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Sample records for tussocks soils beneath

  1. Shifts in the phylogenetic structure and functional capacity of soil microbial communities follow alteration of native tussock grassland ecosystems

    NARCIS (Netherlands)

    Wakelin, Steven A.; Barratt, Barbara I.P.; Gerard, Emily; Gregg, Adrienne L.; Brodie, Eoin L.; Andersen, Gary L.; DeSantis, Todd Z.; Zhou, Jizhong; He, Zhili; Kowalchuk, George A.; O'Callaghan, Maureen

    Globally, tussock-based grasslands are being modified to increase productive capacity. The impacts of cultivation and over-sowing with exotic grass and legumes on soil microbiology were assessed at four sites in New Zealand which differed in soil type, climate and vegetation. Primary alteration of

  2. Soil microbial activities beneath Stipa tenacissima L. and in surrounding bare soil

    Science.gov (United States)

    Novosadová, I.; Ruiz Sinoga, J. D.; Záhora, J.; Fišerová, H.

    2010-05-01

    Open steppes dominated by Stipa tenacissima L. constitute one of the most representative ecosystems of the semi-arid zones of Eastern Mediterranean Basin (Iberian Peninsula, North of Africa). These steppes show a higher degree of variability in composition and structure. Ecosystem functioning is strongly related to the spatial pattern of grass tussocks. Soils beneath S. tenacissima grass show higher fertility and improved microclimatic conditions, favouring the formation of "resource islands" (Maestre et al., 2007). On the other hand in "resource islands" and in surrounding bare soil exists the belowground zone of influence. The competition for water and resources between plants and microorganisms is strong and mediated trough an enormous variety of exudates and resource depletion intended to regulate soil microbial communities in the rhizosphere, control herbivory, encourage beneficial symbioses, and change chemical and physical properties in soil (Pugnaire et Armas, 2008). Secondary compounds and allelopathy restrict other species growth and contribute to patchy plant distribution. Active root segregation affects not only neighbourś growth but also soil microbial activities. The objective of this study was to assess the effect of Stipa tenacissima on the key soil microbial activities under controlled incubation conditions (basal and potential respiration; net nitrogen mineralization). The experimental plots were located in the province Almería in Sierra de los Filabres Mountains near the village Gérgal (southeast Spain) in the small catchment which is situated between 1090 - 1165 m a.s.l. The area with extent of 82 000 m2 is affected by soil degradation. The climate is semiarid Mediterranean. The mean annual rainfall is of about 240 mm mostly concentrated in autumn and spring. The mean annual temperature is 13.9° C. The studied soil has a loam to sandy clay texture and is classified as Lithosol (FAO-ISRIC and ISSS, 1998). The vegetation of these areas is an

  3. Interannual variability of plant phenology in tussock tundra: modelling interactions of plant productivity, plant phenology, snowmelt and soil thaw

    NARCIS (Netherlands)

    Wijk, van M.T.; Williams, M.; Laundre, J.A.; Shaver, G.R.

    2003-01-01

    We present a linked model of plant productivity, plant phenology, snowmelt and soil thaw in order to estimate interannual variability of arctic plant phenology and its effects on plant productivity. The model is tested using 8 years of soil temperature data, and three years of bud break data of Betu

  4. Soil property control of biogeochemical processes beneath two subtropical stormwater infiltration basins

    Science.gov (United States)

    O'Reilly, Andrew M.; Wanielista, Martin P.; Chang, Ni-Bin; Harris, Willie G.; Xuan, Zhemin

    2012-01-01

    Substantially different biogeochemical processes affecting nitrogen fate and transport were observed beneath two stormwater infiltration basins in north-central Florida. Differences are related to soil textural properties that deeply link hydroclimatic conditions with soil moisture variations in a humid, subtropical climate. During 2008, shallow groundwater beneath the basin with predominantly clayey soils (median, 41% silt+clay) exhibited decreases in dissolved oxygen from 3.8 to 0.1 mg L-1 and decreases in nitrate nitrogen (NO3-–N) from 2.7 mg L-1 to -1, followed by manganese and iron reduction, sulfate reduction, and methanogenesis. In contrast, beneath the basin with predominantly sandy soils (median, 2% silt+clay), aerobic conditions persisted from 2007 through 2009 (dissolved oxygen, 5.0–7.8 mg L-1), resulting in NO3-–N of 1.3 to 3.3 mg L-1 in shallow groundwater. Enrichment of d15N and d18O of NO3- combined with water chemistry data indicates denitrification beneath the clayey basin and relatively conservative NO3- transport beneath the sandy basin. Soil-extractable NO3-–N was significantly lower and the copper-containing nitrite reductase gene density was significantly higher beneath the clayey basin. Differences in moisture retention capacity between fine- and coarse-textured soils resulted in median volumetric gas-phase contents of 0.04 beneath the clayey basin and 0.19 beneath the sandy basin, inhibiting surface/subsurface oxygen exchange beneath the clayey basin. Results can inform development of soil amendments to maintain elevated moisture content in shallow soils of stormwater infiltration basins, which can be incorporated in improved best management practices to mitigate NO3- impacts.

  5. Microfungi in the soil beneath common oak and their effect on Armillaria occurrence

    Directory of Open Access Journals (Sweden)

    Hanna Kwaśna

    2014-08-01

    Full Text Available Microfungal assemblages in a soil beneath 30- and 50·year-old oaks and their 2-year-old stumps were studied using the soil dilution plate method. A total of 98 culturable microfungi were isolated. Compared to the living oaks before felling and the control living oaks, the density of Mortierella macrocystis, Penicillium jonczewskii, Pseudogymnoascus roseus Sporothrix schenckii, Tolypoccladiumum inflatum and Umbelopsis vinacea sigificantly inacased in the soil beneath slumps in the 32- and 52-year-old stands. Density of Aspergillus kanagawaensis, Monodictys lepraria, P. daleae and sterile dematiaceous hyphomycetes increased significantly in the 32-year-old stand and Chrysosporium merdarium in the 52·year-old stand. These fungi are known 'stimulants' of Armillaria rhizomorph formation. It is suggested that the increase in density of Armillaria rhizomorph 'stimulants' in a soil beneath oak stumps may increase the possibility of colonization of stumps by Armillaria.

  6. Soil nematode communities are ecologically more mature beneath late- than early-successional stage biological soil crusts

    Science.gov (United States)

    Darby, B.J.; Neher, D.A.; Belnap, J.

    2007-01-01

    Biological soil crusts are key mediators of carbon and nitrogen inputs for arid land soils and often represent a dominant portion of the soil surface cover in arid lands. Free-living soil nematode communities reflect their environment and have been used as biological indicators of soil condition. In this study, we test the hypothesis that nematode communities are successionally more mature beneath well-developed, late-successional stage crusts than immature, early-successional stage crusts. We identified and enumerated nematodes by genus from beneath early- and late-stage crusts from both the Colorado Plateau, Utah (cool, winter rain desert) and Chihuahuan Desert, New Mexico (hot, summer rain desert) at 0-10 and 10-30 cm depths. As hypothesized, nematode abundance, richness, diversity, and successional maturity were greater beneath well-developed crusts than immature crusts. The mechanism of this aboveground-belowground link between biological soil crusts and nematode community composition is likely the increased food, habitat, nutrient inputs, moisture retention, and/or environmental stability provided by late-successional crusts. Canonical correspondence analysis of nematode genera demonstrated that nematode community composition differed greatly between geographic locations that contrast in temperature, precipitation, and soil texture. We found unique assemblages of genera among combinations of location and crust type that reveal a gap in scientific knowledge regarding empirically derived characterization of dominant nematode genera in deserts soils and their functional role in a crust-associated food web. ?? 2006 Elsevier B.V. All rights reserved.

  7. Experimental Relationships between Moduli For Soil Layers Beneath Concrete Pavements

    Science.gov (United States)

    1977-06-01

    Young’s Modulus with Overburden and Void Ratio for a Granular Soil ........... ...... .. ... 45 24 Measured Versus Calculated Deflections for Sand...values, to evaluate the validity of the material characteri,ations. By making comparisions between the "ideal" granular subgrade section and the...components C are dependent on the current total level of stress and strain. The variable modulus models represent materials of the so-called " hypoelastic

  8. Density and stability of soil organic carbon beneath impervious surfaces in urban areas.

    Science.gov (United States)

    Wei, Zongqiang; Wu, Shaohua; Yan, Xiao; Zhou, Shenglu

    2014-01-01

    Installation of impervious surfaces in urban areas has attracted increasing attention due to its potential hazard to urban ecosystems. Urban soils are suggested to have robust carbon (C) sequestration capacity; however, the C stocks and dynamics in the soils covered by impervious surfaces that dominate urban areas are still not well characterized. We compared soil organic C (SOC) densities and their stabilities under impervious surface, determined by a 28-d incubation experiment, with those in open areas in Yixing City, China. The SOC density (0-20 cm) under impervious surfaces was, on average, 68% lower than that in open areas. Furthermore, there was a significantly (Psoils, whereas the correlation was not apparent for the impervious-covered soils, suggesting that the artificial soil sealing in urban areas decoupled the cycle of C and N. Cumulative CO2-C evolved during the 28-d incubation was lower from the impervious-covered soils than from the open soils, and agreed well with a first-order decay model (Ct = C1+C0(1-e-kt)). The model results indicated that the SOC underlying capped surfaces had weaker decomposability and lower turnover rate. Our results confirm the unique character of urban SOC, especially that beneath impervious surface, and suggest that scientific and management views on regional SOC assessment may need to consider the role of urban carbon stocks.

  9. Formation of tussocks by sedges: effects of hydroperiod and nutrients.

    Science.gov (United States)

    Lawrence, Beth A; Zedler, Joy B

    2011-07-01

    Tussock formation is a global phenomenon that enhances microtopography and increases biodiversity by adding structure to ecological communities, but little is known about tussock development in relation to environmental factors. To further efforts to restore wetland microtopography and associated functions, we investigated Carex stricta tussock size in relation to elevation (a proxy for water depth) at a range of sites in southern Wisconsin, USA, and tested the effect of five hydroperiods and N+P addition (15 g N/m2 + 0.37 g P/m2) on tussock formation during a three-year mesocosm experiment. Wet meadows dominated by C. stricta averaged 4.9 tussocks/m2, with a mean volume of 1160 cm3 and height of 15 cm. Within sites, taller tussocks occurred at lower elevations, suggesting a structural adaptation to anoxic conditions. In our mesocosm experiment, C. stricta accelerated tussock formation when inundated, and it increased overall productivity with N + P addition. Within two growing seasons, continuous inundation (+18 cm) in the mesocosms led to tussocks that were nearly as tall as in our field survey (mean height in mesocosms, 10 +/- 1.3 cm; maximum, 17 cm). Plants grown with constant low water (-18 cm) only formed short mounds (mean height = 2 +/- 0.4 cm). After three growing seasons, the volume of the largest tussocks (3274 +/- 376 cm3, grown with +18 cm water depth and N + P addition) was 12 times that of the smallest (275 +/- 38 cm3, grown with -18 cm water depth and no N + P). Though tussock composition varied among hydroperiods, tussocks were predominantly organic (74-94% of dry mass) and composed of leaf bases (46-59%), fine roots (10-31%), and duff (5-13%). Only the plants subjected to high water levels produced the vertically oriented rhizomes and ascending shoot bases that were prevalent in field-collected tussocks. Under continuous or periodic inundation, tussocks achieved similar heights and accumulated similar levels of organic matter (range: 163-394 g C

  10. The detectability of archaeological structures beneath the soil using the ground penetrating radar technique

    Science.gov (United States)

    Ferrara, C.; Barone, P. M.; Pajewski, L.; Pettinelli, E.; Rossi, G.

    2012-04-01

    particular, in the Domus Aurea, in the Domitian Stadium, and in the San Cesario in Palatio church, the processing of the GPR data highlights not only the presence of Roman circular bases/insoles of pillars not yet brought to the light, but also their structural disposition and geometry. These three examples show that GPR technique is a valid support which, in exhaustive way, can underline the unexpected presence of ancient structures beneath the soil, also in well-known archaeological sites.

  11. Influence of the Tussock Growth Form on Arctic Ecosystem Carbon Stocks

    Science.gov (United States)

    Curasi, S.; Rocha, A. V.; Sonnentag, O.; Wullschleger, S. D.; Myers-Smith, I. H.; Fetcher, N.; Mack, M. C.; Natali, S.; Loranty, M. M.; Parker, T.

    2015-12-01

    The influence of plant growth forms on ecosystem carbon (C) cycling has been under appreciated. In arctic tundra, environmental factors and plant traits of the sedge Eriophorum vaginatum cause the formation of mounds that are dense amalgamations of belowground C called tussocks. Tussocks have important implications for arctic ecosystem biogeochemistry and C stocks, but the environmental and biological factors controlling their size and distribution across the landscape are poorly understood. In order to better understand how landscape variation in tussock size and density impact ecosystem C stocks, we formed the Carbon in Arctic Tussock Tundra (CATT) network and recruited an international team to sample locations across the arctic. The CATT network provided a latitudinal and longitudinal gradient along which to improve our understanding of tussocks' influence on ecosystem structure and function. CATT data revealed important insights into tussock formation across the arctic. Tussock density generally declined with latitude, and tussock size exhibited substantial variation across sites. The relationship between height and diameter was similar across CATT sites indicating that both biological and environmental factors control tussock formation. At some sites, C in tussocks comprised a substantial percentage of ecosystem C stocks that may be vulnerable to climate change. It is concluded that the loss of this growth form would offset C gains from projected plant functional shifts from graminoid to shrub tundra. This work highlights the role of plant growth forms on the magnitude and retention of ecosystem C stocks.

  12. Beneath aggregate stability - quantifying thermodynamic properties that drive soil structure dynamics

    Science.gov (United States)

    Hallett, Paul; Ogden, Mike; Karim, Kamal; Schmidt, Sonja; Yoshida, Shuichiro

    2014-05-01

    Soil aggregates are a figment of your energy input and initial boundary conditions, so the basic thermodynamics that drive soil structure formation are needed to understand soil structure dynamics. Using approaches from engineering and materials science, it is possible quantify basic thermodynamic properties, but at present tests are generally limited to highly simplified, often remoulded, soil structures. Although this presents limitations, the understanding of underlying processes driving soil structure dynamics is poor, which could be argued is due to the enormity of the challenge of such an incredibly complex system. Other areas of soil science, particularly soil water physics, relied on simplified structures to develop theories that can now be applied to more complex pore structures. We argue that a similar approach needs to gain prominence in the study of soil aggregates. An overview will be provided of approaches adapted from other disciplines to quantify particle bonding, fracture resistance, rheology and capillary cohesion of soil that drive its aggregation and structure dynamics. All of the tests are limited as they require simplified soil structures, ranging from repacked soils to flat surfaces coated with mineral particles. A brief summary of the different approaches will demonstrate the benefits of collecting basic physical data relevant to soil structure dynamics, including examples where they are vital components of models. The soil treatments we have tested with these engineering and materials science approaches include field soils from a range of management practices with differing clay and organic matters contents, amendment and incubation of soils with a range of microorganisms and substrates in the laboratory, model clay-sand mixes and planar mineral surfaces with different topologies. In addition to advocating the wider adoption of these approaches, we will discuss limitations and hope to stimulate discussion on how approaches could be improved

  13. Sensible heat balance measurements of soil water evaporation beneath a maize canopy

    Science.gov (United States)

    Soil water evaporation is an important component of the water budget in a cropped field. Few methods are available for continuous and independent measurement of soil water evaporation. A sensible heat balance (SHB) approach has recently been demonstrated for continuously determining soil water evapo...

  14. Use of engineered soils beneath low-level radioactive waste disposal facilities

    Energy Technology Data Exchange (ETDEWEB)

    Sandford, T.C.; Humphrey, D.N.; DeMascio, F.A. [Univ. of Maine, Orono, ME (United States). Dept. of Civil Engineering

    1993-03-01

    Current regulations are oriented toward locating low-level radioactive waste disposal facilities on sites that have a substantial natural soil barrier and are above the groundwater table. In some of the northern states, like Maine, the overburden soils are glacially derived and in most places provide a thin cover over bedrock with a high groundwater table. Thus, the orientation of current regulations can severely limit the availability of suitable sites. A common characteristic of many locations in glaciated regions is the rapid change of soil types that may occur and the heterogeneity within a given soil type. In addition, the bedrock may be fractured, providing avenues for water movement. A reliable characterization of these sites can be difficult, even with a detailed subsurface exploration program. Moreover, fluctuating groundwater and frost as well as the natural deposition processes have introduced macro features such as cracks, fissures, sand and silt seams, and root holes. The significant effect that these macro features have on the permeability and adsorptive capacity of a large mass is often ignored or poorly accounted for in the analyses. This paper will examine an alternate approach, which is to use engineered soils as a substitute for some or all of the natural soil and to treat the fractures in the underlying bedrock. The site selection would no longer be primarily determined by the natural soil and rock and could even be placed in locations with no existing soils. Engineered soils can be used for below- or aboveground facilities.

  15. Combined Resistivity and Shear Wave Velocity Soil-type Estimation Beneath a Coastal Protection Levee.

    Science.gov (United States)

    Lorenzo, J. M.; Goff, D.; Hayashi, K.

    2015-12-01

    Unconsolidated Holocene deltaic sediments comprise levee foundation soils in New Orleans, USA. Whereas geotechnical tests at point locations are indispensable for evaluating soil stability, the highly variable sedimentary facies of the Mississippi delta create difficulties to predict soil conditions between test locations. Combined electrical resistivity and seismic shear wave studies, calibrated to geotechnical data, may provide an efficient methodology to predict soil types between geotechnical sites at shallow depths (0- 10 m). The London Avenue Canal levee flank of New Orleans, which failed in the aftermath of Hurricane Katrina, 2005, presents a suitable site in which to pioneer these geophysical relationships. Preliminary cross-plots show electrically resistive, high-shear-wave velocity areas interpreted as low-permeability, resistive silt. In brackish coastal environments, low-resistivity and low-shear-wave-velocity areas may indicate both saturated, unconsolidated sands and low-rigidity clays. Via a polynomial approximation, soil sub-types of sand, silt and clay can be estimated by a cross-plot of S-wave velocity and resistivity. We confirm that existent boring log data fit reasonably well with the polynomial approximation where 2/3 of soil samples fall within their respective bounds—this approach represents a new classification system that could be used for other mid-latitude, fine-grained deltas.

  16. Ionic conductivity anomaly in soil cover——Exploration of blind mineralization beneath regolith cover

    Institute of Scientific and Technical Information of China (English)

    KEELING; John; L.

    2010-01-01

    This paper briefly describes the formation of ionic conductivity anomalies in soil cover, and the characteristics of ionic composition that forms conductivity anomalies, based on the theory of geoelectrochemical halo. Based on some practical results of soluble ions in soil cover and soil conductivity derived from a number of mining areas of both China and overseas, here we present the correlation of a conductivity anomaly with the ionic composition and establish a model for the formation of conductivity anomalies in soil cover. The results indicate that the formation of a conductivity anomaly is not a simple transformation of a secondary geochemical anomaly. A conductivity anomaly is formed as the result of electrochemical and chemical processes, by transformation of orebody into various ionic haloes through four physicochemical processes: 1) dissolution of the orebody, 2) migration of dissolved matter, 3) conversion of matter near the surface, and 4) the formation of ionic conductivity anomalies. The conductivity anomaly, as a physical parameter, essentially represents the integration of various geochemical compositions and is controlled by a set of particular ionic groups.

  17. Effects of over-winter green cover on soil solution nitrate concentrations beneath tillage land.

    Science.gov (United States)

    Premrov, Alina; Coxon, Catherine E; Hackett, Richard; Kirwan, Laura; Richards, Karl G

    2014-02-01

    There is a growing need to reduce nitrogen losses from agricultural systems to increase food production while reducing negative environmental impacts. The efficacy of vegetation cover for reducing nitrate leaching in tillage systems during fallow periods has been widely investigated. Nitrate leaching reductions by natural regeneration (i.e. growth of weeds and crop volunteers) have been investigated to a lesser extent than reductions by planted cover crops. This study compares the efficacy of natural regeneration and a sown cover crop (mustard) relative to no vegetative cover under both a reduced tillage system and conventional plough-based system as potential mitigation measures for reducing over-winter soil solution nitrate concentrations. The study was conducted over three winter fallow seasons on well drained soil, highly susceptible to leaching, under temperate maritime climatic conditions. Mustard cover crop under both reduced tillage and conventional ploughing was observed to be an effective measure for significantly reducing nitrate concentrations. Natural regeneration under reduced tillage was found to significantly reduce the soil solution nitrate concentrations. This was not the case for the natural regeneration under conventional ploughing. The improved efficacy of natural regeneration under reduced tillage could be a consequence of potential stimulation of seedling germination by the autumn reduced tillage practices and improved over-winter plant growth. There was no significant effect of tillage practices on nitrate concentrations. This study shows that over winter covers of mustard and natural regeneration, under reduced tillage, are effective measures for reducing nitrate concentrations in free draining temperate soils.

  18. Variations of Soil Microbial Community Structures Beneath Broadleaved Forest Trees in Temperate and Subtropical Climate Zones.

    Science.gov (United States)

    Yang, Sihang; Zhang, Yuguang; Cong, Jing; Wang, Mengmeng; Zhao, Mengxin; Lu, Hui; Xie, Changyi; Yang, Caiyun; Yuan, Tong; Li, Diqiang; Zhou, Jizhong; Gu, Baohua; Yang, Yunfeng

    2017-01-01

    Global warming has shifted climate zones poleward or upward. However, understanding the responses and mechanism of microbial community structure and functions relevant to natural climate zone succession is challenged by the high complexity of microbial communities. Here, we examined soil microbial community in three broadleaved forests located in the Wulu Mountain (WLM, temperate climate), Funiu Mountain (FNM, at the border of temperate and subtropical climate zones), or Shennongjia Mountain (SNJ, subtropical climate). Although plant species richness decreased with latitudes, the microbial taxonomic α-diversity increased with latitudes, concomitant with increases in soil total and available nitrogen and phosphorus contents. Phylogenetic NRI (Net Relatedness Index) values increased from -0.718 in temperate zone (WLM) to 1.042 in subtropical zone (SNJ), showing a shift from over dispersion to clustering likely caused by environmental filtering such as low pH and nutrients. Similarly, taxonomy-based association networks of subtropical forest samples were larger and tighter, suggesting clustering. In contrast, functional α-diversity was similar among three forests, but functional gene networks of the FNM forest significantly (P < 0.050) differed from the others. A significant correlation (R = 0.616, P < 0.001) between taxonomic and functional β-diversity was observed only in the FNM forest, suggesting low functional redundancy at the border of climate zones. Using a strategy of space-for-time substitution, we predict that poleward climate range shift will lead to decreased microbial taxonomic α-diversities in broadleaved forest.

  19. Soil water storage and groundwater behaviour in a catenary sequence beneath forest in central Amazonia: I. Comparisons between plateau, slope and valley floor

    Directory of Open Access Journals (Sweden)

    M. G. Hodnett

    1997-01-01

    Full Text Available Soil water storage was monitored in three landscape elements in the forest (plateau, slope and valley floor over a 3 year period to identify differences in sub-surface hydrological response. Under the plateau and slope, the changes of storage were very similar and there was no indication of surface runoff on the slope. The mean maximum seasonal storage change was 156 mm in the 2 m profile but it was clear that, in the dry season, the forest was able to take up water from below 3.6 m. Soil water availability was low. Soil water storage changes in the valley were dominated by the behaviour of a shallow water table which, in normal years, varied between 0.1 m below the surface at the end of the wet season and 0.8 m at the end of the dry season. Soil water storage changes were small because root uptake was largely replenished by groundwater flow towards the stream. The groundwater behaviour is controlled mainly by the deep drainage from beneath the plateau and slope areas. The groundwater gradient beneath the slope indicated that recharge beneath the plateau and slope commences only after the soil water deficits from the previous dry season have been replenished. Following a wet season with little recharge, the water table fell, ceasing to influence the valley soil water storage, and the stream dried up. The plateau and slope, a zone of very high porosity between 0.4 and 1.1 m, underlain by a less conductive layer, is a probable route for interflow during, and for a few hours after, heavy and prolonged rainfall.

  20. The soil-water flow system beneath a cotton field in arid north-west China, serviced by mulched drip irrigation using brackish water

    Science.gov (United States)

    Li, Xianwen; Jin, Menggui; Huang, Jinou; Yuan, Jingjing

    2015-02-01

    A field experiment was carried out in southern Xinjiang, China, to reveal soil-water flow pattern beneath a combined plastic-mulch (film) and drip-irrigation system using brackish water. The soil-water flow system (SWFS) was characterized from soil surface to the water table based on observed spatio-temporal distribution of total soil-water potential, water content and electric conductivity. Root suction provided a strong inner sink. The results indicated that SWFS determined the soil salinity and moisture distribution. Drip-irrigation events could leach excess salts from the root zone and provide soil conditions with a tolerable salinity level that supports the growth of cotton. High-salinity strips were formed along the wetting front and at the bare soil surface. Hydrogeology conditions, irrigation regime, climate, plant growth and use of mulch would affect potential sources and sinks, boundary conditions and the size of the SWFS. At depth 0-60 cm, the soil salinity at the end of the irrigation season was 1.9 times that at the beginning. Beneath the mulch cover, the soil-water content in the `wide rows' zone (55 cm between the two rows with no drip line) was higher than that in the `narrow rows' zone (15 cm between the two rows with a drip line) due to the strong root-water uptake. The downward water flow below the divergent curved surface of zero flux before irrigation, and the water-table fluctuation with irrigation events, indicated that excessive irrigation occurred.

  1. Action of Douglas Fir Tussock Moth Larvae and Their Microflora on Dietary Terpenes

    OpenAIRE

    Andrews, R E; Spence, K. D.

    1980-01-01

    A single type of bacterium, tentatively identified as a member of the genus Bacillus, was isolated from 2 of 20 midguts of Douglas fir tussock moth larvae being fed a diet of fir needles. No bacteria could be isolated from most midguts. Although spherically shaped bodies were present in the food bolus, these bodies, if microorganisms, could not be distinguished from spherical bodies associated with the plant tissue. The Douglas fir tussock moth dietary terpenes were altered during their passa...

  2. Extracellular acid phosphatase activities in Eriophorum vaginatum tussocks: A modeling synthesis

    Energy Technology Data Exchange (ETDEWEB)

    Moorhead, D.L. (Texas Tech Univ., Lubbock (United States)); Kroehler, C.J. (Virginia Polytechnic Inst. and State Univ., Blacksburg (United States)); Linkins, A.E. (Clarkson Univ., Potsdan, NY (United States)); Reynolds, J.F. (San Diego State Univ., CA (United States))

    1993-02-01

    Analyses of Eriophorum vaginatum tussocks provided mass and kinetic parameters for a Michaelis-Menten model of phosphatase activities in Alaskan tussock tundra. This model was used to simulate the temporal patterns of phosphatase activities, given a 90-d thawing season and organic phosphorus concentrations of 30 [mu]M in the first and last 10-d intervals; 15 [mu]M at other times. Results indicated that about 28% of the total annual tussock activity (155 mg P released) occurred during the brief period of high substrate availability in autumn; little occurred in spring because most of the tussock was frozen and live root mass was low. Phosphatases associated with living roots of E. vaginatum were responsible for about 4% of the total activity in tussocks (ca. 6 mg P), which is almost twice the annual plant demand (ca. 3.5 mg). These results suggest that (1) E. vaginatum may obtain much of its phosphorus requirement from the activities of root surface phosphatases, and (2) the timing of maximum plant phosphorus uptake (late in year) and growth (early in year) are asynchronous, i.e., E. vaginatum integrates nutrient availabilities across years. 41 refs., 2 figs., 1 tab.

  3. Divergent composition but similar function of soil food webs beneath individual plants: plant species and community effects

    NARCIS (Netherlands)

    Bezemer, T.M.; Fountain, M.T.; Barea, J.M.; Christensen, S.; Dekker, S.C.; Duyts, H.; van Hal, R.; Harvey, J.A.; Hedlund, K.; Maraun, M.; Mikola, J.; Mladenov, A.G.; Robin, C.; de Ruiter, P.C.; Scheu, S.; Setälä, H.; Milauer, P.; Van der Putten, W.H.

    2010-01-01

    Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and

  4. Calcium mineralization in the forest floor and surface soil beneath different tree species in the northeastern US

    NARCIS (Netherlands)

    Dijkstra, F.A.

    2003-01-01

    Calcium (Ca) is an important element for neutralizing soil acidity in temperate forests. The immediate availability of Ca in forested acid soils is largely dependent on mineralization of organic Ca, which may differ significantly among tree species. I estimated net Ca mineralization in the forest

  5. Rapid carbon turnover beneath shrub and tree vegetation is associated with low soil carbon stocks at a subarctic treeline.

    Science.gov (United States)

    Parker, Thomas C; Subke, Jens-Arne; Wookey, Philip A

    2015-05-01

    Climate warming at high northern latitudes has caused substantial increases in plant productivity of tundra vegetation and an expansion of the range of deciduous shrub species. However significant the increase in carbon (C) contained within above-ground shrub biomass, it is modest in comparison with the amount of C stored in the soil in tundra ecosystems. Here, we use a 'space-for-time' approach to test the hypothesis that a shift from lower-productivity tundra heath to higher-productivity deciduous shrub vegetation in the sub-Arctic may lead to a loss of soil C that out-weighs the increase in above-ground shrub biomass. We further hypothesize that a shift from ericoid to ectomycorrhizal systems coincident with this vegetation change provides a mechanism for the loss of soil C. We sampled soil C stocks, soil surface CO2 flux rates and fungal growth rates along replicated natural transitions from birch forest (Betula pubescens), through deciduous shrub tundra (Betula nana) to tundra heaths (Empetrum nigrum) near Abisko, Swedish Lapland. We demonstrate that organic horizon soil organic C (SOCorg ) is significantly lower at shrub (2.98 ± 0.48 kg m(-2) ) and forest (2.04 ± 0.25 kg m(-2) ) plots than at heath plots (7.03 ± 0.79 kg m(-2) ). Shrub vegetation had the highest respiration rates, suggesting that despite higher rates of C assimilation, C turnover was also very high and less C is sequestered in the ecosystem. Growth rates of fungal hyphae increased across the transition from heath to shrub, suggesting that the action of ectomycorrhizal symbionts in the scavenging of organically bound nutrients is an important pathway by which soil C is made available to microbial degradation. The expansion of deciduous shrubs onto potentially vulnerable arctic soils with large stores of C could therefore represent a significant positive feedback to the climate system.

  6. Summer temperature increase has distinct effects on the ectomycorrhizal fungal communities of moist tussock and dry tundra in Arctic Alaska.

    Science.gov (United States)

    Morgado, Luis N; Semenova, Tatiana A; Welker, Jeffrey M; Walker, Marilyn D; Smets, Erik; Geml, József

    2015-02-01

    Arctic regions are experiencing the greatest rates of climate warming on the planet and marked changes have already been observed in terrestrial arctic ecosystems. While most studies have focused on the effects of warming on arctic vegetation and nutrient cycling, little is known about how belowground communities, such as fungi root-associated, respond to warming. Here, we investigate how long-term summer warming affects ectomycorrhizal (ECM) fungal communities. We used Ion Torrent sequencing of the rDNA internal transcribed spacer 2 (ITS2) region to compare ECM fungal communities in plots with and without long-term experimental warming in both dry and moist tussock tundra. Cortinarius was the most OTU-rich genus in the moist tundra, while the most diverse genus in the dry tundra was Tomentella. On the diversity level, in the moist tundra we found significant differences in community composition, and a sharp decrease in the richness of ECM fungi due to warming. On the functional level, our results indicate that warming induces shifts in the extramatrical properties of the communities, where the species with medium-distance exploration type seem to be favored with potential implications for the mobilization of different nutrient pools in the soil. In the dry tundra, neither community richness nor community composition was significantly altered by warming, similar to what had been observed in ECM host plants. There was, however, a marginally significant increase in OTUs identified as ECM fungi with the medium-distance exploration type in the warmed plots. Linking our findings of decreasing richness with previous results of increasing ECM fungal biomass suggests that certain ECM species are favored by warming and may become more abundant, while many other species may go locally extinct due to direct or indirect effects of warming. Such compositional shifts in the community might affect nutrient cycling and soil organic C storage. © 2014 The Authors. Global Change

  7. Annual patterns and budget of CO2 flux in an Alaskan arctic tussock tundra ecosystem at Atqasuk, Alaska

    Science.gov (United States)

    Oechel, W. C.; Kalhori, A. A.; Burba, G. G.; Gioli, B.

    2013-12-01

    Arctic ecosystem functioning is not only critically affected by climate change, but also has the potential for major positive feedbacks on climate. There is however relatively little information available on the role, patterns, and vulnerabilities of CO2 fluxes during the non-summer seasons. Presented here is a year-around study of CO2 fluxes in an Alaskan Arctic tussock tundra ecosystem. Also presented are key environmental controls on CO2 fluxes as well as possible impacts of likely changes in season timing. This is aided by a new empirical quantification of seasons in the Arctic based on net radiation, which can help describe seasonal responses to greenhouse gas fluxes under climate change. The fluxes were computed using standard FluxNet methodology and corrected using standard WPL density terms, adjusted for influences of instrument surface heating. The results showed that the non-summer season comprises a significant source of carbon to the atmosphere. The summer period was a net sink of 10.83 g C m-2 yr-1, while the non-summer seasons released more than four times the CO2 uptake observed in the summer, resulting in a net annual source of 37.6 g C m-2 yr-1 to the atmosphere. This shows a change in this region of the Arctic from a long-term annual sink of CO2 from the atmosphere to an annual source of CO2 from the terrestrial ecosystem and soils to the atmosphere. The results presented here demonstrate that nearly continuous observations may be required in order to accurately calculate the annual NEE of Arctic ecosystems, and to build predictive understanding that can be used to estimate, with confidence, Arctic fluxes under future conditions. Daily CO2 fluxes over the year, average daily net radiation, average daily PAR, average daily air temperature and average daily soil respiration (at -5 cm).

  8. Monk’s tonsure-like gaps in the tussock grass Spartina argentinensis (Gramineae

    Directory of Open Access Journals (Sweden)

    J. P. Lewis

    2001-03-01

    Full Text Available Monk's tonsure-like gaps develop inside gramineans and other plants. The tonsures of Spartina argentinensis originate as a result of tussock development and disturbance. As the tonsure develops the ring of tillers around it breakes down and new tussocks develop from the fragments, regenerating the grassland matrix vegetatively. The microenvironment inside the tonsure is different from the surroundings and microhabitat-specific taxa grow there.Los "claros tipo tonsura de monje" se desarrollan tanto en el interior de matas de gramíneas, como de especies no pertenecientes a dicha familia. Describimos las matas de Spartina argentinensis y sus tonsuras que surgen por el propio desarrollo de la mata y disturbios. A medida que la tonsura se desarrolla, el anillo de culmos que la rodea se rompe y nuevas matas se desarrollan a partir de los fragmentos, regenerando vegetativamente la matriz del pastizal. Los microambientes dentro y fuera de la tonsura son distintos, al igual que las especies que se establecen en ellos.

  9. Nitrogen in soils beneath 18-65 year old stands of subtropical evergreen broad-leaved forests in Laoshan Mountains in Eastern China

    Institute of Scientific and Technical Information of China (English)

    GU Feng; ZHANG Kai; ZHANG Yun-qi; WANG Qin; XU Xiao-niu

    2011-01-01

    Monitoring of soil nitrogen (N) cycling is useful to assess soil quality and to gauge the sustainability of management practices.We studied net N mineralization,nitrification,and soil N availability in the 0-10 cm and 11-30 cm soil horizons in east China during 2006-2007 using an in sito incubation method in four subtropical evergreen broad-leaved forest stands aged 18-,36-,48-,and 65-years.The properties of surface soil and forest floor varied between stand age classes.C:N ratios of surface soil and forest floor decreased,whereas soil total N and total organic C,available P,and soil microbial biomass N increased with stand age.The mineral N pool was small for the young stand and large for the older stands.NO3-N was less than 30% in all stands.Net rates of N mineralization and nitrification were higher in old stands than in younger stands,and higher in the 0-10 cm than in the 11-30 cm horizon.The differences were significant between old and young stands (p <0.031) and between soil horizons (p < 0.005).Relative nitrification was somewhat low in all forest stands and declined with stand age.N transformation seemed to be controlled by soil moisture,soil microbial biomass N,and forest floor C:N ratio.Our results demonstrate that analyses of N cycling can provide insight into the effects of management disturbances on forest ecosystems.

  10. Influence of an Elevated Atmospheric CO2 Content on Soil and Rhizosphere Bacterial Communities Beneath Lolium perenne and Trifolium repens under Field Conditions.

    Science.gov (United States)

    Marilley; Hartwig; Aragno

    1999-07-01

    > Abstract The increase in atmospheric CO2 content alters C3 plant photosynthetic rate, leading to changes in rhizodeposition and other root activities. This may influence the activity, the biomass, and the structure of soil and rhizosphere microbial communities and therefore the nutrient cycling rates and the plant growth. The present paper focuses on bacterial numbers and on community structure. The rhizospheres of two grassland plants, Lolium perenne (ryegrass) and Trifolium repens (white clover), were divided into three fractions: the bulk soil, the rhizospheric soil, and the rhizoplane-endorhizosphere. The elevated atmospheric CO2 content increased the most probable numbers of heterotrophic bacteria in the rhizosphere of L. perenne. However, this effect lasted only at the beginning of the vegetation period for T. repens. Community structure was assessed after isolation of DNA, PCR amplification, and construction of cloned 16S rDNA libraries. Amplified ribosomal DNA restriction analysis (ARDRA) and colony hybridization with an oligonucleotide probe designed to detect Pseudomonas spp. showed under elevated atmospheric CO2 content an increased dominance of pseudomonads in the rhizosphere of L. perenne and a decreased dominance in the rhizosphere of T. repens. This work provides evidence for a CO2-induced alteration in the structure of the rhizosphere bacterial populations, suggesting a possible alteration of the plant-growth-promoting-rhizobacterial (PGPR) effect.http://link.springer-ny.com/link/service/journals/00248/bibs/38n1p39.html

  11. Douglas-Fir Tussock Moth- and Douglas-Fir Beetle-Caused Mortality in a Ponderosa Pine/Douglas-Fir Forest in the Colorado Front Range, USA

    Directory of Open Access Journals (Sweden)

    José F. Negrón

    2014-12-01

    Full Text Available An outbreak of the Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough, occurred in the South Platte River drainage on the Pike-San Isabel National Forest in the Colorado Front Range attacking Douglas-fir, Pseudotsuga menziesii (Mirb. Franco. Stocking levels, species composition, and tree size in heavily and lightly defoliated stands were similar. Douglas-fir tussock moth defoliation resulted in significant Douglas-fir mortality in the heavily defoliated stands, leading to a change in dominance to ponderosa pine, Pinus ponderosa Lawson. Douglas-fir beetle, Dendroctonus pseudotsuqae Hopkins, populations increased following the defoliation event but caused less mortality, and did not differ between heavily and lightly defoliated stands. Douglas-fir tussock moth-related mortality was greatest in trees less than 15 cm dbh (diameter at 1.4 m above the ground that grew in suppressed and intermediate canopy positions. Douglas-fir beetle-related mortality was greatest in trees larger than 15 cm dbh that grew in the dominant and co-dominant crown positions. Although both insects utilize Douglas-fir as its primary host, stand response to infestation is different. The extensive outbreak of the Douglas-fir tussock moth followed by Douglas-fir beetle activity may be associated with a legacy of increased host type growing in overstocked conditions as a result of fire exclusion.

  12. Monitoring larval populations of the Douglas-fir tussock moth and the western spruce budworm on permanent plots: sampling methods and statistical properties of data

    Science.gov (United States)

    A.R. Mason; H.G. Paul

    1994-01-01

    Procedures for monitoring larval populations of the Douglas-fir tussock moth and the western spruce budworm are recommended based on many years experience in sampling these species in eastern Oregon and Washington. It is shown that statistically reliable estimates of larval density can be made for a population by sampling host trees in a series of permanent plots in a...

  13. Determinism beneath Quantum Mechanics

    CERN Document Server

    Hooft, G

    2002-01-01

    Contrary to common belief, it is not difficult to construct deterministic models where stochastic behavior is correctly described by quantum mechanical amplitudes, in precise accordance with the Copenhagen-Bohr-Bohm doctrine. What is difficult however is to obtain a Hamiltonian that is bounded from below, and whose ground state is a vacuum that exhibits complicated vacuum fluctuations, as in the real world. Beneath Quantum Mechanics, there may be a deterministic theory with (local) information loss. This may lead to a sufficiently complex vacuum state, and to an apparent non-locality in the relation between the deterministic ("ontological") states and the quantum states, of the kind needed to explain away the Bell inequalities. Theories of this kind would not only be appealing from a philosophical point of view, but may also be essential for understanding causality at Planckian distance scales.

  14. Grass Cover Influences Hydrophysical Parameters and Heterogeneity of Water Flow in a Sandy Soil

    Institute of Scientific and Technical Information of China (English)

    L. LICHNER; D. J. ELDRIDGE; K. SCHACHT; N. ZHUKOVA; L. HOLKO; M. (S)(I)R; J. PECHO

    2011-01-01

    Vegetation cover has a major effect on water flow in soils.Two sites,separated by distance of about 50 m,were selected to quantify the influence of grass cover on hydrophysical parameters and heterogeneity of water flow in a sandy soil emerging during a heavy rain following a long hot,dry period.A control soil (pure sand) with limited impact of vegetation or organic matter was obtained by sampling at 50 cm depth beneath a glade area,and a grassland soil was covered in a 10 cm thick humic layer and colonised by grasses.The persistence of water repellency was measured using the water drop penetration time test,sorptivity and unsaturated hydraulic conductivity using a mini disk infiltrometer,and saturated hydraulic conductivity using a double-ring infiltrometer.Dye tracer experiments were used to assess the heterogeneity of water flow,and both the modified method for estimating effective cross section and an original method for assessing the degree of preferential flow were used to quantify this heterogeneity from the images of dyed soil profiles.Most hydrophysical parameters were substantially different between the two surfaces.The grassland soil had an index of water repellency about 10 times that of pure sand and the persistence of water repellency almost 350 times that of pure sand.Water and ethanol sorptivities in the grassland soil were 7% and 43%,respectively,of those of the pure sand.Hydraulic conductivity and saturated hydraulic conductivities in the grassland soil were 5% and 16% of those of the pure sand,respectively.Dye tracer experiments revealed a stable flow with "air-draining" condition in pure sand and well-developed preferential flow in grassland soil,corresponding to individual grass tussocks and small micro-depressions.The grassland soil was substantially more water repellent and had 3 times the degree of preferential flow compared to pure sand.The results of this study reinforce our view that the consequences of any change in climate

  15. Soil nitrogen availability in the open steppe with Stipa tenacissima

    Science.gov (United States)

    Novosadova, Irena; Damian Ruiz Sinoga, Jose; Záhora, Jaroslav

    2010-05-01

    Open steppes dominated by Stipa tenacissima L. constitute one of the most representative ecosystems of the semi-arid zones of Iberian Peninsula and show a higher degree of variability in composition and structure (Maestre et al., 2007). Vegetation patchiness, which are seen as mosaics including vegetated and non-vegetated components, is a common feature of such open steppes (Valentin et al., 1999). Ecosystem functioning is strongly related to the spatial pattern of grass tussocks. Soils beneath S. tenacissima grass show higher fertility and improved microclimatic conditions, favouring the formation of "resource islands" (Maestre et al., 2007). First, soil moisture is greater beneath the clumps, due to water harvesting through rainfall interception, uptake by roots from adjacent unvegetated areas and water redistribution from gaps to clumps (Bergkamp et al., 1999; Puigdefá bregas et al., 1999). Second, the canopy diminishes the intense solar radiation (Maestre et al., 2001) avoiding the sun-baking effect, which is an important factor for soil temperature change and physical disruption (Magid et al., 1999). Plant clumps either functioned as microbial hotspots where enhanced microbially driven ecosystem processes took place or as microbial banks capable of undergoing a burst of activity under favourable climatic conditions (Goberna et al., 2007). The competition for water and resources between plants and microorganisms is strong and mediated trough an enormous variety of exudates and resource depletion intended to regulate soil microbial communities in the rhizosphere, control herbivory, encourage beneficial symbioses, and change chemical and physical properties in soil (Pugnaire et Armas, 2008). On the other hand there exists experimental evidence of a non-patchy distribution of certain soil microbial properties in semi-arid Mediterranean patchy ecosystems (Goberna et al., 2007). The microbial nutrient release processes have a fundamental role in ecosystem

  16. Microbial life beneath a high arctic glacier.

    Science.gov (United States)

    Skidmore, M L; Foght, J M; Sharp, M J

    2000-08-01

    The debris-rich basal ice layers of a high Arctic glacier were shown to contain metabolically diverse microbes that could be cultured oligotrophically at low temperatures (0.3 to 4 degrees C). These organisms included aerobic chemoheterotrophs and anaerobic nitrate reducers, sulfate reducers, and methanogens. Colonies purified from subglacial samples at 4 degrees C appeared to be predominantly psychrophilic. Aerobic chemoheterotrophs were metabolically active in unfrozen basal sediments when they were cultured at 0.3 degrees C in the dark (to simulate nearly in situ conditions), producing (14)CO(2) from radiolabeled sodium acetate with minimal organic amendment (> or =38 microM C). In contrast, no activity was observed when samples were cultured at subfreezing temperatures (glacier provides a viable habitat for life and that microbes may be widespread where the basal ice is temperate and water is present at the base of the glacier and where organic carbon from glacially overridden soils is present. Our observations raise the possibility that in situ microbial production of CO(2) and CH(4) beneath ice masses (e.g., the Northern Hemisphere ice sheets) is an important factor in carbon cycling during glacial periods. Moreover, this terrestrial environment may provide a model for viable habitats for life on Mars, since similar conditions may exist or may have existed in the basal sediments beneath the Martian north polar ice cap.

  17. Determinación de nitrógeno inorgánico y fosfatos a distintas profundidades de suelo bajo pilas de abonos Determination of inorganic nitrogen and phosphates at different soil depths beneath manure piles

    Directory of Open Access Journals (Sweden)

    Javier Luis Ferrari

    2012-12-01

    meses de invierno.In the Andean - Patagonian region, nutrient supply for different crops is frequently made using wood chips mixed with manure. These materials are accumulated in piles of 1.5 - 2 m height. As the piles remain for a period of time outdoors, a partial composting may occur, which would be beneficial. Composting is a biooxidative process, involving an organic substrate, a thermophilic phase that must be reached (55°C and a maturity stage. If the manure piles remain outdoors, nutrients can also be transported by water and lost from the soil through percolation (particulary during winter months of higher precipitations. With the objective of studying if extractable phosphorus in NaHCO3 0.5M (P-Ol of phosphorus Olsen and inorganic nitrogen (Nin;ammonium plus nitrates move beneath the piles of manure, composites soil samples were taken from three blocks at different depths in a farm near the town of El Bolsón. The relationship between P-Ol (agronomic threshold and extractable P in 0.01 M CaCl2 (environmental threshold was also studied. Manure temperatures were taken in different seasons. Nin showed a high data dispersion and excessively high mean values up to the 200 cm depth. Average values (of three blocks found for P exceeded the threshold limit of 60 mg kg-1 P-Ol only on the first sampling date in the 0-20cm depth, although individual data for each block reached 52 mg kg-1 in the 40-60 cm depth. A statistically significant linear regression between P-Ol and P-CaCl2 in soils was obtained, and a threshold near 50/60 mg kg-1, similar to the values reported in the literature. High values for both parameters were found in manures. It is advisable to protect piles of manure from rainfall in winter months.

  18. Soil bacterial community composition altered by increased nutrient availability in Arctic tundra soils

    Directory of Open Access Journals (Sweden)

    Akihiro eKoyama

    2014-10-01

    Full Text Available The pool of soil organic carbon (SOC in the Arctic is disproportionally large compared to those in other biomes. This large quantity of SOC accumulated over millennia due to slow rates of decomposition relative to net primary productivity. Decomposition is constrained by low temperatures and nutrient concentrations, which limit soil microbial activity. We investigated how nutrients limit bacterial and fungal biomass and community composition in organic and mineral soils within moist acidic tussock tundra ecosystems. We sampled two experimental arrays of moist acidic tussock tundra that included fertilized and non-fertilized control plots. One array included plots that had been fertilized annually since 1989 and the other since 2006. Fertilization significantly altered overall bacterial community composition and reduced evenness, to a greater degree in organic than mineral soils, and in the 1989 compared to the 2006 site. The relative abundance of copiotrophic α-proteobacteria and β-proteobacteria was higher in fertilized than control soils, and oligotrophic Acidobacteria were less abundant in fertilized than control soils at the 1989 site. Fungal community composition was less sensitive to increased nutrient availability, and fungal responses to fertilization were not consistent between soil horizons and sites. We detected two ectomycorrhizal genera, Russula and Cortinarius spp., associated with shrubs. Their relative abundance was not affected by fertilization despite increased dominance of their host plants in the fertilized plots. Our results indicate that fertilization, which has been commonly used to simulate warming in Arctic tundra, has limited applicability for investigating fungal dynamics under warming.

  19. Soils

    Science.gov (United States)

    Emily Moghaddas; Ken Hubbert

    2014-01-01

    When managing for resilient forests, each soil’s inherent capacity to resist and recover from changes in soil function should be evaluated relative to the anticipated extent and duration of soil disturbance. Application of several key principles will help ensure healthy, resilient soils: (1) minimize physical disturbance using guidelines tailored to specific soil types...

  20. Matrix matters: differences of grand skink metapopulation parameters in native tussock grasslands and exotic pasture grasslands.

    Directory of Open Access Journals (Sweden)

    Konstanze Gebauer

    Full Text Available Modelling metapopulation dynamics is a potentially very powerful tool for conservation biologists. In recent years, scientists have broadened the range of variables incorporated into metapopulation modelling from using almost exclusively habitat patch size and isolation, to the inclusion of attributes of the matrix and habitat patch quality. We investigated the influence of habitat patch and matrix characteristics on the metapopulation parameters of a highly endangered lizard species, the New Zealand endemic grand skink (Oligosoma grande taking into account incomplete detectability. The predictive ability of the developed zxmetapopulation model was assessed through cross-validation of the data and with an independent data-set. Grand skinks occur on scattered rock-outcrops surrounded by indigenous tussock (bunch and pasture grasslands therefore implying a metapopulation structure. We found that the type of matrix surrounding the habitat patch was equally as important as the size of habitat patch for estimating occupancy, colonisation and extinction probabilities. Additionally, the type of matrix was more important than the physical distance between habitat patches for colonisation probabilities. Detection probability differed between habitat patches in the two matrix types and between habitat patches with different attributes such as habitat patch composition and abundance of vegetation on the outcrop. The developed metapopulation models can now be used for management decisions on area protection, monitoring, and the selection of translocation sites for the grand skink. Our study showed that it is important to incorporate not only habitat patch size and distance between habitat patches, but also those matrix type and habitat patch attributes which are vital in the ecology of the target species.

  1. Matrix matters: differences of grand skink metapopulation parameters in native tussock grasslands and exotic pasture grasslands.

    Science.gov (United States)

    Gebauer, Konstanze; Dickinson, Katharine J M; Whigham, Peter A; Seddon, Philip J

    2013-01-01

    Modelling metapopulation dynamics is a potentially very powerful tool for conservation biologists. In recent years, scientists have broadened the range of variables incorporated into metapopulation modelling from using almost exclusively habitat patch size and isolation, to the inclusion of attributes of the matrix and habitat patch quality. We investigated the influence of habitat patch and matrix characteristics on the metapopulation parameters of a highly endangered lizard species, the New Zealand endemic grand skink (Oligosoma grande) taking into account incomplete detectability. The predictive ability of the developed zxmetapopulation model was assessed through cross-validation of the data and with an independent data-set. Grand skinks occur on scattered rock-outcrops surrounded by indigenous tussock (bunch) and pasture grasslands therefore implying a metapopulation structure. We found that the type of matrix surrounding the habitat patch was equally as important as the size of habitat patch for estimating occupancy, colonisation and extinction probabilities. Additionally, the type of matrix was more important than the physical distance between habitat patches for colonisation probabilities. Detection probability differed between habitat patches in the two matrix types and between habitat patches with different attributes such as habitat patch composition and abundance of vegetation on the outcrop. The developed metapopulation models can now be used for management decisions on area protection, monitoring, and the selection of translocation sites for the grand skink. Our study showed that it is important to incorporate not only habitat patch size and distance between habitat patches, but also those matrix type and habitat patch attributes which are vital in the ecology of the target species.

  2. Potential methane reservoirs beneath Antarctica.

    Science.gov (United States)

    Wadham, J L; Arndt, S; Tulaczyk, S; Stibal, M; Tranter, M; Telling, J; Lis, G P; Lawson, E; Ridgwell, A; Dubnick, A; Sharp, M J; Anesio, A M; Butler, C E H

    2012-08-30

    Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick and an estimated 21,000 petagrams (1 Pg equals 10(15) g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage.

  3. Crustal structure beneath Eastern Greenland

    DEFF Research Database (Denmark)

    Reiche, Sönke; Thybo, H.; Kaip, G.

    2011-01-01

    is recorded by 350 Reftek Texan receivers for 10 equidistant shot points along the profile. We use forward ray tracing modelling to construct a two-dimensional velocity model from the observed travel times. These results show the first images of the subsurface velocity structure beneath the Greenland ice...... these mountain belts is needed for assessing the isostatic balance of the crust and to gain insight into possible links between crustal composition, rifting history and present-day topography of the North Atlantic Region. However, the acquisition of geophysical data onshore Greenland is logistically complicated...

  4. Effect of vegetation types on soil arbuscular mycorrhizal fungi and nitrogen-fixing bacterial communities in a karst region.

    Science.gov (United States)

    Liang, Yueming; Pan, Fujing; He, Xunyang; Chen, Xiangbi; Su, Yirong

    2016-09-01

    Arbuscular mycorrhizal (AM) fungi and nitrogen-fixing bacteria play important roles in plant growth and recovery in degraded ecosystems. The desertification in karst regions has become more severe in recent decades. Evaluation of the fungal and bacterial diversity of such regions during vegetation restoration is required for effective protection and restoration in these regions. Therefore, we analyzed relationships among AM fungi and nitrogen-fixing bacteria abundances, plant species diversity, and soil properties in four typical ecosystems of vegetation restoration (tussock (TK), shrub (SB), secondary forest (SF), and primary forest (PF)) in a karst region of southwest China. Abundance of AM fungi and nitrogen-fixing bacteria, plant species diversity, and soil nutrient levels increased from the tussock to the primary forest. The AM fungus, nitrogen-fixing bacterium, and plant community composition differed significantly between vegetation types (p fungi and nitrogen-fixing bacteria, respectively. Available phosphorus, total nitrogen, and soil organic carbon levels and plant richness were positively correlated with the abundance of AM fungi and nitrogen-fixing bacteria (p fungi and nitrogen-fixing bacteria increased from the tussock to the primary forest and highlight the essentiality of these communities for vegetation restoration.

  5. Bacterial community structure and soil properties of a subarctic tundra soil in Council, Alaska.

    Science.gov (United States)

    Kim, Hye Min; Jung, Ji Young; Yergeau, Etienne; Hwang, Chung Yeon; Hinzman, Larry; Nam, Sungjin; Hong, Soon Gyu; Kim, Ok-Sun; Chun, Jongsik; Lee, Yoo Kyung

    2014-08-01

    The subarctic region is highly responsive and vulnerable to climate change. Understanding the structure of subarctic soil microbial communities is essential for predicting the response of the subarctic soil environment to climate change. To determine the composition of the bacterial community and its relationship with soil properties, we investigated the bacterial community structure and properties of surface soil from the moist acidic tussock tundra in Council, Alaska. We collected 70 soil samples with 25-m intervals between sampling points from 0-10 cm to 10-20 cm depths. The bacterial community was analyzed by pyrosequencing of 16S rRNA genes, and the following soil properties were analyzed: soil moisture content (MC), pH, total carbon (TC), total nitrogen (TN), and inorganic nitrogen (NH4+ and NO3-). The community compositions of the two different depths showed that Alphaproteobacteria decreased with soil depth. Among the soil properties measured, soil pH was the most significant factor correlating with bacterial community in both upper and lower-layer soils. Bacterial community similarity based on jackknifed unweighted unifrac distance showed greater similarity across horizontal layers than through the vertical depth. This study showed that soil depth and pH were the most important soil properties determining bacterial community structure of the subarctic tundra soil in Council, Alaska.

  6. Improved quality of beneath-canopy grass in South African savannas: Local and seasonal variation

    NARCIS (Netherlands)

    Treydte, A.C.; Looringh van Beeck, F.A.; Ludwig, F.; Heitkonig, I.M.A.

    2008-01-01

    Questions: Do large trees improve the nutrient content and the structure of the grass layer in savannas? Does the magnitude of this improvement differ with locality ( soil nutrients) and season ( water availability)? Are grass structure and species composition beneath tree canopies influenced by

  7. Arctic Tundra Soils: A Microbial Feast That Shrubs Will Cease

    Science.gov (United States)

    Machmuller, M.; Calderon, F.; Cotrufo, M. F.; Lynch, L.; Paul, E. A.; Wallenstein, M. D.

    2016-12-01

    Rapid climate warming may already be driving rapid decomposition of the vast stocks of carbon in Arctic tundra soils. However, stimulated decomposition may also release nitrogen and support increased plant productivity, potentially counteracting soil carbon losses. At the same time, these two processes interact, with plant derived carbon potentially fueling soil microbes to attack soil organic matter (SOM) to acquire nitrogen- a process known as priming. Thus, differences in the physiology, stoichiometry and microbial interactions among plant species could affect climate-carbon feedbacks. To reconcile these interactive mechanisms, we examined how vegetation type (Betula nana and Eriophorum vaginatum) and fertilization (short-term and long-term) influenced the decomposition of native SOM after labile carbon and nutrient addition. We hypothesized that labile carbon inputs would stimulate the loss of native SOM, but the magnitude of this effect would be indirectly related to soil nitrogen concentrations (e.g. SOM priming would be highest in N-limited soils). We added isotopically enriched (13C) glucose and ammonium nitrate to soils under shrub (B. nana) and tussock (E. vaginatum) vegetation. We found that nitrogen additions stimulated priming only in tussock soils, characterized by lower nutrient concentrations and microbial biomass (ppriming in soils that had been fertilized for >20yrs. Rather, we found that long-term fertilization shifted SOM chemistry towards a greater abundance of recalcitrant SOM, lower microbial biomass, and decreased SOM respiration (ppriming is dependent on vegetation and soil nitrogen concentrations, but this effect may not persist if shrubs increase in abundance under climate warming. Therefore, including nitrogen as a control on SOM decomposition and priming is critical to accurately model the effects of climate change on arctic carbon storage.

  8. The frontier beneath our feet

    Science.gov (United States)

    Grant, Gordon E.; Dietrich, William E.

    2017-04-01

    Following the simple question as to where water goes when it rains leads to one of the most exciting frontiers in earth science: the critical zone—Earth's dynamic skin. The critical zone extends from the top of the vegetation canopy through the soil and down to fresh bedrock and the bottom of the groundwater. Only recently recognized as a distinct zone, it is challenging to study because it is hard to observe directly, and varies widely across biogeoclimatic regions. Yet new ideas, instruments, and observations are revealing surprising and sometimes paradoxical insights, underscoring the value of field campaigns and long-term observatories. These insights bear directly on some of the most pressing societal problems today: maintaining healthy forests, sustaining streamflow during droughts, and restoring productive terrestrial and aquatic ecosystems. The critical zone is critical because it supports all terrestrial life; it is the nexus where water and carbon is cycled, vegetation (hence food) grows, soil develops, landscapes evolve, and we live. No other frontier is so close to home.

  9. Soil mineral N dynamics beneath mixtures of leaves from legume and fruit trees in Central Amazonian multi-strata agroforests Dinâmica do nitrogênio mineral no solo em misturas de folhas de leguminosas arbóreas e de fruteiras em sistemas agroflorestais multiestratificados na Amazônia Central

    Directory of Open Access Journals (Sweden)

    Carol Melanie Schwendener

    2007-01-01

    Full Text Available Long term applications of leguminous green mulch could increase mineralizable nitrogen (N beneath cupuaçu trees produced on the infertile acidic Ultisols and Oxisols of the Amazon Basin. However, low quality standing cupuaçu litter could interfere with green mulch N release and soil N mineralization. This study compared mineral N, total N, and microbial biomass N beneath cupuaçu trees grown in two different agroforestry systems, north of Manaus, Brazil, following seven years of different green mulch application rates. To test for net interactions between green mulch and cupuaçu litter, dried gliricidia and inga leaves were mixed with senescent cupuaçu leaves, surface applied to an Oxisol soil, and incubated in a greenhouse for 162 days. Leaf decomposition, N release and soil N mineralization were periodically measured in the mixed species litter treatments and compared to single species applications. The effect of legume biomass and cupuaçu litter on soil mineral N was additive implying that recommendations for green mulch applications to cupuaçu trees can be based on N dynamics of individual green mulch species. Results demonstrated that residue quality, not quantity, was the dominant factor affecting the rate of N release from leaves and soil N mineralization in a controlled environment. In the field, complex N cycling and other factors, including soil fauna, roots, and microclimatic effects, had a stronger influence on available soil N than residue quality.Aplicações a longo prazo de leguminosas como adubo verde podem aumentar o nitrogênio (N mineralizável sob árvores de cupuaçu em solos pouco férteis e ácidos (Ultisols e Oxisols da Bacia Amazônica. Entretanto, a baixa qualidade da liteira de cupuaçu pode influênciara liberação de N do adubo verde e a mineralização deste no solo. Neste estudo foram comparados o N mineral, N total, e o N da biomassa microbiana sob árvores de cupuaçu cultivadas em dois sistemas

  10. Female-specific wing degeneration caused by ecdysteroid in the Tussock Moth, Orgyia recens: Hormonal and developmental regulation of sexual dimorphism

    Directory of Open Access Journals (Sweden)

    Saori Lobbia

    2003-04-01

    Full Text Available Females of the tussock moth Orgyia recens have vestigial wings, whereas the males have normal wings. During early pupal development, female wings degenerate drastically compared with those of males. To examine whether ecdysteroid is involved in this sex-specific wing development, we cultured pupal wings just after pupation with ecdysteroid (20-hydroxyecdysone, 20E. In the presence of 20E, the female wings degenerated to about one-fifth their original size. In contrast, the male wings cultured with 20E showed only peripheral degeneration just outside the bordering lacuna, as in other butterflies and moths. TUNEL analysis showed that apoptotic signals were induced by 20E over the entire region of female wings, but only in the peripheral region of male wings. Semi-thin sections of the wings cultured with ecdysteroid showed that phagocytotic hemocytes were observed abundantly throughout the female wings, but in only peripheral regions of male wings. These observations indicate that both apoptotic events and phagocytotic activation are triggered by ecdysteroid, in sex-specific and region-specific manners.

  11. Imaging of subducted lithosphere beneath South America

    NARCIS (Netherlands)

    Engdahl, E.R.; Hilst, R.D. van der; Berrocal, J.

    1995-01-01

    Tomographic images are produced for the deep structure of the Andean subduction zone beneath western South America. The data used in the imaging are the delay times of P, pP and pwP phases from relocated teleseismic earthquakes in the region. Regionally, structural features larger than about 150 km

  12. Toxicity of Inorganic Mercury to Native Australian Grass Grown in Three Different Soils.

    Science.gov (United States)

    Mahbub, Khandaker Rayhan; Kader, Mohammed; Krishnan, Kannan; Labbate, Maurizio; Naidu, Ravi; Megharaj, Mallavarapu

    2017-06-01

    In this study, three native Australian grasses namely Iseilema membranaceum (Barcoo), Dichanthium sericeum (Queensland Blue) and Sporobolus africanus (Tussock) were grown in three different soils spiked with different concentrations of inorganic mercury and the root elongation was monitored up to 28 days following the germination. Results showed that mercury at certain concentrations significantly inhibited the root growth of all three tested native grasses grown in three soils, however, the toxicity was less in the soil with high organic carbon content and acidic pH. The calculated EC50 values ranged from 10 to 224 mg/kg total Hg in soil. However, the EC10 values indicated that existing guideline values for mercury may be of protective to the native Australian vegetation. Considering their tolerance to soil mercury, these grass species have the potential for their use in rehabilitation of mercury contaminated sites.

  13. The Ocean Boundary Layer beneath Hurricane Frances

    Science.gov (United States)

    Dasaro, E. A.; Sanford, T. B.; Terrill, E.; Price, J.

    2006-12-01

    The upper ocean beneath the peak winds of Hurricane Frances (57 m/s) was measured using several varieties of air-deployed floats as part of CBLAST. A multilayer structure was observed as the boundary layer deepened from 20m to 120m in about 12 hours. Bubbles generated by breaking waves create a 10m thick surface layer with a density anomaly, due to the bubbles, of about 1 kg/m3. This acts to lubricate the near surface layer. A turbulent boundary layer extends beneath this to about 40 m depth. This is characterized by large turbulent eddies spanning the boundary layer. A stratified boundary layer grows beneath this reaching 120m depth. This is characterized by a gradient Richardson number of 1/4, which is maintained by strong inertial currents generated by the hurricane, and smaller turbulent eddies driven by the shear instead of the wind and waves. There is little evidence of mixing beneath this layer. Heat budgets reveal the boundary layer to be nearly one dimensional through much of the deepening, with horizontal and vertical heat advection becoming important only after the storm had passed. Turbulent kinetic energy measurements support the idea of reduced surface drag at high wind speeds. The PWP model correctly predicts the degree of mixed layer deepening if the surface drag is reduced at high wind speed. Overall, the greatest uncertainty in understanding the ocean boundary layer at these extreme wind speeds is a characterization of the near- surface processes which govern the air-sea fluxes and surface wave properties.

  14. Analysis of groundwater flow beneath ice sheets

    Energy Technology Data Exchange (ETDEWEB)

    Boulton, G. S.; Zatsepin, S.; Maillot, B. [Univ. of Edinburgh (United Kingdom). Dept. of Geology and Geophysics

    2001-03-01

    The large-scale pattern of subglacial groundwater flow beneath European ice sheets was analysed in a previous report. It was based on a two-dimensional flowline model. In this report, the analysis is extended to three dimensions by exploring the interactions between groundwater and tunnel flow. A theory is developed which suggests that the large-scale geometry of the hydraulic system beneath an ice sheet is a coupled, self-organising system. In this system the pressure distribution along tunnels is a function of discharge derived from basal meltwater delivered to tunnels by groundwater flow, and the pressure along tunnels itself sets the base pressure which determines the geometry of catchments and flow towards the tunnel. The large-scale geometry of tunnel distribution is a product of the pattern of basal meltwater production and the transmissive properties of the bed. The tunnel discharge from the ice margin of the glacier, its seasonal fluctuation and the sedimentary characteristics of eskers are largely determined by the discharge of surface meltwater which penetrates to the bed in the terminal zone. The theory explains many of the characteristics of esker systems and can account for tunnel valleys. It is concluded that the large-scale hydraulic regime beneath ice sheets is largely a consequence of groundwater/tunnel flow interactions and that it is essential similar to non-glacial hydraulic regimes. Experimental data from an Icelandic glacier, which demonstrates measured relationships between subglacial tunnel flow and groundwater flow during the transition from summer to winter seasons for a modern glacier, and which support the general conclusions of the theory is summarised in an appendix.

  15. Imaging magma plumbing beneath Askja volcano, Iceland

    Science.gov (United States)

    Greenfield, Tim; White, Robert S.

    2015-04-01

    Volcanoes during repose periods are not commonly monitored by dense instrumentation networks and so activity during periods of unrest is difficult to put in context. We have operated a dense seismic network of 3-component, broadband instruments around Askja, a large central volcano in the Northern Volcanic Zone, Iceland, since 2006. Askja last erupted in 1961, with a relatively small basaltic lava flow. Since 1975 the central caldera has been subsiding and there has been no indication of volcanic activity. Despite this, Askja has been one of the more seismically active volcanoes in Iceland. The majority of these events are due to an extensive geothermal area within the caldera and tectonically induced earthquakes to the northeast which are not related to the magma plumbing system. More intriguing are the less numerous deeper earthquakes at 12-24km depth, situated in three distinct areas within the volcanic system. These earthquakes often show a frequency content which is lower than the shallower activity, but they still show strong P and S wave arrivals indicative of brittle failure, despite their location being well below the brittle-ductile boundary, which, in Askja is ~7km bsl. These earthquakes indicate the presence of melt moving or degassing at depth while the volcano is not inflating, as only high strain rates or increased pore fluid pressures would cause brittle fracture in what is normally an aseismic region in the ductile zone. The lower frequency content must be the result of a slower source time function as earthquakes which are both high frequency and low frequency come from the same cluster, thereby discounting a highly attenuating lower crust. To image the plumbing system beneath Askja, local and regional earthquakes have been used as sources to solve for the velocity structure beneath the volcano. Travel-time tables were created using a finite difference technique and the residuals were used to solve simultaneously for both the earthquake locations

  16. Active convection beneath ridges: a new spin

    Science.gov (United States)

    Katz, R. F.

    2009-12-01

    The role of buoyancy-driven, "active" upwelling beneath mid-ocean ridges has been long debated [1,2,3], with the naysayers holding sway in recent years. Recent work on tomographic imaging of the sub-ridge mantle has revealed patterns in velocity variation that seem inconsistent with what we expect of passive upwelling and melting [4]. The irregular distribution, asymmetry, and off-axis locations of slow regions in tomographic results are suggestive of time-dependent convective flow. Using 2D numerical simulations of internally consistent mantle and magmatic flow plus melting/freezing [5,6], I investigate the parametric subspace in which active convection is expected to occur. For low mantle viscosities, interesting symmetry-breaking behavior is predicted. References: [1] Rabinowicz, et al., EPSL, 1984; [2] Buck & Su, GRL, 1989; [3] Scott & Stevenson, JGR, 1989; [4] Toomey et al., Nature, 2007; [5] McKenzie, J.Pet., 1984; [6] Katz, J.Pet., 2008;

  17. Community structure analysis of soil ammonia oxidizers during vegetation restoration in southwest China.

    Science.gov (United States)

    Liang, Yueming; He, Xunyang; Liang, Shichu; Zhang, Wei; Chen, Xiangbi; Feng, Shuzheng; Su, Yirong

    2014-03-01

    Soil ammonia oxidizers play a critical role in nitrogen cycling and ecological restoration. The composition and structure of soil ammonia oxidizers and their impacting factors were studied in four typical ecosystem soils, tussock (T), shrub (S), secondary forest (SF), and primary forest (PF), during vegetation restoration in the Karst region of Southwest China. The composition and structure of the ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) communities were characterized by sequencing the amoA and arch-amoA genes, respectively. The diversity of soil ammonia oxidizers (except in S) and plant Shannon diversity index gradually increased with vegetation restoration, and the ammonia oxidizer communities differed significantly (p soils. AOB Nitrosospira cluster 3b only appeared in PF and SF soils, while Nitrosospira cluster 3a species were found in all soils. Changes in AOB paralleled the changes in soil ammonium content that occurred with vegetation restoration. Redundancy analysis showed that the distribution of dominant AOB species was linked to pH, soil urease activity, and soil C/N ratio, whereas the distribution of dominant AOA species was mainly influenced by litter nitrogen content and C/N ratio. These results suggested that the composition and structure of the AOB community were more sensitive to changes in vegetation and soil ammonium content, and may be an important indicator of nitrogen availability in Karst ecosystem soils.

  18. Monitoring larval populations of the douglas-fir tussock moth and the western spruce budworm on permanent plots: Sampling methods and statistical properties of data. Forest Service general technical report

    Energy Technology Data Exchange (ETDEWEB)

    Mason, R.R.; Paul, H.G.

    1994-05-01

    Procedures for monitoring Larval populations of the Douglas-fir tussock moth and the western spruce budworm are recommended based on many years experience of sample these species in eastern Oregon and Washington. It is shown that statistically reliable estimates of larval density can be made for a population by sampling host trees in a series of permanent plots in a geographical monitoring unit. The most practical method is to estimate densities of both insect species simultaneously on a plot by the nondestructive sampling of foliage on lower crown branches of host trees. For best results, sampling methods need to be consistent with monitoring done annually to accumulate continuous databases that reflect the behavior of defoliator populations over a long period of time.

  19. Subduction or delamination beneath the Apennines? Evidence from regional tomography

    NARCIS (Netherlands)

    Koulakov, I.; Jakovlev, A.; Zabelina, I.; Roure, F.; Cloetingh, S.; El Khrepy, S.; Al-Arifi, N.

    2015-01-01

    In this study we present a new regional tomography model of the upper mantle beneath Italy and the surrounding area derived from the inversion of travel times of P and S waves from the updated International Seismological Centre (ISC) catalogue. Beneath Italy, we identify a high-velocity anomaly whic

  20. Soil Moisture Spatial Patterns in a Uniform Paulownia Tree Stand

    Science.gov (United States)

    Soil moisture spatial patterns have been studied at length in agricultural fields and pasture/rangelands as part of the USDA soil moisture satellite validation program, but recent research has begun to address the distribution of soil beneath a forest canopy. Forests cover a significant portion of ...

  1. Turbulence beneath finite amplitude water waves

    Energy Technology Data Exchange (ETDEWEB)

    Beya, J.F. [Universidad de Valparaiso, Escuela de Ingenieria Civil Oceanica, Facultad de Ingenieria, Valparaiso (Chile); The University of New South Wales, Water Research Laboratory, School of Civil and Environmental Engineering, Sydney, NSW (Australia); Peirson, W.L. [The University of New South Wales, Water Research Laboratory, School of Civil and Environmental Engineering, Sydney, NSW (Australia); Banner, M.L. [The University of New South Wales, School of Mathematics and Statistics, Sydney, NSW (Australia)

    2012-05-15

    Babanin and Haus (J Phys Oceanogr 39:2675-2679, 2009) recently presented evidence of near-surface turbulence generated below steep non-breaking deep-water waves. They proposed a threshold wave parameter a {sup 2}{omega}/{nu} = 3,000 for the spontaneous occurrence of turbulence beneath surface waves. This is in contrast to conventional understanding that irrotational wave theories provide a good approximation of non-wind-forced wave behaviour as validated by classical experiments. Many laboratory wave experiments were carried out in the early 1960s (e.g. Wiegel 1964). In those experiments, no evidence of turbulence was reported, and steep waves behaved as predicted by the high-order irrotational wave theories within the accuracy of the theories and experimental techniques at the time. This contribution describes flow visualisation experiments for steep non-breaking waves using conventional dye techniques in the wave boundary layer extending above the wave trough level. The measurements showed no evidence of turbulent mixing up to a value of a {sup 2}{omega}/{nu} = 7,000 at which breaking commenced in these experiments. These present findings are in accord with the conventional understandings of wave behaviour. (orig.)

  2. Channelization of plumes beneath ice shelves

    KAUST Repository

    Dallaston, M. C.

    2015-11-11

    © 2015 Cambridge University Press. We study a simplified model of ice-ocean interaction beneath a floating ice shelf, and investigate the possibility for channels to form in the ice shelf base due to spatial variations in conditions at the grounding line. The model combines an extensional thin-film description of viscous ice flow in the shelf, with melting at its base driven by a turbulent ocean plume. Small transverse perturbations to the one-dimensional steady state are considered, driven either by ice thickness or subglacial discharge variations across the grounding line. Either forcing leads to the growth of channels downstream, with melting driven by locally enhanced ocean velocities, and thus heat transfer. Narrow channels are smoothed out due to turbulent mixing in the ocean plume, leading to a preferred wavelength for channel growth. In the absence of perturbations at the grounding line, linear stability analysis suggests that the one-dimensional state is stable to initial perturbations, chiefly due to the background ice advection.

  3. [Guided bone regeneration beneath titanium foils].

    Science.gov (United States)

    Otto, Katharina; Schopper, Christian; Ewers, Rolf; Lambrecht, J Thomas

    2004-01-01

    The aim of this study was to examine the clinical and histological bony healing process beneath titanium foils used for guided tissue regeneration as well as of the Frios Algipore graft which was applied with autologous bone. 66 sinus floor elevations were carried out and examined over a period of three years and eight months. A success rate of 64% was recorded with foil incorporation. Complications occurred in form of primary and secondary disturbances in the healing process caused by exposure of the foil. 12 of the 66 foils had to be removed early. In all but one case, the augmented bone material was macroscopically well integrated despite the loss of the foil. Primary stability of the inserted dental implants into the ossified augmented site after operations of the sinus maxillaris was reached in all cases with absence of post-operative complications, and in 94% when there was postoperative exposure of the membrane. Histologically, a thin layer of connective tissue poor in cells but rich in collagen fibers appeared underneath the titanium foil. This was followed by newly-formed bony tissue transforming into osseous lamella parallel to the membrane underneath the new periost. In 65 out of 66 cases a sufficient amount of stable bone was built up locally suggesting good bio-compatibility and barrier function. Further, the foil also provided mechanical rest and supporting function for the space underneath. However, the occurrence of healing complications in 36% of the cases showed a need to improve on the titanium foils.

  4. Simulation of Snow Processes Beneath a Boreal Scots Pine Canopy

    Institute of Scientific and Technical Information of China (English)

    LI Weiping; LUO Yong; XIA Kun; LIU Xin

    2008-01-01

    A physically-based multi-layer snow model Snow-Atmosphere-Soil-Transfer scheme (SAST) and a land surface model Biosphere-Atmosphere Transfer Scheme (BATS) were employed to investigate how boreal forests influence snow accumulation and ablation under the canopy. Mass balance and energetics of snow beneath a Scots pine canopy in Finland at different stages of the 2003-2004 and 2004-2005 snow seasons are analyzed. For the fairly dense Scots pine forest, drop-off of the canopy-intercepted snow contributes, in some cases, twice as much to the underlying snowpack as the direct throughfall of snow. During early winter snow melting, downward turbulent sensible and condensation heat fluxes play a dominant role together with downward net longwave radiation. In the final stage of snow ablation in middle spring, downward net all-wave radiation dominates the snow melting. Although the downward sensible heat flux is comparable to the net solar radiation during this period, evaporative cooling of the melting snow surface makes the turbulent heat flux weaker than net radiation. Sensitivities of snow processes to leaf area index (LAI) indicate that a denser canopy speeds up early winter snowmelt, but also suppresses melting later in the snow season. Higher LAI increases the interception of snowfall, therefore reduces snow accumulation under the canopy during the snow season; this effect and the enhancement of downward longwave radiation by denser foliage outweighs the increased attenuation of solar radiation, resulting in earlier snow ablation under a denser canopy. The difference in sensitivities to LAI in two snow seasons implies that the impact of canopy density on the underlying snowpack is modulated by interannual variations of climate regimes.

  5. Study of evapotranspiration and evaporation beneath the canopy in a buckwheat field

    Science.gov (United States)

    Yan, Haofang; Zhang, Chuan; Oue, Hiroki; Wang, Guoqing; He, Bin

    2015-11-01

    The determination of evaporation and transpiration separately is very important in improving water use efficiency and developing exact irrigation scheduling. Hourly crop evapotranspiration ( ET c) and soil evaporation ( E g) beneath the buckwheat canopy were measured using Bowen ratio energy balance method and micro-lysimeters, respectively. The total ET c and E g in the whole growth season of buckwheat were 187.4 and 72.1 mm, respectively. Crop coefficient of buckwheat plant was simulated by days after sowing (DAS) and leaf area index (LAI), the average values for four growth stages were 0.58, 0.59, 1.10, and 0.74; and soil evaporation coefficient (the ratio of soil evaporation to reference evapotranspiration) was modeled by soil water content at 5-cm depth by dividing the LAI into two stages. The relationship between the ratio of soil evaporation to actual evapotranspiration ( E g/ ET c) and LAI was decided. It was found that E g/ ET c decreased from 1 to 0.3 with the increase in LAI.

  6. Mantle Structure Beneath Central South America

    Science.gov (United States)

    Vandecar, J. C.; Silver, P. G.; James, D. E.; Assumpcao, M.; Schimmel, M.; Zandt, G.

    2003-12-01

    Making use of 60 digital broadband seismic stations that have operated across central South America in recent years, we have undertaken an inversion for the upper- and uppermost lower-mantle P- and S-wave velocity structures beneath the region. We have combined data from four portable PASSCAL-type experiments as well as the 3 GTSN permanent stations (LPAZ, BDFB and CPUP) and 1 Geoscope station (SPB) located in the region. The portable data were deployed at various times between 1992 and 1999 and include: 28 sites from the Brazilian Lithosphere Seismic Project (BLSP: Carnegie Institution of Washington and Universidade de Sao Paulo), 16 sites from the Broadband ANdean JOint experiment (BANJO: Carnegie Institution of Washington and University of Arizona), 8 sites from the Seismic Exploration of the Deep Altiplano project (SEDA: Lawrence Livermore National Laboratory) and 4 sites from the University of Brasilia. The P- and S-wave relative delay times are independently obtained via a multi-channel cross correlation of band-passed waveforms for each teleseismic event. These data are then inverted using an iterative, robust, non-linear scheme which parameterizes the 3-D velocity variations as splines under tension constrained at over 120,000 nodes across South America between latitudes of 15 and 30 degrees South. Amongst other features, we robustly image the high-velocity subducting Nazca plate penetrating into the lower mantle and the high-velocity root of the ~3.2 Gyr old Sao Francisco Craton extending to depths of 200-300 km. We will discuss the consistency between our tomographic models and predictions of dynamic mantle models based on plate tectonic reconstructions of subduction.

  7. Remote Oil Spill Detection and Monitoring Beneath Sea Ice

    Science.gov (United States)

    Polak, Adam; Marshall, Stephen; Ren, Jinchang; Hwang, Byongjun (Phil); Hagan, Bernard; Stothard, David J. M.

    2016-08-01

    The spillage of oil in Polar Regions is particularly serious due to the threat to the environment and the difficulties in detecting and tracking the full extent of the oil seepage beneath the sea ice. Development of fast and reliable sensing techniques is highly desirable. In this paper hyperspectral imaging combined with signal processing and classification techniques are proposed as a potential tool to detect the presence of oil beneath the sea ice. A small sample, lab based experiment, serving as a proof of concept, resulted in the successful identification of oil presence beneath the thin ice layer as opposed to the other sample with ice only. The paper demonstrates the results of this experiment that granted a financial support to execute full feasibility study of this technology for oil spill detection beneath the sea ice.

  8. Mantle structure beneath the western edge of the Colorado Plateau

    Science.gov (United States)

    Sine, C.R.; Wilson, D.; Gao, W.; Grand, S.P.; Aster, R.; Ni, J.; Baldridge, W.S.

    2008-01-01

    Teleseismic traveltime data are inverted for mantle Vp and Vs variations beneath a 1400 km long line of broadband seismometers extending from eastern New Mexico to western Utah. The model spans 600 km beneath the moho with resolution of ???50 km. Inversions show a sharp, large-magnitude velocity contrast across the Colorado Plateau-Great Basin transition extending ???200 km below the crust. Also imaged is a fast anomaly 300 to 600 km beneath the NW portion of the array. Very slow velocities beneath the Great Basin imply partial melting and/or anomalously wet mantle. We propose that the sharp contrast in mantle velocities across the western edge of the Plateau corresponds to differential lithospheric modification, during and following Farallon subduction, across a boundary defining the western extent of unmodified Proterozoic mantle lithosphere. The deep fast anomaly corresponds to thickened Farallon plate or detached continental lithosphere at transition zone depths. Copyright 2008 by the American Geophysical Union.

  9. Geometric and oceanographic controls on melting beneath Pine Island Glacier

    National Research Council Canada - National Science Library

    De Rydt, J; Holland, P. R; Dutrieux, P; Jenkins, A

    2014-01-01

    .... As a result, a large ocean cavity has formed behind the ridge, strongly controlling the ocean circulation beneath the ice shelf and modulating the ocean water properties that cause ice melting...

  10. Foundering lithosphere imaged beneath the southern Sierra Nevada, California, USA.

    Science.gov (United States)

    Boyd, Oliver S; Jones, Craig H; Sheehan, Anne F

    2004-07-30

    Seismic tomography reveals garnet-rich crust and mantle lithosphere descending into the upper mantle beneath the southeastern Sierra Nevada. The descending lithosphere consists of two layers: an iron-rich eclogite above a magnesium-rich garnet peridotite. These results place descending eclogite above and east of high P wave speed material previously imaged beneath the southern Great Valley, suggesting a previously unsuspected coherence in the lithospheric removal process.

  11. Fate and Transport of 17β-estradiol Beneath Animal Waste Holding Ponds

    Science.gov (United States)

    Gibson, L. A.; Tyner, J. S.; Hawkins, S. A.; Lee, J.; Buchanan, J. R.

    2011-12-01

    Steroidal hormones, such as 17β-estradiol (E2), are prevalent in animal waste and are a common subject of study due to potential stream and groundwater contamination. These particular hormones are labeled as Endocrine Disrupting Chemicals (EDCs) because of their developmental effects in reptiles and amphibians. Dairy waste at concentrated animal feeding operations is typically stored in a pond that is regulated by law to include an underlying soil liner with a minimal hydraulic conductivity to limit leaching beneath the pond, yet some studies have traced stream and groundwater contamination to these ponds. Previous studies have shown that the soil underlying earthen ponds are always unsaturated. This increases the pore water velocity relative to a given flux, which itself is dictated almost entirely by an organic seal that forms at the bottom of a waste pond. This increased velocity results in more rapid transport and less retention time within the vadose zone where E2 could biodegrade into its daughter product, estrone (E1). And since the soil is unsaturated and therefore has a negative pressure, preferential flow should not serve as a method of transport. On the contrary, E2 and E1 may sorb to mobile colloids increasing their mobility. This study will evaluate the use of biochar, an increasingly common activated carbon source, as a soil liner amendment. Biochar has a specific surface area that can exceed 1,500 m2/g and is high in organic matter, which E2 sorbs to strongly. The biochar amendment should be most effective and enduring as a layer located at the bottom of the soil liner so that the leachate has been treated by the soil prior to contact. Another proposed amendment technique is to uniformly mix the biochar within the soil liner to increase the leachate contact time with the biochar, but realistically could prove to be too costly and energy-intensive. Field and laboratory studies were conducted to analyze hormone persistence and transport processes and

  12. Major disruption of D'' beneath Alaska: D'' Beneath Alaska

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Daoyuan [Laboratory of Seismology and Physics of Earth' s Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei Anhui China; National Geophysics Observatory at Mengcheng, Anhui China; Helmberger, Don [Seismological Laboratory, California Institute of Technology, Caltech, Pasadena California USA; Miller, Meghan S. [Department of Earth Sciences, University of Southern California, Los Angeles California USA; Jackson, Jennifer M. [Seismological Laboratory, California Institute of Technology, Caltech, Pasadena California USA

    2016-05-01

    D'' represents one of the most dramatic thermal and compositional layers within our planet. In particular, global tomographic models display relatively fast patches at the base of the mantle along the circum-Pacific which are generally attributed to slab debris. Such distinct patches interact with the bridgmanite (Br) to post-bridgmanite (PBr) phase boundary to generate particularly strong heterogeneity at their edges. Most seismic observations for the D'' come from the lower mantle S wave triplication (Scd). Here we exploit the USArray waveform data to examine one of these sharp transitions in structure beneath Alaska. From west to east beneath Alaska, we observed three different characteristics in D'': (1) the western region with a strong Scd, requiring a sharp δVs = 2.5% increase; (2) the middle region with no clear Scd phases, indicating a lack of D'' (or thin Br-PBr layer); and (3) the eastern region with strong Scd phase, requiring a gradient increase in δVs. To explain such strong lateral variation in the velocity structure, chemical variations must be involved. We suggest that the western region represents relatively normal mantle. In contrast, the eastern region is influenced by a relic slab that has subducted down to the lowermost mantle. In the middle region, we infer an upwelling structure that disrupts the Br-PBr phase boundary. Such an interpretation is based upon a distinct pattern of travel time delays, waveform distortions, and amplitude patterns that reveal a circular-shaped anomaly about 5° across which can be modeled synthetically as a plume-like structure rising about 400 km high with a shear velocity reduction of ~5%, similar to geodynamic modeling predictions of upwellings.

  13. Mantle discontinuities beneath Izu-Bonin and the implications

    Institute of Scientific and Technical Information of China (English)

    臧绍先; 周元泽; 蒋志勇

    2003-01-01

    The SdP, pdP and sdP phases are picked up with the Nth root slant stack method from the digital waveform data recorded by the networks and arrays in USA, Germany and Switzerland for the earthquakes occurring beneath Izu-Bonin and Japan Sea. The mantle discontinuities and the effects of subducting slab on the 660 km and 410 km discontinuities are studied. It is found that there are mantle discontinuities existing at the depths of 170, 220, 300, 410, 660, 850 and 1150 km. Beneath Izu-Bonin, the 410 km discontinuity is elevated, while the 660 km discontinuity is depressed; for both discontinuities, there are regionalized differences. Beneath Japan Sea, however, there is no depth variation of the 410 km discontinuity, and the 660 km discontinuity is depressed without obvious effect of the subducting slab.

  14. Throughfall and its spatial variability beneath xerophytic shrub canopies within water-limited arid desert ecosystems

    Science.gov (United States)

    Zhang, Ya-feng; Wang, Xin-ping; Hu, Rui; Pan, Yan-xia

    2016-08-01

    Throughfall is known to be a critical component of the hydrological and biogeochemical cycles of forested ecosystems with inherently temporal and spatial variability. Yet little is understood concerning the throughfall variability of shrubs and the associated controlling factors in arid desert ecosystems. Here we systematically investigated the variability of throughfall of two morphological distinct xerophytic shrubs (Caragana korshinskii and Artemisia ordosica) within a re-vegetated arid desert ecosystem, and evaluated the effects of shrub structure and rainfall characteristics on throughfall based on heavily gauged throughfall measurements at the event scale. We found that morphological differences were not sufficient to generate significant difference (P decline with the increase in rainfall amount, intensity and duration, and stabilized passing a certain threshold. Our findings highlight the great variability of throughfall beneath the canopies of xerophytic shrubs and the time stability of throughfall pattern among rainfall events. The spatially heterogeneous and temporally stable throughfall is expected to generate a dynamic patchy distribution of soil moisture beneath shrub canopies within arid desert ecosystems.

  15. Seismic imaging of the downwelling Indian lithosphere beneath central Tibet.

    Science.gov (United States)

    Tilmann, Frederik; Ni, James

    2003-05-30

    A tomographic image of the upper mantle beneath central Tibet from INDEPTH data has revealed a subvertical high-velocity zone from approximately 100- to approximately 400-kilometers depth, located approximately south of the Bangong-Nujiang Suture. We interpret this zone to be downwelling Indian mantle lithosphere. This additional lithosphere would account for the total amount of shortening in the Himalayas and Tibet. A consequence of this downwelling would be a deficit of asthenosphere, which should be balanced by an upwelling counterflow, and thus could explain the presence of warm mantle beneath north-central Tibet.

  16. Nitrate in aquifers beneath agricultural systems.

    Science.gov (United States)

    Burkart, M R; Stoner, J D

    2007-01-01

    Research from several regions of the world provides spatially anecdotal evidence to hypothesize which hydrologic and agricultural factors contribute to groundwater vulnerability to nitrate contamination. Analysis of nationally consistent measurements from the U.S. Geological Survey's NAWQA program confirms these hypotheses for a substantial range of agricultural systems. Shallow unconfined aquifers are most susceptible to nitrate contamination associated with agricultural systems. Alluvial and other unconsolidated aquifers are the most vulnerable and also shallow carbonate aquifers that provide a substantial but smaller contamination risk. Where any of these aquifers are overlain by permeable soils the risk of contamination is larger. Irrigated systems can compound this vulnerability by increasing leaching facilitated by additional recharge and additional nutrient applications. The system of corn, soybean, and hogs produced significantly larger concentrations of groundwater nitrate than all other agricultural systems because this system imports the largest amount of N-fertilizer per unit production area. Mean nitrate under dairy, poultry, horticulture, and cattle and grains systems were similar. If trends in the relation between increased fertilizer use and groundwater nitrate in the United States are repeated in other regions of the world, Asia may experience increasing problems because of recent increases in fertilizer use. Groundwater monitoring in Western and Eastern Europe as well as Russia over the next decade may provide data to determine if the trend in increased nitrate contamination can be reversed. If the concentrated livestock trend in the United States is global, it may be accompanied by increasing nitrogen contamination in groundwater. Concentrated livestock provide both point sources in the confinement area and intense non-point sources as fields close to facilities are used for manure disposal. Regions where irrigated cropland is expanding, such as

  17. Soil data for a vegetation gradient located at Bonanza Creek Long Term Ecological Research Site, interior Alaska

    Science.gov (United States)

    Manies, Kristen L.; Harden, Jennifer W.; Fuller, Christopher C.; Xu, Xiaomei; McGeehin, John P.

    2016-07-28

    Boreal soils play an important role in the global carbon cycle owing to the large amount of carbon stored within this northern region. To understand how carbon and nitrogen storage varied among different ecosystems, a vegetation gradient was established in the Bonanza Creek Long Term Ecological Research (LTER) site, located in interior Alaska. The ecosystems represented are a black spruce (Picea mariana)–feather moss (for example, Hylocomium sp.) forest ecosystem, a shrub-dominated ecosystem, a tussock-grass-dominated ecosystem, a sedge-dominated ecosystem, and a rich fen ecosystem. Here, we report the physical, chemical, and descriptive properties for the soil cores collected at these sites. These data have been used to calculate carbon and nitrogen accumulation rates on a long-term (decadal and century) basis (Manies and others, in press).

  18. Homogenization of the soil surface following fire in semiarid grasslands

    Science.gov (United States)

    Carleton S. White

    2011-01-01

    Semiarid grasslands accumulate soil beneath plant "islands" that are raised above bare interspaces. This fine-scale variation in microtopographic relief is plant-induced and is increased with shrub establishment. Research found that fire-induced water repellency enhanced local-scale soil erosion that reduced variation in microtopographic relief, suggesting...

  19. Cyclic biogeochemical processes and nitrogen fate beneath a subtropical stormwater infiltration basin

    Science.gov (United States)

    O'Reilly, Andrew M.; Chang, Ni-Bin; Wanielista, Martin P.

    2012-01-01

    A stormwater infiltration basin in north–central Florida, USA, was monitored from 2007 through 2008 to identify subsurface biogeochemical processes, with emphasis on N cycling, under the highly variable hydrologic conditions common in humid, subtropical climates. Cyclic variations in biogeochemical processes generally coincided with wet and dry hydrologic conditions. Oxidizing conditions in the subsurface persisted for about one month or less at the beginning of wet periods with dissolved O2 and NO3- showing similar temporal patterns. Reducing conditions in the subsurface evolved during prolonged flooding of the basin. At about the same time O2 and NO3- reduction concluded, Mn, Fe and SO42- reduction began, with the onset of methanogenesis one month later. Reducing conditions persisted up to six months, continuing into subsequent dry periods until the next major oxidizing infiltration event. Evidence of denitrification in shallow groundwater at the site is supported by median NO3-–N less than 0.016 mg L-1, excess N2 up to 3 mg L-1 progressively enriched in δ15N during prolonged basin flooding, and isotopically heavy δ15N and δ18O of NO3- (up to 25‰ and 15‰, respectively). Isotopic enrichment of newly infiltrated stormwater suggests denitrification was partially completed within two days. Soil and water chemistry data suggest that a biogeochemically active zone exists in the upper 1.4 m of soil, where organic carbon was the likely electron donor supplied by organic matter in soil solids or dissolved in infiltrating stormwater. The cyclic nature of reducing conditions effectively controlled the N cycle, switching N fate beneath the basin from NO3- leaching to reduction in the shallow saturated zone. Results can inform design of functionalized soil amendments that could replace the native soil in a stormwater infiltration basin and mitigate potential NO3- leaching to groundwater by replicating the biogeochemical conditions under the observed basin.

  20. Subduction beneath Eurasia in connection with the Mesozoic Tethys

    NARCIS (Netherlands)

    Spakman, W.

    2007-01-01

    In this paper we present new results concerning the existence and subduction of Meso-Tethyan oceanic lithosphere in the upper mantle beneath Europe, the Mediterranean and the Middle-East. The results arise from a large scale body wave tomographic analysis of the upper mantle in this region. It is sh

  1. Deep long-period earthquakes beneath Washington and Oregon volcanoes

    Science.gov (United States)

    Nichols, M.L.; Malone, S.D.; Moran, S.C.; Thelen, W.A.; Vidale, J.E.

    2011-01-01

    Deep long-period (DLP) earthquakes are an enigmatic type of seismicity occurring near or beneath volcanoes. They are commonly associated with the presence of magma, and found in some cases to correlate with eruptive activity. To more thoroughly understand and characterize DLP occurrence near volcanoes in Washington and Oregon, we systematically searched the Pacific Northwest Seismic Network (PNSN) triggered earthquake catalog for DLPs occurring between 1980 (when PNSN began collecting digital data) and October 2009. Through our analysis we identified 60 DLPs beneath six Cascade volcanic centers. No DLPs were associated with volcanic activity, including the 1980-1986 and 2004-2008 eruptions at Mount St. Helens. More than half of the events occurred near Mount Baker, where the background flux of magmatic gases is greatest among Washington and Oregon volcanoes. The six volcanoes with DLPs (counts in parentheses) are Mount Baker (31), Glacier Peak (9), Mount Rainier (9), Mount St. Helens (9), Three Sisters (1), and Crater Lake (1). No DLPs were identified beneath Mount Adams, Mount Hood, Mount Jefferson, or Newberry Volcano, although (except at Hood) that may be due in part to poorer network coverage. In cases where the DLPs do not occur directly beneath the volcanic edifice, the locations coincide with large structural faults that extend into the deep crust. Our observations suggest the occurrence of DLPs in these areas could represent fluid and/or magma transport along pre-existing tectonic structures in the middle crust. ?? 2010 Elsevier B.V.

  2. Buckling instabilities of subducted lithosphere beneath the transition zone

    NARCIS (Netherlands)

    Ribe, N.M.; Stutzmann, E.; Ren, Y.; Hilst, R.D. van der

    2007-01-01

    A sheet of viscous fluid poured onto a surface buckles periodically to generate a pile of regular folds. Recent tomographic images beneath subduction zones, together with quantitative fluid mechanical scaling laws, suggest that a similar instability can occur when slabs of subducted oceanic

  3. Tree species effects on calcium cycling: The role of calcium uptake in deep soils

    NARCIS (Netherlands)

    Dijkstra, F.A.; Smits, M.M.

    2002-01-01

    Soil acidity and calcium (Ca) availability in the surface soil differ substantially beneath sugar maple (Acer saccharum) and eastern hemlock (Tsuga canadensis) trees in a mixed forest in northwestern Connecticut. We determined the effect of pumping of Ca from deep soil (rooting zone below 20-cm

  4. Modelling the Crust beneath the Kashmir valley in Northwestern Himalaya

    Science.gov (United States)

    Mir, R. R.; Parvez, I. A.; Gaur, V. K.; A.; Chandra, R.; Romshoo, S. A.

    2015-12-01

    We investigate the crustal structure beneath five broadband seismic stations in the NW-SE trendingoval shaped Kashmir valley sandwiched between the Zanskar and the Pir Panjal ranges of thenorthwestern Himalaya. Three of these sites were located along the southwestern edge of the valley andthe other two adjoined the southeastern. Receiver Functions (RFs) at these sites were calculated usingthe iterative time domain deconvolution method and jointly inverted with surface wave dispersiondata to estimate the shear wave velocity structure beneath each station. To further test the results ofinversion, we applied forward modelling by dividing the crust beneath each station into 4-6homogeneous, isotropic layers. Moho depths were separately calculated at different piercing pointsfrom the inversion of only a few stacked receiver functions of high quality around each piercing point.These uncertainties were further reduced to ±2 km by trial forward modelling as Moho depths werevaried over a range of ±6 km in steps of 2 km and the synthetic receiver functions matched with theinverted ones. The final values were also found to be close to those independently estimated using theH-K stacks. The Moho depths on the eastern edge of the valley and at piercing points in itssouthwestern half are close to 55 km, but increase to about 58 km on the eastern edge, suggesting thathere, as in the central and Nepal Himalaya, the Indian plate dips northeastwards beneath the Himalaya.We also calculated the Vp/Vs ratio beneath these 5 stations which were found to lie between 1.7 and1.76, yielding a Poisson's ratio of ~0.25 which is characteristic of a felsic composition.

  5. Crustal structure beneath northeast India inferred from receiver function modeling

    Science.gov (United States)

    Borah, Kajaljyoti; Bora, Dipok K.; Goyal, Ayush; Kumar, Raju

    2016-09-01

    We estimated crustal shear velocity structure beneath ten broadband seismic stations of northeast India, by using H-Vp/Vs stacking method and a non-linear direct search approach, Neighbourhood Algorithm (NA) technique followed by joint inversion of Rayleigh wave group velocity and receiver function, calculated from teleseismic earthquakes data. Results show significant variations of thickness, shear velocities (Vs) and Vp/Vs ratio in the crust of the study region. The inverted shear wave velocity models show crustal thickness variations of 32-36 km in Shillong Plateau (North), 36-40 in Assam Valley and ∼44 km in Lesser Himalaya (South). Average Vp/Vs ratio in Shillong Plateau is less (1.73-1.77) compared to Assam Valley and Lesser Himalaya (∼1.80). Average crustal shear velocity beneath the study region varies from 3.4 to 3.5 km/s. Sediment structure beneath Shillong Plateau and Assam Valley shows 1-2 km thick sediment layer with low Vs (2.5-2.9 km/s) and high Vp/Vs ratio (1.8-2.1), while it is observed to be of greater thickness (4 km) with similar Vs and high Vp/Vs (∼2.5) in RUP (Lesser Himalaya). Both Shillong Plateau and Assam Valley show thick upper and middle crust (10-20 km), and thin (4-9 km) lower crust. Average Vp/Vs ratio in Assam Valley and Shillong Plateau suggest that the crust is felsic-to-intermediate and intermediate-to-mafic beneath Shillong Plateau and Assam Valley, respectively. Results show that lower crust rocks beneath the Shillong Plateau and Assam Valley lies between mafic granulite and mafic garnet granulite.

  6. Three-dimensional shallow velocity structure beneath Taal Volcano, Philippines

    Science.gov (United States)

    You, Shuei-Huei; Konstantinou, Konstantinos I.; Gung, Yuancheng; Lin, Cheng-Horng

    2017-07-01

    Based on its numerous historical explosive eruptions and high potential hazards to nearby population of millions, Taal Volcano is one of the most dangerous "Decade Volcanoes" in the world. To provide better investigation on local seismicity and seismic structure beneath Taal Volcano, we deployed a temporary seismic network consisting of eight stations from March 2008 to March 2010. In the preliminary data processing stage, three periods showing linear time-drifting of internal clock were clearly identified from noise-derived empirical Green's functions. The time-drifting errors were corrected prior to further data analyses. By using VELEST, 2274 local earthquakes were manually picked and located. Two major earthquake groups are noticed, with one lying beneath the western shore of Taal Lake showing a linear feature, and the other spreading around the eastern flank of Taal Volcano Island at shallower depths. We performed seismic tomography to image the 3D structure beneath Taal Volcano using the LOTOS algorithm. Some interesting features are revealed from the tomographic results, including a solidified magma conduit below the northwestern corner of Taal Volcano Island, indicated by high Vp, Vs, and low Vp/Vs ratio, and a large potential hydrothermal reservoir beneath the center of Taal Volcano Island, suggested by low Vs and high Vp/Vs ratio. Furthermore, combining earthquake distributions and tomographic images, we suggest potential existence of a hydrothermal reservoir beneath the southwestern corner of Taal Lake, and a fluid conduit extending to the northwest. These seismic features have never been proposed in previous studies, implying that new hydrothermal activity might be formed in places away from the historical craters on Taal Volcano Island.

  7. The elastic properties of the lithosphere beneath Scotian basin

    Science.gov (United States)

    Zheng, Ying; Arkani-Hamed, Jafar

    2002-02-01

    To assess the possibility that the North Atlantic Ocean may subduct at Scotian basin east of Canada, we investigate the present compensation state of this deep basin. A Fourier domain analysis of the bathymetry, depth to basement and observed gravity anomalies over the oceanic area east of Nova Scotia indicates that the basin is not isostatically compensated. Moreover, the analysis emphasizes that in addition to the sediments, density perturbations exist beneath the basin. The load produced by the sediments and these density perturbations must have been supported by the lithosphere. We simulate the flexure of the lithosphere under this load by that of a thin elastic plate overlying an inviscid interior. It is shown that a plate with a uniform rigidity does not adequately represent the lithosphere beneath the basin as well as the oceanic lithosphere far from the basin, rather the rigidity of the lithosphere directly beneath the basin is about one to two orders of magnitude smaller than elsewhere. We relate this weakening to the thermal blanketing effects of the thick sediments and the fact that the lithosphere has a temperature-dependent rheology. We suggest that this weak zone would have a controlling effect on the reactivation of normal faults at the hinge zone of the basin, that were formed during the break-up of Africa and North America and were locked in the early stages after the break-up. The weak zone would facilitate reactivation of the faults if tensional stresses were produced by possible reorientation of the spreading direction of the North Atlantic Ocean in the future. The reactivation of the faults would create a free boundary condition at the hinge zone, allowing further bending of the lithosphere beneath the basin and juxtaposition of this lithosphere to the mantle beneath the continent. This may provide a favorable situation for initiation of slow subduction due to subsequent compressional forces.

  8. Contrasting bacterial communities in two indigenous Chionochloa (Poaceae) grassland soils in New Zealand.

    Science.gov (United States)

    Griffith, Jocelyn C; Lee, William G; Orlovich, David A; Summerfield, Tina C

    2017-01-01

    The cultivation of grasslands can modify both bacterial community structure and impact on nutrient cycling as well as the productivity and diversity of plant communities. In this study, two pristine New Zealand grassland sites dominated by indigenous tall tussocks (Chionochloa pallens or C. teretifolia) were examined to investigate the extent and predictability of variation of the bacterial community. The contribution of free-living bacteria to biological nitrogen fixation is predicted to be ecologically significant in these soils; therefore, the diazotrophic community was also examined. The C. teretifolia site had N-poor and poorly-drained peaty soils, and the C. pallens had N-rich and well-drained fertile soils. These soils also differ in the proportion of organic carbon (C), Olsen phosphorus (P) and soil pH. The nutrient-rich soils showed increased relative abundances of some copiotrophic bacterial taxa (including members of the Proteobacteria, Bacteroidetes and Firmicutes phyla). Other copiotrophs, Actinobacteria and the oliogotrophic Acidobacteria showed increased relative abundance in nutrient-poor soils. Greater diversity based on 16S rRNA gene sequences and the Tax4Fun prediction of enhanced spore formation associated with nutrient-rich soils could indicate increased resilience of the bacterial community. The two sites had distinct diazotrophic communities with higher diversity in C. teretifolia soils that had less available nitrate and ammonium, potentially indicating increased resilience of the diazotroph community at this site. The C. teretifolia soils had more 16S rRNA gene and nifH copies per g soil than the nutrient rich site. However, the proportion of the bacterial community that was diazotrophic was similar in the two soils. We suggest that edaphic and vegetation factors are contributing to major differences in the composition and diversity of total bacterial and diazotrophic communities at these sites. We predict the differences in the communities

  9. The elusive lithosphere-asthenosphere boundary (LAB) beneath cratons

    Science.gov (United States)

    Eaton, David W.; Darbyshire, Fiona; Evans, Rob L.; Grütter, Herman; Jones, Alan G.; Yuan, Xiaohui

    2009-04-01

    The lithosphere-asthenosphere boundary (LAB) is a first-order structural discontinuity that accommodates differential motion between tectonic plates and the underlying mantle. Although it is the most extensive type of plate boundary on the planet, its definitive detection, especially beneath cratons, is proving elusive. Different proxies are used to demarcate the LAB, depending on the nature of the measurement. Here we compare interpretations of the LAB beneath three well studied Archean regions: the Kaapvaal craton, the Slave craton and the Fennoscandian Shield. For each location, xenolith and xenocryst thermobarometry define a mantle stratigraphy, as well as a steady-state conductive geotherm that constrains the minimum pressure (depth) of the base of the thermal boundary layer (TBL) to 45-65 kbar (170-245 km). High-temperature xenoliths from northern Lesotho record Fe-, Ca- and Ti-enrichment, grain-size reduction and globally unique supra-adiabatic temperatures at 53-61 kbar (200-230 km depth), all interpreted to result from efficient advection of asthenosphere-derived melts and heat into the TBL. Using a recently compiled suite of olivine creep parameters together with published geotherms, we show that beneath cratons the probable deformation mechanism near the LAB is dislocation creep, consistent with widely observed seismic and electrical anisotropy fabrics. If the LAB is dry, it is probably diffuse (> 50 km thick) and high levels of shear stress (> 2 MPa or > 20 bar) are required to accommodate plate motion. If the LAB is wet, lower shear stress is required to accommodate plate motion and the boundary may be relatively sharp (≤ 20 km thick). The seismic LAB beneath cratons is typically regarded as the base of a high-velocity mantle lid, although some workers infer its location based on a distinct change in seismic anisotropy. Surface-wave inversion studies provide depth-constrained velocity models, but are relatively insensitive to the sharpness of the LAB

  10. Lithospheric thinning beneath rifted regions of Southern California.

    Science.gov (United States)

    Lekic, Vedran; French, Scott W; Fischer, Karen M

    2011-11-11

    The stretching and break-up of tectonic plates by rifting control the evolution of continents and oceans, but the processes by which lithosphere deforms and accommodates strain during rifting remain enigmatic. Using scattering of teleseismic shear waves beneath rifted zones and adjacent areas in Southern California, we resolve the lithosphere-asthenosphere boundary and lithospheric thickness variations to directly constrain this deformation. Substantial and laterally abrupt lithospheric thinning beneath rifted regions suggests efficient strain localization. In the Salton Trough, either the mantle lithosphere has experienced more thinning than the crust, or large volumes of new lithosphere have been created. Lack of a systematic offset between surface and deep lithospheric deformation rules out simple shear along throughgoing unidirectional shallow-dipping shear zones, but is consistent with symmetric extension of the lithosphere.

  11. Temporal moisture content variability beneath and external to a building and the potential effects on vapor intrusion risk assessment.

    Science.gov (United States)

    Tillman, Fred D; Weaver, James W

    2007-06-15

    Migration of vapors from organic chemicals residing in the subsurface into overlying buildings is known as vapor intrusion. Because of the difficulty in evaluating vapor intrusion by indoor air sampling, models are often employed to determine if a potential indoor inhalation exposure pathway exists and, if such a pathway is complete, whether long-term exposure increases the occupants' risk for cancer or other toxic effects to an unacceptable level. For site-specific vapor intrusion assessments, moisture content is, at times, determined from soil cores taken in open spaces between buildings. However, there is little published information on how moisture content measured outside a building structure compares with the moisture content directly beneath the building - where the values are most critical for vapor intrusion assessments. This research begins to address these issues by investigating the movement of soil moisture next to and beneath a building at a contaminated field site and determining the effect on vapor intrusion risk assessment. A two-dimensional, variably-saturated water flow model, HYDRUS-2D, is used with 2 years of hourly, local rainfall data to simulate subsurface moisture content in the vicinity of a hypothetical 10 x 10-m building slab at a contaminated field site. These moisture content values are used in vapor intrusion risk assessment simulations using the Johnson and Ettinger model with instantaneous and averaged moisture contents. Results show that vapor intrusion risk assessments based on moisture content determined from soil cores taken external to a building structure may moderately-to-severely underestimate the vapor intrusion risk from beneath the structure. Soil under the edges of a slab may be influenced by rainfall events and may show reduced vapor intrusion risk as a consequence. Data from a building instrumented with subslab moisture probes showed results similar to the modeling, but with a smaller difference between the subslab and

  12. Temporal moisture content variability beneath and external to a building and the potential effects on vapor intrusion risk assessment

    Energy Technology Data Exchange (ETDEWEB)

    Tillman, Fred D. [National Research Council (United States); U.S. Environmental Protection Agency, National Exposure Research Laboratory, Ecosystems Research Division, 960 College Station Road, Athens, GA 30605-2700 (United States); Weaver, James W. [U.S. Environmental Protection Agency, National Exposure Research Laboratory, Ecosystems Research Division, 960 College Station Road, Athens, GA 30605-2700 (United States)]. E-mail: Weaver.Jim@epa.gov

    2007-06-15

    Migration of vapors from organic chemicals residing in the subsurface into overlying buildings is known as vapor intrusion. Because of the difficulty in evaluating vapor intrusion by indoor air sampling, models are often employed to determine if a potential indoor inhalation exposure pathway exists and, if such a pathway is complete, whether long-term exposure increases the occupants' risk for cancer or other toxic effects to an unacceptable level. For site-specific vapor intrusion assessments, moisture content is, at times, determined from soil cores taken in open spaces between buildings. However, there is little published information on how moisture content measured outside a building structure compares with the moisture content directly beneath the building - where the values are most critical for vapor intrusion assessments. This research begins to address these issues by investigating the movement of soil moisture next to and beneath a building at a contaminated field site and determining the effect on vapor intrusion risk assessment. A two-dimensional, variably-saturated water flow model, HYDRUS-2D, is used with 2 years of hourly, local rainfall data to simulate subsurface moisture content in the vicinity of a hypothetical 10 x 10-m building slab at a contaminated field site. These moisture content values are used in vapor intrusion risk assessment simulations using the Johnson and Ettinger model with instantaneous and averaged moisture contents. Results show that vapor intrusion risk assessments based on moisture content determined from soil cores taken external to a building structure may moderately-to-severely underestimate the vapor intrusion risk from beneath the structure. Soil under the edges of a slab may be influenced by rainfall events and may show reduced vapor intrusion risk as a consequence. Data from a building instrumented with subslab moisture probes showed results similar to the modeling, but with a smaller difference between the

  13. On Irrotational Flows Beneath Periodic Traveling Equatorial Waves

    Science.gov (United States)

    Quirchmayr, Ronald

    2016-08-01

    We discuss some aspects of the velocity field and particle trajectories beneath periodic traveling equatorial surface waves over a flat bed in a flow with uniform underlying currents. The system under study consists of the governing equations for equatorial ocean waves within a non-inertial frame of reference, where Euler's equation of motion has to be suitably adjusted, in order to account for the influence of the earth's rotation.

  14. Detection of Cracks in Aluminum Structure Beneath Inconel Repair Bushings

    Science.gov (United States)

    2008-04-01

    conductivity (i.e. Inconel 718 ) – Primary challenge then becomes detecting the weak eddy current field in the structure beyond the bushing wall...was able to be selected with inspectability as a goal. – Inconel 718 • low permeability (~μ0) • low conductivity (< 2% IACS) • Combined with...Detection of Cracks in Aluminum Structure beneath Inconel Repair Bushings Mr. Kenneth J. LaCivita (USAF) AFRL/RXSA Air Force Research Laboratory

  15. Lithospheric instability beneath the Transverse Ranges of California

    OpenAIRE

    Houseman, Gregory A.; Neil, Emily A.; Kohler, Monica D.

    2000-01-01

    Recent high-resolution seismic experiments reveal that the crust beneath the San Gabriel Mountains portion of the Transverse Ranges thickens by 10–15 km (contrary to earlier studies). Associated with the Transverse Ranges, there is an anomalous ridge of seismically fast upper mantle material extending at least 200 km into the mantle. This high-velocity anomaly has previously been interpreted as a lithospheric downwelling. Both lithospheric downwelling and crustal thickening are associated wit...

  16. On Irrotational Flows Beneath Periodic Traveling Equatorial Waves

    Science.gov (United States)

    Quirchmayr, Ronald

    2017-06-01

    We discuss some aspects of the velocity field and particle trajectories beneath periodic traveling equatorial surface waves over a flat bed in a flow with uniform underlying currents. The system under study consists of the governing equations for equatorial ocean waves within a non-inertial frame of reference, where Euler's equation of motion has to be suitably adjusted, in order to account for the influence of the earth's rotation.

  17. Kelvin-Helmholtz wave generation beneath hovercraft skirts

    Science.gov (United States)

    Sullivan, P. A.; Walsh, C.; Hinchey, M. J.

    1993-05-01

    When a hovercraft is hovering over water, the air flow beneath its skirts can interact with the water surface and generate waves. These, in turn, can cause the hovercraft to undergo violent self-excited heave motions. This note shows that the wave generation is due to the classical Kelvin-Helmholtz mechanism where, beyond a certain air flow rate, small waves at the air water interface extract energy from the air stream and grow.

  18. The Dumbarton Oaks Tlazolteotl: looking beneath the surface

    OpenAIRE

    MacLaren Walsh, Jane

    2014-01-01

    The Dumbarton Oaks Tlazolteotl: looking beneath the surface. Some of the earliest and most revered pre-Columbian artifacts in the world’s major museum and private collections were collected prior to the advent of systematic, scientific archaeological excavation, and have little or no reliable provenience data. They have consistently posed problems for researchers due to anomalies of theme, material, size, technical virtuosity and iconography. This paper offers a historical and scientific appr...

  19. New interpretation of the deep mantle structure beneath eastern China

    Science.gov (United States)

    Ma, Pengfei; Liu, Shaofeng; Lin, Chengfa; Yao, Xiang

    2016-04-01

    Recent study of high resolution seismic tomography presents a large mass of high velocity abnormality beneath eastern China near the phase change depth, expanding more than 1600km-wide in East-west cross-section across the North China plate. This structure high is generally believed to be the subducted slab of Pacific plate beneath the Eurasia continent, while its origin and dynamic effect on the Cenozoic tectonic evolution of eastern China remain to be controversial. We developed a subduction-driven geodynamic mantle convection model that honors a set of global plate reconstruction data since 230Ma to help understand the formation and evolution of mantle structure beneath eastern China. The assimilation of plate kinematics, continuous evolving plate margin, asymmetric subduction zone, and paleo seafloor age data enables the spatial and temporal consistency between the geologic data and the mantle convection model, and guarantees the conservation of the buoyancy flux across the lithosphere and subducted slabs. Our model achieved a first order approximation between predictions and the observed data. Interestingly, the model suggests that the slab material stagnated above discontinuity didn't form until 15Ma, much later than previous expected, and the fast abnormality in the mid-mantle further west in the tomographic image is interpreted to be the remnants of the Mesozoic Izanagi subduction. Moreover, detailed analysis suggests that the accelerated subduction of Philippine Sea plate beneath Eurasia plate along the Ryukyu Trench and Nankai Trough since 15Ma may largely contribute to extending feature above 670km discontinuity. The long distance expansion of the slab material in the East-west direction may be an illusion caused by the approximate spatial perpendicularity between the cross-section and the subduction direction of the Philippine Sea plate. Our model emphasizes the necessity of the re-examination on the geophysical observation and its tectonic and

  20. Lithospheric radial anisotropy beneath the Gulf of Mexico

    Science.gov (United States)

    Chu, Risheng; Ko, Justin Yen-Ting; Wei, Shengji; Zhan, Zhongwen; Helmberger, Don

    2017-05-01

    The Lithosphere-Asthenosphere Boundary (LAB), where a layer of low viscosity asthenosphere decouples with the upper plate motion, plays an essential role in plate tectonics. Most dynamic modeling assumes that the shear velocity can be used as a surrogate for viscosity which provides key information about mantle flow. Here, we derive a shear velocity model for the LAB structure beneath the Gulf of Mexico allowing a detailed comparison with that beneath the Pacific (PAC) and Atlantic (ATL). Our study takes advantage of the USArray data from the March 25th, 2013 Guatemala earthquake at a depth of 200 km. Such data is unique in that we can observe a direct upward traveling lid arrival which remains the first arrival ahead of the triplications beyond 18°. This extra feature in conjunction with upper-mantle triplication sampling allows good depth control of the LAB and a new upper-mantle seismic model ATM, a modification of ATL, to be developed. ATM has a prominent low velocity zone similar to the structure beneath the western Atlantic. The model contains strong radial anisotropy in the lid where VSH is about 6% faster than VSV. This anisotropic feature ends at the bottom of the lithosphere at about the depth of 175 km in contrast to the Pacific where it extends to over 300 km. Another important feature of ATM is the weaker velocity gradient from the depth of 175 to 350 km compared to Pacific models, which may be related to differences in mantle flow.

  1. Why are there few seedlings beneath the myrmecophyte Triplaris americana?

    Science.gov (United States)

    Larrea-Alcázar, Daniel M.; Simonetti, Javier A.

    2007-07-01

    We compared the relative importance of chemical alellopathy, pruning behaviour of resident ants and other non-related agents to ant-plant mutualism for seedling establishment beneath Triplaris americana L. (Polygonaceae), a myrmecophyte plant. We also included a preliminary analysis of effects of fragmentation on these ecological processes. Seeds and seedlings of Theobroma cacao L. (Sterculiaceae) were used as the target species in all experiments. Leaf-tissue extracts of the myrmecophyte plant did not inhibit germination of cacao seeds. Resident Pseudomyrmex triplarinus Weddell (Pseudomyrmecinae) ants did not remove seeds under the canopy of their host plants. The main seed consumer was the leaf-cutting ant Atta sexdens L. (Myrmicinae). Leaves of cacao seedlings were partially or totally pruned by Pseudomyrmex ants mainly in forest fragments studied. We offer evidence pointing to the possibility that the absence of seedlings beneath Triplaris may result from effects of both ant species. We discuss the benefits of pruning behaviour for the resident ant colony and the effects of ant-ant interactions on seedling establishment beneath this ant-plant system.

  2. Crustal structure beneath the southern Korean Peninsula from local earthquakes

    Science.gov (United States)

    Kim, Kwang-Hee; Park, Jung-Ho; Park, Yongcheol; Hao, Tian-Yao; Kim, Han-Joon

    2017-02-01

    The three-dimensional subsurface structure beneath the southern Korean Peninsula is poorly known, even though such information could be key in verifying or rejecting several competing models of the tectonic evolution of East Asia. We constructed a three-dimensional velocity model of the upper crust beneath the southern Korean Peninsula using 19,935 P-wave arrivals from 747 earthquakes recorded by high-density local seismic networks. Results show significant lateral and vertical variations: velocity increases from northwest to southeast at shallow depths, and significant velocity variations are observed across the South Korea Tectonic Line between the Okcheon Fold Belt and the Youngnam Massif. Collision between the North China and South China blocks during the Early Cretaceous might have caused extensive deformation and the observed negative velocity anomalies in the region. The results of the tomographic inversion, combined with the findings of previous studies of Bouguer and isostatic gravity anomalies, indicate the presence of high-density material in the upper and middle crust beneath the Gyeongsang Basin in the southeastern Korean Peninsula. Although our results partially support the indentation tectonic model, it is still premature to discard other tectonic evolution models because our study only covers the southern half of the peninsula.

  3. Descending lithosphere slab beneath the Northwest Dinarides from teleseismic tomography

    Science.gov (United States)

    Šumanovac, Franjo; Dudjak, Darko

    2016-12-01

    The area of study covers the marginal zone between the Adriatic microplate (African plate) and the Pannonian segment (Eurasian plate). We present a tomography model for this area, with special emphasis on the northwest Dinarides. A dense distribution of temporary seismic stations in the area of the Northern Dinarides along with permanent seismic stations located in the area, allowed us to construct this P-wave tomographic model. We assembled our travel-time dataset based on 26 seismic stations were used to collect the dataset. Teleseismic events were recorded for a period of 18 months and a set of 76 distant earthquakes were used to calculate the P-wave travel-time residuals. We calculated relative rather than absolute arrival-time residuals in the inversion to obtain depths of 0-400 km. We imaged a pronounced fast velocity anomaly below the NW Dinarides which directly indicates a lithosphere slab downgoing beneath the Dinarides. This fast anomaly extends towards the NW direction to at least 250 km depth, and we interpreted it as a descending lithosphere slab. The thrusting of the Adriatic microplate may be brought about by sub-lithosphere rising movement beneath the Pannonian region, along with a push from African plate. In our interpretation, the Adriatic lower lithosphere has been detached from the crust, and steeply sinks beneath the Dinarides. A lithosphere model of the contact between the Adriatic microplate and Pannonian tectonic segment was constructed based on the tomographic velocity model and results of previous crustal studies.

  4. What lies beneath the Cerro Prieto geothermal field?

    Energy Technology Data Exchange (ETDEWEB)

    Elders, W.A.; Williams, A.E.; Biehler, S. [Univ. of California, Riverside, CA (United States)

    1997-12-31

    Although the Cerro Prieto geothermal reservoir is one of the world`s largest geothermal developments, conflicting ideas persist about the basement beneath it. The current plan to drill a 6 km deep exploratory well in the eastern part of the field has brought this controversy into sharper focus. This paper discusses criteria which any model of what lies beneath the reservoir must meet, in terms of regional tectonics and geophysics, of the metamorphic and igneous rocks thus far encountered in drilling, and of models of possible heat sources and coupling between the hydrothermal and magmatic systems. Our analysis confirms the interpretation that the crystalline basement beneath the sediments, rather than being granitic, is oceanic in character, resembling an ophiolite complex. The heat source is most likely a cooling gabbroic intrusion, several kilometers in diameter, overlain by a sheeted dike swarm. A 6 km deep bore-hole centered over such an intrusion would not only be one of the world`s deepest geothermal wells but could also be one of the hottest.

  5. Wood stakes as an index of soil organic matter decomposition in a climatic gradient along the Spanish Mediterranean Coast

    Science.gov (United States)

    Jurgensen, M. F.; Page-Dumroese, D. S.; Cerdà, A.; Úbeda, X.; M-Mena, M.; Rey, A.

    2009-04-01

    Organic matter (OM) decomposition is a critical factor in assessing the possible impacts of future climate change and management on soil carbon cycling and sequestration. Soil OM decomposition is a function of abiotic (e.g. moisture, temperature, nutrient content, pH), and biotic (microbial biomass, functional diversity) conditions, which makes this soil process ideally suited to study across a range of soil and climatic conditions. We used wood stakes of four tree species (Populus alba, Populus tremuloides, Pinus halenensis, Pinus taeda) as standard indices of OM decomposition rates on the soil surface and in the mineral soil of three sites along the Spanish Mediterranean Coast with different soils, land use and climatic conditions: 1) Quercus suber forest - 700 mm rainfall /year, 2) Quercus coccifera and Pinus halepenis forest - 300 mm rainfall/year, and 3) tussock grasses - 150 mm rainfall /year. Our results show significant differences in wood stake decomposition as a function of climatic conditions, land use management, and wood stake species.

  6. The preliminary results: Internal seismic velocity structure imaging beneath Mount Lokon

    Science.gov (United States)

    Firmansyah, Rizky; Nugraha, Andri Dian; Kristianto

    2015-04-01

    Historical records that before the 17th century, Mount Lokon had been dormant for approximately 400 years. In the years between 1350 and 1400, eruption ever recorded in Empung, came from Mount Lokon's central crater. Subsequently, in 1750 to 1800, Mount Lokon continued to erupt again and caused soil damage and fall victim. After 1949, Mount Lokon dramatically increased in its frequency: the eruption interval varies between 1 - 5 years, with an average interval of 3 years and a rest interval ranged from 8 - 64 years. Then, on June 26th, 2011, standby alert set by the Center for Volcanology and Geological Hazard Mitigation. Peak activity happened on July 4th, 2011 that Mount Lokon erupted continuously until August 28th, 2011. In this study, we carefully analyzed micro-earthquakes waveform and determined hypocenter location of those events. We then conducted travel time seismic tomographic inversion using SIMULPS12 method to detemine Vp, Vs and Vp/Vs ratio structures beneath Lokon volcano in order to enhance our subsurface geological structure. During the tomographic inversion, we started from 1-D seismic velocities model obtained from VELEST33 method. Our preliminary results show low Vp, low Vs, and high Vp/Vs are observed beneath Mount Lokon-Empung which are may be associated with weak zone or hot material zones. However, in this study we used few station for recording of micro-earthquake events. So, we suggest in the future tomography study, the adding of some seismometers in order to improve ray coverage in the region is profoundly justified.

  7. The preliminary results: Internal seismic velocity structure imaging beneath Mount Lokon

    Energy Technology Data Exchange (ETDEWEB)

    Firmansyah, Rizky, E-mail: rizkyfirmansyah@hotmail.com [Geophysical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Nugraha, Andri Dian, E-mail: nugraha@gf.itb.ac.id [Global Geophysical Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Kristianto, E-mail: kris@vsi.esdm.go.id [Center for Volcanology and Geological Hazard Mitigation (CVGHM), Geological Agency, Bandung, 40122 (Indonesia)

    2015-04-24

    Historical records that before the 17{sup th} century, Mount Lokon had been dormant for approximately 400 years. In the years between 1350 and 1400, eruption ever recorded in Empung, came from Mount Lokon’s central crater. Subsequently, in 1750 to 1800, Mount Lokon continued to erupt again and caused soil damage and fall victim. After 1949, Mount Lokon dramatically increased in its frequency: the eruption interval varies between 1 – 5 years, with an average interval of 3 years and a rest interval ranged from 8 – 64 years. Then, on June 26{sup th}, 2011, standby alert set by the Center for Volcanology and Geological Hazard Mitigation. Peak activity happened on July 4{sup th}, 2011 that Mount Lokon erupted continuously until August 28{sup th}, 2011. In this study, we carefully analyzed micro-earthquakes waveform and determined hypocenter location of those events. We then conducted travel time seismic tomographic inversion using SIMULPS12 method to detemine Vp, Vs and Vp/Vs ratio structures beneath Lokon volcano in order to enhance our subsurface geological structure. During the tomographic inversion, we started from 1-D seismic velocities model obtained from VELEST33 method. Our preliminary results show low Vp, low Vs, and high Vp/Vs are observed beneath Mount Lokon-Empung which are may be associated with weak zone or hot material zones. However, in this study we used few station for recording of micro-earthquake events. So, we suggest in the future tomography study, the adding of some seismometers in order to improve ray coverage in the region is profoundly justified.

  8. Soil seed bank characteristics in relation to rangeland degradation in communal areas of the Eastern Cape, South Africa

    CSIR Research Space (South Africa)

    Lesoli, MS

    2010-07-01

    Full Text Available A soil seed bank is defined as seeds at or beneath the soil surface that are capable of germinating. Soil seed banks are important in ecosystems where grasses account for a large part of the vegetation. This has implications on the future vegetation...

  9. Renforcement de fondations superficielles par soil mixing : Analyses par modélisation physique et numérique

    OpenAIRE

    Dhaybi, Mathieu

    2015-01-01

    The reinforcement of shallow foundations by soil mixing consists on mixing the soil beneath with a hydraulic binder in order to obtain columns with mixed modulus. These columns, which have mechanical properties bounded between those of concrete and those of soil, can improve the soil bearing capacity and reduce excessive settlements as well. This research work is a phenomenological and quantitative study of the behavior of shallow foundations reinforced by soil mixing columns. It leads to ana...

  10. A Bed-Deformation Experiment Beneath Engabreen, Norway

    Science.gov (United States)

    Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Cohen, D.; Jackson, M.; Moore, P. L.; Lappegard, G.; Kohler, J.

    2001-12-01

    Although deformation of sediment beneath ice masses may contribute to their motion and may sometimes enable fast glacier flow, both the kinematics and mechanics of deformation are controversial. This controversy stems, in part, from subglacial measurements that are difficult to interpret. Measurements have been made either beneath ice margins or remotely through boreholes with interpretive limitations caused by uncertain instrument position and performance, uncertain sediment thickness and bed geometry, and unknown disturbance of the bed and stress state by drilling. We have used a different approach made possible by the Svartisen Subglacial Laboratory, which enables human access to the bed of Engabreen, Norway, beneath 230 m of temperate ice. A trough (2 m x 1.5 m x 0.4 m deep) was blasted in the rock bed and filled with sediment (75 percent sand and gravel, 20 percent silt, 5 percent clay). Instruments were placed in the sediment to record shear deformation (tiltmeters), dilation and contraction, total normal stress, and pore-water pressure. Pore pressure was manipulated by feeding water to the base of the sediment with a high-pressure pump, operated in a rock tunnel 4 m below the bed surface. After irregular deformation during closure of ice on the sediment, shear deformation and volume change stopped, and total normal stress became constant at 2.2 MPa. Subsequent pump tests, which lasted several hours, induced pore-water pressures greater than 70 percent of the total normal stress and resulted in shear deformation over most of the sediment thickness with attendant dilation. Ice separated from the sediment when effective normal stress was lowest, arresting shear deformation. Displacement profiles during pump tests were similar to those observed by Boulton and co-workers at Breidamerkurjökull, Iceland, with rates of shear strain increasing upward toward the glacier sole. Such deformation does not require viscous deformation resistance and is expected in a

  11. A magmatic probe of dynamic topography beneath western North America

    Science.gov (United States)

    Klöcking, M.; White, N. J.; Maclennan, J.

    2014-12-01

    A region centered on the Yellowstone hotspot and encompassing the Colorado Plateau sits at an elevation 2 km higher than the cratonic North America. This difference broadly coincides with tomographically observed variations in lithospheric thickness: ~120 km beneath western North America, ~240 km beneath the craton. Thermochronology of the Grand Canyon area, sedimentary flux to the Gulf of Mexico, and river profile inversion all suggest that regional uplift occurred in at least two separate stages. High resolution seismic tomographic models, using USArray data, have identified a ring of low velocity material beneath the edges of the Colorado Plateau. Magmatism coincides with these low velocity zones and shows distinct phases: an overall increase in volume around 40 Ma and a change from lithospheric to asthenospheric signatures around 5 Ma. Volcanism is also observed to migrate north-east with time. Here, we attempt to integrate these different observations with lithospheric thickness. A dynamic topography model of progressive lithospheric erosion over a hot mantle plume might account for uplift as well as the temporal and spatial distribution of magmatism across western North America. Thinning of the lithosphere around the edges of the Colorado Plateau in combination with the hotter mantle potential temperature of a plume could create isostatic and dynamic uplift as well as allowing for melt production. To test this model, we have analysed around 100 samples from volcanic centers across western North America by ICP-MS for rare earth elements (REE). Most of the samples are younger than 5 Ma, and all of them have previously been analysed by XRF. Using trace element ratios such as La/Yb and Nb/Y we assess depth of melting and melt fraction, respectively. In addition, we use REE inversion modelling to estimate melt fractions as a function of depth and temperature of melting. The results are compared to existing constraints on lithospheric thickness and mantle potential

  12. On the Turbulence Beneath Finite Amplitude Water Waves

    CERN Document Server

    Babanin, Alexander V

    2015-01-01

    The paper by Beya et al. (2012, hereinafter BPB) has a general title of Turbulence Beneath Finite Amplitude Water Waves, but is solely dedicated to discussing the experiment by Babanin and Haus (2009, hereinafter BH) who conducted measurements of wave-induced non-breaking turbulence by particle image velocimetry (PIV). The authors of BPB conclude that their observations contradict those of BH. Here we argue that the outcomes of BPB do not contradict BH. In addition, although the main conclusion of BPB is that there is no turbulence observed in their experiment, it actually is observed.

  13. Climate variability effects on urban recharge beneath low impact development

    Science.gov (United States)

    Newcomer, M. E.; Gurdak, J. J.

    2012-12-01

    Groundwater resources in urban and coastal environments are highly vulnerable to human pressures and climate variability and change, and many communities face water shortages and need to find alternative water supplies. Therefore, understanding how low impact development (LID) site planning and integrated/best management practices (BMPs) affect recharge rates and volumes is important because of the increasing use of LID and BMP to reduce stormwater runoff and improve surface-water quality. Often considered a secondary management benefit, many BMPs may also enhance recharge to local aquifers; however these hypothesized benefits have not been thoroughly tested or quantified. In this study, we quantify stormwater capture and recharge enhancement beneath a BMP infiltration trench of the LID research network at San Francisco State University, San Francisco, California. Stormwater capture and retention was analyzed using the SCS TR-55 curve number method and in-situ infiltration rates to assess LID storage. Recharge was quantified using vadose zone monitoring equipment, a detailed water budget analysis, and a Hydrus-2D model. Additionally, the effects of historical and predicted future precipitation on recharge rates were examined using precipitation from the Geophysical Fluid Dynamic Laboratory (GFDL) A1F1 climate scenario. Observed recharge rates beneath the infiltration trench range from 1,600 to 3,700 mm/year and are an order of magnitude greater than recharge beneath an irrigated grass lawn and a natural setting. The Hydrus-2D model results indicate increased recharge under the GFDL A1F1 scenario compared with historical and GFDL modeled 20th century rates because of the higher frequency of large precipitation events that induce runoff into the infiltration trench. However, under a simulated A1F1 El Niño year, recharge calculated by a water budget does not increase compared with current El Niño recharge rates. In comparison, simulated recharge rates were

  14. Carbon dioxide and helium emissions from a reservoir of magmatic gas beneath Mammoth Mountain, California

    Science.gov (United States)

    Sorey, M.L.; Evans, William C.; Kennedy, B.M.; Farrar, C.D.; Hainsworth, L.J.; Hausback, B.

    1998-01-01

    Carbon dioxide and helium with isotopic compositions indicative of a magmatic source (??13C = -4.5 to -5???, 3He/4He = 4.5 to 6.7 RA) are discharging at anomalous rates from Mammoth Mountain, on the southwestern rim of the Long Valley caldera in eastern California. The gas is released mainly as diffuse emissions from normal-temperature soils, but some gas issues from steam vents or leaves the mountain dissolved in cold groundwater. The rate of gas discharge increased significantly in 1989 following a 6-month period of persistent earthquake swarms and associated strain and ground deformation that has been attributed to dike emplacement beneath the mountain. An increase in the magmatic component of helium discharging in a steam vent on the north side of Mammoth Mountain, which also began in 1989, has persisted until the present time. Anomalous CO2 discharge from soils first occurred during the winter of 1990 and was followed by observations of several areas of tree kill and/or heavier than normal needlecast the following summer. Subsequent measurements have confirmed that the tree kills are associated with CO2 concentrations of 30-90% in soil gas and gas flow rates of up to 31,000 g m-2 d-1 at the soil surface. Each of the tree-kill areas and one area of CO2 discharge above tree line occurs in close proximity to one or more normal faults, which may provide conduits for gas flow from depth. We estimate that the total diffuse CO2 flux from the mountain is approximately 520 t/d, and that 30-50 t/d of CO2 are dissolved in cold groundwater flowing off the flanks of the mountain. Isotopic and chemical analyses of soil and fumarolic gas demonstrate a remarkable homogeneity in composition, suggesting that the CO2 and associated helium and excess nitrogen may be derived from a common gas reservoir whose source is associated with some combination of magmatic degassing and thermal metamorphism of metasedimentary rocks. Furthermore, N2/Ar ratios and nitrogen isotopic values

  15. Negative plant soil feedback explaining ring formation in clonal plants.

    Science.gov (United States)

    Cartenì, Fabrizio; Marasco, Addolorata; Bonanomi, Giuliano; Mazzoleni, Stefano; Rietkerk, Max; Giannino, Francesco

    2012-11-21

    Ring shaped patches of clonal plants have been reported in different environments, but the mechanisms underlying such pattern formation are still poorly explained. Water depletion in the inner tussocks zone has been proposed as a possible cause, although ring patterns have been also observed in ecosystems without limiting water conditions. In this work, a spatially explicit model is presented in order to investigate the role of negative plant-soil feedback as an additional explanation for ring formation. The model describes the dynamics of the plant biomass in the presence of toxicity produced by the decomposition of accumulated litter in the soil. Our model qualitatively reproduces the emergence of ring patterns of a single clonal plant species during colonisation of a bare substrate. The model admits two homogeneous stationary solutions representing bare soil and uniform vegetation cover which depend only on the ratio between the biomass death and growth rates. Moreover, differently from other plant spatial patterns models, but in agreement with real field observations of vegetation dynamics, we demonstrated that the pattern dynamics always lead to spatially homogeneous vegetation covers without creation of stable Turing patterns. Analytical results show that ring formation is a function of two main components, the plant specific susceptibility to toxic compounds released in the soil by the accumulated litter and the decay rate of these same compounds, depending on environmental conditions. These components act at the same time and their respective intensities can give rise to the different ring structures observed in nature, ranging from slight reductions of biomass in patch centres, to the appearance of marked rings with bare inner zones, as well as the occurrence of ephemeral waves of plant cover. Our results highlight the potential role of plant-soil negative feedback depending on decomposition processes for the development of transient vegetation patterns.

  16. Shear Wave Splitting Observations Beneath Uturuncu Volcano, Bolivia

    Science.gov (United States)

    Sims, N. E.; Christensen, D. H.; Moore-Driskell, M. M.

    2015-12-01

    Anisotropy in the upper mantle is often associated with mantle flow direction through the lattice preferred orientation of anisotropic minerals such as olivine in the upper mantle material. The flow of the mantle around subduction zones can be particularly complex, and thus difficult to explain. Because of its relationship to anisotropy, analysis of shear wave splitting measurements can help to answer questions regarding the upper mantle flow that surrounds subducting slabs. Here we present SK(K)S shear wave splitting measurements from a temporary broadband network (PLUTONS) of 33 stations deployed from April 2009 to October 2012 on the Altiplano plateau around Uturuncu volcano in Bolivia. The stations are spaced 10-20 km apart, providing a high spatial resolution of the region of the mantle directly below Uturuncu volcano. Despite the lack of numerous splitting results to analyze, preliminary measurements indicate a relatively consistent pattern of fast-polarization directions in a NW-SE orientation of about N80ºW. We think that it is likely that these observations come from anisotropy in the mantle wedge above the subducting Nazca plate indicating a direction of flow in the mantle wedge that is sub-parallel to the subduction direction of the Nazca plate. Although W-E flow beneath the subducting Nazca plate cannot be completely ruled out, these results appear to be consistent with the simple model of two-dimensional corner flow in the mantle wedge and slab-entrained mantle flow beneath the slab.

  17. Subglacial Sediment Deformation: An Experiment Beneath Engabreen, Norway

    Science.gov (United States)

    Fischer, U. H.; Iverson, N. R.; Hooyer, T. S.; Cohen, D.; Jackson, M.; Moore, P. L.; Lappegard, G.; Kohler, J.

    A detailed study of sediment deformation processes was carried out beneath Engabreen, Norway, by taking advantage of unique access to the bed of the glacier beneath 230 m of temperate ice via the Svartisen Subglacial Laboratory. One of the strengths of this novel approach is that many interpretive limitations caused by un- certainties inherent in similarly motivated borehole investigations are eliminated. A trough (approx. 2 m x 1.5 m x 0.4 m deep) was blasted in the rock bed and filled with sediment (75 per cent sand and gravel, 20 per cent silt, 5 per cent clay). Instruments were placed in the sediment to record shear deformation, dilation and contraction, total normal stress, and pore-water pressure. Pore pressure was manipulated by feeding wa- ter to the base of the sediment with a high-pressure pump, operated in a rock tunnel 4 m below the bed surface. After irregular deformation during closure of ice on the sed- iment, shear deformation and volume change stopped, and total normal stress became constant at 2.1 MPa. Pump tests conducted subsequently, which lasted several hours, induced pore-water pressures > 70 per cent of the total normal stress and resulted in shear deformation over most of the sediment thickness with attendant dilation. Ice sep- arated from the sediment when effective pressure was lowest, and shear deformation stopped. Velocity profiles averaged over the duration of pump tests indicate that rates of shear strain increase upward toward the glacier sole.

  18. Anelastic properties beneath the Niigata-Kobe Tectonic Zone, Japan

    Science.gov (United States)

    Nakajima, Junichi; Matsuzawa, Toru

    2017-02-01

    We estimate the three-dimensional (3D) P-wave attenuation structure beneath the Niigata-Kobe Tectonic Zone (NKTZ), central Japan, using high-quality waveform data from a large number of stations. The obtained results confirm the segmentation of the NKTZ into three regions, as suggested by 3D seismic velocity models, and reveal characteristic structures related to surface deformation, shallow subduction of the Philippine Sea slab, and magmatism. The lower crust beneath the NKTZ west of the Itoigawa-Shizuoka Tectonic Line (ISTL) is overall characterized by distinct high attenuation, whereas the upper crust shows marked high attenuation to the east of the ISTL. Differences in the depths of anelastically weakened parts of the crust probably result in a first-order spatial variation in surface deformation, forming wide (width of 100 km) and narrow (width of 25-40 km) deformation zones on the western and eastern sides of the ISTL, respectively. Many M ≥ 6.5 earthquakes occur in the upper crust where seismic attenuation in the underlying lower crust varies sharply, suggesting that spatial variations in rates of anelastic deformation in the lower crust result in stress concentration in the overlying brittle crust. We interpret a moderate- to low-attenuation zone located in the lower crust at the northeast of Biwa Lake to reflect low-temperature conditions that are developed locally as a result of shallow subduction of the cold Philippine Sea slab.

  19. D'' beneath the Arctic from inversion of shear waveforms

    Science.gov (United States)

    Kawai, Kenji; Geller, Robert J.; Fuji, Nobuaki

    2007-11-01

    The structure of the D'' region beneath the Arctic has not previously been studied in detail. Using waveform inversion, we find that the average S-wave velocity in D'' beneath the Arctic is about 0.04 km/s higher than PREM, which is consistent with the existence of post-perovskite (ppv) in D''. It is difficult to strongly constrain the fine structure of S-velocity within D'' due to the small number of stations at epicentral distances Δ weighting those stations heavily in the inversion, we show that the data suggest the existence of high S-velocity in the upper half of D'' and low S-velocity in the lower half, consistent with the possibility of a double crossing (ppv -> pv reverse phase transition) within D''. We conduct a computational experiment to show that resolution of the velocity structure within D'' could be significantly improved by temporary installation of a portable array of seismographs in northern Canada, which would greatly increase the number of stations in the range 70° < Δ < 90°.

  20. Simulation of Wave-Plus-Current Scour beneath Submarine Pipelines

    DEFF Research Database (Denmark)

    Eltard-Larsen, Bjarke; Fuhrman, David R.; Sumer, B. Mutlu

    2016-01-01

    A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed and suspen......A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier–Stokes equations, coupled with k-ω turbulence closure, with additional bed...... and suspended load descriptions forming the basis for seabed morphology. The model was successfully validated against experimental measurements involving scour development and eventual equilibrium in pure-current flows over a range of Shields parameters characteristic of both clear-water and live-bed regimes....... This validation complements previously demonstrated accuracy for the same model in simulating pipeline scour processes in pure-wave environments. The model was subsequently utilized to simulate combined wave-plus-current scour over a wide range of combined Keulegan–Carpenter numbers and relative current strengths...

  1. Shear wave anisotropy in D" region beneath the western Pacific

    Institute of Scientific and Technical Information of China (English)

    DAI Zhi-yang; LIU Bin; WANG Xiao-xiang; ZHA Xian-jie; ZHANG Hu; YANG Feng-qin

    2007-01-01

    Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS, and from 26 northeast Asia and north Pacific events recorded by IRIS, we studied the shear wave anisotropy in D" region beneath the western Pacific utilizing the ScS-S differential travel time method and obtained the splitting time values between the radial and transverse components of each ScS wave corresponding to each core-mantle boundary (CMB) reflection point. We found that most shear waves involved horizontally polarized shear wave components traveling faster than vertically polarized shear wave components through the D" region. The splitting time values of ScS wave range from (0.91 s to 3.21 s with an average value of 1.1 s. The strength of anisotropy varies from (0.45% to 1.56% with an average value of 0.52%. The observations and analyses show that in the D" region beneath the western Pacific the lateral flow is expected to be dominant and the vertical transverse isotropy may be the main anisotropic structure. This structure feature may be explained by the shape preferred orientation of the CMB chemical reaction products or partial melt and the lattice preferred orientation of the lower mantle materials caused by the lateral flow at lowermost mantle.

  2. Locating voids beneath pavement using pulsed electromagnetic waves

    Science.gov (United States)

    Steinway, W. J.; Echard, J. D.; Luke, C. M.

    1981-11-01

    The feasibility of using pulsed electromagnetic wave technology for locating and sizing voids beneath reinforced and nonreinforced portland cement concrete pavements is determined. The data processing techniques developed can be implemented to provide information for void depth and sizing to + or - 1/2 in. and spatial location within + or - 6 in. A very short pulse radar directly connected to a microcomputer was chosen as the equipment necessary to obtain measurements. This equipment has the required accuracy and reliability, and is a cost effective solution for the void locating problem. The radar provides a signal return from voids that has unique characteristics that can be examined to provide information regarding the location, depth, and shape of the void. The microcomputer provides a means of real time processing to extract the information from the radar signal return and record the results. Theoretical modeling of signal returns from voids led to suitable techniques for locating and sizing voids beneath the pavement. Analysis and application of these techniques to radar measurements verified the theoretical predictions that radar can be used to determine the location, size, and shape of actual voids.

  3. Storage of Miscanthus-derived carbon in rhizomes, roots, and soil

    DEFF Research Database (Denmark)

    Christensen, Bent Tolstrup; Lærke, Poul Erik; Jørgensen, Uffe

    2016-01-01

    Compared with annual crops, dedicated perennial bioenergy crops are ascribed additional benefits in terms of reduced greenhouse gas emissions; these benefits include increased carbon (C) storage in soil. We measured Miscanthus-derived C in rhizomes, roots, and 0–100 cm soil beneath three 16-yr-ol...

  4. Fungi obtained on various media from soil under banana trees near Logos in Nigeria

    Directory of Open Access Journals (Sweden)

    Aleksandra Ihnatowicz

    2014-08-01

    Full Text Available From the soil samples collected from beneath various banana plant, Musa paradisiaca L., 96 different species of soil fungi were isolated on medium: Ohio-Agar, Littmans-Agar, Martins Rose Bengal-Agar and identified. Four species of keratinophilic fungi were isolated by means of To-Ka-Va trap-hair method.

  5. Estimating the oxygenated zone beneath building foundations for petroleum vapor intrusion assessment.

    Science.gov (United States)

    Verginelli, Iason; Yao, Yijun; Wang, Yue; Ma, Jie; Suuberg, Eric M

    2016-07-15

    Previous studies show that aerobic biodegradation can effectively reduce hydrocarbon soil gas concentrations by orders of magnitude. Increasingly, oxygen limited biodegradation is being included in petroleum vapor intrusion (PVI) guidance for risk assessment at leaking underground storage tank sites. The application of PVI risk screening tools is aided by the knowledge of subslab oxygen conditions, which, however, are not commonly measured during site investigations. Here we introduce an algebraically explicit analytical method that can estimate oxygen conditions beneath the building slab, for PVI scenarios with impervious or pervious building foundations. Simulation results by this new model are then used to illustrate the role of site-specific conditions in determining the oxygen replenishment below the building for both scenarios. Furthermore, critical slab-width-to-source-depth ratios and critical source depths for the establishment of a subslab "oxygen shadow" (i.e. anoxic zone below the building) are provided as a function of key parameters such as vapor source concentration, effective diffusion coefficients of concrete and building depth. For impervious slab scenarios the obtained results are shown in good agreement with findings by previous studies and further support the recommendation by U.S. EPA about the inapplicability of vertical exclusion distances for scenarios involving large buildings and high source concentrations. For pervious slabs, results by this new model indicate that even relatively low effective diffusion coefficients of concrete can facilitate the oxygen transport into the subsurface below the building and create oxygenated conditions below the whole slab foundation favorable for petroleum vapor biodegradation.

  6. Slab melting and magma formation beneath the southern Cascade arc

    Science.gov (United States)

    Walowski, K. J.; Wallace, P. J.; Clynne, M. A.; Rasmussen, D. J.; Weis, D.

    2016-07-01

    The processes that drive magma formation beneath the Cascade arc and other warm-slab subduction zones have been debated because young oceanic crust is predicted to largely dehydrate beneath the forearc during subduction. In addition, geochemical variability along strike in the Cascades has led to contrasting interpretations about the role of volatiles in magma generation. Here, we focus on the Lassen segment of the Cascade arc, where previous work has demonstrated across-arc geochemical variations related to subduction enrichment, and H-isotope data suggest that H2O in basaltic magmas is derived from the final breakdown of chlorite in the mantle portion of the slab. We use naturally glassy, olivine-hosted melt inclusions (MI) from the tephra deposits of eight primitive (MgO > 7 wt%) basaltic cinder cones to quantify the pre-eruptive volatile contents of mantle-derived melts in this region. The melt inclusions have B concentrations and isotope ratios that are similar to mid-ocean ridge basalt (MORB), suggesting extensive dehydration of the downgoing plate prior to reaching sub-arc depths and little input of slab-derived B into the mantle wedge. However, correlations of volatile and trace element ratios (H2O/Ce, Cl/Nb, Sr/Nd) in the melt inclusions demonstrate that geochemical variability is the result of variable addition of a hydrous subduction component to the mantle wedge. Furthermore, correlations between subduction component tracers and radiogenic isotope ratios show that the subduction component has less radiogenic Sr and Pb than the Lassen sub-arc mantle, which can be explained by melting of subducted Gorda MORB beneath the arc. Agreement between pMELTS melting models and melt inclusion volatile, major, and trace element data suggests that hydrous slab melt addition to the mantle wedge can produce the range in primitive compositions erupted in the Lassen region. Our results provide further evidence that chlorite-derived fluids from the mantle portion of the

  7. Imaging Transition Zone Thickness Beneath South America from SS Precursors

    Science.gov (United States)

    Schmerr, N.; Garnero, E.

    2006-12-01

    We image detailed upper mantle discontinuity structure beneath a number of geologically active regions, including the South American subduction zone, the Scotia plate subduction zone, and several volcanic hotspots (e.g., the Galapagos Islands), in a region ~10,000 km by 10,000 km wide, spanning 70° S to 20° N and 20° W to 110° W. Precursors to the seismic phase SS are analyzed, which form as a result of underside reflections off seismic discontinuities beneath the midpoint of the SS path and are highly sensitive to discontinuity depth and sharpness. Our SS dataset consists of over 15,000 high-quality transverse component broadband displacement seismograms collected from the Incorporated Research Institutions for Seismology (IRIS), the Canadian National Seismic Network (CNSN), as well as data from EarthScope seismic stations, and from the Canadian Northwest Experiment (CANOE) temporary broadband array deployment. This dataset densely samples several regions in our study area and significantly improves the sampling for this area compared to previous precursor studies. Data with common central SS bouncepoints are stacked to enhance precursory phases. Solution discontinuity structure depends on a number of factors, including dominant seismic period, crustal correction, signal-to-noise ratio threshold, and tomography model used for mantle heterogeneity correction. We exclude precursor data predicted to interfere with other seismic phases, such as topside reflections (e.g., s670sS), which have been demonstrated to contaminate final stacks. Solution transition zone thickness is at least 20 km thicker than global average estimates of 242 km along the northwestern portion of the South American subduction complex (Peru, Ecuador, and Columbia); this thickening extends 1000-1500 km to the east beneath the continent, but does not appear to continue south of -20° latitude along the convergent margin. A minimum of 10 km of thickening is imaged to the west of the Scotia

  8. Pn anisotropic tomography and mantle dynamics beneath China

    Science.gov (United States)

    Zhou, Zhigang; Lei, Jianshe

    2016-08-01

    We present a new high-resolution Pn anisotropic tomographic model of the uppermost mantle beneath China inferred from 52,061 Pn arrival-time data manually picked from seismograms recorded at provincial seismic stations in China and temporary stations in Tibet and the Tienshan orogenic belt. Significant features well correlated with surface geology are revealed and provide new insights into the deep dynamics beneath China. Prominent high Pn velocities are visible under the stable cratonic blocks (e.g., the Tarim, Junngar, and Sichuan basins, and the Ordos block), whereas remarkable low Pn velocities are observed in the tectonically active areas (e.g., Pamir, the Tienshan orogenic belt, central Tibet and the Qilian fold belt). A distinct N-S trending low Pn velocity zone around 86°E is revealed under the rift running from the Himalayan block through the Lhasa block to the Qiangtang block, which indicates the hot material upwelling due to the breaking-off of the subducting Indian slab. Two N-S trending low Pn velocity belts with an approximate N-S Pn fast direction along the faults around the Chuan-Dian diamond block suggest that these faults may serve as channels of mantle flow from Tibet. The fast Pn direction changes from N-S in the north across 27°N to E-W in the south, which may reflect different types of mantle deformation. The anisotropy in the south could be caused by the asthenospheric flow resulted from the eastward subduction of the Indian plate down to the mantle transition zone beneath the Burma arc. Across the Talas-Fergana fault in the Tienshan orogenic belt, an obvious difference in velocity and anisotropy is revealed. To the west, high Pn velocities and an arc-shaped fast Pn direction are observed, implying the Indo-Asian collision, whereas to the east low Pn velocities and a range-parallel Pn fast direction are imaged, reflecting the northward underthrusting of the Tarim lithosphere and the southward underthrusting of the Kazakh lithosphere. In

  9. Downbursts and microbursts - An aviation hazard. [downdrafts beneath thunderstorms

    Science.gov (United States)

    Fujita, T. T.

    1980-01-01

    Downburst and microburst phenomena occurring since 1975 are studied, based on meteorological analyses of aircraft accidents, aerial surveys of wind effects left behind downbursts, and studies of sub-mesoscale wind systems. It is concluded that microbursts beneath small, air mass thunderstorms are unpredictable in terms of weather forecast. Most aircraft incidents, however, were found to have occurred in the summer months, June through August. An intense microburst could produce 150 mph horizontal winds as well as 60 fps downflows at the tree-top level. The largest contributing factor to aircraft difficulties seemed to be a combination of the headwind decrease and the downflow. Anemometers and/or pressure sensors placed near runways were found effective for detecting gust fronts, but not for detecting downbursts. It is recommended that new detection systems placed on the ground or airborne, be developed, and that pilots be trained for simulated landing and go-around through microbursts.

  10. Can slabs melt beneath forearcs in hot subduction zones?

    Science.gov (United States)

    Ribeiro, J.; Maury, R.; Gregoire, M.

    2015-12-01

    At subduction zones, thermal modeling predict that the shallow part of the downgoing oceanic crust (test the hypothesis that adakites are pristine slab melts. We find that adakites from Baja California and Philippines formed by two distinct petrogenetic scenarios. In Baja California, hydrous mantle melts mixed/mingled with high-pressure (HP) adakite-type, slab melts within a lower crustal (~30 km depth) magma storage region before stalling into the upper arc crust (~7-15 km depth). In contrast, in the Philippines, primitive mantle melts stalled and crystallized within lower and upper crustal magma storage regions to produce silica-rich melts with an adakitic signature. Thereby, slab melting is not required to produce an adakitic geochemical fingerprint in hot subduction zones. However, our results also suggest that the downgoing crust potentially melted beneath Baja California.

  11. Ocean mixing beneath Pine Island Glacier Ice Shelf

    Science.gov (United States)

    Kimura, Satoshi; Dutrieux, Pierre; Jenkins, Adrian; Forryan, Alexander; Naveira Garabato, Alberto; Firing, Yvonne

    2016-04-01

    Ice shelves around Antarctica are vulnerable to increase in ocean-driven melting, with the melt rate depending on ocean temperature and strength of sub-ice-shelf-cavity circulations. We present repeated measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate and thermal variance dissipation rate beneath Pine Island Glacier Ice Shelf, collected by CTD, ADCP and turbulence sensors mounted on an Autonomous Underwater Vehicle (AUV). The turbulence quantities measured by the AUV outside the ice shelf are in good agreement with ship-based measurements. The highest rate of turbulent kinetic energy dissipation is found near the grounding line, while its temporal fluctuation over seabed ridge within the cavity corresponds to the tidal fluctuation predicted in the Pine Island Bay to the west. The highest thermal variance dissipation rate is found when the AUV was 0.5 m away from the ice, and the thermal variance dissipation generally increases with decreasing distance between the AUV and ice.

  12. Multicomponent seismic forward modeling of gas hydrates beneath the seafloor

    Institute of Scientific and Technical Information of China (English)

    Yang Jia-Jia; He Bing-Shou; Zhang Jian-Zhong

    2014-01-01

    We investigated the effect of microscopic distribution modes of hydrates in porous sediments, and the saturation of hydrates and free gas on the elastic properties of saturated sediments. We simulated the propagation of seismic waves in gas hydrate-bearing sediments beneath the seafloor, and obtained the common receiver gathers of compressional waves (P-waves) and shear waves (S-waves). The numerical results suggest that the interface between sediments containing gas hydrates and free gas produces a large-amplitude bottom-simulating reflector. The analysis of multicomponent common receiver data suggests that ocean-bottom seismometers receive the converted waves of upgoing P-and S-waves, which increases the complexity of the wavefield record.

  13. Subglacial lake drainage detected beneath the Greenland ice sheet.

    Science.gov (United States)

    Palmer, Steven; McMillan, Malcolm; Morlighem, Mathieu

    2015-10-09

    The contribution of the Greenland ice sheet to sea-level rise has accelerated in recent decades. Subglacial lake drainage events can induce an ice sheet dynamic response--a process that has been observed in Antarctica, but not yet in Greenland, where the presence of subglacial lakes has only recently been discovered. Here we investigate the water flow paths from a subglacial lake, which drained beneath the Greenland ice sheet in 2011. Our observations suggest that the lake was fed by surface meltwater flowing down a nearby moulin, and that the draining water reached the ice margin via a subglacial tunnel. Interferometric synthetic aperture radar-derived measurements of ice surface motion acquired in 1995 suggest that a similar event may have occurred 16 years earlier, and we propose that, as the climate warms, increasing volumes of surface meltwater routed to the bed will cause such events to become more common in the future.

  14. Subglacial lake drainage detected beneath the Greenland ice sheet

    Science.gov (United States)

    Palmer, Steven; McMillan, Malcolm; Morlighem, Mathieu

    2015-01-01

    The contribution of the Greenland ice sheet to sea-level rise has accelerated in recent decades. Subglacial lake drainage events can induce an ice sheet dynamic response—a process that has been observed in Antarctica, but not yet in Greenland, where the presence of subglacial lakes has only recently been discovered. Here we investigate the water flow paths from a subglacial lake, which drained beneath the Greenland ice sheet in 2011. Our observations suggest that the lake was fed by surface meltwater flowing down a nearby moulin, and that the draining water reached the ice margin via a subglacial tunnel. Interferometric synthetic aperture radar-derived measurements of ice surface motion acquired in 1995 suggest that a similar event may have occurred 16 years earlier, and we propose that, as the climate warms, increasing volumes of surface meltwater routed to the bed will cause such events to become more common in the future. PMID:26450175

  15. Magma heating by decompression-driven crystallization beneath andesite volcanoes.

    Science.gov (United States)

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

    2006-09-01

    Explosive volcanic eruptions are driven by exsolution of H2O-rich vapour from silicic magma. Eruption dynamics involve a complex interplay between nucleation and growth of vapour bubbles and crystallization, generating highly nonlinear variation in the physical properties of magma as it ascends beneath a volcano. This makes explosive volcanism difficult to model and, ultimately, to predict. A key unknown is the temperature variation in magma rising through the sub-volcanic system, as it loses gas and crystallizes en route. Thermodynamic modelling of magma that degasses, but does not crystallize, indicates that both cooling and heating are possible. Hitherto it has not been possible to evaluate such alternatives because of the difficulty of tracking temperature variations in moving magma several kilometres below the surface. Here we extend recent work on glassy melt inclusions trapped in plagioclase crystals to develop a method for tracking pressure-temperature-crystallinity paths in magma beneath two active andesite volcanoes. We use dissolved H2O in melt inclusions to constrain the pressure of H2O at the time an inclusion became sealed, incompatible trace element concentrations to calculate the corresponding magma crystallinity and plagioclase-melt geothermometry to determine the temperature. These data are allied to ilmenite-magnetite geothermometry to show that the temperature of ascending magma increases by up to 100 degrees C, owing to the release of latent heat of crystallization. This heating can account for several common textural features of andesitic magmas, which might otherwise be erroneously attributed to pre-eruptive magma mixing.

  16. Hydrothermal reservoir beneath Taal Volcano (Philippines): Implications to volcanic activity

    Science.gov (United States)

    Nagao, T.; Alanis, P. B.; Yamaya, Y.; Takeuchi, A.; Bornas, M. V.; Cordon, J. M.; Puertollano, J.; Clarito, C. J.; Hashimoto, T.; Mogi, T.; Sasai, Y.

    2012-12-01

    Taal Volcano is one of the most active volcanoes in the Philippines. The first recorded eruption was in 1573. Since then it has erupted 33 times resulting in thousands of casualties and large damages to property. In 1995, it was declared as one of the 15 Decade Volcanoes. Beginning in the early 1990s it has experienced several phases of abnormal activity, including seismic swarms, episodes of ground deformation, ground fissuring and hydrothermal activities, which continues up to the present. However, it has been noted that past historical eruptions of Taal Volcano may be divided into 2 distinct cycles, depending on the location of the eruption center, either at Main Crater or at the flanks. Between 1572-1645, eruptions occurred at the Main Crater, in 1707 to 1731, they occurred at the flanks. In 1749, eruptions moved back to the Main Crater until 1911. During the 1965 and until the end of the 1977 eruptions, eruptive activity once again shifted to the flanks. As part of the PHIVOLCS-JICA-SATREPS Project magnetotelluric and audio-magnetotelluric surveys were conducted on Volcano Island in March 2011 and March 2012. Two-dimensional (2-D) inversion and 3-D forward modeling reveals a prominent and large zone of relatively high resistivity between 1 to 4 kilometers beneath the volcano almost directly beneath the Main Crater, surrounded by zones of relatively low resistivity. This anomalous zone of high resistivity is hypothesized to be a large hydrothermal reservoir filled with volcanic fluids. The presence of this large hydrothermal reservoir could be related to past activities of Taal Volcano. In particular we believe that the catastrophic explosion described during the 1911 eruption was the result of the hydrothermal reservoir collapsing. During the cycle of Main Crater eruptions, this hydrothermal reservoir is depleted, while during a cycle of flank eruptions this reservoir is replenished with hydrothermal fluids.

  17. SOIL DEGRADATION PROCESSES FROM POLLUTION

    Directory of Open Access Journals (Sweden)

    Popov Leonid

    2012-06-01

    Full Text Available Investigations found HCH and DDT residuals in bottom sediments from several reservoirs and lakes as well as the main rivers, Nistru and Prut (concentrations ranged between 0.2 and 15.8 ppb. The concentration of PCBs in the topsoil collected beneath the capacitors battery at the Vulcănesti substation reached a level of 7100 ppm which is exceeding the MAC by five orders of magnitude (!. With no exception, allowable concentrations of PCBs in soil were exceeded also on the territory of other investigated substations, with peaks registered at the Briceni substation (2545 ppm and the Orhei substation (1959 ppm.

  18. SOIL DEGRADATION PROCESSES FROM POLLUTION

    OpenAIRE

    Popov Leonid; Ciudin Gheorghe; Rotaru Serghei

    2012-01-01

    Investigations found HCH and DDT residuals in bottom sediments from several reservoirs and lakes as well as the main rivers, Nistru and Prut (concentrations ranged between 0.2 and 15.8 ppb). The concentration of PCBs in the topsoil collected beneath the capacitors battery at the Vulcănesti substation reached a level of 7100 ppm which is exceeding the MAC by five orders of magnitude (!). With no exception, allowable concentrations of PCBs in soil were exceeded also on the territory of other in...

  19. Electrical conductivity anomaly beneath Mare Serenitatis detected by Lunokhod 2 and Apollo 16 magnetometers

    Science.gov (United States)

    Vanian, L. L.; Vnuchkova, T. A.; Egorov, I. V.; Basilevskii, A. T.; Eroshenko, E. G.; Fainberg, E. B.; Dyal, P.; Daily, W. D.

    1979-01-01

    Magnetic fluctuations measured by the Lunokhod 2 magnetometer in the Bay Le Monnier are distinctly anisotropic when compared to simultaneous Apollo 16 magnetometer data measured 1100 km away in the Descartes highlands. This anisotropy can be explained by an anomalous electrical conductivity of the upper mantle beneath Mare Serenitatis. A model is presented of anomalously lower electrical conductivity beneath Serenitatis and the simultaneous magnetic data from the Lunokhod 2 site at the mare edge and the Apollo 16 site are compared to the numerically calculated model solutions. This comparison indicates that the anisotropic fluctuations can be modeled by a nonconducting layer in the lunar lithosphere which is 150 km thick beneath the highlands and 300 km thick beneath Mare Serenitatis. A decreased electrical conductivity in the upper mantle beneath the mare may be due to a lower temperature resulting from heat carried out the magma source regions to the surface during mare flooding.

  20. Influence of perennial plants on chemical properties of arid calcareous soils in Iran

    Energy Technology Data Exchange (ETDEWEB)

    Karimian, N.; Razmi, K. (Shiraz Univ. (Iran))

    1990-10-01

    The authors conducted a study in Bajgah to determine the influence of perennial plants on some selected properties of soils formed on the highly calcareous parent material. The major plant genera were determined to be Agropyron, Artemisia, Astragalus, Dianthus, Eryngium, Peganum, Polygonum, Stipa, and Thymus. Tops of plants genera were found to be significantly different in ash, N, P, K, Ca, Mg, Na, Mn, Zn, and Cu; the concentration of Fe was not significantly different. The authors found the plants to differ significantly in their influence on soil properties. Peganum caused an accumulation of organic matter (OM) as high as 7% in the soil, in an environment where the soils typically contain less than 1% OM. Soil concentrations of P, K, Mn, Zn, and Cu were also found to vary significantly beneath different plant genera. They suggest these differences in OM accumulation were caused by plant litter. Concentration of Fe in the soils formed beneath different plant genera was statistically unchanged.

  1. Time-Dependent Flexural Deformation Beneath the Emperor Seamounts

    Science.gov (United States)

    Wessel, P.; Watts, A. B.; Kim, S. S.

    2014-12-01

    The Hawaii-Emperor seamount chain stretches over 6000 km from the Big Island of Hawaii to the subduction cusp off Kamchatka and represents a near-continuous record of hotspot volcanism since the Late Cretaceous. The load of these seamounts and islands has caused the underlying lithosphere to deform, developing a flexural flanking moat that is now largely filled with volcanoclastic sediments. Because the age differences between the seafloor and the seamounts vary by an order of magnitude or more along the chain, the Hawaii-Emperor chain and surrounding area is considered a natural laboratory for lithospheric flexure and has been studied extensively in order to infer the rheology of the oceanic lithosphere. While most investigations have focused on the Hawaiian Islands and proximal seamounts (where data sets are more complete, including seismic reflection and refraction, swath bathymetry and even mapping and dating of drowned reef terraces), far fewer studies have examined the flexural deformation beneath the remote Emperor chain. Preliminary analysis of satellite altimetry data shows the flexural moats to be associated with very large negative gravity anomalies relative to the magnitudes of the positive anomalies over the loads, suggesting considerable viscous or viscoelastic relaxation since the loads were emplaced 50-80 Myr ago. In our study, we will attempt to model the Emperor seamount chain load as a superposition of individual elliptical Gaussian seamounts with separate loading histories. We use Optimal Robust Separation (ORS) techniques to extract the seamount load from the regional background bathymetry and partition the residual load into a set of individual volcanoes. The crustal age grid and available seamount dates are used to construct a temporal loading model and evaluate the flexural response of the lithosphere beneath the Emperor seamounts. We explore a variety of rheological models and loading scenarios that are compatible with the inferred load

  2. Seismic Constraints on the Mantle Viscosity Structure beneath Antarctica

    Science.gov (United States)

    Wiens, Douglas; Heeszel, David; Aster, Richard; Nyblade, Andrew; Wilson, Terry

    2015-04-01

    Lateral variations in upper mantle viscosity structure can have first order effects on glacial isostatic adjustment. These variations are expected to be particularly large for the Antarctic continent because of the stark geological contrast between ancient cratonic and recent tectonically active terrains in East and West Antarctica, respectively. A large misfit between observed and predicted GPS rates for West Antarctica probably results in part from the use of a laterally uniform viscosity structure. Although not linked by a simple relationship, mantle seismic velocities can provide important constraints on mantle viscosity structure, as they are both largely controlled by temperature and water content. Recent higher resolution seismic models for the Antarctic mantle, derived from data acquired by new seismic stations deployed in the AGAP/GAMSEIS and ANET/POLENET projects, offer the opportunity to use the seismic velocity structure to place new constraints on the viscosity of the Antarctic upper mantle. We use an Antarctic shear wave velocity model derived from array analysis of Rayleigh wave phase velocities [Heeszel et al, in prep] and examine a variety of methodologies for relating seismic, thermal and rheological parameters to compute a suite of viscosity models for the Antarctic mantle. A wide variety of viscosity structures can be derived using various assumptions, but they share several robust common elements. There is a viscosity contrast of at least two orders of magnitude between East and West Antarctica at depths of 80-250 km, reflecting the boundary between cold cratonic lithosphere in East Antarctica and warm upper mantle in West Antarctica. The region beneath the Ellsworth-Whitmore Mtns and extending to the Pensacola Mtns. shows intermediate viscosity between the extremes of East and West Antarctica. There are also significant variations between different parts of West Antarctica, with the lowest viscosity occurring beneath the Marie Byrd Land (MBL

  3. Sources and sinks of methane beneath polar ice

    Science.gov (United States)

    Priscu, J. C.; Adams, H. E.; Hand, K. P.; Dore, J. E.; Matheus-Carnevali, P.; Michaud, A. B.; Murray, A. E.; Skidmore, M. L.; Vick-Majors, T.

    2014-12-01

    Several icy moons of the outer solar system carry subsurface oceans containing many times the volume of liquid water on Earth and may provide the greatest volume of habitable space in our solar system. Functional sub-ice polar ecosystems on Earth provide compelling models for the habitability of extraterrestrial sub-ice oceans. A key feature of sub-ice environments is that most of them receive little to no solar energy. Consequently, organisms inhabiting these environments must rely on chemical energy to assimilate either carbon dioxide or organic molecules to support their metabolism. Methane can be utilized by certain bacteria as both a carbon and energy source. Isotopic data show that methane in Earth's polar lakes is derived from both biogenic and thermogenic sources. Thermogenic sources of methane in the thermokarst lakes of the north slope of Alaska yield supersaturated water columns during winter ice cover that support active populations of methanotrophs during the polar night. Methane in the permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica varies widely in concentration and is produced either by contemporary methanogenesis or is a relic from subglacial flow. Rate measurements revealed that microbial methane oxidation occurs beneath the ice in both the arctic and Antarctic lakes. The first samples collected from an Antarctic subglacial environment beneath 800 m of ice (Subglacial Lake Whillans) revealed an active microbial ecosystem that has been isolated from the atmosphere for many thousands of years. The sediments of Lake Whillans contained high levels of methane with an isotopic signature that indicates it was produced via methanogenesis. The source of this methane appears to be from the decomposition of organic carbon deposited when this region of Antarctica was covered by the sea. Collectively, data from these sub-ice environments show that methane transformations play a key role in microbial community metabolism. The discovery of

  4. Lateral variations of crustal structure beneath the Indochina Peninsula

    Science.gov (United States)

    Yu, Youqiang; Hung, Tran D.; Yang, Ting; Xue, Mei; Liu, Kelly H.; Gao, Stephen S.

    2017-08-01

    Crustal thickness (H) and Vp/Vs (κ) measurements obtained by stacking P-to-S receiver functions recorded at 32 broadband seismic stations covering the Indochina Peninsula reveal systematic spatial variations in crustal properties. Mafic bulk crustal composition as indicated by high κ (>1.81) observations is found to exist along major strike-slip faults and the southern part of the Peninsula, where pervasive basaltic magmatism is found and is believed to be the results of lithospheric thinning associated with the indentation of the Indian into the Eurasian plates. In contrast, crust beneath the Khorat Plateau, which occupies the core of the Indochina Block, has relatively large H values with a mean of 36.9 ± 3 km and small κ measurements with an average of 1.74 ± 0.04, which indicates an overall felsic bulk composition. Those observations for the Khorat Plateau are comparable to the undeformed part of the South China Block. The laterally heterogeneous distribution of crustal properties and its correspondence with indentation-related tectonic features suggest that the Indochina lithosphere is extruded as rigid blocks rather than as a viscous flow.

  5. Peeking Beneath the Caldera: Communicating Subsurface Knowledge of Newberry Volcano

    Science.gov (United States)

    Mark-Moser, M.; Rose, K.; Schultz, J.; Cameron, E.

    2016-12-01

    "Imaging the Subsurface: Enhanced Geothermal Systems and Exploring Beneath Newberry Volcano" is an interactive website that presents a three-dimensional subsurface model of Newberry Volcano developed at National Energy Technology Laboratory (NETL). Created using the Story Maps application by ArcGIS Online, this format's dynamic capabilities provide the user the opportunity for multimedia engagement with the datasets and information used to build the subsurface model. This website allows for an interactive experience that the user dictates, including interactive maps, instructive videos and video capture of the subsurface model, and linked information throughout the text. This Story Map offers a general background on the technology of enhanced geothermal systems and the geologic and development history of Newberry Volcano before presenting NETL's modeling efforts that support the installation of enhanced geothermal systems. The model is driven by multiple geologic and geophysical datasets to compare and contrast results which allow for the targeting of potential EGS sites and the reduction of subsurface uncertainty. This Story Map aims to communicate to a broad audience, and provides a platform to effectively introduce the model to researchers and stakeholders.

  6. Crawling beneath the free surface: Water snail locomotion

    CERN Document Server

    Lee, Sungyon; Hosoi, A E; Lauga, Eric

    2008-01-01

    Land snails move via adhesive locomotion. Through muscular contraction and expansion of their foot, they transmit waves of shear stress through a thin layer of mucus onto a solid substrate. Since a free surface cannot support shear stress, adhesive locomotion is not a viable propulsion mechanism for water snails that travel inverted beneath the free surface. Nevertheless, the motion of the freshwater snail, Sorbeoconcha physidae, is reminiscent of that of its terrestrial counterparts, being generated by the undulation of the snail foot that is separated from the free surface by a thin layer of mucus. Here, a lubrication model is used to describe the mucus flow in the limit of small amplitude interfacial deformations. By assuming the shape of the snail foot to be a traveling sine wave and the mucus to be Newtonian, an evolution equation for the interface shape is obtained and the resulting propulsive force on the snail is calculated. This propulsive force is found to be non-zero for moderate values of Capillar...

  7. Investigation of upper crustal structure beneath eastern Java

    Science.gov (United States)

    Martha, Agustya Adi; Widiyantoro, Sri; Cummnins, Phil; Saygin, Erdinc; Masturyono

    2016-05-01

    The complexity of geology structure in eastern Java causes this region has many potential resources as much as the disasters. Therefore, the East Java province represents an interesting area to be explored, especially regarding its upper crustal structure. To investigate this structure, we employ the Ambient Noise Tomography (ANT) method. We have used seismic waveform data from 25 Meteorological, Climatological and Geophysical Agency (BMKG) stationary seismographic stations and 26 portable seismographs installed for 2 to 8 weeks. Inter-station cross-correlation produces more than 800 Rayleigh wave components, which depict the structure beneath eastern Java. Based on the checkerboard resolution test, we found that the optimal grid size is 0.25ox0.25o. Our inversion results for the periods of 1 to 10 s indicate a good agreement with geological and Bouguer anomaly maps. Rembang high depression, most of the southern mountains zone, the northern part of Rembang zone and the central part of the Madura Island, the area of high gravity anomaly and areas dominated with igneous rocks are associated with high velocity zones. On the other hand, Kendeng zone and most of the basin in the Rembang zone are associated with low velocity zones.

  8. Geophysical investigation of seepage beneath an earthen dam.

    Science.gov (United States)

    Ikard, S J; Rittgers, J; Revil, A; Mooney, M A

    2015-01-01

    A hydrogeophysical survey is performed at small earthen dam that overlies a confined aquifer. The structure of the dam has not shown evidence of anomalous seepage internally or through the foundation prior to the survey. However, the surface topography is mounded in a localized zone 150 m downstream, and groundwater discharges from this zone periodically when the reservoir storage is maximum. We use self-potential and electrical resistivity tomography surveys with seismic refraction tomography to (1) determine what underlying hydrogeologic factors, if any, have contributed to the successful long-term operation of the dam without apparent indicators of anomalous seepage through its core and foundation; and (2) investigate the hydraulic connection between the reservoir and the seepage zone to determine whether there exists a potential for this success to be undermined. Geophysical data are informed by hydraulic and geotechnical borehole data. Seismic refraction tomography is performed to determine the geometry of the phreatic surface. The hydro-stratigraphy is mapped with the resistivity data and groundwater flow patterns are determined with self-potential data. A self-potential model is constructed to represent a perpendicular profile extending out from the maximum cross-section of the dam, and self-potential data are inverted to recover the groundwater velocity field. The groundwater flow pattern through the aquifer is controlled by the bedrock topography and a preferential flow pathway exists beneath the dam. It corresponds to a sandy-gravel layer connecting the reservoir to the downstream seepage zone.

  9. Ocean mixing beneath Pine Island Glacier ice shelf, West Antarctica

    Science.gov (United States)

    Kimura, Satoshi; Jenkins, Adrian; Dutrieux, Pierre; Forryan, Alexander; Naveira Garabato, Alberto C.; Firing, Yvonne

    2016-12-01

    Ice shelves around Antarctica are vulnerable to an increase in ocean-driven melting, with the melt rate depending on ocean temperature and the strength of flow inside the ice-shelf cavities. We present measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate, and thermal variance dissipation rate beneath Pine Island Glacier ice shelf, West Antarctica. These measurements were obtained by CTD, ADCP, and turbulence sensors mounted on an Autonomous Underwater Vehicle (AUV). The highest turbulent kinetic energy dissipation rate is found near the grounding line. The thermal variance dissipation rate increases closer to the ice-shelf base, with a maximum value found ˜0.5 m away from the ice. The measurements of turbulent kinetic energy dissipation rate near the ice are used to estimate basal melting of the ice shelf. The dissipation-rate-based melt rate estimates is sensitive to the stability correction parameter in the linear approximation of universal function of the Monin-Obukhov similarity theory for stratified boundary layers. We argue that our estimates of basal melting from dissipation rates are within a range of previous estimates of basal melting.

  10. PN velocity beneath Western New Mexico and Eastern Arizona

    Science.gov (United States)

    Jaksha, L. H.

    1985-01-01

    The experiment involved observing Pn arrivals on an areal array of 7 seismic stations located in the transition zone and along the Jemez lineament. Explosions in coal and copper mines in New Mexico and Arizona were used as energy sources as well as military detonations at White Sands Missile Range, New Mexico, Yuma, Arizona, and the Nevada Test Site. Very preliminary results suggest a Pn velocity of 7.94 km/s (with a fairly large uncertainty) beneath the study area. The Pn delay times, which can be converted to estimates of crustal thickness given knowledge of the velocity structure of the crust increase both to the north and east of Springerville, Arizona. As a constraint on the velocity of Pn, researchers analyzed the reversed refraction line GNOME-HARDHAT which passes through Springerville oriented NW to SE. This analysis resulted in a Pn velocity of 7.9-8.0 km/s for the transition zone. These preliminary results suggest that a normal Pn velocity might persist even though the crust thins (from north to south) by 15 km along the length of the Arizona-New Mexico border. If the upper mantle is currently hot anywhere in western New Mexico or eastern Arizona then the dimensions of the heat source (or sources) might be small compared to the intra-station distances of the seismic arrays used to estimate the velocity of Pn.

  11. Crawling beneath the free surface: Water snail locomotion

    Science.gov (United States)

    Lee, Sungyon; Bush, John W. M.; Hosoi, A. E.; Lauga, Eric

    2008-08-01

    Land snails move via adhesive locomotion. Through muscular contraction and expansion of their foot, they transmit waves of shear stress through a thin layer of mucus onto a solid substrate. Since a free surface cannot support shear stress, adhesive locomotion is not a viable propulsion mechanism for water snails that travel inverted beneath the free surface. Nevertheless, the motion of the freshwater snail, Sorbeoconcha physidae, is reminiscent of that of its terrestrial counterparts, being generated by the undulation of the snail foot that is separated from the free surface by a thin layer of mucus. Here, a lubrication model is used to describe the mucus flow in the limit of small-amplitude interfacial deformations. By assuming the shape of the snail foot to be a traveling sine wave and the mucus to be Newtonian, an evolution equation for the interface shape is obtained and the resulting propulsive force on the snail is calculated. This propulsive force is found to be nonzero for moderate values of the capillary number but vanishes in the limits of high and low capillary number. Physically, this force arises because the snail's foot deforms the free surface, thereby generating curvature pressures and lubrication flows inside the mucus layer that couple to the topography of the foot.

  12. Evaluation of Sources of Nitrate Beneath Food Processing Wastewater-Application Sites near Umatilla, Oregon

    Science.gov (United States)

    Frans, Lonna; Paulson, Anthony; Richerson, Phil; Striz, Elise; Black, Curt

    2009-01-01

    Water samples from wells were collected beneath and downgradient of two food-processing wastewater-application sites near Umatilla, Oregon. These samples were analyzed for nitrate stable isotopes, nutrients, major ions, and age-dating constituents to determine if nitrate-stable isotopes can be used to differentiate food-processing waste from other potential sources of nitrate. Major-ion data from each site were used to determine which samples were associated with the recharge of the food-processing wastewater. End-member mixing analysis was used to determine the relative amounts of each identified end member within the samples collected from the Terrace Farm site. The delta nitrogen-15 (delta 15N) of nitrate generally ranged between +2 and +9 parts per thousand and the delta oxygen-18 (delta 18O) of nitrate generally ranged between -2 and -7 parts per thousand. None of the samples that were determined to be associated with the wastewater were different from the samples that were not affected by the wastewater. The nitrate isotope values measured in this study are also characteristic of ammonium fertilizer, animal and human waste, and soil nitrate; therefore, it was not possible to differentiate between food-processing wastewater and the other nitrate sources. Values of delta 15N and delta 18O of nitrate provided no more information about the sources of nitrate in the Umatilla River basin than did a hydrologic and geochemical understanding of the ground-water system derived from interpreting water-level and major-ion chemistry data.

  13. Bioremediation of RDX in the vadose zone beneath the Pantex Plant

    Energy Technology Data Exchange (ETDEWEB)

    Shull, T.L.; Speitel, G.E. Jr.; McKinney, D.C. [Univ. of Texas, Austin, TX (United States). Dept. of Civil Engineering

    1999-01-01

    The presence of dissolved high explosives (HE), in particular RDX and HMX, is well documented in the perched aquifer beneath the Pantex Plant, but the distribution of HE in the vadose zone has not yet been well defined. Although current remediation activities focus on the contamination in the perched aquifer, eventually regulatory concern is likely to turn to the residual contamination in the vadose zone. Sources of HE include the infiltration of past wastewater discharges from several HE-processing facilities through the ditch drainage system and leachate from former Landfill 3. With limited existing data on the HE distribution in the vadose zone and without preventive action, it must be assumed that residual HE could be leached into infiltrating water, providing a continuing supply of contamination to the perched aquifer. The purpose of this project was to more closely examine the fate and transport of HE in the vadose zone through mathematical modeling and laboratory experimentation. In particular, this report focuses on biodegradation as one possible fate of HE. Biodegradation of RDX in the vadose zone was studied because it is both present in highest concentration and is likely to be of the greatest regulatory concern. This study had several objectives: determine if indigenous soil organisms are capable of RDX biodegradation; determine the impact of electron acceptor availability and nutrient addition on RDX biodegradation; determine the extent of RDX mineralization (i.e., conversion to inorganic carbon) during biodegradation; and estimate the kinetics of RDX biodegradation to provide information for mathematical modeling of fate and transport.

  14. Nutrient Discharge Beneath Urban Lawns To A Sandy Coastal Aquifer, Perth, Western Australia

    Science.gov (United States)

    Sharma, M. L.; Herne, D. E.; Byrne, J. D.; Kin, P. G.

    1996-01-01

    Excess nitrogen and phosphorus leaching beneath urban lawns on sandy soils in metropolitan Perth, Western Australia, may pose a serious threat not only to the quality of the underlying groundwater but also to many surface-water bodies. In this study, suction-driven lysimeters were developed and used to quantify water and nutrient fluxes below the root zone at four urban lawn sites in Perth. The four sites received similar fertiliser treatment but differed in irrigation regimes. Over a period of 12 months, up to 51 percent of incident water passed below the root zone. Annual flow-weighted concentrations of NO3-N in the leachate ranged from 0.8-5.4 mg/L, whereas PO4-P concentrations ranged from 0.003-0.034 mg/L. At most sites, NO3-N concentrations periodically equalled or exceeded the World Health Organization (WHO) drinking-water limit of 10 mg/L; high concentration were maintained for longer periods at two sites with coarser sands and high irrigation regimes. Evidence exists that concentrations of N and P in urban groundwater are reduced through dilution and possibly through chemical transformation and adsorption. It is unlikely that NO3-N concentrations in groundwater will exceed the WHO drinking limit except for relatively short periods of time. However, nutrients (especially N) from fertilised lawns are a threat to wetlands and waterways into which nutrient-rich groundwater is discharged. Modified management practices for urban lawns, or alternative-style home gardens may need to be developed in order to minimise nutrient enrichment of groundwater and water bodies. Some suggestions for these are presented.

  15. Drusen-like beneath retinal deposits in type II mesangiocapillary glomerulonephritis: a review

    Directory of Open Access Journals (Sweden)

    Miguel Hage Amaro

    2015-02-01

    Full Text Available The aim of this paper is to do a review of Drusen-like beneath retinal deposits in type II mesangiocapillary glomerulonephritis. Drusenlike beneath retinal deposits in type II mesangiocapillary glomerulonephritis appear to develop at an early age, often second decade of life different of drusen from age-related macular degeneration (AMD.Long term follow-up of the cases in this disease shows in the most of them, no progression of the of drusen-like beneath retinal deposits in type II mesangiocapillary glomerulonefritis, the most of subjects retain good visual acuity and no specific treatment is indicated.

  16. Effects of Vegetation Removal and Soil Disturbance on Soil Organic and Inorganic Carbon Dynamics in California Desert Ecosystems

    Science.gov (United States)

    Swanson, A. C.; Allen, E. B.; Allen, M. F.; Hernandez, R. R.

    2015-12-01

    Solar energy developments are projected to be deployed over desert wildland areas with deep soil inorganic carbon (SIC) deposits, which often involves elimination of deep-rooted vegetation. This land cover change may systemically alter SIC pools since respired CO2 is the carbon (C) source during SIC formation. We sought to understand how removal of creosote bush scrub affects soil C pools. We hypothesized that vegetation is important for maintaining SIC and soil organic C (SOC) pools and that disturbance to the vegetation and soil will change CO2 flux with increased losses from SIC. Soils were collected from sites that had intact creosote bush scrub habitat adjacent to disturbed, bare areas where the native vegetation had been previously removed. Samples were taken from beneath shrub canopies and interspaces in intact areas, and from random points in the disturbed area. Soils were analyzed for SIC, SOC, microbial and labile C, and δ13C. Soils were also incubated to determine the potential CO2 flux from disturbed and undisturbed soils along with the sources of CO2. Three replicates per soil underwent a control and water addition treatment and flux and δ13C of CO2 were measured continuously. Control replicates yielded no significant CO2 flux. CO2 flux from watered soils was higher beneath shrub canopy (18.57µmol g soil-1 day-1±1.86) than the interspace soils (0.86 µmol g soil-1 day-1±0.17). Soils collected from bare areas had an intermediate flux (5.41 µmol g soil-1 day-1±2.68 and 3.68 µmol g soil-1 day-1±0.85, respectively) lying between shrub canopy and interspace soils. There was no significant difference between the δ13C values of CO2 from shrub canopy and interspace soils, both of which had a very low δ13C values (-22.60‰±0.64 and -23.88‰±0.89, respectively), resembling that of organic C. However, the isotopic values of CO2 from disturbed soils were significantly higher (-16.68‰±1.36 and -15.22‰±2.12, respectively) suggesting that these

  17. Multi-scale Modelling of the Ocean Beneath Ice Shelves

    Science.gov (United States)

    Candy, A. S.; Kimura, S.; Holland, P.; Kramer, S. C.; Piggott, M. D.; Jenkins, A.; Pain, C. C.

    2011-12-01

    Quantitative prediction of future sea-level is currently limited because we lack an understanding of how the mass balance of the Earth's great ice sheets respond to and influence the climate. Understanding the behaviour of the ocean beneath an ice shelf and its interaction with the sheet above presents a great scientific challenge. A solid ice cover, in many places kilometres thick, bars access to the water column, so that observational data can only be obtained by drilling holes through, or launching autonomous vehicles beneath, the ice. In the absence of a comprehensive observational database, numerical modelling can be a key tool to advancing our understanding of the sub-ice-shelf regime. While we have a reasonable understanding of the overall ocean circulation and basic sensitivities, there remain critical processes that are difficult or impossible to represent in current operational models. Resolving these features adequately within a domain that includes the entire ice shelf and continental shelf to the north can be difficult with a structured horizontal resolution. It is currently impossible to adequately represent the key grounding line region, where the water column thickness reduces to zero, with a structured vertical grid. In addition, fronts and pycnoclines, the ice front geometry, shelf basal irregularities and modelling surface pressure all prove difficult in current approaches. The Fluidity-ICOM model (Piggott et al. 2008, doi:10.1002/fld.1663) simulates non-hydrostatic dynamics on meshes that can be unstructured in all three dimensions and uses anisotropic adaptive resolution which optimises the mesh and calculation in response to evolving solution dynamics. These features give it the flexibility required to tackle the challenges outlined above and the opportunity to develop a model that can improve understanding of the physical processes occurring under ice shelves. The approaches taken to develop a multi-scale model of ice shelf ocean cavity

  18. Soils - NRCS Web Soil Survey

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — Web Soil Survey (WSS) provides soil data and information produced by the National Cooperative Soil Survey. It is operated by the USDA Natural Resources Conservation...

  19. Slab melting and magma generation beneath the southern Cascade Arc

    Science.gov (United States)

    Walowski, K. J.; Wallace, P. J.; Clynne, M. A.

    2014-12-01

    Magma formation in subduction zones is interpreted to be caused by flux melting of the mantle wedge by fluids derived from dehydration of the downgoing oceanic lithosphere. In the Cascade Arc and other hot-slab subduction zones, however, most dehydration reactions occur beneath the forearc, necessitating a closer investigation of magma generation processes in this setting. Recent work combining 2-D steady state thermal models and the hydrogen isotope composition of olivine-hosted melt inclusions from the Lassen segment of the Cascades (Walowski et al., 2014; in review) has shown that partial melting of the subducted basaltic crust may be a key part of the subduction component in hot arcs. In this model, fluids from the slab interior (hydrated upper mantle) rise through the slab and cause flux-melting of the already dehydrated MORB volcanics in the upper oceanic crust. In the Shasta and Lassen segments of the southern Cascades, support for this interpretation comes from primitive magmas that have MORB-like Sr isotope compositions that correlate with subduction component tracers (H2O/Ce, Sr/P) (Grove et al. 2002, Borg et al. 2002). In addition, mass balance calculations of the composition of subduction components show ratios of trace elements to H2O that are at the high end of the global arc array (Ruscitto et al. 2012), consistent with the role of a slab-derived melt. Melting of the subducted basaltic crust should contribute a hydrous dacitic or rhyolitic melt (e.g. Jego and Dasgupta, 2013) to the mantle wedge rather than an H2O-rich aqueous fluid. We are using pHMELTS and pMELTS to model the reaction of hydrous slab melts with mantle peridotite as the melts rise through the inverted thermal gradient in the mantle wedge. The results of the modeling will be useful for understanding magma generation processes in arcs that are associated with subduction of relatively young oceanic lithosphere.

  20. Seabed topography beneath Larsen C Ice Shelf from seismic soundings

    Directory of Open Access Journals (Sweden)

    A. M. Brisbourne

    2013-08-01

    Full Text Available Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-shelf bathymetry model derived from the inversion of IceBridge gravity data. A series of lines were collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-shelf oceanic circulation may be affected by ice draft and sub-shelf cavity thickness. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Measured temperatures within the ice column and at the ice base were used to define the velocity profile through the remainder of the ice column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice and water cavity thickness are in general <10 m. Compared with the seismic measurements, the root-mean-square error in the gravimetrically derived bathymetry at the seismic sites is 162 m. The seismic profiles prove the non-existence of several bathymetric features that are indicated in the gravity inversion model, significantly modifying the expected oceanic circulation beneath the ice shelf. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of IceBridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-shelf ocean circulation models.

  1. Seabed topography beneath Larsen C Ice Shelf from seismic soundings

    Science.gov (United States)

    Brisbourne, A. M.; Smith, A. M.; King, E. C.; Nicholls, K. W.; Holland, P. R.; Makinson, K.

    2014-01-01

    Seismic reflection soundings of ice thickness and seabed depth were acquired on the Larsen C Ice Shelf in order to test a sub-ice shelf bathymetry model derived from the inversion of IceBridge gravity data. A series of lines was collected, from the Churchill Peninsula in the north to the Joerg Peninsula in the south, and also towards the ice front. Sites were selected using the bathymetry model derived from the inversion of free-air gravity data to indicate key regions where sub-ice shelf oceanic circulation may be affected by ice draft and seabed depth. The seismic velocity profile in the upper 100 m of firn and ice was derived from shallow refraction surveys at a number of locations. Measured temperatures within the ice column and at the ice base were used to define the velocity profile through the remainder of the ice column. Seismic velocities in the water column were derived from previous in situ measurements. Uncertainties in ice and water cavity thickness are in general model, significantly modifying the expected oceanic circulation beneath the ice shelf. Similar features have previously been shown to be highly significant in affecting basal melt rates predicted by ocean models. The discrepancies between the gravity inversion results and the seismic bathymetry are attributed to the assumption of uniform geology inherent in the gravity inversion process and also the sparsity of IceBridge flight lines. Results indicate that care must be taken when using bathymetry models derived by the inversion of free-air gravity anomalies. The bathymetry results presented here will be used to improve existing sub-ice shelf ocean circulation models.

  2. Fine structure of Pn velocity beneath Sichuan-Yunnan region

    Institute of Scientific and Technical Information of China (English)

    黄金莉; 宋晓东; 汪素云

    2003-01-01

    We use 23298 Pn arrival-time data from Chinese national and provincial earthquake bulletins to invert fine structure of Pn velocity and anisotropy at the top of the mantle beneath the Sichuan-Yunnan and its adjacent region. The results suggest that the Pn velocity in this region shows significant lateral variation; the Pn velocity varies from 7.7 to 8.3 km/s. The Pn-velocity variation correlates well with the tectonic activity and heat flow of the region. Low Pn velocity is observed in southwest Yunnan , Tengchong volcano area, and the Panxi tectonic area. These areas have very active seismicity and tectonic activity with high surface heat flow. On the other hand, high Pn velocity is observed in some stable regions, such as the central region of the Yangtze Platform; the most pronounced high velocity area is located in the Sichuan Basin, south of Chengdu. Pn anisotropy shows a complex pattern of regional deformation. The Pn fast direction shows a prominent clockwise rotation pattern from east of the Tibetan block to the Sichuan-Yunnan diamond block to southwest Yunnan, which may be related to southeastward escape of the Tibetan Plateau material due to the collision of the Indian Plate to the Eurasia Plate. Thus there appears to be strong correlation between the crustal deformation and the upper mantle structure in the region. The delay times of events and stations show that the crust thickness decreases from the Tibetan Plateau to eastern China, which is consistent with the results from deep seismic sounding.

  3. Conflicting Geophysical and Geochemical Indicators of Mantle Temperature Beneath Tibet

    Science.gov (United States)

    Klemperer, S. L.

    2013-12-01

    In Tibet a small number of earthquakes occurs at 75-100 km depth, spanning the Moho, reaching >350 km and >550 km north of the Himalayan front in south-eastern Tibet and western Tibet respectively. 'Earthquake thermometry' implies these deep earthquakes occur in anhydrous lower lithosphere, either anorthitic or ultramafic, at 0.1RA (~1% mantle fluid) are conventionally taken to imply an unequivocal mantle component. Time-averaged upward flow rates calculated from measured 3He/4He ratios (R) and [4He] range from ~1-15 cm/a, implying transport times of 0.5-7 Ma through a 70-km thick crust. Discussion of 3He in Tibet in the western literature has been dominated by a single paper (Hoke et al., EPSL, 2000) that reported modest mantle helium (0.110% mantle fluids are reported 120 km and 150 km south of the northern limit of deep earthquakes in southeastern and western Tibet respectively. These hot springs apparently sampled mantle with T>800°C south of the locations where earthquake thermometry implies Moho temperatures India, Nepal and Pakistan, even though the 800°C isotherm is substantially shallower there than beneath southern Tibet? More plausibly the mantle helium is derived from an Asian mantle wedge above the region of deep earthquakes, in which case underthrusting Indian lithosphere is not intact, but breaks into an upper layer forming the lower crust of the Tibetan Plateau, and a lower seismogenic layer that is subducted more deeply into the mantle. Based on the geothermal springs, an Asian mantle wedge extended south of the Indus Tsangpo suture in SE Tibet and to the Karakoram fault in W Tibet until the latest Miocene, or even more recently.

  4. Soil microbial responses to nitrogen addition in arid ecosystems

    Directory of Open Access Journals (Sweden)

    Robert L Sinsabaugh

    2015-08-01

    Full Text Available The N cycle of arid ecosystems is influenced by low soil organic matter, high soil pH and extremes in water potential and temperature that lead to open canopies and development of biological soil crusts (biocrusts. We investigated the effects of N amendment on soil microbial dynamics in a Larrea tridentata-Ambrosia dumosa shrubland site in southern Nevada USA. Sites were fertilized with a NO3-NH4 mix at 0, 7, and 15 kg ha-1 yr-1 from March 2012 to March 2013. In March 2013, biocrust (0-0.5 cm and bulk soils (0-10 cm were collected beneath Ambrosia canopies and in the interspaces between plants. Biomass responses were assessed as bacterial and fungal SSU rRNA gene copy number and chlorophyll a concentration. Metabolic responses were measured by five ecoenzyme activities (EEA and rates of N transformation. By most measures, nutrient availability, microbial biomass and process rates were greater in soils beneath the shrub canopy compared to the interspace between plants, and greater in the surface biocrust horizon compared to the deeper 10 cm soil profile. Most measures responded positively to experimental N addition. Effect sizes were generally greater for bulk soil than biocrust. Results were incorporated into a meta-analysis of arid ecosystem responses to N.

  5. Tradeoffs between soil, water, and carbon -- a national scale analysis from New Zealand.

    Science.gov (United States)

    Dymond, John R; Ausseil, Anne-Gaelle E; Ekanayake, Jagath C; Kirschbaum, Miko U F

    2012-03-01

    The tradeoffs between the regulation of soil erosion, provision of fresh water, and climate regulation associated with new Pinus radiata forests in New Zealand are explored using national models. These three ecosystem services for which there is strong demand are monetised as commodities (avoided soil erosion is NZ $1 per tonne; water is NZ $1 per cubic metre; and sequestered carbon is assumed to be NZ $73 per tonne). This permits their summation on a spatial basis to produce a national map of the net benefit of these ecosystem services. Net benefit is spatially variable depending primarily on the relative mix of forest growth rates and demand for irrigation water. New P. radiata forests (once mature) generally reduce mass-movement erosion by an order of magnitude. This provides significant benefits for erosion control where there are high natural rates of erosion. Benefits are especially large in catchments where high sedimentation is increasing flood risk and degrading aquatic ecosystems. The generally high growth rates of P. radiata in New Zealand (8.5 tonnesCha(-1)yr(-1) on average for existing forest) add significant environmental benefits of carbon sinks to climate regulation. However, the reduction of water yield associated with new forests (between 30% and 50%) can neutralise these benefits in catchments where there is demand for irrigation water, such as the eastern foothills of the Southern Alps and the tussock grasslands in the South Island.

  6. Liquid Spills on Permeable Soil Surfaces: Experimental Confirmations

    Energy Technology Data Exchange (ETDEWEB)

    Simmons, Carver S.; Keller, Jason M.

    2005-09-29

    Predictive tools for assessing the quantity of a spill on a soil from the observed spreading area could contribute to improving remediation when it is necessary. On a permeable soil, the visible spill area only hints about the amount of liquid that might reside below the surface. An understanding of the physical phenomena involved with spill propagation on a soil surface is key to assessing the liquid amount possibly present beneath the surface. The objective of this study is an improved prediction capability for spill behavior.

  7. Measurement of soil and indoor radon in Italy

    Energy Technology Data Exchange (ETDEWEB)

    Torri, G.; Azimi-Garakani, D.; Oppon, O.C.; Piermattei, S.; Susanna, A.F.; Seidel, J.-L.; Tommasino, L.; Ardanese, L. (ENEA, Rome (Italy))

    1988-01-01

    In spite of the fact that in the majority of cases the most important radon source is the soil and the rock beneath the house, no large scale survey of soil radon has ever been made in Italy. In this paper the results of a large scale survey of soil radon are presented from measurements made in hundreds of different sites in Latium and Campania. For several locations, results of measurements gathered for different years are described and up-dated. As a pilot project for indoor radon survey monthly variations of radon concentrations in typical houses have been investigated. (author).

  8. Imaging Canary Island hotspot material beneath the lithosphere of Morocco and southern Spain

    Science.gov (United States)

    Miller, Meghan S.; O'Driscoll, Leland J.; Butcher, Amber J.; Thomas, Christine

    2015-12-01

    The westernmost Mediterranean has developed into its present day tectonic configuration as a result of complex interactions between late stage subduction of the Neo-Tethys Ocean, continental collision of Africa and Eurasia, and the Canary Island mantle plume. This study utilizes S receiver functions (SRFs) from over 360 broadband seismic stations to seismically image the lithosphere and uppermost mantle from southern Spain through Morocco and the Canary Islands. The lithospheric thickness ranges from ∼65 km beneath the Atlas Mountains and the active volcanic islands to over ∼210 km beneath the cratonic lithosphere in southern Morocco. The common conversion point (CCP) volume of the SRFs indicates that thinned lithosphere extends from beneath the Canary Islands offshore southwestern Morocco, to beneath the continental lithosphere of the Atlas Mountains, and then thickens abruptly at the West African craton. Beneath thin lithosphere between the Canary hot spot and southern Spain, including below the Atlas Mountains and the Alboran Sea, there are distinct pockets of low velocity material, as inferred from high amplitude positive, sub-lithospheric conversions in the SRFs. These regions of low seismic velocity at the base of the lithosphere extend beneath the areas of Pliocene-Quaternary magmatism, which has been linked to a Canary hotspot source via geochemical signatures. However, we find that this volume of low velocity material is discontinuous along strike and occurs only in areas of recent volcanism and where asthenospheric mantle flow is identified with shear wave splitting analyses. We propose that the low velocity structure beneath the lithosphere is material flowing sub-horizontally northeastwards beneath Morocco from the tilted Canary Island plume, and the small, localized volcanoes are the result of small-scale upwellings from this material.

  9. Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

    OpenAIRE

    Livingstone, S.J.; Clark, C. D.; Woodward, J.; Kingslake, J.

    2013-01-01

    We use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of > 60\\% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are ob...

  10. Field-scale evaluation of water fluxes and manure solution leaching in feedlot pen soils.

    Science.gov (United States)

    García, Ana R; Maisonnave, Roberto; Massobrio, Marcelo J; Fabrizio de Iorio, Alicia R

    2012-01-01

    Accumulation of beef cattle manure on feedlot pen surfaces generates large amounts of dissolved solutes that can be mobilized by water fluxes, affecting surface and groundwater quality. Our objective was to examine the long-term impacts of a beef cattle feeding operation on water fluxes and manure leaching in feedlot pens located on sandy loam soils of the subhumid Sandy Pampa region in Argentina. Bulk density, gravimetric moisture content, and chloride concentration were quantified. Rain simulation trials were performed to estimate infiltration and runoff rates. Using chloride ion as a tracer, profile analysis techniques were applied to estimate the soil moisture flux and manure conservative chemical components leaching rates. An organic stratum was found over the surface of the pen soil, separated from the underlying soil by a highly compacted thin layer (the manure-soil interface). The soil beneath the organic layer showed greater bulk density in the A horizon than in the control soil and had greater moisture content. Greater concentrations of chloride were found as a consequence of the partial sealing of the manure-soil interface. Surface runoff was the dominant process in the feedlot pen soil, whereas infiltration was the main process in control soil. Soil moisture flux beneath pens decreased substantially after 15 yr of activity. The estimated minimum leaching rate of chloride was 13 times faster than the estimated soil moisture flux. This difference suggests that chloride ions are not exclusively transported by advective flow under our conditions but also by solute diffusion and preferential flow.

  11. Spatial and temporal variability of microbes in selected soils at the Nevada Test Site

    Energy Technology Data Exchange (ETDEWEB)

    Angerer, J.P.; Winkel, V.K.; Ostler, W.K.; Hall, P.F.

    1993-12-31

    Large areas encompassing almost 800 hectares on the Nevada Test Site, Nellis Air Force Range and the Tonopah Test Range are contaminated with plutonium. Decontamination of plutonium from these sites may involve removal of plants and almost 370,000 cubic meters of soil. The soil may be subjected to a series of processes to remove plutonium. After decontamination, the soils will be returned to the site and revegetated. There is a paucity of information on the spatial and temporal distribution of microbes in soils of the Mojave and Great Basin Deserts. Therefore, this study was initiated to determine the biomass and diversity of microbes in soils prior to decontamination. Soils were collected to a depth of 10 cm along each of five randomly located 30-m transects at each of four sites. To ascertain spatial differences, soils were collected from beneath major shrubs and from associated interspaces. Soils were collected every three to four months to determine temporal (seasonal) differences in microbial parameters. Soils from beneath shrubs generally had greater active fungi and bacteria, and greater non-amended respiration than soils from interspaces. Temporal variability also was found; total and active fungi, and non-amended respiration were correlated with soil moisture at the time of sampling. Information from this study will aid in determining the effects of plutonium decontamination on soil microorganisms, and what measures, if any, will be required to restore microbial populations during revegetation of these sites.

  12. Trench-parallel flow beneath the nazca plate from seismic anisotropy.

    Science.gov (United States)

    Russo, R M; Silver, P G

    1994-02-25

    Shear-wave splitting of S and SKS phases reveals the anisotropy and strain field of the mantle beneath the subducting Nazca plate, Cocos plate, and the Caribbean region. These observations can be used to test models of mantle flow. Two-dimensional entrained mantle flow beneath the subducting Nazca slab is not consistent with the data. Rather, there is evidence for horizontal trench-parallel flow in the mantle beneath the Nazca plate along much of the Andean subduction zone. Trench-parallel flow is attributale utable to retrograde motion of the slab, the decoupling of the slab and underlying mantle, and a partial barrier to flow at depth, resulting in lateral mantle flow beneath the slab. Such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the Pacific basin to the growing mantle reservoir beneath the Atlantic basin. Trenchparallel flow may explain the eastward motions of the Caribbean and Scotia sea plates, the anomalously shallow bathymetry of the eastern Nazca plate, the long-wavelength geoid high over western South America, and it may contribute to the high elevation and intense deformation of the central Andes.

  13. Three-dimensional numerical modeling of thermal regime and slab dehydration beneath Kanto and Tohoku, Japan

    Science.gov (United States)

    Ji, Yingfeng; Yoshioka, Shoichi; Manea, Vlad Constantin; Manea, Marina; Matsumoto, Takumi

    2017-01-01

    Although the thermal regime of the interface between two overlapping subducting plates, such as those beneath Kanto, Japan, is thought to play an important role in affecting the distribution of interplate and intraslab earthquakes, the estimation of the thermal regime remains challenging to date. We constructed a three-dimensional (3-D) thermal convection model to simulate the subduction of the Pacific plate along the Japan Trench and Izu-Bonin Trench, including the subduction of the Philippine Sea beneath Kanto and investigated the slab thermal regime and slab water contents in this complex tectonic setting. Based on the subduction parameters tested in generic models with two flat oceanic plates, a faster or thicker plate subducting in a more trench-normal direction produces a colder slab thermal regime. The interplate temperature of the cold anomaly beneath offshore Kanto was approximately 300°C colder than that beneath offshore Tohoku at a same depth of 40 km and approximately 600°C colder at a depth of 70 km. The convergence between the two subducting plates produces an asymmetric thermal structure in the slab contact zone beneath Kanto, which is characterized by clustered seismicity in the colder southwestern half. The thermo-dehydration state of the mid-ocean ridge basalt near the upper surface of the subducted Pacific plate controls the interplate seismicity beneath the Kanto-Tohoku region according to the spatial concurrence of the thermo-dehydration and seismicity along the megathrust fault zone of the subducted Pacific plate.

  14. Radiation budget and soil heat fluxes in different Arctic tundra vegetation types

    Science.gov (United States)

    Juszak, Inge; Iturrate Garcia, Maitane; Gastellu-Etchegorry, Jean-Philippe; Schaepman, Michael E.; Schaepman-Strub, Gabriela

    2016-04-01

    While solar radiation is one of the primary energy sources for warming and thawing permafrost soil, the amount of shortwave radiation reaching the soil is reduced by vegetation shading. Climate change has led to greening, shrub expansion and encroachment in many Arctic tundra regions and further changes are anticipated. These vegetation changes feed back to the atmosphere and permafrost as they modify the surface energy budget. However, canopy transmittance of solar radiation has rarely been measured or modelled for a variety of tundra vegetation types. We assessed the radiation budget of the most common vegetation types at the Kytalyk field site in North-East Siberia (70.8°N, 147.5°E) with field measurements and 3D radiative transfer modelling and linked it to soil heat fluxes. Our results show that Arctic tundra vegetation types differ in canopy albedo and transmittance as well as in soil heat flux and active layer thickness. Tussock sedges transmitted on average 56% of the incoming light and dwarf shrubs 27%. For wet sedges we found that the litter layer was very important as it reduced the average transmittance to only 6%. Model output indicated that both, albedo and transmittance, also depend on the spatial aggregation of vegetation types. We found that permafrost thaw was more strongly related to soil properties than to canopy shading. The presented radiative transfer model allows quantifying effects of the vegetation layer on the surface radiation budget in permafrost areas. The parametrised model can account for diverse vegetation types and variation of properties within types. Our results highlight small scale radiation budget and permafrost thaw variability which are indicated and partly caused by vegetation. As changes in species composition and biomass increase can influence thaw rates, small scale patterns should be considered in assessments of climate-vegetation-permafrost feedbacks.

  15. Soil water stable isotopes reveal evaporation dynamics at the soil-plant-atmosphere interface of the critical zone

    Science.gov (United States)

    Sprenger, Matthias; Tetzlaff, Doerthe; Soulsby, Chris

    2017-07-01

    Understanding the influence of vegetation on water storage and flux in the upper soil is crucial in assessing the consequences of climate and land use change. We sampled the upper 20 cm of podzolic soils at 5 cm intervals in four sites differing in their vegetation (Scots Pine (Pinus sylvestris) and heather (Calluna sp. and Erica Sp)) and aspect. The sites were located within the Bruntland Burn long-term experimental catchment in the Scottish Highlands, a low energy, wet environment. Sampling took place on 11 occasions between September 2015 and September 2016 to capture seasonal variability in isotope dynamics. The pore waters of soil samples were analyzed for their isotopic composition (δ2H and δ18O) with the direct-equilibration method. Our results show that the soil waters in the top soil are, despite the low potential evaporation rates in such northern latitudes, kinetically fractionated compared to the precipitation input throughout the year. This fractionation signal decreases within the upper 15 cm resulting in the top 5 cm being isotopically differentiated to the soil at 15-20 cm soil depth. There are significant differences in the fractionation signal between soils beneath heather and soils beneath Scots pine, with the latter being more pronounced. But again, this difference diminishes within the upper 15 cm of soil. The enrichment in heavy isotopes in the topsoil follows a seasonal hysteresis pattern, indicating a lag time between the fractionation signal in the soil and the increase/decrease of soil evaporation in spring/autumn. Based on the kinetic enrichment of the soil water isotopes, we estimated the soil evaporation losses to be about 5 and 10 % of the infiltrating water for soils beneath heather and Scots pine, respectively. The high sampling frequency in time (monthly) and depth (5 cm intervals) revealed high temporal and spatial variability of the isotopic composition of soil waters, which can be critical, when using stable isotopes as tracers

  16. Soil friability

    DEFF Research Database (Denmark)

    Munkholm, Lars Juhl

    2011-01-01

    has been found but it is not possible to identify a specific lower critical level of organic matter across soil types. Sustainable management of soil requires continuous and adequate inputs of organic matter to sustain or improve soil friability. Intensive tillage and traffic in unfavorable conditions...... for optimal friability. There is a strong need to get more detailed knowledge about effects of soil water content on soil friability and especially to be able to quantify the least limiting water range for soil friability and therefore soil tillage. A strong relationship between organic matter and friability...

  17. Extensive, water-rich magma reservoir beneath southern Montserrat

    Science.gov (United States)

    Edmonds, M.; Kohn, S. C.; Hauri, E. H.; Humphreys, M. C. S.; Cassidy, M.

    2016-05-01

    South Soufrière Hills and Soufrière Hills volcanoes are 2 km apart at the southern end of the island of Montserrat, West Indies. Their magmas are distinct geochemically, despite these volcanoes having been active contemporaneously at 131-129 ka. We use the water content of pyroxenes and melt inclusion data to reconstruct the bulk water contents of magmas and their depth of storage prior to eruption. Pyroxenes contain up to 281 ppm H2O, with significant variability between crystals and from core to rim in individual crystals. The Al content of the enstatites from Soufrière Hills Volcano (SHV) is used to constrain melt-pyroxene partitioning for H2O. The SHV enstatite cores record melt water contents of 6-9 wt%. Pyroxene and melt inclusion water concentration pairs from South Soufriere Hills basalts independently constrain pyroxene-melt partitioning of water and produces a comparable range in melt water concentrations. Melt inclusions recorded in plagioclase and in pyroxene contain up to 6.3 wt% H2O. When combined with realistic melt CO2 contents, the depth of magma storage for both volcanoes ranges from 5 to 16 km. The data are consistent with a vertically protracted crystal mush in the upper crust beneath the southern part of Montserrat which contains heterogeneous bodies of eruptible magma. The high water contents of the magmas suggest that they contain a high proportion of exsolved fluids, which has implications for the rheology of the mush and timescales for mush reorganisation prior to eruption. A depletion in water in the outer 50-100 μm of a subset of pyroxenes from pumices from a Vulcanian explosion at Soufrière Hills in 2003 is consistent with diffusive loss of hydrogen during magma ascent over 5-13 h. These timescales are similar to the mean time periods between explosions in 1997 and in 2003, raising the possibility that the driving force for this repetitive explosive behaviour lies not in the shallow system, but in the deeper parts of a vertically

  18. Bed-Deformation Experiments Beneath a Temperate Glacier

    Science.gov (United States)

    Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Cohen, D.; Jackson, M.; Moore, P. L.; Lappegard, G.; Kohler, J.

    2002-12-01

    Fast flow of glaciers and genesis of glacial landforms are commonly attributed to shear deformation of subglacial sediment. Although models of this process abound, data gathered subglacially on the kinematics and mechanics of such deformation are difficult to interpret. Major difficulties stem from the necessity of either measuring deformation near glacier margins, where conditions may be abnormal, or at the bottoms of boreholes, where the scope of instrumentation is limited, drilling disturbs sediment, and local boundary conditions are poorly known. A different approach is possible at the Svartisen Subglacial Laboratory, where tunnels melted in the ice provide temporary human access to the bed of Engabreen, a temperate outlet glacier of the Svartisen Ice Cap in Norway. A trough (2 m x 1.5 m x 0.5 m deep) was blasted in the rock bed, where the glacier is 220 m thick and sliding at 0.1-0.2 m/d. During two spring field seasons, this trough was filled with 2.5 tons of simulated till. Instruments in the till recorded shear (tiltmeters), volume change, total normal stress, and pore-water pressure as ice moved across the till surface. Pore pressure was brought to near the total normal stress by feeding water to the base of the till with a high-pressure pump, operated in a rock tunnel 4 m below the bed surface. Results illustrate some fundamental aspects of bed deformation. Permanent shear deformation requires low effective normal stress and hence high pore-water pressure, owing to the frictional nature of till. Shear strain generally increases upward in the bed toward the glacier sole, consistent with previous measurements beneath thinner ice at glacier margins. At low effective normal stresses, ice sometimes decouples from underlying till. Overall, bed deformation accounts for 10-35 % of basal motion, although this range excludes shear in the uppermost 0.05 m of till where shear was not measured. Pump tests with durations ranging from seconds to hours highlight the need

  19. Metastable olivine wedge beneath northeast China and its applications

    Science.gov (United States)

    Jiang, G.; Zhao, D.; Zhang, G.

    2013-12-01

    When the Pacific slab subducted into the mantle transition zone, there might exist a metastable olivine wedge (MOW) inside the slab due to the phase transition. Lots of researchers have adopted such various methods to detect the characteristics of this MOW as the forward modeling of travel times, shear wave amplitude patterns, teleseismic P wave coda, receiver function imaging, thermodynamic simulation and so on. Almost all results could be more or less affected by the source, the receiver and/or the velocity model passed through by the seismic rays. In this study, we have used 21 deep earthquakes, greater than 400 km and locating beneath northeast China, to study the velocity within the MOW. For more precisions, we have done further modifications in two ways based on our previous studies. (1) Double-difference location method is used to relocate all events with an error of 1-2 km with the data recorded by stations both at northeast China and at Japan. All relocated events locate in a zone about 30 km away from the upper boundary of Pacific slab. (2) Double residual travel times, generated by an event-pair at a common station at only Japan, are used to constrain the velocity anomaly rather than the residuals themselves. As a result, we have found that an ultra-lower velocity zone (ULVZ), averagely -7% relative to the iasp91 model, exists within the subducted Pacific slab around the deep earthquakes, which might be represented as the metastable olivine wedge. Because of the lower-velocity corresponding to the lower-density, the MOW would provide upward buoyancy forces which might prevent the slab from free subduction into the mantle transition zone. This feed-back mechanism of MOW to the slab is called ';parachute-effect', which is characterized by other researchers. In addition, the existence of the ULVZ or the MOW in the slab may supply a possible mechanism for triggering deep earthquakes, called ';phase transformation faulting', which was already proposed few

  20. Stratocumulus cloud thickening beneath layers of absorbing smoke aerosol

    Science.gov (United States)

    Wilcox, E. M.

    2010-12-01

    Marine stratocumulus cloud properties, and the free-tropospheric environment above them, are examined in NASA A-Train satellite data for cases where smoke from seasonal burning of the West African savannah overlay the persistent southeast Atlantic stratocumulus cloud deck. CALIPSO space-borne lidar observations show that features identified as layers of aerosol occur predominantly between 2 km and 4 km. Layers identified as cloud features occur predominantly below 1.5 km altitude and beneath the layer of elevated smoke aerosol. The diurnal mean shortwave heating rates attributable to the absorption of solar energy in the aerosol layer is nearly 1.5 K d-1 for an aerosol optical thickness value of 1, and increases to 1.8 K d-1 when the smoke resides above clouds owing to the additional component of upward solar radiation reflected by the cloud. As a consequence of this heating, the 700 hPa air temperature above the cloud deck is warmer by approximately 1 K on average for cases where smoke is present above the cloud compared to cases without smoke above cloud. The warmer conditions in the free-troposphere above the cloud during smoke events coincide with cloud liquid water path values that are greater by 20 g m-2 and cloud tops that are lower for overcast conditions compared to periods with low amounts of smoke. The observed thickening and subsidence of the cloud layer are consistent with published results of large-eddy simulations showing that solar absorption by smoke above stratocumulus clouds increases the buoyancy of free-tropospheric air above the temperature inversion capping the boundary layer. Increased buoyancy inhibits the entrainment of dry air through the cloud-top, thereby helping to preserve humidity and cloud cover in the boundary layer. The direct radiative effect of absorbing aerosols residing over a bright cloud deck is a positive radiative forcing (warming) at the top of the atmosphere. However, the greater liquid water path for cases of smoke

  1. Mantle transition zone shear velocity gradients beneath USArray

    Science.gov (United States)

    Schmandt, Brandon

    2012-11-01

    Broadband P-to-s scattering isolated by teleseismic receiver function analysis is used to investigate shear velocity (VS) gradients in the mantle transition zone beneath USArray. Receiver functions from 2244 stations were filtered in multiple frequency bands and migrated to depth through P and S tomography models. The depth-migrated receiver functions were stacked along their local 410 and 660 km discontinuity depths to reduce stack incoherence and more accurately recover the frequency-dependent amplitudes of P410s and P660s. The stacked waveforms were inverted for one-dimensional VS between 320 and 840 km depth. First, a gradient-based inversion was used to find a least-squares solution and a subsequent Monte Carlo search about that solution constrained the range of VS profiles that provide an acceptable fit to the receiver function stacks. Relative to standard references models, all the acceptable models have diminished VS gradients surrounding the 410, a local VS gradient maximum at 490-500 km depth, and an enhanced VS gradient above the 660. The total 410 VS increase of 6.3% is greater than in reference models, and it occurs over a thickness of 20 km. However, 60% of this VS increase occurs over only 6 km. The 20 km total thickness of the 410 and diminished VS gradients surrounding the 410 are potential indications of high water content in the regional transition zone. An enhanced VS gradient overlying the 660 likely results from remnants of subduction lingering at the base of the transition zone. Cool temperatures from slabs subducted since the late Cretaceous and longer-term accumulation of former ocean crust both may contribute to the high gradient above the 660. The shallow depth of the 520 km discontinuity, 490-500 km, implies that the regional mean temperature in the transition zone is 110-160 K cooler than the global mean. A concentrated Vs gradient maximum centered near 660 km depth and a low VS gradient below 675 km confirms that the ringwoodite to

  2. Cathodic protection beneath thick external coating on flexible pipeline

    Energy Technology Data Exchange (ETDEWEB)

    Festy, Dominique; Choqueuse, Dominique; Leflour, Denise; Lepage, Vincent [Ifremer - Centre de Brest, BP 70 29280 Plouzane (France); Condat, Carol Taravel; Desamais, Nicolas [Technip- FLEXIFRANCE - PED/PEC - Rue Jean Hure, 76580 Le Trait (France); Tribollet, Bernard [UPR 15 du CNRS, Laboratoire LISE, 4 Place Jussieu, 75252 Paris Cedex (France)

    2004-07-01

    Flexible offshore pipelines possess an external polymer sheath to protect the structure against seawater. In case of an accidental damage of the outer sheath, the annulus of the flexible pipe is flooded with seawater. Far from the damage, corrosion and/or corrosion fatigue of armour steel wires in the annulus occur in a strictly deaerated environment; this has been studied for a few years. At the damage location, the steel wires are in direct contact with renewed seawater. In order to protect them against corrosion, a cathodic protection is applied using sacrificial anodes located at the end fittings. The goal of this work is to evaluate the extent of the cathodic protection as well as the electrolyte oxygen concentration beneath the coating around the damage, to know whether or not there is a non protected area with enough oxygen where corrosion and corrosion fatigue can occur. The experimental work was performed with a model cell (2000 x 200 mm{sup 2}), composed of a mild steel plate and a PMMA coat (transparent poly-methyl-methacrylate). The thickness of the gap between the steel plate and the PMMA coat was 0.5 mm. The potential and current density were monitored all along the cell (70 sensors). The oxygen concentration was also recorded. The experiments were performed with natural sea water, and cathodic protection was applied in a reservoir at one extremity of the cell. Another reservoir at the other cell extremity enabled carbon dioxide bubbling to simulate pipeline annular conditions. PROCOR software was used to simulate potential and current density within the gap and a mathematical model was developed to model oxygen concentration evolution. Both model and experimental results show that the extent of the cathodic protection is much greater than that of oxygen. Oxygen depletion is very quick within the gap when seawater fills it and the oxygen concentration is close to zero a few milli-metres from the gap opening. On the other hand, the cathodic protection

  3. Electrical structure beneath the Hangai Dome, Mongolia, from magnetotelluric data

    Science.gov (United States)

    Comeau, Matthew; Käufl, Johannes; Becken, Michael; Kuvshinov, Alexey; Demberel, Sodnomsambuu; Sukhbaatar, Usnikh; Batmagnai, Erdenechimeg; Tserendug, Shoovdor; Nasan, Ochir

    2017-04-01

    The Hangai Dome in west-central Mongolia is an unusual high-elevation intra-continental plateau located far from tectonic plate boundaries and characterized by dispersed, low-volume, basaltic volcanism. This region is an ideal natural laboratory for studying intra-continental orogenic and magmatic processes resulting from crust-mantle interactions. The processes responsible for developing the Hangai Dome remain unexplained, due in part to a lack of high resolution geophysical data over the area. Here we present newly acquired broadband (0.008 - 3,000 s) magnetotelluric (MT) data from a large-scale ( 200 x 450 km) and high resolution (site spacing > 5 km) survey across the Hangai Dome. A total of 125 sites were collected and include full MT sites and telluric-only sites where inter-station transfer functions were computed. The MT data are used to generate an electrical resistivity model of the crust and upper mantle below the Hangai Dome. The model shows that the lower crust ( 30 - 50 km; below the brittle-ductile transition zone) beneath the Hangai Dome contains anomalous discrete pockets of low-resistivity ( 30 ohm-m) material that indicate the presence of local accumulations of fluids and/or low-percent partial melts. These anomalous regions appear to be spatially associated with the surface expressions of past volcanism, hydrothermal activity, and an increase in heat flow. They also correlate with observed crustal low-density and low-velocity anomalies. However they are in contrast to some geochemical and petrological studies which show long-lived crustal melt storage is impossible below the Hangai due to limited crustal assimilation and crustal contamination, arguing for a single parent-source at mantle depths. The upper mantle ( 6%) at this location. The results are consistent with modern geochemical and geophysical data, which show a thin lithosphere below the Hangai region. Furthermore the results agree with geodynamic models that require a low-heat flux

  4. Effects of Tamarisk shrub on physicochemical properties of soil in coastal wetland of the Bohai Sea

    Institute of Scientific and Technical Information of China (English)

    HE Xiuping; WANG Baodong; XIE Linping; XIN Ming; WANG Wei; WANG Zicheng; ZHANG Wenquan; WEI Qinsheng

    2016-01-01

    There are many different and even controversial results concerning the effects of Tamarisk on the physicochemical properties of soil. A year-round monitoring of soil salinity, pH and moisture is conducted beneath the Tamarisk shrub in a coastal wetland in the Bohai Sea in China, to ascertain the effects of Tamarisk on the physicochemical properties of soil in coastal wetland. Compared with the control area, the soil moisture content is lower around the area of the taproot when there is less precipitation in the growing season because of water consumption by Tamarisk shrub. However, the soil moisture content is higher around the taproot when there is more precipitation in the growing season or in the non-growing period because of water conservation by the rhizosphere. The absorption of salt by the Tamarisk shrub reduces the soil salinity temporarily, but eventually salt returns to the soil by the leaching of salt on leaves by rainfall or by fallen leaves. The annual average soil moisture content beneath the Tamarisk shrub is lower than the control area by only 6.4%, indicating that the Tamarisk shrub has little effect on drought or water conservation in soils in the temperate coastal wetland with moderate annual precipitation. The annual average salinity beneath the Tamarisk shrub is 18% greater than that of the control area, indicating that Tamarisk does have an effect of rising soil salinity around Tamarisk shrubs. The soil pH value is as low as 7.3 in summer and as high as 10.2 in winter. The pH of soil near the taproot of the Tamarisk shrubs is one pH unit lower than that in the control area during the growing season. The difference in pH is less different from the control area in the non-growing season, indicating that the Tamarisk shrub does have the effect of reducing the alkalinity of soil in coastal wetland.

  5. Assessment of soil-gas, seep, and soil contamination at the North Range Road Landfill, Fort Gordon, Georgia, 2008-2009

    Science.gov (United States)

    Landmeyer, James E.; Falls, W. Fred; Ratliff, W. Hagan; Wellborn, John B.

    2011-01-01

    Soil gas, seeps, and soil were assessed for contaminants at the North Range Road Landfill at Fort Gordon, Georgia, from October 2008 to September 2009. The assessment included delineating organic contaminants present in soil-gas samples beneath the area estimated to be the landfill and in water samples collected from three seeps at the base of the landfill. Inorganic contaminants were determined in three seep samples and in soil samples. This assessment was conducted to provide environmental contamination data to Fort Gordon pursuant to requirements for the Resource Conservation and Recovery Act Part B Hazardous Waste Permit process.

  6. Soil properties, soil functions and soil security

    Science.gov (United States)

    Poggio, Laura; Gimona, Alessandro

    2017-04-01

    Soil plays a crucial role in the ecosystem functioning such as food production, capture and storage of water, carbon and nutrients and in the realisation of a number of UN Sustainable Developments Goals. In this work we present an approach to spatially and jointly assess the multiple contributions of soil to the delivery of ecosystem services within multiple land-use system. We focussed on the modelling of the impact of soil on sediment retention, carbon storage, storing and filtering of nutrients, habitat for soil organisms and water regulation, taking into account examples of land use and climate scenarios. Simplified models were used for the single components. Spatialised Bayesian Belief networks were used for the jointly assessment and mapping of soil contribution to multiple land use and ecosystem services. We integrated continuous 3D soil information derived from digital soil mapping approaches covering the whole of mainland Scotland, excluding the Northern Islands. Uncertainty was accounted for and propagated across the whole process. The Scottish test case highlights the differences in roles between mineral and organic soils and provides an example of integrated study assessing the contributions of soil. The results show the importance of the multi-functional analysis of the contribution of soils to the ecosystem service delivery and UN SDGs.

  7. Dating Metasomatism in the Lithosphere Beneath North China Craton

    Science.gov (United States)

    Chen, L.; Zhou, X.

    2005-12-01

    Dating of mantle metasomatism had been carried out using zircons in metasomatized mantle xenoliths entrained in kimberlites (Kinny and Dawson, 1992; Rudnick et al., 1999; Konzett et al., 1998, 2000; Liati et al., 2004), because the U-Pb system in zircon can remain closed at high temperature (>900-)(Lee et al., 1997). Here we report a SHRIMP U-Pb dating analysis of zircons from a unique dunite-orthopyroxenite xenolith entrained in Cretaceous high-Mg diorite of Shandong province, which provides a timing constraint for the multi-stage metasomatism in the lithosphere beneath North China craton (NCC). Abundant ultramafic xenoliths had been found in the Tietonggou intrusion, one of the Cretaceous high-Mg diorite-dominated plutons in North China (Chen and Zhou, 2004). The lithology, mineral chemistry, equilibrium temperature (690-790A), and metasomatic characteristics of the ultramafic xenoliths indicate that they might be derived from the shallow lithosphere (the crust-mantle transitional zone or the uppermost lithospheric mantle) and had suffered multi-stage metasomatism (Chen and Zhou, 2004, 2005). Xenolith LW0006 is the most extremely metasomatized sample found so far in the xenolith suite of the Tietonggou pluton. The petrography, mineral chemistry, and major element compositions provide a clear metasomatic record of the composite xenolith: K (and/or Ca) metasomatism, and Si (Na) metasomatism (Chen and Zhou). We found seven zircons range from 100-170 Im in longest dimension, which is reflected in the unusually high Zr content of the bulk rock (49 ppm) of this sample. SHRIMP U-Pb dating reveals that these zircons might be grouped three kinds: Mesozoic (concordia age of 127-A3 Ma, 5 zircons), Paleozoic (430-470 Ma, 1 zircon only) and Mesoproterozoic (1310-1540 Ma, 1 zircon only). Cathodoluminescence (CL) images reveal that a few Mesozoic zircons and the Paleozoic zircons retain oscillatory zoning. The Mesozoic zircons are characterized with high Th, U contents and high

  8. Lithospheric Mantle heterogeneities beneath northern Santa Cruz province, Argentina

    Science.gov (United States)

    Mundl, Andrea; Ntaflos, Theodoros; Bjerg, Ernesto

    2013-04-01

    interstitial clinopyroxene appears to be of metasomatic origin. The clinopyroxene from cumulate dunites has depleted LREE abundances and low HREE indicating that they have been formed from residual melts. In contrast, clinopyroxene from mantle dunites has enriched LREE (10 x PM) and LILE suggesting that the metasomatic agent was fluid-rich silicate melt. Calculated equilibrium conditions cover a wide range, from 800 to 1100 °C. Considering the crustal thickness in the area being around 35 km, a pressure between 12 and 17 kbar can be assumed as reasonable, indicating that xenoliths were extracted from shallow depths, in the order of 40 to 60 km. Model calculations have shown that the Lithospheric Mantle beneath Don Camilo is fertile and that spinel peridotites experienced low degrees of partial melting (2-8% batch melting in the spinel peridotite field). The metasomatic agent was a fluid rich silicate melt presumably similar to that which affected the xenoliths from Cerro Clark locality, north of Don Camilo. The clinopyroxenes with the highest Sr and lowest Nd isotopic signatures suggest that the metasomatism was an old event apparently not associated to the interaction of the Lithospheric Mantle in southern Patagonia with downgoing Nazca and Antarctic plates.

  9. Channelling of Melt Above Plumes and Beneath MORs

    Science.gov (United States)

    Mueller, K.; Schmeling, H.

    2003-12-01

    We investigate melt transportation in partially molten rocks under different stress fields above the head of a mantle plume or beneath a spreading mid-oceanic ridge under hydrous and anhydrous conditions. We model such aggregates with the 2D-FD code FDCON [1] by means of a porous deformable matrix with melt under the influence of a given stress field to clarify the following key questions: Could channeling occur in a matrix containing a random melt distribution under a given stress field? Which orientation does it take? Is it possible to achieve a focusing of melt towards a MOR (dykes)? Does applying simple or pure shear to the matrix result in a difference in the formation and orientation of channels? How does the channel instability evolve during finite simple shear? In a deforming partially molten aggregate, weakening of the solid matrix due to the presence of melt creates an instability in which melt is localized by the following mechanism: regions of initially high melt fraction are areas of low viscosity and pressure, so that melt is drawn into these regions from higher pressure surroundings. This further enhances the melt weakening, producing a self-excited localization mechanism [2]. The channeling developing in models with a random melt distribution of 3.5 +/- 0.5% shows that melt is accumulated preferably in inclined channels. For both, simple as well as pure shear, the growth rate is highest for an orientation parallel to the direction of the maximum compressive stress and proportional to applied stress and the reverse of the Melt Retention Number. This also confirms the theoretical growth rate found by Stevenson [2]. In our isothermal models we found that the influence of water reduces the growth rate, in contrast to non-isothermal models of Hall [3]. Under simple shear melt channels evolve from an irregular melt distribution at angles of 45 degrees to the direction of shear. Upon further straining they rotate out of the orientation of maximum growth

  10. Metasomatism in the oceanic lithosphere beneath La Palma, Canary Islands

    Science.gov (United States)

    Janisch, Astrid; Ntaflos, Theodoros

    2016-04-01

    host basalt) indicate that these veins have been formed prior to their transport to the surface. During to their transport to the surface host basalt infiltration propagated along these veins leading to the breakdown of the amphibole and/or phlogopite and the formation of glass, secondary clinopyroxene and spinel. The glass is of tephra-phonolitic composition in the peridotite and foiditic along the amphibole-phlogopite-veins. Mantle xenoliths from San Antonio reveal that the oceanic lithosphere beneath La Palma has been affected by different metasomatic processes. The metasomatic agents were silicate melts causing the formation of secondary clinopyroxenes and the breakdown of orthopyroxenes, whereas hydrous silica fluids formed the various amphibole and/or phlogopite veins-veinlets. Additionally, the presence of a veinlet containing haüyne and glass is a strong indication for host basalt infiltration since these basalts are haüyne bearing.

  11. Mohorovicic discontinuity depth analysis beneath North Patagonian Massif

    Science.gov (United States)

    Gómez Dacal, M. L.; Tocho, C.; Aragón, E.

    2013-05-01

    The North Patagonian Massif is a 100000 km2, sub-rectangular plateau that stands out 500 to 700 m higher in altitude than the surrounding topography. The creation of this plateau took place during the Oligocene through a sudden uplift without noticeable internal deformation. This quite different mechanical response between the massif and the surrounding back arc, the short time in which this process took place and a regional negative Bouguer anomaly in the massif area, raise the question about the isostatic compensation state of the previously mentioned massif. In the present work, a comparison between different results about the depth of the Mohorovicic discontinuity beneath the North Patagonian Massif and a later analysis is made. It has the objective to analyze the crustal thickness in the area to contribute in the determination of the isostatic balance and the better understanding of the Cenozoic evolution of the mentioned area. The comparison is made between four models; two of these were created with seismic information (Feng et al., 2006 and Bassin et al., 2000), another model with gravity information (Barzaghi et al., 2011) and the last one with a combination of both techniques (Tassara y Etchaurren, 2011). The latter was the result of the adaptation to the work area of a three-dimensional density model made with some additional information, mainly seismic, that constrain the surfaces. The work of restriction and adaptation of this model, the later analysis and comparison with the other three models and the combination of both seismic models to cover the lack of resolution in some areas, is presented here. According the different models, the crustal thickness of the study zone would be between 36 and 45 Km. and thicker than the surrounding areas. These results talk us about a crust thicker than normal and that could behave as a rigid and independent block. Moreover, it can be observed that there are noticeable differences between gravimetric and seismic

  12. Soil carbon and nitrogen dynamics linked to Piliostigma species in ferugino-tropical soils in the Sudano-Sahelian zone of Burkina Faso,West Africa

    Institute of Scientific and Technical Information of China (English)

    Barthélémy Yélémou; Sidzabda Djibril Dayamba; Dasmane Bambara; Georges Yaméogo; Salawu Assimi

    2013-01-01

    In the Sudano-Sahelian zone of Burkina Faso,Piliostigma reticulatum (DC) Hochst and Piliostigma thonningii (Schumach) are precursor species of fallow land colonization and they are used by rural villagers.The present study aimed to assess the contribution of Piliostigma species to soil quality improvement.We quantified organic carbon,total nitrogen,soil microbial biomass,soil basal respiration and metabolic quotient from soil samples taken under and outside Piliostigma canopies.We used one-way ANOVA to test for differences in the above parameters between locations (beneath and outside Piliostigma canopies).We recorded increased total organic carbon under Piliostigma from 31%-105% and in total nitrogen from 23%-66%.Microbial biomass was 13%-266% higher beneath canopies as compared to outside canopies.Basal respiration was also higher beneath canopies.The chemical elements varied by class of soil texture.Metabolic quotient (qCO2) was significantly correlated to clay (r =0.80) and silt (r =0.79) content.Piliostigma stands produced abundant litter due to their leaf biomass.Thus,they contribute to improved total organic carbon and total nitrogen content in the different phytogeographic zones and improve soil fertility

  13. Upper Mantle Flow Beneath the Subducted Nazca Plate: Slab Contortions and Flattening (Invited)

    Science.gov (United States)

    Russo, R. M.

    2010-12-01

    The form of asthenospheric flow beneath subducted lithospheric slabs can be discerned using splitting of shear waves emanating from earthquakes in the slabs themselves. However, the subducted Nazca plate’s abrupt changes in morphology from a planar slab dipping 30° ENE beneath the central Andes to large areas of flat-lying slab beneath Peru, to the north, and Argentina, to the south, are a potential complication to the sub-slab mantle flow. S waves from earthquakes in the Nazca slab reveal details of the upper mantle flow field below and in the vicinity of the slab. Nazca slab earthquakes large enough to be well recorded (M > 5.4, typically), and deep enough to separate S from pS and sS (30-40 km or more), are suitable for such study, and, for events between 1990 and 2010, recording stations are mostly well-distributed azimuthally about the source event. The S waves were recorded at seismic stations at teleseismic distances from the events, and were corrected for known sub-station seismic anisotropy. Thus, the shear wave splitting engendered during their passage through the asthenospheric upper mantle beneath the slab was isolated, and asthenospheric deformation fabrics resulting from plastic flow beneath the slab mapped in some detail. Shear wave splitting fast directions and upper mantle flow beneath the Nazca plate are most often trench-parallel, consistent with trench-parallel upper mantle flow beneath the slab. Fast splitting polarizations at high angle to the strike of the slab occur in the transition regions from flat to normally dipping slab. Upper mantle flow beneath the slab in these regions appears to be channeled by the slab contortion. Upper mantle flow oceanward of the Nazca slab also appears to change abruptly from trends at a high angle to the Peru-Chile trench to trench-parallel as the top of the Nazca slab attains a depth of around 75 km. Trench-parallel sub-slab flow appears to develop once the asthenosphere beneath the Nazca plate is affected

  14. Seismic evidence for a chemically distinct thermochemical reservoir in Earth's deep mantle beneath Hawaii

    Science.gov (United States)

    Zhao, Chunpeng; Garnero, Edward J.; McNamara, Allen K.; Schmerr, Nicholas; Carlson, Richard W.

    2015-09-01

    Nearly antipodal continent-sized zones of reduced seismic shear wave velocities exist at the base of Earth's mantle, one beneath the Pacific Ocean, the other beneath the South Atlantic Ocean and Africa. Geophysicists have attributed the low velocity zones to elevated temperatures associated with large-scale mantle convection processes, specifically, hot mantle upwelling in response to cooler subduction-related downwelling currents. Hypotheses have included superplumes, isochemical heterogeneity, and stable as well as metastable basal thermochemical piles. Here we analyze waveform broadening and travel times of S waves from 11 deep focus earthquakes in the southwest Pacific recorded in North America, resulting in 8500 seismograms studied that sample the deep mantle beneath the Pacific. Waveform broadening is referenced to a mean S-wave shape constructed for each event, to define a relative "misfit". Large misfits are consistent with multipathing that can broaden wave pulses. Misfits of deep mantle sampling S-waves infer that the structure in the northeast part of the low velocity province beneath the Pacific has a sharp side as well as a sloping sharp top to the feature. This sharp boundary morphology is consistent with geodynamic predictions for a stable thermochemical reservoir. The peak of the imaged pile is below Hawaii, supporting the hypothesis of a whole mantle plume beneath the hotspot.

  15. Soil formation.

    NARCIS (Netherlands)

    Breemen, van N.; Buurman, P.

    1998-01-01

    Soil Formation deals with qualitative and quantitative aspects of soil formation (or pedogenesis) and the underlying chemical, biological, and physical processes. The starting point of the text is the process - and not soil classification. Effects of weathering and new formation of minerals, mobilis

  16. Seismic evidence for a crustal magma reservoir beneath the upper east rift zoneof Kilauea volcano, Hawaii

    Science.gov (United States)

    Lin, Guoqing; Amelung, Falk; Lavallee, Yan; Okubo, Paul G.

    2014-01-01

    An anomalous body with low Vp (compressional wave velocity), low Vs (shear wave velocity), and high Vp/Vs anomalies is observed at 8–11 km depth beneath the upper east rift zone of Kilauea volcano in Hawaii by simultaneous inversion of seismic velocity structure and earthquake locations. We interpret this body to be a crustal magma reservoir beneath the volcanic pile, similar to those widely recognized beneath mid-ocean ridge volcanoes. Combined seismic velocity and petrophysical models suggest the presence of 10% melt in a cumulate magma mush. This reservoir could have supplied the magma that intruded into the deep section of the east rift zone and caused its rapid expansion following the 1975 M7.2 Kalapana earthquake.

  17. Simulation of Wave-Plus-Current Induced Scour Beneath Submarine Pipelines

    DEFF Research Database (Denmark)

    Eltard-Larsen, Bjarke; Fuhrman, David R.; Sumer, B. Mutlu

    of combined wave-plus-current scour processes beneath pipelines. The results of 77 simulated wave-plus-current scour cases will be presented and analysed. The cases considered will consist of waves characterized by 10 different Keulegan-Carpenter numbers, KC=UmTw/D and up to eight different values of m......-plus-current environments. The present study, which is published in Larsen et al. (2016) focuses on the numerical simulation of wave-plus-current induced scour beneath submarine pipelines, based on a model solving Reynolds-averaged Navier-Stokes (RANS) equations, fully coupled with turbulence closure, bed and suspended...... load sediment transport descriptions, and a seabed morphological model. The model was utilized in simulating breaker bar development by Jacobsen et al. (2014) and has been used in simulating wave induced scour beneath pipelines by Fuhrman et al. (2014) . The model is utilized for the numerical study...

  18. Subsurface imaging reveals a confined aquifer beneath an ice-sealed Antarctic lake

    DEFF Research Database (Denmark)

    Dugan, H. A.; Doran, P. T.; Tulaczyk, S.;

    2015-01-01

    Liquid water oases are rare under extreme cold desert conditions found in the Antarctic McMurdo Dry Valleys. Here we report geophysical results that indicate that Lake Vida, one of the largest lakes in the region, is nearly frozen and underlain by widespread cryoconcentrated brine. A ground...... Geophysical survey finds low resistivities beneath a lake in Antarctic Dry Valleys Liquid brine abundant beneath Antarctic lake Aquifer provides microbial refugium in cold desert environment...... penetrating radar survey profiled 20 m into lake ice and facilitated bathymetric mapping of the upper lake basin. An airborne transient electromagnetic survey revealed a low-resistivity zone 30-100 m beneath the lake surface. Based on previous knowledge of brine chemistry and local geology, we interpret...

  19. Soil metagenomics and tropical soil productivity

    OpenAIRE

    Karen A Garrett

    2009-01-01

    This presentation summarizes research in the soil metagenomics cross cutting research activity. Soil metagenomics studies soil microbial communities as contributors to soil health.C CCRA-4 (Soil Metagenomics)

  20. Soil microbiology and soil health assessment

    Science.gov (United States)

    Soil scientists have long recognized the importance of soil biology in ecological health. In particular, soil microbes are crucial for many soil functions including decomposition, nutrient cycling, synthesis of plant growth regulators, and degradation of synthetic chemicals. Currently, soil biologis...

  1. Soils - Volusia County Soils (Polygons)

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — Soils: 1:24000 SSURGO Map. Polygon boundaries of Soils in Volusia County, downloaded from SJRWMD and created by NRCS and SJRWMD. This data set is a digital version...

  2. Crust and upper mantle electrical conductivity beneath the Yellowstone Hotspot Track

    Science.gov (United States)

    Kelbert, A.; Egbert, G. D.

    2012-12-01

    We have used high-quality electromagnetic data obtained through the EarthScope USArray project to obtain detailed three-dimensional images of electrical resistivity / conductivity in the crust and upper mantle beneath the Snake River Plain/Yellowstone (SRP/Y) volcanic province (Idaho and Wyoming, United States). The lowest resistivities in the area can only plausibly be explained by partial melt and/or fluids, providing valuable new information about the distribution of these phases deep within the Earth beneath the volcanic system. Unexpectedly, in light of the mantle plume models often used to explain Yellowstone volcanism, the electromagnetic data imply that there is no interconnected melt in the lower crust and uppermost mantle directly beneath the modern Yellowstone caldera. Instead, low resistivities consistent with 1-3% melt in the uppermost mantle (depths of 40-80 km) extend at least 200 km southwest of Yellowstone. Shallower areas of reduced resistivity extend upward into the mid-crust around the edges of the seemingly impermeable Snake River Plain province, including beneath Yellowstone. We suggest that the elevated temperatures beneath the active volcanic center have resulted in greater permeability, allowing magma to ascend to shallower depths and pool in the crust. Little melt is entering the system from below at present, perhaps due to intermittency of supply. We describe these results in the context of larger scale electrical resistivity and seismic tomography models of the western US and employ joint interpretation to formulate hypotheses that would explain this unexpected melt distribution beneath the SRP/Y. Our 3-D model is available at http://www.iris.edu/dms/products/emc/models/SRPY-MT.htm

  3. Mantle seismic anisotropy beneath NE China and implications for the lithospheric delamination hypothesis beneath the southern Great Xing'an range

    Science.gov (United States)

    Chen, Haichao; Niu, Fenglin; Obayashi, Masayuki; Grand, Stephen P.; Kawakatsu, Hitoshi; John Chen, Y.; Ning, Jieyuan; Tanaka, Satoru

    2017-08-01

    We measured shear wave splitting from SKS data recorded by the transcontinental NECESSArray in NE China to constrain lithosphere deformation and sublithospheric flows beneath the area. We selected several hundreds of high quality SKS/SKKS waveforms from 32 teleseismic earthquakes occurring between 09/01/2009 and 08/31/2011 recorded by 125 broadband stations. These stations cover a variety of tectonic terranes, including the Songliao basin, the Changbaishan mountain range and Zhangguancai range in the east, the Great Xing'an range in the west and the Yanshan orogenic belt in the southwest. We assumed each station is underlaid by a single anisotropic layer and employed a signal-to-noise ratio (SNR) weighted multi-event stacking method to estimate the two splitting parameters (the fast polarization direction φ, and delay time, δt) that gives the best fit to all the SKS/SKKS waveforms recorded at each station. Overall, the measured fast polarization direction lies more or less along the NW-SE direction, which significantly differs from the absolute plate motion direction, but is roughly consistent with the regional extension direction. This suggests that lithosphere deformation is likely the general cause of the observed seismic anisotropy. The most complicated anisotropic structure is observed beneath the southern Great Xing'an range and southwest Songliao basin. The observed large variations in splitting parameters and the seismic tomographic images of the area are consistent with ongoing lithospheric delamination beneath this region.

  4. Big mantle wedge, anisotropy, slabs and earthquakes beneath the Japan Sea

    Science.gov (United States)

    Zhao, Dapeng

    2017-09-01

    The Japan Sea is a part of the western Pacific trench-arc-backarc system and has a complex bathymetry and intense seismic activities in the crust and upper mantle. Local seismic tomography revealed strong lateral heterogeneities in the crust and uppermost mantle beneath the eastern margin of the Japan Sea, which was determined using P and S wave arrival times of suboceanic earthquakes relocated precisely with sP depth phases. Ambient-noise tomography revealed a thin crust and a thin lithosphere beneath the Japan Sea and significant low-velocity (low-V) anomalies in the shallow mantle beneath the western and eastern margins of the Japan Sea. Observations with ocean-bottom seismometers and electromagnetometers revealed low-V and high-conductivity anomalies at depths of 200-300 km in the big mantle wedge (BMW) above the subducting Pacific slab, and the anomalies are connected with the low-V zone in the normal mantle wedge beneath NE Japan, suggesting that both shallow and deep slab dehydrations occur and contribute to the arc and back-arc magmatism. The Pacific slab has a simple geometry beneath the Japan Sea, and earthquakes occur actively in the slab down to a depth of ∼600 km beneath the NE Asian margin. Teleseismic P and S wave tomography has revealed that the Philippine Sea plate has subducted aseismically down to the mantle transition zone (MTZ, 410-660 km) depths beneath the southern Japan Sea and the Tsushima Strait, and a slab window is revealed within the aseismic Philippine Sea slab. Seismic anisotropy tomography revealed a NW-SE fast-velocity direction in the BMW, which reflects corner flows induced by the fast deep subduction of the Pacific slab. Large deep earthquakes (M > 7.0; depth > 500 km) occur frequently beneath the Japan Sea western margin, which may be related to the formation of the Changbai and Ulleung intraplate volcanoes. A metastable olivine wedge is revealed within the cold core of the Pacific slab at the MTZ depth, which may be related

  5. Seismic Imaging of the crust and upper mantle beneath Afar, Ethiopia

    Science.gov (United States)

    Hammond, J. O.; Kendall, J. M.; Stuart, G. W.; Ebinger, C. J.

    2009-12-01

    In March 2007 41 seismic stations were deployed in north east Ethiopia. These stations recorded until October 2009, whereupon the array was condensed to 13 stations. Here we show estimates of crustal structure derived from receiver functions and upper mantle velocity structure, derived from tomography and shear-wave splitting using the first 2.5 years of data. Bulk crustal structure has been determined by H-k stacking receiver functions. Crustal Thickness varies from ~45km on the rift margins to ~16km beneath the northeastern Afar stations. Estimates of Vp/Vs show normal continental crust values (1.7-1.8) on the rift margins, and very high values (2.0-2.2) in Afar, similar to results for the Main Ethiopian Rift (MER). This supports ideas of high levels of melt in the crust beneath the Ethiopian Rift. Additionally, we use a common conversion point migration technique to obtain high resolution images of crustal structure beneath the region. Both techniques show a linear region of thin crust (~16km) trending north-south, the same trend as the Red Sea rift. SKS-wave splitting results show a general north east-south west fast direction in the MER, systematically rotating to a more north-south fast direction towards the Red Sea. Additionally, stations close to the recent Dabbahu diking episode show sharp lateral changes over small lateral distances (40° over Danakil microplate. Outside of these focused regions the velocities are relatively fast. Below ~250km the anomaly broadens to cover most of the Afar region with only the rift margins remaining fast. At transition zone depths little anomaly is seen beneath Afar, but some low velocities remain present beneath the MER. These studies suggest that in northern Ethiopia the Red Sea rift is dominant. The presence of thin crust beneath northern Afar suggests that the Red Sea rift is creating oceanic like crust in this region. The lack of deep mantle low velocity anomalies beneath Afar suggest that a typical narrow conduit

  6. Subducted slabs beneath the eastern Indonesia-Tonga region: insights from tomography

    Science.gov (United States)

    Hall, Robert; Spakman, Wim

    2002-07-01

    Tomographic images of mantle structure beneath the region north and northeast of Australia show a number of anomalously fast regions. These are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems. Several strong anomalies are related to current subduction. The inferred slab lengths and positions are consistent with Neogene subduction beneath the New Britain and Halmahera arcs, and at the Tonga and the New Hebrides trenches where there has been rapid rollback of subduction hinges since about 10 Ma. There are several deeper flat-lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by Australia since 25 Ma. Beneath the Bird's Head and Arafura Sea is an anomaly interpreted to be due to north-dipping subduction beneath the Philippines-Halmahera arc between 45 and 25 Ma. A very large anomaly extending from the Papuan peninsula to the New Hebrides, and from the Solomon Islands to the east Australian margin, is interpreted to be the remnant of south-dipping subduction beneath the Melanesian arc between 45 and 25 Ma. This interpretation implies that a flat-lying slab can survive for many tens of millions of years at the bottom of the upper mantle. In the lower mantle there is a huge anomaly beneath the Gulf of Carpentaria and east Papua New Guinea. This is located above the position where the tectonic model interprets a change in polarity of subduction from north-dipping to south-dipping between 45 and 25 Ma. We suggest this deep anomaly may be a slab subducted beneath eastern Australian during the Cretaceous, or subducted north of Australia during the Cenozoic before 45 Ma. The tomography also supports the tectonic interpretation which suggests little Neogene subduction beneath western New Guinea since no slab is imaged south of the New Guinea trench. However, one subduction zone in the tectonic model and many others, that associated with the Trobriand

  7. Receiver Function Analysis of the Lithospheric Structure Beneath the Western Great Plains

    Science.gov (United States)

    Thurner, S.; Zhai, Y.; Levander, A.

    2010-12-01

    The lithosphere in the western Great Plain region of the Southwestern U.S. has been subject to tectonic deformation from the Proterozoic to present day. Proterozoic island arc terranes accreted onto the North American continent between 1.8 and 1.1 Ga, forming the original continent, and there is evidence for Proterozoic continental extension which formed basement penetrating faults between 1.5 and .6 Ga . This was followed by the uplift of the Ancestral Rockies and, most recently, the subduction of the Farallon plate beneath North America. Extension has occurred throughout the Basin and Range and formed the Rio Grand Rift (RGR). However, the relative impact that large scale tectonic forces, regional asthenospheric upwelling, and preexisting structural weaknesses have on the extension of the RGR is still undetermined. This study seeks to better understand the current tectonic system east of the Colorado Plateau beneath the RGR and western Great Plains. We use teleseismic receiver functions to investigate the nature of extension in the RGR as well as its connection to the small-scale convection thought to be occurring beneath the Colorado Plateau-RGR-Great Plains region. Our receiver function images were generated from 85 earthquake events recorded at 187 USArray Transportable Array seismic stations located throughout the western Great Plains (Latitude: 28-48, Longitude: -105-100). Previous studies have indicated crustal thickness between 39 km and 50 km beneath the Great Plains and as thin as 35 km beneath the RGR (Wilson et.al, 2005). Tomography results have shown high velocity anomalies on both sides of the RGR, extending to 600 km depth beneath the western Great Plains, and a low velocity anomaly directly beneath the RGR (Gok et. al, 2003, Wilson et. al, 2005, Gao et. al, Song and Helmberger, 2007). The western Great Plains high velocity anomaly has been interpreted to be part of the downwelling portion of an edge driven convection system induced by a lateral

  8. Soil pollution and soil protection.

    NARCIS (Netherlands)

    Haan, de F.A.M.; Visser-Reijneveld, M.I.

    1996-01-01

    This book was compiled from lecture handouts prepared for the international postgraduate course on soil quality, entitled 'Soil Pollution and Soil Protection' given jointly by the universities of Wageningen (The Netherlands), Gent and Leuven (Belgium), under the auspices of the international

  9. Soil infiltrometer

    Energy Technology Data Exchange (ETDEWEB)

    Mehler, M.R.

    1990-09-18

    This patent describes an infiltrometer useful for field testing soil permeability. It comprises: a large reservoir having an open bottom resting on the soil; a small reservoir having an open bottom resting on the soil, the small reservoir being positioned within the large reservoir; the small reservoir comprising a relatively large receptacle adjacent the soil and a relatively small receptacle connected thereto and extending upwardly therefrom; the volume of the large reservoir greatly exceeding the volume of the small reservoir; the ratio of the upper surface area of liquid in the large reservoir to the surface area of the soil covered thereby greatly exceeding the ratio of the upper surface area of liquid in the relatively small receptacle of the small reservoir to the surface area of the soil covered thereby; and means for determining the amount of liquid from the small reservoir permeating into the soil.

  10. Four-year comparison of water contents beneath a grass ley and a deciduous oak wood overlying Triassic sandstone in lowland England

    Science.gov (United States)

    Green, Julian C.; Reid, Ian; Calder, Ian R.; Nisbet, Thomas R.

    2006-09-01

    SummaryDifferences in the seasonal water dynamics of a sand soil overlying Triassic sandstone have been investigated to a depth of 9 m beneath both a grass ley and a pendunculate oak woodland within Clipstone Forest, Nottinghamshire, England. Fortnightly measurements with a neutron-probe over a four-year period allowed a comparison of the soil-rock water content to depths rarely reported. In spring, the rate of decrease of water content of the uppermost 2 m of soil was much greater under grass than oak woodland. In contrast, the rate of decrease under oak was greater after leafing out in May, while the rate of rewetting in early autumn was lower for this land-use until senescence and leaf-fall in late autumn. In the uppermost 2 m of soil - a depth that includes all plant roots - the soil moisture minima were between 47 and 58 mm lower under oak than grass in each year of monitoring. As a result of both these drier conditions and the comparatively late leaf fall of this species, penetration of the winter-season wetting front to 2 m was delayed by between one and three months at the oak site relative to grass in years of near-average rainfall. Rewetting at 9 m lags by 10-12 months, compared to the surface, giving an average penetration rate for the wetting front to this depth of 25-30 mm day -1, with little observable differences between the land-uses. Preferential flow is evident under both sites, affecting the profile to 3 m in all years and to at least 6 m following winters experiencing exceptional rainfall.

  11. Hanford Science and Technology Program: Reaction Transport Experiments Investigating the Migration of 137Cs in Sediments Beneath the Hanford SX Tank Farm

    Energy Technology Data Exchange (ETDEWEB)

    Carroll, S; Steefel, C; Zhao, P; Roberts, S

    2001-04-18

    Over one million gallons of high-level-waste with more than a million curies of {sup 137}Cs have leaked from Hanford tank farms to the sediments beneath the tanks. Early on, it was assumed that cesium migration would be limited because laboratory experiments had shown that cesium strongly sorbs to phyllosilicate minerals common in soils [1-5]. Additionally, minimal cesium desorption has been observed in contaminated Hanford sediments [6]. However, recent observations beneath the Hanford tank farms show that cesium has migrated to greater depths than expected [7]. Various explanations for enhanced cesium migration include (1) physical processes such as fast flow pathways or bypassing of exchange sites in immobile zones, and (2) chemical processes associated with the very high salt contents and high pH of the tank fluids. Ion exchange processes are clearly indicated in the depth profiles of {sup 137}Cs, and potassium, sodium, calcium, and nitrate (acting as a tracer) from the bore holes beneath tank SX-108 and tank SX-115. Below both tanks, cesium concentration peaks are retarded with respect to potassium and sodium concentration peaks. The importance of cation concentration on ion exchange is illustrated by comparing the sodium and tracer profiles beneath the tanks. Pore water with high sodium concentrations at SX-108 show little or no retardation of sodium, as is indicated by superimposed sodium and nitrate peaks. In contrast, at SX-115 sodium is significantly retarded relative to tracers (nitrate and Tc), presumably due to the lower sodium concentrations of the SX-115 leaks compared to SX-108 leaks. Calcium and magnesium form very distinct peaks at the leading edge of the sodium front under both SX-108 and SX-115. Observations such as these, led Zachara and his co-workers [8] to conduct a series of systematic cesium experiments over a wide range of cesium and salt concentrations to develop an ion exchange model that could be used to predict cesium migration

  12. Seismic imaging of a mid-lithospheric discontinuity beneath Ontong Java Plateau

    Science.gov (United States)

    Tharimena, Saikiran; Rychert, Catherine A.; Harmon, Nicholas

    2016-09-01

    Ontong Java Plateau (OJP) is a huge, completely submerged volcanic edifice that is hypothesized to have formed during large plume melting events ∼90 and 120 My ago. It is currently resisting subduction into the North Solomon trench. The size and buoyancy of the plateau along with its history of plume melting and current interaction with a subduction zone are all similar to the characteristics and hypothesized mechanisms of continent formation. However, the plateau is remote, and enigmatic, and its proto-continent potential is debated. We use SS precursors to image seismic discontinuity structure beneath Ontong Java Plateau. We image a velocity increase with depth at 28 ± 4 km consistent with the Moho. In addition, we image velocity decreases at 80 ± 5 km and 282 ± 7 km depth. Discontinuities at 60-100 km depth are frequently observed both beneath the oceans and the continents. However, the discontinuity at 282 km is anomalous in comparison to surrounding oceanic regions; in the context of previous results it may suggest a thick viscous root beneath OJP. If such a root exists, then the discontinuity at 80 km bears some similarity to the mid-lithospheric discontinuities (MLDs) observed beneath continents. One possibility is that plume melting events, similar to that which formed OJP, may cause discontinuities in the MLD depth range. Plume-plate interaction could be a mechanism for MLD formation in some continents in the Archean prior to the onset of subduction.

  13. Recharge Rates and Chemistry Beneath Playas of the High Plains Aquifer - A Literature Review and Synthesis

    Science.gov (United States)

    Gurdak, Jason J.; Roe, Cassia D.

    2009-01-01

    Playas are ephemeral, closed-basin wetlands that are important zones of recharge to the High Plains (or Ogallala) aquifer and critical habitat for birds and other wildlife in the otherwise semiarid, shortgrass prairie and agricultural landscape. The ephemeral nature of playas, low regional recharge rates, and a strong reliance on ground water from the High Plains aquifer has prompted many questions regarding the contribution of recharge from playas to the regional aquifer. To address these questions and concerns, the U.S. Geological Survey, in cooperation with the Playa Lakes Joint Venture, present a review and synthesis of the more than 175 publications about recharge rates and chemistry beneath playas and interplaya settings. Although a number of questions remain regarding the controls on recharge rates and chemistry beneath playas, the results from most published studies indicate that recharge rates beneath playas are substantially (1 to 2 orders of magnitude) higher than recharge rates beneath interplaya settings. The synthesis presented here supports the conceptual model that playas are important zones of recharge to the High Plains aquifer and are not strictly evaporative pans. The major findings of this synthesis yield science-based implications for the protection and management of playas and ground-water resources of the High Plains aquifer and directions for future research.

  14. Mantle structure beneath Indonesia inferred from high-resolution tomographic imaging

    NARCIS (Netherlands)

    Widiyantoro, Sri; Hilst, R.D. van der

    1997-01-01

    We investigated mantle structure beneath the Indonesian region by means of tomographic inversions of traveltime residuals of direct P and the surface-reflected depth phases pP and pwP. The hypocentres and phase data used in the inversions were derived from the reprocessing of data reported to intern

  15. Tectonic implications of tomographic images of subducted lithosphere beneath northwestern South America

    NARCIS (Netherlands)

    Hilst, R.D. van der; Mann, P.

    1994-01-01

    We used seismic tomography to investigate the complex structure of the upper mantle below northwestern South America. Images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted Caribbean-Pacific lithosphere beneath the study area. B

  16. Depth variations of P-wave azimuthal anisotropy beneath Mainland China.

    Science.gov (United States)

    Wei, Wei; Zhao, Dapeng; Xu, Jiandong; Zhou, Bengang; Shi, Yaolin

    2016-07-19

    A high-resolution model of P-wave anisotropic tomography beneath Mainland China and surrounding regions is determined using a large number of arrival-time data recorded by the China seismic network, the International Seismological Centre (ISC) and temporary seismic arrays deployed on the Tibetan Plateau. Our results provide important new insights into the subducted Indian plate and mantle dynamics in East Asia. Our tomographic images show that the northern limit of the subducting Indian plate has reached the Jinsha River suture in eastern Tibet. A striking variation of P-wave azimuthal anisotropy is revealed in the Indian lithosphere: the fast velocity direction (FVD) is NE-SW beneath the Indian continent, whereas the FVD is arc parallel beneath the Himalaya and Tibetan Plateau, which may reflect re-orientation of minerals due to lithospheric extension, in response to the India-Eurasia collision. There are multiple anisotropic layers with variable FVDs in some parts of the Tibetan Plateau, which may be the cause of the dominant null splitting measurements in these regions. A circular pattern of FVDs is revealed around the Philippine Sea slab beneath SE China, which reflects asthenospheric strain caused by toroidal mantle flow around the edge of the subducting slab.

  17. S-wave attenuation structure beneath the northern Izu-Bonin arc

    Science.gov (United States)

    Takahashi, Tsutomu; Obana, Koichiro; Kodaira, Shuichi

    2016-04-01

    To understand temperature structure or magma distribution in the crust and uppermost mantle, it is essential to know their attenuation structure. This study estimated the 3-D S-wave attenuation structure in the crust and uppermost mantle at the northern Izu-Bonin arc, taking into account the apparent attenuation due to multiple forward scattering. In the uppermost mantle, two areas of high seismic attenuation (high Q -1) imaged beneath the volcanic front were mostly colocated with low-velocity anomalies. This coincidence suggests that these high- Q -1 areas in low-velocity zones are the most likely candidates for high-temperature regions beneath volcanoes. The distribution of random inhomogeneities indicated the presence of three anomalies beneath the volcanic front: Two were in high- Q -1 areas but the third was in a moderate- Q -1 area, indicating a low correlation between random inhomogeneities and Q -1. All three anomalies of random inhomogeneities were rich in short-wavelength spectra. The most probable interpretation of such spectra is the presence of volcanic rock, which would be related to accumulated magma intrusion during episodes of volcanic activity. Therefore, the different distributions of Q -1 and random inhomogeneities imply that the positions of hot regions in the uppermost mantle beneath this arc have changed temporally; therefore, they may provide important constraints on the evolutionary processes of arc crust and volcanoes.

  18. The upper mantle beneath the Gulf of California from surface wave dispersion. Geologica Ultraiectina (299)

    NARCIS (Netherlands)

    Zhang, X.|info:eu-repo/dai/nl/304835773

    2009-01-01

    This thesis is a study on upper mantle shear velocity structure beneath the Gulf of California. Surface wave interstation dispersion data were measured in the Gulf of California area and vicinity to obtain a 3-D shear velocity structure of the upper mantle. This work has particular significance for

  19. The upper mantle beneath the Gulf of California from surface wave dispersion. Geologica Ultraiectina (299)

    NARCIS (Netherlands)

    Zhang, X.

    2009-01-01

    This thesis is a study on upper mantle shear velocity structure beneath the Gulf of California. Surface wave interstation dispersion data were measured in the Gulf of California area and vicinity to obtain a 3-D shear velocity structure of the upper mantle. This work has particular significance for

  20. The crustal structure beneath the Netherlands inferred from ambient seismic noise

    NARCIS (Netherlands)

    Yudistira, T.

    2015-01-01

    A 3-D shear velocity model of the crust beneath the Netherlands is determined from fundamental mode Rayleigh and Love wave group measurements derived from ambient seismic noise recordings. The data are obtained from a temporary array of broad-band seismometers in and around the Netherlands (the NARS

  1. Constraining the crustal root geometry beneath the Rif Cordillera (North Morocco)

    Science.gov (United States)

    Diaz, Jordi; Gil, Alba; Carbonell, Ramon; Gallart, Josep; Harnafi, Mimoun

    2016-04-01

    The analyses of wide-angle reflections of controlled source experiments and receiver functions calculated from teleseismic events provide consistent constraints of an over-thickened crust beneath the Rif Cordillera (North Morocco). Regarding active source data, we investigate now offline arrivals of Moho-reflected phases recorded in RIFSIS project to get new estimations of 3D crustal thickness variations beneath North Morocco. Additional constrains on the onshore-offshore transition are derived from onland recording of marine airgun shots from the coeval Gassis-Topomed profiles. A regional crustal thickness map is computed from all these results. In parallel, we use natural seismicity data collected throughout TopoIberia and PICASSO experiments, and from a new RIFSIS deployment, to obtain teleseismic receiver functions and explore the crustal thickness variations with a H-κ grid-search approach. The use of a larger dataset including new stations covering the complex areas beneath the Rif Cordillera allow us to improve the resolution of previous contributions, revealing abrupt crustal changes beneath the region. A gridded surface is built up by interpolating the Moho depths inferred for each seismic station, then compared with the map from controlled source experiments. A remarkably consistent image is observed in both maps, derived from completely independent data and methods. Both approaches document a large modest root, exceeding 50 km depth in the central part of the Rif, in contrast with the rather small topographic elevations. This large crustal thickness, consistent with the available Bouguer anomaly data, favor models proposing that the high velocity slab imaged by seismic tomography beneath the Alboran Sea is still attached to the lithosphere beneath the Rif, hence pulling down the lithosphere and thickening the crust. The thickened area corresponds to a quiet seismic zone located between the western Morocco arcuate seismic zone, the deep seismicity area

  2. Imaging Lithospheric-scale Structure Beneath Northern Altiplano in Southern Peru and Northern Bolivia

    Science.gov (United States)

    Kumar, A.; Wagner, L. S.; Beck, S. L.; Zandt, G.; Long, M. D.

    2014-12-01

    The northern Altiplano plateau of southern Peru and northern Bolivia is one of the highest topographic features on the Earth, flanked by Western and Eastern Cordillera along its margin. It has strongly influenced the local and far field lithospheric deformation since the early Miocene (Masek et al., 1994). Previous studies have emphasized the importance of both the crust and upper mantle in the evolution of Altiplano plateau (McQuarrie et al., 2005). Early tomographic and receiver function studies, south of 16° S, show significant variations in the crust and upper mantle properties in both perpendicular and along strike direction of the Altiplano plateau (Dorbath et. al., 1993; Myers et al., 1998; Beck and Zandt, 2002). In order to investigate the nature of subsurface lithospheric structure below the northern Altiplano, between 15-18° S, we have determined three-dimensional seismic tomography models for Vp and Vs using P and S-wave travel time data from two recently deployed local seismic networks of CAUGHT and PULSE. We also used data from 8 stations from the PERUSE network (PERU Subduction Experiment). Our preliminary tomographic models show a complex variation in the upper mantle velocity structure with depth, northwest and southeast of lake Titicaca. We see the following trend, at ~85 km depth, northwest of lake Titicaca: low Vp and Vs beneath the Western Cordillera, high Vs beneath the Altiplano and low Vp and Vs beneath the Eastern Cordillera. This low velocity anomaly, beneath Eastern Cordillera, seems to coincide with Kimsachata, a Holocene volcano in southern Peru. At depth greater than ~85 km: we find high velocity anomaly beneath the Western Cordillera and low Vs beneath the Altiplano. This high velocity anomaly, beneath Western Cordillera, coincides with the well-located Wadati-Benioff zone seismicity and perhaps represents the subducting Nazca slab. On the southeast of lake Titicaca, in northern Bolivia, we see a consistently high velocity anomaly

  3. Soil CO2 Uptake in Deserts and Its Implications to the Groundwater Environment

    Directory of Open Access Journals (Sweden)

    Wenfeng Wang

    2016-09-01

    Full Text Available Recent studies of soil carbon cycle in arid and semi-arid ecosystems demonstrated that there exists an abiotic CO2 absorption by saline-alkali soils (Aa at desert ecosystems and suggested potential contributions of CO2 dissolution beneath deserts to the terrestrial ecosystems carbon balance. However, the overall importance of such soil CO2 uptake is still undetermined and its implications to the groundwater environment remain unaddressed. In this manuscript, a simple method is proposed for the direct computation of Aa from the total soil CO2 flux (Fa as well as for the evaluation of Aa importance to Fa. An artificial soil-groundwater system was employed to investigate the implications to groundwater environment and it was found that soil CO2 uptake in deserts can contribute a possible influence on the evolution of the groundwater environment, providing that the absorbed CO2 largely remained in the soil-groundwater system.

  4. Seismic evidence for slab graveyards atop the Core Mantle Boundary beneath the Indian Ocean Geoid Low

    Science.gov (United States)

    Padma Rao, B.; Ravi Kumar, M.

    2014-11-01

    The Indian Ocean Geoid Low (IOGL) that spans a vast areal extent south of the Indian subcontinent is a spectacular feature on the Earth, whose origin still remains ambiguous. In this study, we investigate the seismic character of the lower mantle below this geoid low utilizing the travel time and amplitude residuals of high quality S and ScS phases from 207 earthquakes recorded at 276 stations in the epicentral distance range of 36°-90°. For comparison, we also perform a similar exercise for a region of geoid high in the vicinity. Results reveal large variations in the ScS travel times indicating that the lowermost mantle beneath the IOGL region is heterogeneous. The ScS-S differential travel times are ∼3 s slower than those predicted by the IASP91 model, primarily due to velocity increase in the lowermost mantle beneath the IOGL region and ∼2 s higher than the IASP91 beneath the geoid high region, due to velocity decrease in the lowermost mantle. The largest negative residuals from manual method (-7.72 s) are concentrated below the IOGL. Iterative matching of differential travel time residuals reveals that the maximum positive and negative residuals can be explained in terms of a reduction in shear velocity of 0.9% and an increase of 1.6% respectively in a ∼1000 km thick layer above the Core Mantle Boundary. Further, the ScS/S amplitude residuals beneath the IOGL are positive, implying high impedance contrast at the Core Mantle Boundary, owing to the presence of high velocity material. We attribute these high velocities to the presence of dehydrated high density slab graveyards atop the Core Mantle Boundary beneath the Indian Ocean. Release of water at the mid-to-upper mantle depths due to the dehydration of subducted slabs causing a reduction in density and velocity of the ambient mantle, could be responsible for the geoid low.

  5. Lithospheric structure beneath the High Lava Plains, Oregon, imaged by scattered teleseismic waves

    Science.gov (United States)

    Chen, Chin-Wu; James, David E.; Fouch, Matthew J.; Wagner, Lara S.

    2013-11-01

    We compute high-resolution seismic images from scattered wavefield to detect discontinuities beneath the High Lava Plains (HLP), using data recorded at a dense broadband array. Our images of the HLP and surrounding regions reveal (1) a prominent Moho discontinuity with varying depth, with thinnest crust of 35 km beneath the volcanic track, and thickened crust of ˜45 km beneath the Owyhee Plateau (OP); (2) distinct intracrustal velocity reversals beneath regions of pre-2.0 Ma volcanism and within the OP; and (3) intermittent negative velocity discontinuities in the uppermost mantle beneath regions of Holocene volcanism and volcanic centers near Steens Mountain and Newberry volcano. These features exhibit remarkable similarity with those seen in the surface wave tomography and Ps receiver functions. We fail to find evidence for a ubiquitous regional lithosphere-asthenosphere boundary (LAB). In concert with petrological constraints on the equilibration depths of primitive basaltic melts, our results suggest that the present-day HLP mantle lithosphere is thin or absent, perhaps a consequence of episodes of extensive mantle inflow, lithospheric extension, and possibly melting induced by rapid slab rollback and trench retreat. It remains possible, however, that strong E-W seismic anisotropy reported across this region may reduce the effective S-wave velocity contrast to render the LAB less detectable. In contrast, the Owyhee Plateau exhibits a clear LAB, consistent with it being a block of older preexisting lithosphere. Our images demonstrate the complexity of mantle dynamics in the Cascadian back-arc and the close casual link between subduction-related processes and the origin of HLP volcanism.

  6. The Impact of the Subduction Modeling Beneath Calabria on Seismic Hazard

    Science.gov (United States)

    Morasca, P.; Johnson, W. J.; Del Giudice, T.; Poggi, P.; Traverso, C.; Parker, E. J.

    2014-12-01

    The aim of this work is to better understand the influence of subduction beneath Calabria on seismic hazard, as very little is known about present-day kinematics and the seismogenic potential of the slab interface in the Calabrian Arc region. This evaluation is significant because, depending on stress conditions, subduction zones can vary from being fully coupled to almost entirely decoupled with important consequences in the seismic hazard assessment. Although the debate is still open about the current kinematics of the plates and microplates lying in the region and the degree of coupling of Ionian lithosphere beneath Calabria, GPS data suggest that this subduction is locked in its interface sector. Also the lack of instrumentally recorded thrust earthquakes suggests this zone is locked. The current seismotectonic model developed for the Italian National territory is simplified in this area and does not reflect the possibility of locked subduction beneath the Calabria that could produce infrequent, but very large earthquakes associated with the subduction interface. Because of this we have conducted an independent seismic source analysis to take into account the influence of subduction as part of a regional seismic hazard analysis. Our final model includes two separate provinces for the subduction beneath the Calabria: inslab and interface. From a geometrical point of view the interface province is modeled with a depth between 20-50 km and a dip of 20°, while the inslab one dips 70° between 50 -100 km. Following recent interpretations we take into account that the interface subduction is possibly locked and, in such a case, large events could occur as characteristic earthquakes. The results of the PSHA analysis show that the subduction beneath the Calabrian region has an influence in the total hazard for this region, especially for long return periods. Regional seismotectonic models for this region should account for subduction.

  7. (Contaminated soil)

    Energy Technology Data Exchange (ETDEWEB)

    Siegrist, R.L.

    1991-01-08

    The traveler attended the Third International Conference on Contaminated Soil, held in Karlsruhe, Germany. The Conference was a status conference for worldwide research and practice in contaminated soil assessment and environmental restoration, with more than 1500 attendees representing over 26 countries. The traveler made an oral presentation and presented a poster. At the Federal Institute for Water, Soil and Air Hygiene, the traveler met with Dr. Z. Filip, Director and Professor, and Dr. R. Smed-Hildmann, Research Scientist. Detailed discussions were held regarding the results and conclusions of a collaborative experiment concerning humic substance formation in waste-amended soils.

  8. Soil Solution

    NARCIS (Netherlands)

    Sonneveld, C.; Voogt, W.

    2009-01-01

    The characteristics of the soil solution in the root environment in the greenhouse industry differ much from those for field grown crops. This is caused firstly by the growing conditions in the greenhouse, which strongly differ from those in the field and secondly the function attributed to the soil

  9. Linking soil biodiversity and agricultural soil management

    NARCIS (Netherlands)

    Thiele-Bruhn, S.; Bloem, J.; Vries, de F.T.; Kalbitz, K.; Wagg, C.

    2012-01-01

    Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosystem stability and services. This review presents recent findings in soil biodiversity research focused on interrelations with agricultural soil management. Richness and community structure of soil biota depend o

  10. Linking soil biodiversity and agricultural soil management

    NARCIS (Netherlands)

    Thiele-Bruhn, S.; Bloem, J.; de Vries, F.T.; Kalbitz, K.; Wagg, C.

    2012-01-01

    Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosystem stability and services. This review presents recent findings in soil biodiversity research focused on interrelations with agricultural soil management. Richness and community structure of soil biota depend

  11. Neogene kinematic history of Nazca-Antarctic-Phoenix slab windows beneath Patagonia and the Antarctic Peninsula

    Science.gov (United States)

    Breitsprecher, Katrin; Thorkelson, Derek J.

    2009-01-01

    The Patagonian slab window is a subsurface tectonic feature resulting from subduction of the Nazca-Antarctic spreading-ridge system (Chile Rise) beneath southern South America. The geometry of the slab window had not been rigorously defined, in part because of the complex nature of the history of ridge subduction in the southeast Pacific region, which includes four interrelated spreading-ridge systems since 20 Ma: first, the Nazca-Phoenix ridge beneath South America, then simultaneous subduction of the Nazca-Antarctic and the northern Phoenix-Antarctic spreading-ridge systems beneath South America, and the southern Phoenix-Antarctic spreading-ridge system beneath Antarctica. Spreading-ridge paleo-geographies and rotation poles for all relevant plate pairs (Nazca, Phoenix, Antarctic, South America) are available from 20 Ma onward, and form the mathematical basis of our kinematic reconstruction of the geometry of the Patagonia and Antarctic slab windows through Neogene time. At approximately 18 Ma, the Nazca-Phoenix-Antarctic oceanic (ridge-ridge-ridge) triple junction enters the South American trench; we recognize this condition as an unstable quadruple junction. Heat flow at this junction and for some distance beneath the forearc would be considerably higher than is generally recognized in cases of ridge subduction. From 16 Ma onward, the geometry of the Patagonia slab window developed from the subduction of the trailing arms of the former oceanic triple junction. The majority of the slab window's areal extent and geometry is controlled by the highly oblique (near-parallel) subduction angle of the Nazca-Antarctic ridge system, and by the high contrast in relative convergence rates between these two plates relative to South America. The very slow convergence rate of the Antarctic slab is manifested by the shallow levels achieved by the slab edge (< 45 km); thus no point on the Antarctic slab is sufficiently deep to generate "normal" mantle-derived arc-type magmas

  12. Soil ecosystem functioning under climate change: plant species and community effects.

    Science.gov (United States)

    Kardol, Paul; Cregger, Melissa A; Campany, Courtney E; Classen, Aimee T

    2010-03-01

    Feedbacks of terrestrial ecosystems to atmospheric and climate change depend on soil ecosystem dynamics. Soil ecosystems can directly and indirectly respond to climate change. For example, warming directly alters microbial communities by increasing their activity. Climate change may also alter plant community composition, thus indirectly altering the soil communities that depend on their inputs. To better understand how climate change may directly and indirectly alter soil ecosystem functioning, we investigated old-field plant community and soil ecosystem responses to single and combined effects of elevated [CO2], warming, and precipitation in Tennessee (USA). Specifically, we collected soils at the plot level (plant community soils) and beneath dominant plant species (plant-specific soils). We used microbial enzyme activities and soil nematodes as indicators for soil ecosystem functioning. Our study resulted in two main findings: (1) Overall, while there were some interactions, water, relative to increases in [CO2] and warming, had the largest impact on plant community composition, soil enzyme activity, and soil nematodes. Multiple climate-change factors can interact to shape ecosystems, but in our study, those interactions were largely driven by changes in water. (2) Indirect effects of climate change, via changes in plant communities, had a significant impact on soil ecosystem functioning, and this impact was not obvious when looking at plant community soils. Climate-change effects on enzyme activities and soil nematode abundance and community structure strongly differed between plant community soils and plant-specific soils, but also within plant-specific soils. These results indicate that accurate assessments of climate-change impacts on soil ecosystem functioning require incorporating the concurrent changes in plant function and plant community composition. Climate-change-induced shifts in plant community composition will likely modify or counteract the

  13. Influence of bigleaf maple (Acer Macrophyllum Pursh) on soil properties in a conifer forest of southwest British Columbia

    OpenAIRE

    Chandler, Julia

    2006-01-01

    The overall objective of this research was to detect the influence of bigleaf maple (Acer macrophyllum Pursh) on soils in a conifer forest of southwest British Columbia. Forest floor properties were measured beneath bigleaf maple along six transects and on two 36 m x 36 m plots. Wavelet analysis, kriging, spatial autocorrelation analysis, local indicators of spatial association, and parametric statistics were used to explore and confirm bigleaf maple patterns of influence on surrounding soils...

  14. Melt transport rates in heterogeneous mantle beneath mid-ocean ridges

    CERN Document Server

    Weatherley, Samuel M

    2015-01-01

    Recent insights to melt migration beneath ridges suggest that channelized flow is a consequence of melting of a heterogeneous mantle, and that spreading rate modulates the dynamics of the localized flow. A corollary of this finding is that both mantle het- erogeneity and spreading rate have implications for the speed and time scale of melt migration. Here, we investigate these implications using numerical models of magma flow in heterogeneous mantle beneath spreading plates. The models predict that a broad distribution of magma flow speeds is characteristic of the sub-ridge mantle. Within the melting region, magmatic flow is fastest in regions of average fusibility; surprisingly, magmas from sources of above-average fusibility travel to the ridge in a longer time. Spreading rate has comparatively simple consequences, mainly resulting in faster segregation speeds at higher spreading rates. The computed time scales are short enough to preserve deep origin 230Th disequilibria and, under favourable parameter regi...

  15. Crustal magma pathway beneath Aso caldera inferred from three-dimensional electrical resistivity structure

    Science.gov (United States)

    Hata, Maki; Takakura, Shinichi; Matsushima, Nobuo; Hashimoto, Takeshi; Utsugi, Mitsuru

    2016-10-01

    At Naka-dake cone, Aso caldera, Japan, volcanic activity is raised cyclically, an example of which was a phreatomagmatic eruption in September 2015. Using a three-dimensional model of electrical resistivity, we identify a magma pathway from a series of northward dipping conductive anomalies in the upper crust beneath the caldera. Our resistivity model was created from magnetotelluric measurements conducted in November-December 2015; thus, it provides the latest information about magma reservoir geometry beneath the caldera. The center of the conductive anomalies shifts from the north of Naka-dake at depths >10 km toward Naka-dake, along with a decrease in anomaly depths. The melt fraction is estimated at 13-15% at 2 km depth. Moreover, these anomalies are spatially correlated with the locations of earthquake clusters, which are distributed within resistive blocks on the conductive anomalies in the northwest of Naka-dake but distributed at the resistive sides of resistivity boundaries in the northeast.

  16. Electromagnetic evidence for volatile-rich upwelling beneath the society hotspot, French Polynesia

    Science.gov (United States)

    Tada, Noriko; Tarits, Pascal; Baba, Kiyoshi; Utada, Hisashi; Kasaya, Takafumi; Suetsugu, Daisuke

    2016-12-01

    We have conducted a seafloor magnetotelluric survey that images, for the first time, three-dimensional electrical conductivity structure in the upper mantle beneath the Society hotspot. A striking feature in our model is a high-conductivity anomaly a few hundred kilometers in diameter, which is continuous from the lowest part of the upper mantle to a depth of approximately 50 km below sea level. Using theoretical and experimental results from mineral physics, we interpret the high-conductivity anomaly as evidence of the melt fraction up to 2.2 vol.%, which is robust regardless of assumed temperature, and the existence of carbonated silicate melt beneath the hotspot. Our results suggest that the Society hotspot is a pathway for ascending volatiles from the deeper part of the upper mantle to the surface.

  17. The crustal structure beneath Mauritius from teleseismic P-receiver functions - oceanic or continental?

    Science.gov (United States)

    Singh, Manvendra; Kaviani, Ayoub; Rümpker, Georg

    2016-09-01

    It has recently been suggested that the volcanic island of Mauritius may be underlain by a remnant of continental origin termed "Mauritia". To constrain the crustal thickness beneath Mauritius, we analyzed data from 11 land stations, 10 of which were deployed recently by the RHUM-RUM project. From the recordings, we obtained 382 P-receiver functions (RFs). By applying the H-κ stacking technique, we derive crustal thicknesses of approximately 10-15 km. We observe a considerable variation in the Vp/Vs-ratio caused by a lack of clear multiples. Using forward modeling of RFs, we show that the lack of clear multiples can be explained by a transitional Moho, where the velocity increases gradually. The modeling further indicates that the thickness of this gradient zone is estimated to be approximately 10 km. We argue that our findings suggest oceanic crust thickened by crustal underplating due the mantle plume currently located beneath the La Réunion.

  18. Using Sealed Wells to Measure Water Levels Beneath Streams and Floodplains.

    Science.gov (United States)

    Noorduijn, Saskia L; Cook, Peter G; Wood, Cameron; White, Nick

    2015-01-01

    The design of wells beneath streams and floodplains has often employed with tall standpipes to prevent incursion of surface water into the well during flood events. Here, an approach has been presented to minimise the infrastructure demands in these environments by sealing the well top (e.g., prevent water entering the well) and monitor the total pressure in the water column using an absolute (non-vented) pressure transducer. The sealed well design was tested using a laboratory experiment where the total pressure responses were monitored in both an unsealed and sealed well, while the water level was varied. It is observed that, whether the well is sealed or not, the total pressure at a given depth in the aquifer will be equal to that within the well. This indicates that the sealed well design is a viable alternative to tall standpipes and also facilitates installation of wells beneath streams and floodplains.

  19. Shear-wave velocity structure of the crust and upper mantle beneath the Kola Peninsula

    Science.gov (United States)

    Dricker, I. G.; Roecker, S. W.; Kosarev, G. L.; Vinnik, L. P.

    We determined the shear-wave velocity structure of the crust and upper mantle beneath the central part of the Kola peninsula from the analysis of P-wave receiver functions and mantle P-SV converted phases recorded at stations Apatity (APA) and Lovozero (LVZ). The times of P-SV converted phases from the 410 and 660 km discontinuities are close to those predicted by the IASP91 model. Phase conversions at the crust-mantle boundary beneath the Baltic shield northeast of LVZ and southwest of APA are consistent with a sharp transition from crust to mantle at a depth of 40 km, while conversions from the intervening Khibina plutonic region are consistent with a gradual transition between depths of 20 and 40 km. We infer that short (∼50 km) wavelength lateral variations in the crust-mantle transition persist in this region, despite the inactivity of the Kola peninsula since Devonian times.

  20. Mid-lithosphere discontinuities beneath the western and central North China Craton

    Science.gov (United States)

    Sun, Weijia; Kennett, B. L. N.

    2017-02-01

    By analyzing P reflectivity extracted from stacked autocorrelograms for teleseismic events on a dense seismic profile, we obtain a detailed image of the mid-lithosphere discontinuity (MLD) beneath western and central North China Craton (NCC). This seismic daylight imaging exploits a broad high-frequency band (0.5-4 Hz) to reveal the fine-scale component of multi-scale lithospheric heterogeneity. The depth of the MLD beneath the western and central parts of the NCC ranges 80-120 km, with a good match to the transition to negative S velocity gradient with depth from Rayleigh wave tomography. The MLD inferred from seismic daylight imaging also has good correspondence with the transition from conductive to convective regimes estimated from heat flow data indicating likely thermal control within the seismological lithosphere.

  1. Tomography reveals buoyant asthenosphere accumulating beneath the Juan de Fuca plate

    Science.gov (United States)

    Hawley, William B.; Allen, Richard M.; Richards, Mark A.

    2016-09-01

    The boundary between Earth’s strong lithospheric plates and the underlying mantle asthenosphere corresponds to an abrupt seismic velocity decrease and electrical conductivity increase with depth, perhaps indicating a thin, weak layer that may strongly influence plate motion dynamics. The behavior of such a layer at subduction zones remains unexplored. We present a tomographic model, derived from on- and offshore seismic experiments, that reveals a strong low-velocity feature beneath the subducting Juan de Fuca slab along the entire Cascadia subduction zone. Through simple geodynamic arguments, we propose that this low-velocity feature is the accumulation of material from a thin, weak, buoyant layer present beneath the entire oceanic lithosphere. The presence of this feature could have major implications for our understanding of the asthenosphere and subduction zone dynamics.

  2. Lithosphere-Asthenosphere Boundary Beneath Regions of Recent Volcanism in the Basin and Range Province and Mojave Desert

    Science.gov (United States)

    Forsyth, D. W.; Rau, C. J.; Plank, T.; Gazel, E.; Bendersky, C.

    2010-12-01

    Melt in the asthenosphere may contribute strongly to the development of the lithosphere-asthenosphere boundary (LAB) in some settings. We have compiled a set of vertical shear-velocity profiles beneath centers of recent (<1.0 Ma) volcanic activity in the Basin and Range province based on Rayleigh wave tomography. The classic pattern of a high-velocity lid overlying a low-velocity zone (LVZ) is clear beneath many of the centers. Cima, for example, has a high velocity lid extending to a depth of about 60 km. Beneath Dish Hill and Amboy in the southern Mojave, the lithospheric lid extends to a depth of ~ 90 km. Minimum velocities in the LVZs beneath the higher velocity lids typically are 4.00-4.05 km/s, similar to that beneath the East Pacific Rise and too low to be caused by temperature alone without unreasonably high attenuation. Beneath other centers, like Big Pine, Lathrop Wells and Tahoe, there is no resolvable lid. The lid is either missing or too thin to resolve, but the absence of the lid/LVZ pattern seems to be due to a combination of lower velocities immediately beneath the Moho and higher velocities in the LVZ. Petrological indicators of temperature and depth of melting from basalt composition are in general agreement with the seismological observations, with the depth of last equilibration typically occurring near the top of the LVZ. Beneath Big Pine, for example, the equilibration temperatures are unusually low and the equilibration depth is 40 to 50 km, just below the Moho, in agreement with the lack of a distinct lid. Beneath Cima, equilibration depths are 60-70 km. Beneath Coso, equilibration depths are only slightly deeper than Big Pine, but the temperatures are higher, in agreement with the more pronounced LVZ and the presence of a thin lid. Beneath the Tabernacle Hill/Black Rock volcanic field in west-central Utah, there is a well-developed lid/LVZ structure, but the "high" velocity lid is only ~ 4.10 km/s while the underlying LVZ reaches as low as

  3. Soil mechanics

    Science.gov (United States)

    Mitchell, J. K.; Carrier, W. D., III; Houston, W. N.; Scott, R. F.; Bromwell, L. G.; Durgunoglu, H. T.; Hovland, H. J.; Treadwell, D. D.; Costes, N. C.

    1972-01-01

    Preliminary results are presented of an investigation of the physical and mechanical properties of lunar soil on the Descartes slopes, and the Cayley Plains in the vicinity of the LM for Apollo 16. The soil mechanics data were derived form (1) crew commentary and debriefings, (2) television, (3) lunar surface photography, (4) performance data and observations of interactions between soil and lunar roving vehicle, (5) drive-tube and deep drill samples, (6) sample characteristics, and (7) measurements using the SRP. The general characteristics, stratigraphy and variability are described along with the core samples, penetrometer test results, density, porosity and strength.

  4. Compositions of Upper Mantle Fluids Beneath Eastern China:Implications for Mantle Evolution

    Institute of Scientific and Technical Information of China (English)

    ZHANG Mingjie; WANG Xianbin; LIU Gang; ZHANG Tongwei; BO Wenrui

    2004-01-01

    The composition of gases trapped in olivine, orthopyroxene and clinopyroxene in lherzolite xenoliths collected from different locations in eastern China has been measured by the vacuum stepped-heating mass spectrometry.These xenoliths are hosted in alkali basalts and considered as residues of partial melting of the upper mantle, and may contain evidence of mantle evolution. The results show that various kinds of fluid inclusions in lherzolite xenoliths have been released at distinct times, which could be related to different stages of mantle evolution. In general, primitive fluids of the upper mantle (PFUM) beneath eastern China are dominated by H2, CO2 and CO, and are characterized by high contents of H2 and reduced gases. The compositions of PFUM are highly variable and related to tectonic settings. CO, CO2 and H2 are the main components of the PFUM beneath cratons; the PFUM in the mantle enriched in potassic metasomatism in the northern part of northeastern China has a high content of H2, while CO2 and SO2 are the dominant components of the PFUM in the Su-Lu-Wan (Jiangsu-Shandong-Anhui) region, where recycled crustal fluids were mixed with deeper mantle components. There are several fluids with distinct compositions beneath eastern China, such as primitive fluids of upper mantle (CO, CO2 and H2), partial melting fluids (CO2 and CO) and metasomatic fluids mixed with recycled crustal fluids (CO2, N2, 8O2 and CH4) etc. Fluids of the upper mantle beneath the North China craton are different from that of the South China craton in total gases and chemical compositions: the contents of the reduced gases of the PFUM in the NCC are higher than those in the SCC.

  5. Melt zones beneath five volcanic complexes in California: an assessment of shallow magma occurrences

    Energy Technology Data Exchange (ETDEWEB)

    Goldstein, N.E.; Flexser, S.

    1984-12-01

    Recent geological and geophysical data for five magma-hydrothermal systems were studied for the purpose of developing estimates for the depth, volume and location of magma beneath each area. The areas studied were: (1) Salton Trough, (2) The Geysers-Clear Lake, (3) Long Valley caldera, (4) Coso volcanic field, and (5) Medicine Lake volcano, all located in California and all selected on the basis of recent volcanic activity and published indications of crustal melt zones. 23 figs.

  6. Are assemblages of the fireworm Hermodice carunculata enhanced in sediments beneath offshore fish cages?

    Institute of Scientific and Technical Information of China (English)

    Rodrigo Riera; Oscar Prez; Myriam Rodrguez; Eva Ramos; scar Monterroso

    2014-01-01

    Abundances of the fireworm Hermodice carunculata were counted through a monitoring assessment study of fish cages in Barranco Hondo (NE Tenerife). Seven campaigns were conducted from November 2007 to June 2010 and temporal variations were found, as well as differences among sampling stations. The poly-chaete H. carunculata obtained its highest abundance in sediments beneath fish cages throughout the study period. Thus, the assemblages of this omnivorous species were favoured by the presence of fish cages.

  7. Urban recharge beneath low impact development and effects of climate variability and change

    Science.gov (United States)

    Newcomer, Michelle E.; Gurdak, Jason J.; Sklar, Leonard S.; Nanus, Leora

    2014-02-01

    low impact development (LID) planning and best management practices (BMPs) effects on recharge is important because of the increasing use of LID BMPs to reduce storm water runoff and improve surface-water quality. LID BMPs are microscale, decentralized management techniques such as vegetated systems, pervious pavement, and infiltration trenches to capture, reduce, filter, and slow storm water runoff. Some BMPs may enhance recharge, which has often been considered a secondary management benefit. Here we report results of a field and HYDRUS-2D modeling study in San Francisco, California, USA to quantify urban recharge rates, volumes, and efficiency beneath a LID BMP infiltration trench and irrigated lawn considering historical El Niño/Southern Oscillation (ENSO) variability and future climate change using simulated precipitation from the Geophysical Fluid Dynamic Laboratory (GFDL) A1F1 climate scenario. We find that in situ and modeling methods are complementary, particularly for simulating historical and future recharge scenarios, and the in situ data are critical for accurately estimating recharge under current conditions. Observed (2011-2012) and future (2099-2100) recharge rates beneath the infiltration trench (1750-3710 mm yr-1) were an order of magnitude greater than beneath the irrigated lawn (130-730 mm yr-1). Beneath the infiltration trench, recharge rates ranged from 1390 to 5840 mm yr-1 and averaged 3410 mm yr-1 for El Niño years (1954-2012) and from 1540 to 3330 mm yr-1 and averaged 2430 mm yr-1 for La Niña years. We demonstrate a clear benefit for recharge and local groundwater resources using LID BMPs.

  8. Depth of Cracking beneath Impact Craters: New Constraint for Impact Velocity

    OpenAIRE

    Ahrens, Thomas J.; Xia, Kaiwen; Coker, Demirkan

    2002-01-01

    Both small-scale impact craters in the laboratory and less than 5 km in diameter bowl-shaped craters on the Earth are strength (of rock) controlled. In the strength regime, crater volumes are nearly proportional to impactor kinetic energy. The depth of the cracked rock zone beneath such craters depends on both impactor energy and velocity. Thus determination of the maximum zone of cracking constrains impact velocity. We show this dependency for small-scale laboratory craters where the cracked...

  9. Searching for structure in the mid-mantle: Observations of converted phases beneath Iceland and Europe

    Science.gov (United States)

    Jenkins, J.; Deuss, A. F.; Cottaar, S.

    2016-12-01

    Until recently, most of the lower mantle was considered to be well-mixed with strong heterogeneity restricted to the lowermost several hundred kilometers above the core-mantle boundary, also known as the D'' layer. However, several recent studies have started to hint at a potential change in earth structure at mid-mantle depths, with evidence from both seismic tomography (Fukao and Obayashi 2013, French and Romanowichz, 2015) and global viscosity structure (Rudolph et al., 2015). We present the first continental-wide search for mid-mantle P to S wave converted phases and find most observations come from approximately 1000 km depth beneath Iceland and Western Europe. Conversions are identified using a data set of 50,000 high quality receiver functions which are systematically searched for robust signals from the mid-mantle. Potential P to s conversions are analysed in terms of slowness to determine whether they are true observations from depth or simply surface multiples arriving at similar times. We find broad regions with robust signals from approximately 1000 km depth in several locations; beneath Iceland and across Western Europe, beneath Ireland, Scotland, Eifel and south towards NW Italy and Spain. Similar observations have previously been observed mainly in subduction zone settings, and have been hypothesised to be caused by down-going oceanic crustal material. Here we present observations which correlate with slow seismic velocities in recent tomographic models (Rickers et al., (2013); French and Romanowicz, (2015)). These low velocities appear to be a channel deviating from the broad mantle plume beneath Iceland at mid-mantle depths. We hypothesise that the mid-mantle seismic signals we observe are caused by either a phase transition occurring locally in a specific composition or by small-scale chemical heterogeneities swept along with upwelling material and ponding around 1000 km.

  10. Near-shore talik development beneath shallow water in expanding thermokarst lakes, Old Crow Flats, Yukon

    Science.gov (United States)

    Roy-Leveillee, Pascale; Burn, Christopher R.

    2017-05-01

    It is generally assumed that permafrost is preserved beneath shallow lakes and ponds in the Western North American Arctic where water depth is less than about two thirds of the late-winter lake ice thickness. Here we present field observations of talik development beneath water as shallow as 0.2 m despite a lake ice thickness of 1.5 m, in Old Crow Flats (OCF), YT. Conditions leading to the initiation and development of taliks beneath shallow water were investigated with field measurements of shore erosion rates, bathymetry, ice thickness, snow accumulation, and lake bottom temperature near the shores of two expanding lakes in OCF. The sensitivity of talik development to variations in lake bottom thermal regime was then investigated numerically. Where ice reached the lake bottom, talik development was controlled by the ratio of freezing degree days to thawing degree days at the lake bottom (FDDlb/TDDlb). In some cases, spatial variations in on-ice snow depth had a minimal effect on annual mean lake bottom temperature (Tlb) but caused sufficient variations in FDDlb/TDDlb to influence talik development. Where Tlb was close to but greater than 0°C simulations indicated that the thermal offset allowed permafrost aggradation to occur under certain conditions, resulting in irregular near-shore talik geometries. The results highlight the sensitivity of permafrost to small changes in lake bottom thermal conditions where the water column freezes through in early winter and indicate the occurrence of permafrost degradation beneath very shallow water in the near-shore zone of Arctic ponds and lakes.

  11. Influence of tides on melting and freezing beneath Filchner-Ronne Ice Shelf, Antarctica

    OpenAIRE

    Makinson, Keith; Holland, Paul R.; Jenkins, Adrian; Nicholls, Keith W.; Holland, David M.

    2011-01-01

    An isopycnic coordinate ocean circulation model is applied to the ocean cavity beneath Filchner-Ronne Ice Shelf, investigating the role of tides on sub-ice shelf circulation and ice shelf basal mass balance. Including tidal forcing causes a significant intensification in the sub-ice shelf circulation, with an increase in melting (3-fold) and refreezing (6-fold); the net melt rate and seawater flux through the cavity approximately doubles. With tidal forcing, the spatial pattern and magnitude ...

  12. Hydrologically active palaeofluvial and subglacial channel networks beneath Humboldt Glacier, Greenland

    Science.gov (United States)

    Ely, Jeremy; Livingstone, Stephen; Chu, Winnie; Kingslake, Jonathan

    2017-04-01

    Subglacial drainage systems influence both the flow of overlying ice and the evolution of subglacial landscapes. Yet, the persistence, pattern, origin and spatio-temporal evolution of subglacial drainage remains poorly understood. Whilst the beds of former ice sheets record numerous examples of channelized subglacial drainage systems, any influence these may have had upon ice sheet dynamics is difficult to decipher without contemporary analogues. Therefore, in order to understand the fates of past, present and future ice sheets, further study of contemporary subglacial hydraulic systems is required. Here, we present evidence from satellite imagery, digital elevation models and radio-echo sounding data for previously unknown channelized networks beneath Humboldt Glacier, northern Greenland. We find that two major channel networks exist beneath Humboldt Glacier: (i) a dendritic channel network to the north of the catchment, which extends for over >250 km beneath the ice sheet; and (ii) a series of linear channels in the south of the catchment, which are up to 80 km in length, 2.5 km wide and 400 m deep. These two morphologically contrasting systems likely have separate origins. We interpret the dendritic channel network to be of palaeofluvial origin, whilst the linear channels are likely to be subglacially formed tunnel valleys - analogous to those observed on former ice sheet beds. Radio-echo sounding indicates that basal meltwater is actively being routed along both systems. The dichotomy in subglacial drainage system origin corresponds to a division in ice flow regime, with faster flowing ice occurring over the palaeo-fluvial system. We therefore hypothesise that the large-scale bed channelization by subglacial meltwater erosion, which occurs beneath the slower flowing southern portion of Humboldt, results in a long-term reduction in basal water pressures and ice flow velocities.

  13. Estimates of deep percolation beneath native vegetation, irrigated fields, and the Amargosa-River Channel, Amargosa Desert, Nye County, Nevada

    Science.gov (United States)

    Stonestrom, David A.; Prudic, David E.; Laczniak, Randell J.; Akstin, Katherine C.; Boyd, Robert A.; Henkelman, Katherine K.

    2003-01-01

    The presence and approximate rates of deep percolation beneath areas of native vegetation, irrigated fields, and the Amargosa-River channel in the Amargosa Desert of southern Nevada were evaluated using the chloride mass-balance method and inferred downward velocities of chloride and nitrate peaks. Estimates of deep-percolation rates in the Amargosa Desert are needed for the analysis of regional ground-water flow and transport. An understanding of regional flow patterns is important because ground water originating on the Nevada Test Site may pass through the area before discharging from springs at lower elevations in the Amargosa Desert and in Death Valley. Nine boreholes 10 to 16 meters deep were cored nearly continuously using a hollow-stem auger designed for gravelly sediments. Two boreholes were drilled in each of three irrigated fields in the Amargosa-Farms area, two in the Amargosa-River channel, and one in an undisturbed area of native vegetation. Data from previously cored boreholes beneath undisturbed, native vegetation were compared with the new data to further assess deep percolation under current climatic conditions and provide information on spatial variability. The profiles beneath native vegetation were characterized by large amounts of accumulated chloride just below the root zone with almost no further accumulation at greater depths. This pattern is typical of profiles beneath interfluvial areas in arid alluvial basins of the southwestern United States, where salts have been accumulating since the end of the Pleistocene. The profiles beneath irrigated fields and the Amargosa-River channel contained more than twice the volume of water compared to profiles beneath native vegetation, consistent with active deep percolation beneath these sites. Chloride profiles beneath two older fields (cultivated since the 1960?s) as well as the upstream Amargosa-River site were indicative of long-term, quasi-steady deep percolation. Chloride profiles beneath the

  14. Percutaneous radiofrequency ablation for lung tumors beneath the rib under CT fluoroscopic guidance with gantry tilt

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Takanobu; Yamagami, Takuji; Tanaka, Osamu; Yoshimatsu, Rika; Miura, Hiroshi; Nishimura, Tsunehiko (Dept. of Radiology, Graduate School of Medical Science, Kyoto Prefectural Univ. of Medicine, Kamigyo, Kyoto (Japan)), e-mail: yamagami@koto.kpu-m.ac.jp

    2010-05-15

    Background: Radiofrequency (RF) ablation of lung tumors has become a treatment of choice, especially for unresectable cases. However, RF ablation of small lung lesions located just beneath the rib is difficult. Purpose: To evaluate the efficacy and safety of gantry tilting for the performance of RF ablation of peripheral lesions located beneath the rib. Material and Methods: Our study was based on 18 of 293 lesions in the lung for which RF ablation was performed under CT scan fluoroscopic guidance at our institution between October 2004 and March 2009. For these 18 lesions, RF ablation was performed with gantry tilting because a rib blocked visualization of the RF ablation route even after other attempts had been made to change the relationship between the target and the rib. Results: All RF needles, with only one exception, were successfully advanced to hit the tumor. The commonest complication was a pneumothorax, which occurred in seven procedures. No serious complications occurred. The progression-free rates were 82.4% at 6 months, 62.5% at 12 months, and 30% at 24 months. Mean local progression-free duration was 17.6+-11.6 months (range 4-36 months). Conclusion: RF ablation under CT scan fluoroscopic guidance with gantry tilt is a useful and safe technique for RF ablation of lung nodules located beneath the rib

  15. Attenuation structure beneath the volcanic front in northeastern Japan from broad-band seismograms

    Science.gov (United States)

    Takanami, Tetsuo; Selwyn Sacks, I.; Hasegawa, Akira

    2000-10-01

    Anelastic structure in the asthenosphere beneath the volcanic front in northeastern Japan arc is estimated by using the spectral amplitude ratio data of P and S waves from about 100 events which occurred in the subducting Pacific slab below Japan. These earthquakes occurred within a 90 km radius centered about the station Sawauchi (SWU), with focal depths ranging from 60 to 200 km. Waveforms were recorded by the Carnegie broad-band three-component seismograph and were corrected for instrument responses, crustal reverberations, corner frequencies, and superimposed noise. Ray paths and travel times of P and S waves are calculated using a three-dimensional velocity model [Zhao, D., Hasegawa, A., Horiuchi, S., 1992. J. Geophys. Res. 97, 19909-19928]. We find a low- Q region ( QS˜70) extending down to 55 km depth from the lower crust beneath the volcanic front. Using Q-temperature laboratory results [Sato, H., Sacks, I.S., Murase, T., Muncill, G., Fukushima, H., 1989. J. Geophys. Res. 94, 10647-10661], this implies a temperature of about 130°C higher than the eastern forearc region and about 30°C higher than the western backarc region, in good agreement with the tomographic results of Zhao et al. [Zhao, D., Hasegawa, A., Horiuchi, S., 1992. J. Geophys. Res. 97, 19909-19928]. This suggests that low velocities in the crust and uppermost mantle beneath SWU may be explained by a subsolidus temperature increase without partial melting.

  16. Preliminary result of P-wave speed tomography beneath North Sumatera region

    Science.gov (United States)

    Jatnika, Jajat; Nugraha, Andri Dian; Wandono

    2015-04-01

    The structure of P-wave speed beneath the North Sumatra region was determined using P-wave arrival times compiled by MCGA from time periods of January 2009 to December 2012 combining with PASSCAL data for February to May 1995. In total, there are 2,246 local earthquake events with 10,666 P-wave phases from 63 stations seismic around the study area. Ray tracing to estimate travel time from source to receiver in this study by applying pseudo-bending method while the damped LSQR method was used for the tomographic inversion. Based on assessment of ray coverage, earthquakes and stations distribution, horizontal grid nodes was set up of 30×30 km2 for inside the study area and 80×80 km2 for outside the study area. The tomographic inversion results show low Vp anomaly beneath Toba caldera complex region and around the Sumatra Fault Zones (SFZ). These features are consistent with previous study. The low Vp anomaly beneath Toba caldera complex are observed around Mt. Pusuk Bukit at depths of 5 km down to 100 km. The interpretation is these anomalies may be associated with ascending hot materials from subduction processes at depths of 80 km down to 100 km. The obtained Vp structure from local tomography will give valuable information to enhance understanding of tectonic and volcanic in this study area.

  17. Preliminary result of P-wave speed tomography beneath North Sumatera region

    Energy Technology Data Exchange (ETDEWEB)

    Jatnika, Jajat [Earth Science Study Program, Institute of Technology Bandung (Indonesia); Indonesian Meteorological, Climatological and Geophysical Agency (MCGA), Jakarta (Indonesia); Nugraha, Andri Dian, E-mail: nugraha@gf.itb.ac.id [Global Geophysical Research Group, Faculty of Mining and Petroleum Engineering, Insitute of Technology Bandung (Indonesia); Wandono [Indonesian Meteorological, Climatological and Geophysical Agency (MCGA), Jakarta (Indonesia)

    2015-04-24

    The structure of P-wave speed beneath the North Sumatra region was determined using P-wave arrival times compiled by MCGA from time periods of January 2009 to December 2012 combining with PASSCAL data for February to May 1995. In total, there are 2,246 local earthquake events with 10,666 P-wave phases from 63 stations seismic around the study area. Ray tracing to estimate travel time from source to receiver in this study by applying pseudo-bending method while the damped LSQR method was used for the tomographic inversion. Based on assessment of ray coverage, earthquakes and stations distribution, horizontal grid nodes was set up of 30×30 km2 for inside the study area and 80×80 km2 for outside the study area. The tomographic inversion results show low Vp anomaly beneath Toba caldera complex region and around the Sumatra Fault Zones (SFZ). These features are consistent with previous study. The low Vp anomaly beneath Toba caldera complex are observed around Mt. Pusuk Bukit at depths of 5 km down to 100 km. The interpretation is these anomalies may be associated with ascending hot materials from subduction processes at depths of 80 km down to 100 km. The obtained Vp structure from local tomography will give valuable information to enhance understanding of tectonic and volcanic in this study area.

  18. Anomalous shear wave attenuation in the shallow crust beneath the Coso volcanic regionn, California ( USA).

    Science.gov (United States)

    Sanders, C.; Ho-Liu, P.; Rinn, D.; Hiroo, Kanamori

    1988-01-01

    We use seismograms of local earthquakes to image relative shear wave attenuation structure in the shallow crust beneath the region containing the Coso volcanic-geothermal area of E California. Seismograms of 16 small earthquakes show SV amplitudes which are greatly diminished at some azimuths and takeoff angles, indicating strong lateral variations in S wave attenuation in the area. 3-D images of the relative S wave attenuation structure are obtained from forward modeling and a back projection inversion of the amplitude data. The results indicate regions within a 20 by 30 by 10 km volume of the shallow crust (one shallower than 5 km) that severely attenuate SV waves passing through them. These anomalies lie beneath the Indian Wells Valley, 30 km S of the Coso volcanic field, and are coincident with the epicentral locations of recent earthquake swarms. No anomalous attenuation is seen beneath the Coso volcanic field above about 5 km depth. Geologic relations and the coincidence of anomalously slow P wave velocities suggest that the attenuation anomalies may be related to magmatism along the E Sierra front.-from Authors

  19. Imaging fluid-related subduction processes beneath Central Java (Indonesia) using seismic attenuation tomography

    Science.gov (United States)

    Bohm, Mirjam; Haberland, Christian; Asch, Günter

    2013-04-01

    We use local earthquake data observed by the amphibious, temporary seismic MERAMEX array to derive spatial variations of seismic attenuation (Qp) in the crust and upper mantle beneath Central Java. The path-averaged attenuation values (t∗) of a high quality subset of 84 local earthquakes were calculated by a spectral inversion technique. These 1929 t∗-values inverted by a least-squares tomographic inversion yield the 3D distribution of the specific attenuation (Qp). Analysis of the model resolution matrix and synthetic recovery tests were used to investigate the confidence of the Qp-model. We notice a prominent zone of increased attenuation beneath and north of the modern volcanic arc at depths down to 15 km. Most of this anomaly seems to be related to the Eocene-Miocene Kendeng Basin (mainly in the eastern part of the study area). Enhanced attenuation is also found in the upper crust in the direct vicinity of recent volcanoes pointing towards zones of partial melts, presence of fluids and increased temperatures in the middle to upper crust. The middle and lower crust seems not to be associated with strong heating and the presence of melts throughout the arc. Enhanced attenuation above the subducting slab beneath the marine forearc seems to be due to the presence of fluids.

  20. Constraints on the anisotropic contributions to velocity discontinuities at ˜60 km depth beneath the Pacific

    Science.gov (United States)

    Rychert, Catherine A.; Harmon, Nicholas

    2017-08-01

    Strong, sharp, negative seismic discontinuities, velocity decreases with depth, are observed beneath the Pacific seafloor at ˜60 km depth. It has been suggested that these are caused by an increase in radial anisotropy with depth, which occurs in global surface wave models. Here we test this hypothesis in two ways. We evaluate whether an increase in surface wave radial anisotropy with depth is robust with synthetic resolution tests. We do this by fitting an example surface wave data set near the East Pacific Rise. We also estimate the apparent isotropic seismic velocity discontinuities that could be caused by changes in radial anisotropy in S-to-P and P-to-S receiver functions and SS precursors using synthetic seismograms. We test one model where radial anisotropy is caused by olivine alignment and one model where it is caused by compositional layering. The result of our surface wave inversion suggests strong shallow azimuthal anisotropy beneath 0-10 Ma seafloor, which would also have a radial anisotropy signature. An increase in radial anisotropy with depth at 60 km depth is not well-resolved in surface wave models, and could be artificially observed. Shallow isotropy underlain by strong radial anisotropy could explain moderate apparent velocity drops (effect is diminished if strong anisotropy also exists at 0-60 km depth as suggested by surface waves. Overall, an increase in radial anisotropy with depth may not exist at 60 km beneath the oceans and does not explain the scattered wave observations.

  1. Magmatic underplating beneath the Rajmahal Traps: Gravity signature and derived 3-D configuration

    Indian Academy of Sciences (India)

    A P Singh; Niraj Kumar; Bijendra Singh

    2004-12-01

    The early Cretaceous thermal perturbation beneath the eastern continental margin of the Indian shield resulted in the eruption of the Rajmahal Traps. To understand the impact of the magmatic process that originated in the deep mantle on the lower crustal level of the eastern Indian shield and adjoining Bengal basin the conspicuous gravity anomalies observed over the region have been modelled integrating with available geophysical information. The 3-D gravity modelling has delineated 10–15km thick high-density ( = 3.02 g/cm3) accreted igneous layer at the base of the crust beneath the Rajmahal Traps. Thickness of this layer varies from 16km to the west of the Rajmahal towards north to about 12km near Kharagpur towards south and about 18km to the east of the Raniganj in the central part of the region. The greater thickness of the magmatic body beneath the central part of the region presents itself as the locus of the potential feeder channel for the Rajmahal Traps. It is suggested that the crustal accretion is the imprint of the mantle thermal perturbation, over which the eastern margin of the eastern Indian shield opened around 117Ma ago. The nosing of the crustal accretion in the down south suggests the possible imprint of the subsequent magmatic intrusion along the plume path.

  2. Measurement and Modeling of the Fluctuating Wall Pressure Field Beneath Transitional Boundary Layers

    Science.gov (United States)

    Snarski, Stephen R.

    2001-11-01

    Measurements have been performed to better understand the space-varying character of the fluctuating wall pressure field beneath a transitional boundary layer and to develop an appropriate model for the space-varying (nonhomogeneous) wavenumber-frequency wall pressure spectrum. Although a great deal is understood regarding the structure of the wall pressure field beneath turbulent boundary layers, the current understanding of the wall pressure field beneath the transitional boundary layer is incomplete. Overlooked have been critical issues concerning spatial variations in turbulence structure and the convection and decay of pressure producing disturbances—properties that define the character of the field and resulting form of the wavenumber-frequency spectrum. The experiments involve measurement of the space-time fluctuating wall pressure field across the transition region of a flat plate boundary layer by means of a 64-element linear array of hearing-aid microphones and hot wire velocity measurements in the adjacent laminar, transitional, and turbulent boundary layers. Because the field is nonhomogeneous, wavelet based transform methods are required to appropriately resolve the space-varying structure of the field and form of the nonhomogeneous wavenumber-frequency spectrum.

  3. Simulation of flow in the unsaturated zone beneath Pagany Wash, Yucca Mountain

    Energy Technology Data Exchange (ETDEWEB)

    Kwicklis, E.M.; Healy, R.W. [Geological Survey, Lakewood, CO (United States); Flint, A.L. [Geological Survey, Mercury, NV (United States)

    1994-12-31

    A one-dimensional numerical model was created to simulate water movement beneath Pagany Wash, Yucca Mountain, Nevada. Model stratigraphy and properties were based on data obtained from boreholes UE-25 UZ No. 4 and UE-25 UZ No. 5, which was drilled in the alluvial channel and bedrock sideslope of Pagany Wash. Although unable to account for multidimensional or preferential flowpaths beneath the wash, the model proved a useful conceptual tool with which to develop hypotheses and, in some cases, provide bounding calculations. The model indicated that liquid flux decreases with depth in the upper 120 m beneath the wash, with fluxes of several tens mm/yr in the nonwelded base of the Tiva Canyon Member and fluxes on the order of a tenth mm/yr in the upper Topopah Spring Member. Capillary barrier effects were indicated by the model to significantly delay the entry of large fluxes into the potential repository horizon during periods of increasing net infiltration, and to inhibit rapid drainage of water from the nonwelded and bedded intervals into the potential repository horizon during periods of moisture redistribution. Lateral moisture redistribution can be expected to be promoted by these effects.

  4. Simulation of flow in the unsaturated zone beneath Pagany Wash, Yucca Mountain

    Energy Technology Data Exchange (ETDEWEB)

    Thamir, F.; Kwicklis, E.M. [Geological Survey, Denver, CO (United States); Hampson, D. [Foothills Engineering Consultants Inc., Golden, CO (United States); Anderton, S. [ROCKTECH, West Jordan, UT (United States)

    1994-12-31

    A one-dimensional numerical model was created simulate water movement beneath Pagany Wash, Yucca Mountain, Nevada. Model stratigraphy and properties were on data obtained from boreholes UE-25 UZ {number_sign}4 UE-25 UZ {number_sign}5, which were drilled in the alluvial channel and bedrock sideslope of Pagany Wash. Although unable to account for multidimensional or preferential flowpaths beneath the wash, the model proved a useful conceptual tool with which to develop hypotheses and, in some cases, provide bounding calculations. The model indicated that liquid flux decreases with depth in the upper 120 m beneath the wash, with fluxes of several tens mm/yr in the nonwelded base of the Tiva Canyon Member and fluxes on the order of a tenth mm/yr in the upper Topopah Spring Member. Capillary barrier effects were indicated by the model to significantly delay the entry of large fluxes into the potential repository horizon during periods of increasing net infiltration, and to inhibit rapid drainage of water from the nonwelded and bedded intervals into the potential repository horizon during periods of moisture redistribution. Lateral moisture redistribution can be expected to be promoted by these effects.

  5. Analysis of Fracture in Cores from the Tuff Confining Unit beneath Yucca Flat, Nevada Test Site

    Energy Technology Data Exchange (ETDEWEB)

    Lance Prothro

    2008-03-01

    The role fractures play in the movement of groundwater through zeolitic tuffs that form the tuff confining unit (TCU) beneath Yucca Flat, Nevada Test Site, is poorly known. This is an important uncertainty, because beneath most of Yucca Flat the TCU lies between the sources of radionuclide contaminants produced by historic underground nuclear testing and the regional carbonate aquifer. To gain a better understanding of the role fractures play in the movement of groundwater and radionuclides through the TCU beneath Yucca Flat, a fracture analysis focusing on hydraulic properties was performed on conventional cores from four vertical exploratory holes in Area 7 of Yucca Flat that fully penetrate the TCU. The results of this study indicate that the TCU is poorly fractured. Fracture density for all fractures is 0.27 fractures per vertical meter of core. For open fractures, or those observed to have some aperture, the density is only 0.06 fractures per vertical meter of core. Open fractures are characterized by apertures ranging from 0.1 to 10 millimeter, and averaging 1.1 millimeter. Aperture typically occurs as small isolated openings along the fracture, accounting for only 10 percent of the fracture volume, the rest being completely healed by secondary minerals. Zeolite is the most common secondary mineral occurring in 48 percent of the fractures observed.

  6. Soil ecosystem functioning under climate change: plant species and community effects

    Energy Technology Data Exchange (ETDEWEB)

    Kardol, Paul [ORNL; Cregger, Melissa [ORNL; Campany, Courtney E [ORNL; Classen, Aimee T [ORNL

    2010-01-01

    Feedbacks of terrestrial ecosystems to climate change depend on soil ecosystem dynamics. Soil ecosystems can directly and indirectly respond to climate change. For example, warming directly alters microbial communities by increasing their activity. Climate change may also alter plant community composition, thus indirectly altering the microbial communities that feed on their inputs. To better understand how climate change may directly and indirectly alter soil ecosystem functioning, we investigated old-field plant community and soil ecosystem responses to single and combined effects of elevated [CO2], warming, and water availability. Specifically, we collected soils at the plot level (plant community soils), and beneath dominant plant species (plant-specific soils). We used microbial enzyme activities and soil nematodes as indicators for soil ecosystem functioning. Our study resulted in two main findings: 1) Overall, while there were some interactions, water, relative to increases in [CO2] and warming, had the largest impact on plant community composition, soil enzyme activities, and soil nematodes. Multiple climate change factors can interact to shape ecosystems, but in this case, those interactions were largely driven by changes in water availability. 2) Indirect effects of climate change, via changes in plant communities, had a significant impact on soil ecosystem functioning and this impact was not obvious when looking at plant community soils. Climate change effects on enzyme activities and soil nematode abundance and community structure strongly differed between plant community soils and plant-specific soils, but also within plant-specific soils. In sum, these results indicate that accurate assessments of climate change impacts on soil ecosystem functioning require incorporating the concurrent changes in plant function and plant community composition. Climate change-induced shifts in plant community composition will likely modify or counteract the direct

  7. Agriculture: Soils

    Science.gov (United States)

    Productive soils, a favorable climate, and clean and abundant water resources are essential for growing crops, raising livestock, and for ecosystems to continue to provide the critical provisioning services that humans need.

  8. Preserved Ross-age(?) root beneath the Transantarctic Mountains and origin of the thinner crust beneath the northern Wilkes Subglacial Basin

    Science.gov (United States)

    Jordan, Tom; Ferraccioli, Fausto; Armadillo, Egidio; Bozzo, Emanuele

    2013-04-01

    The Wilkes Subglacial Basin, in the hinterland of the Transantarctic Mountains, represents one of the least understood continental-scale features in Antarctica. Aeromagnetic data suggests that this basin was imposed on a much earlier Ross age back arc region that developed along the former active margin of the East Antarctic Craton (Ferraccioli et al., 2009, Tectonophysics). However, the deeper crustal structure of the basin and its relation with tectonic evolution remains both disputed and poorly constrained. Here, we present new airborne gravity data that reveal the crustal architecture of the northern Wilkes Subglacial Basin. Our gravity models indicate that the crust under the northern Wilkes Subglacial Basin is likely to be 30-35 km thick, i.e. 5-10 km thinner than imaged under the adjacent Transantarctic Mountains, and ~15 km thinner than predicted from some previous flexural and passive seismic models beneath the southern Wilkes Subglacial Basin region. We infer that crustal thickening under northern Victoria Land reflects Ross-age (ca 500 Ma) orogenic events and accretion, followed by partial preservation of the orogenic root since then, as opposed to reflecting the edge of a Mesozoic plateau, which has previously been inferred to have occupied West Antarctica (Bialas et al. 2007, Geology). Airy isostatic anomalies along both flanks of the Wilkes Basin reveal major inherited tectonic structures, which likely controlled the basin location and hence support aeromagnetic interpretations of the Wilkes Subglacial Basin as a structurally controlled basin. The positive anomaly along the western margin of the basin appears to define the tectonic boundary between the East Antarctic Craton and the Ross Orogen, and the anomaly along its eastern flank is interpreted as reflecting high-grade and denser rocks of the central Wilson Terran,e with respect to lower grade meta-sediments and magmatic arc rocks of the western Wilson Terrane and Wilkes Basin region. Our forward

  9. Seismic tomography reveals the upper-mantle structure beneath the Carpathian-Pannonian system

    Science.gov (United States)

    Dando, B. D.; Houseman, G.; Stuart, G. W.; Hegedus, E.; Kovacs, A.; Brueckl, E. P.; Hausmann, H.; Radovanovic, S.

    2009-12-01

    The Carpathian Basins Project (CBP) aims to understand the formation of the Miocene-age extensional basins contained within the convergent arc of the Alpine-Carpathian system. To test competing models for the recent geological evolution of the Carpathian-Pannonian lithosphere and upper mantle, we present a new tomographic determination of P-wave velocity structure to depths of 700 km beneath this region. This model is based on inversion of seismic travel-time residuals from 97 broadband seismic stations. We include CBP data from a 15-month deployment of a high resolution network of 46 stations deployed NW-SE across the Vienna and western Pannonian basins through Austria, Hungary and Serbia, together with 10 broadband stations spread across the Pannonian basin and a further 41 permanent broadband stations. We use P-wave arrival times from 232 teleseismic events. To avoid contamination of our inversion results from crustal velocity variations, deterministic corrections are applied to our travel-time residuals using crustal velocity models obtained from controlled source experiments and sediment thickness maps. Our 3-D velocity model images the fast velocity structure of the eastern Alps down to ~350 km. Beneath the Pannonian basin the velocity variation at 300 km depth is dominated by a fast region which extends eastward from the Alpine anomaly and reaches down into the mantle transition zone (MTZ). This fast structure is limited on the North side by slow material beneath the North Carpathians. At depths greater than 450 km, below the eastern Pannonian basin, a slow anomaly extends to the base of the model. Beneath the same region Hetenyi et al. (submitted to GRL), used receiver functions from the CBP dataset, to show a localised depression of the 660 km discontinuity of up to ~40 km. We aim to address how the depression of the 660 km discontinuity and its associated density and velocity variations affect our tomographic images. Our results will help to provide

  10. Upper mantle structures beneath the Carpathian-Pannonian region: Implications for the geodynamics of continental collision

    Science.gov (United States)

    Ren, Y.; Stuart, G. W.; Houseman, G. A.; Dando, B.; Ionescu, C.; Hegedüs, E.; Radovanović, S.; Shen, Y.; South Carpathian Project Working Group

    2012-10-01

    The Carpathian-Pannonian system of Eastern and Central Europe represents a unique opportunity to study the interaction between surface tectonic processes involving convergence, extension and convective overturn in the upper mantle. Here, we present high-resolution images of upper mantle structure beneath the region from P-wave finite-frequency teleseismic tomography to help constrain such geodynamical interactions. We have selected earthquakes with magnitude greater than 5.5 in the distance range 30°-95°, which occurred between 2006 and 2011. The data were recorded on 54 temporary stations deployed by the South Carpathian Project (2009-2011), 56 temporary stations deployed by the Carpathian Basins Project (2005-2007), and 131 national network broadband stations. The P-wave relative arrival times are measured in two frequency bands (0.5-2.0 Hz and 0.1-0.5 Hz), and are inverted for Vp perturbation maps in the upper mantle. Our images show a sub-vertical slab of fast material beneath the eastern Alps which extends eastward across the Pannonian basin at depths below ˜300km. The fast material extends down into the mantle transition zone (MTZ), where it spreads out beneath the entire basin. Above ˜300km, the upper mantle below the Pannonian basin is dominated by relatively slow velocities, the largest of which extends down to ˜200km. We suggest that cold mantle lithospheric downwelling occurred below the Pannonian Basin before detaching in the mid-Miocene. In the Vrancea Zone of SE Romania, intermediate-depth (75-180 km) seismicity occurs at the NE end of an upper mantle high velocity structure that extends SW under the Moesian Platform, oblique to the southern edge of the South Carpathians. At greater depths (180-400 km), a sub-circular high velocity anomaly is found directly beneath the seismicity. This sub-vertical high-velocity body is bounded by slow anomalies to the NW and SE, which extend down to the top of the MTZ. No clear evidence of a residual slab is

  11. Receiver function structures beneath the deep large faults in the northeastern margin of the Tibetan Plateau

    Science.gov (United States)

    Shen, Xuzhang; Zhou, Yuanze; Zhang, YuanSheng; Mei, Xiuping; Guo, Xiao; Liu, Xuzhou; Qin, Manzhong; Wei, Congxin; Li, Cuiqin

    2014-01-01

    Using the teleseismic P- and S-wave receiver functions of the dense linear temporary seismic array, the crust and uppermost mantle structures beneath the deep large faults in the northeastern margin of the Tibetan Plateau were imaged. The images of the first converted wave and the multiples indicated that the North Fault Zone of West Qinling (NWQ) Mountain and Diebu-Lueyang (DBL) faults cut the Mohorovicic (Moho) Discontinuity and cause an obvious difference feature for the Moho in the two sides of the faults. The higher Vp/Vs ratio and lower velocity layer is found beneath the west portion of the array near the Tibetan Plateau, which implies a lower crust channel flow coming from the Tibetan Plateau. The weak Moho and higher Vp/Vs ratio beneath the eastern portion of the array near the Ordos suggest the upwelling of the hot mantle material. The results also indicate an obvious deformation in the upper crust with the lower Vp/Vs ratio beneath the middle of the array. Such upper crust deformation is closely related to the topography of the surface; therefore, we deduce that the deformation of the brittle upper crust is accompanied by the formation of the local topography during the uplift of the Tibetan Plateau, which is also the primary reason for the active seismicity in the study region. The deformation of the lithosphere-asthenosphere boundary (LAB) can also be associated with the formation of the diapir caused by the upwelling hot materials in the upper mantle due to the uprising of the thrusting plate caused by the subduction of the India Plate. The existence of the lower crust channel flow, the crust shortening, and the mantle diapir in the local region simultaneously implies that the elevation and formation of the Tibetan Plateau cannot be explained with a single model. The higher resolution results for the crust and the mantle, especially beneath the block boundary region, are necessary to construct the completed geodynamic model to understand the formation

  12. Imaging the LAB and other major lithospheric discontinuities beneath South Africa

    Science.gov (United States)

    Sodoudi, Forough; Kind, Rainer; Kaestle, Emanuel

    2013-04-01

    Investigation of the thickness of continental roots, which migrate coherently with plates belongs to the most systematic keys in order to understand the continental evolution. South Africa's lithosphere preserves a nearly un-interrupted geological history of more than 3.5 billion years. It was formed during the break-up of the supercontinent Gondwana over a period of 80 million years and therefore is the longest, best-preserved geological record of the planet Earth. To estimate the LAB and other major lithospheric discontinuities beneath South Africa, we used the novel technique of S receiver function, which employs S-to-P conversions and appears promising for detecting the LAB. This technique has already proven its power for mapping the LAB in the tectonically different regions. Although the South African craton has been extensively studied in recent years, especially by SRFs, the depth extent of the lithosphere and its nature varies somewhat between studies. It seems that several differences in methodology and data selection criteria leading to variations in the SRFs obtained. Some authors observed S-to-P conversions at 25-30 s (~250-300 km) and interpreted them as being from the LAB. In contrast, some other authors found these conversions at shallower depths (~150 km). We calculated SRFs for the data of more than 120 stations within South Africa. Such a huge amount of data has not been yet applied for SRF studies in South Africa. Our results clearly shows 3 different LVZs at about 100 (~10s), 150-220 (15-22 s) km and 300-330 km (30-33 s), which were not seen in any of the previous studies. Based on our preliminary results, the deep and sharp LAB phase at 300-330 km is significantly imaged beneath the cratons (Kaapvaal and Zimbabwe cratons; > 2.7 Ga) and the oldest belt (Limpopo belt ~ 2.7 Ga). This phase may not be visible northward and southward beneath the much younger mobile belts (Mozambique and Namaqua-Natal belt; ~ 1.1 Ga). Instead, a shallower and less

  13. Crustal Structure Beneath the Luangwa Rift, Zambia: Constraints from Potential Field Data

    Science.gov (United States)

    Atekwana, E. A.; Matende, K.; Abdelsalam, M. G.; Mickus, K. L.; Atekwana, E. A.; Gao, S. S.; Sikazwe, O.; Liu, K. H.; Evans, R. L.

    2015-12-01

    We used gravity and magnetic data to examine the thermal and crustal structure beneath the Luangwa Rift Valley (LRV) in Zambia in order to examine the geodynamic controls of its formation.. The LRV lies at the boundary between the Mesoproterozoic-Neoproterozoic Irumide and Southern Irumide orogenic belts between the Zimbabwe craton and the Bangwelu Block. We computed the Curie Point Depth (CPD) using two-dimensional (2D) power spectrum analysis of the aeromagnetic data, and these results were used to estimate heat flow beneath the LRV. We also inverted the aeromagnetic data for three-dimensional (3D) magnetic susceptibility distribution. We further determined the depths to the Moho using 2D power spectrum analysis of the satellite gravity data and 2D forward modeling of the terrestrial gravity data. We found that: (1) there is no consistent pattern of elevated CPD beneath the LRV, and as such no consistent pattern of elevated heat flow anomaly, (2) there are numerous 5-15 km wide magnetic bodies at shallow depth (5-20 km) beneath the LRV and the 2D forward gravity modeling suggests these to be dense intrusive bodies, (3) a thick crust (49-52 km) underlies the northwestern margin of the rift centered beneath the ~ 1 km high Muchinga escarpment which represents the main border fault of the LRV. This thick crust contrasts with the thinner crust (35-45 km) outside the rift, and (4) the thickened crust coincides with a NE-SE elongated belt of 1.05-1.0 Ga granitoids previously interpreted as manifestations of the metacratonization of the southeastern edge of the Bangweulu Block. Our 2D forward gravity model suggests that the thickened crust is due to the presence of possibly Karoo-aged magmatic under-plated mafic body (UPMB) whose thermal anomaly has since decayed. We suggest that the initiation of the LRV was associated with this deep magmatic activity that introduced rheological weaknesses that facilitated strain localization although it never breached the surface. It

  14. Soil moisture dynamics in an eastern Amazonian tropical forest

    Science.gov (United States)

    Bruno, Rogério D.; da Rocha, Humberto R.; de Freitas, Helber C.; Goulden, Michael L.; Miller, Scott D.

    2006-08-01

    We used frequency-domain reflectometry to make continuous, high-resolution measurements for 22 months of the soil moisture to a depth of 10 m in an Amazonian rain forest. We then used these data to determine how soil moisture varies on diel, seasonal and multi-year timescales, and to better understand the quantitative and mechanistic relationships between soil moisture and forest evapotranspiration. The mean annual precipitation at the site was over 1900 mm. The field capacity was approximately 0.53 m3 m-3 and was nearly uniform with soil depth. Soil moisture decreased at all levels during the dry season, with the minimum of 0.38 m3 m-3 at 3 m beneath the surface. The moisture in the upper 1 m showed a strong diel cycle with daytime depletion due to evapotranspiration. The moisture beneath 1 m declined during both day and night due to the combined effects of evapotranspiration, drainage and a nighttime upward movement of water. The depth of active water withdrawal changed markedly over the year. The upper 2 m of soil supplied 56% of the water used for evapotranspiration in the wet season and 28% of the water used in the dry season. The zone of active water withdrawal extended to a depth of at least 10 m. The day-to-day rates of moisture withdrawal from the upper 10 m of soil during rain-free periods agreed well with simultaneous measurements of whole-forest evapotranspiration made by the eddy covariance technique. The forest at the site was well adapted to the normal cycle of wet and dry seasons, and the dry season had only a small effect on the rates of land-atmosphere water vapour exchange.

  15. Longitudinal vibration of pile in layered soil based on Rayleigh-Love rod theory and fictitious soil-pile model

    Institute of Scientific and Technical Information of China (English)

    Lü Shu-hui; WANG Kui-hua; WU Wen-bing; C. J. LEO

    2015-01-01

    The dynamic response of pile in layered soil is theoretically investigated when considering the transverse inertia effect. Firstly, the fictitious soil-pile model is employed to simulate the dynamic interaction between the pile and the soil layers beneath pile toe. The dynamic interactions of adjacent soil layers along the vertical direction are simplified as distributed Voigt models. Meanwhile, the pile and fictitious soil-pile are assumed to be viscoelastic Rayleigh-Love rods, and both the radial and vertical displacement continuity conditions at the soil-pile interface are taken into consideration. On this basis, the analytical solution for dynamic response at the pile head is derived in the frequency domain and the corresponding quasi-analytical solution in the time domain is then obtained by means of the convolution theorem. Following this, the accuracy and parameter value of the hypothetical boundaries for soil-layer interfaces are discussed. Comparisons with published solution and measured data are carried out to verify the rationality of the present solution. Parametric analyses are further conducted by using the present solution to investigate the relationships between the transverse inertia effects and soil-pile parameters.

  16. Phytoremediation of hydrocarbon contaminants in subantarctic soils: an effective management option.

    Science.gov (United States)

    Bramley-Alves, Jessica; Wasley, Jane; King, Catherine K; Powell, Shane; Robinson, Sharon A

    2014-09-01

    Accidental fuel spills on world heritage subantarctic Macquarie Island have caused considerable contamination. Due to the island's high latitude position, its climate, and its fragile ecosystem, traditional methods of remediation are unsuitable for on-site clean up. We investigated the tolerance of a subantarctic native tussock grass, Poa foliosa (Hook. f.), to Special Antarctic Blend (SAB) diesel fuel and its potential to reduce SAB fuel contamination via phytoremediation. Toxicity of SAB fuel to P. foliosa was assessed in an 8 month laboratory growth trial under growth conditions which simulated the island's environment. Single seedlings were planted into 1 L pots of soil spiked with SAB fuel at concentrations of 1000, 5 000, 10,000, 2000 and 40,000 mg/kg (plus control). Plants were harvested at 0, 2, 4 and 8 months and a range of plant productivity endpoints were measured (biomass production, plant morphology and photosynthetic efficiency). Poa foliosa was highly tolerant across all SAB fuel concentrations tested with respect to biomass, although higher concentrations of 20,000 and 40,000 mg SAB/kg soil caused slight reductions in leaf length, width and area. To assess the phytoremediation potential of P. foliosa (to 10 000 mg/kg), soil from the planted pots was compared with that from paired unplanted pots at each SAB fuel concentration. The effect of the plant on SAB fuel concentrations and the associated microbial communities found within the soil (total heterotrophs and hydrocarbon degraders) were compared between planted and unplanted treatments at the 0, 2, 4 and 8 month harvest periods. The presence of plants resulted in significantly less SAB fuel in soils at 2 months and a return to background concentration by 8 months. Microbes did not appear to be the sole driving force behind the observed hydrocarbon loss. This study provides evidence that phytoremediation using P. foliosa is a valuable remediation option for use at Macquarie Island, and may be

  17. Soil sustainability and indigenous soil management practices ...

    African Journals Online (AJOL)

    Soil sustainability and indigenous soil management practices among food crop farmers in Ogun State, Nigeria. ... Journal of Environmental Extension ... describe and analyse the current soil management practices among food crop farmers in ...

  18. Soil Survey Geographic (SSURGO) - Magnesic Soils

    Data.gov (United States)

    California Department of Resources — Magnesic soils is a subset of the SSURGO dataset containing soil family selected based on the magnesic content and serpentinite parent material. The following soil...

  19. Constraining deformation at the lithosphere-asthenosphere boundary beneath the San Andreas fault with Sp phases

    Science.gov (United States)

    Fischer, K. M.; Ford, H. A.; Lekic, V.

    2013-12-01

    The geometry of deformation in the deep mantle lithosphere beneath strike-slip plate boundaries has been enigmatic, with models ranging from localized shear zones that are deep extensions of individual crustal faults to broad zones of diffuse, distributed shear with widths of hundreds of kilometers. Using seismic phases that convert from shear to compressional motion (Sp) at the base of the lithosphere beneath California, we find evidence for strike-slip deformation in the deepest mantle lithosphere beneath the central San Andreas fault that occurs over a horizontal width of 50 km or less. This study is based on over 135,000 Sp receiver functions from 730 seismic stations, including the Northern and Southern California Seismic Networks and the NSF EarthScope Transportable and Flexible Arrays. Individual Sp receiver functions were calculated using an extended-time multi-taper method and were migrated and stacked according to their three-dimensional conversion point locations using a model for crust (Lowry and Pérez-Gussinyé, 2011) and mantle (Obrebski et al., 2010 and 2011) velocity structure beneath each station and a spline-function representation of the Sp Fresnel zone. Sp conversion points at lithosphere-asthenosphere boundary depths are very dense on both sides of the San Andreas fault, and we interpreted the Sp common conversion point stack only at those nodes with information from more than 300 receiver functions. To the east of the plate boundary, a strong coherent Sp phase, indicative of a decrease in shear-wave velocity with depth, is present in the depth range where tomographic studies image the transition from high velocity lithosphere to low velocity asthenosphere. This phase, interpreted as the seismological lithosphere-asthenosphere boundary, has systematically lower amplitudes on the western side of the plate boundary, indicating that the drop in shear velocity from lithosphere to asthenosphere is either smaller or is distributed over a larger

  20. Colonisation of freshly deposited volcanic tephra by soil fungi

    Science.gov (United States)

    Tarasenko, Inga; Opfergelt, Sophie; Stenuit, Benoît; Daily, Hélène; Bonneville, Steeve; Müller, Dirk; Delmelle, Pierre

    2016-04-01

    In active volcanic regions, soils are repeatedly exposed to eruption products, notably tephra emissions. Deposition of volcanic tephra on soil may modify water and gas exchanges between the soil surface and the atmosphere. Through chemical weathering, the silicate glass and mineral components of freshly deposited tephra act as a source of bioavailable potassium and phosphorus. In addition, opportunist fungi may be able to enhance access to these elements via physical and biochemical processes. Altogether, tephra deposition has the potential to affect biological activity and hence, nutrient cycling in the buried soil. Here we present the preliminary results of an ongoing investigation aimed at shedding light on the interaction of soil fungi with freshly deposited tephra. The study site (elevation - 1755 m a.s.l.) is a coniferous forest on the northeastern slope of Etna volcano, Sicily, which received about 20 cm of tephra in November 2013. Soil and tephra samples were collected in September 2014 and October 2015. A variety of biological, chemical and mineralogical analyses were carried out to determine fungal biomass, fungi species and tephra weathering stage. Colonisation of the fresh tephra by fungi is evidenced by the high fungal biomass measured in this material. DNA analyses further indicate that these fungi originate from the soil beneath the tephra layer. While chemical weathering of the tephra material has started, there is no clear indication that fungi colonisation is enhancing this process. We will continue to monitor fungi-tephra interaction on Etna during the next few years.

  1. Schoolground Soil Studies.

    Science.gov (United States)

    Doyle, Charles

    1978-01-01

    Outlined are simple activities for studying soil, which can be conducted in the schoolyard. Concepts include soil profiles, topsoil, soil sizes, making soil, erosion, slope, and water absorption. (SJL)

  2. Rain splash of soil grains as a stochastic advection-dispersion process, with implications for desert plant-soil interactions and land-surface evolution

    Science.gov (United States)

    Furbish, David Jon; Childs, Elise M.; Haff, Peter K.; Schmeeckle, Mark W.

    2009-09-01

    We formulate soil grain transport by rain splash as a stochastic advection-dispersion process. By taking into account the intermittency of grain motions activated by raindrop impacts, the formulation indicates that gradients in raindrop intensity, and thus grain activity (the volume of grains in motion per unit area) can be as important as gradients in grain concentration and surface slope in effecting transport. This idea is confirmed by rain splash experiments and manifest in topographic roughening via mound growth beneath desert shrubs. The formulation provides a framework for describing transport and dispersal of any soil material moveable by rain splash, including soil grains, soil-borne pathogens and nutrients, seeds, or debitage. As such it shows how classic models of topographic "diffusion" reflect effects of slope-dependent grain drift, not diffusion, and it highlights the role of rain splash in the ecological behavior of desert shrubs as "resource islands." Specifically, the growth of mounds beneath shrub canopies, where differential rain splash initially causes more grains to be splashed inward beneath the protective canopy than outward, involves the "harvesting" of nearby soil material, including nutrients. Mounds thus represent temporary storage of soil derived from areas surrounding the shrubs. As the inward grain flux associated with differential rain splash is sustained over the shrub lifetime, mound material is effectively sequestered from erosional processes that might otherwise move this material downslope. With shrub death and loss of the protective canopy, differential rain splash vanishes and the mound material is dispersed to the surrounding area, again subject to downslope movement.

  3. Effects of switchgrass cultivars and intraspecific differences in root structure on soil carbon inputs and accumulation

    Energy Technology Data Exchange (ETDEWEB)

    Adkins, Jaron [Michigan State Univ., East Lansing, MI (United States); Jastrow, Julie D. [Argonne National Lab. (ANL), Argonne, IL (United States); Morris, Geoffrey P. [Kansas State Univ., Manhattan, KS (United States); Six, Johan [Swiss Federal Inst. of Technology, Zurich (Switzerland); de Graaff, Marie-Anne [Boise State Univ., ID (United States)

    2016-01-01

    Switchgrass (Panicum virgatum L), a cellulosic biofuel feedstock, may promote soil C 21 accumulation compared to annual cropping systems by increasing the amount and retention of 22 root-derived soil C inputs. The aim of this study was to assess how different switchgrass 23 cultivars impact soil C inputs and retention, whether these impacts vary with depth, and whether 24 specific root length (SRL) explains these impacts. We collected soil to a depth of 30 cm from six 25 switchgrass cultivars with root systems ranging from high to low SRL. The cultivars (C4 species) 26 were grown for 27 months on soils previously dominated by C3 plants, allowing us to use the 27 natural difference in 13C isotopic signatures between C3 soils and C4 plants to quantify 28 switchgrass-derived C accumulation. The soil was fractionated into coarse particulate organic 29 matter (CPOM), fine particulate organic matter (FPOM), silt, and clay-sized fractions. We 30 measured total C and plant-derived C in all soil fractions across all depths. The study led to two main results: (1) bulk soil C concentrations beneath switchgrass cultivars varied by 40% in the 0-32 10 cm soil depth and by 70% in the 10-20 cm soil depth, and cultivars with high bulk soil C 33 concentrations tended to have relatively high C concentrations in the mineral soil fractions and 34 relatively low C concentrations in the POM fractions; (2) there were significant differences in 35 switchgrass-derived soil C between cultivars at the 0-10 cm depth, where soil C inputs ranged 36 from 1.2 to 3.2 mg C g-1 dry soil. There was also evidence of a positive correlation between SRL 37 and switchgrass-derived C inputs when one outlier data point was removed. These results 38 indicate that switchgrass cultivars differentially impact mechanisms contributing to soil C accumulation.

  4. Broadband Seismic Investigations of the Upper Mantle Beneath the Vienna and Pannonian Basins

    Science.gov (United States)

    Dando, B. D.; Stuart, G. W.; Houseman, G. A.; Team, C.

    2008-12-01

    The Carpathian Basins Project (CBP) aims to understand the origin of the Miocene-age extensional basins contained within the compressional arc of the Alpine-Carpathian system. To test competing models for the recent geological evolution of the Carpathian-Pannonian lithosphere and upper mantle, we present a new determination of P-wave velocity structure to depths of 700 km beneath this region. This model is based on inversion of seismic travel-time residuals from 97 broadband seismic stations. We include CBP data from a 15-month deployment of a high resolution network of 46 stations deployed NW-SE across the Vienna and western Pannonian basins through Austria, Hungary and Serbia, together with 10 broadband stations spread across the Pannonian basin and a further 41 permanent broadband stations. We use P-wave arrival times from approximately 341 teleseismic events. The 3-D velocity variation obtained by tomographic inversion of the P-wave travel-time residuals shows an approximately linear belt of fast material of width about 100 km, orientated WNW-ESE beneath the western Pannonian Basin at sub-lithospheric depths. This feature is apparently continuous with structure beneath the Eastern Alps, but becomes more diffuse into the transition zone. Our initial interpretation of these fast velocities is in terms of mantle downwelling related to the early collision of Adria and Europe. We use receiver functions to assess crustal structure variations. We also determine SKS anisotropy; regionally SKS varies systematically in direction, with a delay time of about 1.0s. E-W fast directions above the fast tomographic anomaly change to NW-SE across the Great Hungarian Plane and the Vienna Basin.

  5. Seismic velocity variations beneath central Mongolia: Evidence for upper mantle plumes?

    Science.gov (United States)

    Zhang, Fengxue; Wu, Qingju; Grand, Stephen P.; Li, Yonghua; Gao, Mengtan; Demberel, Sodnomsambuu; Ulziibat, Munkhuu; Sukhbaatar, Usnikh

    2017-02-01

    Central Mongolia is marked by wide spread recent volcanism as well as significant topographic relief even though it is far from any plate tectonic boundaries. The cause of the recent magmatism and topography remains uncertain partially because little is known of the underlying mantle seismic structure due to the lack of seismic instrumentation in the region. From August 2011 through August 2013, 69 broadband seismic stations were deployed in central Mongolia. Teleseismic traveltime residuals were measured using waveform correlation and were inverted to image upper mantle P and S velocity variations. Significant lateral variations in seismic velocity are imaged in the deep upper mantle (100 to 800 km depth). Most significant are two continuous slow anomalies from the deep upper mantle to near the surface. One slow feature has been imaged previously and may be a zone of deep upwelling bringing warm mantle to beneath the Hangay Dome resulting in uplift and magmatism including the active Khanuy Gol and Middle Gobi volcanoes. The second, deep low velocity anomaly is seen in the east from 800 to 150 km depth. The anomaly ends beneath the Gobi Desert that is found to have fast shallow mantle indicating a relatively thick lithosphere. We interpret the second deep slow anomaly as a mantle upwelling that is deflected by the thick Gobi Desert lithosphere to surrounding regions such as the Hentay Mountains to the north. The upwellings are a means of feeding warmer than normal asthenospheric mantle over a widely distributed region beneath Mongolia resulting in distributed volcanic activity and uplift. There is no indication that the upwellings are rooted in the deep lower mantle i.e. classic plumes. We speculate the upwellings may be related to deep subduction of the Pacific and Indian plates and are thus plumes anchored in the upper mantle.

  6. A journey to the seismic low velocity zone beneath the ocean (Beno Gutenberg Medal Lecture)

    Science.gov (United States)

    Kawakatsu, Hitoshi

    2017-04-01

    The seismic low velocity zone (LVZ), first proposed by Beno Gutenberg, is an enigmatic layer of the Earth that has been drawing attention of earth scientists, most-likely because of its close association with the asthenosphere that enables plate motions in the plate tectonics context. "A journey to the LVZ", therefore, is equivalent to a journey to elucidate the lithosphere-asthenosphere system (LAS) beneath the ocean (at least that is what I mean by this title). Plate tectonics started as a theory of ocean basins nearly 50 years ago, but the mechanical details of how it works are still highly debated. It has been hampered partly by our inability to characterize the physical properties of the LAS beneath the ocean. I will discuss existing observational constraints, including our own results, on the physical properties of the LAS for normal oceanic regions, where plate tectonics is expected to present its simplest form. While a growing number of seismic data on land have provided remarkable advances in large scale pictures, seafloor observations have been shedding new light on the essential details. Particularly, recent advances in ocean bottom broadband seismometry, together with advances in the seismic analysis methodology, have now enabled us to resolve the regional 1-D structure of the entire LAS, from the surface to a depth of 200km, including seismic anisotropy (azimuthal), with deployments of 15 broadband ocean bottom seismometers for 1 2 years. We have thus succeeded to model the entire oceanic LAS without a priori assumption for the shallow-most structure, the assumption often made for the global surface wave tomography. I hope to convince the audience that we are now at an exciting stage that a large-scale array experiment in the ocean (e.g., Pacific Array: http://eri-ndc.eri.u-tokyo.ac.jp/PacificArray/) is becoming approachable to elucidate the enigma of the LVZ, thus the lithosphere-asthenosphere system, beneath the ocean.

  7. P-wave anisotropy, mantle wedge flow and olivine fabrics beneath Japan

    Science.gov (United States)

    Liu, Xin; Zhao, Dapeng

    2017-09-01

    We present a new 3-D anisotropic P-wave velocity (Vp) model for the crust and upper mantle of the Japan subduction zone obtained by inverting a large number of high-quality P-wave traveltime data of local earthquakes and teleseismic events. By assuming orthorhombic anisotropy with a vertical symmetry axis existing in the modeling space, isotropic Vp tomography and 3-D Vp azimuthal and radial anisotropies are determined simultaneously. According to a simple flow field and the obtained Vp anisotropic tomography, we estimate the distribution of olivine fabrics in the mantle wedge. Our results show that the forearc mantle wedge above the subducting Pacific slab beneath NE Japan exhibits an azimuthal anisotropy with trench-parallel fast velocity directions (FVDs) and Vhf > Vv > Vhs (here Vv is Vp in the vertical direction, Vhf and Vhs are P-wave velocities in the fast and slow directions in the horizontal plane), where B-type olivine fabric with vertical trench-parallel flow may dominate. Such an anisotropic feature is not obvious in the forearc mantle wedge above the Philippine Sea (PHS) slab under SW Japan, probably due to higher temperatures and more fluids there associated with the young and warm PHS slab subduction. Trench-normal FVDs and Vhf > Vv > Vhs are generally revealed in the mantle wedge beneath the arc and backarc in Japan, where E-type olivine fabric with FVD-parallel horizontal flow may dominate. Beneath western Honshu, however, the mantle wedge exhibits an anisotropy of Vv > Vhf > Vhs and so C-type olivine fabric may dominate, suggesting that the water content is the highest there, because both the PHS and Pacific slabs exist there and their dehydration reactions release abundant fluids to the overlying mantle wedge.

  8. Verifying Slab-Induced Waveform Effects beneath Central Taiwan by Three-dimensional Simulations

    Science.gov (United States)

    Huang, Yu-Ting; Zaho, Li; Chen, Po-fei; Chiao, Ling-Yun

    2013-04-01

    The Taiwan Island is a result of the convergence between the Eurasia and Philippine Sea plates. To what extent the east-dipping Eurasian slab extends northward beneath central Taiwan and the geometry of the slab east of Taiwan are important issues for understanding the geodynamics of the regional tectonics. However, structures in the upper mantle beneath Taiwan are poorly constrained in regional as well as global tomography models. The TAiwan Integrated GEodynamic Research (TAIGER) project deployed several well designed temporary arrays, and the broadband teleseismic data from stations along a north-south transect across Taiwan has been utilized to examine patterns of the first P waveform variations. The P waveforms observed in central Taiwan are generally characterized by earlier arrival times, reduced amplitudes, and broadened pulse widths relative to those observed in northern Taiwan, indicating the existence of a deep slab beneath central Taiwan. In this study, to verify those observations, we invoke the spectral-element method (SEM) to calculate the synthetic seismogram for the same dataset. Results for the 1D velocity model show that in central Taiwan the observed P waveforms have earlier arrival times, reduced amplitudes, and broadened pulse widths relative to the P waves in 1D model. We then invoke a hybrid model in which we use a regional 3D model as the background and introduce two slabs - an east-dipping slab south of Taiwan and a north-northwest-dipping slab offshore northeast Taiwan - with a suite of different slab configurations to determine the best velocity model that fits the previous observations.

  9. Upper mantle structure beneath the Alpine orogen from high-resolution teleseismic tomography

    Science.gov (United States)

    Lippitsch, Regina; Kissling, Edi; Ansorge, JöRg

    2003-08-01

    To understand the evolution of the Alpine orogen, knowledge of the actual structure of the lithosphere-asthenosphere system is important. We perform high-resolution teleseismic tomography with manually picked P wave arrival times from seismograms recorded in the greater Alpine region. The resulting data set consists of 4199 relative P wave arrivals and 499 absolute P wave arrivals from 76 teleseismic events, corrected for the contribution of the Alpine crust to the travel times. The three-dimensional (3-D) crustal model established from controlled-source seismology data for that purpose represents the large-scale Alpine crustal structure. Absolute P wave arrival times are used to compute an initial reference model for the inversion. Tests with synthetic data document that the combination of nonlinear inversion, high-quality teleseismic data, and usage of an a priori 3-D crustal model allows a reliable resolution of cells at 50 km × 50 km × 30 km. Hence structures as small as two cells can be resolved in the upper mantle. Our tomographic images illuminate the structure of the uppermost mantle to depth of 400 km. Along strike of the Alps, the inversion reveals a high-velocity structure that dips toward the SE beneath the Adriatic microplate in the western and central Alps. In the eastern Alps we observe a northeastward dipping feature, subducting beneath the European plate. We interpret this feature in the western and central Alps as subducted, mainly continental European lower lithosphere. For the east, we propose that parts of the Vardar oceanic basin were subducted toward the NE, forcing continental Adriatic lower lithosphere to subduct northeastward beneath the European plate.

  10. Magnetotelluric investigations of the lithosphere beneath the central Rae craton, mainland Nunavut, Canada

    Science.gov (United States)

    Spratt, Jessica E.; Skulski, Thomas; Craven, James A.; Jones, Alan G.; Snyder, David B.; Kiyan, Duygu

    2014-03-01

    New magnetotelluric soundings at 64 locations throughout the central Rae craton on mainland Nunavut constrain 2-D resistivity models of the crust and lithospheric mantle beneath three regional transects. Responses determined from colocated broadband and long-period magnetotelluric recording instruments enabled resistivity imaging to depths of > 300 km. Strike analysis and distortion decomposition on all data reveal a regional trend of 45-53°, but locally the geoelectric strike angle varies laterally and with depth. The 2-D models reveal a resistive upper crust to depths of 15-35 km that is underlain by a conductive layer that appears to be discontinuous at or near major mapped geological boundaries. Surface projections of the conductive layer coincide with areas of high grade, Archean metasedimentary rocks. Tectonic burial of these rocks and thickening of the crust occurred during the Paleoproterozoic Arrowsmith (2.3 Ga) and Trans-Hudson orogenies (1.85 Ga). Overall, the uppermost mantle of the Rae craton shows resistivity values that range from 3000 Ω m in the northeast (beneath Baffin Island and the Melville Peninsula) to 10,000 Ω m beneath the central Rae craton, to >50,000 Ω m in the south near the Hearne Domain. Near-vertical zones of reduced resistivity are identified within the uppermost mantle lithosphere that may be related to areas affected by mantle melt or metasomatism associated with emplacement of Hudsonian granites. A regional decrease in resistivities to values of 500 Ω m at depths of 180-220 km, increasing to 300 km near the southern margin of the Rae craton, is interpreted as the lithosphere-asthenosphere boundary.

  11. Layered anisotropy within the crust and lithospheric mantle beneath the Sea of Japan

    Science.gov (United States)

    Legendre, C. P.; Zhao, L.; Deschamps, F.; Chen, Q.-F.

    2016-10-01

    Continental rifting during the Oligocene to mid-Miocene caused the opening of the Sea of Japan and the separation between the Japanese Islands and the Eurasian Plate. The tectonic evolution in the Sea of Japan is important for understanding the evolution of back-arc regions in active convergent margins. Here, we use data from the seismic stations surrounding the Sea of Japan to map the Rayleigh-wave azimuthal anisotropy in the crust and lithospheric mantle beneath the Sea of Japan. We explore the variations of Rayleigh-wave phase-velocity beneath the Sea of Japan in a broad period range (30-80 s). Rayleigh-wave dispersion curves are measured by the two-station technique for a total of 231 interstation paths using vertical-component broad-band waveforms at 22 seismic stations around the Sea of Japan from 1411 global earthquakes. The resulting maps of Rayleigh-wave phase velocity and azimuthal anisotropy allow the examination of azimuthal anisotropy at specific periods. They exhibit several regions with different isotropic and anisotropic patterns: the Japan Basin displays fast velocities at shorter periods (30 and 40 s) with NNE-SSW anisotropy, whereas at 60 s and longer, the velocities become slow even if the anisotropy remains NE-SW; the East China Sea shows fast velocities at all periods (30-80 s) with constant NW-SE anisotropy. Trench-normal anisotropy beneath the Japanese Islands is found at short periods (30-40 s) and become trench-parallel at periods of 60 s and longer. Overall, our model resolves two layers of anisotropy, the shallowest and deepest layers being potentially related to frozen deformation due to recent geodynamic events, and asthenospheric flow, respectively.

  12. Stress in the contorted Nazca Plate beneath southern Peru from local earthquakes

    Science.gov (United States)

    Schneider, John F.; Sacks, I. Selwyn

    1987-12-01

    We study earthquake focal mechanisms in a region of highly contorted subducting lithosphere to identify dominant sources of stress in the subduction process. We observe a stress pattern in the contorted Nazca plate beneath southern Peru from an analysis of hypocentral trend and focal mechanisms of intermediate-depth earthquakes. Expanding on previous studies, we examine the hypocentral trend using 1673 of 2178 well-located local events from the nine-station Arequipa network. The dip of the plate beneath southern Peru averages 25°-30° from 25- to 100-km depth. Below this depth there is an 80- to 100-km-wide contortion between a zone of increasing dip (convex) to the southeast and a flat lying (concave) zone to the northwest. Using more than 6000 P wave first motions of events deeper than 50 km, we derive stress orientations from a moving average of composite focal mechanisms across a 200 by 350 km region including the contortion. The in-plate distribution of tension (T) and compression (P) axes reveals a coherent stress pattern. The trend is most clear beneath south-central Peru (NW section) and below 100- km depth in southernmost Peru (SE section). Both T and P axes tend to be dominantly in plate, especially below 100-km depth. T axes orient toward the contortion in a fan-shaped trend, which suggests that the deepest part of the seismic zone, within the convex SE section, is sinking and pulling the more buoyant NW section. We conclude that from 50- to 200-km depth, slab-pull forces are dominant in the observed stress. Our results suggest that a significant amount of plate extension occurs in this region of intermediate-depth subduction.

  13. Nature and extent of lava-flow aquifers beneath Pahute Mesa, Nevada Test Site

    Energy Technology Data Exchange (ETDEWEB)

    Prothro, L.B.; Drellack, S.L. Jr.

    1997-09-01

    Work is currently underway within the Underground Test Area subproject of the US Department of Energy/Nevada Operations Office Environmental Restoration Program to develop corrective action plans in support of the overall corrective action strategy for the Nevada Test Site as established in the Federal Facility Agreement and Consent Order (FFACO, 1996). A closure plan is currently being developed for Pahute Mesa, which has been identified in the FFACO as consisting of the Western and Central Pahute Mesa Corrective Action Units. Part of this effort requires that hydrogeologic data be compiled for inclusion in a regional model that will be used to predict a contaminant boundary for these Corrective Action Units. Hydrogeologic maps have been prepared for use in the model to define the nature and extent of aquifers and confining units that might influence the flow of contaminated groundwater from underground nuclear tests conducted at Pahute Mesa. Much of the groundwater flow beneath Pahute Mesa occurs within lava-flow aquifers. An understanding of the distribution and hydraulic character of these important hydrogeologic units is necessary to accurately model groundwater flow beneath Pahute Mesa. This report summarizes the results of a study by Bechtel Nevada geologists to better define the hydrogeology of lava-flow aquifers at Pahute Mesa. The purpose of this study was twofold: (1) aid in the development of the hydrostratigraphic framework for Pahute Mesa, and (2) provide information on the distribution and hydraulic character of lava-flow aquifers beneath Pahute Mesa for more accurate computer modeling of the Western and Central Pahute Mesa Corrective Action Units.

  14. Rayleigh Wave Phase Velocity in the Upper Mantle Beneath the Indian Ocean

    Science.gov (United States)

    Godfrey, K. E.; Dalton, C. A.; Ritsema, J.

    2016-12-01

    Most of what is currently understood about the seismic properties of oceanic upper mantle is based on either global studies or regional studies of the upper mantle beneath the Pacific Ocean. However, global seismic models and geochemical studies of mid-ocean ridge basalts indicate differences in the properties of the upper mantle beneath the Pacific, Atlantic, and Indian oceans. Though the Indian Ocean is not as well studied seismically, it is host to a number of geologically interesting features including 16,000 km of mid-ocean ridge with a range of spreading rates from 14 mm/yr along the Southwest Indian Ridge to 55-75 mm/yr along the Southeast Indian Ridge. The Indian Ocean also contains multiple volcanic hotspots, the Australian-Antarctic Discordance, and a low geoid anomaly south of India, and it overlies a portion of a large low-shear-velocity province. We are using Rayleigh waves to construct a high-resolution seismic velocity model of the Indian Ocean upper mantle. We utilize a global dataset of phase delays measured at 20 periods, between 37 and 375 seconds; the dataset includes between 700 and 20,000 that traverse our study region exclusively, with a larger number of paths at shorter periods. We explore variations in phase velocity using two separate approaches. One, we allow phase velocity to vary only as a function of seafloor age. Two, we perform a damped least-squares inversion to solve for 2-D phase velocity maps at each period. Preliminary results indicate low velocities along the Southeast Indian Ridge and Central Indian Ridge, but the expected low velocities are less apparent along the slow-spreading Southwest Indian Ridge. We observe a region of fast velocities extending from Antarctica northward between the Kerguelen and Crozet hotspots, and lower than expected velocities beneath the Reunion hotspot. Additionally, we find low velocities associated with a region of extinct seafloor spreading in the Wharton basin.

  15. Evidence for high fluid/melt content beneath Krakatau volcano (Indonesia) from local earthquake tomography

    Science.gov (United States)

    Jaxybulatov, Kairly; Koulakov, Ivan; Seht, Malte Ibs-von; Klinge, Klaus; Reichert, Christian; Dahren, Börje; Troll, Valentin R.

    2011-09-01

    Within the KRAKMON project for multiparameter monitoring of Anak Krakatau volcano (Indonesia), a network of temporary stations was installed on the islands of the Krakatau complex as well as in the surrounding areas of the Sunda Strait, Sumatra and Java. The network was operated from June 2005 until January 2006. More than 700 local events were recorded during this experiment, and travel times from these events were used to perform a tomographic inversion for P and S velocities and for the Vp/Vs ratio. In this study, special attention was paid to the validation of the computed model based on different tests, such as inversion of independent data subsets and synthetic modeling. Although the network configuration and the distribution of the events are not favorable for high-quality tomographic imaging, we have obtained some important and robust features which give information about sources of volcanic activity in the Krakatau complex. The most interesting feature of this study is a zone of high Vp/Vs ratio beneath the Krakatau complex. At depths down to 4 km depth we observe anticorrelation of higher P- and lower S-velocities that leads to Vp/Vs ratio higher than 2. This is a probable indicator of the presence of partially molten and/or with high fluid content material with a composition corresponding to deeper layers. It is important that the anomaly of high Vp/Vs ratio beneath the Krakatau complex appears to be separated in two parts at a depth of 5-6 km. This fits to results of geobarometric analysis that presume the existence of several levels of magma chambers beneath Anak Krakatau.

  16. Probing Earth’s conductivity structure beneath oceans by scalar geomagnetic data: autonomous surface vehicle solution

    DEFF Research Database (Denmark)

    Kuvshinov, Alexey; Matzka, Jürgen; Poedjono, Benny

    2016-01-01

    this method, known as magnetotellurics, to oceanic regions is challenging since only vector instruments placed at the sea bottom can provide such data. Here, we discuss a concept of marine induction surveying which is based on sea-surface scalar magnetic field measurements from a modern position...... to the conductivity structure beneath the ocean. We conclude that the sensitivity, depending on the bathymetry gradient, is typically largest near the coast offshore. We show that such sea-surface marine induction surveys can be performed with the Wave Glider, an easy-to-deploy, autonomous, energy-harvesting floating...

  17. Imaging magma storage reservoirs beneath Sierra Negra volcano, Galápagos, Ecuador

    Science.gov (United States)

    Tepp, G.; Belachew, M.; Ebinger, C. J.; Seats, K.; Ruiz, M. C.; Lawrence, J. F.

    2012-12-01

    Ocean island volcanoes initiate and grow through repeated eruptions and intrusions of primarily basaltic magma that thicken the oceanic crust above melt production zones within the mantle. The movement of oceanic plates over the hot, melt-rich upwellings produces chains of progressively younger basaltic volcanoes, as in the Galapagos Islands. Rates of surface deformation along the chain of 7 active volcanoes in the western Galápagos are some of the most rapid in the world, yet little is known of the subsurface structure of the active volcanic systems. The 16-station SIGNET array deployed between July 2009 and June 2011 provides new insights into the time-averaged structure beneath Sierra Negra, Cerro Azul, and Alcedo volcanoes, and the ocean platform. We use wavespeed tomography to image volcanic island structure, with focus on the magmatic plumbing system beneath Sierra Negra volcano, which has a deep, ~10 km-wide caldera and last erupted in 2005. We compare our results to those of ambient noise tomography. Our 120 x 100 km grid has a variable mesh of 2.5 - 10 km. We have good resolution at depths between 3 and 15 km, with poorer resolution beneath Cerro Azul volcano. Events from Alcedo volcano, which is just outside our array, cause some N-S smearing. Results from wavespeed tomography provide insights into the major island building processes: accretion through extrusive magmatism, magma chamber geometry and depth, radial dike intrusions, and magmatic underplating/sill emplacement. The wide caldera of Sierra Negra is underlain by high velocity (~7 %) material from depths of 5 - 15, and the flanks correspond to low velocity material at all depths. A high velocity zone corresponds to Cerro Azul (~3%). Aligned chains of eruptive centers correlate with elongate high velocity zones, suggesting that radial dikes are the sites of repeated dike intrusions. These chains are preferentially located along ridges linking nearby volcanoes. A comparison of well-resolved zones

  18. Slab detachment of subducted Indo-Australian plate beneath Sunda arc, Indonesia

    Indian Academy of Sciences (India)

    Bhaskar Kundu; V K Gahalaut

    2011-04-01

    Necking, tearing, slab detachment and subsequently slab loss complicate the subduction zone processes and slab architecture. Based on evidences which include patterns of seismicity, seismic tomography and geochemistry of arc volcanoes, we have identified a horizontal slab tear in the subducted Indo-Australian slab beneath the Sunda arc. It strongly reflects on trench migration, and causes along-strike variations in vertical motion and geochemically distinct subduction-related arc magmatism. We also propose a model for the geodynamic evolution of slab detachment.

  19. Upper boundary of the Pacific plate subducting beneath Hokkaido, Japan, estimated from ScSp phase

    OpenAIRE

    Osada, Kinue; Yoshizawa, Kazunori; YOMOGIDA, Kiyoshi

    2010-01-01

    Three-dimensional geometry of the upper boundary of the Pacific plate subducting beneath Hokkaido, Japan, was obtained using the ScSp phase: the phase converted from ScS (S wave reflected at the core-mantle boundary) to P wave at the plate boundary. Taking the advantage of a dense seismic network, "Hi-net", recently deployed across the Japanese islands, we applied several seismic array analyses to the recorded waveform data for a large nearby deep earthquake, in order to enhance very weak ScS...

  20. High-Resolution Imaging of the Mantle Flow Field Beneath Western North America

    Science.gov (United States)

    Fouch, M. J.; West, J. D.

    2008-12-01

    The goal of this study is to provide an improved understanding the nature of deformation in the crust and lithospheric mantle and its relationship to the mantle flow field beneath western North America. We utilize broadband data from regional and portable seismic arrays, including EarthScope's USArray Transportable Array and the ~120 stations of the High Lava Plains seismic array to image seismic anisotropy in the crust and mantle to constrain deformation in the crust, mantle lithosphere, and asthenosphere across the region. Regional shear wave splitting parameters show clear variations with geologic terrane. In the Pacific Northwest, splitting times are large (2.25+ sec) and fast directions are ~E-W with limited variability. Beneath the southern Basin and Range/Colorado Plateau region, splitting times are also large (~1.75+ sec) and fast directions are oriented ~NE-SW (similar to absolute plate motion). Stations near the San Andreas fault exhibit more variability between measurements at individual stations, but regionally exhibit a general rotation toward NW-SE for stations closer to the fault. Analyses from a dense array across the fault near Parkfield exhibit fast direction variations of ~30 degrees over ~15 km, indicating that uppermost crustal structure plays a significant role in some regions. Away from the Pacific-North American plate boundary, and sandwiched between broad regions of simple (i.e., regionally similar fast directions) and strong (i.e., large splitting times) azimuthal anisotropy, stations within the Great Basin exhibit significant complexity. Fast directions show a clear rotation from E-W in the northern Great Basin, to N-S in the eastern Great Basin, to NE-SW in the southeastern Great Basin. Splitting times reduce dramatically, approaching zero within the central Great Basin. At many stations within the Great Basin, particularly those that have been in operation for many years, we observe backazimuthal variations in splitting parameters that

  1. Exploring beneath the PIG Ice Shelf with the Autosub3 AUV

    OpenAIRE

    McPhail, Stephen D.; Furlong, Maaten E; Perrett, James R.; Stevenson, Peter; Webb, Andy; White, Davie

    2009-01-01

    On 31st January 2009, two numbers: “range and bearing” flashing up on a laptop screen, indicated that Autosub3 had returned from its last mission beneath the Pine Island Glacier (PIG) Ice Shelf in the Western Antarctic. The Autosub technical team from NOCS, Southampton, onboard the US ice breaker Nathanial B Palmer breathed a collective sigh of relief. Any significant technical failure would have resulted in total loss of the multi million Euro Autonomous Underwater Vehicle with no hope of re...

  2. Evolution of the Plumbing System Beneath a Primitive Cinder Cone: Volcan Jorullo, Mexico

    Science.gov (United States)

    Johnson, E.; Wallace, P.; Cashman, K.; Delgado Granados, H.

    2006-12-01

    Detailed studies of the explosive products of monogenetic cinder cones can provide insight into the evolution of the plumbing systems beneath these volcanoes. We have studied tephra deposits from the 1759-1774 eruption of Volcan Jorullo in the Trans-Mexican Volcanic Belt. The lava from Jorullo evolved during the eruption from primitive basalts to basaltic andesites (Luhr and Carmichael, 1985). In addition to lava flows, Jorullo erupted explosively, depositing a thick blanket of tephra and ash. We analyzed melt inclusions and their olivine hosts from two thick proximal ash fall sequences. Olivine are abundant as loose crystals in the tephra and their compositions evolve from the base (Fo88-91 cores) to the top (Fo84-87 cores) of the tephra sequence. Crystallization pressures for olivine, obtained from the concentration of CO2 and H2O in melt inclusions, decreased from early (50-4200 bars) to late (40-100 bars) in the eruption. The early erupted olivine crystallized over a much wider range in pressures, and interestingly, the most Fo-rich olivine (Fo90- 91) crystallized at the shallowest depths (~50 bars pressure) beneath the volcano, requiring rapid ascent rates of primitive melts. Olivine zoning profiles allow us to calculate crystal residence times, which increase from the early (~1-45 days) to late (~12-225 days) stages of the eruption. This increase in residence time, combined with the decrease in crystallization depth over time, suggest the formation of a shallow reservoir beneath the volcano as the eruption progressed. Formation of a shallow reservoir of degassed magma in which plagioclase and minor augite fractionation occurred together with assimilation of granitic wall rock is consistent with the temporal changes in lava flow and melt inclusion compositions. While the olivine and melt inclusion compositions evolve throughout our tephra section, we never see the most evolved values present in the lava flows. Although this may be the result of erosion of the

  3. Technology Solutions Case Study: Capillary Break Beneath a Slab: Polyethylene Sheeting over Aggregate, Southwestern Pennsylvania

    Energy Technology Data Exchange (ETDEWEB)

    None

    2014-07-01

    In this project, Building America team IBACOS worked with a builder of single- and multifamily homes in southwestern Pennsylvania (climate zone 5) to understand its methods of successfully using polyethylene sheeting over aggregate as a capillary break beneath the slab in new construction. This builder’s homes vary in terms of whether they have crawlspaces or basements. However, in both cases, the strategy protects the home from water intrusion via capillary action (e.g., water wicking into cracks and spaces in the slab), thereby helping to preserve the durability of the home.

  4. Study on S wave velocity structure beneath part stations in Shanxi Province

    Institute of Scientific and Technical Information of China (English)

    张学民; 束沛镒; 刁桂苓

    2003-01-01

    Based on S wave records of deep teleseisms on Digital Seismic Network of Shanxi Province, shear wave velocity structures beneath 6 stations were obtained by means of S wave waveform fitting. The result shows that the crust is thick in the studied region, reaching 40 km in thickness under 4 stations. The crust all alternatives high velocity layer with low velocity one. There appear varied velocity structures for different stations, and the stations around the same tectonic region exhibit similar structure characteristics. Combined with dominant depth distribution of many small-moderate earthquakes, the correlation between seismogenic layers and crustal structures of high and low velocity layers has been discussed.

  5. Ridge Subduction Beneath the Americas: Synthesis and New Research on Anomalous Tectonism and Magmatism

    Science.gov (United States)

    Thorkelson, D. J.; Madsen, J. K.; Breitsprecher, K.; Groome, W. G.; Sluggett, C.

    2006-12-01

    The west coast of the Americas has been repeatedly affected by ridge-trench interactions from Mesozoic to Recent time. Beneath North America, subduction of the Kula-Farallon, Kula-Resurrection and Farallon- Resurrection spreading ridges resulted in anomalous and time-transgressive forearc to backarc magmatism and related tectonism from the Late Cretaceous to the Eocene. Following consumption and redistribution of the Kula and Resurrection plates, the Neogene Farallon-Pacific ridge system intersected the North American trench in two locations - western Canada and northwestern Mexico / southwestern United States - causing pronounced magmatic and tectonic effects that continue to the present. Beneath Central America, divergent subduction of the Nazca and Cocos plates led to development of a slab window, with a present location beneath Panama and a probable pre-Pliocene position beneath Columbia or Ecuador. Patagonia has been the site of localized ridge subduction from the Eocene to the Recent, with the Phoenix-Farallon ridge subducting from the Eocene to the early Miocene, and the Nazca-Antarctic ridge from the Miocene to the present. Antarctica experienced diverging Antarctic-Phoenix plate subduction from the Eocene to the Pliocene. In all cases, normal arc magmatism was interrupted or eliminated by anomalous igneous activity ranging in signature from adakitic to intraplate. Our current research involves geochemical, tectonic, and thermal modeling of slab window environments. A new geochemical analysis on the effects of Miocene to Recent subduction of the northern segment of the Farallon (Juan de Fuca)-Pacific ridge is underway. A symmetrical arc-intraplate-arc geochemical pattern is evident in a transect from the northern Cascade Arc, through the volcanic fields of British Columbia, Yukon and eastern Alaska, and into the Aleutian Arc. This pattern can be explained by Neogene displacement of the arc-metasomatized mantle wedge caused by upwelling oceanic

  6. New insight into the Upper Mantle Structure Beneath the Pacific Ocean Using PP and SS Precursors

    Science.gov (United States)

    Gurrola, H.; Rogers, K. D.

    2013-12-01

    The passing of the EarthScope Transportable array has provided a dense data set that enabled beam forming of SS and PP data that resultes in improved frequency content to as much a 1 Hz in the imaging of upper mantle structure. This combined with the application of simultaneous iterative deconvolution has resulted in images to as much as 4 Hz. The processing however results in structure being averaged over regions of 60 to 100 km in radius. This is becomes a powerful new tool to image the upper mantle beneath Oceanic regions where locating stations is expensive and difficult. This presentation will summarize work from a number of regions as to new observations of the upper mantle beneath the Pacific and Arctic Oceans. Images from a region of the Pacific Ocean furthest from hot spots or subduction zones (we will refer to this as the 'reference region'). show considerable layering in the upper mantle. The 410 km discontinuity is always imaged using these tools and appears to be a very sharp boundary. It does usually appear as an isolated positive phase. There appears to be a LAB at ~100 km as expected but there is a strong negative phase at ~ 200 km with a positive phase 15 km deeper. This is best explained as a lens of partial melt as expected for this depth based on the geothermal gradient. If so this should be a low friction point and so we would expect it to accommodate plate motion. Imaging of the Aleutian subduction zone does show the 100 km deep LAB as it descends but this 200 km deep horizon appears as a week descending positive anomaly without the shallower negative pulse. In addition to the 410, 100 and 200 km discontinuities there are a number of paired anomalies, between the 200 and 400 km depths, with a negative pulse 15 to 20 km shallower then the positive pulse. We do not believe these are side lobes or we would see side lobes on the 100 km and 410 km discontinuities. We believe these to be the result of friction induced partial melt along zones of

  7. Zircon U-Pb ages of the basement rocks beneath the Songliao Basin, NE China

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The basement of the Songliao Basin is mainly composed of slightly-metamorphosed or unmetamorphosed Paleozoic strata, granites and gneiss. Petrographical studies indicate that the gneiss was originally the granitic intrusions which were deformed in the later stage. One undeformed granitic rock sample gives a U-Pb age of (305±2) Ma, and the mylonitic granite yields a U-Pb age of (165±3) Ma. Both of the two samples contain no inherited zircon, which suggests that there is no large-scale Precambrian crystalline basement beneath the Songliao Basin.

  8. Deep groundwater and potential subsurface habitats beneath an Antarctic dry valley

    DEFF Research Database (Denmark)

    Mikucki, J. A.; Auken, E.; Tulaczyk, S.

    2015-01-01

    The occurrence of groundwater in Antarctica, particularly in the ice-free regions and along the coastal margins is poorly understood. Here we use an airborne transient electromagnetic (AEM) sensor to produce extensive imagery of resistivity beneath Taylor Valley. Regional-scale zones of low...... suitable for microbial life. These inferred brines are widespread within permafrost and extend below glaciers and lakes. One system emanates from below Taylor Glacier into Lake Bonney and a second system connects the ocean with the eastern 18km of the valley. A connection between these two basins...

  9. Upper-Mantle Shear Velocities beneath Southern California Determined from Long-Period Surface Waves

    OpenAIRE

    Polet, J.; Kanamori, H.

    1997-01-01

    We used long-period surface waves from teleseismic earthquakes recorded by the TERRAscope network to determine phase velocity dispersion of Rayleigh waves up to periods of about 170 sec and of Love waves up to about 150 sec. This enabled us to investigate the upper-mantle velocity structure beneath southern California to a depth of about 250 km. Ten and five earthquakes were used for Rayleigh and Love waves, respectively. The observed surface-wave dispersion shows a clear Love/Rayleigh-wave d...

  10. Liquefaction evaluation of dam foundation soils considering overlying structure

    Institute of Scientific and Technical Information of China (English)

    Gang Wang a; Xing Wei b; Hanlong Liu a

    2015-01-01

    The liquefaction analysis procedure conducted at a dam foundation associated with a layer of liquefiable sand is presented. In this case, the effects of the overlying dam and an embedded diaphragm wall on liquefaction potential of foundation soils are considered. The analysis follows the stress-based approach which compares the earthquake-induced cyclic stresses with the cyclic resistance of the soil, and the cyclic resistance of the sand under complex stress condition is the key issue. Comprehensive laboratory monotonic and cyclic triaxial tests are conducted to evaluate the static characteristics, dynamic char-acteristics and the cyclic resistance against liquefaction of the foundation soils. The distribution of the factor of safety considering liquefaction is given. It is found that the zones beneath the dam edges and near the upstream of the diaphragm wall are more susceptible to liquefaction than in free field, whereas the zone beneath the center of the dam is less susceptible to liquefaction than in free field. According to the results, the strategies of ground improvement are proposed to mitigate the liquefaction hazards.

  11. Liquefaction evaluation of dam foundation soils considering overlying structure

    Directory of Open Access Journals (Sweden)

    Gang Wang

    2015-04-01

    Full Text Available The liquefaction analysis procedure conducted at a dam foundation associated with a layer of liquefiable sand is presented. In this case, the effects of the overlying dam and an embedded diaphragm wall on liquefaction potential of foundation soils are considered. The analysis follows the stress-based approach which compares the earthquake-induced cyclic stresses with the cyclic resistance of the soil, and the cyclic resistance of the sand under complex stress condition is the key issue. Comprehensive laboratory monotonic and cyclic triaxial tests are conducted to evaluate the static characteristics, dynamic characteristics and the cyclic resistance against liquefaction of the foundation soils. The distribution of the factor of safety considering liquefaction is given. It is found that the zones beneath the dam edges and near the upstream of the diaphragm wall are more susceptible to liquefaction than in free field, whereas the zone beneath the center of the dam is less susceptible to liquefaction than in free field. According to the results, the strategies of ground improvement are proposed to mitigate the liquefaction hazards.

  12. The influence of flint stones on a soil microbial community in the northern Negev Desert

    Directory of Open Access Journals (Sweden)

    Haggai Wasserstrom

    2017-07-01

    Full Text Available In the Negev Desert ecosystems, flint-stone cover on slopes acts as a barrier against water flow. As a result, soil moisture increases and organic matter accumulates under the stone and in the immediate surroundings, both affecting the duration of soil microbial activity. On the other hand, during the dry season (characterized by approximately 210 dew nights, flint-stone cover plays an important role in the formation of dew, which eventually trickles down beneath the stone, correspondingly enhancing biological activity. The present study examined the possible role of flint stones as hotspots for soil microbial-community activity and diversity. The results were compared with those obtained from the adjacent stone-free soils in the open spaces (OS, which served as controls. Microbial activity (respiration and biomass and functional diversity were determined by the MicroRespTM method. In addition, estimates of genetic diversity and viable counts of bacteria and fungi [colony-forming units (CFUs] were obtained. The soil was significantly wetter and contained more organic matter beneath the flint stones (BFS. As hypothesized, biological activity was enhanced under the stones, as described by CO2 evolution, microbial-community biomass functional diversity, and fungal phylogenetic diversity. BFS environments favored a greater range of catabolic functions. Taxa generally known for their stress resilience were found in the OS habitats. The results of this study elucidate the importance of flint-stone cover to soil microbial biomass, community activity, and functional diversity in the northern Negev Desert.

  13. High resolution image of the Lithosphere-Asthenosphere Boundary of the subducting Nazca plate beneath northern Chile

    Science.gov (United States)

    Sodoudi, F.; Yuan, X.; Asch, G.; Kind, R.

    2010-12-01

    Results obtained from S and P receiver functions produced a clear image of the top and bottom of the subducting Nazca lithosphere beneath northern Chile. Using data from the teleseismic events recorded at 15 permanent IPOC (Integrated Plate boundary Observatory Chile) stations, we were able to obtain new constraints on the shape and thickness of the descending Nazca lithosphere. We observed the subducted crust of the Nazca plate at depths ranging from 40 km beneath the Coastal Cordillera down to 110 km beneath the Western Cordillera. We found significant along-strike variations in the geometry of the Nazca plate beneath northern Chile. On closer inspection, it appears that the oceanic Nazca plate is divided into two distinct segments as it descends beneath the continental South American plate. The transition from the relatively steeper and deeper slab to the north of 21° S to the flatter southern segment is shown reasonably clearly by our data. This feature could well be associated with variations in the curvature of the plate margin and the geometry of the Chile trench, which is mainly curved to the north of 21° S. We have also mapped the continental Moho of the South American plate at depths ranging between 60-70 km to the east of the Longitudinal Valley. Beneath the Coastal Cordillera, this boundary becomes invisible, probably due to the serpentinization of the forearc mantle wedge. The Lithosphere-Astheonsphere Boundary (LAB) of the subducted Nazca plate was clearly identified as a sharp boundary in the results obtained from the P and S receiver functions. The LAB lies at a depth of 80 km beneath the coastal area and dips from a depth of 100 km beneath the Coastal Cordillera to about 150 km underneath the Western Cordillera. High frequency PRF data enabled us to make confident estimates of the top and bottom of the Nazca lithosphere, which results in a lithospheric thickness of 57-60 km. In relation to the age of the Nazca plate, which is assumed to be ~ 50

  14. Mapping the subducted Nazca plate in the lower mantle beneath South America

    Science.gov (United States)

    Contenti, S. M.; Gu, Y. J.; Okeler, A.

    2009-12-01

    Recent improvements in data coverage have enabled high-resolution imaging of the morphology of subduction zones and mantle plumes. In this study, we migrate the SS precursors from over 5000 seismograms to obtain a detailed map of mid- and upper-mantle reflectors beneath the northern portion of the South American subduction zone, where the oceanic Nazca plate is descending below the South American plate. In addition to an elevated 410 and depressed 660 (as expected for a subduction zone), strong mid-mantle reflectors at 800-1100 km depth are also apparent. The amplitudes of these steeply dipping reflectors are comparable to that of the 660-kilometer discontinuity. This anomaly outlines a high-velocity (therefore presumably cold) region present in recent finite-frequency based mantle velocity models, suggesting the extension of slab material into the lower mantle. The strength of the reflection is interpreted to be caused by a relatively sharp velocity change, likely due to a strong temperature gradient in combination with mineral phase transitions, the presence of water, or other chemical heterogeneities. Significant mass and heat exchange is therefore expected between the upper- and lower-mantle beneath the study region.

  15. Mantle upwelling beneath Madagascar: evidence from receiver function analysis and shear wave splitting

    Science.gov (United States)

    Paul, Jonathan D.; Eakin, Caroline M.

    2017-07-01

    Crustal receiver functions have been calculated from 128 events for two three-component broadband seismomenters located on the south coast (FOMA) and in the central High Plateaux (ABPO) of Madagascar. For each station, crustal thickness and V p / V s ratio were estimated from H- κ plots. Self-consistent receiver functions from a smaller back-azimuthal range were then selected, stacked and inverted to determine shear wave velocity structure as a function of depth. These results were corroborated by guided forward modeling and by Monte Carlo error analysis. The crust is found to be thinner (39 ± 0.7 km) beneath the highland center of Madagascar compared to the coast (44 ± 1.6 km), which is the opposite of what would be expected for crustal isostasy, suggesting that present-day long wavelength topography is maintained, at least in part, dynamically. This inference of dynamic support is corroborated by shear wave splitting analyses at the same stations, which produce an overwhelming majority of null results (>96 %), as expected for vertical mantle flow or asthenospheric upwelling beneath the island. These findings suggest a sub-plate origin for dynamic support.

  16. Extreme Mantle Heterogeneity beneath the Jingpohu Area, Northeastern China-Geochemical Evidence of Holocene Basaltic Rock

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Holocene basaltic rocks of the Jingpohu area are located in the "Crater Forest" and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, their petrological characteristics are very different: alkaline olivine basalt without any megacrysts in the former, and leucite tephrite with Ti-amphibole, phlogopite and anorthoclasite megacrysts in the latter. On the basis of their geochemical characteristics, the two types of basaltic rocks should belong to weakly sodian alkaline basalts. But leucite tephrite is characterized by higher Al2O3, Na2O and K2O, higher enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), lower MgO and CaO, compatible elements and moderately compatible elements and lower Mg# values and Na/K ratios in comparison with alkaline olivine basalt. However, the two types of basaltic rocks have similar Sr, Nd, Pb isotopic compositions, which suggests that the mantle beneath the Jingpohu area was homogeneous before undergoing some geological processes about 3490 years ago. As the activity of the mantle plume led to different degrees of metasomatism, extreme mantle source heterogeneities occurred beneath the Jingpohu area. In comparison with alkaline olivine basalt, the leucite tephrite was derived from the more enriched mantle source region and resulted from strong metasomatism.

  17. Repeating deep tremors on the plate interface beneath Kyushu, southwest Japan

    Science.gov (United States)

    Yabe, Suguru; Ide, Satoshi

    2013-01-01

    In the subduction zone south of Kyushu Island, at the western extension of the Nankai subduction zone, southwest Japan, the age of the oceanic crust increases toward the south across the subducting Kyushu-Palau ridge. While tremor activity is very high in Nankai, tectonic tremors have only recently been discovered in Kyushu. In this study, we examined tremors beneath Kyushu using an improved version of the envelope correlation method. In doing so, we distinguished tremors from normal earthquakes and background noise using the criteria of source duration and the spectrum ratio between low and high frequencies. Accurate measurement of S- P times, using cross-correlation between vertical and horizontal seismograms, constrains the tremor depth precisely. Tremor activity is low and within a small region in southern Kyushu, where thick crust of the Kyushu-Palau ridge is being subducted, at depths between 35 and 45 km (i.e., shallower than intra-slab earthquakes by about 20 km), which is consistent with the location of the plate interface within uncertainties proposed in previous studies. Establishing precise depth estimates for tectonic tremors beneath Kyushu, which results from shear slip along the plate interface, is useful in defining the plate interface within the Nankai subduction zone.

  18. Slab mantle dehydrates beneath Kamchatka—Yet recycles water into the deep mantle

    Science.gov (United States)

    Konrad-Schmolke, Matthias; Halama, Ralf; Manea, Vlad C.

    2016-08-01

    The subduction of hydrated slab mantle is the most important and yet weakly constrained factor in the quantification of the Earth's deep geologic water cycle. The most critical unknowns are the initial hydration state and the dehydration behavior of the subducted oceanic mantle. Here we present a combined thermomechanical, thermodynamic, and geochemical model of the Kamchatka subduction zone that indicates significant dehydration of subducted slab mantle beneath Kamchatka. Evidence for the subduction of hydrated oceanic mantle comes from across-arc trends of boron concentrations and isotopic compositions in arc volcanic rocks. Our thermodynamic-geochemical models successfully predict the complex geochemical patterns and the spatial distribution of arc volcanoes in Kamchatka assuming the subduction of hydrated oceanic mantle. Our results show that water content and dehydration behavior of the slab mantle beneath Kamchatka can be directly linked to compositional features in arc volcanic rocks. Depending on hydration depth of the slab mantle, our models yield water recycling rates between 1.1 × 103 and 7.4 × 103 Tg/Ma/km corresponding to values between 0.75 × 106 and 5.2 × 106 Tg/Ma for the entire Kamchatkan subduction zone. These values are up to one order of magnitude lower than previous estimates for Kamchatka, but clearly show that subducted hydrated slab mantle significantly contributes to the water budget in the Kamchatkan subduction zone.

  19. Subduction system and flat slab beneath the Eastern Cordillera of Colombia

    Science.gov (United States)

    Chiarabba, Claudio; De Gori, Pasquale; Faccenna, Claudio; Speranza, Fabio; Seccia, Danilo; Dionicio, Viviana; Prieto, Germán. A.

    2016-01-01

    Seismicity at the northern terminus of the Nazca subduction is diffused over a wide area containing the puzzling seismic feature known as the Bucaramanga nest. We relocate about 5000 earthquakes recorded by the Colombian national seismic network and produce the first 3-D velocity model of the area to define the geometry of the lithosphere subducting below the Colombian Andes. We found lateral velocity heterogeneities and an abrupt offset of the Wadati-Benioff zone at 5°N indicating that the Nazca plate is segmented by an E-W slab tear, that separates a steeper Nazca segment to the south from a flat subduction to the north. The flat Nazca slab extends eastward for about 400 km, before dip increases to ˜50° beneath the Eastern Cordillera, where it yields the Bucaramanga nest. We explain this puzzling locus of intermediate-depth seismicity located beneath the Eastern Cordillera of Colombia as due to a massive dehydration and eclogitization of a thickened oceanic crust. We relate the flat subducting geometry to the entrance at the trench at ca. 10 Ma of a thick - buoyant oceanic crust, likely a volcanic ridge, producing a high coupling with the overriding plate. Sub-horizontal plate subduction is consistent with the abrupt disappearance of volcanism in the Andes of South America at latitudes > 5°N.

  20. S-wave velocity structure beneath Changbaishan volcano inferred from receiver function

    Institute of Scientific and Technical Information of China (English)

    Jianping Wu; Yuehong Ming; Lihua Fang; Weilai Wang

    2009-01-01

    The S wave velocity structure in Changbaishan volcanic region was obtained from teleseismic receiver func-tion modeling. The results show that there exist distinct low velocity layers in crust in volcano area. Beneath WQD station near to the Tianchi caldera the low velocity layer at 8 km depth is 20 km thick with the lowest S-wave velocity about 2.2 km/s. At EDO station located 50 km north of Tianchi caldera, no obvious crustal low velocity layer is detected. In the volcanic re-gion, the thickness of crustal low velocity layer is greater and the lowest velocity is more obvious with the distance shorter to the caldem. It indicates the existence of the high temperature material or magma reservoir in crust near the Tianchi caldera. The receiver functions and inversion result from different back azimuths at CBS permanent seismic station show that the thickness of near surface low velocity layer and Moho depth change with directions. The near surface low velocity layer is obviously thicker in south direction. The Moho depth shows slight uplifting in the direction of the caldera located. We con-sider that the special near surface velocity structure is the main cause of relatively lower prominent frequency of volcanic earthquake waveforms recorded by CBS station. The slight uplifting of Moho beneath Tianchi caldera indicates there is a material exchanging channel between upper mantle and magma reservoir in crust.

  1. Mantle flow geometry from ridge to trench beneath the Gorda-Juan de Fuca plate system

    Science.gov (United States)

    Martin-Short, Robert; Allen, Richard M.; Bastow, Ian D.; Totten, Eoghan; Richards, Mark A.

    2015-12-01

    Tectonic plates are underlain by a low-viscosity mantle layer, the asthenosphere. Asthenospheric flow may be induced by the overriding plate or by deeper mantle convection. Shear strain due to this flow can be inferred using the directional dependence of seismic wave speeds--seismic anisotropy. However, isolation of asthenospheric signals is challenging; most seismometers are located on continents, whose complex structure influences the seismic waves en route to the surface. The Cascadia Initiative, an offshore seismometer deployment in the US Pacific Northwest, offers the opportunity to analyse seismic data recorded on simpler oceanic lithosphere. Here we use measurements of seismic anisotropy across the Juan de Fuca and Gorda plates to reconstruct patterns of asthenospheric mantle shear flow from the Juan de Fuca mid-ocean ridge to the Cascadia subduction zone trench. We find that the direction of fastest seismic wave motion rotates with increasing distance from the mid-ocean ridge to become aligned with the direction of motion of the Juan de Fuca Plate, implying that this plate influences mantle flow. In contrast, asthenospheric mantle flow beneath the Gorda Plate does not align with Gorda Plate motion and instead aligns with the neighbouring Pacific Plate motion. These results show that asthenospheric flow beneath the small, slow-moving Gorda Plate is controlled largely by advection due to the much larger, faster-moving Pacific Plate.

  2. Helioseismic Observations of the Structure and Dynamics of a Rotating Sunspot Beneath the Solar Surface

    Science.gov (United States)

    Zhao, Junwei; Kosovichev, Alexander G.

    2003-01-01

    Time-distance helioseismology is applied to study the subphotospheric structures and dynamics of an unusually fast-rotating sunspot observed by the Michelson Doppler Imager on bead SOH0 in 2000 August. The subsurface sound speed structures and velocity fields are obtained for the sunspot region at different depths from 0 to 12 Mm. By comparing the subsurface sound speed variations with the surface magnetic field, we find evidence for structural twists beneath the visible surface of this active region, which may indicate that magnetic twists often seen at the photosphere also exist beneath the photosphere. We also report on the observation of subsurface horizontal vortical flows that extend to a depth of 5 Mm around this rotating sunspot and present evidence that opposite vortical flows may exist below 9 Mm. It is suggested that the vortical flows around this active region may build up a significant amount of magnetic helicity and energy to power solar eruptions. Monte Carlo simulation has been performed to estimate the error propagation, and in addition the sunspot umbra is masked to test the reliability of our inversion results. On the basis of the three-dimensional velocity fields obtained from the time-distance helioseismology inversions, we estimate the subsurface kinetic helicity at different depths for the first time and conclude that it is comparable to the current helicity estimated from vector magnetograms.

  3. Seismic evidence for a cold serpentinized mantle wedge beneath Mount St Helens.

    Science.gov (United States)

    Hansen, S M; Schmandt, B; Levander, A; Kiser, E; Vidale, J E; Abers, G A; Creager, K C

    2016-11-01

    Mount St Helens is the most active volcano within the Cascade arc; however, its location is unusual because it lies 50 km west of the main axis of arc volcanism. Subduction zone thermal models indicate that the down-going slab is decoupled from the overriding mantle wedge beneath the forearc, resulting in a cold mantle wedge that is unlikely to generate melt. Consequently, the forearc location of Mount St Helens raises questions regarding the extent of the cold mantle wedge and the source region of melts that are responsible for volcanism. Here using, high-resolution active-source seismic data, we show that Mount St Helens sits atop a sharp lateral boundary in Moho reflectivity. Weak-to-absent PmP reflections to the west are attributed to serpentinite in the mantle-wedge, which requires a cold hydrated mantle wedge beneath Mount St Helens (<∼700 °C). These results suggest that the melt source region lies east towards Mount Adams.

  4. Stratified precambrian rocks (sedimentary ) beneath the midcontinent region of the US

    Energy Technology Data Exchange (ETDEWEB)

    Hauser, E.C.

    1993-02-01

    A thick sequence of layered rocks occurs beneath the Phanerozoic platform strata which blanket the US midcontinent. Observed on COCORP deep reflection data in southern Illinois and Indiana and in SW Oklahoma and adjacent Texas, this sequence is locally 1--3 times as thick as the overlying Paleozoic cover, but the origin of this sequence and its ultimate lateral extent are unknown. However, the occurrences of Precambrian layered rocks on both the COCORP profiles and reprocessed industry seismic reflection data from the region lie within regions of generally low amplitude and low frequency aeromagnetic anomaly, suggesting an even greater distribution. Unmetamorphosed Precambrian sedimentary rocks have been recovered from drill holes in southwest Ohio and adjacent northern Kentucky and southwesternmost Indiana. These Precambrian sedimentary rocks lie above and may be part of an underlying package of strongly layered rocks imaged on a short and shallow seismic profile in southwest Ohio. These Precambrian sedimentary rocks were originally viewed as part of a late Precambrian (Keweenawan ) rift; however, in light of Grenville foreland structures seen on the COCORP profile to the north in west central Ohio, these Precambrian strata may (1) be part of a heretofore unrecognized Grenville foreland basin, or (2) indicate that unmetamorphosed Precambrian sedimentary material may be an important constituent of the layered rocks observed on COCORP beneath southern Illinois and Indiana.

  5. Stratified precambrian rocks (sedimentary?) beneath the midcontinent region of the US. Final technical report

    Energy Technology Data Exchange (ETDEWEB)

    Hauser, E.C.

    1993-02-01

    A thick sequence of layered rocks occurs beneath the Phanerozoic platform strata which blanket the US midcontinent. Observed on COCORP deep reflection data in southern Illinois and Indiana and in SW Oklahoma and adjacent Texas, this sequence is locally 1--3 times as thick as the overlying Paleozoic cover, but the origin of this sequence and its ultimate lateral extent are unknown. However, the occurrences of Precambrian layered rocks on both the COCORP profiles and reprocessed industry seismic reflection data from the region lie within regions of generally low amplitude and low frequency aeromagnetic anomaly, suggesting an even greater distribution. Unmetamorphosed Precambrian sedimentary rocks have been recovered from drill holes in southwest Ohio and adjacent northern Kentucky and southwesternmost Indiana. These Precambrian sedimentary rocks lie above and may be part of an underlying package of strongly layered rocks imaged on a short and shallow seismic profile in southwest Ohio. These Precambrian sedimentary rocks were originally viewed as part of a late Precambrian (Keweenawan?) rift; however, in light of Grenville foreland structures seen on the COCORP profile to the north in west central Ohio, these Precambrian strata may (1) be part of a heretofore unrecognized Grenville foreland basin, or (2) indicate that unmetamorphosed Precambrian sedimentary material may be an important constituent of the layered rocks observed on COCORP beneath southern Illinois and Indiana.

  6. A two-layer flow model to represent ice-ocean interactions beneath Antarctic ice shelves

    Science.gov (United States)

    Lee, V.; Payne, A. J.; Gregory, J. M.

    2011-01-01

    We develop a two-dimensional two-layer flow model that can calculate melt rates beneath ice shelves from ocean temperature and salinity fields at the shelf front. The cavity motion is split into two layers where the upper plume layer represents buoyant meltwater-rich water rising along the underside of the ice to the shelf front, while the lower layer represents the ambient water connected to the open ocean circulating beneath the plume. Conservation of momentum has been reduced to a frictional geostrophic balance, which when linearized provides algebraic equations for the plume velocity. The turbulent exchange of heat and salt between the two layers is modelled through an entrainment rate which is directed into the faster flowing layer. The numerical model is tested using an idealized geometry based on the dimensions of Pine Island Ice Shelf. We find that the spatial distribution of melt rates is fairly robust. The rates are at least 2.5 times higher than the mean in fast flowing regions corresponding to the steepest section of the underside of the ice shelf close to the grounding line and to the converged geostrophic flow along the rigid lateral boundary. Precise values depend on a combination of entrainment and plume drag coefficients. The flow of the ambient is slow and the spread of ocean scalar properties is dominated by diffusion.

  7. Evidence for magmatic underplating and partial melt beneath the Canary Islands derived using teleseismic receiver functions

    Science.gov (United States)

    Lodge, A.; Nippress, S. E. J.; Rietbrock, A.; García-Yeguas, A.; Ibáñez, J. M.

    2012-12-01

    In recent years, an increasing number of studies have focussed on resolving the internal structure of ocean island volcanoes. Traditionally, active source seismic experiments have been used to image the volcano edifice. Here we present results using the analysis of compressional to shear (P to S) converted seismic phases from teleseismic events, recorded by stations involved in an active source experiment "TOM-TEIDEVS" (Ibáñez et al., 2008), on the island of Tenerife, Canary Islands. We supplement this data with receiver function (RF) analysis of seismograms from the Canary Islands of Lanzarote and La Palma, applying the extended-time multitaper frequency domain cross-correlation estimation method (Helffrich, 2006). We use the neighbourhood inversion approach of Sambridge (1999a,b) to model the RFs and our results indicate magmatic underplating exists beneath all three islands, ranging from 2 to 8 km, but showing no clear correlation with the age of the island. Beneath both La Palma and Tenerife, we find localized low velocity zones (LVZs), which we interpret as due to partial melt, supported by their correlation with the location of historical earthquakes (La Palma) and recent earthquakes (Tenerife). For Lanzarote, we do not sample the most recently volcanically active region and find no evidence for a LVZ. Instead, we find a simple gradational velocity structure, with discontinuities at ˜4, 10 and 18 km depth, in line with previous studies.

  8. Imaging of magma intrusions beneath Harrat Al-Madinah in Saudi Arabia

    Science.gov (United States)

    Abdelwahed, Mohamed F.; El-Masry, Nabil; Moufti, Mohamed Rashad; Kenedi, Catherine Lewis; Zhao, Dapeng; Zahran, Hani; Shawali, Jamal

    2016-04-01

    High-resolution tomographic images of the crust and upper mantle beneath Harrat Al-Madinah, Saudi Arabia, are obtained by inverting high-quality arrival-time data of local earthquakes and teleseismic events recorded by newly installed borehole seismic stations to investigate the AD 1256 volcanic eruption and the 1999 seismic swarm in the study region. Our tomographic images show the existence of strong heterogeneities marked with low-velocity zones extending beneath the AD 1256 volcanic center and the 1999 seismic swarm area. The low-velocity zone coinciding with the hypocenters of the 1999 seismic swarm suggests the presence of a shallow magma reservoir that is apparently originated from a deeper source (60-100 km depths) and is possibly connected with another reservoir located further north underneath the NNW-aligned scoria cones of the AD 1256 eruption. We suggest that the 1999 seismic swarm may represent an aborted volcanic eruption and that the magmatism along the western margin of Arabia is largely attributed to the uplifting and thinning of its lithosphere by the Red Sea rifting.

  9. Transient rheology of the uppermost mantle beneath the Mojave Desert, California

    Science.gov (United States)

    Pollitz, F.F.

    2003-01-01

    Geodetic data indicate that the M7.1 Hector Mine, California, earthquake was followed by a brief period (a few weeks) of rapid deformation preceding a prolonged phase of slower deformation. We find that the signal contained in continuous and campaign global positioning system data for 2.5 years after the earthquake may be explained with a transient rheology. Quantitative modeling of these data with allowance for transient (linear biviscous) rheology in the lower crust and upper mantle demonstrates that transient rheology in the upper mantle is dominant, its material properties being typified by two characteristic relaxation times ???0.07 and ???2 years. The inferred mantle rheology is a Jeffreys solid in which the transient and steady-state shear moduli are equal. Consideration of a simpler viscoelastic model with a linear univiscous rheology (2 fewer parameters than a biviscous model) shows that it consistently underpredicts the amplitude of the first ???3 months signal, and allowance for a biviscous rheology is significant at the 99.0% confidence level. Another alternative model - deep postseismic afterslip beneath the coseismic rupture - predicts a vertical velocity pattern opposite to the observed pattern at all time periods considered. Despite its plausibility, the advocated biviscous rheology model is non-unique and should be regarded as a viable alternative to the non-linear mantle rheology model for governing postseismic flow beneath the Mojave Desert. Published by Elsevier B.V.

  10. Regionalized difference of the 660 km discontinuity beneath Izu-Bonin

    Institute of Scientific and Technical Information of China (English)

    周元泽; 蒋志勇; 臧绍先

    2002-01-01

    Digital waveform data recorded by the vertical component short period stations at the American networks of SCSN, NCSN and PNSN and three components broadband stations at the Germany and Swiss networks and arrays of GRFN, GRSN and SDSNet for the events between 1981 and 2000 under Izu-Bonin are used as data sets. The N-th root slant stack method was used to pick up the SdP phase converted at the velocity interface beneath source and the regionalized difference of the 660 km discontinuity beneath Izu-Bonin is studied. It is found that while the dip angles of the subducting slab and the maximal depths of sources increase gradually from 35(N to 26(N, the 660 km discontinuity appears regionalized differences. The discontinuity exists at 660 km while there is no effect from subducting slab, but it is depressed to the depth of 720 km while there are obvious effects. The dispersion of converted points is still an unsolved problem which maybe result from the complex structure of the discontinuity, converted phases which were misjudged, or the assumption of one dimensional spherical earth model.

  11. A two-layer flow model to represent ice-ocean interactions beneath Antarctic ice shelves

    Directory of Open Access Journals (Sweden)

    V. Lee

    2011-01-01

    Full Text Available We develop a two-dimensional two-layer flow model that can calculate melt rates beneath ice shelves from ocean temperature and salinity fields at the shelf front. The cavity motion is split into two layers where the upper plume layer represents buoyant meltwater-rich water rising along the underside of the ice to the shelf front, while the lower layer represents the ambient water connected to the open ocean circulating beneath the plume. Conservation of momentum has been reduced to a frictional geostrophic balance, which when linearized provides algebraic equations for the plume velocity. The turbulent exchange of heat and salt between the two layers is modelled through an entrainment rate which is directed into the faster flowing layer.

    The numerical model is tested using an idealized geometry based on the dimensions of Pine Island Ice Shelf. We find that the spatial distribution of melt rates is fairly robust. The rates are at least 2.5 times higher than the mean in fast flowing regions corresponding to the steepest section of the underside of the ice shelf close to the grounding line and to the converged geostrophic flow along the rigid lateral boundary. Precise values depend on a combination of entrainment and plume drag coefficients. The flow of the ambient is slow and the spread of ocean scalar properties is dominated by diffusion.

  12. Grain-size dynamics beneath mid-ocean ridges: Implications for permeability and melt extraction

    CERN Document Server

    Turner, Andrew J; Behn, Mark D

    2014-01-01

    Grain size is an important control on mantle viscosity and permeability, but is difficult or impossible to measure in situ. We construct a two-dimensional, single phase model for the steady-state mean grain size beneath a mid-ocean ridge. The mantle rheology is modelled as a composite of diffusion creep, dislocation creep, dislocation accommodated grain boundary sliding, and a plastic stress limiter. The mean grain size is calculated by the piezometric relationship of Austin and Evans [2007]. We investigate the sensitivity of our model to global variations in grain growth exponent, potential temperature, spreading-rate, and mantle hydration. We interpret the mean mean grain-size field in the context of permeability. The permeability structure due to mean grain size may be approximated as a high permeability region beneath a low permeability region. The transition between high and low permeability regions forms a boundary that is steeply sloped toward the ridge axis. We hypothesise that such a permeability str...

  13. 3-D crustal and uppermost mantle structure beneath NE China revealed by ambient noise adjoint tomography

    Science.gov (United States)

    Liu, Yaning; Niu, Fenglin; Chen, Min; Yang, Wencai

    2017-03-01

    We construct a new 3-D shear wave speed model of the crust and the uppermost mantle beneath Northeast China using the ambient noise adjoint tomography method. Without intermediate steps of measuring phase dispersion, the adjoint tomography inverts for shear wave speeds of the crust and uppermost mantle directly from 6-40 s waveforms of Empirical Green's functions (EGFs) of Rayleigh waves, which are derived from interferometry of two years of ambient noise data recorded by the 127 Northeast China Extended Seismic Array stations. With an initial 3-D model derived from traditional asymptotic surface wave tomography method, adjoint tomography refines the 3-D model by iteratively minimizing the frequency-dependent traveltime misfits between EGFs and synthetic Green's functions measured in four period bands: 6-15 s, 10-20 s, 15-30 s, and 20-40 s. Our new model shows shear wave speed anomalies that are spatially correlated with known tectonic units such as the Great Xing'an range and the Changbaishan mountain range. The new model also reveals low wave speed conduits in the mid-lower crust and the uppermost mantle with a wave speed reduction indicative of partial melting beneath the Halaha, Xilinhot-Abaga, and Jingpohu volcanic complexes, suggesting that the Cenozoic volcanism in the area has a deep origin. Overall, the adjoint tomographic images show more vertically continuous velocity anomalies with larger amplitudes due to the consideration of the finite frequency and 3-D effects.

  14. Active subglacial lakes and channelized water flow beneath the Kamb Ice Stream

    Science.gov (United States)

    Kim, Byeong-Hoon; Lee, Choon-Ki; Seo, Ki-Weon; Lee, Won Sang; Scambos, Ted

    2016-12-01

    We identify two previously unknown subglacial lakes beneath the stagnated trunk of the Kamb Ice Stream (KIS). Rapid fill-drain hydrologic events over several months are inferred from surface height changes measured by CryoSat-2 altimetry and indicate that the lakes are probably connected by a subglacial drainage network, whose structure is inferred from the regional hydraulic potential and probably links the lakes. The sequential fill-drain behavior of the subglacial lakes and concurrent rapid thinning in a channel-like topographic feature near the grounding line implies that the subglacial water repeatedly flows from the region above the trunk to the KIS grounding line and out beneath the Ross Ice Shelf. Ice shelf elevation near the hypothesized outlet is observed to decrease slowly during the study period. Our finding supports a previously published conceptual model of the KIS shutdown stemming from a transition from distributed flow to well-drained channelized flow of subglacial water. However, a water-piracy hypothesis in which the KIS subglacial water system is being starved by drainage in adjacent ice streams is also supported by the fact that the degree of KIS trunk subglacial lake activity is relatively weaker than those of the upstream lakes.

  15. Microbial oxidation as a methane sink beneath the West Antarctic Ice Sheet

    Science.gov (United States)

    Michaud, Alexander B.; Dore, John E.; Achberger, Amanda M.; Christner, Brent C.; Mitchell, Andrew C.; Skidmore, Mark L.; Vick-Majors, Trista J.; Priscu, John C.

    2017-08-01

    Aquatic habitats beneath ice masses contain active microbial ecosystems capable of cycling important greenhouse gases, such as methane (CH4). A large methane reservoir is thought to exist beneath the West Antarctic Ice Sheet, but its quantity, source and ultimate fate are poorly understood. For instance, O2 supplied by basal melting should result in conditions favourable for aerobic methane oxidation. Here we use measurements of methane concentrations and stable isotope compositions along with genomic analyses to assess the sources and cycling of methane in Subglacial Lake Whillans (SLW) in West Antarctica. We show that sub-ice-sheet methane is produced through the biological reduction of CO2 using H2. This methane pool is subsequently consumed by aerobic, bacterial methane oxidation at the SLW sediment-water interface. Bacterial oxidation consumes >99% of the methane and represents a significant methane sink, and source of biomass carbon and metabolic energy to the surficial SLW sediments. We conclude that aerobic methanotrophy may mitigate the release of methane to the atmosphere upon subglacial water drainage to ice sheet margins and during periods of deglaciation.

  16. Anatomy of a meltwater drainage system beneath the ancestral East Antarctic ice sheet

    Science.gov (United States)

    Simkins, Lauren M.; Anderson, John B.; Greenwood, Sarah L.; Gonnermann, Helge M.; Prothro, Lindsay O.; Halberstadt, Anna Ruth W.; Stearns, Leigh A.; Pollard, David; Deconto, Robert M.

    2017-09-01

    Subglacial hydrology is critical to understand the behaviour of ice sheets, yet active meltwater drainage beneath contemporary ice sheets is rarely accessible to direct observation. Using geophysical and sedimentological data from the deglaciated western Ross Sea, we identify a palaeo-subglacial hydrological system active beneath an area formerly covered by the East Antarctic ice sheet. A long channel network repeatedly delivered meltwater to an ice stream grounding line and was a persistent pathway for episodic meltwater drainage events. Embayments within grounding-line landforms coincide with the location of subglacial channels, marking reduced sedimentation and restricted landform growth. Consequently, channelized drainage at the grounding line influenced the degree to which these landforms could provide stability feedbacks to the ice stream. The channel network was connected to upstream subglacial lakes in an area of geologically recent rifting and volcanism, where elevated heat flux would have produced sufficient basal melting to fill the lakes over decades to several centuries; this timescale is consistent with our estimates of the frequency of drainage events at the retreating grounding line. Based on these data, we hypothesize that ice stream dynamics in this region were sensitive to the underlying hydrological system.

  17. Observations and modeling of ocean-induced melt beneath Petermann Glacier Ice Shelf in northwestern Greenland

    Science.gov (United States)

    Cai, Cilan; Rignot, Eric; Menemenlis, Dimitris; Nakayama, Yoshihiro

    2017-08-01

    We update observationally based estimates of subaqueous melt, Qm, beneath Petermann Glacier Ice Shelf (PGIS), Greenland, and model its sensitivity to oceanic thermal forcing, TF, and subglacial runoff, Qsg, using the Massachusetts Institute of Technology general circulation model (MITgcm), in a two-dimensional domain, with 20 m vertical and 40 m horizontal resolution at the grounding line. We adjust the drag coefficient to match the observationally based Qm. With the inclusion of Qsg, the maximum melt rate (Qmmax) is 2 times larger in summer and 1/3 larger annually than in winter. Qmmax increases above linear with TF and below linear with Qsg. We estimate that Qmmax increased by 24% (+8.1 m/yr) beneath PGIS from the 1990s to the 2000s from a 0.21°C warming in ocean temperature and a doubling in Qsg, hence contributing to its thinning. If the PGIS is removed, we estimate that the modeled melt rate near the grounding line will increase 13-16 times.

  18. Slab melting beneath the Cascades Arc driven by dehydration of altered oceanic peridotite

    Science.gov (United States)

    Walowski, Kristina J; Wallace, Paul J.; Hauri, E.H.; Wada, I.; Clynne, Michael A.

    2015-01-01

    Water is returned to Earth’s interior at subduction zones. However, the processes and pathways by which water leaves the subducting plate and causes melting beneath volcanic arcs are complex; the source of the water—subducting sediment, altered oceanic crust, or hydrated mantle in the downgoing plate—is debated; and the role of slab temperature is unclear. Here we analyse the hydrogen-isotope and trace-element signature of melt inclusions in ash samples from the Cascade Arc, where young, hot lithosphere subducts. Comparing these data with published analyses, we find that fluids in the Cascade magmas are sourced from deeper parts of the subducting slab—hydrated mantle peridotite in the slab interior—compared with fluids in magmas from the Marianas Arc, where older, colder lithosphere subducts. We use geodynamic modelling to show that, in the hotter subduction zone, the upper crust of the subducting slab rapidly dehydrates at shallow depths. With continued subduction, fluids released from the deeper plate interior migrate into the dehydrated parts, causing those to melt. These melts in turn migrate into the overlying mantle wedge, where they trigger further melting. Our results provide a physical model to explain melting of the subducted plate and mass transfer from the slab to the mantle beneath arcs where relatively young oceanic lithosphere is subducted.

  19. Radial anisotropy beneath northeast Tibet, implications for lithosphere deformation at a restraining bend in the Kunlun fault and its vicinity

    Science.gov (United States)

    Li, Lun; Li, Aibing; Murphy, Michael A.; Fu, Yuanyuan V.

    2016-09-01

    Three-dimensional shear wave velocity and radial anisotropy models of the crust and upper mantle beneath the NE Tibetan plateau are constructed from new measurements of Love wave dispersions (20-77s) and previously obtained Rayleigh wave dispersions (20-87s) using a two-plane-wave method. The mid-lower crust is characterized with positive anisotropy (VSH > VSV) with large strength beneath the Qinling and Qilian Mountains and small values beneath the Anyemaqen Mountain. The large positive anisotropy can be explained by horizontal alignment of anisotropic minerals in the mid-lower crust due to crustal flow. The mantle lithosphere above 90 km is largely isotropic while weak positive anisotropy appears beneath 90 km, which probably marks the lithosphere-asthenosphere boundary (LAB). A low shear wave velocity anomaly and relatively negative radial anisotropy are imaged in the entire lithosphere beneath the restraining bend in the eastern Kunlun fault, consistent with a weak lithosphere experiencing vertical thickening under horizontal compression. The asthenosphere at the restraining bend is characterized by significant low velocity and positive radial anisotropy, reflecting that the asthenosphere here is probably hotter, has more melts, and deforms more easily than the surrounding region. We propose that the lithosphere at the restraining bend was vertically thickened and subsequently delaminated locally, and induced asthenosphere upwelling. This model explains the observations of velocity and anisotropy anomalies in the lithosphere and asthenosphere as well as geological observations of rapid rock uplift at the restraining bend of the Kunlun fault.

  20. Pile-soil stress ratio in bidirectionally reinforced composite ground by considering soil arching effect

    Institute of Scientific and Technical Information of China (English)

    邹新军; 杨眉; 赵明华; 杨小礼

    2008-01-01

    To discuss the soil arching effect on the load transferring model and sharing ratios by the piles and inter-pile subsoil in the bidirectionally reinforced composite ground, the forming mechanism, mechanical behavior and its effect factors were discussed in detail. Then, the unified strength theory was introduced to set up the elastoplastic equilibrium differential equation of the subsoil under the limit equilibrium state. And from the equation, the solutions were derived with the corresponding formulas presented to calculate the earth pressure over and beneath the horizontal reinforced cushion or pillow, the stress of inter-pile subsoil and the pile-soil stress ratio. Based on the obtained solutions and measured data from an engineering project, the influence rules by the soil property parameters (i.e., the cohesion c and internal friction angle φ) and pile spacing on the pile-soil stress ratio n were discussed respectively. The results show that to improve the load sharing ratio by the piles, the more effective means for filling materials with a larger value of φ is to increase the ratio of pile cap size to spacing, while to reduce the pile spacing properly and increase the value of cohesion c is advisable for those filling materials with a smaller value of φ.

  1. Effects of irrigated agroecosystems: 1. Quantity of soil water and groundwater in the southern High Plains, Texas

    Science.gov (United States)

    Scanlon, B. R.; Reedy, R. C.; Gates, J. B.

    2010-09-01

    Although irrigated agriculture is the primary consumer of global groundwater resources, information on recharge rates and sustainable irrigation is limited. The study objective was to fingerprint irrigation return flow to quantify percolation/recharge and to estimate sustainable irrigation levels. This paper focuses on water quantity; a companion paper addresses water quality. Soil samples from 13 boreholes drilled beneath irrigated agroecosystems in the southern High Plains were analyzed for matric potential and water-extractable Cl and NO3. Unsaturated zone pore water beneath irrigated agroecosystems can be fingerprinted by higher matric potentials (wetter soils, median mp: -40 m) and higher NO3-N (median 71 mg/L) than beneath natural ecosystems (mp -200 m; NO3-N 8.1 mg/L) and by higher Cl (720 mg/L) than beneath rain-fed agroecosystems (8.4 mg/L). The range in percolation/recharge rates beneath irrigated agroecosystems is 18-97 mm/a (median 41 mm/a; 5% of irrigation + precipitation) and occurs primarily in response to extreme precipitation events. Similarity in percolation/recharge rates beneath irrigated and rain-fed (4.8-92 mm/a) agroecosystems was unexpected and is attributed to low irrigation applications (median 300 mm/a) and increased crop yield and evapotranspiration in irrigated areas. Regional water table declines are unsustainably large (≥ 30 m over 10,000 km2) in the north and are much lower in the south. Sustainable irrigation in the south would require reduction of the irrigated area from 23% to 9%. Methods developed for quantifying recharge and sustainable irrigation application rates can be applied to groundwater-fed irrigated areas in semiarid regions globally.

  2. Remediation of PCB contaminated soils at Saglek, Labrador

    Energy Technology Data Exchange (ETDEWEB)

    Maskell, B.; Bordin, D. [Bennett Environmental Inc., Oakville, ON (Canada)

    2005-07-01

    Polychlorinated biphenyl (PCB) contaminated soils were discovered in Saglek in 1986. This paper describes a contract awarded to Bennett Environmental Inc., by the Department of National Defense for the removal of all contaminated soils and debris in the area. Key tasks included removal of all stockpiles of PCB contaminated soil; collection, cleaning and sorting of debris for containerization and removal; remediation of potential contaminated soils beneath the stockpiles; and reinstatement of the staging and clean stone deposition zone area to its natural state. Planning of the project was outlined, including details of partnering sessions and workshops, as well as details of community meetings held in Nain. Details of startup and pre-environmental monitoring were also provided. An outline of the containerization unit used during the project was presented, as well as ship cycle times and soil sampling procedures. Washing and water treatment procedures were reviewed, as well as details of the on-site laboratory, equipped with personal exposure monitoring; an ambient air monitoring network; water sampling and analysis; and continuous monitoring to assess potential exposure to PCB to conform to alarm levels and implement mitigation measures. Shipping procedures were reviewed as well as soil treatment processes at a facility in Cornwall, Ontario. It was concluded that the remediation of the site was successful. All contaminated material was removed and treated. 1 ref., 4 figs.

  3. Deep Background of Wenchuan Earthquake and the Upper Crust Structure beneath the Longmen Shan and Adjacent Areas

    Institute of Scientific and Technical Information of China (English)

    LI Qiusheng; GAO Rui; WANG Haiyan; ZHANG Jisheng; LU Zhanwu; LI Pengwu; GUAN Ye; HE Rizheng

    2009-01-01

    By analyzing the deep seismic sounding profiles across the Longmen Shan, this paper focuses on the study of the relationship between the upper crust structure of the Longmen Shan area and the Wenchuan earthquake. The Longmen Shan thrust belt marks not only the topographical change, but also the lateral velocity variation between the eastern Tibetan Plateau and the Sichuan Basin. A low-velocity layer has consistently been found in the crust beneath the eastern edge of the Tibetan Plateau, and ends beneath the western Sichuan Basin. The low-velocity layer at a depth of -20 km beneath the eastern edge of the Tibetan Plateau has been considered as the deep condition for favoring energy accumulation that formed the great Wenchuan earthquake.

  4. Enzyme leaching of surficial geochemical samples for detecting hydromorphic trace-element anomalies associated with precious-metal mineralized bedrock buried beneath glacial overburden in northern Minnesota

    Science.gov (United States)

    Clark, Robert J.; Meier, A.L.; Riddle, G.; ,

    1990-01-01

    One objective of the International Falls and Roseau, Minnesota, CUSMAP projects was to develop a means of conducting regional-scale geochemical surveys in areas where bedrock is buried beneath complex glacially derived overburden. Partial analysis of B-horizon soils offered hope for detecting subtle hydromorphic trace-element dispersion patterns. An enzyme-based partial leach selectively removes metals from oxide coatings on the surfaces of soil materials without attacking their matrix. Most trace-element concentrations in the resulting solutions are in the part-per-trillion to low part-per-billion range, necessitating determinations by inductively coupled plasma/mass spectrometry. The resulting data show greater contrasts for many trace elements than with other techniques tested. Spatially, many trace metal anomalies are locally discontinuous, but anomalous trends within larger areas are apparent. In many instances, the source for an anomaly seems to be either basal till or bedrock. Ground water flow is probably the most important mechanism for transporting metals toward the surface, although ionic diffusion, electrochemical gradients, and capillary action may play a role in anomaly dispersal. Sample sites near the Rainy Lake-Seine River fault zone, a regional shear zone, often have anomalous concentrations of a variety of metals, commonly including Zn and/or one or more metals which substitute for Zn in sphalerite (Cd, Ge, Ga, and Sn). Shifts in background concentrations of Bi, Sb, and As show a trend across the area indicating a possible regional zoning of lode-Au mineralization. Soil anomalies of Ag, Co, and Tl parallel basement structures, suggesting areas that may have potential for Cobalt/Thunder Baytype silver viens. An area around Baudette, Minnesota, which is underlain by quartz-chlorite-carbonate-altered shear zones, is anomalous in Ag, As, Bi, Co, Mo, Te, Tl, and W. Anomalies of Ag, As, Bi, Te, and W tend to follow the fault zones, suggesting potential

  5. High-resolution image of the geometry and thickness of the subducting Nazca lithosphere beneath northern Chile

    Science.gov (United States)

    Sodoudi, F.; Yuan, X.; Asch, G.; Kind, R.

    2011-04-01

    Results obtained from S and P receiver functions produced a clear image of the top and bottom of the subducting Nazca lithosphere beneath northern Chile. Using data from the teleseismic events recorded at 15 permanent Integrated Plate Boundary Observatory Chile (IPOC) stations, we obtained new constraints on the geometry and thickness of the descending Nazca lithosphere. We observed the subducted crust of the Nazca plate at depths ranging from 50 km beneath the Coastal Cordillera down to 110 km beneath the Western Cordillera. We found significant along-strike variations in the geometry of the Nazca plate beneath northern Chile. On closer inspection, it appears that the oceanic Nazca plate is divided into two distinct segments as it descends beneath the continental South American plate. The transition from the relatively steeper (˜23°) and deeper slab to the north of 21°S to the flatter southern segment (˜19°) is shown reasonably clearly by our data. This feature could well be associated with variations in the curvature of the plate margin and the geometry of the Chile trench, which is mainly curved to the north of 21°S. We have also mapped the continental Moho of the South American plate at depths ranging between 60 and 70 km to the east of the Longitudinal Valley. Beneath the Coastal Cordillera, this boundary becomes invisible, probably due to the serpentinization of the forearc mantle wedge that reduces the velocity in the uppermost mantle. The base of the subducted Nazca plate was clearly identified as a sharp boundary in the results obtained from the P and S receiver functions. The thickness of the subducted oceanic Nazca plate, which has an age of ˜50 My, is estimated to be ˜50 km. Although this thickness is consistent with that predicted by thermal gradients, the explanation of the sharpness of the lithosphere-asthenosphere boundary may require another mechanism such as hydration or melting.

  6. Seismic Anisotropy due to Crust and Uppermost Mantle Deformation Beneath Southern Peru and Bolivia: Constraints from Receiver Functions

    Science.gov (United States)

    Bar, N.; Long, M. D.; Wagner, L. S.; Beck, S. L.; Tavera, H.

    2016-12-01

    Subduction systems play a key role in plate tectonics, but the deformation of the crust and uppermost mantle during subduction and orogenesis in continental subduction systems remains poorly understood. Observations of seismic anisotropy can provide important constraints on dynamic processes in the crust and uppermost mantle in subduction systems. The subduction zone beneath Peru and Bolivia, where the Nazca plate subducts beneath South America, represents a particularly interesting location to study subduction-related deformation, given the complex slab morphology and the along-strike transition from flat to normally dipping subduction. In particular, understanding the structure and deformation of the crust and mantle will yield insight into the relationship between the flat slab and the overriding continental lithosphere. In this study we constrain seismic anisotropy within and above the subducting slab (including the mantle wedge and the overriding plate) beneath southern Peru and Bolivia using transverse component receiver functions. Because anisotropic receiver function analysis can constrain the depth distribution of anisotropy, this analysis is complementary to previous studies of shear wave splitting in this region. We examine data from two dense lines of seismometers from the PULSE and CAUGHT deployments in Peru and Bolivia, each anchored by a long-running permanent station. The northern line overlies the Peru flat slab, while the southern line overlies the normally dipping slab beneath Bolivia. Beneath Peru, our investigation of anisotropic structure along the flat slab will help test the recently suggested hypothesis of a slab tear; beneath Bolivia, we aim to characterize the pattern of flow in the mantle wedge as well as the nature of deformation in the lower crust of the overriding plate.

  7. High-resolution seismic reflection imaging of growth folding and shallow faults beneath the Southern Puget Lowland, Washington State

    Science.gov (United States)

    Odum, Jackson K.; Stephenson, William J.; Pratt, Thomas L.; Blakely, Richard J.

    2016-01-01

    Marine seismic reflection data from southern Puget Sound, Washington, were collected to investigate the nature of shallow structures associated with the Tacoma fault zone and the Olympia structure. Growth folding and probable Holocene surface deformation were imaged within the Tacoma fault zone beneath Case and Carr Inlets. Shallow faults near potential field anomalies associated with the Olympia structure were imaged beneath Budd and Eld Inlets. Beneath Case Inlet, the Tacoma fault zone includes an ∼350-m wide section of south-dipping strata forming the upper part of a fold (kink band) coincident with the southern edge of an uplifted shoreline terrace. An ∼2 m change in the depth of the water bottom, onlapping postglacial sediments, and increasing stratal dips with increasing depth are consistent with late Pleistocene to Holocene postglacial growth folding above a blind fault. Geologic data across a topographic lineament on nearby land indicate recent uplift of late Holocene age. Profiles acquired in Carr Inlet 10 km to the east of Case Inlet showed late Pleistocene or Holocene faulting at one location with ∼3 to 4 m of vertical displacement, south side up. North of this fault the data show several other disruptions and reflector terminations that could mark faults within the broad Tacoma fault zone. Seismic reflection profiles across part of the Olympia structure beneath southern Puget Sound show two apparent faults about 160 m apart having 1 to 2 m of displacement of subhorizontal bedding. Directly beneath one of these faults, a dipping reflector that may mark the base of a glacial channel shows the opposite sense of throw, suggesting strike-slip motion. Deeper seismic reflection profiles show disrupted strata beneath these faults but little apparent vertical offset, consistent with strike-slip faulting. These faults and folds indicate that the Tacoma fault and Olympia structure include active structures with probable postglacial motion.

  8. Mantle transition zone beneath a normal seafloor in the northwestern Pacific: Electrical conductivity, seismic discontinuity, and water content

    Science.gov (United States)

    Matsuno, Tetsuo; Suetsugu, Daisuke; Utada, Hisashi; Baba, Kiyoshi; Tada, Noriko; Shimizu, Hisayoshi; Shiobara, Hajime; Isse, Takehi; Sugioka, Hiroko; Ito, Aki

    2016-04-01

    We conducted a joint electromagnetic and seismic field experiment to probe water content reserved in the mantle transition zone (MTZ) beneath a normal seafloor around the Shatsky Rise in the northwestern Pacific. Specifically for the investigation of the MTZ structure, we developed new ocean bottom instruments for providing higher S/N ratio data and having higher mobility in field experiment than ever. We installed our state-of-the-art instruments in two arrays to the north and south of the Shatsky Rise for 5 years from 2010 to 2015. We first analyzed data obtained in our and previous studies to elucidate an electrical conductivity structure through the magnetotelluric and geomagnetic depth sounding methods and seismic discontinuity depths or thickness of the MTZ through the P-wave receiver function method. An electrical conductivity structure beneath two observational arrays is represented well by an average 1-D model beneath the northern Pacific. A MTZ thickness beneath the north array is thicker than a global average of MTZ thickness by 22 km, and that beneath the south array is similar to the average. For estimating water content in the MTZ, we implemented a series of forward modeling of the electromagnetic responses based on the average 1-D electrical conductivity model, temperature profiles of the MTZ involving temperature anomalies estimated from the MTZ thickness perturbations, and electrical conductivities of dry and hydrous MTZ materials (wadsleyite and ringwoodite). A result of the forward modeling indicates that the maximum water content in the MTZ beneath the north array is 0.5 wt.%.

  9. Layering of the lithospheric mantle beneath the Siberian Craton: Modeling using thermobarometry of mantle xenolith and xenocrysts

    Science.gov (United States)

    Ashchepkov, I. V.; Vladykin, N. N.; Ntaflos, T.; Kostrovitsky, S. I.; Prokopiev, S. A.; Downes, H.; Smelov, A. P.; Agashev, A. M.; Logvinova, A. M.; Kuligin, S. S.; Tychkov, N. S.; Salikhov, R. F.; Stegnitsky, Yu. B.; Alymova, N. V.; Vavilov, M. A.; Minin, V. A.; Babushkina, S. A.; Ovchinnikov, Yu. I.; Karpenko, M. A.; Tolstov, A. V.; Shmarov, G. P.

    2014-11-01

    Single-grain thermobarometric studies of xenocrysts were used to compile local SCLM transects through the major regions of kimberlite magmatism in Siberia and longer transects through the subcontinental mantle lithosphere (SCLM) beneath the Siberian craton. The mantle structure was obtained using P-Fe#, Ca in garnets, oxygen fugacity values fO2 and calculated temperatures T°C. The most detail transect obtained for the Daldyn field on the Udachnaya-Zarnitsa reveals layering showing an inclination of > 35° to Udachnaya. Mantle layering beneath the Alakit field determined from the Krasnopresnenskaya-Sytykanskaya transect shows a moderate inclination from N to S. The inflection near Yubileinaya-Aykhal is also supported by the extreme depletion in peridotites with low-Fe sub-Ca garnets. Beneath the Malo-Botuobinsky field the sharply layered mantle section starts from 5.5 GPa and reveals step-like P-Fe#Ol trends for garnets and ilmenites. The deeper part of SCLM in this field was originally highly depleted but has been regenerated by percolation of protokimberlites and hybrid melts especially beneath Internationalnaya pipe. The three global transects reveal flat layering in granite-greenstone terranes and fluctuations in the granulite-orthogneiss Daldyn collision terranes. The mantle layering beneath the Daldyn - Alakite region may have been created by marginal accretion. Most of southern fields including the Malo-Botuobinsky field reveal flat layering. The primary subduction layering is smoothed beneath the Alakit field. Lower Jurassic kimberlites from the Kharamai-Anabar kimberlite fields reveal a small decrease of the thickness of the SCLM and heating of its base. The Jurassic Kuoyka field shows an uneven base of the SCLM inclined from west to east. SCLM sequences sampled at this time started mainly from depths of 130 km, but some pipes still showed mantle roots to 250 km. The garnet series demonstrates an inclined straight line pyroxenite P-Fe# trend due to

  10. Small variations of soil properties control fire-induced water repellency

    Directory of Open Access Journals (Sweden)

    Jorge Mataix-Solera

    2014-03-01

    Full Text Available Fire induced soil water repellency (WR is controlled by many different factors (temperature reached, amount and type of fuel, etc.. Soil properties may determine the occurrence and intensity of this property in burned soils. The objectives of this paper are to make advances in the study of soil properties as key factors controlling the behaviour of fire-induced WR, and to study the impact of pre-fire SOM content and SOM quality in fire-induced soil WR. In this research, experimental laboratory burnings were carried out using soil samples from different sites with different lithologies, soil types and plant species. Soil samples taken from the same site differ only in quantity and quality of soil organic matter, as they were collected from under different plant species. All soil samples were heated in a muffle furnace at 200, 250, 300 and 350 ºC without the addition of any fuel load. WR was measured using the water drop penetration time test (WDPT. The results showed significant differences between soil types and plant species, indicating that small differences in soil properties may act as key factors controlling the development and persistence of WR reached, with burned soil samples ranging from wettable to extremely water repellent. The main soil property controlling the response was texture, specifically sand content. The quality of organic matter was also observed to have an effect, since soil samples from the same site with similar organic matter contents, but taken from beneath different plant species, showed different WR values after burning.

  11. Lower crustal relaxation beneath the Tibetan Plateau and Qaidam Basin following the 2001 Kokoxili earthquake

    Science.gov (United States)

    Ryder, I.; Burgmann, R.; Pollitz, F.

    2011-01-01

    In 2001 November a magnitude 7.8 earthquake ruptured a 400 km long portion of the Kunlun fault, northeastern Tibet. In this study, we analyse over five years of post-seismic geodetic data and interpret the observed surface deformation in terms of stress relaxation in the thick Tibetan lower crust. We model GPS time-series (first year) and InSAR line of sight measurements (years two to five) and infer that the most likely mechanism of post-seismic stress relaxation is time-dependent distributed creep of viscoelastic material in the lower crust. Since a single relaxation time is not sufficient to model the observed deformation, viscous flow is modelled by a lower crustal Burgers rheology, which has two material relaxation times. The optimum model has a transient viscosity 9 ?? 1017 Pa s, steady-state viscosity 1 ?? 1019 Pa s and a ratio of long term to Maxwell shear modulus of 2:3. This model gives a good fit to GPS stations south of the Kunlun Fault, while displacements at stations north of the fault are over-predicted. We attribute this asymmetry in the GPS residual to lateral heterogeneity in rheological structure across the southern margin of the Qaidam Basin, with thinner crust/higher viscosities beneath the basin than beneath the Tibetan Plateau. Deep afterslip localized in a shear zone beneath the fault rupture gives a reasonable match to the observed InSAR data, but the slip model does not fit the earlier GPS data well. We conclude that while some localized afterslip likely occurred during the early post-seismic phase, the bulk of the observed deformation signal is due to viscous flow in the lower crust. To investigate regional variability in rheological structure, we also analyse post-seismic displacements following the 1997 Manyi earthquake that occurred 250 km west of the Kokoxili rupture. We find that viscoelastic properties are the same as for the Kokoxili area except for the transient viscosity, which is 5 ?? 1017 Pa s. The viscosities estimated for the

  12. Window into the Caledonian orogen: Structure of the crust beneath the East Shetland platform, United Kingdom

    Science.gov (United States)

    McBride, J.H.; England, R.W.

    1999-01-01

    Reprocessing and interpretation of commercial and deep seismic reflection data across the East Shetland platform and its North Sea margin provide a new view of crustal subbasement structure beneath a poorly known region of the British Caledonian orogen. The East Shetland platform, east of the Great Glen strike-slip fault system, is one of the few areas of the offshore British Caledonides that remained relatively insulated from the Mesozoic and later rifting that involved much of the area around the British Isles, thus providing an "acoustic window" into the deep structure of the orogen. Interpretation of the reflection data suggests that the crust beneath the platform retains a significant amount of its original Caledonian and older architecture. The upper to middle crust is typically poorly reflective except for individual prominent dipping reflectors with complex orientations that decrease in dip with depth and merge with a lower crustal layer of high reflectivity. The three-dimensional structural orientation of the reflectors beneath the East Shetland platform is at variance with Caledonian reflector trends observed elsewhere in the Caledonian orogen (e.g., north of the Scottish mainland), emphasizing the unique tectonic character of this part of the orogen. Upper to middle crustal reflectors are interpreted as Caledonian or older thrust surfaces that were possibly reactivated by Devonian extension associated with post-Caledonian orogenic collapse. The appearance of two levels of uneven and diffractive (i.e., corrugated) reflectivity in the lower crust, best developed on east-west-oriented profiles, is characteristic of the East Shetland platform. However, a north-south-oriented profile reveals an interpreted south-vergent folded and imbricated thrust structure in the lower crust that appears to be tied to the two levels of corrugated reflectivity on the east-west profiles. A thrust-belt origin for lower crustal reflectivity would explain its corrugated

  13. Seismic anisotropy and velocity structure beneath the southern half of the Iberian Peninsula

    Science.gov (United States)

    Serrano, I.; Hearn, T. M.; Morales, J.; Torcal, F.

    2005-06-01

    Travel times of 11,612 Pn arrivals collected from 7675 earthquakes are inverted to image the uppermost mantle velocity and anisotropy structure beneath the southern half of the Iberian Peninsula and surrounding regions. Pn phases are routinely identified and picked for epicentral distances from 200 to 1200 km. The method used in this study allows simultaneous imaging of variations of Pn velocity and anisotropy. The results show an average uppermost mantle velocity beneath the study area of 8.0 km/s. The peninsular area covered by the Iberian massif is characterized by high Pn velocity, as expected in tectonically stable regions, indicating areas of the Hercynian belt that have not recently been reactivated. The margins of the Iberian Peninsula have undergone a great number of recent tectonic events and are characterized by a pronouncedly low Pn velocity, as is common in areas greatly affected by recent tectonic and magmatic activity. Our model indicates that the Betic crustal root might be underlined by a negative anomaly beneath the southeastern Iberian Peninsula. In the Atlantic Ocean, we find a sharp variation in the uppermost mantle velocities that coincides with the structural complexity of the European and African plate boundary in the Gulf of Cadiz. Our results show a very pronounced low-velocity anomaly offshore from Cape San Vicente whereas high velocities are distributed along the coast in the Gulf of Cadiz. In the Alboran Sea and northern Morocco, the direction of the fastest Pn velocity found is almost parallel to the Africa-Eurasia plate convergence vector (northwest-southeast) whereas to the north, this direction is almost parallel to the main trend of the Betic Cordillera, i.e. east-west in its central part and north-south in the curvature of the Arc of Gibraltar. This suggests that a significant portion of the uppermost mantle has been involved in the orogenic deformation that produced the arcuate structure of the Betic Cordillera. However, we

  14. Factors contributing to the temperature beneath plaster or fiberglass cast material

    Science.gov (United States)

    Hutchinson, Michael J; Hutchinson, Mark R

    2008-01-01

    Background Most cast materials mature and harden via an exothermic reaction. Although rare, thermal injuries secondary to casting can occur. The purpose of this study was to evaluate factors that contribute to the elevated temperature beneath a cast and, more specifically, evaluate the differences of modern casting materials including fiberglass and prefabricated splints. Methods The temperature beneath various types (plaster, fiberglass, and fiberglass splints), brands, and thickness of cast material were measured after they were applied over thermometer which was on the surface of a single diameter and thickness PVC tube. A single layer of cotton stockinette with variable layers and types of cast padding were placed prior to application of the cast. Serial temperature measurements were made as the cast matured and reached peak temperature. Time to peak, duration of peak, and peak temperature were noted. Additional tests included varying the dip water temperature and assessing external insulating factors. Ambient temperature, ambient humidity and dip water freshness were controlled. Results Outcomes revealed that material type, cast thickness, and dip water temperature played key roles regarding the temperature beneath the cast. Faster setting plasters achieved peak temperature quicker and at a higher level than slower setting plasters. Thicker fiberglass and plaster casts led to greater peak temperature levels. Likewise increasing dip-water temperature led to elevated temperatures. The thickness and type of cast padding had less of an effect for all materials. With a definition of thermal injury risk of skin injury being greater than 49 degrees Celsius, we found that thick casts of extra fast setting plaster consistently approached dangerous levels (greater than 49 degrees for an extended period). Indeed a cast of extra-fast setting plaster, 20 layers thick, placed on a pillow during maturation maintained temperatures over 50 degrees of Celsius for over 20

  15. Extremely depleted lithospheric mantle and diamonds beneath the southern Zimbabwe Craton

    Science.gov (United States)

    Smith, Chris B.; Pearson, D. Graham; Bulanova, Galina P.; Beard, Andrew D.; Carlson, Richard W.; Wittig, Nadine; Sims, Keith; Chimuka, Lovemore; Muchemwa, Ellah

    2009-11-01

    Inclusion-bearing diamonds, mantle xenoliths, and kimberlite concentrates from the Cambrian-aged Murowa and Sese kimberlites have been studied to characterise the nature of the lithospheric mantle beneath the southern Zimbabwe Craton. The diamonds are mostly octahedral, moderately rich in nitrogen with moderate to high aggregation, and contain mainly dunite-harzburgite mineral inclusions. Similarly, dunite xenoliths predominate over harzburgite and lherzolite and carry olivines with Mg/Mg + Fe (Mg#) values of 0.92-0.95, spanning the average signatures for Kaapvaal Craton peridotites. Eclogitic xenoliths are extremely rare, in contrast to the Kaapvaal mantle lithosphere. The Zimbabwe mantle assemblage has been only slightly affected by later silicic metasomatism and re-fertilisation with re-introduction of pyroxenes in contrast to the Kaapvaal and many cratonic lithospheric blocks elsewhere where strong metasomatism and re-fertilisation is widespread. Pyroxene, garnet and spinel thermobarometry suggests an ambient 40 mW m - 2 geotherm, with the lithosphere extending down to 210 km at the time of kimberlite eruption. Whole rock peridotite Re-Os isotope analyses yield T RD model ages of 2.7 to 2.9 Ga, providing minimum estimates of the time of melt depletion, are slightly younger in age than the basement greenstone formation. These model ages coincide with the mean T RD age of > 200 analyses of Kaapvaal Craton peridotites, whereas the average Re-Os model age for the Zimbabwe peridotites is 3.2 Ga. The Os data and low Yb n/Lu n ratios suggest a model whereby thick lithospheric mantle was stabilised during the early stages of crustal development by shallow peridotite melting required for formation of residues with sufficiently high Cr/Al to stabilise chromite which then transforms to low Ca, high Cr garnet. Sulphide inclusions in diamond produce minimum T RD model ages of 3.4 Ga indicating that parts of the lithosphere were present at the earliest stages of crust

  16. 3-D Teleseismic Tomography of the Crust and Upper Mantle Beneath Northern Tasmania, Australia

    Science.gov (United States)

    Rawlinson, N.; Kennett, B. L.; Reading, A. M.

    2004-12-01

    The TIGGER project is a multi-faceted seismic study of Tasmania and southern Victoria (SE Australia) undertaken by the Australian National University in 2001/2002. As part of this project, an array of 72 short period and broadband seismic recorders with a nominal spacing of 15 km was deployed across northern Tasmania for a period of five months. To date, nearly 6,000 relative arrival times from 100 earthquakes have been picked using a newly developed and robust adaptive stacking technique. The azimuthal coverage of teleseisms is generally good, with many events to the north and east (e.g.~Indonesia, Papua New Guinea, New Zealand, Fiji), although fewer from the south and west(e.g.~South Sandwich Islands, mid- Indian ridge). A new iterative non-linear tomographic inversion procedure based on the fast marching method (FMM), a grid based eikonal solver, and a subspace inversion scheme, is used to map traveltime residual patterns as P-wave velocity anomalies from an ak135 reference model. The 3-D model volume beneath the array is parameterized using cubic B-spline functions in spherical coordinates; a total of nearly 10,000 vertices at approximately 15 km grid spacing is used to describe the TIGGER model. Preliminary tomographic results from the TIGGER experiment show significant lateral variations in P-wave velocity structure within the Tasmanian lithosphere. Geological inferences made from these early results include: (1) Within the crust, the first-order E-W velocity variations strongly support the idea that eastern Tasmania is underlain by dense rocks with an oceanic crustal affinity, contrasting with the continentally derived lower crustal rocks of western Tasmania; (2) the Tamar Fracture System, often defined as a lithospheric scale discontinuity, probably does not exist; (3) the elevated crustal velocities beneath the Rocky Cape Group and Arthur Lineament, compared to the Tyennan Element and Mt. Read Volcanics to the east, also support a mafic

  17. Factors contributing to the temperature beneath plaster or fiberglass cast material

    Directory of Open Access Journals (Sweden)

    Hutchinson Mark R

    2008-02-01

    Full Text Available Abstract Background Most cast materials mature and harden via an exothermic reaction. Although rare, thermal injuries secondary to casting can occur. The purpose of this study was to evaluate factors that contribute to the elevated temperature beneath a cast and, more specifically, evaluate the differences of modern casting materials including fiberglass and prefabricated splints. Methods The temperature beneath various types (plaster, fiberglass, and fiberglass splints, brands, and thickness of cast material were measured after they were applied over thermometer which was on the surface of a single diameter and thickness PVC tube. A single layer of cotton stockinette with variable layers and types of cast padding were placed prior to application of the cast. Serial temperature measurements were made as the cast matured and reached peak temperature. Time to peak, duration of peak, and peak temperature were noted. Additional tests included varying the dip water temperature and assessing external insulating factors. Ambient temperature, ambient humidity and dip water freshness were controlled. Results Outcomes revealed that material type, cast thickness, and dip water temperature played key roles regarding the temperature beneath the cast. Faster setting plasters achieved peak temperature quicker and at a higher level than slower setting plasters. Thicker fiberglass and plaster casts led to greater peak temperature levels. Likewise increasing dip-water temperature led to elevated temperatures. The thickness and type of cast padding had less of an effect for all materials. With a definition of thermal injury risk of skin injury being greater than 49 degrees Celsius, we found that thick casts of extra fast setting plaster consistently approached dangerous levels (greater than 49 degrees for an extended period. Indeed a cast of extra-fast setting plaster, 20 layers thick, placed on a pillow during maturation maintained temperatures over 50 degrees of

  18. Complex Crustal Structure Beneath Western Turkey Revealed by 3D Seismic Full Waveform Inversion (FWI)

    Science.gov (United States)

    Cubuk-Sabuncu, Yesim; Taymaz, Tuncay; Fichtner, Andreas

    2016-04-01

    We present a 3D radially anisotropic velocity model of the crust and uppermost mantle structure beneath the Sea of Marmara and surroundings based on the full waveform inversion method. The intense seismic activity and crustal deformation are observed in the Northwest Turkey due to transition tectonics between the strike-slip North Anatolian Fault (NAF) and the extensional Aegean region. We have selected and simulated complete waveforms of 62 earthquakes (Mw > 4.0) occurred during 2007-2015, and recorded at (Δ DAD). The spectral-element solver of the wave equation, SES3D algorithm, is used to simulate seismic wave propagation in 3D spherical coordinates (Fichtner, 2009). The Large Scale Seismic Inversion Framework (LASIF) workflow tool is also used to perform full seismic waveform inversion (Krischer et al., 2015). The initial 3D Earth model is implemented from the multi-scale seismic tomography study of Fichtner et al. (2013). Discrepancies between the observed and simulated synthetic waveforms are determined using the time-frequency misfits which allows a separation between phase and amplitude information (Fichtner et al., 2008). The conjugate gradient optimization method is used to iteratively update the initial Earth model when minimizing the misfit. The inversion is terminated after 19 iterations since no further advances are observed in updated models. Our analysis revealed shear wave velocity variations of the shallow and deeper crustal structure beneath western Turkey down to depths of ~35-40 km. Low shear wave velocity anomalies are observed in the upper and mid crustal depths beneath major fault zones located in the study region. Low velocity zones also tend to mark the outline of young volcanic areas. Our final 3D Earth model is tested using forward wave simulations of earthquakes (M ≥ 3.7) that were not used during the inversion process. The comparison of observed and synthetic seismograms, calculated by initial and final models, showed significant

  19. On the origin of the anisotropy observed beneath the westernmost Mediterranean region

    Science.gov (United States)

    Diaz, Jordi

    2017-04-01

    The Iberian Peninsula and Northern Morocco region provides an excellent opportunity to investigate the origin of subcrustal anisotropy. Following the TopoIberia-Iberarray experiment, anisotropic properties have been explored in a dense network of 60x60 km spaced broad-band stations, resulting in more than 300 sites investigated over an area extending from the Bay of Biscay to the Sahara platform and covering more than 6000.000 km2. The rather uniform N100°E FPD retrieved beneath the Variscan Central Iberian Massif is consistent with global mantle flow models taking into account contributions of surface plate motion, density variations and net lithosphere rotation. The origin of this anisotropy is hence globally related to the lattice preferred orientation of mantle minerals generated by mantle flow at asthenospheric depths, although significant regional variations are observed. The anisotropic parameters retrieved from single events providing high quality data show significant differences for stations located in the Variscan units of NW Iberia, suggesting that the region includes multiple anisotropic layers or complex anisotropy systems have to be considered there. The rotation of the FDE along the Gibraltar arc following the curvature of the Rif-Betic chain has been interpreted as an evidence of mantle flow deflected around the high velocity slab beneath the Gibraltar Arc. Beneath the SW corner of Iberia and the High Atlas zone, small delay times and inconsistent FPD have been detected, suggesting the presence of vertical mantle flow affecting the anisotropic structure of the asthenosphere. Future developments will include a better integration with the anisotropic estimations provided by Pn tomography and, in particular, with those arising from surface wave tomographic inversions using TopoIberia-Ibearray results. Additionally, the contribution of crustal anisotropy could be estimated from the analysis of receiver functions. The detailed knowledge on the

  20. Utilization of humus-rich forest soil (mull) in geochemical exploration for gold

    Science.gov (United States)

    Curtin, Gary C.; Lakin, H.W.; Neuerburg, G.J.; Hubert, A.E.

    1968-01-01

    Distribution of gold in humus-rich forest soil (mull) reflects the known distribution of gold deposits in bedrock in the Empire district, Colorado. Gold from the bedrock is accumulated by pine and aspen trees and is concentrated in the mull by the decay of organic litter from the trees. Anomalies in mull which do not coincide with known gold deposits merit further exploration. The gold anomalies in soil (6- to 12-inch depth) and in float pebbles and cobbles poorly reflect the known distribution of gold deposits in bedrock beneath the extensive cover of colluvium and glacial drift.

  1. Upper mantle low-velocity layers beneath the High Lava Plains imaged by scattered-wavefield migration

    Science.gov (United States)

    Chen, C.; James, D. E.; Wagner, L. S.

    2011-12-01

    The High Lava Plains (HLP) in eastern Oregon represents one of the most active intraplate magmatic provinces on Earth. This region's recent tectonic history is dominated by voluminous mid-Miocene outpourings of the Steens and Columbia River flood basalts, followed by a period of bimodal volcanic activities, generating two roughly orthogonal time-progressive rhyolitic hotspot tracks: the northeastern-trending Snake River Plain and the northwestern-trending High Lava Plains. The causes of this complex tectonomagmatic evolution are not well understood, and geophysical constraints have been lacking regarding the detailed crustal and upper mantle structure in this region. From 2006 to 2009, a passive seismic experiment with the deployment of 118 broadband seismic stations was carried out as part of the multidisciplinary High Lava Plains project, which aims to investigate the causes of continental intraplate tectonomagmatism. These stations covered central and eastern Oregon, northern Nevada, and southwestern Idaho, with average spacing of 15-20 km, yielding unprecedented data density in the HLP region. A number of tomographic and receiver function studies has revealed complex structures beneath HLP. These include irregular Moho topography across the HLP, and concentrated low velocity anomalies in the uppermost mantle beneath regions of Holocene volcanism in southeastern Oregon (including areas of the Owyhee Plateau), as well as beneath volcanic centers near Steens Mountain and Newberry volcano. We complement these previous studies by generating high-resolution seismic images from scattered wavefield to detect seismic discontinuities beneath the HLP. We process 80 high-quality teleseismic events with good azimuthal coverage using a 2-D teleseismic migration algorithm based on the Generalized Radon Transform. The resulting migration images indicate the presence of several main features: 1) a prominent and varying Moho topography: the Moho is at ~40 km depth east of the

  2. Application of teleseismic tomography to the study of shallow structure beneath Shizigou in the western Qaidam basin

    Institute of Scientific and Technical Information of China (English)

    Xiaoming Xu; Yinsheng Ma; Danian Shi; Xiaofeng Wang; Chengming Yin

    2009-01-01

    Teleseismic body wave traveltime tomography is used to inverse the three-dimensional seismic velocity structure beneath Shizigou in the western Qaidam basin. The travel time are picked from the continuous observation data on a small seismic array of stations deployed during 2004-2007. The tomographic results obtained indicate that a NW-trending low velocity anomaly just beneath the target region insert northeastwards with a high dip angle, to the north, northeast and east of the low velocity anomaly, some high-velocity anomalies distribute with the same strike and coverage as those of Shizigou anticline.

  3. Treatment of Chlorinated Solvents in Groundwater Beneath an Occupied Building at the Young-Rainey STAR Center, Pinellas, FL

    Energy Technology Data Exchange (ETDEWEB)

    Daniel, Joe [Navarro Research and Engineering; Surovchak, Scott [Dept. of Energy (DOE), Legacy Management; Tabor, Charles [Navarro Research and Engineering

    2016-03-01

    Groundwater contamination, consisting of two dissolved-phase plumes originating from chlorinated solvent source areas, in the southeastern portion of the Young- Rainey Star Center (also known as the Pinellas County, Florida, Site) in Largo, Florida, has migrated beyond the property boundary, beneath the roadways, and beneath adjacent properties to the south and east. Groundwater contamination will persist as long as the onsite contaminant source remains. The origin of the contamination appears to be multiple long-term point sources beneath Building 100, a 4.5 ha (11 acre) building that housed manufacturing facilities during US DOE operations at the site. The site is now owned by Pinellas County, and most of the space inside the building is leased to private companies, so DOE chose not to conduct characterization or remediation through the floor of the building, instead choosing to conduct all work from outside the building. Injection of emulsified soybean oil and a microbial culture has been used at other areas of the site to accelerate naturally occurring bacterial processes that degrade groundwater contaminants to harmless compounds, and that same approach was chosen for this task. The technical approach consisted of installing horizontal wells from outside the building footprint, extending through and around the identified subsurface treatment areas, and terminating beneath the building. Two 107 m (350 ft) long wells, two 122 m (400 ft) long wells, and four 137 m (450 ft) long wells have been installed to intersect the inferred source areas and confirmed contaminant plumes beneath the building. DOE then injected emulsified vegetable oil and a microbial culture into the horizontal wells at each of several target areas beneath the building where the highest groundwater contaminant concentrations have been detected. The target areas are the northwest corner of the building between the old drum storage pad locations and monitoring well PIN12-S35B, the vicinity of

  4. The South Tibetan Tadpole Zone: Ongoing density sorting at the Moho beneath the Indus-Tsangpo suture zone (and beneath volcanic arcs?)

    Science.gov (United States)

    Kelemen, Peter; Hacker, Bradley

    2016-04-01

    Some Himalayan cross-sections show Indian crust thrust beneath Tibetan crust, with no intervening mantle wedge (e.g., Powell & Conaghan 73), others indicate thickening of both crustal sections, juxtaposed along a steep suture (e.g., Dewey & Burke 73), and many combine features of both end-members (e.g., Argand 24). To understand crustal scale structure and related phenomena, we focus on data from an area in southern Tibet at 28-30°N, 84-91°E. 21st century observations in this area show a horizontal Moho at ca 80 km depth, extending from thickened Indian crust, across a region where Tibetan crust is interpreted to overlie Indian crust, into thickened Tibetan crust (Zhao et al 01; Monsalve et al 08; Wittlinger et al 09; Nabelek et al 09; Kind et al 02; Schulte-Pelkum et al 05; Shi et al 15). About half the subducted Indian crustal volume is present, whereas the other half is missing (Replumaz et al 10). Vp/Vs indicates the alpha-beta quartz transition is at ca 50 km depth (Sheehan et al 13). Miocene lavas include primitive andesites probably formed by interaction of crustal material with mantle peridotite at > 1000°C (Turner et al 93; Williams et al 01, 04; Chung et al 05). Thermobarometry of xenoliths in a 12.7 Ma dike records ~ 1100°C at 2.2-2.6 GPa and 920°C at 1.7 GPa (Chan et al 09). Biotite-rich pyroxenites among the xenoliths, similar to those in central Tibet (Hacker et al 00) and the Pamirs (Hacker et al 05), may form via reaction of hot crustal lithologies and mantle peridotite (e.g., Sekine & Wyllie 82, 83). These data, taken together, indicate Miocene to present day temperatures exceeding 800°C from ca 50 km depth to the Moho, unlike thermal models with a hot mid-crust and cold Moho (McKenzie & Priestley 08, Craig et al 12, Wang et al 13; Nabelek & Nabelek 14), and despite the observation of numerous, near-Moho earthquakes (Chen & Molnar 83; Chen & Yang 04; Monsalve et al 06; Priestley et al 08; Craig et al 12) interpreted by many as brittle failure

  5. Annual emissions of CH4 and N2O, and ecosystem respiration, from eight organic soils in Western Denmark managed by agriculture

    Science.gov (United States)

    Petersen, S. O.; Hoffmann, C. C.; Schäfer, C.-M.; Blicher-Mathiesen, G.; Elsgaard, L.; Kristensen, K.; Larsen, S. E.; Torp, S. B.; Greve, M. H.

    2012-01-01

    The use of organic soils by agriculture involves drainage and tillage, and the resulting increase in C and N turnover can significantly affect their greenhouse gas balance. This study estimated annual fluxes of CH4 and N2O, and ecosystem respiration (Reco), from eight organic soils managed by agriculture. The sites were located in three regions representing different landscape types and climatic conditions, and three land use categories were covered (arable crops, AR, grass in rotation, RG, and permanent grass, PG). The normal management at each site was followed, except that no N inputs occurred during the monitoring period from August 2008 to October 2009. The stratified sampling strategy further included six sampling points in three blocks at each site. Environmental variables (precipitation, PAR, air and soil temperature, soil moisture, groundwater level) were monitored continuously and during sampling campaigns, where also groundwater samples were taken for analysis. Gaseous fluxes were monitored on a three-weekly basis, giving 51, 49 and 38 field campaigns for land use categories AR, PG and RG, respectively. Climatic conditions in each region during monitoring were representative as compared to 20-yr averages. Peat layers were shallow, typically 0.5 to 1 m, and with a pH of 4 to 5. At six sites annual emissions of N2O were in the range 3 to 24 kg N2O-N ha-1, but at two arable sites (spring barley, potato) net emissions of 38 and 61 kg N2O-N ha-1 were recorded. The two high-emitting sites were characterized by fluctuating groundwater, low soil pH and elevated groundwater SO42- concentrations. Annual fluxes of CH4 were generally small, as expected, ranging from 2 to 4 kg CH4 ha-1. However, two permanent grasslands had tussocks of Juncus effusus L. (soft rush) in sampling points that were consistent sources of CH4 throughout the year. Emission factors for organic soils in rotation and with permanent grass, respectively, were estimated to be 0.011 and 0.47 g m-2

  6. Effects of Moisture and Grain Sizes on Rainsplash Transport with Implications for Desert Plant-Soil Interactions

    Science.gov (United States)

    Taube, S. R.; Furbish, D. J.; Roberts, A. S.

    2009-12-01

    Soil mounds beneath desert shrubs can develop from sediment transport associated with rainsplash of soil grains around the plants. As the canopy of a plant protects the underlying soil from the raindrop impacts, sediment accumulates beneath the shrub canopy due to differential rainsplash of grains. Previous work has clarified how rainsplash transport varies with raindrop momentum and with different sizes of dry sediment, focusing on the transfer of momentum of the drops to grains during drop impacts. Details of this transfer of momentum and grain mobilization for moist sediment conditions are not well known, which is important for understanding sediment transport by rainsplash during the progression of storms. Moreover, related work suggests that relatively immobile coarse soil grains are less likely to be splashed beneath shrub canopies than are small grains, so that smaller grains are more likely to accumulate within shrub mounds. However, systematic measurements of sediment grain sizes around and beneath desert shrubs in the Cibola National Forest, New Mexico, suggest that, aside from the coarsest lag material, larger grain sizes (0.5 - 1.5 mm) are preferentially concentrated within the mound surfaces close to the shrubs. This pattern of grain-size sorting is likely associated with effects of moisture, wherein small grains tend to be ejected during drop impacts as grain clumps rather than individually due to surface tension, and thereby behave as relative coarse grains with shorter splash distances. High-speed imaging of drop impacts on sediment reveals this clumping behavior. These results may be useful in determining the dispersal of nutrients and contaminants that preferentially adhere to the smaller grain sizes. This information also extends our understanding of rainsplash transport beyond dry conditions, that is, to storm conditions where soil moisture and grain detachment rates are changing.

  7. Trees and Weathering: Using Soil Petrographic and Chemical Analyses to Compare the Relative Weathering Effects of Gymnosperms and Angiosperms in the Cascade Mountains of Washington State, USA

    Science.gov (United States)

    Andrews, M. Y.; Ague, J. J.; Berner, R. A.

    2006-12-01

    Knowledge of the long-term carbon cycle and its control on atmospheric carbon dioxide levels over the Phanerozoic is crucial to understanding the impending dynamics of contemporary anthropogenic carbon contributions to the atmosphere. One aspect of the long-term carbon cycle that is poorly understood is the role of large vascular plants (trees) in contributing to the chemical weathering of silicate minerals. In particular, little is known about the differences in weathering rates between gymnosperms and angiosperms and how these dissimilarities may have impacted the carbon cycle subsequent to the evolution of angiosperm trees in the Mesozoic. One approach to evaluating these potential differences in weathering is to examine and quantitatively compare the chemistry and petrology of the soil mineral constituents from beneath modern groves of each broad tree type, where the groves have been subject to nearly identical environmental and geological conditions. This particular study focuses on field samples collected along transects through adjacent groves of angiosperms and gymnosperms in the Cascade Mountains of Washington State. Preliminary data demonstrate a significant difference in the soil texture and composition beneath the two types of trees. While soil at each field site has been generated from a homogeneous parent material, and subjected to similar inorganic environmental phenomena, soil density, particle size, and organic content vary across the transects. Soils beneath the angiosperms are denser and have a more clay-like texture, while soils beneath the gymnosperms are more organic-rich and have a sandy texture. Additional macroscopic and microscopic differences in the chemistry and petrology of these soils will illuminate the varied impacts these trees have on the silicate minerals in their immediate environment, and therefore lend insight into the potential impact these groups of organisms have had on the long-term carbon cycle over the past five hundred

  8. Impact of Residential Prairie Gardens on the Physical Properties of Urban Soil in Madison, Wisconsin.

    Science.gov (United States)

    Johnston, Marie R; Balster, Nick J; Zhu, Jun

    2016-01-01

    Prairie gardens have become a common addition to residential communities in the midwestern United States because prairie vegetation is native to the region, requires fewer resources to maintain than turfgrass, and has been promoted to help remediate urban soil. Although prairie systems typically have deeper and more diverse root systems than traditional turfgrass, no one has tested the effect of this vegetation type on the physical properties of urban soil. We hypothesized that residential prairie gardens would yield lower soil bulk density (BD), lower penetration resistance (PR), greater soil organic matter (SOM), and greater saturated hydraulic conductivity () compared with turfgrass lawns. To test this hypothesis, we examined 12 residential properties in Madison, WI, where homeowners had established a prairie garden within their turfgrass lawn. Despite a consistent trend in the difference between vegetation types, no significant main effects were found (i.e., a difference between vegetation types when averaged over depth) for any of the four soil properties measured in this study. Differences were found with depth and depended on a significant interaction with vegetation type. At the surface depth (0-0.15 m), soil beneath prairie gardens had 10% lower mean BD, 15% lower mean PR, 25% greater level of SOM, and 33% greater compared with soil beneath the adjacent lawns. These differences were not detected at deeper sampling intervals of 0.15 to 0.30 m and 0.30 to 0.45 m. Although not statistically significant, the consistent trend and direction among soil variables suggest that residential prairie gardens had changed the surface soil at a rate that marginally outpaced turfgrass and calls for controlled experiments to identify the mechanisms that might enhance these trends.

  9. Soil use and management

    NARCIS (Netherlands)

    Hartemink, A.E.; McBratney, A.B.; White, R.E.

    2009-01-01

    This four-volume set, edited by leading experts in soil science, brings together in one collection a series of papers that have been fundamental to the development of soil science as a defined discipline. Volume 3 on Soil Use and Management covers: - Soil evaluation and land use planning - Soil and

  10. Seismic structure and composition of the crust beneath the southern Scandes, Norway

    DEFF Research Database (Denmark)

    Stratford, Wanda Rose; Thybo, Hans

    2011-01-01

    New results on P and S-wave seismic velocity structure in southern Norway indicate that the crust has an average Poisson's ratio of 0.25, is predominantly of felsic-intermediate composition and lacks a significant mafic lower crust. A crustal scale refraction seismic study (Magnus-Rex — Mantle...... investigations of Norwegian uplift structure, refraction experiment) acquired data along three 300 to 400 km long active source seismic profiles across the Southwest Scandinavian Domain in southern Norway, the youngest section of the Fennoscandian shield. Moho depths in the Domain are 36–40 km, thinning towards...... the continental shelf and Oslo Graben. The high Vp lower crust beneath the Southwest Scandinavian Domain (Vp > 7 km/s) is around 4 km thick. Crustal structure in the adjacent Svecofennian Domain differs significantly; Moho depths reach ~ 50 km and an up to 24 km thick high Vp lower crust is present. Strong P...

  11. Topographies of seismic velocity discontinuities and penetrations of subducting slabs beneath the Sea of Okhotsk

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The existence of discontinuities, the topographies of the 410 km and 660 km discontinuities, and the penetrations of subducting slabs near the 660 km discontinuities beneath the Sea of Okhotsk were studied using Nth root slant stack and digital records from networks in Germany and the western United States. Results show the obvious evidence for reflected and refractive phases associated with the 410 km and 660 km discontinuities. There may be discontinuities at other depths such as 150 km, 220 km and 520 km. The 410 km discontinuity is elevated and the 660 km discontinuity is depressed respectively, consistent with the expected thermal signature of the phase transitions. The subducting slab has penetrated into the lower mantle in the northern part of the Sea of Okhotsk, while it is stagnant on the 660 km discontinuity in the southern part.

  12. Preliminary results of characteristic seismic anisotropy beneath Sunda-Banda subduction-collision zone

    Science.gov (United States)

    Wiyono, Samsul H.; Nugraha, Andri Dian

    2015-04-01

    Determining of seismic anisotropy allowed us for understanding the deformation processes that occured in the past and present. In this study, we performed shear wave splitting to characterize seismic anisotropy beneath Sunda-Banda subduction-collision zone. For about 1,610 XKS waveforms from INATEWS-BMKG networks have been analyzed. From its measurements showed that fast polarization direction is consistent with trench-perpendicular orientation but several stations presented different orientation. We also compared between fast polarization direction with absolute plate motion in the no net rotation and hotspot frame. Its result showed that both absolute plate motion frame had strong correlation with fast polarization direction. Strong correlation between the fast polarization direction and the absolute plate motion can be interpreted as the possibility of dominant anisotropy is in the asthenosphere..

  13. Preliminary results of characteristic seismic anisotropy beneath Sunda-Banda subduction-collision zone

    Energy Technology Data Exchange (ETDEWEB)

    Wiyono, Samsul H., E-mail: samsul.wiyono@bmkg.go.id [Study Program of Earth Sciences, Faculty of Earth Sciences and Technology, Institute of Technology Bandung, Bandung 40132 (Indonesia); Indonesia’s Agency for Meteorology Climatology and Geophysics, Jakarta 10610 (Indonesia); Nugraha, Andri Dian, E-mail: nugraha@gf.itb.ac.id [Indonesia’s Agency for Meteorology Climatology and Geophysics, Jakarta 10610 (Indonesia); Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institute of Technology Bandung, Bandung 40132, Indonesia, Phone: +62-22 2534137 (Indonesia)

    2015-04-24

    Determining of seismic anisotropy allowed us for understanding the deformation processes that occured in the past and present. In this study, we performed shear wave splitting to characterize seismic anisotropy beneath Sunda-Banda subduction-collision zone. For about 1,610 XKS waveforms from INATEWS-BMKG networks have been analyzed. From its measurements showed that fast polarization direction is consistent with trench-perpendicular orientation but several stations presented different orientation. We also compared between fast polarization direction with absolute plate motion in the no net rotation and hotspot frame. Its result showed that both absolute plate motion frame had strong correlation with fast polarization direction. Strong correlation between the fast polarization direction and the absolute plate motion can be interpreted as the possibility of dominant anisotropy is in the asthenosphere.

  14. Upper mantle SH velocity structure beneath Qiangtang Terrane by modeling triplicated phases

    Institute of Scientific and Technical Information of China (English)

    ZHANG RuiQing; WU QingJu; LI YongHua; ZENG RongSheng

    2008-01-01

    We constrain SH wave velocity structure for the upper mantle beneath western Qiangtang Terrane by comparing regional distance seismic triplicated waveforms with synthetic seismograms, based on an intermediate event (~220 km) recorded by the INDEPTH-Ⅲ seismic array. The ATIP model reveals a low-velocity anomaly with up to -4% variation at the depth of 190--270 km and a relatively small ve-locity gradient above the depth of 410 km in the upper mantle, which is in agreement with previous results. In combination with other geological studies, we suggest that the depth of top asthenosphere is 190 km and no large-scale lithosphere thinning occurs in western Qiangtang Terrane, besides, Qiangtang Terrane has the same kind of upper mantle structure as the stable Eurasia.

  15. High-resolution seismic attenuation structures beneath Hokkaido corner, northeastern Japan

    Science.gov (United States)

    Kita, S.; Nakajima, J.; Okada, T.; Hasegawa, A.; Katsumata, K.; Asano, Y.; Uchida, N.

    2013-12-01

    1. Introduction In the Hokkaido corner, the Kuril fore-arc sliver collides with the northeastern Japan arc. Using data from the nationwide Kiban seismic network and a temporary seismic network, Kita et al. [2012] determined high-resolution 3D seismic velocity structure beneath this area for deeper understanding of the collision process of two fore-arcs. The results show that a broad low-V zone (crust material) anomalously descends into the mantle wedge at depths of 30-90 km in the west of the Hidaka main thrust. On the other hand, several high-velocity zones having velocities of mantle materials are distributed in the crust at depths of 10-35 km. These high-velocity zones are inclined eastward, being nearly parallel to each other. Two of the western boundaries of these high-V zones correspond to the fault planes of the 1970 Mj 6.7 Hidaka and the 1982 Mj 7.1 Urakawa-oki earthquakes, respectively. In this study, we merged waveform data from the Kiban-network and from a dense temporary seismic network [Katsumata et al., 2002], and estimated the seismic attenuation structure to compare with the seismic velocity images of Kita et al. [2012]. 2. Data and method We estimated corner frequency for each earthquake by the spectral ratio method using the coda waves [e.g. Mayeda et al., 2007]. Then, we simultaneously determined values of t* and the amplitude level at lower frequencies from the observed spectra after correcting for the source spectrum. Seismic attenuation (Q-1 value) structure was obtained, inverting t* values with the tomographic code of Zhao et al. [1992]. We adopted the geometry of the Pacific plate which was precisely estimated by Kita et al. [2010b]. The study region covers an area of 41-45N, 140.5-146E, and a depth range of 0-200 km. We obtained 131,958 t* from 6,186 events (M>2.5) that occurred during the period from Aug. 1999 to Dec. 2012. The number of stations used is 353. Horizontal and vertical grid nodes were set with spacing of 0.10-0.3 degree and

  16. Radiological status of the ground water beneath the Hanford project, January-December 1979

    Energy Technology Data Exchange (ETDEWEB)

    Eddy, P.A.; Wilbur, J.S.

    1980-04-01

    Operations on the Hanford Site since 1944 have resulted in discharge of large volumes of process cooling water and low-level liquid radioactive waste to the ground. Radioactivity and chemical substances have been carried with these discharges and have reached the Hanford ground water. For may years wells have been used as groundwater sampling structures to gather data on the distribution and movement of these discharges as they interact with the unconfined ground water beneath the site. During 1979, 317 wells were sampled on various frequencies from weekly to annually. This report is one of a series prepared annually to document the evaluation of the status of ground water on the Hanford Site. Data collected during 1979 describe the movement of radionuclide (Tritium and Beta) and nitrate plumes that respond to the influence of groundwater flow, ionic dispersion and radioactive decay.

  17. Detailed crustal thickness variations beneath the Illinois Basin area: Implications for crustal evolution of the midcontinent

    Science.gov (United States)

    Yang, Xiaotao; Pavlis, Gary L.; Hamburger, Michael W.; Marshak, Stephen; Gilbert, Hersh; Rupp, John; Larson, Timothy H.; Chen, Chen; Carpenter, N. Seth

    2017-08-01

    We present high-resolution imaging results of crustal and upper mantle velocity discontinuities across the Illinois Basin area using both common conversion point stacking and plane wave migration methods applied to P wave receiver functions from the EarthScope Ozark, Illinois, Indiana, and Kentucky experiment. The images reveal unusually thick crust (up to 62 km) throughout the central and southeastern Illinois Basin area. A significant Moho gradient underlies the NW trending Ste. Genevieve Fault Zone, which delineates the boundary between the Illinois Basin and Ozark Dome. Relatively thinner crust (convergent margin tectonics around 1.55-1.35 Ga; (3) by Late Precambrian magmatic underplating at the base of older crust, associated with the creation of the Eastern Granite-Rhyolite Province around 1.3 Ga; and (4) through crustal "relamination" during an episode of Proterozoic flat-slab subduction beneath the Illinois Basin, possibly associated with the Grenville Orogeny.

  18. Evidence for a large-scale remnant of subducted lithosphere beneath Fiji.

    Science.gov (United States)

    Chen, W P; Brudzinski, M R

    2001-06-29

    We combine spatial variations of P- and S-wave speeds, 1000 fault plane solutions, and 6600 well-determined hypocenters to investigate the nature of subducted lithosphere and deep earthquakes beneath the Tonga back-arc. We show that perplexing patterns in seismicity and fault plane solutions can be accounted for by the juxtaposition of a steep-dipping Wadati-Benioff zone and a subhorizontal remnant of slab that is no longer attached to the actively subducting lithosphere. The detached slab may be from a previous episode of subduction along the fossil Vitiaz trench about 5 to 8 million years ago. The juxtaposition of slabs retains a large amount of subducted material in the transition zone of the mantle. Such a configuration, if common in the past, would allow the preservation of a primordial component in the lower mantle.

  19. Horizontally opposed trunnion forward engine mount system supported beneath a wing pylon

    Science.gov (United States)

    Seaquist, John D. (Inventor); Culbertson, Chris (Inventor)

    2000-01-01

    The present invention relates to an engine mount assembly for supporting an aircraft engine in aft-cantilevered position beneath the aircraft wing. The assembly includes a pair forward engine mounts positioned on opposite sides of an integrally formed yoke member wrapped about the upper half of the engine casing. Each side of the yoke is preferably configured as an A-shaped frame member with the bottom portions joining each other and the pylon. To prevent backbone bending of the engine trunnion assembly, the forward engine mounts supported at opposite ends of the yoke engage the casing along its centerline. The trunnion assembly is preferably constructed of high strength titanium machined and/or forged.

  20. A one-dimensional model of solid-earth electrical resistivity beneath Florida

    Science.gov (United States)

    Blum, Cletus; Love, Jeffrey J.; Pedrie, Kolby; Bedrosian, Paul A.; Rigler, E. Joshua

    2015-11-19

    An estimated one-dimensional layered model of electrical resistivity beneath Florida was developed from published geological and geophysical information. The resistivity of each layer is represented by plausible upper and lower bounds as well as a geometric mean resistivity. Corresponding impedance transfer functions, Schmucker-Weidelt transfer functions, apparent resistivity, and phase responses are calculated for inducing geomagnetic frequencies ranging from 10−5 to 100 hertz. The resulting one-dimensional model and response functions can be used to make general estimates of time-varying electric fields associated with geomagnetic storms such as might represent induction hazards for electric-power grid operation. The plausible upper- and lower-bound resistivity structures show the uncertainty, giving a wide range of plausible time-varying electric fields.

  1. Experimental and Numerical Study of Wave-Induced Backfilling Beneath Submarine Pipelines

    DEFF Research Database (Denmark)

    Bayraktar, Deniz; Ahmad, Joseph; Eltard-Larsen, Bjarke

    -coupled hydrodynamicand morphodynamic CFD model (Jacobsen et al., 2014),extending previous pipeline scour-related applications ofFuhrman et al. (2014) and Larsen et al. (2016). Comparison of the numerical and experimental results demonstrate the ability of the CFD model to reasonably simulate the current......Through complementary experimental and numerical efforts, the present paper aims to make a significant contribution to the overall understanding of backfilling processes beneath submarine pipelines. For this purpose, we aim to simplify the experimental backfilling process to an elementary two......-stage process: (1) initial scour induced by a pure current, followed by: (2) backfilling induced by pure waves. A steady current is introduced via a re-circulating pump, and is kept constant with a cross-sectional velocity of V = 0.48 m/s until an initial equilibrium scour depth, S0, is reached. Then...

  2. Numerical simulation of wave-induced scour and backfilling processes beneath submarine pipelines

    DEFF Research Database (Denmark)

    Fuhrman, David R.; Baykal, Cüneyt; Sumer, B. Mutlu

    2014-01-01

    A fully-coupled hydrodynamic/morphodynamic numerical model is presented and utilized for the simulation of wave-induced scour and backfilling processes beneath submarine pipelines. The model is based on solutions to Reynolds-averaged Navier–Stokes equations, coupled with k−ω turbulence closure......≤30 demonstrate reasonable match with previous experiments, both in terms of the equilibrium scour depth as well as the scour time scale. Wave-induced backfilling processes are additionally studied by subjecting initial conditions taken from scour simulations with larger KC to new wave climates...... characterized by lower KC values. The simulations considered demonstrate the ability of the model to predict backfilling toward expected equilibrium scour depths based on the new wave climate, in line with experimental expectations. The simulated backfilling process is characterized by two stages: (1...

  3. Seismic structure of the lithosphere beneath the ocean islands near the mid-oceanic ridges

    Science.gov (United States)

    Haldar, C.; Kumar, P.; Kumar, M. Ravi

    2013-10-01

    Deciphering the seismic character of the young lithosphere near the mid-oceanic ridges (MOR) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs, using the P-to-s conversions isolated from good quality data recorded at 5 broadband seismological stations situated on the ocean Islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform modeling of the P receiver function stacks reveal that the crustal thickness varies between 6 and 8 km with the corresponding depths to the lithosphere asthenosphere boundary (LAB) varying between 43 and 68 km. However, the depth to the LAB at Macquire Island is intriguing in view of the observation of a thick (~ 87 km) lithosphere beneath a relatively young crust. At three other stations i.e., Ascension Island, Sao Jorge and Easter Island, we find evidence for an additional deeper low velocity layer probably related to the presence of a hotspot.

  4. A comprehensive analysis of contaminant transport in the vadose zone beneath tank SX-109

    Energy Technology Data Exchange (ETDEWEB)

    Ward, A.L.; Gee, G.W.; White, M.D.

    1997-02-01

    The Vadose Zone Characterization Project is currently investigating the subsurface distribution of gamma-emitting radionuclides in S and SX Waste Management Area (WMA-S-SX) located in the 200 West Area of the US Department of Energy`s Hanford Site in southeastern Washington State. Spectral-gamma logging of boreholes has detected elevated {sup 137}Cs concentrations as deep as 38 m, a depth considered excessive based on the assumed geochemistry of {sup 137}Cs in Hanford sediments. Routine groundwater sampling under the Resource Conservation and Recovery Act (RCRA) have also detected elevated levels of site-specific contaminants downgradient of WMA-S-SX. The objective of this report is to explore the processes controlling the migration of {sup 137}Cs, {sup 99}Tc, and NO{sub 3} through the vadose zone of WMA-S-SX, particularly beneath tank SX-109.

  5. New constraints on the textural and geochemical evolution of the upper mantle beneath the Styrian basin

    Science.gov (United States)

    Aradi, Laszlo; Hidas, Károly; Zanetti, Alberto; János Kovács, István; Patkó, Levente; Szabó, Csaba

    2016-04-01

    Plio-Pleistocene alkali basaltic volcanism sampled sporadically the upper mantle beneath the Carpathian-Pannonian Region (CPR, e.g. [1]). Lavas and pyroclasts often contain mantle derived xenoliths, and the majority of them have been extensively studied [1], except the westernmost Styrian Basin Volcanic Field (SBVF, Eastern Austria and Slovenia). In the SBVF only a few volcanic centers have been studied in details (e.g. Kapfenstein & Tobaj). Based on these studies, the upper mantle beneath the SBVF is consists of dominantly high temperature, texturally and geochemically homogeneous protogranular spinel lherzolite. New major and trace element data from rock-forming minerals of ultramafic xenoliths, coupled with texture and deformation analysis from 12 volcanic outcrops across the SBVF, suggest that the lithospheric roots of the region are more heterogeneous than described previously. The studied xenoliths are predominantly lherzolite, amphibole is a common phase that replaces pyroxenes and spinels and proves modal metasomatism. Phlogopite coupled with apatite is also present in amphibole-rich samples. The texture of the xenoliths is usually coarse-grained and annealed with low abundance of subgrain boundaries in both olivine and pyroxenes. Olivine crystal preferred orientation (CPO) varies between the three most abundant one: [010]-fiber, orthogonal and [100]-fiber symmetry [2]. The CPO of pyroxenes is usually coherent with coeval deformation with olivine, however the CPO of amphibole is suggesting postkinematic epitaxial overgrowth on the precursor pyroxenes. According to equilibrium temperatures, the studied xenolith suite samples a broader temperature range (850-1100 °C) than the literature data, corresponding to mantle depths between 30 and 60 km, which indicates that the xenolith suite only represents the shallower part of the recent 100 km thick lithospheric mantle beneath the SBVF. The equilibrium temperatures show correlation with the varying CPO symmetries

  6. Seismic Evidence for a Low-Velocity Zone in the Upper Crust Beneath Mount Vesuvius

    Science.gov (United States)

    Zollo, A.; Gasparini, P.; Virieux, J.; Le Meur, H.; de Natale, G.; Biella, G.; Boschi, E.; Capuano, P.; de Franco, R.; dell'Aversna, P.; de Matteis, R.; Guerra, I.; Iannaccone, G.; Mirabile, L.; Vilardo, G.

    1996-10-01

    A two-dimensional active seismic experiment was performed on Mount Vesuvius: Explosive charges were set off at three sites, and the seismic signal along a dense line of 82 seismometers was recorded. A high-velocity basement, formed by Mesozoic carbonates, was identified 2 to 3 kilometers beneath the volcano. A slower (P-wave velocity V_P backsimeq 3.4 to 3.8 kilometers per second) and shallower high-velocity zone underlies the central part of the volcano. Large-amplitude late arrivals with a dominant horizontal wave motion and low-frequency content were identified as a P to S phase converted at a depth of about 10 kilometers at the top of a low-velocity zone (V_P < 3 kilometers per second), which might represent a melting zone.

  7. Water exchange between the continental shelf and the cavity beneath Nioghalvfjerdsbræ (79 North Glacier)

    Science.gov (United States)

    Wilson, N. J.; Straneo, F.

    2015-09-01

    The mass loss at Nioghalvfjerdsbræ is primarily due to rapid submarine melting. Ocean data obtained from beneath the Nioghalvfjerdsbræ ice tongue show that melting is driven by the presence of warm (1°C) Atlantic Intermediate Water (AIW). A sill prevents AIW from entering the cavity from Dijmphna Sund, requiring that it flow into the cavity via bathymetric channels to the south at a pinned ice front. Comparison of water properties from the cavity, Dijmphna Sund, and the continental shelf support this conclusion. Overturning circulation rates inferred from observed melt rates and cavity stratification suggest an exchange flow between the cavity and the continental shelf of 38mSv, sufficient to flush cavity waters in under 1 year. These results place upper bounds on the timescales of external variability that can be transmitted to the glacier via the ice tongue cavity.

  8. Evidence for mechanical coupling and strong Indian lower crust beneath southern Tibet.

    Science.gov (United States)

    Copley, Alex; Avouac, Jean-Philippe; Wernicke, Brian P

    2011-04-07

    How surface deformation within mountain ranges relates to tectonic processes at depth is not well understood. The upper crust of the Tibetan Plateau is generally thought to be poorly coupled to the underthrusting Indian crust because of an intervening low-viscosity channel. Here, however, we show that the contrast in tectonic regime between primarily strike-slip faulting in northern Tibet and dominantly normal faulting in southern Tibet requires mechanical coupling between the upper crust of southern Tibet and the underthrusting Indian crust. Such coupling is inconsistent with the presence of active 'channel flow' beneath southern Tibet, and suggests that the Indian crust retains its strength as it underthrusts the plateau. These results shed new light on the debates regarding the mechanical properties of the continental lithosphere, and the deformation of Tibet.

  9. Visual soil evaluation and soil compaction research

    DEFF Research Database (Denmark)

    M.L. Guimarães, Rachel; Keller, Thomas; Munkholm, Lars Juhl

    2017-01-01

    to organize a joint workshop. The present special issue is an outcome from the workshop on “Soil structural quality of tropical soils: Visual evaluation methods and soil compaction prevention strategies” that was held 26–29 May 2014 in Maringá, Paraná, Brazil. There has been a long-lasting interest in Visual...... and climatic conditions, as well as in utilizing VSE methods together with qualitative methods to evaluate the impact of soil management (Munkholm et al., 2013). Soil compaction due to agricultural operations is a serious threat to soil productivity and soil ecological functions and has been a key research...... Soil Evaluation (VSE). An ISTRO working group was established more than 30 years ago with the objectives to exchange knowledge and experiences on field methods of visual-tactile soil assessment and to foster international cooperation on new or refined methods. The three previous meeting of the group...

  10. Decoupling of Pacific subduction zone guided waves beneath central Japan: Evidence for thin slab

    Science.gov (United States)

    Padhy, Simanchal; Furumura, Takashi; Maeda, Takuto

    2014-11-01

    The fine-scale seismic structure of the northeast Japan subduction zone is studied based on waveform analyses of moderate-sized (M4.5-6), deep-focus earthquakes (h >350 km) and the finite difference method (FDM) simulation of high-frequency (up to 8 Hz) wave propagation. Strong regional S wave attenuation anomalies for specific source-receiver paths connecting the cluster of events occurring in central part of the Sea of Japan recorded at fore arc stations in northern and central Japanese Islands (Honshu) are used to model the deeper structure of the subducting Pacific Plate, where recent teleseismic tomography has shown evidence for a possible slab tear westward beneath the Sea of Japan. The character of the observed anomalous S wave attenuation and the following high-frequency coda can be captured with the two-dimensional (2-D) FDM simulation of seismic waves in heterogeneous plate model, incorporating the thinning of the plate at depth, which is also compared with other possible causes of dramatic attenuation of high-frequency S wave due to low-Q or much weaker heterogeneities in the slab. The results of simulation clearly demonstrate that the dramatic loss of high-frequency S wavefield from the plate into the surrounding mantle occurred due to the variation in the plate geometry (i.e., thinning of the plate) at depth near the source rather than due to variation in physical properties, such as due to the lowered-Q and weaker heterogeneities in the plate. The presence of such a thin zone defocuses the high-frequency slab-guided S wave energy from the subducting plate into the surrounding mantle and acts as a geometric antiwaveguide. Based on the sequence of simulation results obtained, we propose thinning of Pacific Plate at depth subducting beneath northeastern Japan, localized to central part of Honshu, in agreement with the observations.

  11. Estimation of the Crustal Bulk Properties Beneath Mainland Portugal from P-Wave Teleseismic Receiver Functions

    Science.gov (United States)

    Dündar, Süleyman; Dias, Nuno A.; Silveira, Graça; Kind, Rainer; Vinnik, Lev; Matias, Luís; Bianchi, Marcelo

    2016-06-01

    In this work, we present results from teleseismic P-wave receiver functions (PRFs) obtained in Portugal, Western Iberia. A dense seismic station deployment conducted between 2010 and 2012, in the scope of the WILAS project and covering the entire country, allowed the most spatially extensive probing on the bulk crustal seismic properties of Portugal up to date. The application of the H- κ stacking algorithm to the PRFs enabled us to estimate the crustal thickness ( H) and the average crustal ratio of the P- and S-waves velocities V p/ V s ( κ) for the region. Observations of Moho conversions indicate that this interface is relatively smooth with the crustal thickness ranging between 24 and 34 km, with an average of 30 km. The highest V p/ V s values are found on the Mesozoic-Cenozoic crust beneath the western and southern coastal domain of Portugal, whereas the lowest values correspond to Palaeozoic crust underlying the remaining part of the subject area. An average V p/ V s is found to be 1.72, ranging 1.63-1.86 across the study area, indicating a predominantly felsic composition. Overall, we systematically observe a decrease of V p/ V s with increasing crustal thickness. Taken as a whole, our results indicate a clear distinction between the geological zones of the Variscan Iberian Massif in Portugal, the overall shape of the anomalies conditioned by the shape of the Ibero-Armorican Arc, and associated Late Paleozoic suture zones, and the Meso-Cenozoic basin associated with Atlantic rifting stages. Thickened crust (30-34 km) across the studied region may be inherited from continental collision during the Paleozoic Variscan orogeny. An anomalous crustal thinning to around 28 km is observed beneath the central part of the Central Iberian Zone and the eastern part of South Portuguese Zone.

  12. Geometry of the Subducting Nazca Plate Beneath Colombia From Relocation of Intermediate-Depth Earthquakes

    Science.gov (United States)

    Chang, Y.; Warren, L. M.; Prieto, G. A.; Grigsby, I.

    2013-12-01

    In subduction zones, earthquakes help distinguish the location of the downgoing slab to hundreds of kilometers depth. However, beneath northwestern South America, the distribution of large intermediate-depth earthquakes in the Global CMT catalog has gaps along the subduction zone, so the position of the subducting Nazca plate is uncertain. In addition, the earthquake focal mechanisms, which range from along-strike compression to down-dip extension, vary over short distances, suggesting that the subducting slab may have a complicated morphology. To clarify the geometry of the subducting Nazca plate beneath Colombia, we relocate regional seismicity recorded by the Colombian National Seismic Network (RSNC). Our data set contains 1231 earthquakes with catalog locations from 0°N-6°N and 72°W-81°W at depths of 0-200 km and magnitudes from M2.5-6.5 that occurred between 1/2010-2/2013. Catalog hypocenters show an ~20 km thick slab subducting to the east, as well as vertical columns extending up from the slab. The shape, thickness, and position of the slab and other features can be refined by using differential travel times to relocate the earthquakes relative to each other. We verify and adjust the network P and S wave picks and pick arrivals at additional or temporary stations, and these arrival times are used to relocate the earthquakes. The hypocenters of the relocated earthquakes are used to generate 3D contours of the subducting plate and visualize bends and folds in the slab.

  13. Dynamics of Caribbean and Nazca Plate Subduction Beneath Colombia from Receiver Function Analysis

    Science.gov (United States)

    Porter, R. C.; Warren, L. M.

    2014-12-01

    The tectonics of northwestern South America are controlled by the complex interactions of the South American, Nazca, and Caribbean plates. In order to better understand subduction within the region, we utilize data recorded by the Colombian National Seismic Network to calculate P-to-S receiver functions at a range of frequencies across the nation of Colombia. Where the station spacing was dense enough, receiver functions were stacked using the Common Conversion Point (CCP) method in order to better image lateral changes in crustal and upper mantle structure. Along the Pacific margin of Colombia, where the Nazca plate is subducting beneath South America, the subducting slab dips too steeply to image it with receiver functions. However, layering and strong negative arrivals are observed in the crust above the subducting slab where active volcanoes are present. The presence of these arrivals is possibly indicative of slab dehydration and the presence of partial melt within the crust. In northeastern Colombia, the Caribbean plate is subducting beneath South America at an oblique angle. Along the direction of convergence, the slab extends ~500 km inland with a relatively shallow dip before steepening. Preliminary receiver function images from this region show a shallowly-dipping negative arrival, interpreted as the top of the slab. This arrival is underlain by a positive conversion, interpreted as the down-going oceanic Moho. As the dip of the seismicity associated with the subducting slab steepens, these arrivals are no longer observed within the receiver function stacks. These cross sections of the Caribbean plate subduction are consistent with the idea that phase changes within the downgoing oceanic crust and mantle are controlling the slab buoyancy and, as a result, the angle of subduction. As the receiver functions are refined and further combined with local earthquake locations, we will better be able to understand the location of earthquakes within the subducting

  14. Exploring information from the topology beneath the Gene Ontology terms to improve semantic similarity measures.

    Science.gov (United States)

    Zhang, Shu-Bo; Lai, Jian-Huang

    2016-07-15

    Measuring the similarity between pairs of biological entities is important in molecular biology. The introduction of Gene Ontology (GO) provides us with a promising approach to quantifying the semantic similarity between two genes or gene products. This kind of similarity measure is closely associated with the GO terms annotated to biological entities under consideration and the structure of the GO graph. However, previous works in this field mainly focused on the upper part of the graph, and seldom concerned about the lower part. In this study, we aim to explore information from the lower part of the GO graph for better semantic similarity. We proposed a framework to quantify the similarity measure beneath a term pair, which takes into account both the information two ancestral terms share and the probability that they co-occur with their common descendants. The effectiveness of our approach was evaluated against seven typical measurements on public platform CESSM, protein-protein interaction and gene expression datasets. Experimental results consistently show that the similarity derived from the lower part contributes to better semantic similarity measure. The promising features of our approach are the following: (1) it provides a mirror model to characterize the information two ancestral terms share with respect to their common descendant; (2) it quantifies the probability that two terms co-occur with their common descendant in an efficient way; and (3) our framework can effectively capture the similarity measure beneath two terms, which can serve as an add-on to improve traditional semantic similarity measure between two GO terms. The algorithm was implemented in Matlab and is freely available from http://ejl.org.cn/bio/GOBeneath/. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. Silt and gas accumulation beneath an artificial recharge spreading basin, Southwestern Utah, U.S.A.

    Science.gov (United States)

    Heilweil, V.M.; Solomon, D.K.; Ortiz, G.

    2009-01-01

    Sand Hollow Reservoir in southwestern Utah, USA, is operated for both surface-water storage and artificial recharge to the underlying Navajo Sandstone. The total volume of estimated artificial recharge between 2002 and 2007 is 85 million cubic meters (69,000 acre-feet). Since 2002, artificial recharge rates have generally been declining and are inversely correlated with the increasing surface area of the reservoir. Permeability testing of core samples retrieved from beneath the reservoir indicates that this decline may not be due to silt accumulation. Artificial recharge rates also show much seasonal variability. Calculations of apparent intrinsic permeability show that these variations can only partly be explained by variation in water viscosity associated with seasonal changes in water temperature. Sporadic seasonal trends in recharge rates and intrinsic permeability during 2002-2004 could be associated with the large fluctuations in reservoir elevation and wetted area. From 2005 through 2007, the reservoir was mostly full and there has been a more consistent seasonal pattern of minimum recharge rates during the summer and maximum rates during the autumn. Total dissolved-gas pressure measurements indicate the presence of biogenic gas bubbles in the shallow sediments beneath the shallower parts of Sand Hollow Reservoir when the water is warmer. Permeability reduction associated with this gas clogging may contribute to the decrease in artificial recharge rates during the spring and summer, with a subsequently increasing recharge rates in the autumn associated with a decline in volume of gas bubbles. Other possible causes for seasonal variation in artificial recharge rates require further investigation.

  16. Compositions and processes of lithospheric mantle beneath the west Cathaysia block, southeast China

    Science.gov (United States)

    Zhang, Hui; Zheng, Jianping; Pan, Shaokui; Lu, Jianggu; Li, Yihe; Xiang, Lu; Lin, Abing

    2017-08-01

    Knowledge about the nature and history of the lithospheric mantle beneath the west Cathaysia block (South China) is still sparse. The major- and trace-element compositions and H2O contents of minerals from peridotite xenoliths entrained in the Cenozoic lamprophyres of the Anyuan area (SE China), were conducted to investigate the nature and evolution of the lithospheric mantle, as well as the factors controlling the distribution of water. The xenoliths including spinel harzburgites and lherzolites are moderately refractory (Mg# Olivine = 90.2-91.2) with minor fertile lherzolites (Mg# Olivine = 89.1-89.9). Clinopyroxenes in lherzolites show variable REE patterns from LREE-depleted to LREE-enriched patterns, and commonly exhibit negative anomalies of U, Pb and Ti. The mantle represented by the xenoliths mostly experienced 1-10% partial melting and obvious subsequent silicate metasomatism. H2O contents of clinopyroxene, orthopyroxene, and olivine in the peridotites are 320-404 ppm, 138-200 ppm, and 11-33 ppm, respectively. The whole-rock H2O contents range from 63 to 120 ppm, similar to that estimated for the MORB source. The negative correlations of H2O contents with Mg# in olivine and lack of correlation correlations with (La/Yb)N in clinopyroxene suggest that the H2O contents are mainly controlled by the partial melting process rather than mantle metasomatism. The fertile and moderately refractory peridotite xenoliths have similar equilibrium temperatures, implying that the lithospheric mantle is not compositionally stratified. Integrated with published data, we suggest that the widespread fertile and moderately refractory lithospheric mantle beneath the studied area (west Cathaysia), even the whole South China, might be eroded or melt-rock reacted by upwelling asthenospheric materials. Finally, the cooling of the upwelled asthenospheric materials resulted in the formation of the accreted lithospheric mantle mixed with pre-existing moderately refractory volumes.

  17. Three-dimensional radial and azimuthal anisotropy beneath the mid-east China

    Science.gov (United States)

    Zhang, Guibin; Jiang, Guoming; Jia, Zhengyuan

    2017-04-01

    The anisotropy media are very common in the Earth, which have been revealed by both seismological observations and laboratory studies. In a model with hexagonal symmetry, the anisotropy parameters will be reduced to three ones from 21 independent elastic moduli. In this work, we have attempted to study 3-D P-wave radial and azimuthal anisotropy beneath the mid-east China. In this region, there exist a mineralization zone in the middle and lower Yangtze region and an ultra-high pressure metamorphic belt in the Qinling-Dabie-Sulu Orogenic belt. Previous studies have shown that both might be caused by the rich exhalation of magma during the Mesozoic period, but various geodynamic models for explaining the mechanism of the Cretaceous magmatism are controversial and even contradictory. We have adopted the anisotropy tomography method of Wang and Zhao (2008, 2013) to the P-wave relative residuals from teleseismic travel time data. As a result, the anisotropy model clearly describes the fast-axis direction of P-wave with 50-700 km deep, which might represent the stress orientation or the motion of asthenospheric flow. The fast-axis direction changes gradually from the east-west at depths of 100-300 km to the north-south at depths of 400-700 km, which is very interesting and we will further explain this result combining with other previous geophysical, geochemical and geological results. This anisotropy result help us discuss the deep geodynamics beneath the mid-east China with more confidence.

  18. Seismic anisotropy of the lithosphere/asthenosphere system beneath the Rwenzori region of the Albertine Rift

    Science.gov (United States)

    Homuth, B.; Löbl, U.; Batte, A. G.; Link, K.; Kasereka, C. M.; Rümpker, G.

    2016-09-01

    Shear-wave splitting measurements from local and teleseismic earthquakes are used to investigate the seismic anisotropy in the upper mantle beneath the Rwenzori region of the East African Rift system. At most stations, shear-wave splitting parameters obtained from individual earthquakes exhibit only minor variations with backazimuth. We therefore employ a joint inversion of SKS waveforms to derive hypothetical one-layer parameters. The corresponding fast polarizations are generally rift parallel and the average delay time is about 1 s. Shear phases from local events within the crust are characterized by an average delay time of 0.04 s. Delay times from local mantle earthquakes are in the range of 0.2 s. This observation suggests that the dominant source region for seismic anisotropy beneath the rift is located within the mantle. We use finite-frequency waveform modeling to test different models of anisotropy within the lithosphere/asthenosphere system of the rift. The results show that the rift-parallel fast polarizations are consistent with horizontal transverse isotropy (HTI anisotropy) caused by rift-parallel magmatic intrusions or lenses located within the lithospheric mantle—as it would be expected during the early stages of continental rifting. Furthermore, the short-scale spatial variations in the fast polarizations observed in the southern part of the study area can be explained by effects due to sedimentary basins of low isotropic velocity in combination with a shift in the orientation of anisotropic fabrics in the upper mantle. A uniform anisotropic layer in relation to large-scale asthenospheric mantle flow is less consistent with the observed splitting parameters.

  19. Autonomous ocean observations beneath Pine Island Glacier Ice Shelf, West Antarctica

    Science.gov (United States)

    Dutrieux, P.; Jenkins, A.; Jacobs, S.; Heywood, K. J.

    2015-12-01

    Warm circumpolar deep water reaching 3.5ºC above the in situ freezing point pervasively fills a network of glacially carved troughs in the Amundsen sea, West Antarctica, and melts and thins neighbouring ice shelves, including Pine Island glacier Ice Shelf (PIIS). Hydrographic, current, and microstructure observations obtained in austral summer 2009 and 2014 by an autonomous underwater vehicle beneath the PIIS are used here to detail the complex ice-ocean interaction and resulting ocean circulation. The theoretical schematic of deeply incoming warm and saline water melting the grounding line and generating a buoyant plume upwelling along the ice draft is generally consistent with observations. The cavity beneath PIIS is clearly divided in two by a seabed ridge, constraining the oceanic circulation and water masses distribution. On the seaward side of the ridge, a thick warm deep water layer circulates cyclonically and is overlaid by a thin meltwater layer. Only intermediate depth waters are allowed to overflow from the ridge top into the inner cavity, where a much thinner warm water layer is now overlaid by a thicker meltwater layer. At the ice/ocean interface, melt induced freshening is forcing an upwelling which in turn injects cyclonic vorticity and participates in creating a vigorous cyclonic recirculation in the inner cavity. The top of the ridge, where warm waters overflow in the inner cavity, is a dynamical boundary characterized by northward along-ridge currents up to 0.2 m/s and enhanced shear, thermal gradient, and mixing. Observations at two points at the ice interface indicate that the ocean remains stratified within 2 meters of the ice.

  20. Seismic structure beneath the Gulf of California: a contribution from group velocity measurements

    Science.gov (United States)

    Di Luccio, F.; Persaud, P.; Clayton, R. W.

    2014-12-01

    Rayleigh wave group velocity dispersion measurements from local and regional earthquakes are used to interpret the lithospheric structure in the Gulf of California region. We compute group velocity maps for Rayleigh waves from 10 to 150 s using earthquakes recorded by broad-band stations of the Network of Autonomously Recording Seismographs in Baja California and Mexico mainland, UNM in Mexico, BOR, DPP and GOR in southern California and TUC in Arizona. The study area is gridded in 120 longitude cells by 180 latitude cells, with an equal spacing of 10 × 10 km. Assuming that each gridpoint is laterally homogeneous, for each period the tomographic maps are inverted to produce a 3-D lithospheric shear wave velocity model for the region. Near the Gulf of California rift axis, we found three prominent low shear wave velocity regions, which are associated with mantle upwelling near the Cerro Prieto volcanic field, the Ballenas Transform Fault and the East Pacific Rise. Upwelling of the mantle at lithospheric and asthenospheric depths characterizes most of the Gulf. This more detailed finding is new when compared to previous surface wave studies in the region. A low-velocity zone in northcentral Baja at ˜28ºN which extends east-south-eastwards is interpreted as an asthenospheric window. In addition, we also identify a well-defined high-velocity zone in the upper mantle beneath central-western Baja California, which correlates with the previously interpreted location of the stalled Guadalupe and Magdalena microplates. We interpret locations of the fossil slab and slab window in light of the distribution of unique post-subduction volcanic rocks in the Gulf of California and Baja California. We also observe a high-velocity anomaly at 50-km depth extending down to ˜130 km near the southwestern Baja coastline and beneath Baja, which may represent another remnant of the Farallon slab.

  1. Uppermost mantle P wavespeed structure beneath eastern China and its surroundings

    Science.gov (United States)

    Sun, Weijia; Kennett, B. L. N.

    2016-06-01

    Pn travel-time tomography provides a way of improving structural information on the uppermost mantle across eastern China exploiting recent developments of dense seismic networks with well recorded seismic events. We used waveforms from 2009 at Chinese stations, supplemented by bulletin arrival times. An initial P wave model was constructed using the crustal model from CRUST1.0 coupled to a P wave model in the mantle derived from the SL2013sv model to capture the broad-scale features. This starting model enables us to compensate for the large contrasts in crustal thickness across the region. All events were relocated using the initial 3-D P model, and after relocation, consistent patterns of travel-time residuals are obtained. We extract Pn as the first arrival in the distance range 1.8 ∘ to 12 ∘. We use the FMTOMO (Fast Marching TOMOgraphy) approach to invert the travel-time results to generate a P wavespeed structure with a resolution of 2 ∘× 2 ∘ down to 75 km. There are considerable variations in Pn wavespeed in the uppermost mantle across the region. The central portion of the North China craton is imaged with particularly slow P wavespeeds, whilst most of the neighbouring Ordos block is fast. Fast P wavespeeds extend through much of the uppermost mantle beneath eastern Central Asia Orogen, northeast China and beneath the Korean peninsula. In the south, the Sichuan Block and the western Yangtze craton show rather fast P wavespeeds. The Tanlu fault system appears to cut through the crust into the mantle with marked slow P wavespeed at its southern end.

  2. Detailed Soils 24K

    Data.gov (United States)

    Kansas Data Access and Support Center — This data set is a digital soil survey and is the most detailed level of soil geographic data developed by the National Cooperative Soil Survey. The information was...

  3. GeologicSoils_SOAG

    Data.gov (United States)

    Vermont Center for Geographic Information — GeologicSoils_SOAG includes a pre-selected subset of SSURGO soil data depicting prime agricultural soils in Vermont. The SSURGO county coverages were joined to the...

  4. Indicators: Soil Chemistry

    Science.gov (United States)

    The chemical makeup of the soil can provide information on wetland condition, wetland water quality and services being provided by the wetland ecosystem. Analyzing soil chemistry reveals if the soil is contaminated with a toxic chemical or heavy metal.

  5. Soil Organic Carbon Stock

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Soil organic carbon (SOC) is the carbon held within soil organic constituents (i.e., products produced as dead plants and animals decompose and the soil microbial...

  6. Complex structure of the lithospheric slab beneath the Banda arc, eastern Indonesia depicted by a seismic tomographic model

    Directory of Open Access Journals (Sweden)

    Sri Widiyantoro

    2011-10-01

    Full Text Available Seismic tomography with a non-linear approach has been successfully applied to image the P-wave velocity structure beneath the Banda arc in detail. Nearly one million compressional phases including the surfacereflected depth phases pP and pwP from events within the Indonesian region have been used. The depth phases have been incorporated in order to improve the sampling of the uppermantle structure, particularly below the Banda Sea in the back-arc regions. For the model parameterization, we have combined a highresolution regional inversion with a low-resolution global inversion to allow detailed images of slab structures within the study region and to minimize the mapping of distant aspherical mantle structure into the volume under study. In this paper, we focus our discussion on the upper mantle and transition zone structure beneath the curved Banda arc. The tomographic images confirm previous observations of the twisting of the slab in the upper mantle, forming a spoon-shaped structure beneath the Banda arc. A slab lying flat on the 660 km discontinuity beneath the Banda Sea is also well imaged. Further interpretations of the resulting tomograms and seismicity data support the scenario of the Banda arc subduction rollback.

  7. What Lies beneath Seemingly Positive Campus Climate Results: Institutional Sexism, Racism, and Male Hostility toward Equity Initiatives and Liberal Bias

    Science.gov (United States)

    Vaccaro, Annemarie

    2010-01-01

    This article presents qualitative results from a campus climate study at one predominately white university. Data analysis uncovered "what lies beneath" a seemingly positive campus climate. Gender differences in survey responses suggest that men and women experienced the climate in vastly different ways. Additionally, lack of deep diversity…

  8. Receiver function images from the Moho and the slab beneath the Altiplano and Puna plateaus in the Central Andes

    Science.gov (United States)

    Wölbern, I.; Heit, B.; Yuan, X.; Asch, G.; Kind, R.; Viramonte, J.; Tawackoli, S.; Wilke, H.

    2009-04-01

    Teleseismic data recorded during one and a half years are investigated with the receiver function technique to determine the crustal and upper-mantle structures underneath the highly elevated Altiplano and Puna plateaus in the central Andes. A series of converting interfaces are determined along two profiles at 21°S and 25.5°S, respectively, with a station spacing of approximately 10 km. The data provide the highest resolution gained from a passive project in this area, so far. The oceanic Nazca plate is detected down to 120 km beneath the Altiplano whereas beneath the Puna, the slab can unexpectedly be traced down to 200 km depth at longer periods. A shallow crustal low-velocity zone is determined beneath both plateaus exhibiting segmentation. In the case of the Altiplano, the segments present vertical offsets and are separated by inclined interfaces, which coincide with major fault systems at the surface. An average depth to Moho of about 70 km is determined for the Altiplano plateau. A strong negative velocity anomaly located directly below the Moho along with local crustal thinning is interpreted beneath the volcanic arc of the Altiplano plateau between 67°W and 68.5°W. A deep section of the Puna profile reveals thinning of the mantle transition zone. Although poorly resolved, the detected anomaly may suggest the presence of a mantle plume, which may constitute the origin of the anomalous temperatures at the depth of the upper-mantle discontinuities.

  9. Characterizing a shallow groundwater system beneath irrigated sugarcane with electrical resistivity and radon (Rn-222), Puunene, Hawaii

    Science.gov (United States)

    In this study, we use a combination of electrical resistivity profiling and radon (222Rn) measurements to characterize a shallow groundwater system beneath the last remaining, large-scale sugarcane plantation on Maui, Hawaii. Hawaiian Commercial & Sugar Company has continuously operated a sugarcane...

  10. What lies beneath: detecting sub-canopy changes in savanna woodlands using a three-dimensional classification method

    CSIR Research Space (South Africa)

    Fisher, JT

    2015-07-01

    Full Text Available Vegetation Science What lies beneath: detecting sub-canopy changes in savanna woodlands using a three-dimensional classification method Jolene T. Fisher, Ed T.F. Witkowski, Barend F.N. Erasmus, Penelope J. Mograbi, Gregory P. Asner, Jan A.N. van...

  11. Understanding seismic heterogeneities in the lower mantle beneath the Americas from seismic tomography and plate tectonic history

    NARCIS (Netherlands)

    Ren, Y.; Stutzmann, E.; Hilst, R.D. van der; Besse, J.

    2007-01-01

    We combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the Americas. Using broadband waveform cross correlation, we measured 37,000 differential P and S traveltimes, 2000 PcP-P and ScS-S times along a wide corrido

  12. Understanding seismic heterogeneities in the lower mantle beneath the Americas from seismic tomography and plate tectonic history

    NARCIS (Netherlands)

    Ren, Y.; Stutzmann, E.; Hilst, R.D. van der; Besse, J.

    2007-01-01

    We combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the Americas. Using broadband waveform cross correlation, we measured 37,000 differential P and S traveltimes, 2000 PcP-P and ScS-S times along a wide corrido

  13. Seismic Character of Moho Beneath the NW Himalaya and Ladakh Inferred from Regional Earthquakes Travel Time Data

    Science.gov (United States)

    Kanna, Nagaraju; Prakasam, K. S.; Gupta, Sandeep

    2017-03-01

    We study the uppermost mantle velocities and dip of Indian Moho beneath the NW Himalaya and Ladakh using 42 regional waveform data recorded on 15 seismographs along a 600 km-long profile. We use the two-way travel time and interstation velocity methods. The apparent Pn and Sn velocities beneath the NW Himalaya are 8.08 ± 0.04 and 4.64 ± 0.07 km/s for earthquakes occurring south of the profile (downdip, western Indian shield) and 8.70 ± 0.13 and 4.76 ± 0.12 km/s for earthquakes from north (updip, western Tibet). Similarly, these velocities beneath Ladakh are 7.18 ± 0.07 and 4.32 ± 0.05 km/s for earthquakes due south (downdip, north Indian shield) and 8.50 ± 0.10 and 4.39 ± 0.12 km/s for earthquakes due north (updip, western Tibet). These velocity variations constrain the Moho dip at 2.4 ± 0.14º beneath the NW Himalaya and 6.6 ± 0.54º beneath Ladakh. Considering the varying dips along the profile, we observe that the true Pn (8.37 ± 0.07 km/s) and Sn (4.70 ± 0.1 km/s) velocities are higher for the NW Himalaya than for Ladakh (7.73 ± 0.08 and 4.33 ± 0.09 km/s). The large variation in interstation Pn velocity is observed between the station pairs near the Indus Zangpo Suture zone due to steep dipping ( 7.1º to 6.26º) of the Indian Moho. In the Himalaya region, the interstation and average values of the velocities and Moho dip are comparable, whereas a variation is observed in different segments of the Ladakh region. The results show that the Indian Moho is underthrusting at a shallow angle ( 2.5º) beneath the Himalaya, steepens abruptly ( 6.6º) further north of the Southern Tibetan Detachment and continues at a shallow angle ( 3.8º) beneath Ladakh.

  14. Annual emissions of CH4 and N2O, and ecosystem respiration, from eight organic soils in Western Denmark managed by agriculture

    Directory of Open Access Journals (Sweden)

    M. H. Greve

    2011-10-01

    Full Text Available The use of organic soils by agriculture involves drainage and tillage, and the resulting increase in C and N turnover can significantly affect their greenhouse gas balance. This study estimated annual fluxes of CH4 and N2O, and ecosystem respiration (Reco, from eight organic soils managed by agriculture. The sites were located in three regions representing different landscape types and climatic conditions, and three land use categories (arable crops, AR, grass in rotation, RG, and permanent grass, PG were covered. The normal management at each site was followed, except that no N inputs occurred during the monitoring period from August 2008 to October 2009. The stratified sampling strategy further included six sampling points in three blocks at each site. Environmental variables (precipitation, PAR, air and soil temperature, soil moisture, groundwater level were monitored continuously and during sampling campaigns, where also groundwater samples were taken for analysis. Gaseous fluxes were monitored on a three-weekly basis, giving 51, 49 and 38 field campaigns for land use categories AR, PG and RG, respectively. Climatic conditions in each region during monitoring were representative based on 20-yr averages. Peat layers were shallow, typically 0.5 to 1 m, and with a pH of 4–5. At six sites annual emissions of N2O were in the range 3 to 24 kg N2O-N ha−1, but at two arable sites (spring barley, potato net emissions of 38 and 61 kg N2O-N ha−1 were recorded. Both were characterized by fluctuating groundwater with elevated SO42− concentrations. Annual fluxes of CH4 were generally small, as expected, ranging from –2 to 4 kg CH4 ha−1. However, two permanent grasslands had tussocks of Juncus effusus (soft rush in sampling points that were consistent sources of CH4 throughout the year. Emission factors for organic soils in rotation and permanent grass, respectively, were estimated to be 0.011 and 0.47 g m−2 for CH4, and 2.5 and 0.5 g m−2

  15. Soils, Soils, Published in 2004, Taylor County.

    Data.gov (United States)

    NSGIC GIS Inventory (aka Ramona) — This Soils dataset, was produced all or in part from Published Reports/Deeds information as of 2004. It is described as 'Soils'. Data by this publisher are often...

  16. Soil Conservation Measures in Rainfed Olive Orchards in South-Eastern Spain:Impacts of Plant Strips on Soil Water Dynamics

    Institute of Scientific and Technical Information of China (English)

    V.H.DURAN ZUAZO; C.R.RODRIGUEZ PLEGUEZUELO,L; ARROYO PANADERO,A; MARTINEZ RAYA, J; R.FRANCIA MARTINEZ; B.CARCELES RODRIGUEZ

    2009-01-01

    Sloping and mountainous olive production systems are widespread,occupying large parts of the Mediterranean landscape prone to water erosion.Soil erosion,runoff,and soil water content patterns over a three-year period were monitored in erosion plots on a mountainside with rainfed olive (Olea europaea cv.Picual) trees under:1) non-tillage with barley strips of 4 m width (BS);2) non-tillage with native vegetation strips of 4 m width (NVS);and 3) non-tillage without plant strips (NT).The erosion plots,located in Lanjaron (Granada,south-eastern Spain),on a 30% slope,were 192 m2 in area.For assessing soil water dynamics in real-time and near-continuons soil water content measurements,multiseusor capacitance probes were installed in the middle of plant strips and beneath the olive tree at five soil depths (10,20,30,50,and 100 cm).The highest erosion and runoff rates were measured under NT,with a mean of 17.3 Mg ha-1 year-1 and 140.0 mm year-1,respectively,over the entire study period.The BS and NVS with respect to the NT reduced erosion by 71% and 59% and runoff by 95% and 94%,respectively.In general,greater available soil water content was found under BS than NVS and NT,especially beneath the olive tree canopies.These results supported the recommendation of non-tillage with barley strips in order to reduce erosion and to preserve soil water for trees in traditional mountainous olive-producing areas,where orchards cover vast tracts of land.

  17. Soil microbial responses to nitrogen addition in arid ecosystems.

    Science.gov (United States)

    Sinsabaugh, Robert L; Belnap, Jayne; Rudgers, Jennifer; Kuske, Cheryl R; Martinez, Noelle; Sandquist, Darren

    2015-01-01

    The N cycle of arid ecosystems is influenced by low soil organic matter, high soil pH, and extremes in water potential and temperature that lead to open canopies and development of biological soil crusts (biocrusts). We investigated the effects of N amendment on soil microbial dynamics in a Larrea tridentata-Ambrosia dumosa shrubland site in southern Nevada USA. Sites were fertilized with a NO3-NH4 mix at 0, 7, and 15 kg N ha(-1) y(-1) from March 2012 to March 2013. In March 2013, biocrust (0-0.5 cm) and bulk soils (0-10 cm) were collected beneath Ambrosia canopies and in the interspaces between plants. Biomass responses were assessed as bacterial and fungal SSU rRNA gene copy number and chlorophyll a concentration. Metabolic responses were measured by five ecoenzyme activities and rates of N transformation. By most measures, nutrient availability, microbial biomass, and process rates were greater in soils beneath the shrub canopy compared to the interspace between plants, and greater in the surface biocrust horizon compared to the deeper 10 cm soil profile. Most measures responded positively to experimental N addition. Effect sizes were generally greater for bulk soil than biocrust. Results were incorporated into a meta-analysis of arid ecosystem responses to N amendment that included data from 14 other studies. Effect sizes were calculated for biomass and metabolic responses. Regressions of effect sizes, calculated for biomass, and metabolic responses, showed similar trends in relation to N application rate and N load (rate × duration). The critical points separating positive from negative treatment effects were 88 kg ha(-1) y(-1) and 159 kg ha(-1), respectively, for biomass, and 70 kg ha(-1) y(-1) and 114 kg ha(-1), respectively, for metabolism. These critical values are comparable to those for microbial biomass, decomposition rates and respiration reported in broader meta-analyses of N amendment effects in mesic ecosystems. However, large effect sizes at low N

  18. Crustal structure beneath the High Lava Plains of eastern Oregon and surrounding regions from receiver function analysis

    Science.gov (United States)

    Eagar, Kevin C.; Fouch, Matthew J.; James, David E.; Carlson, Richard W.

    2011-02-01

    We analyze teleseismic P-to-S receiver functions to image crustal structure beneath the High Lava Plains (HLP) of eastern Oregon and surrounding regions. Coverage from 206 broadband seismic stations provides the first opportunity to resolve variations in crustal composition, thickness, and heterogeneity on scales of a few km in depth and tens of km laterally across the HLP region. We utilize both H - κ stacking and a new Gaussian-weighted common conversion point stacking technique. We find crust that is ≥40 km thick beneath the Cascades, Idaho Batholith, and Owyhee Plateau and thinner (˜31 km) crust beneath the HLP and northern Great Basin. Low Poisson's ratios of ˜0.240 characterize the granitic crust beneath the Idaho Batholith, while the Owyhee Plateau exhibits values of ˜0.270, typical of average continental crust. The Owyhee Plateau is a thick simple crustal block with distinct edges at depth. The western HLP exhibits high average values of 0.304, typical for regions of widespread basaltic volcanism. Combined with other geological and geophysical observations, the areas of abnormally high Poisson's ratios (˜0.320) and low-velocity zones in the crust beneath north-central and southern Oregon are consistent with the presence of partial melt on either side of the HLP trend, suggesting a central zone where crustal melts have drained to the surface, perhaps enabled by the Brothers Fault Zone. Thicker crust and an anomalous N-S band of low Poisson's ratios (˜0.252) skirting the Steens Mountain escarpment is consistent with residuum from a midcrustal magma source of the massive flood basalts, supporting the view of extensive mafic underplating and intraplating of the crust from Cenozoic volcanism.

  19. Facilitation by a Spiny Shrub on a Rhizomatous Clonal Herbaceous in Thicketization-Grassland in Northern China: Increased Soil Resources or Shelter from Herbivores

    Directory of Open Access Journals (Sweden)

    Saixiyala

    2017-05-01

    Full Text Available The formation of fertility islands by shrubs increases soil resources heterogeneity in thicketization-grasslands. Clonal plants, especially rhizomatous or stoloniferous clonal plants, can form large clonal networks and use heterogeneously distributed resources effectively. In addition, shrubs, especially spiny shrubs, may also provide herbaceous plants with protection from herbivores, acting as ‘shelters’. The interaction between pre-dominated clonal herbaceous plants and encroaching shrubs remains unclear in thicketization-grassland under grazing pressure. We hypothesized that clonal herbaceous plants can be facilitated by encroached shrubs as a ‘shelter from herbivores’ and/or as an ‘increased soil resources’ under grazing pressure. To test this hypothesis, a total of 60 quadrats were chosen in a thicket-grassland in northern China that was previously dominated by Leymus chinensis and was encroached upon by the spiny leguminous plant Caragana intermedia. The soil and plant traits beneath and outside the shrub canopies were sampled, investigated and contrasted with an enclosure. The soil organic matter, soil total nitrogen and soil water content were significantly higher in the soil beneath the shrub canopies than in the soil outside the canopies. L. chinensis beneath the shrub canopies had significantly higher plant height, single shoot biomass, leaf length and width than outside the shrub canopies. There were no significantly differences between plant growth in enclosure and outside the shrub canopies. These results suggested that under grazing pressure in a grassland undergoing thicketization, the growth of the rhizomatous clonal herbaceous plant L. chinensis was facilitated by the spiny shrub C. intermedia as a ‘shelter from herbivores’ more than through ‘increased soil resources’. We propose that future studies should focus on the community- and ecosystem-level impacts of plant clonality.

  20. Different Effects of Shrubs and Trees on Seed Bank Richness and Diversity in the Understory Soil (Case Study: Kerman Province, Sharbabak

    Directory of Open Access Journals (Sweden)

    2014-03-01

    Full Text Available This study aimed to investigate the effect of canopy trees and shrubs: Pistacia atlantica, Amygdalus scoparia, Amygdalus eburnean on the species diversity and richness of soil seed bank. Ten individuals of each species were selected and one quadrate was established in and outside of crown canopy of each species. In each plot, soil samples were collected from 0-5 and 5-10 cm depths. GLM was applied to assess the effect of woody species, canopy cover, and depth of sampling on the characteristics of soil seed bank. The paired t-test was used to compare the diversity and richness of soil seed banks beneath and outside the canopy. The results showed that the highest species richness of soil seed bank was related to Pistacia atlantica, 0.24, which was significantly higher than the average species richness of soil seed banks in other species Amygdalus scoparia, Amygdalus eburnea with 0.10 and 0.14, respectively. Pistacia atlantica had the highest species diversity with 0.65 compared to the two other species Amygdalus scoparia and Amygdalus eburnean with 0.48, 0.53, respectively. Paired t-test results showed that canopy of woody species significantly increased soil seed bank diversity and richness beneath their canopy. Our results indicated that canopy of tree and shrub species in arid region affected positively on soil seed bank preservation.

  1. Implementation of deep soil mixing at the Kansas City Plant

    Energy Technology Data Exchange (ETDEWEB)

    Gardner, F.G.; Korte, N. [Oak Ridge National Lab., Grand Junction, CO (United States); Strong-Gunderson, J.; Siegrist, R.L.; West, O.R.; Cline, S.R. [Oak Ridge National Lab., TN (United States). Environmental Sciences Div.; Baker, J. [AlliedSignal, Inc., Kansas City, MO (United States)

    1998-11-01

    In July 1996, the US Department of Energy (DOE) Kansas City Plant (KCP), AlliedSignal Federal Manufacturing and Technologies, and Oak Ridge National Laboratory (ORNL), conducted field-scale tests of in situ soil mixing and treatment technologies within the Northeast Area (NEA) of the KCP at the Former Ponds site. This demonstration, testing, and evaluation effort was conducted as part of the implementation of a deep soil mixing (DSM) innovative remedial technology demonstration project designed to test DSM in the low-permeability clay soils at the KCP. The clay soils and groundwater beneath this area are contaminated by volatile organic compounds (VOCs), primarily trichloroethene (TCE) and 1,2-dichloroethene (1,2-DCE). The demonstration project was originally designed to evaluate TCE and 1,2-DCE removal efficiency using soil mixing coupled with vapor stripping. Treatability study results, however, indicated that mixed region vapor stripping (MRVS) coupled with calcium oxide (dry lime powder) injection would improve TCE and 1,2-DCE removal efficiency in saturated soils. The scope of the KCP DSM demonstration evolved to implement DSM with the following in situ treatment methodologies for contaminant source reduction in soil and groundwater: DSM/MRVS coupled with calcium oxide injection; DSM/bioaugmentation; and DSM/chemical oxidation using potassium permanganate. Laboratory treatability studies were started in 1995 following collection of undisturbed soil cores from the KCP. These studies were conducted at ORNL, and the results provided information on optimum reagent concentrations and mixing ratios for the three in situ treatment agents to be implemented in the field demonstration.

  2. Surfactant adsorption to soil components and soils

    NARCIS (Netherlands)

    Ishiguro, Munehide; Koopal, Luuk K.

    2016-01-01

    Soils are complex and widely varying mixtures of organic matter and inorganic materials; adsorption of surfactants to soils is therefore related to the soil composition. We first discuss the properties of surfactants, including the critical micelle concentration (CMC) and surfactant adsorption on

  3. Soil-structure interaction including nonlinear soil

    OpenAIRE

    Gicev, Vlado

    2008-01-01

    There are two types of models of soil-structure system depending upon the rigidity of foundation: models with rigid and models with flexible foundation. Main features of the soil-structure interaction phenomenon: -wave scattering, -radiation damping, -reduction of the system frequencies. In this presentation, the influence of interaction on the development of nonlinear zones in the soil is studied.

  4. Pervasive and strong effects of plants on soil chemistry: a meta-analysis of individual plant ‘Zinke’ effects

    Science.gov (United States)

    Waring, Bonnie G.; Álvarez-Cansino, Leonor; Barry, Kathryn E.; Becklund, Kristen K.; Dale, Sarah; Gei, Maria G.; Keller, Adrienne B.; Lopez, Omar R.; Markesteijn, Lars; Mangan, Scott; Riggs, Charlotte E.; Rodríguez-Ronderos, María Elizabeth; Segnitz, R. Max; Schnitzer, Stefan A.; Powers, Jennifer S.

    2015-01-01

    Plant species leave a chemical signature in the soils below them, generating fine-scale spatial variation that drives ecological processes. Since the publication of a seminal paper on plant-mediated soil heterogeneity by Paul Zinke in 1962, a robust literature has developed examining effects of individual plants on their local environments (individual plant effects). Here, we synthesize this work using meta-analysis to show that plant effects are strong and pervasive across ecosystems on six continents. Overall, soil properties beneath individual plants differ from those of neighbours by an average of 41%. Although the magnitudes of individual plant effects exhibit weak relationships with climate and latitude, they are significantly stronger in deserts and tundra than forests, and weaker in intensively managed ecosystems. The ubiquitous effects of plant individuals and species on local soil properties imply that individual plant effects have a role in plant–soil feedbacks, linking individual plants with biogeochemical processes at the ecosystem scale. PMID:26224711

  5. Deformation Pattern of Non-cohesive Soil Bases under Foundations with Different Vertical Cross-sectional Shapes

    Directory of Open Access Journals (Sweden)

    Musa Alhassan

    2013-08-01

    Full Text Available Pattern of vertical deformations of soil bases, under shallow foundation modelsof different vertical cross-sectional shapes were experimentally studied on three different modeled non-cohesive subsoilconditions. Foundations models with rectangular, wedge and T shape vertical cross-sections were studied. Result of the study showed that, under the action of vertical load, bulk of the vertical deformation of subsoil bases at the instance of foundations with rectangular vertical cross-sectional shapes, is mostly associated with the soil beneath the foundation, while at the instances of those with wedge and T vertical crosssectional shapes, deformation of the soil occurs both under the foundations’ bases and along their vertical stems. This indicates that, although less loads were generally resisted by the wedge and T shape foundations, using then can help in mobilizing substantial mass of soil above the foundation bases, to function not only as surcharge to the soil below the base, but also in resisting structural loads.

  6. Investigation of sterols as potential biomarkers for the detection of pig (S. s. domesticus) decomposition fluid in soils.

    Science.gov (United States)

    von der Lühe, Barbara; Dawson, Lorna A; Mayes, Robert W; Forbes, Shari L; Fiedler, Sabine

    2013-07-10

    This study was carried out to evaluate the potential of using cholesterol and coprostanol, as indicators for the detection of decomposition fluid of buried pigs (S. s. domesticus) in soils. In May 2007, four pig carcasses (∼35kg) were buried in shallow graves (∼40 cm depth) at the University of Ontario Institute of Technology in Canada. Two pigs were exhumed after three months (Pig 1, Pig 2) and six months (Pig 3, Pig 4) post burial. Soil samples were collected beneath the pig carcasses (∼40cm depth) and from grave walls (∼15-20 cm depth) as well as from a parallel control site. Coprostanol and cholesterol were extracted from soils, purified with solid phase extraction (SPE) and analysed with gas chromatography/mass spectrometry (GC/MS). A significant increase in cholesterol concentrations (psoil located beneath the pig carcasses after three months of burial. It is assumed that during the putrefaction and liquefaction stages of decomposition pig fluid which contains cholesterol and coprostanol is released into the underlying soil. Therefore, cholesterol and coprostanol could be used as potential biomarkers to detect the presence of decomposition fluid three months after burial under comparable soil and environmental conditions. Further research is suggested for additional soil sampling before and after three months to investigate the abundance of these and other sterols.

  7. Effects of vegetation type on soil microbial community structure and catabolic diversity assessed by polyphasic methods in North China

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Soil microbes play a major role in ecological processes and are closely associated with the aboveground plant community. In order to understand the effects of vegetation type on the characteristics of soil microbial communities, the soil microbial communities were assessed by plate counts, phospholipid fatty acid (PLFA) and Biolog microplate techniques in five plant communities, i.e., soybean field (SF), artificial turf (AT), artificial shrub (AS), natural shrub (NS), and maize field (MF) in Jinan, Shandong Province, North China. The results showed that plant diversity had little discernible effect on microbial biomass but a positive impact on the evennessof utilized substrates in Biolog microplate. Legumes could significantly enhance the number of cultural microorganisms, microbial biomass, and community catabolic diversity. Except for SF dominated by legumes, the biomass of fungi and the catabolic diversity of microbial community were higher in less disturbed soil beneath NS than in frequently disturbed soils beneath the other vegetation types. These results confirmed that high number of plant species, legumes, and natural vegetation types tend to support soil microbial communities with higher function. The present study also found a significant correlation between the number of cultured bacteria and catabolic diversity of the bacterial community. Different research methods led to varied results in this study. The combination of several approaches is recommended for accurately describing the characteristics of microbial communities in many respects.

  8. Neotectonic fault detection and lithosphere structure beneath SW of High Atlas (Morocco)

    Science.gov (United States)

    Timoulali, Youssef; Radi, Said; Azguet, Roumaissae; Bachaoui, Mostapha

    2016-08-01

    The High Atlas is a 100 km wide zone defined by E-W to NE-SW trending folds nearly orthogonal to the Atlantic coastline. The major compressional structures in the High Atlas consist of large-scale fold systems which affect Mesozoic and Cainozoic formations. The extreme West of the High Atlas including the region of Agadir is defined as an earthquake Zone. Historical seismicity data shows that the Agadir region was hit by two destructive earthquakes in 1731 and 1960 with magnitude 6.4 and 6.0, respectively. The present study has two main goals: 1) to use remote sensing techniques to detect and map the surface geological structures including faults; 2) to use the local earthquake tomography for imaging the lithosphere (subsurface) and detect deep structures. For the remote sensing techniques we used ETM + Landsat7 images and the SRTM 90 m image as a Digital Terrane Elevation Model. This study focuses on the computerized identification, feature extraction and quantitative interpretation of lineaments over the SW High Atlas. The analysis developed here is based on the numerical enhancement of a Landsat image and on the statistical processing of data generated through enhancement. The results generated by the numerical enhancement and statistical analysis are presented on fault maps, lineament maps, polar diagrams and lineament density maps. The lineaments have a high concentration of orientations around the directions N40E, N80W and N-S. For the subsurface study, seismic data sets were used to define the 3-D velocity structures. We also used local earthquake tomography to obtain the velocity map and crustal structure of the SW High Atlas region. The tomography results show a new and detailed lithosphere structure defined by a high velocity body in the northern of SW High Atlas from 15 to 45 Km depth, dipping to the north beneath the Essaouira basin in the western Meseta with P velocity variations from 6.5 to 7.8 km/s. This anomaly can be interpreted as an old

  9. Seismological Features of the Subducting Slab Beneath the Kii Peninsula, Central Japan, Revealed by Receiver Functions

    Science.gov (United States)

    Shiomi, K.; Park, J.

    2007-12-01

    We report seismological evidence that the subducting Philippine Sea slab (PHS) beneath the Kii Peninsula, central Japan, can be divided into three segments. Offshore the Kii Peninsula, the "Tonankai" and "Nankai" fault segments suffer mega-thrust earthquakes that repeat every 100 to 150 years. The structure of the young, thin, contorted PHS is important to the seismo-tectonics in this region. We apply the receiver function (RF) analysis to 26 Hi-net short-period and 4 F-net broad-band seismographic stations. In the case that dipping velocity discontinuities and/or anisotropic media exist beneath seismometer, both radial RFs and transverse RFs contain useful information to estimate underground structure. For isotropic media with a dipping-slab interface, back- azimuthal variation in RFs depends largely on three parameters, the downdip azimuth, dip angle and the depth of the interface. We stack both radial and transverse RFs with allowance a time-shift caused by the dipping interface, searching for optimal parameters based on the grid-search technique at each station. At some stations located near the eastern coastline of the Kii Peninsula, the dip angle of the interface inferred from RF stacking is much steeper than that estimated by the local seismicity. This discrepancy arises from the interference of two slab-converted phases, suggesting a layer atop the slab. In these cases we refine the stack to distinguish two slab phases and estimate three parameters of each dipping interface separately. Two interfaces with the same dip direction and low dip angle are estimated at these stations, with depth difference near 6 km. Thus, the shallower interface may be related to the layer within the oceanic crust and the deeper one is the slab Moho. These double-layered interfaces are detected only at stations located up-dip of a belt-like distribution of non- volcanic low-frequency tremor. Comparing the interface dips estimated in this study with the direction of slab motion

  10. 3D Imaging of Brittle/Ductile transition of the crust beneath the resurgent calderas

    Science.gov (United States)

    Tizzani, P.; Castaldo, R.; Pepe, S.; Solaro, G.

    2012-04-01

    Rheology is a crucial factor to understand the mechanical behaviour and evolution of the crust in young and tectonically active belts. The aim of this paper is to investigate the rheological properties of the crust beneath resurgent calderas as Long Valley caldera (California USA) and Campi Flegrei (Southern Italy). Through the rheological proprieties of the calderas area, we highlight the driving process that determine the cut off of the local seismicity [K. Ito, 1993]. In this context, we consider the thermal proprieties and mechanical heterogeneity of the crust in order to develop a 3D conductive time dependent thermal model of the upper crust beneath the two calderas. More specifically we integrate geophysical information (gravimetric, seismic and boreholes data) available for the considered area in FEM environment [Manconi A. et al., 2010]. We performed a numerical solution of Fourier equation to carry out an advance optimization of the real measured data. We produce a set of forward models and propose, in order to analyse and solve the statistical problem, the Monte Carlo optimization procedures as Genetic Algorithm [Manconi A. et al., 2009]. In particular we search for the heat production, the volume source distribution and the surface emissivity parameters that providing the best-fit of the geothermal profiles data measured at boreholes, by solving the non stationary heat flow equation (Campanian Ignimbrite eruption about 40 kyr for Campi Flegrei caldera and Bishop tuff eruption about 700 kyr for Long Valley caldera). The performed thermal fields allow us to obtain the rheological stratification of the crust beneath two resurgent calderas; the models suggest that the uprising of a ductile layer which connects the upper mantle to the volcanic feeding system could determine the stress conditions that controlled the distribution of seismicity. In fact, the computed 3D imaging of Brittle/Ductile transition well agrees with the seismic hypocentral distribution

  11. The age of the lithospheric mantle beneath the Northern Kerguelen Plateau

    Science.gov (United States)

    Debaille, V.; Mattielli, N. D.; Weis, D. A.

    2009-12-01

    The Kerguelen Plateau, in the Southern part of the Indian Ocean, provides a unique perspective on the building of Large Igneous Provinces. The Kerguelen Plateau by itself is divided in four parts, each presenting different geochemical characteristics that correspond to the various tectonic stages of the plateau evolution with time. The involvement of continental material has been evidenced in the Cretaceous lavas in the South of the plateau (>100 Myr). In contrast, there is no evidence for continental material in the young, Cenozoic lavas of the Kerguelen Archipelago, located in the Northern part of the plateau (NKP). On the other hand, the presence of subcontinental lithospheric material has been invoked in some basic and ultrabasic xenoliths from the archipelago [1]. These xenoliths, disseminated within alkaline lava series in the Southern and South-East part of the archipelago, have PT conditions generally comprised between 0.6 to 1.8 GPa (10-55 km) and 800 to 1000°C, corresponding to lithospheric conditions. Such petrogenetic conditions reflect underplated basaltic magmas and deep cumulates beneath the Kerguelen Plateau [2]. We have undertaken an Hf-Nd isotopic study on various xenoliths from the South East Province of the archipelago to decipher the fine structure of the mantle and the potential distribution of continental components under the NKP. Preliminary 143Nd/144Nd and 176Hf/177Hf results on websterite and spinel ± sapphirine bearing 2-pyroxenes metagabbro xenoliths show isotopic compositions overlapping those of the depleted ~29.5 Myr oldest lavas from the Archipelago (Mont Bureau). These lavas describe an isotopic alignment between the compositions of the South-East Indian Ridge and the flood basalts from Mont Crozier, which are representative of the enriched signature of the Kerguelen mantle plume. There is no evidence for contamination of the xenoliths from their host during their ascent. The xenoliths analyzed so far do not compare to the

  12. Rapid Mantle Ascent Rates Beneath Brazil: Diamond Bullets from a Smoking Plume?

    Science.gov (United States)

    Walter, M. J.; Frost, D. J.

    2010-12-01

    inclusions in diamonds from Juina also provide evidence for mantle ascent of this magnitude [2, 3]. The questions are (1) over what timeframe do the diamonds ascend? (2) what causes mantle ascent beneath the craton? Bulanova et al [2] were able to obtain a U/Pb age for the J1 perovskite inclusion, giving an astonishingly young model age of 101 ±7 Ma, close to the eruption age of the host kimberlite (93 ±1.5 Ma). From the time and depth differences we calculate ascent rates of about 1 to 50 cm/yr. We suggest that such rapid rates of mantle ascent beneath a craton may be ascribed to buoyant upwelling of mantle material. Diamond speedometry may provide direct evidence for a Cretaceous plume beneath Brazil, which was ultimately responsible for alkaline and kimberlite magmatism, and probably the Trindade magmatic track [6]. 1. Harte et al., Geochem. Soc. Spec. Pub, 1999, 125-153. 2. Bulanova et al., CMP, 2010, DOI:10.1007/s00410-010-0490-6. 3. Harte and Cayzer, Phys. Chem. Min., 2007. 4. Shirey et al., Science, 2002. 297, 1683- 1686. 5. Walter et al., Nature, 2008. 454, 622-625. [6] Gibson et al., J Petrol, 1995, 36, 89-229.

  13. "DOBREfraction'99" - Velocity models of the crust and upper mantle beneath the Donbas Foldbelt (SE Ukraine)

    Science.gov (United States)

    Stephenson, R. A.; Dobrefraction'00 Working Group,.

    2002-12-01

    The Pripyat-Dniepr-Donets basin (PDD) is a Late Devonian rift basin located on the southwestern part of the East-European Craton (EEC). This rift basin strikes in a southeasterly direction and extends from Belarus through Ukraine, where it connects with the Donbas foldbelt and its continuation as the deformed southern margin of the craton (Karpinsky Swell) in southern Russia. The Pripyat and Dniepr-Donets basins are important hydrocarbon provinces. The Donbas foldbelt (DF) is the uplifted and deformed part of the 20-km thick Dniepr-Donets basin. In 1999, an international cooperative deep seismic sounding (DSS) experiment (DOBREfraction'99) was undertaken. This effort involved 11 in-line shotpoints and deployment of some 245 recording stations along a northeast-trending, 360 km long profile extending from the shores of the Azov Sea in the south, across the Azov Massif (Ukrainian Shield), the DF, ending at the Ukraine-Russia border in the Voronezh Massif of the EEC. Particular scientific targets included the nature of the crust-mantle transition and the geometry of crustal/upper mantle structures related to rifting and subsequent basin inversion. Tomographic inversion, as well as, ray-trace based velocity modelling has been carried out. The velocity signature of the sedimentary basin itself is well resolved, indicating an asymmetric form (basement surface dipping more gently towards the center of the basin from the north than from the south) and a total thickness of about 20-km, comparable to estimates derived from previous seismic studies and geological interpretations. A thick (>10-km), high-velocity (>6.9 km/s), lower crustal body lies beneath the rift basin itself. This layer forms a domal structure that is offset slightly to the north compared to the main basin depocenter. A thinner (~5-km) high velocity layer is inferred beneath the southern margin of the Donbas foldbelt and Azov Massif. The former could be related to Permian uplift with the latter being due to

  14. Precambrian crust beneath the Mesozoic northern Canadian Cordillera discovered by Lithoprobe seismic reflection profiling

    Science.gov (United States)

    Cook, Frederick A.; Clowes, Ronald M.; Snyder, David B.; van der Velden, Arie J.; Hall, Kevin W.; Erdmer, Philippe; Evenchick, Carol A.

    2004-04-01

    -British Columbia border, a reflection dips eastward from ˜14.0 s to ˜21.0 s (˜45 to 73 km depth) beneath exposed Eocene magmatic rocks. It is interpreted as a relict subduction surface of the Kula plate. Our interpretation of Proterozoic layered rocks beneath most of the northern Cordillera suggests a much different crustal structure than previously considered: (1) Ancient North American crust comprising up to 25 km of metamorphosed Proterozoic to Paleozoic sediments plus 5-10 km of pre-1.8 Ga crystalline basement projects westward beneath most of the northern Canadian Cordillera. (2) The lateral (500 km by at least 1000 km) and vertical (up to 25 km) extent of the Proterozoic layers and their internal deformation are consistent with a long-lived margin for northwestern North America with alternating episodes of extension and contraction. (3) The detachments that carry deformed rocks of the Mackenzie Mountains and northern Rocky Mountains are largely confined to the upper crustal region above the layering. (4) Accreted terranes include thin klippen that were thrust over North American pericratonic strata (e.g., Yukon-Tanana), and terranes such as Nisling and Stikinia that thicken westward as the underlying Proterozoic layers taper and disappear. (5) The ages of exposed rocks are not necessarily indicative of the ages of underlying crust, a frequent observation in Lithoprobe interpretations, so that estimates of crustal growth based on surface geology may not be representative.

  15. NOrth AMerica Soil (NOAM-SOIL) Database

    Science.gov (United States)

    Miller, D. A.; Waltman, S. W.; Geng, X.; James, D.; Hernandez, L.

    2009-05-01

    NOAM-SOIL is being created by combining the CONUS-SOIL database with pedon data and soil geographic data coverages from Canada and Mexico. Completion of the in-progress NOrth AMerica Soil (NOAM-SOIL) database will provide complete North America coverage comparable to CONUS. Canadian pedons, which number more than 500, have been painstakingly transcribed to a common format, from hardcopy, and key- entered. These data, along with map unit polygons from the 1:1,000,000 Soil Landscapes of Canada, will be used to create the required spatial data coverages. The Mexico data utilizes the INEGI 1:1,000,000 scale soil map that was digitized by U. S. Geological Survey EROS Data Center in the mid 1990's plus about 20,000 pedons. The pedon data were published on the reverse side of the paper 1:250,000 scale Soil Map of Mexico and key entered by USDA and georeferenced by Penn State to develop an attribute database that can be linked to the 1:1,000,000 scale Soil Map of Mexico based on taxonomic information and geographic proximity. The essential properties that will be included in the NOAM-SOIL data base are: layer thickness (depth to bedrock or reported soil depth); available water capacity; sand, silt, clay; rock fragment volume; and bulk density. For quality assurance purposes, Canadian and Mexican soil scientists will provide peer review of the work. The NOAM-SOIL project will provide a standard reference dataset of soil properties for use at 1km resolution by NACP modelers for all of North America. All data resources, including metadata and selected raw data, will be provided through the Penn State web site: Soil Information for Environmental Modeling and Ecosystem Management (www.soilinfo.psu.edu). Progress on database completion is reported.

  16. National-Scale Changes in Soil Profile C and N in New Zealand Pastures are Determined by Land Use

    Science.gov (United States)

    Schipper, L. A.; Parfitt, R.; Ross, C.; Baisden, W. T.; Claydon, J.; Fraser, S.

    2010-12-01

    Grazed pasture is New Zealand’s predominant agricultural land-use and has been relatively recently developed from forest and native grasslands/shrub communities. From the 1850s onwards, land was cleared and exotic pastures established. Phosphorus fertilizer was increasingly used after 1950 which accelerated N fixation by clover. In the last two decades N fertilizers have been used, and grazing intensity has increased, thus affecting soil C and N. Re-sampling of 31 New Zealand soil profiles under grazed pasture measured surprisingly large losses of C and N over the last 2-3 decades (Schipper et al., 2007 Global Change Biology 13:1138-1144). These profiles were predominantly on the most intensively grazed flat land. We extended this re-sampling to 83 profiles (to 90 cm depth), to investigate whether changes in soil C and N stocks also occurred in less intensively managed pasture. Archived soils samples were analysed for total soil C and N alongside the newly collected samples. Intact cores were collected to determine bulk density through the profile. Over an average of 27 years, soils (0-30 cm) in flat dairy pastures significantly lost 0.73±0.16 Mg C ha-1y-1 and 57±16 kg N ha-1y-1 while we observed no change in soil C or N in flat pasture grazed by “dry stock” (e.g., sheep, beef), or in grazed tussock grasslands. Grazed hill country soils (0-30 cm) gained 0.52±0.18 Mg C ha-1y-1 and 66±18 kg N ha-1y-1. The losses of C and N were strongly correlated and C:N ratio has generally declined suggesting soils are becoming N saturated. Losses and gains also occurred in soil layers below 30 cm demonstrating that organic matter throughout the profile was responding to land use. The losses under dairying may be due to greater grazing pressure, fertilizer inputs and exports of C and N. There is evidence that grazing pressure reduces inputs of C below ground, reduces soil microbial C, and that dairy cow urine can mobilise C and N. Gains in hill country pastures may be due

  17. High velocity anomaly beneath the Deccan volcanic province: Evidence from seismic tomography

    Science.gov (United States)

    Iyer, H.M.; Gaur, V.K.; Rai, S.S.; Ramesh, D.S.; Rao, C.V.R.; Srinagesh, D.; Suryaprakasam, K.

    1989-01-01

    Analysis of teleseismic P-wave residuals observed at 15 seismograph stations operated in the Deccan volcanic province (DVP) in west central India points to the existence of a large, deep anomalous region in the upper mantle where the velocity is a few per cent higher than in the surrounding region. The seismic stations were operated in three deployments together with a reference station on precambrian granite at Hyderabad and another common station at Poona. The first group of stations lay along a west-northwesterly profile from Hyderabad through Poona to Bhatsa. The second group roughly formed an L-shaped profile from Poona to Hyderabad through Dharwar and Hospet. The third group of stations lay along a northwesterly profile from Hyderabad to Dhule through Aurangabad and Latur. Relative residuals computed with respect to Hyderabad at all the stations showed two basic features: a large almost linear variation from approximately +1s for teleseisms from the north to-1s for those from the southeast at the western stations, and persistance of the pattern with diminishing magnitudes towards the east. Preliminary ray-plotting and three-dimensional inversion of the P-wave residual data delineate the presence of a 600 km long approximately N-S trending anomalous region of high velocity (1-4% contrast) from a depth of about 100 km in the upper mantle encompassing almost the whole width of the DVP. Inversion of P-wave relative residuals reveal the existence of two prominent features beneath the DVP. The first is a thick high velocity zone (1-4% faster) extending from a depth of about 100 km directly beneath most of the DVP. The second feature is a prominent low velocity region which coincides with the westernmost part of the DVP. A possible explanation for the observed coherent high velocity anomaly is that it forms the root of the lithosphere which coherently translates with the continents during plate motions, an architecture characteristic of precambrian shields. The low

  18. Determination of Nazca slab geometry and state of stress beneath the southern Peru and northern Bolivia

    Science.gov (United States)

    Kumar, A.; Wagner, L. S.; Beck, S. L.; Young, B. E.; Zandt, G.; Long, M. D.; Tavera, H.; Minaya, E.

    2013-12-01

    Subduction of the Nazca plate in the north central Andes beneath southern Peru and northern Bolivia is of prime importance because of the role it plays in the evolution of topographic features since the late Eocene (~40 Ma). Previous studies based on slab event locations constrained only with teleseismic data defined a broad area of flat slab subduction in central and southern Peru, which transitions to a normally dipping slab beneath the northernmost Altiplano Plateau. We present earthquake locations and focal mechanisms using data from two temporary arrays: the network of 50 broadband seismic stations that were part of the NSF-Continental Dynamics-funded project 'CAUGHT' (Central Andean Uplift and the Geodynamics of High Topography) and the 40 station NSF- Geophysics funded 'PULSE' array (PerU Lithosphere and Slab Experiment). Our earthquake locations provide new information about the geometry of subducting Nazca slab between 13°S to 18°S. A significant clustering of intermediate depth earthquakes at ~15.5°S and 18°S suggests strong and localized release of tectonic stress in the slab perhaps due to bending and unbending. There are not enough intra-slab events at depth greater than 100 km to constrain the flat slab width north of 14°S. Our analyses indicate that the flat slab is at least 10 to 12 km shallower than the previous estimates (e.g. Cahill and Isacks, 1992; Ramos, 2009). Focal mechanisms and stress axis orientation of slab events at ~15.5°S indicate down-dip extension, where the dip changes from subhorizontal to steeply dipping slab. The continuity in the trend of stress suggests that the slab is deformed but not torn where it transitions from flat to steeply dipping. Data from local slab events will eventually be incorporated into a local tomographic body wave inversion to better constrain the velocity structure of the mantle lithosphere and asthenosphere below the Altiplano. This in turn will provide the valuable information on the process

  19. Widespread Refreezing of Both Surface and Basal Melt Water Beneath the Greenland Ice Sheet

    Science.gov (United States)

    Bell, R. E.; Tinto, K. J.; Das, I.; Wolovick, M.; Chu, W.; Creyts, T. T.; Frearson, N.

    2013-12-01

    Northeast Ice Stream. The contrasting rheology of glacial and interglacial ice may also enhance the deformation associated with freeze-on beneath large ice sheets. The occurrence of basal units both in the ice sheet interior and in the thermally very different ablation zone indicates refreezing is widespread and can occur in many environments beneath an ice sheet. This process appears to influence the morphology and behavior of the ice sheet from top to bottom.

  20. Permeability Structure Beneath the Lost City Hydrothermal Field, Atlantis Massif Oceanic Core Complex

    Science.gov (United States)

    McCaig, A. M.; Titarenko, S.

    2012-12-01

    The Lost City Hydrothermal Field (LCHF) has been venting low temperature (50-90 °C) alkaline fluids for at least 120,000 years. It is located close to the crest of the transform wall of the Atlantis Massif (30 °N, MAR), and is underlain by detachment fault schists and serpentinized peridotites with minor gabbro. Only 5km to the north, IODP Hole 1309D sampled 1400 m of gabbroic rocks. An almost linear thermal gradient of ~100 °C/km has recently been measured in the Hole during IODP expedition 340T, a unique piece of data in young ocean crust. The combination of a steep conductive gradient in proximity to a long lived hydrothermal system places severe constraints on the permeability structure of the Massif. We have used Comsol Multiphysics to create the first 2-D topographic model of the LCHF using a N-S profile through the vent site and Hole 1309D. Initial models use a constant basal heat flow (0.2 W/m2) which produces a steady state conductive gradient of about 85 °C/km using temperature-dependent conductivity and heat capacity. We include a low permeability basal layer and in some models a lower permeability zone beneath the IODP Hole with a boundary dipping steeply southwards, corresponding to a boundary between gabbro and serpentinite inferred from seismic tomography. We have used two top boundary conditions; (1) a mixed boundary condition in which dT/dz =0 if flow is upwards, and T=0 if flow is downwards, and (2) T=0. The first boundary condition is normally used in hydrothermal modelling but produces serious vent temperature artifacts at low upward flow rates since heat cannot escape conductively. The second boundary condition produces more stable models and has been shown by Wilcock (1998) to reproduce the form of hydrothermal circulation accurately. However vent temperatures can only be approximated due to the upper thermal boundary layer produced. With a constant permeability in the upper part of the model, transient high temperature vents form near the

  1. Upper Mantle Composition Beneath the Petit-Spot Area in Northwestern Pacific: Insights From Electrical Conductivity

    Science.gov (United States)

    Baba, K.; Ichiki, M.; Abe, N.; Hirano, N.

    2007-12-01

    The mantle composition beneath the petit-spot area, where is about 500 km offshore from Japan Trench in northwestern Pacific, is discussed through electrical conductivity obtained by seafloor magnetotelluric (MT) survey. The seafloor MT data were collected using ocean bottom electromagnetometers (OBEMs) at four sites with the spacing of 100-150 km, between May and August, 2005. The survey was conducted as a part of the petit-spot multidsciplinary project. The petit-spot is young volcanic activity on very old (~130 Ma) oceanic plate characterized as a clump of small knolls which erupted strong to moderate alkaline basalt. This volcanic field is associated with neither any plate boundaries nor hot spots. To elucidate the magma generation process of this new-type volcanic activity, a collaborative study of various geophysical and geochemical approaches has been carried out. The MT survey aims to constrain the physical state of the lithosphere and asthenosphere where the petit-spot melt is probably generated. The acquired electromagnetic field variation data were analyzed and the MT responses, which is the transfer function between the electric and magnetic fields, were obtained. The effect for the ocean-land distribution and seafloor topography on the MT responses was modeled and stripped. As the result, the corrected responses indicate that the lateral heterogeneity in electrical conductivity is less significant beneath the survey area. One- dimensional inversion study shows that the data require a peak in conductivity (0.05 S/m) at about 200 km depth. The mantle temperature may be calculated from the conductivity using an experimental result for dry olivine (Constable et al., 1992). The resultant temperature is about 1750 °C which is lower than the dry solidus for garnet peridotite. Instead, assuming the temperature as GDH1 model (Stein and Stein, 1992) for 130 Myr old mantle, we calculate water content in olivine using an experimental result by Wang et al. (2006

  2. Upper mantle discontinuity beneath the SW-Iberia peninsula: A multidisciplinary view.

    Science.gov (United States)

    Palomeras, Imma; de Lis Mancilla, Flor; Ayarza, Puy; Afonso, Juan Carlos; Diaz, Jordi; Morales, Jose; Carbonell, Ramon; Topoiberia Working Group

    2010-05-01

    Evidence for an upper mantle discontinuity located between 60 and 70 km depth have been provided by different seismic data sets acquired in the Southern Iberian peninsula. First indications of such a discontinuity were obtained by the very long offsets seismic refraction shot gathers acquired within the DSS ILIHA project in the early 90's. Clear seismic events recoded by the dense wide-angle seismic reflection shot gathers of the IBERSEIS experiment (2003) provided further constraints on the depth of the discontinuity and first-order estimates of its physical properties beneath the Ossa Morena Zone. Furthermore, the normal incidence Vibroseis deep seismic reflection images of the ALCUDIA transect (2007) extends this structure to the northeast beneath the Central Iberian Zone. This transect images deep laterally discontinuous reflections at upper mantle travel times (19 s) that roughly correspond to depths within the range of 60-70 km. Receiver function studies of the passive seismic recordings acquired by the IBERARRAY (TOPOIBERIA projects) provides additional support for the existence of this upper mantle structure and suggests that this is a relatively large scale regional feature. Two major scenarios need to be addressed when discussing the origin and nature of this deep structure. One is the tectonic scenario in which the structure maybe be related to a major tectonic event such as an old subduction process and therefore represent an ancient slab. A second hypothesis, would relate this feature to a phase change in the mantle. This latter assumption requires this feature ought to be a broader scale boundary which could be identified by different seismic techniques. Reflectivity modeling carried out over the IBERSEIS wide angle reflection data concludes that the observed phase is consistent with an heterogeneous gradient zone located at, approximately, 61-72 km depth. A layered structure with alternating velocities within ranges 8.1 to 8.3 km/s is necessary in

  3. "DOBREfraction'99" - Velocity Model of the Crust and Upper Mantle Beneath the Donbas Foldbelt (east Ukraine)

    Science.gov (United States)

    Omelchenko, V.; Starostenko, V. I.; Stephenson, R. A.; Guterch, A.; Janik, T.; Grad, M.; Stovba, S. M.; Tolkunov, A.; Thybo, H.; Lang, R.; Lyngsie, S. B.; Keller, G. R.

    2001-12-01

    The East European Craton (EEC) contains a classic example of the tectonic inversion of a continental rift zone. The Donbas Foldbelt (DF) is the uplifted and deformed part of the up to 20-km thick Dniepr-Donets Basin that formed as the result of rifting of the EEC in the Late Devonian. The DF, especially its southern margin, was uplifted in Early Permian times, in a (trans)tensional tectonic stress regime while folding and reverse faulting mainly occurred later primarily during the Late Cretaceous. A seismic refraction/wide-angle reflection survey was carried out in 1999 to complement existing Deep Seismic Sounding data from the area that, because maximum offsets were generally not greater than about 150 km, did not record significant Pn phase arrivals. The 1999 main survey comprised some 245 recording stations along a line of 360 km length, with 11 in-line shotpoints, extending from the shores of the Azov Sea in the south, across the Azov Massif of the Ukrainian Shield and the DF, ending at the Ukraine-Russia border in the Voronezh Massif of the EEC. Particular scientific targets included the nature of the crust-mantle transition and the geometry of crustal/upper mantle structures related to rifting and subsequent basin inversion. Tomographic inversion as well as ray-trace based velocity modeling has been carried out. The velocity signature of the sedimentary basin itself is well resolved, indicating an asymmetric form (basement surface dipping more gently towards the center of the basin from the north than from the south) and a total thickness of about 20-km, comparable to estimates derived from previous seismic studies and geological interpretations. A thick ( more 10-km), high velocity (more than 6.9 km/s) lower crustal body lies beneath the rift basin itself (DF) but is offset slightly to the north compared to the main basin depocenter. This layer is most likely related to the earlier rifting processes and may represent magmatic underplating. Velocities in the

  4. A Preliminary Study on the Lithosphere-Asthenosphere Boundary beneath the South China Sea

    Science.gov (United States)

    Lee, T. T. Y.; Chen, C. W.

    2014-12-01

    The lithosphere-asthenosphere boundary (LAB) is an important boundary at which the rigid lithosphere translates coherently upon the viscous asthenosphere. New observations have been made on LAB through detailed seismic analysis, especially that from receiver functions. Previous studies have found LAB depth varies significantly, systematically getting shallower from continental to oceanic lithosphere. In smaller scale, the depth and sharpness of LAB also differ from region to region, suggesting the effects of a combination of thermal and compositional origins. In this study, we investigate the LAB beneath the South China Sea, a region poorly instrumented that conventional seismological are less effective and impractical. The South China Sea is on the Sunda Plate, which is considered to be once the southeastern part of the Eurasia Plate before separating with a distinct moving direction from that of India-Eurasia continental collision. The South China Sea is Phanerozoic in age and continental in nature, but the striped magnetic anomalies observed from the sea floor have suggested multiple spreading events since early Miocene, indicating the presence of latter formed oceanic lithosphere. Previous seismic studies of this region focused mainly on shallow basin structure pertaining to petroleum exploration. The lithospheric structure, particularly the LAB, remains elusive, while it provides important insight into the complex tectonic history in this region. To image the LAB, we use the precursor of SS phase. The precursor bounces at the LAB discontinuity at depth would appear before the SS and presents a signal amenable to analysis for depth and properties. We collect seismic waveform data recorded mainly at Japan and Cocos Islands of corresponding teleseismic events from Southern Sumatera and Japan, with SS and potential precursors bouncing beneath the South China Sea. We employ an analysis technique, velocity spectral analysis (vespagrams), to identify precursory

  5. Composition and evolution of lithosphere beneath the Carpathian Pannonian Region: a review

    Science.gov (United States)

    Szabó, C.; Falus, Gy.; Zajacz, Z.; Kovács, I.; Bali, E.

    2004-11-01

    Our knowledge of the lithosphere beneath the Carpathian-Pannonian Region (CPR) has been greatly improved through petrologic, geochemical and isotopic studies of upper mantle xenoliths hosted by Neogene-Quaternary alkali basalts. These basalts occur at the edge of the Intra-Carpathian Basin System (Styrian Basin, Nógrád-Gömör and Eastern Transylvanian Basin) and its central portion (Little Hungarian Plain, Bakony-Balaton Highland). The xenoliths are mostly spinel lherzolites, accompanied by subordinate pyroxenites, websterites, wehrlites, harzburgites and dunites. The peridotites represent residual mantle material showing textural and geochemical evidence for a complex history of melting and recrystallization, irrespective of location within the region. The lithospheric mantle is more deformed in the center of the studied area than towards the edges. The deformation may be attributed to a combination of extension and asthenospheric upwelling in the late Tertiary, which strongly affected the central part of CPR subcontinental lithosphere. The peridotite xenoliths studied show bulk compositions in the following range: 35-48 wt.% MgO, 0.5-4.0 wt.% CaO and 0.2-4.5 wt.% Al 2O 3 with no significant differences in regard to their geographical location. On the other hand, mineral compositions, particularly of clinopyroxene, vary according to xenolith texture. Clinopyroxenes from less deformed xenoliths show higher contents of 'basaltic' major elements compared to the more deformed xenoliths. However, clinopyroxenes in more deformed xenoliths are relatively enriched in strongly incompatible trace elements such as light rare earth elements (LREE). Modal metasomatic products occur as both hydrous phases, including pargasitic and kearsutitic amphiboles and minor phlogopitic micas, and anhydrous phases — mostly clinopyroxene and orthopyroxene. Vein material is dominated by the two latter phases but may also include amphibole. Amphibole mostly occurs as interstitial phases

  6. Investigation of mantle kinematics beneath the Hellenic-subduction zone with teleseismic direct shear waves

    Science.gov (United States)

    Confal, Judith M.; Eken, Tuna; Tilmann, Frederik; Yolsal-Çevikbilen, Seda; Çubuk-Sabuncu, Yeşim; Saygin, Erdinc; Taymaz, Tuncay

    2016-12-01

    The subduction and roll-back of the African plate beneath the Eurasian plate along the arcuate Hellenic trench is the dominant geodynamic process in the Aegean and western Anatolia. Mantle flow and lithospheric kinematics in this region can potentially be understood better by mapping seismic anisotropy. This study uses direct shear-wave splitting measurements based on the Reference Station Technique in the southern Aegean Sea to reveal seismic anisotropy in the mantle. The technique overcomes possible contamination from source-side anisotropy on direct S-wave signals recorded at a station pair by maximizing the correlation between the seismic traces at reference and target stations after correcting the reference stations for known receiver-side anisotropy and the target stations for arbitrary splitting parameters probed via a grid search. We obtained splitting parameters at 35 stations with good-quality S-wave signals extracted from 81 teleseismic events. Employing direct S-waves enabled more stable and reliable splitting measurements than previously possible, based on sparse SKS data at temporary stations, with one to five events for local SKS studies, compared with an average of 12 events for each station in this study. The fast polarization directions mostly show NNE-SSW orientation with splitting time delays between 1.15 s and 1.62 s. Two stations in the west close to the Hellenic Trench and one in the east show N-S oriented fast polarizations. In the back-arc region three stations exhibit NE-SW orientation. The overall fast polarization variations tend to be similar to those obtained from previous SKS splitting studies in the region but indicate a more consistent pattern, most likely due to the usage of a larger number of individual observations in direct S-wave derived splitting measurements. Splitting analysis on direct shear waves typically resulted in larger split time delays compared to previous studies, possibly because S-waves travel along a longer path

  7. The Lowermost Mantle Beneath Central America Imaged by Kirchhoff Migration of Scatterers and Reflectors

    Science.gov (United States)

    Hutko, A.; Lay, T.; Revenaugh, J.

    2007-05-01

    We use tens of thousands of seismograms from South and Central American earthquakes recorded by western North American seismic networks to image the lowermost mantle beneath Central America using a 3D Kirchhoff migration method. P wave studies of the deep mantle often rely on some form of stacking of many records in order to enhance the signal-to-noise ratio of weak phases generated by deep structure, such as reflections off of the D" discontinuity. These methods, however, often assume one-dimensional structure, which is at odds with the evidence for significant heterogeneity. Kirchhoff migration is a three-dimensional stacking method that allows interactions with structure outside of the source-receiver plane, thus illuminating a much larger volume. The D" discontinuity beneath Central America has been readily observed in S wave studies and may be the result of the shear wave velocity increase associated with the recently discovered perovskite to post-perovskite phase transition. This phase transition is expected to have weaker effects on P wave velocities than on S wave velocities and the sharpness of this transition is unknown. Using data at post-critical distances, we observe structures consistent with a P velocity discontinuity about 200 km above the core-mantle boundary (CMB). Observing this using short period data suggests that the boundary must be less than a few 10s of km thick, while observation with lower frequency broadband data exclude the possibility of it being a thin layer. Whether this discontinuity is co-located for both P and S waves is difficult to resolve. Both the broadband and the short period P wave data sets also reveal a sharp out-of-plane scatterer, which may be located close to the CMB. The short period data also indicate reflectivity about 400 km above the CMB, well above the D" discontinuity, and similar reflectivity is observed under the Central Pacific. This feature appears to be more consistent with a discontinuity than a scatterer

  8. Frequency Dependant P Wave Structure of D" Beneath Central America Imaged by Kirchhoff Migration

    Science.gov (United States)

    Hutko, A. R.; Lay, T.; Revenaugh, J.

    2006-12-01

    We use thousands of seismograms from South and Central American earthquakes recorded by western North American seismic networks to image the lowermost mantle beneath Central America using a 3D Kirchhoff migration scheme. P wave studies of the deep mantle often rely on some form of stacking of many records in order to enhance the signal-to-noise ratio of weak phases generated by deep structure, such as reflections off of the D" discontinuity. These methods, however, often assume one-dimensional structure, which is at odds with the evidence for significant heterogeneity. Kirchhoff migration is a three-dimensional stacking method that allows interactions with structure off of the source-receiver plane, thus imaging a much larger volume and avoiding false projections of scattered arrivals onto specular reflectors. The D" discontinuity beneath Central America has been readily observed in S wave studies and may be the result of the shear wave velocity increase associated with the recently discovered perovskite to post-perovskite phase transition. This phase transition is expected to have weaker effects on P wave velocities than on S wave velocities and the sharpness of this transition is unknown. We observe structures consistent with a discontinuity about 200 km above the core-mantle boundary (CMB). The fact that this is seen at all in short period data suggests that its boundary must be less than 10 to 20 km thick, while observation with broadband data exclude the possibility of it being a thin layer or lamella. Whether the discontinuity is co-located for both P and S waves is difficult to resolve given uncertainties in the long-scale velocity heterogeneity. In addition, both broadband and short period P wave data sets reveal a sharp out-of-plane scatterer, which may be located close to the CMB. The short period data also indicate reflectivity about 400 km above the CMB, well above the aforementioned D" discontinuity, and similar reflectivity is observed under the

  9. Early Carboniferous (˜357 Ma) crust beneath northern Arabia: Tales from Tell Thannoun (southern Syria)

    Science.gov (United States)

    Stern, Robert J.; Ren, Minghua; Ali, Kamal; Förster, Hans-Jürgen; Al Safarjalani, Abdulrahman; Nasir, Sobhi; Whitehouse, Martin J.; Leybourne, Matthew I.; Romer, Rolf L.

    2014-05-01

    Continental crust beneath northern Arabia is deeply buried and poorly known. To advance our knowledge of this crust, we studied 8 xenoliths brought to the surface by Neogene eruptions of Tell Thannoun, S. Syria. The xenolith suite consists of two peridotites, one pyroxenite, four mafic granulites, and one charnockite. The four mafic granulites and charnockite are probably samples of the lower crust, and two mafic granulites gave 2-pyroxene equilibration temperatures of 780-800 °C, which we take to reflect temperatures at the time of formation. Peridotite and pyroxenite gave significantly higher temperatures of ∼900 °C, consistent with derivation from the underlying lithospheric mantle. Fe-rich peridotite yielded T∼800 °C, perhaps representing a cumulate layer in the crust. Three samples spanning the lithologic range of the suite (pyroxenite, mafic granulite, and charnockite) yielded indistinguishable concordant U-Pb zircon ages of ∼357 Ma, interpreted to approximate when these magmas crystallized. These igneous rocks are mostly juvenile additions from the mantle, as indicated by low initial 87Sr/86Sr (0.70312 to 0.70510) and strongly positive initial εNd(357 Ma) (+4 to +9.5). Nd model ages range from 0.55 to 0.71 Ga. We were unable to unequivocally infer a tectonic setting where these melts formed: convergent margin, rift, or hotspot. These xenoliths differ from those of Jordan and Saudi Arabia to the south in four principal ways: 1) age, being least 200 Ma younger than the presumed Neoproterozoic (533-1000 Ma) crust beneath Jordan and Saudi Arabia; 2) the presence of charnockite; 3) abundance of Fe-rich mafic and ultramafic lithologies; and 4) the presence of sapphirine. Our studies indicate that northern Arabian plate lithosphere contains a significant proportion of juvenile Late Paleozoic crust, the extent of which remains to be elucidated. This discovery helps explain fission track resetting documented for rocks from Israel and provides insights into

  10. Anisotropy in the lowermost mantle beneath the circum-Pacific: observations and modelling

    Science.gov (United States)

    Walpole, J.; Wookey, J. M.; Nowacki, A.; Walker, A.; Kendall, J. M.; Masters, G.; Forte, A. M.

    2014-12-01

    The lowermost 300 km of mantle (D'') acts as the lower boundary layer to mantle convection. Numerous observations find that this layer is anisotropic, unlike the bulk of the lower mantle above, which is isotropic. The causal mechanism for this anisotropy remains elusive, though its organisation is likely to be imposed by deformation associated with mantle convection. The subduction of the Tethys ocean (since 180 Ma) is predicted to have deposited slab material in D'' in circum-Pacific regions, making these regions cold, encouraging the phase transformation in the MgSiO3 polymorph bridgmanite to a post-perovskite (ppv) structure. These regions are probably rich in ppv. Here we present new observations of anisotropy from shear wave splitting of ScS phases recorded in the epicentral distance range 50-85 degrees. These observations are corrected for anisotropy in the upper mantle beneath source and receiver. Due to the layout of events and receivers we primarily sample D'' beneath the landward side of the circum-Pacific. A detailed pattern of anisotropy is revealed. Anisotropy predominantly leads to SH fast wave propagation with an inferred average strength of 0.9%. This is consistent with many previous observations. However, we do not limit our observations to the SH/SV system. Many observations show non SH/SV fast polarisation. We interpret these data for tilted transverse isotropy (TTI) style anisotropy. We resolve non-radial anisotropy at unprecedented global scale, in turn placing new constraints on the D'' flow field. We test the ability of the flow model TX2008 (Simmons et al., 2009) to fit our observations. This is achieved by modelling the development of a lattice preferred orientation texture of a ppv layer subject to this flow field using a visco-plastic self consistent theory (Walker et al., 2011). Due to uncertainty in the slip system of ppv three candidate glide planes are trialled: (100)/{110}, (010), and (001). The seismic anisotropy of these models is

  11. Converted phases from sharp 1000 km depth mid-mantle heterogeneity beneath Western Europe

    Science.gov (United States)

    Jenkins, J.; Deuss, A.; Cottaar, S.

    2017-02-01

    Until recently, most of the lower mantle was generally considered to be well-mixed with strong heterogeneity restricted to the lowermost several hundred kilometres above the core-mantle boundary, known as the D″ layer. However several recent studies have started to hint at a potential change in Earth's structure at mid-mantle depths beneath the transition zone. Here we present a continental-wide search of Europe and the North Atlantic for mid-mantle P-to-s wave converted phases. Our data set consists of close to 50,000 high quality receiver functions. These are combined in slowness and depth stacks to identify seismic discontinuities in the range of 800-1400 km depth to determine at which depths and in which tectonic settings these features exist. Receiver functions are computed in different frequency bands to resolve the sharpness of the observed discontinuities. We find most seismic velocity jumps are observed between 975-1050 km depth, localised beneath western Europe and Iceland. The shear wave velocity jumps are roughly 1-2.5% velocity increase with depth occurring over less than 8 km in width. The most robust observations are coincident with areas of active upwelling (under Iceland) and an elongate lateral low velocity anomaly imaged in recent tomographic models which has been interpreted as diverted plume material at depth. The lack of any suggested phase change in a normal pyrolitic mantle composition at around 1000 km depth indicates the presence of regional chemical heterogeneity within the mid-mantle, potentially caused by diverted plume material. We hypothesise that our observations represent either a phase change within chemically distinct plume material itself, or are caused by small scale chemical heterogeneities entrained within the upwelling plume, either in the form of recycled basaltic material or deep sourced chemically distinct material from LLSVPs. Our observations, which cannot be directly linked to an area of either active or ancient

  12. Constraining the thermal structure beneath Lusi: insights from temperature record in erupted clasts

    Science.gov (United States)

    Malvoisin, Benjamin; Mazzini, Adriano; Miller, Stephen

    2016-04-01

    Sedimentary units beneath Lusi from surface to depth are the Pucangan formation, the Upper Kalibeng formation where shales and then volcanoclastic clasts are found, the Kujung-Propuh-Tuban formation composed of carbonates and the Ngimbang formation composed of shales. Water and gas geochemistry as well as surface deformation indicate that Lusi is a hydrothermal system rooted at >4 km depth. However, the thermal structure beneath Lusi is still poorly constrained whereas it has first-order impacts on the physical and chemical processes observed during the eruption. In the framework of the Lusi Lab project (ERC grant n° 308126) and of a project of the Swiss National Science Foundation (n°160050) we studied erupted clasts collected at the crater site to determine their source and temperature record. Three types of clasts were studied based on morphological and mineralogical basis. The first type is limestones mainly composed of Ca- and Fe-bearing carbonates. The clasts of the second type are light grey shales (LGS) containing carbonaceous matter, illite/smectite mixture, plagioclase and quartz. The third type is also a shale with a black colour containing hydrocarbons (black shales, BS) and with the additional presence of Na-rich plagioclase, biotite and chlorite. The presence of these latter minerals indicates hydrothermal activity at relatively high temperature. Better constraints on temperature were obtained by using both Raman spectroscopic carbonaceous material thermometry (RSCM) and chlorite geothermometry. Temperatures below 200°C were determined for the LGS with RSCM. BS recorded two temperatures. The first one, around 170°C, is rather consistent with an extrapolation of the geothermal gradient measured before the eruption up to 4,000 m depth. Combined with mineralogical observations, this suggests that BS originate from the Ngimbang formation. The second recorded higher temperature around 250°C indicates heating, probably through interaction with high

  13. Bacterial diversity and distribution in the southeast edge of the Tengger Desert and their correlation with soil enzyme activities

    Institute of Scientific and Technical Information of China (English)

    Wei Zhang; Gaosen Zhang; Guangxiu Liu; Zhibao Dong; Tuo Chen; Manxiao Zhang; Paul J.Dyson; Lizhe An

    2012-01-01

    The nature of microbial communities and their relation to enzyme activities in desert soils is a neglected area of investigation.To address this,the bacterial diversity and distribution and soil physico-chemical factors were investigated in the soil crust,the soil beneath the crust and rhizosphere soil at the southeast edge of the Tengger Desert,using the denaturing gradient gel electrophoresis of 16S rRNA genes amplified by the polymerase chain reaction.Phylogenetic analysis of the sequenced DGGE bands revealed a great diversity of bacteria.The Proteobacteria,consisting of the α,β,and γ subdivisions,were clearly the dominant group at all depths and in rhizosphere soil.Analysis of the enzyme activities indicated that the rhizosphere soil of Caragana korshinskii exhibited the highest protease and polyphenol oxidase activities,and in the soil crust there were increased activities of catalase,urease,dehydrogenase and sucrase.The bacterial community abundance closely correlated with soil enzyme activities in different soils.The presence of Cyanobacteria correlated with significant increases in protease,catalase and sucrase in the soil crust,and increased urease in the rhizosphere soil of Artemisia ordosica.The occurrence of Acidobacteria was associated with significant increases in urease,dehydrogenase,and sucrase in the rhizosphere soil of C.korshinski.The presence of γ-Proteobacteria correlated with a significant increase in polyphenol oxidase in the rhizosphere soil of A.ordosica.The study indicated a close relationship between the soil bacterial community and soil enzymes,suggesting the necessity of further investigations into bacterial function in this desert ecosystem.

  14. Non-Linear Responses to Precipitation and Shrub Encroachment in Semi-Arid Grassland: Isotopes and CO2 Fluxes Reveal Soil Microsite Alteration as Explanation

    Science.gov (United States)

    Cable, J. M.; Sun, W.; Ogle, K.; Williams, D. G.; Potts, D. L.; Scott, R. L.; Huxman, T. E.

    2006-12-01

    Responses of net ecosystem production (NEP) to growing season rainfall amount is non-linear over a gradient of woody-plant encroachment in semi-arid riparian grassland. NEP is positively correlated with growing season precipitation amount in the grassland, but is negatively correlated with precipitation amount in a former C4 grassland now occupied by large mesquite (Prosopis) individuals. NEP at sites with intermediate stages of mesquite encroachment have a complex, threshold response to precipitation amount. Mesquite encroachment creates patchy soil microsites and spatial variation in rooting depth and activity. We hypothesized that variation in soil microsite properties (e.g., temperature, labile carbon) and root activity affect soil CO2 efflux in such a way that explains the non-linearity in response of NEP to precipitation. We measured soil CO2 efflux during the dry pre-monsoon (early summer) and wet monsoon (mid summer) periods on old floodplain terraces along the San Pedro River in southeastern Arizona. We made intensive spatial and temporal measurements of soil CO2 flux in four microsites associated with woody-plant encroachment: inter-canopy space and beneath the canopies of grasses, medium mesquite, and large mesquite. We also measured the δ13C of soil-respired CO2, which provided insight into the contribution of different sources (e.g., roots vs. microbes) to soil CO2 efflux. Soil respiration was highest beneath large mesquite near the canopy center, and lowest beneath medium mesquite and in inter-canopy spaces. The δ13C data revealed that soil respiration was dominated by a C4 signal during the pre-monsoon, but it switched to being dominated by the C3 mesquite signal during the wet monsoon period. Respiration was most sensitive to precipitation inputs beneath the large mesquite, where labile carbon in the form of mesquite litter is readily available. Conversely, soil respiration was least sensitive to precipitation in the open, inter- canopy space

  15. Fundamentals of soil science

    Science.gov (United States)

    This study guide provides comments and references for professional soil scientists who are studying for the soil science fundamentals exam needed as the first step for certification. The performance objectives were determined by the Soil Science Society of America's Council of Soil Science Examiners...

  16. Hot fire, cool soil

    NARCIS (Netherlands)

    Stoof, C.R.; Moore, D.; Fernandes, P.; Stoorvogel, J.J.; Fernandes, R.; Ferreira, A.J.D.; Ritsema, C.J.

    2013-01-01

    Wildfires greatly increase a landscape's vulnerability to flooding and erosion events by removing vegetation and changing soils. Fire damage to soil increases with increasing soil temperature, and, for fires where smoldering combustion is absent, the current understanding is that soil temperatures i

  17. Decadal and long-term boreal soil carbon and nitrogen sequestration rates across a variety of ecosystems

    Science.gov (United States)

    Manies, Kristen L.; Harden, Jennifer W.; Fuller, Christopher C.; Turetsky, Merritt R.

    2016-08-01

    Boreal soils play a critical role in the global carbon (C) cycle; therefore, it is important to understand the mechanisms that control soil C accumulation and loss for this region. Examining C & nitrogen (N) accumulation rates over decades to centuries may provide additional understanding of the dominant mechanisms for their storage, which can be masked by seasonal and interannual variability when investigated over the short term. We examined longer-term accumulation rates, using 210Pb and 14C to date soil layers, for a wide variety of boreal ecosystems: a black spruce forest, a shrub ecosystem, a tussock grass ecosystem, a sedge-dominated ecosystem, and a rich fen. All ecosystems had similar decadal C accumulation rates, averaging 84 ± 42 gC m-2 yr-1. Long-term (century) C accumulation rates were slower than decadal rates, averaging 14 ± 5 gC m-2 yr-1 for all ecosystems except the rich fen, for which the long-term C accumulation rates was more similar to decadal rates (44 ± 5 and 76 ± 9 gC m-2 yr-1, respectively). The rich fen also had the highest long-term N accumulation rates (2.7 gN m-2 yr-1). The lowest N accumulation rate, on both a decadal and long-term basis, was found in the black spruce forest (0.2 and 1.4 gN m-2 yr-1, respectively). Our results suggest that the controls on long-term C and N cycling at the rich fen is fundamentally different from the other ecosystems, likely due to differences in the predominant drivers of nutrient cycling (oxygen availability, for C) and reduced amounts of disturbance by fire (for C and N). This result implies that most shifts in ecosystem vegetation across the boreal region, driven by either climate or succession, will not significantly impact regional C or N dynamics over years to decades. However, ecosystem transitions to or from a rich fen will promote significant shifts in soil C and N storage.

  18. Decadal and long-term boreal soil carbon and nitrogen sequestration rates across a variety of ecosystems

    Science.gov (United States)

    Manies, Kristen L.; Harden, Jennifer W.; Fuller, Christopher C.; Turetsky, Merritt

    2016-01-01

    Boreal soils play a critical role in the global carbon (C) cycle; therefore, it is important to understand the mechanisms that control soil C accumulation and loss for this region. Examining C & nitrogen (N) accumulation rates over decades to centuries may provide additional understanding of the dominant mechanisms for their storage, which can be masked by seasonal and interannual variability when investigated over the short term. We examined longer-term accumulation rates, using 210Pb and 14C to date soil layers, for a wide variety of boreal ecosystems: a black spruce forest, a shrub ecosystem, a tussock grass ecosystem, a sedge-dominated ecosystem, and a rich fen. All ecosystems had similar decadal C accumulation rates, averaging 84 ± 42 gC m−2 yr−1. Long-term (century) C accumulation rates were slower than decadal rates, averaging 14 ± 5 gC m−2 yr−1 for all ecosystems except the rich fen, for which the long-term C accumulation rates was more similar to decadal rates (44 ± 5 and 76 ± 9 gC m−2 yr−1, respectively). The rich fen also had the highest long-term N accumulation rates (2.7 gN m−2 yr−1). The lowest N accumulation rate, on both a decadal and long-term basis, was found in the black spruce forest (0.2 and 1.4 gN m−2 yr−1, respectively). Our results suggest that the controls on long-term C and N cycling at the rich fen is fundamentally different from the other ecosystems, likely due to differences in the predominant drivers of nutrient cycling (oxygen availability, for C) and reduced amounts of disturbance by fire (for C and N). This result implies that most shifts in ecosystem vegetation across the boreal region, driven by either climate or succession, will not significantly impact regional C or N dynamics over years to decades. However, ecosystem transitions to or from a rich fen will promote significant shifts in soil C and N storage.

  19. Restoring Soil Quality to Mitigate Soil Degradation

    Directory of Open Access Journals (Sweden)

    Rattan Lal

    2015-05-01

    Full Text Available Feeding the world population, 7.3 billion in 2015 and projected to increase to 9.5 billion by 2050, necessitates an increase in agricultural production of ~70% between 2005 and 2050. Soil degradation, characterized by decline in quality and decrease in ecosystem goods and services, is a major constraint to achieving the required increase in agricultural production. Soil is a non-renewable resource on human time scales with its vulnerability to degradation depending on complex interactions between processes, factors and causes occurring at a range of spatial and temporal scales. Among the major soil degradation processes are accelerated erosion, depletion of the soil organic carbon (SOC pool and loss in biodiversity, loss of soil fertility and elemental imbalance, acidification and salinization. Soil degradation trends can be reversed by conversion to a restorative land use and adoption of recommended management practices. The strategy is to minimize soil erosion, create positive SOC and N budgets, enhance activity and species diversity of soil biota (micro, meso, and macro, and improve structural stability and pore geometry. Improving soil quality (i.e., increasing SOC pool, improving soil structure, enhancing soil fertility can reduce risks of soil degradation (physical, chemical, biological and ecological while improving the environment. Increasing the SOC pool to above the critical level (10 to 15 g/kg is essential to set-in-motion the restorative trends. Site-specific techniques of restoring soil quality include conservation agriculture, integrated nutrient management, continuous vegetative cover such as residue mulch and cover cropping, and controlled grazing at appropriate stocking rates. The strategy is to produce “more from less” by reducing losses and increasing soil, water, and nutrient use efficiency.

  20. High-resolution lithospheric structure beneath Mainland China from ambient noise and earthquake surface-wave tomography

    Science.gov (United States)

    Bao, X.; Song, X.; Li, J.

    2016-12-01

    We present a new high-resolution shear-velocity model of the lithosphere (down to about 160 km) beneath China using Rayleigh-wave tomography. We combined ambient noise and earthquake data recorded at 1316 seismic stations, the largest number used for the region to date. More than 700,000 dispersion curves were measured to generate group and phase velocity maps at periods of 10-140s. The resolution of our model is significantly improved over previous models with about 1-2°in eastern China and 2-3°in western China. We also derived models of the study region for crustal thickness and averaged S velocities for upper and mid-lower crust and uppermost mantle. These models reveal important lithospheric features beneath China and provide a fundamental data set for understanding continental dynamics and evolution. Different geological units show distinct features in the Moho depth, lithospheric thickness, and shear velocity. In particular, the North China Craton (NCC) lithosphere shows strong east-west structural variations with thin and low-velocity lithosphere in eastern NCC and thick and high-velocity lithosphere beneath western NCC and the lithosphere of the Ordos Block seems to have undergone strong erosion. The results support the progressive destruction of the NCC lithosphere from east to west at least partly caused by the thermal-chemical erosion of the cratonic lithosphere from the asthenosphere. Another pronounced feature of our model is the strong lateral variations of the mantle lithosphere beneath the Tibetan Plateau (TP). The Indian lithosphere beneath the TP shows variable northward advancement with nearly flat subduction in western and eastern TP and steep subduction in central TP with evidence for the tearing of Indian lithosphere beneath central TP, which may be important for the riftings at the surface in Himalayas and southern TP. The low-velocity zone in northern TP shows strong correlation with the region of the mid-Miocene to Quaternary potassic

  1. Lithosphere/Asthenosphere Structure beneath the Mendocino Triple Junction from the Analysis of Surface Wave, Ambient Noise, and Receiver Functions

    Science.gov (United States)

    Liu, K.; Zhai, Y.; Levander, A.; Porritt, R. W.; Allen, R. M.; Schmandt, B.; Humphreys, E.; O'Driscoll, L.

    2010-12-01

    We have developed a 3-D shear velocity model using finite-frequency Rayleigh wave phase velocity dispersion, PdS receiver functions, and ambient noise tomography to better understand the complex lithosphere/asthenosphere structures in the Mendocino Triple Junction (MTJ) region. Using approximately 100 events (July 2007-December 2008) recorded by the stations of the Flexible Array Mendocino Experiment (FAME), the USArray Transportable Array (TA) network, and the Berkeley Digital Seismograph network, we have obtained the phase velocities (20-100s) from the finite-frequency Rayleigh wave tomography, which agrees well with the ambient noise tomography results (7-40 s, Porritt & Allen, 2010) in the overlapping period range. We subsequently inverted for a 3-D Vs model on a 0.25°x0.25° grid from the combined dispersion datasets, constrained by interface depths from the PdS receiver functions (Zhai & Levander, 2010). The resulting crustal and upper mantle Vs model (~150 km) reveals strong lateral heterogeneity in the subduction and transform regimes of the Mendocino Triple Junction region where the Gorda, Pacific, and North American plates intersect. The subducting Gorda slab is well-imaged as an eastward-dipping high-velocity anomaly to ~100 km depth. At the same depth to the east we observe a large-scale low velocity zone, which is the mantle wedge beneath the North American Plate. The southern edge of the Gorda plate (SEDGE) is imaged at 80-100 km depth and is in excellent agreement with measurements made from PdS receiver functions, body-wave tomography (Schmandt & Humphreys, 2010; Obrebski et al., 2010), and active source studies. At depths greater than 80 km, we interpret low velocities under the Cascadia subduction zone as the asthenosphere below the Gorda plate, in agreement with measured LAB depths from RFs. South of the SEDGE shallow strong low-velocities appear beneath the transform region, which we interpret as the asthenosphere in the slab-gap region left by

  2. Cross-cutting activities: Soil quality and soil metagenomics

    OpenAIRE

    Peter P. Motavalli; Garrett, Karen A.

    2008-01-01

    This presentation reports on the work of the SANREM CRSP cross-cutting activities "Assessing and Managing Soil Quality for Sustainable Agricultural Systems" and "Soil Metagenomics to Construct Indicators of Soil Degradation." The introduction gives an overview of the extensiveness of soil degradation globally and defines soil quality. The objectives of the soil quality cross cutting activity are: CCRA-4 (Soil Metagenomics)

  3. Classification of Ferrallitic Soils in Chinese Soil Taxonomy

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The development of the classification of ferrallitic soils in China is reviewed and the classification of Ferralisols and Ferrisols in Chinese Soil Taxonomy is introduced in order to discuss the correlation between the ferrallitic soil classification in the Chinese Soil Taxonomy and those of the other soil classification systems. In the former soil classification systems of China, the ferrallitic soils were classified into the soil groups of Latosols, Latosolic red soils, Red soils, Yellow soils and Dry red soils, according to the combination of soil forming conditions, soil-forming processes, soil features and soil properties. In the Chinese Soil Taxonomy, most of ferrallitic soils are classified into the soil orders of Ferralisols and Ferrisols based on the diagnostic horizons and/or diagnostic characteristics with quantitatively defined properties. Ferralisols are the soils that have ferralic horizon, and they are merely subdivided into one suborder and two soil groups. Ferrisols are the soils that have LAC-ferric horizon but do not have ferralic horizon, and they are subdivided into three suborders and eleven soil groups. Ferralisols may correspond to part of Latosols and Latosolic red soils. Ferrisols may either correspond to part of Red soils, Yellow soils and Dry red soils, or correspond to part of Latosols and Latosolic red soils.

  4. Current ecological understanding of fungal-like pathogens of fish: what lies beneath?

    Directory of Open Access Journals (Sweden)

    Rodolphe Elie Gozlan

    2014-02-01

    Full Text Available Despite increasingly sophisticated microbiological techniques, and long after the first discovery of microbes, basic knowledge is still lacking to fully appreciate the ecological importance of microbial parasites in fish. This is likely due to the nature of their habitats as many species of fish suffer from living beneath turbid water away from easy recording. However, fishes represent key ecosystem services for millions of people around the world and the absence of a functional ecological understanding of viruses, prokaryotes, and small eukaryotes in the maintenance of fish populations and of their diversity represents an inherent barrier to aquatic conservation and food security. Among recent emerging infectious diseases responsible for severe population declines in plant and animal taxa, fungal and fungal-like microbes have emerged as significant contributors. Here, we review the current knowledge gaps of fungal and fungal-like parasites and pathogens in fish and put them into an ecological perspective with direct implications for the monitoring of fungal fish pathogens in the wild, their phylogeography as well as their associated ecological impact on fish populations. With increasing fish movement around the world for farming, releases into the wild for sport fishing and human-driven habitat changes, it is expected, along with improved environmental monitoring of fungal and fungal-like infections, that the full extent of the impact of these pathogens on wild fish populations will soon emerge as a major threat to freshwater biodiversity.

  5. Low electrical resistivity associated with plunging of the Nazca flat slab beneath Argentina.

    Science.gov (United States)

    Booker, John R; Favetto, Alicia; Pomposiello, M Cristina

    2004-05-27

    Beneath much of the Andes, oceanic lithosphere descends eastward into the mantle at an angle of about 30 degrees (ref. 1). A partially molten region is thought to form in a wedge between this descending slab and the overlying continental lithosphere as volatiles given off by the slab lower the melting temperature of mantle material. This wedge is the ultimate source for magma erupted at the active volcanoes that characterize the Andean margin. But between 28 degrees and 33 degrees S the subducted Nazca plate appears to be anomalously buoyant, as it levels out at about 100 km depth and extends nearly horizontally under the continent. Above this 'flat slab', volcanic activity in the main Andean Cordillera terminated about 9 million years ago as the flattening slab presumably squeezed out the mantle wedge. But it is unknown where slab volatiles go once this happens, and why the flat slab finally rolls over to descend steeply into the mantle 600 km further eastward. Here we present results from a magnetotelluric profile in central Argentina, from which we infer enhanced electrical conductivity along the eastern side of the plunging slab, indicative of the presence of partial melt. This conductivity structure may imply that partial melting occurs to at least 250 km and perhaps to more than 400 km depth, or that melt is supplied from the 410 km discontinuity, consistent with the transition-zone 'water-filter' model of Bercovici and Karato.

  6. Soft-bed experiments beneath Engabreen, Norway: regelation infiltration, basal slip and bed deformation

    Science.gov (United States)

    Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Cohen, D.; Moore, P. L.; Jackson, M.; Lappegard, G.; Kohler, J.

    To avoid some of the limitations of studying soft-bed processes through boreholes, a prism of simulated till (1.8 m × 1.6 m × 0.45 m) with extensive instrumentation was constructed in a trough blasted in the rock bed of Engabreen, a temperate glacier in Norway. Tunnels there provide access to the bed beneath 213 m of ice. Pore-water pressure was regulated in the prism by pumping water to it. During experiments lasting 7-12 days, the glacier regelated downward into the prism to depths of 50- 80 mm, accreting ice-infiltrated till at rates predicted by theory. During periods of sustained high pore water pressure (70-100% of overburden), ice commonly slipped over the prism, due to a water layer at the prism surface. Deformation of the prism was activated when this layer thinned to a sub-millimeter thickness. Shear strain in the till was pervasive and decreased with depth. A model of slip by ploughing of ice-infiltrated till across the prism surface accounts for the slip that occurred when effective pressure was sufficiently low or high. Slip at low effective pressures resulted from water-layer thickening that increased non-linearly with decreasing effective pressure. If sufficiently widespread, such slip over soft glacier beds, which involves no viscous deformation resistance, may instigate abrupt increases in glacier velocity.

  7. Upper crustal structures beneath Yogyakarta imaged by ambient seismic noise tomography

    Science.gov (United States)

    Zulfakriza, Saygin, E.; Cummins, P.; Widiyantoro, S.; Nugraha, Andri Dian

    2013-09-01

    Delineating the upper crustal structures beneath Yogyakarta is necessary for understanding its tectonic setting. The presence of Mt. Merapi, fault line and the alluvial deposits contributes to the complex geology of Yogyakarta. Recently, ambient seismic noise tomography can be used to image the subsurface structure. The cross correlations of ambient seismic noise of pair stations were applied to extract the Green's function. The total of 27 stations from 134 seismic stations available in MERapi Amphibious EXperiment (MERAMEX) covering Yogyakarta region were selected to conduct cross correlation. More than 500 Rayleigh waves of Green's functions could be extracted by cross-correlating available the station pairs of short-period and broad-band seismometers. The group velocities were obtained by filtering the extracted Green's function between 0.5 and 20 s. 2-D inversion was applied to the retrieved travel times. Features in the derived tomographic images correlate with the surface geology of Yogyakarta. The Merapi active volcanoes and alluvial deposit in Yogyakarta are clearly described by lower group velocities. The high velocity anomaly contrasts which are visible in the images obtained from the period range between 1 and 5 s, correspond to subsurface imprints of fault that could be the Opak Fault.

  8. Postcolonial Myth in Salman Rushdie’s The Ground Beneath Her Feet

    Directory of Open Access Journals (Sweden)

    Doncu Roxana Elena

    2014-01-01

    Full Text Available Postcolonial writers like Salman Rushdie often write back to the “empire” by appropriating myth and allegory. In The Ground beneath Her Feet, Rushdie rewrites the mythological story of Orpheus and Eurydice, using katabasis (the trope of the descent into Hell to comment both on the situation of the postcolonial writer from a personal perspective and to attempt a redefinition of postcolonial migrant identity-formation. Hell has a symbolic function, pointing both to the external context of globalization and migration (which results in the characters’ disorientation and to an interior space which can be interpreted either as a source of unrepressed energies and creativity (in a Romantic vein or as the space of the abject (in the manner of Julia Kristeva. The article sets out to investigate the complex ways in which the Orphic myth and katabasis are employed to shed light on the psychology of the creative artist and on the reconfiguration of identity that becomes the task of the postcolonial migrant subject. The journey into the underworld functions simultaneously as an allegory of artistic creation and identity reconstruction.

  9. Crust structure beneath Jilin Province and Liaoning Province in China based on seismic ambient noise tomography

    Science.gov (United States)

    Pang, Guanghua; Feng, Jikun; Lin, Jun

    2016-11-01

    We imaged the crust structure beneath Jilin Province and Liaoning Province in China with fundamental mode Rayleigh waves recorded by 60 broadband stations deployed in the region. Surface-wave empirical Green's functions were retrieved from cross-correlations of inter-station data and phase velocity dispersions were measured using a frequency-time analysis method. Dispersion measurements were then utilized to construct 2D phase velocity maps for periods between 5 and 35 s. Subsequently, the phase-dispersion curves extracted from each cell of the 2D phase velocity maps were inverted to determine the 3D shear wave velocity structures of the crust. The phase velocity maps at different periods reflected the average velocity structures corresponding to different depth ranges. The maps in short periods, in particular, were in excellent agreement with known geological features of the surface. In addition to imaging shear wave velocity structures of the volcanoes, we show that obvious low-velocity anomalies imaged in the Changbaishan-Tianchi Volcano, the Longgang-Jinlongdingzi Volcano, and the system of the Dunmi Fault crossing the Jingbohu Volcano, all of which may be due to geothermal anomalies.

  10. Imaging the Juan de Fuca plate beneath southern Oregon using teleseismic P wave residuals

    Science.gov (United States)

    Harris, R.A.; Iyer, H.M.; Dawson, P.B.

    1991-01-01

    Images the Juan de Fuca plate in southern Oregon using seismic tomography. P wave travel time residuals from a 366-km-long seismic array operated in southern Oregon in 1982 are inverted. The southeast striking array extended from the Coast ranges to the Modoc Plateau and crossed the High Cascades at Crater Lake, Oregon. Three features under the array were imaged: one high-velocity zone and two low-velocity zones. The high-velocity zone is 3-4% faster than the surrounding upper mantle. It dips steeply at 65?? to the east beneath the Cascade Range and extends down to at least 200 km. It is proposed that this high-velocity feature is subducted Juan de Fuca plate. Two low-velocity zones were also imaged, both of which are 3-4% slower than the surrounding earth structure. The southeastern low-velocity zone may be caused by partially molten crust underlying the Crater Lake volcano region. -from Authors

  11. Short length scale mantle heterogeneity beneath Iceland probed by glacial modulation of melting

    Science.gov (United States)

    Sims, Kenneth W. W.; Maclennan, Jo