structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

fault interaction may generate multiple slip vectors on a single fault surface slip vectors of multiple orientations on a single fault surface may be explained by the interaction of crustal scale faults in response to nearby earthquakes field observations of at least five sets of striae on a single planar fault surface can be reproduced in numerical experiments these experimental results suggest that slip vectors having variable orientations may reflect a highly transient local stress state in an otherwise constant regional stress field our results suggest that stress inversion techniques should be applied with caution to areas with complex regional scale fault patterns

stress perturbations associated with active faults penetrated by boreholes possible evidence for near complete stress drop and a new technique for stress magnitude measurement detailed studies of stress induced wellbore breakouts in wells drilled through active faults reveal stress field discontinuities that are apparently associated with recent fault movements these discontinuities are expressed as localized rotations in wellbore breakout orientation in the vicinity of the fault penetrated by the borehole this phenomenon is observed in a variety of tectonic environments and rock types utilizing cases where relatively complete knowledge of the horizontal principal stresses is available from in situ measurements we use three dimensional dislocation modeling to demonstrate that these discontinuities can be explained as the superposition of a reference stress state and a perturbation caused by movement on preexisting faults case studies from normal strike slip and reverse faulting stress states indicate that nearly complete stress drop is required to match the observed breakout orientation anomalies hydraulic fracturing data independently confirm the occurrence of near complete stress drop on some faults penetrated by drilling modeling of the observed interactions between breakouts and fractures can also be used to obtain information about the magnitude of in situ stress

observations and modeling of rotational signals in the p coda constraints on crustal scattering abstract in addition to three classical components vertical north south and east west of ground translations recorded by a broadband seismometer a component of earthquake induced rotational ground motions around the vertical axis is consistently measured by a ring laser sensor located in wettzell southeast germany significant rotations around the vertical axis in the p coda of teleseismic signals are either directly visible or can be inferred through the investigation of cross correlation between the transverse component the component that is perpendicular to the great circle connecting the earthquake and the seismometer of translation acceleration and ring laser rotation rate theoretically in spherically symmetric isotropic media we should not observe rotational signals around the vertical axis before the onset of sh waves possible causes for the observed rotations in the p coda are 1 tilt ring laser coupling 2 anisotropy 3 topographic scattering and 4 p sh scattering in the crust here we show that p sh scattering in the 3d random crust can explain the observations and allow us to constrain crustal scattering properties

stress drop for three m 4 3 4 7 1992 1994 parkfield ca earthquakes in a previous paper fletcher and spudich 1998 we determined the slip distribution for the three m 4 3 to 4 7 parkfield events that occurred between oct 20 1992 and dec 20 1994 the rupture characteristics of these events are of particular interest because they are the largest events to occur at parkfield since the 1966 mainshock to further investigate the rupture process of these events we compute the static stress change or stress drop caused by the slip using a boundary integral method from quin and das 1989 adapted for the forward modeling case of computing stresses from a static slip distribution we find that the initial phase at or very near the hypocenter has the largest stress change in all cases this peak has a value of about 3 8 mpa for the oct 20 1992 event which also has the smallest magnitude of the three at 4 3 and about 45 mpa for the other nov 14 1993 and 60 mpa for the dec 20 1994 event the rest of the stress release is comparatively small and smooth for the nov 14 1993 event which is the deepest event and the most impulsive the pattern of stress release of the other two events oct 20 1992 and dec 20 1994 is more complex with a greater spatial extent the spatial distribution of stress is approximately similar to the spatial distribution of slip but with the larger initial peak in stress drop at the hypocenter

gps derived velocity and strain fields around dome argus antarctica knowledge of the surface topography velocity field and strain field at an ice core site is critical to the accurate interpretation of ice core records at dome argus dome a where a chinese deep ice core drilling project is being carried out we have produced an accurate surface digital elevation model from gps measurements in january 2013 at 47 sites we identify two peaks at dome a with the northern peak 7 cm higher than the southern peak repeat gps measurements at 12 sites in 2008 and 2013 provide a surface velocity field around the dome the surface velocity ranges from 3 1 2 6 to 29 4 1 2 cm a 1 with a mean of 11 1 2 4 cm a 1 the surface flow directions are near perpendicular to the surface elevation contours velocities from gps are lower than derived from satellite radar interferometry insar from gps velocities the accuracy of velocity from the existing insar velocity field is determined resulting in a standard deviation of 0 570 m a 1 in speed and 117 58 in direction this result is consistent with the reported accuracy of insar showing the value of in situ gps measurements for assessing and correcting remote sensing results a surface strain field for the drilling site over dome a is calculated from 24 strain triangles showing north south extension east west compression and vertical layer thinning

on the variation of slip direction during earthquake rupture supporting and conflicting evidence from the 1989 loma prieta earthquake abstract the direction of the slip can change during a rupture episode as a function of time and or of the position on the fault plane in this work we focus on the spatial variations of slip direction during an earthquake theoretically the spatial variations of rake are caused by changes in the direction of the static and dynamic traction the 1989 loma prieta earthquake provides one of the most striking examples of slip direction rotation during the coseismic rupture all the source models obtained by using different inversion procedures show strong spatial partitioning of slip into strike slip motion se of the epicenter and dip slip motion in the nw section in this study we perform both forward waveform modeling and waveform inversion tests to check if the previously observed variations of rake are constrained by seismological data we use the isochrone approach and a tomographic back projection algorithm to solve the forward modeling and the inverse problem respectively results show that observed ground velocities can be well reproduced by source models having spatial slip distribution similar to the beroza9s 1991 inversion solution but having constant rake synthetic inversion tests point out that the inversion procedure does not constrain the slip direction we have analyzed the s wave polarization in order to constrain the direction of slip along the fault this analysis confirms that a predominant strike component rake 160 characterizes the slip direction in the southeastern section while an increase of the reverse component in the northwest section of the fault allows one to explain the observed polarization well an oblique mechanism is consistent with the fault plane solution confirming a spatial variation of the slip direction during the earthquake if the rake actually varied then a nonuniform prestress condition due to a change in fault geometry or to a redistribution of static stress or a spatially inhomogeneous stress release should be proposed in order to explain the observed changes of slip direction we conclude that a nonuniform prestress is a likely explanation for the inferred rake rotations these variations of the direction of slip involve a low value of the initial stress

stability of the rake during the 1992 landers earthquake an indication for a small stress release we use the high quality data set of the landers earthquake to study in detail the ability of strong motion inversions to resolve the rake during the rupture process initially we constrain the rake to be constant on the fault several inversions with different rake values show that a pure strike slip gives the best fit to the data in a second step we have allowed the rake to vary spatially spatial rake variations are well resolved by the data and remain small the data strongly constrain the earthquake to be a pure strike slip event with almost no variation of the rake we assume that the direction of the slip vector is always close to the direction of the applied stress which itself is the vector sum of the pre existing stress and the dynamic stress changes the stability of the rake on a fault with a dynamical rupture process which is clearly heterogeneous suggests that the pre existing stress level is quite homogeneous and that it dominates over the dynamic stress changes

spatial variability of surface mass balance along a traverse route from zhongshan station to dome a antarctica stakes at 2 km intervals were installed in january 1997 and remeasured in february 1998 january 1999 january 2005 and during the 2007 08 austral summer along a 1248 km traverse route from zhongshan station to dome a east antarctica based on topographical parameters meteoro logical features and the records of 650 stakes and six stake arrays the route is divided into five zones we find that the snow accumulation rate decreases with increasing altitude as one progresses inland except in the zone 800 1128 km from the coast where the average annual accumulation rate is higher than in the zone 524 800 km from the coast the dome a zone 1128 1248 km has the lowest accumulation rate 35 kg m 2 a 1 2005 08 due to having the highest elevation and being furthest from the coast the surface mass balance in the region 202 1128 km from the coast exhibits no temporal change from 1999 2005 to 2005 08 but there is a change in the accumulation distribution the zone from 202 to 524 km shows a decrease in surface mass balance from 84 kg m 2 a 1 in 1999 2005 to 67 kg m 2 a 1 in 2005 08 while the zone between 800 and 1128 km shows an increase from 67 kg m 2 a 1 in 1999 2005 to 75 kg m 2 a 1 in 2005 08

coseismic temporal changes of slip direction the effect of absolute stress on dynamic rupture abstract we investigate the dynamics of rupture at low stress level we show that one main difference between the dynamics of high and low stress events is the amount of coseismic temporal rake rotation occurring at given points on the fault curved striations on exposed fault surfaces and earthquake dislocation models derived from ground motion inversion indicate that the slip direction may change with time at a point on the fault during dynamic rupture we use a 3d boundary integral method to model temporal rake variations during dynamic rupture propagation assuming a slip weakening friction law and isotropic friction the points at which the slip rotates most are characterized by an initial shear stress direction substantially different from the average stress direction over the fault plane we show that for a given value of stress drop the level of initial shear stress i e the fractional stress drop determines the amount of rotation in slip direction we infer that seismic events that show evidence of temporal rake rotations are characterized by a low initial shear stress level with spatially variable direction on the fault possibly due to changes in fault surface geometry and an almost complete stress drop our models motivate a new interpretation of curved and cross cutting striations and put new constraints on their analysis the initial rake is in general collinear with the initial stress at the hypocentral zone supporting the assumptions made in stress tensor inversion from first motion analysis at other points on the fault especially away from the hypocenter the initial slip rake may not be collinear with the initial shear stress contradicting a common assumption of structural geology on the other hand the later part of slip in our models is systematically more aligned with the average stress direction than the early slip our modeling suggests that the length of the straight part of curved striations is usually an upper bound of the slip weakening distance if this parameter is uniform over the fault plane and the direction of the late part of slip of curved striations should have more weight in the estimate of initial stress direction

rotational motions for teleseismic surface waves 1 we report the findings for the first teleseismic six degree of freedom 6 dof measurements including three components of rotational motions recorded by a sensitive rotation rate sensor model r 1 made by eentec and three components of translational motions recorded by a traditional seismometer sts 2 at the nacb station in taiwan the consistent observations in waveforms of rotational motions and translational motions in sections of rayleigh and love waves are presented in reference to the analytical solution for these waves in a half space of poisson solid we show that additional information e g rayleigh wave phase velocity shear wave velocity of the surface layer might be exploited from six degree of freedom recordings of teleseismic events at only one station we also find significant errors in the translational records of these teleseismic surface waves due to the sensitivity of inertial translation sensors seismometers to rotational motions the result suggests that the effects of such errors need to be counted in surface wave inversions commonly used to derive earthquake source parameters and earth structure

the 1989 loma prieta earthquake imaged from inversion of geodetic data we invert geodetic measurements of coseismic deformation from the 1989 ms7 1 loma prieta earthquake to determine the geometry of the fault and the distribution of slip on the fault plane the data include electronic distance measurements global positioning system and very long baseline interferometry vectors and elevation changes derived from spirit leveling the fault is modeled as a rectangular dislocation surface in a homogeneous elastic half space first we assume that the slip on the fault is uniform and estimate the position orientation and size of the fault plane using a nonlinear quasi newton algorithm the best fitting dislocation strikes n48 4 w and dips 76 9 sw consistent with the trend of the aftershock zone and moment tensor solutions bootstrap resampling of the data is used to graphically illustrate the uncertainty in the location of the rupture plane the 95 confidence envelope overlaps the aftershock zone arguing that there is not a significant discrepancy between the geodetic data and the aftershock locations second we estimate the slip distribution using the best fitting uniform slip fault orientation but increase the fault length to 40 km and the downdip width to 18 km the fault is divided into 162 subfaults 18 along strike and 9 along dip each subfault is allowed to have constant right lateral and reverse components of slip we then solve for the slip on each subfault that minimizes a linear combination of the norm of the weighted data residual and the roughness of the slip distribution the smoothing parameter which determines the relative weight put on fitting the data versus smoothing the slip distribution is chosen by cross validation simulations indicate that cross validation estimates of the smoothing parameter are nearly optimal the preferred slip distribution is very heterogeneous with maximum strike slip and dip slip of about 5 and 8 m respectively located roughly 10 km north of the hypocenter there is insignificant dip slip in the southeastern most part of the fault causing the rake to vary from nearly pure right lateral in the southeast to oblique right reverse in the northwest the change in rake is consistent with a uniform stress field if the fault dip increases by about 10 toward the southeast as indicated by the aftershock locations there was little slip above 4 km depth consistent with the observation that there was little if any surface rupture

co seismic ruptures of the 12 may 2008 ms 8 0 wenchuan earthquake sichuan east west crustal shortening on oblique parallel thrusts along the eastern edge of tibet abstract the m s 8 0 wenchuan earthquake which devastated the mountainous western rim of the sichuan basin in central china produced a surface rupture over 200 km long with oblique thrust dextral slip and maximum scarp heights of 10 m it thus ranks as one of the world s largest continental mega thrust events in the last 150 yrs field investigation shows clear surface breaks along two of the main branches of the ne trending longmen shan thrust fault system the principal rupture on the nw dipping beichuan fault displays nearly equal amounts of thrust and right lateral slip basin ward of this rupture another continuous surface break is observed for over 70 km on the parallel more shallowly nw dipping pengguan fault slip on this latter fault was pure thrusting with a maximum scarp height of 3 5 m this is one of the very few reported instances of crustal scale co seismic slip partitioning on parallel thrusts this out of sequence event with distributed surface breaks on crustal mega thrusts highlights regional ew directed present day crustal shortening oblique to the longmen shan margin of tibet the long rupture and large offsets with strong horizontal shortening that characterize the wenchuan earthquake herald a re evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau and require a re assessment of seismic hazard along potentially under rated active faults across the densely populated western sichuan basin and mountains

rapid changes of the aftershock p axes 3 years after the 1995 hyogo ken nanbu kobe earthquake aftershock focal mechanisms of the 1995 hyogo ken nanbu earthquake mw 6 9 are analyzed to detect temporal variations in the stress field on the nojima fault and the rokko fault system which ruptured during the mainshock following the mainshock we observe temporal changes in the p axes of aftershocks around the nojima fault p axis orientations of aftershocks which occurred in 1996 and 1997 are almost normal to the fault in contrast aftershocks which occurred after 1998 have p axes consistent with the regional stress around the central part of the rokko fault system p axis directions of aftershocks which occurred in 1996 with focal depths less than 10 km are almost normal to the faults in contrast aftershocks which occurred after 1997 have p axes consistent with the regional stress these results indicate that the nojima fault and the rokko fault system started to accumulate significant shear stress in mid 1998 only 3 years after the mainshock

surficial slip and rupture geometry on the beichuan fault near hongkou during the mw 7 9 wenchuan earthquake chinasurficial slip and rupture geometry on beichuan fault near hongkou during the wenchuan earthquake

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

constraint of fault parameters inferred from nonplanar fault modeling 1 we study the distribution of initial stress and frictional parameters for the 28 june 1992 landers california earthquake through dynamic rupture simulation along a nonplanar fault system we find that observational evidence of large slip distribution near the ground surface requires large nonzero cohesive forces in the depth dependent friction law this is the only way that stress can accumulate and be released at shallow depths we then study the variation of frictional parameters along the strike of the fault for this purpose we mapped into our segmented fault model the initial stress heterogeneity inverted by peyrat et al 2001 using a planar fault model simulations with this initial stress field improved the overall fit of the rupture process to that inferred from kinematic inversions and also improved the fit to the ground motion observed in southern california in order to obtain this fit we had to introduce an additional variations of frictional parameters along the fault the most important is a weak kickapoo fault and a strong johnson valley fault

in situ stress measurement in an earthquake focal area abstract a 2 km deep borehole was drilled into granitic rock where many shallow earthquakes with focal depths from 2 to 15 km have occurred the drill site ashio is 100 km north of tokyo downhole testing and measurements were conducted five times four times after each 500 m drilling and the fifth time after completing the 2000 m borehole measurements of in situ stress orientation and magnitude were conducted by the hydraulic fracturing method stress induced well bore breakout analysis and drilling mud pressure induced hydraulic fracturing analysis breakouts and mud pressure induced hydraulic fractures were observed below 650 m and 1250 m respectively the circular well bore is maintained only in limited spots below 650 m because of breakouts indicating a large differential stress condition between the maximum and the minimum principal stresses the differential stress is calculated at 90 20 mpa at the depth of 2000 m based on the condition under which the breakout with some degree of width appears it is interpreted that this large differential stress is representative of the regional crustal stress condition in the earthquake swarm area each spot of the circular well bore is always adjacent to a fracture zone this suggests that the fracture zone has small differential stress the stress values were measured where the well bore is circular by the hydraulic fracturing method for example the maximum and the minimum horizontal compressive stresses are about 35 mpa and about 25 mpa respectively at the depth of 1650 m giving the differential stress of 10 mpa the water pressure in pre existing fractures was also measured and found that they were nearly equal to the hydrostatic water pressure at the corresponding depths the stress direction estimated from the azimuth of the breakouts and the hydraulic fracture is consistent with that estimated from the earthquake focal mechanisms these results support the following conclusions the differential stress is large in the earthquake swarm region but it is extremely small at narrow zones adjoining fracture zones this is due to the relaxation of the differential stress at fractures of low frictional strength however water pressure is not so large that the low differential stress causes sliding of the fractures clay minerals seems to play an important role in decreasing of the frictional strength

rotational motions observed during an earthquake swarm in april 1998 offshore ito japan abstract we observed six components of ground rotational and translational motions in a near field region during an earthquake swarm in april 1998 offshore ito izu peninsula japan to check the reliability of our observation using a motionpack sensor we installed an 8301f sensor which is an inertial angular displacement sensor with a higher sensitivity than motionpack the noise level of the motionpack is much higher than that of the 8301f but the waveforms of these signal components are quite similar to each other suggesting that the motionpack records rotational rate correctly but with higher noise our observation made known a linear correlation between the maximum rotational displacements around the vertical axis and the maximum translational velocities the waveforms of rotational motion around the vertical axis are analogous to those of translational horizontal velocities suggesting the linear correlation between maximum values these rotational motions are much larger than those calculated by array data at the san andreas fault this large discrepancy might be explained by one or more of the following effects the difference in the spatial scale of rotational motion by single gyro measurement and by array observation the effect of the precipitous topography at the station of the offshore ito swarm and the difference of the degree of maturation between the san andreas fault and the swarm regions of offshore ito

strong ground motion from the michoacan mexico earthquake the network of strong motion accelerographs in mexico includes instruments that were installed under an international cooperative research program in sites selected for the high potenial of a large earthquake the 19 september 1985 earthquake magnitude 8 1 occurred in a seismic gap where an earthquake was expected as a result there is an excellent descripton of the ground motions that caused the disaster

rupture process of the 18 april 1906 california earthquake from near field tsunami waveform inversion abstract the 18 april 1906 m 8 california earthquake generated a small local tsunami that was recorded in the near field by the presidio san francisco tide gauge located near the golden gate we investigate the causative tsunamigenic seismic source by forward modeling and nonlinear inversion of the presidio marigram we use existing seismological and geological observations to fix the fault system geometry and the surface slip on the onland portions of the san andreas fault saf we perform synthetic inversions to show that the single near field marigram constrains the main features of the rupture on the portion of the saf system offshore of the golden gate finally we perform nonlinear inversions for the slip distribution and the timing of the rupture of the 1906 earthquake our results in agreement with previous studies identify a dilatational stepover and show a bilateral rupture possibly originating or propagated through the stepover region we find that little or no coseismic slip on normal faults in the stepover region is required to fit the marigram and we obtain adequate fits when allowing delays in the source initiation times of up to 3 min on the various fault segments we constrain slip to be of about 5 6 m for the onshore portion of the saf to the northwest of the golden gate in agreement with 1906 surface observations of fault offset our results favor the hypothesis of a vertical dip for a currently aseismic saf to the southeast of the golden gate under the san francisco peninsula

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

surface topography and ice flow in the vicinity of the edml deep drilling site antarctica interpretation of ice core records requires accurate knowledge of the past and present surface topography and stress strain fields the european project for ice coring in antarctica epica drilling site 75 00258 s 0 06848 e 2891 7 m in dronning maud land antarctica is located in the immediate vicinity of a transient and forking ice divide a digital elevation model is determined from the combination of kinematic gps measurements with the glas12 datasets from the icesat based on a network of stakes surveyed with static gps the velocity field around the drilling site is calculated the annual mean velocity magnitude of 12 survey points amounts to 0 74ma 1 flow directions mainly vary according to their distance from the ice divide surface strain rates are determined from a pentagonshaped stake network with one center point close to the drilling site the strain field is characterized by along flow compression lateral dilatation and vertical layer thinning

energy partitioning during seismic slip in pseudotachylyte bearing faults gole larghe fault adamello italy thedeterminationoftheearthquakeenergybudgetremainsachallengingissueforearthscientists asunderstandingthepartitioningofenergyisa keytowardsthe understandingthe physicsofearthquakes here weestimatethe partitionofthe mechanical workdensity intoheatandsurfaceenergy energyrequiredtocreatenewfracturesurface duringseismicsliponalocationalongafault earthquakeenergypartitioningisdeterminedfromfield and microstructural analyses of a fault segment decorated by pseudotachylyte solidified friction induced melt produced during seismic slip exhumed from a depth of 10 km typical for earthquake hypocenters in the continental crust frictional heat per unit fault area estimated from the thickness of pseudotachylytes is 27 mj m 2 surface energy estimated from microcrack density inside clast i e cracked grains entrapped in the pseudotachylyte and in the fault wall rock ranges between 0 10 and 0 85 mj m 2 our estimates for the studied fault segment suggest that 97 99 of the energy was dissipated as heat during seismic slip we conclude that at 10 km depth less than 3 of the total mechanical work density is adsorbed as surface energy on the fault plane during earthquake rupture 2008 elsevier b v all rights reserved

on the transient behavior of frictional melt during seismic slip s n and g d t were supported by a european research council starting grant project acronym usems and by a progetti di eccellenza fondazione cassa di risparmio di padova e rovigo we are grateful to nick beeler and to an anonymous referee for their constructive reviews and their help to improve the clarity of the manuscript

inferring rate and state friction parameters from a rupture model of the 1995 hyogo ken nanbu kobe japan earthquake we consider the applicability of laboratory derived rate and state variable friction laws to the dynamic rupture of the 1995 kobe earthquake we analyze the shear stress and slip evolution of ide and takeo s 1997 dislocation model fitting the inferred stress change time histories by calculating the dynamic load and the instantaneous friction at a series of points within the rupture area for points exhibiting a fast weakening behavior the dieterich ruina friction law with values of dc 0 01 0 05 m for critical slip fits the stress change time series well this range of dc is 10 20 times smaller than the slip distance over which the stress is released dc which previous studies have equated with the slip weakening distance the limited resolution and low pass character of the strong motion inversion degrades the resolution of the frictional parameters and suggests that the actual dc is less than this value stress time series at points characterized by a slow weakening behavior are well fitted by the dieterich ruina friction law with values of dc 0 01 0 05 m the apparent fracture energy gc can be estimated from waveform inversions more stably than the other friction parameters we obtain a gc 1 5 l06 j m 2 for the 1995 kobe earthquake in agreement with estimates for previous earthquakes from this estimate and a plausible upper bound for the local rock strength we infer a lower bound for dc of about 0 008 m

near source modeling of the loma prieta earthquake evidence for heterogeneous slip and implications for earthquake hazard i have analyzed records from 20 strong motion instruments that recorded the 1989 loma prieta earthquake ml 6 9 to determine the spatial and temporal distribution of slip using a tomographic back projection technique i find that the earthquake ruptured bilaterally at approximately 80 of the local shear wave velocity over a distance of slightly more than 30 km from 13 km northwest to 20 km southeast of the hypocenter slip within the rupture zone was highly variable both in magnitude and direction slip at the hypocenter and immediately up dip was relatively low about 1 m there were two main areas of concentrated slip one centered 7 km northwest of the hypocenter at a depth of 14 km and the other centered 6 km southeast of the hypocenter at a depth of 12 km peak slip amplitude on these high slip patches exceeded 4 5 m a surprising aspect of the rupture model is that rake varies from being predominately strike slip to the southeast of the hypocenter to being predominately reverse slip to the northwest despite this variation in rake the average rake determined from the strong motion data is in agreement with that determined teleseismically there is a correlation between areas of high slip and areas of low aftershock activity a simple model to explain this observation is that the areas of high slip are also areas of high strength which slip only during infrequent large mainshocks other areas of the fault are weaker and may slip both seismically and aseismically most of the slip in the loma prieta earthquake occurred between 9 and 16 km depth on a structure that dips to the southwest and runs underneath the surface trace of the san andreas fault at a depth of 8 to 10 km this observation complicates the assessment of seismic hazard on the southern santa cruz mountains segment of the san andreas fault

widespread persistent thickening of the east antarctic ice sheet by freezing from the base an international polar year aerogeophysical investigation of the high interior of east antarctica reveals widespread freeze on that drives substantial mass redistribution at the bottom of the ice sheet although the surface accumulation of snow remains the primary mechanism for ice sheet growth beneath dome a 24 of the base by area is frozen on ice in some places up to half of the ice thickness has been added from below these ice packages result from the conductive cooling of water ponded near the gamburtsev subglacial mountain ridges and the supercooling of water forced up steep valley walls persistent freeze on thickens the ice column alters basal ice rheology and fabric and upwarps the overlying ice sheet including the oldest atmospheric climate archive and drives flow behavior not captured in present models

lithospheric elasticity promotes episodic fault activity based on the agreement between geodetic and geological plate velocities interplate fault slip rates are usually considered constant over long periods of time however measurements made at different time scales on intracontinental faults suggest that slip rate evolves with time we examine the slip evolution of a fault embedded in an elastic lithosphere loaded by plate motion we first assume that the fault friction varies due to a climatic cause then we show that high fault stress and low lithospheric stiffness favour large variations of slip rate in the case where fault weakening is controlled by slip rate we find that high loading velocity leads to a low stress constant slip rate while low loading velocity drives the fault slip rate to cycle between high and low values this suggests that paleoseismic slip rate could overpass the loading velocity but also fall to zero for some period of time

three dimensional spontaneous rupture propagation and implications for the earthquake source mechanism summary we consider spontaneous cracks spreading out areally over a fault plane in an infinite medium as a realistic earthquake source model the boundary integral equation technique described in das is used to determine the displacements and stresses everywhere on the crack plane for faults spreading out symmetrically in all four quadrants over infinite planes of constant yield strength we find that the terminal rupture velocity viiicr in the direction of purely anti plane rupture is given by viiicr in the purely in plane direction of rupture propagation we find the terminal rupture velocity viicr to be given by viicr or viicr 0 5 depending on the yield strength we also find that crack propagation in the purely antiplane direction does not influence crack propagation in the purely in plane direction and vice versa for infinitely long shear cracks of finite width the slip at a point is found to grow more slowly after the arrival of a shear wave diffracted from the nearer crack edge the slip virtually ceases after the shear arrival from the further crack edge this implies that for such faults the slip is controlled by the fault width for a rectangular fault in an infinite medium our final dynamic solution is in closer agreement with the static elliptical crack solution of eshelby than with the static rectangular dislocation model solution of chinnery we find the relationship between the average slip and average dynamic stress drop e on such a rectangular fault of half width w to be e c w where c 0 7 the slip at an interior point is again controlled by the fault width for faults that are much longer than wide so that the slip may stop in the region where the fault initiated before the completion of the rupture process this implies that two rectangular faults of varying lengths but of the same width have the same slip for the same average stress drop a fact clearly contradicted by observations that fault slip increases with earthquake size for great earthquakes occurring along the same fault this contradiction is resolved if stress drops are also bigger for bigger earthquakes

growth linkage and termination processes of a 10 km long strike slip fault in jointed granite the gemini fault zone sierra nevada california abstract field based structural analysis of an exhumed 10 km long strike slip fault zone elucidates processes of growth linkage and termination along moderately sized strike slip fault zones in granitic rocks the gemini fault zone is a 9 3 km long left lateral fault system that was active at depths of 8 11 km within the transpressive late cretaceous sierran magmatic arc the fault zone cuts four granitic plutons and is composed of three steeply dipping northeast and southwest striking noncoplanar segments that nucleated and grew along preexisting cooling joints the fault core is bounded by subparallel fault planes that separate highly fractured epidote chlorite and quartz breccias from undeformed protolith the slip profile along the gemini fault zone shows that the fault zone consists of three 2 3 km long segments separated by two zones of local slip minima slip is highest 131 m on the western third of the fault zone and tapers to zero at the eastern termination slip vectors plunge shallowly west southwest and show significant variability along strike and across segment boundaries four types of microstructures reflect compositional changes in protolith along strike and show that deformation was concentrated on narrow slip surfaces at or below greenschist facies conditions taken together we interpret the fault zone to be a segmented linked fault zone in which geometrical complexities of the faults and compositional variations of protolith and fault rock resulted in nonuniform slip orientations complex fault segment interactions and asymmetric slip distance profiles

the antarctica component of postglacial rebound model ice 6g_c vm5a based on gps positioning exposure age dating of ice thicknesses and relative sea level histories

scaling of ground motion parameters state of stress and focal depth the ground motion parametersrv and ra where r is hypocentral distance v is peak velocity is density and a is peak acceleration are found observationally to be strong functions of stress state and linearly related to focal depth z if the stress state and focal depth are properly taken into account then the ground motion parameters depend on the seismic moment m0 as expected from basic scaling principles that is rv m01 3 and ra is independent of earthquake size regression lines fitted to observations covering broad ranges in seismic moment and focal depth indicate that for extensional and compressional tectonic regimes corresponding to normal and thrust or reverse faulting earthquakes respectively peak acceleration is given by ra 1 08 mpa 3 06 mpa km z normal and ra 5 65 mpa 8 76 mpa km z thrust and for peak velocity rv m01 3 10 4 m2 s n m 1 3 3 00 0 69 km 1 z normal and rv m01 3 10 4 m2 s n m 1 3 4 63 1 82 km 1 z thrust for strike slip earthquakes the data currently are insufficient to define regression fits but such lines would definitely lie between those for the normal and thrust stress regimes these equations are appropriate for ground motion at small hypocentral distance as recorded in a whole space it follows that for comparable hypocentral depth peak acceleration in a compressional tectonic regime for example much of the eastern united states is a factor of about 3 greater than in an extensional regime such as nevada and for peak velocity a similar comparison yields a factor of 2 difference the similarity in behavior of the peak acceleration parameter to crustal strength estimated from byerlee s law of friction with respect to depth and stress state indicates that crustal strength is probably the factor governing the seismic source processes that give rise to the high frequency peak ground motion analysis of the peak acceleration data in the context of crustal strength suggests bounds on this ground motion parameter as recorded at a typical surface site that depend on stress state specifically a normal 0 5 g and a thrust 1 9 g thus the state of stress as well as the focal depth clearly is an important factor to be taken into account in the prediction of seismic ground motion

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

advances in 6c seismology applications of combined translational and rotational motion measurements in global and exploration seismology over the past few decades the potential of collocated measurements of 6c data 3c of translational and 3c of rotational motion has been demonstrated in global seismology using high sensitivity observatory based ring laser technology proposed applications of 6c seismology range from tomographic reconstruction of near receiver structure to the reduction of nonuniqueness in seismic source inverse problems applications to exploration problems have so far been hampered by the lack of appropriate sensors but several applications have been proposed and demonstrated with array derived rotational motion estimates with the recent availability of for example fiber optic based high sensitivity rotational motion sensors widespread applications of 6c techniques to exploration problems are in sight potential applications are based on for example the fact that the extended set of combined translational and rotational motion observations enables carrying out array type processing with single station recordings such as wavefield separation and surface wave suppression furthermore measuring the rotational component curl of the seismic wavefield enables direct isolation of the s wave constituents and could significantly improve s wave exploration rotational measurements provide estimates of the spatial wavefield gradient at the free surface that allow carrying out analyses such as local slowness estimation and wavefield reconstruction furthermore rotational motion measurements can help to resolve wavefield infidelity introduced by seismic instruments that are not well coupled to the ground

review progress in rotational ground motion observations from explosions and local earthquakes in taiwan rotational motions generated by large earthquakes in the far field have been successfully measured and observations agree well with the classical elasticity theory however recent rotational measurements in the near field of earthquakes in japan and in taiwan indicate that rotational ground motions are 10 to 100 times larger than expected from the classical elasticity theory the near field strong motion records of the 1999 mw 7 6 chi chi taiwan earthquake suggest that the ground motions along the 100 km rupture are complex some rather arbitrary baseline corrections are necessary in order to obtain reasonable displacement values from double integra tion of the acceleration data because rotational motions can contaminate acceleration observations due to the induced perturbation of the earth s gravitational field we started a modest program to observe rotational ground motions in taiwan three papers have reported the rotational observations in taiwan 1 at the hgsd station liu et al 2009 2 at the n3 site from two taiwan integrated geodynamics research taiger explosions lin et al 2009 and 3 at the taiwan campus of the national chung cheng university nccu wuet al 2009 in addition langston et al 2009 reported the results of analyzing the taiger explosion data as noted by several authors before we found a linear relationship between peak rotational rate prr in mrad sec and peak ground acceleration pga in m sec 2 from local earthquakes in taiwan prr 0 002 1 301 pga with a correlation coefficient of 0 988

coseismic stress changes induced by the 1989 loma prieta california earthquake earthquake focal mechanisms from before and after the 1989 loma prieta california earthquake are used to infer the coseismic stress change before the main shock most earthquakes correspond to right lateral slip on planes sub parallel to the san andreas fault and imply a generally n s most compressional stress axis and a vertical intermediate stress axis aftershocks within the main shock rupture zone however display almost every style and orientation of faulting implying an extremely heterogeneous stress field this suggests that the main shock relieved most if not all of the shear stress acting on its fault plane aftershocks that lie on the perimeter of the rupture agree with spatially uniform stress states but only when considered in three groups north south and above the main shock rupture area in each of these areas the stress state may reflect stress transfer by the main shock

source process of the 1995 kobe earthquake determination of spatio temporal slip distribution by bayesian modeling the kobe hyogo ken nanbu earthquake ms 6 8 occurred on 16 january 1995 in western japan bringing about a tremendous disaster we constructed its source model by determining a spatio temporal slip distribution using strong motion seismograms recorded at a number of stations near the hypocenter the source area is expressed using both a rough and a detailed subfault discretization system and a source time function expanded with a finite number of basis functions at each subfault is determined to perform stable inversions with many parameters we construct a bayesian model with unknown hyperparameters incorporating prior constraints on the smoothness of spatio temporal slip distribution in the observation equation using akaike s bayesian information criterion abic the optimal set of hyperparameters are objectively determined from observed data which enables us to uniquely determine a spatio temporal slip distribution after rough analysis in which the actual rupture area is estimated as 45 20 km we carried out a detailed analysis with a finer subfault discretization system 5 5 km in our final source model most of the slip exists beneath awaji island and the rupture below the city of kobe where the damage was most serious is relatively smaller the large slips of about 2 m in the shallowest subfaults located southwest of the hypocenter correspond to the surface offsets observed along the nojima fault the overall focal mechanism of the source is right lateral strike slip with a small thrust component while total seismic moment is 2 0 1019 nm the source time functions at shallow subfaults show a longer duration than those at deeper ones being hypothesized to represent a possible combined effect of low rupture propagation velocity and varying friction behavior in shallow regions of crust

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

late quaternary slip rates along the sierra nevada frontal fault zone california slip partitioning across the western margin of the eastern california shear zone basin and range province new geologic mapping tectonic geomorphologic and cosmogenic radionuclide geochronologic data provide the fi rst numerical constraints on late quaternary vertical slip and horizontal extension rates across the southern sierra nevada frontal fault zone california this fault zone exposes numerous nnw striking east facing normal fault scarps that offset seven distinct quaternary alluvial surfaces and a rockslide deposit beryllium 10 cosmogenic radionuclide surface exposure dating of these surfaces provides surface abandonment model ages of 123 7 16 6 ka 60 9 6 6 ka 25 8 7 5 ka 4 4 1 1 ka and 4 1 1 0 ka on alluvial fan surfaces and 18 7 3 9 ka on the rockslide deposit these age constraints combined with measurements of vertical surface offset across fault scarps yield preferred late pleistocene to holocene vertical and horizontal extensional slip rates of 0 2 0 3 mm yr and 0 1 0 2 mm yr vertical slip rate estimates in this study are comparable to late pleistocene vertical slip rate estimates across other prominent range front normal faults within the basin and range province these geologic and geochronologic results indicate that the eastern escarpment of the southern sierra nevada has remained tectonically active throughout the late quaternary combining our data with slip data from the owens valley and lone pine faults implies that slip along the eastern escarpment of the sierra nevada block is partitioned into three components dominantly dextral slip along the owens valley fault intermediate oblique slip along the lone pine fault and subordinate normal slip along the sierra nevada frontal fault zone these observations are consistent with global positioning system gps data which indicate that dextral shear strain accumulation dominates today along the western boundary of the eastern california shear zone and basin and range province

comminution and fluidization of granular fault materials implications for fault slip behavior abstract whilst faulting in the shallow crust is inevitably associated with comminution of rocks the mechanical properties of the comminuted granular materials themselves affect the slip behavior of faults therefore the mechanical behavior of any fault progresses along an evolutionary path we analyzed granular fault rocks from four faults and deduced an evolutionary trend of fractal size frequency comminution of fault rocks starts at a fractal dimension close to 1 5 2 d measurement at which a given grain is supported by the maximum number of grains attainable and hence is at its strongest as comminution proceeds the fractal dimension increases and hence comminution itself is a slip weakening mechanism under the appropriate conditions comminuted granular materials may be fluidized during seismic slip events in this paper we develop a new method to identify the granular fault rocks that have experienced fluidization where the detection probability of fragmented counterparts is a key parameter this method was applied to four fault rock samples and a successful result was obtained knowledge from powder technology teaches us that the volume fraction of grains normalized by maximum volume fraction attainable is the most important parameter for dynamic properties of granular materials and once granular fault materials are fluidized the fault plane becomes nearly frictionless a small decrease in the normalized volume fraction of grains from 1 is a necessary condition for the phase transition to fluidization from the deformation mechanism governed by grain friction and crushing by contact stresses this condition can be realized only when shearing proceeds under unconstrained conditions and this demands that the gap between fault walls is widened normal interface vibration proposed by brune et al tectonophysics 218 1993 59 appears to be the most appropriate cause of this and we presented two lines of field evidence that support this mechanism to work in nature

surface characteristics at dome a antarctica first measurements and a guide to future ice coring sites an assessment of the glaciological and meteorological characteristics of dome a the summit of the east antarctic ice sheet is made based on field investigations during the austral summer of 2004 05 knowledge of these characteristics is critical for future international studies such as deep ice core drilling the assessment shows that 1 dome a is characterized by a very low 10m depth firn temperature 58 3 c nearly 3 c lower than at epica dome c and 1 c lower than at vostok 2 automatic weather station aws measurements of snow surface height and reference layers in a snow pit indicate the present day snow accumulation rate at dome a is within the range 1 3 cm w e a 1 densification models suggest a range of 1 2 cm w e a 1 this is lower than at other sites along the ice divide of east antarctica idea annual layers at dome a are thus potentially thinner than at other sites so that a longer record is preserved in a given ice thickness 3 the average wind speed observed at dome a 4 ms 1 is lower than at other sites along idea together these parameters combined with radio echo sounding data and information on the subglacial drainage distribution beneath dome a suggest dome a as a candidate site for obtaining the oldest ice core

fault geometry and the dynamics of the 1999 chi chi taiwan earthquake the 1999 m 7 6 chi chi taiwan earthquake produced a data set of unparalleled size and quality particularly in the near source region where data have been previously quite scarce the large amount of near source data allows the verification of many predictions of thrust fault behavior for faults that intersect the surface of the earth through rigorous three dimensional dynamic models of the chi chi earthquake it can be shown that many aspects of the observed near source ground motion in this event are direct effects of the asymmetrical dipping fault geometry these effects include the hanging wall moving more than the footwall with strongly peaked velocities right at the fault trace and a transition from predominantly thrust motion in the south of the fault to largely left lateral motion in the north building on the work of oglesby and day 2001 the current work helps to delineate the effects of fault geometry nonuniform prestress and dynamic waves on the physics of the chi chi earthquake and dip slip faults in general in particular we find that a completely homogeneous prestress pattern still fits the gross features of the near source ground motion quite well additionally the strike slip component of motion near the fault trace is seen to be a combination of dynamic and static effects finally dynamic overshoot is seen to be much larger for dip slip faults than for otherwise identical vertical faults the results emphasize the necessity of rigorous models that correctly account for both the effects of fault geometry and dynamic waves in the rupture and slip processes manuscript received 31 july 2000

on the inference of absolute stress levels from seismic radiation abstract spudich p k p 1992 on the inference of absolute stress levels from seismic radiation in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 99 106 this paper determines the conditions under which it is possible to learn the absolute stress level at a subset of points on a fault from observation of the fault kinematics specifically the points on a rupturing fault can be divided into two groups those points at which the rake rotates during the rupture process and those points at which the rake does not rotate if it is true that sliding frictional traction is collinear with the instantaneous velocity of one side of a fault then at the former group of points having rotating rakes there is a unique absolute stress consistent with the motion while at the latter group of points having rakes that do not rotate the absolute stress is unspecified by the motion published dislocation solutions for the 1979 imperial valley 1986 north palm springs 1987 whittier narrows and 1989 loma prieta california earthquakes are examined for evidence of temporal rotations of rake at the hypocenters and largest asperities the 1986 north palm springs earthquake shows evidence of a possible rake rotation at the hypocenter this may imply a low absolute stress level

use of fault striations and dislocation models to infer tectonic shear stress during the 1995 hyogo ken nanbu kobe earthquake dislocation models of the 1995 hyogo ken nanbu kobe earthquake derived by yoshida et al 1996 show substantial changes in direction of slip with time at specific points on the nojima and rokko fault systems as do striations we observed on exposures of the nojima fault surface on awaji island spudich 1992 showed that the initial stress that is the shear traction on the fault before the earthquake origin time can be derived at points on the fault where the slip rake rotates with time if slip velocity and stress change are known at these points from yoshida s slip model we calculated dynamic stress changes on the ruptured fault surfaces to estimate errors we compared the slip velocities and dynamic stress changes of several published models of the earthquake the differences between these models had an exponential distribution not gaussian we developed a bayesian method to estimate the probability density function pdf of initial stress from the striations and from yoshida s slip model striations near toshima and hirabayashi give initial stresses of about 13 and 7 mpa respectively we obtained initial stresses of about 7 to 17 mpa at depths of 2 to 10 km on a subset of points on the nojima and rokko fault systems our initial stresses and coseismic stress changes agree well with postearthquake stresses measured by hydrofracturing in deep boreholes near hirabayashi and ogura on awaji island our results indicate that the nojima fault slipped at very low shear stress and fractional stress drop was complete near the surface and about 32 below depths of 2 km our results at depth depend on the accuracy of the rake rotations in yoshida s model which are probably correct on the nojima fault but debatable on the rokko fault our results imply that curved or cross cutting fault striations can be formed in a single earthquake contradicting a common assumption of structural geology

inverting ground motion from a seismometer array to obtain the vertical component of rotation a test using data from explosions to study factors that affect reliability of the derived vertical rotational ground motions about vertical axis from translational array waveforms we have conducted a field test using explosion the dataset was collected on march 4 2008 from an active source experiment of the taiwan geodynamics research project taiger 2008 in which 750 kg of explosives were set off about 500 m away from a specially designed seismic array in free field consisting of 8 tri axial rotational sensors 13 tri axial accelerometers and 12 six channel 24 bit dataloggers with gps receivers our results show that the waveform fits were greatly improved when the explosion induced crustal strains were less than 2 10 5 for our station configuration as a result our modeling for the large amplitude part of the mainshock was not entirely successful however we have successfully recovered the first order features of the later part of the vertical rotational ground motions using translational velocity waveforms in the 0 5 20 hz bandwidth using the spudich and fletcher s procedure 2009 moreover we used a modified jaeger s 1969 formula and derived similar rotational synthetics we found that the best rotational rate waveform fits were derived using a station configuration of a dense small aperture translational array combined with a few largeoffset stations a small aperture array is needed to fulfill the uniform rotation assumption however inverting data from an array of small spatial dimension requires waveforms of high signal to noise ratio and high sampling rates surprisingly large offset translation stations provided additional constraints in time and space helping to fit the low frequency waveforms using the inverted result we forward predicted the vertical translational waveforms not used in the inversion and got excellent fits this suggests that the inverted results are of good quality for predicting the complete translational ground motions even though only horizontal components were used in the inversion array derived or directly measured rotational ground motions can be used to predict translational ground motions in the near by region lessons learned from this study could be helpful for future studies using translational ground motions to derive dynamic ground strains tilts and torsions

mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock aftershock interaction the diverse aftershock sequence of the 1989 loma prieta earthquake is inconsistent with conventional models of mainshock aftershock interaction because the aftershocks do not accommodate mainshock induced stress changes instead the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane this orientation implies that i stress drop in the mainshock was nearly complete ii mainshock induced decreases of fault strength helped were important in controlling the occurrence of after shocks and iii mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip

erratum to surficial slip and rupture geometry on the beichuan fault near hongkou during the mw 7 9 wenchuan earthquake china worldwide occurrence and documentation of reverse type ruptures are sparse near hongkou the wenchuan rupture passes through the broad baisha river valley and provides excellent opportunities to trace the surface faulting in fine details for 13 km distance one of the longest continuous sections along the entire rupture in this paper we present the results of our mapping of the surface rupture in this reach based on the discontinuities in slip and geometry the rupture was divided into four sections for convenience from west to east the shenxi gou the miaoba the gaoyuan and the bajiao miao sections respectively the vertical offset is large in the shenxi gou and the bajiao miao sections locally reaching 5 6 m in maxima and generally low in the miaoba section 1 2 m or less in most places the slip gradient for vertical offset is generally 10 3 locally up to 10 1 similar to that in well documented strike slip ruptures near gaoyuan village the surface rupture con sists of two subparallel branches with the northern one exhibiting right lateral slip with minor southeast side up thrusting while the southern one is almost pure south east side up thrusting this pattern mimics the incomplete slip partitioning of oblique thrusting on parallel faults but at a local scale in addition the sense of vertical throw on these two strands is opposite to the general northwest side up thrusting of the wenchuan rupture we propose that it is likely due to the inheritance at shallow depth from the southeast dipping geological faults and that old fault zone structures can have a strong effect on the dynamic rupture by guiding the rupture propagation onto paths of preexisting though locally unfavorable dipping fault planes we also discuss the cross cutting slickenside striations observed near bajiao miao which indicated temporal rake rotation during dynamic rupture and their geological and seismological implications

planar microstructures in zircon from paleo seismic zones pseudotachylytes resulted from frictional melts associated with ultramylonites in high grade metapelitic rocks from the ivrea verbano zone in the southern alps northern italy were studied with focus on the deformation microstructures in zircon the aims were to investigate the characteristics of zircon deformation in seismic zones and to recognize specific microstructures generated in zircon during earthquakes which could be useful for mineral dating of paleo seismic events helps to understand how seismic energy is released at depth and interacts with metamorphic processes the interior of polished zircon grains ranging from 30 to 150 m in length were investigated with optical microscope and scanning electron microscope sem techniques including secondary electron se backscattered electron bse forward scattered electron fse cathodoluminescence cl imaging and crystallographic orientation mapping by electron backscatter diffraction analysis ebsd grains were studied in situ and as separated fractions embedded in epoxy disks among different cataclastic and crystal plastic deformation microstructures in zircon we identified characteristic planar deformation bands pdbs planar fractures pfs and curviplanar fractures cfs planar deformation bands in zircon are crystallographically controlled planar lattice volumes with misorientation from the host grain which varies from 0 4 to 2 7 pdbs are usually parallel to 100 crystallographic planes have width from 0 3 to 1 m and average spacing of 5 m in 2d sections planar deformation bands appear as contrast lamellae in orientation contrast images and in ebsd maps and in rare cases can be observed with the optical microscope pdbs form in specifically oriented grains due to high differential stresses high temperatures and high strain rates generated in seismically active environment and or due to shearing in the vicinity of frictional melts discovered structures represent a result of crystal plastic deformation of zircon grains with operating dislocations having 010 glide system and misorientation axis therefore they can be classified as a new type 4 lattice distortion pattern according to the existing classification for zircon piazolo et al 2012 kovaleva et al 2014 we have demonstrated that formation of planar fractures in zircon takes place not only during impacts but also in seismically active zones we observe at least two cases of formation of pfs with 100 orientation 1 as a result of evolution of pdbs and 2 as micro cleavage this study demonstrates that planar microstructures in terrestrial zircon do not exclusively form during impact events but also as a result of seismic events at depth due to unusually high differential stress strain rate and temperature according to the new findings pdbs in zircon from the deep crust are supposed to represent newly recognized evidence of seismicity

rotational motions induced by the m8 1 tokachi oki earthquake september 25 2003 1 we report the first consistent observations of rotational motions around a vertical axis induced by distant large earthquakes it is standard in seismology to observe three components up down n s e w of earthquake induced translational ground motions using inertial seismometers however only recently ring laser technology has provided the required sensitivity for observations of the theoretically predicted rotational part of ground motion generated by seismic waves in a wide distance range and frequency band here we show that the rotations observed are consistent in waveform and amplitude with collocated recordings of transverse accelerations recorded by a standard seismometer this suggests that rotations may become a new observable for seismology and related fields with the potential of providing complementary information on earthquake source processes structural properties and ground shaking

tomography of the source area of the 1995 kobe earthquake evidence for fluids at the hypocenter seismic tomography revealed a low seismic velocity 5 and high poisson s ratio 6 anomaly covering about 300 square kilometers at the hypocenter of the 17 january 1995 magnitude 7 2 kobe earthquake in japan this anomaly may be due to an overpressurized fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake

introduction to the special issue on rotational seismology and engineering applications rotational seismology is an emerging field for studying all aspects of ro tational ground motions induced by earthquakes explosions and ambient vibrations it is of interest to a wide range of geophysical disciplines including strong motion seismology broadband seismology earthquake engineering earthquake physics seis mic instrumentation seismic hazards seismotectonics and geodesy as well as to physicists using earth based observatories for detecting gravitational waves generated by astronomical sources predicted by einstein in 1916 in this introduction to the bssa special issue on rotational seismology and engineering applications we will include 1 some background information 2 a summary of the recent events that led to this special issue and 3 an overview of its 51 papers 27 articles 11 short notes 4 reviews 6 tutorials and 3 supplementary articles our comments on these 51 papers are very brief and give just a hint of what the papers are about papers in this special issue demonstrate that earthquake monitoring cannot be limited to measuring only the three components of translational motion we also need to simultaneously measure the three components of rotational motion and the many components of strains a golden opportunity to improve our understanding of earth quakes lies in the near field of large earthquakes within about 25 km of the earthquake ruptures where nonlinear rock and soil response influences ground motions in a com plicated way

dynamic stress drop and rupture dynamics of the october 15 1979 imperial valley california earthquake abstract a dynamic faulting model is constructed to determine the dynamic stress drop and relative strength distribution for the october 15 1989 imperial valley earthquake and to study the dynamics of rupture propagation for this event reproduction of the kinematic quantities of the strike slip rate strike slip final offset rupture time and rupture duration bu varying the dynamic parameters of dynamic stress drop and yield strength is attempted the fault plane is discretized in 1 5 km square grids the model incorporates first order corrections for the effect of the free surface and material property heterogeneity on the calculation of rupture at depth the strike slip particle velocities final offsets and rupture durations of the kinematic model are matched within about 40 everywhere below about 5 km except in the hypocentral region and in a high displacement region 20 km north of the epicenter the strike slip rate of the dynamic model is half and rupture duration double those of the kinematic model in the epicentral region the rupture durations and strike slip final offsets are two thirds those of the kinematic model in a high stress drop region beneath the el centro crossing array two slip concentrations correspond to stress drop concentrations one of about 80 bar at 20 km from the epicenter and at 8 km depth and the other of about 70 bar at 30 km from the epicenter and 10 km depth most of the dynamic stress drop occurs between the depths of 9 and 11 km averaging about 60 bar stress drops in the 7 9 km range vary between 25 and 35 bar while stress drops in the 5 7 km depth range vary between 10 and 15 bar this depth dependence of stress drop was a consistent feature across nearly 20 km of the fault stress drop appeared to be well correlated with rock type negative stress drop was found in the sediment regions and the regions at depth while positive stress drop was found in the metasediment regions between the depths of 5 and 11 km yield strength and rupture velocity are inversely related high yield strength is found in regions of low rupture velocity and vice versa rupture was found to terminate at the northern end of the fault by collision with a high strength barrier a region of supersonic rupture velocity was found to occur in a region of high stress drop and low fracture strength the kinematic rupture velocity at the northern end of the fault was found to be unreasonably low results show that this region reaches its peak stress before the kinematic break time yield strength increased with depth in the seismogenetic zone until the base of the zone was reached below which it tapered off slightly

fluid inclusions in pseudotachylytes from the nojima fault japan pseudotachylytes i e rocks formed by frictional melting have been observed in the nojima fault that was penetrated by the hirabayashi borehole drilled 1 year after the 1995 hyogo ken nanbu kobe earthquake these rocks display millimeter scale banding defined by different pseudotachylyte layers the nature of unmolten crystal fragments k feldspar albite calcite and or quartz allows us to infer a minimum melting temperature of 1200 c the glass has a 8 3 volatile content and a higher cao content than that of the parent granodiorite thus suggesting that pseudotachylyte formation occurred in an already altered calcite bearing and hydrated fault zone fluid inclusions have been observed in the glass and are filled with a dense low salinity 4 3 1 2 wt eq nacl co2 h2o fluid characterized by steep isochoric curves the intersection between the isochores and the measured 24 c km geothermal gradient indicates a minimum 15 km depth for the pseudotachylyte formation such a depth suggests that an important uplift has brought the studied pseudotachylytes to their present position and that these pseudotachylytes are probably pre miocene in age the calculated thermal evolution of a typical millimeter scale pseudotachylyte layer indicates that cooling does not last more than a few seconds this indicates that related seismic processes such as deceleration of fault movement and healing of the fault were both very rapid the geometry and thermal budget of the millimeter thick pseudotachylytes suggest that seismic events of magnitude 6 to 7 are responsible for their formation

constraints on stress and friction from dynamic rupture models of the 1994 northridge california earthquake we have simulated several scenarios of dynamic rupture propagation for the 1994 northridge california earthquake using a three dimensional finite difference method the simulations use a rate and slip weakening friction law starting from a range of initial conditions of stress and frictional parameters a critical balance between initial conditions and friction parameters must be met in order to obtain a moment as well as a final slip distribution in agreement with kinematic slip inversion results we find that the rupture process is strongly controlled by the average stress and connectivity of high stress patches on the fault in particular a strong connectivity of the high stress patches is required in order to promote the rupture propagation from the initial nucleation to the remaining part of the fault moreover we find that a small amount of rate weakening is needed in order to obtain a level of inhomogeneity in the final slip similar to that obtained in the kinematic inversion results however when the amount of rate weakening is increased the overall moment drops dramatically unless the average prestress is raised to unrealistic levels a velocity weakening parameter on the order of 10 cm per second is found to be adequate for an average prestress of about a hundred bars the presence of the free surface and of the uppermost low impedance layers in the model are found to have negligible influence on the rupture dynamics itself because the top of the fault is at a depth of several kilometers the 0 1 0 5 hz radiated waves from the dynamic simulation provides a good fit to strong motion data at sites nwh and ssa underprediction of the recorded peak amplitude at jfp is likely due to omission of near surface low velocity and 3 d basin effects in the simulations

snow accumulation and its moisture origin over dome argus antarctica the spatial and temporal variability of snow accumulation near dome argus antarctica is assessed using new snow pit and stake measurement data together with existing snow pit ice core and automatic weather station records snow accumulation rate shows large inter annual variations but stable multi decadal levels over the last seven centuries spatial variations in snow accumulation within the space of 50 km of dome argus are relatively small probably thanks to the smooth topography a comparison of theses accumulation observations with ecmwf reanalyses era 40 and era interim suggests ecmwf reanalysis captures the seasonal variations but underestimates the overall snow accumulation at dome argus by 50 the moisture sources for precipitation over dome argus are examined by means of a lagrangian moisture source diagnostic based on the tracing of specific humidity changes along air parcel trajectories for the period 2000 2004 using operational ecmwf analysis data dome argus mainly receives moisture from the mid latitude 46 4 s south indian ocean with a seasonal latitudinal shift of about 6 compared to other central east antarctic deep ice core sites such as dome f dome c vostok and epica dronning maud land dome argus has a more southerly moisture origin probably due to topographic influences on the moisture transport paths these results have important implications for the interpretation of future ice cores at dome argus

re establishment of ice surface velocity field and snow surface elevation change around dome argus east antarctica in january 2016 static gps measurements were carried out in a 30 30 km2 area centered around kunlun station at dome argus dome a east antarctica to acquire high precision 3 d geodetic coordinates at 49 sites by comparing the coordinates with previous gps measurements in 2008 and 2013 at the same sites we constructed a detailed and long term record of the ice surface velocity field 2008 2016 around dome a during this time span the estimated ice surface velocity ranges from 0 8 0 3 to 28 7 1 6 cm a 1 with a mean of 10 4 0 3 cm a 1 from 2013 to 2016 the surface elevation of most dome a areas exhibits a rising trend and the maximum increase of snow surface elevation is 84 8 cm the mean snow surface elevation change rate at dome a is estimated to be 6 6 0 7 cm a 1 the difference of 1 0 cm a 1 between the snow surface change rate derived from gps and pole height change rate from surface mass balance is suspected to be a result of a combination of firn densification and basal melt under dome a

directional topographic site response at tarzana observed in aftershocks of the 1994 northridge california earthquake implications for mainshock motions abstract the northridge earthquake caused 1 78 g acceleration in the east west direction at a site in tarzana california located about 6 km south of the mainshock epicenter the accelerograph was located atop a hill about 15 m high 500 m long and 130 m wide striking about n78 e during the aftershock sequence a temporary array of 21 three component geophones was deployed in six radial lines centered on the accelerograph with an average sensor spacing of 35 m station c00 was located about 2 m from the accelerograph we inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion we identified a 3 2 hz resonance that is a transverse oscillation of the hill a directional topographic effect the top base amplification ratio at 3 2 hz is about 4 5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill this resonance is seen most strongly within 50 m of c00 other resonant frequencies were also observed a strong lateral variation in attenuation probably associated with a fault caused substantially lower motion at frequencies above 6 hz at the east end of the hill there may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill causing particle motions not spectral ratios at the top of the hill to be rotated about 20 away from the direction transverse to the hill the resonant frequency but not the amplitude of our observed topographic resonance agrees well with theory even for such a low hill comparisons of our observations with theoretical results indicate that the 3d shape of the hill and its internal structure are important factors affecting its response the strong transverse resonance of the hill does not account for the large east west mainshock motions assuming linear soil response mainshock east west motions at the tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill probable variations in surficial shear wave velocity do not account for the observed differences among mainshock acceleration observed at tarzana and at two different sites within 2 km of tarzana

the gamburtsev mountains and the origin and early evolution of the antarctic ice sheet the manner in which the antarctic ice sheet first formed at a time of rapid global climate change about 34 million years ago has been the subject of considerable speculation several lines of evidence point to central antarctic mountain ranges as the site of the initial ice sheet but our knowledge of the present ice sheet topography is highly restricted in the very zone where ice sheet initiation is most likely along the subglacial gamburtsev mountain range at the centre of the present ice sheet now a detailed survey and analysis of the morphology of the gamburtsev mountains has been performed based on an ice penetrating radar study conducted over two seasons the data reveal a mountain landscape initially incised by rivers then over deepened by ice movement the topography beneath up to 3 000 metres of ice resembles an exploded version of classic alpine valley topography and seems to have developed more than 34 million years ago when mean summer temperatures were about 3 c the nature of initial glaciation on antarctica about 34 million years ago is a mystery results from an intensive radar survey now show that the gamburtsev mountains at dome a at the centre of the present ice sheet were initially incised by rivers and then subsequently overdeepened by ice movement this is suggestive of topographical development before 34 million years ago when mean summer temperatures were about 3 c ice sheet development in antarctica was a result of significant and rapid global climate change about 34 million years ago1 ice sheet and climate modelling suggest reductions in atmospheric carbon dioxide less than three times the pre industrial level of 280 parts per million by volume that in conjunction with the development of the antarctic circumpolar current led to cooling and glaciation paced by changes in earth s orbit2 based on the present subglacial topography numerical models point to ice sheet genesis on mountain massifs of antarctica including the gamburtsev mountains at dome a the centre of the present ice sheet2 3 our lack of knowledge of the present day topography of the gamburtsev mountains4 means however that the nature of early glaciation and subsequent development of a continental sized ice sheet are uncertain here we present radar information about the base of the ice at dome a revealing classic alpine topography with pre existing river valleys overdeepened by valley glaciers formed when the mean summer surface temperature was around 3 c this landscape is likely to have developed during the initial phases of antarctic glaciation according to antarctic climate history estimated from offshore sediment records the gamburtsev mountains are probably older than 34 million years and were the main centre for ice sheet growth moreover the landscape has most probably been preserved beneath the present ice sheet for around 14 million years

ground rotational motions recorded in near source region of earthquakes large rotational motions excited by earthquakes are recorded during an earthquake swarm of march 1997 offshore ito in izu peninsula japan the largest rotational velocity recorded at kaw is 2 6 10 2 rad s around the north south axis during an earthquake of magnitude 5 2 at 14 09 gmt on march 3 the rotational motions around the vertical axis excited by the largest event is 3 3 10 3 rad s considering a spatial variation of slip velocity which directly relates to excitation of a rotational motion we apply a simple point source model to the largest event and succeed in explaining the observed rotational motion around the vertical axis

source times and scaling relations of large earthquakes source time is a kinematic fault parameter corresponding to the duration of seismic source time functions and is accurately determined from phase spectra of long period surface waves source times are determined for 36 large earthquakes during the last three decades scaling relations among source times seismic moments and fault dimensions are derived seismic moment is proportional to the cube of source time and fault dimension is proportional to source time source times for low angle thrust earthquakes along deep sea trenches are found to be longer than those of other types such as intraplate shocks and deep shocks they are also significantly longer than the rupture times expected from a haskell model suggesting that generally there exists an introductory stage of faulting that precedes the main stage of the rupture propagation