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

power law distribution of fault slip rates in southern california 1 the spatial partitioning of deformation in the continental crust and in particular at plate boundary zones is determined by the distribution of fault slip rates analytic and numerical models of strain accumulation in the elastic upper crust have been divided into those that parameterize faulting as localized on a finite length fault system comprised of relatively few fast slip rate faults or as distributed throughout a continuum of relatively slow slip rate faults we demonstrate that in the southern california fault system between the pacific and north american plates both geologically and geodetically constrained fault slip rate catalogs obey a power law frequency distribution using this empirically constrained scaling relationship we derive an analytic expression for the partitioning of potency accumulation rate which determines the distribution and magnitude of slip localization this model describes the kinematics of both micro plate and continuum deformation models and predicts that 97 of the deformation in southern california is accommodated on faults slipping at 1 mm yr which is consistent with models of continental deformation which explicitly represent a large though finite number of deforming structures

vector constraints on western u s deformation from space geodesy neotectonics and plate motions the rate of slip vector on the san andreas fault in central california estimated from geodetic and holocene geological data 34 3 mm yr n41 w 2 is inconsistent with the prediction of rigid plate models such as rm2 56 3 mm yr n35 w 2 this well known san andreas discrepancy is diagnostic of plate deformation distributed both east of the fault in the basin and range and west of the fault along the california continental margin we construct constraints on the integrated deformation rates across these two regions consistent with 1 the kinematical boundary conditions imposed by the rigid plate model 2 neotectonic and paleoseismic estimates of deformation rates 3 ground based geodetic measurements and 4 rates of change observed by very long baseline interferometry along seven baselines to western u s sites the space geodetic data on basin and range extension taken over a 4 year interval are compatible with geological observations averaged over the holocene the best estimate of its integrated deformation rate provided by the joint inversion of both data types is 9 7 2 1 mm yr n56 w 10 too small and in the wrong direction to account entirely for the san andreas discrepancy we therefore attribute much of it to deformation west of the sierra nevada great valley block accommodated for example on faults such as the san gregorio hosgri system of coastal california the integral of this deformation estimated by subtracting the basin and range contribution from the discrepancy vector requires significant right lateral shear parallel to the san andreas 13 5 mm yr and some compression perpendicular to it 9 3 mm yr

block modeling with connected fault network geometries and a linear elastic coupling estimator in spherical coordinates geodetic observations of interseismic deformation provide constraints on the partitioning of fault slip across plate boundary zones the spatial distribution of both elastic and inelastic strain accumulation and the nature of the fault system evolution here we describe linear block theory which decomposes surface velocity fields into four components 1 plate rotations 2 elastic deformation from faults with kinematically consistent slip rates 3 elastic deformation from faults with spatially variable coupling and 4 homogeneous intrablock strain elastic deformation rates are computed for each fault segment in a homogeneous elastic half space using multiple optimal planar cartesian coordinate systems to minimize areal distortion and triangular dislocation elements to accurately represent complex fault system geometry block motions fault slip rates elastic coupling and internal block strain rates are determined simultaneously using a linear estimator with constraints from both geodetically determined velocity fields and geologic fault slip rate estimates we also introduce algorithms for efficiently implementing alternative fault network geometries to quantify parameter sensitivity to nonlinear perturbations in model geometry

formation of patterned ground and fine scale soil development within two late holocene glacial chronosequences jotunheimen norway abstract chronosequences of 250 to 130 years were established on two late holocene glacier forelands in the jotunheimen region of southern norway patterned features occurring within chronologically established time units were studied young patterned features forming 10 20 years after deglaciation are frost active vegetation cover is minimal within the young patterned features consisting of bryophytes organic crusts soil development within patterned ground is also minimal absent because frost action retards horizonization with time and distance from the glaciated ice margin frost activity declines within the patterned features suggesting that a thin active periglacial zone exists near the ice margin initially frost activity decreases at the borders of the features with the centers stabilizing later in time this results in fine scale soil heterogeneity and variations of soil development fine scale pedogenic development is first encountered at the borders of patterned ground that has developed on terrain exposed since the 1930s yet soil development is predominantly absent at the centers of patterned ground with time and distance from the ice margin frost activity declines and allows patterned features to homogenize from border to center positions in regard to soil characteristics across the chronosequences soils within patterned features pedogenically follow previous soil chronosequence studies evolving from usda classifications of entisols into inceptisols frost disturbance within patterned ground however produces a lag effect that results in longer periods of time for pedogenesis to occur and thinner soils than that of the surrounding terrain

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

fast but spatially scattered smectite formation in the proglacial area morteratsch an evaluation using gis proglacial areas in the alps usually cover a time span of deglaciation of about 150 years time since the end of the little ice age in the 1850s in these proglacial areas soils have started to develop due to the continuous retreat of the morteratsch glacier swiss alps the corresponding proglacial area offers a continuous time sequence from 0 to 150 year old surfaces furthermore an optimal digital dataset about the development of vegetation and soils is available for this area the soils have been developing on glacial till having a granitoidic character we investigated the clay mineral assemblage at 35 sites within the glacier forefield smectite can be used as a proxy for weathering intensity in these environments in the proglacial area the smectite concentration in the topsoil steadily increased with time of weathering however this development displayed a strongly scattered trend the complex interplay of biological physical and chemical processes in pedogenesis and clay mineral evolution limits our ability to predict and interpret landscape dynamics we consequently tried to analyse the role of topographic and vegetation modifications on the smectite content sites not or only slightly prone to erosion flattening slope ridge steepening slope ridge or flat morphology promoted the formation of smectite in addition the texture of the soil material influenced soil moisture and hence the degree of weathering and the development of vegetation although vegetation is not a fully independent factor because it is interrelated to the surrounding environmental conditions it seemed to exert its influence on weathering and consequently the formation of smectite green alder stands and grass heath where moister soils develop that have a finer texture or where more organic acids are produced were correlated with a higher smectite content humus forms serve as a proxy for the soil biota and soil organic matter composition at sites having a eumoder and a higher soil organic matter content the smectite concentration was elevated at these sites the production of chelating compounds or organic acids in the soil is believed to promote the development of smectites via an intermediate stage of hydroxy interlayered minerals and the subsequent removal of the hydroxide polymers in this work we have demonstrated that the topographic signature and the effect of vegetation on the formation of smectite and consequent weathering are pervasive our results will serve as a basis for further spatio temporal modelling

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

soil development rates in the transantarctic mountains soil chronosequences were identified at three sites 78 85 s within the transantarctic mountains for determining rates of soil development in cold desert ecosystems more than 175 soils were sampled in xerous and ultraxerous environments on moraines containing sandstone and dolerite and ranging from late holocene ca 6 ka to pre late quaternary ca 250 ka in age based on five linear and nonlinear models highly significant correlations p 0 01 exist between drift age and the following surface boulder weathering features and soil properties percentage of boulders containing desert varnish spalling and pitting depths of staining visible salts ghosts pseudomorphs and coherence in soils electroconductivity in the zone of salt enrichment and total profile salts in the absence of leaching soluble salts readily accumulate in cold desert soils a morphogenetic sequence of soluble salts is presented that relates field observations with laboratory data soil color is highly correlated p 0 01 with dithionite extractable fe within a site the proportion of clasts 15 mm on the surface of the desert pavement increases with time due likely to deflation of fines by strong winds therefore the dominant processes in these cold desert soils are salinization rubification reddening due to oxidation of iron bearing minerals and desert pavement formation

plant communities as a key factor in biogeochemical processes involving micronutrients fe mn co and cu in antarctic soils byers peninsula maritime antarctica abstract the main objective of this study was to establish the effects of plants and microorganisms on soil formation and the geochemical mobility of certain micronutrients in soils from byers peninsula antarctica for this purpose 14 sampling sites were selected to cover the existing range of lithological and geomorphological variability in the area soils were sampled at the surface 0 5 cm and subsurface from 5 cm to 30 cm or until contact with the bedrock or permafrost soil samples were physicochemically characterized by analysis of ph electrical conductivity size particle distribution total organic carbon total nitrogen and dissolved organic carbon sequential extraction of fe and mn and of micronutrients co cu was also carried out the analytical results revealed significant differences between sites in relation to plant cover the total organic carbon was 1 5 times higher the total nitrogen was 1 6 times higher the dissolved organic carbon was more than 3 6 times higher and the ph kcl ph in 0 1 m kcl was lower in the sites colonized by plants mainly mosses than in the sites without any plant cover the sequential extraction of biolimiting nutrients fe mn co and cu also revealed significant differences in the fractions in relation to the presence of plants specifically the most labile and mobile fractions amorphous fe oxyhydroxides easily reducible mn and metals soluble in sodium pyrophosphate were present at higher concentrations in the sites colonized by vegetation than in the sites without plants the latter aspect may be of particular importance within the context of global climate change as increased temperatures will favour expansion of vegetation and the flow of biolimiting nutrients towards oceans and lakes which may have direct effects on primary productivity

pedogenic gradients for iron and aluminum accumulation and phosphorus depletion in arctic and alpine soils as a function of time and climate pedogenically significant chemical extracts of iron aluminum and phosphorus are related mainly to time in chronosequences from baffin island canadian arctic the alpine sierra nevada and wind river range western united states the alpine khumbu glacier area himalaya nepal and the alpine southern alps new zealand based on the accumulation index for fe and al and the depletion index for p in each region the following ranking of chemical pedogenic development is obtained southern alps khumbu glacier area wind river range sierra nevada coastal baffin island inland baffin island the ranking mainly follows regional climate with the greatest accumulation and depletion to the warmest and wettest environment and the least accumulation and depletion in the coldest and driest environment

comparison of geodetic and geologic data from the wasatch region utah and implications for the spectral character of earth deformation at periods of 10 to 10 million years the wasatch fault and adjacent fault zones provide an opportunity to compare present day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows ranging from the last millennium up to 10 myr the three easternmost gps sites of the basin and range geodetic network bargen at this latitude define a 130 km wide region spanning three major normal faults extending east west at a total rate of 2 7 0 4 mm yr with an average regional strain rate estimated to be 21 4 nstrain yr about twice the basin and range average on the wasatch fault the vertical component of the geologic displacement rate is 1 7 0 5 mm yr since 6 ka 0 6 mm yr since 130 ka and 0 5 0 7 mm yr since 10 ma however it appears likely that at the longest timescale rates slowed over time from 1 0 to 1 4 mm yr between 10 and 6 ma to 0 2 to 0 3 mm yr since 6 ma the cumulative vertical displacement record across all three faults also shows time variable strain release ranging from 2 to 4 mm yr since 10 ka to 1 mm yr averaged over the past 130 kyr conventional earthquake recurrence models reid type behavior would require an accordingly large variation in strain accumulation or loading rate on a 10 kyr timescale for which there appears to be no obvious geophysical explanation alternatively seismic strain release given a wide range of plausible constitutive behaviors for frictional sliding may be clustered on the 10 kyr timescale resulting in the high holocene rates with comparatively low uniform strain accumulation rates on the 100 kyr timescale wallace type behavior the latter alternative combined with observations at the million year timescale and the likelihood of a significant contribution of postseismic transients implies maxima of spectral amplitude in the velocity field at periods of 10 myr variations in tectonic loading 10 kyr clustered strain release and of 100 years postseismic transients if so measurements of strain accumulation and strain release may be strongly timescale dependent for any given fault system

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

the motion of crustal blocks driven by flow of the lower lithosphere and implications for slip rates of continental strike slip faults geodetic measurements in actively deforming areas of the continents reveal the pattern of deformation in the lithosphere if the dominant forces acting on crustal blocks are tractions at their bases then the long term motion of each block will be given by the average velocity of the underlying lithosphere slip rates between blocks estimated in this way from recent geodetic measurements across fault zones in the south island of new zealand and southern california are in good agreement with slip rates estimated geologically

soil processes and nutrient bioavailability in the rhizosphere of bolax gummifera in a subantarctic environment martial mountains ushuaia argentina abstract the aim of this study was to explore the effects of plants on the underlying substrate and the possible environmental implications of such effects in an extreme environment for this purpose we sampled the rhizosphere soil of bolax gummifera which is one of the most characteristic vascular plants in the martial mountains tierra del fuego argentina where plant cover is typically sparse superficial 0 5 cm rh5 and subsuperficial 5 15 cm rh15 samples of b gummifera rhizosphere and bulk soil were collected from a small homogeneous area and the following parameters were analyzed particle size ph total organic carbon toc total nitrogen tn total fe tfe fe and al associated with organic matter soluble in sodium pyrophosphate c pyro amorphous fe oxyhydroxides extracted with ammonium oxalate fe oxa crystalline fe oxyhydroxides extracted with sodium dithionite fe dit bioavailable plant nutrients soluble in mehlich 3 extractant and clay mineralogy several differences were found between rhizosphere soil rs and bulk soil the toc was 8 times higher and the tn and c pyro were 4 times higher in the rhizosphere than in the bulk soil mineralogical results suggest a slightly higher degree of chemical weathering mainly affecting biotite and amphibole minerals in the rs than in bulk soil consistent with significantly higher nutrient bioavailability in rs ca mg k co and fe on the other hand the higher concentrations of c and metals extracted with sodium pyrophosphate suggest the formation of more metal organic complexes in the rhizosphere than in the bulk soil this metal fraction is considered as readily mobilizable and available and can be leached from the soil to continental and coastal waters this effect will be enhanced in cold climates by expansion of plant cover due to the increased temperature expected under climate change

active deformation of asia from kinematics to dynamics using estimated strain rates across the actively deforming region of asia to infer variations in viscous stress it is shown that gradients of stress point uphill toward the center of tibet where gravitational potential energy per unit surface area reaches a maximum thus the dynamics of the deformation seem to obey the equation of creeping flow which expresses a balance between gradients in stress and the gravitational body force this balance in the region of the tibetan plateau yields an estimate of 10 22 pascal second for the average viscosity of the tibetan lithosphere which is only about 10 to 100 times greater than the viscosity of the convecting upper mantle

new kinematic models for pacific north america motion from 3 ma to present i evidence for steady motion and biases in the nuvel 1a model we use velocities derived from 2 4 5 years of continuous gps observations at 21 sites on the pacific and north american plates along with a subset of the nuvel 1a data to examine the steadiness of pacific north america motion since 3 16 ma the transfer of baja california to the pacific plate and the magnitude of biases in the nuvel 1a estimate of pacific north america motion we find that pacific north america motion has remained steady since 3 16 ma but at rates significantly faster than predicted by nuvel 1a in the vicinity of baja california our gps derived model and recent seafloor spreading rates in the southern gulf of california both indicate that the nuvel 1a model underestimates pacific north america rates by 4 2 mm yr 1 steady pacific north america motion since 3 16 myr and increasing seafloor spreading rates since 3 58 myr in the gulf of california imply that pacific north america motion was partitioned between seafloor spreading in the gulf of california and decelerating slip along faults in or offshore from the baja peninsula

soil formation in kettle holes from high altitudes in central apennines italy abstract kettle holes are relatively common features of glaciated landscapes and have been widely reported in the literature the work reported here documents the presence of kettle holes at high altitude and low latitude in the central apennines italy and describes the geomorphic and pedogenic processes that originated the soils infilling these depressions the areas selected for this study were located on three of the main massifs of the central apennines italy gran sasso majella and sibillini the kettle holes on these massifs formed at the end of the wurm glaciation appear smaller and shallower than those reported from elsewhere in the northern hemisphere are roughly circular in form and do not contain bogs or lakes in each area the dimensions of 40 kettle holes were measured and three kettle holes were excavated to examine the soils developed inside them the size of the kettle holes was highest in the sibillini massif where the glaciers reached altitudes as low as 1700 m in the very narrow low lying valleys it is hypothesised that at lower elevations the glacier receded more rapidly generating larger blocks of ice and consequently larger kettle holes once formed the kettle hole depressions were very effective as sediment traps and acted as sink for materials washed in from the surrounding slopes or from more distant wind blown sources in the kettle holes from gran sasso and majella massifs small fragments of woody charcoal were found the material filling the kettle holes accumulated inside them in the form of layers soils formed inside the kettle holes showed horizons whose thickness and properties appeared mostly inherited from the amassed layers the only pedogenic process common to the kettle holes of the three massifs was the incorporation of organic matter that as expected from the rather cold climatic conditions was subjected to slow dynamics in the kettle holes of the majella massif the horizons developed from layers rich of materials of volcanic origin and the formation of short range order minerals occurred we conclude that the soils inside the kettle holes are a repository of geomorphic pedogenic and in reference to the source of the charcoal paleo environmental information

germanium silicon ratios in the copper river basin alaska weathering and partitioning in periglacial versus glacial environments 1 glacial to interglacial variation in the germanium to silicon ratio ge si of biogenic opal in oceanic sediment cores has been proposed to record terrestrial silicate weathering intensity however data connecting ge si ratios to weathering are sparse especially for cold regions to characterize ge si of the dissolved loads of rivers draining modern glacial and periglacial regions we measured ge and major element chemistry of more than 30 streams in the copper river basin of south alaska we measured significantly higher ge si in rivers with greater than 15 glacial cover in their basins than in rivers draining areas with less glacial cover which we attribute to preferencial subglacial weathering of biotite we also ran laboratory experiments to investigate the role of differential sorption of ge and si on hydrous iron oxides in moderating the ge si ratio of rivers in recently deglaciated basins these experiments indicate that ge is preferentially adsorbed over si by hydrous iron oxides over a wide range of ph values and support differential sorption as a potentially significant fractionation process our measured high ge si in glaciated basins is in striking contrast to the low ge si in the oceanic record during glacial periods the glacial to interglacial changes in marine ge si cannot simply reflect changes in glacier cover on land as the mineralogy of silicates weathered and processes partitioning ge in soils must also strongly influence the fluvial ge and si inputs to the ocean

amount of extension on small faults an example from the viking graben extension estimates based on palinspastic restoration of only the largest faults in a deformed terrane may be significantly deficient due to neglect of small faults i e unsampled faults most of which have smaller displacements than do sampled faults small faults individually account for little extension but there may be large numbers of them the cumulative extension on small faults can be calculated from the fractal size distributions of fault displacements independent extension estimates support the inference from fault population statistics that small faults account for significant amounts of extension for example restorations of mesozoic faults interpreted from seismic reflection profiles across the viking graben in the north sea yield extension estimates that are only 40 75 of independent estimates the fractal size distribution of fault displacements in the viking graben is consistent with the hypothesis that the remaining 25 60 of extension resulted from displacements on small faults

calcium carbonate nodules in soils 13o 16o and 13c 12c ratios and 14c contents abstract 18 o values 13 c values and 14 c ages were determined in ten caco 3 nodule populations collected from soil and paleosols in the israeli coastal plain the selected soils were carbonate free when formed and the nodules in them represent either reprecipitation of carbonate illuviated from overlying horizons descending mode or precipitated from a raised brackish water table ascending mode the 14 c ages represent the times of migration illuviation or eustatic movement both climate related and the stable isotopic conditions reflect the environmental conditions at such times the 13 c values of most populations were found to have a wide range and cannot be used to reconstruct former climates this wide range is attributed to microvariations of pco 2 in the soil because the 18 o ranges in the same samples are usually comparable to analytical uncertainties and because the 18 o mean values follow an age correlated pattern they permit us to place the soils in one of three categories in two cases where nodules were soft both turned out to be young 1000 years and to have wide ranges in 18 o values the latter are apparently due to continual re equilibration with new soil solutions in three cases of the descending mode of nodule formation 12 000 14 000 year old hard nodules had very narrow 18 o whose means reflect the rainfall value at that time the period between 12 000 14 000 years b p is independently known to be one of higher precipitation evaporation ratio and of more intensive soil formation these ascending mode populations of hard nodules had narrow ranges in 18 o reflecting a mixture of sea water and rainfall and all turned out to be 3 000 4 000 years old at this period the sea reached its highest elevation resulting in raising the nearcoast water table

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

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

pedogenesis in the sorted patterned ground of devon plateau devon island nunavut canada abstract in the high arctic the barren expanses of devon plateau devon island are affected by intense frost action that conditions geomorphic processes at the landscape level soil formation at the profile level and the establishment and distribution of vascular plants at microsites in the high arctic in areas of patterned ground frost action is responsible for both the accumulation of parent material through the segregation of fines in features here called islands of fines and for the development of soil profiles through cryoturbation in these features at the landscape level segregation of fines results in the development of patterned ground specifically in the formation of sorted stripes sorted circles and plugs that repeat themselves on the landscape plugs consist of cylindrical to conical soil masses protruding from the frost permafrost table in the stony areas that may coalesce to form island of fines cryoturbation the dominant soil forming process is manifested by the appearance of convoluted horizons injection of material up heaving of stones and soil mixing but there are also non cryoturbated soils with a b c vertical sequences we have described sampled and analyzed the soils simultaneously present in the islands of fines also we have examined the plugs the stony areas and the stony borders non cryoturbated soils typic haplorthels or brunosolic eutric static cryosols occurred at the edges of the sorted circles once the injection of heaved material has subsided they showed an a horizon grayish brown relatively rich in carbon and nitrogen sandier than the underlying b horizon which is characterized by the presence of illuvial silt caps the c horizon is low in organic carbon and nitrogen and poorly rooted despite wet conditions and impeded drainage because of the high ph low organic matter content and low biological activity oxidation reduction processes are not well expressed c horizon material injected from the frost permafrost table penetrated into the body of the island of fines rupturing horizons and merging at the surface these soils are aquic haploturbels or gleysolic turbic cryosols the major soil forming processes that are acting in the haplorthels or brunosolic cryosols include brunification lessivage and decarbonation carbonation in the aquic haploturbels or gleysolic turbic cryosols the processes are cryoturbation gleying and decarbonation carbonation stony areas play the important role of trapping air born dust that includes mineral and organic components also autochthonous living organisms dwell in these block fields the air born mineral fines together with those left by the receding ice cap and those produced by weathering aliment the formation of plugs islands of fines and the sorted stripes

the formation of caliche in soils of the mojave desert california abstract radiocarbon and 230th 234u dates of calcic horizons from calciorthid soil profiles in the mojave desert were used to calculate the rate of deposition of pedogenic caco3 a major period of caco3 deposition appears to have occurred about 20000 ybp forming calcic horizons below 100 cm depth during a climatic regime with greater effective rainfall than in the present the overall rate of deposition has been 1 0 to 3 5 g caco3 m2 yr during soil formation this rate is consistent with present day rates assuming that the atmospheric deposition of ca limits the process stable isotope ratios in calcic horizons indicate that caco3 precipitated from a soil environment with co2 of 15 5 13 c 12 c vs pdb and h2o of 2 0 18 o 16 o vs smow these values suggest that caco3 precipitates when seasonal drought simultaneously lowers soil pore pco2 and enriches soil water 18o by evaporation the role of soil calcic horizons in the global geochemical cycle of carbon is discussed

a granulometry and secondary mineral fingerprint of chemical weathering in periglacial landscapes and its application to blockfield origins abstract a review of published literature was undertaken to determine if there was a fingerprint of chemical weathering in regoliths subjected to periglacial conditions during their formation if present this fingerprint would be applied to the question of when blockfields in periglacial landscapes were initiated these blocky diamicts are usually considered to represent remnants of regoliths that were chemically weathered under a warm neogene climate and therefore indicate surfaces that have undergone only a few metres to a few 10s of metres of erosion during the quaternary based on a comparison of clay and silt abundances and secondary mineral assemblages from blockfields other regoliths in periglacial settings and regoliths from non periglacial settings a fingerprint of chemical weathering in periglacial landscapes was identified a mobile regolith origin under at least seasonal periglacial conditions is indicated where clay 0 5 silt 8 across a sample batch this contrasts with a mobile regolith origin under non periglacial conditions which is indicated where clay 0 5 silt 6 across a sample batch with clay 0 5 silt 8 in at least one sample a range of secondary minerals which frequently includes interstratified minerals and indicates high local variability in leaching conditions is also commonly present in regoliths exposed to periglacial conditions during their formation clay silt ratios display a threshold response to temperature related to the freezing point of water but there is little response to precipitation or regolith residence time lithology controls clay and silt abundances which increase from felsic through intermediate to mafic compositions but does not control clay silt ratios use of a sedigraph or coulter counter to determine regolith granulometry systematically indicates lower clay abundances and intra site variability than use of a pipette or hydrometer in contrast to clay silt ratios secondary mineral assemblages vary according to regolith residence time temperature and or precipitation a microsystems model is invoked as a conceptual framework in which to interpret the concurrent formation of the observed secondary mineral ranges according to the fingerprint of chemical weathering in periglacial landscapes there is generally no evidence of blockfield origins under warm neogene climates nearly all blockfields appear to be a product of quaternary physical and chemical weathering a more dominant role for periglacial processes in further bevelling elevated low relief non glacial surface remnants in otherwise glacially eroded landscapes is therefore indicated

lithospheric instability in obliquely convergent margins san gabriel mountains southern california 1 oblique convergence across the san andreas fault in southern california has lead to rapid uplift of the san gabriel mountains since 5 ma tomographic models of this region include a sheet like high velocity anomaly extending to depths 200 km one proposed mechanism for the formation of this feature is gravitational instability of the lithosphere resulting in a cold thermal downwelling we present a systematic study of the sensitivity of lithospheric deformation lithospheric downwelling topography deflection of the moho convergent velocity profile to the viscosity structure in 2 d numerical models of lithospheric instability including a pre existing zone of weakness strike parallel strain within a convergent region should create a local zone of weakness due to the non newtonian response of the lithosphere such a weak zone can focus convergent motion increasing and localizing the growth rate of a lithospheric instability we find that the observed characteristics of deformation depend on the width x w and relative viscous weakening factor f w the ratio of crust to mantle lithospheric viscosity eta c eta m and the absolute viscosity of the lithosphere h m for the san gabriel mountains we find that a range of models is capable of reproducing the observed moho deflection and depth extent of the downwelling within the short time since the onset of convergence however only a small subset of models x w 20 km f w 50 100 eta m 7 5 x 10 20 1 5 x 10 21 pa s eta c eta m 100 reproduce both the narrow high topography and horizontal shortening profile

interplay of seismic and aseismic deformations during earthquake swarms an experimental approach observations of earthquake swarms and slow propagating ruptures on related faults suggest a close relation between the two phenomena earthquakes are the signature of fast unstable ruptures initiated on localized asperities while slow aseismic deformations are experienced on large stable segments of the fault plane the spatial proximity and the temporal coincidence of both fault mechanical responses highlight the variability of fault rheology however the mechanism relating earthquakes and aseismic processes is still elusive due to the difficulty of imaging these phenomena of large spatiotemporal variability at depth here we present laboratory experiments that explore in great detail the deformation processes of heterogeneous interfaces in the brittle creep regime we track the evolution of an interfacial crack over 7 orders of magnitude in time and 5 orders of magnitude in space using optical and acoustic sensors we explore the response of the system to slow transient loads and show that slow deformation episodes are systematically accompanied by acoustic emissions due to local fracture energy disorder features of acoustic emission activities and deformation rate distributions of our experimental system are similar to those in natural faults on the basis of an activation energy model we link our results to the rate and state friction model and suggest an active role of local creep deformation in driving the seismic activity of earthquake swarms

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

pedogenic zonation in the well drained soils of the arctic regions abstract pedogenic zonation in the soils of the polar regions is a result of gradients in environmental factors and attendant chemical processes along a latitudinal transect it is best manifested at well drained sites and by soils developed on predominantly silicate rocks selected sites in arctic alaska in the canadian arctic greenland and svalbard adequately fulfill these prerequisites the processes of podzolization decarbonization carbonization pervection and salinization as models of arctic pedogenesis demonstrate that processes occurring in the temperate region also operate in the far north brunification melanization and oxidation are recognized for the first time as current geochemical and pedogenic mechanisms of the arctic region traditional genetic soil names have been retained because they represent a closer relationship to pedogenic processes than the more modern nomenclature the identification the chemical behavior the strength abundance and mobility of the proton donors and conjugate bases are keys to the genesis of soils and the distinction of contrasting soil processes this new approach to the understanding of arctic pedogenesis can be better fulfilled by collecting analyzing and interpreting soil solution obtained in situ

a review of pedogenic zonation in well drained soils of the southern circumpolar region abstract the concept of zonality is used to link well drained mineral soils and processes along a bioclimatic gradient extending from ca 48 to 87 s including southernmost chile the subantarctic islands and maritime and continental antarctica the following environmental factors decline along this gradient mean annual temperature and precipitation and the type and number of plant species six pedological zones along with representative soils are identified along the gradient 1 subantarctic forest zone podzol 2 subantarctic low tundra zone 3 subantarctic high tundra zone subantarctic brown soil without permafrost 4 antarctic sub polar desert zone subantarctic brown soil with permafrost 5 antarctic polar desert zone red ahumisol and 6 cold desert zone ahumisol zonal mineral soils in the subantarctic forest and low tundra zones are rare because large amounts of precipitation 2500 mm and cool summers have led to thick accumulation of peat whereas the processes of rubification melanization and peat accumulation decline in relative magnitude southward the processes of salinization and desert pavement formation increase in relative importance along this bioclimatic gradient carbonation and pervection silt and clay migration are maximized in the subantarctic tundra and antarctic polar desert zones because of the limited amount of land between 40 and 65 s and the presence of the antarctic convergence comparable pedogenic zones occur at lower latitudes in the southern than in the northern circumpolar region

arctic soil properties associated with micro relief forms in the bellsund region spitsbergen abstract the following patterning of the ground surface was observed in the bellsund region sorted circles mud boils cell forms solifluction striped forms and large polygons tundra polygons the soils associated with these forms often have different morphological granulometric and chemical properties and plant covers tundra polygons and surfaces without relief are usually accompanied by relatively well developed brown soils with a dense plant cover 70 100 such forms occur mainly on loamy sands and loams with abundant 1 0 0 1 mm particles brown soils are rich in humus which decreases with depth typical gley soils usually with a sparse plant cover are associated with cell forms sorted circles and mud boils solifluctional forms are usually accompanied by gley like soils rarely by brown like ones gley and gley like soils occur on sediments rich in fractions

deformation kinematics in the western united states determined from quaternary fault slip rates and recent geodetic data we estimate the horizontal velocity gradient tensor field from quaternary fault slip rates and recent global positioning system gps and very long baseline interferometry vlbi velocity solutions in the western united states transform plate boundary zone the total velocity obtained from the quaternary fault slip rate data across the entire plate boundary is within 1 mm yr of the nuvel 1a predicted pacific pa north american na plate motion velocity but directions are 5 6 anticlockwise of directions given by nuvel 1a the total velocity obtained from inversion of recent geodetic data is 2 3 anticlockwise from the nuvel 1a na pa velocity but the difference between the two is not significant at the 95 confidence level the discrepancy between the total pa na motion obtained from the geological data and nuvel 1a indicates that a marginally significant amount of ne sw shortening possibly as much as 5 mm yr is missing overall in the geologic data shortening may occur in the long term in the offshore and coastal areas of california where such shortening is required in the shorter term geodetic solution the seismic moment released in the last 148 years is 59 of the total moment release rate expected from long term strain rate field including both seismic and aseismic deformation derived from the inversion of geological data with nuvel 1a far field pa na motion constraints the accumulated strain in the areas containing the southern san andreas fault san jacinto fault the san francisco bay area and the area containing the ventura basin in the western transverse ranges in the last 148 years is the equivalent to that which could be released by an mw 7 0 earthquake in each 50 100 15 km3 crustal volume if strain is to be released seismically in these areas

community fault model cfm for southern california we present a new three dimensional model of the major fault systems in southern california the model describes the san andreas fault and associated strike slip fault systems in the eastern california shear zone and peninsular ranges as well as active blind thrust and reverse faults in the los angeles basin and transverse ranges the model consists of triangulated surface representations t surfs of more than 140 active faults that are defined based on surfaces traces seismicity seismic reflection profiles wells and geologic cross sections and models the majority of earthquakes and more than 95 of the regional seismic moment release occur along faults represented in the model this suggests that the model describes a comprehen sive set of major earthquake sources in the region the model serves the southern california earthquake center scec as a unified resource for physics based fault systems modeling strong ground motion prediction and probabilistic seismic hazards assessment

dynamics of the pacific north american plate boundary in the western united states the vertically averaged deviatoric stress tensor field within the western united states was determined with topographic data geoid data recent global positioning system observations and strain rate magnitudes and styles from quaternary faults gravitational potential energy differences control the large fault normal compression on the california coast deformation in the basin and range is driven in part by gravitational potential energy differences but extension directions there are modified by plate interaction stresses the california shear zone has relatively low vertically averaged viscosity of about 1021 pascal seconds whereas the basin and range has a higher vertically averaged viscosity of 1022pascal seconds

geochemistry of the neoproterozoic metasedimentary gamble brook formation avalon terrane nova scotia evidence for a rifted arc environment along the west gondwanan margin of rodinia abstract the neoproterozoic gamble brook formation in the avalon terrane of nova scotia consists of quartzitic pelitic and psammitic metasedimentary rocks the formation is generally interpreted to have been deposited in an atlantic type passive margin setting along the amazonian margin of rodinia before the main ca 650 550 ma phase of avalonian subduction related magmatism the geochemical and sm nd isotopic signature of these metasedimentary rocks however shows that although the quartzites are predominantly derived from ancient cratonic basement the pelites and psammites were derived from moderately fractionated mafic to intermediate proto avalonian crust the two contrasting sources for the gamble brook rocks are incompatible with a passive margin setting and are instead interpreted to reflect deposition along a basin margin within a rifted arc environment taken as a whole the amazonian margin of gondwana preserves evidence of episodic subduction in a western pacific like setting between 1000 a

the properties genesis and environmental significance of calcitic pendents from the high arctic spitsbergen abstract calcitic pendents occurring beneath coarse clasts were investigated from a well drained profile near ny alesund spitsbergen developed on fluvio glacial deposits with a few carbonate rock fragments micromorphological study was combined with mineralogical geochemical and isotopic investigations to determine the relationships of calcitic pendent characteristics to soil conditions calcitic pendents are observed at all depths beneath clasts and display a succession of five types of laminae with strongly differentiated overall characteristics the number of laminae and their specific attributes are nearly unchanged with depth and with the petrographic nature of the host clast each lamina consists of weakly differentiated micro laminae that are grouped into six morphological facies precipitation of pedogenic carbonates is shown to be currently active throughout the profile induced by supersaturation of solutes with respect to calcite during the initial stage of freezing this process would form beneath clasts the calcitic pendents that are suggested to successively grow at all depths following the gradual progression of the frost front carbonate dissolution appears to mainly affect the fine soil mass from the surface down to the permafrost level controlled by summer biological activity differences of isotopic values of the whole calcitic pendents from those that would precipitate in equilibrium with present day soil conditions are explained by changes in soil conditions during the accretionary process 14 c values suggest that accretion of the pendents integrates phases which occurred during earlier episodes than the holocene the complex layering of calcitic pendents provides a sequential record of evolving soil forming conditions during a time period possibly longer than the last glacial cycle previous conditions are interpreted in relation to present conditions of precipitation the succession of micro laminae is thought to reflect minor climatic fluctuations and marked changes between adjacent laminae are thought to indicate significant climatic changes

a kinematic model of southern california we propose a kinematic model for southern california based on late quaternary slip rates and orientations of major faults in the region internally consistent motions are determined assuming that these faults bound rigid blocks relative to north america most of california west of the san andreas fault is moving parallel to the san andreas fault through the transverse ranges and not parallel to the motion of the pacific plate this is accomplished by counterclockwise rotation of california south of the san andreas fault and by the westward movement of central california north of the gar lock fault the velocities of the blocks are calculated along several paths in southern california that begin in the mojave desert and end off the california coast a path that crosses the western transverse ranges accumulates the accepted relative north america pacific plate velocity whereas paths to the north and south result in a significant missing component of motion this implies the existence of a zone of active deformation in southern california that is interpreted to include the western transverse ranges and northwest trending predominately strike slip faults close to the coast both north and south of the transverse ranges strain on this system accounts for about a third of the total north america pacific plate motion

small scale variability of soil properties and soil vegetation relationships in patterned ground on different lithologies nw italian alps abstract cryogenic patterned ground represents spectacular periglacial landscapes on the alps sorted nonsorted patterned ground features larger than 1 m formed by deep seasonal cryoturbation with or without permafrost occupy exposed stable surfaces at high altitudes and represent a particularly harsh habitat for plant life we analyzed soils across transects through typical active patterned ground features sorted nonsorted circles and stripes on four common lithotypes calcschists serpentinite gabbros and gneiss in the western italian alps in order to observe the small scale lateral and depth variability in physico chemical properties and their association with cryoturbation plant cover and species distribution cryoturbation was correlated with lateral vertical textural sorting across features mostly visible on silt and coarse sand but with opposite trends on sorted and nonsorted patterned ground types a strong lateral variability in organic carbon was detected with high values near the better vegetated rims and low contents in the centers exchangeable bases heavy metals and nutrients followed the same distribution however the differences inherited from the parent materials were overwhelming climate is the main driver of high altitude ecosystems reducing total plant cover and causing cryoturbation which in turn creates strong edaphic gradients over small distances plant species and communities are well correlated with edaphic properties inherited from the parent materials such as exchangeable ca and heavy metals

microplate versus continuum descriptions of active tectonic deformation whether deformation of continents is more accurately described by the motions of a few small rigid plates or by quasi continuous flow has important implications for lithospheric dynamics fault mechanics and earthquake hazard assessment actively deforming regions of the western united states central asia japan and new zealand show features that argue for both styles of movement but new observations are necessary to determine which is most appropriate and at what scale the description applies geologic geodetic seismic and paleomagnetic measurements tend to sample complementary aspects of the deformation field so an integrated observation program can utilize the strengths of each method and overcome their separate spatial or temporal biases provided the total relative motion across each region is known and the distribution of active faults is well mapped determination of fault slip rates can provide potentially decisive constraints reconnaissance geological studies supply useful slip rate estimates but precise values depend upon detailed intensive investigation of individual sites geodetic survey measurements can determine the spatial pattern of contemporary movements and extract slip rate information but the sometimes elusive effects of cyclic elastic strain buildup and relief must be accounted for in relating current movements to the long term deformation pattern earthquake catalogs can be applied to determine seismic strain rates and relative velocities but must be averaged over large regions and are usually limited by the inadequate duration of historical or instrumental seismicity catalogs paleomagnetic determinations of vertical axis rotations provide estimates of block rotation rates but are often locally variable and averaged over many millions of years which of the two descriptions of continental tectonics is more nearly correct depends on the local rheological stratification of the lithosphere especially the strength and thickness of the elastic crust relative to the ductile lithosphere and dynamical models can provide contrasting forecasts of observable features with testable consequences

effect of north and south exposure on weathering rates and clay mineral formation in alpine soils abstract a comparison was made between two soil climosequences on north and south facing slopes in northern italy to determine the influence of slope aspect on soil processes the climosequences span an elevational gradient ranging from moderate 1200 m a s l to high alpine 2420 m a s l climate zones on surfaces having an age of about 15 000 years the soils were investigated with respect to organic c oxalate and dithionite extractable fe al and si elemental losses ca mg k na fe al si mn and clay minerals the stocks of soil org c as well as of oxalate extractable fe and al was greatest in the subalpine zone near the timberline there are no clear differences in organic c content between the soils on north and south facing sites fe oxalate and to a lesser extent alo stocks were however greater on north facing sites indicating that weathering is greater there eluviation and illuviation of al and fe within the soil profile typical for podzolisation was more distinctly expressed on the n slopes the probability of itm imogolite type material formation in the soil seemed to be greater on south facing sites on the north facing sites element leaching was most intense in the subalpine zone close to the timberline while on the south facing sites this was only the case for the base cations the n slopes exhibited higher leaching of elements which generally indicates a higher weathering intensity on south facing sites typical podzolisation processes were measurable only above 2000 m a s l the development of smectites is also a reflection of the weathering intensity smectite was discernible in the surface horizon at all sites on n slopes but the highest amount was detected in the sub alpine climate zone for the south facing sites only in the alpine climate zone could smectite be detected higher temperatures and an increased number of freeze thaw cycles on south facing slopes should theoretically enhance rates of chemical weathering this could however not be confirmed with our measurements the degree of chemical weathering increases from the south to the north facing sites that are characterised by lower temperatures lower evapotranspiration and consequently by a higher humidity although precipitation in alpine regions is abundant the availability and flux of water through the soil is the prime factor in weathering intensity

from climatic to global change geomorphology contemporary shifts in periglacial geomorphology periglacial geomorphology developed in the 1940s 1960s as a branch of climatic geomorphology focusing first on quaternary studies and palaeoenvironmental reconstructions then on current geomorphi

continental tectonics in the aftermath of plate tectonics the success of plate tectonics required an acceptance of continental drift and thus a reinterpretation of the large scale geological history of most of the earth but the basic tenet of plate tectonics rigid body movements of large plates of lithosphere fails to apply to continental interiors where buoyant continental crust can detach from the underlying mantle to form mountain ranges and broad zones of diffuse tectonic activity

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

fault slip rates effects of elastic heterogeneity on geodetic data and the strength of the lower crust in the salton trough region southern california 1 in southernmost california the salton trough sedimentary basin lies between the subparallel san jacinto and san andreas faults that together with the elsinore fault accommodate 80 of the 50 mm yr of pacific north american relative motion the slip rates on the san andreas and san jacinto faults have been a matter of recent debate and one source of uncertainty has been the influence of crustal strength heterogeneity due to elastically weak basin sediments on geodetic data to evaluate these effects we have modeled regional kinematics with elastic and viscoelastic finite element models that incorporate laterally and vertically varying crustal material properties we find that in general the effects of the sedimentary basin on surface deformation are relatively small and that to explain the geodetic velocity data the slip rate on the san andreas must be higher than that on the san jacinto fault consistent with traditional geologic estimates we also conclude that a relatively strong lower crust of viscosity 5 x 10 19 pa s exists in this region

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

pedogenic carbonate cutans as a record of the holocene history of relic tundra steppes of the upper kolyma valley north eastern asia abstract pendant carbonate cutans on the undersides of coarse rock fragments in a steppe cryoarid soil profile on the steep south facing slope of the valley of the berelekh river in the upper kolyma valley north eastern asia provide a record of the holocene history of the tundra steppe ecosystem on the basis of two radiocarbon dates of cutan carbonate on stones at 40 100 cm depth a model of cutan growth was developed this suggests that the cutans have formed steadily from at least the early holocene until recent times and probably reflect the existence of a local area of stable tundra steppe vegetation throughout the holocene

genesis of soils and landscapes in the ridge and valley province of central pennsylvania abstract the characteristics and properties of the soils on the ridge tops footslopes and adjacent limestone valley areas in the ridge and valley of central pennsylvania have been strongly influenced by their parent material and geomorphic history the ridge top soils have developed in sandstone colluvium which mantles sandstone residuum the upper part of the original residual ridge top soil was truncated during late wisconsinan time and then covered with local colluvium or it was cyroturbated these sandstone parent materials have been stable since the late wisconsinan and have sandy skeletal dystrochrepts and haplorthods developed in them the haplorthods are minor soils and are associated with local concentrations of coniferous vegetation during the late wisconsinan the sandstone colluvium also moved downslope and was mixed with bedrock and residual material from shale and limestone and deposited on the footslope over a pre wisconsinan soil developed in older colluvium or limestone residuum the footslope surface colluvial soils vary in texture and drainage because of their parent material their location in discharge areas and fragipan development the age of the brown surface colluvium is considered late wisconsinan and the age of the pre wisconsinan buried soils is not known the buried soil s bright red rubified color and argillic horizon indicate a much greater degree of soil development than noted in the brown surface colluvium and its age may be correlated with isotope stage 6 the soils developed at the surface in the colluvium are mainly ultisols although some poorly drained soils particularly in limestone material are alfisols the ultisols are parent material ultisols and the poorly drained alfisols have a high base status in their parent material or were recharged with bases from the groundwater the soils of the limestone valleys are developed in residuum the residuum accumulated from the insoluble residues after the caco 3 was leached from the bedrock if the residuum is thick 2 to 3 m the soils date back many hundreds of thousands of years but are still classified as hapludalfs in addition to being old the surface of the hapludalfs has been modified by periglacial truncation and the addition of eolian materials these processes have given the upper 50 cm of the hapludalfs a late wisconsinan age but the bulk of the b horizon is many thousands of years older eolian material has also been added to the ridge top soils as well as the colluvial soils the mineralogy of all the soils in this landscape including the buried paleosols does not show significant clay mineral weathering this appears anomalous considering the degree of oxidation of the buried paleosols and the limestone soils and their estimated age

mineralogy and weathering processes in recent and holocene tephra deposits of the pacific northwest usa abstract weathering and evolution of minerals in tephra deposits in the cascade range of washington state usa are influenced by climate vegetation time microtopography and in the vicinity of mt st helens naturally acidic precipitation we have observed the interaction of these factors in spodosols developed on holocene tephra in the central cascades and in entisols formed on the 1980 pyroclastic flow of mt st helens weathering regimens in these tephritic soils can be qualitatively characterized by the soil solution composition weathering reactions in the spodosol are driven by organic acids in the upper soil horizons and by carbonic acid in the lower b and c horizons the mineral assemblage in the spodosol reflects in part the chemical regimen dictated by each proton donor the presence of smectite in the highly acidic e horizon ph

global positioning system constraints on fault slip rates in the death valley region california and nevada we estimated horizontal velocities at 15 locations in the vicinity of yucca mountain nevada from global positioning system surveys conducted between 1991 and 1996 we used these velocity estimates to infer slip rates on two major quaternary faults within the eastern california shear zone ecsz the hunter mountain and death valley faults the sum of slip rates across the two faults is well determined at 5 1 mm yr 1 between 3 to 5 mm yr of this motion appears to be accommodated along the death valley fault implying 30 50 m of strain accumulation over the next 10 000 yr if so there is potential for 5 to 10 m w 6 5 7 5 earthquakes during this period a finding consistent with paleoseismological studies of the fault zone yucca mountain which lies 50 km east of the ecsz is the proposed location for the disposal of high level nuclear waste in the united states