inverse kinematic and forward dynamic models of the 2002 denali fault earthquake alaska we perform inverse kinematic and forward dynamic models of the m 7 9 2002 denali fault alaska earthquake to shed light on the rupture process and dynamics of this event which took place on a geometrically complex fault system in central alaska we use a combination of local seismic and global positioning system gps data for our kinematic inversion and find that the slip distribution of this event is characterized by three major asperities on the denali fault the rupture nucleated on the susitna glacier thrust fault and after a pause propagated onto the strike slip denali fault approximately 216 km to the east the rupture abandoned the denali fault in favor of the more southwesterly directed totschunda fault three dimensional dynamic models of this event indicate that the abandonment of the denali fault for the totschunda fault can be explained by the totschunda fault s more favorable orientation with respect to the local stress field however a uniform tectonic stress field cannot explain the complex slip pattern in this event we also find that our dynamic models predict discontinuous rupture from the denali to totschunda fault segments such discontinuous rupture helps to qualitatively improve our kinematic inverse models two principal implications of our study are 1 a combination of inverse and forward modeling can bring insight into earthquake processes that are not possible with either technique alone and 2 the stress field on geometrically complex fault systems is most likely not due to a uniform tectonic stress field that is resolved onto fault segments of different orientations rather other forms of stress heterogeneity must be invoked to explain the observed slip patterns

the effect of bandwidth limitations on the inference of earthquake slip weakening distance from seismograms numerous researchers have obtained estimates of slip weakening distance dc and fracture energy for recent earthquakes dc is often observed to be a significant fraction of the total slip and tends to correlate with total slip although these observations may well be true of real earthquakes we show that low pass filtering of strong motion seismograms can also produce some of these effects in inverted rupture models we test the accuracy of dc estimates by calculating them in low pass filtered versions of models a and b of guatteri and spudich 2000 models a and b are two different rupture models for a hypothetical m 6 5 earthquake and they have nearly identical rupture time slip and stress drop distributions and nearly identical predicted seismograms but dc for model b is about twice that for model a by low pass filtering slip models a and b at 1 0 hz we simulate the blurring effects of band limited waveform inversions on these slip models at each point on a fault graphic 1 is defined to be the slip at the time of the peak slip speed at that point low pass filtering the slip models causes an upward bias in dc inferred from stress slip curves and it causes an artificial correlation between graphic 2 and the total slip low pass filtering might also bias fracture energy high and radiated energy low these biases should be considered when interpreting dc derived from band limited slip models of real earthquakes 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

a re examination of evidence for the north atlantic 1500 year cycle at site 609 ice rafting evidence for a 1500 year cycle sparked considerable debate on millennial scale climate change and the role of solar variability here we reinterpret the last 70 000 years of the subpolar north atlantic record focusing on classic dsdp site 609 in the context of newly available raw data the latest radiocarbon calibration marine09 and ice core chronology gicc05 and a wider range of statistical methodologies a w1500 year oscillation is primarily limited to the short glacial stage 4 the age of which is derived solely from an ice flow model ss09sea subject to uncertainty and offset most from the original chronology results from the most well dated younger interval suggest that the original 1500 500 year cycle may actually be an admixture of the w1000 and w2000 cycles that are observed within the holocene at multiple locations in holocene sections these variations are coherent with 14 c and 10 be estimates of solar variability our new results suggest that the 1500 year cycle may be a transient phenomenon whose origin could be due for example to ice sheet boundary conditions for the interval in which it is observed we therefore question whether it is necessary to invoke such exotic explanations as heterodyne frequencies or combination tones to explain a phenomenon of such fleeting occurrence that is potentially an artifact of arithmetic averaging

impact of backstop thickness lateral variations on the tectonic architecture of orogens insights from sandbox analogue modeling and application to the pyrenees 1 we performed sandbox analogue models to investigate the influence of along strike tapering of the backstop on the three dimensional architecture of natural doubly vergent thrust fold belts applying the results to a natural example as the pyrenees available geological and geophysical data indicate that the european crust which provided the backstop in the pyrenean orogen has a westward tapering on both the upper westward thickening of the mesozoic cover rocks and the lower westward rising of the moho envelope surfaces accordingly we performed laboratory models characterized by backstops with an along strike tapering of either the upper or the lower surface our results indicate a significant impact of backstop lateral tapering in thrust wedge architecture in terms of the outward propagation of the deformation fronts the width and elevation of the axial zone and the timing of thrust polarity reversal along strike when compared to the pyrenees our results support the inferred westward tapering of the european basement and its commonly accepted backstop role in the pyrenean orogen moreover comparison between the map pattern of the pyrenees and of laboratory experiments suggests that the along strike tapering of the bottom envelope surface of the backstop played a most important role on the three dimensional thrust wedge architecture than the tapering of the upper envelope surface

the dependence of traction evolution on the earthquake source time function adopted in kinematic rupture models 1 we compute the temporal evolution of traction by solving the elasto dynamic equation and by using the slip velocity history as a boundary condition on the fault plane we use different source time functions to derive a suite of kinematic source models to image the spatial distribution of dynamic and breakdown stress drop strength excess and critical slip weakening distance d c our results show that the source time functions adopted in kinematic source models affect the inferred dynamic parameters the critical slip weakening distance characterizing the constitutive relation ranges between 30 and 80 of the total slip the ratio between d c and total slip depends on the adopted source time functions and in these applications is nearly constant over the fault we propose that source time functions compatible with earthquake dynamics should be used to inter the traction time history

three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

laboratory earthquakes along inhomogeneous faults directionality and supershear we report on the experimental observation of spontaneously nucleated ruptures occurring on frictionally held bimaterial interfaces with small amounts of wave speed mismatch rupture is always found to be asymmetric bilateral in one direction rupture always propagates at the generalized rayleigh wave speed whereas in the opposite direction it is subshear or it transitions to supershear the lack of a preferred rupture direction and the conditions leading to supershear are discussed in relation to existing theory and to the earthquake sequence in parkfield california and in north anatolia

dynamic source inversion of the m6 5 intermediate depth zumpango earthquake in central mexico a parallel genetic algorithm we introduce a method for imaging the earthquake source dynamics from the inversion of ground motion records based on a parallel genetic algorithm the source model follows an elliptical patch approach and uses the staggered grid split node method to simulate the earthquake dynamics a statistical analysis is used to estimate errors in both inverted and derived source parameters synthetic inversion tests reveal that the average rupture speed vr the rupture area and the stress drop may be determined with formal errors of 30 12 and 10 respectively in contrast derived parameters such as the radiated energy er the radiation efficiency r and the fracture energy g have larger errors around 70 40 and 25 respectively we applied the method to the mw 6 5 intermediate depth 62 km normal faulting earthquake of 11 december 2011 in guerrero mexico inferred values of 29 2 6 2 mpa and r 0 26 0 1 are significantly higher and lower respectively than those of typical subduction thrust events fracture energy is large so that more than 73 of the available potential energy for the dynamic process of faulting was deposited in the focal region i e g 14 4 3 5 1014j producing a slow rupture process vr vs 0 47 0 09 despite the relatively high energy radiation er 0 54 0 31 1015 j and energy moment ratio er m0 5 7 10 5 it is interesting to point out that such a slow and inefficient rupture along with the large stress drop in a small focal region are features also observed in both the 1994 deep bolivian earthquake and the seismicity of the intermediate depth bucaramanga nest

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

dynamic faulting studied by a finite difference method we have developed a finite difference method that is especially adapted to the study of dynamic shear cracks we studied a number of simple earthquake source models in two and three dimensions with special emphasis on the modeling of the stress field we compared our numerical results for semi infinite and self similar shear cracks with the few exact solutions that are available in the literature we then studied spontaneous rupture propagation with the help of a maximum stress criterion from dimensional arguments and a few simple examples we showed that the maximum stress criterion depended on the physical dimensions of the fault for a given maximum stress intensity the finer the numerical mesh the higher the maximum stress that had to be adopted a study of in plane cracks showed that at high rupture velocities the numerical results did not resolve the stress concentration due to the rupture front from the stress peak associated with the shear wave propagating in front of the crack we suggest that this is the reason why transonic rupture velocities are found in the numerical solutions of in plane faulting when the rupture resistance is rather low finally we studied the spontaneous propagation of an initially circular rupture two distinct modes of nucleation of the rupture were studied in the first a plane circular shear crack was formed instantaneously in a uniformly prestressed medium after a while once stress concentrations had developed around the crack edge the rupture started to grow in the second type of nucleation a preexisting circular crack became unstable at time t 0 and started to grow the latter model appeared to us as a more realistic simulation of earthquake triggering in this case the initial stress was nonuniform and was the static field of the preexisting fault

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

photo acoustic study of subshear and supershear ruptures in the laboratory abstract we report supershear ruptures observed in spontaneously nucleating laboratory microearthquakes and describe the signature of the associated mach wavefront radiation transducers detect the wavefield both close and at a distance from the fault the rupture velocities are inferred from either photoelastic high speed imaging or using the acoustic recordings both methods yield compatible estimates of sufficient accuracy to discriminate between sub shear and supershear ruptures the acoustic records allow to characterize the mach wavefront radiated from the supershear rupture front in particular its amplitude and decay velocity functions recovered by integrating high frequency accelerometer signals in the case of supershear ruptures consist in a double pulse function a first pulse traveling at supershear velocity followed by a second pulse traveling at the rayleigh wave velocity conversely the sub shear event is characterized by a single pulse finally we perform numerical simulations of our experiment using a prescribed supershear rupture velocity the synthetic waveforms obtained from these simulations including the mach wave amplitude and phase yield a satisfactory fit to the experimental results

constitutive relations between dynamic physical parameters near a tip of the propagating slip zone during stick slip shear failure abstract constitutive relations between physical parameters in the cohesive zone during stick slip shear failure are experimentally investigated stick slip was generated along a 40 cm long precut fault in tsukuba granite samples using a servocontrolled biaxial loading apparatus dynamic behavior during local breakdown processes near a tip of the slipping zone is revealed the slip velocity and acceleration are given as a function of the slip displacement and the cohesive or breakdown shear stress as a function of the slip velocity a cycle of the breakdown and restrengthening process of stick slip is composed of five phases characterized in terms of the cohesive strength and the slip velocity the cohesive strength can degrade regardless of the slip velocity during slip instabilities the maximum slip acceleration u max and the maximum slip velocity u max are obtained experimentally as u max 2 u c u max 2 and u max b g v where u c is the critical displacement b the breakdown stress drop g the rigidity and v the rupture velocity these relations are consistent with ida s theoretical estimation based on the cohesive zone model the above formula gives good estimates for the maximum slip acceleration of actual earthquakes the cutoff frequency max of the power spectral density of the slip acceleration increases with increasing normal stress in particular max is found to be directly proportional to the normal stress n within the normal stress range less than 17 mpa as max khz 4 0 n mpa n max increase with an increase in u max or u max all these results lead to the conclusion that u max u max and max increase with increasing normal stress this is consistent with a previous observation that b increases with increasing normal stress the above empirical linear relation between max and n can be explained by a linear dependence of b on n the size scale dependence of physical parameters is discussed and such size scale dependent parameters as u max and apparent fracture energy are scaled to the breakdown zone size regarded as a characteristic length to extend the results obtained in the laboratory to an earthquake failure in the earth

estimation of dynamic rupture parameters from the radiated seismic energy and apparent stress we propose a new procedure for estimating the critical slip weakening distance dc by evaluating the spatio temporal distribution of the apparent stress calculated from the spatio temporal distribution of the slip velocity function on the fault plane obtained from a kinematic inversion of the earthquake source the idea is based on the fact that the apparent stress can be related to the difference between the earthquake average stress and the frictional dynamical stress on the fault plane during the rupture process from the cumulative slip apparent stress relationship we estimate the critical slip dc of the 1992 landers earthquake we find that the critical slip weakening plays an important role in controlling the rupture velocity in the case of the landers earthquake the very low rupture velocity in the central segment could be explained by the large dc value obtained for the main asperity on that segment

dynamic rupture modeling of the transition from thrust to strike slip motion in the 2002 denali fault earthquake alaska we use three dimensional dynamic spontaneous rupture models to investigate the nearly simultaneous ruptures of the susitna glacier thrust fault and the denali strike slip fault with the 1957 m w 8 3 gobi altay mongolia earthquake as the only other well documented case of significant nearly simultaneous rupture of both thrust and strike slip faults this feature of the 2002 denali fault earthquake provides a unique opportunity to investigate the mechanisms responsible for development of these large complex events we find that the geometry of the faults and the orientation of the regional stress field caused slip on the susitna glacier fault to load the denali fault several different stress orientations with oblique right lateral motion on the susitna glacier fault replicate the triggering of rupture on the denali fault about 10 sec after the rupture nucleates on the susitna glacier fault however generating slip directions compatible with measured surface offsets and kinematic source inversions requires perturbing the stress orientation from that determined with focal mechanisms of regional events adjusting the vertical component of the principal stress tensor for the regional stress field so that it is more consistent with a mixture of strike slip and reverse faulting significantly improves the fit of the slip rake angles to the data rotating the maximum horizontal compressive stress direction westward appears to improve the fit even further

how fast is rupture during an earthquake new insights from the 1999 turkey earthquakes we report that during the two devastating 1999 earthquakes in turkey rupture propagated over a large part of the nearly 200km long fault zone at supershear speed approaching 5km s we present observations and modeling which confirm the original inference of supershear rupture during the izmit earthquake and we show that supershear rupture also occurred during the duzce earthquake we show that the rupture velocity measured about 2 times the shear wave velocity is the value predicted by theoretical studies in fracture dynamics we look for clues to explain these observations

slip weakening distance estimated at near fault stations we estimated the slip weakening distance from the seismograms recorded at near fault stations considering the effect of spatio temporal filtering for a continuous propagation of rupture this effect is usually observed at some distance away from the fault we used a green s function for 2 d anti plane rupture propagating with constant rupture velocity and instantaneous slip at the crack tip as a source time function we used a regularized yoffe function which is a kinematically good approximation of dynamic slip weakening behavior by convolving these functions near fault waveforms are computed as a proxy of slip weakening distance d c we used d c which is defined as a slip at the time of peak slip velocity then d c values can be computed as a function of the distance from the fault this procedure is applied to the observation of the 2000 western tottori japan earthquake m w 6 6 as well as the 2002 denali alaska earthquake m w 7 9 we estimated d at about 0 3 m at gsh station 100 m away from the fault for the tottori earthquake and that at about 2 5 m at ps10 station 3 km away from the fault for the denali earthquake we confirmed that both estimates are not affected by the spatio temporal smoothing

supershear mach waves expose the fault breakdown slip abstract mikumo et al 2003 showed that it is possible to estimate the breakdown slip dc as the slip at the time of the peak slip rate for rupture propagation with subshear speeds cruz atienza et al 2009 later attempted to extend this method to extract information about dc as the displacement at the time of the peak particle velocity from seismic strong motion records however a reasonably accurate estimate of dc was only possible in a narrow zone adjacent to the fault typically on the order of hundreds of meters due to the fast decay with distance from the fault of the seismic energy related to the stress breakdown process when the rupture propagates with supershear speeds on the other hand this energy is carried much farther away from the fault by mach waves in particular rayleigh mach waves when rupture reaches the earth s surface dunham and bhat 2008 here we present a new approach to estimate dc from strong motion records containing mach waves first we show that the method by mikumo et al is valid for supershear rupture propagation this method is then used to estimate dc via an asymptotic approximation of the slip and slip rate time histories from the mach waves using spontaneous rupture simulations we demonstrate that for a visco elastic half space model dc can be estimated within an error of 40 from mach waves that have propagated a distance of at least 3 km from the fault the method is applied to estimate dc for the 2002 mw7 9 denali alaska earthquake 1 5 m and for the 1999 mw7 6 izmit turkey earthquake 1 7 m

attenuation of radiated ground motion and stresses from three dimensional supershear ruptures 1 radiating shear and rayleigh waves from supershear ruptures form mach waves that transmit large amplitude ground motion and stresses to locations far from the fault we simulate bilateral ruptures on a finite width vertical strike slip fault of width w and half length l with l w breaking the surface of an elastic half space and focus on the wavefield out to distances comparable to l at distances much smaller than w two dimensional plane strain slip pulse models i e models in which the lateral extent of the slip zone is unbounded accurately predict the subsurface wavefield amplitudes in the shear mach wedge of those models are undiminished with distance from the fault when viewed from distances far greater than w rupture is accurately modeled as a moving point source that produces a shear mach cone and on the free surface rayleigh wave mach fronts geometrical spreading of the shear mach cone occurs radially and amplitudes there decrease with the inverse square root of distance the transition between these two asymptotic limits occurs at distances comparable to w similar considerations suggest that rayleigh mach waves suffer no attenuation in the ideally elastic medium studied here the rate at which fault strength weakens at the rupture front exerts a strong influence on the off fault fields only in the immediate vicinity of the fault for both sub rayleigh and supershear ruptures and at the mach fronts of supershear ruptures more rapid weakening generates larger amplitudes at the mach fronts

slip dependent friction law and nucleation processes in earthquake rupture abstract matsu ura m kataoka h and shibazaki b 1992 slip dependent friction law and nucleation processes in earthquake rupture in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 135 148 we developed a physical model that interprets slip strengthening and slip weakening processes in brittle shear fracture by considering the microscopic interaction between statistically self similar fault surfaces our model successfully describes general features of the constitutive behaviour observed in laboratory experiments of stick slip with the progress of fault slip frictional stress first increases rapidly up to a peak value and then decreases gradually to a constant level the first slip strengthening process can be explained by the increase of frictional resistance in transition from the in phase contact to the random phase contact of fault surfaces the latter slip weakening process can be explained by the decrease of frictional resistance due to the abrasion of surface asperities the trade off between these two processes determines the peak stress and the critical displacement over which the slip weakening proceeds we examined the nucleation process proceeding in a seismogenic zone with the increase of external shear stress through numerical simulations in our model the seismogenic zone is represented by a broad weak zone with a locally strong part asperity on a fault plane the basic equations governing the nucleation process are the equation of equilibrium and the constitutive relation between frictional stress and fault slip we obtained the following results the nucleation process first proceeds quasi statically at the weak portions with the increase of external shear stress then if the constitutive relation at the asperity has a high and narrow peak of stress brittle dynamic rupture occurs in a limited area around the asperity when the constitutive relation has a low and broad peak the dynamic rupture of the asperity does not occur the process is completely aseismic when the peak of stress is high and broad the dynamic rupture of the asperity leads to the catastrophic rupture which extends over the whole region from these results it is concluded that diversity in the nucleation process can be ascribed to difference in the variation of constitutive behaviour along the fault

terashake2 spontaneous rupture simulations of mw 7 7 earthquakes on the southern san andreas fault abstract previous numerical simulations terashake1 of large m w 7 7 southern san andreas fault earthquakes predicted localized areas of strong amplification in the los angeles area associated with directivity and wave guide effects from northwestward propagating rupture scenarios the terashake1 source was derived from inversions of the 2002 m w 7 9 denali alaska earthquake that source was relatively smooth in its slip distribution and rupture characteristics owing both to resolution limits of the inversions and simplifications imposed by the kinematic parameterization new simulations terashake2 with a more complex source derived from spontaneous rupture modeling with small scale stress drop heterogeneity predict a similar spatial pattern of peak ground velocity pgv but with the pgv extremes decreased by factors of 2 3 relative to terashake1 the terashake2 source excites a less coherent wave field with reduced along strike directivity accompanied by streaks of elevated ground motion extending away from the fault trace the source complexity entails abrupt changes in the direction and speed of rupture correlated to changes in slip velocity amplitude and waveform features that might prove challenging to capture in a purely kinematic parameterization despite the reduced pgv extremes northwest rupturing terashake2 simulations still predict entrainment by basin structure of a strong directivity pulse with pgvs in los angeles and san gabriel basins that are much higher than predicted by empirical methods significant areas of those basins have predicted pgv above the 2 probability of exceedance poe level relative to current attenuation relationships even when the latter includes a site term to account for local sediment depth and wave guide focusing produces localized areas with pgv at roughly 0 1 0 2 poe about a factor of 4 5 above the median in contrast at rock sites in the 0 100 km distance range the median terashake2 pgvs are in very close agreement with the median empirical prediction and extremes nowhere reach the 2 poe level the rock site agreement lends credibility to some of our source modeling assumptions including overall stress drop level and the manner in which we assigned dynamic parameters to represent the mechanical weakness of near surface material future efforts should focus on validating and refining these findings assessing their probabilities of occurrence relative to alternative rupture scenarios for the southern san andreas fault and incorporating them into seismic hazard estimation for southern california

coherence of mach fronts during heterogeneous supershear earthquake rupture propagation simulations and comparison with observations 1 we study how heterogeneous rupture propagation affects the coherence of shear and rayleigh mach wavefronts radiated by supershear earthquakes we address this question using numerical simulations of ruptures on a planar vertical strike slip fault embedded in a three dimensional homogeneous linear elastic half space ruptures propagate spontaneously in accordance with a linear slip weakening friction law through both homogeneous and heterogeneous initial shear stress fields in the 3 d homogeneous case rupture fronts are curved owing to interactions with the free surface and the finite fault width however this curvature does not greatly diminish the coherence of mach fronts relative to cases in which the rupture front is constrained to be straight as studied by dunham and bhat 2008a introducing heterogeneity in the initial shear stress distribution causes ruptures to propagate at speeds that locally fluctuate above and below the shear wave speed calculations of the fourier amplitude spectra fas of ground velocity time histories corroborate the kinematic results of bizzarri and spudich 2008a 1 the ground motion of a supershear rupture is richer in high frequency with respect to a subshear one 2 when a mach pulse is present its high frequency content overwhelms that arising from stress heterogeneity present numerical experiments indicate that a mach pulse causes approximately an 1 7 high frequency falloff in the fas of ground displacement moreover within the context of the employed representation of heterogeneities and over the range of parameter space that is accessible with current computational resources our simulations suggest that while heterogeneities reduce peak ground velocity and diminish the coherence of the mach fronts ground motion at stations experiencing mach pulses should be richer in high frequencies compared to stations without mach pulses in contrast to the foregoing theoretical results we find no average elevation of 5 damped absolute response spectral accelerations sa in the period band 0 05 0 4 s observed at stations that presumably experienced mach pulses during the 1979 imperial valley 1999 kocaeli and 2002 denali fault earthquakes compared to sa observed at non mach pulse stations in the same earthquakes a 20 amplification of short period sa is seen only at a few of the imperial valley stations closest to the fault this lack of elevated sa suggests that either mach pulses in real earthquakes are even more incoherent that in our simulations or that mach pulses are vulnerable to attenuation through nonlinear soil response in any case this result might imply that current engineering models of high frequency earthquake ground motions do not need to be modified by more than 20 close to the fault to account for mach pulses provided that the existing data are adequately representative of ground motions from supershear earthquakes

the 14 november 2001 kokoxili tibet earthquake high frequency seismic radiation originating from the transitions between sub rayleigh and supershear rupture velocity regimes seismic array based analysis of the major kokoxili earthquake tibet 14 november 2001 yields an unambiguous reconstruction of the seismic rupture history and relates it to the generated seismic radiation we demonstrate that after a classical sub rayleigh velocity stage the rupture speed has jumped to supershear values close to compressional wave velocity over a 175 km long fault segment before abruptly slowing down in the late part of the earthquake the transition locations between these three phases are correlated with the fault geometry and are associated with the most energetic radiation this observation proves that the rupture velocity changes as theoretically predicted are a primary source of high frequency seismic radiation this result requires reconsidering the origins of seismic damage generally attributed to slip variations

cretaceous tertiary tectonic inversion of the cotiella basin southern pyrenees spain the cotiella nappe includes one of the most important mesozoic basins of the southern pyrenees which was subsequently inverted during the tertiary compression the late cretaceous cotiella basin is here interpreted as the western sector of the cretaceous cotiella boixols basin 100 20 km wide located in the central part of the southern pyrenees the present day complex structure of the cotiella nappe is the result of the inversion process linked to the emplacement of basement thrust sheets of the axial zone in its western sector the cotiella nappe consists of several superimposed thrust sheets with complex geometry becoming simpler towards the east with a single thrust surface and smaller displacements the cotiella boixols basin underwent strong subsidence during the early cretaceous at its eastern sector and its depocentre migrated westward during the late cretaceous the reconstruction of the sedimentary basin to the pre compressional stage shows that during the mesozoic the cotiella boixols basin was located to the south of a basement high which later became the pyrenean axial zone from a balanced cross section it can be inferred that the cotiella north verging extensional system was connected with the north pyrenean rift by means of a 10 km deep horizontal detachment the compressional tertiary detachment within the upper crust was shallower than the extensional detachment and individualised four basement thrust sheets which form the axial zone antiform

estimation of the breakdown slip from strong motion seismograms insights from numerical experiments fukuyama and mikumo 2007 presented a method to extract informa tion about the friction controlling earthquake rupture directly from near field seismo grams recorded out to several kilometers from a fault this method computes a parameter d 00 approximating the breakdown slip dc from the rake parallel dis placement at the time of the peak particle velocity the validation of the method was based on simple 2d steady state green s functions an approach lacking sufficient physics of the rupture process to support their conclusions here we use 3d simula tions of subshear strike slip spontaneous rupture propagation to demonstrate that d 00 is almost always controlled by rupture and wave propagation effects rather than the fault friction process only if rupture reaches the earth s surface and within a short distance from the fault rc is it possible to extract information about dc from strong motion data due to the fast decay with distance from the fault of the seismic energy related to the stress breakdown process beyond rc d 00 is controlled by the dynamic stress drop from the earthquake rupture without information about dc rc is comparable to the length of the fault cohesive zone where the breakdown process takes place during rupture and approximately equal to 80 of the wavelength associated with the break down frequency defined as the reciprocal of the time span required by the stress to drop to the dynamic level our findings suggest that the dc estimate by fukuyama and mikumo 2007 for the 2000 mw 6 6 tottori earthquake is unrelated to the breakdown slip moreover the very narrow widths for rc obtained from our simulations are in agreement with previous studies challenging the resolution of bandlimited strong motion data to estimate dc from kinematic rupture models guatteri and spudich 2000 spudich and guatteri 2004

modeling dynamic rupture in a 3d earthquake fault model we propose a fourth order staggered grid finite difference method to study dynamic faulting in three dimensions the method uses an implementation of the boundary conditions on the fault that allows the use of general friction models including slip weakening and rate dependence because the staggered grid method defines stresses and particle velocities at different grid points we preserve symmetry by implementing a two grid row thick fault zone slip is computed between points located at the borders of the fault zone while the two components of shear traction on the fault are forced to be symmetric inside the fault zone we study the properties of the numerical method comparing our simulations with well known properties of seismic ruptures in 3d among the properties that are well modeled by our method are full elastic wave interactions frictional instability rupture initiation from a finite initial patch spontaneous rupture growth at subsonic and supersonic speeds as well as healing by either stopping phases or rate dependent friction we use this method for simulating spontaneous rupture propagation along an arbitrarily loaded planar fault starting from a localized asperity on circular and rectangular faults the shape of the rupture front is close to elliptical and is systematically elongated in the in plane direction of traction drop this elongation is due to the presence of a strong shear stress peak that moves ahead of the rupture in the in plane direction at high initial stresses the rupture front becomes unstable and jumps to super shear speeds in the direction of in plane shear another interesting effect is the development of relatively narrow rupture fronts due to the presence of rate weakening friction the solutions for the thick fault boundary conditions scale with the slip weakening distance do and are stable and reproducible for do greater than about 4 in terms of 2t t ax finally a comparison of scalar and vector boundary conditions for the friction shows that slip is dominant along the direction of the prestress with the largest deviations in slip rate direction occurring near the rupture front and the edges of the fault

effects of supershear rupture speed on the high frequency content of s waves investigated using spontaneous dynamic rupture models and isochrone theory 1 in this paper we achieve three goals 1 we demonstrate that crack tips governed by friction laws including slip weakening rate and state dependent laws and thermal pressurization of pore fluids propagating at supershear speed have slip velocity functions with reduced high frequency content compared to crack tips traveling at subshear speeds this is demonstrated using a fully dynamic spontaneous three dimensional earthquake model in which we calculate fault slip velocity at nine points locations distributed along a quarter circle on the fault where the rupture is traveling at supershear speed in the in plane direction and subshear speed in the antiplane direction this holds for a fault governed by the linear slip weakening constitutive equation by slip weakening with thermal pressurization of pore fluid and by rate and state dependent laws with thermal pressurization the same is also true even assuming a highly heterogeneous initial shear stress field on the fault 2 using isochrone theory we derive a general expression for the spectral characteristics and geometric spreading of two pulses arising from supershear rupture the well known mach wave and a second lesser known pulse caused by rupture acceleration 3 we demonstrate that the mach cone amplification of high frequencies overwhelms the de amplification of high frequency content in the slip velocity functions in supershear ruptures consequently when earthquake ruptures travel at supershear speed a net enhancement of high frequency radiation is expected and the alleged low peak accelerations observed for the 2002 denali and other large earthquakes are probably not caused by diminished high frequency content in the slip velocity function as has been speculated

dynamic modeling of the 1992 landers earthquake we have used observed band pass filtered accelerograms and a previously determined slip distribution to invert for the dynamic rupture propagation of the 1992 landers earthquake in our simulations dynamic rupture grows under the simultaneous control of initial stress and rupture resistance by friction which we modeled using a simple slip weakening law we used a simplified landers fault model where the fault segments were combined into a single vertical planar fault by trial and error we modified an initial stress field inferred from the kinematic slip distribution proposed by wald and heaton 1994 until dynamic rupture generated a rupture history and final slip distribution that approximately matched those determined by the kinematic inversion we found that rupture propagation was extremely sensitive to small changes in the distribution of prestress and that a delicate balance with energy release rate controls the average rupture speed for the inversion we generated synthetic 0 5 hz ground displacements using an efficient green s function propagator method axitra this method enables us to propagate the radiation generated by the dynamic rupture to distances greater than those feasible using the finite difference method the dynamic model built by trial and error inversion provides a very satisfactory fit between synthetics and strong motion data we validated this model using records from stations used in the slip inversion as well as some which were not included we also inverted for a complementary model that fits the data just as well but in which the initial stress was perfectly uniform while rupture resistance was heterogeneous this demonstrates that inversion of ground motion is nonunique

seismic imaging of the 1999 izmit turkey rupture inferred from the near fault recordings we use near fault accelerograms to infer the space time history of rupture on the fault during the izmit earthquake the records show that the ground displacement and velocity near the fault were surprisingly simple rupture propagated toward the west at a velocity of about 3 km s and toward the east at a remarkably high average velocity of 4 7 km s over a distance of about 45 km before decelerating to about 3 1 km s on the eastern segment slip on the fault is particularly large down to a depth of 20 km on the central portion of the fault where it reaches about 7 m slip is large also below 10 km on the eastern fault segment and this may have contributed to the loading of shear stress on the duzce fault on the western fault segment large slip seems confined to shallow depths

the aftershock signature of supershear earthquakes recent studies show that earthquake faults may rupture at speeds exceeding the shear wave velocity of rocks this supershear rupture produces in the ground a seismic shock wave similar to the sonic boom produced by a supersonic airplane this shock wave may increase the destruction caused by the earthquake we report that supershear earthquakes are characterized by a specific pattern of aftershocks the fault plane itself is remarkably quiet whereas aftershocks cluster off the fault on secondary structures that are activated by the supershear rupture the post earthquake quiescence of the fault shows that friction is relatively uniform over supershear segments whereas the activation of off fault structures is explained by the shock wave radiation which produces high stresses over a wide zone surrounding the fault

near source ground motion from steady state dynamic rupture pulses 1 ground motion from two dimensional steady state dynamic ruptures is examined for both subshear and supershear rupture velocities synthetic seismograms demonstrate that coherent high frequency information about the source process rapidly attenuates with distance from the fault for subshear ruptures such records provide almost no resolution of the spatial extent of the stress breakdown zone at supershear speeds s waves radiate away from the fault preserving the full source spectrum and carrying an exact history of the slip velocity on both the fault parallel and fault normal components of motion whose amplitudes are given by a function of rupture speed that vanishes at times the s wave speed the energy liberated from the strain field by the passage of a supershear rupture is partitioned into fracture energy dissipated within the fault zone and far field s wave radiation the partition depends on both the rupture velocity and the size of the breakdown zone

stress breakdown time and slip weakening distance inferred from slip velocity functions on earthquake faults we estimate the critical slip weakening distance on earthquake faults by using a new approach which is independent of the estimate of fracture energy or radiated seismic energy the approach is to find a physically based relation between the breakdown time of shear stress tb the time of peak slip velocity tpv and the slip weakening distance dc from the time histories of shear stress slip and slip velocity at each point on the fault which can be obtained from dynamic rupture calculations using a simple slip weakening friction law numerical calculations are carried out for a dynamic shear crack propagating either spontaneously or at a fixed rupture velocity on a vertical fault located in a 3d half space and a more realistic horizontally layered structure with finite difference schemes the results show that tpv is well correlated with tb for faults even with a heterogeneous stress drop dis tribution except at locations near strong barriers and the fault edges we also inves tigate this relation for different types of slip weakening behavior we have applied the method to two recent strike slip earthquakes in western japan the 2000 tottori and the 1995 kobe events we integrated the slip velocity functions on the vertical fault obtained from kinematic waveform inversion of strong motion and teleseismic records from the arrival time of rupture tr to the time of the peak slip velocity tpv and we then corrected the slip obtained at tpv for the errors expected from the dynamic calculations it was found that the slip weakening dis tance d c estimated in the frequency window between 0 05 and 0 5 hz ranges between 40 and 90 cm on the two earthquake faults however if we consider the limited frequency resolution of the observed waveforms probable time errors in the slip velocity functions obtained from kinematic inversion and the uncertainty of the slip weakening behavior the above estimates may be those located between the minimum resolvable limit and the upper bound of their real values the estimated dc values do not necessarily seem to indicate larger values in the shallower part and smaller values in the deeper part of the fault but rather a spatially heterogeneous distribution that appears to be dependent on the local maximum slip this possible dependence might be interpreted by the frictional properties of the fault such as the degree of roughness or the thickness of gouge layers in addition to stress heterogeneities

the 1999 izmit earthquake sequence in turkey seismological and tectonic aspects the izmit duzce earthquake sequence is the largest sequence recorded by modern digital networks in the history of turkish earthquakes the m w 7 4 izmit mainshock occurred at 29 967 e and 40 729 n and 13 km depth at 00 hr 01 min 38 7 sec utc on 17 august 1999 and was preceded by at least eight immediate foreshocks of magnitude m l 3 0 aftershock locations show that a large region has become seismically very energetic following the mainshock and that most of the aftershock zone developed quickly in the first 3 days the distribution of the aftershocks illuminates numerous seismotectonic structures associated with the various branches of the north anatolian fault naf in the aftershock zone the seismicity pattern defines a rupture plane that extends about 80 km east and 75 km west of the mainshock epicenter confirming bilateral rupture during the mainshock the western aftershock activity is almost entirely located offshore extending along the axis of the izmit bay we show that the westernmost extent of the mainshock rupture reached the offshore region just 10 km south of the princes islands the dominance of strike slip motion is one of the main characteristics of the izmit sequence a number of significant aftershock clusters occur off the inferred mainshock rupture plane the spatial and temporal occurrence of these clusters show that they are triggered by the complex redistribution of stresses and dynamic strains imposed by the dislocation of the mainshock the focal mechanisms of the events located in the western end of the rupture zone show both strike slip and normal faulting mechanisms we infer that the yalova cluster was triggered by the mainshock the dominance of the normal faulting mechanisms supports the notion that dynamic extensional strains played a major role in triggering this cluster four events located off the princes islands indicate similar source mechanisms characterized by right lateral strike slip motion parallel to the strike of the northern boundary fault nbf and local trend of aftershock distribution this observation leads to a first order seismotectonic evidence that the nature of the nbf which is known to be a transtensional feature at the surface is dominated by strike slip motion at depth the coexistence of strike slip and extensional seismotectonic features in the sea of marmara highlights the importance of strain partitioning amongst shallow transtentional structures accommodating north south extension and deeper structures associated with the naf accommodating east west right lateral shear manuscript received 22 september 2000

episodic accretion and strain partitioning in a model sand wedge we model led thrust wedge accretion and deformation partitioning in a passively layered sand detached and shortened above a smooth rigid decollement the thrust wedge accretes in piggyback style during forward advance of a rear wall the passively layered sand accommodates the shortening penetratively by kinking ramp folding and by imbrication in single layers the style of compression changes with time and or stratigraphic position within the sand prism initial penetrative layer shortening above a slipped zone of decollement is succeeded by formation of monoclinal or conjugate shear bands at temporary terminations of decollement the shear bands subsequently narrow down and lock as thrust ramps the model sand wedge accrets episodically rather than steadily episodicity is controlled by the stick slip mode of decollement propagation and by volume loss and compaction of the wedge material in response to convergence this results in formation of a wedge with a convex upwards cross sectional topography

near source ground motions from simulations of sustained intersonic and supersonic fault ruptures we examine the long period near source ground motions from simulations of m 7 4 events on a strike slip fault using kinematic ruptures with rupture speeds that range from subshear speeds through intersonic speeds to supersonic speeds the strong along strike shear wave directivity present in scenarios with subshear rupture speeds disappears in the scenarios with ruptures propagating faster than the shear wave speed furthermore the maximum horizontal displacements and velocities rotate from generally fault perpendicular orientations at subshear rupture speeds to generally fault parallel orientations at supersonic rupture speeds for rupture speeds just above the shear wave speed the orientations are spatially heterogeneous as a result of the random nature of our assumed slip model at locations within a few kilometers of the rupture the time histories of the polarization of the horizontal motion provide a better diagnostic with which to gauge the rupture speed than the orientation of the peak motion subshear ruptures are associated with significant fault perpendicular motion before fault parallel motion close to the fault supershear ruptures are associated with fault perpendicular motion after significant fault parallel motion consistent with previous studies we do not find evidence for prolonged supershear rupture in the long period 2 sec ground motions from the 1979 imperial valley earthquake however we are unable to resolve the issue of whether a limited portion of the rupture approximately 10 km in length propagated faster than the shear wave speed additionally a recording from the 2002 denali fault earthquake does appear to be qualitatively consistent with locally supershear rupture stronger evidence for supershear rupture in earthquakes may require very dense station coverage in order to capture these potentially distinguishing traits

paleomagnetic structural and stratigraphic constraints on transverse fault kinematics during basin inversion the pamplona fault pyrenees north spain 1 the pamplona fault in the pyrenees is a major transverse structure that has been classically interpreted as a strike slip fault however lack of consensus concerning the sense of movement casts doubt on its actual kinematics and as a consequence its role in the cenozoic evolution of the pyrenees remains controversial in order to assess its kinematics we have conducted a paleomagnetic structural and stratigraphic study focused on the mesozoic and tertiary sedimentary rocks that outcrop around the southern segment of the fault restoration of balanced cross sections allows us to examine the present day spatial relationship of the sedimentary sequences on both sides of the fault and to reconstruct the geometry of the extensional basins formed during mesozoic rifting episodes in the bay of biscay and pyrenean domains paleomagnetic results indicate that no significant tectonic rotations occurred around the fault during tertiary inversion of the pyrenees the lack of tectonic rotations and revaluation of previous hypotheses argues against a strike slip movement of the fault we propose a new model in which the pamplona fault is treated as a large scale hanging wall drop fault whose kinematics was determined by variations in the geometry and thickness of mesozoic sequences on both sides of the fault these variations influenced the geometry of the thrust sheet developed during tertiary compression we are unaware of any other transverse fault that has been interpreted in this fashion thus the pamplona fault serves as a case study for the evolution of transverse faults involved in basin inversion processes

space and time evolution of rupture and faulting during the 1999 izmit turkey earthquake we use the records of the ground motion obtained at near fault accelerometers to study the space and time evolution of rupture and faulting during the izmit earthquake we find that the rupture propagated at the sub rayleigh speed of about 3 km sec on the western and eastern segments of the fault but that the central segment izmit sapanca lake sakarya nearly 50 km long broke at the supershear speed of about 4 8 km sec this value within the range of uncertainties is the one theoretically predicted sqrt 2 v mathrm s in fracture dynamics for stable shear crack growth at intersonic speed we infer an average fault slip of about 2 9 m over a total rupture length of about 150 km with the largest values of up to 6 m occurring in the golcuk area to the west and in the sakarya region to the east the strong motion data also indicate that the slip diminished gradually to the west beyond the hersek peninsula over about 30 km whereas it stopped abruptly at depth at the termination of the eastern karadere segment the slip duration is between 2 and 4 sec except in the hypocentral area which slipped in about 1 sec the seismic moment inferred is about 2 5 10 20 n m

gravity anomaly map of the pyrenean region and a comparison of the deep geological structure of the western and eastern pyrenees abstract a gravity anomaly map based on over 13 000 observations accurately delineates the major features of the pyrenean region an extensive gravity anomaly low in the south of the region appears to result from crustal thickening associated with the pyrenean mountain building episode several large positive gravity anomalies are apparent in the north pyrenean zone in the centre and west of the mountain chain but are absent in the east the interpretation of a series of gravity anomaly profiles along the pyrenees has been controlled by existing geophysical data the interpretations confirm the cause of the southern gravity anomaly low as thickened iberian crust and demonstrate as shown by previous seismic investigations that the transition to much thinner european crust is quite abrupt the sources of the positive anomalies in the north pyrenean zone are bodies in the upper crust with densities too high to be explained in terms of crustal materials these are interpreted as segments of upper mantle that originated in transtensional n s separation across the north pyrenean fault and were emplaced at shallow levels by thrusting during pyrenean orogenesis this is the first time that evidence has been presented for the presence of such mantle bodies in the pyrenees it is suggested that their absence in the east is caused by less extension between iberia and europe in this region during the transform motion between them prior to orogenesis allowing only limited ascent of deep material the greater extension in the west would have allowed the ascent of upper mantle into the space between iberia and europe which would have been further elevated during the thrusting associated with pyrenean orogenesis

slip weakening distance in dynamic rupture of in slab normal faulting earthquakes we apply the above method to three large in slab normal faulting earthquakes in the mexican subduction zone to do this we calculate the spatial distribution of slip velocity functions and final slip from kinematic waveform inversion of strong motion and teleseismic records and the stress history and final stress change from dynamic rupture calculations by integrating the slip velocity functions obtained from the inversion from the rupture arrival time to the time of peak slip velocity we obtain slip dat t pv and then correct it for dc at t b through dynamic calculations we also estimate the lowest resolvable limit and probable errors of dc from the slip velocity functions and its upper bound from a theoretical constraint between the dynamic stress drop and dc we found that the slip weakening distance dc estimated in the frequency band between 0 05 and 0 5 hz ranges between 40 and 120 cm on the in slab fault of the 1999 oaxaca earthquake mw 7 5 the largest dc is detected in the central fault and in part of the deeper sections and dc in the zone around the hypocentre ranges between 50 and 70 cm the estimated dc values appear to be less depth dependent but are rather more dependent on the local maximum slip this possible slip dependence might be interpreted by the degree of fault roughness in addition to stress heterogeneities the fracture energy g in the central section and in the hypocentral zone are roughly estimated to be of the order of 10 15 and 5 8 mj m 2 respectively both of the estimated dc and g values are somewhat larger than those on the vertical fault of two recent shallow strike slip earthquakes in western japan

extensional fault systems in sedimentary basins a review of analogue model studies abstract scaled analogue models have provided graphic new insights into the progressive development of extensional fault systems this paper reviews recent results of an on going analogue modelling programme and compares the structural styles in the models with examples of natural extensional fault systems four fundamental model styles scaled to simulate deformation in brittle sedimentary rocks in the upper 10 km of the crust are reviewed extension above a basal detachment which undergoes stretching over a limited are produces an asymmetric rift graben bounded by planar faults and in which the internal deformation is accommodated by rotational domino faults these experimental results are directly comparable to structures found in intracontinental rifts extension above a basal detechment which undergoes extension under the whole model and which has no constraints at the ends produces domino style fault arrays in the pre rift sequence and listric growth faults in the syn rift sequence these results compare with highly extended rift basins and terranes such as the basin and range province usa extension above a simple listric fault produces a characteristic hangingwall roll over and crestal collapse graben system at high values of extension superposed crestal collapse grabens occur and a fan of listric growth faults is developed these structures bear striking similarities to growth faults in progradational delta systems ramp flat listric extensional fault systems using sand mica models produce a characteristic family of structures with an upper roll over crestal collapse system a ramp syncline and reverse fault fold zone and a lower roll over crestal collapse system an example of a ramp flat fault system from the gulf coast usa is presented as a comparison with the analogue model results preliminary results of three dimensional extensional model experiments are presented to illustrate the complexities in such fault systems in all of the experimental models it is found that the geometry of the underlying detachment system exerts fundamental control on structures produced in the hangingwall the analogue models illustrated in this review provide valid geometric and kinematic templates for the progressive evolution of extensional fault systems in sedimentary basins

evidence for a supershear transient during the 2002 denali fault earthquake elastodynamic considerations suggest that the acceleration of ruptures to supershear velocities is accompanied by the release of rayleigh waves along the fault from the stress breakdown zone these waves generate a secondary slip pulse trailing the rupture front but manifest almost entirely in ground motion perpendicular to the fault in the near source region we construct a spontaneously propagating rupture model exhibiting these features and use it to explain ground motions recorded during the 2002 denali fault earthquake at pump station 10 located 3 km from the fault we show that the initial pulses on both the fault normal and fault parallel components are due to the supershear stress release on the fault whereas the later arriving fault normal pulses result from the trailing subshear slip pulse on the fault online material mpeg movies of rupture history and ground motion

dynamics of sediment subduction accretion at convergent margins short term modes long term deformation and tectonic implications a conceptual model is proposed for the short term operation of subduction accretion systems at convergent margins the operation is described in terms of the mass fluxes among the four system components namely the accretionary or prowedge wedge p an uplifted plug u a retrowedge r and the subduction zone the latter consists of a conduit c of slowly moving and deforming material and an underlying subduction channel where material moves and deforms more rapidly a broad range of convergent margin types can be accommodated within the conceptual model framework with differing short term modes that depend on which of the p u r c components that are active finite element geodynamical model experiments are used to investigate whether these modes are dynamically feasible these experiments determine excitation of modes under controls that include model entry and exit mass fluxes flexural loading by accreted material and slab pull forces boundary velocities corresponding to subduction and subduction zone advance retreat distribution thickness and density of accreted sediment and internal frictional properties of the coulomb sediments that all modes with the exception of p in which only a prowedge is created are seen in the models provides support for the concepts and allows conditions that favor particular modes to be recognized in addition the finite deformation predicted by the models is used to infer the long term tectonic styles associated with both single mode evolutions and those that exhibit mode switching a steady state mass balance can occur for modes 0 pure subduction p c i e where components p and c are active or other modes when the surface mass denudation plus the subduction flux balances accretion plus tectonic underplating the p c mode is favored by subduction zone retreat and or an increasing subduction load and creates an apparent landward dipping backstop p u c is predicted to be the most common mode and it creates an apparent seaward dipping backstop p u r c is an inefficient mode but is favored by easily detached retrocrust or sediment and or a decreasing subduction load

3d finite difference dynamic rupture modeling along nonplanar faults properunderstandingofseismicemissionsassociatedwiththe growth of complexly shaped microearthquake networks and larger scale nonplanar fault ruptures both in arbitrarily heterogeneousmedia requiresaccuratemodelingoftheunderlyingdynamic processes we present a new 3d dynamic rupture finitedifference model called the finite difference fault element fdfe method it simulates the dynamic rupture of nonplanar faults subjected to regional loads in complex media fdfe is based on a 3d methodology for applying dynamic rupture boundary conditions along the fault surface the fault is discretizedbyasetofparallelepipedfaultelementsinwhichspecific boundary conditions are applied these conditions are applied to the stress tensor once transformed into a local fault reference frame numerically determined weight functions multiplying particle velocities around each element allow accurate estimates offaultkinematicparametersi e slipandsliprateindependent of faulting mechanism assuming a coulomb like slip weakeningfrictionlaw aparametricstudysuggeststhatthefdfemethod converges toward a unique solution provided that the cohesive zone behind the rupture front is well resolved i e four or more elements inside this zone solutions are free of relevant numerical artifacts for grid sizes smaller than approximately 70 m results yielded by the fdfe approach are in good quantitative agreement with those obtained by a semianalytical boundaryintegralmethodalongplanarandnonplanarparabola shaped faults thefdfemethodthusprovidesquantitative accurateresults for spontaneous rupture simulations on intricate fault geometries