laboratory earthquakes the sub rayleigh to supershear rupture transition we report on the experimental observation of spontaneously nucleated supershear rupture and on the visualization of sub rayleigh to supershear rupture transitions in frictionally held interfaces the laboratory experiments mimic natural earthquakes the results suggest that under certain conditions supershear rupture propagation can be facilitated during large earthquake events

finite faults and inverse theory with applications to the 1979 imperial valley earthquake abstract using a representation theorem from elastodynamics subsurface slip on a known fault is formulated as the solution to an inverse problem in which recorded surface ground motion is the data two methods of solution are presented the least squares method which minimizes the squared differences between theory and data and the constrained least squares method which simultaneously maintains a set of linear inequalities instabilities in the solution are effectively eliminated in both methods and the sensitivity of the solution to small changes in the data is quantitatively stated the inversion methodology is applied to 77 components of near field ground acceleration recorded during the 15 october 1979 imperial valley earthquake the faulting is constrained to propagate bilaterally away from the epicenter at an average velocity of 90 per cent of the shear wave speed on a vertical fault plane extending from the surface to 10 km depth inequality constraints are used to keep the faulting sequence physically reasonable by maintaining right lateral motion and positive slip velocity the preferred solution is stable and provides a good fit to the data it is also realistic and consistent with observed surface offsets and independent estimates of seismic moment

self healing slip pulses in dynamic rupture models due to velocity dependent strength abstract seismological observations of short slip duration on faults short rise time on seismograms during earthquakes are not consistent with conventional crack models of dynamic rupture and fault slip in these models the leading edge of rupture stops only when a strong region is encountered and slip at an interior point ceases only when waves from the stopped edge of slip propagate back to that point in contrast some seismological evidence suggests that the duration of slip is too short for waves to propagate from the nearest edge of the ruptured surface perhaps even if the distance used is an asperity size instead of the entire rupture dimension what controls slip duration if not dimensions of the fault or of asperities in this study dynamic earthquake rupture and slip are represented by a propagating shear crack for all propagating shear cracks slip velocity is highest near the rupture front and at a small distance behind the rupture front the slip velocity decreases as pointed out by heaton 1990 if the crack obeys a negative slip rate dependent strength relation the lower slip velocity behind the rupture front will lead to strengthening that further reduces the velocity and under certain circumstances healing of slip can occur the boundary element method of hamano 1974 is used in a program adapted from andrews 1985 for numerical simulations of mode ii rupture with two different velocity dependent strength functions for the first function after a slip weakening displacement the crack follows an exponential velocity weakening relation the characteristic velocity v 0 of the exponential determines the magnitude of the velocity dependence at dynamic velocities the velocity dependence at high velocity is essentially zero when v 0 is small and the resulting slip velocity distribution is similar to slip weakening if v 0 is larger rupture propagation initially resembles slip weakening but spontaneous healing occurs behind the rupture front the rise time and rupture propagation velocity depend on the choice of constitutive parameters the second strength function is a natural log velocity dependent form similar to constitutive laws that fit experimental rock friction data at lower velocities slip pulses also arise with this function for a reasonable choice of constitutive parameters slip pulses with this function do not propagate at speeds greater than the raleighwave velocity the calculated slip pulses are similar in many aspects to seismic observations of short rise time in all cases of self healing slip pulses the residual stress increases with distance behind the trailing edge of the pulse so that the final stress drop is much less than the dynamic stress drop in agreement with the model of brune 1976 and some recent seismological observations of rupture

a supershear transition mechanism for cracks seismic data indicate that fault ruptures follow complicated paths with variable velocity because of inhomogeneities in initial stress or fracture energy we report a phenomenon unique to three dimensional cracks locally stronger fault sections rather than slowing ruptures drive them forward at velocities exceeding the shear wave speed this supershear mechanism differentiates barrier and asperity models of fault heterogeneity which previously have been regarded as indistinguishable high strength barriers concentrate energy producing potentially destructive pulses of strong ground motion

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

dependence of boundary layer structure near an ice edge coastal front upon geostrophic wind direction the dependence of boundary layer bl features within a coastal front created by temperature and roughness differences across a surface interface upon the direction of a large scale geostrophic wind is examined with idealized simulations using parameters appropriate to an ice edge maximum vertical velocities and strongest horizontal gradients occur when the vertically averaged bl velocity near the ice edge parallels the ice edge this occurs at the on ice geostrophic angle for which frictional modification of the geostrophic wind optimally counters thermally induced cross interface flow at the ice edge this optimal angle is greater for ice on right when looking downwind assuming northern hemisphere rotation flow than for ice on left flow due to asymmetry introduced by surface friction the associated vertical velocity maxima also vary asymmetrically with geostrophic wind direction the optimal angle depends upon the average surface roughness at the interface whereas the vertical velocity maxima depend upon the differential surface roughness across the interface for a prototype ice edge the optimal on ice angle is 20 larger and its vertical velocity maximum 3 times larger for ice on right flow with differential surface roughness accounting for nearly half of the magnitude asymmetry along ice velocity jets develop only when the large scale geostrophic wind nearly parallels the ice edge the curl of the surface stress is sensitive to changes in geostrophic wind direction changing sign over the water when the large scale geostrophic wind approximately parallels the ice edge because of frontal collapse the width of the surface transition region has a relatively minor influence on these results

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

source rupture process of the 2004 chuetsu mid niigata prefecture japan earthquake inferred from waveform inversion with dense strong motion data abstract the kinematic source rupture process of the 2004 chuetsu mid niigata prefecture japan earthquake is estimated from strong motion data by the linear waveform inversion method in order to develop appropriate green s functions one dimensional velocity structure models for each station are constructed by modeling the aftershock waveforms the estimated top of the bedrock is deeper at the western side of the fault and relatively shallow at the eastern side this tendency coincides with other investigations of seismic tomography and microtremor array observations the obtained source model shows large slips in the vicinity of the hypocenter the reverse slipping rupture originated from the deeper part of the fault and propagated toward the up dip and southwest directions the near surface slip is small two tests are demonstrated to check the stability of the obtained source model the first test examines the effects of the number of available stations on the solution and the second test examines how the difference in the target waveform type affects the solution the number of stations affects the variation of slip amount and more than 12 stations appear to be sufficient to obtain a stable solution in this case the difference in the target wave type in the data set does not significantly affect the solution if the number of stations is sufficient and the green s functions are well calibrated the model obtained using calibrated velocity structure models shows clear image of high slip area compared to the model obtained using a single velocity structure model

distribution of dynamic and static stress changes during 2000 tottori japan earthquake brief interpretation of the earthquake sequences foreshocks mainshock and aftershocks 1 the dynamic and static stress changes during the 2000 tottori earthquake have been recovered from the results of waveform inversion we use the dem to solve the elastodynamic equation specifying the slip along the fault obtained by a kinematic fault model the resulting shear stress distribution suggests an explanation of the foreshock and aftershock distributions we conclude that the fault zone heterogeneity is strong and most of the foreshocks and aftershocks were located in the zone of negative stress drop and mainly in the area surrounding the asperity this suggests that the asperity behaved as a barrier during the foreshocks and after the main shock the stress in the area surrounding the asperity increased and triggered most of the aftershocks the foreshock distribution was confined to a finite localized zone in the central part of the fault suggesting that this zone was bordered by barriers

dynamic modeling of the 2004 mw 6 0 parkfield california earthquake 1 we present two spontaneous rupture models of the 2004 mw 6 0 parkfield earthquake constrained by near source ground motions we start with a stress drop distribution calculated from a kinematic slip distribution using a linear slip weakening friction law we utilize trial and error to obtain both the stress conditions and frictional parameters on the fault that produce synthetics consistent with records the material contrast across the san andreas fault is incorporated using different one dimensional velocity structures on each side of the fault an approximately constant s parameter of 0 3 and a uniform slip weakening distance of 0 15 m are used in the dynamic models in our preferred dynamic model consistent with the ground motion and gps the slip is bounded by seismicity streaks at 5 and 10 km depths confirming a locked zone at depth the stress drop is approximately 10 mpa in the hypocentral region and about 2 mpa elsewhere the material contrast across the fault causes significant normal stress variations 1 mpa leading to a larger strength drop to the southeast than to the northwest the main rupture front propagates at nearly a constant subshear rupture velocity 3 km s in both directions the total radiated energy determined from the preferred dynamic model is 1 1 1013 j seismic moment is 1 0 1018 nm and fracture energy is 3 0 1013 j the limited number of aftershocks in the slipped area suggests the important role of stress on the distribution of seismicity in the locked zone

imaging surface contacts power law contact distributions and contact stresses in quartz calcite glass and acrylic plastic a procedure has been developed to obtain microscope images of regions of contact between roughened surfaces of transparent materials while the surfaces are subjected to static loads or undergoing frictional slip static loading experiments with quartz calcite soda lime glass and acrylic plastic at normal stresses to 30 mpa yield power law distributions of contact areas from the smallest contacts that can be resolved 3 5 m2 up to a limiting size that correlates with the grain size of the abrasive grit used to roughen the surfaces in each material increasing normal stress results in a roughly linear increase of the real area of contact mechanisms of contact area increase are by growth of existing contacts coalescence of contacts and appearance of new contacts mean contacts stresses are consistent with the indentation strength of each material contact size distributions are insensitive to normal stress indicating that the increase of contact area is approximately self similar the contact images and contact distributions are modeled using simulations of surfaces with random fractal topographies the contact process for model fractal surfaces is represented by the simple expedient of removing material at regions where surface irregularities overlap synthetic contact images created by this approach reproduce observed characteristics of the contacts and demonstrate that the exponent in the power law distributions depends on the scaling exponent used to generate the surface topography

surface rupturing and buried dynamic rupture models calibrated with statistical observations of past earthquakes in the context of the slip weakening friction model and simplified asper ity models for stress state we calibrate dynamic rupture models for buried and surface rupturing earthquakes constrained with statistical observations of past earth quakes these observations are the kinematic source models derived from source in versions of ground motion and empirical source models of seismic moment and rupture area the calibrated parameters are the stress drop distribution on the fault and average stress drop we develop a set of dynamic rupture models that consist of asperities and surrounding background areas the distribution of dynamic stress drop outside the asperity is characterized by a fraction of the stress drop on the as perity from this set of models we identify dynamic fault models with defined stress drop characteristics that satisfy the observations the selected dynamic fault models show that surface rupturing earthquakes are characterized by a large area of negative stress drop surrounding the asperities while buried earthquakes present positive or zero stress drop in addition the calibrated fault models that match the observations show that the average stress drop is independent of earthquake size for buried earth quakes but scale dependent for surface rupturing earthquakes this suggests that in the context of our parameterization buried earthquakes follow self similarity scaling and surface rupturing earthquakes break this self similarity we apply the calibrated dynamic models to simulate near source ground motion consistent with observations that suggest that buried earthquakes generate stronger ground motion than surface rupturing earthquakes at high frequency we propose possible mechanisms that satisfy this observation as follows buried rupture has a hypocenter location below the as perity this can produce strong directivity of the slip velocity function toward the free surface that effect in addition to a reduced fault area and low fracture energy during rupture may be significant in enhancing high frequency ground motion on the other hand surface rupturing earthquakes have a shallow hypocenter large fracture energy on the asperities and enhanced energy absorption due to large areas of negative stress drop in the background area these characteristics of large earthquakes inhibit severe directivity effects on the slip velocity function directly toward the free surface redu cing the high frequency ground motion

rupture reactivation during the 2011 mw 9 0 tohoku earthquake dynamic rupture and ground motion simulations near source ground motion observations and kinematic source inversions suggest that the rupture process of the 2011 m w 9 0 tohoku earthquake involved rupture reactivation that is repeated rupture nucleation in the same hypocentral area this unusual phenomenon may have provided a second breath to the rupture that enhanced its final size here we propose that rupture reactivation may have been governed by a slip weakening friction model with two sequential strength drops the second one being activated at large slip such frictional behavior has been previously observed in laboratory experiments and attributed to pressurization of fault zone fluids by mineral decomposition reactions activated by shear heating such as dehydration and decarbonation further evidence of this double slip weakening friction model is obtained here from the dynamic stress changes in the hypocentral region derived from a finite source inversion model we incorporate this friction model in a dynamic rupture simulation comprising two main asperities constrained by source inversion models and several deep small asperities constrained by backprojection source imaging studies our simulation produces ground motion patterns along the japanese coast consistent with observations and rupture patterns consistent with a kinematic source model featuring rupture reactivation the deep small asperities serve as a bridge to connect the two main asperities and the rupture reactivation mechanism is needed to reproduce the observed ground motion pattern therefore we argue that rupture reactivation during the 2011 tohoku earthquake is consistent with a second strength drop possibly caused by activation of thermochemical weakening processes at large slip online material movie of simulated rupture and wave propagation and ground velocities recorded at the kik net and k net seismic networks

kinematic inversion of physically plausible earthquake source models obtained from dynamic rupture simulations one approach to investigate earthquake source processes is to produce kinematic source models from inversion of seismic records and geodetic data the setup of the inversion requires a variety of assumptions and constraints to restrict the range of possible models here we evaluate to what extent physically plausible earth quake scenarios are reliably restituted in spite of these restrictions we study which characteristics of ruptures such as rupture velocity slip distribution stress drop rise time and slip function can be reliably determined from the inversion of near field seismic and geodetic data using spontaneous dynamic rupture simulations we gen erate five earthquake scenarios each of which has different characteristics of the source process then we conduct a blind test by modeling the synthetic near source data using a standard inversion scheme that optimizes the fit to the observations while searching for solutions with minimum roughness the inversion procedure assumes a rupture front propagating away from the hypocenter with variable rupture velocity and a simple cosine slip time function our results show that overall slip distribution and stress drop are reasonably well determined even for input models with relatively complex histories such as a subshear rupture transitioning to supershear speeds depth averaged rupture velocities are also reasonably well resolved although their estimate progressively deteriorates away from the hypocenter the local rise time and slip function are not well resolved but there is some sensitivity to the rupture pulse width which can be used to differentiate between pulse like and crack like ruptures our test for understanding the inaccuracies in green s functions shows that random 3d perturbations of 5 standard deviation do not lead to significant degradation of the estimation of earthquake source parameters as remedies to the current limitations we propose smoothing slip function parameters and using more complicated inversion schemes only if data necessitates them online material figures showing snapshots of forward and inverse modeling of rupture l curves slip models and waveform fits

the 2004 mw6 0 parkfield california earthquake inversion of near source ground motion using multiple data sets on 28 september 2004 the m w 6 0 parkfield earthquake became the most densely recorded earthquake for near source ground motion to infer the kinematic nature of this event we invert the strong motion data the non linear global inversion yields slip amplitude slip rake average rupture velocity and rise time over the fault by using subsets of the data we study the dependence of the kinematic solutions on data input the inversions reveal that the slip amplitude was less than 0 65 m and outline two major areas of slip one that laterally surrounds the hypocenter preferentially extending to its se the other 10 to 20 km nw of the hypocenter at a depth between 2 and 8 km the slip amplitude we obtain for each point on the fault varies less than 0 15 m depending on data set used the rake angle variability is less than 40 degrees

influence of the rupture initiation on the intersonic transition crack like versus pulse like modes we numerically investigate the supershear transition of inplane rupture under slip weakening friction and tectonic loading using a non smooth spectral element method nucleation of the rupture in the vicinity of an initial stress concentration is consistently solved together with the dynamic propagation nucleation is shown to influence the transition to the supershear propagation and depending upon the initiation process and the level of the stress out of the nucleating asperity crack like or pulse like solutions can be selected in the intersonic regime pulses are triggered by dynamic unloading of the traction ahead of the rayleigh wave and tend to become metastable the asymptotic numerical solution is always a crack propagating close to p wave speed the rupture front and the arrest velocities are numerically characterized we argue that the nucleation phase introduces a trade off with the state of the stress in determining the distance at which supershear appears

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

complexity of seismicity due to highly rate dependent friction we study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid in order to understand the origin of seismic source heterogeneity in the presence of nonlinear rate dependent friction all the mechanical properties of the medium and friction are assumed to be homogeneous starting from a heterogeneous initial stress distribution we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for more than 20 000 events in some cases the style of seismicity produced by this model is determined by a control parameter which measures the degree of rate dependence of friction for classical friction models with rate independent friction no complexity appears and seismicity is perfectly periodic for weakly rate dependent friction seismicity becomes slightly nonperiodic but most events are still characteristic earthquakes when friction is highly rate dependent seismicity is completely irregular and ruptures of all sizes occur inside the fault highly rate dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop premature healing causes rupture to take the form of narrow propagating slip episodes the so called heaton s 1990 pulses partial stress drop produces large variations in the state of stress which in turn produce earthquakes of different sizes we make the conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity

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

dynamic rupture analysis inversion for the source process of the 1990 izu oshima japan earthquake m 6 5 a waveform inversion has been applied to strong motion data using a dynamic shear crack model we studied the 1990 izu oshima earthquake mjma 6 5 which has vertical strike slip faulting with unilateral rupture propagation the inversion has two steps a waveform inversion and a crack inversion that are applied iteratively a waveform inversion is used to determine the distribution of rupture starting times and slip dislocations using the slip functions calculated by the initial crack model or by previous crack inversion a crack inversion is used to calculate dynamic crack propagation that explains the results of the above inversion in this step we use the estimated rupture times as a locking fracture criterion the maximum shear stress attained before a fault segment breaks gives a lower bound estimate of the peak shear strength at each fault segment then the dynamic stress drop distribution is estimated from the slip distribution obtained from waveform inversion assuming a dynamic crack model from the results we determine the rise time distribution and the distribution of a dimensionless stress ratio s defined as strength excess stress drop our analysis gives the following picture of the rupture process of the 1990 izu oshima earthquake 1 an asperity type faulting having large slip and high stress drop was detected in the region around the initiation point of rupture 2 south of the asperity zone barrier type faulting characterized by incoherent propagating rupture small slip long rise time and high strength excess was detected this zone corresponds to the intersection of the fault with the 1978 earthquake mjma 7 0

a spatial random field model to characterize complexity in earthquake slip 1 finite fault source inversions reveal the spatial complexity of earthquake slip over the fault plane we develop a stochastic characterization of earthquake slip complexity based on published finite source rupture models in which we model the distribution of slip as a spatial random field the model most consistent with the data follows a von karman autocorrelation function acf for which the correlation lengths a increase with source dimension for earthquakes with large fault aspect ratios we observe substantial differences of the correlation length in the along strike a x and downdip a z directions increasing correlation length with increasing magnitude can be understood using concepts of dynamic rupture propagation the power spectrum of the slip distribution can also be well described with a power law decay i e a fractal distribution in which the fractal dimension d remains scale invariant with a median value d 2 29 0 23 while the comer wave number k c which is inversely proportional to source size decreases with earthquake magnitude accounting for larger slip patches for large magnitude events our stochastic slip model can be used to generate realizations of scenario earthquakes for near source ground motion simulations

dynamic faulting under rate dependent friction we discuss the effects of rate dependent friction on the propagation of seismic rupture on active faults several physicists using burridge and knopoff s box and spring model of faulting have proposed that fault complexity may arise from the spontaneous development of a self similar stress distribution on the fault plane if this model proves to be correct it has important consequences for the origin of the complexity of seismic sources in order to test these ideas on a more realistic earthquake model we developed a new boundary integral equation method for studying rupture propagation along an antiplane fault in the presence of nonlinear rate dependent friction we study rupture dynamics of models with single and twin asperities in our models asperities are places on the fault with a higher value of prestress othewise all fault parameters are homogeneous we show that for models with such asperities a slip velocity weakening friction leads to the propagation of supersonic healing phases and to the spontaneous arrest of fracture if the prestress outside the asperities is low enough for models with asperities we can also observe narrow slip velocity pulses qualitatively similar to the so called heaton pulses observed in some earthquake accelerograms we also observe a complex distribution of stress after the rupture that depends on details of the initial distribution of asperities and on the details of the friction law

the dynamic rupture process of the 1993 kushiro oki earthquake we have constructed a dynamic rapture model of the 1993 kushiro oki earthquake mw 7 6 that is consistent with the observed seismograms this earthquake occurred beneath the city of kushiro japan at a depth of about 100 km and the aftershocks are limited to a horizontal plane between a double seismic zone in the subducting slab excellent near field strong motion records are available in our analysis a kinematic inversion is followed by a dynamic crack calculation and this pair of operations is repeated until convergence to the data is obtained two different conditions concerning the dynamic stress drop were considered in the dynamic calculation and a dynamic model was constructed for each condition the difference in these conditions has little effect on the results the final dynamic model shows that this earthquake occurred with a localized high stress drop of about 40 mpa in the subducting slab which indicates that the region between the double seismic zone is strong enough to sustain such a high stress one of the two high strength regions in the final model lies near the upper plane of the double seismic zone and represents a barrier due to a substantial change of stress state in the slab in the region where the initial breaks occurred 5 s before the main rupture both the strength and the stress drop are smaller than in the adjacent region this implies that before the main rupture the accumulated stress had already been released in the area of the initial breaks the aftershocks tend to occur near the high strength area in some of them the p wave first motions are opposite to those of the main shock

kinematic inversion of the 2004 m 6 0 parkfield earthquake including an approximation to site effects the 2004 m 6 0 parkfield earthquake yielded one of the largest amounts of near source strong ground motion seismic data ever we invert strong motion seismograms to obtain a model for the space time distribution of coseismic slip on the fault to reduce noise in the inversion we take into account local amplifications that affect each station by using records of the 1983 m 6 5 coalinga earthquake site amplification correlates well with large peak ground velocities registered during the 2004 parkfield mainshock the inversion for a kinematic rupture model yields a nonunique solution we therefore analyze various rupture models that explain the data equally well our preferred rupture model identifies a primary zone of high slip surrounding the hypocenter where the maximum slip is 57 cm a secondary slip area over which contours are not well resolved is located northwest of the hypo center the rupture speed is highly heterogeneous we infer an average rupture ve locity of 2 8 km sec close to the hypocenter and of 3 3 km sec in the secondary region of large slip to the northwest of the hypocenter by correlation of our rupture model with both microseismicity and velocity structure we identify six patches on the fault plane that behave in seismically distinct ways online material kinematic rupture model parameters

pulse like and crack like ruptures in experiments mimicking crustal earthquakes theoretical studies have shown that the issue of rupture modes has important implications for fault constitutive laws stress conditions on faults energy partition and heat generation during earthquakes scaling laws and spatiotemporal complexity of fault slip early theoretical models treated earthquakes as crack like ruptures but seismic inversions indicate that earthquake ruptures may propagate in a self healing pulse like mode a number of explanations for the existence of slip pulses have been proposed and continue to be vigorously debated this study presents experimental observations of spontaneous pulse like ruptures in a homogeneous linear elastic setting that mimics crustal earthquakes reveals how different rupture modes are selected based on the level of fault prestress demonstrates that both rupture modes can transition to supershear speeds and advocates based on comparison with theoretical studies the importance of velocity weakening friction for earthquake dynamics

what the exercise of the spice source inversion validation blindtest 1 did not tell you summary uncertainties of earthquake finite fault inversions based upon strong motion data are investigated using the source inversion validation blindtest 1 exercise of the spice seismic wave propagation and imaging in complex media a european network project motivated by previous counterintuitive results the distribution of slip and the shapes of asymmetric slip rate functions are simultaneously inverted by matching 10 or 33 broad band three component velocity waveforms within the period ranging from 0 02 to 2hz using a finite fault method that carries out the waveform inversion in the wavelet domain the effects of subfault size data noise and the number of stations have been explored our results suggest 1 although there are inevitable discrepancies between the inverted model and the target model because of ignoring the spatial slip variations within individual subfaults the fault slip and rise time distributions can be well constrained even with the data including large gaussian noise 2 it is crucial for source studies to develop new inversion schemes that can properly honour the frequency and time dependent energy distribution of seismic radiation and data noise for instance inversions using the variance reduction function of velocity waveforms as the objective function have low sensitivities to the total seismic moment and peak slip 3 although the relative value of the objective function is guided in the inversion the absolute value of the objective function cannot be used to evaluate the quality of an inverted model 4 because the source inversion is based on surface observations the spatiotemporal resolution of source inversion is affected not only by the data quality but also by the earthquake itself for vertical strike slip faults the along strike resolution is better than that along the downdip direction

effects of three dimensional crustal structure and smoothing constraint on earthquake slip inversions case study of the mw6 3 2009 l aquila earthquake earthquake slip inversions aiming to retrieve kinematic rupture characteristics typically assume 1 d velocity models and a flat earth surface however heterogeneous nature of the crust and presence of rough topography lead to seismic scattering and other wave propagation phenomena introducing complex 3 d effects on ground motions here we investigate how the use of imprecise green s functions achieved by including 3 d velocity perturbations and topography affect slip inversion results we create sets of synthetic seismograms including 3 d heterogeneous earth structure and topography and then invert these synthetics using green s functions computed for a horizontally layered 1 d earth model we apply a linear inversion regularized by smoothing and positivity constraint and examine in detail how smoothing effects perturb the solution among others our tests and resolution analyses demonstrate how imprecise green s functions introduce artificial slip rate multiples especially at shallow depths and that the timing of the peak slip rate is hardly affected by the chosen smoothing the investigation is extended to recordings of the 2009 mw6 3 l aquila earthquake considering both strong motion and high rate gps stations we interpret the inversion results taking into account the lessons learned from the synthetic tests the retrieved slip model resembles previously published solutions using geodetic data showing a large slip asperity southeast of the hypocenter in agreement with other studies we find evidence for fast but subshear rupture propagation in updip direction followed by a delayed propagation along strike we conjecture that rupture was partially inhibited by a deep localized velocity strengthening patch that subsequently experienced afterslip

rupture modes in laboratory earthquakes effect of fault prestress and nucleation conditions seismic inversions show that earthquake risetimes may be much shorter than the overall rupture duration indicating that earthquakes may propagate as self healing pulse like ruptures several mechanisms for producing pulse like ruptures have been proposed including velocity weakening friction interaction of dynamic rupture with fault geometry and local heterogeneity and effect of bimaterial contrast we present experimental results on rupture mode selection in laboratory earthquakes occurring on frictional interfaces which were prestressed both in compression and in shear our experiments demonstrate that pulse like ruptures can exist in the absence of a bimaterial effect or of local heterogeneities we find a systematic variation from crack like to pulse like rupture modes with both 1 decreasing nondimensional shear prestress and 2 decreasing absolute levels of shear and normal prestress for the same value of nondimensional shear prestress both pulse like and crack like ruptures can propagate with either sub rayleigh or supershear rupture speeds our experimental results are consistent with theories of ruptures on velocity weakening interfaces implying that velocity weakening friction plays an important role in governing the dynamic behavior of earthquake ruptures we show that there is no measurable fault normal stress decrease on the fault plane due to the nucleation procedure employed in experiments and hence this is not a factor in the rupture mode selection we find that pulse like ruptures correspond to the levels of nondimensional shear prestress significantly lower than the static friction coefficient suggesting that faults hosting pulse like ruptures may operate at low levels of prestress compared to their static strength

stochastic modeling of slip spatial complexities for the 1979 imperial valley california earthquake 1 finite fault source inversions reveal the spatial complexity of earthquake slip or prestress distribution over the fault surface in this paper we discuss a stochastic model that reproduces the spatial variability and the long range spatial correlation of the slip distribution of the 1979 imperial valley earthquake we have found that stochastic models based on non gaussian distributions are better suited to describe the spatial variability of the slip amplitude over the fault we also show that a stochastic modeling of the slip amplitude based on a gaussian distribution fails to reproduce the spatial variability observed in the original slip distribution the stochastic models can be used to deduce ground motion from other earthquakes statistically similar to imperial valley

dynamics of fault interaction parallel strike slip faults we use a two dimensional finite difference computer program to study the effect of fault steps on dynamic ruptures our results indicate that a strike slip earthquake is unlikely to jump a fault step wider than 5 km in correlation with field observations of moderate to great sized earthquakes we also find that dynamically propagating ruptures can jump both compressional and dilational fault steps although wider dilational fault steps can be jumped dilational steps tend to delay the rupture for a longer time than compressional steps do this delay leads to a slower apparent rupture velocity in the vicinity of dilational steps these dry cases assumed hydrostatic or greater pore pressures but did not include the effects of changing pore pressures in an additional study we simulated the dynamic effects of a fault rupture on undrained pore fluids to test sibson s 1985 1986 suggestion that wet dilational steps are a barrier to rupture propagation our numerical results validate sibson s hypothesis by demonstrating that the effect of the rupture on the undrained pore fluids is to inhibit the rupture from jumping dilational stepovers the basis of our result differs from sibson s hypothesis in that our model is purely elastic and does not necessitate the opening of extension fractures between the fault segments

the effect of asymmetric damage on dynamic shear rupture propagation ii with mismatch in bulk elasticity high speed digital photography was used to study rupture propagation on the interface between transparent damaged and undamaged photoelastic plates bilateral ruptures were nucleated on pre machined faults at an angle to the uniaxial loading axis stress concentration at the crack tips produced fringes in polarized laser light that allowed their positions to be measured in successive photos we found that fracture damage introduces a strong asymmetry in propagation speed different from that expected due to the lower elastic stiffness in the damaged material alone when the tensile lobe of a rupture tip propagated through the damaged material the velocity of that rupture was reduced or stopped by contrast when the compressive lobe of a rupture tip passed through the damage the velocity of that rupture was unaffected by the damage a physical interpretation is that passage of a tensile lobe through the damage expends energy by lowering the normal stress on pre existing cracks thus allowing frictional sliding along the crack surfaces when the compressive lobe of the rupture passes through the damage compressive stresses prevent sliding only minor energy is dissipated and the damage has almost no effect on the velocity this effect can produce asymmetric propagation for earthquake ruptures on slip surfaces near the edge of a highly damaged fault zone

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

uncertainty in earthquake source imaging due to variations in source time function and earth structure abstract one way to improve the accuracy and reliability of kinematic earthquake source imaging is to investigate the origin of uncertainty and to minimize their effects the difficulties in kinematic source inversion arise from the nonlinearity of the problem nonunique choices in the parameterization and observational errors we analyze particularly the uncertainty related to the choice of the source time function stf and the variability in earth structure we consider a synthetic data set generated from a spontaneous dynamic rupture calculation using bayesian inference we map the solution space of peak slip rate rupture time and rise time to characterize the kinematic rupture in terms of posterior density functions our test to investigate the effect of the choice of stf reveals that all three tested stfs isosceles triangle regularized yoffe with acceleration time of 0 1 and 0 3 s retrieve the patch of high slip and slip rate around the hypocenter however the use of an isosceles triangle as stf artificially accelerates the rupture to propagate faster than the target solution it additionally generates an artificial linear correlation between rupture onset time and rise time these appear to compensate for the dynamic source effects that are not included in the symmetric triangular stf the exact rise time for the tested stfs is difficult to resolve due to the small amount of radiated seismic moment in the tail of stf to highlight the effect of earth structure variability we perform inversions including the uncertainty in the wavespeed only and variability in both wavespeed and layer depth we find that little difference is noticeable between the resulting rupture model uncertainties from these two parameterizations both significantly broaden the posterior densities and cause faster rupture propagation particularly near the hypocenter due to the major velocity change at the depth where the fault is located online material figures of inverted rupture models trade off curve and posterior probability density function

self healing pulse like shear ruptures in the laboratory models predict that dynamic shear ruptures during earthquake faulting occur as either sliding cracks where a large section of the interface slides behind a fast moving rupture front or self healing slip pulses where the fault relocks shortly behind the rupture front we report experimental visualizations of crack like pulse like and mixed rupture modes propagating along frictionally held incoherent interfaces separating identical solids and we describe the conditions under which those modes develop a combination of simultaneously performed measurements via dynamic photoelasticity and laser interferometry reveals the rupture mode type the exact point of rupture initiation the sliding velocity history and the rupture propagation speed

short slip duration in dynamic rupture in the presence of heterogeneous fault properties recent studies of strong motion data consistently show that the risetime duration of slip at particular locations on the fault is significantly shorter than the overall rupture duration the physical explanation for this observation and its implications have become central issues in earthquake source studies two classes of mechanisms have been proposed to explain short risetimes one explanation is that velocity weakening frictional behavior on the fault surface causes the fault to self heal this possibility is suggested by rate dependent friction observed in laboratory experiments and by some two dimensional dynamic numerical simulations of earthquake rupture it has recently been demonstrated however that the velocity dependence of friction observed in the laboratory is too weak to cause faults to self heal an alternative explanation for short risetimes is that spatially heterogeneous fault strength e g barriers limit the slip duration in this paper we investigate this second explanation for short risetimes by constructing a three dimensional dynamic rupture model for the 1984 morgan hill california earthquake mw 6 2 using a kinematic model previously obtained from waveform inversion of strong motion data we assume velocity independent friction and a critical stress fracture criterion and derive a dynamic model specified by the spatial distribution of dynamic stress drop and strength excess that reproduces the slip and rupture time of the kinematic model the slip velocity time functions calculated from this dynamic model are then used in a subsequent inversion to fit the strong motion data by alternating between dynamic and kinematic modeling we obtain a dynamic model that provides an acceptable fit to the recorded waveforms in this dynamic model the risetime is short over most of the fault which is attributable entirely to the short scale length slip stress drop heterogeneity required by the strong motion data a self healing mechanism such as strongly velocity dependent friction is not required to explain the short risetimes observed in this earthquake

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

identifying the unique ground motion signatures of supershear earthquakes theory and experiments the near field ground motion signatures associated with sub rayleigh and supershear ruptures are investigated using the laboratory earthquake experiment originally developed by rosakis and co workers xia et al 2004 2005a lu et al 2007 rosakis et al 2007 heterodyne laser interferometers enable continuous high bandwidth measurements of fault normal fn fault parallel fp and vertical v particle velocity ground motion records at discrete locations on the surface of a homalite 100 test specimen as a sub rayleigh or a supershear rupture sweeps along the frictional fault photoelastic interference fringes acquired using high speed digital photography provide a synchronized spatially resolved whole field view of the advancing rupture tip and surrounding maximum shear stress field the first phase of experimental investigations examine and verify the ground motion signatures of supershear ruptures experimental results demonstrate that a shear mach front produced by a stable supershear rupture is characterized by a dominant fp velocity component the situation is shown to reverse in the sub rayleigh rupture speed regime whereby the fn particle velocity component dominates the ground motion record additional distinguishing particle velocity signatures consistent with theoretical and numerical predictions and repeatedly observed in experimental records are 1 a pronounced peak in the fp velocity record induced by the leading dilatational field which sweeps the measurement station in advance of the shear mach front and 2 a pronounced velocity swing in the fn record associated with the arrival of a trailing rayleigh sub rayleigh secondary rupture which follows the arrival of the shear mach front analysis of the particle velocity records also confirms 2d steady state theoretical predictions pertaining to the separation attenuation and radiation partitioning of the shear and dilatational portions of the rupture velocity field components the second phase of our experimental investigations re examine the 2002 mw7 9 denali fault earthquake and the remarkable set of near source ground motion records obtained at ps10 located approximately 85 km east of the epicenter and just 3 km north of the fault along the alaska pipeline motivated by the analysis and interpretation of these records by ellsworth et al 2004 dunham and archuleta 2004 2005 we attempt to mimic the denali strike slip rupture scenario and replicate the ps10 ground motion signatures using a laboratory earthquake experiment the experiments feature a left to right west to east propagating right lateral rupture within a homalite 100 test specimen with particle velocity data collected at a near field station situated just above north of the fault both sub rayleigh and supershear laboratory earthquake experiments are conducted using the denali ps10 configuration in order to compare and contrast the resulting particle velocity signatures supershear laboratory records capture all of the prominent features displayed within the ps10 ground motion records noted velocity signatures are correlated to the location of the rupture fronts and their noted arrival times in the synchronized photoelastic image sequence scaling relationships are also presented which transform the laboratory records through six orders of magnitude in time to match the scale of the ps10 ground motion records the strong correlation between the scaled experimental records and the actual ps10 ground motion records support the hypothesis that the denali strike slip fault exhibited a supershear burst finally we present a 2d steady state stress velocity formulation that relates the fp and fn particle velocity records measured close to the fault to the evolution of the stress tensor at the same location a locally steady state condition is assumed within a restricted time interval in order to invoke these relationships and estimate the dynamic stresses xx t and t at the near fault station dynamic stress measurements enable a new class of friction investigations using the laboratory earthquake configuration experimental findings are presented which capture the temporal and spatial distributions of xx and evolution of the dynamic friction coefficient and velocity weakening behavior of a supershear slip pulse

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

dynamic stress changes during earthquake rupture we assess two competing dynamic interpretations that have been pro posed for the short slip durations characteristic of kinematic earthquake models de rived by inversion of earthquake waveform and geodetic data the first interpretation would require a fault constitutive relationship in which rapid dynamic restrengthen ing of the fault surface occurs after passage of the rupture front a hypothesized mechanical behavior that has been referred to as self healing the second inter pretation would require sufficient spatial heterogeneity of stress drop to permit rapid equilibration of elastic stresses with the residual dynamic friction level a condition we refer to as geometrical constraint these interpretations imply contrasting pre dictions for the time dependence of the fault plane shear stresses we compare these predictions with dynamic shear stress changes for the 1992 landers m 7 3 1994 northridge m 6 7 and 1995 kobe m 6 9 earthquakes stress changes are com puted from kinematic slip models of these earthquakes using a finite difference method for each event static stress drop is highly variable spatially with high stress drop patches embedded in a background of low and largely negative stress drop the time histories of stress change show predominantly monotonic stress change after passage of the rupture front settling to a residual level without significant evidence for dynamic restrengthening the stress change at the rupture front is usu ally gradual rather than abrupt probably reflecting the limited resolution inherent in the underlying kinematic inversions on the basis of this analysis as well as recent similar results obtained independently for the kobe and morgan hill earthquakes we conclude that at the present time the self healing hypothesis is unnecessary to explain earthquake kinematics

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

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

a support operator method for 3 d rupture dynamics summary we present a numerical method to simulate spontaneous shear crack propagation within a heterogeneous 3 d viscoelastic medium wave motions are computed on a logically rectangular hexahedral mesh using the generalized finite difference method of support operators som this approach enables modelling of non planar surfaces and non planar fault ruptures our implementation the support operator rupture dynamics sord code is highly scalable enabling large scale multiprocessors calculations the fault surface is modelled by coupled double nodes where rupture occurs as dictated by the local stress conditions and a frictional failure law the method successfully performs test problems developed for the southern california earthquake center scec u s geological survey usgs dynamic earthquake rupture code validation exercise showing good agreement with semi analytical boundary integral method results we undertake further dynamic rupture tests to quantify numerical errors introduced by shear deformations to the hexahedral mesh we generate a family of meshes distorted by simple shearing in the along strike direction up to a maximum of 73 for scec usgs validation problem number 3 grid induced errors increase with mesh shear angle with the logarithm of error approximately proportional to angle over the range tested at 73 rms misfits are about 10 per cent for peak slip rate and 0 5 per cent for both rupture time and total slip indicating that the method which up to now we have applied mainly to near vertical strike slip faulting is also capable of handling geometries appropriate to low angle surface rupturing thrust earthquakes additionally we demonstrate non planar rupture effects by modifying the test geometry to include respectively cylindrical curvature and sharp kinks

bayesian imaging of the 2000 western tottori japan earthquake through fitting of strong motion and gps data summary we image the rupture process of the 2000 western tottori earthquake m w 6 6 through fitting of strong motion and gps data we consider an observational network consisting of 18 strong motion and 16 gps stations located within three fault lengths from the epicentre we assume a planar fault and compute green s functions for a 1 d velocity model the earthquake rupture is described as a shear dislocation parameterized in terms of peak slip velocity rake angle rupture time and rise time defined on a regular grid of nodes on the fault surface and derived at inner points through bilinear interpolation our inversion procedure is based on a bayesian approach the solution of the inverse problem is stated in terms of a posterior probability density function pdf representing the conjunction of prior information with information contained in the data and in the physical law relating model parameters with data inferences on model parameters are thus expressed in terms of posterior marginal pdfs due to the non linearity of the problem we use a markov chain monte carlo mcmc method based on the metropolis algorithm to compute posterior marginals except for a few cases posterior marginals do not show a gaussian like distribution this prevents us from providing a mean model and from characterizing uncertainties in terms of standard deviations only resolution on each single parameter is analysed by looking at the difference between prior and posterior marginal pdfs posterior marginals indicate that the best resolved feature is a major slip patch peak value of 311 140 cm located between the hypocentre and the top edge of the fault centered at a depth of 4 5 km this shallow slip patch is triggered about 3 s after the earthquake nucleated and required about 4 s to reach its final slip value the presence of this shallow slip patch is common to all previous studies in contrast to some previous studies we do not identify any significant slip 1 m at the bottom of the fault we also compare inferences from both strong motion and gps data with inferences derived from strong motion data only in both cases the shallow slip patch is identified at other locations the main effect of the gps data is in reducing the probability associated with high values of slip gps data reduce the presence of spurious fault slip and therefore strongly influence the resulting final seismic moment

magnetic properties of fault pseudotachylytes in granites 1 we investigate the petrographic geochemical and magnetic properties of fault pseudotachylytes formed by frictional melting in granitic rocks from southern california the italian alps and kyushyu japan the main magnetic remanence carriers are mixtures of grain sizes of fine grained magnetite these ferrimagnetic grains record a stable multicomponent magnetization that consists of one or more of the following coseismic thermal remanent magnetization coseismic lightning isothermal remanent magnetization and post seismic chemical remanent magnetization fault pseudotachylytes from the three localities display contrasting magnetic properties which suggests that oxygen fugacity and host rock composition ultimately control the magnetic assemblage

the influence of the lithospheric thickness on bilateral slip summary a 2 d model of slip formation and dynamic propagation in an elastic lithospheric plate coupled to the asthenosphere and having a fault plane is investigated using a finite element method slip is nucleated at a weak portion of the fault plane and propagates bilaterally at the edges slip is assumed to develop according to a critical shear stress criterion combined with a slip weakening law except for the weak portion the slip resistance is constant along the fault plane the influence of resistive stresses from the asthenosphere at the bottom of the plate is taken into account the results indicate that bilateral slip lengths are limited to about the lithospheric plate thickness or somewhat larger such lengths will only be reached for sufficiently high tectonic loading after maximum slip length has been reached the slipping region is split into two regions of unidirectional slip moving in opposite directions the results thus illustrate one mechanism which limits the maximum amount of slip during an earthquake even in the absence of strong barriers

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

the mw 7 8 2001 kunlunshan earthquake extreme rupture speed variability and effect of fault geometry 1 by analyzing body wave seismograms we show that the rupture speed on the main kunlun fault during the mw 7 8 2001 kunlunshan tibet earthquake was highly variable and the rupture process consisted of three stages in the first stage the rupture accelerated from rest to an average speed of 3 3 km s over a distance of 120 km the rupture then propagated for another 150 km at an apparent rupture speed exceeding the p wave speed in the final stage the earthquake fault bifurcates and the rupture front slowed down the region of highest rupture velocity is found to coincide with the region of highest fault slip has the longest slip duration and is where off fault ground cracking is observed in the field stress drops are found to be higher in regions of higher rupture speeds the greatest concentration of aftershocks is located near the fault bifurcation zone and hence coincides with the region of highest fault slip highest stress drop and highest rupture velocity the fault width is no more than 10 km in most places and is about 20 km in the region of highest slip this narrow fault width is attributed to the fact that crust below this depth is sufficiently warm not to permit brittle failure to occur the remarkable similarity of this earthquake with the 1906 california earthquake in spite of occurring in very different tectonic regimes is discussed

synthetic source inversion tests with the full complexity of earthquake source processes including both supershear rupture and slip reactivation recent studies in dynamic source modeling and kinematic source inversion show that earthquake rupture may contain greater complexity than we previously anticipated including multiple slipping at a given point on a fault finite source inversion methods suffer from the nonuniqueness of solutions and it may become more serious if we aim to resolve more complex rupture models in this study we perform synthetic inversion tests with dynamically generated complex rupture models including both supershear rupture and slip reactivation to understand the possibility of resolving complex rupture processes by inverting seismic waveform data we adopt a linear source inversion method with multiple windows allowing for slipping from the nucleation of rupture to the termination at all locations along a fault we regularize the model space effectively in the bayesian framework and perform multiple inversion tests by considering the effect of inaccurate green s functions and station distributions we also perform a spectral stability analysis our results show that it may be possible to resolve both a supershear rupture front and reactivated secondary slipping using the linear inversion method if those complex features are well separated from the main rupture and produce a fair amount of seismic energy it may be desirable to assume the full complexity of an earthquake rupture when we first develop finite source models after a major event occurs and then assume a simple rupture model for stability if the estimated models do not show a clear pattern of complex rupture processes

supershear transition due to a free surface in 3 d simulations of spontaneous dynamic rupture on vertical strike slip faults supershear rupture propagation has been inferred from seismic observations for natural faults and observed in laboratory experiments we study the effect of the free surface on the transition of earthquake rupture from subshear to supershear speeds using simulations of spontaneous dynamic rupture on vertical strike slip faults we find that locally supershear rupture near the free surface can occur due to i the generalized burridge andrews mechanism that is a supershear loading field between p and sv wave arrivals generated by the main rupture front at depths and ii the phase conversion of sv to p diffracted waves at the free surface weaker supershear slip due to the generalized burridge andrews mechanism is caused by the low strength at shallow portions of the fault relative to deeper ones dominant supershear rupture is supported by the additional supershear loading field produced by phase conversion locally supershear propagation at the free surface occurs regardless of the level of prestress and can cause transition to supershear propagation over the entire seismogenic depth such global supershear transition which depends on prestress can occur under prestress levels lower than the theoretical estimates for models with no free surface although the effectiveness of supershear transition due to the free surface can be diminished by several potentially important factors it may play an important role on natural faults at least in those strike slip earthquakes that accumulate significant surface slip

a simple dynamic model for the 1995 kobe japan earthquake 1 we investigate the dynamic rupture process of the 16 january 1995 kobe earthquake mw 6 9 by spontaneous rupture modeling of a 3 d dynamic shear crack that reproduces the slip distribution found from kinematic waveform inversion of strong motion data we find that using the heterogeneous initial stress field obtained from the kinematic slip model and relatively uniform fracture energy distribution successfully generates a dynamic model with slip and rupture time distributions that are consistent with the kinematic source inversion our results suggest that we may be able to produce realistic dynamic rupture models with simpler assumptions for dynamic source parameters such as the fracture energy than have been used in most dynamic rupture models to date

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

generation of new cracks accompanied by the dynamic shear rupture propagation of the 2000 tottori japan earthquake the 2000 tottori japan earthquake caused fracture zones of surface rupture at some places away from the trace of the main causative fault in order to explain this observation the 3d dynamic rupture process of the 2000 tottori japan earthquake was simulated the attractive feature of the problem under consideration is the possibility of introducing internal new cracks that propagate under tensile stress as a consequence of the dynamic process of shear slip propagation the discrete element method was used to solve this problem because it can introduce internal tensile cracks for the shear rupture propagation the simple slip weakening model was used as a friction law on the fault the new tensile cracks occur following the classical griffith theory when the critical value of tensile fracture surface energy has been reached the first step to solve the problem was the estimation of the dynamic parameters such as stress drop strength excess and critical slip which were recov ered from the results of waveform inversion in the second step a shear dynamic rupture process was simulated assuming that shear slip occurs only on the pre existing fault and the tensile stress concentration resulting from shear slip causes the new cracks that propagate away from the pre existing fault the results which are consistent with the observations show a free surface rupture caused by the new cracks and the development of a flowerlike structure springing from the borders of the pre existing fault and main asperity

the transition of dynamic rupture styles in elastic media under velocity weakening friction although kinematic earthquake source inversions show dominantly pulse like subshear rupture behavior seismological observations laboratory experiments and theoretical models indicate that earthquakes can operate with different rupture styles either as pulses or cracks that propagate at subshear or supershear speeds the determination of rupture style and speed has important implications for ground motions and may inform about the state of stress and strength of active fault zones we conduct 2d in plane dynamic rupture simulations with a spectral element method to investigate the diversity of rupture styles on faults governed by velocity and state dependent friction with dramatic velocity weakening at high slip rate our rupture models are governed by uniform initial stresses and are artificially initiated we identify the conditions that lead to different rupture styles by investigating the transitions between decaying steady state and growing pulses cracks sub shear and super shear ruptures as a function of background stress nucleation size and characteristic velocity at the onset of severe weakening our models show that small changes of background stress or nucleation size may lead to dramatic changes of rupture style we characterize the asymptotic properties of steady state and self similar pulses as a function of background stress we show that an earthquake may not be restricted to a single rupture style but that complex rupture patterns may emerge that consist of multiple rupture fronts possibly involving different styles and back propagating fronts we also demonstrate the possibility of a super shear transition for pulse like ruptures finally we draw connections between our findings and recent seismological observations

earthquakes on dipping faults the effects of broken symmetry dynamic simulations of earthquakes on dipping faults show asymmetric near source ground motion caused by the asymmetric geometry of such faults the ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more given identical initial stress magnitudes the motion of the hanging wall is larger than that of the footwall in both thrust reverse and normal earthquakes the asymmetry between normal and thrust reverse faults results from time dependent normal stress caused by the interaction of the earthquake generated stress field with earth s free surface the asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault

rupture history of the 2009 l aquila italy earthquake from non linear joint inversion of strong motion and gps data 1 we image the rupture history of the 2009 l aquila central italy earthquake using a nonlinear joint inversion of strong motion and gps data this earthquake ruptured a normal fault striking along the apennines axis and dipping to the sw the inferred slip distribution is heterogeneous and characterized by a small shallow slip patch located up dip from the hypocenter 9 5 km depth and a large deeper patch located southeastward the rupture velocity is larger in the up dip than in the along strike direction this difference can be partially accounted by the crustal structure which is characterized by a high velocity layer above the hypocenter and a lower velocity below the latter velocity seems to have affected the along strike propagation since the largest slip patch is located at depths between 9 and 14 km the imaged slip distribution correlates well with the on fault aftershock pattern as well as with mapped surface breakages

a global search inversion for earthquake kinematic rupture history application to the 2000 western tottori japan earthquake 1 we present a two stage nonlinear technique to invert strong motions records and geodetic data to retrieve the rupture history of an earthquake on a finite fault to account for the actual rupture complexity the fault parameters are spatially variable peak slip velocity slip direction rupture time and risetime the unknown parameters are given at the nodes of the subfaults whereas the parameters within a subfault are allowed to vary through a bilinear interpolation of the nodal values the forward modeling is performed with a discrete wave number technique whose green s functions include the complete response of the vertically varying earth structure during the first stage an algorithm based on the heat bath simulated annealing generates an ensemble of models that efficiently sample the good data fitting regions of parameter space in the second stage appraisal the algorithm performs a statistical analysis of the model ensemble and computes a weighted mean model and its standard deviation this technique rather than simply looking at the best model extracts the most stable features of the earthquake rupture that are consistent with the data and gives an estimate of the variability of each model parameter we present some synthetic tests to show the effectiveness of the method and its robustness to uncertainty of the adopted crustal model finally we apply this inverse technique to the well recorded 2000 western tottori japan earthquake mw 6 6 we confirm that the rupture process is characterized by large slip 3 4 m at very shallow depths but differently from previous studies we imaged a new slip patch 2 2 5 m located deeper between 14 and 18 km depth

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

slip distribution of the 1992 landers earthquake and its implications for earthquake source mechanics we use near source 10 to 164 km displacement seismograms to image the slip distribution and rupture history of the 28 june 1992 mw 7 3 landers california earthquake aftershock seismograms from similar distances are modeled to find the velocity model and frequency range 0 05 to 0 25 hz over which theoretical green s functions are most accurate and the measure of fit is used as an upper bound on theoretical error in the mainshock inversion we represent the rupture surface with three planar segments divided into 3 by 3 km elements extending from the surface to 18 km depth and solve for the slip distribution and the rupture time model that minimizes misfit to both recorded seismograms and mapped surface displacement in a least squares sense we investigate two faulting models one with a uniformly short 3 sec rise time everywhere on the fault surface and the other with a variable rise time 2 to 6 sec we perform sensitivity tests using synthetic data from a hypothetical earthquake to evaluate model resolution and solution stability in the sensitivity tests both fault models recover similar slip and rupture features but neither is capable of imaging details of the rise time for the landers earthquake we find an average rupture velocity of 2 5 km sec and use this average for a starting model in a linearized inversion for rupture time in our solutions of slip amplitude distribution the southernmost johnson valley fault segment has 20 of the total seismic moment 6 to 8 1019 n m with small displacements near the hypocenter the homestead valley segment contributes half of the moment with the largest slip amplitudes 25 to 35 km northwest of the hypocenter at 4 to 12 km depth and the camp rock emerson segment contributes the remaining moment with the largest slip amplitude 35 to 50 km northwest of the hypocenter in the shallow crust 9 km there is some evidence that the rupture front is delayed as it encounters high slip regions suggesting that prior to the mainshock these areas were further from failure owing either to greater strength or lower prestress

heterogeneous distribution of dynamic stress drop and relative fault strength recovered from the results of waveform inversion the 1984 morgan hill california earthquake the dynamic rupture process of the 1984 morgan hill california earthquake m 6 2 has been investigated on the basis of a three dimensional 3d dynamic shear crack model from previous waveform inversion results for this purpose a locking fracture criterion is introduced for rupture propagation from which a lower bound of the peak shear stress just before rupturing and hence of the relative fault strength has been estimated at each fault segment the distribution of static and dynamic stress drops has also been independently evaluated from that of fault slips by linear and nonlinear inversion procedures respectively the results show that large slips located from the hypocenter to about 10 km and 14 to 17 km along the strike at depths between 8 and 12 km result from local dynamic stress drops exceeding 40 and 140 bars respectively negative stress drops down to 15 bars are required to explain very low slips over a shallow fault section if a non negative stress drop condition is imposed somewhat larger slips are obtained there than those from the waveform inversion the above results suggest that there could be a zone of velocity strengthening frictional behavior in the shallow crust which may have arrested slip motion during rupture propagation the strength excess is found to be generally small but somewhat larger at a small zone that has delayed rupture propagation the dynamic rupture initiated from a small nucleus zone with a low stress drop propagated southeastward breaking the deeper fault section with high stress drop and then broke a relatively high strength zone after a short time of arrest with highest stress drop

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

evidence of large scale repeating slip during the 2011 tohoku oki earthquake 1 the repetition of slip during rupture process of earthquake is a debate issue which had never been confirmed clearly in the past big events due to the lack of dense near field observations and limited resolution in time of source model the 2011 m9 0 tohoku oki earthquake generated a wealth seismic records which provided us an unprecedented opportunity to study the rupture evolution of giant earthquake at a high spatio temporal resolution here we use teleseismic local strong motion and near field coseismic geodetic data to investigate the source rupture process of this event based on the parallel inversion technique the results reveal a broad slip zone with remarkable large scale repeating slip during the earthquake the inverted source model shows several time periods of energy release with three main peaks these energy bursts and temporal rupture snapshots suggest repetition of a large scale slip on the biggest asperity this rupture behavior resulted in 50 m slips on the slip zone and prolonged the entire rupture process for a long duration of 160 seconds the proposed source model is in a good agreement with the aftershock distribution and can interpret the characteristics of local strong motions further investigations of repeating slip during this event are crucial which will deeply transform earthquake science from dynamic point of view

a unified source model for the 1906 san francisco earthquake abstract we reconcile two previously discordant source models of the 1906 san francisco earthquake and obtain a model that satisfies both triangulation and seismic data by allowing the rupture velocity to exceed the shear wave velocity employing a projection method to remove the dependence on initial station positions allowed us to make use of a more stable triangulation network including nonrepeated angle observations along the northern san andreas fault this strengthens the case for significant slip over the entire northern segment of the san andreas fault from san juan bautista to cape mendocino during the 1906 earthquake we also found that the teleseismic body wave data can be reconciled with the geodetically derived slip model by allowing supershear rupture this resolves a longstanding conflict between the two previous slip models geodetic and seismic of this earthquake supershear rupture has long been recognized as a theoretical possibility for strike slip faulting and it has been observed in several recent large strike slip earthquakes which raises the prospect that it might be typical for such events supershear rupture leads to substantially different strong ground motion and as a result may need to be taken into account when developing ground motion prediction relations for large strike slip earthquakes our final slip model has a seismic moment of 7 9 10 20 n m which corresponds to a moment magnitude of m w 7 9

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

earthquake in a maze compressional rupture branching during the 2012 mw 8 6 sumatra earthquake seismological observations of the 2012 moment magnitude 8 6 sumatra earthquake reveal unprecedented complexity of dynamic rupture the surprisingly large magnitude results from the combination of deep extent high stress drop and rupture of multiple faults back projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system with relatively slow rupture speed the east southeast west northwest ruptures add a new dimension to the seismotectonics of the wharton basin which was previously thought to be controlled by north south strike slip faulting the rupture turned twice into the compressive quadrant against the preferred branching direction predicted by dynamic coulomb stress calculations orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure insensitive strength of the deep oceanic lithosphere

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

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

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

dependency of supershear transition and ground motion on the autocorrelation of initial stress abstract theoretical and observational studies show that earthquakes on strike slip faults can have rupture speeds exceeding the shear wave speed due to the close relationship between the rupture velocity and the radiated wave field it is important to understand the conditions leading to supershear ruptures and their effect on the resulting ground motion we compute dynamic strike slip ruptures in a 3d elastic half space using heterogeneous frictional properties on faults that are 60 km long we use a grid spacing of 60 m allowing us to compute ground motion for frequencies from 0 to 5 hz we analyze the resulting ground motion using isochrones to explain phenomena we observe we model the amplitudes of the initial shear stress as a self similar random field with cauchy distributed amplitudes the wavenumber amplitude spectrum of initial stress decays as a power law with exponent that controls the decay and the spatial correlation of the initial stress the faster the decay corresponding to larger value of the more correlated is the stress on the fault i e the stress field appears spatially smoother the strength on the fault is computed under the assumption of a constant s factor where s is the ratio of strength excess over stress drop on a fault with uniform strength and stress drop the s factor has to be less than a critical value for the supershear transition to occur for models with heterogeneous initial stress we find that both the s factor and the value of the spectral decay constant affect the occurrence of supershear rupture we observe that for a given but small enough s factor a smooth model 2 can run at supershear speed while a rough model 1 will rupture at subshear speeds for the same s factor based on the theory of fracture a non dimensional number was introduced to quantify the condition when a transition to supershear rupture velocity can occur during an earthquake transition will occur when exceeds a critical value we introduce a modified dimensionless parameter ac that is based on the original parameter the parameter ac incorporates a length scale w ac that reflects the degree of the autocorrelation of the stress field we compute ac for a large number of available dynamic ruptures that propagate at subshear and supershear speeds and find i there is a critical value ac c below which all ruptures propagate subshear ii for values larger than ac c there is only a finite probability that the rupture goes supershear i e it is a necessary but not a sufficient condition for the occurrence of supershear rupture propagation

three dimensional finite difference simulation of fault dynamics rectangular faults with fixed rupture velocity we analyze three dimensional finite difference solutions for a simple shear crack model of faulting to determine the effects of fault length and width on the earthquake slip function the fault model is dynamic with only rupture velocity fault dimensions and dynamic stress drop prescribed the numerical solutions are accurate for frequencies up to 5 hz and are combined with asymptotic results for shear cracks in order to characterize the slip function at higher frequencies near the hypocenter the slip velocity exhibits a square root singularity whose intensity increases with hypocentral distance at distances greater than the fault width w growth of the velocity intensity ceases and the slip function becomes nearly invariant with distance along the fault length closed form expressions are developed for the dependence of static slip s slip rise time tr and slip velocity intensity v on fault geometry along the center line of a long narrow fault at hypocentral distances exceeding w these expressions reduce to s w tr 0 5 w vr and v w 2 vr where is the dynamic stress drop the shear modulus and vr the rupture velocity the numerical results imply that uniform dislocation kinematic earthquake models in which slip is represented by a ramp time function will underpredict high frequency ground motion relative to low frequency ground motion a further implication of the numerical solutions is that the nature of inelastic processes at the advancing edge of a long fault will depend on fault width but will be independent of rupture length

source description of the 1999 hector mine california earthquake part ii complexity of slip history we present a rupture model of the hector mine earthquake m 7 1 determined from the joint inversion of strong motion records p and sh teleseismic body waves global positioning system gps displacement vectors and measured surface offset we solve for variable local slip rake angle rise time and rupture velocity of a finite fault model involving multiple segments the inversion methodology developed in a companion article ji et al 2002 combines a wavelet transform approach with a nonlinear simulated annealing algorithm the final model is checked by forward simulating the interferometric synthetic aperture radar insar data our estimation to the seismic moment is 6 28 10 19 n m which is distributed along three segments from north to south releasing 37 41 and 22 of the total moment respectively the average slip is 1 5 m with peak amplitudes as high as 7 m the fault rupture has an average rise time of 3 5 sec and a relatively slow average rupture velocity 1 9 km sec resulting in a 14 sec rupture propagation history our approach permits large variation in rupture velocity and rise time and indicates that rise time appears to be roughly proportional to slip and shorter rise times are associated with the initiation of asperity rupture we also find evidence for nearly simultaneous rupture of the two northern branches