widespread fault creep in the northern san francisco bay area revealed by multistation cluster detection of repeating earthquakes we search for repeating earthquakes res in the northern san francisco bay area in 1984 2016 by comparing over 670 000 waveforms from 75 000 events we identify candidate clusters of events whos

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

thirty five year creep rates for the creeping segment of the san andreas fault and the effects of the 2004 parkfield earthquake constraints from alignment arrays continuous global positioning system and creepmeters we present results from differential global positioning system gps surveys of seven alignment arrays and four continuous gps sites along the creeping segment of the san andreas fault surveys of four alignment arrays from the central creeping segment yield 33 to 36 year average minimum slip rates of 21 26 mm yr these rates are consistent with previous alignment array surveys spanning a 10 year period and with rates determined by creepmeters indicating approximate steady state creep along the central creeping segment for at least 35 years motion between continuous gps sites that span the central creeping segment is 28 2 0 5 mm yr for two sites that are 1 km apart and 33 6 1 mm yr for two sites that are 70 km apart slip rates therefore increase with distance from the creeping segment of the san andreas fault all rates reported here are significantly slower than the 39 2 mm yr rate predicted for motion between the sierra nevada great valley block and the pacific plate repeat surveys of three alignment arrays following the 2004 parkfield earthquake demonstrate that its coseismic and short term postseismic offsets decrease rapidly with distance from the epicenter from 150 mm to 15 mm to 5 mm at respective distances of 9 36 and 54 km to the northwest continuous gps data confirm that little coseismic and postseismic slip occurred along the central creeping segment geodetic and geologic slip rates are compared and different models for the accommodation of transcurrent deformation across the creeping segment are discussed

a large silent earthquake in the guerrero seismic gap mexico 1 geodetic measurements from a network of permanent gps stations along the pacific coast of mexico reveal a large silent earthquake along the segment of the cocos north american plate interface identified as the guerrero seismic gap the event began in october of 2001 and lasted for 6 7 months average slip of 10 cm produced measurable displacements over an area of 550 250 km2 the equivalent moment magnitude of the event was mw 7 5 recognition of this and previous slow event here indicate that the seismogenic portion of the plate interface is not loading steadily as hitherto believed but is rather partitioning the stress buildup with episodic as opposed to steady state or periodic slip downdip of the seismogenic zone this process increases the stress at the base of the seismogenic zone bringing it closer to failure these results call for a reassessment of the seismic potential of guerrero and other seismic gaps in mexico

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

spatial and temporal variations in creep rate along the el pilar fault at the caribbean south american plate boundary venezuela from insar in eastern venezuela the caribbean south american plate boundary follows the el pilar fault system previous studies based on three gps campaigns 2003 2005 2013 demonstrated that the el pilar fault accommodates the whole relative displacement between the two tectonic plates 20 mm yr and proposed that 50 60 of the slip is aseismic jouanne et al 2011 reinoza et al 2015 in order to quantify the possible variations of the aseismic creep in time and space we conducted an insar time series analysis using the nsbas method on 18 images from the alos 1 satellite spanning the 2007 2011 period during this 3 5 year period insar observations show that aseismic slip decreases eastwards along the fault the creep rate of the western segment reaches 25 3 9 4 mm yr on average compared to 13 4 6 9 mm yr on average for the eastern segment this is interpreted through slip distribution models as being related to coupled and un coupled areas between the surface and ca 20 km in depth insar observations also show significant temporal creep rate variations accelerations during the considered time span along the western segment the transient behavior of the creep is not consistent with typical postseismic afterslip following the 1997 ms 6 8 earthquake the creep is thus interpreted as persistent aseismic slip during an interseismic period which have a pulse or transient like behavior

geologic versus geodetic deformation adjacent to the san andreas fault central california we combine geologic and global positioning system gps data to characterize the style and magnitude of off fault deformation across the san andreas fault system in central california geologic structures record 12 km of both fault parallel and fault perpendicular displacements across creeping and locked portions of the san andreas fault analysis of 150 gps site velocities suggests that the borderlands record 4 6 mm yr of fault parallel and 3 5 mm yr of fault perpendicular motion alongside the creeping segment where elastic strain is minimized the distribution of both long term geologic and short term geodetic deformation is affected by basement type where more deformation is concentrated northeast of the san andreas fault on franciscan basement we suggest that at least half the fault parallel gps deformation measured by gps bordering the creeping segment must be accommodated by geologic structures this permanent deformation needs to be incorporated into dynamic models of the fault system elastic modeling of the san andreas fault in central california which incorporates its well known transition from locked to creeping behavior near parkfield predicts first order variations in the gps velocity field along the fault and corresponding variations in dilatational strain rates the strain rate pattern is dominated by a large contractional region northeast of the transition from locked to creeping behavior and a large extensional region southwest of the transition the former coincides with the coalinga and kettleman hills anticlines the growth and development of which seem to have occurred under at least two kinematic conditions we suggest that the onset of fault creep in central california promoted the growth of these folds by implication fault creep has been active over geologic time scales

aseismic slip and seismogenic coupling along the central san andreas fault we use high resolution synthetic aperture radar and gps derived observations of surface displacements to derive the first probabilistic estimates of fault coupling along the creeping section of the san andreas fault in between the terminations of the 1857 and 1906 magnitude 7 9 earthquakes using a fully bayesian approach enables unequaled resolution and allows us to infer a high probability of significant fault locking along the creeping section the inferred discreet locked asperities are consistent with evidence for magnitude 6 earthquakes over the past century in this area and may be associated with the initiation phase of the 1857 earthquake as creeping segments may be related to the initiation and termination of seismic ruptures such distribution of locked and creeping asperities highlights the central role of the creeping section on the occurrence of major earthquakes along the san andreas fault

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

a slow thrust slip event following the two 1996 hyuganada earthquakes beneath the bungo channel southwest japan we report a slow thrust slip event that occurred beneath the bungo channel region southwestern japan on oct and dec 1996 two hyuganada earthquakes both mw 6 7 followed by afterslips occurred in addition a crustal movement characterized by an extremely slow rise was observed around the bungo channel about 200 km north from the epicenters and continued for about 300 days long assuming a slow slip on the plate boundary we estimate its duration and surface displacements from gps time series data by curve fitting and then determine the fault slip distribution we found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the hyuganada earthquakes occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling

landslide susceptibility mapping using lidar and dmc data a case study in the three gorges area china the objective of this study is to map landslide susceptibility in zigui segment of the yangtze three gorges area that is known as one of the most landslide prone areas in china by using data from light detection and ranging lidar and digital mapping camera dmc the likelihood ratio lr and logistic regression model lrm were used in this study the work is divided into three phases the first phase consists of data processing and analysis in this phase lidar and dmc data and geological maps were processed and the landslide controlling factors were derived such as landslide density digital elevation model dem slope angle aspect lithology land use and distance from drainage among these the landslide inventories land use and drainage were constructed with both lidar and dmc data dem slope angle and aspect were constructed with lidar data lithology was taken from the 1 250 000 scale geological maps the second phase is the logistic regression analysis in this phase the lr was applied to find the correlation between the landslide locations and the landslide controlling factors whereas the lrm was used to predict the occurrence of landslides based on six factors to calculate the coefficients of lrm 13 290 553 pixels was used 29 5 of the total pixels the logical regression coefficients of landslide controlling factors were obtained by logical regression analysis with spss 17 0 software the accuracy of the lrm was 88 8 on the whole the third phase is landslide susceptibility mapping and verification the mapping result was verified using the landslide location data and 64 4 landslide pixels distributed in extremely high zone and high zone in addition verification was performed using a success rate curve the verification result show clearly that landslide susceptibility zones were in close agreement with actual landslide areas in the field it is also shown that the factors that were applied in this study are appropriate lithology elevation and distance from drainage are primary factors for the landslide susceptibility mapping in the area while slope angle aspect and land use are secondary

coseismic and postseismic slip of the 2004 parkfield earthquake from space geodetic data we invert interferometric synthetic aperture radar insar data jointly with campaign and continuous global positioning system gps data for slip in the coseismic and postseismic periods of the 2004 parkfield earthquake the insar dataset consists of eight interferograms from data collected by the envisat and radarsat satellites spanning the time of the earthquake and variable amounts of the postseismic period the two datasets complement each other with the insar providing dense sampling of motion in the range direction of the satellite and the gps providing more sparse but three dimensional measurements of ground motion the model assumes exponential decay of the postseismic slip with a decay time constant of 0 087 years determined from time series modeling of continuous gps and creepmeter data we find a geodetic moment magnitude of m 6 2 for a 1 day coseismic model and m w 6 1 for the entire postseismic period the coseismic rupture occurred mainly in two slip asperities one near the hypocenter and the other 15 20 km north postseismic slip occurred on the shallow portions of the fault and near the rupture areas of two m 5 0 aftershocks a comparison of the geodetic slip models with seismic moment estimates suggests that the coseismic moment release of the parkfield earthquake is as little as 25 of the total this underlines the importance of aseismic slip in the slip budget for the parkfield segment online material complete data tables and supplemental tables

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

detection and monitoring of ongoing aseismic slip in the tokai region central japan analysis of global positioning system data shows that the rate of crustal deformations in the tokai region of japan a seismic gap area changed over the past 18 months kalman filtering analysis shows aseismic slip on the plate boundary in the western tokai region centered on lake hamana adjacent to the anticipated tokai earthquake source area the cumulative moment magnitude reaches 6 7 in june 2002 with a relative slip increase northeast of lake haman from january 2002 an existence of aseismic slip in the western tokai supports the hypothesis of a silent event as the cause of uplifting several days before the 1944 tonankai earthquake

debris flow generated tsunamis and their dependence on debris flow dynamics abstract debris flow generated tsunamis can be extremely dangerous for lakeside settlements and infrastructure debris flow composition strongly affects debris flow thickness and velocity and therefore also the generated tsunami this interaction is however poorly understood we investigate the effects of debris flow volume composition gravel sand clay water and subaerial outflow slope on wave celerity and amplitude in a small scale physical model consisting of an inclined outflow channel which transits into a three dimensional water reservoir we find that upon debouching a debris flow pushes the water forward until wave celerity exceeds subaqueous debris flow velocity i e froude number wave celerity has the strongest relation with debris flow velocity debris flow velocity increases with increasing water and clay content up to 22 which both lubricate the flow far field leading wave amplitude has the strongest relation with debris flow momentum velocity times effective mass which is mostly a function of debris flow thickness water and clay content we test the applicability of published semi empirical equations for predicting tsunami amplitude generated by dry landslides and show that they are to some extent also applicable to debris flow potential scale effects especially considering the smallest waves and water depths could influence the applicability of these predictors and translation of the results to the field scale our results demonstrate the importance of debris flow composition on tsunami generation and evolution and thus the necessity of including flow composition in predictive simulation models

topography correlated atmospheric delay correction in radar interferometry using wavelet transforms 1 atmospheric delay is one of the major sources of error in repeat pass interferometry we propose a new approach for correcting the topography correlated components of this artifact to this aim we use multiresolution wavelet analysis to identify the components of the unwrapped interferogram that correlate with topography by using a forward wavelet transform we break down the digital elevation model and the unwrapped interferogram into their building blocks based on their frequency properties we apply a cross correlation analysis to identify correlated coefficients that represent the effect of the atmospheric delay thus the correction to the unwrapped interferogram is obtained by down weighting the correlated coefficients during inverse wavelet transform we test this approach on real and synthetic data sets that are generated over the san francisco bay area we find that even in the presence of tectonic signals this method is able to reduce the correlated component of the atmospheric delay by up to 75 and improves the signal in areas of high relief the remaining part is most likely due to 3d heterogeneities of the atmosphere and can be reduced by integrating temporal information or using complementary observations or models of atmospheric delay

mechanical evolution of transpression zones affected by fault interactions insights from 3d elasto plastic finite element models abstract the mechanical evolution of transpression zones affected by fault interactions is investigated by a 3d elasto plastic mechanical model solved with the finite element method ductile transpression between non rigid walls implies an upward and lateral extrusion the model results demonstrate that a transpression zone evolves in a 3d strain field along non coaxial strain paths distributed plastic strain slip transfer and maximum plastic strain occur within the transpression zone outside the transpression zone fault slip is reduced because deformation is accommodated by distributed plastic shear with progressive deformation the 3 axis the minimum compressive stress rotates within the transpression zone to form an oblique angle to the regional transport direction 9 10 the magnitude of displacement increases faster within the transpression zone than outside it rotation of the displacement vectors of oblique convergence with time suggests that transpression zone evolves toward an overall non plane strain deformation the slip decreases along fault segments and with increasing depth this can be attributed to the accommodation of bulk shortening over adjacent fault segments the model result shows an almost symmetrical domal uplift due to off fault deformation generating a doubly plunging fold and a positive flower structure outside the overlap zone expanding asymmetric basins subside to negative flower structures on both sides of the transpression zone and are called transpressional basins deflection at fault segments causes the fault dip fall to less than 90 86 89 near the surface 1 5 km this results in a pure shear dominated triclinic and discontinuous heterogeneous flow of the transpression zone

an aseismic slip transient on the north anatolian fault constellations of synthetic aperture radar sar satellites with short repeat time acquisitions allow exploration of active faults behavior with unprecedented temporal resolution along the north anatolian fault naf in turkey an 80 km long section has been creeping at least since the 1944 m w 7 3 earthquake near ismetpasa with a current interferometric synthetic aperture radar insar derived average creep rate of 8 3 mm yr i e a third of the naf long term slip rate we use a dense set of sar images acquired by the cosmo skymed constellation to quantify the spatial distribution and temporal evolution of creep over 1 year we identify a major burst of aseismic slip spanning 31 days with a maximum slip of 2 cm between the surface and 4 km depth this result shows that fault creep along this section of the naf does not occur at a steady rate as previously thought highlighting a need to revise our understanding of the underlying fault mechanics

shallow flank deformation at cumbre vieja volcano canary islands implications on the stability of steep sided volcano flanks at oceanic islands abstract volcano flank instability has been recognized at many volcanoes around the globe structural morphological geodetic and geophysical evidence supports the continuous deformation of their flanks while identification of instability has been recognized in well documented examples until recently the initial stages of such processes have been difficult to capture using a combination of geological geodetic and geophysical data analysis we study the stability of the cumbre vieja new descending radar interferometric data covering a volcanologically quiet period between 1992 and 2008 at cumbre vieja indicate movement away from the satellite on the western volcano flank using an inversion of stacked velocity maps we determine the geometry and slip for a near horizontal dislocation beneath the western flank of cumbre vieja our ground deformation modelling results position and depth are in agreement with a low density anomaly constrained by gravity data the previously undetected intereruptive ground deformation at cumbre vieja volcano flanks was explained as an indicator of a kinematic passive response model of the flank where the flanks were mobilized only during periods of magmatic activity shallow dike intrusions and remained stable and undeformed during intereruptive periods here we present new results indicating that active creeping stress release due to gravitational loading is also a dominant deformation mechanism for current intereruptive periods at cumbre vieja which would contribute positively to the stabilization of the edifice and reduce the associated hazard related to the volcano flank dynamics this study at cumbre vieja can be considered as a prototype for similar volcanoes around the macaronesian islands group e g fogo teide el hierro pico and elsewhere

clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield california the san andreas fault at parkfield california apparently late in an interval between repeating magnitude 6 earthquakes is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters 20 meter radius of microearthquakes within these clusters which account for 63 of the earthquakes in a 1987 92 study interval virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second the rate of earthquake occurrence particularly at depth increased significantly during the study period but the fraction of earthquakes that were cluster members decreased

a transient subduction zone slip episode in southwest japan observed by the nationwide gps array 1 we investigate the spatiotemporal variation of fault slip on the subduction interface in southwest japan following the two 1996 hyuganada earthquakes m 6 7 using continuous gps observations a silent thrust slip event has been reported by hirose et al 1999 following these earthquakes approximately 100 km to the north beneath the bungo channel we employ the network inversion filter to rigorously invert for the fault slip distribution in space and time the gps time series is modeled as a sum of 1 secular deformation 2 coseismic station displacements 3 transient fault slip 4 random benchmark motion 5 reference frame shifts and 6 observational errors nonnegativity constraints effectively prohibit normal faulting on the subduction interface spatial and temporal smoothing parameters are estimated by the extended kalman filter the estimated fault slip rate images postseismic slip following the two hyuganada earthquakes slip associated with the silent thrust event began roughly 1 month after the second earthquake but initiated 100 km to the northeast of the hyuganada earthquakes the slow event propagated southwest and downdip beneath the bungo channel lasting approximately 1 year with maximum slip rates of 0 6 m yr the equivalent seismic moment was mw 7 2 we can rule out the possibility that slip propagated from the source region of the hyuganada earthquakes to the location of the silent earthquake however the timing of the events suggests a causal connection perhaps due to static stress transfer this kind of transient event or silent earthquake may reflect different fault zone characteristics and may be responsible for accommodating strain that would otherwise be released in large earthquakes

periodic pulsing of characteristic microearthquakes on the san andreas fault deep fault slip information from characteristically repeating microearthquakes reveals previously unrecognized patterns of extensive large amplitude long duration quasiperiodic repetition of aseismic events along much of a 175 kilometer segment of the central san andreas fault pulsing occurs both in conjunction with and independent of transient slip from larger earthquakes it extends to depths of 10 to 11 kilometers but may be deeper and it may be related to similar phenomena occurring in subduction zones over much of the study area pulse onset periods also show a higher probability of larger earthquakes which may provide useful information for earthquake forecasting

episodic creep events on the san andreas fault caused by pore pressure variations recent seismic and geodetic observations indicate that interseismic creep rate varies in both time and space the spatial extent of creep pinpoints locked asperities while its temporary accelerations known as slow slip events may trigger earthquakes although the conditions promoting fault creep are well studied the mechanisms for initiating episodic slow slip events are enigmatic here we investigate surface deformation measured by radar interferometry along the central san andreas fault between 2003 and 2010 to constrain the temporal evolution of creep we show that slow slip events are ensembles of localized creep bursts that aseismically rupture isolated fault compartments using a rate and state friction model we show that effective normal stress is temporally variable on the fault and support this using seismic observations we propose that compaction driven elevated pore fluid pressure in hydraulically isolated fault zone and subsequent frictional dilation cause the observed slow slip episodes we further suggest that the 2004 mw6 parkfield earthquake might have been triggered by a slow slip event which increased the coulomb failure stress by up to 0 45 bar per year this implies that while creeping segments are suggested to act as seismic rupture barriers slow slip events on these zones might promote seismicity on adjacent locked segments

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

slow slip slow earthquakes period two cycles full and partial ruptures and deterministic chaos in a single asperity fault abstract the assimilation of geological geophysical and laboratory data in physics based models of fault dynamics promises increasingly realistic simulations of the seismic cycle to assist this effort i explore the dynamics of a single velocity weakening asperity to delineate the relationship between a fault physical properties and the style of faulting during the seismic cycle based on a micro physical model of rate and state friction from a dimensional analysis four non dimensional parameters control the characteristics of slip events and the behavior during the interseismic period including the dieterich ruina rice number ru which is proportional to the ratio of asperity to critical nucleation size w h and rb b a b where a and b control the direct and local evolutionary effects respectively for sufficiently large rb the ru number controls the spectrum of fault slip from periodic slow slip events to aperiodic fast ruptures in finite faults but not in semi infinite faults the transition between these end members includes a bifurcation that involves period two period four period six cycles and deterministic chaos with increasing ru macroscopic fault slip is stabilized as rb vanishes even as ru 1 for finite faults but not for semi infinite faults the transition between slow and fast ruptures for increasing rb includes another type of bifurcation with period two and period four cycles of slow and fast ruptures for 0

seismological studies at parkfield iii microearthquake clusters in the study of fault zone dynamics abstract more than half of the microearthquakes that occur near parkfield california when located with high resolution methods are seen to define some 80 small clusters of 2 to 12 similar events each cluster occupies a patch typically 100 to 200 m in length within the fault zone cluster members have nearly identical waveforms correlation coefficient of 0 9 or greater to frequencies of 50 to 100 hz as recorded by the borehole installed seismographic network the clusters are distributed throughout the fault zone around the presumed nucleation region in the locked section to the se and in the creeping part of the nw of the previous m 6 hypocenter they are also found in the salinian block several kilometers sw of the fault zone the total area occupied by all of the clusters constitutes only a small fraction 1 to 2 of the fault zone approaching failure at parkfield such clusters provide insight into the dynamics of the failure process through their spatial temporal characteristics and their mechanisms they also serve as highly repetitive sources distributed throughout the fault zone suitable for monitoring the nucleation zone for possible precursory changes in physical properties that affect wave propagation in this article we demonstrate these applications with a detailed analysis of selected clusters

frictional properties on the san andreas fault near parkfield california inferred from models of afterslip following the 2004 earthquake the abundance of geodetic and seismic data recording postseismic deformation following the 2004 parkfield earthquake provides an unprecedented opportunity to resolve frictional properties on the parkfield section of the san andreas fault the parkfield segment is a transition between the locked section to the southeast that last ruptured in the 1857 fort tejon earthquake and the creeping section to the northwest we develop three dimensional rate and state dependent friction models of afterslip following the 2004 earthquake to investigate the frictional behavior of the fault it is assumed that the coseismic rupture occurred on an area of the fault surrounded by aseismic creep that accelerated after the earthquake we estimate the distribution of coseismic slip afterslip and rate state frictional parameters by inverting a two step slip model in the model we 1 estimate the coseismic slip distribution from 1 hz global positioning system gps data and 2 use the corresponding coseismic shear stress change on the fault as input into a numerical afterslip model governed by rate state friction we find the rate state frictional parameter a b an indicator of frictional stability is in the range 10 4 10 3 at 50 mpa normal stress which is near the transition from potentially unstable negative a b to nominally stable positive a b friction the estimate of a b values falls within a wide range of experimental values reported for serpentinite which crops out along the san andreas fault zone the critical slip distance d c which characterizes the distance over which strength breaks down during a slip event is in the range 0 01 0 1 m consistent with seismic estimates and a fault gouge thickness of 1 10 m the afterslip model reproduces most features observed in the gps time series data including high surface velocities in the first few months after the earthquake and lower rates at later times as well as the cumulative postseismic displacement the model tends to underpredict the displacement data at later times suggesting that perhaps the modeled afterslip period ends too quickly or an unmodeled deformation process dominates the signal at later times

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

time dependent model of creep on the hayward fault from joint inversion of 18 years of insar and surface creep data 1 spatial and temporal variations of aseismic fault creep influence the size and timing of large earthquakes along partially coupled faults to solve for a time dependent model of creep on the hayward fault we invert 18 years of surface deformation data 1992 2010 obtained by interferometric processing of 52 and 50 sar images acquired by the ers1 2 and envisat satellites respectively and surface creep data obtained at 19 alinement and 4 creepmeter stations for multi temporal analysis of the sar data we developed a method for identifying stable pixels using wavelet multi resolution analysis we also implement a variety of wavelet based filters for reducing the effects of environmental artifacts using a reweighted least squares approach we inverted the interferometric data to generate a time series of surface deformation over the san francisco bay area with a precision of better than a few millimeters to jointly invert the insar displacement time series and the surface creep data for a time dependent model of fault creep we use a robust inversion approach combined with a kalman filter the time dependent model constrains a zone of high slip deficit that may represent the locked rupture asperity of past and future m 7 earthquakes we identify several additional temporal variations in creep rate along the hayward fault the most important one being a zone of accelerating slip just northwest of the major locked zone we estimate that a slip rate deficit equivalent to mw 6 3 6 8 has accumulated on the fault since the last event in 1868

analysis of deformation data at parkfield california detection of a long term strain transient analysis of more than a decade of high quality data particularly those from the two color electronic distance meter edm in the parkfield california area reveals a significant transient in slip rate along the san andreas fault this transient consists of an increase in fault slip rate of 3 3 0 9 mm yr during 1993 0 to 1998 0 the most reliable fault creep instruments show a comparable increase in slip rate suggesting that the deformation is localized to the fault which breaks the surface there was also an increase in precipitation around 1993 it is unlikely however that this anomaly is due directly to hydrology as its spatial distribution is what would be expected for increased slip on the san andreas fault the increase in slip rate corresponds temporally to a dramatic increase in seismicity including the four largest earthquakes in the period 1984 1999 that occurred along a 6 km segment of the fault just to the north of the edm network there was also a previously reported anomaly in borehole shear strain gwyther et al 1996 that closely corresponds temporally to the transient in edm data solely on the basis of edm data the transient can be modeled as a slip event on a 10 km long segment of the fault the calculated shear strains from this model however are not consistent with the observed ones a compatible model can be found if there is increased aseismic slip to the northwest in conjunction with the four earthquakes support for this northwestern slip is provided by a recent study of slip rate based on microearthquake activity we speculate that this northwestern event served to load the fault to the southeast with the stress being partially released by the observed slip

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

deep slow slip events promote seismicity in northeastern japan megathrust abstract the sliding movement between oceanic and crustal plates in subduction zones is accommodated through both earthquakes and quasi static or transient aseismic slip on northeastern japan megathrust aseismic transients known as slow slip events are suggested to precede and trigger major earthquakes in their immediate surroundings however the geodetic evidence for these episodic slow slip events as well as their link to the seismicity on neighboring locked segments of the megathrust is missing here we combine the on shore geodetic data set with seismic observations during the interseismic period of 1996 2003 and demonstrate that episodic slow slip events are prevalent across the down dip portion 30 70 km depth of the megathrust and the associated stress changes modulate the seismicity rate on the neighboring seismogenic zone consequently small to moderate size earthquakes are periodically triggered whose interaction through a domino effect might occasionally lead to major earthquakes this observation has a profound impact on the estimation of seismic hazard in the region introducing a new triggering mechanism that acts across the megathrust to the extent that has not been acknowledged before

aseismic slip and fault normal strain along the central creeping section of the san andreas fault 1 we use gps data to measure the aseismic slip along the central san andreas fault csaf and the deformation across adjacent faults comparison of edm and gps data sets implies that except for small scale transients the fault motion has been steady over the last 40 years we add 42 new gps velocities along the csaf to constrain the regional strain distribution shear strain rates are less than 0 083 0 010 strain yr adjacent to the creeping saf with 1 4 5 mm yr of contraction across the coast ranges dislocation modeling of the data gives a deep long term slip rate of 31 35 mm yr and a shallow 0 12 km creep rate of 28 mm yr along the central portion of the csaf consistent with surface creep measurements the lower shallow slip rate may be due to the effect of partial locking along the csaf or reflect reduced creep rates late in the earthquake cycle of the adjoining saf rupture zones

triggered afterslip on the southern hikurangi subduction interface following the 2016 kaikōura earthquake from insar time series with atmospheric corrections abstract the 2016 mw 7 8 kaik ura earthquake represents an extremely complex event involving over ten major crustal faults altering conventional understanding of multi fault ruptures although evidence for coseismic slip on the hikurangi subduction interface is controversial we present afterslip on the subduction zone beneath marlborough using 13 months of interferometric synthetic aperture radar insar and global positioning system gps observations the spatially and temporally correlated atmospheric errors in sar interferograms are problematic and hence a new insar time series approach combining the generic atmospheric correction online service gacos with a spatial temporal atmospheric phase screen aps filter to facilitate the insar time series analysis is developed for interferograms with over 250 km spatial extent we achieve a 0 77 cm displacement rms difference against gps improving 61 from the conventional insar time series method ts comparisons between the overlapping region of two independent tracks show an rms difference of 1 1 cm for the ts gacos aps combined method improving 54 from the ts method and 27 from using ts with an aps filter only the aps filter reduces the short wavelength residuals substantially but fails to remove the long wavelength error even after the ramp removal revealing that the gacos correction has played a key role in mitigating long wavelength atmospheric effects the resultant insar displacements together with the gps displacements are used to recover the time dependent afterslip distribution on the hikurangi subduction interface which provides insights for reviewing the co seismic slip sources the present status of the subduction plate boundary and future seismic hazards

inversion of gps data for spatially variable slip rate on the san andreas fault near parkfield ca we analyze gps data collected from 1991 1998 at 35 sites near the parkeld segment of the san andreas fault inverting the resultant site velocities for the distri bution of interseismic slip rate on the san andreas reveals an area of low slip rate on thefault extendingfrom between middle mountain and carr hill to southeast of gold hill this slip rate patternis similar to thatfoundbyharris and segall 1987 using trilateration data collected between 1966 and 1984 we infer a deep slip rate 33 mm yr and depth of the transition between seismogenic and non seismogenic slip 14km thatagree betterwithindependentgeologic ev idence than those found in the 1987 study in contrast to harris and segall 1987 wendnoevidenceoffault normal contraction

subsidence derived volumetric strain models for mapping extensional fissures and constraining rock mechanical properties in the san joaquin valley california large scale subsidence due to aquifer overdraft is an ongoing hazard in the san joaquin valley subsidence continues to cause damage to infrastructure and increases the risk of extensional fissures here we use insar derived vertical land motion vlm to model the volumetric strain rate due to groundwater storage change during the 2007 2010 drought in the san joaquin valley central valley california we then use this volumetric strain rate model to calculate surface tensile stress in order to predict regions that are at the highest risk for hazardous tensile surface fissures we find a maximum volumetric strain rate of 232 microstrain yr at a depth of 0 to 200 m in tulare and kings county california the highest risk of tensile fissure development occurs at the periphery of the largest subsiding zones particularly in tulare county and merced county finally we assume that subsidence is likely due to aquifer pressure change which is calculated using groundwater level changes observed at 300 wells during this drought we combine pressure data from selected wells with our volumetric strain maps to estimate the quasi static bulk modulus k a poroelastic parameter applicable when pressure change within the aquifer is inducing volumetric strain this parameter is reflective of a slow deformation process and is one to two orders of magnitude lower than typical values for the bulk modulus found using seismic velocity data the results of this study highlight the importance of large scale high resolution vlm measurements in evaluating aquifer system dynamics hazards associated with overdraft and in estimating important poroelastic parameters

landslide susceptibility assessment using logistic regression and its comparison with a rock mass classification system along a road section in the northern himalayas india landslide studies are commonly guided by ground knowledge and field measurements of rock strength and slope failure criteria with increasing sophistication of gis based statistical methods however landslide susceptibility studies benefit from the integration of data collected from various sources and methods at different scales this study presents a logistic regression method for landslide susceptibility mapping and verifies the result by comparing it with the geotechnical based slope stability probability classification sspc methodology the study was carried out in a landslide prone national highway road section in the northern himalayas india logistic regression model performance was assessed by the receiver operator characteristics roc curve showing an area under the curve equal to 0 83 field validation of the sspc results showed a correspondence of 72 between the high and very high susceptibility classes with present landslide occurrences a spatial comparison of the two susceptibility maps revealed the significance of the geotechnical based sspc method as 90 of the area classified as high and very high susceptible zones by the logistic regression method corresponds to the high and very high class in the sspc method on the other hand only 34 of the area classified as high and very high by the sspc method falls in the high and very high classes of the logistic regression method the underestimation by the logistic regression method can be attributed to the generalisation made by the statistical methods so that a number of slopes existing in critical equilibrium condition might not be classified as high or very high susceptible zones

long term creep rates on the hayward fault evidence for controls on the size and frequency of large earthquakes the hayward fault hf in california exhibits large m w 6 5 7 1 earthquakes with short recurrence times 161 65 yr probably kept short by a 26 78 aseismic release rate including postseismic its interseismic release rate varies locally over time as we infer from many decades of surface creep data earliest estimates of creep rate primarily from infrequent surveys of offset cultural features revealed distinct spatial variation in rates along the fault but no detectable temporal variation since the 1989 m w 6 9 loma prieta earthquake lpe monitoring on 32 alinement arrays and 5 creepmeters has greatly improved the spatial and temporal resolution of creep rate we now identify significant temporal variations mostly associated with local and regional earthquakes the largest rate change was a 6 yr cessation of creep along a 5 km length near the south end of the hf attributed to a regional stress drop from the lpe ending in 1996 with a 2 cm creep event north of there near union city starting in 1991 rates apparently increased by 25 above pre lpe levels on a 16 km long reach of the fault near oakland in 2007 an m w 4 2 earthquake initiated a 1 2 cm creep event extending 10 15 km along the fault using new better constrained long term creep rates we updated earlier estimates of depth to locking along the hf the locking depths outline a single 50 km long locked or retarded patch with the potential for an m w 6 8 event equaling the 1868 hf earthquake we propose that this inferred patch regulates the size and frequency of large earthquakes on hf online material 2007 event creep models plots of creepmeter data maps and cross sections of relocated microearthquakes and active fault traces and iterative solutions for depth of creep

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

time dependent model of aseismic slip on the central san andreas fault from insar time series and repeating earthquakes the central segment of san andreas fault csaf is characterized by a nearly continuous right lateral aseismic slip however observations of the creep rate obtained using small characteristically repeating earthquakes cres show pulses of creep along the csaf which may indicate spatially and temporally variable seismic hazard along the csaf therefore the goal of this study is to obtain a high resolution time dependent model of creep along the csaf to examine this hypothesis to this end we apply a time dependent creep modeling approach which combines interferometric synthetic aperture radar insar surface deformation time series and observations of fault creep obtained from cres the sar data set includes c band scenes acquired by the ers 2 and envisat satellites between 2003 and 2011 the resulting creep rate distribution implies a peak rate up to 32 mm yr along the central part of the csaf afterslip due to the 2004 parkfield earthquake on the southeastern segment of the csaf is also manifest in the model and there is clear evidence of creep pulsing along strike and depth of the csaf estimated annual rate of slip deficit accumulation is equivalent to a magnitude 5 6 5 7 earthquake taking advantage of the time dependence of our model we also refine the scaling relationship which associates the released seismic moment due to a cre event with the amount of creep on the fault surrounding the cre patches this study provides the first kinematic model of creep pulsing constrained using geodetic and seismic data which can enhance time dependent seismic hazard maps and improve earthquake operational forecast models

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses

earthquake deformation cycle on the san andreas fault near parkfield california six moderate earthquakes are thought to have ruptured the parkfield segment of the san andreas fault since 1857 the similar characteristics of the three seismically recorded events together with the quasi regular 22 year recurrence interval have led to the forecast of a similar event in 1988 5 years in this study the potential for the hypothesized earthquake is assessed by estimating the time required for interseismic straining to recover the strain energy released by the most recent june 1966 parkfield earthquake for a simple model of the earthquake cycle this interval is proportional to the ratio of the 1966 seismic moment to the interseismic moment deficit rate baseline lengths measured before and after the 1966 earthquake are inverted to estimate the magnitude and distribution of the combined coseismic and transient postseismic slip although the geodetic data determine only broad spatial averages of the fault slip they do require that slip at depth exceeded the surface offsets measured in 1966 inversions with extreme prior models are calculated to assess the range of seismic moment and moment deficit rates consistent with the available geodetic data inversions assuming only that the slip distributions are to some degree smooth yield strain energy recovery intervals of 14 25 years extreme values range from as little as 6 years to as much as 29 years in comparison historic recurrence intervals of parkfield earthquakes range from 12 to 32 years these results are consistent with the expectation of a magnitude 5 6 earthquake near parkfield by 1993

large scale relocation of two decades of northern california seismicity using cross correlation and double difference methods 1 we simultaneously reanalyzed two decades 1984 2003 of the digital seismic archive of northern california using waveform cross correlation cc and double difference dd methods to improve the resolution in hypocenter locations in the existing earthquake catalog generated at the northern california seismic network ncsn by up to three orders of magnitude we used a combination of 3 billion cc differential times measured from all correlated pairs of events that are separated by less than 5 km and 7 million p wave arrival time picks listed in the ncsn bulletin data were inverted for precise relative locations of 311 273 events using the dd method the relocated catalog is able to image the fine scale structure of seismicity associated with active faults and revealed characteristic spatiotemporal structures such as streaks and repeating earthquakes we found that 90 of the earthquakes have correlated p wave and s wave trains at common stations and that 12 are colocated repeating events an analysis of the repeating events indicates that uncertainties at the 95 confidence level in the existing network locations are on average 0 7 km laterally and 2 km vertically correlation characteristics and relative location improvement are remarkably similar across most of northern california implying the general applicability of these techniques to image high resolution seismicity caused by a variety of plate tectonic and anthropogenic processes we show that consistent long term seismic monitoring and data archiving practices are key to increase resolution in existing hypocenter catalogs and to estimate the precise location of future events on a routine basis

applicability of sentinel 1 terrain observation by progressive scans multitemporal interferometry for monitoring slow ground motions in the san francisco bay area 2017 american geophysical union all rights reserved data from the sentinel 1 satellite have already proven useful for investigating seismic and volcanic events since its launch in april 2014 the requirement of ultrahigh coregistration accuracy and the current relatively short time of sentinel 1 acquisitions make its application challenging for studying slow deformation processes such as fault creep and land subsidence here we analyze a set of 14 sar images over the san francisco bay area spanning 1 year from early 2015 to 2016 we show that implementing an existing enhanced spectral diversity algorithm or using precise orbits together with a reference digital elevation model both yield the required coregistration accuracy for making use of the phase measurements in time series analysis of ground deformation following a thorough validation test we update our estimates of hayward fault creep rate and confirm uplift due to recharge of the santa clara valley aquifer system during the final summer of 4 year drought

postseismic deformation due to the mw 6 0 2004 parkfield earthquake stress driven creep on a fault with spatially variable rate and state friction parameters 1 we investigate the coseismic and postseismic deformation due to the m w 6 0 2004 parkfield california earthquake we produce coseismic and postseismic slip models by inverting data from an array of 14 continuous gps stations from the scign network kinematic inversions of postseismic gps data over a time period of 3 years show that afterslip occurred in areas of low seismicity and low coseismic slip predominantly at a depth of 5 km inversions suggest that coseismic stress increases were relaxed by predominantly aseismic afterslip on a fault plane the kinetics of afterslip is consistent with a velocity strengthening friction generalized to include the case of infinitesimal velocities we performed simulations of stress driven creep using a numerical model that evaluates the time dependent deformation due to coseismic stress changes in a viscoelastoplastic half space starting with a coseismic slip distribution we compute the time dependent evolution of afterslip on a fault plane and the associated displacements at the gps stations data are best explained by a rate strengthening model with frictional parameter a b 7 x 10 3 at a high end of values observed in laboratory experiments we also find that the geodetic moment due to creep is a factor of 100 greater than the cumulative seismic moment of aftershocks the rate of aftershocks in the top 10 km of the seismogenic zone mirrors the kinetics of afterslip suggesting that postearthquake seismicity is governed by loading from the nearby aseismic creep the san andreas fault around parkfield is deduced to have large along strike variations in rate and state frictional properties velocity strengthening areas may be responsible for the separation of the coseismic slip in two distinct asperities and for the ongoing aseismic creep occurring between the velocity weakening patches after the 2004 rupture

a unified source model for the 1906 san francisco earthquake abstract we reconcile two previously discordant source models of the 1906 san francisco earthquake and obtain a model that satisfies both triangulation and seismic data by allowing the rupture velocity to exceed the shear wave velocity employing a projection method to remove the dependence on initial station positions allowed us to make use of a more stable triangulation network including nonrepeated angle observations along the northern san andreas fault this strengthens the case for significant slip over the entire northern segment of the san andreas fault from san juan bautista to cape mendocino during the 1906 earthquake we also found that the teleseismic body wave data can be reconciled with the geodetically derived slip model by allowing supershear rupture this resolves a longstanding conflict between the two previous slip models geodetic and seismic of this earthquake supershear rupture has long been recognized as a theoretical possibility for strike slip faulting and it has been observed in several recent large strike slip earthquakes which raises the prospect that it might be typical for such events supershear rupture leads to substantially different strong ground motion and as a result may need to be taken into account when developing ground motion prediction relations for large strike slip earthquakes our final slip model has a seismic moment of 7 9 10 20 n m which corresponds to a moment magnitude of m w 7 9

afterslip and only afterslip following the 2004 parkfield california earthquake 1 an analysis of the first two years of postseismic surface deformations from gps reveals that afterslip is the only mechanism significantly contributing to postseismic deformation following the 2004 m6 parkfield california earthquake finite element modeling shows this event to have been too small to significantly stress the lower crust and upper mantle thus viscoelastic relaxation did not lead to detectable surface displacements similarly coseismically induced pressure changes in the upper crust were not sufficient to induce a measurable poroelastic response from 10 days to two years after the parkfield earthquake postseismic displacements at all gps stations experience the same characteristic decay time 2 weeks this suggests that only afterslip was activated and the distribution of slip remained unchanged in this time period afterslip was found to be broadly distributed in the upper 15 km of the crust and associated with a moment release of much greater magnitude than the coseismic rupture

fault coupling and potential for earthquakes on the creeping section of the central san andreas fault the 150 km long central section of the san andreas fault csaf in central california creeps at the surface and has not produced a large earthquake historically however sections of the san andreas fault to the north and south are known to have ruptured repeatedly in m 7 8 earthquakes it is currently unclear whether the creeping csaf could rupture in large earthquakes either individually or along with earthquakes on the locked sections to the north and south we invert global positioning system and interferometric synthetic aperture radar data with elastic block models to estimate the degree of locking on the csaf and place bounds on the moment accumulation rate on the fault we find that the inferred moment accumulation rate is highly dependent on the long term fault slip rate which is poorly constrained along the csaf the inferred moment accumulation rate normalized by shear modulus ranges from 3 28 104 to 5 85 107 m3 yr which is equivalent to a mw 5 5 7 2 earthquake every 150 years for a long term slip rate of 26 mm yr and mw 7 3 7 65 for a long term slip rate of 34 mm yr the comparisons of slip distributions with microseismicity and repeating earthquakes indicate a possible locked patch between 10 and 20 km depth on the csaf that could potentially rupture with mw 6 5

evidence for postseismic deformation of the lower crust following the 2004 mw6 0 parkfield earthquake previous studies have shown that postseismic relaxation following the 2004 mw6 0 parkfield ca earthquake is dominated by afterslip however we show that some fraction of the afterslip inferred from kinematic inversion to have occurred immediately below the seismically ruptured area may in fact be a substitute for viscous postseismic deformation of the lower crust using continuous gps and synthetic aperture radar interferometry we estimate the relative contribution of shallow afterslip at depth less than 20km and deeper seated deformation required to account for observed postseismic surface displacements exploiting the possible separation in space and time of the time series of displacements predicted from viscoelastic relaxation we devise a linear inversion scheme that allows inverting jointly for the contribution of afterslip and viscoelastic flow as a function of time we find that a wide range of models involving variable amounts of viscoelastic deformation can fit the observations equally well provided that they allow some fraction of deep seated deformation at depth larger than 20 km these models require that the moment released by postseismic relaxation over 5 years following the earthquake reached nearly as much as 200 of the coseismic moment all the models show a remarkable complementarity of coseismic and shallow afterslip distributions some significant deformation at lower crustal depth 20 26 km is required to fit the geodetic data the condition that postseismic deformation cannot exceed complete relaxation places a constraint on the amount of deep seated deformation the analysis requires an effective viscosity of at least 10 18 pa s of the lower crust assuming a semi infinite homogeneous viscous domain this deep seated deformation is consistent with the depth range of tremors which also show a transient postseismic response and could explain as much as 50 of the total postseismic geodetic moment the remaining fraction being due to afterslip at depth shallower than 20 km lower crustal postseismic deformation could reflect a combination of localized ductile deformation and aseismic frictional sliding

postseismic response of repeating aftershocks the recurrence intervals of repeating earthquakes on the san andreas fault in the loma prieta aftershock zone follow the characteristic 1 t decay of omori s law a model in which these earthquakes occur on isolated patches of the fault that fail in stick slip with creep around them can explain this observation in this model the recurrence interval is inversely proportional to the loading rate due to creep logarithmic velocity strengthening friction predicts 1 t decay in creep rate following the mainshock the time dependence of recurrence is inconsistent with a simple viscous constitutive relationship which predicts an exponential decay of loading rate thus our observations imply postseismic slip at seismogenic depth under a power law rheology the time dependence of postseismic deformation measured geodetically may be diagnostic of whether postseismic deformation is caused by creep or possible viscoelastic deformation at greater depths

spatiotemporal evolution of a transient slip event on the san andreas fault near parkfield california 1 in 1993 several baselines of the two color electronic distance meter edm network at parkfield california deviated from their long term rates coincident with anomalous observations from nearby strain meters and a creep meter as well as an increase in microseismicity between october 1992 and december 1994 three m 4 5 earthquakes occurred beneath middle mountain near the hypocenter of the 1934 and 1966 parkfield m6 events we analyzed the two color edm data using a kalman filtering based technique to image the spatiotemporal evolution of slip on the fault at parkfield between the mid 1980s and 2003 this method accounts for localized random walk motion of the geodetic monuments and a prominent seasonal signal that affects many baselines we find that a slip rate increase occurred between january 1993 and july 1996 on the upper 8 km of the fault near middle mountain the peak estimated slip rate during this time was 49 mm yr which exceeds the long term geologic rate of 35 mm yr the slip rate evolution appears episodic with an initial modest increase after the m4 3 earthquake and a much larger jump following the shallower m4 7 event in december 1994 this temporal correlation between inferred slip and seismicity suggests that the moderate earthquakes triggered the aseismic fault slip the edm data cannot resolve whether transient slip propagated across the nucleation zone of the 1934 and 1966 m6 parkfield earthquakes however transient slip and its associated stress release in the hypocentral area of previous parkfield events is consistent with the nucleation of the 2004 m6 parkfield earthquake elsewhere on the fault

spatial variations in slip deficit on the central san andreas fault from insar summary we use ers insar measurements to record spatial variations in creep rate along the creeping segment of the san andreas fault saf california between 1992 and 2001 inversion of geodetic data yields a slip rate distribution along the creeping segment which is used for firstorder moment release and deficit calculations we present a time averaged spatial picture of surface deformation and associated subsurface creep an interferometric stack is constructed from 12 interferograms that show good coherence for the decade of observation the total right lateral offset spanned by the data is 34 mm yr 1 along most of the length of the creeping segment this offset occurs within a narrow 2 km zone close to the fault trace in the northern part a minor part of the offset is taken up by the nearby calaveras paicines fault in general the observed rates of surface creep are consistent with those obtained by several other studies for a longer and or earlier period of time using different geodetic methods this suggests that the average creep rate has been constant over a period of almost four decades a joint gps insar inversion implies that the shallow creep rate is variable along strike reaching up to 31 5 1m m yr 1 in the central section of the creeping segment tapering off along strike to the south and becoming partitioned across two subparallel faults in the north the deep slip rate beneath the seismogenic layer is 33 3m m yr 1 the difference between shallow and deep slip rates suggests that there is a shallow slip deficit on the creeping segment of the saf csaf moment release rate due to aseismic slip is approximately three orders of magnitude greater than seismic moment release the annual creep on the csaf is equivalent to the moment released in a m 6 earthquake the equivalent moment of the slip deficit relative to the deep slip rate is between 4 1 10 17 and 8 4 10 17 nm yr 1 which is equivalent to a magnitude 5 7 5 9 earthquake over a 150 yr period the deficit is equivalent to a m 7 2 7 4 earthquake this slip deficit may be compensated by intermittent moderate sized events or by accelerated afterslip following large events on nearby fault segments