new slip rate estimates for the creeping segment of the san andreas fault california new continuous and differential global positioning system gps measurements of recent slip rates and 30 yr alignment array offsets from the central creeping segment of the san andreas fault yield a maximum right lateral slip rate of 25 1 mm yr this slip rate is 20 slower than the 30 mm yr slip rate accepted for this segment of the fault and 35 slower than the 39 mm yr slip rate predicted between the sierra nevada great valley block and the pacific plate new continuous gps measurements between pairs of sites that flank the creeping segment at intersite distances of 1 0 km and 70 km give relative fault parallel slip rates of 28 2 and 30 2 mm yr respectively these observations indicate that right lateral deformation rates increase with distance from the fault possible explanations for the gradient observed in the geodetic data are elastic strain accumulation along the creeping segment or significant distributed deformation on off fault structures

size distribution of parkfield s microearthquakes reflects changes in surface creep rate s u m m a r y the nucleation area of the series of m6 events in parkfield has been shown to be characterized by low b values throughout the seismic cycle since low b values represent high differential stresses the asperity structure seems to be always stably stressed and even unaffected by the latest main shock in 2004 however because fault loading rates and applied shear stress vary with time some degree of temporal variability of the b value within stable blocks is to be expected we discuss in this study adequate techniques and uncertainty treatment for a detailed analysis of the temporal evolution of b values we show that the derived signal for the parkfield asperity correlates with changes in surface creep suggesting a sensitive time resolution of the b value stress meter and confirming near critical loading conditions within the parkfield asperity

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

streaks multiplets and holes high resolution spatio temporal behavior of parkfield seismicity 1 double difference locations of 8000 earthquakes from 1969 2002 on the parkfield section of the san andreas fault reveal detailed fault structures and seismicity that is although complex highly organized in both space and time distinctive features of the seismicity include 1 multiple recurrence of earthquakes of the same size at precisely the same location on the fault multiplets implying frictional or geometric controls on their location and size 2 sub horizontal alignments of hypocenters along the fault plane streaks suggestive of rheological transitions within the fault zone and or stress concentrations between locked and creeping areas 3 regions devoid of microearthquakes with typical dimensions of 1 5 km holes one of which contains the m6 1966 parkfield earthquake hypocenter these features represent long lived structures that persist through many cycles of individual events

how similar were the 1934 and 1966 parkfield earthquakes bakun and mcevilly 1984 showed that surface waves from the 1934 and 1966 parkfield earthquakes are remarkably similar this observation together with other seismic and geologic data led to the forecast of a repeat of a characteristic parkfield earthquake by 1993 in this paper we model near field geodetic measurements collected before and after the 1934 and 1966 parkfield earthquakes the slip in 1934 on the northwestern half of the rupture is poorly constrained due to the limited station coverage in this part of the rupture near the hypocenter the geodetic measurements permit the two earthquakes to have the same slip distribution on the other hand the data clearly show that the 1966 earthquake ruptured through the right step in the surface trace of the fault while the 1934 earthquake stopped northwest of the step if we assume only that the slip distribution is to some degree smooth we find that the centroid of the 1934 slip distribution could be as much as 10 km northwest of the centroid of the 1966 slip the data are consistent with but do not demand the largest slip in 1934 occurring in a region of low slip in 1966 the geodetically determined moments of the two earthquakes from smooth inversions are indistinguishable m0 4 4 0 4 1018 n m we also examine inversions in which we assume that the two earthquakes start identically and estimate how far down the fault the two earthquakes could have remained the same we find that the 1934 event could have had the same slip as in 1966 up to the fault step the 1934 earthquake must have stopped at the step whereas the 1966 event slipped southeast of the step in this quasi characteristic model m0 of the 1934 quake is only 60 of that in 1966 the difference presumably occurring as afterslip in 1966 if the 1934 geodetic moment was indeed less than in 1966 and the loading rate was constant this observation could explain the early occurrence of the 1934 earthquake

slip budget and potential for a m7 earthquake in central california the slip rate budget of the san andreas fault saf in central california which is approximately 33 mm yr is accounted for by a change in the slip release mechanism along the fault in the nw section of the fault between bear valley and monarch peak creep apparently accounts for the slip budget with the seismicity contributing negligibly the section at parkfield marks the transition from a creeping to a locked fault trace since the m8 1857 earthquake five m6 earthquakes have occurred but have not completely accounted for the slip budget southeast of parkfield the saf has been locked since 1857 from cholame to bitterwater valley this section now lags the deep slip by the amount of slip released in 1857 consequently faulting in this section could occur at the time of the next parkfield earthquake if this earthquake releases the slip deficit accumulated in the transition zone and in the locked zone the earthquake will have a moment magnitude m7 2

historic surface slip along the san andreas fault near parkfield california the parkfield earthquake prediction experiment is focusing close attention on the 44 km long section of the san andreas fault that last ruptured seismically in 1966 ms 6 0 the 20 km long central segment of the 1966 parkfield rupture extending from the mainshock epicenter at middle mountain southeastward to gold hill forms a 1 to 2 km salient northeastward away from the dominant n40 w strike following the 1966 earthquake afterslip aseismic slip has been nearly constant moderate parkfield earthquakes have recurred on average every 21 years since 1857 when a great earthquake m 8 ruptured at least as far north as the southern parkfield segment many measurements of slip have been made near parkfield since 1966 nevertheless much of the history of surface slip remained uncertain especially the total amount associated with the 1966 event in 1985 we measured accumulated slip on the four oldest cultural features offset by the fault along the 1966 parkfield rupture segment we interpret net slip on each feature as a sum of event slip sum of coseismic and rapid preseismic and postseismic slip from parkfield earthquakes and steady interseismic slip as measured over the last 20 years on nearby alinement arrays creep meters and trilateration lines we assumed for each site that event slip was identical for the 1922 1934 and 1966 parkfield events and that long term average rate of interseismic slip was constant between all events two fences on the southern segment southeast of gold hill indicate event slip of 13 and 15 cm and interseismic slip rate of 0 36 and 0 30 cm yr since 1959 and 1908 respectively at these sites redundant independent data support our assumption that both event and interseismic slip occur uniformly on the central segment near parkfield both the 1934 and the 1966 ruptures offset a bridge built in 1932 interseismic slip rate near the bridge has been about 1 1 cm yr since 1966 thus we deduce an average event slip of 31 cm for the 1934 and 1966 earthquakes on a parallel fault trace 1 km to the southwest slip was about 8 cm in 1966 thus total event slip summed across the entire fault zone near parkfield was nearly 40 cm on middle mountain 4 km north of the 1966 mainshock epicenter an offset fence indicates 17 cm of slip in 1966 and a 2 26 cm yr interseismic slip rate since circa 1946 thus the central segment of the 1966 rupture is characterized by much larger event slip 40 cm than both distal segments 15 cm this amount of surface slip per event is about twice what had been previously assumed larger 1966 surface slip in the central part of the rupture is geodetically compatible with a coseismic slip of 65 10 cm slip on a narrow buried asperity between middle mountain and gold hill that has been inferred from the depth distribution of early aftershocks assuming our characteristic surface slip model one can further deduce a deficit in slip since the great 1857 earthquake taking the long term slip rate as 3 3 cm yr the surface slip deficit is 3 0 2 m south of gold hill but only 0 3 0 3 m northward from parkfield

probabilistic seismic hazard in the san francisco bay area based on a simplified viscoelastic cycle model of fault interactions 1 we construct a viscoelastic cycle model of plate boundary deformation that includes the effect of time dependent interseismic strain accumulation coseismic strain release and viscoelastic relaxation of the substrate beneath the seismogenic crust for a given fault system time averaged stress changes at any point not on a fault are constrained to zero that is kinematic consistency is enforced for the fault system the dates of last rupture mean recurrence times and the slip distributions of the assumed repeating ruptures are key inputs into the viscoelastic cycle model this simple formulation allows construction of stress evolution at all points in the plate boundary zone for purposes of probabilistic seismic hazard analysis psha stress evolution is combined with a coulomb failure stress threshold at representative points on the fault segments to estimate the times of their respective future ruptures in our psha we consider uncertainties in a four dimensional parameter space the rupture peridocities slip distributions time of last earthquake for prehistoric ruptures and coulomb failure stress thresholds we apply this methodology to the san francisco bay region using a recently determined fault chronology of area faults assuming single segment rupture scenarios we find that future rupture probabilities of area faults in the coming decades are the highest for the southern hayward rodgers creek and northern calaveras faults this conclusion is qualitatively similar to that of working group on california earthquake probabilities but the probabilities derived here are significantly higher given that fault rupture probabilities are highly model dependent no single model should be used to assess to time dependent rupture probabilities we suggest that several models including the present one be used in a comprehensive psha methodology as was done by working group on california earthquake probabilities

seismicity around parkfield correlates with static shear stress changes following the 2003 mw6 5 san simeon earthquake 1 earthquakes trigger other earthquakes but the physical mechanism of the triggering is currently debated most studies of earthquake triggering rely on earthquakes listed in catalogs which are known to be incomplete around the origin times of large earthquakes and therefore missing potentially triggered events here we apply a waveform matched filter technique to systematically detect earthquakes along the parkfield section of the san andreas fault from 46 days before to 31 days after the nearby 2003 mw6 5 san simeon earthquake after removing all possible false detections we identify 8 times more earthquakes than in the northern california seismic network catalog the newly identified events along the creeping section of the san andreas fault show a statistically significant decrease following the san simeon main shock which correlates well with the negative static stress changes i e stress shadow cast by the main shock in comparison the seismicity rate around parkfield increased moderately where the static stress changes are positive the seismicity rate changes correlate well with the static shear stress changes induced by the san simeon main shock suggesting a low friction in the seismogenic zone along the parkfield section of the san andreas fault

rupture characteristics of the three m 4 7 1992 1994 parkfield earthquakes slip on the san andreas fault was determined for three m 4 7 earthquakes using a tomographic inverse system beroza and spudich 1988 to invert seismic source time functions stfs from s waves stfs were obtained by deconvolving mainshock accelerograms by those from collocated smaller earthquakes accelerograms were from the u s geological survey parkfield small aperture array upsar and from a distributed array of digital accelerometer stations at parkfield eight or nine stfs are used in each of the three inversions stfs are typically symmetrical pulses with a duration of about 0 3 0 5 s in the inversion mainshock rise time was set to 0 05 s and we allowed the rupture time to vary slightly from a constant rupture velocity of approximately 0 85 rupture for all three events which are located in or close to the middle mountain preparation zone or box mmb quickly reaches a local maximum in slip and then propagates outward to peaks ridges or plateaus in the slip distribution slip for the october 20 1992 event located just inside the southern edge of the mmb propagates from an initial spike north and updip along a curving ridge for about 2 km the initial spike continued to grow in the november 14 1993 event located north of the october 20 1992 event just beneath the hypocenter of the 1966 parkfield earthquake which shows little directivity although there is a smaller patch of slip updip and to the south in contrast rupture for the december 20 1994 event located just south of the october 20 1992 event propagated north and slightly updip creating a rough plateau in slip a few kilometers wide on a side directivity for this event also is to the north directivity for all three events points in the approximate direction of the 1966 hypocenter small pulses which comprise a coda are found on the stfs for several seconds after the initial impulsive event several tests based on the assumption that the average of all stfs from upsar for each event is an estimate of the true slip at the source suggest that the codas in the stfs are s waves from a long duration source rather than uncorrected site response an initiation phase is found on the array average for the november 14 1993 and december 20 1994 events these precursory phases are the result of a spike in slip at the hypocenter a value of 2 4 4 mm is obtained for d c the slip weakening distance by interpreting the initial spike as a critical patch the few aftershocks for the october 20 1992 event are distributed to the north and updip of the mainshock but the november 14 1993 event had a strong burst of aftershock activity that propagated to the north of its hypocenter at roughly the same depth aftershocks of the december 20 1994 event are mostly updip the november 14 1993 event had the simplest slip distribution appeared to be the most impulsive and had the most active aftershock sequence and the greatest depth if the eventual parkfield earthquake initiates near the 1966 hypocenter then the directivity of the three events studied here will have pointed to it however it is certainly possible that both the initiation of characteristic parkfield shocks and the directivity of smaller events are controlled by fault properties on a larger scale such as by fault bends or jogs

high resolution image of calaveras fault seismicity 1 by measuring relative earthquake arrival times using waveform cross correlation and locating earthquakes using the double difference technique we are able to reduce hypocentral errors by 1 to 2 orders of magnitude over routine locations for nearly 8000 events along a 35 km section of the calaveras fault this represents 92 of all seismicity since 1984 and includes the rupture zone of the m 6 2 1984 morgan hill california earthquake the relocated seismicity forms highly organized structures that were previously obscured by location errors there are abundant repeating earthquake sequences as well as linear clusters of earthquakes large voids in seismicity appear with dimensions of kilometers that have been aseismic over the 30 year time interval suggesting that these portions of the fault are either locked or creeping the area of greatest slip in the morgan hill main shock coincides with the most prominent of these voids suggesting that this part of the fault may be locked between large earthquakes we find that the calaveras fault at depth is extremely thin with an average upper bound on fault zone width of 75 m given the location error however this width is not resolvably different from zero the relocations reveal active secondary faults which we use to solve for the stress field in the immediate vicinity of the calaveras fault we find that the maximum compressive stress is at a high angle only 13 from the fault normal supporting previous interpretations that this fault is weak

slip rate increase at parkfield in 1993 detected by high precision edm and borehole tensor strainmeters on two of the instrument networks at parkfield california the two color electronic distance meter edm network and borehole tensor strainmeter btsm network we have detected a rate change starting in 1993 that has persisted at least 5 years these and other instruments capable of measuring crustal deformation were installed at parkfield in anticipation of a moderate m6 earthquake on the san andreas fault many of these instruments have been in operation since the mid 1980s and have established an excellent baseline to judge changes in rate of deformation and the coherence of such changes between instruments the onset of the observed rate change corresponds in time to two other changes at parkfield from late 1992 through late 1994 the parkfield region had an increase in number of m4 to m5 earthquakes relative to the preceding 6 years the deformation rate change also coincides with the end of a 7 year period of sub normal rainfall both the spatial coherence of the rate change and hydrological modeling suggest a tectonic explanation for the rate change from these observations we infer that the rate of slip increased over the period 1993 1998

correlated errors in geodetic time series implications for time dependent deformation analysis of frequent trilateration observations from the two color electronic distance measuring networks in california demonstrate that the noise power spectra are dominated by white noise at higher frequencies and power law behavior at lower frequencies in contrast earth scientists typically have assumed that only white noise is present in a geodetic time series since a combination of infrequent measurements and low precision usually preclude identifying the time correlated signature in such data after removing a linear trend from the two color data it becomes evident that there are primarily two recognizable types of time correlated noise present in the residuals the first type is a seasonal variation in displacement which is probably a result of measuring to shallow surface monuments installed in clayey soil which responds to seasonally occurring rainfall this noise is significant only for a small fraction of the sites analyzed the second type of correlated noise becomes evident only after spectral analysis of line length changes and shows a functional relation at long periods between power and frequency of 1 where is frequency and 2 with 2 this type of correlated noise is termed random walk noise and its source is mainly thought to be small random motions of geodetic monuments with respect to the earth s crust though other sources are possible because the line length changes in the two color networks are measured at irregular intervals power spectral techniques cannot reliably estimate the level of 1 noise rather we also use here a maximum likelihood estimation technique which assumes that there are only two sources of noise in the residual time series white noise and random walk noise and estimates the amount of each from this analysis we find that the random walk noise level averages about 1 3 mm yr and that our estimates of the white noise component confirm theoretical limitations of the measurement technique in addition the seasonal noise can be as large as 3 mm in amplitude but typically is less than 0 5 mm because of the presence of random walk noise in these time series modeling and interpretation of the geodetic data must account for this source of error by way of example we show that estimating the time varying strain tensor a form of spatial averaging from geodetic data having both random walk and white noise error components results in seemingly significant variations in the rate of strain accumulation spatial averaging does reduce the size of both noise components but not their relative influence on the resulting strain accumulation model

irregular earthquake cycle along the southern tianshan front aksu area china 1 a long deformation record 16 5 ka showing nonsteady earthquake recurrence is established for the aksu thrust tianshan china on the basis of cosmogenic 10be dating of faulted surfaces topographic leveling across the aksu fault scarp indicates up to 10 m uplift across a moraine abandoned 16 5 ka and similar uplift of 6 m across two inset surfaces yielding ages of 12 5 and 5 ka successively smaller uplifts of terraces younger than 5 ka indicate that three or more major earthquakes occurred during this period these data show that the aksu thrust fault was quiet for at least 7500 years and active in the last 5000 years and probably in the interval 16 5 12 5 ka the seismic cycle along the aksu thrust fault over the last 16 500 years was thus strongly irregular showing long quiescence and clustering which is a challenge for paleoseismology and hazard assessment this irregularity also makes it more difficult to estimate long term shortening rates nevertheless we are able to constrain a minimum total shortening rate 7 mm yr across the southern tianshan front for the last 12 500 years that is about a third of the total geodetic rate for the western tianshan 20 mm yr

a high frequency secondary event during the 2004 parkfield earthquake by using seismic records of the 2004 magnitude 6 0 parkfield earthquake we identified a burst of high frequency seismic radiation that occurred about 13 kilometers northwest of the hypocenter and 5 seconds after rupture initiation we imaged this event in three dimensions by using a waveform back projection method as well as by timing distinct arrivals visible on many of the seismograms the high frequency event is located near the south edge of a large slip patch seen in most seismic and geodetic inversions indicating that slip may have grown abruptly at this point the time history obtained from full waveform back projection suggests a rupture velocity of 2 5 kilometers per second energy estimates for the subevent together with long period slip inversions indicate a lower average stress drop for the northern part of the parkfield earthquake compared with that for the region near its hypocenter which is in agreement with stress drop estimates obtained from small magnitude aftershocks

interseismic coupling and refined earthquake potential on the hayward calaveras fault zone interseismic strain accumulation and fault creep is usually estimated from gps and alignment arrays data which provide precise but spatially sparse measurements here we use interferometric synthetic aperture radar to resolve the interseismic deformation associated with the hayward and calaveras faults hf and cf in the east san francisco bay area the large 1992 2011 sar data set permits evaluation of short and long wavelength deformation larger than 2 mm yr without alignment of the velocity field to a gps based model our time series approach in which the interferogram selection is based on the spatial coherence enables deformation mapping in vegetated areas and leads to refined estimates of along fault surface creep rates creep rates vary from 0 2 mm yr on the northern cf to 14 2 mm yr on the central cf south of the hf surface junction we estimate the long term slip rates by inverting the long wavelength deformation and the distribution of shallow slip due to creep by inverting the remaining velocity field this distribution of slip reveals the locations of locked and slowly creeping patches with potential for a m6 8 0 3 on the hf near san leandro a m6 6 0 2 on the northern cf near dublin a m6 5 0 1 on the hf south of fremont and a m6 2 0 2 on the central cf near morgan hill with cascading multisegment ruptures the hf rupturing from berkeley to the cf junction could produce a m6 9 0 1 the northern cf a m6 6 0 1 the central cf a m6 9 0 2 from the junction to gilroy and a joint rupture of the hf and central cf could produce a m7 1 0 1

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

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

coseismic and initial postseismic deformation from the 2004 parkfield california earthquake observed by global positioning system electronic distance meter creepmeters and borehole strainmeters global positioning system gps electronic distance meter creepmeter and strainmeter measurements spanning the m 6 0 parkfield california earthquake are examined using these data from 100 sec through 9 months following the mainshock the omori s law with rate inversely related to time 1 t p and p ranging between 0 7 and 1 3 characterizes the time dependent deformation during the postseismic period these results are consistent with creep models for elastic solids with an accurate function of postseismic response the coseismic displacements can be estimated from the high rate 1 min sampling gps and the coseismic displacements are approximately 75 of those estimated from the daily solutions consequently fault slip models using daily solutions overestimate coseismic slip in addition at 2 months and at 8 months following the mainshock postseismic displacements are modeled as slip on the san andreas fault with a lower bound on the moment exceeding that of the coseismic moment online material data description and supplementary figures tables and data used in models and time series analysis

tectonically driven late paleocene 57 9 54 7 ma transgression and climatically forced latest middle eocene 41 3 38 0 ma regression on the indian subcontinent abstract cenozoic era was the turning point in the geological history of the indian subcontinent when india experienced maximum isolation before it collided with asia and there occurred a great mountain building activity shaping the himalaya in the cenozoic era the sedimentation commenced in the late paleocene 57 9 ma in the pericratonic basins of the western india as well as the foreland basins of the himalaya that marks the beginning of a major transgression on the indian subcontinent till now it is not sure whether this transgression was forced by tectonics or climate we have interpreted that the primary driver for this transgression was the tectonics that marks the beginning of the india asia convergence a major regression of similar magnitude occurred during latest middle eocene 41 3 38 0 ma that corresponds to global sea level fall this regression is global and can be identified even in the cenozoic basins developed within the african plate it is interpreted that this regression was driven by the global cooling during latest middle eocene late eocene possibly associated with the nucleation of the antarctica ice sheets coupled with the uplift of the himalaya

high rate real time gps network at parkfield utility for detecting fault slip and seismic displacements 1 a network of 13 continuous gps stations near parkfield california has been converted from 30 second to 1 second sampling with positions of the stations estimated in real time relative to a master station most stations are near the trace of the san andreas fault which exhibits creep the noise spectra of the instantaneous 1 hz positions show flicker noise at high frequencies and change to frequency independence at low frequencies the change in character occurs between 6 to 8 hours our analysis indicates that 1 second sampled gps can estimate horizontal displacements of order 6 mm at the 99 confidence level from a few seconds to a few hours high frequency gps can augment existing measurements in capturing large creep events and postseismic slip that would exceed the range of existing creepmeters and can detect large seismic displacements

distribution of interseismic slip rates and the potential for significant earthquakes on the calaveras fault central california 1 the calaveras fault is a major component of the san andreas fault system in the san francisco bay area that generated 13 earthquakes of ml 5 since 1850 in most recent ml 5 events premain shock and postmain shock microseismicity is sparse in the region of coseismic slip these aseismic areas are believed to represent locked patches of the fault that are accumulating strain to be released in ml 5 events we analyze geodetic data to better characterize the spatial distribution of interseismic slip rates on the calaveras fault modeling the slip distribution in the seismogenic zone by inversion of over 25 years of surface deformation data we use a regional fault model with the seismogenic zone of the calaveras fault discretized into 6 km 3 km elements employing a weighted least squares approach with smoothing and positivity constraints our discretized fault slip model consistently identifies regions of slip deficit in the seismogenic zone of the calaveras fault that generally correspond to regions of decreased microseismicity and ruptures of previous moderate earthquakes in particular we find correspondence with the 1979 coyote lake and 1984 morgan hill events as well as regions where historical earthquakes on the coyote and the sunol san ramon segments have occurred moment magnitude calculations based on the estimated slip deficit fault area and recurrence intervals agree with measured magnitudes of modern events and interpreted historical magnitudes the results suggest that a combination of geodetically derived fault slip models and microseismicity distribution can be used to characterize seismic hazard

probabilistic estimates of surface coseismic slip and afterslip for hayward fault earthquakes we examine the partition of long term geologic slip on the hayward fault into interseismic creep coseismic slip and afterslip using monte carlo simulations we compute expected coseismic slip and afterslip at three alinement array sites for hayward fault earthquakes with nominal moment magnitudes ranging from about 6 5 to 7 1 we consider how interseismic creep might affect the coseismic slip distribution as well as the variability in locations of large and small slip patches and the magnitude of an earthquake for a given rupture area we calibrate the estimates to be consistent with the ratio of interseismic creep rate at the alinement array sites to the geologic slip rate for the hayward fault we find that the coseismic slip at the surface is expected to comprise only a small fraction of the long term geologic slip the median values of coseismic slip are less than 0 2 m in nearly all cases as a result of the influence of interseismic creep and afterslip however afterslip makes a substantial contribution to the long term geologic slip and may be responsible for up to 0 5 1 5 m median plus one standard deviation s d of additional slip following an earthquake rupture thus utility and transportation infrastructure could be severely impacted by afterslip in the hours and days following a large earthquake on the hayward fault that generated little coseismic slip inherent spatial variability in earthquake slip combined with the uncertainty in how interseismic creep affects coseismic slip results in large uncertainties in these slip estimates

inverting for slip on three dimensional fault surfaces using angular dislocations the increasing quality of geodetic data synthetic aperture radar interferometry insar dense global positioning system gps arrays now available to geophysicists and geologists are not fully exploited in slip inversion procedures most common methods of inversion use rectangular dislocation segments to model fault ruptures and therefore oversimplify fault geometries these geometric simplifications can lead to inconsistencies when inverting for slip on earthquake faults and they preclude a more complete understanding of the role of fault geometry in the earthquake process we have developed a new three dimensional slip inversion method based on the analytical solution for an angular dislocation in a linear elastic homogeneous isotropic half space the approach uses the boundary element code poly3d that employs a set of planar triangular elements of constant displacement discontinuity to model fault surfaces the use of triangulated surfaces as discontinuities permits one to construct fault models that better approximate curved three dimensional surfaces bounded by curved tiplines shapes that commonly are imaged by three dimensional reflection seismic data and inferred from relocated aftershock data we demonstrate the method s ability to model three dimensional rupture geometries by inverting for slip associated with the 1999 hector mine earthquake the resulting model avoids displacement anomalies associated with the overlapping rectangular dislocations used in previous models improving the fit to the geodetic data by 32 and honors the observed surface ruptures thereby allowing more direct comparisons between geologic and geodetic data on slip distributions online material hector mine input files and file format description

equatorial long wave characteristics determined from satellite sea surface temperature and in situ data sea surface temperature sst maps and imagery derived from the noaa 6 satellite advanced very high resolution radiometer avhrr for june and july 1981 in the eastern tropical pacific portray the wavelike structure of the cool water along the equator from 93 w to 125 w cusped waves of approximately 1000 km zonal wavelength and 25 day period propagated westward with a phase speed of 40 km day the observed meridional extent between the crest and trough of the waves is about 300 km details in the imagery show cooler water at the cusps advected north and then east with the north equatorial countercurrent necc consistent with the suggestion of a series of anticyclonic eddies occupying the shear zone between the necc and the westward flowing south equatorial current absolute sst estimates from the avhrr data agree to within 0 6 c with shipboard data taken along 110 w between 5 n and 5 s the wavelike structures in the sst maps are also in agreement at the surface with a vertical expendable bathythermograph temperature section made along the equator between 93 w and 125 w which shows the phase of the waves tilting westward with increasing depth over the upper 75 m such a phase shift if it extended 100 200 km meridionally in either direction from the equator would be associated with an equatorward flux of heat similar phase shifts appear in temperature time series at depths of 20 and 50 m from a mooring at 0 33 n 110 30 w near surface currents measured at this and a second mooring on the equator at 109 40 w indicate a regular pattern of northward advection when wave cusps pass them followed by southwest flow during the passage of wave troughs again consistent with an equatorward flux of heat as well as with earlier theoretical and drift buoy findings

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

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

high interseismic coupling in the eastern makran pakistan subduction zone estimating the extent of interseismic coupling along subduction zone megathrusts is essential for quantitative assessments of seismic and tsunami hazards up to now quantifying the seismogenic potential of the eastern makran subduction zone at the northern edge of the indian ocean has remained elusive due to a paucity of geodetic observations furthermore non tectonic processes obscure the signature of accumulating elastic strain historical earthquakes of magnitudes greater than 7 have been reported in particular the 1945 mw 8 1 earthquake resulted in a significant tsunami that swept the shores of the arabian sea and the indian ocean a quantitative estimate of elastic strain accumulation along the subduction plate boundary in eastern makran is needed to confront previous indirect and contradictory conclusions about the seismic potential in the region here we infer the distribution of interseismic coupling on the eastern makran megathrust from time series of satellite interferometric synthetic aperture radar insar images acquired between 2003 and 2010 applying a consistent series of corrections to extract the low amplitude long wavelength deformation signal associated with elastic strain on the megathrust we find high interseismic coupling i e the megathrust does not slip and elastic strain accumulates in the central section of eastern makran where the 1945 earthquake occurred while lower coupling coincides spatially with the subduction of the sonne fault zone the inferred accumulation of elastic strain since the 1945 earthquake is consistent with the future occurrence of magnitude 7 earthquakes and we cannot exclude the possibility of a multi segment rupture mw 8 however the likelihood for such scenarios might be modulated by partitioning of plate convergence between slip on the megathrust and internal deformation of the overlying actively deforming accretionary wedge

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

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

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

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

slip in the 1868 hayward earthquake from the analysis of historical triangulation data despite the importance of the hayward fault for earthquake hazards in the san francisco bay area neither the rupture length nor the average coseismic slip in the most recent major earthquake which occurred in 1868 is well known we estimate slip in the 1868 earthquake by analyzing triangulation data collected between 1853 1860 and 1876 1891 we apply a denuisancing procedure that projects out the dependence of that data on station coordinates allowing their displacements to be estimated directly the best fit to the data is obtained with a 52 km long by 10 km deep rupture that extends from warm springs to near berkeley considerably longer than the 30 km of reported surface breakage the estimated slip for an earthquake of this length is 1 9 0 4 m and the seismic moment is m0 3 0 0 7 1019 n m corresponding to mw 7 0 the data are inconsistent with regionally high strain rate prior to the 1906 earthquake as had been previously suggested the triangulation data record northeastward displacement of station loma prieta presumably as a result of the 1865 earthquake the fault normal displacement is not easily explained by slip on either the san andreas fault or the 1989 loma prieta rupture surface this observation is however consistent with an mw 6 3 4 thrust event northeast of the san andreas fault in the southern santa cruz mountains thrust belt

slip partitioning of the calaveras fault california and prospects for future earthquakes examination of main shock and microearthquake data from the calaveras fault during the last 20 years reveals that main shock hypocenters occur at depths of 8 9 km near the base of the zone of microearthquakes the spatial pattern of pre main shock microseismicity surrounding the coyote lake and morgan hill hypocenters is similar to the pattern of the post main shock microseismicity microseismicity extends between depths of 4 and 10 km and defines zones of concentrated microseismicity and aseismic zones estimates of the fault regions which slipped during the coyote lake and morgan hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic we propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes from the pattern of microearthquake locations we recognize six aseismic zones where we expect future main shocks will rupture the calaveras fault from an analysis of historic seismic data we establish the main shock rupture history for each aseismic zone and identify two zones that are the most likely sites for the next m 5 earthquakes the first zone is located near gilroy and was last ruptured by a m5 2 earthquake in 1949 the second zone is located south of calaveras reservoir and north of the 1988 m5 1 alum rock earthquake it has not slipped seismically since at least 1903 and the size of the aseismic region is sufficiently large to sustain a m5 5 earthquake

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

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

variations in fault slip and strain accumulation at parkfield california initial results using two color geodimeter measurements 1984 1988 repeated length measurements of several geodetic baselines near parkfield california have revealed significant variations in the local rates of shallow fault slip and strain this network of baselines surveyed several times each week straddles the san andreas fault in the transition zone between the creeping section to the northwest and the locked section to the southeast the length measurements characterized by a precision approaching 0 1 ppm reveal large fluctuations in the rates of baseline extension principal mode analysis of the length change data indicates that the two largest components of the signal are 1 secular extensions and contractions consistent with surface slip on the main strand of the san andreas fault and 2 a large seasonal oscillation with no obvious spatial coherence on most of these baselines the second component appears to be in phase with seasonal rainfall when data from the baselines with the largest amplitude of the seasonal signal are excluded the remaining data can be modeled in terms of both spatial and temporal variations in surface slip variations in the components of the changes in uniform strain and the possible displacement of the central monument in this radial network in parameterizing this model the spatial variation of slip beneath the near surface is reflected by changes in shear strain although the computed secular shear is highly dependent upon the specified parameterization of surface slip the data are consistent with the hypothesis that slip at intermediate depths lags behind the surface slip rate however the range in models that fit the data does not necessarily imply that there is a deficit in slip at depth relative to the surface comparison of the inferred values of surface slip from the model with the observed fault slip measured by very short baseline creep meters indicates close agreement in secular rates but the short term variations observed with the creep meters are either highly attenuated or nonexistent in the modeled slip since the modeled slip is a spatial average which smooths out possible short wavelength variations in the surface slip for which the creep instruments are most sensitive an interesting conclusion from the two color data is that surface slip on the san andreas fault appears to be spread over a 2 km wide zone on the south flank of middle mountain but is confined to a very narrow zone to the south as the fault passes through the center of the network this conclusion is dependent upon the assumption that a few critical monuments are stable and track tectonic displacements in the long term finally the largest observed strain change is an extensional strain coincident with the kettleman hills earthquake m5 5 in august 1985

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

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

six similar sequential ruptures of the san andreas fault carrizo plain california we document the precise sizes but not the dates of the six latest offsets across the san andreas fault at wallace creek california three and perhaps four of these including the latest in 1857 show dextral offset of 7 5 8 m the third and fourth offsets however are just 1 4 and 5 2 m the predominance of similar offsets for the latest six events suggests that the fundamental properties of the fault system that control slip size do not vary greatly from event to event the large offsets imply that ruptures involving this site are typically more than 200 km long

comparison of various inversion techniques as applied to the determination of a geophysical deformation model for the 1983 borah peak earthquake abstract a number of techniques are employed to overcome nonuniqueness and instability inherent in linear inverse problems to test the factors that enter into the selection of an inversion technique for fault slip distribution we used a penalty function with smoothness pf s a damped least squares method dls damped least squares method with a positivity constraint dls p and a penalty function with smoothness and a positivity constraint pf s p for inverting the elevation changes for slip associated with the 1983 borah peak earthquake unlike solving an ill posed inverse problem using a gradient technique ward and barrientos 1986 we have restored the well posed character between the elevation changes and normal slip distribution studies showed that the constraints based on sound understanding of the physical nature of the problem are crucial in the derivation of a meaningful solution and dictates primarily the selection of a particular inversion technique all available geological and geophysical information were used to determine a geophysical deformation model for the earthquake it is suggested that the pf s p solution for a fault length of 75 km is the preferred model the long wavelength features in the estimated slip distribution are similar to those obtained by ward and barrientos 1986 whereas the shorter wavelength features differ between two solutions the fault dips 49 to the southwest the slipped zones deepen from the surface at the northwest to about 20 km downdip depth at the southeast the fault extends to the southeast beyond the epicenter of the mainshock it is also shown that only the long wavelength features of the slip distribution are well resolved the resolution is better at shallower levels than at deeper levels the resolution deteriorates when the deformation sources are away from the leveling lines smoothness constraints provide better resolution than damping does at depth the addition of a positivity constraint significantly improves the model resolution

surface slip associated with the 2004 parkfield california earthquake measured on alinement arrays although still continuing surface slip from the 2004 parkfield earth quake as measured on alinement arrays appears to be approaching about 30 35 cm between parkfield and gold hill this includes slip along the main trace and the southwest fracture zone swfz slip here was higher in 1966 at about 40 cm the distribution of 2004 slip appears to have a shape similar to that of the 1966 event but final slip is expected to be lower in 2004 by about 3 15 cm even when continuing slip is accounted for proportionately this difference is most notable at the south end at highway 46 where the 1966 event slip was 13 cm compared to the 2004 slip of 4 cm continuous global positioning system and creepmeters suggest that significant surface coseismic slip apparently occurred mainly on the swfz and perhaps on middle mountain the latter possibly caused by shaking langbein et al 2005 creepmeters indicate only minor 0 2 cm surface coseismic slip occurred on the main trace between parkfield and gold hill we infer that 3 6 cm slip accumulated across our arrays in the first 24 hr at highway 46 slip appears complete whereas the remaining sites are expected to take 2 6 years to reach their background creep rates following the 1966 event afterslip at one site persisted as much as 5 10 years the much longer recurrence intervals between the past two parkfield earthquakes and the decreasing slip per event may suggest that larger slip deficits are now growing along the parkfield segment

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

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