evidence from precise earthquake hypocenters for segmentation of the san andreas fault in san gorgonio pass we use precise hypocenter patterns and focal mechanisms to investigate the presence or absence of a continuous strike slip fault at depth connecting the san bernardino strand of the san andreas fault with the coachella valley segment of the banning fault we inverted 560 000 arrival times from 23 000 earthquakes 1981 1993 for high quality hypocenters and three dimensional p wave velocity structure in a 1 by 2 area centered on the san gorgonio pass cross sectional plots of relocated earthquakes reveal an abrupt 5 to 7 km high step in the maximum depth of hypocenters the step riser defines a near vertical locally curved surface that extends westerly more than 60 km from the coachella valley segment of the san andreas fault to the san jacinto fault a hypothetical continuous vertical san andreas fault through san gorgonio pass would cross the step at an oblique angle we suggest that the step is the expression of the contact between different basement rock types juxtaposed by large scale right slip motion on the ancestral san andreas fault south of the step in peninsular ranges type basement intrusives brittle failure occurs down to about 20 km depth while north of the step in san bernardino type basement pelona schist brittle failure occurs to only about 13 km depth the step provides a piercing plane that should be offset about 3 km right laterally by an active continuous vertical san andreas fault within the resolution of our mapping the step is not offset in this manner implying either that there has not been a throughgoing vertical fault at depth that a throughgoing fault has not experienced enough slip to offset the step or that a throughgoing fault is not vertical and dips north over the top of the step hypocentral patterns and focal mechanisms indicate distributed deformation thrust normal and strike slip faulting over a large volume in the san gorgonio pass region there is no evidence of hypocenter or slip vector alignments that would indicate a throughgoing continuous near vertical san andreas fault in summary we find no evidence indicating a continuous fault at seismogenic depth connecting the san bernardino strand and coachella valley segment of the san andreas fault zone we speculate that this is because the 3 km of right slip on the san bernardino stand of the san andreas fault and coachella valley segment of the banning fault has not been sufficient to form a single new structure through the 15 to 20 km gap between the two previously unconnected segments this implies that large earthquake rupture on the san andreas fault may be inhibited from propagating through san gorgonio pass thus limiting the maximum magnitudes on the southern san andreas fault

the seismogenic thickness of the southern california crust the average seismogenic thickness measured from the surface down to maximum depth of earthquake rupture for the southern california crust is 15 0 km 1 2 1 1 km we determine the seismogenic thickness using the depth distribution of the seismic moment release of 19 years of seismicity we calibrate the depth distribution of moment release from background seismicity by comparing the maximum depth of rupture during moderate to large magnitude earthquakes to the premainshock background seismicity of the respective mainshock region the calibration shows that the depth above which 99 9 of the moment release of background seismicity occurs reliably estimates the maximum depth of rupture during moderate to large earthquakes locally the seismogenic thickness is highly variable ranging from less than 10 km in the salton trough to greater than 25 km at the southwestern edge of the san joaquin valley similarly the seismogenic thickness along the major strike slip faults can vary significantly along strike changes in seismogenic thickness along strike do not correspond to the mapped surface segmentation of the major southern california strike slip fault systems in the future such estimates of the seismogenic thickness can be used to refine existing seismic hazard estimates for southern california

soil geomorphic research a selective overview abstract much soil geomorphologic research involves tracking the development of soils with time otherwise known as soil chronosequences most of these have been undertaken on landforms underlain by quaternary depsits of varying ages in general there is a predictable variation in both soil horizon sequence and amounts of constituents such as clay fe and caco 3 with time the rate at which these constituents accumulate in the soil is a function of parent material bioclimate and atmospheric dust influx and because of the latter soils in aridic regions can form at rapid rates profile properties can be used to estimate the ages of deposits and faulting events but the error on the estimated age can be 50 or greater the position of salt accumulations in soil profiles is one of the best indications of climatic change and these can be modelled to compare with various climatic parameters present and past profile characteristics due to pedogenic thresholds however can mimic those due to climatic change so close dating is necessary to differentiate the effects of both soil geomorphic data are essential to understand the origin of ancient paleosols in the sedimentary rock records but a major problem still is one of recognition of these features as soils and to separate the effects of pedogenesis from those of diagenesis

viscosity structure of the crust and upper mantle in western nevada from isostatic rebound patterns of the late pleistocene lake lahontan high shoreline received 13 july 2005 revised 26 october 2006 accepted 31 january 2007 published 8 june 2007 1 large lakes can both produce and record significant crustal deformation we present an analysis of the isostatic rebound pattern recorded in the shorelines of paleolake lahontan in western nevada using a layered maxwell viscoelastic model the inferred viscosity structure depends on loading history we use three variants of a well documented lake surface elevation model as input and recover corresponding estimates of viscosity and density structure a simple two layer model with an elastic plate over an inviscid half space fits the observed elevation pattern quite well with a residual variance of 32 of the data variance using multilayered finite viscosity models the residual variance is reduced to 20 of the data variance which is very near to the noise level in the higher resolution models the viscosity is below 10 18 pa s over the depth range from 80 to 160 km the minimum viscosity is very similar to the value that has been seen in the eastern great basin from similar analyses of lake bonneville shorelines but the lowviscosity zone is thinner beneath bonneville making small adjustments to a seismically derived density structure allows an improved fit to the shoreline observations additionally we find that small variations in proposed loading models can result in presumably spurious density inversions and suggest that this modeling approach provides a test for loading histories

relative contributions of crustal temperature and composition to controlling the depth of earthquakes in southern california 1 control of the 13 km range of the maximum depth of earthquakes in southern california has been attributed previously to lateral variations in either crustal temperature or crustal rock composition here i compare heat flow a proxy for crustal temperature local maximum depths of earthquakes d95 and best guess crustal rock compositions plotting heat flow versus d95 produces distinct trends for each rock composition with each trend representing an isotherm marking the onset of plastic behavior offsets between the trends measure the differences in the plastic behavior temperatures of each rock composition these offsets are comparable to the d95 variations with heat flow thus crustal temperature and composition contribute about equally to the control of the maximum depths of earthquakes the observed isotherm slopes imply vertical variations in crustal composition in addition to the lateral variations

mapping apparent stress and energy radiation over fault zones of major earthquakes using published slip models for five major earthquakes 1979 imperial valley 1989 loma prieta 1992 landers 1994 northridge and 1995 kobe we produce maps of apparent stress and radiated seismic energy over their fault surfaces the slip models obtained by inverting seismic and geodetic data entail the division of the fault surfaces into many subfaults for which the time histories of seismic slip are determined to estimate the seismic energy radiated by each subfault we measure the near fault seismic energy flux from the time dependent slip there and then multiply by a function of rupture velocity to obtain the corresponding energy that propagates into the far field this function the ratio of far field to near fault energy is typically less than 1 3 inasmuch as most of the near fault energy remains near the fault and is associated with permanent earthquake deformation adding the energy contributions from all of the subfaults yields an estimate of the total seismic energy which can be compared with independent energy estimates based on seismic energy flux measured in the far field often at teleseismic distances estimates of seismic energy based on slip models are robust in that different models for a given earthquake yield energy estimates that are in close agreement moreover the slip model estimates of energy are generally in good accord with independent estimates by others based on regional or teleseismic data apparent stress is estimated for each subfault by dividing the corresponding seismic moment into the radiated energy distributions of apparent stress over an earthquake fault zone show considerable heterogeneity with peak values that are typically about double the whole earthquake values based on the ratio of seismic energy to seismic moment the range of apparent stresses estimated for subfaults of the events studied here is similar to the range of apparent stresses for earthquakes in continental settings with peak values of about 8 mpa in each case for earthquakes in compressional tectonic settings peak apparent stresses at a given depth are substantially greater than corresponding peak values from events in extensional settings this suggests that crustal strength inferred from laboratory measurements may be a limiting factor lower bounds on shear stresses inferred from the apparent stress distribution of the 1995 kobe earthquake are consistent with tectonic stress estimates reported by spudich et al 1998 based partly on slip vector rake changes manuscript received 21 february 2001

constraints on the stress state of the san andreas fault with analysis based on core and cuttings from san andreas fault observatory at depth safod drilling phases 1 and 2 stress state constraints on the saf

fine structure of the landers fault zone segmentation and the rupture process observations and modeling of 3 to 6 hertz seismic shear waves trapped within the fault zone of the 1992 landers earthquake series allow the fine structure and continuity of the zone to be evaluated the fault to a depth of at least 12 kilometers is marked by a zone 100 to 200 meters wide where shear velocity is reduced by 30 to 50 percent this zone forms a seismic waveguide that extends along the southern 30 kilometers of the landers rupture surface and ends at the fault bend about 18 kilometers north of the main shock epicenter another fault plane waveguide disconnected from the first exists along the northern rupture surface these observations in conjunction with surface slip detailed seismicity patterns and the progression of rupture along the fault suggest that several simple rupture planes were involved in the landers earthquake and that the inferred rupture front hesitated or slowed at the location where the rupture jumped from one to the next plane reduction in rupture velocity can tentatively be attributed to fault plane complexity and variations in moment release can be attributed to variations in available energy

locking depth slip rate and seismicity distribution along the daofu kangding segment of the xianshuihe fault system eastern tibetan plateau abstract in this study 1338 relocated earthquakes ms 1 6 from 1981 to 2018 and 53 gps velocities from 2004 to 2017 were processed to obtain the geometry and kinematic characteristics of the daofu kangding segment of the xianshuihe fault system in southwestern china by analyzing the seismicity depth distribution of the selaha kangding fault we inferred its three branches the yalahe fault selaha fault and zheduotang fault converged into one fault at a depth of approximately 15 km and that a flower shaped structure was observed above this depth furthermore based on a 2d elastic dislocation model the creep rates creep depths slip rates and locking depths of the daofu kangding segment were analyzed in case of the daofu qianning fault the obtained left lateral slip rate was 4 5 1 1 mm a and the locking depth was 5 3 1 9 km because the fault creep rate from a depth of 2 6 km to the surface was 1 3 1 0 mm a the daofu qianning fault cannot generate earthquakes having magnitudes of greater than 7 in the near future however the slip rates were 7 5 1 6 2 3 1 5 and 1 9 1 5 mm a by assuming a locking depth of 15 km for the selaha fault yalahe fault and zheduotang fault respectively furthermore because the creep depth of the selaha fault was 3 4 1 6 km and the creep rate was 7 5 2 8 mm a the accumulated seismic moment since 1725 corresponded to a mw7 1 earthquake

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

using the accumulation of cbd extractable iron and clay content to estimate soil age on stable surfaces and nearby slopes front range colorado abstract in many transport limited environments morphology pedogenic iron and clay content provide a basis for estimating the exposure age of soils and associated landforms we measured citrate buffered dithionite cbd extractable fe fe d and clay concentration in fresh rock saprolite morainal and colluvial materials and soil horizons from stable surfaces and hillslopes in the colorado front range fresh igneous and high grade metamorphic rocks contain d and 1 to 5 clay as bedrock and surficial deposits age fe d and clay accumulate from weathering and dustfall late holocene regolith at warm dry sites contains small amounts of fe d and clay but relatively moist soils developed on early holocene cirque deposits contain as much as 1 5 fe d and 8 clay concentrations and total profile accumulation of fe d and clay increase with age in soils developed on stable surfaces of glacial deposits as old as 130 kyr on stable sites fe d and clay accumulation from weathering and dust is 0 02 g cm 2 kyr 1 and 0 2 g cm 2 kyr 1 respectively we used the fe d and clay inventory in soil profiles at dated stable front range surfaces to calculate accumulation functions which allowed us to estimate soil age at hillslope sites heterogeneous parent material particularly on hillslopes and climate related effects add to variability in measured relations mobile regolith in gordon gulch one of the boulder creek critical zone observatory czo catchments yields profile ages from about 0 5 to 5 10 4 yr comparable to values measured using other techniques calculated profile ages are older on a north vs south facing slope and increase from the drainage divide to the footslope ages calculated for stabilized colluvium and well developed buried profiles at nearby hillslope sites lefthand ward and rollinsville suggest that these soils have stabilized over periods 10 5 yr in the absence of radiometric ages the accumulation of fe d and clay in soils on stable sites and hillslopes provides a useful local chronofunction for 10 3 to 3 10 5 yr local footslope thickening of mobile regolith buried soils and areas of fe d and clay rich stabilized colluvium suggest that steady state models of hillslope regolith must be modified to account for observed soil properties

deep drilling at vostok station antarctica history and recent events deep drilling into the ice sheet at vostok station antarctica was started by specialists of the leningrad mining institute since 1991 st petersburg state mining institute in 1970 five deep holes were cored hole no 1 to 952 m hole no 2 to 450 4 m hole no 3g 3g 1 3g 2 to 2201 7 m hole no 4g 4g 1 4g 2 to 2546 4 m and hole no 5g 5g 1 to 3650 2 m depth drilling of hole 5g 1 is not yet complete the deep drilling at vostok station has had successes and problems all the deep holes at vostok have undergone at least one offset drilling operation because of problems with lost drills these deviations were made successfully using a thermal drilling technique several drilling records have been achieved at vostok station the deepest dry hole no 1 952 m was made during soviet antarctic expedition sae 17 in 1972 the deepest fluid filled hole no 5g 1 made by a thermal drill tbzs 132 reached 2755 m during sae 38 in 1993 the deepest fluid filled hole in ice no 5g 1 was drilled with a kems 132 electromechanical drill and was stopped above vostok subglacial lake at 3650 2 m depth during russian antarctic expedition rae 51 in 2006

a large deep freshwater lake beneath the ice of central east antarctica in 1974 75 an airborne radio echo survey of ice depths over central east antarctica led to the discovery of a sub ice lake of unknown depth and composition with an area of about 10 000km2 and lying beneath 4km of ice1 in 1993 altimetric data from satellite measurements2 provided independent evidence of the lake s areal extent thus confirming it to be the largest known sub ice lake by an order of magnitude here we analyse new altimetric and radio echo data along with existing seismic data3 to show that the lake is deep mean depth of 125 m or more and fresh and that it has an area that exceeds previous estimates by about 50 dimensions comparable with those of lake ontario we estimate that the residence time of the water in the lake is of the order of tens of thousands of years and that the mean age of water in the lake since deposition as surface ice is about one million years regional ice dynamics can be explained in terms of steady state ice flow along and over the lake

identification of subglacial lakes using ers 1 radar altimeter radar altimeter data from ers 1 allow detailed topographic mapping of antarctica to 82 degrees s to be carried out revealing several notable surface features among these is the large subglacial lake near vostok which is mapped here in detail the central part of the lake is found to have an exceptionally smooth surface with r m s elevation variations of less than 0 2 m a search for other large antarctic lakes in the data is made based on the smoothness and low gradient of the surface a number of other flat areas are identified with lake locations previously determined from radio echo sounding observations however radar altimeter observations show that a minimum lake size of 20 km is required for a surface above a lake to become flat numerous bowl like features can be seen in the surface topography and these may be associated with intermediate sized subglacial lakes it is determined that high spatial resolution radar altimetery could be used to identify subglacial lakes greater than 10 km in lateral extent flat regions of the ice sheet are particularly useful as they may be used as height reference surfaces to help fix the orbits of radar altimeter satellites

short term geomorphological evolution of proglacial systems proglacial systems are amongst the most rapidly changing landscapes on earth as glacier mass loss permafrost degradation and more episodes of intense rainfall progress with climate change this review addresses the urgent need to quantitatively define proglacial systems not only in terms of spatial extent but also in terms of functional processes it firstly provides a critical appraisal of prevailing conceptual models of proglacial systems and uses this to justify compiling data on rates of landform change in terms of planform horizontal motion elevation changes and sediment budgets these data permit us to produce novel summary conceptual diagrams that consider proglacial landscape evolution in terms of a balance of longitudinal and lateral water and sediment fluxes throughout we give examples of newly emerging datasets and data processing methods because these have the potential to assist with the issues of i a lack of knowledge of proglacial systems within high mountain arctic and polar regions ii considerable inter and intra catchment variability in the geomorphology and functioning of proglacial systems iii problems with the magnitude of short term geomorphological changes being at the threshold of detection iv separating short term variability from longer term trends and v of the representativeness of plot scale field measurements for regionalisation and for upscaling we consider that understanding of future climate change effects on proglacial systems requires holistic process based modelling to explicitly consider feedbacks and linkages especially between hillslope and valley floor components such modelling must be informed by a new generation of repeated distributed topographic surveys to detect and quantify short term geomorphological changes

the seismogenic thickness in italy constraints on potential magnitude and seismic hazard the thickness of the seismogenic layer is a key parameter for seismic hazard since it can be used to constrain the maximum depth of faulting and the potential magnitude in this study we compute the seismogenic thickness in the italian region by defining the lower seismicity cutoff using high quality hypocentral locations of earthquakes that occurred in the past decade along the eastern alps the seismogenic thickness is about 12 14 km laterally homogeneous along the entire south verging thrust front in the apennines extensional belt lateral changes in seismogenic thickness are evident and correlate with changes in the seismic energy released by past earthquakes the potential magnitude is larger in the southern apennines where the seismogenic thickness is greater 16 18 km than in the northern apennines where it is less 6 10 km and seismic energy is partially released by the creeping of faults this article is protected by copyright all rights reserved

rapid weathering processes of a 120 year old chronosequence in the hailuogou glacier foreland mt gongga sw china increasing numbers of young soil chronosequences have become exposed in global alpine areas as glaciers have retreated due to climate warming since the industrial revolution however knowledge on the initial stages of weathering at the decadal time scale is limited our aim is to reveal the weathering processes and influential factors in a 120 year old chronosequence on mt gongga in southwest china sixty nine soil samples and 17 water samples were collected from 6 sites with different exposure ages 0 30 40 52 80 and 120 years mineral compositions were determined using x ray diffractometry and four mineral pools i e 1 exchangeable cations 2 carbonates and apatite 3 biotite and hornblende and 4 refractory minerals were separated using a sequential extraction method the results reveal that the soil particle sizes of 2 mu m clay in the a horizons increased and the particle sizes of 20 2000 mu m sand decreased significantly with time the soil organic carbon accumulation rate was up to 14 g m 2 yr which is relatively high compared with other chronosequences of similar age the weathering can be generally divided into two stages the first stage was dominated by the weathering of carbonates and was present at sites with an exposure age of 52 years the second stage was characterized by the intense weathering of biotite hornblende and apatite and was present at the 80 and 120 year old sites where coniferous trees were the dominant plants the rapid weathering was a result of the interactions of the lithology rapid vegetation succession and climate in the hailuogou chronosequence fine silt was produced in large quantities by the strong glacial abrasion and freeze thaw cycles providing rich materials for the subsequent chemical and biogeochemical weathering the decarbonation and the rapid establishment of the conifer forest due to relatively high temperatures and precipitation promote mineral weathering by decreasing soil ph from 8 5 0 years to 4 8 120 years the high permeability of the soil horizons due to the high content of rock fragments and abundant precipitation allows water and organic acids to infiltrate and dissolve mineral soils above the impervious bedrock this study highlights the importance of carbonate weathering in alpine biogeochemical cycling during the initial stage of weathering in granitoid rock areas furthermore our results indicate that the weathering intensity increases with exposure age due to vegetation succession in the early stages of weathering c 2015 elsevier b v all rights reserved

pro glacial soil variability and geomorphic activity the case of three swiss valleys soils in pro glacial areas are often approached from a chronosequence viewpoint in the chronosequence approach the objective is to derive rates of soil formation from differences in properties between soils of different age for this reason in chronosequence studies soils are sampled in locations that are assumed geomorphically stable and that have different age as a result these studies do not necessarily yield a complete view of soil variability in pro glacial areas and may miss important relations between geomorphology and soil development in this contribution we present new soil observations from three closely related pro glacial areas in switzerland these observations were intended to get closer to a complete view of soil variability and to assess impacts from factors other than time on soil development about 40 soils were visited in each pro glacial valley in a combined design convenience sampling scheme and described in the field linear modelling was used to assess effects of time and topographic factors on soil properties the time since glacial retreat turned out to rarely explain more than half of the variation in soil properties and a linear model combining effects of time and topographic variables explained typically about half of the variation in each pro glacial valley models differed and were not transferable between valleys apparently time and the present day shape of the landscape combined are insufficient information to accurately predict soil properties field evidence points to the importance of the geomorphic history and regime of the valleys as a reason for this copyright c 2014 john wiley sons ltd

ice cover landscape setting and geological framework of lake vostok east antarctica abstract lake vostok located beneath more than 4 km of ice in the middle of east antarctica is a unique subglacial habitat and may contain microorganisms with distinct adaptations to such an extreme environment melting and freezing at the base of the ice sheet which slowly flows across the lake controls the flux of water biota and sediment particles through the lake the influx of thermal energy however is limited to contributions from below thus the geological origin of lake vostok is a critical boundary condition for the subglacial ecosystem we present the first comprehensive maps of ice surface ice thickness and subglacial topography around lake vostok the ice flow across the lake and the landscape setting are closely linked to the geological origin of lake vostok our data show that lake vostok is located along a major geological boundary magnetic and gravity data are distinct east and west of the lake as is the roughness of the subglacial topography the physiographic setting of the lake has important consequences for the ice flow and thus the melting and freezing pattern and the lake s circulation lake vostok is a tectonically controlled subglacial lake the tectonic processes provided the space for a unique habitat and recent minor tectonic activity could have the potential to introduce small but significant amounts of thermal energy into the lake

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

exploring links between vadose zone hydrology and chemical weathering in the boulder creek critical zone observatory understanding the relationship between subsurface flow paths on hillslopes and chemical weathering of bedrock is fundamental to understanding the timing and mechanisms that weather bedrock to saprolite the link between chemical weathering of bedrock and contact time with reactive water along flow paths motivates this study water drives the chemical alteration of rock into saprolite yet connected porosity generally declines with depth into the weathered profile saprolite formation therefore reflects coupled weathering and permeability development over time this study uses numerical modeling and soil moisture monitoring to explore the hydrology of the unsaturated zone and the influence of fracture density hillslope gradient and permeability contrasts within the saprolite development horizon on saprolite development

earthquake cycle simulations with rate and state friction and power law viscoelasticity abstract we simulate earthquake cycles with rate and state fault friction and off fault power law viscoelasticity for the classic 2d antiplane shear problem of a vertical strike slip plate boundary fault we investigate the interaction between fault slip and bulk viscous flow with experimentally based flow laws for quartz diorite and olivine for the crust and mantle respectively simulations using three linear geotherms dt dz 20 25 and 30 k km produce different deformation styles at depth ranging from significant interseismic fault creep to purely bulk viscous flow however they have almost identical earthquake recurrence interval nucleation depth and down dip coseismic slip limit despite these similarities variations in the predicted surface deformation might permit discrimination of the deformation mechanism using geodetic observations additionally in the 25 and 30 k km simulations the crust drags the mantle the 20 k km simulation also predicts this except within 10 km of the fault where the reverse occurs however basal tractions play a minor role in the overall force balance of the lithosphere at least for the flow laws used in our study therefore the depth integrated stress on the fault is balanced primarily by shear stress on vertical fault parallel planes because strain rates are higher directly below the fault than far from it stresses are also higher thus the upper crust far from the fault bears a substantial part of the tectonic load resulting in unrealistically high stresses in the real earth this might lead to distributed plastic deformation or formation of subparallel faults alternatively fault pore pressures in excess of hydrostatic and or weakening mechanisms such as grain size reduction and thermo mechanical coupling could lower the strength of the ductile fault root in the lower crust and concomitantly off fault upper crustal stresses

widespread persistent thickening of the east antarctic ice sheet by freezing from the base an international polar year aerogeophysical investigation of the high interior of east antarctica reveals widespread freeze on that drives substantial mass redistribution at the bottom of the ice sheet although the surface accumulation of snow remains the primary mechanism for ice sheet growth beneath dome a 24 of the base by area is frozen on ice in some places up to half of the ice thickness has been added from below these ice packages result from the conductive cooling of water ponded near the gamburtsev subglacial mountain ridges and the supercooling of water forced up steep valley walls persistent freeze on thickens the ice column alters basal ice rheology and fabric and upwarps the overlying ice sheet including the oldest atmospheric climate archive and drives flow behavior not captured in present models

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

the 1992 landers earthquake sequence earthquake occurrence and structural heterogeneities the june 28 1992 mw 7 3 landers earthquake occurred in the southeastern mojave desert california over 10 000 aftershocks of the earthquake were recorded by the caltech usgs southern california seismic network scsn in 1992 to investigate the relationship between complexities in the crustal structure and variations in seismicity we have used a tomographic method to invert 145 098 p wave arrival times from 3740 landers earthquake aftershocks and 1148 other events recorded by 60 permanent and temporary scsn stations we determined a detailed p wave tomographic image with a spatial resolution of about 5 km and relocated the hypocenters with the obtained 3 d velocity model the results show a correlation between seismicity patterns and velocity patterns and a tendency for regions rich in seismicity to be associated with higher velocities the higher velocity areas are considered to be strong and brittle parts of the fault zone which are apt to generate earthquakes in contrast low velocity areas are probably more ductile and weaker allowing aseismic slippage

state of stress from focal mechanisms before and after the 1992 landers earthquake sequence the state of stress in the eastern california shear zone ecsz changed significantly because of the occurrence of the 1992 m w 6 1 joshua tree and the m w 7 3 landers earthquakes to quantify this change focal mechanisms from the 1975 galway lake sequence the 1979 homestead valley sequence background seismicity from 1981 to 1991 and the 1992 landers sequence are inverted for the state of stress in all cases the intermediate principal stress axis s2 remained vertical and changes in the state of stress consisted of variations in the trend of maximum and minimum principal stress axes s 1 and s 3 and small variations in the value of the relative stress magnitudes in general the stress state in the ecsz has s 1 trending east of north and 0 43 to 0 65 suggesting that the ecsz is a moderate stress refractor and the style of faulting is transtensional south of the pinto mountain fault in the region of the 1992 joshua tree earthquake the stress state determined from the 1981 to 1991 background seismicity changed on 23 april and again on 28 june 1992 in the central zone s 1 rotated from n14 5 e to n28 5 e on 23 april and back again to n16 5 e on 28 june thus the landers mainshock in effect recharged some of the shear stress in the region of the m w 6 1 joshua tree earthquake comparison of the state of stress before and after 28 june 1992 along the landers mainshock rupture zone showed that the mainshock changed the stress orientation the s1 trend rotated 7 to 20 clockwise and became progressively more fault normal from south to north along the emerson camp rock faults the variation was so prominent that the focal mechanisms of aftershocks could not be fit by a single deviatoric stress tensor the complex distribution of p and t axes suggests that most of the uniform component of the applied shear stress along the northern part of the rupture zone was released in the mainshock the san bernardino mountains region of the m w 6 2 big bear earthquake has a distinctively different state of stress as compared to the landers region with s 1 trending n3 5 w this region did not show any significant change in the state of stress following the 1992 m w 6 2 big bear sequence

plate rigidity inversion in southern california using interseismic gps velocity field summary this paper presents an inversion method using the interseismic velocity field to determine effective rigidity of the lithosphere the method is based on the minimization of a cost function defined as the quadratic measure of the difference between measured and modelled velocity fields on a discrete set of points the continuous mapping of the rigidity is fulfilled with a limited set of parameters and the forward solution is achieved using a plane stress finite element code the computation of the cost function gradient in the parameters space allows one to iteratively find the best parameters set through a suitable optimization algorithm we first design a benchmark including an abrupt rigidity variation that cannot be described by a continuous function for such a case we show that increasing the number of parameters is a way to accurately describe sharp variations of the rigidity map then we use a dense gps velocity field over the southwestern united states to estimate the corresponding rigidity variations for different spatial resolutions of the parameters grid we analyse the conceptual and practical difficulties associated with our methodology finally rigidity maps obtained by our inversion method in southwestern united states and particularly across the san andreas fault system are reviewed and compared to current plate rigidity estimates and geophysical data over this area

tectonically controlled subglacial lakes on the flanks of the gamburtsev subglacial mountains east antarctica 1 the morphology of surface lakes strongly influences their ecology and limnology wetzel 2001 this morphology is a result of both the geologic processes that produce topographic basins and the regional climatic and local hydrologic processes that control water depth and sediment infilling carroll and bohacs 1999 although basin forming processes range from glacial scour to meteorite impacts cohen 2003 the deepest oldest surface lakes are tectonically controlled meybeck 1995 and contain diverse exotic ecosystems rossiterm and kawanabe 2000 subglacial lakes are also thought to be ancient systems that may contain exotic biota bulat et al 2004 karl et al 1999 priscu et al 1999 here we present evidence for the scale and configuration of 2 large subglacial lakes in east antarctica that together with lake vostok define a province of major lakes on the flanks of the gamburtsev subglacial mountains spatially defined in the new moderate resolution imaging spectroradiometer modis imagery of antarctica t scambos et al a modis based mosaic of antarctica moa submitted to remote sensing of environment 2005 hereinafter referred to as scambos et al submitted manuscript 2005 these lakes are aligned parallel to lake vostok other data shows that they are distinguished by distinct gravity lows flat ice surface slopes and have estimated water depths of at least 900 m surface elevation data indicates that large deep subglacial lakes have a profound influence on the regional ice sheet topography and probably ice sheet flow these deep subglacial lakes with elongate rectilinear morphology are tectonically controlled features unlike the shallow lakes in west antarctica and beneath dome concordia these deep subglacial lakes remained stable environments through many glacial cycles since their origin 10 35 ma enabling the development of novel ecosystems

thermal constraints on earthquake depths in california the high quality databases for california seismicity from the southern and northern california earthquake centers and an extensive compilation of thermal measurements in california are used to quantify the concept of temperature as a fundamental parameter for determining the thickness of the seismogenic zone the base of this zone below which only a small percentage of crustal earthquakes occur is termed the cutout depth and it is at or near the brittle ductile transition in the crust based on laboratory deformation studies this transition should be temperature strain rate lithology and stress state dependent in this study qualitative comparisons between the heat flow in california and earthquake hypocentral distributions show first that as expected earthquake cutout depths are inversely related to heat flow second the epicentral distributions tend to parallel thermal transitions this correlation is probably related to stress concentrations in these locations an ancillary observation is that the cooler western mojave block in southern california appears to be behaving similarly to the tibetan indenter block in asia as faults tend to go around it into areas of higher heat flow where the seismogenic zone is thinner and the crust may be weaker and it is pushed toward and under the southern cold sierra nevada block third to quantitatively compare the data sets temperatures for the seismicity cutout depth in california were calculated using the steady state 1d heat conduction equation with the variables based on published values for heat flow heat generation and thermal conductivity the analysis was restricted to profiles along which the heat flow and earthquake databases were constrained which allowed the error in the temperature calculation to be determined using monte carlo simulations the results show that two distinct ranges of temperatures dependent upon location describe the cutout depth d 99 of seismicity for california 450 50 c and 260 40 c the 450 50 c cutout depth temperature is most widespread geographically occurs within many provinces and is higher than the frequently referenced temperature of 300 50 c for the brittle ductile transition the lower temperature 260 c seems to be restricted to provinces where the heat flow is near or below 50 mw m 2 such as the mojave block and sierra nevada the differences in these cutout temperatures suggest that additional factors such as strain rate stress regime and or lithology may contribute to the seismicity cutout depth fourth along a profile with significant seismic activity and a 450 c cutout temperature the envelope for the maximum energy released by earthquakes falls at or below the 300 c isotherm detailed characterization of the heat flow and earthquake synergy in this manner furthers the understanding of the earthquake process and can aid in the estimation of the maximum depth of rupture for great earthquakes particularly in areas of low seismicity thus reducing uncertainties in hazard calculations manuscript received 26 february 2003

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

testing a soil development model against southern norway soil chronosequences abstract the first results of modeling soil development in marine sediments in s norway using the model soilgen are compared to measured properties of two soil chronosequences on the western and eastern side of oslofjord respectively the aim of this work is to test how well soil development under well defined environmental conditions can be modeled such testing reveals to what degree soil forming processes are understood allowing formulation of adequate calculations reflecting these processes the model predicts particle size distribution reasonably well although clay depletion in the upper parts of the soils as a result of clay migration is overestimated the model tends to underestimate contents of organic carbon and cec in the a horizons below modeled cec matches well with measured cec base saturation is overestimated in the upper 40 cm and underestimated below apparently leaching of bases proceeds less rapidly in reality than is predicted by the model due to strong soil structure of the b horizons causing preferential flow and base leaching around the aggregates whereas bases inside the aggregates are only slightly affected by leaching difficulties and possibilities for improvements are identified some related to model input data and some to the model itself input data could be improved by determining the amounts of organic carbon in organic surface horizons and by quantifying effects of bioturbation a big challenge is the implementation of soil structure formation in the model quantitative data on the development of soil structure with time that can be included in a model are required amounts distribution and connectivity of macro pores need to be defined for each stage of soil development and zones of low and high base leaching need to be distinguished in the model for each time step the long term aim of this work is to model soil development with different sets of soil forming factors e g different climatic conditions in order to reliably predict soil development under different climate scenarios and related sets of soil forming factors the results of the first model runs and the identified possible improvements suggest that this aim is generally achievable

constraints on the stress state of the san andreas fault with analysis based on core and cuttings from san andreas fault observatory at depth safod drilling phases 1 and 2 1 analysis of field data has led different investigators to conclude that the san andreas fault saf has either anomalously low frictional sliding strength 0 6 arguments for the apparent weakness of the saf generally hinge on conceptual models involving intrinsically weak gouge or elevated pore pressure within the fault zone some models assert that weak gouge and or high pore pressure exist under static conditions while others consider strength loss or fluid pressure increase due to rapid coseismic fault slip the present paper is composed of three parts first we develop generalized equations based on and consistent with the rice 1992 fault zone model to relate stress orientation and magnitude to depth dependent coefficient of friction and pore pressure second we present temperature and pressure dependent friction measurements from wet illite rich fault gouge extracted from san andreas fault observatory at depth safod phase 1 core samples and from weak minerals associated with the san andreas fault third we reevaluate the state of stress on the san andreas fault in light of new constraints imposed by safod borehole data pure talc 0 1 had the lowest strength considered and was sufficiently weak to satisfy weak fault heat flow and stress orientation constraints with hydrostatic pore pressure other fault gouges showed a systematic increase in strength with increasing temperature and pressure in this case heat flow and stress orientation constraints would require elevated pore pressure and in some cases fault zone pore pressure in excess of vertical stress

height changes over subglacial lake vostok east antarctica insights from gnss observations height changes of the ice surface above subglacial lake vostok east antarctica reflect the integral effect of different processes within the subglacial environment and the ice sheet repeated gnss global navigation satellite systems observations on 56 surface markers in the lake vostok region spanning 11 years and continuous gnss observations at vostok station over 5 years are used to determine the vertical firn particle movement vertical marker velocities are derived with an accuracy of 1 cm yr or better repeated measurements of surface height profiles around vostok station using kinematic gnss observations on a snowmobile allow the quantification of surface height changes at 308 crossover points the height change rate was determined at 1 5 mm yr thus indicating a stable ice surface height over the last decade it is concluded that both the local mass balance of the ice and the lake level of the entire lake have been stable throughout the observation period the continuous gnss observations demonstrate that the particle heights vary linearly with time nonlinear height changes do not exceed 1 cm at vostok station and constrain the magnitude of spatiotemporal lake level variations icesat laser altimetry data confirm that the amplitude of the surface deformations over the lake is restricted to a few centimeters assuming the ice sheet to be in steady state over the entire lake estimates for the surface accumulation on basal accretion melt rates and on flux divergence are derived

the evolution of the seismic aseismic transition during the earthquake cycle constraints from the time dependent depth distribution of aftershocks 1 using the example of the 1992 m 7 3 landers earthquake we show that in the aftermath of a large earthquake the depth extent of aftershocks shows an immediate deepening from pre earthquake levels followed by a time dependent postseismic shallowing we use these seismic data to constrain the change in the depth of the seismic aseismic transition with time throughout the earthquake cycle most studies of the seismic aseismic transition have focussed on the effects of temperature and or lithology on the transition either from brittle faulting to viscous flow or from unstable to stable sliding a strain rate dependent transient deepening of the brittle ductile transition following a major earthquake is predicted by geological and laboratory observations by analyzing the time dependent depth distributions of aftershocks we identify and quantify the temporal evolution of this transition in the example of the landers earthquake its depth changes by as much as 3 km over the course of 4 years

locking depths estimated from geodesy and seismology along the san andreas fault system implications for seismic moment release 1 the depth of the seismogenic zone is a critical parameter for earthquake hazard models independent observations from seismology and geodesy can provide insight into the depths of faulting but these depths do not always agree here we inspect variations in fault depths of 12 segments of the southern san andreas fault system derived from over 1000 gps velocities and 66 000 relocated earthquake hypocenters geodetically determined locking depths range from 6 to 22 km while seismogenic thicknesses are largely limited to depths of 11 20km theseseismogenicdepthsbestmatchthegeodeticlockingdepthswhenestimated at the 95 cutoff depth in seismicity and most fault segment depths agree to within 2 km however the imperial coyote creek and borrego segments have significant discrepancies in these cases the geodetically inferred locking depths are much shallower than the seismogenic depths we also examine variations in seismic moment accumulation rate per unit fault length as suggested by seismicity and geodesy and find that both approaches yield high rates 1 5 1 8 1 0 13 nm yr km along the mojave and carrizo segments and low rates 0 2 10 13 nm yr km along several san jacinto segments the largest difference in seismic moment between models is calculated for the imperial segment where the moment rate from seismic depths is a factor of 2 5 larger than that from geodetic depths such variability has important implications for the accuracy to which future major earthquake magnitudes can be estimated

antarctic subglacial lakes abstract antarctic subglacial lakes were first identified by robin et al 1970 after airborne radio echo sounding res investigations of the ice sheet interior recently satellite altimetry was used to measure anomalous near flat regions on the ice sheet surface that represent a manifestation of the subglacial lake beneath using res and satellite altimetry the location and extent of antarctic subglacial lakes can be identified the largest subglacial lake exists beneath vostok station and is 14 000 km2 in area the combined area of additional subglacial lakes beneath dome c is 15 000 km2 and at least 15 000 km2 of lake surface lies beneath the remainder of the ice sheet the water depth of subglacial lakes can be estimated through seismic investigations although data exist only for lake vostok and consideration of the bedrock slopes that border subglacial lakes the depths of many subglacial lakes are of the order of 10 s 100 s of metres the total volume of water held beneath the ice sheet is estimated between 4000 and 12 000 km3 to date there are six known examples of radio echo reflections from the lake floors at a depth of no more than 20 m since e m attenuation through water is related to the salinity these data indicate that subglacial water is very pure and fresh some near flat surface regions that usually occur over lakes have been observed where no lakes exist such features are may be caused by water saturated basal sediments rather than subglacial lakes finally the spatial variation in geothermal heat flux around the central regions of antarctica can be established estimated by employing a simple thermal model of the ice sheet under an assumption that the basal ice temperature above subglacial lakes is equal to the pressure melting value calculations indicate that the geothermal heat flux varies spatially over the antarctic plate between 37 and 65 mw m 2

the 1992 landers earthquake sequence seismological observations the m w 6 1 7 3 6 2 1992 landers earthquakes began on april 23 with the m w6 1 1992 joshua tree preshock and form the most substantial earthquake sequence to occur in california in the last 40 years this sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long the faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the san andreas fault the m w6 1 joshua tree preshock at 33 n58 and 116 w19 on 0451 ut april 23 was preceded by a tightly clustered foreshock sequence m 4 6 beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks the aftershocks extended along a northerly trend from about 10 km north of the san andreas fault northwest of indio to the east striking pinto mountain fault the m w7 3 landers mainshock occurred at 34 n13 and 116 w26 at 1158 ut june 28 1992 and was preceded for 12 hours by 25 small m 3 earthquakes at the mainshock epicenter the distribution of more than 20 000 aftershocks analyzed in this study and short period focal mechanisms illuminate a complex sequence of faulting the aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults and 40 km to the south crossing the pinto mountain fault through the joshua tree aftershock zone towards the san andreas fault near indio the rupture initiated in the depth range of 3 6 km similar to previous m 5 earthquakes in the region although the maximum depth of aftershocks is about 15 km the mainshock focal mechanism showed right lateral strike slip faulting with a strike of n10 w on an almost vertical fault the rupture formed an arclike zone well defined by both surficial faulting and aftershocks with more westerly faulting to the north this change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west a 20 km long linear cluster of aftershocks occurred 10 20 km north of barstow or 30 40 km north of the end of the mainshock rupture the most prominent off fault aftershock cluster occurred 30 km to the west of the landers mainshock the largest aftershock was within this cluster the m w6 2 big bear aftershock occurring at 34 n10 and 116 w49 at 1505 ut june 28 it exhibited left lateral strike slip faulting on a northeast striking and steeply dipping plane the big bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north the landers mainshock occurred near the southernmost extent of the eastern california shear zone an 80 km wide more than 400 km long zone of deformation this zone extends into the death valley region and accommodates about 10 to 20 of the plate motion between the pacific and north american plates the joshua tree preshock its aftershocks and landers aftershocks form a previously missing link that connects the eastern california shear zone to the southern san andreas fault

bedmap a new ice thickness and subglacial topographic model of antarctica measurements of ice thickness on the antarctic ice sheet collected during surveys undertaken over the past 50 years have been brought together into a single database from these data a seamless suite of digital topographic models have been compiled for antarctica and its surrounding ocean this includes grids of ice sheet thickness over the grounded ice sheet and ice shelves water column thickness beneath the floating ice shelves bed elevation beneath the grounded ice sheet and bathymetry to 60 s including the sub ice shelf cavities these grids are consistent with a recent high resolution surface elevation model of antarctica while the digital models have a nominal spatial resolution of 5 km such high resolution is justified by the original data density only over a few parts of the ice sheet the suite does however provide an unparalleled vision of the geosphere beneath the ice sheet and a more reliable basis for ice sheet modeling than earlier maps the total volume of the antarctic ice sheet calculated from the bedmap grid is 25 4 million km3 and the total sea level equivalent derived from the amount of ice contained within the grounded ice sheet is 57 m comprising 52 m from the east antarctic ice sheet and 5 m from the west antarctic ice sheet slightly less than earlier estimates the gridded data sets can be obtained from the authors

initial stages of weathering and soil formation in the morteratsch proglacial area upper engadine switzerland investigations in alpine soils indicate that mineral weathering is much faster in young soils 1000 yr than in old soils 10 000 yr however little is known about the initial stages of weathering and soil formation i e during the first decades of soil genesis in this study we investigated rock forming minerals weathering at very early stages of soil formation due to the continuous retreat of the morteratsch glacier upper engadine swiss alps the proglacial area offers a full time sequence from 0 to 150 yr old surfaces a low slope and the absence of glacier which might have interrupted soil formation processes contributed to the choice of the morteratsch proglacial valley for this case study the area is well documented regarding vegetation and soils the tectonic unit is the bernina crystalline which is mainly constituted of granitoid rocks consequently the glacial till has an acidic character mineralogical measurements were carried out on the soil fraction 2 mm using xrd and drift for qualitative and quantitative phase analysis in addition chemical analyses of the stream water from the main channel tributaries and of rainwater were performed with a special focus on ca sr and sr isotope ratios 87sr 86sr furthermore the accumulation of organic matter within the time sequence and physical soil properties were measured decreasing grain size with time shows active physical weathering processes soil organic matter has been accumulated during 150 yr at very high rates special emphasis has been given to chemical weathering and to the formation and transformation mechanisms of minerals of special interest were biotite chlorite epidote plagioclase and calcite biotite has been continuously transformed into illite like components within 150 yr the concentration of epidote significantly decreased the high ca sr as well as 87sr 86sr ratios in the stream and spring waters confirmed that ca bearing minerals are weathering and transforming at very high rates in the proglacial area also in cryic ice free environments chemical weathering rates are high leading to the formation and transformation of minerals disseminated calcite in granitoid rocks not confined to sedimentary carbonate rocks also plays a role in subglacial environments it is however not known for how long such an influence is significant and measurable the high ca na and ca sr ratio in the stream and tributary waters showed that calcite contributes to the supply of soluble ca although the ion activity product calculations clearly demonstrated that the waters were undersaturated with respect to this mineral

evidence of power law flow in the mojave desert mantle studies of the earth s response to large earthquakes can be viewed as large rock deformation experiments in which sudden stress changes induce viscous flow in the lower crust and upper mantle that lead to observable postseismic surface deformation laboratory experiments suggest that viscous flow of deforming hot lithospheric rocks is characterized by a power law in which strain rate is proportional to stress raised to a power n refs 2 3 most geodynamic models of flow in the lower crust and upper mantle however resort to newtonian linear stress strain rate relations here we show that a power law model of viscous flow in the mantle with n 3 5 successfully explains the spatial and temporal evolution of transient surface deformation following the 1992 landers and 1999 hector mine earthquakes in southern california a power law rheology implies that viscosity varies spatially with stress causing localization of strain and varies temporally as stress evolves rendering newtonian models untenable our findings are consistent with laboratory derived flow law parameters for hot and wet olivine the most abundant mineral in the upper mantle and support the contention that at least beneath the mojave desert the upper mantle is weaker than the lower crust

temperature and the seismic aseismic transition observations from the 1992 landers earthquake an important constraint on the size and destructive potential of earthquakes is the depth extent of rupture laboratory studies of the transition from unstable to stable sliding along with observed relationships between surface heat flow and the thickness of the seismogenic crust provide strong evidence for the significance of temperature in determining the maximum nucleation depth of large earthquakes the june 28 1992 mw 7 3 landers earthquake ruptured fault segments within 20 km of 11 pre existing heat flow measurements and shallowing of the base of aftershock seismicity along strike correlates with an increase in heat flow crustal geotherms estimated from these measurements place the base of seismicity along the 250 c isotherm this temperature is consistent with predictions from laboratory studies of the frictional stability of westerly granite but estimated temperatures for the seismic aseismic transition along other faults within the san andreas fault system are in the range of 350 to 400 c variations in country rock and fault gouge composition together with higher slip rates may account for this difference although part of the landers seismogenic crust might remain unruptured

silent play in a loud theatre dominantly time dependent soil development in the geomorphically active proglacial area of the gepatsch glacier austria climate change over the last century expressed as temperature increase is substantially stronger in the european alps than the average for the northern hemisphere this leads to fast glacial retreat and permafrost degradation and hence to increased rates and risks of mass wasting more extreme floods in spring and lower base flow in summer we do not know enough about the interplay between increased proglacial mass wasting and geomorphic activity on the one hand and soil development on proglacial areas on the other hand both processes affect the attenuation of storm flow provision of base flow and the future geo pedo and biodiversity of alpine valleys however despite the known importance of soil landscape interactions soils and landscapes have so far only been studied in isolation our objective was to assess whether soil development the silent play in a geomorphically active proglacial area the loud theatre was nonetheless dominantly a function of time since glacial retreat as often observed in geomorphically inactive proglacial areas we used conditional latin hypercube sampling to select 97 locations in the gepatsch glacier proglacial area in the west of austria that best cover variation in soil age and topographic position standard soil observations were done in all locations soil development indicators were then related to time since glacial retreat and a range of geomorphic variables results indicate that time since glacial retreat indeed remains an important explanatory variable and that soil development in the gepatsch glacier proglacial area roughly equals that in some other well studied valleys geomorphic variables were found to be significant co determinants of soil development with a strong scale dependency variation in soil properties increased over time and the storage of organic matter in the proglacial area is currently in the order of 330 kg per year

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

airborne radar survey above vostok region east central antarctica ice thickness and lake vostok geometry during the 1999 2000 italian expedition an airborne radar survey was performed along 12 transects across lake vostok antarctica and its western and eastern margins ice thickness subglacial elevation and the precise location of lake boundaries were determined radar data confirm the geometry derived from previous surveys but with some slight differences we measured a length of up to 260 km a maximum width of 81 km and an area of roughly 14 000 km 2 along the major axis from north to south the ice thickness varies from 3800 to 4250 m with a decreasing gradient from west to east the ice thickness is fairly constant except for two narrow strips located on the western and eastern margins where it increases with high thickening rate over the lake the surface elevation increases from 3476 m a s l south to 3525 north with a decreasing gradient while the lake surface elevation decreases from 315 to 750 m a s l with a decreasing gradient absolute value the ice surface and lake ceiling slopes suggest that the lake is in a state of hydrostatic equilibrium

modelling soil landscape genesis a time split approach for hummocky agricultural landscapes abstract here we present a scheme for modelling soil landscape development in hummocky agricultural landscapes of formerly glaciated terrains soil landscape development is regarded as discontinuous over time long term progressive soil development during the holocene was replaced abruptly by an intense period of regressive pedogenesis during the last 50 years which is deduced from published 137 cs data and catchment scale mass balances consequently our primary working hypothesis is that the recent soil pattern is mainly a result of human influence during the last 50 years the paradigm behind our approach is that we have to couple geological historical information with recent dynamics of relevant processes to understand soil landscape development spatially distributed erosion and sedimentation are the most important processes during that period the intensity and extent of these processes is however also a function of the spatial pattern of soils erodibility which evolved in the progressive period therefore we developed a time split modelling approach for the progressive period relevant pedogenic processes de carbonatization silicate weathering clay translocation have to be quantified by a spatially distributed coupled water flow and solute transport model based on reconstructed initial and upper boundary conditions geomorphic units climate history relevant outputs e g topsoil textural properties are used as a spatially distributed input for the model of the regressive period for the latter we use a modified version of the dynamic physically based erosion 3d model schmidt j von werner m michael a 1996 erosion 2d 3d a computer model to simulate water erosion in german sachsische landesanstalt fur landwirtschaft dresden which allows spatially distributed modelling of water related soil erosion and deposition relevant topsoil properties are iteratively adapted to the rates of spatially distributed erosion and deposition preliminary results suggest that a coupling with tillage erosion plays an important role in our landscapes explicit analyses of the soil pattern using digital soil mapping techniques will be applied for model validation

co seismic displacements of the 1992 landers earthquake sequence we present co seismic displacement vectors derived from global positioning system gps measurements of 92 stations in southern california these gps results are combined with five well determined gps displacement vectors from continuously tracking stations of the permanent gps geodetic array as well as line length changes from usgs geodolite and two color laser trilateration observations to determine a self consistent set of geodetic data for the earthquake these combined displacements are modeled by an elastic dislocation representation of the primary fault rupture planes on average the model residuals are about twice the estimated measurement errors

slip distribution of the 1992 landers earthquake and its implications for earthquake source mechanics we use near source 10 to 164 km displacement seismograms to image the slip distribution and rupture history of the 28 june 1992 mw 7 3 landers california earthquake aftershock seismograms from similar distances are modeled to find the velocity model and frequency range 0 05 to 0 25 hz over which theoretical green s functions are most accurate and the measure of fit is used as an upper bound on theoretical error in the mainshock inversion we represent the rupture surface with three planar segments divided into 3 by 3 km elements extending from the surface to 18 km depth and solve for the slip distribution and the rupture time model that minimizes misfit to both recorded seismograms and mapped surface displacement in a least squares sense we investigate two faulting models one with a uniformly short 3 sec rise time everywhere on the fault surface and the other with a variable rise time 2 to 6 sec we perform sensitivity tests using synthetic data from a hypothetical earthquake to evaluate model resolution and solution stability in the sensitivity tests both fault models recover similar slip and rupture features but neither is capable of imaging details of the rise time for the landers earthquake we find an average rupture velocity of 2 5 km sec and use this average for a starting model in a linearized inversion for rupture time in our solutions of slip amplitude distribution the southernmost johnson valley fault segment has 20 of the total seismic moment 6 to 8 1019 n m with small displacements near the hypocenter the homestead valley segment contributes half of the moment with the largest slip amplitudes 25 to 35 km northwest of the hypocenter at 4 to 12 km depth and the camp rock emerson segment contributes the remaining moment with the largest slip amplitude 35 to 50 km northwest of the hypocenter in the shallow crust 9 km there is some evidence that the rupture front is delayed as it encounters high slip regions suggesting that prior to the mainshock these areas were further from failure owing either to greater strength or lower prestress

velocity of radio wave propagation in ice at vostok station antarctica during the austral summer field season of the russian antarctic expedition in 1999 2000 wide angle reflections experiments were performed in the vicinity of the russian station vostok a 60 mhz ice radar system with 12 bit digital recording was used the measurements were taken along two perpendicular lines directed south north and east west with a distance of 200 m between marks we used a one layer model without snow firn zone influence for the calculations we calculate that the average velocity of radio wave propagation in the ice sheet is 168 4 0 5 m s 1 the same velocity was derived from hyperbolic diffractions from internal discontinuities the results allow more accurate depth interpretation of radio echo soundings

glaciology ice sheet plumbing in antarctica it s not easy to work out what is going on beneath four kilometres of ice but remote imaging has enabled the discovery of the long distance discharge of water from one subglacial lake to another in antarctica

time since deglaciation and geomorphological disturbances determine the patterns of geochemical mineralogical and microbial successions in an icelandic foreland abstract glacier forelands are an ideal natural laboratory to study the initial stages of pedogenesis here we document a build up in organic carbon c nitrogen n and phosphorous p an increase in bacterial communities as well as a progression of physical and chemical weathering along a 2 km long and 122 yr old chronosequence in the glacier foreland of flaajokull in south eastern iceland we complemented this chronosequence dataset with an assessment of the variability in soils that were affected by geomorphological disturbances along a 175 m long toposequence transect while soils at the crest of the toposequence moraines were anomalously under developed due to frequent erosion the soils at the footslopes were characterized by a more advanced successional stage in that they benefited from an ample supply of nutrients fine and more weathered materials as well as higher moisture the large variability in soil properties across the toposequence demonstrates that even across short distances disturbances driven by hillslope and glacio fluvial processes can lead to substantial heterogeneities in soil development in glacier forelands we emphasize that the geochemical and biological features of soil development and patterns of succession in glacier forelands should be interpreted as the result of both changes in time since deglaciation and geomorphological disturbances

subglacial lake vostok not expected to discharge water the question whether antarctica s largest lake subglacial lake vostok exchanges water is of interdisciplinary relevance but has been undecided so far we present the potential pathway outlet location and threshold height of subglacial water discharge from this lake based on a quantitative evaluation of the fluid potential if water left lake vostok it would flow toward ross ice shelf discharge would occur first to the east of the southern tip of the lake at this location the bedrock threshold is 91 23 m higher than the hydrostatic equipotential level of lake vostok it is concluded that lake vostok is not likely to reach this level within climatic timescales and that no discharge of liquid water is to be expected we show that in absence of the ice sheet the lake vostok depression would harbor a lake significantly deeper and larger than the present aquifer

spatial variation of seismogenic depths of crustal earthquakes in the taiwan region implications for seismic hazard assessment abstract this paper presents the first whole taiwan scale spatial variation of the seismogenic zone using a high quality crustal seismicity catalog the seismicity onset and cutoff depths i e seismogenic depths are determined by the earthquake depth moment distribution and used to define the upper and lower boundaries of the seismogenic zone respectively together with the published fault geometries and fault area moment magnitude relations the depth difference in the onset and cutoff depths i e seismogenic thickness is used as the fault width to determine the moment magnitudes of potential earthquakes for the major seismogenic faults results show that the largest mw7 9 8 0 potential earthquake may occur along the changhua fault in western taiwan where the seismic risk is relatively high and seismic hazard mitigation should be a matter of urgent concern in addition the first motion focal mechanism catalog is used to examine the relation between the seismogenic depths and earthquake source parameters for crustal earthquakes 50 km the shallowest onset and cutoff depths are observed for normal and strike slip events respectively this observation is different from the prediction of the conventional continental rheology model which states that thrust events have the shallowest cutoff depth thus a more sophisticated rheology model is necessary to explain our observed dependence of the seismogenic depths on faulting types meanwhile for intermediate to large crustal mw 4 depth 50 km earthquakes thrust events tend to occur at the bottom region of the seismogenic zone but normal and strike slip events distribute at a large depth range

integrating soils and geomorphology in mountains an example from the front range of colorado soil distribution in high mountains reflects the impact of several soil forming factors soil geomorphologists use key pedological properties to estimate ages of quaternary deposits of various depositional environments estimate long term stability and instability of landscapes and make inferences on past climatic change once the influence of the soil forming factors is known soils can be used to help interpret some aspects of landscape evolution that otherwise might go undetected the front range of colorado rises from the plains of the colorado piedmont at about 1700 m past a widespread dissected tertiary erosion surface between 2300 and 2800 m up to an alpine continental divide at 3600 to over 4000 m pleistocene valley glaciers reached the western edge of the erosion surface parent rocks are broadly uniform granitic and gneissic climate varies from 46 cm mean annual precipitation map and 11 jc mean annual temperature mat in the plains to 102 cm and 4 jc respectively near the range crest vegetation follows climate with grassland in the plains forest in the mountains and tundra above 3450 m soils reflect the bioclimatic transect from plains to divide a bw or bt bk or k grassland to a e bw or bt c forest to a bw c tundra corresponding soil ph values decrease from 8 to less than 5 with increasing elevation the pedogenic clay minerals dominant in each major vegetation zone are smectite grassland vermiculite forest and 1 0 1 8 nm mixed layer clays tundra within the lower forested zone the topographic factor aspect results in more leached colder soils with relatively thin o horizons well expressed e horizons and bt horizons alfisols on n facing slopes whereas soils with thicker a horizons less developed or no e horizons and bw or bt horizons mollisols are more common on s facing slopes the topographic factor in the tundra results in soil patterns as a consequence of wind redistributed snow and the amount of time it lingers on the landscape an important parent material factor is airborne dust which results in fine grained surface horizons and if infiltrated contributes to clay accumulation in some bt horizons the time factor is evaluated by soil chronosequence studies of quaternary deposits in tundra upper forest and plains grassland few soils in the study area are 10 000 years old in the tundra 100 000 years old in the forest and 2 million years old in the grassland stages of granite weathering vary with distance from the continental divide and the best developed is grus near the sedimentary granitic rock contact just west of the mountain front grus takes a minimum of 100 000 years to form

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

subglacial floods beneath ice sheets subglacial floods jokulhlaups are well documented as occurring beneath present day glaciers and ice caps in addition it is known that massive floods have occurred from ice dammed lakes proximal to the laurentide ice sheet during the last ice age and it has been suggested that at least one such flood below the waning ice sheet was responsible for a dramatic cooling event some 8000 years ago we propose that drainage of lakes from beneath ice sheets will generally occur in a time periodic fashion and that such floods can be of severe magnitude such hydraulic eruptions are likely to have caused severe climatic disturbances in the past and may well do so in the future

retreating ice research in pro glacial areas matters glacier forefields are landscapes in transition from glacial to non glacial conditions this implies intense geomorphic hydrological and ecological dynamics with important on and off site effects this special issue collects 13 papers covering recent research in both sub polar and alpine proglacial environments that focus on i proglacial sediment sources ii proglacial rivers iii proglacial lakes iv ground water and ice and v the development of soil and vegetation in its interplay with morphodynamics advances in mapping surveying and geophysical techniques form the basis for research perspectives related to the historical evolution of proglacial areas the understanding of complex interactions of multiple processes and the effects of continued glacier recession

the gamburtsev mountains and the origin and early evolution of the antarctic ice sheet the manner in which the antarctic ice sheet first formed at a time of rapid global climate change about 34 million years ago has been the subject of considerable speculation several lines of evidence point to central antarctic mountain ranges as the site of the initial ice sheet but our knowledge of the present ice sheet topography is highly restricted in the very zone where ice sheet initiation is most likely along the subglacial gamburtsev mountain range at the centre of the present ice sheet now a detailed survey and analysis of the morphology of the gamburtsev mountains has been performed based on an ice penetrating radar study conducted over two seasons the data reveal a mountain landscape initially incised by rivers then over deepened by ice movement the topography beneath up to 3 000 metres of ice resembles an exploded version of classic alpine valley topography and seems to have developed more than 34 million years ago when mean summer temperatures were about 3 c the nature of initial glaciation on antarctica about 34 million years ago is a mystery results from an intensive radar survey now show that the gamburtsev mountains at dome a at the centre of the present ice sheet were initially incised by rivers and then subsequently overdeepened by ice movement this is suggestive of topographical development before 34 million years ago when mean summer temperatures were about 3 c ice sheet development in antarctica was a result of significant and rapid global climate change about 34 million years ago1 ice sheet and climate modelling suggest reductions in atmospheric carbon dioxide less than three times the pre industrial level of 280 parts per million by volume that in conjunction with the development of the antarctic circumpolar current led to cooling and glaciation paced by changes in earth s orbit2 based on the present subglacial topography numerical models point to ice sheet genesis on mountain massifs of antarctica including the gamburtsev mountains at dome a the centre of the present ice sheet2 3 our lack of knowledge of the present day topography of the gamburtsev mountains4 means however that the nature of early glaciation and subsequent development of a continental sized ice sheet are uncertain here we present radar information about the base of the ice at dome a revealing classic alpine topography with pre existing river valleys overdeepened by valley glaciers formed when the mean summer surface temperature was around 3 c this landscape is likely to have developed during the initial phases of antarctic glaciation according to antarctic climate history estimated from offshore sediment records the gamburtsev mountains are probably older than 34 million years and were the main centre for ice sheet growth moreover the landscape has most probably been preserved beneath the present ice sheet for around 14 million years

slicing up the san francisco bay area block kinematics and fault slip rates from gps derived surface velocities received 26 october 2004 revised 11 february 2005 accepted 10 march 2005 published 16 june 2005 i observations of surface deformation allow us to determine the kinematics of faults in the san francisco bay area we present the bay area velocity unification bavu bay view a compilation of over 200 horizontal surface velocities computed from campaign style and continuous global positioning system gps observations from 1993 to 2003 we interpret this interseismic velocity field using a three dimensional block model to determine the relative contributions of block motion elastic strain accumulation and shallow aseismic creep the total relative motion between the pacific plate and the rigid sierra nevada great valley sngv microplate is 37 9 0 6 mm yr 1 directed toward n30 4 w 0 8 at san francisco 2 fault slip rates from our preferred model are typically within the error bounds of geologic estimates but provide a better fit to geodetic data notable right lateral slip rates in mm yr 1 san gregorio fault 2 4 1 0 west napa fault 4 0 3 0 zone of faulting along the eastern margin of the coast range 5 4 1 0 and mount diablo thrust 3 9 1 0 of reverse slip and 4 0 0 2 of right lateral strike slip slip on the northern calaveras is partitioned between both the west napa and concord green valley fault systems the total convergence across the bay area is negligible poles of rotation for bay area blocks progress systematically from the north america pacific to north america sngv poles the resulting present day relative motion cannot explain the strike of most bay area faults but fault strike does loosely correlate with inferred plate motions at the time each fault initiated

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults