Shallow seismicity in volcanic system: what role does the edifice play?

Science.gov (United States)

Bean, Chris; Lokmer, Ivan

2017-04-01

Seismicity in the upper two kilometres in volcanic systems is complex and very diverse in nature. The origins lie in the multi-physics nature of source processes and in the often extreme heterogeneity in near surface structure, which introduces strong seismic wave propagation path effects that often 'hide' the source itself. Other complicating factors are that we are often in the seismic near-field so waveforms can be intrinsically more complex than in far-field earthquake seismology. The traditional focus for an explanation of the diverse nature of shallow seismic signals is to call on the direct action of fluids in the system. Fits to model data are then used to elucidate properties of the plumbing system. Here we show that solutions based on these conceptual models are not unique and that models based on a diverse range of quasi-brittle failure of low stiffness near surface structures are equally valid from a data fit perspective. These earthquake-like sources also explain aspects of edifice deformation that are as yet poorly quantified.

Seismic Model and Geological Interpretation of the Basement Beneath the Doupovske Hory Volcanic Complex (NW Czech Republic)

Czech Academy of Sciences Publication Activity Database

Valenta, Jan; Brož, Milan; Málek, Jiří; Mlčoch, B.; Rapprich, V.; Skácelová, Z.

2011-01-01

Roč. 59, č. 3 (2011), s. 597-617 ISSN 1895-6572 R&D Projects: GA AV ČR IAA300460602 Institutional research plan: CEZ:AV0Z30460519 Keywords : seismic refraction * seismic tomography * Doupovske Hory Volcanic Complex Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.617, year: 2011

Seismic tremors and magma wagging during explosive volcanism.

Science.gov (United States)

Jellinek, A Mark; Bercovici, David

2011-02-24

Volcanic tremor is a ubiquitous feature of explosive eruptions. This oscillation persists for minutes to weeks and is characterized by a remarkably narrow band of frequencies from about 0.5 Hz to 7 Hz (refs 1-4). Before major eruptions, tremor can occur in concert with increased gas flux and related ground deformation. Volcanic tremor is thus of particular value for eruption forecasting. Most models for volcanic tremor rely on specific properties of the geometry, structure and constitution of volcanic conduits as well as the gas content of the erupting magma. Because neither the initial structure nor the evolution of the magma-conduit system will be the same from one volcano to the next, it is surprising that tremor characteristics are so consistent among different volcanoes. Indeed, this universality of tremor properties remains a major enigma. Here we employ the contemporary view that silicic magma rises in the conduit as a columnar plug surrounded by a highly vesicular annulus of sheared bubbles. We demonstrate that, for most geologically relevant conditions, the magma column will oscillate or 'wag' against the restoring 'gas-spring' force of the annulus at observed tremor frequencies. In contrast to previous models, the magma-wagging oscillation is relatively insensitive to the conduit structure and geometry, which explains the narrow band of tremor frequencies observed around the world. Moreover, the model predicts that as an eruption proceeds there will be an upward drift in both the maximum frequency and the total signal frequency bandwidth, the nature of which depends on the explosivity of the eruption, as is often observed.

Seismicity pattern: an indicator of source region of volcanism at convergent plate margins

Czech Academy of Sciences Publication Activity Database

Špičák, Aleš; Hanuš, Václav; Vaněk, Jiří

2004-01-01

Roč. 141, č. 4 (2004), s. 303-326 ISSN 0031-9201 R&D Projects: GA AV ČR IAA3012002; GA AV ČR IAA3012303; GA AV ČR KSK3012103 Institutional research plan: CEZ:AV0Z3012916 Keywords : seismicity pattern * volcanism * aseismic gap Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.370, year: 2004

Seismicity at Old Faithful Geyser: an isolated source of geothermal noise and possible analogue of volcanic seismicity

Science.gov (United States)

Kieffer, Susan Werner

1984-09-01

Old Faithful Geyser in Yellowstone National Park, U.S.A., is a relatively isolated source of seismic noise and exhibits seismic behavior similar to that observed at many volcanoes, including "bubblequakes" that resemble B-type "earthquakes", harmonic tremor before and during eruptions, and periods of seismic quiet prior to eruptions. Although Old Faithful differs from volcanoes in that the conduit is continuously open, that rock-fracturing is not a process responsible for seismicity, and that the erupting fluid is inviscid H 2O rather than viscous magma, there are also remarkable similarities in the problems of heat and mass recharge to the system, in the eruption dynamics, and in the seismicity. Water rises irregularly into the immediate reservoir of Old Faithful as recharge occurs, a fact that suggests that there are two enlarged storage regions: one between 18 and 22 m (the base of the immediate reservoir) and one between about 10 and 12 m depth. Transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water, and by episodes of convective overturn. An eruption occurs when the temperature of the near-surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure-release waves (rarefactions) down the column can bring the liquid water onto the boiling curve. The process of conversion of the liquid water in the conduit at the onset of an eruption into a two-phase liquid-vapor mixture takes on the order of 30 s. The seismicity is directly related to the sequence of filling and heating during the recharge cycle, and to the fluid mechanics of the eruption. Short (0.2-0.3 s), monochromatic, high-frequency events (20-60 Hz) resembling unsustained harmonic tremor and, in some instances, B-type volcanic earthquakes, occur when exploding or imploding

The persistent signature of tropical cyclones in ambient seismic noise

KAUST Repository

Gualtieri, Lucia; Camargo, Suzana J.; Pascale, Salvatore; Pons, Flavio M.E.; Ekströ m, Gö ran

2017-01-01

The spectrum of ambient seismic noise shows strong signals associated with tropical cyclones, yet a detailed understanding of these signals and the relationship between them and the storms is currently lacking. Through the analysis of more than a decade of seismic data recorded at several stations located in and adjacent to the northwest Pacific Ocean, here we show that there is a persistent and frequency-dependent signature of tropical cyclones in ambient seismic noise that depends on characteristics of the storm and on the detailed location of the station relative to the storm. An adaptive statistical model shows that the spectral amplitude of ambient seismic noise, and notably of the short-period secondary microseisms, has a strong relationship with tropical cyclone intensity and can be employed to extract information on the tropical cyclones.

The persistent signature of tropical cyclones in ambient seismic noise

KAUST Repository

Gualtieri, Lucia

2017-12-28

The spectrum of ambient seismic noise shows strong signals associated with tropical cyclones, yet a detailed understanding of these signals and the relationship between them and the storms is currently lacking. Through the analysis of more than a decade of seismic data recorded at several stations located in and adjacent to the northwest Pacific Ocean, here we show that there is a persistent and frequency-dependent signature of tropical cyclones in ambient seismic noise that depends on characteristics of the storm and on the detailed location of the station relative to the storm. An adaptive statistical model shows that the spectral amplitude of ambient seismic noise, and notably of the short-period secondary microseisms, has a strong relationship with tropical cyclone intensity and can be employed to extract information on the tropical cyclones.

Submarine seismic monitoring of El Hierro volcanic eruption with a 3C-geophone string: applying new acquisition and data processing techniques to volcano monitoring

Science.gov (United States)

Jurado, Maria Jose; Ripepe, Maurizio; Lopez, Carmen; Blanco, Maria Jose; Crespo, Jose

2015-04-01

A submarine volcanic eruption took place near the southernmost emerged land of the El Hierro Island (Canary Islands, Spain), from October 2011 to February 2012. The Instituto Geografico Nacional (IGN) seismic stations network evidenced seismic unrest since July 2011 and was a reference also to follow the evolution of the seismic activity associated with the volcanic eruption. Right after the eruption onset, in October 2011 a geophone string was deployed by the CSIC-IGN to monitor seismic activity. Monitoring with the seismic array continued till May 2012. The array was installed less than 2 km away from the new vol¬cano, next to La Restinga village shore in the harbor from 6 to 12m deep into the water. Our purpose was to record seismic activity related to the volcanic activity, continuously and with special interest on high frequency events. The seismic array was endowed with 8, high frequency, 3 component, 250 Hz, geophone cable string with a separation of 6 m between them. Each geophone consists on a 3-component module based on 3 orthogonal independent sensors that measures ground velocity. Some of the geophones were placed directly on the seabed, some were buried. Due to different factors, as the irregular characteristics of the seafloor. The data was recorded on the surface with a seismometer and stored on a laptop computer. We show how acoustic data collected underwater show a great correlation with the seismic data recorded on land. Finally we compare our data analysis results with the observed sea surface activity (ash and lava emission and degassing). This evidence is disclosing new and innovative tecniques on monitoring submarine volcanic activity. Reference Instituto Geográfico Nacional (IGN), "Serie El Hierro." Internet: http://www.ign.es/ign/resources /volcanologia/HIERRO.html [May, 17. 2013

Preliminary review and summary of the potential for tectonic, seismic, and volcanic activity at the Nevada Test Site defense waste disposal site

International Nuclear Information System (INIS)

Metcalf, L.A.

1983-03-01

A change from compressional to extensional tectonics, which occurred about 17 m.y. ago, marks the emergence of the present tectonic regime in the southern Great Basin. Crustal extension is continuing at the present time, oriented in a NW-SE direction in the NTS region. Concurrently with the onset of crustal extension a system of NW- and NE-trending shear zones developed, along which mutual offset has occurred. Present seismic and tectonic activity in the NTS region is concentrated along the intersections of the shear zones and in areas of deep basin formation. Natural historic seismicity of the NTS region has been low to moderate. Seismic hazard assessments suggest a maximum magnitude 6-7 earthquake, associated with a maximum peak acceleration of 0.7 to 0.9 g, is probable for the NTS. A return period of 12,700 to 15,000 y for the maximum peak acceleration indicates a relatively low seismic hazard. Silicic volcanism in the NTS region was active from 16 to 6 m.y. ago, followed by a transition to basaltic volcanism. The tectonic settings most favorable for Quaternary basaltic activity are areas of young basin-range extension, caldera ring fracture zones, and intersections of conjugate shear zones. Probability calculations for the Yucca Mountain waste repository result in a volcanic disruption hazard of 10 - 8 to 10 - 9 /y. This value is extremely low and is probably representative of the hazard at Frenchman Flat. However, due to its tectonic setting, Frenchman Flat may be an area conducive to future basaltic volcanism; further investigation is needed to properly assess volcanic hazard

Characteristics of Helicopter-Generated and Volcano-Related Seismic Tremor Signals

Science.gov (United States)

Eibl, Eva P. S.; Lokmer, Ivan; Bean, Christopher J.; Akerlie, Eggert; Vogfjörd, Kristin S.

2017-04-01

In volcanic environments it is crucial to distinguish between man-made seismic signals and signals created by the volcano. We compare volcanic, seismic signals with helicopter generated, seismic signals recorded in the last 2.5 years in Iceland. In both cases a long-lasting, emergent seismic signal, that can be referred to as seismic tremor, was generated. In the case of a helicopter, the rotating blades generate pressure pulses that travel through the air and excite Rayleigh waves at up to 40 km distance depending on wind speed, wind direction and topographic features. The longest helicopter related seismic signal we recorded was at the order of 40 minutes long. The tremor usually has a fundamental frequency of more than 10 Hz and overtones at integers of the fundamental frequency. Changes in distance lead to either increases or decreases of the frequency due to the Doppler Effect and are strongest for small source-receiver distances. The volcanic tremor signal was recorded during the Bardarbunga eruption at Holuhraun in 2014/15. For volcano-related seismic signals it is usually more difficult to determine the source process that generated the tremor. The pre-eruptive tremor persists for 2 weeks, while the co-eruptive tremor lasted for 6 months. We observed no frequency changes, most energy between 1 and 2 Hz and no or very little energy above 5 Hz. We compare the different characteristics of helicopter-related and volcano-related seismic signals and discuss how they can be distinguished. In addition we discuss how we can determine if a frequency change is related to a moving source or change in repeat time or a change in the geometry of the resonating body.

Study of structural change in volcanic and geothermal areas using seismic tomography

Science.gov (United States)

Mhana, Najwa; Foulger, Gillian; Julian, Bruce; peirce, Christine

2014-05-01

Long Valley caldera is a large silicic volcano. It has been in a state of volcanic and seismic unrest since 1978. Farther escalation of this unrest could pose a threat to the 5,000 residents and the tens of thousands of tourists who visit the area. We have studied the crustal structure beneath 28 km X 16 km area using seismic tomography. We performed tomographic inversions for the years 2009 and 2010 with a view to differencing it with the 1997 result to look for structural changes with time and whether repeat tomography is a capable of determining the changes in structure in volcanic and geothermal reservoirs. Thus, it might provide a useful tool to monitoring physical changes in volcanoes and exploited geothermal reservoirs. Up to 600 earthquakes, selected from the best-quality events, were used for the inversion. The inversions were performed using program simulps12 [Thurber, 1983]. Our initial results show that changes in both V p and V s were consistent with the migration of CO2 into the upper 2 km or so. Our ongoing work will also invert pairs of years simultaneously using a new program, tomo4d [Julian and Foulger, 2010]. This program inverts for the differences in structure between two epochs so it can provide a more reliable measure of structural change than simply differencing the results of individual years.

The attenuation of seismic intensity in the Etna region and comparison with other Italian volcanic districts

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T. Tuvè

2006-06-01

Full Text Available A detailed analysis of the intensity attenuation in the Etna and other Italian volcanic districts, was performed using the most recent and complete intensity datasets. Attenuation laws were derived through empirical models fitting ?I (the difference between epicentral I0 and site Ix intensities average values versus hypocentral site distances by the least-square method. The huge amount of data available for the Etna area allowed us to elaborate bi-linear and logarithmic attenuation models, also taking source effects into account. Furthermore, the coefficients of the Grandori formulation have been re-calculated to verify the ones previously defined for seismic hazard purposes. Among the tested relationships, the logarithmic one is simple and fairly stable, so it was also adopted for the other volcanic Italian areas. The analysis showed different attenuation trends: on the one hand, Etna and Ischia show the highest decay of intensity (?I=4 in the first 20 km; on the contrary, the Aeolian Islands and Albani Hills present a slight intensity attenuation (?I=2 at 20 km from the hypocentre; finally, Vesuvius seems to have an intermediate behaviour between the two groups. The proposed regionalization gives a significantly better image of near-field damage in volcanic regions and is easily applicable to probabilistic seismic hazard analyses.

Seismic evidence for arc segmentation, active magmatic intrusions and syn-rift fault system in the northern Ryukyu volcanic arc

Science.gov (United States)

Arai, Ryuta; Kodaira, Shuichi; Takahashi, Tsutomu; Miura, Seiichi; Kaneda, Yoshiyuki

2018-04-01

Tectonic and volcanic structures of the northern Ryukyu arc are investigated on the basis of multichannel seismic (MCS) reflection data. The study area forms an active volcanic front in parallel to the non-volcanic island chain in the eastern margin of the Eurasian plate and has been undergoing regional extension on its back-arc side. We carried out a MCS reflection experiment along two across-arc lines, and one of the profiles was laid out across the Tokara Channel, a linear bathymetric depression which demarcates the northern and central Ryukyu arcs. The reflection image reveals that beneath this topographic valley there exists a 3-km-deep sedimentary basin atop the arc crust, suggesting that the arc segment boundary was formed by rapid and focused subsidence of the arc crust driven by the arc-parallel extension. Around the volcanic front, magmatic conduits represented by tubular transparent bodies in the reflection images are well developed within the shallow sediments and some of them are accompanied by small fragments of dipping seismic reflectors indicating intruded sills at their bottoms. The spatial distribution of the conduits may suggest that the arc volcanism has multiple active outlets on the seafloor which bifurcate at crustal depths and/or that the location of the volcanic front has been migrating trenchward over time. Further distant from the volcanic front toward the back-arc (> 30 km away), these volcanic features vanish, and alternatively wide rift basins become predominant where rapid transitions from normal-fault-dominant regions to strike-slip-fault-dominant regions occur. This spatial variation in faulting patterns indicates complex stress regimes associated with arc/back-arc rifting in the northern Okinawa Trough.[Figure not available: see fulltext.

Multi-scale seismic tomography of the Merapi-Merbabu volcanic complex, Indonesia

Science.gov (United States)

Mujid Abdullah, Nur; Valette, Bernard; Potin, Bertrand; Ramdhan, Mohamad

2017-04-01

Merapi-Merbabu volcanic complex is the most active volcano located on Java Island, Indonesia, where the Indian plate subducts beneath Eurasian plate. We present a preliminary study of a multi-scale seismic tomography of the substructures of the volcanic complex. The main objective of our study is to image the feeding paths of the volcanic complex at an intermediate scale by using the data from the dense network (about 5 km spacing) constituted by 53 stations of the French-Indonesian DOMERAPI experiment complemented by the data of the German-Indonesian MERAMEX project (134 stations) and of the Indonesia Tsunami Early Warning System (InaTEWS) located in the vicinity of the complex. The inversion was performed using the INSIGHT algorithm, which follows a non-linear least squares approach based on a stochastic description of data and model. In total, 1883 events and 41846 phases (26647 P and 15199 S) have been processed, and a two-scale approach was adopted. The model obtained at regional scale is consistent with the previous studies. We selected the most reliable regional model as a prior model for the local tomography performed with a variant of the INSIGHT code. The algorithm of this code is based on the fact that inverting differences of data when transporting the errors in probability is equivalent to inverting initial data while introducing specific correlation terms in the data covariance matrix. The local tomography provides images of the substructure of the volcanic complex with a sufficiently good resolution to allow identification of a probable magma chamber at about 20 km.

Neogene seismites and seismic volcanic rocks in the Linqu area, Shandong Province, E China

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Tian H.S.

2014-07-01

Full Text Available The Yishu Fault Zone runs through the centre of Shandong Province (E China; it is a deep-seated large fault system that still is active. Two volcanic faulted basins (the Shanwang and Linqu Basins in the Linqu area, west of the fault zone, are exposed to rifting, which process is accompanied by a series of tectonic and volcanic earthquakes with a magnitude of 5-8. Lacustrine sediments in the basins were affected by these earthquakes so that seismites with a variety of soft-sediment deformation structures originated. The seismites form part of the Shanwang Formation of the Linqu Group. Semi-consolidated fluvial conglomerates became deformed in a brittle way; these seismites are present at the base of the Yaoshan Formation. Intense earthquakes triggered by volcanic activity left their traces in the form of seismic volcanic rocks associated with liquefied-sand veins in the basalt/sand intercalations at the base of the Yaoshan Formation. These palaeo-earthquake records are dated around 14-10 Ma; they are responses to the intense tectonic extension and the basin rifting in this area and even the activity of the Yishu Fault Zone in the Himalayan tectonic cycle.

Seismicity and volcanic activity in Japan based on crustal thermal activity. 1; Chikaku no netsukatsudo ni motozuku Nippon no jishin kazan katsudo. 1

Energy Technology Data Exchange (ETDEWEB)

Hayakawa, M [Tokai Univ., Tokyo (Japan). School of Marine Science and Technology

1996-05-01

This paper describes the following matters about correlation between seismic and volcanic activities and thermal energy. Investigations on the status of seismic and volcanic activities in the Japanese archipelago during about 400 years in the past reveals the following matters: noticing earthquakes with magnitudes of upper M6 to about M7, flows of energy going outward from deep crust of the earth repeat ups and downs, whereas several prominent rising periods having certain time widths can be seen; volcanic activities are included in the rising period at the same rank as seismic activities; with regard to years 1900 and on, the similar fact can be seen if the Japanese archipelago is divided into a north portion, a south portion, and an extremely south portion southern than the Hiuga area; and the present time is going toward a period of rise in energy flows. In other words, it is thought that the crust and the uppermost portion of the mantle form one body like an organic body, making an action like a geyser releasing the energy outward. 3 refs., 2 figs., 1 tab.

Seismically active column and volcanic plumbing system beneath the island arc of the Izu-Bonin subduction zone

Science.gov (United States)

Špičák, Aleš; Vaněk, Jiří; Hanuš, Václav

2009-12-01

A detailed spatio-temporal analysis of teleseismic earthquake occurrence (mb > 4.0) along the convergent margin of the Izu-Bonin-Mariana arc system reveals an anomalously high concentration of events between 27° and 30.5°N, beneath a chain of seamounts between Tori-shima and Nishino-shima volcanoes. This seismicity is dominated by the 1985/1986 earthquake swarm represented in the Engdahl-van der Hilst-Buland database by 146 earthquakes in the body wave magnitude range 4.3-5.8 and focal depth range 1-100 km. The epicentral cluster of the swarm is elongated parallel to the volcanic chain. Available focal mechanisms are consistent with an extensional tectonic regime and reveal nodal planes with azimuths close to that of the epicentral cluster. Earthquakes of the 1985/1986 swarm occurred in seven time phases. Seismic activity migrated in space from one phase to the other. Earthquake foci belonging to individual phases of the swarm aligned in vertically disposed seismically active columns. The epicentral zones of the columns are located in the immediate vicinity of seamounts Suiyo and Mokuyo, recently reported by the Japanese Meteorological Agency as volcanically active. The three observations-episodic character of earthquake occurrence, column-like vertically arranged seismicity pattern, and existence of volcanic seamounts at the seafloor above the earthquake foci-led us to interpret the 1985/1986 swarm as a consequence of subduction-related magmatic and/or fluid activity. A modification of the shallow earthquake swarm magmatic model of D. Hill fits earthquake foci distribution, tectonic stress orientation and fault plane solutions. The 1985/1986 deep-rooted earthquake swarm in the Izu-Bonin region represents an uncommon phenomenon of plate tectonics. The portion of the lithospheric wedge that was affected by the swarm should be composed of fractured rigid, brittle material so that the source of magma and/or fluids which might induce the swarm should be situated at a

Retrieving robust noise-based seismic velocity changes from sparse data sets: synthetic tests and application to Klyuchevskoy volcanic group (Kamchatka)

Science.gov (United States)

Gómez-García, C.; Brenguier, F.; Boué, P.; Shapiro, N. M.; Droznin, D. V.; Droznina, S. Ya; Senyukov, S. L.; Gordeev, E. I.

2018-05-01

Continuous noise-based monitoring of seismic velocity changes provides insights into volcanic unrest, earthquake mechanisms and fluid injection in the sub-surface. The standard monitoring approach relies on measuring travel time changes of late coda arrivals between daily and reference noise cross-correlations, usually chosen as stacks of daily cross-correlations. The main assumption of this method is that the shape of the noise correlations does not change over time or, in other terms, that the ambient-noise sources are stationary through time. These conditions are not fulfilled when a strong episodic source of noise, such as a volcanic tremor for example, perturbs the reconstructed Green's function. In this paper we propose a general formulation for retrieving continuous time series of noise-based seismic velocity changes without the requirement of any arbitrary reference cross-correlation function. Instead, we measure the changes between all possible pairs of daily cross-correlations and invert them using different smoothing parameters to obtain the final velocity change curve. We perform synthetic tests in order to establish a general framework for future applications of this technique. In particular, we study the reliability of velocity change measurements versus the stability of noise cross-correlation functions. We apply this approach to a complex dataset of noise cross-correlations at Klyuchevskoy volcanic group (Kamchatka), hampered by loss of data and the presence of highly non-stationary seismic tremors.

Seismicity, focal mechanisms, and stress distribution in the Tres Virgenes volcanic and geothermal region, Baja California Sur, Mexico

Energy Technology Data Exchange (ETDEWEB)

Wong, Victor; Munguia, Luis [Centro de Investigacion Cientifica y de Educacion Superior de Ensenada (Mexico)

2006-01-15

In October 1993 we carried out a seismic monitoring in the Tres Virgenes volcanic region in order to record the background seismicity associated with the volcanic structures, the geothermal field and the tectonic features of the area. Hypocenters for 257 microearthquakes were located in the volcanic edifices and along the northwest right-lateral, strike-slip La Virgen fault. Focal depths range from close to the Earth surface to about 8 km. Shallow depths occur mainly in the volcanic edifices. Deeper seismic events occurred outside the volcanic area. The duration magnitudes of the located microearthquakes range between 1 and 3. The Vp/Vs ratio and the low-Q values estimated suggest heterogeneous material properties in the volcanic structures mainly toward the El Azufre fault and the El Aguajito Caldera, where hydrothermal activity has been reported. The P- and T-axes of focal mechanisms for 90 microearthquakes suggest that the region is under N-S compression and E-W extension, in agreement with the regional tectonic stress field of the NW-SE right-lateral strike-slip transform fault system of the Gulf of California. [Spanish] En octubre de 1993 se llevo a cabo un monitoreo sismico en la region volcanica Las Tres Virgenes con el proposito de registrar la actividad sismica asociada a las estructuras volcanicas, al campo geotermico y a la tectonica local. Se localizaron 257 microsismos con hipocentros en los edificios volcanicos y a lo largo de la falla de rumbo, lateral derecha conocida como falla La Virgen. La profundidad focal de los sismos varia desde los muy cercanos a la superficie de la Tierra hasta los 8 km. Las profundidades someras ocurren principalmente en los edificios volcanicos. Los sismos mas profundos ocurren fuera del area volcanica. La magnitud de duracion de los microsismos localizados varia entre 1 y 3. La razon Vp/Vs y los valores bajos de Q que se estimaron en la zona sugieren un material con propiedades heterogeneas bajo las estructuras

Seismic reflection data processing in active volcanic areas: an application to Campi Flegrei and Somma Vesuvius offshore (Southern Italy

Directory of Open Access Journals (Sweden)

A. Rapolla

2002-06-01

Full Text Available The Campanian volcanism develops near the sea. Therefore, the geophysical study of the marine environment is a key to a better understanding of the tectonic evolution and the origin of volcanism in the area. An abundance of high quality seismic data in the marine sector, where little direct information is available, is critical to the study of Campanian volcanism. This paper concerns the reprocessing of a seismic reflection dataset acquired in Naples Bay and processed during 1973. Even though the overall data quality was high for that time, of course their acquisition technological limits have been overcome by the new processing. Our reprocessing aimed at: 1 reduction of random noise in the data; 2 removal of unwanted coherent events; 3 reduction of spatial aliasing by means of trace interpolation on Commod Shot Point (CSP gathering; 4 improvement of resolution of the seismic wavelet with spiking deconvolution algorithms and finally 5 reposition of reflectors in their correct locations in the space-TWT domain by means of dip moveout and post-stack time migration. A comparison between the new and old data shows that the new sections are characterized by a much higher S/N ratio. Diffraction hyperbole has been collapsed. Reverberations, ghosts and multiples have been removed or greatly attenuated, especially between the reflectors of interest, allowing us to follow them with more detail and with greater continuity. Furthermore, data resolution has been boosted by the reprocessing, allowing the interpreter to evaluate reflector position and continuity in greater detail. The reinterpretation phase of such lines, that is already in an advanced stage, will therefore allow us to gain new insights into the structural setting of the bay, with the aim of exploring the connection between tectonics and volcanism.

New Approach for Monitoring Seismic and Volcanic Activities Using Microwave Radiometer Data

Science.gov (United States)

Maeda, Takashi; Takano, Tadashi

Interferograms formed from the data of satellite-borne synthetic aperture radar (SAR) enable us to detect slight land-surface deformations related to volcanic eruptions and earthquakes. Currently, however, we cannot determine when land-surface deformations occurred with high time resolution since the time lag between two scenes of SAR used to form interferograms is longer than the recurrent period of the satellite carrying it (several tens of days). In order to solve this problem, we are investigating new approach to monitor seismic and vol-canic activities with higher time resolution from satellite-borne sensor data, and now focusing on a satellite-borne microwave radiometer. It is less subject to clouds and rainfalls over the ground than an infrared spectrometer, so more suitable to observe an emission from land sur-faces. With this advantage, we can expect that thermal microwave energy by increasing land surface temperatures is detected before a volcanic eruption. Additionally, laboratory experi-ments recently confirmed that rocks emit microwave energy when fractured. This microwave energy may result from micro discharges in the destruction of materials, or fragment motions with charged surfaces of materials. We first extrapolated the microwave signal power gener-ated by rock failures in an earthquake from the experimental results and concluded that the microwave signals generated by rock failures near the land surface are strong enough to be detected by a satellite-borne radiometer. Accordingly, microwave energy generated by rock failures associated with a seismic activity is likely to be detected as well. However, a satellite-borne microwave radiometer has a serious problem that its spatial res-olution is too coarse compared to SAR or an infrared spectrometer. In order to raise the possibility of detection, a new methodology to compensate the coarse spatial resolution is es-sential. Therefore, we investigated and developed an analysis method to detect local

Seismically active column and volcanic plumbing system beneath the island arc of the Izu-Bonin subduction zone

Czech Academy of Sciences Publication Activity Database

Špičák, Aleš; Vaněk, Jiří; Hanuš, Václav

2009-01-01

Roč. 179, č. 3 (2009), s. 1301-1312 ISSN 0956-540X Institutional research plan: CEZ:AV0Z30120515 Keywords : seismicity and tectonics * volcano seismology * subduction zone processes * volcanic arc processes * magma migration and fragmentation * Pacific Ocean Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.435, year: 2009

Seismic tomography of Basse-Terre volcanic island, Guadeloupe, Lesser Antilles, using earthquake travel times and noise correlations

Science.gov (United States)

Barnoud, Anne; Coutant, Olivier; Bouligand, Claire; Massin, Frédérick; Stehly, Laurent

2015-04-01

We image the volcanic island of Basse-Terre, Guadeloupe, Lesser Antilles, using both earthquake travel times and noise correlations. (1) A new earthquake catalog was recently compiled for the Lesser Antilles by the CDSA/OVSG/IPGP (Massin et al., EGU General Assembly 2014) and allows us to perform classical travel time tomography to obtain smooth 3D body wave velocity models. The geometrical configuration of the volcanic arc controls the resolution of the model in our zone of interest. (2) Surface wave tomography using noise correlations was successfully applied to volcanoes (Brenguier et al., Geophys. Res. Lett. 2007). We use seismic noise recorded at 16 broad-band stations and 9 short-period stations from Basse-Terre over a period of six years (2007-2012). For each station pair, we extract a dispersion curve from the noise correlation to get surface wave velocity models. The inversion of the dispersion curves produces a 3D S-wave velocity model of the island. The spatial distribution of seismic stations accross the island is highly heterogeneous, leading to higher resolution near the dome of the Soufrière of Guadeloupe volcano. Resulting velocity models are compared with densities obtained by 3D inversion of gravimetric data (Barnoud et al., AGU Fall Meeting 2013). Further work should include simultaneous inversion of seismic and gravimetric datasets to overcome resolution limitations.

Magma displacements under insular volcanic fields, applications to eruption forecasting: El Hierro, Canary Islands, 2011-2013

Science.gov (United States)

García, A.; Fernández-Ros, A.; Berrocoso, M.; Marrero, J. M.; Prates, G.; De la Cruz-Reyna, S.; Ortiz, R.

2014-04-01

Significant deformations, followed by increased seismicity detected since 2011 July at El Hierro, Canary Islands, Spain, prompted the deployment of additional monitoring equipment. The climax of this unrest was a submarine eruption first detected on 2011 October 10, and located at about 2 km SW of La Restinga, southernmost village of El Hierro Island. The eruption ceased on 2012 March 5, after the volcanic tremor signals persistently weakened through 2012 February. However, the seismic activity did not end with the eruption, as several other seismic crises followed. The seismic episodes presented a characteristic pattern: over a few days the number and magnitude of seismic event increased persistently, culminating in seismic events severe enough to be felt all over the island. Those crises occurred in 2011 November, 2012 June and September, 2012 December to 2013 January and in 2013 March-April. In all cases the seismic unrest was preceded by significant deformations measured on the island's surface that continued during the whole episode. Analysis of the available GPS and seismic data suggests that several magma displacement processes occurred at depth from the beginning of the unrest. The first main magma movement or `injection' culminated with the 2011 October submarine eruption. A model combining the geometry of the magma injection process and the variations in seismic energy release has allowed successful forecasting of the new-vent opening.

Shear-wave velocity models and seismic sources in Campanian volcanic areas: Vesuvius and Phlegraean fields

Energy Technology Data Exchange (ETDEWEB)

Guidarelli, M; Zille, A; Sarao, A [Dipartimento di Scienze della Terra, Universita degli Studi di Trieste, Trieste (Italy); Natale, M; Nunziata, C [Dipartimento di Geofisica e Vulcanologia, Universita di Napoli ' Federico II' , Napoli (Italy); Panza, G F [Dipartimento di Scienze della Terra, Universita degli Studi di Trieste, Trieste (Italy); Abdus Salam International Centre for Theoretical Physics, Trieste (Italy)

2006-12-15

This chapter summarizes a comparative study of shear-wave velocity models and seismic sources in the Campanian volcanic areas of Vesuvius and Phlegraean Fields. These velocity models were obtained through the nonlinear inversion of surface-wave tomography data, using as a priori constraints the relevant information available in the literature. Local group velocity data were obtained by means of the frequency-time analysis for the time period between 0.3 and 2 s and were combined with the group velocity data for the time period between 10 and 35 s from the regional events located in the Italian peninsula and bordering areas and two station phase velocity data corresponding to the time period between 25 and 100 s. In order to invert Rayleigh wave dispersion curves, we applied the nonlinear inversion method called hedgehog and retrieved average models for the first 30-35 km of the lithosphere, with the lower part of the upper mantle being kept fixed on the basis of existing regional models. A feature that is common to the two volcanic areas is a low shear velocity layer which is centered at the depth of about 10 km, while on the outside of the cone and along a path in the northeastern part of the Vesuvius area this layer is absent. This low velocity can be associated with the presence of partial melting and, therefore, may represent a quite diffused crustal magma reservoir which is fed by a deeper one that is regional in character and located in the uppermost mantle. The study of seismic source in terms of the moment tensor is suitable for an investigation of physical processes within a volcano; indeed, its components, double couple, compensated linear vector dipole, and volumetric, can be related to the movements of magma and fluids within the volcanic system. Although for many recent earthquake events the percentage of double couple component is high, our results also show the presence of significant non-double couple components in both volcanic areas. (author)

Crustal structure, evolution, and volcanic unrest of the Alban Hills, Central Italy

Science.gov (United States)

Chiarabba, C.; Amato, A.; Delaney, P.T.

1997-01-01

The Alban Hills, a Quaternary volcanic center lying west of the central Apennines, 15-25 km southeast of Rome, last erupted 19ka and has produced approximately 290 km3 of eruptive deposits since the inception of volcanism at 580 ka. Earthquakes of moderate intensity have been generated there at least since the Roman age. Modern observations show that intermittent periods of swarm activity originate primarily beneath the youngest features, the phreatomagmatic craters on the west side of the volcano. Results from seismic tomography allow identification of a low-velocity region, perhaps still hot or partially molten, more than 6 km beneath the youngest craters and a high-velocity region, probably a solidified magma body, beneath the older central volcanic construct. Thirty centimeters of uplift measured by releveling supports the contention that high levels of seismicity during the 1980s and 1990s resulted from accumulation of magma beneath these craters. The volume of magma accumulation and the amount of maximum uplift was probably at least 40 ?? 106 m3 and 40 cm, respectively. Comparison of newer levelings with those completed in 1891 and 1927 suggests earlier episodes of uplift. The magma chamber beneath the western Alban Hills is probably responsible for much of the past 200 ka of eruptive activity, is still receiving intermittent batches of magma, and is, therefore, continuing to generate modest levels of volcanic unrest. Bending of overburden is the most likely cause of the persistent earthquakes, which generally have hypocenters above the 6-km-deep top of the magma reservoir. In this view, the most recent uplift and seismicity are probably characteristic and not precursors of more intense activity.

Mainshock-Aftershocks Clustering Detection in Volcanic Regions

Science.gov (United States)

Garza Giron, R.; Brodsky, E. E.; Prejean, S. G.

2017-12-01

Crustal earthquakes tend to break their general Poissonean process behavior by gathering into two main kinds of seismic bursts: swarms and mainshock-aftershocks sequences. The former is commonly related to volcanic or geothermal processes whereas the latter is a characteristic feature of tectonically driven seismicity. We explore the mainshock-aftershock clustering behavior of different active volcanic regions in Japan and its comparison to non-volcanic regions. We find that aftershock production in volcanoes shows mainshock-aftershocks clustering similar to what is observed in non-volcanic areas. The ratio of volanic areas that cluster in mainshock-aftershocks sequences vs the areas that do not is comparable to the ratio of non-volcanic regions that show clustering vs the ones that do not. Furthermore, the level of production of aftershocks for most volcanic areas where clustering is present seems to be of the same order of magnitude, or slightly higher, as the median of the non-volcanic regions. An interesting example of highly aftershock-productive volcanoes emerges from the 2000 Miyakejima dike intrusion. A big seismic cluster started to build up rapidly in the south-west flank of Miyakejima to later propagate to the north-west towards the Kozushima and Niijima volcanoes. In Miyakejima the seismicity showed a swarm-like signature with a constant earthquake rate, whereas Kozushima and Niijima both had expressions of highly productive mainshock-aftershocks sequences. These findings are surprising given the alternative mechanisms available in volcanic systems for releasing deviatoric strain. We speculate that aftershock behavior might hold a relationship with the rheological properties of the rocks of each system and with the capacity of a system to accumulate or release the internal pressures caused by magmatic or hydrothermal systems.

Late Cretaceous sub-volcanic structure in the continental shelf off Portugal and its implications on tectonics and seismicity

Science.gov (United States)

Neres, Marta; Terrinha, Pedro; Custódio, Susana; Noiva, João; Brito, Pedro; Santos, Joana; Carrilho, Fernando

2017-04-01

Long-lasting and widespread alkaline magmatism is recognized in the west Portuguese margin. Offshore, several volcanic seamounts punctuate the Tore-Madeira Rise and the Estremadura Spur, with known ages between 80 and 100 Ma. Onshore, the major events are the Monchique (69-73 Ma), Sines (75-77 Ma) and Sintra (75-82 Ma) plutons - whose location (aligned along 200 km) and age discrepancy inspired some geodynamic models for Iberia during the Cretaceous - and the Lisbon Volcanic Complex (90-100 Ma). Structural links between them have been proposed but no direct evidence was yet found for it. In this work we present new magnetic data from recent marine magnetic surveys (ROCHEL and MINEPLAT project) conducted off the west Portuguese coast on the continental shelf and slope. A total area of about 3000 km2 between Sintra and Sines was surveyed with line spacing of 1 mile. Very high-resolution multi-channel seismic profiles were simultaneously acquired with the magnetics covering an area of 400 km2 off Sines. Two main primary outcomes arise from these data. On one hand, higher-resolution mapping in regions where magnetic anomalies were already known allows a better understanding of the buried sub-volcanic system. On the other hand, previously unknown NNW-SSE aligned magnetic anomalies were identified along the coast off Sines, possibly corresponding to buried Late Cretaceous alkaline magmatic intrusives. The presence of magmatic bodies was up to now unknown in this region, and these findings reignite the discussion about a structural link connecting the three main on land intrusive complexes, Sintra, Sines and Monchique. In addition to the structural control of the magmatic complexes, seismicity is also an issue as a cluster of seismicity coincident with the Monchique complex has long been known. Smaller clusters coincide with the magnetic anomalies mapped during the ROCHEL and MINEPLAT surveys, as well. We interpret these results in the light of the tectono-magmatism of

Ambient Seismic Noise Interferometry on the Island of Hawai`i

Science.gov (United States)

Ballmer, Silke

Ambient seismic noise interferometry has been successfully applied in a variety of tectonic settings to gain information about the subsurface. As a passive seismic technique, it extracts the coherent part of ambient seismic noise in-between pairs of seismic receivers. Measurements of subtle temporal changes in seismic velocities, and high-resolution tomographic imaging are then possible - two applications of particular interest for volcano monitoring. Promising results from other volcanic settings motivate its application in Hawai'i, with this work being the first to explore its potential. The dataset used for this purpose was recorded by the Hawaiian Volcano Observatory's permanent seismic network on the Island of Hawai'i. It spans 2.5 years from 5/2007 to 12/2009 and covers two distinct sources of volcanic tremor. After applying standard processing for ambient seismic noise interferometry, we find that volcanic tremor strongly affects the extracted noise information not only close to the tremor source, but unexpectedly, throughout the island-wide network. Besides demonstrating how this long-range observability of volcanic tremor can be used to monitor volcanic activity in the absence of a dense seismic array, our results suggest that care must be taken when applying ambient seismic noise interferometry in volcanic settings. In a second step, we thus exclude days that show signs of volcanic tremor, reducing the dataset to three months, and perform ambient seismic noise tomography. The resulting two-dimensional Rayleigh wave group velocity maps for 0.1 - 0.9 Hz compare very well with images from previous travel time tomography, both, for the main volcanic structures at low frequencies as well as for smaller features at mid-to-high frequencies - a remarkable observation for the temporally truncated dataset. These robust results suggest that ambient seismic noise tomography in Hawai'i is suitable 1) to provide a three-dimensional S-wave model for the volcanoes and 2

Monitoring Persistent Volcanic Emissions from Sulphur Springs, Saint Lucia: A Community Approach to Disaster Risk Reduction

Science.gov (United States)

Joseph, E. P.; Beckles, D. M.; Cox, L.; Jackson, V. B.; Alexander, D.

2014-12-01

Volcanic and geothermal emissions are known natural sources of volatiles to the atmosphere. Volcanogenic air pollutants known to cause the most serious impact are carbon dioxide (CO2), sulphur dioxide (SO2), hydrogen chloride (HCl) and hydrogen fluoride (HF). Some studies into the potential for volcanic emissions to produce chronic diseases in humans indicate that areas of major concern include respiratory problems, particularly silicosis (Allen et al. 2000; Baxter et al. 1999; Buist et al. 1986), psychological stress (Shore et al. 1986), and chemical impacts of gas or ash (Giammanco et al. 1998). Sulphur Springs Park in Saint Lucia has a very high recreational value with >200,000 visitors annually, while the nearby town of Soufrière has >8,400 residents. Residents and visitors have raised concerns about the volcanic emissions and its health effects. As part of the volcanic surveillance programme undertaken by the UWI, Seismic Research Centre (SRC) in Saint Lucia, a new monitoring network has been established for quantifying the ambient SO2 in air, to which staff and visitors at the volcanic park are exposed to. The implementation and continued operation of this network has involved the training of local personnel in the active field sampling and analytical techniques required for the assessment of ambient SO2 concentrations, using a low cost monitor as well as commercial passive samplers. This approach recognizes that environmental hazards are a usual part of life and productive livelihoods, and to minimize post-disaster response and recovery it is beneficial to promote preparedness and mitigation, which is best achieved at the local level with community involvement. It is also intended that the volcanic emissions monitoring network could be used as a method to establish and maintain community-based initiatives that would also be helpful when volcanic threat manifests.

Seismic activity around and under Krakatau volcano, Sunda Arc: constraints to the source region of island arc volcanics

Czech Academy of Sciences Publication Activity Database

Špičák, Aleš; Hanuš, Václav; Vaněk, Jiří

2002-01-01

Roč. 46, č. 3 (2002), s. 545-565 ISSN 0039-3169 R&D Projects: GA ČR GA205/97/0898; GA AV ČR IAA3012002 Institutional research plan: CEZ:AV0Z3012916 Keywords : Krakatau * Sunda Strait seismicity * island arc volcanism * subduction * Wadati-Benioff zone Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.571, year: 2002

Evidence for sub-lacustrine volcanic activity in Lake Bolsena (central Italy) revealed by high resolution seismic data sets

Science.gov (United States)

Lindhorst, Katja; Krastel, Sebastian; Wagner, Bernd; Schuerer, Anke

2017-06-01

The Bolsena caldera that formed between 0.6 and 0.2 Ma has a well preserved structural rim, which makes it an ideal site to study the tectonic and volcanic evolution of calderas. However, the main area is covered by a 150 m deep lake which makes it rather difficult to investigate the subsurface structure directly. To overcome this problem new high resolution hydro-acoustic surveys using a multichannel reflection seismic system and a sediment echo-sounder system were conducted in September 2012. As space was limited we used a rowing boat towed by a rubber boat to handle a 36 m long and 24 channel streamer to receive seismic reflections produced using a Mini GI-Gun (0.25 l). The subsurface structure of Lake Bolsena was imaged up to a sediment depth of 190 m, which is estimated to have filled over a period of 333 kyrs. However, massive pyroclastic flow deposits found in the deeper parts of the basin indicate an initial infill of volcanic deposits from two adjacent younger calderas, the Latera (W) and Montefiascone (SE) calderas. Our data suggest that the caldera has a long history of active volcanism, because the lacustrine sediments show post-sedimentary influences of geothermal fluids. We mapped several mound structures at various stratigraphic depths. Two volcanic structures outcrop at the modern lake surface implying recent activity. One of these structures is hardly covered by sediments and has a crater-like feature in its summit. The other structure shows a pockmark-like depression on top. Another observable feature is a partially sediment filled crater located in the western part of the lake which further implies the existence of a magma chamber located beneath the Bolsena caldera. Since the late Pleistocene and Holocene, the sedimentation was mainly hemipelagic evidenced by a sediment drape of up to 10 m thick sediment drape on the uppermost sediments. Beneath the drape we found evidence for a distal tephra layer likely related to an explosive eruption from

Studies of crustal structure, seismic precursors to volcanic eruptions and earthquake hazard in the eastern provinces of the Democratic Republic of Congo

CSIR Research Space (South Africa)

Mavonga, T

2010-11-01

Full Text Available In recent decades, civil wars in the eastern provinces of the Democratic Republic of Congo have caused massive social disruptions, which have been exacerbated by volcanic and earthquake disasters. Seismic data were gathered and analysed as part...

[US Geological Survey research in radioactive waste disposal, fiscal year 1980:] Tectonics, seismicity, volcanism, and erosion rates in the southern Great Basin

International Nuclear Information System (INIS)

Carr, W.J.; Rogers, A.M.

1982-01-01

The objective is to assess the potential for faulting, damaging earthquakes, recurrence of volcanism, and local acceleration of erosion in parts of the southern Great Basin. The following approaches are being used: (1) investigating the rate, intensity, and distribution of faulting during approximately the last 25 m.y., with emphasis on the last 10 m.y.; (2) monitoring and interpreting present seismicity; (3) studying the history of volcanism; and (4) evaluating past rates of erosion and deposition. Progress is reported

An FP7 "Space" project: Aphorism "Advanced PRocedures for volcanic and Seismic Monitoring"

Science.gov (United States)

Di Iorio, A., Sr.; Stramondo, S.; Bignami, C.; Corradini, S.; Merucci, L.

2014-12-01

APHORISM project proposes the development and testing of two new methods to combine Earth Observation satellite data from different sensors, and ground data. The aim is to demonstrate that this two types of data, appropriately managed and integrated, can provide new improved GMES products useful for seismic and volcanic crisis management. The first method, APE - A Priori information for Earthquake damage mapping, concerns the generation of maps to address the detection and estimate of damage caused by a seism. The use of satellite data to investigate earthquake damages is not an innovative issue. We can find a wide literature and projects concerning such issue, but usually the approach is only based on change detection techniques and classifications algorithms. The novelty of APE relies on the exploitation of a priori information derived by InSAR time series to measure surface movements, shake maps obtained from seismological data, and vulnerability information. This a priori information is then integrated with change detection map to improve accuracy and to limit false alarms. The second method deals with volcanic crisis management. The method, MACE - Multi-platform volcanic Ash Cloud Estimation, concerns the exploitation of GEO (Geosynchronous Earth Orbit) sensor platform, LEO (Low Earth Orbit) satellite sensors and ground measures to improve the ash detection and retrieval and to characterize the volcanic ash clouds. The basic idea of MACE consists of an improvement of volcanic ash retrievals at the space-time scale by using both the LEO and GEO estimations and in-situ data. Indeed the standard ash thermal infrared retrieval is integrated with data coming from a wider spectral range from visible to microwave. The ash detection is also extended in case of cloudy atmosphere or steam plumes. APE and MACE methods have been defined in order to provide products oriented toward the next ESA Sentinels satellite missions.The project is funded under the European Union FP7

3D upper crustal seismic structure across Santorini volcanic field: Constraints on magmatic and tectonic interactions

Science.gov (United States)

Heath, B.; Hooft, E. E. E.; Toomey, D. R.; Papazachos, C. V.; Walls, K.; Paulatto, M.; Morgan, J. V.; Nomikou, P.; Warner, M.

2017-12-01

To investigate magmatic-tectonic interactions at an arc volcano, we collected a dense, active-source, seismic dataset across the Santorini Volcano, Greece, with 90 ocean bottom seismometers, 65 land seismometers, and 14,300 marine sound sources. We use over 140,000 travel-time picks to obtain a P-wave tomography model of the upper crustal structure of the Santorini volcano and surrounding tectonically extended region. Regionally, the shallow (Bouguer gravity anomalies and preliminary shallow attenuation results (using waveform amplitudes and t* values). We find regional Pliocene and younger faults bounding basement grabens and horsts to be predominately oriented in a NE-SW direction with Santorini itself located in a graben bounded by faults striking in this direction. In contrast, volcanic vents and dikes expressed at the surface seem to strike about 20° clockwise relative to these regional faults. In the northern caldera of Santorini, a 4-km wide region of anomalously low velocities and high attenuation directly overlies an inferred source of 2011-2012 inflation (4-4.5 km depth), however it is located at shallower depths ( 1-2km). The imaged low-velocity anomaly may correspond to hydrothermal activity (due to increased porosity and alteration) and/or brecciation from a prior episode of caldera collapse. It is bounded by anomalously fast velocities (at 1-2 km depth) that parallel the regional fault orientation and are correspondingly rotated 20° to surface dikes. At 4-5 km depth beneath the northern caldera basin, low-velocity anomalies and attenuated seismic arrivals provide preliminary evidence for a magma body; the low-velocity anomaly is elongated in the same direction as regional volcanic vents. The difference in strike of volcanic and tectonic features indicates oblique extension and potential time-variation in the minimum stress direction.

The 2014, MW6.9 North Aegean earthquake: seismic and geodetic evidence for coseismic slip on persistent asperities

Science.gov (United States)

Konca, Ali Ozgun; Cetin, Seda; Karabulut, Hayrullah; Reilinger, Robert; Dogan, Ugur; Ergintav, Semih; Cakir, Ziyadin; Tari, Ergin

2018-05-01

We report that asperities with the highest coseismic slip in the 2014 MW6.9 North Aegean earthquake persisted through the interseismic, coseismic and immediate post-seismic periods. We use GPS and seismic data to obtain the source model of the 2014 earthquake, which is located on the western extension of the North Anatolian Fault (NAF). The earthquake ruptured a bilateral, 90 km strike-slip fault with three slip patches: one asperity located west of the hypocentre and two to the east with a rupture duration of 40 s. Relocated pre-earthquake seismicity and aftershocks show that zones with significant coseismic slip were relatively quiet during both the 7 yr of interseismic and the 3-month aftershock periods, while the surrounding regions generated significant seismicity during both the interseismic and post-seismic periods. We interpret the unusually long fault length and source duration, and distribution of pre- and post-main-shock seismicity as evidence for a rupture of asperities that persisted through strain accumulation and coseismic strain release in a partially coupled fault zone. We further suggest that the association of seismicity with fault creep may characterize the adjacent Izmit, Marmara Sea and Saros segments of the NAF. Similar behaviour has been reported for sections of the San Andreas Fault, and some large subduction zones, suggesting that the association of seismicity with creeping fault segments and rapid relocking of asperities may characterize many large earthquake faults.

Shear-wave velocities beneath the Harrat Rahat volcanic field, Saudi Arabia, using ambient seismic noise analysis

Science.gov (United States)

Civilini, F.; Mooney, W.; Savage, M. K.; Townend, J.; Zahran, H. M.

2017-12-01

We present seismic shear-velocities for Harrat Rahat, a Cenozoic bimodal alkaline volcanic field in west-central Saudi Arabia, using seismic tomography from natural ambient noise. This project is part of an overall effort by the Saudi Geological Survey and the United States Geological Survey to describe the subsurface structure and assess hazards within the Saudi Arabian shield. Volcanism at Harrat Rahat began approximately 10 Ma, with at least three pulses around 10, 5, and 2 Ma, and at least several pulses in the Quaternary from 1.9 Ma to the present. This area is instrumented by 14 broadband Nanometrics Trillium T120 instruments across an array aperture of approximately 130 kilometers. We used a year of recorded natural ambient noise to determine group and phase velocity surface wave dispersion maps with a 0.1 decimal degree resolution for radial-radial, transverse-transverse, and vertical-vertical components of the empirical Green's function. A grid-search method was used to carry out 1D shear-velocity inversions at each latitude-longitude point and the results were interpolated to produce pseudo-3D shear velocity models. The dispersion maps resolved a zone of slow surface wave velocity south-east of the city of Medina spatially correlated with the 1256 CE eruption. A crustal layer interface at approximately 20 km depth was determined by the inversions for all components, matching the results of prior seismic-refraction studies. Cross-sections of the 3D shear velocity models were compared to gravity measurements obtained in the south-east edge of the field. We found that measurements of low gravity qualitatively correlate with low values of shear-velocity below 20 km along the cross-section profile. We apply these methods to obtain preliminary tomography results on the entire Arabian Shield.

Volcano seismicity and ground deformation unveil the gravity-driven magma discharge dynamics of a volcanic eruption.

Science.gov (United States)

Ripepe, Maurizio; Donne, Dario Delle; Genco, Riccardo; Maggio, Giuseppe; Pistolesi, Marco; Marchetti, Emanuele; Lacanna, Giorgio; Ulivieri, Giacomo; Poggi, Pasquale

2015-05-18

Effusive eruptions are explained as the mechanism by which volcanoes restore the equilibrium perturbed by magma rising in a chamber deep in the crust. Seismic, ground deformation and topographic measurements are compared with effusion rate during the 2007 Stromboli eruption, drawing an eruptive scenario that shifts our attention from the interior of the crust to the surface. The eruption is modelled as a gravity-driven drainage of magma stored in the volcanic edifice with a minor contribution of magma supplied at a steady rate from a deep reservoir. Here we show that the discharge rate can be predicted by the contraction of the volcano edifice and that the very-long-period seismicity migrates downwards, tracking the residual volume of magma in the shallow reservoir. Gravity-driven magma discharge dynamics explain the initially high discharge rates observed during eruptive crises and greatly influence our ability to predict the evolution of effusive eruptions.

GeoNetGIS: a Geodetic Network Geographical Information System to manage GPS networks in seismic and volcanic areas

Science.gov (United States)

Cristofoletti, P.; Esposito, A.; Anzidei, M.

2003-04-01

This paper presents the methodologies and issues involved in the use of GIS techniques to manage geodetic information derived from networks in seismic and volcanic areas. Organization and manipulation of different geodetical, geological and seismic database, give us a new challenge in interpretation of information that has several dimensions, including spatial and temporal variations, also the flexibility and brand range of tools available in GeoNetGIS, make it an attractive platform for earthquake risk assessment. During the last decade the use of geodetic networks based on the Global Positioning System, devoted to geophysical applications, especially for crustal deformation monitoring in seismic and volcanic areas, increased dramatically. The large amount of data provided by these networks, combined with different and independent observations, such as epicentre distribution of recent and historical earthquakes, geological and structural data, photo interpretation of aerial and satellite images, can aid for the detection and parameterization of seismogenic sources. In particular we applied our geodetic oriented GIS to a new GPS network recently set up and surveyed in the Central Apennine region: the CA-GeoNet. GeoNetGIS is designed to analyze in three and four dimensions GPS sources and to improve crustal deformation analysis and interpretation related with tectonic structures and seismicity. It manages many database (DBMS) consisting of different classes, such as Geodesy, Topography, Seismicity, Geology, Geography and Raster Images, administrated according to Thematic Layers. GeoNetGIS represents a powerful research tool allowing to join the analysis of all data layers to integrate the different data base which aid for the identification of the activity of known faults or structures and suggesting the new evidences of active tectonics. A new approach to data integration given by GeoNetGIS capabilities, allow us to create and deliver a wide range of maps, digital

Seismic imaging of North China: insight into intraplate volcanism and seismotectonics

Science.gov (United States)

Zhao, D.

2004-12-01

We used seismic tomography to study the detailed three-dimensional (3-D) seismic velocity structure of the crust and mantle beneath North China for understanding the intraplate volcanism and seismotectonics of the Asian continent. Two active volcanoes, Changbai and Wudalianchi, exist in Northeast China and they have erupted several times in the last 1000 years. The origin of the active intraplate volcanoes is still unclear. Global tomography shows that the subducting Pacific slab becomes stagnant under NE Asia and strong low-velocity (low-V) anomalies exist in the upper mantle under the two volcanoes (Zhao, 2004). Recently we determined a 3-D P-wave velocity structure under the Changbai volcano using teleseismic data recorded by 19 portable seismic stations in NE China (Zhao et al., 2004). Our result shows a columnar low-V anomaly extending to 400 km depth and high-velocity anomalies in the mantle transition zone with deep-focus earthquakes of about 600 km depth. These results indicatie that the Changbai and Wudalianchi volcanoes are not hotspot like Hawaii but a kind of back-arc volcano related to the deep subduction and stagnancy of the Pacific slab under NE Asia. A detailed 3-D P-wave tomography of the crust and uppermost mantle under the Beijing region is determined by using local earthquake arrival times recorded by the newly installed Chinese Capital Seismic Network with 101 short-period seismic stations coving the region densely and uniformly (Huang and Zhao, 2004). The results show that large crustal earthquakes, such as the 1679 Sanhe earthquake (M 8.0) and the 1976 Tangshan earthquake (M 7.8), generally occurred in high-velocity areas in the upper to middle crust. In the lower crust to the uppermost mantle under the source zones of the large earthquakes, however, low-velocity and high-conductivity anomalies exist, which are considered to be associated with fluids. The fluids in the lower crust may cause the weakening of the seismogenic layer in the upper

Crustal seismicity associated to rpid surface uplift at Laguna del Maule Volcanic Complex, Southern Volcanic Zone of the Andes

Science.gov (United States)

Cardona, Carlos; Tassara, Andrés; Gil-Cruz, Fernando; Lara, Luis; Morales, Sergio; Kohler, Paulina; Franco, Luis

2018-03-01

Laguna del Maule Volcanic Complex (LMVC, Southern Andes of Chile) has been experiencing large rates (ca. 30 cm/yr) of surface uplift as detected since 2008 by satellite geodetic measurements. Previous works have modeled the source of this deformation as an inflating rectangular sub-horizontal sill underlying LMVC at 5 km depth, which is supposedly related to an active process of magmatic replenishment of a shallow silicic reservoir. However little is known about the tectonic context on which this activity is taking place, particularly its relation with crustal seismicity that could help understanding and monitoring the current deformation process. Here we present the first detailed characterization of the seismic activity taking place at LMVC and integrate it with structural data acquired in the field in order to illuminate the possible connection between the ongoing process of surface uplift and the activation of crustal faults. Our main finding is the recognition of repetitive volcano-tectonic (VT) seismic swarms that occur periodically between 2011 and 2014 near the SW corner of the sill modeled by InSAR studies. A cross-correlation analysis of the waveforms recorded for these VT events allows identifying three different seismic families. Families F1 and F3 share some common features in the stacked waveform and its locations, which markedly differ from those of family F2. Swarms belonging to this later family are more energetic and its energy was increasing since 2011 to a peak in January 2013, which coincide with maximum vertical velocities detected by local GPS stations. This points to a common process relating both phenomena. The location of VT seismic swarms roughly coincides with the intersection of a NE-SW lineament with a WNW-ESE lineament. The former shows clear field evidences of dextral strike-slip that are fully consistent with one nodal plane of focal mechanism for well-recorded F2 events. The conjugate nodal plane of these focal mechanisms could

Crustal Structure of the Tengchong Intra-plate Volcanic Area

Science.gov (United States)

Qian, Rongyi; Tong, Vincent C. H.

2015-09-01

We here provide an overview of our current understanding of the crustal structure of Tengchong in southwest China, a key intra-plate volcanic area along the Himalayan geothermal belt. Given that there is hitherto a lack of information about the near-surface structure of intra-plate volcanic areas, we present the first seismic reflection and velocity constraints on the shallow crust between intra-plate volcanoes. Our near-surface seismic images reveal the existence of dome-shaped seismic reflectors (DSRs) in the shallow crust between intra-plate volcanic clusters in Tengchong. The two DSRs are both ~2 km wide, and the shallowest parts of the DSRs are found at the depth of 200-300 m. The velocity model shows that the shallow low-velocity layer (<4 km/s) is anomalously thick (~1 km) in the region where the DSRs are observed. The presence of DSRs indicates significant levels of intra-plate magmatism beneath the along-axis gap separating two volcano clusters. Along-axis gaps between volcano clusters are therefore not necessarily an indicator of lower levels of magmatism. The seismic images obtained in this technically challenging area for controlled-source seismology allow us to conclude that shallow crustal structures are crucial for understanding the along-axis variations of magmatism and hydrothermal activities in intra-plate volcanic areas.

Eocene volcanism and the origin of horizon A

Science.gov (United States)

Gibson, T.G.; Towe, K.M.

1971-01-01

A series of closely time-equivalent deposits that correlate with seismic reflector horizon A exists along the coast of eastern North America. These sediments of Late-Early to Early-Middle Eocene age contain an authigenic mineral suite indicative of the alteration of volcanic glass. A volcanic origin for these siliceous deposits onshore is consistent with a volcanic origin for the cherts of horizon A offshore.

Volcanic tremor and local earthquakes at Copahue volcanic complex, Southern Andes, Argentina

Science.gov (United States)

Ibáñez, J. M.; Del Pezzo, E.; Bengoa, C.; Caselli, A.; Badi, G.; Almendros, J.

2008-07-01

In the present paper we describe the results of a seismic field survey carried out at Copahue Volcano, Southern Andes, Argentina, using a small-aperture, dense seismic antenna. Copahue Volcano is an active volcano that exhibited a few phreatic eruptions in the last 20 years. The aim of this experiment was to record and classify the background seismic activity of this volcanic area, and locate the sources of local earthquakes and volcanic tremor. Data consist of several volcano-tectonic (VT) earthquakes, and many samples of back-ground seismic noise. We use both ordinary spectral, and multi-spectral techniques to measure the spectral content, and an array technique [Zero Lag Cross Correlation technique] to measure the back-azimuth and apparent slowness of the signals propagating across the array. We locate VT earthquakes using a procedure based on the estimate of slowness vector components and S-P time. VT events are located mainly along the border of the Caviahue caldera lake, positioned at the South-East of Copahue volcano, in a depth interval of 1-3 km below the surface. The background noise shows the presence of many transients with high correlation among the array stations in the frequency band centered at 2.5 Hz. These transients are superimposed to an uncorrelated background seismic signal. Array solutions for these transients show a predominant slowness vector pointing to the exploited geothermal field of "Las Maquinitas" and "Copahue Village", located about 6 km north of the array site. We interpret this coherent signal as a tremor generated by the activity of the geothermal field.

Scientific results from the deepened Lopra-1 borehole, Faroe Islands: Borehole seismic studies of a volcanic succession from the Lopra-1/1A borehole in the Faroe Islands, northern North Atlantic

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Cowper, David

2006-07-01

Full Text Available Extruded basalt flows overlying sedimentary sequences present a challenge to hydrocarbon exploration using reflection seismic techniques. The Lopra-1/1A re-entry well on the Faroese island of Suðuroy allowed us to study the seismic characteristics of a thick sequence of basalt flows from well logs and borehole seismic recordings. Data acquired during the deepening operation in 1996 are presented here.The re-entry well found that the seismic event at 2340 m, prognosed from the pre-drill Vertical Seismic Profile (VSP as a decrease in impedance, was not base basalt and the deepened well remainedwithin the lower series basalts. Nonetheless, compressional and shear sonic logs and a density log were recorded over the full open hole interval. These allowed a firm tie to be made with the reflectedwavefield from a new VSP. The sonic logs show a compressional to shear wavespeed ratio of 1.84 which is almost constant with depth. Sonic compressional wavespeeds are 3% higher than seismicvelocities, suggesting dispersion in the basalt flows. Azimuthal anisotropy was weakly indicated by the shear sonic log but its orientation is consistent with the directions of mapped master joints in the vicinity of the well.The VSP downgoing compressional wavelet shows good persistence, retaining a dominant period of 28 ms at 3510 m depth. Average vertical velocity is 5248 m/s, higher than previously reported.Attenuation can largely be modelled by geometrical spreading and scattering loss, consistent with other studies. Within the piled flows, the effective Q from scattering is about 35. Elastic layeredmedium modelling shows some hope that a mode-converted shear wave may be observed at moderate offsets. Like its predecessor, the 1996 VSP indicates a decrease in impedance below the final depth ofthe well. However, it is unlikely to be basement or sediment and is probably an event within the volcanic sequence.

Diffuse Helium Emission as a Precursory Sign of Volcanic Unrest

Science.gov (United States)

Padron, E.; Perez, N.; Hernandez Perez, P. A.; Sumino, H.; Melian Rodriguez, G.; Barrancos, J.; Nolasco, D.; Padilla, G.; Dionis, S.; Rodriguez, F.; Hernandez, I.; Calvo, D.; Peraza, M.; Nagao, K.

2012-12-01

Since July 16, 2011, an anomalous seismicity at El Hierro island, the youngest and smallest of the Canary Islands, was recorded by IGN seismic network. After the occurrence of more than 10,000 seismic events, volcanic tremor was recorded since 05:15 of the October 10, by all of the seismic stations on the island, with highest amplitudes recorded in the southernmost station. During the afternoon of October 12 a large light-green coloured area was observed in the sea to the souht of La Restinga village (at the southernmost part of El Hierro island), suggesting the existence of a submarine eruption. Since October 12, frequent episodes of, turbulent gas emission and foaming, and the appearance of steamy lava fragments has been observed on the sea surface. As part of the volcanic surveillance of the island, the Instituto Volcanologico de Canarias (INVOLCAN) geochemical monitoring program is carrying out diffuse helium surveys on the surface environment of El Hierro (soil atmosphere). This nobel gas has been investigated because it has been considered an almost ideal geochemical indicator because it is chemically inert, physically stable, nonbiogenic, sparingly soluble in water under ambient conditions and almost non-adsorbable. At each survey, 600 sampling sites covering the whole island and following an homogeneous distribution are selected for helium measurements in the soil gases, The helium concentration gradients with respect to its value on air (5.24 ppm) allow us to estimate a pure diffusive emission rate of helium throughout the island. The first survey was carried out on the summer of 2003, when the island was on a quiescence period. At this survey, the amount of helium released by the volcanic system of El Hierro was estimated in 6 kg/d. Since the beginning of the seismic unrest, 13 helium emission surveys have been carried out. The helium emission rate has shown an excellent agreement with the evolution of the volcanic crisis of the island, reaching 30 kg

Small instrument to volcanic seismic signals

Science.gov (United States)

Carreras, Normandino; Gomariz, Spartacus; Manuel, Antoni

2014-05-01

Currently, the presence of volcanoes represents a threat to their local populations, and for this reason, scientific communities invest resources to monitor seismic activity of an area, and to obtain information to identify risk situations. To perform such monitoring, it can use different general purpose acquisition systems commercially available, but these devices do not meet to the specifications of reduced dimensions, low weight, low power consumption and low cost. These features allow the system works in autonomous mode for a long period of time, and it makes easy to be carried and to be installed. In the line of designing a volcanic acquisition system with the previously mentioned specifications, exists the Volcanology Department of CSIC, developers of a system with some of these specifications. The objective of this work is to improve the energy consumption requirements of the previous system, providing three channels of data acquisition and with the possibility to transmit data acquisition via radio frequency to a base station, allowing operation it in remote mode. The developed acquisition system consists of three very low-power acquisition modules of Texas Instruments (ADS1246), and this is designed to capture information of the three coordinate axes. A microprocessor also of Texas Instruments (MSP430F5438) is used to work in low-power, due to it is ready to run this consumption and also takes advantage the power save mode in certain moments when system is not working. This system is configurable by serial port, and it has a SD memory to storage data. Contrast to the previous system, it has a RF communication module incorporated specially to work in remote mode of Lynx (YLX-TRM8053-025-05), and boasts also with a GPS module which keeps the time reference synchronized with module of SANAV (GM-1315LA). Thanks to this last selection of components, it is designed a small system about 106 x 106 mm. Assuming that the power supply system is working during all the

2014 volcanic activity in Alaska: Summary of events and response of the Alaska Volcano Observatory

Science.gov (United States)

Cameron, Cheryl E.; Dixon, James P.; Neal, Christina A.; Waythomas, Christopher F.; Schaefer, Janet R.; McGimsey, Robert G.

2017-09-07

The Alaska Volcano Observatory (AVO) responded to eruptions, possible eruptions, volcanic unrest or suspected unrest, and seismic events at 18 volcanic centers in Alaska during 2014. The most notable volcanic activity consisted of intermittent ash eruptions from long-active Cleveland and Shishaldin Volcanoes in the Aleutian Islands, and two eruptive episodes at Pavlof Volcano on the Alaska Peninsula. Semisopochnoi and Akutan volcanoes had seismic swarms, both likely the result of magmatic intrusion. The AVO also installed seismometers and infrasound instruments at Mount Cleveland during 2014.

A generalized formulation for noise-based seismic velocity change measurements

Science.gov (United States)

Gómez-García, C.; Brenguier, F.; Boué, P.; Shapiro, N.; Droznin, D.; Droznina, S.; Senyukov, S.; Gordeev, E.

2017-12-01

The observation of continuous seismic velocity changes is a powerful tool for detecting seasonal variations in crustal structure, volcanic unrest, co- and post-seismic evolution of stress in fault areas or the effects of fluid injection. The standard approach for measuring such velocity changes relies on comparison of travel times in the coda of a set of seismic signals, usually noise-based cross-correlations retrieved at different dates, and a reference trace, usually a averaged function over dates. A good stability in both space and time of the noise sources is then the main assumption for reliable measurements. Unfortunately, these conditions are often not fulfilled, as it happens when ambient-noise sources are non-stationary, such as the emissions of low-frequency volcanic tremors.We propose a generalized formulation for retrieving continuous time series of noise-based seismic velocity changes without any arbitrary reference cross-correlation function. We set up a general framework for future applications of this technique performing synthetic tests. In particular, we study the reliability of the retrieved velocity changes in case of seasonal-type trends, transient effects (similar to those produced as a result of an earthquake or a volcanic eruption) and sudden velocity drops and recoveries as the effects of transient local source emissions. Finally, we apply this approach to a real dataset of noise cross-correlations. We choose the Klyuchevskoy volcanic group (Kamchatka) as a case study where the recorded wavefield is hampered by loss of data and dominated by strongly localized volcanic tremor sources. Despite the mentioned wavefield contaminations, we retrieve clear seismic velocity drops associated with the eruptions of the Klyuchevskoy an the Tolbachik volcanoes in 2010 and 2012, respectively.

Anomalous crustal movements with low seismic efficiency - Campi Flegrei, Italy and some examples in Japan

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A. Nazzaro

2002-06-01

Full Text Available Campi Flegrei is a unique volcanic region located near Naples, Italy. Anomalous crustal movements at Pozzuoli in Campi Flegrei have been documented since the Roman period. The movements were gradual and have continued to the present, occasionally accompanying swarms of local earthquakes and volcanic eruptions. Generally the movements proceed with low seismicity. After the 1538 eruption of Monte Nuovo, Pozzuoli had subsided monotonously, but it changed to uplift abruptly in 1969. The uplift accelerated in 1983 and 1984 reaching more than 2 m, and thereafter began to subside. Many discussions of this event have been published. In Japan, we have examples of deformations similar to those at Campi Flegrei, mainly in volcanic areas, and rarely in non-volcanic areas. The former includes Iwojima, Miyakejima and Aira caldera while the latter is represented by Cape Omaezaki. Iwojima is a volcano island, and its secular uplifts since the 18th century are recognized as an unusual event. Miyakejima volcano and Aira caldera exhibited anomalous movements with low seismicity after their eruptions. Cape Omaezaki is not situated in volcanic zone but near a subduction zone, and gradually and continuously subsides as a precursor to a large earthquake. In such cases as Campi Flegrei and the Japanese localities, we would question whether the deformations are accompanied by normal seismicity or low seismicity. To examine quantitatively the relationship between seismicity and related deformation, seismic efficiency is generally useful. The crustal deformations in all the regions cited above are characterized by exceptionally low seismic efficiencies. In the present paper, the deformations at Pozzuoli and Iwojima are mainly described and a comparative discussion among these and other localities in Japan is supplemented. It is concluded that such anomalous phenomena in volcanic areas are attributable to peculiar rheological aspects of the material composing the local

Time-reversibility in seismic sequences: Application to the seismicity of Mexican subduction zone

Science.gov (United States)

Telesca, L.; Flores-Márquez, E. L.; Ramírez-Rojas, A.

2018-02-01

In this paper we investigate the time-reversibility of series associated with the seismicity of five seismic areas of the subduction zone beneath the Southwest Pacific Mexican coast, applying the horizontal visibility graph method to the series of earthquake magnitudes, interevent times, interdistances and magnitude increments. We applied the Kullback-Leibler divergence D that is a metric for quantifying the degree of time-irreversibility in time series. Our findings suggest that among the five seismic areas, Jalisco-Colima is characterized by time-reversibility in all the four seismic series. Our results are consistent with the peculiar seismo-tectonic characteristics of Jalisco-Colima, which is the closest to the Middle American Trench and belongs to the Mexican volcanic arc.

Initial results from the Volcanic Risk in Saudi Arabia project: Microearthquakes in the northern Harrat Rahat monogenetic volcanic field, Madinah, Saudi Arabia

Science.gov (United States)

Kenedi, C. L.; Alvarez, M. G.; Abdelwahed, M. F.; Aboud, E.; Lindsay, J. M.; Mokhtar, T. A.; Moufti, M. R.

2012-12-01

An 8-station borehole seismic research array is recording microearthquake data in northern Harrat Rahat. This recently active monogenetic volcanic field lies southeast of the Islamic holy city of Madinah, Kingdom of Saudi Arabia. The VORiSA seismographs are operated in collaboration between King Abdulaziz University in Jeddah and the Institute of Earth Science and Engineering, University of Auckland, in New Zealand. The goal of the VORiSA project is to evaluate the seismic and volcanic hazard around Madinah. To this end, we will evaluate the local earthquake activity including the extent to which local earthquakes are tectonic or volcanic. We also will use seismicity to understand the subsurface structure. The analytical goals of the seismic research array are the following: (1) Calculate a new seismic velocity model, (2) Map subsurface structures using seismic tomography, and (3) Explore for fracture zones using shear wave splitting analysis. As compared to seismographs installed on the surface, borehole seismometers detect smaller and more numerous microearthquake signals. The sensitivity and location of the borehole sensors in the VORiSA array are designed to detect these weak signals. The array has a total aperture of 17 km with station spacing at 5 - 10 km. The seismometers are housed in IESE model S21g-2.0, two Hz, 3-component borehole sondes. Sensor depths range from 107 - 121 m. The data acquisition system at each stand-alone station consists of a Reftek 130-01, 6-channel, 24 bit data logger which records at 250 samples per second. The power source is a deep cycle battery with solar recharge. Local temperatures reach extremes of 0° to 50°C, so the battery and recorder are contained in a specially designed underground vault. The vault also provides security in the remote and sparsely populated volcanic field. Recording began on 31 March 2012. An average of one earthquake every three days suggests that currently this is not a highly seismic area. However

Seismic instrumentation plan for the Hawaiian Volcano Observatory

Science.gov (United States)

Thelen, Weston A.

2014-01-01

The seismic network operated by the U.S. Geological Survey’s Hawaiian Volcano Observatory (HVO) is the main source of authoritative data for reporting earthquakes in the State of Hawaii, including those that occur on the State’s six active volcanoes (Kīlauea, Mauna Loa, Hualālai, Mauna Kea, Haleakalā, Lō‘ihi). Of these volcanoes, Kīlauea and Mauna Loa are considered “very high threat” in a report on the rationale for a National Volcanic Early Warning System (NVEWS) (Ewert and others, 2005). This seismic instrumentation plan assesses the current state of HVO’s seismic network with respect to the State’s active volcanoes and calculates the number of stations that are needed to upgrade the current network to provide a seismic early warning capability for forecasting volcanic activity. Further, the report provides proposed priorities for upgrading the seismic network and a cost assessment for both the installation costs and maintenance costs of the improved network that are required to fully realize the potential of the early warning system.

New seismic sources parameterization in El Salvador. Implications to seismic hazard.

OpenAIRE

Alonso-Henar, Jorge; Staller, A.; Martínez Díaz, José J.; Benito, Belén; Álvarez Gómez, José Antonio; Canora Catalán, Carolina

2014-01-01

El Salvador is located at the pacific active margin of Central America, here, the subduction of the Cocos Plate under the Caribbean Plate at a rate of 80 mm/yr is the main seismic source. Although the seismic sources located in the Central American Volcanic Arc have been responsible for some of the most damaging earthquakes in El Salvador. The El Salvador Fault Zone is the main geological structure in El Salvador and accommodates 14 mm/yr of horizontal displacement between the Caribbean Plate...

Development of a time synchronization methodology for a wireless seismic array

Science.gov (United States)

Moure-García, David; Torres-González, Pedro; del Río, Joaquín; Mihai, Daniel; Domínguez Cerdeña, Itahiza

2017-04-01

Seismic arrays have multiple applications. In the past, the main use was nuclear tests monitoring that began in mid-twentieth century. The major difference with a seismic network is the hypocenter location procedure. With a seismic network the hypocenter's 3D coordinates are calculated while using an array, the source direction of the seismic signal is determined. Seismic arrays are used in volcanology to obtain the source azimuth of volcanic signals related to fluids movement, magma and/or gases, that do not show a clear seismic phases' onset. A key condition in the seismic array operativity is the temporal synchronization of all the sensors, better than 1 microsecond. Because of that, usually all sensors are connected to the acquisition system by cable to ensure an identical sampling time. In this work we present the design of a wireless low-cost and low-power consumption volcanic monitoring seismic array where all nodes (sensors) acquire data synchronously and transmit them to the center node where a coherent signal is pursued in near real time.

Experimental and theoretical fracture mechanics applied to volcanic conduits and domes

Science.gov (United States)

Sammonds, P.; Matthews, C.; Kilburn, C.; Smith, R.; Tuffen, H.; Meredith, P.

2008-12-01

We present an integrated modelling and experimental approach to magma deformation and fracture, which we attempt to validate against field observations of seismicity. The importance of fracture processes in magma ascent dynamics and lava dome growth and collapse are apparent from the associated seismicity. Our laboratory experiments have shown that brittle fracture of magma can occur at high temperature and stress conditions prevalent in the shallow volcanic system. Here, we use a fracture mechanics approach to model seismicity preceding volcanic eruptions. Starting with the fracture mechanics concept of a crack in an elastic body, we model crack growth around the volcanic conduit through the processes of crack interactions, leading either to the propagation and linkage of cracks, or crack avoidance and the inhibition of crack propagation. The nature of that interaction is governed by the temperature and plasticity of the magma. We find that fracture mechanics rules can account for the style of seismicity preceding eruptions. We have derived the changes in seismic b-value predicted by the model and interpret these in terms of the style of fracturing, fluid flow and heat transport. We compare our model with results from our laboratory experiments where we have deformed lava at high temperatures under triaxial stresses. These experiments were conducted in dry and water saturated conditions at effective pressures up to 10 MPa, temperatures up to 1000°C and strain rates from 10-4 s-1 to 10-6 s-1. The behaviour of these magmas was largely brittle under these conditions. We monitored the acoustic emission emitted and calculate the change in micro-seismic b-value with deformation. These we find are in accord with volcano seismicity and our fracture mechanics model.

Lichen Persistence and Recovery in Response to Varied Volcanic Disturbances

Science.gov (United States)

Nelson, P.; Wheeler, T. B.

2015-12-01

Volcanic eruptions produce many ecological disturbances that structure vegetation. While lichens are sensitive to disturbances, little is known about their responses to volcanic disturbances, except for colonization of lava. We examined lichen community responses through time to different disturbances produced by the May 1, 2008 eruption of Volcan Chaiten in south-central Chile. Pre-eruption vegetation near the volcano was old-growth Valdivian temperate rainforest dominated by closed-canopy Nothofagus sp... In 2012, we installed thirteen 1-acre plots across volcanic disturbance zones on which a time-constrained search was done for all macrolichen species, each of which was assigned an approximate log10 categorical abundance. We also installed a 0.2 m2 quadrat on two representative trees per plot for repeat photography of lichen cover. We remeasured at least one plot per disturbance zone in 2014 and re-photographed tree quadrats in 2013 and 2014. We then analyzed species composition and abundance differences among disturbance zones. In 2012, the blast (pyroclastic density flow), scorch (standing scorched forest at the edge of the blast) and deep tephra (>10 cm) zones had the lowest lichen species richness (5-13 species), followed by reference (unimpacted) and shallow (lichen species since 2012 while the light tephra and reference were essentially unchanged. Gravel rain, gravel rain + pumice and flooded forest plots all had about the same number of species in 2014 as 2012. Lichen colonization and growth in tree quadrats varied widely, from very little colonization in the blast to prolific colonization in the gravel rain + pumice zone. Lichen's varied responses to different volcanic disturbances were attributable to varying degrees of mortality and subsequent availability of substrate, quantity of light and removal of competitors. While sensitive to disturbance, lichens are apparently resilient to and can quickly recolonize after a variety of large, violent volcanic

Spontaneous non-volcanic tremor detected in the Anza Seismic Gap of San Jacinto Fault

Science.gov (United States)

Hutchison, A. A.; Ghosh, A.

2017-12-01

Non-volcanic tremor (NVT), a type of slow earthquake, is becoming more frequently detected along plate boundaries, particularly in subduction zones, and is also observed along the San Andreas Fault [e.g. Nadeau & Dolenc, 2005]. NVT is typically associated with transient deformation (i.e. slow slip) in the transition zone [e.g. Ide et al., 2007], and at times it is observed with deep creep along faults [e.g. Beroza & Ide, 2011]. Using several independent location and detection methods including multi-beam backprojection [Ghosh et al., 2009a; 2012], envelope cross correlation [Wech & Creager, 2008], spectral analyses and visual inspection of existing network stations and high-density mini seismic array data, we detect multiple discrete spontaneous tremor events in the Anza Gap of the San Jacinto Fault (SJF) in June, 2011. The events occur on the SJF where the Hot Springs Fault terminates, on the northwestern boundary of the Anza Gap, below the inferred seismogenic zone characterized by velocity weakening frictional behavior [e.g. Lindsay et al., 2014]. The location methods provide consistent locations for each event in our catalog. Low slowness values help rule-out surface noise that may result in false detections. Analyses of frequency spectra show these time windows are depleted in high frequency energy in the displacement amplitude spectrum compared to small local regular (fast) earthquakes. This spectral pattern is characteristic of tremor [Shelly et al., 2007]. We interpret this tremor to be a seismic manifestation of slow-slip events below the seismogenic zone. Recently, an independent geodetic study suggests that the 2010 El Mayor-Cucupah earthquake triggered a slow-slip event in the Anza Gap [Inbal et al., 2017]. In addition, multiple studies infer deep creep in the SJF [e.g. Meng & Peng et al., 2016; Jiang & Fialko, 2016] indicating that this fault is capable of producing slow slip events. Transient tectonic behavior like tremor and slow slip may be playing

Rescaled Range analysis of Induced Seismicity: rapid classification of clusters in seismic crisis

Science.gov (United States)

Bejar-Pizarro, M.; Perez Lopez, R.; Benito-Parejo, M.; Guardiola-Albert, C.; Herraiz, M.

2017-12-01

Different underground fluid operations, mainly gas storing, fracking and water pumping, can trigger Induced Seismicity (IS). This seismicity is normally featured by small-sized earthquakes (M<2.5), although particular cases reach magnitude as great as 5. It has been up for debate whether earthquakes greater than 5 can be triggered by IS or this level of magnitude only corresponds to tectonic earthquakes caused by stress change. Whatever the case, the characterization of IS for seismic clusters and seismic series recorded close but not into the gas storage, is still under discussion. Time-series of earthquakes obey non-linear patterns where the Hurst exponent describes the persistency or anti-persistency of the sequence. Natural seismic sequences have an H-exponent close to 0.7, which combined with the b-value time evolution during the time clusters, give us valuable information about the stationarity of the phenomena. Tectonic earthquakes consist in a main shock with a decay of time-occurrence of seismic shocks obeying the Omori's empirical law. On the contrary, IS does not exhibit a main shock and the time occurrence depends on the injection operations instead of on the tectonic energy released. In this context, the H-exponent can give information about the origin of the sequence. In 2013, a seismic crisis was declared from the Castor underground gas storing located off-shore in the Mediterranean Sea, close to the Northeastern Spanish cost. The greatest induced earthquake was 3.7. However, a 4.2 earthquake, probably of tectonic origin, occurred few days after the operations stopped. In this work, we have compared the H-exponent and the b-value time evolution according to the timeline of gas injection. Moreover, we have divided the seismic sequence into two groups: (1) Induced Seismicity and (2) Triggered Seismicity. The rescaled range analysis allows the differentiation between natural and induced seismicity and gives information about the persistency and long

Observations of volcanic earthquakes and tremor at Deception Island - Antarctica

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J. Morales

1999-06-01

Full Text Available Deception Island - South Shetlands, Antarctica is site of active volcanism. Since 1988 field surveys have been carried out with the aim of seismic monitoring, and in 1994 a seismic array was set up near the site of the Spanish summer base in order to better constrain the source location and spectral properties of the seismic events related to the volcanic activity. The array was maintained during the Antarctic summer of 1995 and the last field survey was carried out in 1996. Data show the existence of three different groups (or families of seismic events: 1 long period events, with a quasi-monochromatic spectral content (1-3 Hz peak frequency and a duration of more than 50 s, often occurring in small swarms lasting from several minutes to some day; 2 volcanic tremor, with a spectral shape similar to the long period events but with a duration of several minutes (2-10; 3 hybrid events, with a waveform characterised by the presence of a high frequency initial phase, followed by a low frequency phase with characteristics similar to those of the long period events. The high frequency phase of the hybrid events was analysed using polarisation techniques, showing the presence of P waves. This phase is presumably located at short epicentral distances and shallow source depth. All the analysed seismic events show back-azimuths between 120 and 330 degrees from north (corresponding to zones of volcanic activity showing no seismic activity in the middle of the caldera. Particle motion, Fourier spectral and spectrogram analysis show that the low frequency part of the three groups of the seismic signals have similar patterns. Moreover careful observations show that the high frequency phase which characterises the hybrid events is present in the long period and in the tremor events, even with lower signal to noise ratios. This evidence suggests that long period events are events in which the high frequency part is simply difficult to observe, due to a very

Satellite Monitoring of Accumulation of Strain in the Earth's Crust Related to Seismic and Volcanic Activity

Science.gov (United States)

Arellano-Baeza, A. A.

2009-12-01

Our studies have shown that the strain energy accumulation deep in the Earth’s crust that precedes seismic and volcanic activity can be detected by applying a lineament extraction technique to the high-resolution multispectral satellite images. A lineament is a straight or a somewhat curved feature in a satellite image, which it is possible to detect by a special processing of images based on directional filtering and or Hough transform. We analyzed tens of earthquakes occurred in the Pacific coast of the South America with the magnitude > 4 Mw, using ASTER/TERRA multispectral satellite images for detection and analysis of changes in the system of lineaments previous to a strong earthquake. All events were located in the regions with small seasonal variations and limited vegetation to facilitate the tracking of features associated with the seismic activity only. It was found that the number and orientation of lineaments changed significantly about one month before an earthquake approximately, and a few months later the system returns to its initial state. This effect increases with the earthquake magnitude. It also was shown that the behavior of lineaments associated to the volcano seismic activity is opposite to that obtained previously for earthquakes. This discrepancy can be explained assuming that in the last case the main reason of earthquakes is compression and accumulation of strength in the Earth’s crust due to subduction of tectonic plates, whereas in the first case we deal with the inflation of a volcano edifice due to elevation of pressure and magma intrusion. The results obtained made it possible to include this research as a part of scientific program of Chilean Remote Sensing Satellite mission to be launched in 2010.

Comparative analysis of seismic persistence of Hindu Kush nests (Afghanistan) and Los Santos (Colombia) using fractal dimension

Science.gov (United States)

Prada, D. A.; Sanabria, M. P.; Torres, A. F.; Álvarez, M. A.; Gómez, J.

2018-04-01

The study of persistence in time series in seismic events in two of the most important nets such as Hindu Kush in Afghanistan and Los Santos Santander in Colombia generate great interest due to its high presence of telluric activity. The data were taken from the global seismological network. Using the Jarque-Bera test the presence of gaussian distribution was analyzed, and because the distribution in the series was asymmetric, without presence of mesocurtisity, the Hurst coefficient was calculated using the rescaled range method, with which it was found the fractal dimension associated to these time series and under what is possible to determine the persistence, antipersistence and volatility in these phenomena.

Improved techniques in data analysis and interpretation of potential fields: examples of application in volcanic and seismically active areas

Directory of Open Access Journals (Sweden)

G. Florio

2002-06-01

Full Text Available Geopotential data may be interpreted by many different techniques, depending on the nature of the mathematical equations correlating specific unknown ground parameters to the measured data set. The investigation based on the study of the gravity and magnetic anomaly fields represents one of the most important geophysical approaches in the earth sciences. It has now evolved aimed both at improving of known methods and testing other new and reliable techniques. This paper outlines a general framework for several applications of recent techniques in the study of the potential methods for the earth sciences. Most of them are here described and significant case histories are shown to illustrate their reliability on active seismic and volcanic areas.

The seismic reassessment Mochovce NPP

International Nuclear Information System (INIS)

Baumeister, P.

2004-01-01

The design of Mochovce NPP was based on the Novo-Voronez type WWER-440/213 reactor - twin units. Seismic characteristic of this region is characterized by very low activity. Mochovce NPP site is located on the rock soil with volcanic layer (andesit). Seismic reassessment of Mochovce NPP was done in two steps: deterministic approach up to commissioning confirmed value Horizontal Peak Ground Acceleration HPGA=0.1 g and activities after commissioning as a consequence of the IAEA mission indicate higher hazard values. (author)

Supercomputer modeling of volcanic eruption dynamics

Energy Technology Data Exchange (ETDEWEB)

Kieffer, S.W. [Arizona State Univ., Tempe, AZ (United States); Valentine, G.A. [Los Alamos National Lab., NM (United States); Woo, Mahn-Ling [Arizona State Univ., Tempe, AZ (United States)

1995-06-01

Our specific goals are to: (1) provide a set of models based on well-defined assumptions about initial and boundary conditions to constrain interpretations of observations of active volcanic eruptions--including movies of flow front velocities, satellite observations of temperature in plumes vs. time, and still photographs of the dimensions of erupting plumes and flows on Earth and other planets; (2) to examine the influence of subsurface conditions on exit plane conditions and plume characteristics, and to compare the models of subsurface fluid flow with seismic constraints where possible; (3) to relate equations-of-state for magma-gas mixtures to flow dynamics; (4) to examine, in some detail, the interaction of the flowing fluid with the conduit walls and ground topography through boundary layer theory so that field observations of erosion and deposition can be related to fluid processes; and (5) to test the applicability of existing two-phase flow codes for problems related to the generation of volcanic long-period seismic signals; (6) to extend our understanding and simulation capability to problems associated with emplacement of fragmental ejecta from large meteorite impacts.

Neotectonics of Graciosa island (Azores: a contribution to seismic hazard assessment of a volcanic area in a complex geodynamic setting

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Ana Hipólito

2014-02-01

Full Text Available Graciosa is a mid-Pleistocene to Holocene volcanic island that lies in a complex plate boundary between the North American, Eurasian, and Nubian plates. Large fault scarps displace the oldest (Middle Pleistocene volcanic units, but in the younger areas recent volcanism (Holocene to Upper Pleistocene conceals the surface expression of faulting, limiting neotectonic observations. The large displacement accumulated by the older volcanic units when compared with the younger formations suggests a variability of deformation rates and the possibility of alternating periods of higher and lower tectonic deformation rates; this would increase the recurrence interval of surface rupturing earthquakes. Nevertheless, in historical times a few destructive earthquakes affected the island attesting for its seismic hazard. Regarding the structural data, two main fault systems, incompatible with a single stress field, were identified at Graciosa Island. Thus, it is proposed that the region is affected by two alternating stress fields. The stress field #1 corresponds to the regional stress regime proposed by several authors for the interplate shear zone that constitutes the Azorean segment of the Eurasia-Nubia plate boundary. It is suggested that the stress field #2 will act when the area under the influence of the regional stress field #1 narrows as a result of variations in the differential spreading rates north and south of Azores. The islands closer to the edge of the sheared region will temporarily come under the influence of a different (external stress field (stress field #2. Such data support the concept that, in the Azores, the Eurasia-Nubia boundary corresponds to a complex and wide deformation zone, variable in time.

Soil gas radon and volcanic activity at El Hierro (Canary Islands) before and after the 2011-2012 submarine eruption

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Barrancos, J.; Padilla, G.; Hernandez Perez, P. A.; Padron, E.; Perez, N.; Melian Rodriguez, G.; Nolasco, D.; Dionis, S.; Rodriguez, F.; Calvo, D.; Hernandez, I.

2012-12-01

El Hierro is the youngest and southernmost island of the Canarian archipelago and represents the summit of a volcanic shield elevating from the surrounding seafloor at depth of 4000 m to up to 1501 m above sea level. The island is believed to be near the present hotspot location in the Canaries with the oldest subaerial rocks dated at 1.12 Ma. The subaerial parts of the El Hierro rift zones (NE, NW and S Ridges) are characterized by tightly aligned dyke complexes with clusters of cinder cones as their surface expressions. Since July 16, 2011, an anomalous seismicity at El Hierro Island was recorded by IGN seismic network. Volcanic tremor started at 05:15 hours on October 10, followed on the afternoon of October 12 by a green discolouration of seawater, strong bubbling and degassing indicating the initial stage of submarine volcanic eruption at approximately 2 km off the coast of La Restinga, El Hierro. Soil gas 222Rn and 220Rn activities were continuously measured during the period of the recent volcanic unrest occurred at El Hierro, at two different geochemical stations, HIE02 and HIE03. Significant increases in soil 222Rn activity and 222Rn/220Rn ratio from the soil were observed at both stations prior the submarine eruption off the coast of El Hierro, showing the highest increases before the eruption onset and the occurrence of the strongest seismic event (M=4.6). A statistical analysis showed that the long-term trend of the filtered data corresponded closely to the seismic energy released during the volcanic unrest. The observed increases of 222Rn are related to the rock fracturing processes (seismic activity) and the magmatic CO2 outflow increase, as observed in HIE03 station. Under these results, we find that continuous soil radon studies are important for evaluating the volcanic activity of El Hierro and they demonstrate the potential of applying continuous monitoring of soil radon to improve and optimize the detection of early warning signals of future

Linking Volcanism and Gas Release from the North East Atlantic Volcanic Province to the PETM: Challenges and Updates

Science.gov (United States)

Svensen, H.; Jones, M. T.; Jerram, D. A.; Planke, S.; Kjoberg, S.; Schmid, D. W.; Iyer, K.; Tegner, C.

2016-12-01

The main phase of the development of the North East Atlantic Volcanic Province took place about 56 Ma and coincides with the Paleocene Eocene Thermal Maximum (PETM). The volcanic activity was characterized by voluminous flood basalts, large plutonic complexes, sub-marine eruptions, widespread tephra deposition, and emplacement of sills and dikes along the continental margins of Norway, Greenland, Ireland, and the UK. Here we review the style and tempo of volcanism during this important period of Earth's history and discuss the sources and volumes of the carbon gases emitted to the ocean and atmosphere. Moreover, we present new data and models from 1) West Greenland showing the impact on sill intrusions on gas generation from heated Cretaceous mudstones, 2) a 3D seismic survey of gas release structures offshore Norway, and 3) Paleocene-Eocene tephra layers from Svalbard and Denmark. Gas migrated out of the contact aureoles by either explosive venting or by slower seepage towards the seafloor as demonstrated by 3D seismic data. Some of the gas was permanently trapped (dry gas and CO2-rich gas) in the source rocks and aureoles. Combined with high-precision zircon ages and a time model for the PETM, our approach may give robust fluxes that can explain both the onset and the body of the PETM.

An assessment of seismic monitoring in the United States; requirement for an Advanced National Seismic System

Science.gov (United States)

,

1999-01-01

This report assesses the status, needs, and associated costs of seismic monitoring in the United States. It sets down the requirement for an effective, national seismic monitoring strategy and an advanced system linking national, regional, and urban monitoring networks. Modernized seismic monitoring can provide alerts of imminent strong earthquake shaking; rapid assessment of distribution and severity of earthquake shaking (for use in emergency response); warnings of a possible tsunami from an offshore earthquake; warnings of volcanic eruptions; information for correctly characterizing earthquake hazards and for improving building codes; and data on response of buildings and structures during earthquakes, for safe, cost-effective design, engineering, and construction practices in earthquake-prone regions.

Uncertainties for seismic moment tensors and applications to nuclear explosions, volcanic events, and earthquakes

Science.gov (United States)

Tape, C.; Alvizuri, C. R.; Silwal, V.; Tape, W.

2017-12-01

When considered as a point source, a seismic source can be characterized in terms of its origin time, hypocenter, moment tensor, and source time function. The seismologist's task is to estimate these parameters--and their uncertainties--from three-component ground motion recorded at irregularly spaced stations. We will focus on one portion of this problem: the estimation of the moment tensor and its uncertainties. With magnitude estimated separately, we are left with five parameters describing the normalized moment tensor. A lune of normalized eigenvalue triples can be used to visualize the two parameters (lune longitude and lune latitude) describing the source type, while the conventional strike, dip, and rake angles can be used to characterize the orientation. Slight modifications of these five parameters lead to a uniform parameterization of moment tensors--uniform in the sense that equal volumes in the coordinate domain of the parameterization correspond to equal volumes of moment tensors. For a moment tensor m that we have inferred from seismic data for an earthquake, we define P(V) to be the probability that the true moment tensor for the earthquake lies in the neighborhood of m that has fractional volume V. The average value of P(V) is then a measure of our confidence in our inference of m. The calculation of P(V) requires knowing both the probability P(w) and the fractional volume V(w) of the set of moment tensors within a given angular radius w of m. We apply this approach to several different data sets, including nuclear explosions from the Nevada Test Site, volcanic events from Uturuncu (Bolivia), and earthquakes. Several challenges remain: choosing an appropriate misfit function, handling time shifts between data and synthetic waveforms, and extending the uncertainty estimation to include more source parameters (e.g., hypocenter and source time function).

Quantifying the Plutonic to Volcanic Relationship Along the Puna Plateau: Implications for Cordilleran Plateau Evolution

Science.gov (United States)

Ward, K. M.; Delph, J. R.; Zandt, G.; Beck, S. L.; Ducea, M. N.

2016-12-01

Quantifying well constrained plutonic to volcanic (P:V) ratios is inherently difficult because the tectonic processes that exhume intrusive bodies rarely preserve their extrusive equivalents. Conversely, active magmatic systems that have well-preserved volcanic deposits require sophisticated geophysical or geochemical approaches to estimate their plutonic roots and even when these sophisticated approaches are available, it is not always clear what constitutes a plutonic volume. Further complicating the enigmatic plutonic to volcanic relationship is the highly episodic nature of pluton emplacement where magmatic flare-ups produce several orders of magnitude more magmatism when compared against magmatic lulls. Despite this inherent difficulty, a growing body of independently measured P:V ratios (e.g. seismic tomography, geomorphic modeling, geological mapping/dating, and Zircon age spectra modeling) suggests the contribution of magmatic addition as an uplift mechanism in Cordilleran systems is much larger than is currently accepted. However, it remains unclear if these studies can be generalized to represent type behavior in Cordilleran systems or result from the non-uniform sampling imposed by the ability to measure large P:V ratios in only a few select and potentially anomalous regions of the American Cordillera. To better examine the role of magmatic processes in building Cordilleran high plateaus, we image the crustal seismic shear-wave velocity for an 800 km section (20.5°-28°S) of the active South American Cordillera (Puna Plateau). When placed in the context of existing geological and geophysical datasets, our seismic model reveals numerous mid-crustal low-velocity zones that we unambiguously interpret as the plutonic underpinnings associated with the voluminous silicic volcanics of the Puna Plateau. These larger P:V ratios are consistent with recent thermomechanical modeling of granitic magma intrusions that support the existence of long-lived, partially

Global positioning system survey data for active seismic and volcanic areas of eastern Sicily, 1994 to 2013

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Bonforte, Alessandro; Fagone, Sonia; Giardina, Carmelo; Genovese, Simone; Aiesi, Gianpiero; Calvagna, Francesco; Cantarero, Massimo; Consoli, Orazio; Consoli, Salvatore; Guglielmino, Francesco; Puglisi, Biagio; Puglisi, Giuseppe; Saraceno, Benedetto

2016-08-01

This work presents and describes a 20-year long database of GPS data collected by geodetic surveys over the seismically and volcanically active eastern Sicily, for a total of more than 6300 measurements. Raw data were initially collected from the various archives at the Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania—Osservatorio Etneo and organized in a single repository. Here, quality and completeness checks were performed, while all necessary supplementary information were searched, collected, validated and organized together with the relevant data. Once all data and information collections were completed, raw binary data were converted into the universal ASCII RINEX format; all data are provided in this format with the necessary information for precise processing. In order to make the data archive readily consultable, we developed software allowing the user to easily search and obtain the needed data by simple alphanumeric and geographic queries.

Global positioning system survey data for active seismic and volcanic areas of eastern Sicily, 1994 to 2013.

Science.gov (United States)

Bonforte, Alessandro; Fagone, Sonia; Giardina, Carmelo; Genovese, Simone; Aiesi, Gianpiero; Calvagna, Francesco; Cantarero, Massimo; Consoli, Orazio; Consoli, Salvatore; Guglielmino, Francesco; Puglisi, Biagio; Puglisi, Giuseppe; Saraceno, Benedetto

2016-08-01

This work presents and describes a 20-year long database of GPS data collected by geodetic surveys over the seismically and volcanically active eastern Sicily, for a total of more than 6300 measurements. Raw data were initially collected from the various archives at the Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania-Osservatorio Etneo and organized in a single repository. Here, quality and completeness checks were performed, while all necessary supplementary information were searched, collected, validated and organized together with the relevant data. Once all data and information collections were completed, raw binary data were converted into the universal ASCII RINEX format; all data are provided in this format with the necessary information for precise processing. In order to make the data archive readily consultable, we developed software allowing the user to easily search and obtain the needed data by simple alphanumeric and geographic queries.

Soil radon concentration and volcanic activity of Mt. Etna before and after the 2002 eruption

International Nuclear Information System (INIS)

Imme, G.; La Delfa, S.; Lo Nigro, S.; Morelli, D.; Patane, G.

2006-01-01

Soil radon investigation, using a continuous measurement device, has been performed on Mt. Etna in order to observe possible anomalies due to seismic and/or volcanic activity. In October 2002 an eruptive event occurred. Measurements, performed on the NE flank, have shown a possible correlation between eruptive activity of the volcano and soil radon concentration anomaly. The study of the seismic activity recorded in the same flank has, also, allowed to characterize the volcano dynamics and to correlate it with the variations of radon. The obtained results seem to indicate a possible dependence on volcanic activity of the radon concentration

The effect of deformation after backarc spreading between the rear arc and current volcanic front in Shikoku Basin obtained by seismic reflection survey

Science.gov (United States)

Yamashita, M.; Takahashi, N.; Nakanishi, A.; Kodaira, S.; Tamura, Y.

2012-12-01

Detailed crustal structure information of a back-arc basin must be obtained to elucidate the mechanism of its opening. Especially, the Shikoku Basin, which occupies the northern part of the Philippine Sea Plate between the Kyushu-Palau Ridge and the Izu-Bonin (Ogasawara) Arc, is an important area to understand the evolution of the back-arc basins as a part of the growth process of the Philippine Sea. Especially, the crustal structure oft the east side of Shikoku Basin is complicated by colliding to the Izu Peninsula Japan Agency for Marine-Earth Science and Technology has been carried out many multi-channel seismic reflection surveys since 2004 in Izu-Bonin region. Kodaira et al. (2008) reported the results of a refraction seismic survey along a north-south profile within paleoarc in the rear arc (i.e., the Nishi-shichito ridge) about 150 km west of current volcanic front. According to their results, the variation relationship of crustal thickness between the rear arc and volcanic front is suggested the evidence of rifting from current volcanic arc. There is the en-echelon arrangement is located in the eastern side of Shikoku Basin from current arc to rear arc, and it is known to activate after ceased spreading at 15 Ma (Okino et al., 1994) of Shikoku Basin by geologic sampling of Ishizuka et al. (2003). Our MCS results are also recognized the recent lateral fault zone is located in east side of Shikoku Basin. We carried out high density grid multi-channel seismic reflection (MCS) survey using tuned airgun in order to obtain the relationship between the lateral faults and en-echelon arrangement in KR08-04 cruise. We identified the deformation of sediments in Shikoku Basin after activity of Kanbun seamount at 8 Ma in MCS profile. It is estimated to activate a part of the eastern side of Shikoku Basin after construction of en-echelon arrangement and termination of Shikoku Basin spreading. Based on analyses of magnetic and gravity anomalies, Yamazaki and Yuasa (1998

Seismic imaging for an ocean drilling site survey and its verification in the Izu rear arc

Science.gov (United States)

Yamashita, Mikiya; Takahashi, Narumi; Tamura, Yoshihiko; Miura, Seiichi; Kodaira, Shuichi

2018-01-01

To evaluate the crustal structure of a site proposed for International Ocean Discovery Program drilling, the Japan Agency for Marine-Earth Science and Technology carried out seismic surveys in the Izu rear arc between 2006 and 2008, using research vessels Kaiyo and Kairei. High-resolution dense grid surveys, consisting of three kinds of reflection surveys, generated clear seismic profiles, together with a seismic velocity image obtained from a seismic refraction survey. In this paper, we compare the seismic profiles with the geological column obtained from the drilling. Five volcaniclastic sedimentary units were identified in seismic reflection profiles above the 5 km/s and 6 km/s contours of P-wave velocity obtained from the velocity image from the seismic refraction survey. However, some of the unit boundaries interpreted from the seismic images were not recognised in the drilling core, highlighting the difficulties of geological target identification in volcanic regions from seismic images alone. The geological core derived from drilling consisted of seven lithological units (labelled I to VII). Units I to V were aged at 0-9 Ma, and units VI and VII, from 1320-1806.5 m below seafloor (mbsf) had ages from 9 to ~15 Ma. The strong heterogeneity of volcanic sediments beneath the drilling site U1437 was also identified from coherence, calculated using cross-spectral analysis between grid survey lines. Our results suggest that use of a dense grid configuration is important in site surveys for ocean drilling in volcanic rear-arc situations, in order to recognise heterogeneous crustal structure, such as sediments from different origins.

Constraining the dynamics of 2014-15 Bardarbunga-Holuhraun intrusion and eruption using seismic noise

Science.gov (United States)

Caudron, Corentin; Donaldson, Clare; White, Robert

2016-04-01

The 2010 Eyjafjallajokull volcanic eruption explosively emitted a large quantity of ash in the atmosphere and paralysed the European airspace for weeks. Several seismic scientific studies already contributed to the understanding of this complex eruption (e.g., Tarasewicz et al., 2012). Although an excellent network of seismometers recorded this eruption, some volcanological and seismological aspects are still poorly understood. In order to gain further constraints on the dynamics of this ground-breaking eruptions, we mine the seismic dataset using the seismic ambient noise technique between pairs of stations and the Seismic Amplitude Ratio Analysis (SARA). Our preliminary results reveal a strong contamination of the Cross Correlation Functions (CCF) by the volcanic tremor, particularly above 0.5 Hz even for station pairs located >50 km from the volcano. Although this volcanic tremor precludes the monitoring of the seismic velocities, it literally illuminated the medium. The two phases of the eruptions (i.e., effusive and explosive) are clearly distinguished in these functions due to their different locations. During the explosive phase, an intriguing shift of the main peaks of the cross correlation functions is evidenced (early May 2010). It is remarkably consistent with the downward migration proposed by Tarasewicz et al. (2012) and is interpreted as a migration of the volcanic tremor. SARA methodology, which is continuously imaging and tracking any significant seismicity at a 10-min time scale (Taisne et al., 2010), is applied in the 5-15 Hz frequency band in order to image to continuously migrating microseismicity. The analysis displays several shallow migrations (above 5 km of depth, in March 2010) preceding the effusive phase of the eruption. Interestingly, the results also evidence a fast and deep migration (> 5 km) starting a few hours before the beginning of the explosive phase (13 April 2010). These preliminary results may shed light on the triggering of

Monitoring diffuse degassing in monogenetic volcanic field during seismic-volcanic unrest: the case of Tenerife North-West Rift Zone (NWRZ), Canary Islands, Spain

Science.gov (United States)

García, E.; Botelho, A. H.; Regnier, G. S. G.; Rodríguez, F.; Alonso Cótchico, M.; Melián, G.; Asensio-Ramos, M.; Padrón, E.; Hernández, P. A.; Pérez, N. M.

2017-12-01

factors and it shows a clear temporal correlation with the onsets of seismic activity (Hernández et al., 2017, Bull. Volcanol.). Monitoring the diffuse CO2 emission contributes to detect early warning signals of volcanic unrest at the Tenerife North-West Rift-Zone volcano.

Using faults for PSHA in a volcanic context: the Etna case (Southern Italy)

Science.gov (United States)

Azzaro, Raffaele; D'Amico, Salvatore; Gee, Robin; Pace, Bruno; Peruzza, Laura

2016-04-01

At Mt. Etna volcano (Southern Italy), recurrent volcano-tectonic earthquakes affect the urbanised areas, with an overall population of about 400,000 and with important infrastructures and lifelines. For this reason, seismic hazard analyses have been undertaken in the last decade focusing on the capability of local faults to generate damaging earthquakes especially in the short-term (30-5 yrs); these results have to be intended as complementary to the regulatory seismic hazard maps, and devoted to establish priority in the seismic retrofitting of the exposed municipalities. Starting from past experience, in the framework of the V3 Project funded by the Italian Department of Civil Defense we performed a fully probabilistic seismic hazard assessment by using an original definition of seismic sources and ground-motion prediction equations specifically derived for this volcanic area; calculations are referred to a new brand topographic surface (Mt. Etna reaches more than 3,000 m in elevation, in less than 20 km from the coast), and to both Poissonian and time-dependent occurrence models. We present at first the process of defining seismic sources that includes individual faults, seismic zones and gridded seismicity; they are obtained by integrating geological field data with long-term (the historical macroseismic catalogue) and short-term earthquake data (the instrumental catalogue). The analysis of the Frequency Magnitude Distribution identifies areas in the volcanic complex, with a- and b-values of the Gutenberg-Richter relationship representative of different dynamic processes. Then, we discuss the variability of the mean occurrence times of major earthquakes along the main Etnean faults estimated by using a purely geologic approach. This analysis has been carried out through the software code FISH, a Matlab® tool developed to turn fault data representative of the seismogenic process into hazard models. The utilization of a magnitude-size scaling relationship

Geologic field-trip guide to the volcanic and hydrothermal landscape of the Yellowstone Plateau

Science.gov (United States)

Morgan Morzel, Lisa Ann; Shanks, W. C. Pat; Lowenstern, Jacob B.; Farrell, Jamie M.; Robinson, Joel E.

2017-11-20

Yellowstone National Park, a nearly 9,000 km2 (~3,468 mi2) area, was preserved in 1872 as the world’s first national park for its unique, extraordinary, and magnificent natural features. Rimmed by a crescent of older mountainous terrain, Yellowstone National Park has at its core the Quaternary Yellowstone Plateau, an undulating landscape shaped by forces of late Cenozoic explosive and effusive volcanism, on-going tectonism, glaciation, and hydrothermal activity. The Yellowstone Caldera is the centerpiece of the Yellowstone Plateau. The Yellowstone Plateau lies at the most northeastern front of the 17-Ma Yellowstone hot spot track, one of the few places on Earth where time-transgressive processes on continental crust can be observed in the volcanic and tectonic (faulting and uplift) record at the rate and direction predicted by plate motion. Over six days, this field trip presents an intensive overview into volcanism, tectonism, and hydrothermal activity on the Yellowstone Plateau (fig. 1). Field stops are linked directly to conceptual models related to monitoring of the various volcanic, geochemical, hydrothermal, and tectonic aspects of the greater Yellowstone system. Recent interest in young and possible future volcanism at Yellowstone as well as new discoveries and synthesis of previous studies, (for example, tomographic, deformation, gas, aeromagnetic, bathymetric, and seismic surveys), provide a framework in which to discuss volcanic, hydrothermal, and seismic activity in this dynamic region.

Seismic response in archaeological areas: the case-histories of Rome

Science.gov (United States)

Donati, Stefano; Funiciello, Renato; Rovelli, Antonio

1999-03-01

Rome is affected by earthquakes associated to three different seismogenic districts: the Central Apennines area, the Colli Albani volcanic area and the Roman area. The major effects were exclusively due to Apennine seismicity and reached in some cases felt intensities up to VII-VIII degree (MCS scale). The predominant role in the damage distribution seems to be played by the local geological conditions. The historical centre of the city is characterized by the presence of two geomorphologic domains: the alluvial plain of Tiber river and the topographic relieves of Roman Hills, where tradition indicates the first site of the city foundation. In particular, the right river side is characterized by the outcropping of the regional bedrock along the Monte Mario-Gianicolo ridge, while the eastern relieves are the remnants of the Sabatini and Albani volcanic plateau, deeply eroded by the Tiber river and its tributaries during the last glacial low-stand (Würm). These domains are characterized by a large difference in seismic response, due to the high impedance contrast between Holocene coarse deposits filling the Tiber Valley and sedimentary and volcanic Plio-Pleistocene units. Seismic damage observed in 150 monuments of downtown Rome was indicating a significant concentration on alluvial recent deposits. This result was confirmed by the geographical distribution of conservation and retrofitting activities subsequent to main earthquakes, mostly related to local geological conditions. The cases of Marcus Aurelius' Column and Colosseum confirmed the influence of the Holocene alluvial network in local seismic response. During 2500 years of history, the monuments of Rome have `memorized' the seismic effects of historical earthquakes. In some cases, the integration of historical and geological research and macroseismic observations may provide original and useful indications to seismologists to define the seismic response of the city. Local site effects represent a serious

Seismicity and volcanic activity in Japan based on crustal thermal activity . 2; Chikaku no netsukatsudo ni motozuku Nippon no Jishin kazan katsudo. 2

Energy Technology Data Exchange (ETDEWEB)

Hayakawa, M [Tokai Univ., Tokyo (Japan). School of Marine Science and Technology

1996-05-01

This paper describes the following matters about seismic and volcanic activities in Japan. The previous paper has reported a view that energy is transported from deep portions of the earth`s crust toward outer portions, and the stored energy thrusts up collectively in a certain time period (a rising period). A fact may be accounted for as one of the endorsements thereof that earthquakes and volcanic eruptions take place successively over a wide area from Okinawa to Hokkaido in a short period of time (included in the rising period). When viewed by limiting the time period and areas, a great earthquake would not occur suddenly, but stored energy is released wholly at a certain time while it has been released little by little. Referring to the Kanto Great Earthquake (1923) and the Tokai and Nankai Earthquakes (1944 and 1946), it is found that earthquakes had been occurring successively in the surrounding areas since about 20 years before the occurrence of these great earthquakes. Similar phenomena may be seen in the great earthquakes of Ansei (1854) and An-ei (1707). 5 figs.

Seismic energy data analysis of Merapi volcano to test the eruption time prediction using materials failure forecast method (FFM)

Science.gov (United States)

Anggraeni, Novia Antika

2015-04-01

The test of eruption time prediction is an effort to prepare volcanic disaster mitigation, especially in the volcano's inhabited slope area, such as Merapi Volcano. The test can be conducted by observing the increase of volcanic activity, such as seismicity degree, deformation and SO2 gas emission. One of methods that can be used to predict the time of eruption is Materials Failure Forecast Method (FFM). Materials Failure Forecast Method (FFM) is a predictive method to determine the time of volcanic eruption which was introduced by Voight (1988). This method requires an increase in the rate of change, or acceleration of the observed volcanic activity parameters. The parameter used in this study is the seismic energy value of Merapi Volcano from 1990 - 2012. The data was plotted in form of graphs of seismic energy rate inverse versus time with FFM graphical technique approach uses simple linear regression. The data quality control used to increase the time precision employs the data correlation coefficient value of the seismic energy rate inverse versus time. From the results of graph analysis, the precision of prediction time toward the real time of eruption vary between -2.86 up to 5.49 days.

Diffuse CO_{2} degassing monitoring of the oceanic active volcanic island of El Hierro, Canary Islands, Spain

Science.gov (United States)

Hernández, Pedro A.; Norrie, Janice; Withoos, Yannick; García-Merino, Marta; Melián, Gladys; Padrón, Eleazar; Barrancos, José; Padilla, Germán; Rodríguez, Fátima; Pérez, Nemesio M.

2017-04-01

Even during repose periods, volcanoes release large amounts of gases from both visible (fumaroles, solfataras, plumes) and non-visible emanations (diffuse degassing). In the last 20 years, there has been considerable interest in the study of diffuse degassing as a powerful tool in volcano monitoring programs, particularly in those volcanic areas where there are no visible volcanic-hydrothermal gas emissions. Historically, soil gas and diffuse degassing surveys in volcanic environments have focused mainly on CO2 because it is, after water vapor, the most abundant gas dissolved in magma. As CO2 travels upward by advective-diffusive transport mechanisms and manifests itself at the surface, changes in its flux pattern over time provide important information for monitoring volcanic and seismic activity. Since 1998, diffuse CO2 emission has been monitored at El Hierro Island, the smallest and south westernmost island of the Canarian archipelago with an area of 278 km2. As no visible emanations occur at the surface environment of El Hierro, diffuse degassing studies have become the most useful geochemical tool to monitor the volcanic activity in this volcanic island. The island experienced a volcano-seismic unrest that began in July 2011, characterized by the location of a large number of relatively small earthquakes (MHierro at depths between 8 and 15 km. On October 12, 2011, a submarine eruption was confirmed during the afternoon of October 12, 2011 by visual observations off the coast of El Hierro, about 2 km south of the small village of La Restinga in the southernmost part of the island. During the pre-eruptive and eruptive periods, the time series of the diffuse CO2 emission released by the whole island experienced two significant increases. The first started almost 2 weeks before the onset of the submarine eruption, reflecting a clear geochemical anomaly in CO2 emission, most likely due to increasing release of deep seated magmatic gases to the surface. The second

Unrest of Chiles - Cerro Negro volcanic complex: A binational Ecuador - Colombia effort

Science.gov (United States)

Ruiz, M. C.; Gomez, D.; Torres, R.; Cadena, O.; Mothes, P. A.; Anzieta, J. C.; Pacheco, D. A.; Bernard, B.; Acero, W.; Hidalgo, S.; Enriquez, W.; Cordova, A.

2014-12-01

The increasing seismic activity at the area of Chiles - Cerro Negro volcanic complex, located at the Ecuador-Colombian border, has been jointly monitored by the Instituto Geofisico - Ecuador and the Observatorio Vulcanologico y Sismologico de Pasto OVSP, a division of the Servicio Geologico Colombiano. Since April 2013, three seismic swarms have been detected in this area and more than 100.000 events are recorded since November 2013. The largest and more recent swarm has a daily average of 676 events between March and June 2014. Currently a seismic network of 8 seismic stations (5 in the Colombian and 3 in Ecuadorean side) are deployed in this area. Epicenters of more than 315 seismic events with magnitudes Ml>2.0 and 10 or more phases are located in an area 1-4 km south of Chiles volcano with shallow depths (up to 14 km). Most of events have magnitudes between 1.0 to 4.0. Nine events have magnitudes larger than 4.0 and the largest event occurred on April 30. 2014 with a local magnitude of 4.7 and inverse-transcurrent component focal mechanism. Waveforms and spectral patterns define these events as volcano-tectonic. Events with large magnitudes (above 3.0) show a very long-period component. Hot spring and deformation measurements also show signals of volcanic unrest.

Earthquakes and Volcanic Processes at San Miguel Volcano, El Salvador, Determined from a Small, Temporary Seismic Network

Science.gov (United States)

Hernandez, S.; Schiek, C. G.; Zeiler, C. P.; Velasco, A. A.; Hurtado, J. M.

2008-12-01

The San Miguel volcano lies within the Central American volcanic chain in eastern El Salvador. The volcano has experienced at least 29 eruptions with Volcano Explosivity Index (VEI) of 2. Since 1970, however, eruptions have decreased in intensity to an average of VEI 1, with the most recent eruption occurring in 2002. Eruptions at San Miguel volcano consist mostly of central vent and phreatic eruptions. A critical challenge related to the explosive nature of this volcano is to understand the relationships between precursory surface deformation, earthquake activity, and volcanic activity. In this project, we seek to determine sub-surface structures within and near the volcano, relate the local deformation to these structures, and better understand the hazard that the volcano presents in the region. To accomplish these goals, we deployed a six station, broadband seismic network around San Miguel volcano in collaboration with researchers from Servicio Nacional de Estudios Territoriales (SNET). This network operated continuously from 23 March 2007 to 15 January 2008 and had a high data recovery rate. The data were processed to determine earthquake locations, magnitudes, and, for some of the larger events, focal mechanisms. We obtained high precision locations using a double-difference approach and identified at least 25 events near the volcano. Ongoing analysis will seek to identify earthquake types (e.g., long period, tectonic, and hybrid events) that occurred in the vicinity of San Miguel volcano. These results will be combined with radar interferometric measurements of surface deformation in order to determine the relationship between surface and subsurface processes at the volcano.

Backprojection of volcanic tremor

Science.gov (United States)

Haney, Matthew M.

2014-01-01

Backprojection has become a powerful tool for imaging the rupture process of global earthquakes. We demonstrate the ability of backprojection to illuminate and track volcanic sources as well. We apply the method to the seismic network from Okmok Volcano, Alaska, at the time of an escalation in tremor during the 2008 eruption. Although we are able to focus the wavefield close to the location of the active cone, the network array response lacks sufficient resolution to reveal kilometer-scale changes in tremor location. By deconvolving the response in successive backprojection images, we enhance resolution and find that the tremor source moved toward an intracaldera lake prior to its escalation. The increased tremor therefore resulted from magma-water interaction, in agreement with the overall phreatomagmatic character of the eruption. Imaging of eruption tremor shows that time reversal methods, such as backprojection, can provide new insights into the temporal evolution of volcanic sources.

Volcanic Alert System (VAS) developed during the (2011-2013) El Hierro (Canary Islands) volcanic process

Science.gov (United States)

Ortiz, Ramon; Berrocoso, Manuel; Marrero, Jose Manuel; Fernandez-Ros, Alberto; Prates, Gonçalo; De la Cruz-Reyna, Servando; Garcia, Alicia

2014-05-01

In volcanic areas with long repose periods (as El Hierro), recently installed monitoring networks offer no instrumental record of past eruptions nor experience in handling a volcanic crisis. Both conditions, uncertainty and inexperience, contribute to make the communication of hazard more difficult. In fact, in the initial phases of the unrest at El Hierro, the perception of volcanic risk was somewhat distorted, as even relatively low volcanic hazards caused a high political impact. The need of a Volcanic Alert System became then evident. In general, the Volcanic Alert System is comprised of the monitoring network, the software tools for the analysis of the observables, the management of the Volcanic Activity Level, and the assessment of the threat. The Volcanic Alert System presented here places special emphasis on phenomena associated to moderate eruptions, as well as on volcano-tectonic earthquakes and landslides, which in some cases, as in El Hierro, may be more destructive than an eruption itself. As part of the Volcanic Alert System, we introduce here the Volcanic Activity Level which continuously applies a routine analysis of monitoring data (particularly seismic and deformation data) to detect data trend changes or monitoring network failures. The data trend changes are quantified according to the Failure Forecast Method (FFM). When data changes and/or malfunctions are detected, by an automated watchdog, warnings are automatically issued to the Monitoring Scientific Team. Changes in the data patterns are then translated by the Monitoring Scientific Team into a simple Volcanic Activity Level, that is easy to use and understand by the scientists and technicians in charge for the technical management of the unrest. The main feature of the Volcanic Activity Level is its objectivity, as it does not depend on expert opinions, which are left to the Scientific Committee, and its capabilities for early detection of precursors. As a consequence of the El Hierro

The January 2006 Volcanic-Tectonic Earthquake Swarm at Mount Martin, Alaska

Science.gov (United States)

Dixon, James P.; Power, John A.

2009-01-01

On January 8, 2006, a swarm of volcanic-tectonic earthquakes began beneath Mount Martin at the southern end of the Katmai volcanic cluster. This was the first recorded swarm at Mount Martin since continuous seismic monitoring began in 1996. The number of located earthquakes increased during the next four days, reaching a peak on January 11. For the next two days, the seismic activity decreased, and on January 14, the number of events increased to twice the previous day's total. Following this increase in activity, seismicity declined, returning to background levels by the end of the month. The Alaska Volcano Observatory located 860 earthquakes near Mount Martin during January 2006. No additional signs of volcanic unrest were noted in association with this earthquake swarm. The earthquakes in the Mount Martin swarm, relocated using the double difference technique, formed an elongated cluster dipping to the southwest. Focal mechanisms beneath Mount Martin show a mix of normal, thrust, and strike-slip solutions, with normal focal mechanisms dominating. For earthquakes more than 1 km from Mount Martin, all focal mechanisms showed normal faulting. The calculated b-value for the Mount Martin swarm is 0.98 and showed no significant change before, during, or after the swarm. The triggering mechanism for the Mount Martin swarm is unknown. The time-history of earthquake occurrence is indicative of a volcanic cause; however, there were no low-frequency events or observations, such as increased steaming associated with the swarm. During the swarm, there was no change in the b-value, and the distribution and type of focal mechanisms were similar to those in the period before the anomalous activity. The short duration of the swarm, the similarity in observed focal mechanisms, and the lack of additional signs of unrest suggest this swarm did not result from a large influx of magma within the shallow crust beneath Mount Martin.

Reassessment of the historical seismic activity with major impact on S. Miguel Island (Azores

Directory of Open Access Journals (Sweden)

D. Silveira

2003-01-01

Full Text Available On account of its tectonic setting, both seismic and volcanic events are frequent in the Azores archipelago. During the historical period earthquakes and seismic swarms of tectonic and/or volcanic origin have struck S. Miguel Island causing a significant number of casualties and severe damages. The information present in historical records made possible a new macroseismic analysis of these major events using the European Macroseismic Scale-1998 (EMS-98. Among the strongest earthquakes of tectonic origin that affected S. Miguel Island, six events were selected for this study. The isoseismal maps drawn for these events enabled the identification of areas characterized by anomalous values of seismic intensity, either positive or negative, to constrain epicentre locations and to identify some new seismogenic areas. Regarding seismic activity associated with volcanic phenomena six cases were also selected. For each of the studied cases cumulative intensity values were assessed for each locality. The distribution of local intensity values shows that the effects are not homogeneous within a certain distance from the eruptive centre, the area of major impacts relates with the eruptive style and damages equivalent to high intensities may occur in Furnas and Sete Cidades calderas. Combining all the historical macroseismic data, a maximum intensity map was produced for S. Miguel Island.

The Volcanism Ontology (VO): a model of the volcanic system

Science.gov (United States)

Myer, J.; Babaie, H. A.

2017-12-01

We have modeled a part of the complex material and process entities and properties of the volcanic system in the Volcanism Ontology (VO) applying several top-level ontologies such as Basic Formal Ontology (BFO), SWEET, and Ontology of Physics for Biology (OPB) within a single framework. The continuant concepts in BFO describe features with instances that persist as wholes through time and have qualities (attributes) that may change (e.g., state, composition, and location). In VO, the continuants include lava, volcanic rock, and volcano. The occurrent concepts in BFO include processes, their temporal boundaries, and the spatio-temporal regions within which they occur. In VO, these include eruption (process), the onset of pyroclastic flow (temporal boundary), and the space and time span of the crystallization of lava in a lava tube (spatio-temporal region). These processes can be of physical (e.g., debris flow, crystallization, injection), atmospheric (e.g., vapor emission, ash particles blocking solar radiation), hydrological (e.g., diffusion of water vapor, hot spring), thermal (e.g., cooling of lava) and other types. The properties (predicates) relate continuants to other continuants, occurrents to continuants, and occurrents to occurrents. The ontology also models other concepts such as laboratory and field procedures by volcanologists, sampling by sensors, and the type of instruments applied in monitoring volcanic activity. When deployed on the web, VO will be used to explicitly and formally annotate data and information collected by volcanologists based on domain knowledge. This will enable the integration of global volcanic data and improve the interoperability of software that deal with such data.

A seismic network to investigate the sedimentary hosted hydrothermal Lusi system

Science.gov (United States)

Javad Fallahi, Mohammad; Mazzini, Adriano; Lupi, Matteo; Obermann, Anne; Karyono, Karyono

2016-04-01

The 29th of May 2006 marked the beginning of the sedimentary hosted hydrothermal Lusi system. During the last 10 years we witnessed numerous alterations of the Lusi system behavior that coincide with the frequent seismic and volcanic activity occurring in the region. In order to monitor the effect that the seismicity and the activity of the volcanic arc have on Lusi, we deployed a ad hoc seismic network. This temporary network consist of 10 broadband and 21 short period stations and is currently operating around the Arjuno-Welirang volcanic complex, along the Watukosek fault system and around Lusi, in the East Java basin since January 2015. We exploit this dataset to investigate surface wave and shear wave velocity structure of the upper-crust beneath the Arjuno-Welirang-Lusi complex in the framework of the Lusi Lab project (ERC grant n° 308126). Rayleigh and Love waves travelling between each station-pair are extracted by cross-correlating long time series of ambient noise data recorded at the stations. Group and phase velocity dispersion curves are obtained by time-frequency analysis of cross-correlation functions, and are tomographically inverted to provide 2D velocity maps corresponding to different sampling depths. 3D shear wave velocity structure is then acquired by inverting the group velocity maps.

Combining Geological and Geophysical Data in Volcanic Hazard Estimation for Dominica, Lesser Antilles

Science.gov (United States)

George, O.; Latchman, J. L.; Connor, C.; Malservisi, R.; Connor, L.

2014-12-01

Risk posed by volcanic eruptions are generally quantified in a few ways; in the short term geophysical data such as seismic activity or ground deformation are used to assess the state of volcanic unrest while statistical approaches such as spatial density estimates are used for long term hazard assessment. Spatial density estimates have been used in a number of monogenetic volcanic fields for hazard map generation and utilize the age, location and volumes of previous eruptions to calculate the probability of a new event occurring at a given location within this field. In a previously unpublished study, spatial density estimates of the Lesser Antilles volcanic arc showed the island of Dominica to have the highest likelihood of future vent formation. In this current study, this technique was used in combination with relocated seismic events occurring beneath Dominica within the last ~ 20 years as well as InSAR images of ground deformation to generate a hazard map which not only takes into consideration the past events but also the current state of unrest. Here, geophysical data serve as a weighting factor in the estimates with those centers showing more vigorous activity receiving stronger favorability in the assessment for future activity. In addition to this weighting, the bandwidth utilized in the 2D-radially symmetric kernel density function was optimized using the SAMSE method so as to find the value which best minimizes the error in the estimate. The end results of this study are dynamic volcanic hazards maps which will be readily updatable as changes in volcanic unrest occurs within the system.

Seismic energy data analysis of Merapi volcano to test the eruption time prediction using materials failure forecast method (FFM)

International Nuclear Information System (INIS)

Anggraeni, Novia Antika

2015-01-01

The test of eruption time prediction is an effort to prepare volcanic disaster mitigation, especially in the volcano’s inhabited slope area, such as Merapi Volcano. The test can be conducted by observing the increase of volcanic activity, such as seismicity degree, deformation and SO2 gas emission. One of methods that can be used to predict the time of eruption is Materials Failure Forecast Method (FFM). Materials Failure Forecast Method (FFM) is a predictive method to determine the time of volcanic eruption which was introduced by Voight (1988). This method requires an increase in the rate of change, or acceleration of the observed volcanic activity parameters. The parameter used in this study is the seismic energy value of Merapi Volcano from 1990 – 2012. The data was plotted in form of graphs of seismic energy rate inverse versus time with FFM graphical technique approach uses simple linear regression. The data quality control used to increase the time precision employs the data correlation coefficient value of the seismic energy rate inverse versus time. From the results of graph analysis, the precision of prediction time toward the real time of eruption vary between −2.86 up to 5.49 days

Seismic energy data analysis of Merapi volcano to test the eruption time prediction using materials failure forecast method (FFM)

Energy Technology Data Exchange (ETDEWEB)

Anggraeni, Novia Antika, E-mail: novia.antika.a@gmail.com [Geophysics Sub-department, Physics Department, Faculty of Mathematic and Natural Science, Universitas Gadjah Mada. BLS 21 Yogyakarta 55281 (Indonesia)

2015-04-24

The test of eruption time prediction is an effort to prepare volcanic disaster mitigation, especially in the volcano’s inhabited slope area, such as Merapi Volcano. The test can be conducted by observing the increase of volcanic activity, such as seismicity degree, deformation and SO2 gas emission. One of methods that can be used to predict the time of eruption is Materials Failure Forecast Method (FFM). Materials Failure Forecast Method (FFM) is a predictive method to determine the time of volcanic eruption which was introduced by Voight (1988). This method requires an increase in the rate of change, or acceleration of the observed volcanic activity parameters. The parameter used in this study is the seismic energy value of Merapi Volcano from 1990 – 2012. The data was plotted in form of graphs of seismic energy rate inverse versus time with FFM graphical technique approach uses simple linear regression. The data quality control used to increase the time precision employs the data correlation coefficient value of the seismic energy rate inverse versus time. From the results of graph analysis, the precision of prediction time toward the real time of eruption vary between −2.86 up to 5.49 days.

Volcanic Hazard Assessments for Nuclear Installations: Methods and Examples in Site Evaluation

International Nuclear Information System (INIS)

2016-07-01

To provide guidance on the protection of nuclear installations against the effects of volcanoes, the IAEA published in 2012 IAEA Safety Standards Series No. SSG-21, Volcanic Hazards in Site Evaluation for Nuclear Installations. SSG-21 addresses hazards relating to volcanic phenomena, and provides recommendations and general guidance for evaluation of these hazards. Unlike seismic hazard assessments, models for volcanic hazard assessment have not undergone decades of review, evaluation and testing for suitability in evaluating hazards at proposed nuclear installations. Currently in volcanology, scientific developments and detailed methodologies to model volcanic phenomena are evolving rapidly.This publication provides information on detailed methodologies and examples in the application of volcanic hazard assessment to site evaluation for nuclear installations, thereby addressing the recommendations in SSG-21. Although SSG-21 develops a logical framework for conducting a volcanic hazard assessment, this publication demonstrates the practicability of evaluating the recommendations in SSG-21 through a systematic volcanic hazard assessment and examples from Member States. The results of this hazard assessment can be used to derive the appropriate design bases and operational considerations for specific nuclear installations

Deployment of a seismic array for volcano monitoring during the ongoing submarine eruption at El Hierro, Canary Islands

Science.gov (United States)

Abella, R.; Almendros, J.; Carmona, E.; Martin, R.

2012-04-01

On 17 July 2011 there was an important increase of the seismic activity at El Hierro (Canary Islands, Spain). This increase was detected by the Volcano Monitoring Network (Spanish national seismic network) run by the Instituto Geográfico Nacional (IGN). As a consequence, the IGN immediately deployed a dense, complete monitoring network that included seismometers, GPS stations, geochemical equipment, magnetometers, and gravity meters. During the first three months of activity, the seismic network recorded over ten thousand volcano-tectonic earthquakes, with a maximum magnitude of 4.6. On 10 October 2011 an intense volcanic tremor started. It was a monochromatic signal, with variable amplitude and frequency content centered at about 1-2 Hz. The tremor onset was correlated with the initial stages of the submarine eruption that occurred from a vent located south of El Hierro island, near the village of La Restinga. At that point the IGN, in collaboration with the Instituto Andaluz de Geofísica, deployed a seismic array intended for volcanic tremor monitoring and analysis. The seismic array is located about 7 km NW of the submarine vent. It has a 12-channel, 24-bit data acquisition system sampling each channel at 100 sps. The array is composed by 1 three-component and 9 vertical-component seismometers, distributed in a flat area with an aperture of 360 m. The data provided by the seismic array are going to be processed using two different approaches: (1) near-real-time, to produce information that can be useful in the management of the volcanic crisis; and (2) detailed investigations, to study the volcanic tremor characteristics and relate them to the eruption dynamics. At this stage we are mostly dedicated to produce fast, near-real-time estimates. Preliminary results have been obtained using the maximum average cross-correlation method. They indicate that the tremor wavefronts are highly coherent among array stations and propagate across the seismic array with an

Seismic velocity variation along the Izu-Bonin arc estaimated from traveltime tomography using OBS data

Science.gov (United States)

Obana, K.; Tamura, Y.; Takahashi, T.; Kodaira, S.

2014-12-01

The Izu-Bonin (Ogasawara) arc is an intra-oceanic island arc along the convergent plate boundary between the subducting Pacific and overriding Philippine Sea plates. Recent active seismic studies in the Izu-Bonin arc reveal significant along-arc variations in crustal structure [Kodaira et al., 2007]. The thickness of the arc crust shows a remarkable change between thicker Izu (~30 km) and thinner Bonin (~10 km) arcs. In addition to this, several geological and geophysical contrasts, such as seafloor topography and chemical composition of volcanic rocks, between Izu and Bonin arc have been reported [e.g., Yuasa 1992]. We have conducted earthquake observations using ocean bottom seismographs (OBSs) to reveal seismic velocity structure of the crust and mantle wedge in the Izu-Bonin arc and to investigate origin of the along-arc structure variations. We deployed 40 short-period OBSs in Izu and Bonin area in 2006 and 2009, respectively. The OBS data were processed with seismic data recorded at routine seismic stations on Hachijo-jima, Aoga-shima, and Chichi-jima operated by National Research Institute for Earth Science and Disaster Prevention (NIED). More than 5000 earthquakes were observed during about three-months observation period in each experiment. We conducted three-dimensional seismic tomography using manually picked P- and S-wave arrival time data. The obtained image shows a different seismic velocity structures in the mantle beneath the volcanic front between Izu and Bonin arcs. Low P-wave velocity anomalies in the mantle beneath the volcanic front in the Izu arc are limited at depths deeper than those in the Bonin arc. On the other hand, P-wave velocity in the low velocity anomalies beneath volcanic front in the Bonin arc is slower than that in the Izu arc. These large-scale along-arc structure variations in the mantle could relate to the geological and geophysical contrasts between Izu and Bonin arcs.

2015 Volcanic activity in Alaska—Summary of events and response of the Alaska Volcano Observatory

Science.gov (United States)

Dixon, James P.; Cameron, Cheryl E.; Iezzi, Alexandra M.; Wallace, Kristi

2017-09-28

The Alaska Volcano Observatory (AVO) responded to eruptions, volcanic unrest or suspected unrest, and seismic events at 14 volcanic centers in Alaska during 2015. The most notable volcanic activity consisted of continuing intermittent ash eruptions from Cleveland and Shishaldin volcanoes in the Aleutian Islands. Two eruptive episodes, at Veniaminof and Pavlof, on the Alaska Peninsula ended in 2015. During 2015, AVO re-established the seismograph network at Aniakchak, installed six new broadband seismometers throughout the Aleutian Islands, and added a Multiple component Gas Analyzer System (MultiGAS) station on Augustine.

Geologic aspects of seismic hazards assessment at the Idaho National Engineering Laboratory, southeastern Idaho

International Nuclear Information System (INIS)

Smith, R.P.; Hackett, W.R.; Rodgers, D.W.

1989-01-01

The Idaho National Engineering Laboratory (INEL), located on the northwestern side of the Eastern Snake River Plain (ESRP), lies in an area influenced by two distinct geologic provinces. The ESRP province is a northeast-trending zone of late Tertiary and Quaternary volcanism which transects the northwest-trending, block-fault mountain ranges of the Basin and Range province. An understanding of the interaction of these two provinces is important for realistic geologic hazards assessment. Of particular importance for seismic hazards analysis is the relationship of volcanic rift zones on the ESRP to basin-and-range faults north of the plain. The Arco Rift Zone, a 20-km-long belt of deformation and volcanism on the plain just west of the INEL, is colinear with the basin-and-range Lost River fault. Recent field studies have demonstrated that Arco Rift Zone deformation is typical of that induced by dike injection in other volcanic rift zones. The deformation is characterized by a predominance of dilational fissuring with less extensive development of faults and grabens. Cumulative vertical displacements over the past 0.6 Ma are an order of magnitude lower than those associated with the Arco Segment of the Lost River fault to the northwest. The evidence suggests that the northeast-directed extension that produces the block fault mountains of the Basin and Range is expressed by dike injection and volcanic rift zone development in the ESRP. Seismicity associated with dike injection during rift zone development is typically of low magnitude and would represent only minor hazard compared to that associated with the block faulting. Since the ESRP responds to extension in a manner distinct from basin-and-range faulting, it is not appropriate to consider the volcanic rift zones as extensions of basin-and-range faults for seismic hazard analysis

Evidence for a continental unstable triple junction as an alternate model for Vrancea seismicity

International Nuclear Information System (INIS)

Besutiu, L.

2002-01-01

The Vrancea active seismic zone located in the bending area of Romanian Carpathians stands for a long time as a challenge to geoscientists all over the world. Deep seismicity in continental collision circumstances is rather rare and always constraints on dynamics of subduction. The pattern of the intermediate-depth seismicity in the Vrancea region suggests a confined prismatic nearly vertical seismic body. The small size and geometry of the seismic zone have made it difficult to interpret the kinematics of subduction and continental collision in the area. During the years, several models, almost all subduction-related, have more or less successfully tried to explain this phenomenon. The paper represents an attempt to explain the Vrancea intermediate depth seismicity starting from a new concept, as introduced by the plate tectonics theory: the triple junction. A continental unstable triple junction is proposed as an alternate model to explain the unusual seismicity in the Vrancea seismic area. Three tectonic plates / microplates seem to join in the region: East European Plate (EEP), Moesian microplate (MoP), and the Intra-Alpine microplate (IaP). Their edges are geophysically documented and their motion is evidenced. The differentiation in their relative velocities generated an unstable transform-transform-compression triple junction that determined the vertical collapse of the lithospheric segment to which the intermediate seismicity within Vrancea zone is associated. Three major plates' wedges bound the seismic body: Tornquist-Teissyere zone, Peceneaga-Camena fault, and Trans-Getica fault. Temperature accommodation phenomena associated to the sinking lithospheric body into the hotter upper mantle environment (such as convective cells, phase-transform processes, and devolatilization) could be responsible for the earthquakes occurrence. The problem of the missing subduction related volcanism within Vrancea triple junction (VTJ) area is definitely solved in the case

Integration of potential field and seismic data for hydrocarbon exploration in the Miguasha area, Appalachian Gaspe belt, Quebec

Energy Technology Data Exchange (ETDEWEB)

St-Laurent, C.; Adam, E. [Hydro-Quebec, Ste-Foy, PQ (Canada). Petrole et Gaz

2005-07-01

In 2003, Hydro-Quebec acquired about 100 km of seismic data and 2,300 km{sup 2} of aeromagnetic data to begin exploration for oil and gas in the Miguasha area of the southwestern part of the Gaspe Peninsula. A discrepancy exists within the prospective area between the observed orientation of formational contacts in outcrop and moderately-dipping reflectors observed on seismic surveys. According to magnetic data, there is only 1 weakly-magnetic zone that is composed of felsic to intermediate volcanic rocks. A 3-D inversion of the total magnetic field was undertaken to obtain the subsurface distribution of magnetic rocks before drilling 2 exploratory wells in 2004. The inversion results were validated by performing 2.5-D modelling along selected traverses and through correlation with depth-converted seismic sections. The 3-D magnetic inversion is a cost-effective method of obtaining a 3-D subsurface image of this weakly-magnetic volcanic zone. Valuable information regarding the depth of the magnetic zone was obtained by combining magnetic inversion results with the seismic data. This study revealed the effectiveness of this approach in discriminating sediments with potential hydrocarbon reservoirs from non-prospective, magnetic volcanic rocks.

The Online GVP/USGS Weekly Volcanic Activity Report: Providing Timely Information About Worldwide Volcanism

Science.gov (United States)

Mayberry, G. C.; Guffanti, M. C.; Luhr, J. F.; Venzke, E. A.; Wunderman, R. L.

2001-12-01

The awesome power and intricate inner workings of volcanoes have made them a popular subject with scientists and the general public alike. About 1500 known volcanoes have been active on Earth during the Holocene, approximately 50 of which erupt per year. With so much activity occurring around the world, often in remote locations, it can be difficult to find up-to-date information about current volcanism from a reliable source. To satisfy the desire for timely volcano-related information the Smithsonian Institution and US Geological Survey combined their strengths to create the Weekly Volcanic Activity Report. The Smithsonian's Global Volcanism Program (GVP) has developed a network of correspondents while reporting worldwide volcanism for over 30 years in their monthly Bulletin of the Global Volcanism Network. The US Geological Survey's Volcano Hazards Program studies and monitors volcanoes in the United States and responds (upon invitation) to selected volcanic crises in other countries. The Weekly Volcanic Activity Report is one of the most popular sites on both organization's websites. The core of the Weekly Volcanic Activity Report is the brief summaries of current volcanic activity around the world. In addition to discussing various types of volcanism, the summaries also describe precursory activity (e.g. volcanic seismicity, deformation, and gas emissions), secondary activity (e.g. debris flows, mass wasting, and rockfalls), volcanic ash hazards to aviation, and preventative measures. The summaries are supplemented by links to definitions of technical terms found in the USGS photoglossary of volcano terms, links to information sources, and background information about reported volcanoes. The site also includes maps that highlight the location of reported volcanoes, an archive of weekly reports sorted by volcano and date, and links to commonly used acronyms. Since the Weekly Volcanic Activity Report's inception in November 2000, activity has been reported at

Anomalous changes of diffuse CO_{2} emission and seismic activity at Teide volcano, Tenerife, Canary Islands

Science.gov (United States)

García-Hernández, Rubén; Melián, Gladys; D'Auria, Luca; Asensio-Ramos, María; Alonso, Mar; Padilla, Germán D.; Rodríguez, Fátima; Padrón, Eleazar; Barrancos, José; García-Merino, Marta; Amonte, Cecilia; Pérez, Aarón; Calvo, David; Hernández, Pedro A.; Pérez, Nemesio M.

2017-04-01

Tenerife (2034 km2) is the largest of the Canary Islands and hosts four main active volcanic edifices: three volcanic rifts and a central volcanic complex, Las Cañadas, which is characterized by the eruption of differentiated magmas. Laying inside Las Cañadas a twin stratovolcanoes system, Pico Viejo and Teide, has been developed. Although there are no visible gas emanations along the volcanic rifts of Tenerife, the existence of a volcanic-hydrothermal system beneath Teide volcano is suggested by the occurrence of a weak fumarolic system, steamy ground and high rates of diffuse CO2 degassing all around the summit cone of Teide. Soil CO2 efflux surveys have been performed at the summit crater of Teide volcano since 1999, to determine the diffuse CO2 emission from the summit crater and to evaluate the temporal variations of CO2 efflux and their relationships with seismic-volcanic activity. Soil CO2 efflux and soil temperature have been always measured at the same 38 observation sites homogeneously distributed within an area of about 6,972 m2 inside the summit crater. Soil CO2 diffuse effluxes were estimated according to the accumulation chamber method by means of a non-dispersive infrared (NDIR) LICOR-820 CO2 analyzer. Historical seismic activity in Tenerife has been characterized by low- to moderate-magnitude events (M de Canarias (INVOLCAN) registered an earthquake of M 2.5 located in the vertical of Teide volcano with a depth of 6.6 km. It was the strongest earthquake located inside Cañadas caldera since 2004. Between October 11 and December 13, 2016, a continuous increase on the diffuse CO2 emission was registered, from 21.3 ± 2.0 to 101.7 ± 20.7 t d-1, suggesting the occurrence of future increase in the seismic-volcanic activity. In fact, this precursory signal preceded the occurrence of the 2.5 seismic event and no significant horizontal and vertical displacements were registered by the Canary GPS network belonged to INVOLCAN. This seismic event was

Volcanism/tectonics working group summary

International Nuclear Information System (INIS)

Kovach, L.A.; Young, S.R.

1995-01-01

This article is a summary of the proceedings of a group discussion which took place at the Workshop on the Role of Natural Analogs in Geologic Disposal of High-Level Nuclear Waste in San Antonio, Texas on July 22-25, 1991. The working group concentrated on the subject of the impacts of earthquakes, fault rupture, and volcanic eruption on the underground repository disposal of high-level radioactive wastes. The tectonics and seismic history of the Yucca Mountain site in Nevada is discussed and geologic analogs to that site are described

Seismic velocity structure of the crust and shallow mantle of the Central and Eastern United States by seismic surface wave imaging

Science.gov (United States)

Pollitz, Fred; Mooney, Walter D.

2016-01-01

Seismic surface waves from the Transportable Array of EarthScope's USArray are used to estimate phase velocity structure of 18 to 125 s Rayleigh waves, then inverted to obtain three-dimensional crust and upper mantle structure of the Central and Eastern United States (CEUS) down to ∼200 km. The obtained lithosphere structure confirms previously imaged CEUS features, e.g., the low seismic-velocity signature of the Cambrian Reelfoot Rift and the very low velocity at >150 km depth below an Eocene volcanic center in northwestern Virginia. New features include high-velocity mantle stretching from the Archean Superior Craton well into the Proterozoic terranes and deep low-velocity zones in central Texas (associated with the late Cretaceous Travis and Uvalde volcanic fields) and beneath the South Georgia Rift (which contains Jurassic basalts). Hot spot tracks may be associated with several imaged low-velocity zones, particularly those close to the former rifted Laurentia margin.

Seismic swarm associated with the 2008 eruption of Kasatochi Volcano, Alaska: earthquake locations and source parameters

Science.gov (United States)

Ruppert, Natalia G.; Prejean, Stephanie G.; Hansen, Roger A.

2011-01-01

An energetic seismic swarm accompanied an eruption of Kasatochi Volcano in the central Aleutian volcanic arc in August of 2008. In retrospect, the first earthquakes in the swarm were detected about 1 month prior to the eruption onset. Activity in the swarm quickly intensified less than 48 h prior to the first large explosion and subsequently subsided with decline of eruptive activity. The largest earthquake measured as moment magnitude 5.8, and a dozen additional earthquakes were larger than magnitude 4. The swarm exhibited both tectonic and volcanic characteristics. Its shear failure earthquake features were b value = 0.9, most earthquakes with impulsive P and S arrivals and higher-frequency content, and earthquake faulting parameters consistent with regional tectonic stresses. Its volcanic or fluid-influenced seismicity features were volcanic tremor, large CLVD components in moment tensor solutions, and increasing magnitudes with time. Earthquake location tests suggest that the earthquakes occurred in a distributed volume elongated in the NS direction either directly under the volcano or within 5-10 km south of it. Following the MW 5.8 event, earthquakes occurred in a new crustal volume slightly east and north of the previous earthquakes. The central Aleutian Arc is a tectonically active region with seismicity occurring in the crusts of the Pacific and North American plates in addition to interplate events. We postulate that the Kasatochi seismic swarm was a manifestation of the complex interaction of tectonic and magmatic processes in the Earth's crust. Although magmatic intrusion triggered the earthquakes in the swarm, the earthquakes failed in context of the regional stress field.

A dynamical analysis of the seismic activity of Villarrica volcano (Chile) during September-October 2000

Energy Technology Data Exchange (ETDEWEB)

Tarraga, Marta [Departamento de Volcanologia. Museo Nacional de Ciencias Naturales, CSIC, Madrid (Spain)], E-mail: martat@mncn.csic.es; Carniel, Roberto [Dipartimento di Georisorse e Territorio, Universita di Udine, Via Cotonificio 114, 33100 Udine (Italy)], E-mail: roberto.carniel@uniud.it; Ortiz, Ramon; Garcia, Alicia [Departamento de Volcanologia. Museo Nacional de Ciencias Naturales, CSIC, Madrid (Spain); Moreno, Hugo [Observatorio Volcanologico de los Andes del Sur (OVDAS), Servicio Nacional de Geologia y Mineria de Chile (SERNAGEOMIN), Temuco, IX Region (Chile)

2008-09-15

Although Villarrica volcano in Chile is one of the most active in the southern Andes, the literature studying its seismic activity is relatively scarce. An interesting problem recently tackled is the possibility for a regional tectonic event to trigger a change in the volcanic activity of this basaltic to basaltic-andesitic volcano, which is in turn reflected in the time evolution of the properly volcanic seismicity, especially in the form of a continuous volcanic tremor. In this work, we conduct a spectral, dynamical and statistical analysis of the tremor recorded during September and October 2000, in order to characterize the anomalous behaviour of the volcano following a tectonic event recorded on 20th September 2000. The observed dynamical transitions are compared with remote sensing and visual observations describing the changes in the eruptive style of the volcano.

A dynamical analysis of the seismic activity of Villarrica volcano (Chile) during September-October 2000

International Nuclear Information System (INIS)

Tarraga, Marta; Carniel, Roberto; Ortiz, Ramon; Garcia, Alicia; Moreno, Hugo

2008-01-01

Although Villarrica volcano in Chile is one of the most active in the southern Andes, the literature studying its seismic activity is relatively scarce. An interesting problem recently tackled is the possibility for a regional tectonic event to trigger a change in the volcanic activity of this basaltic to basaltic-andesitic volcano, which is in turn reflected in the time evolution of the properly volcanic seismicity, especially in the form of a continuous volcanic tremor. In this work, we conduct a spectral, dynamical and statistical analysis of the tremor recorded during September and October 2000, in order to characterize the anomalous behaviour of the volcano following a tectonic event recorded on 20th September 2000. The observed dynamical transitions are compared with remote sensing and visual observations describing the changes in the eruptive style of the volcano

Medieval Irish chronicles reveal persistent volcanic forcing of severe winter cold events, 431–1649 CE

International Nuclear Information System (INIS)

Ludlow, Francis; Stine, Alexander R; Leahy, Paul; Kiely, Gerard; Murphy, Enda; Mayewski, Paul A; Taylor, David; Killen, James; Hennessy, Mark; Baillie, Michael G L

2013-01-01

Explosive volcanism resulting in stratospheric injection of sulfate aerosol is a major driver of regional to global climatic variability on interannual and longer timescales. However, much of our knowledge of the climatic impact of volcanism derives from the limited number of eruptions that have occurred in the modern period during which meteorological instrumental records are available. We present a uniquely long historical record of severe short-term cold events from Irish chronicles, 431–1649 CE, and test the association between cold event occurrence and explosive volcanism. Thirty eight (79%) of 48 volcanic events identified in the sulfate deposition record of the Greenland Ice Sheet Project 2 ice-core correspond to 37 (54%) of 69 cold events in this 1219 year period. We show this association to be statistically significant at the 99.7% confidence level, revealing both the consistency of response to explosive volcanism for Ireland’s climatically sensitive Northeast Atlantic location and the large proportional contribution of volcanism to historic cold event frequencies here. Our results expose, moreover, the extent to which volcanism has impacted winter-season climate for the region, and can help to further resolve the complex spatial patterns of Northern Hemisphere winter-season cooling versus warming after major eruptions. (letter)

Persistent pre-seismic signature detected by means of Na-K-Mg geothermometry records in a saline spring of Vrancea area (Romania

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H. Mitrofan

2010-02-01

Full Text Available A six year-long hydrochemical monitoring operation was conducted in Vrancea seismic zone (Romania, addressing a saline spring that proved to be suitable for Na-K-Mg geothermometry diagnosis. During the considered time-interval (2003–2009, only one important earthquake (m_b=5.8 occurred in Vrancea region, this circumstance providing an unambiguous reference-moment between pre-seismic and post-seismic periods. On occurrence of that earthquake, an anomalous fluctuation of the Na-K temperature was detected – a result largely similar to previous ones recorded worldwide (California, southwest Egypt, northeast India. Yet such fluctuations may not necessarily be induced by earthquake-associated processes: they can occur also "routinely", possibly reflecting some environmental, meteorologically-induced "noise". It was therefore important to examine whether the variations observed in the data values could be plausibly related to a seismogenesis process. By additionally investigating (in a "scattterplot" diagram the correlation between the Na-K temperatures and the values of a so-called "maturity index", a specific pattern emerged, with pre-seismic data-points plotting in a distinct domain of the diagram; moreover, those data-points appeared to describe a "drift away" pathway with respect to the remaining data-points "cluster", recorded during the subsequent 4 years of post-seismic monitoring. The "drift away" pattern persistently evolved for at least 18 months, ending just before the m_b=5.8 earthquake and consequently suggesting the existence of some kind of long-term precursory phenomenon.

Asthenospheric flow and origin of volcanism in the Baikal rift area

NARCIS (Netherlands)

Lebedev, S.; Meier, T.; Hilst, R.D. van der

2006-01-01

The origin of low-volume, hotspot-like volcanism often observed in continental rift areas is debated, as is the nature of the flow in the mantle beneath. In this paper we assemble seismic constraints on the mantle flow below the Baikal Rift Zone. We combine new evidence from upper-mantle

The seismic monitoring network of Mt. Vesuvius

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Massimo Orazi

2013-11-01

Full Text Available Mt. Vesuvius (southern Italy is one of the most hazardous volcanoes in the world. Its activity is currently characterized by moderate seismicity, with hypocenters located beneath the crater zone with depth rarely exceeding 5 km and magnitudes generally less than 3. The current configuration of the seismic monitoring network of Mt. Vesuvius consists of 18 seismic stations and 7 infrasound microphones. During the period 2006-2010 a seismic array with 48 channels was also operative. The station distribution provides appropriate coverage of the area around the volcanic edifice. The current development of the network and its geometry, under conditions of low seismic noise, allows locating seismic events with M<1. Remote instruments continuously transmit data to the main acquisition center in Naples. Data transmission is realized using different technological solutions based on UHF, Wi-Fi radio links, and TCP/IP client-server applications. Data are collected in the monitoring center of the Osservatorio Vesuviano (Italian National Institute of Geophysics and Volcanology, Naples section, which is equipped with systems for displaying and analyzing signals, using both real-time automatic and manual procedures. 24-hour surveillance allows to immediately communicate any significant anomaly to the Civil Protection authorities.

WOVOdat: A New Tool for Managing and Accessing Data of Worldwide Volcanic Unrest

Science.gov (United States)

Venezky, D. Y.; Malone, S. D.; Newhall, C. G.

2002-12-01

WOVOdat (World Organization of Volcano Observatories database of volcanic unrest) will for the first time bring together data of worldwide volcanic seismicity, ground deformation, fumarolic activity, and other changes within or adjacent to a volcanic system. Although a large body of data and experience has been built over the past century, currently, we have no means of accessing that collective experience for use during crises and for research. WOVOdat will be the central resource of a data management system; other components will include utilities for data input and archiving, structured data retrieval, and data mining; educational modules; and links to institutional databases such as IRIS (global seismicity), UNAVCO (global GPS coordinates and strain vectors), and Smithsonian's Global Volcanism Program (historical eruptions). Data will be geospatially and time-referenced, to provide four dimensional images of how volcanic systems respond to magma intrusion, regional strain, and other disturbances prior to and during eruption. As part of the design phase, a small WOVOdat team is currently collecting information from observatories about their data types, formats, and local data management. The database schema is being designed such that responses to common, yet complex, queries are rapid (e.g., where else has similar unrest occurred and what was the outcome?) while also allowing for more detailed research analysis of relationships between various parameters (e.g., what do temporal relations between long-period earthquakes, transient deformation, and spikes in gas emission tell us about the geometry and physical properties of magma and a volcanic edifice?). We are excited by the potential of WOVOdat, and we invite participation in its design and development. Next steps involve formalizing and testing the design, and, developing utilities for translating data of various formats into common formats. The large job of populating the database will follow, and eventually

The forearc crustal evolution of Izu-Bonin (Ogasawara) region obtained by seismic reflection and refraction surveys

Science.gov (United States)

Yamashita, M.; Kodaira, S.; Takahashi, N.; Tatsumi, Y.; Kaneda, Y.

2009-12-01

The Izu-Bonin (Ogasawara)-Mariana (IBM) arc is known to the typical oceanic island arc, and it is the most suitable area to understand the growth process of island arc. By previous seismic survey and deep sea drilling, convex basements are distributed along North-South direction in present forearc region. The convex basements are reported to be formed during Oligocene and Eocene (Taylor, 1992). In IBM forearc region, the middle crust with 6 km/s is recognized by seismic survey using OBSs. In IBM region, four IODP drilling sites are proposed in order to understand comprehensive growth process of arc and continental crust evolution. Two of them are located in forearc region. Japan Agency for Marine-Earth Science and Technology (JAMSTEC) carried out multi-channel seismic reflection survey using 7,800/12,000 cu.in. air gun and 5-6 km streamer with 444/204 ch hydrophones in the IBM region since 2004. We investigate the crustal structure beneath the Izu-Bonin forearc region for contribution of IBM drilling site along five long survey lines, which are across from present volcanic front to forearc basin. Seismic refraction survey is also conducted across forearc region using 84 OBSs every 1 km interval. Shallow crustal structure can be classified four units including basement which compared between previous drilling results and obtained seismic profiles. In IBM forearc region, thick sedimentary basin distribute from east side of volcanic front. Two convex basement peaks are indicated in across profile of forearc region. These peaks are estimated the top of paleoarc (Oligocene and Eocene) by previous ODP drilling. The half graben structure with major displacement is identified from west side of present volcanic front to the top of Oligocene arc. On the other hand, there is no displacement of sediments between the Oligocene arc and Eocene arc. This result shows the same origin of basement between the present volcanic front and Oligocene arc. There is long time difference of

Numerical simulations (2D) on the influence of pre-existing local structures and seismic source characteristics in earthquake-volcano interactions

Science.gov (United States)

Farías, Cristian; Galván, Boris; Miller, Stephen A.

2017-09-01

Earthquake triggering of hydrothermal and volcanic systems is ubiquitous, but the underlying processes driving these systems are not well-understood. We numerically investigate the influence of seismic wave interaction with volcanic systems simulated as a trapped, high-pressure fluid reservoir connected to a fluid-filled fault system in a 2-D poroelastic medium. Different orientations and earthquake magnitudes are studied to quantify dynamic and static stress, and pore pressure changes induced by a seismic event. Results show that although the response of the system is mainly dominated by characteristics of the radiated seismic waves, local structures can also play an important role on the system dynamics. The fluid reservoir affects the seismic wave front, distorts the static overpressure pattern induced by the earthquake, and concentrates the kinetic energy of the incoming wave on its boundaries. The static volumetric stress pattern inside the fault system is also affected by the local structures. Our results show that local faults play an important role in earthquake-volcanic systems dynamics by concentrating kinetic energy inside and acting as wave-guides that have a breakwater-like behavior. This generates sudden changes in pore pressure, volumetric expansion, and stress gradients. Local structures also influence the regional Coulomb yield function. Our results show that local structures affect the dynamics of volcanic and hydrothermal systems, and should be taken into account when investigating triggering of these systems from nearby or distant earthquakes.

Integrating passive seismicity with Web-Based GIS for a new perspective on volcano imaging and monitoring: the case study of Mt. Etna

Science.gov (United States)

Guardo, Roberto; De Siena, Luca

2017-04-01

The timely estimation of short- and long-term volcanic hazard relies on the existence of detailed 3D geophysical images of volcanic structures. High-resolution seismic models of the absorbing uppermost conduit systems and highly-heterogeneous shallowest volcanic layers, while particularly challenging to obtain, provide important data to locate feasible eruptive centers and forecast flank collapses and lava ascending paths. Here, we model the volcanic structures of Mt. Etna (Sicily, Italy) and its outskirts using the Horizontal to Vertical Spectral Ratio method, generally applied to industrial and engineering settings. The integration of this technique with Web-based Geographic Information System improves precision during the acquisition phase. It also integrates geological and geophysical visualization of 3D surface and subsurface structures in a queryable environment representing their exact three-dimensional geographic position, enhancing interpretation. The results show high-resolution 3D images of the shallowest volcanic and feeding systems, which complement (1) deeper seismic tomography imaging and (2) the results of recent remote sensing imaging. The main novelty with respect to previous model is the presence of a vertical structure that divides the pre-existing volcanic complexes of Ellittico and Cuvigghiuni. This could be interpreted as a transitional phase between the two systems. A comparison with recent remote sensing and geological results, however, shows clear connections between the anomaly and dynamic active during the last 15 years. We infer that seismic noise measurements from miniaturized instruments, when combined with remote sensing techniques, represent an important resource when monitoring volcanic media and eruptions, reducing the risk of loss of human lives and instrumentation.

Abstracts for the October 2012 meeting on Volcanism in the American Southwest, Flagstaff, Arizona

Science.gov (United States)

Lowenstern, Jacob B.

2013-01-01

Though volcanic eruptions are comparatively rare in the American Southwest, the States of Arizona, Colorado, New Mexico, Nevada, and Utah host Holocene volcanic eruption deposits and are vulnerable to future volcanic activity. Compared with other parts of the western United States, comparatively little research has been focused on this area, and eruption probabilities are poorly constrained. Monitoring infrastructure consists of a variety of local seismic networks, and ”backbone“ geodetic networks with little integration. Emergency response planning for volcanic unrest has received little attention by either Federal or State agencies. On October 18–20, 2012, 90 people met at the U.S. Geological Survey campus in Flagstaff, Arizona, providing an opportunity for volcanologists, land managers, and emergency responders to meet, converse, and begin to plan protocols for any future activity. Geologists contributed data on recent findings of eruptive ages, eruption probabilities, and hazards extents (plume heights, ash dispersal). Geophysicists discussed evidence for magma intrusions from seismic, geodetic, and other geophysical techniques. Network operators publicized their recent work and the relevance of their equipment to volcanic regions. Land managers and emergency responders shared their experiences with emergency planning for earthquakes. The meeting was organized out of the recognition that little attention had been paid to planning for or mitigation of volcanic hazards in the American Southwest. Moreover, few geological meetings have hosted a session specifically devoted to this topic. This volume represents one official outcome of the meeting—a collection of abstracts related to talks and poster presentations shared during the first two days of the meeting. In addition, this report includes the meeting agenda as a record of the proceedings. One additional intended outcome will be greater discussion and coordination among emergency responders, geologists

Georgia-Armenia Transboarder seismicity studies

Science.gov (United States)

Godoladze, T.; Tvaradze, N.; Javakishvili, Z.; Elashvili, M.; Durgaryan, R.; Arakelyan, A.; Gevorgyan, M.

2012-12-01

In the presented study we performed Comprehensive seismic analyses for the Armenian-Georgian transboarder active seismic fault starting on Armenian territory, cutting the state boarder and having possibly northern termination on Adjara-Triealeti frontal structure in Georgia. In the scope of International projects: ISTC A-1418 "Open network of scientific Centers for mitigation risk of natural hazards in the Southern Caucasus and Central Asia" and NATO SfP- 983284 Project "Caucasus Seismic Emergency Response" in Akhalkalaki (Georgia) seismic center, Regional Summer school trainings and intensive filed investigations were conducted. Main goal was multidisciplinary study of the Javakheti fault structure and better understanding seismicity of the area. Young scientists from Turkey, Armenia, Azerbaijan and Georgia were participated in the deployment of temporal seismic network in order to monitor seisimity on the Javakheti highland and particularly delineate fault scarf and identify active seismic structures. In the scope of international collaboration the common seismic database has been created in the southern Caucasus and collected data from the field works is available now online. Javakheti highland, which is located in the central part of the Caucasus, belongs to the structure of the lesser Caucasus and represents a history of neotectonic volcanism existed in the area. Jasvakheti highland is seismicalu active region devastating from several severe earthquakes(1088, 1283, 1899…). Hypocenters located during analogue network were highly scattered and did not describe real pattern of seismicity of the highland. We relocated hypocenters of the region and improved local velocity model. The hypocenters derived from recently deployed local seismic network in the Javakheti highland, clearly identified seismically active structures. Fault plane solutions of analogue data of the Soviet times have been carefully analyzed and examined. Moment tensor inversion were preformed

Cluster Computing For Real Time Seismic Array Analysis.

Science.gov (United States)

Martini, M.; Giudicepietro, F.

A seismic array is an instrument composed by a dense distribution of seismic sen- sors that allow to measure the directional properties of the wavefield (slowness or wavenumber vector) radiated by a seismic source. Over the last years arrays have been widely used in different fields of seismological researches. In particular they are applied in the investigation of seismic sources on volcanoes where they can be suc- cessfully used for studying the volcanic microtremor and long period events which are critical for getting information on the volcanic systems evolution. For this reason arrays could be usefully employed for the volcanoes monitoring, however the huge amount of data produced by this type of instruments and the processing techniques which are quite time consuming limited their potentiality for this application. In order to favor a direct application of arrays techniques to continuous volcano monitoring we designed and built a small PC cluster able to near real time computing the kinematics properties of the wavefield (slowness or wavenumber vector) produced by local seis- mic source. The cluster is composed of 8 Intel Pentium-III bi-processors PC working at 550 MHz, and has 4 Gigabytes of RAM memory. It runs under Linux operating system. The developed analysis software package is based on the Multiple SIgnal Classification (MUSIC) algorithm and is written in Fortran. The message-passing part is based upon the LAM programming environment package, an open-source imple- mentation of the Message Passing Interface (MPI). The developed software system includes modules devote to receiving date by internet and graphical applications for the continuous displaying of the processing results. The system has been tested with a data set collected during a seismic experiment conducted on Etna in 1999 when two dense seismic arrays have been deployed on the northeast and the southeast flanks of this volcano. A real time continuous acquisition system has been simulated by

Earth modeling and estimation of the local seismic ground motion due to site geology in complex volcanoclastic areas

Directory of Open Access Journals (Sweden)

V. Di Fiore

2002-06-01

Full Text Available Volcanic areas often show complex behaviour as far as seismic waves propagation and seismic motion at surface are concerned. In fact, the finite lateral extent of surface layers such as lava flows, blocks, differential welding and/or zeolitization within pyroclastic deposits, introduces in the propagation of seismic waves effects such as the generation of surface waves at the edge, resonance in lateral direction, diffractions and scattering of energy, which tend to modify the amplitude as well as the duration of the ground motion. The irregular topographic surface, typical of volcanic areas, also strongly influences the seismic site response. Despite this heterogeneity, it is unfortunately a common geophysical and engineering practice to evaluate even in volcanic environments the subsurface velocity field with monodimensional investigation method (i.e. geognostic soundings, refraction survey, down-hole, etc. prior to the seismic site response computation which in a such cases is obviously also made with 1D algorithms. This approach often leads to highly inaccurate results. In this paper we use a different approach, i.e. a fully 2D P-wave Çturning rayÈ tomographic survey followed by 2D seismic site response modeling. We report here the results of this approach in three sites located at short distance from Mt. Vesuvius and Campi Flegrei and characterized by overburdens constituted by volcanoclastic deposits with large lateral and vertical variations of their elastic properties. Comparison between 1D and 2D Dynamic Amplification Factor shows in all reported cases entirely different results, both in terms of peak period and spectral contents, as expected from the clear bidimensionality of the geological section. Therefore, these studies suggest evaluating carefully the subsoil geological structures in areas characterized by possible large lateral and vertical variations of the elastic properties in order to reach correct seismic site response

Shallow repeating seismic events under an alpine glacier at Mount Rainier, Washington, USA

Science.gov (United States)

Thelen, Weston A.; Allstadt, Kate E.; De Angelis, Silvio; Malone, Stephen D.; Moran, Seth C.; Vidale, John

2013-01-01

We observed several swarms of repeating low-frequency (1–5 Hz) seismic events during a 3 week period in May–June 2010, near the summit of Mount Rainier, Washington, USA, that likely were a result of stick–slip motion at the base of alpine glaciers. The dominant set of repeating events ('multiplets') featured >4000 individual events and did not exhibit daytime variations in recurrence interval or amplitude. Volcanoes and glaciers around the world are known to produce seismic signals with great variability in both frequency content and size. The low-frequency character and periodic recurrence of the Mount Rainier multiplets mimic long-period seismicity often seen at volcanoes, particularly during periods of unrest. However, their near-surface location, lack of common spectral peaks across the recording network, rapid attenuation of amplitudes with distance, and temporal correlation with weather systems all indicate that ice-related source mechanisms are the most likely explanation. We interpret the low-frequency character of these multiplets to be the result of trapping of seismic energy under glacial ice as it propagates through the highly heterogeneous and attenuating volcanic material. The Mount Rainier multiplet sequences underscore the difficulties in differentiating low-frequency signals due to glacial processes from those caused by volcanic processes on glacier-clad volcanoes.

Crustal deformation and volcanism at active plate boundaries

Science.gov (United States)

Geirsson, Halldor

Most of Earth's volcanoes are located near active tectonic plate boundaries, where the tectonic plates move relative to each other resulting in deformation. Likewise, subsurface magma movement and pressure changes in magmatic systems can cause measurable deformation of the Earth's surface. The study of the shape of Earth and therefore studies of surface deformation is called geodesy. Modern geodetic techniques allow precise measurements (˜1 mm accuracy) of deformation of tectonic and magmatic systems. Because of the spatial correlation between tectonic boundaries and volcanism, the tectonic and volcanic deformation signals can become intertwined. Thus it is often important to study both tectonic and volcanic deformation processes simultaneously, when one is trying to study one of the systems individually. In this thesis, I present research on crustal deformation and magmatic processes at active plate boundaries. The study areas cover divergent and transform plate boundaries in south Iceland and convergent and transform plate boundaries in Central America, specifically Nicaragua and El Salvador. The study is composed of four main chapters: two of the chapters focus on the magma plumbing system of Hekla volcano, Iceland and the plate boundary in south Iceland; one chapter focuses on shallow controls of explosive volcanism at Telica volcano, Nicaragua; and the fourth chapter focuses on co- and post-seismic deformation from a Mw = 7.3 earthquake which occurred offshore El Salvador in 2012. Hekla volcano is located at the intersection of a transform zone and a rift zone in Iceland and thus is affected by a combination of shear and extensional strains, in addition to co-seismic and co-rifting deformation. The inter-eruptive deformation signal from Hekla is subtle, as observed by a decade (2000-2010) of GPS data in south Iceland. A simultaneous inversion of this data for parameters describing the geometry and source characteristics of the magma chamber at Hekla, and

The Lanzarote Geodynamic Laboratory: new capabilities for monitoring of volcanic activity at Canary Islands

Science.gov (United States)

Arnoso, J.; Vélez, E. J.; Soler, V.; Montesinos, F. G.; Benavent, M.

2012-04-01

The volcanic island of Lanzarote is located at the northeastern end of the Canary Islands. Together with Fuerteventura Island, Lanzarote constitutes the emergent part of the East Canary Ridge, which presents a NNE-SSW volcanic alignment. Last eruptive events took place in 1824 and during the period 1730-1736, which is the largest to occur in the archipelago and throw out about 1.3 km3 of volcanic materials. The Lanzarote Geodynamic Laboratory (LGL) was created in 1986 with the idea of making Lanzarote as a natural laboratory to carry out studies in order to acquire more knowledge about its origin, present status and evolution (Vieira et al., 1991; 2006). The LGL has a multidisciplinary scientific purpose and, among others, various objectives are devoted to investigate mass distribution in the Earth system and surface displacements associated to volcanic and/or seismic activity in the island. The influence of LGL is extended throughout the whole geographical area of Lanzarote, including small islands located at the north. The laboratory has 3 observing modules distributed along the island according to its infrastructure and scientific objectives, where more than 70 sensors are recording continuously gravity variations, ground deformations, sea level, seismic activity, meteorological parameters, etc. All these observations are supplemented by periodic measurement of geodetic and geophysical networks that allow us to make studies at local, insular and regional scales. The application of geodetic and geophysical techniques to identify geodynamic signals related to volcanic processes is then a permanent research activity of the laboratory. Nowadays, this fact becomes more interesting due to the ongoing volcanic eruption that is taking place in other island of the Canary Archipelago, El Hierro, since past July 2011. That is, the multidisciplinary research carry on up to now at the LGL allow us to apply multiparameter observations of different kinds of volcanic

Three decades of seismic activity at Mt. Vesuvius: 1972-1999

International Nuclear Information System (INIS)

De Natale, Giuseppe; Troise, Claudia; Kuznetzov, Igor; Kronrod, Tanya; Peresan, Antonella; Sarao, Angela; Panza, Gluliano F.

2002-06-01

We analyse the seismic catalogue of the local earthquakes which occurred at Somma- Vesuvius volcano in the past three decades (1972-2000). The seismicity in this period can be described as composed by a background level, characterised by a low and rather uniform rate of energy release and by sporadic periods of increased seismic activity. Such relatively intense seismicity periods are characterised by energy rates and magnitudes progressively increasing in the critical periods. The analyses of the b value in the whole period evidences a well defined pattern, with values of b progressively decreasing, from about 1.8, at the beginning of the considered period, to about 1.0 at present. This steady variation indicates an increasing dynamics in the volcanic system. Within this general trend it is possible to identity a sub-structure in the time sequence of the seismic events, formed by the alternating episodes of quiescence and activity. The analysis of the source moment tensor of the largest earthquakes shows that the processes at the seismic source are generally not consistent with simple double-couples, but that they are compatible with large isotropic components, mostly indicating volumetric expansion. These components are shown to be statistically significant for almost all the analysed events. Such focal mechanisms can be interpreted as the effect of explosion phenomena, possibly related to volatile exsolution from the crystallising magma. The availability of a reduced amount of high quality data necessary for the inversion of the source moment tensor, the still limited period of systematic observation of Vesuvius micro- earthquakes and, above all, the absence of eruptive events during such interval of time, cannot obviously permit to outline any formal premonitory signal. Nevertheless, the analysis reported in this paper indicates a progressively evolving dynamics, characterised by a general increasing trend in the seismic activity in the volcanic system and by a

When probabilistic seismic hazard climbs volcanoes: the Mt. Etna case, Italy - Part 1: Model components for sources parameterization

Science.gov (United States)

Azzaro, Raffaele; Barberi, Graziella; D'Amico, Salvatore; Pace, Bruno; Peruzza, Laura; Tuvè, Tiziana

2017-11-01

The volcanic region of Mt. Etna (Sicily, Italy) represents a perfect lab for testing innovative approaches to seismic hazard assessment. This is largely due to the long record of historical and recent observations of seismic and tectonic phenomena, the high quality of various geophysical monitoring and particularly the rapid geodynamics clearly demonstrate some seismotectonic processes. We present here the model components and the procedures adopted for defining seismic sources to be used in a new generation of probabilistic seismic hazard assessment (PSHA), the first results and maps of which are presented in a companion paper, Peruzza et al. (2017). The sources include, with increasing complexity, seismic zones, individual faults and gridded point sources that are obtained by integrating geological field data with long and short earthquake datasets (the historical macroseismic catalogue, which covers about 3 centuries, and a high-quality instrumental location database for the last decades). The analysis of the frequency-magnitude distribution identifies two main fault systems within the volcanic complex featuring different seismic rates that are controlled essentially by volcano-tectonic processes. We discuss the variability of the mean occurrence times of major earthquakes along the main Etnean faults by using an historical approach and a purely geologic method. We derive a magnitude-size scaling relationship specifically for this volcanic area, which has been implemented into a recently developed software tool - FiSH (Pace et al., 2016) - that we use to calculate the characteristic magnitudes and the related mean recurrence times expected for each fault. Results suggest that for the Mt. Etna area, the traditional assumptions of uniform and Poissonian seismicity can be relaxed; a time-dependent fault-based modeling, joined with a 3-D imaging of volcano-tectonic sources depicted by the recent instrumental seismicity, can therefore be implemented in PSHA maps

Magma wagging and whirling in volcanic conduits

Science.gov (United States)

Liao, Yang; Bercovici, David; Jellinek, Mark

2018-02-01

Seismic tremor characterized by 0.5-7 Hz ground oscillations commonly occur before and during eruptions at silicic volcanoes with widely ranging vent geometries and edifice structures. The ubiquitous characteristics of this tremor imply that its causes are potentially common to silicic volcanoes. Here we revisit and extend to three dimensions the magma-wagging model for tremor (Jellinek and Bercovici, 2011; Bercovici et al., 2013), wherein a stiff magma column rising in a vertical conduit oscillates against a surrounding foamy annulus of bubbly magma, giving rise to tremor. While prior studies were restricted to two-dimensional lateral oscillations, here we explore three-dimensional motion and additional modes of oscillations. In the absence of viscous damping, the magma column undergoes 'whirling' motion: the center of each horizontal section of the column traces an elliptical trajectory. In the presence of viscous effect we identify new 'coiling' and 'uncoiling' column bending shapes with relatively higher and comparable rates of dissipation to the original two-dimensional magma wagging model. We also calculate the seismic P-wave response of the crustal material around the volcanic conduit to the new whirling motions and propose seismic diagnostics for different wagging patterns using the time-lag between seismic stations. We test our model by analyzing pre-eruptive seismic data from the 2009 eruption of Redoubt Volcano. In addition to suggesting that the occurrence of elliptical whirling motion more than 1 week before the eruption, our analysis of seismic time-lags also implies that the 2009 eruption was accompanied by qualitative changes in the magma wagging behavior including fluctuations in eccentricity and a reversal in the direction of elliptical whirling motion when the eruption was immediately impending.

Characteristics of Volcanic Soils in Landslide during the 2016 Kumamoto Earthquake, Japan

Science.gov (United States)

Hazarika, H.; Fukuoka, H.; Kokusho, T.; Sumartini, O.; Bhoopendra, D.

2017-12-01

There were many seismic subsidence, debris flows, landslides and slope failures, which occurred in Aso area due to the 2016 Kumamoto earthquake, Japan. This research aims to determine the failure mechanism of many mild slopes, and elucidate the strength characteristics of volcanic soils collected from the sites. A series of undrained static and cyclic triaxial tests, ring shear tests and direct shear tests were performed. Also, for further understanding of volcanic soils' material strength, X-ray powder diffraction analysis (XRD), X-ray fluorescence analysis (XRF), and Scanning electron microscope analysis (SEM) were performed. In this paper, preliminary results of the experimental testing program are discussed.

VOLCANIC TSUNAMI GENERATING SOURCE MECHANISMS IN THE EASTERN CARIBBEAN REGION

Directory of Open Access Journals (Sweden)

George Pararas-Carayannis

2004-01-01

Full Text Available Earthquakes, volcanic eruptions, volcanic island flank failures and underwater slides have generated numerous destructive tsunamis in the Caribbean region. Convergent, compressional and collisional tectonic activity caused primarily from the eastward movement of the Caribbean Plate in relation to the North American, Atlantic and South American Plates, is responsible for zones of subduction in the region, the formation of island arcs and the evolution of particular volcanic centers on the overlying plate. The inter-plate tectonic interaction and deformation along these marginal boundaries result in moderate seismic and volcanic events that can generate tsunamis by a number of different mechanisms. The active geo-dynamic processes have created the Lesser Antilles, an arc of small islands with volcanoes characterized by both effusive and explosive activity. Eruption mechanisms of these Caribbean volcanoes are complex and often anomalous. Collapses of lava domes often precede major eruptions, which may vary in intensity from Strombolian to Plinian. Locally catastrophic, short-period tsunami-like waves can be generated directly by lateral, direct or channelized volcanic blast episodes, or in combination with collateral air pressure perturbations, nuéss ardentes, pyroclastic flows, lahars, or cascading debris avalanches. Submarine volcanic caldera collapses can also generate locally destructive tsunami waves. Volcanoes in the Eastern Caribbean Region have unstable flanks. Destructive local tsunamis may be generated from aerial and submarine volcanic edifice mass edifice flank failures, which may be triggered by volcanic episodes, lava dome collapses, or simply by gravitational instabilities. The present report evaluates volcanic mechanisms, resulting flank failure processes and their potential for tsunami generation. More specifically, the report evaluates recent volcanic eruption mechanisms of the Soufriere Hills volcano on Montserrat, of Mt. Pel

Deformation and seismic anisotropy of the subcontinental lithospheric mantle in NE Spain: EBSD data on xenoliths from the Catalan Volcanic Zone

Science.gov (United States)

Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

2017-02-01

Mantle xenoliths in Neogene-Quaternary basaltic rocks related to the European Cenozoic Rift System serve to assess the evolution of the subcontinental lithospheric mantle beneath the Catalan Volcanic Zone in NE Spain. Crystallographic preferred orientations, major element composition of minerals, and temperature and pressure estimates have been used to this end. The mantle consists of spinel lherzolites, harzburgites and subordinate websterites. Protogranular microstructures are found in all peridotites and websterites, but lherzolites also display finer-grained porphyroclastic and equigranular microstructures. The dominant olivine deformation fabric is [010] fiber, but subordinate orthorhombic and [100]-fiber types are also present, especially in porphyroclastic and equigranular lherzolites. The fabric strength (J index = 10.12-1.91), equilibrium temperature and pressure are higher in xenoliths with [010]-fiber fabric and decrease in those with orthorhombic and [100]-fiber type. Incoherence between olivine and pyroxene deformation fabric is mostly found in porphyroclastic and equigranular lherzolites. Seismic anisotropy, estimated from the crystal preferred orientations, also decreases (AVp = 10.2-2.60%; AVs max = 7.95-2.19%) in porphyroclastic and equigranular lherzolites. The olivine [010]-fiber fabric points to deformation by simple shear or transpression which is likely to have occured during the development of late-Hercynian strike-slip shear zones, and to subsequent annealing during late Hercynian decompression, Permian and Cretaceous rifting. Also, it cannot be excluded that the percolation of mafic magmas during these extensional events provoked the refertilization of the lithospheric mantle. However, no clear relationship has been observed between fabric strength and mineral mode and composition. Later transtensional deformation during late Alpine orogenesis, at higher stress and decreasing temperature and pressure, transformed the earlier fabric into

Flood, Seismic or Volcanic Deposits? New Insights from X-Ray Computed Tomography

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Van Daele, M. E.; Moernaut, J.; Vermassen, F.; Llurba, M.; Praet, N.; Strupler, M. M.; Anselmetti, F.; Cnudde, V.; Haeussler, P. J.; Pino, M.; Urrutia, R.; De Batist, M. A. O.

2014-12-01

Event deposits, such as e.g. turbidites incorporated in marine or lacustrine sediment sequences, may be caused by a wide range of possible triggering processes: failure of underwater slopes - either spontaneous or in response to earthquake shaking, hyperpycnal flows and floods, volcanic processes, etc. Determining the exact triggering process remains, however, a major challenge. Especially when studying the event deposits on sediment cores, which typically have diameters of only a few cm, only a small spatial window is available to analyze diagnostic textural and facies characteristics. We have performed X-ray CT scans on sediment cores from Chilean, Alaskan and Swiss lakes. Even when using relatively low-resolution CT scans (0.6 mm voxel size), many sedimentary structures and fabrics that are not visible by eye, are revealed. For example, the CT scans allow to distinguish tephra layers that are deposited by fall-out, from those that reached the basin by river transport or mud flows and from tephra layers that have been reworked and re-deposited by turbidity currents. The 3D data generated by the CT scans also allow to examine relative orientations of sedimentary structures (e.g. convolute lamination) and fabrics (e.g. imbricated mud clasts), which can be used to reconstruct flow directions. Such relative flow directions allow to determine whether a deposit (e.g. a turbidite) had one or several source areas, the latter being typical for seismically triggered turbidites. When the sediment core can be oriented (e.g. using geomagnetic properties), absolute flow directions can be reconstructed. X-ray CT scanning, at different resolution, is thus becoming an increasingly important tool for discriminating the exact origin of EDs, as it can help determining whether e.g. an ash layer was deposited as fall out from an ash cloud or fluvially washed into the lake, or whether a turbidite was triggered by an earthquake or a flood.

An Overview of the Dynamics of the Volcanic Paroxysmal Explosive Activity, and Related Seismicity, at Andesitic and Dacitic Volcanoes (1960–2010

Directory of Open Access Journals (Sweden)

Vyacheslav M. Zobin

2018-05-01

Full Text Available Understanding volcanic paroxysmal explosive activity requires the knowledge of many associated processes. An overview of the dynamics of paroxysmal explosive eruptions (PEEs at andesitic and dacitic volcanoes occurring between 1960 and 2010 is presented here. This overview is based mainly on a description of the pre-eruptive and eruptive events, as well as on the related seismic measurements. The selected eruptions are grouped according to their Volcanic Explosivity Index (VEI. A first group includes three eruptions of VEI 5-6 (Mount St. Helens, 1980; El Chichón, 1982; Pinatubo, 1991 and a second group includes three eruptions of VEI 3 (Usu volcano, 1977; Soufriere Hills Volcano (SHV, 1996, and Volcán de Colima, 2005. The PEEs of the first group have similarity in their developments that allows to propose a 5-stage scheme of their dynamics process. Between these stages are: long (more than 120 years period of quiescence (stage 1, preliminary volcano-tectonic (VT earthquake swarm (stage 2, period of phreatic explosions (stage 3 and then, PEE appearance (stage 4. It was shown also that the PEEs of this group during their Plinian stage “triggered” the earthquake sequences beneath the volcanic structures with the maximum magnitude of earthquakes proportional to the volume of ejecta of PEEs (stage 5. Three discussed PEEs of the second group with lower VEI developed in more individual styles, not keeping within any general scheme. Among these, one PEE (SHV may be considered as partly following in development to the PEEs of the first group, having stages 1, 3, and 4. The PEEs of Usu volcano and of Volcán de Colima had no preliminary long-term stages of quiescence. The PEE at Usu volcano came just at the end of the preceding short swarm of VT earthquakes. At Volcán de Colima, no preceding swarm of VT occurred. This absence of any regularity in development of lower VEI eruptions may refer, among other reasons, to different conditions of opening

Short-term volcano-tectonic earthquake forecasts based on a moving mean recurrence time algorithm: the El Hierro seismo-volcanic crisis experience

Science.gov (United States)

García, Alicia; De la Cruz-Reyna, Servando; Marrero, José M.; Ortiz, Ramón

2016-05-01

Under certain conditions, volcano-tectonic (VT) earthquakes may pose significant hazards to people living in or near active volcanic regions, especially on volcanic islands; however, hazard arising from VT activity caused by localized volcanic sources is rarely addressed in the literature. The evolution of VT earthquakes resulting from a magmatic intrusion shows some orderly behaviour that may allow the occurrence and magnitude of major events to be forecast. Thus governmental decision makers can be supplied with warnings of the increased probability of larger-magnitude earthquakes on the short-term timescale. We present here a methodology for forecasting the occurrence of large-magnitude VT events during volcanic crises; it is based on a mean recurrence time (MRT) algorithm that translates the Gutenberg-Richter distribution parameter fluctuations into time windows of increased probability of a major VT earthquake. The MRT forecasting algorithm was developed after observing a repetitive pattern in the seismic swarm episodes occurring between July and November 2011 at El Hierro (Canary Islands). From then on, this methodology has been applied to the consecutive seismic crises registered at El Hierro, achieving a high success rate in the real-time forecasting, within 10-day time windows, of volcano-tectonic earthquakes.

Preliminary volcano-hazard assessment for the Katmai volcanic cluster, Alaska

Science.gov (United States)

Fierstein, Judy; Hildreth, Wes

2000-01-01

, 1999, 2000, 2001; Hildreth and Fierstein, 2000), only half of which had been named previously—the four stratovolcanoes Mounts Katmai, Mageik, Martin, and Griggs; the cone cluster called Trident Volcano; Snowy Mountain; and the three lava domes Novarupta, Mount Cerberus, and Falling Mountain. The most recent eruptions were from Trident Volcano (1953–74), but there have been at least eight other, probably larger, explosive events from the volcanoes of this area in the past 10,000 years. This report summarizes what has been learned about the volcanic histories and styles of eruption of all these volcanoes. Many large earthquakes occurred before and during the 1912 eruption, and the cluster of Katmai volcanoes remains seismically active. Because we expect an increase in seismicity before eruptions, seismic monitoring efforts to detect volcanic unrest and procedures for eruption notification and dissemination of information are included in this report. Most at risk from future eruptions of the Katmai volcanic cluster are (1) air-traffic corridors of the North Pacific, including those approaching Anchorage, one of the Pacific’s busiest international airports, (2) several regional airports and military air bases, (3) fisheries and navigation on the Naknek Lake system and Shelikof Strait, (4) pristine wildlife habitat, particularly that of the Alaskan brown bear, and (5) tourist facilities in and near Katmai National Park.

The Canarian Seismic Monitoring Network: design, development and first result

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D'Auria, Luca; Barrancos, José; Padilla, Germán D.; García-Hernández, Rubén; Pérez, Aaron; Pérez, Nemesio M.

2017-04-01

Tenerife is an active volcanic island which experienced several eruptions of moderate intensity in historical times, and few explosive eruptions in the Holocene. The increasing population density and the consistent number of tourists are constantly raising the volcanic risk. In June 2016 Instituto Volcanologico de Canarias started the deployment of a seismological volcano monitoring network consisting of 15 broadband seismic stations. The network began its full operativity in November 2016. The aim of the network are both volcano monitoring and scientific research. Currently data are continuously recorded and processed in real-time. Seismograms, hypocentral parameters, statistical informations about the seismicity and other data are published on a web page. We show the technical characteristics of the network and an estimate of its detection threshold and earthquake location performances. Furthermore we present other near-real time procedures on the data: analysis of the ambient noise for determining the shallow velocity model and temporal velocity variations, detection of earthquake multiplets through massive data mining of the seismograms and automatic relocation of events through double-difference location.

Different deformation patterns using GPS in the volcanic process of El Hierro (Canary Island) 2011-2013

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García-Cañada, Laura; José García-Arias, María; Pereda de Pablo, Jorge; Lamolda, Héctor; López, Carmen

2014-05-01

Ground deformation is one of the most important parameter in volcano monitoring. The detected deformations in volcanic areas can be precursors of a volcanic activity and contribute with useful information to study the evolution of an unrest, eruption or any volcanic process. GPS is the most common technique used to measure volcano deformations. It can be used to detect slow displacement rates or much larger and faster deformations associated with any volcanic process. In volcanoes the deformation is expected to be a mixed of nature; during periods of quiescence it will be slow or not present, while increased activity slow displacement rates can be detected or much larger and faster deformations can be measure due to magma intrusion, for example in the hours to days prior a eruption beginning. In response to the anomalous seismicity detected at El Hierro in July 2011, the Instituto Geográfico Nacional (IGN) improved its volcano monitoring network in the island with continuous GPS that had been used to measure the ground deformation associated with the precursory unrest since summer 2011, submarine eruption (October 2011-March 2012) and the following unrest periods (2012-2013). The continuous GPS time series, together with other techniques, had been used to evaluate the activity and to detect changes in the process. We investigate changes in the direction and module of the deformation obtained by GPS and they show different patterns in every unrest period, very close to the seismicity locations and migrations.

Timing and compositional evolution of Late Pleistocene to Holocene volcanism within the Harrat Rahat volcanic field, Kingdom of Saudi Arabia

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Stelten, M. E.; Downs, D. T.; Dietterich, H. R.

2017-12-01

Harrat Rahat is one of the largest ( 20,000 km2) of 15 active Cenozoic volcanic fields that stretch 3,000 km along the western Arabian Peninsula from Yemen to Syria. The Harrat Rahat volcanic field is 310 km long (N-S) by 75 km wide (E-W), and is dominated by alkalic basalts with minor hawaiite, mugearite, benmoreite, and trachyte eruptives. The timing of volcanism within greater Harrat Rahat is poorly constrained, but field relations and geochronology indicate that northern Harrat Rahat hosted the most recent eruptions. To better constrain the timing and compositional evolution of Harrat Rahat during this recent phase, we present 743 geochemical analyses, 144 40Ar/39Ar ages, and 9 36Cl exposure ages for volcanic strata from northernmost Harrat Rahat. These data demonstrate that volcanism has been ongoing from at least 1.2 Ma to the present, with the most recent eruption known from historical accounts at 1256 CE. Basalt has erupted persistently from 1.2 Ma to the present, but more evolved volcanism has been episodic. Benmoreite erupted at 1.1 Ma and between 550 to 400 ka. Trachytic volcanism has only occurred over the past 150 ka, with the most recent eruption at 5 ka. Aside from the well-documented basaltic eruption at 1256 CE, prior workers interpreted 6 additional basaltic eruptions during the Holocene. However, our 36Cl exposure ages demonstrate that these erupted between 60 to 13 ka. Interestingly, in the northern part of our field area, where the spatial density of volcanic vents is low, young volcanism (<150 ka) is dominated by basaltic eruptions. Conversely, young volcanism in the southern part of our field area, where volcanic vent density is high, is dominated by trachyte. This observation is consistent with a process wherein the time-integrated effects of basaltic influx into the crust in the south produced a mafic intrusive complex, through which younger basaltic magmas cannot ascend. Instead, these magmas stall and produce trachyte, likely through

Heterogeneity in Subducting Slab Influences Fluid Properties, Plate Coupling and Volcanism: Hikurangi Subduction Zone, New Zealand

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Eberhart-Phillips, D. M.; Reyners, M.; Bannister, S. C.

2017-12-01

Seismicity distribution and 3-D models of P- and S-attenuation (1/Q) in the Hikurangi subduction zone, in the North Island of New Zealand, show large variation along-arc in the fluid properties of the subducting slab. Volcanism is also non-uniform, with extremely productive rhyolitic volcanism localized to the central Taupo Volcanic zone, and subduction without volcanism in the southern North Island. Plate coupling varies with heterogeneous slip deficit in the northern section, low slip deficit in the central section, and high slip deficit (strong coupling) in the south. Heterogeneous initial hydration and varied dehydration history both are inferred to play roles. The Hikurangi Plateau (large igneous province) has been subducted beneath New Zealand twice - firstly at ca. 105-100 Ma during north-south convergence with Gondwana, and currently during east-west convergence between the Pacific and Australian plates along the Hikurangi subduction zone. It has an uneven downdip edge which has produced spatially and temporally localized stalls in subduction rate. The mantle wedge under the rhyolitic section has a very low Q feature centred at 50-125 km depth, which directly overlies a 150-km long zone of dense seismicity. This seismicity occurs below a sharp transition in the downdip extent of the Hikurangi Plateau, where difficulty subducting the buoyant plateau would have created a zone of increased faulting and hydration that spent a longer time in the outer-rise yielding zone, compared with areas to the north and south. At shallow depths this section has unusually high fracture permeability from the two episodes of bending, but it did not experience dehydration during Gondwana subduction. This central section at plate interface depths less than 50-km has low Q in the slab crust, showing that it is extremely fluid rich, and it exhibits weak plate coupling with both deep and shallow slow-slip events. In contrast in the southern section, where there is a large deficit in

3D absolute hypocentral determination - 13 years of seismicity in Ecuadorian subduction zone

Science.gov (United States)

Font, Yvonne; Segovia, Monica; Theunissen, Thomas

2010-05-01

In Ecuador, the Nazca plate is subducting beneath the North Andean Block. This subduction triggered, during the last century, 4 major earthquakes of magnitude greater than 7.7. Between 1994 and 2007, the Geophysical Institute (Escuela National Politecnica, Quito) recorded about 40 000 events in whole Ecuador ranging from Mb 1.5 to 6.9. Unfortunately, the local network shows great density discrepancy between the Coastal and Andean regions where numerous stations were installed to survey volcanic activity. Consequently, seismicity in and around the interplate seismogenic zone - producer of the most destructive earthquakes and tsunamis - is not well constrained. This study aims to improve the location of 13 years seismicity occurred during an interseismic period in order to better localize the seismic deformation and gaps. The first step consists in the construction of a 3D "georealistic" velocity model. Because local tomography cannot provide satisfactory model, we combined all local crustal/lithospheric information on the geometry and velocity properties of different geological units. Those information cover the oceanic Nazca plate and sedimentary coverture the subducting plate dip angle; the North Andean Block margin composed of accreted oceanic plateaus (the Moho depth is approximated using gravity modeling); the metamorphic volcanic chain (oceanic nature for the occidental cordillera and inter-andean valley, continental one for the oriental cordillera); The continental Guyana shield and sedimentary basins. The resulting 3D velocity model extends from 2°N to 6.5°S and 277°E to 283°E and reaches a depth of 300 km. It is discretized in constant velocity blocks of 12 x 12 x 3 km in x, y and z, respectively. The second step consists in selecting an adequate sub-set of seismic stations in order to correct the effect of station density disequilibrium between coastal and volcanic regions. Consequently, we only keep the most representative volcanic stations in terms

Seismicity Induced by Groundwater Recharge at Mt. Hood, Oregon, and its Implications for Hydrogeologic Properties.

Science.gov (United States)

Saar, M. O.; Manga, M.

2002-12-01

Earthquakes induced by human-caused changes in fluid pressure have been documented for many years. Examples include seismicity induced by filling reservoirs and by fluid injection or extraction. Less well-documented are seismic events that potentially are triggered by natural variations in groundwater recharge rates (e.g., Wolf et al., BSSA, 1997; Jimenez and Garcia-Fernandez, JVGR, 2000; Audin et al., GRL, 2002). Large groundwater recharge rates can occur in Volcanic Arcs such as the Oregon Cascades where annual precipitation is > 2 m of which > 50 % infiltrates the ground mostly during snowmelt in spring. As a result, infiltration rates of > 1 m per year concentrated during a few months can occur. Near-surface porosities are about 5-10 %. Thus, groundwater levels may fluctuate annually by about 10-20 m resulting in seasonal pore fluid pressure variations of about 1-2 x 105 Pa. Such large-amplitude, narrow-duration fluid pressure signals may allow investigation of seismicity induced by pore fluid pressure diffusion without the influence of engineered systems such as reservoirs. This kind of in-situ study of natural systems over large representative elementary volumes may allow determination of hydrologic parameters at spatial and temporal scales that are relevant for regional hydrogeology. Furthermore, natural hydrologic triggering of earthquakes that persist for decades provides insight into the state of stress in the crust and suggest long-term near-critical failure conditions. Here, we approximate the temporal variations in groundwater recharge with discharge in runoff-dominated streams at high elevations that show a peak in discharge during snow melt. Seismicity is evaluated as time series of daily number of earthquakes and seismic moments. Both stream discharge and seismicity are compared at equivalent frequency bands by applying segmented least-squares polynomial fits to the data. We find statistically significant correlation between groundwater recharge and

Spatio-temporal evolution of volcano seismicity: A laboratory study

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Benson, Philip M.; Vinciguerra, Sergio; Meredith, Philip G.; Young, R. Paul

2010-08-01

We report a laboratory and microstructural study of a suite of deformation experiments in which basalt from Mount Etna volcano is deformed and fractured at an effective confining pressure representative of conditions under a volcanic edifice (40 MPa). Particular attention was paid to the formation of a fracture and damage zone with which to stimulate coupled hydro-mechanical interactions that create the various types of seismicity recorded on volcanic edifices, and which usually precede eruption. Location of AE events through time shows the formation of a fault plane during which waveforms exhibit the typical high frequency characteristics of volcano-tectonic (VT) earthquakes. We found that these VT earthquakes were particularly pronounced when generated using dry samples, compared to samples saturated with a pore fluid (water). VT events generated during deformation of water saturated sample are characterised by a distinctive high frequency onset and a longer, low frequency coda exhibiting properties often seen in the field as hybrid events. We present evidence that hybrid events are, in fact, the common type of volcanic seismic event with either VT or low frequency (LF) events representing end members, and whose proportion depend on pore fluid being present in the rock type being deformed, as well as how close the rock is to failure. We find a notable trend of reducing instances of hybrid events leading up to the failure stage in our experiments, suggesting that during this stage, the pore fluid present in the rock moves sufficiently quickly to provide a resonance, seen as a LF coda. Our data supports recent modeling and field studies that postulate that hybrid events generated in volcanic areas are likely to be generated through the interaction of hydrothermal fluids moving through a combination of pre-existing microcrack networks and larger faults, such as those we observe in forensic (post-test) examination.

International Collaboration on Building Local Technical Capacities for Monitoring Volcanic Activity at Pacaya Volcano, Guatemala.

Science.gov (United States)

Escobar-Wolf, R. P.; Chigna, G.; Morales, H.; Waite, G. P.; Oommen, T.; Lechner, H. N.

2015-12-01

Pacaya volcano is a frequently active and potentially dangerous volcano situated in the Guatemalan volcanic arc. It is also a National Park and a major touristic attraction, constituting an important economic resource for local municipality and the nearby communities. Recent eruptions have caused fatalities and extensive damage to nearby communities, highlighting the need for risk management and loss reduction from the volcanic activity. Volcanic monitoring at Pacaya is done by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), instrumentally through one short period seismic station, and visually by the Parque Nacional Volcan de Pacaya y Laguna de Calderas (PNVPLC) personnel. We carry out a project to increase the local technical capacities for monitoring volcanic activity at Pacaya. Funding for the project comes from the Society of Exploration Geophysicists through the Geoscientists Without Borders program. Three seismic and continuous GPS stations will be installed at locations within 5 km from the main vent at Pacaya, and one webcam will aid in the visual monitoring tasks. Local educational and outreach components of the project include technical workshops on data monitoring use, and short thesis projects with the San Carlos University in Guatemala. A small permanent exhibit at the PNVPLC museum or visitor center, focusing on the volcano's history, hazards and resources, will also be established as part of the project. The strategy to involve a diverse group of local collaborators in Guatemala aims to increase the chances for long term sustainability of the project, and relies not only on transferring technology but also the "know-how" to make that technology useful. Although not a primary research project, it builds on a relationship of years of joint research projects at Pacaya between the participants, and could be a model of how to increase the broader impacts of such long term collaboration partnerships.

Yellowstone-Snake River Plain seismic profilling experiment: Crustal structure of the eastern Snake River Plain

International Nuclear Information System (INIS)

Braile, L.W.; Smith, R.B.; Ansorge, J.; Baker, M.R.; Sparlin, M.A.; Prodehl, C.; Schilly, M.M.; Healy, J.H.; Mueller, S.; Olsen, K.H.

1982-01-01

Seismic refraction profiles recorded along the eastern Snake River Plain (ESRP) in southeastern Idaho during the 1978 Yellowstone-Snake River Plain cooperative seismic profiling experiment are interpreted to infer the crustal velocity and attenuation (Q-1) structure of the ESRP. Travel-time and synthetic seismogram modeling of a 250 km reversed refraction profile as well as a 100 km detailed profile indicate that the crust of the ESRP is highly anomalous. Approximately 3 to 6 km of volcanic rocks (with some interbedded sediments) overlie an upper-crustal layer (compressional velocity approx. =6.1 km/s) which thins southwestward along the ESRP from a thickness of 10 km near Island Park Caldera to 2 to 3 km beneath the central and southwestern portions of the ESRP. An intermediate-velocity (approx. =6.5 km/s) layer extends from approx. =10 to approx. =20 km depth. a thick (approx. =22 km) lower crust of compressional velocity 6.8 km/s, a total crustall thickness of approx. =42 km, and a P/sub n/ velocity of approx. =7.9 km/s is observed in the ESRP, similar to the western Snake River Plain and the Rocky Mountains Provinces. High attenuation is evident on the amplitude corrected seismic data due to low-Q values in the volcanic rocks (Q/sub p/ = 20 to 200) and throughout the crust (Q/sub p/ = 160 to 300). Based on these characteristics of the crustal structure and volcanic-age progression data, it is suggested that the ESRP has resulted from an intensitive period of intrusion of mantle-derived basaltic magma into the upper crust generating explosive silicic volcanism and associated regional uplift and caldera collapse. This activity began about 15 m.y. ago in southwestern Idaho and has migrated northeast to its present position at Yellowstone. Subsequent cooling of the intruded upper crust results in the 6.5 km/s velocity intermediate layer. Crustal subsidence and periodic basaltic volcanism as represented by the ESRP complete the sequence of crustal evolution

Seismic hydraulic fracture migration originated by successive deep magma pulses: The 2011-2013 seismic series associated to the volcanic activity of El Hierro Island

Science.gov (United States)

Díaz-Moreno, A.; Ibáñez, J. M.; De Angelis, S.; García-Yeguas, A.; Prudencio, J.; Morales, J.; Tuvè, T.; García, L.

2015-11-01

In this manuscript we present a new interpretation of the seismic series that accompanied eruptive activity off the coast of El Hierro, Canary Islands, during 2011-2013. We estimated temporal variations of the Gutenberg-Richter b value throughout the period of analysis, and performed high-precision relocations of the preeruptive and syneruptive seismicity using a realistic 3-D velocity model. Our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust. These magma pulses occurred within a small and well-defined volume resulting in the emplacement of fresh magma along the crust-mantle boundary underneath El Hierro. We analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust. Our results suggest that very high earthquake rates underneath El Hierro represent the response of a stable lower crust to stress perturbations with pulsatory character, linked to the injection of magma from the mantle. Magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms. The absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity, had diffusive character. We conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill. Our conceptual model considers pulsatory magma injection from the upper mantle and its propagation along the Moho. We suggest, within this framework, that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement.

Seismic attenuation and scattering tomography of rock samples using stochastic wavefields: linking seismology, volcanology, and rock physics.

Science.gov (United States)

Fazio, Marco; De Siena, Luca; Benson, Phillip

2016-04-01

Seismic attenuation and scattering are two attributes that can be linked with porosity and permeability in laboratory experiments. When measuring these two quantities using seismic waveforms recorder at lithospheric and volcanic scales the areas of highest heterogeneity, as batches of melt and zones of high deformation, produce anomalous values of the measured quantities, the seismic quality factor and scattering coefficient. When employed as indicators of heterogeneity and absorption in volcanic areas these anomalous effects become strong indicators of magma accumulation and tectonic boundaries, shaping magmatic chambers and conduit systems. We perform attenuation and scattering measurements and imaging using seismic waveforms produced in laboratory experiments, at frequencies ranging between the kHz and MHz. As attenuation and scattering are measured from the shape of the envelopes, disregarding phases, we are able to connect the observations with the micro fracturing and petrological quantities previously measured on the sample. Connecting the imaging of dry and saturated samples via these novel attributes with the burst of low-period events with increasing saturation and deformation is a challenge. Its solution could plant the seed for better relating attenuation and scattering tomography measurements to the presence of fluids and gas, therefore creating a novel path for reliable porosity and permeability tomography. In particular for volcanoes, being able to relate attenuation/scattering measurements with low-period micro seismicity could deliver new data to settle the debate about if both source and medium can produce seismic resonance.

Micro-seismicity and seismic moment release within the Coso Geothermal Field, California

Science.gov (United States)

Kaven, Joern; Hickman, Stephen H.; Davatzes, Nicholas C.

2014-01-01

We relocate 16 years of seismicity in the Coso Geothermal Field (CGF) using differential travel times and simultaneously invert for seismic velocities to improve our knowledge of the subsurface geologic and hydrologic structure. We expand on our previous results by doubling the number of relocated events from April 1996 through May 2012 using a new field-wide 3-D velocity model. Relocated micro-seismicity sharpens in many portions of the active geothermal reservoir, likely defining large-scale fault zones and fluid pressure compartment boundaries. However, a significant fraction of seismicity remains diffuse and does not cluster into sharply defined structures, suggesting that permeability is maintained within the reservoir through distributed brittle failure. The seismic velocity structure reveals heterogeneous distributions of compressional (Vp) and shear (Vs) wave speed, with Vs generally higher in the Main Field and East Flank and Vp remaining relatively uniform across the CGF, but with significant local variations. The Vp/Vs ratio appears to outline the two main producing compartments of the reservoir at depths below mean ground level of approximately 1 to 2.5 km, with a ridge of relatively high Vp/Vs separating the Main Field from the East Flank. Detailed analyses of spatial and temporal variations in earthquake relocations and cumulative seismic moment release in the East Flank reveal three regions with persistently high rates of seismic activity. Two of these regions exhibit sharp, stationary boundaries at the margins of the East Flank that likely represent barriers to fluid flow and advective heat transport. However, seismicity and moment release in a third region at the northern end of the East Flank spread over time to form an elongated NE to SW structure, roughly parallel both to an elongated cluster of seismicity at the southern end of the East Flank and to regional fault traces mapped at the surface. Our results indicate that high

The 2007 Nazko, British Columbia, earthquake sequence: Injection of magma deep in the crust beneath the Anahim volcanic belt

Science.gov (United States)

Cassidy, J.F.; Balfour, N.; Hickson, C.; Kao, H.; White, Rickie; Caplan-Auerbach, J.; Mazzotti, S.; Rogers, Gary C.; Al-Khoubbi, I.; Bird, A.L.; Esteban, L.; Kelman, M.; Hutchinson, J.; McCormack, D.

2011-01-01

On 9 October 2007, an unusual sequence of earthquakes began in central British Columbia about 20 km west of the Nazko cone, the most recent (circa 7200 yr) volcanic center in the Anahim volcanic belt. Within 25 hr, eight earthquakes of magnitude 2.3-2.9 occurred in a region where no earthquakes had previously been recorded. During the next three weeks, more than 800 microearthquakes were located (and many more detected), most at a depth of 25-31 km and within a radius of about 5 km. After about two months, almost all activity ceased. The clear P- and S-wave arrivals indicated that these were high-frequency (volcanic-tectonic) earthquakes and the b value of 1.9 that we calculated is anomalous for crustal earthquakes but consistent with volcanic-related events. Analysis of receiver functions at a station immediately above the seismicity indicated a Moho near 30 km depth. Precise relocation of the seismicity using a double-difference method suggested a horizontal migration at the rate of about 0:5 km=d, with almost all events within the lowermost crust. Neither harmonic tremor nor long-period events were observed; however, some spasmodic bursts were recorded and determined to be colocated with the earthquake hypocenters. These observations are all very similar to a deep earthquake sequence recorded beneath Lake Tahoe, California, in 2003-2004. Based on these remarkable similarities, we interpret the Nazko sequence as an indication of an injection of magma into the lower crust beneath the Anahim volcanic belt. This magma injection fractures rock, producing high-frequency, volcanic-tectonic earthquakes and spasmodic bursts.

Three-dimensional seismic velocity structure and earthquake relocations at Katmai, Alaska

Science.gov (United States)

Murphy, Rachel; Thurber, Clifford; Prejean, Stephanie G.; Bennington, Ninfa

2014-01-01

We invert arrival time data from local earthquakes occurring between September 2004 and May 2009 to determine the three-dimensional (3D) upper crustal seismic structure in the Katmai volcanic region. Waveforms for the study come from the Alaska Volcano Observatory's permanent network of 20 seismic stations in the area (predominantly single-component, short period instruments) plus a densely spaced temporary array of 11 broadband, 3-component stations. The absolute and relative arrival times are used in a double-difference seismic tomography inversion to solve for 3D P- and S-wave velocity models for an area encompassing the main volcanic centers. The relocated hypocenters provide insight into the geometry of seismogenic structures in the area, revealing clustering of events into four distinct zones associated with Martin, Mageik, Trident-Novarupta, and Mount Katmai. The seismic activity extends from about sea level to 2 km depth (all depths referenced to mean sea level) beneath Martin, is concentrated near 2 km depth beneath Mageik, and lies mainly between 2 and 4 km depth below Katmai and Trident-Novarupta. Many new features are apparent within these earthquake clusters. In particular, linear features are visible within all clusters, some associated with swarm activity, including an observation of earthquake migration near Trident in 2008. The final velocity model reveals a possible zone of magma storage beneath Mageik, but there is no clear evidence for magma beneath the Katmai-Novarupta area where the 1912 eruptive activity occurred, suggesting that the storage zone for that eruption may have largely been evacuated, or remnant magma has solidified.

Evolution of the 2015 Cotopaxi eruption revealed by combined geochemical & seismic observations

Science.gov (United States)

Hidalgo, Silvana; Battaglia, Jean; Arellano, Santiago; Sierra, Daniel; Bernard, Benjamin; Parra, Rene; Kelly, Peter; Dinger, Florian; Barrington, Charlotte; Samaniego, Pablo

2018-01-01

Through integration of multiple data streams to monitor volcanic unrest scientists are able to make more robust eruption forecast and to obtain a more holistic interpretation of volcanic systems. We examined gas emission and gas geochemistry, seismic and petrologic data recorded during the 2015 unrest of Cotopaxi (Ecuador) in order to decipher the origin and temporal evolution of this eruption. Identification of families of similar seismic events and the use of seismic amplitude ratios reveals temporal changes in volcanic processes. SO2 (300 to 24000 t/d), BrO/SO2 (5-10 x10-5), SO2/HCl (5.8 ± 4.8 and 6.6 ± 3.0) and CO2/SO2 (0.6 to 2.1) measured throughout the eruption indicate a shallow magmatic source. Bulk ash and glass chemistry indicate a homogenous andesitic (SiO2 wt%=56.94 ± 0.25) magma having undergone extensive S-exsolution and degassing during ascent. These data lead us to interpret this eruption as a magma intrusion and ascend to shallow levels. The intrusion progressively interacted with the hydrothermal system, boiled off water, and produced hydromagmatic explosions. A small volume of this intrusion continued to fragment and produced episodic ash emissions until it was sufficiently degassed and rheologically stiff. Based on the 470 kt of measured SO2 we estimate that ~ 65.3 x106 m3 of magma were required to supply the emitted gases. This volume exceeds the volume of erupted juvenile material by a factor of 50. This result emphasizes the importance of careful monitoring of Cotopaxi to identify the intrusion of a new batch of magma, which could rejuvenate the non-erupted material.

Understanding cyclic seismicity and ground deformation patterns at volcanoes: Intriguing lessons from Tungurahua volcano, Ecuador

Science.gov (United States)

Neuberg, Jürgen W.; Collinson, Amy S. D.; Mothes, Patricia A.; Ruiz, Mario C.; Aguaiza, Santiago

2018-01-01

Cyclic seismicity and ground deformation patterns are observed on many volcanoes worldwide where seismic swarms and the tilt of the volcanic flanks provide sensitive tools to assess the state of volcanic activity. Ground deformation at active volcanoes is often interpreted as pressure changes in a magmatic reservoir, and tilt is simply translated accordingly into inflation and deflation of such a reservoir. Tilt data recorded by an instrument in the summit area of Tungurahua volcano in Ecuador, however, show an intriguing and unexpected behaviour on several occasions: prior to a Vulcanian explosion when a pressurisation of the system would be expected, the tilt signal declines significantly, hence indicating depressurisation. At the same time, seismicity increases drastically. Envisaging that such a pattern could carry the potential to forecast Vulcanian explosions on Tungurahua, we use numerical modelling and reproduce the observed tilt patterns in both space and time. We demonstrate that the tilt signal can be more easily explained as caused by shear stress due to viscous flow resistance, rather than by pressurisation of the magmatic plumbing system. In general, our numerical models prove that if magma shear viscosity and ascent rate are high enough, the resulting shear stress is sufficient to generate a tilt signal as observed on Tungurahua. Furthermore, we address the interdependence of tilt and seismicity through shear stress partitioning and suggest that a joint interpretation of tilt and seismicity can shed new light on the eruption potential of silicic volcanoes.

ACTIVITY AND Vp/Vs RATIO OF VOLCANO-TECTONIC SEISMIC SWARM ZONES AT NEVADO DEL RUIZ VOLCANO, COLOMBIA

Directory of Open Access Journals (Sweden)

Londoño B. John Makario

2010-06-01

Full Text Available An analysis of the seismic activity for volcano-tectonic earthquake (VT swarms zones at Nevado del Ruiz Volcano (NRV was carried out for the interval 1985- 2002, which is the most seismic active period at NRV until now (2010. The swarm-like seismicity of NRV was frequently concentrated in very well defined clusters around the volcano. The seismic swarm zone located at the active crater was the most active during the entire time. The seismic swarm zone located to the west of the volcano suggested some relationship with the volcanic crises. It was active before and after the two eruptions occurred in November 1985 and September 1989. It is believed that this seismic activity may be used as a monitoring tool of volcanic activity. For each seismic swarm zone the Vp/Vs ratio was also calculated by grouping of earthquakes and stations. It was found that each seismic swarm zone had a distinct Vp/Vs ratio with respect to the others, except for the crater and west swarm zones, which had the same value. The average Vp/Vs ratios for the seismic swarm zones located at the active crater and to the west of the volcano are about 6-7% lower than that for the north swarm zone, and about 3% lower than that for the south swarm zone. We suggest that the reduction of the Vp/Vs ratio is due to degassing phenomena inside the central and western earthquake swarm zones, or due to the presence of microcracks inside the volcano. This supposition is in agreement with other studies of geophysics, geochemistry and drilling surveys carried out at NRV.

Seismic observations of Redoubt Volcano, Alaska - 1989-2010 and a conceptual model of the Redoubt magmatic system

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Power, John A.; Stihler, Scott D.; Chouet, Bernard A.; Haney, Matthew M.; Ketner, D.M.

2013-01-01

Seismic activity at Redoubt Volcano, Alaska, has been closely monitored since 1989 by a network of five to ten seismometers within 22 km of the volcano's summit. Major eruptions occurred in 1989-1990 and 2009 and were characterized by large volcanic explosions, episodes of lava dome growth and failure, pyroclastic flows, and lahars. Seismic features of the 1989-1990 eruption were 1) weak precursory tremor and a short, 23-hour-long, intense swarm of repetitive shallow long-period (LP) events centered 1.4 km below the crater floor, 2) shallow volcano-tectonic (VT) and hybrid earthquakes that separated early episodes of dome growth, 3) 13 additional swarms of LP events at shallow depths precursory to many of the 25 explosions that occurred over the more than 128 day duration of eruptive activity, and 4) a persistent cluster of VT earthquakes at 6 to 9 km depth. In contrast the 2009 eruption was preceded by a pronounced increase in deep-LP (DLP) events at lower crustal depths (25 to 38 km) that began in mid-December 2008, two months of discontinuous shallow volcanic tremor that started on January 23, 2009, a strong phreatic explosion on March 15, and a 58-hour-long swarm of repetitive shallow LP events. The 2009 eruption consisted of at least 23 major explosions between March 23 and April 5, again accompanied by shallow VT earthquakes, several episodes of shallow repetitive LP events and dome growth continuing until mid July. Increased VT earthquakes at 4 to 9 km depth began slowly in early April, possibly defining a mid-crustal magma source zone. Magmatic processes associated with the 2009 eruption seismically activated the same portions of the Redoubt magmatic system as the 1989-1990 eruption, although the time scales and intensity vary considerably among the two eruptions. The occurrence of precursory DLP events suggests that the 2009 eruption may have involved the rise of magma from lower crustal depths. Based on the evolution of seismicity during the 1989-1990 and

From 3D to 4D seismic tomography at El Hierro Island (Canary Islands, Spain)

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Garcia-Yeguas, A.; Koulakov, I.; Jakovlev, A.; Ibáñez, J. M.

2012-04-01

In this work we are going to show the advantages of a dynamic tomography 4D, versus a static image 3D related with a volcanic reactivation and eruption at El Hierro island (Canary Islands, Spain). In this process a high number of earthquakes before and during the eruptive processes have been registered. We are going to show a 3D image as an average of the velocity structure and then the characteristics and physical properties on the medium, including the presence or not of magma. This image will be complemented with its evolution along the time, observing its volcanic dynamic and its influence over the medium properties, including its power as an important element on early warnings protocols. After more than forty years of quiet at Canary Islands, since 1971 with Teneguía eruption at La Palma Island, and more than 200 years on El Hierro Island (The last eruption known at El Hierro took place in 1793, volcán de Lomo Negro), on 19th July on 2011 the Spanish seismic national network, administered by IGN (Instituto Geográfico Nacional), detected an increase of local seismic activity below El Hierro island (Canary Islands, Spain). Since this moment an intense swarm took place, with more than 11000 events, until 11th December, with magnitudes (MLg) from 0.2 to 4.4. In this period two eruptive processes have been declared in front of the South coast of El Hierro island, and they have not finished yet. This seismic swarm has allowed carrying out a 3D seismic tomography, using P and S waves traveltimes. It has showed a low velocity from the North to the South. On the other hand, we have performed a 4D seismic tomography, taking the events occurred at different intervals of time. We can observe the evolution of the negative anomaly along the time, from the North to the South, where has taken place La Restinga submarine eruption. 4D seismic tomography is an innovative and powerful tool able to show the evolution in time of a volcanic process.

Geomorphological features in the southern Canary Island Volcanic Province: The importance of volcanic processes and massive slope instabilities associated with seamounts

Science.gov (United States)

Palomino, Desirée; Vázquez, Juan-Tomás; Somoza, Luis; León, Ricardo; López-González, Nieves; Medialdea, Teresa; Fernández-Salas, Luis-Miguel; González, Francisco-Javier; Rengel, Juan Antonio

2016-02-01

The margin of the continental slope of the Volcanic Province of Canary Islands is characterised by seamounts, submarine hills and large landslides. The seabed morphology including detailed morphology of the seamounts and hills was analysed using multibeam bathymetry and backscatter data, and very high resolution seismic profiles. Some of the elevation data are reported here for the first time. The shape and distribution of characteristics features such as volcanic cones, ridges, slides scars, gullies and channels indicate evolutionary differences. Special attention was paid to recent geological processes that influenced the seamounts. We defined various morpho-sedimentary units, which are mainly due to massive slope instability that disrupt the pelagic sedimentary cover. We also studied other processes such as the role of deep bottom currents in determining sediment distribution. The sediments are interpreted as the result of a complex mixture of material derived from a) slope failures on seamounts and submarine hills; and b) slides and slumps on the continental slope.

Correlating the electrification of volcanic plumes with ashfall textures at Sakurajima Volcano, Japan

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Smith, Cassandra M.; Van Eaton, Alexa R.; Charbonnier, Sylvain; McNutt, Stephen R.; Behnke, Sonja A.; Thomas, Ronald J.; Edens, Harald E.; Thompson, Glenn

2018-06-01

Volcanic lightning detection has become a useful resource for monitoring remote, under-instrumented volcanoes. Previous studies have shown that the behavior of volcanic plume electrification responds to changes in the eruptive processes and products. However, there has not yet been a study to quantify the links between ash textures and plume electrification during an actively monitored eruption. In this study, we examine a sequence of vulcanian eruptions from Sakurajima Volcano in Japan to compare ash textural properties (grain size, shape, componentry, and groundmass crystallinity) to plume electrification using a lightning mapping array and other monitoring data. We show that the presence of the continual radio frequency (CRF) signal is more likely to occur during eruptions that produce large seismic amplitudes (>7 μm) and glass-rich volcanic ash with more equant particle shapes. We show that CRF is generated during energetic, impulsive eruptions, where charge buildup is enhanced by secondary fragmentation (milling) as particles travel out of the conduit and into the gas-thrust region of the plume. We show that the CRF signal is influenced by a different electrification process than later volcanic lightning. By using volcanic CRF and lightning to better understand the eruptive event and its products these key observations will help the monitoring community better utilize volcanic electrification as a method for monitoring and understanding ongoing explosive eruptions.

Collateral variations between the concentrations of mercury and other water soluble ions in volcanic ash samples and volcanic activity during the 2014-2016 eruptive episodes at Aso volcano, Japan

Science.gov (United States)

Marumoto, Kohji; Sudo, Yasuaki; Nagamatsu, Yoshizumi

2017-07-01

During 2014-2016, the Aso volcano, located in the center of the Kyushu Islands, Japan, erupted and emitted large amounts of volcanic gases and ash. Two episodes of the eruption were observed; firstly Strombolian magmatic eruptive episodes from 25 November 2014 to the middle of May 2015, and secondly phreatomagmatic and phreatic eruptive episodes from September 2015 to February 2016. Bulk chemical analyses on total mercury (Hg) and major ions in water soluble fraction in volcanic ash fall samples were conducted. During the Strombolian magmatic eruptive episodes, total Hg concentrations averaged 1.69 ± 0.87 ng g- 1 (N = 33), with a range from 0.47 to 3.8 ng g- 1. In addition, the temporal variation of total Hg concentrations in volcanic ash varied with the amplitude change of seismic signals. In the Aso volcano, the volcanic tremors are always observed during eruptive stages and quiet interludes, and the amplitudes of tremors increase at eruptive stages. So, the temporal variation of total Hg concentrations could provide an indication of the level of volcanic activity. During the phreatomagmatic and phreatic eruptive episodes, on the other hand, total Hg concentrations in the volcanic ash fall samples averaged 220 ± 88 ng g- 1 (N = 5), corresponding to 100 times higher than those during the Strombolian eruptive episode. Therefore, it is possible that total Hg concentrations in volcanic ash samples are largely varied depending on the eruptive type. In addition, the ash fall amounts were also largely different among the two eruptive episodes. This can be also one of the factors controlling Hg concentrations in volcanic ash.

Two types of SDR recognised in pre-stack velocity analysis of ultra-long-offset seismic reflection data in the South Atlantic

Science.gov (United States)

Collier, J.; McDermott, C.; Lonergan, L.; McDermott, K.; Bellingham, P.

2017-12-01

Our understanding of continental breakup at volcanic margins has lagged behind that of non-volcanic margins in recent years. This is largely due to seismic imaging problems caused by the presence of thick packages of Seaward-Dipping Reflectors (SDRs) in the continent-ocean transition zone. These packages consist of interbedded tholeiitic lava flows, volcanic tuffs and terrestrial sediment that results in scattering, peg-leg multiples and defocusing of seismic energy. Here we analyse three ultra-long-offset (10.2 km), wide-bandwidth (5-100 Hz) seismic reflection profiles acquired by ION-GXT offshore South America during 2009-12 to gain new insights into the velocity structure of the SDRs and hence pattern of magmatism during continental breakup. We observe two seismic velocity patterns within the SDRs. The most landward packages show high velocity anomaly "bulls-eyes" of up to 1 km s-1. These highs occur where the stacked section shows them to thicken at the down-dip end of individual packages that are bounded by faults. All lines show 5-6 velocity highs spaced approximately 10 km apart. We interpret the velocity bulls-eyes as depleted mafic or ultramafic bodies that fed the sub-aerial tholeiitic lava flows during continental stretching. Similar relationships have been observed in outcrop onshore but have not been previously demonstrated in seismic data. The bulls-eye packages pass laterally into SDR packages that show no velocity highs. These packages are not associated with faulting and become more extensive going north towards the impact point of the Tristan da Cunha hotspot. This second type of SDR coincides with linear magnetic anomalies. We interpret these SDRs as the products of sub-aerial oceanic spreading similar to those seen on Iceland and described in the classic "Hinz model" and marine geophysical literature. Our work demonstrates that these SDRs are preceded by ones generated during an earlier phase of mechanical thinning of the continental crust. The

Geophysical techniques for detecting magmas and high-temperature fluids. Their application to the Onikobe-Narugo volcanic region and the southern Kii Peninsula

International Nuclear Information System (INIS)

Asamori, Koichi; Umeda, Koji

2005-01-01

The effects of volcanism on the geological environments include a dynamic destruction and subsidence of basement rocks, caused by the intrusion and eruption of magma. To ensure the long-term stability of geological disposal system, a possibility of renewed volcanism at the site might be examined based on the geotectonic data of the deep underground using geophysical and geochemical approaches. This paper describes an overview of geophysical approaches for detecting magmas and/or high temperature fluids related to volcanism within the crust and uppermost mantle. Moreover, we present the images of the seismic velocity and electrical resistivity structure beneath the Onikobe-Narugo volcanic region and the southern Kii Peninsula, carried out in JNC's R and D program. (author)

Erosion influences the seismicity of active thrust faults.

Science.gov (United States)

Steer, Philippe; Simoes, Martine; Cattin, Rodolphe; Shyu, J Bruce H

2014-11-21

Assessing seismic hazards remains one of the most challenging scientific issues in Earth sciences. Deep tectonic processes are classically considered as the only persistent mechanism driving the stress loading of active faults over a seismic cycle. Here we show via a mechanical model that erosion also significantly influences the stress loading of thrust faults at the timescale of a seismic cycle. Indeed, erosion rates of about ~0.1-20 mm yr(-1), as documented in Taiwan and in other active compressional orogens, can raise the Coulomb stress by ~0.1-10 bar on the nearby thrust faults over the inter-seismic phase. Mass transfers induced by surface processes in general, during continuous or short-lived and intense events, represent a prominent mechanism for inter-seismic stress loading of faults near the surface. Such stresses are probably sufficient to trigger shallow seismicity or promote the rupture of deep continental earthquakes up to the surface.

New Insights on the Structure of the Cascadia Subduction Zone from Amphibious Seismic Data

Science.gov (United States)

Janiszewski, Helen Anne

A new onshore-offshore seismic dataset from the Cascadia subduction zone was used to characterize mantle lithosphere structure from the ridge to the volcanic arc, and plate interface structure offshore within the seismogenic zone. The Cascadia Initiative (CI) covered the Juan de Fuca plate offshore the northwest coast of the United States with an ocean bottom seismometer (OBS) array for four years; this was complemented by a simultaneous onshore seismic array. Teleseismic data recorded by this array allows the unprecedented imaging of an entire tectonic plate from its creation at the ridge through subduction initiation and back beyond the volcanic arc along the entire strike of the Cascadia subduction zone. Higher frequency active source seismic data also provides constraints on the crustal structure along the plate interface offshore. Two seismic datasets were used to image the plate interface structure along a line extending 100 km offshore central Washington. These are wide-angle reflections from ship-to-shore seismic data from the Ridge-To-Trench seismic cruise and receiver functions calculated from a densely spaced CI OBS focus array in a similar region. Active source seismic observations are consistent with reflections from the plate interface offshore indicating the presence of a P-wave velocity discontinuity. Until recently, there has been limited success in using the receiver function technique on OBS data. I avoid these traditional challenges by using OBS constructed with shielding deployed in shallow water on the continental shelf. These data have quieter horizontals and avoid water- and sediment-multiple contamination at the examined frequencies. The receiver functions are consistently modeled with a velocity structure that has a low velocity zone (LVZ) with elevated P to S-wave velocity ratios at the plate interface. A similar LVZ structure has been observed onshore and interpreted as a combination of elevated pore-fluid pressures or metasediments

Mega-rings Surrounding Timber Mountain Nested Calderas, Geophysical Anomalies: Rethinking Structure and Volcanism Near Yucca Mountain (YM), Nevada

Science.gov (United States)

Tynan, M. C.; Smith, K. D.; Savino, J. M.; Vogt, T. J.

2004-12-01

Observed regional mega-rings define a zone ˜80-100 km in diameter centered on Timber Mountain (TM). The mega-rings encompass known smaller rhyolitic nested Miocene calderas ( ˜11-15 my, structural relationships. Mega-rings consist of arcuate faulted blocks with deformation (some remain active structures) patterns showing a genetic relationship to the TM volcanic system; they appear to be spatially associated and temporally correlated with Miocene volcanism and two geophysically identified crustal/upper mantle features. A 50+ km diameter pipe-like high velocity anomaly extends from crustal depth to over 200 km beneath TM (evidence for 400km depth to NE). The pipe is located between two ˜100 km sub-parallel N/S linear trends of small-magnitude earthquake activity, one extending through the central NV Test Site, and a second located near Beatty, NV. Neither the kinematics nor relational mechanism of 100km seismically active N/S linear zones, pipe, and mega-rings are understood. Interpreted mega-rings are: 1) Similar in size to larger terrestrial volcanic complexes (e.g., Yellowstone, Indonesia's Toba system); 2) Located in the region of structural transition from the Mohave block to the south, N/S Basin and Range features to the north, Walker Lane to the NW, and the Las Vegas Valley shear zone to the SE; 3) Associated with the two seismically active zones (similar to other caldera fault-bounded sags), the mantle high velocity feature, and possibly a regional bouguer gravity anomaly; 4) Nearly coincident with area hydrologic basins and sub-basins; 5) Similar to features described from terrestrial and planetary caldera-collapse studies, and as modeled in laboratory scaled investigations (ice melt, balloon/sand). Post Mid-Miocene basalts commonly occur within or adjacent to the older rhyolitic caldera moats; other basaltic material occurs marginal to both the outer rings of the interpreted mega-ring system and high velocity pipe. The YM repository may be situated in

Timing and climate forcing of volcanic eruptions for the past 2,500 years.

Science.gov (United States)

Sigl, M; Winstrup, M; McConnell, J R; Welten, K C; Plunkett, G; Ludlow, F; Büntgen, U; Caffee, M; Chellman, N; Dahl-Jensen, D; Fischer, H; Kipfstuhl, S; Kostick, C; Maselli, O J; Mekhaldi, F; Mulvaney, R; Muscheler, R; Pasteris, D R; Pilcher, J R; Salzer, M; Schüpbach, S; Steffensen, J P; Vinther, B M; Woodruff, T E

2015-07-30

Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

A shallow crustal earthquake doublet from the Trans-Mexican volcanic belt (Central Mexico)

Science.gov (United States)

Quintanar, L.; Rodríguez-González, M.; Campos-Enríquez, O.

2003-04-01

The trans-Mexican volcanic belt is an active volcanic arc related to subduction along the Middle America trench and characterized by shallow seismicity and synvolcanic to postvolcanic extensional arc-parallel faulting. The Mezquital graben is a major intra-arc basin of the central trans-Mexican volcanic belt. A doublet of moderate shallow shocks occurred in March and October 1976 in the region of this graben. These earthquakes were recorded by the Mexican National Seismological network, in particular by the Bosch-Omori seismograph (T_0 = 18 s) at the Tacubaya Observatory in Mexico City. We have carefully relocated the two main shocks and their major aftershocks by reading the original records and using a modified crustal velocity model for this region. A difference of ˜50 km is observed between the locations reported by the Mexican Seismological Service and those obtained in this study, which are additionally supported by the damage distribution of these earthquakes. A first motion analysis, based on regional and teleseismic records, defines for the March and October shocks normal fault mechanisms, characterized by E-W striking fault planes, which coincides with the orientation of the master faults of the Mezquital graben. After calculating the instrumental response, the source parameters were obtained from the Bosch-Omori seismograph records by body-wave modeling. For the March earthquake, we estimate a seismic moment of 4.5×1023 dyne-cm (equivalent to M_w=5.0) and a stress drop of 0.7 MPa assuming a circular rupture model (radius = 3 km). Given the poor quality of the Bosch-Omori record for the October earthquake, we used the comparison, between both events, of long-period (T=20 sec) teleseismic records at 2 stations to obtain its corresponding source parameters. By assuming a similar stress drop as for the March event, we obtain a M_0 of 5.6×1023 dyne-cm and M_w = 5.1 with a rupture length of 6.5 km. According to gravity data, the regional E-W faults are

Non-Volcanic release of CO2 in Italy: quantification, conceptual models and gas hazard

Science.gov (United States)

Chiodini, G.; Cardellini, C.; Caliro, S.; Avino, R.

2011-12-01

Central and South Italy are characterized by the presence of many reservoirs naturally recharged by CO2 of deep provenance. In the western sector, the reservoirs feed hundreds of gas emissions at the surface. Many studies in the last years were devoted to (i) elaborating a map of CO2 Earth degassing of the region; (ii) to asses the gas hazard; (iii) to develop methods suitable for the measurement of the gas fluxes from different types of emissions; (iv) to elaborate the conceptual model of Earth degassing and its relation with the seismic activity of the region and (v) to develop physical numerical models of CO2 air dispersion. The main results obtained are: 1) A general, regional map of CO2 Earth degassing in Central Italy has been elaborated. The total flux of CO2 in the area has been estimated in ~ 10 Mt/a which are released to the atmosphere trough numerous dangerous gas emissions or by degassing spring waters (~ 10 % of the CO2 globally estimated to be released by the Earth trough volcanic activity). 2) An on line, open access, georeferenced database of the main CO2 emissions (~ 250) was settled up (http://googas.ov.ingv.it). CO2 flux > 100 t/d characterise 14% of the degassing sites while CO2 fluxes from 100 t/d to 10 t/d have been estimated for about 35% of the gas emissions. 3) The sites of the gas emissions are not suitable for life: the gas causes many accidents to animals and people. In order to mitigate the gas hazard a specific model of CO2 air dispersion has been developed and applied to the main degassing sites. A relevant application regarded Mefite d'Ansanto, southern Apennines, which is the largest natural emission of low temperature CO2 rich gases, from non-volcanic environment, ever measured in the Earth (˜2000 t/d). Under low wind conditions, the gas flows along a narrow natural channel producing a persistent gas river which has killed over a period of time many people and animals. The application of the physical numerical model allowed us to

Driving magma to the surface: The 2011-2012 El Hierro Volcanic Eruption

Science.gov (United States)

López, Carmen; Benito-Saz, Maria A.; Martí, Joan; del-Fresno, Carmen; García-Cañada, Laura; Albert, Helena; Lamolda, Héctor

2017-08-01

We reanalyzed the seismic and deformation data corresponding to the preeruptive unrest on El Hierro (Canary Islands) in 2011. We considered new information about the internal structure of the island. We updated the seismic catalog to estimate the full evolution of the released seismic energy and demonstrate the importance of nonlocated earthquakes. Using seismic data and GPS displacements, we characterized the shear-tensile type of the predominant fracturing and modeled the strain and stress fields for different time periods. This enabled us to identify a prolonged first phase characterized by hydraulic tensile fracturing, which we interpret as being related to the emplacement of new magma below the volcanic edifice on El Hierro. This was followed by postinjection unidirectional migration, probably controlled by the stress field and the distribution of the structural discontinuities. We identified the effects of energetic magmatic pulses occurring a few days before the eruption that induced shear seismicity on preexisting faults within the volcano and raised the Coulomb stress over the whole crust. We suggest that these magmatic pulses reflect the crossing of the Moho discontinuity, as well as changes in the path geometry of the dyke migration toward the surface. The final phase involved magma ascent through a prefractured crust.

Full moment tensor retrieval and fluid dynamics in volcanic areas: The case of phlegraean field (south Italy)

International Nuclear Information System (INIS)

Campus, P.; Cespuglio, G.

1994-04-01

When studying seismicity in volcanic areas it is appropriate to treat the seismic source in a form a priori not restricted to a double couple, since its mechanism may reflect not only small scale tectonics but also fluid dynamics. The monitoring of fluid dynamics can be therefore attempted from the retrieval of the rupture processes. It is not possible to use standard methods, based on the distribution of polarities of first arrivals to determine the non double-couple components of the seismic source. The new method presented here is based on the wave form inversion of the dominant part of the seismograms, where the signal to noise ratio is very large and allows the inversion of the full seismic moment tensor. The results of a pilot study in the Phlegraean Fields (South Italy) are presented. 13 refs, 10 figs, 4 tabs

Sub-crustal seismic activity beneath Klyuchevskoy Volcano

Science.gov (United States)

Carr, M. J.; Droznina, S.; Levin, V. L.; Senyukov, S.

2013-12-01

Seismic activity is extremely vigorous beneath the Klyuchevskoy Volcanic Group (KVG). The unique aspect is the distribution in depth. In addition to upper-crustal seismicity, earthquakes take place at depths in excess of 20 km. Similar observations are known in other volcanic regions, however the KVG is unique in both the number of earthquakes and that they occur continuously. Most other instances of deep seismicity beneath volcanoes appear to be episodic or transient. Digital recording of seismic signals started at the KVG in early 2000s.The dense local network reliably locates earthquakes as small as ML~1. We selected records of 20 earthquakes located at depths over 20 km. Selection was based on the quality of the routine locations and the visual clarity of the records. Arrivals of P and S waves were re-picked, and hypocentral parameters re-established. Newl locations fell within the ranges outlined by historical seismicity, confirming the existence of two distinct seismically active regions. A shallower zone is at ~20 km depth, and all hypocenters are to the northeast of KVG, in a region between KVG and Shiveluch volcano. A deeper zone is at ~30 km, and all hypocenters cluster directly beneath the edifice of the Kyuchevskoy volcano. Examination of individual records shows that earthquakes in both zones are tectonic, with well-defined P and S waves - another distinction of the deep seismicity beneath KVG. While the upper seismic zone is unquestionably within the crust, the provenance of the deeper earthquakes is enigmatic. The crustal structure beneath KVG is highly complex, with no agreed-upon definition of the crust-mantle boundary. Rather, a range of values, from under 30 to over 40 km, exists in the literature. Similarly, a range of velocity structures has been reported. Teleseismic receiver functions (RFs) provide a way to position the earthquakes with respect to the crust-mantle boundary. We compare the differential travel times of S and P waves from deep

Geodynamic Constraints on the Sources of Seismic Anisotropy Beneath Madagascar

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Rajaonarison, T. A.; Stamps, D. S.; Fishwick, S.

2017-12-01

The rheological structure of the lithosphere-asthenosphere system controls the degree in which the mantle drives surface motions. Seismic anisotropy is a proxy to infer information about previous tectonic events imprinted in lithospheric structures and/or asthenospheric flow pattern in regions absent of active volcanism, however, distinguishing between the shallow and deeper sources, respectively, remains ambiguous. Madagascar is an ideal natural laboratory to study the sources of anisotropy and the rheological implications for lithosphere-asthenosphere system because 1) active volcanism is minimal or absent, 2) there are well-exposed tectonic fabrics for comparison, and 3) numerous geological and geophysical observations provides evidence of present-day tectonic activities. Recent studies suggest new seismic anisotropy observations in southern Madagascar are sourced from both fossilized lithospheric structure and asthenospheric flow driven by rigid lithospheric plate motion. In this work we compare geodynamic simulations of the lithosphere-asthenosphere system with seismic anisotropy data set that includes all of Madagascar. We use the numerical code Advanced Solver for Problems in Earth's ConvecTion (ASPECT) to calculate instantaneous deformation in the lithosphere and edge-driven convective flow in the asthenosphere accounting for variations in buoyancy forces and temperature dependent viscosity. The initial temperature conditions are based on interpretations from high resolution regional surface wave tomography. We assume visco-plastic rheology for a uniform crust, dislocation creep for a laterally varying mantle lithospheric structure, and diffusion creep for the asthenosphere. To test for the source of anisotropy we compare our velocity solution azimuths with azimuths of anisotropy at 25 km depth intervals. Calculated asthenospheric flow aligns with measured seismic anisotropy with a 15° WRMS at 175 km depth and possibly down to 250 km suggesting the

Missing Magmas: A Multidisciplinary Effort to Understand a Seismic Anomaly in the Chilean Flat Slab (28°-33°S)

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Domino, J.; Bourke, J. R.; Naslund, H. R.; Nikulin, A.

2017-12-01

A gap in the volcanic arc across the Pampean section of the Chilean subduction zone (28-33°S) breaks up the otherwise predictable pattern of South American volcanism. This gap in the volcanic front, accompanied by diminished interplate seismic activity, correlates to the onset of flat slab subduction of the segmented Nazca Plate. We present results of a multidisciplinary study combining geophysical and petrologic observations, focused on the processes influencing subduction zone geometry in Central Chile and their impact on regional seismic and volcanic activity. Through a broad-scale receiver function survey obtained from existing permanent stations in Central Chile, we imaged the position of the subducting Nazca Plate beneath South America and created corresponding depth-converted images to further interpret the underlying structure. This survey reveals evidence of a highly anisotropic layer above the subducting slab beneath station GO03 of the Chilean National Seismic Network, possibly indicating an area of extensive hydration triggered by fluid release from the subducting plate. By imaging the interplate region to the north of the flat slab, we constrained the lateral extent of the anisotropic layer and made an attempt to correlate the character of the identified geophysical anomaly to geochemical patterns exhibited by active volcanoes in the region. A detailed compilation of available geochemical data was done to understand any existing cross-arc or along-arc variations that could be attributed to the geometry of the subducting slab over time, focused on trace element trends that are indicative of interactions with hydrated mantle. Our results indicate a correlation between the observed anisotropic layer and changes in the geochemistry of the closest spatial volcanism through time as the geometry of flat slab subduction evolved. By combining the receiver function results with initial petrologic observations, it is our goal to further constrain the inherent

Processing of radon time series in underground environments: Implications for volcanic surveillance in the island of Tenerife, Canary Islands, Spain

International Nuclear Information System (INIS)

Vinas, Ronaldo; Eff-Darwich, Antonio; Soler, Vicente; Martin-Luis, Maria C.; Quesada, Maria L.; Nuez, Julio de la

2007-01-01

The analysis of temporal and spatial variations in the flux of soil gases across the soil-air interface is a useful tool to study geo-dynamical processes associated with volcanic and/or seismic activity. However, many of these variations are induced by external variables, such as temperature, barometric pressure, rainfall and other meteorological variables. In an attempt to filter out non-endogenous variations in the emissions of gases, the optimal choice of the monitoring sites with numerical filtering techniques based on multi-variate and frequency domain analysis of the time series for gaseous emissions were combined, in the case of radon ( 222 Rn). Monitoring sites are located in underground galleries in the volcanic island of Tenerife, Canary Islands, Spain. Since the effect of wind, rainfall and temperature variations are very small inside galleries, a first natural filtering process of external parameters in the emissions of gases was achieved. This new approach has been successfully tested and as a result, the background level for radon emissions at various locations has been defined, by which correlations between gaseous emissions and the volcanic and/or seismic activity could be carried out

Characteristics of the seismicity of Vesuvius and Campi Flegrei during the year 2000

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G. Talarico

2001-06-01

Full Text Available This paper describes the characteristics of the seismicity in the volcanic Neapolitan area during the year 2000 recorded by the monitoring seismic network of the Osservatorio Vesuviano. In particular, a detailed analysis of the seismicity of Vesuvius is presented. We compared the seismic velocity models available for the Vesuvius area locating the earthquakes recorded in the year 2000 and on the basis of the results, we introduce for routine earthquake location the new velocity model obtained by the seismic tomography experiments (TomoVes performed in the area. We also determined the focal mechanisms and analysed the seismicity rate, comparing the results with those obtained for the past years. After the introduction of the new acquisition system at the Osservatorio Vesuviano, a re-calibration of the duration magnitude scale was necessary to avoid biases related to the different instrumental response. Consequently, we re-calibrated the magnitude relation used for the Vesuvius earthquakes, obtaining a new formula to be used for the earthquakes recorded by the new acquisition system. Finally, we give a description of the seismic activity in the Campi Flegrei area during the summer of 2000.

Sedimentation influx and volcanic interactions in the Fuji Five Lakes: implications for paleoseismological records

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Lamair, Laura; Hubert-Ferrari, Aurélia; Yamamoto, Shinya; El Ouahabi, Meriam; Garrett, Ed; Shishikura, Masanobu; Schmidt, Sabine; Boes, Evelien; Obrochta, Stephen; Nakamura, Atsunori; Miyairi, Yosuke; Yokoyama, Yusuke; De Batist, Marc; Heyvaert, Vanessa M. A.

2017-04-01

The Fuji Fives Lakes are located at the foot of Mount Fuji volcano close to the triple junction, where the North American Plate, the Eurasian plate and the Philippine Sea Plate meet. These lakes are ideally situated to study Mount Fuji volcanism and the interaction between volcanism, changes in lake sedimentation rates and the ability of lakes to record paleoearthquakes. Here, we present newly acquired geological data of Lake Yamanaka and Lake Motosu, including seismic reflection profiles, gravity and piston cores. These two lakes and their respective watersheds were affected by several eruptions of Mount Fuji. Lake Yamanaka, a very shallow lake (max. depth 14 m), was heavily impacted by the scoria fall-out of the A.D. 1707 Hoei eruption of Mount Fuji. A detailed investigation of the effect of the Hoei eruption was conducted on short gravity cores, using high resolution XRD, C/N and 210Pb/137Cs analyses. The preliminary results suggest that the sedimentation rate of Lake Yamanaka drastically reduced after the Hoei eruption, followed by an increase until the present day. Similarly, lacustrine sedimentation in Lake Motosu (max. depth 122 m) was disturbed by Mount Fuji volcanism at a larger scale. The watershed of Lake Motosu was impacted by several lava flows and scoria cones. For example, the Omuro scoria cone reduced the catchment size of Lake Motosu and modified its physiography. The related scoria fall out covered an extensive part of the lake catchment and reduced terrigenous sedimentary influx to Lake Motosu. Within the deep basin of Lake Motosu, seismic reflection data shows two different periods that are distinguished by a major change in the dominant sedimentary processes. During the first period, sublacustrine landslides and turbidity currents were the dominant sedimentation processes. During the second one, the seismic stratigraphy evidences only deposition of numerous turbidites interrupting the hemipelagic sedimentation. Changes in sedimentary processes

Multiteide Project: Multiparametric characterization of the activity of Teide-Pico Viejo volcanic system

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Domínguez Cerdeña, Itahiza; Villasante-Marcos, Victor; Meletlidis, Stavros; Sainz-Maza, Sergio; Abella, Rafael; Torres, Pedro A.; Sánchez, Nieves; Luengo-Oroz, Natividad; José Blanco, María; García-Cañada, Laura; Pereda de Pablo, Jorge; Lamolda, Héctor; Moure, David; Del Fresno, Carmen; Finizola, Anthony; Felepto, Alicia

2017-04-01

Teide-Pico Viejo complex stands for one of the major natural volcanic hazards in the Canary Islands, due to the expected types of eruptions in the area and the high number of inhabitants in Tenerife Island. Therefore, it is necessary to have a volcanic alert system able to afford a precise assessment of the current state of the complex. For this purpose, the knowledge of the expected signals at each volcanic activity level is required. Moreover, the external effects that can affect the measurements shall be distinguished, external influences as the atmosphere are qualitatively known but have not been quantified yet. The objective of the project is to collect, analyze and jointly and continuously evaluate over time geophysical, geodetic, geochemical and meteorological data from the Teide-Pico Viejo complex and its surroundings. A continuous multiparametric network have been deployed in the area, which, together with the data provided by the Volcano Monitoring Network of the Instituto Geográfico Nacional (IGN) and data from other institutions will provide a comprehensive set of data with high resolution in both space and time. This multiparametric network includes a seismic array, two self-potential lines for continuous measurements, five magnetometers and two weather stations. The network will be complemented with 8 CGPS stations, one tiltmeter, 10 seismic stations, and four thermometric stations on the fumaroles of Teide volcano that IGN already manage in Tenerife. The data will be completed with the results from different repeated surveys of self potential, soil temperature and CO2 diffuse flux in several pre-established areas on top of Teide throughout the entire duration of project. During the project, new computation tools will be developed to study the correlation between the different parameters analyzed. The results obtained will characterize the possible seasonal fluctuations of each parameter and the variations related to meteorological phenomena. In

Seismic constraints on caldera dynamics from the 2015 Axial Seamount eruption.

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Wilcock, William S D; Tolstoy, Maya; Waldhauser, Felix; Garcia, Charles; Tan, Yen Joe; Bohnenstiehl, DelWayne R; Caplan-Auerbach, Jacqueline; Dziak, Robert P; Arnulf, Adrien F; Mann, M Everett

2016-12-16

Seismic observations in volcanically active calderas are challenging. A new cabled observatory atop Axial Seamount on the Juan de Fuca ridge allows unprecedented real-time monitoring of a submarine caldera. Beginning on 24 April 2015, the seismic network captured an eruption that culminated in explosive acoustic signals where lava erupted on the seafloor. Extensive seismic activity preceding the eruption shows that inflation is accommodated by the reactivation of an outward-dipping caldera ring fault, with strong tidal triggering indicating a critically stressed system. The ring fault accommodated deflation during the eruption and provided a pathway for a dike that propagated south and north beneath the caldera's east wall. Once north of the caldera, the eruption stepped westward, and a dike propagated along the extensional north rift. Copyright © 2016, American Association for the Advancement of Science.

When probabilistic seismic hazard climbs volcanoes: the Mt. Etna case, Italy – Part 1: Model components for sources parameterization

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R. Azzaro

2017-11-01

Full Text Available The volcanic region of Mt. Etna (Sicily, Italy represents a perfect lab for testing innovative approaches to seismic hazard assessment. This is largely due to the long record of historical and recent observations of seismic and tectonic phenomena, the high quality of various geophysical monitoring and particularly the rapid geodynamics clearly demonstrate some seismotectonic processes. We present here the model components and the procedures adopted for defining seismic sources to be used in a new generation of probabilistic seismic hazard assessment (PSHA, the first results and maps of which are presented in a companion paper, Peruzza et al. (2017. The sources include, with increasing complexity, seismic zones, individual faults and gridded point sources that are obtained by integrating geological field data with long and short earthquake datasets (the historical macroseismic catalogue, which covers about 3 centuries, and a high-quality instrumental location database for the last decades. The analysis of the frequency–magnitude distribution identifies two main fault systems within the volcanic complex featuring different seismic rates that are controlled essentially by volcano-tectonic processes. We discuss the variability of the mean occurrence times of major earthquakes along the main Etnean faults by using an historical approach and a purely geologic method. We derive a magnitude–size scaling relationship specifically for this volcanic area, which has been implemented into a recently developed software tool – FiSH (Pace et al., 2016 – that we use to calculate the characteristic magnitudes and the related mean recurrence times expected for each fault. Results suggest that for the Mt. Etna area, the traditional assumptions of uniform and Poissonian seismicity can be relaxed; a time-dependent fault-based modeling, joined with a 3-D imaging of volcano-tectonic sources depicted by the recent instrumental seismicity, can therefore be

Glacial removal of late Cenozoic subglacially emplaced volcanic edifices by the West Antarctic ice sheet

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Behrendt, John C.; Blankenship, D.D.; Damaske, D.; Cooper, A. K.

1995-01-01

Local maxima of the horizontal gradient of pseudogravity from closely spaced aeromagnetic surveys over the Ross Sea, northwestern Ross Ice Shelf, and the West Antarctic ice sheet, reveal a linear magnetic rift fabric and numerous subcircular, high-amplitude anomalies. Geophysical data indicate two or three youthful volcanic edifices at widely separated areas beneath the sea and ice cover in the West Antarctic rift system. In contrast, we suggest glacial removal of edifices of volcanic sources of many more anomalies. Magnetic models, controlled by marine seismic reflection and radar ice-sounding data, allow us to infer that glacial removal of the associated late Cenozoic volcanic edifices (probably debris, comprising pillow breccias, and hyaloclastites) has occurred essentially concomitantly with their subglacial eruption. "Removal' of unconsolidated volcanic debris erupted beneath the ice is probably a more appropriate term than "erosion', given its fragmented, ice-contact origin. The exposed volcanoes may have been protected from erosion by the surrounding ice sheet because of more competent rock or high elevation above the ice sheet. -from Authors

Volcanic Eruptions and Climate

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LeGrande, Allegra N.; Anchukaitis, Kevin J.

2015-01-01

Volcanic eruptions represent some of the most climatically important and societally disruptive short-term events in human history. Large eruptions inject ash, dust, sulfurous gases (e.g. SO2, H2S), halogens (e.g. Hcl and Hbr), and water vapor into the Earth's atmosphere. Sulfurous emissions principally interact with the climate by converting into sulfate aerosols that reduce incoming solar radiation, warming the stratosphere and altering ozone creation, reducing global mean surface temperature, and suppressing the hydrological cycle. In this issue, we focus on the history, processes, and consequences of these large eruptions that inject enough material into the stratosphere to significantly affect the climate system. In terms of the changes wrought on the energy balance of the Earth System, these transient events can temporarily have a radiative forcing magnitude larger than the range of solar, greenhouse gas, and land use variability over the last millennium. In simulations as well as modern and paleoclimate observations, volcanic eruptions cause large inter-annual to decadal-scale changes in climate. Active debates persist concerning their role in longer-term (multi-decadal to centennial) modification of the Earth System, however.

Soil gas 222Rn and volcanic activity at El Hierro (Canary Islands) before and after the 2011 submarine eruption

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Padilla, G.; Hernández, P. A.; Padrón, E.; Barrancos, J.; Melián, G.; Dionis, S.; Rodríguez, F.; Nolasco, D.; Calvo, D.; Hernández, I.; Pereza, M. D.; Pérez, N. M.

2012-04-01

El Hierro (278 km2) is the southwesternmost island of the Canarian archipelago. From June 19, 2011 to January 2012, more than 11,950 seismic events have been detected by the seismic network of IGN. On 10 October 2011 the earthquake swarm changed its behaviour and produced a harmonic tremor due to magma movement, indicating that a submarine eruption located at 2 km south of La Restinga had started which is still in progress. Since 2003, the ITER Environmental Research Division now integrated in the Instituto Volcanológico de Canarias, INVOLCAN, has regularly performed soil gas surveys at El Hierro as a geochemical tool for volcanic surveillance. Among the investigated gases, soil gas radon (222Rn) and thoron (220Rn) have played a special attention. Both gases are characterized to ascend towards the surface mainly through cracks or faults via diffusion or advection, mechanisms dependent of both soil porosity and permeability, which in turn vary as a function of the stress/strain changes at depth. Years before the starts of the volcanic-seismic crisis on July 17, 2011, a volcanic multidisciplinary surveillance program was implemented at El Hierro including discrete and continuous measurements of 222Rn and 220Rn. Two soil gas 222Rn surveys had been carried out at El Hierro in 2003 and 2011, and four continuous geochemical monitoring stations for 222Rn and 220Rn measurements had been installed (HIE02, HIE03, HIE04 and HIE08). Soil gas 222Rn surveys were carried out at the surface environment of El Hierro after selecting 600 sampling observation sites (about 40 cm depth). Geochemical stations measure 222Rn and 220Rn activities by pumping the gas from a PVC pipe inserted 1m in the ground and thermally isolated. The results of the 2003 and 2011 soil gas 222Rn surveys show clearly a relatively higher observed 222Rn activities in the surface environment on 2011 than those observed on 2003 when no anomalous seismicity were taking place beneath El Hierro. The observed

Imaging an off-axis volcanic field in the Main Ethiopian Rift using 3-D magnetotellurics

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Huebert, J.; Whaler, K. A.; Fisseha, S.; Hogg, C.

2017-12-01

In active continental rifts, asthenospheric upwelling and crustal thinning result in the ascent of melt through the crust to the surface. In the Main Ethiopian Rift (MER), most volcanic activity is located in magmatic segments in the rift centre, but there are areas of significant off-axis magmatism as well. The Butajira volcanic field is part of the Silti Debre Zeyt Fault (SDZF) zone in the western Main Ethiopian Rift. It is characterized by densely clustered volcanic vents (mostly scoria cones) and by limited seismic activity, which is mainly located along the big border faults that form the edge of a steep escarpment. Seismic P-Wave tomography reveals a crustal low velocity anomaly in this area. We present newly collected Magnetotelluric (MT) data to image the electrical conductivity structure of the area. We deployed 12 LMT instruments and 27 broadband stations in the western flank of the rift to further investigate the along-rift and depth extent of a highly conductive region under the SDZF which was previously identified by MT data collected on the central volcano Aluto and along a cross-rift transverse. This large conductor was interpreted as potential pathways for magma and fluid in the crust. MT Stations were positioned in five NW-SE running 50 km long profiles, covering overall 100km along the rift and providing good coverage for a 3-D inversion of the data to image this enigmatic area of the MER.

Toward Assessing the Causes of Volcanic Diversity in the Cascades Arc

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Till, C. B.; Kent, A. J.; Abers, G. A.; Pitcher, B.; Janiszewski, H. A.; Schmandt, B.

2017-12-01

and quantities of evolved magma. When we compare our Quaternary heat flux calculations to a variety of geophysical observations, we find that regions of calculated higher volcanic heat flux coincide with regions of significantly lower crustal seismic wave speeds beneath and behind the arc, as well as with regions of significantly higher heat flow.

Seismic Structure of the Oceanic Plate Entering the Central Part of the Japan Trench Obtained from Ocean-Bottom Seismic Data

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Ohira, A.; Kodaira, S.; Fujie, G.; No, T.; Nakamura, Y.; Miura, S.

2017-12-01

In trench-outer rise regions, the normal faults develop due to the bending of the incoming plate, which cause numerous normal-faulting earthquakes and systematic structural variations toward trenches. In addition to the effects on the bend-related normal fault, structural variations which are interpreted to be attributed to pseudofaults, a fracture zone, and petit-spot volcanic activities are observed in the oceanic plate entering the central part of the Japan Trench, off Miyagi. In May-June 2017, to understand detail structural variations and systematic structural changes of the oceanic plate toward the trench, we conducted an active-source seismic survey off Miyagi using R/V Kaimei, a new research vessel of JAMSTEC. Along a 100 km-long seismic profile which is approximately perpendicular to the trench axis, we deployed 40 ocean-bottom seismometers at intervals of 2 km and fired a large airgun array (total volume 10,600 cubic inches) with 100 m shooting intervals. Multi-channel seismic reflection data were also collected along the profile. On OBS records we observed refractions from the sedimentary layer and the oceanic crust (Pg), wide-angle reflections from the crust-mantle boundary (PmP), and refractions from the uppermost mantle (Pn). Pg is typically observed clearly at near offsets (approximately 20 km) but it highly attenuates at far offsets (> 20 km). A triplication of Pg-PmP-Pn with strong amplitudes is observed at ranges from 30 km to 60 km offsets. Pn is typically weak and its apparent velocity is approximately 8 km/sec. High attenuation of Pg and weak Pn may indicate the complex crustal structure related to petit-spot volcanic activities and/or a fracture zone, which are recognized in bathymetry data around the profile.

Monitoring diffuse volcanic degassing during volcanic unrests: the case of Campi Flegrei (Italy).

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Cardellini, C; Chiodini, G; Frondini, F; Avino, R; Bagnato, E; Caliro, S; Lelli, M; Rosiello, A

2017-07-28

In volcanoes with active hydrothermal systems, diffuse CO 2 degassing may constitute the primary mode of volcanic degassing. The monitoring of CO 2 emissions can provide important clues in understanding the evolution of volcanic activity especially at calderas where the interpretation of unrest signals is often complex. Here, we report eighteen years of CO 2 fluxes from the soil at Solfatara of Pozzuoli, located in the restless Campi Flegrei caldera. The entire dataset, one of the largest of diffuse CO 2 degassing ever produced, is made available for the scientific community. We show that, from 2003 to 2016, the area releasing deep-sourced CO 2 tripled its extent. This expansion was accompanied by an increase of the background CO 2 flux, over most of the surveyed area (1.4 km 2 ), with increased contributions from non-biogenic source. Concurrently, the amount of diffusively released CO 2 increased up to values typical of persistently degassing active volcanoes (up to 3000 t d -1 ). These variations are consistent with the increase in the flux of magmatic fluids injected into the hydrothermal system, which cause pressure increase and, in turn, condensation within the vapor plume feeding the Solfatara emission.

Seismic moment tensor for anisotropic media: implication for Non-double-couple earthquakes

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Cai, X.; Chen, X.; Chen, Y.; Cai, M.

2008-12-01

It is often found that the inversion results of seismic moment tensor from real seismic recorded data show the trace of seismic moment tensor M is not zero, a phenomenon called non-double-couple earthquake sources mechanism. Recently we have derived the analytical expressions of M in transversely isotropic media with the titled axis of symmetry and the results shows even only pure shear-motion of fault can lead to the implosive components determined by several combined anisotropic elastic constants. Many non-double-couple earthquakes from observations often appear in volcanic and geothermal areas (Julian, 1998), where there exist a mount of stress-aligned fluid-saturated parallel vertical micro-cracks identical to transversely isotropic media (Crampin, 2008), this stress-aligned crack will modify the seismic moment tensor. In another word, non-double-couple earthquakes don't mean to have a seismic failure movement perpendicular to the fault plane, while traditional research of seismic moment tensor focus on the case of isotropy, which cannot provide correct interpretation of seismic source mechanism. Reference: Julian, B.R., Miller, A.D. and Foulger, G.R., 1998. Non-double-couple earthquakes,1. Theory, Rev. Geophys., 36, 525¨C549. Crampin,S., Peacock,S., 2008, A review of the current understanding of seismic shear-wave splitting in the Earth's crust and common fallacies in interpretation, wave motion, 45,675-722

The ascent of magma as determined by seismic tomography. The visualization of velocity structure and magma distribution from upper mantle to upper crust in Hakone volcano, northern Izu peninsula

International Nuclear Information System (INIS)

Abe, Shintaro; Aoyagi, Yasuhira; Toshida, Kiyoshi; Oda, Yoshiya

2003-01-01

Three-dimensional seismic reflection and refraction survey was carried out in Hakone volcanic area, northern part of Izu peninsula. The region is one of the most famous hot spring areas in Japan. Hakone volcano morphologically resembles one big caldera. However, the depression of the volcano consists of several small calderas which has been formed by multiple eruptions. Although sprouts of fumarolic gas and steam are identified in a few areas of the volcano, there is no historical record of volcanic eruption. Main purpose of our study is to determine the 3-dimensional deep velocity structure around the volcano using the seismic tomography processing. We deployed 44 sets of temporal offline seismic stations and a line of multi-channels seismic reflection survey cable. The seismic waves generated by some natural earthquakes and 14 dynamite explosions were observed, and their data were processed for tomography. The observation coverage was 20 km in diameter. Our result demonstrates the usefulness of high dense seismic observation in identifying and locating low velocity zones beneath the particular area. According to our tomography, low velocity zone was identified only in surface layer of the old caldera part of the volcano. We could not identify any remarkable reflector in deeper crust, as the result of wide-angle reflection survey using explosive shots. Moreover, we could not identify any other low velocity zone as far as 32 km depth by incorporating the results of other study. In other words, we think that magma is no longer supplied to Hakone volcanic area. (author)

Time-resolved seismic tomography detects magma intrusions at Mount Etna.

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Patanè, D; Barberi, G; Cocina, O; De Gori, P; Chiarabba, C

2006-08-11

The continuous volcanic and seismic activity at Mount Etna makes this volcano an important laboratory for seismological and geophysical studies. We used repeated three-dimensional tomography to detect variations in elastic parameters during different volcanic cycles, before and during the October 2002-January 2003 flank eruption. Well-defined anomalous low P- to S-wave velocity ratio volumes were revealed. Absent during the pre-eruptive period, the anomalies trace the intrusion of volatile-rich (>/=4 weight percent) basaltic magma, most of which rose up only a few months before the onset of eruption. The observed time changes of velocity anomalies suggest that four-dimensional tomography provides a basis for more efficient volcano monitoring and short- and midterm eruption forecasting of explosive activity.

Seismicity Structure of the Downgoing Nazca Slab in Northern Chile

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Sippl, C.; Schurr, B.

2017-12-01

We applied an automatized earthquake detection and location algorithm to 8 years of continuous seismic data from the IPOC network in Northern Chile, located in the forearc between about 18.5°S and 24°S. The resulting seismicity catalog contains more than 113k double-difference relocated earthquake hypocenters and features a completeness magnitude around 2.8. Despite the occurrence of two megathrust earthquakes with vigorous aftershock seismicity in the studied time period (the 2007 Tocopilla and the 2014 Iquique earthquakes), >60% of the retrieved seismicity is located in a highly active band of intermediate-depth earthquakes (80-120 km deep) within the downgoing Nazca slab.We obtain a triple seismic zone in the updip part of the slab, with the three parallel dipping planes corresponding to the plate interface, the oceanic Moho (ca. 8 km below the interface) and a third band in the mantle lithosphere 26-28 km beneath the slab top. The plate interface seismicity terminates abruptly at a depth of 55 km. At about 80-90 km depth, the remaining two planes of seismicity then merge into the single, 20 km thick cluster of vigorous seismicity mentioned above, which terminates at 120 km depth. This cluster is located directly beneath the volcanic arc and shows a pronounced kink in the slab dipping angle. Intra-slab seismicity is most likely related to metamorphic dehydration reactions, hence our high-resolution earthquake distribution can be considered a map of metamorphic reactions (although a possibly incomplete one, since not all reactions necessarily invoke seismicity). By correlating this distribution with isotherms from thermal models as well as geophysical imaging results from previous studies, we attempt to get a glimpse at the processes that produce the different patches of intraslab seismicity at intermediate depths.

Seasonal patterns of seismicity and deformation at the Alutu geothermal reservoir, Ethiopia, induced by hydrological loading

Science.gov (United States)

Birhanu, Yelebe; Wilks, Matthew; Biggs, Juliet; Kendall, J.-Michael; Ayele, Atalay; Lewi, Elias

2018-05-01

Seasonal variations in the seismicity of volcanic and geothermal reservoirs are usually attributed to the hydrological cycle. Here, we focus on the Aluto-Langano geothermal system, Ethiopia, where the climate is monsoonal and there is abundant shallow seismicity. We deployed temporary networks of seismometers and GPS receivers to understand the drivers of unrest. First, we show that a statistically significant peak in seismicity occurred 2-3 months after the main rainy season, with a second, smaller peak of variable timing. Seasonal seismicity is commonly attributed to variations in either surface loading or reservoir pore pressure. As loading will cause subsidence and overpressure will cause uplift, comparing seismicity rates with continuous GPS, enables us to distinguish between mechanisms. At Aluto, the major peak in seismicity is coincident with the high stand of nearby lakes and maximum subsidence, indicating that it is driven by surface loading. The magnitude of loading is insufficient to trigger widespread crustal seismicity but the geothermal reservoir at Aluto is likely sensitive to small perturbations in the stress field. Thus we demonstrate that monsoonal loading can produce seismicity in geothermal reservoirs, and the likelihood of both triggered and induced seismicity varies seasonally.

Analysis of the geometry of diabase sills of the Serra Geral magmatism, by 2D seismic interpretation, in Guareí region, São Paulo, Paraná basin, Brazil

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Diego Felipe Bezerra da Costa

Full Text Available ABSTRACT: The Paraná Basin holds in its stratigraphic record a thick layer of volcanic rocks related to the opening of the Gondwana Supercontinent, which occurred during the Eocretaceous. Based on the interpretation of three two-dimensional (2D seismic lines in the region of Guareí, East-Central São Paulo state, in the Southeast of Brazil, the subsurface geometries of these volcanic rocks were identified. Since the original seismic resolution quality was low, alternative techniques were utilized to improve the seismic imaging, such as isolating maximum and minimum amplitude values by manipulating the color scale, and using the root mean square (RMS attribute and the Amplitude Volume technique (tecVA, which emphasize the seismic signature of igneous rocks in relation to sedimentary layers. The use of such techniques allowed the identification of different geometries of diabase sills and showed a relationship between these intrusive and organic matter maturation of the source rock.

Plagioclase-dominated Seismic Anisotropy in the Basin and Range Lower Crust

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Bernard, R. E.; Behr, W. M.

2017-12-01

Observations of seismic anisotropy have the ability to provide important information on deformation and structures within the lithosphere. While the mechanisms controlling seismic anisotropy in the upper mantle are fairly well understood (i.e., olivine "lattice preferred orientation" or LPO), less is known about the minerals and structures controlling regional lower crustal anisotropy. We use lower crustal xenoliths from young cinder cones in the eastern Mojave/western Basin and Range to investigate mineral LPOs and their effect on seismic anisotropy. Lower crustal gabbros were collected from two areas roughly 80 km apart — the Cima and Deadman Lake Volcanic Fields. Lower crustal fabrics measured using EBSD are dominated by LPOs in plagioclase associated with both plastic deformation and magmatic flow. In all fabric types, plagioclase LPOs produce seismic fast axes oriented perpendicular to the foliation plane. This is in contrast to mantle peridotite xenoliths from the same locations, which preserve olivine LPOs with fast axes aligned parallel to the foliation plane. The orthogonal orientations of mantle and lower crustal fast axes relative to foliation implies that even where fabric development in both layers is coeval and kinematically compatible, their measured anisotropies can be perpendicular to each other, therefore appearing anti-correlated when measured seismically. Furthermore, our observation of plagioclase-dominated LPO and negligible concentrations of mica is at odds with the common assumption that lower crustal anisotropy is dominated by micaceous minerals, whose slow axes reliably align parallel to lineation or flow. In contrast, our data show that for plagioclase, fast axes align perpendicular to flow and the slow axes are variably aligned within the foliation plane. Therefore, for a crustal section dominated by plagioclase LPO with assumed horizontal foliation, there would be a vertical rather than a horizontal axis of symmetry, resulting in a

When probabilistic seismic hazard climbs volcanoes: the Mt. Etna case, Italy - Part 2: Computational implementation and first results

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Peruzza, Laura; Azzaro, Raffaele; Gee, Robin; D'Amico, Salvatore; Langer, Horst; Lombardo, Giuseppe; Pace, Bruno; Pagani, Marco; Panzera, Francesco; Ordaz, Mario; Suarez, Miguel Leonardo; Tusa, Giuseppina

2017-11-01

This paper describes the model implementation and presents results of a probabilistic seismic hazard assessment (PSHA) for the Mt. Etna volcanic region in Sicily, Italy, considering local volcano-tectonic earthquakes. Working in a volcanic region presents new challenges not typically faced in standard PSHA, which are broadly due to the nature of the local volcano-tectonic earthquakes, the cone shape of the volcano and the attenuation properties of seismic waves in the volcanic region. These have been accounted for through the development of a seismic source model that integrates data from different disciplines (historical and instrumental earthquake datasets, tectonic data, etc.; presented in Part 1, by Azzaro et al., 2017) and through the development and software implementation of original tools for the computation, such as a new ground-motion prediction equation and magnitude-scaling relationship specifically derived for this volcanic area, and the capability to account for the surficial topography in the hazard calculation, which influences source-to-site distances. Hazard calculations have been carried out after updating the most recent releases of two widely used PSHA software packages (CRISIS, as in Ordaz et al., 2013; the OpenQuake engine, as in Pagani et al., 2014). Results are computed for short- to mid-term exposure times (10 % probability of exceedance in 5 and 30 years, Poisson and time dependent) and spectral amplitudes of engineering interest. A preliminary exploration of the impact of site-specific response is also presented for the densely inhabited Etna's eastern flank, and the change in expected ground motion is finally commented on. These results do not account for M > 6 regional seismogenic sources which control the hazard at long return periods. However, by focusing on the impact of M risk reduction.

Seismic environment of Deccan Volcanic Province (DVP) and its suitability for location of new nuclear power plants in India - a few geoscientific opinions

International Nuclear Information System (INIS)

Sinha, D.K.; Parihar, P.S.

2014-01-01

India has an ambitious programme to expand the nuclear power capacity to 60 GWe by 2032 and 655 GWe by 2050. Such an exponential growth of nuclear power generation warranty identification of suitable sites for nuclear power reactors. Perhaps the 6000 km long vast coastline is the best choice for siting new NPPs because of ready availability of sea water and a quiet seismic environment. Large inland areas with adequate water resources provide additional locations to cater the power requirements of Central and Northern India. In this perspective, the potentials of Deccan Volcanic Province (DVP) for siting new NPPs is discussed. Five zones delineated as safer sites of nuclear power plants on Deccan Trap, are the first hand targets identified by this study. Two of them are situated to the north of Narmada-Son Lineament and have large areas. Chambal and Betwa river systems of Ganga Basin are perennial source of water along with several dams constructed on their course. The other three zones are located to the south of Narmada-Son Lineament and are small in size. The Konkan Coastal Lineament (N-S) in the west and Kurduwadi Lineament (NW-SE) in the east are major tectonic features bordering these zones. The Godavari and Krishna rivers are perennial water sources. Presence of reservoirs within the delineated zones stands advantageous considering their potential as ultimate heat sinks. All the five zones are devoid of any known major seismicity. Thick basalt cover provides good foundation conditions and engineerability for these zones. Considering above characteristics, proposed five zones could be good candidate sites for future NPPs, after their detailed geotechnical investigations. (author)

Origin of seamount volcanism in northeast Indian Ocean with emphasis on Christmas Island

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Taneja, R.; O'Neill, C.; Rushmer, T. A.; Jourdan, F.; Blichert-Toft, J.; Turner, S.; Lackie, M. A.

2012-12-01

The Northeast Indian Ocean has been a central point of research in the recent past due to its intraplate geophysical and geochemical characteristics. It is dominated by sub-aerial volcanic islands and submerged guyots and two islands, namely, Cocos (Keeling) Island and Christmas Island. Christmas Island, the focus of this study, consists of limestone and mafic intraplate volcanics. The origin of most of the features in northeast Indian Ocean is not fully understood. Christmas Island has experienced multiple stages of intraplate volcanic activity as previously established by 40Ar/39Ar radioisotopic analyses of basalts from the island (Hoernl et al., 2011). Here, we present new 40Ar/39Ar ages where the rock samples from Waterfall Spring (WS), Ethel Beach (EB) & Dolly Beach (DB) on the east coast of the island yielded plateau and mini-plateau ages of 37.75±0.77 Ma, 37.10±0.66 Ma and 43.37±0.45 Ma respectively, whereas a sample from Flying Fish Cove (FFC) in the north of the island yielded a minimum age of 38.6±0.5 Ma. All these units are part of the Lower Volcanics Series. The samples from the west coast (Winifred Beach, WB) are younger with an age of 4.32 ± 0.17 Ma, and are part of the Upper Volcanic Series. This confirms two stages of volcanism at the island with a gap of around 38 Ma. The 40Ar/39Ar radioisotopic ages were overlayed on Gplates and seismic tomography models to determine its paleo motion. The present position of the island is 10.5°S, 105.5°E. During Eocene its reconstructed position was 30°S latitude. Seismic tomography models have highlighted a low velocity zone beneath the island during Eocene. Geochemically, the two volcanic suites (Upper & Lower) are mostly similar in their major and trace element composition. The majority of localities (WS, EB, and WB) are basanites; where as that from Dolly Beach is basaltic. The Dale's (west coast), are trachyte and appear evolved with high SiO2. They also have low Ba and Sr ~25ppm, whereas those from

Crustal rifting and magmatic underplating in the Izu-Ogasawara (Bonin) intra-oceanic arc detected by active source seismic studies

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Takahashi, N.; Kodaira, S.; Yamashita, M.; Miura, S.; Sato, T.; No, T.; Tatsumi, Y.; Kaneda, Y.

2009-12-01

Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has carried out seismic experiments using a multichannel reflection system and ocean bottom seismographs (OBSs) in the Izu-Ogasawara (Bonin)-Mariana (IBM) arc region since 2002 to understand growth process of continental crust. The source was an airgun array with a total capacity of 12,000 cubic inches and the OBSs as the receiver were deployed with an interval of 5 km for all seismic refraction experiments. As the results, we obtained crustal structures across the whole IBM arc with an interval of 50 km and detected the structural characteristics showing the crustal growth process. The IBM arc is one of typical oceanic island arc, which crustal growth started from subduction of an oceanic crust beneath the other oceanic crust. The arc crust has developed through repeatedly magmatic accretion from subduction slab and backarc opening. The volcanism has activated in Eocene, Oligocene, Miocene and Quaternary (e.g., Taylor, 1992), however, these detailed locations of past volcanic arc has been remained as one of unknown issues. In addition, a role of crustal rifting for the crustal growth has also been still unknown issue yet. Our seismic structures show three rows of past volcanic arc crusts except current arc. A rear arc and a forearc side have one and two, respectively. The first one, which was already reported by Kodaira et al. (2008), distributes in northern side from 27 N of the rear arc region. The second one, which develops in the forearc region next to the recent volcanic front, distributes in whole of the Izu-Ogasawara arc having crustal variation along arc direction. Ones of them sometimes have thicker crust than that beneath current volcanic front and no clear topographic high. Last one in the forearc connects to the Ogasawara Ridge. However, thickest crust is not always located beneath these volcanic arcs. The initial rifting region like the northern end of the Mariana Trough and the Sumisu

Geophysical Evidence for the Locations, Shapes and Sizes, and Internal Structures of Magma Chambers beneath Regions of Quaternary Volcanism

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Iyer, H. M.

1984-04-01

This paper is a review of seismic, gravity, magnetic and electromagnetic techniques to detect and delineate magma chambers of a few cubic kilometres to several thousand cubic kilometres volume. A dramatic decrease in density and seismic velocity, and an increase in seismic attenuation and electrical conductivity occurs at the onset of partial melting in rocks. The geophysical techniques are based on detecting these differences in physical properties between solid and partially molten rock. Although seismic refraction techniques, with sophisticated instrumentation and analytical procedures, are routinely used for detailed studies of crustal structure in volcanic regions, their application for magma detection has been quite limited. In one study, in Yellowstone National Park, U.S.A., fan-shooting and time-term techniques have been used to detect an upper-crustal magma chamber. Attenuation and velocity changes in seismic waves from explosions and earthquakes diffracted around magma chambers are observed near some volcanoes in Kamchatka. Strong attenuation of shear waves from regional earthquakes, interpreted as a diffraction effect, has been used to model magma chambers in Alaska, Kamchatka, Iceland, and New Zealand. One of the most powerful techniques in modern seismology, the seismic reflection technique with vibrators, was used to confirm the existence of a strong reflector in the crust near Socorro, New Mexico, in the Rio Grande Rift. This reflector, discovered earlier from data from local earthquakes, is interpreted as a sill-like magma body. In the Kilauea volcano, Hawaii, mapping seismicity patterns in the upper crust has enabled the modelling of the complex magma conduits in the crust and upper mantle. On the other hand, in the Usu volcano, Japan, the magma conduits are delineated by zones of seismic quiescence. Three-dimensional modelling of laterally varying structures using teleseismic residuals is proving to be a very promising technique for detecting and

Seismic properties of fluid bearing formations in magmatic geothermal systems: can we directly detect geothermal activity with seismic methods?

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Grab, Melchior; Scott, Samuel; Quintal, Beatriz; Caspari, Eva; Maurer, Hansruedi; Greenhalgh, Stewart

2016-04-01

Seismic methods are amongst the most common techniques to explore the earth's subsurface. Seismic properties such as velocities, impedance contrasts and attenuation enable the characterization of the rocks in a geothermal system. The most important goal of geothermal exploration, however, is to describe the enthalpy state of the pore fluids, which act as the main transport medium for the geothermal heat, and to detect permeable structures such as fracture networks, which control the movement of these pore fluids in the subsurface. Since the quantities measured with seismic methods are only indirectly related with the fluid state and the rock permeability, the interpretation of seismic datasets is difficult and usually delivers ambiguous results. To help overcome this problem, we use a numerical modeling tool that quantifies the seismic properties of fractured rock formations that are typically found in magmatic geothermal systems. We incorporate the physics of the pore fluids, ranging from the liquid to the boiling and ultimately vapor state. Furthermore, we consider the hydromechanics of permeable structures at different scales from small cooling joints to large caldera faults as are known to be present in volcanic systems. Our modeling techniques simulate oscillatory compressibility and shear tests and yield the P- and S-wave velocities and attenuation factors of fluid saturated fractured rock volumes. To apply this modeling technique to realistic scenarios, numerous input parameters need to be indentified. The properties of the rock matrix and individual fractures were derived from extensive literature research including a large number of laboratory-based studies. The geometries of fracture networks were provided by structural geologists from their published studies of outcrops. Finally, the physical properties of the pore fluid, ranging from those at ambient pressures and temperatures up to the supercritical conditions, were taken from the fluid physics

Time lag between deformation and seismicity along monogenetic volcanic unrest periods: The case of El Hierro Island (Canary Islands)

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Lamolda, Héctor; Felpeto, Alicia; Bethencourt, Abelardo

2017-07-01

Between 2011 and 2014 there were at least seven episodes of magmatic intrusion in El Hierro Island, but only the first one led to a submarine eruption in 2011-2012. In order to study the relationship between GPS deformation and seismicity during these episodes, we compare the temporal evolution of the deformation with the cumulative seismic energy released. In some of the episodes both deformation and seismicity evolve in a very similar way, but in others a time lag appears between them, in which the deformation precedes the seismicity. Furthermore, a linear correlation between decimal logarithm of intruded magma volume and decimal logarithm of total seismic energy released along the different episodes has been observed. Therefore, if a future magmatic intrusion in El Hierro Island follows this behavior with a proper time lag, we could have an a priori estimate on the order of magnitude the seismic energy released would reach.

Geochemical and geophysical monitoring activities in Campo de Calatrava Volcanic Field (Spain)

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Luengo-Oroz, Natividad; Villasante-Marcos, Víctor; López-Díaz, Rubén; Calvo, Marta; Albert, Helena; Domínguez Cerdeña, Itahiza

2017-04-01

The Campo de Calatrava Volcanic Field (CCVF) or Spanish Central Volcanic Zone is located in central continental Spain (Ciudad Real province) and covers about 5000 km2. It includes around 240 eruptive centers, mainly monogenetic basaltic cones but also explosive maar structures. According to K-Ar geochronology, its main activity phase occurred during Pliocene and Pleistocene epochs (between 5 and 1.7 Ma) and involved alkaline to ultraalkaline magmas, although an older ultrapotassic phase is dated around 8.7-6.4 Ma. However, some recent works have proposed Holocene ages for some of the volcanic products, opening the possibility of considering the CCVF "active" according to international standards. Responding to this situation, the Instituto Geográfico Nacional (IGN) has initiated geochemical and geophysical monitoring activities in the CCVF. Here, we describe these ongoing efforts and we report results about groundwater geochemistry at several natural highly-gaseous springs in the area (hervideros), as well as soil temperature, CO2 diffuse flux from the soil and electrical self-potential data mapped on a small degassing structure called La Sima. In order to analyze microseismicity or any seismic anomaly in the CCVF, a seismic station has also been installed close to this degassing structure. Physicochemical parameters (temperature, pH, Eh and electric conductivity) were measured in situ in four springs and samples were taken in order to analyze major ions and trace elements. Total composition of dissolved gases and helium isotopic ratios were also determined. To complete soil temperature, self-potential and gas prospections performed in La Sima, soil gases were sampled at the bottom of the structure at a depth of 20 cm. Analysis of the total gas composition found 957400 ppm of CO2. Low values of O2 and N2 were also detected (5600 and 24800 ppm respectively).

Seismic evidence for deep fluid circulation in the overriding plate of subduction zones

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Tauzin, B.; Reynard, B.; Bodin, T.; Perrillat, J. P.; Debayle, E.

2015-12-01

In subduction zones, non-volcanic tremors are associated with fluid circulations (Obara, 2002). Their sources are often located on the interplate boundary (Rogers and Dragert, 2003; Shelly et al, 2006; La Rocca, 2009), consistent with fluids released by the dehydration of subducted plates (Hacker et al., 2003). Reports of tremors in the overriding continental crust of several subduction zones in the world (Kao et al., 2005; Payero et al., 2008; Ide, 2012) suggest fluid circulation at shallower depths but potential fluid paths are poorly documented. Here we obtained seismic observations from receiver functions that evidence the close association between the shallow tremor zone, electrical conductivity, and tectonic features of the Cascadia overriding plate. A seismic discontinuity near 15 km depth in the crust of the overriding North American plate is attributed to the Conrad discontinuity. This interface is segmented, and its interruption is spatially correlated with conductive regions and shallow swarms of seismicity and non-volcanic tremors. These observations suggest that shallow fluid circulation, tremors and seismicity are controlled by fault zones limiting blocks of accreted terranes in the overriding plate (Brudzinski and Allen, 2007). These zones constitute fluid "escape" routes that may contribute unloading fluid pressure on the megathrust. Obara, K. (2002). Science, 296, 1679-1681. Rogers, G., & Dragert, H. (2003). Science, 300, 1942-1943. Shelly, D. R., et al. (2006). Nature, 442, 188-191. La Rocca, M., et al. (2009). Science, 323, 620-623. Kao, H., et al. (2005). Nature, 436, 841-844. Payero, J. S., et al. (2008). Geophysical Research Letters, 35. Ide, S. (2012). Journal of Geophysical Research: Solid Earth, 117. Brudzinski, M. R., & Allen, R. M. (2007). Geology, 35, 907-910.

Seismic monitoring at Deception Island volcano (Antarctica): the 2010-2011 survey

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Martín, R.; Carmona, E.; Almendros, J.; Serrano, I.; Villaseñor, A.; Galeano, J.

2012-04-01

the seismic activity and an efficient seismo-volcanic surveillance. The data are processed and analyzed using the SEISAN database management software. In addition to the seismic network, we deployed a small-aperture seismic array south of Fumarole Bay. It is composed by 9 vertical and 1 three-component short-period stations. The 24-bit data acquisition system samples these 12 channels at 100 sps. There is also a permanent seismic station operating since 2008 and located near GdC, that is very useful for the preliminary evaluation of the seismicity at the start of the survey. This station is composed by a 16-s electrolytic seismometer (Eentec SP400) and a 24-bit datalogger (Eentec DR4000) sampling at 100 sps. During the 2010-2011 survey we identified 33 regional earthquakes, 80 volcano-tectonic (VT) earthquakes, and 929 long-period (LP) events. The volcanic alert system has remained green (the lowest level) at all times. The seismic activity has been similar to previous surveys and remained within limits that are normal for the island.

Earthquake swarm in the non-volcanic area north of Harrat Lunayyir, western Saudi Arabia: observations and imaging

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Youssof, M.; Mai, P. M.; Parisi, L.; Tang, Z.; Zahran, H. M.; El-Hadidy, S. Y.; Al-Raddadi, W.; Sami, M.; El-Hadidy, M. S. Y.

2017-12-01

We report on an unusual earthquake swarm in a non-volcanic area of western Saudi Arabia. Since March 2017, hundreds of earthquakes were recorded, reaching magnitude Ml 3.7, which occurred within a very narrowly defined rock volume. The seismicity is shallow, mostly between 4 to 8 km depths, with some events reaching as deep as 16 km. One set of events aligns into a well-defined horizontal tube of 2 km height, 1 km width, and 4-5 km E-W extent. Other event clusters exist, but are less well-defined. The focal mechanism solutions of the largest earthquakes indicate normal faulting, which agree with the regional stress field. The earthquake swarm occurs 75 km NW of Harrat Lunayyir. However, the area of interest doesn't seem to be associated with the well-known volcanic area of Harrat Lunayyir, which experienced a magmatic dike intrusion in 2009 with intense seismic activity (including a surface rupturing Mw 5.7 earthquake). Furthermore, the study area is characterized by a complex shear system, which host gold mineralization. Therefore, the exact origin of the swarm sequence is enigmatic as it's the first of its kind in this region. By using continuous seismological data recorded by the Saudi Geological Survey (SGS) that operates three permanent seismic stations and a temporary network of 11 broadband sensors, we analyze the seismic patterns in space and time. For the verified detected events, we assemble the body wave arrival times that are inverted for the velocity structures along with events hypocenters to investigate possible causes of this swarm sequence, that is, whether the activity is of tectonic- or hydro-thermal origin.

Full-Wave Ambient Noise Tomography of the Long Valley Volcanic Region (California)

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Flinders, A. F.; Shelly, D. R.; Dawson, P. B.; Hill, D. P.; Shen, Y.

2017-12-01

In the late 1970s, and throughout the 1990s, Long Valley Caldera (California) experienced intense periods of unrest characterized by uplift of the resurgent dome, earthquake swarms, and CO2 emissions around Mammoth Mountain. While modeling of the uplift and gravity changes support the possibility of new magmatic intrusions beneath the caldera, geologic interpretations conclude that the magmatic system underlying the caldera is moribund. Geophysical studies yield diverse versions of a sizable but poorly resolved low-velocity zone at depth (> 6km), yet whether this zone is indicative of a significant volume of crystal mush, smaller isolated pockets of partial melt, or magmatic fluids, is inconclusive. The nature of this low-velocity zone, and the state of volcano's magmatic system, carry important implications for the significance of resurgent-dome inflation and the nature of associated hazards. To better characterize this low-velocity zone we present preliminary results from a 3D full-waveform ambient-noise seismic tomography model derived from the past 25 years of vertical component broadband and short-period seismic data. This new study uses fully numerical solutions of the wave equation to account for the complex wave propagation in a heterogeneous, 3D earth model, including wave interaction with topography. The method ensures that wave propagation is modeled accurately in 3D, enabling the full use of seismic records. By using empirical Green's functions, derived from ambient noise and modeled as Rayleigh surface waves, we are able to extend model resolution to depths beyond the limits of previous local earthquake studies. The model encompasses not only the Long Valley Caldera, but the entire Long Valley Volcanic Region, including Mammoth Mountain and the Mono Crater/Inyo Domes volcanic chain.

Seismic Evidence of Ancient Westward Residual Slab Subduction Beneath Southern Taiwan

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Cheng-Horng Lin

2015-01-01

Full Text Available The northeastern convergence of the Philippine Sea plate toward the Eurasian plate causes the major western Philippine Sea plate boundary to subduct toward the northwest or west directions. However, this phenomenon is not clearly observed along the plate boundary between Luzon and Taiwan. Careful examination of deep seismicity in the southern Taiwan area from the earthquake catalog reported by the Central Weather Bureau shows two seismic zones dipping toward the opposing directions. The first dips toward the east from the surface down to 150 km in depth, while the second dips westward at depths between 150 and 200 km. These two seismic zones are confirmed further by seismogram observation and modeling results generated by two deep faults in the southern Taiwan area. The eastward seismic zone clearly results from the Eurasia plate subduction along the Manila trench, while a small section of the westward seismic zone might likely be a residual slab from the ancient subducted Philippine Sea plate. Based on the subduction speed obtained from GPS observations and the subducted Eurasian plate geometry, we can further estimate the eastward Eurasian plate subduction started at least 3.35 million years ago. This result is roughly consistent with the volcanic ages (3 - 4 Ma observed in the arc between Luzon and Taiwan.

MARGATS cruise: investigation of the deep internal structure and the heterogeneous margins of the Demerara plateau reveals a polyphased volcanic history

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Graindorge, D.; Museur, T.; Roest, W. R.; Klingelhoefer, F.; Loncke, L.; Basile, C.; Poetisi, E.; Deverchere, J.; Heuret, A.; Jean-Frederic, L.; Perrot, J.

2017-12-01

The MARGATS scientific cruise was carried out from October 20th to November 16th 2016 on board the R/V L'Atalante, offshore Suriname and French Guiana. This cruise is part of a program dedicated to the geological investigation of the continental margin, including the Demerara plateau, following the GUYAPLAC (2003), IGUANES (2013) and DRADEM (2016) cruises. The aim of MARGATS was to image the internal structure of the Demerara plateau and its different margins using coincident deep penetrating wide angle refraction and multi channel reflection seismic (MCS) methods. During the MARGATS experiment 171 OBS deployments were distributed along 4 wide-angle lines. Along each wide-angle line we also recorded coincident MCS data using a 3 km long 480 channel streamer. The dataset was completed by three MCS lines along the eastern part of the Demerara plateau. MCS MAR007 line which is coincident with line OBS MAR-3 was extended on land by 13 land stations deployed along the Maroni River. This line, together with MCS MAR001 and the coincident OBS MAR-1 line reveal the highly homogeneous deep structure of the internal part of the plateau. MCS MAR005 line, which is coincident with OBS MAR-2, MCS MAR006 line coincident with OBS MAR-4, MCS MAR002, MCS MAR003 and MCS MAR004 helps to elucidate the structural complexity of the northern transform margin and the eastern divergent margin of the plateau. These new datasets are highly complementary to the DRADEM dredge results which provide evidence for mid Jurassic volcanic rocks along the plateau and significant vertical displacements along the transform margin. These results allow to interpret the plateau as the remains of a huge jurassic volcanic divergent margin along the Central Atlantic ocean to the west, possibly remobilized during the cretaceous opening of the Equatorial Atlantic ocean as an highly oblique margin to the north and a divergent margin to the east in persistent presence of volcanism. This AGU session will be a great

Micro-seismic earthquakes characteristics at natural and exploited hydrothermal systems in West Java, Indonesia

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Jousset, P. G.; Jaya, M. S.; Sule, R.; Diningrat, W.; Gassner, A.; Akbar, F.; Ryannugroho, R.; Hendryana, A.; Kusnadi, Y.; Syahbana, D.; Nugraha, A. D.; Umar, M.; Indrinanto, Y.; Erbas, K.

2013-12-01

The assessment of geothermal resources requires the understanding of the structure and the dynamics of geothermal reservoirs. We deployed a multidisciplinary geophysical network around geothermal areas in the south of Bandung, West Java, Indonesia. The first deployment included a network of 30 broadband and 4 short-period seismic stations with Güralp and Trillium sensors (0.008 - 100 Hz) since October 2012. In a second step, we extended the network in June 2013 with 16 short-period (1 Hz) seismometers. We describe the set-up of the seismic networks and discuss first observations and results. The co-existence of a large variety of intense surface manifestations like geysers, hot-steaming grounds, hot water pools, and active volcanoes suggest an intimate coupling between volcanic, tectonic and hydrothermal processes in this area. Preliminary location of earthquakes is performed using a non-linear algorithm, which allows us to define at least 3 seismic clusters. We discuss this seismic pattern within the geothermal fields.

Spatial and temporal variations of diffuse CO2 degassing at El Hierro volcanic system: Relation to the 2011-2012 submarine eruption

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Melián, Gladys; Hernández, Pedro A.; Padrón, Eleazar; Pérez, Nemesio M.; Barrancos, José; Padilla, Germán.; Dionis, Samara; Rodríguez, Fátima; Calvo, David; Nolasco, Dacil

2014-09-01

We report herein the results of extensive diffuse CO2 emission surveys performed on El Hierro Island in the period 1998-2012. More than 17,000 measurements of the diffuse CO2 efflux were carried out, most of them during the volcanic unrest period that started in July 2011. Two significant precursory signals based on geochemical and geodetical studies suggest that a magma intrusion processes might have started before 2011 in El Hierro Island. During the preeruptive and eruptive periods, the time series of the diffuse CO2 emission released by the whole island experienced two significant increases. The first started almost 2 weeks before the onset of the submarine eruption, reflecting a clear geochemical anomaly in CO2 emission, most likely due to increasing release of deep-seated magmatic gases to the surface. The second one, between 24 October and 27 November 2011, started before the most energetic seismic events of the volcanic-seismic unrest. The data presented here demonstrate that combined continuous monitoring studies and discrete surveys of diffuse CO2 emission provide important information to optimize the early warning system in volcano monitoring programs and to monitor the evolution of an ongoing volcanic eruption, even though it is a submarine eruption.

Los efectos del terremoto de Sámara y otros dos grandes terremotos tectónicos en los volcanes de Centroamérica en el 2012

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González Ilama, Gino

2014-06-01

the volcanologist was: could these earthquakes trigger some volcanic unrest? In this manuscript analyze the volcanic activity before and after this seismic crisis by recording a the name of the volcano in unrest after the earthquakes, b time lapsed in days between and the onset of the volcanic unrest, c the distance in kilometers between the volcano and the epicenters, d the type of change of the unrest of the volcano, which were divided into three: 1 increase in seismic activity, 2 combination of increased seismic activity, temperature and degassing and/or the occurrence of phreatic eruptions, 3 large eruptions with ash fall. From this, found that thirteen volcanoes of Central America were some volcanic unrest. Of those, six volcanoes showed changes of type 1, four volcanoes with changes of type 2 and three volcanoes with changes of type 3. Based on those facts, establish an apparent correlation as tectonic earthquakes can cause changes in the volcanoes and thus could understand future seismic crisis and aftermath in the volcanic systems

Assessment of pre-crisis and syn-crisis seismic hazard at Campi Flegrei and Mt. Vesuvius volcanoes, Campania, southern Italy

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Convertito, Vincenzo; Zollo, Aldo

2011-08-01

In this study, we address the issue of short-term to medium-term probabilistic seismic hazard analysis for two volcanic areas, Campi Flegrei caldera and Mt. Vesuvius in the Campania region of southern Italy. Two different phases of the volcanic activity are considered. The first, which we term the pre-crisis phase, concerns the present quiescent state of the volcanoes that is characterized by low-to-moderate seismicity. The second phase, syn-crisis, concerns the unrest phase that can potentially lead to eruption. For the Campi Flegrei case study, we analyzed the pattern of seismicity during the 1982-1984 ground uplift episode (bradyseism). For Mt. Vesuvius, two different time-evolutionary models for seismicity were adopted, corresponding to different ways in which the volcano might erupt. We performed a site-specific analysis, linked with the hazard map, to investigate the effects of input parameters, in terms of source geometry, mean activity rate, periods of data collection, and return periods, for the syn-crisis phase. The analysis in the present study of the pre-crisis phase allowed a comparison of the results of probabilistic seismic hazard analysis for the two study areas with those provided in the Italian national hazard map. For the Mt. Vesuvius area in particular, the results show that the hazard can be greater than that reported in the national hazard map when information at a local scale is used. For the syn-crisis phase, the main result is that the data recorded during the early months of the unrest phase are substantially representative of the seismic hazard during the whole duration of the crisis.

Secular Variations of Soil CO2 Efflux at Santa Ana-Izalco-Coatepeque Volcanic Complex, El Salvador, Central America

Science.gov (United States)

Olmos, R.; Barahona, F.; Cartagena, R.; Soriano, T.; Salazar, J.; Hernandez, P.; Perez, N.; Lopez, D.

2002-12-01

The Santa Ana-Izalco-Coatepeque volcanic complex (2,365 m elevation), located 40 Km west of San Salvador, consists of the Coatepeque collapse caldera (a 6.5 x 10.5 Km elliptical depression), the Santa Ana and Izalco stratovolcanoes, as well as numerous cinder cones and explosion craters. The summit of the Santa Ana volcano contains an acid lake where hot springs, gas bubbling and intense fumarolic emissions occur. A volcanic plume, usually driven by the NE trades, may be seen rising up to 500 m from the summit crater of the Santa Ana volcano. The goal of this study is to provide a multidisciplinary approach for the volcanic surveillance by means of performing geochemical continuous monitoring of diffuse CO2 emission rate in addition to seismic monitoring. Temporal variations of soil CO2 efflux measured at Cerro Pacho dome, Coatepeque caldera, by means of the accumulation chamber method and using a CO2 efflux continuous monitoring station developed by WEST Systems (Italy). From May 2001 till May 2002, CO2 efflux ranged from 4.3 to 327 gm-2d-1, with a median value of 98 and a quartile range of 26 gm-2d-1. Two distinct diffuse CO2 degassing periods have been observed: (1) an increasing trend from May to July 2001, and (2) a stationary period from November 2001 to May 2002. The increasing-trend period may be due to the anomalous plume degassing at the Santa Ana volcano during 2001 and soon after the January and February 2001 earthquakes. Temporal variations of CO2 efllux during the second period seem to be coupled with those of barometric pressure and wind speed at different time scales, though most of the variance is contained at diurnal and semi-diurnal frequencies. These observations can help to explain the existence of a persistent behavior (Hurst exponent, H=0.934 +/- 0.0039) within the diffuse CO2 degassing phenomena. However, further observations are in progress to understand the long-term memory of diffuse CO2 degassing at the Santa Ana volcanic complex.

The recent seismicity of Teide volcano, Tenerife (Canary Islands, Spain)

Science.gov (United States)

D'Auria, L.; Albert, G. W.; Calvert, M. M.; Gray, A.; Vidic, C.; Barrancos, J.; Padilla, G.; García-Hernández, R.; Perez, N. M.

2017-12-01

Tenerife is an active volcanic island which experienced several eruptions of moderate intensity in historical times, and few explosive eruptions in the Holocene. The increasing population density and the consistent number of tourists are constantly raising the volcanic risk of the island.On 02/10/2016 a remarkable swarm of long-period events was recorded and was interpreted as the effect of a transient massive fluid discharge episode occurring within the deep hydrothermal system of Teide volcano. Actually, since Oct. 2016, the hydrothermal system of the volcano underwent a progressive pressurization, testified by the marked variation of different geochemical parameters. The most striking observation is the increase in the diffuse CO2 emission from the summit crater of Teide volcano which started increasing from a background value of about 20 tons/day and reaching a peak of 175 tons/day in Feb. 2017.The pressurization process has been accompanied by an increase in the volcano-tectonic seismicity of. Teide volcano, recorded by the Red Sísmica Canaria, managed by Instituto Volcanológico de Canarias (INVOLCAN). The network began its full operativity in Nov. 2016 and currently consists of 15 broadband seismic stations. Since Nov. 2016 the network detected more than 100 small magnitude earthquakes, located beneath Teide volcano at depths usually ranging between 5 and 15 km. On January 6th 2017 a M=2.5 earthquake was recorded in the area, being one of the strongest ever recorded since decades. Most of the events show typical features of the microseismicity of hydrothermal systems: high spatial and temporal clustering and similar waveforms of individual events which often are overlapped.We present the spatial and temporal distribution of the seismicity of Teide volcano since Nov. 2016, comparing it also with the past seismicity of the volcano. Furthermore we analyze the statistical properties of the numerous swarms recorded until now with the aid of a template

Seismic and gravity signature of the Ischia Island Caldera (Italy)

Science.gov (United States)

Capuano, P.; de Matteis, R.; Russo, G.

2009-04-01

The Campania (Italy) coasts are characterized by the presence of several volcanoes. The island of Ischia, located at the northwestern end of the Gulf of Naples, belongs to the Neapolitan Volcanic District together with Phlegrean Fields and Vesuvius, having all these Pleistocene volcanoes erupted in historical times, and it is characterized by diffuse hydrothermal phenomena The island represents the emergent part of a more extensive volcanic area developed mainly westward of the island, with underwater volcanoes aligned along regional fault patterns. The activity of Ischia volcano is testified by the occurrence of eruptions in historical times, the presence of intense hydrothermal phenomena, and by seismic activity (e.g. the 1883 Casamicciola earthquake). Ischia is populated by about 50,000 inhabitants increasing, mainly in the summer, due to thriving tourism business, partially due to its active volcanic state. Hazard assessment at active, densely populated volcanoes is critically based on knowledge of the volcanoes past behavior and the definition of its present state. As a contribution to the definition of the present state of the Ischia island volcano, we obtain a model of the shallow crust using geophysical observables through seismic tomography and 3D gravity inversion. In particular we use travel times collected during the Serapis experiment on the island and its surroundings and free air anomaly. A new 3D gravity inversion procedure has been developed to take better into account the shape and the effects of topography approximating it by a triangular mesh. Below each triangle, a sequence of triangular prisms is built, the uppermost prism having the upper face coincident with the triangle following the topography. The inversion is performed searching for a regularized solution using the minimum norm stabilizer. The main results inferable from the 3D seismic and gravity images are the definition of the caldera rims hypothesize by many authors along the

Pockets, conduits, channels, and plumes: links to volcanism and orogeny in the rollback dominated western Mediterranean

Science.gov (United States)

Miller, Meghan S.; Sun, Daoyuan; O'Driscoll, Leland; Becker, Thorsten W.; Holt, Adam; Diaz, Jordi; Thomas, Christine

2015-04-01

Detailed mantle and lithospheric structure from the Canary Islands to Iberia have been imaged with data from recent temporary deployments and select permanent stations from over 300 broadband seismometers. The stations extended across Morocco and Spain as part of the PICASSO, IberArray, and Morocco-Münster experiments. We present results from S receiver functions (SRF), shear wave splitting, waveform modeling, and geodynamic models that help constrain the tectonic evolution of the westernmost Mediterranean, including orogenesis of the Atlas Mountains and occurrence of localized alkaline volcanism. Our receiver function images, in agreement with previous geophysical modeling, show that the lithosphere is thin (~65 km) beneath the Atlas, but thickens (~100 km) over a very short length scale at the flanks of the mountains. We find that these dramatic changes in lithospheric thickness also correspond to dramatic decreases in delay times inferred from S and SKS splitting observations of seismic anisotropy. Pockets and conduits of low seismic velocity material below the lithosphere extend along much of the Atlas to Southern Spain and correlate with the locations of Pliocene-Quaternary magmatism. Waveform analysis from the USC linear seismic array across the Atlas Mountains constrains the position, shape, and physical characteristics of one localized, low velocity conduit that extends from the uppermost mantle (~200 km depth) up to the volcanoes in the Middle Atlas. The shape, position and temperature of these seismically imaged low velocity anomalies, topography of the base of the lithosphere, morphology of the subducted slab beneath the Alboran Sea, position of the West African Craton and correlation with mantle flow inferred from shear wave splitting suggest that the unusually high topography of the Atlas Mountains and isolated recent volcanics are due to active mantle support that may be from material channeled from the Canary Island plume.

Using Digital Cameras to Detect Warning Signs of Volcanic Eruptions

Science.gov (United States)

Girona, T.; Huber, C.; Trinh, K. T.; Protti, M.; Pacheco, J. F.

2017-12-01

Monitoring volcanic outgassing is fundamental to improve the forecasting of volcanic eruptions. Recent efforts have led to the advent of new methods to measure the concentration and flux of volcanic gases with unprecedented temporal resolution, thus allowing us to obtain reliable high-frequency (up to 1 Hz) time series of outgassing activity. These high-frequency methods have shown that volcanic outgassing can be periodic sometimes (with periodicities ranging from 101 s to 103 s), although it remains unknown whether the spectral features of outgassing reflect the processes that ultimately trigger volcanic unrest and eruptions. In this study, we explore the evolution of the spectral content of the outgassing activity of Turrialba volcano (Costa Rica) using digital images (with digital brightness as a proxy for the emissions of water vapor [Girona et al., 2015]). Images were taken at 1 km distance with 1 Hz sampling rate, and the time period analyzed (from April 2016 to April 2017) is characterized by episodes of quiescent outgassing, ash explosions, and sporadic eruptions of ballistics. Our preliminary results show that: 1) quiescent states of Turrialba volcano are characterized by outgassing frequency spectra with fractal distribution; 2) superimposed onto the fractal frequency spectra, well-defined pulses with period around 100 s emerge hours to days before some of the eruptions of ballistics. An important conclusion of this study is that digital cameras can be potentially used in real-time volcano monitoring to detect warning signs of eruptions, as well as to better understand subsurface processes and track the changing conditions below volcanic craters. Our ongoing study also explores the correlation between the evolution of the spectral content of outgassing, infrasound data, and shallow seismicity. Girona, T., F. Costa, B. Taisne, B. Aggangan, and S. Ildefonso (2015), Fractal degassing from Erebus and Mayon volcanoes revealed by a new method to monitor H2O

Volcano-tectonic interactions at Sabancaya and other Peruvian volcanoes revealed by InSAR and seismicity

Science.gov (United States)

Jay, J.; Pritchard, M. E.; Aron, F.; Delgado, F.; Macedo, O.; Aguilar, V.

2013-12-01

An InSAR survey of all 13 Holocene volcanoes in the Andean Central Volcanic Zone of Peru reveals previously undocumented surface deformation that is occasionally accompanied by seismic activity. Our survey utilizes SAR data spanning from 1992 to the present from the ERS-1, ERS-2, and Envisat satellites, as well as selected data from the TerraSAR-X satellite. We find that the recent unrest at Sabancaya volcano (heightened seismicity since 22 February 2013 and increased fumarolic output) has been accompanied by surface deformation. We also find two distinct deformation episodes near Sabancaya that are likely associated with an earthquake swarm in February 2013 and a M6 normal fault earthquake that occurred on 17 July 2013. Preliminary modeling suggests that faulting from the observed seismic moment can account for nearly all of the observed deformation and thus we have not yet found clear evidence for recent magma intrusion. We also document an earlier episode of deformation that occurred between December 2002 and September 2003 which may be associated with a M5.3 earthquake that occurred on 13 December 2002 on the Solarpampa fault, a large EW-striking normal fault located about 25 km northwest of Sabancaya volcano. All of the deformation episodes between 2002 and 2013 are spatially distinct from the inflation seen near Sabancaya from 1992 to 1997. In addition to the activity at Sabancaya, we also observe deformation near Coropuna volcano, in the Andagua Valley, and in the region between Ticsani and Tutupaca volcanoes. InSAR images reveal surface deformation that is possibly related to an earthquake swarm near Coropuna and Sabancaya volcanoes in December 2001. We also find persistent deformation in the scoria cone and lava field along the Andagua Valley, located 40 km east of Corpuna. An earthquake swarm near Ticsani volcano in 2005 produced surface deformation centered northwest of the volcano and was accompanied by a north-south elongated subsidence signal to the

Seismic tomography model reveals mantle magma sources of recent volcanic activity at El Hierro Island (Canary Islands, Spain)

Science.gov (United States)

García-Yeguas, Araceli; Ibáñez, Jesús M.; Koulakov, Ivan; Jakovlev, Andrey; Romero-Ruiz, M. Carmen; Prudencio, Janire

2014-12-01

We present a 3-D model of P and S velocities beneath El Hierro Island, constructed using the traveltime data of more than 13 000 local earthquakes recorded by the Instituto Geográfico Nacional (IGN, Spain) in the period from 2011 July to 2012 September. The velocity models were performed using the LOTOS code for iterative passive source tomography. The results of inversion were thoroughly verified using different resolution and robustness tests. The results reveal that the majority of the onshore area of El Hierro is associated with a high-velocity anomaly observed down to 10-12-km depth. This anomaly is interpreted as the accumulation of solid igneous rocks erupted during the last 1 Myr and intrusive magmatic bodies. Below this high-velocity pattern, we observe a low-velocity anomaly, interpreted as a batch of magma coming from the mantle located beneath El Hierro. The boundary between the low- and high-velocity anomalies is marked by a prominent seismicity cluster, thought to represent anomalous stresses due to the interaction of the batch of magma with crust material. The areas of recent eruptions, Orchilla and La Restinga, are associated with low-velocity anomalies surrounding the main high-velocity block. These eruptions took place around the island where the crust is much weaker than the onshore area and where the melted material cannot penetrate. These results put constraints on the geological model that could explain the origin of the volcanism in oceanic islands, such as in the Canaries, which is not yet clearly understood.

Acoustic waves in the atmosphere and ground generated by volcanic activity

International Nuclear Information System (INIS)

Ichihara, Mie; Lyons, John; Oikawa, Jun; Takeo, Minoru

2012-01-01

This paper reports an interesting sequence of harmonic tremor observed in the 2011 eruption of Shinmoe-dake volcano, southern Japan. The main eruptive activity started with ashcloud forming explosive eruptions, followed by lava effusion. Harmonic tremor was transmitted into the ground and observed as seismic waves at the last stage of the effusive eruption. The tremor observed at this stage had unclear and fluctuating harmonic modes. In the atmosphere, on the other hand, many impulsive acoustic waves indicating small surface explosions were observed. When the effusion stopped and the erupted lava began explosive degassing, harmonic tremor started to be transmitted also to the atmosphere and observed as acoustic waves. Then the harmonic modes became clearer and more stable. This sequence of harmonic tremor is interpreted as a process in which volcanic degassing generates an open connection between the volcanic conduit and the atmosphere. In order to test this hypothesis, a laboratory experiment was performed and the essential features were successfully reproduced.

Acoustic waves in the atmosphere and ground generated by volcanic activity

Energy Technology Data Exchange (ETDEWEB)

Ichihara, Mie; Lyons, John; Oikawa, Jun; Takeo, Minoru [Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032 (Japan); Instituto Geofisico, Escuela Politecnica Nacional, Ladron de Guevara E11-253, Aptdo 2759, Quito (Ecuador); Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032 (Japan)

2012-09-04

This paper reports an interesting sequence of harmonic tremor observed in the 2011 eruption of Shinmoe-dake volcano, southern Japan. The main eruptive activity started with ashcloud forming explosive eruptions, followed by lava effusion. Harmonic tremor was transmitted into the ground and observed as seismic waves at the last stage of the effusive eruption. The tremor observed at this stage had unclear and fluctuating harmonic modes. In the atmosphere, on the other hand, many impulsive acoustic waves indicating small surface explosions were observed. When the effusion stopped and the erupted lava began explosive degassing, harmonic tremor started to be transmitted also to the atmosphere and observed as acoustic waves. Then the harmonic modes became clearer and more stable. This sequence of harmonic tremor is interpreted as a process in which volcanic degassing generates an open connection between the volcanic conduit and the atmosphere. In order to test this hypothesis, a laboratory experiment was performed and the essential features were successfully reproduced.

Volcanic spreading forcing and feedback in geothermal reservoir development, Amiata Volcano, Italia

Science.gov (United States)

Borgia, Andrea; Mazzoldi, Alberto; Brunori, Carlo Alberto; Allocca, Carmine; Delcroix, Carlo; Micheli, Luigi; Vercellino, Alberto; Grieco, Giovanni

2014-09-01

-water aquifer) and the rocks of the geothermal field, constitute ideal pathways for water recharge during vapour extraction for geothermal energy production. We think that volcanic spreading could maintain faults in a critically stressed state, facilitating the occurrence of induced and triggered seismicity.

Influences of volcanism on coal quality - Examples from the western United States

International Nuclear Information System (INIS)

Hildebrand, R.T.; Affolter, R.H.

1986-01-01

Several small Tertiary coal deposits in Idaho, Nevada, and Washington formed in fresh-water basins located near active continental (salic) volcanic centers. Metastable glassy material (tephra) ejected during volcanic eruptions was introduced into the coal-forming environment of these basins as ash falls. This tephra contributed to the high ash content of many of the coal beds, formed laterally persistent partings (''tonsteins'') in the coal, and constitutes a large part of the strata enclosing the deposits. In order to study the possible relationships between the presence of tephra and coal quality, chemical data for 65 coal samples from 12 of these deposits were compiled and statistically analyzed. The results indicate that, in addition to the high ash content, coal from Tertiary deposits containing appreciable amounts of tephra generally is enriched in many elements compared to 460 coal samples from 11 deposits of similar ages remote from volcanic activity

Eighteen years of geochemical monitoring at the oceanic active volcanic island of El Hierro (Canary Islands, Spain)

Science.gov (United States)

Asensio-Ramos, María; Alonso, Mar; Sharp, Emerson; Woods, Hannah; Barrancos, José; Pérez, Nemesio M.

2016-04-01

We report herein the latest results of a diffuse CO2 efflux survey at El Hierro volcanic system carried out during the summer period of 2015 to constrain the total CO2 output from the studied area a during post-eruptive period. El Hierro Island (278 km2) is the youngest and the SW-most of the Canary Islands. On July 16, 2011, a seismic-volcanic crisis started with the occurrence of more than 11,900 seismic events and significant deformation along the island. On October 10, 2011, the dominant character of seismicity changed dramatically from discrete earthquakes to continuous tremor, a clear indication that magma was rapidly approaching the surface immediately before the onset of the eruption, October 12. Eruption was declared over on 5 March, 2012. In order to monitor the volcanic activity of El Hierro Island, from 1998 to 2015 diffuse CO2 emission studies have been performed at El Hierro volcanic system in a yearly basis (˜600 observation sites) according to the accumulation chamber method. Spatial distribution maps were constructed following the sequential Gaussian simulation (sGs) procedure. To quantify the total CO2 emission from the studied area, 100 simulations for each survey have been performed. During the eruption period, soil CO2 efflux values range from non-detectable (˜0.5 g m-2 d-1) up to 457 g m-2 d-1, reaching in November 27, 2011, the maximum CO2 output estimated value of all time series, 2,398 t d-1, just before the episodes of maximum degassing observed as vigorous bubbling at the sea surface and an increment in the amplitude of the tremor signal. During the 2015 survey, soil CO2 efflux values ranged from non-detectable up to 41 g m-2 d-1. The spatial distribution of diffuse CO2 emission values seemed to be controlled by the main volcano structural features of the island. The total diffuse CO2 output released to atmosphere was estimated at 575 ± 24 t d-1, value slightly higher that the background CO2 emission estimated at 422 t d-1 (Melián et

Multi-decadal satellite measurements of passive and eruptive volcanic SO2 emissions

Science.gov (United States)

Carn, Simon; Yang, Kai; Krotkov, Nickolay; Prata, Fred; Telling, Jennifer

2015-04-01

strongest volcanic SO2 sources between 2004 and 2015. OMI measurements are most sensitive to SO2 emission rates on the order of ~1000 tons/day or more, and thus the satellite data provide new constraints on the location and persistence of major volcanic SO2 sources. We find that OMI has detected non-eruptive SO2 emissions from at least ~60 volcanoes since 2004. Results of our analysis reveal the emergence of several major tropospheric SO2 sources that are not prominent in existing inventories (Ambrym, Nyiragongo, Turrialba, Ubinas), the persistence of some well-known sources (Etna, Kilauea) and a possible decline in emissions at others (e.g., Lascar). The OMI measurements provide particularly valuable information in regions lacking regular ground-based monitoring such as Indonesia, Melanesia and Kamchatka. We describe how the OMI measurements of SO2 total column, and their probability density function, can be used to infer SO2 emission rates for compatibility with existing emissions data and assimilation into chemical transport models. The satellite-derived SO2 emission rates are in good agreement with ground-based measurements from frequently monitored volcanoes (e.g., from the NOVAC network), but differ for other volcanoes. We conclude that some ground-based SO2 measurements may be biased high if collected during periods of elevated unrest, and hence may not be representative of long-term average emissions.

Astor Pass Seismic Surveys Preliminary Report

Energy Technology Data Exchange (ETDEWEB)

Louie, John [UNR; Pullammanappallil, Satish [Optim; Faulds, James; Eisses, Amy; Kell, Annie; Frary, Roxanna; Kent, Graham

2011-08-05

In collaboration with the Pyramid Lake Paiute Tribe (PLPT), the University of Nevada, Reno (UNR) and Optim re-processed, or collected and processed, over 24 miles of 2d seismic-reflection data near the northwest corner of Pyramid Lake, Nevada. The network of 2d land surveys achieved a near-3d density at the Astor Pass geothermal prospect that the PLPT drilled during Nov. 2010 to Feb. 2011. The Bureau of Indian Affairs funded additional seismic work around the Lake, and an extensive, detailed single-channel marine survey producing more than 300 miles of section, imaging more than 120 ft below the Lake bottom. Optim’s land data collection utilized multiple heavy vibrators and recorded over 200 channels live, providing a state-of-the-art reflection-refraction data set. After advanced seismic analysis including first-arrival velocity optimization and prestack depth migration, the 2d sections show clear fault-plane reflections, in some areas as deep as 4000 ft, tying to distinct terminations of the mostly volcanic stratigraphy. Some lines achieved velocity control to 3000 ft depth; all lines show reflections and terminations to 5000 ft depth. Three separate sets of normal faults appear in an initial interpretation of fault reflections and stratigraphic terminations, after loading the data into the OpendTect 3d seismic visualization system. Each preliminary fault set includes a continuous trace more than 3000 ft long, and a swarm of short fault strands. The three preliminary normal-fault sets strike northerly with westward dip, northwesterly with northeast dip, and easterly with north dip. An intersection of all three fault systems documented in the seismic sections at the end of Phase I helped to locate the APS-2 and APS-3 slimholes. The seismic sections do not show the faults connected to the Astor Pass tufa spire, suggesting that we have imaged mostly Tertiary-aged faults. We hypothesize that the Recent, active faults that produced the tufa through hotspring

New Seismic Monitoring Station at Mohawk Ridge, Valles Caldera

Energy Technology Data Exchange (ETDEWEB)

Roberts, Peter Morse [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-09-20

Two new broadband digital seismic stations were installed in the Valles Caldera in 2011 and 2012. The first is located on the summit of Cerros del Abrigo (station code CDAB) and the second is located on the flanks of San Antonio Mountain (station code SAMT). Seismic monitoring stations in the caldera serve multiple purposes. These stations augment and expand the current coverage of the Los Alamos Seismic Network (LASN), which is operated to support seismic and volcanic hazards studies for LANL and northern New Mexico (Figure 1). They also provide unique continuous seismic data within the caldera that can be used for scientific studies of the caldera’s substructure and detection of very small seismic signals that may indicate changes in the current and evolving state of remnant magma that is known to exist beneath the caldera. Since the installation of CDAB and SAMT, several very small earthquakes have already been detected near San Antonio Mountain just west of SAMT (Figure 2). These are the first events to be seen in that area. Caldera stations also improve the detection and epicenter determination quality for larger local earthquakes on the Pajarito Fault System east of the Preserve and the Nacimiento Uplift to the west. These larger earthquakes are a concern to LANL Seismic Hazards assessments and seismic monitoring of the Los Alamos region, including the VCNP, is a DOE requirement. Currently the next closest seismic stations to the caldera are on Pipeline Road (PPR) just west of Los Alamos, and Peralta Ridge (PER) south of the caldera. There is no station coverage near the resurgent dome, Redondo Peak, in the center of the caldera. Filling this “hole” is the highest priority for the next new LASN station. We propose to install this station in 2018 on Mohawk Ridge just east of Redondito, in the same area already occupied by other scientific installations, such as the MCON flux tower operated by UNM.

Fractal behaviour of the seismicity in the Southern Iberian Peninsula

Directory of Open Access Journals (Sweden)

X. Lana

2005-01-01

Full Text Available The fractal behaviour of the seismicity in the Southern Iberian Peninsula is analysed by considering two different series of data: the distance and the elapsed time between consecutive seismic events recorded by the seismic network of the Andalusian Institute of Geophysics (AIG. The fractal analyses have been repeated by considering four threshold magnitudes of 2.5, 3.0, 3.5 and 4.0. The re-scaled analysis lets to determine if the seismicity shows strong randomness or if it is characterised by time-persistence and the cluster dimension indicates the degree of time and spatial clustering of the seismicity. Another analysis, based on the reconstruction theorem, permits to evaluate the minimum number of nonlinear equations describing the dynamical mechanism of the seismicity, its 'loss of memory', its chaotic character and the instability of a possible predicting algorithm. The results obtained depict some differences depending on distances or elapsed times and the different threshold levels of magnitude also lead to slightly different results. Additionally, only a part of the fractal tools, the re-scaled analysis, have been applied to five seismic crises in the same area.

Volcanism on Io

Science.gov (United States)

Davies, Ashley Gerard

2014-03-01

Preface; Introduction; Part I. Io, 1610 to 1995: Galileo to Galileo: 1. Io, 1610-1979; 2. Between Voyager and Galileo: 1979-95; 3. Galileo at Io; Part II. Planetary Volcanism: Evolution and Composition: 4. Io and Earth: formation, evolution, and interior structure; 5. Magmas and volatiles; Part III. Observing and Modeling Volcanic Activity: 6. Observations: thermal remote sensing of volcanic activity; 7. Models of effusive eruption processes; 8. Thermal evolution of volcanic eruptions; Part IV. Galileo at Io: the Volcanic Bestiary: 9. The view from Galileo; 10. The lava lake at Pele; 11. Pillan and Tvashtar: lava fountains and flows; 12. Prometheus and Amirani: Effusive activity and insulated flows; 13. Loki Patera: Io's powerhouse; 14. Other volcanoes and eruptions; Part V. Volcanism on Io: The Global View: 15. Geomorphology: paterae, shields, flows and mountains; 16. Volcanic plumes; 17. Hot spots; Part VI. Io after Galileo: 18. Volcanism on Io: a post-Galileo view; 19. The future of Io observations; Appendix 1; Appendix 2; References; Index.

Volcanic Ash Hazards and Risk in Argentina: Scientific and Social Collaborative Approaches.

Science.gov (United States)

Rovere, E. I., II; Violante, R. A.; Vazquez Herrera, M. D.; Martinez Fernandez, M. D. L. P.

2015-12-01

Due to the absence of alerts or volcanic impacts during 60 years (from 1932, Quizapu-Descabezado Grande -one of the major eruptions of the XX Century- until 1991 Hudson eruption) there was mild remembrance of volcanic hazards in the collective memory of the Argentina citizens. Since then and until April 2015, the social perception changed according to different factors: age, location, education, culture, vulnerability. This variability produces a maze of challenges that go beyond the scientific knowledge. Volcanic health hazards began to be understood in 2008 after the eruption of Chaiten volcano. The particle size of ashfall (concern on epidemiological monitoring. In 2011 the volcanic complex Puyehue - Cordon Caulle eruption produced ashfall through plumes that reached densely populated cities like San Carlos de Bariloche and Buenos Aires. Farther away in South Africa and New Zealand ash plumes forced airlines to cancel local and international flights for several weeks. The fear of another eruption did not wait long when Calbuco volcano started activity in April 2015, it came at a time when Villarrica volcano was also in an eruptive phase, and the SERNAGEOMIN Chile, through the Observatory OVDAS of the Southern Andes, faced multiple natural disasters at the same time, 3 volcanoes in activity, lahars, pyroclastic flows and floods in the North. In Argentina, critical infrastructure, farming, livestock and primary supplies were affected mainly in the western region. Copahue volcano, is increasing unstability on seismic and geochemistry data since 2012. Caviahue resort village, distant only 8 Km. from the active vent happens to be a high vulnerable location. In 2014 GEVAS (Geology, Volcanoes, Environment and Health) Network ARGENTINA Civil Association started collaborative activities with SEGEMAR and in 2015 with the IAPG (Geoethics, Argentina), intending to promote Best Practices in volcanic and geological hazards. Geoscientists and the volcano vulnerable population

On the relation between crustal deformation and seismicity during the 2012-2014 magmatic intrusions in El Hierro island.

Science.gov (United States)

Domínguez Cerdeña, Itahiza; García-Cañada, Laura; Ángeles Benito Saz, María; Del Fresno, Carmen

2017-04-01

The last volcanic eruption in the Canary Islands took place in 2011 less than 2 km offshore El Hierro island, after 3 months of measuring surface deformation (up to 5 cm) and locating more than 10 000 earthquakes. In the two years following the end of the submarine eruption on 5 March 2012, six deep magmatic intrusions were recorded beneath the island. Despite the short time duration of these intrusions, these events have been more energetic that the 2011 pre-eruptive intrusive event but none of them ended in a new eruption. These post-eruptive reactivations are some of the few examples in the world of well monitored magmatic intrusions related with monogenetic volcanism. In order to understand these processes we have analyzed the geodetic and seismic data with different techniques. First, we did a joint hypocentral relocation of the six seismic swarms, including more than 6 300 events, to analyze the relative distribution of the earthquakes from different intrusions. The uncertainties of the earthquakes relocations was reduced to an average value of 300 m. New earthquakes' distribution shows the alignments of the different intrusions and a temporal migration of the events to larger depths. Moreover, we show the results of the ground deformation using GPS data from the network installed on the island (for each of the six intrusive events) and their inversion considering spherical models. In most of the intrusions the optimal source model was shallower and southern than the corresponding seismicity hypocenters. The intruded magma volume ranges from 0.02 to 0.13 km3. Finally, we also computed the b value from the Gutenberg Richter equation by means of a bootstrap method. The spatial and temporal evolution of the b value for the seismicity show a clear correlation with the temporal evolution of the crustal deformation. The six magma intrusions can be grouped, depending on their location, in three pairs each one associated with each of the three active rifts of El

Borehole Array Observations of Non-Volcanic Tremor at SAFOD

Science.gov (United States)

Ellsworth, W. L.; Luetgert, J. H.; Oppenheimer, D. H.

2005-12-01

We report on the observation of non-volcanic tremor made in the San Andreas Fault Observatory at Depth in May, 2005 during the deployment of a multi-level borehole seismic array in the SAFOD main hole. The seismic array consisted of 80 levels of hydraulically-clamped 3-component, 15 Hz omni-directional geophones spaced 15.24 m apart along a 1200 m section of the inclined borehole between 1538 and 2363 m below the ground surface. The array was provided by Paulsson Geophysical Services, Inc. (P/GSI), and recorded at a sample rate of 4000 sps on 24-bit Geode digital recorders provided by Geometrics, Inc. More than 2 TB of continuous data were recorded during the 2-week deployment. Selected local earthquakes and explosions recorded by the array are available at the Northern California Earthquake Data Center, and the entire unedited data set is available as assembled data at the IRIS Data Management Center. Both data sets are currently in the industry standard SEG2 format. Episodes of non-volcanic tremor are common along this reach of the San Andreas Fault according to Nadeau and Dolenc [2004, DOI: 10.1126/science.1107142], with many originating about 30 km southeast of SAFOD beneath the southern end of the Parkfield segment and northern end of the Simmler segment of the fault. We identified tremor episodes using spectrograms routinely produced by the Northern California Seismic Network (http://quake.usgs.gov/cgi-bin/sgrampark.pl) on which they appear as periods of elevated noise relative to the background. A particularly strong tremor episode occurred on May 10, 2005 between 19:39 and 20:00 UTC. In SAFOD, tremor spectral levels exceed the instrumental noise floor to at least 40 Hz. The spatially unaliased recording of the tremor wavefield on the P/GSI array reveal individual phases that can be tracked continuously across the array. The wavefield is composed of both up- and down-going shear waves that form quasi-stationary interference patterns in which areas of

Network-Based Detection and Classification of Seismovolcanic Tremors: Example From the Klyuchevskoy Volcanic Group in Kamchatka

Science.gov (United States)

Soubestre, Jean; Shapiro, Nikolai M.; Seydoux, Léonard; de Rosny, Julien; Droznin, Dmitry V.; Droznina, Svetlana Ya.; Senyukov, Sergey L.; Gordeev, Evgeniy I.

2018-01-01

We develop a network-based method for detecting and classifying seismovolcanic tremors. The proposed approach exploits the coherence of tremor signals across the network that is estimated from the array covariance matrix. The method is applied to four and a half years of continuous seismic data recorded by 19 permanent seismic stations in the vicinity of the Klyuchevskoy volcanic group in Kamchatka (Russia), where five volcanoes were erupting during the considered time period. We compute and analyze daily covariance matrices together with their eigenvalues and eigenvectors. As a first step, most coherent signals corresponding to dominating tremor sources are detected based on the width of the covariance matrix eigenvalues distribution. Thus, volcanic tremors of the two volcanoes known as most active during the considered period, Klyuchevskoy and Tolbachik, are efficiently detected. As a next step, we consider the daily array covariance matrix's first eigenvector. Our main hypothesis is that these eigenvectors represent the principal components of the daily seismic wavefield and, for days with tremor activity, characterize dominant tremor sources. Those daily first eigenvectors, which can be used as network-based fingerprints of tremor sources, are then grouped into clusters using correlation coefficient as a measure of the vector similarity. As a result, we identify seven clusters associated with different periods of activity of four volcanoes: Tolbachik, Klyuchevskoy, Shiveluch, and Kizimen. The developed method does not require a priori knowledge and is fully automatic; and the database of the network-based tremor fingerprints can be continuously enriched with newly available data.

Median Filtering Methods for Non-volcanic Tremor Detection

Science.gov (United States)

Damiao, L. G.; Nadeau, R. M.; Dreger, D. S.; Luna, B.; Zhang, H.

2016-12-01

Various properties of median filtering over time and space are used to address challenges posed by the Non-volcanic tremor detection problem. As part of a "Big-Data" effort to characterize the spatial and temporal distribution of ambient tremor throughout the Northern San Andreas Fault system, continuous seismic data from multiple seismic networks with contrasting operational characteristics and distributed over a variety of regions are being used. Automated median filtering methods that are flexible enough to work consistently with these data are required. Tremor is characterized by a low-amplitude, long-duration signal-train whose shape is coherent at multiple stations distributed over a large area. There are no consistent phase arrivals or mechanisms in a given tremor's signal and even the durations and shapes among different tremors vary considerably. A myriad of masquerading noise, anthropogenic and natural-event signals must also be discriminated in order to obtain accurate tremor detections. We present here results of the median methods applied to data from four regions of the San Andreas Fault system in northern California (Geysers Geothermal Field, Napa, Bitterwater and Parkfield) to illustrate the ability of the methods to detect tremor under diverse conditions.

Volcanic risk perception in the Campi Flegrei area

Science.gov (United States)

Ricci, T.; Barberi, F.; Davis, M. S.; Isaia, R.; Nave, R.

2013-03-01

The Campi Flegrei which includes part of the city of Naples, is an active volcanic system; its last eruption occurred in 1538 AD. More recently two significant crises occurred between 1969 and 72 and 1982-84 and were accompanied by ground movements (bradyseism) and seismic activity, forcing people of the town of Pozzuoli to be evacuated. Since 1984 development of a volcanic emergency plan has been underway. In 2000 Civil Protection published a risk map which defined the Red Zone, an area highly at risk from pyroclastic flows, which would need to be evacuated before an eruption. The first study to evaluate the volcanic risk perceptions of the people living within the Campi Flegrei area was completed in spring 2006, resulting in the largest sample ever studied on this topic except for one on Vesuvio area residents by Barberi et al. (2008). A 46 item questionnaire was distributed to 2000 of the approximately 300,000 residents of the Campi Flegrei Red Zone, which includes three towns and four neighborhoods within the city of Naples. A total of 1161 questionnaires were returned, for an overall response rate of 58%. Surveys were distributed to junior high and high school students, as well as to adult members of the general population. Results indicated that unlike issues such as crime, traffic, trash, and unemployment, volcanic hazards are not spontaneously mentioned as a major problem facing their community. However, when asked specific questions about volcanic risks, respondents believe that an eruption is likely and could have serious consequences for themselves and their communities and they are quite worried about the threat. Considering the events of 1969-72 and 1982-84, it was not surprising that respondents indicated earthquakes and ground deformations as more serious threats than eruptive phenomena. Of significant importance is that only 17% of the sample knows about the existence of the Emergency Plan, announced in 2001, and 65% said that they have not received

Mantle upwellings and convective instabilities revealed by seismic tomography and helium isotope geochemistry beneath eastern Africa

Science.gov (United States)

Montagner, Jean-Paul; Marty, Bernard; Stutzmann, Eléonore; Sicilia, Déborah; Cara, Michel; Pik, Raphael; Lévêque, Jean-Jacques; Roult, Geneviève; Beucler, Eric; Debayle, Eric

2007-11-01

The relationship between intraplate volcanism and continental tectonics has been investigated for North and East Africa using a high resolution three-dimensional anisotropic tomographic model derived from seismic data of a French experiment ``Horn of Africa'' and existing broadband data. The joint inversion for seismic velocity and anisotropy of the upper 400 km of the mantle, and geochemical data reveals a complex interaction between mantle upwellings, and lithosphere. Two kinds of mantle upwellings can be distinguished: The first one, the Afar ``plume'' originates from deeper than 400 km and is characterized by enrichment in primordial 3He and 3He/4He ratios higher than those along mid-ocean ridges (MOR). The second one, associated with other Cenozoic volcanic provinces (Darfur, Tibesti, Hoggar, Cameroon), with 3He/4He ratios similar to, or lower than MOR, is a consequence of shallower upwelling. The presumed asthenospheric convective instabilities are oriented in an east-west direction, resulting from interaction between south-north asthenospheric mantle flow, main plume head and topography on the base of lithosphere.

The Hawaiian Volcano Observatory: a natural laboratory for studying basaltic volcanism: Chapter 1 in Characteristics of Hawaiian volcanoes

Science.gov (United States)

Tilling, Robert I.; Kauahikaua, James P.; Brantley, Steven R.; Neal, Christina A.; Poland, Michael P.; Takahashi, T. Jane; Landowski, Claire M.

2014-01-01

In the beginning of the 20th century, geologist Thomas A. Jaggar, Jr., argued that, to fully understand volcanic and associated hazards, the expeditionary mode of studying eruptions only after they occurred was inadequate. Instead, he fervently advocated the use of permanent observatories to record and measure volcanic phenomena—at and below the surface—before, during, and after eruptions to obtain the basic scientific information needed to protect people and property from volcanic hazards. With the crucial early help of American volcanologist Frank Alvord Perret and the Hawaiian business community, the Hawaiian Volcano Observatory (HVO) was established in 1912, and Jaggar’s vision became reality. From its inception, HVO’s mission has centered on several goals: (1) measuring and documenting the seismic, eruptive, and geodetic processes of active Hawaiian volcanoes (principally Kīlauea and Mauna Loa); (2) geological mapping and dating of deposits to reconstruct volcanic histories, understand island evolution, and determine eruptive frequencies and volcanic hazards; (3) systematically collecting eruptive products, including gases, for laboratory analysis; and (4) widely disseminating observatory-acquired data and analysis, reports, and hazard warnings to the global scientific community, emergency-management authorities, news media, and the public. The long-term focus on these goals by HVO scientists, in collaboration with investigators from many other organizations, continues to fulfill Jaggar’s career-long vision of reducing risks from volcanic and earthquake hazards across the globe.

Stress barriers controlling lateral migration of magma revealed by seismic tomography

OpenAIRE

Mart?, J.; Villase?or, A.; Geyer, A.; L?pez, C.; Tryggvason, A.

2017-01-01

Understanding how monogenetic volcanic systems work requires full comprehension of the local and regional stresses that govern magma migration inside them and why/how they seem to change from one eruption to another. During the 2011-2012 El Hierro eruption (Canary Islands) the characteristics of unrest, including a continuous change in the location of seismicity, made the location of the future vent unpredictable, so short term hazard assessment was highly imprecise. A 3D P-wave velocity mode...

Characterizing Volcanic Eruptions on Venus: Some Realistic (?) Scenarios

Science.gov (United States)

Stofan, E. R.; Glaze, L. S.; Grinspoon, D. H.

2011-01-01

When Pioneer Venus arrived at Venus in 1978, it detected anomalously high concentrations of SO2 at the top of the troposphere, which subsequently declined over the next five years. This decline in SO2 was linked to some sort of dynamic process, possibly a volcanic eruption. Observations of SO2 variability have persisted since Pioneer Venus. More recently, scientists from the Venus Express mission announced that the SPICAV (Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus) instrument had measured varying amounts of SO2 in the upper atmosphere; VIRTIS (Visible and Infrared Thermal Imaging Spectrometer) measured no similar variations in the lower atmosphere (ESA, 4 April, 2008). In addition, Fegley and Prinn stated that venusian volcanoes must replenish SO2 to the atmosphere, or it would react with calcite and disappear within 1.9 my. Fegley and Tremain suggested an eruption rate on the order of approx 1 cubic km/year to maintain atmospheric SO2; Bullock and Grinspoon posit that volcanism must have occurred within the last 20-50 my to maintain the sulfuric acid/water clouds on Venus. The abundance of volcanic deposits on Venus and the likely thermal history of the planet suggest that it is still geologically active, although at rates lower than Earth. Current estimates of resurfacing rates range from approx 0.01 cubic km/yr to approx 2 cubic km/yr. Demonstrating definitively that Venus is still volcanically active, and at what rate, would help to constrain models of evolution of the surface and interior, and help to focus future exploration of Venus.

Timing and Duration of Volcanism in the North Atlantic Igneous Province: Implications for Geodynamics and Links to the Iceland Hotspot

DEFF Research Database (Denmark)

Storey, M.; Duncan, R. A.; Tegner, Christian

2007-01-01

estimates of erupted magmas and their cumulates to calculate melt production rates for the early Tertiary flood basalts of East Greenland and the Faeroes Islands. The lavas lie at opposite ends of the Greenland-Iceland-Faeroes Ridge, the postulated Iceland hotspot track, and record volcanic activity leading...... of plate separation. The upper part of this crust comprises seismically imaged, seaward-dipping, subaerially erupted lavas. By  50 Ma, eruption rates had diminished drastically and volcanic activity had narrowed to a much restricted portion of the East Greenland margin, at the western end of the Greenland......We combine new and published 40Ar/39Ar age determinations from incremental heating experiments on whole rocks and mineral separates to assess the timing, duration and distribution of volcanic activity during construction of the North Atlantic Igneous Province. We use these ages together with volume...

Geochemical differentiation processes for arc magma of the Sengan volcanic cluster, Northeastern Japan, constrained from principal component analysis

Science.gov (United States)

Ueki, Kenta; Iwamori, Hikaru

2017-10-01

In this study, with a view of understanding the structure of high-dimensional geochemical data and discussing the chemical processes at work in the evolution of arc magmas, we employed principal component analysis (PCA) to evaluate the compositional variations of volcanic rocks from the Sengan volcanic cluster of the Northeastern Japan Arc. We analyzed the trace element compositions of various arc volcanic rocks, sampled from 17 different volcanoes in a volcanic cluster. The PCA results demonstrated that the first three principal components accounted for 86% of the geochemical variation in the magma of the Sengan region. Based on the relationships between the principal components and the major elements, the mass-balance relationships with respect to the contributions of minerals, the composition of plagioclase phenocrysts, geothermal gradient, and seismic velocity structure in the crust, the first, the second, and the third principal components appear to represent magma mixing, crystallizations of olivine/pyroxene, and crystallizations of plagioclase, respectively. These represented 59%, 20%, and 6%, respectively, of the variance in the entire compositional range, indicating that magma mixing accounted for the largest variance in the geochemical variation of the arc magma. Our result indicated that crustal processes dominate the geochemical variation of magma in the Sengan volcanic cluster.

Modernization of the USGS Hawaiian Volcano Observatory Seismic Processing Infrastructure

Science.gov (United States)

Antolik, L.; Shiro, B.; Friberg, P. A.

2016-12-01

The USGS Hawaiian Volcano Observatory (HVO) operates a Tier 1 Advanced National Seismic System (ANSS) seismic network to monitor, characterize, and report on volcanic and earthquake activity in the State of Hawaii. Upgrades at the observatory since 2009 have improved the digital telemetry network, computing resources, and seismic data processing with the adoption of the ANSS Quake Management System (AQMS) system. HVO aims to build on these efforts by further modernizing its seismic processing infrastructure and strengthen its ability to meet ANSS performance standards. Most notably, this will also allow HVO to support redundant systems, both onsite and offsite, in order to provide better continuity of operation during intermittent power and network outages. We are in the process of implementing a number of upgrades and improvements on HVO's seismic processing infrastructure, including: 1) Virtualization of AQMS physical servers; 2) Migration of server operating systems from Solaris to Linux; 3) Consolidation of AQMS real-time and post-processing services to a single server; 4) Upgrading database from Oracle 10 to Oracle 12; and 5) Upgrading to the latest Earthworm and AQMS software. These improvements will make server administration more efficient, minimize hardware resources required by AQMS, simplify the Oracle replication setup, and provide better integration with HVO's existing state of health monitoring tools and backup system. Ultimately, it will provide HVO with the latest and most secure software available while making the software easier to deploy and support.

Seismic swarms and fluid flow offshore Central America

Science.gov (United States)

Dzierma, Yvonne; Thorwart, Martin; Hensen, Christian; Rabbel, Wolfgang; Wolf, Florian

2010-05-01

Offshore Nicaragua and Northern Costa Rica, the Cocos Plate subducts beneath the Caribbean Plate, carrying with it a large amount of fluids and volatiles. While some of these are set free at great depth beneath the volcanic arc, causing the extremely high water content observed in Nicaraguan mafic magmas (Carr et al., 2003; Kutterolf et al., 2007), some early dehydration reactions already release fluids from the subducting plate underneath the continental slope. Unlike in accretionary margins, where these fluids migrate up along the decollement towards the deformation front, fluid release at erosional margins seems to occur through fractures in the overriding plate (Ranero et al., 2008). Fluid seeps in this region have be observed at seafloor mounds, appearing as side-scan sonar backscatter anomalies or revealed by the presence of chemosynthetic communities (Sahling et al., 2008). In the framework of the General Research Area SFB 574 "Volatiles and Fluids in Subduction Zones", a network of 20 ocean-bottom-stations was deployed offshore Sta Elena Peninsula, Northern Costa Rica, from December 2005 to June 2006. Several distinct swarms of small earthquakes were observed at the seismic stations, which occurred clustered over a time period of several days and have very similar seismic waveforms. Since a correlation of fluid-release sites with the occurrence of sporadic seismic swarms would indicate that fluid migration and fracturing is the mechanism responsible for triggering the earthquake swarms, the events are re-analysed by double-difference localisation to enhance the resolution of the earthquake locations. The results are then considered to estimate the migration velocity and direction and compare the localisations with the known mound sites. Carr, M., Feigenson, M. D., Patino, L. C., and Walker, J. A., 2003: Volcanism and geochemistry in Central America: Progress and problems, in Eiler, J. (ed.), Inside the subduction factory, pp. 153-179, American Geophysical

Seismic attenuation structure beneath Nazca Plate subduction zone in southern Peru

Science.gov (United States)

Jang, H.; Kim, Y.; Clayton, R. W.

2017-12-01

We estimate seismic attenuation in terms of quality factors, QP and QS using P and S phases, respectively, beneath Nazca Plate subduction zone between 10°S and 18.5°S latitude in southern Peru. We first relocate 298 earthquakes with magnitude ranges of 4.0-6.5 and depth ranges of 20-280 km. We measure t*, which is an integrated attenuation through the seismic raypath between the regional earthquakes and stations. The measured t* are inverted to construct three-dimensional attenuation structures of southern Peru. Checkerboard test results for both QP and QS structures ensure good resolution in the slab-dip transition zone between flat and normal slab subduction down to a depth of 200 km. Both QP and QS results show higher attenuation continued down to a depth of 50 km beneath volcanic arc and also beneath the Quimsachata volcano, the northernmost young volcano, located far east of the main volcanic front. We also observe high attenuation in mantle wedge especially beneath the normal subduction region in both QP and QS (100-130 in QP and 100-125 in QS) and slightly higher QP and QS beneath the flat-subduction and slab-dip transition regions. We plan to relate measured attenuation in the mantle wedge to material properties such as viscosity to understand the subduction zone dynamics.

APhoRISM FP7 project: the Multi-platform volcanic Ash Cloud Estimation (MACE) infrastructure

Science.gov (United States)

Merucci, Luca; Corradini, Stefano; Bignami, Christian; Stramondo, Salvatore

2014-05-01

APHORISM is an FP7 project that aims to develop innovative products to support the management and mitigation of the volcanic and the seismic crisis. Satellite and ground measurements will be managed in a novel manner to provide new and improved products in terms of accuracy and quality of information. The Multi-platform volcanic Ash Cloud Estimation (MACE) infrastructure will exploit the complementarity between geostationary, and polar satellite sensors and ground measurements to improve the ash detection and retrieval and to fully characterize the volcanic ash clouds from source to the atmosphere. The basic idea behind the proposed method consists to manage in a novel manner, the volcanic ash retrievals at the space-time scale of typical geostationary observations using both the polar satellite estimations and in-situ measurements. The typical ash thermal infrared (TIR) retrieval will be integrated by using a wider spectral range from visible (VIS) to microwave (MW) and the ash detection will be extended also in case of cloudy atmosphere or steam plumes. All the MACE ash products will be tested on three recent eruptions representative of different eruption styles in different clear or cloudy atmospheric conditions: Eyjafjallajokull (Iceland) 2010, Grimsvotn (Iceland) 2011 and Etna (Italy) 2011-2012. The MACE infrastructure will be suitable to be implemented in the next generation of ESA Sentinels satellite missions.

Magnetic properties of frictional volcanic materials

Science.gov (United States)

Kendrick, Jackie E.; Lavallée, Yan; Biggin, Andrew; Ferk, Annika; Leonhardt, Roman

2015-04-01

During dome-building volcanic eruptions, highly viscous magma extends through the upper conduit in a solid-like state. The outer margins of the magma column accommodate the majority of the strain, while the bulk of the magma is able to extrude, largely undeformed, to produce magma spines. Spine extrusion is often characterised by the emission of repetitive seismicity, produced in the upper <1 km by magma failure and slip at the conduit margins. The rheology of the magma controls the depth at which fracture can occur, while the frictional properties of the magma are important in controlling subsequent marginal slip processes. Upon extrusion, spines are coated by a carapace of volcanic fault rocks which provide insights into the deeper conduit processes. Frictional samples from magma spines at Mount St. Helens (USA), Soufriere Hills (Montserrat) and Mount Unzen (Japan) have been examined using structural, thermal and magnetic analyses to reveal a history of comminution, frictional heating, melting and cooling to form volcanic pseudotachylyte. Pseudotachylyte has rarely been noted in volcanic materials, and the recent observation of its syn-eruptive formation in dome-building volcanoes was unprecedented. The uniquely high thermal conditions of volcanic environments means that frictional melt remains at elevated temperatures for longer than usual, causing slow crystallisation, preventing the development of some signature "quench" characteristics. As such, rock-magnetic tests have proven to be some of the most useful tools in distinguishing pseudotachylytes from their andesite/ dacite hosts. In volcanic pseudotachylyte the mass normalised natural remanent magnetisation (NRM) when further normalised with the concentration dependent saturation remanence (Mrs) was found to be higher than the host rock. Remanence carriers are defined as low coercive materials across all samples, and while the remanence of the host rock displays similarities to an anhysteretic remanent

Innovations in seismic tomography, their applications and induced seismic events in carbon sequestration

Science.gov (United States)

Li, Peng

algorithm with the inclusion of full topography that is integrated from the Digital Elevation Model data. We present both synthetic and real data tests based on the compressional (P) wave arrival time data for Kilauea volcano in Hawai'i. A total of 33,768 events with 515,711 P-picks recorded by 35 stations at the Hawaiian Volcano Observatory are used in these tests. The comparison between the new and traditional methods based on the synthetic test shows that our new algorithm significantly improves the accuracy of the velocity model, especially at shallow depths. In the real data test, the P-wave velocity model of Kilauea shows some intriguing features. Velocity decrease from the surface to 2 km depth beneath Kilauea caldera indicates a state change of the basalt. Low velocity zones beneath Pu'u'O'o, Heiheiahulu and the Hilina fault system between 5 and 12 km are possible partial melting zones. High velocity anomalies are resolved below 6 km depth beneath the summit caldera, which may suggest the presence of consolidated gabbro-ultramafic cumulates. In the third work, we installed three broadband seismic stations (Test1, Test2 and Test3) in an Enhanced Oil Recovery field to monitor the potential seismic events associated with CO 2 injection. In the two years of continuous seismic data between October 2011 and October 2013, we observed a type of long duration (LD) events instead of typical micro earthquakes, with an average daily rate of 12. The LD events have the following characteristics: (1) their duration varies from ˜30 to ˜300 sec; (2) the amplitude changes smoothly from the beginning to the end of the LD event window; (3) they are local seismic events and were not recorded by regional seismic stations (e.g., ˜200 km away); (4) the waveforms are very different from those of typical earthquakes, but similar to volcanic tremors; (5) the frequency content is mainly concentrated between 0.5 and 6 Hz, which is similar to the frequency band of volcanic tremors; and (6

Estimating seismic moment magnitude (Mw) of tremor bursts in northern Cascadia: Implications for the “seismic efficiency” of episodic tremor and slip

Science.gov (United States)

Kao, Honn; Wang, Kelin; Dragert, Herb; Kao, Jason Y.; Rogers, Garry

2010-10-01

We develop a method to estimate the seismic moments of deep non-volcanic tremor bursts observed in northern Cascadia. For each tremor burst, the maximum amplitudes at individual stations within a time window ±5 s around the predicted arrivals of the S phase are measured and compared to the maximum S amplitudes measured from synthetic seismograms. The proposed method is thoroughly calibrated using 464 local earthquakes and the results show excellent consistency between the reported ML and the estimated Mw. We apply the method to northern Cascadia tremors and infer that most bursts have Mw˜1.0-1.7. The corresponding b value appears to be 1, consistent with that of ordinary earthquakes but over a narrower Mw range. Comparison of cumulative tremor Mw and the Mw estimated from the accompanying slow slip suggests that the “seismic efficiency” of the Episodic Tremor and Slip (ETS) is of the order of 0.1% or less.

Automatic Classification of volcano-seismic events based on Deep Neural Networks.

Science.gov (United States)

Titos Luzón, M.; Bueno Rodriguez, A.; Garcia Martinez, L.; Benitez, C.; Ibáñez, J. M.

2017-12-01

Seismic monitoring of active volcanoes is a popular remote sensing technique to detect seismic activity, often associated to energy exchanges between the volcano and the environment. As a result, seismographs register a wide range of volcano-seismic signals that reflect the nature and underlying physics of volcanic processes. Machine learning and signal processing techniques provide an appropriate framework to analyze such data. In this research, we propose a new classification framework for seismic events based on deep neural networks. Deep neural networks are composed by multiple processing layers, and can discover intrinsic patterns from the data itself. Internal parameters can be initialized using a greedy unsupervised pre-training stage, leading to an efficient training of fully connected architectures. We aim to determine the robustness of these architectures as classifiers of seven different types of seismic events recorded at "Volcán de Fuego" (Colima, Mexico). Two deep neural networks with different pre-training strategies are studied: stacked denoising autoencoder and deep belief networks. Results are compared to existing machine learning algorithms (SVM, Random Forest, Multilayer Perceptron). We used 5 LPC coefficients over three non-overlapping segments as training features in order to characterize temporal evolution, avoid redundancy and encode the signal, regardless of its duration. Experimental results show that deep architectures can classify seismic events with higher accuracy than classical algorithms, attaining up to 92% recognition accuracy. Pre-training initialization helps these models to detect events that occur simultaneously in time (such explosions and rockfalls), increase robustness against noisy inputs, and provide better generalization. These results demonstrate deep neural networks are robust classifiers, and can be deployed in real-environments to monitor the seismicity of restless volcanoes.

Methodology for the study of the Mexican Volcanic Belt; Metodologia para el estudio del Cinturon Volcanico Mexicano

Energy Technology Data Exchange (ETDEWEB)

Pal Verma, Surendra [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)

1991-12-31

The Mexican Volcanic Belt (MVB) is an structure 20 to 150 kilometers wide an {approx}1000 km long, oriented approximately east-west, from nearby Puerto Vallarta up until Veracruz; it contains a great number ({approx}7000) of volcanic apparatus or volcanic centers (Verma, 1987a, and the cited references in this paper). Fig. 1 represents the location of some of its main volcanic centers. The MVB forms part of the ring of fire that extends all along the circumpacific region (see Fig. 2) named this way because it refers to a very high volcanoes population (many of them active volcanoes), to its seismic activity and to the large geothermal manifestations. [Espanol] El Cinturon Volcanico Mexicano (CVM) es una estructura de 20 a 150 kilometros de ancho, {approx}1,000 km de largo, orientada aproximadamente este-oeste desde cerca de Puerto Vallarta hasta Veracruz; contiene gran numero ({approx}7,000) de aparatos o centros volcanicos (Verma, 1987a, y las referencias citadas en este trabajo). La figura 1 presenta la localizacion de algunos de sus principales centros volcanicos. El CVM forma parte del llamado anillo del fuego, que se extiende a todo lo largo de la region circumpacifica (vease la Fig. 2), denominada asi porque se trata de una poblacion muy alta de volcanes (mucho de ellos activos), de la actividad sismica y de grandes manifestaciones geotermicas.

Methodology for the study of the Mexican Volcanic Belt; Metodologia para el estudio del Cinturon Volcanico Mexicano

Energy Technology Data Exchange (ETDEWEB)

Pal Verma, Surendra [Instituto de Investigaciones Electricas, Cuernavaca (Mexico)

1990-12-31

The Mexican Volcanic Belt (MVB) is an structure 20 to 150 kilometers wide an {approx}1000 km long, oriented approximately east-west, from nearby Puerto Vallarta up until Veracruz; it contains a great number ({approx}7000) of volcanic apparatus or volcanic centers (Verma, 1987a, and the cited references in this paper). Fig. 1 represents the location of some of its main volcanic centers. The MVB forms part of the ring of fire that extends all along the circumpacific region (see Fig. 2) named this way because it refers to a very high volcanoes population (many of them active volcanoes), to its seismic activity and to the large geothermal manifestations. [Espanol] El Cinturon Volcanico Mexicano (CVM) es una estructura de 20 a 150 kilometros de ancho, {approx}1,000 km de largo, orientada aproximadamente este-oeste desde cerca de Puerto Vallarta hasta Veracruz; contiene gran numero ({approx}7,000) de aparatos o centros volcanicos (Verma, 1987a, y las referencias citadas en este trabajo). La figura 1 presenta la localizacion de algunos de sus principales centros volcanicos. El CVM forma parte del llamado anillo del fuego, que se extiende a todo lo largo de la region circumpacifica (vease la Fig. 2), denominada asi porque se trata de una poblacion muy alta de volcanes (mucho de ellos activos), de la actividad sismica y de grandes manifestaciones geotermicas.

Volcanic stratigraphy: A review

Science.gov (United States)

Martí, Joan; Groppelli, Gianluca; Brum da Silveira, Antonio

2018-05-01

Volcanic stratigraphy is a fundamental component of geological mapping in volcanic areas as it yields the basic criteria and essential data for identifying the spatial and temporal relationships between volcanic products and intra/inter-eruptive processes (earth-surface, tectonic and climatic), which in turn provides greater understanding of the geological evolution of a region. Establishing precise stratigraphic relationships in volcanic successions is not only essential for understanding the past behaviour of volcanoes and for predicting how they might behave in the future, but is also critical for establishing guidelines for exploring economic and energy resources associated with volcanic systems or for reconstructing the evolution of sedimentary basins in which volcanism has played a significant role. Like classical stratigraphy, volcanic stratigraphy should also be defined using a systematic methodology that can provide an organised and comprehensive description of the temporal and spatial evolution of volcanic terrain. This review explores different methods employed in studies of volcanic stratigraphy, examines four case studies that use differing stratigraphic approaches, and recommends methods for using systematic volcanic stratigraphy based on the application of the concepts of traditional stratigraphy but adapted to the needs of volcanological environment.

Development of mobile sensor for volcanic observation "HOMURA": Test campaigns for a long-term operation

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Kaneko, K.; Iwahori, K.; Ito, K.; Sagi, H.

2016-12-01

Unmanned robots are useful to observe volcanic phenomena near active volcanic vents, to learn symptoms and transitions of eruptions, and to mitigate volcanic disasters. We have been trying to develop a practical UGV robot for flexible observation of active volcanic vents. We named this system "Homura". In this presentation, we report results of test campaigns of Homura for observation in a volcanic field. We have developed a prototype of Homura, which is a small robot vehicle with six wheels (75 x 43 x 31 cm and a weight of about 12 kg). It is remotely controlled with mobile phone radio waves; it can move in volcanic fields and send real time data of sensors (camera and gas sensors) equipped in the vehicle to the base station. Homura has a small solar panel (4 W). Power consumption of Homura is about 4 W in operation of sensors and less than 0.1 W in idle state, so that Homura can work outdoors for a long time by intermittent operation.We carried out two test campaigns of Homura at Iwo-yama to examine if Homura can work for a few month in natural volcanic fields (however, it had no solar panel in these campaigns). Iwo-yama is one of craters in the Kirishima volcanic field, SW Japan; the area within 1 km from the crater was an off-limit area from Oct., 2014 to May, 2015 and from Feb. to Mar., 2016 because of strong volcanic seismicity. On Feb. 19th, 2015 and Mar. 7th, 2016, we carried and put Homura at the rim of the crater. Unfortunately, mobile phone connectivity was not entirely stable around Iwo-yama. Then, we did not move Homura and only obtain real time data of the sensors. In the two campaigns, we operated Homura at our office for a few hours every day for 49 and 37 days, respectively. Although the weather was often bad (rain, fog, or cold temperature) during the campaigns, Homura perfectly worked. The results of these campaigns indicate that Homura is useful as s simple monitoring station in volcanic fields where mobile phone connection is available.

Characteristics of volcanic reservoirs and distribution rules of effective reservoirs in the Changling fault depression, Songliao Basin

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Pujun Wang

2015-11-01

Full Text Available In the Songliao Basin, volcanic oil and gas reservoirs are important exploration domains. Based on drilling, logging, and 3D seismic (1495 km2 data, 546 sets of measured physical properties and gas testing productivity of 66 wells in the Changling fault depression, Songliao Basin, eruptive cycles and sub-lithofacies were distinguished after lithologic correction of the 19,384 m volcanic well intervals, so that a quantitative analysis was conducted on the relation between the eruptive cycles, lithologies and lithofacies and the distribution of effective reservoirs. After the relationship was established between lithologies, lithofacies & cycles and reservoir physical properties & oil and gas bearing situations, an analysis was conducted on the characteristics of volcanic reservoirs and the distribution rules of effective reservoirs. It is indicated that 10 eruptive cycles of 3 sections are totally developed in this area, and the effective reservoirs are mainly distributed at the top cycles of eruptive sequences, with those of the 1st and 3rd Members of Yingcheng Formation presenting the best reservoir properties. In this area, there are mainly 11 types of volcanic rocks, among which rhyolite, rhyolitic tuff, rhyolitic tuffo lava and rhyolitic volcanic breccia are the dominant lithologies of effective reservoirs. In the target area are mainly developed 4 volcanic lithofacies (11 sub-lithofacies, among which upper sub-lithofacies of effusive facies and thermal clastic sub-lithofacies of explosion lithofacies are predominant in effective reservoirs. There is an obvious corresponding relationship between the physical properties of volcanic reservoirs and the development degree of effective reservoirs. The distribution of effective reservoirs is controlled by reservoir physical properties, and the formation of effective reservoirs is influenced more by porosity than by permeability. It is concluded that deep volcanic gas exploration presents a good

Fault-magma interactions during early continental rifting: Seismicity of the Magadi-Natron-Manyara basins, Africa

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Weinstein, A.; Oliva, S. J.; Ebinger, C. J.; Roecker, S.; Tiberi, C.; Aman, M.; Lambert, C.; Witkin, E.; Albaric, J.; Gautier, S.; Peyrat, S.; Muirhead, J. D.; Muzuka, A. N. N.; Mulibo, G.; Kianji, G.; Ferdinand-Wambura, R.; Msabi, M.; Rodzianko, A.; Hadfield, R.; Illsley-Kemp, F.; Fischer, T. P.

2017-10-01

Although magmatism may occur during the earliest stages of continental rifting, its role in strain accommodation remains weakly constrained by largely 2-D studies. We analyze seismicity data from a 13 month, 39-station broadband seismic array to determine the role of magma intrusion on state-of-stress and strain localization, and their along-strike variations. Precise earthquake locations using cluster analyses and a new 3-D velocity model reveal lower crustal earthquakes beneath the central basins and along projections of steep border faults that degas CO2. Seismicity forms several disks interpreted as sills at 6-10 km below a monogenetic cone field. The sills overlie a lower crustal magma chamber that may feed eruptions at Oldoinyo Lengai volcano. After determining a new ML scaling relation, we determine a b-value of 0.87 ± 0.03. Focal mechanisms for 65 earthquakes, and 13 from a catalogue prior to our array reveal an along-axis stress rotation of ˜60° in the magmatically active zone. New and prior mechanisms show predominantly normal slip along steep nodal planes, with extension directions ˜N90°E north and south of an active volcanic chain consistent with geodetic data, and ˜N150°E in the volcanic chain. The stress rotation facilitates strain transfer from border fault systems, the locus of early-stage deformation, to the zone of magma intrusion in the central rift. Our seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Results indicate that earthquakes are largely driven by stress state around inflating magma bodies.

The Origin of Widespread Long-lived Volcanism Across the Galapagos Volcanic Province

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O'Connor, J. M.; Stoffers, P.; Wijbrans, J. R.; Worthington, T. J.

2005-12-01

40Ar/39Ar ages for rocks dredged (SO144 PAGANINI expedition) and drilled (DSDP) from the Galapagos Volcanic Province (Cocos, Carnegie, Coiba and Malpelo aseismic ridges and associated seamounts) show evidence of 1) increasing age with distance from the Galapagos Archipelago, 2) long-lived episodic volcanism at many locations, and 3) broad overlapping regions of coeval volcanism. The widespread nature of synchronous volcanism across the Galapagos Volcanic Province (GVP) suggests a correspondingly large Galapagos hotspot melting anomaly (O'Connor et al., 2004). Development of the GVP via Cocos and Nazca plate migration and divergence over this broad melting anomaly would explain continued multiple phases of volcanism over millions of years following the initial onset of hotspot volcanism. The question arising from these observations is whether long-lived GVP episodic volcanism is equivalent to `rejuvenescent' or a `post-erosional' phase of volcanism that occurs hundreds of thousands or million years after the main shield-building phase documented on many mid-plate seamount chains, most notably along the Hawaiian-Emperor Seamount Chain? Thus, investigating the process responsible for long-lived episodic GVP volcanism provides the opportunity to evaluate this little understood process of rejuvenation in a physical setting very different to the Hawaiian-Emperor Chain (i.e. on/near spreading axis versus mid-plate). We consider here timing and geochemical information to test the various geodynamic models proposed to explain the origin of GVP hotspot volcanism, especially the possibility of rejuvenated phases that erupt long after initial shield-building.

Historical and Paleo Events as an input for Seismic And Associated Natural Hazard Assessment of Javakheti highland (South Georgia)

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Elashvili, M.; Javakhishvili, Z.; Godoladze, T.; Karakhanyan, A.; Sukhishvili, L.; Nikolaeva, E.; Sokhadze, G.; Avanesyan, M.

2012-12-01

Current study concerns Javakheti area in the Lesser Caucasus. This area comprises a volcanic plateau with more than 20 volcanoes, several of them dated as having erupted during the Holocene. In the region the upper part of Lava complex is represented by Middle-Upper Quaternary formations. The region is an area of young deformations in the Alpine belt. Formation of relief began at the neotectonic stage (Sarmatian) and continues at present. Javakheti is one of the most seismically active regions in the Caucasus, earthquakes of 1899 and 1986 with magnitudes up to 6.0, causing severe damage and hundreds of casualties, occurred there. Historical data on earthquakes in 1088 and 1899 locate them in the same region, highlighting the importance on learning about the location and characteristics of their seismic sources. Javakheti highland seems to be actively populated at least from the Bronze Age period, forming a local culture to be strongly affected by Natural catastrophes and significant changes in Landscapes and climate. Study of potential seismic and associated natural hazards, such as landslide and rockfalls, possible volcanic activity in the region, including paleo and historical evidences, were addressed by number of International Projects (ISTC A-1418, NATO SFP # 983284 ) and multidisciplinary studies carried out by the Institute of Earth Sciences. Data gathered after the Installation of local GPS and Seismic networks have provided new look on seismicity pattern of the region and major seismic sources, while field studies (Geophysical survey, Paleo trenching, Archaeological studies, etc.) have provided new information on the dramatic Natural disasters which occurred in the region and probably played a vital role in its history. Remote sensing techniques became widely used in geological investigations during the decades. Interferometric synthetic aperture radar (InSAR), aerial and optical data analysis have contributed to the development of this work.. Case studies

Event recognition by detrended fluctuation analysis: An application to Teide-Pico Viejo volcanic complex, Tenerife, Spain

International Nuclear Information System (INIS)

Del Pin, Enrico; Carniel, Roberto; Tarraga, Marta

2008-01-01

In this work we investigate the application of the detrended fluctuation analysis (DFA) to seismic data recorded in the island of Tenerife (Canary Islands, Spain) during the month of July 2004, in a phase of possible unrest of the Teide-Pico Viejo volcanic complex. Tectonic events recorded in the area are recognized and located by the Spanish national agency Instituto Geografico Nacional (IGN) and their catalogue is the only currently available dataset, whose completeness unfortunately suffers from the strong presence of anthropogenic noise. In this paper we propose the use of DFA to help to automatically identify events. The evaluation of this case study proves DFA to be a promising tool to be used for rapidly screening large seismic datasets and highlighting time windows with the potential presence of discrete events

Potential Magma Chambers beneath the Tatun Volcanic Area, Taiwan: Results from Magnetotelluric Survey and Monitoring

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Chen, C.

2013-12-01

Previous earthquakes analysis indicated existing seismicity anomaly beneath Tatun volcano, Taiwan, possibly caused by the fluid activity of the volcano. Helium isotope studies also indicated that over 60% of the fumarolic gases and vapors originated from deep mantle in the Tatun volcano area. The chemistry of the fumarolic gases and vapors and seismicity anomaly are important issues in view of possible magma chamber in the Tatun volcano, where is in the vicinity of metropolitan Taipei, only 15 km north of the capital city. In this study magnetotelluric (MT) soundings and monitoring were deployed to understand the geoelectric structures in the Tatun volcano as Electromagnetic methods are sensitive to conductivity contrasts and can be used as a supplementary tool to delineate reservoir boundaries. An anticline extending more than 10 km beneath the Chih-Shin-Shan and Da-You-Kan areas was recognized. Low resistivity at a shallow and highly porous layer 500m thick might indicate circulation of heated water. However, a high resistivity layer at depth between 2 and 6 km was detected. This layer could be associated with high micro-earthquakes zone. The characteristics of this layer produced by either the magma chamber or other geothermal activity were similar to that of some other active volcanic areas in the world. At 6 km underground was a dome structure of medium resistivity. This structure could be interpreted as a magma chamber in which the magma is possibly cooling down, as judged by its relatively high resistivity. The exact attributes of the magma chamber were not precisely determined from the limited MT soundings. At present, a joint monitors including seismic activity, ground deformation, volcanic gases, and changes in water levels and chemistry are conducted by universities and government agencies. When unusual activity is detected, a response team may do more ground surveys to better determine if an eruption is likely.

Inter-Rifting and Inter-Seismic Strain Accumulation in a Propagating Ridge System: A Geodetic Study from South Iceland

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Travis, M. E.; La Femina, P. C.; Geirsson, H.

2012-12-01

The Mid-Atlantic Ridge, a slow spreading (~19 mm/yr) mid-ocean ridge boundary between the North American and Eurasian plates, is exposed subaerially in Iceland as the result of ridge-hotspot interaction. Plate spreading in Iceland is accommodated along neovolcanic zones comprised of central volcanoes and their fissure swarms. In south Iceland plate motion is partitioned between the Western Volcanic Zone (WVZ) and Eastern Volcanic Zone (EVZ). The EVZ is propagating to the southwest, while the WVZ is dying out from the northeast. Plate motion across both systems has been accommodated by repeated rifting events and fissure eruptions. In this study we investigate whether the WVZ is active and accumulating strain, and how strain is partitioned between the WVZ and EVZ. We also test how strain is accumulating along fissure swarms within the EVZ (i.e. is strain accumulation localized to one fissure swarm, or are multiple systems active?). We use GPS data and elastic block models run using the program DEFNODE to investigate these issues. GPS data are processed using the GIPSY-OASIS II software, and have been truncated to the 2000.5-2011 time period to avoid co-seismic displacement from the two June 2000 South Iceland Seismic Zone earthquakes. We also truncate the time series for sites within 20 km of Eyjafjallajökull to the beginning of 2010 to eliminate deformation associated with the March 2010 eruption of that volcano. We correct for co-seismic displacement from the two May 2008 SISZ earthquakes, inflation at Hekla volcano and the horizontal component of glacial isostatic rebound (GIA). Our best-fit model for inter-rifting and inter-seismic elastic strain accumulation suggests 80-90% of spreading is accommodated in the EVZ with the other 10-20% accommodated by the WVZ. The best-fit location of the EVZ is between Veidivotn and Lakigigar in an area of no Holocene volcanic activity. We suggest the WVZ is only active at Hengill and its associated fissure swarm. Geologic and

Intra-arc Seismicity: Geometry and Kinematic Constraints of Active Faulting along Northern Liquiñe-Ofqui and Andean Transverse Fault Systems [38º and 40ºS, Southern Andes

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Sielfeld, G.; Lange, D.; Cembrano, J. M.

2017-12-01

Intra-arc crustal seismicity documents the schizosphere tectonic state along active magmatic arcs. At oblique-convergent margins, a significant portion of bulk transpressional deformation is accommodated in intra-arc regions, as a consequence of stress and strain partitioning. Simultaneously, crustal fluid migration mechanisms may be controlled by the geometry and kinematics of crustal high strain domains. In such domains shallow earthquakes have been associated with either margin-parallel strike-slip faults or to volcano-tectonic activity. However, very little is known on the nature and kinematics of Southern Andes intra-arc crustal seismicity and its relation with crustal faults. Here we present results of a passive seismicity study based on 16 months of data collected from 33 seismometers deployed along the intra-arc region of Southern Andes between 38˚S and 40˚S. This region is characterized by a long-lived interplay among margin-parallel strike-slip faults (Liquiñe-Ofqui Fault System, LOFS), second order Andean-transverse-faults (ATF), volcanism and hydrothermal activity. Seismic signals recorded by our network document small magnitude (0.2P and 2,796 S phase arrival times have been located with NonLinLoc. First arrival polarities and amplitude ratios of well-constrained events, were used for focal mechanism inversion. Local seismicity occurs at shallow levels down to depth of ca. 16 km, associated either with stratovolcanoes or to master, N10˚E, and subsidiary, NE to ENE, striking branches of the LOFS. Strike-slip focal mechanisms are consistent with the long-term kinematics documented by field structural-geology studies. Unexpected, well-defined NW-SE elongated clusters are also reported. In particular, a 72-hour-long, N60˚W-oriented seismicity swarm took place at Caburgua Lake area, describing a ca. 36x12x1km3 faulting crustal volume. Results imply a unique snapshot on shallow crustal tectonics, contributing to the understanding of faulting processes

An interdisciplinary approach to volcanic risk reduction under conditions of uncertainty: a case study of Tristan da Cunha

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Hicks, A.; Barclay, J.; Simmons, P.; Loughlin, S.

2013-12-01

This research project adopted an interdisciplinary approach to volcanic risk reduction on the remote volcanic island of Tristan da Cunha (South Atlantic). New data were produced that: (1) established no spatio-temporal pattern to recent volcanic activity; (2) quantified the high degree of scientific uncertainty around future eruptive scenarios; (3) analysed the physical vulnerability of the community as a consequence of their geographical isolation and exposure to volcanic hazards; (4) evaluated social and cultural influences on vulnerability and resilience. Despite their isolation and prolonged periods of hardship, islanders have demonstrated an ability to cope with and recover from adverse events. This resilience is likely a function of remoteness, strong kinship ties, bonding social capital, and persistence of shared values and principles established at community inception. While there is good knowledge of the styles of volcanic activity on Tristan, given the high degree of scientific uncertainty about the timing, size and location of future volcanism, a qualitative scenario planning approach was used as a vehicle to convey this information to the islanders. This deliberative, anticipatory method allowed on-island decision makers to take ownership of risk identification, management and capacity building within their community. This paper demonstrates the value of integrating social and physical sciences with development of effective, tailored communication strategies in volcanic risk reduction.

Forearc oceanic crust in the Izu-Bonin arc - new insights from active-source seismic survey -

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Kodaira, S.; Noguchi, N.; Takahashi, N.; Ishizuka, O.; Kaneda, Y.

2009-12-01

Petrological studies have suggested that oceanic crust is formed in forearc areas during the initial stage of subduction. However, there is little geophysical evidence for the formation of oceanic crust in those regions. In order to examine crustal formation process associated with a subduction initiation process, we conducted an active-source seismic survey at a forearc region in the Izu-Bonin intra-oceanic arc. The resultant seismic image shows a remarkably thin crust (less than 10 km) at the northern half of the Bonin ridge (at the north of the Chichi-jima) and abrupt thickening the crust (~ 20 km thick) toward the south (at the Haha-jima). Comparison of velocity-depth profiles of the thin forearc crust of the Bonin ridge with those of typical oceanic crusts showed them to be seismologically identical. The observed structural variation also well corresponds to magmatic activities along the forearc. Boninitic magmatism is evident in the area of thin crust and tholeiitic-calcalkaline andesitic volcanism in the area of thick crust. Based on high precision dating studies of those volcanic rocks, we interpreted that the oceanic-type thin crust associated with boninitic volcanism has been created soon after the initiation of subduction (45-48 Ma) and and that the nonoceanic thick crust was created by tholeiitic-calcalkaline andesitic magmatism after the boninitic magmatism was ceased. The above seismological evidences strongly support the idea of forearc oceanic crust (or phiolite) created by forearc spreading in the initial stage of subduction along the intra-oceanic arc.

Aeromagnetic Study of the Nortern Acambay Graben and Amealco Caldera, Central Mexican Volcanic Belt

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Gonzalez, T.

2011-12-01

The Mexican Volcanic Belt (MVB) is characterized by E-W striking faults which form a series of en echelon graben along its length. In the central region of the MVB is located the Acambay graben an intra-arc tectonic depression structure, of apparent Quaternary age, which gives rise to pronounced scarps over a distance of about 80 Km. and 15 to 35 Km wide. The general arrangement of the faults that constitute the Acambay graben shows E-W trend which defines the fronts of the graben exhibits a major fault discontinuity. The graben is limited of the north by the Acambay- Tixmadeje and Epitafio Huerta faults and in the south by the Pastores and Venta de Bravo faults.. In the northern wall in the graben is located the Amealco caldera. This volcanic center (approximately 10 km in diameter) was formed by several discrete volcanic events, which produced an ignimbrite which covers the area. It is partially cut by a regional fault and the southern portion of the Amealco Caldera was displaced by a normal faulting along a segment of the Epitafio Huerta system. Continued tectonic activity in the Acambay area is confirmed by recent seismic episodes The Amealco tuff is the most important volcanic unit because of its volume and distribution. Aeromagnetic data was obtained and analyzed the anomalies. The anomaly map was compared with the surface geology and larger anomalies were correlated with major volcanic features. Since our main interest was in mapping the subsurface intrusive and volcanic bodies, the total field magnetic anomalies were reduced to the pole by using the double integral Fourier method. The reduced to the pole anomaly map results in a simplified pattern of isolated positive and negative anomalies, which show an improved correlation with all major volcanic structures. For the analysis and interpretation of the anomalies, the reduced to the pole anomalies were continued upward at various reference levels. These operations result in smoothing of the anomaly field by

Volcanic features of Io

International Nuclear Information System (INIS)

Carr, M.H.; Masursky, H.; Strom, R.G.; Terrile, R.J.

1979-01-01

The volcanic features of Io as detected during the Voyager mission are discussed. The volcanic activity is apparently higher than on any other body in the Solar System. Its volcanic landforms are compared with features on Earth to indicate the type of volcanism present on Io. (U.K.)

Seismo-volcanic monitoring at Furnas Volcano (Azores): radon (222Rn) concentration in groundwater

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Silva, Catarina; Virgílio Cruz, José; Ferreira, Teresa; Viveiros, Fátima; Freire, Pedro; Allard, Patrick

2017-04-01

The Azores archipelago, located in the middle of the North Atlantic Ocean, is composed of nine volcanic islands that formed at the triple junction of the North American, Eurasian and African (Nubian) tectonic plates. These volcanic islands were the sites of several eruptions and destructive earthquakes since human settlement in the 15th century. S. Miguel Island, the largest and most densely populated island of the Azores, hosts three active strato-volcanoes with calderas. Furnas Volcano is one of these. Its eruptive activity has been essentially explosive, involving magmas with trachytic (s.l.) composition. In the last 5000 years at least 10 explosive eruptions occurred inside the caldera of Furnas. The last one occurred in 1630 and was subplinian in character. Since then an intense hydrothermal activity has persisted, involving four main fumarolic fields, thermal springs, CO2-rich springs, several soil diffuse degassing areas (CO2 and 222Rn), as well as occasional hydrothermal explosions. In the past decade we have developed a radon survey of Furnas hydrothermal manifestations. Here we report on the radon survey of twelve water springs, located inside the caldera, and representative of the different water types encountered at the volcano (orthothermal, thermal and CO2-rich springs). Bimonthly sampling and determination of radon activity and water temperature was performed in the selected springs between years 2007 and 2011. At each sampling point two water samples were collected for radon dosing in laboratory with the RAD7 equipment. A decay correction was applied to each sample. The average radon activities were found to vary between 1.15 Bq/L and 29.77 Bq/L, while water temperatures ranged between 16.5 °C and 76.2 °C. As a whole radon activities inversely correlate with water temperature, with orthothermal springs showing higher radon activity than thermal springs. Temporal variations in both parameters appear to be mainly determined by seasonal variations of

When probabilistic seismic hazard climbs volcanoes: the Mt. Etna case, Italy – Part 2: Computational implementation and first results

Directory of Open Access Journals (Sweden)

L. Peruzza

2017-11-01

Full Text Available This paper describes the model implementation and presents results of a probabilistic seismic hazard assessment (PSHA for the Mt. Etna volcanic region in Sicily, Italy, considering local volcano-tectonic earthquakes. Working in a volcanic region presents new challenges not typically faced in standard PSHA, which are broadly due to the nature of the local volcano-tectonic earthquakes, the cone shape of the volcano and the attenuation properties of seismic waves in the volcanic region. These have been accounted for through the development of a seismic source model that integrates data from different disciplines (historical and instrumental earthquake datasets, tectonic data, etc.; presented in Part 1, by Azzaro et al., 2017 and through the development and software implementation of original tools for the computation, such as a new ground-motion prediction equation and magnitude–scaling relationship specifically derived for this volcanic area, and the capability to account for the surficial topography in the hazard calculation, which influences source-to-site distances. Hazard calculations have been carried out after updating the most recent releases of two widely used PSHA software packages (CRISIS, as in Ordaz et al., 2013; the OpenQuake engine, as in Pagani et al., 2014. Results are computed for short- to mid-term exposure times (10 % probability of exceedance in 5 and 30 years, Poisson and time dependent and spectral amplitudes of engineering interest. A preliminary exploration of the impact of site-specific response is also presented for the densely inhabited Etna's eastern flank, and the change in expected ground motion is finally commented on. These results do not account for M  >  6 regional seismogenic sources which control the hazard at long return periods. However, by focusing on the impact of M  <  6 local volcano-tectonic earthquakes, which dominate the hazard at the short- to mid-term exposure times considered

Crustal Seismicity and Geomorphic Observations of the Chiripa-Haciendas Fault System: The Guanacaste Volcanic Arc Sliver of Western Costa Rica

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Lewis, J. C.; Montero Pohly, W. K.; Araya, M. C.

2017-12-01

It has recently been shown that contemporary northwest motion of the Nicoya Peninsula of Costa Rica reflects a tectonic sliver that includes much of the upper-plate arc, referred to as the Guanacaste Volcanic Arc Sliver (GVAS). Here we characterize historical seismicity and geomorphic expressions of faults that define the northeastern margin of the GVAS. Several crustal earthquakes and their aftershocks provide constraints on the geometry and/or kinematics of the fault system. These include the Armenia earthquake of July 12, 2011, the Bijagua earthquake of January 27, 2002, the Tilarán earthquake of April 13, 1973 and two much older events. We summarize these earthquakes in the context of recent fault mapping and focal mechanism solutions, and suggest that most of the deformation can be explained by slip on steeply dipping NW-striking fault planes accommodating dextral slip. Streams that cross the major fault traces we have mapped also show deflections consistent with dextral slip. These include map-view apparent offsets of 6.5 km for the Haciendas River, 1.0 km for the Orosi River and 0.6 km for the Pizote River. Although preservation is poor, we document stream terrace risers that reveal truncations and/or offsets consistent with dextral slip. Additional constraints on the fault system are apparent as it is traced into Lake Nicaragua. Previous workers have shown that earthquake clusters accommodate a combination of dextral slip on NW-strike faults and sinistral slip NE-strike faults, the latter described as part of a system of bookshelf fault blocks. Whether the northeastern margin of the GVAS under Lake Nicaragua is a single fault strand or an array of bookshelf blocks remains an open question. An equally important gap in our understanding is the kinematic link of the fault system to the east where the GVAS originates. Our results set the stage for expanded studies that will be essential to understanding the relative contributions of Cocos Ridge collision and

Characterizing the deformation of reservoirs using interferometry, gravity, and seismic analyses

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Schiek, Cara Gina

In this dissertation, I characterize how reservoirs deform using surface and subsurface techniques. The surface technique I employ is radar interferometry, also known as InSAR (Interferometric Synthetic Aperture Radar). The subsurface analyses I explore include gravity modeling and seismic techniques consisting of determining earthquake locations from a small-temporary seismic network of six seismometers. These techniques were used in two different projects to determine how reservoirs deform in the subsurface and how this deformation relates to its remotely sensed surface deformation. The first project uses InSAR to determine land subsidence in the Mimbres basin near Deming, NM. The land subsidence measurements are visually compared to gravity models in order to determine the influence of near surface faults on the subsidence and the physical properties of the aquifers in these basins. Elastic storage coefficients were calculated for the Mimbres basin to aid in determining the stress regime of the aquifers. In the Mimbres basin, I determine that it is experiencing elastic deformation at differing compaction rates. The west side of the Mimbres basin is deforming faster, 17 mm/yr, while the east side of the basin is compacting at a rate of 11 mm/yr. The second project focuses on San Miguel volcano, El Salvador. Here, I integrate InSAR with earthquake locations using surface deformation forward modeling to investigate the explosive volcanism in this region. This investigation determined the areas around the volcano that are undergoing deformation, and that could lead to volcanic hazards such as slope failure from a fractured volcano interior. I use the earthquake epicenters with field data to define the subsurface geometry of the deformation source, which I forward model to produce synthetic interferograms. Residuals between the synthetic and observed interferograms demonstrate that the observed deformation is a direct result of the seismic activity along the San

Seismic structure from multi-channel seismic reflection and wide-angle data of Transect 0E in the Southern Gulf of California

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Paramo, P.; Holbrook, W.; Brown, H.; Lizarralde, D.; Fletcher, J.; Umhoefer, P.; Kent, G.; Harding, A.; Gonzalez, A.; Axen, G.

2005-12-01

We present a velocity model from wide-angle data along with coincident prestack depth migration sections from seismic reflection data collected in the southern Gulf of California. Transect 0E runs NE to SW from the hills of Sierra Madre in mainland Mexico near Mazatlan to approximately 115 km into Gulf of California waters. Wide-angle data were recorded by 9 ocean bottom seismometers, deployed by the R/V New Horizon and 10 Reftek seismometers located along onshore extension of the transect. The average spacing for the OBS and Refteks is ~12 km and shots were fired from the R/V Maurice Ewing at 150 m intervals. Transect 0E crosses what it is believed to be extended continental crust and lies in the initial direction of extension characteristic of the proto-gulf. Preliminary results from the velocity model show upper crustal velocities of 6.1-6.3 km/s and lower crustal velocities of 6.7-7.0 km/s along the entire transect. Seismic velocities and crustal thicknesses observed along transect 0E are characteristic of non-volcanic margins.

The role of magmatic loads and rift jumps in generating seaward dipping reflectors on volcanic rifted margins

Science.gov (United States)

Buck, W. Roger

2017-05-01

The largest volcanic constructs on Earth are the seismically imaged seaward dipping reflector (SDR) units found offshore of many rifted continental margins, including most that border the Atlantic Ocean. Whether their formation requires large magnitude (i.e. 10 s of km) of normal fault slip or results from the deflection of the lithosphere by the weight of volcanic flows is controversial. Though there is evidence for faulting associated with some SDRs, this paper considers the range of structures that can be produced by magmatic and volcanic loading alone. To do this an idealized mechanical model for the construction of rift-related volcanic flow structures is developed. Dikes open as plates move away from the center of a model rift and volcanic flows fill the depression produced by the load caused by dike solidification. The thin elastic plate flexure approximation allows a closed form description of the shape of both the contacts between flows and between the flows and underlying dikes. The model depends on two independent parameters: the flexure parameter, α, and the maximum isostatically supported extrusive layer thickness, w0. For reasonable values of these parameters the model reproduces the observed down-dip thickening of flows and the range of reflector dip angles. A numerical scheme using the analytic results allows simulation of the effect of temporal changes in the locus of magmatic spreading as well as changes in the amount of volcanic infill. Either jumps in the location of the center of diking or periods with no volcanism result in separate units or "packages" of model SDRs, in which the flow-dike contact dips landward, consistent with observations previously attributed only to listric normal fault offset. When jumps in the spreading center are small (i.e. less than α) they result in thicker, narrower volcanic units on one side of a rift compared to those on the other side. This is similar to the asymmetric distributions of volcanic packages seen

The effects of subduction termination on the continental lithosphere: Linking volcanism, deformation, surface uplift, and slab tearing in central Anatolia

Science.gov (United States)

Delph, Jonathan R.; Abgarmi, Bijan; Ward, Kevin M.; Beck, Susan L.; Arda Ozacar, A.; Zandt, George; Sandvol, Eric; Turkelli, Niyazi; Kalafat, Dogan

2017-04-01

The lithospheric evolution of Anatolia is largely defined by processes associated with the terminal stages of subduction along its southern margin. Central Anatolia represents the transition from the subduction of oceanic lithosphere at the Aegean trench in the west to the Arabian - Eurasian continental collision in the east. In the overriding plate, this complicated transition is contemporaneous with uplift along the southern margin of central Anatolia (2 km in 6 Myr), voluminous felsic-intermediate ignimbrite eruptions (>1000 km3), extension, and tectonic deformation reflected by abundant low-magnitude seismic activity. The addition of 72 seismic stations as part of the Continental Dynamics - Central Anatolian Tectonics project, along with development of a new approach to the joint inversion of receiver functions and dispersion data, enables us obtain a high-resolution 3D shear wave velocity model of central Anatolia down to 150 km. This new velocity model has important implications for the complex interactions between the downgoing, segmenting African lithosphere and the overriding Anatolian Plate. These results reveal that the lithosphere of central Anatolia and the northern Arabian Plate is thin (4.5 km/s), indicating the presence of the Cyprean slab beneath central Anatolia. Thus, uplift of the Central Taurus Mountains may be due to slab rebound after the detachment of the oceanic portion of the Cyprean slab beneath Anatolia rather than the presence of shallow asthenospheric material. These fast velocities extend to the northern margin of the Central Taurus Mountains, giving way to a NE-SW trend of very slow upper mantle shear wave velocities (interpreted to be shallow, warm asthenosphere in which melt is present. The combination of a shallow asthenosphere and lithospheric-scale weaknesses associated with relict tectonic structures formed during the assembly of Anatolia are responsible for the spatial distribution of volcanism in the Central Anatolian

Fine crustal and uppermost mantle S-wave velocity structure beneath the Tengchong volcanic area inferred from receiver function and surface-wave dispersion: constraints on magma chamber distribution

Science.gov (United States)

Li, Mengkui; Zhang, Shuangxi; Wu, Tengfei; Hua, Yujin; Zhang, Bo

2018-03-01

The Tengchong volcanic area is located in the southeastern margin of the collision zone between the Indian and Eurasian Plates. It is one of the youngest intraplate volcano groups in mainland China. Imaging the S-wave velocity structure of the crustal and uppermost mantle beneath the Tengchong volcanic area is an important means of improving our understanding of its volcanic activity and seismicity. In this study, we analyze teleseismic data from nine broadband seismic stations in the Tengchong Earthquake Monitoring Network. We then image the crustal and uppermost mantle S-wave velocity structure by joint analysis of receiver functions and surface-wave dispersion. The results reveal widely distributed low-velocity zones. We find four possible magma chambers in the upper-to-middle crust and one in the uppermost mantle. The chamber in the uppermost mantle locates in the depth range from 55 to 70 km. The four magma chambers in the crust occur at different depths, ranging from the depth of 7 to 25 km in general. They may be the heat sources for the high geothermal activity at the surface. Based on the fine crustal and uppermost mantle S-wave velocity structure, we propose a model for the distribution of the magma chambers.

A Proposed Community Network For Monitoring Volcanic Emissions In Saint Lucia, Lesser Antilles

Science.gov (United States)

Joseph, E. P.; Beckles, D. M.; Robertson, R. E.; Latchman, J. L.; Edwards, S.

2013-12-01

Systematic geochemical monitoring of volcanic systems in the English-speaking islands of the Lesser Antilles was initiated by the UWI Seismic Research Centre (SRC) in 2000, as part of its volcanic surveillance programme for the English-speaking islands of the Lesser Antilles. This programme provided the first time-series observations used for the purpose of volcano monitoring in Dominica and Saint Lucia, permitted the characterization of the geothermal fluids associated with them, and established baseline studies for understanding of the hydrothermal systems during periods of quiescence (Joseph et al., 2011; Joseph et al., 2013). As part of efforts to improve and expand the capacity of SRC to provide volcanic surveillance through its geothermal monitoring programme, it is necessary to develop economically sustainable options for the monitoring of volcanic emissions/pollutants. Towards this effort we intend to work in collaboration with local authorities in Saint Lucia, to develop a monitoring network for quantifying the background exposure levels of ambient concentrations of volcanic pollutants, SO2 in air and As in waters (as health significant marker elements in the geothermal emissions) that would serve as a model for the emissions monitoring network for other volcanic islands. This programme would facilitate the building of local capacity and training to monitor the hazardous exposure, through the application and transfer of a regionally available low-cost and low-technology SO2 measurement/detection system in Saint Lucia. Existing monitoring technologies to inform evidence based health practices are too costly for small island Caribbean states, and no government policies or health services measures currently exist to address/mitigate these influences. Gases, aerosols and toxic elements from eruptive and non-eruptive volcanic activity are known to adversely affect human health and the environment (Baxter, 2000; Zhang et al., 2008). Investigations into the

Shear-wave velocity of marine sediments offshore Taiwan using ambient seismic noise

Science.gov (United States)

Lin, Yu-Tse; Lin, Jing-Yi; Kuo-Chen, Hao; Yeh, Yi-Chin; Cheng, Win-Bin

2017-04-01

Seismic ambient noise technology has many advantages over the traditional two-station method. The most important one is that noise is happening all the time and it can be widely and evenly distributed. Thus, the Green's Function of any station pair can be obtained through the data cross-correlation process. Many related studies have been performed to estimate the velocity structures based on the inland area. Only a few studies were reported for the marine area due to the relatively shorter recording time of ocean bottom seismometers (OBS) deployment and the high cost of the marine experiment. However, the understanding about the shear-wave velocity (Vs) of the marine sediments is very crucial for the hazard assessment related to submarine landslides, particularly with the growing of submarine resources exploration. In this study, we applied the ambient noise technique to four OBS seismic networks located offshore Taiwan in the aim of getting more information about the noise sources and having the preliminary estimation for the Vs of the marine sediments. Two of the seismic networks were deployed in the NE part of Taiwan, near the Ryukyu subduction system, whereas the others were in the SW area, on the continental margin rich in gas hydrate. Generally, ambient seismic noise could be associated with wind, ocean waves, rock fracturing and anthropogenic activity. In the southwestern Taiwan, the cross-correlation function obtained from two seismic networks indicate similar direction, suggestion that the source from the south part of the network could be the origin of the noise. However, the two networks in the northeastern Taiwan show various source direction, which could be caused by the abrupt change of bathymetry or the volcanic degassing effect frequently observed by the marine geophysical method in the area. The Vs determined from the dispersion curve shows a relatively higher value for the networks in the Okinawa Trough (OT) off NE Taiwan than that in the

Development of mobile sensor for volcanic observation "HOMURA": Test campaign at Kirishima Iwo-yama, SW Japan

Science.gov (United States)

Kaneko, K.; Ito, K.; Iwahori, K.; Anbe, Y.

2015-12-01

Monitoring volcanoes near active craters is important to know symptoms and transitions of volcanic eruptions. In order to observe volcanic phenomena near craters according to the circumstance, monitoring system with unmanned robots are useful. We have been trying to develop a practical UGV-type robot, and have completed a prototype, which we named "Homura". Homura is a small-sized, vehicle-type robot with six wheels (750 x 430 x 310 mm in dimensions and a weight of about 12 kg). Homura is remotely controlled with mobile phone radio waves; it can move in volcanic fields and send real time data of sensors equipped in the vehicle to the base station. We carried out a test campaign of Homura from Feb. 19th to Apr. 8th, 2015 at Iwo-yama to examine if Homura can work for a few month in natural volcanic fields. Iwo-yama is one of craters in the Kirishima volcanic field, SW Japan; the area within 1 km from the crater was an off-limit area from Oct. 24th, 2014 to May 5th, 2015 because volcanic seismicity there was active and eruption might occur. On Feb. 19th, we carried and put Homura at the rim of the crater. Unfortunately, mobile phone connectivity was not entirely stable around Iwo-yama. Then, we decided not to move Homura and only to obtain real time data of the sensors (a camera, CO2 gas sensor, and thermometer). After we returned to our office, we operated Homura for one to two hours every day until Apr. 8th. Although the weather was often bad (rain, fog, or cold temperature) during the test campaign, we could completely operate Homura without any trouble. On Apr. 8th, the battery in Homura ran down. After we collected Homura from Iwo-yama and recharged the battery, Homura perfectly worked again. The results of this campaign indicate that Homura stably operates for a long time in volcanic field. Homura is useful as simple monitoring station in volcanic fields where mobile phone connection is available.

Long-term autonomous volcanic gas monitoring with Multi-GAS at Mount St. Helens, Washington, and Augustine Volcano, Alaska

Science.gov (United States)

Kelly, P. J.; Ketner, D. M.; Kern, C.; Lahusen, R. G.; Lockett, C.; Parker, T.; Paskievitch, J.; Pauk, B.; Rinehart, A.; Werner, C. A.

2015-12-01

In recent years, the USGS Volcano Hazards Program has worked to implement continuous real-time in situ volcanic gas monitoring at volcanoes in the Cascade Range and Alaska. The main goal of this ongoing effort is to better link the compositions of volcanic gases to other real-time monitoring data, such as seismicity and deformation, in order to improve baseline monitoring and early detection of volcanic unrest. Due to the remote and difficult-to-access nature of volcanic-gas monitoring sites in the Cascades and Alaska, we developed Multi-GAS instruments that can operate unattended for long periods of time with minimal direct maintenance from field personnel. Our Multi-GAS stations measure H2O, CO2, SO2, and H2S gas concentrations, are comprised entirely of commercial off-the-shelf components, and are powered by small solar energy systems. One notable feature of our Multi-GAS stations is that they include a unique capability to perform automated CO2, SO2, and H2S sensor verifications using portable gas standards while deployed in the field, thereby allowing for rigorous tracking of sensor performances. In addition, we have developed novel onboard data-processing routines that allow diagnostic and monitoring data - including gas ratios (e.g. CO2/SO2) - to be streamed in real time to internal observatory and public web pages without user input. Here we present over one year of continuous data from a permanent Multi-GAS station installed in August 2014 in the crater of Mount St. Helens, Washington, and several months of data from a station installed near the summit of Augustine Volcano, Alaska in June 2015. Data from the Mount St. Helens Multi-GAS station has been streaming to a public USGS site since early 2015, a first for a permanent Multi-GAS site. Neither station has detected significant changes in gas concentrations or compositions since they were installed, consistent with low levels of seismicity and deformation.

Persistent volcanic signature observed around Barren Island, Andaman Sea, India

Digital Repository Service at National Institute of Oceanography (India)

Laluraj, C.M.; Balachandran, K.K.; Sabu, P.S.; Panampunnayil, U.

in the Andaman Sea during the period 25 to 30th October 2005. It is evident that during this period, the local winds were weak and northerly (Figure 3c), consistent with the orientation of the warm air pool. The heat source feeding the warm air mass may.... 1976). The intensity and movement of this hot air mass depends on the strength and endurance of eruption and the winds (Mass and Portman, 1989). Persistence of a warm air pool in the Andaman Sea, especially in the winter season is significant because...

Moments, magnitudes, and radiated energies of non-volcanic tremor near Cholame, CA, from ground motion spectra at UPSAR

Science.gov (United States)

Fletcher, J. B.; McGarr, A.

2011-08-01

By averaging the spectra of events within two episodes of tremor (on Jan. 21 and 24, 2005) across the 12 stations of UPSAR, we improved the S/N sufficiently to define source spectra. Analysis of eleven impulsive events revealed attenuation-corrected spectra of displacement similar to those of earthquakes, with a low-frequency plateau, a corner frequency, and a high frequency decay proportional to f-2. Seismic moments, M0, estimated from these spectra range from about 3 to 10 × 1011 N-m or moment magnitudes in the range 1.6 to 1.9. The corner frequencies range from 2.6 to 7.2 Hz and, if interpreted in the same way as for earthquakes, indicate low stress drops that vary from 0.001 to 0.04 MPa. Seismic energies, estimated from the ground motion spectra, vary from 0.2 × 105 to 4.4 × 105 J, or apparent stresses in the range 0.002 to 0.02 MPa. The low stress parameters are consistent with a weak fault zone in the lower crust at the depth of tremor. In contrast, the same analysis on a micro-earthquake, located near Cholame (depth = 10.3 km), revealed a stress drop of 0.5 MPa and an apparent stress of 0.02 MPa. Residual spectra from ω-2 model fits to the displacement spectra of the non-volcanic tremor events show peaks near 4 Hz that are not apparent in the spectra for the microearthquake nor for the spectrum of earth noise. These spectral peaks may indicate that tremor entails more than shear failure reminiscent of mechanisms, possibly entailing fluid flow, associated with volcanic tremor or deep volcanic earthquakes.

From the Atlas to the Rif a Crustal seismic image across Morocco: The SIMA & RIFSEIS control source wide-angle seismic reflection data

Science.gov (United States)

Carbonell, Ramon; Ayarza, Puy; Gallart, Josep; Diaz, Jordi; Harnafi, Mimoun; Levander, Alan; Teixell, Antonio

2014-05-01

The velocity structure of the crust and the geometry of the Moho across Morocco has been the main target of two recently acquired wide-angle seismic reflection transects. One is the SIMA experiment which provided seismic constraints beneath the Atlas Mountains and the second has been the RIFSEIS experiment which sampled the RIF orogen. Jointly these controlled source wide-angle seismic reflection data results in an almost 700 km, seismic profile going from the the Sahara craton across the High and Middle Atlas and Rif Mountain till the Gibraltar-Arc (Alboran). Current work on the interpretation of the seismic data-set is based on forward modeling, ray-tracing, as well as low fold wide-angle stacking. The data has resulted in a detailed crustal structure and velocity model for the Atlas Mountains and a 700 km transect revealing the irregular topography of the Moho beneath these two mountain orogens. Results indicate that the High Atlas features a moderate crustal thickness and that shortening is resolved at depth through a crustal root where the Saharan crust under-thrusts below the Moroccan crust, defining a lower crust imbrication which locally places the Moho boundary at, approximately, 40 km depth. The P-wave velocity model is characterized, in averaged, by relatively low velocities. These low deep crustal velocities together with other geophysical observables such as: conductivity estimates derived from Mt measurements; moderate Bouguer gravity anomaly; surface exposures of recent alkaline volcanics; lead the interpretation to propose that partial melts are currently emplaced in the deep crustal levels and in the upper mantle. The Moho discontinuity defines a crust which is in average relatively thin beneath the Atlas which is almost a 4000 m high orogenic belt. The resulting model supports existence of mantle upwelling as a possible mechanism that contributes, significantly, to maintain the High Atlas topography.

The Marsili Volcanic Seamount (Southern Tyrrhenian Sea: A Potential Offshore Geothermal Resource

Directory of Open Access Journals (Sweden)

Francesco Italiano

2014-06-01

Full Text Available Italy has a strong geothermal potential for power generation, although, at present, the only two geothermal fields being exploited are Larderello-Travale/Radicondoli and Mt. Amiata in the Tyrrhenian pre-Apennine volcanic district of Southern Tuscany. A new target for geothermal exploration and exploitation in Italy is represented by the Southern Tyrrhenian submarine volcanic district, a geologically young basin (Upper Pliocene-Pleistocene characterised by tectonic extension where many seamounts have developed. Heat-flow data from that area show significant anomalies comparable to those of onshore geothermal fields. Fractured basaltic rocks facilitate seawater infiltration and circulation of hot water chemically altered by rock/water interactions, as shown by the widespread presence of hydrothermal deposits. The persistence of active hydrothermal activity is consistently shown by many different sources of evidence, including: heat-flow data, gravity and magnetic anomalies, widespread presence of hydrothermal-derived gases (CO2, CO, CH4, 3He/4He isotopic ratios, as well as broadband OBS/H seismological information, which demonstrates persistence of volcano-tectonic events and High Frequency Tremor (HFT. The Marsili and Tyrrhenian seamounts are thus an important—and likely long-lasting-renewable energy resource. This raises the possibility of future development of the world’s first offshore geothermal power plant.

Degassing during quiescence as a trigger of magma ascent and volcanic eruptions.

Science.gov (United States)

Girona, Társilo; Costa, Fidel; Schubert, Gerald

2015-12-15

Understanding the mechanisms that control the start-up of volcanic unrest is crucial to improve the forecasting of eruptions at active volcanoes. Among the most active volcanoes in the world are the so-called persistently degassing ones (e.g., Etna, Italy; Merapi, Indonesia), which emit massive amounts of gas during quiescence (several kilotonnes per day) and erupt every few months or years. The hyperactivity of these volcanoes results from frequent pressurizations of the shallow magma plumbing system, which in most cases are thought to occur by the ascent of magma from deep to shallow reservoirs. However, the driving force that causes magma ascent from depth remains unknown. Here we demonstrate that magma ascent can be triggered by the passive release of gas during quiescence, which induces the opening of pathways connecting deep and shallow magma reservoirs. This top-down mechanism for volcanic eruptions contrasts with the more common bottom-up mechanisms in which magma ascent is only driven by processes occurring at depth. A cause-effect relationship between passive degassing and magma ascent can explain the fact that repose times are typically much longer than unrest times preceding eruptions, and may account for the so frequent unrest episodes of persistently degassing volcanoes.

Mantle updrafts and mechanisms of oceanic volcanism

Science.gov (United States)

Anderson, Don L.; Natland, James H.

2014-10-01

Convection in an isolated planet is characterized by narrow downwellings and broad updrafts-consequences of Archimedes' principle, the cooling required by the second law of thermodynamics, and the effect of compression on material properties. A mature cooling planet with a conductive low-viscosity core develops a thick insulating surface boundary layer with a thermal maximum, a subadiabatic interior, and a cooling highly conductive but thin boundary layer above the core. Parts of the surface layer sink into the interior, displacing older, colder material, which is entrained by spreading ridges. Magma characteristics of intraplate volcanoes are derived from within the upper boundary layer. Upper mantle features revealed by seismic tomography and that are apparently related to surface volcanoes are intrinsically broad and are not due to unresolved narrow jets. Their morphology, aspect ratio, inferred ascent rate, and temperature show that they are passively responding to downward fluxes, as appropriate for a cooling planet that is losing more heat through its surface than is being provided from its core or from radioactive heating. Response to doward flux is the inverse of the heat-pipe/mantle-plume mode of planetary cooling. Shear-driven melt extraction from the surface boundary layer explains volcanic provinces such as Yellowstone, Hawaii, and Samoa. Passive upwellings from deeper in the upper mantle feed ridges and near-ridge hotspots, and others interact with the sheared and metasomatized surface layer. Normal plate tectonic processes are responsible both for plate boundary and intraplate swells and volcanism.

Volcanic unrest and hazard communication in Long Valley Volcanic Region, California

Science.gov (United States)

Hill, David P.; Mangan, Margaret T.; McNutt, Stephen R.

2017-01-01

�emissions. Initial response plans developed by county and state agencies in response to the volcanic unrest began with “The Mono County Volcano Contingency Plan” and “Plan Caldera” by the California Office of Emergency Services in 1982–84. They subsequently became integrated in the regularly updated County Emergency Operation Plan. The alert level system employed by the USGS also evolved from the three-level “Notice-Watch-Warning” system of the early 1980s through a five level color-code to the current “Normal-Advisory-Watch-Warning” ground-based system in conjunction with the international 4-level aviation color-code for volcanic ash hazards. Field trips led by the scientists proved to be a particularly effective means of acquainting local residents and officials with the geologically active environment in which they reside. Relative caldera quiescence from 2000 through 2011 required continued efforts to remind an evolving population that the hazards posed by the 1980–2000 unrest persisted. Renewed uplift of the resurgent dome from 2011 to 2014 was accompanied by an increase in low-level earthquake activity in the caldera and beneath Mammoth Mountain and continues through May 2016. As unrest levels continue to wax and wane, so will the communication challenges.

Sentinel-1 automatic processing chain for volcanic and seismic areas monitoring within the Geohazards Exploitation Platform (GEP)

Science.gov (United States)

De Luca, Claudio; Zinno, Ivana; Manunta, Michele; Lanari, Riccardo; Casu, Francesco

2016-04-01

The microwave remote sensing scenario is rapidly evolving through development of new sensor technology for Earth Observation (EO). In particular, Sentinel-1A (S1A) is the first of a sensors' constellation designed to provide a satellite data stream for the Copernicus European program. Sentinel-1A has been specifically designed to provide, over land, Differential Interferometric Synthetic Aperture Radar (DInSAR) products to analyze and investigate Earth's surface displacements. S1A peculiarities include wide ground coverage (250 km of swath), C-band operational frequency and short revisit time (that will reduce from 12 to 6 days when the twin system Sentinel-1B will be placed in orbit during 2016). Such characteristics, together with the global coverage acquisition policy, make the Sentinel-1 constellation to be extremely suitable for volcanic and seismic areas studying and monitoring worldwide, thus allowing the generation of both ground displacement information with increasing rapidity and new geological understanding. The main acquisition mode over land is the so called Interferometric Wide Swath (IWS) that is based on the Terrain Observation by Progressive Scans (TOPS) technique and that guarantees the mentioned S1A large coverage characteristics at expense of a not trivial interferometric processing. Moreover, the satellite spatial coverage and the reduced revisit time will lead to an exponential increase of the data archives that, after the launch of Sentine-1B, will reach about 3TB per day. Therefore, the EO scientific community needs from the one hand automated and effective DInSAR tools able to address the S1A processing complexity, and from the other hand the computing and storage capacities to face out the expected large amount of data. Then, it is becoming more crucial to move processors and tools close to the satellite archives, being not efficient anymore the approach of downloading and processing data with in-house computing facilities. To address

Subsurface geology of the Lusi region: preliminary results from a comprehensive seismic-stratigraphic study.

Science.gov (United States)

Moscariello, Andrea; Do Couto, Damien; Lupi, Matteo; Mazzini, Adriano

2016-04-01

We investigate the subsurface data of a large sector in the Sidoarjo district (East Java, Indonesia) where the sudden catastrophic Lusi eruption started the 26th May 2006. Our goal is to understand the stratigraphic and structural features which can be genetically related to the surface manifestations of deep hydrothermal fluids and thus allow us to predict possible future similar phenomena in the region. In the framework of the Lusi Lab project (ERC grant n° 308126) we examined a series of densely spaced 2D reflection commercial seismic lines This allowed the reconstruction of the lateral variability of key stratigraphic horizons as well as the main tectonic features. In particular, we shed light on the deep structure of the Watukosek fault system and the associated fracture corridors crossing the entire stratigraphic successions. To the South-West, when approaching the volcanic complex, we could identify a clear contrast in seismic facies between chaotic volcanoclastic wedges and clastic-prone sedimentary successions as well as between the deeper stratigraphic units consisting of carbonates and lateral shales units. The latter show possible ductile deformation associated to fault-controlled diapirism which control in turns deformation of overlying stratigraphic units and deep geo-fluids circulation. Large collapse structures recognized in the study area (e.g. well PRG-1) are interpreted as the results of shale movement at depth. Similarly to Lusi, vertical deformation zones ("pipes"), likely associated with deeply rooted strike-slip systems seem to be often located at the interface between harder carbonate rocks forming isolated build ups and the laterally nearby clastic (shale-prone)-units. The mechanisms of deformation of structural features (strike vs dip slip systems) which may affect either the basement rock or the overlying deeper stratigraphic rocks is also being investigated to understand the relationship between deep and shallower (i.e. meteoric) fluid

New seismic sources parameterization in El Salvador. Implications to seismic hazard.

Science.gov (United States)

Alonso-Henar, Jorge; Staller, Alejandra; Jesús Martínez-Díaz, José; Benito, Belén; Álvarez-Gómez, José Antonio; Canora, Carolina

2014-05-01

El Salvador is located at the pacific active margin of Central America, here, the subduction of the Cocos Plate under the Caribbean Plate at a rate of ~80 mm/yr is the main seismic source. Although the seismic sources located in the Central American Volcanic Arc have been responsible for some of the most damaging earthquakes in El Salvador. The El Salvador Fault Zone is the main geological structure in El Salvador and accommodates 14 mm/yr of horizontal displacement between the Caribbean Plate and the forearc sliver. The ESFZ is a right lateral strike-slip fault zone c. 150 km long and 20 km wide .This shear band distributes the deformation among strike-slip faults trending N90º-100ºE and secondary normal faults trending N120º- N170º. The ESFZ is relieved westward by the Jalpatagua Fault and becomes less clear eastward disappearing at Golfo de Fonseca. Five sections have been proposed for the whole fault zone. These fault sections are (from west to east): ESFZ Western Section, San Vicente Section, Lempa Section, Berlin Section and San Miguel Section. Paleoseismic studies carried out in the Berlin and San Vicente Segments reveal an important amount of quaternary deformation and paleoearthquakes up to Mw 7.6. In this study we present 45 capable seismic sources in El Salvador and their preliminary slip-rate from geological and GPS data. The GPS data detailled results are presented by Staller et al., 2014 in a complimentary communication. The calculated preliminary slip-rates range from 0.5 to 8 mm/yr for individualized faults within the ESFZ. We calculated maximum magnitudes from the mapped lengths and paleoseismic observations.We propose different earthquakes scenario including the potential combined rupture of different fault sections of the ESFZ, resulting in maximum earthquake magnitudes of Mw 7.6. We used deterministic models to calculate acceleration distribution related with maximum earthquakes of the different proposed scenario. The spatial distribution of

Estimation of full moment tensors, including uncertainties, for earthquakes, volcanic events, and nuclear explosions

Science.gov (United States)

Alvizuri, Celso R.

We present a catalog of full seismic moment tensors for 63 events from Uturuncu volcano in Bolivia. The events were recorded during 2011-2012 in the PLUTONS seismic array of 24 broadband stations. Most events had magnitudes between 0.5 and 2.0 and did not generate discernible surface waves; the largest event was Mw 2.8. For each event we computed the misfit between observed and synthetic waveforms, and we used first-motion polarity measurements to reduce the number of possible solutions. Each moment tensor solution was obtained using a grid search over the six-dimensional space of moment tensors. For each event we show the misfit function in eigenvalue space, represented by a lune. We identify three subsets of the catalog: (1) 6 isotropic events, (2) 5 tensional crack events, and (3) a swarm of 14 events southeast of the volcanic center that appear to be double couples. The occurrence of positively isotropic events is consistent with other published results from volcanic and geothermal regions. Several of these previous results, as well as our results, cannot be interpreted within the context of either an oblique opening crack or a crack-plus-double-couple model. Proper characterization of uncertainties for full moment tensors is critical for distinguishing among physical models of source processes. A seismic moment tensor is a 3x3 symmetric matrix that provides a compact representation of a seismic source. We develop an algorithm to estimate moment tensors and their uncertainties from observed seismic data. For a given event, the algorithm performs a grid search over the six-dimensional space of moment tensors by generating synthetic waveforms for each moment tensor and then evaluating a misfit function between the observed and synthetic waveforms. 'The' moment tensor M0 for the event is then the moment tensor with minimum misfit. To describe the uncertainty associated with M0, we first convert the misfit function to a probability function. The uncertainty, or

Constraint on the magma sources in Luzon Island Philippines by using P and S wave local seismic tomography

Science.gov (United States)

Nghia, N. C.; Huang, B. S.; Chen, P. F.

2017-12-01

The subduction of South China Sea beneath the Luzon Island has caused a complex setting of seismicity and magmatism because of the proposed ridge subduction and slab tearing. To constrain the validity of slab tearing induced by ridge subduction and their effect, we performed a P and S wave seismic tomography travel time inversion using LOTOS code. The dataset has been retrieved from International Seismological Centre from 1960 to 2008. A 1D velocity inverted by using VELEST with a Vp/Vs ratio of 1.74 is used as the starting input velocity for tomographic inversion. Total of 20905 P readings and 8126 S readings from 2355 earthquakes events were used to invert for velocity structure beneath Luzon Island. The horizontal tomographic results show low-velocity, high Vp/Vs regions at the shallow depth less than 50 km which are interpreted as the magmatic chambers of the volcanic system in Luzon. At the suspected region of slab tearing at 16oN to 18oN, two sources of magma have been indentified: slab window magma at shallow depth (< 50 km) and magma induced by mantle wedge partial melting from higher depth. This slab melting may have changed the composition of magmatic to become more silicic with high viscosity, which explains the volcanic gap in this region. At the region of 14oN to 15oN, large magma chambers under active volcanos are identified which explain the active volcanism in this region. Contrast to the region of slab tearing, in this region, the magma chambers are fed by only magma from partial melting of mantle wedge from the depth higher than 100 km. These observations are consistent with previous work on the slab tearing of South China Sea and the activities of volcanism in the Luzon Island.

Fifteen years of seismic monitoring at the Las Tres Virgenes, BCS, geothermal field; Quince anos de monitoreo sismico en el campo geotermico de Las Tres Virgenes, BCS

Energy Technology Data Exchange (ETDEWEB)

Ortiz Prieto, Irais; Lorenzo Pulido, Cecilia [Comision Federal de Electricidad, Gerencia de Proyectos Geotermoelectricos, Morelia, Michoacan (Mexico)]. E-mail: cecilia.lorenzo@cfe.gob.mx

2009-07-15

Seismic monitoring at the Las Tres Virgenes, BCS, geothermal field started in 1992 with an analog station of vertical components detecting a large number of earthquakes of varying magnitudes. In February 1993, a seismic network was installed, composed of six digital stations DR-2000-with S-6000 and S-5000 sensors and three registration channels (N-S, E-W and vertical). This was the basis for the development of a program to correct arrival-time data for P and S waves due to instrument drift. From January to April 1994 and May to August 1995, based on the 170 seismic events recorded, a velocity model was proposed. From December 1995 to July 1996, seismic data were processed and interpreted, and zones of occurrence were determined for events according to magnitude and the predominant noise in the field. From September 2003 to December 2004, 10 seismic stations (permanent and temporary) were installed and monitored and it was concluded the most active fault system was El Volcan. From September to December 2004, production wells LV-4 and LV-13 were acid-stimulated and seismic monitoring during this period allowed for the definition of two important seismic zones, both related to the El Volcan fault system and to injection well LV-8. After reopening these production wells, it was concluded an increase in seismic activity had occurred. From May to August 2006, information was compiled from the seismic network and it was concluded El Partido had became the most active fault system. Presently the seismic network in this field is composed of one SARA station and four K2 units. The SARA station is telemetrically connected to the base station. [Spanish] En el campo geotermico de Las Tres Virgenes, BCS, el monitoreo sismico empezo a partir de 1992 con una sola estacion analogica de registro vertical, la cual detecto una gran cantidad de temblores de distintas magnitudes. En febrero de 1993 se instalo una red sismica con seis estaciones digitales DR-2000 con sensores S-6000 y S

The lithosphere structure and deep processes of the Mesozoic metallogenic belt in eastern China: constraints from passive and active seismic methods

Science.gov (United States)

Lu, Q.; Shi, D.; Jiang, G.; Yan, J.

2013-12-01

The lithosphere structure and deep processes are keys to understanding mineral system and ore-forming processes. Lithosphere-scale process could create big footprints or signatures which can be observed by geophysics methods. SinoProbe-03 has conducted a Transect exploration across middle and lower Yangtze Metallogenic Belt (YMT) in Eastern China. Broadband seismic, reflection seismic, wide-angle reflection and magnetotellurics survey were carried out along the Transect. Seismic reflection profiles and MT survey were also performed in Luzong, Tongling and Ningwu ore districts to construct 3D geological model. The resulting geophysical data provides new information which help to better understanding the lithosphere structure, deep processes and deformation history of the Metallogenic Belt. The major results are: (1) Lower velocity body at the top of upper mantle and a SE dipping high velocity body were imaged by teleseismic tomography beneath YMB; (2) Shear wave splitting results show NE parallel fast-wave polarization direction which parallel with tectonic lineament; (3) The reflection seismic data support the crustal-detachment model, the lower and upper crust was detached during contraction deformation near Tanlu fault and Ningwu volcanic basin; (4) Broadband and reflection seismic confirm the shallow Moho beneath YMB; (5) Strong correlation of lower crust reflectivity with magmatism; (6) The lower crust below Luzong Volcanics shows obvious reflective anisotropy both at the crust-mantle transition and the brittle-ductile transition in the crust. All these features suggest that introcontinental subduction, lithosphere delamination, mantle sources magmatic underplating, and MASH process are responsible for the formation of this Mesozoic metallogenic belt. Acknowledgment: We acknowledge the financial support of SinoProbe by the Ministry of Finance and Ministry of Land and Resources, P. R. China, under Grant sinoprobe-03, and financial support by National Natural

Recent geophysical investigation at Somma-Vesuvio volcanic complex

Science.gov (United States)

Berrino, Giovanna; Coppa, Ugo; De Natale, Giuseppe; Pingue, Folco

1993-11-01

Activity at Somma-Vesuvio volcanic area in southern Italy is monitored by seismic stations and periodic geodetic and gravity surveys. The seismic network, which consists at present of four vertical stations and one three-component station, recorded an increase in earthquake activity in 1978 and between November 1988 and March 1989. During the later activity, earthquakes were located in a cluster about 3 km beneath the summit of the volcano. Two tide gauges, two tiltmeters and a recording gravimeter are also operating at Somma-Vesuvio. Yearly levelling surveys are conducted along several closed routes that extend from as much as 6 km from the base of the volcano to the summit area. Survey results reveal no significant ground movement since 1959, except for a slight subsidence around the rim of the summit crater. Gravity changes have been larger than the expected 10 μGal uncertainty of the measurements. The lack of contemporary elevation changes implies that the observed gravity changes are the result of a slight change in density structure. The cone of Somma-Vesuvio has been very stable for the last few decades, showing no indications of a buildup to activity. The lack of surface movement should rule out a magma-supply rate to this volcano at the historic eruptive rate of 0.002 km 3/yr.

Inferring Shallow Subsurface Density Structure from Surface and Underground Gravity Measurements: Calibrating Models for Relatively Undeformed Volcanic Strata at the Jemez Volcanic Field, New Mexico, USA

Science.gov (United States)

Roy, Mousumi; Lewis, Megan; Johnson, Alex; George, Nicolas; Rowe, Charlotte; Guardincerri, Elena

2018-03-01

Imaging shallow subsurface density structure is an important goal in a variety of applications, from hydrogeology to seismic and volcanic hazard assessment. We assess the effectiveness of surface and subsurface gravity measurements in estimating the density structure of a well-characterized rock volume: the mesa (a small, flat-topped plateau) upon which the town of Los Alamos, New Mexico, USA is located. Our gravity measurements were made on the mesa surface above a horizontal tunnel and underground, within the tunnel. We demonstrate that, in the absence of other geophysical data such as seismic data or muon attenuation, subsurface (tunnel) gravity measurements are critical to accurately recovering geologic structure. Without the tunnel data, our resolution is limited to roughly the surface gravity station spacing, but by including the tunnel data we can resolve structure to a depth of 10 times the surface gravity station spacing. Densities were obtained using both forward modeling and a Bayesian inverse modeling approach, incorporating relevant constraints from geologic observations. We find that Bayesian inversion, with geologically relevant prior, is a superior approach to the forward models in terms of both robustness and efficiency and correctly predicts the orientation and elevation of important geologic features.

Sources of Quaternary volcanism in the Itasy and Ankaratra volcanic fields, Madagascar

Science.gov (United States)

Rasoazanamparany, C.; Widom, E.; Kuentz, D. C.; Raharimahefa, T.; Rakotondrazafy, F. M. A.; Rakotondravelo, K. M.

2017-12-01

We present new major and trace element and Sr, Nd, Pb and Os isotope data for Quaternary basaltic lavas and tephra from the Itasy and Ankaratra volcanic fields, representing the most recent volcanism in Madagascar. Mafic magmas from Itasy and Ankaratra exhibit significant inter- and intra-volcanic field geochemical heterogeneity. The Itasy eruptive products range in composition from foidite to phonotephrite whereas Ankaratra lavas range from basanite to trachybasalts. Trace element signatures of samples from both volcanic fields are very similar to those of ocean island basalts (OIB), with significant enrichment in Nb and Ta, depletion in Rb, Cs, and K, and relatively high Nb/U and Ce/Pb. However, the Itasy volcanic rocks show enrichment relative to those of Ankaratra in most incompatible elements, indicative of a more enriched source and/or lower degrees of partial melting. Significant inter- and intra-volcanic field heterogeneity is also observed in Sr, Nd, Pb and Os isotope signatures. The Itasy volcanic rocks generally have less radiogenic Sr and Nd isotopic ratios but more radiogenic Pb isotopic signatures than the Ankaratra volcanic field. Together, the Itasy and Ankaratra volcanic rocks form a well-defined negative correlation in Sr vs. Pb isotopes that could be attributed to lithospheric contamination or variable degrees of mixing between distinct mantle sources. However, the lack of correlation between isotopes and indices of crustal contamination (e.g. MgO and Nb/U) are inconsistent with shallow lithospheric contamination, and instead suggest mixing between compositionally distinct mantle sources. Furthermore, although Sr-Pb isotope systematics are apparently consistent with mixing between two different sources, distinct trends in Sr vs. Nd isotopes displayed by samples from Itasy and Ankaratra, respectively, argue for more complex source mixing involving three or more sources. The current data demonstrate that although the Itasy and Ankaratra volcanic

Volcanic hotspots of the central and southern Andes as seen from space by ASTER and MODVOLC between the years 2000-2011

Science.gov (United States)

Jay, J.; Pritchard, M. E.; Mares, P. J.; Mnich, M. E.; Welch, M. D.; Melkonian, A. K.; Aguilera, F.; Naranjo, J.; Sunagua, M.; Clavero, J. E.

2011-12-01

order to investigate the relationship between seismic and thermal volcanic activity, we examine seismic data for 5 of the volcanoes (Uturuncu, Olca-Paruma, Ollague, Irruputuncu, and Sol de Mañana) as well as seismological reports from the Chilean geological survey SERNAGEOMIN for 11 additional volcanoes. Although there were 7 earthquakes with Mw > 7 in our study area from 2000-2010, there is essentially no evidence from ASTER or MODVOLC that the thermal anomalies were affected by seismic shaking.

Electric effects induced by artificial seismic sources at Somma-Vesuvius volcano

Directory of Open Access Journals (Sweden)

Rosa Di Maio

2013-11-01

Full Text Available In this paper, we present a series of self-potential measurements at Somma-Vesuvius volcanic area acquired in conjunction with an active seismic tomography survey. The aim of our study is both to provide further confirmation to the occurrence of seismo-electric coupling and to identify sites suitable for self-potential signal monitoring at Somma-Vesuvius district. The data, which were collected along two perpendicular dipoles, show significant changes on the natural electric field pattern. These variations, attributable to electrokinetic processes triggered by the artificial seismic waves, were observed after explosions occurred at a distance less than 5 km from the SP dipole arrays. In particular, we found that the NW-SE component of the natural electric field was more sensible to the shots than the NE-SW one, and the major effects did not correspond to the nearest shots. Such evidences were interpreted considering the underground electrical properties as deduced by previous detailed resistivity and self-potential surveys performed in the study area.

Automated detection and characterization of harmonic tremor in continuous seismic data

Science.gov (United States)

Roman, Diana C.

2017-06-01

Harmonic tremor is a common feature of volcanic, hydrothermal, and ice sheet seismicity and is thus an important proxy for monitoring changes in these systems. However, no automated methods for detecting harmonic tremor currently exist. Because harmonic tremor shares characteristics with speech and music, digital signal processing techniques for analyzing these signals can be adapted. I develop a novel pitch-detection-based algorithm to automatically identify occurrences of harmonic tremor and characterize their frequency content. The algorithm is applied to seismic data from Popocatepetl Volcano, Mexico, and benchmarked against a monthlong manually detected catalog of harmonic tremor events. During a period of heightened eruptive activity from December 2014 to May 2015, the algorithm detects 1465 min of harmonic tremor, which generally precede periods of heightened explosive activity. These results demonstrate the algorithm's ability to accurately characterize harmonic tremor while highlighting the need for additional work to understand its causes and implications at restless volcanoes.

Monte Carlo Volcano Seismic Moment Tensors

Science.gov (United States)

Waite, G. P.; Brill, K. A.; Lanza, F.

2015-12-01

Inverse modeling of volcano seismic sources can provide insight into the geometry and dynamics of volcanic conduits. But given the logistical challenges of working on an active volcano, seismic networks are typically deficient in spatial and temporal coverage; this potentially leads to large errors in source models. In addition, uncertainties in the centroid location and moment-tensor components, including volumetric components, are difficult to constrain from the linear inversion results, which leads to a poor understanding of the model space. In this study, we employ a nonlinear inversion using a Monte Carlo scheme with the objective of defining robustly resolved elements of model space. The model space is randomized by centroid location and moment tensor eigenvectors. Point sources densely sample the summit area and moment tensors are constrained to a randomly chosen geometry within the inversion; Green's functions for the random moment tensors are all calculated from modeled single forces, making the nonlinear inversion computationally reasonable. We apply this method to very-long-period (VLP) seismic events that accompany minor eruptions at Fuego volcano, Guatemala. The library of single force Green's functions is computed with a 3D finite-difference modeling algorithm through a homogeneous velocity-density model that includes topography, for a 3D grid of nodes, spaced 40 m apart, within the summit region. The homogenous velocity and density model is justified by long wavelength of VLP data. The nonlinear inversion reveals well resolved model features and informs the interpretation through a better understanding of the possible models. This approach can also be used to evaluate possible station geometries in order to optimize networks prior to deployment.

The PROTEUS Experiment: Active Source Seismic Imaging of the Crustal Magma Plumbing Structure of the Santorini Arc Volcano

Science.gov (United States)

Hooft, E. E. E.; Morgan, J. V.; Nomikou, P.; Toomey, D. R.; Papazachos, C. V.; Warner, M.; Heath, B.; Christopoulou, M. E.; Lampridou, D.; Kementzetzidou, D.

2016-12-01

The goal of the PROTEUS seismic experiment (Plumbing Reservoirs Of The Earth Under Santorini) is to examine the entire crustal magma plumbing system beneath a continental arc volcano and determine the magma geometry and connections throughout the crust. These physical parameters control magma migration, storage, and eruption and inform the question of how physical and chemical processing of magma at arc volcanoes forms the andesitic rock compositions that dominate the lower continental crust. These physical parameters are also important to understand volcanic-tectonic interactions and geohazards. Santorini is ideal for these goals because the continental crust has been thinned by extension and so the deep magmatic system is more accessible, also it is geologically well studied. Since the volcano is a semi-submerged, it was possible to collect a unique 3D marine-land active source seismic dataset. During the PROTEUS experiment in November-December of 2015, we recorded 14,300 marine sound sources from the US R/V Langseth on 89 OBSIP short period ocean bottom seismometers and 60 German and 5 Greek land seismometers. The experiment was designed for high-density spatial sampling of the seismic wavefield to allow us to apply two state-of-the-art 3D inversion methods: travel time tomography and full waveform inversion. A preliminary travel time tomography model of the upper crustal seismic velocity structure of the volcano and surrounding region is presented in an accompanying poster. We also made marine geophysical maps of the seafloor using multi-beam bathymetry and of the gravity and magnetic fields. The new seafloor map reveals the detailed structure of the major fault system between Santorini and Amorgos, of associated landslides, and of newly discovered volcanic features. The PROTEUS project will provide new insights into the structure of the whole crustal magmatic system of a continental arc volcano and its evolution within the surrounding tectonic setting.

Effects of Regulation on Induced Seismicity in Southern Kansas

Science.gov (United States)

Rubinstein, J. L.; Ellsworth, W. L.; Dougherty, S. L.

2016-12-01

The appearance of seismicity concurrent with the expansion of oil and gas activities in southern Kansas since September 2012 suggests that industrial operations are inducing earthquakes there. Much of the seismicity can be related to high-rate injection wells within 5 km of the earthquakes. There is significant complexity to the situation, though. Some of the seismicity, including the 2014 M4.8 Milan earthquake, the largest earthquake to occur in the area, lies at least 10km from high-rate injection wells. Additionally, the presence of high-rate wells does not guarantee that there will be nearby seismicity. Many of the highest-rate injection wells are located to the southwest of our study area, where there is minimal seismicity. We have also seen changes in earthquake rates shortly following the March 2015 enactment of new limits on the rate of wastewater disposal in five areas in southern Kansas. Overall, the earthquake rate has decreased significantly since these rules went into place. In more detail, however, earthquake rates within the five areas decreased, but the rate outside the five zones increased. It is likely that fluid-pressure diffusion is responsible for the migration of seismicity outside the areas of reduced injection because there is little injection in the areas unaffected by the new injection rules. This increase is also a reminder that seismicity can persist long after the reduction or cessation of injection. In addition to the effect of the new injection rules, it is possible that the reduction in injection may be partially caused by economic factors that have resulted in a decrease in the production of oil and gas. We have yet to disentangle the effects of the new injection rules and the low prices of oil and gas on the induced seismicity in southern Kansas.

Earthquake and volcanic risks: issues for the Bataan Nuclear Power Plant

International Nuclear Information System (INIS)

Solidum, Dr. Renato U.

2009-01-01

The proposed re-commissioning of the mothballed Bataan Nuclear Power Plant (BNPP) has raised objections that include the perceived unsafe siting of the BNPP on Mt. Natib, a potentially active volcano, in an earthquake-prone region. This concern must be evaluated through thorough seismological, paleo-seismic, volcanological and engineering studies. The BNPP sits on Napot Point on the southwest foot slope of Mt. Natib, an andesitic to dacitic stratovolcano just 30 kms south of Mt. Pinatubo. Natib's evolution is poorly known, but involved at least 3 explosive summit eruptions that formed a 6 km-diameter coalescent caldera and a younger 2-km diameter caldera. Pyroclastic flows define the cone surface, and available age dating includes a ±27 ka 14C age for a deposit on the eastern flanks and an 11-18 ka relative dating for suspected pyroclastic deposits in Subic Bay (1). Whether these represent the most recent eruptions is uncertain. A detailed magmatic/eruptive history defining magmatic recharge and eruption recurrence rates, from which probabilities for future eruptive activity can be analyzed, will be necessary for quantifying volcanic risk. Furthermore, Natib,Pinatubo and adjacent Mariveles are part of the Luzon Arc and associated with ongoing subduction along the Manila Trench. Subduction earthquakes are common, but apart from these, seismic risk is also being attributted to tectonic structures inland that include reported on site faults inferred from drilling, basin faults seen in reflection profiles (1), the Subic Bay Fault Zone delineated by magmatic studies (2) and various lineaments inferred from satellite imageries. These, plus seismicity in the region are being argued as indicators of earthquake threat. However, much emphasis is given maximum seismic magnitudes rather than peak ground accelerations (PGAs), epicentral rather than focal sources,and the inference of faults/lineaments rather than paleoseismic evidence of recent faulting. Paleoseismic studies of

Data from investigation on seismic Sea-waves events in the Eastern Mediterranean from the Birth of Christ to 500 A.D.

Directory of Open Access Journals (Sweden)

J. ANTONOPOULOS

1980-06-01

Full Text Available The Eastern Mediterranean has a long history of damaging seismic sea
waves (Tsunamis but a great number of them which are locally generated are small. They have caused no serious damage to the coasts because their
energy is confined by many islands of the Greek Archipelagos. However,
some of them have been rather severe and destructive to property and
human life.
This paper is comprised of data from an investigation into the activity
of seismic sea waves in the Eastern Mediterranean from the Birth of
Christ to 500 A.D. It contains a great amount of information concerning
earthquakes, volcanic eruptions and seismic sea waves.
All the available information has been compiled from historical accounts,
archives, press reports, magazines and related works.

Triggered Seismicity in Utah from the November 3, 2002, Denali Fault Earthquake

Science.gov (United States)

Pankow, K. L.; Nava, S. J.; Pechmann, J. C.; Arabasz, W. J.

2002-12-01

important to investigate because well-documented evidence for triggering of seismicity by distant earthquakes comes primarily from areas characterized by recent volcanic or geothermal activity. The regions of apparent triggered seismicity from the DFE in Utah fall into neither of these two categories.

Frictional melting and stick-slip behavior in volcanic conduits

Science.gov (United States)

Kendrick, Jackie Evan; Lavallee, Yan; Hirose, Takehiro; di Toro, Giulio; Hornby, Adrian Jakob; Hess, Kai-Uwe; Dingwell, Donald Bruce

2013-04-01

fixed spatial locus that explains the repetitive drumbeat seismicity and the occurrence of "families" of similar seismic events. We conclude that stick-slip motion in volcanic conduits is a self-driving, frictional-melt-regulated force common to many dome building volcanoes.

Monitoring unrest in a large silicic caldera, the long Valley-inyo craters volcanic complex in east-central California

Science.gov (United States)

Hill, D. P.

1984-06-01

Recent patterns of geologic unrest in long Valley caldera in east-central California emphasize that this large, silicic volcanic system and the adjacent, geologically youthful Inyo-Mono Craters volcanic chain are still active and capable of producing locally hazardous volcanic eruptions. A series of four magnitude -6 earthquakes in May 1980 called attention to this current episode of unrest, and subsequent activity has included numerous earthquake swarms in the south moat of the caldera accompanied by inflation of the resurgent dome by more than 50 cm over the last five years. The seismicity associated with this unrest is currently monitored by a network of 31 telemetered seismic stations with an automatic processing system that yelds hypocentral locations and earthquake magnitudes in near-real time. Deformation of the ground is monitored by a) a series of overlapping trilateration networks that provide coverage ranging from annual measurements of regional deformation to daily measurements of deformation local to the active, southern section of the caldera, b) a regional network of level lines surveyed annually, c) a regional network of precise gravity stations occupied annually, d) local, L-shaped level figures surveyed every few months, and e) a network of fourteen borehole tiltmeter clusters (two instruments in each cluster) and a borehole dilatometer, the telemetered signals from which provide continuous data on deformation rates. Additional telemetered data provide continuous information on fluctuations in the local magnetic field, hydrogen gas emission rates at three sites, and water level and temperatures in three wells. Continuous data on disharge rates and temperatures from hot springs and fumaroles are collected by several on-site recorders within the caldera, and samples for liquid and gas chemistry are collected several times per year from selected hot springs and fumaroles.

Earthquake clustering in modern seismicity and its relationship with strong historical earthquakes around Beijing, China

Science.gov (United States)

Wang, Jian; Main, Ian G.; Musson, Roger M. W.

2017-11-01

Beijing, China's capital city, is located in a typical intraplate seismic belt, with relatively high-quality instrumental catalogue data available since 1970. The Chinese historical earthquake catalogue contains six strong historical earthquakes of Ms ≥ 6 around Beijing, the earliest in 294 AD. This poses a significant potential hazard to one of the most densely populated and economically active parts of China. In some intraplate areas, persistent clusters of events associated with historical events can occur over centuries, for example, the ongoing sequence in the New Madrid zone of the eastern US. Here we will examine the evidence for such persistent clusters around Beijing. We introduce a metric known as the `seismic density index' that quantifies the degree of clustering of seismic energy release. For a given map location, this multi-dimensional index depends on the number of events, their magnitudes, and the distances to the locations of the surrounding population of earthquakes. We apply the index to modern instrumental catalogue data between 1970 and 2014, and identify six clear candidate zones. We then compare these locations to earthquake epicentre and seismic intensity data for the six largest historical earthquakes. Each candidate zone contains one of the six historical events, and the location of peak intensity is within 5 km or so of the reported epicentre in five of these cases. In one case—the great Ms 8 earthquake of 1679—the peak is closer to the area of strongest shaking (Intensity XI or more) than the reported epicentre. The present-day event rates are similar to those predicted by the modified Omori law but there is no evidence of ongoing decay in event rates. Accordingly, the index is more likely to be picking out the location of persistent weaknesses in the lithosphere. Our results imply zones of high seismic density index could be used in principle to indicate the location of unrecorded historical of palaeoseismic events, in China and

Active spreading processes at ultraslow mid-ocean ridges: The 1999-2001 seismo-volcanic episode at 85°E Gakkel ridge, Arctic Ocean

Science.gov (United States)

Schlindwein, Vera; Riedel, Carsten; Korger, Edith; Läderach, Christine

2010-05-01

The rate of magma and crustal production at mid-ocean ridges is thought to decrease with decreasing spreading rate. At ultraslow spreading rates below 10-20 mm/y full rate, heat loss by conduction greatly reduces melt production with less melt produced at increasingly greater depths. Gakkel Ridge, the actively spreading mid-ocean ridge in the Arctic Ocean, opens at rates of 14 mm/y in the west decreasing to less than 6 mm/y at its eastern termination and demonstrates that magma production is not only a function of spreading rate. Whereas amagmatic spreading takes place at rates of about 12-10 mm/y, focussed melt production occurs at even lower spreading rates in long-lived discrete volcanic centres. One such centre is the 85°E volcanic complex at eastern Gakkel ridge where in 1999 a teleseismically recorded earthquake swarm consisting of more than 250 earthquakes over 9 months signalled the onset of an active spreading episode. The earthquake swarm is believed to be associated with volcanic activity although no concurrent lava effusion was found. We analysed the teleseismic earthquake swarm together with visual observation and microseismic data recorded at this site in 2001 and 2007 and noted the following characteristics which may be indicative for volcanic spreading events at the still poorly explored ultraslow spreading ridges: - unusual duration: The 1999 earthquake swarm lasted over 9 months rather than a few weeks as observed on faster spreading ridges. In addition, in 2001 seismoacoustic sounds which we interpret as gas discharge in Strombolian eruptions and a giant event plume maintained over more than one year indicate waxing and waning volcanic activity since 1999. - unusual strength: The earthquake swarm was detected at teleseismic distances of more than 1000 km and included 11 events with a magnitude >5. No other confirmed mid-ocean ridge eruption released a comparable seismic moment. Rather than focussing in a narrow area or showing pronounced

On the climate impacts from the volcanic and solar forcings

Science.gov (United States)

Varotsos, Costas A.; Lovejoy, Shaun

2016-04-01

The observed and the modelled estimations show that the main forcings on the atmosphere are of volcanic and solar origins, which act however in an opposite way. The former can be very strong and decrease at short time scales, whereas, the latter increase with time scale. On the contrary, the observed fluctuations in temperatures increase at long scales (e.g. centennial and millennial), and the solar forcings do increase with scale. The common practice is to reduce forcings to radiative equivalents assuming that their combination is linear. In order to clarify the validity of the linearity assumption and determine its range of validity, we systematically compare the statistical properties of solar only, volcanic only and combined solar and volcanic forcings over the range of time scales from one to 1000 years. Additionally, we attempt to investigate plausible reasons for the discrepancies observed between the measured and modeled anomalies of tropospheric temperatures in the tropics. For this purpose, we analyse tropospheric temperature anomalies for both the measured and modeled time series. The results obtained show that the measured temperature fluctuations reveal white noise behavior, while the modeled ones exhibit long-range power law correlations. We suggest that the persistent signal, should be removed from the modeled values in order to achieve better agreement with observations. Keywords: Scaling, Nonlinear variability, Climate system, Solar radiation

Advanced Seismic Data Analysis Program (The Hot Pot Project), DOE Award: DE-EE0002839, Phase 1 Report

Energy Technology Data Exchange (ETDEWEB)

Oski Energy, LLC,

2013-03-28

A five-line (23 mile) reflection- seismic survey was conducted at the Hot Pot geothermal prospect area in north-central Nevada under the USDOE (United States Department of Energy) Geothermal Technologies Program. The project objective was to utilize innovative seismic data processing, integrated with existing geological, geophysical and geochemical information, to identify high-potential drilling targets and to reduce drilling risk. Data acquisition and interpretation took place between October 2010 and April 2011. The first round of data processing resulted in large areas of relatively poor data, and obvious reflectors known from existing subsurface information either did not appear on the seismic profiles or appeared at the wrong depth. To resolve these issues, the velocity model was adjusted to include geologic input, and the lines were reprocessed. The resulting products were significantly improved, and additional detail was recovered within the high-velocity and in part acoustically isotropic basement. Features visible on the improved seismic images include interpreted low angle thrust faults within the Paleozoic Valmy Formation, which potentially are reactivated in the current stress field. Intermediate-depth wells are currently targeted to test these features. The seismic images also suggest the existence of Paleogene sedimentary and volcanic rocks which potentially may function as a near- surface reservoir, charged by deeper structures in Paleozoic rocks.

Tectonic History and Deep Structure of the Demerara Plateau from Combined Wide-Angle and Reflection Seismic Data and Plate Kinematic Reconstructions

Science.gov (United States)

Klingelhoefer, F.; Museur, T.; Roest, W. R.; Graindorge, D.; Chauvet, F.; Loncke, L.; Basile, C.; Poetisi, E.; Deverchere, J.; Lebrun, J. F.; Perrot, J.; Heuret, A.

2017-12-01

Many transform margins have associated intermediate depth marginal plateaus, which are commonly located between two oceanic basins. The Demerara plateau is located offshore Surinam and French Guiana. Plate kinematic reconstructions show that the plateau is located between the central and equatorial Atlantic in a position conjugate to the Guinean Plateau. In the fall of 2016, the MARGATS cruise acquired geophysical data along the 400 km wide Demerara plateau. The main objective of the cruise was to image the deep structure of the Demerara plateau and to study its tectonic history. A set of 4 combined wide-angle and reflection seismic profiles was acquired along the plateau, using 80 ocean-bottom seismometers, a 3 km long seismic streamer and a 8000 cu inch tuned airgun array. Forward modelling of the wide-angle seismic data on a profile, located in the eastern part of the plateau and oriented in a NE-SW direction, images the crustal structure of the plateau, the transition zone and the neighbouring crust of oceanic origin, up to a depth of 40 km. The plateau itself is characterised by a crust of 30 km thickness, subdivided into three distinct layers. However, the velocities and velocity gradients do not fit typical continental crust, with a lower crustal layer showing untypically high velocities and an upper layer having a steep velocity gradient. From this model we propose that the lowermost layer is probably formed from volcanic underplated material and that the upper crustal layer likely consists of the corresponding extrusive volcanic material, forming thick seaward-dipping reflector sequences on the plateau. A basement high is imaged at the foot of the slope and forms the ocean-continent transition zone. Further oceanward, a 5-6 km thick crust is imaged with velocities and velocity gradients corresponding to a thin oceanic crust. A compilation of magnetic data from the MARGATS and 3 previous cruises shows a high amplitude magnetic anomaly along the northern

Sediment transport dynamics in steep, tropical volcanic catchments

Science.gov (United States)

Birkel, Christian; Solano Rivera, Vanessa; Granados Bolaños, Sebastian; Brenes Cambronero, Liz; Sánchez Murillo, Ricardo; Geris, Josie

2017-04-01

How volcanic landforms in tropical mountainous regions are eroded, and how eroded materials move through these mostly steep landscapes from the headwaters to affect sediment fluxes are critical to water resources management in their downstream rivers. Volcanic landscapes are of particular importance because of the short timescales (transform. Owing to volcanism and seismic activity, landslides and other mass movements frequently occur. These processes are amplified by high intensity precipitation inputs resulting in significant, but natural runoff, erosion and sediment fluxes. Sediment transport is also directly linked to carbon and solute export. However, knowledge on the sediment sources and transport dynamics in the humid tropics remains limited and their fluxes largely unquantified. In order to increase our understanding of the dominant erosion and sediment transport dynamics in humid tropical volcanic landscapes, we conducted an extensive monitoring effort in a pristine and protected (biological reserve Alberto Manuel Brenes, ReBAMB) tropical forest catchment (3.2 km2), located in the Central Volcanic Cordillera of Costa Rica (Figure 1A). Typical for tropical volcanic and montane regions, deeply incised V-form headwaters (Figure 1B) deliver the majority of water (>70%) and sediments to downstream rivers. At the catchment outlet (Figure 1C) of the San Lorencito stream, we established high temporal resolution (5min) water quantity and sediment monitoring (turbidity). We also surveyed the river network on various occasions to characterize fluvial geomorphology including material properties. We could show that the rainfall-runoff-sediment relationships and their characteristic hysteresis patterns are directly linked to variations in the climatic input (storm intensity and duration) and the size, form and mineralogy of the transported material. Such a relationship allowed us to gain the following insights: (i) periodic landslides contribute significant volumes of

Volcanic sulfur dioxide index and volcanic explosivity index inferred from eruptive volume of volcanoes in Jeju Island, Korea: application to volcanic hazard mitigation

Science.gov (United States)

Ko, Bokyun; Yun, Sung-Hyo

2016-04-01

Jeju Island located in the southwestern part of Korea Peninsula is a volcanic island composed of lavaflows, pyroclasts, and around 450 monogenetic volcanoes. The volcanic activity of the island commenced with phreatomagmatic eruptions under subaqueous condition ca. 1.8-2.0 Ma and lasted until ca. 1,000 year BP. For evaluating volcanic activity of the most recently erupted volcanoes with reported age, volcanic explosivity index (VEI) and volcanic sulfur dioxide index (VSI) of three volcanoes (Ilchulbong tuff cone, Songaksan tuff ring, and Biyangdo scoria cone) are inferred from their eruptive volumes. The quantity of eruptive materials such as tuff, lavaflow, scoria, and so on, is calculated using a model developed in Auckland Volcanic Field which has similar volcanic setting to the island. The eruptive volumes of them are 11,911,534 m3, 24,987,557 m3, and 9,652,025 m3, which correspond to VEI of 3, 3, and 2, respectively. According to the correlation between VEI and VSI, the average quantity of SO2 emission during an eruption with VEI of 3 is 2-8 × 103 kiloton considering that the island was formed under intraplate tectonic setting. Jeju Island was regarded as an extinct volcano, however, several studies have recently reported some volcanic eruption ages within 10,000 year BP owing to the development in age dating technique. Thus, the island is a dormant volcano potentially implying high probability to erupt again in the future. The volcanoes might have explosive eruptions (vulcanian to plinian) with the possibility that SO2 emitted by the eruption reaches stratosphere causing climate change due to backscattering incoming solar radiation, increase in cloud reflectivity, etc. Consequently, recommencement of volcanic eruption in the island is able to result in serious volcanic hazard and this study provides fundamental and important data for volcanic hazard mitigation of East Asia as well as the island. ACKNOWLEDGMENTS: This research was supported by a grant [MPSS

Seismic Fracture Characterization Methodologies for Enhanced Geothermal Systems

Energy Technology Data Exchange (ETDEWEB)

Queen, John H. [Hi-Geophysical, Inc., Ponca, OK (United States)

2016-05-09

Executive Summary The overall objective of this work was the development of surface and borehole seismic methodologies using both compressional and shear waves for characterizing faults and fractures in Enhanced Geothermal Systems. We used both surface seismic and vertical seismic profile (VSP) methods. We adapted these methods to the unique conditions encountered in Enhanced Geothermal Systems (EGS) creation. These conditions include geological environments with volcanic cover, highly altered rocks, severe structure, extreme near surface velocity contrasts and lack of distinct velocity contrasts at depth. One of the objectives was the development of methods for identifying more appropriate seismic acquisition parameters for overcoming problems associated with these geological factors. Because temperatures up to 300º C are often encountered in these systems, another objective was the testing of VSP borehole tools capable of operating at depths in excess of 1,000 m and at temperatures in excess of 200º C. A final objective was the development of new processing and interpretation techniques based on scattering and time-frequency analysis, as well as the application of modern seismic migration imaging algorithms to seismic data acquired over geothermal areas. The use of surface seismic reflection data at Brady's Hot Springs was found useful in building a geological model, but only when combined with other extensive geological and geophysical data. The use of fine source and geophone spacing was critical in producing useful images. The surface seismic reflection data gave no information about the internal structure (extent, thickness and filling) of faults and fractures, and modeling suggests that they are unlikely to do so. Time-frequency analysis was applied to these data, but was not found to be significantly useful in their interpretation. Modeling does indicate that VSP and other seismic methods with sensors located at depth in wells will be the most

Friction in volcanic environments

Science.gov (United States)

Kendrick, Jackie E.; Lavallée, Yan

2016-04-01

Volcanic landscapes are amongst the most dynamic on Earth and, as such, are particularly susceptible to failure and frictional processes. In rocks, damage accumulation is frequently accompanied by the release of seismic energy, which has been shown to accelerate in the approach to failure on both a field and laboratory scale. The point at which failure occurs is highly dependent upon strain-rate, which also dictates the slip-zone properties that pertain beyond failure, in scenarios such as sector collapse and pyroclastic flows as well as the ascent of viscous magma. High-velocity rotary shear (HVR) experiments have provided new opportunities to overcome the grand challenge of understanding faulting processes during volcanic phenomena. Work on granular ash material demonstrates that at ambient temperatures, ash gouge behaves according to Byerlee's rule at low slip velocities, but is slip-weakening, becoming increasingly lubricating as slip ensues. In absence of ash along a slip plane, rock-rock friction induces cataclasis and heating which, if sufficient, may induce melting (producing pseudotachylyte) and importantly, vesiculation. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The shear-thinning behaviour and viscoelasticity of frictional melts yield a tendency for extremely unstable slip, and occurrence of frictional melt fragmentation. This velocity-dependence acts as an important feedback mechanism on the slip plane, in addition to the bulk composition, mineralogy and glass content of the magma, that all influence frictional behaviour. During sector collapse events and in pyroclastic density currents it is the frictional properties of the rocks and ash that, in-part, control the run-out distance and associated risk. In addition, friction plays an important role in the eruption of viscous magmas: In the conduit, the rheology of magma is integral

Controls on Magmatic and Hydrothermal Processes at Yellowstone Supervolcano: The Wideband Magnetotelluric Component of an Integrated MT/Seismic Investigation

Science.gov (United States)

Schultz, A.; Bennington, N. L.; Bowles-martinez, E.; Imamura, N.; Cronin, R. A.; Miller, D. J.; Hart, L.; Gurrola, R. M.; Neal, B. A.; Scholz, K.; Fry, B.; Carbonari, R.

2017-12-01

Previous seismic and magnetotelluric (MT) studies beneath Yellowstone (YS) have provided insight into the origin and migration of magmatic fluids within the volcanic system. However, important questions remain concerning the generation of magmatism at YS, the migration and storage of these magmatic fluids, as well as their relationships to hydrothermal expressions. Analysis of regional-scale EarthScope MT data collected previously suggests a relative absence of continuity in crustal partial melt accumulations directly beneath YS. This is in contrast to some seismic interpretations, although such long-period MT data have limited resolving power in the upper-to-mid crustal section. A wideband MT experiment was designed as a component of an integrated MT/seismic project to examine: the origin and location of magmatic fluids at upper mantle/lower crustal depths, the preferred path of migration for these magmatic fluids into the mid- to upper-crust, the resulting distribution of the magma reservoir, the composition of the magma reservoir, and implications for future volcanism at YS. A high-resolution wideband MT survey was carried out in the YS region in the summer of 2017, with more than forty-five wideband stations installed within and immediately surrounding the YS National Park boundary. These data provided nearly six decades of bandwidth ( 10-3 Hz -to- 103 Hz). Extraordinary permitting restrictions prevented us from using conventional installation methods at many of our sites, and an innovative "no-dig" subaerial method of wideband MT was developed and used successfully. Using these new data along with existing MT datasets, we are inverting for the 3D resistivity structure at upper crustal through upper mantle scales at YS. Complementary to this MT work, a joint inversion for the 3D crustal velocity structure is being carried out using both ambient noise and earthquake travel time data. Taken together, these data should better constrain the crustal velocity

Detecting hidden volcanic explosions from Mt. Cleveland Volcano, Alaska with infrasound and ground-couples airwaves

Science.gov (United States)

De Angelis, Slivio; Fee, David; Haney, Matthew; Schneider, David

2012-01-01

In Alaska, where many active volcanoes exist without ground-based instrumentation, the use of techniques suitable for distant monitoring is pivotal. In this study we report regional-scale seismic and infrasound observations of volcanic activity at Mt. Cleveland between December 2011 and August 2012. During this period, twenty explosions were detected by infrasound sensors as far away as 1827 km from the active vent, and ground-coupled acoustic waves were recorded at seismic stations across the Aleutian Arc. Several events resulting from the explosive disruption of small lava domes within the summit crater were confirmed by analysis of satellite remote sensing data. However, many explosions eluded initial, automated, analyses of satellite data due to poor weather conditions. Infrasound and seismic monitoring provided effective means for detecting these hidden events. We present results from the implementation of automatic infrasound and seismo-acoustic eruption detection algorithms, and review the challenges of real-time volcano monitoring operations in remote regions. We also model acoustic propagation in the Northern Pacific, showing how tropospheric ducting effects allow infrasound to travel long distances across the Aleutian Arc. The successful results of our investigation provide motivation for expanded efforts in infrasound monitoring across the Aleutians and contributes to our knowledge of the number and style of vulcanian eruptions at Mt. Cleveland.

Lower Crustal Seismicity, Volatiles, and Evolving Strain Fields During the Initial Stages of Cratonic Rifting

Science.gov (United States)

Lambert, C.; Muirhead, J.; Ebinger, C. J.; Tiberi, C.; Roecker, S. W.; Ferdinand-Wambura, R.; Kianji, G.; Mulibo, G. D.

2014-12-01

The volcanically active East African rift system in southern Kenya and northern Tanzania transects thick cratonic lithosphere, and comprises several basins characterized by deep crustal seismicity. The US-French-Tanzania-Kenya CRAFTI project aims to understand the role of magma and volatile movement during the initiation and evolution of rifting in cratonic lithosphere. Our 38-station broadband network spans all or parts of fault-bounded rift segments, enabling comparison of lithospheric structure, fault kinematics, and seismogenic layer thickness with age and proximity to the deeply rooted Archaen craton. Seismicity levels are high in all basins, but we find profound differences in seismogenic layer thickness along the length of the rift. Seismicity in the Manyara basin occurs almost exclusively within the lower crust, and in spatial clusters that have been active since 1990. In contrast, seismicity in the ~ 5 My older Magadi basin is localized in the upper crust, and the long border fault bounding the west side of the basin is seismically inactive. Between these two basins lies the Natron rift segment, which shows seismicity between ~ 20 and ~2 km depth, and high concentrations at Oldoinyo Lengai and Gelai volcanoes. Older volcanoes on the uplifted western flank (e.g., Ngorongoro) experience swarms of activity, suggesting that active magmatism and degassing are widespread. Focal mechanisms of the frequent earthquakes recorded across the array are spatially variable, and indicate a stress field strongly influenced by (1) Holocene volcanoes, (2) mechanical interactions between adjacent rift basins, and (3) a far-field ESE-WNW extensional stress regime. We explore the spatial correlation between zones of intense degassing along fault systems and seismicity, and examine the influence of high gas pressures on lower and upper crustal seismicity in this youthful cratonic rift zone.

Moving towards persistent identification in the seismological community

Science.gov (United States)

Quinteros, Javier; Evans, Peter; Strollo, Angelo; Ulbricht, Damian; Elger, Kirsten; Bertelmann, Roland

2016-04-01

The GEOFON data centre and others in the seismological community have been archiving seismic waveforms for many years. The amount of seismic data available continuously increases due to the use of higher sampling rates and the growing number of stations. In recent years, there is a trend towards standardization of the protocols and formats to improve and homogenise access to these data [FDSN, 2013]. The seismological community has begun assigning a particular persistent identifier (PID), the Digital Object Identifier (DOI), to seismic networks as a first step for properly and consistently attributing the use of data from seismic networks in scientific articles [Evans et al., 2015]. This was codified in a recommendation by the international Federation of Digital Seismic Networks [FDSN, 2014]; DOIs for networks now appear in community web pages. However, our community, in common with other fields of science, still struggles with issues such as: supporting reproducibility of results; providing proper attribution (data citation) for data sets; and measuring the impact (by tracking their use) of, those data sets. Seismological data sets used for research are frequently created "on-the-fly" based on particular user requirements such as location or time period; users prepare requests to select subsets of the data held in seismic networks; the data actually provided may even be held at many different data centres [EIDA, 2016]. These subsets also require careful citation. For persistency, a request must receive exactly the same data when repeated at a later time. However, if data are curated between requests, the data set delivered may differ, severely complicating the ability to reproduce a result. Transmission problems or configuration problems may also inadvertently modify the response to a request. With this in mind, our next step is the assignment of additional EPIC-PIDs to daily data files (currently over 28 million in the GEOFON archive) for use within the data

Geophysical Analysis of Young Monogenetic Volcanoes in the San Francisco Volcanic Field, Arizona

Science.gov (United States)

Rees, S.; Porter, R. C.; Riggs, N.

2017-12-01

The San Francisco Volcanic Field (SFVF), located in northern Arizona, USA, contains some of the youngest intracontinental volcanism within the United States and, given its recent eruptive history, presents an excellent opportunity to better understand how these systems behave. Geophysical techniques such as magnetics, paleomagnetics, and seismic refraction can be used to understand eruptive behavior and image shallow subsurface structures. As such, they present an opportunity to understand eruptive processes associated with the monogenetic volcanism that is common within the SFVF. These techniques are especially beneficial in areas where erosion has not exposed shallow eruptive features within the volcano. We focus on two volcanoes within the SFVF, Merriam Crater and Crater 120 for this work. These are thought to be some of the youngest volcanoes in the field and, as such, are well preserved. Aside from being young, they both exhibit interesting features such as multiple vents, apparent vent alignment, and lack of erosional features that are present at many of the other volcanoes in the SFVF, making them ideal for this work. Initial results show that shallow subsurface basaltic masses can be located using geophysical techniques. These masses are interpreted as dikes or lava flows that are covered by younger scoria. Propagating dikes drive eruptions at monogenetic volcanoes, which often appear in aligned clusters. Locating these features will further the understanding of how magma is transported and how eruptions may have progressed.

Sustained weight loss in patients treated with mifepristone for Cushing's syndrome: a follow-up analysis of the SEISMIC study and long-term extension.

Science.gov (United States)

Fein, Henry G; Vaughan, T Brooks; Kushner, Harvey; Cram, David; Nguyen, Dat

2015-10-27

Overweight and obesity are common among patients with Cushing's syndrome (CS) and may persist in some patients even after ostensibly curative surgery, contributing to cardiometabolic dysfunction and increased cardiovascular risk. Mifepristone, a selective glucocorticoid receptor antagonist, was effective in controlling hyperglycemia in a 24-week trial of adults (N = 50) with endogenous CS and associated type 2 diabetes mellitus/impaired glucose tolerance or hypertension who had failed or were not candidates for surgery (SEISMIC, Study of the Efficacy and Safety of Mifepristone in the Treatment of Endogenous Cushing's Syndrome). This analysis examines long-term weight change among patients who received mifepristone in SEISMIC and enrolled in a long-term safety extension (LTE) study. Patients completing the 24-week SEISMIC study and subsequent 6-week off-drug safety evaluation were invited to enroll in the LTE study. Mifepristone doses at the end of SEISMIC were the LTE starting doses. Body weight measures were reviewed at baseline and week 24 of SEISMIC and at LTE month 6, 12, 18, 24, and final visit (last observation collected during the LTE study). Of the 30 patients enrolled in the LTE, evaluable weight data were available for 29 (20/29 female; mean age of 44.7 ± 11.2 years). These patients received mifepristone for a median of 29.2 months (range 8.4-41.9). Mean ± SD weight from SEISMIC baseline to LTE final visit decreased by 10.3 ± 16.3 kg (mean 105.4 ± 34.3 kg to 95.1 ± 32.9 kg), a 9.3 % decrease from baseline weight (P = 0.0008). Of the 29 LTE patients, 18 (62.1 %) lost ≥ 5 % of body weight by the end of the initial 24-week treatment period; this ≥5 % weight loss persisted in 83.3 % (15/18) at LTE final visit. Ten patients (34.5 %) lost ≥ 10 % of initial body weight by week 24 of SEISMIC, which persisted in 80 % at LTE final visit. No new safety signals were detected with long-term mifepristone use. Clinically meaningful weight loss achieved during

Spreading of Somma-Vesuvio Volcanic Complex: is the Hazard for Plinian Eruptions being reduced?

Science.gov (United States)

Borgia, A.; Tizzani, P.; Solaro, G.; Luongo, G.; Fusi, N.

2003-12-01

Contrary to what is the common knowledge, a detailed structural study of active faulting and rifting of the summit area of Somma-Vesuvio volcanic complex, combined with INSAR, levelling data and seismic profiling at sea suggests that the present-day long-term dynamic behaviour of the complex and of its summit caldera is characterized by volcanic spreading. The structural evolution is controlled by a number of asymmetric, intersecting leaf-grabens. The boundary faults of these grabens intersect at different angles the Somma caldera walls generating a set of wedge-horsts. While normal faulting characterizes the Somma caldera walls, the lavas of the past 150 years, infilling the caldera, have been rifted all around the southern, eastern and northern base of Vesuvio's cone, which, in turn, is being displaced seaward. Associated to the subsidence and extension of the summit area, relative uplift occurs along the coast; in addition, deformation of recent sediments 6-18 km offshore also indicate compression and uplift, which appears to be unrelated to regional tectonics. A preliminary evaluation indicates that rifting of the lavas is in the order of 1-2 mm/a with a southwestward average direction of displacement. Based on these data, we suggest that a wide sector of Somma-Vesuvio is spreading on its plastic sedimentary substratum, which have been identified by drilling. Volcanic spreading appears to have controlled the magmatic evolution and the energy decrease of major historic explosive eruptions since 79 AD. If our interpretation is correct, major plinian eruptions should not occur in the near future. On the other hand, rifting around the caldera suggests that volcanic activity could soon be renewed.

Hurst analysis of seismicity in Corinth rift and Mygdonia graben (Greece)

International Nuclear Information System (INIS)

Gkarlaouni, Charikleia; Lasocki, Stanislaw; Papadimitriou, Eleftheria; George, Tsaklidis

2017-01-01

Highlights: • Long-term memory properties of seismicity are investigated using R/S analysis. • Small and moderate earthquake interevent times exhibit strong interdependence. • Strong earthquake occurrence indicates a memoryless process. • Seismicity variations in time are associated with Hurst temporal fluctuations. - Abstract: Temporal and spatial analysis of seismicity is performed via the Rescaled Range (R/S) analysis for revealing the hidden characteristics of long memory dependence and clustering between earthquakes. The analysis is applied in two seismogenic units belonging to the extensional Aegean back-arc region, namely the Corinth rift and the Mygdonian graben. The Hurst exponent estimations were used for the interpretation of earthquake collective properties, regarding magnitude, interevent time and interevent epicentral distance for consecutive events. Additional stochastic tools were then engaged for the validation of the results. Τhe analysis outcome is a significant long memory content in the seismic process of both areas, especially for the interevent time of recent micro seismicity and moderate earthquakes in the last decades. This property is not ascertained for the strong (M ≥ 6.0) historical earthquakes indicating that stronger events are rather independent, whereas the weaker ones may be primary carriers of persistence in the seismogenesis process.

Volcanic signatures in time gravity variations during the volcanic unrest on El Hierro (Canary Islands)

Science.gov (United States)

Sainz-Maza Aparicio, S.; Arnoso Sampedro, J.; Gonzalez Montesinos, F.; Martí Molist, J.

2014-06-01

Gravity changes occurring during the initial stage of the 2011-2012 El Hierro submarine eruption are interpreted in terms of the preeruptive signatures during the episode of unrest. Continuous gravity measurements were made at two sites on the island using the relative spring gravimeter LaCoste and Romberg gPhone-054. On 15 September 2011, an observed gravity decrease of 45 μGal, associated with the southward migration of seismic epicenters, is consistent with a lateral magma migration that occurred beneath the volcanic edifice, an apparently clear precursor of the eruption that took place 25 days later on 10 October 2011. High-frequency gravity signals also appeared on 6-11 October 2011, pointing to an occurring interaction between a magmatic intrusion and the ocean floor. These important gravity changes, with amplitudes varying from 10 to -90 μGal, during the first 3 days following the onset of the eruption are consistent with the northward migration of the eruptive focus along an active eruptive fissure. An apparent correlation of gravity variations with body tide vertical strain was also noted, which could indicate that concurrent tidal triggering occurred during the initial stage of the eruption.

Seismic isolation - efficient procedure for seismic response assessement

International Nuclear Information System (INIS)

Zamfir, M. A.; Androne, M.

2016-01-01

The aim of this analysis is to reduce the dynamic response of a structure. The seismic isolation solution must take into consideration the specific site ground motion. In this paper will be presented results obtained by applying the seismic isolation method. Based on the obtained results, important conclusions can be outlined: the seismic isolation device has the ability to reduce seismic acceleration of the seismic isolated structure to values that no longer present a danger to people and environment; the seismic isolation solution is limiting devices deformations to safety values for ensuring structural integrity and stability of the entire system; the effective seismic energy dissipation and with no side effects both for the seismic isolated building and for the devices used, and the return to the initial position before earthquake occurence are obtained with acceptable permanent displacement. (authors)

Numerical Simulation of a Non-volcanic Hydrothermal System Caused by Formation of a High Permeability Fracture Zone

Science.gov (United States)

Oka, Daisuke; Ehara, Sachio; Fujimitsu, Yasuhiro

2010-05-01

Because in the Japanese islands the earth crust activity is very active, a disposal stratum for high-level radioactive waste produced by reprocessing the spent nuclear fuel from nuclear power plants will be selected in the tectonically stable areas in which the waste can be disposed underground safely for a long term and there is no influence of earthquakes, seismic activities, volcanic activities, upheaval, sedimentation, erosion, climate and global sea level change and so on, which causes the risk of the inflow of the groundwater to destroy the disposal site or the outflow to the ground surface. However, even if the disposal stratum in such condition will be chosen, in case that a new high permeability fracture zone is formed by the earthquake, and a new hydrothermal system may be formed for a long term (thousands or millions years) and the system may affect the disposal site. Therefore, we have to understand the feature of the non-volcanic hydrothermal system through the high permeability fracture zone. We estimated such influence by using HYDROTHERM Ver2.2 (Hayba & Ingebritsen, 1994), which is a three-dimensional numerical reservoir simulator. The model field is the northwestern part of Kego Fault, which was formed by a series of earthquakes called "the 2005 Fukuoka Prefecture Western Offshore Earthquakes" (the main shock of Mjma 7.0 on 20 March 2005) in Kyushu, Japan. The results of the numerical simulations show the development of a low temperature hydrothermal system as a new fracture zone is formed, in case that there is no volcanic heat source. The results of the simulations up to 100,000 years after formation of the fracture zone show that the higher heat flow and the wider and more permeable fracture zone accelerate the development of the hydrothermal system in the fracture zone. As a result of calculation of up to10 million years, we clarified the evolutional process of the non-volcanic hydrothermal system through the high permeability fracture zone. At

Volcanic hazards to airports

Science.gov (United States)

Guffanti, M.; Mayberry, G.C.; Casadevall, T.J.; Wunderman, R.

2009-01-01

Volcanic activity has caused significant hazards to numerous airports worldwide, with local to far-ranging effects on travelers and commerce. Analysis of a new compilation of incidents of airports impacted by volcanic activity from 1944 through 2006 reveals that, at a minimum, 101 airports in 28 countries were affected on 171 occasions by eruptions at 46 volcanoes. Since 1980, five airports per year on average have been affected by volcanic activity, which indicates that volcanic hazards to airports are not rare on a worldwide basis. The main hazard to airports is ashfall, with accumulations of only a few millimeters sufficient to force temporary closures of some airports. A substantial portion of incidents has been caused by ash in airspace in the vicinity of airports, without accumulation of ash on the ground. On a few occasions, airports have been impacted by hazards other than ash (pyroclastic flow, lava flow, gas emission, and phreatic explosion). Several airports have been affected repeatedly by volcanic hazards. Four airports have been affected the most often and likely will continue to be among the most vulnerable owing to continued nearby volcanic activity: Fontanarossa International Airport in Catania, Italy; Ted Stevens Anchorage International Airport in Alaska, USA; Mariscal Sucre International Airport in Quito, Ecuador; and Tokua Airport in Kokopo, Papua New Guinea. The USA has the most airports affected by volcanic activity (17) on the most occasions (33) and hosts the second highest number of volcanoes that have caused the disruptions (5, after Indonesia with 7). One-fifth of the affected airports are within 30 km of the source volcanoes, approximately half are located within 150 km of the source volcanoes, and about three-quarters are within 300 km; nearly one-fifth are located more than 500 km away from the source volcanoes. The volcanoes that have caused the most impacts are Soufriere Hills on the island of Montserrat in the British West Indies

Petrologic Modeling of Magmatic Evolution in The Elysium Volcanic Province

Science.gov (United States)

Susko, D.; Karunatillake, S.; Hood, D.

2017-12-01

The Elysium Volcanic Province (EVP) on Mars is a massive expanse of land made up of many hundreds of lava flows of various ages1. The variable surface ages within this volcanic province have distinct elemental compositions based on the derived values from the Gamma Ray Spectrometer (GRS) suite2. Without seismic data or ophiolite sequences on Mars, the compositions of lavas on the surface provide some of the only information to study the properties of the interior of the planet. The Amazonian surface age and isolated nature of the EVP in the northern lowlands of Mars make it ideal for analyzing the mantle beneath Elysium during the most recent geologic era on Mars. The MELTS algorithm is one of the most commonly used programs for simulating compositions and mineral phases of basaltic melt crystallization3. It has been used extensively for both terrestrial applications4 and for other planetary bodies3,5. The pMELTS calibration of the algorithm allows for higher pressure (10-30 kbars) regimes, and is more appropriate for modeling melt compositions and equilibrium conditions for a source within the martian mantle. We use the pMELTS program to model how partial melting of the martian mantle could evolve magmas into the surface compositions derived from the GRS instrument, and how the mantle beneath Elysium has changed over time. We attribute changes to lithospheric loading by long term, episodic volcanism within the EVP throughout its history. 1. Vaucher, J. et al. The volcanic history of central Elysium Planitia: Implications for martian magmatism. Icarus 204, 418-442 (2009). 2. Susko, D. et al. A record of igneous evolution in Elysium, a major martian volcanic province. Scientific Reports 7, 43177 (2017). 3. El Maarry, M. R. et al. Gamma-ray constraints on the chemical composition of the martian surface in the Tharsis region: A signature of partial melting of the mantle? Journal of Volcanology and Geothermal Research 185, 116-122 (2009). 4. Ding, S. & Dasgupta, R. The

Major and micro seismo-volcanic crises in the Asal Rift, Djibouti

Science.gov (United States)

Peltzer, G.; Doubre, C.; Tomic, J.

2009-05-01

The Asal-Ghoubbet Rift is located on the eastern branch of the Afar triple junction between the Arabia, Somalia, and Nubia tectonic plates. The last major seismo-volcanic crisis on this segment occurred in November 1978, involving two earthquakes of mb=5+, a basaltic fissure eruption, the development of many open fissures across the rift and up to 80 cm of vertical slip on the bordering faults. Geodetic leveling revealed ~2 m of horizontal opening of the rift accompanied by ~70 cm of subsidence of the inner-floor, consistent with models of the elastic deformation produced by the injection of magma in a system of two dykes. InSAR data acquired at 24-day intervals during the last 12 years by the Canadian Radarsat satellite over the Asal Rift show that the two main faults activated in 1978 continue to slip with periods of steady creep at rates of 0.3-1.3 mm/yr, interrupted by sudden slip events of a few millimeters, in 2000 and 2003. Slip events are coincident with bursts of micro earthquakes distributed around and over the Fieale volcanic center in the eastern part of the Asal Rift. In both cases (the 1978 crisis and micro-slip events), the observed geodetic moment released by fault slip exceeds by a few orders of magnitude the total seismic moment released by earthquakes over the same period. Aseismic fault slip is likely to be the faults response to a changing stress field associated with a volcanic process and not due to dry friction on faults. Sustained injection of magma (1978 crisis) and/or crustal fluids (micro-slip events) in dykes and fissures is a plausible mechanism to control fluid pressure in the basal parts of faults and trigger aseismic slip. In this respect, the micro-events observed by InSAR during a 12-year period of low activity in the rift and the 1978 seismo-volcanic episode are of same nature.

Investigation of persistent Multiplets at the EGS reservoir of Soultz-Sous-Forêts, France

Science.gov (United States)

Lengliné, O.; Cauchie, L.; Schmittbuhl, J.

2017-12-01

During the exploitation of geothermal reservoirs, abundant seismicity is generally observed, especially during phases of hydraulic stimulations. The induced seismicity at the Enhanced Geothermal System of Soultz-Sous-Forêts in France, has been thoroughly studied over the years of exploitation. The mechanism at its origin has been related to both fluid pressure increases during stimulation and aseismic creeping movements. The fluid-induced seismic events often exhibit a high degree of similarity and the mechanism at the origin of these repeated events is thought to be associated with slow slip process where asperities on the rupture zone act several times.To have a better understanding of the mechanisms associated with such events and on the damaged zones involved during the hydraulic stimulations, we investigate the behavior of the multiplets and their persistent nature over several water injection intervals. For this purpose, we analyzed large datasets recorded from a borehole seismic network for several water injection periods (1993, 2000). For each stimulation interval, thousands of events are recorded at depth. We detected the events using a STA/LTA approach and classified them into families of comparable waveforms using an approach based on cross-correlation analysis. Classification of the seismic events is then improved depending on their location within the multiplets. For this purpose, inter-event distances within multiplets are examined and determined from cross-correlation analysis between pairs of events. These distances are then compared to the source dimensions derived from the estimation of the corner frequencies estimation. The multiplets properties (location, events size) are then investigated within and over several hydraulic tests. Hopefully these steps will lead to increase the knowledge on the repetitive nature of these events and the investigation of their persistence will outline the heterogeneities of the structures (regional stress

Diffuse Carbon Dioxide Degassing Monitoring at Santa Ana-Izalco-Coatepeque Volcanic System, El Salvador, Central America

Science.gov (United States)

Olmos, R.; Barahona, F.; Cartagena, R.; Soriano, T.; Salazar, J.; Hernandez, P.; Perez, N.; Notsu, K.; Lopez, D.

2001-12-01

Santa Ana volcanic complex (0.22 Ma), located 40 Km west of San Salvador, comprises Santa Ana, Izalco, and Cerro Verde stratovolcanoes, the Coatepeque collapse caldera, as well as several cinder cones and explosion craters. Most recent activity has occurred at Izalco (1966) and Santa Ana which shows a permanent acidic crater lake with an intense fumarolic activity. In addition, Santa Ana exhibits a SO2-rich rising plume though no local seismicity has been reported. Weak fumarolic activity is also present at two locations within the Santa Ana volcanic complex: the summit crater of Izalco and Cerro Pacho at Coatepeque caldera. Other important structural features of this volcanic complex are two fault/fissure systems running NNW-SSE that can be identified by the alignment of the stratovolcanoes and numerous cinder cones and explosion craters. In January 2001, a 7.6 magnitude earthquake occurred about 150 Km SE of Santa Ana volcano. A soil gas and CO2 efflux survey was performed to evaluate the impact of this seismic event upon the diffuse degassing rates in Santa Ana volcanic complex in March 2001. A total of 450 soil gas and diffuse CO2 efflux measurements were carried out covering an area of 209.5 Km2. CO2 efflux ranged from non-detectable values to 293 gm-2d-1, with a median of 8.9 gm-2d-1 and an upper quartile of 5.2 gm-2d-1. The CO2 efflux spatial distribution reveals the existence of areas with CO2 efflux higher than 60 gm-2d-1 associated to the fault/fissure systems of NNW-SSE orientation. One of these areas, Cerro Pacho, was selected for the continuous monitoring of diffuse CO2 efflux in late May 2001. Secular variations of diffuse CO2 efflux ranged from 27.4 to 329 gm-2d-1 with a median of 130 gm-2d-1 and a quartile range of 59.3 gm-2d-1. An increasing trend of 43 gm-2d-1 was observed between May and August 2001 overlapped to high-frequency minor fluctuations related to meteorological variables' changes. However, a larger observation time-span is needed to

Gravity in extensional regimes: A case study in the Central Volcanic Region, New Zealand

Science.gov (United States)

Greve, A.; Stern, T. A.

2017-12-01

Using the interpretation of a large crustal seismic experiment conducted in 2009 as boundary model, we produced a sequence of new 2D gravity models for the central North Island in New Zealand. The Bouguer gravity field in the region ranges from -100 to 60 mGal and is dominated by the long wavelength signals of the subduction of the Pacific beneath the Australian plate along the Hikurangi margin and the transition from continental to oceanic lithosphere about the Bay of Plenty coast (NE New Zealand). Removal of these broad regional trends reveals the presence of a triangular shaped area, within the lines Taranaki-Coromandel and Taranaki - White Island, with negative anomalies between -30 and 60 mGal and positive anomalies around 10 mGal along the margins. This area, commonly referred to as the Central Volcanic Region (CVR) represents the continental continuation of the Lau-Havre, oceanic, back-arc rift basin. The Taupo Volcanic Zone forms the active eastern half of the CVR, where anomalously high heat output, geothermal activity and active volcanism occur. The new gravity model includes the presence of a 90km wide, ca. 10 km thick rift pillow of new underplated, lower crust between the depths of 15 and 25 km. A positive density contrast of 300 kg/m3 for this body is consistent with the observed seismic velocities (6.8 ≤ Vp ≤ 7.1 km/s). A ca. 2.5 km deep basin dominates the upper crustal structure and is about 50 km wide, infilled by low density volcaniclastics, with adopted average negative densities of -425 kg/m3. In the mid-crustal region, between 2.5 and 15 km depth, isostatic compensation requires a small density contrast of -110 kg/m3. This density contrast, with respect to a standard crustal model, can be ascribed to the presence of low density intrusives, within the old and now stretched crust. On the basis of this new crustal structure model we estimate a stretching factor (ß) for the old crust of 2-2.4. The intruded mid crust and the underplated new

Crustal evolution of Eocene paleo arc around Ogasawara region obtained by seismic reflection survey

Science.gov (United States)

Yamashita, M.; Takahashi, N.; Kodaira, S.; Miura, S.; Ishizuka, O.; Tatsumi, Y.

2011-12-01

The Izu-Bonin (Ogasawara)-Mariana (IBM) arc is known to the typical oceanic island arc, and it is the most suitable area to understand the growth process of island arc. The existence of two paleo arc which consists of Oligocene and Eocene paleo age is known in IBM forearc region by geological and geophysical studies. The Ogasawara ridge is also known to locate the initial structure of arc evolution from geologic sampling of research submersible. In this region, IODP drilling site: IBM-2 is proposed in order to understand the temporal and spatial change in arc crust composition from 50 to 40Ma magmatism. Site IBM-2 consists of two offset drilling holes (BON-1, BON-2). BON-1 designed to first encounter forearc basalt and will reach the sheeted dykes. BON-2 will start in boninites and finish in fore arc basalts. The purpose of these drilling is sampling the full volcanic stratigraphy from gabbro to boninite. There is no seismic data around BON-1 and BON-2, therefore it is need to conduct the multi-channel seismic reflection survey. Japan Agency for Marine-Earth Science and Technology carried out multi-channel seismic reflection survey and wide-angle reflection survey using 7,800 cu.in. air gun, 5 km streamer with 444 ch hydrophones and 40 OBSs in March 2011. We obtained two seismic reflection profiles of lines KT06 and KT07 along the paleo arc around Ogasawara ridge. Line KT06 located the north side of Ogasawara ridge. Line KT07 located the trench side of Ogasawara ridge. Lines KT06 is also deployed the OBSs every 5 km interval. Thin sediments are covered with basement in both survey lines. There are some sediment filled in depression topography. The low-frequency reflection from the top of subducting Pacific plate is recognized in line KT06. The continuity of this reflection is not clear due to the complicated bathymetry. The displacement of basement in northern side of Ogasawara ridge is identified along the lineament of bathymetry in Line 06. This structure is

Degassing Processes at Persistently Active Explosive Volcanoes

Science.gov (United States)

Smekens, Jean-Francois

Among volcanic gases, sulfur dioxide (SO2) is by far the most commonly measured. More than a monitoring proxy for volcanic degassing, SO 2 has the potential to alter climate patterns. Persistently active explosive volcanoes are characterized by short explosive bursts, which often occur at periodic intervals numerous times per day, spanning years to decades. SO 2 emissions at those volcanoes are poorly constrained, in large part because the current satellite monitoring techniques are unable to detect or quantify plumes of low concentration in the troposphere. Eruption plumes also often show high concentrations of ash and/or aerosols, which further inhibit the detection methods. In this work I focus on quantifying volcanic gas emissions at persistently active explosive volcanoes and their variations over short timescales (minutes to hours), in order to document their contribution to natural SO2 flux as well as investigate the physical processes that control their behavior. In order to make these measurements, I first develop and assemble a UV ground-based instrument, and validate it against an independently measured source of SO2 at a coal-burning power plant in Arizona. I establish a measurement protocol and demonstrate that the instrument measures SO 2 fluxes with Indonesia), a volcano that has been producing cycles of repeated explosions with periods of minutes to hours for the past several decades. Semeru produces an average of 21-71 tons of SO2 per day, amounting to a yearly output of 8-26 Mt. Using the Semeru data, along with a 1-D transient numerical model of magma ascent, I test the validity of a model in which a viscous plug at the top of the conduit produces cycles of eruption and gas release. I find that it can be a valid hypothesis to explain the observed patterns of degassing at Semeru. Periodic behavior in such a system occurs for a very narrow range of conditions, for which the mass balance between magma flux and open-system gas escape repeatedly

What goes up might come down: Backflow in the conduits of persistently degassing volcanoes and ramifications for melt-inclusion analysis

Science.gov (United States)

Suckale, J.; Qin, Z.; Picchi, D.; Keller, T.

2017-12-01

Many active volcanoes erupt significantly less magma than they degas, implying that large quantities of magma must descend back into the plumbing system after degassing. The resulting bidirectional flow field in the volcanic conduit is fundamentally unstable. These instabilities are important to understand, because they likely control the episodicity of eruptive behavior observed at persistently degassing volcanoes. Laboratory experiments have provided invaluable insights into the flow regimes that may arise in volcanic conduits, but are not straightforward to scale up to volcanic systems. The goal of this study is to use direct numerical simulations to virtually reproduce the analogue experiments by Stevenson and Blake, 1998, compare them to simple analytical models and gain insights into the different flow regimes and interface instabilities observed in actual volcanic conduits. Direct numerical simulations provide a compelling complement to analogue experiments, because they are not constrained by the scales or flow properties achievable in a laboratory setting. By linking virtual and analogue experiments, we show that the interface between ascending and descending fluid is not usually stationary in volcanic conduits (see fig). The intuition that buoyant, volatile-rich magma moves up while heavy, degassed magma moves down is hence not generally true in bidirectional conduit flow. Instead, our results show that a potentially significant portion of the volatile-rich magma flows downwards despite its positive buoyancy - a process commonly referred to as backflow. The existence of backflow in volcanic conduits has potentially important ramifications for understanding melt-inclusion trends, because it affects exsolved and dissolved volatile components differently. Our preliminary results suggest that carbon dioxide bubbles exsolved at depth tend to decouple from the backflow and escape into the upward moving portion of the fluid, while dissolved water is recycled

Seismic testing

International Nuclear Information System (INIS)

Sollogoub, Pierre

2001-01-01

This lecture deals with: qualification methods for seismic testing; objectives of seismic testing; seismic testing standards including examples; main content of standard; testing means; and some important elements of seismic testing

Mass movement processes associated with volcanic structures in Mexico City

Directory of Open Access Journals (Sweden)

Víctor Carlos Valerio

2012-11-01

Full Text Available Mexico City, one of the most populated areas of the world, has been affected by various hazards of natural origin, such as subsidence and cracking of the soil, seismicity, floods and mass movement processes (MMPs. Owing to the lack of space on the plain, in recent years urban growth has been concentrated particularly on the slopes of the surrounding mountain ranges, and this has significantly modified the dynamics of the relief as well as the hydrogeological conditions. The specific character of natural susceptibility to mass movements is strongly dependent on the geological–structural and morphological characteristics of the volcanic bodies that form the mountainous relief. This natural susceptibility, combined with the characteristics of vulnerability of the society, creates risk conditions that can generate severe consequences for the population and the economy. Hence, based on an inventory of mass movement processes comprising 95 data points, the present study aimed to achieve a zoning of the areas susceptible to these processes, as well as to characterize the mechanisms of instability in the volcanic structures that form the relief of the area in question. The results of this work clearly show the role of the lithology, the mode of emplacement and the morpho–structural characteristics of the volcanic structures, in the types of mass movement processes. In addition, it identifies the diverse activities of anthropogenic origin that favour slope instability in the zone: deforestation and burning of rubbish, felling of timber on the slopes for building infrastructure and dwellings, leakages of water, vibrations of vehicles, rotating machinery and the use of explosives in mining works, overloading the heads of the slopes, disturbance of the geohydrological regime, generation of rubbish tips, terracing of the slopes for cultivation, inadequate building regulations, and the use of counterproductive or ineffectual stabilization measures.

Hydrological sensitivity of volcanically disturbed watersheds—a lesson reinforced at Pinatubo

Science.gov (United States)

Major, J. J.; Janda, R. J.

2016-12-01

The climactic June 1991 eruption of Mount Pinatubo devastated many surrounding catchments with thick pyroclastic fall and flow deposits, and subsequent hydrogeomorphic responses were dramatic and persisted for years. But in the 24 hours preceding the climactic eruption there was less devastating eruptive activity that had more subtle, yet significant, impact on catchment hydrology. Stratigraphic relations show damaging lahars swept all major channels east of the volcano, starting late on June 14 and continuing through (and in some instances after) midday on June 15, before the climactic phase of the eruption began and before Typhoon Yunya struck the region. These early lahars were preceded by relatively small explosions and pyroclastic surges that emplaced fine-grained ash in the upper catchments, locally damaged or destroyed vegetation, reduced hillside infiltration capacity, and smoothed surface roughness. Thus the lahars, likely triggered by typical afternoon monsoon storms perhaps enhanced by local thermal influences of fresh volcanic deposits, did not result from extraordinary tropical rainfall or exceptional volcaniclastic deposition. Instead, direct rainfall-runoff volume increased substantially as a consequence of vegetation damage and moderate deposition of fine ash. Rapid runoff from hillsides to channels initiated hillside and bank erosion as well as channel scour, producing debris flows and hyperconcentrated flows. Timing of some lahars varied across catchments as well as downstream within catchments with respect to climactic pumice fall, demonstrating complex interplay among volcanic processes, variations in catchment disturbance, and rainfall timing and intensity. Occurrence of these early lahars supports the hypothesis that eruptions that deposit fine ash in volcanic catchments can instigate major hydrogeomorphic responses even when volcanic disturbances are modest—an effect that can be masked by later eruption impacts.

Seismic structure of the western U.S. mantle and its relation to regional tectonic and magmatic activity

Science.gov (United States)

Schmandt, Brandon

Vigorous convective activity in the western U.S. mantle has long been inferred from the region's widespread intra-plate crustal deformation, volcanism, and high elevations, but the specific form of convective activity and the degree and nature of lithospheric involvement have been strongly debated. I design a seismic travel-time tomography method and implement it with seismic data from the EarthScope Transportable Array and complementary arrays to constrain three-dimensional seismic structure beneath the western U.S. Tomographic images of variations in compressional velocity, shear velocity, and the ratio of shear to compressional velocity in the western U.S. mantle to a depth of 1000 km are produced. Using these results I investigate mantle physical properties, Cenozoic subduction history, and the influence of small-scale lithospheric convection on regional tectonic and magmatic activity, with particular focus on southern California and the Pacific Northwest. This dissertation includes previously published co-authored material. Chapter II presents a travel-time tomography method I designed and first implemented with data from southern California and the surrounding southwestern U.S. The resulting images provide a new level of constraint on upper mantle seismic anomalies beneath the Transverse Ranges, southern Great Valley, Salton Trough, and southwestern Nevada volcanic field. Chapter III presents tomographic images of the western U.S. mantle, identifies upper mantle volumes where partial melt is probable, and discusses implications of the apparently widespread occurrence of gravitational instabilities of continental lithsophere and the complex geometry and buoyancy of subducted ocean lithosphere imaged beneath the western U.S. In Chapter IV, tomography images are used in conjunction with geologic constraints on major transitions in crustal deformation and magmatism to construct a model for Pacific Northwest evolution since the Cretaceous. Accretion in the Pacific

Soft-sediment deformation in New Zealand: Structures resulting from the 2010/11 Christchurch earthquakes and comparison with Pleistocene sediments of the Taupo Volcanic Zone (TVZ)

Science.gov (United States)

Scholz, C.; Downs, D. T.; Gravley, D.; Quigley, M.; Rowland, J. V.

2011-12-01

The distinction between seismites and other event-related soft-sediment deformation is a challenging problem. Recognition and interpretation is aided by comparison of recent examples produced during known seismic events and those generated experimentally. Seismites are important features, once recognized in a rock, for interpretations of paleotectonic environment, tectonic relationships of sediments in basins, sedimentary facies analysis, evaluation of earthquake frequency and hazard and consequent land managment. Two examples of soft-sediment deformation, potentially generated through ground shaking and associated liquefaction, are described from within the TVZ: 1) Near Matata on the western margin of the Whakatane Graben. This location has a complicated en-echelon fault history and large earthquakes occur from time to time (e.g., 1987 ML6.3 Edgecumbe event). The structures occur in ~550 ka volcanic sediments, and represent soft-sediment deformation within stratigraphically-bounded layers. Based on paleoenvironment, appearance, and diagnostic criteria described by other authors (Sims 1975; Hempton and Dewey 1983), we interpret these features to have formed by ground shaking related to an earthquake and/or possibly accompanying large volcanic eruptions, rather than by slope failure. 2) Near Taupo, 3 km from the active Kaiapo fault. Lakeward dipping, nearly horizontal lacustrine sediments overlay Taupo Ignimbrite (1.8 ka). At one outcrop the lake beds have subsided into the underlying substrate resulting in kidney-shaped features. These structures formed as a result of liquefaction of the underlying substrate, which may have been caused by ground shaking related to either seismic or volcanic activity. However, inferred time relationships are more consistent with seismic-induced ground shaking. We compare and contrast the form and geometry of the above structures with seismites generated during the recent Christchurch earthquakes (Sep. 2010 and Feb. 2011). Hempton, M

seismic-py: Reading seismic data with Python

Directory of Open Access Journals (Sweden)

2008-08-01

Full Text Available The field of seismic exploration of the Earth has changed
dramatically over the last half a century. The Society of Exploration
Geophysicists (SEG has worked to create standards to store the vast
amounts of seismic data in a way that will be portable across computer
architectures. However, it has been impossible to predict the needs of the
immense range of seismic data acquisition systems. As a result, vendors have
had to bend the rules to accommodate the needs of new instruments and
experiment types. For low level access to seismic data, there is need for a
standard open source library to allow access to a wide range of vendor data
files that can handle all of the variations. A new seismic software package,
seismic-py, provides an infrastructure for creating and managing drivers for
each particular format. Drivers can be derived from one of the known formats
and altered to handle any slight variations. Alternatively drivers can be
developed from scratch for formats that are very different from any previously
defined format. Python has been the key to making driver development easy
and efficient to implement. The goal of seismic-py is to be the base system
that will power a wide range of experimentation with seismic data and at the
same time provide clear documentation for the historical record of seismic
data formats.

Subduction factory 1. Theoretical mineralogy, densities, seismic wave speeds, and H2O contents

Science.gov (United States)

Hacker, Bradley R.; Abers, Geoffrey A.; Peacock, Simon M.

2003-01-01

We present a new compilation of physical properties of minerals relevant to subduction zones and new phase diagrams for mid-ocean ridge basalt, lherzolite, depleted lherzolite, harzburgite, and serpentinite. We use these data to calculate H2O content, density and seismic wave speeds of subduction zone rocks. These calculations provide a new basis for evaluating the subduction factory, including (1) the presence of hydrous phases and the distribution of H2O within a subduction zone; (2) the densification of the subducting slab and resultant effects on measured gravity and slab shape; and (3) the variations in seismic wave speeds resulting from thermal and metamorphic processes at depth. In considering specific examples, we find that for ocean basins worldwide the lower oceanic crust is partially hydrated (measurements. Subducted hydrous crust in cold slabs can persist to several gigapascals at seismic velocities that are several percent slower than the surrounding mantle. Seismic velocities and VP/VS ratios indicate that mantle wedges locally reach 60-80% hydration.

Volcanic signals in oceans

KAUST Repository

Stenchikov, Georgiy L.

2009-08-22

Sulfate aerosols resulting from strong volcanic explosions last for 2–3 years in the lower stratosphere. Therefore it was traditionally believed that volcanic impacts produce mainly short-term, transient climate perturbations. However, the ocean integrates volcanic radiative cooling and responds over a wide range of time scales. The associated processes, especially ocean heat uptake, play a key role in ongoing climate change. However, they are not well constrained by observations, and attempts to simulate them in current climate models used for climate predictions yield a range of uncertainty. Volcanic impacts on the ocean provide an independent means of assessing these processes. This study focuses on quantification of the seasonal to multidecadal time scale response of the ocean to explosive volcanism. It employs the coupled climate model CM2.1, developed recently at the National Oceanic and Atmospheric Administration\\'s Geophysical Fluid Dynamics Laboratory, to simulate the response to the 1991 Pinatubo and the 1815 Tambora eruptions, which were the largest in the 20th and 19th centuries, respectively. The simulated climate perturbations compare well with available observations for the Pinatubo period. The stronger Tambora forcing produces responses with higher signal-to-noise ratio. Volcanic cooling tends to strengthen the Atlantic meridional overturning circulation. Sea ice extent appears to be sensitive to volcanic forcing, especially during the warm season. Because of the extremely long relaxation time of ocean subsurface temperature and sea level, the perturbations caused by the Tambora eruption could have lasted well into the 20th century.

Application of a Hybrid Detection and Location Scheme to Volcanic Systems

Science.gov (United States)

Thurber, C. H.; Lanza, F.; Roecker, S. W.

2017-12-01

We are using a hybrid method for automated detection and onset estimation, called REST, that combines a modified version of the nearest-neighbor similarity scheme of Rawles and Thurber (2015; RT15) with the regression approach of Kushnir et al. (1990; K90). This approach incorporates some of the windowing ideas proposed by RT15 into the regression techniques described in K90. The K90 and RT15 algorithms both define an onset as that sample where a segment of noise at earlier times is most "unlike" a segment of data at later times; the main difference between the approaches is how one defines "likeness." Hence, it is fairly straightforward to adapt the RT15 ideas to a K90 approach. We also incorporated the running mean normalization scheme of Bensen et al. (2007), used in ambient noise pre-processing, to reduce the effects of coherent signals (such as earthquakes) in defining noise segments. This is especially useful for aftershock sequences, when the persistent high amplitudes due to many earthquakes biases the true noise level. We use the fall-off of the K90 estimation function to assign uncertainties and the asymmetry of the function as a causality constraint. The detection and onset estimation stage is followed by iterative pick association and event location using a grid-search method. Some fine-tuning of some parameters is generally required for optimal results. We present 2 applications of this scheme to data from volcanic systems: Makushin volcano, Alaska, and Laguna del Maule (LdM), Chile. In both cases, there are permanent seismic networks, operated by the Alaska Volcano Observatory (AVO) and Observatorio Volcanológico de Los Andes del Sur (OVDAS), respectively, and temporary seismic arrays were deployed for a year or more. For Makushin, we have analyzed a year of data, from summer 2015 to summer 2016. The AVO catalog has 691 events in our study volume; REST processing yields 1784 more events. After quality control, the event numbers are 151 AVO events and

In-situ monitoring of deformation of clayey and volcanic sequences in the lacustrine plain of Iztapalapa, Mexico City

Science.gov (United States)

Carreon-Freyre, D.; Cerca, M.; Barrientos, B.; Gutierrez, R.; Blancas, D.

2012-12-01

Major cities of Central Mexico with lowering of land elevation problems are located in inter-volcanic and fault bounded basins within the central Trans-Mexican Volcanic Belt (TMVB). The most representative and studied case of ground deformation is Mexico City, where the Iztapalapa Municipality presents the highest population density. This area is located over the geological contact between the "Sierra de Santa Catarina" volcanic range and a lacustrine plain. Filling of lacustrine basins includes silty and clayey sediments as well as pyroclastic deposits (coarse and fine grained) and volcanic rocks layers. We used Ground Penetrating Radar (GPR) and MASW prospection to evaluate contrasts in the physical properties of fine grained soils and identify geometry of the deformational features and implemented a mechanical system for in situ monitoring in fractured sites. Deformational features in this basin reflect an interplay between the geological history (depositional conditions), load history, seismic activity, and faulting. Plastic mechanical behaviour predominates in these clayey sediments and differential deformation locally triggers brittle fracturing and/or subsidence of the surface. In this work we present the results of monitoring and characterization of ground deformation and fracturing in different sequences, our results show a dynamic interplay between the mechanisms of ground fracturing and the stress history of sedimentary sequences. Relating the mechanical behaviour of the studied sequences with variations of physical and geological properties should be taken into account to estimate land level lowering and risk of fracturing for urban development planning.

Seismic Amplitude Ratio Analysis of the 2014-2015 Bár∂arbunga-Holuhraun Dike Propagation and Eruption

Science.gov (United States)

Caudron, Corentin; White, Robert S.; Green, Robert G.; Woods, Jennifer; Ágústsdóttir, Thorbjörg; Donaldson, Clare; Greenfield, Tim; Rivalta, Eleonora; Brandsdóttir, Bryndís.

2018-01-01

Magma is transported in brittle rock through dikes and sills. This movement may be accompanied by the release of seismic energy that can be tracked from the Earth's surface. Locating dikes and deciphering their dynamics is therefore of prime importance in understanding and potentially forecasting volcanic eruptions. The Seismic Amplitude Ratio Analysis (SARA) method aims to track melt propagation using the amplitudes recorded across a seismic network without picking the arrival times of individual earthquake phases. This study validates this methodology by comparing SARA locations (filtered between 2 and 16 Hz) with the earthquake locations (same frequency band) recorded during the 2014-2015 Bár∂arbunga-Holuhraun dike intrusion and eruption in Iceland. Integrating both approaches also provides the opportunity to investigate the spatiotemporal characteristics of magma migration during the dike intrusion and ensuing eruption. During the intrusion SARA locations correspond remarkably well to the locations of earthquakes. Several exceptions are, however, observed. (1) A low-frequency signal was possibly associated with a subglacial eruption on 23 August. (2) A systematic retreat of the seismicity was also observed to the back of each active segment during stalled phases and was associated with a larger spatial extent of the seismic energy source. This behavior may be controlled by the dike's shape and/or by dike inflation. (3) During the eruption SARA locations consistently focused at the eruptive site. (4) Tremor-rich signal close to ice cauldrons occurred on 3 September. This study demonstrates the power of the SARA methodology, provided robust site amplification; Quality Factors and seismic velocities are available.

Final recommendations of the Peer Review Panel on the use of seismic methods for characterizing Yucca Mountain and vicinity

International Nuclear Information System (INIS)

1991-01-01

The Peer Review Panel was charged with deciding whether seismic methods, which had been utilized at Yucca Mountain with mixed results in the past, could provide useful information about the Tertiary structure in the Yucca Mountain area. The objectives of using seismic methods at Yucca Mountain are to: (a) obtain information about the structural character of the Paleozoic-Tertiary (Pz-T) contact, and (b) obtain information about the structural and volcanic details within the Tertiary and Quaternary section. The Panel recommends that a four part program be undertaken to test the utility of seismic reflection data for characterizing the structural setting of the Yucca Mountain area. The Panel feels strongly that all four parts of the program must be completed in order to provide the highest probability of success. The four parts of the program are: (a) drill or extend a deep hole in Crater Flat to provide depth control and allow for the identification of seismic reflectors in an area where good quality seismic reflection data are expected; (b) undertake a full seismic noise test in Crater Flat, test 2D receiver arrays as well as linear arrays; perform an expanding spread test using both P and S wave sources to obtain a quick look at the reflection quality in the area and see if shear wave reflections might provide structural information in areas of unsaturated rock; (c) acquire a P wave seismic reflection profile across Crater Flat through the deep control well, across Yucca Mountain, and continuing into Jackass Flats; and (d) acquire a standard VSP (vertical seismic profiling) in the deep control well to tie the seismic data into depth and to identify reflectors correctly

Monitoring diffuse degassing in monogentic volcanic field during magmatic reactivation: the case of El Hierro (Canary Islands, Spain)

Science.gov (United States)

Morales-Ocaña, C.; Feldman, R. C.; Pointer, Z. R.; Rodríguez, F.; Asensio-Ramos, M.; Melián, G.; Padrón, E.; Hernández, P. A.; Pérez, N. M.

2017-12-01

El Hierro (278 km2), the younger, smallest and westernmost island of the Canarian archipelago, is a 5-km-high edifice constructed by rapid constructive and destructive processes in 1.12 Ma, with a truncated trihedron shape and three convergent ridges of volcanic cones. It experienced a submarine eruption from 12 October, 2011 and 5 March 2012, off its southern coast that was the first one to be monitored from the beginning in the Canary Islands. As no visible emanations occur at the surface environment of El Hierro, diffuse degassing studies have become a useful geochemical tool to monitor the volcanic activity in this volcanic island. Diffuse CO2 emission has been monitored at El Hierro Island since 1998 in a yearly basis, with much higher frequency in the period 2011-2012. At each survey, about 600 sampling sites were selected to obtain a homogeneous distribution. Measurements of soil CO2 efflux were performed in situ following the accumulation chamber method. During pre-eruptive and eruptive periods, the diffuse CO2 emission released by the whole island experienced significant increases before the onset of the submarine eruption and the most energetic seismic events of the volcanic-seismic unrest (Melián et al., 2014. J. Geophys. Res. Solid Earth, 119, 6976-6991). The soil CO2 efflux values of the 2017 survey ranged from non-detectable to 53.1 g m-2 d-1. Statistical-graphical analysis of the data show two different geochemical populations; background (B) and peak (P) represented by 77.6% and 22.4% of the total data, respectively, with geometric means of 1.8 and 9.2 g m-2 d-1, respectively. Most of the area showed B values while the P values were mainly observed at the interception center of the three convergent ridges and the north of the island. To estimate the diffuse CO2 emission for the 2017 survey, we ran about 100 sGs simulations. The estimated 2017 diffuse CO2 output released to atmosphere by El Hierro was at 1,150 ± 42 t d-1, value higher than the

Northeastern Brazilian margin: Regional tectonic evolution based on integrated analysis of seismic reflection and potential field data and modelling

Science.gov (United States)

Blaich, Olav A.; Tsikalas, Filippos; Faleide, Jan Inge

2008-10-01

Integration of regional seismic reflection and potential field data along the northeastern Brazilian margin, complemented by crustal-scale gravity modelling, is used to reveal and illustrate onshore-offshore crustal structure correlation, the character of the continent-ocean boundary, and the relationship of crustal structure to regional variation of potential field anomalies. The study reveals distinct along-margin structural and magmatic changes that are spatially related to a number of conjugate Brazil-West Africa transfer systems, governing the margin segmentation and evolution. Several conceptual tectonic models are invoked to explain the structural evolution of the different margin segments in a conjugate margin context. Furthermore, the constructed transects, the observed and modelled Moho relief, and the potential field anomalies indicate that the Recôncavo, Tucano and Jatobá rift system may reflect a polyphase deformation rifting-mode associated with a complex time-dependent thermal structure of the lithosphere. The constructed transects and available seismic reflection profiles, indicate that the northern part of the study area lacks major breakup-related magmatic activity, suggesting a rifted non-volcanic margin affinity. In contrast, the southern part of the study area is characterized by abrupt crustal thinning and evidence for breakup magmatic activity, suggesting that this region evolved, partially, with a rifted volcanic margin affinity and character.

4-D Visualization of Seismic and Geodetic Data of the Big Island of Hawai'i

Science.gov (United States)

Burstein, J. A.; Smith-Konter, B. R.; Aryal, A.

2017-12-01

For decades Hawai'i has served as a natural laboratory for studying complex interactions between magmatic and seismic processes. Investigating characteristics of these processes, as well as the crustal response to major Hawaiian earthquakes, requires a synthesis of seismic and geodetic data and models. Here, we present a 4-D visualization of the Big Island of Hawai'i that investigates geospatial and temporal relationships of seismicity, seismic velocity structure, and GPS crustal motions to known volcanic and seismically active features. Using the QPS Fledermaus visualization package, we compile 90 m resolution topographic data from NASA's Shuttle Radar Topography Mission (SRTM) and 50 m resolution bathymetric data from the Hawaiian Mapping Research Group (HMRG) with a high-precision earthquake catalog of more than 130,000 events from 1992-2009 [Matoza et al., 2013] and a 3-D seismic velocity model of Hawai'i [Lin et al., 2014] based on seismic data from the Hawaiian Volcano Observatory (HVO). Long-term crustal motion vectors are integrated into the visualization from HVO GPS time-series data. These interactive data sets reveal well-defined seismic structure near the summit areas of Mauna Loa and Kilauea volcanoes, where high Vp and high Vp/Vs anomalies at 5-12 km depth, as well as clusters of low magnitude (M data are also used to help identify seismic clusters associated with the steady crustal detachment of the south flank of Kilauea's East Rift Zone. We also investigate the fault geometry of the 2006 M6.7 Kiholo Bay earthquake event by analyzing elastic dislocation deformation modeling results [Okada, 1985] and HVO GPS and seismic data of this event. We demonstrate the 3-D fault mechanisms of the Kiholo Bay main shock as a combination of strike-slip and dip-slip components (net slip 0.55 m) delineating a 30 km east-west striking, southward-dipping fault plane, occurring at 39 km depth. This visualization serves as a resource for advancing scientific analyses of

Acceleration to failure in geophysical signals prior to laboratory rock failure and volcanic eruptions (Invited)

Science.gov (United States)

Main, I. G.; Bell, A. F.; Greenhough, J.; Heap, M. J.; Meredith, P. G.

2010-12-01

The nucleation processes that ultimately lead to earthquakes, volcanic eruptions, rock bursts in mines, and landslides from cliff slopes are likely to be controlled at some scale by brittle failure of the Earth’s crust. In laboratory brittle deformation experiments geophysical signals commonly exhibit an accelerating trend prior to dynamic failure. Similar signals have been observed prior to volcanic eruptions, including volcano-tectonic earthquake event and moment release rates. Despite a large amount of effort in the search, no such statistically robust systematic trend is found prior to natural earthquakes. Here we describe the results of a suite of laboratory tests on Mount Etna Basalt and other rocks to examine the nature of the non-linear scaling from laboratory to field conditions, notably using laboratory ‘creep’ tests to reduce the boundary strain rate to conditions more similar to those in the field. Seismic event rate, seismic moment release rate and rate of porosity change show a classic ‘bathtub’ graph that can be derived from a simple damage model based on separate transient and accelerating sub-critical crack growth mechanisms, resulting from separate processes of negative and positive feedback in the population dynamics. The signals exhibit clear precursors based on formal statistical model tests using maximum likelihood techniques with Poisson errors. After correcting for the finite loading time of the signal, the results show a transient creep rate that decays as a classic Omori law for earthquake aftershocks, and remarkably with an exponent near unity, as commonly observed for natural earthquake sequences. The accelerating trend follows an inverse power law when fitted in retrospect, i.e. with prior knowledge of the failure time. In contrast the strain measured on the sample boundary shows a less obvious but still accelerating signal that is often absent altogether in natural strain data prior to volcanic eruptions. To test the

The 2011 volcanic crisis at El Hierro (Canary Islands): monitoring ground deformation through tiltmeter and gravimetric observations

Science.gov (United States)

Arnoso, J.; Montesinos, F. G.; Benavent, M.; Vélez, E. J.

2012-04-01

El Hierro is an ocean island located at the western end of the Canary Islands, and along with Tenerife and La Palma islands have been the most geologically active in the recent past. The island has a triple armed rift and, presently, is at the stage of growth, representing the summit of a volcanic shield elevating from the seafloor at depth of 4000 m up to 1501 m above the sea level (Münn et al., 2006; Carracedo et al., 1999). Since July 19th, 2011 seismic activity has produced more than 11950 events up to date. The seismic crisis resulted in a volcanic eruption that began on October 10th, being still currently active. The new volcano is located 2 km off the coast and about 300 m depth, in the submarine flank of the southern rift of the island, which is extended some 40 km length. Since September 2004 until November 2010 two continuous tilt stations were installed at the north, Balneario site (BA), and at the center of the island, Aula de la Naturaleza (AU) site. Both stations were used to assess the pattern of local ground movements in the island. When seismic swarm started on past July 2011, we have reinstalled both tilt stations (BA and AU) and 2 new ones located at the south of the island, namely Montaña Quemada (MQ) and Restinga (RE) sites. We have used short base platform tiltmeters that measure ground tilts with resolutions varying from 0.1 up to 0.01 microradians (µrad). On October 8th, a 4.4 magnitude earthquake took place and is supposed that fractured the ocean crust at some 8-10 km off the south coast of the island and about 1000 m depth. Typical spike signals were observed at the tilt stations. Two days after, the eruption onset was recorded also at tilt stations through a remarkable increase of the high frequency signal, being of large amplitude the components (radial) orientated towards the new volcano edifice. When compared with previous tiltmeter records in the island, tilt pattern were clearly modified several times at the stations when strong

Volcanic signals in oceans

KAUST Repository

Stenchikov, Georgiy L.; Delworth, Thomas L.; Ramaswamy, V.; Stouffer, Ronald J.; Wittenberg, Andrew; Zeng, Fanrong

2009-01-01

Sulfate aerosols resulting from strong volcanic explosions last for 2–3 years in the lower stratosphere. Therefore it was traditionally believed that volcanic impacts produce mainly short-term, transient climate perturbations. However, the ocean

Remotely triggered seismicity in north China following the 2008 M w 7.9 Wenchuan earthquake

Science.gov (United States)

Peng, Zhigang; Wang, Weijun; Chen, Qi-Fu; Jiang, Tao

2010-11-01

We conduct a systematic survey of remote triggering of earthquakes in north China following the 2008 M w 7.9 Wenchuan earthquake. We identify triggered earthquakes as impulsive seismic energies with clear P and S arrivals on 5 Hz high-pass-filtered three-component velocity seismograms during and immediately after the passage of teleseismic waves. We find clearly triggered seismic activity near the Babaoshan and Huangzhuang-Gaoliying faults southwest of Beijing, and near the aftershock zone of the 1976 M W 7.6 Tangshan earthquake. While several earthquakes occur during and immediately after the teleseismic waves in the aftershock zone of the 1975 M w 7.0 Haicheng earthquake, the change of seismicity is not significant enough to establish the direct triggering relationship. Our results suggest that intraplate regions with active faults associated with major earthquakes during historic or recent times are susceptible to remote triggering. We note that this does not always guarantee the triggering to occur, indicating that other conditions are needed. Since none of these regions is associated with any active geothermal or volcanic activity, we infer that dynamic triggering could be ubiquitous and occur in a wide range of tectonic environments.

Robust satellite techniques (RST for the thermal monitoring of earthquake prone areas: the case of Umbria-Marche October, 1997 seismic events

Directory of Open Access Journals (Sweden)

V. Tramutoli

2008-06-01

Full Text Available Several authors claim a space-time correlation between increases in Earth’s emitted Thermal Infra-Red (TIR radiation and earthquake occurrence. The main problems of such studies regard data analysis and interpretation, which are often done without a validation/confutation control. In this context, a robust data analysis technique (RST, i.e. Robust Satellite Techniques is proposed which permits a statistically based definition of TIR «anomaly » and uses a validation/confutation approach. This technique was already applied to satellite TIR surveys in seismic regions for about twenty earthquakes that occurred in the world. In this work RST is applied for the first time to a time sequence of seismic events. Nine years of Meteosat TIR observations have been analyzed to characterize the unperturbed TIR signal behaviour at specific observation times and locations. The main seismic events of the October 1997 Umbria-Marche sequence have been considered for validation, and relatively unperturbed periods (no earthquakes with Mb ? 4 were taken for confutation purposes. Positive time-space persistent TIR anomalies were observed during seismic periods, generally overlapping the principal tectonic lineaments of the region and sometimes focusing on the vicinity of the epicentre. No similar (in terms of relative intensity and space-time persistence TIR anomalies were detected during seismically unperturbed periods.

Study on structural seismic margin and probabilistic seismic risk. Development of a structural capacity-seismic risk diagram

International Nuclear Information System (INIS)

Nakajima, Masato; Ohtori, Yasuki; Hirata, Kazuta

2010-01-01

Seismic margin is extremely important index and information when we evaluate and account seismic safety of critical structures, systems and components quantitatively. Therefore, it is required that electric power companies evaluate the seismic margin of each plant in back-check of nuclear power plants in Japan. The seismic margin of structures is usually defined as a structural capacity margin corresponding to design earthquake ground motion. However, there is little agreement as to the definition of the seismic margin and we have no knowledge about a relationship between the seismic margin and seismic risk (annual failure probability) which is obtained in PSA (Probabilistic Safety Assessment). The purpose of this report is to discuss a definition of structural seismic margin and to develop a diagram which can identify a relation between seismic margin and seismic risk. The main results of this paper are described as follows: (1) We develop seismic margin which is defined based on the fact that intensity of earthquake ground motion is more appropriate than the conventional definition (i.e., the response-based seismic margin) for the following reasons: -seismic margin based on earthquake ground motion is invariant where different typed structures are considered, -stakeholders can understand the seismic margin based on the earthquake ground motion better than the response-based one. (2) The developed seismic margin-risk diagram facilitates us to judge easily whether we need to perform detailed probabilistic risk analysis or only deterministic analysis, given that the reference risk level although information on the uncertainty parameter beta is not obtained. (3) We have performed numerical simulations based on the developed method for four sites in Japan. The structural capacity-risk diagram differs depending on each location because the diagram is greatly influenced by seismic hazard information for a target site. Furthermore, the required structural capacity

Seismic Ecology

Science.gov (United States)

Seleznev, V. S.; Soloviev, V. M.; Emanov, A. F.

The paper is devoted to researches of influence of seismic actions for industrial and civil buildings and people. The seismic actions bring influence directly on the people (vibration actions, force shocks at earthquakes) or indirectly through various build- ings and the constructions and can be strong (be felt by people) and weak (be fixed by sensing devices). The great number of work is devoted to influence of violent seismic actions (first of all of earthquakes) on people and various constructions. This work is devoted to study weak, but long seismic actions on various buildings and people. There is a need to take into account seismic oscillations, acting on the territory, at construction of various buildings on urbanized territories. Essential influence, except for violent earthquakes, man-caused seismic actions: the explosions, seismic noise, emitted by plant facilities and moving transport, radiation from high-rise buildings and constructions under action of a wind, etc. can exert. Materials on increase of man- caused seismicity in a number of regions in Russia, which earlier were not seismic, are presented in the paper. Along with maps of seismic microzoning maps to be built indicating a variation of amplitude spectra of seismic noise within day, months, years. The presence of an information about amplitudes and frequencies of oscillations from possible earthquakes and man-caused oscillations in concrete regions allows carry- ing out soundly designing and construction of industrial and civil housing projects. The construction of buildings even in not seismically dangerous regions, which have one from resonance frequencies coincident on magnitude to frequency of oscillations, emitted in this place by man-caused objects, can end in failure of these buildings and heaviest consequences for the people. The practical examples of detail of engineering- seismological investigation of large industrial and civil housing projects of Siberia territory (hydro power

The analysis and interpretation of very-long-period seismic signals on volcanoes

Science.gov (United States)

Sindija, Dinko; Neuberg, Jurgen; Smith, Patrick

2017-04-01

The study of very long period (VLP) seismic signals became possible with the widespread use of broadband instruments. VLP seismic signals are caused by transients of pressure in the volcanic edifice and have periods ranging from several seconds to several minutes. For the VLP events recorded in March 2012 and 2014 at Soufriere Hills Volcano, Montserrat, we model the ground displacement using several source time functions: a step function using Richards growth equation, Küpper wavelet, and a damped sine wave to which an instrument response is then applied. This way we get a synthetic velocity seismogram which is directly comparable to the data. After the full vector field of ground displacement is determined, we model the source mechanism to determine the relationship between the source mechanism and the observed VLP waveforms. Emphasis of the research is on how different VLP waveforms are related to the volcano environment and the instrumentation used and on the processing steps in this low frequency band to get most out of broadband instruments.

Candidate constructional volcanic edifices on Mercury

OpenAIRE

Wright, J.; Rothery, D. A.; Balme, M. R.; Conway, S. J.

2018-01-01

[Introduction] Studies using MESSENGER data suggest that Mercury’s crust is predominantly a product of effusive volcanism that occurred in the first billion years following the planet’s formation. Despite this planet-wide effusive volcanism, no constructional volcanic edifices, characterized by a topographic rise, have hitherto been robustly identified on Mercury, whereas constructional volcanoes are common on other planetary bodies in the solar system with volcanic histories. Here, we descri...

Disruptive event analysis: volcanism and igneous intrusion

International Nuclear Information System (INIS)

Crowe, B.M.

1980-08-01

An evaluation is made of the disruptive effects of volcanic activity with respect to long term isolation of radioactive waste through deep geologic storage. Three major questions are considered. First, what is the range of disruption effects of a radioactive waste repository by volcanic activity. Second, is it possible, by selective siting of a repository, to reduce the risk of disruption by future volcanic activity. And third, can the probability of repository disruption by volcanic activity be quantified. The main variables involved in the evaluation of the consequences of repository disruption by volcanic activity are the geometry of the magma-repository intersection (partly controlled by depth of burial) and the nature of volcanism. Potential radionuclide dispersal by volcanic transport within the biosphere ranges in distance from several kilometers to global. Risk from the most catastrophic types of eruptions can be reduced by careful site selection to maximize lag time prior to the onset of activity. Certain areas or volcanic provinces within the western United States have been sites of significant volcanism and should be avoided as potential sites for a radioactive waste repository. Examples of projection of future sites of active volcanism are discussed for three areas of the western United States. Probability calculations require two types of data: a numerical rate or frequency of volcanic activity and a numerical evaluation of the areal extent of volcanic disruption for a designated region. The former is clearly beyond the current state of art in volcanology. The latter can be approximated with a reasonable degree of satisfaction. In this report, simplified probability calculations are attempted for areas of past volcanic activity

A New Structural Model for the Red Sea from Seismic Data

Science.gov (United States)

Mooney, W. D.; Yao, Z.; Zahran, H. M.; El-Hadidy, S. Y.

2017-12-01

We present a new structureal model for the Red Sea that shows opening on an east-dipping low-angle detachment fault. We measured phase velocities using Rayleigh-wave data recorded at recently-installed, dense broadband seismic stations in the Arabian shield and determined the shear-wave velocity structure. Our results clearly reveal a 300-km wide upper mantle seismic low-velocity zone (LVZ) beneath the western Arabian shield at a depth of 60 km and with a thickness of 130 km. The LVZ has a north-south trend and follows the late-Cenozoic volcanic areas. The lithosphere beneath the western Arabian shield is remarkably thin (60-90 km). The 130-km thick mantle LVZ does not appear beneath the western Red Sea and the spreading axis. Thus, the Red Sea at 20°- 26° N is an asymmetric rift, with thin lithosphere located east of the Red Sea axis, as predicted by the low-angle detachment model for rift development. Passive rifting at the Red Sea and extensional stresses in the shield are probably driven by slab pull from the Zagros subduction zone. The low shear-wave velocity (4.0-4.2 km/s) and the geometry of LVZ beneath the western shield indicate northward flow of hot asthenosphere from the Afar hot spot. The upwelling of basaltic melt in fractures or zones of localized lithospheric thinning has produced extensive late Cenozoic volcanism on the western edge of the shield, and the buoyant LVZ has caused pronounced topography uplift there. Thus, the evolution of the Red Sea and the Arabian shield is driven by subduction of the Arabian plate along its northeastern boundary, and the Red Sea opened on a east-dipping low-angle detachment fault.

Mapping Inherited Fractures in the Critical Zone Using Seismic Anisotropy From Circular Surveys

Science.gov (United States)

Novitsky, Christopher G.; Holbrook, W. Steven; Carr, Bradley J.; Pasquet, Sylvain; Okaya, David; Flinchum, Brady A.

2018-04-01

Weathering and hydrological processes in Earth's shallow subsurface are influenced by inherited bedrock structures, such as bedding planes, faults, joints, and fractures. However, these structures are difficult to observe in soil-mantled landscapes. Steeply dipping structures with a dominant orientation are detectable by seismic anisotropy, with fast wave speeds along the strike of structures. We measured shallow ( 2-4 m) seismic anisotropy using "circle shots," geophones deployed in a circle around a central shot point, in a weathered granite terrain in the Laramie Range of Wyoming. The inferred remnant fracture orientations agree with brittle fracture orientations measured at tens of meters depth in boreholes, demonstrating that bedrock fractures persist through the weathering process into the shallow critical zone. Seismic anisotropy positively correlates with saprolite thickness, suggesting that inherited bedrock fractures may control saprolite thickness by providing preferential pathways for corrosive meteoric waters to access the deep critical zone.

Multiple Seismic Array Observations for Tracing Deep Tremor Activity in Western Shikoku, Japan

Science.gov (United States)

Takeda, T.; Matsuzawa, T.; Shiomi, K.; Obara, K.

2011-12-01

Deep non-volcanic tremors become very active during episodic slow-slip events in western Japan and Cascadia. The episodic tremor and slow-slip events in western Shikoku, Japan, occur at a typical interval of 6 months. Recently, it has been reported that tremor migration activity is complex and shows different migrating directions depending on time scales (Ghosh et al., 2010). Such characteristics of tremor are important to understand the mechanism of tremor and the relationship between tremor and SSEs. However it is difficult to determine the location of tremors with high accuracy because tremors show faint signals and make the identification of P/S-wave arrivals difficult. Seismic array analysis is useful to evaluate tremor activity, especially to estimate the arrival direction of seismic energy (e.g. Ueno et al., 2010, Ghosh et al., 2010), as it can distinguish multiple tremor sources occurring simultaneously. Here, we have conducted seismic array observation and analyzed seismic data during tremor activity by applying the MUSIC method to trace tremor location and its migration in western Shikoku. We have installed five seismic arrays in western Shikoku since January 2011. One of the arrays contains 30 stations with 3-component seismometers with a natural frequency of 2 Hz (Type-L array). The array aperture size is 2 km and the mean interval between stations is approximately 200 m. Each of the other arrays (Type-S array) contains 9 seismic stations with the same type of seismometers of the Type-L array, and is deployed surrounding the Type-L array. The small array aperture size is 800 m and its mean station interval is approximately 150 m. All array stations have recorded continuous waveform data at a sampling of 200Hz. In May 2011, an episodic tremor and a short-term slip event occurred for the first time during the observation period. We could retrieve the array seismic data during the whole tremor episode. The analysis of data from the type-L array confirms

Imaging pockets and conduits of low velocity material beneath the lithosphere of the Atlas Mountains of Morocco: links to volcanism and orogenesis

Science.gov (United States)

Miller, M. S.; Sun, D.; O'Driscoll, L.; Holt, A.; Butcher, A.; Becker, T. W.; Diaz Cusi, J.; Thomas, C.

2014-12-01

The Atlas Mountains of Morocco have unusually high topography, with no apparent deep crustal root, and regions of localized Cenozoic alkaline volcanism. Previous seismic imaging and geophysical studies have implied a hot mantle upwelling as the source of the volcanism and high elevation, but the existence and physical properties of such an upwelling are debated. Recent temporary deployments of over 100 broadband seismometers that extended across Morocco as part of the PICASSO, Morocco-Münster, and IberArray experiments along with select permanent stations have provided a dataset to image the detailed mantle and lithospheric structure beneath the Atlas. We present results from S receiver functions (SRF), shear wave splitting, waveform modeling, and geodynamic models that help constrain the tectonic evolution of the Atlas and the localized alkaline volcanism. The receiver functions show that the lithosphere is thin (~65 km) beneath the Atlas, but thickens (~105 km) over a very short length scale at the flanks of the mountains and near the Quaternary volcanoes. These changes in lithospheric thickness also correspond to dramatic decreases in delay times inferred from S and SKS splitting observations. SRFs also indicate a broad, low seismic velocity anomaly (~150 km) below the shallow lithosphere that extends along much of the Atlas and beneath the Anti-Atlas and correlates with the location of Pliocene-Quaternary magmatism. Waveform analysis from the linear array across the Middle and High Atlas constrains the position, shape, and physical characteristics of a localized, low velocity conduit that extends up from the uppermost mantle (~200 km). The shape, position and temperature of the imaged low velocity anomaly, offsets in the lithosphere-asthenosphere boundary, and correlation with mantle flow inferred from shear wave splitting suggest that the unusually high topography of the Atlas Mountains is due to active mantle support.

Seismic Tremors and Three-Dimensional Magma Wagging

Science.gov (United States)

Liao, Y.; Bercovici, D.

2015-12-01

Seismic tremor is a feature shared by many silicic volcanoes and is a precursor of volcanic eruption. Many of the characteristics of tremors, including their frequency band from 0.5 Hz to 7 Hz, are common for volcanoes with very different geophysical and geochemical properties. The ubiquitous characteristics of tremor imply that it results from some generation mechanism that is common to all volcanoes, instead of being unique to each volcano. Here we present new analysis on the magma-wagging mechanism that has been proposed to generate tremor. The model is based on the suggestion given by previous work (Jellinek & Bercovici 2011; Bercovici et.al. 2013) that the magma column is surrounded by a compressible, bubble-rich foam annulus while rising inside the volcanic conduit, and that the lateral oscillation of the magma inside the annulus causes observable tremor. Unlike the previous two-dimensional wagging model where the displacement of the magma column is restricted to one vertical plane, the three-dimensional model we employ allows the magma column to bend in different directions and has angular motion as well. Our preliminary results show that, without damping from viscous deformation of the magma column, the system retains angular momentum and develops elliptical motion (i.e., the horizontal displacement traces an ellipse). In this ''inviscid'' limit, the magma column can also develop instabilities with higher frequencies than what is found in the original two-dimensional model. Lateral motion can also be out of phase for various depths in the magma column leading to a coiled wagging motion. For the viscous-magma model, we predict a similar damping rate for the uncoiled magma column as in the two-dimensional model, and faster damping for the coiled magma column. The higher damping thus requires the existence of a forcing mechanism to sustain the oscillation, for example the gas-driven Bernoulli effect proposed by Bercovici et al (2013). Finally, using our new 3

Seismic monitoring during acid stimulation of wells LV-4 and LV-13 at the Las Tres Virgenes geothermal field, BCS, Mexico; Monitoreo sismico durante la estimulacion acida de los pozos LV-4 y LV-13 del campo geotermico de Las Tres Virgenes, BCS, Mexico

Energy Technology Data Exchange (ETDEWEB)

Venegas Salgado, Saul; Arredondo Fragoso, Jesus; Ramirez Silva, German; Flores Armenta, Magaly; Ramirez Montes, Miguel [Comision Federal de Electricidad, Gerencia de Proyectos Geotermoelectricos, Morelia, Michoacan (Mexico)]. E-mail: magaly.flores@cfe.gob.mx

2006-07-15

From September through December 2004 a seismic monitoring in the Las Tres Virgenes, BCS, geothermal field was carried out simultaneously with the acid stimulation of wells LV-4 and LV-13. The seismic network had four digital seismographs and recorded 174 local seismic events, 131 regional ones and many more volcanic signals at seismic station TV20 during the acid stimulation. Additionally, 37 seismic events were located, 22 of them inside the most important geothermal zone at depths between 0.4 and 4 km with typically low magnitudes (0.7 to 2.2 Md). Two relevant zones were determined: Zone A related to the El Volcan fault system and Zone B related to injection well LV-8. In Zone A the well-induction stage and the operation start of the wells LV-4 and LV-13 after acidification on October 30 and November 17, 2004, increased seismic activity to a maximum of 12 daily events in early December. When the two wells in Zone B were cooled before the acidification, the seismic events recorded there increased to a maximum of 6 daily events on October 2, and then decreased. Also in Zone B the seismic activity increased after well-induction and the start of well production once they were acidified, recording up to 11 daily events in late November. According to the seismic distribution, we may conclude that the most active fault systems are El Volcan and El Viejo. New proposals for well locations in the field are supported by these results. [Spanish] De septiembre a diciembre de 2004 se realizo un estudio de monitoreo sismico en el campo geotermico de Las Tres Virgenes, BCS, simultaneamente con las estimulaciones acidas de los pozos LV-4 y LV-13. Se utilizo una red sismica conformada por cuatro sismografos digitales, logrando registrar en la estacion sismica TV20 un total de 174 sismos locales, 131 sismos regionales y muchas mas senales de tipo volcanico, durante el periodo del monitoreo de la estimulacion acida. Ademas, se localizaron un total de 37 sismos, de los cuales 22 se

Use of Logistic Regression for Forecasting Short-Term Volcanic Activity

Directory of Open Access Journals (Sweden)

Mark T. Woods

2012-08-01

Full Text Available An algorithm that forecasts volcanic activity using an event tree decision making framework and logistic regression has been developed, characterized, and validated. The suite of empirical models that drive the system were derived from a sparse and geographically diverse dataset comprised of source modeling results, volcano monitoring data, and historic information from analog volcanoes. Bootstrapping techniques were applied to the training dataset to allow for the estimation of robust logistic model coefficients. Probabilities generated from the logistic models increase with positive modeling results, escalating seismicity, and rising eruption frequency. Cross validation yielded a series of receiver operating characteristic curves with areas ranging between 0.78 and 0.81, indicating that the algorithm has good forecasting capabilities. Our results suggest that the logistic models are highly transportable and can compete with, and in some cases outperform, non-transportable empirical models trained with site specific information.

Volcanic gas impacts on vegetation at Turrialba Volcano, Costa Rica

Science.gov (United States)

Teasdale, R.; Jenkins, M.; Pushnik, J.; Houpis, J. L.; Brown, D. L.

2010-12-01

Turrialba volcano is an active composite stratovolcano that is located approximately 40 km east of San Jose, Costa Rica. Seismic activity and degassing have increased since 2005, and gas compositions reflect further increased activity since 2007 peaking in January 2010 with a phreatic eruption. Gas fumes dispersed by trade winds toward the west, northwest, and southwest flanks of Turrialba volcano have caused significant vegetation kill zones, in areas important to local agriculture, including dairy pastures and potato fields, wildlife and human populations. In addition to extensive vegetative degradation is the potential for soil and water contamination and soil erosion. Summit fumarole temperatures have been measured over 200 degrees C and gas emissions are dominated by SO2; gas and vapor plumes reach up to 2 km (fumaroles and gases are measured regularly by OVSICORI-UNA). A recent network of passive air sampling, monitoring of water temperatures of hydrothermal systems, and soil pH measurements coupled with measurement of the physiological status of surrounding plants using gas exchange and fluorescence measurements to: (1) identify physiological correlations between leaf-level gas exchange and chlorophyll fluorescence measurements of plants under long term stress induced by the volcanic gas emissions, and (2) use measurements in tandem with remotely sensed reflectance-derived fluorescence ratio indices to track natural photo inhibition caused by volcanic gas emissions, for use in monitoring plant stress and photosynthetic function. Results may prove helpful in developing potential land management strategies to maintain the biological health of the area.

Mapping local singularities using magnetic data to investigate the volcanic rocks of the Qikou depression, Dagang oilfield, eastern China

Directory of Open Access Journals (Sweden)

G. Chen

2013-07-01

Full Text Available The spatial structural characteristics of geological anomaly, including singularity and self-similarity, can be analysed using fractal or multifractal modelling. Here we apply the multifractal methods to potential fields to demonstrate that singularities can characterise geological bodies, including rock density and magnetic susceptibility. In addition to enhancing weak gravity and magnetic anomalies with respect to either strong or weak background levels, the local singularity index (α ≈ 2 can be used to delineate the edges of geological bodies. Two models were established to evaluate the effectiveness of mapping singularities for extracting weak anomalies and delineating edges of buried geological bodies. The Qikou depression of the Dagang oilfield in eastern China has been chosen as a study area for demonstrating the extraction of weak anomalies of volcanic rocks, using the singularity mapping technique to analyse complex magnetic anomalies caused by complex geological background. The results have shown that the singularities of magnetic data mapped in the paper are associated with buried volcanic rocks, which have been verified by both drilling and seismic survey, and the S–N and E–W faults in the region. The targets delineated for deeply seated faults and volcanic rocks in the Qikou depression should be further investigated for the potential application in undiscovered oil and gas reservoirs exploration.

A new seismic station in Romania the Bucovina seismic array

International Nuclear Information System (INIS)

Grigore, Adrian; Grecu, Bogdan; Ionescu, Constantin; Ghica, Daniela; Popa, Mihaela; Rizescu, Mihaela

2002-01-01

Recently, a new seismic monitoring station, the Bucovina Seismic Array, has been established in the northern part of Romania, in a joint effort of the Air Force Technical Applications Center, USA, and the National Institute for Earth Physics, Romania. The array consists of 10 seismic sensors (9 short-period and one broad band) located in boreholes and distributed in a 5 x 5 km area. On July 24, 2002 the official Opening Ceremony of Bucovina Seismic Array took place in the area near the city of Campulung Moldovenesc in the presence of Romanian Prime Minister, Adrian Nastase. Starting with this date, the new seismic monitoring system became fully operational by continuous recording and transmitting data in real-time to the National Data Center of Romania, in Bucharest and to the National Data Center of USA, in Florida. Bucovina Seismic Array, added to the present Seismic Network, will provide much better seismic monitoring coverage of Romania's territory, on-scale recording for weak-to-strong events, and will contribute to advanced seismological studies on seismic hazard and risk, local effects and microzonation, seismic source physics, Earth structure. (authors)

Volcanic Surface Deformation in Dominica From GPS Geodesy: Results From the 2007 NSF- REU Site

Science.gov (United States)

Murphy, R.; James, S.; Styron, R. H.; Turner, H. L.; Ashlock, A.; Cavness, C.; Collier, X.; Fauria, K.; Feinstein, R.; Staisch, L.; Williams, B.; Mattioli, G. S.; Jansma, P. E.; Cothren, J.

2007-12-01

GPS measurements have been collected on the island of Dominica in the Lesser Antilles between 2001 and 2007, with five month-long campaigns completed in June of each year supported in part by a NSF REU Site award for the past two years. All GPS data were collected using dual-frequency, code-phase receivers and geodetic-quality antenna, primarily choke rings. Three consecutive 24 hr observation days were normally obtained for each site. Precise station positions were estimated with GIPSY-OASISII using an absolute point positioning strategy and final, precise orbits, clocks, earth orientation parameters, and x-files. All position estimates were updated to ITRF05 and a revised Caribbean Euler pole was used to place our observations in a CAR-fixed frame. Time series were created to determine the velocity of each station. Forward and inverse elastic half-space models with planar (i.e. dike) and Mogi (i.e. point) sources were investigated. Inverse modeling was completed using a downhill simplex method of function minimization. Selected site velocities were used to create appropriate models for specific regions of Dominica, which correspond to known centers of pre-historic volcanic or recent shallow, seismic activity. Because of the current distribution of GPS sites with robust velocity estimates, we limit our models to possible magmatic activity in the northern, proximal to the volcanic centers of Morne Diablotins and Morne aux Diables, and southern, proximal to volcanic centers of Soufriere and Morne Plat Pays, regions of the island. Surface deformation data from the northernmost sites may be fit with the development of a several km-long dike trending approximately northeast- southwest. Activity in the southern volcanic centers is best modeled by an expanding point source at approximately 1 km depth.

Volcanoes and climate: Krakatoa's signature persists in the ocean.

Science.gov (United States)

Gleckler, P J; Wigley, T M L; Santer, B D; Gregory, J M; Achutarao, K; Taylor, K E

2006-02-09

We have analysed a suite of 12 state-of-the-art climate models and show that ocean warming and sea-level rise in the twentieth century were substantially reduced by the colossal eruption in 1883 of the volcano Krakatoa in the Sunda strait, Indonesia. Volcanically induced cooling of the ocean surface penetrated into deeper layers, where it persisted for decades after the event. This remarkable effect on oceanic thermal structure is longer lasting than has previously been suspected and is sufficient to offset a large fraction of ocean warming and sea-level rise caused by anthropogenic influences.

Approximate Seismic Diffusive Models of Near-Receiver Geology: Applications from Lab Scale to Field

Science.gov (United States)

King, Thomas; Benson, Philip; De Siena, Luca; Vinciguerra, Sergio

2017-04-01

This paper presents a novel and simple method of seismic envelope analysis that can be applied at multiple scales, e.g. field, m to km scale and laboratory, mm to cm scale, and utilises the diffusive approximation of the seismic wavefield (Wegler, 2003). Coefficient values for diffusion and attenuation are obtained from seismic coda energies and are used to describe the rate at which seismic energy is scattered and attenuated into the local medium around a receiver. Values are acquired by performing a linear least squares inversion of coda energies calculated in successive time windows along a seismic trace. Acoustic emission data were taken from piezoelectric transducers (PZT) with typical resonance frequency of 1-5MHz glued around rock samples during deformation laboratory experiments carried out using a servo-controlled triaxial testing machine, where a shear/damage zone is generated under compression after the nucleation, growth and coalescence of microcracks. Passive field data were collected from conventional geophones during the 2004-2008 eruption of Mount St. Helens volcano (MSH), USA where a sudden reawakening of the volcanic activity and a new dome growth has occurred. The laboratory study shows a strong correlation between variations of the coefficients over time and the increase of differential stress as the experiment progresses. The field study links structural variations present in the near-surface geology, including those seen in previous geophysical studies of the area, to these same coefficients. Both studies show a correlation between frequency and structural feature size, i.e. landslide slip-planes and microcracks, with higher frequencies being much more sensitive to smaller scale features and vice-versa.

The Alboran volcanic arc archipelago isolated the Mediterranean during the Messinian salinity crisis forming the land bridge for biota dispersal across the western Mediterranean

Science.gov (United States)

Booth-Rea, Guillermo; Ranero, Cesar R.; Grevemeyer, Ingo

2017-04-01

The Mediterranean Sea desiccation during isolation from the world oceans created the well-known Messinian salinity crisis but also landbridges that permitted the exchange of terrestrial biota between Africa and Iberia contributing to the present biodiversity of the Mediterranean region. The hypotheses for the cause chocking the Mediterranean have typically sought to explain geological features, particularly the giant salt deposits, but the implications of the faunal changes occurring around that time remain inadequately integrated by current geological models. We present wide-angle seismic data that constrain for the first time the 16-18 km thick crust structure of a volcanic arc formed mostly between 10 to 6 Ma across the eastern region of the Alboran basin. The crustal structure supports that the arc created an archipelago forming a land bridge across the basin that largely isolated the Mediterranean. After the cessation of volcanic activity, the archipelago progressively submerged by thermal subsidence and accompanying sediment loading, having emerged islands that persisted into the Pleistocene time and shallow straits forming sills during the early Pliocene. The presence of an archipelago in the eastern region of the basin may explain a number of puzzling observations previously inexplicable by the proposed barriers closing the Gibraltar arc west of Alboran. The progressive volcanic build up of the archipelago together with the closure of the Betic and Rifean marine corridors would explain the initial isolation of the Mediterranean since 7.1 Ma and the exchange of terrestrial biota since 6.2 Ma, i.e. before desiccation, which diversified radiating from SE Iberia and the opposite segment of the eastern Rif. In addition, an eastern barrier agrees with the continuous Messinian-age open marine sediments drilled at ODP site 976 in the western Alboran basin, which may have been the refuge of typical Mediterranean taxa that rapidly repopulated the Mediterranean in the

Investigating Crustal Scale Fault Systems Controlling Volcanic and Hydrothermal Fluid Processes in the South-Central Andes, First Results from a Magnetotelluric Survey

Science.gov (United States)

Pearce, R.; Mitchell, T. M.; Moorkamp, M.; Araya, J.; Cembrano, J. M.; Yanez, G. A.; Hammond, J. O. S.

2017-12-01

At convergent plate boundaries, volcanic orogeny is largely controlled by major thrust fault systems that act as magmatic and hydrothermal fluid conduits through the crust. In the south-central Andes, the volcanically and seismically active Tinguiririca and Planchon-Peteroa volcanoes are considered to be tectonically related to the major El Fierro thrust fault system. These large scale reverse faults are characterized by 500 - 1000m wide hydrothermally altered fault cores, which possess a distinct conductive signature relative to surrounding lithology. In order to establish the subsurface architecture of these fault systems, such conductivity contrasts can be detected using the magnetotelluric method. In this study, LEMI fluxgate-magnetometer long-period and Metronix broadband MT data were collected at 21 sites in a 40km2 survey grid that surrounds this fault system and associated volcanic complexes. Multi-remote referencing techniques is used together with robust processing to obtain reliable impedance estimates between 100 Hz and 1,000s. Our preliminary inversion results provide evidence of structures within the 10 - 20 km depth range that are attributed to this fault system. Further inversions will be conducted to determine the approximate depth extent of these features, and ultimately provide constraints for future geophysical studies aimed to deduce the role of these faults in volcanic orogeny and hydrothermal fluid migration processes in this region of the Andes.

Patterns in Seismicity at Mt St Helens and Mt Unzen

Science.gov (United States)

Lamb, Oliver; De Angelis, Silvio; Lavallee, Yan

2014-05-01

seismic behaviour at both volcanoes with a focus on comparisons with changes in activity with the hope of gaining a greater understanding of sub-surface processes occurring within the volcanic systems. This approach and the techniques above were successfully implemented at Redoubt Volcano (USA) [2] which also concluded that these techniques may serve an important role in future real-time eruption monitoring efforts. [1] Lamb O., Varley N., Mather T. et al., in prep Similar Cyclic Behaviour at two lava domes, Volcán de Colima (Mexico) and Soufrière Hills volcano (Montserrat), with implications for monitoring. [2] Ketner, D. & Power, J., 2013. Characterization of seismic events during the 2009 eruption of Redoubt Volcano, Alaska. Journal of Volcanology and Geothermal Research, 259, pp.45-62

Passive seismic experiment in the Olduvai Gorge and Laetoli region (Ngorongoro Conservation Area), Northern Tanzania.

Science.gov (United States)

Parisi, Laura; Lombardo, Luigi; Tang, Zheng; Mai, P. Martin

2017-04-01

The Olduvai Gorge and Laetoli basins, located within the Ngorogoro Conservation Area (NCA), are a cornerstone for understanding the evolution of early humans and are two paleo-antropological excavation sites of global importance. NCA is located at the boundary between the Tanzanian Craton and East African Rift (EAR), in the vicinity of Ngorongoro Crater and other major volcanic edifices. Thus, understanding the geology and tectonics of the NCA may shed light onto the question why early Hominins settled in this region. Environmental and geological conditions in the Olduvai and Laetoli region that promoted human settlement and development are still debated by geologists and paleo-anthropologists. Paleo-geographical reconstructions of the study area of the last 2 million years may take advantage of modern passive seismology. Therefore, we installed a dense seismic network covering a surface of approximately 30 x 40 km within the NCA to map the depth extent of known faults, and to identify seismically active faults that have no surface expression. Our ten seismic stations, equipped with Trillium Compact 120 s sensors, started to operate in June 2016 and will continue for a total of 2 years. At the end of the first year, other 5 stations will densify our network. Here we analyse data quality of the first four months of continuous recordings. Our network provides good quality 3-C waveforms in the frequency range of 0.7-50 Hz. Vertical component seismograms record frequencies reliably down to 8 mHz. Preliminary results of the seismicity obtained with standard location procedures show that NCA is characterised by frequent tectonic seismicity (not volcano-related) with Ml between 0.5 and 2.0. Seismic activity is more frequent in the South (Laetoli region) where major fault systems have not been recognised at the surface yet.

The Seismic Analyzer: Interpreting and Illustrating 2D Seismic Data

OpenAIRE

Patel, Daniel; Giertsen, Christopher; Thurmond, John; Gjelberg, John; Gröller, Eduard

2008-01-01

We present a toolbox for quickly interpreting and illustrating 2D slices of seismic volumetric reflection data. Searching for oil and gas involves creating a structural overview of seismic reflection data to identify hydrocarbon reservoirs. We improve the search of seismic structures by precalculating the horizon structures of the seismic data prior to interpretation. We improve the annotation of seismic structures by applying novel illustrative rendering algorithms tailored to seism...

TOMO-ETNA MED-SUV.ISES an active seismic and passive seismic experiment at Mt. Etna volcano. An integrated marine and onland geophysical survey.

Science.gov (United States)

Ibáñez, Jesus. M.; Patane, Domenico; Puglisi, Guisseppe; Zuccarello, Lucciano; Bianco, Francesca; Luehr, Birger; Diaz-Moreno, Alejandro; Prudencio, Janire; Koulakov, Ivan; Del Pezzo, Edoardo; Cocina, Ornella; Coltelli, Mauro; Scarfi, Lucciano; De Gori, Pascuale; Carrion, Francisco

2014-05-01

An active seismic experiment to study the internal structure of Etna Volcano is going to carried out on Sicily and Aeolian islands. The main objective of the TOMO-ETNA MED-SUV.ISES experiment, beginning in summer 2014, is to perform a high resolution seismic tomography, in velocity and attenuation, in Southern Italy, by using active and passive seismic data, in an area encompassing outstanding volcanoes as Mt. Etna, and Aeolian volcanoes. The achievement of this objective is based on the integration and sharing of the in-situ marine and land experiments and observations and on the implementation of new instruments and monitoring systems. For the purpose, onshore and offshore seismic stations and passive and active seismic data generated both in marine and terrestrial environment will be used. Additionally, other geophysical data, mainly magnetic and gravimetric data will be considered to obtain a joint Upper Mantle-Crust structure that could permit to make progress in the understanding of the dynamic of the region. This multinational experiment which involves institutions from Spain, Italy, Germany, United Kingdom, Ireland, France, Malta, Portugal, Russia, USA and Mexico. During the experiment more than 6.600 air gun shots performed by the Spanish Oceanographic vessel "Sarmiento de Gamboa" will be recorder on a dense local seismic network consisting of 100 on land non-permanent stations, 70 on land permanent stations and 20-25 OBSs. Contemporaneously other marine geophysical measures will be performed using a marine Gravimeter LaCoste&Romberg Air-Sea Gravity System II and a Marine Magnetometer SeaSPY. The experiments will provide a unique data set in terms of data quantity and quality, and it will provide a detailed velocity and attenuation structural image of volcano edifice. The results will be essential in the development and interpretation of future volcanic models. It is noteworthy that this project is fully transversal, multidisciplinary and crosses several

Using Volcanic Lightning Measurements to Discern Variations in Explosive Volcanic Activity

Science.gov (United States)

Behnke, S. A.; Thomas, R. J.; McNutt, S. R.; Edens, H. E.; Krehbiel, P. R.; Rison, W.

2013-12-01

VHF observations of volcanic lightning have been made during the recent eruptions of Augustine Volcano (2006, Alaska, USA), Redoubt Volcano (2009, Alaska, USA), and Eyjafjallajökull (2010, Iceland). These show that electrical activity occurs both on small scales at the vent of the volcano, concurrent with an eruptive event and on large scales throughout the eruption column during and subsequent to an eruptive event. The small-scale discharges at the vent of the volcano are often referred to as 'vent discharges' and are on the order of 10-100 meters in length and occur at rates on the order of 1000 per second. The high rate of vent discharges produces a distinct VHF signature that is sometimes referred to as 'continuous RF' radiation. VHF radiation from vent discharges has been observed at sensors placed as far as 100 km from the volcano. VHF and infrasound measurements have shown that vent discharges occur simultaneously with the onset of eruption, making their detection an unambiguous indicator of explosive volcanic activity. The fact that vent discharges are observed concurrent with explosive volcanic activity indicates that volcanic ejecta are charged upon eruption. VHF observations have shown that the intensity of vent discharges varies between eruptive events, suggesting that fluctuations in eruptive processes affect the electrification processes giving rise to vent discharges. These fluctuations may be variations in eruptive vigor or variations in the type of eruption; however, the data obtained so far do not show a clear relationship between eruption parameters and the intensity or occurrence of vent discharges. Further study is needed to clarify the link between vent discharges and eruptive behavior, such as more detailed lightning observations concurrent with tephra measurements and other measures of eruptive strength. Observations of vent discharges, and volcanic lightning observations in general, are a valuable tool for volcano monitoring, providing a

Are volcanic seismic b-values high, and if so when?

Science.gov (United States)

Roberts, Nick S.; Bell, Andrew F.; Main, Ian G.

2015-12-01

The Gutenberg-Richter exponent b is a measure of the relative proportion of large and small earthquakes. It is commonly used to infer material properties such as heterogeneity, or mechanical properties such as the state of stress from earthquake populations. It is 'well known' that the b-value tends to be high or very high for volcanic earthquake populations relative to b = 1 for those of tectonic earthquakes, and that b varies significantly with time during periods of unrest. We first review the supporting evidence from 34 case studies, and identify weaknesses in this argument due predominantly to small sample size, the narrow bandwidth of magnitude scales available, variability in the methods used to assess the minimum or cutoff magnitude Mc, and to infer b. Informed by this, we use synthetic realisations to quantify the effect of choice of the cutoff magnitude on maximum likelihood estimates of b, and suggest a new work flow for this choice. We present the first quantitative estimate of the error in b introduced by uncertainties in estimating Mc, as a function of the number of events and the b-value itself. This error can significantly exceed the commonly-quoted statistical error in the estimated b-value, especially for the case that the underlying b-value is high. We apply the new methods to data sets from recent periods of unrest in El Hierro and Mount Etna. For El Hierro we confirm significantly high b-values of 1.5-2.5 prior to the 10 October 2011 eruption. For Mount Etna the b-values are indistinguishable from b = 1 within error, except during the flank eruptions at Mount Etna in 2001-2003, when 1.5 forecasting informed by b-value variability, in particular in assessing the significance of b-value variations identified by sample sizes with fewer than 200 events above the completeness threshold.

Active crustal deformation of the El Salvador Fault Zone (ESFZ) using GPS data: Implications in seismic hazard assessment

Science.gov (United States)

Staller, Alejandra; Benito, Belen; Jesús Martínez-Díaz, José; Hernández, Douglas; Hernández-Rey, Román; Alonso-Henar, Jorge

2014-05-01

El Salvador, Central America, is part of the Chortis block in the northwestern boundary of the Caribbean plate. This block is interacting with a diffuse triple junction point with the Cocos and North American plates. Among the structures that cut the Miocene to Pleistocene volcanic deposits stands out the El Salvador Fault Zone (ESFZ): It is oriented in N90º-100ºE direction, and it is composed of several structural segments that deform Quaternary deposits with right-lateral and oblique slip motions. The ESFZ is seismically active and capable of producing earthquakes such as the February 13, 2001 with Mw 6.6 (Martínez-Díaz et al., 2004), that seriously affected the population, leaving many casualties. This structure plays an important role in the tectonics of the Chortis block, since its motion is directly related to the drift of the Caribbean plate to the east and not with the partitioning of the deformation of the Cocos subduction (here not coupled) (Álvarez-Gómez et al., 2008). Together with the volcanic arc of El Salvador, this zone constitutes a weakness area that allows the motion of forearc block toward the NW. The geometry and the degree of activity of the ESFZ are not studied enough. However their knowledge is essential to understand the seismic hazard associated to this important seismogenic structure. For this reason, since 2007 a GPS dense network was established along the ESFZ (ZFESNet) in order to obtain GPS velocity measurements which are later used to explain the nature of strain accumulation on major faults along the ESFZ. The current work aims at understanding active crustal deformation of the ESFZ through kinematic model. The results provide significant information to be included in a new estimation of seismic hazard taking into account the major structures in ESFZ.

Recurrence models of volcanic events: Applications to volcanic risk assessment

International Nuclear Information System (INIS)

Crowe, B.M.; Picard, R.; Valentine, G.; Perry, F.V.

1992-01-01

An assessment of the risk of future volcanism has been conducted for isolation of high-level radioactive waste at the potential Yucca Mountain site in southern Nevada. Risk used in this context refers to a combined assessment of the probability and consequences of future volcanic activity. Past studies established bounds on the probability of magmatic disruption of a repository. These bounds were revised as additional data were gathered from site characterization studies. The probability of direct intersection of a potential repository located in an eight km 2 area of Yucca Mountain by ascending basalt magma was bounded by the range of 10 -8 to 10 -10 yr -1 2 . The consequences of magmatic disruption of a repository were estimated in previous studies to be limited. The exact releases from such an event are dependent on the strike of an intruding basalt dike relative to the repository geometry, the timing of the basaltic event relative to the age of the radioactive waste and the mechanisms of release and dispersal of the waste radionuclides in the accessible environment. The combined low probability of repository disruption and the limited releases associated with this event established the basis for the judgement that the risk of future volcanism was relatively low. It was reasoned that that risk of future volcanism was not likely to result in disqualification of the potential Yucca Mountain site

Volcanic Plume Measurements with UAV (Invited)

Science.gov (United States)

Shinohara, H.; Kaneko, T.; Ohminato, T.

2013-12-01

Volatiles in magmas are the driving force of volcanic eruptions and quantification of volcanic gas flux and composition is important for the volcano monitoring. Recently we developed a portable gas sensor system (Multi-GAS) to quantify the volcanic gas composition by measuring volcanic plumes and obtained volcanic gas compositions of actively degassing volcanoes. As the Multi-GAS measures variation of volcanic gas component concentrations in the pumped air (volcanic plume), we need to bring the apparatus into the volcanic plume. Commonly the observer brings the apparatus to the summit crater by himself but such measurements are not possible under conditions of high risk of volcanic eruption or difficulty to approach the summit due to topography etc. In order to overcome these difficulties, volcanic plume measurements were performed by using manned and unmanned aerial vehicles. The volcanic plume measurements by manned aerial vehicles, however, are also not possible under high risk of eruption. The strict regulation against the modification of the aircraft, such as installing sampling pipes, also causes difficulty due to the high cost. Application of the UAVs for the volcanic plume measurements has a big advantage to avoid these problems. The Multi-GAS consists of IR-CO2 and H2O gas analyzer, SO2-H2O chemical sensors and H2 semiconductor sensor and the total weight ranges 3-6 kg including batteries. The necessary conditions of the UAV for the volcanic plumes measurements with the Multi-GAS are the payloads larger than 3 kg, maximum altitude larger than the plume height and installation of the sampling pipe without contamination of the exhaust gases, as the exhaust gases contain high concentrations of H2, SO2 and CO2. Up to now, three different types of UAVs were applied for the measurements; Kite-plane (Sky Remote) at Miyakejima operated by JMA, Unmanned airplane (Air Photo Service) at Shinomoedake, Kirishima volcano, and Unmanned helicopter (Yamaha) at Sakurajima

CO2 driven weathering vs plume driven weathering as inferred from the groundwater of a persistently degassing basaltic volcano: Mt. Etna

Science.gov (United States)

Liotta, Marcello; D'Alessandro, Walter

2016-04-01

At Mt. Etna the presence of a persistent volcanic plume provides large amounts of volcanogenic elements to the bulk deposition along its flanks. The volcanic plume consists of solid particles, acidic droplets and gaseous species. After H2O and CO2, S, Cl and F represent the most abundant volatile elements emitted as gaseous species from the craters. During rain events acidic gases interact rapidly with droplets lowering the pH of rain. This process favors the dissolution and dissociation of the most acidic gases. Under these conditions, the chemical weathering of volcanic rocks and ashes is promoted by the acid rain during its infiltration. Subsequently during groundwater circulation, chemical weathering of volcanic rocks is also driven by the huge amount of deep magmatic carbon dioxide (CO2) coming up through the volcanic edifice and dissolving in the water. These two different weathering steps occur under very different conditions. The former occurs in a highly acidic environment (pH rates depend strongly on the pH, while the latter usually occurs under slightly acidic conditions since the pH has been already neutralized by the interaction with volcanics rocks. The high content of chlorine is mainly derived from interactions between the plume and rainwater, while the total alkalinity can be completely ascribed to the dissociation of carbonic acid (H2CO3) after the hydration of CO2. The relative contributions of plume-derived elements/weathering and CO2-driven weathering has been computed for each element. In addition, the comparison between the chemical compositions of the bulk deposition and of groundwater provides a new understanding about the mobility of volatile elements. Other processes such as ion exchange, iddingsite formation, and carbonate precipitation can also play roles, but only to minor extents. The proposed approach has revealed that the persistent plume strongly affects the chemical composition of groundwater at Mt. Etna and probably also at other

Monitoring of Volcanic Activity by Sub-mm Geodetic Analyses

Science.gov (United States)

Miura, S.; Mare, Y.; Ichiki, M.; Demachi, T.; Tachibana, K.; Nishimura, T.

2017-12-01

Volcanic earthquakes have been occurring beneath Zao volcano in northern Honshu, Japan since 2013, following the increase of deep low frequency earthquakes from 2012. On account of a burst of seismicity initiated in April 2015, the JMA announced a warning of eruption, however, the seismicity gradually decreased for the next two months and the warning was canceled in June. In the same time period, minor expansive deformation was observed by GNSS. Small earthquakes are still occurring, and low-freq. earthquakes (LPE) occur sometimes accompanied by static tilt changes. In this study, we try to extract the sub-mm displacements from the LPE waveforms observed by broadband seismometers (BBS) and utilize them for geodetic inversion to monitor volcanic activities. Thun et al. (2015, 2016) devised an efficient method using a running median filter (RMF) to remove LP noises, which contaminate displacement waveforms. They demonstrated the reproducibility of the waveforms corresponding to the experimentally given sub-mm displacements in the laboratory. They also apply the method to the field LPE data obtained from several volcanoes to show static displacements. The procedure is outlined as follows: (1) Unfiltered removal of the instrument response, (2) LP noise estimate by LPF with a corner frequency of 5/M, where M (seconds) is the time window of the RMF and should be at least three times the length of the rise time. (3) Subtract the noise estimated from step (2). (4) Integrate to obtain displacement waveforms. We apply the method to the BBS waveform at a distance of about 1.5 km ESE from the summit crater of Zao Volcano associated with a LPE on April 1, 2017. Assuming the time window M as 300 seconds, we successfully obtained the displacement history: taking the rise time of about 2 minutes, the site was gradually uplifted with the amount of about 50-60 µm and then subsided with HF displacements in the next 2 minutes resulting about 20-30 µm static upheaval. Comparing the

Crustal Thickness Beneath Libya and the Origin of Partial Melt Beneath AS Sawda Volcanic Province From Receiver Function Constraints

Science.gov (United States)

Lemnifi, Awad A.; Elshaafi, Abdelsalam; Browning, John; Aouad, Nassib S.; El Ebaidi, Saad K.; Liu, Kelly K.; Gudmundsson, Agust

2017-12-01

This study investigates crustal thickness and properties within the Libyan region. Results obtained from 15 seismic stations belonging to the Libyan Center for Remote Sensing and Space Science are reported, in addition to 3 seismic stations publically available, using receiver functions. The results show crustal thicknesses ranging from 24 km to 36 km (with uncertainties ranging between ±0.10 km and ±0.90 km). More specifically, crustal thickness ranges from 32 km to 36 km in the southern portion of the Libyan territory then becomes thinner, between 24 km and 30 km, in the coastal areas of Libya and thinnest, between 24 km and 28 km, in the Sirt Basin. The observed high Vp/Vs value of 1.91 at one station located at the AS Sawda Volcanic Province in central Libya indicates the presence of either partial melt or an abnormally warm area. This finding suggests that magma reservoirs beneath the Libyan territory may still be partially molten and active, thereby posing significant earthquake and volcanic risks. The hypothesis of an active magma source is further demonstrated though the presence of asthenospheric upwelling and extension of the Sirt Basin. This study provides a new calculation of unconsolidated sediment layers by using the arrival time of the P to S converted phases. The results show sediments thicknesses of 0.4 km to 3.7 km, with the Vp/Vs values ranging from 2.2 to 4.8. The variations in crustal thickness throughout the region are correlated with surface elevation and Bouguer gravity anomalies, which suggest that they are isostatically compensated.

Conceptual model of volcanism and volcanic hazards of the region of Ararat valley, Armenia

Science.gov (United States)

Meliksetian, Khachatur; Connor, Charles; Savov, Ivan; Connor, Laura; Navasardyan, Gevorg; Manucharyan, Davit; Ghukasyan, Yura; Gevorgyan, Hripsime

2015-04-01

Armenia and the adjacent volcanically active regions in Iran, Turkey and Georgia are located in the collision zone between the Arabian and Eurasian lithospheric plates. The majority of studies of regional collision related volcanism use the model proposed by Keskin, (2003) where volcanism is driven by Neo-Tethyan slab break-off. In Armenia, >500 Quaternary-Holocene volcanoes from the Gegham, Vardenis and Syunik volcanic fields are hosted within pull-apart structures formed by active faults and their segments (Karakhanyan et al., 2002), while tectonic position of the large in volume basalt-dacite Aragats volcano and periphery volcanic plateaus is different and its position away from major fault lines necessitates more complex volcano-tectonic setup. Our detailed volcanological, petrological and geochemical studies provide insight into the nature of such volcanic activity in the region of Ararat Valley. Most magmas, such as those erupted in Armenia are volatile-poor and erupt fairly hot. Here we report newly discovered tephra sequences in Ararat valley, that were erupted from historically active Ararat stratovolcano and provide evidence for explosive eruption of young, mid K2O calc-alkaline and volatile-rich (>4.6 wt% H2O; amph-bearing) magmas. Such young eruptions, in addition to the ignimbrite and lava flow hazards from Gegham and Aragats, present a threat to the >1.4 million people (~ ½ of the population of Armenia). We will report numerical simulations of potential volcanic hazards for the region of Ararat valley near Yerevan that will include including tephra fallout, lava flows and opening of new vents. Connor et al. (2012) J. Applied Volcanology 1:3, 1-19; Karakhanian et al. (2002), JVGR, 113, 319-344; Keskin, M. (2003) Geophys. Res. Lett. 30, 24, 8046.

Dynamic triggering of volcano drumbeat-like seismicity at the Tatun volcano group in Taiwan

Science.gov (United States)

Lin, Cheng-Horng

2017-07-01

Periodical seismicity during eruptions has been observed at several volcanoes, such as Mount St. Helens and Soufrière Hills. Movement of magma is often considered one of the most important factors in its generation. Without any magma movement, drumbeat-like (or heartbeat-like) periodical seismicity was detected twice beneath one of the strongest fumarole sites (Dayoukeng) among the Tatun volcano group in northern Taiwan in 2015. Both incidences of drumbeat-like seismicity were respectively started after felt earthquakes in Taiwan, and then persisted for 1-2 d afterward with repetition intervals of ∼18 min between any two adjacent events. The phenomena suggest both drumbeat-like (heartbeat-like) seismicity sequences were likely triggered by dynamic waves generated by the two felt earthquakes. Thus, rather than any involvement of magma, a simplified pumping system within a degassing conduit is proposed to explain the generation of drumbeat-like seismicity. The collapsed rocks within the conduit act as a piston, which was repeatedly lifted up by ascending gas from a deeper reservoir and dropped down when the ascending gas was escaping later. These phenomena show that the degassing process is still very strong in the Tatun volcano group in Taiwan, even though it has been dormant for about several thousand years.

Seismic Microzonation for Refinement of Seismic Load Parameters

Energy Technology Data Exchange (ETDEWEB)

Savich, A. I.; Bugaevskii, A. G., E-mail: office@geodyn.ru, E-mail: bugaevskiy@geodyn.ru [Center of the Office of Geodynamic Observations in the Power Sector, an affiliate of JSC “Institut Gidroproekt” (Russian Federation)

2016-05-15

Functional dependencies are established for the characteristics of seismic transients recorded at various points of a studied site, which are used to propose a new approach to seismic microzonation (SMZ) that enables the creation of new SMZ maps of strong seismic motion, with due regard for dynamic parameters of recorded transients during weak earthquakes.

The seismic analyzer: interpreting and illustrating 2D seismic data.

Science.gov (United States)

Patel, Daniel; Giertsen, Christopher; Thurmond, John; Gjelberg, John; Gröller, M Eduard

2008-01-01

We present a toolbox for quickly interpreting and illustrating 2D slices of seismic volumetric reflection data. Searching for oil and gas involves creating a structural overview of seismic reflection data to identify hydrocarbon reservoirs. We improve the search of seismic structures by precalculating the horizon structures of the seismic data prior to interpretation. We improve the annotation of seismic structures by applying novel illustrative rendering algorithms tailored to seismic data, such as deformed texturing and line and texture transfer functions. The illustrative rendering results in multi-attribute and scale invariant visualizations where features are represented clearly in both highly zoomed in and zoomed out views. Thumbnail views in combination with interactive appearance control allows for a quick overview of the data before detailed interpretation takes place. These techniques help reduce the work of seismic illustrators and interpreters.

Separating volcanic deformation and atmospheric signals at Mount St. Helens using Persistent Scatterer InSAR

Science.gov (United States)

Welch, Mark D.; Schmidt, David A.

2017-09-01

Over the past two decades, GPS and leveling surveys have recorded cycles of inflation and deflation associated with dome building eruptions at Mount St. Helens. Due to spatial and temporal limitations of the data, it remains unknown whether any deformation occurred prior to the most recent eruption of 2004, information which could help anticipate future eruptions. Interferometric Synthetic Aperture Radar (InSAR), which boasts fine spatial resolution over large areas, has the potential to resolve pre-eruptive deformation that may have occurred, but eluded detection by campaign GPS surveys because it was localized to the edifice or crater. Traditional InSAR methods are challenging to apply in the Cascades volcanic arc because of a combination of environmental factors, and past attempts to observe deformation at Mount St. Helens were unable to make reliable observations in the crater or on much of the edifice. In this study, Persistent Scatterer InSAR, known to mitigate issues of decorrelation caused by environmental factors, is applied to four SAR data sets in an attempt to resolve localized sources of deformation on the volcano between 1995 and 2010. Many interferograms are strongly influenced by phase delay from atmospheric water vapor and require correction, evidenced by a correlation between phase and topography. To assess the bias imposed by the atmosphere, we perform sensitivity tests on a suite of atmospheric correction techniques, including several that rely on the correlation of phase delay to elevation, and explore approaches that directly estimate phase delay using the ERA-Interim and NARR climate reanalysis data sets. We find that different correction methods produce velocities on the edifice of Mount St. Helens that differ by up to 1 cm/yr due to variability in how atmospheric artifacts are treated in individual interferograms. Additionally, simple phase-based techniques run the risk of minimizing any surface deformation signals that may themselves be

Lithology and temperature: How key mantle variables control rift volcanism

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Shorttle, O.; Hoggard, M.; Matthews, S.; Maclennan, J.

2015-12-01

Continental rifting is often associated with extensive magmatic activity, emplacing millions of cubic kilometres of basalt and triggering environmental change. The lasting geological record of this volcanic catastrophism are the large igneous provinces found at the margins of many continents and abrupt extinctions in the fossil record, most strikingly that found at the Permo-Triassic boundary. Rather than being considered purely a passive plate tectonic phenomenon, these episodes are frequently explained by the involvement of mantle plumes, upwellings of mantle rock made buoyant by their high temperatures. However, there has been debate over the relative role of the mantle's temperature and composition in generating the large volumes of magma involved in rift and intra-plate volcanism, and even when the mantle is inferred to be hot, this has been variously attributed to mantle plumes or continental insulation effects. To help resolve these uncertainties we have combined geochemical, geophysical and modelling results in a two stage approach: Firstly, we have investigated how mantle composition and temperature contribute to melting beneath Iceland, the present day manifestation of the mantle plume implicated in the 54Ma break up of the North Atlantic. By considering both the igneous crustal production on Iceland and the chemistry of its basalts we have been able to place stringent constraints on the viable temperature and lithology of the Icelandic mantle. Although a >100°C excess temperature is required to generate Iceland's thick igneous crust, geochemistry also indicates that pyroxenite comprises 10% of its source. Therefore, the dynamics of rifting on Iceland are modulated both by thermal and compositional mantle anomalies. Secondly, we have performed a global assessment of the mantle's post break-up thermal history to determine the amplitude and longevity of continental insulation in driving excess volcanism. Using seismically constrained igneous crustal

Seismicity and seismic monitoring in the Asse salt mine

International Nuclear Information System (INIS)

Flach, D.; Gommlich, G.; Hente, B.

1987-01-01

Seismicity analyses are made in order to assess the safety of candidate sites for ultimate disposal of hazardous wastes. The report in hand reviews the seismicity history of the Asse salt mine and presents recent results of a measuring campaign made in the area. The monitoring network installed at the site supplies data and information on the regional seismicity, on seismic amplitudes under ground and above ground, and on microseismic activities. (DG) [de

Diagnosis of time of increased probability of volcanic earthquakes at Mt. Vesuvius zone

International Nuclear Information System (INIS)

Rotwain, I.; Kuznetsov, I.; De Natale, G.; Peresan, A.; Panza, G.F.

2003-06-01

The possibility of intermediate-term earthquake prediction at Mt. Vesuvius by means of the algorithm CN is explored. CN was originally designed to identify the Times of Increased Probability (TIPs) for the occurrence of strong tectonic earthquakes, with magnitude M ≥ M 0 , within a region a priori delimited. Here the algorithm CN is applied, for the first time, to the analysis of volcanic seismicity. The earthquakes recorded at Mt. Vesuvius, during the period from February 1972 to October 2002, are considered and the magnitude threshold M 0 , selecting the events to be predicted, is varied within the range: 3.0 - 3.3. Satisfactory prediction results are obtained, by retrospective analysis, when a time scaling is introduced. In particular, when the length of the time windows is reduced by a factor 2.5 - 3, with respect to the standard version of CN algorithm, more than 90% of the events with M ≥ M 0 occur within the TIP intervals, with TIPs occupying about 30% of the total time considered. The control experiment 'Seismic History' demonstrates the stability of the obtained results and indicates that the algorithm CN can be applied to monitor the preparation of impending earthquakes with M ≥ 3.0 at Mt. Vesuvius. (author)

Volcano dome dynamics at Mount St. Helens: Deformation and intermittent subsidence monitored by seismicity and camera imagery pixel offsets

Science.gov (United States)

Salzer, Jacqueline T.; Thelen, Weston A.; James, Mike R.; Walter, Thomas R.; Moran, Seth C.; Denlinger, Roger P.

2016-01-01

The surface deformation field measured at volcanic domes provides insights into the effects of magmatic processes, gravity- and gas-driven processes, and the development and distribution of internal dome structures. Here we study short-term dome deformation associated with earthquakes at Mount St. Helens, recorded by a permanent optical camera and seismic monitoring network. We use Digital Image Correlation (DIC) to compute the displacement field between successive images and compare the results to the occurrence and characteristics of seismic events during a 6 week period of dome growth in 2006. The results reveal that dome growth at Mount St. Helens was repeatedly interrupted by short-term meter-scale downward displacements at the dome surface, which were associated in time with low-frequency, large-magnitude seismic events followed by a tremor-like signal. The tremor was only recorded by the seismic stations closest to the dome. We find a correlation between the magnitudes of the camera-derived displacements and the spectral amplitudes of the associated tremor. We use the DIC results from two cameras and a high-resolution topographic model to derive full 3-D displacement maps, which reveals internal dome structures and the effect of the seismic activity on daily surface velocities. We postulate that the tremor is recording the gravity-driven response of the upper dome due to mechanical collapse or depressurization and fault-controlled slumping. Our results highlight the different scales and structural expressions during growth and disintegration of lava domes and the relationships between seismic and deformation signals.

German seismic regulations

International Nuclear Information System (INIS)

Danisch, Ruediger

2002-01-01

Rules and regulations for seismic design in Germany cover the following: seismic design of conventional buildings; and seismic design of nuclear facilities. Safety criteria for NPPs, accident guidelines, and guidelines for PWRs as well as safety standards are cited. Safety standards concerned with NPPs seismic design include basic principles, soil analysis, design of building structures, design of mechanical and electrical components, seismic instrumentation, and measures to be undertaken after the earthquake

Centennial-scale climate change from decadally-paced explosive volcanism: a coupled sea ice-ocean mechanism

Energy Technology Data Exchange (ETDEWEB)

Zhong, Y. [University of Colorado, INSTAAR, Boulder, CO (United States); Miller, G.H. [University of Colorado, INSTAAR, Boulder, CO (United States); University of Colorado, Department of Geological Sciences, Boulder, CO (United States); Otto-Bliesner, B.L.; Holland, M.M.; Bailey, D.A. [NCAR, Boulder, CO (United States); Schneider, D.P. [NCAR, Boulder, CO (United States); University of Colorado, CIRES, Boulder, CO (United States); Geirsdottir, A. [University of Iceland, Department of Earth Sciences and Institute of Earth Sciences, Reykjavik (Iceland)

2011-12-15

Northern Hemisphere summer cooling through the Holocene is largely driven by the steady decrease in summer insolation tied to the precession of the equinoxes. However, centennial-scale climate departures, such as the Little Ice Age, must be caused by other forcings, most likely explosive volcanism and changes in solar irradiance. Stratospheric volcanic aerosols have the stronger forcing, but their short residence time likely precludes a lasting climate impact from a single eruption. Decadally paced explosive volcanism may produce a greater climate impact because the long response time of ocean surface waters allows for a cumulative decrease in sea-surface temperatures that exceeds that of any single eruption. Here we use a global climate model to evaluate the potential long-term climate impacts from four decadally paced large tropical eruptions. Direct forcing results in a rapid expansion of Arctic Ocean sea ice that persists throughout the eruption period. The expanded sea ice increases the flux of sea ice exported to the northern North Atlantic long enough that it reduces the convective warming of surface waters in the subpolar North Atlantic. In two of our four simulations the cooler surface waters being advected into the Arctic Ocean reduced the rate of basal sea-ice melt in the Atlantic sector of the Arctic Ocean, allowing sea ice to remain in an expanded state for > 100 model years after volcanic aerosols were removed from the stratosphere. In these simulations the coupled sea ice-ocean mechanism maintains the strong positive feedbacks of an expanded Arctic Ocean sea ice cover, allowing the initial cooling related to the direct effect of volcanic aerosols to be perpetuated, potentially resulting in a centennial-scale or longer change of state in Arctic climate. The fact that the sea ice-ocean mechanism was not established in two of our four simulations suggests that a long-term sea ice response to volcanic forcing is sensitive to the stability of the seawater

Establishing seismic design criteria to achieve an acceptable seismic margin

International Nuclear Information System (INIS)

Kennedy, R.P.

1997-01-01

In order to develop a risk based seismic design criteria the following four issues must be addressed: (1) What target annual probability of seismic induced unacceptable performance is acceptable? (2). What minimum seismic margin is acceptable? (3) Given the decisions made under Issues 1 and 2, at what annual frequency of exceedance should the Safe Shutdown Earthquake ground motion be defined? (4) What seismic design criteria should be established to reasonably achieve the seismic margin defined under Issue 2? The first issue is purely a policy decision and is not addressed in this paper. Each of the other three issues are addressed. Issues 2 and 3 are integrally tied together so that a very large number of possible combinations of responses to these two issues can be used to achieve the target goal defined under Issue 1. Section 2 lays out a combined approach to these two issues and presents three potentially attractive combined resolutions of these two issues which reasonably achieves the target goal. The remainder of the paper discusses an approach which can be used to develop seismic design criteria aimed at achieving the desired seismic margin defined in resolution of Issue 2. Suggestions for revising existing seismic design criteria to more consistently achieve the desired seismic margin are presented

Seismic capacity of a reinforced concrete frame structure without seismic detailing and limited ductility seismic design in moderate seismicity

International Nuclear Information System (INIS)

Kim, J. K.; Kim, I. H.

1999-01-01

A four-story reinforced concrete frame building model is designed for the gravity loads only. Static nonlinear pushover analyses are performed in two orthogonal horizontal directions. The overall capacity curves are converted into ADRS spectra and compared with demand spectra. At several points the deformed shape, moment and shear distribution are calculated. Based on these results limited ductility seismic design concept is proposed as an alternative seismic design approach in moderate seismicity resign

Closer look at lunar volcanism

International Nuclear Information System (INIS)

Vaniman, D.T.; Heiken, G.; Taylor, G.J.

1984-01-01

Although the American Apollo and Soviet Luna missions concentrated on mare basalt samples, major questions remain about lunar volcanism. Lunar field work will be indispensable for resolving the scientific questions about ages, compositions, and eruption processes of lunar volcanism. From a utilitarian standpoint, a better knowledge of lunar volcanism will also yield profitable returns in lunar base construction (e.g., exploitation of rille or lava-tube structures) and in access to materials such as volatile elements, pure glass, or ilmenite for lunar industry

Burar seismic station: evaluation of seismic performance

International Nuclear Information System (INIS)

Ghica, Daniela; Popa, Mihaela

2005-01-01

A new seismic monitoring system, the Bucovina Seismic Array (BURAR), has been established since July 2002, in the Northern part of Romania, in a joint effort of the Air Force Technical Applications Center, USA, and the National Institute for Earth Physics (NIEP), Romania. The small-aperture array consists of 10 seismic sensors (9 vertical short-period and one three-component broad band) located in boreholes and distributed in a 5 x 5 km 2 area. At present, the seismic data are continuously recorded by the BURAR and transmitted in real-time to the Romanian National Data Center in Bucharest and National Data Center of the USA, in Florida. Based on the BURAR seismic information gathered at the National Data Center, NIEP (ROM N DC), in the August 2002 - December 2004 time interval, analysis and statistical assessments were performed. Following the preliminary processing of the data, several observations on the global performance of the BURAR system were emphasized. Data investigation showed an excellent efficiency of the BURAR system particularly in detecting teleseismic and regional events. Also, a statistical analysis for the BURAR detection capability of the local Vrancea events was performed in terms of depth and magnitude for the year 2004. The high signal detection capability of the BURAR resulted, generally, in improving the location solutions for the Vrancea seismic events. The location solution accuracy is enhanced when adding BURAR recordings, especially in the case of low magnitude events (recorded by few stations). The location accuracy is increased, both in terms of constraining hypocenter depth and epicentral coordinates. Our analysis certifies the importance of the BURAR system in NIEP efforts to elaborate seismic bulletins. Furthermore, the specific procedures for array data processing (beam forming, f-k analysis) increase significantly the signal-to-noise ratio by summing up the coherent signals from the array components, and ensure a better accuracy

Volcanic alert system (VAS) developed during the 2011-2014 El Hierro (Canary Islands) volcanic process

Science.gov (United States)

García, Alicia; Berrocoso, Manuel; Marrero, José M.; Fernández-Ros, Alberto; Prates, Gonçalo; De la Cruz-Reyna, Servando; Ortiz, Ramón

2014-06-01

The 2011 volcanic unrest at El Hierro Island illustrated the need for a Volcanic Alert System (VAS) specifically designed for the management of volcanic crises developing after long repose periods. The VAS comprises the monitoring network, the software tools for analysis of the monitoring parameters, the Volcanic Activity Level (VAL) management, and the assessment of hazard. The VAS presented here focuses on phenomena related to moderate eruptions, and on potentially destructive volcano-tectonic earthquakes and landslides. We introduce a set of new data analysis tools, aimed to detect data trend changes, as well as spurious signals related to instrumental failure. When data-trend changes and/or malfunctions are detected, a watchdog is triggered, issuing a watch-out warning (WOW) to the Monitoring Scientific Team (MST). The changes in data patterns are then translated by the MST into a VAL that is easy to use and understand by scientists, technicians, and decision-makers. Although the VAS was designed specifically for the unrest episodes at El Hierro, the methodologies may prove useful at other volcanic systems.

Validating predictions made by a thermo-mechanical model of melt segregation in sub-volcanic systems

Science.gov (United States)

Roele, Katarina; Jackson, Matthew; Morgan, Joanna

2014-05-01

A quantitative understanding of the spatial and temporal evolution of melt distribution in the crust is crucial in providing insights into the development of sub-volcanic crustal stratigraphy and composition. This work aims to relate numerical models that describe the base of volcanic systems with geophysical observations. Recent modelling has shown that the repetitive emplacement of mantle-derived basaltic sills, at the base of the lower crust, acts as a heat source for anatectic melt generation, buoyancy-driven melt segregation and mobilisation. These processes form the lowermost architecture of complex sub-volcanic networks as upward migrating melt produces high melt fraction layers. These 'porosity waves' are separated by zones with high compaction rates and have distinctive polybaric chemical signatures that suggest mixed crust and mantle origins. A thermo-mechanical model produced by Solano et al in 2012 has been used to predict the temperatures and melt fractions of successive high porosity layers within the crust. This model was used as it accounts for the dynamic evolution of melt during segregation and migration through the crust; a significant process that has been neglected in previous models. The results were used to input starting compositions for each of the layers into the rhyolite-MELTS thermodynamic simulation. MELTS then determined the approximate bulk composition of the layers once they had cooled and solidified. The mean seismic wave velocities of the polymineralic layers were then calculated using the relevant Voight-Reuss-Hill mixture rules, whilst accounting for the pressure and temperature dependence of seismic wave velocity. The predicted results were then compared with real examples of reflectivity for areas including the UK, where lower crustal layering is observed. A comparison between the impedance contrasts at compositional boundaries is presented as it confirms the extent to which modelling is able to make predictions that are

Lidar sounding of volcanic plumes

Science.gov (United States)

Fiorani, Luca; Aiuppa, Alessandro; Angelini, Federico; Borelli, Rodolfo; Del Franco, Mario; Murra, Daniele; Pistilli, Marco; Puiu, Adriana; Santoro, Simone

2013-10-01

Accurate knowledge of gas composition in volcanic plumes has high scientific and societal value. On the one hand, it gives information on the geophysical processes taking place inside volcanos; on the other hand, it provides alert on possible eruptions. For this reasons, it has been suggested to monitor volcanic plumes by lidar. In particular, one of the aims of the FP7 ERC project BRIDGE is the measurement of CO2 concentration in volcanic gases by differential absorption lidar. This is a very challenging task due to the harsh environment, the narrowness and weakness of the CO2 absorption lines and the difficulty to procure a suitable laser source. This paper, after a review on remote sensing of volcanic plumes, reports on the current progress of the lidar system.

Gas measurements from the Costa Rica-Nicaragua volcanic segment suggest possible along-arc variations in volcanic gas chemistry

Science.gov (United States)

Aiuppa, A.; Robidoux, P.; Tamburello, G.; Conde, V.; Galle, B.; Avard, G.; Bagnato, E.; De Moor, J. M.; Martínez, M.; Muñóz, A.

2014-12-01

Obtaining accurate estimates of the CO2 output from arc volcanism requires a precise understanding of the potential along-arc variations in volcanic gas chemistry, and ultimately of the magmatic gas signature of each individual arc segment. In an attempt to more fully constrain the magmatic gas signature of the Central America Volcanic Arc (CAVA), we present here the results of a volcanic gas survey performed during March and April 2013 at five degassing volcanoes within the Costa Rica-Nicaragua volcanic segment (CNVS). Observations of the volcanic gas plume made with a multicomponent gas analyzer system (Multi-GAS) have allowed characterization of the CO2/SO2-ratio signature of the plumes at Poás (0.30±0.06, mean ± SD), Rincón de la Vieja (27.0±15.3), and Turrialba (2.2±0.8) in Costa Rica, and at Telica (3.0±0.9) and San Cristóbal (4.2±1.3) in Nicaragua (all ratios on molar basis). By scaling these plume compositions to simultaneously measured SO2 fluxes, we estimate that the CO2 outputs at CNVS volcanoes range from low (25.5±11.0 tons/day at Poás) to moderate (918 to 1270 tons/day at Turrialba). These results add a new information to the still fragmentary volcanic CO2 output data set, and allow estimating the total CO2 output from the CNVS at 2835±1364 tons/day. Our novel results, with previously available information about gas emissions in Central America, are suggestive of distinct volcanic gas CO2/ST (= SO2 + H2S)-ratio signature for magmatic volatiles in Nicaragua (∼3) relative to Costa Rica (∼0.5-1.0). We also provide additional evidence for the earlier theory relating the CO2-richer signature of Nicaragua volcanism to increased contributions from slab-derived fluids, relative to more-MORB-like volcanism in Costa Rica. The sizeable along-arc variations in magmatic gas chemistry that the present study has suggested indicate that additional gas observations are urgently needed to more-precisely confine the volcanic CO2 from the CAVA, and from

Structural control of monogenetic volcanism in the Garrotxa volcanic field (Northeastern Spain) from gravity and self-potential measurements

Science.gov (United States)

Barde-Cabusson, S.; Gottsmann, J.; Martí, J.; Bolós, X.; Camacho, A. G.; Geyer, A.; Planagumà, Ll.; Ronchin, E.; Sánchez, A.

2014-01-01

We report new geophysical observations on the distribution of subsurface structures associated with monogenetic volcanism in the Garrotxa volcanic field (Northern Spain). As part of the Catalan Volcanic Zone, this Quaternary volcanic field is associated with the European rifts system. It contains the most recent and best preserved volcanic edifices of the Catalan Volcanic Zone with 38 monogenetic volcanoes identified in the Garrotxa Natural Park. We conducted new gravimetric and self-potential surveys to enhance our understanding of the relationship between the local geology and the spatial distribution of the monogenetic volcanoes. The main finding of this study is that the central part of the volcanic field is dominated by a broad negative Bouguer anomaly of around -0.5 mGal, within which a series of gravity minima are found with amplitudes of up to -2.3 mGal. Inverse modelling of the Bouguer data suggests that surficial low-density material dominates the volcanic field, most likely associated with effusive and explosive surface deposits. In contrast, an arcuate cluster of gravity minima to the NW of the Croscat volcano, the youngest volcano of this zone, is modelled by vertically extended low-density bodies, which we interpret as a complex ensemble of fault damage zones and the roots of young scoria cones. A ground-water infiltration zone identified by a self-potential anomaly is associated with a steep horizontal Bouguer gravity gradient and interpreted as a fault zone and/or magmatic fissure, which fed the most recent volcanic activity in the Garrotxa. Gravimetric and self-potential data are well correlated and indicate a control on the locations of scoria cones by NNE-SSW and NNW-SSE striking tectonic features, which intersect the main structural boundaries of the study area to the north and south. Our interpretation of the data is that faults facilitated magma ascent to the surface. Our findings have major implications for understanding the relationship

Seismic hazard estimation based on the distributed seismicity in northern China

Science.gov (United States)

Yang, Yong; Shi, Bao-Ping; Sun, Liang

2008-03-01

In this paper, we have proposed an alternative seismic hazard modeling by using distributed seismicites. The distributed seismicity model does not need delineation of seismic source zones, and simplify the methodology of probabilistic seismic hazard analysis. Based on the devastating earthquake catalogue, we established three seismicity model, derived the distribution of a-value in northern China by using Gaussian smoothing function, and calculated peak ground acceleration distributions for this area with 2%, 5% and 10% probability of exceedance in a 50-year period by using three attenuation models, respectively. In general, the peak ground motion distribution patterns are consistent with current seismic hazard map of China, but in some specific seismic zones which include Shanxi Province and Shijiazhuang areas, our results indicated a little bit higher peak ground motions and zonation characters which are in agreement with seismicity distribution patterns in these areas. The hazard curves have been developed for Beijing, Tianjin, Taiyuan, Tangshan, and Ji’nan, the metropolitan cities in the northern China. The results showed that Tangshan, Taiyuan, Beijing has a higher seismic hazard than that of other cities mentioned above.

New geological interpretation of multi-channel seismic profiles from the Pacific Margin of the Antarctic Peninsula

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Okoń Jan

2016-06-01

Full Text Available The Polish Geophysical Expedition to West Antarctica in 1979–1980 was carried out by the Institute of Geophysics, Polish Academy of Sciences. Beside deep seismic soundings, 12 multi-channel seismic profiles, with a total length of ca 1000 km have been recorded north and east of the South Shetland Islands and in the Bransfield Strait, but they have never before been completely interpreted and published. All profiles have been processed with modern processing flow including time migration. Profiles crossing the South Shetland Trench revealed distinct reflector inside continental slope, which has been interpreted as border between buried accretionary prism and overlying slope sediments of glacial-marine origin. Profiles in the Bransfield Strait show traces of the Last Glacial Maximum (LGM in the form of glacial foreground valleys, with some of them used as weak spots for young age volcanic intrusions. This paper is the first comprehensive geological interpretation of collected dataset and differences between results from other expeditions are discussed.

Volcanic Hazards in Site Evaluation for Nuclear Installations

Energy Technology Data Exchange (ETDEWEB)

NONE

2012-10-15

This publication provides comprehensive and updated guidance for site evaluation in relation to volcanic hazards. It includes recommendations on assessing the volcanic hazards at a nuclear installation site, in order to identify and characterize, in a comprehensive manner, all potentially hazardous phenomena that may be associated with future volcanic events. It describes how some of these volcanic phenomena may affect the acceptability of the selected site, resulting in exclusion of a site or determining the corresponding design basis parameters for the installation. This Safety Guide is applicable to both existing and new sites, and a graded approach is recommended to cater for all types of nuclear installations. Contents: 1. Introduction; 2. Overview of volcanic hazard assessment; 3. General recommendations; 4. Necessary information and investigations (database); 5. Screening of volcanic hazards; 6. Site specific volcanic hazard assessment; 7. Nuclear installations other than nuclear power plants; 8. Monitoring and preparation for response; 9. Management system for volcanic hazard assessment; Annex I: Volcanic hazard scenarios; Annex II: Worldwide sources of information.

Volcanic ash in ancient Maya ceramics of the limestone lowlands: implications for prehistoric volcanic activity in the Guatemala highlands

Science.gov (United States)

Ford, Anabel; Rose, William I.

1995-07-01

In the spirit of collaborative research, Glicken and Ford embarked on the problem of identifying the source of volcanic ash used as temper in prehistoric Maya ceramics. Verification of the presence of glass shards and associated volcanic mineralogy in thin sections of Maya ceramics was straightforward and pointed to the Guatemala Highland volcanic chain. Considering seasonal wind rose patterns, target volcanoes include those from the area west of and including Guatemala City. Joint field research conducted in 1983 by Glicken and Ford in the limestone lowlands of Belize and neighboring Guatemala, 300 km north of the volcanic zone and 150 km from the nearest identified ash deposits, was unsuccessful in discovering local volcanic ash deposits. The abundance of the ash in common Maya ceramic vessels coupled with the difficulties of long-distance procurement without draft animals lead Glicken to suggest that ashfall into the lowlands would most parsimoniously explain prehistoric procurement; it literally dropped into their hands. A major archaeological problem with this explanation is that the use of volcanic ash occurring over several centuries of the Late Classic Period (ca. 600-900 AD). To accept the ashfall hypothesis for ancient Maya volcanic ash procurement, one would have to demonstrate a long span of consistent volcanic activity in the Guatemala Highlands for the last half of the first millennium AD. Should this be documented through careful petrographic, microprobe and tephrachronological studies, a number of related archaeological phenomena would be explained. In addition, the proposed model of volcanic activity has implications for understanding volcanism and potential volcanic hazards in Central America over a significantly longer time span than the historic period. These avenues are explored and a call for further collaborative research of this interdisciplinary problem is extended in this paper.

Automating Hyperspectral Data for Rapid Response in Volcanic Emergencies

Science.gov (United States)

Davies, Ashley G.; Doubleday, Joshua R.; Chien, Steve A.

2013-01-01

In a volcanic emergency, time is of the essence. It is vital to quantify eruption parameters (thermal emission, effusion rate, location of activity) and distribute this information as quickly as possible to decision-makers in order to enable effective evaluation of eruption-related risk and hazard. The goal of this work was to automate and streamline processing of spacecraft hyperspectral data, automate product generation, and automate distribution of products. Visible and Short-Wave Infrared Images of volcanic eruption in Iceland in May 2010." class="caption" align="right">The software rapidly processes hyperspectral data, correcting for incident sunlight where necessary, and atmospheric transmission; detects thermally anomalous pixels; fits data with model black-body thermal emission spectra to determine radiant flux; calculates atmospheric convection thermal removal; and then calculates total heat loss. From these results, an estimation of effusion rate is made. Maps are generated of thermal emission and location (see figure). Products are posted online, and relevant parties notified. Effusion rate data are added to historical record and plotted to identify spikes in activity for persistently active eruptions. The entire process from start to end is autonomous. Future spacecraft, especially those in deep space, can react to detection of transient processes without the need to communicate with Earth, thus increasing science return. Terrestrially, this removes the need for human intervention.

Progressive Seismic Failure, Seismic Gap, and Great Seismic Risk across the Densely Populated North China Basin

Science.gov (United States)