anatomy of strong ground motion near source records and three dimensional physics based numerical simulations of the mw 6 0 2012 may 29 po plain earthquake italy

in situ measurement of velocity stress sensitivity using crosswell continuous active source seismic monitoring abstractthe ability to characterize time varying reservoir properties such as the state of stress has fundamental implications in subsurface engineering relevant to geologic sequestration of co2 stress variation here in the form of changes in pore fluid pressure is one factor known to affect seismic velocity induced variations in velocity have been used in seismic studies to determine and monitor changes in the stress state previous studies conducted to determine velocity stress sensitivity at reservoir conditions rely primarily on laboratory measurements of core samples or theoretical relationships we have developed a novel field scale experiment designed to study the in situ relationship between pore fluid pressure and seismic velocity using a crosswell continuous active source seismic monitoring cassm system at the cranfield mississippi co2 sequestration field site we actively monitored seismic response for five days with a temporal resolution of 5 min the target was a 26 m thick inject

delineation of faulting and basin geometry along a seismic reflection transect in urbanized san bernardino valley california fourteen kilometers of continuous shallow seismic reflection data acquired through the urbanized san bernardino valley california have revealed numerous faults between the san jacinto and san andreas faults as well as a complex pattern of downdropped and uplifted blocks these data also indicate that the loma linda fault continues northeastward at least 4 5 km beyond its last mapped location on the southern edge of the valley and to within at least 2 km of downtown san bernardino previously undetected faults within the valley northeast of the san jacinto fault are also imaged including the inferred western extension of the banning fault and several unnamed faults the rialto colton fault is interpreted southwest of the san jacinto fault the seismic data image the top of the crystalline basement complex across 70 of the profile length and show that the basement has an overall dip of roughly 10 southwest between perris hill and the san jacinto fault gravity and aeromagnetic data corroborate the interpreted location of the san jacinto fault and better constrain the basin depth along the seismic profile to be as deep as 1 7 km these data also corroborate other fault locations and the general dip of the basement surface at least 1 2 km of apparent vertical displacement on the basement is observed across the san jacinto fault at the profile location the basin geometry delineated by these data was used to generate modeled ground motions that show peak horizontal amplifications of 2 3 5 above bedrock response in the 0 05 to 1 0 hz frequency band which is consistent with recorded earthquake data in the valley

auto correlation analysis of coda waves from local earthquakes for detecting temporal changes in shallow subsurface structures the 2011 tohoku oki japan earthquake for monitoring temporal changes in subsurface structures i propose to use auto correlation functions of coda waves from local earthquakes recorded at surface receivers which probably contain more body waves than surface waves use of coda waves requires earthquakes resulting in decreased time resolution for monitoring nonetheless it may be possible to monitor subsurface structures in sufficient time resolutions in regions with high seismicity in studying the 2011 tohoku oki japan earthquake mw 9 0 for which velocity changes have been previously reported i try to validate the method kik net stations in northern honshu are used in this analysis for each moderate earthquake normalized auto correlation functions of surface records are stacked with respect to time windows in the s wave coda aligning the stacked normalized auto correlation functions with time i search for changes in phases arrival times the phases at lag times of 1 s are studied because changes at shallow depths are focused temporal variations in the arrival times are measured at the stations based on the stretching method clear phase delays are found to be associated with the mainshock and to gradually recover with time the amounts of the phase delays are 10 on average with the maximum of about 50 at some stations the deconvolution analysis using surface and subsurface records at the same stations is conducted for validation the results show the phase delays from the deconvolution analysis are slightly smaller than those from the auto correlation analysis which implies that the phases on the auto correlations are caused by larger velocity changes at shallower depths the auto correlation analysis seems to have an accuracy of about several percent which is much larger than methods using earthquake doublets and borehole array data so this analysis might be applicable in detecting larger changes in spite of these disadvantages this analysis is still attractive because it can be applied to many records on the surface in regions where no boreholes are available

crustal strains in the japanese islands as deduced from dense gps array data from the nationwide continuous gps network operated by the geographical survey institute of japan were used to estimate crustal strains in the japanese islands we used horizontal velocity vectors at 610 sites for the period april 1996 to march 1997 and employed the least squares prediction method to interpolate the velocities to a uniform 7km 7km grid over japan the gridded velocities were then differentiated in space to calculate principal components of strains results clearly portray tectonic strainings of the japanese islands in one year 1 dilatational strains show that the japanese islands are under a compressive strain regime induced by the subducting oceanic plates 2 distribution of high maximum shear strains coincides with the regions of crustal activities and 3 principal axes of the strains indicate influences of e w and nw se compression due to the converging oceanic plates north south extension in kyushu is also visible

global mapping of topography on the 660 km discontinuity long period precursors to the ss seismic phase are used to produce global maps of topography for the discontinuity at 660 km depth in the upper mantle these maps indicate discontinuity depth variations of up to 30 km and suggest a correlation between regional depressions in the 660 km discontinuity and subduction zones a result more consistent with models in which the subducting slabs are deflected horizontally at the discontinuity than with models of unhindered slab penetration into the lower mantle

towards a mechanical model for the formation of the pannonian basin abstract new maps showing crustal and lithospheric thickness variations in the pannonian basin and the surrounding east alpine carpathian and dinaric mountains have been prepared on the basis of recent seismic seismologic and electromagnetic data a map presenting miocene faults of regional significance has been also constructed for the same region by using a wealth of recently available national and or more local studies it is suggested that observed crustal and lithospheric structural contrasts have been controlled primarily by neogene kinematic history of the region kinematic history is characterized by the following main patterns 1 1 indentation by adria and large scale backthrusting in the southern alps 2 2 eastward escape and extension of the eastern alps 3 3 extensional collapse in the pannonian basin area 4 4 formation of broad wrench fault systems along strike in the dinarides and southern carpathians and the western carpathians with dextral and sinistral shear respectively 5 5 compression and accretion of the external thrust and fold belt in the eastern carpathians these kinematic patterns are thought to be interrelated and all are manifestations of the late stage evolution of an overthickened orogenic wedge in order to arrive at a better understanding of the mechanism of extension which formed the pannonian basin deep crustal seismic profiles hydrocarbon exploration reflection lines and borehole data have been analyzed in the little hungarian plain this plain represents the transition zone between the alps and the pannonian lowlands and the results are illustrated by eight interpreted cross sections one result of regional importance is the clear recognition that the transdanubian central range at the southeastern flank of the little hungarian plain is composed of alpine pre senonian thrust sheets this finding marks the end of a century of debate the allochthony of the substrata of the pannonian basin can be now considered proven another result of more general interest is that these cross sections document the mode of lithospheric extension preexisting compressional detachment planes reactivate as low angle normal faults and lead to tectonic unroofing of deeply buried metamorphic terranes characterized by ductile flow along subhorizontal lineation

in situ observations of velocity changes in response to tidal deformation from analysis of the high frequency ambient wavefield we report systematic seismic velocity variations in response to tidal deformation measurements are made on correlation functions of the ambient seismic wavefield at 2 8 hz recorded by a dense array at the site of the pinon flat observatory southern california the key observation is the dependence of the response on the component of wave motion and coda lapse time measurements on the vertical correlation component indicate reduced wave speeds during periods of volumetric compression whereas data from horizontal components show the opposite behavior compatible with previous observations these effects are amplified by the directional sensitivities of the different surface wave types constituting the early coda of vertical and horizontal correlation components to the anisotropic behavior of the compliant layer the decrease of the velocity volumetric strain sensitivity s with indicates that this response is constrained to shallow depths the observed velocity dependence on strain implies nonlinear behavior but conclusions regarding elasticity are more ambiguous the anisotropic response is possibly associated with inelastic dilatancy of the unconsolidated low velocity material above the granitic basement however equal polarity of vertical component velocity changes and deformation in the vertical direction indicate that a nonlinear poisson effect is similarly compatible with the observed response pattern peak relative velocity changes at small are 0 03 which translates into an absolute velocity strain sensitivity of s 5 10 3 and a stress sensitivity of 0 5 mpa 1 the potentially evolving velocity strain sensitivity of crustal and fault zone materials can be studied with the method introduced here

earthquake ground motion prediction using the ambient seismic field 1 the waves generated by faulting represent the primary threat posed by most large earthquakes the effect of complex geological structures such as sedimentary basins on earthquake ground motion is a source of particular concern we show that it is possible to extract reliable phase and amplitude response that includes the effects of complex structure for the elastodynamic green s function from the ambient seismic field using deconvolution we demonstrate the accuracy of the approach by predicting complex ground motion for a moderate mw 4 6 earthquake in southern california as recorded in the los angeles basin this suggests a novel approach to seismic hazard analysis in which ground motion from hypothetical future earthquakes is simulated directly without the need for modeling the detailed heterogeneity of the earth s crust as an intermediate step

ground motion simulation and validation of the 2008 chino hills california earthquake we present a simulation of the 2008 m w 5 4 chino hills earthquake for a maximum frequency up to 4 hz and a minimum shear wave velocity down to 200 m s and perform a validation study comparing data obtained from seismic networks with simulation synthetics on more than 300 recording stations the simulation was done using a parallel computing code for earthquake simulations that implements a finite element solution to anelastic wave propagation in heterogeneous media the source model corresponds to that of an independent inversion study and the material model used is a community velocity model cvm developed by the southern california earthquake center scec our results for the goodness of fit measure of the synthetics indicate that from a regional perspective the simulation starts to deviate from the data at frequencies above 1 and 2 hz at particular locations or station clusters however the synthetics yield very good results even at frequencies between 2 and 4 hz the best results are obtained between 0 1 and 0 25 hz over the entire region and up to 1 hz within the major basins these and other results from comparisons at boreholes biases of the peak surface response and the differences in the strong phase duration of the waveforms and the arrival time of p waves suggest a strong sensitivity to seismic velocities in particular the cvm used seems to misrepresent the shallow soil deposits and overestimate seismic velocities in the upper layers outside the basins these observations are helpful in identifying regions where the velocity model may need to be revised overall this study shows that extending the maximum frequency for deterministic earthquake simulations beyond 1 hz is an effort worth pursuing

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

dense array recordings in the san bernardino valley of landers big bear aftershocks basin surface waves moho reflections and three dimensional simulations abstract fourteen geos seismic recorders were deployed in the san bernardino valley to study the propagation of short period t 1 to 3 sec surface waves and moho reflections three dense arrays were used to determine the direction and speed of propagation of arrivals in the seismograms the seismograms for a shallow d 1 km m 4 9 aftershock of the big bear earthquake exhibit a very long duration 60 sec of sustained shaking at periods of about 2 sec array analysis indicates that these late arrivals are dominated by surface waves traveling in various directions across the valley some energy is arriving from a direction 180 from the epicenter and was apparently reflected from the edge of the valley opposite the source a close in aftershock 25 km depth 7 km displays substantial short period surface waves at deep soil sites a three dimensional 3d finite difference simulation produces synthetic seismograms with durations similar to those of the observed records for this event indicating the importance of s wave to surface wave conversion near the edge of the basin flat layered models severely underpredict the duration and spectral amplification of this deep soil site i show an example where the coda wave amplitude ratio at 1 to 2 hz between a deep soil and a rock site does not equal the s wave amplitude ratio because of the presence of surface waves in the coda of the deep soil site for one of the events studied 90 km there are sizable phases that are critically reflected from the moho pmp and sms at one of the rock sites the sms phase has a more peaked spectrum that the direct s wave

unified structural representation of the southern california crust and upper mantle we present a new 3d description of crust and upper mantle velocity structure in southern california implemented as a unified structural representation usr the usr is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity vp vs measurements and incorporates the locations and displacement of major fault zones that influence basin structure these basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure which were subsequently iterated and improved using 3d waveform adjoint tomography a geotechnical layer gtl based on vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component the resulting model provides a detailed description of the structure of the southern california crust and upper mantle that reflects the complex tectonic history of the region the crust thickens eastward as moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust deep sedimentary basins and underlying areas of thin crust reflect neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late pliocene to illustrate the impact of this complex structure on strong ground motion forecasting we simulate rupture of a proposed m 7 9 earthquake source in the western transverse ranges the results show distinct basin amplification and focusing of energy that reflects crustal structure described by the usr that is not captured by simpler velocity descriptions we anticipate that the usr will be useful for a broad range of simulation and modeling efforts including strong ground motion forecasting dynamic rupture simulations and fault system modeling the usr is available through the southern california earthquake center scec website http www scec org

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

the shakeout earthquake scenario verification of three simulation sets summary this paper presents a verification of three simulations of the shakeout scenario an mw 7 8 earthquake on a portion of the san andreas fault in southern california conducted by three different groups at the southern california earthquake center using the scec community velocity model for this region we conducted two simulations using the finite difference method and one by the finite element method and performed qualitative and quantitative comparisons between the corresponding results the results are in good agreement with each other only small differences occur both in amplitude and phase between the various synthetics at ten observation points located near and away from the fault as far as 150 km away from the fault using an available goodness of fit criterion all the comparisons scored above 8 with most above 9 2 this score would be regarded as excellent if the measurements were between recorded and synthetic seismograms we also report results of comparisons based on time frequency misfit criteria results from these two criteria can be used for calibrating the two methods for comparing seismograms in those cases in which noticeable discrepancies occurred between the seismograms generated by the three groups we found that they were the product of inherent characteristics of the various numerical methods used and their implementations in particular we found that the major source of discrepancy lies in the difference between mesh and grid representations of the same material model overall however even the largest differences in the synthetic seismograms are small thus given the complexity of the simulations used in this verification it appears that the three schemes are consistent reliable and sufficiently accurate and robust for use in future large scale simulations

seismic evidence of nonlinear crustal deformation during a large slow slip event in mexico repeated cross correlations of ambient seismic noise indicate a long term seismic velocity change associated with the 2006 m7 5 slow slip event sse in the guerrero region mexico because the sse does not radiate seismic waves the measured velocity change cannot be associated with the response of superficial soil layers to strong shaking as observed for regular earthquakes the perturbation observed maximized at periods between 7 s and 17 s which correspond to surface waves with sensitivity to the upper and middle crust the amplitude of the relative velocity change 10 3 was much larger than the volumetric deformation 10 6 at the depths probed 5 20 km moreover the time dependence of the velocity perturbation indicated that it was related to the strain rate rather than the strain itself this suggests that during strong slow slip events the deformation of the overlying crust shows significant nonlinear elastic behavior

a detailed receiver function image of the upper mantle discontinuities in the japan subduction zone abstract we have imaged the upper mantle discontinuities in a 30 20 large region at the active continental margin of the japan subduction zone and neighboring areas using p to s converted phases from teleseismic records of permanent broadband stations the 410 km discontinuity is detected within 10 km of its global average position an interesting exception in its observation is a gap near 135 e very close to the slab penetration of the 410 km discontinuity and in an area where we have rather high data density the 660 km discontinuity reaches 700 km depth at two places where it is hit directly by the slab these data generally show good agreement with tomographic results both the 660 km discontinuity depression and the p velocity anomalies suggest about 400 500 k temperature deficit within the slab however no downward bending of the 660 km discontinuity is observed in eastern china where the flat lying slab is imaged by tomography this suggests that the slab does not cool the 660 km discontinuity in this region therefore the positive buoyancy required to keep the slab lying flat cannot have been provided by the negative clapeyron slope of the spinel perovskite phase transition another mechanism is needed which could possibly be metastable olivine in the cold core of the slab we have also imaged the shallower portion of the slab down to about 150 km underneath some seismic stations likely because metastable gabbro is still existing to this depth providing a sufficient velocity contrast a strong negative converted phase is observed at 150 200 km depth underneath a volcanic region in japan if real observed at one station only the zone which produces this conversion and which may begin exactly above the slab would require fluid fed melting

a site conditions map for california based on geology and shear wave velocity one simple way of accounting for site conditions in calculating seismic hazards is to use the shear wave velocity in the shallow subsurface to classify materials the average shear wave velocity to 30 m v 30s has been used to develop site categories that can be used for modifying a calculated ground motion to account for site conditions we have prepared a site category map of california by first classifying the geologic units shown on 1 250 000 scale geologic maps our classification of geologic units is based on v 30s measured in 556 profiles and geological similarities between units for which we have v s data and the vast majority of units for which we have no data we then digitized the geologic boundaries from those maps that separated units with different site classifications v s data for california shows that several widespread geologic units have ranges of v 30s values that cross the boundaries between nehrp ubc site categories the franciscan complex has v 30s values across ubc categories b and c with a mean value near the boundary between those two categories older alluvium and late tertiary bedrock have v 30s values that range from about 300 to about 450 m sec across the boundary between categories c and d to accommodate these units we have created intermediate categories which we informally call bc and cd geologic units that have or are interpreted to have v 30s values near the boundary of the ubc categories are placed in these intermediate units in testing our map against the available v 30s measurements we have found that 74 of the measured v 30s values fall within the range assigned to the v s category where they fall on the map this ratio is quite good considering the inherent problems in plotting site specific data on a regional map and the variability of physical properties in geologic units we have also calculated the mean and distribution of v 30s for each of our map units and prepared composite profiles showing the variation of v s in the upper 100 m from the available v s data these data show that the map categories that we have defined based on geologic units have different v s properties that can be taken into account in calculating seismic hazards

the seismic response of the san bernardino basin region during the 2001 big bear lake earthquake abstract the 2001 big bear lake earthquake m w 4 63 was recorded by over 30 strong motion instruments in the san bernardino basin region of southern california at periods longer than about 1 sec the ground motions in the central portion of the basin have significantly larger amplitudes and extended durations of strong shaking relative to sites outside the basin in many cases the peak motions at the basin sites occur 10 or more seconds after the direct s wave arrival suggesting that these arrivals are controlled by basin generated surface waves to model these motions i have performed finite difference simulations using a 3d representation of the basin velocity structure the basin structure has a minimum shear velocity of 250 m sec which coupled with the model grid spacing of 50 m yields a bandwidth resolution limit of t 1 sec for the numerical simulations the simulations do quite well at reproducing the observed waveforms amplitudes and durations at periods of 3 sec and longer at shorter periods 1 2 sec the fit to the recorded motions is less well resolved especially in matching the waveforms of the later arriving phases this suggests that in regions of complex geology deterministic waveform modeling at periods approaching 1 sec involves more than simply reducing the minimum velocity threshold and in particular requires knowledge of the subsurface structure and distribution of seismic velocities at relatively short length scales on the order of 50 m

three dimensional seismic velocity structure in the sichuan basin china we present a new three dimensional velocity model of the crust in the eastern margin of the tibetan plateau the model describes the velocity structure of the sichuan basin and surrounding thrust belts the model consists of 3 d surfaces representing major geologic unit contacts and faults and is parameterized with vp velocity depth functions calibrated using sonic logs the model incorporates data from 1166 oil wells industry isopach maps geological maps and a digital elevation model the geological surfaces were modeled based on structure contour maps for various units from oil wells and seismic reflection profiles these surfaces include base quaternary mesozoic paleozoic and proterozoic horizons the horizons locally exhibit major offsets that are compatible with the locations and displacements of important faults systems this layered upper crustal 3 d model extends down to 10 15 km depth and illustrates lateral and vertical variations of velocity that reflect the complex evolution of tectonics and sedimentation in the basin the model also incorporates 3 d descriptions of vs and density for sediments that are obtained from empirical relationships with vp using direct measurements of these properties in borehole logs to illustrate the impact of our basin model on earthquake hazards assessment we use it to calculate ground motions and compare these with observations for the 2013 lushan earthquake the result demonstrates the effects of basin amplification in the western sichuan basin the sichuan cvm model is intended to facilitate fault systems analysis strong ground motion prediction and earthquake hazards assessment for the densely populated sichuan region

seismic wave velocity changes and stress build up in the crust of the kanto tokai region we show there are large temporal p wave velocity changes in the crust of the kanto tokai region in japan from repeated observations of explosions we find that the variation is the response of the crustal rocks to two components of stress change the tidal stress and the secular stress accumulation the inferred annual rate of fractional velocity change year caused by the stress accumulation in the upper crust is of the order of 10 3 year the results indicate that the build up of stress in the crust can be monitored by precise observations of seismic wave velocities

full 3d tomography for the crustal structure of the los angeles region we apply full 3d tomography f3dt to a regional dataset in the los angeles area in f3dt the starting model as well as the model perturbation is three dimensional and the sensitivity frechet kernels are computed using numerical schemes that account for the full physics of 3d wave propagation f3dt can account for the nonlinearity of structural inverse problem through iteration thus providing the most efficient means for assimilating seismic observations into dynamic ground motion models we have successfully applied a scattering integral si formulation of f3dt to improve a 3d elastic structure model the southern california earthquake center scec community velocity model version 3 0 cvm3 0 with lowest shear velocity clamped at 1 km sec in the los angeles region our data are time and frequency localized measurements of phase delay anomalies relative to synthetics computed from the 3d elastic starting model the frechet kernels for our measurements were computed by convolving the earthquake wave fields generated by point earthquake sources with the receiver green tensors rgts which are the spatial temporal fields produced by three orthogonal unit impulsive point forces acting at the receiver locations we inverted 7364 phase delay measurements of p and s body waves by using the lsqr method the revised 3d model laf3d provides substantially better fit to the observed waveform data than the 3d starting model to our knowledge this study is the first successful application of f3dt using real data in structural seismology

seismic velocity structures in the southern california plate boundary environment from double difference tomography summary we present tomographic images of crustal structures in the southern california plate boundary area with a focus on the san jacinto fault zone sjfz based on double difference inversions of earthquake arrival times absolute arrival times of 247 472 p and 105 448 s wave phase picks for 5493 earthquakes recorded at 139 stations in southern california are used starting with a layered 1 d model and continuing in later iterations with various updated initial models we invert the data for vp and vs in a 270 km long 105 km wide and 35 km deep volume around the sjfz using a spatially variable grid with higher density around the sjfz the examined volume stretches from cajon pass to the northernmost imperial fault zone and includes portions of the southern san andreas fault saf the elsinore fault and the brawley seismic zone in the salton trough because differential traveltimes used in the double difference inversions are most sensitive to near source structures we obtain high resolution around the earthquake sources after 30 iterations we improve the average traveltime misfit by a factor of 16 though ray coverage is limited at shallow depths we obtain detailed images of seismic velocities from 3 to 20 km throughout much of the study area our final velocity results show zones of low velocity and anomalous vp vs ratios associated with various fault strands and sedimentary basins along with clear velocity contrasts across the sjfz and the southern saf the velocity reductions in fault zone regions are generally highest in geometrically complex areas up to 30 50 per cent in the top few kilometres are higher for vs than for vp and follow a flower type pattern with depth in the central section of the sjfz from the san jacinto valley to the trifurcation area the northeast side of the fault has generally higher seismic velocities than the southwest block the obtained contrasts of vp are more persistent and higher up to 20 per cent than the contrasts of vs up to 15 per cent although the differences may stem at least partially from the higher resolution of vp images in the sjfz sections to the northwest and southeast there are patches with reversed velocities contrasts especially in the shallow crust near the san jacinto valley and other basins along the banning fault there is no clear velocity contrast for the southern saf the northeast side has generally lower seismic velocities in the seismogenic zone with patches of contrast reversals in the shallow crust in the brawley seismic zone the northeast side has somewhat lower velocities in the 20 km section near the southern saf and higher velocities farther to the southwest the imaged features have important implications for various aspects of earthquake and crustal dynamics in the region

ground motion simulation and validation of the 2008 chino hills california earthquake using different velocity models abstract we present a set of ground motion simulations of the 2008 m w 5 4 chino hills earthquake using different seismic velocity models available for southern california the simulations are tailored for a maximum frequency of 4 hz and a minimum shear wave velocity of 200 m s we use the community models developed by the southern california earthquake center cvm s and cvm h in the case of cvm h we use two available alternatives with and without considering the geotechnical layers gtl we compare the simulation results obtained with the models against each other and validate the synthetics with recordings obtained at more than 300 stations the comparisons are used to gain insight into the sensitivity of the results to differences in the models and to make conclusions about the strengths of each model s description of the crustal structure and the gtl in the region the validation is done using a goodness of fit gof criterion we find the gof values show a better match at frequencies below 1 hz within the basins and below 0 5 hz in general the models however do not converge at frequencies lower than 0 5 hz and the areas where each model leads to better results do not always coincide the synthetics start to deviate significantly from observations at frequencies above 1 and 2 hz although very good agreement with data can still be found at individual locations even at the higher frequencies cvm s yields the best results at frequencies up to 0 25 hz our results reveal significant sensitivity of the ground motion to the differences in the structural representation of basins and shallow layers in the models this indicates the models need to be cross referenced we close by offering suggestions on the type of improvements that could be adopted in the future

propagation mechanism of long period ground motions for offshore earthquakes along the nankai trough effects of the accretionary wedge a thick accretionary wedge with low seismic velocity overlying a subducting plate is an important factor affecting the amplitudes and durations of long period ground motions for great offshore earthquakes we performed a series of 3d long period ground motion simulations to obtain a better understanding of the effects of the accretionary wedge along the nankai trough japan the simulation results demonstrate that the accretionary wedge has the effect of decreasing the peak amplitude and velocity response but amplifying and elongating later phases of long period ground motions in the land area these effects depend significantly on the focal depth and are pronounced for shallow seismic sources the amplified and elongated later phases originate mainly from prominent basin induced surface waves excited near the trough axis we also identified hard sediments with intermediate s wave velocity in the accretionary wedge as a key layer that enhances the propagation of long period ground motions from offshore to onshore in the case of the nankai trough the hard sediments allow long period ground motions developed inside the accretionary wedge to be efficiently transmitted outward in the longer period than 10 s comparisons between the observed and simulated records suggest that for more accurate predictions of long period ground motions velocity structure models of not only the accretionary wedge but also the surrounding upper crust should be validated and revised using seafloor observations

testing long period ground motion simulations of scenario earthquakes using the mw 7 2 el mayor cucapah mainshock evaluation of finite fault rupture characterization and 3d seismic velocity models using a suite of five hypothetical finite fault rupture models we test the ability of long period t 2 0 s ground motion simulations of scenario earthquakes to produce waveforms throughout southern california consistent with those recorded during the 4 april 2010 m w 7 2 el mayor cucapah earthquake the hypothetical ruptures are generated using the methodology proposed by graves and pitarka 2010 and require as inputs only a general description of the fault location and geometry event magnitude and hypocenter as would be done for a scenario event for each rupture model two southern california earthquake center three dimensional community seismic velocity models cvm 4m and cvm h62 are used resulting in a total of 10 ground motion simulations which we compare with recorded ground motions while the details of the motions vary across the simulations the median levels match the observed peak ground velocities reasonably well with the standard deviation of the residuals generally within 50 of the median simulations with the cvm 4m model yield somewhat lower variance than those with the cvm h62 model both models tend to overpredict motions in the san diego region and underpredict motions in the mojave desert within the greater los angeles basin the cvm 4m model generally matches the level of observed motions whereas the cvm h62 model tends to overpredict the motions particularly in the southern portion of the basin the variance in the peak velocity residuals is lowest for a rupture that has significant shallow slip 5 km depth whereas the variance in the residuals is greatest for ruptures with large asperities below 10 km depth overall these results are encouraging and provide confidence in the predictive capabilities of the simulation methodology while also suggesting some regions in which the seismic velocity models may need improvement

p wave seismic velocity structure derived from sonic logs and industry reflection data in the los angeles basin california 1 we present a new three dimensional seismic p wave velocity model of the los angeles basin that is based on more than 150 sonic logs and 7000 stacking velocities from industry reflection profiles the model was developed using kriging techniques implemented in gocad a commercial application specializing in the construction of surfaces the analysis of spatially distributed data and the modeling or simulation of properties and is characterized by a heterogeneous spatial varying velocity gradient with maximum velocities of 5000 m s in the sedimentary section variability of the observed p wave velocities increases with depth reflecting complex structural and sedimentological controls the model contains a new representation of the basin shape as defined by the sediment basement interface which was mapped using well control and seismic reflection profiles our model differs substantially in approach and outcome from previous representations of crustal velocity structure in southern california

using repeated sources to quantitatively determine temporal change of medium properties theory and an example 1 we develop a theory of using difference wavefields of repeated sources to locate and quantify temporal medium change and apply the theory to locate temporal change of seismic properties beneath the japan subduction zone using repeated earthquakes our theory states the difference wavefields of two repeated sources in a temporally changed medium can be equivalently treated as wavefields propagating from conceptual sources with their location at the place of temporal change and their strengths equal to the product of magnitude of medium property change and magnitude of the initial wavefields from the repeated sources when the medium change extends to a finite region the conceptual sources become volumetric sources distributed over the region of the medium change and propagating in the direction of the initial wave the conceptualization establishes a theoretical framework for possible applications of using difference wavefields to locate and quantify temporal medium changes in geological sciences ultrasonic experiments civil engineering and medical imaging we search repeating earthquakes occurring in the japan subduction zone formulate an empirical procedure to extract the difference wavefields between repeating earthquakes and determine temporal change of seismic properties using a back projection method we locate the temporal change of seismic properties beneath the japan subduction zone to be at 37 2 n 142 e and estimate the magnitude of the conceptual body force associated with the temporal change to be 1 15 1010n or as a reference a 0 87 density change for an assumed volume of temporal change of 103 km3

time dependent seismic tomography summary of methods for measuring temporal changes in seismic wave speeds in the earth seismic tomography is among those that offer the highest spatial resolution 3 d tomographic methods are commonly applied in this context by inverting seismic wave arrival time data sets from different epochs independently and assuming that differences in the derived structures represent real temporal variations this assumption is dangerous because the results of independent inversions would differ even if the structure in the earth did not change due to observational errors and differences in the seismic ray distributions the latter effect may be especially severe when data sets include earthquake swarms or aftershock sequences and may produce the appearance of correlation between structural changes and seismicity when the wave speeds are actually temporally invariant a better approach which makes it possible to assess what changes are truly required by the data is to invert multiple data sets simultaneously minimizing the difference between models for different epochs as well as the rms arrival time residuals this problem leads in the case of two epochs to a system of normal equations whose order is twice as great as for a single epoch the direct solution of this system would require twice as much memory and four times as much computational effort as would independent inversions we present an algorithm tomo4d that takes advantage of the structure and sparseness of the system to obtain the solution with essentially no more effort than independent inversions require

experimental determination of the effect of h2o on the 410 km seismic discontinuity abstract due to the high solubility of h 2 o in the mineral wadsleyite it has been recognized that the presence of h 2 o in the mantle could influence the pressure and pressure interval of the olivine to wadsleyite phase transformation that is generally considered to be the cause of the 410 km seismic discontinuity we have performed multianvil experiments in the mg 2 sio 4 h 2 o system in order to quantify the expansion of the wadsleyite stability field as a result of the presence of h 2 o at 1200 c we find that the wadsleyite stability field expands to lower pressures by approximately 1 gpa under h 2 o rich fluid saturated conditions at 1400 c the expansion is approximately 0 4 gpa and no expansion can be detected at 1600 c a thermodynamic model based on recent h 2 o solubility measurements and crystallographic observations predicts an expansion of the wadsleyite stability field that is in good agreement with the experimental results when these results are combined with phase relations in the mg 2 sio 4 fe 2 sio 4 system it can be shown that significant effects on the pressure and pressure interval of the olivine to wadsleyite transformation i e on the depth and width of the 410 km discontinuity are only expected at lower than ambient mantle temperatures 2 o concentrations that are substantially greater than 0 2 wt areas of the mantle where the 410 km discontinuity appears to occur over a depth interval of over 20 km can only be explained if the temperature in these regions is at or below 1200 c and water concentrations are close to the level where olivine would become h 2 o saturated i e 0 5 wt the presence of ferric fe in the mantle however may also play a role in the broadening of the 410 km discontinuity that is as yet unquantified

observed and simulated ground motions in the san bernardino basin region for the hector mine california earthquake during the m w 7 1 hector mine earthquake peak ground velocities recorded at sites in the central san bernardino basin region were up to 2 times larger and had significantly longer durations of strong shaking than sites just outside the basin to better understand the effects of 3d structure on the long period ground motion response in this region we have performed finite difference simulations for this earthquake the simulations are numerically accurate for periods of 2 sec and longer and incorporate the detailed spatial and temporal heterogeneity of source rupture as well as complex 3d basin structure here we analyze three models of the san bernardino basin model a with structural constraints from gravity and seismic reflection data model f water well and seismic refraction data and the southern california earthquake center version 3 model hydrologic and seismic refraction data models a and f are characterized by a gradual increase in sediment thickness toward the south with an abrupt step up in the basement surface across the san jacinto fault the basin structure in the scec version 3 model has a nearly uniform sediment thickness of 1 km with little basement topography along the san jacinto fault in models a and f we impose a layered velocity structure within the sediments based on the seismic refraction data and an assumed depth dependent v p v s ratio sediment velocities within the scec version 3 model are given by a smoothly varying rule based function that is calibrated to the seismic refraction measurements due to computational limitations the minimum shear wave velocity is fixed at 600 m sec in all of the models ground motion simulations for both models a and f provide a reasonably good match to the amplitude and waveform characteristics of the recorded motions in these models surface waves are generated as energy enters the basin through the gradually sloping northern margin due to the basement step along the san jacinto fault the surface wave energy is confined to the region north of this structure consistent with the observations the scec version 3 model lacking the basin geometry complexity present in the other two models fails to provide a satisfactory match to the characteristics of the observed motions our study demonstrates the importance of using detailed and accurate basin geometry for predicting ground motions and also highlights the utility of integrating geological geophysical and seismological observations in the development and validation of 3d velocity models

a finite difference simulation of wave propagation in two dimensional random media a finite difference algorithm is used to generate synthetic seismograms for waves propagating through two dimensional random media the media have a significant component of their material properties varying randomly over length scales smaller than the seismic wavelength and are meant to approximate the heterogeneity of the crust and upper mantle the finite difference technique retains all multiply scattered and diffracted waves and also accounts for transmission losses the synthetic seismograms clearly exhibit coda and apparent attenuation caused by scattering for a medium with a white wavenumber spectrum of velocity fluctuations the coda is higher frequency than the initial pulse the apparent attenuation is greatest when the scatterer size is comparable to the seismic wavelength the spectra of the coda generally increase in frequency as the scatterers decrease in size examples demonstrate how scattering can produce spectra with broad peaks and sharp fall offs that can make the determination of the source spectra and corner frequencies of small earthquakes extremely difficult

anomalously deep mantle transition zone below central europe evidence of lithospheric instability 1 the depths of the 410 and 660 km phase transitions provide critical information on the thermal state of the mantle transition zone mtz and by implication on the circulation of the upper mantle we analyze converted seismic waves to produce a high resolution image of these discontinuities beneath the pannonian basin of central europe models to explain the extension of the basin in the middle miocene involve subduction roll back and gravitational instability of an over thickened lithosphere we find that cold dense material appears to have accumulated in the mtz consistent with the idea of supply from several subduction episodes or upper mantle overturn variation in depth of the 660 km discontinuity by as much as 40 km suggests that cold lithospheric mantle is ponding on top of this phase transition where the phase transition is deepest eventual transfer of this material into the lower mantle may be expected to develop

ground motion modeling of the 1906 san francisco earthquake part i validation using the 1989 loma prieta earthquake we compute ground motions for the beroza 1991 and wald et al 1991 source models of the 1989 magnitude 6 9 loma prieta earthquake using four different wave propagation codes and recently developed 3d geologic and seismic velocity models in preparation for modeling the 1906 san francisco earthquake we use this well recorded earthquake to characterize how well our ground motion simulations reproduce the observed shaking intensities and amplitude and durations of recorded motions throughout the san francisco bay area all of the simulations generate ground motions consistent with the large scale spatial variations in shaking associated with rupture directivity and the geologic structure we attribute the small variations among the synthetics to the minimum shear wave speed permitted in the simulations and how they accommodate topography our long period simulations on average under predict shaking intensities by about one half modified mercalli inten sity mmi units 25 35 in peak velocity while our broadband simulations on average under predict the shaking intensities by one fourth mmi units 16 in peak velocity discrepancies with observations arise due to errors in the source models and geologic structure the consistency in the synthetic waveforms across the wave propagation codes for a given source model suggests the uncertainty in the source parameters tends to exceed the uncertainty in the seismic velocity structure in agree ment with earlier studies we find that a source model with slip more evenly distributed northwest and southeast of the hypocenter would be preferable to both the beroza and wald source models although the new 3d seismic velocity model improves upon previous velocity models we identify two areas needing improvement nevertheless we find that the seismic velocity model and the wave propagation codes are suitable for modeling the 1906 earthquake and scenario events in the san francisco bay area online material modified mercalli intensities and velocity waveforms and a movie of simulated wave propagation