dynamic earthquake rupture modelled with an unstructured 3 d spectral element method applied to the 2011 m9 tohoku earthquake an important goal of computational seismology is to simulate dynamic earthquake rupture and strong ground motion in realistic models that include crustal heterogeneities and complex fault geometries to accomplish this we incorporate dynamic rupture modelling capabilities in a spectral element solver on unstructured meshes the 3 d open source code specfem3d and employ state of the art software for the generation of unstructured meshes of hexahedral elements these tools provide high flexibility in representing fault systems with complex geometries including faults with branches and non planar faults the domain size is extended with progressive mesh coarsening to maintain an accurate resolution of the static field our implementation of dynamic rupture does not affect the parallel scalability of the code we verify our implementation by comparing our results to those of two finite element codes on benchmark problems including branched faults finally we present a preliminary dynamic rupture model of the 2011 m w 9 0 tohoku earthquake including a non planar plate interface with heterogeneous frictional properties and initial stresses our simulation reproduces qualitatively the depth dependent frequency content of the source and the large slip close to the trench observed for this earthquake

dynamically modeling fault step overs using various friction laws it is well known that fault step overs can under some circumstances allow through going rupture and under other circumstances cause rupture to terminate however the effects of different friction law formulations on jumping rupture have not been extensively explored in this study we use the 2 d dynamic finite element method to investigate how different frictional parameterizations affect the ability of rupture to jump a step over in both extensional and compressional settings we compare linear slip weakening friction and three forms of rate and state dependent friction the aging law slip law and slip law with strong rate weakening we have found that for friction parameterizations with the same effective slip weakening distance the functional forms of such friction laws can have a significant effect on maximum jump distance with friction laws scaled to have equivalent fracture energies we find that the functional forms of such friction laws have a second order effect on jumping rupture finally with our specific parameterizations we find that delays in rupture across the step over systems can lead to a previously unseen mode of supershear transition once the rupture renucleates on the secondary fault segment even if the initial stress field precludes such a transition studies using multiple friction laws in complex geometries such as fault step overs can lead to better understanding of the dependence of rupture properties on the type of friction law utilized in models and statistical analysis

a shallow fault zone structure illuminated by trapped waves in the karadere duzce branch of the north anatolian fault western turkey summary we discuss the subsurface structure of the karadere duzce branch of the north anatolian fault based on analysis of a large seismic data set recorded by a local passcal network in the 6 months following the mw 7 4 1999 izmit earthquake seismograms observed at stations located in the immediate vicinity of the rupture zone show motion amplification and long period oscillations in both p and s wave trains that do not exist in nearby off fault stations examination of thousands of waveforms reveals that these characteristics are commonly generated by events that are well outside the fault zone the anomalous features in fault zone seismograms produced by events not necessarily in the fault may be referred to generally as fault zone related site effects the oscillatory shear wave trains after the direct s arrival in these seismograms are analysed as trapped waves propagating in a low velocity fault zone layer the time difference between the s arrival and trapped waves group does not grow systematically with increasing source receiver separation along the fault these observations imply that the trapping of seismic energy in the karadere duzce rupture zone is generated by a shallow fault zone layer traveltime analysis and synthetic waveform modelling indicate that the depth of the trapping structure is approximately 3 4 km the synthetic waveform modelling indicates further that the shallow trapping structure has effective waveguide properties consisting of thickness of the order of 100 m a velocity decrease relative to the surrounding rock of approximately 50 per cent and an s wave quality factor of 10 15 the results are supported by large 2 d and 3 d parameter space studies and are compatible with recent analyses of trapped waves in a number of other faults and rupture zones the inferred shallow trapping structure is likely to be a common structural element of fault zones and may correspond to the top part of a flower type structure the motion amplification associated with fault zone related site effects increases the seismic shaking hazard near fault zone structures the effect may be significant since the volume of sources capable of generating motion amplification in shallow trapping structures is large

en echelon and orthogonal fault ruptures of the 11 april 2012 great intraplate earthquakes the magnitude 8 7 earthquake that occurred off the coast of the sumatra subduction zone on 11 april 2012 is shown to have had an extraordinarily complex four fault rupture these great ruptures represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates on 11 april 2012 two of the largest strike slip earthquakes ever recorded at magnitudes of 8 7 and 8 2 occurred in the northeastern indian ocean a few hundred kilometres off the coast of sumatra three groups now report the analysis of seismic data from the days and months before and after these events as well as the events themselves matthias delescluse and co authors show that these earthquakes are part of the ongoing boost of intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes they conclude that the australian plate driven by slab pull forces at the sunda trench is gradually detaching from the indian plate han yue and colleagues show that the 11 april event involved a complex four fault rupture lasting several minutes followed two hours later by a magnitude 8 2 aftershock these great ruptures on a lattice of strike slip faults that extends through the crust and into the upper mantle represent large lithospheric deformation that may eventually create a localized boundary between the indian and australian plates fred pollitz and colleagues show that in the six days following 11 april the global rate of remote earthquakes with magnitudes greater than 5 5 increased nearly fivefold and events up to magnitude 7 seem to have been triggered the unprecedented delayed triggering power of this earthquake may arise from its strike slip source geometry or because it struck at a time of an unusually low global earthquake rate and increased the number of nucleation sites that were very close to failure the indo australian plate is undergoing distributed internal deformation caused by the lateral transition along its northern boundary from an environment of continental collision to an island arc subduction zone1 2 on 11 april 2012 one of the largest strike slip earthquakes ever recorded seismic moment magnitude mw 8 7 occurred about 100 200 kilometres southwest of the sumatra subduction zone occurrence of great intraplate strike slip faulting located seaward of a subduction zone is unusual it results from northwest southeast compression within the plate caused by the india eurasia continental collision to the northwest together with northeast southwest extension associated with slab pull stresses as the plate underthrusts sumatra to the northeast here we use seismic wave analyses to reveal that the 11 april 2012 event had an extraordinarily complex four fault rupture lasting about 160 seconds and was followed approximately two hours later by a great mw 8 2 aftershock the mainshock rupture initially expanded bilaterally with large slip 20 30 metres on a right lateral strike slip fault trending west northwest to east southeast wnw ese and then bilateral rupture was triggered on an orthogonal left lateral strike slip fault trending north northeast to south southwest nne ssw that crosses the first fault this was followed by westward rupture on a second wnw ese strike slip fault offset about 150 kilometres towards the southwest from the first fault finally rupture was triggered on another en echelon wnw ese fault about 330 kilometres west of the epicentre crossing the ninetyeast ridge the great aftershock with an epicentre located 185 kilometres to the ssw of the mainshock epicentre ruptured bilaterally on a nne ssw fault the complex faulting limits our resolution of the slip distribution these great ruptures on a lattice of strike slip faults that extend through the crust and a further 30 40 kilometres into the upper mantle represent large lithospheric deformation that may eventually lead to a localized boundary between the indian and australian plates

near field deformation from the el mayor cucapah earthquake revealed by differential lidar large moment magnitude m w 7 continental earthquakes often generate complex multifault ruptures linked by enigmatic zones of distributed deformation here we report the collection and results of a high resolution nine returns per square meter airborne light detection and ranging lidar topographic survey of the 2010 m w 7 2 el mayor cucapah earthquake that produced a 120 kilometer long multifault rupture through northernmost baja california mexico this differential lidar survey completely captures an earthquake surface rupture in a sparsely vegetated region with pre earthquake lower resolution 5 meter pixel lidar data the postevent survey reveals numerous surface ruptures including previously undocumented blind faults within thick sediments of the colorado river delta differential elevation changes show distributed kilometer scale bending strains as large as 10 3 microstrains in response to slip along discontinuous faults cutting crystalline bedrock of the sierra cucapah

climate system transition from glacial to interglacial state around the beginning of the last termination evidence from a centennial to millennial scale climate rhythm a periodic variation on a centennial to millennial scale was observed in the manganese and iron contents of lake suigetsu sediments in japan dating from 19 0 to 5 7 cal kyr b p calibrated thousand years before present the increased manganese and iron contents which mainly indicate the relative abundance of siderite result from a greater vertical circulation in the lake during a cold period with a higher mass of manganese and iron oxide being precipitated the cold periods inferred from the increased manganese and iron contents coincide with the timing of ice rafting debris ird events in the north atlantic which span from the last termination to the holocene suggesting that the climate shift was hemispheric or probably global in nature the manganese variation resembles the residual atmospheric 14c production 14c data of the holocene that reflect variation in solar activity and its periodicities correspond with those of solar related climate changes from paleoproxy records in the north atlantic and east asia from the last cold stage to the holocene in particular the mn variation was larger in amplitude and shorter in timescale during the last cold stage when compared with those during the last termination and the holocene thereby possibly showing a significant difference in climate response to solar irradiance the transition of the climate system from a glacial to an interglacial state corresponds to the beginning of the last termination

nucleation of rupture under slip dependent friction law simple models of fault zone the initiation of frictional instability is investigated for simple models of fault zone using a linearized perturbation analysis the fault interface is assumed to obey a linear slip weakening law the fault is initially prestressed uniformly at the sliding threshold in the case of antiplane shear between two homogeneous linearly elastic media space time and spectral solutions are obtained and shown to be consistent the nucleation is characterized by 1 a long wavelength unstable spectrum bounded by a critical wave number 2 an exponential growth of the unstable modes and 3 an induced off fault deformation that remains trapped within a bounded zone in the vicinity of the fault these phenomena are characterized in terms of the elastic parameters of the surrounding medium and a nucleation length that results from the coupling between the frictional interface and the bulk elasticity these results are extended to other geometries within the same formalism and implications for three dimensional rupture are discussed finally internal fault structures are investigated in terms of a fault parallel damaged zone spectral solutions are obtained for both a smooth and a layered distribution of damage for natural faults the nucleation is shown to depend strongly on the existence of a internal damaged layer this nucleation can be described in terms of an effective homogeneous model in all cases frictional trapping of the deformation out of the fault can lead to the property that arbitrarily long wavelengths remain sensitive to the existence of a fault zone

heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults 1 we combine a viscoelastic model for the interseismic process and an elastodynamic model for the coseismic process to explore the dynamics over multiple earthquake cycles of two parallel strike slip faults embedded in a two dimensional full space the step over fault geometry results in a buildup of heterogeneous fault stress near the step over this heterogeneous stress accumulates at the early stage of the evolution of the fault system and finally stabilizes after a number of earthquake cycles the heterogeneity in fault stress varies with the geometrical parameters e g width and along strike overlap gap of the step over as well as the rupture history of the fault system this heterogeneous fault stress from previous earthquakes has significant effects on earthquake rupture initiation propagation and termination the locations with a low normal stress level near a step over are favorable points for earthquake initiation rupture can jump a 4 km wide compressional step over and a 8 km or wider dilational step over if the fault system has historically experienced many earthquakes a young step over with less induced heterogeneity allows rupture to jump only smaller step over widths these results may have important implications for seismic hazard analysis in areas where segmented strikeslip faults predominate particularly for estimating maximum earthquake potential citation duan b and d d oglesby 2006 heterogeneous fault stresses from previous earthquakes and the effect on dynamics of parallel strike slip faults j geophys res 111 b05309 doi 10 1029 2005jb004138

rupture termination and jump on parallel offset faults proper evaluation of seismic hazard depends on accurate estimates of potential earthquake size in areas with complex multisegment fault systems such an estimate in turn depends on an ability to predict the circumstances under which rupture may jump between fault segments many observational and numerical studies have analyzed the phenomenon of jumping rupture but none has focused on how the process of rupture termination on the primary nucleating fault segment affects the ability of rupture to jump to a secondary fault segment in the current study i model the dynamics of a simple 2d strike slip fault system with two parallel segments arranged with either a compressional or extensional stepover i vary the suddenness with which the initial shear stress tapers to zero on the primary section if the initial shear stress goes to zero over a very small 100 m distance rupture readily jumps both compressional and extensional stepovers of 1 km if the initial shear stress tapers to zero over 1 km rupture can jump the compressional stepover but not the extensional stepover if the initial shear stress tapers to zero over 2 5 km rupture cannot jump either the compressional or the extensional stepover the results illustrate the importance of the slip gradient and the resultant static stress field and the acceleration of the rupture front and the resultant generation of stopping phases in determining the probability of jumping rupture

complex multifault rupture during the 2016 mw 7 8 kaikōura earthquake new zealand the 2016 moment magnitude m w 7 8 kaik ura earthquake was one of the largest ever to hit new zealand hamling et al show with a new slip model that it was an incredibly complex event unlike most earthquakes multiple faults ruptured to generate the ground shaking a remarkable 12 faults ruptured overall with the rupture jumping between faults located up to 15 km away from each other the earthquake should motivate rethinking of certain seismic hazard models which do not presently allow for this unusual complex rupture pattern science this issue p eaam7194 1 1 lookup doi 10 1126 science aam7194

superficial simplicity of the 2010 el mayor cucapah earthquake of baja california in mexico the geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation propagation and arrest of seismic ruptures the fault system that runs from southern california into mexico is a simple strike slip boundary the west side of california and mexico moves northwards with respect to the east however the m w 7 2 2010 el mayor cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike slip fault here we use geodetic remote sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake we find that the earthquake produced a straight 120 km long fault trace that cut through the cucapah mountain range and across the colorado river delta however at depth the fault is made up of two different segments connected by a small extensional fault both segments strike n130 e but dip in opposite directions the earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike slip motion we show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves we conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone

dynamic 3d simulations of earthquakes on en echelon faults one of the mysteries of earthquake mechanics is why earthquakes stop this process determines the difference between small and devastating ruptures one possibility is that fault geometry controls earthquake size we test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three dimensional medium and apply our knowledge to two california fault zones we find that the size difference between the 1934 and 1966 parkfield california earthquakes may be the product of a stepover at the southern end of the 1934 earthquake and show how the 1992 landers california earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event if there are no linking structures such as transfer faults then strike slip earthquakes are unlikely to propagate through stepover s 5 km wide

earthquake ruptures modulated by waves in damaged fault zones faults are usually surrounded by damaged zones of lower elastic moduli and seismic wave velocities than their host rocks if the interface between the damaged rocks and host rocks is sharp enough earthquakes happening inside the fault zone generate reflected waves and head waves which can interact with earthquake ruptures and modulate rupture properties such as rupture speed slip rate and rise time we find through 2 d dynamic rupture simulations the following 1 reflected waves can induce multiple slip pulses the rise time of the primary pulse is controlled by fault zone properties rather than by frictional properties 2 head waves can cause oscillations of rupture speed and in a certain range of fault zone widths a permanent transition to supershear rupture with speeds that would be unstable in homogeneous media 3 large attenuation smears the slip rate function and delays the initial acceleration of rupture speed but does not affect significantly the rise time or the period of rupture speed oscillations 4 fault zones cause a rotation of the background stress field and can induce plastic deformations on both extensional and compressional sides of the fault the plastic deformations are accumulated both inside and outside the fault zone which indicates a correlation between fault zone development and repeating ruptures spatially periodic patterns of plastic deformations are formed due to oscillating rupture speed which may leave a permanent signature in the geological record our results indicate that damaged fault zones with sharp boundaries promote multiple slip pulses and supershear ruptures

seismotectonics of the southern apennines and adriatic foreland insights on active regional e w shear zones from analogue modeling 1 the active tectonics at the front of the southern apennines and in the adriatic foreland is characterized by e w striking right lateral seismogenic faults interpreted as reactivated inherited discontinuities the best studied among these is the molise gondola shear zone the interaction of these shear zones with the apennines chain is not yet clear to address this open question we developed a set of scaled analogue experiments aimed at analyzing 1 how dextral strike slip motion along a preexisting zone of weakness within the foreland propagates toward the surface and affects the orogenic wedge 2 the propagation of deformation as a function of displacement and 3 any insights on the active tectonics of southern italy our results stress the primary role played by these inherited structures when reactivated and confirm that regional e w dextral shear zones are a plausible way of explaining the seismotectonic setting of the external areas of the southern apennines

mapping 3d fault geometry in earthquakes using high resolution topography examples from the 2010 el mayor cucapah mexico and 2013 balochistan pakistan earthquakes fault dips are usually measured from outcrops in the field or inferred through geodetic or seismological modeling here we apply the classic structural geology approach of calculating dip from a fault s 3 d surface trace using recent high resolution topography a test study applied to the 2010 el mayor cucapah earthquake shows very good agreement between our results and those previously determined from field measurements to obtain a reliable estimate a fault segment 120 m long with a topographic variation 15 m is suggested we then applied this method to the 2013 balochistan earthquake getting dips similar to previous estimates our dip estimates show a switch from north to south dipping at the southern end of the main trace which appears to be a response to local extension within a stepover we suggest that this previously unidentified geometrical complexity may act as the endpoint of earthquake ruptures for the southern end of the hoshab fault

origin chemical and isotopic evolution of formation water in geopressured zones in the pannonian basin hungary abstract in the central part of the pannonian basin we investigate formation waters from two deep sub basins with sedimentary sequences up to 7000 m thick and from fields above basement highs where the total thickness of the sediments is only 2000 m in each study region the depth interval involves the lower lower part of the upper miocene and upper upper part of the upper miocene and pliocene pannonian sediments separated with a widespread aquitard named the algy formation at the top of the lower pannonian however in the fields above basement highs it occasionally contains sand lenses sedimentological discontinuities faults and fractures resulting in a more conductive character we investigate the sources and evolution of the formation waters in two geological settings in sub basins and in fields above an elevated basement we distinguish nahco3 type water in the sub basins and nacl dominated water in the fields above the elevated basement the isotopic composition of most nahco3 type samples indicates a pure paleometeoric origin while a few samples are a mixture of paleometeoric and non meteoric waters the nacl type samples all have a non meteoric contribution we have developed a model for the origin and evolution of the formation water that operates for both water types and both geological conditions the cl dominated water is a mixture of ascending pre pannonian evaporated water and freshening lake pannon water trapped during the late miocene and pliocene sedimentation in the area above the elevated basement where in some places the algy formation is conductive the source and evolution of the nahco3 non meteoric water in the sub basins are similar to those of the nacl water with the main difference being the aquitard character of the algy formation in the sub basins the aquitard consists of siltstone and clay marl which has resulted in overpressure in the layers under the algy formation the ascending pre pannonian water which mixes with in situ pore water squeezed through the compacted clay by overpressure is exposed to microfiltration the cl remains behind and the squeezed water is depleted of the heavier isotopes these processes are shown by recent chemical and isotopic data 18o and d as well as by archival chemical and hydrological data

critical jump distance for propagating earthquake ruptures across step overs the geometry of a strike slip fault system is an important component that influences the kinematics and interactions of the various faults within the system discontinuities and bends in the fault geometry not only determine the types of structures and the physiography that we observe along the fault system but also have a significant influence on the propagation of earthquake ruptures a precise knowledge of the fault geometry especially how it is segmented and other physical parameters is essential for seismic hazard analysis it is known that earthquake ruptures sometimes propagate over multiple faults by jumping from one segment to the next a fault jump is a sudden dynamic coalescence of two faults separated by a step over field observations suggest that a step over width of 5 km is an appropriate maximum jump distance our study shows that between 2 5 and 6 5 km of step over width the probability of fault jump for both releasing and restraining step overs decreases significantly from 100 to 10

predicting rupture arrests rupture jumps and cascading earthquakes the devastation inflicted by recent earthquakes demonstrates the danger of under predicting the size of earthquakes unfortunately earthquakes may rupture fault sections larger than previously observed making it essential to develop predictive rupture models we present numerical models based on earthquake physics and fault zone data that determine whether a rupture on a segmented fault could cascade and grow into a devastating multisegment earthquake we demonstrate that weakened damaged fault zones and bi material interfaces promote rupture propagation and greatly increase the risk of cascading ruptures and triggered seismicity this result provides a feasible explanation for the outstanding observation of a very large 10 km rupture jump documented in the mw7 8 2001 kunlun china earthquake however enhanced inter seismic deformation and energy dissipation at fault tips suppress rupture propagation and may turn even small discontinuities into effective earthquake barriers by assessing fault stability identifying rupture barriers and foreseeing multisegment earthquakes we provide a tool to improve earthquake prediction and hazard analysis

how much can off fault deformation contribute to the slip rate discrepancy within the eastern california shear zone kinematic assumptions of geodetic inversions for fault slip require that the slip sums to the plate boundary velocity this assumption neglects permanent off fault deformation which could account for discrepancies between geologic and geodetic estimates we use three dimensional mechanical models to assess if unaccounted permanent strain surrounding faults could contribute to slip rate discrepancies across disconnected faults within the mojave desert california usa portion of the eastern california shear zone ecsz we modified fault configurations derived from the southern california earthquake center community fault model to better represent the disconnected nature of active faults in the ecsz south of the garlock fault the models with revised fault geometry produce slip rates that better match geologic strike slip rates thus validating the revisions within these models off fault deformation accounts for 40 23 of the total strain across the ecsz this suggests that a significant portion of the discrepancy between the geologic and geodetically modeled slip rates in the ecsz could be due to the geodetic inversion model assumption of zero permanent off fault deformation

the length to which an earthquake will go to rupture abstract using a database of 22 historical strike slip surface rupture earthquakes an apparent upper limit is observed in the number of steps through which an earthquake is likely to rupture the number of ruptures is also observed to decrease as a function of the number of steps through which the respective earthquakes propagated the observations may be important for assessing the expected length of earthquake ruptures where fault sections interact on mapped fault systems

evidence from coseismic slip gradients for dynamic control on rupture propagation and arrest through stepovers received 30 july 2008 revised 14 november 2008 accepted 18 december 2008 published 27 february 2009 1 analysis of historic slip distributions from large magnitude continental strike slip earthquake ruptures reveals a pronounced correlation between the distance over which slip decreases as a rupture approaches a structural step in the fault and the ability of the rupture to propagate through the step our analysis of coseismic slip gradients near these stepovers indicates that in earthquakes in which slip decreases gradually toward a step rupture will not continue on the next segment conversely in earthquakes in which slip decreases abruptly rupture commonly renucleates on the next segment the fact that ruptures that stopped had low slip gradients near stepovers relative to those that continued indicates that rupture dynamics control the propagation of rupture through stepovers these results corroborate dynamic rupture models that show that ruptures in which slip decreases abruptly at a step generate strong seismic waves that serve to renucleate rupture on the opposite side of the structural step there are several potential causes for gradual decrease of displacement as rupture approaches a stepover including transference of deformation onto subsidiary structures rheological contrasts that could dictate favored rupture propagation directions the existence of stress shadows from previous earthquakes within the system or other material or frictional heterogeneities all of these are potentially observable and if mapped systematically could provide the basis for a strong constraint on the likely end points of future earthquakes inasmuch as earthquake magnitude is strongly dependent on the size of the rupture such predictions would be of great utility as a basic component of scenario based earthquake rupture forecasts

the dynamics of strike slip step overs with linking dip slip faults fault step overs with linking dip slip faults are common features on long strike slip fault systems worldwide it has been noted by various researchers that under some circumstances earthquakes can jump across fault step overs to cascade into large events while under other circumstances rupture is arrested at step overs there is also evidence that fault step overs may be preferential locations for earthquake nucleation the present work uses the 3d finite element method to model the dynamics of strike slip fault systems with step overs and linking dip slip faults i find that the presence of a linking normal or thrust fault greatly increases the ability of earthquake rupture to propagate across the step over leading to a larger event additionally dilational step overs with linking normal faults are more prone to through going rupture than compressional step overs with linking thrust faults this difference is due to the sign of the normal stress increment on the dip slip fault caused by slip on the strike slip segments slip on the strike slip segments causes a negative unclamping normal stress increment on the linking normal fault in a dilational step over whereas the opposite effect occurs on the linking thrust fault in a compressional step over even in cases for which both dilational and compressional step overs can experience through going rupture dilational step overs typically experience higher slip particularly on the linking normal fault in the compressional case rupture nucleation on the linking thrust fault may increase the likelihood of through going rupture compared to nucleation on one of the strike slip segments near the intersections between the fault segments the stress interaction between the fault segments also causes a significant rotation of rake away from that which would be inferred from the regional stress field the results help to emphasize the importance of two way interactions between nearby fault segments during the earthquake rupture process the results also may have implications for the probability of large earthquakes along geometrically complex strike slip fault systems and may help explain why step overs sometimes act as barriers and other times as nucleation locations for large earthquakes

active faulting in apparently stable peninsular india rift inversion and a holocene age great earthquake on the tapti fault we present observations of active faulting within peninsular india far from the surrounding plate boundaries offset alluvial fan surfaces indicate one or more magnitude 7 6 8 4 thrust faulting earthquakes on the tapti fault maharashtra western india during the holocene the high ratio of fault displacement to length on the alluvial fan offsets implies high stress drop faulting as has been observed elsewhere in the peninsula the along strike extent of the fan offsets is similar to the thickness of the seismogenic layer suggesting a roughly equidimensional fault rupture the subsiding footwall of the fault is likely to have been responsible for altering the continental scale drainage pattern in central india and creating the large west flowing catchment of the tapti river a preexisting sedimentary basin in the uplifting hanging wall implies that the tapti fault was active as a normal fault during the mesozoic and has been reactivated as a thrust highlighting the role of preexisting structures in determining the rheology and deformation of the lithosphere the slip sense of faults and earthquakes in india suggests that deformation south of the ganges foreland basin is driven by the compressive force transmitted between india and the tibetan plateau the along strike continuation of faulting to the east of the holocene ruptures we have studied represents a significant seismic hazard in central india

reevaluation of surface rupture parameters and faulting segmentation of the 2001 kunlunshan earthquake mw7 8 northern tibetan plateau china the 14 november 2001 m w 7 8 kunlunshan earthquake ruptured the westernmost part of the kunlun fault northern tibetan plateau the main segment affected by this event was the kusaihu segment field investigations allowed us to constrain the length the width and the coseismic horizontal displacement distribution of the kunlunshan earthquake rupture zone the mapped surface rupture zone starts from 90 257 e in the west and ends at 94 795 e in the east with a total length of 426 km it consists of three main sections the western strike slip section the transtensional section and the eastern strike slip section the rupture zone is oriented n100 10 e on average the distribution of the coseismic horizontal displacements is characterized by multiple peaks departing clearly from a general bell shaped distribution reassessment of the maximum coseismic horizontal left lateral displacement yields a value of 7 6 0 4 m at the site 35 767 n 93 323 e consistent with independent measurements derived from interferometric synthetic aperture radar and seismology from this site the horizontal displacement decreases unevenly to both the west and east coseismic vertical reverse displacement is also noted at the eastern end of the rupture but it remains much smaller than the horizontal component the width of the rupture zone varies from site to site from several meters to few kilometers the maximum width measured reaches 8 km along the yuxi feng subsection where a large number of shaking related cracks were well developed

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

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

fault steps and the dynamic rupture process 2 d numerical simulations of a spontaneously propagating shear fracture fault steps may have controlled the sizes of the 1966 parkfield 1968 borrego mountain 1979 imperial valley 1979 coyote lake and the 1987 superstition hills earthquakes this project investigates the effect of fault steps of various geometries on the dynamic rupture process we have used a finite difference code to simulate spontaneous rupture propagation in two dimensions we employ a slip weakening fracture criterion as the condition for rupture propagation and examine how rupture on one plane initiates rupture on parallel fault planes the geometry of the two parallel fault planes allows for stepover widths of 0 5 to 10 0 km and overlaps of 5 to 5 km our results demonstrate that the spontaneous rupture on the first fault segment continues to propagate onto the second fault segment for a range of geometries for both compressional and dilational fault steps a major difference between the compressional and dilational cases is that a dilational step requires a longer time delay between the rupture front reaching the end of the first fault segment and initiating rupture on the second segment therefore our dynamic study implies that a compressional step will be jumped quickly whereas a dilational step will cause a time delay leading to a lower apparent rupture velocity we also find that the rupture is capable of jumping a wider dilational step than compressional step

the effects of d0 on rupture propagation on fault stepovers abstract according to the slip weakening friction law andrews 1976a fault friction drops from a static value to a sliding value over some slip weakening distance d 0 laboratory studies of fault friction confirm this weakening but do not settle on a single value for d 0 however this parameter is a critical input in dynamic earthquake models as it affects rupture nucleation and propagation we use the 2d finite element method to test how the specific value of d 0 affects rupture behavior we consider the ability of rupture to jump from segment to segment of a disconnected stepover or to propagate through the double bends of a connected stepover as a way to gauge rupture energy and behavior we find the stepover width or bend angle through which rupture can propagate is affected by the choice of d 0 but it is not a linear relationship this is true regardless of whether the stepover is connected or disconnected compressional or extensional or whether the initial rupture velocity is supershear or subshear we do find however that scaling the intensity of the regional stress field up or down does linearly correspond to scaling d 0 down or up we interpret the nonlinearity of the d 0 scaling results to be related to the area of the secondary fault that intersects the lobe of failure level coulomb stress change induced by rupture of the first fault segment because 1 the d 0 controlled critical patch size for renucleation must be exceeded on the second segment and 2 the area of this overlap also does not change linearly with distance from the first fault

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

diversity of fault zone damage and trapping structures in the parkfield section of the san andreas fault from comprehensive analysis of near fault seismograms summary we perform comprehensive analyses of trapped waves and signals of damaged fault zone rocks associated with time delays of body waves along the parkfield section of the san andreas fault saf waveforms generated by thousands of earthquakes and recorded by near fault stations in several permanent and temporary deployments are examined with attention to the possible influence of a lithology contrast across the fault on signals of the low velocity damage zone clear candidate trapped waves are identified at only three stations mmnb and two of the other near fault stations flip and pies further to the nw clear candidate trapped waves are not seen at any of the near fault stations to the se of mmnb the locations of the events generating good candidate trapped waves at mmnb and the other two stations are not distributed broadly in space but clustered in a small number of locations moreover events that generate clear candidate trapped waves at one station do not typically generate trapped waves at the other two stations these observations imply that the damage zone is highly variable along strike and that a coherent connected waveguide does not exist for distances along strike larger than at most 3 5 km the distance between stations synthetic waveform fits for observed trapped waves at stations mmnb and flip indicate that the most likely parameters of the trapping structures at these locations are widths of about 150 m depths of about 3 km velocity reductions of 30 40 per cent and q values of 10 40 synthetic calculations of trapped waves demonstrate that if there is a contrast of seismic velocity across the fault the trapped waves are delayed relative to the s wave arrival trapped waves at station mmnb and to a lesser extent also at stations flip and pies in the nw section show this characteristic this suggests a lithology contrast in the top few km at these locations in agreement with results from tomography and studies of head waves in the parkfield area at several mini across fault arrays where trapped waves are not observed a low velocity damage zone is detected from the delay in the arrival time of body wave phases relative to a nearby off fault station the observed delay of the s wave is greater than the p wave delay consistent with the existence of a damage zone with poisson ratio of about 0 33 the observations of time delays without trapped waves indicate that parts of the damage zone are insufficiently coherent to generate trapped waves a broader damage zone may exist in the region between the saf and the south west fracture zone the results highlight the diversity of damage structures along the 40 km of the saf examined in this study and imply that fault imaging based on data at single sites does not necessarily apply to a larger section

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

on the initiation of sustained slip weakening ruptures by localized stresses numerical simulations of dynamic earthquake rupture require an artificial initiation procedure if they are not integrated in long term earthquake cycle simulations a widely applied procedure involves an overstressed asperity a localized region stressed beyond the static frictional strength the physical properties of the asperity size shape and overstress may significantly impact rupture propagation in particular to induce a sustained rupture the asperity size needs to exceed a critical value although criteria for estimating the critical nucleation size under linear slip weakening friction have been proposed for 2 d and 3 d problems based on simplifying assumptions they do not provide general rules for designing 3 d numerical simulations we conduct a parametric study to estimate parameters of the asperity that minimize numerical artefacts e g changes of rupture shape and speed artificial supershear transition higher slip rate amplitudes we examine the critical size of square circular and elliptical asperities as a function of asperity overstress and background off asperity stress for a given overstress we find that asperity area controls rupture initiation while asperity shape is of lesser importance the critical area obtained from our numerical results contrasts with published theoretical estimates when background stress is low therefore we derive two new theoretical estimates of the critical size under low background stress while also accounting for overstress our numerical results suggest that setting the asperity overstress and area close to their critical values eliminates strong numerical artefacts even when the overstress is large we also find that properly chosen asperity size or overstress may significantly shorten the duration of the initiation overall our results provide guidelines for determining the size of the asperity and overstress to minimize the effects of the forced initiation on the subsequent spontaneous rupture propagation

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

damage in step overs may enable large cascading earthquakes seismic hazard analysis relies on the ability to predict whether an earthquake will terminate at a fault tip or propagate onto adjacent faults cascading into a larger more devastating event while ruptures are expected to arrest at fault discontinuities larger than 4 5 km scientists are often puzzled by much larger rupture jumps here we show that material properties between faults significantly affect the ability to arrest propagating ruptures earthquake simulations accounting for fault step over zones weakened by accumulated damage provide new insights into rupture propagation revealing that lowered rigidity and material interfaces promote rupture propagation our models show for the first time that step overs as wide as 10 km may not constitute effective earthquake barriers our results call for re evaluation of seismic hazard analyses that predict rupture length and earthquake magnitude based on historic records and fault segmentation models

deeper penetration of large earthquakes on seismically quiescent faults why many major strike slip faults known to have had large earthquakes are silent in the interseismic period is a long standing enigma one would expect small earthquakes to occur at least at the bottom of the seismogenic zone where deeper aseismic deformation concentrates loading we suggest that the absence of such concentrated microseismicity indicates deep rupture past the seismogenic zone in previous large earthquakes we support this conclusion with numerical simulations of fault behavior and observations of recent major events our modeling implies that the 1857 fort tejon earthquake on the san andreas fault in southern california penetrated below the seismogenic zone by at least 3 to 5 kilometers our findings suggest that such deeper ruptures may occur on other major fault segments potentially increasing the associated seismic hazard

a possible explanation for difference in stress drop between intraplate and interplate earthquakes 1 it is known from observations that stress drop of intraplate earthquakes is larger than that of interplate earthquakes on average i present a mechanical model for explaining the difference in stress drop where an intraplate fault is assumed to be loaded uniformly while a locked area an asperity on a plate boundary is nonuniformly loaded by surrounding aseismic sliding a numerical simulation is conducted to quantitatively evaluate the difference in stress drop for different loading processes because the model intraplate fault is uniformly loaded stress drop is uniform over the fault with a larger average value in contrast stress concentration is generated at a boundary region between locked area and aseismic sliding area for a model interplate earthquake this stress concentration hastens earthquake occurrence resulting in lower average stress drop the stress drop of simulated intraplate earthquakes is several tens percent larger than that of simulated interplate earthquakes

effect of seismogenic depth and background stress on physical limits of earthquake rupture across fault step overs earthquakes can rupture geometrically complex fault systems by breaching fault step overs quantifying the likelihood of rupture jump across step overs is important to evaluate earthquake hazard and to understand the interactions between dynamic rupture and fault growth processes here we investigate the role of seismogenic depth and background stress on physical limits of earthquake rupture across fault step overs our computational and theoretical study is focused on the canonical case of two parallel strike slip faults with large aspect ratio uniform prestress and friction properties we conduct a systematic set of 3 d dynamic rupture simulations with different seismogenic depth step over distance and initial stresses we find that the maximum step over distance h c that a rupture can jump depends on seismogenic depth w and strength excess to stress drop ratio s commonly used to evaluate probable rupture velocity as h c w s n where n 2 when h c w 1 5 and n 1 otherwise the critical nucleation size largely controlled by frictional properties has a second order effect on h c rupture on the secondary fault is mainly triggered by the stopping phase emanated from the rupture end on the primary fault asymptotic analysis of the peak amplitude of stopping phases sheds light on the mechanical origin of the relations between h c w and s and leads to the scaling regime with n 1 in far field and n 2 in near field the results suggest that strike slip earthquakes on faults with large seismogenic depth or operating at high shear stresses can jump wider step overs than observed so far in continental interplate earthquakes

probabilities for jumping fault segment stepovers 1 seismic hazard analysis relies heavily on the segmentation of faults the ability of ruptures to break multiple segments has a big impact on estimated hazard current practice for estimating multiple segment breakage relies on panels of experts voting on their opinions for each case here we explore the probability of elastodynamic ruptures jumping segment stepovers in numerical simulations of segmented fault systems we find a simple functional form for the probability of jumping a segment stepover as a function of stepover distance an exponential falloff with distance we suggest this simple parameterization of jumping probabilities combined with sparse observational data to fix the lengthscale parameter as a new approach to estimating multisegment earthquake hazard

dynamic shear rupture interactions with fault bends and off axis secondary faulting 1 on the basis of elastodynamic stress fields for singular crack and nonsingular slip weakening models of propagating rupture we develop preliminary answers to such questions as follows if a rupturing fault is intersected by another providing a possible bend in the failure path when will stressing be consistent with rupture along the bend what secondary fault locations and orientations in a damaged region bordering a major fault will be stressed to failure by the main rupture stresses that could initiate rupture on a bend are shown to increase dramatically with crack speed especially near the limiting speed rayleigh for mode ii shear for mode iii whether a bend path once begun can be continued to larger scales depends on principal stress directions and ratios in the prestress field conditions should often be met in mode ii for which bend paths encouraged by stressing very near the rupture tip are discouraged by the larger scale stressing a basis for intermittent rupture propagation and spontaneous arrest secondary failure in the damage zone likewise increases markedly as the limiting speed is approached such may make the fracture energy much greater than for slip on a single surface the extent of secondary faulting is strongly affected by prestress directions and the ratio of residual to peak strength for mode ii prestress controls whether activation occurs primarily on the extensional side which we show to be the typical case or on the compressional side too natural examples are consistent with the concepts developed

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

modeling megathrust earthquakes across scales one way coupling from geodynamics and seismic cycles to dynamic rupture abstract taking the full complexity of subduction zones into account is important for realistic modelling and hazard assessment of subduction zone seismicity and associated tsunamis studying seismicity requires numerical methods that span a large range of spatial and temporal scales we present the first coupled framework that resolves subduction dynamics over millions of years and earthquake dynamics down to fractions of a second using a two dimensional geodynamic seismic cycle sc method we model 4 million years of subduction followed by cycles of spontaneous megathrust events at the initiation of one such sc event we export the self consistent fault and surface geometry fault stress and strength and heterogeneous material properties to a dynamic rupture dr model coupling leads to spontaneous dynamic rupture nucleation propagation and arrest with the same spatial characteristics as in the sc model it also results in a similar material dependent stress drop although dynamic slip is significantly larger the dr event shows a high degree of complexity featuring various rupture styles and speeds precursory phases and fault reactivation compared to a coupled model with homogeneous material properties accounting for realistic lithological contrasts doubles the amount of maximum slip introduces local pulse like rupture episodes and relocates the peak slip from near the downdip limit of the seismogenic zone to the updip limit when an sc splay fault is included in the dr model the rupture prefers the splay over the shallow megathrust although wave reflections do activate the megathrust afterwards

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

pulse like ruptures induced by low velocity fault zones low velocity fault zones lvfzs are found in most mature faults they are usually 100 400 m wide and have 20 60 wave velocity reductions relative to the country rock to study the effect of lvfzs on earthquake rupture and the radiated wavefield we conducted two dimensional 2 d simulations of dynamic rupture on faults that bisect a lvfz considering a range of velocity reductions and widths most earthquakes apparently have slip rise times much shorter than their overall rupture duration a number of dynamic mechanisms for such pulse like ruptures have been proposed including frictional self healing fault strength heterogeneities and bimaterial effects we find that ruptures in lvfzs with strong enough wave velocity contrast behave as pulses these pulses are generated by fault locking induced by waves reflected from the boundaries of the lvfz this mechanism of pulse generation is robust to variations of initial stress smoothness of the lvfz structure rupture mode and exclusion of frictional healing moreover we find that lvfzs can generate complex rupture patterns lvfzs with low velocity reduction induce multiple rupture fronts involving coexisting pulses and cracks lvfzs with certain widths can accelerate the transition to supershear rupture speed these additional effects of lvfzs on dynamic rupture can contribute to the complexity of high frequency ground motions

possible earthquake rupture connections on mapped california faults ranked by calculated coulomb linking stresses probabilistic seismic hazard assessment is requiring an increasingly broad compilation of earthquake sources fault systems are often divided into char acteristic ruptures based on geometric features such as bends or steps though events such as the 2002 m 7 9 denali and 2011 m 9 0 tohoku oki earthquakes raise the possibility that earthquakes can involve subsidiary faults and or rupture through iden tified geometric barriers here we introduce a method to discriminate among a wide range of possible earthquakes within a large fault system and to quantify the prob ability of a rupture passing through a bend or step we note that many of the conditions favoring earthquake rupture propagation can be simulated using a static coulomb stress change approximation such an approach lacks inertial effects inherent in a full dynamic simulation but does capture many of the empirical observations drawn from examining past ruptures such as continuity of rake and strike as well as distance across gaps or stepovers we make calculations for a test region in northern california and find that the method provides a quantitative basis for ranking possible ruptures within localized fault systems

spectral element modeling of spontaneous earthquake rupture on rate and state faults effect of velocity strengthening friction at shallow depths we develop a spectral element methodology sem for simulating dynamic rupture on rate and state faults and use it to study how the rupture is affected by a shallow fault region of steady state velocity strengthening friction our comparison of the developed sem and a spectral boundary integral method bim for an anti plane two dimensional test problem shows that the two methods produce virtually identical solutions for the finest resolution we use and that the convergence with grid reduction of the developed sem methodology is comparable to that of bim we also use the test problem to compare numerical resolution required for different state evolution laws and for linear slip weakening friction using our three dimensional implementation of the methodology we find that a shallow velocity strengthening fault region can significantly alter dynamic rupture and ground motion the velocity strengthening region suppresses supershear propagation at the free surface occurring in the absence of such region which could explain the lack of universally observed supershear rupture near the free surface in addition the velocity strengthening region promotes faster fall off of slip velocity behind the rupture front and decreases final slip throughout the entire fault causing a smaller average stress drop the slip decrease is largest in the shallow parts of the fault resulting in the depth profile of slip qualitatively consistent with observations of shallow co seismic slip deficit the shallow velocity strengthening region also reduces the amplification of strong ground motion due to a low velocity bulk structure

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults