analytical solutions of seawater intrusion in sloping confined and unconfined coastal aquifers sloping coastal aquifers in reality are ubiquitous and well documented steady state sharp interface analytical solutions for describing seawater intrusion in sloping confined and unconfined coastal aquifers are developed based on the dupuit forchheimer approximation specifically analytical solutions based on the constant flux inland boundary condition are derived by solving the discharge equation for the interface zone with the continuity conditions of the head and flux applied at the interface between the freshwater zone and the interface zone analytical solutions for the constant head inland boundary are then obtained by developing the relationship between the inland freshwater flux and hydraulic head and combining this relationship with the solutions of the constant flux inland boundary it is found that for the constant flux inland boundary the shape of the saltwater interface is independent of the geometry of the bottom confining layer for both aquifer types despite that the geometry of the bottom confining layer determines the location of the interface tip this is attributed to that the hydraulic head at the interface is identical to that of the coastal boundary so the shape of the bed below the interface is irrelevant to the interface position moreover developed analytical solutions with an empirical factor on the density factor are in good agreement with the results of variable density flow numerical modelling analytical solutions developed in this study provide a powerful tool for assessment of seawater intrusion in sloping coastal aquifers as well as in coastal aquifers with a known freshwater flux but an arbitrary geometry of the bottom confining layer this article is protected by copyright all rights reserved

paleomagnetic and 40ar 39ar geochronologic data bearing on the structural evolution of the silver peak extensional complex west central nevada the silver peak extensional complex located in the silver peak range of west central nevada is a displacement transfer system linking the furnace creek fish lake valley fault system and transcurrent faults of the central walker lane late neogene northwest directed motion of an upper plate composed of lower paleozoic sedimentary rocks and late tertiary volcanic and volcaniclastic strata exhumed a lower plate assemblage of metamorphic tectonites with proterozoic and mesozoic protoliths paleomagnetic investigation of miocene pliocene pyroclastic and sedimentary rocks of the upper plate and miocene mafic dikes in the lower plate reveals modest horizontal axis tilting northwest side up and vertical axis rotation clockwise within the extensional complex eight to ten samples from each of 123 sites were demagnetized 95 sites yielded interpretable results dual polarity results from one population of mafic dikes in the lower plate assemblage indicate moderate northwest side up tilting declination d 329 inclination i 37 95 4 3 number n 30 sites in situ 95 the confidence limit for the calculated mean direction expressed as an angular radius from the calculated mean direction some dikes yield exclusively normal polarity results that are interpreted to indicate modest clockwise vertical axis rotation d 021 i 57 95 4 3 n 19 sites in situ concurrent with uplift of the lower plate rocks and nine sites yield magnetization directions that are north directed with positive inclinations of moderate steepness similar to an expected miocene field late miocene pyroclastic rocks in the upper plate yield normal polarity magnetizations suggestive of moderate clockwise vertical axis rotation d 032 i 53 95 8 8 n 10 sites the apparent clockwise rotation is unlikely to result from incomplete sampling of the geomagnetic field because the overall dispersion of the vgp virtual geomagnetic pole positions is high for the latitude of the site location middle miocene sedimentary rocks probably were remagnetized shortly after deposition of eight 40ar 39ar determinations from mafic dikes in the lower plate five groundmass concentrates yield saddle shaped age spectra and one separate provided a plateau date of low confidence isochron analysis reveals that all six groundmass concentrates contain excess ar if rapid cooling and ar retention below 250 c are assumed the preferred age estimate for mafic intrusions is provided by isochron dates and suggests emplacement between 12 and 10 5 ma the 40ar 39ar age spectrum data are consistent with existing fission track cooling and k ar isotopic age information from lower plate granitic rocks and indicate rapid cooling of the lower plate assemblage from well above 300 c to 100 c between 13 and 5 ma rapid cooling may explain the overall distribution of paleomagnetic results from lower plate intrusions such that the earliest acquired magnetizations reflect both northwest side up tilt and clockwise rotation and the younger magnetizations reflect northwest side up tilt overall the paleomagnetic data from the silver peak extensional complex are interpreted to suggest that vertical axis rotation of crustal scale blocks associated with displacement transfer in the central walker lane may play an integral part in accommodating strain within a continental displacement transfer system

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

spatial and temporal constancy of seismic strain release along an evolving segment of the pacific north america plate boundary abstract three new slip rates from the death valley fish lake valley dvflv fault contribute to an exceptionally detailed record of lateral rate variations on this 300 km long system from south to north these three new sites are south mud canyon cucomongo canyon and indian creek slip rates were determined by combining offsets measured with 1 m resolution airborne lidar data with 10be cosmogenic nuclide surface exposure and optically stimulated luminescence ages from displaced alluvial fans the offset fans date to 17 4 2 3 ka at south mud canyon 39 3 ka at cucomongo canyon and 6 3 1 8 ka at indian creek yielding slip rates of 2 1 0 5 0 4 mm yr 6 1 1 3 1 0 mm yr and 2 2 0 8 0 6 mm yr respectively at indian creek the holocene 6 ka and late quaternary 70 ka slip rates are the same within uncertainty suggesting temporal constancy of seismic strain release along the northern dvflv fault zone over these time spans when combined with slip rates determined in earlier companion studies these results show that the late quaternary slip rate decreases northward and southward from the central part of the fault as slip is transferred onto north trending zones of distributed normal faulting towards the northeast and southwest of the central zone of rapid deformation this complex pattern of strain accommodation may reflect structural evolution towards a straighter structurally simpler zone of dextral shear that locally utilizes well established dextral faults that are linked where necessary by nascent zones of deformation summation of the rates of all major faults in the eastern california shear zone ecsz at the 37 n latitude of red wall canyon in northern death valley shows that the cumulative geologic rate of 8 5 10 mm yr is indistinguishable from the 9 mm yr geodetic rate although the cumulative rate on the major faults of the ecsz is slower to the north and south this probably reflects more distributed deformation in these areas rather than transient strain accumulation these results demonstrate the importance of obtaining multiple slip rates to effectively document the behavior of any fault system especially in studies of seismic hazard assessment and comparisons of geologic and geodetic rate data

effects of episodic rainfall on a subterranean estuary numerical simulations were conducted to examine the effect of episodic rainfall on nearshore groundwater dynamics in a tidally influenced unconfined coastal aquifer with a focus on both long yearly and short term daily behaviour of submarine groundwater discharge sgd and seawater intrusion swi the results showed non linear interactions among the processes driven by rainfall tides and density gradients rainfall induced infiltration increased the yearly averaged fresh groundwater discharge to the ocean but reduced the extents of the saltwater wedge and upper saline plume as well as the total rate of seawater circulation through both zones overall the net effect of the interactions led to an increase of the sgd the nearshore groundwater responded to individual rainfall events in a delayed and cumulative fashion as evident in the variations of daily averaged sgd and salt stored in the saltwater wedge quantifying the extent of swi a generalized linear model glm along with a gamma distribution function was developed to describe the delayed and prolonged effect of rainfall events on short term groundwater behaviour this model validated with results of daily averaged sgd and swi from the simulations of groundwater and solute transport using independent rainfall datasets performed well in predicting the behaviour of the nearshore groundwater system under the combined influence of episodic rainfall tides and density gradients the findings and developed glm form a basis for evaluating and predicting sgd swi and associated mass fluxes from unconfined coastal aquifers under natural conditions including episodic rainfall

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

steady contemporary deformation of the central basin and range province western united states we use data from western u s gps networks to estimate the rate pattern and style of tectonic deformation of the central basin and range province brp previous geodetic investigations have found the crust of eastern nevada and western utah to act as a rigid microplate with zero deformation rates to within measurement uncertainty observed transients in gps time series have led others to propose a megadetachment model predicting that the central brp behaves as a microplate but with time varying translation here we reassess these hypotheses benefiting from a significant increase in gps stations and time span and innovations in analysis techniques our results show that the brp crust deforms everywhere and all the time in a group of 24 stations between longitude 113 5 and 116 8 we find strain rates of 1 9 0 2 10 9 yr 1 extension directed n55 w and 2 2 0 2 10 9 yr 1 contraction directed n35 e inconsistent with microplate behavior the linearity of time series of strain from gps station triplets is inconsistent with episodic translation of quasi rigid domains one exception is station egan that exhibits nonlinear motion not found in adjacent stations the dominant signal in nevada is distributed shear consistent with pacific north america relative plate motion suggesting that stresses are transmitted through the lithosphere at least 800 km from the plate boundary the observed active extension is consistent with earthquake focal mechanisms and is in agreement with integrated rates estimated from earthquake geology our results do not support the proposed megadetachment in the brp

transience of seawater intrusion in response to sea level rise 1 understanding seawater intrusion swi induced by sea level rise slr is important for the future management of many coastal aquifers only simplified steady state sharp interface analyses of generalized slr swi exist in the literature and the important issue of associated time scales has been neglected we employ numerical modeling in order to explore the transience of dispersive slr swi in common unconfined coastal aquifer settings an instantaneous slr is adopted to compare with the instantaneous sea level drop sld case of a previous sld swi analysis temporal asymmetry between the swi responses to slr and sld is observed a slr swi simulation series indicates that toe representative response times time to reach 95 of new steady state range from decades to centuries for a 1 m slr significant discrepancies between the representative response times of various swi quantitative indicators e g toe position wedge center of mass are observed this demonstrates that the indication of steady state swi conditions depends upon the monitoring approach and thus holds implications for studies reporting that swi steady state has been attained we adopt 100 years as a typical planning time frame and compare 100 year and steady state slr swi as expected the simplified steady state sharp interface solution overpredicts the 100 year landward toe shift in most cases however some simulations exhibit temporary overshoot of the steady state interface position this is in contradiction to the presumption that steady state swi is the worst case steady state sharp interface estimates appear to be at best useful as initial approximations of slr swi given that they span 40 250 of 100 year dispersive interface results for the cases considered

quaternary faulting in queen valley california nevada implications for kinematics of fault slip transfer in the eastern california shear zone walker lane belt new geologic map tectonic geomorphologic and terrestrial cosmogenic nuclide tcn geochronologic data document the geometry style kinematics and slip rates on late quaternary faults within the queen valley california nevada area these data provide important insight into the kinematics of fault slip transfer from the dextral white mountains fault zone northward into the mina defl ection queen valley is an 16 kmlong ne trending basin bounded to the south by the white mountains and underlain by four major pleistocene to holocene alluvialfan surfaces four different fault types and orientations cut and offset all but the youngest surfaces 1 the normal slip queen valley fault which consists of a set of ne striking nw and se dipping normal fault scarps that cut across the se side of the valley and offset all but the youngest surfaces 2 discontinuous ne striking sinistral faults exposed on the north side of the valley 3 the nw striking dextral coyote springs fault which merges into 4 a set of e w striking thrust faults measured offsets across normal fault scarps developed within 10 be tcn dated surfaces yield minimum late pleistocene horizontal extension rates of 0 1 0 3 mm yr documented fault geometries and slip orientations across queen valley suggest that fault slip transfer models such as the extensional displacement transfer block rotation and simple shear models within the dextral fault system proposed for the eastern california shear zone walker lane belt are not applicable to this part of the mina defl ection rather dextral fault slip is transferred by both a restraining westward step and a releasing eastward step restraining and releasing bends have been extensively documented at a range of scales in strike slip fault tectonic settings globally and they have been simulated in analog models thus it is not surprising to document both within the 630 km long dextral shear zone that makes up the northern eastern california shear zone walker lane belt our results combined with published slip rates for the dextral white mountain fault zone and the eastern sinistral coaldale fault suggest that transfer of dextral slip into the mina defl ection is partitioned into three different components horizontal extension along the queen valley fault thrust faulting that merges into the dominantly dextral slip along the coyote springs fault and dominantly sinistral slip along the coaldale fault a velocity vector diagram of fault slip partitioning across queen valley predicts a small component of contraction across the coyote springs and western coaldale faults contraction across the mina defl ection is consistent with global positioning system data an observed reduction in late pleistocene fault slip rates at the northern end of the eastern california shear zone and across the southwestern part of the mina defl ection may be explained by distribution of slip across a much broader zone than generally thought

late pleistocene and holocene faulting in the western truckee basin north of truckee california evidence for active faulting in the truckee basin north of lake tahoe is observed in a meadow containing a scarp and small closed depression shallow hand dug trenches show offset marsh stratigraphy of holocene age lithostratigraphy descriptions and radiocarbon dates indicate the meadow was a marsh during the late quaternary that was abruptly infilled with the deposition of the 7000 yr b p tsoyawata tephra mt mazama the tephra is offset up to 80 cm across a narrow sub vertical north south striking fault zone additional offset of 30 cm occurred across the same structure during the late pleistocene our study provides direct stratigraphic evidence for at least one surface faulting event during the holocene and another in the late pleistocene within the truckee fault zone and provides new constraints on seismic sources capable of significant ground rupture and or shaking in the greater reno tahoe truckee area

morphological characterization of cluster microforms a field study was conducted on two mountain streams in the cascade mountains of washington state on the morphological characterization of cluster microforms morphological characterization of clusters is presented in terms of i cluster shape ii cluster geometric properties and iii the spatial arrangement of clusters in the horizontal plane clusters were differentiated from other microtopography features such as reticulate structures and transverse ribs and identified clusters were categorized by shape as being of pebble line comet heap or ring type the complex spatial arrangement of clusters at the sites was characterized by using a two dimensional correlation function which allowed for measurement of the average cluster spacing properties for the rivers examined pebble shaped clusters were the most frequently observed cluster shape cluster geometric properties were found to be controlled by particles of the largest size fraction in the bed and the projected frontal width of the cluster with cluster length being linearly related to cluster width for cluster width to height ratios 3 5 results of the cluster spacing analysis suggest that cluster spacing increases with cluster size and decreases with local slope application of this principle to the available spacing data shows that cluster spacing scales with the ratio of s d0 such that s d0 constant where s is the local slope and d0 the diameter of the largest particle in the cluster

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

effects of a pebble cluster on the turbulent structure of a depth limited flow in a gravel bed river pebble clusters are important morphological features of gravel bed rivers and have a significant effect on the spatial and temporal response of the flow this paper presents original results from measurements of velocity taken at a high spatial and temporal resolution in a turbulent flow upstream and downstream from a pebble cluster three electromagnetic current meters 0 013 m in diameter mounted on a wading rod were deployed upstream and downstream of an isolated pebble cluster along 31 vertical profiles that contained between 7 and 13 points in a 5 m long section the high sampling resolutions in a natural environment permitted characterization of the complex dynamics of the turbulent flow in the vicinity of the cluster the description of these dynamics is based on the interpretation of contour maps of several turbulence statistics including moments of velocity distributions reynolds shear stress quadrant analysis and autocorrelation function downstream from the cluster flow is decelerated the intensity of turbulence increases and zones of strong vertical motions are present the superimposition of the maps allowed us to decompose the field of turbulent flow around a pebble cluster into distinct regions in a downstream direction from the cluster we observed zones of flow acceleration recirculation vortex shedding flow reattachment fluid upwelling and flow recovering results indicate the existence of highly dynamic boundaries between zones where strong intermittent events are generated they also highlight the difference between shedding and upwelling motions of the flow

present day pattern of cordilleran deformation in the western united states we present the first detailed geodetic image of the entire western united states south of lat 42 n merging both campaign and continuous global positioning system gps and very long baseline interferometry vlbi data sets in a combined solution for station velocities having a single uniform reference frame the results are consistent with a number of features previously observed through local geodetic studies and very sparse space geodetic studies including a dominant pattern of right lateral shear associated with the san andreas fault rates of the westernmost sites along the california coast of 46 48 mm yr relative to a north america reference frame and some 11 13 mm yr of deformation accommodated east of the sierra nevada in the basin and range province north of lat 36 n south of 36 n the solution also shows that the southernmost san andreas fault system accommodates effectively all interplate motion and that the southern basin and range is not deforming significantly at lat 37 n the eastern california shear zone appears to exhibit simple shear oriented between n20 w and n40 w relative to north america with a fairly well defined transition zone from localized shear to diffuse spreading in the basin and range enigmatically this transition involves a significant component of contraction normal to the overall shear zone trend sites in the great basin move southwestward at up to 5 mm yr toward sites within the eastern california shear zone to the north in contrast there appears to be a relatively smooth transition from east west spreading within the eastern great basin to northwest southeast shear across the westernmost basin and range

delineation of gravel bed clusters via factorial kriging abstract gravel bed clusters are the most prevalent microforms that affect local flows and sediment transport a growing consensus is that the practice of cluster delineation should be based primarily on bed topography rather than grain sizes here we present a novel approach for cluster delineation using patch scale high resolution digital elevation models dems we use a geostatistical interpolation method i e factorial kriging to decompose the short and long range grain and microform scale dems the required parameters are determined directly from the scales of the nested variograms the short range dem exhibits a flat bed topography yet individual grains are sharply outlined making the short range dem a useful aid for grain segmentation the long range dem exhibits a smoother topography than the original full dem yet groupings of particles emerge as small scale bedforms making the contour percentile levels of the long range dem a useful tool for cluster identification individual clusters are delineated using the segmented grains and identified clusters via a range of contour percentile levels our results reveal that the density and total area of delineated clusters decrease with increasing contour percentile level while the mean grain size of clusters and average size of anchor clast i e the largest particle in a cluster increase with the contour percentile level these results support the interpretation that larger particles group as clusters and protrude higher above the bed than other smaller grains a striking feature of the delineated clusters is that anchor clasts are invariably greater than the d90 of the grain sizes even though a threshold anchor size was not adopted herein the average areal fractal dimensions hausdorff besicovich dimensions of the projected areas of individual clusters however demonstrate that clusters delineated with different contour percentile levels exhibit similar planform morphologies comparisons with a compilation of existing field data show consistency with the cluster properties documented in a wide variety of settings this study thus points toward a promising alternative dem based approach to characterizing sediment structures in gravel bed rivers

particle clusters in gravel bed rivers an experimental morphological approach to bed material transport and stability concepts structured gravel river beds clearly exert a major influence on bed stability indexing structural stability by field measurements of bed strength neglects the processes operating to entrain and transport bed material in different parts of each structure this study takes a morphological approach to interpreting the critical processes using particle tracing to determine the movement of individual cluster particles over a range of flood event magnitudes and durations the experiment was carried out on the river south tyne uk it uses flow hydrographs measured nearby and also benefits from previous studies of historical development channel morphology and sediment transport at the same site more than 30 clusters were monitored over a seven month period during which clusters occupied 7 16 per cent of the bed threshold flows delimiting three apparently contrasting bed sediment process regimes for cluster particles are tentatively set at 100 m3 s 1 and 183 m3 s 1 durations of flow at these levels are critical for cluster development rather than flow peak values wake particles are transported most easily flow straightening in the wandering channel planform reduces the stability of clusters since mechanical strength is markedly reduced by this change of direction the overall area covered by clusters between significant transport events varies little implying a dynamic equilibrium condition copyright 2005 john wiley sons ltd

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

patterns and timing of late quaternary faulting in the great basin province and relation to some regional tectonic features large scale surface faulting events each tens of kilometers long and involving more than a meter of displacement of late quaternary age have not been uniformly distributed but have been concentrated in subprovincial and smaller belts and areas within the great basin province furthermore faulting apparently has not been uniformly distributed over time the average recurrence interval of large scale faulting events on individual faults in the province is measured in thousands or tens of thousands of years in contrast to such long recurrence intervals in the central nevada and eastern california seismic belts large scale faulting events have occurred during the last 111 years in an apparently coherent sequential belt filling pulse of activity in which events were separated by only a few years or a few decades the questions are where are other pulses of large scale faulting likely to occur and what controls the localization of such belts and areas characterized by higher rates of faulting two examples of tectonic subprovinces that may play a role in delimiting smaller zones of faulting are the black rock carson sink zone of extension and the central nevada downwarp the central nevada seismic belt lies along the dividing line between these two subprovinces and the northwest margin of the black rock carson sink zone of extension coincides with the margin of a fingerlike belt of dense faulting in northwestern nevada

distributed extensional deformation in a zone of right lateral shear implications for geodetic versus geologic rates of deformation in the eastern california shear zone walker lane 1 the eastern california shear zone ecsz walker lane belt represents an important evolving component of the pacific north america plate boundary geodetic data suggest the northern ecsz is accumulating dextral shear at a rate of 9 3 mm a more than double the total measured late pleistocene rate at 37 5 n at this latitude the silver peak lone mountain splm extensional complex plays an important role in accommodating and transferring slip among the strike slip and normal faults of the ecsz and walker lane to better understand the recent geodynamic evolution of this region we determined late pleistocene extension rates for the clayton valley fault zone one of a series of down to the northwest normal faults comprising the splm using geologic mapping differential gps fault scarp surveys and cosmogenic nuclide geochronology extension rates along the clayton valley fault zone are time invariant at 0 1 0 1 to 0 3 0 1 mm a depending on fault dip since 137 ka when combined with other published fault slip rates at this latitude the cumulative late pleistocene geologic slip rate is 3 3 to 5 2 mm a this rate is lower than both the geodetic rate of dextral shear and other long term slip rate budgets in the northern ecsz our results suggest that deformation in clayton valley is spread across a diffuse set of normal faults and that not all of the deformation is recorded in the surficial geology we suggest that the low cumulative geologic slip rate in the northern ecsz may be a result of this distributed extension which can cause long term rates of deformation to be significantly underestimated

accommodation of missing shear strain in the central walker lane western north america constraints from dense gps measurements abstract we present 264 new interseismic gps velocities from the mobile array of gps for nevada transtension magnet and continuous gps networks that measure pacific north american plate boundary deformation in the central walker lane relative to a north america fixed reference frame northwestward velocities increase smoothly from 4 mm yr in the basin and range province to 12 2 mm yr in the central sierra nevada resulting in a central walker lane deformation budget of 8 mm yr we use an elastic block model to estimate fault slip and block rotation rates and patterns of deformation from the gps velocities right lateral shear is distributed throughout the central walker lane with strike slip rates generally

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

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

apatite u th he thermochronometry as an innovative geothermal exploration tool a case study from the southern wassuk range nevada abstract extensional type geothermal systems are complicated by the interrelation between footwall advection during exhumation and the subsequent redistribution of heat by migrating hydrothermal fluids in the hanging wall the southern wassuk range wr hanging wall hosts a moderate temperature extensional type geothermal system and is ideal for studying this duality by analyzing a suite of apatite ahe and zircon zhe helium samples from the footwall and hanging wall of the southern wr young 3 4 ma ahe ages along the wr front are concentrated along the se corners of segmented footwall blocks marking the location of focused mio pliocene transtension fracture dilation and advection hydrothermally reset ahe ages along the footwall range front suggest that the hawthorne geothermal system 85 135 c is long lived and has resided at a prominent structural boundary in the wr footwall marked by localized advection and range front deformation in contrast the presence of both hydrothermally reset and non reset ahe ages from a 1 4 km deep borehole in the hanging wall basin probably indicate that the geothermal plumbing system and current manifestation as a thermal anomaly 113 c are juvenile and are controlled by the generation of newly formed faults in the hanging wall ahe ages have been shown here to greatly enhance the focusing of regional scale geothermal exploration efforts and for the first time have been used to identify and estimate the temperature of unseen hydrothermal fluids

neotectonics geodesy and seismic hazard in the northern walker lane of western north america thirty kilometers of crustal shear and no strike slip article i nfo roughly 30 km of cumulative right lateral crustal displacement and 5 6 mm yr of the ongoing relative right lateral motion between the pacific and north american plates are observed in the northern walker lane the right lateral shear has been accommodated in large part by the development of a set of discontinuous en echelon normal fault bounded basins and perhaps significant vertical axis rotations of the intervening crust the observations provide an illustrative example of how large amounts of crustal shear may be accom modated in the absence of strike slip faults and point to difficulties attendant to melding geologic and geo detic observations in the analysis of seismic hazard in this particular case the assumption that all geodetically observed shear across the area will be recorded by earthquake displacements may be flawed

clustering of velocities in a gps network spanning the sierra nevada block the northern walker lane belt and the central nevada seismic belt california nevada 1 the deformation across the sierra nevada block the walker lane belt and the central nevada seismic belt cnsb between 38 5 n and 40 5 n has been analyzed by clustering gps velocities to identify coherent blocks cluster analysis determines the number of clusters required and assigns the gps stations to the proper clusters the clusters are shown on a fault map by symbols located at the positions of the gps stations each symbol representing the cluster to which the velocity of that gps station belongs fault systems that separate the clusters are readily identified on such a map four significant clusters are identified those clusters are strips separated by from west to east the mohawk valley genoa fault system the pyramid lake wassuk fault system and the central nevada seismic belt the strain rates within the westernmost three clusters approximate simple right lateral shear 13 nstrain a across vertical planes roughly parallel to the cluster boundaries clustering does not recognize the longitudinal segmentation of the walker lane belt into domains dominated by either northwesterly trending right lateral faults or northeasterly trending left lateral faults

a note on cluster bedform behaviour in a gravel bed river abstract the behaviour of cluster bedforms was investigated in the farma r central italy a study reach was surveyed and the three components of the pebble clusters occuring on the surface of a gravel bar were painted using different colours before and after each flood all the clusters were photographed and a comparison was made this simple methodology allowed the evolution of the painted clusters to be followed and also allowed a survey of the dislodgment of the clusters particles and the addition of new ones the experiment shows that the mobility of the wake grains is higher than that of the stoss particles a pebble cluster generally loses the wake grain first followed by the stoss pebbles the obstacel clast is commonly the last to be entrained and acts as a single particle after the wake and stoss particles have been dislodged different explanations of this unexpected behaviour are postulated and the interaction of pebble with bed armouring and bedload size distribution is discussed

kinematics of the southern walker lane belt and motion of the sierra nevada block california deformation in the southern walker lane belt region of the southwestern great basin accommodates significant portions of both pacific north america transform motion and basin and range extension apparent kinematic inconsistencies between geodetic and fault slip data in this region have made it difficult to understand the nature of the interaction between these deformation processes and to infer the regional kinematics we model the kinematics of this region in a manner that enforces kinematic consistency and includes fault geometry and slip rate data global positioning system gps survey data and very long baseline interferometry very long baseline array vlbi vlba site velocity data a model is found that is consistent with the set of available data and this model differs significantly from prior models for the region our model has the sierra nevada block which bounds the western margin of the great basin moving n50 w 5 at 12 7 1 5 mm yr with only minor amounts of counterclockwise rotation left lateral slip on the western garlock fault is a consequence of the relatively great westerly component of sierra nevada velocity we also find that the basin and range extension east of our study area occurs at a rate of about 2 5 mm yr which is slower than the rate in the central great basin

an apparent shear zone trending north northwest across the mojave desert into owens valley eastern california strain rates measured at four geodetic networks in eastern california situated between northern owens valley and transverse ranges along a small circle drawn about the pacific north america pole of rotation are remarkably consistent each exhibits 0 14 mu rad yr simple right lateral engineering shear strain accumulation across the local vertical plane tangent to the small circle local faults e g owens valley garlock helendale traversing these networks are not as closely aligned with the vertical planes of maximum shear strain accumulation as is the local tangent to the small circle a fifth network slightly east of the small circle shows no significant strain accumulation thus a shear zone trending n35 degree w from near the eastern end of the big bend of the san andreas fault to northern owens valley is indicated by these data this corresponds to the eastern california shear zone proposed on geological evidence by dokka and travis the shear zone carries approximately 8 mm yr of the pacific north america relative plate motion from the san andreas fault north northwest across the mojave desert into owens valley and the northern basin and range province the shear zone observed at the surface may be a manifestation of a through going subcrustal fault

active megadetachment beneath the western united states geodetic data interpreted in light of seismic imaging seismicity xenolith studies and the late quaternary geologic history of the northern great basin suggest that a subcontinental scale extensional detachment is localized near the moho to first order seismic yielding in the upper crust at any given latitude in this region occurs via an m7 earthquake every 100 years here we develop the hypothesis that since 1996 the region has undergone a cycle of strain accumulation and release similar to slow slip events observed on subduction megathrusts but yielding occurred on a subhorizontal surface 5 10 times larger in the slip direction and at temperatures 800 c net slip was variable ranging from 5 to 10 mm over most of the region strain energy with moment magnitude equivalent to an m7 earthquake was released along this megadetachment primarily between 2000 0 and 2005 5 slip initiated in late 1998 to mid 1999 in northeastern nevada and is best expressed in late 2003 during a magma injection event at moho depth beneath the sierra nevada accompanied by more rapid eastward relative displacement across the entire region the event ended in the east at 2004 0 and in the remainder of the network at about 2005 5 strain energy thus appears to have been transmitted from the cordilleran interior toward the plate boundary from high gravitational potential to low via yielding on the megadetachment the size and kinematic function of the proposed structure in light of various proxies for lithospheric thickness imply that the subcrustal lithosphere beneath nevada is a strong thin plate even though it resides in a high heat flow tectonic regime a strong lowermost crust and upper mantle is consistent with patterns of postseismic relaxation in the southern great basin deformation microstructures and low water content in dunite xenoliths in young lavas in central nevada and high temperature microstructures in analog surface exposures of deformed lower crust large scale decoupling between crust and upper mantle is consistent with the broad distribution of strain in the upper crust versus the more localized distribution in the subcrustal lithosphere as inferred by such proxies as low p wave velocity and mafic magmatism

the importance of bed sediment sand content for the structure of a static armor layer in a gravel bed river the surface structure of static armor layers generated from water worked gravel bed channels was investigated with primary focus on the influence of sand content and flow rate flume experiments were conducted in which four sediment mixtures with sand contents between 1 and 38 were armored under one of three different flow rates first and second order statistical analyses were applied to digital elevation models of unarmored armored and clustered bed surface areas to identify changes in surface structure results were combined with data from previous research to create an extended data set of armored bed surfaces water worked unarmored bed surfaces established under a dynamic equilibrium flow rate impacted the topographic variability and structure of the armored beds surface complexity decreased with armor formation as surface grains preferentially aligned with the flow direction the bed surface became smoother and where sediment mixture sand content was constant there was greater smoothing of the surface during higher armoring flows as grains rearranged more easily as bulk sand content increased statistical analyses of the expanded data set showed that beds with very little sand content developed static armor layers that remained rough and had greater topographic variability than armor layers from sediments with higher sand contents the bulk sediment sand content exerted a stronger influence over the change in surface roughness and structure upon armoring than that of the flow rate during armor formation when combined with the knowledge of the local flow regime the sand content may aid in predictions related to armored bed surface structure

sea level rise impact on fresh groundwater lenses in two layer small islands the fresh groundwater lenses fgls of small islands can be highly vulnerable to climate change impacts including sea level rise slr many real cases of atoll or sandy islands involve two layer hydrogeological conceptualizations in this paper the influential factors that affect fgls in two layer small islands subject to slr are investigated an analytical solution describing fgls in circular islands composed of two geological layers is developed for the simplified case of steady state and sharp interface conditions an application of the developed model is demonstrated to estimate the fgl thickness of some real world islands by comparison with existing fgl thickness data furthermore numerical modelling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases sensitivity analyses are used to assess the importance of land surface inundation caused by slr relative to other parameters i e thickness of aquifer layers hydraulic conductivity recharge rate and land surface slope that influence the fgl dimensionless parameters are used to generalize the findings the results demonstrate that land surface inundation has a considerable impact on a fgl influenced by slr as expected although the fgl volume is more sensitive to recharge aquifer thickness and hydraulic conductivity than slr impacts considering typical parameter ranges the methodology presented in this study provides water resource managers with a rapid assessment tool for evaluating the likely impacts of slr and accompanying lsi on fgls

the unusual temporal and spatial slip history of the wassuk range normal fault western nevada usa implications for seismic hazard and walker lane deformation we document temporal and spatial variations in vertical displacement rate across 6 temporal orders of magnitude to better understand how the 100 km long east dipping wassuk range normal fault system has accommodated strain in the context of the walker lane a tectonically active nnw trending zone of dextral and extensional deformation that affects significant portions of western nevada and eastern california we combine 10 be and 26 al cosmonuclide exposure ages with shallow seismic and gravity data from the buried hanging wall of the wassuk fault to derive a post 113 ka 10 5 yr time scale vertical displacement rate of 0 82 0 16 mm yr we also perform large scale fault scarp analysis to constrain the long term 1 ma 10 6 yr time scale displacement rate our fault scarp analysis results imply similar vertical displacement rates with higher long term vertical displacement rates along the southern fault 1 1 mm yr relative to the northern fault vertical displacement rate data at the 10 6 10 5 10 3 and 10 1 yr time scales this study and others support a constant vertical displacement rate between 0 75 and 1 0 mm yr for the wassuk range fault since ca 4 ma an anomalously high vertical displacement rate at the 10 4 yr time scale is best explained by an earthquake cluster between ca 15 5 ka and ca 10 5 ka potentially linked to rapid filling of the walker lake basin immediately prior to the ca 13 ka sehoo highstand of ancestral lake lahontan we hypothesize that this flood event induced seismicity by placing an additional load on the hanging wall of the wassuk range fault and by increasing the pore fluid pressure within and adjacent to the fault although an earthquake cluster like this is consistent with wallace type fault behavior we suggest that a nontectonic stressor induced the cluster resulting in the apparent discrepancy in vertical displacement rate at the 10 4 yr time scale thus we posit that the long term slip along wassuk fault is better explained by slip predictable reid type behavior which deviates from the behavior of other well documented fault systems based on these results we suggest that similar unrecognized nontectonic stressors may influence rates of strain release along other major fault systems worldwide finally we present a revised model of central walker lane kinematics based on data from this and other recent studies

kinematics of the southwestern u s deformation zone inferred from gps motion data 1 we have estimated the surface deformation field of the southwestern u s deformation zone in terms of the velocity gradient field and surface creep simultaneously by inversion of 497 geodetic velocities the model shows aseismic fault motion consistent with aseismic creep measurements and a sense of motion consistent with geological observations we deduce that our surface deformation field shows distributed deformation in a zone around the faults containing shear strains and rotations the eastern california shear zone acts as a distinct fault zone bounded by more rigid blocks the faults within the zone partition the shear motion while right lateral shear strain rates and clockwise rotations are concentrated between the bounding faults in the same way the san jacinto and southern san andreas faults act as bounding faults of a fault zone the mojave desert is dominated by right lateral shear whereas the western transverse ranges wtr is subjected to contraction we find significant localization of deformation east of the san andreas fault between the transverse ranges and the san francisco bay we attribute this to a relative rigidity contrast across the fault of 1 8 finally a moment deficit analysis shows an accumulation of moment deficit between 1973 and 2000 corresponding to a mw 6 1 6 3 earthquake along the san andreas fault just north of the big bend around the imperial and southern san andreas faults and in the san francisco bay area along the hayward and southern calaveras faults

three dimensional flow structure around small scale bedforms in a simulated gravel bed environment pebble clusters are common small scale morphological features in gravel bed rivers occupying as much as 10 per cent of the bed surface important links exist between the presence of pebble clusters and the development of flow structures these links are poorly understood at the three dimensional level particularly neglected has been the effect of clusters on the lateral flow characteristics a laboratory study was conducted using a hydraulic flume within which simulated pebble clusters were superimposed onto a plane bed of gravel material high resolution three dimensional flow data were collected above the bed at two different flow depths using an acoustic doppler velocimeter the results present evidence of the importance of lateral flow in the development of turbulent flow structure narrow regions of high lateral and downstream turbulence intensity exist to both sides of clusters and in a three dimensional separation zone in their lee this may indicate the presence of horseshoe type vortical structures analogous to those identified in less hydraulically rough environments however it is likely that these structures are more complicated given the mutual interference of the surrounding medium the lateral flow was also identified as a key component in the upwelling identified by other authors in the lee of pebble clusters the results of the vertical flow analysis confirm the hypothesis that six regions with distinct vertical flow characteristics exist above clusters flow acceleration up the stoss side of the cluster recirculation behind the cluster in the wake region vortex shedding from the pebble crest and shear layer flow reattachment downstream of the cluster upwelling of flow downstream of the point of reattachment and recovery of flow copyright 2001 john wiley sons ltd

regional coseismic deformation from the june 28 1992 landers california earthquake results from the mojave gps network the 1992 landers california earthquake sequence and its aftershocks delineate an active part of the eastern california shear zone the surface rupture lies within the mojave desert providing a unique opportunity to characterize far field deformation with a regional global positioning system gps network that was installed and occupied in may 1991 with uncertainties of less than 1 cm on interstation baseline vectors changes in absolute displacement vectors on the decimetre and centimetre level were determined for individual sites providing more samples of the sparsely sampled landers displacement field measured displacements result from secular strain across the mojave desert coseismic elastic recovery and postseismic deformation during the six weeks between the earthquake and the gps experiment secular strain and postseismic displacement are relatively small thus first order modeling of these fields allows calculation and subtraction of their signals leaving a coseismic residual field the gps determined far field coseismic displacements differ significantly from elastic half space models offering new insight on the role of regional scale heterogeneity in crustal structure

assessment of the impact of sea level rise on seawater intrusion in sloping confined coastal aquifers abstract previous studies of the impact of sea level rise on seawater intrusion slr swi are mostly based on horizontal coastal aquifers despite that most coastal aquifers are sloping a recent study has shown that the effect of aquifer slope can not be neglected when assessing slr swi in unconfined coastal aquifers however the effect of slope in confined aquifers has not been evaluated in this study we apply existing analytical solutions to quantify the effect of the slope of both upper and lower confining layers on slr swi the results show that for flux controlled sloping confined coastal aquifer systems slr does not change the steady state interface location consistent with previous findings for horizontal aquifers therefore our analysis focuses on head controlled sloping confined coastal aquifer systems for which we find the assumption of horizontal confining units causes significant errors we demonstrate this by assessing the sensitivities of the seawater toe location and seawater volume to slr for various combinations of sloping confining layers the results indicate that the influence of the slope on slr swi is small in thin confined aquifers however the slope is an important factor in thick confined aquifers the influence of the slope in the lower confining layer on slr swi is much greater than that of the upper confining layer aquifers that thin towards the sea are most susceptible to slr swi whereas those that thin towards inland are least susceptible the assessment of slr swi in sloping confined coastal aquifers in the current study demonstrates application of a rapid first order assessment tool that can be applied to a wide range of other sloping coastal confined aquifer problems

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

investigating the role of clasts on the movement of sand in gravel bed rivers the bed morphology of mountain rivers is characterized primarily by the presence of distinguishable isolated roughness elements such boulders or clasts the objective of this experimental study was to provide a unique insight into the role of an array of clasts in regulating sand movement over gravel beds for low relative submergence conditions h dc 1 and flow depth h to the diameter of the clast dc a process that has not been studied thoroughly to assess the role of clasts in controlling incoming sand movement detailed flume experiments were conducted by placing 40 equally spaced clasts atop a well packed glass bead bed for replicating the isolated roughness flow regime the experiments were performed for moderate 2 50 cr where cr is the critical dimensionless bed shear stress and high 5 50 cr applied bed shear stress conditions representative of gravel bed rivers for comparison purposes experiments were also repeated for nearly identical flow conditions but without the presence of

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

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

quantifying dextral shear on the bristol granite mountains fault zone successful geologic prediction from kinematic compatibility of the eastern california shear zone abstractfor regional kinematic compatibility to be a valid boundary condition for continental tectonic reconstructions there must be tests that validate or invalidate kinematic model predictions in several reconstructions of western north america the displacement history of the mojave block continues to be unresolved the magnitude of displacement along the bristol granite mountains fault zone bgmfz which is the eastern margin of the eastern california shear zone ecsz in the mojave block is a key example of a long standing kinematic prediction that has defied a positive field test until now the ecsz is a network of late neogene and quaternary right lateral strike slip faults that extend from the gulf of california north through the mojave desert linking pacific north america plate motion with basin and range extension this network of faults accounts for 15 of post 16 ma plate transform motion geologic estimates of net dextral offset along the mojave portion of the ecsz 53 6 km are appro

transitional field clusters from uppermost oligocene volcanic rocks in the central walker lane western nevada abstract three sections of the candelaria hills volcanic sequence west central nevada appear to have recorded parts of two transitional field records or reversal excursions paleomagnetic data and 40 ar 39 ar laser fusion sanidine age estimates for pyroclastic rocks and associated flows show that these rocks recorded the unusual field behavior at about 25 7 ma and about 23 8 ma fifteen sites yield northeast declination moderate to shallow negative inclination mean directions and 16 sites yield west to southwest declination moderate negative inclination directions both populations of site mean directions representing a total of 12 independent eruptive units are highly discordant to a time averaged late tertiary field direction and neither can be explained by a geologically reasonable magnitude of vertical axis rotation virtual paleomagnetic poles vgps estimated from the directional data lie at low to intermediate latitudes 29 of the 31 flows at intermediate latitudes

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

a reappraisal of the significance of obstacle clasts in cluster bedform dispersal the dispersal of cluster bedforms is examined in a short partially braided reach of the river quoich northeast scotland after minor flood events in 1989 and 1990 in all cases the eventual dispersal of clusters occurred without prior removal of the obstacle clast since none of the obstacle clasts was dispersed in 1989 and only two thirds by 1990 obstacle clasts probably form a less significant delay to sediment entrainment than previously assumed and represent a relatively immobile component of bed sediment

a new hypothesis for the amount and distribution of dextral displacement along the fish lake valley northern death valley furnace creek fault zone california nevada 1 the fish lake valley northern death valley furnace creek fault zone a 250 km long predominantly right lateral structure in california and nevada is a key element in tectonic reconstructions of the death valley area eastern california shear zone and walker lane and central basin and range province total displacement on the fault zone is contested however with estimates ranging from 30 to 63 km or more here we present a new synthesis of available constraints preextensional thrust faults folds and igneous rocks indicate that offset reaches a maximum of 50 km neogene rocks constrain its partitioning over time most offset is interpreted as 13 10 ma accruing at 3 5 mm yr in the middle of the fault zone and more slowly toward the tips the offset markers imply 68 14 km of translation between the cottonwood mountains and resting spring nopah range 60 14 km since 15 ma through a combination of strike slip and crustal extension this suggests that a previous interpretation of 104 7 km based on the middle miocene eagle mountain formation is an overestimate by 50 our results also help to mitigate a discrepancy in the 12 0 ma strain budget for the eastern california shear zone displacement has previously been estimated at 100 10 km and 67 6 km for the basin and range and mojave portions of the shear zone respectively our new estimate of 74 17 km for the basin and range is within the uncertainty of the mojave estimate

replenishing an unconfined coastal aquifer to control seawater intrusion injection or infiltration in this study we compare the performances of well injection and pond infiltration in controlling seawater intrusion in an unconfined coastal aquifer through two scenario groups 1 a single injection well vs an elliptic infiltration pond and 2 an injection extraction well pair system vs an elliptic infiltration pond extraction well system comparison is based on quantitative indicators that include the interface toe location saltwater volume and maximum net extraction rate for scenario 2 we introduce a method to determine the maximum net extraction rate for cases where the locations of stagnation points cannot be easily derived analytical analysis shows that the performances of injection and infiltration are the same provided that the pond shape is circular the examination of scenario group 1 suggests that the shape of the infiltration pond has a minor effect on the interface toe location as well as the reduction in the saltwater volume given the same total recharge rate the investigation of scenario group 2 indicates by contrast that the maximum net extraction rate increases significantly with the increasing ratio of b to a where a and b are semi axes of the ellipse parallel and perpendicular to the coastline respectively specifically for a typical aquifer assumed an increase of 40 is obtained for the maximum net extraction when b a increases from 1 200 to 200 despite that the study is based on a simplified model the results provide initial guidance for practitioners when planning to use an aquifer recharge strategy to restore a salinized unconfined coastal aquifer

sea level rise impacts on seawater intrusion in coastal aquifers review and integration summary sea level rise slr influences groundwater hydraulics and in particular seawater intrusion swi in many coastal aquifers the quantification of the combined and relative impacts of influential factors on swi has not previously been considered in coastal aquifers in the present study a systematic review of the available literature on this topic is first provided then the potential remaining challenges are scrutinized open questions on the effects of more realistic complexities such as gradual slr parameter uncertainties and the associated influences in decision making models are issues requiring further investigation we assess and quantify the seawater toe location under the impacts of slr in combination with recharge rate variations land surface inundation lsi due to slr aquifer bed slope variation and changing landward boundary conditions lwbcs this is the first study to include all of these factors in a single analysis framework both analytical and numerical models are used for these sensitivity assessments it is demonstrated that 1 lsi caused by slr has a significant incremental impact on the seawater toe location especially in the flatter coasts and the flux controlled fc lwbcs however this impact is less than the reported orders of magnitude differences which were estimated using only analytical solutions 2 lwbcs significantly influence the slr impacts under almost all conditions considered in this study 3 the main controlling factors of seawater toe location are the magnitudes of fresh groundwater discharge to sea and recharge rate regional freshwater flux entering from the landward boundary and the groundwater hydraulic gradient are the major contributors of fresh groundwater discharge to sea for both fc and head controlled hc systems respectively 4 a larger response of the aquifer and larger seawater toe location changes are demonstrable for a larger ratio of the aquifer thickness to the aquifer length particularly in the hc systems 5 the lowest sensitivity of seawater toe location is found for the density difference ratio of the seawater and freshwater and also for the aquifer bed slope 6 the early time observations show seawater fingers below the inundated lands due to slr which are diminished and ultimately extinguished and 7 a less than 2 reversal effect on the seawater toe location after overshoot mechanism is observed in the transient simulations which suggests that this mechanism is an insignificant and impractical factor compared to other more significant factors

geometry kinematics and landscape characteristics of an active transtension zone karakoram fault system southwest tibet abstract we investigate the style of active transtensional deformation and characteristics of the landscape along the southern segment of the karakoram fault system through field mapping structural analysis and examination of digital topography srtm aster multi spectral aster landsat 7 and panchromatic corona photography imagery our data suggests that wrench dominated transtension is occurring within a 90 km wide zone simple shear within the zone is accommodated by right lateral r and p shears as well as left lateral r shears vertical shortening is accommodated by north striking extensional shear zones and horizontal shortening is accommodated by east west trending transtension related corrugations drainage divides strike at high angles and subparallel to the transtension zone those that strike at high angles to the zone can be explained by movement along north striking extensional fault systems while the geometry of drainage divides subparallel to the zone are consistent with uplift of corrugations as well as rapid uplift of mountain ranges by normal right slip faulting

the influence of microform bed roughness elements on flow and sediment transport in gravel bed rivers a reply clifford et al 1992 argue that differences in hydraulic conditions at the moment of sediment entrainment in turkey brook flood by flood are attributable to variations in the form drag that arises from cluster microforms while not denying the possibility of variable cluster concentration we show that the time dependent bed consolidation and cementation that arises as a function of interstitial matrix development can also account for variation in the traction threshold clifford et al further postulate that the growth of pebble clusters just prior to bedload entrainment is a cause of the observed differences in traction thresholds at the start and finish of bedload during a flood event this merits further examination however we point out that clusters are not only observed at low flow and therefore already present and able to contribute significant form drag as the next bedload generating flood waxes but that they are known both to survive more or less intact and to entrap mobile particles during bed disturbing events the revelation by clifford et al that flow structure in the river quarme reflects differences in bed rugosity between riffles and pools and that it relates in scale to bed roughness elements perhaps clusters is not surprising there is however some difficulty in distinguishing the precedence of chicken and egg when using this data set to elucidate the cause of cluster spacing nevertheless the inference that flow and form are dynamically linked is in sympathy with our own conclusions that cluster spacing is an equilibrium condition governed by the interplay of flow resistance and sediment transport

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

contact metamorphism of the white mountain peak metavolcanic complex eastern california the nnw trending white inyo range represents the eastern continuation of the sierran volcanic plutonic arc along the central california nevada state line south of white mountain peak the ne trending steeply se dipping barcroft structural break transects the orogenic belt this high angle reverse fault downdropped deformed weakly recrystallized mid mesozoic mildly alkaline white mountain peak mafic and felsic metavolcanic flows interlayered volcanogenic metasedimentary strata and minor subvolcanic plugs against a folded neoproterozoic lower paleozoic quartzite and carbonate metasedimentary section on the south the middle jurassic barcroft granodioritic pluton later intruded the barcroft break the middle jurassic cottonwood and late cretaceous mcafee creek pellisier flat granitoids also invaded the superjacent section on the ne heating of the white mountain peak metavolcanic complex by the barcroft and nearby plutons caused a southeastward progressive increase in metamorphic grade producing neoblastic biotite epidote and hornblende in mafic volcanic rocks minor hypabyssal stocks and biotite epidote andalusite in felsic volcanic rocks volcaniclastic strata gradual increases in biotite ti and plagioclase an contents reflect this se metamorphic zonation utilizing hornblende actinolite muscovite celadonite and biotite solid solutions thermobarometry indicates lithostatic pressures of 2 3 kbar during recrystallization with temperatures ranging from a background value of 350 c far from the barcroft pluton to 500 c along the intrusive contact physical conditions were similar to those developed in the neoproterozoic lower paleozoic platform strata directly south of the barcroft granodiorite the region constitutes a typical example of the p t evolution of the late mesozoic californian crustal margin where episodic magma emplacement caused widespread contact metamorphism

assessment of the impact of sea level rise on steady state seawater intrusion in a layered coastal aquifer abstract previous studies on the impact of sea level rise slr on seawater intrusion swi are mostly based on the assumption of a homogeneous coastal aquifer in this study we extend those studies by investigating slr induced swi in a layered coastal aquifer using the analytical method developed by strack and ausk 2015 we provide analytical solutions for steady state swi in confined and unconfined coastal aquifers where both constant head and constant flux inland boundary conditions are considered the analysis based on a three layer aquifer indicates that in general aquifer stratification affects either or both the initial location and response distance of the interface toe specifically for flux controlled unconfined coastal systems the toe response distance driven by slr is a linear function of the hydraulic conductivity of the top layer and independent of hydraulic conductivities of lower layers using an equivalent homogeneous hydraulic conductivity derived based on the initial interface toe location before slr would result in overestimation or underestimation of the toe response distance depending on the hydraulic conductivities and thicknesses of the layers for flux controlled confined layered coastal systems by contrast slr can not cause variation of the steady state interface toe location which is consistent with previous findings for homogeneous coastal aquifers the interface toe location in head controlled layered coastal systems is only a function of relative hydraulic conductivities between the layers moreover the effect of the layer thickness on the interface toe location and response distance in the head controlled system exhibits a more complicated pattern than in the flux controlled coastal system as changing the layer thickness changes both the overall aquifer transmissivity and inland freshwater flux the results obtained enhance the understanding of the impact of slr on swi which could provide a first order assessment tool for relevant practitioners

experiments on surface structure and partial sediment transport on a gravel bed eight flume experiments were conducted to study the development of bed surface texture and structure in the presence of partial bed material transport the experiments have two phases a no feed degradational phase followed by a feeding phase a surface structure of irregular reticulate stone nets and clusters was developed before sediment feeding commenced bed load transport equaled or slightly exceeded the fed supply except at the highest feed rate the bed structure was maintained but bed surface texture fined with increasing sediment load the two phenomena may coexist because the largest grains on the bed moved only very sporadically the actual sediment transport rates were much less than the expected rate calculated from the ratio of bed surface grain size to transported grain size the difference reflects the increase in bed stability introduced by the bed structure between 17 and 47 of the bed shear stress is estimated to be carried by the structure 4 being absorbed by the load while the bed grains carried the balance of the stress bed material transport is exceedingly sensitive to bed surface structure and grain size which raises concerns about the realizable precision of grain size measurements and characterization of the structure

spatiotemporal patterns of fault slip rates across the central sierra nevada frontal fault zone abstract patterns in fault slip rates through time and space are examined across the transition from the sierra nevada to the eastern california shear zone walker lane belt at each of four sites along the eastern sierra nevada frontal fault zone between 38 and 39 n latitude geomorphic markers such as glacial moraines and outwash terraces are displaced by a suite of range front normal faults using geomorphic mapping surveying and 10 be surface exposure dating mean fault slip rates are defined and by utilizing markers of different ages generally 20 ka and 150 ka rates through time and interactions among multiple faults are examined over 10 4 10 5 year timescales at each site for which data are available for the last 150 ky mean slip rates across the sierra nevada frontal fault zone have probably not varied by more than a factor of two over time spans equal to half of the total time interval 20 ky and 150 ky timescales 0 3 0 1 mm year 1 mode and 95 ci at both buckeye creek in the bridgeport basin and sonora junction and 0 4 0 3 0 1 mm year 1 along the west fork of the carson river at woodfords data permit rates that are relatively constant over the time scales examined in contrast slip rates are highly variable in space over the last 20 ky slip rates decrease by a factor of 3 5 northward over a distance of 20 km between the northern mono basin 1 3 0 6 0 3 mm year 1 at lundy canyon site to the bridgeport basin 0 3 0 1 mm year 1 the 3 fold decrease in the slip rate on the sierra nevada frontal fault zone northward from mono basin is indicative of a change in the character of faulting north of the mina deflection as extension is transferred eastward onto normal faults between the sierra nevada and walker lane belt a compilation of regional deformation rates reveals that the spatial pattern of extension rates changes along strike of the eastern california shear zone walker lane belt south of the mina deflection extension is accommodated within a diffuse zone of normal and oblique faults with extension rates increasing northward on the fish lake valley fault where faults of the eastern california shear zone terminate northward into the mina deflection extension rates increase northward along the sierra nevada frontal fault zone to 0 7 mm year 1 in northern mono basin this spatial pattern suggests that extension is transferred from more easterly fault systems e g fish lake valley fault and localized on the sierra nevada frontal fault zone as the eastern california shear zone walker lane belt faulting is transferred through the mina deflection

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

flow heterogeneity over 3d cluster microform laboratory and numerical investigation the present study examines the flow around a self occurring cluster bed form and the use of general computation fluid dynamics methods for hydraulic and geophysical flow applications this is accomplished through a comprehensive experimental numerical investigation in the laboratory cluster bed forms are first formed from movable sediment and laser doppler velocimeter measurements of two dimensional fluid velocity are then taken around a formed cluster a three dimensional 3d reynolds averaged navier stokes simulation of the physical cluster and flow conditions is then conducted using near wall shear stress transport sst turbulence modeling with the inclusion of hydraulic roughness ks r 31 150 ks h 0 1 ks 274 i e in the fully rough regime sst near wall modeling is advantageous compared to the more widely used wall functions approach for flows with significant roughness and flow separation because the model equations can be integrated down to the wall therefore sst near wall model

sediment transporting flows in headwater streams the equilibrium alluvial stream channel has a geometry that allows it to pass the water and sediment supplied from the watershed at the same time the equilibrium alluvial channel is built and maintained by the flows and sediment delivered to it a prerequisite for understanding the creation of the equilibrium channel is an understanding of the sediment conveyance and competence of the flows the channel receives this study describes the bed load transport regime as it is linked to hydrology and geomorphology in 23 headwater gravel bed streams in snowmelt dominated parts of central and northern idaho at sites drainage areas range from 1 29 to 381 km 2 stream gradients range from 0 0042 to 0 0747 and median bed surface particle sizes range from 4 to 207 mm stream architecture includes riffle pool planar and step pool beds the bed load is much finer than the surface and subsurface material suggesting selective transport of the finer sizes nonetheless the majority of the load is sand at all flow discharges progressively coarser sediment was collected as flow discharge increased and painted rock experiments documented the transport of coarser particles at higher discharges the supply of sediment to the streams appears limited as indicated by observed clockwise hysteresis in bed load transport rates during each spring snowmelt and by the coarse surface armor observed at sites flows above bankfull discharge move 37 of the bed load whereas flows between mean annual discharge and bankfull move 57 of the bed load the bed load effective discharge has a recurrence interval that averages 1 4 yr and the magnitude of effective discharge averages 80 of bankfull discharge the recurrence interval of bankfull discharge averages 2 0 yr the ratio of effective discharge to bankfull discharge is independent of basin size grain size and gradient although the ratio increases with the relative magnitude of large infrequent events

seawater intrusion in response to sea level rise in a coastal aquifer with a general head inland boundary seawater intrusion in response to sea level rise has been studied extensively in recent years by assuming largely a constant head or constant flux inland boundary condition however these two types of boundary conditions are not sufficient when the inland edge of the model domain is neither natural groundwater nor known hydraulic boundaries under these circumstances a general head inland boundary condition capable of characterizing the hydraulic response of model boundaries is needed previous studies adopting the general head inland boundary condition to assess coastal aquifer vulnerability to sea level rise are limited and all based on numerical modeling in this study we derive analytical solutions of the interface toe location in both confined and unconfined coastal systems with a general head inland boundary condition comparison among the performances of the three different types of inland boundary conditions in evaluating the sea level rise impact on aquifer salinization is carried out by assuming the same initial system condition it is found that the displacement of the interface toe predicted using a general head inland boundary is between those of using a constant head upper bound and constant flux lower bound inland boundary depending on the values of two general head boundary parameters i e hydraulic conductance and reference head more importantly analytical solutions developed could serve as a tool for calibrating the two boundary parameters defined in the general head boundary condition for site specific assessments

laboratory study on the evolution of gravel bed surfaces in bed armoring processes abstract cluster microforms in bed armoring have important implications for bedload transport in this study two sets of flume experiments were carried out to study the evolution of the cluster microforms in the bed armoring and their influences on the bedload transport dynamically stable armor layers were formed by applying a staged hydrograph on a mobile sediment bed consisted of poorly sorted sand and gravel thus enabling the investigation of the cluster microforms associated with different flow characteristics simulated in these experiments the size and the planimetric positions of the large particles on the bed surface were extracted using photogrammetric technique allowing analysis of surface grain size distribution and particle clustering pattern of the bed the results showed a tendency towards a coarsened and clustered bed surface which is likely responsible for the declining bedload transport rate the cluster microforms evolved with increasing bed shear stress in the following sequence flat bed pebble cluster line cluster heap cluster reticulate structure we found a bed armoring statistics that can partially explain the declining bedload transport rate under constant discharge nonetheless additional parameters are needed to simulate the fluctuation in the bedload transport rate under changing flow conditions

analysis of small scale gravel bed topography during armoring 1 in evaluating the resistance of sediment particles to entrainment by the action of the flow in a river the grain geometry is usually characterized using representative sizes this approach has been dictated initially by lack of physical insight but more recently by the lack of analytical tools able to describe the 3 d nature of surface grain organization on water worked sediment beds laboratory experiments are presented where mixed grain size beds were mobilized under a range of hydraulic and sediment input conditions detailed bed topography was measured at various stages statistical tools have been adopted which describe the degree of surface organization on water worked sediment bed surfaces the degree of particle organization and the bed stability can be evaluated in relative terms using the properties of the probability density distribution of the bed surface elevations and in absolute terms using a properly defined 2 d structure function the methods described can be applied directly to natural water worked surfaces given the availability of appropriate bed surface elevation data sets

holocene earthquakes and late pleistocene slip rate estimates on the wassuk range fault zone nevada the wassuk range fault zone is an 80 km long east dipping high angle normal fault that flanks the eastern margin of the wassuk range in central nevada observations from two alluvial fan systems truncated by the fault yield information on the vertical slip rate and holocene earthquake history along the range front at the apex of the rose creek alluvial fan radiocarbon dating of offset stratigraphy exposed in two fault trenches shows that multiple earthquakes resulted in 7 0 m of vertical offset along the fault since 9400 cal b p these data yield a holocene vertical slip rate of 0 7 0 1 mm yr the south trench exposure records at least two faulting events since 9400 cal b p with the most recent displacement postdating 2810 cal b p the north trench exposure records an 1 m offset between 610 cal b p and a d 1850 a 1 3 m minimum offset prior to 1460 cal b p and one earlier undated earthquake of a similar size variations in stratigraphy and limited datable material preclude a unique correlation of paleoevents between the two trenches approximately 25 km north the range front fault has truncated and uplifted a remnant of the penrod canyon fan by 40 m since the surface was deposited 113 ka based on cosmogenic dating of two large boulders these data allow an estimate of the minimum late pleistocene vertical slip rate at 0 3 0 4 mm yr for the wassuk range fault zone online material tables summarizing radiocarbon and cosmogenic analyses photos of rocks sampled for cosmogenic analyses and figures summarizing cosmogenic exposure age estimates

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 slip rate along the owens valley fault eastern california 1 the owens valley fault zone ovf is one of the primary structures accommodating dextral shear across the eastern california shear zone ecsz previous estimates of the holocene slip rate along this structure rely on paleoseismic data and yield rates 2 3 times lower than those implied by geodetic velocities using displaced lava flows along the flank of crater mountain we present the first estimate of slip rate along the ovf during the late pleistocene subsurface characterization of the flow margin using a ground penetrating radar gpr allows for relatively precise determination of dextral displacement and terrestrial cosmogenic 36cl exposure ages of samples from the flow surface yield slip rates between 2 8 4 5 mm yr over the past 55 80 kyr our results suggest either that paleoseismic slip rate estimates underestimate the long term slip rate or that rates of strain release have not been steady during the latter part of the quaternary

the role of sediment specific gravity and availability on cluster evolution the objective of this experimental study was to account for the role of sediment availability and specific gravity on cluster formation and cluster geometric characteristics spacing and size to isolate the effects of sediment availability and specific gravity on cluster evolution mono sized spheres were used to simulate the cluster evolutionary cycle overall twelve experimental runs were carried out in the laboratory flume six of these tests were performed by using glass spheres specific gravity sg 2 58 and the other six by employing an equal combination of glass and teflon spheres sg 2 12 of the same diameter to evaluate the role of specific gravity on cluster evolution the three sediment availability conditions that were investigated here simulated isolated gravel elements pool riffle sequences and densely packed gravel bed an advanced image analysis technique was employed to track the evolution of cluster microforms and provide quantitative information about the size and shape of clusters and the number of clusters per unit area the results of this study showed that 1 sediment availability affects the architecture and size of cluster microforms and 2 clusters consisting of mono sized sediments start disintegrating at twice the incipient conditions by performing complementary tests for the isolated gravel elements case it was found that the evolutionary cycle of individual clusters could be described as follows in order of increasing stress no cluster two particle cluster comet triangle rhomboid break up copyright 2003 john wiley sons ltd

seawater intrusion vulnerability indicators for freshwater lenses in strip islands freshwater lenses on small islands are some of the most vulnerable aquifer systems in the world however there is currently little guidance on methods for rapidly assessing the vulnerability of freshwater lenses to the potential effects of climate change we address this gap using a simple steady state analytic modelling approach to develop seawater intrusion swi vulnerability indicator equations which quantify the propensity for swi to occur in strip islands due to recharge change and sea level rise slr incorporating the effect of land surface inundation lsi the following inferences about swi vulnerability in freshwater lenses can be made from the analysis 1 swi vulnerability indicators for slr under flux controlled conditions are proportional to lens thickness or volume and the rate of lsi and inversely proportional to island width 2 swi vulnerability indicators for recharge change under flux controlled conditions are proportional to lens thickness or volume and inversely proportional to recharge and 3 slr has greater impact under head controlled conditions rather than flux controlled conditions whereas the opposite is the case for lsi and recharge change example applications to several case studies illustrate use of the method for rapidly ranking lenses according to vulnerability thereby allowing for prioritisation of areas where further and more detailed swi investigations may be required

thermochronometrically constrained anatomy and evolution of a miocene extensional accommodation zone and tilt domain boundary the southern wassuk range nevada 1 apatite ahe and zircon zhe u th he thermochronometric data from the southern wassuk range wr coupled with 40ar 39ar age data from the overlying tilted tertiary section are used to constrain the thermal evolution of an extensional accommodation zone and tilt domain boundary ahe and zhe data record two episodes of rapid cooling related to the tectonic exhumation of the wr fault block beginning at 15 and 4 ma extension was accommodated through fault block rotation and variably tilted the southern wr to the west from 60 70 in the central wr to 15 35 in the southernmost wr and pine grove hills and minimal tilting in the anchorite hills and along the mina deflection to the south middle miocene geothermal gradient estimates record heating immediately prior to large magnitude extension that was likely coeval with the extrusion of the lincoln flat andesite at 14 8 ma geothermal gradients increase from 19 4 c km to 65 20 c km toward the mina deflection suggesting that it was the focus of middle miocene arc magmatism in the upper crust the decreasing thickness of tilt blocks toward the south resulted from a shallowing brittle ductile transition zone postmagmatic middle miocene extension and fault block advection were focused in the northern and central wr and coincidentally moderated the large lateral thermal gradient within the uppermost crust

interferometric synthetic aperture radar observations of the 1994 double spring flat nevada earthquake m5 9 main shock accompanied by triggered slip on a conjugate fault 1 the 1994 double spring flat dsf earthquake m5 9 was the largest earthquake to strike nevada in more than 30 years it occurred in the sierra nevada basin and range transition zone within a step over region between two major normal faults descending and ascending ers interferograms show a maximum range change of 8 5 cm which is the coseismic ground displacement associated with this normal oblique slip moderatesized earthquake elastic inverse modeling and surface displacements across coseismic ground cracks suggest that two different event sources could account for the observed deformation the first source was the main shock with right oblique slip on the northnorthwest striking dsf fault the second source was normal faulting on a shallow northnortheast striking elongated plane conjugate to the dsf fault these two sources are consistent with the pattern of postevent seismicity and we suggest that the second source represents seismic and aseismic slip triggered by the main shock calculations of changes in coulomb failure stress show that the main shock encouraged normal slip on this plane index terms 1206 geodesy and gravity crustal movements interplate 8155 1241 geodesy and gravity satellite orbits 1242 geodesy and gravity seismic deformations 7205 1299 geodesy and gravity general or miscellaneous 7212 seismology earthquake ground motions and engineering

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