potential for larger earthquakes in the east san francisco bay area due to the direct connection between the hayward and calaveras faults the hayward and calaveras faults two strike slip faults of the san andreas system located in the east san francisco bay area are commonly considered independent structures for seismic hazard assessment we use interferometric synthetic aperture radar to show that surface creep on the hayward fault continues 15 km farther south than previously known revealing new potential for rupture and damage south of fremont the extended trace of the hayward fault also illuminated by shallow repeating micro earthquakes documents a surface connection with the calaveras fault at depths greater than 3 5 km repeating micro earthquakes located 10 km north of the surface connection highlight the 3 d wedge geometry of the junction our new model of the hayward and calaveras faults argues that they should be treated as a single system with potential for earthquake ruptures generating events with magnitudes greater than 7 posing a higher seismic hazard to the east san francisco bay area than previously considered

interseismic ground deformation and fault slip rates in the greater san francisco bay area from two decades of space geodetic data author s xu w wu s materna k nadeau r floyd m funning g chaussard e johnson cw murray jr ding x burgmann r abstract 2018 american geophysical union all rights reserved the detailed spatial variations of strain accumulation and creep on major faults in the northern san francisco bay area north bay which are important for seismic potential and evaluation of natural hazards remain poorly understood here we combine interferometric synthetic aperture radar data from the ers 1 2 and envisat satellites between 1992 and 2010 with continuous and campaign gps data to obtain a high spatial and temporal coverage of ground deformation of the north bay the sar data from both ascending and descending orbits are combined to separate horizontal and vertical components of the deformation we jointly invert the horizontal component of the mean velocities derived from these data to infer the deep strike slip rates on major locked faults we use the estimated deep rates to simulate the long wavelength deformation due to interseismic elastic strain accumulation along these locked faults after removing the long wavelength signal from the insar horizontal mean velocity field we estimate fault parallel surface creep rates of up to 2 mm year along the central section of the rodgers creek fault and surface creep rates ranging between 2 and 4 mm year along the concord fault no surface creep is geodetically resolved along the west napa and green valley fault zones we identified characteristically repeating earthquakes on the rodgers creek fault the west napa fault the green valley fault and the concord fault nontectonic deformation in the geysers geothermal field and in late cenozoic basins rohnert park and sonoma basins are also observed likely due to hydrological and sediment compaction processes respectively

slow and go pulsing slip rates on the creeping section of the san andreas fault rising and falling slip rates on the creeping section of the san andreas fault have been inferred from variations of recurrence intervals of characteristically repeating microearthquakes but this observation has not previously been confirmed using modern geodetic data here we report on observations of this pulsing slip obtained from advanced multitemporal interferometric synthetic aperture radar insar data confirmed using continuous gps sites of the plate boundary observatory the surface deformation time series show a strong correlation to the previously documented slip rate variations derived from repeating earthquakes on the fault interface at various spatial and temporal scales time series and spectral analyses of repeating earthquake and insar data reveal a quasiperiodic pulsing with a roughly 2 year period along some sections of the fault with the earthquakes on the fault interface lagging behind the far field deformation by about 6 months this suggests a temporal delay between the pulsing crustal strain generated by deep seated shear and the time variable slip on the shallow fault interface and that at least in some places this process may be cyclical there exist potential impacts for time dependent seismic hazard forecasting in california and as it becomes better validated in the richly instrumented natural laboratory of the central san andreas fault the process used here will be even more helpful in characterizing hazard and fault zone rheology in areas without california s geodetic infrastructure

temporal changes in attenuation associated with the 2004 m6 0 parkfield earthquake 1 elevated seismic attenuation is often observed in fault zones due to the high degree of fracturing and fluid content however temporal changes in attenuation at the time of an earthquake are poorly constrained but can give indications of fracture damage and healing in this study spectral ratios between earthquakes within repeating clusters are calculated in an attempt to resolve temporal variations in attenuation at the time of the 2004 m6 0 parkfield earthquake a sharp increase in attenuation is observed immediately after the earthquake which then decays over the next 2 years influences of intercluster magnitude variations time window length and previously reported postseismic velocity changes are investigated the postseismic decay is fit by a logarithmic function the timescale of the decay is found to be similar to that in gps data and ambient seismic noise velocities following the 2004 m6 0 parkfield earthquake the amplitude of the attenuation change corresponds to a decrease of approximately 10 in qp at the time of the earthquake the greatest changes are recorded on the northeast of the fault trace consistent with preferential damage in the extensional quadrant behind a north westerly propagating rupture tip our analysis suggests that significant changes in seismic attenuation and hence fracture dilatancy during coseismic rupture are limited to depths of less than about 5 km

kinematic source parameters for the 1989 loma prieta earthquake from the nonlinear inversion of accelerograms we describe a technique to infer the kinematic parameters of the earth quake rupture process by the nonlinear inversion of near source high frequency seis mic records the model assumes that each point on the fault plane slips when the rupture front passes with a variable slip amplitude for a given rupture model syn thetic seismograms are computed by using the ray theory and a plane layered velocity structure the rupture velocity and the final slip are specified at a set of control points on the fault plane and the values at any point on the fault are then obtained by a bicubic interpolation the final slip and rupture velocity at the fault grid nodes are determined by searching for the minimum of a misfit function by using the genetic algorithm the number of control points is progressively increased to move from a high to low wavelength description of final slip and rupture velocity on the fault plane the optimal model parameter set is chosen according to the minimum of the corrected akaike information criterion parameter the uncertainty on the source parameters has been estimated through the analysis of cross correlation of the misfit function in the neighborhood of the final best fit rupture model the method is applied to near source strong motion records of the 1989 loma prieta earthquake we find that the most earthquake slip occurred in two regions located northwest and southeast of the hypocenter consistent with previous models obtained using other data and techniques moreover we find that the rupture propagated faster toward the southeast than in the northwest direction the total duration of the rupture is found to be approximately 9 sec

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

a two layer wind driven coastal circulation model a simple two layer water circulation model is developed for the application in homogeneous coastal regions the objective is to develop a two layer model with a relatively thin upper layer that can respond better than a depth averaged model to a changing wind field hence give better predictions of the near surface velocity the governing equations for each water layer are derived from depth averaging of the navier stokes equations coupling between the upper and lower water layers is through the mass and momentum transfer at the interface to obtain the stress transfer function at the interface the problem of wind driven circulations in finite water depth is solved with a bilinear eddy viscosity model that assumes the vertical eddy viscosity to increase linearly with the distance from both the water surface and the bottom boundary it is found that the stresses at the interface i can be related to the mean flows above and below the interface v1 and v2 by a simple constitutive law i 0 18 u s v1 v2 where is the water density and u s is the shear velocity at the water surface comparisons of the two layer circulation model with commonly used depth averaged models for the prediction of coastal circulation reveal that the use of the two layer model gives more realistic predictions of the water motion as an example the upper water layer of the two layer model is coupled with that of an ice circulation model and it is found that the coupled ice water circulation model gives accurate predictions of ice floe movements obtained from field measurements

a time series of vent fluid compositions from 21 n east pacific rise 1979 1981 1985 and the guaymas basin gulf of california 1982 1985 a time series study of four hot spring fields at 21 n on the east pacific rise demonstrates that the solution compositions of mid ocean ridge hydrothermal vents are stable on a decadal time scale the ocean bottom seismometer obs national geographic smoker ngs and south west sw vents show no significant changes in the major element composition of their end member fluids since 1979 two of the vents obs and sw have maintained exit temperatures near 350 c since 1979 the ngs vent has remained close to 270 c since 1981 after cooling from 350 c in 1979 only one vent hanging gardens shows important changes in solution chemistry from 1981 to 1985 in 1985 this vent appears to have cooled 10 c relative to the other vents the depth of the reaction zone as determined by quartz geobarometry has increased by about 1 km at this vent the large fluxes of compositionally stable fluids from these vents cannot be explained by transient conditions and unique circumstances rather the constancy of small interfield variations in solution composition is more consistent with control by rock buffering a 4 year time series study of hydrothermal vents in the guaymas basin also shows no significant changes in the major element composition of the end member fluids interfield differences in solution chemistry have been maintained from 1982 to 1985 this phenomenon is best explained in terms of an equilibrium model

pb isotopes in sulfides from mid ocean ridge hydrothermal sites the authors report pb isotope ratios of sulfides deposited at seven recently active mid ocean ridge mor hydrothermal vents sulfides from three sediment starved sites on the juan de fuca ridge contain pb with isotope ratios identical to their local basaltic sources lead in two deposits from the sediment covered escanaba trough gorda ridge is derived from the sediments and does not appear to contain any basaltic component there is a range of isotope ratios in a guaymas basin deposit consistent with a mixture of sediment and mor basalt pb lead in a galapagos deposit differs slightly from known galapagos basalt pb isotope values the faithful record of pb isotope signatures of local sources in mor sulfides indicates that isotope ratios from ancient analogues ca be used as accurate reflections of ancient oceanic crustal values in ophiolite hosted deposits and continental crustal averages in sediment hosted deposits the preservation of primary ophiolitic or continental crustal pb isotope signatures in ancient mor sulfides provides a powerful tool for investigation of crustal evolution and for fingerprinting ancient terranes

variability of fault slip behavior along the san andreas fault in the san juan bautista region an improved understanding of the time history of fault slip at depth is an essential step toward understanding the underlying mechanics of the faulting process using a waveform cross correlation approach we document spatially and temporally varying fault slip along the northernmost creeping section of the san andreas fault near san juan bautista sjb california by systematically examining spatiotemporal behaviors of characteristically repeating earthquakes cres the spatial distribution of pre 1998 sjb earthquake 1984 1998 fault slip rate inferred from the cres reveals a 15 km long low creep or partially locked section located near the 1998 mw 5 1 sjb earthquake rupture a finite fault slip inversion reveals that the rupture of the 1998 sjb earthquake is characterized by the failure of a compact 4 km2 asperity with a maximum slip of about 90 cm and corresponding peak stress drop of up to 50 mpa whereas the mean stress drop is about 15 mpa following the 1998 earthquake the cre activity was significantly increased in a 5 10 km deep zone extending 2 7 km northwest of the main shock which indicates triggering of substantial aseismic slip the postseismic slip inferred from the cre activity primarily propagated to the northwest and released a maximum slip of 9 cm in this 5 10 km depth range the estimated postseismic moment release is 8 6 1016 n m which is equivalent to mw 5 22 the aseismic slip distribution following the 1998 earthquake is not consistent with coseismic stress driven afterslip but represents a triggered long lasting slow earthquake

fractal dimension and b value on creeping and locked patches of the san andreas fault near parkfield california we tested the hypotheses 1 that the fractal dimension d of hypocenters are different in a locked and a creeping segment of the san andreas fault and 2 that the relationship d 2b holds approximately where b is the slope of the frequency magnitude relationship the test area was the 30 to 50 km fault segment north of park eld for which two earthquake catalogs exist the borehole high resolution seismic network data and the u s geological survey data which have a minimum magnitude of completeness of mc 0 4 and mc 1 0 1 2 respectively the relative location errors in the two catalogs are estimated as 0 25 km and less than 1 km respectively the periods of high quality data available extend from 1987 to 1998 5 and 1981 to 2000 2 respectively furnishing 2609 and 3775 events for analysis in the two catalogs in the locked part 0 5 b 0 7 and 0 96 d 1 14 whereas in the creeping segment 1 1 b 1 6 and 1 45 d 1 72 however the spatial distribution of the hypocenters in the creeping segment is not well approximated by a fractal distribution we conclude 1 that the frequency magnitude distribution as described by b as well as the fractal dimension d are different in the locked and creeping segments near park eld 2 that the spatial distribution in the creeping segment is not well approximated by a fractal distribution and 3 that the relationship d 2b holds in the locked segment where both parameters can be measured accurately thus we propose that the heterogeneity of seismogenic volumes lead to differences in d and b and that these differences where established by high quality data may furnish clues concerning properties of fault zones

seismic velocity variations along the rupture zone of the 1989 loma prieta earthquake california 1 we revisit the rupture zone of the 1989 mw6 9 loma prieta earthquake central california by developing high resolution three dimensional 3 d vp and vp vs models we apply the simul2000 inversion method and algorithm to a set of composite events which have greater number of picks per event and reduced random picking errors compared with traditional master events our final p wave velocity model generally agrees with previous studies showing a high velocity body of above 6 7 km s in the southeast rupture zone of the main shock the 3 dvp vs model however has different features with low vp vs in the upper crust and high vp vs anomalies in deeper layers of the rupture zone we interpret the low vp vs at shallow depths to be granitic rocks whereas at greater depths the areas of higher vp vs around 1 725 1 75 presumably are mafic rocks the resulting 3 d velocity model was used to improve absolute locations for all local events between 1984 and 2010 in our study area we then applied a similar event cluster analysis waveform cross correlation and differential time relocation methods to improve relative event location accuracy over 88 of the seismicity falls into similar event clusters a dramatic sharpening of seismicity patterns is obtained after using these methods the medians of the relative location uncertainties calculated by using the bootstrap approach are 5 m for horizontal and 8 m for vertical differential times from cross correlation are used to estimatein situnear sourcevp vsratio within each event cluster the high resolutionvp vs method confirms the trend of the velocity variations from the tomographic results although absolute values are slightly different

towards a universal rule on the recurrence interval scaling of repeating earthquakes 1 a recent analysis of recurrence properties of small repeating earthquakes on a creeping oblique thrust fault in eastern taiwan reveals a weak variation in recurrence interval tr with seismic moment mo compared to the scaling of tr with mo from repeating earthquake data near parkfield in california the repeating data from eastern taiwan has recurrence intervals that are 2 times shorter also in northeastern japan tr of repeating quakes are 4 times shorter than those expected from the parkfield scaling law when adjusted to account for differences in the geodetically derived slip rates for the three fault zones however the tr mo scaling is remarkably consistent among the three regions it suggests that the tectonic loading rate is likely the most important factor that controls the repeat time it also suggests that there seems to exist a universal rule on recurrence interval scaling of repeating earthquakes in diverse tectonic settings

a dual origin for the hydrothermal component in a metalliferous sediment core from the mid atlantic ridge a highly metalliferous sediment core collected from tag 26 n mid atlantic ridge has been analyzed for uranium series isotopes rare earth elements ree and radiogenic isotopes two types of deposition of hydrothermal material have been identified and characterized the first is sulfide material which has been rapidly deposited and is sometimes clearly turbiditic this material exhibits high u fe and eu sm ratios and low 230th fe and ree fe ratios it is proposed that u is incorporated into the sulfides by diffusion through the oxidized coating with reductive fixation near the sulfide oxide boundary the second hydrothermal component is particulate fallout from the neutrally buoyant plume which is diluted by the background pelagic sedimentation this component exhibits u fe ratios around 2 10 5 an order of magnitude greater than reported plume particulate levels but the 230th fe ree fe and eu sm ratios are similar to plume values nd and pb isotopes have been used to differentiate the hydrothermal and pelagic end members within this sediment core

near source modeling of the loma prieta earthquake evidence for heterogeneous slip and implications for earthquake hazard i have analyzed records from 20 strong motion instruments that recorded the 1989 loma prieta earthquake ml 6 9 to determine the spatial and temporal distribution of slip using a tomographic back projection technique i find that the earthquake ruptured bilaterally at approximately 80 of the local shear wave velocity over a distance of slightly more than 30 km from 13 km northwest to 20 km southeast of the hypocenter slip within the rupture zone was highly variable both in magnitude and direction slip at the hypocenter and immediately up dip was relatively low about 1 m there were two main areas of concentrated slip one centered 7 km northwest of the hypocenter at a depth of 14 km and the other centered 6 km southeast of the hypocenter at a depth of 12 km peak slip amplitude on these high slip patches exceeded 4 5 m a surprising aspect of the rupture model is that rake varies from being predominately strike slip to the southeast of the hypocenter to being predominately reverse slip to the northwest despite this variation in rake the average rake determined from the strong motion data is in agreement with that determined teleseismically there is a correlation between areas of high slip and areas of low aftershock activity a simple model to explain this observation is that the areas of high slip are also areas of high strength which slip only during infrequent large mainshocks other areas of the fault are weaker and may slip both seismically and aseismically most of the slip in the loma prieta earthquake occurred between 9 and 16 km depth on a structure that dips to the southwest and runs underneath the surface trace of the san andreas fault at a depth of 8 to 10 km this observation complicates the assessment of seismic hazard on the southern santa cruz mountains segment of the san andreas fault

rupture history of the 1989 loma prieta california earthquake strong motion records of the 1989 loma prieta earthquake are inverted to determine a model of the rupture history uncorrected horizontal and vertical accelerograms are integrated to particle velocity time histories for 38 stations within an epicentral range of 75 km the time histories are bandpassed filtered with corners at 0 05 and 1 0 hz these bandpassed time histories are inverted using a nonlinear method to solve for the distribution of slip amplitudes and rupture times at specified locations on the fault plane the fault plane is specified a priori 38 km long and 17 km wide extending from 3 to 19 km depth at a constant dip of 70 starting models have rupture times based on constant rupture velocities of 2 5 2 8 and 3 0 km sec and uniform slip with rise times of 0 5 1 0 1 5 and 3 0 sec the waveform inversion results show the strike slip displacement is concentrated at the southern end of the rupture rake 156 and the dip slip displacement is concentrated at the northern end of the rupture rake 115 the average total slip is partitioned almost equally between strike slip and dip slip rake 137 the hypocentral area has an unusually small amount of slip with almost no slip in a region just to the north and up dip from the hypocenter the rupture front is complex propagating up dip to the south faster than it propagates to the north the region of maximum strike slip to the southeast radiates simultaneously with the region of maximum dip slip to the northwest the average rupture velocity is 3 0 km sec approximately 0 83 times the local shear wave speed the calculated seismic moment is 3 5 0 5 1026 dyne cm

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

repeating earthquake finite source models strong asperities revealed on the san andreas fault 1 we investigate the rupture process of a sequence of repeating mw 2 1 earthquakes on the san andreas fault in parkfield spanning the occurrence of the september 28 2004 mainshock by inverting seismic moment rate functions obtained from empirical green s function deconvolution the results show that these events have extremely concentrated slip patches with radii on the order of 10 20 m with peak slip between 8 4 and 11 4 cm the rupture speed and rise time are consistent with values of larger earthquakes the spatial distribution of stress drop for the events shows low average values 2 5 5 6 mpa and very large peak values of 66 7 93 9 mpa the results show that strong asperities can exist at small scales on an otherwise weak fault and helps reconcile differences between traditional spectra based and tectonic loading methods for determining the stress drop of small repeating earthquakes

uranium enrichment in metalliferous sediments from the mid atlantic ridge abstract previous studies of metal rich sediments at mid ocean ridge spreading centres have suggested that u fe ratios are relatively constant from site to site a suite of cores from the mid atlantic ridge has been analysed for u and fe content and most samples exhibit constant u fe ratios sulphide bearing parts of one core however contain excess u compared with that observed in other metalliferous sediments but apparently only during oxidative alteration of pyrite phases fission track registration has demonstrated that this excess u is intimately associated with sulphide grains in the sediment scanning electron microscope examination indicates that this u enrichment is limited to very small areas within the oxidation layer and is associated with an enhanced p concentration ion probe analyses allow semi quantitative analyses of various elements through a u rich grain the observed distribution of u coupled with its specific enrichment suggests that microbial mediation might be controlling this enrichment u fe ratios in fully oxidised tag sediments are constant and approximately an order of magnitude higher than in young plume particulates this discrepancy is attributed to a second type of post depositional u enrichment producing an homogeneous distribution of u throughout the sediment

triggering of repeating earthquakes in central california dynamic stresses carried by transient seismic waves have been found capable of triggering earthquakes instantly in various tectonic settings delayed triggering may be even more common but the mechanisms are not well understood catalogs of repeating earthquakes earthquakes that recur repeatedly at the same location provide ideal data sets to test the effects of transient dynamic perturbations on the timing of earthquake occurrence here we employ a catalog of 165 families containing 2500 total repeating earthquakes to test whether dynamic perturbations from local regional and teleseismic earthquakes change recurrence intervals the distance to the earthquake generating the perturbing waves is a proxy for the relative potential contributions of static and dynamic deformations because static deformations decay more rapidly with distance clear changes followed the nearby 2004 mw6 parkfield earthquake so we study only repeaters prior to its origin time we apply a monte carlo approach to compare the observed number of shortened recurrence intervals following dynamic perturbations with the distribution of this number estimated for randomized perturbation times we examine the comparison for a series of dynamic stress peak amplitude and distance thresholds the results suggest a weak correlation between dynamic perturbations in excess of 20 kpa and shortened recurrence intervals for both nearby and remote perturbations

scaling of small repeating earthquakes explained by interaction of seismic and aseismic slip in a rate and state fault model because of short recurrence times and known locations small repeating earthquakes present a rare predictable opportunity for detailed field observations they are used to study fault creeping velocities earthquake nucleation stress drops and other aspects of tectonophysics earthquake mechanics and seismology an intriguing observation about repeating earthquakes is their scaling of recurrence time with seismic moment which is significantly different from the scaling based on a simple conceptual model of circular ruptures with stress drop independent of seismic moment and no aseismic slip here we show that a model of repeating earthquakes based on laboratory derived rate and state friction laws reproduces the observed scaling in the model a small fault patch governed by steady state velocity weakening friction is surrounded by a much larger velocity strengthening region long term slip behavior of the fault is simulated using a methodology that fully accounts for both aseismic slip and inertial effects of occasional seismic events the model results in repeating earthquakes with typical stress drops and sizes comparable with observations for a fixed set of friction parameters the observed scaling is reproduced by varying the size of the velocity weakening patch in simulations a significant part of slip on the velocity weakening patches is accumulated aseismically even though the patches also produce seismic events the proposed model supplies a laboratory based framework for interpreting the wealth of observations about repeating earthquakes provides indirect evidence that rate and state friction acts on natural faults and has important implications for possible scenarios of slip partition into seismic and aseismic parts

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

lithospheric rheology constrained from twenty five years of postseismic deformation following the 1989 mw 6 9 loma prieta earthquake abstract the october 17 1989 m w 6 9 loma prieta earthquake provides the first opportunity of probing the crustal and upper mantle rheology in the san francisco bay area since the 1906 m w 7 9 san francisco earthquake here we use geodetic observations including gps and insar to characterize the loma prieta earthquake postseismic displacements from 1989 to 2013 pre earthquake deformation rates are constrained by nearly 20 yr of usgs trilateration measurements and removed from the postseismic measurements prior to the analysis we observe gps horizontal displacements at mean rates of 1 4 mm yr toward loma prieta mountain until 2000 and 2 mm yr surface subsidence of the northern santa cruz mountains between 1992 and 2002 shown by insar which is not associated with the seasonal and longer term hydrological deformation in the adjoining santa clara valley previous work indicates afterslip dominated in the early 1989 1994 postseismic period so we focus on modeling the postseismic viscoelastic relaxation constrained by the geodetic observations after 1994 the best fitting model shows an elastic 19 km thick upper crust above an 11 km thick viscoelastic lower crust with viscosity of 6 10 18 pa s underlain by a viscous upper mantle with viscosity between 3 10 18 and 2 10 19 pa s the millimeter scale postseismic deformation does not resolve the viscosity in the different layers very well and the lower crustal relaxation may be localized in a narrow shear zone however the inferred lithospheric rheology is consistent with previous estimates based on post 1906 san francisco earthquake measurements along the san andreas fault system the viscoelastic relaxation may also contribute to the enduring increase of aseismic slip and repeating earthquake activity on the san andreas fault near san juan bautista which continued for at least a decade after the loma prieta event

rare earth element geochemistry of standard sediments a study using inductively coupled plasma spectrometry the rare earth elements ree and y have been determined in 15 international standard sediments from france german democratic republic canada and the u s a samples were prepared using conventional rock dissolution techniques and the ree and y were separated from other constituents using cation exchange chromatography the ree la ce pr nd sm eu gd dy ho er yb lu and y were analysed simultaneously by inductively coupled plasma atomic emission spectrometry results indicate that u s g s standard shale sco 1 cody shale is a good reference material to use for the normalisation of the ree distributions of sediments data normalised to sco 1 are more readily interpreted than those normalised to existing estimates of average shale the ree patterns of standard sediments vary considerably in shape span an order of magnitude in absolute concentration and provide valuable reference values for the ree analysis of other sedimentary materials

pb and sr isotopic systematics of some basalts and sulfides from the east pacific rise at 21 n project rita abstract tholeiitic basalts and sulfide deposits from the cyana and alvin diving programs rita project on the east pacific rise were analyzed for pb and sr isotopes the basalt data plot within the field defined previously by other east pacific rise basalts 206 pb 204 pb 18 35 18 58 207 pb 204 pb 15 48 15 53 208 pb 204 pb 37 8 38 1 87 sr 86 sr 0 7022 0 7025 pb u and sr contents 0 5 0 05 and 110 ppm respectively and values 6 are typical of morb whereas th u ratios 3 5 are significantly higher the pb isotopic ratios of the sulfide samples are very homogeneous 206 pb 204 pb 18 47 207 pb 204 pb 15 49 208 pb 204 pb 37 90 and plot in the middle of the basalt field this indicates that 1 the sulfide pb was derived from the basaltic crust without any significant contribution from either seawater or hemipelagic sediments and 2 the solutions from which the sulfides were deposited had uniform pb isotopic composition the pb contents of three sulfide samples is relatively high 170 1310 ppm the sr contents of five sulfide samples are widely scattered from 12 to 210 ppm with 87 sr 86 sr ratios intermediate between basaltic and seawater values 0 70554 0 00005 to0 70795 0 00011 leaching experiments show that both basalt derived sr and seawater sr were present in the solutions which deposited the sulfides in some cases sr was also adsorbed from seawater onto the sulfides following their deposition basalt derived sr and seawater sr are also present in associated non sulfide phases

aseismic slip and fault interaction from repeating earthquakes in the loma prieta aftershock zone 1 along creeping sections of the san andreas and other faults small asperities in the fault zone load and fail in characteristic repeating earthquake sequences which can be used as subsurface creepmeters here we use these virtual creepmeters to examine and compare deep slip rates on both the northwestern end of the creeping section of the san andreas fault near san juan bautista and on the nearby subparallel sargent fault while creep on the san andreas increased dramatically due to static stress changes in response to the 1989 loma prieta earthquake the sargent showed very little immediate response consistent with loma prieta finite slip models that put this section of the fault in a region of less than 3 bar coulomb stress increase after about 10 years the san andreas creep rate fell back close to the interseismic rate and variations in creep became coherent in time with the sargent indicating a mutual driving force in the system

seawater metasomatism in hydrothermal sediments escanaba trough northeast pacific abstract hydrothermal sediments from the nesca vent field escanaba trough are enriched in a number of typical vent fluid metals for which fluid data for the same sediment hosted site exhibit anomalous depletion these results are consistent with cooling of rising fluids and precipitation of various metal sulphide sulphate and oxide phases in situ within the sediment column prior to expulsion of the fluids from the seabed significant enrichments of mg and u elements which are quantitatively removed from high temperature vent fluids are also observed in the escanaba trough sediments however enrichments of these elements cannot derive from simple conductive cooling of the rising vent fluids but instead are believed to result from extensive seawater metasomatism as relatively fresh unreached seawater is heated from below by hot sediments and or percolating vent fluids in the upper levels of the circulation system calculated seawater sediment interaction ratios range from 5 1 to 2500 l of seawater per gram of sediment pb sr and nd isotope distributions for the escanaba sediments are consistent with combined sediment fluid and seawater sediment interactions pb isotope ratios for hydrothermal and background sediments coincide with local sulphide deposits but are much more radiogenic than local morb this indicates not only that complete isotopic re equilibration must occur between the hot rising fluids and the host sediments but in addition that sediment composition appears to dominate the pb isotopic composition of these fluids sr and nd isotope ratios in the hydrothermally altered sediments which are distinct from background ratios coincide closely with modern seawater values providing confirmatory evidence that extensive interactions must also have occurred between these hydrothermal sediments and relatively fresh unreacted seawater

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

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

seismicity controlled by a frictional afterslip during a small magnitude seismic sequence m l 5 on the chihshang fault taiwan we report evidence for frictional afterslip at shallow depths about 5 to 7 km during a small magnitude seismic sequence with ml 5 along the chihshang fault a main active structure of the longitudinal valley in southeast taiwan the afterslip which was recorded by a nearby borehole dilatometer lasted about a month with a cumulative geodetic moment magnitude of 4 8 0 2 the afterslip comprised two stages and controlled the aftershock sequence the first postseismic stage which followed a ml 4 6 earthquake lasted about 6 h and mostly controlled the ruptures of neighboring asperities e g multiplets near the hypocenter then a 4 week duration large afterslip event following a ml 4 9 earthquake controlled the rate of aftershocks during its first 2 days through brittle creep the study presents a rare case of simultaneous seismological and geodetic observations for afterslip following earthquakes with magnitude lower than 5 furthermore the geodetic moment of the postseismic phase is at least equivalent to the coseismic moment of the sequence

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

fault creep and microseismicity on the hayward fault california implications for asperity size 1 the hayward fault is documented to undergo significant creep with some patches accommodating 50 or more of the long term fault displacement in spite of this the fault has also experienced moderate to large earthquakes by comparing the patterns of microseismicity observed on the fault with models of fault zone creep we can investigate the long term displacement deformation history of the fault in terms of the relative roles of aseismic creep fault slip accommodated through microseismicity and strain accumulation slip deficit we find that microseismicity on the hayward fault produces a negligible percentage of the seismic moment dissipated on the fault combining seismicity with our fault creep models allows us to calculate the size of asperities on the creeping fault for small asperities associated with repeating earthquakes on the hayward fault the rupture areas of these asperities range from 20 to 60 m2

behavior of repeating earthquake sequences in central california and the implications for subsurface fault creep repeating earthquakes res are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth we investigate the occurrence of these res along faults in central california to determine which faults exhibit creep and the spatiotemporal distribution of this creep at the juncture of the san andreas and southern calaveras paicines faults both faults as well as a smaller secondary fault the quien sabe fault are observed to produce res over the observation period of march 1984 through may 2005 res in this area reflect a heterogeneous creep distribution along the fault plane with significant variations in time cumulative slip over the observation period at individual sequence locations is determined to range from 5 5 58 2 cm on the san andreas fault from 4 8 14 1 cm on the southern calaveras paicines fault and from 4 9 24 8 cm on the quien sabe fault creep at depth appears to mimic the behaviors seen for creep on the surface in that evidence of steady slip triggered slip and episodic slip phenomena are also observed in the re sequences for comparison we investigate the occurrence of res west of the san andreas fault within the southern coast range events within these re sequences occurred only minutes to weeks apart from each other and then did not repeat again over the observation period suggesting that res in this area are not produced by steady aseismic creep of the surrounding fault surface

bayesian inversion of seismic spectral ratio for source scaling application to a persistent multiplet in the western corinth rift we propose a method to precisely estimate earthquake source parameters as magnitude size of rupture stress drop and coseismic slip and their uncertainties this method that relies on a bayesian approach allows the determination of the scalar seismic moment corner frequency fc and their associated uncertainties by inverting ratios between seismic displacement spectra of nearby located earthquakes we apply this method to a large earthquake multiplet 56 events located under the northern coast of the corinth gulf at 8 km depth this multiplet is regularly active between 2001 and 2007 results show fcp fcs ratios globally between 1 0 and 1 5 which is compatible with the values predicted by madariagas circular rupture model in details 6 earthquakes however exhibit corner frequency variations as a function of the station azimuth compatible with linear rupture propagation magnitude ranges 1 08 and 2 80 with a b value of 1 04 source rupture length globally ranges between 40 and 170 m for stress drop between 1 and 100 mpa we show that the number of ruptures and the cumulated coseismic slip are maximal at the center of the multiplet this suggests that multiplet 866 could be seen as a weak seismogenic patch surrounded by a locked fault how ever the large value of the maximum coseismic slip cumulated over the period 2000 2008 10 cm rather suggests creep allowing rapid stress reloading and repeated earthquakes with short delays we therefore propose that multiplet 866 is surrounded by a heterogeneous fault surface with both locked and creeping areas

joint estimation of afterslip rate and postseismic relaxation following the 1989 loma prieta earthquake global positioning system gps data from campaigns carried out over the 5 years following the 1989 loma prieta earthquake and leveling data measured in 1990 and 1992 define the postseismic velocity field around the loma prieta rupture zone subtraction of a background velocity field yields a residual velocity pattern which we interpret as the product of two physical processes 1 slow afterslip along distinct planes in the upper cru st and 2 viscoelastic relaxation of the lower crust and upper mantle biirgmann et al 1997 previously derived an afterslip model involving uniform afterslip on two optimally determined planes in cluding oblique reverse slip on the coseismic rupture and reverse slip on a shallow thrust fault to the northeast of the san andreas fault we further consider models of distributed slip on these two fault planes plus a viscoelastic relaxation pattern which depends on a suitable cose ismic rupture model and crust and mantle viscosities several fault models from the literature were considered for the 1989 coseismic rupture with nearly identical impact on the results simultaneous maximum likelihood inversion of the gps and leveling data for afterslip distri bution and viscosity yields the following results 1 a good fit to the data is obtained by smooth afterslip distributions without any viscoelastic relaxation being required 2 tangible broad scale viscoelastic relaxation of the lower crust and upper mantle are present in this data set at 97 confidence and a lower crustal viscosity of 1029 pa s is obtained however the viscosity of both the lower crust and upper mantle are poorly constrained 3 for a given misfit 20 less integrated afterslip and smoother afterslip distributions result when viscoelas tic relaxation is included 4 maximum slip rates on the slip distributed models are 3 5 crn yr the dominant patches estimated on the two planes fill in the entire depth range 4 13 km without significant overlap and deeper afterslip is not required the afterslip distribution on the coseismic rupture plane is strongly dominated by reverse slip immediately southeast of the main center of coseismic reverse slip