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

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

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

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

reassessment of isotaches compression concept and isotaches consolidation models abstracta substantial body of laboratory and field observations on compression and consolidation of soft clay and silt deposits as well as organic soils suggest a soil behavior according to hypoth

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

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

predominance of unilateral rupture for a global catalog of large earthquakes the manner in which an earthquake rupture propagates across a fault reflects both the initial properties of the fault and the dynamical stresses produced by the rupture we quantify the propagation of an earthquake rupture using the second moments of the earthquake space time distribution in particular the second moments provide a simple way to differentiate between approximately bilateral and predominantly unilateral ruptures we determined the second moments for a catalog of m w 7 earthquakes that have occurred since 1994 the results show that approximately 80 of large shallow ruptures are predominantly unilateral our result agrees well with strong motion inversions from previous studies on moderate and large earthquakes the predominance of unilateral propagation in large earthquakes is explained by a simple characteristic earthquake model in which large events rupture an entire structurally defined fault segment and nucleation points are uniformly distributed along the fault the predominance of unilateral rupture may also be enhanced by the dynamic stress field produced by contrasts in the elastic properties between the two sides of plate boundary faults manuscript received 16 november 2001

evaluating damage during shear tests of rock joints using acoustic emissions abstract the acoustic emission ae signals generated during direct shear test were evaluated on different types of joints rock rock rock concrete and concrete concrete several boreholes were cored from a dam body rock mass and interface between dam and rock mass and the samples were prepared and tested under direct shear test a laser profilometer scanner was used for scanning the joint surfaces in order to assess surface roughness by correlating the ae signals with the shear graphs one can predict the starting point of shearing during direct shear test count and energy parameters were analyzed in two different methods to monitor the shear behavior of the joints a graph of the count and energy rates and a graph of cumulative count and energy four separated periods were observed for bonded and non bonded joints linear pre peak period non linear pre peak period post peak period and residual period this study showed that ae has enough accuracy to monitor the shear behavior of the joints and it can be used in site confidently

geological and geomorphologic asymmetry across the rupture zones of the 1943 and 1944 earthquakes on the north anatolian fault possible signals for preferred earthquake propagation direction summary the east and west rupture directions of the 1943 and 1944 earthquakes on the north anatolian fault naf are hypothesized to represent respectively long term preferred propagation directions on the corresponding sections of the naf fault sections with preferred rupture direction are expected to have an asymmetric damage structure with respect to the slipping zone to test the above hypothesis we study geological and geomorphologic manifestations of structural asymmetry with respect to the active trace of the naf along the 1943 and 1944 sections the following fault zone elements are mapped gouge fabric in the cm scale fault core structure in a metre scale and secondary faults and fault rocks in tens of metres scale mapping results at three sites on the 1943 rupture and one site on the 1944 rupture are consistent with accumulation of more rock damage on the south side of the 1943 section and on the north side of the 1944 section erosion patterns adjacent to the fault that are not correlated with the distribution of intrinsic and extrinsic erosion controlling variables e g rock type are interpreted as morphologic responses to the damage content of rocks and its impact on rock erodibility the valleys of 11 rivers are parallel to the studied fault sections about 75 per cent of the total river valleys length along the 1943 rupture is on the south side of the fault and about 89 per cent of the total river valleys length along the 1944 rupture is on the north side of the fault morphometric analysis of watersheds in two correlative terrains displaced along the 1944 rupture section shows that stream erosion is considerably more intense in the terrain north of the fault with drainage density values almost double in the north compare to the south badland topography at two sites along the 1943 rupture section is substantially more developed at the 100 m scale on the south side of fault our observations along the 1943 1944 rupture sections including various types of signals that span a large range of scales are systematically compatible with an opposite sense of damage asymmetry between the two fault sections these observations are consistent with opposite preferred direction of ruptures for the two sections similar to the propagation directions of the two recent earthquakes if those rupture directions are dictated by the velocity structure at depth we infer that the south side of the 1943 rupture has faster seismic velocity at seismogenic depth than the north side and that the sense of velocity contrast is reversed along the 1944 rupture zone

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

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

bimaterial effects in an earthquake cycle model using rate and state friction we have developed a computational framework to study earthquake cycles in 2 d plane strain and apply it to faults separating dissimilar material we consider a planar strike slip fault governed by rate and state friction where quasi dynamic events nucleate spontaneously due to remote tectonic loading we investigate the influence of material contrast over the course of many hundreds of years for the parameters we consider we find that the presence of bimaterial properties influences the earthquake nucleation site such that rupture in the preferred direction that is in the direction of particle motion of the side of the fault with lower shear wave velocity is favorable for large values of the critical slip distance dc events propagating in the preferred rupture direction occur for a wide range of material contrasts for smaller values of dc small events emerge even in the monomaterial case with material mismatch present some of these small events propagate in the nonpreferred direction made possible by a favorable stress distribution left on the fault from previous ruptures these results may shed light on our understanding of rupture directivity on large strike slip faults like the san andreas fault in california which occasionally host events rupturing in the nonpreferred direction

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

effects of a low velocity zone on a dynamic rupture dynamic crack earthquake simulations generally assume that the crustal material surrounding faults is laterally homogeneous tomographic and near fault seismic studies indicate that the crust near faults is instead comprised of rocks of varying material velocities we have tested the effects of adding material velocity variation to simulations of spontaneously propagating earthquakes we used two dimensional plane strain conditions coupled with a slip weakening fracture criterion and examined earthquakes on faults that bisect finite width low velocity zones embedded in country rock and earthquakes on faults that bound two different velocity materials when a fault bisects a low velocity zone the normal stress remains unchanged but both the rupture velocity and slip velocity pulse shape are perturbed the presence of the low velocity zone induces high frequency oscillations in the slip function near the rupture front when the fault is on the edge of the low velocity zone the oscillations are more pronounced and repeated sticking and slipping can occur near the rupture front for the slip weakening velocity independent friction model however the temporary sticking does not lead to permanent arrest of slip and slip duration is still controlled by the overall rupture dimension when an earthquake ruptures a fault juxtaposing a lower velocity material against a higher velocity material the normal stress across the fault near the crack tip is perturbed the sign of the normal stress perturbation depends on the direction of rupture leading in some cases to a directional dependence of rupture velocity when slip is accompanied by stress reduction a positive feedback develops between the normal and shear stress changes as previously noted by andrews and ben zion 1997 resulting in an apparently unavoidable grid size dependence in computation of stress change near the rupture front numerical experiments indicate however that the rupture velocity is insensitive to this zone size dependence which is highly localized immediately behind the crack tip the factors controlling the rupture velocity in the simulations including directional dependence are further elucidated by a new analytical solution for rupture of an asperity on a frictionless interface

rupture dynamics on a bimaterial interface for dipping faults dip slip faulting may juxtapose different geologic materials with differ ent properties such that a strong material contrast will naturally tend to form both the material contrast across a fault and dip slip motion on a nonvertical fault lead to normal stress variations during earthquake rupture this normal stress variation will significantly affect dynamic rupture propagation to demonstrate this we model dynamic rupture propagation on two dimensional 2d reverse and normal faults 30 45 and 60 dipping with 20 material contrasts for predominantly up dip rupture propagation we find that normal stress variations due to the free surface and material contrast can either reinforce or counteract each other depending on the configuration for reverse faults we find a larger strength drop for a more com pliant hanging wall and a lower strength drop for a more compliant footwall for normal faults we find a larger strength drop for a more compliant footwall and a lower strength drop for a more compliant hanging wall for both reverse and normal faults ground motion will be more symmetric between the hanging wall and footwall with compliant material on the footwall and more asymmetric if more compliant materials are on the hanging wall our results have important implications for the dynamics of crustal and perhaps subduction zone earthquake faulting where strong bimaterial contrasts across dipping faults are possible in continental settings reverse faulting will tend to advect rigid materials from greater depth onto the hanging wall such that the effects of fault dip and material contrast will counteract one another in subduction zones the hanging wall is likely to be more compliant and hence the material and geometric effects may reinforce one another

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

ground motion signatures of supershear ruptures in the burridge andrews and free surface induced mechanisms abstract we analyze the ground motions of supershear ruptures in the burridge andrews bam and free surface induced fsi mechanisms bam supershear ruptures require higher initial shear stress than fsi supershear ruptures thus cause faster rupture speed the supershear slip pulse initiates at the free surface or upper boundary of a fault for fsi and at the hypocenter depth in the in plane direction for bam in homogeneous models both bam and fsi supershear ruptures can generate mach waves and the rayleigh wave field the bam and the faster fsi supershear ruptures can make stronger shear mach waves the shear mach waves show a larger amplitude of negative component for a faster fsi supershear rupture the fsi supershear ruptures make the strongest dilatational wave next to the fault while it is at a distance away from the fault for the bam supershear ruptures the different shapes of supershear rupture front locations of supershear triggered and the rupture speeds contribute to these contrasts and we find that the bam and the faster fsi supershear ruptures can trigger more high frequency radiation due to the sharper and stronger shear mach waves finally the comparisons between the simulated seismograms and the records of ps10 indicate that the 2002 denali earthquake may represent a supershear one with the fsi mechanism and a slow supershear rupture speed

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

earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod 1 arrival time data from 453 local earthquakes and 6 explosions at parkfield ca are inverted for earthquake locations and three dimensional vp and vp vs structure the structure is dominated by the velocity contrast across the saf with the southwest side about 20 25 faster consistent with previous studies nearly all the earthquakes occur almost directly beneath the fault trace we find high vp vs anomalies that correlate with low resistivity features in a magnetotelluric model that are interpreted to represent fluids we locate a magnitude 2 earthquake that is a potential target event for the final stage of safod drilling yielding a depth of 3 1 km below surface and an epicenter 100 m southwest of the fault trace nonlinear analyses indicate 95 confidence relative and absolute uncertainties on the order of 500 700 m vertically and 200 300 m horizontally for this target earthquake

the 1999 izmit turkey earthquake a 3d dynamic stress transfer model of intraearthquake triggering before the august 1999 izmit kocaeli turkey earthquake theoretical studies of earthquake ruptures and geological observations had provided estimates of how far an earthquake might jump to get to a neighboring fault both numerical simulations and geological observations suggested that 5 km might be the upper limit if there were no transfer faults the izmit earthquake appears to have followed these expectations it did not jump across any step over wider than 5 km and was instead stopped by a narrower step over at its eastern end and possibly by a stress shadow caused by a historic large earthquake at its western end our 3d spontaneous rupture simulations of the 1999 izmit earthquake provide two new insights 1 the west to east striking fault segments of this part of the north anatolian fault are oriented so as to be low stress faults and 2 the easternmost segment involved in the august 1999 rupture may be dipping an interesting feature of the izmit earthquake is that a 5 km long gap in surface rupture and an adjacent 25 restraining bend in the fault zone did not stop the earthquake the latter observation is a warning that significant fault bends in strike slip faults may not arrest future earthquakes manuscript received 30 august 2000