relationships among seismic velocity metamorphism and seismic and aseismic fault slip in the salton sea geothermal field region the salton sea geothermal field is one of the most geothermally and seismically active areas in california and presents an opportunity to study the effect of high temperature metamorphism on the properties of seismogenic faults the area includes numerous active tectonic faults that have recently been imaged with active source seismic reflection and refraction we utilize the active source surveys along with the abundant microseismicity data from a dense borehole seismic network to image the 3 d variations in seismic velocity in the upper 5 km of the crust there are strong velocity variations up to 30 that correlate spatially with the distribution of shallow heat flow patterns the combination of hydrothermal circulation and high temperature contact metamorphism has significantly altered the shallow sandstone sedimentary layers within the geothermal field to denser more feldspathic rock with higher p wave velocity as is seen in the numerous exploration wells within the field this alteration appears to have a first order effect on the frictional stability of shallow faults in 2005 a large earthquake swarm and deformation event occurred analysis of interferometric synthetic aperture radar data and earthquake relocations indicates that the shallow aseismic fault creep that occurred in 2005 was localized on the kalin fault system that lies just outside the region of high temperature metamorphism in contrast the earthquake swarm which includes all of the m 4 earthquakes to have occurred within the salton sea geothermal field in the last 15 years ruptured the main central fault mcf system that is localized in the heart of the geothermal anomaly the background microseismicity induced by the geothermal operations is also concentrated in the high temperature regions in the vicinity of operational wells however while this microseismicity occurs over a few kilometer scale region much of it is clustered in earthquake swarms that last from hours to a few days and are localized near the mcf system

evolution and thickness of the lithosphere beneath coastal california many of the tectonic features of the california coast ranges are directly related to the northward migration of the mendocino triple junction along the western edge of north america during the past 20 to 30 m y at the triple junction the western edge of the north american plate slides off the relative northward moving and subducting gorda plate leaving the thin western edge in direct contact with asthenosphere upwelling to fill the space vacated by the underlying gorda plate two dimensional time dependent thermal modeling of this process constrained by teleseismic delay studies is used to construct a map of lithospheric thickness of coastal california among the implications of this map are that 1 the high heat flow in the coast ranges can be almost entirely accounted for by the asthenospheric upwelling associated with the migrating mendocino triple junction 2 the general elevation and the late cenozoic volcanism in the california coast ranges are responses to a zone of unusually thin 20 to 45 km lithosphere that extends southward behind the mendocino triple junction and 3 the course of some segments of the san andreas fault in both central and southern california appear to deviate from a deeper more fundamental transform boundary separating the pacific and north american plates

joint analysis of the 2014 kangding southwest china earthquake sequence with seismicity relocation and insar inversion over 1000 earthquakes struck the northwest of kangding on the xianshuihe fault in southwest china between 22 and 29 november 2014 including two largest events of mw 5 9 and mw 5 6 the hypocenters of 799 relocated earthquakes suggest that two independent main shock aftershock subsequences occurred on the selaha and zheduotang branches of the xianshuihe fault respectively fault slip inversion results from one interferometric synthetic aperture radar insar interferogram 26 september 2014 to 5 december 2014 show that the mw 5 9 main shock produced a maximum slip of 0 47 m at the depth of 9 km however there is no distinct slip associated with the mw 5 6 main shock the insar determined moment is 2 36 1018 nm with a rigidity of 30 gpa equivalent to mw 6 2 which is about twofold the total seismic moment of all the recorded earthquakes during the insar time span this large discrepancy between geodetic and seismic moment estimates indicates that there was probably rapid aseismic afterslip in the 2 weeks following the mw 5 9 main shock the released seismic energy of this earthquake sequence is far less than the accumulated strain energy since the 1955 m 712 earthquake on the same fault branch which implies that the seismic risk on the selaha kangding segment of the xianshuihe fault remains high

arrest and recovery of frictional creep on the southern hayward fault triggered by the 1989 loma prieta california earthquake and implications for future earthquakes 1 theodolite measurements across the right lateral hayward fault san francisco bay california show a dramatic reduction in surface creep rate from 5 to 10 mm yr before the 1989 loma prieta earthquake to nearly zero creep rate after the earthquake a 6 year period of nearly zero surface creep was followed by sudden fault creep that accumulated about 20 25 mm of right lateral displacement followed by an eventual return to a steady creep by year 2000 this creep behavior can be explained as a result of a sudden shear stress reduction on the fault and is consistent with model predictions for a fault imbedded in an elastic medium with slip governed by laboratory derived friction laws we infer friction parameters on the fault using a spring slider model and a boundary element model with the rate and state dependent friction laws the state healing term in the friction law is critical for reproducing the observed evolution of surface creep a popular simplified rate dependent friction law is insufficient results suggest that the creep event extended to a depth of 4 7 5 km the inferred critical slip distance dc is 1 2 orders of magnitude larger than lab values and inferred a values imply low effective fault normal stresses of 5 30 mpa this range of effective normal stress and inversion results for a b imply very small values for a b of 10 5 to 10 3 suggesting the fault has nearly velocity neutral frictional properties earthquake simulations with such small a b values show that creeping areas on the hayward fault may be capable of rupturing during earthquakes

estimation of seismic and aseismic deformation in mexicali valley baja california mexico in the 2006 2009 period using precise leveling dinsar geotechnical instruments data and modeling ground deformation and seismicity in mexicali valley baja california mexico the southern part of the mexicali imperial valley are influenced by active tectonics and human activity in this study data from two successive leveling surveys in 2006 and 2009 2010 are used to estimate the total deformation occurred in mexicali valley during 2006 2009 the leveling data span more than 3 5 years and include deformation from several natural and anthropogenic sources that acted at different temporal and spatial scales during the analyzed period because of its large magnitude the aseismic anthropogenic deformation caused by fluid extraction in the cerro prieto geothermal field obscures the deformation caused by other mechanisms and sources the method of differential interferograms stacking was used to estimate the aseismic interseismic tectonic and anthropogenic components of the observed displacement using sar images taken in 2007 during a period when no significant seismicity occurred in the study area after removing the estimated aseismic signal from the leveling data residual vertical displacement remained and to identify possible sources and mechanisms of this displacement a detailed analysis of records from tiltmeters and creepmeters was performed the results of this analysis suggest that the residual displacement is mainly caused by moderate sized seismicity in the area of study modeling of the vertical ground deformation caused by the coseismic slip on source fault primary mechanism of the two most important earthquakes may 24 2006 mw 5 4 and december 30 2009 mw 5 8 was performed the modeling results together with the analysis of geotechnical instruments data suggests that this moderate sized seismicity influences the deformation in the study area by coseismic slip on the source fault triggered slip on secondary faults and soft sediments deformation

long term monitoring of creep rate along the hayward fault and evidence for a lasting creep response to 1989 loma prieta earthquake we present results from over 30 yr of precise surveys of creep along the hayward fault along most of the fault spatial variability in long term creep rates is well determined by these data and can help constrain 3d models of the depth of the creeping zone however creep at the south end of the fault stopped completely for more than 6 years after the m7 1989 loma prieta earthquake lpeq perhaps delayed by stress drop imposed by this event with a decade of detailed data before lpeq and a decade after it we report that creep response to that event does indeed indicate the expected deficit in creep

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

large scale right slip displacement on the east san francisco bay region fault system california implications for location of late miocene to pliocene pacific plate boundary a belt of northwardly younging neogene and quaternary volcanic rocks and hydrothermal vein systems together with a distinctive cretaceous terrane of the franciscan complex the permanente terrane exhibits about 160 to 170 km of cumulative dextral offset across faults of the east san francisco bay region esfbr fault system the offset hydrothermal veins and volcanic rocks range in age from 01 ma at the northwest end to about 17 6 ma at the southeast end in the fault block between the san andreas and esfbr fault systems where volcanic rocks are scarce hydrothermal vein system ages clearly indicate that the northward younging thermal overprint affected these rocks beginning about 18 ma the age progression of these volcanic rocks and hydrothermal vein systems is consistent with previously proposed models that relate northward propagation of the san andreas transform to the opening of an asthenospheric window beneath the north american plate margin in the wake of subducting lithosphere the similarity in the amount of offset of the permanente terrane across the esfbr fault system to that derived by restoring continuity in the northward younging age progression of volcanic rocks and hydrothermal veins suggests a model in which 80 110 km of offset are taken up 8 to 6 ma on a fault aligned with the bloomfield tolay franklin concord sunol calaveras faults an additional 50 70 km of cumulative slip are taken up 6 ma by the rogers creek hayward and concord franklin sunol calaveras faults an alternative model in which the permanente terrane is offset about 80 km by pre miocene faults does not adequately restore the distribution of 8 12 ma volcanic rocks and hydrothermal veins to a single northwardly younging age trend if 80 110 km of slip was taken up by the esfbr fault system between 8 and 6 ma dextral slip rates were 40 55 mm yr such high rates might occur if the esfbr fault system rather than the san andreas fault acted as the transform margin at this time major transpression across the boundary between the pacific and north american plates at about 3 to 5 ma would have resulted in the transfer of significant slip back to the san francisco peninsula segment of the san andreas fault since that time the esfbr fault system has continued to slip at rates of 11 14 mm yr if this interpretation is valid the esfbr fault system was the pacific north american plate boundary between 8 and 6 ma and this boundary has migrated both eastward and westward with time in response to changing plate margin geometry and plate motions

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

under the hood of the earthquake machine toward predictive modeling of the seismic cycle advances in observational laboratory and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power to explore that possibility we developed an integrative and fully dynamic model of the parkfield segment of the san andreas fault the model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude m w 6 0 main shocks including events similar to the ones in 1966 and 2004 and provides an excellent match for the detailed interseismic coseismic and postseismic observations collected along this fault during the most recent earthquake cycle such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins

spatial and temporal variations in creep rate along the el pilar fault at the caribbean south american plate boundary venezuela from insar in eastern venezuela the caribbean south american plate boundary follows the el pilar fault system previous studies based on three gps campaigns 2003 2005 2013 demonstrated that the el pilar fault accommodates the whole relative displacement between the two tectonic plates 20 mm yr and proposed that 50 60 of the slip is aseismic jouanne et al 2011 reinoza et al 2015 in order to quantify the possible variations of the aseismic creep in time and space we conducted an insar time series analysis using the nsbas method on 18 images from the alos 1 satellite spanning the 2007 2011 period during this 3 5 year period insar observations show that aseismic slip decreases eastwards along the fault the creep rate of the western segment reaches 25 3 9 4 mm yr on average compared to 13 4 6 9 mm yr on average for the eastern segment this is interpreted through slip distribution models as being related to coupled and un coupled areas between the surface and ca 20 km in depth insar observations also show significant temporal creep rate variations accelerations during the considered time span along the western segment the transient behavior of the creep is not consistent with typical postseismic afterslip following the 1997 ms 6 8 earthquake the creep is thus interpreted as persistent aseismic slip during an interseismic period which have a pulse or transient like behavior

frictional properties and 3 d stress analysis of the southern alpine fault new zealand abstract new zealand s alpine fault af ruptures quasi periodically in large magnitude earthquakes paleoseismological evidence suggests that about half of all recognized af earthquakes terminated at the boundary between the central and south westland sections of the fault there fault geometry and the polarity of uplift change the south westland af exhibits oblique normal fault motion on a structure oriented 052 82 se that for at least 35 km along strike contains saponite rich principal slip zone gouges new hydrothermal friction experiments reveal that the saponite fault gouge is frictionally weak exhibiting friction coefficients between 0 12 and 0 16 for a range of temperatures t 25 210 c and effective normal stresses n 31 2 93 6 mpa the saponite gouge is rate strengthening in all velocity steps performed at velocities between 0 01 and 3 0 m s behavior conducive to aseismic creep a three dimensional stress analysis shows that the south westland af is favorably oriented with respect to the regional stress field for slip within the frictionally weak saponite fault gouge geometrically the fault is severely misoriented for slip in any fault forming materials with friction coefficients exceeding 0 5 the combination of weak gouges prone to aseismic creep strong asperities and low resolved shear stress may impede earthquake rupture propagation along the south westland alpine fault

coseismic and postseismic deformation due to the 2007 m5 5 ghazaband fault earthquake balochistan pakistan time series analysis of interferometric synthetic aperture radar data reveals coseismic and postseismic surface displacements associated with the 2007 m5 5 earthquake along the southern ghazaband fault a major but little studied fault in pakistan modeling indicates that the coseismic surface deformation was caused by 9 cm of strike slip displacement along a shallow subvertical fault the earthquake was followed by at least 1 year of afterslip releasing 70 of the moment of the main event equivalent to a m5 4 earthquake this high aseismic relative to the seismic moment release is consistent with previous observations for moderate earthquakes m 6 and suggests that smaller earthquakes are associated with a higher aseismic relative to seismic moment release than larger earthquakes

surface creep on the north anatolian fault at ismetpasa turkey 1944 2016 we re evaluate the 72 year history of surface slip on the north anatolian fault at ismetpasa since the mw 7 4 1944 bolu gerede earthquake a revised analysis of published observations suggests that days after the earthquake the fault had been offset by 3 7 m and 6 years later by an additional 0 74 m creep was first recognized on the fault in 1969 as a 0 13 m offset of a wall constructed in 1957 that now 2016 has been offset by 0 52 m a carbon rod creep meter operated across the fault in the past two years confirms results from an invar wire creep meter operated 1982 1991 that surface slip is episodic months of fault inactivity are interrupted by slow slip 10 m day or multiple creep events with cumulative amplitudes of 2 10 mm durations of several weeks and with slip rates briefly exceeding 2 5 mm hour creep events accommodate 80 of the surface slip and individually release 10 6 shear strain on the flanks of the uppermost 3 7 km of the fault gps and insar methods yield a current fault slip rate of 7 6 1 mm yr suggesting that creep meters incompletely sample the full width of the surface shear zone the slip rate has slowed from 10 mm yr in 1969 to 6 1 mm year at present 4 65 mm yr of which appears to be due to steady interseismic creep driven by plate boundary stressing rates we calculate that a further 1 m of aseismic surface slip will precede the next major earthquake on the fault assuming a 260 year mainshock recurrence interval on this segment

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

thermal evolution of coastal california with application to hydrocarbon maturation coastal california has evolved through a series of plate tectonic interactions that significantly affected the geologic thermal and hydrocarbon maturation histories of the area numerical solutions for steady state heat transfer are used to estimate temperature suppression resulting from plate subduction along coastal california and to model thermal refraction within the pismo basin numerical solutions for time dependent heat transfer estimate the thermal effect of the passage of the mendocino triple junction with consequent upwelling of asthenosphere thermal solutions vary for different areas along coastal california depending on the magnitude of the temperature suppression due to subduction the geometry of the space into which the asthenosphere upwells the time s nce passage of the triple junction and the specific depositional history of each basin paleo temperatures are calculated for the pismo basin predicting that the basal 300 m of source rocks have generated hydrocarbons

present day kinematic behaviour of active faults in the eastern alps abstract the neogene to quaternary lateral extrusion of the eastern alps towards the pannonian basin is accommodated by a system of strike slip faults despite decades lasting gps observations no information on contemporary kinematic behaviour of these faults has been available therefore we had monitored subsidiary and or conjugated faults associated to these major fault systems in six caves throughout the eastern alps over a 1 5 2 5 year observation period by means of high resolution three dimensional moire extensometers tm71 we confirmed that the monitored faults revealed present day aseismic displacements at a micrometer level during several activity phases that usually also coincided with periods of increased local seismicity the annual displacement rates of the monitored faults were mostly about an order of magnitude smaller than the rates of the entire crustal wedges revealed from gnss the particular displacements consisted of a variety mechanisms and faulting regimes fault dilations and compressions were mostly associated with thermal volumetric variations normal dip slips and downward hanging wall displacements originated due to gravitational relaxation or mass movement displacements with the same mechanisms as the geologically documented fault systems or with an upward component were attributed to tectonic creep and strain built up during the interseismic period on the other hand the countervailing displacements opposite to the master fault kinematics were most probably caused by elastic rebound they were usually registered few days in advance to distinct local earthquakes that were simultaneously activated at locked segments within the same deformation band therefore the countervailing events could be considered an indicator of impending near earthquake within the rebound zone their better understanding and real time detecting could be a step forward to an effective earthquake early warning in similar geological settings

earthquake rupture propagation inferred from the spatial distribution of fault rock frictional properties abstract the frictional properties of fault rocks that rupture during earthquakes are expected to affect the nucleation and propagation of seismic slip but these properties and their variation under in situ earthquake conditions are typically unknown here we present experimental results on the variation of frictional properties of fault rocks from the alhama de murcia fault amf in se spain which ruptured in the 2011 lorca earthquake in the epicentral area the fault zone is characterized by the presence of abundant phyllosilicate rich gouges that surround more competent fractured lenses of the phyllitic basement measurements of lineaments and orientations of r shears in the gouges are consistent with cmt solutions of the 2011 lorca earthquake suggesting that the bulk of displacement on the amf was accommodated within similar gouges at depth in order to evaluate the frictional properties of the fault rocks of the amf we performed rotary shear experiments under hydrothermal conditions of samples obtained from surface outcrops of the amf zone progressively simulating deeper levels in the crust by stepping temperature effective normal stress and fluid pressure a negative velocity dependence of friction expressed as a negative value of the rate and state friction rsf parameter a b and which is a prerequisite for the nucleation of an instability was observed only for samples derived from competent lenses under hydrothermal conditions gouge derived samples exhibited only velocity strengthening properties i e positive values of a b which increase with deeper conditions in particular with increasing effective normal stress combined with our outcrop observation of the anastomosing nature of gouges surrounding more competent lenses of fractured protolith our results suggest that the 2011 lorca earthquake nucleated in the competent lenses followed by propagation of slip into the frictionally weaker gouges the inferred upward propagation direction of the 2011 lorca earthquake is consistent with propagation of the rupture into the velocity strengthening gouges which at shallower levels provide a smaller barrier to seismic slip due to lower values of effective normal stress and a b our results suggest that the spatial variation of the frictional properties along the amf was an important factor controlling the nucleation and propagation of seismic slip which together with the shallow hypocenter close to the city of lorca led to serious damage we infer that understanding of such variations in frictional properties may significantly improve seismic hazard evaluations in tectonically active regions

an aseismic slip transient on the north anatolian fault constellations of synthetic aperture radar sar satellites with short repeat time acquisitions allow exploration of active faults behavior with unprecedented temporal resolution along the north anatolian fault naf in turkey an 80 km long section has been creeping at least since the 1944 m w 7 3 earthquake near ismetpasa with a current interferometric synthetic aperture radar insar derived average creep rate of 8 3 mm yr i e a third of the naf long term slip rate we use a dense set of sar images acquired by the cosmo skymed constellation to quantify the spatial distribution and temporal evolution of creep over 1 year we identify a major burst of aseismic slip spanning 31 days with a maximum slip of 2 cm between the surface and 4 km depth this result shows that fault creep along this section of the naf does not occur at a steady rate as previously thought highlighting a need to revise our understanding of the underlying fault mechanics

fault slip in southern california measurements of slip on major faults in southern california have been performed over the past 18 yr using principally theodolite alignment arrays and tautwire extensometers they provide geodetic control within a few hundred meters of the fault traces which complements measurements made by other techniques at larger distances approximately constant slip rates of from 0 5 to 5 mm yr over periods of several years have been found for the southwestern portion of the garlock fault the banning and san andreas faults in the coachella valley the coyote creek fault the superstition hills fault and an unnamed fault 20 km west of el centro these slip rates are typically an order of magnitude below displacement rates that have been geodetically measured between points at greater distances from the fault traces exponentially decaying postseismic slip in the horizontal and vertical directions due to the 1979 imperial valley earthquake has been measured it is similar in magnitude to the coseismic displacements analysis of seismic activity adjacent to slipping faults has shown that accumulated seismic moment is insufficient to explain either the constant or the decaying postseismic slip thus the mechanism of motion may differ from that of slipping faults in central california which move at rates close to the plate motion and are accompanied by sufficient seismic moment seismic activity removed from the slipping faults in southern california may be driving their relatively aseismic motion

talc bearing serpentinite and the creeping section of the san andreas fault the section of the san andreas fault located between cholame valley and san juan bautista in central california creeps at a rate as high as 28 mm yr 1 ref 1 and it is also the segment that yields the best evidence for being a weak fault embedded in a strong crust serpentinized ultramafic rocks have been associated with creeping faults in central and northern california and serpentinite is commonly invoked as the cause of the creep and the low strength of this section of the san andreas fault however the frictional strengths of serpentine minerals are too high to satisfy the limitations on fault strength and these minerals also have the potential for unstable slip under some conditions here we report the discovery of talc in cuttings of serpentinite collected from the probable active trace of the san andreas fault that was intersected during drilling of the san andreas fault observatory at depth safod main hole in 2005 we infer that the talc is forming as a result of the reaction of serpentine minerals with silica saturated hydrothermal fluids that migrate up the fault zone and the talc commonly occurs in sheared serpentinite this discovery is significant as the frictional strength of talc at elevated temperatures is sufficiently low to meet the constraints on the shear strength of the fault and its inherently stable sliding behaviour is consistent with fault creep talc may therefore provide the connection between serpentinite and creep in the san andreas fault if shear at depth can become localized along a talc rich principal slip surface within serpentinite entrained in the fault zone

thermal modeling of the geometry of subduction with implications for the tectonics of the overriding plate the path which subducting lithosphere follows can be broken into three zones zone i a subhorizontal region of nearly constant dip near the trench zone ii a region of rapidly increasing dip and zone iii a region generally deeper than 125 km again of nearly constant dip we have modeled the thermal evolution of slabs as they pass through these three zones using the method of lines a numerical technique well suited to the solution of time dependent partial differential equations by use of appropriate initial conditions and time dependent boundary conditions we can simulate subduction with variations in age of subducting lithosphere slab velocities and paths followed by the slab thermal modeling results indicate that the geometry of the slab in region ii can be empirically related directly to the thermal structure of the slab in that region and thus indirectly to age and velocity it follows that low angle subduction can extend several hundred kilometers inland only in cases of high convergent velocities 15 cm yr 1 and old 120 m y lithosphere we further suggest that rapid variations in the convergence velocities can provide an enabling mechanism for back arc spreading while slow changes in convergence velocities and or age variations in the subducting lithosphere lead to migration of volcanic arcs

relationships between thermal maturity indices calculated using arrhenius equation and lopatin method implications for petroleum exploration thermal maturity can be calculated with time temperature indices tti based on the arrhenius equation using kinetics applicable to a range of types ii and iii kerogens these ttis are compared with tti calculations based on the lopatin method and are related theoretically and empirically via vitrinite reflectance to the petroleum generation window the ttis for both methods are expressed mathematically as integrals of temperature combined with variable linear heating rates for selected temperature intervals heating rates control the thermal maturation trends of buried sediments relative to arrhenius ttis lopatin ttis tend to underestimate thermal maturity at high heating rates and overestimate it as low heating rates complex burial histories applicable to a range of tectonic environments illustrate the different exploration decisions that might be made on the basis of independent results of these two thermal maturation models

integrating strike slip tectonism with three dimensional basin and petroleum system analysis of the salinas basin california the salinas basin is a strike slip basin in central california with stratigraphy dominantly composed of miocene monterey formation despite a long history of oil production aspects of petroleum system development in the basin remain poorly understood of the seven main oil fields one san ardo field has produced more than 500 million bbl of oil or 99 of all oil found in the basin the evolution of this basin was profoundly influenced by strike slip movement on the rinconada fault which bisected the depocenter beginning circa 15 ma to address the influence of strike slip motion on petroleum system development we constructed a three dimensional 3 d basin and petroleum system model that incorporates strike slip displacement seismic reflection profiles from a 3 d survey reveal four main tectonic stages that correspond to events in petroleum system evolution petroleum generation from type ii kerogen source rock began circa 11 ma approximately 4 m y after strike slip faulting began to offset a once contiguous sedimentary depocenter two separate petroleum provinces an eastern one and a western one developed and the fault zone likely was a conduit for petroleum if nonsealing most accumulated petroleum was derived from the eastern pod of active source rock because of greater sedimentary burial east of the fault our model roughly replicates the skewed distribution in oil field size factors controlling field size distribution include trap size and connectivity to source

an efficient numerical method for earthquake cycles in heterogeneous media alternating subbasin and surface rupturing events on faults crossing a sedimentary basin we present an efficient numerical method for earthquake cycle simulations that employs a finite difference discretization of the off fault material to accommodate spatially variable elastic properties the method is developed for the two dimensional antiplane shear problem of a vertical strike slip fault with rate and state friction we compare earthquake cycles in a homogeneous half space with those in which the upper portion of the fault cuts through a sedimentary basin in both cases we assume velocity weakening behavior over the full seismogenic depth even in the basin to isolate the influence of elastic heterogeneity in a homogeneous half space events rupturing the full seismogenic depth occur periodically event sequences are more complex in basin models with one or several subbasin events confined to the lower section of the fault followed by a much larger surface rupturing event that breaks through the basin this phenomenology emerges only for sufficiently compliant and deep basins predicted surface velocities are essentially identical before subbasin events and surface rupturing events suggesting that geodetic observations would not be useful in predicting the rupture mode the alternating sequence of subbasin and surface rupturing events would complicate interpretation of paleoseismic data our results also offer one potential explanation for the shallow slip deficit observed in many recent earthquakes namely that these events which lack appreciable surface slip are simply one style of rupture subsequent events on these faults might be larger with slip extending all the way to the surface the 1940 mw 7 0 and 1979 mw 6 5 imperial valley events might be considered as examples of these two rupture styles

thermal history of alberta deep basin comparative study of fluid inclusion and vitrinite reflectance data the thermal history of the alberta deep basin the gas saturated westernmost part of the western canadian sedimentary basin has been studied by analyzing aqueous and hydrocarbon fluid inclusions in diagenetic cements and comparing the results with coal maturity data results indicate that most of the diagenetic quartz druse precipitated from low salinity fluids 2 3 wt at a temperature of 170 195 c calcite cement precipitated after quartz druse during uplift and cooling at temperatures of 108 169 c inclusions rich in larger hydrocarbon molecules occur in cements that precipitated at 150 c whereas methane rich inclusions occur in cements that precipitated at 165 c or at lower temperatures after significant uplift and cooling of the b sin maximum burial temperatures tmb calculated from vitrinite reflectance data using the lopatin waples tti ro calibration are significantly lower 150 c than the temperature at which quartz druse precipitated in the same area 190 c an equation directly relating tmb and ro proposed by barker and pawlewicz in 1986 yields maximum burial temperatures 200 210 c only slightly higher than the fluid temperatures the results from this study suggest that hot fluids migrated updip along permeable conglomerates and bedding plane fractures to produce unexpectedly high geothermal gradients 38 c km in the western part of the study area the apparent restriction of hot fluids to the western part of the study area sugge ts that convective heat transfer by fluids may have operated on a scale of only tens of kilometers in lower cretaceous rocks of the alberta deep basin

episodic creep events on the san andreas fault caused by pore pressure variations recent seismic and geodetic observations indicate that interseismic creep rate varies in both time and space the spatial extent of creep pinpoints locked asperities while its temporary accelerations known as slow slip events may trigger earthquakes although the conditions promoting fault creep are well studied the mechanisms for initiating episodic slow slip events are enigmatic here we investigate surface deformation measured by radar interferometry along the central san andreas fault between 2003 and 2010 to constrain the temporal evolution of creep we show that slow slip events are ensembles of localized creep bursts that aseismically rupture isolated fault compartments using a rate and state friction model we show that effective normal stress is temporally variable on the fault and support this using seismic observations we propose that compaction driven elevated pore fluid pressure in hydraulically isolated fault zone and subsequent frictional dilation cause the observed slow slip episodes we further suggest that the 2004 mw6 parkfield earthquake might have been triggered by a slow slip event which increased the coulomb failure stress by up to 0 45 bar per year this implies that while creeping segments are suggested to act as seismic rupture barriers slow slip events on these zones might promote seismicity on adjacent locked segments

seismicity along st lawrence paleorift faults overprinted by a meteorite impact structure in charlevoix quebec eastern canada abstract the charlevoix seismic zone csz in quebec has the highest number of earthquakes in eastern canada with cataloged events diffusely distributed between the st lawrence paleorift faults in this study we relocate 1242 out of 1639 earthquakes in the csz from 1988 to 2010 using double difference relocations with phase arrivals from manual picks and waveform cross correlations and requiring a strict set of quality control criteria our results show a diffuse distribution of earthquakes beneath the st lawrence river within a meteorite impact structure and clear lineations of event hypocenters outside the inner boundary of the impact structure the diffuse seismicity distribution coupled with a lower cumulative seismic moment within the impact structure despite a higher number of events suggests the presence of highly fractured crust and weakened pre existing faults a lack of m n 4 0 earthquakes and a wide variation of focal mechanism p axis orientations also provide evidence for weakened pre existing faults relocated earthquakes beneath the north shore of the st lawrence river illuminate a broad southeast trending linear structure suggesting the geometry of the gouffre northwest river fault a paucity of seismicity between the north shore and the river may correspond to fault controlled basins of unconsolidated sediments at the surface and volumes of high seismic velocity material at midcrustal depths online material earthquake catalogs

lithospheric behavior with triple junction migration an example based on the mendocino triple junction abstract the northward migration of the mendocino triple junction along the western margin of the north american plate produces a region of thin lithosphere in association with the growth of the san andreas transform numerical modeling of the resultant thermal regime in conjunction with modeling of the mechanical response of the region indicate the role of lithospheric thinning in the tectonism along the western margin of north america the geometry of the region of thin lithosphere is inherited from the previous subduction regime with resulting implications for the mechanical response the elevation of the california coast ranges is maintained primarily by flexure from buoyant loading from below additionally sporadic volcanism associated with the passage of the triple junction is a likely consequence of super solidus mantle emplaced at shallow depths after the removal of the subducting slab

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

source scaling relations and along strike segmentation of slow slip events in a 3 d subduction fault model scaling between slip event duration and equivalent moment is diagnostic of the underlying physics of rupture process for episodic slow slip events sses in subduction zones their moment duration relation is not clearly defined and shows considerable variation among individual margins where multiple episodes of sses are geodetically detected here i set up a 3 d planar thrust fault model within the framework of rate state friction to study the spatiotemporal evolution of slip and stress during sses sse source properties including along strike length duration equivalent moment and stress drop are quantified and their scaling relations are compared to observations modeled sses have nearly constant stress drops of 0 001 to 0 01 mpa due to near lithostatic pore pressure at the sse depths the modeled moment duration scaling is between 1 linear and 2 squared when multiple sses appear simultaneously along the strike the stress interaction between approaching slip fronts results in higher average propagation speeds for longer lengths which leads to a scaling close to 2 when sses are well offset in space and time stress interaction is negligible and the scaling is close to 1 two types of sse along strike segmentation gaps are identified from model results the primary gaps are persistent segmentation boundaries due to along strike variation of effective normal stress while the secondary gaps evolve through sse cycles and reflect the stress condition within a primary segment this implies that some geodetically inferred sse segmentation boundaries may result from slower slip velocities below the resolution limits of geodetic inversion models

slow slip slow earthquakes period two cycles full and partial ruptures and deterministic chaos in a single asperity fault abstract the assimilation of geological geophysical and laboratory data in physics based models of fault dynamics promises increasingly realistic simulations of the seismic cycle to assist this effort i explore the dynamics of a single velocity weakening asperity to delineate the relationship between a fault physical properties and the style of faulting during the seismic cycle based on a micro physical model of rate and state friction from a dimensional analysis four non dimensional parameters control the characteristics of slip events and the behavior during the interseismic period including the dieterich ruina rice number ru which is proportional to the ratio of asperity to critical nucleation size w h and rb b a b where a and b control the direct and local evolutionary effects respectively for sufficiently large rb the ru number controls the spectrum of fault slip from periodic slow slip events to aperiodic fast ruptures in finite faults but not in semi infinite faults the transition between these end members includes a bifurcation that involves period two period four period six cycles and deterministic chaos with increasing ru macroscopic fault slip is stabilized as rb vanishes even as ru 1 for finite faults but not for semi infinite faults the transition between slow and fast ruptures for increasing rb includes another type of bifurcation with period two and period four cycles of slow and fast ruptures for 0

characteristics of short period wavelike features near 87 km altitude from airglow and lidar observations over maui 1 small scale less than 15 km horizontal wavelength wavelike structures known as ripples are a common occurrence in oh airglow images recent case studies attribute their origin to the presence of either convective or dynamical instabilities however little is known about their frequency of occurrence and period the maui malt observatory located at mt haleakala is instrumented with a na wind temperature lidar which allows the determination of whether the atmosphere is dynamically or convectively unstable and a fast oh airglow camera which takes images every 3 s with a sensitivity high enough to see the ripples this study reports on 2 months of observations in october november 2003 and in august 2004 eight nights of which also included na lidar measurements the imager results suggest that instability features occur in the 85 to 90 km region of the atmosphere for around 20 of the time the nominal observed period for the ripples is between 2 and 4 min while there are clear night to night variations the average observed period is similar for both the 2003 and 2004 observations in addition a few of the small scale structures are not ripples caused by instabilities but rather have features consistent with their being short horizontal wavelength evanescent waves their fractional intensity fluctuations are as large or larger than those of the ripple instabilities unlike the instabilities the origin of the evanescent waves is not determined

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event

increase of creep interevent intervals a conceptual model abstract creep event sequences on shallow faults are studied here by means of a one dimensional fault model assuming that the aseismic section is extended from the surface down to few hundreds metres depth the sequences of creep events on a fault are qualitatively described in terms of sequences of stick slip movements relaxation oscillations of a spring block system with very low velocity peaks the model is based on the nonlinear rate and state dependent frictional properties of faults where time dependent coefficients can be considered during this study it was necessary to define the properties of friction at low velocity thereby avoiding the singularity implied by previous formulations in order to study the deformations near the fault the effect of rock elastic nonlinearity is modeled by ascribing a nonlinear elastic characteristic to the spring of the model if the system parameters do not depend explicitly on time the system undergoes relaxation oscillations with a constant period a temporal variation of the fault parameters can be successfully used in order to explain increasing intervals of time between velocity peaks in creep event sequences in particular allowing the sliding section to extend with time provides an increase in the intervals between creep events

laboratory micro seismic signature of shear faulting and fault slip in shale this article reports the results of a triaxial deformation experiment conducted on a transversely isotropic shale specimen this specimen was instrumented with ultrasonic transducers to monitor the evolution of the micro seismic activity induced by shear faulting triaxial failure and subsequent fault slip at two different rates the strain data demonstrate the anisotropy of the mechanical quasi static compliance of the shale the p wave velocity data demonstrate the anisotropy of the elastic dynamic compliance of the shale the spatio temporal evolution of the micro seismic activity suggests the development of two distinct but overlapping shear faults a feature similar to relay ramps observed in large scale structural geology the shear faulting of the shale specimen appears quasi aseismic at least in the 0 5 mhz range of sensitivity of the ultrasonic transducers used in the experiment concomitantly the rate of micro seismic activity is strongly correlated with the imposed slip rate and the evolution of the axial stress the moment tensor inversion of the focal mechanism of the high quality micro seismic events recorded suggests a transition from a non shear dominated to a shear dominated micro seismic activity when the rock evolves from initial failure to larger and faster slip along the fault the frictional behaviour of the shear faults highlights the possible interactions between small asperities and slow slip of a velocity strengthening fault which could be considered as a realistic experimental analogue of natural observations of non volcanic tremors and very low frequency earthquakes triggered by slow slip events

surface slip subsequent to the 24 november 1987 superstition hills california earthquake monitored by digital creepmeters three creepmeters of new design were operated on the superstition hills fault following the 24 november 1987 earthquake each creepmeter consists of a digital displacement sensor interrogated periodically by a computer at the end of each hour the computer determines a recording rate appropriate to the velocity of the slip on the fault in that hour no data are recorded if the fault is inactive data are recorded at a maximum rate of one sample per minute if slip on the fault is detected the resolution and range of the creepmeters are 10 m and 15 cm respectively fault activity is observed to be confined to periods of episodic slip creep events with mean amplitudes 3 to 6 mm and durations less than 4 hr a total of 80 creep events were recorded during the first week following the earthquake creep events occurred several times each day after 6 months events occurred every 3 weeks this increase in the mean time interval between creep events results in the observed decay in afterslip rate between creep events the fault is inactive although more than 200 microstrain of fault zone deformation may accumulate before each event although creep events were observed to propagate unilaterally in both directions along the fault the most impulsive events appeared to propagate bilaterally from a dilatant offset separating the northern and southern halves of the 24 km long fault zone maximum propagation velocities of 30 m sec were observed aftershocks 2 m 4 7 were observed to occur near the creepmeters following 6 to 9 cm of surface slip on the fault a future aftershock in this region is anticipated in mid 1989 based on afterslip rates in the year following the main shock

continental margin tectonics submarine accretionary prisms submarine accretionary prisms are sites of incipient mountain building where sediments and rocks of the deep ocean are uplifted deformed and ultimately transformed to continental crust accretionary prisms develop at sites of lithospheric convergence that is subduction zones commonly accretionary prisms form along continental margins although accretionary prisms may also occur adjacent to island arcs which are ultimately coalesced into continental landmasses here we review the studies of submarine accretionary prisms during the past four years with primary focus on the contributions of geoscientists from the united states

a nonplanar slow rupture episode during the 2000 miyakejima dike intrusion magmatic intrusions release extensional strain in the earth s crust upon availability of magma intrusions are typically accompanied by earthquake swarms and by surface faulting that is often larger than what is expected from the magnitude of the induced earthquakes the 2000 miyakejima dike intrusion triggered the largest volcanic earthquake swarm monitored so far with five ml 6 earthquakes we analyze the seismicity and deformation induced by the miyakejima dike with the aim of constraining the timescale and mechanisms of slow strain release during the episode in six earthquake bursts lasting few hours and migrating at 1 km h 1 we find candidates for slow earthquakes each burst nucleated at the tips of previous bursts suggesting stress interaction the variability of fault plane solutions indicates that the bursts occurred on a complex system of fractures consistent with weakly consolidated surface layers strained by spatially inhomogneous stresses that change in time such as those induced by a dike based on dislocation models we find that deformation is best explained by aseismic slip in addition to the seismic burst with a moment 1 3 to 2 3 times larger than the earthquakes seismic moment and opening of 0 20 0 07 m on the dike the aseismic slip occurred over a few hours with moment duration and migration velocity consistent with that of previously observed slow slip events we argue that the seismic bursts are likely driven by slow slip sharing most properties with tectonic slow slip events and swarms but occurring on a set of nonaligned faults

thermal regime from bottom simulating reflectors along the north ecuador south colombia margin relation to margin segmentation and great subduction earthquakes 1 the north ecuador south colombia nesc margin has three transverse morphotectonic segments the manglares tumaco and patia segments each with different tectonic and structural patterns following the 1906 subduction earthquake the nesc margin has been the site of three megathrust events in 1942 1958 and 1979 for which the rupture zones abut one another we first investigated variations in heat flow derived from bottom simulating reflectors bsr observed along multichannel seismic lines sampling the three morphotectonic segments strong along strike variations of the bsr derived heat flow just landward of the deformation front suggest that each morphotectonic segment has a specific thermal regime finite element thermal models show that these variations are mainly produced by changes in the age and the dip of the oceanic plate and local hydrothermal cooling we then examined the relationship between seismogenesis and thermal structure along the plate boundary the updip limits of the 1942 and 1979 seismogenic zones estimated from the aftershock area and rupture zone reach the trench where the temperature at the top of the subducting plate appears to be 50 60 c between these events the seismogenic zone of the 1958 earthquake is restricted to a region landward of a prominent outer basement high where the temperature appears to be 100 120 c we propose that on the nesc margin the updip limit of the seismogenic zone is primarily controlled by low temperature processes except for the 1958 event for which the seismogenic updip limit appears to be related to a structural feature in the upper plate

earthquake supercycles as part of a spectrum of normal fault slip styles like thrust boundaries in subduction zones some normal faults show evidence of temporally transient slip patterns such as temporally clustered earthquakes or periods of elevated creep rate we create rate and state friction numerical models to assess whether typical distributions of frictional parameters can explain transient slip on normal faults we constrain our models with geometry from the wasatch fault zone where 5 10 kyr timescale earthquake clusters are recorded on fault scarps we use numerical models to test whether these earthquake clusters could be the geologic representation of supercycles which we define as long period stress cycles containing multiple seismic cycles field observations laboratory data and analogue experiments suggest that the ratio of velocity weakening to velocity strengthening material varies with the ratio of brittle to ductile material in the shear zone we therefore employ a linear transition of frictional parameters with depth to simulate bulk frictional properties of the shear zone we find that for generalized normal faults rate and state friction predicts a spectrum of slip behaviors including steady aseismic creep aseismic transients clustered earthquakes and regular seismic cycle earthquakes the dominant control on slip behavior is the degree of weakening material in the potentially seismogenic fault patch earthquake clusters occur with higher proportions of velocity weakening material which correspond to more competent less ductile shear zone assemblages we find that rate and state friction predicts a wider spectrum of slip behavior on active normal faults than has been previously recognized potentially due to geologic preservation and identification issues

geologic heterogeneity can produce aseismic slip transients 1 slow slip and tectonic tremor in subduction zones take place at depths where there is abundant evidence for distributed shear over broad zones 10 103 m composed of rocks with marked differences in mechanical properties here we model quasi dynamic rupture along faults composed of material mixtures characterized by different rate and state dependent frictional properties to determine the parameter regime capable of producing slow slip in an idealized subduction zone setting keeping other parameters fixed the relative proportions of velocity weakening vw and velocity strengthening vs materials control the sliding character stable slow or dynamic along the fault the stability boundary between slow and dynamic is accurately described by linear analysis of a double spring slider system with vw and vs blocks our results place bounds on the volume fractions of vw material present in heterogeneous geological assemblages that host slow slip and tremor in subduction zones

dynamic triggering of shallow slip on forearc faults constrained by monitoring surface displacement with the ipoc creepmeter array abstract the m w 8 8 maule earthquake of february 27 2010 remotely triggered minor surface displacement along the atacama fault system in northern chile located 1500 1800 km from the epicenter here we present evidence that surface displacement events recorded by the ipoc integrated plate boundary observatory in n chile creepmeter array are related to earthquakes on the underlying subduction zone interface or to large earthquakes around the world our observations document dynamic triggering of shallow slip on faults in a forearc setting continuous monitoring revealed that up to 30 displacement events per year occur on the monitored fault segments 90 of them triggered by earthquakes in the near or far field synchronous to the passage of the seismic wave we can clearly attribute far field triggering to the passage of the surface wave and near field triggering to the passage of the body wave the most distant triggered displacement event monitored occurred after the 2011 m w 9 0 tohoku oki earthquake located 16 468 km away following the passage of large amplitude ss waves comparing the triggered displacement events with other triggered phenomena like seismicity volcanic eruptions hydrological changes as well as with data from the california creepmeter array we find that the seismic energy density appropriately describes a magnitude distance scaling relationship of slip triggering finally the observed surface displacement is found to not occur by continuous creep but rather through nearly exclusively discrete displacement events

implications of measured thermal gradients for water movement through the northeast japan accretionary prism thermal gradients of 24 36 c km have been found in the slope cover sediments of the accretionary prism off northeast japan deep sea drilling project dsdp sites 438a 439 and 440 these gradients lead to the prediction of temperatures in excess of 400 c at depths of 15 km using an increase in thermal conductivity with depth due to the decrease in porosity such temperatures conflict with the predictions of temperatures of 150 c at even greater depths from conductive thermal models and petrologic studies of low temperature blueschists at similar ancient margins one dimensional steady state conduction and advection via darcian water flow of heat up through the prism was simulated numerically the measured thermal gradients can be reconciled with temperatures less than 125 c at the prism base by water flowing upward at rates of the order of 10 10 m s such velocities imply that the total volume of water available from compaction of sediments subducted beneath the northeast japan prism would flow up through a 10 km width of the prism perpendicular to the trench and would require the dsdp sites to have been located fortuitously over the localized zone s of water flow smaller velocities will reproduce the measured gradients and thus greater widths through which water flow occurs are predicted if the temperature at the prism base is higher and or if the prism is thinner and a subduction channel several kilometers high separates the accreted sediments from the descending plate where water flow is significant as likely wherever abundant water rich sediments are subducted thermal gradients below a few kilometers in accretionary prisms may be much lower than near surface values this has profound implications for the thermal structure of the prism off northeast japan and elsewhere

modulation of fault strength during the seismic cycle by grain size evolution around contact junctions abstract earthquake prediction is fundamentally hampered by insufficient knowledge of the constitutive behavior of faults laboratory and theoretical work by dieterich 1978 and ruina 1983 formed the basis of rate and state friction a constitutive framework that captures the healing and weakening of frictional contacts the rate and state law successfully explains the frictional behavior of a wide range of rocks and many phenomena associated with fault slip the physics underlying the rate and state friction law is not fully understood but it is generally accepted that several micro mechanisms operate depending on the texture maturity fluid content and other physical and kinematic conditions of the fault here i formulate a constitutive framework that unifies a number of laboratory experiments on silicate rocks and the gouges derived from these rocks that describe the effect of grain size temperature real area of contact gouge thickness and fault roughness fundamental to the model is that fault strength is controlled by the area of the interfacial contact junctions that support the shear and normal loads the curvature of asperities weakly controls the area of their contact junction and the resulting fault strength as a result the dynamics of grain size evolution around micro asperities enables the seismic cycle the model quantitatively explains the correlation between the characteristic weakening distance and the gouge thickness marone and kilgore 1993 the correlation of the static friction coefficient with the rate dependence parameters ikari et al 2011 the dependence of frictional resistance to sub solidus temperatures chester 1994 and predicts a range of grain sizes that is compatible with observations at exposed fault zones however the dynamics of grain size evolution is still challenging to verify experimentally the model features a regularization at vanishing slip speeds that implies distinct dynamics at low strength for friction coefficients lower than 0 1 seismic cycle simulations predict the emergence of frictional instabilities with complex source time functions this is a significant departure from the predictions of rate and state friction that is most relevant to the dynamics of decollements serpentinized shear zones and other low strength faults

dynamic triggering of creep events in the salton trough southern california by regional m 5 4 earthquakes constrained by geodetic observations and numerical simulations abstract since a regional earthquake in 1951 shallow creep events on strike slip faults within the salton trough southern california have been triggered at least 10 times by m 5 4 earthquakes within 200 km the high earthquake and creep activity and the long history of digital recording within the salton trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes here we document the history of fault creep events on the superstition hills fault based on data from creepmeters insar and field surveys since 1988 we focus on a subset of these creep events that were triggered by significant nearby earthquakes we model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate and state dependent friction we find that the static stress changes from the causal earthquakes are less than 0 1 mpa and too small to instantaneously trigger creep events in contrast we can reproduce the characteristics of triggered slip with dynamic perturbations alone the instantaneous triggering of creep events depends on the peak and the time integrated amplitudes of the dynamic coulomb stress change based on observations and simulations the stress change amplitude required to trigger a creep event of a 0 01 mm surface slip is about 0 6 mpa this threshold is at least an order of magnitude larger than the reported triggering threshold of non volcanic tremors 2 60 kpa and earthquakes in geothermal fields 5 kpa and near shale gas production sites 0 2 0 4 kpa which may result from differences in effective normal stress fault friction the density of nucleation sites in these systems or triggering mechanisms we conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the superstition hills fault

millimeter level precision in a seafloor geodesy experiment at the discovery transform fault east pacific rise 1 direct path acoustic ranging is a promising seafloor geodetic technique for continuous high resolution monitoring of geodynamical process such as fault slip and magma intrusion here we report on a yearlong acoustic ranging experiment conducted across the discovery transform fault at 4 s on the east pacific rise the ranging instruments utilized a novel acoustic signal designed to enhance precision we find that after correcting for variations in sound speed at the path end points the ranging measurements have a precision of 1 mm over baselines approaching 1 km in length the primary difficulty in this particular experiment was with the physical stability of the benchmarks which were deployed free fall from a ship despite the stability issues it appears that the portion of the transform fault that the array covered was locked during the year of our survey the primary obstacle to continuous high sample rate high precision geodetic monitoring of oceanic ridges and transform faults is now limited to the construction of geodetic monuments that are well anchored into bedrock

effects of subduction parameters on geothermal gradients in forearcs with an application to franciscan subduction in california geothermal gradients in forearcs are often suppressed below normal values because of the cooling effect of the relatively cold downgoing plate in this paper finite difference thermal modeling is used to evaluate the influence on forearc gradients of variations in six potentially important subduction zone parameters variations in forearc radiogenic heat production over the general range likely in forearc rocks 0 to 1 5 10 6 w m 3 cause only minor changes in temperatures at the base of the forearc about 2 to 35 depending on other parameters and thus have relatively little effect on pressure temperature pt conditions of metamorphism however their effect on gradients at shallow levels and thus on surface heat flows may be greater up to about 100 likely variations in forearc thermal conductivity 1 5 to 3 5 w m 1 c 1 similarly change temperatures at the base of the forearc only modestly 10 25 but change surface heat flows more substantially 1 45 1 75 times decreasing the subduction angle from 27 to 3 6 increases gradients by about a factor of 2 at both deep and shallow levels decreasing the subduction rate by a factor of 8 160 to 20 km m y increases gradients by about a factor of 2 when frictional heating at the plate contact is excluded and less when modest amounts of frictional heating are included forearc gradients increase virtually linearly with the presubduction geothermal gradient in the subducting slab and thus are higher above a younger slab when frictional heating is excluded forearc gradients are 2 0 2 8 times higher above a 10 m y old slab than above a 150 m y old slab again the relative effect is lessened when frictional heating is incorporated the amount of frictional heating at the plate contact potentially has the greatest influence on forearc gradients the frictional heat production h is given by h vs where is the shear stress along the plate contact and vs is the subduction rate the modeling shows that forearc gradients increase linearly with unless plate contact shear stresses are only a small fraction of those expected with frictional sliding of dry rocks outer parts of forearcs would be the sites of pervasive low p t metamorphism greenschist facies rather than high p t metamorphism blueschist facies very high fluid pressures along the plate contact are probably the way shear stresses are reduced pressure temperature conditions of blueschist facies metamorphism in the franciscan subduction complex of california are easily explained with typical subduction rates and slab ages with plate contact shear stresses of the order of 10 mpa equivalent to around 3 of lithostatic pressure but stresses within the range zero to a few tens of megapascals are probably permitted by the thermal constraints speculative application of the modeling results assuming a shear stress of 4 of lithostatic pressure to plate motion reconstructions for the franciscan forearc suggests that forearc gradients were about 8 c km around 85 ma when the subducting slab was perhaps 145 m y old and the subduction rate was perhaps 95 km m y gradients increased moderately through the latest cretaceous to middle tertiary as subduction became slower and the subducting slab became younger reaching about 16 c km at 28 ma when the slab age was about 11 m y and the subduction rate was about 48 km m y the slab age subduction rate and forearc gradient then remained fairly constant until 5 ma when subduction slowed to about 32 km m y and the slab age decreased to about 8 m y causing gradients to rise to about 20 c km

dynamics of fault creep observations along the surface traces of active faults in california and elsewhere indicate that tectonic displacement can occur as seismic slip or as aseismic fault creep fault creep occurs as secular displacement and as displacement episodes called creep events which last a few hours to days and include from a millimeter or less to a few tens of millimeters of displacement instrumental measurements of displacement versus time during creep events show that many events have a characteristic simple form including a steep beginning followed by a gradual decay in the rate of displacement some creep events display small amounts of precursory slip and many seem to be composed of several discrete simple events propagation of creep events along the san andreas calaveras and imperial faults in california has been inferred from the nearly simultaneous observation of creep events at nearby creepmeters and from kinematic modeling of continuous measurements of strain during creep events fault creep can be viewed as arising from the interplay of three factors stress applied to the fault from external sources stress caused by the geometry and distribution of displacement on the fault arising from the elastic response of the surrounding medium to the displacements within the anelastic fault zone itself and the constitutive relations characterizing the resistance to slip on the fault analytic solutions are presented for a simple rectangular dislocation quasi static model of nonpropagating fault creep assuming viscous and quasi plastic power law creep fault zone rheology and for a multi element composed of several rectangular or striplike dislocation surfaces quasi static model assuming a viscous rheology viscous rheology implies solutions composed of exponentials that decay with time the simple one element quasi plastic model is in agreement with the form of creep events observed at melendy ranch california a matrix formulation is presented to calculate dislocation stresses on a fault zone in a half space or plate the formulation involves the division of the dislocation surface into strips or rectangles and the use of published solutions to calculate the stress resulting from displacement on each individual element results from the matrix method agree with analytic results for equilibrium displacements on stress free cracks the matrix formulation is then used as the basis for a numerical method to simulate one and two dimensional propagating creep assuming a quasi plastic rheology on the fault zone results from this method agree reasonably well with observations of afterslip from the 1966 parkfield 1975 oroville and 1979 imperial valley california earthquakes and of a propagating creep event observed along the southern calaveras fault central california during july 1977 this method of analysis and the assumption that creep at each point on the fault zone follows a power law rheology after the applied stress reaches a spatially varying yield stress can explain the secular and episodic nature of fault creep afterslip the simple shape of some individual events and the multiple composite shape of others and the propagation of creep events on the southern calaveras fault observations of propagating creep indicate a yield stress near zero at the surface and throughout much of the fault zone however they also indicate the presence of a zone at a depth of about 0 5 km and about 5 km long with a yield stress of about 15 bars 1 5 mpa the methods of solution presented here should be applicable to many problems in the dynamics of faulting

nucleation process of magnitude 2 repeating earthquakes on the san andreas fault predicted by rate and state fault models with safod drill core data recent laboratory shear slip experiments conducted on a nominally flat frictional interface reported the intriguing details of a two phase nucleation of stick slip motion that precedes the dynamic rupture propagation this behavior was subsequently reproduced by a physics based model incorporating laboratory derived rate and state friction laws however applying the laboratory and theoretical results to the nucleation of crustal earthquakes remains challenging due to poorly constrained physical and friction properties of fault zone rocks at seismogenic depths here we apply the same physics based model to simulate the nucleation process of crustal earthquakes using unique data acquired during the san andreas fault observatory at depth safod experiment and new and existing measurements of friction properties of safod drill core samples using this well constrained model we predict what the nucleation phase will look like for magnitude 2 repeating earthquakes on segments of the san andreas fault at a 2 8 km depth we find that despite up to three orders of magnitude difference in the physical and friction parameters and stress conditions the behavior of the modeled nucleation is qualitatively similar to that of laboratory earthquakes with the nucleation consisting of two distinct phases our results further suggest that precursory slow slip associated with the earthquake nucleation phase may be observable in the hours before the occurrence of the magnitude 2 earthquakes by strain measurements close a few hundreds meters to the hypocenter in a position reached by the existing borehole

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

break of slope in earthquake size distribution and creep rate along the san andreas fault system crustal faults accommodate slip either by a succession of earthquakes or continuous slip and in most instances both these seismic and aseismic processes coexist recorded seismicity and geodetic measurements are therefore two complementary data sets that together document ongoing deformation along active tectonic structures here we study the influence of stable sliding on earthquake statistics we show that creep along the san andreas fault is responsible for a break of slope in the earthquake size distribution this slope increases with an increasing creep rate for larger magnitude ranges whereas it shows no systematic dependence on creep rate for smaller magnitude ranges this is interpreted as a deficit of large events under conditions of faster creep where seismic ruptures are less likely to propagate these results suggest that the earthquake size distribution does not only depend on the level of stress but also on the type of deformation

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

slow and fast ruptures on a laboratory fault controlled by loading characteristics recent geodetic observations indicate that a single fault may slip slowly and silently or fast and seismically in different circumstances we report laboratory experiments that demonstrate how the mode of faulting can alternate between fast stick slip events 70 to 500 mm s sliding rates and slow silent events 0 001 to 30 mm s as a result of loading conditions rather than friction properties or stiffness of the loading machine the 760 mm long granite sample is close to the critical nucleation length scale for unstable slip so small variations in nucleation properties result in measurable differences in slip events slow events occur when instability cannot fully nucleate before reaching the sample ends dynamic events occur after long healing times or abrupt increases in loading rate which suggests that these factors shrink the spatial and temporal extents of the nucleation zone arrays of slip strain and ground motion sensors installed on the sample allow us to quantify seismic coupling and study details of premonitory slip and afterslip we find that seismic coupling decreases when slip rates fall below about 70 mm s the slow slip events we observe are primarily aseismic less than 1 of the seismic coupling of faster events and produce swarms of very small m 6 to m 8 events these mechanical and seismic interactions suggest that faults with transitional behavior where creep small earthquakes and tremor are often observed could become seismically coupled if loaded rapidly either by a slow slip front or dynamic rupture of an earthquake that nucleated elsewhere

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

spatiotemporal evolution of slow slip events in a nonplanar fault model for northern cascadia subduction zone slow slip events sses are identified as the quasi stable fault deformation in the deep transition zone from locked to continuous sliding in many subduction zones in the well instrumented cascadia margin a class of mw6 0 slow slip events arise beneath port angeles every 14 months as inferred from two decades of continuous geodetic monitoring the along strike bending of the incoming oceanic plate beneath north washington is a unique geometric feature whose influence on slow slip processes is still unknown here we incorporate a realistic fault geometry of northern cascadia in the framework of rate and state dependent friction law to simulate the spatiotemporal evolution of slow slip events on a nonplanar subduction fault the modeled sses capture the major characteristics revealed by gps observations the central 150 km long fault segment beneath port angeles acts as a repetitive slip patch where sses appear every 1 5 years with a maximum slip of 2 5 cm two minor slip patches with smaller areas and cumulative slips straddle this central slip patch the along strike segmentation of slow slip is inversely related to the local fault dip and strike angles of the slow slip zone suggesting strong geometrical control on the slow slip process this correlation holds even after removing the effect of w h ratio between velocity weakening sse fault width and characteristic nucleation size besides the gps detectable fast spreading phase we find that each sse cycle consists of deep pre sse preparation and post sse relaxation phases which may be the driving mechanism for the deep tremor activity between major sse episodes discovered in cascadia

strong ground motions generated by earthquakes on creeping faults a tenet of earthquake science is that faults are locked in position until they abruptly slip during the sudden strain relieving events that are earthquakes whereas it is expected that locked faults when they finally do slip will produce noticeable ground shaking what is uncertain is how the ground shakes during earthquakes on creeping faults creeping faults are rare throughout much of the earth s continental crust but there is a group of them in the san andreas fault system here we evaluate the strongest ground motions from the largest well recorded earthquakes on creeping faults we find that the peak ground motions generated by the creeping fault earthquakes are similar to the peak ground motions generated by earthquakes on locked faults our findings imply that buildings near creeping faults need to be designed to withstand the same level of shaking as those constructed near locked faults

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

san luis obispo transform fault and middle miocene rotation of the western transverse ranges california a fault disrupted linear belt of lower middle miocene pyroclastic and volcanic rocks was erupted 15 17 m y b p along a trend 140 to 200 km long in the southern coast ranges and along the northern flank of the western transverse ranges of california offset segments of the belt are coincident with the oceanic west huasna santa maria river little pine and lompoc solvang fault zones the volcanic rocks thin eastward and also vary in thickness along strike the latter reflecting the undulation of porpoising highs and lows of basins to account for the linear distribution of over 3000 km2 of bimodal volcanic rock types it is proposed that they were intruded extruded and ejected into a continental submarine margin environment along a feature here named the san luis obispo transform slot the fault was near the mid miocene continental margin and evidently joined the early mid miocene mendocino triple junction with the crest of the east pacific rise subduction of the farallon plate had stopped along the adjacent continental margin before miocene magmatism in this region the inferred position of the east pacific rise crest was too far to the south and the inferred position of the mendocino triple junction was too far to the north between 15 and 20 m y b p to have been directly related to the miocene volcanic event near 35 n latitude at that time a part of the western transverse ranges was transported northwestward immediately following miocene volcanism earlier movement is possible but evidence is inconclusive microplate transport was concurrent with the development of pull apart structures and the 12 to 16 m y old period of volcanism along the southern margin of the microplate within the los angeles basin variable paleomagnetic directions that display clockwise deflections in the oligocene e g morro rock islay hill complex and miocene igneous rocks e g western transverse ranges in the vicinity of slot can be accounted for by extension and rotational tectonics during pull apart development rotation of blocks between faults during the northwestward transport of the western transverse ranges along slot and by rotation and possible northward translation of a part of the western transverse ranges

slow slip evolves into megathrust earthquakes in 2d numerical simulations 1 slow slip events sse in many subduction zones incrementally stress the adjacent locked megathrust suggesting that they could potentially either trigger or evolve into damaging earthquakes we explore this with 2d quasi dynamic simulations with rate state friction dilatancy and coupled 1d pore fluid and heat transport steady state weakening friction allows transient slip to nucleate but is inhibited by dilatant strengthening and destabilized by thermal pressurization sse spontaneously nucleate in low effective stress velocity weakening lesvw regions if the dimension of the lesvw is relatively small the sse are trapped at its updip end imparting a strong stress concentration in the locked zone after several centuries sse penetrate into the region of higher effective stress where thermal pressurization eventually leads to dynamic rupture for larger lesvw regions sse tend to increase in length with time ultimately higher slip speeds enhance thermal weakening leading to dynamic instability within the sse zone in both cases the onset of the ultimate sse is essentially indistinguishable from preceding events

surface creep and slip behavior segmentation along the northwestern xianshuihe fault zone of southwestern china determined from decades of fault crossing short baseline and short level surveys abstract this study examines the 200 km long northwestern xianshuihe fault zone nwxfz southwestern china using more than three decades of geodetic observations from fault crossing short baseline and short leveling surveys at seven sites these data enable estimates of creep rates and depths and examination of the long term slip behavior the surface motion of the nwxfz is dominated by sinistral creep although sinistral transverse and vertical slip components show spatio temporal variations combining these slip variations with data of earthquake rupture coseismic slip seismicity fault geometry and far fault movement velocity and using the velocity and state friction theory our analysis indicates that the surface slip behavior of the nwxfz is segmented along strike the 1973 rupture section of this fault zone exhibits spatio temporally variable slip behavior showing time decaying post 1973 afterslip on the northwestern and southeastern parts of the rupture at depths above 5 8 7 0 km with average sinistral creep rates of 1 3 and 3 5 mm yr respectively but being relocked in the central part of the rupture the 1923 1981 rupture section is generally in locking state with postseismic and interseismic sinistral creep at 1 1 mm yr on its central part at depths above 2 0 2 8 km the 1893 rupture section has been tightly locked without creep since at least the early 1980s the thickness of the shallow velocity strengthening or creep layer and the restraining bend geometry of the nwxfz are the key factors that control spatio temporal variations in surface creep rates two surface observed locked fault portions are located within two different restraining bends in the nwxfz both of which act as compressive asperities and hence have enabled the long term locking of these portions creep along the nwxfz has also been affected to varying degrees by m6 5 mw9 2 earthquakes at distances of 50 3800 km from the fault zone most of these effects have been removed from our estimates of the long term average creep rates