formulation of a fault governing law at high sliding speeds inferences from dynamic rupture models understanding the behavior of natural faults at cosesimic slip velocities v 1 10 m s or more has become a challenging achievement for experimentalists and modelers of earthquake instabilities the rate and state dependent friction laws originally obtained in slow slip rate conditions have been widely adopted in dynamic rupture models by assuming their validity well above the experimental range of observations in this paper we consider a modification at high speeds in which the steady state friction becomes independent of v above a transitional value vt our results show that this modification has dramatic effects on the dynamic propagation as long as vt decreases the breakdown stress drop decreases as well as the slip weakening distance and the fracture energy density moreover we found that the subshear regime is favored as vt decreases we found that for the strength parameter s greater than 1 482 the supershear rupture propagation is inhibited finally we demonstrate that the exponential weakening often observed in laboratory experiments can be theoretically explained in the framework of the rate and state laws

effect of slip weakening distance on selected seismic source parameters of mining induced fault slip abstract fault slip caused by mining activities in underground mines could cause severe damage to nearby mine openings due to seismic waves arising from the fault slip a better understanding of seismic source parameters such as seismically radiated energy and the maximum slip rate is of pivotal importance in estimating the damage induced by the fault slip it is widely recognized that dynamic behaviour of fault slip is largely affected by slip weakening behaviour in the present study the effect of the slip weakening behaviour on selected seismic source parameters of fault slip is investigated using a mine wide numerical model encompassing a fault running parallel to an orebody a linear slip weakening law is employed in a parametrical study with respect to characteristic slip weakening distance d 0 assuming two types of fault slip a zonal fault slip taking place across the fault b local fault slip taking place within limited areas of the fault i e it is assumed that fault slip is arrested by surrounding rockmasses results obtained from the dynamic analysis indicate that seismically radiated energy and slip rates are significantly affected by d 0 for both types of fault slip on the other hand the seismic moment is susceptible to d 0 only for zonal fault slip given that d 0 is smaller than the maximum shear displacement increment during the fault slip these results imply that considering slip weakening distance is critical in estimating seismically radiated energy and slip rates whereas slip weakening behaviour might not have a large influence on seismic moment of local fault slip

ground motion prediction equation for small to moderate events at short hypocentral distances with application to induced seismicity hazards abstract the evaluation of seismic hazard from induced seismicity requires the development of ground motion prediction equations gmpes that are tuned to the key magnitude distance range for such applications i use events of m 3 6 at hypocentral distances less than 40 km drawn from the next generation attenuation west 2 nga west 2 database to develop a gmpe that accounts correctly for point source scaling in both magnitude and distance space for such events the developed gmpe is in demonstrable agreement with the nga west 2 database and with the predictions of a stochastic point source simulation model the database is sparse at close distances implying epistemic uncertainty of as much as a factor of 2 in ground motion amplitudes within 10 km of the hypocenter an important conclusion from this study is that the ground motion amplitudes for moderate induced events could be much larger near the epicenter than predicted by most of the nga west 2 gmpes the potential for large motions is a consequence of the shallow depth of induced events which places the earthquake fault only a short distance beneath the epicenter

earthquake clusters in southern california i identification and stability 1 we use recent results on statistical analysis of seismicity to present a robust method for comprehensive detection and analysis of earthquake clusters the method is based on nearest neighbor distances of events in space time energy domain the method is applied to a 1981 2011 relocated seismicity catalog of southern california having 111 981 events with magnitudes m 2 and corresponding synthetic catalogs produced by the epidemic type aftershock sequence etas model analysis of the etas model demonstrates that the cluster detection results are accurate and stable with respect to 1 three numerical parameters of the method 2 variations of the minimal reported magnitude 3 catalog incompleteness and 4 location errors application of the method to the observed catalog separates the 111 981 examined earthquakes into 41 393 statistically significant clusters comprised of foreshocks mainshocks and aftershocks the results reproduce the essential known statistical properties of earthquake clusters which provide overall support for the proposed technique in addition systematic analysis with our method allows us to detect several new features of seismicity that include 1 existence of a significant population of single event clusters 2 existence of foreshock activity in natural seismicity that exceeds expectation based on the etas model and 3 dependence of all cluster properties except area on the magnitude difference of events from mainshocks but not on their absolute values the classification of detected clusters into several major types generally corresponding to singles burst like and swarm like sequences and correlations between different cluster types and geographic locations is addressed in a companion paper

how does seismic rupture accelerate observational insights from earthquake source time functions observation of the seismic process for a large earthquake population is of key interest to detect potential magnitude dependent behaviors and more generally to quantify how seismic rupture develops in contrast with studies focusing on the first radiated waves we here propose to characterize the growing phase leading to the main seismic moment release episode s which we refer to as the development phase our analysis uses the 2 221 teleseismic source time functions stfs of shallow dip slip earthquakes provided by the global scardec database and consists in measuring the moment acceleration during the development phase at prescribed moment rates this approach is therefore insensitive to hypocentral time uncertainties and aims at quantifying how seismic ruptures accelerate independently of when they accelerate our results first show that rupture acceleration does not exhibit any magnitude dependent signal emerging above the intrinsic measurements variability we thus use the full stf catalog to characterize the moment rate m d of the development phase and show that on average m d t t n d with n d equal to 2 7 this time evolution therefore does not follow the steady t 2 growth expected for classical circular crack models which indicates that stress drop and or rupture velocity transiently vary during the development phase we finally illustrate with a synthetic stf catalog that due to initial rupture variability approaches based on hypocentral time are not expected to fully characterize the behavior of the development phase

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

including foreshocks and aftershocks in time independent probabilistic seismic hazard analyses time independent probabilistic seismic hazard analysis treats each source as being temporally and spatially independent hence foreshocks and aftershocks which are both spatially and temporally dependent on the mainshock are removed from earthquake catalogs yet intuitively these earthquakes should be considered part of the seismic hazard capable of producing damaging ground motions in this study i consider the mainshock and its dependents as a time independent cluster each cluster being temporally and spatially independent from any other the cluster has a recurrence time of the mainshock and by considering the earthquakes in the cluster as a union of events dependent events have an opportunity to contribute to seismic ground motions and hazard based on the methods of the u s geological survey for a high hazard site the inclusion of dependent events causes ground motions that are exceeded at probability levels of engineering interest to increase by about 10 but could be as high as 20 if variations in aftershock productivity can be accounted for reliably

geochemistry and thermodynamics of an earthquake a case study of pseudotachylites within mylonitic granitoid abstract pseudotachylites are melts produced by frictional heating during seismic slip understanding their origin and their influence on slip behavior is critical to understanding the physics of earthquakes to provide insight into this topic we conducted a case study in the proto mylonitic to mylonitic asbestos mountain granitoid in the eastern peninsular ranges batholith california which records both ductile mylonites and brittle deformation features pseudotachylites and ultracataclasites u pb chronology and zr thermometry of titanite porphyroblasts in the mylonites indicate that mylonitization of the plutons occurred at near solidus conditions 750 c over a 10 ma interval from 89 to 78 ma mylonitization resulted in recrystallization of quartz plagioclase and biotite with the biotite concentrated into biotite rich foliation planes subsequent brittle deformation is superimposed on the ductile fabrics micro xrf elemental mapping and in situ la icp ms analyses on these brittle deformation products show that the pseudotachylites are more mafic lower si but higher fe and k rich than the host mylonite while the ultracataclasites are intermediate between the host and the pseudotachylites inverse mass balance calculations show that both brittle deformation products are depleted in quartz but enriched in biotite with the pseudotachylites showing the most significant enrichment in biotite indicating preferential involvement of biotite during brittle deformation we suggest that biotite rich layers generated during ductile deformation may have been the preferred locus of subsequent brittle deformation presumably because such layers represent zones of weakness frictional heating associated with slip along such planes results in melting which causes a decrease in viscosity in turn leading to further strain localization during the short time span of an earthquake frictional melting appears to be a disequilibrium process in which the minerals are melted in order of their melting points from biotite 800 c to plagioclase 1400 c and finally to quartz 1700 c rather than by equilibrium melting which results in silicic eutectoid melts at lower temperatures 650 c thus with progressive slip melt composition should evolve from mafic to felsic eventually approaching the bulk composition of the host rock the mafic composition of the pseudotachylites thus indicates that they formed between the melting point of biotite and plagioclase 800 1400 c our chemical and modeling analyses on the pseudotachylites suggest that the chemical composition of pseudotachylites can potentially be used to constrain the thermodynamic conditions in the shear zone as well as earthquake source mechanics

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

correlation of earthquake source parameters inferred from dynamic rupture simulations 1 we analyzed 315 dynamic strike slip rupture models computed up to 5 0 hz to get a quantitative understanding of the correlation and amplitude distributions of parameters describing the earthquake source such as slip and rupture velocity to account for the epistemic uncertainty of the problem we constructed a database of dynamic ruptures computed by ourselves and other authors this database contains ruptures computed using different models of initial stress peak stress and critical slip weakening distance using the set of computed ruptures we constructed probability density functions pdfs for the amplitude distributions of the source parameters and for the correlation between the source parameters we tried to extract parameter pairs that showed a small variability in the spatial correlation given the large epistemic uncertainty in the input we only analyzed the areas on the fault with subshear propagation speed the principal findings are as follows 1 final slip amplitude does not show correlation with the local rupture velocity 2 final slip amplitude correlates well with risetime 3 rupture velocity correlates well with peak slip rate and the duration of the impulsive part of the slip rate function 4 the pdf of rupture velocity risetime and peak slip rate depends on the distance from the nucleation zone 5 fracture energy is not the single controlling factor for the rupture velocity the slope of the linear slip weakening curve has a significant effect on the rupture velocity 6 the crack length length that is slipping at a given time decreases with the distance from the nucleation zone

on the deterministic description of earthquakes 1 the quantitative estimate of earthquake damage due to ground shaking is of pivotal importance in geosciences and its knowledge should hopefully lead to the formulation of improved strategies for seismic hazard assessment numerical models of the processes occurring during seismogenic faulting represent a powerful tool to explore realistic scenarios that are often far from being fully reproduced in laboratory experiments because of intrinsic technical limitations in this paper we discuss the prominent role of the fault governing model which describes the behavior of the fault traction during a dynamic slip failure and accounts for the different and potentially competing chemical and physical dissipative mechanisms we show in a comprehensive sketch the large number of constitutive models adopted in dynamic modeling of seismic events and we emphasize their prominent features limitations and specific advantages in a quantitative comparison we show through numerical simulations that spontaneous dynamic ruptures obeying the idealized linear slip weakening sw equation and a more elaborated rate and state dependent friction law produce very similar results in terms of rupture times peaks slip velocity developed slip and stress drops provided that the frictional parameters are adequately comparable and more importantly that the fracture energy density is the same our numerical experiments also illustrate that the different models predict fault slip velocity time histories characterized by a similar frequency content a feeble predominance of high frequencies in the sw case emerges in the frequency ranges 0 3 1 and 11 50 hz these simulations clearly indicate that even forgiving the frequency band limitation it would be very difficult virtually impossible to discriminate between two different but energetically identical constitutive models on the basis of the seismograms recorded after a natural earthquake

dynamic modelling of induced seismicity by using seismic efficiency constraints and a new scaling law for slip weakening distance in the numerical simulation of induced seismicity much attention is generally paid to the calibration of the frictional resistance of the causative fault to obtain a seismic moment consistent with that of the actual event whereas sufficient investigation is not made in the estimation of the slip weakening distance dc as well as in the calibration of seismically radiated energy the present study addresses this problem by numerically and analytically investigating the relation between dc and seismic source parameters first this study performs the dynamic simulation of an induced seismic event caused by a decrease in the effective normal stress the analysis demonstrated that seismic efficiency can be used to improve the accuracy of estimating the critical slip weakening distance and the coefficient of kinetic friction d whilst considering not only seismic moment but also radiated energy in the calibration this gave insight into the development of the new calibration method for induced seismicity that considers energy related seismic source parameters furthermore a new scaling law of the slip weakening distance was derived from the theoretical expression of seismic efficiency considering seismic moment mo and scaled energy hat e the proposed scaling law can yield the relation between dc and mo which is shown to be similar to that obtained from a previous study but additionally considers the relation between seismically radiated energy and dc the dependency of dc on seismically radiated energy implied from the proposed scaling law has been verified from the dynamic analyses where 0 06 was used to place a constraint on dc for seismic events with different magnitudes the developed numerical simulation methodology of induced seismicity as well as the scaling law considering the energy indices significantly contributes to improving the accuracy of back analysis thus leading to a more accurate estimation of the mechanical properties of faults and or shear zones in seismically active regions of deep underground mines or reservoirs composed of discontinuous hard rock masses

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

using the etas model for catalog declustering and seismic background assessment the concept of background seismicity is strictly related to the identification of spontaneous and triggered earthquakes the definition of foreshocks main shocks and aftershocks is currently based on procedures depending on parameters whose values are notoriously assumed by subjective criteria we propose a method for recognizing the background and the induced seismicity statistically rather than using a binary distinction of the events in these two categories we prefer to assign to each of them a probability of being independent or triggered this probability comes from an algorithm based on the etas model a certain degree of subjectivity is still present in this procedure but it is limited by the possibility of adjusting the free parameters of the algorithm by rigorous statistical criteria such as maximum likelihood we applied the method to the seismicity of southern california and analyzed the sensitivity of the results to the free parameters in the algorithm finally we show how our statistical declustering algorithm may be used for mapping the background seismicity or the moment rate in a seismic area

source properties of dynamic rupture pulses with off fault plasticity large dynamic stresses near earthquake rupture fronts may induce an inelastic response of the surrounding materials leading to increased energy absorption that may affect dynamic rupture we systematically investigate the effects of off fault plastic energy dissipation in 2 d in plane dynamic rupture simulations under velocity and state dependent friction with severe weakening at high slip velocity we find that plasticity does not alter the nature of the transitions between different rupture styles decaying versus growing pulse like versus crack like and subshear versus supershear ruptures but increases their required background stress and nucleation size we systematically quantify the effect of amplitude and orientation of background shear stresses on the asymptotic properties of self similar pulse like ruptures peak slip rate rupture speed healing front speed slip gradient and the relative contribution of plastic strain to seismic moment peak slip velocity and rupture speed remain bounded from fracture mechanics arguments we derive a nonlinear relation between their limiting values appropriate also for crack like and supershear ruptures at low background stress plasticity turns self similar pulses into steady state pulses for which plastic strain contributes significantly to the seismic moment we find that the closeness to failure of the background stress state is an adequate predictor of rupture speed for relatively slow events our proposed relations between state of stress and earthquake source properties in the presence of off fault plasticity may contribute to the improved interpretation of earthquake observations and to pseudodynamic source modeling for ground motion prediction

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

mechanics of 3 d shear cracks between rayleigh and shear wave rupture speeds abstract though mode ii shear fractures primarily strike slip earthquakes can not only exceed the shear wave speed of the medium but can even reach the compressional wave speed steady state calculations showed that speeds between the rayleigh and shear wave speeds were not possible thus defining a forbidden zone for more than 30 years it was believed that this result in which the rupture jumps over the forbidden zone also holds for 3 d ruptures in which mode ii and mode iii mainly dip slip faulting are mixed using unprecedentedly fine spatial and temporal grids we show that even in the simple configuration of homogeneous fault properties and linear slip weakening friction law a realistic 3 d rupture which starts from rest and accelerates to some higher velocity actually does pass smoothly through this forbidden zone but very fast the energy flux from the rupture tip is always positive even within the so called forbidden zone contrary to the 2 d case finally our results show that the width of the cohesive zone initially decreases then increases as the rupture exceeds the shear wave speed and finally again decreases as the rupture accelerates to a speed of 90 of the compressional wave speed

seismicity declustering and hazard analysis of the oklahoma kansas regionseismicity declustering and hazard analysis of the oklahoma kansas region

jet flow over foredunes jet flows which are localized flows exhibiting a high speed maxima are relatively common in nature and in many devices they have only been occasionally observed on dunes and their dynamics are poorly known this paper examines computational fluid dynamic cfd two dimensional 2d modelling of jet flow over a foredune topography flow was simulated in 10 increments from onshore 0 to highly oblique alongshore 70 incident wind approach angles cfd modelling reveals that the formation of a jet is not dependent on a critical wind speed and an increase in incident wind velocity does not affect the magnitude of jet flow a jet is first formed at 1 0m seawards of the foredune crest on the prince edward island foredune morphology example examined here a jet is not developed when the incident wind is from an oblique approach angle greater than 50 because there is significantly less flow acceleration across a much lower slope at this incident angle the presence of a scarp does influence the structure of the crest jet in that the jet is more pronounced where a scarp is present surface roughness affects the magnitude of jet expansion and jets are better developed on bare surfaces compared to vegetated ones

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

single link cluster analysis of earthquake aftershocks decay laws and regional variations using single link cluster analysis the authors investigate how various properties of aftershock sequences depend on their tectonic regime and focal depth for international seismological centre earthquakes of m sub b ge 4 8 they find that earthquakes deeper than 70 km have the fewest and smallest aftershock sequences even after accounting for differences in detectability and maximum magnitude they find that ridge transform earthquakes have smaller aftershock sequences that shallow subduction zone earthquakes among different subduction zones they find that zones with high moment release rates possess larger aftershock sequences comparing ridge transform zones they find those with slower spreading rates possess larger aftershock sequences by transposing origin times of several different aftershock sequences as if all had main shocks occurring at time zero they are able to study the properties of aftershock sequences which individually have too few aftershocks to study by other means secondary events determined by single link cluster analysis follow a modified omori s power law decay for time separations of 0 1 day to 20 days from the parent event with p values ranging from 0 539 plus minus 0 022 intermediate and deep focus earthquakes to 0 928 plus minus 0 024 ridge transform earthquakes they find that earthquake foreshocks and multiplets also follow a modified omori s law atmore greater times from the main shock the decay is steeper than a power law decay more like an exponential decay aftershocks in the adak catalog m sub b ge 2 0 show a marked decrease in activity between 40 and 50 km depth they speculate that the observed differences in number of aftershocks and p values may be caused by variations in fault heterogeneity or in fluid pressures less

dynamic seismic ruptures on melting fault zones 1 we present a physical model that describes the behavior of spontaneous earthquake ruptures dynamically propagating on a fault zone and that accounts for the presence of frictional melt produced by the sliding surfaces first we analytically derive the solution for the temperature evolution inside the melt layer which generalizes previous approximations then we incorporate such a solution into a numerical code for the solution of the elastodynamic problem when a melt layer is formed the linear slip weakening law initially governing the fault and relying on the coulomb friction is no longer valid therefore we introduce on the fault a linearly viscous rheology with a temperature dependent dynamic viscosity we explore through numerical simulations the resulting behavior of the traction evolution in the cohesive zone before and after the transition from coulomb friction and viscous rheology the predictions of our model are in general agreement with the data from exhumed faults we also find that the fault after undergoing the breakdown stress drop controlled by the slip weakening constitutive equation experiences a second traction drop controlled by the exponential weakening of fault resistance due to the viscous rheology this further drop enhances the instability of the fault increasing the rupture speeds the peaks in fault slip velocity and the fracture energy density

rupture speed and slip velocity what can we learn from simulated earthquakes abstract in this paper we consider a wide catalog of synthetic earthquakes numerically modeled as spontaneous fully dynamic 3 d ruptures on extended faults governed by different friction laws including slip dependent and rate and state dependent equations we analyze the spatial correlations between the peak of fault slip velocity vpeak and the rupture speed vr at which the earthquake spreads over the fault we found that vpeak positively correlates with vr and that the increase of vpeak is roughly quadratic we found that near the transition between sub and supershear regimes vpeak significantly diminishes and then starts to increase again with the square of vr this holds for all the governing models we consider and for both homogeneous and heterogeneous configurations moreover we found that on average vpeak increases with the magnitude of the event vpeak m00 18 our results can be incorporated as constraints in the inverse modeling of faults

an efficient mechanism to avert frictional melts during seismic ruptures abstract we consider the spatio temporal evolution of temperature due to frictional heating caused by the spontaneous propagation of 3 d dynamic seismic ruptures on planar faults in our numerical experiments which characterize typical crustal earthquakes we assume that fault friction is controlled by different linear and nonlinear slip dependent friction laws in this paper we confirm that a necessary condition to prevent melting is to have a nearly complete breakdown stress drop our simulations which employ a nonlinear slip dependent governing equation recently inferred from laboratory experiments by sone and shimamoto 2009 reproduce such a dramatic fault weakening and represent a plausible explanation for the prevention of melting during earthquake ruptures we also demonstrate that low friction alone although necessary is not a sufficient condition to avert melts the linear or classical slip weakening sw law would produce melting even assuming the same lengthscales and frictional levels to avoid melting with linear sw law we have to impose a specific value of the sw distance this reveals the prominent role of the time evolution of traction within the cohesive zone where the stress release is realized and of the value of the fracture energy density

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

near source ground motion along strike slip faults insights into magnitude saturation of pgv and pga empirical data suggest that peak ground acceleration pga and peak ground velocity pgv saturate as a function of magnitude for large magnitude ruptures close to the fault because data are sparse in the near source region of large magnitude events we have explored this question by simulating large magnitude strike slip earthquakes we use kinematic simulations to generate ground motion for a strike slip fault that has a large aspect ratio length width we consider both homogeneous or heterogeneous rupture models we find that close to the fault along strike profiles of pgv and pga increase to a maximum at a certain epicentral distance and then decrease to an asymptotic level beyond this distance critical factors for predicting ground motion are the position of an observer along strike the depth of the hypocenter below the top of the fault and the ratio of rupture velocity to shear wave velocity to understand the cause of the amplitude variation of along strike profiles of pgv and pga we use the isochrone method and the concept of the critical point to investigate how the geometry and kinematic parameters interact to produce the computed ground motion we construct a predictor based on the critical point that does well in predicting the position of the maximum of pgv and pga for stations close to the fault for heterogeneous rupture models we find that the behavior is more complex though the general observation that along strike profiles of pgv and pga increase to a maximum and then decrease still holds this has implications for empirical attenuation relationships that essentially average the ground motion for all stations along strike with the same distance to the fault

off fault damage patterns due to supershear ruptures with application to the 2001 mw 8 1 kokoxili kunlun tibet earthquake 1 we extend a model of a two dimensional self healing slip pulse propagating dynamically in steady state with slip weakening failure criterion to the supershear regime in order to study the off fault stressing induced by such a slip pulse and investigate features unique to the supershear range specifically we show that there exists a nonattenuating stress field behind the mach front that radiates high stresses arbitrarily far from the fault practically this would be limited to distances comparable to the depth of the seismogenic zone thus being capable of creating fresh damage or inducing coulomb failure in known structures at large distances away from the main fault we allow for both strike slip and dip slip failure induced by such a slip pulse we show that off fault damage is controlled by the speed of the slip pulse scaled stress drop and principal stress orientation of the prestress field we apply this model to study damage features induced during the 2001 kokoxili kunlun event in tibet for which it has been suggested that much of the rupture was supershear we argue that an interval of simultaneous induced normal faulting is more likely due to a slip partitioning mechanism suggested previously than to the special features of supershear rupture however those features do provide an explanation for otherwise anomalous ground cracking at several kilometers from the main fault we also make some estimates of fracture energy which for a given net slip and dynamic stress drop is lower than for a sub rayleigh slip pulse because part of the energy fed by the far field stress is radiated back along the mach fronts

dynamic behaviour of mining induced fault slip abstract fault slip bursts induced by mining activities could inflict severe damage to nearby mine developments considering a variety of factors that might exert an influence on the fault slip dynamic numerical analyses are conducted for models having a fault parallel to a tabular ore deposit the results obtained from the analyses show that the maximum dynamic shear displacement increment induced by stope extraction is significantly affected by the friction angle of the fault as well as mining depth and position of fault with respect to the orebody while the stiffness and the dilation angle of the fault do not have as much influence seismic source parameters are computed based on the numerical results and as is the case with the maximum relative shear displacements the position and friction angle of the fault appear to have the strongest influence on seismic moment and energy released by fault slip the limitations of mohr coulomb criterion as applied to the dynamic analysis of fault slip bursts are discussed in light of the results obtained lastly slip rates and rupture velocity are investigated the results show that the maximum slip rates are associated with the maximum increments of relative dynamic shear displacement it is shown that extremely high rupture velocity could be induced by stope extraction this could be the cause for a severe seismic event

single link cluster analysis as a method to evaluate spatial and temporal properties of earthquake catalogues summary single link cluster analysis is a straightforward method to quantitatively measure the degree of clustering or isolation of groups of elements in a set such as a catalogue of earthquakes to apply single link cluster analysis to a set of n earthquakes individual earthquakes are first linked to their nearest neighbours to form event sub groups the process is then repeated and each sub group linked to its nearest neighbour recursively until n 1 links are found to join all the earthquakes this paper shows how knowledge of these links can be used to divide a group of earthquakes into any number of spatial clusters with various modifications this analysis can identify earthquake nests isolated events aftershock sequences and zones of seismic quiescence to illustrate this method we apply it to i a global data set of 2178 earthquakes having mb of 5 8 or greater reported by the international seismological centre isc between 1964 and february 1986 and ii sets of earthquakes having mb of 4 9 and greater as reported by the isc occurring in central america and in the aleutians to facilitate comparison with real data this study also investigates the distribution of link lengths for synthetic events placed randomly on 1 d circular line 2 d circular area and 3 d spherical volume geometries if we remove links between nuclear explosions from the isc data the resulting link distribution is quite similar to that for synthetic events placed along a 1 d fault for the shortest links the similarity improves markedly if the synthetic fault has a finite width or if relative location errors cause events to be located away from the fault trace with a standard deviation of about 15 km

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

accounting for fault roughness in pseudo dynamic ground motion simulations geological faults comprise large scale segmentation and small scale roughness these multi scale geometrical complexities determine the dynamics of the earthquake rupture process and therefore affect the radiated seismic wavefield in this study we examine how different parameterizations of fault roughness lead to variability in the rupture evolution and the resulting near fault ground motions rupture incoherence naturally induced by fault roughness generates high frequency radiation that follows an 2 decay in displacement amplitude spectra because dynamic rupture simulations are computationally expensive we test several kinematic source approximations designed to emulate the observed dynamic behavior when simplifying the rough fault geometry we find that perturbations in local moment tensor orientation are important while perturbations in local source location are not thus a planar fault can be assumed if the local strike dip and rake are maintained we observe that dynamic rake angle variations are anti correlated with the local dip angles testing two parameterizations of dynamically consistent yoffe type source time function we show that the seismic wavefield of the approximated kinematic ruptures well reproduces the radiated seismic waves of the complete dynamic source process this finding opens a new avenue for an improved pseudo dynamic source characterization that captures the effects of fault roughness on earthquake rupture evolution by including also the correlations between kinematic source parameters we outline a new pseudo dynamic rupture modeling approach for broadband ground motion simulation