subcontinental scale crustal velocity changes along the pacific north america plate boundary transient tectonic deformation has long been noted within approx100 km of plate boundary fault zones and within active volcanic regions but it is unknown whether transient motions also occur at larger scales within plates relatively localized transients are known to occur as both seismic and episodic aseismic events and are generally ascribed to motions of magma bodies aseismic creep on faults or elastic or viscoelastic effects associated with earthquakes however triggering phenomena and systematic patterns of seismic strain release at subcontinental 1 000 km scale along diffuse plate boundaries have long suggested that energy transfer occurs at larger scale such transfer appears to occur by the interaction of stresses induced by surface wave propagation and magma or groundwater in the crust or from large scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes here we report geodetic evidence for a coherent subcontinental scale change in tectonic velocity along a diffuse 1 000 km wide deformation zone our observations are derived from continuous gps global positioning system data collected over the past decade across the basin and range province which absorbs approximately 25 per cent of pacific north america relative plate motion the observed changes in site velocity define a sharp boundary near the centre of the province oriented roughly parallel to the north northwest relative plate motion vector we show that sites to the west of this boundary slowed relative to sites east of it by 1 mm yr 1 starting in late 1999

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

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

late quaternary paleoenvironments and growth of intrusive ice in eastern beringia eagle river valley northern yukon canada in this study the sediments exposed in a fluvial terrace and in the headwall of a thaw slump in the eagle river valley northern yukon provide new data about the timing of flooding of glacial lake old crow the formation of massive ground ice bodies and the vegetation and the fauna in eastern beringia during the late quaternary the stratigraphy and radiocarbon ages establish the following chronology of events 1 a gravel fluvial terrace was deposited by an overflow from glacial lake hughes into glacial lake old crow 2 a carbonate silty clay was deposited during the maximum level of glacial lake old crow at 15 120 14c year bp 3 permafrost and large intrusive ice bodies aggraded through the glaciolacustrine and underlying sediments following the drainage of glacial lake old crow from the site 4 at 11 290 14c year bp a shrub sedge tundra colonized an uneven surface deformed by the bodies of ground ice 5 a thaw lake drained at 6730 14c year bp after flooding the site 6 during the early h

geodetically constrained models of viscoelastic stress transfer and earthquake triggering along the north anatolian fault over the past 80 years 8 mw 6 7 strike slip earthquakes west of 40 longitude have ruptured the north anatolian fault naf from east to west the series began with the 1939 erzincan earthquake in eastern turkey and the most recent 1999 mw 7 4 izmit earthquake extended the pattern of ruptures into the sea of marmara in western turkey the mean time between seismic events in this westward progression is 8 5 11 years 67 confidence interval much greater than the timescale of seismic wave propagation seconds to minutes the delayed triggering of these earthquakes may be explained by the propagation of earthquake generated diffusive viscoelastic fronts within the upper mantle that slowly increase the coulomb failure stress change cfs at adjacent hypocenters here we develop three dimensional stress transfer models with an elastic upper crust coupled to a viscoelastic burgers rheology mantle both the maxwell m 4 1018 1 1019 pa s and kelvin k 1 1018 1 1019 pa s viscosities are constrained by studies of geodetic observations before and after the 1999 izmit earthquake we combine this geodetically constrained rheological model with the observed sequence of large earthquakes since 1939 to calculate the time evolution of cfs changes along the north anatolian fault due to viscoelastic stress transfer apparent threshold values of mean cfs at which the earthquakes in the eight decade sequence occur are between 0 02 to 3 15 mpa and may exceed the magnitude of static cfs values by as much as 177 by 2023 we infer that the mean time dependent stress change along the northern naf strand in the marmara sea near istanbul which may have previously ruptured in 1766 may reach the mean apparent time dependent stress thresholds of the previous naf earthquakes

core complex geometries and regional scale flow in the lower crust a simple flexural model that treats the lithosphere as a thin elastic plate overlying a fluid asthenosphere produces an excellent fit to the domal detachment fault geometries observed in typical core complexes of the basin and range province however this mode of isostatic compensation requires an unacceptably large reduction in local topographic elevation 3 5 km above core complex structures because topographic lows of this magnitude are not observed above core complexes today it requires mountain ranges 3 5 km higher than the surrounding areas to have existed at the site of each future core complex and requires these mountain ranges to have had large crustal roots that were subsequently uplifted to form a flat moho as the core complexes developed an alternate mode of isostatic compensation whereby compensation occurs primarily by regional scale flow of material within the lower crust beneath an elastic midcrust provides an equally good fit to the observed detachment fault geometries while requiring little reduction in local topographic elevation above developing core complex structures and providing an obvious means of maintaining a flat moho beneath these zones of upper crustal doming if this interpretation is correct then the effective elastic plate thickness below the basin and range province probably cannot exceed a maximum of about 4 km with a best guess estimate of about 0 5 to 1 km computation of the temperature structure associated with crustal flow during doming shows that an increase in temperature at the moho of about 100 c follows doming by several million years perhaps explaining the observed coincidence of core complexes with crustally derived igneous rocks subsequent cooling of the mid to lower crust beneath the core complex could result in freezing of the initially ductile lower crust within the core of the dome effectively locking the domal shape into the crust even after the detachment surface is cut by younger faults

the behavior of trace elements during schwertmannite precipitation and subsequent transformation into goethite and jarosite schwertmannite is a ubiquitous mineral formed from acid rock drainage ard and plays a major role in controlling the water chemistry of many acid streams the formation of schwertmannite was investigated in the acid discharge of the monte romero abandoned mine iberian pyrite belt sw spain schwertmannite precipitated from supersaturated solutions mainly owing to the oxidation of fe ii to fe iii and transformed with time into goethite and jarosite in a few hours schwertmannite precipitation removed more than half of the arsenic load from solution whereas the concentration of divalent trace metals zn cu pb cd ni and co remained almost unchanged in the laboratory natural schwertmannite was kept in contact with its coexisting acid water in a flask with a solid liquid mass ratio of 1 5 for 353 days during this time the ph of the solution dropped from 3 07 to 1 74 and the concentrations of sulfate and fe increased during the first 164 days schwertmannite transformed into goethite plus h3o jarosite but subsequently goethite was the only mineral to form some of the trace elements such as al cu pb and as were depleted in solution during the first stage as schwertmannite transformed into goethite plus h3o jarosite on the contrary the transformation of schwertmannite to goethite with no jarosite during the second stage released al cu and as to the solution despite the variation in their concentrations in solution approximately 80 of the total al and cu inventories and more than 99 as and pb remained in the solid phase throughout the entire aging process

relating viscosities from postseismic relaxation to a realistic viscosity structure for the lithosphere summary models of geodetic observations of postseismic relaxation most often represent the lithosphere with only a few layers with constant viscosity this is surpr ising because rock mechanical experiments consistently demonstrate that we should expect a profound vertical gradient in lithospheric viscosities due to the geothermal gradient i n this thermal boundary layer we isolate the effect of lower crustal flow where the effect of visc osity gradients has the largest impact on surface deformation we therefore explore postseismic deformation in models with realistic vertical viscosity gradients and seek to illustrate th e differences between these models and those with idealized uniform viscosity layers by means of synthetic experiments with a semianalytical viscoelastic relaxation model we show how for a given earthquake the averaged viscosity value obtained for a thick viscoelastic layer is d ependent on both the layout of the geodetic network and on the observation time window

simple data processing of tripotential apparent resistivity measurements as an aid to the interpretation of subsurface structure the advantages of the wenner tripotential method carpenter 1955 for apparent resistivity profiling are described and two new data processing techniques introduced as an aid to the interpretation of apparent resistivity sections pseudo sections these techniques were developed from model data computed using a two dimensional finite difference method oscillatory components present in anomalies on tripotential profiles and related to electrode spacing are shown to be effectively removed by linear filtering that also simplifies their form and aids recognition furthermore it is shown that the ratio of the beta and gamma apparent resistivities is a good indicator of resistivity variation and is particularly sensitive to lateral change model data indicates that over a wide range of conditions enough subsurface information can be obtained by inspection of tripotential resistivity and ratio profiles and from space sections to make possible a useful and sometimes semi quantitative interpretation a rationale for the general interpretation of tripotential data is developed field data are described from an area of weathered granite basement in nigeria a model of the subsurface is developed using parameters derived from the processed observations the observed and calculated apparent resistivity space sections are very similar

northwest basin and range tectonic deformation observed with the global positioning system 1999 2003 1 we use geodetic velocities obtained with the global positioning system gps to quantify tectonic deformation of the northwest basin and range province of the western united states the results are based on gps data collected in 1999 and 2003 across five new quasi linear networks in northern nevada northeast california and southeast oregon the velocities show 3 mm yr westward movement of northern nevada with respect to stable north america west of longitude 119 w the velocities increase and turn northwest parallel to sierra nevada great valley microplate motion and similar to velocities previously obtained to the south the observations are explained by a kinematic model with three domains that rotate around euler poles in eastern oregon and western idaho northeast california experiences internal dextral shear deformation 11 2 3 6 nstrain yr subparallel to pacific north america motion relative motions of the domains imply 2 5 mm yr approximately east west extension in northwest nevada and 1 4 mm yr approximately north south contraction near the california oregon border the northward decreasing approximately east west extension in northwest nevada is consistent with the northern termination of basin and range deformation faulting and characteristic topography no significant extension is detected in the oregon basin and range the oregon cascade arc moves north at 3 5 mm yr and is possibly influenced by the approximately eastward motion of the juan de fuca plate these results disagree with secular northwest trenchward motion of the oregon forearc inferred from paleomagnetic rotations south of latitude 43 however trenchward motion exists and is consistent with block rotations approximately east west basin and range extension and northwest sierra nevada translation

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

a geochemical characterization of cold water natural acid rock drainage at the zn pb xy deposit yukon canada abstract acid rock drainage ard is considered to be temperature limited due to the diminished activity of fe ii oxidizing microbes at low temperatures nonetheless ard streams are present in cold climates this study presents a geochemical characterization of a cold climate ard creek at the zn pb xy deposit in yukon canada which showed highly elevated concentrations of dissolved zinc up to 475 mg l acid rock drainage at the xy deposit is likely generated via subsurface abiotic and biotic oxidation of sulfide minerals and then exits as seeps at the headwaters of the creek the uppermost reaches of the creek have the lowest ph levels ph 3 3 and highest metal concentrations with prolific precipitation of iron hydroxysulfate and oxyhydroxide mineral precipitates schwertmannite jarosite and goethite present as terraced iron formations tifs at one sampling location the lower reaches of the creek show a progressive ph increase up to ph level 4 9 which occurs due to fe iii and al hydrolysis the neutralizing influence of carbonate rich strata and or ground waters and dilution by surface waters entering the creek progressive ph neutralization causes a change in precipitate mineralogy to x ray amorphous al hydroxysulfates with a composition similar to aluminite and hydrobasaluminite and amorphous al oh 3 natural attenuation of cd zn and pb occurred downstream from the headwater seeps which was likely influenced by adsorption reactions involving both metal sulfate anions and metal sulfate ternary complexes generally the concentrations of cd zn and pb in the mineral precipitates followed trends in ph aqueous concentration predicted speciation and mineralogy of the precipitates however anomalous trace metal concentrations were observed in the precipitates at 120 m downstream and potentially reflect a local ground water input overall the geochemistry of this cold climate ard creek was similar to ard in more temperate climates although low temperatures appear to retard the kinetics of ferrous iron oxidation and seasonal hydrodynamics may influence the formation of tifs in these highly saturated waters

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

resistivity and percolation study of preferential flow in vadose zone at bokhorst germany traditional nondestructive resistivity techniques have been applied in combination with tracer displacement and conventional soil moisture recording methods i e buried tensiometer and time domain reflectometry tdr for studying flow processes at an arable site in bokhorst germany three water infiltration experiments were carried out using tap water spiked with a nonreactive tracer at different concentrations the study aimed at exploring the capabilities of these combined techniques for tracing the preferential movement of water in the uppermost 1 5 m of the highly heterogeneous vadose zone the results illustrate that the applied tensiometer and tdr techniques can detect the relatively fast flow process at their position points and thus only tentatively trace the preferential flow the additional application of the resistivity method can trace the preferential flow paths continuously along the plane of measurements the results of the individual applied methods complement and confirm each other

viscoelastic gravitational deformation by a rectangular thrust fault in a layered earth previous papers in this series have been concerned with developing the numerical techniques required for the evaluation of vertical displacements which are the result of thrust faulting in a layered elastic gravitational earth model this paper extends these methods to the calculation of fully time dependent vertical surface deformation from a rectangular dipping thrust fault in an elastic gravitational layer over a viscoelastic gravitational half space the elastic gravitational solutions are used together with the correspondence principle of linear viscoelasticity to give the solution in the laplace transform domain the technique used here to invert the displacements into the time domain is the prony series technique wherein the transformed solution is fit to the transformed representation of a truncated series of decaying exponentials purely viscoelastic results obtained are checked against results found previously using a different inverse transform method and agreement is excellent the major advantage in using the prony series technique is that deformations can be computed for arbitrary time intervals a series of results are obtained for a rectangular 30 dipping thrust fault in an elastic gravitational layer over viscoelastic gravitational half space time dependent displacements are calculated out to 50 half space relaxation times a or 100 maxwell times 2 m a significant effects due to gravity are shown to exist in the solutions as early as several a the difference between the purely viscoelastic solution and the viscoelastic gravitational solutions grows as time progresses typically the solutions with gravity reach an equilibrium value after 10 20 relaxation times when the purely viscoelastic solutions are still changing significantly additionally the length scaling which was apparent in the purely viscoelastic problem breaks down in the viscoelastic gravitational problem two independent length scales one of which changes with time are now seen to characterize the problem

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

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

oxygen and sulfur isotope geochemistry of acidic groundwater discharge in british columbia yukon and district of mackenzie canada the paint pots in kootenay national park british columbia appear to derive the fe zn pb and contents of their water from sulfide mineralization in lower and middle cambrian carbonates the fe zn ni and contents of groundwater discharging into a tributary of engineer creek yukon are likely derived from sulfide mineralization in devonian or ordovician black shales exposed in the area the high fe and contents of a natrojarosite deposit northeast of fort norman northwest territories are probably derived from pyritiferous cretaceous shales in that area isotope analyses of water and of dissolved and precipitated sulfur species from these three sites where acidic heavy metal bearing groundwater is being discharged revealed that between 38 and 74 of the oxygen used in the subsurface oxidation of metal sulfides is supplied by h2o molecules rather than by molecular dissolved oxygen the available data also suggest that lower percentages of water oxygen in the secondary sulfates reflect increasing

spatial distribution of soil surface coverage on north and south facing hillslopes along a mediterranean to extreme arid climatic gradient four research sites were established along a climatic gradient in israel representing mediterranean xeric mediterranean arid and extreme arid climate conditions the cover percentage of eight soil surface components vegetation annual and perennial forms biogenic crust mosses lichens cyanobacteria and dwarf grass stones and bare soil patches were measured transects along hillslopes on each of two opposite aspects south and north facing slopes were established at each site altogether eight transects dominance and soil surface cover diversity indices and similarity coefficients between the transects were calculated high similarity values in soil surface cover were found between the south facing slopes located in the xeric mediterranean arid and extreme arid areas these hillslopes are dominated by stones and bare soil patches in contrast lower similarity values were found between the northern slope aspects dominated by biotic components vegetation and biogenic crusts the study along a climatic gradient together with the comparison between northern and southern aspects provide useful information that can be utilized for evaluation of changes in soil surface cover characteristics given various scenarios of future climate regimes in that region

impacts of hillslope thaw slumps on the geochemistry of permafrost catchments stony creek watershed nwt canada abstract retrogressive thaw slumps are one of the most dramatic thermokarst landforms in periglacial regions this study investigates the impacts of one stable and two active thaw slumps on the geochemistry of streams in the stony creek watershed peel plateau nwt canada the objective of this study is to elucidate the geochemical processes associated with ground ice ablation in retrogressive thaw slumps and the geochemical evolution of slump runoff to streams this is accomplished by describing the geochemical composition of runoff across active mega slumps impacted and pristine tundra streams as well as that of the ice rich permafrost exposed in the slump headwalls in the stony creek watershed runoff derived from active and stable thaw slumps is characterized by a ca mg so 4 geochemical facies with conductivity and solute concentrations approximately one order of magnitude higher than in pristine streams the elevated solute concentrations in the slump runoff are directly related to thawing of highly weatherable late pleistocene age ice rich and solute rich permafrost exposed in the headwalls of slumps which has solute concentrations nearly 100 times higher than those measured in the uppermost 1 2 m i e above the early holocene thaw unconformity an examination of ionic relations revealed a strong relation between ca 2 and so 4 2 and ca 2 mg 2 so 4 2 suggestive that sulfate dissolution is the main process responsible for the geochemical composition of slump impacted streams thaw slumps significantly impact the geochemistry of streams by increasing their solute load well above that of pristine streams along any reach of impacted streams unlike shallow active layer disturbances the thaw slumps can degrade permafrost to depths of 10 m or more and the impacts of abundant slump activity on stream geochemistry can be detected at the 10 2 km 2 watershed scale

vertical deformation associated with normal fault systems evolved over coseismic postseismic and multiseismic periods vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways sparse but robust geodetic seismic and geologic observations in the basin and range province of the western united states indicate that immediately after an earthquake vertical change primarily occurs as subsidence of the normal fault hanging wall a few decades later a 100 km wide zone is symmetrically uplifted the preserved topography of long term rifting shows bent and tilted footwall flanks rising high above deep basins we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting we replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust a 60 dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width 10 km which is predicted to take place within 1 2 decades after each large earthquake thus the best preserved topographic signature of rifting is expected to occur early in the postseismic period the relatively stronger lower crust in our models is necessary to replicate broader postseismic uplift that is observed geodetically in subsequent decades

environmental controls of the seasonal variation in oxygen uptake in sulfidic tailings deposited in a permafrost affected area oxygen consumption sulfide oxidation and acid mine drainage amd of pyritic mine tailings were investigated at nanisivik mine which is located in an area with continuous permafrost on baffin island in northern canada tailings of varying age and water content have been deposited under alkaline conditions one area consisting of tailings deposited on land in 1992 was selected for detailed measurements of in situ oxygen uptake rates at the tailing surface in the summers 1998 and 1999 and periodically during autumn and winter in 1998 measurements included oxygen gas water content and temperature in profiles as well as chemical analyses of pore solution and solids additional oxygen consumption rates were measured under controlled temperature conditions on columns filled with partly oxidized tailings on the basis of temperature dependency of pyrite oxidation observed in the laboratory an arrhenius diffusion equation with soil temperature as input was used to simulate the observed temporal variation in oxygen uptake field data reveal that the ongoing sulfide oxidation of well drained tailings primarily takes place in the upper 30 cm and that oxidation has resulted in a depletion of pyrite carbonates and metals from this reaction zone the model provides a reasonable fit to the observed trend in oxygen consumption and documents that oxidation of sulfide minerals in tailings is not reduced to neglectable levels at o c the amd generation rate has been quantified based on the changes in concentration of oxidation products in the pore water and oxidation rates based on in situ measurements of oxygen consumption the two rate descriptions provide comparable estimates of seasonal amd generation and provide detailed information on weather related controls of amd generation i e ground temperature freezing water content and snow cover these environmental controls are crucial for the design of frozen cover schemes in permafrost regions where the aim is to force the frost table to the top of the tailings maintaining tailings at subzero temperatures year round and thereby controlling the amd generation

state of stress and modern deformation of the northern basin and range province constraints on the current stress regime of the actively extending northern basin and range province are provided by deformation data focal mechanisms and fault slip studies hydraulic fracturing in situ stress measurements borehole elongation breakouts analyses and alignment of young volcanic vents the integrated data indicate significant variations both in principal stress orientations and magnitudes an approximately e w least principal stress direction appears to characterize both the eastern and western margins of the basin and range province whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented nw to n60 w the contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins active deformation along the southeastern and western province margins is characterized by a combination of strike slip and normal faulting focal mechanisms along northeastern province margin wasatch front and in central nevada indicate a combination of normal and oblique normal faulting temporal regional and depth dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles however some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated evidence for significant temporal variation or multiple cycles of variation in relative stress magnitude comes from the sierran front basin and range boundary region where recent earthquakes are predominantly strike slip whereas the profound relative vertical relief across the sierra frontal fault zone in the last 9 10 m y implies a normal faulting stress regime using the best data on stress orientation relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements analysis of well constrained slip vectors in the owens valley california area indicate that large temporal variations in the magnitude of the approximately n s oriented maximum horizontal stress are required to explain dominantly dip slip and strike slip offsets on subparallel faults similar faulting relations are observed throughout much of the boundary zone between the basin and range sierra nevada including the walker lane belt along the eastern province margin in the wasatch front area in utah available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of 4 5 km earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth furthermore superimposed sets of young fault striae along a segment of the wasatch fault also indicate temporal variations of relative stress magnitudes sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion thermally induced flow and the influence of the san andreas plate boundary although difficult to date accurately the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle 1000 5000 years and multiple earthquake cycles 10 000 years

evidence for localized active extension in the central apennines italy from global positioning system observations to assess how contemporary crustal extension is accommodated in the central apennines we use a new continuous and survey style global positioning system velocity solution and model the velocity field using a bicubic spline interpolation method the partitioning of contemporary deformation over the 100 km wide central apennines belt reveals a pattern of strain accumulation that largely reflects the spatial distribution of historic and recent seismicity the highest gradients of horizontal velocities are observed across those faults associated with m 6 historical earthquakes dislocation modeling shows that interseismic elastic loading in which creep occurs below the seismogenic upper crust on the downdip extensions of historically active faults reproduces the observed velocity gradients the current resolution level of quaternary fault slip rates estimates hinders the comparison with past deformation patterns and in particular the discrimination between 1 migrating episodes of short term focused activity 2 a distributed pattern of simultaneous deformation on parallel fault systems or 3 long term localization of active extension taking into account geomorphological evidence we propose that the geodetically observed deformation spatially corresponds with a long term localization of strain along the long wavelength 100 km topographic bulge caused by its highest gravitation potential energy relative to surrounding lowlands

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

note natural heavy metal release by sulphide oxidation in the high arctic an assessment of the environmental impact of the weathering of sulphide rich rocks at citronen fjord north greenland provided information on sulphide oxidation rates and metal release from outcrops of sediment hosted stratiform ore that may be mined for its zinc content in situ oxygen uptake rates were measured at the surface of partly weathered sulphide rich outcrops and compared with metal contents in streams and soil water the oxygen uptake rates measured during august 1996 were of the same order of magnitude as those reported from mine tailings at lower latitudes the variation in metal concentrations and ph of the drainage waters reflects the spatial variation in sulphide oxidation and carbonate buffering high weathering rates of sulphide minerals occur in the high arctic during the summer and release of heavy metals must be considered a potential environmental issue if mining is initiated key words sulphide oxidation pyrite sphalerite oxygen high arctic zinc

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

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

interseismic deformation associated with three dimensional faults in the greater los angeles region california 1 existing interseismic models are not well suited to simulate deformation within the network of finite intersecting nonplanar faults observed in the greater los angeles region instead of applying fault slip rates to a model a priori we allow three dimensional fault surfaces to interact and accumulate mechanically viable slip distributions and then use the deep nonseismogenic portion of slip to calculate interseismic deformation we apply this approach to the los angeles region and find that the geologic timescale model results match well geologic slip rate data and the interseismic timescale model results match well the heterogeneous gps velocity pattern in the los angeles region model results suggest that localized geodetic convergence in the san gabriel basin can be achieved with slip on multiple active fault surfaces in the los angeles region including relatively fast slip on the sierra madre fault and slow slip on the puente hills thrusts in agreement with geologic data the ability of the three dimensional model to reproduce well both geologic slip rates and interseismic geodetic velocity patterns suggests that current day contraction rates in the greater los angeles region are compatible with long term geologic deformation rates and disputes suggestions of significant temporal variations in fault slip rates inferred from existing investigations

surface faulting of the 1954 fairview peak ms 7 2 and dixie valley ms 6 8 earthquakes central nevada abstract the 1954 fairview peak earthquake was followed 4 min and 20 sec later by the dixie valley earthquake surface ruptures were distributed among six different faults that define a complex north trending zone 100 km long and over 15 km wide the rupture sequence progressed from south to north the initial event produced a 32 km rupture of right oblique slip along the east dipping fairview fault where the components of right lateral offset and vertical separation reached 2 9 and 3 8 m respectively the northernmost ruptures occurred during the subsequent event along a 46 km portion of the east dipping dixie valley fault where the sense of slip was normal and reached a maximum vertical separation of 2 8 m average surface offset for both events is about 1 2 m the west dipping west gate louderback mountains and gold king faults also ruptured during the earthquake sequence these faults form a complex structural linkage within a 15 km left step that separates the surface traces of the fairview and dixie valley faults the west dipping faults likely played an important role in the redistribution of static stress from the fairview peak earthquake and subsequent triggering of the dixie valley earthquake right lateral offsets of more than a meter occurred along both the west gate and louder back mountains faults slip was limited to normal motion of 1 m or less along the gold king fault the change from right oblique motion along the fairview fault to pure normal motion on the dixie valley fault may reflect the transition from principally northwest extension in the south to more westerly extension in the north alternatively slip at the latitude of the dixie valley fault may be partitioned between pure normal slip along the dixie valley fault and strike slip motion on faults immediately to the west observations of fault dip provide insight to the complex three dimensional geometry of the rupture sequence of particular note a significant section of the dixie valley fault appears to be characterized by dip angles as low as 25 at the surface slip variation or earthquake endpoints do not generally appear to have been influenced by changes in bedrock type we do not observe systematic relations between slip variation and aspects of fault trace geometry such as salients and reentrants yet the relative competence of footwall bedrock appears to have influenced the long term development of large salients and reentrants along both the dixie valley and the fairview faults as well as the style of rupture along the southern portion of the dixie valley fault

strain accumulation across the central nevada seismic zone 1973 1994 five trilateration networks extending for 280 km along the central nevada seismic zone 1915 pleasant valley m 7 3 1954 dixie valley m 6 8 1954 stillwater m 6 8 1954 rainbow mountain m 6 6 1954 fairview peak m 7 1 and 1932 cedar mountain m 7 2 have been surveyed 6 times since 1973 to determine deformation along the zone within the precision of measurement the deformation appears uniform along the zone and is described by the principal strain rates 0 036 0 008 strain yr n60 w 3 and 0 031 0 008 strain yr n30 e 3 extension reckoned positive the observed strain rates are consistent with simple right lateral tensor shear at the rate of 0 033 strain yr across a shear zone striking n15 w this central nevada shear zone appears to be the northward continuation of the eastern california shear zone the orientation of the strike slip and normal slip ruptures within the central nevada seismic zone are consistent with principal stress axes parallel to the measured principal strain rate axes space based geodetic measurements very long baseline interferometry indicate that the relative motion accommodated across the basin and range province west of ely nevada is about 9 1 1 5 mm yr n16 w 8 dixon et al 1995 notice that the right lateral shear zone postulated to explain deformation in the central nevada seismic zone is properly oriented to accommodate that relative motion however a 135 km effective width of the shear zone would be required to accommodate all of the 9 1 mm yr relative motion at the strain rates observed in the nevada seismic zone only about 3 mm yr of that relative motion is accommodated within the span of the trilateration networks

microtopographic and depth controls on active layer chemistry in arctic polygonal ground polygonal ground is a signature characteristic of arctic lowlands and carbon release from permafrost thaw can alter feedbacks to arctic ecosystems and climate this study describes the first comprehensive spatial examination of active layer biogeochemistry that extends across high and low centered ice wedge polygons their features and with depth water chemistry measurements of 54 analytes were made on surface and active layer pore waters collected near barrow alaska usa significant differences were observed between high and low centered polygons suggesting that polygon types may be useful for landscape scale geochemical classification however differences were found for polygon features centers and troughs for analytes that were not significant for polygon type suggesting that finer scale features affect biogeochemistry differently from polygon types depth variations were also significant demonstrating important multidimensional aspects of polygonal ground biogeochemistry these results have major implications for understanding how polygonal ground ecosystems function and how they may respond to future change

the dynamics of the eastern mediterranean and eastern turkey summary in this study we investigate the dynamics of the region that includes greece the aegean sea and asia minor in a least squares inversion we solve for a continuous strain rate field and corresponding velocity field that satisfies 872 gps data the estimate of the geodetic strain rate field provides constraints for our dynamic analysis next we separately solve the depth integrated 3 d force balance equations for depth integrated deviatoric stresses within the lithosphere in which body force input comes from differences in vertically integrated vertical stress or differences in gravitational potential energy per unit area gpe these gpe estimates calibrate the absolute magnitudes of deviatoric stresses that are acting within the lithosphere further we investigate the sensitivity of our stress field solutions by using two different crustal structure models one from compiled crustal structure estimates obtained primarily from relatively recent seismic observations and the other from the crust 2 0 model in an iterative least squares inversion we then solve for stress field boundary conditions that when added to the contribution of deviatoric stresses associated with gpe differences provides a best fit to the directions of principal axes and relative magnitudes of the principal axes of the rates of strain obtained in the kinematic analysis robust features that arise from the boundary condition solution are nne forcing along the southern boundary east of about 33 e 0 5 1 2 1012 n m 1 with a rapid anticlockwise rotation of forces to the west of this along with an outward pulling force 0 4 1012 n m 1 directed ssw along the entire hellenic arc segment this force system along the hellenic arc can be interpreted as a result of slab rollback the total depth integrated 3 d deviatoric stresses in the final dynamic solution provides an excellent match to the deformation indicators throughout the region with vertically integrated stress magnitudes of order 0 5 2 5 1012 n m 1 we use constraints from derived stress magnitudes together with gps defined scalar values of strain rate magnitude to define bulk effective viscosities of the lithosphere depth averaged effective viscosities for the entire lithosphere are high within the black sea of order 0 7 3 1023 pa s relative to surrounding continental lithosphere north anatolian shear zone northern aegean sea and gulf of corinth are characterized by low depth averaged viscosities of order 1 5 1021 pa s deviatoric stresses from gpe differences and boundary condition effects combine in surprising ways in some regions resulting in near total stress cancellation in areas such as the southern aegean sea and portions of the central anatolian block gpe differences combine with boundary condition effects along the eastern segment of the north anatolian fault naf in a way that is compatible with the hypothesis that motion on the naf was facilitated by slab detachment beneath east anatolia and dynamic uplift of east anatolian plateau in general gpe differences play a nearly equal role as boundary condition influences in their contribution to the total deviatoric stress field the low depth integrated deviatoric stress magnitudes throughout the region suggest that zones of active deformation are facilitated by dramatic weakening mechanisms throughout the lithosphere

geomorphological and geochemistry changes in permafrost after the 2002 tundra wildfire in kougarok seward peninsula alaska geomorphological and thermo hydrological changes to tundra caused by a wildfire in 2002 on the central seward peninsula of alaska were investigated as a case study for understanding the response from ice rich permafrost terrain to surface disturbance frozen and unfrozen soil samples were collected at burned and unburned areas and then water isotope geochemistry and cryostratigraphy of the active layer and near surface permafrost were analyzed to investigate past hydrological and freeze thaw conditions and how this information could be recorded within the permafrost the development of thermokarst subsidence due to ice wedge melting after the fire was clear from analyses of historical sub meter resolution remote sensing imagery long term monitoring of thermo hydrological conditions within the active layer in situ surveys of micro relief and geochemical signals recorded in the near surface permafrost the resulting polygonal relief coincided with depression lines along an underground ice wedge network and cumulative subsidence to 2013 was estimated as at least 10 1 to 12 1 cm 0 9 1 1 cm year eleven year average profiles of water geochemistry in the ground indicated mixing or replenishment of older permafrost water with newer meteoric water as a consequence of the increase in active layer thickness due to wildfire or past thaw event our geocryological analysis of cores suggests that permafrost could be used to reconstruct the permafrost degradation history for the study site distinct hydrogen and oxygen isotopic compositions above the global meteoric water line were found for water from these sites where permafrost degradation with geomorphological change and prolonged surface inundation were suggested

acid drainage generation and seasonal recycling in disturbed permafrost near eagle plains northern yukon territory canada abstract acidic so 4 ca fe waters are discharging from sandstone bedrock overlying pyrite rich shales along the dempster highway near eagle plains northern yukon territory although evidence of acid drainage was present prior to the construction of the dempster highway in the 1970 s the removal of surficial sediments during its construction amplified the release of acidity by allowing the active layer to penetrate into the freshly exposed pyrite rich shale acid drainage originating from the excavated area has a ph value averaging 3 1 0 3 and over 5 g l of dissolved solids so 4 2 3915 mg l fe total 459 mg l ca 2 418 mg l and al total 83 6 mg l whereas the unaffected drainage has a ph greater than 4 4 and total dissolved solids in the 100 to 200 mg l range geochemical modeling of the surface waters and active layer pore water using phreeqc hydrogeochemical computer code predicted saturation in fe hydroxide and fe sulfate minerals which is confirmed by the observation of abundant ferrihydrite precipitates along the acidified stream the solute concentrations of the acidified stream and active layer soluble ions versus so 4 plot on very similar slopes suggesting a recycling of solutes it is suggested that the effect of seasonal freeze thaw of the active layer plays an important role in sustaining acidity in the stream freeze back of the acid waters in the active layer produces both fe sulfate minerals and residual sulfuric acid during the thaw season this acidity is released thus enhancing further dissolution of alumino silicate minerals the release of these contaminants including acidity not only causes a perturbation of the water quality but also has a negative impact on the sensitive arctic ecosystem by disturbing the local permafrost conditions

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

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

slip rate variations on faults during glacial loading and post glacial unloading implications for the viscosity structure of the lithosphere abstract many active faults in extensional and contractional tectonic settings experienced a slip rate increase after the last glacial period when the volume of nearby glaciers and lakes decreased this post glacial slip rate increase is caused by transient stresses that are generated by the unloading induced rebound and superimposed on the tectonic background stress field as the latter is different for normal and thrust faults the response to loading and unloading should depend on the fault type here we use finite element models including a fault in rheologically layered lithosphere to explore the conditions under which both normal and thrust faults experience a post glacial slip rate increase the results show that a post glacial slip rate increase occurs on normal faults if the lower crust is stronger than the lithospheric mantle whereas thrust faults accelerate if the lower crust is weaker than the lithospheric mantle these findings imply that the response of faults to mass fluctuations on the earth9s surface may provide constraints on the rheological stratification of the lithosphere we use our results to make predictions on the viscosity structure of the basin and range province and northern scandinavia where palaeoseismological data document a pronounced increase in seismicity as a result of post glacial unloading and rebound

hydrogeology of the central mackenzie valley abstract more than 100 springs seeps and mineralized ponds in the central mackenzie valley have been investigated using chemistry field observations and a general knowledge of the geology in conjunction with environmental isotopes 2 h and 18 o values indicate precipitation primarily snowmelt as the source for all groundwaters sampled chemical analyses of the waters indicate that there are three major components ca 2 so 4 2 dominates followed by na cl and ca 2 mg 2 hco 3 the chemical data in combination with 34 s data indicate that the devonian bear rock formation is the major aquifer throughout the valley other important bedrock aquifers include the mt kindle franklin mountain and saline river formations recharge is directly into bedrock through solution channels or karst systems within the franklin mountains discharge from the bedrock units is controlled by fold and fault structures permafrost is a major factor controlling groundwater recharge but does not significantly affect the location of groundwater discharge

application of the multifrequency horizontal loop em method in overburden investigations1 in recent years geophysical methods shallow seismic electromagnetic resistivity ground penetrating radar have been increasingly applied to overburden investigations their effectiveness has been found to depend significantly on local geological conditions compared with advanced seismic techniques em methods are faster and hence more cost effective but they have not been considered sufficiently accurate analysis is carried out of data obtained with the multifrequency horizontal loop method hlem in northeastern ontario where the overburden consists of quaternary glacial and glaciolacustrine sediments surveying along 1 6 km long profiles permitted recognition of bedrock inhomogeneities and selection of sites suitable for hlem data interpretation using the layered model phasor diagrams and computer inversion based on the ridge regression technique were used to interpret hlem soundings obtained at eight frequencies interpreted layer resistivities and thicknesses were correlated with the results of rotasonic drilling at 70 sites relatively accurate estimates of overburden thickness within 10 could be obtained in about 80 of the cases nine examples of hlem soundings are given and discussed three each of one two and three layer situations an appropriate interpretation model cannot be selected simply by minimizing the rms error or by analysing the parameter resolution matrix frequently the most effective way of evaluating a solution is to consider whether resistivity values determined by inversion fit any of the ranges determined by statistical analyses of sediment resistivities a previously published study of electrical properties of quaternary sediments indicated that resistivities of clay till and sand are stable within a fairly large area such as the one under investigation while the application of hlem methods to mapping of quaternary sediments can be considered a success interpretation of em data in regions covered by glacial sediments is more difficult than in weathered terrains where near surface layering is more predictable the problem of equivalence causes non uniqueness in interpretation thickness equivalence which results in poor resistivity estimates was found to affect areas convered by sand and till conductance equivalence caused poor resolution of thickness and resistivity for thin clay layers less than 10 m

the signature of depth dependent viscosity structure in post seismic deformation summary geodetic observations of post seismic ground motion reflect the integrated effects of several relaxation mechanisms to evaluate the viscous relaxation component accurately the crustal viscosity structure beneath a region must be estimated in this study using a 3 d finite element model we describe the viscoelastic relaxation that follows an instantaneous strike slip faulting event in a crustal layer whose viscosity decreases exponentially with depth at any surface observation point the depth dependent viscosity ddv model displacement history closely fits the history predicted for a uniform viscosity unv model the difference can be minimized to obtain the unv viscosity u that best fits the ddv model displacement at that location the differences in displacement histories between ddv and best fit unv models are minor but depend on distance from fault the viscosity gradient and the fault configuration in the near field the ddv model prediction can be well approximated by the unv model regardless of the viscosity gradient and fault configuration on the other hand in the far field small differences between ddv model and best fit unv model become apparent the displacements are controlled by greater viscosities in later phases and the differences are greater for ddv models with greater viscosity gradient the more important result we obtain is that apparent viscosity u decreases with distance from the fault and its rate of decrease is directly diagnostic of the vertical viscosity gradient this result points to a practical method of analysing post seismic ground displacement data for the variation of viscosity in the ductile crust the apparent crustal viscosity should be determined at a series of points at increasing distance from the fault the variation of apparent viscosity with distance can then be used to directly infer the vertical gradient of viscosity in the crust

contrasting strike slip motions on thrust and normal faults implications for space geodetic monitoring of surface deformation recent global positioning system gps records of surface deformation caused by earthquakes on intracontinental dip slip faults revealed in unprecedented detail a significant strike slip component near the fault tips that is markedly different for thrust and normal faults in the hanging wall of the thrust fault ruptured during the a d 2003 chengkung taiwan earthquake a divergent displacement pattern was recorded in contrast a convergent slip pattern was observed in the hanging wall of the normal fault that produced the 2009 l aquila italy earthquake such convergent slip patterns are also evident in field records of cumulative fault slip from central italy which underlines the coseismic origin of cumulative displacement patterns here we use three dimensional numerical modeling to demonstrate that the observed fault parallel motions are a characteristic feature of the coseismic slip pattern on normal and thrust faults modeled slip vectors converge toward the center of normal faults whereas they diverge for thrust faults this causes contrasting fault parallel displacements at the model surface our model also predicts divergent movements in normal fault footwalls which were recorded for the first time during the l aquila earthquake during the postseismic phase viscous flow in the lower crust induces fault parallel surface displacements which have the same direction as the coseismic displacements but are distributed over a larger area that extends far beyond the fault tips therefore detecting this signal requires gps stations in the prolongation of the fault strike postseismic velocities vary over several orders of magnitude depending on the lower crustal viscosity and may reach tens of millimeters per year for low viscosities our study establishes the link between coseismic and cumulative slip patterns on normal and thrust faults and emphasizes that understanding fault parallel slip components and associated surface displacements is essential for inferring regional deformation patterns from space geodetic and fault slip data

environmental impact of mineralised black shales abstract black shales are sedimentary rocks containing 0 5 of organic carbon they host polymetallic deposits which have been mined for cu ni zn mn p mo v u au and pge platinum group elements even sub economic occurrences provide potential risk of acid rock drainage when exposed to oxic surface environment the natural acid neutralisation potential varies depending on the adjacent rock units especially on the presence of calcareous rocks the chemical and mineralogical composition of black shale is reflected in the quality of the surface waters and groundwater cu ni pb u and zn are recognised as major pollutants though the environmental impact is characteristically polymetallic just like the black shale occurrences hence the environmental impacts have to be evaluated in each occurrence the proterozoic ni zn cu co deposit at talvivaara finland is reviewed in more detail as an example of a large low grade deposit that is currently exploited with open pit mining and a bioleaching process together with the proterozoic central african copperbelt the cambrian u mo deposits in sweden the cambrian ni mo pge deposits in china and the cambrian ordovician u deposits in south korea the devonian ni zn pge occurrences in yukon canada and kentucky usa and the permian cu ag deposits in poland and germany the mineralised horizons may be merely few centimetres thick like in yukon or hundreds of metres thick like at talvivaara both natural and anthropogenic environmental impacts of black shales are reviewed world wide and based on the overview of the state of the art an integrated research approach is suggested for the comprehensive assessment of the risk black shales are natural sources of soil and water contamination at talvivaara the geochemical background includes higher than average concentrations of ni cu zn and mn in glacial till peat surface waters and groundwater as well as in stream and lake sediments bioaccumulation by plants has been reported in china and korea even endemic diseases have been proposed to be linked with the contamination derived from the weathering and leaching of harmful elements from black shale anthropogenic actions exposing the black shale bedrock and associated soils to oxic conditions further intensifies acid rock drainage regional or nation wide mapping of the black shales is recommended to detect potential risk areas finland has recently completed the country wide mapping program of black shales with airborne geophysics integrated with geological petrophysical and geochemical studies the black shale database is actively used in regional planning and by environmental authorities research institutes and consulting companies in the case of the historical black shale mining areas like in the kupferschiefer in germany restoration measures have been applied to prevent further acid mine drainage in active and future mining projects a comprehensive environmental impact assessment with effective monitoring programmes and closure plans play a crucial role in the prevention of acid mine drainage from the black shale associated deposits

grouping and migration of surface faulting and variations in slip rates on faults in the great basin province abstract nonuniformity of the occurrence of large slip events producing surface ruptures on seismogenic faults and variations in slip rate probably characterize seismogenic faulting in the great basin province western united states examples include the grouping of faulting events along the lost river fault idaho changes in tilt rates of the east range and cortez mountains nevada extension of slip along a fault on the northwest flank of the humboldt range nevada and migration or shifting of slip back and forth from one fault to another along subparallel range front faults in dixie valley nevada

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

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

oxidation of mine tailings from rankin inlet nunavut at subzero temperatures acid generating sulphidic tailings from a ni cu mine were exposed on the shores of hudson bay for 30 years before burial in a drained bedrock basin to determine if encapsulation in permafrost will maintain the tailings and their saline pore water in a chemically inert state a field and experimental program was employed three years after burial several boreholes were drilled to collect tailings and pore water samples and to initiate long term thermal monitoring columns charged with pyrrhotite bearing unsaturated tailings were studied at temperatures between 30 c and 10 c oxygen consumption was measured directly to determine the effect of low temperatures on oxidation rate results of the column experiments indicate that significant oxidation of the rankin inlet tailings occurs at 30 c but at lower temperatures this rate is substantially reduced at 10 c unfrozen water was still present in the columns but oxygen consumption was below the detection limit the highest measured oxygen flux corr

weak ductile shear zone beneath a major strike slip fault inferences from earthquake cycle model constrained by geodetic observations of the western north anatolian fault zone gps data before and after the 1999 izmit duzce earthquakes on the north anatolian fault zone turkey reveal a preseismic strain localization within about 25 km of the fault and a rapid postseismic transient using 3 d finite element calculations of the earthquake cycle in an idealized model of the crust comprising elastic above maxwell viscoelastic layers we show that spatially varying viscosity in the crust can explain these observations depth dependent viscosity without lateral variations can reproduce some of the observations but cannot explain the proximity to the fault of maximum postseismic velocities a localized weak zone beneath the faulted elastic lid satisfactorily explains the observations if the weak zone extends down to midcrustal depths and the ratio of relaxation time to earthquake repeat time ranges from 0 005 to 0 01 for weak zone widths of 24 and 40 km respectively in the weakened domain and greater than 1 0 elsewhere corresponding to viscosities of 1018 0 3 pa s and greater than 1020 pa s models with sharp weak zone boundaries fit the data better than those with a smooth viscosity increase away from the fault implying that the weak zone may be bounded by a relatively abrupt change in material properties such a change might result from lithological contrast grain size reduction fabric development or water content in addition to any effects from shear heating our models also imply that viscosities inferred from postseismic studies primarily reflect the rheology of the weak zone and should not be used to infer the mechanical properties of normal crust

bias in estimates of lithosphere viscosity from interseismic deformation 1 the estimation of uniform viscosities representing the lower crust and uppermost mantle from postseismic or interseismic deformation i e apparent viscosities is inherently biased with respect to a depth dependence of the viscosities within each layer estimates are biased toward a more viscous lower crust or a less viscous lithospheric mantle depending on the relative geometric mean viscosities of the two layers when there is a low viscosity shear zone beneath the fault apparent viscosities are close to that of the shear zone immediately after the earthquake although the apparent viscosities increase significantly during the later interseismic period inferences made from interseismic deformation that the lower crust is more viscous than the upper mantle may be entirely consistent with depth dependent viscosity profiles that have a significant increase in viscosity from the lowermost crust to the uppermost mantle

western u s upper mantle structure regional three dimensional inversions of upper mande p wave velocity structure are created from teleseismic p wave travel time residuals recorded by many of the high density high frequency regional arrays operated within the western united states these inversions are adjusted to a global international seismic centre reference and merged to obtain an image of the upper mantle beneath western united states the p wave velocities in the upper mantle are slow on average and the structure is very heterogeneous where resolution is good coherent upper mantle structures are imaged that extend as deep as 200 km the juan de fuca and gorda slabs which penetrate to greater depths are exceptions and deviate from the average velocity at a given depth by as much as 4 lateral resolution of these structures usually is very good although the magnitude of the actual seismic variations is probably greater than that imaged the long wavelength part of the imaged mantle structure defines coherent elongate features with wavelengths of 200 500 km within 250 km of the pacific coast these structures have a wavelength of 250 km and trend parallel to the surface physiography and young tectonic structures beneath the continental interior where use is made of additional seismic studies to infer average structure in regions of poor teleseismic data coverage structures have a wavelength of 500 km and trend northeasterly this northeast orientation is discordant with young tectonic structures but aligns with young volcanic activity

detecting small scale targets by the 2d inversion of two sided three electrode data application to an archaeological survey abstractthe detecting capabilities of some electrical arrays for the estimation of position sizeand depth of small scale targets were examined in view of the results obtained from2d inversions of apparent resistivity data the two sided three electrode apparent resistivity data are obtained by the application of left and right hand pole dipolearrays that also permit the computation of four electrode and dipole dipoleapparent resistivity values without actually measuring them synthetic apparent resistivity data sets of the dipole dipole four electrode and two sided three electrodearrays are calculated for models that simulate buried tombs the results of two dimensional inversions are compared with regard to the resolution in detecting theexact location size and depth of the target showing some advantage for the two sided three electrode array a field application was carried out in the archaeologicalsite known as alaca hoyuk a religious temple area of the hittite period the two dimensional inversion of the two sided three electrode apparent resistivity data hasled to locating a part of the city wall and a buried small room the validity of theinterpretation has been checked against the results of subsequent archaeologicalexcavations introductionthe two dimensional 2d inversion of direct current dc sounding data has become a standard tool for the investiga tion of targets buried at shallow and intermediate depths theapplications include archaeology environmental and hydro geological works mining exploration and engineeringstudies when using the traditional electrode arrays thedata acquisition is usually carried out by expanding electro des along a measurement profile the apparent resistivitydata obtained from all soundings are then used as the input ofa 2d inversion algorithm pelton rijo and swift 1978 andsasaki 1981 first introduced inversion algorithms applied tothe dipole dipole and schlumberger arrays respectively later loke and barker 1996 introduced a fast 2d inversionmethod for the wenner and dipole dipole electrode arrays this algorithm is based on a quasi newton method whichcalculates an approximate value of partial derivatives of theapparent resistivity data with respect to model parameters the finite difference technique is used for the computation ofthe model response one of the remarkable developments in dc methods is theuse of modern measuring systems with multicore cableswhich allows automatic switching between electrodes forpractical field operations the electrodes are located at equallyspaced measurement stations for example morris ronningand lile 1997 described a data acquisition system thatsimultaneously collects schlumberger and two dipole dipoledata however they did not indicate a quantitative inter pretation tool acworth and griffiths 1985 and griffithsand turnbull 1985 described wenner tripotential apparent resistivity measurements to reduce the number of ambiguitiesarising in the qualitative interpretation of apparent resistivitypseudosections the tripotential method produces threeapparent resistivity measurements for each position of acollinear equispaced quadripole of electrodes they used the

characteristics and consequences of flow in the lower crust in some places there is strong evidence that the lower continental crust has flowed so as to smooth out variations in crustal thickness caused by differential crustal extension or shortening in order to better understand the processes involved we investigate the behavior of a fluid layer over a fluid half space to see how such a system responds to the deformation of its upper and lower boundaries this simple system can be used to study both the decay of crustal thickness contrasts and the behavior of a thin lithospheric sheet the changing response of the system to variations in density and viscosity contrasts and to different boundary conditions imposed on the fluid interface can easily be studied analytically the most important results are that variations in crustal thickness on a wavelength of a few times the thickness of the flowing channel will decay quickest and that large lateral variations in crustal thickness cause the fluid to develop a steep front which may cause a topographic step above it at the earth s surface deformation within the channel will be principally by simple shear the clear association of lower crustal flow with regions of thickened crust and magmatic activity suggests that both can reduce the viscosity of the lower crust to levels at which flow can occur the smoothing of crustal thickness contrasts leads to differential vertical motions and is thus a method by which substantial tilting can occur without faulting this differential uplift may be responsible for rotating and exhuming some of the detachment faults in metamorphic core complexes in the basin and range province of the western united states it is also a method of causing structural inversion in basins that does not require the reactivation of normal faults as thrusts or reverse faults

secondary sulfate minerals associated with acid drainage in the eastern us recycling of metals and acidity in surficial environments weathering of metal sulfide minerals produces suites of variably soluble efflorescent sulfate salts at a number of localities in the eastern united states the salts which are present on mine wastes tailings piles and outcrops include minerals that incorporate heavy metals in solid solution primarily the highly soluble members of the melanterite rozenite epsomite halotrichite and copiapite groups the minerals were identified by a combination of powder x ray diffraction xrd scanning electron microscopy sem and electron microprobe base metal salts are rare at these localities and cu zn and co are commonly sequestered as solid solutions within fe and fe al sulfate minerals salt dissolution affects the surfacewater chemistry at abandoned mines that exploited the massive sulfide deposits in the vermont copper belt the mineral district of central virginia the copper basin ducktown mining district of tennessee and where sulfide bearing metamorphic rocks undisturbed by mining are exposed in great smoky mountains national park in north carolina and tennessee dissolution experiments on composite salt samples from three minesites and two outcrops of metamorphic rock showed that in all cases the ph of the leachates rapidly declined from 6 9 to b3 7 and specific conductance increased gradually over 24 h leachates analyzed after 24 h dissolution experiments indicated that all of the salts provided ready sources of dissolved al n30 mg l 1 fe n47 mg l 1 sulfate n1000 mg l 1 and base metals n1000 mg l 1 for minesites and 2 mg l 1 for other sites geochemical modeling of surface waters mine waste leachates and salt leachates using phreeqc software predicted saturation in the observed ochre minerals but significant concentration by evaporation would be needed to reach saturation in most of the sulfate salts periodic surface water monitoring at vermont minesites indicated peak annual metal loads during spring runoff at the virginia site where no winter long snowpack develops metal loads were highest during summer months when salts were dissolved periodically by rainstorms following sustained evaporation during dry spells despite the relatively humid climate of the eastern united states where precipitation typically exceeds evaporation salts form intermittently in open

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

omori like decay of postseismic velocities following continental earthquakes various mechanisms have been proposed to explain the transient enhanced surface deformation rates following earthquakes unfortunately these different mechanisms can produce very similar surface deformation patterns leading to difficulty in distinguishing between them here we return to the observations themselves and compile near field postseismic velocity measurements following moderate to large continental earthquakes we find that these velocities have a remarkably consistent pattern with velocity inversely proportional to time since the earthquake this suggests that postseismic velocities show an omori like decay and that postseismic displacements increase logarithmically over time these observations are inconsistent with simple linear maxwell or burgers body viscoelastic relaxation mechanisms but are consistent with rate and state frictional afterslip models and power law shear zone models the results imply that near field postseismic surface deformation measurements are primarily the result of fault zone processes and therefore that the inference of lower crustal viscosities from near field postseismic deformation requires care

influence of water fugacity and activation volume on the flow properties of fine grained anorthite aggregates 1 to specify quantitatively the effect of pressure and water weakening on the flow strength of feldspar we performed triaxial creep experiments in a gas deformation apparatus at temperatures of 1000 1150 c confining pressures of 100 450 mpa and axial stresses of 10 400 mpa resulting in strain rates of 6 10 7 to 3 10 3 s 1 dense samples with a grain size of 3 m were prepared by hot isostatic pressing of anorthite glass powder hydrous samples contain about 0 33 0 14 wt h2o and dry specimens 0 0005 0 02 wt h2o the estimated residual glass content of wet samples is 2 vol samples deformed by grain boundary diffusion controlled creep at low stresses and dislocation creep at stresses 150 mpa we estimate an activation volume of v 24 cm3mol 1 for anhydrous samples deforming in diffusion creep for wet samples deformed in hydrous conditions with varying buffers fixing oxygen fugacity the activation volume is about 38 cm3 mol 1 creep rate of hydrous anorthite aggregates depends on water fugacity raised to a power of r 1 0 0 3 suggesting hydrolysis of oxygen bonds considering the effect of activation volume and water fugacity on extrapolation of constitutive laws to conditions prevailing in the continental lower crust viscosities of hydrous feldspar aggregates increase by a factor of 3

sulfate mineral crusts from pyrite weathering and acid rock drainage in the dakota formation and graneros shale jefferson county nebraska pyrite weathering in the uppermost dakota formation and lower graneros shale cretaceous near fairbury nebraska produces acid materials and soils typically ph 6 acid rock drainage ph 2 5 and surface crusts of gypsum and the hydrated fe3 and al sulfate minerals copiapite alunogen metahohmannite coquimbite paracoquimbite and meta alunogen the fe and al minerals produced by acid sulfate weathering are relatively rare heretofore undocumented from nebraska and form in quantity only during episodes of dry weather lasting up to several weeks the maturation of mineral crusts on the dakota formation involves the dehydration of hydrous fe3 and al minerals precursor fe2 sulfates as found in many other cases of pyrite weathering were not observed in surface crusts during the study period surficial mineral crusts on the graneros shale consist only of gypsum with included clay minerals and quartz derived from the underlying shale the processes described herein are noteworthy in a regional geochemical and hydrogeological context and also by virtue of their apparent dependency on weather conditions the acid sulfate weathering sites described herein seem to be relatively unique in the surrounding region nonetheless the study of these sites suggests that there are potentially widespread effects of natural acid sulfate weathering associated with the dakota formation and other pyritiferous cretaceous strata in the region and that the localized effects of anthropogenically induced acid sulfate weathering in roadcuts quarries and other excavations can present engineering problems acid sulfate weathering is likely to have influenced the development of regional groundwater chemistry during the quaternary and may create adverse engineering and environmental conditions such as the retardation of vegetation cover encouragement of subsoil gypsum growth acceleration of shale slaking and possibly even the corrosion of roadbed materials

ground motion measurement in the lake mead area nevada by differential synthetic aperture radar interferometry time series analysis probing the lithosphere rheological structure 1 we measure ground motion around the lake mead nevada using synthetic aperture radar interferometry the lake water level has fluctuated through time since impoundment in 1935 to quantify the deformation due to water level variations over the past decade and to constrain the crust and mantle rheological parameters in the lake area we analyze 241 interferograms based on 43 ers images acquired between 1992 and 2002 all interferograms have a high coherence due to arid conditions most of them show strong atmospheric artefacts tropospheric phase delays are estimated and corrected for each interferogram by analyzing the phase elevation correlation corrections are validated using data from the era40 global atmospheric reanalysis corrected interferograms are inverted pixel by pixel to solve for the time series of ground motion in the lake area temporal smoothing is added to reduce random atmospheric artefacts the observed deformation is nonlinear in time and spreads over a 50 50 km2 area we observe a 16 mm subsidence between 1995 and 1998 due to an 11 m water level increase followed by an uplift due to the water level drop after 2000 we model the deformation taking into account the loading history of the lake since 1935 a simple elastic model with parameters constrained by seismic wave velocities does not explain the amplitude of the observed motion the two layer viscoelastic model proposed by kaufmann and amelung 2000 with a mantle viscosity of 1018 pa s adjusts well the data amplitude and its spatiotemporal shape

a relation among geology tectonics and velocity structure western to central nevada basin and range in the northwestern to central nevada basin and range there are correlations between velocity and specific geologic structures of the crust mapped range bounding faults at the surface can be traced to appreciable 10 km depths based on velocity variations and are consistent with subsurface projections of the faults based on seismic reflection images the limiting depth of the faults as indicated by the velocity variations corresponds to the maximum depth of earthquakes along the seismic profile correlations between velocity and the surface geology show that in the upper crust the pre cenozoic rocks are underlain by high velocity 6 0 km s rocks whereas the tertiary ranges are underlain by lower velocity 4 0 5 7 km s rocks to depths as great as 10 km although the tertiary rocks differ in composition from the mesozoic rocks the lower velocity tertiary rocks may also be attributed to rock masses which are broken 4 0 5 7 km s and the higher velocity mesozoic rocks 6 0 km s may be attributed to largely unbroken rock masses the regional seismicity pattern is consistent with this interpretation as earthquakes are largely confined within or near the base of the low velocity rocks these low velocity highly fractured rocks are laterally distributed in discrete zones suggesting that extension is not uniformly distributed but occurs in discrete highly extended zones beneath these highly extended zones the lower crustal layers show structural evidence of extension and velocity measurements suggest that the lowermost crust has been magmatically underplated the superposition of tertiary volcanic rocks highly fractured upper crust and lower crustal magmatic underplating suggests that the tertiary volcanic rocks originated from lower crustal magmas that migrated to the surface via the highly extended zones the velocity structure of one of the highly extended zones and the lahonton basin resembles that of many continental rifts the velocity structure beneath central nevada however is much more like normal continental crust on the basis of isotopic studies it is concluded that the transition between highly extended crust and more normal crust occurs in the area inferred to be the edge of the north american craton

application of the fast fourier transform to interpret geoelectric anomalies preliminary results archaeological structures are commonly buried at shallow depths nevertheless their geophysical signatures measured at the surface may be weak and contaminated with noise thus difficult to interpret however regional residual separation techniques commonly used in gravity and magnetics to enhance the signal of interest also can be applied to the interpretation of one dimensional resistivity profile data such a process is done based on a frequency analysis the resistivity response of synthetic models has been computed analytically by the images method for a wenner array different curves were analysed varying the observation step p the width t of two vertical layers the resistivity p of the media and the electrodes interval a the fourier transform is applied to the theoretical resistivity profiles to compute and analyse its amplitude spectrum such a function presented three regions of interest a low frequency zone was selected to design a low pass filter to calculate the regional of the resistivity curve a residual resistivity anomaly was calculated by taking the difference between that and the observed profile such an anomaly depicted highs that corresponded to the location of the resistive interfaces after assessing the technique with theoretical data an application to a real case was studied the real data are from the city of denia alicante located in the eastern coast of spain in the mediterranean sea the area of interest was covered by eight resistivity profiles two of them lay on a road under construction where remains of a roman structure were discovered during the construction works residual resistivity anomalies were computed by applying the method of regional residual separation in the wave number domain a correlation process between the computed residual and the theoretical response of the wall model was carried out to locate the position of the boundaries of the village foundations the geophysical interpretation enabled the archaeological work to discover the remains of a warehouse complex related to the ancient roman port of dianium buried close to the surface below the road so far no excavation has been undertaken in the reminder electrical profiles

from coseismic offsets to fault block mountains in the basin and range extensional province of the western united states coseismic offsets under the influence of gravity display predominantly subsidence of the basin side fault hanging wall with comparatively little or no uplift of the mountainside fault footwall a few decades later geodetic measurements gps and interferometric synthetic aperture radar insar show broad 100 km aseismic uplift symmetrically spanning the fault zone finally after millions of years and hundreds of fault offsets the mountain blocks display large uplift and tilting over a breadth of only about 10 km these sparse but robust observations pose a problem in that the coesismic uplifts of the footwall are small and inadequate to raise the mountain blocks to address this paradox we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift which is predicted to take place within one to two decades after each large earthquake thus the best preserved topographic signature of earthquakes is expected to occur early in the postseismic period

geochemistry of the active layer and near surface permafrost mackenzie delta region northwest territories canada the soluble ion content of the active layer and near surface permafrost was determined at 41 sites in the mackenzie delta region northwest territories canada in delta soils ca2 and mg2 are the dominant soluble cations but the quantity and relative abundance of na increase with proximity to the beaufort sea coast soils beneath frequently flooded surfaces are ion rich in comparison with ground above the level of decadal flooding within a terrain type near surface permafrost soil solute concentrations are similar between paired cores spaced 1 m apart but at greater distances cores spaced 3 13 m apart solute concentrations are significantly different comparatively low soil solute concentrations in old upland surfaces near inuvik may be a result of progressive removal of soluble materials from the active layer and permafrost during periods of deeper thaw in sandy silt alluvium solutes excluded during downward freezing may accumulate at the base of the active layer and be sequestered by a ris

inference of multiple earthquake cycle relaxation timescales from irregular geodetic sampling of interseismic deformation abstract characterizing surface deformation throughout a full earthquake cycle is a challenge due to the lack of high resolution geodetic observations of duration comparable to that of characteristic earthquake recurrence intervals 250 10 000 years here we approach this problem by comparing long term geologic slip rates with geodetically derived fault slip rates by sampling only a short fraction 0 001 0 1 of a complete earthquake cycle along 15 continental strike slip faults geodetic observations provide snapshots of surface deformation from different times through the earthquake cycle the timing of the last earthquake on many of these faults is poorly known and may vary greatly from fault to fault assuming that the underlying mechanics of the seismic cycle are similar for all faults geodetic observations from different faults may be interpreted as samples over a significantly larger fraction of the earthquake cycle than could be obtained from the geodetic record along any one fault alone as an ensemble we find that geologically and geodetically inferred slip rates agree well with a linear relation of 0 94 0 09 to simultaneously explain both the ensemble agreement between geologic and geodetic slip rate estimates with observations of rapid postseismic deformation we consider the predictions from simple two layer earthquake cycle models with both maxwell and burgers viscoelastic rheologies we find that a two layer burgers model with two relaxation timescales is consistent with observations of deformation throughout the earthquake cycle whereas the widely used two layer maxwell model with a single relaxation timescale is not suggesting that the earthquake cycle is effectively characterized by a largely stress recoverable rapid postseismic stage and a much more slowly varying interseismic stage

how vein sealing boosts fracture widening rates the buckling enhanced aperture growth mechanism for syn tectonic veins abstract the paper introduces the mechanism of buckling enhanced aperture growth for syn tectonic veins that formed in simple shear dominated kinematic frameworks in the middle or lower crust apart from the well understood concepts of fracture widening driven by effective tensile stresses buckling enhanced fracture aperture growth relates widening to active outward buckling of more viscous incipient cement layers precipitated as hydrothermal minerals for the pore fluid on the walls of juvenile syn tectonic veins driven by fracture parallel compressive creep strain in the host rocks thus the mechanism proposed here follows similar principles as tectonic folding although important differences exist inspired by the structural record of low aspect ratio veins exposed in hp lt metamorphic rocks cropping out on south evia island greece generic numerical models are calculated to study development of buckling instabilities in such incompletely cemented veins and their impact on aperture growth rates the models indicate 1 that aperture growth rates increase with increasing viscosity contrast between the host rocks and the cement layers 2 an increase in the thickness of the cement layers cause acceleration of aperture growth 3 that support of restraining forces at the vein tips offered by the host rocks against buckling of the cement layers cause fully compressive states of stress ahead the fracture tips and 4 that fracture aperture growth is possible against fully compressive fracture normal stresses the buckling enhanced vein aperture growth mechanism yields important implications for the maintenance and decay of fracture bound permeability and for the mechanical state of the middle and lower crust in seismically active regions

a new method for the computation of global viscoelastic post seismic deformation in a realistic earth model i vertical displacement and gravity variation summary we introduce a new method by which to compute global post seismic deformation psd in a spherically symmetric self gravitating viscoelastic earth model previous methods are based on simplified earth models that neglect compressibility and or the continuous variation of the radial structure of earth this is because the previous mode summation technique cannot avoid intrinsic numerical difficulties caused by the innumerable poles that appear in a realistic earth model that considers such effects in contrast the proposed method enables both of these effects to be taken into account simultaneously we carry out numerical inverse laplace integration which allows evaluation of the contribution from all of the innumerable modes of the realistic earth model using this method a complete set of green s functions is obtained including functions of the time variation of the displacement gravity change and the geoid height change at the surface for strike slip dip slip horizontal and vertical tensile point dislocations as an earth model we employ the preliminary reference earth model prem and a convex viscosity profile further we investigate the effects of fine layering of the viscoelastic structure and compressibility on a time series of psd using the green s function for a dip slip fault the result indicates that the effect of increasing number of layers is saturated at several tens of layers even when compressibility is taken into account and that the effect of compressibility is detectable with modern observational techniques for a shallower large earthquake mw 8 as an application the psd due to the sumatra andaman islands earthquake mw 9 3 is estimated we show that the rate of post seismic vertical displacement and gravity change is possibly detected in the far field where the epicentral distance exceeds 400 km

weathering of sulfidic shale and copper mine waste secondary minerals and metal cycling in great smoky mountains national park tennessee and north carolina usa metal cycling via physical and chemical weathering of discrete sources copper mines and regional non point sources sulfide rich shale is evaluated by examining the mineralogy and chemistry of weathering products in great smoky mountains national park tennessee and north carolina usa the elements in copper mine waste secondary minerals stream sediments and waters that are most likely to have negative impacts on aquatic ecosystems are aluminum copper zinc and arsenic because these elements locally exceed toxicity guidelines for surface waters or for stream sediments acid mine drainage has not developed in streams draining inactive copper mines acid rock drainage and chemical weathering processes that accompany debris flows or human disturbances of sulfidic rocks are comparable to processes that develop acid mine drainage elsewhere despite the high rainfall in the mountain range sheltered areas and intermittent dry spells provide local venues for development of secondary weathering products that can impact aquatic ecosystems

downward water movement into frozen ground western arctic coast canada field studies carried out mainly since 1975 in permafrost areas of alaska canada china and the soviet union have been combined with the results of laboratory investigations to show that in summer water can move from the thawing active layer into the subjacent frozen active layer and under certain conditions even into the top of permafrost direct field evidence discussed includes data from drilling and neutron probe logging which show a summer increase in the ice content of already frozen ground summer heave of heavemeters with heave occurring in the frozen active layer and increase in the ice content of the subjacent frozen ground in both permafrost and non permafrost areas caused by snowmelt infiltration indirect field and laboratory evidence is also added to support the direct lines of evidence the conditions that favor the downward migration of water from thawed to frozen ground are examined in terms of thermally induced hydraulic gradients hydraulic conductivity content of unfrozen pore

potential application of oxygen 18 and deuterium in mining effluent and acid rock drainage studies oxygen 18 18o and deuterium d or 2h are routinely used in hydrologic climatologic and geothermal studies in hydrology stable isotopes provide information on the type and topology altitude and latitude of the recharge waters and the historical effects on water related to such physical processes as evaporation in ponds melting of snow or ice condensation evapotranspiration and mixing in geothermal studies stable isotopes provide key information related to recharge and the various temperature dependent water rock isotope exchange reactions the latter is assessed through the oxygen shift in the 18o d correlation at acid rock drainage ard sites water rock interactions are primarily controlled by ph and oxidation potential using the isotopic characteristics of the rocks and the recharge waters as a basis the relative oxygen shift of the ard effluent can provide information on 1 the residence time 2 the rate of water rock reactions and 3 the actual ph at the rock water interface this paper offers a methodology for conducting oxygen and hydrogen isotope studies related to ard and other mineral effluent problems the methodology is based on 1 comprehensive sampling of regional waters ard effluent and major contributing minerals and rocks 2 isotopic and elemental analysis and 3 data interpretation on the basis of a zero dimensional mass balance multi component mixing model