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

shallow creep on the haiyuan fault gansu china revealed by sar interferometry interferometric synthetic aperture radar data are used to map the interseismic velocity field along the haiyuan fault system hfs at the north eastern boundary of the tibetan plateau two m 8 earthquakes ruptured the hfs in 1920 and 1927 but its 260 km long central section known as the tianzhu seismic gap remains unbroken since 1000 years the envisat sar data spanning the 2003 2009 period cover about 200 300 km2 along three descending and two ascending tracks interferograms are processed using an adapted version of roi pac the signal due to stratified atmospheric phase delay is empirically corrected together with orbital residuals mean line of sight velocity maps are computed using a constrained time series analysis after selection of interferograms with low atmospheric noise these maps show a dominant left lateral motion across the hfs and reveal a narrow 35 km long zone of high velocity gradient across the fault in between the tianzhu gap and the 1920 rupture we model the observed velocity field using a discretized fault creeping at shallow depth and a least squares inversion the inferred shallow slip rate distribution reveals aseismic slip in between two fully locked segments the average creep rate is 5 mm yr 1 comparable in magnitude with the estimated loading rate at depth suggesting no strain accumulation on this segment the modeled creep rate locally exceeds the long term rate reaching 8 mm yr 1 suggesting transient creep episodes the present study emphasizes the need for continuous monitoring of the surface velocity in the vicinity of major seismic gaps in terms of seismic hazard assessment

biogenic silica accumulation in the ross sea and the importance of antarctic continental shelf deposits in the marine silica budget abstract thirty five box cores were collected from the continental shelf in the ross sea during cruises in january and february 1983 pb 210 and pu 239 240 geochronologies coupled with biogenic silica measurements were used to calculate accumulation rates of biogenic silica sediment in the southern ross sea accumulates at rates ranging from 0 6 to 2 7 mm y with the highest values occurring in the southwestern ross sea biogenic silica content in surface sediments ranges from 2 by weight in sulzberger bay and the eastern ross sea to 41 in the southwestern ross sea biogenic silica accumulation in the southwestern ross sea averages 2 7 10 2 g cm2 y and is comparable to accumulation rates in high productivity upwelling environments from low latitude continental margins e g gulf of california coast of peru the total rate of biogenic silica accumulation in the southern ross sea is approximately 0 2 1014 g y with most of the accumulation occurring in basins 500 1000 m water depth if biogenic silica accumulation in the southern ross sea continental shelf is typical of other basins on the antarctic continental shelf as much as 1 2 1014 g y of silica could be accumulating in these deposits biogenic silica accumulation on the antarctic continental shelf may account for as much as a fourth of the dissolved silica supplied to the world ocean by rivers and hydrothermal vents

paleocene plutonism and its tectonic implications north cascades washington u pb zircon geochronology has identified a northwest trending belt of paleocene 68 59 ma plutons within the crystalline core of the north cascades most of these plutons show amphibolite facies assemblages and solid state foiliation they document extensive paleogene dynamothermal metamorphism in the core and combined with other recent studies demonstrate ongoing metamorphism from mid cretaceous to mid eocene time the paleocene plutons were emplaced during an interval that marked a magmatic lull throughout much of the northern cordillera the distribution of latest cretaceous and paleocene plutons suggests that magmatism in the north cascades core records the same eastward retreat that occurred farther north in the cordillera

testing the inference of creep on the northern rodgers creek fault california using ascending and descending persistent scatterer insar data author s jin l funning gj abstract 2017 american geophysical union all rights reserved we revisit the question of whether the rodgers creek fault in northern california is creeping a question with implications for seismic hazard using imagery acquired by envisat between 2003 and 2010 we process two persistent scatterer interferometric synthetic aperture radar insar data sets one from an ascending track and the other from a descending track covering the northernmost segment of the rodgers creek fault between the cities of santa rosa and healdsburg the two different viewing geometries provided by the two different tracks allow us to distinguish vertical velocities which may reflect nontectonic deformation processes from fault parallel velocities which can be used to identify creep by measuring offsets in insar line of sight velocity from 12 fault perpendicular profiles through both data sets we identify seven locations where we have a high degree of confidence that creep is occurring estimated creep rate is more than two standard deviations above zero the preferred creep rates at these locations are in the range 1 9 6 7 mm yr consistent within uncertainty with alignment array measurements creep is probable p 0 70 at another three locations defining a creeping zone 20 km long in total extending northwest from santa rosa we also estimate the map patterns of fault parallel and vertical velocities in the region covered by both data sets these suggest that the rodgers creek fault immediately southeast of santa rosa remains locked

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

creep on the rodgers creek fault northern san francisco bay area from a 10 year ps insar dataset 1 deformation in the northern san francisco bay area is dominated by a series of sub parallel strike slip faults existing gps observations provide some constraint on the slip rates of these faults however these have only limited resolution for resolving shallow fault behavior such as brittle creep we use a 30 image permanent scatterer insar ps insar dataset spanning the time interval 1992 2001 to dramatically increase the density of surface deformation observations we find a discontinuity in observed surface velocities across the rodgers creek fault around santa rosa and further north consistent with shallow creep at rates of up to 6 mm yr the creeping segments are located in areas of local transtension suggesting that lowered normal stresses may play a role in the distribution of creep the existence of creep could significantly reduce expected moment release in future earthquakes on the rodgers creek fault and thus has implications for seismic hazard assessment

budgets and behaviors of uranium and thorium series isotopes in santa monica basin sediments abstract nine natural decay series isotopes were measured in six box cores collected from a transect across the santa monica basin the 210 pb derived sedimentation rate decreases from 80 mg cm 2 yr at the slope to 20 mg cm 2 yr in the deep central basin sediment mixing prevails in sites underlying oxic waters but is subdued in the anoxic deep basin below the sill depth uranium contents in sediments are controlled by levels of authigenic u which are higher in the more reduced condition in the deep basin most of the authigenic u results from precipitation within the sediments the 232 th 228 th disequilibrium in sediments indicates that 228 ra is lost from the sediments from a depth of 10 cm upward modelling the distribution of excess 228 th and 234 th in the surficial layers of the deep basin sediments results in a mean sediment mixing coefficient of 0 2 cm 2 yr and a sedimentation rate close to that based on 210 pb there is no evidence of changing sedimentation rate in the central basin during the past century fluxes of excess 210 pb 230 th and 231 pa to the central santa monica basin sediments are much higher than what can be predicted from local supply advective input of open ocean waters coupled with enhanced scavenging of these reactive nuclides at the ocean margin is considered to be the primary cause

distribution of aseismic slip rate on the hayward fault inferred from seismic and geodetic data 1 we solve for the slip rate distribution on the hayward fault by performing a least squares inversion of geodetic and seismic data sets our analysis focuses on the northern 60 km of the fault interferometric synthetic aperture radar insar data from 13 independent ers interferograms are stacked to obtain range change rates from 1992 to 2000 horizontal surface displacement rates at 141 bench marks are measured using gps from 1994 to 2003 surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion the fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface south of the city of hayward a steeply east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth the inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of 5 mm yr to a depth of 4 6 km the interferometric synthetic aperture radar insar data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath point pinole although the insar data might be complicated by a small dip slip component at this location a low slip rate patch of 1 mm yr is inferred beneath san leandro consistent with the source location of the 1868 earthquake we calculate that the entire fault is accumulating a slip rate deficit equivalent to a mw 6 77 0 05 per century however this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip

plutonium 241am and 137cs ratios inventories and vertical profiles in washington and oregon continental shelf sediments abstract continental shelf sediments from nine locations off washington and oregon have 239 240 pu inventories which average 8 0 2 6 mci km 2 the columbia river and seawaters advecting over the shelf supply pu which is removed to underlying sediments principally through scavenging by inorganic paniculate matter mass balance calculations argue that less than 20 percent of the advected pu need be scavenged from the water column to balance river input and total shelf sediment inventories the percentage of the pu removed through scavenging is consistent with observed participate concentrations in shelf waters and published sediment water distribution coefficients no marked separation of pu from 137 cs is observed with depth in pacific shelf sediments as has been reported in atlantic coastal sediments this interocean distinctness can be explained by differences in particle mixing and downward diffusion of cs in sediments of varying porosities the transuranic inventories and pu cs ratios in the pacific sediments do not support the hypothesis of livingston and bowen that pu is remobilized within the sediment column by complexone formation with principally organic substances excess 210 pb 239 240 pu inventory ratios in eight representative cores from the washington shelf average 100 19 even though absolute values of both inventories vary by much larger factors this reasonably constant ratio for a given water depth permits estimation of total pu inventories and prediction of sites of unusual pu accumulation from data on the more easily measured natural radionuclide

origin of k poor leucosomes in a metasedimentary migmatite complex by ultrametamorphism syn metamorphic magmatism and subsolidus processes two types of stromatic leucosomes are identified in metasedimentary rocks from the skagit migmatite complex north cascades washington state u s a both types are trondhjemitic and appear similar in outcrop but although both contain low abundances of ree one type consists of leucosomes that are relatively ree enriched compared to the other and contains 1 small 700 c water rich fluid present inferences about the origin of the above listed mineralogical and fluid inclusion features and modeling of leucosome trace element abundances the second type of leucosome is interpreted to have formed entirely by subsolidus processes e g metamorphic differentiation because these leucosomes lack features consistent with an origin by partial melting k poor tonalitic trondhjemitic leucosomes associated with metasedimentary biotite bearing source rocks may form by water saturated partial melting or by subsolidus processes both general leucosome forming mechanisms may operate at different times during upper amphibolite facies regional metamorphism partial melting may be initiated by syn metamorphic magmatic activity if crystallizing plutons serve as external sources of the water rich fluid necessary for ultrametamorphism in the middle crust during orogenesis large scale migmatite complexes such as the skagit migmatites may form at least in part in response to contact effects of plutonism associated with high grade metamorphism so although migmatite complexes are a volumetrically substantial part of many orogenic belts they may not themselves represent a significant original source of magma for larger scale igneous bodies

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

iso kinematic maps from statistical analysis of ps insar data of piemonte nw italy comparison with geological kinematic trends abstract sar interferometry based on permanent scatterers ps insar is used here to study the present crustal mobility of a large area of nw italy in the piemonte region thirty eight satellite scenes ers sar taken from may 1992 to january 2001 were analysed for detecting more than 2 million ps on the study area continuous velocity surface maps iso kinematic maps ikm were obtained from geo statistical and spatial cluster techniques hot spot analysis of ps short period data to identify relative ground motions and to compare them with long period tectonic mobility trends i e those inferred at regional scale over geological times some million years the comparison was made by individuation of homogeneous kinematic areas represented in the ikm and characterization of the boundaries between them iso kinematic boundaries ikb the ikb were used as tools to asses if the ps insar data on present day crustal mobility could fit with the distribution of real tectonic structures or field geological elements ikm were drawn for uplifting geological sectors of piemonte maritime alps gran paradiso langhe where moderate to very low seismicity is recorded and gravitational instabilities of rock mass on mountain slopes are widespread the land sectors have been chosen in order to test the suitability of ikm in very different geo morphological conditions different types of correspondence between the ikm and the geological kinematic trend were found a first type in which the kinematic trend of short period a decade of years i e the ps insar detection time span is in agreement with a long period tectonic trend some million years and seem to be driven by well known faults subparallel to the ikb these kinematic trends can be hidden by the slope movement due to gravitational instabilities a second type in which the kinematic trend of short period does not strictly correspond to the long period trend but can be considered as minor order uplifting subsidence cycles even if in contrast with the long period kinematic trend alternatively the short period kinematic trends could reflect the action of deep seated geological forces or structures not yet known or inferable at least with the recorded ps insar velocities on the basis of the available geological data and models

the most recent large earthquake on the rodgers creek fault san francisco bay area the rodgers creek fault rcf is a principal component of the san andreas fault system north of san francisco no evidence appears in the historical record of a large earthquake on the rcf implying that the most recent earthquake mre occurred before 1824 when a franciscan mission was built near the fault at sonoma and probably before 1776 when a mission and presidio were built in san francisco the first appearance of nonnative pollen in the stratigraphic record at the triangle g ranch study site on the south central reach of the rcf confirms that the mre occurred before local settlement and the beginning of livestock grazing chronological modeling of earthquake age using radiocarbon dated charcoal from near the top of a faulted alluvial sequence at the site indicates that the mre occurred no earlier than a d 1690 and most likely occurred after a d 1715 with these age constraints we know that the elapsed time since the mre on the rcf is more than 181 years and less than 315 years and is probably between 229 and 290 years this elapsed time is similar to published recurrence interval estimates of 131 to 370 years preferred value of 230 years and 136 to 345 years mean of 205 years calculated from geologic data and a regional earthquake model respectively importantly then the elapsed time may have reached or exceeded the average recurrence time for the fault the age of the mre on the rcf is similar to the age of prehistoric surface rupture on the northern and southern sections of the hayward fault to the south this suggests possible rupture scenarios that involve simultaneous rupture of the rodgers creek and hayward faults a buried channel is offset 2 2 1 2 0 8 m along one side of a pressure ridge at the triangle g ranch site this provides a minimum estimate of right lateral slip during the mre at this location total slip at the site may be similar to but is probably greater than the 2 0 3 0 2 m measured previously at the nearby beebe ranch site

detailed mapping and rupture implications of the 1 km releasing bend in the rodgers creek fault at santa rosa northern california airborne light detection and ranging lidar topography reveals for the first time the trace of the rodgers creek fault rcf through the center of santa rosa the largest city in the northern san francisco bay area vertical deformation of the santa rosa creek floodplain expresses a composite pull apart basin beneath the urban cover that is part of a broader 1 km wide right releasing bend in the fault high resolution geophysical data illuminate subsurface conditions that may be responsible for the complex pattern of surface faulting as well as for the distribution of seismicity and possibly for creep behavior we identify a dense magnetic basement body bounded by the rcf beneath santa rosa that we interpret as a strong asperity likely part of a larger locked patch of the fault to the south a local increase in frictional resistance associated with the basement body appears to explain 1 distributed fault normal extension above where the rcf intersects the body 2 earthquake activity around the northern end of the body notably the 1969 m l 5 6 and 5 7 events and aftershocks and 3 creep rates on the rcf that are higher to the north of santa rosa than to the south there is a significant probability of a major earthquake on the rcf in the coming decades and earthquakes associated with the proposed asperity have the potential to release seismic energy into the cotati basin beneath santa rosa already known from damaging historical earthquakes to produce amplified ground shaking

fluxes of uranium and thorium series isotopes in the santa barbara basin abstract samples from the manop santa barbara basin sediment trap intercomparison were analyzed for the isotopes of uranium thorium radium lead and polonium all of the traps showed approximately the same compositions and isotopic ratios indicating that they trapped similar materials the234th flux via falling particles was very close to the flux predicted from the production and scavenging rates of234th from the water column the210pb content of the trapped particles and the surface sediments were the same however the measured flux of210pb was seven times greater than the predicted flux predicted and measured fluxes of228th and210po were similarly out of balance to explain this apparent inconsistency we suggest as others have done that the santa barbara basin is an area where scavenging from the water column is intensified and where sediments deposited initially on the margins may be physically remobilized on a short time scale these two effects increase the apparent area from which the basin derives the longer lived isotopes but does not increase significantly the supply of the short lived234th

mid crustal magmatic sheets in the cascades mountains washington implications for magma ascent abstract diking diapirism ascent along faults and ascent during heterogeneous ductile flow have all been championed as the most important means of magma ascent in the crust we suggest that these mechanisms are end members in a complex spectrum of ascent processes in an attempt to evaluate which combination of ascent processes formed sheet like bodies in the mid crustal 20 25 km entiat pluton washington we examined the tip regions of these sheets the sheets have length width ratios ranging from 6 to 75 with increasing ratios strongly correlated to decreasing sheet tip radii from 850 to 100 m and decreasing ratios of tip diameter sheet width from 0 66 to 0 33 thus these bodies have geometries falling between those of dikes and those associated with elliptical diapirs the sheets are not associated with faults or fracture zones extending from their tips instead sheet walls are oriented parallel to the axial planes of upright syn emplacement folds in sheets with high length width ratios magmatic foliations in sheets are folded or parallel to axial planes of host rock folds with decreasing length width ratios margin parallel foliations in both sheet and host rock are increasingly common our studies indicate that the sheets are emplaced at high angles to 1 not 3 as proposed in elastic dike models and are always associated with complex viscoelastic flow of host rock these observations rule out elastic dike and fault models and instead favor diapiric rise of magma sheets during viscoelastic behavior of host rock

spatio temporal evolution of aseismic slip along the haiyuan fault china implications for fault frictional properties article history we use 20 years of synthetic aperture radar acquisitions by the ers and envisat satellites to investigate the spatial and temporal variations of strain rates along the 35 km long creeping section of the haiyuan fault at the north eastern boundary of the tibetan plateau we then use the derived displacements to infer the fault s frictional properties and discuss the relationship between creep and the seismic behavior of the fault located in between a millennial seismic gap and the 1920 m8 surface rupture trace this section has an average creep rate of 5 1m m yr about the interseismic loading rate the comparison of average surface velocity profiles derived from sar interferometry across the creeping section reveals a creep rate increase and or a creep migration to shallower depth between the 1990s and the 2000s we apply a smoothed time series analysis scheme on envisat insar data to investigate the creep rate variations during the 2004 2009 time period our analysis reveals that the creep rate accelerated in 2007 although data resolution does not allow to better constrain the onset of creep acceleration and its amplitude both decadal and short term transient behaviors are coeval with the largest earthquakes m 4 5 along the fault segment in recent years from the precise mapping of the surface fault trace we use the fault strike variations and the mohr circle construction to compute the along strike distribution of the friction coefficient along the creeping segment and compare it with the observed distribution of the creep rate we find that the creep rate scales logarithmically with the friction coefficient in agreement with the rate and state friction law in a rate strengthening regime the estimated value of log v 2 10 3 indicates that the earthquakes occurring along the creeping section cannot be the cause for a significant change in the overall segment s creep rate and that the recorded micro seismicity is most likely creep driven finally given the size and frictional properties of the creeping section we estimate based on previous models of dynamic rupture simulations a 0 20 probability for a rupture to break through this section together with the geometrical configuration of the haiyuan fault these results suggest that the creeping segment may act as a persistent barrier to earthquake propagation

squeesar and gps ground deformation monitoring of santorini volcano 1992 2012 tectonic implications abstract the santorini volcanic complex svc has been in a dormant state for the last 60 years until january 2011 when upward influx of magma reawakened the volcano with intense radial ground deformation and inter caldera seismicity that lasted until january 2012 but declined afterwards this paper aims to study the ground deformation and the inferred tectonic implications of the svc for the period 1992 2012 mainly based on the squeesar technique and dgps campaign results of our local network which incorporates available data on internet from several continuous gps stations established on the island the spatial deformation of the svc during the quiet period 1992 2010 was deduced by joint analysis of ers1 and 2 and envisat it was found that the intra caldera palaea kammeni shield volcano was being uplifted 2 3 mm yr with increasing rate whilst the adjacent nea kammeni shield volcano was being subsided up to 6 mm yr with increasing rate the rest of the svc showed a velocity field varying from 1 to 2 mm yr indicating a rather linear deformation during that period the results from the gps network are in full agreement with the squeesar results based on the results of squeesar analysis of 12 envisat images and dgps cgps data to end 2012 the deformation for the unrest period 2011 2012 was non linear being characterized by strong radial deformation in the northern part of the caldera 50 120 mm yr and accelerating values 130 mm yr 2 combined gps squeesar mogi modeling indicated a source located north of nea kammeni at a shallow depth however a progressively decreasing rate in deformation was noted at most gps cgps station components after january 2012 indicating magma settlement consistent with the constantly decreasing rate of the inter caldera seismicity the faulting features seem to have a key role in the evolution of the deformation which continues up the end 2012 but at a very low level

tectonic implications of syn and post emplacement deformation of the mount stuart batholith for mid cretaceous orogenesis in the north cascades the 93 96 ma mount stuart batholith intruded across the boundary between the northwest cascades thrust system and the crystalline core of the north cascades although previously considered posttectonic the northeast margin of the mount stuart batholith and its wall rocks have been involved in syn to post emplacement southwest directed thrusting and folding and west northwest stretching contraction ended shortly after emplacement as indicated by high temperature recrystallization in thrust related mylonites of the pluton and by geochronological data whereas west northwest stretching continued for an unknown period of time this is the best documented mid cretaceous contractional belt in the main part of the crystalline core the shortening direction and timing are identical to that of southwest vergent thrusts in the offset continuation of the core in british columbia the contractional belt provides a link between thrusting in the northwest cascades thrust system and deformation in the crystalline

evidence for differential degradation of alkenones under contrasting bottom water oxygen conditions implication for paleotemperature reconstruction abstract the successful reconstruction of sea surface temperatures using alkenone paleothermometry u37k has relied on the premise that there is no significant differential degradation of alkenones with different states of unsaturation during diagenetic processes to test this assumption we conducted a comparative study of contemporary sediments in oxic and anoxic bottom waters from the santa monica basin offshore california long chain alkenones were quantified and sea surface temperature were calculated using the calibrated u37k t relationship of prahl et al 1988 our results show that temperature record from the oxic sediments is higher by as much as 4 c compared to those from time equivalent anoxic sediments as a result of differential degradation of long chain unsaturated alkenones and bioturbation mixing in the oxic sediments the differential degradation of c37 3 vs c37 2 alone could account for up to 2 5 c difference between these two records this finding has significant implication in the interpretation of paleo sea surface temperature data using alkenone paleothermometry

exploiting uavsar for a comprehensive analysis of subsidence in the sacramento delta abstract the sacramento san joaquin delta like other heavily engineered deltas throughout the world has undergone substantial subsidence since the late 1800s when the natural estuary was leveed to form islands today islands within the delta have subsided to the point where most lie below mean sea level long term sustainability of the delta requires reversal of subsidence but spatially comprehensive maps of subsidence have not been available to inform and monitor remediation reported here is the first spatially dense map of recent subsidence rates across the delta based on synthetic aperture radar interferometry and constrained by gnss observations the analysis uses a temporally dense and spatially overlapping set of data acquired by the uninhabited aerial vehicle sar uavsar sensor in 2009 2015 on average the delta is subsiding by 9 2 4 4 mm yr with high variability even at the sub island scale including peak subsidence of 160 4 4 mm yr occurring just inland of the levee of the westernmost island and average subsidence of 11 mm yr along the planned path of water conveyance tunnels through the delta the results are compared to local sea level rise slr measured at a tidal gauge in san francisco bay to show that subsidence is currently the dominant contributor to local relative sea level rise rslr by nearly a factor of five based on recently measured and modeled acceleration of slr subsidence in the delta is likely to dominate rslr until the middle of the 21th century

geodetic exploration of the elastic properties across and within the northern san andreas fault zone abstract relying on densely spaced gps data collected between 1996 and 2007 and on insar data spanning the 1992 2001 time period we explore the effects of lateral rheological heterogeneities across the san andreas fault near point reyes on the interseismic velocity field we evaluate heterogeneous elastic dislocation models including an asymmetric model with contrasting rigidities on either side of the san andreas fault and models with a narrow compliant fault zone that lead to high near fault strain rates we show that we cannot resolve a compliant zone from interseismic surface displacement measurements unless independent constraints on the locking depth exist we infer an 18 1 mm yr 1 slip rate on the san andreas fault with a 10 2 km locking depth and a 40 higher rigidity to the sw of the fault at bodega bay gps and edm data suggest a compliant zone on the saf with a 50 to 60 rigidity decrease but 25 km further south we find no evidence for a weak fault zone this suggests substantial variability in fault zone properties along the san andreas fault

a silent mw 4 7 slip event of october 2006 on the superstition hills fault southern california 1 during october 2006 the 20 km long superstition hills fault shf in the salton trough southern california slipped aseismically producing a maximum offset of 27 mm as recorded by a creepmeter we investigate this creep event as well as the spatial and temporal variations in slip history since 1992 using ers 1 2 and envisat satellite data during a 15 year period steady creep is punctuated by at least three events the first two events were dynamically triggered by the 1992 landers and 1999 hector mine earthquakes in contrast there is no obvious triggering mechanism for the october 2006 event field measurements of fault offset after the 1999 and 2006 events are in good agreement with the interferometric synthetic aperture radar data indicating that creep occurred along the 20 km long fault above 4 km depth with most of the slip occurring at the surface the moment released during this event is equivalent to a mw 4 7 earthquake this event produced no detectable aftershocks and was not recorded by the continuous gps stations that were 9 km away modeling of the long term creep from 1992 to 2007 creep using stacked ers 1 2 interferograms also shows a maximum creep depth of 2 4 km with slip tapering with depth considering that the sediment thickness varies between 3 km and 5 km along the shf our results are consistent with previous studies suggesting that shallow creep is controlled by sediment depth perhaps due to high pore pressures in the unconsolidated sediments

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

monitoring deformation at the geysers geothermal field california using c band and x band interferometric synthetic aperture radar monitoring deformation at the geysers geothermal field california using c band and x band interferometric synthetic aperture radar d w vasco jonny rutqvist alessandro ferretti alessio rucci fernando bellotti patrick dobson curtis oldenburg julio garcia mark walters and craig hartline d w vasco jonny rutqvist patrick dobson curtis oldenburg earth sciences di vision building 74 berkeley laboratory 1 cyclotron road berkeley ca 94720 e mail dwvasco lbl gov jrutqvist lbl gov pfdobson lbl gov cmoldenburg lbl gov alessandro ferretti alessio rucci and fernando bellotti tele rilevamento europa via vittoria colonna 7 20149 milano italy e mail alessandro ferretti treuropa com alessio rucci treuropa com fernando bellotti treuropa com julio garcia mark walters and craig hartline calpine corporation 10350 socrates mine road middletown ca 95461 e mail julio garcia calpine com mark walters calpine com craig hartline calpine com

high pressure metamorphism in the western cordillera of north america the skagit gneiss a major component of the crystalline core of the north cascades was metamorphosed during a mid cretaceous to early tertiary high p event driven by the collision of the insular and intermontane superterranes maximum pressures recorded by metapelitic rocks are 8 10 kbar at 650 725 c high pressures are also indicated by coexisting staurolite and hornblende in amphibolites in the skagit gneiss and adjacent cascade river schist mineral reactions continued during nearly isothermal decompression from 8 10 kbar to c 3 5 kbar early high p minerals e g kyanite are present as armoured relics in garnet in gneisses that contain sillimanite and cordierite in the groundmass skeletal relics of kyanite are also present in the groundmass of lower grade staurolite bearing schists that contain texturally later cordierite this matrix kyanite may have been preserved as a result of rapid uplift following initial decompression at high temperature these results represent a revision of the metamorphic history of the skagit gneiss which was formerly thought to have experienced only relatively low p barrovian metamorphism qualitative estimates of metamorphic conditions based on stable matrix mineral assemblages result in an underestimation of maximum pressures because mineral reactions continued during decompression geobarometric results for the skagit gneiss are interpreted as evidence for major crustal thickening in the north cascades recognition that pressures of c 9 kbar were attained supports a contractional model for north cascades orogenesis and requires that tectonic syntheses account for the burial of the skagit gneiss protoliths to a depth of c 25 30 km

persistent scatterers interferometry detects and measures ground subsidence in lisbon abstract results from the application of persistent scatterers interferometry in lisbon metropolitan area revealed two previously unknown subsiding urban areas one laranjeiras is located in the center of lisbon another vialonga is to be found toward the north in an industrial region crossed by lisbon s main highway and railway lines the two subsiding sectors are bordered by sharp velocity gradients and the subsidence pattern appears partially delimited by mapped geologic faults surface geology and urbanization alone are unable to explain the phenomena in the vialonga area the historical record of water pore pressure shows a clear decline of the levels up to 65 m in 27 years providing evidence of over exploitation of groundwater resources limited information from wells drilled inside and outside the subsidence area points to a spatial correlation between the subsidence and the water pressure levels and suggests that faults could be acting as hydraulic barriers in the aquifer system the surface subsidence detected is probably caused by compaction of a clay rich oligocene aged aquitard led by over exploitation of adjacent aquifers the same oligocene aquitard layer is present in the laranjeiras area immediately bellow a multi layered sand clay limestone miocene aquifer but further work is needed to diagnose the possibility of over exploitation of groundwater here in this work we were able to independently confirm the psi results by comparing autonomous psi results processed for the same geographical areas and by comparing psi with leveling and continuous gps derived subsidence velocities whose close match provided further ground validation of the space borne psi technique

resolving vertical tectonics in the san francisco bay area from permanent scatterer insar and gps analysis using a combination of gps measured horizontal velocities of 200 sites and 115 487 range change rates determined with the permanent scatterer interferometric synthetic aperture radar insar method in the san francisco bay area we resolve vertical motions in the region at sub mm yr precision the highest displacement rates are due to nontectonic processes such as active landslides subsidence and rebound over aquifers and rapid settling of unconsolidated sediments along the bay margins residual displacement rates are determined by removing the contribution of the gps derived horizontal velocity field from the insar range change rates to isolate vertical tectonic rates we use only those insar measurements made on material that was not quaternary substrate which is susceptible to nontectonic and seasonally varying ground motions the insar residuals indicate significant uplift over the southern foothills of the active mount diablo anticlinorium the mission hills stepover region of the hayward and calaveras faults and the central and southern santa cruz mountains located along a restraining bend of the san andreas fault

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

deformation across the pacific north america plate boundary near san francisco california we have detected a narrow zone of compression between the coast ranges and the great valley and we have estimated slip rates for the san andreas rodgers creek and green valley faults just north of san francisco these results are based on an analysis of campaign and continuous global positioning system gps data collected between 1992 and 2000 in central california the zone of compression between the coast ranges and the great valley is 25 km wide the observations clearly show 3 8 1 5 mm yr 1 of shortening over this narrow zone the strike slip components are best fit by a model with 20 8 1 9 mm yr 1 slip on the san andreas fault 10 3 2 6 mm yr 1 on the rodgers creek fault and 8 1 2 1 mm yr 1 on the green valley fault the pacific sierra nevada great valley motion totals 39 2 3 8 mm yr 1 across a zone that is 120 km wide at the latitude of san francisco standard deviations are one the geodetic results suggest a higher than geologic rate for the green valley fault the geodetic results also suggest an inconsistency between geologic estimates of the san andreas rate and seismologic estimates of the depth of locking on the san andreas fault the only convergence observed is in the narrow zone along the border between the great valley and the coast ranges

p t t evidence for mechanisms of vertical tectonic motion in a contractional orogen north western us and canadian cordillera the 1800 km long coast mountains north cascades orogen of the canadian cordillera and north western us developed as a continental magmatic arc metamorphic rocks in the orogen contain widespread evidence for burial of supracrustal rocks to depths of c 40 km followed by nearly isothermal decompression to depths of 10 km near many shallowly emplaced mid cretaceous plutons low pressure contact metamorphic effects were overprinted by high pressure regional metamorphic minerals and textures as evidenced by kyanite staurolite pseudomorphs after andalusite in metapelitic rocks therefore near pluton rocks record the loading history of the orogen metapelitic rocks not associated with plutons only preserve evidence for high pressure conditions and or high temperature decompression as indicated for example by sillimanite and cordierite after kyanite and garnet respectively petrological evidence for burial and decompression is therefore recorded in different rocks various regions of the orogen differ in timing of metamorphism the overall shape of p t paths and the relative timing and regional extent of the high pressure event but most of these data and observations are consistent with thrusting and or pure shear thickening as primary loading mechanisms throughout the orogen as opposed to magma dominated loading this interpretation is further supported by comparison with thermal models which demonstrate that the p t paths are consistent with simultaneous thrusting and folding at a high initial geothermal gradient 35 40 c km 1 in much of the orogen a high geothermal gradient supports tectonic models invoking intra arc contraction and suggests that magmatism played an important role in regional temperature time paths this tectonic thermal history may be typical of other contractional orogens and illustrates the importance of large vertical displacement of crust in magmatic arcs

slip rate earthquake recurrence and seismogenic potential of the rodgers creek fault zone northern california initial results instrumental seismicity defines a seismic gap along the rodgers creek fault zone rcfz between santa rose and san pablo bay results of a paleoseismicity study within the gap using offset channels in late holocene alluvial deposits as piercing points indicate a minimum slip rate of 2 1 to 5 8 mm yr for the past 1 300 years a preferred range for the maximum recurrence interval of 248 to 679 years and a surface offset of 2 0 3 minus 0 2 m during the most recent event the rcfz has produced past m7 earthquakes and historical seismicity data indicate a minimum elapsed time of 182 years since the most recent earthquake of this size

using surface creep rate to infer fraction locked for sections of the san andreas fault system in northern california from alignment array and gps data surface creep rate observed along five branches of the dextral san andreas fault system in northern california varies considerably from one section to the next indicating that so too may the depth at which the faults are locked we model locking on 29 fault sections using each section s mean long term creep rate and the consensus values of fault width and geologic slip rate surface creep rate observations from 111 short range alignment and trilateration arrays and 48 near fault global positioning system station pairs are used to estimate depth of creep assuming an elastic half space model and adjusting depth of creep iteratively by trial and error to match the creep observations along fault sections fault sections are delineated either by geometric discontinuities between them or by distinctly different creeping behaviors we remove transient rate changes associated with five large m 5 5 regional earthquakes estimates of fraction locked the ratio of moment accumulation rate to loading rate on each section of the fault system provide a uniform means to inform source parameters relevant to seismic hazard assessment from its mean creep rates we infer the main branch the san andreas fault ranges from only 20 10 locked on its central creeping section to 99 100 on the north coast from mean accumulation rates we infer that four urban faults appear to have accumulated enough seismic moment to produce major earthquakes the northern calaveras m 6 8 hayward m 6 8 rodgers creek m 7 1 and green valley m 7 1 the latter three faults are nearing or past their mean recurrence interval online material high resolution fault system map and tables of creep observations and geographic coordinates of fault model

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

radionuclide concentrations fluxes and residence times at santa monica and san pedro basins our participation in the california basin study cabs in 1986 1988 has produced a radionuclide data base that allows us to trace the particle and water movement in the santa monica and the san pedro basins these data enable us to calculate the radionuclide inventories in the three compartments of the basin the water column the settling particles and the sediments we have also determined the fluxes of several radionuclides associated with the sinking particles the residence time in the water column and the rate of deposition in the sediments the biogeochemical environment of the santa monica basin is uniquely suited to the application of tracer techniques to study the sedimentation processes subtle but measurable changes in the distribution of fallout of 137cs from 1977 to 1988 were noted in the water column compared to the decay corrected measurement in 1973 1977 at the geosecs and farallon islands stations off the coast of california 137cs inventory in the water column in santa monica basin has not changed significantly for the past decade increases in the deep water concentration profiles of 137cs particle transport and diagenetic release of cesium in the deep water the major 137cs inventory 70 resides in the upper 400m of water with a mean residence time of 480 90 years less than 11 of the total 137cs inventory was found in the sediments at water depths of 900m in 1987 unlike 137cs more than 80 of the fallout 239 240pu has been deposited in the santa monica basin sediments a mean residence time of 13 2 years was measured for 239 240pu in the basin water the ubiquitous 239 240pu subsurface concentration maximum observed in the pacific oceanic waters at about 350m depth is also evident in the basin water we have no definitive explanation for the persistence of the subsurface maximum except that it appears to be correlated with the density gradient at 26 5 to 26 9 sigma t the 239 240pu flux for settling particles correlates remarkably well with mass flux and it increases with depth in the water column plutonium deposition in anoxic sediments also appears to be useful as a time marker for age dating of sediments and estimating the sediment accumulation rates the sedimentation rates determined by plutonium are shown to be comparable to those estimated by excess 210pb in the cores radionuclide fluxes measured from sediment trap particles in 1986 1988 were lower by a factor of 0 6 0 2 compared to the average fluxes determined from the box core samples radionuclides such as 210pb 137cs and 239 240pu have been shown to be useful tools in the study of biogeochemical processes in the santa monica basin

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

southern california inner basin sediment trap calibration the deployment of particle interceptor traps pits in the three inner basins of the southern california bight santa barbara santa monica and san pedro where preserved laminated bottom sediments occur provides a natural calibration between the parameters determined with the pits and those derived from the historical sedimentary deposits the accumulation rates and chemical composition of the pit materials compare favorably with these recently deposited bottom sediments the ratio of the measured particle collection rate to the sediment accumulation rate for these three basins averaged0 93 0 20 radionuclide 210pb 228th 232th and trace element fe cu zn cd pb compositions of the pit materials and surface sediments agree within generally 30 in each basin an application of pits as a sampling system in an outer basin san nicolas where the sedimentary record has been obscured by bioturbation is also presented to further demonstrate the utility of pits for spatial and temporal studies of various aspects of particle transport and sediment deposition based on the calibration of the pits in the three inner basins we conclude from the comparison of the radionuclide and trace element compositions between the pit materials and surface sediments from the san nicolas basin that recently deposited sedimentary material has been mixed by bioturbation with older material from the last several hundred years excess210pb and the228th 232th activity ratio in the pit material are 6 and 15 times higher than in the surface sediment total pb and1n hno3 leachable pb are 4 and 8 fold higher in the pit material

variations in creep rate along the hayward fault california interpreted as changes in depth of creep variations in surface creep rate along the hayward fault are modeled as changes in locking depth using 3d boundary elements model creep is driven by screw dislocations at 12 km depth under the hayward and other regional faults inferred depth to locking varies along strike from 4 12 km 12 km implies no locking our models require locked patches under the central hayward fault consistent with a m6 8 earthquake in 1868 but the geometry and extent of locking under the north and south ends depend critically on assumptions regarding continuity and creep behavior of the fault at its ends for the northern onshore part of the fault our models contain 1 4 1 7 times more stored moment than the model of burgmann et al 2000 45 57 of this stored moment resides in creeping areas it is important for seismic hazard estimation to know how much of this moment is released coseismically or as aseismic afterslip

a mid crustal contractional stepover zone in a major strike slip system north cascades washington abstract the segmentation of strike slip faults at the earth s surface is well known but the geometry of these faults in the mid crust is poorly understood as are the intervening stepover zones a mid crustal example of a segmented strike slip fault is present within the 500 km long ross lake fault system where the nw striking twisp river fault zone and gabriel peak tectonic belt occur as overlapping left stepping dextral strike slip shear zones the contractional stepover between these structures is occupied by the black peak batholith which is riddled by ductile shear zones that are typically 0 5 1 5 m thick and are restricted to the stepover gently to moderately nw dipping reverse slip ductile shear zones in the center of the stepover strike at a high angle to the twisp river fault zone and gabriel peak tectonic belt and lie in an appropriate position to transfer most of the displacement between the strike slip segments the orientation of the reverse slip ductile shear zones relative to the strike slip segments is broadly similar to that of folds and thrusts in upper crustal stepovers the stepover width is relatively large however in comparison to many active stepovers emplacement of the black peak batholith across an originally narrower stepover or bend in the fault system may have created a rigid buttress and subsequent deformation jumped to the mechanically weak southwest margin of the body because plutons are commonly intruded into strike slip zones such partitioning of later displacements may be widespread

basin structure beneath the santa rosa plain northern california implications for damage caused by the 1969 santa rosa and 1906 san francisco earthquakes regional gravity data in the northern san francisco bay region reflect a complex basin configuration beneath the santa rosa plain that likely contributed to the significant damage to the city of santa rosa caused by the 1969 m 5 6 5 7 santa rosa earthquakes and the 1906 m 7 9 san francisco earthquake inversion of these data indicates that the santa rosa plain is underlain by two sedimentary basins about 2 km deep separated by the trenton ridge a shallow west northwest striking bedrock ridge west of santa rosa the city of santa rosa is situated above the 2 km wide protruding northeast corner of the southern basin where damage from both the 1969 and 1906 earthquakes was concentrated ground motion simulations of the 1969 and 1906 earthquakes two events with opposing azimuths using the gravity defined basin surface show enhanced ground motions along the northeastern edge of this corner suggesting that basin edge effects contributed to the concentration of shaking damage in this area in the past and may also contribute to strong shaking during future earthquakes

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

remotely sensing large and small scale ground subsidence a case study of the guangdong hong kong macao greater bay area of china abstract as the world s largest city cluster the guangdong hong kong macao greater bay area gba is vulnerable to significant subsidence the widely distributed sediments and rapid urbanization in the gba result in the concurrence of large and small scale subsidence mono sensor synthetic aperture radar sar images usually suffer from the limitation of either low resolution or small coverage and thus are not applicable to completely monitoring the gba in this study we used sentinel 1 s1 cosmo skymed csk and terrasar x tsx images jointly to reveal multi scale subsidence of the gba the overall subsidence ranged from 0 to 112 3 mm yr derived from the 2015 2017 s1 images three regional subsidence bowls zhuhai zhongshan jiangmen and guangzhou zhongshan formed in the western alluvial plain the high correlation between regional subsidence and quaternary sediments confirms that sediment consolidation is the main cause of subsidence the land use and numerical modeling results suggest that groundwater extraction and artificial loading are the triggering factors two representative local subsidence cases were analyzed using high resolution images reclamation settlement at the hong kong international airport hkia and sinkhole subsidence due to the excavation of the shenzhen wenbo skyscraper foundation pit the validation at the hkia showed that the measurements from the csk and s1 data both agreed well with the leveling data however csk outperformed s1 in the sense that it increased the point density by a factor of 5 improved the height precision by a factor of 4 and showed fewer false alarms csk is therefore more applicable to monitoring the local subsidence of key infrastructures the cross heading tracks of tsx and csk images detected precursory subsidence before the sinkhole collapse from two sides indicating that the cross heading tracks benefit the comprehensive monitoring of local subsidence in high rise and high density built environments in summary the synergistic use of multi sensor sar images demonstrates the practicability of the operational surveillance of multi scale subsidence from regional surveying to the fine monitoring of local areas in the gba

large earthquakes and creeping faults faults are ubiquitous throughout the earth s crust the majority are silent for decades to centuries until they suddenly rupture and produce earthquakes with a focus on shallow continental active tectonic regions this paper reviews a subset of faults that have a different behavior these unusual faults slowly creep for long periods of time and produce many small earthquakes the presence of fault creep and the related microseismicity helps illuminate faults that might not otherwise be located in fine detail but there is also the question of how creeping faults contribute to seismic hazard it appears that well recorded creeping fault earthquakes of up to magnitude 6 6 that have occurred in shallow continental regions produce similar fault surface rupture areas and similar peak ground shaking as their locked fault counterparts of the same earthquake magnitude the behavior of much larger earthquakes on shallow creeping continental faults is less well known because there is a dearth of comprehensive observations computational simulations provide an opportunity to fill the gaps in our understanding particularly of the dynamic processes that occur during large earthquake rupture and arrest

a search in strainmeter data for slow slip associated with triggered and ambient tremor near parkfield california 1 we test the hypothesis that as in subduction zones slow slip facilitates triggered and ambient tremor in the transform boundary setting of california our study builds on the study of peng et al 2009 of triggered and ambient tremor near parkfield california during time intervals surrounding 31 potentially triggering m 7 5 teleseismic earthquakes waves from 10 of these triggered tremor and 29 occurred in periods of ambient tremor activity we look for transient slow slip during 3 month windows that include 11 of these triggering and nontriggering teleseisms using continuous strain data recorded on two borehole gladwin tensor strainmeters gtsm located within the distribution of tremor epicenters we model the gtsm data assuming only tidal and drift signals are present and find no detectable slow slip either ongoing when the teleseismic waves passed or triggered by them we infer a conservative detection threshold of about 5 nanostrain for abrupt changes and about twice this for slowly evolving signals this could be lowered slightly by adding analyses of other data types modeled slow slip signals and gtsm data calibration detection of slow slip also depends on the slipping fault s location and size which we describe in terms of equivalent earthquake moment magnitude m in the best case of the gtsm above a very shallow slipping fault detectable slip events must exceed m 2 and if the slow slip is beneath the seismogenic zone below 15 km depth even m 5 events are likely to remain hidden

coseismic deformation from the 1999 mw 7 1 hector mine california earthquake as inferred from insar and gps observations we use interferometric synthetic aperture radar insar and global positioning system gps observations to investigate static deformation due to the 1999 m w 7 1 hector mine earthquake that occurred in the eastern california shear zone interferometric decorrelation phase and azimuth offset measurements indicate regions of surface and near surface slip which we use to constrain the geometry of surface rupture the inferred geometry is spatially complex with multiple strands the southern third of the rupture zone consists of three subparallel segments extending about 20 km in length in a n45 w direction the central segment is the simplest with a single strand crossing the bullion mountains and a strike of n10 w the northern third of the rupture zone is characterized by multiple splays with directions subparallel to strikes in the southern and central the average strike for the entire rupture is about n30 w the interferograms indicate significant along strike variations in strain which are consistent with variations in the ground based slip measurements using a variable resolution data sampling routine to reduce the computational burden we invert the insar and gps data for the fault geometry and distribution of slip we compare results from assuming an elastic half space and a layered elastic space results from these two elastic models are similar although the layered space model predicts more slip at depth than does the half space model the layered model predicts a maximum coseismic slip of more than 5 m at a depth of 3 to 6 km contrary to preliminary reports the northern part of the hector mine rupture accommodates the maximum slip our model predictions for the surface fault offset and total seismic moment agree with both field mapping results and recent seismic models the inferred shallow slip deficit is enigmatic and may suggest that distributed inelastic yielding occurred in the uppermost few kilometers of the crust during or soon after the earthquake

metamorphism and deformation at different structural levels in a strike slip fault zone ross lake fault north cascades usa continental crust is displaced in strike slip fault zones through lateral and vertical movement that together drive burial and exhumation pressure temperature deformation p t d histories of orogenic crust exhumed in transcurrent zones record the mechanisms and conditions of these processes the skagit gneiss complex a migmatitic unit of the north cascades washington usa was metamorphosed at depths of 25 30 km in a continental arc under contraction and is bounded on its eastern side by the long lived transcurrent ross lake fault zone rlfz the p t d conditions recorded by rocks on either side of the rlfz vary along the length of the fault zone but most typically the fault separates high grade gneiss and plutons from lower grade rocks the ruby mt elijah ridge area at the eastern margin of the skagit gneiss exposes tectonic contacts between gneiss and overlying rocks the latter rocks including slivers of methow basin deposits are metamorphosed and record higher grade metamorphism than in correlative rocks along strike along the rlfz in this area the skagit gneiss and overlying units all yield maximum p t conditions of 8 10 kbar at 650 c indicating that slices of basin rocks were buried to similar mid crustal depths as the gneiss after exhumation of fault zone rocks to 15 km depth intrusion of granitoid plutons drove contact metamorphism resulting in texturally late andalusite cordierite in garnet schist in the elijah ridge area of the rlfz an overlapping step over or series of step overs that evolved through time may have facilitated burial and exhumation of a deep slice of the methow basin indicating that strike slip faults can have major vertical displacement tens of kilometres that is significant during the crustal thickening and exhumation stages of orogeny

slicing up the san francisco bay area block kinematics and fault slip rates from gps derived surface velocities received 26 october 2004 revised 11 february 2005 accepted 10 march 2005 published 16 june 2005 i observations of surface deformation allow us to determine the kinematics of faults in the san francisco bay area we present the bay area velocity unification bavu bay view a compilation of over 200 horizontal surface velocities computed from campaign style and continuous global positioning system gps observations from 1993 to 2003 we interpret this interseismic velocity field using a three dimensional block model to determine the relative contributions of block motion elastic strain accumulation and shallow aseismic creep the total relative motion between the pacific plate and the rigid sierra nevada great valley sngv microplate is 37 9 0 6 mm yr 1 directed toward n30 4 w 0 8 at san francisco 2 fault slip rates from our preferred model are typically within the error bounds of geologic estimates but provide a better fit to geodetic data notable right lateral slip rates in mm yr 1 san gregorio fault 2 4 1 0 west napa fault 4 0 3 0 zone of faulting along the eastern margin of the coast range 5 4 1 0 and mount diablo thrust 3 9 1 0 of reverse slip and 4 0 0 2 of right lateral strike slip slip on the northern calaveras is partitioned between both the west napa and concord green valley fault systems the total convergence across the bay area is negligible poles of rotation for bay area blocks progress systematically from the north america pacific to north america sngv poles the resulting present day relative motion cannot explain the strike of most bay area faults but fault strike does loosely correlate with inferred plate motions at the time each fault initiated

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr