coseismic and postseismic slip from the 2003 san simeon earthquake and their effects on backthrust slip and the 2004 parkfield earthquake 1 the 2003 m6 5 san simeon earthquake occurred less than a year before and 50 km west of the long awaited parkfield earthquake of 2004 aftershocks of the san simeon event occurred not only on the presumptive rupture plane but also delineated subconjugate structures to the east backthrusts insar data show a complex pattern of deformation during the postseismic time interval and suggest that shallow postseismic slip may have occurred on the backthrust structures in this paper we present a model inversion for slip during and after the earthquake from four interferograms and gps data we find that the data are well fit when coseismic slip is allowed on two planes the main rupture plane and a backthrust structure to the south the backthrust structure accommodates slip amounting to about one third of the coseismic moment release shallow postseismic slip also occurred on the main rupture plane updip from the coseismic slip and on the southern backthrust postseismic slip on the more northern backthrust structure is not well constrained and the data is fit nearly as well without including it the areas of postseismic slip on the backthrusts correspond well with areas that experienced unclamping and little slip is found in regions of clamping no value for the coefficient of friction below 1 0 results in a coulomb failure stress field that matches the aseismic slip distributions better than the normal stress alone we also investigate whether static stress changes from the san simeon earthquake acted to encourage right lateral strike slip on the parkfield segment of the san andreas fault we find that the san simeon earthquake s rupture planes were oriented in such a way that the maximum increase in coulomb failure stress on the san andreas fault occurred on the parkfield segment the 2004 parkfield earthquake differed from its expected behavior by nucleating in the southern portion of the parkfield segment an area that experienced increased shear stress of 0 1 0 14 bars from coseismic slip in the san simeon earthquake postseismic slip from san simeon further loaded the southern portion of the parkfield segment preferentially over the northern portion though the size of the stress changes was small 0 03 0 04 bars

a study of secondary pyrite deformation and calcite veins in safod damage zone with implications for aseismic creep deformation mechanism at depths 3 km abstract previous studies of the san andreas fault damage zone samples from the san andreas fault observatory at depth safod have identified a variety of tectonic microstructures including pressure solution cleavage calcite sealed fractures vein fabric and pyrite and anhydrite hydrothermal fracture sealing understanding the deformation provenance of the damage zone rocks and operative deformation mechanism s based on preserved microstructures provide insight into overall deformation behavior of the entire seismogenic zone in the creeping section of this transform fault we analysed the deformation of hydrothermal secondary pyrite in connection with network of calcite veins in a sample of foliated ultracataclasites bordering the actively creeping southwestern deforming zone sdz using sem ebsd and cl microscopy the results show that calcite veins associated with the pressure solution cleavage are crosscut by the secondary pyrite deformed under a range of p t conditions relatively undeformed secondary pyrite is found sealing implosion microbreccia our review of previously available data indicates that the damage zone rocks may represent a collage of structural and compositional domains from both locked and creeping sections of the saf this interpretation together with results of this study suggest that weak clay frictional deformation mechanism s is likely to be the predominant aseismic creep mechanism at depths below the safod

localized shear in the deep lithosphere beneath the san andreas fault system seismic images of the base of the lithosphere across the san andreas fault system california usa yield new constraints on the distribution of deformation in the deep lithosphere beneath this strikeslip plate boundary we show that conversions of shear to compressional waves sp across the base of the lithosphere are systematically weaker on the western side of the plate boundary indicating that the drop in seismic shear wave velocity from lithosphere to asthenosphere is either smaller or occurs over a larger depth range in central and northern california the lithosphere asthenosphere boundary changes character across a distance of 50 km and does so directly beneath the san andreas fault along its simple central segment and beneath the calaveras green valley bartlett springs faults to the north given the absolute velocities of the north america and pacific plates and low viscosities inferred for the asthenosphere these results indicate the juxtaposition of mantle lithospheres with different properties across these faults the spatial correlation between the central san andreas fault and the laterally abrupt change in the velocity structure of the deepest mantle lithosphere points to the accommodation of relative plate motion on a narrow shear zone 50 km in width and a rheology that enables strain localization throughout the thickness of the lithosphere

thirty five year creep rates for the creeping segment of the san andreas fault and the effects of the 2004 parkfield earthquake constraints from alignment arrays continuous global positioning system and creepmeters we present results from differential global positioning system gps surveys of seven alignment arrays and four continuous gps sites along the creeping segment of the san andreas fault surveys of four alignment arrays from the central creeping segment yield 33 to 36 year average minimum slip rates of 21 26 mm yr these rates are consistent with previous alignment array surveys spanning a 10 year period and with rates determined by creepmeters indicating approximate steady state creep along the central creeping segment for at least 35 years motion between continuous gps sites that span the central creeping segment is 28 2 0 5 mm yr for two sites that are 1 km apart and 33 6 1 mm yr for two sites that are 70 km apart slip rates therefore increase with distance from the creeping segment of the san andreas fault all rates reported here are significantly slower than the 39 2 mm yr rate predicted for motion between the sierra nevada great valley block and the pacific plate repeat surveys of three alignment arrays following the 2004 parkfield earthquake demonstrate that its coseismic and short term postseismic offsets decrease rapidly with distance from the epicenter from 150 mm to 15 mm to 5 mm at respective distances of 9 36 and 54 km to the northwest continuous gps data confirm that little coseismic and postseismic slip occurred along the central creeping segment geodetic and geologic slip rates are compared and different models for the accommodation of transcurrent deformation across the creeping segment are discussed

viscoelastic cycle model of interseismic deformation in the northwestern united states summary we apply a viscoelastic cycle model to a compilation of gps velocity fields in order to address the kinematics of deformation in the northwestern united states a viscoelastic cycle model accounts for time dependent deformation following large crustal earthquakes and is an alternative to block models for explaining the interseismic crustal velocity field building on the approach taken in pollitz et al we construct a deformation model for the entire western united states based on combined fault slip and distributed deformation and focus on the implications for the mendocino triple junction mtj cascadia megathrust and western washington we find significant partitioning between strike slip and dip slip motion near the mtj as the tectonic environment shifts from northwest directed shear along the san andreas fault system to east west convergence along the juan de fuca plate by better accounting for the budget of aseismic and seismic slip along the cascadia subduction interface in conjunction with an assumed rheology we revise a previous model of slip for the m 9 1700 cascadia earthquake in western washington we infer slip rates on a number of strike slip and dip slip faults that accommodate northward convergence of the oregon coast block and northwestward convergence of the juan de fuca plate lateral variations in first order mechanical properties e g mantle viscosity vertically averaged rigidity explain to a large extent crustal strain that cannot be rationalized with cyclic deformation on a laterally homogeneous viscoelastic structure our analysis also shows that present crustal deformation measurements particularly with the addition of the plate boundary observatory can constrain such lateral variations

measurements of the strain field associated with episodic creep events on the san andreas fault at san juan bautista california over the past 6 years repeated strain steps recorded on a tensor strainmeter installed close to the san andreas fault trace at san juan bautista in california correlated closely with episodic creep events registered on a nearby creepmeter the strain events were remarkably similar in character were of about 1 hour duration and were followed within hours to days by creep events of 2 6 days duration the episodic slip of a source region from 200 m to 500 m in depth and at most a few kilometers in length is consistent with the observed strain and creep data we postulate that the additional stress transferred to this region by the loma prieta earthquake is giving rise to an increased rate of accumulation of shear strain around a locked patch beneath the creep source region thus accounting for the increased frequency of the creep strain events following the loma prieta earthquake

creep and quakes on the northern transition zone of the san andreas fault from gps and insar data 1 the san juan bautista sjb segment forms the northern transition zone of the creeping section of the san andreas fault it is an area of moderate seismicity the largest instrumentally recorded earthquakes have been m5 5 however historic records suggest six m 6 earthquakes occurred near the sjb segment between 1840 and 1899 it is also an area that has experienced several slow earthquakes we perform a joint inversion of gps and insar data to determine the current rate and distribution of interseismic creep we find two low slip locked segments at mid seismogenic depths that may represent source regions for the 19th century earthquakes we find that the sjb segment is currently accumulating strain energy at the rate of one m6 3 6 7 earthquake per century at this rate the 1840 1899 sequence released 135 510 years of accumulated moment deficit

a slow earthquake sequence on the san andreas fault earthquakes typically release stored strain energy on timescales of the order of seconds limited by the velocity of sound in rock over the past 20 years observations1 13 and laboratory experiments14 have indicated that rupture can also occur more slowly with durations up to hours such events may be important in earthquake nucleation15 and in accounting for the excess of plate convergence over seismic slip in subduction zones the detection of events with larger timescales requires near field deformation measurements in december 1992 two borehole strainmeters close to the san andreas fault in california recorded a slow strain event of about a week in duration and we show here that the strain changes were produced by a slow earthquake sequence equivalent magnitude 4 8 with complexity similar to that of regular earthquakes the largest earthquakes associated with these slow events were small local magnitude 3 7 and contributed negligible strain release the importance of slow earthquakes in the seismogenic process remains an open question but these observations extend the observed timescale for slow events by two orders of magnitude

using vertical axis rotations to characterize off fault deformation across the san andreas fault system central california we use vertical axis rotations from new paleomagnetic data to constrain off fault deformation within the san andreas fault system in central california samples were collected from 177 sites in the miocene monterey formation adjacent to the rinconada fault reliable means from 57 sites have 3 prominent patterns 1 the largest clockwise rotations are close to the rinconada and nacimiento faults 2 no significant rotation is observed near the san andreas fault and 3 counterclockwise rotations are observed at several sites northwest of paso robles these paleomagnetic results are compared to two other measures of off fault deformation where rotation can be calculated results from a fold based kinematic model show increasing clockwise rotations toward the rinconada fault consistent with pattern 1 few folds are observed in rocks on salinian basement near the san andreas fault suggesting that little deformation has occurred and providing an explanation for the negligible paleomagnetic rotations in pattern 2 rotations calculated from the global positioning system velocity field predict counterclockwise rotations that coincide with those observed from paleomagnetic data in pattern 3 broad patterns in the velocity field appear to be controlled by the transition from creeping to locked behavior along the san andreas fault and the region of counterclockwise rotation is linked to this transition thus we suggest that the creeping segment has been aseismic over geologic time scales in order to produce the observed paleomagnetic rotations the integration of all three data sets demonstrates that the san andreas fault borderlands record an important portion of fault parallel plate motion over geologic and geodetic time scales

geologic versus geodetic deformation adjacent to the san andreas fault central california we combine geologic and global positioning system gps data to characterize the style and magnitude of off fault deformation across the san andreas fault system in central california geologic structures record 12 km of both fault parallel and fault perpendicular displacements across creeping and locked portions of the san andreas fault analysis of 150 gps site velocities suggests that the borderlands record 4 6 mm yr of fault parallel and 3 5 mm yr of fault perpendicular motion alongside the creeping segment where elastic strain is minimized the distribution of both long term geologic and short term geodetic deformation is affected by basement type where more deformation is concentrated northeast of the san andreas fault on franciscan basement we suggest that at least half the fault parallel gps deformation measured by gps bordering the creeping segment must be accommodated by geologic structures this permanent deformation needs to be incorporated into dynamic models of the fault system elastic modeling of the san andreas fault in central california which incorporates its well known transition from locked to creeping behavior near parkfield predicts first order variations in the gps velocity field along the fault and corresponding variations in dilatational strain rates the strain rate pattern is dominated by a large contractional region northeast of the transition from locked to creeping behavior and a large extensional region southwest of the transition the former coincides with the coalinga and kettleman hills anticlines the growth and development of which seem to have occurred under at least two kinematic conditions we suggest that the onset of fault creep in central california promoted the growth of these folds by implication fault creep has been active over geologic time scales

coseismic and postseismic slip of the 2004 parkfield earthquake from space geodetic data we invert interferometric synthetic aperture radar insar data jointly with campaign and continuous global positioning system gps data for slip in the coseismic and postseismic periods of the 2004 parkfield earthquake the insar dataset consists of eight interferograms from data collected by the envisat and radarsat satellites spanning the time of the earthquake and variable amounts of the postseismic period the two datasets complement each other with the insar providing dense sampling of motion in the range direction of the satellite and the gps providing more sparse but three dimensional measurements of ground motion the model assumes exponential decay of the postseismic slip with a decay time constant of 0 087 years determined from time series modeling of continuous gps and creepmeter data we find a geodetic moment magnitude of m 6 2 for a 1 day coseismic model and m w 6 1 for the entire postseismic period the coseismic rupture occurred mainly in two slip asperities one near the hypocenter and the other 15 20 km north postseismic slip occurred on the shallow portions of the fault and near the rupture areas of two m 5 0 aftershocks a comparison of the geodetic slip models with seismic moment estimates suggests that the coseismic moment release of the parkfield earthquake is as little as 25 of the total this underlines the importance of aseismic slip in the slip budget for the parkfield segment online material complete data tables and supplemental tables

a decadal scale deformation transient prior to the 2011 mw 9 0 tohoku oki earthquake gps time series in northeast japan exhibit nonlinear trends from 1996 to 2011 before the mw 9 0 2011 tohoku oki earthquake after removing reference frame noise we model time series as linear trends plus constant acceleration correcting for coseismic and postseismic effects from the numerous mw 6 5 earthquakes during this period we find spatially coherent and statistically significant accelerations throughout northern honshu large areas of japan outside the tohoku region show insignificant accelerations demonstrating that the observation is not due to network wide artifacts while the accelerations in northern tohoku sanriku area can be explained by decaying postseismic deformation from pre 1996 earthquakes the accelerations in south central tohoku appear unrelated to postseismic effects the latter accelerations are associated with a decrease in average trench normal strain rate and can be explained by increasing slip rate on the japan trench plate interface and or updip migration of deep aseismic slip in the decades before the 2011 tohoku oki earthquake

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

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

length displacement scaling and fault growth abstract following an earthquake in a fault zone commonly the co seismic rupture length and the slip are measured similarly in a structural analysis of major faults the total fault length and displacement are measured when possible it is well known that typical rupture length slip ratios are generally orders of magnitude larger than typical fault length displacement ratios so far however most of the measured co seismic ruptures and faults have been from different areas and commonly hosted by rocks of widely different mechanical properties which have strong effects on these ratios here we present new results on length displacement ratios from 7 fault zones in holocene lava flows on the flanks of the volcano etna italy as well as 10 co seismic rupture length slips and compare them with fault data from iceland the displacement and slip data from etna are mostly from the same fault zones and hosted by rocks with largely the same mechanical properties for the co seismic ruptures the average length is 3657 m the average slip 0 31 m and the average length slip ratio 19 595 for the faults the average length is 6341 m the average displacement 73 m and the average length displacement ratio 130 thus the average rupture slip ratio is about 150 times larger than the average length displacement ratio we propose a model where the differences between the length slip and the length displacement ratios can be partly explained by the dynamic young s modulus of a fault zone being 101 2 times greater than its static modulus in this model the dynamic modulus controls the length slip ratios whereas the static modulus controls the length displacement ratio we suggest that the common aseismic slip in fault zones is partly related to adjustment of the short term seismogenic length slip ratios to the long term length displacement ratios fault displacement is here regarded as analogous to plastic flow in which case the long term displacement can be very large so long as sufficient shear stress concentrates in the fault

subglacial jokulhlaup deposition jotunheimen norway abstract the aim of this paper is to discuss the origin of a linear boulder deposit near the mjolkedalsbreen jotunheimen norway subglacial fluvial deposition is suggested by palaeoflow indicators showing flow directions uphill along the axis of a ridge like deposit and the close association of this deposit with an ice contact boulder delta peak discharges of repeated jokulhlaups from the former ice dammed ovre mjolkedalsvatn were estimated at 1188 m3 s 1 using evidence derived from the proglacial jokulhlaup routeway former ice tunnel dimensions and flow conditions associated with the ridge like deposit were derived from a simple pipe flow equation flow velocities of 9 8 11 6 m s 1 and shear stresses of 1440 2018 n m2 were reconstructed for a tunnel less than 3 m in average height and 45 m wide such flows would have been capable of transporting boulders of greater than 3 m in diameter as traction load and material of gravel cobble size in suspension material of this size has been deposited downflow as an ice contact delta linear ridges of boulder gravel with up slope gradients found in association with ice contact deposits in other formerly glaciated areas may similarly be of jokulhlaup origin

interaction of the san andreas fault creeping segment with adjacent great rupture zones and earthquake recurrence at parkfield three dimensional finite element calculations are employed to study interactions in space and time between the creeping segment of the san andreas fault in central california and the adjacent currently locked zones of the 1857 and 1906 great earthquakes vertically the model consists of an elastic upper crust over a maxwell viscoelastic region representing the entire lower crust or a narrower horizontal detachment layer and a stiffer and more viscous upper mantle the crust has a single vertical fault extending to the top of the mantle at 25 km depth in zones along strike corresponding to the 1857 and 1906 events the top 12 5 km of the fault is locked against slip except in great earthquakes below the locked zones and everywhere along the creeping region between them the fault is freely slipping the model parameters are compatible with seismological and geological observations and with a ratio of maxwell relaxation time to the relaxing layer thickness in the range 1 to 2 yr km as established by li and rice 1987 and fares and rice 1988 based on fits to geodetic data along the san andreas fault an imposed constant far field shear motion and periodic 1857 and 1906 type earthquakes generate slip rates along the creeping fault segment that evolve in time throughout the entire earthquake cycle shortly after an adjacent great earthquake slip rates in the creeping zone are higher than the far field velocity while later in the cycle they are lower hence time dependency should be accounted for when measurements of fault slip are used to estimate the plate motion if parkfield earthquakes are a response to a time dependent loading of the type simulated here their recurrence interval would tend to lengthen with time since the 1857 event thus the hypothesis of characteristic periodic earthquakes at parkfield may not provide the best estimate of the occurrence time of the next event using for example the statistics of past events and assuming that parkfield earthquakes are a response to a slip deficit near middle mountain and that the elastic crustal layer is 17 5 km thick we find that the next event is predicted for about 1992 9 years if the lower crust is a 7 5 km thick layer having a material relaxation time of 15 years and 1995 11 years if the 7 5 km thick lower crust is characterized by a relaxation time of 7 5 years these values may be compared to the 1988 7 years estimate based on periodicity in time the modeling results also indicate that the interaction between the 1857 and 1906 rupture zones is small

change of apparent segmentation of the san andreas fault around parkfield from space geodetic observations across multiple periods sequences of earthquakes are commonly represented as a succession of periods of interseismic stress accumulation followed by coseismic and postseismic phases of stress release because the recurrence time of large earthquakes is often greater than the available span of space geodetic data it has been challenging to monitor the evolution of interseismic loading in its entire duration here we analyze large data sets of surface deformation at different key episodes around the cholame parkfield and creeping segments of the san andreas fault that show evidence of significant deceleration of fault slip during the interseismic period we compare the average fault slip rates before and after the 2004 mw6 parkfield earthquake in the 1986 2004 and 2006 2012 periods respectively avoiding 2 years of postseismic deformation after 2004 using a combination of gps data from the plate boundary observatory the southern california earthquake center crustal motion map and the bay area velocity unification networks and interferometric synthetic aperture radar from the advanced land observing satellite alos and envisat satellites we show that the area of coupling at the transition between the parkfield and cholame segments appears larger later in the interseismic period than it does earlier on while strong plate coupling is uniform across the parkfield and cholame segments in the 1986 2004 period creep occurs south of the 2004 epicenter after 2006 making segmentation of the san andreas fault south of parkfield more clearly apparent these observations indicate that analyses of surface deformation late in the earthquake cycle may overestimate the area of plate coupling a fault surface creeping much below plate rate may in some case be a region that does not promote earthquake nucleation but rather just be at a slower stage of its evolution our analysis also shows signs of large variation of slip velocity above and below plate rate in the creeping segment indicating that cycles of weakening and hardening can also be at play in dominantly aseismic areas

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

when faults communicate viscoelastic coupling and earthquake clustering in a simple two fault system 1 3 d finite element models of a simplified northern and southern san andreas type fault system are presented with the goal of better understanding how great earthquakes m 7 5 on one major segment of a fault can affect the earthquake cycle on another colinear fault segment separated from the first by an asesimically creeping segment we find that the earthquake cycles of the two seismogenic fault segments become coupled as the lower crustal viscosity and or the fault separation distance are decreased further models with a 10 30 difference in relative fault breaking strengths exhibit a bi modal distribution of repeat times for each fault resulting in earthquakes that appear clustered in time

amino acid geochronology applied to the correlation and dating of central european loess deposits abstract numerous localities in the czech republic slovakia and austria have been sampled for fossil gastropod shells for the purpose of an aminostratigraphic evaluation of loess sequences in all three regions alloisoleucine isoleucine aile ile ratios are observed to be significantly higher in shells from loess deposited during the penultimate glacial period cycle c relative to samples from loess of the last glaciation cycle b the difference in aile ile ratio reflects both difference in age of the samples plus the impact on the older samples of the relatively high effective temperature of the last interglacial period amino acid data support the previous correlation suggested between pk ii iii in the czech republic and slovakia and the stillfried a in austria samples have also been recovered from older loess units and previously published correlations within the czech and slovak republics are tested aiie ile ratios appear to distinguish between samples from loess of the last four glacial cycles beyond cycle e 18o stages 10 and 11 the increase in alle ile ratio is relatively small from cycle to cycle in addition shells tend to be poorly preserved and are absent at many localities nevertheless amino acid geochronology offers a means of resolving ages of loess units in the critical time period that is beyond the range of radiocarbon and thermoluminescence methods but post dates the brunhes matuyama paleomagnetic reversal

stable isotopic compositions of recent freshwater cyanobacterial carbonates from the british isles local and regional environmental controls recent 50 years old freshwater cyanobacterial carbonates from diverse environments streams lakes waterfalls throughout britain and ireland were analysed for their stable carbon and oxygen isotope compositions the mean 18o value of 5 9 pdb for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central britain 7 5 smow assuming a mean water temperature of 9 c the mean 18o of lake data 4 5 pdb is statistically different reflecting the effects of residence time and or variations in the oxygen isotopic composition of rainfall carbon isotopes have wide variations in both fluviatile and lake data sets 3 to 12 pdb these variations are principally controlled in the fluviatile samples by contribution of isotopically light soil zone carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution lake samples have the heaviest carbon isotope values reflecting a trend toward isotopic equilibrium between atmospheric co2 and aqueous hco 3 we infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information although the effects of stabilization and diagenesis on primary 18o values will need careful consideration primary carbon isotope compositions should be well preserved although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate

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

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

a unified analysis of crustal motion in southern california 1970 2004 the scec crustal motion map 1 to determine crustal motions in and around southern california we have processed and combined trilateration data collected from 1970 to 1992 vlbi data from 1979 to 1992 and gps data from 1986 to 2004 a long temporal coverage required in part by the occurrence of several large earthquakes in this region from a series of solutions for station positions we have estimated interseismic velocities coseismic displacements and postseismic motions within the region from 31 n to 38 n and east to 114 w the final product includes estimated horizontal velocities for 1009 gps 190 trilateration and 16 vlbi points with ties between some of these used to stabilize the solution all motions are relative to the stable north american reference frame snarf as realized through the velocities of 20 gps stations this provides a relatively dense set of horizontal velocity estimates with well tested errors for the past quarter century over the plate boundary from 31 n to 36 5 n these velocities agree well with those from the plate boundary observatory which apply to a later time period we also estimated vertical velocities 533 of which have errors below 2 mm yr most of these velocities are less than 1 mm yr but they show 2 4 mm yr subsidence in the ventura and los angeles basins and in the salton trough our analysis also included estimates of coseismic and postseismic motions related to the 1992 landers 1994 northridge 1999 hector mine and 2003 san simeon earthquakes postseismic motions increase logarithmically over time with a time constant of about 10 days and generally mimic the direction and relative amplitude of the coseismic offsets

a late middle pleistocene temperate periglacial temperate sequence oxygen isotope stages 7 5e near marsworth buckinghamshire uk abstract river channel and colluvial deposits near marsworth buckinghamshire record a temperate periglacial temperate sequence during the late middle pleistocene the deposits of a lower channel contain tufa clasts bearing leaf impressions that include acer sp and sorbus aucuparia and containing temperate arboreal pollen attributed to ash dominated woodland the tufa probably formed at the mouth of a limestone spring before being redeposited in a small river whose deposits contain plant remains mollusca coleoptera ostracoda and vertebrate bones of temperate affinities the sediments sedimentary structures and limited biological remains above the lower channel deposits indicate that fluvial deposition preceded climatic cooling into periglacial conditions fluvial deposition recurred during a later temperate episode as shown by the mammalian bone assemblage in stratigraphically higher channel deposits the upper channel deposits are confidently attributed to oxygen isotope sub stage 5e ipswichian on the basis of their vertebrate remains however the age of the lower channel deposits is less clear the mammalian and coleopteran remains in the lower channel strongly suggest correlation with oxygen isotope stage 7 on the basis of their similarities to other sites whose stratigraphy is better known and the clear difference of the lower channel assemblage from well established faunas of ipswichian or any other age by contrast u th dating of the tufa clasts suggests an age post 160 ka bp while aile ile ratios on mollusca point to an ipswichian age and younger four ways of interpreting this age discrepancy are considered the preferred one correlating the lower channel deposits with oxygen isotope stage 7

the response of creeping parts of the san andreas fault to earthquakes on nearby faults two examples rates of shallow slip on creeping sections of the san andreas fault have been perturbed on a number of occasions by earthquakes occurring on nearby faults one example of such perturbations occurred during the 26 january 1986 magnitude 5 3 tres pinos earthquake located about 10 km southeast of hollister california seven creepmeters on the san andreas fault showed creep steps either during or soon after the shock both left lateral ll and right lateral rl steps were observed a rectangular dislocation in an elastic half space was used to model the coseismic fault offset at the hypocenter for a model based on the preliminary focal mechanism the predicted changes in static shear stress on the plane of the san andreas fault agreed in sense ll or rl with the observed slip directions at all seven meters for a model based on a refined focal mechanism six of the seven meters showed the correct sense of motion two possible explanations for such coseismic and postseismic steps are 1 that slip was triggered by the earthquake shaking or 2 that slip occurred in response to the changes in static stress fields accompanying the earthquake in the tres pinos example the observed steps may have been of both the triggered and responsive kinds a second example is provided by the 2 may 1983 magnitude 6 7 coalinga earthquake which profoundly altered slip rates at five creepmeters on the san andreas fault for a period of months to years the xmm1 meter 9 km northwest of parkfield california recorded ll creep for more than a year after the event to simulate the temporal behavior of the xmm1 meter and to view the stress perturbation provided by the coalinga earthquake in the context of steady state deformation on the san andreas fault a simple time evolving dislocation model was constructed the model was driven by a single long vertical dislocation below 15 km in depth that was forced to slip at 35 mm yr in a rl sense a dislocation element placed in the seismogenic layer under xmm1 was given a finite breaking strength of sufficient magnitude to produce a parkfield like earthquake every 22 years when stress changes equivalent to a coalinga earthquake were superposed on the model running in a steady state mode the effect was to make a segment under xmm1 that could slip in a linear viscous fashion creep ll and to delay the onset of the next parkfield like earthquake by a year or more if static stress changes imposed by earthquakes off the san andreas can indeed advance or delay earthquakes on the san andreas by months or years then such changes must be considered in intermediate term prediction efforts

fault zone controls on the spatial distribution of slow moving landslides slow moving landslides earthflows can dominate hillslope sediment flux and landscape erosion in hilly terrain with mechanically weak fine grained rock controls on the occurrence of slow moving landslides are poorly constrained and need to be understood for landscape evolution models sediment budgets and infrastructure and hazards planning here we use airborne interferometric synthetic aperture radar insar and aerial photographs to document 150 previously unidentified active earthflows along the central creeping portion of the san andreas fault california the earthflows move seasonally in response to winter rainfall occur on hillslopes at 20 40 gradients less than typically associated with rapid catastrophic landslides and have similar morphological characteristics to earthflows in different climatic and tectonic settings although our data extend up to 10 km from the fault trace 75 of detected landslides occur within 2 km of the active fault topographic precipitation and rock type metrics alone are not enough to explain the observed spatial distribution of earthflows instead we hypothesize that earthflows cluster near the creeping san andreas fault because of a fault induced zone of reduced bulk rock strength that increases hillslope susceptibility to failure in addition similar lithology topography and climate exist north of the creeping section of the fault yet earthflows there are rare this may be due to large magnitude earthquakes episodically triggering coseismic rapid landslides which preferentially remove weak rock from the fault damage zone our analysis suggests that the necessary conditions for earthflow formation in central california include some combination of reduced rock strength fine grained sedimentary rock threshold precipitation and relief and possibly the absence of large magnitude earthquakes these conditions likely hold for earthflow development in other areas and our work suggests that local variations in rock strength and seismicity such as those associated with fault zones need to be taken into account in order to accurately predict earthflow occurrence

is there a discrepancy between geological and geodetic slip rates along the san andreas fault system previous inversions for slip rate along the san andreas fault system safs based on elastic half space models show a discrepancy between the geologic and geodetic slip rates along a few major fault segments in this study we use an earthquake cycle model representing an elastic plate over a viscoelastic half space to demonstrate that there is no significant discrepancy between long term geologic and geodetic slip rates the california statewide model includes 41 major fault segments having steady slip from the base of the locked zone to the base of the elastic plate and episodic shallow slip based on known historical ruptures and geologic recurrence intervals the slip rates are constrained by 1981 secular velocity measurements from gps and l band intereferometric synthetic aperture radar a model with a thick elastic layer 60 km and half space viscosity of 1019pa s is preferred because it produces the smallest misfit to both the geologic and the geodetic data we find that the geodetic slip rates from the thick plate model agrees to within the bounds of the geologic slip rates while the rates from the elastic half space model disagree on specific important fault segments such as the mojave and the north coast segment of the san andreas fault the viscoelastic earthquake cycle models have generally higher slip rates than the half space model because most of the faults along the safs are late in the earthquake cycle so today they are moving slower than the long term cycle averaged velocity as governed by the viscoelastic relaxation process

coseismic slip distribution of the 2003 mw 6 6 san simeon earthquake california determined from gps measurements and seismic waveform data 1 we combine geodetic and seismic data sets to constrain the coseismic slip distribution of the mw6 6 san simeon earthquake which occurred in the central california coast ranges on december 22 2003 we use continuous and survey mode gps observations along with seismic waveform data from the california integrated seismic network cisn we invert both data sets for the distribution of finite fault slip in a layered earth model the inversion results indicate that the rupture extends to the southeast of the epicenter for approximately 25 30 km and occurred in a relatively shallow depth range between 1 to 10 km the average and peak slip are 0 61 m and 2 37 m respectively the scalar seismic moment is 7 85e18 nm and the static stress drop 1 7 mpa this thrust earthquake is characterized by its shallow along strike extended slip

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

aseismic slip and fault normal strain along the central creeping section of the san andreas fault 1 we use gps data to measure the aseismic slip along the central san andreas fault csaf and the deformation across adjacent faults comparison of edm and gps data sets implies that except for small scale transients the fault motion has been steady over the last 40 years we add 42 new gps velocities along the csaf to constrain the regional strain distribution shear strain rates are less than 0 083 0 010 strain yr adjacent to the creeping saf with 1 4 5 mm yr of contraction across the coast ranges dislocation modeling of the data gives a deep long term slip rate of 31 35 mm yr and a shallow 0 12 km creep rate of 28 mm yr along the central portion of the csaf consistent with surface creep measurements the lower shallow slip rate may be due to the effect of partial locking along the csaf or reflect reduced creep rates late in the earthquake cycle of the adjoining saf rupture zones

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

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

a preliminary report on the stanton harcourt channel deposits oxfordshire england geological context vertebrate remains and palaeolithic stone artefacts a summary is given of the geological faunal and archaeological information obtained during excavations in the stanton harcourt channel deposits from 1990 to 1995 the channel deposits underlie the cold climate stanton harcourt gravel member of the summertown radley terrace formation the channel sediments are attributed to oxygen isotope stage 7 when the thames was undergoing down dip migration and eroding the weymouth member of the oxford clay upper jurassic the contemporary jurassic corallian escarpment being near to stanton harcourt at that time abundant large vertebrate remains have been recovered mainly from the base of the channel deposits where a cobble and boulder bed rests on thin silt or sand horizons or in scour hollows in the clay bedrock smaller bones occur throughout the deposits which are mainly poorly sorted gravels but especially at erosive horizons several palaeolithic artefacts have been found in the same contexts many of the bones and some of the artefacts appear not to have been transported far although the artefacts cannot be linked directly with the bones a study of them adds to our knowledge of the middle pleistocene human settlement of the upper thames valley it is of interest that mammoth is abundant as part of the interglacial faunal assemblage and the significance of this is discussed the environment clearly included substantial areas of open grassland although there was also some forest in the vicinity evidence appears to be accumulating for important faunal and floral differences between particular interglacial events during the british middle and late pleistocene

time dependent model of aseismic slip on the central san andreas fault from insar time series and repeating earthquakes the central segment of san andreas fault csaf is characterized by a nearly continuous right lateral aseismic slip however observations of the creep rate obtained using small characteristically repeating earthquakes cres show pulses of creep along the csaf which may indicate spatially and temporally variable seismic hazard along the csaf therefore the goal of this study is to obtain a high resolution time dependent model of creep along the csaf to examine this hypothesis to this end we apply a time dependent creep modeling approach which combines interferometric synthetic aperture radar insar surface deformation time series and observations of fault creep obtained from cres the sar data set includes c band scenes acquired by the ers 2 and envisat satellites between 2003 and 2011 the resulting creep rate distribution implies a peak rate up to 32 mm yr along the central part of the csaf afterslip due to the 2004 parkfield earthquake on the southeastern segment of the csaf is also manifest in the model and there is clear evidence of creep pulsing along strike and depth of the csaf estimated annual rate of slip deficit accumulation is equivalent to a magnitude 5 6 5 7 earthquake taking advantage of the time dependence of our model we also refine the scaling relationship which associates the released seismic moment due to a cre event with the amount of creep on the fault surrounding the cre patches this study provides the first kinematic model of creep pulsing constrained using geodetic and seismic data which can enhance time dependent seismic hazard maps and improve earthquake operational forecast models

crustal deformation across and beyond the los angeles basin from geodetic measurements we combine 6 years of global positioning system gps data with 20 years of trilateration data and a century of triangulation taped distance and astronomic azimuth measurements to derive 66 interseismic station velocities in the greater los angeles region we interpolate the velocities to construct a regional strain rate map beyond the los angeles basin our results generally agree with the model proposed by the working group on california earthquake probabilities in 1995 important regional findings of this study are as follows 1 there is a significant n s convergence and e w extension about 0 22 and 0 17 0 05 strain yr respectively for the two components along the southern frontal fault system of the san gabriel mountains 2 the crustal deformation around the big bend of the san andreas fault saf cannot be explained solely by wrench style motion across the saf remaining motion could be part of a nw se extension which is the response to nfsw compression in the central transverse ranges region alternatively it could be caused by left lateral faulting on an oblique blind thrust beneath the san gabriel mountains 3 low strain rates axe found along the elsinore fault and newport inglewood 4 north south compression decreases from the raymond hill fault westward to the santa monica fault there is little east west extension along this fault system

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

fault network modeling of crustal deformation in california constrained using gps and geologic observations abstract we have developed a kinematic fault network model of crustal deformation in an elastic half space surface deformation is calculated using this model assuming each fault segment slipping beneath a locking depth each fault segment connects to its adjacent elements with slip vector continuity imposed at fault nodes or intersections the degree of the constraints determines whether deformation is block like or not we apply this model to invert gps observations for slip rates on major faults in california with geological rate constraints based on the f test result we find that lesser block like models fit the data significantly better than the strictly block like model our final inversion shows a slip rate varying from 20 to 23 mm yr along the northern san andreas from the santa cruz to the north coast segment slip rates vary from 9 to 13 mm yr along the hayward to the maacama fault segment and from 15 to 3 mm yr along the central calaveras to the west napa fault segment for the central california creeping zone the result suggests a depth dependent creep rate with an average of 22 mm yr over the top 5 km and 32 mm yr underneath from the mojave to san bernardino mountain segments we also find a significant decrease in slip rate along the san andreas in comparison with the geologic rates in contrast to a significant increase in slip rate on faults along the eastern california shear zone along the southern san andreas slip rates vary from 21 to 25 mm yr from the coachella valley to imperial valley segments slip rates range from 0 to 3 mm yr across the western transverse ranges faults which is consistent with the regional crustal thickening overall slip rates derived from geodetic observations correlate strongly with the geologic slip rates statistically suggesting high compatibility between geodetic and geologic observations

strain partitioning along the western margin of north america abstract this paper describes an elastic block model for the interseismic horizontal crustal velocity field occurring in that part of the united states located west of longitude 100 w and between latitudes 31 n and 49 n we developed the model by simultaneously inverting 6873 gps derived velocity vectors and 166 geological fault slip rates for the angular velocities i e the euler poles relative to the north america plate of 46 elastic blocks horizontal strain rate tensors for 38 of these blocks and the spatially variable elastic coupling coefficients on faults that bound adjacent blocks while the model covers all of the western united states located between canada and mexico this paper focuses on the region residing south of cape mendocino where plate boundary deformation is accommodated predominantly by slip on the san andreas fault system block strain rates which account for deformation associated with distributed faults within blocks are systematically higher in blocks located in the western part of the model and adjacent to the plate boundary strain rate magnitudes range from over 10 7 yr for some blocks adjacent to the san andreas fault system to values of about 10 9 yr for blocks located in eastern nevada and western utah blocks adjacent to the san andreas fault system are characterized by strain rate tensors that correspond to uniaxial contraction perpendicular to the local strike of the san andreas the highest rates of fault normal contraction are associated with the northern end of the fault north of san francisco and in the southern end south of los angeles the central san andreas including the creeping segment of the fault is characterized by strain rate tensors more consistent with dextral shear thus the northern and southern ends of the fault are consistent with a transpressional strain partitioning model with strike slip occurring on the san andreas fault system and distributed shortening occurring within the blocks adjacent to this fault system there is no evidence of strain partitioning in the central san andreas

present tectonic motion across the coast ranges and san andreas fault system in central california geodetic results from very long baseline interferometry vlbi satellite laser ranging slr and the global positioning system gps are used to estimate angular velocities between the sierran microplate pacific plate and north american plate the sierra pacific pole of rotation lies nearer to the san andreas fault than does the pacific north america pole of rotation and leads to different tectonic implications than if the latter is used the angular velocities show that the san andreas fault system and central california coast ranges accommodate motion of 39 2 mm yr mainly by strike slip faulting all confidence limits following signs in this paper are 95 confidence limits fault normal motion is small is mainly convergent at rates up to 3 3 1 0 mm yr and varies along the coast but is divergent at 2 6 1 2 mm yr across san pablo bay and associated topographic lows across which the sierran and central valley watershed drains to the pacific ocean the mountain ranges tend to be larger where the fault normal convergence rates are larger the low convergence rate 0 5 1 8 mm yr normal to the san andreas fault in the carrizo plain differs sharply from that previously inferred 8 2 1 2 mm yr and 4 9 1 6 mm yr by feigl et al 1993 the difference is due to differences between their and our elastic strain accumulation models and between how their and our pacific plate reference frames are defined the ranges in most places require a minimum of 4 2 1 m y of fault normal convergence at the present rate to attain their present cross sectional area if erosion is neglected more if it is not the amount of convergence previously estimated from a balanced cross section across the diablo range in central california requires 10 8 3 m y of convergence at the present rate the former is consistent with widely held views about the onset of the coast range orogeny but the latter is not both are consistent however with the recent plate reconstructions by s cande j stock and colleagues which indicate that pacific plate motion relative to north america changed to a more convergent direction 20 25 clockwise of its prior direction at ca 8 to 6 ma and not at 3 5 ma as had been previously inferred the inferred change in direction of plate motion is large compared with the present angle of convergence across the straight and narrow segment of the san andreas fault of 0 7 4 7 from which we infer that the sierran microplate changed motion relative to north america at the same time ca 8 to 6 ma as did the pacific plate we further infer that the motion accommodated across the great basin must also have changed at the same time we also examine the hypothesis that stable sliding occurs along the san andreas fault and other northwest striking strike slip faults in central california where the fault normal convergence rate is low or negative and that these faults are unstable where the fault normal convergence rate is high such a relationship appears to hold in general but fails in detail in particular there are substantial sections of fault with small inferred rates of fault normal convergence across which the san andreas fault is locked moreover the creeping section of the san andreas fault i e the section between parkfield and the calaveras junction is the locus of greater fault normal convergence 3 2 1 4 mm yr than is the locked part of the fault 0 5 1 8 mm yr south of parkfield thus this hypothesis is at best a partial explanation for the observed distribution of locked and nonlocked sections of the fault

spatiotemporal evolution of surface creep in the parkfield region of the san andreas fault 1993 2004 from synthetic aperture radar the parkfield section of the san andreas fault saf is defined as a transitional portion of the fault between slip release behavior types in the creeping section of the saf to the northwest and the apparently locked section to the southeast the parkfield section is characterized by complex frictional fault behavior because it represents a transition zone from aseismic creep to stick slip regime at least six historic earthquakes of mw 6 have occurred in this area in 1881 1901 1922 1934 1966 and 2004 it was observed in the 2004 mw 6 0 parkfield earthquake that 70 of the total coseismic and postseismic moment release occurred aseismically to understand the saf behavior in this area it is of particular interest to measure and analyze not only the spatial evolution of the surface displacement in this area but also its evolution over time using radar data acquired by the european space agency s european remote sensing ers1 2 satellites we constructed descending interferograms and retrieved time series of surface displacements along the central saf for the decade preceding the 2004 parkfield earthquake we focus on characterizing the space and time evolution of surface creep in the parkfield and cholame sections the spatial pattern of the interseismic displacement rate indicates that tectonic strain was not uniformly distributed along the strike of the fault between 1993 and 2004 our data indicate not only a decrease in the creep rate from the parkfield section to south of highway 46 from 1 4 0 3 cm y to 0 6 0 3 cm y but also a small but significant creep rate increase in the cholame section to 0 2 0 1 cm y the evidence for episodic creep in the cholame section of the saf south east of parkfield is in contrast with previously published interpretations of gps and trilateration data the cholame section of the saf merits close monitoring because it was likely the nucleation site of the 1857 fort tejon earthquake and because it has shown recent evidence of deep slow slip as revealed by deep tremors

the chronology palaeogeography and archaeological significance of the marine quaternary record of the west sussex coastal plain southern england u k abstract the quaternary sediments of the west sussex coastal plain have produced a wide range of floral faunal and archaeological remains these sediments consist of marine sands and gravels exhibiting transgressive and regressive trends which occur from present day sea level to c 43 0 m o d and are overlain by terrestrial silts and cold climate periglacial sediments at the present day coastline channel fill deposits occur below modern beach levels new field observations coupled with a re investigation of old sites and literature suggest that five discrete high stands of sea level may be preserved in the area of the west sussex coastal plain age estimates for these deposits suggest that they span large parts of the middle and upper pleistocene oxygen isotope stages 13 to 5 conformable relationships between many of the marine and terrestrial sediments suggest that the potential exists within the area to correlate the marine and terrestrial quaternary stratigraphic records in addition sediments associated with two of these high sea level stands are associated with extensive buried landsurfaces covering large areas of the coastal plain at some locations these intact landsurfaces are associated with evidence for human activity and represent stratigraphic and cultural resources of international importance

persistent termini of 2004 and 2005 like ruptures of the sunda megathrust to gain insight into the longevity of subduction zone segmentation we use coral microatolls to examine an 1100 year record of large earthquakes across the boundary of the great 2004 and 2005 sunda megathrust ruptures simeulue a 100 km long island off the west coast of northern sumatra indonesia straddles this boundary northern simeulue was uplifted in the 2004 earthquake whereas southern simeulue rose in 2005 northern simeulue corals reveal that predecessors of the 2004 earthquake occurred in the 10th century ad in ad 1394 2 and in ad 1450 3 corals from southern simeulue indicate that none of the major uplifts inferred on northern simeulue in the past 1100 years extended to southern simeulue the two largest uplifts recognized at a south central simeulue site around ad 1422 and in 2005 involved little or no uplift of northern simeulue the distribution of uplift and strong shaking during a historical earthquake in 1861 suggests the 1861 rupture area was also restricted to south of central simeulue as in 2005 the strikingly different histories of the two adjacent patches demonstrate that this boundary has persisted as an impediment to rupture through at least seven earthquakes in the past 1100 years this implies that the rupture lengths and hence sizes of at least some future great earthquakes and tsunamis can be forecast these microatolls also provide insight into megathrust behavior between earthquakes revealing sudden and substantial changes in interseismic strain accumulation rates

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

spatial variations in slip deficit on the central san andreas fault from insar summary we use ers insar measurements to record spatial variations in creep rate along the creeping segment of the san andreas fault saf california between 1992 and 2001 inversion of geodetic data yields a slip rate distribution along the creeping segment which is used for firstorder moment release and deficit calculations we present a time averaged spatial picture of surface deformation and associated subsurface creep an interferometric stack is constructed from 12 interferograms that show good coherence for the decade of observation the total right lateral offset spanned by the data is 34 mm yr 1 along most of the length of the creeping segment this offset occurs within a narrow 2 km zone close to the fault trace in the northern part a minor part of the offset is taken up by the nearby calaveras paicines fault in general the observed rates of surface creep are consistent with those obtained by several other studies for a longer and or earlier period of time using different geodetic methods this suggests that the average creep rate has been constant over a period of almost four decades a joint gps insar inversion implies that the shallow creep rate is variable along strike reaching up to 31 5 1m m yr 1 in the central section of the creeping segment tapering off along strike to the south and becoming partitioned across two subparallel faults in the north the deep slip rate beneath the seismogenic layer is 33 3m m yr 1 the difference between shallow and deep slip rates suggests that there is a shallow slip deficit on the creeping segment of the saf csaf moment release rate due to aseismic slip is approximately three orders of magnitude greater than seismic moment release the annual creep on the csaf is equivalent to the moment released in a m 6 earthquake the equivalent moment of the slip deficit relative to the deep slip rate is between 4 1 10 17 and 8 4 10 17 nm yr 1 which is equivalent to a magnitude 5 7 5 9 earthquake over a 150 yr period the deficit is equivalent to a m 7 2 7 4 earthquake this slip deficit may be compensated by intermittent moderate sized events or by accelerated afterslip following large events on nearby fault segments