Body wave travel times and amplitudes for present-day seismic model of Mars
Raevskiy, Sergey; Gudkova, Tamara
At the moment Martian interior structure models are constrained by the satellite observational data (the mass, the moment of inertia factor, the Love number k _{2}) (Konopliv et al., 2011) and high pressure experimental data (Bertka and Fei, 1997). Seismological observations could provide unparalleled capability for studying Martian interiors. Future missions include seismic experiments on Mars (Lognonné et al., 2012). The main instrument for these seismic experiments is a broadband seismometer (Robert et al., 2012). When seismic measurements are not yet available, physically consistent interior models, characterized by properties of relevant minerals, make possible to study of the seismic response of the planet. \\To estimate travel times for direct P, S, core reflected PcP, ScS and core refracted PKP body waves as a function of epicentral distance and hypocentral depth, as well as their amplitudes at the surface for a given marsquake, software product was developed in MatLab, as it encompasses many plotting routines that plot resulting travel times and ray paths. The computational results have been compared with the program TTBox (Knapmeyer, 2004). The code computes seismic ray paths and travel times for a one-dimentional spherical interior model (density and seismic velocities are functions of a radius only). Calculations of travel times tables for direct P, S, core reflected PcP, ScS and core refracted PKP waves and their amplitudes are carried out for a trial seismic model of Mars M14_3 from (Zharkov et al., 2009): the core radius is 1800 km, the thickness of the crust is 50 km. Direct and core reflected P and S waves are recorded to a maximum epicentral distance equal to about 100(°) , and PKP arrivals can be detected for epicental distances larger than 150(°) . The shadow zone is getting wider in comparison with previous results (Knapmeyer, 2010), as the liquid core radius of the seismic model under consideration is larger. Based on the estimates of
Ellipticity and crustal corrections for seismic body wave paths: application to Mars and Moon
Hempel, S.; Garcia, R.; Wieczorek, M. A.
2015-12-01
Forward modeling of seismic body wave travel times and ray parameters for a given density and seismic velocity model is an important tool to investigate the interior structure of planets. The popular toolbox TauP by Crotwell et al. (1999) facilitates application to planets other than Earth, but does not consider a planet's ellipticity nor its surface topography. Due to their ellipticity, smaller radii and larger relative surface topography, these corrections become more significant in predicting seismic observations for celestial bodies like the Moon and Mars. In preparation for NASA's INSIGHT discovery mission (launch in March 2016), we include ellipticity corrections, geometrical spreading and topography corrections into TauP. The respective TauP extensions, as well as Lunar and Martian applications are presented: Previously, Lunar and Martian seismic velocity models have been proposed based on mass, moment of inertia, Love numbers and estimated bulk composition, and in case of the Moon also based on seismic data acquired during the Apollo Program (1969-1977). Due to the lack of direct seismic evidence, current Martian seismic velocity models vary widely and exhibit large travel time excursions, as well as considerable variations in epicentral distance ranges for which a given body wave is predicted to arrive. We discuss the effects of Lunar and Martian ellipticity and crustal structure on seismic travel times for a set of seismic velocity models and compare these to variations observed between the different 1D models. This comparison demonstrates the relevance of modeling the effects of ellipticity and crustal thickness during interpretation of seismic data acquired on planets like Mars or Moon.
Body-wave retrieval and imaging from ambient seismic fields with very dense arrays
Nakata, N.; Boué, P.; Beroza, G. C.
2015-12-01
Correlation-based analyses of ambient seismic wavefields is a powerful tool for retrieving subsurface information such as stiffness, anisotropy, and heterogeneity at a variety of scales. These analyses can be considered to be data-driven wavefield modeling. Studies of ambient-field tomography have been mostly focused on the surface waves, especially fundamental-mode Rayleigh waves. Although the surface-wave tomography is useful to model 3D velocities, the spatial resolution is limited due to the extended depth sensitivity of the surface wave measurements. Moreover, to represent elastic media, we need at least two stiffness parameters (e.g., shear and bulk moduli). We develop a technique to retrieve P diving waves from the ambient field observed by the dense geophone network (~2500 receivers with 100-m spacing) at Long Beach, California. With two-step filtering, we improve the signal-to-noise ratio of body waves to extract P wave observations that we use for tomography to estimate 3D P-wave velocity structure. The small scale-length heterogeneity of the velocity model follows a power law with ellipsoidal anisotropy. We also discuss possibilities to retrieve reflected waves from the ambient field and show other applications of the body-wave extraction at different locations and scales. Note that reflected waves penetrate deeper than diving waves and have the potential to provide much higher spatial resolution.
Making Waves: Seismic Waves Activities and Demonstrations
Braile, S. J.; Braile, L. W.
2011-12-01
The nature and propagation of seismic waves are fundamental concepts necessary for understanding the exploration of Earth's interior structure and properties, plate tectonics, earthquakes, and seismic hazards. Investigating seismic waves is also an engaging approach to learning basic principles of the physics of waves and wave propagation. Several effective educational activities and demonstrations are available for teaching about seismic waves, including the stretching of a spring to demonstrate elasticity; slinky wave propagation activities for compressional, shear, Rayleigh and Love waves; the human wave activity to demonstrate P- and S- waves in solids and liquids; waves in water in a simple wave tank; seismic wave computer animations; simple shake table demonstrations of model building responses to seismic waves to illustrate earthquake damage to structures; processing and analysis of seismograms using free and easy to use software; and seismic wave simulation software for viewing wave propagation in a spherical Earth. The use of multiple methods for teaching about seismic waves is useful because it provides reinforcement of the fundamental concepts, is adaptable to variable classroom situations and diverse learning styles, and allows one or more methods to be used for authentic assessment. The methods described here have been used effectively with a broad range of audiences, including K-12 students and teachers, undergraduate students in introductory geosciences courses, and geosciences majors.
Analysis of seismic body waves excited by the Mount Saint Helens eruption of May 18, 1980
Kanamori, H.; Given, J. W.; Lay, T.
Seismic body waves which were excited by eruption of Mt. St. Helens, and recorded by the Global Digital Seismographic Network (GDSN) stations are analyzed to determine the nature and the time sequence of the events associated with the eruption. The polarity of teleseismic P waves (period 20 sec) is identical at six stations which are distributed over a wide azimuthal range. This observation, together with a very small S to P amplitude ratio (at 20 sec), suggests that the source is a nearly vertical single force that represents the counter force of the eruption. The time history of the vertical force suggests two distinct groups of events, about two minutes apart, each consisting of several subevents with a duration of about 25 sec. The magnitude of the force is approximately 2.6 to the 17th power dyne. this vertical force is in contrast with the long period (approximately 150 sec) southward horizontal single force which was determined by a previous study and interpreted to be due to the massive landslide.
Seismic waves and seismic barriers
Kuznetsov, S. V.
2011-05-01
The basic idea of seismic barrier is to protect an area occupied by a building or a group of buildings from seismic waves. Depending on nature of seismic waves that are most probable in a specific region, different kinds of seismic barriers are suggested. For example, vertical barriers resembling a wall in a soil can protect from Rayleigh and bulk waves. The FEM simulation reveals that to be effective, such a barrier should be (i) composed of layers with contrast physical properties allowing "trapping" of the wave energy inside some of the layers, and (ii) depth of the barrier should be comparable or greater than the considered seismic wave length. Another type of seismic barrier represents a relatively thin surface layer that prevents some types of surface seismic waves from propagating. The ideas for these barriers are based on one Chadwick's result concerning non-propagation condition for Rayleigh waves in a clamped half-space, and Love's theorem that describes condition of non-existence for Love waves. The numerical simulations reveal that to be effective the length of the horizontal barriers should be comparable to the typical wavelength.
Body-wave seismic interferometry applied to earthquake- and storm-induced wavefield
Ruigrok, E.N.
2012-01-01
Seismology is the study of the vibration of the Earth. Seismologists pay much attention to the main source of Earth vibration: earthquakes. But also other seismic sources, like mining blasts, ocean storms and windmills, are studied. All these sources induce seismic waves, which can eventually be
Gribler, G.; Liberty, L. M.
2014-12-01
We present earthquake site response results from a 48-channel multicomponent seismic land streamer and large weight drop system. We acquired data along a grid of city streets in western Idaho at a rate of a few km per day where we derived shear wave velocity profiles to a depth of 40-50 m by incorporating vertical and radial geophone signals to capture the complete elliptical Rayleigh wave motion. We also obtained robust p-wave reflection and refraction results by capturing the returned signals that arrive at non-vertical incidence angles that result from the high-velocity road surface layer. By integrating the derived shear wave velocity profiles with p-wave reflection results, we include depositional and tectonic boundaries from the upper few hundred meters into our analysis to help assess whether ground motions may be amplified by shallow bedrock. By including p-wave refraction information into the analysis, we can identify zones of high liquefaction potential by comparing shear wave and p-wave velocity (Vp/Vs) measurements relative to refraction-derived water table depths. The utilization of multicomponent land streamer data improves signal-noise levels over single component data with no additional field effort. The added multicomponent data processing step can be as simple as calculating the magnitude of the vector for surface wave and refraction arrivals or rotating the reflected signals to the maximum emergence angle based on near surface p-wave velocity information. We show example data from a number of Idaho communities where historical earthquakes have been recorded. We also present numerical models and systematic field tests that show the effects of a high velocity road surface layer in surface and body wave measurements. We conclude that multicomponent seismic information derived from seismic land streamers can provide a significant improvement in earthquake hazard assessment over a standard single component approach with only a small addition in
Near-source attenuation of high-frequency body waves beneath the New Madrid Seismic Zone
Pezeshk, Shahram; Sedaghati, Farhad; Nazemi, Nima
2018-03-01
Attenuation characteristics in the New Madrid Seismic Zone (NMSZ) are estimated from 157 local seismograph recordings out of 46 earthquakes of 2.6 ≤ M ≤ 4.1 with hypocentral distances up to 60 km and focal depths down to 25 km. Digital waveform seismograms were obtained from local earthquakes in the NMSZ recorded by the Center for Earthquake Research and Information (CERI) at the University of Memphis. Using the coda normalization method, we tried to determine Q values and geometrical spreading exponents at 13 center frequencies. The scatter of the data and trade-off between the geometrical spreading and the quality factor did not allow us to simultaneously derive both these parameters from inversion. Assuming 1/ R 1.0 as the geometrical spreading function in the NMSZ, the Q P and Q S estimates increase with increasing frequency from 354 and 426 at 4 Hz to 729 and 1091 at 24 Hz, respectively. Fitting a power law equation to the Q estimates, we found the attenuation models for the P waves and S waves in the frequency range of 4 to 24 Hz as Q P = (115.80 ± 1.36) f (0.495 ± 0.129) and Q S = (161.34 ± 1.73) f (0.613 ± 0.067), respectively. We did not consider Q estimates from the coda normalization method for frequencies less than 4 Hz in the regression analysis since the decay of coda amplitude was not observed at most bandpass filtered seismograms for these frequencies. Q S/ Q P > 1, for 4 ≤ f ≤ 24 Hz as well as strong intrinsic attenuation, suggest that the crust beneath the NMSZ is partially fluid-saturated. Further, high scattering attenuation indicates the presence of a high level of small-scale heterogeneities inside the crust in this region.
Detection and monitoring of shear crack growth using S-P conversion of seismic waves
Modiriasari, A.; Bobet, A.; Pyrak-Nolte, L. J.
2017-12-01
, which causes energy partitioning into P, S, and P-to-S or S-to-P waves. This finding provides a diagnostic method for detecting shear crack initiation and growth using seismic wave conversions. Acknowledgments: This material is based upon work supported by the National Science Foundation, Geomechanics and Geotechnical Systems Program (award No. CMMI-1162082).
Automatic picking of direct P, S seismic phases and fault zone head waves
Ross, Z. E.; Ben-Zion, Y.
2014-10-01
We develop a set of algorithms for automatic detection and picking of direct P and S waves, as well as fault zone head waves (FZHW), generated by earthquakes on faults that separate different lithologies and recorded by local seismic networks. The S-wave picks are performed using polarization analysis and related filters to remove P-wave energy from the seismograms, and utilize STA/LTA and kurtosis detectors in tandem to lock on the phase arrival. The early portions of P waveforms are processed with STA/LTA, kurtosis and skewness detectors for possible first-arriving FZHW. Identification and picking of direct P and FZHW is performed by a multistage algorithm that accounts for basic characteristics (motion polarities, time difference, sharpness and amplitudes) of the two phases. The algorithm is shown to perform well on synthetic seismograms produced by a model with a velocity contrast across the fault, and observed data generated by earthquakes along the Parkfield section of the San Andreas fault and the Hayward fault. The developed techniques can be used for systematic processing of large seismic waveform data sets recorded near major faults.
Seismic Wave Propagation in Layered Viscoelastic Media
Borcherdt, R. D.
2008-12-01
Advances in the general theory of wave propagation in layered viscoelastic media reveal new insights regarding seismic waves in the Earth. For example, the theory predicts: 1) P and S waves are predominantly inhomogeneous in a layered anelastic Earth with seismic travel times, particle-motion orbits, energy speeds, Q, and amplitude characteristics that vary with angle of incidence and hence, travel path through the layers, 2) two types of shear waves exist, one with linear and the other with elliptical particle motions each with different absorption coefficients, and 3) surface waves with amplitude and particle motion characteristics not predicted by elasticity, such as Rayleigh-Type waves with tilted elliptical particle motion orbits and Love-Type waves with superimposed sinusoidal amplitude dependencies that decay exponentially with depth. The general theory provides closed-form analytic solutions for body waves, reflection-refraction problems, response of multiple layers, and surface wave problems valid for any material with a viscoelastic response, including the infinite number of models, derivable from various configurations of springs and dashpots, such as elastic, Voight, Maxwell, and Standard Linear. The theory provides solutions independent of the amount of intrinsic absorption and explicit analytic expressions for physical characteristics of body waves in low-loss media such as the deep Earth. The results explain laboratory and seismic observations, such as travel-time and wide-angle reflection amplitude anomalies, not explained by elasticity or one dimensional Q models. They have important implications for some forward modeling and inverse problems. Theoretical advances and corresponding numerical results as recently compiled (Borcherdt, 2008, Viscoelastic Waves in Layered Media, Cambridge University Press) will be reviewed.
Body and Surface Wave Modeling of Observed Seismic Events Part 3.
1987-05-13
of the Seismic Waves L. and R. across Australia, Nature, vol. 180, pp. 495, 1957. -116- Bollinger , G. A., Attenuation of the L. Phases and... Paris , FRANCE Reston, VA 22092 Dr. Pierre Hechler Dr. Frode Ringdal Societe Radiomana NTNF/NORSAR 27, Rue Claude Bernard P.O. Box 51 75005, Paris , FRANCE...5- I% ~~ ~ .P.. .P K *- ~~ ~ 6 ’*P K Ph. K Dr. G.A. Bollinger Dr. Nuawia Barazangi Department of Geological Sciences Geological Sciences Virginia
Korneev, Valeri A [LaFayette, CA
2009-05-05
The detailed analysis of cross well seismic data for a gas reservoir in Texas revealed two newly detected seismic wave effects, recorded approximately 2000 feet above the reservoir. A tube-wave (150) is initiated in a source well (110) by a source (111), travels in the source well (110), is coupled to a geological feature (140), propagates (151) through the geological feature (140), is coupled back to a tube-wave (152) at a receiver well (120), and is and received by receiver(s) (121) in either the same (110) or a different receiving well (120). The tube-wave has been shown to be extremely sensitive to changes in reservoir characteristics. Tube-waves appear to couple most effectively to reservoirs where the well casing is perforated, allowing direct fluid contact from the interior of a well case to the reservoir.
Body and Surface Wave Modeling of Observed Seismic Events Part 1.
1987-05-11
1977), Nakanishi et al. (1977), and Mantovani (1978) considered S., Stephens and Isacks (1977) considered the transverse component of S., and Cansi and...parallel to the strike of the Andes. They also observed conversion of Oceanic S, to L. in areas of crustal thickening. Isacks and Stephens (1975) also...Center for Seismic Studies P.O. box 51 1300 North 17th Street N-2007 Kjeller, NORWAY Suite 1450 Arlington, VA 22209-2308 Dr. Carl Newton Los Alamos
Shear-wave anisotropy reveals pore fluid pressure-induced seismicity in the U.S. midcontinent.
Nolte, Keith A; Tsoflias, George P; Bidgoli, Tandis S; Watney, W Lynn
2017-12-01
Seismicity in the U.S. midcontinent has increased by orders of magnitude over the past decade. Spatiotemporal correlations of seismicity to wastewater injection operations have suggested that injection-related pore fluid pressure increases are inducing the earthquakes. We present direct evidence linking earthquake occurrence to pore pressure increase in the U.S. midcontinent through time-lapse shear-wave ( S -wave) anisotropy analysis. Since the onset of the observation period in 2010, the orientation of the fast S -wave polarization has flipped from inline with the maximum horizontal stress to inline with the minimum horizontal stress, a change known to be associated with critical pore pressure buildup. The time delay between fast and slow S -wave arrivals exhibits increased variance through time, which is common in critical pore fluid settings. Near-basement borehole fluid pressure measurements indicate pore pressure increase in the region over the earthquake monitoring period.
Comte, D.; Carrizo, D.; Roecker, S. W.; Peyrat, S.; Arriaza, R.; Chi, R. K.; Baeza, S.
2015-12-01
Partly in anticipation of an imminent megathrust earthquake, a significant amount of seismic data has been collected over the past several years in northern Chile by local deployments of seismometers. In this study we generate elastic wavespeed images of the crust and upper mantle using a combination of body wave arrival times and surface wave dispersion curves. The body wave data set consists of 130000 P and 108000 S wave arrival times generated by 12000 earthquakes recorded locally over a period of 25 years by networks comprising about 360 stations. The surface wave data set consists of Rayleigh wave dispersion curves determined from ambient noise recorded by 60 broad band stations from three different networks over a period of three years. Transit time biases due to an uneven distribution of noise were estimated using a technique based on that of Yao and van der Hilst (2009) and found to be as high as 5% for some station pairs. We jointly invert the body and surface wave observations to both improve the overall resolution of the crustal images and reduce the trade-off between shallow and deep structures in the images of the subducted slab. Of particular interest in these images are three regions of anomalous Vp/Vs: (1) An extensive zone of low Vp/Vs (1.68) correlates with trench-parallel magmatic belts emplaced in the upper continental crust. In the region of the coast and continental slope, low Vp/Vs corresponds to batholithic structures in the Jurassic-Cretaceous magmatic arc. Between the central depression and Domeyko Cordillera, low Vp/Vs correlates with the distribution of magmatic arcs of Paleocene-Oligocene and Eocene-Oligocene age. Low Vp/Vs also correlates with the location of the Mejillones Peninsula. (2) A region of high Vp/Vs occurs in what is most likely the serpentinized wedge of the subduction zone. (3) An additional zone of low Vp/Vs is located in the middle of the double seismic zone at depths of 90-110 km. This region may exist all along the
Vallée, M.; Charléty, J.; Ferreira, A. M. G.; Delouis, B.; Vergoz, J.
2011-01-01
Accurate and fast magnitude determination for large, shallow earthquakes is of key importance for post-seismic response and tsumami alert purposes. When no local real-time data are available, which is today the case for most subduction earthquakes, the first information comes from teleseismic body waves. Standard body-wave methods give accurate magnitudes for earthquakes up to Mw= 7-7.5. For larger earthquakes, the analysis is more complex, because of the non-validity of the point-source approximation and of the interaction between direct and surface-reflected phases. The latter effect acts as a strong high-pass filter, which complicates the magnitude determination. We here propose an automated deconvolutive approach, which does not impose any simplifying assumptions about the rupture process, thus being well adapted to large earthquakes. We first determine the source duration based on the length of the high frequency (1-3 Hz) signal content. The deconvolution of synthetic double-couple point source signals—depending on the four earthquake parameters strike, dip, rake and depth—from the windowed real data body-wave signals (including P, PcP, PP, SH and ScS waves) gives the apparent source time function (STF). We search the optimal combination of these four parameters that respects the physical features of any STF: causality, positivity and stability of the seismic moment at all stations. Once this combination is retrieved, the integration of the STFs gives directly the moment magnitude. We apply this new approach, referred as the SCARDEC method, to most of the major subduction earthquakes in the period 1990-2010. Magnitude differences between the Global Centroid Moment Tensor (CMT) and the SCARDEC method may reach 0.2, but values are found consistent if we take into account that the Global CMT solutions for large, shallow earthquakes suffer from a known trade-off between dip and seismic moment. We show by modelling long-period surface waves of these events that
Simulations of Seismic Wave Propagation on Mars
Bozdağ, Ebru; Ruan, Youyi; Metthez, Nathan; Khan, Amir; Leng, Kuangdai; van Driel, Martin; Wieczorek, Mark; Rivoldini, Attilio; Larmat, Carène S.; Giardini, Domenico; Tromp, Jeroen; Lognonné, Philippe; Banerdt, Bruce W.
2017-10-01
We present global and regional synthetic seismograms computed for 1D and 3D Mars models based on the spectral-element method. For global simulations, we implemented a radially-symmetric Mars model with a 110 km thick crust (Sohl and Spohn in J. Geophys. Res., Planets 102(E1):1613-1635, 1997). For this 1D model, we successfully benchmarked the 3D seismic wave propagation solver SPECFEM3D_GLOBE (Komatitsch and Tromp in Geophys. J. Int. 149(2):390-412, 2002a; 150(1):303-318, 2002b) against the 2D axisymmetric wave propagation solver AxiSEM (Nissen-Meyer et al. in Solid Earth 5(1):425-445, 2014) at periods down to 10 s. We also present higher-resolution body-wave simulations with AxiSEM down to 1 s in a model with a more complex 1D crust, revealing wave propagation effects that would have been difficult to interpret based on ray theory. For 3D global simulations based on SPECFEM3D_GLOBE, we superimposed 3D crustal thickness variations capturing the distinct crustal dichotomy between Mars' northern and southern hemispheres, as well as topography, ellipticity, gravity, and rotation. The global simulations clearly indicate that the 3D crust speeds up body waves compared to the reference 1D model, whereas it significantly changes surface waveforms and their dispersive character depending on its thickness. We also perform regional simulations with the solver SES3D (Fichtner et al. Geophys. J. Int. 179:1703-1725, 2009) based on 3D crustal models derived from surface composition, thereby addressing the effects of various distinct crustal features down to 2 s. The regional simulations confirm the strong effects of crustal variations on waveforms. We conclude that the numerical tools are ready for examining more scenarios, including various other seismic models and sources.
Body and Surface Wave Modeling of Observed Seismic Events. Part 2.
1987-05-12
Claude Bernard Mail Stop 928 National Center 75005, Paris , FRANCE Reston, VA 22092 Dr. Pierre Mechler Dr. Frode Ringdal Societe Radiomana NTNF/NORSAR...27, Rue Claude Bernard P.O. Box 51 75005, Paris , FRANCE N-2007 Kjeller, ORIJAY Mr. Jack Kurphy Dr. George H. Rothe S-CUBED Chief, Research Division...47907 -5- Dr. G.A. Bollinger Dr. Muawia Barazaiigi Department of Geological Sciences Geological Sciences Virginia Polytechnical Institute Cornell
1987-03-01
Massinon Dr. Frode Ringdal Societe Radiomana NTNF/NORSAR 27, Rue Claude Bernard P.O. Box 51 75005, Paris , FRANCE N-2007 Kjeller, NORWAY Dr. George H... Paris , FRANCE Applications Center Patrick AFB, Florida 32925-6001 Mr. Jack Murphy S-CUBED Dr. Alan S. Ryall, Jr. Reston Geophysics Office Center for...West Lafayette, IN 47907 -5- Dr. G.A. Bollinger Dr. Muawia Barazangi Department of Geological Sciences Geological Sciences Virginia Polytechnical
Czech Academy of Sciences Publication Activity Database
Plomerová, Jaroslava; Babuška, Vladislav; Vecsey, Luděk; Kouba, Daniel
2002-01-01
Roč. 360, 1/4 (2002), s. 89-114 ISSN 0040-1951 R&D Projects: GA AV ČR IAA3012908; GA ČR GV205/98/K004 Institutional research plan: CEZ:AV0Z3012916 Keywords : shear-wave splitting * seismic anisotropy * subcrustal lithosphere Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.409, year: 2002
Thangraj, J. S.; Quiros, D.; Pulliam, J.
2017-12-01
that exhibit dispersive behavior, which we interpret to be Rayleigh waves. Current efforts are focused on extending the spatial range of the airgun-generated seismic energy further inland (> 70 km) by creating more VSG, to obtain a body wave velocity model along the transect. Similarly, we are inverting the Rayleigh waves in the VSG to obtain a shear wave velocity model.
Extension of Seismic Scanning Tunneling Macroscope to Elastic Waves
Tarhini, Ahmad
2017-11-06
The theory for the seismic scanning tunneling macroscope is extended from acoustic body waves to elastic body-wave propagation. We show that, similar to the acoustic case, near-field superresolution imaging from elastic body waves results from the O(1/R) term, where R is the distance between the source and near-field scatterer. The higher-order contributions R−n for n>1 are cancelled in the near-field region for a point source with normal stress.
1976-08-01
in 1976) ESTPirmiRA DE LOS ANDES CENTRALES A TRAVES DE REST DUOS Y ATENUACTON DE ONDAS P y S. Tesis de Grado , Universidad »«avor de San Andres...ES- PESOR DE LA CORTEZA TERPESTRE MEDTANTE DTSPERRTON DE ONDAS PAYLETQf. Tests de Grado , Universidad Mayor de San Andres, Rodrfquez, Ren^ and Vega
Huang, Y.; Yao, H.; Wu, F. T.; Liang, W.; Huang, B.; Lin, C.; Wen, K.
2013-12-01
Although orogeny seems to have stopped in western Taiwan large and small earthquakes do occur in the Taiwan Strait. Limited studies have focused on this region before and were barely within reach for comprehensive projects like TAICRUST and TAIGER for logistical reasons; thus, the overall crustal structures of the Taiwan Strait remain unknown. Time domain empirical Green's function (TDEGF) from ambient seismic noise to determine crustal velocity structure allows us to study an area using station pairs on its periphery. This research aims to resolve 1-D average crustal and upper mantle S-wave velocity (Vs) structures alone paths of several broadband station-pairs across the Taiwan Strait; 5-120 s Rayleigh wave phase velocity dispersion data derived by combining TDEGF and traditional surface wave two-station method (TS). The average Vs structures show significant differences in the upper 15 km as expected. In general, the highest Vs are observed in the coastal area of Mainland China and the lowest Vs appear along the southwest offshore of the Taiwan Island; they differ by about 0.6-1.1 km/s. For different parts of the Strait, the Vs are lower in the middle by about 0.1-0.2 km/s relative to those in the northern and southern parts. The overall crustal thickness is approximately 30 km, much thinner and less variable than under the Taiwan Island.
Examples of law of seismic wave attenuation
Czech Academy of Sciences Publication Activity Database
Kaláb, Zdeněk; Pandula, B.; Stolárik, Martin; Kondela, J.
2013-01-01
Roč. 52, č. 3 (2013), s. 387-390 ISSN 0543-5846 R&D Projects: GA ČR(CZ) GA105/09/1415 Institutional support: RVO:68145535 Keywords : blasting operation * vibration velocity * seismic wave attenuation Subject RIV: DH - Mining, incl. Coal Mining Impact factor: 0.755, year: 2013 http://public.carnet.hr/metalurg/Metalurgija/2013_vol_52/No_3/MET_52_3_387-390_Kalab.pdf
Attenuation Characteristics of High Frequency Seismic Waves in Southern India
Sivaram, K.; Utpal, Saikia; Kanna, Nagaraju; Kumar, Dinesh
2017-07-01
We present a systematic study of seismic attenuation and its related Q structure derived from the spectral analysis of P-, S-waves in the southern India. The study region is separated into parts of EDC (Eastern Dharwar Craton), Western Dharwar Craton (WDC) and Southern Granulite Terrain (SGT). The study is carried out in the frequency range 1-20 Hz, using a single-station spectral ratio technique. We make use of about 45 earthquakes, recorded in a network of about 32 broadband 3-component seismograph-stations, having magnitudes ( M L) varying from 1.6 to 4.5, to estimate the average seismic body wave attenuation quality factors; Q P and Q S. Their estimated average values are observed to be fitting to the power law form of Q = Q 0 f n . The averaged power law relations for Southern Indian region (as a whole) are obtained as Q P = (95 ± 1.12) f (1.32±0.01); Q S = (128 ± 1.84) f (1.49±0.01). Based on the stations and recorded local earthquakes, for parts of EDC, WDC and SGT, the average power law estimates are obtained as: Q P = (97 ± 5) f (1.40±0.03), Q S = (116 ± 1.5) f (1.48±0.01) for EDC region; Q P = (130 ± 7) f (1.20±0.03), Q S = (103 ± 3) f (1.49±0.02) for WDC region; Q P = (68 ± 2) f (1.4±0.02), Q S = (152 ± 6) f (1.48±0.02) for SGT region. These estimates are weighed against coda Q ( Q C) estimates, using the coda decay technique, which is based on a weak backscattering of S-waves. A major observation in the study of body wave analysis is the low body wave Q ( Q 0 0.5) and Q S/ Q P ≫ 1, suggesting lateral stretches of dominant scattering mode of seismic wave propagation. This primarily could be attributed to possible thermal anomalies and spread of partially fluid-saturated rock-masses in the crust and upper mantle of the southern Indian region, which, however, needs further laboratory studies. Such physical conditions might partly be correlated to the active seismicity and intraplate tectonism, especially in SGT and EDC regions, as per the
Numerical simulations of passing seismic waves at the Larderello-Travale Geothermal Field, Italy
Lupi, Matteo; Fuchs, Florian; Saenger, Erik H.
2017-06-01
Passing seismic waves released by large-magnitude earthquakes may affect geological systems located thousands of miles far from the epicenter. The M9.0 Tohoku earthquake struck on 11 March 2011 in Japan. We detected local seismic activity at the Larderello-Travale geothermal field, Italy, coinciding with the maximum amplitudes of the Rayleigh waves generated by the Tohoku earthquake. We suggest that the earthquakes were triggered by passing Rayleigh waves that induced locally a maximum vertical displacement of approximately 7.5 mm (for waves with period of 100 s). The estimated dynamic stress was about 8 kPa for a measured peak ground velocity of 0.8 mm/s. Previous similar observations pointed out local seismicity at the Larderello-Travale Geothermal Field triggered by the 2012 Mw5.9 Po Plain earthquake. We conducted forward numerical modeling to investigate the effects caused by passing P, S, Love, and Rayleigh waves through the known velocity structure of the geothermal field. Results indicate that maximum displacements focus differently when considering body or surface waves, with displacement values being higher within the first 2 km of depth. The focusing of the displacement below 3 km seems to be strongly controlled by the velocity structure of the Larderello-Travale geothermal field. We propose that seismic activity triggered by passing seismic waves may be related to a clock-advancing mechanism for local seismic events that may have occurred in any case. Furthermore, our analysis shows that local anisotropies in the velocity structure of the Larderello-Travale geothermal field (possibly linked to compartments of elevated pore pressures) strongly control the reactivation of regions of the geothermal field affected by passing seismic waves.
Tutorial review of seismic surface waves' phenomenology
Levshin, A. L.; Barmin, M. P.; Ritzwoller, M. H.
2018-03-01
In recent years, surface wave seismology has become one of the leading directions in seismological investigations of the Earth's structure and seismic sources. Various applications cover a wide spectrum of goals, dealing with differences in sources of seismic excitation, penetration depths, frequency ranges, and interpretation techniques. Observed seismic data demonstrates the great variability of phenomenology which can produce difficulties in interpretation for beginners. This tutorial review is based on the many years' experience of authors in processing and interpretation of seismic surface wave observations and the lectures of one of the authors (ALL) at Workshops on Seismic Wave Excitation, Propagation and Interpretation held at the Abdus Salam International Center for Theoretical Physics (Trieste, Italy) in 1990-2012. We present some typical examples of wave patterns which could be encountered in different applications and which can serve as a guide to analysis of observed seismograms.
Seismic Wave Propagation on the Tablet Computer
Emoto, K.
2015-12-01
Tablet computers widely used in recent years. The performance of the tablet computer is improving year by year. Some of them have performance comparable to the personal computer of a few years ago with respect to the calculation speed and the memory size. The convenience and the intuitive operation are the advantage of the tablet computer compared to the desktop PC. I developed the iPad application of the numerical simulation of the seismic wave propagation. The numerical simulation is based on the 2D finite difference method with the staggered-grid scheme. The number of the grid points is 512 x 384 = 196,608. The grid space is 200m in both horizontal and vertical directions. That is the calculation area is 102km x 77km. The time step is 0.01s. In order to reduce the user waiting time, the image of the wave field is drawn simultaneously with the calculation rather than playing the movie after the whole calculation. P and S wave energies are plotted on the screen every 20 steps (0.2s). There is the trade-off between the smooth simulation and the resolution of the wave field image. In the current setting, it takes about 30s to calculate the 10s wave propagation (50 times image updates). The seismogram at the receiver is displayed below of the wave field updated in real time. The default medium structure consists of 3 layers. The layer boundary is defined by 10 movable points with linear interpolation. Users can intuitively change to the arbitrary boundary shape by moving the point. Also users can easily change the source and the receiver positions. The favorite structure can be saved and loaded. For the advance simulation, users can introduce the random velocity fluctuation whose spectrum can be changed to the arbitrary shape. By using this application, everyone can simulate the seismic wave propagation without the special knowledge of the elastic wave equation. So far, the Japanese version of the application is released on the App Store. Now I am preparing the
Coupled seismic and electromagnetic wave propagation
Schakel, M.D.
2011-01-01
Coupled seismic and electromagnetic wave propagation is studied theoretically and experimentally. This coupling arises because of the electrochemical double layer, which exists along the solid-grain/fluid-electrolyte boundaries of porous media. Within the double layer, charge is redistributed,
GyPSuM: A Detailed Tomographic Model of Mantle Density and Seismic Wave Speeds
Energy Technology Data Exchange (ETDEWEB)
Simmons, N A; Forte, A M; Boschi, L; Grand, S P
2010-03-30
GyPSuM is a tomographic model fo mantle seismic shear wave (S) speeds, compressional wave (P) speeds and detailed density anomalies that drive mantle flow. the model is developed through simultaneous inversion of seismic body wave travel times (P and S) and geodynamic observations while considering realistic mineral physics parameters linking the relative behavior of mantle properties (wave speeds and density). Geodynamic observations include the (up to degree 16) global free-air gravity field, divergence of the tectonic plates, dynamic topography of the free surface, and the flow-induced excess ellipticity of the core-mantle boundary. GyPSuM is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution. Models of the density field from Earth's free oscillations have provided great insight into the density configuration of the mantle; but are limited to very long-wavelength solutions. Alternatively, simply scaling higher resolution seismic images to density anomalies generates density fields that do not satisfy geodynamic observations. The current study provides detailed density structures in the mantle while directly satisfying geodynamic observations through a joint seismic-geodynamic inversion process. Notable density field observations include high-density piles at the base of the superplume structures, supporting the fundamental results of past normal mode studies. However, these features are more localized and lower amplitude than past studies would suggest. When we consider all seismic anomalies in GyPSuM, we find that P and S-wave speeds are strongly correlated throughout the mantle. However, correlations between the high-velocity S zones in the deep mantle ({approx} 2000 km depth) and corresponding P-wave anomalies are very low suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies. Nevertheless, they argue that temperature variations are
Polom, U.; Guenther, A.; Arsyad, I.; Wiyono, P.; Krawczyk, C. M.
2009-12-01
After the big 2004 Sumatra-Andaman earthquake, the massive reconstruction activities in the Aceh province (Northern Sumatra) were promoted by the Republic of Indonesia and the Federal Ministry of Economic Cooperation and Development. The aims of the project MANGEONAD (Management of Georisk Nanggroe Aceh Darussalam). are to establish geoscientific on the ground support for a sustainable development and management of save building constructions, lifelines, infrastructure and also natural resources. Therefore, shallow shear-wave reflection seismics was applied in close combination to engineering geology investigations in the period between 2005-2009 since depth and internal structure of the Krueng Aceh River delta (mainly young alluvial sediments) were widely unknown. Due to the requirements in the densely populated Banda Aceh region, lacking also traffic infrastructure, a small and lightweight engineering seismic setup of high mobility and high subsurface resolution capability was chosen. The S-wave land streamer system with 48 channels was applied successfully together with the ELVIS vibratory source using S- and P-waves on paved roads within the city of Banda Aceh. The performance of the S-wave system enabled the detailed seismic investigation of the shallow subsurface down to 50-150 m depth generating shaking frequencies between 20 Hz to 200 Hz. This also provides depth information extending the maximum depths of boreholes and Standard Penetrometer Testings (SPT), which could only be applied to max. 20 m depth. To integrate the results gained from all three methods, and further to provide a fast statistical analysis tool for engineering use, the Information System Engineering Geology (ISEG, BGR) was developed. This geospatial information tool includes the seismic data, all borehole information, geotechnical SPT and laboratory results from samples available in the investigation area. Thereby, the geotechnical 3D analysis of the subsurface units is enabled. The
Models for seismic wave propagation in periodically layered porous media
Kudarova, A.; Van Dalen, K.N.; Drijkoningen, G.G.
2014-01-01
Several models are discussed for seismic wave propagation in periodically layered poroelastic media where layers represent mesoscopic-scale heterogeneities that are larger than the pore and grain sizes but smaller than the wavelength. The layers behave according to Biot’s theory. Wave propagation
Li, Wei; Chen, Yun; Yuan, Xiaohui; Schurr, Bernd; Mechie, James; Oimahmadov, Ilhomjon; Fu, Bihong
2018-01-01
The Pamir has experienced more intense deformation and shortening than Tibet, although it has a similar history of terrane accretion. Subduction as a primary way to accommodate lithospheric shortening beneath the Pamir has induced the intermediate-depth seismicity, which is rare in Tibet. Here we construct a 3D S-wave velocity model of the lithosphere beneath the Pamir by surface wave tomography using data of the TIPAGE (Tien Shan-Pamir Geodynamic program) and other seismic networks in the area. We imaged a large-scale low velocity anomaly in the crust at 20-50 km depth in the Pamir overlain by a high velocity anomaly at a depth shallower than 15 km. The high velocity anomalies colocate with exposed gneiss domes, which may imply a similar history of crustal deformation, partial melting and exhumation in the hinterland, as has occurred in the Himalaya/Tibet system. At mantle depths, where the intermediate-depth earthquakes are located, a low velocity zone is clearly observed extending to about 180 km and 150 km depth in the Hindu Kush and eastern Pamir, respectively. Moreover, the geometry of the low-velocity anomaly suggests that lower crustal material has been pulled down into the mantle by the subducting Asian and Indian lithospheric mantle beneath the Pamir and Hindu Kush, respectively. Metamorphic processes in the subducting lower crust may cause the intermediate-depth seismicity down to 150-180 km depth beneath the Pamir and Hindu Kush. We inverted focal mechanisms in the seismic zone for the stress field. Differences in the stress field between the upper and lower parts of the Indian slab imply that subduction and detachment of the Indian lithosphere might cause intense seismicity associated with the thermal shear instability in the deep Hindu Kush.
Attenuation of seismic waves in Central Egypt
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Mamdouh Abbas Morsy
2013-06-01
Full Text Available Attenuation of seismic waves in central Egypt had never been studied before. The results of the research on the seismic attenuation are based upon the information collected by the seismological network from 1998 to 2011. 855 earthquakes were selected from the Egyptian seismological catalog, with their epicenter distances between 15 and 150 km, their magnitudes ranging from 2 and 4.1 and focal depths reaching up to 30 km. The first systematic study of attenuation derived from the P-, S- and coda wave in the frequency range 1–24 Hz is presented. In the interpretation of the results both single and multiple scattering in a half space are considered. The single scattering model proposed by Sato (1977 was used. Two methods, the coda (Qc and the Multiple Lapse Time Window (MLTW method are used. The aim of this study is to validate these interpretations in the region and to try to identify the effects of attenuation due to intrinsic (Qi and scattering attenuation (Qsc. The mean Qc value calculated was Qc = (39 ± 1f1.0±0.009. The average Qc at 1.5 Hz is (53 ± 6 and Qc = (900 ± 195 at 24 Hz with Qo ranging between 23 and 107, where η ranging between 0.9 and 1.3. The quality factor (Q was estimated from spectra of P- and S-waves by applying a spectral ratio technique. The results show variations in Qp and QS as a function of frequency, according to the power law Q = 56η1.1. The seismic albedo is 0.7 at all stations and it mean that the earthquake activity is due to tectonic origin. The attenuation and frequency dependency for different paths and the correlation of the results with the geotectonic of the region are presented. The Qc values were calculated and correlated with the geology and tectonics of the area. The relatively low Qo and the high frequency dependency agree with the values of a region characterized by a low tectonic activity and vise versa.
Experiments on seismic metamaterials: molding surface waves.
Brûlé, S; Javelaud, E H; Enoch, S; Guenneau, S
2014-04-04
Materials engineered at the micro- and nanometer scales have had a tremendous and lasting impact in photonics and phononics. At much larger scales, natural soils civil engineered at decimeter to meter scales may interact with seismic waves when the global properties of the medium are modified, or alternatively thanks to a seismic metamaterial constituted of a mesh of vertical empty inclusions bored in the initial soil. Here, we show the experimental results of a seismic test carried out using seismic waves generated by a monochromatic vibrocompaction probe. Measurements of the particles' velocities show a modification of the seismic energy distribution in the presence of the metamaterial in agreement with numerical simulations using an approximate plate model. For complex natural materials such as soils, this large-scale experiment was needed to show the practical feasibility of seismic metamaterials and to stress their importance for applications in civil engineering. We anticipate this experiment to be a starting point for smart devices for anthropic and natural vibrations.
Experiments on Seismic Metamaterials: Molding Surface Waves
Brûlé, S.; Javelaud, E. H.; Enoch, S.; Guenneau, S.
2014-04-01
Materials engineered at the micro- and nanometer scales have had a tremendous and lasting impact in photonics and phononics. At much larger scales, natural soils civil engineered at decimeter to meter scales may interact with seismic waves when the global properties of the medium are modified, or alternatively thanks to a seismic metamaterial constituted of a mesh of vertical empty inclusions bored in the initial soil. Here, we show the experimental results of a seismic test carried out using seismic waves generated by a monochromatic vibrocompaction probe. Measurements of the particles' velocities show a modification of the seismic energy distribution in the presence of the metamaterial in agreement with numerical simulations using an approximate plate model. For complex natural materials such as soils, this large-scale experiment was needed to show the practical feasibility of seismic metamaterials and to stress their importance for applications in civil engineering. We anticipate this experiment to be a starting point for smart devices for anthropic and natural vibrations.
Rajendra Prasad, B.; Behera, Laxmidhar; Rao, P. Koteswara
2006-07-01
We present a 2-D tomographic P and S wave velocity (Vp and Vs) image with Vp/Vs ratios along N-S trending 220 km long deep seismic profile acquired in 2005, which traverses across major shear and tectonically disturbed zones in southern granulite terrain (SGT), India. The 2-D velocity model constrained down to maximum 8 km depth shows velocity anomalies (>0.2 km/s) beneath major shear zones with good spatial resolution (>0.05 km/s). The presence of high Vp (6.3-6.5 km/s), Vs (3.5-3.8 km/s), Vp/Vs (>1.75) and Poisson's ratio (0.25-0.29) indicate significant compositional changes of rocks at shallow depths (0.5 to 8 km) reveal rapid crustal exhumation of mid to lower crustal rocks. This crustal exhumation could be responsible due to Pan-African tectonothermal activity during Neoproterozoic period.
In Situ Observations of Seismic Wave Propagation
Hudson, Kenneth Stewart
Instrumented geotechnical field sites are designed to capture the infrequent but critically important in situ case histories of ground response, deformation, and liquefaction during significant earthquakes that generate high intensity ground shaking and large strains. The University of California at Santa Barbara has been monitoring densely instrumented geotechnical array field sites for almost three decades, with continuous recording now for more than a decade. When seismic waves travel into soil with sufficiently large ground motions, the soil behaves nonlinearly meaning the shear modulus of the material decreases from the linear value observed during weak ground motions. The degraded shear modulus can continue to affect a site for a period of time by changing the soil response during smaller ground motions after the large event. Decreased shear modulus is inferred when a decrease of shear wave velocity between two sensors in a vertical downhole array is observed. This velocity is calculated by measuring the difference in shear wave arrival times between the sensors using normalized cross correlation. The trend of decreasing shear wave velocity with increasing peak ground acceleration is observed at multiple geotechnical array field sites. The length of time the decreased velocity remains following stronger shaking is analyzed using more than 450 events over more than a decade at the Wildlife Liquefaction Array (WLA). Using both monthly and yearly velocity averages between sensors, there is evidence that suggests the shear wave velocity remains low over a period of months following larger significant shaking events at the site. In addition, at WLA there is evidence that the decrease in shear wave velocity can be detected at ground motion levels as low as 20 cm/s2. Additionally at the Garner Valley Downhole Array, a permanent cross-hole experiment is used to measure velocity changes in the soil with changing water table height. An underground hammer source swings
Frequency-Dependent Seismic Waves in Fluid-Saturated Fractured Rock
Korneev, V. A.; Goloshubin, G.
2015-12-01
Fractures are the natural and essential elements of rock. Fracture systems are the most important features that define rock permeability and strength, as well as their anisotropy properties. Recent advancement in induced fracturing is a core part of the gas/oil shale technology, where fracture monitoring and control became a special topic of interest. Krauklis wave (K-wave) is the result of interaction between a fluid mass and elasticity of fracture walls, and it propagates primarily along the fracture systems in the fluid. At the fracture tips and fracture intersections it partially converts into the body waves. It is quite clear that incorporation of K-waves in a theory of wave propagation in fractured rock is one of the most important problems to solve for understanding of their seismic properties. One of the most fundamental properties of fractured rock is a fractal fracture distribution and it is rarely, if ever, taken into account in existing wave propagation theories. However, this property exists on a widest variety of scales and in particular reveals itself in a form of Gutenberg-Richter Law experimentally proven, starting from laboratory measurements and up to the global seismicity. We computed P and S-wave velocities of the rock containing fluid (and proppant) filled fractures, considering the effect of extremely slow and dispersive wave propagation within individual fractures. This was made possible by introducing the concept of "effective fracture-wave volume," and by evaluating the elastic constants of rock containing a complex, fractal network of fractures. These velocities were used to compute seismic waves reflected normally from a fractured reservoir. We demonstrate that by taking into account the Krauklis wave phenomenon for the fractally distributed fluid-filled fractures, it is possible to explain the observed low-frequency anomalies above the underground natural reservoirs. These anomalies include increase of amplitude and a phase delay of
Hirata, Naoshi; Sakai, Shin'ichi; Nakagawa, Shigeki; Panayotopoulos, Yannis; Ishikawa, Masahiro; Sato, Hiroshi; Kasahara, Keiji; Kimura, Hisanor; Honda, Ryou
2013-04-01
The Central Disaster Management Council of Japan estimates the next great M7+ earthquake in the Tokyo metropolitan region will cause 11,000 fatalities and 112 trillion yen (1 trillion US) economic loss at worst case if it occur beneath northern Tokyo bay with M7.3. However, the estimate is based on a source fault model by conventional studies about the PSP geometry. To evaluate seismic hazard due to the great quake we need to clarify the geometry of PSP and also the Pacific palate (PAP) that subducs beneath PSP. We identify those plates with use of seismic tomography and available deep seismic reflection profiling and borehole data in southern Kanto area. We deployed about 300 seismic stations in the greater Tokyo urban region under the Special Project for Earthquake Disaster Mitigation in Tokyo Metropolitan Area. We obtain clear P- and S- wave velocity (Vp and Vs) and Q tomograms which show a clear image of PSP and PAP. A depth to the top of PSP, 20 to 30 kilometer beneath northern part of Tokyo bay, is about 10 km shallower than previous estimates based on the distribution of seismicity (Ishida, 1992). This shallower plate geometry changes estimations of strong ground motion for seismic hazards analysis within the Tokyo region. Based on elastic wave velocities of rocks and minerals, we interpreted the tomographic images as petrologic images. Tomographic images revealed the presence of two stepwise velocity increase of the top layer of the subducting PSP slab. Rock velocity data reveals that subducting PSP crust transforms from blueschists to amphibolites at depth of 30km and amphibolites to eclogites at depth of 50km, which suggest that dehydration reactions occurs in subducting crust of basaltic compositions during prograde metamorphism and water is released from the subducting PSP crust. Tomograms show evidence for a low-velocity zone (LVZ) beneath the area just north of Tokyo bay. A Q tomogram show a low Q zone in PSP slab. We interpret the LVZ as a
Bubbles attenuate elastic waves at seismic frequencies
Tisato, Nicola; Quintal, Beatriz; Chapman, Samuel; Podladchikov, Yury; Burg, Jean-Pierre
2016-04-01
The vertical migration of multiphase fluids in the crust can cause hazardous events such as eruptions, explosions, pollution and earthquakes. Although seismic tomography could potentially provide a detailed image of such fluid-saturated regions, the interpretation of the tomographic signals is often controversial and fails in providing a conclusive map of the subsurface saturation. Seismic tomography should be improved considering seismic wave attenuation (1/Q) and the dispersive elastic moduli which allow accounting for the energy lost by the propagating elastic wave. In particular, in saturated media a significant portion of the energy carried by the propagating wave is dissipated by the wave-induced-fluid-flow and the wave-induced-gas-exsolution-dissolution (WIGED) mechanisms. The WIGED mechanism describes how a propagating wave modifies the thermodynamic equillibrium between different fluid phases causing the exsolution and the dissolution of the gas in the liquid, which in turn causes a significant frequency dependent 1/Q and moduli dispersion. The WIGED theory was initially postulated for bubbly magmas but only recently was extended to bubbly water and experimentally demonstrated. Here we report these theory and laboratory experiments. Specifically, we present i) attenuation measurements performed by means of the Broad Band Attenuation Vessel on porous media saturated with water and different gases, and ii) numerical experiments validating the laboratory observations. Finally, we will extend the theory to fluids and to pressure-temperature conditions which are typical of phreatomagmatic and hydrocarbon domains and we will compare the propagation of seismic waves in bubble-free and bubble-bearing subsurface domains. With the present contribution we extend the knowledge about attenuation in rocks which are saturated with multiphase fluid demonstrating that the WIGED mechanism could be extremely important to image subsurface gas plumes.
Seismic rotation waves: basic elements of theory and recording
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P. Palangio
2003-06-01
Full Text Available Returning to the old problem of observed rotation effects, we present the recording system and basic elements of the theory related to the rotation fi eld and its association with seismic waves. There can be many different causes leading to observed/recorded rotation effects; we can group them as follows: generation of micro-displacement motion due to asymmetry of source processes and/or due to interaction between seismic body/surface waves and medium structure; interaction between incident seismic waves and objects situated on the ground surface. New recording techniques and advanced theory of deformation in media with defects and internal (e.g., granular structure make it possible to focus our attention on the fi rst group, related to microdisplacement motion recording, which includes both rotation and twist motions. Surface rotations and twists caused directly by the action of emerging seismic waves on some objects situated on the ground surface are considered here only in the historical aspects of the problem. We present some examples of experimental results related to recording of rotation and twist components at the Ojcow Observatory, Poland, and L'Aquila Observatory, Italy, and we discuss some prospects for further research.
Directory of Open Access Journals (Sweden)
A. E. Vinogradov
2008-01-01
Full Text Available An induction seismic receiver is widely applied in many guarding devices (1К18 «Realiya», PS-75 «Gerb» and others which are used for detection of moving surface objects. The receiver makes it possible to register soil vibrations caused by the object action. An inertial element of such seismic receiver is a cylindrical coil connected with the body by means of two flat springs.The paper proposes a method for calculation of electromotive force (EMF at induction seismic receiver output when it is exposed to seismic Relay wave on the basis of a differential equation for motion of the inertial element with due account of transient processes of forced vibrations and damping. The seismic receiver damping is a coil form where k of the spool, in which surface Foucault currents are induced.Results of modeling and experimental investigations have shown that the proposed methodology for EMF calculation, which is induced in the seismic receiver, allows faithfully to model signals at induction seismic receiver output that can be rather useful for mathematical modeling of surface object motion seismograms.
Seismic shear waves as Foucault pendulum
Snieder, Roel; Sens-Schönfelder, Christoph; Ruigrok, Elmer; Shiomi, Katsuhiko
2016-03-01
Earth's rotation causes splitting of normal modes. Wave fronts and rays are, however, not affected by Earth's rotation, as we show theoretically and with observations made with USArray. We derive that the Coriolis force causes a small transverse component for P waves and a small longitudinal component for S waves. More importantly, Earth's rotation leads to a slow rotation of the transverse polarization of S waves; during the propagation of S waves the particle motion behaves just like a Foucault pendulum. The polarization plane of shear waves counteracts Earth's rotation and rotates clockwise in the Northern Hemisphere. The rotation rate is independent of the wave frequency and is purely geometric, like the Berry phase. Using the polarization of ScS and ScS2 waves, we show that the Foucault-like rotation of the S wave polarization can be observed. This can affect the determination of source mechanisms and the interpretation of observed SKS splitting.
Comparison of recent S-wave indicating methods
Hubicka, Katarzyna; Sokolowski, Jakub
2018-01-01
Seismic event consists of surface waves and body waves. Due to the fact that the body waves are faster (P-waves) and more energetic (S-waves) in literature the problem of their analysis is taken more often. The most universal information that is received from the recorded wave is its moment of arrival. When this information is obtained from at least four seismometers in different locations, the epicentre of the particular event can be estimated [1]. Since the recorded body waves may overlap in signal, the problem of wave onset moment is considered more often for faster P-wave than S-wave. This however does not mean that the issue of S-wave arrival time is not taken at all. As the process of manual picking is time-consuming, methods of automatic detection are recommended (these however may be less accurate). In this paper four recently developed methods estimating S-wave arrival are compared: the method operating on empirical mode decomposition and Teager-Kaiser operator [2], the modification of STA/LTA algorithm [3], the method using a nearest neighbour-based approach [4] and the algorithm operating on characteristic of signals' second moments. The methods will be also compared to wellknown algorithm based on the autoregressive model [5]. The algorithms will be tested in terms of their S-wave arrival identification accuracy on real data originating from International Research Institutions for Seismology (IRIS) database.
Seismic waves and earthquakes in a global monolithic model
Roubíček, Tomáš
2018-03-01
The philosophy that a single "monolithic" model can "asymptotically" replace and couple in a simple elegant way several specialized models relevant on various Earth layers is presented and, in special situations, also rigorously justified. In particular, global seismicity and tectonics is coupled to capture, e.g., (here by a simplified model) ruptures of lithospheric faults generating seismic waves which then propagate through the solid-like mantle and inner core both as shear (S) or pressure (P) waves, while S-waves are suppressed in the fluidic outer core and also in the oceans. The "monolithic-type" models have the capacity to describe all the mentioned features globally in a unified way together with corresponding interfacial conditions implicitly involved, only when scaling its parameters appropriately in different Earth's layers. Coupling of seismic waves with seismic sources due to tectonic events is thus an automatic side effect. The global ansatz is here based, rather for an illustration, only on a relatively simple Jeffreys' viscoelastic damageable material at small strains whose various scaling (limits) can lead to Boger's viscoelastic fluid or even to purely elastic (inviscid) fluid. Self-induced gravity field, Coriolis, centrifugal, and tidal forces are counted in our global model, as well. The rigorous mathematical analysis as far as the existence of solutions, convergence of the mentioned scalings, and energy conservation is briefly presented.
Seismic wave interaction with underground cavities
Schneider, Felix M.; Esterhazy, Sofi; Perugia, Ilaria; Bokelmann, Götz
2016-04-01
Realization of the future Comprehensive Nuclear Test Ban Treaty (CTBT) will require ensuring its compliance, making the CTBT a prime example of forensic seismology. Following indications of a nuclear explosion obtained on the basis of the (IMS) monitoring network further evidence needs to be sought at the location of the suspicious event. For such an On-Site Inspection (OSI) at a possible nuclear test site the treaty lists several techniques that can be carried out by the inspection team, including aftershock monitoring and the conduction of active seismic surveys. While those techniques are already well established, a third group of methods labeled as "resonance seismometry" is less well defined and needs further elaboration. A prime structural target that is expected to be present as a remnant of an underground nuclear explosion is a cavity at the location and depth the bomb was fired. Originally "resonance seismometry" referred to resonant seismic emission of the cavity within the medium that could be stimulated by an incident seismic wave of the right frequency and observed as peaks in the spectrum of seismic stations in the vicinity of the cavity. However, it is not yet clear which are the conditions for which resonant emissions of the cavity could be observed. In order to define distance-, frequency- and amplitude ranges at which resonant emissions could be observed we study the interaction of seismic waves with underground cavities. As a generic model for possible resonances we use a spherical acoustic cavity in an elastic full-space. To solve the forward problem for the full elastic wave field around acoustic spherical inclusions, we implemented an analytical solution (Korneev, 1993). This yields the possibility of generating scattering cross-sections, amplitude spectrums and synthetic seismograms for plane incident waves. Here, we focus on the questions whether or not we can expect resonant responses in the wave field scattered from the cavity. We show
Seismic Wave Velocity in Earth's Shallow Core
Alexandrakis, C.; Eaton, D. W.
2008-12-01
Studies of the outer core indicate that it is composed of liquid Fe and Ni alloyed with a ~10% fraction of light elements such as O, S or Si. Recently, unusual features, such as sediment accumulation, immiscible fluid layers or stagnant convection, have been predicted in the shallow core region. Secular cooling and compositional buoyancy drive vigorous convection that sustains the geodynamo, although critical details of light-element composition and thermal regime remain uncertain. Seismic velocity models can provide important constraints on the light element composition, however global reference models, such as Preliminary Reference Earth Model (PREM), IASP91 and AK135 vary significantly in the 200 km below the core-mantle boundary. Past studies of the outermost core velocity structure have been hampered by traveltime uncertainties due to lowermost mantle heterogeneities. The recently published Empirical Transfer Function (ETF) method has been shown to reduce the uncertainty using a waveform stacking approach to improve global observations of SmKS teleseismic waves. Here, we apply the ETF method to achieve a precise top-of-core velocity measurement of 8.05 ± 0.03 km/s. This new model accords well with PREM. Since PREM is based on the adiabatic form of the Adams-Williamson equation, it assumes a well mixed (i.e. homogeneous) composition. This result suggests a lack of heterogeneity in the outermost core due to layering or stagnant convection.
Seismic Wave Propagation in Icy Ocean Worlds
Stähler, Simon C.; Panning, Mark P.; Vance, Steven D.; Lorenz, Ralph D.; vanÂ Driel, Martin; Nissen-Meyer, Tarje; Kedar, Sharon
2018-01-01
Seismology was developed on Earth and shaped our model of the Earth's interior over the twentieth century. With the exception of the Philae lander, all in situ extraterrestrial seismological effort to date was limited to other terrestrial planets. All have in common a rigid crust above a solid mantle. The coming years may see the installation of seismometers on Europa, Titan, and Enceladus, so it is necessary to adapt seismological concepts to the setting of worlds with global oceans covered in ice. Here we use waveform analyses to identify and classify wave types, developing a lexicon for icy ocean world seismology intended to be useful to both seismologists and planetary scientists. We use results from spectral-element simulations of broadband seismic wavefields to adapt seismological concepts to icy ocean worlds. We present a concise naming scheme for seismic waves and an overview of the features of the seismic wavefield on Europa, Titan, Ganymede, and Enceladus. In close connection with geophysical interior models, we analyze simulated seismic measurements of Europa and Titan that might be used to constrain geochemical parameters governing the habitability of a sub-ice ocean.
Array processing for seismic surface waves
International Nuclear Information System (INIS)
Marano, S.
2013-01-01
This dissertation submitted to the Swiss Federal Institute of Technology ETH in Zurich takes a look at the analysis of surface wave properties which allows geophysicists to gain insight into the structure of the subsoil, thus avoiding more expensive invasive techniques such as borehole drilling. This thesis aims at improving signal processing techniques for the analysis of surface waves in various directions. One main contribution of this work is the development of a method for the analysis of seismic surface waves. The method also deals with the simultaneous presence of multiple waves. Several computational approaches to minimize costs are presented and compared. Finally, numerical experiments that verify the effectiveness of the proposed cost function and resulting array geometry designs are presented. These lead to greatly improved estimation performance in comparison to arbitrary array geometries
Yasui, M.; Matsumoto, E.; Arakawa, M.; Matsue, K.; Kobayashi, N.
2014-07-01
Introduction: A seismic wave survey is a direct method to investigate the sub-surface structures of solid bodies, so we measured and analyzed these seismic waves propagating through these interiors. Earthquake and Moonquake are the only two phenomena that have been observed to explore these interiors until now, while the future surveys on the other bodies, (solid planets and/or asteroids) are now planned. To complete a seismic wave survey during the mission period, an artificial method that activates the seismic wave is necessary and one candidate is a projectile collision on the target body. However, to utilize the artificial seismic wave generated on the target body, the relationship between the impact energy and the amplitude and the decay process of the seismic wave should be examined. If these relationships are clarified, we can estimate the required sensitivity of seismometers installed on the target body and the possible distance from the seismic origin measurable for the seismometer. Furthermore, if we can estimate the impact energy from the observed seismic wave, we expect to be able to estimate the impact flux of impactors that collided on the target body. McGarr et al. (1969) did impact experiments by using the lexan projectile and two targets, quartz sand and sand bonded by epoxy cement, at 0.8-7 km/s. They found a difference of seismic wave properties between the two targets, and calculated the conversion efficiency to discuss the capability of detection of seismic waves on the Moon. However, they did not examine the excitation and propagation properties of the seismic waves in detail. In this study, we carried out impact experiments in the laboratory to observe the seismic waves by accelerometers, and examined the effects of projectile properties on the excitation and propagation properties of the seismic waves. Experimental methods: We made impact experiments by using a one-stage gas gun at Kobe University. Projectiles were a polycarbonate cylinder
Seismic wave extrapolation using lowrank symbol approximation
Fomel, Sergey
2012-04-30
We consider the problem of constructing a wave extrapolation operator in a variable and possibly anisotropic medium. Our construction involves Fourier transforms in space combined with the help of a lowrank approximation of the space-wavenumber wave-propagator matrix. A lowrank approximation implies selecting a small set of representative spatial locations and a small set of representative wavenumbers. We present a mathematical derivation of this method, a description of the lowrank approximation algorithm and numerical examples that confirm the validity of the proposed approach. Wave extrapolation using lowrank approximation can be applied to seismic imaging by reverse-time migration in 3D heterogeneous isotropic or anisotropic media. © 2012 European Association of Geoscientists & Engineers.
Horizontal Acoustic Barriers for Protection from Seismic Waves
Directory of Open Access Journals (Sweden)
Sergey V. Kuznetsov
2011-01-01
Full Text Available The basic idea of a seismic barrier is to protect an area occupied by a building or a group of buildings from seismic waves. Depending on nature of seismic waves that are most probable in a specific region, different kinds of seismic barriers can be suggested. Herein, we consider a kind of a seismic barrier that represents a relatively thin surface layer that prevents surface seismic waves from propagating. The ideas for these barriers are based on one Chadwick's result concerning nonpropagation condition for Rayleigh waves in a clamped half-space, and Love's theorem that describes condition of nonexistence for Love waves. The numerical simulations reveal that to be effective the length of the horizontal barriers should be comparable to the typical wavelength.
Eliminating time dispersion from seismic wave modeling
Koene, Erik F. M.; Robertsson, Johan O. A.; Broggini, Filippo; Andersson, Fredrik
2018-04-01
We derive an expression for the error introduced by the second-order accurate temporal finite-difference (FD) operator, as present in the FD, pseudospectral and spectral element methods for seismic wave modeling applied to time-invariant media. The `time-dispersion' error speeds up the signal as a function of frequency and time step only. Time dispersion is thus independent of the propagation path, medium or spatial modeling error. We derive two transforms to either add or remove time dispersion from synthetic seismograms after a simulation. The transforms are compared to previous related work and demonstrated on wave modeling in acoustic as well as elastic media. In addition, an application to imaging is shown. The transforms enable accurate computation of synthetic seismograms at reduced cost, benefitting modeling applications in both exploration and global seismology.
Yeguas, A. García.; Almendros, J.; Abella, R.; Ibáñez, J. M.
2011-02-01
We analyse shot data recorded by eight seismic arrays during an active-source seismic experiment carried out at Deception Island (Antarctica) in 2005 January. For each source we estimate the apparent slowness and propagation azimuth of the first wave arrival. Since both source and receiver positions are accurately known, we are able to interpret the results in terms of the effect of the heterogeneities of the medium on wave propagation. The results show the presence of significant propagation anomalies. Nearby shots produce large apparent slowness values above 0.6 s km-1, while distant shots produce small values, down to about 0.15-0.20 s km-1. These values are different for each array, which shows the importance of the local structure under the receiver. The spatial distributions of apparent slowness are not radial as we would expect in a flat-layered medium. And again, these distributions are different for each array. The azimuth anomalies defined as the difference between the empirical estimates and the values expected in a 1-D model (i.e. the source-array directions) suggest ubiquitous wave front distortions. We have detected both positive and negative anomalies. For some shot-array geometries, azimuth anomalies are quite large with values up to 60°. The distribution of the anomalies depends on the position of the array. Some of these features can be interpreted in terms of a shallow magma chamber and shallow rigid bodies imaged by high-resolution seismic tomography. However several details remain unexplained. Further work is required, including modelling of synthetic wavefields on realistic models of Deception Island and/or apparent slowness vector tomography.
Catchings, R.
2017-12-01
P- and S-wave propagation differ in varying materials in the Earth's crust. As a result, combined measurements of P- and S-wave data can be used to infer properties of the shallow crust, including bulk composition, fluid saturation, faulting and fracturing, seismic velocities, reflectivity, and general structures. Ratios of P- to S-wave velocities and Poisson's ratio, which can be derived from the P- and S-wave data, can be particularly diagnostic of subsurface materials and their physical state. In field studies, S-wave data can be obtained directly with S-wave sources or from surface waves associated with P-wave sources. P- and S-wave data can be processed using reflection, refraction, and surface-wave-analysis methods. With the combined data, unconsolidated sediments, consolidated sediments, and rocks can be differentiated on the basis of seismic velocities and their ratios, as can saturated versus unsaturated sediments. We summarize studies where we have used combined P- and S-wave measurements to reliably map the top of ground water, prospect for minerals, locate subsurface faults, locate basement interfaces, determine basin shapes, and measure shear-wave velocities (with calculated Vs30), and other features of the crust that are important for hazards, engineering, and exploration purposes. When compared directly, we find that body waves provide more accurate measures than surface waves.
Karakostas, F. G.; Rakoto, V.; Lognonne, P. H.
2015-12-01
Meteor impacts are a very important seismic source for planetary seismology, since their locations and, in some cases, their occurence times can be accurately known from orbiters, tracking or optical observations. Their importance becomes greater in the case of a seismic experiment with one seismometer, as the SEIS (Seismic Experiment of Interior Structure) of the future Martian mission "InSight", as the known location allows a direct inversion of differential travel times and wave forms in terms of structure. Meteor impacts generate body and surface seismic waves when they reach the surface of a planet. But when they explode into the atmosphere, due to ablation, they generate shock waves, which are converted into linear, seismic waves in the solid part and acoustic waves in the atmosphere. This effect can be modeled when the amplitude of Rayleigh and other Spheroidal normal modes is made with the atmospheric/ground coupling effects. In this study, meteor impacts are modeled as seismic sources in a comparative analysis for the cases of Earth and Mars. Using the computed seismograms, calculated by the summation of the normal modes of the full planet (e.g. with atmosphere) the properties of the seismic source can be obtained. Its duration is typically associated to the radiation duration of shock waves until they reach the linear regime of propagation. These transition times are comparatively analyzed, for providing constraints on the seismic source duration on Earth and Mars. In the case of Earth, we test our approach with the Chelyabinsk superbolide. The computed seismograms are used in order to perform the inversion of the source, by comparison with the data of the Global Seismographic Network. The results are interpreted and compared with other observations. In the case of Mars, equivalent sources are similarly modeled in different atmospheric, impact size and lithospheric conditions.
DEFF Research Database (Denmark)
Soliman, Mohammad Youssof Ahmad; Yuan, Xiaohui; Tilmann, Frederik
2015-01-01
are related to the impact of asthenosphere-lithosphere interaction, (plume-related features), on the continental areas and the evolution of the continent-ocean transition that followed the break-up of Gondwana. This process is supposed to leave its imprint as distinct seismic signature in the upper mantle....... Utilizing 3D sensitivity kernels, we invert traveltime residuals to image velocity perturbations in the upper mantle down to 1000 km depth. To test the robustness of our tomographic image we employed various resolution tests which allow us to evaluate the extent of smearing effects and help defining...... structures. We present detailed tomographic images of the oceanic and continental lithosphere beneath the study area. The fast lithospheric keel of the Congo Craton reaches a depth of ∼250 km. Relatively low velocity perturbations have been imaged within the orogenic Damara Belt down to a depth of ∼150 km...
Linking Spe Body-Wave Amplitudes and Site Characterization
Mellors, R. J.; Walter, W. R.; Ford, S. R.; Pitarka, A.; Wagoner, J. L.; Matzel, E.; Hauk, T. F.
2013-12-01
The purpose of the Source Physics Experiments is to investigate the generation and propagation of seismic waves from buried underground chemical explosions. Here we present results from an analysis of the tests up to date with emphasis on implications for discrimination and yield estimation using seismic data at very local (appear to discriminate well using P/S ratios at some stations. We attempt to correlate variations in body wave amplitudes as a function of azimuth observed at very local ranges (effects; 2) path effects; 3) path topography; and 4) near-source (effects using both observations and modeling as a guide. Possible path effects are evaluated using a combination of existing geologic models combined with seismic velocity/attenuation models constructed using ambient noise tomography. Modeling is conducted with a finite-difference code capable of handling topographic effects. Near-source effects will rely on measurements of near-source geology, velocity models, and near-field observations (including spall) with focus on azimuthal variations.
The effects of core-reflected waves on finite fault inversions with teleseismic body wave data
Qian, Yunyi; Ni, Sidao; Wei, Shengji; Almeida, Rafael; Zhang, Han
2017-11-01
Teleseismic body waves are essential for imaging rupture processes of large earthquakes. Earthquake source parameters are usually characterized by waveform analyses such as finite fault inversions using only turning (direct) P and SH waves without considering the reflected phases from the core-mantle boundary (CMB). However, core-reflected waves such as ScS usually have amplitudes comparable to direct S waves due to the total reflection from the CMB and might interfere with the S waves used for inversion, especially at large epicentral distances for long duration earthquakes. In order to understand how core-reflected waves affect teleseismic body wave inversion results, we develop a procedure named Multitel3 to compute Green's functions that contain turning waves (direct P, pP, sP, direct S, sS and reverberations in the crust) and core-reflected waves (PcP, pPcP, sPcP, ScS, sScS and associated reflected phases from the CMB). This ray-based method can efficiently generate synthetic seismograms for turning and core-reflected waves independently, with the flexibility to take into account the 3-D Earth structure effect on the timing between these phases. The performance of this approach is assessed through a series of numerical inversion tests on synthetic waveforms of the 2008 Mw7.9 Wenchuan earthquake and the 2015 Mw7.8 Nepal earthquake. We also compare this improved method with the turning-wave only inversions and explore the stability of the new procedure when there are uncertainties in a priori information (such as fault geometry and epicentre location) or arrival time of core-reflected phases. Finally, a finite fault inversion of the 2005 Mw8.7 Nias-Simeulue earthquake is carried out using the improved Green's functions. Using enhanced Green's functions yields better inversion results as expected. While the finite source inversion with conventional P and SH waves is able to recover large-scale characteristics of the earthquake source, by adding PcP and ScS phases
Diagnostic possibilities of body waves for studying the interior structure of mars
Raevskiy, S. N.; Gudkova, T. V.; Zharkov, V. N.
2015-01-01
The diagnostic possibilities of body waves for refining the models of the Martian interior structure are explored. The MATLAB-based software is developed for calculating the theoretical travel time curves and estimating the amplitudes of P- and S-waves for the predicted values of seismic moments of the marsquakes. The traveltimes of the P- and S-waves, as well as the reflected phases and the phases that passed through the core as the functions of epicentral distance, are compared for different test models of the interior of Mars.
Regional velocity structure in northern California from inversion of scattered seismic surface waves
Pollitz, Fred F.
1999-07-01
Seismic surface waves recorded by the Berkeley Digital Seismic Network have been analyzed in order to constrain three-dimensional lateral heterogeneity of the upper mantle under northern California. A total of 2164 seismograms from 173 teleseismic events were windowed for the fundamental mode Rayleigh wave, followed by estimation of complex amplitude spectra over the period range 16 to 100 s using a multiple-taper method. Since Rayleigh waves at shorter periods, particularly below 35 s, suffer from serious multipathing or "non-plane" wave arrivals, these amplitude spectra have been interpreted as the product of wavefront distortion along the teleseismic propagation path and seismic structure beneath the network. The amplitude spectra are first modeled in terms of non-plane incoming wavefields and structural phase velocity perturbations period by period. After corrections for Moho and surface topography, the phase velocity maps are inverted for three-dimensional shear velocity perturbations δνs down to a depth of 200 km. The δνs maps are in good agreement with the results of body studies over a broad spatial scale. The dominant signals are associated with the thermal effects of the active Gorda and fossil Farallon subducted slab stretching from Mount Shasta through the western Sierran foothills to the southern Great Valley and asthenospheric upwelling beneath the northern Coast Ranges. The southern Sierra Nevada Range is characterized by fast δνs down to ˜50 km and slow velocities between ˜60 and 120 km depth, in agreement with independent inferences of a cold crust and warm upper mantle, which may provide the buoyancy forces necessary to support the elevation of the range.
A Shear-Wave Seismic System to Look Ahead of a Tunnel Boring Machine
Bharadwaj, Pawan; Drijkoningen, G.G.; Mulder, W.A.; Tscharner, Thomas; Jenneskens, Rob
2016-01-01
The Earth’s properties, composition and structure ahead of a tunnel boring machine (TBM) should be mapped for hazard assessment during excavation. We study the use of seismic-exploration techniques for this purpose. We focus on a seismic system for soft soils, where shear waves are better and easier
Jiang, T.; Yue, Y.
2017-12-01
It is well known that the mono-frequency directional seismic wave technology can concentrate seismic waves into a beam. However, little work on the method and effect of variable frequency directional seismic wave under complex geological conditions have been done .We studied the variable frequency directional wave theory in several aspects. Firstly, we studied the relation between directional parameters and the direction of the main beam. Secondly, we analyzed the parameters that affect the beam width of main beam significantly, such as spacing of vibrator, wavelet dominant frequency, and number of vibrator. In addition, we will study different characteristics of variable frequency directional seismic wave in typical velocity models. In order to examine the propagation characteristics of directional seismic wave, we designed appropriate parameters according to the character of direction parameters, which is capable to enhance the energy of the main beam direction. Further study on directional seismic wave was discussed in the viewpoint of power spectral. The results indicate that the energy intensity of main beam direction increased 2 to 6 times for a multi-ore body velocity model. It showed us that the variable frequency directional seismic technology provided an effective way to strengthen the target signals under complex geological conditions. For concave interface model, we introduced complicated directional seismic technology which supports multiple main beams to obtain high quality data. Finally, we applied the 9-element variable frequency directional seismic wave technology to process the raw data acquired in a oil-shale exploration area. The results show that the depth of exploration increased 4 times with directional seismic wave method. Based on the above analysis, we draw the conclusion that the variable frequency directional seismic wave technology can improve the target signals of different geologic conditions and increase exploration depth with little
Sources of Error and the Statistical Formulation of M S: m b Seismic Event Screening Analysis
Anderson, D. N.; Patton, H. J.; Taylor, S. R.; Bonner, J. L.; Selby, N. D.
2014-03-01
The Comprehensive Nuclear-Test-Ban Treaty (CTBT), a global ban on nuclear explosions, is currently in a ratification phase. Under the CTBT, an International Monitoring System (IMS) of seismic, hydroacoustic, infrasonic and radionuclide sensors is operational, and the data from the IMS is analysed by the International Data Centre (IDC). The IDC provides CTBT signatories basic seismic event parameters and a screening analysis indicating whether an event exhibits explosion characteristics (for example, shallow depth). An important component of the screening analysis is a statistical test of the null hypothesis H 0: explosion characteristics using empirical measurements of seismic energy (magnitudes). The established magnitude used for event size is the body-wave magnitude (denoted m b) computed from the initial segment of a seismic waveform. IDC screening analysis is applied to events with m b greater than 3.5. The Rayleigh wave magnitude (denoted M S) is a measure of later arriving surface wave energy. Magnitudes are measurements of seismic energy that include adjustments (physical correction model) for path and distance effects between event and station. Relative to m b, earthquakes generally have a larger M S magnitude than explosions. This article proposes a hypothesis test (screening analysis) using M S and m b that expressly accounts for physical correction model inadequacy in the standard error of the test statistic. With this hypothesis test formulation, the 2009 Democratic Peoples Republic of Korea announced nuclear weapon test fails to reject the null hypothesis H 0: explosion characteristics.
Optimal wave focusing for seismic source imaging
Bazargani, Farhad
In both global and exploration seismology, studying seismic sources provides geophysicists with invaluable insight into the physics of earthquakes and faulting processes. One way to characterize the seismic source is to directly image it. Time-reversal (TR) focusing provides a simple and robust solution to the source imaging problem. However, for recovering a well- resolved image, TR requires a full-aperture receiver array that surrounds the source and adequately samples the wavefield. This requirement often cannot be realized in practice. In most source imaging experiments, the receiver geometry, due to the limited aperture and sparsity of the stations, does not allow adequate sampling of the source wavefield. Incomplete acquisition and imbalanced illumination of the imaging target limit the resolving power of the TR process. The main focus of this thesis is to offer an alternative approach to source imaging with the goal of mitigating the adverse effects of incomplete acquisition on the TR modeling. To this end, I propose a new method, named Backus-Gilbert (BG) source imaging, to optimally focus the wavefield onto the source position using a given receiver geometry. I first introduce BG as a method for focusing waves in acoustic media at a desired location and time. Then, by exploiting the source-receiver reciprocity of the Green function and the linearity of the problem, I show that BG focusing can be adapted and used as a source-imaging tool. Following this, I generalize the BG theory for elastic waves. Applying BG formalism for source imaging requires a model for the wave propagation properties of the earth and an estimate of the source location. Using numerical tests, I next examine the robustness and sensitivity of the proposed method with respect to errors in the earth model, uncertainty in the source location, and noise in data. The BG method can image extended sources as well as point sources. It can also retrieve the source mechanism. These features of
Mesoscopics of ultrasound and seismic waves: application to passive imaging
Larose, É.
2006-05-01
This manuscript deals with different aspects of the propagation of acoustic and seismic waves in heterogeneous media, both simply and multiply scattering ones. After a short introduction on conventional imaging techniques, we describe two observations that demonstrate the presence of multiple scattering in seismic records: the equipartition principle, and the coherent backscattering effect (Chap. 2). Multiple scattering is related to the mesoscopic nature of seismic and acoustic waves, and is a strong limitation for conventional techniques like medical or seismic imaging. In the following part of the manuscript (Chaps. 3 5), we present an application of mesoscopic physics to acoustic and seismic waves: the principle of passive imaging. By correlating records of ambient noise or diffuse waves obtained at two passive sensors, it is possible to reconstruct the impulse response of the medium as if a source was placed at one sensor. This provides the opportunity of doing acoustics and seismology without a source. Several aspects of this technique are presented here, starting with theoretical considerations and numerical simulations (Chaps. 3, 4). Then we present experimental applications (Chap. 5) to ultrasound (passive tomography of a layered medium) and to seismic waves (passive imaging of California, and the Moon, with micro-seismic noise). Physique mésoscopique des ultrasons et des ondes sismiques : application à l'imagerie passive. Cet article de revue rassemble plusieurs aspects fondamentaux et appliqués de la propagation des ondes acoustiques et élastiques dans les milieux hétérogènes, en régime de diffusion simple ou multiple. Après une introduction sur les techniques conventionelles d'imagerie sismique et ultrasonore, nous présentons deux expériences qui mettent en évidence la présence de diffusion multiple dans les enregistrements sismologiques : l'équipartition des ondes, et la rétrodiffusion cohérente (Chap. 2). La diffusion multiple des
Flat lens effect on seismic waves propagation in the subsoil.
Brûlé, Stéphane; Javelaud, Emmanuel H; Enoch, Stefan; Guenneau, Sébastien
2017-12-22
We show that seismic energy simulated by an artificial source that mainly propagates Rayleigh surface waves, is focused in structured soil made of a grid of holes distributed in the ground. We carry out large-scale field tests with a structured soil made of a grid consisting of cylindrical and vertical holes in the ground and a low frequency artificial source (seismic metamaterials to counteract partially or totally the most devastating components of seismic signals.
Body waves separation in the time-frequency domain
Herrera, R. H.; Tary, J.; Van der Baan, M.
2013-12-01
Arrival times of body waves generated by small magnitude microseismic events are usually very close and their limited bandwidth can cause even partial overlap in the time and frequency domains. The separation of P and S waves is then a challenging task that if solved could bring more insights about nature and location of the generating source. Differences in arrival times and frequency content of P and S waves can be seen by using time-frequency decomposition. The traditional time-frequency representation based on the Fourier Transform is limited by its trade-off between time and frequency resolutions, while other alternatives like the Wavelet Transform are still limited by the Heisenberg box. A new derivation of the Continuous Wavelet Transform, called Synchrosqueezing, stretches these boundaries using a mixture of the reassignment method with instantaneous frequency, giving a better frequency representation with improved time localization. Furthermore, all the individual components of the signal are separated in the time domain. This means that we are able to isolate the waveforms of a complex microseismic trace. Each spectral component can then be matched with a body wave plus its associated coda. Proper parameters have to be selected prior to the computation, such as the central frequency and bandwidth of the mother wavelet. We thus include a signal characterization first to find the best matching mother wavelet. In this paper we use the Synchrosqueezing transform to perform the time frequency representation of short brittle events recorded during microseismic experiments. Decomposition results for these examples show that the Synchrosqueezing transform outperforms the Short-Time Fourier Transform. The different components of each body waves (first arrival, coda, frequency components) can then be identified in the time-frequency plane. For some microseismic events, a first P-wave arrival is followed by another arrival at lower frequency that could be a P-wave
Detection of sinkholes or anomalies using full seismic wave fields.
2013-04-01
This research presents an application of two-dimensional (2-D) time-domain waveform tomography for detection of embedded sinkholes and anomalies. The measured seismic surface wave fields were inverted using a full waveform inversion (FWI) technique, ...
Wave-equation migration velocity inversion using passive seismic sources
Witten, B.; Shragge, J. C.
2015-12-01
Seismic monitoring at injection sites (e.g., CO2 sequestration, waste water disposal, hydraulic fracturing) has become an increasingly important tool for hazard identification and avoidance. The information obtained from this data is often limited to seismic event properties (e.g., location, approximate time, moment tensor), the accuracy of which greatly depends on the estimated elastic velocity models. However, creating accurate velocity models from passive array data remains a challenging problem. Common techniques rely on picking arrivals or matching waveforms requiring high signal-to-noise data that is often not available for the magnitude earthquakes observed over injection sites. We present a new method for obtaining elastic velocity information from earthquakes though full-wavefield wave-equation imaging and adjoint-state tomography. The technique exploits the fact that the P- and S-wave arrivals originate at the same time and location in the subsurface. We generate image volumes by back-propagating P- and S-wave data through initial Earth models and then applying a correlation-based extended-imaging condition. Energy focusing away from zero lag in the extended image volume is used as a (penalized) residual in an adjoint-state tomography scheme to update the P- and S-wave velocity models. We use an acousto-elastic approximation to greatly reduce the computational cost. Because the method requires neither an initial source location or origin time estimate nor picking of arrivals, it is suitable for low signal-to-noise datasets, such as microseismic data. Synthetic results show that with a realistic distribution of microseismic sources, P- and S-velocity perturbations can be recovered. Although demonstrated at an oil and gas reservoir scale, the technique can be applied to problems of all scales from geologic core samples to global seismology.
A Hammer-Impact, Aluminum, Shear-Wave Seismic Source
Haines, Seth S.
2007-01-01
Near-surface seismic surveys often employ hammer impacts to create seismic energy. Shear-wave surveys using horizontally polarized waves require horizontal hammer impacts against a rigid object (the source) that is coupled to the ground surface. I have designed, built, and tested a source made out of aluminum and equipped with spikes to improve coupling. The source is effective in a variety of settings, and it is relatively simple and inexpensive to build.
A new instrumentation to measure seismic waves attenuation
Tisato, N.; Madonna, C.; Boutareaud, S.; Burg, J.
2010-12-01
Attenuation of seismic waves is the general expression describing the loss of energy of an elastic perturbation during its propagation in a medium. As a geophysical method, measuring the attenuation of seismic waves is a key to uncover essential information about fluid saturation of buried rocks. Attenuation of seismic waves depends on several mechanisms. In the case of saturated rock, fluids play an important role. Seismic waves create zones of overpressure by mobilizing the fluids in the pores of the rock. Starting from Gassmann-Biot theory (Gassman, 1951), several models (e.g. White, 1975; Mavko and Jizba, 1991) have been formulated to describe the energy absorption by flow of fluids. According to Mavko et al. (1998) for rock with permeability equals or less than 1 D, fluid viscosity between 1 cP and 10 cP and low frequencies seismic wave ( 100 KPa) in less than 10 ms. The vessel is equipped with 5 pressure sensors buried within the rock sample, a load cell and a strain sensor to measure axial shortening while the motor generates the seismic waves. The sensor conditioning system has been designed and realized by us and the acquisition software has been developed in Matlab. We present the first results, at room pressure and temperature, based on the measurements of pore fluid pressure increase in a sandstone sample with a permeability of 200 to 500 mD and partially saturated with water and air. These preliminary results show the reliability of this new instrumentation to measure seismic wave attenuation at low frequency and to verify the pore fluid flow driven by seismic waves.
Almendros, J.; Chouet, B.; Dawson, P.; Huber, Caleb G.
2002-01-01
Seismic antennas constitute a powerful tool for the analysis of complex wave fields. Well-designed antennas can identify and separate components of a complex wave field based on their distinct propagation properties. The combination of several antennas provides the basis for a more complete understanding of volcanic wave fields, including an estimate of the location of each individual wave-field component identified simultaneously by at least two antennas. We used frequency-slowness analyses of data from three antennas to identify and locate the different components contributing to the wave fields recorded at Kilauea volcano, Hawaii, in February 1997. The wave-field components identified are (1) a sustained background volcanic tremor in the form of body waves generated in a shallow hydrothermal system located below the northeastern edge of the Halemaumau pit crater; (2) surface waves generated along the path between this hydrothermal source and the antennas; (3) back-scattered surface wave energy from a shallow reflector located near the southeastern rim of Kilauea caldera; (4) evidence for diffracted wave components originating at the southeastern edge of Halemaumau; and (5) body waves reflecting the activation of a deeper tremor source between 02 hr 00 min and 16 hr 00 min Hawaii Standard Time on 11 February.
Retrieval of Body-Wave Reflections Using Ambient Noise Interferometry Using a Small-Scale Experiment
Dantas, Odmaksuel Anísio Bezerra; do Nascimento, Aderson Farias; Schimmel, Martin
2018-02-01
We report the retrieval of body-wave reflections from noise records using a small-scale experiment over a mature oil field. The reflections are obtained by cross-correlation and stacking of the data. We used the stacked correlograms to create virtual source-to-receiver common shot gathers and are able to obtain body-wave reflections. Surface waves that obliterate the body-waves in our noise correlations were attenuated following a standard procedure from active source seismics. Further different strategies were employed to cross-correlate and stack the data: classical geometrical normalized cross-correlation (CCGN), phase cross-correlation (PCC), linear stacking**** and phase weighted stacking (PWS). PCC and PWS are based on the instantaneous phase coherence of analytic signals. The four approaches are independent and reveal the reflections; nevertheless, the combination of PWS and CCGN provided the best results. Our analysis is based on 2145 cross-correlations of 600 s data segments. We also compare the resulted virtual shot gathers with an active 2D seismic line near the passive experiment. It is shown that our ambient noise analysis reproduces reflections which are present in the active seismic data.
Numerical estimates of seismic effects after collisions of small bodies with the Earth atmosphere
Svetsov, Vladimir; Shuvalov, Valery
Small bodies - meteoroids, asteroids or cometary objects of moderate size (10 - 100 m) every so often do not survive the entry through the planetary atmosphere and release their energy at some altitudes. Then the aerial blast waves reach the ground and generate Rayleigh seismic surface waves. The magnitude of the following earthquake can be significant as in the cases of the Tunguska event of 30 June 1908 or the Chelyabinsk airburst of 15 February 2013. If the pressure on the ground is known as a function of coordinates and time, the energy of seismic waves can be calculated using a solution of Lamb’s problem of the response to vertical load acting on the surface of an elastic half-space. The numerical procedure includes calculations of pressure spectra and integrals which are proportional to the energy of seismic waves. The final formula for the calculation of earthquake magnitudes was calibrated using published results of measurements made during nuclear tests on Novaya Zemlya in 1961 - 1962. We carried out numerical simulations of the aerial shock waves in Chelyabinsk event of 15 February 2013, using hydrodynamic codes. The energy input along the atmospheric trajectory inclined at 19° to the Earth surface was assumed to be proportional to the radiation intensity derived from numerous video records. The calculated magnitude of the seismic source proved to be 3.85 on the assumption that the initial kinetic energy of the asteroid was 300 kt TNT. For the energy of 500 kt TNT the magnitude was 4.0. These values are in agreement with the results of magnitude records within the measurement errors. We also calculated the magnitudes of earthquakes caused by spherical explosions with the energies from 30 kt to 30 Mt TNT (bodies from ~7 to 70 m in size) at altitudes from 5 to 45 km. The earthquake magnitude of the Chelyabinsk event corresponds to a spherical explosion at an altitude of about 35 km. For the Tunguska event of 1908, we obtained the earthquake magnitudes
Directory of Open Access Journals (Sweden)
S. I. Sherman
2013-01-01
Full Text Available Deformation waves as a trigger mechanism of seismic activity and migration of earthquake foci have been under discussion by researchers in seismology and geodynamics for over 50 years. Four sections of this article present available principal data on impacts of wave processes on seismicity and new data. The first section reviews analytical and experimental studies aimed at identification of relationships between wave processes in the lithosphere and seismic activity manifested as space-and-time migration of individual earthquake foci or clusters of earthquakes. It is concluded that with a systematic approach, instead of using a variety of terms to denote waves that trigger seismic process in the lithosphere, it is reasonable to apply the concise definition of ‘deformation waves’, which is most often used in fact.The second section contains a description of deformation waves considered as the trigger mechanism of seismic activity. It is concluded that a variety of methods are applied to identify deformation waves, and such methods are based on various research methods and concepts that naturally differ in sensitivity concerning detection of waves and/or impact of the waves on seismic process. Epicenters of strong earthquakes are grouped into specific linear or arc-shaped systems, which common criterion is the same time interval of the occurrence of events under analysis. On site the systems compose zones with similar time sequences, which correspond to the physical notion of moving waves (Fig. 9. Periods of manifestation of such waves are estimated as millions of years, and a direct consideration of the presence of waves and wave parameters is highly challenging. In the current state-of-the-art, geodynamics and seismology cannot provide any other solution yet.The third section presents a solution considering record of deformation waves in the lithosphere. With account of the fact that all the earthquakes with М≥3.0 are associated with
Borcherdt, Roger D.; Glassmoyer, Gary; Wennerberg, Leif
1986-10-01
A general computer code, developed to calculate anelastic reflection-refraction coefficients, energy flow, and the physical characteristics for general P, S-I, and S-II waves, quantitatively describes physical characteristics for wave fields in anelastic media that do not exist in elastic media. Consideration of wave fields incident on boundaries between anelastic media shows that scattered wave fields experience reductions in phase and energy speeds, increases in maximum attenuation and Q-1, and directions of maximum energy flow distinct from phase propagation. Each of these changes in physical characteristics are shown to vary with angle of incidence. Finite relaxation times for anelastic media result in energy flow due to interaction of superimposed radiation fields and contribute to energy flow across anelastic boundaries for all angles of incidence. Agreement of theoretical and numerical results with laboratory measurements argues for the validity of the theoretical and numerical formulations incorporating inhomogeneous wave fields. The agreement attests to the applicability of the model and helps confirm the existence of inhomogeneous body waves and their associated set of distinct physical characteristics in the earth. The existence of such body waves in layered, low-loss anelastic solids implies the need to reformulate some seismological models of the earth. The exact anelastic formulation for a liquid-solid interface with no low-loss approximations predicts the existence of a range of angles of incidence or an anelastic Rayleigh window, through which significant amounts of energy are transmitted across the boundary. The window accounts for the discrepancy apparent between measured reflection data presented in early textbooks and predictions based on classical elasticity theory. Characteristics of the anelastic Rayleigh window are expected to be evident in certain sets of wide-angle, ocean-bottom reflection data and to be useful in estimating Q-1 for some
Engineered metabarrier as shield from seismic surface waves.
Palermo, Antonio; Krödel, Sebastian; Marzani, Alessandro; Daraio, Chiara
2016-12-20
Resonant metamaterials have been proposed to reflect or redirect elastic waves at different length scales, ranging from thermal vibrations to seismic excitation. However, for seismic excitation, where energy is mostly carried by surface waves, energy reflection and redirection might lead to harming surrounding regions. Here, we propose a seismic metabarrier able to convert seismic Rayleigh waves into shear bulk waves that propagate away from the soil surface. The metabarrier is realized by burying sub-wavelength resonant structures under the soil surface. Each resonant structure consists of a cylindrical mass suspended by elastomeric springs within a concrete case and can be tuned to the resonance frequency of interest. The design allows controlling seismic waves with wavelengths from 10-to-100 m with meter-sized resonant structures. We develop an analytical model based on effective medium theory able to capture the mode conversion mechanism. The model is used to guide the design of metabarriers for varying soil conditions and validated using finite-element simulations. We investigate the shielding performance of a metabarrier in a scaled experimental model and demonstrate that surface ground motion can be reduced up to 50% in frequency regions below 10 Hz, relevant for the protection of buildings and civil infrastructures.
Using seismic coda waves to resolve intrinsic and scattering attenuation
Wang, W.; Shearer, P. M.
2016-12-01
Seismic attenuation is caused by two factors, scattering and intrinsic absorption. Characterizing scattering and absorbing properties and the power spectrum of crustal heterogeneity is a fundamental problem for informing strong ground motion estimates at high frequencies, where scattering and attenuation effects are critical. Determining the relative amount of attenuation caused by scattering and intrinsic absorption has been a long-standing problem in seismology. The wavetrain following the direct body wave phases is called the coda, which is caused by scattered energy. Many studies have analyzed the coda of local events to constrain crustal and upper-mantle scattering strength and intrinsic attenuation. Here we examine two popular attenuation inversion methods, the Multiple Lapse Time Window Method (MLTWM) and the Coda Qc Method. First, based on our previous work on California attenuation structure, we apply an efficient and accurate method, the Monte Carlo Approach, to synthesize seismic envelope functions. We use this code to generate a series of synthetic data based on several complex and realistic forward models. Although the MLTWM assumes a uniform whole space, we use the MLTWM to invert for both scattering and intrinsic attenuation from the synthetic data to test how accurately it can recover the attenuation models. Results for the coda Qc method depend on choices for the length and starting time of the coda-wave time window. Here we explore the relation between the inversion results for Qc, the windowing parameters, and the intrinsic and scattering Q structure of our synthetic model. These results should help assess the practicality and accuracy of the Multiple Lapse Time Window Method and Coda Qc Method when applied to realistic crustal velocity and attenuation models.
Energy Technology Data Exchange (ETDEWEB)
Inazaki, T. [Public Works Research Institute, Tsukuba (Japan)
1997-05-27
With an objective to measure a behavior of the surface ground during a strong earthquake directly on the actual ground and make evaluation thereon, a proposal was made on an original location measuring and analyzing method using an S-wave vibrator and seismic cones. This system consists of an S-wave vibrator and a static cone penetrating machine, and different types of measuring cones. A large number of measuring cones are inserted initially in the object bed of the ground, and variation in the vibration generated by the vibrator is measured. This method can derive decrease in rigidity rate of the actual ground according to dynamic strain levels, or in other words, the dynamic nonlinearity. The strain levels can be controlled with a range from 10 {sup -5} to 10 {sup -3} by varying the distance from the S-wave vibrator. Furthermore, the decrease in the rigidity rate can be derived by measuring variations in the S-wave velocity by using the plank hammering method during the vibration. Field measurement is as easy as it can be completed in about half a day including preparatory works, and the data analysis is also simple. The method is superior in mobility and workability. 9 figs.
Czech Academy of Sciences Publication Activity Database
Brokešová, J.; Málek, Jiří
2015-01-01
Roč. 19, č. 2 (2015), s. 511-539 ISSN 1383-4649 R&D Projects: GA ČR GAP210/10/0925; GA MŠk LM2010008; GA ČR GAP210/12/2336; GA ČR GA15-02363S Institutional support: RVO:67985891 Keywords : seismic rotation * near-source region * rotational seismometer * microearthquakes * West Bohemia/Vogtland region * Gulf of Corinth * Katla region Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.550, year: 2015
Directory of Open Access Journals (Sweden)
Hao Wang
2015-06-01
Full Text Available As one of the main characteristics of seismic waves, apparent wave velocity has great influence on seismic responses of long-span suspension bridges. Understanding these influences is important for seismic design. In this article, the critical issues concerning the traveling wave effect analysis are first reviewed. Taizhou Bridge, the longest triple-tower suspension bridge in the world, is then taken as an example for this investigation. A three-dimensional finite element model of the bridge is established in ABAQUS, and the LANCZOS eigenvalue solver is employed to calculate the structural dynamic characteristics. Traveling wave effect on seismic responses of these long-span triple-tower suspension bridges is investigated. Envelopes of seismic shear force and moment in the longitudinal direction along the three towers, relative displacements between the towers and the girder, and reaction forces at the bottoms of the three towers under different apparent wave velocities are calculated and presented in detail. The results show that the effect of apparent wave velocity on the seismic responses of triple-tower suspension bridge fluctuates when the velocity is lower than 2000 m/s, and the effects turn stable when the velocity becomes larger. In addition, the effects of traveling wave are closely related to spectral characteristics and propagation direction of the seismic wave, and seismic responses of components closer to the source are relatively larger. Therefore, reliable estimation of the seismic input and apparent wave velocity according to the characteristics of the bridge site are significant for accurate prediction of seismic responses. This study provides critical reference for seismic analysis and design of long-span triple-tower suspension bridges.
Experimental illustrations of seismic-wave properties of interest for hydrogeological studies
Bodet, L.; Pasquet, S.; Bergamo, P.; Martin, R.; Mourgues, R.; Tournat, V.
2015-12-01
The joint study of pressure (P-) and shear (S-) wave velocities (VP and VS, respectively), as well as their ratio (VP/VS), has been used for many years at large scales (compared to near-surface applications) to study fluids in earth materials. Theoretical and experimental developments have been aimed at understanding the effect of saturation and pore fluids on body wave velocities, more particularly in consolidated media. In the field of hydrocarbon exploration for instance, the measurement of VP/VS ratio helps discriminating different pore fluids in reservoirs. But it is only until recently that this approach has been successfully applied to the characterization of hydrosystems. We showed, thanks to controlled field experiments, the ability of VP/VS ratio in imaging spatial and/or temporal variations of water content at the critical zone scale. These promising results still lack quantitative links between water saturation and seismic properties in such materials and context. We consequently developed laboratory experiments to simulate seismic acquisitions on small-scale controlled granular media with varying water levels. The first results clearly showed the influence of the water level on first arrival times, dispersion and amplitude of the recorded wavefields, and how these measurements could be used as monitoring tools.
Excitation of seismic waves by a tornado
Valovcin, A.; Tanimoto, T.; Twardzik, C.
2016-12-01
Tornadoes are among the most common natural disasters to occur in the United States. Various methods are currently used in tornado forecasting, including surface weather stations, weather balloons and satellite and Doppler radar. These methods work for detecting possible locations of tornadoes and funnel clouds, but knowing when a tornado has touched down still strongly relies on reports from spotters. Studying tornadoes seismically offers an opportunity to know when a tornado has touched down without requiring an eyewitness report. With the installation of Earthscope's Transportable Array (TA), there have been an increased number of tornadoes that have come within close range of seismometers. We have identified seismic signals corresponding to three tornadoes that occurred in 2011 in the central US. These signals were recorded by the TA station closest to each of the tornado tracks. For each tornado, the amplitudes of the seismic signals increase when the storm is in contact with the ground, and continue until the tornado lifts off some time later. This occurs at both high and low frequencies. In this study we will model the seismic signal generated by a tornado at low frequencies (below 0.1 Hz). We will begin by modeling the signal from the Joplin tornado, an EF5 rated tornado which occurred in Missouri on May 22, 2011. By approximating the tornado as a vertical force, we model the generated signal as the tornado moves along its track and changes in strength. By modeling the seismic waveform generated by a tornado, we can better understand the seismic-excitation process. It could also provide a way to quantitatively compare tornadoes. Additional tornadoes to model include the Calumet-El Reno-Piedmont-Guthrie (CEPG) and Chickasa-Blanchard-Newcastle (CBN) tornadoes, both of which occurred on May 24, 2011 in Oklahoma.
Lowrank seismic-wave extrapolation on a staggered grid
Fang, Gang
2014-05-01
© 2014 Society of Exploration Geophysicists. We evaluated a new spectral method and a new finite-difference (FD) method for seismic-wave extrapolation in time. Using staggered temporal and spatial grids, we derived a wave-extrapolation operator using a lowrank decomposition for a first-order system of wave equations and designed the corresponding FD scheme. The proposed methods extend previously proposed lowrank and lowrank FD wave extrapolation methods from the cases of constant density to those of variable density. Dispersion analysis demonstrated that the proposed methods have high accuracy for a wide wavenumber range and significantly reduce the numerical dispersion. The method of manufactured solutions coupled with mesh refinement was used to verify each method and to compare numerical errors. Tests on 2D synthetic examples demonstrated that the proposed method is highly accurate and stable. The proposed methods can be used for seismic modeling or reverse-time migration.
Seismic shear waves as Foucault pendulum
Snieder, Roel; Sens-Schönfelder, C.; Ruigrok, E.; Shiomi, K.
2016-01-01
Earth's rotation causes splitting of normal modes. Wave fronts and rays are, however, not affected by Earth's rotation, as we show theoretically and with observations made with USArray. We derive that the Coriolis force causes a small transverse component for P waves and a small longitudinal
Levshin, Anatoli L.; Barmin, Mikhail P.; Moschetti, Morgan P.; Mendoza, Carlos; Ritzwoller, Michael H.
2012-01-01
The purpose of this study is to develop and test a modiﬁcation to a previous method of regional seismic event location based on Empirical Green’s Functions (EGFs) produced from ambient seismic noise. Elastic EGFs between pairs of seismic stations are determined by cross-correlating long ambient noise time-series recorded at the two stations. The EGFs principally contain Rayleigh- and Love-wave energy on the vertical and transverse components, respectively, and we utilize these signals between about 5 and 12 s period. The previous method, based exclusively on Rayleigh waves, may yield biased epicentral locations for certain event types with hypocentral depths between 2 and 5 km. Here we present theoretical arguments that show how Love waves can be introduced to reduce or potentially eliminate the bias. We also present applications of Rayleigh- and Love-wave EGFs to locate 10 reference events in the western United States. The separate Rayleigh and Love epicentral locations and the joint locations using a combination of the two waves agree to within 1 km distance, on average, but conﬁdence ellipses are smallest when both types of waves are used.
rock physics investigation of seismic wave absorption in reservoir ...
African Journals Online (AJOL)
Admin
ROCK PHYSICS INVESTIGATION OF SEISMIC WAVE ABSORPTION. IN RESERVOIR ROCKS. W. O. RAJI AND A. RIETBROCK. (Received 2, January 2009; Revision Accepted 19, January 2009). ABSTRACT. This research provides insight into the process of pore- fluid induced absorption which is important for absorption ...
S. Pellegrino and Brasimone seismic stations
International Nuclear Information System (INIS)
Capocecera, P.; Tedeschi, E.; Vitiello, F.
1988-07-01
The paper describes the technical features relative to the S. Pellegrino and Brasimone seismic stations. The stations have been modified in order to realize a central data acquisition system; in this way seismic signals are sent to Brasimone Center through telephone pair and are recorded in continuous form. (author)
SeismoDome: Sonic and visual representation of earthquakes and seismic waves in the planetarium
Holtzman, B. K.; Candler, J.; Repetto, D.; Pratt, M. J.; Paté, A.; Turk, M.; Gualtieri, L.; Peter, D. B.; Trakinski, V.; Ebel, D. S. S.; Gossmann, J.; Lem, N.
2017-12-01
Since 2014, we have produced four "Seismodome" public programs in the Hayden Planetarium at the American Museum of Natural History in New York City. To teach the general public about the dynamics of the Earth, we use a range of seismic data (seismicity catalogs, surface and body wave fields, ambient noise, free oscillations) to generate movies and sounds conveying aspects of the physics of earthquakes and seismic waves. The narrative aims to stretch people's sense of time and scale, starting with 2 billion years of convection, then zooming in seismicity over days to twenty years at different length scales, to hours of global seismic wave propagation, all compressed to minute long movies. To optimize the experience in the planetarium, the 180-degree fisheye screen corresponds directly to the surface of the Earth, such that the audience is inside the planet. The program consists of three main elements (1) Using sonified and animated seismicity catalogs, comparison of several years of earthquakes on different plate boundaries conveys the dramatic differences in their dynamics and the nature of great and "normal" earthquakes. (2) Animations of USArray data (based on "Ground Motion Visualizations" methods from IRIS but in 3D, with added sound) convey the basic observations of seismic wave fields, with which we raise questions about what they tell us about earthquake physics and the Earth's interior structure. (3) Movies of spectral element simulations of global seismic wave fields synchronized with sonified natural data push these questions further, especially when viewed from the interior of the planet. Other elements include (4) sounds of the global ambient noise field coupled to movies of mean ocean wave height (related to the noise source) and (5) three months of free oscillations / normal modes ringing after the Tohoku earthquake. We use and develop a wide range of sonification and animation methods, written mostly in python. Flat-screen versions of these movies
Numerical simulation of seismic wave field in graded geological media containing multiple cavities
Fontara, Ioanna-Kleoniki; Dineva, Petia S.; Manolis, George D.; Wuttke, Frank
2016-08-01
In this study, we develop an efficient boundary integral equation method for estimation of seismic motion in a graded medium with multiple cavities under antiplane strain conditions. This inhomogeneous and heterogeneous medium is subjected to either time-harmonic incident shear seismic waves or to body waves radiating from a point seismic source. Three different types of soil material gradient are considered: (i) density and shear modulus vary proportionally as quadratic functions of depth, but the wave velocity remains constant; (ii) the soil material is viscoelastic, with a shear modulus and density that vary with respect to the spatial coordinates in an arbitrary fashion, so that the wave velocity is both frequency and position-dependent and (iii) the soil material has position-dependent shear modulus and constant density, yielding a linear profile for the wave velocity. Three different, frequency-dependent boundary integral equation schemes are respectively developed for the aforementioned three types of graded soil materials based on: (i) Green's function for the quadratically graded elastic half-plane; (ii) a fundamental solution for the viscoelastic full-plane with position-dependent wave speed profiles and (iii) a fundamental solution for an elastic full-plane with a linearly varying wave speed profile. Next, a number of cases involving geological media with position-dependent material properties and any number of cavities of various shapes and geometry are solved in the frequency domain. The numerical results reveal the dependency of the wave fields and zones of stress concentration on the following key factors: (i) type and properties of the soil material gradient; (ii) type and characteristics of the applied seismic load; (iii) shape, position and number of cavities and (iv) interaction phenomena between the cavities and the free surface.
Inelastic processes in seismic wave generation by underground explosions
Energy Technology Data Exchange (ETDEWEB)
Rodean, H.C.
1980-08-01
Theories, computer calculations, and measurements of spherical stress waves from explosions are described and compared, with emphasis on the transition from inelastic to almost-elastic relations between stress and strain. Two aspects of nonspherical explosion geometry are considered: tectonic strain release and surface spall. Tectonic strain release affects the generation of surface waves; spall closure may also. The reduced-displacement potential is a common solution (the equivalent elastic source) of the forward and inverse problems, assuming a spherical source. Measured reduced-displacement potentials are compared with potentials calculated as solutions of the direct and inverse problems; there are significant differences between the results of the two types of calculations and between calculations and measurements. The simple spherical model of an explosion is not sufficient to account for observations of explosions over wide ranges of depth and yield. The explosion environment can have a large effect on explosion detection and yield estimation. The best sets of seismic observations for use in developing discrimination techniques are for high-magnitude high-yield explosions; the identification problem is most difficult for low-magnitude low-yield explosions. Most of the presently available explosion data (time, medium, depth, yield, etc.) are for explosions in a few media at the Nevada Test Site; some key questions concerning magnitude vs yield and m/sub b/ vs M/sub s/ relations can be answered only by data for explosions in other media at other locations.
Inelastic processes in seismic wave generation by underground explosions
International Nuclear Information System (INIS)
Rodean, H.C.
1980-01-01
Theories, computer calculations, and measurements of spherical stress waves from explosions are described and compared, with emphasis on the transition from inelastic to almost-elastic relations between stress and strain. Two aspects of nonspherical explosion geometry are considered: tectonic strain release and surface spall. Tectonic strain release affects the generation of surface waves; spall closure may also. The reduced-displacement potential is a common solution (the equivalent elastic source) of the forward and inverse problems, assuming a spherical source. Measured reduced-displacement potentials are compared with potentials calculated as solutions of the direct and inverse problems; there are significant differences between the results of the two types of calculations and between calculations and measurements. The simple spherical model of an explosion is not sufficient to account for observations of explosions over wide ranges of depth and yield. The explosion environment can have a large effect on explosion detection and yield estimation. The best sets of seismic observations for use in developing discrimination techniques are for high-magnitude high-yield explosions; the identification problem is most difficult for low-magnitude low-yield explosions. Most of the presently available explosion data (time, medium, depth, yield, etc.) are for explosions in a few media at the Nevada Test Site; some key questions concerning magnitude vs yield and m/sub b/ vs M/sub s/ relations can be answered only by data for explosions in other media at other locations
Nixon, C.; Kofman, R.; Schmitt, D. R.; Lofi, J.; Gulick, S. P. S.; Christeson, G. L.; Saustrup, S., Sr.; Morgan, J. V.
2017-12-01
We acquired a closely-spaced vertical seismic profile (VSP) in the Chicxulub K-Pg Impact Crater drilling program borehole to calibrate the existing surface seismic profiles and provide complementary measurements of in situ seismic wave speeds. Downhole seismic records were obtained at spacings ranging from 1.25 m to 5 m along the borehole from 47.5 m to 1325 mwsf (meters wireline below sea floor) (Fig 1a) using a Sercel SlimwaveTM geophone chain (University of Alberta). The seismic source was a 30/30ci Sercel Mini GI airgun (University of Texas), fired a minimum of 5 times per station. Seismic data processing used a combination of a commercial processing package (Schlumberger's VISTA) and MatlabTM codes. The VSP displays detailed reflectivity (Fig. 1a) with the strongest reflection seen at 600 mwsf (280 ms one-way time), geologically corresponding to the sharp contact between the post-impact sediments and the target peak ring rock, thus confirming the pre-drilling interpretations of the seismic profiles. A two-way time trace extracted from the separated up-going wavefield matches the major reflection both in travel time and character. In the granitic rocks that form the peak ring of the Chicxulub impact crater, we observe P-wave velocities of 4000-4500 m/s which are significantly less than the expected values of granitoids ( 6000 m/s) (Fig. 1b). The VSP measured wave speeds are confirmed against downhole sonic logging and in laboratory velocimetry measurements; these data provide additional evidence that the crustal material displaced by the impact experienced a significant amount of damage. Samples and data provided by IODP. Samples can be requested at http://web.iodp.tamu.edu/sdrm after 19 October 2017. Expedition 364 was jointly funded by ECORD, ICDP, and IODP with contributions and logistical support from the Yucatan State Government and UNAM. The downhole seismic chain and wireline system is funded by grants to DRS from the Canada Foundation for Innovation and
Removing Love waves from shallow seismic SH-wave data
Van Zanen, L.F.
2004-01-01
Geophysical exploration measurements are used to obtain an image of the geological structures of the subsurface, as detailed as possible. To this end, a wavefield is generated by a seismic source. This wavefield propagates through the subsurface, and will partly reflect on boundaries between layers
Seismic anisotropy in deforming salt bodies
Prasse, P.; Wookey, J. M.; Kendall, J. M.; Dutko, M.
2017-12-01
Salt is often involved in forming hydrocarbon traps. Studying salt dynamics and the deformation processes is important for the exploration industry. We have performed numerical texture simulations of single halite crystals deformed by simple shear and axial extension using the visco-plastic self consistent approach (VPSC). A methodology from subduction studies to estimate strain in a geodynamic simulation is applied to a complex high-resolution salt diapir model. The salt diapir deformation is modelled with the ELFEN software by our industrial partner Rockfield, which is based on a finite-element code. High strain areas at the bottom of the head-like strctures of the salt diapir show high amount of seismic anisotropy due to LPO development of halite crystals. The results demonstrate that a significant degree of seismic anisotropy can be generated, validating the view that this should be accounted for in the treatment of seismic data in, for example, salt diapir settings.
Aquatic vertebrate locomotion : Wakes from body waves
Videler, JJ; Muller, UK; Stamhuis, EJ
1999-01-01
Vertebrates swimming with undulations of the body and tail have inflection points where the curvature of the body changes from concave to convex or vice versa. These inflection paints travel down the body at the speed of the running wave of bending, In movements with increasing amplitudes, the body
The impact of crustal density variations on seismic wave propagation
Plonka, A.; Fichtner, A.
2014-12-01
Lateral density variations are the source of mass transport in the Earth at all scales, acting as drivers of convective motion. However, the density structure of the Earth remains largely unknown since classic seismic observables and gravity provide only weak constraints with strong trade-offs. Current density models are therefore often based on velocity scaling, making strong assumptions on the origin of structural heterogeneities, which may not necessarily be correct.We propose to develop a seismic tomography technique that directly inverts for density, using complete seismograms rather than arrival times of certain waves only. The first task in this challenge is to systematically study the imprints of density on synthetic seismograms.To compute the full seismic wavefield in a 3D heterogeneous medium without making significant approximations, we usenumerical wave propagation based on a spectral-element discretization of the seismic wave equation. We consider a 2000 by 1000 km wide and 500 km deep spherical section, with the 1D Earth model PREM (with 40 km crust thickness) as a background. Onto this (in the uppermost 40 km) we superimpose 3D randomly generated velocity and density heterogeneities of various magnitudes and correlation lenghts. We use different random realizations of heterogeneity distribution.We compare the synthetic seismograms for 3D velocity and density structure with 3D velocity structure and with the 1D background, calculating relative amplitude differences and timeshifts as functions of time and frequency.Our analyses indicate that reasonably sized density variations within the crust can leave a strong imprint on both traveltimes and amplitudes. This suggests (1) that crustal tomography can be significantly biased when density heterogeneities are not properly accounted for, and (2) that the solution of the seismic inverse problem for density may become feasible.
Spectral properties of Seismic waves during quarry blasts
Czech Academy of Sciences Publication Activity Database
Holub, Karel; Knejzlík, Jaromír; Rušajová, Jana
2006-01-01
Roč. 6, č. 2 (2006), s. 133-141 ISSN 1213-1962. [Nové poznatky a měření v seismologii, inženýrské geofyzice a geotechnice/15./. Ostrava, 11.04.2006-13.04.2006] R&D Projects: GA ČR GA205/03/0999 Institutional research plan: CEZ:AV0Z30860518 Keywords : quarry blasts * spectral analysis * body and surface waves Subject RIV: DC - Siesmology, Volcanology, Earth Structure
Energy Technology Data Exchange (ETDEWEB)
Inazaki, T. [Public Works Research Institute, Tsukuba (Japan)
1996-05-01
For the purpose of evaluating liquefaction in situ, it was proposed that an S-wave vibrator designed to serve as a source in a reflection exploration method be utilized as a strong vibration generating source, and measurement was conducted in this connection. Equipment used in this test included an S-wave vibrator, static cone penetration machine, and various measuring cones. A multiplicity of measuring cones had been inserted beforehand into the target layers and comparison layers, and changes upon vibrator activation were measured. On a dry bed of the Tonegawa river, a 40m{sup 2} field was set up, and 41 cone penetration tests were conducted, with the cones positioned zigzag at 5m intervals. In this way, the ground structure was disclosed from the surface to the 10m-deep level. For the measurement, 3-component cones and seismic cones were placed at prescribed depths, and fluctuations and waveforms presented by pore water pressure at each level were determined with the vibration source changing its place. It was found that the changes in the pore water pressure exposed to vibration assume characteristic patterns corresponding to the conditions of vibration application. 5 figs., 1 tab.
SH-wave seismic reflection at a landslide (Patigno, NW Italy) integrated with P-wave
Stucchi, E.; Tognarelli, A.; Ribolini, A.
2017-11-01
The aim of this paper is to present the acquisition and processing up to the depth migrated section of an SH-wave reflection seismic profile. This experience is conducted on a deep-seated gravitational slope deformation located in the Northern Apennines in Italy. The SH-wave depth-migrated image in the investigated area provides a detailed description of the small reactivation slip surfaces delineating minor landslides at shallow depths, which are responsible for the major damages observed. These results are integrated with a recently acquired P-wave seismic reflection profile investigating the same slope and delineating the highly deformed layer at depth, liable for the deep-seated gravitational slope deformation. The combined use of P-waves and SH-waves allows to gain a deeper knowledge of the landslide internal setting that is necessary to mitigate the risk associated with the mass movement.
MIGRATION OF SEISMIC AND VOLCANIC ACTIVITY AS DISPLAY OF WAVE GEODYNAMIC PROCESS
Directory of Open Access Journals (Sweden)
Alexander V. Vikulin
2012-01-01
Full Text Available Publications about the earthquake foci migration have been reviewed. An important result of such studies is establishment of wave nature of seismic activity migration that is manifested by two types of rotational waves; such waves are responsible for interaction between earthquakes foci and propagate with different velocities. Waves determining long-range interaction of earthquake foci are classified as Type 1; their limiting velocities range from 1 to 10 cm/s. Waves determining short-range interaction of foreshocks and aftershocks of individual earthquakes are classified as Type 2; their velocities range from 1 to 10 km/s. According to the classification described in [Bykov, 2005], these two types of migration waves correspond to slow and fast tectonic waves. The most complete data on earthquakes (for a period over 4.1 million of years and volcanic eruptions (for 12 thousand years of the planet are consolidated in a unified systematic format and analyzed by methods developed by the authors. For the Pacific margin, Alpine-Himalayan belt and the Mid-Atlantic Ridge, which are the three most active zones of the Earth, new patterns of spatial and temporal distribution of seismic and volcanic activity are revealed; they correspond to Type 1 of rotational waves. The wave nature of the migration of seismic and volcanic activity is confirmed. A new approach to solving problems of geodynamics is proposed with application of the data on migration of seismic and volcanic activity, which are consolidated in this study, in combination with data on velocities of movement of tectonic plate boundaries. This approach is based on the concept of integration of seismic, volcanic and tectonic processes that develop in the block geomedium and interact with each other through rotating waves with a symmetric stress tensor. The data obtained in this study give grounds to suggest that a geodynamic value, that is mechanically analogous to an impulse
Polarized seismic and solitary waves run-up at the sea bed
Energy Technology Data Exchange (ETDEWEB)
Dennis, L. C.C.; Zainal, A. A.; Faisal, S. Y. [Universiti Teknologi PETRONAS, 31750 Tronoh, Perak (Malaysia); Universiti Teknologi Malaysia, 81310 Johor Bahru (Malaysia)
2012-09-26
The polarization effects in hydrodynamics are studied. Hydrodynamic equation for the nonlinear wave is used along with the polarized solitary waves and seismic waves act as initial waves. The model is then solved by Fourier spectral and Runge-Kutta 4 methods, and the surface plot is drawn. The output demonstrates the inundation behaviors. Consequently, the polarized seismic waves along with the polarized solitary waves tend to generate dissimilar inundation which is more disastrous.
Air-coupled seismic waves at long range from Apollo launchings.
Donn, W. L.; Dalins, I.; Mccarty, V.; Ewing, M.; Kaschak , G.
1971-01-01
Microphones and seismographs were co-located in arrays on Skidaway Island, Georgia, for the launchings of Apollo 13 and 14, 374 km to the south. Simultaneous acoustic and seismic waves were recorded for both events at times appropriate to the arrival of the acoustic waves from the source. The acoustic signal is relatively broadband compared to the nearly monochromatic seismic signal; the seismic signal is much more continuous than the more pulse-like acoustic signal; ground loading from the pressure variations of the acoustic waves is shown to be too small to account for the seismic waves; and the measured phase velocities of both acoustic and seismic waves across the local instrument arrays differ by less than 6 per cent and possibly 3 per cent if experimental error is included. It is concluded that the seismic waves are generated by resonant coupling to the acoustic waves along some 10 km of path on Skidaway Island.
Body Wave and Ambient Noise Tomography of Makushin Volcano, Alaska
Lanza, F.; Thurber, C. H.; Syracuse, E. M.; Ghosh, A.; LI, B.; Power, J. A.
2017-12-01
Located in the eastern portion of the Alaska-Aleutian subduction zone, Makushin Volcano is among the most active volcanoes in the United States and has been classified as high threat based on eruptive history and proximity to the City of Unalaska and international air routes. In 2015, five individual seismic stations and three mini seismic arrays of 15 stations each were deployed on Unalaska island to supplement the Alaska Volcano Observatory (AVO) permanent seismic network. This temporary array was operational for one year. Taking advantage of the increased azimuthal coverage and the array's increased earthquake detection capability, we developed body-wave Vp and Vp/Vs seismic images of the velocity structure beneath the volcano. Body-wave tomography results show a complex structure with the upper 5 km of the crust dominated by both positive and negative Vp anomalies. The shallow high-Vp features possibly delineate remnant magma pathways or conduits. Low-Vp regions are found east of the caldera at approximately 6-9 km depth. This is in agreement with previous tomographic work and geodetic models, obtained using InSAR data, which had identified this region as a possible long-term source of magma. We also observe a high Vp/Vs feature extending between 7 and 12 km depth below the caldera, possibly indicating partial melting, although the resolution is diminished at these depths. The distributed stations allow us to further complement body-wave tomography with ambient noise imaging and to obtain higher quality of Vs images. Our data processing includes single station data preparation and station-pair cross-correlation steps (Bensen et al., 2007), and the use of the phase weighted stacking method (Schimmel and Gallart, 2007) to improve the signal-to-noise ratio of the cross-correlations. We will show surface-wave dispersion curves, group velocity maps, and ultimately a 3D Vs image. By performing both body wave and ambient noise tomography, we provide a high
Olugboji, T. M.; Lekic, V.; McDonough, W.
2017-07-01
We present a new approach for evaluating existing crustal models using ambient noise data sets and its associated uncertainties. We use a transdimensional hierarchical Bayesian inversion approach to invert ambient noise surface wave phase dispersion maps for Love and Rayleigh waves using measurements obtained from Ekström (2014). Spatiospectral analysis shows that our results are comparable to a linear least squares inverse approach (except at higher harmonic degrees), but the procedure has additional advantages: (1) it yields an autoadaptive parameterization that follows Earth structure without making restricting assumptions on model resolution (regularization or damping) and data errors; (2) it can recover non-Gaussian phase velocity probability distributions while quantifying the sources of uncertainties in the data measurements and modeling procedure; and (3) it enables statistical assessments of different crustal models (e.g., CRUST1.0, LITHO1.0, and NACr14) using variable resolution residual and standard deviation maps estimated from the ensemble. These assessments show that in the stable old crust of the Archean, the misfits are statistically negligible, requiring no significant update to crustal models from the ambient noise data set. In other regions of the U.S., significant updates to regionalization and crustal structure are expected especially in the shallow sedimentary basins and the tectonically active regions, where the differences between model predictions and data are statistically significant.
Preliminary Modeling of Global Seismic Wave Propagation in the Whole Mars
Toyokuni, G.; Ishihara, Y.; Takenaka, H.
2011-03-01
Global seismic wave propagation in the whole Mars is simulated by an accurate and efficient numerical scheme which has been developed for the Earth. Simple Mars models are used to obtain preliminary results of martian seismic waveform modeling.
Finite-frequency sensitivity kernels of seismic waves to fault zone structures
Allam, A. A.; Tape, C.; Ben-Zion, Y.
2015-12-01
We analyse the volumetric sensitivity of fault zone seismic head and trapped waves by constructing finite-frequency sensitivity (Fréchet) kernels for these phases using a suite of idealized and tomographically derived velocity models of fault zones. We first validate numerical calculations by waveform comparisons with analytical results for two simple fault zone models: a vertical bimaterial interface separating two solids of differing elastic properties, and a `vertical sandwich' with a vertical low velocity zone surrounded on both sides by higher velocity media. Establishing numerical accuracy up to 12 Hz, we compute sensitivity kernels for various phases that arise in these and more realistic models. In contrast to direct P body waves, which have little or no sensitivity to the internal fault zone structure, the sensitivity kernels for head waves have sharp peaks with high values near the fault in the faster medium. Surface wave kernels show the broadest spatial distribution of sensitivity, while trapped wave kernels are extremely narrow with sensitivity focused entirely inside the low-velocity fault zone layer. Trapped waves are shown to exhibit sensitivity patterns similar to Love waves, with decreasing width as a function of frequency and multiple Fresnel zones of alternating polarity. In models that include smoothing of the boundaries of the low velocity zone, there is little effect on the trapped wave kernels, which are focused in the central core of the low velocity zone. When the source is located outside a shallow fault zone layer, trapped waves propagate through the surrounding medium with body wave sensitivity before becoming confined. The results provide building blocks for full waveform tomography of fault zone regions combining high-frequency head, trapped, body, and surface waves. Such an imaging approach can constrain fault zone structure across a larger range of scales than has previously been possible.
Assessment of seismic wave effects on soil-structure interaction
International Nuclear Information System (INIS)
Bernreuter, D.L.
1977-01-01
One of the most common hypotheses made for soil-structure interaction analyses is that the earthquake input motion is identical at all points beneath the structure. Several papers have recently shown that this assumption may be overly conservative and that the effect of wave passage is extremely important. These studies typically employ a relatively simple model, namely, the basemat is represented by a rectangular rigid foundation resting on top of the soil and connected to the soil by a continuously distributed set of soil springs. The seismic input is applied at the base of the soil springs and is assumed to be traveling at a constant wave velocity across the site. It ispossible to improve on the soil/structure model by use of finite element methods; however, little is known about how to model the input seismic energy and typically a simple travelling wave is used. In this paper, the author examines the available data to determine: (i) the appropriate wave velocity to use, and (ii) if the currently availble analytic models are adequate. (Auth.)
Sardina, V.
2017-12-01
The Pacific Tsunami Warning Center's round the clock operations rely on the rapid determination of the source parameters of earthquakes occurring around the world. To rapidly estimate source parameters such as earthquake location and magnitude the PTWC analyzes data streams ingested in near-real time from a global network of more than 700 seismic stations. Both the density of this network and the data latency of its member stations at any given time have a direct impact on the speed at which the PTWC scientists on duty can locate an earthquake and estimate its magnitude. In this context, it turns operationally advantageous to have the ability of assessing how quickly the PTWC operational system can reasonably detect and locate and earthquake, estimate its magnitude, and send the corresponding tsunami message whenever appropriate. For this purpose, we designed and implemented a multithreaded C++ software package to generate detection time grids for both P- and S-waves after taking into consideration the seismic network topology and the data latency of its member stations. We first encapsulate all the parameters of interest at a given geographic point, such as geographic coordinates, P- and S-waves detection time in at least a minimum number of stations, and maximum allowed azimuth gap into a DetectionTimePoint class. Then we apply composition and inheritance to define a DetectionTimeLine class that handles a vector of DetectionTimePoint objects along a given latitude. A DetectionTimesGrid class in turn handles the dynamic allocation of new TravelTimeLine objects and assigning the calculation of the corresponding P- and S-waves' detection times to new threads. Finally, we added a GUI that allows the user to interactively set all initial calculation parameters and output options. Initial testing in an eight core system shows that generation of a global 2D grid at 1 degree resolution setting detection on at least 5 stations and no azimuth gap restriction takes under 25
MEASUREMENT OF COMPRESSIONAL-WAVE SEISMIC VELOCITIES IN 29 WELLS AT THE HANFORD SITE
Energy Technology Data Exchange (ETDEWEB)
PETERSON SW
2010-10-08
Check shot seismic velocity surveys were collected in 100 B/C, 200 East, 200-PO-1 Operational Unit (OU), and the Gable Gap areas in order to provide time-depth correlation information to aid the interpretation of existing seismic reflection data acquired at the Hanford Site (Figure 1). This report details results from 5 wells surveyed in fiscal year (FY) 2008, 7 wells in FY 2009, and 17 wells in FY 2010 and provides summary compressional-wave seismic velocity information to help guide future seismic survey design as well as improve current interpretations of the seismic data (SSC 1979/1980; SGW-39675; SGW-43746). Augmenting the check shot database are four surveys acquired in 2007 in support of the Bechtel National, Inc. Waste Treatment Plant construction design (PNNL-16559, PNNL-16652), and check shot surveys in three wells to support seismic testing in the 200 West Area (Waddell et al., 1999). Additional sonic logging was conducted during the late 1970s and early 1980s as part of the Basalt Waste Isolation Program (BWIP) (SSC 1979/1980) and check shot/sonic surveys as part of the safety report for the Skagit/Hanford Nuclear project (RDH/10-AMCP-0164). Check shot surveys are used to obtain an in situ measure of compressional-wave seismic velocity for sediment and rock in the vicinity of the well point, and provide the seismic-wave travel time to geologic horizons of interest. The check shot method deploys a downhole seismic receiver (geophone) to record the arrival of seismic waves generated by a source at the ground surface. The travel time of the first arriving seismic-wave is determined and used to create a time-depth function to correlate encountered geologic intervals with the seismic data. This critical tie with the underlying geology improves the interpretation of seismic reflection profile information. Fieldwork for this investigation was conducted by in house staff during the weeks of September 22, 2008 for 5 wells in the 200 East Area (Figure 2); June 1
Wu, S.; Yang, Y.; Wang, K.
2017-12-01
The Tien Shan orogeny, situated in central Asia about 2000 km away from the collision boundary between Indian plate and Eurasian plate, is one of the highest, youngest, and most active intracontinental mountain belts on the earth. It first formed during the Paleozoic times and became reactivated at about 20Ma. Although many studies on the dynamic processes of the Tien Shan orogeny have been carried out before, its tectonic rejuvenation and uplift mechanism are still being debated. A high-resolution model of crust and mantle beneath Tien Shan is critical to discern among competing models for the mountain building. In this study, we collect and process seismic data recorded by several seismic arrays in the central and western Tien Shan region to generate surface wave dispersion curves at 6-140 s period using ambient noise tomography (ANT) and two-plane surface wave tomography (TPWT) methods. Using these dispersion curves, we construct a high-resolution 3-D image of shear wave velocity (Vs) in the crust and upper mantle up to 300 km depth. Our current model constrained only by surface waves shows that, under the Tien Shan orogenic belt, a strong low S-wave velocity anomaly exists in the uppermost mantle down to the depth of 200km, supporting the model that the hot upper mantle is upwelling under the Tien Shan orogenic belt, which may be responsible for the mountain building. To the west of central Tien Shan across the Talas-Fergana fault, low S-wave velocity anomalies in the upper mantle become much weaker and finally disappear beneath the Fergana basin. Because surface waves are insensitive to the structures below 300 km, body wave arrival times will be included for a joint inversion with surface waves to generate S-wave velocity structure from the surface down to the mantle transition zone. The joint inversion of both body and surface waves provide complementary constraints on structures at different depths and helps to achieve a more realistic model compared with
Le Merrer, Marie; Clanet, Christophe; Quéré, David; Raphaël, Élie; Chevy, Frédéric
2011-01-01
We measure the deceleration of liquid nitrogen drops floating at the surface of a liquid bath. On water, the friction force is found to be about 10 to 100 times larger than on a solid substrate, which is shown to arise from wave resistance. We investigate the influence of the bath viscosity and show that the dissipation decreases as the viscosity is increased, owing to wave damping. The measured resistance is well predicted by a model imposing a vertical force (i.e., the drop weight) on a finite area, as long as the wake can be considered stationary. PMID:21876186
Hartzell, S.; Carver, D.; Williams, R.A.; Harmsen, S.; Zerva, A.
2003-01-01
Ground-motion records from a 52-element dense seismic array near San Jose, California, are analyzed to obtain site response, shallow shear-wave velocity, and plane-wave propagation characteristics. The array, located on the eastern side of the Santa Clara Valley south of the San Francisco Bay, is sited over the Evergreen basin, a 7-km-deep depression with Miocene and younger deposits. Site response values below 4 Hz are up to a factor of 2 greater when larger, regional records are included in the analysis, due to strong surface-wave development within the Santa Clara Valley. The pattern of site amplification is the same, however, with local or regional events. Site amplification increases away from the eastern edge of the Santa Clara Valley, reaching a maximum over the western edge of the Evergreen basin, where the pre-Cenozoic basement shallows rapidly. Amplification then decreases further to the west. This pattern may be caused by lower shallow shear-wave velocities and thicker Quaternary deposits further from the edge of the Santa Clara Valley and generation/trapping of surface waves above the shallowing basement of the western Evergreen basin. Shear-wave velocities from the inversion of site response spectra based on smaller, local earthquakes compare well with those obtained independently from our seismic reflection/refraction measurements. Velocities from the inversion of site spectra that include larger, regional records do not compare well with these measurements. A mix of local and regional events, however, is appropriate for determination of site response to be used in seismic hazard evaluation, since large damaging events would excite both body and surface waves with a wide range in ray parameters. Frequency-wavenumber, plane-wave analysis is used to determine the backazimuth and apparent velocity of coherent phases at the array. Conventional, high-resolution, and multiple signal characterization f-k power spectra and stacked slowness power spectra are
High-resolution seismic wave propagation using local time stepping
Peter, Daniel
2017-03-13
High-resolution seismic wave simulations often require local refinements in numerical meshes to accurately capture e.g. steep topography or complex fault geometry. Together with explicit time schemes, this dramatically reduces the global time step size for ground-motion simulations due to numerical stability conditions. To alleviate this problem, local time stepping (LTS) algorithms allow an explicit time stepping scheme to adapt the time step to the element size, allowing nearoptimal time steps everywhere in the mesh. This can potentially lead to significantly faster simulation runtimes.
Torpey, Megan Elizabeth
The Maule, Chile 2010 Mw 8.8 earthquake afforded the opportunity to study the rupture zone (33°S-38°S) in detail using aftershocks recorded by the rapid-response IRIS CHAMP seismic network. We used measurements of differential S to P seismic attenuation to characterize the attenuation structure of the South American crust and upper mantle wedge. We implemented an evolving time window to determine Qs-1 values using a spectral ratio method and incorporated these measurements into a bounded linear inequality least squares inversion to solve for Qs -1 in a 3D volume. On a large-scale, we observe an east-dipping low attenuation feature, consistent with the location of the Nazca oceanic slab, and image progressively greater attenuation as we move towards the surface of our model. A dramatic feature in our model is a large, low-attenuation body in the same location where Hicks et al. (2014) resolved a high P wave velocity anomaly in their velocity tomography model. We calculated the shear wave splitting intensity of the Maule rupture zone by implementing the multichannel method of Chevrot (2000) which calculates the splitting intensity of teleseismic SK(K)S phases and splitting parameters, ϕ and deltat. The results we obtained show an overall fast direction with a strong component of trench parallel splitting and very few trench normal splits. The fast directions do not parallel the Nazca APM, but are instead dominated by splits rotated 40°-50° counter-clockwise from Nazca APM. Based on these data, we see little evidence for sub-slab entrained mantle flow and invoke the trench-parallel retrograde flow model as an explanation for our measurements. We developed an extended splitting intensity method to allow for use of the upgoing S phase from Maule aftershocks, utilizing the initial event polarization. For this local dataset, we observe three dominant fast directions oriented N20°W, N40°E, and N10°W-20°E and a subset of fast directions trending N60°-90°E which
Eilon, Zachary; Fischer, Karen M.; Dalton, Colleen A.
2018-04-01
We present a methodology for 1-D imaging of upper mantle structure using a Bayesian approach that incorporates a novel combination of seismic data types and an adaptive parameterisation based on piecewise discontinuous splines. Our inversion algorithm lays the groundwork for improved seismic velocity models of the lithosphere and asthenosphere by harnessing the recent expansion of large seismic arrays and computational power alongside sophisticated data analysis. Careful processing of P- and S-wave arrivals isolates converted phases generated at velocity gradients between the mid-crust and 300 km depth. This data is allied with ambient noise and earthquake Rayleigh wave phase velocities to obtain detailed VS and VP velocity models. Synthetic tests demonstrate that converted phases are necessary to accurately constrain velocity gradients, and S-p phases are particularly important for resolving mantle structure, while surface waves are necessary for capturing absolute velocities. We apply the method to several stations in the northwest and north-central United States, finding that the imaged structure improves upon existing models by sharpening the vertical resolution of absolute velocity profiles, offering robust uncertainty estimates, and revealing mid-lithospheric velocity gradients indicative of thermochemical cratonic layering. This flexible method holds promise for increasingly detailed understanding of the upper mantle.
Assessment of seismic wave effects on soil-structure interaction
International Nuclear Information System (INIS)
Bernreuter, D.L.
1977-03-01
It is normally assumed in the seismic analysis of structures that the free-field motion which is used as input is the same for all points on a given level beneath the foundation mat. This represents a simplification, as not all particles of soil describe the same motion simultaneously. As the foundation mat of the structure is rigid in the horizontal direction, it will tend to average the ground motion. Abandoning the assumption of the uniformity of the input motion may lead to a reduction of the translational motion which a foundation mat will experience, as the displacement components will cancel each other to a certain extent. This is of considerable interest for the design of nuclear power plants which are very stiff, large structures. To investigate these effects, the extremely complex phenomenon of the passage of a seismic wave has to be simplified considerably. It is the purpose of this paper to determine if wave passage effects can be determined from the simplified analyses currently used
Seismic waves and acoustic waves: from earthquake to music
D'Addezio, Giuliana; Marsili, Antonella; Ingrid Hunstad, Ingrid; Burrato, Pierfrancesco; Casale, Paolo; Vallocchia, Massimiliano; Fracassi, Umberto; Ventura, Guido
2011-01-01
INGV is currently the largest European scientific institution dealing with Earth Sciences research and real-time surveillance, early warning, and forecast activities in geophysics and volcanology. The Laboratorio Didattica e Divulgazione Scientifica of INGV organizes every year rich educational and outreach activities with schools of different levels and with general public to convey scientific knowledge and to promote research on science and nature, focusing on volcanic and s...
Characterization of tsunamigenic earthquake in Java region based on seismic wave calculation
International Nuclear Information System (INIS)
Pribadi, Sugeng; Afnimar,; Puspito, Nanang T.; Ibrahim, Gunawan
2014-01-01
This study is to characterize the source mechanism of tsunamigenic earthquake based on seismic wave calculation. The source parameter used are the ratio (Θ) between the radiated seismic energy (E) and seismic moment (M o ), moment magnitude (M W ), rupture duration (T o ) and focal mechanism. These determine the types of tsunamigenic earthquake and tsunami earthquake. We calculate the formula using the teleseismic wave signal processing with the initial phase of P wave with bandpass filter 0.001 Hz to 5 Hz. The amount of station is 84 broadband seismometer with far distance of 30° to 90°. The 2 June 1994 Banyuwangi earthquake with M W =7.8 and the 17 July 2006 Pangandaran earthquake with M W =7.7 include the criteria as a tsunami earthquake which distributed about ratio Θ=−6.1, long rupture duration To>100 s and high tsunami H>7 m. The 2 September 2009 Tasikmalaya earthquake with M W =7.2, Θ=−5.1 and To=27 s which characterized as a small tsunamigenic earthquake
Observations of short period seismic scattered waves by small seismic arrays
Directory of Open Access Journals (Sweden)
M. Simini
1997-06-01
Full Text Available The most recent observations of well correlated seismic phases in the high frequency coda of local earthquakes recorded throughout the world are reported. In particular the main results, obtained on two active volcanoes, Teide and Deception, using small array are described. The ZLC (Zero Lag Cross-correlation method and polarization analysis have been applied to the data in order to distinguish the main phases in the recorded seismograms and their azimuths and apparent velocities. The results obtained at the Teide volcano demonstrate that the uncorrelated part of the seismograms may be produced by multiple scattering from randomly distributed heterogeneity, while the well correlated part, showing SH type polarization or the possible presence of Rayleigh surface waves, may be generated by single scattering by strong scatterers. At the Deception Volcano strong scattering, strongly focused in a precise direction, is deduced from the data. In that case, all the coda radiation is composed of surface waves.
High resolution Rayleigh wave group velocity tomography in North-China from ambient seismic noise
International Nuclear Information System (INIS)
Fang Lihua; Wu Jianping; Ding Zhifeng; Panza, G.F.
2009-03-01
This study presents the results of the Rayleigh wave group velocity tomography in North-China performed using ambient seismic noise observed at 190 broadband and 10 very broadband stations of the North-China Seismic Array. All available vertical component time-series for the 14 months span between January, 2007 and February, 2008 are cross-correlated to obtain empirical Rayleigh wave Green functions that are subsequently processed, with the multiple filter method, to isolate the group velocity dispersion curves of the fundamental mode of Rayleigh wave. Tomographic maps, with a grid spacing of 0.25 deg. x 0.25 deg., are computed at the periods of 4.5s, 12s, 20s, 28s. The maps at short periods reveal an evident lateral heterogeneity in the crust of North-China, quite well in agreement with known geological and tectonic features. The North China Basin is imaged as a broad low velocity area, while the Taihangshan and Yanshan uplifts and Ordos block are imaged as high velocity zones, and the Quaternary intermountain basins show up as small low-velocity anomalies. The group velocity contours at 4.5s, 12s and 20s are consistent with the Bouguer gravity anomalies measured in the area of the Taihangshan fault, that cuts through the lower crust at least. Most of the historical strong earthquakes (M≥6.0) are located where the tomographic maps show zones with moderate velocity gradient. (author)
Wanniarachchi, W A M; Ranjith, P G; Perera, M S A; Rathnaweera, T D; Lyu, Q; Mahanta, B
2017-10-01
The mechanical properties of any substance are essential facts to understand its behaviour and make the maximum use of the particular substance. Rocks are indeed an important substance, as they are of significant use in the energy industry, specifically for fossil fuels and geothermal energy. Attenuation of seismic waves is a non-destructive technique to investigate mechanical properties of reservoir rocks under different conditions. The attenuation characteristics of five different rock types, siltstone, shale, Australian sandstone, Indian sandstone and granite, were investigated in the laboratory using ultrasonic and acoustic emission instruments in a frequency range of 0.1-1 MHz. The pulse transmission technique and spectral ratios were used to calculate the attenuation coefficient ( α ) and quality factor ( Q ) values for the five selected rock types for both primary ( P ) and secondary ( S ) waves, relative to the reference steel sample. For all the rock types, the attenuation coefficient was linearly proportional to the frequency of both the P and S waves. Interestingly, the attenuation coefficient of granite is more than 22% higher than that of siltstone, sandstone and shale for both P and S waves. The P and S wave velocities were calculated based on their recorded travel time, and these velocities were then used to calculate the dynamic mechanical properties including elastic modulus ( E ), bulk modulus ( K ), shear modulus ( µ ) and Poisson's ratio ( ν ). The P and S wave velocities for the selected rock types varied in the ranges of 2.43-4.61 km s -1 and 1.43-2.41 km h -1 , respectively. Furthermore, it was observed that the P wave velocity was always greater than the S wave velocity, and this confirmed the first arrival of P waves to the sensor. According to the experimental results, the dynamic E value is generally higher than the static E value obtained by unconfined compressive strength tests.
Wanniarachchi, W. A. M.; Ranjith, P. G.; Perera, M. S. A.; Rathnaweera, T. D.; Lyu, Q.; Mahanta, B.
2017-10-01
The mechanical properties of any substance are essential facts to understand its behaviour and make the maximum use of the particular substance. Rocks are indeed an important substance, as they are of significant use in the energy industry, specifically for fossil fuels and geothermal energy. Attenuation of seismic waves is a non-destructive technique to investigate mechanical properties of reservoir rocks under different conditions. The attenuation characteristics of five different rock types, siltstone, shale, Australian sandstone, Indian sandstone and granite, were investigated in the laboratory using ultrasonic and acoustic emission instruments in a frequency range of 0.1-1 MHz. The pulse transmission technique and spectral ratios were used to calculate the attenuation coefficient (α) and quality factor (Q) values for the five selected rock types for both primary (P) and secondary (S) waves, relative to the reference steel sample. For all the rock types, the attenuation coefficient was linearly proportional to the frequency of both the P and S waves. Interestingly, the attenuation coefficient of granite is more than 22% higher than that of siltstone, sandstone and shale for both P and S waves. The P and S wave velocities were calculated based on their recorded travel time, and these velocities were then used to calculate the dynamic mechanical properties including elastic modulus (E), bulk modulus (K), shear modulus (µ) and Poisson's ratio (ν). The P and S wave velocities for the selected rock types varied in the ranges of 2.43-4.61 km s-1 and 1.43-2.41 km h-1, respectively. Furthermore, it was observed that the P wave velocity was always greater than the S wave velocity, and this confirmed the first arrival of P waves to the sensor. According to the experimental results, the dynamic E value is generally higher than the static E value obtained by unconfined compressive strength tests.
Matrix Approach of Seismic Wave Imaging: Application to Erebus Volcano
Blondel, T.; Chaput, J.; Derode, A.; Campillo, M.; Aubry, A.
2017-12-01
This work aims at extending to seismic imaging a matrix approach of wave propagation in heterogeneous media, previously developed in acoustics and optics. More specifically, we will apply this approach to the imaging of the Erebus volcano in Antarctica. Volcanoes are actually among the most challenging media to explore seismically in light of highly localized and abrupt variations in density and wave velocity, extreme topography, extensive fractures, and the presence of magma. In this strongly scattering regime, conventional imaging methods suffer from the multiple scattering of waves. Our approach experimentally relies on the measurement of a reflection matrix associated with an array of geophones located at the surface of the volcano. Although these sensors are purely passive, a set of Green's functions can be measured between all pairs of geophones from ice-quake coda cross-correlations (1-10 Hz) and forms the reflection matrix. A set of matrix operations can then be applied for imaging purposes. First, the reflection matrix is projected, at each time of flight, in the ballistic focal plane by applying adaptive focusing at emission and reception. It yields a response matrix associated with an array of virtual geophones located at the ballistic depth. This basis allows us to get rid of most of the multiple scattering contribution by applying a confocal filter to seismic data. Iterative time reversal is then applied to detect and image the strongest scatterers. Mathematically, it consists in performing a singular value decomposition of the reflection matrix. The presence of a potential target is assessed from a statistical analysis of the singular values, while the corresponding eigenvectors yield the corresponding target images. When stacked, the results obtained at each depth give a three-dimensional image of the volcano. While conventional imaging methods lead to a speckle image with no connection to the actual medium's reflectivity, our method enables to
Database of seismic wave travel times in the Bohemian Massif
Czech Academy of Sciences Publication Activity Database
Růžek, Bohuslav; Zedník, Jan; Hrubcová, Pavla
2005-01-01
Roč. 5, č. 2 (2005), s. 145-152 ISSN 1213-1962. [Nové poznatky a měření v seizmologii, inženýrské geofyzice a geotechnice. Ostrava, 12.04.2005-13.04.2005] Institutional research plan: CEZ:AV0Z30120515 Keywords : refraction seismic experiments * Bohemian Massif * database Subject RIV: DC - Siesmology, Volcanology, Earth Structure
Numerical simulation of seismic wave propagation from land-excited large volume air-gun source
Cao, W.; Zhang, W.
2017-12-01
The land-excited large volume air-gun source can be used to study regional underground structures and to detect temporal velocity changes. The air-gun source is characterized by rich low frequency energy (from bubble oscillation, 2-8Hz) and high repeatability. It can be excited in rivers, reservoirs or man-made pool. Numerical simulation of the seismic wave propagation from the air-gun source helps to understand the energy partitioning and characteristics of the waveform records at stations. However, the effective energy recorded at a distance station is from the process of bubble oscillation, which can not be approximated by a single point source. We propose a method to simulate the seismic wave propagation from the land-excited large volume air-gun source by finite difference method. The process can be divided into three parts: bubble oscillation and source coupling, solid-fluid coupling and the propagation in the solid medium. For the first part, the wavelet of the bubble oscillation can be simulated by bubble model. We use wave injection method combining the bubble wavelet with elastic wave equation to achieve the source coupling. Then, the solid-fluid boundary condition is implemented along the water bottom. And the last part is the seismic wave propagation in the solid medium, which can be readily implemented by the finite difference method. Our method can get accuracy waveform of land-excited large volume air-gun source. Based on the above forward modeling technology, we analysis the effect of the excited P wave and the energy of converted S wave due to different water shapes. We study two land-excited large volume air-gun fields, one is Binchuan in Yunnan, and the other is Hutubi in Xinjiang. The station in Binchuan, Yunnan is located in a large irregular reservoir, the waveform records have a clear S wave. Nevertheless, the station in Hutubi, Xinjiang is located in a small man-made pool, the waveform records have very weak S wave. Better understanding of
Petronio, Lorenzo; Boaga, Jacopo; Cassiani, Giorgio
2016-05-01
The mechanisms of the disastrous Vajont rockslide (North-Eastern Italy, October 9, 1963) have been studied in great detail over the past five decades. Nevertheless, the reconstruction of the rockslide dynamics still presents several uncertainties, including those related to the accurate estimation of the actual landslide mass. This work presents the results of a geophysical characterization of the Vajont landslide body in terms of material properties and buried geometry. Both aspects add new information to the existing dataset and will help a better understanding of the rockslide failure mechanisms and dynamics. In addition, some general considerations concerning the intricacies of landslide characterization can be drawn, with due attention to potential pitfalls. The employed techniques are: (i) high resolution P-wave reflection, (ii) high resolution SH-wave reflection, (iii) controlled source surface wave analysis. We adopted as a seismic source a vibrator both for P waves and SH waves, using vertical and horizontal geophones respectively. For the surface wave seismic survey we used a heavy drop-weight source and low frequency receivers. Despite the high noise level caused by the fractured conditions of the large rock body, a common situation in landslide studies, we managed to achieve a satisfying imaging quality of the landslide structure thanks to the large number of active channels, the short receiver interval and the test of appropriate seismic sources. The joint use of different seismic techniques help focus the investigation on the rock mass mechanical properties. Results are in good agreement with the available borehole data, the geological sections and the mechanical properties of the rockmass estimated by other studies. In general the proposed approach is likely to be applicable successfully to similar situations where scattering and other noise sources are a typical bottleneck to geophysical data acquisition on landslide bodies.
DEFF Research Database (Denmark)
Dahl, Jens Peder; Varro, S.; Wolf, A.
2007-01-01
We derive explicit expressions for the Wigner function of wave functions in D dimensions which depend on the hyperradius-that is, of s waves. They are based either on the position or the momentum representation of the s wave. The corresponding Wigner function depends on three variables......: the absolute value of the D-dimensional position and momentum vectors and the angle between them. We illustrate these expressions by calculating and discussing the Wigner functions of an elementary s wave and the energy eigenfunction of a free particle....
Seismic reflection and refraction methods
Digital Repository Service at National Institute of Oceanography (India)
Chaubey, A.K.
of noise that we attempt to suppress. In all of the remaining discussion about seismic waves, we will consider only body waves. 216 Factors affecting the amplitude of seismic waves Many factors affect the amplitude of seismic waves and some.... Factors which affect amplitude of seismic wave. Absorption is another factor, which affects amplitude. The loss of energy in the Earth due to absorption is described in various ways viz., i) by a quantity called ‘Q’ (the amount of energy in a seismic...
Esteve, C.; Schaeffer, A. J.; Audet, P.
2017-12-01
Over the past number of decades, the Slave Craton (Canada) has been extensively studied for its diamondiferous kimberlites. Not only are diamonds a valuable resource, but their kimberlitic host rocks provide an otherwise unique direct source of information on the deep upper mantle (and potentially transition zone). Many of the Canadian Diamond mines are located within the Slave Craton. As a result of the propensity for diamondiferous kimberlites, it is imperative to probe the deep mantle structure beneath the Slave Craton. This work is further motivated by the increase in high-quality broadband seismic data across the Northern Canadian Cordillera over the past decade. To this end we have generated a P and S body wave tomography model of the Slave Craton and its surroundings. Furthermore, tomographic inversion techniques are growing ever more capable of producing high resolution Earth models which capture detailed structure and dynamics across a range of scale lengths. Here, we present preliminary results on the structure of the upper mantle underlying the Slave Craton. These results are generated using data from eight different seismic networks such as the Canadian National Seismic Network (CNSN), Yukon Northwest Seismic Network (YNSN), older Portable Observatories for Lithospheric Analysis and Reseach Investigating Seismicity (POLARIS), Regional Alberta Observatory for Earthquake Studies Network (RV), USArray Transportable Array (TA), older Canadian Northwest Experiment (CANOE), Batholith Broadband (XY) and the Yukon Observatory (YO). This regional model brings new insights about the upper mantle structure beneath the Slave Craton, Canada.
Saito, Tatsuhiko; Tsushima, Hiroaki
2016-11-01
The present study proposes a method for synthesizing the ocean bottom pressure records during a tsunamigenic earthquake. First, a linear seismic wave simulation is conducted with a kinematic earthquake fault model as a source. Then, a nonlinear tsunami simulation is conducted using the sea bottom movement calculated in the seismic wave simulation. By using these simulation results, this method can provide realistic ocean bottom pressure change data, including both seismic and tsunami contributions. A simple theoretical consideration indicates that the dynamic pressure change caused by the sea bottom acceleration can contribute significantly until the duration of 90 s for a depth of 4000 m in the ocean. The performance of a tsunami monitoring system was investigated using the synthesized ocean bottom pressure records. It indicates that the system based on the hydrostatic approximation could not measure the actual tsunami height when the time does not elapse enough. The dynamic pressure change and the permanent sea bottom deformation inside the source region break the condition of a simple hydrostatic approximation. A tsunami source estimation method of tFISH is also examined. Even though the synthesized records contain a large dynamic pressure change, which is not considered in the algorithm, tFISH showed a satisfactory performance 5 min after the earthquake occurrence. The pressure records synthesized in this study, including both seismic wave and tsunami contributions, are more practical for evaluating the performance of our monitoring ability, whereas most tsunami monitoring tests neglect the seismic wave contribution.
A seismic waves velocity model for Gran Canaria Island from ambient noise correlations
García-Jerez, Antonio; Almendros, Javier; Martínez-Arévalo, Carmen; de Lis Mancilla, Flor; Luzón, Francisco; Carmona, Enrique; Martín, Rosa; Sánchez, Nieves
2014-05-01
We have analysed continuous ambient seismic noise recorded by a temporary array in Gran Canaria (Canary Islands, Spain) in order to find a velocity model for the top few kilometers. The SISTEVOTENCAN-IGN seismic array consisted of five broadband stations surrounding a sixth central one placed close to Pico de las Nieves, at the center of the island. The array had a radius of 12-14 km, with interstation distances ranging from 10 to 27 km. This network was operative from December 2009 to November 2011. The Green's functions between the 15 pairs of stations have been estimated in the time domain by stacking cross-correlations of 60-s time windows for the whole recording period (~2 years). The effects of several processing adjustments such as 1-bit normalization and spectral whitening are discussed. We observe significant differences (mainly in amplitude) between causal and acausal parts of the estimated Green's functions, which can be associated to an uneven distribution of the seismic noise sources. The application of a phase-matched filter based on an average dispersion curve allowed the effective reduction of some spurious early arrivals and the selection of fundamental-mode Rayleigh wave pulses, making possible an automatic extraction of their group velocities. Then, Rayleigh-wave dispersion curves were retrieved for the set of paths by using frequency-time analysis (FTAN) as well as by following the procedure described by Herrin and Goforth (1977, BSSA) based on the iterative fitting of a phase-matched filter which optimally undisperses the signal. Reliable curves were obtained from 1 s to 6-7 s with group velocities ranging between 1.5 and 2.2 km/s. Some lateral variations in velocity have been detected in spite of the limited spatial coverage and path density, which substantially restricted the resolution. A mean S-wave velocity model has been inverted for this area down to ~3 km.
Joint Inversion of Surface Waves Dispersion and Receiver Function at Cuba Seismic Stations
International Nuclear Information System (INIS)
Gonzalez, O'Leary; Moreno, Bladimir; Romanelli, Fabio; Panza, Giuliano F.
2010-06-01
Joint inversion of Rayleigh wave group velocity dispersion and receiver functions have been used to estimate the crust and upper mantle structure at eight seismic stations in Cuba. Receiver functions have been computed from teleseismic recordings of earthquakes at epicentral (angular) distances between 30 o and 90 o and Rayleigh wave group velocity dispersion have been taken from a surface-wave tomography study of the Caribbean area. The thickest crust (around 27 km) is found at Cascorro (CCC), Soroa (SOR), Moa (MOA) and Maisi (MAS) stations while the thinnest crust (around 18 km) is found at stations Rio Carpintero (RCC) and Guantanamo Bay (GTBY), in the southeastern of Cuba; this result is in agreement with the southward gradual thinning of the crust revealed by previous studies. The inversion shows a crystalline crust with S-wave velocity between 2.9 km/s and 3.9 km/s and at the crust-mantle transition zone the shear wave velocity varies from 3.9 km/s and 4.3 km/s. The lithospheric thickness varies from 74 km, in the youngest lithosphere, to 200 km in the middle of the Cuban island. Evidences of a subducted slab possibly belonging to the Caribbean plate are present below the stations Las Mercedes (LMG), RCC and GTBY and a thicker slab is present below the SOR station. (author)
Pulli, J. J.; Kofford, A. S.; Newman, K. R.; Krumhansl, P. A.
2012-12-01
T-wave signals from sub-sea earthquakes are often recorded on coastal or island seismic stations (Linehan, 1940; Okal, 2008). The physical process of the acoustic-to-seismic conversion is poorly understood but likely depends on factors such as seafloor relief and sediment thickness at the location where the interaction occurs. Quantification of the conversion process is necessary to understand and interpret the seismic recordings, and allow for the calculation of in-water acoustic levels from these recordings where no in-water sensor recordings are available. Applications for this knowledge would include the calculation of in-water explosion yields and seismic airgun source levels. Here we present the measurement of the acoustic-to-seismic transfer functions at Ascension Island and Diego Garcia using hydroacoustic data from the International Monitoring System and broadband seismic data from the Global Seismic Network. For Ascension Island, a volcanic island formed above magmatic plumes, we used T-wave signals from earthquakes on the Central Mid-Atlantic Ridge and associated fracture zones. For Diego Garcia, an atoll of carbonate sequences and no volcanism, we used T-wave signals from earthquakes along the Sumatran Subduction Zone, the Indian Ocean Ridges, and the Chagos Arch. The methodology is based on the smoothed cross-spectra over a frequency band that is common to the acoustic and seismic recordings, typically 2-18 Hz. Preliminary results indicate that at 5 Hz the acoustic-to-seismic conversion is 2-4 times more efficient at Ascension Island than at Diego Garcia (124 nm/s/Pa vs. 51 nm/s/Pa, respectively), but nearly equal at 10 Hz (20 nm/s/Pa). At 15 Hz the conversion is more efficient at Diego Garcia (13 nm/s/Pa vs. 8 nm/s/Pa at Ascension). We also investigate the azimuthal variance of this transfer function, as well as the differences between the three components of seismic motion. As a verification of the methodology, we use the equivalent time domain
Implicit finite-difference simulations of seismic wave propagation
Chu, Chunlei
2012-03-01
We propose a new finite-difference modeling method, implicit both in space and in time, for the scalar wave equation. We use a three-level implicit splitting time integration method for the temporal derivative and implicit finite-difference operators of arbitrary order for the spatial derivatives. Both the implicit splitting time integration method and the implicit spatial finite-difference operators require solving systems of linear equations. We show that it is possible to merge these two sets of linear systems, one from implicit temporal discretizations and the other from implicit spatial discretizations, to reduce the amount of computations to develop a highly efficient and accurate seismic modeling algorithm. We give the complete derivations of the implicit splitting time integration method and the implicit spatial finite-difference operators, and present the resulting discretized formulas for the scalar wave equation. We conduct a thorough numerical analysis on grid dispersions of this new implicit modeling method. We show that implicit spatial finite-difference operators greatly improve the accuracy of the implicit splitting time integration simulation results with only a slight increase in computational time, compared with explicit spatial finite-difference operators. We further verify this conclusion by both 2D and 3D numerical examples. © 2012 Society of Exploration Geophysicists.
Seismic wave speed structure of the Ontong Java Plateau
Covellone, Brian M.; Savage, Brian; Shen, Yang
2015-06-01
The Ontong Java Plateau (OJP) represents the result of a significant event in the Earth's geologic history. Limited geophysical and geochemical data, as well as the plateau's relative isolation in the Pacific ocean, have made interpretation of the modern day geologic structure and its 120 Ma formation history difficult. Here we present the highest resolution image to date of the wave speed structure of the OJP region. We use a data set that combines Rayleigh waves extracted from both ambient noise and earthquake waveforms and an iterative finite-frequency tomography methodology. The combination of datasets allow us to best exploit the limited station distribution in the Pacific and image wave speed structures between 35 km and 300 km into the Earth. We image a region of fast shear wave speeds, greater than 4.75 km/s, that extends to greater than 100 km beneath the plateau. The wave speeds are similar to as observed in cratonic environments and are consistent with a compositional anomaly that resulted from the residuum of eclogite entrainment during the plateau's formation. The combination of our imaged wave speed structure and previous geochemical work suggest that a surfacing plume head entrained eclogite from the deep mantle and accounts for the anomalous buoyancy characteristics of the plateau and observed fast wave speeds.
Seismic wave propagation on heterogeneous systems with CHAPEL
Gokhberg, Alexey; Fichtner, Andreas
2014-05-01
Simulations of seismic wave propagation play a key role in the exploration of the Earth's internal structure, the prediction of earthquake-induced ground motion, and numerous other applications. In order to harness modern heterogeneous HPC systems, we implement a spectral-element discretization of the seismic wave equation using the emerging parallel programming language Chapel. High-performance massively parallel computing systems are widely used for solving seismological problems. A recent trend in the evolution of such systems is a transition from homogeneous architectures based on the conventional CPU to faster and more energy-efficient heterogeneous architectures that combine CPU with the special purpose GPU accelerators. These new heterogeneous architectures have much higher hardware complexity and are thus more difficult to program. Therefore transition to heterogeneous computing systems widens the well known gap between the performance of the new hardware and the programmers' productivity. In particular, programming heterogeneous systems typically involves a mix of various programming technologies like MPI, CUDA, or OpenACC. This conventional approach increases complexity of application code, limits its portability and reduces the programmers' productivity. We are approaching this problem by introducing a unified high-level programming model suitable for both conventional and hybrid architectures. Our model is based on the Partitioned Global Address Space (PGAS) paradigm used by several modern parallel programming languages. We implemented this model by extending Chapel, the emerging parallel programming language created at Cray Inc. In particular, we introduced the language abstractions for GPU-based domain mapping and extended the open source Chapel compiler (version 1.8.0) with facilities designed to translate Chapel high-level parallel programming constructs into CUDA kernels. We used this extended Chapel implementation to re-program the package for the
Premlet, B.; Sabu, S.; Kamarudheen, R.; Subair, S.
2017-12-01
Since the first nuclear test on 15 July 1945 , there have been over 2,051 other weapon tests around the world . The waveforms of a natural earthquake which generates strong S waves and an underground explosion which is dominated by P waves were distinguished from the analysis of data corresponding to a 2005 M5.0 Earthquake and a 2016 North Korean nuclear test , both at similar distances from seismometer . Further differences between the seismograms were evaluated and successfully distinguished between the origins of the elastic waves through the data using Moment Tensor Solution using stations BJT , HIA and INCN . North Korea has developed a nuclear fuel cycle capability and has both plutonium and enriched uranium programs at Pyongyang . Seismic recordings of vertical ground motion at Global Seismographic Network station IC.MDJ of the 4 seismic events at Punggye-ri , North Korea , which occurred on the 9th of October 2006 , 25th of May 2009, 12th of February 2013 and on the 6th of January and 9th of September , 2016 were examined and the P waves of these seismic waves , which show very similar wave form , were inspected and compared to the seismic data of the latest underground nuclear test on the 3rd of September 2017 at 03:30 UTC at the same site which is many times more powerful than the previous tests . The country , which is the only nation to have tested nuclear weapons in this millennium , has successfully prevented the release of radioactive isotopes and hampered data collection but further studies were done using acoustic data which was analysed from sonograms of the 4 North Korean tests at station MDJ. The latest explosion data from 3rd September was also compared to 42 presumed underground explosions which occurred in China , India , the U.S.S.R , Iran , Turkey and recorded at Arkansas Seismic Network.
International Nuclear Information System (INIS)
Macia, R.; Correig, A.M.
1987-01-01
Seismic wave propagation is described by a second order differential equation for medium displacement. By Fourier transforming with respect to time and space, wave equation transforms into a system of first order linear differential equations for the Fourier transform of displacement and stress. This system of differential equations is solved by means of Matrix Propagator and applied to the propagation of body waves in stratified media. The matrix propagators corresponding to P-SV and SH waves in homogeneous medium are found as an intermediate step to obtain the spectral response of body waves propagating through a stratified medium with homogeneous layers. (author) 14 refs
Maruyama, Takashi; Shinagawa, Hiroyuki
2014-05-01
After the M 9.0 Tohoku-oki earthquake in 2011, strong deformation of ionogram echo traces, forming multiple cusp signatures (MCSs), were observed at three stations 790-1880 km from the epicenter. The vertical structure of the ionospheric disturbances was determined by true height analysis and compared with broadband seismograph records at stations close to the ionosondes. These ionospheric disturbances were caused by vertically propagating acoustic waves excited by the up/down ground motion of seismic waves. Numerical simulations have shown that acoustic waves with a period of 15-40 s and amplitude of order 1 mm/s at the ground level were sufficient to create MCSs as sharp as those observed. These acoustic wave parameters are consistent with the seismic records if the motion of the air mass on the ground level is assumed to be the same as the ground motion. The travel time diagram of the seismic records along the line connecting the epicenter and ionosondes showed that the first MCS ionogram detected at each station was caused by P waves, while the others were caused by Rayleigh waves.
Accelerating Simulation of Seismic Wave Propagation by Multi-GPUs (Invited)
Okamoto, T.; Takenaka, H.; Nakamura, T.; Aoki, T.
2010-12-01
Simulation of seismic wave propagation is essential in modern seismology: the effects of irregular topography of the surface, internal discontinuities and heterogeneity on the seismic waveforms must be precisely modeled in order to probe the Earth's and other planets' interiors, to study the earthquake sources, and to evaluate the strong ground motions due to earthquakes. Devices with high computing performance are necessary because in large scale simulations more than one billion of grid points are required. GPU (Graphics Processing Unit) is a remarkable device for its many core architecture with more-than-one-hundred processing units, and its high memory bandwidth. Now GPU delivers extremely high computing performance (more than one tera-flops in single-precision arithmetic) at a reduced power and cost compared to conventional CPUs. The simulation of seismic wave propagation is a memory intensive problem which involves large amount of data transfer between the memory and the arithmetic units while the number of arithmetic calculations is relatively small. Therefore the simulation should benefit from the high memory bandwidth of the GPU. Thus several approaches to adopt GPU to the simulation of seismic wave propagation have been emerging (e.g., Komatitsch et al., 2009; Micikevicius, 2009; Michea and Komatitsch, 2010; Aoi et al., SSJ 2009, JPGU 2010; Okamoto et al., SSJ 2009, SACSIS 2010). In this paper we describe our approach to accelerate the simulation of seismic wave propagation based on the finite-difference method (FDM) by adopting multi-GPU computing. The finite-difference scheme we use is the three-dimensional, velocity-stress staggered grid scheme (e.g., Grave 1996; Moczo et al., 2007) for heterogeneous medium with perfect elasticity (incorporation of an-elasticity is underway). We use the GPUs (NVIDIA S1070, 1.44 GHz) installed in the TSUBAME grid cluster in the Global Scientific Information and Computing Center, Tokyo Institute of Technology and NVIDIA
Seismic Wave Propagation in Southern and Central Africa
National Research Council Canada - National Science Library
Langston, Charles
1997-01-01
Structure of the crust and upper mantle in southern and central Africa is investigated using seismic data from the Global Seismic Network and a special PASSCAL deployment of stations in Tanzania, East Africa...
Czech Academy of Sciences Publication Activity Database
Svitek, Tomáš; Vavryčuk, Václav; Lokajíček, Tomáš; Petružálek, Matěj
2014-01-01
Roč. 199, č. 3 (2014), s. 1682-1697 ISSN 0956-540X R&D Projects: GA MŠk LH13102; GA ČR(CZ) GAP104/12/0915; GA ČR(CZ) GAP210/12/1491; GA ČR GA13-13967S Institutional support: RVO:67985831 ; RVO:67985530 Keywords : geomechanics * microstructures * body waves * seismic anisotropy * wave propagation Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.724, year: 2013
Pn seismic wave travel time at the Semipalatinsk Test Site - Borovoe seismic station trace
International Nuclear Information System (INIS)
An, V.A.; Kaazik, P.B.; Ovchinnikov, V.M.
2001-01-01
This paper preparation involved 160 explosions at the Degelen Site conducted in 1961-1989 and 89 explosions at the Balapan Site conducted in 1968-1989. Pn wave travel time was tied to the sea level in accordance with velocity characteristics of the explosion hypocenter medium; and to average epicentral distance for every site basing on their local travel time curves of Pn wave relative to Borovoe station. Maximum amplitude of mean-year travel times variations is 0.3-0.5 s as at the Nevada Test Site - Borovoe trace and Mirniy (Antarctica). However, the linear trend in contrast to previous traces has negative sign (0.08 s for Degelen and 0.1 s for Balapan). Thus, Pn wave velocity increases with calendar time. (author)
Dickinson, Alex; White, N. J.; Caulfield, C. P.
2017-12-01
Bright reflections are observed within the upper 1,000 m of the water column along a seismic reflection profile that traverses the northern margin of the Gulf of Mexico. Independent hydrographic calibration demonstrates that these reflections are primarily caused by temperature changes associated with different water masses that are entrained into the Gulf along the Loop Current. The internal wave field is analyzed by automatically tracking 1,171 reflections, each of which is greater than 2 km in length. Power spectra of the horizontal gradient of isopycnal displacement, ϕξx, are calculated from these tracked reflections. At low horizontal wave numbers (kx<10-2 cpm), ϕξx∝kx-0.2±0.6, in agreement with hydrographic observations of the internal wave field. The turbulent spectral subrange is rarely observed. Diapycnal diffusivity, K, is estimated from the observed internal wave spectral subrange of each tracked reflection using a fine-scale parametrization of turbulent mixing. Calculated values of K vary between 10-8 and 10-4 m2 s-1 with a mean value of K˜4×10-6 m2 s-1. The spatial distribution of turbulent mixing shows that K˜10-7 m2 s-1 away from the shelf edge in the upper 300 m where stratification is strong. Mixing is enhanced by up to 4 orders of magnitude adjacent to the shoaling bathymetry of the continental slope. This overall pattern matches that determined by analyzing nearby suites of CTD casts. However, the range of values recovered by spectral analysis of the seismic image is greater as a consequence of significantly better horizontal resolution.
3D Numerical Simulation on the Sloshing Waves Excited by the Seismic Shacking
Zhang, Lin; Wu, Tso-Ren
2016-04-01
importantly, the amount of water loosed in the event. The simulated water movement excited by the seismic acceleration was visually similar to the video clip mentioned before. From the simulation results, we observed that the water was mainly leaked at the corner of the water tank with a nonlinear curve of the free-surface. This phenomenon can't be found in the conventional studies with acceleration in a sole direction. We also studied the effect from a porous body placed on the lower part of the tank. Detailed results and discussion will be presented in the full paper. Keywords Sloshing, Splash3D, LES, Breaking waves, VOF, spent fuel pool, Nuclear power plant
Effects of seismic anisotropy on P-velocity tomography of the Baltic Shield
Czech Academy of Sciences Publication Activity Database
Eken, T.; Plomerová, Jaroslava; Vecsey, Luděk; Babuška, Vladislav; Roberts, R.; Shomali, H.; Bodvarsson, R.
2012-01-01
Roč. 188, č. 2 (2012), s. 600-612 ISSN 0956-540X R&D Projects: GA AV ČR IAA300120709 Institutional research plan: CEZ:AV0Z30120515 Keywords : body waves * seismic anisotropy * seismic tomography * cratons Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.853, year: 2012
A test of a mechanical multi-impact shear-wave seismic source
Worley, David M.; Odum, Jack K.; Williams, Robert A.; Stephenson, William J.
2001-01-01
We modified two gasoline-engine-powered earth tampers, commonly used as compressional-(P) wave seismic energy sources for shallow reflection studies, for use as shear(S)-wave energy sources. This new configuration, termed ?Hacker? (horizontal Wacker?), is evaluated as an alternative to the manual sledgehammer typically used in conjunction with a large timber held down by the front wheels of a vehicle. The Hacker maximizes the use of existing equipment by a quick changeover of bolt-on accessories as opposed to the handling of a separate source, and is intended to improve the depth of penetration of S-wave data by stacking hundreds of impacts over a two to three minute period. Records were made with a variety of configurations involving up to two Hackers simultaneously then compared to a reference record made with a sledgehammer. Preliminary results indicate moderate success by the higher amplitude S-waves recorded with the Hacker as compared to the hammer method. False triggers generated by the backswing of the Hacker add unwanted noise and we are currently working to modify the device to eliminate this effect. Correlation noise caused by insufficient randomness of the Hacker impact sequence is also a significant noise problem that we hope to reduce by improving the coupling of the Hacker to the timber so that the operator has more control over the impact sequence.
Energy Technology Data Exchange (ETDEWEB)
Hansen, S; Gaherty, J; Schwartz, S; Rodgers, A; Al-Amri, A
2007-07-25
We investigate the lithospheric and upper mantle structure as well as the depth-dependence of anisotropy along the Red Sea and beneath the Arabian Peninsula using receiver function constraints and phase velocities of surface waves traversing two transects of stations from the Saudi Arabian National Digital Seismic Network. Frequency-dependent phase delays of fundamental-mode Love and Rayleigh waves, measured using a cross-correlation procedure, require very slow shear velocities and the presence of anisotropy throughout the upper mantle. Linearized inversion of these data produce path-averaged 1D radially anisotropic models with about 4% anisotropy in the lithosphere, increasing to about 4.8% anisotropy across the lithosphere-asthenosphere boundary (LAB). Models with reasonable crustal velocities in which the mantle lithosphere is isotropic cannot satisfy the data. The lithospheric lid, which ranges in thickness from about 70 km near the Red Sea coast to about 90 km beneath the Arabian Shield, is underlain by a pronounced low-velocity zone with shear velocities as low as 4.1 km/s. Forward models, which are constructed from previously determined shear-wave splitting estimates, can reconcile surface and body wave observations of anisotropy. The low shear velocity values are similar to many other continental rift and oceanic ridge environments. These low velocities combined with the sharp velocity contrast across the LAB may indicate the presence of partial melt beneath Arabia. The anisotropic signature primarily reflects a combination of plate- and density-driven flow associated with active rifting processes in the Red Sea.
Seismic, satellite, and site observations of internal solitary waves in the NE South China Sea.
Tang, Qunshu; Wang, Caixia; Wang, Dongxiao; Pawlowicz, Rich
2014-06-20
Internal solitary waves (ISWs) in the NE South China Sea (SCS) are tidally generated at the Luzon Strait. Their propagation, evolution, and dissipation processes involve numerous issues still poorly understood. Here, a novel method of seismic oceanography capable of capturing oceanic finescale structures is used to study ISWs in the slope region of the NE SCS. Near-simultaneous observations of two ISWs were acquired using seismic and satellite imaging, and water column measurements. The vertical and horizontal length scales of the seismic observed ISWs are around 50 m and 1-2 km, respectively. Wave phase speeds calculated from seismic observations, satellite images, and water column data are consistent with each other. Observed waveforms and vertical velocities also correspond well with those estimated using KdV theory. These results suggest that the seismic method, a new option to oceanographers, can be further applied to resolve other important issues related to ISWs.
Rayleigh wave tomography of the British Isles from ambient seismic noise
Nicolson, Heather; Curtis, Andrew; Baptie, Brian
2014-08-01
We present the first Rayleigh wave group speed maps of the British Isles constructed from ambient seismic noise. The maps also constitute the first surface wave tomography study of the crust under the British Isles at a relatively high resolution. We computed interferometric, interstation Rayleigh waves from vertical component records of ambient seismic noise recorded on 63 broad-band and short-period stations across the UK and Ireland. Group velocity measurements were made from the resulting surface wave dispersion curves between 5 and 25 s using a multiple phase-matched filter method. Uncertainties in the group velocities were computed by calculating the standard deviation of four dispersion curves constructed by stacking a random selection of daily cross-correlations. Where an uncertainty could not be obtained for a ray path using this method, we estimated it as a function of the interreceiver distance. Group velocity maps were computed for 5-25-s period using the Fast Marching forward solution of the eikonal equation and iterative, linearized inversion. At short and intermediate periods, the maps show remarkable agreement with the major geological features of the British Isles including: terrane boundaries in Scotland; regions of late Palaeozoic basement uplift; areas of exposed late Proterozoic/early Palaeozoic rocks in southwest Scotland, northern England and northwest Wales and, sedimentary basins formed during the Mesozoic such as the Irish Sea Basin, the Chester Basin, the Worcester Graben and the Wessex Basin. The maps also show a consistent low-velocity anomaly in the region of the Midlands Platform, a Proterozoic crustal block in the English Midlands. At longer periods, which are sensitive velocities in the lower crustal/upper mantle, the maps suggest that the depth of Moho beneath the British Isles decreases towards the north and west. Areas of fast velocity in the lower crust also coincide with areas thought to be associated with underplating of the
Galiana-Merino, J. J.; Rosa-Herranz, J. L.; Rosa-Cintas, S.; Martinez-Espla, J. J.
2013-01-01
A MATLAB-based computer code has been developed for the simultaneous wavelet analysis and filtering of multichannel seismic data. The considered time-frequency transforms include the continuous wavelet transform, the discrete wavelet transform and the discrete wavelet packet transform. The developed approaches provide a fast and precise time-frequency examination of the seismograms at different frequency bands. Moreover, filtering methods for noise, transients or even baseline removal, are implemented. The primary motivation is to support seismologists with a user-friendly and fast program for the wavelet analysis, providing practical and understandable results. Program summaryProgram title: SeismicWaveTool Catalogue identifier: AENG_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AENG_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 611072 No. of bytes in distributed program, including test data, etc.: 14688355 Distribution format: tar.gz Programming language: MATLAB (MathWorks Inc.) version 7.8.0.347 (R2009a) or higher. Wavelet Toolbox is required. Computer: Developed on a MacBook Pro. Tested on Mac and PC. No computer-specific optimization was performed. Operating system: Any supporting MATLAB (MathWorks Inc.) v7.8.0.347 (R2009a) or higher. Tested on Mac OS X 10.6.8, Windows XP and Vista. Classification: 13. Nature of problem: Numerous research works have developed a great number of free or commercial wavelet based software, which provide specific solutions for the analysis of seismic data. On the other hand, standard toolboxes, packages or libraries, such as the MathWorks' Wavelet Toolbox for MATLAB, offer command line functions and interfaces for the wavelet analysis of one-component signals. Thus, software usually is focused on very specific problems
Energy Technology Data Exchange (ETDEWEB)
Wardaya, P. D., E-mail: pongga.wardaya@utp.edu.my; Noh, K. A. B. M., E-mail: pongga.wardaya@utp.edu.my; Yusoff, W. I. B. W., E-mail: pongga.wardaya@utp.edu.my [Petroleum Geosciences Department, Universiti Teknologi PETRONAS, Tronoh, Perak, 31750 (Malaysia); Ridha, S. [Petroleum Engineering Department, Universiti Teknologi PETRONAS, Tronoh, Perak, 31750 (Malaysia); Nurhandoko, B. E. B. [Wave Inversion and Subsurface Fluid Imaging Research Laboratory (WISFIR), Dept. of Physics, Institute of Technology Bandung, Bandung, Indonesia and Rock Fluid Imaging Lab, Bandung (Indonesia)
2014-09-25
This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, an advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic
Nurhandoko, Bagus Endar B.; Wardaya, Pongga Dikdya; Adler, John; Siahaan, Kisko R.
2012-06-01
Seismic wave parameter plays very important role to characterize reservoir properties whereas pore parameter is one of the most important parameter of reservoir. Therefore, wave propagation phenomena in pore media is important to be studied. By referring this study, in-direct pore measurement method based on seismic wave propagation can be developed. Porosity play important role in reservoir, because the porosity can be as compartment of fluid. Many type of porosity like primary as well as secondary porosity. Carbonate rock consist many type of porosity, i.e.: inter granular porosity, moldic porosity and also fracture porosity. The complexity of pore type in carbonate rocks make the wave propagation in these rocks is more complex than sand reservoir. We have studied numerically wave propagation in carbonate rock by finite difference modeling in time-space domain. The medium of wave propagation was modeled by base on the result of pattern recognition using artificial neural network. The image of thin slice of carbonate rock is then translated into the velocity matrix. Each mineral contents including pore of thin slice image are translated to velocity since mineral has unique velocity. After matrix velocity model has been developed, the seismic wave is propagated numerically in this model. The phenomena diffraction is clearly shown while wave propagates in this complex carbonate medium. The seismic wave is modeled in various frequencies. The result shows dispersive phenomena where high frequency wave tends to propagate in matrix instead pores. In the other hand, the low frequency waves tend to propagate through pore space even though the velocity of pore is very low. Therefore, this dispersive phenomena of seismic wave propagation can be the future indirect measurement technology for predicting the existence or intensity of pore space in reservoir rock. It will be very useful for the future reservoir characterization.
Numerical Simulation of Floating Bodies in Extreme Free Surface Waves
Hu, Zheng Zheng; Causon, Derek; Mingham, Clive; Qiang, Ling
2010-05-01
and efficient. Firstly, extreme design wave conditions are generated in an empty NWT and compared with physical experiments as a precursor to calculations to investigate the survivability of the Bobber device operating in a challenging wave climate. Secondly, we consider a bench-mark test case involving in a first order regular wave maker acting on a fixed cylinder and Pelamis. Finally, a floating Bobber has been simulated under extreme wave conditions. These results will be reported at the meeting. Causon D.M., Ingram D.M., Mingham C.G., Yang G. Pearson R.V. (2000). Calculation of shallow water flows using a Cartesian cut cell approach. Advances in Water resources, 23: 545-562. Causon D.M., Ingram D.M., Mingham C.G. (2000). A Cartesian cut cell method for shallow water flows with moving boundaries. Advances in Water resources, 24: 899-911. Dalzell J.F. 1999 A note on finite depth second-order wave-wave interactions. Appl. Ocean Res. 21, 105-111. Ning D.Z., Zang J., Liu S.X. Eatock Taylor R. Teng B. & Taylor P.H. 2009 Free surface and wave kinematics for nonlinear focused wave groups. J. Ocean Engineering. Accepted. Hu Z.Z., Causon D.M., Mingham C.M. and Qian L.(2009). Numerical wave tank study of a wave energy converter in heave. Proceedlings 19th ISOPE conference, Osaka, Japan Qian L., Causon D.M. & Mingham C.G., Ingram D.M. 2006 A free-surface capturing method for two fluid flows with moving bodies. Proc. Roy. Soc. London, Vol. A 462 21-42.
Directionality analysis and Rayleigh wave tomography of ambient seismic noise in southern Norway
Köhler, Andreas; Weidle, Christian; Maupin, Valérie
2011-01-01
We process seismic broad-band data from southern Norway by cross correlation of ambient seismic noise in view of getting a better image of the crustal structure in the area. The main data set sterns from the temporary MAGNUS network which operated continuously from 2006 September to 2008 June. Additionally, data from permanent stations of the National Norwegian Seismic Network, the NORSAR array and GSN stations in the region are used. We compute vertical component cross-correlation functions using 41 receivers for 3-month time windows. Evaluation of the azimuthal and temporal variation of signal-to-noise ratios (SNRs) and f-k analysis of data from NORSAR array between 3 and 25 s period shows that the dominant source areas of seismic noise are located to the west and north of the network during most of the measurement time, which corresponds well to the Norwegian coast line. During summer months, the SNRs decrease but the azimuthal distribution becomes more uniform between 7 and 12 s period, suggesting a more diffuse character of the wavefield. Primary ocean microseisms above 12 s show different dominant source azimuths during this time period compared to the winter months. Time-frequency analysis is applied to measure Rayleigh wave group velocity dispersion curves between each station pair for each 3-month correlation stack and the mean and variance of all dispersion curves is computed for each path. After rejection of low-quality data, a careful analysis shows that the group velocities are not biased by noise directionality. We invert the data for group velocity maps at period bands between 3 and 25 s. At short periods, we find an average Rayleigh wave group speed of about 3 km s-1 and velocity anomalies that correlate very well with local surface geology. While higher velocities (+5 per cent) can be associated with the Caledonian nappes in the central part of southern Norway, the Oslo Graben is reflected by negative velocity anomalies (-3 to -5 per cent). At
Parallel 3D Simulation of Seismic Wave Propagation in the Structure of Nobi Plain, Central Japan
Kotani, A.; Furumura, T.; Hirahara, K.
2003-12-01
We performed large-scale parallel simulations of the seismic wave propagation to understand the complex wave behavior in the 3D basin structure of the Nobi Plain, which is one of the high population cities in central Japan. In this area, many large earthquakes occurred in the past, such as the 1891 Nobi earthquake (M8.0), the 1944 Tonankai earthquake (M7.9) and the 1945 Mikawa earthquake (M6.8). In order to mitigate the potential disasters for future earthquakes, 3D subsurface structure of Nobi Plain has recently been investigated by local governments. We referred to this model together with bouguer anomaly data to construct a detail 3D basin structure model for Nobi plain, and conducted computer simulations of ground motions. We first evaluated the ground motions for two small earthquakes (M4~5); one occurred just beneath the basin edge at west, and the other occurred at south. The ground motions from these earthquakes were well recorded by the strong motion networks; K-net, Kik-net, and seismic intensity instruments operated by local governments. We compare the observed seismograms with simulations to validate the 3D model. For the 3D simulation we sliced the 3D model into a number of layers to assign to many processors for concurrent computing. The equation of motions are solved using a high order (32nd) staggered-grid FDM in horizontal directions, and a conventional (4th-order) FDM in vertical direction with the MPI inter-processor communications between neighbor region. The simulation model is 128km by 128km by 43km, which is discritized at variable grid size of 62.5-125m in horizontal directions and of 31.25-62.5m in vertical direction. We assigned a minimum shear wave velocity is Vs=0.4km/s, at the top of the sedimentary basin. The seismic sources for the small events are approximated by double-couple point source and we simulate the seismic wave propagation at maximum frequency of 2Hz. We used the Earth Simulator (JAMSTEC, Yokohama Inst) to conduct such
Analysis of Seismic Anisotropy Across Central Anatolia by Shear Wave Splitting
Pamir, Dilekcan; Abgarmi, Bizhan; Arda Özacar, A.
2014-05-01
Analysis of Seismic Anisotropy Across Central Anatolia by Shear Wave Splitting Dilekcan Pamir, Bizhan Abgarmi, A. Arda Özacar Department of Geological Engineering, Middle East Technical University (METU), Dumlupinar Bulvari 1, 06800 Ankara, Turkey Central Anatolia holds the key to connect the theories about the ongoing tectonic escape, the African Plate subduction along Cyprus Arc and the indenter-style collision of Arabian Plate along Bitlis Suture. However, the shear wave splitting measurements which are needed to characterize seismic anisotropy are very sparse in the region. Recently, seismic data recorded by national seismic networks (KOERI, ERI-DAD) with dense coverage, provided a unique opportunity to analyze the effect of present slab geometry (slab tears, slab break-off) on mantle deformation and test different models of anisotropy forming mechanisms. In this study, the anisotropic structure beneath the Central Anatolia is investigated via splitting of SKS and SKKS phases recorded at 46 broadband seismic stations. Our measurements yielded 1171 well-constrained splitting and 433 null results. Overall, the region displays NE-SW trending fast splitting directions and delay times on the order of 1 sec. On the other hand, a large number of stations which are spatially correlated with Cyprus Slab, Neogene volcanism and major tectonic structures present significant back azimuthal variations on splitting parameters that cannot be explained by one-layered anisotropy with horizontal symmetry. Thus, we have modeled anisotropy for two-layered structures using a forward approach and identified NE-SW trending fast splitting directions with delay times close to 1 sec at the lower layer and N-S, NW-SE trending fast splitting with limited time delays (0.1 - 0.3 sec) at the upper layer. Fast directions and delay times of the lower layer are similar to one-layered anisotropy and parallel or sub-parallel to the absolute plate motions which favors asthenospheric flow model
Saito, S.; Ishikawa, M.; Shibata, S.; Akizuki, R.; Arima, M.; Tatsumi, Y.; Arai, S.
2010-12-01
Evaluation of rock velocities and comparison with velocity profiles defined by seismic refraction experiments are a crucial approach for understanding the petrological structure of the crust. In this study, we calculated the seismic wave velocities of various types of rocks from the Oman ophiolite in order to constrain a petrological structure of the oceanic crust. Christensen & Smewing (1981, JGR) have reported experimental elastic velocities of rocks from the Oman ophiolite under oceanic crust-mantle conditions (6-430 MPa). However, in their relatively low-pressure experiments, internal pore-spaces might affect the velocity and resulted in lower values than the intrinsic velocity of sample. In this study we calculated the velocities of samples based on their modal proportions and chemical compositions of mineral constituents. Our calculated velocities represent the ‘pore-space-free’ intrinsic velocities of the sample. We calculated seismic velocities of rocks from the Oman ophiolite including pillow lavas, dolerites, plagiogranites, gabbros and peridotites at high-pressure-temperature conditions with an Excel macro (Hacker & Avers 2004, G-cubed). The minerals used for calculations for pillow lavas, dolerites and plagiogranites were Qtz, Pl, Prh, Pmp, Chl, Ep, Act, Hbl, Cpx and Mag. Pl, Hbl, Cpx, Opx and Ol were used for the calculations for gabbros and peridotites. Assuming thermal gradient of 20° C/km and pressure gradient of 25 MPa/km, the velocities were calculated in the ranges from the atmospheric pressure (0° C) to 200 MPa (160° C). The calculation yielded P-wave velocities (Vp) of 6.5-6.7 km/s for the pillow lavas, 6.6-6.8 km/s for the dolerites, 6.1-6.3 km/s for the plagiogranites, 6.9-7.5 km/s for the gabbros and 8.1-8.2 km/s for the peridotites. On the other hand, experimental results reported by Christensen & Smewing (1981, JGR) were 4.5-5.9 km/s for the pillow lavas, 5.5-6.3 km/s for the dolerites, 6.1-6.3 km/s for the plagiogranites, 6
Matsuzawa, T.; Obara, K.; Maeda, T.
2008-12-01
A nationwide seismic network in Japan detected long period microtremors from the northern Atlantic region. It is reported that a cyclone generate ocean swells which excite microtremors. If the microtremors have sufficient intensity, the seismic waves propagate far from the source. Such propagation was sometimes observed at the high-sensitivity accelerometers of Hi-net, NIED. In this study, a migration of the source location with a cyclone is estimated by an array analysis technique, combining broadband seismic data of another array. In the middle of March 2007, anomalous seismic waves were continuously arrived from the north direction in Japan. Such waves were automatically detected by the array analysis of Hi-net data. The automated analysis also shows that the seismic wave is originated far from Japan because the propagation is well approximated to plane waves rather than cylindrical waves. The waves are especially predominant at the period of around 20 s. In addition, from a semblance analysis, apparent velocity is estimated to 3.4--3.6 km/s and 3.8--4.0 km/s in radial and transverse components, respectively. This suggests that the observed waves are composed both of Rayleigh and Love waves. To discuss the more accurate direction and the temporal change, we apply a multiple signal classification (MUSIC) method to the data of high-sensitivity accelerometers. The arrival direction rotated to several degrees clockwise from the azimuth of -15 degrees. In addition, we analyze broadband seismic data of the Graefenberg-array (GRF array) in Germany, and also obtain an evident rotation of the arrival direction from - 40 to -5 degrees. The result of array analysis suggests that the source of seismic wave moves to the north direction at the North Sea and the Norwegian Sea. The location of the source is estimated as the intersections of the expected ray paths from two arrays. To calculate a ray path, we assumed the Rayleigh wave velocity at the period of 35 s. The shooting
International Nuclear Information System (INIS)
Erlangga, Mokhammad Puput
2015-01-01
Separation between signal and noise, incoherent or coherent, is important in seismic data processing. Although we have processed the seismic data, the coherent noise is still mixing with the primary signal. Multiple reflections are a kind of coherent noise. In this research, we processed seismic data to attenuate multiple reflections in the both synthetic and real seismic data of Mentawai. There are several methods to attenuate multiple reflection, one of them is Radon filter method that discriminates between primary reflection and multiple reflection in the τ-p domain based on move out difference between primary reflection and multiple reflection. However, in case where the move out difference is too small, the Radon filter method is not enough to attenuate the multiple reflections. The Radon filter also produces the artifacts on the gathers data. Except the Radon filter method, we also use the Wave Equation Multiple Elimination (WEMR) method to attenuate the long period multiple reflection. The WEMR method can attenuate the long period multiple reflection based on wave equation inversion. Refer to the inversion of wave equation and the magnitude of the seismic wave amplitude that observed on the free surface, we get the water bottom reflectivity which is used to eliminate the multiple reflections. The WEMR method does not depend on the move out difference to attenuate the long period multiple reflection. Therefore, the WEMR method can be applied to the seismic data which has small move out difference as the Mentawai seismic data. The small move out difference on the Mentawai seismic data is caused by the restrictiveness of far offset, which is only 705 meter. We compared the real free multiple stacking data after processing with Radon filter and WEMR process. The conclusion is the WEMR method can more attenuate the long period multiple reflection than the Radon filter method on the real (Mentawai) seismic data
Han, Fengqin; Jia, Ruizhi; Fu, Yuanyuan V.
2017-08-01
Love wave dispersion maps across the southeastern margin of the Tibetan Plateau are obtained using earthquake data recorded by the temporary ChinArray and permanent China Digital Seismic Array. Fundamental mode Love wave phase velocity curves are measured by inverting Love wave amplitude and phase with the two-plane-wave method. The phase velocity maps with resolution better than 150 km are presented at periods of 20-100 s, which is unprecedented in the study area. The maps agree well with each other and show clear correlations with major tectonic structures. The Love wave phase velocity could provide new information about structures in the crust and upper mantle beneath the southeast margin of Tibetan Plateau, like the radial anisotropy.
Development of S-wave portable vibrator; S ha potable vibrator shingen no kaihatsu
Energy Technology Data Exchange (ETDEWEB)
Kaida, Y.; Matsubara, Y. [OYO Corp., Tokyo (Japan); Nijhof, V.; Brouwer, J.
1996-05-01
An S-wave portable vibrator to serve as a seismic source has been developed for the purpose of applying the shallow-layer reflection method to the study of the soil ground. The author, et al., who previously developed a P-wave portable vibrator has now developed an S-wave version, considering the advantage of the S-wave over the P-wave in that, for example, the S-wave velocity may be directly compared with the N-value representing ground strength and that the S-wave travels more slowly than the P-wave through sticky soil promising a higher-resolution exploration. The experimentally constructed S-wave vibrator consists of a conventional P-wave vibrator and an L-type wooden base plate combined therewith. Serving as the monitor for vibration is a conventional accelerometer without any modification. The applicability test was carried out at a location where a plank hammering test was once conducted for reflection aided exploration, and the result was compared with that of the plank hammering test. As the result, it was found that after some preliminary treatment the results of the two tests were roughly the same but that both reflected waves were a little sharper in the S-wave vibrator test than in the plank hammering test. 4 refs., 9 figs., 1 tab.
A collision-based model for measuring bedload transport from the seismic waves generated by rivers
Roth, D. L.; Finnegan, N. J.; Brodsky, E. E.; Stark, C. P.
2011-12-01
Accurately predicting rates of coarse sediment transport in river channels is a central goal of fluvial geomorphology and civil engineering. However, it is difficult to evaluate sediment transport and bedrock abrasion models in large rivers because quantitative measures of bedload transport are labor intensive and often dangerous to obtain in floods. Two recent studies show that the amplitude of seismic waves near rivers may record bedload flux, indicating that seismometers near rivers provide a potential means of monitoring bedload transport. In an effort to better interpret seismic waves generated by rivers, we seek a relationship between the variables governing bedload transport and seismic waves. Our approach relies on the fact that elastic waves are generated when momentum is transferred to the bed during a bedload particle impact. For an impacting particle of known mass and velocity, the momentum transfer can be computed from Hertzian impact theory. Here we combine analytic results based on Hertzian and elastic wave theories with empirical equations developed to describe the ballistics of bedload particles in terms of fluid shear stress and grain size. From this synthesis we arrive at a semi-analytic expression that predicts how the characteristic frequencies and amplitudes of seismic waves generated from saltating bedload particles should scale with fluid shear stress, grain size, and coarse sediment flux. Preliminary tests of our predictions using previously published and newly acquired laboratory data indicate that seismic signals near rivers can record information about the size, velocity and number of particles impacting the bed. Additionally, our analytical results help identify bedload transport events in seismic data collected along the Chijiawan River in Taiwan. Here the river is evolving rapidly in response to a dam removal - resulting in predictable changes in bedload transport efficiency in time and space that we can compare to local seismic data.
Seismic Waves from Light Trucks Moving Over Terrain
National Research Council Canada - National Science Library
Ketcham, Stephen A; Moran, Mark L; Lacombe, James
2004-01-01
...). Seismic sensors possess the advantage of beyond-line-of-sight sensing. They can detect ground vibrations generated by moving vehicles or personnel, and they can be used to cue other sensors or possibly to classify or even identify targets...
DEFF Research Database (Denmark)
Kammann, Janina; Hübscher, Christian; Nielsen, Lars
The Carlsberg Fault zone is located in the N-S striking Höllviken Graben and traverses the city of Copenhagen. The fault zone is a NNW-SSE striking structure in direct vicinity to the transition zone of the Danish Basin and the Baltic Shield. Recent small earthquakes indicate activity in the area......, although none of the mapped earthquakes appear to have occurred on the Carlsberg Fault. We examined the fault evolution by a combination of very high resolution onshore shear-wave seismic data, one conventional onshore seismic profile and marine reflection seismic profiles. The chalk stratigraphy...... and the localization of the fault zone at depth was inferred from previous studies by other authors. We extrapolated the Jurassic and Triassic stratigraphy from the Pomeranian Bay to the area of investigation. The fault zone shows a flower structure in the Triassic as well as in Cretaceous sediments. The faulting...
Three-dimensional S-wave tomography under Axial Seamount
Baillard, C.; Wilcock, W. S. D.; Arnulf, A. F.; Tolstoy, M.; Waldhauser, F.
2017-12-01
Axial Seamount is a submarine volcano located at the intersection of the Juande Fuca Ridge and the Cobb-Eickelberg hotspot 500 km off the coast of thenorthwestern United States. The seamount, which rises 1 km above the seafloor, ischaracterized by a shallow caldera that is elongated in the N-S direction, measure 8km by 3 km and sits on top of a 14 km by 3 km magma reservoir. Two eruptive eventsin 1998 and 2011 motivated the deployment in 2014 of a real time cabled observatorywithin the Axial caldera, as part of the Ocean Observatories Initiative (OOI).Theobservatory includes a network of seven seismometers that span the southern half ofthe caldera. Five months after the observatory came on-line in November 2014, thevolcano erupted on April 24, 2015. Well over 100,000 events were located in thevicinity of the caldera, delineating an outward dipping ring fault that extends fromnear the surface to the magma body at 2 km depth and which accommodatesinflation and deflation of the volcano.The initial earthquake locations have beenobtained with a one-dimensional velocity model but the travel time residuals suggeststrong heterogeneities. A three-dimensional P-wave velocity model, obtained bycombining multichannel and ocean bottom seismometer refraction data, is being usedto refine locations but the three-dimensional S-wave structure is presently unknown.In most mid-ocean ridge settings, the distribution of earthquakes is not conducive forjoint inversions for S-wave velocity and hypocentral parameters because there are fewcrossing ray paths but at Axial the presence of a ring fault that is seismically active atall depths on both the east and west side of the caldera, provides a reasonablegeometry for such efforts. We will present the results of joint inversions that assumethe existing three-dimensional P wave velocity model and solve for VP/VS structure andhypocentral parameters using LOTOS, an algorithm that solves the forward problemusing ray bending.The resulting model
Accuracy of finite-difference modeling of seismic waves : Simulation versus laboratory measurements
Arntsen, B.
2017-12-01
The finite-difference technique for numerical modeling of seismic waves is still important and for some areas extensively used.For exploration purposes is finite-difference simulation at the core of both traditional imaging techniques such as reverse-time migration and more elaborate Full-Waveform Inversion techniques.The accuracy and fidelity of finite-difference simulation of seismic waves are hard to quantify and meaningfully error analysis is really onlyeasily available for simplistic media. A possible alternative to theoretical error analysis is provided by comparing finite-difference simulated data with laboratory data created using a scale model. The advantage of this approach is the accurate knowledge of the model, within measurement precision, and the location of sources and receivers.We use a model made of PVC immersed in water and containing horizontal and tilted interfaces together with several spherical objects to generateultrasonic pressure reflection measurements. The physical dimensions of the model is of the order of a meter, which after scaling represents a model with dimensions of the order of 10 kilometer and frequencies in the range of one to thirty hertz.We find that for plane horizontal interfaces the laboratory data can be reproduced by the finite-difference scheme with relatively small error, but for steeply tilted interfaces the error increases. For spherical interfaces the discrepancy between laboratory data and simulated data is sometimes much more severe, to the extent that it is not possible to simulate reflections from parts of highly curved bodies. The results are important in view of the fact that finite-difference modeling is often at the core of imaging and inversion algorithms tackling complicatedgeological areas with highly curved interfaces.
Statistical distributions of earthquakes and related non-linear features in seismic waves
International Nuclear Information System (INIS)
Apostol, B.-F.
2006-01-01
A few basic facts in the science of the earthquakes are briefly reviewed. An accumulation, or growth, model is put forward for the focal mechanisms and the critical focal zone of the earthquakes, which relates the earthquake average recurrence time to the released seismic energy. The temporal statistical distribution for average recurrence time is introduced for earthquakes, and, on this basis, the Omori-type distribution in energy is derived, as well as the distribution in magnitude, by making use of the semi-empirical Gutenberg-Richter law relating seismic energy to earthquake magnitude. On geometric grounds, the accumulation model suggests the value r = 1/3 for the Omori parameter in the power-law of energy distribution, which leads to β = 1,17 for the coefficient in the Gutenberg-Richter recurrence law, in fair agreement with the statistical analysis of the empirical data. Making use of this value, the empirical Bath's law is discussed for the average magnitude of the aftershocks (which is 1.2 less than the magnitude of the main seismic shock), by assuming that the aftershocks are relaxation events of the seismic zone. The time distribution of the earthquakes with a fixed average recurrence time is also derived, the earthquake occurrence prediction is discussed by means of the average recurrence time and the seismicity rate, and application of this discussion to the seismic region Vrancea, Romania, is outlined. Finally, a special effect of non-linear behaviour of the seismic waves is discussed, by describing an exact solution derived recently for the elastic waves equation with cubic anharmonicities, its relevance, and its connection to the approximate quasi-plane waves picture. The properties of the seismic activity accompanying a main seismic shock, both like foreshocks and aftershocks, are relegated to forthcoming publications. (author)
The dynamic reaction of containment structures (Sarcophagus) to seismic waves and vibrations
International Nuclear Information System (INIS)
Nemchinov Marenkov, U.I.
1995-01-01
This work deals with the dynamic reaction of containment structures (sarcophagus) to seismic waves and vibrations. It shows the results of experimental vibration measurements of the turbogenerators. It gives an analysis of the level of seismic and vibration effects on the load bearing structures of the sarcophagus and it puts forward recommendations relating to a permissible operating level for any vibroactive machinery which may be used during the reconstruction and transformation of the structure. (O.L.). 6 refs., 3 figs., 2 tabs
Shallow shear-wave reflection seismics in the tsunami struck Krueng Aceh River Basin, Sumatra
Directory of Open Access Journals (Sweden)
U. Polom
2008-01-01
Full Text Available As part of the project "Management of Georisk" (MANGEONAD of the Federal Institute for Geosciences and Natural Resources (BGR, Hanover, high resolution shallow shear-wave reflection seismics was applied in the Indonesian province Nanggroe Aceh Darussalam, North Sumatra in cooperation with the Government of Indonesia, local counterparts, and the Leibniz Institute for Applied Geosciences, Hanover. The investigations were expected to support classification of earthquake site effects for the reconstruction of buildings and infrastructure as well as for groundwater exploration. The study focussed on the city of Banda Aceh and the surroundings of Aceh Besar. The shear-wave seismic surveys were done parallel to standard geoengineering investigations like cone penetrometer tests to support subsequent site specific statistical calibration. They were also partly supplemented by shallow p-wave seismics for the identification of (a elastic subsurface parameters and (b zones with abundance of groundwater. Evaluation of seismic site effects based on shallow reflection seismics has in fact been found to be a highly useful method in Aceh province. In particular, use of a vibratory seismic source was essential for successful application of shear-wave seismics in the city of Banda Aceh and in areas with compacted ground like on farm tracks in the surroundings, presenting mostly agricultural land use areas. We thus were able to explore the mechanical stiffness of the subsurface down to 100 m depth, occasionally even deeper, with remarkably high resolution. The results were transferred into geotechnical site classification in terms of the International Building Code (IBC, 2003. The seismic images give also insights into the history of the basin sedimentation processes of the Krueng Aceh River delta, which is relevant for the exploration of new areas for construction of safe foundations of buildings and for identification of fresh water aquifers in the tsunami
A local adaptive method for the numerical approximation in seismic wave modelling
Directory of Open Access Journals (Sweden)
Galuzzi Bruno G.
2017-12-01
Full Text Available We propose a new numerical approach for the solution of the 2D acoustic wave equation to model the predicted data in the field of active-source seismic inverse problems. This method consists in using an explicit finite difference technique with an adaptive order of approximation of the spatial derivatives that takes into account the local velocity at the grid nodes. Testing our method to simulate the recorded seismograms in a marine seismic acquisition, we found that the low computational time and the low approximation error of the proposed approach make it suitable in the context of seismic inversion problems.
Some features of seismic waves observed in the territory of Northern Moravia and Silesia
Czech Academy of Sciences Publication Activity Database
Holub, Karel; Knejzlík, Jaromír; Růžek, Bohuslav; Rušajová, Jana; Novotný, O.
2006-01-01
Roč. 3, 3/143/ (2006), s. 97-107 ISSN 1214-9705. [Czech-Polish Workshop on Recent Geodynamics of the Sudeten and Adjacent Areas /7./. Ramzová, 02.11.2005-05.11.2005] R&D Projects: GA ČR GA205/03/0999 Institutional research plan: CEZ:AV0Z30860518; CEZ:AV0Z30120515 Keywords : Moravo-Silesian region * body waves * surface waves Subject RIV: DC - Siesmology, Volcanology, Earth Structure
Modeling the Excitation of Seismic Waves by the Joplin Tornado
Valovcin, Anne; Tanimoto, Toshiro
2017-10-01
Tornadoes generate seismic signals when they contact the ground. Here we examine the signals excited by the Joplin tornado, which passed within 2 km of a station in the Earthscope Transportable Array. We model the tornado-generated vertical seismic signal at low frequencies (0.01-0.03 Hz) and solve for the strength of the seismic source. The resulting source amplitude is largest when the tornado was reported to be strongest (EF 4-5), and the amplitude is smallest when the tornado was weak (EF 0-2). A further understanding of the relationship between source amplitude and tornado intensity could open up new ways to study tornadoes from the ground.
Directory of Open Access Journals (Sweden)
Mingwei Zhang
2018-01-01
Full Text Available Based on the energy attenuation characteristics of residual wave in deep rock, a method was developed to determine the microseismic focus energy. Differential energy loss in infinitesimal spreading distance is logically deduced, upon which energy attenuation equation was established. With a logarithmic transformation, a linear relation of the residual seismic energy with distance is formulated. Its intercept was used to determine the microseismic focus energy. The result is compared with that determined by the energy density method. The reliability of the determined focus energy and the impact of the built-in velocity threshold on the residual wave energy computation are discussed. Meanwhile, the energy absorption coefficient used for representing the absorption characteristics of the rock medium in the mining region under study is also clarified. Key findings show that the microseismic focus energy confirmed by the residual wave attenuation is reliable. The result’s accuracy is quite high, especially for the events in deep rock with great homogeneity. The developed focus energy computation method is closely dependent on the integrity of waveform, accuracy of repositioning, and reliability of effective components extraction. The new method has been shown to be effective and practical.
Regional seismic-wave propagation from the M5.8 23 August 2011, Mineral, Virginia, earthquake
Pollitz, Fred; Mooney, Walter D.
2015-01-01
The M5.8 23 August 2011 Mineral, Virginia, earthquake was felt over nearly the entire eastern United States and was recorded by a wide array of seismic broadband instruments. The earthquake occurred ~200 km southeast of the boundary between two distinct geologic belts, the Piedmont and Blue Ridge terranes to the southeast and the Valley and Ridge Province to the northwest. At a dominant period of 3 s, coherent postcritical P-wave (i.e., direct longitudinal waves trapped in the crustal waveguide) arrivals persist to a much greater distance for propagation paths toward the northwest quadrant than toward other directions; this is probably related to the relatively high crustal thickness beneath and west of the Appalachian Mountains. The seismic surface-wave arrivals comprise two distinct classes: those with weakly dispersed Rayleigh waves and those with strongly dispersed Rayleigh waves. We attribute the character of Rayleigh wave arrivals in the first class to wave propagation through a predominantly crystalline crust (Blue Ridge Mountains and Piedmont terranes) with a relatively thin veneer of sedimentary rock, whereas the temporal extent of the Rayleigh wave arrivals in the second class are well explained as the effect of the thick sedimentary cover of the Valley and Ridge Province and adjacent Appalachian Plateau province to its northwest. Broadband surface-wave ground velocity is amplified along both north-northwest and northeast azimuths from the Mineral, Virginia, source. The former may arise from lateral focusing effects arising from locally thick sedimentary cover in the Appalachian Basin, and the latter may result from directivity effects due to a northeast rupture propagation along the finite fault plane.
Germán Rubino, J; Monachesi, Leonardo B; Müller, Tobias M; Guarracino, Luis; Holliger, Klaus
2013-12-01
Oscillatory fluid movements in heterogeneous porous rocks induced by seismic waves cause dissipation of wave field energy. The resulting seismic signature depends not only on the rock compressibility distribution, but also on a statistically averaged permeability. This so-called equivalent seismic permeability does not, however, coincide with the respective equivalent flow permeability. While this issue has been analyzed for one-dimensional (1D) media, the corresponding two-dimensional (2D) and three-dimensional (3D) cases remain unexplored. In this work, this topic is analyzed for 2D random medium realizations having strong permeability fluctuations. With this objective, oscillatory compressibility simulations based on the quasi-static poroelasticity equations are performed. Numerical analysis shows that strong permeability fluctuations diminish the magnitude of attenuation and velocity dispersion due to fluid flow, while the frequency range where these effects are significant gets broader. By comparing the acoustic responses obtained using different permeability averages, it is also shown that at very low frequencies the equivalent seismic permeability is similar to the equivalent flow permeability, while for very high frequencies this parameter approaches the arithmetic average of the permeability field. These seemingly generic findings have potentially important implications with regard to the estimation of equivalent flow permeability from seismic data.
Joint Inversion of Earthquake Source Parameters with local and teleseismic body waves
Chen, W.; Ni, S.; Wang, Z.
2011-12-01
In the classical source parameter inversion algorithm of CAP (Cut and Paste method, by Zhao and Helmberger), waveform data at near distances (typically less than 500km) are partitioned into Pnl and surface waves to account for uncertainties in the crustal models and different amplitude weight of body and surface waves. The classical CAP algorithms have proven effective for resolving source parameters (focal mechanisms, depth and moment) for earthquakes well recorded on relatively dense seismic network. However for regions covered with sparse stations, it is challenging to achieve precise source parameters . In this case, a moderate earthquake of ~M6 is usually recorded on only one or two local stations with epicentral distances less than 500 km. Fortunately, an earthquake of ~M6 can be well recorded on global seismic networks. Since the ray paths for teleseismic and local body waves sample different portions of the focal sphere, combination of teleseismic and local body wave data helps constrain source parameters better. Here we present a new CAP mothod (CAPjoint), which emploits both teleseismic body waveforms (P and SH waves) and local waveforms (Pnl, Rayleigh and Love waves) to determine source parameters. For an earthquake in Nevada that is well recorded with dense local network (USArray stations), we compare the results from CAPjoint with those from the traditional CAP method involving only of local waveforms , and explore the efficiency with bootstraping statistics to prove the results derived by CAPjoint are stable and reliable. Even with one local station included in joint inversion, accuracy of source parameters such as moment and strike can be much better improved.
Seismic Interface Waves in Coastal Waters: A Review
1980-11-15
is more interested in the phenomenological or experimental aspects of seismic sensing of the sea floor may simply skip those chapters without...retically and experimentally the shallow-water edge with different, quite- small, taper - or "beach" - angles. In acco dance both with simplified
Precise seismic-wave velocity atop Earth's core: No evidence for outer-core stratification
Alexandrakis, Catherine; Eaton, David W.
2010-05-01
Earth's outer core is composed of liquid Fe and Ni alloyed with a ˜10% fraction of light elements such as O, S, or Si. Secular cooling and compositional buoyancy drive vigorous convection that sustains the geodynamo, but critical details of light-element composition and thermal regime remain uncertain. Seismic velocities can provide important observational constraints on these parameters, but global reference models such as Preliminary Reference Earth Model ( PREM), IASP91 and AK135 exhibit significant discrepancies in the outermost ˜200 km of the core. Here, we apply an Empirical Transfer Function method to obtain precise arrival times for SmKS waves, a whispering-gallery mode that propagates near the underside of the core-mantle boundary. Models that fit our data are all characterized by seismic velocities and depth gradients in the outermost 200 km of the core that correspond best with PREM. This similarity to PREM, which has a smooth velocity profile that satisfies the adiabatic Adams and Williamson equation, argues against the presence of an anomalous layer of light material near the top of the core as suggested in some previous studies. A new model, AE09, is proposed as a slight modification to PREM for use as a reference model of the outermost core.
3-D P- and S-wave velocity structure along the central Alpine Fault, South Island, New Zealand
Guo, B.; Thurber, C. H.; Roecker, S. W.; Townend, J.; Rawles, C.; Chamberlain, C. J.; Boese, C. M.; Bannister, S.; Feenstra, J.; Eccles, J. D.
2017-05-01
The Deep Fault Drilling Project (DFDP) on the central Alpine Fault, South Island, New Zealand, has motivated a broad range of geophysical and geological studies intended to characterize the fault system in the locality of the drill site at various scales. In order to better understand the structural features of the central Alpine Fault, we have developed 3-D P- and S-wave velocity (VP and VS) models of the region by double-difference tomography using data sets from multiple seismic networks. In previous work, the quality of the S-wave model has been poor due to the small number of available S-wave picks. We have utilized a new high-accuracy automatic S-wave picker to increase the number of usable S-wave arrivals by more than a factor of two, thereby substantially improving the VS model. Compared to previous studies, our new higher-resolution VP model based on more observations shows a clear VP contrast (higher VP on the southeast hanging wall side) at depths of 5-10 km near the DFDP drill sites. With our better resolved VS model, in the same region, we detect a sharply defined high VS body (VS > 3.7 km s-1) within the hanging wall. Our earthquake relocations reveal the presence of clusters within and around low-velocity zones in the hanging wall southeast of the Alpine Fault. Together with the improved earthquake locations, the P- and S-wave tomography results reveal the Alpine Fault to be marked by a velocity contrast throughout most of the study region. The fault dips southeastwards at about 50° from 5 to 15 km depth, as inferred from the velocity structure, seismicity and observations of fault zone guided waves.
Combined effects of traveling seismic waves and soil nonlinearity on nuclear power plant response
International Nuclear Information System (INIS)
Lee, T.H.; Charman, C.M.
1981-01-01
The effects of ground motion nonuniformity on the seismic input have been actively studied in recent years by considering the passage of traveling seismic waves. These studies gave rise to a new class of soil-structure interaction problems in which the seismic input is modified as a result of the spatial variations of ground motion. The phenomena were usually studied by using the elastic half-space simulation or discrete spring-models for modeling the soil medium. Finite element methods were also used recently on a limited scope. Results obtained from these investigations are often manifested by an attenuation of translational excitation along with an addition of rotational ground motion input. The decrease in structural response resulting from the input loss in the translational component was often insignificant since the response reduction tends to be offset by the effects from rotational input. The traveling wave effects have, so far, been investigated within the framework of linear theory with soil nonlinearity ignored. Conversely, the incorporation of soil nonlinearity in soil-structure interaction analyses has been done without including wave effect. Seismic analyses considering the hysteretic behavior of soil have been performed using highly idealized models for steady-state solution. More elaborate nonlinear seismic models deal with only the strain-dependent soil modulus rather than the transient unloading-reloading type of hysteretic characteristics of soil under a time-function input of earthquake trace. Apparently, the traveling wave effect and soil nonlinearity have been separately treated in the past. The purpose of this paper is to demonstrate that these two major effects can be combined in one model such that the influence of wave passage is reflected through the hysteretic behavior of soil particles, and thereby achieving significant reduction in seismic loads. (orig./RW)
P- and S-wave Receiver Function Imaging with Scattering Kernels
Hansen, S. M.; Schmandt, B.
2017-12-01
Full waveform inversion provides a flexible approach to the seismic parameter estimation problem and can account for the full physics of wave propagation using numeric simulations. However, this approach requires significant computational resources due to the demanding nature of solving the forward and adjoint problems. This issue is particularly acute for temporary passive-source seismic experiments (e.g. PASSCAL) that have traditionally relied on teleseismic earthquakes as sources resulting in a global scale forward problem. Various approximation strategies have been proposed to reduce the computational burden such as hybrid methods that embed a heterogeneous regional scale model in a 1D global model. In this study, we focus specifically on the problem of scattered wave imaging (migration) using both P- and S-wave receiver function data. The proposed method relies on body-wave scattering kernels that are derived from the adjoint data sensitivity kernels which are typically used for full waveform inversion. The forward problem is approximated using ray theory yielding a computationally efficient imaging algorithm that can resolve dipping and discontinuous velocity interfaces in 3D. From the imaging perspective, this approach is closely related to elastic reverse time migration. An energy stable finite-difference method is used to simulate elastic wave propagation in a 2D hypothetical subduction zone model. The resulting synthetic P- and S-wave receiver function datasets are used to validate the imaging method. The kernel images are compared with those generated by the Generalized Radon Transform (GRT) and Common Conversion Point stacking (CCP) methods. These results demonstrate the potential of the kernel imaging approach to constrain lithospheric structure in complex geologic environments with sufficiently dense recordings of teleseismic data. This is demonstrated using a receiver function dataset from the Central California Seismic Experiment which shows several
Shear wave velocity versus quality factor: results from seismic noise recordings
Boxberger, Tobias; Pilz, Marco; Parolai, Stefano
2017-08-01
The assessment of the shear wave velocity (vs) and shear wave quality factor (Qs) for the shallow structure below a site is necessary to characterize its site response. In the past, methods based on the analysis of seismic noise have been shown to be very efficient for providing a sufficiently accurate estimation of the vs versus depth at reasonable costs for engineering seismology purposes. In addition, a slight modification of the same method has proved to be able to provide realistic Qs versus depth estimates. In this study, data sets of seismic noise recorded by microarrays of seismic stations in different geological environments of Europe and Central Asia are used to calculate both vs and Qs versus depth profiles. Analogous to the generally adopted approach in seismic hazard assessment for mapping the average shear wave velocity in the uppermost 30 m (vs30) as a proxy of the site response, this approach was also applied to the quality factor within the uppermost 30 m (Qs30). A slightly inverse correlation between both parameters is found based on a methodological consistent determination for different sites. Consequently, a combined assessment of vs and Qs by seismic noise analysis has the potential to provide a more comprehensive description of the geological structure below a site.
Compressional seismic waves recorded during underground nuclear explosion tests in HOGGAR
International Nuclear Information System (INIS)
Ferrieux, Henri
1970-01-01
The seismic measurement device was the following: - a movable apparatus in the shot area, - at larger distances, two stations at permanent places. The radial compression wave is examined from the beginning of the pseudo-elastical behaviour of the medium to a distance of fifty kilometers. The amplitude laws evolution is conformed to the theory predictions. The shots energy and the observation distance influence on the amplitude spectra of the compression waves, is studied. (author)
Joint body- and surface-wave tomography of Yucca Flat, Nevada
Toney, L. D.; Abbott, R. E.; Preston, L. A.
2017-12-01
In 2015, Sandia National Laboratories conducted an active-source seismic survey of Yucca Flat (YF), Nevada, on the Nevada National Security Site. YF hosted over 650 underground nuclear tests (UGTs) between 1957 and 1992. Data from this survey will help characterize the geologic structure and bulk properties of the region, informing models for the next phase of the Source Physics Experiments. The survey source was a 13,000-kg weight drop at 91 locations along a 19-km N-S transect and 56 locations along an 11-km E-W transect. Over 350 three-component 2-Hz geophones were variably spaced at 10, 20, and 100 m along each line; we used a roll-along survey geometry to ensure 10-m receiver spacing within 2 km of the source. We applied the multiple filter technique to the dataset using a comb of 30 narrow bandpass filters with center frequencies ranging from 1 to 50 Hz. After manually windowing out the fundamental Rayleigh-wave arrival, we picked group-velocity dispersion curves for 50,000 source-receiver pairs. We performed a joint inversion of group-velocity dispersion and existing body-wave travel-time picks for the shear- and compressional-wave velocity structure of YF. Our final models reveal significant Vp / Vs anomalies in the vicinities of legacy UGT sites. The velocity structures corroborate existing seismo-stratigraphic models of YF derived from borehole and gravity data. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.
The finite-difference and finite-element modeling of seismic wave propagation and earthquake motion
International Nuclear Information System (INIS)
Moszo, P.; Kristek, J.; Galis, M.; Pazak, P.; Balazovijech, M.
2006-01-01
Numerical modeling of seismic wave propagation and earthquake motion is an irreplaceable tool in investigation of the Earth's structure, processes in the Earth, and particularly earthquake phenomena. Among various numerical methods, the finite-difference method is the dominant method in the modeling of earthquake motion. Moreover, it is becoming more important in the seismic exploration and structural modeling. At the same time we are convinced that the best time of the finite-difference method in seismology is in the future. This monograph provides tutorial and detailed introduction to the application of the finite-difference, finite-element, and hybrid finite-difference-finite-element methods to the modeling of seismic wave propagation and earthquake motion. The text does not cover all topics and aspects of the methods. We focus on those to which we have contributed. (Author)
Seismic wave propagation in non-homogeneous elastic media by boundary elements
Manolis, George D; Rangelov, Tsviatko V; Wuttke, Frank
2017-01-01
This book focuses on the mathematical potential and computational efficiency of the Boundary Element Method (BEM) for modeling seismic wave propagation in either continuous or discrete inhomogeneous elastic/viscoelastic, isotropic/anisotropic media containing multiple cavities, cracks, inclusions and surface topography. BEM models may take into account the entire seismic wave path from the seismic source through the geological deposits all the way up to the local site under consideration. The general presentation of the theoretical basis of elastodynamics for inhomogeneous and heterogeneous continua in the first part is followed by the analytical derivation of fundamental solutions and Green's functions for the governing field equations by the usage of Fourier and Radon transforms. The numerical implementation of the BEM is for antiplane in the second part as well as for plane strain boundary value problems in the third part. Verification studies and parametric analysis appear throughout the book, as do both ...
Comina, Cesare; Krawczyk, Charlotte M.; Polom, Ulrich; Socco, Laura Valentina
2017-09-01
Quick clay is a water-saturated formation originally formed through flocculation and deposition in a marine to brackish environment. It is subsequently leached to low salinity by freshwater flow. If its strength decreases, then the flocculated structure collapses leading to landslides of varying destructiveness. Leaching can result in a reduction of the undisturbed shear strength of these clays and suggestions exist that a reduction in shear wave velocities is also possible. Integration of SH seismic reflection and Love-wave dispersion data was undertaken, in an area near the Göta River in southwest Sweden, to evaluate the potential of shear wave velocity imaging for detecting quick clays. Seismic reflection processing evidenced several geologically interesting interfaces related to the probable presence of quick clays (locally confirmed by boreholes) and sand-gravelly layers strongly contributing to water circulation within them. Dispersion data were extracted with a Gaussian windowing approach and inverted with a laterally constrained inversion using a priori information from the seismic reflection imaging. The inversion of dispersion curves has evidenced the presence of a low velocity layer (lvl, with a velocity reduction of ca. 30 per cent) probably associable to quick clays. This velocity reduction is enough to produce detectable phase-velocity differences in the field data and to achieve a better velocity resolution if compared to reflection seismic velocity analyses. The proposed approach has the potential of a comprehensive determination of the shear wave velocity distribution in the shallow subsurface. A sensitivity analysis of Love-wave dispersion data is also presented underlining that, despite limited dispersion of the data set and the velocity-reducing effect of quick-clay leaching, the proposed interpretation procedure arises as a valuable approach in quick clay and other lvl identification.
Realistic Modeling of Seismic Wave Ground Motion in Beijing City
Ding, Z.; Romanelli, F.; Chen, Y. T.; Panza, G. F.
Algorithms for the calculation of synthetic seismograms in laterally heterogeneous anelastic media have been applied to model the ground motion in Beijing City. The synthetic signals are compared with the few available seismic recordings (1998, Zhangbei earthquake) and with the distribution of observed macroseismic intensity (1976, Tangshan earthquake). The synthetic three-component seismograms have been computed for the Xiji area and Beijing City. The numerical results show that the thick Tertiary and Quaternary sediments are responsible for the severe amplification of the seismic ground motion. Such a result is well correlated with the abnormally high macroseismic intensity zone in the Xiji area associated with the 1976 Tangshan earthquake as well as with the ground motion recorded in Beijing city in the wake of the 1998 Zhangbei earthquake.
Realistic modeling of seismic wave ground motion in Beijing City
International Nuclear Information System (INIS)
Ding, Z.; Chen, Y.T.; Romanelli, F.; Panza, G.F.
2002-05-01
Advanced algorithms for the calculation of synthetic seismograms in laterally heterogeneous anelastic media have been applied to model the ground motion in Beijing City. The synthetic signals are compared with the few available seismic recordings (1998, Zhangbei earthquake) and with the distribution of the observed macroseismic intensity (1976, Tangshan earthquake). The synthetic 3-component seismograms have been computed in the Xiji area and in Beijing town. The numerical results show that the thick Tertiary and Quaternary sediments are responsible of the severe amplification of the seismic ground motion. Such a result is well correlated with the abnormally high macroseismic intensity zone (Xiji area) associated to the 1976 Tangshan earthquake and with the records in Beijing town, associated to the 1998 Zhangbei earthquake. (author)
Energy Technology Data Exchange (ETDEWEB)
Telegin, A.N.; Bulatov, M.G.
1982-01-01
An algorithm is proposed for determining effective velocities in the process of diffraction transformation of seismic waves. It is based on summation with conjugate recordings. Results of the study of velocities are indicated in materials of Sakhalin. A difference is noted in the procedures for computing effective velocities in the OGT method and diffraction transformation.
Surface-wave separation and its impact on seismic survey design
Ishiyama, T.
2015-01-01
Surface waves in seismic data are often dominant and mask primaries in land or shallow-water environments. Separating them from the primaries is of great importance either for removing them as noise for reservoir imaging and characterization, or for considering them as signal for near-surface
Miyoshi, Takayuki
2017-04-01
depth of 30 km. We found distinct low wave-speed patterns in S-wave structure. One of the patterns extends in the E-W direction around a depth of 40 km. This zone was interpreted as the serpentinized mantle above the Philippine Sea slab (e.g. Kamiya and Kobayashi 2000). We also obtained the low wave-speed zone around the depth of 5 km. It seems this area extends along the Median tectonic line and this area is correspond to the sedimentary layer. We thank the NIED for providing seismic data, and also thank the researchers for providing the SPECFEM Cartesian program package.
High-Resolution Body Wave Tomography of the Ross Sea Embayment, Antarctica
White-Gaynor, A.; Nyblade, A.; Wiens, D. A.; Aster, R. C.; Gerstoft, P.; Bromirski, P. D.; Stephen, R. A.
2017-12-01
The West Antarctic Rift System (WARS) is one of the least understood continental rift system on the planet. The 1000 km wide WARS includes the Ross Sea Embayment between Marie Byrd Land and the Transantarctic Mountains (TAMS). Active volcanism on Ross Island continues to challenge our understanding of the generally quiescent rift system. Previous regional-scale body wave tomographic investigations have identified areas of low seismic wave speeds to 200 km depth beneath Ross Island. However, the spatial extent of the low velocity structure across the entirety of the WARS remains poorly constrained due to the insufficient resolution of upper mantle structure under the Ross Sea Embayment away from Ross Island. We utilize teleseismic P wave observations recorded on the RIS/DRIS network, which consists of 34 seismometers deployed across the Ross Ice Shelf, along with data from nearby POLENET and TAMSEIS stations to better resolve this region. Relative P wave travel time residuals from 1300 teleseismic events, obtained using a multichannel cross-correlation method, have been inverted for a seismic velocity model of the upper mantle throughout the Ross Sea Embayment. Our results suggest that the low wave speed structure under Ross Island extends roughly halfway across the Embayment and south along the Transantarctic Mountains. This observation is consistent with a two-phase rifting history for the WARS in which broad, late Cretaceous rifting between Marie Byrd Land and the TAMS transitioned to more focused rifting along the TAMS margin in the Cenozoic.
Shiina, T.; Nakajima, J.; Toyokuni, G.; Kita, S.; Matsuzawa, T.
2014-12-01
A subducting crust contains a large amount of water as a form of hydrous minerals (e.g., Hacker et al., 2003), and the crust plays important roles for water transportation and seismogenesis in subduction zones at intermediate depths (e.g., Kirby et al., 1996; Iwamori, 2007). Therefore, the investigation of seismic structure in the crust is important to understand ongoing physical processes with subduction of oceanic lithosphere. A guided wave which propagates in the subducting crust is recorded in seismograms at Hokkaido, northern Japan (Shiina et al., 2014). Here, we estimated P- and S-wave velocity in the crust with guided waves, and obtained P-wave velocity of 6.6-7.3 km/s and S-wave velocity of 3.6-4.2 km/s at depths of 50-90 km. Moreover, Vp/Vs ratio in the crust is calculated to be 1.80-1.85 in that depth range. The obtained P-wave velocity about 6.6km/s at depths of 50-70 km is consistent with those estimated in Tohoku, northeast Japan (Shiina et al., 2013), and this the P-wave velocity is lower than those expected from models of subducting crustal compositions, such as metamorphosed MORB model (Hacker et al., 2003). In contrast, at greater depths (>80 km), the P-wave velocity marks higher velocity than the case of NE Japan and the velocity is roughly comparable to those of the MORB model. The obtained S-wave velocity distribution also shows characteristics similar to P waves. This regional variation may be caused by a small variation in thermal regime of the Pacific slab beneath the two regions as a result of the normal subduction in Tohoku and oblique subduction in Hokkaido. In addition, the effect of seismic anisotropy in the subducting crust would not be ruled out because rays used in the analysis in Hokkaido propagate mostly in the trench-parallel direction, while those in Tohoku are sufficiently criss-crossed.
Attenuation of seismic waves in rocks saturated with multiphase fluids: theory and experiments
Tisato, N.; Quintal, B.; Chapman, S.; Podladchikov, Y.; Burg, J. P.
2016-12-01
Albeit seismic tomography could provide a detailed image of subsurface fluid distribution, the interpretation of the tomographic signals is often controversial and fails in providing a conclusive map of the subsurface saturation. However, tomographic information is important because the upward migration of multiphase fluids through the crust of the Earth can cause hazardous events such as eruptions, explosions, soil-pollution and earthquakes. In addition, multiphase fluids, such as hydrocarbons, represent important resources for economy. Seismic tomography can be improved considering complex elastic moduli and the attenuation of seismic waves (1/Q) that quantifies the energy lost by propagating elastic waves. In particular, a significant portion of the energy carried by the propagating wave is dissipated in saturated media by the wave-induced-fluid-flow (WIFF) and the wave-induced-gas-exsolution-dissolution (WIGED) mechanism. The latter describes how a propagating wave modifies the thermodynamic equilibrium between different fluid phases causing exsolution and dissolution of gas bubbles in the liquid, which in turn causes a significant frequency-dependent 1/Q and moduli dispersion. The WIGED theory was initially postulated for bubbly magmas but was only recently demonstrated and extended to bubbly water. We report the theory and laboratory experiments that have been performed to confirm the WIGED theory. In particular, we present i) attenuation measurements performed by means of the Broad Band Attenuation Vessel on porous media saturated with water and different gases, and ii) numerical experiments validating the laboratory observations. Then, we extend the theory to fluids and pressure-temperature conditions which are typical of phreatomagmatic and hydrocarbon domains and we compare the propagation of seismic waves in bubble-free and bubble-bearing subsurface domains. This work etends the knowledge of attenuation in rocks saturated with multiphase fluid and
Induced Electromagnetic Field by Seismic Waves in Stratified Media in Earth's Magnetic Field
Yamazaki, K.
2017-12-01
Seismic waves accompany electromagnetic (EM) variations because Earth's crust involves a variety of EM properties such as finite electrical conductivity and ion contents. If we can catch the EM variations just after the earthquake rupture, we will know the occurrence of earthquake before the arrival of seismic waves at observation point. However, quantitative aspects of EM variations arising from seismic waves have not sufficiently understood. Together with observational works, theoretical works have been made to simulate EM variations arising from seismic waves. The generation mechanisms of EM variations include electrokinetic effect (Pride, 1994), motional induction (Gao et al., 2014), piezo-electric effect (Ogawa and Utada, 2000), piezo-magnetic effect (Yamazaki, 2016), etc. It is widely accepted that the electrokinetic effect is the dominant mechanism. Theoretical calculation of EM variations assuming the electrokinetic effect roughly explains the observed EM variations accompanying with earthquake ground motions (e.g. Gao et al. 2016). However, there are a significant disagreement between observed and predicted EM variations. In the present study, I focus on the motional induction mechanism that possibly explain some parts of EM variations accompanying with seismic waves. A theoretical work on EM variations arising from the motional induction has been presented by Gao et al. (2014), but their work assumed uniform full-space medium. In contrast, the present work assumes stratified media which correctly incorporate the effect of the ground surface. I apply a calculating method developed in seismology (e.g. Kennett, 2013) and in EM studies (Haartsen and Pride, 1997), and derive a set of expressions describing the spatial-temporal variations of the EM field after the onset of rupture. The derived formula is used to calculate EM variations for actual earthquakes to compare the theoretical prediction to observed EM variations.
The finite-difference and finite-element modeling of seismic wave propagation and earthquake motion
International Nuclear Information System (INIS)
Moczo, P.; Kristek, J.; Pazak, P.; Balazovjech, M.; Moczo, P.; Kristek, J.; Galis, M.
2007-01-01
Numerical modeling of seismic wave propagation and earthquake motion is an irreplaceable tool in investigation of the Earth's structure, processes in the Earth, and particularly earthquake phenomena. Among various numerical methods, the finite-difference method is the dominant method in the modeling of earthquake motion. Moreover, it is becoming more important in the seismic exploration and structural modeling. At the same time we are convinced that the best time of the finite-difference method in seismology is in the future. This monograph provides tutorial and detailed introduction to the application of the finite difference (FD), finite-element (FE), and hybrid FD-FE methods to the modeling of seismic wave propagation and earthquake motion. The text does not cover all topics and aspects of the methods. We focus on those to which we have contributed. We present alternative formulations of equation of motion for a smooth elastic continuum. We then develop alternative formulations for a canonical problem with a welded material interface and free surface. We continue with a model of an earthquake source. We complete the general theoretical introduction by a chapter on the constitutive laws for elastic and viscoelastic media, and brief review of strong formulations of the equation of motion. What follows is a block of chapters on the finite-difference and finite-element methods. We develop FD targets for the free surface and welded material interface. We then present various FD schemes for a smooth continuum, free surface, and welded interface. We focus on the staggered-grid and mainly optimally-accurate FD schemes. We also present alternative formulations of the FE method. We include the FD and FE implementations of the traction-at-split-nodes method for simulation of dynamic rupture propagation. The FD modeling is applied to the model of the deep sedimentary Grenoble basin, France. The FD and FE methods are combined in the hybrid FD-FE method. The hybrid
Esterhazy, Sofi; Schneider, Felix; Perugia, Ilaria; Bokelmann, Götz
2017-04-01
Motivated by the need to detect an underground cavity within the procedure of an On-Site-Inspection (OSI) of the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), which might be caused by a nuclear explosion/weapon testing, we aim to provide a basic numerical study of the wave propagation around and inside such an underground cavity. One method to investigate the geophysical properties of an underground cavity allowed by the Comprehensive Nuclear-test Ban Treaty is referred to as "resonance seismometry" - a resonance method that uses passive or active seismic techniques, relying on seismic cavity vibrations. This method is in fact not yet entirely determined by the Treaty and so far, there are only very few experimental examples that have been suitably documented to build a proper scientific groundwork. This motivates to investigate this problem on a purely numerical level and to simulate these events based on recent advances in numerical modeling of wave propagation problems. Our numerical study includes the full elastic wave field in three dimensions. We consider the effects from an incoming plane wave as well as point source located in the surrounding of the cavity at the surface. While the former can be considered as passive source like a tele-seismic earthquake, the latter represents a man-made explosion or a viborseis as used for/in active seismic techniques. Further we want to demonstrate the specific characteristics of the scattered wave field from a P-waves and S-wave separately. For our simulations in 3D we use the discontinuous Galerkin Spectral Element Code SPEED developed by MOX (The Laboratory for Modeling and Scientific Computing, Department of Mathematics) and DICA (Department of Civil and Environmental Engineering) at the Politecnico di Milano. The computations are carried out on the Vienna Scientific Cluster (VSC). The accurate numerical modeling can facilitate the development of proper analysis techniques to detect the remnants of an
Real-time fracture monitoring in Engineered Geothermal Systems with seismic waves
Energy Technology Data Exchange (ETDEWEB)
Jose A. Rial; Jonathan Lees
2009-03-31
As proposed, the main effort in this project is the development of software capable of performing real-time monitoring of micro-seismic activity recorded by an array of sensors deployed around an EGS. The main milestones are defined by the development of software to perform the following tasks: • Real-time micro-earthquake detection and location • Real-time detection of shear-wave splitting • Delayed-time inversion of shear-wave splitting These algorithms, which are discussed in detail in this report, make possible the automatic and real-time monitoring of subsurface fracture systems in geothermal fields from data collected by an array of seismic sensors. Shear wave splitting (SWS) is parameterized in terms of the polarization of the fast shear wave and the time delay between the fast and slow shear waves, which are automatically measured and stored. The measured parameters are then combined with previously measured SWS parameters at the same station and used to invert for the orientation (strike and dip) and intensity of cracks under that station. In addition, this grant allowed the collection of seismic data from several geothermal regions in the US (Coso) and Iceland (Hengill) to use in the development and testing of the software.
Modeling Seismic Wave Propagation Using Time-Dependent Cauchy-Navier Splines
Kammann, P.
2005-12-01
Our intention is the modeling of seismic wave propagation from displacement measurements by seismographs at the Earth's surface. The elastic behaviour of the Earth is usually described by the Cauchy-Navier equation. A system of fundamental solutions for the Fourier transformed Cauchy-Navier equation are the Hansen vectors L, M and N. We apply an inverse Fourier transform to obtain an orthonormal function system depending on time and space. By means of this system we construct certain splines, which are then used for interpolating the given data. Compared to polynomial interpolation, splines have the advantage that they minimize some curvature measure and are, therefore, smoother. First, we test this method on a synthetic wave function. Afterwards, we apply it to realistic earthquake data. (P. Kammann, Modelling Seismic Wave Propagation Using Time-Dependent Cauchy-Navier Splines, Diploma Thesis, Geomathematics Group, Department of Mathematics, University of Kaiserslautern, 2005)
Neural Network-Based Laser Interferometer Compensation for Seismic Signal Detection
Directory of Open Access Journals (Sweden)
Kyunghyun Lee
2018-01-01
Full Text Available We propose a seismic wave detection method in the frequency domain using a heterodyne laser interferometer, which is used in ultraprecision fields as a displacement measurement device. In seismology, it is important to accurately measure seismic waves. To overcome the limited frequency range and low resolution of accelerometers and velocimeters and to enhance the precision of seismic data analysis, we use the heterodyne laser interferometer as a seismic detection apparatus. We apply the data fusion algorithm with the adaptive standard deviation ratio (ς derived from the neural network to improve the laser interferometer’s measurement precision. Moreover, by using the interferometric characteristics, we analyze the seismic data in the frequency domain. To determine the location of the epicenter from the body wave propagation analysis, we apply the STA/LTA algorithm to the measurement data. The effectiveness of the proposed laser interferometric seismometer is shown through experiments to locate the precise epicenter.
Seismic surface wave tomography of waste sites. 1997 annual progress report
International Nuclear Information System (INIS)
Long, T.L.
1997-01-01
'The objective of the Seismic Surface Wave Tomography of Waste Sites is to develop a robust technique for field acquisition and analysis of surface wave data for the interpretation of shallow structures, such as those associated with the burial of wastes. The analysis technique is to be developed and tested on an existing set of seismic data covering the K-901 burial site at the East Tennessee Technology Park. Also, a portable prototype for a field acquisition system will be designed and developed to obtain additional data for analysis and testing of the technique. The K-901 data have been examined and a preliminary Single Valued Decomposition inversion has been obtained. The preliminary data indicates a need for additional seismic data to ground-truth the inversion. The originally proposed gravity data acquisition has been dropped because sufficient gravity data are now available for a preliminary analysis and because the seismic data are considered more critical to the interpretation. The proposed prototype for the portable acquisition and analysis system was developed during the first year and will be used in part of the acquisition of additional seismic data.'
Three-Dimensional Sensitivity Kernels of Z/H Amplitude Ratios of Surface and Body Waves
Bao, X.; Shen, Y.
2017-12-01
The ellipticity of Rayleigh wave particle motion, or Z/H amplitude ratio, has received increasing attention in inversion for shallow Earth structures. Previous studies of the Z/H ratio assumed one-dimensional (1D) velocity structures beneath the receiver, ignoring the effects of three-dimensional (3D) heterogeneities on wave amplitudes. This simplification may introduce bias in the resulting models. Here we present 3D sensitivity kernels of the Z/H ratio to Vs, Vp, and density perturbations, based on finite-difference modeling of wave propagation in 3D structures and the scattering-integral method. Our full-wave approach overcomes two main issues in previous studies of Rayleigh wave ellipticity: (1) the finite-frequency effects of wave propagation in 3D Earth structures, and (2) isolation of the fundamental mode Rayleigh waves from Rayleigh wave overtones and converted Love waves. In contrast to the 1D depth sensitivity kernels in previous studies, our 3D sensitivity kernels exhibit patterns that vary with azimuths and distances to the receiver. The laterally-summed 3D sensitivity kernels and 1D depth sensitivity kernels, based on the same homogeneous reference model, are nearly identical with small differences that are attributable to the single period of the 1D kernels and a finite period range of the 3D kernels. We further verify the 3D sensitivity kernels by comparing the predictions from the kernels with the measurements from numerical simulations of wave propagation for models with various small-scale perturbations. We also calculate and verify the amplitude kernels for P waves. This study shows that both Rayleigh and body wave Z/H ratios provide vertical and lateral constraints on the structure near the receiver. With seismic arrays, the 3D kernels afford a powerful tool to use the Z/H ratios to obtain accurate and high-resolution Earth models.
Chan, J. H.; Catchings, R.; Strayer, L. M.; Goldman, M.; Criley, C.; Sickler, R. R.; Boatwright, J.
2017-12-01
We conducted an active-source seismic investigation across the Napa Valley (Napa Valley Seismic Investigation-16) in September of 2016 consisting of two basin-wide seismic profiles; one profile was 20 km long and N-S-trending (338°), and the other 15 km long and E-W-trending (80°) (see Catchings et al., 2017). Data from the NVSI-16 seismic investigation were recorded using a total of 666 vertical- and horizontal-component seismographs, spaced 100 m apart on both seismic profiles. Seismic sources were generated by a total of 36 buried explosions spaced 1 km apart. The two seismic profiles intersected in downtown Napa, where a large number of buildings were red-tagged by the City following the 24 August 2014 Mw 6.0 South Napa earthquake. From the recorded Rayleigh and Love waves, we developed 2-Dimensional S-wave velocity models to depths of about 0.5 km using the multichannel analysis of surface waves (MASW) method. Our MASW (Rayleigh) and MALW (Love) models show two prominent low-velocity (Vs = 350 to 1300 m/s) sub-basins that were also previously identified from gravity studies (Langenheim et al., 2010). These basins trend N-W and also coincide with the locations of more than 1500 red- and yellow-tagged buildings within the City of Napa that were tagged after the 2014 South Napa earthquake. The observed correlation between low-Vs, deep basins, and the red-and yellow-tagged buildings in Napa suggests similar large-scale seismic investigations can be performed. These correlations provide insights into the likely locations of significant structural damage resulting from future earthquakes that occur adjacent to or within sedimentary basins.
Fucugauchi, J. U.; Ortiz-Aleman, C.; Martin, R.
2017-12-01
Large complex craters are characterized by central uplifts that represent large-scale differential movement of deep basement from the transient cavity. Here we investigate the central sector of the large multiring Chicxulub crater, which has been surveyed by an array of marine, aerial and land-borne geophysical methods. Despite high contrasts in physical properties,contrasting results for the central uplift have been obtained, with seismic reflection surveys showing lack of resolution in the central zone. We develop an integrated seismic and gravity model for the main structural elements, imaging the central basement uplift and melt and breccia units. The 3-D velocity model built from interpolation of seismic data is validated using perfectly matched layer seismic acoustic wave propagation modeling, optimized at grazing incidence using shift in the frequency domain. Modeling shows significant lack of illumination in the central sector, masking presence of the central uplift. Seismic energy remains trapped in an upper low velocity zone corresponding to the sedimentary infill, melt/breccias and surrounding faulted blocks. After conversion of seismic velocities into a volume of density values, we use massive parallel forward gravity modeling to constrain the size and shape of the central uplift that lies at 4.5 km depth, providing a high-resolution image of crater structure.The Bouguer anomaly and gravity response of modeled units show asymmetries, corresponding to the crater structure and distribution of post-impact carbonates, breccias, melt and target sediments
Burdick, S.; Waszek, L.; Lekic, V.
2017-12-01
Studies of body waves and normal modes have revealed strong quasi-hemispheric variations in seismic velocity, anisotropy and attenuation in the inner core. A rigorous mapping of the hemispheric boundaries and smaller scale heterogeneity within the hemispheres is crucial for distinguishing between hypotheses about inner core formation and evolution. However, the relatively sparse and heterogeneous distribution of paths piercing the inner core creates difficulties in constraining the boundaries and sub-hemispheric variations with body wave tomography. Damped tomographic inversions tend to smooth out strong structural gradients and risk carrying the imprint of sparse path coverage, while under-parametrized models can miss pertinent small-scale variations. For these reasons, we apply a probabilistic and transdimensional (THB) tomography method on core-sensitive differential P-wave traveltimes. The THB approach is well-suited to the problem of inner core tomography since 1) it remains parsimonious by allowing the parametrization to be determined the requirements of the data and 2) it preserves sharp boundaries in seismic properties, allowing it to capture both short-wavelength structure and the strong hemispheric dichotomy. Furthermore, the approach yields estimates of uncertainty in isotropic and anisotropic velocity, hemispheric boundary geometry, anisotropy axis and the tradeoffs between these properties. We quantify the effects of mantle heterogeneity with inner core structure and place constraints on inner core dynamics and minerology.
Micromechanics of seismic wave propagation in granular materials
O’Donovan, J.; Ibraim, E.; O’Sullivan, C.; Hamlin, S.; Muir Wood, D.; Marketos, G.
2016-01-01
In this study experimental data on a model soil in a cubical cell are compared with both discrete element (DEM) simulations and continuum analyses. The experiments and simulations used point source transmitters and receivers to evaluate the shear and compression wave velocities of the samples, from
Seismic wave propagation in fractured media: A discontinuous Galerkin approach
De Basabe, Jonás D.
2011-01-01
We formulate and implement a discontinuous Galekin method for elastic wave propagation that allows for discontinuities in the displacement field to simulate fractures or faults using the linear- slip model. We show numerical results using a 2D model with one linear- slip discontinuity and different frequencies. The results show a good agreement with analytic solutions. © 2011 Society of Exploration Geophysicists.
Directory of Open Access Journals (Sweden)
Glangeaud F.
2006-11-01
of upgoing waves and sensitivity to first arrival time estimates. La plupart des algorithmes utilisés pour la séparation des ondes montantes et descendantes en PSV font l'hypothèse que le signal est stationnaire en fonction de la profondeur sur toutes les traces utilisées dans le filtre de séparation. Cependant, le signal ne peut plus être supposé stationnaire lorsque les filtres sont appliqués sur une fenêtre en profondeur trop grande (100-200 m. Par contre, la stationnarité du signal peut être considérée comme une hypothèse physiquement raisonnable pour deux positions voisines de la sonde (5-20 m. Cet article présente trois algorithmes pour la séparation des ondes montantes et descendantes, qui ne nécessitent que deux traces adjacentes et les temps de première arrivée sur chacune des traces. Dans la mesure où il n'existe pas de discontinuités géologiques entre ces traces, les algorithmes sont indépendants de la distance en profondeur entre traces. Le premier algorithme (solution pseudo-théorique travaille dans le domaine fréquentiel. La séparation des ondes est obtenue par résolution d'un système de deux équations à deux inconnues pour chaque fréquence. Cette opération est effectuée dans la bande passante correspondant à la meilleure cohérence. Le second algorithme (solution simple réalise une addition et soustraction, basées sur la semblance des signaux, des traces décalées en temps. Le troisième algorithme (solution de Wiener utilise un filtre de Wiener pour prédire le champ d'ondes le plus énergique, qui correspond généralement aux ondes descendantes. Les ondes montantes sont ensuite obtenues par soustraction des ondes montantes estimées, au champ d'ondes total. Le filtre de Wiener peut être ensuite de nouveau appliqué aux ondes montantes de façon à les renforcer. La solution pseudo-théorique et la solution simple réalisent des filtres en vitesse apparente de bande passante étroite, et sont applicables aux PSV
International Nuclear Information System (INIS)
Blom, M.R.; Beker, M.G.; Bertolini, A.; Brand, J.F.J. van den; Bulten, H.J.; Hennes, E.; Mul, F.A.; Rabeling, D.S.; Schimmel, A.
2013-01-01
In November 2011 a major upgrade of the Virgo gravitational wave detector was started. After these improvements the detector's sensitivity will have increased by an order of magnitude, increasing the expected event rate by 10 3 compared to its predecessor. Extensive noise studies showed that this improvement can only be accomplished if a number of optical benches, hosting ancillary optics and optical sensors for the alignment of the interferometer, are isolated from seismic ground motion to reduce the amount of beam jitter and control noise they introduce. Here we present the first of these systems: the External Injection Bench Seismic Attenuation System, or EIB-SAS, which is able to reduce seismically induced motion of the external injection bench (last bench before laser beam enters the vacuum system) by more than 40 dB above 10 Hz in 6 degrees of freedom
Integral anomalous effect of an oil and gas deposit in a seismic wave field
Energy Technology Data Exchange (ETDEWEB)
Korostyshevskiy, M.B.; Nabokov, G.N.
1981-01-01
The basic precepts of an elaborated version of a procedure for forecasting (direct exploration) of oil and gas deposits according to seismic prospecting data MOV are examined. This procedure was previously called the procedure of analysis of the integral affect of an oil and gas deposit in a seismic wave field (MIIEZ-VP). The procedure is implemented in the form of an automated system ASOM-VP for the BESM-4 computer in a standard configuration equipped with standard input-output devices for seismic information (''Potok'', MVU, ''Atlas''). The entire procedure of processing from input of data into the computer to output of resulting maps and graphs on graph plotter ''Atlas'' is automated. Results of testing of procedure MIIEZ-VP and system ASOM-VP on drilled areas of Kazakhstan, Azerbaydzhan and Uzbekistan are cited.
Energy Technology Data Exchange (ETDEWEB)
Pineda Porras, Omar Andrey [Los Alamos National Laboratory
2009-01-01
Over the past three decades, seismic fragility fonnulations for buried pipeline systems have been developed following two tendencies: the use of earthquake damage scenarios from several pipeline systems to create general pipeline fragility functions; and, the use of damage scenarios from one pipeline system to create specific-system fragility functions. In this paper, the advantages and disadvantages of both tendencies are analyzed and discussed; in addition, a summary of what can be considered the new challenges for developing better pipeline seismic fragility formulations is discussed. The most important conclusion of this paper states that more efforts are needed to improve the estimation of transient ground strain -the main cause of pipeline damage due to seismic wave propagation; with relevant advances in that research field, new and better fragility formulations could be developed.
Wilken, Dennis; Wölz, Susanne; Müller, Christof; Rabbel, Wolfgang
2009-05-01
along the acquired profiles correlate well with the reflection seismic stratigraphy and document three shear-wave velocity units ranging from 130 m/s to 420 m/s.
Allowable Pressure In Soils and Rocks by Seismic Wave Velocities
International Nuclear Information System (INIS)
Tezcan, S.; Keceli, A.; Oezdemir, Z.
2007-01-01
Firstly, the historical background is presented for the determination of ultimate bearing capacity of shallow foundations. The principles of plastic equilibrium used in the classical formulation of the ultimate bearing capacity are reviewed, followed by a discussion about the sources of approximations inherent in the classical theory. Secondly, based on a variety of case histories of site investigations, including extensive bore hole data, laboratory testing and geophysical prospecting, an empirical formulation is proposed for the determination of allowable bearing capacity of shallow foundations. The proposed expression corroborates consistently with the results of the classical theory and is proven to be reliable and safe, also from the view point of maximum allowable settlements. It consists of only two soil parameters, namely, the Institut measured shear wave velocity, and the unit weight. The unit weight may be also determined with sufficient accuracy, by means of another empirical expression, using the P-wave velocity. It is indicated that once the shear and P-wave velocities are measured Institut by an appropriate geophysical survey, the allowable bearing capacity is determined reliably through a single step operation. Such an approach, is considerably cost and time-saving, in practice
The objective of this paper is to study the feasibility of using a seismic surface wave method to investigate seasonal and weather effects on shallow surface soils. In the study, temporal variations of subsurface soil properties were measured and monitored by using a combination of a new seismic su...
Pore-fluid effects on seismic waves in vertically fractured earth with orthotropic symmetry
Energy Technology Data Exchange (ETDEWEB)
Berryman, J.G.
2010-05-15
For elastically noninteracting vertical-fracture sets at arbitrary orientation angles to each other, a detailed model is presented in which the resulting anisotropic fractured medium generally has orthorhombic symmetry overall. Some of the analysis methods and ideas of Schoenberg are emphasized, together with their connections to other similarly motivated and conceptually related methods by Sayers and Kachanov, among others. Examples show how parallel vertical-fracture sets having HTI (horizontal transversely isotropic) symmetry transform into orthotropic fractured media if some subsets of the vertical fractures are misaligned with the others, and then the fractured system can have VTI (vertical transversely isotropic) symmetry if all of the fractures are aligned randomly or half parallel and half perpendicular to a given vertical plane. An orthotropic example having vertical fractures in an otherwise VTI earth system (studied previously by Schoenberg and Helbig) is compared with the other examples treated and it is finally shown how fluids in the fractures affect the orthotropic poroelastic system response to seismic waves. The key result is that fracture-influence parameters are multiplied by a factor of (1-B), where 0 {le} B < 1 is Skempton's second coefficient for poroelastic media. Skempton's B coefficient is itself a measurable characteristic of fluid-saturated porous rocks, depending on porosity, solid moduli, and the pore-fluid bulk modulus. For heterogeneous porous media, connections between the present work and earlier related results of Brown and Korringa are also established.
Seismic microzoning of Santiago de Cuba: An approach by SH waves modelling
International Nuclear Information System (INIS)
Alvarez, Leonardo; Garcia, Julio; Gonzalez, Bertha; Reyes, Carmen; Femandez, Barbara; Zapata, Jose A.; Arango, Enrique; Vaccari, Franco; Panza, Giuliano F.; Pico, Ramon
2002-07-01
The expected ground motion in Santiago de Cuba basin from earthquakes which occurred in the Oriente fault zone is studied. Synthetic SH-waves seismograms have been calculated along four profiles in the basin by the hybrid approach (modal summation for the path source-profile and finite differences for the profile) for a maximum frequency of 1 Hz. The response spectra ratio (RSR) has been determined in 49 sites, distributed along all considered profiles with a spacing of 900 m. The corresponding RSR versus frequency curves have been classified using a logical-combinatorial algorithm. The results of the classification, in combination with the uppermost geological setting (geotechnical information and geological geometry of the subsoil) are used for the seismic microzoning of the city. Three different main zones are identified, and a small sector characterised by big resonance effects, due to the particular structural conditions. Each zone is characterized in terms of its expected ground motion parameters for the most probable strong earthquake (M S =7), and for the maximum possible (M S =8). (author)
A Full-Wave Seismic Tomography for the Crustal Structure in the Metropolitan Beijing Region
Sun, A.; Zhao, L.; Chen, Q.
2008-12-01
The greater Beijing metropolitan region is located in an old cratonic block in northeast China with complex geology and several large historic earthquakes, such as the Sanhe-Pinggu earthquake (~M8.0) in 1679, the Xingtai earthquake (M7.2) in 1966, and the Tangshan earthquake (M7.8) in 1976. To enhance our understanding of the crustal structure and the seismotectonics under this region, we conduct a full-wave three-dimensional (3D) tomographic study of this region using the waveforms recorded by the newly established Beijing metropolitan digital seismic network. Since the Beijing network was put into operation in October 2001, there have been 89 local earthquakes of magnitude 3.0 and above. From these, we selected 23 events of magnitude 3.2 and above and obtained their waveform records at 50 stations within our area of interest. The types of instruments at these stations include broadband, short-period and very broadband. First-motion focal mechanisms were determined for these events. We used a regional 3D model obtained by seismic reflection surveys as the reference model and calculated the synthetic seismograms by the finite-difference method. In this first attempt at finite- frequency tomography for the Beijing region, we focus on the variation of the P-wave speed using the first- arriving P waves. We measure the frequency-dependent traveltime anomalies of the P waves by the cross- correlation between observed and synthetic P waveforms within several discrete frequency bands between 20-sec and 5-sec periods. The sensitivity or Frechet kernels of these measurements for the perturbations in P-wave speed were computed by the same finite-difference method. We will present the preliminary result in our full-wave seismic tomography for the Beijing region.
Obrebski, M.; Allen, R.M.; Pollitz, F.; Hung, S.-H.
2011-01-01
The relation between the complex geological history of the western margin of the North American plate and the processes in the mantle is still not fully documented and understood. Several pre-USArray local seismic studies showed how the characteristics of key geological features such as the Colorado Plateau and the Yellowstone Snake River Plains are linked to their deep mantle structure. Recent body-wave models based on the deployment of the high density, large aperture USArray have provided far more details on the mantle structure while surface-wave tomography (ballistic waves and noise correlations) informs us on the shallow structure. Here we combine constraints from these two data sets to image and study the link between the geology of the western United States, the shallow structure of the Earth and the convective processes in mantle. Our multiphase DNA10-S model provides new constraints on the extent of the Archean lithosphere imaged as a large, deeply rooted fast body that encompasses the stable Great Plains and a large portion of the Northern and Central Rocky Mountains. Widespread slow anomalies are found in the lower crust and upper mantle, suggesting that low-density rocks isostatically sustain part of the high topography of the western United States. The Yellowstone anomaly is imaged as a large slow body rising from the lower mantle, intruding the overlying lithosphere and controlling locally the seismicity and the topography. The large E-W extent of the USArray used in this study allows imaging the 'slab graveyard', a sequence of Farallon fragments aligned with the currently subducting Juan de Fuca Slab, north of the Mendocino Triple Junction. The lithospheric root of the Colorado Plateau has apparently been weakened and partly removed through dripping. The distribution of the slower regions around the Colorado Plateau and other rigid blocks follows closely the trend of Cenozoic volcanic fields and ancient lithospheric sutures, suggesting that the
Mikesell, T. Dylan; Malcolm, Alison E.; Yang, Di; Haney, Matthew M.
2015-01-01
Time-shift estimation between arrivals in two seismic traces before and after a velocity perturbation is a crucial step in many seismic methods. The accuracy of the estimated velocity perturbation location and amplitude depend on this time shift. Windowed cross correlation and trace stretching are two techniques commonly used to estimate local time shifts in seismic signals. In the work presented here, we implement Dynamic Time Warping (DTW) to estimate the warping function – a vector of local time shifts that globally minimizes the misfit between two seismic traces. We illustrate the differences of all three methods compared to one another using acoustic numerical experiments. We show that DTW is comparable to or better than the other two methods when the velocity perturbation is homogeneous and the signal-to-noise ratio is high. When the signal-to-noise ratio is low, we find that DTW and windowed cross correlation are more accurate than the stretching method. Finally, we show that the DTW algorithm has better time resolution when identifying small differences in the seismic traces for a model with an isolated velocity perturbation. These results impact current methods that utilize not only time shifts between (multiply) scattered waves, but also amplitude and decoherence measurements. DTW is a new tool that may find new applications in seismology and other geophysical methods (e.g., as a waveform inversion misfit function).
Rayleigh wave tomography in North-China from ambient seismic noise
Fang, Lihua
2010-01-01
2008/2009 The theory and methodology of ambient noise tomography has been studied and applied to North-China successfully. Continuous vertical-component seismograms, spanning the period from January 1, 2007 to February 28, 2008 recorded by 190 broadband stations and 10 very broadband stations, have been used. The cross correlation technique has been applied to ambient noise data recorded by North-China Seismic Array for each station pairs of the array. Rayleigh wave group ve...
S-Band Doppler Wave Radar System
Directory of Open Access Journals (Sweden)
Zezong Chen
2017-12-01
Full Text Available In this paper, a novel shore-based S-band microwave Doppler coherent wave radar (Microwave Ocean Remote SEnsor (MORSE is designed to improve wave measurements. Marine radars, which operate in the X band, have been widely used for ocean monitoring because of their low cost, small size and flexibility. However, because of the non-coherent measurements and strong absorption of X-band radio waves by rain, these radar systems suffer considerable performance loss in moist weather. Furthermore, frequent calibrations to modify the modulation transfer function are required. To overcome these shortcomings, MORSE, which operates in the S band, was developed by Wuhan University. Because of the coherent measurements of this sensor, it is able to measure the radial velocity of water particles via the Doppler effect. Then the relation between the velocity spectrum and wave height spectrum can be used to obtain the wave height spectra. Finally, wave parameters are estimated from the wave height spectra by the spectrum moment method. Comparisons between MORSE and Waverider MKIII are conducted in this study, and the results, including the non-directional wave height spectra, significant wave height and average wave period, are calculated and displayed. The correlation coefficient of the significant wave height is larger than 0.9, whereas that of the average wave period is approximately 0.4, demonstrating the effectiveness of MORSE for the continuous monitoring of ocean areas with high accuracy.
Directory of Open Access Journals (Sweden)
A. A. Stepashko
2013-01-01
mantle lense (Fig 6, A; it is one of four main tectonical units that compose the basement of the Siberian craton [Mironyuk, Zagruzina, 1983]. As evidenced by the zonal composition of the mantle lense, the centre of the lense is highly dense, and this explains the location of a seismic anomaly there (Fig. 6, B which is determined to a depth of about 50–60 km [Pavlenkova G.A., Pavlenkova N.I., 2006]. The high-velocity root located in this segment of the craton is traced by seismic tomography [Koulakov, Bushenkova, 2010] to a depth of about 600 km (Fig. 7. The southward-stretching edge of the sub-cratonic mantle has played a major role in the evolution of the Central Asian orogenic belt. In the Paleozoic, the position and the configuration of the accretional margin of the Siberian paleocontinent were determined by the hidden boundary of the craton (Fig. 8, A. Along the craton’s boundary, rifting zones of various ages are located, and intrusions are concentrated, which genesis was related to extension settings (Fig. 8, B. The Cenozoic sedimentary basins are located above the hidden edge of the Siberian craton, which gives evidence of involvement of the deep lithospheric structure in the formation of the recent destruction zone. The basin of Lake Baikal is located along the mantle edge of the Siberian craton, and the basin’s crescent shape accentuates the strike of the mantle edge.In the region under study, the wave nature of seismicity is most evidently manifested by the cyclicity of the strongest earthquakes in the Baikal zone (Table 2. Three seismic cycles are distinguished as follows: (1 at the turn of the 20th century (earthquakes in the period from 1885 to 1931, M=6.6–8.2, (2 the middle of the 20th century (earthquakes from 1950 to 1967, M=6.8–8.1, and (3 at the turn of the 21st century (earthquakes from 1991 to 2012, M=6.3–7.3. While moving in the mantle, the deformation front collapses with the craton’s basement, partially releases its energy to the
The use of multiwavelets for uncertainty estimation in seismic surface wave dispersion.
Energy Technology Data Exchange (ETDEWEB)
Poppeliers, Christian [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2017-12-01
This report describes a new single-station analysis method to estimate the dispersion and uncer- tainty of seismic surface waves using the multiwavelet transform. Typically, when estimating the dispersion of a surface wave using only a single seismic station, the seismogram is decomposed into a series of narrow-band realizations using a bank of narrow-band filters. By then enveloping and normalizing the filtered seismograms and identifying the maximum power as a function of frequency, the group velocity can be estimated if the source-receiver distance is known. However, using the filter bank method, there is no robust way to estimate uncertainty. In this report, I in- troduce a new method of estimating the group velocity that includes an estimate of uncertainty. The method is similar to the conventional filter bank method, but uses a class of functions, called Slepian wavelets, to compute a series of wavelet transforms of the data. Each wavelet transform is mathematically similar to a filter bank, however, the time-frequency tradeoff is optimized. By taking multiple wavelet transforms, I form a population of dispersion estimates from which stan- dard statistical methods can be used to estimate uncertainty. I demonstrate the utility of this new method by applying it to synthetic data as well as ambient-noise surface-wave cross-correlelograms recorded by the University of Nevada Seismic Network.
Numerical investigation of wake-collapse internal waves generated by a submerged moving body
Liang, Jianjun; Du, Tao; Huang, Weigen; He, Mingxia
2017-07-01
The state-of-the-art OpenFOAM technology is used to develop a numerical model that can be devoted to numerically investigating wake-collapse internal waves generated by a submerged moving body. The model incorporates body geometry, propeller forcing, and stratification magnitude of seawater. The generation mechanism and wave properties are discussed based on model results. It was found that the generation of the wave and its properties depend greatly on the body speed. Only when that speed exceeds some critical value, between 1.5 and 4.5 m/s, can the moving body generate wake-collapse internal waves, and with increases of this speed, the time of generation advances and wave amplitude increases. The generated wake-collapse internal waves are confirmed to have characteristics of the second baroclinic mode. As the body speed increases, wave amplitude and length increase and its waveform tends to take on a regular sinusoidal shape. For three linearly temperature-stratified profiles examined, the weaker the stratification, the stronger the wake-collapse internal wave.
Gravitational waves from periodic three-body systems.
Dmitrašinović, V; Suvakov, Milovan; Hudomal, Ana
2014-09-05
Three bodies moving in a periodic orbit under the influence of Newtonian gravity ought to emit gravitational waves. We have calculated the gravitational radiation quadrupolar waveforms and the corresponding luminosities for the 13+11 recently discovered three-body periodic orbits in Newtonian gravity. These waves clearly allow one to distinguish between their sources: all 13+11 orbits have different waveforms and their luminosities (evaluated at the same orbit energy and body mass) vary by up to 13 orders of magnitude in the mean, and up to 20 orders of magnitude for the peak values.
Servali, A.; Long, M. D.; Benoit, M.
2017-12-01
The eastern margin of North America has been affected by a series of mountain building and rifting events that have likely shaped the deep structure of the lithosphere. Observations of seismic anisotropy can provide insight into lithospheric deformation associated with these past tectonic events, as well as into present-day patterns of mantle flow beneath the passive margin. Previous work on SKS splitting beneath eastern North America has revealed fast splitting directions parallel to the strike of the Appalachian orogen in the central and southern Appalachians. A major challenge to the interpretation of SKS splitting measurements, however, is the lack of vertical resolution; isolating anisotropic structures at different depths is therefore difficult. Complementary constraints on the depth distribution of anisotropy can be provided by surface waves. In this study, we analyze the scattering of Love wave energy to Rayleigh waves, which is generated via sharp lateral gradients in anisotropic structure along the ray path. The scattered phases, known as quasi-Love (QL) waves, exhibit amplitude behavior that depend on the strength of the anisotropic contrast as well as the angle between the propagation azimuth and the anisotropic symmetry axis. We analyze data collected by the dense MAGIC seismic array across the central Appalachians. We examine teleseismic earthquakes of magnitude 6.7 and greater over a range of backazimuths, and isolate surface waves at periods between 100 and 500 seconds. We compare the data to synthetic seismograms generated by the Princeton Global ShakeMovie initiative to identify anomalous QL arrivals. We find evidence significant QL arrivals at MAGIC stations, with amplitudes depending on propagation azimuth and station location. Preliminary results are consistent with a sharp lateral gradient in seismic anisotropy across the Appalachian Mountains in the depth range between 100-200 km.
Where no wave has gone before: unconventional elastic wave fields in exotic regimes
Bohlen, T.
2012-04-01
Nowadays, elastic wave fields are acquired on land, at the sea or or within tunnels and boreholes. The increasing availability of computational resources allow to use their full information content, e.g., P- and S-waves, converted waves, guided and interface waves, to image geological discontinuities and/or to reconstruct multi-parameter models. For the full consideration of elastic wave propagation effects the efficient forward simulation in 3-D complex media gains in importance. Full wave field modelling is essential for seismic imaging and inversion but also to invent and verify new seismic reconstruction techniques. Innovative seismic methods sometimes use unconventional elastic wave fields having very specific properties and being the only solution for some exotic applications. Such unconventional elastic wave fields, for example, are exploited for the seismic prediction ahead of tunnels. Tunnel surface-waves that arrive at the front face of the tunnel are converted into body-waves. Reflected body-waves are later back-converted into tunnel surface-waves. Imaging methods based on these wave fields can successfully detect geological discontinuities ahead. The conversion of interface waves and body waves can also be observed in fluid-filled boreholes and can be used for seismic prediction while drilling. Other unconventional waves in an exotic regime are marine Scholte waves that can be excited by airguns. Scholte waves are interface waves propagating along the sea floor and can be used to reconstruct the shear-wave velocity of shallow water marine sediments - an important parameter to characterize the stability of the marine sediments for offshore constructions. The ultimative goal, however, is the consistent consideration of both unconven¬tional waves as well as all other possible elastic wave propagation effects by full waveform inversion (FWI). Over the last several years, computer resources have brought 3D elastic FWI computations within reach. Some early
Confinement-induced p-wave resonances from s-wave interactions
International Nuclear Information System (INIS)
Nishida, Yusuke; Tan, Shina
2010-01-01
We show that a purely s-wave interaction in three dimensions (3D) can induce higher partial-wave resonances in mixed dimensions. We develop two-body scattering theories in all three cases of 0D-3D, 1D-3D, and 2D-3D mixtures and determine the positions of higher partial-wave resonances in terms of the 3D s-wave scattering length assuming a harmonic confinement potential. We also compute the low-energy scattering parameters in the p-wave channel (scattering volume and effective momentum) that are necessary for the low-energy effective theory of the p-wave resonance. We point out that some of the resonances observed in the Florence group experiment [Phys. Rev. Lett. 104, 153202 (2010)] can be interpreted as the p-wave resonances in the 2D-3D mixed dimensions. Our study paves the way for a variety of physics, such as Anderson localization of matter waves under p-wave resonant scatterers.
Energy Technology Data Exchange (ETDEWEB)
Kim, Jung Yul; Hyun, Hye ja; Kim, Yoo Sung [Korea Institute of Geology Mining and Materials, Taejon (Korea, Republic of)
1997-12-01
In petroleum exploration seismic reflection method is by far the most widely used. The resulting seismogram or seismic trace consists of many wavelets with different strengths and arrival times, due to the wavefront that have traveled different source-to receiver paths. In this sense, the seismic trace may be represented as a convolution of a wavelet with an impulse response denoting the various wavelet amplitudes and arrival times present in the trace. However, the wavelet suffers different attenuations while traveling through the earth layers. For example, the weathered layer (near-surface structure : e.g. valley) affect the propagating seismic wave in ways that cannot be simply modeled, but rather described in terms of an overall time delay and significant distortion of the source wavelet as it travels downward. Of course, the weathered layer will also affect the upgoing wave. Thus, the reflection method does not always lead to a desirable resolution in reflection section, because some specific constraints on the illumination of the deeper reflectors can be often imposed by the near-surface effect. Among other things, the mechanism for attenuation in many types of rocks is not very well understood. The present work is then mostly focussed on studying problems of wave propagation especially dealing with the near-surface structure problem by using physical modeling. An attempt was made to compare the measured data in detail with those from numerical method (ray theory). Besides, various kinds of physical models were additionally built to simulate the complex geological structures comprising wavy layer, coal seam structure, absorbing inhomogeneities, gradient layer that are not simply amenable to theory. Hereby, an attention was given on the reflection and transmission responses. The results illustrated in this work will provide a basis for the future oil exploration in Korea and demonstrate the potential of physical modeling as well. (author). 7 refs., 4 tabs., 62
International Nuclear Information System (INIS)
Wasiu, M.
2003-01-01
Interface scattering of seismic wavefield is an important phenomenon which affects the phase and/or amplitude of seismic signal and hence the quality of final seismic image. Irregular interface which causes interface scattering are widespread in nature. Practical examples of such are the interfaces between under-compacted mobile shale and sand, salt body and sand, basalt flows etc. This has been known constitute major imagery problem in the past. The weathered zone is a well known scatterer in land seismic data, and it is known to be highly spatially irregular. To be able to understand this phenomenon better, seismic wavefield scattering from a statistically random rough interface in a multi-layered homogeneous medium is studied in 3-D. The influence of surface roughness on the incident wavefield is analyzed numerically by employing a finite difference operator in the acoustic domain. Since interface scattering in real practical sense is a 3-D phenomenon, we showed that the scattering response of a random rough interface is not the same in 3-D situations as compared with 2-D case as described in most earlier works. For a given interface roughness height in 3-D, it requires an interface of at least about three times higher to produce an equivalent phase scattering effect in 2-D situation. We also showed that the phase scattering is not negligible in 3-D when the scale of the surface roughness to the incident wavefield is 1/1 0 as is generally assumed. Based on observation from spectral analysis of synthetic and real seismic data, we showed that interface scattering principally results in de-phasing and frequency band-limiting of the incident wavefield, the frequency band-limiting properties being comparable to cases reported in the literature for absorption and thin layer filtering. This phenomenon should be critically considered when using amplitude and phase information of seismic signal during inversion process
Integrate urban‐scale seismic hazard analyses with the U.S. National Seismic Hazard Model
Moschetti, Morgan P.; Luco, Nicolas; Frankel, Arthur; Petersen, Mark D.; Aagaard, Brad T.; Baltay, Annemarie S.; Blanpied, Michael; Boyd, Oliver; Briggs, Richard; Gold, Ryan D.; Graves, Robert; Hartzell, Stephen; Rezaeian, Sanaz; Stephenson, William J.; Wald, David J.; Williams, Robert A.; Withers, Kyle
2018-01-01
For more than 20 yrs, damage patterns and instrumental recordings have highlighted the influence of the local 3D geologic structure on earthquake ground motions (e.g., M">M 6.7 Northridge, California, Gao et al., 1996; M">M 6.9 Kobe, Japan, Kawase, 1996; M">M 6.8 Nisqually, Washington, Frankel, Carver, and Williams, 2002). Although this and other local‐scale features are critical to improving seismic hazard forecasts, historically they have not been explicitly incorporated into the U.S. National Seismic Hazard Model (NSHM, national model and maps), primarily because the necessary basin maps and methodologies were not available at the national scale. Instead,...
First-order P-wave ray synthetic seismograms in inhomogeneous, weakly anisotropic, layered media
Czech Academy of Sciences Publication Activity Database
Pšenčík, Ivan; Farra, V.
2014-01-01
Roč. 198, č. 1 (2014), s. 298-307 ISSN 0956-540X R&D Projects: GA ČR(CZ) GAP210/11/0117 Institutional support: RVO:67985530 Keywords : body waves * seismic anisotropy * wave propagation Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.724, year: 2013
Czech Academy of Sciences Publication Activity Database
Farra, V.; Pšenčík, Ivan
2010-01-01
Roč. 183, č. 3 (2010), s. 1443-1454 ISSN 0956-540X R&D Projects: GA ČR GA205/08/0332 Institutional research plan: CEZ:AV0Z30120515 Keywords : body waves * seismic anisotropy * wave propagation Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.411, year: 2010
Receiver function analysis and preliminary body wave tomography of the MACOMO network in Madagascar
Pratt, M. J.; Wysession, M. E.; Wiens, D. A.; Nyblade, A.; Aleqabi, G. I.; Shore, P.; Rambolamana, G.; Sy Tanjona Andriampenomanana ny Ony, F.; Rakotondraibe, T.
2013-12-01
We present results from a set of seismological studies of the continental island of Madagascar using new seismic data from the NSF-funded MACOMO (MAdagascar, COmores, and MOzambique) IRIS PASSCAL broadband seismometer array. MACOMO involved the deployment during 2011-2013 of 26 broadband seismometers in Madagascar and 6 seismometers in Mozambique, providing the first seismic imaging across the world's 4th-largest island. We present preliminary crustal structure variations from receiver function analyses and body wave tomography results. We calculate radial receiver functions for all Madagascar stations and use the weighted linear regression methodology of Herrmann and Ammon [2002] to invert for shear velocity. Upper mantle and crustal structures from the receiver function analyses are used to help determine starting models for the teleseismic travel-time tomography. The tectonic structure of Madagascar is generally divided into four crustal blocks. Initial seismic imaging shows that the Archean Antongil block that runs along the east of the island has the thickest crust (>40 km) and three Proterozoic terranes that make up the central highlands and are bounded by fault and shear zones are closer to the average crustal thickness (35 km). There has been late Cenozoic intraplate volcanism in northern and central Madagascar (as recently as 1 million years ago), and different hypotheses for its origin will be evaluated by the preliminary results from the three different seismic studies. Complete analyses will be done incorporating seismic data from simultaneous and complementary array of both land- and ocean-based seismometers from French and German deployments.
Seismic observations at the Sodankylä Geophysical Observatory: history, present, and the future
Kozlovskaya, Elena; Narkilahti, Janne; Nevalainen, Jouni; Hurskainen, Riitta; Silvennoinen, Hanna
2016-08-01
Instrumental seismic observations in northern Finland started in the 1950s. They were originally initiated by the Institute of Seismology of the University of Helsinki (ISUH), but the staff of Sodankylä Geophysical Observatory (SGO) and later geophysicists of the University of Oulu (UO) were involved in the development of seismological observations and research in northern Finland from the very beginning. This close cooperation between seismologists and the technical staff of ISUH, UO, and SGO continued in many significant international projects and enabled a high level of seismological research in Finland. In our paper, we present history and current status of seismic observations and seismological research in northern Finland at the UO and SGO. These include both seismic observations at permanent seismic stations and temporary seismic experiments with portable seismic equipment. We describe the present seismic instrumentation and major research topics of the seismic group at SGO and discuss plans for future development of permanent seismological observations and portable seismic instrumentation at SGO as part of the European Plate Observing System (EPOS) research infrastructure. We also present the research topics of the recently organized Laboratory of Applied Seismology, and show examples of seismic observations performed by new seismic equipment located at this laboratory and selected results of time-lapse seismic body wave travel-time tomography using the data of microseismic monitoring in the Pyhäsalmi Mine (northern Finland).
Monitoring southwest Greenland’s ice sheet melt with ambient seismic noise
Mordret, Aurélien; Mikesell, T. Dylan; Harig, Christopher; Lipovsky, Bradley P.; Prieto, Germán A.
2016-01-01
The Greenland ice sheet presently accounts for ~70% of global ice sheet mass loss. Because this mass loss is associated with sea-level rise at a rate of 0.7 mm/year, the development of improved monitoring techniques to observe ongoing changes in ice sheet mass balance is of paramount concern. Spaceborne mass balance techniques are commonly used; however, they are inadequate for many purposes because of their low spatial and/or temporal resolution. We demonstrate that small variations in seismic wave speed in Earth’s crust, as measured with the correlation of seismic noise, may be used to infer seasonal ice sheet mass balance. Seasonal loading and unloading of glacial mass induces strain in the crust, and these strains then result in seismic velocity changes due to poroelastic processes. Our method provides a new and independent way of monitoring (in near real time) ice sheet mass balance, yielding new constraints on ice sheet evolution and its contribution to global sea-level changes. An increased number of seismic stations in the vicinity of ice sheets will enhance our ability to create detailed space-time records of ice mass variations. PMID:27386524
Self-Assembling Sup-porosity: The Effect On Fluid Flow And Seismic Wave Propagation
Energy Technology Data Exchange (ETDEWEB)
Pyrak-Nolte, Laura J. [Purdue University
2013-04-27
Fractures and joints in the field often contain debris within the void spaces. Debris originates from many different mechanisms: organic and/or inorganic chemical reactions/mineralization, sediment transport, formation of a fracture, mechanical weathering or combinations of these processes. In many cases, the presence of debris forms a sub-porosity within the fracture void space. This sub-porosity often is composed of material that differs from the fracture walls in mineralogy and morphology. The sub-porosity may partially fill voids that are on the order of hundreds of microns and thereby reduce the local porosity to lengths scales on the order of sub-microns to tens of microns. It is quite clear that a sub-porosity affects fracture porosity, permeability and storativity. What is not known is how the existence/formation of a sub-porosity affects seismic wave propagation and consequently our ability to probe changes in the subsurface caused by the formation or alteration of a sub-porosity. If seismic techniques are to be developed to monitor the injection and containment of phases in sequestration reservoirs or the propping of hydraulically induced fracture to enhance oil & gas production, it is important to understand how a sub-porosity within a fracture affects macroscopic seismic and hydraulic measurements. A sub-porosity will directly affect the interrelationship between the seismic and hydraulic properties of a fracture. This reports contains the results of the three main topics of research that were performed (1) to determine the effect of a sub-porosity composed of spherical grains on seismic wave propagation across fractures, (2) to determine the effect of biofilm growth in pores and between grains on seismic wave propagation in sediment, and (3) to determine the effect of the scale of observation (field-of-view) on monitoring alteration the pore space within a fracture caused by reactive flow. A brief summary of the results for each topic is contained in
Shear-wave velocity of marine sediments offshore Taiwan using ambient seismic noise
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
Bouchaala, Fateh; Y Ali, Mohammed; Matsushima, Jun
2017-04-01
Many methods for quantitative interpretation of seismic data are based on the analysis of amplitudes of seismic waves. Seismic attenuation along the ray path of wave significantly affects this amplitude information. As such, understanding of this phenomenon has a huge impact for seismic studies. The main sources of seismic attenuation are scattering and intrinsic attenuation. The former is an elastic phenomenon where the energy undergoes new redistribution due to subsurface heterogeneities, however the total energy of the wavefield is conserved [Wu 1982]. The intrinsic attenuation is an anelastic phenomenon where the energy is converted to heat due to fluid-solid friction [eg. Müller et al. 2010]. Therefore, seismic attenuation can potentially improve geophysical interpretation in saturated media, such as reservoir zones. Nevertheless, accurate estimation and separation between scattering and intrinsic attenuation is challenging due to misunderstanding of their mechanism and their high sensitivity to data noise. The sum of scattering and intrinsic attenuation is called total attenuation [Schoenberger and Levin 1974]. This latter is usually estimated from field data by using widely used methods in the frequency domain such as, spectral ratio [Bath, 1974] and Modified Median Frequency Shift (MMFS) [Frazer et al. 1997]. The scattering is usually estimated by applying the same methods on synthetic data generated by using Goupillaud model [Goupillaud, 1961]. Then, the intrinsic attenuation is estimated by subtracting the scattering from the total attenuation. In this study we combine new signal processing flow and a novel method to estimate scattering and intrinsic attenuation separately. The signal processing flow is based on common midpoint (CMP) approach which increases the signal to noise ratio (SNR) of data. The novel method is a further improvement of MMFS method [Matsushima et al. 2016]. Numerical study showed that the proposed method provides better depth
Kayen, R.; Moss, R.E.S.; Thompson, E.M.; Seed, R.B.; Cetin, K.O.; Der Kiureghian, A.; Tanaka, Y.; Tokimatsu, K.
2013-01-01
Shear-wave velocity (Vs) offers a means to determine the seismic resistance of soil to liquefaction by a fundamental soil property. This paper presents the results of an 11-year international project to gather new Vs site data and develop probabilistic correlations for seismic soil liquefaction occurrence. Toward that objective, shear-wave velocity test sites were identified, and measurements made for 301 new liquefaction field case histories in China, Japan, Taiwan, Greece, and the United States over a decade. The majority of these new case histories reoccupy those previously investigated by penetration testing. These new data are combined with previously published case histories to build a global catalog of 422 case histories of Vs liquefaction performance. Bayesian regression and structural reliability methods facilitate a probabilistic treatment of the Vs catalog for performance-based engineering applications. Where possible, uncertainties of the variables comprising both the seismic demand and the soil capacity were estimated and included in the analysis, resulting in greatly reduced overall model uncertainty relative to previous studies. The presented data set and probabilistic analysis also help resolve the ancillary issues of adjustment for soil fines content and magnitude scaling factors.
Surface and body waves from surface and underground explosions
International Nuclear Information System (INIS)
Kusubov, A.S.
1976-06-01
The characteristics of surface and ground waves were recorded for surface and underground explosions up to 100 tons and 40 kt in magnitude, respectively, and a preliminary analysis of these results is presented. The experiments were conducted at NTS in the Yucca Flats, Nevada. Ground motions were detected with triaxial geophones along seismic lines extending up to 16 miles from the point of explosions. A comparison of Rayleigh waves generated by surface and underground explosions in the same lake bed is presented indicating a very different behavior of surface and ground waves from the two types of explosions. The magnitude of the transverse wave for surface shots was smaller by a factor of two than its longitudinal counterpart. The dependence of apparent periods on the blast energy was not apparent at a fixed distance from the explosions. Changes in the apparent period with distance for both types of explosion are compared indicating a strong layering effect of the lake bed. The ground motion study was complimented by excavation of cavities generated by the explosions
International Nuclear Information System (INIS)
Zeuch, W.R.; Wang, C.Y.
1985-01-01
This paper presents some of the current capabilities of the three-dimensional piping code SHAPS and demonstrates their usefulness in handling analyses encountered in typical LMFBR studies. Several examples demonstrate the utility of the SHAPS code for problems involving fluid-structure interactions and seismic-related events occurring in three-dimensional piping networks. Results of two studies of pressure wave propagation demonstrate the dynamic coupling of pipes and elbows producing global motion and rigorous treatment of physical quantities such as changes in density, pressure, and strain energy. Results of the seismic analysis demonstrate the capability of SHAPS to handle dynamic structural response within a piping network over an extended transient period of several seconds. Variation in dominant stress frequencies and global translational frequencies were easily handled with the code. 4 refs., 10 figs
Modeling seismic wave propagation using staggered-grid mimetic finite differences
Directory of Open Access Journals (Sweden)
Freysimar Solano-Feo
2017-04-01
Full Text Available Mimetic finite difference (MFD approximations of continuous gradient and divergence operators satisfy a discrete version of the Gauss-Divergence theorem on staggered grids. On the mimetic approximation of this integral conservation principle, an unique boundary flux operator is introduced that also intervenes on the discretization of a given boundary value problem (BVP. In this work, we present a second-order MFD scheme for seismic wave propagation on staggered grids that discretized free surface and absorbing boundary conditions (ABC with same accuracy order. This scheme is time explicit after coupling a central three-level finite difference (FD stencil for numerical integration. Here, we briefly discuss the convergence properties of this scheme and show its higher accuracy on a challenging test when compared to a traditional FD method. Preliminary applications to 2-D seismic scenarios are also presented and show the potential of the mimetic finite difference method.
Riding the waves : the role of the body wave in undulatory fish swimming
Muller, UK; Stamhuis, EJ; Videler, JJ
2002-01-01
A continuously swimming mullet modulates its thrust production by changing slip-the ratio between its swimming speed U and the speed V with which the body wave travels down its body. This variation in thrust is reflected in the wake of the fish. We obtained 2-dimensional impressions of the wake
Numerical simulation of floating bodies in extreme free surface waves
Directory of Open Access Journals (Sweden)
Z. Z. Hu
2011-02-01
Full Text Available In this paper, we use the in-house Computational Fluid Dynamics (CFD flow code AMAZON-SC as a numerical wave tank (NWT to study wave loading on a wave energy converter (WEC device in heave motion. This is a surface-capturing method for two fluid flows that treats the free surface as contact surface in the density field that is captured automatically without special provision. A time-accurate artificial compressibility method and high resolution Godunov-type scheme are employed in both fluid regions (air/water. The Cartesian cut cell method can provide a boundary-fitted mesh for a complex geometry with no requirement to re-mesh globally or even locally for moving geometry, requiring only changes to cut cell data at the body contour. Extreme wave boundary conditions are prescribed in an empty NWT and compared with physical experiments prior to calculations of extreme waves acting on a floating Bobber-type device. The validation work also includes the wave force on a fixed cylinder compared with theoretical and experimental data under regular waves. Results include free surface elevations, vertical displacement of the float, induced vertical velocity and heave force for a typical Bobber geometry with a hemispherical base under extreme wave conditions.
Detailed study of seismic wave attenuation from four oilfields in Abu Dhabi, United Arab Emirates
Bouchaala, F.; Ali, M. Y.; Matsushima, J.
2018-02-01
In the present study, we provide a detailed study of seismic wave attenuation obtained from four oilfields. The reservoir zones of these oilfields are complicated due to complex fracture networks, the presence of tar mat and high heterogeneity of carbonate rocks of which the subsurface of Abu Dhabi is mainly composed. These complexities decrease signal-to-noise ratio and make attenuation estimation difficult. We obtained high-resolution attenuation profiles from vertical seismic profiling (VSP) and sonic waveform data. The VSP data were recorded in all four oilfields and the sonic data were acquired in the reservoir zones of oilfields I and IV. We found that the VSP scattering attenuation ({Q}{{S}{{c}}{{a}}{{t}}}-1) varies from -0.080 to 0.180 over a depth range of 400-3500 m. We attributed this significant scattering to the high heterogeneity of carbonate rocks. The scattering profiles seem to be sensitive to fractures, lithology heterogeneity and tar mat, but their effect is superimposed. The VSP intrinsic attenuation varies from -0.15 to 0.246 with high variation within each formation. Since intrinsic attenuation is closely related to fluids, we assumed that this variation is due to the non-uniform distribution of fluids caused by the complex porosity network of the subsurface. The sonic monopole attenuation ({Q}{{M}{{f}}}-1) in the reservoir zones ranges between 0.033-0.094 and dipole inline attenuation ({Q}{{I}{{n}}{{l}}}-1) ranges from 0.040-0.138. The sonic attenuation appears to be sensitive to the presence of fluid and type of fractures, where it shows high attenuation for open fractures and low attenuation for resistive fractures. The zones with high clay content display high sonic intrinsic attenuation in the reservoir of oilfield II. We explain this by the frictional movement between the clay and carbonates due to the elasticity contrast of these two materials. Therefore, the solid grain friction may be the dominant attenuation mechanism in those zones.
Shear-wave seismic reflection imaging and impedance inversion for a near-surface point-bar
Benton, N. W.; Morrison, M.; Lorenzo, J. M.; Odom, B.; Clift, P. D.; Olson, E.; Gostic, A.
2017-12-01
Imaging and inversion of SH-waves are useful to detect, map, and quantitatively characterize near-surface point-bar strata. We conduct a horizontally-polarized (SH) reflection survey across and along a near-surface (9 - 40 m) downstream point-bar. We invert for shear-impedance profiles and correlate our interpretation to electrical conductivity (EC) logs in adjacent wells to study the internal architecture and lithology of point-bars. We acquire two common-midpoint (CMP) SH-wave seismic reflection lines at False River (Point Coupee Parish, Louisiana). A 104 m long seismic line (L1) is oriented orthogonal (NW - SE) to point-bar strike. A second line (L2) is 48 m long and set parallel to point-bar strike (NE - SW). Two EC wells lie 33 m apart. Both wells are parallel with respect to the L1 survey and offset from it by 15 m. EC log measurements range from 1 - 25 m depth. Interference of Love-waves prevents seismic imaging at depths less than 9 m. The L1 and L2 data sets are inverted for shear-impedance using a model-based band-limited impedance (BLIMP) algorithm that incorporates a low-frequency velocity model. This model is also used for the depthing processing. The L1 cross-section shows coherent dipping reflection events ( 4 - 7º) from 0.15 - 0.35 s (10 - 40 m). The corresponding shear-impedance profile also reveals coherent and dipping impedance contrasts that grow in magnitude with increasing depth. The L2 cross-section shows comparatively less dip ( 1º) as well as sharper and shallower continuity of reflection events (0.1 - 0.28 s TWT or 9 - 25 m). Depth-converted (TVD) seismic amplitudes and impedance values correlate to near-surface point-bar geology via superposition of log data. The first well (W5) shows distinct EC local maxima (+50 - 70 mS/m) at 14.5 and 15.5 m depth that correlate well with the seismic amplitudes and impedance values from both L1 and L2 data sets. The second well (W7) shows comparatively lower local maxima (+40 - 60 mS/m) but at greater
Köhler, Andreas; Weidle, Christian; Maupin, Valérie
2012-12-01
We use ambient seismic noise and earthquake recordings on a temporary regional network in southern Norway to produce Rayleigh and Love wave phase velocity maps from 3 to 67 s period. Local dispersion curves are then jointly inverted for a 3-D shear wave velocity model of the region. We perform a two-step inversion approach. First, a direct search, Monte Carlo algorithm is applied to find best fitting isotropic velocity depth profiles. Those profiles are then used as initial models for a linearised inversion which takes into account radial anisotropy in the shear wave structure. Results reveal crustal as well as uppermost mantle structures in the studied region. Velocity anomalies in the upper crust are rather small in amplitude and can in most parts be related to surface geology in terms of rock densities. Old tectonic units like the Oslo Graben (300-240 Ma) and the Caledonian nappes (440-410 Ma) are clearly imaged. Furthermore, we find clear indications for localized crustal anisotropy of about 3 per cent. Despite generally poor resolution of interface depths in surface wave inversion, we find lateral variation of crustal thickness in agreement with previous studies. We are able to confirm and locate the transition from a slow lithospheric upper mantle underneath southern Norway to a fast shield-like mantle towards Sweden.
Determination of the upper crustal structure using seismic waves from quarry blasts
Broz, M.; Brokesova, J.; Malek, J.; Novotny, O.; Strunc, J.; Zanda, L.
2003-04-01
The territory of the Czech Republic is covered with a relatively dense network of quarries using blasting for rock disintegration. Blasts of large extent (more then 200 kg of explosive) take place mainly in coal open-pit mines, limestone quarries and basalt quarries. Seismic waves generated by industrial blasts are recorded by sensitive stations up to the distance of 200 km. Seismograms up to 120 km contain a clear Pg onset and in some cases Sg onset can also be recognized. A typical feature at these epicentral distances is the presence of very intensive surface waves, which frequently forms the dominant phase on the seismogram. In the recent years we started project, which aims to use seismograms generated by quarry blasts for developing of 3-D model of Bohemian Massif and for study of anisotropy in this region. An accurate determination of the origin time was one of the problems. This problem has been solved by developing of special seismograph BUMPRECORDER, for recording seismic waves very close to the blast (tens of meters).
WAVE EQUATION DATUMING TO CORRECT TOPOGRAPHY EFFECT ON FOOTHILL SEISMIC DATA
Directory of Open Access Journals (Sweden)
Montes Vides Luis Alfredo
2005-08-01
Full Text Available The current seismic processing applies Static Corrections to overcome the effects associated to rough topography, based in the assumption that velocity in near surface is lower than in the substratum, which force going up rays travel near to vertical. However, when the velocity contrast between these layers is not large enough, the trajectory of the up going rays deviate from vertical raveling the reflectors erroneously. A better alternative to correct this is to continue the wave field to a datum, because it does not assume vertical ray trajectory and solves the acoustic wave equation to extrapolate sources and receivers. The Kirchhoff approach was tested in synthetic shots continuing their wave field to a datum and finally it was applied instead of Static Corrections in real data acquired in foothill zones. First shot and receiver gathers were downward continued to the base of weathering layer and later upward continued to a final flat datum. Comparing the obtained results we observed that continuation approach provides a noticeable enhancement of reflectors in seismic records, displaying a better continuity of the reflectors and an increment in frequency content.
Louie, J. N.; Basler-Reeder, K.; Kent, G. M.; Pullammanappallil, S. K.
2015-12-01
Simultaneous joint seismic-gravity optimization improves P-wave velocity models in areas with sharp lateral velocity contrasts. Optimization is achieved using simulated annealing, a metaheuristic global optimization algorithm that does not require an accurate initial model. Balancing the seismic-gravity objective function is accomplished by a novel approach based on analysis of Pareto charts. Gravity modeling uses a newly developed convolution algorithm, while seismic modeling utilizes the highly efficient Vidale eikonal equation traveltime generation technique. Synthetic tests show that joint optimization improves velocity model accuracy and provides velocity control below the deepest headwave raypath. Detailed first arrival picking followed by trial velocity modeling remediates inconsistent data. We use a set of highly refined first arrival picks to compare results of a convergent joint seismic-gravity optimization to the Plotrefa™ and SeisOpt® Pro™ velocity modeling packages. Plotrefa™ uses a nonlinear least squares approach that is initial model dependent and produces shallow velocity artifacts. SeisOpt® Pro™ utilizes the simulated annealing algorithm and is limited to depths above the deepest raypath. Joint optimization increases the depth of constrained velocities, improving reflector coherency at depth. Kirchoff prestack depth migrations reveal that joint optimization ameliorates shallow velocity artifacts caused by limitations in refraction ray coverage. Seismic and gravity data from the San Emidio Geothermal field of the northwest Basin and Range province demonstrate that joint optimization changes interpretation outcomes. The prior shallow-valley interpretation gives way to a deep valley model, while shallow antiformal reflectors that could have been interpreted as antiformal folds are flattened. Furthermore, joint optimization provides a clearer image of the rangefront fault. This technique can readily be applied to existing datasets and could
New seismic events identified in the Apollo lunar data by application of a Hidden Markov Model
Knapmeyer-Endrun, B.; Hammer, C.
2015-10-01
The Apollo astronauts installed seismic stations on the Moon during Apollo missions 11, 12, 14, 15 and 16. The stations consisted of a three-component long- period seismometer (eigenperiod 15 s) and a vertical short-period sensor (eigenperiod 1 s). Until today, the Apollo seismic network provides the only confirmed recordings of seismic events from any extrater-restrial. The recorded event waveforms differ significantly from what had been expected based on Earth data, mainly by their long duration body wave codas caused by strong near-surface scattering and weak attenuation due to lack of fluids. The main lunar event types are deep moonquakes, impacts, and the rare shallow moonquakes.
Maeda, Takuto; Takemura, Shunsuke; Furumura, Takashi
2017-07-01
We have developed an open-source software package, Open-source Seismic Wave Propagation Code (OpenSWPC), for parallel numerical simulations of seismic wave propagation in 3D and 2D (P-SV and SH) viscoelastic media based on the finite difference method in local-to-regional scales. This code is equipped with a frequency-independent attenuation model based on the generalized Zener body and an efficient perfectly matched layer for absorbing boundary condition. A hybrid-style programming using OpenMP and the Message Passing Interface (MPI) is adopted for efficient parallel computation. OpenSWPC has wide applicability for seismological studies and great portability to allowing excellent performance from PC clusters to supercomputers. Without modifying the code, users can conduct seismic wave propagation simulations using their own velocity structure models and the necessary source representations by specifying them in an input parameter file. The code has various modes for different types of velocity structure model input and different source representations such as single force, moment tensor and plane-wave incidence, which can easily be selected via the input parameters. Widely used binary data formats, the Network Common Data Form (NetCDF) and the Seismic Analysis Code (SAC) are adopted for the input of the heterogeneous structure model and the outputs of the simulation results, so users can easily handle the input/output datasets. All codes are written in Fortran 2003 and are available with detailed documents in a public repository.[Figure not available: see fulltext.
Seismic attenuation in the African LLSVP estimated from PcS phases
Liu, Chujie; Grand, Stephen P.
2018-05-01
Seismic tomography models have revealed two broad regions in the lowermost mantle marked by ∼3% slower shear velocity than normal beneath the south central Pacific and southern Africa. These two regions are known as large-low-shear-velocity provinces (LLSVP). There is debate over whether the LLSVPs can be explained by purely thermal variations or whether they must be chemically distinct from normal mantle. Elastic properties alone, have been unable to distinguish the thermal from chemical interpretations. Anelastic structure, however, can help discriminate among models of the LLSVPs since intrinsic attenuation is more sensitive to temperature than to chemical variations. Here we estimate Qμ (the shear wave quality factor) in the African LLSVP using PcS waves generated from a Scotia Arc earthquake, recorded by broadband seismometers deployed in Southern Africa during the Kaapvaal experiment. The upward leg of the PcS waves sweeps from normal mantle into the African LLSVP across the array. We use the spectral ratio (SR) and instantaneous frequency matching (IFM) techniques to measure the differential attenuation (Δt*) between waves sampling the African LLSVP and the waves that sample normal lower mantle. Using both methods for estimating Δt* we find that PcS waves sampling the LLSVP are more attenuated than the waves that miss the LLSVP yielding a Δt* difference of more than 1 s. Using the Δt* measurements we estimate the average Qμ in the LLSVP to be about 110. Using a range of activation enthalpy (H*) estimates, we find an average temperature anomaly within the LLSVP ranging from +250 to +800 K. Our estimated temperature anomaly range overlaps previous isochemical geodynamic studies that explain the LLSVP as a purely thermal structure although the large uncertainties cannot rule out chemical variations as well.
S-wave velocity structures of the Taipei Basin, Taiwan, using microtremor array measurements
Huang, Huey-Chu; Wu, Cheng-Feng; Lee, Feng-Mei; Hwang, Ruey-Der
2015-04-01
The S-wave velocity structures of the Taipei Basin in Taiwan are investigated using the array records of microtremors at 15 sites. Dispersion curves at these sites are calculated using the frequency-wavenumber (F-K) spectrum method. The S-wave velocity structures in the Taipei Basin are then estimated by employing surface wave inversion technique. Harder strata sites have higher phase velocities than softer sites. If the S-wave velocity of the Tertiary Basement is assumed to be 1000 m/s, then the Quaternary alluvial thicknesses in the Taipei Basin are between about 100 m and 650 m. The thickness of the alluvium gradually increases from the southeast to the northwest. The inversion results are also in good agreement with well-logging data and seismic reflection studies of the Taipei Basin. The study concludes that microtremor array measurement is a useful tool for estimating S-wave velocity structure.
Wave-free floating body forms for a shallow sea area; Senkaiiki no naminashi futai keijo ni tsuite
Energy Technology Data Exchange (ETDEWEB)
Kyozuka, Y.; Nariai, Y. [Kyushu University, Fukuoka (Japan)
1997-10-01
In column footing or semi-submergible type marine structures, a vertical wave force vanishes at a specific period of waves. This phenomenon is called wave-free characteristics. This wave-free characteristics make it possible to design marine structures superior in oscillation performance in waves. Since Bessho`s wave-free theory is useful only for an infinite water depth, this paper studied the wave-free theory for a shallow sea area. On a wave-free singularity and required floating body form, 2-D and 3-D axisymmetric floating body forms were determined, and vertical wave force characteristics of the obtained body forms were calculated and verified experimentally. Since the source term of the wave-free singularity was weaker in a shallow sea area than an infinite deep water area, resulting in the narrow width of the obtained wave-free body forms in a shallow sea area. The wave-free theory for a shallow sea area was verified by both numerical calculation based on a singularity distribution method and model experiment for these floating body forms. 3 refs., 10 figs.
Seismic verification of underground explosions
International Nuclear Information System (INIS)
Glenn, L.A.
1986-01-01
The principal tools for monitoring compliance with a comprehensive test ban treaty (CTBT), prohibiting all testing of nuclear weapons, are seismic networks and surveillance satellites. On-site inspections might also be required to resolve ambiguous events. The critical element of the monitoring system is the network of seismic stations, and in particular the in-country station. Internal stations provide much more useful data than do stations outside the borders of testing nations. For large events that are not eliminated by depth or location, one of the most useful discriminants is based on the ratio of surface-wave to body-wave magnitudes (M /sub s/ :m /sub b/ ). If an explosion and an earthquake have the same body-wave magnitude, the surface-wave magnitude for the earthquake is generally larger. It has yet to be proven that M /sub s/ :m /sub b/ is useful at low magnitudes, expecially when explosions are set off in long tunnels or odd-shaped cavities. A number of other promising regional discriminants have been suggested. Evasion opportunities and cavity decoupling are discussed
Wave Dynamic Analysis of the Seismic Response of a Reinforced Concrete Building
International Nuclear Information System (INIS)
Astroza, Rodrigo; Saragoni, G. Rodolfo
2008-01-01
This paper evaluates the response of the seven-story instrumented building, Holiday Inn Hotel, during the 1994 Northridge earthquake through the wave propagation dynamic analysis. The building has been instrumented during other earthquakes, the most important of these was the 1971 San Fernando earthquake, where the building was located only 22 [km] from the epicenter and didn't showing structural damage. From the accelerograms analysis is detected the propagation of Rayleigh and soil waves in the building, where the first has a polarized particle motion on a vertical plane and the second has a coupled particle motion in the horizontal plane. Both waves impose their frequencies to the building response, whose fundamental frequency (1.4 [Hz] according to ambient vibration test) is less than the frequencies of the identified waves. Due to the impact that these observations have in the seismic design of buildings, as a first attempt, a simple method is proposed to estimate the drift produced by the propagation of a Rayleigh wave in buildings
Moon meteoritic seismic hum: Steady state prediction
Lognonne, P.; Feuvre, M.L.; Johnson, C.L.; Weber, R.C.
2009-01-01
We use three different statistical models describing the frequency of meteoroid impacts on Earth to estimate the seismic background noise due to impacts on the lunar surface. Because of diffraction, seismic events on the Moon are typically characterized by long codas, lasting 1 h or more. We find that the small but frequent impacts generate seismic signals whose codas overlap in time, resulting in a permanent seismic noise that we term the "lunar hum" by analogy with the Earth's continuous seismic background seismic hum. We find that the Apollo era impact detection rates and amplitudes are well explained by a model that parameterizes (1) the net seismic impulse due to the impactor and resulting ejecta and (2) the effects of diffraction and attenuation. The formulation permits the calculation of a composite waveform at any point on the Moon due to simulated impacts at any epicentral distance. The root-mean-square amplitude of this waveform yields a background noise level that is about 100 times lower than the resolution of the Apollo long-period seismometers. At 2 s periods, this noise level is more than 1000 times lower than the low noise model prediction for Earth's microseismic noise. Sufficiently sensitive seismometers will allow the future detection of several impacts per day at body wave frequencies. Copyright 2009 by the American Geophysical Union.
Feng, Lei; Zhang, Yugui
2017-08-01
Dispersion analysis is an important part of in-seam seismic data processing, and the calculation accuracy of the dispersion curve directly influences pickup errors of channel wave travel time. To extract an accurate channel wave dispersion curve from in-seam seismic two-component signals, we proposed a time-frequency analysis method based on single-trace signal processing; in addition, we formulated a dispersion calculation equation, based on S-transform, with a freely adjusted filter window width. To unify the azimuth of seismic wave propagation received by a two-component geophone, the original in-seam seismic data undergoes coordinate rotation. The rotation angle can be calculated based on P-wave characteristics, with high energy in the wave propagation direction and weak energy in the vertical direction. With this angle acquisition, a two-component signal can be converted to horizontal and vertical directions. Because Love channel waves have a particle vibration track perpendicular to the wave propagation direction, the signal in the horizontal and vertical directions is mainly Love channel waves. More accurate dispersion characters of Love channel waves can be extracted after the coordinate rotation of two-component signals.
Hirakawa, E. T.; Ezzedine, S. M.
2017-12-01
Recorded motions from underground chemical explosions are complicated by long duration seismic coda as well as motion in the tangential direction. The inability to distinguish the origins of these complexities as either source or path effects comprises a limitation to effective monitoring of underground chemical explosions. With numerical models, it is possible to conduct rigorous sensitivity analyses for chemical explosive sources and their resulting ground motions under the influence of many attributes, including but not limited to complex velocity structure, topography, and non-linear source characteristics. Previously we found that topography can cause significant scattering in the direct wave but leads to relatively little motion in the coda. Here, we aim to investigate the contribution from the low-velocity weathered layer that exists in the shallow subsurface apart from and in combination with surface topography. We use SW4, an anelastic anisotropic fourth order finite difference code to simulate chemical explosive source in a 1D velocity structure consisting of a single weathered layer over a half space. A range of velocity magnitudes are used for the upper weathered layer with the velocities always being lower than that of the granitic underlaying layer. We find that for lower weathered layer velocities, the wave train is highly dispersed and causes a large percentage of energy to be contained in the coda in relation to the entire time series. The percentage of energy contained in the coda grows with distance from the source but saturates at a certain distance that depends on weathered layer velocity and thickness. The saturation onset distance increases with decreasing layer thickness and increasing velocity of the upper layer. Measurements of relative coda energy and coda saturation onset distance from real recordings can provide an additional constraint on the properties of the weathered layer in remote sites as well as test sites like the Nevada
Directory of Open Access Journals (Sweden)
Masaki Kanao
2012-01-01
Full Text Available Several kinds of natural source signals are recorded by seismic exploration stations on the continental ice sheet in Eastern Dronning Maud Land, East Antarctica, during 2002 austral summer. They include not only tectonic earthquakes, but also ice-related phenomena possibly involving recent global climate change. The recorded signals are classified into (1 teleseismic events, (2 local ice quakes, and (3 unidentified events (X-phases. The teleseismic waves show the high signal-to-noise ratio in spite of the small magnitude of the event; this indicates that it is highly feasible to study not only the local shallow structure but also the deep structure of the earth by using teleseismic events. Frequency spectra of the all waveforms represent discordances along the observation seismic profile. The abrupt change of topography in the valley along the seismic profile might cause both the anomalous frequency content and travel times. Finally, an origin of the X-phases is speculated as the intraplate earthquakes or possibly large ice-quakes (glacial earthquakes around Antarctica, involving global warming appeared in polar region.
Cao, Yi; Jung, Haemyeong; Song, Shuguang
2018-01-01
Though extensively studied, the roles of olivine crystal preferred orientations (CPOs or fabrics) in affecting the seismic anisotropies in the Earth's upper mantle are rather complicated and still not fully known. In this study, we attempted to address this issue by analyzing the seismic anisotropies [e.g., P-wave anisotropy (AVp), S-wave polarization anisotropy (AVs), radial anisotropy (ξ), and Rayleigh wave anisotropy (G)] of the Songshugou peridotites (dunite dominated) in the Qinling orogen in central China, based on our previously reported olivine CPOs. The seismic anisotropy patterns of olivine aggregates in our studied samples are well consistent with the prediction for their olivine CPO types; and the magnitude of seismic anisotropies shows a striking positive correlation with equilibrium pressure and temperature (P-T) conditions. Significant reductions of seismic anisotropies (AVp, max. AVs, and G) are observed in porphyroclastic dunite compared to coarse- and fine-grained dunites, as the results of olivine CPO transition (from A-/D-type in coarse-grained dunite, through AG-type-like in porphyroclastic dunite, to B-type-like in fine-grained dunite) and strength variation (weakening: A-/D-type → AG-type-like; strengthening: AG-type-like → B-type-like) during dynamic recrystallization. The transition of olivine CPOs from A-/D-type to B-/AG-type-like in the forearc mantle may weaken the seismic anisotropies and deviate the fast velocity direction and the fast S-wave polarization direction from trench-perpendicular to trench-oblique direction with the cooling and aging of forearc mantle. Depending on the size and distribution of the peridotite body such as the Songshugou peridotites, B- and AG-type-like olivine CPOs can be an additional (despite minor) local contributor to the orogen-parallel fast velocity direction and fast shear-wave polarization direction in the orogenic crust such as in the Songshugou area in Qinling orogen.
A 3D Numerical Survey of Seismic Waves Inside and Around an Underground Cavity
Esterhazy, S.; Schneider, F. M.; Perugia, I.; Bokelmann, G.
2016-12-01
Motivated by the need to detect an underground cavity within the procedure of an On-Site-Inspection (OSI) of the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO), which might be caused by a nuclear explo- sion/weapon testing, we present our findings of a numerical study on the elastic wave propagation inside and around such an underground cavity.The aim of the CTBTO is to ban all nuclear explosions of any size anywhere, by anyone. Therefore, it is essential to build a powerful strategy to efficiently investigate and detect critical signatures such as gas filled cavities, rubble zones and fracture networks below the surface. One method to investigate the geophysical properties of an under- ground cavity allowed by the Comprehensive Nuclear-test Ban Treaty is referred to as "resonance seismometry" - a resonance method that uses passive or active seismic techniques, relying on seismic cavity vibrations. This method is in fact not yet entirely determined by the Treaty and there are also only few experimental examples that have been suitably documented to build a proper scientific groundwork. This motivates to investigate this problem on a purely numerical level and to simulate these events based on recent advances in the mathematical understanding of the underlying physical phenomena.Our numerical study includes the full elastic wave field in three dimensions. We consider the effects from an in- coming plane wave as well as point source located in the surrounding of the cavity at the surface. While the former can be considered as passive source like a tele-seismic earthquake, the latter represents a man-made explosion or a viborseis as used for/in active seismic techniques. For our simulations in 3D we use the discontinuous Galerkin Spectral Element Code SPEED developed by MOX (The Laboratory for Modeling and Scientific Computing, Department of Mathematics) and DICA (Department of Civil and Environmental Engineering) at the Politecnico di Milano. The
Three-dimensional seismic velocity model of theWest Bohemia/Vogtland seismoactive region
Czech Academy of Sciences Publication Activity Database
Růžek, Bohuslav; Horálek, Josef
2013-01-01
Roč. 195, č. 2 (2013), s. 1251-1266 ISSN 0956-540X R&D Projects: GA ČR GAP210/12/2336; GA MŠk LM2010008 Institutional support: RVO:67985530 Keywords : controlled source seismology * body waves * seismic tomography * crustal structure Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.724, year: 2013
TIDAL DISSIPATION COMPARED TO SEISMIC DISSIPATION: IN SMALL BODIES, EARTHS, AND SUPER-EARTHS
International Nuclear Information System (INIS)
Efroimsky, Michael
2012-01-01
While the seismic quality factor and phase lag are defined solely by the bulk properties of the mantle, their tidal counterparts are determined by both the bulk properties and the size effect (self-gravitation of a body as a whole). For a qualitative estimate, we model the body with a homogeneous sphere, and express the tidal phase lag through the lag in a sample of material. Although simplistic, our model is sufficient to understand that the lags are not identical. The difference emerges because self-gravitation pulls the tidal bulge down. At low frequencies, this reduces strain and the damping rate, making tidal damping less efficient in larger objects. At higher frequencies, competition between self-gravitation and rheology becomes more complex, though for sufficiently large super-Earths the same rule applies: the larger the planet, the weaker the tidal dissipation in it. Being negligible for small terrestrial planets and moons, the difference between the seismic and tidal lagging (and likewise between the seismic and tidal damping) becomes very considerable for large exoplanets (super-Earths). In those, it is much lower than what one might expect from using a seismic quality factor. The tidal damping rate deviates from the seismic damping rate, especially in the zero-frequency limit, and this difference takes place for bodies of any size. So the equal in magnitude but opposite in sign tidal torques, exerted on one another by the primary and the secondary, have their orbital averages going smoothly through zero as the secondary crosses the synchronous orbit. We describe the mantle rheology with the Andrade model, allowing it to lean toward the Maxwell model at the lowest frequencies. To implement this additional flexibility, we reformulate the Andrade model by endowing it with a free parameter ζ which is the ratio of the anelastic timescale to the viscoelastic Maxwell time of the mantle. Some uncertainty in this parameter's frequency dependence does not
Asymmetric radiation of seismic waves from an atoll: nuclear tests in French Polynesia
Weber, Michael; Wicks, Charles W.; Krüger, Frank; Jahnke, Gunnar; Schlittenhardt, Jörg
1998-01-01
Seismic records of nuclear tests detonated in the Mururoa Atoll in French Polynesia show large unpredicted arrivals 2.2 and 4.5 seconds (X1 and X2) after the P-wave at the Australian Warramunga Array. These arrivals are not observed at the Canadian Yellowknife Array. X1 and X2 are also absent on Warramunga Array recordings of tests carried out at the Fangataufa Atoll situated 40 km SSE of Mururoa. Array analysis shows that X1 and X2 are produced within the source area. The layered crustal structure of the atoll, significant local inhomogeneities, and focusing effects due to the elongated shape and the steep flanks of the Mururoa Atoll are most likely responsible for X1 and X2. The form of Mururoa (28 × 10 km) and its East-West orientation is due to its location on the Austral Fracture Zone (AFZ). The Fangataufa Atoll on the other hand is almost circular (10 km diameter) and is unaffected by the dynamics along the AFZ. Our observations demonstrate that complicated structures in the source area can significantly alter the wave field at teleseismic distances and produce a large magnitude (mb) bias. A better understanding of the exact cause of these unusual seismic observations will only become possible, if the coordinates of the tests and information on the detailed 3-D structure of the atolls are released.
The effect of frequency on Young's modulus and seismic wave attenuation
International Nuclear Information System (INIS)
Price, R.H.
1994-07-01
Laboratory experiments were performed to measure the effect of frequency, water-saturation, and strain amplitude on Young's modulus and seismic wave attenuation on rock cores recovered on or near the site of a potential nuclear waste repository at Yucca Mountain, Nevada. The purpose of this investigation is to perform the measurements using four techniques: cyclic loading, waveform inversion, resonant bar, and ultrasonic velocity. The measurements ranged in frequency between 10 -2 and 10 6 Hz. For the dry specimens Young's modulus and attenuation were independent of frequency; that is, all four techniques yielded nearly the same values for modulus and attenuation. For saturated specimens, a frequency dependence for both Young's modulus and attenuation was observed. In general, saturation reduced Young's modulus and increased seismic wave attenuation. The effect of strain amplitude on Young's modulus and attenuation was measured using the cyclic loading technique at a frequency of 10 -1 Hz. The effect of strain amplitude in all cases was small. For some rocks, such as the potential repository horizon of the Topopah Spring Member tuff (TSw2), the effect of strain amplitude on both attenuation and modulus was minimal
Mathematical modeling of seismic explosion waves impact on rock mass with a working
Directory of Open Access Journals (Sweden)
А. П. Господариков
2017-08-01
Full Text Available In the article, within the framework of the dynamic theory of elasticity, a mathematical model of the impact of seismic blast waves on rock mass is presented, including a working. The increase in the volume of mining operations in complex mining and geological conditions, taking into account the influence of the explosion energy, is closely connected with the analysis of the main parameters of the stress-strain state of the rock massif including a working. The latter leads to the need to determine the safe parameters of drilling and blasting operations that ensure the operational state of mining. The main danger in detonation of an explosive charge near an active working is a seismic explosive wave which characteristics are determined by the properties of soil and parameters of drilling and blasting operations. The determination of stress fields and displacement velocities in rock mass requires the use of a modern mathematical apparatus for its solution. For numerical solution of the given boundary value problem by the method of finite differences, an original calculation-difference scheme is constructed. The application of the splitting method for solving a two-dimensional boundary value problem is reduced to the solution of spatially one-dimensional differential equations. For the obtained numerical algorithm, an effective computational software has been developed. Numerical solutions of the model problem are given for the case when the shape of the working has a form of an ellipse.
Seismic Oceanography in the Tyrrhenian Sea: Thermohaline Staircases, Eddies, and Internal Waves
Buffett, G. G.; Krahmann, G.; Klaeschen, D.; Schroeder, K.; Sallarès, V.; Papenberg, C.; Ranero, C. R.; Zitellini, N.
2017-11-01
We use seismic oceanography to document and analyze oceanic thermohaline fine structure across the Tyrrhenian Sea. Multichannel seismic (MCS) reflection data were acquired during the MEDiterranean OCcidental survey in April-May 2010. We deployed along-track expendable bathythermograph probes simultaneous with MCS acquisition. At nearby locations we gathered conductivity-temperature-depth data. An autonomous glider survey added in situ measurements of oceanic properties. The seismic reflectivity clearly delineates thermohaline fine structure in the upper 2,000 m of the water column, indicating the interfaces between Atlantic Water/Winter Intermediate Water, Levantine Intermediate Water, and Tyrrhenian Deep Water. We observe the Northern Tyrrhenian Anticyclone, a near-surface mesoscale eddy, plus laterally and vertically extensive thermohaline staircases. Using MCS, we are able to fully image the anticyclone to a depth of 800 m and to confirm the horizontal continuity of the thermohaline staircases of more than 200 km. The staircases show the clearest step-like gradients in the center of the basin while they become more diffuse toward the periphery and bottom, where impedance gradients become too small to be detected by MCS. We quantify the internal wave field and find it to be weak in the region of the eddy and in the center of the staircases, while it is stronger near the coastlines. Our results indicate this is because of the influence of the boundary currents, which disrupt the formation of staircases by preventing diffusive convection. In the interior of the basin, the staircases are clearer and the internal wave field weaker, suggesting that other mixing processes such as double diffusion prevail.
Viscoelastic shock wave in ballistic gelatin behind soft body armor.
Liu, Li; Fan, Yurun; Li, Wei
2014-06-01
Ballistic gelatins are widely used as a surrogate of biological tissue in blunt trauma tests. Non-penetration impact tests of handgun bullets on the 10wt% ballistic gelatin block behind soft armor were carried out in which a high-speed camera recorded the crater׳s movement and pressure sensors imbedded in the gelatin block recorded the pressure waves at different locations. The observed shock wave attenuation indicates the necessity of considering the gelatin׳s viscoelasticity. A three-element viscoelastic constitutive model was adopted, in which the relevant parameters were obtained via fitting the damping free oscillations at the beginning of the creep-mode of rheological measurement, and by examining the data of published split Hopkinson pressure bar (SHPB) experiments. The viscoelastic model is determined by a retardation time of 5.5×10(-5)s for high oscillation frequencies and a stress relaxation time of 2.0-4.5×10(-7)s for shock wave attenuation. Using the characteristic-line method and the spherical wave assumption, the propagation of impact pressure wave front and the subsequent unloading profile can be simulated using the experimental velocity boundary condition. The established viscoelastic model considerably improves the prediction of shock wave attenuation in the ballistic gelatin. Copyright © 2014 Elsevier Ltd. All rights reserved.
Hejrani, Babak; Balling, Niels; Holm Jacobsen, Bo; Kind, Rainer; Tilmann, Frederik; England, Richard; Bom Nielsen, Søren
2014-05-01
set for Europe.Geophysical Journal International, 173, 465-472. England, R. W.; Ebbing, J., 2012, Crustal structure of central Norway and Sweden from integrated modelling of teleseismic receiver functions and the gravity anomaly.GEOPHYSICAL JOURNAL INTERNATIONAL, 191, 1-11. Gregersen S., Voss P., TOR Working Group, 2002. Summary of project TOR: delineation of a stepwise, sharp, deep lithosphere transition across Germany-Denmark-Sweden, Tectonophysics, 360, 61-73. Hejrani, B., Jacobsen, B. H., Balling,N. and England, R. W.. 2012, A seismic tomography study of lithospheric structure under the Norwegian Caledonides.Geophysical Research Abstracts, 14, 4334. Hejrani, B.; Jacobsen, B.H.; Balling, N.;Tilmann, F.; Kind, R., 2013, Upper-mantle velocity structure beneathJutland, Denmark and northern Germany:Preliminary results. Joint Assembly Gothenburg Abstract S401S2.01, Medhus, A. B., Balling, N., Jacobsen, B. H., Weidle, C., England, R. W., Kind, R., Thybo, H., Voss, P. (2012a): Upper-mantle structure beneath the Southern Scandes Mountains and the Northern Tornquist Zone revealed by P-wave traveltime tomography. Geophysical Journal International, 189, 3, 1315-1334. Medhus, Jacobsen, B. H.,A. B., Balling, N., 2012b, Bias Problems in Existing Teleseismic Travel Time Databases: Ignore or Repair? Seismological Research Letters, 83, 1030-1037. Sandoval, S., Kissling, E. &Ansorge, J., 2003.High-resolution body wave tomography beneath the SVEKALAPKO array: I. A priori three-dimensional crustal model and associated traveltime effects on teleseismic wave fronts, Geophys. J. Int., 153, 75-87. Weidle, C., Maupin, V., Ritter, J.,Kværna, T., Schweitzer J., Balling, N.,Thybo, H.,Faleide, J. I.,and,Wenzel, F., 2010, MAGNUS-A Seismological Broadband Experiment to Resolve Crustal and Upper Mantle Structure beneath the Southern Scandes Mountains in Norway. SEISMOLOGICAL RESEARCH LETTERS, 81, 76-84.
Seismic imaging of Q structures by a trans-dimensional coda-wave analysis
Takahashi, Tsutomu
2017-04-01
Wave scattering and intrinsic attenuation are important processes to describe incoherent and complex wave trains of high frequency seismic wave (>1Hz). The multiple lapse time window analysis (MLTWA) has been used to estimate scattering and intrinsic Q values by assuming constant Q in a study area (e.g., Hoshiba 1993). This study generalizes this MLTWA to estimate lateral variations of Q values under the Bayesian framework in dimension variable space. Study area is partitioned into small areas by means of the Voronoi tessellation. Scattering and intrinsic Q in each small area are constant. We define a misfit function for spatiotemporal variations of wave energy as with the original MLTWA, and maximize the posterior probability with changing not only Q values but the number and spatial layout of the Voronoi cells. This maximization is conducted by means of the reversible jump Markov chain Monte Carlo (rjMCMC) (Green 1995) since the number of unknown parameters (i.e., dimension of posterior probability) is variable. After a convergence to the maximum posterior, we estimate Q structures from the ensemble averages of MCMC samples around the maximum posterior probability. Synthetic tests showed stable reconstructions of input structures with reasonable error distributions. We applied this method for seismic waveform data recorded by ocean bottom seismograms at the outer-rise area off Tohoku, and estimated Q values at 4-8Hz, 8-16Hz and 16-32Hz. Intrinsic Q are nearly constant at all frequency bands, and scattering Q shows two distinct strong scattering regions at petit spot area and high seismicity area. These strong scattering are probably related to magma inclusions and fractured structure, respectively. Difference between these two areas becomes clear at high frequencies. It means that scale dependences of inhomogeneities or smaller scale inhomogeneity is important to discuss medium property and origins of structural variations. While the generalized MLTWA is based on
Smith, J. A.; Peter, D. B.; Tromp, J.; Komatitsch, D.; Lefebvre, M. P.
2015-12-01
We present both SPECFEM3D_Cartesian and SPECFEM3D_GLOBE open-source codes, representing high-performance numerical wave solvers simulating seismic wave propagation for local-, regional-, and global-scale application. These codes are suitable for both forward propagation in complex media and tomographic imaging. Both solvers compute highly accurate seismic wave fields using the continuous Galerkin spectral-element method on unstructured meshes. Lateral variations in compressional- and shear-wave speeds, density, as well as 3D attenuation Q models, topography and fluid-solid coupling are all readily included in both codes. For global simulations, effects due to rotation, ellipticity, the oceans, 3D crustal models, and self-gravitation are additionally included. Both packages provide forward and adjoint functionality suitable for adjoint tomography on high-performance computing architectures. We highlight the most recent release of the global version which includes improved performance, simultaneous MPI runs, OpenCL and CUDA support via an automatic source-to-source transformation library (BOAST), parallel I/O readers and writers for databases using ADIOS and seismograms using the recently developed Adaptable Seismic Data Format (ASDF) with built-in provenance. This makes our spectral-element solvers current state-of-the-art, open-source community codes for high-performance seismic wave propagation on arbitrarily complex 3D models. Together with these solvers, we provide full-waveform inversion tools to image the Earth's interior at unprecedented resolution.
Seismic source characterization for the 2014 update of the U.S. National Seismic Hazard Model
Moschetti, Morgan P.; Powers, Peter; Petersen, Mark D.; Boyd, Oliver; Chen, Rui; Field, Edward H.; Frankel, Arthur; Haller, Kathleen; Harmsen, Stephen; Mueller, Charles S.; Wheeler, Russell; Zeng, Yuehua
2015-01-01
We present the updated seismic source characterization (SSC) for the 2014 update of the National Seismic Hazard Model (NSHM) for the conterminous United States. Construction of the seismic source models employs the methodology that was developed for the 1996 NSHM but includes new and updated data, data types, source models, and source parameters that reflect the current state of knowledge of earthquake occurrence and state of practice for seismic hazard analyses. We review the SSC parameterization and describe the methods used to estimate earthquake rates, magnitudes, locations, and geometries for all seismic source models, with an emphasis on new source model components. We highlight the effects that two new model components—incorporation of slip rates from combined geodetic-geologic inversions and the incorporation of adaptively smoothed seismicity models—have on probabilistic ground motions, because these sources span multiple regions of the conterminous United States and provide important additional epistemic uncertainty for the 2014 NSHM.
Simulation of Seismic Waves from Underground Explosions in Geologic Media: FY2009 Progress Report
Energy Technology Data Exchange (ETDEWEB)
Rodgers, A; Vorobiev, O; Sjogreen, B; Petersson, N A
2009-11-09
This report summarizes work done after one year on project LL09-Sim-NDD-02 entitled 'Exploratory Research: Advanced Simulation of Low Yield Underground Nuclear Explosions To Improve Seismic Yield Estimation and Source Identification'. Work on this effort proceeded in two thrusts: (1) parametric studies of underground explosion generated motions with GEODYN; and (2) coupling of GEODYN to WPP. GEODYN is a code for modeling hydrodynamic (shock-wave) motions in a wide variety of materials, including earth materials. WPP is an anelastic finite difference code for modeling seismic motions. The sensitivity of seismic motions to emplacement conditions was investigated with a series of parametric studies of low-yield (0.2-4 kiloton) chemical high-explosive shots at a range of burial depths in four canonical geologic media (granite, limestone, tuff and alluvium). Results indicate that the material has a strong impact on the seismic motions consistent with previous reports. Motions computed with GEODYN in realistically complex material models are very consistent with reported motions from nuclear tests by Perret and Bass (1975). The amplitude, frequency content and cavity size resulting from explosions are all strongly sensitive to the material strength. Explosions in high-strength (granite) resulted in the highest amplitude, shortest duration pulse and smallest cavities, whereas explosions in low-strength material (alluvium) resulted in the lowest amplitudes, longest duration pulse and larger cavities. The corner frequencies of P-wave motions at take-off angles corresponding to propagation to teleseismic distances show corresponding behavior, with high-strength materials having the highest corner frequency and low-strength materials having low corner frequency. Gravity has an important effect on the cavity size and outgoing motions due work done against lithostatic stress. In fact without gravity the cavity radius and elastic motions are largely insensitive to
1983-09-30
inversion schemes surface waves were used to determine the source mechanism [Dziewonski and Gilbert, 1974; Patton and Aki, 1979; Kafka and Weidner, 1979...important because several recent seismicity studies [Buyukasikoglu, 1980; Rotstein and Kafka , 1982] have used ISC locations of earthquakes with...primarily by teams from France and England [Ambraseys, 1981; King and Vita-Finzi, 1981; Ouyed et al., 1981, 1984; Yielding et al., 1981; Philip and
Time-Lapse Monitoring with 4D Seismic Coda Waves in Active, Passive and Ambient Noise Data
Lumley, D. E.; Kamei, R.; Saygin, E.; Shragge, J. C.
2017-12-01
The Earth's subsurface is continuously changing, due to temporal variations in fluid flow, stress, temperature, geomechanics and geochemistry, for example. These physical changes occur at broad tectonic and earthquake scales, and also at very detailed near-surface and reservoir scales. Changes in the physical states of the earth cause time-varying changes in the physical properties of rocks and fluids, which can be monitored with natural or manmade seismic waves. Time-lapse (4D) seismic monitoring is important for applications related to natural and induced seismicity, hydrocarbon and groundwater reservoir depletion, CO2 sequestration etc. An exciting new research area involves moving beyond traditional methods in order to use the full complex time-lapse scattered wavefield (4D coda waves) for both manmade active-source 3D/4D seismic data, and also to use continuous recordings of natural-source passive seismic data, especially (micro) earthquakes and ocean ambient noise. This research involves full wave-equation approaches including waveform inversion (FWI), interferometry, Large N sensor arrays, "big data" information theory, and high performance supercomputing (HPC). I will present high-level concepts and recent data results that are quite spectacular and highly encouraging.
African Cenozoic hotpot tectonism: new insights from continent-scale body-wave tomography
Bastow, I. D.; Boyce, A.; Caunt, E.; Guilloud De Courbeville, J.; Desai, S.; Kounoudis, R.; Golos, E. M.; Burdick, S.; van der Hilst, R. D.
2017-12-01
The African plate is an ideal study locale for mantle plumes and Cenozoic hotspot tectonism. On the eastern side of the continent, the uplifted East African and Ethiopian plateaus, and the 30Ma Ethiopian Traps, are widely considered to be the result of the African Superplume: a broad thermochemical anomaly that originates below southern Africa. Precisely where and how the superplume traverses the mantle transition zone is debated however. On the western side of the continent, the Cameroon Volcanic Line is a hotspot track with no age-progression; it is less easily attributed to the effects of a mantle plume. Central to our understanding of these issues is an improved picture of mantle seismic structure. Body-wave studies of African mantle wave-speed structure are typically limited to regional relative arrival-time studies that utilize data from temporary seismograph networks of aperture less than 1000km. The resulting tomographic images are higher resolution than continent-scale surface-wave models, but anomaly amplitudes cannot be compared from region to region using the relative arrival-time approach: the 0% contour in each region refers to the regional, not global mean. The challenge is thus to incorporate the often-noisy body-wave data from temporary seismograph networks into a continent-scale absolute delay-time model. We achieve this using the new Absolute Arrival-time Recovery Method (AARM) method of Boyce et. al., (2017) and the tomographic inversion approach described by Li et. al., (2008). We invert for mantle wavespeed structure using data recorded since 1990 by temporary networks in the Atlas Mountains, Cameroon, South Africa, East African Rift system, Ethiopia and Madagascar. Our model is well resolved to lower mantle depths beneath these temporary networks, and offers the most detailed picture yet of mantle wavespeed structure beneath Africa. The contrast between East African and Cameroon mantle structure suggests multiple development mechanisms for
Roeloffs, E.
2002-12-01
That seismic waves trigger microseismicity in hydrothermal settings hundreds of km from the epicenter is plausibly linked to seismic-wave-induced fluid pressure changes at these distances. Although fluid pressure decreases have been observed in diverse settings, in the hydrothermal system at Long Valley, California, that seismic waves from earthquakes increase fluid pressure or discharge. Other published data, from thermal springs in Japan, Yellowstone, and Klamath Falls, Oregon, support the idea that seismic waves have induced pressure and discharge changes and that, in hydrothermal systems, these changes are usually increases. Temperature increases in seafloor hydrothermal vents within days after earthquakes as distant as 220 km imply, moreover, that seismic waves enhance conductance of vertical fluid flow pathways. The influence of seismic waves (wavelengths of km), on hot, fluid-filled subsurface fractures (apertures of mm to cm) could proceed by several mechanisms. Local fluid flow induced at crack walls could remove mineral seals. Spatially uniform acceleration can move gas bubbles relative to denser liquid and solid phases. Thermal expansion can elevate pressure around hot fluid that has penetrated upward. By lowering effective stress and directly weakening faults that are themselves flow paths, seismic waves could initiate processes leading to volcanic eruptions or other earthquakes where sufficient subsurface magma or elastic strain energy have previously accumulated. This type of earthquake-volcano linkage could explain why volcanos statistically erupt more frequently up to 5 years after M>7 earthquakes hundreds of km distant. For example, 11 months elapsed after the Ms 7.8 Luzon (Phillipines) earthquake before Mount Pinatubo erupted on June 15, 1991, 100 km away. Steam emission and 3 M4+ earthquakes in the Pinatubo area followed within days of the Luzon event, however, and a hydrothermal explosion on April 2 started the continuous unrest that built to
Comparison of laboratory and field measurements of P and S wave velocities of a peridotite rock
Czech Academy of Sciences Publication Activity Database
Vilhelm, J.; Ivankina, T.; Lokajíček, Tomáš; Rudajev, V.
2016-01-01
Roč. 88, October (2016), s. 235-241 ISSN 1365-1609 R&D Projects: GA MŠk LH13102; GA ČR(CZ) GAP104/12/0915; GA ČR GA13-13967S Institutional support: RVO:67985831 Keywords : elastic waves * peridotite rocks * seismic anisotropy * neutron diffraction * pulse-transmission technique Subject RIV: DB - Geology ; Mineralogy Impact factor: 2.268, year: 2016
An effective absorbing layer for the boundary condition in acoustic seismic wave simulation
Yao, Gang; da Silva, Nuno V.; Wu, Di
2018-04-01
Efficient numerical simulation of seismic wavefields generally involves truncating the Earth model in order to keep computing time and memory requirements down. Absorbing boundary conditions, therefore, are applied to remove the boundary reflections caused by this truncation, thereby allowing for accurate modeling of wavefields. In this paper, we derive an effective absorbing boundary condition for both acoustic and elastic wave simulation, through the simplification of the damping term of the split perfectly matched layer (SPML) boundary condition. This new boundary condition is accurate, cost-effective, and easily implemented, especially for high-performance computing. Stability analysis shows that this boundary condition is effectively as stable as normal (non-absorbing) wave equations for explicit time-stepping finite differences. We found that for full-waveform inversion (FWI), the strengths of the effective absorbing layer—a reduction of the computational and memory cost coupled with a simplistic implementation—significantly outweighs the limitation of incomplete absorption of outgoing waves relative to the SPML. More importantly, we demonstrate that this limitation can easily be overcome through the use of two strategies in FWI, namely variable cell size and model extension thereby fully compensating for the imperfectness of the proposed absorbing boundary condition.
Watanabe, Kohei; Pisano, F.; Jeremi, Boris
2016-01-01
Presented here is a numerical investigation that (re-)appraises standard rules for space/time discretization in seismic wave propagation analyses. Although the issue is almost off the table of research, situations are often encountered where (established) discretization criteria are not observed and
Wang, Chun-Yong; Mooney, W.D.; Ding, Z.; Yang, J.; Yao, Z.; Lou, H.
2009-01-01
The shallow seismic velocity structure of the Kunlun fault zone (KLFZ) was jointly deduced from seismic refraction profiling and the records of trapped waves that were excited by five explosions. The data were collected after the 2001 Kunlun M s8.1 earthquake in the northern Tibetan Plateau. Seismic phases for the in-line record sections (26 records up to a distance of 15 km) along the fault zone were analysed, and 1-D P- and S-wave velocity models of shallow crust within the fault zone were determined by using the seismic refraction method. Sixteen seismic stations were deployed along the off-line profile perpendicular to the fault zone. Fault-zone trapped waves appear clearly on the record sections, which were simulated with a 3-D finite difference algorithm. Quantitative analysis of the correlation coefficients of the synthetic and observed trapped waveforms indicates that the Kunlun fault-zone width is 300 m, and S-wave quality factor Q within the fault zone is 15. Significantly, S-wave velocities within the fault zone are reduced by 30-45 per cent from surrounding rocks to a depth of at least 1-2 km, while P-wave velocities are reduced by 7-20 per cent. A fault-zone with such P- and S-low velocities is an indication of high fluid pressure because Vs is affected more than Vp. The low-velocity and low-Q zone in the KLFZ model is the effect of multiple ruptures along the fault trace of the 2001 M s8.1 Kunlun earthquake. ?? 2009 The Authors Journal compilation ?? 2009 RAS.
Acoustic wave therapy for cellulite, body shaping and fat reduction.
Hexsel, Doris; Camozzato, Fernanda Oliveira; Silva, Aline Flor; Siega, Carolina
2017-06-01
Cellulite is a common aesthetic condition that affects almost every woman. To evaluate the efficacy of acoustic wave therapy (AWT) for cellulite and body shaping. In this open-label, single-centre trial, 30 women presenting moderate or severe cellulite underwent 12 sessions of AWT on the gluteus and back of the thighs, over six weeks. The following assessments were performed at baseline, and up to 12 weeks after treatment: Cellulite Severity Scale (CSS), body circumference measurements, subcutaneous fat thickness by magnetic resonance imaging (MRI), quality of life related by Celluqol ® and a satisfaction questionnaire. The treatment reduced cellulite severity from baseline up to 12 weeks after the last treatment session (subjects presenting severe cellulite: 60% to 38%). The mean CSS shifted from 11.1 to 9.5 (p cellulite appearance and reduce body circumferences.
Long Period Seismic Waves Developped at Local Distances and Their Importance for EEWs
Kalkan Ertan, Esra; Pınar, Ali
2017-04-01
Long period ground motions is an highly importance topic nowadays because of the number of the large-scale structures increases day by day in metropolitan areas. Their effect on the large-scale structure (high rise buildings, suspension bridges, off-shore oil drilling platforms etc.) are more perceivable than small structures. Studies show that long period ground motions especially occurs in distant sedimentary basins with the help of the path effects. (Koketsu and Miyake, 2008) Period of the waves is ranging from several to ten seconds and that causes dramatic resonance and severe damage to the structures which are located in deep sedimentary basins (Furumura et al., 2013). There are so many examples of how destructive these waves can be. A devastating example is Mexico City, which is located 400 km away from the 1985 Michoacan Earthquake (Mw=8.0) epicenter, where 300 buldings collapsed and 800 buildings were demolished beyond repair. (Celebi et al, 1987). Another example is 2003 Tokachi-oki Earthquake associated with severe damage on large oil tanks, and fires lasting two days at the city of Tomakomani 250 km away from the source (Koketsu et al, 2005). Lots of studies revealed that the sedimentary basins amplifiy the long period seismic waves. In the case of Marmara Region, three important basins namely Çınarcık, Central and Tekirdaǧ Basins exist in Marmara Sea. The primary objective of the proposed study is to investigate if any relations exist between basins structures and generation of long period seismic waves which can be effective in Istanbul Metropolitan Area and develop reliable early warning applications or systems for structures which are under such risk. Three types of algorithms are in use for EEW applications used for this study, Virtual Seismologist, PRESTo and ELARMS2. The early warning signal is communicated to the appropriate server shut-down systems of the recipient facilities, that automatically decide proper action based on the alarm
Dai, W. P.; Hung, S. H.; Wu, S. M.; Hsu, Y. J.
2017-12-01
Owing to the rapid development in ambient noise seismology, time-lapse variations in delay time and waveform decorrelation of coda derived from noise cross correlation (NCF) have been proved very effective to monitor slight changes in seismic velocity and scattering properties of the crust induced by various loadings such as the earthquake and healing process. In this study, we employ coda wave interferometry to detect the crustal perturbations immediately preceding and following the 2013 Mw 6.2 Ruisui Earthquake which struck the northern segment of the Longitudinal Valley Fault in eastern Taiwan, a seismically very active thrust suture zone separating the Eurasian and Philippine Sea Plate. By comparing the pre- and post-event coda waves extracted from the auto- and cross-correlation functions (ACFs and CCFs) of ambient seismic and strain fields recorded by the seismometers and borehole strainmeters, respectively, in the vicinity of the source region, we present a strong case that not only coseismic velocity reduction but also preceding decorrelation of waveforms are explicitly revealed in both the seismic and strain CCFs filtered in the secondary microseism frequency band of 0.1-0.9 Hz. Such precursory signals susceptible to the scattering properties of the crust are more unequivocally identified in the coda retrieved from the strainmeter data, suggesting that the ambient strain field can act as a more sensible probe to detect tiny structural perturbations in the critically stressed fault zone at the verge of failure. In addition to coseismic velocity changes detected in both the seismic and strain NCFs, we find quasi-periodic velocity variations that only appear in the strain retrieved coda signals, with a predominant cycle of 3-4 months correlating with the groundwater fluctuations observed at Ruisui.
S-wave scattering of fermion revisited
International Nuclear Information System (INIS)
Rahaman, Anisur
2011-01-01
A model where a Dirac fermion is coupled to background dilaton field is considered to study s-wave scattering of fermion by a back ground dilaton black hole. It is found that an uncomfortable situation towards information loss scenario arises when one loop correction gets involved during bosonization.
Seismic microzoning of Santiago de Cuba An approach by SH waves modelling
Alvarez, L; Femandez, B; García, J; González, B; Panza, G F; Pico, R; Reyes, C; Vaccari, F; Zapata, R J A
2002-01-01
The expected ground motion in Santiago de Cuba basin from earthquakes which occurred in the Oriente fault zone is studied. Synthetic SH-waves seismograms have been calculated along four profiles in the basin by the hybrid approach (modal summation for the path source-profile and finite differences for the profile) for a maximum frequency of 1 Hz. The response spectra ratio (RSR) has been determined in 49 sites, distributed along all considered profiles with a spacing of 900 m. The corresponding RSR versus frequency curves have been classified using a logical-combinatorial algorithm. The results of the classification, in combination with the uppermost geological setting (geotechnical information and geological geometry of the subsoil) are used for the seismic microzoning of the city. Three different main zones are identified, and a small sector characterised by big resonance effects, due to the particular structural conditions. Each zone is characterized in terms of its expected ground motion parameters for th...
Attenuation of seismic waves and the universal rheological model of the Earth's mantle
Birger, B. I.
2007-08-01
Analysis of results of laboratory studies on creep of mantle rocks, data on seismic wave attenuation in the mantle, and rheological micromechanisms shows that the universal, i.e., relevant to all time scales, rheological model of the mantle can be represented as four rheological elements connected in series. These elements account for elasticity, diffusion rheology, high temperature dislocation rheology, and low temperature dislocation rheology. The diffusion rheology element is described in terms of a Newtonian viscous fluid. The high temperature dislocation rheology element is described by the rheological model previously proposed by the author. This model is a combination of a power-law non-Newtonian fluid model for stationary flows and the linear hereditary Andrade model for flows associated with small strains. The low temperature dislocation rheology element is described by the linear hereditary Lomnitz model.
Clustering P-Wave Receiver Functions To Constrain Subsurface Seismic Structure
Chai, C.; Larmat, C. S.; Maceira, M.; Ammon, C. J.; He, R.; Zhang, H.
2017-12-01
The acquisition of high-quality data from permanent and temporary dense seismic networks provides the opportunity to apply statistical and machine learning techniques to a broad range of geophysical observations. Lekic and Romanowicz (2011) used clustering analysis on tomographic velocity models of the western United States to perform tectonic regionalization and the velocity-profile clusters agree well with known geomorphic provinces. A complementary and somewhat less restrictive approach is to apply cluster analysis directly to geophysical observations. In this presentation, we apply clustering analysis to teleseismic P-wave receiver functions (RFs) continuing efforts of Larmat et al. (2015) and Maceira et al. (2015). These earlier studies validated the approach with surface waves and stacked EARS RFs from the USArray stations. In this study, we experiment with both the K-means and hierarchical clustering algorithms. We also test different distance metrics defined in the vector space of RFs following Lekic and Romanowicz (2011). We cluster data from two distinct data sets. The first, corresponding to the western US, was by smoothing/interpolation of receiver-function wavefield (Chai et al. 2015). Spatial coherence and agreement with geologic region increase with this simpler, spatially smoothed set of observations. The second data set is composed of RFs for more than 800 stations of the China Digital Seismic Network (CSN). Preliminary results show a first order agreement between clusters and tectonic region and each region cluster includes a distinct Ps arrival, which probably reflects differences in crustal thickness. Regionalization remains an important step to characterize a model prior to application of full waveform and/or stochastic imaging techniques because of the computational expense of these types of studies. Machine learning techniques can provide valuable information that can be used to design and characterize formal geophysical inversion, providing
Darbyshire, F. A.; Bastow, I. D.; Forte, A. M.; Hobbs, T. E.; Calvel, A.; Gonzalez-Monteza, A.; Schow, B.
2015-12-01
Measurements of seismic anisotropy in continental regions are frequently interpreted with respect to past tectonic processes, preserved in the lithosphere as "fossil" fabrics. Models of the present-day sublithospheric flow (often using absolute plate motion as a proxy) are also used to explain the observations. Discriminating between these different sources of seismic anisotropy is particularly challenging beneath shields, whose thick (≥200 km) lithospheric roots may record a protracted history of deformation and strongly influence underlying mantle flow. Eastern Canada, where the geological record spans ˜3 Ga of Earth history, is an ideal region to address this issue. We use shear wave splitting measurements of core phases such as SKS to define upper mantle anisotropy using the orientation of the fast-polarization direction ϕ and delay time δt between fast and slow shear wave arrivals. Comparison with structural trends in surface geology and aeromagnetic data helps to determine the contribution of fossil lithospheric fabrics to the anisotropy. We also assess the influence of sublithospheric mantle flow via flow directions derived from global geodynamic models. Fast-polarization orientations are generally ENE-WSW to ESE-WNW across the region, but significant lateral variability in splitting parameters on a ≤100 km scale implies a lithospheric contribution to the results. Correlations with structural geologic and magnetic trends are not ubiquitous, however, nor are correlations with geodynamically predicted mantle flow directions. We therefore consider that the splitting parameters likely record a combination of the present-day mantle flow and older lithospheric fabrics. Consideration of both sources of anisotropy is critical in shield regions when interpreting splitting observations.
Chen, Xin; Chen, Wenchao; Wang, Xiaokai; Wang, Wei
2017-10-01
Low-frequency oscillatory ground-roll is regarded as one of the main regular interference waves, which obscures primary reflections in land seismic data. Suppressing the ground-roll can reasonably improve the signal-to-noise ratio of seismic data. Conventional suppression methods, such as high-pass and various f-k filtering, usually cause waveform distortions and loss of body wave information because of their simple cut-off operation. In this study, a sparsity-optimized separation of body waves and ground-roll, which is based on morphological component analysis theory, is realized by constructing dictionaries using tunable Q-factor wavelet transforms with different Q-factors. Our separation model is grounded on the fact that the input seismic data are composed of low-oscillatory body waves and high-oscillatory ground-roll. Two different waveform dictionaries using a low Q-factor and a high Q-factor, respectively, are confirmed as able to sparsely represent each component based on their diverse morphologies. Thus, seismic data including body waves and ground-roll can be nonlinearly decomposed into low-oscillatory and high-oscillatory components. This is a new noise attenuation approach according to the oscillatory behaviour of the signal rather than the scale or frequency. We illustrate the method using both synthetic and field shot data. Compared with results from conventional high-pass and f-k filtering, the results of the proposed method prove this method to be effective and advantageous in preserving the waveform and bandwidth of reflections.
International Nuclear Information System (INIS)
Wardaya, P. D.; Noh, K. A. B. M.; Yusoff, W. I. B. W.; Ridha, S.; Nurhandoko, B. E. B.
2014-01-01
This paper discusses a new approach for investigating the seismic wave velocity of rock, specifically carbonates, as affected by their pore structures. While the conventional routine of seismic velocity measurement highly depends on the extensive laboratory experiment, the proposed approach utilizes the digital rock physics view which lies on the numerical experiment. Thus, instead of using core sample, we use the thin section image of carbonate rock to measure the effective seismic wave velocity when travelling on it. In the numerical experiment, thin section images act as the medium on which wave propagation will be simulated. For the modeling, an advanced technique based on artificial neural network was employed for building the velocity and density profile, replacing image's RGB pixel value with the seismic velocity and density of each rock constituent. Then, ultrasonic wave was simulated to propagate in the thin section image by using finite difference time domain method, based on assumption of an acoustic-isotropic medium. Effective velocities were drawn from the recorded signal and being compared to the velocity modeling from Wyllie time average model and Kuster-Toksoz rock physics model. To perform the modeling, image analysis routines were undertaken for quantifying the pore aspect ratio that is assumed to represent the rocks pore structure. In addition, porosity and mineral fraction required for velocity modeling were also quantified by using integrated neural network and image analysis technique. It was found that the Kuster-Toksoz gives the closer prediction to the measured velocity as compared to the Wyllie time average model. We also conclude that Wyllie time average that does not incorporate the pore structure parameter deviates significantly for samples having more than 40% porosity. Utilizing this approach we found a good agreement between numerical experiment and theoretically derived rock physics model for estimating the effective seismic wave
Czech Academy of Sciences Publication Activity Database
Wcislo, Milosz; Pšenčík, Ivan
2017-01-01
Roč. 27 (2017), s. 83-92 ISSN 2336-3827 R&D Projects: GA ČR(CZ) GA16-05237S Institutional support: RVO:67985530 Keywords : ANRAY Subject RIV: DC - Siesmology, Volcanology, Earth Structure OBOR OECD: Volcanology
International Nuclear Information System (INIS)
Sorokin, L.
2017-01-01
The natural high intensity sub-millisecond electromagnetic pulses associated with seismic waves from earthquakes can trigger +CG, -CG and IC lightning discharges, transient luminous events (TLEs) and non luminous events as TGFS. The lightning discharges with higher peak currents are more probable during the moments when seismic waves from earthquakes pass through a place of lightning. Huge charge transfer of triggered +CG, -CG and IC lightning discharges can radiate powerful electromagnetic emission. Space-time analysis of the seismic wave’s propagation and WWLLN data was done together with the second Fermi GBM Terrestrial Gamma-ray Flashes (TGF) Catalog. A total number of 1203 events from the WWLLN associations table were associated with the entrance the exact seismic waves from earthquakes in the place of lightning. Only 11 events from 1214 associations were rejected. After that the full list of 1049 TGFs has been checked out. As the result the 1038 TGFS has been associated with earthquakes. Among them 42 events with time difference exceeding ±100 sec were found. As the result 996 events get inside the time interval for the space-time analysis ±100 sec, they correspond to 95% from the total number of 1049 TGFS. The probability density function for the Time difference data was calculated and more preferably can be explained by the probability density functions of Cauchy distribution. The Phases of Seismic Waves and earthquakes magnitude associated with selected 996 TGFS from WWLLN associations table were studied. (author)
Taylor, G.; Rost, S.; Houseman, G. A.; Hillers, G.
2017-12-01
By utilising short period surface waves present in the noise field, we can construct images of shallow structure in the Earth's upper crust: a depth-range that is usually poorly resolved in earthquake tomography. Here, we use data from a dense seismic array (Dense Array for Northern Anatolia - DANA) deployed across the North Anatolian Fault Zone (NAFZ) in the source region of the 1999 magnitude 7.6 Izmit earthquake in western Turkey. The NAFZ is a major strike-slip system that extends 1200 km across northern Turkey and continues to pose a high level of seismic hazard, in particular to the mega-city of Istanbul. We obtain maps of group velocity variation using surface wave tomography applied to short period (1- 6 s) Rayleigh and Love waves to construct high-resolution images of SV and SH-wave velocity in the upper 5 km of a 70 km x 35 km region centred on the eastern end of the fault segment that ruptured in the 1999 Izmit earthquake. The average Rayleigh wave group velocities in the region vary between 1.8 km/s at 1.5 s period, to 2.2 km/s at 6 s period. The NAFZ bifurcates into northern and southern strands in this region; both are active but only the northern strand ruptured in the 1999 event. The signatures of both the northern and southern branches of the NAFZ are clearly associated with strong gradients in seismic velocity that also denote the boundaries of major tectonic units. This observation implies that the fault zone exploits the pre-existing structure of the Intra-Pontide suture zone. To the north of the NAFZ, we observe low S-wave velocities ( 2.0 km/s) associated with the unconsolidated sediments of the Adapazari basin, and blocks of weathered terrigenous clastic sediments. To the south of the northern branch of the NAFZ in the Armutlu block, we detect higher velocities ( 2.9 km/s) associated with a shallow crystalline basement, in particular a block of metamorphosed schists and marbles that bound the northern branch of the NAFZ.
A new AVA attribute based on P-wave and S-wave reflectivities for overpressure prediction
Aleardi, Mattia; Mapelli, Luca; Mazzotti, Alfredo
2017-05-01
Pore pressure prediction is a key step for safe well drilling operations and is usually performed by deriving a velocity-pressure relationship calibrated to a reference well. However, in the last few decades, other seismic-based methods, such as the Amplitude versus Angle (AVA) technique, have been extended to predict anomalous pressure values. Concerning AVA analysis, in this work, we show that the expected pressure effect on the elastic rock properties is very different from the fluid effect, thus making the classical AVA attributes used for fluid prediction ineffective at highlighting pressure anomalies. Therefore, we propose a new AVA attribute to evidence the decrease in P-wave and S-wave reflectivity that usually occurs when passing from an overlying formation to an underlying overpressured one. This attribute can be easily derived from the intercept and gradient values extracted from the recorded seismic pre-stack data by means of the Shuey equation. To demonstrate the applicability of this new attribute for pore pressure prediction we show examples on synthetic seismic data and three applications to different field datasets over already drilled prospects. In the case of overpressured layers, this attribute shows anomalous responses, thus demonstrating its effectiveness in highlighting anomalous pore pressure regimes. In contrast, no anomalous attribute values are observed in cases characterized by a hydrostatic pore pressure regime.
Directory of Open Access Journals (Sweden)
Bor-Shouh Huang
2011-01-01
Full Text Available Extant paper records of the early analog seismic network of Taiwan represent a large resource for earthquake studies in several disciplines. In this study, we report on T waves generated from offshore earthquakes, based on analog observations. The T phases were identified from their stable apparent velocity of about 1.5 km s-1 and other observations using data recorded by stations in eastern Taiwan and on two nearby islands. The observed T phases are recorded for the first time from Taiwan, and in particular are observed by the network in the distal range of local earthquakes. Most of the T waves are observed at island stations at epicentral distances greater than 100 km. For earthquakes that occurred a great distance east of Taiwan, the T phases are always the most dominant phases observed at island stations east of Taiwan, and are also seen at some inland stations with smaller amplitudes. No T phases from inland events were observed by stations on Taiwan or on nearby islands. The observations indicate that the amplitude of the T phase is highly attenuated on its land path and that the propagation direction of the T phase is affected by water depth.
Energy Technology Data Exchange (ETDEWEB)
Kano, N.; Yamaguchi, K.; Yokota, T.; Kiguchi, T. [Geological Survey of Japan, Tsukuba (Japan)
1996-10-01
Anisotropy has been investigated using S-wave as a technique for detecting fractures. In this study, fundamental experiments were carried out with slightly changing the measuring conditions at a place where anisotropy was expected. This paper describes the fundamental data acquisition of anisotropy analysis using S-wave, and a part of the results. The experiments were conducted on the agricultural road in Yamadera district, Matsuyama-machi, Yamagata Prefecture. Two flat unpaved roads meeting at right angles were used as traverse lines. In this place, several reflection surfaces were certainly detected by P-wave, and anisotropy of S-wave was confirmed from the velocity of refracted wave of S-wave. Data were processed for individual traverse lines meeting at right angles. Firstly, signal sweeping, correlation, and vertical superposition were made. Six kinds of data were prepared, i.e., three-component receiving records of data at 0{degree} of generating direction and three-component receiving records of data at 90{degree} of generating direction. Records of T-component at 0{degree} and R-component at 90{degree} were used for processing of the seismic reflection method. These records would be considered to be data of SH-wave and SV-wave, respectively. 4 figs.
Bartrand, J.; Abbott, R. E.
2017-12-01
We present data and analysis of a seismic data collect at the site of a historical underground nuclear explosion at Yucca Flat, a sedimentary basin on the Nevada National Security Site, USA. The data presented here consist of active-source, six degree-of-freedom seismic signals. The translational signals were collected with a Nanometrics Trillium Compact Posthole seismometer and the rotational signals were collected with an ATA Proto-SMHD, a prototype rotational ground motion sensor. The source for the experiment was the Seismic Hammer (a 13,000 kg weight-drop), deployed on two-kilometer, orthogonal arms centered on the site of the nuclear explosion. By leveraging the fact that compressional waves have no rotational component, we generated a map of subsurface scattering and compared the results to known subsurface features. To determine scattering intensity, signals were cut to include only the P-wave and its coda. The ratio of the time-domain signal magnitudes of angular velocity and translational acceleration were sectioned into three time windows within the coda and averaged within each window. Preliminary results indicate an increased rotation/translation ratio in the vicinity of the explosion-generated chimney, suggesting mode conversion of P-wave energy to S-wave energy at that location. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.
Geophysical imaging of near-surface structure using electromagnetic and seismic waves
Chen, Yongping
of tomograms to interpret plume morphology. In my second study I developed a passive-seismic method to image shear-wave velocity, which is an important geotechnical property commonly correlated with soil type or lithology. I inverted shear-wave velocity profiles from the phase velocity dispersion of Rayleigh waves based on passive seismic observations (microtremors). I used several sets of microtremor data which were collected at different sites. I obtained the phase velocity dispersion curve by the Extended Spatial Autocorrelation (ESPAC) method. I used simulated annealing method is used to invert the subsurface shear-wave velocity profile from the fundamental phase velocity dispersion curve. The field-experimental and synthetic results indicated that the microtremor approach can provide valuable information for quantitative geotechnical and hydrologic characterization. In my third study I developed a method to image vadose-zone dynamics using GPR. Flow in the unsaturated zone is important for predicting groundwater recharge, contaminant migration, and chemical/microbiological processes. However, it is difficult to characterize or monitor with conventional hydrologic measurements, which provide information at sparse locations. The purpose of this study was to image changes in moisture content, as well as aquifer structure based on the relation between dielectric constant and water content. The objective was to calibrate a flow model to field-experimental, time-lapse GPR data collected during an infiltration experiment. To this end, (1) I constructed a VS2DT model based on aquifer structure interpreted from static GPR reflection profiles; (2) I manually calibrated the model to reproduce observed changes in GPR data during infiltration; and (3) I used a time-domain electromagnetic finite-difference model to simulate experimental observations for comparison. The results of this work indicate that time-lapse GPR can monitor changes in water content on the order of a few
Detailed Study of Seismic Wave Attenuation in Carbonate Rocks: Application on Abu Dhabi Oil Fields
Bouchaala, F.; Ali, M. Y.; Matsushima, J.
2015-12-01
Seismic wave attenuation is a promising attribute for the petroleum exploration, thanks to its high sensitivity to physical properties of subsurface. It can be used to enhance the seismic imaging and improve the geophysical interpretation which is crucial for reservoir characterization. However getting an accurate attenuation profile is not an easy task, this is due to complex mechanism of this parameter, although that many studies were carried out to understand it. The degree of difficulty increases for the media composed of carbonate rocks, known to be highly heterogeneous and with complex lithology. That is why few attenuation studies were done successfully in carbonate rocks. The main objectives of this study are, Getting an accurate and high resolution attenuation profiles from several oil fields. The resolution is very important target for us, because many reservoirs in Abu Dhabi oil fields are tight.Separation between different modes of wave attenuation (scattering and intrinsic attenuations).Correlation between the attenuation profiles and other logs (Porosity, resistivity, oil saturation…), in order to establish a relationship which can be used to detect the reservoir properties from the attenuation profiles.Comparison of attenuation estimated from VSP and sonic waveforms. Provide spatial distribution of attenuation in Abu Dhabi oil fields.To reach these objectives we implemented a robust processing flow and new methodology to estimate the attenuation from the downgoing waves of the compressional VSP data and waveforms acquired from several wells drilled in Abu Dhabi. The subsurface geology of this area is primarily composed of carbonate rocks and it is known to be highly fractured which complicates more the situation, then we separated successfully the intrinsic attenuation from the scattering. The results show that the scattering is significant and cannot be ignored. We found also a very interesting correlation between the attenuation profiles and the
S-wave velocity measurements along levees in New Orleans using passive surface wave methods
Hayashi, K.; Lorenzo, J. M.; Craig, M. S.; Gostic, A.
2017-12-01
In order to develop non-invasive methods for levee inspection, geophysical investigations were carried out at four sites along levees in the New Orleans area: 17th Street Canal, London Avenue Canal, Marrero Levee, and Industrial Canal. Three of the four sites sustained damage from Hurricane Katrina in 2005 and have since been rebuilt. The geophysical methods used include active and passive surface wave methods, and capacitively coupled resistivity. This paper summarizes the acquisition and analysis of the 1D and 2D passive surface wave data. Twelve wireless seismic data acquisition units with 2 Hz vertical component geophones were used to record data. Each unit includes a GPS receiver so that all units can be synchronized over any distance without cables. The 1D passive method used L shaped arrays of three different sizes with geophone spacing ranging from 5 to 340 m. Ten minutes to one hour of ambient noise was recorded with each array, and total data acquisition took approximately two hours at each site. The 2D method used a linear array with a geophone spacing of 5m. Four geophones were moved forward every 10 minutes along 400 1000 m length lines. Data acquisition took several hours for each line. Recorded ambient noise was processed using the spatial autocorrelation method and clear dispersion curves were obtained at all sites (Figure 1a). Minimum frequencies ranged from 0.4 to 0.7 Hz and maximum frequencies ranged from 10 to 30 Hz depending on the site. Non-linear inversion was performed and 1D and 2D S-wave velocity models were obtained. The 1D method penetrated to depths ranging from 200 to 500 m depending on the site (Figure 1b). The 2D method penetrated to a depth of 40 60 m and provided 400 1000 m cross sections along the levees (Figure 2). The interpretation focused on identifying zones beneath the levees or canal walls having low S-wave velocities corresponding to saturated, unconsolidated sands, or low-rigidity clays. Resultant S-wave velocity profiles
Directory of Open Access Journals (Sweden)
Emanuele Casarotti
2016-12-01
Full Text Available We present here the first application of the fast reacting framework for 3D simulations of seismic wave propagation generated by earthquakes in the Italian region with magnitude Mw 5. The driven motivation is to offer a visualization of the natural phenomenon to the general public but also to provide preliminary modeling to expert and civil protection operators. We report here a description of this framework during the emergency of 24 August 2016 Mw 6.0 central Italy Earthquake, a discussion on the accuracy of the simulation for this seismic event and a preliminary critical analysis of the visualization structure and of the reaction of the public.
Sherman, Christopher Scott
Naturally occurring geologic heterogeneity is an important, but often overlooked, aspect of seismic wave propagation. This dissertation presents a strategy for modeling the effects of heterogeneity using a combination of geostatistics and Finite Difference simulation. In the first chapter, I discuss my motivations for studying geologic heterogeneity and seis- mic wave propagation. Models based upon fractal statistics are powerful tools in geophysics for modeling heterogeneity. The important features of these fractal models are illustrated using borehole log data from an oil well and geomorphological observations from a site in Death Valley, California. A large part of the computational work presented in this disserta- tion was completed using the Finite Difference Code E3D. I discuss the Python-based user interface for E3D and the computational strategies for working with heterogeneous models developed over the course of this research. The second chapter explores a phenomenon observed for wave propagation in heteroge- neous media - the generation of unexpected shear wave phases in the near-source region. In spite of their popularity amongst seismic researchers, approximate methods for modeling wave propagation in these media, such as the Born and Rytov methods or Radiative Trans- fer Theory, are incapable of explaining these shear waves. This is primarily due to these method's assumptions regarding the coupling of near-source terms with the heterogeneities and mode conversion. To determine the source of these shear waves, I generate a suite of 3D synthetic heterogeneous fractal geologic models and use E3D to simulate the wave propaga- tion for a vertical point force on the surface of the models. I also present a methodology for calculating the effective source radiation patterns from the models. The numerical results show that, due to a combination of mode conversion and coupling with near-source hetero- geneity, shear wave energy on the order of 10% of the
Is the seismic moment tensor ambiguous at a material interface?
Czech Academy of Sciences Publication Activity Database
Vavryčuk, Václav
2013-01-01
Roč. 194, č. 1 (2013), s. 395-400 ISSN 0956-540X R&D Projects: GA ČR(CZ) GAP210/12/1491 EU Projects: European Commission(XE) 230669 - AIM Institutional support: RVO:67985530 Keywords : earthquake dynamics * earthquake source observations * body waves * seismic anisotropy * dynamics and mechanics of faulting Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.724, year: 2013
Static corrections for enhanced signal detection at IMS seismic arrays
Wilkins, Neil; Wookey, James; Selby, Neil
2016-04-01
Seismic monitoring forms an important part of the International Monitoring System (IMS) for verifying the Comprehensive nuclear Test Ban Treaty (CTBT). Analysis of seismic data can be used to discriminate between nuclear explosions and the tens of thousands of natural earthquakes of similar magnitude that occur every year. This is known as "forensic seismology", and techniques include measuring the P-to-S wave amplitude ratio, the body-to-surface wave magnitude ratio (mb/Ms), and source depth. Measurement of these seismic discriminants requires very high signal-to-noise ratio (SNR) data, and this has led to the development and deployment of seismic arrays as part of the IMS. Array processing methodologies such as stacking can be used, but optimum SNR improvement needs an accurate estimate of the arrival time of the particular seismic phase. To enhance the imaging capability of IMS arrays, we aim to develop site-specific static corrections to the arrival time as a function of frequency, slowness and backazimuth. Here, we present initial results for the IMS TORD array in Niger. Vespagrams are calculated for various events using the F-statistic to clearly identify seismic phases and measure their arrival times. Observed arrival times are compared with those predicted by 1D and 3D velocity models, and residuals are calculated for a range of backazimuths and slownesses. Finally, we demonstrate the improvement in signal fidelity provided by these corrections.
Seismic waves modeling with the Fourier pseudo-spectral method on massively parallel machines.
Klin, Peter
2015-04-01
The Fourier pseudo-spectral method (FPSM) is an approach for the 3D numerical modeling of the wave propagation, which is based on the discretization of the spatial domain in a structured grid and relies on global spatial differential operators for the solution of the wave equation. This last peculiarity is advantageous from the accuracy point of view but poses difficulties for an efficient implementation of the method to be run on parallel computers with distributed memory architecture. The 1D spatial domain decomposition approach has been so far commonly adopted in the parallel implementations of the FPSM, but it implies an intensive data exchange among all the processors involved in the computation, which can degrade the performance because of communication latencies. Moreover, the scalability of the 1D domain decomposition is limited, since the number of processors can not exceed the number of grid points along the directions in which the domain is partitioned. This limitation inhibits an efficient exploitation of the computational environments with a very large number of processors. In order to overcome the limitations of the 1D domain decomposition we implemented a parallel version of the FPSM based on a 2D domain decomposition, which allows to achieve a higher degree of parallelism and scalability on massively parallel machines with several thousands of processing elements. The parallel programming is essentially achieved using the MPI protocol but OpenMP parts are also included in order to exploit the single processor multi - threading capabilities, when available. The developed tool is aimed at the numerical simulation of the seismic waves propagation and in particular is intended for earthquake ground motion research. We show the scalability tests performed up to 16k processing elements on the IBM Blue Gene/Q computer at CINECA (Italy), as well as the application to the simulation of the earthquake ground motion in the alluvial plain of the Po river (Italy).
Energy Technology Data Exchange (ETDEWEB)
Fujimoto, M.; Watanabe, T.; Ashida, Y.; Sassa, K. [Kyoto University, Kyoto (Japan). Faculty of Engineering
1997-05-27
With regard to the elastic wave exploration, discussions have been given on the relationship between frequency and resolution in P-wave velocity tomography using the initial travel time. The discussions were carried out by using a new analysis method which incorporates the concept of Fresnel volume into tomography analysis. The following two arrangements were used in the calculation: a cross hole arrangement, in which seismic source and vibration receiving points were arranged so as to surround the three directions of a region extending 250 m in the horizontal direction and 500 m in the vertical direction, and observation is performed between two wells, and a permeation VSP arrangement in which the seismic source is installed on the ground surface and receiving points installed in wells. Restructuring was performed on the velocity structure by using a total of 819 observation travel times. This method has derived results of the restructuring according to frequencies of the seismic source used for the exploration. The resolution shown in the result of the restructuring has become higher as elastic waves with higher frequency are used, and the size of the structure identified from the restructuring result has decreased. This fact reveals that sufficient considerations must be given on frequencies of elastic waves used according to size of objects to be explored. 4 refs., 4 figs.
Energy Technology Data Exchange (ETDEWEB)
Brauchler, R.; Doetsch, J.; Dietrich, P.; Sauter, M.
2012-01-10
In this study, hydraulic and seismic tomographic measurements were used to derive a site-specific relationship between the geophysical parameter p-wave velocity and the hydraulic parameters, diffusivity and specific storage. Our field study includes diffusivity tomograms derived from hydraulic travel time tomography, specific storage tomograms, derived from hydraulic attenuation tomography, and p-wave velocity tomograms, derived from seismic tomography. The tomographic inversion was performed in all three cases with the SIRT (Simultaneous Iterative Reconstruction Technique) algorithm, using a ray tracing technique with curved trajectories. The experimental set-up was designed such that the p-wave velocity tomogram overlaps the hydraulic tomograms by half. The experiments were performed at a wellcharacterized sand and gravel aquifer, located in the Leine River valley near Göttingen, Germany. Access to the shallow subsurface was provided by direct-push technology. The high spatial resolution of hydraulic and seismic tomography was exploited to derive representative site-specific relationships between the hydraulic and geophysical parameters, based on the area where geophysical and hydraulic tests were performed. The transformation of the p-wave velocities into hydraulic properties was undertaken using a k-means cluster analysis. Results demonstrate that the combination of hydraulic and geophysical tomographic data is a promising approach to improve hydrogeophysical site characterization.
Sun, Yao-Chong; Zhang, Wei; Xu, Jian-Kuan; Chen, Xiaofei
2017-09-01
This study simulates seismic wave propagation across a 2-D topographic fluid (acoustic) and solid (elastic) interface at the sea bottom by the finite-difference method (FDM). In this method, seismic waves in sea water are governed by acoustic wave equations, whereas seismic waves in solid earth are governed by elastic wave equations. The fluid-solid interface condition is implemented on the interface. Body-conforming grids are used to fit the topographic fluid-solid interface which naturally avoids spurious diffractions due to staircase approximation. A collocated-grid MacCormack FDM is utilized to update the wavefields in the fluid and solid media. The fluid-solid interface condition is explicitly implemented by decomposing the velocity and stress components to the normal and tangential directions with respect to the interface within a fourth-order Runge-Kutta time-marching scheme. The algorithm solutions for both flat and topographic fluid-solid interface models are compared with analytical solutions and spectral element solutions to validate the proposed method. Results show a suitable agreement with the reference solutions and hence confirms the validity of this method. The proposed FDM enforces the numerical solutions to satisfy the exact interface condition and it is more accurate than the conventional FDM that uses effective media parameters to approximate the interface condition.
The VERCE Science Gateway: Enabling User Friendly HPC Seismic Wave Simulations.
Casarotti, E.; Spinuso, A.; Matser, J.; Leong, S. H.; Magnoni, F.; Krause, A.; Garcia, C. R.; Muraleedharan, V.; Krischer, L.; Anthes, C.
2014-12-01
The EU-funded project VERCE (Virtual Earthquake and seismology Research Community in Europe) aims to deploy technologies which satisfy the HPC and data-intensive requirements of modern seismology.As a result of VERCE official collaboration with the EU project SCI-BUS, access to computational resources, like local clusters and international infrastructures (EGI and PRACE), is made homogeneous and integrated within a dedicated science gateway based on the gUSE framework. In this presentation we give a detailed overview on the progress achieved with the developments of the VERCE Science Gateway, according to a use-case driven implementation strategy. More specifically, we show how the computational technologies and data services have been integrated within a tool for Seismic Forward Modelling, whose objective is to offer the possibility to performsimulations of seismic waves as a service to the seismological community.We will introduce the interactive components of the OGC map based web interface and how it supports the user with setting up the simulation. We will go through the selection of input data, which are either fetched from federated seismological web services, adopting community standards, or provided by the users themselves by accessing their own document data store. The HPC scientific codes can be selected from a number of waveform simulators, currently available to the seismological community as batch tools or with limited configuration capabilities in their interactive online versions.The results will be staged out via a secure GridFTP transfer to a VERCE data layer managed by iRODS. The provenance information of the simulation will be automatically cataloged by the data layer via NoSQL techonologies.Finally, we will show the example of how the visualisation output of the gateway could be enhanced by the connection with immersive projection technology at the Virtual Reality and Visualisation Centre of Leibniz Supercomputing Centre (LRZ).
Seismic Wave Attenuation in Fractured Reservoir: Application on Abu Dhabi Oil Fields.
Bouchaala, F.; Ali, M.; Matsushima, J.
2016-12-01
There is a close link between fractures network and fluids circulation so information about nature and geometry of fractures in the reservoir zone is benificial for the petroleum industry. However the immaturity of the methodology and the complication of fractures network in some reservoirs like those of Abu Dhabi oil fields, make getting such information challenging. Since several studies showed the close link between physical properties of the subsurface and seismic wave attenuation (eg. Müller et al. 2010), we use this parameter in this study to assess its potentiality on fractures detection and characterization, even though its use is not common for reservoir characterization and even less for fractures characterization. To get an accurate attenuation profiles, we use a robust methods recently developed to estimate accurately attenuation from Vertical Seismic Profiling (VSP) (Matsushima et al. 2016) and sonic waveforms (Suziki and Matsushima 2013) in the reservoir zones. The data were acquired from many wells located in offshore and onshore oil fields of Abu Dhabi region. The subsurface of this region is mainly composed of carbonate rocks, such media are known to be highly heterogeneous. Scattering and intrinsic attenuation profiles were compared to interpreted fractures by using Formation Micro-imager (FMI). The comparison shows a correlation between these two parameters and fractures characteristic, such as their density and dipping. We also performed Alford rotation on dipole data to estimate the attenuation from fast and slow shear waveforms. The anisotropy is proportional to the dispersion of the points plotted from the ratio between the intrinsic attenuation of fast and slow shear over the depth, from the line (Qslow /Qfast=1), which corresponds to the isotropic case. We noticed that the zones with low fractures density display less dispersion than those of high density. Even though our results show potentiality of the attenuation for fractured
TUNING IN TO FISH SWIMMING WAVES - BODY FORM, SWIMMING MODE AND MUSCLE FUNCTION
WARDLE, CS; VIDELER, JJ; ALTRINGHAM, JD
Most fish species swim with lateral body undulations running from head to tail, These waves run more slowly than the waves of muscle activation causing them, reflecting the effect of the interaction between the fish's body and the reactive forces from the water, The coupling between both waves
Non-overlapped P- and S-wave Poynting vectors and its solution on Grid Method
Lu, Yong Ming
2017-12-12
Poynting vector represents the local directional energy flux density of seismic waves in geophysics. It is widely used in elastic reverse time migration (RTM) to analyze source illumination, suppress low-wavenumber noise, correct for image polarity and extract angle-domain common imaging gather (ADCIG). However, the P and S waves are mixed together during wavefield propagation such that the P and S energy fluxes are not clean everywhere, especially at the overlapped points. In this paper, we use a modified elastic wave equation in which the P and S vector wavefields are naturally separated. Then, we develop an efficient method to evaluate the separable P and S poynting vectors, respectively, based on the view that the group velocity and phase velocity have the same direction in isotropic elastic media. We furthermore formulate our method using an unstructured mesh based modeling method named the grid method. Finally, we verify our method using two numerical examples.
The Formation of Laurentia: Evidence from Shear Wave Splitting and Seismic Tomography
Liddell, M. V.; Bastow, I. D.; Rawlinson, N.; Darbyshire, F. A.; Gilligan, A.
2017-12-01
The northern Hudson Bay region of Canada comprises several Archean cratonic nuclei, assembled by Paleoproterozoic orogenies including the 1.8 Ga Trans-Hudson Orogen (THO) and Rinkian-Nagssugtoqidian Orogen (NO). Questions remain about how similar in scale and nature these orogens were compared to modern orogens like the Himalayas. Also in question is whether the thick Laurentian cratonic root below Hudson Bay is stratified, with a seismically-fast Archean core underlain by a lower, younger, thermal layer. We investigate these problems via shear-wave splitting and teleseismic tomography using up to 25 years of data from 65 broadband seismic stations across northern Hudson Bay. The results of the complementary studies comprise the most comprehensive study to date of mantle seismic velocity and anisotropy in northern Laurentia. Splitting parameter patterns are used to interpret multiple layers, lithospheric boundaries, dipping anisotropy, and deformation zone limits for the THO and NO. Source-side waveguide effects from Japan and the Aleutian trench are observed despite the tomographic data being exclusively relative arrival time. Mitigating steps to ensure data quality are explained and enforced. In the Hudson Strait, anisotropic fast directions (φ) generally parallel the THO, which appears in tomographic images as a strong low velocity feature relative to the neighbouring Archean cratons. Several islands in northern Hudson Bay show short length-scale changes in φ coincident with strong velocity contrasts. These are interpreted as distinct lithospheric blocks with unique deformational histories, and point to a complex, rather than simple 2-plate, collisional history for the THO. Strong evidence is presented for multiple anisotropic layers beneath Archean zones, consistent with the episodic development model of cratonic keels (e.g., Yuan & Romanowicz 2010). We show via both tomographic inversion models and SKS splitting patterns that southern Baffin Island was
Carvalho, João; Ghose, R.; Alves, D.; Leote, J
2016-01-01
Expressions of ductile, soft-sediment deformations induced by ground movements due to past earthquakes are difficult to recognize in near-surface soils. We have carried out shallow S-wave reflection studies in a seismically active area located northeast of metropolitan Lisbon, Portugal. Identifying
Application of random seismic inversion method based on tectonic model in thin sand body research
Dianju, W.; Jianghai, L.; Qingkai, F.
2017-12-01
The oil and gas exploitation at Songliao Basin, Northeast China have already progressed to the period with high water production. The previous detailed reservoir description that based on seismic image, sediment core, borehole logging has great limitations in small scale structural interpretation and thin sand body characterization. Thus, precise guidance for petroleum exploration is badly in need of a more advanced method. To do so, we derived the method of random seismic inversion constrained by tectonic model.It can effectively improve the depicting ability of thin sand bodies, combining numerical simulation techniques, which can credibly reducing the blindness of reservoir analysis from the whole to the local and from the macroscopic to the microscopic. At the same time, this can reduce the limitations of the study under the constraints of different geological conditions of the reservoir, accomplish probably the exact estimation for the effective reservoir. Based on the research, this paper has optimized the regional effective reservoir evaluation and the productive location adjustment of applicability, combined with the practical exploration and development in Aonan oil field.
International Nuclear Information System (INIS)
Dupuy, B.
2011-11-01
Seismic wave propagation in multiphasic porous media have various environmental (natural risks, geotechnics, groundwater pollutions...) and resources (aquifers, oil and gas, CO 2 storage...) issues. When seismic waves are crossing a given material, they are distorted and thus contain information on fluid and solid phases. This work focuses on the characteristics of seismic waves propagating in multiphasic media, from the physical complex description to the parameter characterisation by inversion, including 2D numerical modelling of the wave propagation. The first part consists in the description of the physics of multiphasic media (each phase and their interactions), using several up-scaling methods, in order to obtain an equivalent mesoscale medium defined by seven parameters. Thus, in simple porosity saturated media and in complex media (double porosity, patchy saturation, visco-poro-elasticity), I can compute seismic wave propagation without any approximation. Indeed, I use a frequency-space domain for the numerical method, which allows to consider all the frequency dependent terms. The spatial discretization employs a discontinuous finite elements method (discontinuous Galerkin), which allows to take into account complex interfaces.The computation of the seismic attributes (velocities and attenuations) of complex porous media shows strong variations in respect with the frequency. Waveforms, computed without approximation, are strongly different if we take into account the full description of the medium or an homogenisation by averages. The last part of this work deals with the poro-elastic parameters characterisation by inversion. For this, I develop a two-steps method: the first one consists in a classical inversion (tomography, full waveform inversion) of seismograms data to obtain macro-scale parameters (seismic attributes). The second step allows to recover, from the macro-scale parameters, the poro-elastic micro-scale properties. This down-scaling step
Sharma, Antara; Baruah, Santanu; Piccinini, Davide; Saikia, Sowrav; Phukan, Manoj K.; Chetia, Monisha; Kayal, J. R.
2017-10-01
We present crustal anisotropy estimates constrained by shear wave splitting (SWS) analysis using local earthquakes in the Shillong plateau and Assam valley area, North East India (NE India) region. Splitting parameters are determined using an automated cross-correlation (CC) method. We located 330 earthquakes recorded by 17 broadband seismic stations during 2001-2014 in the study area. Out of these 330 events, seismograms of 163 events are selected for the SWS analysis. Relatively small average delay times (0.039-0.084 s) indicate existence of moderate crack density in the crust below the study area. It is found that fast polarization directions vary from station to station depending on the regional stress system as well as geological conditions. The spatial pattern of crustal anisotropy in the area is controlled mostly by tectonic movement of the Indian plate towards NE. Presence of several E-W and N-S trending active faults in the area also play an important role on the observed pattern of crustal anisotropy.
Determination of S-wave slowness from a linear array of borehole receivers
Czech Academy of Sciences Publication Activity Database
Eisner, L.; Fischer, Tomáš; Rutledge, J. T.
2009-01-01
Roč. 176, č. 1 (2009), s. 31-39 ISSN 0956-540X Grant - others:EC(XE) MTKI-CT-2004-517242 Institutional research plan: CEZ:AV0Z30120515 Keywords : downhole methods * controlled source seismology * body waves * wave propagation Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.435, year: 2009
Margerin, L.; Campillo, M.; Van Tiggelen, B. A.; Hennino, R.
2009-05-01
the low-velocity structure, the drop of the energy ratios WS/WP and V2/H2 is controlled by the change of ellipticity of the Rayleigh wave and the large contribution of the fundamental Love mode. At higher frequencies, the interplay between Rayleigh and Love modes trapped in shallow low-velocity layers is responsible for the abrupt increase of the kinetic energy ratio V2/H2. Our study demonstrates that the partition of energy in the seismic coda contains information on the local geological structure.
Fu, Lei
2017-05-11
Full-waveform inversion of land seismic data tends to get stuck in a local minimum associated with the waveform misfit function. This problem can be partly mitigated by using an initial velocity model that is close to the true velocity model. This initial starting model can be obtained by inverting traveltimes with ray-tracing traveltime tomography (RT) or wave-equation traveltime (WT) inversion. We have found that WT can provide a more accurate tomogram than RT by inverting the first-arrival traveltimes, and empirical tests suggest that RT is more sensitive to the additive noise in the input data than WT. We present two examples of applying WT and RT to land seismic data acquired in western Saudi Arabia. One of the seismic experiments investigated the water-table depth, and the other one attempted to detect the location of a buried fault. The seismic land data were inverted by WT and RT to generate the P-velocity tomograms, from which we can clearly identify the water table depth along the seismic survey line in the first example and the fault location in the second example.
Petrov, P.; Newman, G. A.
2011-12-01
Recent developments in high resolution imaging technology of subsurface objects involves a combination of different geophysical measurements (gravity, EM and seismic). A joint image of the subsurface geophysical attributes (velocity, electrical conductivity and density) requires the consistent treatment of the different geophysical data due to their differing physical nature. For example, in conducting media, which is typical of the Earth's interior, EM energy propagation is defined by a diffusive mechanism and may be characterized by two specific length scales: wavelength and skin depth. However, the propagation of seismic signals is a multiwave process and is characterized by a set of wavelengths. Thus, to consistently treat seismic and electromagnetic data an additional length scale is needed for seismic data that does not directly depend on a wavelength and describes a diffusive process, similar to EM wave propagation in the subsurface. Works by Brown et al.(2005), Shin and Cha(2008), and Shin and Ha(2008) suggest that an artificial damping of seismic wave fields via Laplace-Fourier transformation can be an effective approach to obtain a seismic data that have similar spatial resolution to EM data. The key benefit of such transformation is that diffusive wave-field inversion works well for both data sets: seismic (Brown et al.,2005; Shin and Cha,2008) and electromagnetic (Commer and Newman,2008; Newman et al.,2010). With the recent interest in the Laplace-Fourier domain full waveform inversion, 3D fourth and second-order finite-difference schemes for modeling of seismic wave propagation have been developed (Petrov and Newman, 2010). Incorporation of attenuation and anisotropy into a velocity model is a necessary step for a more realistic description of subsurface media. Here we consider the extension of our method which includes attenuation and VTI anisotropy. Our approach is based on the integro-interpolation technique for velocity-stress formulation. Seven
Lay, T.; Yue, H.; Rivera, L. A.; Yamazaki, Y.; Cheung, K.; Bai, Y.; Li, L.; Hill, E.; Sieh, K.; Kongko, W.; Muhari, A.
2013-12-01
The 25 October 2010 Mentawai, Indonesia earthquake (Mw 7.8) ruptured the near-trench portion of the subduction zone seaward of the Mentawai islands, off-shore of Sumatra, generating 3 to 9 m tsunami run-up along the southwestern coasts of the Pagai Islands and taking at least 431 lives. The location of the main slip area varies in published models and is critical to the tsunami generation mechanism. We constrain the slip model using iterative modeling of high-rate (1 sample/s) GPS observations and teleseismic body wave signals, along with tsunami recordings at buoys and tide gauges. The hr-GPS data, from SuGAR network stations on the Mentawai Islands, recorded the complete ground displacement field produced by the earthquake. The closest station is located ~40 km from the hypocenter, with the time-varying (seismic) portion of the signal constraining the location of the slip. The near-field ground displacement data show a ramp-like initial phase followed by several short period strong oscillations, which suggests that the earthquake is primarily a tsunami earthquake that triggered abrupt subevents. Finite-fault models, inverted jointly from hr-GPS and teleseismic datasets, indicate that the main rupture area extends ~100 km along strike and ~50 km along dip, with a seismic moment of 8×10**21 Nm (Mw = 7.85). An isolated off-shore slip patch with large slip amplitude (~4 m) is apparent later in the rupture. This subevent radiated relatively short-period seismic energy detected in the hr-GPS data. It appears that local regions along the prism toe, perhaps associated with subducted plate bathymetry, can be strongly locked and rupture as a regular event, while most of the toe region has smoother rupture.
Balvantín, A J; Diosdado-De-la-Peña, J A; Limon-Leyva, P A; Hernández-Rodríguez, E
2018-02-01
In this work, fundamental symmetric Lamb wave S0 mode is characterized in terms of its velocity variation as function of the interfacial conditions between solid bodies in contact. Imperfect contact conditions are numerically and experimentally determined by using ultrasonic Lamb wave propagation parameters. For the study, an experimental system was used, formed by two solid aluminum rods (25.4mm in diameter) axially loading a thin aluminum plate to control contact interfacial stiffness. The axially applied load on the aluminum plate was varied from 0MPa to 10MPa. Experimental Lamb wave signals were excited on the plate through two longitudinal contact transducers (1MHz of central frequency) using a pitch-catch configuration. Numerical simulations of contact conditions and Lamb wave propagation were performed through Finite Element Analysis (FEA) in commercial software, ANSYS 15®. Simulated Lamb wave signals were generated by means of a 5 cycles tone burst signals with different frequency values. Results indicate a velocity change in both, experimental and simulated Lamb wave signals as function of the applied load. Finally, a comparison between numerical results and experimental measurements was performed obtaining a good agreement. Copyright © 2017 Elsevier B.V. All rights reserved.
International Nuclear Information System (INIS)
Nakanishi, K.K.; Sherman, N.W.
1982-09-01
Tectonic strain release affects both the amplitude and phase of seismic waves from underground nuclear explosions. Surface wave magnitudes are strongly affected by the component of tectonic strain release in the explosion. Amplitudes and radiation patterns of surface waves from explosions with even small tectonic components change magnitudes significantly and show a strong dependence on receiver locations. A thrust-slip source superimposed on an isotropic explosion can explain observed reversals in waveform at different azimuths and phase delays between normal and reversed Rayleigh waves. The mechanism of this reversal is due to the phase relationship between reasonable explosion and tectonic release sources. Spallation or an unusual source time function are not required. The observations of Shagan River events imply thrust-slip motion along faults in a northwest-southeast direction, which is consistent with regional tectonics
A mixed-grid finite element method with PML absorbing boundary conditions for seismic wave modelling
International Nuclear Information System (INIS)
Liu, Shaolin; Li, Xiaofan; Liu, Youshan; Wang, Wenshuai
2014-01-01
We have developed a mixed-grid finite element method (MGFEM) to simulate seismic wave propagation in 2D structurally complex media. This method divides the physical domain into two subdomains. One subdomain covering the major part of the physical domain is divided by regular quadrilateral elements, while the other subdomain uses triangular elements to correctly fit a rugged free surface topography. The local stiffness matrix of any quadrilateral element is identical and matrix-vector production is calculated using an element-by-element technique, which avoids assembling a huge global stiffness matrix. As only a few triangular elements exist in the subdomain containing the rugged free surface topography, the memory requirements for storing the assembled subdomain global stiffness matrix are significantly reduced. To eliminate artificial boundary reflections, the MGFEM is also implemented to solve the system equations of PML absorbing boundary conditions (PML ABC). The accuracy and efficiency of the MGFEM is tested in numerical experiments by comparing it with conventional methods, and numerical comparisons also indicate its tremendous ability to describe rugged surfaces. (paper)
International Nuclear Information System (INIS)
Chung, D.H.; Bernreuter, D.L.
1981-10-01
Attenuation is caused by geometric spreading and absorption. Geometric spreading is almost independent of crustal geology and physiographic region, but absorption depends strongly on crustal geology and the state of the earth's upper mantle. Except for very high frequency waves, absorption does not affect ground motion at distances less than about 25 to 50 km. Thus, in the near-field zone, the attenuation in the eastern United States is similar to that in the western United States. Beyond the near field, differences in ground motion can best be accounted for by differences in attenuation caused by differences in absorption. The stress drop of eastern earthquakes may be higher than for western earthquakes of the same seismic moment, which would affect the high-frequency spectral content. But we believe this factor is of much less significance than differences in absorption in explaining the differences in ground motion between the East and the West. The characteristics of strong ground motion in the conterminous United States are discussed in light of these considerations, and estimates are made of the epicentral ground motions in the central and eastern United States. (author)
Seismic excitation by space shuttles
Kanamori, H.; Mori, J.; Sturtevant, B.; Anderson, D.L.; Heaton, T.
1992-01-01
Shock waves generated by the space shuttles Columbia (August 13, 1989), Atlantis (April 11, 1991) and Discovery (September 18, 1991) on their return to Edwards Air Force Base, California, were recorded by TERRAscope (Caltech's broadband seismic network), the Caltech-U.S.G.S Southern California Seismic Network (SCSN), and the University of Southern California (USC) Los Angeles Basin Seismic Network. The spatial pattern of the arrival times exhibits hyperbolic shock fronts from which the path, velocity and altitude of the space shuttle could be determined. The shock wave was acoustically coupled to the ground, converted to a seismic wave, and recorded clearly at the broadband TERRAscope stations. The acoustic coupling occurred very differently depending on the conditions of the Earth's surface surrounding the station. For a seismic station located on hard bedrock, the shock wave (N wave) was clearly recorded with little distortion. Aside from the N wave, very little acoustic coupling of the shock wave energy to the ground occurred at these sites. The observed N wave record was used to estimate the overpressure of the shock wave accurately; a pressure change of 0.5 to 2.2 mbars was obtained. For a seismic station located close to the ocean or soft sedimentary basins, a significant amount of shock wave energy was transferred to the ground through acoustic coupling of the shock wave and the oceanic Rayleigh wave. A distinct topography such as a mountain range was found effective to couple the shock wave energy to the ground. Shock wave energy was also coupled to the ground very effectively through large man made structures such as high rise buildings and offshore oil drilling platforms. For the space shuttle Columbia, in particular, a distinct pulse having a period of about 2 to 3 seconds was observed, 12.5 s before the shock wave, with a broadband seismograph in Pasadena. This pulse was probably excited by the high rise buildings in downtown Los Angeles which were
A 1.8 trillion degrees-of-freedom, 1.24 petaflops global seismic wave simulation on the K computer
Tsuboi, Seiji
2016-03-01
We present high-performance simulations of global seismic wave propagation with an unprecedented accuracy of 1.2 s seismic period for a realistic three-dimensional Earth model using the spectral element method on the K computer. Our seismic simulations use a total of 665.2 billion grid points and resolve 1.8 trillion degrees of freedom. To realize these large-scale computations, we optimize a widely used community software code to efficiently address all hardware parallelization, especially thread-level parallelization to solve the bottleneck of memory usage for coarse-grained parallelization. The new code exhibits excellent strong scaling for the time stepping loop, that is, parallel efficiency on 82,134 nodes relative to 36,504 nodes is 99.54%. Sustained performance of these computations on the K computer is 1.24 petaflops, which is 11.84% of its peak performance. The obtained seismograms with an accuracy of 1.2 s for the entire globe should help us to better understand rupture mechanisms of devastating earthquakes.
Seismic Window Selection and Misfit Measurements for Global Adjoint Tomography
Lei, W.; Bozdag, E.; Lefebvre, M.; Podhorszki, N.; Smith, J. A.; Tromp, J.
2013-12-01
Global Adjoint Tomography requires fast parallel processing of large datasets. After obtaing the preprocessed observed and synthetic seismograms, we use the open source software packages FLEXWIN (Maggi et al. 2007) to select time windows and MEASURE_ADJ to make measurements. These measurements define adjoint sources for data assimilation. Previous versions of these tools work on a pair of SAC files---observed and synthetic seismic data for the same component and station, and loop over all seismic records associated with one earthquake. Given the large number of stations and earthquakes, the frequent read and write operations create severe I/O bottlenecks on modern computing platforms. We present new versions of these tools utilizing a new seismic data format, namely the Adaptive Seismic Data Format(ASDF). This new format shows superior scalability for applications on high-performance computers and accommodates various types of data, including earthquake, industry and seismic interferometry datasets. ASDF also provides user-friendly APIs, which can be easily integrated into the adjoint tomography workflow and combined with other data processing tools. In addition to solving the I/O bottleneck, we are making several improvements to these tools. For example, FLEXWIN is tuned to select windows for different types of earthquakes. To capture their distinct features, we categorize earthquakes by their depths and frequency bands. Moreover, instead of only picking phases between the first P arrival and the surface-wave arrivals, our aim is to select and assimilate many other later prominent phases in adjoint tomography. For example, in the body-wave band (17 s - 60 s), we include SKS, sSKS and their multiple, while in the surface-wave band (60 s - 120 s) we incorporate major-arc surface waves.
Alkhalifah, Tariq Ali
2016-12-17
The leading component of the high-frequency asymptotic description of the wavefield, given by the travel time, is governed by the eikonal equation. In anisotropic media, traveltime measurements from seismic experiments conducted along one surface cannot constrain the long-wavelength attribute of the medium along the orthogonal-to-the-surface direction, as anisotropy introduces an independent parameter controlling wave propagation in the orthogonal direction. Since travel times measured on the Earth\\'s surface in transversely isotropic media with a vertical symmetry axis are mainly insensitive to the absolute value of the anisotropic parameter responsible for relating these observations to depth δ, the travel time was perturbed laterally to investigate the traveltime sensitivity to lateral variations in δ. This formulation can be used to develop inversion strategies for lateral variations in δ in acoustic transversely isotropic media, as the surface-recorded data are sensitive to it even if the model is described by the normal moveout velocity and horizontal velocity, or the anellipticity parameter η. Numerical tests demonstrate the enhanced sensitivity of our data when the model is parameterised with a lateral change in δ.
Haines, S.S.; Pidlisecky, Adam; Knight, R.
2009-01-01
With the goal of improving the understanding of the subsurface structure beneath the Harkins Slough recharge pond in Pajaro Valley, California, USA, we have undertaken a multimodal approach to develop a robust velocity model to yield an accurate seismic reflection section. Our shear-wave reflection section helps us identify and map an important and previously unknown flow barrier at depth; it also helps us map other relevant structure within the surficial aquifer. Development of an accurate velocity model is essential for depth conversion and interpretation of the reflection section. We incorporate information provided by shear-wave seismic methods along with cone penetrometer testing and seismic cone penetrometer testing measurements. One velocity model is based on reflected and refracted arrivals and provides reliable velocity estimates for the full depth range of interest when anchored on interface depths determined from cone data and borehole drillers' logs. A second velocity model is based on seismic cone penetrometer testing data that provide higher-resolution ID velocity columns with error estimates within the depth range of the cone penetrometer testing. Comparison of the reflection/refraction model with the seismic cone penetrometer testing model also suggests that the mass of the cone truck can influence velocity with the equivalent effect of approximately one metre of extra overburden stress. Together, these velocity models and the depth-converted reflection section result in a better constrained hydrologic model of the subsurface and illustrate the pivotal role that cone data can provide in the reflection processing workflow. ?? 2009 European Association of Geoscientists & Engineers.
S/WAVES: The Radio and Plasma Wave Investigation on the STEREO Mission
Czech Academy of Sciences Publication Activity Database
Bougeret, J. L.; Goetz, K.; Kaiser, M. L.; Bale, S. D.; Kellogg, P. J.; Maksimovic, M.; Monge, N.; Monson, S. J.; Astier, P. L.; Davy, S.; Dekkali, M.; Hinze, J. J.; Manning, R. E.; Aguilar-Rodriguez, E.; Bonnin, X.; Briand, C.; Cairns, I. H.; Cattell, C. A.; Cecconi, B.; Eastwood, J.; Ergun, R. E.; Fainberg, J.; Hoang, S.; Huttunen, K. E. J.; Krucker, S.; Lecacheux, A.; MacDowall, R. J.; Macher, W.; Mangeney, A.; Meetre, C. A.; Moussas, X.; Nguyen, Q. N.; Oswald, T. H.; Pulupa, M.; Reiner, M. J.; Robinson, P. A.; Rucker, H.; Salem, c.; Santolík, Ondřej; Silvis, J. M.; Ullrich, R.; Zarka, P.; Zouganelis, I.
2008-01-01
Roč. 136, 1-4 (2008), s. 487-528 ISSN 0038-6308 Grant - others:NASA(US) NAS5-03076 Institutional research plan: CEZ:AV0Z30420517 Keywords : S/WAVES * STEREO * plasma waves * radio waves Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.372, year: 2008
Spinuso, Alessandro; Krause, Amy; Ramos Garcia, Clàudia; Casarotti, Emanuele; Magnoni, Federica; Klampanos, Iraklis A.; Frobert, Laurent; Krischer, Lion; Trani, Luca; David, Mario; Leong, Siew Hoon; Muraleedharan, Visakh
2014-05-01
The EU-funded project VERCE (Virtual Earthquake and seismology Research Community in Europe) aims to deploy technologies which satisfy the HPC and data-intensive requirements of modern seismology. As a result of VERCE's official collaboration with the EU project SCI-BUS, access to computational resources, like local clusters and international infrastructures (EGI and PRACE), is made homogeneous and integrated within a dedicated science gateway based on the gUSE framework. In this presentation we give a detailed overview on the progress achieved with the developments of the VERCE Science Gateway, according to a use-case driven implementation strategy. More specifically, we show how the computational technologies and data services have been integrated within a tool for Seismic Forward Modelling, whose objective is to offer the possibility to perform simulations of seismic waves as a service to the seismological community. We will introduce the interactive components of the OGC map based web interface and how it supports the user with setting up the simulation. We will go through the selection of input data, which are either fetched from federated seismological web services, adopting community standards, or provided by the users themselves by accessing their own document data store. The HPC scientific codes can be selected from a number of waveform simulators, currently available to the seismological community as batch tools or with limited configuration capabilities in their interactive online versions. The results will be staged out from the HPC via a secure GridFTP transfer to a VERCE data layer managed by iRODS. The provenance information of the simulation will be automatically cataloged by the data layer via NoSQL techonologies. We will try to demonstrate how data access, validation and visualisation can be supported by a general purpose provenance framework which, besides common provenance concepts imported from the OPM and the W3C-PROV initiatives, also offers
Apparent splitting of S waves propagating through an isotropic lowermost mantle
Parisi, Laura
2018-03-24
Observations of shear‐wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D” layer), based on differences in the arrival times of vertically (SV) and horizontally (SH) polarized shear waves. By computing waveforms at period > 6 s for a wide range of 1‐D and 3‐D Earth structures we illustrate that a time shift (i.e., apparent splitting) between SV and SH may appear in purely isotropic simulations. This may be misinterpreted as shear wave anisotropy. For near‐surface earthquakes, apparent shear wave splitting can result from the interference of S with the surface reflection sS. For deep earthquakes, apparent splitting can be due to the S‐wave triplication in D”, reflections off discontinuities in the upper mantle and 3‐D heterogeneity. The wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations.
Simulation of Collision Contacts among Disjoined Soil-Structure Bodies Under Seismic Motions
Wang, Ching-Jong
Structure bodies and surrounding soils in certain types of bridges and tunnels may be prone to collisions during earthquake. A dynamic system composed of discrete and finite elements is developed using explicit formulation for equations of motion, and nonlinearities in soils and at interfaces of disjoined regions are implemented. Time history solutions are carried out to examine the plastic deformation in soils as well as the integrity of structures. Two case studies are presented in which collisions among disjoined regions are anticipated in the event of extremely large earthquakes. Case one is based on a replica from a quake-stricken bridge, to illustrate that a backfill with moderate soil strength may be used as an energy-dissipating buffer to contain the shaken loose decks. The other case involves an underground subway station box with slurry walls alongside, to exemplify the seismic resistance of the dual-wall system.
International Nuclear Information System (INIS)
Masopust, R.
1983-01-01
The paper presents only the results related to the first part of the research program directed toward the development of engineering methods and computer programs for assessing the effects of travelling seismic waves on the response of nuclear power plant civil structures. Phenomena related to travelling seismic waves are briefly summarized on the basis of many foregoing studies. Two basic approximate methods - direct and indirect - currently being used in a dynamic analysis and taking structure-soil interaction and travelling wave effects into account are discussed as well. In the second part of the paper, the rigid or hybrid finite element model and method are proposed for this purpose. Both the structure and the soil are modelled not only by means of conventional deformable finite elements, but as well considerably using rigid finite elements in a single system. The hybrid finite element method proposed herein is basically the direct method which can efficiently simulate structure-soil interaction and travelling wave effects. The corresponding single finite element system has three differently discretizated subsystems: the structure, the near-field and the far-field of the soil. An accurate using of the rigid finite elements in the structure and in the far-field of the soil permits to reduce essentially the total number of degrees of freedom for all the system which is the most important advantage in comparison with the classical finite element modelling. (orig./HP)
Virtual source reflection imaging of the Socorro Magma Body, New Mexico, using a dense seismic array
Finlay, T. S.; Worthington, L. L.; Schmandt, B.; Hansen, S. M.; Bilek, S. L.; Aster, R. C.; Ranasinghe, N. R.
2017-12-01
The Socorro Magma Body (SMB) is one of the largest known actively inflating continental magmatic intrusions. Previous studies have relied on sparse instrument coverage to determine its spatial extent, depth, and seismic signature, which characterized the body as a thin sill with a surface at 19 km below the Earth's surface. However, over the last two decades, InSAR and magneto-telluric (MT) studies have shed new light on the SMB and invigorated the scientific debate of the spatial distribution and uplift rate of the SMB. We return to seismic imaging of the SMB with the Sevilleta Array, a 12-day deployment of approximately 800 vertical component, 10-Hz geophones north of Socorro, New Mexico above and around the estimated northern half of the SMB. Teleseismic virtual source reflection profiling (TVR) employs the free surface reflection off of a teleseismic P as a virtual source in dense arrays, and has been used successfully to image basin structure and the Moho in multiple tectonic environments. The Sevilleta Array recorded 62 teleseismic events greater than M5. Applying TVR to the data collected by the Sevilleta Array, we present stacks from four events that produced the with high signal-to-noise ratios and simple source-time functions: the February 11, 2015 M6.7 in northern Argentina, the February 19, 2015 M5.4 in Kamchatka, Russia, and the February 21, 2015 M5.1 and February 22, 2015 M5.5 in western Colombia. Preliminary results suggest eastward-dipping reflectors at approximately 5 km depth near the Sierra Ladrones range in the northwestern corner of the array. Further analysis will focus on creating profiles across the area of maximum SMB uplift and constraining basin geometry.
International Nuclear Information System (INIS)
Trichandi, Rahmantara; Yudistira, Tedi; Nugraha, Andri Dian; Zulhan, Zulfakriza; Saygin, Erdinc
2015-01-01
Ambient noise tomography is relatively a new method for imaging the shallow structure of the Earth subsurface. We presents the application of this method to produce a Rayleigh wave group velocity maps around the Merapi Volcano, Central Java. Rayleigh waves group velocity maps were reconstructed from the cross-correlation of ambient noise recorded by the DOMERAPI array which consists 43 broadband seismometers. In the processing stage, we first filtered the observation data to separatethe noise from the signal that dominated by the strong volcanic activities. Next, we cross-correlate the filtered data and stack to obtain the Green’s function for all possible station pairs. Then we carefully picked the peak of each Green’s function to estimate the dispersion trend and appliedMultiple Filter Technique to obtain the dispersion curve. Inter-station group velocity curvesare inverted to produceRayleigh wave group velocity maps for periods 1 to 10 s. The resulted Rayleigh group velocity maps show the interesting features around the Merapi Volcano which generally agree with the previous studies. Merapi-Lawu Anomaly (MLA) is emerged as a relatively low anomaly in our group velocity maps
Energy Technology Data Exchange (ETDEWEB)
Trichandi, Rahmantara, E-mail: rachmantara.tri@gmail.com [Geophysical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, 40132, Bandung (Indonesia); Yudistira, Tedi; Nugraha, Andri Dian [Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Zulhan, Zulfakriza [Earth Science Graduate Program, Faculty of Earth Science and Technology, Institut Teknologi Bandung, Bandung, 40132 (Indonesia); Saygin, Erdinc [Research School of Earth Sciences, The Australian National University, Canberra ACT 0200 (Australia)
2015-04-24
Ambient noise tomography is relatively a new method for imaging the shallow structure of the Earth subsurface. We presents the application of this method to produce a Rayleigh wave group velocity maps around the Merapi Volcano, Central Java. Rayleigh waves group velocity maps were reconstructed from the cross-correlation of ambient noise recorded by the DOMERAPI array which consists 43 broadband seismometers. In the processing stage, we first filtered the observation data to separatethe noise from the signal that dominated by the strong volcanic activities. Next, we cross-correlate the filtered data and stack to obtain the Green’s function for all possible station pairs. Then we carefully picked the peak of each Green’s function to estimate the dispersion trend and appliedMultiple Filter Technique to obtain the dispersion curve. Inter-station group velocity curvesare inverted to produceRayleigh wave group velocity maps for periods 1 to 10 s. The resulted Rayleigh group velocity maps show the interesting features around the Merapi Volcano which generally agree with the previous studies. Merapi-Lawu Anomaly (MLA) is emerged as a relatively low anomaly in our group velocity maps.
Laboratory measurements of P- and S-wave anisotropy in synthetic rocks by 3D printing
Kong, L.; Ostadhassan, M.; Tamimi, N.; Li, C.; Alexeyev, A.
2017-12-01
Synthetic rocks have been widely used to realize the models with controlled factors in rock physics and geomechanics experiments. Additive manufacturing technology, known as 3D printing, is becoming a popular method to produce the synthetic rocks as the advantages of timesaving, economics, and control. In terms of mechanical properties, the duplicability of 3D printed rock towards a natural rock has been studied whereas the seismic anisotropy still remains unknown as being the key factor in conducting rock physics experiments. This study utilized a 3D printer with gypsum as the ink to manufacture a series of synthetic rocks that have the shapes of octagonal prisms, with half of them printed from lateral and another half from the bottom. An ultrasonic investigation system was set up to measure the P- and S- wave velocities at different frequencies while samples were under dry conditions. The results show the impact of layered property on the P- and S- wave velocities. The measurement results were compared with the predicted results of Hudson model, demonstrating that the synthetic rock from 3D printing is a transverse isotropic model. The seismic anisotropy indicates that the availability of using 3D printed rocks to duplicate natural rocks for the purpose of recreating the experiments of rock physics. Future experiments will be performed on the dependence of seismic anisotropy on fracture geometry and density in 3D printed synthetic rocks.
Syracuse, E. M.; Zhang, H.; Maceira, M.
2017-10-01
We present a method for using any combination of body wave arrival time measurements, surface wave dispersion observations, and gravity data to simultaneously invert for three-dimensional P- and S-wave velocity models. The simultaneous use of disparate data types takes advantage of the differing sensitivities of each data type, resulting in a comprehensive and higher resolution three-dimensional geophysical model. In a case study for Utah, we combine body wave first arrivals mainly from the USArray Transportable Array, Rayleigh wave group and phase velocity dispersion data, and Bouguer gravity anomalies to invert for crustal and upper mantle structure of the region. Results show clear delineations, visible in both P- and S-wave velocities, between the three main tectonic provinces in the region. Without the inclusion of the surface wave and gravity constraints, these delineations are less clear, particularly for S-wave velocities. Indeed, checkerboard tests confirm that the inclusion of the additional datasets dramatically improves S-wave velocity recovery, with more subtle improvements to P-wave velocity recovery, demonstrating the strength of the method in successfully recovering seismic velocity structure from multiple types of constraints.
Tang, Qunshu; Hobbs, Richard; Zheng, Chan; Biescas, Berta; Caiado, Camila
2016-06-01
Marine seismic reflection technique is used to observe the strong ocean dynamic process of nonlinear internal solitary waves (ISWs or solitons) in the near-surface water. Analysis of ISWs is problematical because of their transient nature and limitations of classical physical oceanography methods. This work explores a Markov Chain Monte Carlo (MCMC) approach to recover the temperature and salinity of ISW field using the seismic reflectivity data and in situ hydrographic data. The MCMC approach is designed to directly sample the posterior probability distributions of temperature and salinity which are the solutions of the system under investigation. The principle improvement is the capability of incorporating uncertainties in observations and prior models which then provide quantified uncertainties in the output model parameters. We tested the MCMC approach on two acoustic reflectivity data sets one synthesized from a CTD cast and the other derived from multichannel seismic reflections. This method finds the solutions faithfully within the significantly narrowed confidence intervals from the provided priors. Combined with a low frequency initial model interpreted from seismic horizons of ISWs, the MCMC method is used to compute the finescale temperature, salinity, acoustic velocity, and density of ISW field. The statistically derived results are equivalent to the conventional linearized inversion method. However, the former provides us the quantified uncertainties of the temperature and salinity along the whole section whilst the latter does not. These results are the first time ISWs have been mapped with sufficient detail for further analysis of their dynamic properties.
Bouchaala, Fateh; Ali, Mohammed Y.; Farid, Asam
2014-07-01
The subsurface geology of Abu Dhabi in the United Arab Emirates is primarily composed of carbonate rocks. Such media are known to be highly heterogeneous. Very few studies have attempted to estimate attenuation in carbonate rocks. In Abu Dhabi no attenuation profile has been published. This study provides the first seismic wave attenuation profiles in Abu Dhabi using dense array of VSP data. We estimated three attenuation profiles: the apparent, the scattering, and the intrinsic attenuations. The apparent attenuation profile was computed using amplitude decay and spectral-ratio methods. The scattering attenuation profile was estimated using a generalized reflection-transmission matrix forward model. It is usually estimated from the sonic log, but to be more consistent with the apparent attenuation, we succeeded in this paper to estimate it from the VSP data. We subtracted the scattering attenuation from the apparent attenuation to deduce the intrinsic attenuation. The results of the study indicate that the scattering attenuation is significant compared to the published studies that are mainly based on clastic rocks. The high scattering attenuation can reach up to 0.02. It can be explained by the strong heterogeneity of the carbonate rocks. This study demonstrates that the Simsima and Rus Formations have considerable scattering and intrinsic attenuations. These formations are considered aquifers in Abu Dhabi; we therefore interpreted this high intrinsic attenuation zones to be due to the heterogeneity and to the fluids contained in these formations. The Umm-Er-Radhuma Formation is a more homogenous formation with limited aquifer potential. Hence, scattering and intrinsic attenuations of the Umm-Er-Radhuma Formation are low.
Bozdag, H.E.
2009-01-01
We have reached a stage in seismic tomography where further refinements with classical techniques become very difficult. Advances in numerical methods and computational facilities are providing new opportunities in seismic tomography to enhance the resolution of tomographic mantle images. 3-D
DEFF Research Database (Denmark)
Khan, A.; Koch, S.; Shankland, T. J.
2015-01-01
We present maps of the three-dimensional density (ρ), electrical conductivity (σ), and shear-wave speed (VS) structure of the mantle beneath Australia and surrounding ocean in the depth range of 100–800 km. These maps derived from stochastic inversion of seismic surface-wave dispersion data, ther...
Kenyon, P. M.; Orantes, E. J.; Grynewize, S.; Tedesco, M.
2016-12-01
The drainage of supraglacial lakes over the Greenland ice sheet has been shown to have a significant impact on ice dynamics and subglacial hydrology. As supraglacial lakes drain, they produce seismic waves that can be detected on both local and regional scales. Studying such waves and the originating phenomena has the potential to advance our understanding of the subglacial processes involved. Here we present the results of an analysis of high frequency seismic waves generated during the drainage of two supraglacial lakes in southwestern Greenland. The two lakes drained by contrasting mechanisms. One (Lake Half Moon) drained slowly by overflow into an existing moulin. Here GPS data, recorded during the drainage, show an increase in ice sheet velocity that begins well before the time of maximum lake depth. The other lake (Lake Ponting) drained suddenly by hydrofracture through the lake bed. In this case, the GPS data show an increase in velocity that is essentially simultaneous with the maximum lake depth. In both cases, vertical component seismograms were obtained from the Greenland Ice Sheet Monitoring Network (GLISN) for several hours before and after the lake drainage. Arrival times were picked manually, using the criterion that an arrival must have a minimum amplitude of twice the noise level. The arrivals were then plotted on graphs of time versus distance from the lake in question. Several linear trends are visible on each graph. The velocities calculated from the slopes of these trends are unexpectedly low. We suggest that one explanation for this might be that the waves are traveling in a layer of till at the base of the ice sheet, that forms a low velocity channel. When compared with GPS and lake depth data, the origin times of the waves coincide with the velocity increase in both cases. Therefore, we conclude that the waves are being generated by stick-slip processes involving the slippage of the ice sheet on an underlying layer of till.
Directory of Open Access Journals (Sweden)
Moikwathai Dax Moidaki
2014-02-01
Full Text Available A total of 93 well-defined PKS, 54 SKKS, and 126 SKS shear-wave splitting parameters are determined at 25 broadband seismic stations in an approximately 1000 by 1000 km2 area centered at the New Madrid seismic zone (NMSZ in order to test the existence of two anisotropic layers and to map the direction and strength of mantle fabrics. The individual splitting parameters suggest a significant and systematic spatial and azimuthal variation in the splitting parameters. The azimuthal variations at most stations can be explained as the results of present SW ward asthenospheric flow and NNE trending lithospheric fabrics formed during past orogenic events. In the NMSZ, rift-parallel fast directions (potentially related to a long-rift flow and rift-orthogonal fast directions from small-scale mantle convection are not observed. In addition, reduction in splitting times as a result of vertical asthenospheric flow is not observed.
Mengxuan, Zhong
2017-06-01
The gradient preconditioning algorithms based on Hessian matrices in time-domain full waveform inversion (FWI) are widely used now, but consume a lot of memory and do not fit the FWI of large models or actual seismic data well. To avoid the huge storage consumption, the gradient preconditioning approach based on seismic wave energy has been proposed it simulates the “approximated wave field” with the acoustic wave equation and uses the energy of the simulated wavefield to precondition the gradient. The method does not require computing and storing the Hessian matrix or its inverse and can effectively eliminate the effect caused by geometric diffusion and uneven illumination on gradient. The result of experiments in this article with field data from South China Sea confirms that the time-domain FWI using the gradient preconditioning based on seismic wave energy (GPWE) can achieve higher inversion accuracy for the deep high-velocity model and its underlying strata.
Directory of Open Access Journals (Sweden)
T. Maruyama
2016-02-01
Full Text Available The vertical ground motion of seismic surface waves launches acoustic waves into the atmosphere and induces ionospheric disturbances. Disturbances due to Rayleigh waves near the short-period Airy phase appear as wavy fluctuations in the virtual height of an ionogram and have a multiple-cusp signature (MCS when the fluctuation amplitude is increased. An extremely developed MCS was observed at Kazan, Russia, after the 2010 M 8.8 Chile earthquake. The ionogram exhibited steep satellite traces for which the virtual heights increased rapidly with frequency starting near the top of cusps and continuing for 0.1–0.2 MHz. This complicated ionogram was analyzed by applying a ray tracing technique to the radio wave propagation in the ionosphere that was perturbed by acoustic waves. Acoustic wavefronts were inclined by the effects of finite Rayleigh wave velocity and sound speed in the thermosphere. The satellite echo traces were reproduced by oblique returns from the inclined wavefronts, in addition to the nearly vertical returns that are responsible for the main trace.
Kochemasov, G. G.
2012-09-01
The wave planetology [1-3 & others] states that along with tectonic segmentation (dichotomy, 2πRs tructure) and s ectoring (πR-structure) cosmic bodies display tectonic granulations caused by warping waves lengths of which are inversely proportional to orbital frequencies. The warping waves (and their overtones) appear due to movements of all bodies in non-circular orbits with changing accelerations. Arising warping waves have stationary character and 4 crossing interfering directions (ortho- and diagonal, Fig. 1). Produced by this interference tectonic granules (craters) dispose themselves in grids, alignments, often spoiled by superposed impacts, but nevertheless distinguished in many cases. An alignment of square shaped craters shows their wave origin. Wave produced craters and ring forms must be taken out of the crater size-frequency statistics to make it real [3]. Below are some examples of the wave woven forms proving their ubiquities (Fig. 2- 10). Remark various classes of cosmic bodies.
Hartzell, Stephen; Leeds, Alena L.; Ramirez-Guzman, Leonardo; Allen, James P.; Schmitt, Robert G.
2016-01-01
Thirty‐two accelerometers were deployed in the Livermore Valley, California, for approximately one year to study sedimentary basin effects. Many local and near‐regional earthquakes were recorded, including the 24 August 2014 Mw 6.0 Napa, California, earthquake. The resulting ground‐motion data set is used to quantify the seismic response of the Livermore basin, a major structural depression in the California Coast Range Province bounded by active faults. Site response is calculated by two methods: the reference‐site spectral ratio method and a source‐site spectral inversion method. Longer‐period (≥1 s) amplification factors follow the same general pattern as Bouguer gravity anomaly contours. Site response spectra are inverted for shallow shear‐wave velocity profiles, which are consistent with independent information. Frequency–wavenumber analysis is used to analyze plane‐wave propagation across the Livermore Valley and to identify basin‐edge‐induced surface waves with back azimuths different from the source back azimuth. Finite‐element simulations in a 3D velocity model of the region illustrate the generation of basin‐edge‐induced surface waves and point out strips of elevated ground velocities along the margins of the basin.
Attenuation of S-waves in the lithosphere of the Sea of Crete according to OBS observations
Kovachev, S. A.; Kuzin, I. P.; Shoda, O. Yu.; Soloviev, S. L.
1991-11-01
Five OBS were installed in the Sea of Crete in 1987. During a period of nine days 430 local earthquakes were recorded. Hypocentres were determined for 85 microearthquakes. A correlation between magnitude ML and duration of seismic events on the records of the ocean bottom seismographs (OBS) was found from data of 14 shocks recorded simultaneously by OBS and some land-based Greek stations. A magnitude-frequency relationship for earthquakes recorded by OBS was obtained in the magnitude range ML = 2-4. Amplitude curves describing the attenuation of body waves in the lithosphere of the Sea of Crete were compiled. Assessment of quality factor Qs was made by comparison of empirical and theoretical amplitude curves. The values of Qs for the lithosphere of the Sea of Crete were calculated and found equal to 200-300. Low values of Qs and consequently strong attenuation of S-waves in the lithosphere of the Sea of Crete could be explained by extension of the lithosphere accompanied by its partial contamination with melted magma.
Study of Spectral Attenuation Laws of Seismic Waves for Michoacán state, México
Vazquez Rosas, R.; Aguirre, J.; Mijares Arellano, H.
2009-12-01
Several attenuation relationships have been developed for Mexico, mostly after the earthquake of September 19, 1985, an event that gave great impetus to the development of engineering seismology in Mexico. Since 1985, the number of seismic stations in the country has increased significantly, especially between the Coast of Guerrero and Mexico City. This is due to the infamous large amplifications observed in the lake area of Mexico City with respect to hard ground sites. Some studies have analyzed how seismic waves are attenuated or amplified from the Pacific Coast toward the inland. The attenuation relationship used for seismic hazard assessment in Mexico is that of Ordaz (1989), which uses data from the Guerrero acceleration network. Another recent study is that of García et al. (2005), which uses more recent data from intraplate earthquakes recorded at the Guerrero acceleration network. It is important to note that, since these relations were derived for only part of the Mexican subduction zone and for certain types of seismic sources, caution should be exercised when using them for earthquake risk studies in other regions of Mexico. In the present work, we study the state of Michoacán, one of the most important seimogenic zones in Mexico. Three kinds of sources exist in the state, producing tectonic earthquakes, volcanic earthquakes, and events due to local faults in the region. For this reason, it is of vital importance to study the propagation of seismic waves within Michoacán state, and in this paper in particular we study their attenuation. We installed a temporary network consisting of 7 accelerograph stations across the state, at the following locations: Faro de Brucerías, Aguililla, Apatzingán, Taretán, Pátzcuaro, Morelia, and Maravatío. The stations form a line that is perpendicular to the coastline and has a total length of 366 km, while the distance between neighboring stations varies from 60 to 80 km. Among all the seismic events recorded at
InSight detection of a Lithospheric Low Seismic Velocity Zone in Mars
Zheng, Y.; Nimmo, F.; Lay, T.
2014-12-01
Most seismological models for the interior of Mars lack an upper mantle low velocity zone. However, there is expected to be a large thermal gradient across the stagnant conductive lid (lithosphere) of Mars. This gradient should tend to decrease elastic wave velocities with increasing depth, with this effect dominating the opposing tendency caused by increasing pressure with depth because Mars has low gravity. An upper mantle lithosphere with a low velocity zone (LVZ) beneath a thin high velocity "seismic lid" is thus predicted. The upcoming NASA InSight mission includes a three-component seismometer, which should provide the first opportunity to directly detect any lithospheric LVZ in Mars. Seismic wavefields expected for Mars mantle velocity structures with or without a strong LVZ are very distinct and may be distinguished by observing a modest number of seismic sources at different epicentral ranges. The LVZ models predict shadow zones for high-frequency seismic body wave phases such as P, S, PP and SS, etc. The most diagnostic waves that can be used to evaluate presence of a lithospheric LVZ given a single seismometer are intermediate period surface waves, which travel along the great circle from a seismic source to the seismometer along both minor- and (if the source is large enough) major-arc directions. An LVZ produces distinctive dispersion, with a Rayleigh wave Airy phase around 100 s period and very different surface wave seismograms compared to a model with no LVZ. Even a single observation of long-period surface waves from a known range can be diagnostic of the lithospheric structure. Establishing the existence of an LVZ has major implications for thermal evolution, volatile content and internal dynamics of the planet.
Statics correction methods for 3D converted-wave (PS) seismic reflection
Strong, Shaun; Hearn, Steve
2017-04-01
One of the most difficult steps in the PS processing sequence is estimation of the S-wave receiver statics. This process is particularly important at the coal scale, due to the need for higher frequency content (better resolution). We present an analysis of three approaches for estimating 3D PS statics. These include a surface-consistent inversion algorithm (analogous to the residual-statics method used in conventional P-wave processing), PPS refraction statics, and a so-called robust statistical method. This analysis is achieved through the use of synthetic models, and a coal-scale 3D-3C survey acquired in the Bowen Basin. The presented datasets demonstrate that the surface-consistent inversion method can become unstable in certain environments. This is likely due to parameter leakage between receiver and structural terms, caused by the highly asymmetric nature of the shallow PS reflection paths. The robust statistical method appears reliable for determination of short-wavelength receiver statics, and hence is useful for continuity enhancement. The PPS refraction approach can provide both short-wavelength and long-wavelength solutions, provided the PPS arrivals can be picked reliably. As with P-wave analysis, a combination of algorithms may provide the most effective production tool for determination of PS receiver statics.
On seismic response characteristics of floating nuclear plant barge, (1)
International Nuclear Information System (INIS)
Hagiwara, Yutaka; Masuko, Yoshio; Nakamura, Shuuji; Matsuura, Shinichi; Shiojiri, Hiroo
1986-01-01
Since Floating Nuclear Plants (FNP) are considered to be isolated from horizontal seismic motion, reduction and standardization of the aseismic design conditions of the floating plants are anticipated. However, studies on FNP in closed and shallow basin have almost not been executed to data, and there are many problems remaining unsolved. The purpose of the present report is to obtain sufficient elementary data and materials on the seismic response of floating body in the closed and shallow basin. Some interesting points to be extracted from shaking table tests, finite element analyses and simplified analyses are summarized as follows: 1) The seismic isolation characteristics of the floating body are remarkable to short period horizontal seismic motion. 2) Resonances of the floating body's motion, which coupled with surface waves, are induced by long period horizontal seismic motion. 3) Vertical seismic motion is transmitted directly to the floating body. (author)
Liang, C.; Prochnow, B. N.; OReilly, O. J.; Dunham, E. M.; Karlstrom, L.
2016-12-01
Oscillation of magma in volcanic conduits connected to cracks (dikes and sills) has been suggested as an explanation for very long period (VLP) seismic signals recorded at active basaltic volcanoes such as. Kilauea, Hawaii, and Erebus, Antarctica. We investigate the VLP seismicity using a linearized model for waves in and associated eigenmodes of a coupled conduit-crack system filled with multiphase magma, an extension of the Karlstrom and Dunham (2016) model for acoustic-gravity waves in volcanic conduits. We find that the long period surface displacement (as recorded on broadband seismometers) is dominated by opening/closing of the crack rather than the deformation of the conduit conduit walls. While the fundamental eigenmode is sensitive to the fluid properties and the geometry of the magma plumbing system, a closer scrutiny of various resonant modes reveals that the surface displacement is often more sensitive to higher modes. Here we present a systematic analysis of various long period acoustic-gravity wave resonant modes of a coupled conduit-crack system that the surface displacement is most sensitive to. We extend our previous work on a quasi-one-dimensional conduit model with inviscid magma to a more general axisymmetric conduit model that properly accounts for viscous boundary layers near the conduit walls, based on the numerical method developed by Prochnow et al. (submitted to Computers and Fluids, 2016). The surface displacement is dominated by either the fundamental or higher eigenmodes, depending on magma properties and the geometry of conduit and crack. An examination of the energetics of these modes reveals the complex interplay of different restoring forces (magma compressibility in the conduit, gravity, and elasticity of the crack) driving the VLP oscillations. Both nonequilibrium bubble growth and resorption and viscosity contribute to the damping of VLP signals. Our models thus provide a means to infer properties of open-vent basaltic volcanoes
Observations of exotic inner core waves
Waszek, Lauren; Deuss, A.F.
2015-01-01
The seismic structure of Earth’s inner core is highly complex, displaying strong anisotropy and further regional variations. However, few seismic waves are sensitive to the inner core and fundamental questions regarding the origin of the observed seismic features remain unanswered. Thus, new
Elastic-Wavefield Seismic Stratigraphy: A New Seismic Imaging Technology
Energy Technology Data Exchange (ETDEWEB)
Bob A. Hardage; Milo M. Backus; Michael V. DeAngelo; Sergey Fomel; Khaled Fouad; Robert J. Graebner; Paul E. Murray; Randy Remington; Diana Sava
2006-07-31
The purpose of our research has been to develop and demonstrate a seismic technology that will provide the oil and gas industry a better methodology for understanding reservoir and seal architectures and for improving interpretations of hydrocarbon systems. Our research goal was to expand the valuable science of seismic stratigraphy beyond the constraints of compressional (P-P) seismic data by using all modes (P-P, P-SV, SH-SH, SV-SV, SV-P) of a seismic elastic wavefield to define depositional sequences and facies. Our objective was to demonstrate that one or more modes of an elastic wavefield may image stratal surfaces across some stratigraphic intervals that are not seen by companion wave modes and thus provide different, but equally valid, information regarding depositional sequences and sedimentary facies within that interval. We use the term elastic wavefield stratigraphy to describe the methodology we use to integrate seismic sequences and seismic facies from all modes of an elastic wavefield into a seismic interpretation. We interpreted both onshore and marine multicomponent seismic surveys to select the data examples that we use to document the principles of elastic wavefield stratigraphy. We have also used examples from published papers that illustrate some concepts better than did the multicomponent seismic data that were available for our analysis. In each interpretation study, we used rock physics modeling to explain how and why certain geological conditions caused differences in P and S reflectivities that resulted in P-wave seismic sequences and facies being different from depth-equivalent S-wave sequences and facies across the targets we studied.
Investigating Near Surface S-Wave Velocity Properties Using Ambient Noise in Southwestern Taiwan
Directory of Open Access Journals (Sweden)
Chun-Hsiang Kuo
2015-01-01
Full Text Available Ambient noise is typically used to estimate seismic site effects and velocity profiles instead of earthquake recordings, especially in areas with limited seismic data. The dominant Horizontal to Vertical Spectral Ratio (HVSR frequency of ambient noise is correlated to Vs30, which is the average S-wave velocity in the top 30 m. Vs30 is a widely used parameter for defining seismic amplification in earthquake engineering. HVSR can detect the vertical discontinuity of velocities, that is, the interfaces between hard bedrock and soft sediments. In southwestern Taiwan most strong motion stations are located in the plains and show a dominant frequency lower than 3 Hz. Several stations near the coast have low dominant frequencies of less than 1 Hz. The dominant frequencies are higher than 4 Hz at piedmont stations. The stations in the mountains with dominant frequencies over 8 Hz are typically located on very hard sites. This study analyzed the HVSR characteristics under different seismic site conditions considering the Vs30 from previous study (Kuo et al. 2012. The result implies that HVSRs are a better tool than Vs30 to classify the sites where bedrock is deeper than 30 m. Furthermore, we found a linear correlation between Vs30 and dominant HVSR frequency which could be used as a proxy of Vs30. The Vs30 map in this area was derived using the Engineering Geological Database for Taiwan Strong Motion Instrumentation Program (EGDT. The comparable distribution pattern between the dominant frequency and Vs30 demonstrate that HVSR can recognize S-wave velocity properties at the shallow subsurface.
S-Wave Velocity Structure of the Puli Basin, Taiwan, Using the Array Records of Microtremors
Wu, C.; Huang, H.
2009-12-01
The September 21, 1999 Chi-Chi earthquake induced strong shaking, resulting in severe damage in the Puli area. According to Huang and Tarng (2005), the collapse of many structures during the earthquake was very closely related to the site effects. The Shallow Shear-wave velocities have widely been used for earthquake ground-motion site characterization. Thus, the S-wave velocity structures of the Puli area are investigated using the array records of microtremors at 16 sites. The dispersion curves at these sites are calculated using the F-K method (Capon, 1969); then, the S-wave velocity structures at the Puli area are estimated by employing the surface wave inversion technique (Herrmann, 1991). If the S-wave velocity of bedrock is assumed to be 2000m/sec, the depths of the alluvium at the Puli area are between 360m (ZHO) and 810m (AIL, DAH). Besides, there are 3~4 distinct interfaces in the shallow velocity structure (0~1000m). The depth of the alluvium gradually increases from east to west and the deepest one appears at stations AIL and DAH. The results in this study are similar to those using the seismic exploration method (Wang et al., 2003; Huang, 2008) in the Puli area and the well-logging method at LAC.
Effects of body mass index on gastric slow wave: a magnetogastrographic study
International Nuclear Information System (INIS)
Somarajan, S; Cassilly, S; Obioha, C; Bradshaw, L A; Richards, W O
2014-01-01
We measured gastric slow wave activity simultaneously with magnetogastrogram (MGG), mucosal electromyogram (EMG) and electrogastrogram (EGG) in human subjects with varying body mass index (BMI) before and after a meal. In order to investigate the effect of BMI on gastric slow wave parameters, each subject's BMI was calculated and divided into two groups: subjects with BMI ≤ 27 and BMI > 27. Signals were processed with Fourier spectral analysis and second-order blind identification (SOBI) techniques. Our results showed that increased BMI does not affect signal characteristics such as frequency and amplitude of EMG and MGG. Comparison of the postprandial EGG power, on the other hand, showed a statistically significant reduction in subjects with BMI > 27 compared with BMI ≤ 27. In addition to the frequency and amplitude, the use of SOBI-computed propagation maps from MGG data allowed us to visualize the propagating slow wave and compute the propagation velocity in both BMI groups. No significant change in velocity with increasing BMI or meal was observed in our study. In conclusion, multichannel MGG provides an assessment of frequency, amplitude and propagation velocity of the slow wave in subjects with differing BMI categories and was observed to be independent of BMI. (paper)
Seismic signal and noise on Europa and how to use it
Panning, M. P.; Stähler, S. C.; Bills, B. G.; Castillo, J.; Huang, H. H.; Husker, A. L.; Kedar, S.; Lorenz, R. D.; Pike, W. T.; Schmerr, N. C.; Tsai, V. C.; Vance, S.
2017-12-01
Seismology is one of our best tools for detailing interior structure of planetary bodies, and a seismometer is included in the baseline and threshold mission design for a potential Europa lander mission. Guiding mission design and planning for adequate science return, though, requires modeling of both the anticipated signal and noise. Assuming ice seismicity on Europa behaves according to statistical properties observed in Earth catalogs and scaling cumulative seismic moment release to the moon, we simulate long seismic records and estimate background noise and peak signal amplitudes (Panning et al., 2017). This suggests a sensitive instrument comparable to many broadband terrestrial instruments or the SP instrument from the InSight mission to Mars will be able to record signals, while high frequency geophones are likely inadequate. We extend this analysis to also begin incorporation of spatial and temporal variation due to the tidal cycle, which can help inform landing site selection. We also begin exploration of how chaotic terrane at the bottom of the ice shell and inter-ice heterogeneities (i.e. internal melt structures) may affect predicted seismic observations using 2D numerical seismic simulations. We also show some of the key seismic observations to determine interior properties of Europa (Stähler et al., 2017). M. P. Panning, S. C. Stähler, H.-H. Huang, S. D. Vance, S. Kedar, V. C. Tsai, W. T. Pike, R. D. Lorenz, "Expected seismicity and the seismic noise environment of Europa," J. Geophys. Res., in revision, 2017. S. C. Stähler, M. P. Panning, S. D. Vance, R. D. Lorenz, M. van Driel, T. Nissen-Meyer, S. Kedar, "Seismic wave propagation in icy ocean worlds," J. Geophys. Res., in revision, 2017.
Seismic loads on tunnels and buried pipelines
International Nuclear Information System (INIS)
Ionita, M.V.; Volpe, F.; Castellani, A.
1983-01-01
In soil dynamics analysis under earthquake excitation it is an accepted procedure to assume that: a) the free field seismic waves propagate vertically as plane waves; b) the soil local or 'intrinsic' dissipation is represented by a viscous damping, the constant ranging from 0.05 to 0.1 relative to the critical one; c) a horizontal rigid bedrock is present at a depth of the order of some embedment lengths. The paper shows that the above assumptions are not always at the safe side when a long span embedded structures is concerned. In particular, body waves - P or S - propagating both vertically and horizontally may provide larger loads than a vertically propagating wave does. Besides, for the same free field surface motion, higher damping values of soil will result in higher earth pressures. On the other hand, the hypothesis of the presence of a rigid bedrock may overestimate the seismic effects. Therefore a soil dynamic model was developed allowing to remove the assumptions (a), (b) and (c) above. It works in time domain, and plane geometry. A lumped parameter model was also developed to the same purpose. Typical results are shown. (orig./HP)
Rayleigh-wave Tomography and Seismic Anisotropic Structures in the Region of the Philippine Sea
Lee, Hsin-Yu; Legendre, Cédric P.; Chang, Emmy T. Y.
2016-04-01
The Philippine Sea Plate (PSP) is surrounded by convergent boundaries, the Pacific plate is subducting beneath the PSP along the Izu-Bonin and Mariana trenches at the east, whereas the PSP is subducting beneath the Eurasian plate along the Nankai trough, Ryukyu trench and Philippine trench at the west. The PSP can be divided by three oceanic basins: the oldest West Philippine basin developing in 35-45 Ma in the west, and the Shikoku and Parece Vela basins in 15-30 Ma in the east. Previous studies show a large variety of the seismic anisotropy structures in the region of the PSP, which correspond different scenarios of tectonic evolution for this area. In this study, we analyze both isotropic and anisotropic Rayleigh-wave velocity structures of the PSP by means of two-station method. The earthquakes of magnitude (Mw) greater than 5.0 in-between the years 1998-2014 were acquired. Totally, 7914 teleseismic events are adopted to form the measurements of Rayleigh-wave dispersion curves along 467 station-pairs over the PSP. The measured dispersion curves are then inverted into the isotropic and azimuthally anisotropic (2ψ) velocity maps at different periods with the damped, lateral smoothing LSQR inversion. The inversion is framed by the triangular grids which knots are of 200 km spacing. The consequent velocity anomalies are referenced to the average of the phase velocity at the periods between 50 and 100 seconds. The resulting velocity anomalies show a consistent pattern with the locations of the sub-basins in the PSP at the periods of 50 and 60 sec, which can be considered to be the association of lithospheric velocity structure with basin ages. The positive velocity anomalies are seen in the West Philippine basin associating the relatively old lithosphere; whereas the negative anomalies are found in the Shikoku and Parece Vela basins which the lithospheric structures are relatively young. On the other hand, the resultant azimuthal anisotropy reveals an apparent
Validation of a Wave-Body Interaction Model by Experimental Tests
DEFF Research Database (Denmark)
Ferri, Francesco; Kramer, Morten; Pecher, Arthur
2013-01-01
Within the wave energy field, numerical simulation has recently acquired a worldwide consent as being a useful tool, besides physical model testing. The main goal of this work is the validation of a numerical model by experimental results. The numerical model is based on a linear wave-body intera......-body interaction theory, applied for a point absorber wave energy converter. The results show that the ratio floater size/wave amplitude is a key parameter for the validity of the applied theory....
Czech Academy of Sciences Publication Activity Database
Plomerová, Jaroslava; Vecsey, Luděk; Babuška, Vladislav
2012-01-01
Roč. 564-565, Sep 5 (2012), s. 38-53 ISSN 0040-1951 R&D Projects: GA AV ČR IAA300120709; GA ČR GA205/07/1088 Institutional research plan: CEZ:AV0Z30120515 Keywords : lithospheric mantle * seismic anisotropy of body waves * joint inversion * 3D self-consistent models * domains of fossil anisotropy Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.684, year: 2012
Seismic anisotropy - a key to resolve fabrics of mantle lithosphere of Fennoscandia
Czech Academy of Sciences Publication Activity Database
Plomerová, Jaroslava; Babuška, Vladislav; Kozlovskaya, E.; Vecsey, Luděk; Hyvönen, L. T.
2008-01-01
Roč. 462, č. 1-4 (2008), s. 125-136 ISSN 0040-1951 R&D Projects: GA AV ČR IAA3012405; GA AV ČR IAA300120709 Institutional research plan: CEZ:AV0Z30120515 Keywords : seismic anisotropy * body waves * mantle lithosphere * lithospheric thickness * early plate tectonics Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.677, year: 2008
Numerical simulation of wave-induced fluid flow seismic attenuation based on the Cole-Cole model.
Picotti, Stefano; Carcione, José M
2017-07-01
The acoustic behavior of porous media can be simulated more realistically using a stress-strain relation based on the Cole-Cole model. In particular, seismic velocity dispersion and attenuation in porous rocks is well described by mesoscopic-loss models. Using the Zener model to simulate wave propagation is a rough approximation, while the Cole-Cole model provides an optimal description of the physics. Here, a time-domain algorithm is proposed based on the Grünwald-Letnikov numerical approximation of the fractional derivative involved in the time-domain representation of the Cole-Cole model, while the spatial derivatives are computed with the Fourier pseudospectral method. The numerical solution is successfully tested against an analytical solution. The methodology is applied to a model of saline aquifer, where carbon dioxide (CO 2 ) is injected. To follow the migration of the gas and detect possible leakages, seismic monitoring surveys should be carried out periodically. To this aim, the sensitivity of the seismic method must be carefully assessed for the specific case. The simulated test considers a possible leakage in the overburden, above the caprock, where the sandstone is partially saturated with gas and brine. The numerical examples illustrate the implementation of the theory.
Niu, F.
2011-12-01
China is a country with high levels of seismic activity, and has a history of strong earthquakes that caused great loss in both life and property. While it is generally believed that the high seismicity is the result of the prolonged collision between India and Eurasia plates in the west, and the continuous rollback of the Pacific subduction in the east, there are, however, no quantitative explanations on the distribution of the observed seismicity. In this study, we intend to seek a possible relationship between the seismicity and lithospheric structure at large scale (~100km). We developed a new method that uses ScS reverberation data from deep earthquakes to image the lithosphere and asthenosphere boundary (LAB). More specifically, we used more than 600 CEArray records (The CEArray consists of 31 regional networks operated by the China Earthquake Administration (CEA)) from a large deep earthquake occurring beneath the Sea of Okhotsk on July 5 of 2008. Multiple reflections of SH waves between the free surface and the core-mantle boundary (ScS1, ScS2, ScS3) can be clearly identified from all the individual records. We used the upperside reflections at the LAB (ScSm_SdS), which arrive after the main ScS multiples (ScSm), to estimate the depth of the boundary. We employed a common-reflection-point (CRP) stacking technique to the ScS reverberation data to enhance the signal-to-noise ratio (SNR) of the LAB reflections. At an assuming LAB depth, d, for each source-receiver pair, we first computed the reflection points of ScSm_SdS and the time moveouts of the ScSm_SdS with respect to ScSm by ray tracing the iasp91 velocity model. We further included corrections computed from 3D crustal and mantle velocity models. We divided the study area (18°N to 54°N, 75°E to 134°E) into meshed grid of 1° by 1°, and used a circular cap with a radius of 1 degree for gathering the ScS reverberations. We then summed all the reverberation data within a 0.5 s window centered on the
Directory of Open Access Journals (Sweden)
P. Alfaro
2012-12-01
Full Text Available A ~1000 m^{3} rockslide occurred close to Lorca (SE Spain during the main shock (M_{w} = 5.1 of the May 2011 seismic sequence. The location of the rockslide, within 10 km of the earthquake epicenter and along the southern slope of a valley in which similar geological conditions occur on both slopes of the valley, suggests a significant near-field effect due to local seismic response. This could be related to the specific interaction between the topography and the obliquely propagating seismic waves.
A dynamic stress strain numerical model was constructed using the FLAC 7.0 finite difference code to back analyze the Lorca rockslide event and relate its occurrence to both the local seismic amplification and the interaction between seismic waves and local topography. The results indicate that only for seismic waves with incidence angles in the range 0°–50° are the occurred slope instabilities expected. These results do not significantly change when varying the values for either stiffness or strength parameters within the range of the experimental data.
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.
U.S. Nuclear Regulatory Commission seismic regulations, research, and emerging trends
Energy Technology Data Exchange (ETDEWEB)
Chokshi, N.C.; Shao, L.C. [Nuclear Regulatory Commission, Washington, DC (United States). Office of Nuclear Regulatory Research; Apostolakis, G.
1997-03-01
Historically in the United States, seismic issues have played an important role in determining site suitability and, in some cases, have determined the ultimate fate of power plants. During the late 1960s and early 1970s, a seismic design philosophy evolved as the licensing of the earlier plants was in progress. Concepts such as the Safe Shutdown Earthquake (SSE) and the Operating Basis Earthquake (OBE) emerged and were codified into the federal regulations with the publication in December 1973 of Appendix A, `Seismic and Geologic Siting Criteria for Nuclear Power Plants,` to 10 CFR Part 100, `Reactor Site Criteria.` Seismic considerations are also important in siting and design of other fuel cycle and waste facilities. In this paper, a brief overview of the current seismic siting and design regulations are described along with some recent and planned changes based on the past experience, advancement in the state-of-the-art, and research results. In particular, the recently revised siting rule and use of the probabilistic seismic hazard analysis in implementation of the rule will be described in more detail. The paper includes discussion of some recent seismic issues and research activities, including issues related to aging. Some emerging trends are highlighted. In particular, the paper focuses on use of `expert opinion` in the probabilistic analysis and risk informed regulations and their implications to the seismic design. An additional focus is on international cooperative programs and how to initiate such programs such that better use can be made of limited resources to resolve issues of common interest. (author)
U.S. Nuclear Regulatory Commission seismic regulations, research, and emerging trends
International Nuclear Information System (INIS)
Chokshi, N.C.; Shao, L.C.; Apostolakis, G.
1997-01-01
Historically in the United States, seismic issues have played an important role in determining site suitability and, in some cases, have determined the ultimate fate of power plants. During the late 1960s and early 1970s, a seismic design philosophy evolved as the licensing of the earlier plants was in progress. Concepts such as the Safe Shutdown Earthquake (SSE) and the Operating Basis Earthquake (OBE) emerged and were codified into the federal regulations with the publication in December 1973 of Appendix A, 'Seismic and Geologic Siting Criteria for Nuclear Power Plants,' to 10 CFR Part 100, 'Reactor Site Criteria.' Seismic considerations are also important in siting and design of other fuel cycle and waste facilities. In this paper, a brief overview of the current seismic siting and design regulations are described along with some recent and planned changes based on the past experience, advancement in the state-of-the-art, and research results. In particular, the recently revised siting rule and use of the probabilistic seismic hazard analysis in implementation of the rule will be described in more detail. The paper includes discussion of some recent seismic issues and research activities, including issues related to aging. Some emerging trends are highlighted. In particular, the paper focuses on use of 'expert opinion' in the probabilistic analysis and risk informed regulations and their implications to the seismic design. An additional focus is on international cooperative programs and how to initiate such programs such that better use can be made of limited resources to resolve issues of common interest. (author)
The correlation between the amplitude of Osborn wave and core body temperature.
Omar, Hesham R; Camporesi, Enrico M
2015-08-01
Several reports illustrate an inverse correlation between the Osborn wave (J wave) amplitude and core body temperature. We attempted to study the strength of this correlation. We reviewed all articles reporting hypothermic J waves from 1950-2014 for patient demographics, core body temperature in Celsius (°C), amplitude of the J wave in millimeters (mm), lead with the highest amplitude of J wave, presence of acidosis, PO2, electrolytes and outcome. In cases with more than one electrocardiogram (ECG), the respective core body temperature and J wave amplitude of each ECG were recorded. The main study outcome is to evaluate the correlation between the J wave amplitude and core body temperature in the admission ECG. We have also examined the strength of this relationship in cases with more than one ECG. We attempted to find the most frequent lead that recorded the highest amplitude of the J wave in addition to the correlation between the amplitude of J wave and pH. We found 64 articles comprising a total of 68 cases. When analyzing only cases with more than one reported ECG, there was a strong inverse correlation (r = - 0.682, ptemperature: however, when analyzing admission ECG of all cases, the correlation was only moderate (r = - 0.410, ptemperature. © The European Society of Cardiology 2014.
Basin amplification of seismic waves in the city of Pahrump, Nevada.
Energy Technology Data Exchange (ETDEWEB)
Abbott, Robert E.
2005-07-01
Sedimentary basins can increase the magnitude and extend the duration of seismic shaking. This potential for seismic amplification is investigated for Pahrump Valley, Nevada-California. The Pahrump Valley is located approximately 50 km northwest of Las Vegas and 75 km south of the Nevada Test Site. Gravity data suggest that the city of Pahrump sits atop a narrow, approximately 5 km deep sub-basin within the valley. The seismic amplification, or ''site effect'', was investigated using a combination of in situ velocity modeling and comparison of the waveforms and spectra of weak ground motion recorded in the city of Pahrump, Nevada, and those recorded in the nearby mountains. Resulting spectral ratios indicate seismic amplification factors of 3-6 over the deepest portion of Pahrump Valley. This amplification predominantly occurs at 2-2.5 Hz. Amplification over the deep sub-basin is lower than amplification at the sub-basin edge, location of the John Blume and Associates PAHA seismic station, which recorded many underground nuclear tests at the Nevada Test Site. A comprehensive analysis of basin amplification for the city of Pahrump should include 3-D basin modeling, due to the extreme basement topography of the Pahrump Valley.
Zaroli, C.; Nolet, G.; Charlety, J.; Debayle, E.; Sambridge, M.
2011-12-01
To better constrain the structure of the Earth's interior, new theoretical developments on seismic wave propagation have emerged in recent years, and received increasing attention in global tomography. A recent focus has been to take into account the "Finite-Frequency" (FF) behaviour of seismic waves (e.g. wavefront-healing). We have chosen to use the FF approach by Dahlen et al. (2000) in multiple frequency bands, based on a ray-Born approximation, also known as Multiple-Frequency Tomography (MFT). The principle of MFT is to invert delay times measured in several frequency bands, using 3-D FF sensitivity kernels for modeling single-scattering phenomena undergone by seismic waves. Such FF effects are intrinsically always present in delay times measured by waveform cross-correlation (as opposed to onset measurements in ray theory). In this study, we pose the question how much MFT really contributes to improving the 3-D imaging of the deep Earth structure? We investigate the role of the model parameterization and regularization when using MFT, in our ability/unability to map the structural dispersion present in the data into a tomographic model. Our data consist of 274 066 globally distributed S, ScS and SS time residuals measured at 10, 15, 22 and 34 s period (Zaroli et al., 2010). Two ways of parameterizing the Earth's mantle, and their implications on the model obtained using MFT, are presented. One is based on irregularly spaced spherical triangular prisms, with nodes spacing ranging from 200 to 900 km, i.e. a "coarse" parameterization. The other is based on a "cubed Earth", that consists of cubic cells of 70 km size near the top, down to 35 km near the base of the mantle, i.e. a "fine" parameterization. We also investigate how the model regularization (i.e. choice of the damping parameter in the inversion) may prevent us from fully exploiting the extra information, on the 3-D structure, present in our multi-band dataset. We present a comparison of a multi
García-Yeguas, A.; Sánchez-Alzola, A.; De Siena, L.; Prudencio, J.; Díaz-Moreno, A.; Ibáñez, J. M.
2018-03-01
We present a P-wave scattering image of the volcanic structures under Tenerife Island using the autocorrelation functions of P-wave vertical velocity fluctuations. We have applied a cluster analysis to total quality factor attenuation ( {Q}_t^{-1} ) and scattering quality factor attenuation ( {Q}_{PSc}^{-1} ) images to interpret the structures in terms of intrinsic and scattering attenuation variations on a 2D plane, corresponding to a depth of 2000 m, and check the robustness of the scattering imaging. The results show that scattering patterns are similar to total attenuation patterns in the south of the island. There are two main areas where patterns differ: at Cañadas-Teide-Pico Viejo Complex, high total attenuation and average-to-low scattering values are observed. We interpret the difference as induced by intrinsic attenuation. In the Santiago Ridge Zone (SRZ) region, high scattering values correspond to average total attenuation. In our interpretation, the anomaly is induced by an extended scatterer, geometrically related to the surficial traces of Garachico and El Chinyero historical eruptions and the area of highest seismic activity during the 2004-2008 seismic crises.
Oral, Elif; Gélis, Céline; Bonilla, Luis Fabián; Delavaud, Elise
2017-12-01
Numerical modelling of seismic wave propagation, considering soil nonlinearity, has become a major topic in seismic hazard studies when strong shaking is involved under particular soil conditions. Indeed, when strong ground motion propagates in saturated soils, pore pressure is another important parameter to take into account when successive phases of contractive and dilatant soil behaviour are expected. Here, we model 1-D seismic wave propagation in linear and nonlinear media using the spectral element numerical method. The study uses a three-component (3C) nonlinear rheology and includes pore-pressure excess. The 1-D-3C model is used to study the 1987 Superstition Hills earthquake (ML 6.6), which was recorded at the Wildlife Refuge Liquefaction Array, USA. The data of this event present strong soil nonlinearity involving pore-pressure effects. The ground motion is numerically modelled for different assumptions on soil rheology and input motion (1C versus 3C), using the recorded borehole signals as input motion. The computed acceleration-time histories show low-frequency amplification and strong high-frequency damping due to the development of pore pressure in one of the soil layers. Furthermore, the soil is found to be more nonlinear and more dilatant under triaxial loading compared to the classical 1C analysis, and significant differences in surface displacements are observed between the 1C and 3C approaches. This study contributes to identify and understand the dominant phenomena occurring in superficial layers, depending on local soil properties and input motions, conditions relevant for site-specific studies.
Energy Technology Data Exchange (ETDEWEB)
Apsel, R.J.; Frazier, G.A.; Jurkevics, A.; Fried, J.C.
1980-09-30
This report assesses the relative difference between seismic ground motion in the Eastern (EUS) and Western (WUS) regions of the United States; and provides the necessary input to soil-structure interaction codes concerning type and propagation direction for incoming seismic waves. Implicit is the relevance to the Zion Nuclear Power Plant (ZNPP) site. The relative differences between seismic ground motions in EUS and WUS are assumed to be principally caused by differences in material attenuation. Earthquake rupture and wave propagation through the earth were simulated by performing numerical calculations. Typical results for a Western United States earth structure indicate that essentially no seismic energy emerges at angles shallower than 45 degrees except for low frequency emission from shallow zones of earthquake rupture. The same simulations are repeated for the ZNPP earth structure. The effective incoming waves are seen to be emerging within ten degrees of vertical at Zion for all source/receiver geometries and all frequencies of interest. At high frequency, the reduced material attenuation (corresponding to the higher EUS quality factors) additionally constrains the effective incoming waves to emerge within five degrees of vertical.
Studies of Seismic Sources in Antarctica Using an Extensive Deployment of Broadband Seismographs
Lough, Amanda Colleen
This dissertation is the first comprehensive study reporting the seismicity of Antarctica utilizing year-round recordings from autonomous instruments installed on the continent itself. I first examine the general seismic nature of the continent using locally deployed seismographs in both East Antarctica and West Antarctica. I detect and locate seismic events using the traditional first arriving impulsive P and S waves as well as events classified as 'slow' earthquakes with no impulsive P-waves. I find evidence of tectonic events in East Antarctica (representing intraplate earthquakes within a stable craton), icequake events in the Transantarctic Mountains (associated with active alpine glaciers), and icequake events at calving glaciers along the coastline. In West Antarctica I find tectonic earthquakes, icequakes, and tectonic events related to volcanism. I do not find evidence of tectonic events in West Antarctica that would indicate rifting is currently active. I also find two main sources of 'slow' seismicity: calving along Vanderford glacier and tidally modulated stick-slip motion of the Whillans Ice Stream. I further examine two types of events found through my review of the seismicity of Antarctica. I show that a cluster of events located in West Antarctica near the Marie Byrd Land linear volcanic chain the Executive Committee Range (ECR) are deep long period seismic events associated with the ongoing volcanism of the ECR. I provide several lines of evidence including the age progression of the exposed volcanic line as well as radar images featuring a recent ash layer supporting the continued magmatic activity in the ECR. My final investigation is into a new type of icequake in East Antarctica associated with wind-glazed small-scale crevasse features. The wave trains are dominated by surface wave energy and an apparent lack of body wave energy. I demonstrate that these events are sourced in the upper firn layers and can be used to determine firn thickness in
Automated Processing Workflow for Ambient Seismic Recordings
Girard, A. J.; Shragge, J.
2017-12-01
Structural imaging using body-wave energy present in ambient seismic data remains a challenging task, largely because these wave modes are commonly much weaker than surface wave energy. In a number of situations body-wave energy has been extracted successfully; however, (nearly) all successful body-wave extraction and imaging approaches have focused on cross-correlation processing. While this is useful for interferometric purposes, it can also lead to the inclusion of unwanted noise events that dominate the resulting stack, leaving body-wave energy overpowered by the coherent noise. Conversely, wave-equation imaging can be applied directly on non-correlated ambient data that has been preprocessed to mitigate unwanted energy (i.e., surface waves, burst-like and electromechanical noise) to enhance body-wave arrivals. Following this approach, though, requires a significant preprocessing effort on often Terabytes of ambient seismic data, which is expensive and requires automation to be a feasible approach. In this work we outline an automated processing workflow designed to optimize body wave energy from an ambient seismic data set acquired on a large-N array at a mine site near Lalor Lake, Manitoba, Canada. We show that processing ambient seismic data in the recording domain, rather than the cross-correlation domain, allows us to mitigate energy that is inappropriate for body-wave imaging. We first develop a method for window selection that automatically identifies and removes data contaminated by coherent high-energy bursts. We then apply time- and frequency-domain debursting techniques to mitigate the effects of remaining strong amplitude and/or monochromatic energy without severely degrading the overall waveforms. After each processing step we implement a QC check to investigate improvements in the convergence rates - and the emergence of reflection events - in the cross-correlation plus stack waveforms over hour-long windows. Overall, the QC analyses suggest that
Spatial wavefield gradient-based seismic wavefield separation
Van Renterghem, C.; Schmelzbach, C.; Sollberger, D.; Robertsson, J. OA
2018-03-01
Measurements of the horizontal and vertical components of particle motion combined with estimates of the spatial gradients of the seismic wavefield enable seismic data to be acquired and processed using single dedicated multicomponent stations (e.g. rotational sensors) and/or small receiver groups instead of large receiver arrays. Here, we present seismic wavefield decomposition techniques that use spatial wavefield gradient data to separate land and ocean bottom data into their upgoing/downgoing and P/S constituents. Our method is based on the elastodynamic representation theorem with the derived filters requiring local measurements of the wavefield and its spatial gradients only. We demonstrate with synthetic data and a land seismic field data example that combining translational measurements with spatial wavefield gradient estimates allows separating seismic data recorded either at the Earth's free-surface or at the sea bottom into upgoing/downgoing and P/S wavefield constituents for typical incidence angle ranges of body waves. A key finding is that the filter application only requires knowledge of the elastic properties exactly at the recording locations and is valid for a wide elastic property range.
[Experimental study on conduction of Gong tonality vibromusic sound wave in the healthy human body].
Wei, Yu-lin; Tu, Yi-wen; Liang, Tian-tian; Han, Biao; Liu, Wei
2005-02-01
To study the conduction of Gong tonality vibromusic sound wave along meridians in healthy human body, and investigate differences of the sensitivity of different meridians and genders to this vibromusic message. Emit the Gong tonality music signal under the water and then investigate the responses of different acupoints and control points at the tissue of the same level to the vibromusic sound wave. There were differences of sensitivity to music waves at source acupoints on the foot, sensitivity of Zusanli (ST 36) was significantly higher than its control point (P music sound wave. Gong tonality vibromusic sound wave can conduct along meridians in healthy human body, and there are differences between different meridians and different genders in the sensitivity to the music sound wave.
Seismic monitoring of soft-rock landslides: the Super-Sauze and Valoria case studies
Tonnellier, Alice; Helmstetter, Agnès; Malet, Jean-Philippe; Schmittbuhl, Jean; Corsini, Alessandro; Joswig, Manfred
2013-06-01
This work focuses on the characterization of seismic sources observed in clay-shale landslides. Two landslides are considered: Super-Sauze (France) and Valoria (Italy). The two landslides are developed in reworked clay-shales but differ in terms of dimensions and displacement rates. Thousands of seismic signals have been identified by a small seismic array in spite of the high-seismic attenuation of the material. Several detection methods are tested. A semi-automatic detection method is validated by the comparison with a manual detection. Seismic signals are classified in three groups based on the frequency content, the apparent velocity and the differentiation of P and S waves. It is supposed that the first group of seismic signals is associated to shearing or fracture events within the landslide bodies, while the second group may correspond to rockfalls or debris flows. A last group corresponds to external earthquakes. Seismic sources are located with an automatic beam-forming location method. Sources are clustered in several parts of the landslide in agreement with geomorphological observations. We found that the rate of rockfall and fracture events increases after periods of heavy rainfall or snowmelt. The rate of microseismicity and rockfall activity is also positively correlated with landslide displacement rates. External earthquakes did not influence the microseismic activity or the landslide movement, probably because the earthquake ground motion was too weak to trigger landslide events during the observation periods.
Effects of Mooring Systems on the Performance of a Wave Activated Body Energy Converter
DEFF Research Database (Denmark)
Zanuttigh, Barbara; Angelelli, Elisa; Kofoed, Jens Peter
2013-01-01
Aim of this paper is to analyse the power and hydraulic performance of a floating Wave Energy Converter with the purpose at optimising its design for installation in arrays. The paper presents new experiments carried out in 1:30 scale on a single device of the Wave Activated Body type in the deep-water...
Tornado Detection Based on Seismic Signal.
Tatom, Frank B.; Knupp, Kevin R.; Vitton, Stanley J.
1995-02-01
At the present time the only generally accepted method for detecting when a tornado is on the ground is human observation. Based on theoretical considerations combined with eyewitness testimony, there is strong reason to believe that a tornado in contact with the ground transfers a significant amount of energy into the ground. The amount of energy transferred depends upon the intensity of the tornado and the characteristics of the surface. Some portion of this energy takes the form of seismic waves, both body and surface waves. Surface waves (Rayleigh and possibly Love) represent the most likely type of seismic signal to be detected. Based on the existence of such a signal, a seismic tornado detector appears conceptually possible. The major concerns for designing such a detector are range of detection and discrimination between the tornadic signal and other types of surface waves generated by ground transportation equipment, high winds, or other nontornadic sources.
Stanciu, Adrian Christian
Proposed mechanisms for the unusual seismicity ~100 km southeast of the contact between the Transylvanian Basin and the Eastern Carpathians in Romania have included tearing and rollback of a subducted slab of oceanic lithosphere and gravitational instability and delamination of continental lithosphere. We examined the upper mantle fabrics using shear wave splitting of SK(K)S phases recorded at four broadband seismic stations in the Transylvanian Basin. Our results indicate a regional NW-SE splitting trend, with measurements that reflect an abrupt change from this regional flow field in the vicinity of the Vrancea body to a NE-SW trend that is consistent with redirection of mantle flow. Crustal thickness measurements show 28-30 km in the western part of the Transylvanian Basin, 34-39 km at the contact with the Eastern Carpathians, and 40-45 km further east. These results, along with previous estimates, constrain the locus of the inferred Miocene suture between the southeastern-most portion of the Tisza-Dacia terrane and the East European Platform. The second convergent margin system represented here is in the North American Cordillera in Idaho and Oregon, where subduction and accretion of exotic terranes have modified the western margin of North America. We used teleseismic receiver functions from 85 broadband stations to analyze the geometry of the Salmon River suture zone, the western Idaho shear zone, and the Grouse Creek-Farmington zone boundary. Results show a clear break in crustal thickness from ~28 km beneath the accreted terranes to 36 km east of the surface expression of the WISZ. A strong mid-crustal converter at ~20 km depth is consistent with tectonic wedging during accretion of the Blue Mountains terranes. An eastern Moho offset of ~6 km is consistent with the Archean Grouse Creek-Farmington zone boundary. We used deep converted phases generated beneath the study area to image the mantle transition zone. We observe a continuous high amplitude P410s
Czech Academy of Sciences Publication Activity Database
Růžek, Bohuslav; Plomerová, Jaroslava; Babuška, Vladislav
2012-01-01
Roč. 56, č. 1 (2012), s. 107-140 ISSN 0039-3169 R&D Projects: GA ČR GA205/07/1088; GA AV ČR IAA300120709; GA MŠk LM2010008 Institutional research plan: CEZ:AV0Z30120515 Keywords : receiver function * seismic noise * joint inversion * Bohemian Massif * velocity structure Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.975, year: 2012
Slip heterogeneity, body-wave spectra, and directivity of earthquake ruptures
Bernard, P.; Herrero, A.
1994-01-01
We present a broadband kinematic model based on a self-similar k-square distribution of the coseismic slip, with an instantaneous rise-time and a constant rupture velocity. The phase of the slip spectrum at high wave number is random. This model generates an ?-squared body-wave radiation, and a particular directivity factor C2d scaling the amplitude of the body-wave spectra, where Cd is the standard directivity factor. Considering the source models with a propagating pulse and a finite rise-t...
Czech Academy of Sciences Publication Activity Database
Dal Moro, Giancarlo
2015-01-01
Roč. 254, JUL 1 (2015), s. 338-349 ISSN 0019-1035 Institutional support: RVO:67985891 Keywords : moon * Regoliths * geophysics * surface- wave Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 3.383, year: 2015
Directory of Open Access Journals (Sweden)
Teuku Reza Ferasyi
2014-04-01
Full Text Available This report was aimed to describe the behavioral changes of catfish as observed before two different earthquakes hit the Province of Aceh, Indonesia in year of 2012. A number of 5 African’s catfish (Clarias gariepinus were placed in an aquarium located in Gapang, Sukakarya Sub-district of Sabang Town, Aceh. Their behavior activities were observed manually at three different times (08.00 AM, 01.00 PM, and 05.00 PM every day from 1st March up to 11th April 2012. The result of observation showed that the activity of catfish was different between all of them from 1st March 2012 up to morning observation on 11th April 2012. Most of those activities was not showed as very active behavior. However, their behavior was very active in the same pattern when observed at noon and afternoon times on 11 April 2012. On this date, there were two consecutive earthquakes happened at magnitude of >8 Richter Scale at 03.38 PM and 05.43 PM. The epicenter of this earthquake was in Simeulue, with the distance of more and less of 390 km from observation station of catfish in Gapang. It was noted that this abnormal behavior possibly showed as an indication of their ability to detect the increase of pre-seismic activity at 2.38 hours and 43 minutes before the two earthquakes. Perhaps, it is the result of their response to the increase of pre-seismic electromagnetic wave. Further continuous observation and research is needed to ensure the role of African’s catfish (Clarias gariepinus as abio-sensor for the increase of seismic activity.
Seismological implications of a lithospheric low seismic velocity zone in Mars
Zheng, Yingcai; Nimmo, Francis; Lay, Thorne
2015-03-01
Most seismological models for the interior of Mars lack an upper mantle low velocity zone. However, there is expected to be a large thermal gradient across the stagnant conductive lid (lithosphere) of Mars. This gradient should tend to decrease elastic wave velocities with increasing depth, with this effect dominating the opposing tendency caused by increasing pressure with depth because Mars has low gravity. An upper mantle lithosphere with a low velocity zone (LVZ) beneath a thin high velocity "seismic lid" is thus predicted. The upcoming NASA InSight mission includes a three-component seismometer, which should provide the first opportunity to directly detect any lithospheric LVZ in Mars. Seismic wavefields expected for Mars mantle velocity structures with or without a strong LVZ are very distinct. The LVZ models predict shadow zones for high-frequency seismic body wave phases such as P, S, PP and SS, etc. The most diagnostic waves that can be used to evaluate presence of a lithospheric LVZ given a single seismometer are intermediate-period global surface waves, which travel along the great circle from a seismic source to the seismometer. An LVZ produces distinctive dispersion, with a Rayleigh wave Airy phase around 100 s period and very different surface wave seismograms compared to a model with no LVZ. Even a single observation of long-period surface waves from a known range can be diagnostic of the lithospheric structure. Establishing the existence of an LVZ has major implications for thermal evolution, volatile content and internal dynamics of the planet.
A photoelastic study of the effects of an impulsive seismic wave on a nuclear containment vessel
International Nuclear Information System (INIS)
Burger, C.P.
1981-01-01
A dynamic photoelastic study of the progressive movement of a dilatational P-wave into a model of a nuclear containment vessel,is studied. The reflections at the dome abutments are observed and the strong flexural wave that deforms the dome itself is studied with photoelasticity and with dynamic strain gage procedures. (E.G.) [pt
U.S. Seismic Design Maps Web Application
Martinez, E.; Fee, J.
2015-12-01
The application computes earthquake ground motion design parameters compatible with the International Building Code and other seismic design provisions. It is the primary method for design engineers to obtain ground motion parameters for multiple building codes across the country. When designing new buildings and other structures, engineers around the country use the application. Users specify the design code of interest, location, and other parameters to obtain necessary ground motion information consisting of a high-level executive summary as well as detailed information including maps, data, and graphs. Results are formatted such that they can be directly included in a final engineering report. In addition to single-site analysis, the application supports a batch mode for simultaneous consideration of multiple locations. Finally, an application programming interface (API) is available which allows other application developers to integrate this application's results into larger applications for additional processing. Development on the application has proceeded in an iterative manner working with engineers through email, meetings, and workshops. Each iteration provided new features, improved performance, and usability enhancements. This development approach positioned the application to be integral to the structural design process and is now used to produce over 1800 reports daily. Recent efforts have enhanced the application to be a data-driven, mobile-first, responsive web application. Development is ongoing, and source code has recently been published into the open-source community on GitHub. Open-sourcing the code facilitates improved incorporation of user feedback to add new features ensuring the application's continued success.
Nonlinear Wave Radiation and Diffraction by a Near-Surface Body
Ananthakrishnan, P.
1997-11-01
Physics of surface-wave and rigid-body interactions is of importance in naval architecture, in that a good understanding of wave-body interactions is necessary for the design of hulls with minimum ship-motion and resistance characteristics. Particular topics of contemporary research such as generation of spray and breaking waves by a surface ship and control of ship motion in high seas are however highly nonlinear, rendering analysis a challenging task. Using a robust numerical algorithm developed for analyzing fully nonlinear free-surface flow in a viscous fluid (see P. Ananthakrishnan, Three-dimensional wave-body interactions in a viscous fluid, Proc. of ISOPE'97 Conference, Hawaii), we have investigated diffraction and radiation of waves by floating and submerged rigid bodies. In the numerical model, the Navier-Stokes equations subject to exact free-surface and body boundary conditions are solved in primitive variables using a fractional-step finite-difference method which is implemented using curvilinear coordinates. Approximate conditions are however used to model the open boundary and the movement of the contact line. Results presented shed light to a better understanding of generation and ensuing spatial-temporal evolution of vortices under the influence of a free surface, vortical and potential components of hydrodynamics forces, symmetry-breaking in the case of large-amplitude oscillations, generation and damping of super-harmonic waves, and parameter ranges in which effect of viscosity is significant.
The contribution of activated processes to Q. [stress corrosion cracking in seismic wave attenuation
Spetzler, H. A.; Getting, I. C.; Swanson, P. L.
1980-01-01
The possible role of activated processes in seismic attenuation is investigated. In this study, a solid is modeled by a parallel and series configuration of dashpots and springs. The contribution of stress and temperature activated processes to the long term dissipative behavior of this system is analyzed. Data from brittle rock deformation experiments suggest that one such process, stress corrosion cracking, may make a significant contribution to the attenuation factor, Q, especially for long period oscillations under significant tectonic stress.
The Body and the Beautiful: Health, Attractiveness and Body Composition in Men’s and Women’s Bodies
Brierley, Mary-Ellen; Brooks, Kevin R.; Mond, Jonathan; Stevenson, Richard J.
2016-01-01
The dominant evolutionary theory of physical attraction posits that attractiveness reflects physiological health, and attraction is a mechanism for identifying a healthy mate. Previous studies have found that perceptions of the healthiest body mass index (weight scaled for height; BMI) for women are close to healthy BMI guidelines, while the most attractive BMI is significantly lower, possibly pointing to an influence of sociocultural factors in determining attractive BMI. However, less is known about ideal body size for men. Further, research has not addressed the role of body fat and muscle, which have distinct relationships with health and are conflated in BMI, in determining perceived health and attractiveness. Here, we hypothesised that, if attractiveness reflects physiological health, the most attractive and healthy appearing body composition should be in line with physiologically healthy body composition. Thirty female and 33 male observers were instructed to manipulate 15 female and 15 male body images in terms of their fat and muscle to optimise perceived health and, separately, attractiveness. Observers were unaware that they were manipulating the muscle and fat content of bodies. The most attractive apparent fat mass for female bodies was significantly lower than the healthiest appearing fat mass (and was lower than the physiologically healthy range), with no significant difference for muscle mass. The optimal fat and muscle mass for men’s bodies was in line with the healthy range. Male observers preferred a significantly lower overall male body mass than did female observers. While the body fat and muscle associated with healthy and attractive appearance is broadly in line with physiologically healthy values, deviations from this pattern suggest that future research should examine a possible role for internalization of body ideals in influencing perceptions of attractive body composition, particularly in women. PMID:27257677
Can we derive a continental growth curve from global S seismic tomography?
Poupinet, G.; Shapiro, N.
2007-05-01
The origin of continents is a standard question in geology; the worldwide application of geochronology lead to propose several models for the rate of formation of continental surfaces: see Hurley and Rand (1969), Amstrong (1981), Allègre (1982), McLennan and Taylor (1982), McCulloch and Bennett(1994), Condie (1998) ... In a diagram plotting the percentage of continental surface as a function of surface rock age, each model is characterized by a different curve - see Rino et al (2004) for example. In seismology, the structure of the continental lithosphere has been mapped in detail on all continents during the last 20 years. Large scale studies suggest a close relationship between the average P and S vertical travel times across the lithosphere inside continents and the age of surface rocks. The vertical travel time is directly related to the velocity and to the thickness of the lithosphere. It is correlated to the geotherm which is also known to be nearly dependent on the age of the continents. Using such a vertical traveltime - age relationship, it is straightforward to build a seismological curve which would be the seismic equivalent of the crustal growth curve familiar to geochronologists. This curve relates the percentage of continental surface to the average S vertical travel time and indirectly to age. We present various attempts to build such a curve. Our basic input is the S-tomography model obtained from global surface wave measurements by Shapiro and Ritzwoller (2002). P-delays derived from ISC residuals could in principle be used but they are a local measurement. S-tomography models have the advantage that they are surface measurements. We finally compare our growth curve with standard crustal growth curves and find that it is an "intermediate" curve. The S-tomography derived growth curve does not exhibit fast growth episodes as in McCulloch and Bennett (1994) and Condie (1998). A regular rate of formation of continents seems the most probable
Roecker, S. W.; Priestley, K. F.; Tatar, M.
2014-12-01
The Iranian Plateau forms a broad zone of deformation between the colliding Arabian and Eurasian plates. The convergence is accommodated in the Zagros Mountains of SW Iran, the Alborz Mountains of northern Iran, and the Kopeh Dagh Mountains of NE Iran. These deforming belts are separated by relatively aseismic depressions such as the Lut Block. It has been suggested that the Arabia-Eurasia collision is similar to the Indo-Eurasia collision but at a early point of development and therefore, it may provide clues to our understanding of the earlier stages of the continent-continent collision process. We present results of the analysis of seismic data collected along two NE-SW trending transects across the Iranian Plateau. The first profile extends from near Bushere on the Persian Gulf coast to near to the Iran-Turkmenistan border north of Mashad, and consists of seismic recordings along the SW portion of the line in 2000-2001 and recording along the NE portion of the line in 2003 and 2006-2008. The second profile extends from near the Iran-Iraq border near the Dezfel embayment to the south Caspian Sea coast north of Tehran. We apply the combined 2.5D finite element waveform tomography algorithm of Baker and Roecker [2014] to jointly invert teleseismic body and surface waves to determine the elastic wavespeed structures of these areas. The joint inversion of these different types of waves affords similar types of advantages that are common to combined surface wave dispersion/receiver function inversions in compensating for intrinsic weaknesses in horizontal and vertical resolution capabilities. We compare results recovered from a finite difference approach to document the effects of various assumptions related to their application, such as the inclusion of topography, on the models recovered. We also apply several different inverse methods, starting with simple gradient techniques to the more sophisticated pseudo-Hessian or L-BFGS approach, and find that the latter are
Wada, N.; Kawakata, H.; Murakami, O.; Doi, I.; Yoshimitsu, N.; Nakatani, M.; Yabe, Y.; Naoi, M. M.; Miyakawa, K.; Miyake, H.; Ide, S.; Igarashi, T.; Morema, G.; Pinder, E.; Ogasawara, H.
2011-12-01
Scaling relationship between corner frequencies, fc, and seismic moments, Mo is an important clue to understand the seismic source characteristics. Aki (1967) showed that Mo is proportional to fc-3 for large earthquakes (cubic law). Iio (1986) claimed breakdown of the cubic law between fc and Mo for smaller earthquakes (Mw law holds even for micro earthquakes (-1 4) by using high quality data observed at a deep borehole (Abercrombie, 1995; Ogasawara et al., 2001; Hiramatsu et al., 2002; Yamada et al., 2007). In order to clarify the scaling relationship for smaller earthquakes (Mw Africa. We used 4 tri-axial accelerometers of three-component that have a flat response up to 25 kHz. They were installed to be 10 to 30 meters apart from each other at 3,300 meters deep. During the period from 2008/10/14 to 2008/10/30 (17 days), 8,927 events were recorded. We estimated fc and Mo for 60 events (-3 Common practice is using direct waves from adjacent events. However, there were only 5 event pairs with the distance between them less than 20 meters and Mw difference over one. In addition, the observation array is very small (radius less than 30 m), which means that effects of directivity and radiation pattern on direct waves are similar at all stations. Hence, we used spectral ratio of coda waves, since these effects are averaged and will be effectively reduced (Mayeda et al., 2007; Somei et al., 2010). Coda analysis was attempted only for relatively large 20 events (we call "coda events" hereafter) that have coda energy large enough for analysis. The results agree with those of the direct S-wave analysis for the same events, though the latter showed more scattering in fc-Mo trend. So, we combine the results from the both analyses to examine the fc-Mo trend down to very small events. Therefore, we adopted fc and (relative) Mo estimated from coda spectral ratios for coda events, while we adopted them from direct spectra for other events despite of their lower reliability. We
Zotov, O. D.; Zavyalov, A. D.; Guglielmi, A. V.; Lavrov, I. P.
2018-01-01
Based on the observation data for hundreds of the main shocks and thousands of aftershocks, the existence of effect of round-the-world surface seismic waves is demonstrated (let us conditionally refer to them as a round-the-world seismic echo) and the manifestations of this effect in the dynamics of the repeated shocks of strong earthquakes are analyzed. At the same time, we by no means believe this effect has been fully proven. We only present a version of our own understanding of the physical causes of the observed phenomenon and analyze the regularities in its manifestation. The effect is that the surface waves excited in the Earth by the main shock make a full revolution around the Earth and excite a strong aftershock in the epicentral zone of the main shock. In our opinion, the physical nature of this phenomenon consists in the fact that the superposition leads to a concentration of wave energy when the convergent surface waves reach the epicentral zone (cumulative effect). The effect of the first seismic echo is most manifest. Thus, the present work supports our hypothesis of the activation of rock failure under the cumulative impact of an round-the-world seismic echo on the source area which is releasing ("cooling") after the main shock. The spatial regularities in the manifestations of this effect are established, and the independence of the probability of its occurrence on the main shock magnitude is revealed. The effect of a round-the-world seismic echo can be used to improve the reliability of the forecasts of strong aftershocks in determining the scenario for the seismic process developing in the epicentral zone of a strong earthquake that has taken place.
Gao, Longfei
2017-10-26
We consider the long-time instability issue associated with finite difference simulation of seismic acoustic wave equations on discontinuous grids. This issue is exhibited by a prototype algebraic problem abstracted from practical application settings. Analysis of this algebraic problem leads to better understanding of the cause of the instability and provides guidance for its treatment. Specifically, we use the concept of discrete energy to derive the proper solution transfer operators and design an effective way to damp the unstable solution modes. Our investigation shows that the interpolation operators need to be matched with their companion restriction operators in order to properly couple the coarse and fine grids. Moreover, to provide effective damping, specially designed diffusive terms are introduced to the equations at designated locations and discretized with specially designed schemes. These techniques are applied to simulations in practical settings and are shown to lead to superior results in terms of both stability and accuracy.
Evasion of HSR in S-wave charmonium decaying to P-wave light hadrons
Energy Technology Data Exchange (ETDEWEB)
Li, Gang [Qufu Normal University, Department of Physics, Qufu (China); Liu, Xiao-Hai [Peking University, Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Beijing (China); Zhao, Qiang [Chinese Academy of Sciences, Institute of High Energy Physics, Beijing (China); CAS, Theoretical Physics Center for Science Facilities, Beijing (China)
2013-09-15
The S-wave charmonium decaying to a P-wave and S-wave light hadron pairs are supposed to be suppressed by the helicity selection rule in the perturbative QCD framework. With an effective Lagrangian method, we show that the intermediate charmed meson loops can provide a possible mechanism for the evasion of the helicity selection rule, and result in sizeable decay branching ratios in some of those channels. The theoretical predictions can be examined by the forthcoming BES-III data in the near future. (orig.)
U.S. experience in seismic re-evaluation and verification programs
International Nuclear Information System (INIS)
Stevenson, J.D.
1995-01-01
The purpose of this paper is to present a summary of the development of a seismic re-evaluation program for older nuclear power plants in the U.S. The principal focus of this reevaluation is the use of actual strong motion earthquake response data for structures and mechanical and electrical systems and components. These data are supplemented by generic shake table test results. Use of this type of seismic re-evaluation has led to major cost reductions as compared to more conventional analytical and component specific testing procedures. (author)
Attanayake, J.; Ghosh, A.; Amosu, A.
2010-12-01
Students of this generation are markedly different from their predecessors because they grow up and learn in a world of visual technology populated by touch screens and smart boards. Recent studies have found that the attention span of university students whose medium of instruction is traditional teaching methods is roughly fifteen minutes and that there is a significant drop in the number of students paying attention over time in a lecture. On the other hand, when carefully segmented and learner-paced, animated visualizations can enhance the learning experience. Therefore, the instructors are faced with the difficult task of designing more complex teaching environments to improve learner productivity. We have developed an animated visualization of earthquake wave propagation across a generic transect of the Transportable Array of the USArray from a magnitude 6.9 event that occurred in the Gulf of California on August 3rd 2009. Despite the fact that the proto-type tool is built in MATLAB - one of the most popular programming environments among the seismology community, the movies can be run as a standalone stream with any built-in media player that supports .avi file format. We infer continuous ground motion along the transect through a projection and interpolation mechanism based on data from stations within 100 km of the transect. In the movies we identify the arrival of surface waves that have high amplitudes. However, over time, although typical Rayleigh type ground motion can be observed, the motion at any given point becomes complex owing to interference of different wave types and different seismic properties of the subsurface. This clearly is different from simple representations of seismic wave propagation in most introductory textbooks. Further, we find a noisy station that shows unusually high amplitude. We refrain from deleting this station in order to demonstrate that in a real world experiment, generally, there will be complexities arising from
Seismic Coupling of Short-Period Wind Noise Through Mars’ Regolith for NASA’s InSight Lander
Teanby, N. A.; Stevanović, J.; Wookey, J.; Murdoch, Naomi; Hurley, J.; Myhill, R.; Bowles, N. E.; Calcutt, S. B.; Pike, William T.
2017-01-01
NASA’s InSight lander will deploy a tripod-mounted seismometer package onto the surface of Mars in late 2018. Mars is expected to have lower seismic activity than the Earth, so minimisation of environmental seismic noise will be critical for maximising observations of seismicity and scientific return from the mission. Therefore, the seismometers will be protected by a Wind and Thermal Shield (WTS), also mounted on a tripod. Nevertheless, wind impinging on the WTS will cause vibration noise, w...
Scattering of quasi seismic waves between self-reinforced and triclinic media
Kumari, Pato
2017-10-01
Present work explores scattering of two-dimensional plane quasi longitudinal and quasi shear vertical waves through a triclinic medium laid over by a self-reinforced half space. The analytical expressions for velocity of all the scattered waves are derived in compact form. Reflection and transmission angles along with scattered velocities are computed numerically for particular model and the variations in same have been studied against propagation angle of incident qP/qSV wave. The variation of reflection/transmission angles and velocity versus incident angle for unconstrained and constrained conditions are plotted using MATLAB plots. Critical angle for grazing phenomenon is found for both incident qP and qSV waves. The present work has its utility in reflection problems where highly anisotropic source region encounters reinforced layered obstruction.
The Detection of Vertical Cracks in Asphalt Using Seismic Surface Wave Methods
International Nuclear Information System (INIS)
Iodice, M; Muggleton, J; Rustighi, E
2016-01-01
Assessment of the location and of the extension of cracking in road surfaces is important for determining the potential level of deterioration in the road overall and the infrastructure buried beneath it. Damage in a pavement structure is usually initiated in the tarmac layers, making the Rayleigh wave ideally suited for the detection of shallow surface defects. This paper presents an investigation of two surface wave methods to detect and locate top-down cracks in asphalt layers. The aim of the study is to compare the results from the well- established Multichannel Analysis of Surface Waves (MASW) and the more recent Multiple Impact of Surface Waves (MISW) in the presence of a discontinuity and to suggest the best surface wave technique for evaluating the presence and the extension of vertical cracks in roads. The study is conducted through numerical simulations alongside experimental investigations and it considers the cases for which the cracking is internal and external to the deployment of sensors. MISW is found to enhance the visibility of the reflected waves in the frequency wavenumber ( f-k ) spectrum, helping with the detection of the discontinuity. In some cases, by looking at the f-k spectrum obtained with MISW it is possible to extract information regarding the location and the depth of the cracking. (paper)
Proceedings of the Japan - U.S. Seminar on HTGR Safety Technology - Seismic Research. Volume 1
Energy Technology Data Exchange (ETDEWEB)
None, None
1977-09-15
These volumes constitute the proceedings of the f i r s t Japan-United States HTGR Safety Technology Seminar sponsored by the U. S. Nuclear Regulatory Commission, which was held at Brookhaven National Laboratory, Upton, New York, on September 15 and 16, 1977. This Seminar was held within the framework of the technical information exchange agreement in the area of HTGR safety research between the United States Nuclear Regulatory Commission and the Japan Atomic Energy Bureau. The agreement covers many aspects of HTGR safety res'earch, including: accident delineation, fuel cycle safety, primary coolant impurities, seismic effects, 'material properties, fission product release and transport and graphite oxidation. This f i r s t Seminar covered the safety research being carried out i n the areas of seismic effects and helium technology. in Japan and the United States. The Seminar was divided into two parallel sessions, one for Seismic Research and the second for Helium Technology. The papers presented i n the Seismic Research.session constitute Volume I of the proceedings, and the papers of the Helium Technology session constitute Volume 11. I t is hoped that these papers will form the basis for future cooperation between the Japanese and American scientific and engineering community in 'HTGR safety research.
Influence of Lightning on the Observation of Seismic Electromagnetic Wave Anomalies
Directory of Open Access Journals (Sweden)
Jun Izutsu
2007-01-01
Full Text Available For two decades, many researchers have been claiming that pre-seismic electromagnetic phenomena may be useful in short-term earthquake prediction. Despite much effort, however, the relationship between anomalous electromagnetic signals and earthquakes has not been proven. In this paper, we examine LF- and VLF-range electromagnetic-pulse data accumulated by Kyoto University since 1981, with special emphasis on the influence of lightning. Our data on electromagnetic pulses were compared with available lightning data to evaluate the influence of lightning.
Lognonne, P.; Gudkova, T.; Le Feuvre, M.; Garcia, R. F.; Kawamura, T.; Banerdt, B.; Kobayashi, N.
2011-12-01
Natural Impacts occurring on the surface of telluric planets are important seismic sources for constraining the crustal and upper mantle structure, especially when their impact location and impacting time can be determined by other complementing experiments, such as Earth based flash detection for the Moon or differential orbital imaging of the surface for Mars. When these complementary data are not available, which was the case of Apollo with the exception of artificial impacts, the location of impact as compared to quake is easier, as only their geographical location must be determined from seismic data. We present recent results of the analysis of impact related seismic data gathered by the Apollo Lunar seismic network during the 70th. By using the artificial impact, we first develop a calibrated analysis for extracting the impulse (i.e. mass time impact velocity) from the amplitude of seismic waves, and point out the effect of the generation of ejecta in the seismic impulse. This approach not only allows to constrain the mass of the impacts, but also to constrain the impact frequency-impactor mass relation. By combining both the Apollo long period and short period data, further analysis can be made on the dynamic of the seismic source. The combination of these date provides indeed broadband seismic analysis have been made allowing to constraint the seismic cut-off frequency and source spectrum associated with both natural and artificial impacts. We show that the source cut-off is, as compared to moonquakes, relatively low and around a few Hz for remotely detected impacts. It is also depending not only on the impact size, but also on the impact location, as the seismic radiation of the shock wave depends on the most-upper regolith layers. We finally use our results and forward modeling to prepare the GEMS seismic mission to Mars, considered by NASA for a launch in 2016. In order to have a robust estimation of the rates of seismic detection of impacts, we analyze
ESTIMA, Neutron Width Level Spacing, Neutron Strength Function of S- Wave, P-Wave Resonances
International Nuclear Information System (INIS)
Fort, E.
1982-01-01
1 - Description of problem or function: ESTIMA calculates level spacing and neutron strength function of a mixed sequence of s- and p-wave resonances given a set of neutron widths as input parameters. Three algorithms are used, two of which calculate s-wave average parameters and assume that the reduced widths obey a Porter-Thomas distribution truncated by a minimum detection threshold. The third performs a maximum likelihood fit to a truncated chi-squared distribution of any specified number of degrees of freedom, i.e. it can be used for calculating s-wave or p-wave average parameters. Resonances of undeclared angular orbital momentum are divided into groups of probable s-wave and probable p-wave by a simple application of Bayes' Theorem. 2 - Method of solution: Three algorithms are used: i) GAMN method, based on simple moments properties of a Porter-Thomas distribution. ii) Missing Level Estimator, a simplified version of the algorithm used by the program BAYESZ. iii) ESTIMA, a maximum likelihood fit. 3 - Restrictions on the complexity of the problem: A maximum of 400 resonances is allowed in the version available from NEADB, however this restriction can be relaxed by increasing array dimensions
Zeng, Zhi-Ping; Zhao, Yan-Gang; Xu, Wen-Tao; Yu, Zhi-Wu; Chen, Ling-Kun; Lou, Ping
2015-04-01
The frequent use of bridges in high-speed railway lines greatly increases the probability that trains are running on bridges when earthquakes occur. This paper investigates the random vibrations of a high-speed train traversing a slab track on a continuous girder bridge subjected to track irregularities and traveling seismic waves by the pseudo-excitation method (PEM). To derive the equations of motion of the train-slab track-bridge interaction system, the multibody dynamics and finite element method models are used for the train and the track and bridge, respectively. By assuming track irregularities to be fully coherent random excitations with time lags between different wheels and seismic accelerations to be uniformly modulated, non-stationary random excitations with time lags between different foundations, the random load vectors of the equations of motion are transformed into a series of deterministic pseudo-excitations based on PEM and the wheel-rail contact relationship. A computer code is developed to obtain the time-dependent random responses of the entire system. As a case study, the random vibration characteristics of an ICE-3 high-speed train traversing a seven-span continuous girder bridge simultaneously excited by track irregularities and traveling seismic waves are analyzed. The influence of train speed and seismic wave propagation velocity on the random vibration characteristics of the bridge and train are discussed.
Oblique shock waves in granular flows over bluff bodies
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Gopan Nandu
2017-01-01
Full Text Available Granular flows around an object have been the focus of numerous analytical, experimental and simulation studies. The structure and nature of the oblique shock wave developed when a quasi-two dimensional flow of spherical granular particles streams past an immersed, fixed cylindrical obstacle forms the focus of this study. The binary granular mixture, consisting of particles of the same diameter but different material properties, is investigated by using a modified LIGGGHTS package as the simulation engine. Variations in the solid fraction and granular temperature within the resulting flow are studied. The Mach number is calculated and is used to distinguish between the subsonic and the supersonic regions of the bow shock.
Loads on a 3D body due to second order waves and a current
DEFF Research Database (Denmark)
Skourup, Jesper; Cheung, K. F.; Bingham, Harry B.
2000-01-01
Non-linear loads on a fixed body due to waves and a current are investigated. Potential theory is used to describe the flow, and a three-dimensional (3D) boundary element method (BEM), combined with a time-stepping procedure, is used to solve the problem. The exact free-surface boundary conditions...... are expanded about the still-water level by Taylor series so that the solution is evaluated on a time-invariant geometry. A formulation correct to second order in the wave steepness and to first order in the current speed is used. Numerical results are obtained for the first-order and the second......-order oscillatory forces and for the second-order mean force on a fixed vertical circular cylinder in waves and a current. The second-order oscillatory forces on the body in waves and current are new results, while the remaining force components are verified by comparison with established numerical and analytical...
Asymptotic form of three-body (dtμ)+ and (ddμ)+ wave functions
International Nuclear Information System (INIS)
Kino, Y.; Shimamura, I.; Armour, E.A.G.; Kamimura, M.
1996-01-01
In order to investigate a discrepancy between existing literature values for the normalization constant in the asymptotic form of three-body wave functions for (DTμ) + , we report the results of a new calculation of the normalization constants for this system as well as the related system (DDμ) + . These were obtained by fitting to accurate variational wave functions with special care being taken to describe the long-range behavior. (orig.)
Magnetopause Waves Controlling the Dynamics of Earth’s Magnetosphere
Directory of Open Access Journals (Sweden)
Kyoung-Joo Hwang
2015-03-01
Full Text Available Earth’s magnetopause separating the fast and often turbulent magnetosheath and the relatively stagnant magnetosphere provides various forms of free energy that generate low-frequency surface waves. The source mechanism of this energy includes current-driven kinetic physical processes such as magnetic reconnection on the dayside magnetopause and flux transfer events drifting along the magnetopause, and velocity shear-driven (Kelvin-Helmholtz instability or density/ pressure gradient-driven (Rayleigh-Taylor instability magnetohydro-dynamics (MHD instabilities. The solar wind external perturbations (impulsive transient pressure pulses or quasi-periodic dynamic pressure variations act as seed fluctuations for the magnetopause waves and trigger ULF pulsations inside the magnetosphere via global modes or mode conversion at the magnetopause. The magnetopause waves thus play an important role in the solar wind-magnetosphere coupling, which is the key to space weather. This paper presents recent findings regarding the generation of surface waves (e.g., Kelvin- Helmholtz waves at the Earth’s magnetopause and analytic and observational studies accountable for the linking of the magnetopause waves and inner magnetospheric ULF pulsations, and the impacts of magnetopause waves on the dynamics of the magnetopause and on the inner magnetosphere.
Shallow S-Wave Velocity Structures in the Western Coastal Plain of Taiwan
Directory of Open Access Journals (Sweden)
Che-Min Lin
2009-01-01
Full Text Available The western coastal plain of Taiwan borders the Western Foot hills, which is a fold-and-thrust zone and one of Taiwan's major seismic zones. Earth quakes from the Western Foot hills are a frequent cause of disaster in the western coastal plain. In this study, array measurements of microtremors were conducted at seven sites through out the western coastal plain. At each site, four arrays (S, M, L, and XL arrays of different sizes were considered. The largest radius of each array ranged from 32 m to 1 km. The Maximum Likelihood Method of Frequency-Wavenumber (F-K analyses was used to obtain phase velocity dispersion curves. After the inversion of the dispersion curves with the initial models decided by Genetic Algorithm (GA searching, shallow S-wave velocity structures for the western coastal plain were estimated.
Recent Impacts on Mars: Cluster Properties and Seismic Signal Predictions
Justine Daubar, Ingrid; Schmerr, Nicholas; Banks, Maria; Marusiak, Angela; Golombek, Matthew P.
2016-10-01
Impacts are a key source of seismic waves that are a primary constraint on the formation, evolution, and dynamics of planetary objects. Geophysical missions such as InSight (Banerdt et al., 2013) will monitor seismic signals from internal and external sources. New martian craters have been identified in orbital images (Malin et al., 2006; Daubar et al., 2013). Seismically detecting such impacts and subsequently imaging the resulting craters will provide extremely accurate epicenters and source crater sizes, enabling calibration of seismic velocities, the efficiency of impact-seismic coupling, and retrieval of detailed regional and local internal structure.To investigate recent impact-induced seismicity on Mars, we have assessed ~100 new, dated impact sites. In approximately half of new impacts, the bolide partially disintegrates in the atmosphere, forming multiple craters in a cluster. We incorporate the resulting, more complex, seismic effects in our model. To characterize the variation between sites, we focus on clustered impacts. We report statistics of craters within clusters: diameters, morphometry indicating subsurface layering, strewn-field azimuths indicating impact direction, and dispersion within clusters indicating combined effects of bolide strength and elevation of breakup.Measured parameters are converted to seismic predictions for impact sources using a scaling law relating crater diameter to the momentum and source duration, calibrated for impacts recorded by Apollo (Lognonne et al., 2009). We use plausible ranges for target properties, bolide densities, and impact velocities to bound the seismic moment. The expected seismic sources are modeled in the near field using a 3-D wave propagation code (Petersson et al., 2010) and in the far field using a 1-D wave propagation code (Friederich et al., 1995), for a martian seismic model. Thus we calculate the amplitudes of seismic phases at varying distances, which can be used to evaluate the detectability
Reflection imaging of the Moon's interior using deep-moonquake seismic interferometry
Nishitsuji, Y.; Rowe, CA; Wapenaar, C.P.A.; Draganov, D.S.
2016-01-01
The internal structure of the Moon has been investigated over many years using a variety of seismic methods, such as travel time analysis, receiver functions, and tomography. Here we propose to apply body-wave seismic interferometry to deep moonquakes in order to retrieve zero-offset reflection
International Nuclear Information System (INIS)
Herbreteau, L.; Giraud, D.
1994-01-01
This device comprises reception modulus of these signals having an oscillator giving an electric wave, a mixing device and a band-pass filter or a low-pass filter giving the mean value of the output signal. By comparison with two predetermined values a signal is given when this mean value is out of these limits. 5 figs
Lin, Cheng-Horng
2016-12-23
There are more than 7 million people living near the Tatun volcano group in northern Taiwan. For the safety of the Taipei metropolis, in particular, it has been debated for decades whether or not these volcanoes are active. Here I show evidence of a deep magma reservoir beneath the Taipei metropolis from both S-wave shadows and P-wave delays. The reservoir is probably composed of either a thin magma layer overlay or many molten sills within thick partially molten rocks. Assuming that 40% of the reservoir is partially molten, its total volume could be approximately 350 km 3 . The exact location and geometry of the magma reservoir will be obtained after dense seismic arrays are deployed in 2017-2020.
Lin, Cheng-Horng
2016-12-01
There are more than 7 million people living near the Tatun volcano group in northern Taiwan. For the safety of the Taipei metropolis, in particular, it has been debated for decades whether or not these volcanoes are active. Here I show evidence of a deep magma reservoir beneath the Taipei metropolis from both S-wave shadows and P-wave delays. The reservoir is probably composed of either a thin magma layer overlay or many molten sills within thick partially molten rocks. Assuming that 40% of the reservoir is partially molten, its total volume could be approximately 350 km3. The exact location and geometry of the magma reservoir will be obtained after dense seismic arrays are deployed in 2017-2020.
Four-body wave function of π3He-system at the threshold energy
International Nuclear Information System (INIS)
Pupyshev, V.V.; Rakityanskij, S.A.
1985-01-01
On the basis of approximate four-body equations the wave function of π 3 He-system is calculated at zero kinetic energy of the pion. In the case when distances between all four particles are comparable with the nucleus size a strong distortion of the wave function of (3N)-subsystem caused by the presence of the pion is found. The calculated four-body function is represented in a semianalytical form, which makes it possible to apply it in different calculations
Dissipation-preserving spectral element method for damped seismic wave equations
Cai, Wenjun; Zhang, Huai; Wang, Yushun
2017-12-01
This article describes the extension of the conformal symplectic method to solve the damped acoustic wave equation and the elastic wave equations in the framework of the spectral element method. The conformal symplectic method is a variation of conventional symplectic methods to treat non-conservative time evolution problems, which has superior behaviors in long-time stability and dissipation preservation. To reveal the intrinsic dissipative properties of the model equations, we first reformulate the original systems in their equivalent conformal multi-symplectic structures and derive the corresponding conformal symplectic conservation laws. We thereafter separate each system into a conservative Hamiltonian system and a purely dissipative ordinary differential equation system. Based on the splitting methodology, we solve the two subsystems respectively. The dissipative one is cheaply solved by its analytic solution. While for the conservative system, we combine a fourth-order symplectic Nyström method in time and the spectral element method in space to cover the circumstances in realistic geological structures involving complex free-surface topography. The Strang composition method is adopted thereby to concatenate the corresponding two parts of solutions and generate the completed conformal symplectic method. A relative larger Courant number than that of the traditional Newmark scheme is found in the numerical experiments in conjunction with a spatial sampling of approximately 5 points per wavelength. A benchmark test for the damped acoustic wave equation validates the effectiveness of our proposed method in precisely capturing dissipation rate. The classical Lamb problem is used to demonstrate the ability of modeling Rayleigh wave in elastic wave propagation. More comprehensive numerical experiments are presented to investigate the long-time simulation, low dispersion and energy conservation properties of the conformal symplectic methods in both the attenuating
Provost, Floriane; Hibert, Clément; Malet, Jean-Philippe; Stumpf, André; Doubre, Cécile
2016-04-01
Different studies have shown the presence of microseismic activity in soft-rock landslides. The seismic signals exhibit significantly different features in the time and frequency domains which allow their classification and interpretation. Most of the classes could be associated with different mechanisms of deformation occurring within and at the surface (e.g. rockfall, slide-quake, fissure opening, fluid circulation). However, some signals remain not fully understood and some classes contain few examples that prevent any interpretation. To move toward a more complete interpretation of the links between the dynamics of soft-rock landslides and the physical processes controlling their behaviour, a complete catalog of the endogeneous seismicity is needed. We propose a multi-class detection method based on the random forests algorithm to automatically classify the source of seismic signals. Random forests is a supervised machine learning technique that is based on the computation of a large number of decision trees. The multiple decision trees are constructed from training sets including each of the target classes. In the case of seismic signals, these attributes may encompass spectral features but also waveform characteristics, multi-stations observations and other relevant information. The Random Forest classifier is used because it provides state-of-the-art performance when compared with other machine learning techniques (e.g. SVM, Neural Networks) and requires no fine tuning. Furthermore it is relatively fast, robust, easy to parallelize, and inherently suitable for multi-class problems. In this work, we present the first results of the classification method applied to the seismicity recorded at the Super-Sauze landslide between 2013 and 2015. We selected a dozen of seismic signal features that characterize precisely its spectral content (e.g. central frequency, spectrum width, energy in several frequency bands, spectrogram shape, spectrum local and global maxima
User's manual for seismic analysis code 'SONATINA-2V'
Energy Technology Data Exchange (ETDEWEB)
Hanawa, Satoshi; Iyoku, Tatsuo [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment
2001-08-01
The seismic analysis code, SONATINA-2V, has been developed to analyze the behavior of the HTTR core graphite components under seismic excitation. The SONATINA-2V code is a two-dimensional computer program capable of analyzing the vertical arrangement of the HTTR graphite components, such as fuel blocks, replaceable reflector blocks, permanent reflector blocks, as well as their restraint structures. In the analytical model, each block is treated as rigid body and is restrained by dowel pins which restrict relative horizontal movement but allow vertical and rocking motions between upper and lower blocks. Moreover, the SONATINA-2V code is capable of analyzing the core vibration behavior under both simultaneous excitations of vertical and horizontal directions. The SONATINA-2V code is composed of the main program, pri-processor for making the input data to SONATINA-2V and post-processor for data processing and making the graphics from analytical results. Though the SONATINA-2V code was developed in order to work in the MSP computer system of Japan Atomic Energy Research Institute (JAERI), the computer system was abolished with the technical progress of computer. Therefore, improvement of this analysis code was carried out in order to operate the code under the UNIX machine, SR8000 computer system, of the JAERI. The users manual for seismic analysis code, SONATINA-2V, including pri- and post-processor is given in the present report. (author)
Directory of Open Access Journals (Sweden)
Boris M. Chikov
2010-01-01
Full Text Available In our study, an earthquake focus is viewed as a 3D zone of the Earth’s crust, wherein the discharge of mechanical loading is accompanied by recordable destruction and qualitative transformation of the geological medium. The purpose of the present publication is to make an attempt to reveal a direct relationship between seismicity and deformation-metamorphic processes which took place in the Earth’s crust. Traditional and alternative interpretations of geomechanics of seismic-foci situations are discussed. The problems of geodynamics and geostatics of the seismic-foci systems and their concentrations, as well as anthropogenic models and mechanisms of focus medium structuring are reviewed. The relationship between seismicity and mechanisms of «regional shearing» or formation of crustal deformation-metamorphic structures of lineament type is outlined in the example of the Chuya seismic system of earthquakes which occurred in 2003 and afterwards in the Altai region.
Multi-component joint analysis of surface waves
Czech Academy of Sciences Publication Activity Database
Dal Moro, Giancarlo; Moura, R.M.M.; Moustafa, S.S.R.
2015-01-01
Roč. 119, AUG (2015), s. 128-138 ISSN 0926-9851 Institutional support: RVO:67985891 Keywords : surface waves * surface wave dispersion * seismic data acquisition * seismic data inversion * velocity spectrum Subject RIV: DB - Geology ; Mineralogy Impact factor: 1.355, year: 2015
Tracing the Farallon plate through seismic imaging with USArray
Porritt, Robert William
The Farallon plate system has been subducting off the western United States since at least the middle Mesozoic. This plate has undergone virtually every subduction process during this time including a long episode of flat-slab subduction, generation of microplates, and formation of oceanic plateaus. The shallow remains of this plate are two small microplates, the Gorda and Juan de Fuca, in the Pacific Northwest. The anomalous nature of these two small plates and the missing deeper evidence of subduction has motivated this study. The USArray seismic experiment has provided unprecedented spatial sampling of the seismic wavefield in the continuous United States. Utilizing this dataset, new imaging methods have been implemented and older imaging methods have been revitalized. This study first uses ambient seismic noise in the Pacific Northwest to extract short period Rayleigh waves which are sensitive to lithospheric scale structure. Phase velocities from this model are then combined with teleseismic delay times of body waves and surface waves to image the structure of the continuous United States from the surface through the mantle transition zone. The resolving power of this model allows tracing of the Farallon plate from the trench to the lower mantle. The seismic velocity structure of the continuous United States is broadly composed of a slow western half and fast eastern half separated by the Rocky Mountain Front. The low velocity of the western U.S. contains several high velocity anomalies. While previous work has focused on individual anomalies and suggested they represent lithospheric instabilities, a larger regional view indicates that these are the western remnants of the Farallon plate. Below the thick cratonic lithosphere of the eastern U.S., the Farallon plate contains significant topography due to a subducted heterogeneity of the oceanic plate and a viscosity contrast through the mantle transition zone. The velocity models presented herein provide a
International Nuclear Information System (INIS)
Bertolini, A.; Cella, G.; Chenyang, W.; Salvo, R. de; Kovalik, J.; Marka, S.; Sannibale, V.; Takamori, A.; Tariq, H.; Viboud, N.
2001-01-01
High-performance Seismic Isolation Systems in gravitational wave interferometers are needed not only to increase the sensitivity of the detectors but also to guarantee long periods of stable operation. SAS is essentially a system which produces the required in-band seismic isolation by use of passive mechanical filters and actively reduces the out of band seismic noise using inertial damping. The passive isolation is achieved for all the 6 degrees of freedom, with an Inverted Pendulum and a chain of single wire pendula whose masses are the Geometrical Anti-Spring Filters (GASF). The active control is applied to reduce mainly the noise below 4 Hz and to damp the resonances of the chain acting from the inverted pendulum table. Here we present a brief overview of SAS and recent results achieved from the full scale SAS prototype
Transient waves in visco-elastic media
Ricker, Norman
1977-01-01
Developments in Solid Earth Geophysics 10: Transient Waves in Visco-Elastic Media deals with the propagation of transient elastic disturbances in visco-elastic media. More specifically, it explores the visco-elastic behavior of a medium, whether gaseous, liquid, or solid, for very-small-amplitude disturbances. This volume provides a historical overview of the theory of the propagation of elastic waves in solid bodies, along with seismic prospecting and the nature of seismograms. It also discusses the seismic experiments, the behavior of waves propagated in accordance with the Stokes wave
Systolic Time Interval Estimation Using Continuous Wave Radar With On-Body Antennas.
Buxi, Dilpreet; Hermeling, Evelien; Mercuri, Marco; Beutel, Fabian; van der Westen, Roberto Garcia; Torfs, Tom; Redoute, Jean-Michel; Yuce, Mehmet Rasit
2018-01-01
The estimation of systolic time intervals (STIs) is done using continuous wave (CW) radar at 2.45 GHz with an on-body antenna. In the state of the art, typically bioimpedance, heart sounds and/or ultrasound are used to measure STIs. All three methods suffer from insufficient accuracy of STI estimation due to various reasons. CW radar is investigated for its ability to overcome the deficiencies in the state of the art. Ten healthy male subjects aged 25-45 were asked to lie down at a 30 incline. Recordings of 60 s were taken without breathing and with paced breathing. Heart sounds, electrocardiogram, respiration, and impedance cardiogram were measured simultaneously as reference. The radar antennas were placed at two positions on the chest. The antennas were placed directly on the body as well as with cotton textile in between. The beat to beat STIs have been determined from the reference signals as well as CW radar signals. The results indicate that CW radar can be used to estimate STIs in ambulatory monitoring. The results pave way to a potentially more compact method of estimating STIs, which can be integrated into a wearable device.
Optimal Configurations of Wave Energy Converter Arrays with a Floating Body
Directory of Open Access Journals (Sweden)
Zhang Wanchao
2016-10-01
Full Text Available An array of floating point-absorbing wave energy converters (WECs is usually employed for extracting efficiently ocean wave energy. For deep water environment, it is more feasible and convenient to connect the absorbers array with a floating body, such as a semi-submersible bottom-moored disk, whose function is to act as the virtual seabed. In the present work, an array of identical floating symmetrically distributed cylinders in a coaxial moored disk as a wave energy device is proposed The power take-off (PTO system in the wave energy device is assumed to be composed of a linear/nonlinear damper activated by the buoys heaving motion. Hydrodynamic analysis of the examined floating system is implemented in frequency domain. Hydrodynamic interferences between the oscillating bodies are accounted for in the corresponding coupled equations. The array layouts under the constraint of the disk, incidence wave directions, separating distance between the absorbers and the PTO damping are considered to optimize this kind of WECs. Numerical results with regular waves are presented and discussed for the axisymmetric system utilizing heave mode with these interaction factors, in terms of a specific numbers of cylinders and expected power production.
DEFF Research Database (Denmark)
Ibsen, Lars Bo
2008-01-01
Estimates for the amount of potential wave energy in the world range from 1-10 TW. The World Energy Council estimates that a potential 2TW of energy is available from the world’s oceans, which is the equivalent of twice the world’s electricity production. Whilst the recoverable resource is many...
Liu, T.; Klemperer, S. L.; Yu, C.; Ning, J.
2017-12-01
In the past decades, P wave receiver functions (PRF) have been routinely used to image the Moho, although it is well known that PRFs are susceptible to contamination from sedimentary multiples. Recently, Virtual Deep Seismic Sounding (VDSS) emerged as a novel method to image the Moho. However, despite successful applications of VDSS on multiple datasets from different areas, how sedimentary basins affect the waveforms of post-critical SsPmp, the Moho reflection phase used in VDSS, is not widely understood. Here, motivated by a dataset collected in the Ordos plateau, which shows distinct effects of sedimentary basins on SsPmp and Pms waveforms, we use synthetic seismograms to study the effects of sedimentary basins on SsPmp and Pms, the phases used in VDSS and PRF respectively. The results show that when the sedimentary thickness is on the same order of magnitude as the dominant wavelength of the incident S wave, SsPmp amplitude decreases significantly with S velocity of the sedimentary layer, whereas increasing sedimentary thickness has little effect in SsPmp amplitude. Our explanation is that the low S velocity layer at the virtual source reduces the incident angle of S wave at the free surface, thus decreases the S-to-P reflection coefficient at the virtual source. In addition, transmission loss associated with the bottom of sedimentary basins also contributes to reducing SsPmp amplitude. This explains not only our observations from the Ordos plateau, but also observations from other areas where post-critical SsPmp is expected to be observable, but instead is too weak to be identified. As for Pms, we observe that increasing sedimentary thickness and decreasing sedimentary velocities both can cause interference between sedimentary multiples and Pms, rendering the Moho depths inferred from Pms arrival times unreliable. The reason is that although Pms amplitude does not vary with sedimentary thickness or velocities, as sedimentary velocities decrease and thickness
Gamage, S.S.N.; Umino, N.; Hasegawa, A.; Kirby, S.H.
2009-01-01
We detected the sP depth phase at small epicentral distances of about 150 km or more in the seismograms of shallow earthquakes in the NE Japan forearc region. The focal depths of 1078 M > 3 earthquakes that occurred from 2000 to 2006 were precisely determined using the time delay of the sP phase from the initial P-wave arrival. The distribution of relocated hypocentres clearly shows the configuration of a double-planed shallow seismic zone beneath the Pacific Ocean. The upper plane has a low dip angle near the Japan Trench, increasing gradually to ???30?? at approximately 100 km landward of the Japan Trench. The lower plane is approximately parallel to the upper plane, and appears to be the near-trench counterpart of the lower plane of the double-planed deep seismic zone beneath the land area. The distance between the upper and lower planes is 28-32 km, which is approximately the same as or slightly smaller than that of the double-planed deep seismic zone beneath the land area. Focal mechanism solutions of the relocated earthquakes are determined from P-wave initial motion data. Although P-wave initial motion data for these offshore events are not ideally distributed on the focal sphere, we found that the upper-plane events that occur near the Japan Trench are characterized by normal faulting, whereas lower-plane events are characterized by thrust faulting. This focal mechanism distribution is the opposite to that of the double-planed deep seismic zone beneath the land area. The characteristics of these focal mechanisms for the shallow and deep doubled-planed seismic zones can be explained by a bending-unbending model of the subducting Pacific plate. Some of relocated earthquakes took place in the source area of the 1933 Mw8.4 Sanriku earthquake at depths of 10-23 km. The available focal mechanisms for these events are characterized by normal faulting. Given that the 1933 event was a large normal-fault event that occurred along a fault plane dipping landward, the
Statistical analysis of s-wave neutron reduced widths
International Nuclear Information System (INIS)
Pandita Anita; Agrawal, H.M.
1992-01-01
The fluctuations of the s-wave neutron reduced widths for many nuclei have been analyzed with emphasis on recent measurements by a statistical procedure which is based on the method of maximum likelihood. It is shown that the s-wave neutron reduced widths of nuclei follow single channel Porter Thomas distribution (x 2 -distribution with degree of freedom ν = 1) for most of the cases. However there are apparent deviations from ν = 1 and possible explanation and significance of this deviation is given. These considerations are likely to modify the evaluation of neutron cross section. (author)
CSIR Research Space (South Africa)
Shatalov, MY
2011-01-01
Full Text Available -1 Journal of Sound and Vibration Volume 330, Issue 1, 3 January 2011, Pages 127-135 The influence of mass imperfections on the evolution of standing waves in slowly rotating spherical bodies Michael Y. Shatalova, b, Stephan V. Jouberta...
Yeluru, P. M.; Baker, G. S.
2008-12-01
The geology of Earth's moon has previously been examined via telescopic observations, orbiting spacecraft readings, lunar sample analysis, and also from some geophysical data. Previous researchers have examined layering of the moon and models exist explaining the velocity variations in the mantle and core. However, no studies (or datasets) currently exist regarding the engineering properties of the shallow (channel Analysis of Surface Wave (MASW), has greatly increased our ability to map subsurface variations in physical properties. The MASW method involves deployment of multiple seismometers to acquire 1-D or 2-D shear wave velocity profiles that can be directly related to various engineering properties. The advantage of this technique over drilling boreholes or any other geophysical technique is that it is less intensive, non-invasive, more cost- effective, and more robust because strong surface-wave records are almost guaranteed. In addition, data processing and analysis is fairly straightforward, and the MASW method allows for analysis of a large area of interest as compared to drilling boreholes. A new scheme using randomly distributed geophones (likely deployed from a mortar-type device) instead of a conventional linear array will be presented. A random array is necessary for lunar exploration because of the logistical constraints involved in deploying a linear or circular array robotically or by astronaut. Initial results indicate that robust dispersion curves (and thus subsurface models of engineering properties) can be obtained from the random array geometry. This random geometry will also be evaluated (a) for potential improvements in the resolution of the dispersion image and (b) as more accurate method for assessing azimuthal variations in the subsurface geology. Based on the extreme logistics imposed by lunar exploration and the anticipated engineering needs of lunar exploration, information obtained on the moon using this technique should prove to be
Total body irradiation: what schedule(s)
International Nuclear Information System (INIS)
Cosset, J.M.
1993-01-01
In this article, the author explains why a whole-body irradiation is still an essential step before a bone marrow graft. He presents irradiation protocols for acute myeloid leukemia and chronic myeloid leukemia. 14 refs
Kawase, Hiroshi; Mori, Yuta; Nagashima, Fumiaki
2018-01-01
We have been discussing the validity of using the horizontal-to-vertical spectral ratios (HVRs) as a substitute for S-wave amplifications after Nakamura first proposed the idea in 1989. So far a formula for HVRs had not been derived that fully utilized their physical characteristics until a recent proposal based on the diffuse field concept. There is another source of confusion that comes from the mixed use of HVRs from earthquake and microtremors, although their wave fields are hardly the same. In this study, we compared HVRs from observed microtremors (MHVR) and those from observed earthquake motions (EHVR) at one hundred K-NET and KiK-net stations. We found that MHVR and EHVR share similarities, especially until their first peak frequency, but have significant differences in the higher frequency range. This is because microtremors mainly consist of surface waves so that peaks associated with higher modes would not be prominent, while seismic motions mainly consist of upwardly propagating plain body waves so that higher mode resonances can be seen in high frequency. We defined here the spectral amplitude ratio between them as EMR and calculated their average. We categorize all the sites into five bins by their fundamental peak frequencies in MHVR. Once we obtained EMRs for five categories, we back-calculated EHVRs from MHVRs, which we call pseudo-EHVRs (pEHVR). We found that pEHVR is much closer to EHVR than MHVR. Then we use our inversion code to invert the one-dimensional S-wave velocity structures from EHVRs based on the diffuse field concept. We also applied the same code to pEHVRs and MHVRs for comparison. We found that pEHVRs yield velocity structures much closer to those by EHVRs than those by MHVRs. This is natural since what we have done up to here is circular except for the average operation in EMRs. Finally, we showed independent examples of data not used in the EMR calculation, where better ground structures were successfully identified from p
Innovative Approaches for Seismic Studies of Mars (Invited)
Banerdt, B.
2010-12-01
In addition to its intrinsic interest, Mars is particularly well-suited for studying the full range of processes and phenomena related to early terrestrial planet evolution, from initial differentiation to the start of plate tectonics. It is large and complex enough to have undergone most of the processes that affected early Earth but, unlike the Earth, has apparently not undergone extensive plate tectonics or other major reworking that erased the imprint of early events (as evidenced by the presence of cratered surfaces older than 4 Ga). The martian mantle should have Earth-like polymorphic phase transitions and may even support a perovskite layer near the core (depending on the actual core radius), a characteristic that would have major implications for core cooling and mantle convection. Thus even the most basic measurements of planetary structure, such as crustal thickness, core radius and state (solid/liquid), and gross mantle velocity structure would provide invaluable constraints on models of early planetary evolution. Despite this strong scientific motivation (and several failed attempts), Mars remains terra incognita from a seismic standpoint. This is due to an unfortunate convergence of circumstances, prominent among which are our uncertainty in the level of seismic activity and the relatively high cost of landing multiple long-lived spacecraft on Mars to comprise a seismic network for body-wave travel-time analysis; typically four to ten stations are considered necessary for this type of experiment. In this presentation I will address both of these issues. In order to overcome the concern about a possible lack of marsquakes with which to work, it is useful to identify alternative methods for using seismic techniques to probe the interior. Seismology without quakes can be accomplished in a number of ways. “Unconventional” sources of seismic energy include meteorites (which strike the surface of Mars at a relatively high rate), artificial projectiles
s -wave scattering length of a Gaussian potential
Jeszenszki, Peter; Cherny, Alexander Yu.; Brand, Joachim
2018-04-01
We provide accurate expressions for the s -wave scattering length for a Gaussian potential well in one, two, and three spatial dimensions. The Gaussian potential is widely used as a pseudopotential in the theoretical description of ultracold-atomic gases, where the s -wave scattering length is a physically relevant parameter. We first describe a numerical procedure to compute the value of the s -wave scattering length from the parameters of the Gaussian, but find that its accuracy is limited in the vicinity of singularities that result from the formation of new bound states. We then derive simple analytical expressions that capture the correct asymptotic behavior of the s -wave scattering length near the bound states. Expressions that are increasingly accurate in wide parameter regimes are found by a hierarchy of approximations that capture an increasing number of bound states. The small number of numerical coefficients that enter these expressions is determined from accurate numerical calculations. The approximate formulas combine the advantages of the numerical and approximate expressions, yielding an accurate and simple description from the weakly to the strongly interacting limit.