insar analysis of the 2008 reno mogul earthquake swarm evidence for westward migration of walker lane style dextral faulting and post seismic slip over an area of more than 150 km 2 this earthquake is one of the smallest magnitude events modeled with insar to date in the seismically active western basin and range and it provides new insights into regional neotectonic relations inverse modeling of the insar data suggests that the earthquake swarm was generated by 25 75 cm of dextral displacement on a n44wstriking fault with a 3 km rupture length and a rupture depth of 2 km the insar detected strike slip ground deformation is unique for the reno basin which is in the purely extensional domain of the sierra nevada basin and range transition zone an area dominated by north striking normal faults the insar modeling of the 2008 earthquake swarmsupports the concept of westward migration of walker lane transcurrent faulting and overprinting of extensional basin and range structures in this case the westward migration of dextral shear associated with the northern walker lane into the extension dominated reno basin citation bell j w f amelung and c d henry 2012 insar analysis of the 2008 reno mogul earthquake swarm evidence for westward migration of walker lane style dextral faulting geophys res lett 39 l18306 doi 10 1029 2012gl052795

block models of crustal motion in southern california constrained by gps measurements 1 we estimate slip rates on major active faults in southern california using a block model constrained by global positioning system measurements of interseismic deformation the block model includes the effects of block rotation and elastic strain accumulation consistent with a simple model of the earthquake cycle our estimates of the right lateral strike slip rate on the san andreas fault vary by at least a factor of 5 from a high of 35 9 0 5 mm yr in the carrizo plain to a low of 5 1 1 5 mm yr through the san bernadino segment shortening across the puente hills thrust and left lateral slip on the raymond hill fault are consistent with both thickening and escape tectonics in the los angeles basin discrepancies between geodetic and geologic slip rate estimates along the san andreas and san jacinto faults as well as in the eastern california shear zone may be explained by a temporal change in fault system behavior we find no substantial evidence for long term postseismic relaxation and infer that the viscosity of the lower crust upper mantle may be relatively high 1019 pa s

dislocation models of interseismic deformation in the western united states 1 the gps derived crustal velocity field of the western united states is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation the interseismic velocity field is constrained by 1052 gps velocity vectors spanning the 2500 km long plate boundary zone adjacent to the san andreas fault and cascadia subduction zone and extending 1000 km into the plate interior the gps data set is compiled from u s geological survey campaign data plate boundary observatory data and the western u s cordillera velocity field of bennett et al 1999 in the context of viscoelastic cycle models of postearthquake deformation the interseismic velocity field is modeled with a combination of earthquake sources on 100 known faults plus broadly distributed sources models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins viscoelastic relaxation from distributed faulting in the plate interior as well as lateral variations in depth averaged rigidity in the elastic lithosphere resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the san andreas fault saf system primary deformation characteristics are captured along the entire saf system eastern california shear zone walker lane the mendocino triple junction the cascadia margin and the plate interior up to 1000 km from the major plate boundaries

strain partitioning in the northern walker lane western nevada and northeastern california abstract paleomagnetic studies constrain both the kinematics and the timing of neogene intracontinental strain in the walker lane of northwestern nevada northeastern california the northwest trending walker lane is a zone of complex faulting and dextral offset along the boundary between the sierra nevada and the basin and range here an extensive tertiary volcanic section provides a paleomagnetic test for vertical axis rotation the 25 1 ma nine hill tuff covered the two structural domains of northern walker lane and parts of the adjacent provinces in the northernmost domain the pyramid lake domain the nine hill tuff is unrotated or rotated slightly counter clockwise in contrast nine hill tuff is rotated 35 44 clockwise in the northeastern part of the adjacent carson domain usable exposures of the tuff are lacking elsewhere in the carson domain but 9 13 ma basalts record 37 51 clockwise vertical axis rotation these basalts were sampled at three sites encompassing the n s length of the carson domain younger basalts from the carson domain show smaller clockwise rotations the paleomagnetic studies show that the deformation in the northern walker lane is partitioned into domains dominated by translation rotation and extension dextral slip along the walker lane is accommodated primarily by northwestward translation in the pyramid lake domain and by clockwise vertical axis rotation in the carson domain some neogene extension is also accommodated in the walker lane but most of it is occurring to the west of the walker lane along the edge of the sierra nevada comparison of paleomagnetic results from rocks of different ages constrains the timing of the present deformation regime in the walker lane the similar rotations recorded in 25 ma and 9 13 ma rocks indicates that virtually all of the rotation in the carson domain occurred after the eruption of the 9 13 ma basalts smaller rotations recorded in younger rocks constrain rotation rate

constraints from gps measurements on the dynamics of the zone of convergence between arabia and eurasia we investigate the dynamics of deformation in the zone of convergence between the arabian and eurasian plates using a physical model that treats the lithosphere as a thin fluid sheet deforming in response to lateral variations in gravitational potential energy gpe this model has two free material parameters the power law exponent n of the vertically averaged rheology of the lithosphere and the argand number ar which expresses the relative importance of gpe and stresses required to deform the lithosphere with boundary conditions described by three free parameters the model fits the observed deformation as measured by 367 gps velocities with a root mean square residual of 2 4 mm yr we find negligible improvement when variations in material properties are introduced that represent increases or decreases in the lithospheric strength of the central iranian and turkish iranian plateaux and the zagros mountains effective viscosity of the lithosphere ranges from 5 1022 pa s at 10 nanostrain yr to 1022 pa s at 100 nanostrain yr as well as matching the decadal timescale predominantly interseismic strain rates determined from gps the computed distribution of strain rates is also consistent with the distribution and types of earthquake focal mechanism significant historical earthquake activity is seen in regions with strain rates lower than 20 nanostrain yr implying that it is prudent to base assessments of seismic hazard on regional strain rates

transtensional model for the sierra nevada frontal fault system eastern california active strike slip and normal faults along the eastern margin of the sierra nevada primarily accommodate northwestward translation of the sierra nevada central valley i e sierran microplate with respect to stable north america strike slip faults bordering the eastern sierran microplate are subparallel to small circles about the sierra nevada north american euler pole normal faults of the sierra nevada frontal fault system strike 45 clockwise of the small circle trajectories and exhibit well defined left stepping en echelon patterns consistent with formation in dextral transcurrent regime major graben bordering the northeastern sierran microplate are located in regions where the locus of range front deformation steps abruptly eastward in a releasing geometry relative to sierra nevada north american motion crustal shortening occurs at the northern end of the sierran microplate where a component of northwest dextral shear steps westward in a left restraining geometry across the sierran crest to the sacramento valley kinematic inversions of earthquake focal mechanisms from the walker lane belt bordering the eastern sierra nevada indicate that seismogenic deformation primarily is characterized by horizontal shearing and oblique crustal thinning directions of macroscopic dextral shear inferred from the inversions are subparallel to the trajectories of small circles about the sierra nevada north american euler pole normal faulting along most of the eastern sierran range front thus appears to primarily accommodate microplate translation rather than sierran uplift or regional basin and range extension

60 k y record of extension across the western boundary of the basin and range province estimate of slip rates from offset shoreline terraces and a catastrophic slide beneath lake tahoe deformation across three major fault strands within the lake tahoe basin has been mapped by using a novel combination of high resolution seismic chirp airborne laser and acoustic multibeam derived bathymetry and deep and shallow water sediment cores submerged erosional terraces of late pleistocene age 19 2 6 1 8 ka record vertical de formation across fault strands that ranges between 10 and 15 m offset of 10 m is observed across the southern part of the west tahoe fault avalanche deposits from the catastrophic mckinney bay slide ca 60 ka are offset across the stateline fault by at least 21 25 m the submerged shoreline terraces and debris avalanche provide marker beds with which to constrain the extensional history of the region for the past 60 k y this history is then used to assess the future seismic hazard of the region data on deformation across these two important marker beds combined with chronological control from 14 c and optically stimulated luminescence measurements yield an estimate of extension across the lake tahoe basin that is 0 4 0 5 mm yr on the basis of these measurements there exists the potential for a large seiche wave generating m7 earthquake every 3 k y late pleisto cene and holocene vertical deformation rates within the tahoe basin are characteristic of basin and range faulting and place the tahoe basin within the western limits of the extensional basin and range province

block kinematics of the pacific north america plate boundary in the southwestern united states from inversion of gps seismological and geologic data 1 the active deformation of the southwestern united states 30 41 n is represented by a finite number of rotating elastic plastic spherical caps gps derived horizontal velocities geologic fault slip rates transform fault azimuths and earthquake derived fault slip vector azimuths are inverted for block angular velocities creep on block bounding faults permanent strain rates within the blocks and the rotations of 11 published gps velocity fields into to a common north american reference frame gps velocities are considered to be a combination of rigid block rotations recoverable elastic strain rates resulting from friction on block bounding faults and nonrecoverable strain rates resulting from slip on faults within the blocks the resulting pacific north america angular velocity is similar to some published estimates and satisfies transform azimuths and one spreading rate in the gulf of california earthquake slip vectors in the gulf of california and alaska and gps velocities along coastal california and within the pacific basin published fault slip rates are satisfied except in the southern mojave desert where the motion of the mohave block relative to north america is faster than can be explained by mapped faults the largest blocks the sierra nevada great valley and the eastern basin and range show permanent strain rates after removing elastic strain of only a few nanostrain per year demonstrating approximately rigid behavior observed horizontal strain rates correlate strongly with predicted strain rates from known faults suggesting that the short term strains evident in gps velocities are largely elastic in only about 20 of the region is distributed deformation needed to match the data indicating that a plate tectonic style description of the deformation of the western united states is plausible most blocks rotate about vertical axes at approximately the same rate as the pacific relative to north america suggesting that locally spin rates are communicated from block to block arguing against both floating block and ball bearing mechanisms of block rotation the similarities of the blocks spin rates to that of the pacific suggests that the pacific strongly influences their motions through edge tractions however it is shown that the blocks cannot rotate about the pacific north america pole without spinning counter to the sense of pacific north america shear unlike some other broad plate boundaries in the western united states vertical axis rotations take up very little of the slip rate budget across the region

active faulting in the north valleys region of reno nevada a distributed zone within the northern walker lane abstract at the latitude of reno nevada usa 15 25 of the pacific north american plate boundary strain is accommodated east of the sierra nevada through a combination of normal oblique dextral slip along the eastern sierra nevada range front and dextral slip along faults in the northern walker lane the north valleys region sits within the northern walker lane directly east of the sierra range front and is characterized by a series of small north striking basins bound by quaternary active faults that accommodate dextral oblique extension geodetic studies of the north valleys estimate that the faults collectively accommodate 0 9 1 7 mm y of extension and in this paper geologic observations on the tectonic geomorphic expression and relative activity of faults within and bounding the north valleys are described including the last chance petersen mountain fred s mountain and spanish springs valley fault zones and several un named faults in lemmon and hungry valleys geologic observations from the interpretation of lidar derived hillshade images aerial photographs satellite imagery and field reconnaissance indicate that the faults all exhibit evidence of late quaternary deformation including offset alluvial fan deposits and abrupt range front escarpments the results indicate that the faults of the north valleys are capable seismic sources characterized by extension rates on the order of hundredths to tenths of millimeters per year the faults act to transfer slip from the sierra nevada range front to the northeastern walker lane by accommodating dextral oblique extension consistent with pull apart basin kinematics within a simple shear right lateral system

active transtensional boundary zone between the western great basin and sierra nevada block western u s cordillera the walker lane and northern part of the eastern california shear zone form a boundary zone accommodating differential motion between the sierra nevada and western great basin within the boundary zone global positioning system velocities show a westward increase from 2 3 mm yr in the central great basin to 14 mm yr in the sierra nevada and a clockwise rotation from west northwest to northwest in the same region incremental extensional strain axes recorded by earthquake focal mechanisms and fault slip inversion show an east to west counterclockwise rotation of 50 from parallel with the velocity field in the central great basin to nearly orthogonal to the velocity field along the eastern flank of the sierra nevada unlike plane strain deformation within the central great basin the progressive deviation between the orientation of extension axes and the velocity field in the boundary zone is a product of nonplane strain the boundary zone records active constriction formed in conditions varying from wrench dominated to extension dominated transtension

transtensional deformation in the lake tahoe region california and nevada usa dextral transtensional deformation is occurring along the sierra nevada great basin boundary zone sngbbz at the eastern edge of the sierra nevada microplate in the lake tahoe region of the sngbbz transtension is partitioned spatially and temporally into domains of north south striking normal faults and transitional domains with conjugate strike slip faults the normal fault domains which have had large holocene earthquakes but account only for background seismicity in the historic period primarily accommodate east west extension while the transitional domains which have had moderate holocene and historic earthquakes and are currently seismically active primarily record north south shortening through partitioned slip the upper crust in this region undergoes overall constrictional strain major fault zones within the lake tahoe basin include two normal fault zones the northwest trending tahoe sierra frontal fault zone tsffz and the north trending west tahoe dollar point fault zone most faults in these zones show eastside down displacements both of these fault zones show evidence of holocene earthquakes but are relatively quiet seismically through the historic record the northeast trending north tahoe incline village fault zone is a major normal to sinistral oblique fault zone this fault zone shows evidence for large holocene earthquakes and based on the historic record is seismically active at the microearthquake level the zone forms the boundary between the lake tahoe normal fault domain to the south and the truckee transition zone to the north several lines of evidence including both geology and historic seismicity indicate that the seismically active truckee and gardnerville transition zones north and southeast of lake tahoe basin respectively are undergoing north south shortening in addition the central carson range a major north trending range block between two large normal fault zones shows internal fault patterns that suggest the range is undergoing north south shortening in addition to east west extension a model capable of explaining the spatial and temporal partitioning of slip suggests that seismic behavior in the region alternates between two modes one mode characterized by an east west minimum principal stress and a north south maximum principal stress as at present in this mode seismicity and small scale faulting reflecting north south shortening concentrate in mechanically weak transition zones with primarily strike slip faulting in relatively small magnitude events and domains with major normal faults are relatively quiet a second mode occurs after sufficient north south shortening reduces the north south shmax in magnitude until it is less than sv at which point sv becomes the maximum principal stress this second mode is then characterized by large earthquakes on major normal faults in the large normal fault domains which dominate the overall moment release in the region producing significant east west extension

how the continents deform the evidence from tectonic geodesy space geodesy now provides quantitative maps of the surface velocity field within tectonically active regions supplying constraints on the spatial distribution of deformation the forces that drive it and the brittle and ductile properties of continental lithosphere deformation is usefully described as relative motions among elastic blocks and is block like because major faults are weaker than adjacent intact crust despite similarities continental block kinematics differs from global plate tectonics blocks are much smaller typically 100 1000 km in size departures from block rigidity are sometimes measurable and blocks evolve over 1 10 ma timescales particularly near their often geometrically irregular boundaries quantitatively relating deformation to the forces that drive it requires simplifying assumptions about the strength distribution in the lithosphere if brittle elastic crust is strongest interactions among blocks control the deformation if ductile lithosphere is the stronger its fl

block modeling of crustal deformation of the northern walker lane and basin and range from gps velocities 1 we infer rates of crustal deformation in the northern walker lane nwl and western basin and range using data from the mobile array of gps for nevada transtension and other continuous gps networks including the earthscope plate boundary observatory we present 224 new gps velocities correct them for the effects of viscoelastic postseismic relaxation and use them to constrain a block model to estimate fault slip rates the data segregate the nwl into domains based on differences in deformation rate pattern and style deformation is transtensional with highest rates near the western and eastern edges of the nwl some basins e g tahoe experience shear deformation and extension normal slip is distributed throughout the nwl and basin and range where 11 subparallel range bounding normal fault systems have an average horizontal extension rate of 0 1 mm yr comparison between geologic and geodetic slip rates indicates that out of 12 published geologic rates 10 agree with geodetic rates to within uncertainties this suggests that smaller crustal blocks move steadily similar to larger lithospheric plates and that geodetic measurements of slip rates are reliable in zones of complex crustal deformation for the two slip rates that disagree geologic rates are greater the vertical axis rotation rate of the carson domain is 1 3 0 1 my clockwise lower than the 3 to 6 my obtained in paleomagnetic measurements this suggests that vertical axis rotation rates may have decreased over the last 9 13 my as the role of faulting has increased at the expense of rigid rotations

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

paleoseismology and global positioning system earthquake cycle effects and geodetic versus geologic fault slip rates in the eastern california shear zone published slip rates for the owens valley fault zone in eastern california based on geodetic data and elastic half space models 5 7 mm yr are faster than longer term geologic rates 2 3 mm yr we use global positioning system data spanning the central owens valley a more realistic rheological model with an elastic upper crust over a viscoelastic lower crust and upper mantle and paleoseismic data from adjacent faults to show that this difference could reflect earthquake cycle effects we estimate a long term rate 2 1 0 7 mm yr and earthquake recurrence interval 2750 350 1000 yr from the geodetic data both in agreement with independent geologic estimates

paleoseismic and slip rate observations along the honey lake fault zone northeastern california usa the honey lake fault is a major strike slip fault in northeastern california that accommodates northwest directed right lateral shear in the northern walker lane we reexamine the fault s paleoseismic history and slip rate by evaluating a natural stream bank exposure of the fault and offset terrace riser structural and stratigraphic relations within the modern stream cut radiocarbon ages and a detailed topographic survey of the offset terrace riser are used to estimate a holocene fault slip rate of 1 7 0 6 mm yr or more we also interpret the occurrence of at least four surface rupturing earthquakes during the last 7025 calendar years before present b p three of the surface rupturing earthquakes occurred prior to 4670 calendar years b p and have interevent times that range between 730 and 990 yr the stratigraphic record is limited after 4670 calendar years b p and records evidence for at least one more subsequent surface rupturing earthquake

the san andreas and walker lane fault systems western north america transpression transtension cumulative slip and the structural evolution of a major transform plate boundary abstract relative right lateral pacific north american transform motion across the western us is largely taken up by the san andreas and walker lane fault systems cumulative lateral displacement on active strands of the san andreas system is 3 4 or more times greater than across faults of the walker lane the san andreas system is transpressional while the walker lane system is transtensional the relatively more complex discontinuous and broader system of faults composing the walker lane system is attributed to lower cumulative slip and an attendant extensional component of motion greater slip accompanied by a small component of contraction has yielded the simpler more continuous and generally throughgoing set of faults that comprise the san andreas system with respect to the contrasting amounts of cumulative slip the san andreas is at a more mature stage of structural development than the walker lane despite differences in gross patterns of faulting the systems also share similarities in deformation style slip along each is locally accommodated by clockwise rotation of crustal blocks that has produced structural basins and oblique components of slip are commonly partitioned into subparallel strike slip and dip slip faults

dislocation model for aseismic crustal deformation at hollister california geodetic observations at many active plate margins reveal relatively steady aseismic motion during the time between major earthquakes we model the aseismic motion by the relative motion between several blocks that suffer frictional resistance in the upper crust frictional drag is represented by uniform dislocation on a fault surface we assume that friction occurs only on the upper brittle zone of each block boundary and that frictionless sliding occurs below this zone using a bayesian inversion procedure we invert geodetic data to determine the parameters of the block and dislocation model parameters to be estimated include the two horizontal components of velocity for each block and the dislocation rate dip angle slip angle and width of each rectangular fault patch for hollister we assume five blocks and nine rectangular fault patches rates of length change on 92 lines observed by trilateration make up the data triangulation leveling very long baseline interferometry satellite ranging and global positioning system data can also be easily included in our model our inversion procedure uses prior estimates of all block and fault parameters based on geological and seismological data the block parameters are estimated from geological observations of fault displacement rates while the widths of the fault patches are estimated from earthquake hypocentral depths we choose prior estimates of the dislocation rate to match observed creep rates the estimated block motion is well resolved by the geodetic data and agrees well with the geological estimates this suggests that the block motion is steady on time scales from 10 years to 1 m y the net motion across the san andreas calaveras fault system is 38 3 mm yr oriented s38 e thus some additional displacement possibly offshore is needed to match the rate of 56 mm yr predicted by plate tectonic models the depth of the transition from frictional to free sliding varies considerably from 0 4 km on the southern calaveras to 11 km on the central san andreas fault two segments of the san andreas north of 36 50 and south of 36 40 have the greatest potential for moderate to large earthquakes

geodetic observations of interseismic strain segmentation at the sumatra subduction zone deformation above the sumatra subduction zone revealed by global positioning system gps geodetic surveys shows nearly complete coupling of the forearc to the subducting plate south of 0 5 s and half as much to the north the abrupt change in plate coupling coincides with the boundary between the rupture zones of the 1833 and 1861 mw 8 thrust earthquakes the rupture boundary appears as an abrupt change in strain accumulation well into the interseismic cycle suggesting that seismic segmentation is controlled by properties of the plate interface that persist through more than one earthquake cycle structural evidence indicates that differences in basal shear stress may be related to elevated pore pressure in the north

far reaching transient motions after mojave earthquakes require broad mantle flow beneath a strong crust 1 geodeticallyobservedpostseismicsurfacedisplacements in the 7 years following the 1999 hector mine earthquake demonstrate a previously unrecognized broad pattern of transient deformation throughout southern california and into nevada more than 200 km from the epicenter unlike previous postseismic observations in which trade offs between postseismic mechanisms and the depth of flow lead to non unique solutions this deformation pattern can only be explained by viscoelastic flow in a region of the mantle 100s of km wide and below a depth of 40 km this result enables two robust conclusions regarding the nature of lithospheric strength in this region the mantle is weaker than the lower crust and flow occurs over a wide region of mantle as opposed to within a narrow shear zone beneath

behavior of the brittle crust in wide plate boundary zones in wide and active continental plate boundary zones ductile flow in the deeper and strong parts of the lithosphere may control crustal deformation this is likely if average resistive shear stresses on faults in the brittle crust are much less than 108 pa and the underlying bulk effective viscosity is much greater than 1021 pa s in this case a simple model of distributed deformation referred to as the floating block model may be useful this treats the crust as an array of rotating and translating rigid blocks which are floating on an underlying continuous flow with a constant rheology the model is analyzed in detail in this paper because it has the potential to link detailed observations of crustal deformation with the large scale flow crustal blocks are defined by at least two sets of faults the kinematics of crustal deformation can be described in terms of the motions of these blocks both the relative motion on block boundaries faults and block tilting about a horizontal axis can be described in terms of the underlying flow and block rotation about a vertical axis however rotations about a vertical axis which are an important component of the crustal deformation will depend not only on the underlying flow but also on the shape orientation and arrangement of the crustal blocks the average rotation rate about a vertical axis over finite rotations will be significantly different from that predicted at any instant also the rotation history is considerably complicated if as is likely the underlying flow field or block shape has changed with time these aspects of crustal deformation are discussed with reference to real zones of active deformation in new zealand greece and western north america

source parameters of earthquakes in the nevada seismic zone 1915 1943 the nevada seismic zone has historically been one of the most active seismic regions of the intermountain west although all large m 7 0 earthquakes located within this zone occurred prior to the establishment of a worldwide seismograph network most have been well recorded instrumentally this study uses available instrumental data to determine the source parameters for some of the earliest earthquakes occurring within the region namely the 1915 m 7 6 pleasant valley and 1932 m 7 2 cedar mountain earthquakes and several smaller events of 5 5 m 6 5 occurring within the cedar mountain region between 1934 and 1943 results of body waveform inversions suggest that the pleasant valley earthquake at the northern end of the nevada seismic zone is a complex event best fit by a multiple source time function waveform and first motion information for the cedar mountain earthquake located within the walker lane suggest the earthquake was composed of two events each having significant components of right lateral strike slip motion rakes of 176 to 179 waveforms of the m 6 5 excelsior mountain earthquake located only 40 km southwest of cedar mountain suggest the earthquake was a simple rupture along a normal fault rake of 90 20 although surface faulting indicates that the event had a component of left lateral strike slip motion

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

present day kinematics of the eastern california shear zone from a geodetically constrained block model we use global positioning system gps data from 1993 2000 to determine horizontal velocities of 65 stations in eastern california and western nevada between 35 and 37 n we relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km the velocity of the sierra nevada block with respect to nevada is 11 1 0 3 mm yr with slip partitioned across the death valley 2 8 0 5 mm yr panamint valley 2 5 0 8 mm yr and airport lake owens valley 5 3 0 7 4 6 0 5 mm yr faults the western mojave block rotates at 2 1 0 8 my clockwise with 3 7 0 7 mm yr of left lateral motion across the western garlock fault we infer 11 2 mm yr of right lateral motion across the mojave region of the eastern california shear zone

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

fault orientations in extensional and conjugate strike slip environments and their implications seismically active conjugate strike slip faults in california and japan typically have mutually orthogonal right and left lateral fault planes normal fault dips at earthquake nucleation depths are concentrated between 40 and 50 the observed orientations and their strong clustering are surprising because conventional faulting theory suggests fault initiation with conjugate 60 and 120 intersecting planes and 60 normal fault dip or fault reactivation with a broad range of permitted orientations the observations place new constraints on the mechanics of fault initiation rotation and evolutionary development we speculate that the data could be explained by fault rotation into the observed orientations and deactivation for greater rotation or by formation of localized shear zones beneath the brittle ductile transition in earth9s crust initiation as weak frictional faults seems unlikely

paleoseismic transect across the northern great basin 1 the relationship of strain accumulation to strain release over different timescales provides insight to the dynamics structural development and spatial and temporal pattern of earthquake recurrence in regions of active tectonics the great basin physiographic province of the western united states is one of the earth s broadest regions of ongoing continental extension encompassing an area reaching 800 km in width between the sierra nevada to the west and wasatch mountains to the east we present observations arising from excavations scarp profiling optically stimulated luminescence and radiocarbon dating to place limits on the late pleistocene paleoseismic history of faults bounding eight ranges across the interior of the northern great basin specifically the shawave hot springs humboldt sonoma shoshone tuscarora dry hills and pequop ranges combining the observations with similar previously published studies within and at the margins of the great basin yields a transect that extends eastward across the basin between the 40th and 41st parallels the sum of observations provides a picture of the patterns and rates of earthquake recurrence over the region during the last 20 45 kyr that may be compared to patterns of contemporary seismicity and recently reported measures of strain accumulation across the area using gps the recurrence rate of large surface rupture paleoearthquakes along ranges at the margins of the great basin is systematically greater than observed along ranges in the interior the pattern is similar to seismological and geodetic measurements that show levels of background seismicity and strain accumulation are also concentrated along the margins of the great basin an east west extension rate across the interior of the great basin on the order of 1 2 mm yr 1 strain rate of 1 nstrain yr 1 over the last 20 45 kyr is estimated by summing the record of paleoseismic displacements across the 400 km breadth of the transect as compared to 2m m yr 1 of strain accumulation indicated by a recently reported analysis of a collinear gps survey the comparison is hindered by significant uncertainties coupled to the geologic rate estimate the transect also crosses the northern limit of the central nevada seismic belt the central nevada seismic belt is defined by a north northeast trending alignment of historical surface rupture earthquakes increased levels of background seismicity and strain accumulation rates greater than observed elsewhere in the interior of the great basin the reported recurrence rate of late pleistocene surface rupture earthquakes within the central nevada seismic belt is also generally greater than observed along our transect the observations when taken together suggest that the characteristics of strain release observed historically within the central nevada seismic belt have been operative over the latest pleistocene and that the apparently greater rates of strain accumulation and release in the central nevada seismic belt are diminished or less localized in regions to the north and east thus while the historical alignment of surface ruptures that defines the central nevada seismic belt remains a unique clustering of earthquakes in time and space the likelihood of the cluster at its observed location appears greater than would be expected to the north or eastward in the interior of the great basin

active displacement transfer and differential block motion within the central walker lane western great basin velocities determined for 50 global positioning system sites within the central walker lane indicate differential motion among tectonic blocks forming a boundary zone between the great basin extensional province and the sierra nevada the velocity field is related to displacement transfer from the owens valley and furnace creek fault systems of east ern california to transtensional structures of the walker lane and extensional faults of the central nevada seismic belt block boundaries are sharp and appear to be inherited from pre tertiary crustal structure the block geometries exert strong influence on dif ferential displacements concentrated along boundaries as belts of divergent transcurrent and convergent motion the aggregate velocity accounts for about 25 of the relative motion between the pacific and north american plates about 5 mm yr of the motion is localized along the eastern margin of the sierra nevada whereas about 10 mm yr is stepped 100 km east along a belt of east northeast trending transtensional faults that merge with northwest trending transcurrent structures of the walker lane about 6 mm yr of the velocity field is transferred to north northeast trending extensional faults of the central nevada seismic belt the heterogeneous distribution of motions is consistent with partitioning of a regional velocity field formed by westward extension and n408w directed shear

hydrodynamics of mountain river confluences and its relationship to sediment transport mountain confluences are characterized by narrow and steep tributaries that provide important sediment load to the confluence whereas themain channel supplies the dominant flow discharge this results in a marked bed discordance between the tributary and main channel which induces key differences in the hydromorphodynamics of the confluence when compared to concordant bed and some common types of discordant bed confluences the processes of initiation and maintenance of the morphology of confluences are still unknown and research linking morphodynamics and hydrodynamics of river confluences is required to understand these phenomena in this paper eddy resolving simulations based on laboratory experiments made in a live bed model of a mountain river confluence are used to provide a detailed description of flow hydrodynamics and implications for morphodynamics the test case study corresponds to a confluence with an angle of 70 numerical simulations are performed for two extreme bathymetric conditions those at the start of the experiment and when equilibriummorphological conditions are reached results of the simulations and experimental observations are used tomake inferences on erosion mechanisms during the initial and final states of the erosion deposition process the relationship between the coherent structures present in the near bed region in the instantaneous and mean flow fields and sediment entrainment transport is described the present paper demonstrates the critical role played by large scale turbulence generated in the shear layers forming on the side of the tributary flow as it enters the main channel by the main vortex forming over the discordant bed region surrounding the downstream end of the tributary as well as by several near bed vortices induced by the deflection of the tributary flow by the incoming flow in the main channel the predicted patterns of bed shear stress are linked to pathways of sediment movement

current sierra nevada north america motion from very long baseline interferometry implications for the kinematics of the western united states we use geodetic measurements from very long baseline interferometry to estimate the motion of the sierra nevadan microplate which is composed of the sierra nevada and the great valley the motion of the sierra nevadan microplate relative to the north american plate is described by a right handed rotation of 0 61 m y about lat 32 n long 128 w this euler pole lies only 10 southwest of the sierra nevadan microplate and predicts a significant counterclockwise rotation about a local vertical axis it further predicts a velocity of the eastern edge of the sierra nevada at 38 0 n 119 3 w relative to stable north america of 11 1 mm yr toward n36 3 w quoted uncertainties are plus or minus one standard error which accounts for about one fourth of the velocity between the pacific and north american plates and is 25 clockwise of many prior estimates the velocity nearly parallels the boundary between the sierra nevada and the great basin which implies that current motion within the great basin results in a rotational noncoaxial deformation we use this velocity to estimate how motion is distributed across the broad deforming zone taking up pacific north america plate motion we find that the vector sum of strike slip along the san andreas fault and motion of the sierra nevada relative to stable north america taken up by deformation within the great basin differs little from the pacific north america plate velocity the difference can be described at 36 n along the san andreas fault by a vector of 6 mm yr directed toward n20 w this vector resolves into components of 5 mm yr parallel to the fault and 2 mm yr perpendicular to the fault with 95 confidence intervals of 0 to 10 mm yr and 1 to 5 mm yr respectively the component perpendicular to the fault is several times smaller than found in prior studies and places a small upper bound on fault perpendicular shortening we conclude that motion previously inferred to be taken up by deformation other than strike slip along the san andreas fault or deformation within the great basin is much smaller than previously thought

postseismic relaxation across the central nevada seismic belt 1 two gps geodetic surveys across the basin and range br province of western north america have detected an anomalous compression east of the central nevada seismic belt cnsb the first network installed by the u s geological survey along an east west trending transect across the br at approximately 40 n consisted of 63 monuments observed campaign style in 1992 1996 and 1998 the second network installed by the california institute of technology consisted of 50 continuously operating gps receivers 18 of which were roughly along the same transect as the campaign survey we have used a viscoelastic postseismic relaxation model of the four largest earthquakes in the cnsb on the pleasant valley fault in 1915 the cedar mountain fault in 1932 and on the fairview peak and dixie valley faults in 1954 to interpret the geodetic velocities observed across the cnsb a model of postseismic relaxation with a lower crustal maxwell viscosity of 5 50 1018 pa s can explain the apparent compression regardless of the assumed mantle viscosity the geodetic velocities that we determined after removing the postseismic contribution indicate that within current gps detection limits the br is stable east of the cnsb and is undergoing rapid right lateral shear west of the cnsb

pattern and rates of faulting in the central nevada seismic belt and paleoseismic evidence for prior beltlike behavior the central nevada seismic belt cnsb is a concentration of historical 1915 1932 1954 surface faulting in the western basin and range province forming a linear nearly continuous 300 km long rupture zone previous results are integrated in this study with new paleoseismic and exploratory trenching data from the historical zones to look for evidence of older similar beltlike patterns or elevated slip rates that could indicate whether the cnsb is a zone of focused long term crustal strain the data show that the continuous rupture belt produced by the seven earthquakes occurring between 1915 and 1954 is unique in the available paleoseismic record at the 1954 fairview peak fault the lack of prehistorical faulting in deposits containing the wilson creek bed 19 tephra eliminates the possibility of an identical seismic belt in the past 35 4 ka our studies also show that the faults have net slip rates ranging from a low of 0 09 mm yr on the fairview peak fault to a high of 0 7 mm yr on the 1932 cedar mountain fault these are considered moderate to low rates that are similar to most late quaternary faults in the western basin and range province a space time comparison shows that the paleoseismic histories for these multiple rupture zones are diverse and the number and timing of events in each of the zones indicate that there is little evidence for older contemporaneous ruptures of these same faults based on these results we reach several conclusions regarding the longer term holocene behavior of the cnsb although paleoseismic data preclude an older identical rupture belt among the historical zones consideration of associated holocene faults within the greater cnsb region indicates that several similar but not identical beltlike rupture patterns are plausible during the past 13 ka although each requires seismic gaps in the along strike pattern although long term strain represented by density of young faults does appear to increase from east to west into the cnsb the slip rate data demonstrate that the cnsb is not a belt of concentrated or elevated crustal strain compared with areas that extend west to the sierra nevada the increase in the distribution of holocene fault activity from east to west into the cnsb is consistent with a marked increase in the 1992 2002 gps velocity field at the latitude of the 1954 rupture sequence however a comparison of the geologic rates across the belt at this same latitude indicates that the extension rates 0 59 1 37 mm yr are systematically lower than both the campaign and continuous gps rates 2 20 3 13 mm yr by factors of 2 5 these discrepancies may be due to postseismic strain or to some form of off fault deformation we conclude that the results of our study of fault behavior in the cnsb best support the belt migration model proposed by wallace 1987 for the western basin and range province in which temporal tectonic pulses are believed to migrate regionally activating different beltlike combinations of late quaternary faults in an as yet unknown pattern of migration

comparison of seismic and geodetic scalar moment rates across the basin and range province scalar moment rates estimated from a 146 year seismicity catalog agree within uncertainties with the deformation rate of the basin and range province determined by using space geodesy seismic moment rates have been estimated from a new catalog of earthquakes complete for m 5 the catalog was compiled from 15 preexisting catalogs supplemented by the review of 44 journal articles throughout the catalog compilation care was taken to obtain the moment magnitude or a reasonable and not inflated equivalent seventy six percent of the moment release occurred during 10 earthquakes of magnitude m w 6 79 the spatial distribution of earthquakes and their moment release matches the geodetic pattern of deformation all three are concentrated in a 200 km wide zone along the western boundary of the great basin with this zone widening to the north several techniques ultimately traceable to kostrov and brune are used to translate the geodetic strain rates into rates of seismic moment release the agreement between geodetic and seismic moment rate suggests that within uncertainties the rate of historic earthquakes within the basin and range province taken as a whole provides a reasonable estimate for the future rate of seismicity these results support the hypothesis that even a few years of detailed geodetic monitoring can provide a good constraint on earthquake occurrence rate estimates for large enough regions

holocene slip rate and earthquake recurrence on the honey lake fault zone northeastern california the honey lake fault zone a major right lateral fault in the basin and range province of eastern california is one of a broad system of faults that accommodate some of the relative motion between the pacific and north american plates these right lateral faults may have significantly higher slip rates and thus greater earthquake hazards than the normal faults for which the basin and range is more commonly known in the honey lake valley the fault forms a 50 km long zone of landforms typical of active strike slip faults right lateral offset of an incised creek channel is used to estimate a holocene slip rate of between 1 1 and 2 6 mm yr a fault exposure in holocene alluvium shows evidence for at least four late holocene surface faulting earthquakes

strain accumulation and rotation in western nevada 1993 2000 1 the positions of 44 gps monuments in an array extending from the sierra nevada at the latitude of reno to near austin nevada have been measured several times in the 1993 2000 interval the western half of the array spans the walker lane belt whereas the eastern half spans the central nevada seismic zone cnsz the principal strain rates in the walker lane belt are 29 6 5 3 nstrain yr 1 n88 4 e 5 4 and 12 8 6 0 nanostrain yr 1 n01 6 w 5 4 extension reckoned positive and the clockwise as seen from above the earth rotation rate about a vertical axis is 13 6 4 0 nrad yr 1 the quoted uncertainties are standard deviations the motion in the walker lane belt can then be represented by a zone striking n35 w subject to 16 8 4 9 nstrain yr 1 extension perpendicular to it and 19 5 4 0 nstrain yr 1 right lateral simple shear across it the n35 w strike of the zone is the same as the direction of the local tangent to the small circle drawn about the pacific north america pole of rotation the principal strain rates for the cnsz are 46 2 11 0 nstrain yr 1 n49 9 w 6 0 and 13 6 6 1 nstrain yr 1 n40 1 e 6 0 and the clockwise rotation rate about a vertical axis is 20 3 6 3 nrad yr 1 the motion across the cnsz can then be represented by a zone striking n12 e subject to 32 6 11 0 nstrain yr 1 extension perpendicular to it and 25 1 6 3 nstrain yr 1 right lateral simple shear across it the n12 e strike of the zone is similar to the strikes of the faults rainbow mountain fairview peak and dixie valley within it

late pleistocene fault slip rate earthquake recurrence and recency of slip along the pyramid lake fault zone northern walker lane united states 1 up to 25 of pacific north america plate relative transform motion is accommodated east of the sierra nevada most of that 25 is taken up by deformation in the walker lane a discontinuous zone of strike slip and normal faults approximately parallel to the san andreas the pyramid lake fault zone is a northwest trending right lateral fault in the northern walker lane nevada recent geodetic surveys report 6 2 mm year of right lateral shear strain accumulation across the northern walker lane interpretation of displaced geomorphic features preserved in post lake lahontan 15 500 cal yr b p surfaces indicate the pyramid lake fault zone has accommodated at least 2 6 0 3 mm year of right lateral shear during the late pleistocene additionally a minimum of two earthquakes have occurred since deposition of the mazama tephra 7630 cal yr b p and at least four earthquakes have occurred on the fault after desiccation of lake lahontan 15 5 ka with the most recent earthquake occurring after 1705 175 cal yr b p the observations indicate that the pyramid lake fault zone accommodates the major portion 25 70 of right lateral slip east of the sierra nevada at the latitude of 39 45 n

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

mobility of continental mantle evidence from postseismic geodetic observations following the 1992 landers earthquake the crust around the rupture zone of the 1992 landers earthquake has continued to deform in the years following the earthquake at rates 3 times greater than pre earthquake rates we use a combination of global positioning system gps and synthetic aperture radar insar data collected during a 3 year epoch following the earthquake in order to investigate postseismic mechanisms responsible for the high transient velocities in order to maximize the potential signal from viscoelastic relaxation we evaluate and model postseismic relaxation following the first few months of documented accelerated deformation the combination of gps and insar data allows us to establish viscoelastic relaxation of the lower crust and upper mantle as the dominant postseismic process and to discriminate among possible viscoelastic models the data particularly require the presence of a highly ductile uppermost mantle beneath the central mojave domain with temperature between the wet and dry basalt solidus this is consistent with independent seismic and geochemical inferences of a regionally warm uppermost mantle further consideration of seismic velocity variations in conjunction with faulting patterns within the mojave desert suggests that the primary faulting characteristics of the mojave desert namely the pervasive late cenozoic deformation within the eastern california shear zone versus the near absence of faults in the western mojave domain are controlled by the rheology of the uppermost mantle

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

postseismic mantle relaxation in the central nevada seismic belt holocene acceleration of deformation and postseismic relaxation are two hypotheses to explain the present day deformation in the central nevada seismic belt cnsb discriminating between these two mechanisms is critical for understanding the dynamics and seismic potential of the basin and range province interferometric synthetic aperture radar detected a broad area of uplift 2 to 3 millimeters per year that can be explained by postseismic mantle relaxation after a sequence of large crustal earthquakes from 1915 to 1954 the results lead to a broad agreement between geologic and geodetic strain indicators and support a model of a rigid basin and range between the cnsb and the wasatch fault

surface faulting and paleoseismic history of the 1932 cedar mountain earthquake area west central nevada and implications for modern tectonics of the walker lane the 1932 cedar mountain earthquake m s 7 2 was one of the largest historical events in the walker lane region of western nevada and it produced a complicated strike slip rupture pattern on multiple quaternary faults distributed through three valleys primary right lateral surface ruptures occurred on north striking faults in monte cristo valley small scale lateral and normal offsets occurred in stewart valley and secondary normal faulting occurred on north northeast striking faults in the gabbs valley epicentral region a reexamination of the surface ruptures provides new displacement and fault zone data maximum cumulative offset is estimated to be 2 7 m and newly recognized faults extend the maximum width and end to end length of the rupture zone to 17 and 75 km respectively a detailed quaternary allostratigraphic chronology based on regional alluvial geomorphic relationships tephrochronology and radiocarbon dating provides a framework for interpreting the paleoseismic history of the fault zone a late wisconsinan alluvial fan and piedmont unit containing a 32 36 ka tephra layer is a key stratigraphic datum for paleoseismic measurements exploratory trenching and radiocarbon dating of tectonic stratigraphy provide the first estimates for timing of late quaternary faulting along the cedar mountain fault zone three trenches display evidence for six faulting events including that in 1932 during the past 32 36 ka radiocarbon dating of organic soils interstratified with tectonically ponded silts establishes best fit ages of the pre 1932 events at 4 5 12 15 and 18 ka each with 2 ka uncertainties on the basis of an estimated cumulative net slip of 6 12 m for the six faulting events minimum and maximum late quaternary slip rates are 0 2 and 0 7 mm yr respectively and the preferred rate is 0 4 0 5 mm yr the average recurrence interseismic interval is 3600 yr the relatively uniform thickness of the ponded deposits suggests that similar size characteristic rupture events may characterize late quaternary slip on the zone a comparison of event timing with the average late quaternary recurrence interval indicates that slip has been largely regular periodic rather than temporally clustered to account for the spatial separation of the primary surface faulting in monte cristo valley from the epicenter and for a factor of two to three disparity between the instrumentally and geologically determined seismic moments associated with the earthquake we hypothesize two alternative tectonic models containing undetected subevents either model would adequately account for the observed faulting on the basis of wrench fault kinematics that may be associated with the walker lane the 1932 cedar mountain earthquake is considered an important modern analogue for seismotectonic modeling and estimating seismic hazard in the walker lane region in contrast to most other historical events in the basin and range province the 1932 event did not occur along a major range bounding fault and no single throughgoing basement structure can account for the observed rupture pattern the 1932 faulting supports the concept that major earthquakes in the basin and range province can exhibit complicated distributive rupture patterns and that slip rate may not be a reliable criterion for modeling seismic hazard

nearly frictionless faulting by unclamping in long term interaction models in defiance of direct rock friction observations some transform faults appear to slide with little resistance in this paper finite element models are used to show how strain energy is minimized by interacting faults that can cause long term reduction in fault normal stresses unclamping a model fault contained within a sheared elastic medium concentrates stress at its end points with increasing slip if accommodating structures free up the ends then the fault responds by rotating lengthening and unclamping this concept is illustrated by a comparison between simple strike slip faulting and a mid ocean ridge model with the same total transform length calculations show that the more complex system unclamps the transforms and operates at lower energy in another example the overlapping san andreas fault system in the san francisco bay region is modeled this system is complicated by junctions and stepovers a finite element model indicates that the normal stress along parts of the faults could be reduced to hydrostatic levels after 60 100 k y of system wide slip if this process occurs in the earth then parts of major transform fault zones could appear nearly frictionless

modern strain localization in the central walker lane western united states implications for the evolution of intraplate deformation in transtensional settings abstract approximately 25 of the differential motion between the pacific and north american plates occurs in the walker lane a zone of dextral motion within the western margin of the basin and range province at the latitude of lake tahoe the central walker lane has been considered a zone of transtension with strain accommodated by dip slip strike slip and oblique slip faults geologic data indicate that extension and strike slip motion are partitioned across the central walker lane with dip slip motion resulting in e w to ese wnw extension along the present day western margin of the central walker lane since approximately 15 ma and dextral strike slip motion across a zone further east since as early as 24 ma gps velocity data suggest that present day strain continues to be strongly partitioned and localized across the same regions established by geologic data velocity data across the central walker lane suggest a minimum of 2 mm yr extensional strain focused along the western margin of the belt with very little extension across either the central or eastern portions of the walker lane these data indicate very little dextral motion across the central and western portions of the domain with dextral motion of 3 5 mm yr presently focused along a discrete zone of the eastern part of the central walker lane coincident with existing mapped strike slip faults historic seismic data reveal little seismic activity in areas of late holocene dip slip motion in the west or dextral motion in the east suggesting a period of quiescence in the earthquake cycle and the likelihood of future activity in both areas based on this and previous studies it is likely that a combination of pre cenozoic crustal structure a relatively weak lithosphere beneath the walker lane and long term low stress ratios in the crust have permitted the long term partitioning of dextral and extensional strain exhibited across the central walker lane the present day location of dextral strain in the central walker lane is subparallel with dextral deformation documented in the northern walker lane suggesting that as strain continues to accumulate these two discrete zones could become a continuous strike slip system which will play a more important role in the future accommodation of relative pacific north american plate motion

kinematics of the northern walker lane an incipient transform fault along the pacific north american plate boundary in the western great basin of north america a system of dextral faults accommodates 15 25 of the pacific north american plate motion the northern walker lane in northwest nevada and northeast california occupies the northern terminus of this system this young evolving part of the plate boundary offers insight into how strike slip fault systems develop and may reflect the birth of a transform fault a belt of overlapping left stepping dextral faults dominates the northern walker lane offset segments of a w trending oligocene paleovalley suggest 20 30 km of cumulative dextral slip beginning ca 9 3 ma the inferred long term slip rate of 2 10 mm yr is compatible with global positioning system observations of the current strain field we interpret the left stepping faults as macroscopic riedel shears developing above a nascent lithospheric scale transform fault the strike slip faults end in arrays of n striking normal faults suggesting that dextral shear diffuses into extension in the great basin coeval extension and dextral shear have induced slight counterclockwise fault block rotations which may ultimately rotate riedel shears toward the main shear zone at depth thus facilitating development of a throughgoing strike slip fault

active faulting in the walker lane 1 deformation across the san andreas and walker lane fault systems accounts for most relative pacific north american transform plate motion the walker lane is composed of discontinuous sets of right slip faults that are located to the east and strike approximately parallel to the san andreas fault system mapping of active faults in the central walker lane shows that right lateral shear is locally accommodated by rotation of crustal blocks bounded by steep dipping east striking left slip faults the left slip and clockwise rotation of crustal blocks bounded by the east striking faults has produced major basins in the area including rattlesnake and garfield flats teels columbus and rhodes salt marshes and queen valley the benton springs and petrified springs faults are the major northwest striking structures currently accommodating transform motion in the central walker lane right lateral offsets of late pleistocene surfaces along the two faults point to slip rates of at least 1 mm yr the northern limit of northwest trending strike slip faults in the central walker lane is abrupt and reflects transfer of strike slip to dip slip deformation in the western basin and range and transformation of right slip into rotation of crustal blocks to the north the transfer of strike slip in the central walker lane to dip slip in the western basin and range correlates to a northward broadening of the modern strain field suggested by geodesy and appears to be a long lived feature of the deformation field the complexity of faulting and apparent rotation of crustal blocks within the walker lane is consistent with the concept of a partially detached and elastic brittle crust that is being transported on a continuously deforming layer below the regional pattern of faulting within the walker lane is more complex than observed along the san andreas fault system to the west the difference is attributed to the relatively less cumulative slip that has occurred across the walker lane and that oblique components of displacement are of opposite sense along the walker lane extension and san andreas contraction respectively despite the gross differences in fault pattern the walker lane and san andreas also share similarities in deformation style including clockwise rotations of crustal blocks leading to development of structural basins and the partitioning of oblique components of slip onto subparallel strike slip and dip slip faults

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

effect of viscoelastic postseismic relaxation on estimates of interseismic crustal strain accumulation at yucca mountain nevada 1 we estimate the long term crustal strain rate at yucca mountain ym nevada from gps velocities taking into account viscoelastic relaxation following recent earthquakes to remove bias associated with transient deformation the ym data reveal postseismic relaxation in time series non linearity and geographic variation of the transient signal from the data we estimate best fitting lower crust and upper mantle viscosities of 1019 5 pa s and 1018 5 pa s respectively once the relaxation model predictions are subtracted from the data the long term shear strain accumulation rate is between 16 3 and 25 1 nanostrains year ns yr to 99 confidence a range much larger than the formal uncertainties from gps measurement we conclude that 1 a maxwell viscoelastic model cannot explain all the deformation observed at ym 2 uncertainty in viscosities dominates uncertainty in ym strain rates and 3 the effects of large recent earthquakes must be accounted for in seismic hazard studies using gps

large magnitude late holocene earthquakes on the genoa fault west central nevada and eastern california the genoa fault a principal normal fault of the transition zone between the basin and range province and the northern sierra nevada displays a large and conspicuous prehistoric scarp three trenches excavated across this scarp exposed two large displacement late holocene events two of the trenches contained multiple layers of stratified charcoal yielding radiocarbon ages suggesting the most recent and penultimate events on the main part of the fault occurred 500 600 cal b p and 2000 2200 cal b p respectively normal slip offsets of 3 5 5 m per event along much of the rupture length are comparable to the largest historical basin and range province earthquakes suggesting these paleoearthquakes were on the order of magnitude 7 2 7 5 the apparent late holocene slip rate 2 3 mm yr is one of the highest in the basin and range province based on structural and behavioral differences the genoa fault is here divided into four principal sections the sierra diamond valley carson valley and jacks valley sections and is distinguished from three northeast striking faults in the carson city area the kings canyon carson city and indian hill faults the conspicuous scarp extends for nearly 25 km the combined length of the carson valley and jacks valley sections the diamond valley section lacks the conspicuous scarp and older alluvial fans and bedrock outcrops on the downthrown side of the fault indicate a lower activity rate activity further decreases to the south along the sierra section which consists of numerous distributed faults all three northeast striking faults in the carson city area ruptured within the past few thousand years and one or more may have ruptured during recent events on the genoa fault

ensemble approach to develop landslide susceptibility map in landslide dominated sikkim himalayan region india the landslide is a downward movement of soil and rock and one of the most destructive geo hazards that causes losses in lives environment and economy all over the world landslide susceptibility mapping is a scientific method to evaluate the landslide probability zones and causative factors the main objective of the present study was to introduce ensemble landslide susceptibility models which are developed on the basis of two statistical models evidential belief function and geographically weighted regression and one machine learning model random forest for spatial prediction of landslide of the upper rangit river basin sikkim india totally 102 landslide locations have been identified and randomly classified into 70 and 30 as training and validating database respectively total 16 landslide causative factors are considered and grouped into four categories geomorphological hydrological geological and environmental factors the evidential belief function ebf geographically weighted regression gwr and random forest rf method and their ensemble methods rf ebf and rf gwr models have been applied with the help of training landslide and non landslide dataset and spatial database of landslide causative factors five landslide susceptibility maps have been generated by the said model and the maps have been validated by validating dataset with the help of sensitivity specificity accuracy kappa index and area under curve auc of receiver operating characteristic roc tools the ensemble methods have the best degree of fit and prediction performance than single methods i e rf ebf and rf gwr model have 91 8 and 89 9 prediction capabilities the result of the relative importance of factor showed that land use land cover lulc distance to river soil drainage density and road density factors have played the key role in the occurrence of the landslide the result of the study can be used by local planning dicession makers and the methods of landslide susceptibility can be applied in other areas

inescapable slow slip on the altyn tagh fault 1 gps surveys conducted in 1994 1998 and 2002 on the central portion of the altyn tagh fault confirm left lateral slip rates of 9 4 mm yr significantly slower than geological estimates of slip rate for the past several thousand years the measurements were obtained on a 300 km long profile between 88 and 91 e within one fault dimension of the mw 7 6 and mw 7 8 kunlun earthquakes of 1997 and 2001 the inferred elastic displacements from these events are incorporated into the interpreted 1994 2002 velocity field the recent serendipitous occurrence of these two large earthquakes on a sub parallel fault system suggests that slip on the kunlun fault may have recently accelerated thereby reducing the slip rate on the altyn tagh fault however geodetic data from northern tibet prior to the 2001 earthquake indicate present day rates similar to long term rates this suggests that systematic errors may be present in published geologic slip rate estimates for the altyn tagh fault

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

crustal deformation across the sierra nevada northern walker lane basin and range transition western united states measured with gps 2000 2004 1 global positioning system gps data collected in campaigns in 2000 and 2004 were processed and interpreted with other gps data in the western basin and range province to provide new constraints on the rate style and pattern of deformation of the central and northern walker lane wl which lies near the western boundary of the basin and range across the central wl near 38n latitude the velocities with respect to north america increase westward by 10 mm yr inducing dextral shear farther north between 40 and 41n latitude a western zone of 7 mm yr relative motion undergoes dextral shear and an eastern zone of 3 mm yr relative motion undergoes extension and shear these data show that the northern wl is essentially a dextral shear zone experiencing minor net dilatation ed 2 6 0 8 nstrain yr near most holocene normal faults dilatation inferred from the velocity field is not greater than the uncertainties however near the central nevada seismic belt we detect significant dilatation expressed as extension in a direction approximately normal to the range fronts ed 23 0 3 9 nstrain yr some of which is attributable to transient postseismic deformation following large historic earthquakes a block model constrained by velocities corrected for transient effects shows that the sum of dextral slip rates across the honey lake warm springs east pyramid fault system and mohawk valley faults is 7 mm yr the wl is a zone whose width and dilatation rate increase northwestward consistent with counterclockwise rotation of the sierra nevada microplate and transfer of deformation into the pacific northwest

global positioning system constraints on fault slip rates in southern california and northern baja mexico we use global positioning system gps estimates of horizontal site velocity to constrain slip rates on faults comprising the pacific north america plate boundary in southern california and northern mexico we enlist a simple elastic block model to parameterize the distribution and sum of deformation within and across the plate boundary we estimate a pacific north america relative plate motion rate of 49 3 mm yr one standard deviation consistent with nuvel 1a estimates we are able to resolve robust slip rate estimates for the southernmost san andreas san jacinto and elsinore faults 26 2 9 2 and 6 2 mm yr respectively and for the imperial and cerro prieto faults 35 2 and 42 1 mm yr respectively accounting for about 86 of the total plate motion the remaining 14 appears to be accommodated to the west of these fault systems probably via slip along the san clemente fault and or the san miguel vallecitos rose canyon and newport inglewood fault systems these results are highly consistent with paleoseismic estimates for slip rates implying that off fault strain accumulation within the deforming zone of the plate boundary is largely elastic we estimate that the seismically quiescent southernmost san andreas fault has incurred about 8 2 m of slip deficit over the last few hundred years presumably to be recovered during a future large earthquake