double beam imaging mapping lower mantle heterogeneities using combinations of source and receiver arrays we present a new technique for imaging spatially distributed heterogeneities using information from combinations of source and receiver arrays the method is based on the single scattering assumption and is closely related to the double beam method of kruger et al 1993 1995 1996 in that it exploits amplitude delay time slowness and azimuth information in two arrays simultaneously a crucial step in the method is the application of static time corrections for a chosen reference phase here pcp one type of image is obtained as a spatial likelihood distribution for prescribed source and receiver array slowness and azimuth values and delay times with respect to a reference phase this allows the determination of the spatial origin of coherent phases in the p coda in a complementary approach we perform a double beam stack migration according to the theoretical slowness and azimuth values for candidate scatterers distributed over a three dimensional 3 d grid the scattering strength is expressed as the resulting beam power beam amplitude or semblance in a time window determined from the theoretical delay time with respect to the reference phase while likelihood mapping provides an image reflecting the probability of a region to explain observed kinematic phase properties by single scattering double beam migration provides information about the scattering strength the method is applied to nuclear explosion sources in eastern kazakhstan recorded at the yellowknife array in northern canada we identify several scattering volumes within the lower mantle below the arctic producing individual anomalous lower mantle phases in the p coda these anomalies range in depth from the core mantle boundary cmb up to 500 km into the lowermost mantle and are mainly located under the eurasian side of the arctic the joint interpretation of these results with the results of previous studies suggests a connection of these anomalies to the cenozoic and mesozoic subduction of the pacific plate and the kula plate the determination of the nature of such 3 d anomalies necessitates further array studies with better azimuthal coverage

an efficient algorithm for double difference tomography and location in heterogeneous media with an application to the kilauea volcano 1 improving our understanding of crustal processes requires a better knowledge of the geometry and the position of geological bodies in this study we have designed a method based upon double difference relocation and tomography to image as accurately as possible a heterogeneous medium containing seismogenic objects our approach consisted not only of incorporating double difference in tomography but also partly in revisiting tomographic schemes for choosing accurate and stable numerical strategies adapted to the use of cross spectral time delays we used a finite difference solution to the eikonal equation for travel time computation and a tarantola valette approach for both the classical and double difference three dimensional tomographic inversion to find accurate earthquake locations and seismic velocity estimates we estimated efficiently the square root of the inverse model s covariance matrix in the case of a gaussian correlation function it allows the use of correlation length and a priori model variance criteria to determine the optimal solution double difference relocation of similar earthquakes is performed in the optimal velocity model making absolute and relative locations less biased by the velocity model double difference tomography is achieved by using high accuracy time delay measurements these algorithms have been applied to earthquake data recorded in the vicinity of kilauea and mauna loa volcanoes for imaging the volcanic structures stable and detailed velocity models are obtained the regional tomography unambiguously highlights the structure of the island of hawaii and the double difference tomography shows a detailed image of the southern kilauea caldera upper east rift zone magmatic complex

the computation of body wave synthetic seismograms in laterally homogeneous media synthetic seismograms computed for realistic horizontally stratified media are now routinely used as an aid to seismic interpretation this paper reviews the theoretical background to these methods and presents comparisons of the two popular algorithms reflectivity and wkbj seismograms for a variety of earth models the transformed wave equations are developed from the equations for a spherical gravitating medium in a symmetric form suitable for body wave calculations four methods of solving these equations in general inhomogeneous layers are described the wkbj and langer asymptotic expansions and the wkbj and langer iterative solutions together with the earth flattening transformation and the ray expansion transformed solutions for body waves can then be obtained for realistic layered media four methods of inverting the frequency and wave number transformations are also described the real and complex spectral and slowness methods although realistic seismic models are normally sufficiently complicated that numerical calculations are essential before proceeding with numerical comparisons we have included a review of the canonical signals included in body wave seismograms these analytic results for direct rays partial and total reflections turning rays on forward and reversed branches head waves interface waves airy caustics and fresnel and interface shadows are useful to anticipate and understand numerical problems and results finally a comparison of green s functions for crustal mantle and whole earth models calculated using the wkbj and reflectivity algorithms is included

comparison of prestack stereotomography and nip wave tomography for velocity model building instances from the messinian evaporites velocity model determination during seismic data processing is crucial for any kind of depth imaging we compared two approaches of grid tomography prestack stereotomography and normal incidence point nip wave tomography whereas nip wave tomography is based on wavefield attributes obtained during the common reflection surface stack and thus on the underlying hyperbolic second order traveltime approximation prestack stereotomography describes traveltimes by local slopes i e linearly in the prestack data domain to analyze the impact of the different traveltime approximations and the different input data domains on velocity model building we applied two implementations of these techniques to two profiles of a field marine data set from the levante basin eastern mediterranean because ofthe presence of a thick tabular mobile unit of the messinian evaporites strong vertical and lateral velocity contrasts had been expected the velocity models revealed the reconstruction of high velocity contrasts

love mode dispersion across subduction zones by finite element modelling summary phase velocity and mode conversion of love waves with normal incidence across a subduction zone have been studied with the use of the finite element algorithm previously developed for seismic waves through anomalous earth structures two rather different models are considered representing subduction slabs under japan and the north island of new zealand fundamental mode love wave dispersion curves have been calculated for wave periods between 5 and 60s comparison with phase velocity curves for the adjacent ocean and island regions shows that the phase velocity for the subduction zones is in general slightly less than the mean of the phase velocities of the adjacent regions for example at a period of 20 s the phase velocity in the model of the subduction zone of japan is 4 1 57 km s and the mean of the phase velocities in the regions at the ends of the model is 4 245 km sc1 at the same period the phase velocity in the new zealand subduction model is 3 895 km s and the mean of the phase velocities at the ends of the model is 4 150 km s at a period of 10 s only 5 per cent of the energy of the incident fundamental love mode is transmitted in the fundamental mode across the model of the subduction zone of japan at a period of 15 s 18 per cent of the energy of the incident fundamental love mode is transmitted in the fundamental mode across the new zealand subduction zone at these periods a subduction zone significantly scatters the energy of the fundamental love mode in the same way as a continental margin scatters it the relevance of these results for the inversion of dispersion measurements of surface waves with circumglobal paths is that subduction zones have a negligible effect on the phase velocity of the fundamental love mode and that scattering of the fundamental love mode at subduction zones and at continental margins is important only at periods less than approximately 40 s

synthetic sh seismograms in a laterally varying medium by the discrete wavenumber method summary we present a new method to calculate the sh wavefield produced by a seismic source in a half space with an irregular buried interface the diffractiog interface is represented by a distribution of body forces the green s functions needed to solve the boundary conditions are evaluated using the discrete wavenumber method our approach relies on the introduction of a periodicity in the source medium configuration and on the discretization of the interface at regular spacing the technique developed is applicable to boundaries of arbitrary shapes and is valid at all frequencies some examples of calculation in simple configurations are presented showing the capabilities of the method

interferometric daylight seismic imaging summary claerbout s daylight imaging concept is generalized to a theory of interferometric seismic imaging ii interferometric seismic imaging is defined to be any algorithm that inverts correlated seismic data for the reflectivity or source distribution as examples we show that ii can image reflectivity distributions by migrating ghost reflections in passive seismic data and generalizes the receiver function imaging method used by seismologists interferometric seismic imaging can also migrate free surface multiples in common depth point cdp data and image source distributions from passive seismic data both synthetic and field data examples are used to illustrate the different possibilities of ii the key advantage of ii is that it can image source locations or reflectivity distributions from passive seismic data where the source position or wavelet is unknown in some cases it can mitigate defocusing errors as a result of statics or an incorrect migration velocity the main drawback with ii is that severe migration artefacts can be created by partial focusing of virtual multiples

double beam analysis of anomalies in the core mantle boundary region seismic p waves from nuclear explosions at the kazakhstan test site in eastern kazakhstan kts observed at the yellowknife array yka canada are used to analyze the structure at the base of the mantle under severnaya zemlya arctic sea 18 events at the degelen subsite and 9 events at the shagan river subsite of kts are studied the simple waveforms and well controlled source parameters of nuclear explosions allow the use of the events as source arrays in addition to the usual receiver array configuration a new method double beamforming integrating both concepts is presented this method increases the resolution considerably for the degelen yka path one anomalous arrival 1 9 s before pcp slowness between p and pcp slowness is observed smaller anomalous arrivals are found 6 5 s degelen yka and 8 1 s before pcp shagan river yka these anomalous phases cannot be explained with standard earth models they are produced by reflections from an inhomogeneity in the lowermost mantle at 82 3n 107 5e under the area north of severnaya zemlya the strong variations between the wavefields for the two source receiver combinations indicate a heterogeneous structure in the lower mantle the anomaly found here is located close to an anomaly in the lowermost mantle beneath the nansen basin

cross correlation weighted migration towards high resolution mapping of mantle heterogeneities summary we present a new type of born migration scheme to obtain a high resolution image of smallscale scatterers in the mantle seismic migration is a technique that projects scattered energy back to its origin by shifting and stacking seismograms using theoretical traveltimes migration methods in global seismology because of the limited distribution of sources and receivers tend to suffer from considerable smearing owing to isochronal artefacts this type of artefacts is caused by migration grids that have the set of theoretical traveltimes from a given source to all receivers similar to that for a true scattering point previously the information of slowness and backazimuth was explicitly explored to reduce such migration artefacts here we propose a simpler and more computationally efficient method but with similar effects in which the coherency of shifted seismograms measured by cross correlation is exploited to suppress isochronal artefacts the new migration scheme makes it possible to compute a large number of migrated images efficiently and thus evaluate the robustness of observed scattering objects by statistical approaches such as bootstrap resampling

modified topographic amplification factors for a single faced slope due to kinematic soil structure interaction in this paper we evaluate the additive effects of topography soil nonlinearity and soil structure interaction ssi along the crest of an idealized 40 m high cliff type topographic feature with slope inclination 300 where excessive damage was observed during the athens 1999 earthquake the objective of this paper is to investigate the relative contribution of topographic amplification and kinematic ssi as a function of the incident motion frequency content and geotechnical site conditions for a surface and an embedded structure located at the cliff crest for this purpose we perform elastic parametric and nonlinear site specific two dimensional finite element simulations using three profiles and six input motions we illustrate the role of ssi in altering the response at the location of peak topographic amplification potential behind the crest the effects of incident motion incoherency on the transient structural response and the beneficial contribution of structural embedment we finally suggest that empirical models for base slab averaging of shallow foundations developed as a function of site conditions structural dimensions and center line location could be combined with topographic amplification factors to predict realistic design spectra for structures located on irregular topographic features

an example of two dimensional synthetic seismogram modeling abstract synthetic seismograms for laterally inhomogeneous velocity and q structures can be calculated by the disk ray theory drt method ray tracing through the model provides travel time distance slowness and ray amplitude data which are combined to synthesize seismic record sections by drt the amplitude factors include geometrical spreading attenuation due to q 1 reflection and transmission coefficients and the free surface conversion coefficient comparison of drt synthetic seismograms with those calculated by the reflectivity method for a layer over a half space model shows excellent agreement in both amplitude and waveform character of all arrivals direct reflected p to s converted multiply reflected and head waves may be synthesized by the drt method in an application of two dimensional synthetic seismogram modeling using the drt method synthetic seismogram record sections were calculated for a complicated geological model of the crust in the eastern snake river plain idaho and compared with observed seismic data in this application we find that a small modification of the snake river plain velocity model which was interpreted from travel time data produces drt synthetic seismograms which compare well with the amplitude and waveform character of the observed seismograms

hybrid modeling of p sv seismic motion at inhomogeneous viscoelastic topographic structures a new hybrid two step method for computation of p sv seismic motion at inhomogeneous viscoelastic topographic structure is presented the method is based on a combination of the discrete wavenumber dw finite difference fd and finite element fe methods in the first step the dw method is used to calculate the source radiation and wave propagation in the background 1d medium in the second step the fd fe algorithm is used to compute the wave propagation along the topographic structure the accuracy of the method has been separately tested for inclusion of the attenuation and for inclusion of the free surface topography through numerical comparisons with analytical and independent numerical methods the method is a generalization of the hybrid dw fd method of zahradnik and moczo 1996 for localized structures with a flat free surface numerical computations for a ridge sediment valley and the ridge neighboring the sediment valley show that a ridge can considerably influence the response of the neighboring sediment valley this means that the neighboring topographic feature should be taken into account even when we are only interested in the valley response

calculation of synthetic seismograms in a laterally varying medium by the boundary element discrete wavenumber method abstract we investigate the propagation of lg waves in laterally varying crustal structures by numerical simulation the method of calculation is formulated in terms of boundary integral equations where the green9s functions are evaluated by wavenumber summation the approach is well suited to study the propagation of seismic waves in a layered medium where the interfaces are flat in some regions and irregular in others we investigate the effect of a crustal fault with vertical offset and study the case of a lateral change in crustal thickness the results show that the lg wave amplitude is only slightly affected by the presence of these heterogeneities they confirm the robustness of lg wave propagation in presence of lateral heterogeneities observed in other numerical simulations they show that large scale geometric features of the crust cannot account alone for the strong attenuation of lg waves observed in many regions the results also suggest a possible relation between the level of lg wave coda and the degree of roughness of the moho they further indicate the importance of backscattering and suggest a possible use of the backscattered wave field to map strong crustal heterogeneities

predicting permeability and gas production of hydraulically fractured tight sands from microseismic data the main objective of hydraulic well stimulation is creating fractures in a tight rock that enhance its natural permeability and make hydrocarbon production economic because the geometry of fractures and the permeability of treated formation influence the subsequent production their assessment is important for the development of tight gas fields the fracture shapes and orientations are inferred conventionally from microseismic data acquired in the process of well stimulation but the same data also can be used to estimate the formation permeability we have compared two techniques for permeability estimation that utilize different aspects of information contained in the observed microseismicity we applied those techniques to data recorded in the course of the hydraulic fracturing of four wells drilled in the pinedale field wyoming u s a then we used the obtained permeabilities to predict the gas rates from 20 treatment stages at which the number of identified microseismic events was sufficient to perform our analysis the predictions of both techniques correlate with production and allow us to establish the characteristics of rocks and hydraulic fractures that make good producers at pinedale

a review of numerical experiments on seismic wave scattering this paper reviews applications of the finite difference and finite element methods to the study of seismic wave scattering in both simple and complex velocity models these numerical simulations have improved our understanding of seismic scattering in portions of the earth where there is significant lateral heterogeneity such as the crust the methods propagate complete seismic wavefields through highly complex media and include multiply scattered waves and converted phases e g p tosv sv top body wave to surface wave the numerical methods have been especially useful in cases of moderate and strong scattering in complex media where multiple scattering becomes important progress has been made with numerical methods in understanding how near surface low velocity basin structures scatter surface waves and vertically incident body waves the numerical methods have proven useful in evaluating scattering of surface waves and body waves from topography of both the free surface and interfaces buried at depth numerical studies have demonstrated the importance of conversions from body waves to surface waves andvice versa when lateral heterogeneities and topographic relief are present in the uppermost crust recently several investigations have applied numerical methods to study seismic wave propagation in velocity models which vary randomly in space this stochastic approach seeks to understand the effects of small scale complexity in the earth which cannot be resolved deterministically these experiments have quantified the relationships between the statistical properties of the random heterogeneity and the measurable properties of high frequency 1 hz seismograms these simulations have been applied to the study of many features observed in actual high frequency seismic waves including the amplitude and time decay of seismic coda the apparent attenuation from scattering the dispersion of waveforms and the travel time and waveform variations across arrays of receivers

time reversal imaging of seismic sources and application to the great sumatra earthquake the increasing power of computers and numerical methods like spectral element methods allows continuously improving modelization of the propagation of seismic waves in heterogeneous media and the development of new applications in particular time reversal in the three dimensional earth the concept of time reversal hereafter referred to as tr was previously successfully applied for acoustic waves in many fields like medical imaging underwater acoustics and non destructive testing we present here the first application at the global scale of tr with associated reverse movies of seismic waves propagation by sending back long period time reversed seismograms we show that seismic wave energy is refocused at the right location and the right time of the earthquake when tr is applied to the sumatra andaman earthquake 26 dec 2004 the migration of the rupture from the south towards the north is retrieved therefore tr is potentially interesting for constraining the spatio temporal history of complex earthquakes

effects of topographic amplification induced by a u shaped canyon on seismic waves abstract the series solution of wave functions for 2d scattering and diffraction of plane sh shear horizontal waves induced by a u shaped canyon is proposed herein to account for the topographic effect of such a canyon the wave function expansion method has been frequently employed to study the topographic effect because it can reveal the physics of the wave scattering and can test the accuracy of other methods through a new domain decomposition strategy the half space having a u shaped canyon is divided into three subregions hence we defined three cylindrical coordinate systems in each coordinate system the wave field satisfying the helmholtz equation was represented by means of the separation of variables method in terms of the series of both bessel functions and hankel functions with unknown complex coefficients then three wave fields are all represented in the same coordinate system using the graf addition theorem the unknown coefficients are solved by satisfying the continuity conditions of the auxiliary boundary and the traction free boundary conditions on the bottom of the canyon to show the effects of symmetrical and nonsymmetrical u shaped canyons on the surface ground motion a parametric analysis is carried out in the frequency domain surface and subsurface transient responses in the time domain demonstrate the phenomenon of wave propagating and scattering it is found that a zone of amplification can obviously take place at the bottom of a u shaped canyon with nearly vertical walls

reverse modelling for seismic event characterization summary the localization of seismic events is of utmost importance in seismology and exploration current techniques rely on the fact that the recorded event is detectable at most of the stations of a seismic network weak events not visible in the individual seismogram of the network are missed out we present an approach where no picking of events in the seismograms of the recording network is required the observed wavefield of the network is reversed in time and then considered as the boundary value for the reverse modelling assuming the correct velocity model the reversely modelled wavefield focuses on the hypocentre of the seismic event the origin time of the event is given by the time where maximum focussing is observed the spatial extent of the focus resembles the resolution power of the recorded wavefield and the acquisition this automatically provides the uncertainty in the localization with respect to the bandwidth of the recorded data the method is particularly useful for the upcoming large passive networks since no picking is required it has great potential for localizing very weak events not detectable in the individual seismogram since the reverse modelling sums the energy of all recorded traces and therefore enhances the signal to noise ratio similar to stacking in seismic exploration the method is demonstrated by 2 d and 3 d numerical case studies which show the potential of the technique events with a s n ratio smaller than 1 where the events cannot be identified in the individual seismogram of the network are localized very well by the method

topographic effects on the seismic response of steep slopes a frequency domain parametric study using generalized consistent transmitting boundaries has been performed to evaluate the significance of topographic effects on the seismic response of steep slopes the results show that the peak amplification of motion at the crest of a slope occurs at a normalized frequency h 0 2 where h is the slope height and is the wavelength of the motion the importance of the natural site frequency is illustrated by the analysis of a stepped layer over a half space it was found that the natural frequency of the region behind the crest can dominate the response relative to the topographic effect for the conditions studied moreover the effect of topography can be handled separately from the amplification due to the natural frequency of the deposit behind the crest of the slope this concept of separating the amplification caused by topography from that caused by the natural frequency is advantageous to the development of a simplified method to estimate topographic effects

elastic finite difference modeling of cross hole seismic data cross hole seismic data exhibit unique characteristics not seen in surface survey data or even in vertical seismic profile data these are to a large extent due to the near horizontal propagation involved transmitted reflected evanescent guided and converted waves are all prominent these require an elastic algorithm for realistic simulation elastic finite differences are used to synthesize responses both fixed time snapshots and seismogram profiles for a series of two dimensional models of increasing complexity special emphasis is given to guided waves in continuous and segmented low velocity zones

the application of finite element analysis to body wave propagation problems summary the finite element method is shown to be a powerful tool for the numerical modelling of seismic body wave propagation problems applications extend to both problems on a scale of interest to engineers and also to large scale seismological problems solutions are sought in the time domain efficient programs have been written to accomplish this the scope of numerical solutions has been greatly enhanced by the use of a previously reported scheme for exactly cancelling reflections at the boundaries of the model the finite difference results of boore and the analytical results of trifunac for the amplification due to a mountain and an alluvial valley respectively are compared with new finite element results the new results agree well although there are some difficulties with resonance in the alluvial valley problem boore s sh results have been extended to vertical p and sv incidence a deep earthquake zone has been modelled realistically in two dimensions and earthquakes simulated at depth it is suggested that the variation in observed amplitude across the top of the zone due to refraction away from the slab may be used to provide an estimate of the thickness of the slab from long period observations of local earthquakes

migration velocity analysis from locally coherent events in 2 d laterally heterogeneous media part i theoretical aspects we present a new method based on migration velocity analysis mva to estimate 2 d velocity models from seismic reflection data with no assumption on reflector geometry or the background velocity field classical approaches using picking on common image gathers cigs must consider continuous events over the whole panel this interpretive step may be difficult particularly for applications on real data sets we propose to overcome the limiting factor by considering locally coherent events a locally coherent event can be defined whenever the imaged reflectivity locally shows lateral coherency at some location in the image cube in the prestack depth migrated volume obtained for an a priori velocity model locally coherent events are picked automatically without interpretation and are characterized by their positions and slopes tangent to the event even a single locally coherent event has information on the unknown velocity model carried by the value of the slope measured in the cig the velocity is e

2 dreflectivity method and synthetic seismograms for irregularly layered structures i sh wave generation summary the reflectivity method for complete sh seismograms has been extended to two dimensionally layered structures the aki larner technique is generalized to solve the integral equations for 2 d boundary conditions and propagator matrices are enlarged to express a total sh wavefield synthetic seismograms in a soft basin are calculated for an incident plane wave they compare favourably with the results of the finiteeiement and finitedifference methods even in the later portion where asymptotic ray and beam theories break down synthetic seismograms due to a line force and a point dislocation are also presented

seismic radiation from an sh line source in a laterally heterogeneous planar fault zone a solution to the class of problems in which an sh line source is operating in a medium consisting of two quarter spaces with an arbitrary number of semi infinite vertical layers in between is given in a frequency wavenumber domain the general result is applied to a model with a single vertical layer and synthetic seismograms are calculated for a source specified as an sh line dislocation at the interface between the vertical layer and the faster quarter space the numerical examples demonstrate that moderate fault normal material heterogeneity can have significant effects on the seismic response of a medium the overall distribution of travel times amplitudes and motion polarities in the presence of fault zone material heterogeneity is different from a corresponding distribution in a homogeneous half space the effects are most prominent near the fault zone where head waves surface waves and trapped modes result in waveform complexities large amplifications over an order of magnitude in the fault zone itself and first motion polarities which are reversed from homogeneous medium predictions the results imply that material heterogeneity should be included in fault zone models which are used for the interpretation of observed seismic data and theoretical calculations of near fault responses such models can be utilized to obtain important fault zone and earthquake source parameters

slowness backazimuth weighted migration a new array approach to a high resolution image summary we have developed a new array method combining conventional migration with a slownessbackazimuth deviation weighting scheme all seismic traces are shifted based on the theoretical traveltime of the scattered wave from specific gridpoints in a 3 d volume observed slowness and backazimuth are calculated for each raypath and compared with theoretical values in order to estimate slowness and backazimuth deviations subsequently stacked energy calculated by a conventional migration method is weighted by the slowness and backazimuth deviations to suppress any arrival energy whose slowness and backazimuth are inconsistent with the expected theoretical values this new method was applied to two p wave data sets which comprise 1 underside reflections at the 410 and 660 km mantle discontinuities and 2 d reflections as well as their corresponding synthetic data sets the results show that the weighting scheme dramatically increases the resolution of the migrated images and enables us to obtain wellconstrained focused images making upper mantle discontinuities and d reflections more

ground motion observations at hotel montana during the m 7 0 2010 haiti earthquake topography or soil amplification unusually severe structural damage was reported during the 2010 m 7 0 haiti earthquake in the vicinity of hotel montana located on top of a ridge in the district of petionville prompted by the observations u s geological survey seismic stations were deployed and aftershock recordings indicated ground motion amplification on the top of the hill compared to adjacent stations on reference site conditions the presence of topographic relief has been shown to significantly aggravate the consequences of strong ground motion during past events and topographic effects were brought forward to explain the observations in this paper we test the hypothesis of topographic amplification as the dominant factor that contributed to the damage concentration in the vicinity of hotel montana we initially conduct numerical simulations of the ridge seismic response assuming elastic homogeneous site conditions and show that numerical predictions of topographic amplification disagree with the field data both in amplitude and in frequency conversely while 1d ground response analyses for the site conditions at the hilltop predict amplification in the same frequency range as the field data they significantly underestimate the recorded amplitude we then conduct numerical simulations of the foothill ridge response to seismic motion while accounting for soil layering and qualitatively demonstrate that the recorded amplification is most likely attributed to coupled site topographic amplification effects namely to seismic waves trapped in the soft soil layers of the near surface amplified as a consequence of reverberations and further modified due to diffraction and scattering upon incidence on the irregular ground surface parametric investigations of the topography soil amplification coupling effects are then conducted and our results show that when accounting for a hypothetical soil bedrock interface at 100 m depth predictions are in excellent agreement with the observed motion

effect of a simple mountain range on underground seismic motion summary the influence of a simple mountain range on seismic ground motion is studied a two dimensional model of the medium and vertically incident plane sh waves are considered attention is devoted not only lo the wavefield along the earth s surface but also within the medium the wavefield is computed in two steps i the computation of the impulse response by the finite difference method 2 the computation of the response to a time variation of the incident wave approximately corresponding to a hundred yeai local earthquake a the sitc numerical results the impulse 1 esponse the transfer function the accelerograms and their spectra indicate strong spatial variability of the wavefield due to the topographical anomaly the differences as large as 100 per cent in the peak amplitudes of the accelerograms and of the order of 5 hz in their predominant frequencies at closely 200 m spaccd internal points of the medium have been found attention is focused also on the effect of causal absorption even unrealistically strong absorption seems to be unable to reduce significantly the spatial variability of the ground niotion caused by the topography a variability like this implying the occurrence of underground differential strains might be of engineering inipoi lance in the antiseismic desigti of underground structures tunnels for example in mountainous seismic i egions the groundmotion variability along the surface of the mountain is considerably smaller than within the medium

the effect of underground structure on seismic motions of the ground surface summary two dimensional finite element modelling of underground structural anomalies at shallow depths has been done to obtain the response at the ground surface to damped vertically incident sh waves power spectral ratios are examined to determine what effects the position shape depth and size of the anomaly have on the surface seismograms based on the results gathered from a number of models inferences are made with respect to the inverse problem given the seismic motion of the ground surface what can be said about the underground structure

imaging complex geologic structure with single arrival kirchhoff prestack depth migration we compare various forms of single arrival kirchhoff prestack depth migration to a full waveform finite difference migration image using synthetic seismic data generated from the structurally complex 2 d marmousi velocity model first arrival traveltime kirchhoff migration produces severe artifacts and image contamination in regions of the depth model where significant reflection energy propagates as late or multiple arrivals in the total reflection wavefield kirchhoff migrations using maximum energy arrival traveltime trajectories significantly improve the image in the complex zone of the marmousi model but are not as coherent as the finite difference migration image by carefully incorporating continuous phase estimates with the associated maximum energy arrival traveltimes we obtain single arrival kirchhoff images that are similar in quality to the finite difference migration image furthermore maximum energy green s function traveltime and phase values calculated within the seismic frequency ban

ground motion at mountains and sedimentary basins with vertical seismic velocity gradient summary the boundary integral gaussian beam method benites aki 1989 is applied to study the ground motion in 2 d structures that exhibit irregular topography and interface and whose shear wave velocity varies linearly with depth for incident plane sh waves in our first example of application the model is a half space whose free surface topography is a ridge of cosine shape with vertical shear wave velocity gradient in the second the model is a semi cylindrical sedimentary basin in a homogeneous half space in which the shear wave velocity of the sediments increases with depth our results for the case of the mountain show that the amplification on its top predicted by the 2 d modelling when the velocity is constant is enhanced when the velocity gradient is present for all frequencies and by a factor up to 3 in the case of the basin results show that the velocity gradient 1 enhances the amplification at the edges of the valley 2 makes the reverberations due to 2 d resonance have larger amplitudes and shorter intervals between arrivals 3 shortens the total duration of the seismograms at all stations within the basin

single station location of seismic events a review and a plea for more research abstract traveltime based location methods are ineffective for locating regional seismic events which are recorded by few stations however the comprehensive test ban treaty ctbt makes it imperative that we monitor sparsely observed events this paper reviews the current status of single station location ssl methods the location of seismic events using records from one three component broadband digital station we argue here that ssl methods may ultimately provide the most effective and economical means for monitoring small magnitude m 3 seismic events over most of the earth potentially station event distance and focal depth may be determined accurately by utilizing broadband three component data and matching observed and synthetic waveforms station event azimuth is determinable from the polarization of the p wave arrival and p coda however more research is required before ssl methods become a practical alternative to traveltime based methods currently the most significant problem is that regional seismograms are strongly dependent on regional crustal structure thus future research efforts should focus both on determining appropriate crustal models in specific regions and also on improved methods for dealing with regional variations in crustal structure a second important problem concerns location errors with ssl they may involve 180 errors in station event azimuth or other highly non gaussian blunders

hypocenter velocity structure coupling in local earthquake tomography abstract local earthquake tomography involves the use of seismic wave arrival times from earthquake sources with uncertain locations for the inference of three dimensional variations in seismic velocity formally this inverse problem contains explicit coupling between the earthquake hypocenters and the velocity structure however many studies fail to treat the hypocenter velocity structure coupling explicitly an examination of previous studies provides evidence that this failure can lead to significant bias in the resulting velocity model a set of simple hypothetical test cases clearly demonstrates the seriousness of the potential bias when coupling is neglected producing models that underestimate the actual velocity perturbations by about a factor of four under the same conditions strict simultaneous inversion and simultaneous inversion with parameter separation both produce accurate inverted models the use of appropriate station corrections and iteration of the solution can improve the results when the coupling is ignored but velocity anomalies will still be underestimated by about a factor of two at best

fast location of seismicity a migration type approach with application to hydraulic fracturing data we propose a new approach for the location of seismic sources using a technique inspired by gaussian beam migration of three component data this approach requires only the preliminary picking of time intervals around a detected event and is much less sensitive to the picking precision than standard location procedures furthermore this approach is characterized by a high degree of automation the polarization information of three component data is estimated and used to perform initial value ray tracing by weighting the energy of the signal using gaussian beams around these rays the stacking is restricted to physically relevant regions only event locations correspond to regions of maximum energy in the resulting image we have successfully applied the method to synthetic data examples with 20 30 white noise and to real data of a hydraulic fracturing experiment where events with comparatively small magnitudes 0 were recorded

numerical modeling of fault zone trapped waves acoustic case abstract we have obtained numerical results for an acoustic wave propagating in a 3d medium with mixed boundary conditions the specific model involves a vertical low velocity fault zone of varying thickness embedded in an otherwise homogeneous half space at the fault zone boundary the stress and displacement are continuous on the free surface the stress is zero a pseudo spectrum method is employed to achieve sufficient resolution with reasonable computation time on a cray results show the development of guided waves trapped in the fault zone these guided waves display large amplitudes and lengthening waveforms they propagate at lower velocity with amplitudes that drop off mainly due to energy leakage out of the fault zone as the width of the fault zone varies the wave energy tends to funnel into the new low velocity wave guide at large distance these guided waves become the dominant arrivals on seismograms the waveforms are useful to recover the geometry and properties of the fault zone

refining the image of the san andreas fault near parkfield california using a finite difference travel time computation technique abstract the parkfield area seismic observatory paso was a dense telemetered seismic array that operated for nearly 2 years in a 15 km aperture centered on the san andreas fault observatory at depth safod drill site the main objective of this deployment was to refine the locations of earthquakes that will serve as potential targets for safod drilling and in the process develop a high for passive seismological techniques resolution image of the fault zone structure a challenging aspect of the analysis of this data set was the known existence of large 20 25 contrasts in seismic wavespeed across the san andreas fault the resultant distortion of raypaths could challenge the applicability of approximate ray tracing techniques in order to test the sensitivity of our hypocenter locations and tomographic image to the particular ray tracing and inversion technique employed we compare an initial determination of locations and structure developed using a coarse grid and an approximate ray tracer thurber c roecker s roberts k gold m powell m l and rittger k 2003 earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod geophys res lett 30 3 10 1029 2002gl016004 with one derived from a relatively fine grid and an application of a finite difference algorithm hole j a and zelt b c 1995 3 d finite difference reflection traveltimes geophys j int 121 2 427 434 in both cases we inverted arrival time data from about 686 local earthquakes and 23 shots simultaneously for earthquake locations and three dimensional vp and vp vs structure included are data from an active source seismic experiment around the safod site as well as from a vertical array of geophones installed in the 2 km deep safod pilot hole drilled in summer 2002 our results show that the main features of the original analysis are robust hypocenters are located beneath the trace of the fault in the vicinity of the drill site and the positions of major contrasts in wavespeed are largely the same at the same time we determine that shear wave speeds in the upper 2 km of the fault zone are significantly lower than previously estimated and our estimate of the depth of the main part of the seismogenic zone decreases in places by 100 m tests using virtual earthquakes borehole receiver gathers of picks for surface shots indicate that our event locations near the borehole currently are accurate to about a few tens of meters horizontally and vertically

acoustic imaging of earthquake sources from the chalfant valley 1986 aftershock series summary following the chalfant valley earthquake of 1986 july 21 ml 6 4 the usgs deployed 120 vertical component seismometers to obtain dense array recordings of aftershocks from this data set we selected three events with the best station coverage to obtain acoustic images of the earthquake sources the events were relocated using a layered velocity model and models with a constant velocity and a constant gradient to obtain minimum traveltime residuals all models performed similarly well preprocessing of the data prior to the extrapolation consisted of applying static corrections lowpass filtering and spatial interpolation as well as spatial tapering at the edges of the recording line for the back projection of the recorded wavefield we used a second order finite difference reverse time extrapolation technique similar to mcmechan 1982 while for two events no focusing of the energy could be obtained an acoustic image of one earthquake source was retrieved in order to obtain a better understanding of the physical meaning of acoustic imaging we applied the same processing and extrapolation scheme to synthetic seismograms calculated using the reflectivity method for the present data set these tests indicate that the influence of the 1 d velocity model on the focusing quality is very low the most severe limitations however are due to the finite aperture and gaps of the recording line the spatial sampling of the wavefield limits the frequency range used for extrapolation so that the resolution is beyond the scale of the source processes the finite aperture leads to polarity reversals in the final source image which makes an interpretation of the radiation pattern at the time of focusing from the reconstructed image impossible

two dimensional analysis of the effect of subsurface anomalies on the free surface response to incident sh waves summary two dimensional finite element modelling of subsurface anomalies at shallow depth has been done to obtain the response to incident sh waves vertically incident sh and obliquely incident sh have been examined power spectral ratios were studied to determine the effect on the surface seismograms of the position shape depth size and material composition of the anomaly a number of relationships between the surface response and the anomaly has been identified these relationships may be used in solving the inverse problem given the seismic motion of the ground surface determine the physical properties of the underground structure

geometrical constraints of the 1980 mount st helens intrusion from analogue models the 1980 mount st helens cryptodome intrusion has been simulated by scaled experiments silicone used as a magma analogue was intruded into a cohesive cone that models the edifice measuring surface deformation features associated with variations of injection rate and depth of cryptodome initiation revealed linear relationships with the intrusion characteristics scaled to mount st helens dimensions the 1980 cryptodome is found to have had a maximum e w width of 850 m an initial depth of 680 to 835 m it had an ascending velocity of 5 7 7 3 m day that corresponds to a vertical displacement of 330 380 m toward the surface within the two months of deformation this brought the intrusion to less than 250 m below the crater floor at the point when the north flank failed on may 18 1980

rapid three dimensional hypocentral determination using a master station method a master station ms method is presented in this paper to rapidly determine hypocenters in three dimensional 3 d heterogeneous velocities an equal differential time edt surface is defined as the collection of all spatial points that satisfy the time difference between two arrivals which can be two picks at two stations or two different phase picks at one station the edt surface is independent of the origin time and will contain the hypocenter for an event with j arrivals there are j 1 independent edt surfaces the ms method determines the hypocenter that satisfies two types of constraints to be traversed by most edt surfaces and to yield minimum travel time residual statistics the statistics include both the residual variance and the amplitude of the origin time error the combined use of the edt surfaces and residual statistics allows for a unique determination of the hypocenter and origin time using different types of phase arrivals in principle only three arrivals are minimally required to constrain a unique solution if three different stations are used for a 3 d velocity model the edt surfaces and the residual statistics can be computed efficiently using a reference file created by moser s 1991 ray tracing method an illustration of the ms method is given for 27 small events that occurred in southern california using a p wave velocity model modified from that of magistrale et al 1992 the average misfit between the bulletin hypocenters and the new solutions is 3 8 km if a 3 d velocity model is accurate the ms method can be a viable means of hypocenter determination

teleseismic p wave imaging of the 26 december 2004 sumatra andaman and 28 march 2005 sumatra earthquake ruptures using the hi net array 1 seismograms from a dense high quality seismic network in japan are used to investigate the characteristics of the 26 december 2004 sumatra andaman and the 28 march 2005 sumatran earthquakes the onset of the p waveforms are aligned through cross correlation and a simple concept of back projecting seismic energy to a grid of potential source locations is applied the waveform alignment removes the effects due to lateral variations in wave speed between the hypocenter and each station to better approximate the effects of three dimensional heterogeneity for paths originating from grid points away from the hypocenter cross correlation results of the p waveforms from aftershocks are introduced this additional information leads to improved resolution of smaller scale features near many of the aftershocks by reducing wavefront distortion the back projection analysis provides a quick assessment of the spatiotemporal extent and variability of relative high frequency energy release which can be translated into an estimate of the moment magnitude as well as an unparalleled view of high frequency rupture propagation the results are in general consistent with those obtained from more involved source inversion methods the 2004 sumatra andaman earthquake released most energy in a region northwest of the sumatra island and the rupture extended to the northern andaman islands about 1300 km from the epicenter this northern portion of the rupture radiated a considerable amount of energy but there is little evidence of slow slip the 2005 event is imaged to have bilateral rupture with northwestern slip occurring for about 50 s before it moved to the southeast of the epicenter

three dimensional geometrical ray theory and modelling of transmitted seismic energy of data from the nevada test site this paper presents a geometrically based algorithm for computing synthetic seismograms for energy transmitted through a 3 d velocity distribution 3 d ray tracing is performed to compute the traveltimes and geometrical spreading amplitude the formulations of both kinematic and dynamic ray tracing systems are presented the two point ray tracing problem is solved by systematically updating the initial conditions and adjusting the ray direction until the ray intersects the specified endpoint the amount of adjustment required depends on the derivatives of the position with respect to the given starting angles between consecutive rays the algorithm uses derivatives to define the steepest descent direction and to update the initial directions the convergence rate depends on the complexity of the model test seismograms compare favourably with those from a 2 d asymptotic ray theory algorithm and a 3 d gaussian beam algorithm the algorithm is flexible in modelling arbitrary source and recorder geometries for various smoothly varying 3 d velocity distributions the algorithm is further tested by simulating surface to tunnel vibroseis field data shear waves as well as compressional waves may be approximately included application of the algorithm to a data set from the rainier mesa of the nevada test site produced a good fit to the transmitted first arrival traveltimes and amplitudes with approximately 15 per cent variation in the local 3 d velocity

elastic wave propagation and site amplification in the salt lake valley utah from simulated normal faulting earthquakes the two dimensional seismic response of the salt lake valley to near and far field earthquakes has been investigated from simulations of vertically incident plane waves and from normal faulting earthquakes generated on the basin bounding wasatch fault the response to normal faulting earthquakes was simulated using a two dimensional finite element method and the plane wave response was calculated from two dimensional finite difference simulations the plane wave simulations were then compared with observed site amplifications in the salt lake valley based on seismic recordings from nuclear explosions in southern nevada that show 10 times greater amplification within the basin than measured values on hard rock sites while previous studies attribute this increased site amplification to the near surface unconsolidated consolidated alluvial fill contact our synthetic seismograms suggest that in the frequency band 0 3 to 1 5 hz at least one half the site amplification can be attributed to the impedance contrast between the basin sediments and higher velocity basement rocks synthetic seismograms from vertically incident plane wave sources and buried double couple sources predict large amplitude rayleigh wave propagation from the edges of the basin and in general uniform site amplification in contrast near field simulations of basin bounding normal faulting earthquakes predict large amplitude rayleigh waves propagating westward from the fault across the basin spectra of synthetic accelerograms computed from the normal faulting earthquakes shows that spectral amplification within the basin is primarily due to source directivity with a maxima near the surface projection of the fault that decays rapidly away from the fault importantly the synthetic modeling of near field earthquake sources show that near field directivity effects are important and should be considered in an earthquake hazard assessment of the salt lake valley and similar geologic settings along the wasatch front

earthquake ground motion and structural response in alluvial valleys this paper is concerned with the problem of soil amplification and structural damage due to local site conditions in sedimentary valleys during earthquakes it focuses on a small valley in kirovakan for which 1d wave propagation analyses have failed to provide adequate answers for the large extent and spatial distribution of damage during the 1988 armenia earthquake a more realistic 2d finite element analysis is performed herein in search of an explanation of the observed behavior using as input an inferred rock accelerogram the response of the valley is calculated for a vertically incident sh wave synthetic accelerograms of the surface ground motion are presented for different sites these accelerograms are then used to determine the amplification ratios of the surface response with respect to that of the free field motion of the rock outcrop for different frequencies and for a continuous set of sites in addition response spectra are evaluated for simple oscillators representing structures located at various sites results of the 2d simulations show striking differences with respect to those from 1d analyses in particular 1 while the resonant frequencies exhibited by a 1d model for a given site also appear in the 2d model the peak ground response and structural response are almost twice as large for the 2d as for the 1d model 2 the 2d model exhibits in addition a new set of resonant frequencies and concomitant mode shapes across the valley which are directly related to its finite width and 3 due to these additional resonances the ground amplification ratio tends to oscillate very rapidly both spatially and with frequency leading to the observation that two identical structures located in the same vicinity or two slightly different structures located essentially on the same site can be subjected to significantly different seismic forces even if the underlying soils have very similar characteristics these results provide a meaningful explanation for the observed damage and thus serve to exemplify a situation in which site effects caused by the finite lateral extent of a valley must be taken into consideration in order to model satisfactorily seismic behavior

the effect of topography on earthquake ground motion a review and new results a brief review of experimental and theoretical results about the effect of topography on seismic motion shows that they are consistent only on a qualitative basis amplification at mountain tops for wavelengths comparable with mountain widths is predicted and observed but the numerical simulations often underestimate the actual observed effects we propose that this disagreement is because current models are not complex enough we therefore computed the response to incident sh waves of a set of different complex configurations that include two dimensional surface topography with or without periodic ridges and subsurface layering the results show that 1 the topographic effect in itself is difficult to isolate from other effects like surface layering and therefore the amplification on top of geomorphologically complex sites cannot be predicted by a priori estimations based solely on topography and 2 the high crest base amplification ratio observed in the field cannot usually be matched even with complex two dimensional structures with incident plane sh waves which suggests that more complex models are needed to incorporate more complex wave fields e g sv surface and three dimensional geologic configurations

real time earthquake location using kirchhoff reconstruction real time location of earthquakes can be achieved by using direct imaging of the recorded wave field based on a kirchhoff reconstruction method similar to that used in the migration of seismic reflection data the standard method of event location requires the wave arrival at each sensor to be picked and associated with an event by using direct imaging the event is identified once in the imaged wave field the computation is independent of the level of seismic activity and can be carried out on a typical desktop computer the procedure has been successfully demonstrated in two and three dimensions using data from the southern california seismic network trinet at higher resolutions the reconstruction method can identify finite source effects further work considers extending the method by implementing full elastic theory and solving for moment tensors at all locations in the mesh

effects of local soil conditions on the topographic aggravation of seismic motion parametric investigation and recorded field evidence from the 1999 athens earthquake during the 1999 athens earthquake the town of adames located on the eastern side of the kifissos river canyon experienced unexpectedly heavy damage despite the particular geometry of the slope that caused significant motion amplification topography effects alone cannot explain the uneven damage distribution within a 300 m zone parallel to the canyon s crest which is characterized by a rather uniform structural quality in this article we illustrate the important role of soil stratigraphy and material heterogeneity on the topographic aggravation of surface ground motion for this purpose we first conduct an extensive time domain parametric study using idealized stratified profiles and gaussian stochastic fields to characterize the spatial distribution of soil properties and using ricker wavelets to describe the seismic input motion the results show that both topography and local soil conditions significantly affect the spatial variability of seismic motion we next perform elastic two dimensional wave propagation analyses based on available local geotechnical and seismological data and validate our results by comparison with aftershock recordings

the seismic response of a steep slope high resolution observations with a dense three component seismic array we deployed an array of 35 three component seismographs to measure site effects associated with a 50 m high slope that is the highwall of an abandoned surface coal mine near sullivan indiana the strip mine pit had filled with water to within 10 m of the top of the highwall our array was deployed over this slope and recorded 10 underwater explosions detonated in the lake 800 m away the raw data show a site resonance revealed by ringy waveforms observed at stations near the slope crest the ringing is seen on the vertical component immediately following the p arrival and on the horizontal components immediately following what we interpret as a secondary p arrival formed by a direct wave propagating through the water three dimensional particle motion analysis demonstrates that the p wave signal is linearly polarized on the flat ground behind the slope but becomes strongly elliptical for stations on the slope the direct wave through the water is nearly horizontally polarized and shows a pronounced amplification of about a factor of 2 for stations at the top of the slope we quantify the variations in the site resonance by using spectral ratios we observe a factor of 2 amplification at about 9 hz that we interpret as a fundamental mode of the slope face online material animations of 3d and 4d visualizations manuscript received 8 june 2001