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

tectonic implications of a dense continuous gps velocity field at yucca mountain nevada 1 a dense continuous gps network was established in the yucca mountain area in 1999 to provide the most reliable measurements possible of geodetic strain patterns across the nation s only proposed permanent repository for high level radioactive waste the network lies astride a boundary between the geodetically stable central great basin and the active western great basin which at the latitude of yucca mountain is undergoing distributed right lateral shear at a rate of 60 nstrain yr monitoring from 1999 to 2003 3 75 years yields a velocity field characterized by nearly homogenous n20 w rightlateral shear of 20 2 nstrain yr net velocity contrast of 1 2 mm yr across a 60 km aperture in the vicinity of the proposed repository site comparison of time series of continuous results with earlier campaign surveys indicating 50 nstrain yr of westnorthwest extension from 1991 to 1997 suggests that the more rapid rates were in part transient motions associated with the 1992 ms 5 4 little skull mountain earthquake postseismic motions do not appear to affect the 1999 2003 velocity field in either campaign or continuous data the magnitude of the velocity contrast across the area the overall linearity of the gradient and the large area of undeforming crust to the east of yucca mountain are difficult to explain by elastic bending of the crust associated with the death valley fault zone a major right lateral strike slip fault about 50 km west of the repository site these observations along with apparent local variations in the velocity gradient suggest that significant right lateral strain accumulation with displacement rate in the 1 mm yr range may be associated with structures in the yucca mountain area the absence of structures in the area with equivalent late quaternary displacement rates underscores the problem of reconciling discrepancies between geologic and geodetic estimates of deformation rates index terms 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8107 tectonophysics continental neotectonics 8109 tectonophysics continental tectonics extensional 0905 keywords geodesy tectonics yucca mountain

recurrence rates of large earthquakes in the south carolina coastal plain based on paleoliquefaction data we present a reanalysis of results of 15 years of paleoliquefaction investigations in the south carolina coastal plain all earlier radiocarbon age data and locations of organic material collected by various investigators were reviewed and recalibrated to obtain a uniform data set the calibrated dates and the spatial extent of the sandblows having similar dates were used to estimate ages and magnitudes of prehistoric earthquake episodes the results of this analysis suggest seven episodes episodes a g of prehistoric liquefaction in the past 6000 years and two possible scenarios for their occurrence in the first scenario three seismic sources exist within the coastal plain of south carolina at charleston a b e and g with magnitudes m 71 georgetown c and f and bluffton d with magnitudes m 6 in the second scenario episodes c and d are combined into one episode episode c9 in this scenario all earthquakes occurred at charleston and with m 71 episodes a and b seem to be more representative of the earthquake cycle and suggest a recurrence time of 500 600 years for m 71 earthquakes at charleston the recurrence times and magnitudes for episodes c and d are estimated at 2000 years and 6 0 respectively the older episodes are less frequent a fact that may be attributable to times of low ground water table before 6000 years b p the ground water table was too low to permit observable liquefaction features to develop at the surface

surface slip during large owens valley earthquakes data sets and expanded results contributing to this study are available in the supporting information the earthscope southern and eastern california lidar project available online at http opentopo sdsc edu involved data acquisition and processing for the plate boundary observatory pbo by ncalm http www ncalm org unavco operates the pbo for earthscope http www earthscope org supported by the national science foundation ear 0350028 and ear 0732947 funding for this study was provided by the southern california earthquake center scec project 12140 the geological society of america graduate student research fund the community foundation of san bernardino county and the western washington university geology department we thank g seitz m price and k morgan for assistance in the field and s bacon j arrowsmith r weldon k scharer j unruh c madden madugo and d haddad for helpful discussions constructive reviews by d schwartz r briggs e schermer d clark and one anonymous reviewer substantially improved the paper we also thank the staff at the uc white mountain research center for facilitating this work any use of trade firm or product names is for descriptive purposes only and does not imply endorsement by the u s government

rapid incision of a small coarse and steep fan delta in response to base level fall the case of nahal qedem the dead sea israel the dead sea has been continuously dropping 0 4 1 0 m yr 1 since the middle of the 20th century and thus provides a unique field laboratory for studying in real time the response of drainage systems to a non tectonic base level fall the aim of this work is to study the short term ongoing erosive response to a rapid base level drop in a small steep fronted erodible fan delta setting the work explores the controls of the steep qedem fan delta guided by its clinoform structure on its incision longitudinal profiles of the fan delta and of its entrenched channel were measured in the field sedimentary facies changes fluviatile shallow lacustrine and beach were followed along exposures the existence of large boulders provided an opportunity to examine the uncertain role of armouring and boulder flux on incision the field study was combined with digital elevation models dems that were extracted from pairs of overlapping aerial photos maps of erosion and deposition were prepared using a change detection algorithm the longitudinal profile of the entrenched channel was found to be steep and linear the outlet temporarily hangs elevated and ungraded above the retreating lake level indicating years without incision flow events which cause lags in response to the rapid lake level drop in spite of the large boulders the small drainage basin and precipitation volume over the basin of the qedem the recorded vertical incision rates in the unconsolidated sediments are as high as 0 8 m yr 1 i e similar to those of the largest wadis draining to the dead sea the steep front of the fan delta is suggested to be a main factor controlling the efficient incision a unique transport mechanism of rolling boulders following undercutting contributed to the entrenchment efficiency copyright 2010 john wiley sons ltd

mechanical deformation model of the western united states instantaneous strain rate field summary we present a relationship between the long term fault slip rates and instantaneous velocities as measured by global positioning system gps or other geodetic measurements over a short time span the main elements are the secularly increasing forces imposed by the bounding pacific and juan de fuca jdf plates on the north american plate viscoelastic relaxation following selected large earthquakes occurring on faults that are locked during their respective interseismic periods and steady slip along creeping portions of faults in the context of a thin plate system in detail the physical model allows separate treatments of faults with known geometry and slip history faults with incomplete characterization i e fault geometry but not necessarily slip history is available creeping faults and dislocation sources distributed between the faults we model the western united states strain rate field derived from 746 gps velocity vectors in order to test the importance of the relaxation from historic events and characterize the tectonic forces imposed by the bounding pacific and jdf plates relaxation following major earthquakes m 8 0 strongly shapes the present strain rate field over most of the plate boundary zone equally important are lateral shear transmitted across the pacific north america plate boundary along 1000 km of the continental shelf downdip forces distributed along the cascadia subduction interface and distributed slip in the lower lithosphere post earthquake relaxation and tectonic forcing combined with distributed deep slip constructively interfere near the western margin of the plate boundary zone producing locally large strain accumulation along the san andreas fault saf system however they destructively interfere further into the plate interior resulting in smaller and more variable strain accumulation patterns in the eastern part of the plate boundary zone much of the rightlateral strain accumulation along the saf system is systematically underpredicted by models which account only for relaxation from known large earthquakes this strongly suggests that in addition to viscoelastic cycle effects steady deep slip in the lower lithosphere is needed to explain the observed strain rate field

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

the 2013 seismic swarm in chihuahua mexico evidence of active extensional deformation in the southern basin and range abstract an earthquake swarm took place from 27 august 2013 to december 2013 in the southern basin and range province of chihuahua mexico during this period the seismological service of mexico located approximately 60 earthquakes in the region the largest earthquake took place on 21 september 2013 m w 5 3 a temporary seismic network was installed in the area for a period of two weeks the hypocenters were relocated using the double difference algorithm the results show a cluster of seismicity along the vallecillo fault where most of the seismicity took place and on the penasco fault these two faults lie within the foothills of the sierras of the same name that bound the el caballo desert basin the seismicity suggests that both faults bounding the el caballo basin slipped during the swarm the main event of 27 august 2013 apparently took place on the vallecillo fault a third cluster of seismicity was located on sierra la mezcalera about 20 km to the south of the vallecillo fault at the western end of the la boquilla dam focal mechanisms of the larger events indicate right lateral slip with extensional deformation on the vallecillo fault with t axes oriented in a northeast southwest direction these source mechanisms reflect a regime of extensional tectonics in the southern basin and range province the vallecillo and penasco fault system is exposed for approximately 12 km along strike scaling relations suggest that earthquakes as large as m w 6 4 may take place on them this magnitude is similar to that of the 1928 parral earthquake that occurred about 125 km to the south of the swarm however segmented faults may rupture sequentially and generate a larger earthquake than the one predicted on the basis of the length of individual mapped faults

lake levels and sedimentary environments during deposition of the trego hot springs and wono tephras in the lake lahontan basin nevada usa abstract the wono and trego hot springs ths tephras are widespread in the lahontan basin and have been identified in a variety of sedimentary environments at different elevations davis 1983 reported lake level to be at about 1256 m when the ths tephra was deposited an interpretation questioned by benson et al 1997 who interpreted lake level to be 1177 m at that time this is a significant difference in lake size with important implications for interpreting the climate that prevailed at that time based on new interpretations of depositional settings of the ths bed at multiple sites the larger lake size is correct additional sites containing the wono tephra indicate that it was deposited when lake level was at about 1217 m in the western subbasins and at about 1205 m in the carson sink sedimentary features associated with progressively deeper paleowater depths follow a predictable pattern that is modulated by proximity to sediment sources and local slope fine to coarse sands with wave formed features are commonly associated with relatively shallow water silty clay or clay dominates in paleowater depths 25 m with thin laminae of sand and ostracods at sites located adjacent to or downslope from steep mountain fronts

coulomb stress evolution in a diffuse plate boundary 1400 years of earthquakes in eastern california and western nevada usa diffuse plate boundaries are characterized by deformation distributed over a wide area in a complex network of active faults and by relatively low strain rates these characteristics make it difficult to understand the spatial and temporal distribution of seismicity the area east of the sierra nevada between longitudes 121 degrees w and 116 degrees w is part of a diffuse plate boundary at least 17 major surface rupturing earthquakes have happened here in the last 1400 years our purpose is to determine whether these events influence each other or whether they are randomly distributed in time and space we model the evolution of coseismic and postseismic coulomb failure stress changes delta cfs produced by these earthquakes and we also model interseismic stresses on the entire fault network our results show that 80 of the earthquake ruptures are located in areas of combined coseismic and postseismic delta cfs 0 2 bar this relationship is robust as shown by the control tests that we carried out using random earthquake sequences we also show that the fish lake valley pyramid lake and honey lake faults have accumulated 45 37 and 27 bars respectively of total delta cfs i e coseismic postseismic interseismic in the last 1400 years such values are comparable to the average stress drop in a major earthquake and these three faults may be therefore close to failure

quaternary sedimentology of the rose creek fan delta walker lake nevada usa and implications to fan delta facies models the 3 2 km long rose creek fan delta of west central nevada is prograding from an active rift margin into the 32 m deep walker lake a case study of the forms processes and facies of this fan delta reveals that the proximal and medial zones mainly are of sub aerial origin and the distal zone is of lacustrine origin pebbly to bouldery rock avalanche mounds 100 m thick facies a and muddy to bouldery debris flow levees 0 5 to 2 0 m thick facies b dominate the proximal zone whereas mostly matrix supported cobbly pebbly debris flow lobes 0 1 to 1 0 m thick facies c typify the medial zone surficial pebble lags and gully fills facies d are widespread in both zones but in exposures comprise only partings or lenticles between debris flow units the distal fan delta mainly consists of lakeshore to lake bottom tracts formed by extensive wave reworking of debris flow facies nearshore deposits include erosional cobbly boulder lag beaches facies e pebbly constructional beaches attached at headcuts or on barrier spits facies f pebbly upper shoreface facies g and sandy lower shoreface facies h tracts positioned lakeward of the beach and pebbly landward dipping foresets facies i and backshore pond sand and mud facies j present landward of the spits erosional lag beaches fringe the windward north side of the fan delta front attached constructional beaches characterize the central zone and southward elongating barrier spits typify the leeward south side extending from the zone of greatest projection of the fan delta into the lake shoreline facies asymmetry results from largely unidirectional longshore drift caused by high fetch to the north and minimal fetch to the south combined with the arcuate shape of the fan delta front the spits overlie a platform deposited below common wave base consisting of south east trending cones of pebbly gilbert foresets facies k and sandy toesets facies l typically slumped silt and mud facies m fringe both this platform and lower shoreface sand in deeper water this case demonstrates facies types and patterns that are inconsistent with the widely promoted fan delta facies model having a front consisting of an apron of radially directed gilbert foresets deposited where sub aerial flows enter the lake the rose creek fan delta front instead features a sharp contact between sub aerial and lakeshore facies formed where waves erode sort and redistribute heterogeneous debris flow sediment into the various shallow to deep lake facies gilbert foresets are present only in the lee of the fan delta where sediment moving by longshore drift reaches the brink of the spit front this facies scenario results from the infrequency of fan building events versus nearly constant wind induced waves a scenario that in contrast to the popular gilbert model probably is the norm for fan deltas the level of walker lake and thus the position of wave reworking on the rose creek fan delta fluctuated over a range of 157 m during the last 18 kyr producing complex interfingering between sub aerial and lakeshore facies across a 1700 m wide radial belt typifying a wave modified freestand lacustrine fan delta

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

variability of displacement at a point implications for earthquake size distribution and rupture hazard on faults abstract to investigate the nature of earthquake magnitude distributions on faults we compare the interevent variability of surface displacement at a point on a fault from a composite global data set of paleoseismic observations with the variability expected from two prevailing magnitude frequency distributions the truncated exponential model and the characteristic earthquake model we use forward modeling to predict the coefficient of variation cv for the alternative earthquake distributions incorporating factors that would effect observations of displacement at a site the characteristic earthquake model with a characteristic magnitude range of 0 25 produces cv values consistent with the data cv 0 5 only if the variability for a given earthquake magnitude is small this condition implies that rupture patterns on a fault are stable in keeping with the concept behind the model this constraint also bears upon fault rupture hazard analysis which for lack of point specific information has used global scaling relations to infer variability in average displacement for a given size earthquake exponential distributions of earthquakes from m 5 to the maximum magnitude give rise to cv values that are significantly larger than the empirical constraint a version of the model truncated at m 7 however yields values consistent with a larger cv 0 6 determined for small displacement sites although this result allows for a difference in the magnitude distribution of smaller surface rupturing earthquakes it may reflect in part less stability in the displacement profile of smaller ruptures and or the tails of larger ruptures online material global surface displacement data and identified sources of uncertainty

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

historic surface faulting and paleoseismicity in the area of the 1954 rainbow mountain stillwater earthquake sequence central nevada the rainbow mountain area was the site of three surface rupturing earthquakes on 6 july and 23 august 1954 more than 50 field measurements of surface offsets constrain the distribution of slip along the discontinuous and distrib uted rupture zone that formed during the earthquake sequence vertical offsets reach a maximum of 0 8 m with the average vertical offset being 0 2 m in contrast to original reports we see evidence for a right lateral component of slip along portions of the rupture zone including offset stream channels 0 5 1 0 m left stepping en echelon scarps and a well preserved 100 m long mole track the right slip com ponent is consistent with focal plane solutions for the events and recent geodetic results previously unmapped surface ruptures now extend the known rupture length of the sequence by 25 km to a total of 70 km surface ruptures along the previously unmapped fourmile flat fault are subparallel to and form a 10 km left step to the southeast of the rainbow mountain fault event locations and anecdotal information indicate that the fourmile flat ruptures represent minor primary surface rupture associated with the large 6 july aftershock triggered 11 hr after the initial 6 july rainbow mountain event the paleoseismic histories of the rainbow mountain and fourmile flat faults as recorded in natural and trench exposures are different although both faults experi enced three post 15 ka surface rupturing events including 1954 bracketing ages for triultimate events on both faults do not overlap however constraints on the penultimate event for the rainbow mountain and triultimate event for the fourmile flat fault do overlap slightly allowing the possibility that they may have ruptured close in time as in 1954 the holocene slip rate for the fourmile flat fault 0 40 mm yr is similar to the post latest pleistocene rate for the rainbow mountain fault 0 20 0 46 mm yr even though the total length of the fourmile flat 10 km is much shorter than the overall length of the rainbow mountain rupture zone 60 km indicating that even minor faults can be important for assessing regional strain rates and patterns

long term fault slip rates distributed deformation rates and forecast of seismicity in the western united states from joint fitting of community geologic geodetic and stress direction data sets 1 the long term average velocity field of the western united states is computed with a kinematic finite element code community data sets include fault traces geologic offset rates geodetic velocities principal stress directions and euler poles there is an irreducible minimum amount of distributed permanent deformation which accommodates one third of pacific north america relative motion in california much of this may be due to slip on faults not included in the model all data sets are fit at a common rms level of 1 8 datum standard deviations experiments with alternate weights fault sets and euler poles define a suite of acceptable community models in pseudoprospective tests fault offset rates are compared to 126 additional published rates not used in the computation 44 are consistent another 48 have discrepancies under 1 mm a 1 and 8 have larger discrepancies updated models are then computed novel predictions include dextral slip at 2 3 mm a 1 in the brothers fault zone two alternative solutions for the mendocino triple junction slower slip on some trains of the san andreas fault than in recent hazard models and clockwise rotation of some domains in the eastern california shear zone long term seismicity is computed by assigning each fault and finite element the seismicity parameters coupled thickness corner magnitude and spectral slope of the most comparable type of plate boundary this long term seismicity forecast is retrospectively compared to instrumental seismicity the western united states has been 37 below its long term average seismicity during 1977 2008 primarily because of temporary reduced activity in the cascadia subduction zone and san andreas fault system

the relationship between the instantaneous velocity field and the rate of moment release in the lithosphere summary instantaneous velocity gradients within the continental lithosphere are often related to the tectonic driving forces this relationship is direct if the forces are secular as for the case of loading of a locked section of a subduction interface by the downgoing plate if the forces are static as for the case of lateral variations in gravitational potential energy then velocity gradients can be produced only if the lithosphere has on average zero strength the static force model may be related to the long term velocity field but not the instantaneous velocity field typically measured geodetically over a period of several years because over short time intervals the upper lithosphere behaves elastically in order to describe both the short and long term behaviour of an elastic lithosphere viscoelastic asthenosphere system in a selfconsistent manner i construct a deformation model termed the expected interseismic velocity eiv model assuming that the lithosphere is populated with faults that rupture continually each with a definite mean recurrence time and that the earth is well approximated as a linear elastic viscoelastic coupled system i derive a simple relationship between the instantaneous velocity field and the average rate of moment release in the lithosphere examples with synthetic fault networks demonstrate that velocity gradients in actively deforming regions may to a large extent be the product of compounded viscoelastic relaxation from past earthquakes on hundreds of faults distributed over large 10 6 km 2 areas

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

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

geologic context of geodetic data across a basin and range normal fault crescent valley nevada geodetic strain and late quaternary faulting in the basin and range province is distributed over a region much wider than historic seismicity which is localized near the margins of the province in the relatively aseismic interior both the magnitude and direction of geodetic strain may be inconsistent with the holocene faulting record we document the best example of such a disagreement across the ne striking 55 nw dipping crescent normal fault where a nw oriented 70 km geodetic baseline records contemporary shortening of 2 mm yr orthogonal to the fault trace in contrast our geomorphic paleoseismic and geochronologic analyses of the crescent fault suggest that a large extensional rupture occurred during the late holocene epoch an excavation across the fault at fourmile canyon reveals that the most recent event occurred at 2 8 0 1 ka with net vertical tectonic displacement of 4 6 0 4 m at this location corresponding to the release of 3 m of accumulated nw se extension measured alluvial scarp profiles suggest a minimum rupture length of 30 km along the range front for the event implying a moment magnitude m w of at least 6 6 no prior event occurred between 2 8 ka and 6 4 0 1 ka the 14 c calender age of strata near the base of the exposed section assuming typical slip rates for basin and range faults 0 3 mm yr these results imply that up to one third or 1 m of the extensional strain released in the previous earthquake could have reaccumulated across the fault since 2 8 ka however the contemporary shortening implies that the fault is unloading due to a transient process whose duration is limited to between 6 years geodetic recording time and 2 8 ka the age of the most recent event these results emphasize the importance of providing accurate geologic data on the timescale of the earthquake cycle in order to evaluate geodetic measurements

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

late pleistocene regional extension rate derived from earthquake geology of late quaternary faults across the great basin nevada between 38 5 n and 40 n latitude maps showing quaternary deposits and active fault traces paleoseismic trenches scarp diffusion analyses and soil characteristics in displaced alluvial surfaces are combined with previous paleoseismic studies to examine the character of late pleistocene earthquake recurrence and estimate the net extension rate across the interior of the great basin of the western united states at the latitude of 39 n the study area includes faults bounding the desatoya toiyabe monitor simpson park toquima antelope fish creek butte egan and schell creek ranges the rate of earthquake recurrence is documented to be significantly less than observed within the walker lane central nevada seismic belt and along the wasatch which respectively define the western and eastern boundaries of the interior of the great basin late pleistocene extension across the interior of the great basin is calculated to equal 1 mm yr across the 450 km transect and is consistent with rates defined by recent geodetic studies the agreement in extension rate estimates over different time scales indicates that tectonic deformation in the great basin has been characterized by relatively slow and consistent extension through the late pleistocene to the present the internal deformation of the great basin and the pattern of strain release may reflect a broad transition zone from northwest directed shear in the west to extension along the eastern edge of the pacific north american plate boundary

did plinian eruptions in california lead to debris flows in nevada an intriguing stratigraphic connection a common association of thin late holocene mono and inyo crater tephra beds buried by debris flows within a 250 km long corridor of western nevada suggests that there has been at times a genetic link between these two otherwise independent processes the unambiguous depositional relations and the undisturbed character of the tephra beds at more than 20 sites indicate that tephra deposition was often followed by burial under debris flows produced by intense precipitation considering that average return periods are hundreds of years for such storms it is highly improbable that this stratigraphic association is random coincidence we propose that the most plausible explanation for this association is that some plinian ash columns produced intense thunderstorms resulting in large debris flows that buried the tephra beds