triggered slip along the san andreas fault after the 8 july 1986 north palm springs earthquake in addition to minor surface cracks in the region of the 8 july 1986 north palm springs earthquake minor aseismic surficial rupture occurred along three segments of the san andreas fault 44 to 86 km southeast of the epicenter data from a creepmeter and a tiltmeter at one locality suggest that triggered slip occurred coseismically beneath the instruments but took 33 hr to propagate to the surface that slippage occurred coseismically at depth favors mechanisms for triggered slip that involve dynamic or static strain changes rather than creep migrating from the source region the distribution of slip along the san andreas fault associated with the north palm springs earthquake differed significantly from that recorded after the moderate 1968 borrego mountain california and 1979 imperial valley california earthquakes during these earthquakes triggered slip occurred along the san andreas fault in the durmid hill area and in the mecca hills triggered slip associated with the north palm springs earthquake occurred in these two areas again but also extended farther northwest into the indio hills where as much as 9 mm of dextral slip occurred in the mecca hills surface cracks in 1986 appeared over a shorter fault length than in previous events and the dextral displacement was smaller with maximum values of only 2 to 3 mm on durmid hill surface cracks in 1986 were localized along a 200 m long stretch of the fault spanning the mecca beach creepmeter and extending about 150 m to the southeast right lateral displacements on surface cracks in this area were 1 4 to 2 0 mm smaller than those observed in previous events although the mechanism of triggered aseismic slip is poorly understood examination of displacement rates for the past several decades to centuries may indicate whether the aseismic slip rate is constant or represents accelerating premonitory failiure of the southernmost san andreas fault

triggered surface slips in the salton trough associated with the 1999 hector mine california earthquake surface fracturing occurred along the southern san andreas superstition hills and imperial faults in association with the 16 october 1999 mw 7 1 hector mine earthquake making this at least the eighth time in the past 31 years that a regional earthquake has triggered slip along faults in the salton trough fractures associated with the event formed discontinuous breaks over a 39 km long stretch of the san andreas fault from the mecca hills southeastward to salt creek and durmid hill a distance from the epicenter of 107 to 139 km sense of slip was right lateral only locally was there a minor 1 mm vertical component of slip dextral slip ranged from 1 to 13 mm maximum slip values in 1999 and earlier triggered slips are most common in the central mecca hills field evidence indicates a transient opening as the hector mine seismic waves passed the southern san andreas fault comparison of nearby strong motion records indicates several periods of relative opening with passage of the hector mine seismic wave a similar process may have contributed to the field evidence of a transient opening slip on the superstition hills fault extended at least 9 km at a distance from the hector mine epicenter of about 188 to 196 km this length of slip is a minimum value because we saw fresh surface breakage extending farther northwest than our measurement sites sense of slip was right lateral locally there was a minor 1 mm vertical component of slip dextral slip ranged from 1 to 18 mm with the largest amounts found distributed or skewed away from the hector mine earthquake source slip triggered on the superstition hills fault commonly is skewed away from the earthquake source most notably in 1968 1979 and 1999 surface slip on the imperial fault and within the imperial valley extended about 22 km representing a distance from the hector mine epicenter of about 204 to 226 km sense of slip dominantly was right lateral the right lateral component of slip ranged from 1 to 19 mm locally there was a minor 1 2 mm vertical component of slip larger proportions of vertical slip up to 10 mm occurred in mesquite basin where scarps indicate long term oblique slip motion for this part of the imperial fault slip triggered on the imperial fault appears randomly distributed relative to location along the fault and source direction multiple surface slips both primary and triggered slip indicate that slip repeatedly is small at locations of structural complexity

postseismic deformation following the mw 7 2 23 october 2011 van earthquake turkey evidence for aseismic fault reactivation geodetic measurements following the 23 october 2011 mw 7 2 van eastern turkey earthquake reveal that a fault splay on the footwall block of the coseismic thrust fault was reactivated and slipped aseismically for more than 1 5 years following the earthquake although long lasting aseismic slip on coseismic ruptures has been documented following many large earthquakes long lasting triggered slip on neighboring faults that did not rupture during the earthquake has not been reported previously elastic dislocation and coulomb stress modeling indicate that the postseismic deformation can be adequately explained by shallow slip on both the coseismic and splay fault and is likely driven mostly by coseismic stress changes thus the slip deficit on the shallow section of the coseismic fault indicated by interferometric synthetic aperture radar based models has been partially filled by aseismic slip suggesting a lower likelihood for a large earthquake on the shallow section of the van fault than suggested by previous studies

locally and remotely triggered aseismic slip on the central san jacinto fault near anza ca from joint inversion of seismicity and strainmeter data we study deep aseismic slip along the central section of the san jacinto fault near the anza seismic gap in southern california elevated strain rates following the remote m w7 2 4 april 2010 el mayor cucapah and the local m w5 4 7 july 2010 collins valley earthquakes were recorded by plate boundary observatory borehole strainmeters near anza and were accompanied by vigorous aftershock sequences we introduce a method to infer the distribution of triggered aseismic slip from combined seismicity and geodetic data based on a rate and state friction model that maps observed changes in seismicity rates into stress changes we invert for the cumulative slip in the 10 day period following each main shock synthetic tests show that the effect of aftershock interactions on the inferred slip distribution is negligible the joint data set is more consistent with a model in which aseismic slip on a principal fault triggers seismicity on adjacent faults than with one in which aseismic slip and seismicity are coplanar our results indicate that aseismic slip primarily occurs along the rim of two seismicity clusters adjacent to anza gap as well as beneath the anza gap itself at depths larger than 10 km the triggered aseismic slip generated by the two main shocks has little overlap a pattern also found in sequences of large earthquakes occurring on a same fault stresses inferred from seismic activity leading to the collins valley main shock suggest that this earthquake was triggered by stresses imposed by the el mayor cucapah remote triggered aseismic slip which persisted for more than 2 months

behavior of the southernmost san andreas fault during the past 300 years surficial creep occurs at low rates along the coachella valley segment of the san andreas fault which has not produced a large earthquake during the period of historical record geodetic data indicate however that the crust adjacent to this segment of the san andreas fault is accumulating strain at a high rate furthermore neotectonic and paleoseismic data indicate that the fault does produce very large earthquakes every two to three centuries in view of its long term behavior the occurrence of creep along the surficial trace of the fault in the coachella valley is of particular interest along two short reaches of the san andreas fault in the coachella valley measurements of offset geological deposits and man made structures and from alignment arrays and creep meters show that slip rates of 2 4 mm yr near indio and near the salton sea have persisted for the past three centuries this slow aseismic surficial creep is not a transient precursor to seismic failure of this segment of the fault we suggest that the coachella valley segment of the san andreas fault creeps in its upper few kilometers this behavior may be due to tectonically induced high pore pressures in the coarse sediments that abut the fault

interseismic strain accumulation and the earthquake potential on the southern san andreas fault system the southern section of the san andreas fault is the only part of the fault that hasn t ruptured in historic times for this reason it is believed to pose the largest seismic risk in california although whether tectonic stress is actually accumulating there is a topic of heated debate using data from radar interferometry satellites yuri fialko has produced a detailed map of surface deformation in the area that shows that elastic stress is accumulating at a fairly high rate during the past 300 years a displacement of 6 to 9 metres has built up this suggests that the southern san andreas fault is nearing the end of the interseismic phase of the earthquake cycle and that increased seismic activity of some kind can be expected the san andreas fault in california is a mature continental transform fault that accommodates a significant fraction of motion between the north american and pacific plates the two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857 respectively the southern section of the fault however has not produced a great earthquake in historic times for at least 250 years assuming the average slip rate of a few centimetres per year typical of the rest of the san andreas fault the minimum amount of slip deficit accrued on the southern section is of the order of 7 10 metres comparable to the maximum co seismic offset ever documented on the fault1 2 here i present high resolution measurements of interseismic deformation across the southern san andreas fault system using a well populated catalogue of space borne synthetic aperture radar data the data reveal a nearly equal partitioning of deformation between the southern san andreas and san jacinto faults with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces the observed strain rates confirm that the southern section of the san andreas fault may be approaching the end of the interseismic phase of the earthquake cycle

interseismic strain localization in the san jacinto fault zone we investigate interseismic deformation across the san jacinto fault at anza california where previous geodetic observations have indicated an anomalously high shear strain rate we present an updated set of secular velocities from gps and insar observations that reveal a 2 3 km wide shear zone deforming at a rate that exceeds the background strain rate by more than a factor of two gps occupations of an alignment array installed in 1990 across the fault trace at anza allow us to rule out shallow creep as a possible contributor to the observed strain rate using a dislocation model in a heterogeneous elastic half space we show that a reduction in shear modulus within the fault zone by a factor of 1 2 1 6 as imaged tomographically by allam and ben zion geophys j int 190 1181 1196 2012 can explain about 50 of the observed anomalous strain rate however the best fitting locking depth in this case 10 4 1 3 km is significantly less than the local depth extent of seismicity 14 18 km we show that a deep fault zone with a shear modulus reduction of at least a factor of 2 4 would be required to explain fully the geodetic strain rate assuming the locking depth is 15 km two alternative possibilities include fault creep at a substantial fraction of the long term slip rate within the region of deep microseismicity or a reduced yield strength within the upper fault zone leading to distributed plastic failure during the interseismic period

shallow slip deficit due to large strike slip earthquakes in dynamic rupture simulations with elasto plastic off fault response summary slip inversions of geodetic data from several large magnitude 7 strike slip earthquakes point to coseismic slip deficit at shallow depths 3 4 km that is coseismic slip appears to decrease towards the earth surface while the inferred slip distribution may be consistent with laboratory derived rate and state friction laws suggesting that the uppermost brittle crust may be velocity strengthening there remains a question of how the coseismic slip deficit is accommodated throughout the earthquake cycle the consequence of velocity strengthening fault friction at shallow depths is that the deficit of coseismic slip is relieved by post seismic afterslip and interseismic creep however many seismic events with inferred shallow slip deficit were not associated with either resolvable shallow interseismic creep or robust shallow afterslip hence the origin of shallow slip deficit remains uncertain in this study we investigate whether inelastic failure in the shallow crust due to dynamic earthquake rupture can explain the inferred deficit of shallow slip evidence for such failure is emerging from geologic seismic and geodetic observations we find that the amount of shallow slip deficit is proportional to the amount of inelastic deformation near the earth surface such deformation occurs under a wide range of parameters that characterize rock strength in the upper crust however the largest magnitude of slip deficit in models accounting for off fault yielding is 2 4 times smaller than that inferred from kinematic inversions of geodetic data to explain this discrepancy we further explore to what extent assumptions in the kinematic inversions may bias the inferred slip distributions inelastic deformation in the shallow crust reduces coseismic strain near the fault introducing an additional artificial deficit of up to 10 per cent of the maximum slip in inversions of geodetic data that are based on purely elastic models the largest magnitude of slip deficit in our models combined with the bias in inversions accounts for up to 25 per cent of shallow slip deficit which is comparable but still smaller than 30 60 per cent deficit inferred from kinematic inversions we discuss potential mechanisms that may account for the remaining discrepancy between slip deficit predicted by elasto plastic rupture models and that inferred from inversions of space geodetic data

surface ruptures on cross faults in the 24 november 1987 superstition hills california earthquake sequence left lateral slip occurred on individual surface breaks along northeast trending faults associated with the 24 november 1987 earthquake sequence in the superstition hills imperial valley california this sequence included the m s 6 2 event on a left lateral northeast trending cross fault between the superstition hills fault shf and brawley seismic zone which was spatially associated with the left lateral surface breaks six distinct subparallel cross faults broke at the surface with rupture lengths ranging from about formula to 10 km and maximum displacements ranging from 30 to 130 mm about half a day after the m s 6 2 event an m s 6 6 earthquake nucleated near the intersection of the cross faults with the shf and rupture propagated southeast along the shf whereas right lateral slip on the shf occurred dominantly on a single trace in a narrow zone the cross fault surface slip was distributed over several stands across a 10 km wide zone also whereas afterslip accounted for a large proportion of total slip on the shf there is no evidence for afterslip on the cross faults we present documentation of these surface ruptures a simple mechanical model of faulting illustrates how the foreshock sequence may have triggered the main rupture displacement on other cross faults could trigger an event on the southern san andreas fault by a similar mechanism in the future

stability assessment of slopes in rock governed by the hoek brown strength criterion abstract instabilities in rock slopes are often triggered along planar joints with weakened shear strength inducing translational failures in intact rocks however the kinematics of failure may exhibit rotation which is a more common occurrence also in soil slopes a slope instability in a geomaterial governed by the hoek brown failure criterion is analyzed and two measures of the slope safety are considered the stability number and the factor of safety a consistent method is developed to arrive at the factor of safety for geomaterials with nonlinear strength envelopes an argument is presented to justify the application of plasticity theorems in rocks and a collapse mechanism is developed consistent with the hoek brown failure criterion and the normality flow rule not surprisingly the kinematic approach of limit analysis indicates that the safety measures for slopes are greatly dependent on the geological strength index of the rock although the limit analysis used in the paper does not allow calculation of the true stress distribution in the rock the method allows approximately estimating the stress vector on the rupture surface it appears that for gentle slopes the stress vector is predominantly in the compression regime but with an increase in the slope inclination the range of the rupture surface with tensile stress increases this may very well be the chief reason why steeper slopes are more prone to failures results of calculations presented in the paper indicate that the stability numbers based on the proposed method are generally higher compared to those from the limit equilibrium and finite element methods and the factors of safety are lower considering that the method used yields a strict upper bound to the factor of safety and lower bound to the stability number this observation imparts confidence in the method of analysis presented in the paper

radionuclide migration in the experimental polygon of the red forest waste site in the chernobyl zone part 1 characterization of the waste trench fuel particle transformation processes in soils biogenic fluxes and effects on biota abstract this review article introduces an experimental site located within the chernobyl exclusion zone that is equipped to study radionuclide behavior in the environment after disposal of radioactive waste into shallow subsurface storage trenches this paper presents how the site is equipped and the methodology that was followed in order to understand and reproduce the observed 90sr contaminant plume downstream from a shallow waste trench in an area about 2 5 km west of the chernobyl nuclear power plant chnpp called the red forest the main results include identification of the radionuclide source term the distribution and inventories of radionuclides in the trench the description of the physical and chemical properties of the fuel particles encountered in the waste trench and a model of fuel particle dissolution and subsequent radionuclide leaching into the soil solution the biogenic migration of radionuclides from the trench to and effects of radiation on plants scots pine are also described

parallel fault strands at 9 km depth resolved on the imperial fault southern california 1 precision relocation of hundreds of small earthquakes occurring along the imperial fault in southern california during the last two decades reveals parallel steaks of seismicity at 9 km depth these strands are spaced about 0 5 km apart within a 2 km wide zone of earthquakes near the brittle ductile transition between the shallow locked part of the fault and a creeping zone at depth these results suggest that the lower crustal shear zone below the imperial fault site of major earthquakes in 1940 and 1979 must be at least two kilometers wide

transient deformation in california from two decades of gps displacements implications for a three dimensional kinematic reference frame our understanding of plate boundary deformation has been enhanced by transient signals observed against the backdrop of time independent secular motions we make use of a new analysis of displacement time series from about 1 000 continuous global positioning system gps stations in california from 1999 to 2018 to distinguish tectonic and nontectonic transients from secular motion a primary objective is to define a high resolution three dimensional reference frame datum for california that can be rapidly maintained with geodetic data to accommodate both secular and time dependent motions to this end we compare the displacements to those predicted by a horizontal secular fault slip model for the region and construct displacement and strain rate fields over the past 19 years california has experienced 19 geodetically detectable earthquakes and widespread postseismic deformation we observe postseismic strain rate variations as large as 1 000 nstrain year with moment releases equivalent up to an mw6 8 earthquake we find significant secular differences up to 10 mm year with the fault slip model from the mendocino triple junction to the southern cascadia subduction zone the northern basin and range and the santa barbara channel secular vertical uplift is observed across the transverse ranges coastal ranges sierra nevada as well as large scale postseismic uplift after the 1999 mw7 1 hector mine and 2010 mw7 2 el mayor cucapah earthquakes we also identify areas of vertical land motions due to anthropogenic natural and magmatic processes finally we demonstrate the utility of the kinematic datum by improving the accuracy of high spatial resolution 12 day repeat cycle sentinel 1 interferometric synthetic aperture radar displacement and velocity maps

the 2012 brawley swarm triggered by injection induced aseismic slip it has long been known that fluid injection or withdrawal can induce earthquakes but the underlying mechanisms remain elusive for example the 2012 brawley swarm which produced two strike slip shocks with magnitudes larger than 5 3 and surface ruptures in the close vicinity of a geothermal field started with earthquakes about 5 km deeper than the injection depth 1 5 km this makes the causality between the injection and seismicity unclear here we jointly analyze broadband and strong motion waveforms uavsar leveling measurements and field observations to reveal the detailed seismic and aseismic faulting behaviors associated with the 2012 brawley swarm in particular path calibration established from smaller events in the swarm allows waveform inversion to be conducted up to 3 hz to resolve finite rupture process of the mw 4 7 normal event our results show that the 2012 earthquake sequence was preceded by aseismic slip on a shallow normal fault beneath the geothermal field aseismic slip initiated in 2010 when injection rate rapidly increased and triggered the following earthquakes subsequently including unusually shallow and relatively high frequency seismic excitations on the normal fault in this example seismicity is induced indirectly by fluid injection a result of mediation by aseismic creep rather than directly by a pore pressure increase at the location of the earthquakes

stability of tunnels according to depth and variability of rock mass parameters abstract even with the most recent advances in rock mechanics the stability assessment of underground tunnels continues to involve many uncertainties in the parameters which can significantly affect the calculated factors of safety in the present work a straight characterization which can help to evaluate the risk of a tunnel collapse with respect to the depth of excavation is proposed following a consolidated limit analysis approach and by means of the hoek brown failure criterion the galleries are divided into shallow intermediate and deep according to the variability of the mechanical parameters of the rock mass with depth a solution to the problem of impending collapse in the case of variable rock properties is proposed and examples are presented and discussed both from an analytical and a numerical standpoint

a seismic refraction survey of the imperial valley region california the u s geological survey conducted an extensive seismic refraction survey in the imperial valley region of california in 1979 the imperial valley is located in the salton trough an active rift between the pacific and north american plates forty shots fired at seven shot points were recorded by 100 portable seismic instruments at typical spacing of 0 5 1 km more than 1300 recording locations were occupied and more than 3000 usable seismograms were obtained we analyzed five profiles using a standard ray tracing program constructed a contour map of reduced travel times from our most widely recorded shot point and modeled an existing gravity profile across the salton trough results are itemized 1 all models have in common a sedimentary layer vp 1 8 5 0 km s a transition zone vp 5 0 5 65 km s a basement vp 5 65 km s in the imperial valley 5 9 km s on the bordering mesas and subbasement vp 7 2 km s 2 the sedimentary layer ranges in thickness along the axis of the salton trough from 3 7 km salton sea to 4 8 km u s mexican border on the bordering mesas it is quite variable in thickness 3 the transition zone is about 1 km thick in most places in the imperial valley there are no marked velocity discontinuities in this zone between the sedimentary layer and basement on the bordering mesas however there is a discontinuity at the top of this zone 4 there are apparently two types of basement on the bordering mesas basement is crystalline igneous and metamorphic rocks in the imperial valley basement is mostly lower greenshist facies sedimentary rocks based primarily on the smooth transition in character from sediment to basement arrivals the low value of basement velocity and the fact that deep 4 km wells in the valley penetrate only the upper part of the known cenozoic stratigraphic column for the salton trough 5 the subbasement or intermediate crustal layer ranges in depth along the axis of the salton trough from 16 km salton sea to 10 km u s mexican border gravity modeling requires that this layer deepen and or pinch out beneath the bordering mesas and mountain ranges based on its high velocity and the presence of intrusive basaltic rocks in the sedimentary section in the imperial valley the subbasement is thought to be a mafic intrusive complex similar to oceanic middle crust 6 several structures are seen that affect basement transition zone and deeper parts of the sedimentary layer they include a scarp along the imperial fault as much as 1 km down to the northeast and a scarp passing roughly along the topographic boundary between the imperial valley and the bordering mesa to the west as much as 3 km down to the east we interpret the latter scarp to be the suture or rift boundary between the older crystalline basement on the mesa and the younger metasedimentary basement in the imperial valley 7 on a contour map of reduced travel time from our most widely recorded shot point subtle patches of early arrivals among otherwise late arrivals in the central imperial valley correlate well with known geothermal resource areas having reservoir temperatures of more than 150 c apparently the salton trough is a location where new crust is being generated as the rift opens mafic intrusive rocks fill it from below as sedimentary rocks fill it from above rifting and intrusion produce high heat flow that metamorphoses the sedimentary rocks to shallow depth metasedimentary basement in the imperial valley and thus consolidates the new crust

uavsar observations of triggered slip on the imperial superstition hills and east elmore ranch faults associated with the 2010 m 7 2 el mayor cucapah earthquake the 4 april 2010 m 7 2 el mayor cucapah earthquake that occurred in baja california mexico and terminated near the u s mexican border caused slip on the imperial superstition hills and east elmore ranch faults the pattern of slip was observed using radar interferometry from nasa s uninhabited aerial vehicle synthetic aperture radar uavsar instrument collected on 20 21 october 2009 and 12 13 april 2010 right lateral slip of 36 9 and 14 2 mm occurred on the imperial and superstition hills faults respectively left lateral slip of 9 2 mm occurred on the east elmore ranch fault the widths of the zones of displacement increase northward suggesting successively more buried fault motion to the north the observations show a decreasing pattern of slip northward on a series of faults in the salton trough stepping between the el mayor cucapah rupture and san andreas fault most of the motion occurred at the time of the m 7 2 earthquake and the uavsar observations are consistent with field creepmeter gps and envisat observations an additional 28 1 mm of slip at the southern end of the imperial fault over a 1 km wide zone was observed over a 1 day span a week after the earthquake suggesting that the fault continued to slip at depth following the mainshock the total moment release on the three faults is 2 3 1023 1 2 1024 dyne cm equivalent to a moment magnitude release of 4 9 5 3 assuming shallow slip depths ranging from 1 to 5 km

triggered surface slips in the coachella valley area associated with the 1992 joshua tree and landers california earthquakes the coachella valley area was strongly shaken by the 1992 joshua tree 23 april and landers 28 june earthquakes and both events caused triggered slip on active faults within the area triggered slip associated with the joshua tree earth quake was on a newly recognized fault the east wide canyon fault near the south western edge of the little san bernardino mountains slip associated with the land ers earthquake formed along the san andreas fault in the southeastern coachella valley surface fractures formed along the east wide canyon fault in association with the joshua tree earthquake the fractures extended discontinuously over a 1 5 km stretch of the fault near its southern end sense of slip was consistently right oblique west side down similar to the long term style of faulting measured offset values were small with right lateral and vertical components of slip ranging from 1 to 6 mm and 1 to 4 mm respectively this is the first documented historic slip on the east wide canyon fault which was first mapped only months before the joshua tree earthquake surface slip associated with the joshua tree earthquake most likely de veloped as triggered slip given its 5 km distance from the joshua tree epicenter and aftershocks as revealed in a trench investigation slip formed in an area with only a thin 3 m thick veneer of alluvium in contrast to earlier documented triggered slip events in this region all in the deep basins of the salton trough a paleoseismic trench study in an area of 1992 surface slip revealed evidence of two and possibly three surface faulting events on the east wide canyon fault during the late quaternary probably latest pleistocene first event and mid to late holocene second two events about two months after the joshua tree earthquake the landers earthquake then triggered slip on many faults including the san andreas fault in the southeastern coachella valley surface fractures associated with this event formed discontinuous breaks over a 54 km long stretch of the fault from the indio hills southeastward to durmid hill sense of slip was right lateral only locally was there a minor 1 mm vertical component of slip measured dextral displacement values ranged from 1 to 20 mm with the largest amounts found in the mecca hills where large slip values have been measured following past triggered slip events

probing the mechanical properties of seismically active crust with space geodesy study of the coseismic deformation due to the 1992 mw7 3 landers southern california earthquake 1 the coseismic deformation due to the 1992 m w 7 3 landers earthquake southern california is investigated using synthetic aperture radar sar and global positioning system gps measurements the ers 1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components east north up of the coseismic surface displacement field the coseismic displacement field exhibits symmetries with respect to the rupture plane that are suggestive of a linear relationship between stress and strain in the crust interferometric synthetic aperture radar insar data show small scale deformation on nearby faults of the eastern california shear zone some of these faults in particular the calico rodman and pinto mountain faults were also subsequently strained by the 1999 m w 7 1 hector mine earthquake i test the hypothesis that the anomalous fault strain represents essentially an elastic response of kilometer scale compliant fault zones to stressing by nearby earthquakes fialko et al 2002 the coseismic stress perturbations due to the landers earthquake are computed using a slip model derived from inversions of the insar and gps data calculations are performed for both homogeneous and transversely isotropic half space models the compliant zone model that best explains the deformation on the calico and pinto mountain faults due to the hector mine earthquake successfully predicts the coseismic displacements on these faults induced by the landers earthquake deformation on the calico and pinto mountain faults implies about a factor of 2 reduction in the effective shear modulus within the similar to 2 km wide fault zones the depth extent of the low rigidity zones is poorly constrained but is likely in excess of a few kilometers the same type of structure is able to explain high gradients in the radar line of sight displacements observed on other faults adjacent to the landers rupture in particular the lenwood fault north of the soggy lake has likely experienced a few centimeters of left lateral motion across 1 km wide compliant fault zone having the rigidity reduction of more than a factor of 2 the inferred compliant fault zones are interpreted to be a result of extensive damage due to past earthquakes

a two layer model for aseismic slip on the superstition hills fault california a new differential creepmeter on the superstition hills fault reveals that afterslip at approximately 28 mm year consists of episodic creep events super imposed on a slow stable slip component of 2 4 mm year the relative contribution from this background slip 8 5 of the total aseismic surface slip has remained approximately constant for the past 2 years to account for this observed behavior we proposed a two layer model for aseismic slip in which stable sliding occurs from the surface to a transition depth below which episodic creep events are initiated these creep events propagate to the surface through the stable sliding layer from the ratio of background slip velocity to total afterslip velocity we estimate the ratio of depths of stable sliding to episodic slip regions to be approximately 1 10 thus assuming that episodic slip extends to 3 km we infer that background surface creep is moderated by processes in the uppermost 300 m we speculate that the transition depth is sensitive to applied fault normal stresses and suggest that the ratio of stable sliding to episodic slip velocities may provide an indication of secular variations in tectonic stress since the background creep is evidently continuous and little affected by episodic events its velocity may provide a sensitive indication of applied tectonic strain in the period range days to years

seismic velocity change patterns along the san jacinto fault zone following the 2010 m7 2 el mayor cucapah and m5 4 collins valley earthquakes

late holocene rupture history of the rose canyon fault in old town san diego implications for cascading earthquakes on the newport inglewood rose canyon fault system

coseismic slip variation assessed from terrestrial lidar scans of the el mayor cucapah surface rupture abstract we analyze high resolution 103 points m2 terrestrial lidar surveys of the 4 april 2010 el mayor cucapah earthquake rupture baja california mexico collected at three sites 12 18 days after the event using point cloud based tools in an immersive visualization environment we quantify coseismic fault slip for hundreds of meters along strike and construct densely constrained along strike slip distributions from measurements of offset landforms uncertainty bounds for each offset determined empirically by repeatedly measuring offsets at each site sequentially illuminate measurement uncertainties that are difficult to quantify in the field these uncertainties are used to define length scales over which variability in slip distributions may be assumed to reflect either recognizable earthquake mechanisms or measurement noise at two sites characterized by 2 3 m of concentrated right oblique slip repeat measurements yield 2 uncertainties of 11 12 each site encompasses 200 m along strike and a smoothed linear slip gradient satisfies all measurement distributions implying along fault strains of 10 3 conversely the common practice of defining the slip curve by the local slip maxima distorts the curve overestimates along fault strain and may overestimate actual fault slip by favoring measurements with large positive uncertainties at a third site characterized by 1 2 5 m of diffuse normal slip repeat measurements of fault throw summed along fault perpendicular profiles yield 2 uncertainties of 17 here a low order polynomial fit through the measurement averages best approximates surface slip however independent measurements of off fault strain accommodated by hanging wall flexure suggest that over the 200 m length of this site a linear interpolation through the average values for the slip maxima at either end of this site most accurately represents subsurface displacement in aggregate these datasets show that given uncertainties of greater than 11 2 slip distributions over shorter scales are likely to be less uneven than those derived from a single set of field or lidar based measurements this suggests that the relatively smooth slip curves we obtain over 102 m distances reflect real physical phenomena whereas short wavelength variability over 100 101 m distances can be attributed to measurement uncertainty

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

the 2010 m w 7 2 el mayor cucapah earthquake sequence baja california mexico and southernmost california usa active seismotectonics along the mexican pacific margin the el mayor cucapah earthquake sequence started with a few foreshocks in march 2010 and a second sequence of 15 foreshocks of m 2 up to m4 4 that occurred during the 24 h preceding the mainshock the foreshocks occurred along a north south trend near the mainshock epicenter the mw 7 2 mainshock on april 4 exhibited complex faulting possibly starting with a m6 normal faulting event followed 15 s later by the main event which included simultaneous normal and right lateral strike slip faulting the aftershock zone extends for 120 km from the south end of the elsinore fault zone north of the us mexico border almost to the northern tip of the gulf of california the waveform relocated aftershocks form two abutting clusters each about 50 km long as well as a 10 km north south aftershock zone just north of the epicenter of the mainshock even though the baja california data are included the magnitude of completeness and the hypocentral errors increase gradually with distance south of the international border the spatial distribution of large aftershocks is asymmetric with five m5 aftershocks located to the south of the mainshock and only one m5 7 aftershock but numerous smaller aftershocks to the north further the northwest aftershock cluster exhibits complex faulting on both northwest and northeast planes thus the aftershocks also express a complex pattern of stress release along strike the overall rate of decay of the aftershocks is similar to the rate of decay of a generic california aftershock sequence in addition some triggered seismicity was recorded along the elsinore and san jacinto faults to the north but significant northward migration of aftershocks has not occurred the synthesis of the el mayor cucapah sequence reveals transtensional regional tectonics including the westward growth of the mexicali valley and the transfer of pacific north america plate motion from the gulf of california in the south into the southernmost san andreas fault system to the north we propose that the location of the 2010 el mayor cucapah as well as the 1992 landers and 1999 hector mine earthquakes may have been controlled by the bends in the plate boundary

insar imaging of displacement on flexural slip faults triggered by the 2013 mw 6 6 lake grassmere earthquake central new zealand interferometric synthetic aperture radar insar data reveal surface slip on multiple faults triggered by the 2013 mw 6 6 lake grassmere earthquake new zealand surface offsets of 1 2 cm occurred on previously inferred flexural slip faults located 4 km from the epicenter we document dip slip on at least three different northeast striking northwest dipping flexural slip faults located in the western limb of a syncline the along strike extent of the triggered slip is 1 1 5 km for each fault dislocation models suggest that triggered slip is confined to shallow depths 800 m coulomb stress analysis indicates that slip was not triggered by the static stress change of the main shock but was likely caused by dynamic shaking during the passage of seismic waves our finding also provides an important clue on how some slip on shallow flexural slip faults takes place

san andreas fault zone california m 5 5 earthquake history the san andreas fault zone has been a very significant source of major california earthquakes from 1812 to 1906 it generated four major earthquakes of m 7 or larger in two pairs on two major portions of the fault a pair of major earthquakes occurred on the central to southern region where the 1857 faulting overlapped the 1812 earthquake faulting a pair of major earthquakes occurred on the northern region where the 1906 faulting overlapped the 1838 earthquake faulting also earthquakes of m 7 occurred in the san francisco bay area on the hayward fault in 1868 and the santa cruz mountains near loma prieta in 1989 and on the imperial fault near the border with mexico in 1940 the 1838 earthquake s damage effects throughout the bay area from san francisco to santa clara valley and monterey were unequalled by any historical earthquake other than the 1906 event this and numerous strong possible aftershocks during the following 3 years in the san juan bautista vicinity suggest 1838 faulting from san francisco to san juan bautista cycles of seismicity and quiescence were associated with the bay area earthquakes of 1868 1906 and 1989 the 1868 earthquake on the hayward fault was preceded by 12 earthquakes of m 5 5 from 1855 to 1866 within 60 km of the hayward fault and was followed by 13 quiet years the 1906 san andreas fault event was preceded from 1881 to 1903 by 18 earthquakes of m 5 5 and was followed by quiescence with only three earthquakes of m 5 5 until 1954 the bay area has been seismically quiet at the m 5 5 level since the 1989 loma prieta earthquake and its 1990 aftershocks which contrasts with the 10 years before 1989 when five m 5 5 6 2 events occurred the loma prieta earthquake is of similar magnitude to the 1868 hayward event and could be followed by a similarly short quiet period the 1857 earthquake had immediate foreshocks in the lonoak bitterwater region 50 km northwest of parkfield in the northern end zone of the 1857 rupture extending southeast from bitterwater 70 km to parkfield the rate of seismic moment release has decreased with time since 1857 this may reflect the decay with time of the stress loading due to the 9 m 1857 fault displacements 80 km southeast of parkfield and explain why the predicted earthquake which was based on the assumption of regular recurrence of parkfield earthquakes has not yet occurred the extent of the 1812 earthquake fault rupture is not well defined jacoby et al 1988 estimated that it extended 170 km from cajon pass to tejon pass based on this estimate we present the hypothesis that the rupture occurred in two segments in december 1812 the eastern segment generated the 8 december earthquake that damaged san juan capistrano san gabriel san fernando and san buenaventura thirteen days later the western segment ruptured generating the earthquake that damaged san fernando and san buenaventura again as well as santa barbara santa ynez and purisima concepcion

radar determination of fault slip and location in partially decorrelated images faced with the challenge of thousands of frames of radar interferometric images automated feature extraction promises to spur data understanding and highlight geophysically active land regions for further study we have developed techniques for automatically determining surface fault slip and location using deformation images from the nasa uninhabited aerial vehicle synthetic aperture radar uavsar which is similar to satellite based sar but has more mission flexibility and higher resolution pixels are approximately 7 m this radar interferometry provides a highly sensitive method clearly indicating faults slipping at levels of 10 mm or less but interferometric images are subject to decorrelation between revisit times creating spots of bad data in the image our method begins with freely available data products from the uavsar mission chiefly unwrapped interferograms coherence images and flight metadata the computer vision techniques we use assume no data gaps or holes so a preliminary step detects and removes spots of bad data and fills these holes by interpolation and blurring detected and partially validated surface fractures from earthquake main shocks aftershocks and aseismic induced slip are shown for faults in california including el mayor cucapah m7 2 2010 the ocotillo aftershock m5 7 2010 and south napa m6 0 2014 aseismic slip is detected on the san andreas fault from the el mayor cucapah earthquake in regions of highly patterned partial decorrelation validation is performed by comparing slip estimates from two interferograms with published ground truth measurements

global positioning system measurements of deformations associated with the 1987 superstition hills earthquake evidence for conjugate faulting large station displacements observed from imperial valley global positioning system gps campaigns are attributed to the november 24 1987 superstition hills earthquake sequence thirty sites from a 42 station gps network established in 1986 have been reoccupied during 1988 and or 1990 displacements at three sites within 3 km of the surface rupture approach 0 5 m eight additional stations within 20 km of the seismic zone are displaced at least 10 cm this is the first occurrence of a large earthquake ms 6 6 within a preexisting gps network best fitting uniform slip models of rectangular dislocations in an elastic half space indicate 130 8 cm right lateral displacement along the northwest trending superstition hills fault and 30 10 cm left lateral displacement along the conjugate northeast trending elmore ranch fault the geodetic moments are 9 4 1025 dyn cm and 2 3 1025 dyn cm for the superstition hills and elmore ranch faults respectively consistent with teleseismic source parameters the data also suggest that postseismic slip along the superstition hills fault is concentrated at shallow depths distributed slip solutions using singular value decomposition indicate near uniform displacement along the elmore ranch fault and concentrated slip to the northwest and southeast along the superstition hills fault a significant component of nonseismic secular displacement is observed across the imperial valley which is attributed to interseismic plate boundary deformation

three dimensional roof collapse analysis in circular tunnels in rock abstract collapse of a roof in circular cross section tunnels is analyzed the kinematic approach of limit analysis is utilized with strength of the rock described by the hoek brown failure criterion the parametric form of the hoek brown function is used to avoid introduction of an alternative explicit form of the shear strength criterion three measures of safety are considered stability number the factor of safety and the support pressure needed to assure roof stability the shape of the rock block in the failure mechanism consists of a right elliptic cone with a piece wise linear generatrix and a prismatic section inserted between the two halves of the cone the complexity of the cross section of the block with the tunnel makes for an intricate integration of the rates of the dissipated work and the work of external forces all three measures of safety are strongly dependent on the quality of rock described in the geological strength index whereas the dependence on the rock type captured in coefficient mi is less distinct the length of the roof failure mechanism is subject to a constraint dependent on the spacing of the supporting ribs in the tunnel all measures of safety or stability are distinctly dependent on the length constraint the shorter the spacing between the ribs the safer the tunnel against roof collapse the 2d analysis yields the most conservative outcome

pattern informatics and its application for optimal forecasting of large earthquakes in japan pattern informatics pi technique can be used to detect precursory seismic activation or quiescence and make an earthquake forecast here we apply the pi method for optimal forecasting of large earthquakes in japan using the data catalogue maintained by the japan meteorological agency the pi method is tested to forecast large magnitude m 5 earthquakes spanning the time period 1995 2004 in the kobe region visual inspection and statistical testing show that the optimized pi method has forecasting skill relative to the seismic intensity data often used as a standard null hypothesis moreover we find in a retrospective forecast that the 1995 kobe earthquake m 7 2 falls in a seismically anomalous area another approach to test the forecasting algorithm is to create a future potential map for large m 5 earthquake events this is illustrated using the kobe and tokyo regions for the forecast period 2000 2009 based on the resulting kobe map we point out several forecasted areas the epicentral area of the 1995 kobe earthquake the wakayama area the mie area and the aichi area the tokyo forecast map was created prior to the occurrence of the oct 23 2004 niigata earthquake m 6 8 and the principal aftershocks with 5 0 m we find that these events were close to in a forecasted area on the tokyo map the pi technique for regional seismicity observation substantiates an example showing considerable promise as an intermediate term earthquake forecasting in japan

hierarchical interlocked orthogonal faulting in the 2019 ridgecrest earthquake sequence a nearly 20 year hiatus in major seismic activity in southern california ended on 4 july 2019 with a sequence of intersecting earthquakes near the city of ridgecrest california this sequence included a foreshock with a moment magnitude mw of 6 4 followed by a mw 7 1 mainshock nearly 34 hours later geodetic seismic and seismicity data provided an integrative view of this sequence which ruptured an unmapped multiscale network of interlaced orthogonal faults this complex fault geometry persists over the entire seismogenic depth range the rupture of the mainshock terminated only a few kilometers from the major regional garlock fault triggering shallow creep and a substantial earthquake swarm the repeated occurrence of multifault ruptures as revealed by modern instrumentation and analysis techniques poses a formidable challenge in quantifying regional seismic hazards

the 2016 kumamoto mw 7 0 earthquake a significant event in a fault volcano system the 2016 kumamoto earthquake sequence occurred on the futagawa hinagu fault zone near the aso volcano on kyushu island the sequence was initiated with two major m w 6 0 foreshocks and the mainshock m w 7 0 occurred 25 h after the second major foreshock we combine gps strong motion synthetic aperture radar images and surface offset data in a joint inversion to resolve the kinematic rupture process of the mainshock and coseismic displacement of the foreshocks the joint inversion results reveal a unilateral rupture process for the mainshock involving sequential rupture of four major asperities the slip area of the foreshocks and mainshock and the aftershock loci form a detailed complementary pattern the mainshock rupture terminates near the rim of the caldera leaving a 10 km long gap of aftershocks this area is characterized by high temperature and low shear wave velocity density and resistivity which may be related to the partially melted geothermal condition ductile material property near the volcano may act as a material barrier to the dynamic rupture topographic weight of the caldera increases compressional normal stress on the fault plane which may behave as a stress barrier long term seismic hazard and deformation behaviors related to these two types of barriers are discussed in terms of the associated frictional mechanism significant postseismic creeps observed near the volcano area indicates a velocity strengthening frictional behavior near the rupture termination which confirms that the material barrier mechanism is likely the dominant rupture termination mechanism

slip on faults in the imperial valley triggered by the 4 april 2010 mw 7 2 el mayor cucapah earthquake revealed by insar 1 radar interferometry insar field measurements and creepmeters reveal surface slip on multiple faults in the imperial valley triggered by the main shock of the 4 april 2010 el mayor cucapah mw 7 2 earthquake co seismic offsets occurred on the san andreas superstition hills imperial elmore ranch wienert coyote creek elsinore yuha and several minor faults near the town of ocotillo at the northern end of the mainshock rupture we documented right lateral slip 40 mm on northwest striking faults and left lateral slip 40 mm on southwest striking faults slip occurred on 15 km and 20 km long segments of the san andreas fault in the mecca hills 50 mm and durmid hill 10 mm respectively and on 25 km of the superstition hills fault 37 mm field measurements of slip on the superstition hills fault agree with insar and creepmeter measurements to within a few millimeters dislocation models of the insar data from the superstition hills fault confirm that creep in this sequence as in previous slip events is confined to shallow depths 3 km

seismic evidence for conjugate slip and block rotation within the san andreas fault system southern california the pattern of seismicity in southern california indicates that much of the activity is presently occurring on secondary structures several of which are oriented nearly orthogonal to the strikes of the major through going faults slip along these secondary transverse features is predominantly left lateral and is consistent with the reactivation of conjugate faults by the current regional stress field near the intersection of the san jacinto and san andreas faults however these active left lateral faults appear to define a set of small crustal blocks which in conjunction with both normal and reverse faulting earthquakes suggests contemporary clockwise rotation as a result of regional right lateral shear other left lateral faults representing additional rotating block systems are identified in adjacent areas from geologic and seismologic data many of these structures predate the modern san andreas system and may control the pattern of strain accumulation in southern california geodetic and paleomagnetic evidence confirm that block rotation by strike slip faulting is nearly ubiquitous particularly in areas where shear is distributed and that it accommodates both short term elastic and long term nonelastic strain a rotating block model accounts for a number of structural styles characteristic of strike slip deformation in california including variable slip rates and alternating transtensional and transpressional features observed along strike of major wrench faults domains of evenly spaced antithetic faults that terminate against major fault boundaries continued development of bends in faults with large lateral displacements anomalous focal mechanisms and differential uplift in areas otherwise expected to experience extension and subsidence since block rotation requires a detachment surface at depth to permit rotational movement low angle structures like detachments of either local or regional extent may be involved in the contemporary strike slip deformation of southern california a block nature of the crust also implies that not only will strains be inhomogeneous and likely concentrated along edge bounding faults but that local stress orientations will largely be responding to local kinematic constraints of block rotation and fault interaction this behavior coupled with the presence of possible regional detachments accounts for some of the precursory changes observed at considerable distances prior to large earthquakes and the triggering of seismicity or slip on nearby faults or around adjacent block edges although fault displacements along secondary structures associated with block rotations remain small they may still influence the nucleation and the characteristic rupture length of large earthquakes a more complete description of what these structures are and how they interact may prove critical to any fundamental understanding of the earthquake process and any realistic assessment of the regional seismic hazard

sedimentation and crustal recycling along an active oblique rift margin salton trough and northern gulf of california transtensional basins embedded in the san andreas fault system of southern california united states and northwestern mexico are fi lled with sediment derived from the colorado river which drains a large area of the western u s interior the sediment is rapidly buried heated and mingled with intrusions in the deep basins to form a new generation of recycled crust along the active plate boundary using a range of values for total basin depth relative volume of mantle derived intrusions and composition of early rift deposits the volume of colorado river derived sediment in the basins is bracketed between 2 2 and 3 4 10 5 km 3 similar to the volume of rock that likely was eroded from the colorado river catchment over the past 5 6 m y the volumetric rate of crustal growth by sedimentation is 80 130 km 3 m y km comparable to growth rates in subductionrelated island arcs and slow seafl oor spreading centers sedimentary and basinal processes thus play a major role in crustal evolution and recycling in this setting and may be important at other rifted margins where a large river system is captured following tectonic collapse of a prerift orogenic highland

dynamic rupture modeling of the m7 2 2010 el mayor cucapah earthquake comparison with a geodetic model author s kyriakopoulos c oglesby dd funning gj ryan kj abstract 2017 american geophysical union all rights reserved the 2010 mw 7 2 el mayor cucapah earthquake is the largest event recorded in the broader southern california baja california region in the last 18nyears here we try to analyze primary features of this type of event by using dynamic rupture simulations based on a multifault interface and later compare our results with space geodetic models our results show that starting from homogeneous prestress conditions slip heterogeneity can be achieved as a result of variable dip angle along strike and the modulation imposed by step over segments we also considered effects from a topographic free surface and find that although this does not produce significant first order effects for this earthquake even a low topographic dome such as the cucapah range can affect the rupture front pattern and fault slip rate finally we inverted available interferometric synthetic aperture radar data using the same geometry as the dynamic rupture model and retrieved the space geodetic slip distribution that serves to constrain the dynamic rupture models the one to one comparison of the final fault slip pattern generated with dynamic rupture models and the space geodetic inversion show good agreement our results lead us to the following conclusion in a possible multifault rupture scenario and if we have first order geometry constraints dynamic rupture models can be very efficient in predicting large scale slip heterogeneities that are important for the correct assessment of seismic hazard and the magnitude of future events our work contributes to understanding the complex nature of multifault systems

rapid drought induced land subsidence and its impact on the california aqueduct abstract the central valley in california is characterized by a semi arid climate prone to droughts a variable surface water supply and immense agricultural areas dependent on groundwater irrigation the groundwater is stored in a complex aquifer system composed of alternating layers of coarse sediments and fine grained sediments acting as confining materials groundwater fluctuations are coupled with both the elastic and inelastic land surface deformation historically observed in the central valley surface deformation poses a hazard to the california aqueduct which supports central valley agriculture and large urban populations in southern california the risk of reduced aqueduct efficacy and expensive repairs compels water resource managers to carefully monitor land deformation in the valley a persistent drought in the region began in 2012 intensified in 2014 and was abruptly alleviated by a wet period from dec 2016 to feb 2018 nasa s uavsar l band synthetic aperture radar acquired 31 high resolution radar images between may 2013 and nov 2018 the interferometric phase difference between acquisitions is used to develop a time series of vertical displacement and identify and track a rapidly forming subsidence feature adjacent to the california aqueduct the surface area of the feature that subsided 10 cm or more by the end of the time series reaches 4452 ha and a 10 5 km segment of the aqueduct this study also incorporates extensometer measurements precise leveling surveys sentinel 1a displacement concurrent water elevation data well construction reports nearby extensometer measurements aquifer material characterization and environmental conditions spatiotemporal data availability limits the appropriateness of calculations and models able to be performed for different sites along the aqueduct we aim to offer insight into heterogeneous subsurface properties and mechanics estimate the permanent loss of aquifer storage volume and identify additional data that would aid water management

a silent mw 4 7 slip event of october 2006 on the superstition hills fault southern california 1 during october 2006 the 20 km long superstition hills fault shf in the salton trough southern california slipped aseismically producing a maximum offset of 27 mm as recorded by a creepmeter we investigate this creep event as well as the spatial and temporal variations in slip history since 1992 using ers 1 2 and envisat satellite data during a 15 year period steady creep is punctuated by at least three events the first two events were dynamically triggered by the 1992 landers and 1999 hector mine earthquakes in contrast there is no obvious triggering mechanism for the october 2006 event field measurements of fault offset after the 1999 and 2006 events are in good agreement with the interferometric synthetic aperture radar data indicating that creep occurred along the 20 km long fault above 4 km depth with most of the slip occurring at the surface the moment released during this event is equivalent to a mw 4 7 earthquake this event produced no detectable aftershocks and was not recorded by the continuous gps stations that were 9 km away modeling of the long term creep from 1992 to 2007 creep using stacked ers 1 2 interferograms also shows a maximum creep depth of 2 4 km with slip tapering with depth considering that the sediment thickness varies between 3 km and 5 km along the shf our results are consistent with previous studies suggesting that shallow creep is controlled by sediment depth perhaps due to high pore pressures in the unconsolidated sediments

the 2018 mw6 4 hualien earthquake dynamic slip partitioning reveals the spatial transition from mountain building to subduction abstract the hualien earthquake of 6 february 2018 occurred on the east coast of taiwan in the collision zone between the eurasia and philippine sea plates even though an event with a moderate magnitude of mw6 4 it caused widespread surface rupture in and around the city of hualien leading to significant loss of life and property damages in this study we investigate the rupture process of this earthquake using teleseismic strong motion gps and sar observations we first employ the geodetic data to search for the geometry of multiple fault planes followed by a multi point source inversion using teleseismic and strong motion waveforms to determine the possible change in mechanism during the rupture process we parameterize the fault model with three curved segments to represent the complicated fault system involved in the rupture process an offshore fault was ruptured by the hualien earthquake showing a curved geometry with the dip angle changing from shallow 45 in the north to sub vertical 80 in the south evidence from tomographic velocity model indicates that the offshore fault is the boundary between the subducted coastal range and meilun tableland which is also a plate interface finally a joint inversion is carried out to constrain the complete rupture process the inversion result reveals that the rupture initiated on the offshore fault interface and propagated unilaterally towards south southwest the rupture then jumped on to the sub vertical meilun fault and reached the ground surface significant dynamic slip partitioning occurred during the rupture process near the meilun fault with the majority of thrust and strike slip motions occurring on the off shore fault and the meilun fault respectively the afterslip model is inverted with sar timeseries spanning 6 months after the mainshock the afterslip model shows a strong complementary pattern with co seismic slips the comparison between the 1951 and 2018 hualien earthquake shows that the rupture behavior of the meilun fault does not follow a repeating earthquake pattern thrust motion may occur on the two side walls of the meilun tableland with a teeterboard uplift pattern in different earthquake cycles the change in geometry and slip on the inter plate fault appears to be related to the transition of the coastal range from mountain building to subduction

spatial localization of moment deficits in southern california 1 the balance between interseismic elastic strain accumulation and coseismic release defines the extent to which a fault system exhibits a surplus or deficit of large earthquakes we calculate the regional moment accumulation rate in southern california based on a fault slip rate catalog estimated from a block model of interseismic deformation constrained by gps measurements the scalar moment accumulation rate 17 8 1 1 1018 n m yr is approximately 50 larger than the average moment release rate over the last 200 years differences between the accumulated and released elastic displacement fields are consistent with moment deficits that are localized in three regions the southern san andreas and san jacinto faults offshore faults and the los angeles and ventura basins and the eastern california shear zone the moment budget could be balanced by coseismic events with a composite magnitude of mw 8

sawtooth segmentation and deformation processes on the southern san andreas fault california five contiguous 12 13 km fault segments form a sawtooth geometry on the south ernmost san andreas fault the kinematic and morphologic properties of each segment depend on fault strike despite differences of strike between segments of as little as 3 degrees oblique slip transpression of fault segments within the indio hills mecca hills and durmid hill results from an inferred 8 1 ratio of dex tral slip to convergence across the fault zone triggered slip and creep are confined almost en tirely to transpressive segments of the fault durmid hill has been formed in the last 28 n 6 ka by uplift at an average rate of 3 1 mm a

locating distributed faulting contributions from insar imaging to probabilistic fault displacement hazard analysis pfdha abstract prediction of location and amount of slip for distributed faulting associated to strong earthquakes is a recently explored issue with major implications in terms of hazard assessment currently the best practice involves the applications of probabilistic fault displacement hazard analysis pfdha whose results fit sufficiently well real data in the near range of the primary fault but show considerable inaccuracies in the far range we believe that this inaccuracy descends from the biased earthquake databases used for regression analysis whose data relative to old earthquakes were largely collected only by field surveys focused close to the primary fault i e near range remotely sensed data i e interferometric radar imaging insar offer the opportunity to precisely measure the surface deformation induced by strong earthquakes and thus to explore its possible relation with distributed faulting we analyze the l aquila earthquake case study 29th april 2009 mw 6 3 and explore the correlation between location and slip on distributed faulting and insar derived deformation field we find a significant correlation between occurrence of distributed faulting and profile curvature of the dislocation field in spite of the distance from the primary fault moreover distributed faults tend to occur within the area deformed by the earthquake as imaged by insar data and whose extent is directly proportional to the earthquake magnitude mw according to a dataset of 30 recent earthquakes we then propose that these observations have to be incorporated into the present pfdha practice as limit boundaries to possible scenarios of probabilistic analysis and that an integrated use of field based and remotely data collection have to be implemented following strong earthquakes

statistical physics approach to understanding the multiscale dynamics of earthquake fault systems 1 earthquakes and the faults upon which they occur interact over a wide range of spatial and temporal scales in addition many aspects of regional seismicity appear to be stochastic both in space and time however within this complexity there is considerable self organization we argue that the occurrence of earthquakes is a problem that can be attacked using the fundamentals of statistical physics concepts of statistical physics associated with phase changes and critical points have been successfully applied to a variety of cellular automata models examples include sandpile models forest fire models and particularly slider block models these models exhibit avalanche behavior very similar to observed seismicity a fundamental question is whether variations in seismicity can be used to successfully forecast the occurrence of earthquakes several attempts have been made to utilize precursory seismic activation and quiescence to make earthquake forecasts some of which show promise

roof stability in deep rock tunnels abstract a method is presented addressing quantitative assessment of tunnel roof stability based on the kinematic approach of limit analysis long tunnels with both rectangular flat ceiling and circular cross sections are considered the rock is governed by the hoek brown strength envelope and the normality flow rule and it is assumed to provide enough ductility at failure making plasticity theorems applicable a failing block in the collapse mechanism is separated from the stationary rock by a deformation band with a large gradient of velocity across its width the shape of the block in the critical mechanism is found from the requirement of the mechanism s kinematic admissibility and an optimization procedure consistent with respective measures of stability the stability number and the supporting pressure needed for tunnel stability are calculated first although less commonly used in rock engineering a procedure is developed for estimating the factor of safety defined as the ratio of the rock shear strength determined from the hoek brown criterion to the demand on the strength curiously for flat ceiling tunnels such definition of the factor of safety yields results equivalent to the ratio of a dimensionless group dependent on the uniaxial compressive strength and the size of the tunnel to the stability number such an equivalency does not hold for tunnels with ceilings of finite curvature not surprisingly all measures of tunnel roof stability are strongly dependent on the geological strength index that describes the quality of the rock

flexural slip folding along the eastern elmore ranch fault in the superstition hills earthquake sequence of november 1987 co seismic flexural slip folding of a small anticline along the eastern elmore ranch fault associated with the superstition hills earthquake sequence demonstrates that variations in left lateral slip can be explained locally by folding surface rupture on the eastern branch of the elmore ranch fault was greatest to the northeast of the fold but decreased to zero across the southern limb a kilometer long surface slip gap exists just southwest of the fold being bounded on the northeast with 75 mm of slip and to the southwest with about 60 mm of slip lateral slip continues southwesterly to the faults intersection with the superstition hills fault the gentle to openly folded moderately plunging upright asymmetric anticline experienced left lateral slip on the northern limb and right oblique slip on the southern limb with maximum documented lateral slip along bedding planes of 10 mm slip values were greatest on the limbs and decreased to zero at the fold hinge which is consistent with the flexural slip folding process secondary left lateral faults ruptured both limbs of the anticline and bedding plane slip was not observed hingeward of these faults these data suggest that left lateral strain associated with seismogenic fault rupture was continuous in the subsurface but was accommodated locally by folding at the surface

from geodetic imaging of seismic and aseismic fault slip to dynamic modeling of the seismic cycle understanding the partitioning of seismic and aseismic fault slip is central to seismotectonics as it ultimately determines the seismic potential of faults thanks to advances in tectonic geodesy it is now possible to develop kinematic models of the spatiotemporal evolution of slip over the seismic cycle and to determine the budget of seismic and aseismic slip studies of subduction zones and continental faults have shown that aseismic creep is common and sometimes prevalent within the seismogenic depth range interseismic coupling is generally observed to be spatially heterogeneous defining locked patches of stress accumulation to be released in future earthquakes or aseismic transients surrounded by creeping areas clay rich tectonites high temperature and elevated pore fluid pressure seem to be key factors promoting aseismic creep the generally logarithmic time evolution of afterslip is a distinctive feature of creeping faults that suggests a logarithmic dependency of fault friction on slip rate

dense gnss profiles across the northwestern tip of the india asia collision zone triggered slip and westward flow of the peter the first range pamir into the tajik depression

complex crustal deformation of the 2016 kaikoura new zealand earthquake revealed by alos 2complex crustal deformation of the 2016 kaikoura new zealand earthquake revealed by alos 2

slip on the elmore ranch fault during the past 330 years and its relation to slip on the superstition hills fault abstract the elmore ranch fault is a left lateral fault that strikes northeast within the right lateral transform boundary that strikes northwest through southern california it lies transverse and adjacent to the segment of the superstition hills fault that ruptured in 1987 rupture of the elmore ranch fault m s 6 2 preceded rupture of the superstition hills fault m s 6 6 by about 11 4 hr the elmore ranch fault slipped at the surface in 1987 with left lateral displacements of up to 130 mm geological data indicate that it had slipped prehistorically sometime after about 1660 a d probably in a single event excavations at three sites enable the following comparisons at these sites the only significant component of dip slip down to the southeast was found on the west strand for slip previous to 1987 the superstition hills fault has also been documented to have experienced one slip event between 1660 and 1987 thus these slip events on the elmore ranch and superstition hills faults may have occurred in a sequence similar to that in 1987 neither the main fault nor the cross fault however appear to have exactly duplicated their previous surficial slip previous slip was probably smaller on the superstition hills fault and larger on the elmore ranch fault zone than in the 1987 event because the temporal correlation between previous slip events is not proven rupture sequences other than a doublet in which main fault rupture follows cross fault rupture are possible

dynamic triggering of creep events in the salton trough southern california by regional m 5 4 earthquakes constrained by geodetic observations and numerical simulations abstract since a regional earthquake in 1951 shallow creep events on strike slip faults within the salton trough southern california have been triggered at least 10 times by m 5 4 earthquakes within 200 km the high earthquake and creep activity and the long history of digital recording within the salton trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes here we document the history of fault creep events on the superstition hills fault based on data from creepmeters insar and field surveys since 1988 we focus on a subset of these creep events that were triggered by significant nearby earthquakes we model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate and state dependent friction we find that the static stress changes from the causal earthquakes are less than 0 1 mpa and too small to instantaneously trigger creep events in contrast we can reproduce the characteristics of triggered slip with dynamic perturbations alone the instantaneous triggering of creep events depends on the peak and the time integrated amplitudes of the dynamic coulomb stress change based on observations and simulations the stress change amplitude required to trigger a creep event of a 0 01 mm surface slip is about 0 6 mpa this threshold is at least an order of magnitude larger than the reported triggering threshold of non volcanic tremors 2 60 kpa and earthquakes in geothermal fields 5 kpa and near shale gas production sites 0 2 0 4 kpa which may result from differences in effective normal stress fault friction the density of nucleation sites in these systems or triggering mechanisms we conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the superstition hills fault

waveform relocated earthquake catalog for southern california 1981 to june 2011 we determine a new relocated catalog hys catalog 2011 for southern california from 1981 through june 2011 about 75 3 of the hypocenters are calculated with absolute and differential travel time picks and 24 7 could be relocated only by using absolute travel time picks with 3d or 1d velocity models the total catalog consists of more than 502 000 earthquakes in the region extending from baja california in the south to coalinga and owens valley in the north the catalog consists of three m 7 1 m 7 2 and m 7 3 mainshocks their foreshocks and aftershocks and background seismicity caused by tectonic and other processes in the southern california crust hypocenters in the new relocated catalog exhibit tighter spatial clustering of seismicity than does the routinely generated catalog and the depth distribution is tighter and reflects the thickness of the seismogenic zone more accurately compared to the standard catalog the relocated hypocenters are more easily related to other data sets such as mapped late quaternary faults

variability in magnitude of paleoearthquakes revealed by trenching and historical records along the haiyuan fault china paleoseismology provides fundamental data for generalizing earthquake recurrence behavior by revealing past surface rupturing events determining the size of paleoseismic events is notoriously more challenging than their timing paleoearthquakes exposed in trenches are vaguely defined as large enough to break to the surface and often assumed to be similar in size here we show an example where the paleoseismic record includes events of both moderate and large magnitudes at the salt lake site on the active left lateral haiyuan fault northern tibetan plateau a high resolution stratigraphic sequence recorded three and possibly four events since a d 1500 constrained by accelerator mass spectrometry 14 c dating historical accounts of earthquake damage in the study region suggest that several earthquakes exposed in the trenches markedly differ in magnitude with the exception of the most recent m 8 earthquake that occurred in a d 1920 two earlier events which occurred in a d 1760 or 1709 and 1638 respectively are considerably smaller with magnitude m 7 and more likely m 6 or less thus this section of the haiyuan fault that broke during moderate magnitude events failed again after a short interval during a large m w 7 8 8 3 earthquake as part of a larger multisegment rupture our study shows that moderate magnitude events can be preserved in the stratigraphy and exposed by paleoseismic trenching under ideal conditions for instance if sedimentation is fast enough and there is no hiatus in deposition eventually the data presented add to the growing body of paleoseismic records containing events of different magnitudes with a large variability in rupture length and coseismic slip

high resolution mapping of near field deformation with airborne earth observation data a comparison study we present an investigation into different approaches for high resolution mapping of near field surface displacement for strike slip earthquakes airborne laser scanning als and optical imagery are two common sources of earth observation data available to geoscientists for earthquake documentation and studies optical image correlation and point cloud differencing techniques are among the most widely used methods for retrieving displacement signals in the near field we compare the performances of these techniques for estimating near field deformation using pre and postevent high resolution als and airborne imagery of the august 24 2014 mw 6 0 napa california earthquake estimates of deformation agree with field observations within a decimeter at the expected accuracy level of the data we show that the correlation of intensity images from als data can unveil the near field deformation successfully and outperforms optical image correlation in vegetated areas as well as in the absence of geodetic markers man made structures furthermore we illustrate that the point clouds generated with structure from motion perform comparably to als point clouds for retrieving the displacement signal in unvegetated areas overall we conclude that als data are generally better than imagery for estimating near field deformation regardless of the estimation methodology and that the iterative closest point algorithm was more effective at recovering the displacement signal

refining the spatial and temporal signatures of creep and co seismic slip along the southern san andreas fault using very high resolution uas imagery and sfm derived topography coachella valley california abstract the current interseismic period for an event on the coachella valley segment of the san andreas fault saf is 300 years much greater than the best estimated average recurrence interval of 180 years prompting questions regarding earthquake recurrence and fault behavior digital surface models dsms generated using structure from motion multiview stereo sfm mvs techniques on unmanned aerial systems uas imagery and very high resolution uas orthomosaics were used to identify and measure fault related offsets of small geomorphic features and develop a model of late holocene slip per event for the southern saf ssaf in the coachella valley we aim to better constrain slip estimates from recent earthquakes along the ssaf and combine new slip data with ages of past earthquakes from paleoseismic studies to understand earthquake recurrence slip per event for paleoearthquakes which ruptured this segment of the ssaf and the relationship between co seismic slip events creep or afterslip and triggered slip were evaluated examination of offsets suggests that five 5 large surface rupturing events produced average displacements of 2 6 3 1 m per event gaussian distribution analysis revealed small scale offset clusters that we attribute to climate modulated channel incision across the fault and subsequent creep these offset clusters support a creep rate of 3 mm yr in the mecca hills averaged over the past 160 years

fault slip rates effects of elastic heterogeneity on geodetic data and the strength of the lower crust in the salton trough region southern california 1 in southernmost california the salton trough sedimentary basin lies between the subparallel san jacinto and san andreas faults that together with the elsinore fault accommodate 80 of the 50 mm yr of pacific north american relative motion the slip rates on the san andreas and san jacinto faults have been a matter of recent debate and one source of uncertainty has been the influence of crustal strength heterogeneity due to elastically weak basin sediments on geodetic data to evaluate these effects we have modeled regional kinematics with elastic and viscoelastic finite element models that incorporate laterally and vertically varying crustal material properties we find that in general the effects of the sedimentary basin on surface deformation are relatively small and that to explain the geodetic velocity data the slip rate on the san andreas must be higher than that on the san jacinto fault consistent with traditional geologic estimates we also conclude that a relatively strong lower crust of viscosity 5 x 10 19 pa s exists in this region

characterization of subsurface geometry and radioactivity distribution in the trench containing chernobyl clean up wastes several radiometric and geophysical methods were applied to characterize the subsurface geometry and radioactivity distribution especially 137cs in a trench with low level wastes at the chernobyl site while surface dose rate measurements and electromagnetic soil conductivity survey produced uninterpretable fields of signals the ground penetrating radar appeared to be an efficient method for characterization of the subsurface geometry of the waste burial it was established that the trench had the following dimensions the length was 70 m average width 6 8 m and depth 2 2 5 m data on 137cs distribution in the trench were obtained by means of a borehole gamma logging technique the total inventory of 137cs was estimated at 600 200 gbq geostatistical analysis using the semivariogram function has shown regular spatial correlation patterns for the logarithm transformed 137cs activity of waste material the correlation length along the trench was 17 m while across the trench and in the vertical direction it was 4 m the observed correlation patterns supposedly were caused by the method used to dispose the contaminated topsoil the bulldozing in the direction perpendicular to a trench axis obtained results may be useful for selecting a characterization method and for optimization of sampling strategies for similar waste sites

radionuclide migration at experimental polygon at red forest waste site in chernobyl zone part 2 hydrogeological characterization and groundwater transport modeling abstract this article represents the second of two articles which review the main results of the international radioecological projects chernobyl pilot site project 1999 2003 and experimental platform in chernobyl 2004 2008 these projects studied radionuclide migration from the near surface radioactive waste trench at the red forest waste dump in the chernobyl zone which contained nuclear fuel particles this article presents results from the comprehensive hydrogeological site characterization program including the following issues geological structure of the study site hydraulic properties of the deposits tracer tests in the aquifer results of groundwater monitoring and unsaturated zone regime studies as well as data on the 90sr distribution in the unsaturated zone and aquifer and analyses of 90sr sorption behavior the derived parameters were used to develop and calibrate 1d flow tube and 2d cross section models describing the migration of 90sr from the studied waste trench to the unsaturated zone and aquifer over a 16 a period 1986 2002 the models involved the following sub models 1 the geostatistical structural model for radioactivity distribution in the trench using gslib and 2 the radionuclide source term model sterm1d describing dissolution of fuel particles and a 1d of radionuclide redistribution in the trench body and unsaturated zone the modflow mt3d codes were used to model the 2d 90sr transport in the aquifer cross section calibration of the 1d model with respect to kds and dispersivities allowed quite accurate reproduction of 90sr migration behavior for the early period 1995 1998 the less perfect fit between the 1d and 2d modeling results and monitoring data for the later period 1999 2002 suggests the need to improve the conceptual radionuclide migration model i e to account for transient hydraulic and geochemical regimes of the waste site

triggered aseismic fault slip from nearby earthquakes static or dynamic effect 1 observations show that an earthquake can affect aseismic slip behavior of nearby faults and produce triggered aseismic fault slip two types of stress changes are often examined by researchers as possible triggering sources one is the static stress change associated with the faulting process and the other is the dynamic stress change or transient deformation generated by the passage of seismic waves no consensus has been reached however regarding the mechanism s of triggered aseismic fault slip we evaluate the possible triggering role of static stress changes by examining observations made after 10 large earthquakes in california most of the nearby fault segments that slipped aseismically were encouraged to move by the imposed positive changes in static coulomb failure stress cfs nonetheless three discrepancies or failures with this model exist which implies that static stress triggering either is or is not the sole mechanism causing the observed triggered slip we then use a spring slider system as a simplified fault model to study its slip behavior and the impact of transient dynamic loading on it we show that a two state variable rate dependent and state dependent frictional law can generate creep events transient loads are then put into the system certain types of them can cause a large time advance of or trigger the next creep event while our work examines triggered creep events near the surface it may well have implications for the occurrence of similar events near the bottom of the seismogenic zone where a transition in frictional stability occurs index terms 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling 8168 tectonophysics evolution of the earth stresses general

surface creep and slip behavior segmentation along the northwestern xianshuihe fault zone of southwestern china determined from decades of fault crossing short baseline and short level surveys abstract this study examines the 200 km long northwestern xianshuihe fault zone nwxfz southwestern china using more than three decades of geodetic observations from fault crossing short baseline and short leveling surveys at seven sites these data enable estimates of creep rates and depths and examination of the long term slip behavior the surface motion of the nwxfz is dominated by sinistral creep although sinistral transverse and vertical slip components show spatio temporal variations combining these slip variations with data of earthquake rupture coseismic slip seismicity fault geometry and far fault movement velocity and using the velocity and state friction theory our analysis indicates that the surface slip behavior of the nwxfz is segmented along strike the 1973 rupture section of this fault zone exhibits spatio temporally variable slip behavior showing time decaying post 1973 afterslip on the northwestern and southeastern parts of the rupture at depths above 5 8 7 0 km with average sinistral creep rates of 1 3 and 3 5 mm yr respectively but being relocked in the central part of the rupture the 1923 1981 rupture section is generally in locking state with postseismic and interseismic sinistral creep at 1 1 mm yr on its central part at depths above 2 0 2 8 km the 1893 rupture section has been tightly locked without creep since at least the early 1980s the thickness of the shallow velocity strengthening or creep layer and the restraining bend geometry of the nwxfz are the key factors that control spatio temporal variations in surface creep rates two surface observed locked fault portions are located within two different restraining bends in the nwxfz both of which act as compressive asperities and hence have enabled the long term locking of these portions creep along the nwxfz has also been affected to varying degrees by m6 5 mw9 2 earthquakes at distances of 50 3800 km from the fault zone most of these effects have been removed from our estimates of the long term average creep rates