regional moment tensor inversion for strong aftershocks of the august 17 1999 izmit earthquake mw 7 4 we analyzed the source mechanisms of the thirty largest aftershocks 4 0 ml 6 2 of the august 17 1999 izmit earthquake mw 7 4 by applying the regional moment tensor inversion method using data from near regional broadband stations the inversion solutions were compared to 17 well constrained first motion solutions and were seen to be in good agreement we found that the dominance of strike slip motion is the main characteristic of the izmit earthquake sequence significant aftershock activity was recorded to the west and east of the un ruptured extremities in the east the aftershocks located near the town of duzce represent an early replica of the november 12 1999 duzce earthquake mw 7 2 in terms of locations and source mechanisms in the marmara sea where the fault geometry is still very poorly resolved most aftershocks have right lateral strike slip solutions with strike direction parallel to the submerged branches of the north anatolian fault

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

effect of fault rupture characteristics on near fault strong ground motions the effect of fault rupture characteristics on near fault strong ground motions is investigated using a kinematic modeling approach in an attempt to identify physical processes that lead to specific ground motion patterns the shear stress distribution on the causative fault plane of four well documented seismic events i e 1979 imperial valley 1985 michoacan 1989 loma prieta and 1999 izmit is calculated based on fault slip models available in the literature using the methodology proposed by bouchon 1997 for stress field computations in order to associate the fault rupture characteristics i e slip rupture velocity state of stress of the investigated earthquakes with near fault ground motions generated by the events forward ground motion simulations are performed using the discrete wavenumber representation method and the concept of the s wave isochrones is exploited the results indicate that the seismic energy radiated from the high isochrone velocity region of the fault arrives at the receiver within a time interval that coincides with the time window of the long period ground motion pulse recorded at the site furthermore the near fault ground motion pulses are strongly correlated with large slip on the fault plane locally driven by high stress drop in addition the local rupture velocity seems to be inversely correlated to the spatial distribution of the strength excess over the fault plane confirming findings of previous studies for various events the area of the fault that contributes to the formation of the near fault pulse encompasses more than one patch of significant moment release subevent e g 1979 imperial valley 1989 loma prieta this observation explains why a dislocation model with average properties i e slip rise time etc reproduces successfully near fault ground motions for strike slip faults and for dip slip faults with intermediate to large earthquake magnitudes aki 1979 however for very large earthquakes such as megathrust events on subduction zones e g 1985 michoacan the fault region that contributes to the pulse formation encompasses individual subevents and consequently cracklike slip functions rather than dislocation models may be more appropriate for the simulation of the near fault ground motions

seismic velocity models for the denali fault zone along the richardson highway alaska crustal scale seismic velocity models across the denali fault zone along the richardson highway show a 50 km thick crust a near vertical fault trace and a 5 km wide damage zone associated with the fault near trans alaska pipeline pump station 10 which provided the closest strong ground motion recordings of the 2002 denali fault earthquake we compare models derived from seismic reflection and refraction surveys acquired in 1986 and 1987 to laboratory measurements of seismic velocities for typical metamorphic rocks exposed along the profiles our model for the 1986 seismic reflection profile indicates a 5 km wide low velocity zone in the upper 1 km of the denali fault zone which we interpret as fault gouge deeper refractions from our 1987 line image a 40 km wide 5 km deep low velocity zone along the denali fault and nearby associated fault strands which we attribute to a composite damage zone along several strands of the denali fault zone and to the obliquity of the seismic line to the fault zone our velocity model and other geophysical data indicate a nearly vertical denali fault zone to a depth of 30 km aftershocks of the 2002 denali fault earthquake and our velocity model provide evidence for a flower structure along the fault zone consisting of faults dipping toward and truncated by the denali fault wide angle reflections indicate that the crustal thickness beneath the denali fault is transitional between the 60 km thick crust beneath the alaska range to the south and the extended 30 km thick crust of the yukon tanana terrane to the north online material tables of locations for the tact 1986 and tact 1987 lines

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

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

the seismicity in the eastern marmara sea after the 17 august 1999 izmit earthquake we used seismic stations that we deployed after the izmit earthquake along the shores and islands of the izmit bay cinarcik basin to study the seismic activity that took place after the earthquake in the eastern marmara sea the aftershock distribution indicates the existence of three clusters of activity there in the days that followed the earthquake one of the clusters shows the extension of the e w trending izmit rupture into the eastern marmara sea the seismic activity there clearly outlines the fault plane of the main rupture and shows its termination 35 km beyond the hersek peninsula two other clusters of activity are present in the region one is in the armutlu peninsula and the other one is located a few kilometers southwest of the tuzla peninsula beneath the northern slope of the cinarcik basin the focal mechanism solutions indicate strike slip faulting along the main branch of the izmit rupture and normal faulting within the two swarms the presence of the different mechanisms suggests the existence of slip partitioning in the region a remarkable feature of the aftershock data is the absence of seismicity above 4 km in the marmara sea manuscript received 30 august 2000

aftershocks of the 2012 off coast of sumatra earthquake sequence abstract aftershocks of the 2012 off coast of sumatra earthquake sequence exhibit a complex and diffuse spatial distribution the first order complexity in aftershock distribution is clear and well beyond the influence of typical earthquake location uncertainty the sequence included rupture of multiple fault segments spatially separated we use surface wave based relative centroid locations to examine whether at the small scale the distribution of the aftershocks was influenced by location errors surface wave based relative location has delineated precise oceanic transform fault earthquake locations in multiple regions however the relocated aftershocks off the coast of sumatra seldom align along simple linear trends that are compatible with the corresponding fault strikes as estimated for the gcmt catalog the relocation of roughly 60 moderate earthquake epicentroids suggests that the faulting involved in the 2012 earthquake aftershock sequence included strain release along many short fault segments statistical analysis and temporal variations of aftershocks show a typical decay of the aftershocks but a relatively low number of aftershocks as is common for intraplate oceanic earthquakes coulomb stress calculations indicate that most of the moderate magnitude aftershocks are compatible with stress changes predicted by the large event slip models the patterns in the aftershocks suggest that the formation of the boundary and eventual localization of deformation between the indian and australian plate is a complicated process

distribution of seismic velocities and attenuation in the crust beneath the north anatolian fault turkey from local earthquake tomography we investigate the crustal structure beneath the western part of the north anatolian fault zone nafz an area where at least five damaging earthquakes occurred during the twentieth century this study is based on local earthquake tomography using the data from aftershocks of the izmit event 17 august 1999 m 7 4 recorded by stations of permanent and temporary networks we derive the distribution of v p v s and the v p v s ratio based on the iterative inversion for both v p v s and v p v p v s using the lotos code innovatively in this study we perform an inversion for frequency dependent s wave attenuation 1 q s the reliability of the results is assessed through synthetic tests the distributions of the resulting seismic parameters v p v s v p v s and q s highlight important geodynamical features in the study area the low velocity and high attenuation patterns mostly correlate with the fracturing zones of the nafz low velocities are also observed beneath the main sedimentary basins e g adapazari duzce and kuzuluk high velocity and low attenuation patterns correlate with blocks presumed to be rigid kocaeli armutlu and almacik blocks the rupture traces of the largest earthquakes in this area pass generally in the transition areas between high and low velocities while moderate and weak seismicity is mostly concentrated in low velocity areas based on these results we propose and discuss the role that the almacik block could have played in producing the largest earthquakes in the study area in the twentieth century

imaging supershear rupture for the 2014 mw 6 9 northern aegean earthquake by backprojection of strong motion waveforms the seismic source spatiotemporal evolution of the mw 6 9 event on 24 may 2014 in northern aegean is imaged by backprojection of strong motion envelopes the results indicate that the event ruptured on two different fault segments in the first one rupture propagated from the hypocenter westward for 20 km in the second delayed segment to the east rupture propagated eastward for 65 km with a supershear velocity 5 5 km s at the end of this rupture the largest stacking amplitudes are imaged associated with possible stopping phases from the abrupt cessation of a fast slip low aftershock seismicity on the supershear segment implies a simple and linear fault geometry there this is the third large event in the northern aegean trough northern anatolian fault zones that has ruptured with supershear speed this characteristic should be taken into account in studying past events and estimating seismic hazard in this area

evolution of the seismicity in the eastern marmara sea a decade before and after the 17 august 1999 izmit earthquake we review the long term evolution of seismicity in the eastern marmara sea over a decade before and after the 1999 mw 7 6 izmit earthquake we analyze large scale space time variations of seismicity in the region and illustrate the impact of the recent large strike slip earthquakes on the background activity composed of distinct pre existing seismic clusters two types of aftershocks activity are observed the first type of enhancement is on strike slip fault segments izmit fault princes island section of the main marmara fault gemlik fault immediately following the main shock and related to coulomb stress transfer the second type of enhancement is attached to extensional clusters yalova tuzla with a few days delay in the onset of strong activation probably related to pore pressure increase we observe a fast decay of the activity on strike slip segments and slower evolution of seismic clusters with extensional features two years after the izmit earthquake seismic activity returned to the pre earthquake pattern with most of the activity occurring within extensional clusters it appears that the influence of the last large strike slip event on the spatial seismicity distribution in the eastern marmara sea is less significant than the effect of the long term regional extension

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

statistical analysis of the 2002 mw 7 9 denali earthquake aftershock sequence we study the scaling properties of the aftershock sequence of the 2002 m w 7 9 denali earthquake the sequence exhibits nontrivial scaling behavior in magnitude aftershock decay rates and aftershock inter occurrence times in particular we observe a marked variability in the gutenberg richter gr exponent the b value in space between early and late times after the mainshock and over different magnitude ranges we find strong indications that certain aspects of this variability might be ascribed to the occurrence of some of the aftershocks on and around a supershear rupture associated with this event particularly we observe a statistically higher b value for the aftershocks that occurred in the zone surrounding the supershear rupture we further outline a method to obtain an average b value consistent with the theory and statistical properties of the data we find a significant difference between the magnitude of the largest aftershock and the mainshock this is analyzed and discussed using the modified bath s law it is observed that the aftershock decay rate can be approximated by the modified omori law the distribution of inter occurrence times is studied and we show that it can be explained in terms of a nonhomogeneous poisson process through time we further observe that the rescaled inter occurrence time distributions for various magnitude thresholds collapse into a universal functional form which indicates that the aftershock sequence exhibits self similarity in both magnitude and time in particular the statistical features of the aftershock sequence show that the rupture process or the preconditions that lead to it may influence aftershock statistics

the surface rupture and slip distribution of the 17 august 1999 izmit earthquake m 7 4 north anatolian fault the 17 august 1999 izmit earthquake occurred on the northern strand of the north anatolian fault zone the earthquake is associated with a 145 km long surface rupture that extends from southwest of duzce in the east to west of hersek delta in the west detailed mapping of the surface rupture shows that it consists of five segments separated by releasing step overs herein named the hersek karamursel golcuk izmit sapanca lake sapanca akyazi and karadere segments from west to east respectively the hersek segment which cuts the tip of a large delta plain in the western end of the rupture zone has an orientation of n80 the n70 80 e trending karamursel golcuk segment extends along the linear southern coasts of the izmit gulf between karamursel and golcuk and produced the 470 cm maximum displacement in golcuk the northwest southeast striking golcuk normal fault between the karamursel golcuk and izmit sapanca segments has 2 3 m maximum vertical displacement the maximum dextral offset along the izmit sapanca lake segment was measured to be about 3 5 m and its trend varies between n80 e and east west the sapanca akyazi segment trends n75 85 w and expresses a maximum displacement of 5 2 m the karadere segment trends n65 e and produced up to 1 5 m maximum displacement the karadere and sapanca akyazi segments form fan shape or splaying ruptures near their eastern ends where the displacement also diminished

back propagating super shear rupture in the 2016 mw7 1 romanche transform fault earthquake how an earthquake rupture propagates strongly influences the potentially destructive ground shaking complex ruptures often involve slip along multiple faults which masks information on the frictional behaviour of fault zones geometrically smooth ocean transform fault plate boundaries offer a favourable environment to study fault dynamics because strain is accommodated along a single wide fault zone that offsets the homogeneous geology here we present an analysis of the 2016 mw 7 1 earthquake on the romanche fracture zone in the equatorial atlantic using data from both nearby seafloor seismometers and global seismic networks we show that this rupture had two phases 1 upward and eastward propagation towards a weaker region where the transform fault intersects the mid ocean ridge and then 2 an unusual back propagation westwards at a supershear speed towards the centre of the fault we suggest that deep rupture into weak fault segments facilitated greater seismic slip on shallow locked zones this highlights that even earthquakes along a single distinct fault zone can be highly dynamic observations of back propagating ruptures are sparse and the possibility of reverse propagation is largely absent in rupture simulations and unaccounted for in hazard assessments in one earthquake an oceanic transform fault ruptured in one direction and then backwards at a speed exceeding that of shear wave propagation according to an analysis of data recorded by nearby seafloor and global seismometers

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

rupture process of the 1999 november 12 duzce turkey earthquake deduced from strong motion and global positioning system measurements summary we use the strong motion data recorded at near fault accelerometers combined with global positioning system gps measurements to infer the space and time evolution of the mw 7 2 1999 november 12 duzce turkey earthquake we confirm that the rupture is subshear towards the west whereas it overpassed the shear speed towards the east the mechanism of the earthquake is predominantly right lateral on a 65 north dipping fault the strike slip we infer represents at least 75 of the total seismic moment we stress that the use of strong motion data allows us to constrain a strong spatial variation of the slip direction during faulting to the west of the hypocentral region the slip is oblique accompanied by a significant normal component in the central and eastern part of the activated fault the slip is almost pure right lateral this result is consistent both with the surface offset observations and with the long term morphology of the fault neither strong motion data nor gps data can resolve the complexity of the eastern termination of the duzce rupture

earthquake fault superhighways abstract motivated by the observation that the rare earthquakes which propagated for significant distances at supershear speeds occurred on very long straight segments of faults we examine every known major active strike slip fault system on land worldwide and identify those with long 100 km straight portions capable not only of sustained supershear rupture speeds but having the potential to reach compressional wave speeds over significant distances and call them fault superhighways the criteria used for identifying these are discussed these superhighways include portions of the 1000 km long red river fault in china and vietnam passing through hanoi the 1050 km long san andreas fault in california passing close to los angeles santa barbara and san francisco the 1100 km long chaman fault system in pakistan north of karachi the 700 km long sagaing fault connecting the first and second cities of burma rangoon and mandalay the 1600 km great sumatra fault and the 1000 km dead sea fault of the 11 faults so classified nine are in asia and two in north america with seven located near areas of very dense populations based on the current population distribution within 50 km of each fault superhighway we find that more than 60 million people today have increased seismic hazards due to them

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

two go together near simultaneous moment release of two asperities during the 2016 mw 6 6 muji china earthquake abstract on 25 november 2016 a mw 6 6 earthquake ruptured the muji fault in western xinjiang china we investigate the earthquake rupture independently using geodetic observations from interferometric synthetic aperture radar insar and regional seismic recordings to constrain the fault geometry and slip distribution we test different combinations of fault dip and slip direction to reproduce insar observations both insar observations and optimal distributed slip model suggest buried rupture of two asperities separated by a gap of greater than 5 km additional seismic gaps exist at the end of both asperities that failed in the 2016 earthquake to reveal the dynamic history of asperity failure we inverted regional seismic waveforms for multiple centroid moment tensors and construct a moment rate function the results show a small centroid time gap of 2 6 s between the two sub events considering the 5 km gap between the two asperities and short time interval we propose that the two asperities failed near simultaneously rather than in a cascading rupture propagation style the second sub event locates 39 km to the east of the epicenter and the centroid time is at 10 7 s it leads to an estimate of average velocity of 3 7 km s as an upper bound consistent with upper crust shear wave velocity in this region we interpret that the rupture front is propagating at sub shear wave velocities but that the second sub event has a reduced or asymmetric rupture time leading to the apparent near simultaneous moment release of the two asperities

implications of delta retreat on wave propagation and longshore sediment transport guadalfeo case study southern spain abstract the influence of both natural and human induced changes on the evolution of worldwide deltas has been widely addressed however the variations of the submerged morphology of the delta and their implications on coastal dynamics have received limited attention this work details the spatial and temporal variability of the mouth of the guadalfeo river southern spain and focuses on the influence of submerged morphological changes partly due to watershed regulation in 2004 on wave propagation and longshore sediment transport bathymetric measurements were carried out over a 15 year period 1999 2014 a wave propagation model was calibrated and applied and an updated expression for longshore sediment transport was applied using downscaling techniques to obtain the complete littoral drift time series the results show that the river damming led to coastline retreat and bed level erosion up to 3 m along a 1 km section around the river mouth with maximum erosion rates in excess of 760 m 3 m these subtidal morphological changes reduced wave refraction and led to higher breaking wave energy variations in wave climate during the study period have also played a role in influencing the coastline dynamics although the erosion around the river mouth has decreased since 2008 partly due to a sediment pulse in 2010 eastward longshore sediment transport rates under westerly storm wave conditions have significantly increased since then this has led to the propagation of the sediment deficit towards the east of the mouth endangering urban developments at this location this paper provides insights into the shift from wave river dominated deltas towards deltaic coasts increasingly controlled by wave directionality and longshore sediment transport and represents an advance on the understanding of the dynamics of many worldwide deltas where the river sediment supply has decreased due to human activities

the 14 november 2001 kokoxili kunlunshan tibet earthquake rupture transfer through a large extensional step over the 14 november 2001 kokoxili tibet earthquake m w 7 8 ruptured 400 km of the western kunlun fault in northern tibet we apply two inversion methods to p and sh waves recorded by the global seismographic network to recover the spatial and temporal history of the rupture process the observed surface rupture consists of two strike slip segments offset by an extensional step over little surface rupture was observed in the graben system in this step over which is approximately 45 km long and over 10 km wide our results imply that the rupture did not jump this large gap but that the rupture was continuous through the graben the earthquake began with a small strike slip subevent presumably along the westernmost of the two segments this was followed 5 sec later by a subevent of about the same magnitude but having an oblique mechanism with a large normal faulting component the likely location for this subevent is within the graben this oblique slip event probably enabled transfer of the rupture onto the main kunlun fault the main moment release began 18 sec after rupture initiation and propagated over 350 km eastward along the kunlun fault slip on this segment was very heterogeneous averaging 2 m for the first 200 km followed by a sharp increase to a maximum of 7 5 m within the next 50 km and then a rapid decline the average rupture velocity along the main segment was high 3 6 km sec 1 and probably exceeded the local shear wave velocity the m w 7 8 kokoxili earthquake had a longer surface rupture and faster average rupture velocity radiated more energy and probably had a lower average fracture energy than the november 2002 m w 7 9 denali fault alaska earthquake evidence suggests that the velocity of the rupture front dropped significantly after passing the point of maximum slip implying a large difference in frictional strength between the two ends of the fault online material waveform fits to teleseismic body waves

steady activity of microfractures on geological faults loaded by mining stress abstract acoustic emissions ae down to m w 4 were recorded at a site 1 km beneath the surface in the cooke 4 mine south africa several planar ae clusters with lateral extent of 10 100 m were identified most of them were located several tens of meters away from the mining front and exhibited steady activity during the analysis period of about two months some of the clusters coincided with mapped faults the planar cluster aes were sharply aggregated within a thickness of several decimeters likely delineating the fracture interface of the fault and its higher order morphology such as branches bends and stepovers the composite focal mechanism evaluated for each cluster was consistent with slip events on the fracture interface these results imply that numerous shear microfractures occur steadily on a natural fault surface subjected to a mining related stress increase the planar clusters consist of very small aes 99 7 were smaller than m w 2 exhibiting high b values much exceeding unity this contrasts with the more usual b values of the stope cluster aes which were aggregated within 20 m of the mining front and exhibited a more scattered distribution the size distribution of microfractures on a fracture interface may directly reflect fine scale irregularities of the interface on the other hand many other mapped faults near the planar ae clusters were not accompanied by ae activities despite the fact that these quiet faults were subjected to a similar stress history the presence or absence of ae activities on a fault may reflect different states of the fault including stress and strength

supershear rupture of the 5 january 2013 craig alaska mw 7 5 earthquake supershear rupture in which a fracture s crack tip expansion velocity exceeds the elastic shear wave velocity has been extensively investigated theoretically and experimentally and previously inferred from seismic wave observations for six continental strike slip earthquakes we find extensive evidence of supershear rupture expansion of an oceanic interplate earthquake the 5 january 2013 mw 7 5 craig alaska earthquake this asymmetric bilateral strike slip rupture occurred on the queen charlotte fault offshore of southeastern alaska observations of first arriving sn and sg shear waves originating from positions on the fault closer than the hypocenter for several regional seismic stations with path calibrations provided by an empirical green s function approach indicate a supershear rupture process several waveform inversion and modeling techniques were further applied to determine the rupture velocity and space time distribution of slip using regional seismic and geodetic observations both theoretical and empirical green s functions were used in the analyses with all results being consistent with a rupture velocity of 5 5 to 6 km s exceeding the crustal and upper mantle s wave velocity and approaching the crustal p wave velocity supershear rupture occurred along 100 km of the northern portion of the rupture zone but not along the shorter southern rupture extension the direction in which supershear rupture developed may be related to the strong material contrast across the continental oceanic plate boundary as predicted theoretically and experimentally the shear and surface wave mach waves involve strongly enhanced ground motions at azimuths oblique to the rupture direction emphasizing the enhanced hazard posed by supershear rupture of large strike slip earthquakes

geophysical data reveal the crustal structure of the alaska range orogen within the aftershock zone of the mw 7 9 denali fault earthquake geophysical information including deep crustal seismic reflection magnetotelluric mt gravity and magnetic data cross the aftershock zone of the 3 november 2002 mw 7 9 denali fault earthquake these data and aftershock seis micity jointly interpreted reveal the crustal structure of the right lateral slip denali fault and the eastern alaska range orogen as well as the relationship between this structure and seismicity north of the denali fault strong seismic reflections from within the alaska range orogen show features that dip as steeply as 25 north and extend downward to depths between 20 and 25 km these reflections reveal crustal structures probably ductile shear zones that most likely formed during the late cretaceous but these structures appear to be inactive having produced little seis micity during the past 20 years furthermore seismic reflections mainly dip north whereas alignments in aftershock hypocenters dip south the denali fault is nonre flective but modeling of mt gravity and magnetic data suggests that the denali fault dips steeply to vertically however in an alternative structural model the denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the alaska range orogen modeling of mt data indicates a rock body having low electrical resistivity 10 xm that lies mainly at depths greater than 10 km directly beneath aftershocks of the denali fault earthquake the maxi mum depth of aftershocks along the denali fault is 10 km this shallow depth may arise from a higher than normal geothermal gradient alternatively the low electrical resistivity of deep rocks along the denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the after shock zone

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

seismicity distribution in conjunction with spatiotemporal variations of coseismic slip and postseismic creep along the combined 1999 izmit duzce rupture abstract the north anatolian fault zone nafz in nw turkey as one of the most active and best studied strike slip faults provides a unique opportunity to study earthquake related relaxation processes through analyzing co and postseismic deformation we study the spatial and temporal distributions of seismicity related to the two consecutive 1999 m 7 izmit and duzce earthquakes a high resolution aftershock catalogue including 10 000 hypocenters extending along the combined rupture zone and extending from prior to the izmit event to after the duzce event is studied spatial and temporal distributions of events allow to identify distinct seismically active and inactive fault patches their location is related to the co and postseismic deformation within and below the seismogenic layer respectively four seismically inactive patches extending 30 50 km along the rupture zone and down to 10 km depth are identified with a systematic spatial shift between them introduced by the duzce mainshock the cumulative distribution of sub areas hosting coseismic slip aftershock clusters and postseismic creep shows that the entire upper seismogenic and lower ductile portions of the crust along the combined izmit and duzce rupture zone are activated between rupture initiation and a two year postseismic period this observation was only achieved due to the subsequent occurrence of two adjacent m 7 strike slip earthquakes in combination with a distinct local seismic and geodetic monitoring our findings suggest that a coseismically introduced lateral and vertical slip deficit is systematically compensated postseismically in both the brittle and ductile portions of the crust

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

finite element simulations of dynamic shear rupture experiments and dynamic path selection along kinked and branched faults we analyze the nucleation and propagation of shear cracks along nonplanar kinked and branched fault paths corresponding to the configurations used in recent laboratory fracture studies by rousseau and rosakis 2003 2009 the aim is to reproduce numerically those shear rupture experiments and from that provide an insight into processes which are active when a crack initially propagating in mode ii along a straight path interacts with a bend in the fault or a branching junction the experiments involved impact loading of thin homalite 100 a photoelastic polymer plates which had been cut along bent or branched paths and weakly glued back together everywhere except along a starter notch near the impact site strain gage recordings and high speed photography of isochromatic lines provided characterization of the transient deformation fields associated with the impact and fracture propagation we found that dynamic explicit 2 d plane stress finite element analyses with a simple linear slip weakening description of cohesive and frictional strength of the bonded interfaces can reproduce the qualitative rupture behavior past the bend and branch junctions in most cases and reproduce the principal features revealed by the photographs of dynamic isochromatic line patterns the presence of a kink or branch can cause an abrupt change in rupture propagation velocity additionally the finite element results allow comparison between total slip accumulated along the main and inclined fault segments we found that slip along inclined faults can be substantially less than slip along the main fault and the amount depends on the branch angle and kink or branch configuration

fault slip source models for the 2014 mw 6 9 samothraki gokceada earthquake north aegean trough combining geodetic and seismological observations the 24 may 2014 mw 6 9 samothraki gokceada shallow depth 11 km earthquake along the north aegean trough nat at the westward extension of the north anatolian fault zone nafz is investigated using constraints from seismological and geodetic data a point source solution based on teleseismic long period p and sh waveforms suggests an essentially strike slip faulting mechanism consisting of two subevents while from a finite fault inversion of broadband data the rupture area and slip history were estimated analysis of data from 11 permanent gps stations indicated significant coseismic horizontal displacement but no significant vertical or postseismic slip okada type inversion of horizontal slip vectors using the new topological inversion algorithm allowed precise modeling of the fault rupture both as single and preferably as double strike slip faulting reaching the surface variable slip models were also computed the independent seismological and geodetic fault rupture models are broadly consistent with each other and with structural and seismological data and indicate reactivation of two adjacent fault segments separated by a bend of the nat the 2014 earthquake was associated with remote clusters of low magnitude aftershocks produced low accelerations and filled a gap in seismicity along the nat in the last 50 years faulting in the nat seems not directly related to the sequence of recent faulting farther east along the nafz and the seismic gap in the marmara sea near istanbul

seismicity distribution and locking depth along the main marmara fault turkey the seismicity along the main marmara fault mmf below the marmara sea is analyzed during the 2007 2012 period to provide insights on the recent evolution of this important regional seismic gap high precision locations show that seismicity is strongly varying along strike and depth providing fine details of the fault behavior that are inaccessible from geodetic observations the activity strongly clusters at the regions of transition between basins the central basin shows significant seismicity located below the shallow locking depth inferred from gps measurements its b value is low and the average seismic slip is high all observations are consistent with a deep creep of this segment on the contrary the kumburgaz basin at the center of the fault shows sparse seismicity with the hallmarks of a locked segment in the eastern marmara sea the seismicity distribution along the princes island segment in the cinarcik basin is consistent with the geodetic locking depth of 10 km and a low contribution to the regional seismic energy release the assessment of the locked segment areas provide an estimate of the magnitude of the main forthcoming event to be about 7 3 assuming that the rupture will not enter significantly within creeping domains

ground motion modeling of hayward fault scenario earthquakes part ii simulation of long period and broadband ground motions abstract we simulate long period t 1 0 2 0 s and broadband t 0 1 s ground motions for 39 scenario earthquakes m w 6 7 7 2 involving the hayward calaveras and rodgers creek faults for rupture on the hayward fault we consider the effects of creep on coseismic slip using two different approaches both of which reduce the ground motions compared with neglecting the influence of creep nevertheless the scenario earthquakes generate strong shaking throughout the san francisco bay area with about 50 of the urban area experiencing modified mercalli intensity vii or greater for the magnitude 7 0 scenario events long period simulations of the 2007 m w 4 18 oakland earthquake and the 2007 m w 5 45 alum rock earthquake show that the u s geological survey s bay area velocity model version 08 3 0 permits simulation of the amplitude and duration of shaking throughout the san francisco bay area for hayward fault earthquakes with the greatest accuracy in the santa clara valley san jose area the ground motions for the suite of scenarios exhibit a strong sensitivity to the rupture length or magnitude hypocenter or rupture directivity and slip distribution the ground motions display a much weaker sensitivity to the rise time and rupture speed peak velocities peak accelerations and spectral accelerations from the synthetic broadband ground motions are on average slightly higher than the next generation attenuation nga ground motion prediction equations we attribute much of this difference to the seismic velocity structure in the san francisco bay area and how the nga models account for basin amplification the nga relations may underpredict amplification in shallow sedimentary basins the simulations also suggest that the spudich and chiou 2008 directivity corrections to the nga relations could be improved by increasing the areal extent of rupture directivity with period

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

aftershock patterns of ms 7 earthquakes in the india asia collision belt anomalous results from the muzaffarabad earthquake sequence kashmir 2005 the seismicity rate triggered by the muzaffarabad kashmir 2005 m w 7 6 m s 7 7 earthquake is above the average when analyzing the aftershock rate of the 18 m s 7 0 events in the india asia collision belt between 1973 and 2008 all 17 m s 7 0 events occurred within 10 latitude and 20 longitude distance from the 2005 muzaffarabad earthquake epicenter we determined the huge aftershock productivity for this earthquake is not driven by a specific omori law parameter this anomaly in aftershock rate value corresponds to a relatively higher rate decay as measured by the p value and a larger density value in a higher background seismicity rate setting prestress conditions than the other 17 sequences respectively after normalizing by the mainshock size and by the magnitude range of observation we resolved the anomalies with a 95 confidence level for five aftershock sequences for either the duration the productivity the density or the background seismicity rate when we did not include the local processes that drive these specific anomalies two other global results emerged for the averaged data from the 18 m s 7 0 aftershock sequences first for all sequences background seismicity and duration are anticorrelated graphic 1 within the framework of rate and state friction law this result supports the assertion that the observed background seismicity rate can be used as a proxy for the stressing rate dieterich 1994 second we robustly resolve the dependence of aftershock productivity on the mainshock faulting styles for example the aftershock productivity for strike slip mainshocks is on average four times smaller than the productivity of thrust faulting mainshocks 1 embed inline graphic 1 gif

dynamic path selection along branched faults experiments involving sub rayleigh and supershear ruptures building upon previous laboratory earthquake experiments of dynamic shear rupture growth taking place along faults with simple kinks new and complex fault geometries involving cohesively held fault branches are studied asymmetric impact at the specimen boundaries controls the incoming shear ruptures which are manipulated to propagate at either sub rayleigh or supershear velocities high speed photography and dynamic photoelasticity are used with a model material homalite 100 to monitor incoming and outgoing rupture propagation acceleration deceleration or arrest at the vicinity of the branch location differences and similarities of rupture velocity history between cases involving faults with either simple kinks or branches on the one hand and sub rayleigh and supershear incoming ruptures on the other are highlighted and explained results of the experiments show a clear general bias toward large branch inclination smaller branch angles appearing to be overshadowed and suppressed by the stress field associated with the main fault of great interest also is the sustenance of rupture propagation along a branch by the mach cone when the initial rupture is supershear driven generally higher rupture speeds favors larger arrays of branching angles to be triggered a companion analysis by templeton et al 2009 featuring detailed numerical simulations of these experiments provides further insight into the observed phenomena

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

seismotectonics of the central denali fault alaska and the 2002 denali fault earthquake sequence in this article we analyze the spatial and temporal variations in the seismicity and stress state within the central denali fault system alaska before and during the 2002 denali fault earthquake sequence seismicity for 30 years prior to the 2002 earthquake sequence along the denali fault was very light with an average of four events with magnitude m l 3 per year we observe a significant increase in the seismicity rate prior to the m w 7 9 event of 3 november 2002 within its epicentral region starting about 8 months before its occurrence the majority of the aftershocks of the m w 7 9 event are located within the upper 11 km of the crust and form several persistent clusters with a few aseismic patches along the ruptured fault the most active aftershock source is associated with the epicentral region of the earthquake the overall b value of the aftershock sequence is 0 96 with the highest b values within the epicentral region we estimate that it will take 14 years for the seismicity rate to drop back to the background level the stress regime across the region varies in space and time the inferred stress regime prior to the 2002 sequence is predominately strike slip along the central part of the rupture zone the orientations of the least and intermediate stress axes are reversed after the 2002 earthquake sequence the maximum compressive stresses along the denali fault rotate clockwise by up to 35 the greatest rotations occur in the area of the rupture step over from the denali to the totschunda fault the inferred stress regime after the 2002 sequence reflects an interchanging thrusting and strike slip faulting along the ruptured fault the thrust faulting is concentrated in the epicentral region of the m w 7 9 event and along the rupture segments showing the largest surface offsets

faulting characteristics of supershear earthquakes article i nfo recent observations of large continental strike slip earthquakes show that different fault segments may rupture at different speeds and that rupture may propagate faster than the shear wave velocity of surrounding rocks we report that all the documented occurrences of supershear rupture are associated with faults which have simple geometry the surface trace of these faults is described in the field or seen on satellite images as remarkably linear continuous and narrow segmentation features along these segments are small or absent and the deformation is highly localized as theoretically predicted supershear is clearly associated with mode ii rupture

rupture process of the 1999 mw 7 1 duzce earthquake from joint analysis of spot gps insar strong motion and teleseismic data a supershear rupture with variable rupture velocity we analyze the rupture process of the 1999 m w 7 1 duzce earthquake using seismological remote sensing and geodetic data ground deformation measured from the subpixel cross correlation of satellite pour l observation de la terre spot images reveals a 55 km long fault trace and smooth surface slip distribution peaking at 3 5 4 m the westernmost segment overlaps for over 10 km with ruptures from the m w 7 4 izmit earthquake the 15 km long easternmost segment which cuts across mountainous topography had not been reported previously we determine a well constrained source model using a four segment fault geometry using constraints on surface fault slip and inverting global positioning system and interferometric synthetic aperture radar data along with strong motion records our results show that some variability of the rupture velocity and an eastward supershear velocity are required to fit the strong motion data the rise time up to 6 sec correlates with cumulative slip suggesting a sliding velocity of about 1 m sec the source model predicts teleseismic waveforms well although early by 2 sec this time shift is probably due to the weak beginning of the earthquake that is not observable at teleseismic distances strong motion records are relatively well predicted from a source model derived from the teleseismic data using the fault geometry derived from the satellite images this study demonstrates the benefit of using accurate fault geometries to determine finite fault source models

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

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

stochastic strong ground motion simulation of the 12 november 1999 duzce turkey earthquake using a dynamic corner frequency approach on 12 november 1999 only three months after the 17 august 1999 kocaeli earthquake mw 7 4 an earthquake of mw 7 1 occurred immediately to the east of the kocaeli rupture in northwestern turkey resulting in extensive structural damage in the city of duzce and its surrounding area it was reported to be a right lateral strike slip event on the previously unbroken segment of the north anatolian fault zone with a north dipping fault plane this paper presents stochastic finite fault simulation of near field ground motions from this earthquake at selected near fault stations based on a dynamic corner frequency approach using the computer program exsim motazedian and atkinson 2005 the method requires region specific source path and site characterizations as input model parameters the source mech anism of the 1999 duzce event and regional path effects are well constrained from previous studies of the earthquake the local site effects at the selected stations are studied as a combination of the kappa operator and frequency dependent soil ampli fication the model parameters are validated against recordings and a stress drop value of 100 bars is estimated for the 1999 duzce earthquake the validated model is then used to compute synthetic records around the fault distribution of peak ground motion parameters is observed to be consistent with the building damage dis tribution in the near fault region most affected by the seismic shaking the attenuation of synthetic ground motion parameters is compared with recent ground motion pre diction equations proposed for the region by gulkan and kalkan 2002 ulusay et al 2004 and akkar and bommer 2007 as well as two next generation attenuation models by boore and atkinson 2007 and campbell and bozorgnia 2007 despite discrepancies at several stations stochastic finite fault modeling based on a dynamic corner frequency approach confirms to be a practical tool to reproduce the ground motions of large earthquakes

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

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

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

twenty thousand aftershocks of a very small m 2 earthquake and their relation to the mainshock rupture and geological structures we have determined the locations of more than 20 000 aftershocks as small as moment magnitude mw 4 4 or even smaller following an m 2 event in a south african gold mine using manually picked arrival times spatial clustering into fivegroupswasclearlydiscerned amajorityoftheaftershocksformedaplanarcluster 4 m in apparent thickness 100 80 m in areal extent this cluster is thought to delineate the rupture area of the mainshock because its orientation and spatial extent wereconsistent with thenodalplaneofthecentroid moment tensor cmt solution and withthecornerfrequencyofthemainshock respectively thecluster sattitudesuggests that the mainshock was a mohr coulomb failure or formation of a shear rupture sur faceinintactrockatananglethatobeysthecoulombfailurecriterion thattookplacein a vertical compression stress field that is indicated by borehole breakout patterns the aftershock distribution also shows that the mainshock rupture was largely confined to the interior of a 25 m thick vertical dike although there are indications of interactions taking place between the rupture and the dike s material boundary with the host rock

stress and structure induced shear wave anisotropy along the 1999 izmit rupture northwest turkey abstract we perform a shear wave splitting analysis using seismograms of aftershocks following the 1999 m w 7 4 izmit earthquake to delineate between stress and structure controlled anisotropic mechanisms in the upper crust beneath the northwest north anatolian fault zone nafz the splitting analysis is performed on direct shear wave arrivals using a cross correlation technique to calculate the fast shear wave polarization and the delay time between fast and slow shear wave arrivals five stations located both within 1 km the nafz yield a combined 333 quality shear wave splitting measurements the shear wave splitting measurements indicate that it is occasionally possible to delineate between the two anisotropic mechanisms stations greater than 1 km from the nafz tend to have dominant fast shear wave polarizations parallel or subparallel to the regional strike of the maximum horizontal compressive stress which suggests a stress controlled anisotropic mechanism the single station within 1 km of the nafz yields a bimodal dominant fast shear wave polarization that is both parallel and perpendicular to the strike of the nearby mudurnu fault we interpret the fault parallel mode as representing a structure controlled anisotropic mechanism from the mudurnu fault the average delay time for all earthquakes is 0 038 0 031 s and anisotropic intervals do not appear to extend below 8 km the fast shear wave polarizations and delay times suggest a heterogeneous anisotropic distribution within the recording array and that the physical properties of the upper crust vary between the nafz and surrounding area

significant lateral dip changes may have limited the scale of the 2015 mw 7 8 gorkha earthquake the 2015 mw 7 8 gorkha earthquake has drawn interest due to its complex fault geometry both geodetic and geologic studies have focused on the dip variations in this study we invert the coseismic geodetic data for the 2 d dip variations of the earthquake the best fit model confirms that the dip varies with depth and suggests that there is a significant lateral dip anomaly along strike the depth dependent dip variation suggests that the earthquake ruptured a ramp flat fault the shallow ramp may have prevented the rupture breaking through the surface in addition a lateral large dip anomaly is found in the northeastern corner of the slip area which supports the previous findings of inferred interseismic fault coupling coseismic high frequency radiations and the aftershock mechanisms this lateral dip anomaly is likely associated with local tearing within the indian slab it may have blocked the east southeastward rupture propagations of the gorkha earthquake implying important controls on the earthquake scale and the spatial limits of ruptures

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

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

evidence of supershear during the 2018 magnitude 7 5 palu earthquake from space geodesy a magnitude 7 5 earthquake hit the city of palu in sulawesi indonesia on 28 september 2018 at 10 02 43 coordinated universal time it was followed a few minutes later by a 4 7 m high tsunami palu is situated in a narrow pull apart basin surrounded by high mountains of up to 2 000 m altitude this morphology has been created by a releasing bend in the palu koro fault a rapidly moving left lateral strike slip fault here we present observations derived from optical and radar satellite imagery that constrain the ground surface displacements associated with the earthquake in great detail mapping of the main rupture and associated secondary structures shows that the slip initiated on a structurally complex and previously unknown fault to the north extended southwards over 180 km and passed through two major releasing bends the 30 km section of the rupture south of palu city is extremely linear and slightly offset from the mapped geological fault at the surface this part of the rupture accommodates a large and smooth surface slip of 4 7 m with no shallow slip deficit almost no aftershock seismicity was recorded from this section of the fault as these characteristics are similar to those from known supershear segments we conclude that the palu earthquake probably ruptured this segment at supershear velocities the devastating 2018 magnitude 7 5 earthquake in palu indonesia ruptured at supershear speeds according to evidence from space geodesy

impacts of wave energy and littoral currents on shoreline erosion accretion along the south west coast of kanyakumari tamil nadu using dsas and geospatial technology the present study investigates the impact of wave energy and littoral current on shorelines along the south west coast of kanyakumari tamil nadu india the multi temporal landsat tm etm images acquired from 1999 to 2011 were used to demarcate the rate of shoreline shift using gis based digital shoreline analysis system the statistical analysis such as net shoreline movement and end point rate were determined from the multi temporal shoreline layers moreover the wave energy and seasonal littoral current velocity were calculated for each coastal zone using mathematical equations the results reveal that the coastal zones which include kanyakumari kovalam manavalakurichi and thengapattinam coasts consisting of maximum wave energy along with high velocity of littoral current have faced continuous erosion processes the estimated wave energy along these zones ranges from 6 5 to 8 5 kj km2 and the observed current velocity varies from 0 22 to 0 32 m s during south west and north east monsoons the cumulative effect of these coastal processes in the study area leads to severe erosion that is estimated as 300 63 69 92 54 12 and 66 11 m respectively however the coastal zones namely rajakkamangalam ganapathipuram muttam and colachel have experienced sediment deposits due to current movement during the north east monsoon however the trend changes during the south west monsoon as a result of sediment drift through backwash the spatial variation of shoreline and its impact on wave energy and the littoral current have been mapped using the geo spatial technology this study envisages the impact of coastal processes on site specific shorelines hence the study will be effective for sustainable coastal zone management

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

are stress drop and rupture velocity of earthquakes independent insight from observed ground motion variability we demonstrate that the variability of the peak ground acceleration pga generated by earthquakes can be simply related to the variability of stress drop rupture velocity vr and their correlation by compiling recent observations of variability of and vr we show that the hypothesis of independence between and vr leads to an overestimation of the pga variability we suggest that and vr must be anticorrelated so as to match recent observations of pga variability

high resolution satellite imagery mapping of the surface rupture and slip distribution of the mw 7 8 14 november 2001 kokoxili earthquake kunlun fault northern tibet china the mw 7 8 kokoxili earthquake of 14 november 2001 which ruptured a 450 km long stretch of the sinistral kunlun strike slip fault at the northeastern edge of the tibet plateau china ranks as the largest strike slip event ever recorded instrumentally in asia newly available high resolution satellite hrs images pixel size 1 m acquired in the months following the earthquake proved a powerful tool to complement field investigations and to produce the most accurate map to date of the coseismic displacements along the central kusai hu segment of the rupture the coseismic rupture geometry south and west of buka daban feng near the earthquake epicenter was also investigated in detail along the kusai hu segment slip parti tioning is for the first time observed to occur simultaneously during a single event with two parallel strands 2 km apart localizing almost pure strike slip and normal faulting in all 83 new hrs coseismic offset measurements some of which calibrated by field work show large well constrained variations 100 of the slip function over distances of only25 km tension cracks opening ahead of the shear dislocation and later offset by the upward propagating strike slip rupture were observed dem onstrating that the rupture front propagated faster at depth than near the surface the triple junction between the central kusai hu segment the kunlun pass fault where the rupture ended and the xidatan dongdatan segment which could be the next segment to fail along the main kunlun fault acted as a strong barrier implying that direct triggering of earthquake rupture on the xidatan dongdatan segment by kokoxili type earthquakes may not be the rule

seismic characteristics of supershear and sub rayleigh earthquakes implication from simple cases numerous investigations of supershear earthquakes make a conclusion that a supershear earthquake produces a seismic shock wave on the ground that may increase the resulting destruction we investigate a supershear rupture promoted by the free surface and find out that although the seismic energy of a supershear earthquake can be transmitted further with large amplitudes the peak slip velocity on a fault near the free surface is smaller than that caused by a subshear rupture earthquake our results show that the free surface induced supershear rupture mitigates the amplitudes of ground motions near the fault plane compared with the subshear rupture the coulomb failure change derived from dynamic modeling further suggests that this free surface induced supershear reduces aftershock potential compared to a subshear rupture both ground motion at near fault and aftershock possibility show low risk for the free surface induced supershear rupture earthquake than subshear earthquake contrary to the traditional concept