the 2007 m5 4 alum rock california earthquake implications for future earthquakes on the central and southern calaveras fault 1 the similarity of seismograms recorded by two seismic stations demonstrate that the 31 october 2007 moment magnitude m5 4 alum rock earthquake is a repeat of a 1955 ml5 5 earthquake both occurred on oppenheimer et al s 1990 zone v stuck patch on the central calaveras fault providing new support for their model of calaveras fault earthquake activity we suggest that zone v fails only in a family of recurring m 5 4 5 5 earthquakes the 1955 and 2007 earthquakes are the penultimate and ultimate zone v events earthquakes in 1891 and 1864 are possible earlier zone v events the next zone v event is not expected in the next few decades assuming a time dependent recurrence model the mean forecast date is 2064 2035 2104 95 confidence range we further suggest that zones i ii iii and iv fail in recurring m 5 1 5 3 m 5 6 5 8 m 6 1 6 3 and m 4 9 5 0 earthquakes respectively if our earthquake recurrence model is correct the next zone i event is overdue and could occur anytime and m5 6 earthquakes should not occur on zones ii iii and iv before 2014 2012 and 2026 respectively we cannot rule out the possibility that zone vi which lies at the southern end of the mission seismic trend where the southern hayward and central calaveras faults appear to connect at depth fails aseismically or in large events on the southern hayward fault such as last occurred in 1868 or in large events on the adjoining northern calaveras fault segment

surface slip and off fault deformation patterns in the 2013 mw 7 7 balochistan pakistan earthquake implications for controls on the distribution of near surface coseismic slip comparison of 398 fault offsets measured by visual analysis of worldview high resolution satellite imagery with deformation maps produced by cosi corr subpixel image correlation of landsat 8 and spot5 imagery reveals significant complexity and distributed deformation along the 2013 mw 7 7 balochistan pakistan earthquake average slip along the main trace of the fault was 4 2 m with local maximum offsets up to 11 4 m comparison of slip measured from offset geomorphic features which record localized slip along the main strand of the fault to the total displacement across the entire width of the surface deformation zone from cosi corr reveals 45 off fault deformation while previous studies have shown that the structural maturity of the fault exerts a primary control on the total percentage of off fault surface deformation large along strike variations in the percentage of strain localization observed in the 2013 rupture imply the influence of important secondary controls one such possible secondary control is the type of near surface material through which the rupture propagated we therefore compared the percentage off fault deformation to the type of material bedrock old alluvium and young alluvium at the surface and the distance of the fault to the nearest bedrock outcrop a proxy for sediment thickness along this hybrid strike slip reverse slip fault we find significantly more off fault deformation in younger and or thicker sediments accounting for and predicting such off fault deformation patterns has important implications for the interpretation of geologic slip rates especially for their use in probabilistic seismic hazard assessments the behavior of near surface materials during coseismic deformation and the future development of microzonation protocols for the built environment

seismic activity of the san francisco bay region moment magnitude m with objective confidence level uncertainties are estimated for felt san francisco bay region earthquakes using bakun and went worth s 1997 analysis strategy for seismic intensity observations the frequency magnitude distribution is well described for m 5 5 events since 1850 by a gutenberg richter relation with a b value of 0 90 the seismic moment rate m yr since 1836 is 2 68 1018 n m yr 95 confidence range 1 29 1018 n m yr to 4 07 1018 n m yr the seismic moment rate since 1850 is nearly the same m yr in the 56 years before 1906 is about 10 times that in the 70 years after 1906 in contrast m yr since 1977 is about equal that in the 56 years before 1906 80 1 14 of the plate motion moment accumulation rate is available for release in earthquakes the historical m yr and the portion of the plate motion moment accumulation rate available for release in earthquakes are used in a seismic cycle model to estimate the rate of seismic activity in the twenty first century high and low rates of future seismic activity are both permissible given the range of possible seismic cycle recurrence times t and the uncertainties in the historical m and in the percentage of plate motion available for release in earthquakes if the historical seismic moment rate is not greater than the estimated 2 68 1018 n m yr and the percentage of the plate motion moment accumulation available for release in earthquakes is not less than the estimated 80 then for all t the rate of seismic moment release from now until the next 1906 sized shock will be comparable to the rate from 1836 to 1905 when m 6 1 2 shocks occurred every 15 to 20 years

seasonal variations in wave characteristics around a coral reef island south maalhosmadulu atoll maldives synchronous measurements of waves were made at six locations around a small reef platform island in the maldives during both westerly and northeast monsoon conditions summary statistics of wave records indicated similar hs values propagating onto windward and leeward reef surfaces and a distinct growth in wave height as waves shoal toward island shorelines waves up to 0 78 m were recorded impacting the island shoreline wave energy on the reef platform was strongly modulated by seasonal winds with wave energy during the westerly monsoon an order of magnitude larger than wave conditions in the northeast monsoon spectral analysis of wave records highlighted spatial differences in wave energy around the island windward reefs and shorelines are dominated by waves at wind and swell frequencies whereas wind wave energy is absent from leeward shorelines consequently windward shorelines have up to twice the gross energy input than leeward shorelines results have significant implications for geomorphic processes longer duration and greater incident wave energy during the westerly monsoon has promoted higher growth of the western reef flat 0 2 m and more energetic shoreline runup processes have produced markedly higher western island ridges 0 7 m incident shoreline wave processes are sufficient to entrain beach sediments during both monsoon periods although periods of active sediment mobilisation are constrained to mid to high tide stages the windward leeward gradient in shoreline wave energy is likely to drive littoral sediment flux seasonal modulation of the shoreline wave energy gradients account for observed oscillations in beach position around island shorelines large differences in incident wave energy between monsoons is considered to affect the rate of beach change around island shorelines rather than the total volumetric movement of island beaches

riedel shear structures in the co seismic surface rupture zone produced by the 2001 mw 7 8 kunlun earthquake northern tibetan plateau abstract we present a case study of riedel shear structures related to the co seismic surface ruptures produced during the 2001 mw 7 8 kunlun earthquake in northern tibet which are related to strike slip movement along the kunlun fault field investigations and interpretations of high resolution remote sensing images show that the 2001 co seismic surface ruptures striking wnw ese are mainly characterized by riedel shear structures including t fractures and r y and p shears a left lateral shear sense is indicated to assess the riedel shear fabrics quantitatively we measured the azimuth of 19 455 co seismic surface rupture strands the width of rupture zones at 474 profiles and 336 fold axes of mole track structures using 1 m resolution ikonos and 0 61 m resolution quickbird images acquired soon after the earthquake the analytical results show that i the co seismic surface ruptures are generally concentrated in up to five subparallel sub rupture zones with individual sub rupture zones varying in width from 3 to 350 m generally 1 2 km iii t fractures are mainly developed within the alluvial deposits at counterclockwise angles of 15 40 relative to the general trend of the rupture zone iv p shears are also mainly found in the alluvial deposits but at counterclockwise to clockwise angles of 5 10 relative to the general trend and v y and r shears are developed within both the alluvial deposits and basement rocks mainly representing the reactivation of pre existing fault traces the results demonstrate that the co seismic riedel shear structures are primarily controlled by the local geology during surface rupture formation consistent with the idea that riedel shear structures are common fault patterns within strike slip shear zones and that their development is related to the early stages of fault evolution

retardations in fault creep rates before local moderate earthquakes along the san andreas fault system central california records of shallow aseismic slip fault creep obtained along parts of the san andreas and calaveras faults in central california demonstrate that significant changes in creep rates often have been associated with local moderate earthquakes an immediate postearthquake increase followed by gradual long term decay back to a previous background rate is generally the most obvious earthquake effect on fault creep this phenomenon identified as aseismic afterslip usually is characterized by above average creep rates for several months to a few years in several cases minor step like movements called coseismic slip events have occurred at or near the times of mainshocks one extreme case of coseismic slip recorded at cienega winery on the san andreas fault 17 5 km southeast of san juan bautista consisted of 11 mm of sudden displacement coincident with earthquakes ofm l 5 3 andm l 5 2 that occurred 2 5 minutes apart on 9 april 1961 at least one of these shocks originated on the main fault beneath the winery creep activity subsequently stopped at the winery for 19 months then gradually returned to a nearly steady rate slightly below the previous long term average

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

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

three dimensional surface displacements and rotations from differencing pre and post earthquake lidar point clouds 1 the recent explosion in sub meter resolution airborne lidar data raises the possibility of mapping detailed changes to earth s topography we present a new method that determines three dimensional 3 d coseismic surface displacements and rotations from differencing pre and post earthquake airborne lidar point clouds using the iterative closest point icp algorithm tested on simulated earthquake displacements added to real lidar data along the san andreas fault the method reproduces the input deformation for a grid size of 50 m with horizontal and vertical accuracies of 20 cm and 4 cm values that mimic errors in the original spot height measurements the technique also measures rotations directly resolving the detailed kinematics of distributed zones of faulting where block rotations are common by capturing near fault deformation in 3 d the method offers new constraints on shallow fault slip and rupture zone deformation in turn aiding research into fault zone rheology and long term earthquake repeatability

pervasive cracking of the northern chilean coastal cordillera new evidence for forearc extension despite convergence across the strongly coupled seismogenic interface between the south american and nazca plates the dominant neotectonic signature in the forearc of northern chile is arc normal extension we have used 1 m resolution ikonos satellite imagery to map nearly 37 000 cracks over an area of 500 km2 near the salar grande 21 s these features which are best preserved in a ubiquitous gypcrete surface layer have both nontectonic and tectonic origins however their strong preferred orientation perpendicular to the plate convergence vector suggests that the majority owe their formation to approximate east west extension associated with plate boundary processes such as interseismic loading coseismic and postseismic strain and long term instability resulting from subduction erosion similar structures were formed during or shortly after the 1995 mw 8 0 earthquake near the city of antofagasta south of salar grande and in conjunction with the 2001 mw 8 2 8 4 arequipa peru event cracks such as these may form in other forearcs but remain largely unexposed because of vegetative cover or marked fluvial erosion factors that are absent in northern chile as a result of its hyperarid climate

kinematic gps solutions for aircraft trajectories identifying and minimizing systematic height errors associated with atmospheric propagation delays 1 when kinematic gps processing software is used to estimate the trajectory of an aircraft unless the delays imposed on the gps signals by the atmosphere are either estimated or calibrated via external observations then vertical height errors of decimeters can occur this problem is clearly manifested when the aircraft is positioned against multiple base stations in areas of pronounced topography because the aircraft height solutions obtained using different base stations will tend to be mutually offset or biased in proportion to the elevation differences between the base stations when performing kinematic surveys in areas with significant topography it should be standard procedure to use multiple base stations and to separate them vertically to the maximum extent possible since it will then be much easier to detect mis modeling of the atmosphere

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

how well do surface slip measurements track slip at depth in large strike slip earthquakes the importance of fault structural maturity in controlling on fault slip versus off fault surface deformation abstract comparisons of observed surface displacements with geodetically inferred slip at depth in six large m w 7 1 strike slip earthquakes reveal a correlation between the structural maturity of the fault and the ratio of deep slip to surface slip that occurs on localized zones of surface rupture specifically structurally immature faults 25 km of total displacement manifest only 50 60 of total slip on narrow fault surface traces versus 85 95 for structurally mature faults 85 km total slip the same pattern holds when structurally simple parts of a surface rupture are analyzed separately from parts that exhibit obvious structural complexity e g discontinuous or multiple traces or significant dip slip these results imply that geologic measurements of surface slip along structurally immature faults are likely to significantly underestimate the true slip at depth in large earthquakes this observation has implications for a number of important problems including determination of fault slip rates which are based on surface offsets earthquake probability assessments which are based on geologic fault slip rates comparisons of geologic and geodetic rate data in the search for strain transients the structural evolution of fault zones estimation of paleo earthquake magnitudes based on geomorphic offsets analyses of the relative importance of faulting vs distributed deformation in accommodating relative plate motions in continental crust the design and construction of infrastructure built near active faults and possibly for the prediction of strong ground motions which may at least partially depend on the degree of slip localization to the surface

from decades to epochs spanning the gap between geodesy and structural geology of active mountain belts geodetic data from the global navigation satellite system gnss and from satellite interferometric radar insar are revolutionizing how we look at instantaneous tectonic deformation but the significance for long term finite strain in orogenic belts is less clear we review two different ways of analyzing geodetic data velocity gradient fields from which one can extract strain dilatation and rotation rate and elastic block modeling which assumes that deformation is not continuous but occurs primarily on networks of interconnected faults separating quasi rigid blocks these methods are complementary velocity gradients are purely kinematic and yield information about regional deformation the calculation does not take into account either faults or rigid blocks but where gnss data are dense enough active fault zones and stable blocks emerge naturally in the solution block modeling integrates known structural geometry with idealized earthquake cycle models to predict slip rates on active faults future technological advances should overcome many of today s uncertainties and provide rich new data to mine by providing denser more uniform and temporally continuous observations

fault zone structure from topography signatures of en echelon fault slip at mustang ridge on the san andreas fault monterey county california 1 we used high resolution topography to quantify the spatial distribution of scarps linear valleys topographic sinks and oversteepened stream channels formed along an extensional step over on the san andreas fault saf at mustang ridge california this location provides detail of both creeping fault landform development and complex fault zone kinematics here the saf creeps 10 14 mm yr slower than at locations 20 km along the fault in either direction this spatial change in creep rate is coincident with a series of en echelon oblique normal faults that strike obliquely to the saf and may accommodate the missing deformation this study presents a suite of analyses that are helpful for proper mapping of faults in locations where high resolution topographic data are available furthermore our analyses indicate that two large subsidiary faults near the center of the step over zone appear to carry significant distributed deformation based on their large apparent vertical offsets the presence of associated sag ponds and fluvial knickpoints and the observation that they are rotating a segment of the main saf several subsidiary faults in the southeastern portion of mustang ridge are likely less active they have few associated sag ponds and have older scarp morphologic ages and subdued channel knickpoints several faults in the northwestern part of mustang ridge though relatively small are likely also actively accommodating active fault slip based on their young morphologic ages and the presence of associated sag ponds

inferences drawn from two decades of alinement array measurements of creep on faults in the san francisco bay region we summarize over 20 years of monitoring surface creep on faults of the san andreas system in the san francisco bay region using alinement arrays the san andreas fault is fully locked at five sites northwest from san juan bautista the southern end of the 1906 earthquake rupture that is no creep 1 mm yr is observed likewise the san gregorio rodgers creek and west napa faults show no creep the measured creep rate on the calaveras paicines fault from hollister southward is either 6 or 10 mm yr depending on whether the arrays cross all of the creeping traces northward of hollister the central calaveras creep rate reaches 14 2 mm yr but drops to 2 mm yr near calaveras reservoir where slip transfers to the southern hayward fault at a maximum creep rate of 9 mm yr at its south end however the hayward fault averages only 4 6 mm yr over most of its length the northern calaveras fault now creeping at 3 4 mm yr steps right to the concord fault which has a similar rate 2 5 3 5 mm yr which is slightly slower than the 4 4 mm yr rate on its northward continuation the green valley fault the maacama fault creeps at 4 4 mm yr near ukiah and 6 5 mm yr in willits the central and southern segments of the calaveras fault are predominantly creeping whereas the hayward northern calaveras and maacama faults are partly locked and along with the rodgers creek and san andreas have high potential for major earthquakes manuscript received 6 november 2002

coseismic fault zone deformation revealed with differential lidar examples from japanese mw 7 intraplate earthquakes abstract we use two recent japanese earthquakes to demonstrate the rich potential as well as some of the challenges of differencing repeat airborne light detection and ranging lidar topographic data to measure coseismic fault zone deformation we focus on densely vegetated sections of the 14 june 2008 iwate miyagi m w 6 9 and 11 april 2011 fukushima hamadori m w 7 1 earthquake ruptures each covered by 2 m resolution pre event and 1 m resolution post event bare earth digital terrain models dtms obtained from commercial lidar providers three dimensional displacements and rotations were extracted from these datasets using an adaptation of the iterative closest point icp algorithm these displacements remain coherent close to surface fault breaks as well as within dense forest despite intervals of 2 years iwate miyagi and 4 years fukushima hamadori encompassed by the lidar scenes differential lidar analysis is thus complementary to interferometric synthetic aperture radar insar and sub pixel correlation techniques which often break down under conditions of long time intervals dense vegetation or steep displacement gradients although the icp displacements are much noisier than overlapping insar line of sight displacements they still provide powerful constraints on near surface fault slip in the fukushima hamadori case near fault displacements and rotations are consistent with decreased primary fault slip at very shallow depths of a few tens of meters helping to account for the large along strike heterogeneity in surface offsets observed in the field this displacement field also captures long wavelength deformation resulting from the 11 march 2011 tohoku great earthquake

seismicity and source parameters of earthquakes in the region of the large tolbachik fissure eruption this study discusses the focal mechanisms of 61 earthquakes and dynamic parameters of 97 earthquakes mi 2 0 and focal depths 0 20 km occurring in the region of the large tolbachik fissure eruption in 1975 1978 variations of these parameters during the different eruptive stages are examined three stages can be distinguished 1 june 27 july 2 1975 from the beginning of the seismic preparation to the large earthquakes of july 2nd withm 5 0 2 july 2nd july 6th 1975 before the onset of eruption 3 from july 6th 1975 to the end of 1976 during the eruption

is stress accumulating on the creeping section of the san andreas fault 1 the creeping section of the san andreas fault csaf in central california is a proposed barrier to propagation of large earthquakes yet recent studies show that the creeping section is not entirely uncoupled but is accumulating slip deficit at a rate equivalent to a mw 7 2 7 4 earthquake every 150years a critical piece to understanding earthquake potential on the csaf is determining whether slip deficit is occurring with stress accumulation on stick slip regions or without stress accumulation on stable sliding regions shadowed by surrounding locked areas we use a physical model to estimate the spatial distribution of locked stress accumulating areas of the fault constrained by surface creep rate measurements and gps derived velocities we find that the area of the fault accumulating stress if ruptured every 150years would release slip equivalent to at most a mw 6 75 earthquake significantly less than the mw 7 2 7 4 150year equivalent total slip deficit rate

high resolution interseismic velocity data along the san andreas fault from gps and insar 1 we compared four interseismic velocity models of the san andreas fault based on gps observations the standard deviations of the predicted secular velocity from the four models are larger north of the san francisco bay area near the creeping segment in central california and along the san jacinto fault and the east california shear zone in southern california a coherence spectrum analysis of the secular velocity fields indicates relatively high correlation among the four models at longer wavelengths 15 40 km with lower correlation at shorter wavelengths to improve the short wavelength accuracy of the interseismic velocity model we integrated interferometric synthetic aperture radar insar observations initially from advanced land observing satellite alos ascending data spanning from the middle of 2006 to the end of 2010 totaling more than 1100 interferograms with gps observations using a sum remove filter restore approach the final insar line of sight data match the point gps observations with a mean absolute deviation of 1 5 mm yr we systematically evaluated the fault creep rates along major faults of the san andreas fault and compared them with creepmeters and alignment array data compiled in uniform california earthquake rupture forecast version 2 ucerf2 moreover this insar line of sight dataset can constrain rapid velocity gradients near the faults which are critical for understanding the along strike variations in stress accumulation rate and associated earthquake hazard

episodic fault creep events in california controlled by shallow frictional heterogeneity stable fault slip or creep is thought to occur in unconsolidated sediments that form shallow parts of continental strike slip faults numerical simulations show that creep events observed on faults in california also require the presence of a shallow unstable layer of rock the thickness of which influences the duration of the creep event

slip on the san andreas fault at parkfield california over two earthquake cycles and the implications for seismic hazard parkfield california which experienced m 6 0 earthquakes in 1934 1966 and 2004 is one of the few locales for which geodetic observations span multiple earthquake cycles we undertake a comprehensive study of deformation over the most recent earthquake cycle and explore the results in the context of geodetic data collected prior to the 1966 event through joint inversion of the variety of parkfield geodetic measurements trilateration two color laser and global positioning system including previously unpublished two color data we estimate the spatial distribution of slip and slip rate along the san andreas using a fault geometry based on precisely relocated seismicity although the three most recent parkfield earthquakes appear complementary in their along strike distributions of slip they do not produce uniform strain release along strike over multiple seismic cycles since the 1934 earthquake more than 1 m of slip deficit has accumulated on portions of the fault that slipped in the 1966 and 2004 earthquakes and an average of 2 m of slip deficit exists on the 33 km of the fault southeast of gold hill to be released in a future perhaps larger earthquake it appears that the fault is capable of partially releasing stored strain in moderate earthquakes maintaining a disequilibrium through multiple earthquake cycles this complicates the application of simple earthquake recurrence models that assume only the strain accumulated since the most recent event is relevant to the size or timing of an upcoming earthquake our findings further emphasize that accumulated slip deficit is not sufficient for earthquake nucleation online material model fault geometry fit to the data for the inversions and model resolution

localized and distributed creep along the southern san andreas fault we investigate the spatial pattern of surface creep and off fault deformation along the southern segment of the san andreas fault using a combination of multiple interferometric synthetic aperture radar viewing geometries and survey mode gps occupations of a dense array crossing the fault radar observations from envisat during the period 2003 2010 were used to separate the pattern of horizontal and vertical motion providing a high resolution image of uplift and shallow creep along the fault trace the data reveal pervasive shallow creep along the southernmost 50 km of the fault creep is localized on a well defined fault trace only in the mecca hills and durmid hill areas while elsewhere creep appears to be distributed over a 1 2 km wide zone surrounding the fault the degree of strain localization is correlated with variations in the local fault strike using a two dimensional boundary element model we show that stresses resulting from slip on a curved fault can promote or inhibit inelastic failure within the fault zone in a pattern matching the observations the occurrence of shallow localized interseismic fault creep within mature fault zones may thus be partly controlled by the local fault geometry and normal stress with implications for models of fault zone evolution shallow coseismic slip deficit and geologic estimates of long term slip rates

reassessment of a slip budget along the parkfield segment of the san andreas fault historically the parkfield segment has represented a transition in fault behavior along the san andreas fault saf despite a 33 mm yr long term slip rate along the saf slip has not been observed on the cholame segment since the great 1857 fort tejon earthquake during that time the parkfield segment has experienced slip from at least six m 6 0 earthquakes aseismic fault creep and from minor earthquakes data from aseismic slip rate studies and historical earthquake studies allow us to estimate the total slip released along this portion of the saf since 1857 assuming the saf should slip at the long term slip rate a slip deficit of 5 m exists along the cholame segment since 1857 the slip deficit is approximately equivalent to 1857 offsets measured on the cholame and the southeast portion of the parkfield segment thus the slip deficit in southeast parkfield and cholame may be as great as the slip accommodated along these segments in 1857 the slip deficit abruptly decreases to the northwest across the parkfield segment it is 2 m near the town of parkfield and 0 m northwest of middle mountain an m 7 event rupturing all or part of the cholame segment and the southeastern parkfield segment slip decreasing to the northwest would release the accumulated slip and is plausible importantly this study also shows that the change in the pattern of strain release occurs in the middle of the parkfield segment rather than at its ends online material tables showing aseismic and coseismic slip estimations and calculations

surface fault slip associated with the 2004 parkfield california earthquake surface fracturing occurred along the san andreas fault the subparallel southwest fracture zone and six secondary faults in association with the 28 september 2004 m 6 0 parkfield earthquake fractures formed discontinuous breaks along a 32 km long stretch of the san andreas fault sense of slip was right lateral only locally was there a minor 1 11 mm vertical component of slip right lateral slip in the first few weeks after the event early in its afterslip period ranged from 1 to 44 mm our observations in the weeks following the earthquake indicated that the highest slip values are in the middle mountain area northwest of the mainshock epicenter creepmeter measurements indicate a similar distribution of slip surface slip along the san andreas fault developed soon after the mainshock field checks in the area near parkfield and about 5 km to the southeast indicated that surface slip developed more than 1 hr but generally less than 1 day after the event slip along the southwest fracture zone developed coseismically and extended about 8 km sense of slip was right lateral locally there was a minor to moderate 1 29 mm vertical component of slip right lateral slip ranged from 1 to 41 mm surface slip along secondary faults was right lateral the right lateral component of slip ranged from 3 to 5 mm surface slip in the 1966 and 2004 events occurred along both the san andreas fault and the southwest fracture zone in 1966 the length of ground breakage along the san andreas fault extended 5 km longer than that mapped in 2004 in contrast the length of ground breakage along the southwest fracture zone was the same in both events yet the surface fractures were more continuous in 2004 surface slip on secondary faults in 2004 indicated previously unmapped structural connections between the san andreas fault and the southwest fracture zone further revealing aspects of the structural setting and fault interactions in the parkfield area