untested carbonate buildups in the bermejo field ecuador a potential new play type in the western oriente basin we identified a previously unknown carbonate buildup in the cretaceous m1 limestone in the bermejo field northwestern oriente basin of ecuador thinner carbonate builduplike features are also seen in the deeper a limestone which has produced small volumes of oil in the northern bermejo field the carbonate buildups can represent a significant new play type in the western oriente basin where limestones have been known principally as a source rock the m1 carbonate buildup imaged as a lenslike event in three dimensional seismic data forms a circular feature in the isopach amplitude and dip maps it is characterized by generally high but variable seismic amplitude and its thicknesses 20 to 40 m 66 to 131 ft exhibit a complicated pattern suggesting weathering and or localized carbonate growth the dark and rough top surface and irregular edges of the m1 carbonate buildup revealed by the dip map probably suggest the formation of fracture cavity karst type reservoirs the late cretaceous convergence along the western oriente basin may have further fractured the carbonates in the area the m1 carbonate buildup assuming a porosity of 10 can contain more than 4 0 107 bbl of liquid which is particularly significant in the bermejo field where production has been marginal

ice dams outburst floods and glacial incision at the western margin of the tibetan plateau a 100 k y chronology from the shyok valley karakoram some of the largest and most erosive floods on earth result from the failure of glacial dams while potentially cataclysmic ice dams are recognized to have repeatedly formed along ice sheet margins much less is known about the frequency and longevity of ice dams caused by mountain glaciers and their impact on landscape evolution here we present field observations and results from cosmogenic nuclide dating that allow reconstructing a 100 k y long history of glacial damming in the shyok valley eastern karakoram south asia our field observations provide evidence that asia s second longest glacier the siachen once extended for over 180 km and blocked the shyok river during the penultimate glacial period leading to upstream deposition of a more than 400 m thick fluvio lacustrine valley fill 10 be depth profile modeling indicates that glacial damming ended with the onset of the eemian interglacial and that the shyok river subsequently incised the valley fill at an average rate of 4 7 m k y 1 comparison with contemporary ice dammed lakes in the karakoram and elsewhere suggests recurring outburst floods during the aggradation period while over 25 cycles of fining upward lake deposits within the valley fill indicate impounding of floods from farther upstream despite prolonged damming the net effect of this and probably earlier damming episodes by the siachen glacier is dominated by glacial erosion in excess of fluvial incision as evidenced by a pronounced overdeepening that follows the glaciated valley reach strikingly similar overdeepened valleys at all major confluences of the shyok and indus rivers with karakoram tributaries indicate that glacial dams and subsequent outburst floods have been widespread and frequent in this region during the quaternary our study suggests that the interaction of karakoram glaciers with the shyok and indus rivers promoted valley incision and headward erosion into the western margin of the tibetan plateau

probabilistic lithofacies prediction from prestack seismic data in a heterogeneous carbonate reservoir abstractwe mapped probabilities of lithology and fluid based on seismic and well observations in a heterogeneous carbonate reservoir of the sichuan basin southwest china thus characterizing the reservoir complexity and identifying the potential sweet spot rock physical analysis showed that the presence of a vuggy fracture porosity system combined with the fluids effect complicate the elastic responses of heterogeneous carbonates this also gives physical insight into how the elastic properties of different lithofluid classes can be distinguished with the application of bayesian linearized amplitude variation with offset inversion we found that the posterior distribution of p and s wave velocities were reliably extracted whereas the inverted density tended to show high uncertainty due to a lack of wide angle data in the migrated seismic gathers finally a bayesian approach was implemented to propagate uncertainty from prestack seismic data to lithofluid classes in an integrated framework the gas

empirical ground motion relations for subduction zone earthquakes and their application to cascadia and other regions ground motion relations for earthquakes that occur in subduction zones are an important input to seismic hazard analyses in many parts of the world in the cascadia region washington oregon northern california and british columbia for example there is a significant hazard from megathrust earthquakes along the subduction interface and from large events within the subducting slab these hazards are in addition to the hazard from shallow earthquakes in the overlying crust we have compiled a response spectra database from thousands of strong motion record ings from events of moment magnitude m 5 8 3 occurring in subduction zones around the world including both interface and in slab events the 2001 m 6 8 nis qually and 1999 m 5 9 satsop earthquakes are included in the database as are many records from subduction zones in japan kyoshin net data mexico guerrero data and central america the size of the database is four times larger than that available for previous empirical regressions to determine ground motion relations for subduc tion zone earthquakes the large dataset enables improved determination of attenu ation parameters and magnitude scaling for both interface and in slab events soil response parameters are also better determined by the data we use the database to develop global ground motion relations for interface and in slab earthquakes using a maximum likelihood regression method we analyze regional variability of ground motion amplitudes across the global database and find that there are significant regional differences in particular amplitudes in cascadia differ by more than a factor of 2 from those in japan for the same magnitude distance event type and national earthquake hazards reduction program nehrp soil class this is believed to be due to regional differences in the depth of the soil profile which are not captured by the nehrp site classification scheme regional correction factors to account for these differences are proposed for cascadia and japan the results of this study differ significantly from previous analyses based on more limited data and have important implications for seismic hazard analysis the ground motion relations predict that a great megathrust earthquake m 8 at a fault distance of about 100 km would produce pseudoacceleration psa 5 damped horizontal component on soil sites of about 110 cm sec 2 at 0 5 hz 660 cm sec 2 at 2 5 hz and 410 cm sec 2 at 5 hz with a peak ground acceleration of about 180 cm sec 2 these damaging levels of motion would be experienced over a very large area corresponding to a rectangular area about 300 km wide by 500 km long large in slab events m 7 5 would produce even higher psa values within 100 km of the fault but the in slab motions attenuate much more rapidly with distance thus the hazard posed by moderate to large in slab events such as the 2001 nisqually earth quake is modest compared to that of a cascadia megathrust earthquake of m 8 in terms of the area that would experience damaging levels of ground motion

the recent deglaciation of kolahoi valley in kashmir himalaya india in response to the changing climate abstract in the present study the retreat of kolahoi glacier was mapped from the satellite observations and historical maps supplemented by the extensive field observations to understand the recent deglaciation of the kolahoi valley kashmir himalaya india the glacier has retreated by 2 85 km during the last 157 years from 1857 to 2014 with an average retreat of about 18 2 m year 1 however the glacier snout has shown higher recession during the last decade the geomorphological evidence reveals glaciation of the kolahoi valley during the quaternary these evidences include glacial till at pahalgam and aru besides terminal and lateral moraines at lidderwat satlanjan and kolahoi gunj in the kolahoi valley the glacier has shrunk by 2 81 km2 during the last 51 years 1962 2013 losing an ice volume of 0 30 km3 the observed glacier changes were correlated with the climate data from pmip3 cmip5 models the temperatures are predicted to increase almost ten times more than that observed during the last glacial maximum lgm the future temperature is predicted to rise between 0 18 c and 0 61 c per decade under rcp 2 6 and rcp 8 5 respectively the projected rise in the temperature if realized will have an adverse effect on the glaciers and would in all likelihood adversely affect the water availability for various sectors in the region

numerical simulations of glacial valley longitudinal profile evolution glaciers shape alpine landscapes they broaden valley bottoms enhance local valley relief generate multiple steps overdeepen valley floors and cause tributary valleys to hang these distinctive glacial signatures result from 10 4 10 5 yr of erosion during which swings in climate drive advances and retreats of alpine glaciers we use a numerical model of glacial erosion to explore the development of the longitudinal profiles of glaciated valleys the model is driven by the past 400 k y of variable climate because both sliding speed which dictates abrasion rate and water pressure fluctuations which strongly modulate quarrying rate should peak at the equilibrium line altitude ela we expect the locus of most rapid erosion to follow the transient ela simulations of a single glacial valley show rapid flattening of the longitudinal profile inclusion of a tributary glacier creates a step immediately downvalley of the tributary junction that persists over multiple glaciations and commonly leaves the tributary valley hanging steps and overdeepenings result from an increase in ice discharge immediately below the tributary junction which is accommodated primarily by increased ice thickness and hence sliding rate the size of the step increases with the ratio of tributary to trunk ice discharge while the height of a hanging valley reflects the difference in the time integrated ice discharge in tributary and trunk valleys and therefore increases as the discharge ratio decreases

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

sediment evacuation and glacial erosion rates at a small alpine glacier 1 glacial erosion is known to be driven by sliding which occurs in brief episodes in the melt season what is not known is how well this sliding history is reflected in the sediment output from a glacier and to what degree temporary sediment storage in the glacier smoothes the history of sediment production we document sediment evacuation rates for three seasons at bench glacier a small temperate alpine glacier in the chugach range of alaska two lines of evidence suggest that subglacial sediment storage is small strong hysteresis in the relationship between sediment and water discharge argues for sediment exhaustion from the subglacial system on seasonal and flood event timescales uplift of the glacier surface during periods of enhanced basal motion reflects intimate contact of the glacier sole with up glacier inclined stoss slopes of bedrock bumps sediment evacuation rates at bench glacier should therefore closely track glacial erosion rates over annual timescales much of the sediment emerges in a major pulse that closely follows the termination of enhanced sliding each year suggesting that the conduits and well connected cavities that allowed removal of englacial water to terminate sliding also promoted efficient transport of sediment this small glacier efficiently modifies the landscape lowering its bed by 1 2 mm yr while sliding only 1 2 m yr our sparse measurements of instantaneous bed load discharge average 41 of concurrent suspended sediment discharge assuming that half of the suspended load derives from abrasion of subglacially quarried clasts roughly two thirds of the sediment evacuated can be attributed to quarrying

numerical modeling of the development of u shaped valleys by glacial erosion the steep sided valleys and overdeepened basins of alpine landscapes are well known products of glaciation yet relatively little is known about how the dynamics of ice flow and glacial erosion interact to give rise to such landforms by linking a finite element model for ice flow through a glacier cross section with an erosion model it is possible to investigate the development of one of the most striking glacial landforms the u shaped valley in addition to providing a detailed understanding of landform development such modeling provides a way to test current understanding of the controls on glacial sliding and erosion to simulate valley development i first model flow through an initial glacier cross section and calculate the glaciological parameters that govern erosion i then numerically simulate erosion to produce a modified transverse profile for which a new flow field and erosion pattern are computed a number of iterations permits examination of the progressive transformation of cross section form which can be compared with field data model predictions of the cross section flow field are in close accord with data from the athabasca glacier and include marked lateral variations in sliding velocity with an erosion law dependent on basal velocity the model predicts the rapid transformation of a v shaped cross section into a recognizably glacial form over a time period on the order of 10 4 yr and the eventual development of a steady state quasi parabolic glacier cross section better agreement with empirical data from glaciated valleys is obtained by including temporal variations in ice discharge in order to mimic the characteristics of 100 000 yr glacial cycles the high discharge phase dominates form development and at low discharges cross section form is essentially inherited from the central part of the form that developed during the preceding high discharge phase

lame parameters of common rocks in the earth s crust and upper mantle 1 lame parameter and shear modulus are the most important intrinsic elastic properties of rocks the lame parameter which relates stresses and strains in perpendicular directions is closely related to the incompressibility and contains a high proportion of information about the resistance to a change in volume caused by a change in pressure recent studies have emphasized the roles played by in the discrimination of gas sands from carbonates and shale in sedimentary basins and in the seismic reflection of crustal fault zones here we analyze the equivalent isotropic elastic data of 475 natural rocks in order to characterize values for common types of crystalline rocks in the earth s crust and upper mantle and their variations with pressure p temperature t and mineralogical composition when no partial melting metamorphic reaction dehydration or phase transformation occurs of a crystalline rock as a function of p and t can be described by a d dp p c exp kp d dt t where a is the projected value at zero pressure if microcracks were fully closed d dp is the pressure derivative in the linear elastic regime c is the initial drop caused by the presence of microcracks at zero pressure k is a decay constant of the drop in the nonlinear poroelastic regime and d dt is the temperature derivative the parameter increases nonlinearly and linearly with increasing pressure at low 300 mpa pressures respectively in the regime of high pressures decreases quasi linearly with increasing temperature with d dt values in the range of 1 10 10 3 gpa c approaching the quartz transition temperature quartzite displays negative values in the density and plots the main categories of lithology can be clearly distinguished the ultramafic rocks display systematic decreases in both and with increasing the degree of serpentinization eclogites mafic rocks gabbro diabase mafic granulite and mafic gneiss and felsic rocks granite diorite felsic gneiss intermediate gneiss and metasediments are characterized by high moderate and low and values respectively for pyroxene and olivine both and increase but decreases with increasing the fe mg ratios in the plagioclase series both and increases with increasing the anorthite content increases in the contents of garnets sillimanite rutile zircon ilmenite and spinel result systematically in an increase in rock s and values the present results provide improved constraints on the discrimination of composition for crustal and upper mantle rocks in terms of and

a new surface processes model combining glacial and fluvial erosion we have developed a new surface processes model incorporating large scale fluvial processes local hill slope processes and glacial erosion ice thickness and velocity are calculated under a shallow ice approximation simulation experiments in fast growing orogens comparing the efficiencies of fluvial and glacial erosion where the two are operating simultaneously over several glacial cycles show that glacial landscapes can support greater ice masses than fluvial landscapes glacial valley and lake shapes create a disequilibrium between landform and land forming process that leads to pulses of high erosion at the end of glacial periods glacial erosion rates can reach a constant value in a uniformly growing orogen and glacial erosion is capable of eroding drainage divides when the ice is moderately thick

hillslope glacier coupling the interplay of topography and glacial dynamics in high asia 1 high asian glacial landscapes have large variations in topographic relief and the size and steepness of snow accumulation areas associated differences in glacial cover and dynamics allow a first order determination of the dominant processes shaping these landscapes here we provide a regional synthesis of the topography and flow characteristics of 287 glaciers across high asia using digital elevation analysis and remotely sensed glacier surface velocities glaciers situated in low relief areas on the tibetan plateau are mainly nourished by direct snowfall have little or no debris cover and have a relatively symmetrical distribution of velocities along their length in contrast avalanche fed glaciers with steep accumulation areas which occur at the deeply incised edges of the tibetan plateau are heavily covered with supraglacial debris and flow velocities are highest along short segments near their headwalls but greatly reduced along their debris mantled lower parts the downstream distribution of flow velocities suggests that the glacial erosion potential is progressively shifted upstream as accumulation areas get steeper and hillslope debris fluxes increase our data suggest that the coupling of hillslopes and glacial dynamics increases with topographic steepness and debris cover the melt lowering effect of thick debris cover allows the existence of glaciers even when they are located entirely below the snow line however slow velocities limit the erosion potential of such glaciers and their main landscape shaping contribution may simply be the evacuation of debris from the base of glacial headwalls which inhibits the formation of scree slopes and thereby allows ongoing headwall retreat by periglacial hillslope processes we propose a conceptual model in which glacially influenced plateau margins evolve from low relief to high relief landscapes with distinctive contributions of hillslope processes and glaciers to relief production and decay

small valley glaciers and the effectiveness of the glacial buzzsaw in the northern basin and range usa the glacial buzzsaw hypothesis suggests that efficient erosion limits topographic elevations in extensively glaciated orogens studies to date have largely focussed on regions where large glaciers tens of kilometres long have been active in light of recent studies emphasising the importance of lateral glacial erosion in lowering peaks and ridgelines we examine the effectiveness of small glaciers in limiting topography under both relatively slow and rapid rock uplift conditions four ranges in the northern basin and range idaho montana and wyoming usa were chosen for this analysis estimates of maximum pleistocene slip rates along normal faults bounding the beaverhead bitterroot mountains similar to 0 14 mm y 1 lemhi range similar to 0 3 mm y 1 and lost river range similar to 0 3 mm y 1 are an order of magnitude lower than those on the teton fault similar to 2 mm y 1 we compare the distribution of glacial erosion estimated from cirque floor elevations and last glacial maximum lgm equilibrium line altitude ela reconstructions and fault slip rate with three metrics of topography in each range the along strike maximum elevation swath profile hypsometry and slope elevation profiles in the slowly uplifting beaverhead bitterroot mountains and lemhi and lost river ranges trends in maximum elevation parallel elas independent of variations in fault slip rate maximum elevations are offset similar to 500 m from lgm elas in the lost river range lemhi range and northern beaverhead bitterroot mountains and by similar to 350 m in the southern beaverhead bitterroot mountains where glacial extents were less the offset between maximum topography and mean quaternary elas inferred from cirque floor elevations is similar to 350 m in the lost river and lemhi ranges and 200 250 m in the beaverhead bitterroot mountains additionally slope elevation profiles are flattened and hypsometry profiles show a peak in surface areas close to the ela in the lemhi range and beaverhead bitterroot mountains suggesting that small glaciers efficiently limit topography the situation in the lost river range is less clear as a glacial signature is not apparent in either slope elevation profiles or the hypsometry in the rapidly uplifting teton range the distribution of elas appears superficially to correspond to maximum topography hypsometry and slope elevations profiles with regression lines on maximum elevations offset by similar to 700 and similar to 350 m from the lgm and mean quaternary ela respectively however grand teton and mt moran represent high elevation teflon peaks that appear impervious to glacial erosion formed in the hard crystalline bedrock at the core of the range glacier size and drainage density rock uplift rate and bedrock lithology are all important considerations when assessing the ability of glaciers to limit mountain range topography in the northern basin and range it is only under exceptional circumstances in the teton range that small glaciers appear to be incapable of imposing a fully efficient glacial buzzsaw emphasising that high peaks represent an important caveat to the glacial buzzsaw hypothesis c 2008 elsevier b v all rights reserved

numerical modeling of glacial erosion and headwall processes in alpine valleys abstract how rock relief is developed by glacial erosion in alpine landscapes is a key question in understanding the controls on mountain range topography any generation of relief by glaciers at the highest elevations in mountain ranges can affect the distribution of precipitation in alpine landscapes creating feedbacks between glacier mass balance and glacial erosion relief production at high elevation mountain crests is addressed using a numerical model that incorporates glacier dynamics and subglacial erosion as well as relevant hillslope processes blowing snow from a valley bounding plateau and avalanching onto the accumulation zone of the glacier is included in the model furthermore temperature dependent frost cracking is used as a proxy for headwall backwearing the parameterization of subglacial erosion produces about 500 m of erosion over the 400 ka of each numerical simulation in steady and varying climate scenarios valley floors flatten as headwalls increase in height and retreat headward over time headwall slopes increase in simulations in which quarrying is explicitly incorporated rates of quarrying are high near the base of the headwall increasing headwall length and slope as a result of valley floor lowering high rates of subglacial erosion and production of headwall relief also result when elastic flexural uplift occurs in response to mass unloading small overdeepenings form at the base of the headwall in steady climate simulations when the glacier is small at the end of the model run while the final profiles are relatively insensitive to the erosion rule used quarrying is most effective near the head of the glacier whereas rates of abrasion reflect the instantaneous pattern of integrated ice discharge or ice flux in simulations in which cirques are formed the equilibrium line altitude is hundreds of meters above the cirque floor however the time averaged horizontal position of the equilibrium line corresponds well with the downvalley position of the cirques

recent applications of avo to carbonate reservoirs in the western canadian sedimentary basin carbonates make up about half of the sedimentary rock in the western canada sedimentary basin wcsb and range from cambrian to early jurassic in geologic age large oil and gas reserves exist in devonian and early carboniferous carbonate formations middle and upper devonian carbonate rocks alone have known reserve of about 15 billion barrels of oil and 35 trillion cubic feet of natural gas a variety of carbonate reservoirs exist in the wcsb mostly reef and platform types these reservoirs are formed by porous limestones or platforms that were dolomitized prior to basin wide hydro carbon maturation and migration fractured reservoirs were formed by natural fractures due to regional or local stress regimes or by local overpressure until recently seismic analysis of data from carbonate reservoirs relied mainly on interpreting zero offset stacked volumes common knowledge within the world of avo suggests that zero offset information is often insufficient to differentiate shale from carbonate porosity or to discriminate gas saturated from brine saturated reservoirs however in the last a few years great efforts have been made to apply avo analysis to carbonate reservoir characterization but several issues must be addressed in investigating the feasibility potential and sensitivity of the response of carbonate rock properties to porosity and fluid first a lack of carbonate rock property information is considered an obstacle in applying avo to carbonate reservoir characterization second the differences between clastic avo and carbonate avo need to be clarified third procedures and calibration in seismic data processing and interpretation need to be developed the situation has been greatly improved due to recent significant acquisition of dipole sonic logs that sample a variety of reservoirs and formations directly associated with carbonates this newly acquired information provides in situ reservoir and nonreservoir measurements that are beyond laboratory and theoretical rock property predictions on the seismic side experience in

fluvial incision into bedrock insights from morphometric analysis and numerical modeling of gorges incising glacial hanging valleys western alps france bedrock gorges incising glacial hanging valleys potentially allow measurements of fluvial bedrock incision in mountainous relief using digital elevation models topographic maps and field reconnaissance we identified and characterized 30 tributary hanging valleys incised by gorges near their confluence with trunk streams in the romanche watershed french western alps longitudinal profiles of these tributaries are all convex and have abrupt knickpoints at the upper limit of oversteepened gorge reaches we reconstructed initial glacial profiles from glacially polished bedrock knobs surrounding the gorges in order to quantify the amount of fluvial incision and knickpoint retreat from morphometric analyses we find that mean channel gradients and widths as well as knickpoint retreat rates display a drainage area dependence modulated by bedrock lithology however there appears to be no relation between horizontal retreat and vertical downwearing of knickpoints assuming a postglacial origin of these gorges our results imply high postglacial fluvial incision 0 5 15 mm yr 1 and knickpoint retreat 1 200 mm yr 1 rates that are however consistent with previous estimates numerical modeling was used to test the capacity of different fluvial incision models to predict the inferred evolution of the gorges results from simple end member models suggest transport limited behavior of the bedrock gorges a more sophisticated model including dynamic width adjustment and sediment dependent incision rates predicts present day channel geometry only if a significant supply of sediment from the gorge sidewalls 10 mm yr 1 is triggered by gorge deepening combined with pronounced inhibition of bedrock incision by sediment transport and deposition

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

testing the efficacy of the glacial buzzsaw insights from the sredinny mountains kamchatka abstract peak altitudes hypsometry geology and former equilibrium line altitudes elas are analysed across the sredinny mountains kamchatka overall evidence is found to suggest that the glacial buzzsaw has operated to shape the topography of this mountain range but the strength of this signature is not spatially uniform in the southern sector of the mountains we see evidence that an efficient glacial buzzsaw has acted to impose constraints upon topography limiting peak altitudes and concentrating land surface area hypsometric maxima close to palaeo elas by contrast in the northern sector of the mountains a number of peaks rise high above the surrounding topography and land surface area is concentrated well below palaeo elas this deviation from a classic buzzsaw signature in the northern sector of the mountains is considered to reflect volcanic construction during the quaternary resulting in a series of high altitude peaks combined with the action of dynamic glaciers acting to skew basin topography toward low altitudes well below palaeo elas these glaciers are considered to have been particularly dynamic because of their off shore termination their proximity to moisture bearing air masses from the north pacific and because accumulation was supplemented by snow and ice avalanching from local high altitude peaks overall the data suggest that the buzzsaw remains a valid mechanism to generally explain landscape evolution in mountain regions but its signature is significantly weakened in mountain basins that experience both volcanic construction and climatic conditions favouring dynamic glaciation

temporal constraints on glacial valley cross profile evolution two thumb range central southern alps new zealand abstract a key problem in understanding valley evolution in alpine landscapes has been the lack of an independent timescale against which to measure morphological change here we outline that by using space as a proxy for time the role of glaciation in producing classic u shaped valleys can be quantified the two thumb range in new zealand s central southern alps is undergoing rapid tectonic transport and uplift as it is advected towards the alpine fault repeated cycles of glacial erosion during the quaternary have fashioned an alpine landscape in the north of the range close to the main divide and alpine fault while valleys in the less glaciated south of the range have rounded divides and convex fluvial cross profiles using known rates of tectonic transport and uplift of the southern alps coupled with an offshore oxygen isotope 18o record from the chatham rise and glacio geological reconstructions time constraints can be applied to the erosional development of valleys it is possible to estimate the duration of glacial occupancy of valleys in the two thumb range and the pattern is one of very limited glaciation of the southern valleys with glacial occupancy increasing northwards the key trend identifiable is that valley cross profiles become u shaped with c 400 600 kyr of glacial occupancy other models have shown a flattening of valley long profiles with increased glaciation implying glaciers erode larger volumes of rock from mountains than rivers from a cross profile perspective the simple change in geometry from v to u shape concurs with these models indeed the transition from v to u shape with increasing relief and glaciation indicates glaciers may erode greater volumes of rock from mountain belts than rivers

uncertainty in vs30 based site response abstract methods that account for site response range in complexity from simple linear categorical adjustment factors to sophisticated nonlinear constitutive models seismic hazard analysis usually relies on ground motion prediction equations gmpes within this framework site response is modeled statistically with simplified site parameters that include the time averaged shear wave velocity to 30 m v s 30 and basin depth parameters because v s 30 is not known in most locations it must be interpolated or inferred through secondary information such as geology or topography in this article we analyze a subset of stations for which v s 30 has been measured to address effects of v s 30 proxies on the uncertainty in the ground motions as modeled by gmpes the stations we analyze also include multiple recordings which allow us to compute the repeatable site effects or empirical amplification factors eafs from the ground motions although all methods exhibit similar bias the proxy methods only reduce the ground motion standard deviations at long periods when compared to gmpes without a site term whereas measured v s 30 values reduce the standard deviations at all periods the standard deviation of the ground motions are much lower when the eafs are used indicating that future refinements of the site term in gmpes have the potential to substantially reduce the overall uncertainty in the prediction of ground motions by gmpes

post little ice age record of coarse and fine clastic sedimentation in an alaskan proglacial lake many assessments of glacial sediment yield rely solely on mea surements of fine grained suspended sediment we show that sus pended sediment contributes 20 of the total clastic sediment discharge into iceberg lake an alaskan proglacial lake drainage of this lake in 1999 exposed outcrops of varved lacustrine sediment that record suspended sediment deposition since a little ice age highstand two centuries ago lake level has dropped in four abrupt spillway controlled events that are recorded stratigraphically as transient increases in the basinwide deposition of unusually fine grained sediments varve counting constrains ages of these events and hence of each abandoned shoreline and associated delta vol umes of deltaic and lake floor sediments constrain specific yields from four multidecadal intervals between a d 1825 and 1999 to tal yield ranges from 3 8 to 4 9 3 10 3 t km 22 yr 21 and most of the sediment 81 86 is sand and gravel now in the deltas a range of evidence suggests that sediment yield faithfully records up stream sediment production in this small 66 km 2 and heavily gla cierized basin implying an effective subglacial erosion rate of 1 6 mm yr these data show that estimates of total yield based upon suspended sediment alone are subject to large errors and suggest that quarrying accounts for a large fraction of the glacial erosion in this system

testing a glacial erosion rule using hang heights of hanging valleys jasper national park alberta canada 1 in most models of glacial erosion glacier sliding velocity is hypothesized to control rates of bedrock erosion if this hypothesis is correct then the elevation difference between hanging and trunk valley floors the hang height should be dictated by the relative sliding velocities of the glaciers that occupied these valleys by considering sliding velocity to be proportional to balance velocity and using mass continuity hang height is expressed in terms of glacier catchment areas slopes and widths which can be estimated for past glaciers from the morphology of glacial valleys these parameters were estimated for 46 hanging valleys and their trunk valleys in three adjacent regions of jasper national park the variability in valley morphology can account for 55 85 of the hang height variability if erosion rate scales with balance velocity raised to a power of 1 3 this correspondence is in spite of spatial variations in glaciation duration snow accumulation rates and other variables that likely affected hang heights but cannot be readily estimated and so are not included in our formulation thus it appears that balance velocity and by extension sliding velocity if the two are proportional may be a reasonable control variable for assessing erosion rate

flow and structure in a dendritic glacier with bedrock steps sherpa romeo green journal open access article creative commons attribution 4 0 international cc by 4 0 applies

ground motion prediction equation for the chilean subduction zone abstract a ground motion prediction equation for the horizontal component of the response spectral values from the chilean subduction zone is developed the dataset contains 3774 recordings from 473 earthquakes including the latest megathrust events that occurred in the country i e 2010 m w 8 8 maule 2014 m w 8 1 iquique and 2015 m w 8 3 illapel the functional form for the median model follows the proposal by abrahamson et al 2016 site effects are estimated based on v s 30 an additional model is built using only ground motions associated with measured values of v s 30 and reliable m w estimates termed the high quality hq model the standard deviation of the hq model is much lower than the main model particularly the component of the standard deviation that corresponds to site to site variability indicating that better site characterization can significantly reduce the overall uncertainty in ground motion estimation electronic supplement tables of regression coefficients for the high quality hq model and 95 confidence intervals for model s coefficients and matlab implementation of the ground motion prediction equation gmpe

ice cap erosion patterns from bedrock 10be and 26al southeastern tibetan plateau quantifying glacial erosion contributes to our understanding of landscape evolution and topographic relief production in high altitude and high latitude areas combining in situ be 10 and al 26 ana

numerical modeling of glacial sediment production and transport during deglaciation abstract we aim to improve the understanding of sediment fluxes originating from ice sheet outlet glaciers in order to explain the evolution of sedimentary fjord fills a numerical glacial erosion and sediment flux process model has been developed to quantify sediment generation and subglacial transport dynamic ice sheet cover is generated from topography and climate parameters affecting the glacial net mass balance pressure temperature and velocity characteristics of the ice sheet force erosion at the glacier bed bed erodability depends on bedrock hardness and potential shielding by sediment after erosion sediment is either stored at the bed or transported either by meltwater or englacially within basal ice model experiments show ice retreat is driven by valley topography rapid retreat occurs in the flatter valley stretches and slower retreat in the steeper parts of a glacial valley distinct depocenters of exposed sediment develop during retreat predicted erosion rates in the glaciated valley range from 37 to 56 mm yr for different climate scenarios which is well within the range of reported field reconstructions erosion is significantly accelerated beneath warm based ice and the effect of an enlarged warm based footprint during warming compensates for decreasing ice mass topographic shielding of bedrock by previously eroded material in large areas constrains erosion by a factor 4 simulated glacier retreat and melt water flux initially occur at a high rate and subsequently decelerate while sediment delivery exhibits a distinct lagging of several thousands of years behind the meltwater flux upon the transition from glaciation to deglaciation the subglacial system is in a sediment starved state late deglacial erosion and sub and englacial sediment storage cause a lagging sediment delivery to downstream periglacial fluvial and lacustrine domains

acoustic properties of carbonates effects of rock texture and implications for fluid substitution more than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of miocene tortonian age were quantitatively analyzed for texture mineralogy and acoustic properties we measured the p and s waves of carbonate rocks under dry humidified and brine saturated conditions at 10 mpa effective pressure with an ultrasonic pulse transmission technique 1 mhz the data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences two major textural groups were distinguished on the basis of trends in plots of compressional wave velocity versus poisson s ratio a specific ratio of p wave over s wave velocity in granular rocks the framework of depositional grains is the main medium for acoustic wave propagation in crystalline rocks this medium is provided by a framework of interlocking crystals formed during diagenesis rock textures are connected to primary depositionalparameters and a diagenetic ov

intermittent glacial sliding velocities explain variations in long timescale denudation abstract quantifying controls on glacial erosion over geologic timescales is central to understanding the role of cenozoic climate change on the development of modern mountain belts yet the mechanisms that produce the distinct relief and topography visible in glaciated regions remain poorly constrained we test the hypothesis that commonly assumed glacial sliding parameterizations control denudation rates over geologic timescales we do this by modeling glacier dynamics over a glacial interglacial cycle and compare with a dense dataset of u th he thermochronometer derived denudation rates from the southern coast mountains bc results indicate zones of rapid quaternary erosion correspond to locations where the model predicts the highest averaged sliding velocities the results are consistent with the hypothesis that sliding influences the rate of glacial erosion regression between sliding predicted by the model and erosion rates shows a statistically significant correlation r 2 0 6 the coefficient of the regression 10 5 is smaller than previous estimates based on data from much shorter timescales the model results also reveal that for a specific location active subglacial sliding and hence erosion occurs for only 10 20 of a glacial interglacial cycle suggesting high temporal variations in erosion rates this intermittency of erosion requires instantaneous erosion rates to be greater than long term averages explaining how timescale averaging can impact estimates of glacial erosion rates

features of glacial valley profiles simply explained 1 glacial occupation of alpine valleys results in a distinct signature in the long valley profile including steepening of the profile in the headwaters flattening at lower elevations and a step in the profile at the convergence of headwater tributaries we present analytic results for glacial erosion patterns by making the following assumptions 1 the initial profile is linear 2 the width of the valley is uniform 3 the annual mass balance varies linearly with elevation 4 the glacier at any time is quasi steady 5 the erosion rate is proportional to ice discharge per unit valley width and 6 glacial erosion rates far exceed fluvial erosion rates a steady glacier under these conditions would erode a parabolic divot in the longitudinal valley profile with its maximum depth coinciding with the down valley position of the equilibrium line altitude ela the calculated flattening of the valley floor down valley of the ela and the steepening of it up valley captures the essence of the glacial signature when a reasonable probability distribution of elas is allowed the predicted erosion peaks at 30 40 of the down valley distance to the glacial limit and the pattern merges smoothly with the steeper fluvial profile downstream of the glacial limit profiles of mass balance that are capped at a maximum value produce shorter glaciers and a slight asymmetry in the expected erosion pattern only when we mimic the tributaries of glacial headwaters by specifying a valley width distribution do we obtain the upper step observed in many valley profiles

potential effects of subglacial water pressure fluctuations on quarrying water pressure fluctuations beneath glaciers may accelerate rock fracture by redistributing stresses on subglacial bedrock and changing the pressure of water in bedrock cracks to study the potential influence of water pressure fluctuations on the fracture of subglacial bedrock ice flow over a small bedrock step with a water filled cavity in its lee is numerically modeled and stresses on the bedrock surface are calculated as a function of transient water pressures in the cavity stresses on the bed are then used to calculate principal stress differences within the step rapid reductions in cavity water pressure increase principal stress differences in the bed increasing the likelihood of crack growth in the step and the formation of predominantly vertical fractures relatively impermeable bedrock may be most susceptible to fracturing during water pressure reductions because high water pressure in cracks within the rock can be maintained as water pressure decreases in cavities these results when considered in conjunction with the strong likelihood that increases in water pressure accelerate the removal of rock fragments loosened from the bed suggest that in zones of ice bed separation where water pressure fluctuations typically are large rates of quarrying may be higher than along other parts of glacier beds

the relationship between subglacial water pressure and velocity of findelengletscher switzerland during its advance and retreat findelengletscher switzerland advanced about 250 m between 1979 and 1985 and retreated thereafter subglacial water pressure surface velocity and surface strain rate were determined at several sites the measurements were made early in the melt seasons of 1980 1982 1985 and 1994 and in the autumn of 1983 and the winter of 1984 changes of surface geometry were assessed from aerial photographs the estimated basal shear stress changed little between 1982 and 1994 nevertheless large changes in the relationship of subglacial water pressure and surface velocity were observed which cannot be reconciled with the most commonly used sliding law unless it is modified substantially consideration of possible reasons indicales that a change in the subglacial drainage system occurred probably involving a change in the degree of cavity interconnection isolated cavities damp the variations in sliding velocity that normally result from changes in water pressure because the pressure in isolated cavities decreases as the sliding speed increases in contrast by transmitting water pressure fluctuations to a larger area of the bed interconnected cavities amplify the effect of water pressure fluctuations on sliding speed thus we suggest that an observed decrease in velocity for a given water pressure between 1982 and 1994 was a consequence of a decrease in the interconnectedness of the subglacial cavity system

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

attenuation relations of strong ground motion in japan using site classification based on predominant period a spectral acceleration attenuation model for japan is presented in the present study the data set includes a very large number of strong ground motion records up to the 2003 off tokach main and aftershocks site class terms instead of individual site correction terms are used the site classes of recording stations are from a recent study on site classification for strong motion recording stations in japan according to a classification scheme that has been used in japanese engineering design the use of site class terms enables tectonic source type effects to be identified and accounted for in the present model the effects of a faulting mechanism for crustal earthquakes also are accounted for for crustal and interface earthquakes a simple form of an attenuation model with respect to distance is able to capture the main strong motion characteristics and achieves unbiased estimates for subduction slab events a simple distance modification factor is employed to achieve plausible and unbiased predictions the effects of source depth tectonic source type and faulting mechanism of crustal earthquakes are significant the need for magnitude squared terms is evaluated and the use of magnitude squared terms reduces the interevent error further

glacial hydrology and erosion patterns a mechanism for carving glacial valleys article i nfo article history most glacial erosion models assume that erosion rates are proportional to ice sliding velocity while recent studies have shown that water plays a major role in modulating sliding velocities the impact it might have on erosion rates is still unclear here we incorporate subglacial hydrology into a glacial erosion model that is based on a sliding rule our results explicitly highlight that adding subglacial hydrology has profound impacts on the temporal and spatial patterns of glacial erosion first it suggests that erosion might mainly occur during melting seasons when subglacial water pressure is large and effective pressure is low i e before the channels fully develop and reduce the water pressure at the ice bedrock interface which promotes sliding and erosion second the distribution of erosion is bimodal with a peak at the equilibrium line altitude and as we demonstrate enhanced erosion at much lower altitudes within the ablation area where water due to melting abounds this has important implications because it explains why glacial erosion can simultaneously

dynamics of an alpine cirque glacier alpine cirques are excavated by glacial erosion a process that depends in turn on the movement of ice by basal sliding cirque glacier flow is usually depicted as rotational sliding of a rigid block but this model is based on little evidence and implies unorthodox glacier behavior given typical cirque dimensions the small 1 km2 temperate west washmawapta glacier occupies an archetypal overdeepened and armchair shaped cirque in the canadian rockies we measured 1 the annual surface velocity field 2 ice thickness 3 sliding and internal deformation at one borehole and 4 sliding in a marginal cavity the glacier moves slowly with surface velocities of 3 to 10 m yr the maximum ice thickness 185 m occurs in the center of the cirque basin and roughly coincides with the position of greatest ice flux using our field measurements a standard constitutive relation for ice and simplifying assumptions related to the depth distribution of strain rates we approximated the driving and resisting forces acting on sections of the glacier and inferred the general pattern of basal sliding sliding is minimum in the center of the cirque and increases toward the margins especially up the stoss side of the riegel internal deformation accounts for all motion in the cirque center even if an unusually low viscosity for temperate ice is assumed basal shear stresses tend toward 105 pa everywhere a typical value for mountain glaciers transverse and longitudinal straining are significant in some parts of the glacier although a component of rotational flow must occur internally the glacier does not conform to the rotational sliding model in any essential respect

ice thickness and topographic relief in glaciated landscapes of the western usa abstract the development of relief in glaciated landscapes plays a crucial role in hypotheses relating climate change and tectonic processes in particular glaciers can only be responsible for peak uplift if they are capable of generating significant relief in formerly nonglaciated landscapes previous work has suggested that relief in glaciated landscapes should scale with the thickness of the ice here we summarise a field based test of this hypothesis in two mountain ranges in the western united states the sierra nevada california and the sangre de cristo range colorado these areas exhibit a range of degrees of glacial occupation during the quaternary including some drainage basins essentially unoccupied by ice allowing a detailed exploration of how relief in different parts of a drainage basin evolves in response to glacial modification we mapped last glacial maximum lgm trimlines to estimate the ice thickness at the equilibrium line altitude during the lgm and determined several metrics of relief for drainage basins across the full spectrum of lgm ice extents comparison between measures of relief and ice thickness estimates indicates that relief production in glaciated mountain belts scales with ice thickness and consequently also drainage area we extended our study to the bitterroot range in idaho montana and the teton range in wyoming for a more comprehensive understanding of sub ridgeline relief or missing mass this measure of mean relief is surprisingly little affected by either the degree of glacial modification or the total material removed by glaciers but appears to be influenced by the more active tectonics of the teton range while the effects of glacial modification on the landscape are clear valley widening hanging valley formation the overall change in the relief structure of the mountain ranges studied here is surprisingly modest

on the mathematical description of glaciated valley cross sections morphometric analyses of glaciated valleys typically involve attempts to fit empirical data from valley cross profiles to quadratic parabolic or power law equations with the choice of equation depending on the goal of the analysis in assessing the relative merits of these two types of equations some confusion has arisen because of apparent variations in coordinate system datums between studies which have made use of the power law equation however we show that this confusion relates to a simple mathematical error rather than any true difference in methodology of more significance however is the fact that in fitting a power law equation to observed profiles significant bias is introduced by the use of a logarithmic data transformation because of this implicit bias power law equation parameters are influenced most strongly by data points close in elevation to the centre of the valley and so failure to account for the depositional elements which frequently occur in these areas can lead to significant errors if the aim of the analysis is to characterize the form of the erosional profile

spatial and temporal variations of glacial erosion in the rhone valley swiss alps insights from numerical modeling the present day topography of the european alps shows evidence of intense glacial reshaping however significant questions regarding alpine landscape evolution during glaciations still persist in this study we focus on the rhone valley swiss alps and use a numerical model to estimate patterns and magnitudes of glacial erosion comparing modeling results on a reconstructed pre glacial topography and the present day landforms we find that the landscape response to glaciation is more complex than a simple buzzsaw mechanism by which glacial erosion sets the height of mountain ranges or increase of relief due to localized valley incision instead glacial erosion propagates headward as the landforms evolve from a fluvial to a glacial state leading to an initial increase of local relief followed by subsequent erosion at high elevations it has also been proposed that the mid pleistocene climatic transition of glacial interglacial oscillations from periods of 40 kyr with symmetric shapes to periods of 100 kyr with asymmetric shapes promoted glacial erosion within the alps although this change of climate periodicity may have contributed to enhance glacial erosion our results suggest that other factors such as an increase in rock uplift and or progressive climate cooling are required to explain enhanced glacial carving at view the mathml source 1ma

ground motion attenuation relationships for subduction zone earthquakes in northeastern taiwan subduction zone earthquakes have not been taken into special consid eration in most previous probabilistic seismic hazard analyses psha in taiwan however they may be critical to properly analyze the earthquake hazard in metro politan taipei so they need to be studied strong motion data from subduction zone earthquakes of both interface and intraslab types obtained by the tsmip and smart1 arrays in northeastern taiwan are used to establish the attenuation equa tions for peak ground acceleration pga and response spectral acceleration sa the resultant pga and sa attenuation equations include two site classes and two earth quake source types the ground motion values predicted by these attenuation equa tions are higher than those obtained from the crustal earthquake attenuation equations previously used in taiwan but are lower than those predicted by the attenuation equa tions for worldwide subduction zone earthquakes

testing 3d landform quantification methods with synthetic drumlins in a real digital elevation model metrics such as height and volume quantifying the 3d morphology of landforms are important observations that reflect and constrain earth surface processes errors in such measurements are however poorly understood a novel approach using statistically valid synthetic landscapes to quantify the errors is presented the utility of the approach is illustrated using a case study of 184 drumlins observed in scotland as quantified from a digital elevation model dem by the cookie cutter extraction method to create the synthetic dems observed drumlins were removed from the measured dem and replaced by elongate 3d gaussian ones of equivalent dimensions positioned randomly with respect to the noise e g trees and regional trends e g hills that cause the errors then errors in the cookie cutter extraction method were investigated by using it to quantify these synthetic drumlins whose location and size is known thus the approach determines which key metrics are recovered accurately for example mean height of 6 8 m is recovered poorly at 12 5 0 6 2 m but mean volume is recovered correctly additionally quantification methods can be compared a variant on the cookie cutter using an un tensioned spline induced about twice 1 79 as much error finally a previously reportedly statistically significant p 0 007 difference in mean volume between sub populations of different ages which may reflect formational processes is demonstrated to be only 30 50 likely to exist in reality critically the synthetic dems are demonstrated to realistically model parameter recovery primarily because they are still almost entirely the original landscape results are insensitive to the exact method used to create the synthetic dems and the approach could be readily adapted to assess a variety of landforms e g craters dunes and volcanoes