an automated time window selection algorithm for seismic tomography we present flexwin an open source algorithm for the automated selection of time windows on pairs of observed and synthetic seismograms the algorithm was designed specifically to accommodate synthetic seismograms produced from 3 d wavefield simulations which capture complex phases that do not necessarily exist in 1 d simulations or traditional traveltime curves relying on signal processing tools and several user tuned parameters the algorithm is able to include these new phases and to maximize the number of measurements made on each seismic record while avoiding seismic noise our motivation is to use the algorithm for iterative tomographic inversions in which the synthetic seismograms change from one iteration to the next hence automation is needed to handle the volume of measurements and to allow for an increasing number of windows at each model iteration the algorithm is sufficiently flexible to be adapted to many tomographic applications and seismological scenarios including those based on synthetics generated from 1 d models we illustrate the algorithm using data sets from three distinct regions the entire globe the japan subduction zone and southern california

imaging alpine crust using ambient noise wave equation tomography we present an improved crustal vs model and moho depth map using ambient noise wave equation tomography the so called ambient noise wave equation tomography is a method to invert seismic ambient noise phase dispersion data based on elastic waveform simulation which accounts for 3 d and finite frequency effects we use cross correlations of up to four years of continuous vertical component ambient seismic noise recordings from 304 high quality broadband stations in the alpine region we use model lsp eucrust1 0 obtained from traditional ambient noise tomography as initial model and we iteratively improve the initial model by minimizing frequency dependent phase traveltime differences between the observed and synthetic waveforms of rayleigh waves in the period range 10 50 s we obtain the final model after 15 iterations with 65 total misfit reduction compared to the initial model at crustal depth the final model significantly enhances the amplitudes and adjusts the shapes of velocity anomalies at moho and upper mantle depth the final model corrects an obvious systematic velocity shift of the initial model the resulting iso velocity moho map confirms a moho step along the external side of the external crystalline massifs of the northwestern alps and reveals underplated gabbroic plutons in the lower most crust of the central and eastern alps ambient noise wave equation tomography turns out to be a useful tool to refine shear wave velocity models obtained by traditional ambient noise tomography based on ray theory

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

structure of the california coast ranges and san andreas fault at safod from seismic waveform inversion and reflection imaging 1 a seismic reflection and refraction survey across the san andreas fault saf near parkfield provides a detailed characterization of crustal structure across the location of the san andreas fault observatory at depth safod steep dip prestack migration and frequency domain acoustic waveform tomography were applied to obtain highly resolved images of the upper 5 km of the crust for 15 km on either side of the saf the resulting velocity model constrains the top of the salinian granite with great detail steep dip reflection seismic images show several strong amplitude vertical reflectors in the uppermost crust near safod that define an 2 km wide zone comprising the main saf and two or more local faults another prominent subvertical reflector at 2 4 km depth 9 km to the northeast of the saf marks the boundary between the franciscan terrane and the great valley sequence a deep seismic section of low resolution shows several reflectors in the salinian crust west of the saf two horizontal reflectors around 10 km depth correlate with strains of seismicity observed along strike of the saf they represent midcrustal shear zones partially decoupling the ductile lower crust from the brittle upper crust the deepest reflections from 25 km depth are interpreted as crust mantle boundary

an approach to improve rayleigh wave ellipticity estimates from seismic noise application to the los angeles basin s u m m a r y we present an approach for seismic noise which improves rayleigh wave ellipticity estimates by reducing the influences from body waves and love waves the method requires three component seismographs and uses the phase shift information between the vertical and horizontal components we select data that show the phase shift of about 90 in order to separate rayleigh waves from body waves and love waves in comparison to the usual h v approach the estimates for rayleigh wave ellipticity are systematically different by about 20 per cent because the existence of s waves and love waves systematically increases horizontal amplitudes the differences in the inverted s wave velocity structure reach up to about 20 per cent in the upper 20 km the method is limited to a relatively low frequency range below 0 3 hz as the 90 phase shift peaks become difficult to identify above 0 3 hz despite this limitation in the frequency range this approach can improve the s wave velocity structure in the upper 5 10 km which should lead to a better prediction of long period ground motions for periods of about 5 10 s an improved prediction of such long period ground motion is important for hazard mitigation in the world s metropolitan areas with high rise buildings this approach is applied to the structure in the broader los angeles basin in southern california and improvement of the reference velocity structure in the upper 5 10 km is demonstrated

variations in the zn si record over the last interglacial glacial transition we examined the zinc content of diatom frustules as an indicator of past changes in surface seawater zn2 concentration zn si data of samples from three cores located in the south atlantic sector of the southern ocean spanning the last interglacial glacial transition are presented changes in the zn si record are linked to changes in the surface water zn2 concentration the source of variation in zn2 concentration appears to be via changes in deep water upwelling and circulation we rule out changes in phytoplankton productivity and aeolian dust input as a source of variation in the zn si record likewise the zn si data are not linked to shifts in the diatom species composition of the sediment or sediment preservation effects the zn si results presented do not support the zinc hypothesis there is no link between the uptake of co2 by phytoplankton as inferred from the 13c record and the zn si record

regional scale 3d ground motion simulations of mw 7 earthquakes on the hayward fault northern california resolving frequencies 0 10 hz and including site response corrections

seismic attenuation beneath europe and the north atlantic implications for water in the mantle abstract it is well known that anelasticity has significant effects on the propagation of seismic waves as manifested by physical dispersion and dissipation investigations of anelasticity provide complementary constraints on the physical properties of earth materials but contrary to imaging with elastic waves progress in mapping earth s anelasticity has been relatively slow and there is only limited agreement between different studies or methodologies here within the framework of adjoint tomography we use frequency dependent phase and amplitude anomalies between observed and simulated seismograms to simultaneously constrain upper mantle wavespeeds and attenuation beneath the european continent and the north atlantic ocean in the sea floor spreading environment beneath the north atlantic we find enhanced attenuation in the asthenosphere and within the mantle transition zone mtz in subduction zone settings for example beneath the hellenic arc elevated attenuation is observed along the top of the subducting slab down to the mtz no prominent reductions in wavespeeds are correlated with these distinct attenuation features suggesting that non thermal effects may play an important role in these environments a plausible explanation invokes the transport of water into the deep earth by relatively cold subducting slabs leading to a hydrated mtz as previously suggested by mineral physics and geodynamics studies

integrated model of the crustal structure in the gulf of california extensional province abstract a method of constructing 3d earth models from a suite of 1d profiles is demonstrated using delaunay triangulation accurate crustal models are required to correct for crustal contamination in seismic tomography of the mantle and can be used as starting points for higher resolution tomography of the lithosphere and asthenosphere using a simple input data set 1d vertical profiles provides for rapid prototyping model building and modification any structural length scale in the final 3d model is possible using this method through precise placement of 1d profiles and triangulation collections of layers within the 1d profiles are grouped and identified by keys called superlayers allowing for 3d discontinuities and variations along these important interfaces the method was applied to the gulf extensional province and baja california regions to account for the laterally discontinuous crustal variations during a tomographic inversion for mantle structure use of the 3d model and appropriate regional crustal wave speeds minimizes wave speed variations in the tomographic model and assists interpretation of the final model

full waveform tomography for radially anisotropic structure new insights into present and past states of the australasian upper mantle article i nfo we combine spectral element simulations and adjoint techniques in a non linear full seismic waveform tomography for the radially anisotropic structure of the australasian upper mantle our method allows us to explain 30 s waveforms in detail and it yields tomographic images with locally 2 lateral resolution in the course of 19 conjugate gradient iterations the total number of exploitable waveforms increased from 2200 to nearly 3000 the final model amsan 19 thus explains data that were not initially included in the inversion this is strong evidence for the effectiveness of the inversion scheme and the physical consistency of the tomographic model amsan 19 confirms long wavelength heterogeneities found in previous studies and it allows us to draw the following inferences concerning the past and present states of the australian upper mantle and the formation of seismic anisotropy 1 small scale neutral to low velocity patches beneath central australia are likely to be related to localised paleozoic intraplate deformation 2 increasing seismic velocities between the moho and 150 km depth are found beneath parts of proterozoic australia suggesting thermochemical variations related to the formation and fragmentation of a centralian superbasin 3 radial anisotropy above 150 km depth reveals a clear ocean continent dichotomy we find strong vshnvsv beneath the coral and tasman seas the anisotropy is strongest at the top of the inferred asthenospheric flow channel where strain is expected to be largest radial anisotropy beneath the continent is weaker but more variable localised patches with vshbvsv appear in accord with small scale intraplate deformation 4 the ocean continent dichotomy disappears gradually between 150 and 250 km depth where the continental lithospheric mantle and the oceanic asthenosphere pass into the underlying convecting mantle 5 significant anisotropy exists below 250 km depth its character can be explained by sublithospheric small scale convection and a change in the dominant glide system of olivine

adjoint tomography of the southern california crust using an inversion strategy based on adjoint methods we developed a three dimensional seismological model of the southern california crust the resulting model involved 16 tomographic iterations which required 6800 wavefield simulations and a total of 0 8 million central processing unit hours the new crustal model reveals strong heterogeneity including local changes of 30 with respect to the initial three dimensional model provided by the southern california earthquake center the model illuminates shallow features such as sedimentary basins and compositional contrasts across faults it also reveals crustal features at depth that aid in the tectonic reconstruction of southern california such as subduction captured oceanic crustal fragments the new model enables more realistic and accurate assessments of seismic hazard

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

shakeout d ground motion estimates using an ensemble of large earthquakes on the southern san andreas fault with spontaneous rupture propagation 1 we simulate ground motion in southern california from an ensemble of 7 spontaneous rupture models of large mw7 8 northwest propagating earthquakes on the southern san andreas fault shakeout d compared to long period spectral accelerations from the next generation attenuation nga empirical relations shakeout d predicts similar average rock site values i e within roughly their epistemic uncertainty but significantly larger values in los angeles and ventura basins due to wave guide focusing effects the shakeout d ground motion predictions differ from those of a kinematically parameterized geometrically similar scenario rupture 1 the kinematic rock site predictions depart significantly from the common distance attenuation trend of the nga and shakeout d results and 2 shakeout d predictions of long period spectral acceleration within the basins of the greater los angeles area are lower by factors of 2 3 than the corresponding kinematic predictions we attribute these differences to a less coherent wavefield excited by the complex rupture paths of the shakeout d sources

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

a seismic refraction survey of the imperial valley region california the u s geological survey conducted an extensive seismic refraction survey in the imperial valley region of california in 1979 the imperial valley is located in the salton trough an active rift between the pacific and north american plates forty shots fired at seven shot points were recorded by 100 portable seismic instruments at typical spacing of 0 5 1 km more than 1300 recording locations were occupied and more than 3000 usable seismograms were obtained we analyzed five profiles using a standard ray tracing program constructed a contour map of reduced travel times from our most widely recorded shot point and modeled an existing gravity profile across the salton trough results are itemized 1 all models have in common a sedimentary layer vp 1 8 5 0 km s a transition zone vp 5 0 5 65 km s a basement vp 5 65 km s in the imperial valley 5 9 km s on the bordering mesas and subbasement vp 7 2 km s 2 the sedimentary layer ranges in thickness along the axis of the salton trough from 3 7 km salton sea to 4 8 km u s mexican border on the bordering mesas it is quite variable in thickness 3 the transition zone is about 1 km thick in most places in the imperial valley there are no marked velocity discontinuities in this zone between the sedimentary layer and basement on the bordering mesas however there is a discontinuity at the top of this zone 4 there are apparently two types of basement on the bordering mesas basement is crystalline igneous and metamorphic rocks in the imperial valley basement is mostly lower greenshist facies sedimentary rocks based primarily on the smooth transition in character from sediment to basement arrivals the low value of basement velocity and the fact that deep 4 km wells in the valley penetrate only the upper part of the known cenozoic stratigraphic column for the salton trough 5 the subbasement or intermediate crustal layer ranges in depth along the axis of the salton trough from 16 km salton sea to 10 km u s mexican border gravity modeling requires that this layer deepen and or pinch out beneath the bordering mesas and mountain ranges based on its high velocity and the presence of intrusive basaltic rocks in the sedimentary section in the imperial valley the subbasement is thought to be a mafic intrusive complex similar to oceanic middle crust 6 several structures are seen that affect basement transition zone and deeper parts of the sedimentary layer they include a scarp along the imperial fault as much as 1 km down to the northeast and a scarp passing roughly along the topographic boundary between the imperial valley and the bordering mesa to the west as much as 3 km down to the east we interpret the latter scarp to be the suture or rift boundary between the older crystalline basement on the mesa and the younger metasedimentary basement in the imperial valley 7 on a contour map of reduced travel time from our most widely recorded shot point subtle patches of early arrivals among otherwise late arrivals in the central imperial valley correlate well with known geothermal resource areas having reservoir temperatures of more than 150 c apparently the salton trough is a location where new crust is being generated as the rift opens mafic intrusive rocks fill it from below as sedimentary rocks fill it from above rifting and intrusion produce high heat flow that metamorphoses the sedimentary rocks to shallow depth metasedimentary basement in the imperial valley and thus consolidates the new crust

estimation of q for long period 2 sec waves in the los angeles basin we simulate 0 to 0 5 hz 3d wave propagation through the southern california earthquake center seismic velocity reference model version 2 for the 1994 northridge earthquake in order to examine the effects of anelastic attenuation and amplification within the near surface sediments we use a fourth order finite difference staggered grid method with the coarse grained frequency independent anelastic scheme of day and bradley 2001 and a variable slip distribution from kinematic inversion for the northridge earthquake we find that the near surface material with s wave velocity v s as low as 500 m sec significantly affects the long period peak ground velocities compared with simulations in which the s wave velocity is constrained to 1 km sec and greater anelastic attenuation also has a strong effect on ground motion amplitudes reducing the predicted peak velocity by a factor of up to 2 5 relative to lossless simulations our preferred q model is q s v s 0 02 v s in meters per second for v s less than 1 2 km sec and much larger q s v s 0 1 v s in meters per second for layers with higher velocities the simple model reduces the standard deviation of the residuals between synthetic and observed natural log of peak velocity from 1 13 to 0 26 relative to simulations for the lossless case the anelastic losses have their largest effect on short period surface waves propagating in the los angeles basin which are principally sensitive to q s in the low velocity near surface sediments of the basin the low frequency ground motion simulated here is relatively insensitive to q p as well as to the values of q s at depths greater than roughly that of the 2 km sec s wave velocity isosurface

detecting hazardous new zealand faults at depth using seismic velocity gradients abstract many large damaging earthquakes occur along previously unmapped faults because it is difficult to locate active faults that have slow average slip rates long recurrence intervals and weak surface expression we use recently collected seismic wave velocity data from new zealand to test whether there is a strong correlation between seismic velocity gradients deep in the earth s crust known active faults and large shallow historical earthquakes the correlation with active faults is significant at the 99 confidence level suggesting that seismic velocity gradients at depth can pinpoint active and in some cases unmapped faults that may reactivate and rupture in infrequent earthquakes in addition all eight of the post 1840 m w 7 upper crustal earthquakes in new zealand within the region of good tomographic coverage are spatially correlated with mid crustal seismic velocity gradients and ruptured faults that intersect them many of the seismic velocity gradients coincide with the faulted edges of strong blocks within basement rocks consistent with these marking preferred sites for fault reactivation owing to inherited strength contrasts we propose that seismic velocity gradients provide a means to map potentially hazardous undiscovered faults at mid crustal depths in advance of their activation in future damaging earthquakes

ground motion and intraevent variability from 3d deterministic broadband 0 7 5 hz simulations along a nonplanar strike slip faultground motion and intraevent variability from 3d deterministic broadband simulations

seismic wavespeed images across the iapetus and tornquist suture zones 1 closures of the iapetus ocean and the tornquist sea lead to the collision of the paleocontinents of laurentia baltica and eastern avalonia during the caledonian orogeny it has been speculated that relicts of these two closures may be preserved within the crust or upper mantle over the past decades numerous wide angle seismic profiles were gathered in northwestern europe to search for related subsurface features although active source studies revealed detailed crustal structures across the iapetus and tornquist suture zones there are relatively few clear three dimensional upper mantle images beneath this region we use a new european crust and upper mantle model eu30 determined based on continental scale nonlinear adjoint tomography to explore upper mantle structures across these two suture zones model eu30 reveals two fast anomalies within the upper mantle one dips in a northwesterly direction down to approximately 400 km beneath the north sea and the other dips in a southwesterly direction down to nearly 250 km across the tornquist suture zone in addition we observe a gap between the lithospheres of laurentia and eastern avalonia across the iapetus suture zone beneath the central british isles these seismic images suggest that heterogeneity related to the closures of the iapetus ocean and the tornquist sea have been preserved within the upper mantle over hundreds of millions of years

assessing past changes in bioavailable zinc from a terrestrial zn si opal record historical changes in bioavailable zn concentrations of the surface waters of lake geneva were assessed by analyzing the zinc content of fossil diatoms the measured ratios of zn to si in the opal zn si opal were consistent with both data obtained for cultured freshwater diatoms that were representative of lake geneva and with field data reconstructed variations suggested that increased zn uptake by phytoplankton occurred in the period from 1960 1980 resulting from an increased loading of zn to the lake nonetheless observed concentrations were sufficiently low that no adverse effects were expected on the pelagic community the data presented here suggest that zn si opal records may become a valuable tool to assess past changes in bioavailable zn concentrations in freshwater systems

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

seismic tomography of the southern california crust based on spectral element and adjoint methods we iteratively improve a 3 d tomographic model of the southern california crust using numerical simulations of seismic wave propagation based on a spectral element method sem in combination with an adjoint method the initial 3 d model is provided by the southern california earthquake center the data set comprises three component seismic waveforms i e both body and surface waves filtered over the period range 2 30 s from 143 local earthquakes recorded by a network of 203 stations time windows for measurements are automatically selected by the flexwin algorithm the misfit function in the tomographic inversion is based on frequency dependent multitaper traveltime differences the gradient of the misfit function and related finite frequency sensitivity kernels for each earthquake are computed using an adjoint technique the kernels are combined using a source subspace projection method to compute a model update at each iteration of a gradient based minimization algorithm the inversion involved 16 iterations which required 6800 wavefield simulations the new crustal model m 16 is described in terms of independent shear v s and bulk sound v b wave speed variations it exhibits strong heterogeneity including local changes of 30 per cent with respect to the initial 3 d model the model reveals several features that relate to geological observations such as sedimentary basins exhumed batholiths and contrasting lithologies across faults the quality of the new model is validated by quantifying waveform misfits of full length seismograms from 91 earthquakes that were not used in the tomographic inversion the new model provides more accurate synthetic seismograms that will benefit seismic hazard assessment

the zn abundance and isotopic composition of diatom frustules a proxy for zn availability in ocean surface seawater we have developed cleaning methods for extracting diatomopal from bulk marine sediment samples for measurement of both zinc zn abundance and isotope composition this cleaning technique was then applied to a set of holocene core top samples from the southern ocean the measured 66zn reported relative to the jmclyon standard and zn si ratios from the southern ocean diatomopal samples range from 0 7 to 1 5 and from 14 to 0 9 mol mol respectively the zn abundance and isotope composition data show a clear correlation with opal burial rates and other oceanographic parameters in common with previous work we interpret the systematic changes in the zn si ratio to be linked to the variability in the concentrations of bioavailable zn in the ambient surface seawater where the diatom opal is formed this variability is likely to be primarily controlled by the degree to which zn is taken up into phytoplankton biomass the observed systematic pattern in the 66zn compositions of the diatomopal core top samples is similarly likely to reflect changes in the 66zn composition of the ambient zn in the surface waters above the core top sites which is progressively driven towards isotopically heavier values by preferential incorporation of the lighter isotopes into phytoplankton organic material thus the systematic relationship between zn isotopes and abundance observed in the core top diatomopal samples suggests a potential tool for investigating the biogeochemical cycling of zn in the past surface ocean for down core diatomopal material in this respect it may be possible to test hypotheses that attribute variations in atmospheric co2 on glacial interglacial timescales to the degree to which trace metals limited primary productivity in hnlc zones

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

tidal influence on self potential measurements long term surface and borehole self potential sp monitoring was conducted in the uk chalk aquifer at two sites the coastal site is c 1 7 km from the coast and the inland site is c 80 km from the coast at both sites power spectral density analysis revealed that sp data contain the main ocean tidal periodic components however the principal lunar component m2 the dominant ocean tidal component was most significant at the coastal site the m2 signal in surface referenced sp data at the inland site was partly due to telluric currents caused by the geomagnetic ocean dynamo earth and or atmospheric tides also contributed as the sp power spectrum was not typical of a telluric electric field the m2 component in borehole referenced data at the inland site was below the significance level of the analysis method and was two orders of magnitude smaller than the m2 signal in borehole referenced sp data at the coastal site the tidal response of the sp data in the coastal borehole is therefore primarily driven by ocean tides these cause changes in fluid pressure and chemical concentration gradients within the coastal aquifer leading to time varying electrokinetic and exclusion diffusion potentials borehole referenced sp measurements could be used to characterize and monitor tidal processes in coastal aquifers such as the intrusion of seawater

probabilistic point source inversion of strong motion data in 3 d media using pattern recognition a case study for the 2008 mw 5 4 chino hills earthquake despite the ever increasing availability of computational power real time source inversions based on physical modeling of wave propagation in realistic media remain challenging we investigate how a nonlinear bayesian approach based on pattern recognition and synthetic 3 d green s functions can be used to rapidly invert strong motion data for point source parameters by means of a case study for a fault system in the los angeles basin the probabilistic inverse mapping is represented in compact form by a neural network which yields probability distributions over source parameters it can therefore be evaluated rapidly and with very moderate cpu and memory requirements we present a simulated real time inversion of data for the 2008 mw 5 4 chino hills event initial estimates of epicentral location and magnitude are available 14 s after origin time the estimate can be refined as more data arrive by 40 s fault strike and source depth can also be determined with relatively high certainty

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

waveform tomography reveals channeled flow at the base of the oceanic asthenosphere understanding the relationship between different scales of convection that drive plate motions and hotspot volcanism still eludes geophysicists using full waveform seismic tomography we imaged a pattern of horizontally elongated bands of low shear velocity most prominent between 200 and 350 kilometers depth which extends below the well developed low velocity zone these quasi periodic fingerlike structures of wavelength 2000 kilometers align parallel to the direction of absolute plate motion for thousands of kilometers below 400 kilometers depth velocity structure is organized into fewer undulating but vertically coherent low velocity plumelike features which appear rooted in the lower mantle this suggests the presence of a dynamic interplay between plate driven flow in the low velocity zone and active influx of low rigidity material from deep mantle sources deflected horizontally beneath the moving top boundary layer

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

tomographic image of the southern california mantle p wave teleseismic travel time delays recorded by the southern california array are inverted by the method of backprojection tomography to obtain images of variations in the p wave velocity structure to a depth of 750 km two major upper mantle features arc resolved one beneath the transverse ranges region and another beneath the salton trough region the transverse ranges feature appears as a curtainlike east trending high velocity anomaly this feature is 60 km thick extends most deeply on its eastern end to 250 km and attains a maximum velocity 3 greater than average southern california mantle of the same depth the salton trough feature which is not as well resolved as the transverse ranges feature is composed of low velocities in the upper 70 100 km these p wave velocities arc depressed 3 4 compared to average southern california mantle tests of the inversion indicate the major aspects of the imaged structure are authentic

mantle heterogeneities and the scec reference three dimensional seismic velocity model version 3 we determine upper mantle seismic velocity heterogeneities below southern california from the inversion of teleseismic travel time residuals teleseismic p wave arrival times are obtained from three temporary passive experiments and southern california seismic network scsn stations producing good raypath coverage the inversion is performed using a damped least squares conjugate gradient method lsqr the inversion model element spacing is 20 km before the inversion the effects of crustal velocity heterogeneities represented by the southern california earthquake center scec seismic velocity model version 2 are removed from the teleseismic travel times the p wave inversion produces a variance reduction of 43 s wave velocities are determined from laboratory vp vs ratios the most prominent features imaged in the results are high p wave velocities 3 in the uppermost mantle beneath the northern los angeles basin and the previously reported tabular high velocity anomaly 3 to depths of 200 km beneath the transverse ranges crosscutting the san andreas fault we incorporate the upper mantle seismic velocity heterogeneities into the scec southern california reference seismic velocity model the prior accounting for the crustal velocity heterogeneity demonstrates the utility of the top down method of the scec seismic velocity model development

change of apparent segmentation of the san andreas fault around parkfield from space geodetic observations across multiple periods sequences of earthquakes are commonly represented as a succession of periods of interseismic stress accumulation followed by coseismic and postseismic phases of stress release because the recurrence time of large earthquakes is often greater than the available span of space geodetic data it has been challenging to monitor the evolution of interseismic loading in its entire duration here we analyze large data sets of surface deformation at different key episodes around the cholame parkfield and creeping segments of the san andreas fault that show evidence of significant deceleration of fault slip during the interseismic period we compare the average fault slip rates before and after the 2004 mw6 parkfield earthquake in the 1986 2004 and 2006 2012 periods respectively avoiding 2 years of postseismic deformation after 2004 using a combination of gps data from the plate boundary observatory the southern california earthquake center crustal motion map and the bay area velocity unification networks and interferometric synthetic aperture radar from the advanced land observing satellite alos and envisat satellites we show that the area of coupling at the transition between the parkfield and cholame segments appears larger later in the interseismic period than it does earlier on while strong plate coupling is uniform across the parkfield and cholame segments in the 1986 2004 period creep occurs south of the 2004 epicenter after 2006 making segmentation of the san andreas fault south of parkfield more clearly apparent these observations indicate that analyses of surface deformation late in the earthquake cycle may overestimate the area of plate coupling a fault surface creeping much below plate rate may in some case be a region that does not promote earthquake nucleation but rather just be at a slower stage of its evolution our analysis also shows signs of large variation of slip velocity above and below plate rate in the creeping segment indicating that cycles of weakening and hardening can also be at play in dominantly aseismic areas

continental rupture and the creation of new crust in the salton trough rift southern california and northern mexico results from the salton seismic imaging project a refraction and wide angle reflection seismic profile along the axis of the salton trough california and mexico was analyzed to constrain crustal and upper mantle seismic velocity structure during active continental rifting from the northern salton sea to the southern imperial valley the crust is 17 18 km thick and approximately one dimensional the transition at depth from colorado river sediment to underlying crystalline rock is gradual and is not a depositional surface the crystalline rock from 3 to 8 km depth is interpreted as sediment metamorphosed by high heat flow deeper felsic crystalline rock could be stretched preexisting crust or higher grade metamorphosed sediment the lower crust below 12 km depth is interpreted to be gabbro emplaced by rift related magmatic intrusion by underplating low upper mantle velocity indicates high temperature and partial melting under the coachella valley sediment thins to the north and the underlying crystalline rock is interpreted as granitic basement mafic rock does not exist at 12 18 km depth as it does to the south and a weak reflection suggests moho at 28 km depth structure in adjacent mexico has slower midcrustal velocity and rocks with mantle velocity must be much deeper than in the imperial valley slower velocity and thicker crust in the coachella and mexicali valleys define the rift zone between them to be 100 km wide in the direction of plate motion north american lithosphere in the central salton trough has been rifted apart and is being replaced by new crust created by magmatism sedimentation and metamorphism

the zinc isotopic composition of siliceous marine sponges investigating nature s sediment traps article i nfo the zinc zn content and isotopic composition of marine biogenic opal have the potential to yield informa tion about the nutrient availability utilization and export of particulate organic matter from surface to deep waters here we report the first measurements of the zn isotopic composition of deep sea marine sponge skeletal elements spicules collected in the southern ocean our results highlight different zn uptake and isotopic fractionation behavior between the two major siliceous sponge clades hexactinellids and demosponges which is most likely linked to sponge feeding strategy hexactinellid spicule zn isotopic com positions are not fractionated with respect to seawater most likely due to zn transport via the open internal structure of the sponges in contrast demosponge spicules exhibit a wide range of zn isotopic compositions that are related to the opal zn concentration most likely reflecting variable zn isotope compositions in the organic matter particles on which they feed and internal fractionation processes

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

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

lithosphere rigidity by adjoint based inversion of interseismic gps data application to the western united states while vertical motion induced by long term geological loads is often used to estimate the flexural rigidity of the lithosphere we intend to evaluate the shear rigidity of the lithosphere using horizontal motion our approach considers that the rigidity of the lithosphere may be defined as its resistance to horizontal tectonic lateral forces in this case a spatial distribution of an effective shear rigidity can be estimated from the analysis of the interseismic velocity fields we consider the western united states zone where weakly strained areas e g the sierra nevada are connected with areas of large strain rate e g san andreas fault system by inverting interseismic strain distribution measured by geodetic methods we infer the effective shear rigidity of the lithosphere the forward problem is defined using the equations of linear elasticity the inversion relies on the minimization of the sum of a quadratic measure of the differences between measured and modelled velocity fields the functional also includes regularization terms for the parameters of the model the gradient of the functional with respect to the minimization parameters is computed using an adjoint formulation this permits the treatment of large dimensional minimization problems finally a measure of the uncertainty of our inversion is illustrated through the covariance matrix of the parameters at the optimum the optimization chart is validated on two synthetic velocity distributions then the effective shear rigidity variations of the western united states are estimated using the cmm3 interseismic velocities the inversion displays low effective rigidities along the san andreas fault system the mojave desert and in the eastern california shear zone while rigid areas are found in the sierra nevada and in the south basin and range finally we discuss the differences between our strain rate and rigidity maps with previously published results for the western united states

rupture process and energy budget of the 29 july 2008 mw 5 4 chino hills california earthquake the source model of the 2008 m w 5 4 chino hills california earthquake is constrained using near field seismic body waves recorded by the california integrated seismic network cisn finite fault inversions are preformed for the two fault models based on the nodal planes derived from the cisn moment tensor solution the northeast dipping plane strike 289 dip 62 which has a similar strike as the nearby whittier fault is chosen as the causative fault because it fits the data significantly better our inversion result indicates that the majority of the chino hills earthquake rupture occurred in a compact area in particular 48 of the total seismic moment 1 6 10 17 nm was released by the failure of a 1 8 km 2 asperity located east of the hypocenter in a short time window from 0 4 to 0 8 s after the rupture initiation the average slip is approximately 0 5 m but the maximum slip is 1 8 m the average rupture velocity is 1 9 km s the static stress drop calculated using the slip model is up to 80 mpa and the average stress drop changes from 19 to 38 mpa depending on the average schemes the weighted average slip velocity is 6 5 m s for entire rupture and is 11 m s for the east asperity the inferred available energy and radiated energy are 8 10 13 j and 2 5 10 13 j respectively radiation efficiency is then 0 31 which is moderately low compared with previous earthquakes but consistent with the inferred high average fracture energy density ranging from 6 5 to 14 8 mj m 2

developing a map of geologically defined site condition categories for california consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion the importance of amplification by soil conditions has long been recognized but though many seismic instrument sites have been characterized by their geologic conditions there has been no consistent simple classification applied to all sites as classification of sites by shear wave velocity has become more common the need to go back and provide a simple uniform classification for all stations has become apparent within the pacific earthquake engineering research center s next generation attenuation equation project developers of attenuation equations recognized the need to consider site conditions and asked that the california geological survey provide site conditions information for all stations that have recorded earthquake ground motion in california to provide these estimates we sorted the available shear wave velocity data by geologic unit generalized the geologic units and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials this new map is different from the california geological survey preliminary site conditions map of california in that 19 geologically defined categories are used rather than national earthquake hazards reduction program categories although this map does not yet cover all of california when completed it may provide a basis for more precise consideration of site conditions in ground motion calculations

microplate capture rotation of the western transverse ranges and initiation of the san andreas transform as a low angle fault system tectonic rotation of the western transverse ranges block is explained by capture of the partially subducted monterey microplate by the pacific plate at about anomaly 6 time ca 20 ma as pacific monterey spreading slowed and eventually ceased the slip vector along the gently northeast dipping subduction interface beneath the california margin changed from slightly oblique subduction to transtensional dextral transform motion this change in slip vector and a shift of pacific plate motion eastward along the already subducted monterey plate interface imply that the san andreas transform began as a system of low angle faults that locally subjected the overriding continental margin to distributed basal shear and crustal extension this basal shear produced the rotated western transverse ranges this model helps explain the timing of initial rotation and basin formation the sudden appearance of widely distributed transform motion well inland of the margin in early miocene time why the western transverse ranges uniquely rotated as a large coherent crustal block and several fundamental structural characteristics of central and southern california the model also provides major constraints on the amount of pacific north america strike slip motion the position through time of offshore oceanic plates relative to onshore geology and a general explanation for what may happen as a spreading ridge approaches a trench and the subduction zone evolves into a transform system

zn si records in diatom opal from prydz bay east antarctica abstract the zn si records of diatom opal from prydz bay were investigated the results show that the zn si ratios range from 8 to 53 mol mol 1 the ratio from the continental slope is higher than those from the shelf the difference in zn si records could be attributed to the change of bioavailable zn via the upwelling of zn2 rich deep water or the influence of oceanic water on the slope however phytoplankton productivity influences zn si records on the continental shelf increased productivity leads to elevated zn pumping and eventually to higher zn si ratio in diatom opal in this case it is suggested that zn si proxy could be a signal of marine productivity on the continental shelf of prydz bay the down core profile of zn si records shows an increase in marine productivity over the last century

evolution of the southern san joaquin basin and mid tertiary transitional tectonics central california a cenozoic tectonic and sedimentary history is proposed for the southern san joaquin basin ssjb and tehachapi mountains that evolved adjacent to the plate margin off central california seismic reflection borehole field biostratigraphic and paleomagnetic data are integrated into geologic and fault structure maps cross sections and geohistory plots and are analyzed with previous work in the region to develop a model relating the sequence timing and distribution of complex tectonically linked events the largely buried structures and strata in the ssjb preserve an unusually complete record of the mid tertiary transition from convergent to transform plate boundary as well as the regional transition to contraction during the pliocene significant structural relief existing across both extensional and contractile features is preserved in the subsurface and an active fold thrust belt propagates basinward along the margin of the u shaped tejon embayment the cenozoic evolution of the ssjb reflects the regional deformation of central california as different tectonic events followed each other along the adjacent north american plate margin five oligocene miocene basin phases are identified in the ssjb 1 late oligocene early miocene extensional subsidence with high and low angle normal faulting accompanied by volcanism and deposition of coarse syntectonic conglomerates 2 middle miocene uplift 3 later mid miocene transtensional subsidence to lower bathyal depths 4 alternating subsidence and uplift until the late miocene and 5 flexural subsidence due to pliocene to recent contraction reconstructions of mid tertiary california place the southern san joaquin tehachapi extensional terrane as a paleotectonic block located between the western mojave terrane then to the east and the western california terrane then to the south and west regional extension occurred during a long transition period between convergent and transform boundaries along the north american plate margin significant slip along the san andreas transform postdates this extensional event its origin apparently coincided with a regional middle miocene uplift event indicating that the san andreas fault is younger than previously supposed the tertiary ssjb has subsided due to extension transtension crustal tilting and thrust related loading the maricopa subbasin floor is likely composed of ensimatic and mafic rocks like those along the west side of the sierra nevada and locally has subsided beyond 12 km in contrast the relatively stable tejon embayment underlain by sierran crystalline crust achieved its maximum subsidence in the miocene since pliocene time the ssjb has filled and continued to deepen after the basin was tectonically shut off from the pacific ocean

thermal constraints on earthquake depths in california the high quality databases for california seismicity from the southern and northern california earthquake centers and an extensive compilation of thermal measurements in california are used to quantify the concept of temperature as a fundamental parameter for determining the thickness of the seismogenic zone the base of this zone below which only a small percentage of crustal earthquakes occur is termed the cutout depth and it is at or near the brittle ductile transition in the crust based on laboratory deformation studies this transition should be temperature strain rate lithology and stress state dependent in this study qualitative comparisons between the heat flow in california and earthquake hypocentral distributions show first that as expected earthquake cutout depths are inversely related to heat flow second the epicentral distributions tend to parallel thermal transitions this correlation is probably related to stress concentrations in these locations an ancillary observation is that the cooler western mojave block in southern california appears to be behaving similarly to the tibetan indenter block in asia as faults tend to go around it into areas of higher heat flow where the seismogenic zone is thinner and the crust may be weaker and it is pushed toward and under the southern cold sierra nevada block third to quantitatively compare the data sets temperatures for the seismicity cutout depth in california were calculated using the steady state 1d heat conduction equation with the variables based on published values for heat flow heat generation and thermal conductivity the analysis was restricted to profiles along which the heat flow and earthquake databases were constrained which allowed the error in the temperature calculation to be determined using monte carlo simulations the results show that two distinct ranges of temperatures dependent upon location describe the cutout depth d 99 of seismicity for california 450 50 c and 260 40 c the 450 50 c cutout depth temperature is most widespread geographically occurs within many provinces and is higher than the frequently referenced temperature of 300 50 c for the brittle ductile transition the lower temperature 260 c seems to be restricted to provinces where the heat flow is near or below 50 mw m 2 such as the mojave block and sierra nevada the differences in these cutout temperatures suggest that additional factors such as strain rate stress regime and or lithology may contribute to the seismicity cutout depth fourth along a profile with significant seismic activity and a 450 c cutout temperature the envelope for the maximum energy released by earthquakes falls at or below the 300 c isotherm detailed characterization of the heat flow and earthquake synergy in this manner furthers the understanding of the earthquake process and can aid in the estimation of the maximum depth of rupture for great earthquakes particularly in areas of low seismicity thus reducing uncertainties in hazard calculations manuscript received 26 february 2003

on shore amplification of the electric field induced by a coastal sea current abstract numerical techniques for the model approximating the earth by conducting and resistive thin sheets that are underlain by a perfect conductor are used to study the on shore amplification of the electric field induced by the norwegian coastal current the electric field is induced by sea water movement in the earth s magnetic field and decreases away from the sea current however numerical modelling suggests that the electric field is increased significantly on shore due to the conductivity contrast between the sea and the land results of the modelling indicate the significant in land decrease of the electric field anomaly controlled by the adjustment distance depending on the conductance of the first layer and the transverse resistance of the second one the coastal electric field anomaly ranges up to 10 mv km 1 which is large enough to be measured by 5 10 km long receiving antenna

opal zn si ratios as a nearshore geochemical proxy in coastal antarctica during the last 50 years the antarctic peninsula has experienced rapid warming with associated retreat of 87 of marine and tidewater glacier fronts accelerated glacial retreat and iceberg calving may have a significant impact on the freshwater and nutrient supply to the phytoplankton communities of the highly productive coastal regions however commonly used biogenic carbonate proxies for nutrient and salinity conditions are not preserved in sediments from coastal antarctica here we describe a method for the measurement of zinc to silicon ratios in diatom opal zn si opal which is a potential archive in antarctic marine sediments a core top calibration from the west antarctic peninsula shows zn si opal is a proxy for mixed layer salinity we present down core zn si opal paleosalinity records from two rapidly accumulating sites taken from nearshore environments off the west antarctic peninsula which show an increase in meltwater input in recent decades our records show that the recent melting in this region is unprecedented for over 120 years

the distribution of dissolved zinc in the atlantic sector of the southern ocean the distribution of dissolved zinc zn was investigated in the atlantic sector of the southern ocean in the austral autumn of 2008 as part of the ipy geotraces expedition zero drake research focused on transects across the major frontal systems along the zero meridian and across the drake passage there was a strong gradient in surface zinc concentrations observed across the antarctic polar front along both transects and high zinc levels were found in surface waters throughout the southern ocean vertical profiles for dissolved zinc showed the presence of local minima and maxima in the upper 200 m consistent with significant uptake by phytoplankton and release by zooplankton grazing respectively highest deep water zinc concentrations were found in the centre of the weddell gyre associated with central intermediate water ciw a water mass which is depleted in o2 elevated in co2 and is regionally a cfc minimum our data suggests that the remineralization of sinking particles is a key control on the distribution of zn in the southern ocean disappearance ratios of zinc to phosphate zn p in the upper water column increased southwards along both transects and based on laboratory studies they suggest slower growth rates of phytoplankton due to iron or light limitation zinc and silicate were strongly correlated throughout the study region but the disappearance ratio zn si was relatively uniform overall except for the region close to the ice edge on the zero meridian

a geology based 3d velocity model of the los angeles basin sediments abstract seismic hazard studies of the los angeles basin area require a realistic seismic velocity model we use geologic information about depth to crystalline basement depths to sedimentary horizons uplift of sediments and surface geology in a velocity depth age function to construct a three dimensional velocity model in earthquake location tests the model predicts travel times satisfactorily and in earthquake ground motion simulations the model correctly determines the timing and amplitude of late arriving waves

global mantle tomography progress status in the past 10 years abstract we review the present status of global mantle tomography and discuss two main classes of models that have been developed in the past 10 years p velocity models based on large datasets of travel times from the international seismological centre bulletins often referred to as high resolution models and s velocity models based on a combination of surface wave and hand picked body wave travel times or waveforms referred to as long wavelength models we discuss their respective strengths and weaknesses as well as progress in the resolution of other physical parameters such as anisotropy anelasticity density and bulk sound velocity using tomographic approaches we present the view that future improvements in global seismic tomography require the utilization of the rich information contained in complete broadband seismic waveforms this is presently within our reach owing to theoretical progress as well as the increase in computational power in recent years

attenuation models qp and qs in three dimensions of the southern california crust inferred fluid saturation at seismogenic depths we analyze high dynamic range waveform spectra to determine t values for both p and s waves from earthquakes in southern california we invert the t values for three dimensional 3 d frequency independent q p and q s regional models of the crust the models have 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth and extend from the u s mexico border to the coast ranges in the south and sierra nevada in the north in general qp and qs increase rapidly with depth consistent with crustal densities and velocities the 3 d q p and q s models image the major tectonic structures and to a much lesser extent the thermal structure of the southern california crust the near surface low q p and q s zones coincide with major sedimentary basins such as the san bernardino chino san gabriel valley los angeles ventura and santa maria basins and the salton trough in contrast at shallow depths beneath the peninsular ranges southern mojave desert and southern sierras we image high q p and q s zones which correspond to the dense and high velocity rocks of the mountain ranges several clear transition zones of rapidly varying q p and q s coincide with major late quaternary faults and connect regions of high and low q p and q s at midcrustal depths the q p and q s exhibit modest variation in slightly higher and lower qp or qs zones which is consistent with reported crustal reflectivity in general for the southern california crust q s q p is greater than 1 0 suggesting partially fluid saturated crust a few limited regions of q s q p less than 1 0 correspond to areas mostly outside the major sedimentary basins including areas around the san jacinto fault suggesting a larger reduction in the shear modulus compared to the bulk modulus or almost complete fluid saturation

a three dimensional crustal seismic velocity model for southern california from a composite event method we present a new crustal seismic velocity model for southern california derived from p and s arrival times from local earthquakes and explosions to reduce the volume of data and ensure a more uniform source distribution we compute composite event picks for 2597 distributed master events that include pick information for other events within spheres of 2 km radius the approach reduces random picking error and maximizes the number of s wave picks to constrain absolute event locations and shallow velocity structure we also use times from controlled sources including both refraction shots and quarries we implement the simulps tomography algorithm to obtain three dimensional 3 d v p and v p v s structure and hypocenter locations of the composite events our new velocity model in general agrees with previous studies resolving low velocity features at shallow depths in the basins and some high velocity features in the midcrust using our velocity model and 3 d ray tracing we relocate about 450 000 earthquakes from 1981 to 2005 we observe a weak correlation between seismic velocities and earthquake occurrence with shallow earthquakes mostly occurring in high p velocity regions and midcrustal earthquakes occurring in low p velocity regions in addition most seismicity occurs in regions with relatively low v p v s ratios although aftershock sequences following large earthquakes are often an exception to this pattern

community fault model cfm for southern california we present a new three dimensional model of the major fault systems in southern california the model describes the san andreas fault and associated strike slip fault systems in the eastern california shear zone and peninsular ranges as well as active blind thrust and reverse faults in the los angeles basin and transverse ranges the model consists of triangulated surface representations t surfs of more than 140 active faults that are defined based on surfaces traces seismicity seismic reflection profiles wells and geologic cross sections and models the majority of earthquakes and more than 95 of the regional seismic moment release occur along faults represented in the model this suggests that the model describes a comprehen sive set of major earthquake sources in the region the model serves the southern california earthquake center scec as a unified resource for physics based fault systems modeling strong ground motion prediction and probabilistic seismic hazards assessment

delineating shallow s wave velocity structure using multiple ambient noise surface wave methods an example from western junggar china abstract aiming for a geophysical survey to around 1 5 km depth we conduct a passive source surface wave survey along a 70 km long line on the western side of the junggar basin in northwest china we use frequency time analysis and spatial autocorrelation methods to extract surface wave dispersion curves from ambient noise data of station pairs as well as ambient noise multichannel analysis of surface waves from multistations dispersion curves corresponding to the same positions obtained by these three methods independently are comparable which shows the validity of using these methods after inverting more than 400 dispersion curves and aligning their results together we construct a 2d shear s wave velocity image around 1 5 km deep and 60 km long a less than 6 difference between the inverted s wave velocity profile and the borehole data in situ shows the relatively high accuracy of our method the 2d s wave velocity image clearly delineates the main geologic structures including transition of landform intrusion of rock mass and shape of bedrock beneath the survey line

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

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

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

full waveform tomography of the upper mantle in the south atlantic region imaging a westward fluxing shallow asthenosphere abstract a prominent feature of the south atlantic region is its strongly asymmetric residual bathymetry across the ocean basin it has been suggested that the residual bathymetry is dynamic in nature arising from the large slow velocity seismic anomaly located in the lower mantle beneath the african plate unfortunately the pattern of mantle heterogeneity particularly in the upper mantle is not well known owing to the sparsity of seismic stations and the existence of large aseismic regions on the african and south american plates here we present a new seismic tomographic study of the south atlantic upper mantle our model is based on a full seismic waveform inversion of 4000 high quality seismograms for isotropic 3 d seismic structure using a powerful adjoint methodology capable of extracting maximum information from each seismogram the theory requires simulation of seismic wave propagation in 3 d heterogeneous earth models computed with a spectral element method where the differences between observed and synthetic seismograms are quantified using phase misfits obtained through a time frequency transform the model images a continuous channel of pronounced slow seismic velocity in the shallow sublithospheric mantle between 150 and 300 km depth that branches in between the cratonic roots under the african and south american continents at greater depth below 300 350 km the slow anomalies are less pronounced and a change in the convective planform is indicated by isolated round shaped patches in an overall faster mantle it is possible that the depthwise change of the convective planform from vertical to horizontal advection of hot buoyant material in a low viscosity asthenosphere can reconcile the anomalous residual bathymetry in the region and we present a simple fluid dynamic model of pressure driven flow to assess the feasibility of this scenario

controls on ostracod valve geochemistry part 1 variations of environmental parameters in ostracod micro habitats abstract the variations of environmental conditions t ph 13 c dic dic 18 o mg ca and sr ca of ostracod habitats were examined to determine the controls of environmental parameters on the chemical and isotopic composition of ostracod valves results of a one year monitoring of environmental parameters at five sites with depths of between 2 and 70 m in lake geneva indicate that in littoral to sub littoral zones 2 5 and 13 m the chemical composition of bottom water varies seasonally in concert with changes in temperature and photosynthetic activity an increase of temperature and photosynthetic activity leads to an increase in 13 c values of dic and to precipitation of authigenic calcite which results in a concomitant increase of mg ca and sr ca ratios of water in deeper sites 33 and 70 m the composition of bottom water remains constant throughout the year and isotopic values and trace element contents are similar to those of deep water within the lake the chemical composition of interstitial pore water also does not reflect seasonal variations but is controlled by calcite dissolution aerobic respiration anaerobic respiration with reduction of sulphate and or nitrate and methanogenesis that may occur in the sediment pores relative influence of each of these factors on the pore water geochemistry depends on sediment thickness and texture oxygen content in bottom as well as pore water variations of chemical compositions of the ostracod valves of this study vary according to the specific ecology of the ostracod species analysed that is its life cycle and its micro habitat littoral species have compositions that are related to the seasonal variations of temperature 13 c values of dic and of mg ca and sr ca ratios of water in contrast the compositions of profundal species are largely controlled by variations of pore fluids along sediment depth profiles according to the specific depth preference of the species the control on the geochemistry of sub littoral species is a combination of controls for the littoral and profundal species as well as the specific ecology of the species

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

theoretical background for continental and global scale full waveform inversion in the time frequency domain summary we propose a new approach to full seismic waveform inversion on continental and global scales this is based on the time frequency transform of both data and synthetic seismograms with the use of time and frequency dependent phase and envelope misfits these misfits allow us to provide a complete quantification of the differences between data and synthetics while separating phase and amplitude information the result is an efficient exploitation of waveform information that is robust and quasi linearly related to earth s structure thus the phase and envelope misfits are usable for continental and global scale tomography that is in a scenario where the seismic wavefield is spatially undersampled and where a 3 d reference model is usually unavailable body waves surface waves and interfering phases are naturally included in the analysis we discuss and illustrate technical details of phase measurements such as the treatment of phase jumps and instability in the case of small amplitudes the frechet kernels for phase and envelope misfits can be expressed in terms of their corresponding adjoint wavefields and the forward wavefield the adjoint wavefields are uniquely determined by their respective adjoint source time functions we derive the adjoint source time functions for phase and envelope misfits the adjoint sources can be expressed as inverse time frequency transforms of a weighted phase difference or a weighted envelope difference in a comparative study we establish connections between the phase and envelope misfits and the following widely used measures of seismic waveform differences 1 cross correlation time shifts 2 relative rms amplitude differences 3 generalized seismological data functionals and 4 the l2 distance between data and synthetics used in time domain full waveform inversion we illustrate the computation of frechet kernels for phase and envelope misfits with data from an event in the west irian region of indonesia recorded on the australian continent the synthetic seismograms are computed for a heterogeneous 3 d velocity model of the australian upper mantle with a spectral element method the examples include p body waves rayleigh waves and s waves interfering with higher mode surface waves all the kernels differ from the more familar kernels for cross correlation time shifts or relative rms amplitude differences the differences arise from interference effects 3 d earth s structure and waveform dissimilarities that are due to waveform dispersion in the heterogeneous earth

compressional and shear wave velocity versus depth relations for common rock types in northern california abstract this article presents new empirical compressional and shear wave velocity vp and vs versus depth relationships for the most common rock types in northern california vp versus depth relations were developed from borehole laboratory seismic refraction and tomography and density measurements and were converted to vs versus depth relations using new empirical relations between vp and vs the relations proposed here account for increasing overburden pressure but not for variations in other factors that can influence velocity over short distance scales such as lithology consolidation induration porosity and stratigraphic age standard deviations of the misfits predicted by these relations thus provide a measure of the importance of the variability in vp and vs caused by these other factors because gabbros greenstones basalts and other mafic rocks have a different vp and vs relationship than sedimentary and granitic rocks the differences in vs between these rock types at depths below 6 or 7 km are generally small the new relations were used to derive the 2005 u s geological survey seismic velocity model for northern california employed in the broadband strong motion simulations of the 1989 loma prieta and 1906 san francisco earthquakes initial tests of the model indicate that the vp model generally compares favorably to regional seismic tomography models but that the vp and vs values proposed for the franciscan complex may be about 5 too high

rupture dynamics and ground motion from 3 d rough fault simulations 1 we perform three dimensional 3 d numerical calculations of dynamic rupture along non planar faults to study the effects of fault roughness on rupture propagation and resultant ground motion the fault roughness model follows a self similar fractal distribution over length scales spanning three orders of magnitude from 102 to 105 m the fault is governed by a strongly rate weakening friction and the bulk material is subject to drucker prager viscoplasticity fault roughness promotes the development of self healing rupture pulses and a heterogeneous distribution of fault slip at the free surface and at depth the inelastic deformation generated by the large dynamic stress near rupture fronts occurs in a narrow volume around the fault with heterogeneous thickness correlated to local roughness slopes inelastic deformation near the free surface however is induced by the stress waves originated from dynamic rupture at depth and spreads to large distances 10 km away from the fault the present simulations model seismic wave excitation up to 10 hz with rupture lengths of 100 km permitting comparisons with empirical studies of ground motion intensity measures of engineering interest characteristics of site averaged synthetic response spectra including the distance and period dependence of the median values absolute level and intra event standard deviation are comparable to appropriate empirical estimates throughout the period range 0 1 3 0 s this class of model may provide a viable representation of the ground motion excitation process over a wide frequency range in a large spatial domain with potential applications to the numerical prediction of source and path specific effects on earthquake ground motion

teleseismic surface wave study for s wave velocity structure under an array southern california summary teleseismic surface wave data from the dense seismographic network in southern california cisn california integrated seismic network are used to construct s wave velocity maps for the region surface wave phase velocity measurements are achieved by way of a waveform matching spectral domain technique that was developed for use within the cisn array a two station phase velocity measurement technique was developed which takes advantage of the fact that for surface wave arrivals from any azimuth there are multiple pairs of cisn stations which are almost exactly on the same great circle paths to ensure the validity of this assumption particle motions were analysed for measured pairs within the network showing that the deviation between expected backazimuth from ray theory and observed backazimuths are small enough to be analysed by a simple distance correction this method was applied to 114 large earthquakes for time periods between 1999 and 2002 and led to the retrieval of phase velocity maps for rayleigh waves between 20 and 55 mhz and for love waves between 25 and 45 mhz finite frequency effect for propagating surface waves was approximately taken into consideration using a geometrical technique an ellipse determined by wavelength and great circle distance between the source and receiver can describe an influence zone for the finite frequency effect phase velocity map reconstructions using a method which incorporates this effect show minimal changes in phase velocity maps for our region but do extend solvable velocity regions inversion for s wave velocity distribution with depth shows that deep structural contrast across the san andreas extends into the upper mantle a slow velocity anomaly is evident under the southern sierras and the salton sea the latter region indicating the northward extension of tectonic activity in the gulf of california fast velocity roots that reach 60 km are found under the western part of transverse ranges and the northern peninsular ranges reconstruction of past location of the western transverse range microplate implies that these two ranges may have been adjacent to one another historically both the western transverse range fast velocity root and the peninsular range fast velocity root may be a remnant of old oceanic plate

numerically stable computation of complete synthetic seismograms including the static displacement in plane layered media summary we present a new method for calculating dynamic and static displacements arising from a buried point source in a plane layered isotropic elastic half space we avoid the problem of the loss of precision in solutions for p sv wave motion by integrating a system of minor vector equations with solutions constructed from pairs of solutions to the equations of motion in the frequency wavenumber domain the resulting algorithm is efficient and numerically stable at zero frequency and at high frequencies and thus can be used to compute complete synthetic seismograms that include the static offset for the special case of the static deformation of a homogeneous half space we show that our results are equivalent to formulae that are often currently used in the geodetic community an advantage of our method is that a single algorithm can be used to model both seismological and geodetic measurements of ground motion we illustrate one seismological application of our method using continuous global positioning system gps data obtained for a recent earthquake seismograms calculated in a realistic layered crustal model emulate the observed dynamic and static displacements well if the calculation is only carried out at 0 hz we obtain an image of the static surface deformation and thus our method also has potential applications in the modelling of coseismic surface displacements measured with for example synthetic aperture radar interferometry

interseismic strain accumulation on faults beneath los angeles california geodetic data show that the los angeles metropolitan area is undergoing 8 9 mm year of north south tectonic shortening associated with the big bend of the san andreas fault this shortening has been linked to multiple damaging twentieth century thrust earthquakes as well as possible mw 7 0 holocene thrust events beneath central los angeles to better characterize this seismic hazard we assess how this shortening is being accommodated by interseismic strain accumulation on subsurface faults incorporating detailed seismology and geology based models of fault geometry and the low stiffness los angeles sedimentary basin we find that strain accumulation on local strike slip faults likely contributes no more than 1 2 mm year of the shortening we formally invert the geodetic data for the pattern of interseismic strain accumulation on the north dipping sierra madre puente hills and compton thrust faults and a master decollement we explore the impact of the assumed material model strain accumulation on faults to the west and east and other model assumptions we infer that the three faults slip at 3 4 mm year over the long term and are currently partially or fully locked and accruing interseismic strain on their upper sections this locking implies an annual deficit of seismic moment 1 6 1 3 0 5 10 17 nm year in total which is presumably balanced over the long term average by the moment released in earthquakes the depth distribution of moment deficit accumulation rate matches that of seismicity rates in los angeles to first order in part because the models incorporate the blind nature of the puente hills and compton faults

development and testing of a 3d seismic velocity model of the po plain sedimentary basin italy abstract we built a 3d seismic model of the po plain and neighboring regions of northern italy covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid we started by collecting an extensive and diverse set of geological and geophysical data including seismic reflection and refraction profiles borehole logs and available geological information major geological boundaries and discontinuities have thus been identified and mapped into the model we used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness seismic wave properties have been assigned to each unit using a rule based system and v p v s and derived from other studies sedimentary strata although with varying levels of compaction and hence material properties may locally reach a thickness of 15 km and give rise to significant effects in seismic wave propagation we have used our new model to compute the seismic response for two recent earthquakes to test its performance results show that the 3d model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments whereas paths outside the basin may be well fit by more homogeneous 1d hard rock structure we conclude that the new model is suited for simulation of wave propagation mostly for t 3 s and may serve well as a constraint for earthquake location and further improvements via body or surface wave inversion

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