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

control of rupture by fault geometry during the 1966 parkfield earthquake a reanalysis of the available data for the 1966 parkfleld california earthquake mr 5 suggests that although the ground breakage and aftershocks extended about 40 km along the san andreas fault the initial dynamic rupture was only 20 to 25 km in length the foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault detailed analysis of the p wave first motions from these events at the gold hill station 20 km southeast indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at parkfield analysis of the strong motion records suggests that the rupture stopped at another discontinuity in the fault plane an en echeion offset near gold hill that lies at the boundary on the san andreas fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred foreshocks to the 1857 earthquake occurred in this area sieh 1978 and the epicenter of the main shock may have coincided with the offset zone if it did a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do

block modeling with connected fault network geometries and a linear elastic coupling estimator in spherical coordinates geodetic observations of interseismic deformation provide constraints on the partitioning of fault slip across plate boundary zones the spatial distribution of both elastic and inelastic strain accumulation and the nature of the fault system evolution here we describe linear block theory which decomposes surface velocity fields into four components 1 plate rotations 2 elastic deformation from faults with kinematically consistent slip rates 3 elastic deformation from faults with spatially variable coupling and 4 homogeneous intrablock strain elastic deformation rates are computed for each fault segment in a homogeneous elastic half space using multiple optimal planar cartesian coordinate systems to minimize areal distortion and triangular dislocation elements to accurately represent complex fault system geometry block motions fault slip rates elastic coupling and internal block strain rates are determined simultaneously using a linear estimator with constraints from both geodetically determined velocity fields and geologic fault slip rate estimates we also introduce algorithms for efficiently implementing alternative fault network geometries to quantify parameter sensitivity to nonlinear perturbations in model geometry

asperities and barriers on the seismogenic zone in north chile state of the art after the 2007 mw 7 7 tocopilla earthquake inferred by gps and insar data the mw 7 7 2007 november 14 earthquake had an epicentre located close to the city of tocopilla at the southern end of a known seismic gap in north chile through modelling of global positioning system gps and radar interferometry insar data we show that this event ruptured the deeper part of the seismogenic interface 30 50 km and did not reach the surface the earthquake initiated at the hypocentre and was arrested 150 km south beneath the mejillones peninsula an area already identified as an important structural barrier between two segments of the peru chile subduction zone our preferred models for the tocopilla main shock show slip concentrated in two main asperities consistent with previous inversions of seismological data slip appears to have propagated towards relatively shallow depths at its southern extremity under the mejillones peninsula our analysis of post seismic deformation suggests that small but still significant post seismic slip occurred within the first 10 d after the main shock and that it was mostly concentrated at the southern end of the rupture the post seismic deformation occurring in this period represents 12 19 per cent of the coseismic deformation of which 30 55 per cent has been released aseismically post seismic slip appears to concentrate within regions that exhibit low coseismic slip suggesting that the afterslip distribution during the first month of the post seismic interval complements the coseismic slip the 2007 tocopilla earthquake released only 2 5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500 km long north chile seismic gap

temporal changes in microseismicity and creep near parkfield california the 25 km long section of the san andreas fault near parkfield california ruptured in similar magnitude 6 earthquakes in 1881 1901 1922 1934 and 1966 on the basis of a number of lines of seismological evidence a section of the san andreas fault now termed the parkfield preparation zone has been identified as the locus of the next parkfield earthquake1 3 here we describe coincident changes in surface creep rates and deep seismicity near the parkfield preparation zone following the 2 may 1983 coalinga earthquake and suggest that both respond to the same stimuli these changes were concentrated near the point of initiation of the magnitude 6 characteristic parkfield earthquakes lending credence to the hypothesis that this section of the san andreas fault is characterized by a unique set of physical properties4 6 which make it ideal for earthquake prediction studies and which may also be useful for identifying hypocentral regions in other areas

subduction earthquake deformation associated with 14 november 2007 mw 7 8 tocopilla earthquake in chile results from insar and aftershocks abstract on 14 november 2007 a subduction thrust earthquake magnitude mw 7 8 occurred in the coastal region of northern chile causing substantial damage to the city of tocopilla we investigate the source fault of the earthquake slip distribution and fault interaction by integrating aftershock locations satellite interferometry data and stress model simulations aftershock measurements allow us to locate the area and geometry of the rupture plane in the coastal region between the cities of tocopilla and antofagasta combining two satellite viewing geometries acquired in envisat s wide swath and image modes we observe decimetre scale coseismic deformation the maximum line of sight displacement is found to be about 40 cm located at the mejillones peninsula slip inversions using elastic half space models with geometry constrained by aftershocks suggest rupturing of an area of 160 km by 50 km along the nazca south america convergent margin between latitudes 22 s and 23 5 s the main slip is concentrated on two asperities the largest being located in the southern part of the rupture area at a depth of approximately 30 50 km with a magnitude of about 2 5 m because aftershock distribution may also suggest a region of shallow crustal deformation activity located offshore we investigate whether the 2007 tocopilla earthquake also involved shallow crustal fault slip offshore although we find that the latter assumption is supported by coulomb stress modelling and geologic inferences our geodetic and seismic data provide insufficient constraints to resolve the exact geometry and kinematics of dislocation on this structure

characteristics on fault coupling along the solomon megathrust based on gps observations from 2011 to 2014 the solomon megathrust along the western solomon arc generated two megathrust earthquakes in the past decade mw 8 1 in 2007 and mw 7 1 in 2010 to investigate the interseismic deformation and inferred coupling on the megathrust we deployed the first continuous gps network in the western solomon islands our 2011 2014 gps data and the back slip inversion model show coupling ratio as high as 73 along the southeastern 2007 rupture segment but only 10 on average along the segment of 2010 event based on the spatial distribution of coseismic slip aftershock clusters derived coupling pattern and paleo geodetic records we discovered the former as a semi permanent asperity and the latter as a potential megathrust barrier we propose that a characteristic earthquake of magnitude not less than mw 8 will recur in an interval of 100 or more years by either single or doublet earthquake

effects of layered crust on the coseismic slip inversion and related cff variations hints from the 2012 emilia romagna earthquake abstract the 2012 emilia romagna italy seismic sequence has been extensively studied given the occurrence of two mainshocks both temporally and spatially close to each other the recent literature accounts for several fault models obtained with different inversion methods and different datasets several authors investigated the possibility that the second event was triggered by the first mainshock with elusive results in this work we consider all the available insar and gps datasets and two planar fault geometries which are based on both seismological and geological constraints we account for a layered elastic half space hosting the dislocation and compare the slip distribution resulting from the inversion and the related changes in coulomb failure function cff obtained with both a homogeneous and layered half space finally we focus on the interaction between the two main events discriminating the contributions of coseismic and early postseismic slip of the mainshock on the generation of the second event and discuss the spatio temporal distribution of the seismic sequence when accounting for both insar and gps geodetic data we are able to reproduce a detailed coseismic slip distribution for the two mainshocks that is in accordance with the overall aftershock seismicity distribution furthermore we see that an elastic medium with depth dependent rigidity better accounts for the lack of the shallow seismicity amplifying with respect to the homogeneous case the mechanical interaction of the two mainshocks

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

source parameters for the 1952 kern county earthquake california a joint inversion of leveling and triangulation observations coseismic leveling and triangulation observations are used to determine the faulting geometry and slip distribution of the july 21 1952 mw 7 3 kern county earthquake on the white wolf fault a singular value decomposition inversion is used to assess the ability of the geodetic network to resolve slip along a multisegment fault and shows that the network is sufficient to resolve slip along the surface rupture to a depth of 10 km below 10 km the network can only resolve dip slip near the fault ends the preferred source model is a two segment right stepping fault with a strike of 51 and a dip of 75 sw the epicentral patch has deep 6 27 km left lateral oblique slip while the northeastern patch has shallow 1 12 5 km reverse slip there is nearly uniform reverse slip epicentral 1 6 m northeast 1 9 m with 3 6 m of left lateral strike slip limited to the epicentral patch the seismic moment is m0 9 2 0 5 1019 n m mw 7 2 the signal to noise ratio of the leveling and triangulation data is reduced by 96 and 49 respectively the slip distribution from the preferred model matches regional geomorphic features and may provide a driving mechanism for regional shortening across the comanche thrust and structural continuity with the scodie seismic lineament to the northeast

strain accumulation in southern california 1973 1980 frequent surveys of seven trilateration networks in southern california over the interval 1973 1980 suggest that a regional increment in strain may have occurred in 1978 1979 prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north south compression this secular trend was interrupted sometime in 1978 1979 by an increment in both north south and east west extension in five of the seven networks the onset of this change appears to have occurred first in the networks farthest south the changes occurred without any unusual seismicity within the networks but the overall seismicity in southern california was unusually low prior to and has been unusually high since the occurrence the average principal strain rates for the seven networks in the 1973 1980 interval are 0 17 mu strain yr north south contraction and 0 08 mu strain yr east west extension although the observed increment in strain could be related to unidentifed systematic error in the measuring system a careful review of the measurements and comparison with three other measuring systems reveal no appreciable cumulative systematic error

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

the determination of displacement fields from geodetic data along a strike slip fault observations of angles or distances between stations of a geodetic network are commonly used to infer information about the movement of the surface of the earth the absence of any observations external to the network leads to an ambiguous displacement field existing techniques for eliminating this ambiguity are all unsatisfactory in some respect the best technique an inner coordinate solution is not appropriate for networks located in a strike slip fault environment the inner coordinate solution zeros the rotation of all stations about their center of mass along a strike slip fault like the san andreas however motion normal to the fault is less likely than motion parallel to the fault the solution presented here an outer coordinate solution finds the rotation of the network that minimizes the components of displacement normal to the fault since motion along a strike slip fault is generally expected to be parallel to the fault the displacements obtained with the outer coordinate solution are more reasonable than those obtained with other techniques examination of a trilateration network near san francisco bay demonstrates the large effect that the choice of adjustment technique can have on the inferred relative motion of the two sides of the fault the inner coordinate solution gave a rate of about 1 mm yr whereas the preferred outer coordinate solution rate was 36 mm yr

forecast model for moderate earthquakes near parkfield california earthquake instability models have possible application to earthquake forecasting because the models simulate both preseismic and coseismic changes of fault slip and ground deformation in the forecast procedure proposed here repeated measurements of preseismic fault slip and ground deformation constrain the values of model parameters the early part of the model simulation corresponds to the available field data and the subsequent part constitutes an estimate of future faulting and ground deformation in particular the time location and size of unstable faulting are estimates of the pending earthquake parameters the forecast accuracy depends on the model realism and parameter resolution the forecast procedure is applied to fault creep and trilateration data measured near parkfield california where at least five magnitude 5 5 to 6 earthquakes have occurred regularly since 1881 the last in 1966 the quasi static model consists of a flat vertical plane embedded in an elastic half space spacially variable fault slip of strike slip sense is driven by an increasing regional shear stress but is impeded by a relatively strong patch of brittle strain softening fault the field data are consistent with these approximate values of patch parameters radius of 3 km patch center 5 km deep and 8 km southeast of the 1966 epicenter and maximum brittle strength of 26 bars fluctuations in the available field data prevent estimating the earthquake time with any more precision than use of the 21 8 year recurrence interval however the model may later give a more precise estimate of the earthquake time if the fault slip rate near the inferred patch increases before the earthquake as predicted by the model

source analysis of the crandall canyon utah mine collapse analysis of seismograms from a magnitude 3 9 seismic event on 6 august 2007 in central utah reveals an anomalous radiation pattern that is contrary to that expected for a tectonic earthquake and which is dominated by an implosive component the results show that the seismic event is best modeled as a shallow underground collapse interestingly large transverse surface waves require a smaller additional noncollapse source component that might represent either faulting in the rocks above the mine workings or deformation of the medium surrounding the mine seismic moment tensor results for nuclear explosions explosion and other mining cavity collapses and tectonic earthquakes are compared and the separation of the different populations indicates that the seismic moment tensor may be used for source type discrimination

preliminary determination of pacfic north america relative motion in the southern gulf of calfornia using the global positioning system global positioning system gps data from experiments conducted in 1985 and 1989 in the southern gulf of california mexico allow a determination of relative motion between the pacific and north american plates the data indicate motion of cabo san lucas on the pacific plate relative to north america at a rate of 47 7 mrn yr and azimuth of 57 6 west of north 1 errors equivalent within uncertainties to the nuvel 1 global plate motion model

earthquake potential along the northern hayward fault california the hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace dislocation models of the surface deformation adjacent to the hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at 7 millimeters per year to the bottom of the seismogenic zone along a 20 kilometer long northern fault segment microearthquakes with the same waveform repeatedly occur at 4 to 10 kilometer depths and indicate deep creep at 5 to 7 millimeters per year the difference between current creep rates and the long term slip rate of 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern hayward fault adjacent to the locked 1868 earthquake rupture which broke the southern 40 to 50 kilometers of the fault the potential for a major independent earthquake of the northern hayward fault might be less than previously thought

coseismic deformation revealed by inversion of strong motion and gps data the 2003 chengkung earthquake in eastern taiwan summary a moderate earthquake of mw 6 8 occurred on 2003 december 10 it ruptured the chihshang fault in eastern taiwan which is the most active segment of the longitudinal fault as a plate suture fault between the luzon arc of the philippine sea plate and the eurasian plate the largest coseismic displacements were 13 cm horizontal and 26 cm vertical we analyse 40 strong motion and 91 gps data to model the fault geometry and coseismic dislocations the most realistic shape of the chihshang fault surface is listric in type the dipping angle of the seismic zone is steep about 60 70 at depths shallower than 10 km and then gradually decreases to 40 50 at depths of 20 30 km thus the polygonal elements in poly3d are well suited for modelling complex surfaces with curving boundaries using the strong motion data the displacement reaches 1 2 m dip slip on the chihshang fault and decreases to 0 1 m near surface the slip averages 0 34 m releasing a scalar moment of 1 6e26 dyne cm for gps data our model reveals that the maximal dislocation is 1 8 m dip slip the dislocations decrease to 0 1 m near the surface the average slip is 0 48 m giving a scalar moment of 2 2e26 dyne cm regarding post seismic deformation a displacements of 0 5 m were observed near the chihshang fault indicating the strain had not been totally released as a probable result of near surface locking of the fault zone

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

slip deficit on the san andreas fault at parkfield california as revealed by inversion of geodetic data a network of geodetic lines spanning the san andreas fault near the rupture zone of the 1966 parkfield california earthquake magnitude m 6 has been repeatedly surveyed since 1959 in the study reported here the average rates of line length change since 1966 were inverted to determine the distribution of interseismic slip rate on the fault these results indicate that the parkfield rupture surface has not slipped significantly since 1966 comparison of the geodetically determined seismic moment of the 1966 earthquake with the interseismic slip deficit rate suggests that the strain released by the latest shock will most likely be restored between 1984 and 1989 although this may not occur until 1995 these results lend independent support to the earlier forecast of an m 6 earthquake near parkfield within 5 years of 1988

long term fault creep observations in central california the u s geological survey usgs has been monitoring aseismic fault slip in central california for more than 10 years as part of an earthquake prediction experiment since 1968 the usgs creep network has grown from one creep meter at the cienega winery south of hollister to a 44 station network that stretches from hayward east of san francisco bay to palmdale in southern california in general the long term slip pattern is most variable on sections of the faults where several magnitude 4 and larger earthquakes occurred during the recording period e g calaveras fault near hollister and san andreas fault between san juan bautista and bear valley these fault sections are the most difficult to characterize with a single long term slip rate in contrast sections of the faults that are seismically relatively quiet e g san andreas fault between bear valley and parkfield produce the steadiest creep records and are easiest to fit with a single long term slip rate appendix is available with entire article on microfiche order from the american geophysical union 2000 florida avenue n w washington d c 20009 document j82 004 1 00 payment must accompany order

the co seismic slip distribution of the landers earthquake we derived a model for the co seismic slip distribution on the faults which ruptured during the landers earthquake sequence of 28 june 1992 the model is based on the inversion of surface geodetic measurements primarily vector displacements measured using the global positioning system gps the inversion procedure assumes that the slip distribution is to some extent smooth and purely right lateral strike slip for a given fault geometry a family of so lutions of varying smoothness can be generated we choose the optimal model from this family based on cross validation which measures the predictive power of the data and the trade off of misfit and roughness solutions which give roughly equal weight to misfit and smoothness are preferred and have certain features in common 1 there are two main patches of slip on the johnson valley fault and on the homestead valley emerson and camp rock faults 2 virtually all slip is in the upper 10 to 12 km and 3 the model reproduces the general features of the geologically measured sur face displacements without prior constraints on the surface slip in all models regardless of smoothing very little slip is required on the fault that represents the big bear event and the total moment of the landers event is 9 1019 n m the nearly simultaneous rupture of multiple distinct faults suggests that much of the crust in this region must have been close to failure prior to the earthquake

an interpretation of episodic slip on the calaveras fault near hollister california data from a precision multi wavelength distance measuring mwdm instrument located near hollister california have been analyzed in terms of strike slip faulting in the region covered by the network four episodes of deformation that are readily identifiable in the mwdm data for the year following september 1975 can be modeled as slip on the calaveras fault creepmeter data tend to support this interpretation since the creep events and the observed episodes of deformation appear to be correlated in a temporal sense lower bounds on the moment for each episode of slip can be determined from the mwdm data by the technique of linear programing the results indicate that aseismic slip is the dominant mechanism for strain release since the combined moment of 1 16 1024 dyn cm for the four episodes far exceeds the moment of all of the earthquakes that occurred during the year creepmeter data and geologic evidence that are taken in conjunction with the lower bound of the moment indicate that the depth of aseismic slip for some of the episodes of fault slip could extend to below the greatest depth of earthquake hypocenters for this region of central california

interactions between the landers and hector mine california earthquakes from space geodesy boundary element modeling and time dependent friction the m w 7 1 hector mine earthquake happened 7 years after the 1992 m w 7 3 landers earthquake within a system of right lateral strike slip faults comprising the eastern california shear zone because estimates of recurrence intervals of m 7 earthquakes on these faults range anywhere from 1500 to 50 000 years the close temporal spacing of these two earthquakes suggests that there is some interaction between the two current models of simple coulomb static stress interactions between the earthquake ruptures do not predict an obvious cause and effect relationship the interaction between the computed normal and right lateral shear stress reductions induced by the landers earthquake at the hector mine hypocenter is unclear we use a combination of space geodesy boundary element modeling and computer modeling of time dependent fault friction to investigate the interaction between the two earthquakes we compare stress changes on the hector mine rupture plane induced by the landers earthquake with the detailed slip distribution inferred using a combination of gps and insar data the slip distributions of both earthquakes are also used to infer the magnitude of the shear stress drop on each earthquake rupture and the orientation of the remote background stress consistent with these two recent events for each earthquake the azimuth of the remote maximum compressive stress was approximately 17 6 and the magnitude of the shear stress drop was 8 1 mpa on the landers rupture and 10 2 mpa on the hector mine rupture using a simple spring and slider model as a proxy for the rate and state frictional response of the hector mine faults to landers earthquake imposed stress steps we find that while a decrease in normal stress at the hector mine hypocenter would by itself have caused the hector mine earthquake to nucleate immediately the simultaneous decrease in shear stress may have caused a delay in the peak shear loading consideration of an acceptable range of rate and state friction parameters secular strain rates and crustal stiffnesses leads us to conclude that this delay could have been 0 to 40 years

locking depths estimated from geodesy and seismology along the san andreas fault system implications for seismic moment release 1 the depth of the seismogenic zone is a critical parameter for earthquake hazard models independent observations from seismology and geodesy can provide insight into the depths of faulting but these depths do not always agree here we inspect variations in fault depths of 12 segments of the southern san andreas fault system derived from over 1000 gps velocities and 66 000 relocated earthquake hypocenters geodetically determined locking depths range from 6 to 22 km while seismogenic thicknesses are largely limited to depths of 11 20km theseseismogenicdepthsbestmatchthegeodeticlockingdepthswhenestimated at the 95 cutoff depth in seismicity and most fault segment depths agree to within 2 km however the imperial coyote creek and borrego segments have significant discrepancies in these cases the geodetically inferred locking depths are much shallower than the seismogenic depths we also examine variations in seismic moment accumulation rate per unit fault length as suggested by seismicity and geodesy and find that both approaches yield high rates 1 5 1 8 1 0 13 nm yr km along the mojave and carrizo segments and low rates 0 2 10 13 nm yr km along several san jacinto segments the largest difference in seismic moment between models is calculated for the imperial segment where the moment rate from seismic depths is a factor of 2 5 larger than that from geodetic depths such variability has important implications for the accuracy to which future major earthquake magnitudes can be estimated

deformation near the junction of the creeping and locked segments of the san andreas fault cholame valley california 1970 1980 we have constructed a simple dislocation model of the san andreas fault near cholame california that reproduces the observed deformation of nearby geodetic networks as well as the transition from quasi continuous slip fault creep to a no slip locked condition on the surface trace the model is specified by the slip rates imposed on the fault surface slip on the surface trace is given by the observed fault creep rates and slip at depths greater than 12 6 km is taken to 30 mm yr along the entire length of the fault i e beneath creeping and locked sections alike slip at intermediate depths is assigned by a rather arbitrary extrapolation of the surface creep values this postulated distribution of slip on the fault is tested by using it in a dislocation model to predict the deformation in two geodetic networks a trilateration network 20 km aperture and a 20 km long level line the calculated deformation of the trilateration network agrees with the observed deformation within the observational error agreement between the predicted and observed elevation changes along the level line was satisfactory in the sense that the predicted values were below the level of detection and the observed changes were not significant

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

the link between grain size components and depositional processes in a modern clastic lake it is widely recognized that lake sediment grain size distributions tend to be polymodal and consist of two or more grain size components however for specific cases the genesis of each component usually is poorly understood in this study the grain size components of the surface sediments of hulun lake inner mongolia were partitioned using the log normal distribution function method and the relationship between the identity of each grain size component and the hydraulic condition of the lake was investigated in order to relate the constituent components to specific depositional processes in the lake the data indicate that the modern clastic sediments of hulun lake contain six distinct unimodal grain size distributions representing six grainsize components each of the components retains its identity including modal size manner of transportation and environment of deposition although the relative percentage varies with the hydraulic conditions throughout the lake these components are specified from fine to coarse modes as long term suspension clay offshore suspension fine silt and medium to coarse silt and nearshore suspension fine sand saltation medium sand and traction coarse sand the percentage contribution of several grain size components interpreted as being indicative of nearshore environments is shown to be correlated negatively with water depth across the modern lake bed this suggests that the proportion of these components in core data might be useful as a proxy for water depth this possibility was tested using a sediment core from hulun lake where high percentages of the nearshore grain size components were found to be correlated with low regional precipitation reconstructed from the pollen profile of the same core the coincidence of two independent proxies does not only demonstrate the validity of log normal distribution function in partitioning polymodal sediments but reveals the potential of lake sediment grain size components for the research of lake level fluctuations during the geological past

geodetic measurements near parkfield california 1959 1984 trilateration measurements have been made by various agencies since 1959 near parkfield california in the transition zone between the central creeping section and the southern locked section of the san andreas fault within the transition zone there are several creep meters and alignment arrays four small aperture trilateration networks and a broad trilateration network extending 70 km southwest from the san andreas fault to the pacific coast line length changes observed after the 1966 ml 5 6 parkfield earthquake indicate a geodetic moment of 4 5 1 0 1025 dyn cm the data are consistent with either 91 8 cm slip on a rupture zone which is 30 km long and extends from 3 to 8 km below the surface or 59 5 cm on a 30 km long zone 2 10 km deep this moment estimate includes some postseismic slip and is a factor of 2 4 greater than the moment determined from seismic surface waves the post 1966 data set is well suited to discriminate between the effects of surface and deep slip surface slip rates determined by creep meters alinement arrays and small aperture trilateration networks decrease from 29 mm yr at slack canyon to zero south of highway 46 a gradient of roughly 0 48 0 01 mm yr km deformation of a subset of the trilateration network between cholame and san luis obispo is consistent with shallow slip of 2 9 1 2 mm yr from the surface to a depth of 16 km and 33 4 5 5 mm yr below 16 km the trilateration data alone do not uniquely constrain both the transition depth from shallow to deep slip and the deep slip rate a transition depth near 16 km is preferred because it provides the best fit to the data and because the predicted slip rate is consistent with independent estimates of the total slip rate across the san andreas fault this simple two dimensional model neglects along strike variations in the deformation the data show no evidence for significant strike slip deformation across faults between the san andreas and the pacific coast

an increment of volcano collapse kinematics of the 1975 kalapana hawaii earthquake abstract earthquakes on kilauea volcano can be even more hazardous than volcanic eruptions the most recent large earthquake was the 1975 kalapana quake which generated a locally damaging tsunami over 8 m of horizontal surface displacement and 3 m of subsidence at the coast the seismic magnitude estimates for this earthquake range from ms 7 2 to mw 7 7 the complexity of the seismic data is matched by the complex surface deformation that was observed with a combination of leveling tilt and electronic distance measurements edm the geodetic data shows evidence of collapse of the caldera due to magma withdrawal localized subsidence over the rift zone normal faulting associated with shallow slumping along the hilina pali and displacement on the basal detachment fault we model the summit caldera rift zones and basal detachment fault as dislocations in an elastic half space to better quantify the sources of deformation related to this devastating event using inversion techniques that allow us to let the data constrain the geometry and magnitude of these sources we find 0 04 km3 of magma withdrawal at the summit between 3 5 m of opening along the rift zone and 7 1 m of slip along the basal detachment at 8 3 km depth models that allow for finer spatial resolution of slip on the detachment show that the largest slip occurred west of the seismically recorded earthquake hypocenter along the region of the fault below the coast and that the majority of the fault slip occurred south of the region of microseismicity our best fitting model has a geodetic moment of 4 1 1020 nm mw 7 7 which is consistent with tsunami models and recent analysis of long period seismic data the residual displacements of sites located in the hanging wall of the hilina pali slump system which were not used in the inversion of the other sources suggest that triggered shallow slumping contributed several meters of horizontal displacement to the coseismic displacement at these sites

inferring fault characteristics using fold geometry constrained by airborne laser swath mapping at raplee ridge utah 1 we used airborne laser swath mapping alsm data to define the geometry of strata in raplee ridge in southeastern utah that were likely deformed by slip on an underlying fault the fold geometry was used to infer the fault geometry and loading responsible for the folding using the boundary element model poly3d monte carlo markov chain mcmc methods created probability density functions pdfs that reveal the most likely fault geometry and loading conditions and their uncertainties despite the restrictive assumptions of poly3d in which body deformations occur from slip on displacement discontinuities in a homogeneous linear elastic half space the strata deflections are matched remarkably well and the resulting inferences of fault geometry and stress field appear reasonable we propose that similar methods may be used with models that include more complicated rheologies and heterogeneous and anisotropic material properties to estimate fault geometries and loading conditions where only deflection of strata record these parameters

time dependent triggered afterslip following the 1989 loma prieta earthquake we employ a modified version of the network inversion filter to investigate time dependent slip following the 1989 loma prieta earthquake previous analysis of global positioning system gps and leveling data suggests afterslip on the loma prieta rupture as well as aseismic slip on a thrust fault northeast of the san andreas fault which we identify with the foothills thrust belt we analyzed 173 daily gps solution files at 62 stations collected from 1989 8 to 1998 3 a total of 1 134 three dimensional relative baseline determinations the observed position changes are assumed to result from secular deformation random benchmark motions and temporally varying fault slip the data reveal temporal variations in slip rate but poorly resolve spatial variations in fault slip the amount of temporal smoothing is estimated by maximum likelihood conditional on this estimate reverse slip on the foothills thrust decays from 45 12 mm yr immediately after the earthquake to zero by 1992 reverse slip on the loma prieta rupture surface decays from 57 11 mm yr to zero by 1994 right lateral slip on the loma prieta rupture surface decays monotonically from 30 10 mm yr to zero by 1994 these results suggest that 1 triggered afterslip can occur off the main rupture zone on adjacent faults 2 shallow afterslip dominated the postseismic deformation for the 8 years following the earthquake and 3 postseismic slip on the foothills thrust may account for a significant portion of its total slip budget

earthquake failure sequences along a cellular fault zone in a three dimensional elastic solid containing asperity and nonasperity regions numerical simulations of earthquake failure sequences along a discrete cellular fault zone are performed for a three dimensional 3 d model representing approximately the central san andreas fault the model consists of an upper crust overlying a lower crust and mantle region together defining an elastic half space with a vertical half plane fault the fault contains a region where slip is calculated on a uniform grid of cells governed by a static kinetic friction law and regions where slip is prescribed so as to represent tectonic loading aseismic fault creep and adjacent great earthquakes the computational region models a 70 km long and 17 5 km deep section of the san andreas fault to the nw of the great 1857 rupture zone different distributions of stress drops on failing computational cells are used to model asperity parkfield asperity and nonasperity fault regions the model is inherently discrete and corresponds to a situation in which a characteristic size of geometric disorder within the fault i e cell size here a few hundreds of meters is much larger than the nucleation size of the order of tens of centimeters to tens of meters based on slip weakening or state evolution slip distances the computational grid is loaded by a constant plate motion imposed at the lower crust upper mantle and creeping fault regions and by a staircase slip history imposed at the 1857 and 1906 rupture zones stress transfer along and outside the fault due to the imposed loadings and failure episodes along the computational grid is calculated using 3 d elastic dislocation theory the resulting displacement field in the computational region is compatible with geodetic and seismological observations only when the asperity and nonasperity regions are characterized by significantly different average stress drops the frequency magnitude statistics of the simulated failure episodes are approximately self similar for small events with b 1 2 the b value of statistics based on rupture area ba is about 1 but are strongly enhanced with respect to self similarity for events larger than a critical size this is interpreted as a direct manifestation of our 3 d elastic stress transfer calculations beyond certain rupture area and potency seismic moment divided by rigidity release values the event is usually unstoppable and it continues to grow to a size limited by a characteristic model dimension this effect is not accounted for by cellular automata and block spring models in which the adopted simplified stress transfer laws fail to scale properly with increasing rupture size the simulations suggest that local maxima in observed frequency magnitude statistics correspond to dimensions of coherent brittle zones such as the width of the seismogenic layer or the length of a fault segment bounded by barriers the analysis indicates that a single cell size representing approximately a single scale of geometric disorder cannot induce self similarity in a 3 d elastic model over a broad range of magnitudes a representation of geometric disorder covering a range of scales may thus be required to generate a wide domain of self similar gutenberg richter statistics our simulations show a great diversity in the mode of failure of the parkfield asperity the earthquakes themselves define an irregular sequence of events the modeling like many other discrete fault models suggests that expectations for periodic parkfield earthquakes and or simple precursory patterns repeating from one event to the other are unrealistic

anomalous shear strain at parkfield during 1993 94 three borehole tensor strainmeters btsm installed near parkfield and separated by more than 5km have established a good baseline of data spanning the past eight years a significant change in the accumulation rate of shear strain 0 5 and 1 0 microstrain per year at two of the sites commencing approximately in mid 1993 and continuing to 1995 is evident in these data some supporting evidence for a change in the strain rate at that time is seen in dilatometer data geodetic measurements fault zone properties and microearthquake locations there was also an increase in medium level seismic activity m 4 7 on 10 20 92 m 3 9 on 10 26 92 m 3 5 on 3 13 93 m 4 4 on 4 3 93 m 4 8 on 11 14 93 in the middle mountain area while a rainfall induced strain may have caused the observed strain anomaly we propose a more likely explanation is that aseismic slip at depth on a section of the fault south of middle mountain produced the observed strain anomaly this anomaly is unique in the current data set

the parkfield california earthquake prediction experiment five moderate magnitude 6 earthquakes with similar features have occurred on the parkfield section of the san andreas fault in central california since 1857 the next moderate parkfield earthquake is expected to occur before 1993 the parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process observations and reports of seismicity and aseismic slip associated with the last moderate parkfield earthquake in 1966 constitute much of the basis of the design of the experiment

gps measurement of postseismic deformation following the 1999 chi chi taiwan earthquake 1 in the 15 month period september 1999 to december 2000 after the 1999 chi chi taiwan earthquake mw 7 6 about 80 campaign surveyed gps stations in central taiwan were occupied up to seven times furthermore seven continuous gps stations were put into operation in the epicentral region mostly within three weeks after the main shock gps data from these near field stations and some pre existing far field stations were utilized to study the postseismic deformation following the chi chi earthquake the postseismic displacements of the gps stations were approximated by a combination of an exponential transient decay function with a relaxation time of 86 days and a postseismic linear rate change stations on the hanging wall displayed west northwesterly horizontal displacements of up to 252 mm and uplift as large as 229 mm postseismic displacements are much larger to the south near the epicenter of chi chi main shock than in the north where the maximum coseismic displacement occurred stations on the footwall show only small displacements the postseismic gps data were inverted to infer the deeper fault geometry and afterslip distribution based on a four segment fault model with its shallow part constrained by coseismic fault geometry deduced from gps and seismological studies the optimal model requires the lower fault segment to be a horizontal plane at a depth of 10 4 km consistent with a model based on gps data taken during the first three months after the main shock and other geological or geophysical studies the maximum afterslip 459 mm occurs in the hypocentral region and in the northern part of the decollement slip of about 430 mm also occurs in the southern part of the decollement the afterslip moment inferred from 15 months of gps data is 4 7 1019 n m approximately 2 3 times the seismic moment released by aftershocks this implies that a major part of the postseismic deformation is aseismic

a bayesian method for incorporating self similarity into earthquake slip inversions distributions of coseismic slip help illuminate many properties of earthquakes including fault geometry stress changes frictional properties and potential future hazard slip inversions take observations and calculate slip at depth but there are a number of commonly adopted assumptions such as minimizing the second spatial derivative of slip the laplacian that have little physical basis and potentially bias the result in light of growing evidence that fault slip shows fractal properties we suggest that this information should be incorporated into slip inversions as a form of regularization instead of laplacian smoothing we have developed a bayesian approach to efficiently solve for slip incorporating von karman regularization in synthetic tests our approach retrieves fractal slip better than laplacian regularization as expected but even performs comparably or better when the input slip is not fractal we apply this to the 2014 mw 6 0 napa valley earthquake on a two segment fault using interferometric synthetic aperture radar insar and global positioning system gps data we find the von karman and laplacian inversions give similar slip magnitude but in different locations and the von karman solution has much tighter confidence bounds on slip than the laplacian solution differences in earthquake slip due to the regularization technique could have important implications for the interpretation and modeling of stress changes on the causative and neighboring faults we therefore recommend that choice of regularization method should be routinely made explicit and justified and that von karman regularization is a better default than laplacian