the deep structure of the north anatolian fault zone abstract multi scale full waveform inversion of complete continental and regional scale seismograms reveals the crustal and upper mantle signature of the north anatolian fault zone which shapes the neotectonics of turkey and the eastern mediterranean within the crust the fault zone is mostly bounded by several high velocity blocks suggesting that it developed along the edges of continental fragments with high rigidity below the crust the surface expression of the eastern and central parts of the north anatolian fault zone correlate with a pronounced low velocity band that extends laterally over 600 km around 100 km depth the low velocity band merges into the shallow anatolian asthenosphere thereby providing a link to the kirka afyon isparta volcanic field and the central anatolian volcanics we interpret the low velocity band beneath the north anatolian fault zone as the upper mantle expression of the tethyan sutures that formed 60 15 ma ago as a result of africa eurasian convergence the structurally weak suture facilitated the formation of the younger less than 10 ma crustal fault zone in this sense the north anatolian fault zone is not only a crustal feature but a narrow zone of weakness that extends into the upper mantle

frechet kernels for imaging regional earth structure based on three dimensional reference models high resolution images of three dimensional 3d seismicstructuresare not only of scientific interest but also of practical importance in predicting strong ground motion after large earthquakes given the source and station distributions resolutions in current regional seismic tomography studies have been limited by two types of simplifying practices the adoption of high frequency approximations such as the ray theory and the use of one dimensional 1d reference starting models we have developed a new approach to compute accurate finite frequency 3d frechet sensitivity kernels of observed travel time and amplitude anomalies relative to 3d reference models in our approach we use a fourth order staggered grid finite difference method to model the seismic wave propagation in 3d media and the reciprocity property of the green s tensor to reduce the number of numerical simu lations this approach accounts for the perturbations in compressional and shear wave speeds in the same way leading to a capability of inverting for the shear wave speed directly from seismic data the algorithm is readily parallelized to allow for realistic regional high resolution 3d tomography inversions we have implemented the algorithm for the southern california earthquake center scec community velocity model scec cvm 3 0 a complex 3d model for southern california in cluding a number of sedimentary basins by enabling the inversion of 3d structural perturbations to 3d reference models our approach provides a practical means of iteratively solving the nonlinear regional tomography problems

strong shaking in los angeles expected from southern san andreas earthquake 1 the southernmost san andreas fault has a high probability of rupturing in a large greater than magnitude 7 5 earthquake sometime during the next few decades new simulations show that the chain of sedimentary basins between san bernardino and downtown los angeles form an effective waveguide that channels love waves along the southern edge of the san bernardino and san gabriel mountains earthquake scenarios with northward rupture in which the guided wave is efficiently excited produce unusually high long period ground motions over much of the greater los angeles region including intense localized amplitude modulations arising from variations in waveguide cross section

interseismic strain accumulation and the earthquake potential on the southern san andreas fault system the southern section of the san andreas fault is the only part of the fault that hasn t ruptured in historic times for this reason it is believed to pose the largest seismic risk in california although whether tectonic stress is actually accumulating there is a topic of heated debate using data from radar interferometry satellites yuri fialko has produced a detailed map of surface deformation in the area that shows that elastic stress is accumulating at a fairly high rate during the past 300 years a displacement of 6 to 9 metres has built up this suggests that the southern san andreas fault is nearing the end of the interseismic phase of the earthquake cycle and that increased seismic activity of some kind can be expected the san andreas fault in california is a mature continental transform fault that accommodates a significant fraction of motion between the north american and pacific plates the two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857 respectively the southern section of the fault however has not produced a great earthquake in historic times for at least 250 years assuming the average slip rate of a few centimetres per year typical of the rest of the san andreas fault the minimum amount of slip deficit accrued on the southern section is of the order of 7 10 metres comparable to the maximum co seismic offset ever documented on the fault1 2 here i present high resolution measurements of interseismic deformation across the southern san andreas fault system using a well populated catalogue of space borne synthetic aperture radar data the data reveal a nearly equal partitioning of deformation between the southern san andreas and san jacinto faults with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces the observed strain rates confirm that the southern section of the san andreas fault may be approaching the end of the interseismic phase of the earthquake cycle

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

separation of s wave and p wave reflections offshore western florida hard water bottom marine environments such as offshore western florida have presented particular problems in the acquisition and processing of seismic reflection data one problem has been the limited angle of incidence less than critical available to p wave penetration into the subsurface mode conversion from p wave to s waves sv however is quite efficient over a broad range of angles of incidence after the success of a previously reported physical model experiment an experimental line was acquired offshore western florida the 19 mile line located approximately 100 miles west of key west florida was shot and processed three key factors have contributed to the successful recording of mode converted s wave reflections 1 recognition of the effect of the group length on attenuation of energy arriving at large angles of incidence 2 tau p processing techniques that allow separation of energy by angle of incidence and 3 velocity filtering over a range of hyperbolic normal moveout nmo

high resolution seismic images of potentially seismogenic structures beneath the northwest canterbury plains new zealand 1 the transpressional boundary between the australian and pacific plates in the central south island of new zealand comprises the alpine fault and a broad region of distributed strain concentrated in the southern alps but encompassing regions further to the east including the northwest canterbury plains low to moderate levels of seismicity e g 2 m 5 events since 1974 and 2 m 4 0 in 2009 and holocene sediments offset or disrupted along rare exposed active fault segments are evidence for ongoing tectonism in the northwest plains the surface topography of which is remarkably flat and even because the geology underlying the late quaternary alluvial fan deposits that carpet most of the plains is not established the detailed tectonic evolution of this region and the potential for larger earthquakes is only poorly understood to address these issues we have processed and interpreted high resolution 2 5 m subsurface sampling interval seismic data acquired along lines strategically located relative to extensive rock exposures to the north west and southwest and rare exposures to the east geological information provided by these rock exposures offer important constraints on the interpretation of the seismic data the processed seismic reflection sections image a variably thick layer of generally undisturbed younger i e 59 ka quaternary sedimentary sequence that shows evidence of moderate faulting and folding during and subsequent to deposition these quaternary units are in unconformable contact with late cretaceous tertiary interbedded sedimentary and volcanic rocks that are highly faulted folded and tilted the lowest imaged unit is largely reflection free permian triassic basement rocks quaternary age deformation has affected all the rocks underlying the younger alluvial sediments and there is evidence for ongoing deformation eight primary and numerous secondary faults as well as a major anticlinal fold are revealed on the seismic sections folded sedimentary and volcanic units are observed in the hanging walls and footwalls of most faults five of the primary faults represent plausible extensions of mapped faults three of which are active the major anticlinal fold is the probable continuation of known active structure a magnitude 7 1 earthquake occurred on 4 september 2010 near the southeastern edge of our study area this predominantly right lateral strike slip event and numerous aftershocks ten with magnitudes 5 within one week of the main event highlight the primary message of our paper that the generally flat and topographically featureless canterbury plains is underlain by a network of active faults that have the potential to generate significant earthquakes

high resolution relocation of aftershocks of the mw 7 1 darfield new zealand earthquake and implications for fault activity 1 low slip rate regions often represent under recognized hazards and understanding the progression of seismicity when faults in such areas rupture will help us to better understand earthquake rupture patterns the 3 september 2010 utc mw 7 1 darfield earthquake revealed a formerly unrecognized set of faults in the canterbury region of new zealand an area that had previously been mapped as one of the lower hazard areas in the country in this study we analyze the first four months of its aftershock sequence to identify active faults and temporal changes in seismicity along them we jointly invert for three dimensional p wave and s wave velocities and hypocentral locations using data for 2840 aftershocks recorded at 36 temporary and permanent seismic stations within 70 km of the main shock epicenter these relocations delineate eight individual faults active prior to the 22 february 2011 mw 6 3 christchurch earthquake the largest aftershock of the darfield earthquake two of these faults are in the christchurch region one of which corresponds to geodetically determined rupture planes of the christchurch earthquake using focal mechanisms calculated from first motion polarities we find mainly strike slip faulting events with some reverse and normal faulting events as well we compare the orientations of these faults to the prevailing regional stress directions to identify which faults may have been active prior to the darfield earthquake and which may be newly developed

resolving fault plane ambiguity for small earthquakes summary we have developed an automated procedure to resolve fault plane ambiguity for small to medium sized earthquakes 2 5 ml 5 using synthetic green s tensors computed in a 3 d earth structure model and applied this procedure to 35 earthquakes in the los angeles area for 69 per cent of the events we resolved fault plane ambiguity of our cmt solutions at 70 per cent or higher probability for some earthquakes the fault planes selected by our automated procedure were confirmed by the distributions of relocated aftershock hypocentres in regions where there are no precisely relocated aftershocks or for earthquakes with few aftershocks we expect our method to provide the most convenient means for resolving fault plane ambiguity our procedure does not rely on detecting directivity effects therefore it is applicable to any types of earthquakes

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

extraction of p and s waves from the vertical component of the particle velocity at the sea floor at the boundary between two solid media in welded contact all three components of particle velocity and vertical traction are continuous through the boundary across the boundary between a fluid and a solid however only the vertical component of particle velocity is continuous while the horizontal components can be discontinuous furthermore the pressure in the fluid is the negative of the vertical component of traction in the solid while the horizontal components of traction vanish at the interface taking advantage of this latter fact the authors show that total p and s waves can be computed from the vertical component of the particle velocity recorded by single component geophones planted on the sea floor in the case when the sea floor is transversely isotropic with a vertical axis of symmetry the computation requires the five independent elastic stiffness components and the density however when the sea floor material is fully isotropic the only material parameter needed is the local shear wave velocity the analysis of the extraction problem is done in the slowness domain they show however that the s wave section can be obtained by a filtering operation in the space frequency domain the p wave section is then the difference between themore vertical component of the particle velocity and the s wave component a synthetic data example demonstrates the performance of the algorithm less

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

using regional moment tensors to constrain the kinematics and stress evolution of the 2010 2013 canterbury earthquake sequence south island new zealand abstract on september 3 2010 a m w 7 0 u s geological survey moment magnitude earthquake ruptured across the canterbury plains in south island new zealand since then new zealand gns science has recorded over 10 000 aftershocks m l 2 0 and larger including three destructive m w 6 0 earthquakes near christchurch we treat the canterbury earthquake sequence as an intraplate earthquake sequence and compare its kinematics to an andersonian model for fault slip in a uniform stress field we determined moment magnitudes and double couple solutions for 150 earthquakes having m w 3 7 and larger through the use of a waveform inversion technique using data from broadband seismic stations on south island new zealand the majority 126 of these double couple solutions have strike slip focal mechanisms with right lateral slip on ene fault planes or equivalently left lateral slip on sse fault planes the remaining focal mechanisms indicate reverse faulting except for two normal faulting events the strike slip segments have compatible orientations for slip in a stress field with a horizontal 1 oriented n115 e and horizontal 3 the preference for right lateral strike slip earthquakes suggests that these structures are inherited from previous stages of deformation reverse slip is interpreted to have occurred on previously existing structures in regions with an absence of existing structures optimally oriented for strike slip deformation despite the variations in slip direction and faulting style most aftershocks had nearly the same p axis orientation consistent with the regional 1 there is no evidence for significant changes in these stress orientations throughout the canterbury earthquake sequence

stress and the direction of slip on fault planes the shear stress direction on a fault plane depends only on four of the six components of the stress tensor assuming only that the slip direction marks the shear stress direction on any fault plane and that stress is homogeneous it is possible to estimate these four stress parameters from populations of fault planes with known slip directions as several workers have observed different formulations of the problem may yield varying best fitting stresses and estimates of uncertainty in the simplest case no assumptions are made regarding the orientations of fault planes relative to the stress tensor thus the technique allows for the possibility that the fault planes may be very weak here we present simple analytical and graphical descriptions of the field of admissible fault geometries relative to any four parameter stress model which can be used to illustrate the significance of various inverse strategies in particular this paper explores the effects of using two alternative measures of misfit between an observed fault datum and stress model 1 the pole rotation the angle between the observed and predicted slip direction on the observed fault plane and 2 the minimum rotation the smallest angle between the observed fault geometry and any fault geometry which is consistent with the model by allowing for variation of the fault plane as well as the slip vector the minimum rotation procedure generally achieves a more stable and presumably realistic estimate of the actual discrepancy between a fault observation and stress model than the pole rotation procedure in a test case using 17 earthquake focal mechanisms from the yuii region of eastern taiwan separate inversions based on the two misfit criteria yield different optimum stress models and uncertainty estimates additional constraints on the stress tensor such as the effect of friction can be superimposed on the ones used here

introduction seismic wave scattering in three dimensionally heterogeneous earth the classical earth model of spherical symmetry or layered structure is undergoing a revolution the earth has been revealed to be laterally heterogeneous everywhere from the crust mantle to the core with scale from the grain size of rocks to the lowest orders of global spherical harmonics figure 1 shows the strength and scale length of heterogeneities in the crust and mantle of the earth in terms of v the perturbation index of seismic p or s wave speed defined as the r m s fractional variations of wave speed over the measured region the scale length of heterogeneities revealed by seismic waves not including the laboratory measurements of rock samples spans 8 orders of magnitude these heterogeneities with different scales have different effects to seismic waves the velocity and density heterogeneities can cause the change in waveform phase or travel time and amplitude fluctuation as well as apparent attenuation of the direct arrivals they can also generate coda waves such as the p coda s coda and lg coda caused by the lithospheric heterogeneities and precursory waves such as the scattered pkp waves as the precursors to pkikp caused by the heterogeneities near the core mantle boundary the near source or near receiver structures can modify the seismic waveforms by resonance and other effect rough topography or rough interface can cause the coupling between body wave and surface wave aligned cracks in the crust can produce the effective anisotrophy a great complexity arises when heterogeneities have interaction with anisotrophy and nonlinearity

decomposition of multicomponent sea floor data into upgoing and downgoing p and s waves a method for decomposing multicomponent sea floor measurements into upgoing and downgoing p and s waves is presented we assume that a marine survey employing a marine source in the water layer is conducted over a plane layered medium from recordings of the pressure just above the sea floor and the particle velocity vector just below the sea floor decomposition filters can be determined by plane wave analysis the decomposition filter coefficients depend on the p and s wave velocities and the density at the sea bottom we show how to decompose the multicomponent measurements into upgoing and downgoing p and s vertical traction components vertical particle velocity components and horizontal particle velocity components the decomposition filters are applied with good results to synthetic data modeled in a plane layered medium

resolution limits for crosswell migration and traveltime tomography summary equations are derived for the point scatterer response of the crosswell migration and traveltime tomography operators these formulas are used to estimate the limits of spatial resolution in reflection migration images and traveltime tomograms in particular for a crosswell geometry with borehole length l well offset 2x0 source wavelength and a centred point scatterer i show the following 1 the vertical resolution zmig of the reflection migration image is equal to 2 x0 l under the far field approximation under the fresnel approximation zmig 2 x0 l 2 2 l which says that images become better resolved with an increase in aperture and a decrease in wavelength and well offset 2 the horizontal resolution zmig of the migration image is equal to 16 x02 l2 the lateral resolution of the migrated image is worse than the vertical resolution by a factor of 8x0 l where x0 l 1 under the far field approximation 3 the vertical resolution ztomo of the traveltime velocity tomogram is proportional to x0 this estimate agrees with that of a previous study however the tomographic image of the slowness perturbation behaves as a non local cosine function along the depth axis whereas the migration image behaves as a localized squared sine function in the depth coordinate this is consistent with the empirical observation that interface boundaries are more sharply resolved by migration than by traveltime tomography 4 the horizontal resolution of the slowness image in a traveltime tomogram is equal to 4x0 l 3x0 4 a factor more than 4x0 l worse than the vertical resolution 5 for ns sources and ng geophones the dynamic range of the migrated image is proportional to nsng the dynamic range of the slowness tomogram is proportional to ngns many of the estimates for the resolution limits have simple geometrical interpretations for example the minimum vertical horizontal resolution in a migrated reflectivity section corresponds to the minimum vertical horizontal stretch that a migrated wavelet undergoes in going from the time domain to the depth domain in addition the minimum vertical horizontal resolution in a traveltime tomogram corresponds to the minimum vertical horizontal width of the wavepath at the scatterer location

seismic structure of the upper mantle in a central pacific corridor the seismic structure of the tonga hawaii corridor has been investigated by combining two data sets revenaugh and jordan s reflectivity profile from scs reverberations which provides travel times to and impedance contrasts across the major mantle discontinuities and 1500 new observations of frequency dependent phase delays for the three component s ss and sss body waves and the r1 and g1 surface waves which constrain the velocity structure within this layered framework the shear waves turning in the upper mantle showed significant splitting of the sh and sv components indicative of shallow polarization anisotropy the data set was inverted in conjunction with attenuation and mineralogical constraints to obtain a complete spherically symmetric radially anisotropic structure the final model pa5 is characterized by a high velocity anisotropic lid bounded at 68 km depth by a large negative g discontinuity a low velocity anisotropic layer below g extending to a small l discontinuity at 166 km an isotropic steep gradient region between 166 km and 415 km and transition zone discontinuities at 415 507 and 651 km the depth of the radial anisotropy in pa5 is shallower than in most previous studies based on surface waves and higher modes the average value of radial shear anisotropy in the lid 3 7 is consistent with the magnitude expected from the spreading controlled models of olivine orientation while anisotropy in the low velocity zone which is required by our data set could be induced either by paleostrains that took place near the ridge crest or by shearing in the asthenosphere as a result of present day plate motions on the basis of recent work by hirth and kohlstedt we suggest that the g discontinuity is caused by a rapid increase in the water content of mantle minerals with depth marking the fossilized lower boundary of the melt separation zone active during crust formation the high gradient zone between 200 and 400 km is a characteristic feature of convecting oceanic upper mantle and is probably controlled by a steady decrease in the homologous temperature over this depth interval the average shear velocity gradient in the transition zone is lower than in most previous seismic models in better agreement with the predictions for a pyrolitic composition

continuing megathrust earthquake potential in chile after the 2014 iquique earthquake the 2014 iquique event was not the earthquake that had been expected to fill the regional seismic gap given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure the seismic gap theory1 identifies regions of elevated hazard based on a lack of recent seismicity in comparison with other portions of a fault it has successfully explained past earthquakes see for example ref 2 and is useful for qualitatively describing where large earthquakes might occur a large earthquake had been expected in the subduction zone adjacent to northern chile3 4 5 6 which had not ruptured in a megathrust earthquake since a m 8 8 event in 1877 on 1 april 2014 a m 8 2 earthquake occurred within this seismic gap here we present an assessment of the seismotectonics of the march april 2014 iquique sequence including analyses of earthquake relocations moment tensors finite fault models moment deficit calculations and cumulative coulomb stress transfer this ensemble of information allows us to place the sequence within the context of regional seismicity and to identify areas of remaining and or elevated hazard our results constrain the size and spatial extent of rupture and indicate that this was not the earthquake that had been anticipated significant sections of the northern chile subduction zone have not ruptured in almost 150 years so it is likely that future megathrust earthquakes will occur to the south and potentially to the north of the 2014 iquique sequence

revisiting the canterbury earthquake sequence after the 14 february 2016 mw 5 7 event on 14 february 2016 an mw 5 7 gns science moment magnitude earthquake ruptured offshore east of christchurch new zealand this earthquake occurred in an area that had previously experienced significant seismicity from 2010 to 2012 during the canterbury earthquake sequence starting with the 2010 mw 7 0 darfield earthquake and including four mw 6 0 earthquakes near christchurch we determine source parameters for the february 2016 event and its aftershocks relocate the recent events along with the canterbury earthquakes and compute coulomb stress changes resolved onto the recent events and throughout the greater christchurch region because the february 2016 earthquake occurred close to previous seismicity the coulomb stress changes resolved onto its nodal planes are uncertain however in the greater christchurch region there are areas that remain positively loaded including beneath the city of christchurch the recent earthquake and regional stress changes suggest that faults in these regions may pose a continuing seismic hazard

significance of stress transfer in time dependent earthquake probability calculations 1 a sudden change in stress is seen to modify earthquake rates but should it also revise earthquake probability data used to derive input parameters permit an array of forecasts so how large a static stress change is required to cause a statistically significant earthquake probability change to answer that question effects of parameter and philosophical choices are examined through all phases of sample calculations drawing at random from distributions of recurrence aperiodicity pairs identifies many that recreate long paleoseismic and historic earthquake catalogs probability density functions built from the recurrence aperiodicity pairs give the range of possible earthquake forecasts under a point process renewal model consequences of choices made in stress transfer calculations such as different slip models fault rake dip and friction are tracked for interactions among large faults calculated peak stress changes may be localized with most of the receiving fault area changed less than the mean thus to avoid overstating probability change on segments stress change values should be drawn from a distribution reflecting the spatial pattern rather than using the segment mean disparity resulting from interaction probability methodology is also examined for a fault with a well understood earthquake history a minimum stress change to stressing rate ratio of 10 1 to 20 1 is required to significantly skew probabilities with 80 85 confidence that ratio must be closer to 50 1 to exceed 90 95 confidence levels thus revision to earthquake probability is achievable when a perturbing event is very close to the fault in question or the tectonic stressing rate is low

global upper mantle structure from long period differential travel times we have made over ten thousand measurements of pp p and ss s differential travel times from long period global digital seismograph network recordings of all events with mb 5 5 which occurred during the years 1976 to 1986 we have obtained reasonable global coverage with very good sampling of several regions of the world the residuals range from 5 to 5 s for pp p and 12 to 12 s for ss s and reveal a large scale pattern of heterogeneity when plotted at the reflected phase s bounce point our experiments indicate that lower mantle structure and source receiver structure can each contribute approximately 0 5 s to our measured pp p residuals so there is considerable signal to be explained the pattern observed in the pp p measurements is similar to the pattern observed in the ss s measurements with the ss s residuals 2 to 4 times larger in magnitude comparisons of our measured residuals to those predicted by the upper mantle models of woodhouse and dziewonski show that the overall patterns are quite similar but the amplitude of the model residuals is roughly a factor of 2 too small comparisons with the predictions of a whole mantle model of tanimoto again shows that the predicted pattern of residuals is reasonably consistent with the observations but now the predicted residuals are too large by about a factor of 2 this variation in predicted amplitudes is probably mainly due to differences in the near surface structure of the models we have also binned our measurements according to the tectonic regionalization gtr1 of jordan and find a qualitative correlation of average residual with tectonic region in particular precambrian shields show a strong anomaly and there is a correlation of residual size with the age of oceanic crust at the bounce point for all tectonic regions the ratio of ss s to pp p residuals is approximately 2 this ratio is consistent with a thermal origin for the observed signal finally our measurements show no compelling evidence for azimuthal anisotropy which might be related to fossil spreading direction or the direction of absolute plate motion such a signal is probably overwhelmed by the large signal from three dimensional structure

monitoring the earthquake source process in north america with the implementation of the usgs national earthquake information center prompt assessment of global earthquakes for response system pager rapid determination of earthquake moment magnitude is essential especially for earthquakes that are felt within the contiguous united states we report an implementation of moment tensor processing for application to broad seismically active areas of north america this effort focuses on the selection of regional crustal velocity models codification of data quality tests and the development of procedures for rapid computation of the seismic moment tensor we systematically apply these techniques to earthquakes with reported magnitude greater than 3 5 in continental north america that are not associated with a tectonic plate boundary using the 0 02 0 10 hz passband we can usually determine with few exceptions moment tensor solutions for earthquakes with m w as small as 3 7 the threshold is significantly influenced by the density of stations the location of the earthquake relative to the seismic stations and of course the signal to noise ratio with the existing permanent broadband stations in north america operated for rapid earthquake response the seismic moment tensor of most earthquakes that are m w 4 or larger can be routinely computed as expected the nonuniform spatial pattern of these solutions reflects the seismicity pattern however the orientation of the direction of maximum compressive stress and the predominant style of faulting is spatially coherent across large regions of the continent

decomposition of multicomponent seismic data into primary p and s wave responses1 inversion of multicomponent seismic data can be subdivided in three main processes 1 surface related preprocessing decomposition of the multicomponent data into primary p and s wave responses 2 prestack migration of the primary p and s wave responses yielding the angle dependent p p p s s p and s s reflectivity of the subsurface 3 target related post processing transformation of the reflectivity into the rock and pore parameters in the target this paper deals with the theoretical aspects of surface related preprocessing which consists of two steps 1 decomposition of the multicomponent data pseudo p and s wave responses into true p and s wave responses 2 elimination of the surface related multiple reflections and conversions

wide area imaging from obs multiples the subseafloor structure offshore western canada was imaged using first order water layer multiples from oceanbottom seismometer obs data and the results were compared to conventional imaging using primary reflections this multiple migration mirror imaging method uses the downgoingpressurewavefieldjustabovetheseafloor which is devoid of any primary reflections but consists of receiverside ghosts of these primary reflections the mirror imaging method employs a primaries only kirchhoff prestack depth migration algorithm to image the receiver ghosts the additional travel path of the multiples through the water layer is accountedforbyasimplemanipulationofthevelocitymodel and processing datum the receivers lie not on the seabed but on a sea surface twice as high as the true water column migration results show that the multiple migrated image provides a much broader illumination of the subsurface than is possible for conventional imaging using the primaries especially for the very shallow reflections and sparse obs spacing the resulting image from mirror imaging has illumination comparable to the vertical incidence surface streamer single channelreflectiondata

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

seismic waveform inversion in the frequency domain part 2 fault delineation in sediments using crosshole data a crosshole experiment was carried out in a layered sedimentary environment in which a normal fault is known to cut through the section initial traveltime inversions produced stable but low resolution images from which the fault could be only vaguely inferred to image the fault wavefield inversion was used to produce a velocity model consistent with the detailed phase and amplitude of the data at a number of frequencies our wavefield inversion scheme uses a classical descent type algorithm for decreasing the data misfit by iteratively computing the gradient of this misfit by repeated forward and backward propagations our propagator is a full wave equation frequency domain acoustic finite difference method the use of the frequency space domain yields computational advantages for multisource data and allows an easy incorporation of viscous effects by running wavefield inversion on the field data a quantitative velocity image was produced that yielded a significantly improved image of the fault when compared with the original traveltime inversions because the original field data were noisy and contained a high degree of multiple scattering from the layering of the sediments the transmitted arrivals were selectively windowed to enhance the image the sediments at the site were strongly attenuating we therefore used a viscoacoustic model during the modeling and the inversion that correctly simulated the observed decrease in amplitude with increasing frequency and source receiver offset furthermore since the traveltime inversion indicated a high degree of anisotropy at the site a fixed homogeneous level of anisotropy was used during the inversion tests at varying levels of anisotropy confirmed the improvement in image quality and in data fit when anisotropy was incorporated the final image was verified by examining the distribution of the residuals in the frequency domain by comparing time domain modeled wavefields with the observed data and by direct comparison with borehole logs

finite moment tensor of the 3 september 2002 yorba linda earthquake we have developed procedures for inverting broadband waveforms for the finite moment tensors fmts of regional earthquakes the fmt is defined in terms of second order polynomial moments of the source space time function it removes the fault plane ambiguity of the centroid moment tensor cmt and yields several additional parameters of seismological interest the characteristic length lc width wc and duration tc of the faulting as well as the directivity vector v d of the fault slip following mcguire et al 2001 we represent the observed waveform relative to the synthetic in terms of two frequency dependent differential times a phase delay p and an amplitude reduction time q which we measure using the generalized seismological data functional gsdf method gee and jordan 1992 we numerically calculate the fmt partial derivatives which allows us to use synthetics computed by using any forward modeling tools we have tested our methodology on southern california seismic network scsn recordings of the 03 september 2002 yorba linda earthquake m w 4 3 using 1d synthetic green s functions we determined the cmt and resolved fault plane ambiguity to resolve the details of source finiteness we employed a joint inversion technique that recovers the cmt parameters of the aftershocks and the cmt and fmt parameters of the mainshock the joint system of equations relating the data to the source parameters of the mainshock aftershock cluster is denuisanced for path anomalies in both observables this projection operation effectively corrects the mainshock data for path related anomalies in a way similar to but more flexible than empirical green s function egf techniques our results indicate that the yorba linda rupture occurred as left lateral slip on a fault patch conjugate to the nearby right lateral whittier fault we obtained source dimensions of lc 0 7 0 1 km wc 0 4 0 1 km and tc 0 2 0 05 sec implying a stress drop of about 3 2 mpa and we found a directivity of 0 8 0 2 oriented up and to the northeast the inferred fault plane is consistent with the mainshock aftershock distribution relocated by hauksson et al 2002

long aftershock sequences within continents and implications for earthquake hazard assessment one of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries plate tectonics gives no insight however into where and when earthquakes will occur within plates because the interiors of ideal plates should not deform as a result within plate interiors assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes here however we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago we present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries these predictions are in accord with observations so the common practice of treating continental earthquakes as steady state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere

full wave seismic data assimilation theoretical background and recent advances the seismological inverse problem has much in common with the data assimilation problem found in meteorology and oceanography using the data assimilation methodology i will formulate the seismological inverse problem for estimating seismic source and earth structure parameters in the form of weak constraint generalized inverse in which the seismic wave equation and the associated initial and boundary conditions are allowed to contain errors the resulting euler lagrange equations are closely related to the adjoint method and the scattering integral method which have been successfully applied in full 3d full wave seismic tomography and earthquake source parameter inversions i will review some recent applications of the full wave methodology in seismic tomography and seismic source parameter inversions and discuss some challenging issues related to the computational implementation and the effective exploitation of seismic waveform data

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

structural constraints on the spatial distribution of aftershocks 1 calculations of static stress changes due to large earthquakes have shown that the spatial distribution of aftershocks is predictable to first order with aftershocks primarily occurring in areas experiencing positive stress changes delineation of these areas relies on resolving the stress perturbation onto planes with known orientations common practice is to use poorly constrained regional stress information to compute optimally oriented failure planes assuming that they exist everywhere here we show that this assumption is not supported by observation but rather that aftershock failure planes are controlled by geological structure we argue that useful aftershock hazard estimates are better made by replacing information on regional stress with statistical measures of structural orientations

cumulative coulomb stress triggering as an explanation for the canterbury new zealand aftershock sequence initial conditions are everything using 2 years of aftershock data and three fault plane solutions for each of the initial m7 1 darfield earthquake and the larger m 6 aftershocks we conduct a detailed examination of coulomb stress transfer in the canterbury 2010 2011 earthquake sequence moment tensor solutions exist for 283 of the events with m ge 3 6 while 713 other events of m ge 3 6 have only hypocentre and magnitude information available we look at various methods for deciding between the two possible mechanisms for the 283 events with moment tensor solutions including conformation to observed surface faulting and maximum delta cff transfer from the darfield main shock for the remaining events imputation methods for the mechanism including nearest neighbour kernel smoothing and optimal plane methods are considered fault length width and depth are arrived at via a suite of scaling relations a large 50 70 proportion of the faults considered were calculated to have initial loading in excess of the final stress drop the majority of faults that accumulated positive delta cff during the sequence were encouraged by the main shock failure but on the other hand of the faults that failed during the sequence more than 50 of faults appeared to have accumulated a negative delta cff from all preceding failures during the sequence these results were qualitatively insensitive to any of the factors considered we conclude that there is much unknown about how coulomb stress triggering works in practice

onto what planes should coulomb stress perturbations be resolved 1 coulomb stress maps are produced by computing the tensorial stress perturbation due to an earthquake rupture and resolving this tensor onto planes of a particular orientation it is often assumed that aftershock fault planes are optimally oriented in other words the regional stress and coseismic stress change are used to compute the orientation of planes most likely to fail and the coseismic stress is resolved onto these orientations this practice assumes that faults capable of sustaining aftershocks exist at all orientations an assumption contradicted by the observation that aftershock focal mechanisms have strong preferred orientations consistent with mapped structural trends here we systematically investigate the best planes onto which stress should be resolved for the landers hector mine loma prieta and northridge earthquakes by quantitatively comparing observed aftershock distributions with stress maps based on optimally oriented planes two and three dimensional main shock orientation and regional structural trend we find that the best model differs between different tectonic regions but that in all cases models that incorporate the regional stress field tend to produce stress maps that best fit the observed aftershock distributions although not all such models do so equally well our results suggest that when the regional stress field is poorly defined or in structurally complex areas the best model may be to fix the strike of the planes upon which the stress is to be resolved to that of the main shock but allow the dip and rake to vary

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

full waveform tomography for lithospheric imaging results from a blind test in a realistic crustal model summary a comprehensive validation of 2 d frequency domain acoustic wave equation tomography was undertaken in a blind test using third party realistic elastic wave equation data the synthetic 2 d wide angle seismic data were provided prior to a recent workshop on the methods of controlled source seismology the true model was not revealed to the authors until after the presentation of our waveform tomography results the original model was specified on a detailed grid with variable p wave velocity s wave velocity density and viscoelastic q factor structure designed to simulate a section of continental crust 250 km long and 40 km deep synthetic vertical and horizontal component data were available for 51 shot locations spaced every 5 km recorded at 2779 receivers spaced every 90 m evenly spread along the surface of the model the data contained energy from 0 2 to 15 hz waveform tomography a combination of traveltime tomography and 2 d waveform inversion of the early arrivals of the seismic waveforms was used to recover crustal p velocity structure from the vertical component data using data from 51 sources 1390 receivers and frequencies between 0 8 and 7 0 hz the waveform tomography result contained apparent structure at wavelength scale resolution that was not evident on the traveltime tomography result the predicted acoustic waveforms in the final result matched the original elastic data to a high degree of accuracy during the workshop the exact model was revealed over much of the model the waveform tomography results provided a good correspondence with the true model from large to intermediate wavelength scales with a resolution limit on the order of 1 km a significant near surface low velocity zone invisible to traveltime methods was correctly recovered the results also provided a high resolution image of the complex structure of the entire crust and the depth and nature of the crust mantle transition some inaccuracies were observed near the edges of the images due to the limited ray coverage inherent to the footprint of the survey geometry several aspects of the waveform tomography strategy were critical to the success of the acoustic method with realistic synthetic viscoelastic data i the accuracy of the starting model from traveltime tomography ii implementation in the frequency domain iii the use of complex valued frequencies to effect time damping of the data residuals iv the selection of a suitable subset of data and data frequencies v progressive inversion of low to high frequency components of the data vi initial pre inversion matching of the amplitudes between observed and modelled data and vii sufficient preconditioning of both the data and the update images combined these strategies were effectively equivalent to a multiscale approach that mitigated the non linearity of the seismic inverse problem during the inversion we carried out repeated forward modelling to ensure our modelled waveforms matched the observed data as closely as possible in both frequency and time domains the synthetic data set used in this paper provides a benchmark for future testing of modelling inversion and imaging algorithms for wide angle lithospheric imaging

teleseismic inversion for the second degree moments of earthquake space time distributions summary determining detailed descriptions of the space time distribution of an earthquake s rupture using only teleseismic data is often a difficult and non unique process however a description of an earthquake that goes beyond a point source is often needed for many seismotectonic problems we have developed a method that inverts measurements of the shifts in traveltime and amplitude of various seismic phases at global stations for the second degree polynomial moments of an event s space time distribution our values for the second moments of the 1995 mw 8 0 jalisco mexico thrust event correspond to a characteristic rupture length of 121t10 km along strike a characteristic rupture width of 76t11 km downdip a characteristic duration of 29t2 s and a direction of rupture propagation along the strike of the subduction zone to the nw for the 1995 mw 7 2 gulf of aqaba earthquake our estimates of the second moments correspond to a characteristic rupture length of 53t2 km a characteristic duration of 12t1 s and rupture propagation to the ne along the strike of the dead sea transform our estimates of the first and second moments agree well with values from local seismic and geodetic networks for both the jalisco and aqaba events we are able to resolve the fault plane ambiguity associated with the events moment tensors using our estimates of the second spatial moment

extraction of the normal component of the particle velocity from marine pressure data the authors present a general wave theoretical method for extracting the normal component of the particle velocity from marine pressure data a possible use of the normal component of the particle velocity and the pressure is the separation of upgoing and downgoing waves at the receivers for one special acquisition geometry the source wavelet can also be estimated the method in principle is exact no information about the properties of the elastic earth is required when the pressure data are recorded on a single surface it is necessary to known the source signatures if the source array location is above the receiver surface if the sources are located below the signatures need not be known the locations of the individual receivers must be specified and the reflecting properties of the sea surface must be known when the receiver surface is plane and horizontal the extraction process can be performed in the frequency horizontal wavenumber domain the normal component of the particle velocity can furthermore be extracted from pressure data recorded at two surfaces at different depths in this case the reflectivity of the sea surface does not come into play it is only the medium properties between the two receiver surfacesmore that enter the problem the actual depths of the receivers need not be known only their relative distances if the sources are located above the uppermost receiver surface the source signatures can also be estimated a simple synthetic data example demonstrates the extraction of the normal component of the pressure from the pressure field recorded along a dipping receiver line below a free surface less

diffraction tomography and multisource holography applied to seismic imaging seismic tomography is emerging as an imaging method for determining subsurface structure when the view angle coverage is limited and the scale of the medium inhomogeneities is comparable with the wavelength as is often true in geophysical applications the performance of ordinary ray tomography becomes poor other tomographic methods are needed to improve the imaging process here we study diffraction tomography and multisource holography and evaluate their performances for surface reflection profiling srp vertical seismic profiling vsp and cross hole measurements theoretical formulations are derived for two dimensional geometry in terms of line sources along a source line and line receivers along a receiver line the theory for diffraction tomography is based on the born or rytov approximation the performances of diffraction tomography and multisource holography are evaluated by examining the information coverage in the spatial frequency domain and by numerical examples multisource holography

marine pssp reflections with a bottom velocity transition zone marine shear wave reflection methods using the conventional data acquisition system i e source and receiver in water rely on two mode conversions at the water bottom to produce shear reflections such as pssp some theoretical considerations and the results of a marine check shot survey conducted in the gulf of mexico demonstrate that the difficulty in observing pssp events is attributable to weak p s and s p conversion at the bottom in regions with very low shear velocity a few hundred ft s or less sediments at the bottom for a simple water bottom with a low shear wave velocity water over a uniform half space the ps conversion factor is proportional to vs and the sp conversion factor is proportional to vs2 where vs is the bottom shear velocity for vs 1500ft s their product gives pssp reflections that can be comparable in amplitude to typical pppp events for vs 500ft s the pssp events should be about 30 db weaker and probably not visible for typical gulf of mexico sediments with a shear velo

balancing the plate motion budget in the south island new zealand using gps geological and seismological data summary the landmass of new zealand exists as a consequence of transpressional collision between the australian and pacific plates providing an excellent opportunity to quantify the kinematics of deformation at this type of tectonic boundary we interpret gps geological and seismological data describing the active deformation in the south island new zealand by using an elastic rotating block approach that automatically balances the pacific australia relative plate motion budget the data in new zealand are fit to within uncertainty when inverted simultaneously for angular velocities of rotating tectonic blocks and the degree of coupling on faults bounding the blocks we find that most of the plate motion budget has been accounted for in previous geological studies although we suggest that the porter s pass amberley fault zone in north canterbury and a zone of faults in the foothills of the southern alps may have slip rates about twice that of the geological estimates up to 5 mm yr 1 of active deformation on faults distributed within the southern alps 100 km to the east of the alpine fault is possible the role of tectonic block rotations in partitioning plate boundary deformation is less pronounced in the south island compared to the north island vertical axis rotation rates of tectonic blocks in the south island are similar to that of the pacific plate suggesting that edge forces dominate the block kinematics there the southward migrating chatham rise exerts a major influence on the evolution of the new zealand plate boundary we discuss a model for the development of the marlborough fault system and hikurangi subduction zone in the context of this migration

full 3 d tomography for crustal structure in southern california based on the scattering integral and the adjoint wavefield methods we have successfully applied full 3 d tomography f3dt based on a combination of the scattering integral method si f3dt and the adjoint wavefield method aw f3dt to iteratively improve a 3 d starting model the southern california earthquake center scec community velocity model version 4 0 cvm s4 in f3dt the sensitivity frechet kernels are computed using numerical solutions of the 3 d elastodynamic equation and the nonlinearity of the structural inversion problem is accounted for through an iterative tomographic navigation process more than half a million misfit measurements made on about 38 000 earthquake seismograms and 12 000 ambient noise correlagrams have been assimilated into our inversion after 26 f3dt iterations synthetic seismograms computed using our latest model cvm s4 26 show substantially better fit to observed seismograms at frequencies below 0 2 hz than those computed using our 3 d starting model cvm s4 and the other scec cvm cvm h11 9 which was improved through 16 iterations of aw f3dt cvm s4 26 has revealed strong crustal heterogeneities throughout southern california some of which are completely missing in cvm s4 and cvm h11 9 but exist in models obtained from previous crustal scale 2 d active source refraction tomography models at shallow depths our model shows strong correlation with sedimentary basins and reveals velocity contrasts across major mapped strike slip and dip slip faults at middle to lower crustal depths structural features in our model may provide new insights into regional tectonics when combined with physics based seismic hazard analysis tools we expect our model to provide more accurate estimates of seismic hazards in southern california

insights into the kinematics of a volcanic caldera drop probabilistic finite source inversion of the 1996 bardarbunga iceland earthquake article i nfo the accurate modelling and prediction of volcanic eruptions depends critically on information concerning the interaction between the caldera and the underlying magma chamber knowledge concerning the kinematics of a caldera in the course of an eruption is therefore essential here we provide detailed seismological constraints on the kinematics of a volcanic caldera drop and the geometry of a caldera ring fault for this we performed a finite source inversion of the september 29 1996 bardarbunga iceland earthquake that was caused by caldera subsidence our methodology is based on spectral element simulations of seismic wave propagation through a realistic model of the icelandic crust and upper mantle a particularly robust feature is the initiation of the rupture in the north western part of the ring fault that is about 10 km in diameter from there it spread to the other fault segments within about 3 s without invoking super shear propagation sensu stricto we can explain this unusually fast rupture propagation by the triggering of fault segments through p waves that propagated across the caldera our results favour outward dipping fault segments in the western half of the ring fault while the eastern half is preferentially inward dipping this variability may reflect structural heterogeneities or an irregular magma chamber geometry the individual segments of the caldera ring fault radiated approximately equal amounts of energy this indicates that the caldera dropped coherently as one single block the work presented here is intended to aid in the design of realistic models of magma chamber and caldera dynamics