ground ice and slope sediments archiving late quaternary paleoenvironment and paleoclimate signals at the margins of el gygytgyn impact crater ne siberia an accumulation terrace close to the el gygytgyn impact crater in northeastern siberia contains stratigraphic and periglacial evidence of the paleoenvironmental and paleoclimatic history and permafrost dynamics during late quaternary time a succession of paleo active layer deposits that mirror environmental changes records periods favorable for the establishment and growth of ice wedge polygonal networks and sediment variations these two elements of the periglacial landscape serve as complementary paleoenvironmental archives that can be traced back to 14 000 cal yr bp the slope sediments and the ground ice contained therein have prominent relative maxima and minima in properties grain size total organic content oxygen isotopes they document a regional early holocene thermal maximum at about 9000 cal yr bp followed by a transition to slightly cooler conditions and a subsequent transition to slightly warmer conditions after about 4000 cal yr bp results from sedimentary analysis resemble morphological and geochemical oxygen and hydrogen isotopes results from ice wedge studies in which successive generations of ice wedge polygonal networks record warmer winters in late holocene time moreover peaks of light soluble cation contents and quartz grain surface textures reveal distinct traces of cryogenic weathering we propose a conclusive sedimentation model illustrating terrace formation in a permafrost terrain

earthquake ground motion estimation using strong motion records a review of equations for the estimation of peak ground acceleration and response spectral ordinates abstract engineering seismology is the link between earth sciences and engineering the main input of engineering seismology in engineering design are loading conditions which must satisfy certain conditions regarding their level and frequency of occurrence during the lifetime of a structure one method for estimating these loading conditions is through equations based on strong ground motion recorded during previous earthquakes these equations have a handful of independent parameters such as magnitude and source to site distance and a dependent parameter such as peak ground acceleration pga or spectral acceleration and the coefficients in the equation are usually found by regression analysis this review examines such equations in terms of data selection accelerogram processing techniques of the strong motion records used to construct the equations the characterisation of earthquake source travel path and local site used and regression techniques employed to find the final equations it is found that little agreement has been reached in the past 30 years of ground motion estimation relation studies workers have chosen their techniques based on the available data which varies greatly with geographical region also it is noted that there is a need to include more independent parameters into ground motion estimation equations if the large uncertainties associated with such equations are to be significantly reduced the data required to do this is unfortunately scarce

prediction of rotational ground motion for mining induced seismicity case study from upper silesian coal basin poland abstract for decades coal mining in the upper silesian coal basin uscb in poland has been inducing annually more than 150 seismic events with local magnitude m 2 two sets of sensors were installed in the uscb in poland to measure angular velocities and translational accelerations from seismic events induced by underground coal mining in the period from december 2015 to november 2016 503 seismic events were recorded with local magnitude m between 1 1 and 3 5 analysis of measurement data for induced seismicity confirmed a strong linear correlation between peak ground acceleration of shear s waves pga and peak ground motion of angular velocity prv the observed correlation can be a result of previously observed coupling between the angular instantaneous velocity vector and the respective displacement vector at the ground surface three types of empirical equations for induced seismicity in upper silesia in poland were developed to predict the peak rotational ground motion of the vertical torsion horizontal rocking and instantaneous 3d xyz components the prediction values of horizontal peak angular velocity ground motion indicate that for strong mining induced seismic events in the uscb with a magnitude of m 3 5 we can expect that the mean values of prvh will reach 7 5 mrad s in the epicentral area r 500 m and with magnitude m 4 respectively will reach 19 7 mrad s such values of ground rotation may substantially contribute to the overall seismic response of civil infrastructure particularly for tall buildings the study of angular velocity ground motion is important not only from the cognitive point of view but also from practical significance for assessing the seismic impact on very high buildings chimneys and stability of slopes

magnitude dependent variance of peak ground acceleration abstract we examine the variability of peak horizontal and vertical accelerations of the large california strong motion data set for the time period 1957 to 1991 and find a statistically significant dependence of the standard error on earthquake magnitude specifically the standard error decreases with increasing magnitude the analysis was conducted using a rigorous methodology that examines both earthquake to earthquake inter event variability and within earthquake intra event variability the magnitude dependence is stronger for inter event variability than intra event variability and stronger for horizontal peak acceleration than for vertical peak acceleration the data from the recent landers big bear and northridge earthquakes are consistent with these results

multiple water isotope proxy reconstruction of extremely low last glacial temperatures in eastern beringia western arctic abstract precipitation isotopes are commonly used for paleothermometry in high latitude regions here we present multiple water isotope proxies from the same sedimentary context perennially frozen loess deposits in the klondike goldfields in central yukon canada representing parts of marine isotope stages mis 4 3 and 2 allowing us to uniquely corroborate fractionations and temperature conversions during these late pleistocene cold stages we include new and existing proxy data from relict wedge ice a direct archive for snowmelt relict pore ice an archive for bulk soil water integrating year round precipitation and hydrated volcanic glass shards and fossil plant waxes which are also thought to integrate year round precipitation but are subject to large fractionations in some cases our temperature estimates based on existing proxy data are much cooler than previously estimated due to our use of source water corrections for the glacial ocean new transfer functions calibrated specifically for northern north america d precip 3 1 c 1 t 155 and 18 o precip 0 41 c 1 t 20 2 and novel insights on the apparent net fractionation correction for eastern beringian steppe tundra plant waxes e wax precip 59 10 the snowmelt origin of wedge ice ensures a relatively constrained winter spring seasonality of contributing precipitation as supported by the consistency between water isotope measurements from late holocene wedge ice and modern winter spring precipitation wedge ice dating to the transitional mis 3 2 is isotopically depleted relative to modern spring winter precipitation by an amount that indicates a temperature depression of 14 5 c below modern the soil water origin of pore ice and other proxies integrating year round precipitation from soil water allows for a more variable precipitation seasonality the isotopic composition of modern pore ice is consistent with mean annual precipitation however the isotopic composition of pore ice during mis 3 2 converges on wedge ice values signalling an increase in the ratio of cold to warm season precipitation integrated by pore ice during glacial times possibly due to drier summers as supported by the fossil record and climate model simulations in the study region water isotope proxies integrating year round precipitation may overestimate annual temperature differences between today and recent cold stages due to transient precipitation seasonality as detected here and thus are best interpreted as upper bound estimates based on these proxies we estimate that annual temperatures during mis 4 3 2 and 2 were depressed below the modern climate to a maximum of 18 c 16 c and 21 c 4 5 c respectively our study highlights the value of multiple water isotope proxies towards understanding changes in precipitation seasonality and developing robust reconstructions of past climate and may be particularly important for studies of the major climate transformations over glacial interglacial timescales

modeling of wave propagation in northern los angeles basin abstract the los angeles basin is characterized by deep structural complexity and is the site of numerous earthquakes we analyze the amplitude and waveform data of earthquakes recorded in the los angeles basin in order to identify the structurally controlled path effects this has been done in order to determine which features of the structure affect the observations and to generate improved models in different parts of the basin increasing our capabilities of predicting seismic hazard several structural models of the l a basin that are based on regional subsurface studies exposed sections scattered oil wells and other limited geophysical data have recently become available in this study we have used seismic modeling techniques together with geologic models to attempt to explain site variations in some important data bases we have modeled waveforms of 1 the 19 january 1989 malibu earthquake data recorded in pasadena 2 an m 2 8 earthquake recorded by the usc downhole array in the baldwin hills southern california and 3 two aftershocks of the whittier narrows earthquake recorded at five stations along a profile the modeling of the malibu earthquake results in a layered one dimensional model representing 6 5 km of layered sediment underlain by a high velocity basement direct arrivals basin reflected phases and multiple reverberations are modeled fairly well by this one dimensional model the downhole array data in the baldwin hills show a significant near surface amplification that can be modeled by very low velocity near surface materials a series of aftershocks of the whittier narrows earthquake recorded at close distances at temporary recording sites shows a wide variation in peak accelerations due both to radiation pattern and propagation effects the effect of lateral heterogeneity is evident in the travel time where stations within the basin show later arrival times than those away from the basin for the same epicentral distance seismograms recorded at different sites show variation in waveforms due to multi pathing of rays we use such triplicated arrivals to constrain the structure of different interfaces using these criteria and the synthetic seismograms calculated by ray theory and finite difference methods we have been able to model the tangential seismograms due to two of these events recorded at five stations along a two dimensional profile all three modeling exercises helped us understand wave propagation in the basin environment a basin reflected phase was identified in the seismogram from the malibu earthquake which was used to derive an effective depth of the basement near surface amplification of the waves observed in the downhole data could be explained by constructive interference of the multiply reflected waves through the thin near surface low velocity layer similarly site dependent variation of waveform and travel time shown by the seismograms from the aftershocks of the whittier narrows california earthquake could be accounted for when a laterally varying structure was used

explosive origin of silicic lava textural and δd h2o evidence for pyroclastic degassing during rhyolite effusion a long standing challenge in volcanology is to explain why explosive eruptions of silicic magma give way to lava a widely cited idea is that the explosive to effusive transition manifests a two stage degassing history whereby lava is the product of non explosive open system gas release following initial explosive closed system degassing direct observations of rhyolite eruptions indicate that effusive rhyolites are in fact highly explosive as they erupt simultaneously with violent volcanic blasts and pyroclastic fountains for months from a common vent this explosive and effusive overlap suggests that pyroclastic processes play a key role in rendering silicic magma sufficiently degassed to generate lava here we use precise h isotope and magmatic h2o measurements and textural evidence to demonstrate that effusion results from explosion s lavas are the direct product of brittle deformation that fosters batched degassing into transient pyroclastic channels tuffisites that repetitively and explosively vent from effusing lava our measurements show specifically that d h ratios and h2o contents of a broad suite of explosive and effusive samples from chaiten volcano hydrous bombs plinian pyroclasts tuffisite veins and lava define a single and continuous degassing trend that links wet explosive pyroclasts 1 6 wt h2o d 76 4 to dry obsidian lavas 0 13 wt h2o d 145 7 this geochemical pattern is best fit with batched degassing model that comprises small repeated closed system degassing steps followed by pulses of vapour extraction this degassing mechanism is made possible by the action of tuffisite veins which by tapping already vesicular or brecciated magma allow batches of exsolved gas to rapidly and explosively escape from relatively isolated closed system domains and large tracts of conduit magma by giving them long range connectivity even though tuffisite veins render magma degassed and capable of effusing they are nonetheless the avenues of violent gas and particle transport and thus have the potential to drive explosions when they become blocked or welded shut thus the effusion of silicic lava traditionally thought to be relatively benign process presents a particularly hazardous form of explosive volcanism

formation evolution and inversion of the middle tertiary diligencia basin orocopia mountains southern california the diligencia basin located in the eastern orocopia mountains of southern california contains 1500 2000 m of oligocene miocene continental siliciclastic sedimentary rocks and subordinate limestone and evaporite deposits intercalated with basaltic lavas these rocks are locally intensely folded and faulted defining in present day coordinates an elongate east west trending basin and are unconformably overlain by flat lying late pliocene and pleistocene alluvial deposits the sedimentological stratigraphic and structural history of the basin is compatible with late oligocene early miocene formation as a half graben basin produced by orthogonal basin and range type extension and latest miocene to pliocene basin inversion in either a localized transpressional transverse range regime or a more diffuse compressional regime associated with north south shortening of the entire mojave block facies associations in the lower part of the diligencia basin display a distinctly asymmetric distribution across the basin indicating deposition in a half graben with a steep possibly fault controlled south facing northern escarpment and a more gentle north facing southern slope paleocurrent data particularly from high energy deposits on the northern basin margin indicate stream flow toward the southeast to south southeast oblique to the deformed basin margins and suggest an approximate northeast to east northeast strike for the basin before deformation previously published paleomagnetic data however indicate that the elongate currently east west trending fault block containing the diligencia basin has rotated clockwise by as much as 110 about a vertical axis angle depends on data and model used since deposition ceased if correct this would suggest that the basin may have originally opened to between the northeast and east northeast subparallel to well documented extension directions in miocene age basins in the mojave desert to the east clockwise rotation on east west fault blocks exposed in this region has previously been bracketed as between ca 10 and 4 5 ma structural and paleomagnetic data indicate that inversion of the diligencia basin occurred after block rotation implying a latest miocene to pliocene age for inversion we speculate that basin inversion within a north south and still active compressive stress field resulted from the locking and subsequent internal deformation of this previously passively rotating elongate crustal block

influence of changing atmospheric circulation on precipitation δ18o temperature relations in canada during the holocene postglacial precipitation 18o history has been reconstructed for two regions of canada long term shifts in the oxygen isotope composition of annual precipitation 18op in southern ontario appear to have occurred with a consistent isotope temperature relation throughout the past 11 50014c yr the modern isotope temperature relation in central canada near present boreal treeline evidently became established between 5000 and 4000 years ago although the relation during the last glacial maximum and deglaciation may also have been similar to present in the early holocene however unusually high 18opapparently persisted in spite of low temperature locally probably associated with high zonal index a rudimentary sensitivity analysis suggests that a small reduction in distillation of moisture in pacific air masses traversing the western cordillera perhaps accompanied by a higher summer winter precipitation ratio could have been responsible for the observed effect equivalent isotope temperature anomalies apparently occurred elsewhere in western north america in response to changing early holocene atmospheric circulation patterns suggesting that a time slice map of 18opfor north america during this period might provide a useful target for testing and validation of atmospheric general circulation model simulations using isotopic water tracers

estimation of ground motion variability in the central and eastern united states using deterministic physics based syntheticsestimation of ground motion variability in the ceus using deterministic physics based synthetics

pollen based continental climate reconstructions at 6 and 21 ka a global synthesis subfossil pollen and plant macrofossil data derived from 14c dated sediment profiles can provide quantitative information on glacial and interglacial climates the data allow climate variables related to growing season warmth winter cold and plant available moisture to be reconstructed continental scale reconstructions have been made for the mid holocene mh around 6 ka and last glacial maximum lgm around 21 ka allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth assessment report ar5 of the intergovernmental panel on climate change the synthesis of the available mh and lgm climate reconstructions and their uncertainties obtained using modern analogue regression and model inversion techniques is presented for four temperature variables and two moisture variables reconstructions of the same variables based on surface pollen assemblages are shown to be accurate and unbiased reconstructed lgm and mh climate anomaly patterns are coherent consistent between variables and robust with respect to the choice of technique they support a conceptual model of the controls of late quaternary climate change whereby the first order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance

cryostratigraphy of the klondike muck deposits west central yukon territory four late quaternary cryostratigraphic units are recognized in the unconsolidated valley bottom deposits of the klondike area yukon territory three of the units in ice rich loessal sediments of pre wisconsinan or wisconsinan age collectively compose the king solomon formation they are overlain by a holocene organic unit the units are distinguished by their cryostratigraphic characteristics and oxygen isotope ratios of included ground ice the basal unit is the last chance creek member a pre late wisconsinan deposit containing preserved ice wedges 18o 28 to 26 d 225 to 209 the overlying quartz creek member a late wisconsinan unit is dominated by organic rich loess massive ice is noticeably absent although the sediments are ice rich the isotopic composition of ice in this unit is characteristic of full glacial conditions 18o 32 to 29 d 234 to 257 an abrupt change to warmer and wetter conditions at the end of glaciation prior to the holocene is recorded by the i

stable isotopic evidence for neogene surface downdrop in the central basin and range province authigenic calcite and smectite stable isotopic records were determined for five neogene terrestrial stratigraphic sections from the central basin and range province and surrounding regions we recognized a general pattern of increasing authigenic mineral 18 o values with decreasing age since the middle miocene throughout the region we suggest this pattern results from regional elevation decrease and associated changes in atmospheric circulation patterns an anomalous pattern of decreasing 18 o values with decreasing age is observed in the miocene horse spring formation exposed in the lake mead basin which is contemporaneous with local magmatic activity we suggest this pattern results from surficial uplift of local highlands feeding water into the horse spring depositional system the topographic histories suggested here provide insight into the response of the land surface to crustal processes neogene extensional deformation in the central basin and range province resulted in a net regional elevation decrease

a catalogue of late cenozoic tephra beds in the klondike goldfields and adjacent areas yukon territory preece s j westgate j a froese d g pearce n j g perkins w t 2011 a catlogue of late cenozioc tephra beds in the klondike goldfields and adjacent areas yukon canadian journal of earth sciences 48 10 1386 1418

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

the duparquet formation sedimentation in a late archean successor basin abitibi greenstone belt quebec canada in the south central part of the abitibi greenstone belt a succession of archean epiclastic sediments at least 2 km thick was deposited in the duparquet basin the destor porcupine fault and a secondary fault that splays off the major fault define the margins of this basin which is at least 15 km long and up to 2 5 km wide sedimentary evidence of tectonic influence includes i rapid vertical and lateral facies changes over tens of metres ii cyclic repetition of facies associations iii mixed fining upward coarsening upward fining upward sequences in conglomerate units iv local derivation of most clasts and v asymmetric distribution of fan deltas and braid deltas along the strike of the fault bounded basin three basic facies associations are recognized i conglomerate sandstone facies association csfa ii sandstone argillite facies association safa and iii argillite sandstone facies association asfa the csfa which predominates at the faulted basin margins constitutes 60

comparison of soil derived tetraether membrane lipid distributions and plant wax δd compositions for reconstruction of canadian arctic temperatures abstract polar amplification of climate warming has received much attention as these rapidly rising temperatures have the potential to alter ecosystem function and biogeochemical cycles in particular carbon preserved in arctic tundra soil and permafrost may be especially vulnerable resulting in carbon cycle perturbations providing an additional positive feedback to climate change reliable methods for reconstructing past temperature changes in polar regions have been established from ice cores and marine sediments however techniques for the continental terrestrial environments are lacking but are imperative to examine polar amplification of climate warming here we compare two molecular methods for reconstructing continental annual mean air temperature mat for the canadian arctic based on the distribution of soil bacterial derived glycerol dialkyl glycerol tetraether gdgt membrane lipids mbt cbt proxy and the hydrogen isotopic composition d of plant wax derived n alkanes these two proxies were applied to both modern soil and paleosols collected from the yukon territory canada to evaluate both the accuracy of the reconstructed absolute temperatures as well as the relative change in temperature between the last glacial and the holocene branched gdgt based estimates using the recently revised mbt cbt calibration are overall higher by ca 6 c compared to the original calibration mat estimates for modern soils based on the original mbt cbt calibration are comparable with those based on the d of extracted c29 n alkanes and instrumental data however produced a 6 c higher temperature signal for the glacial paleosols therefore branched gdgt based temperature reconstructions for glacial soils in the high arctic may represent the higher temperatures at the time of soil formation when bacterial activity was optimal whereas d of c29 n alkane plant lipids appear to integrate an average annual signal when used in tandem these geochemical proxies may provide a more comprehensive method for reconstructing arctic paleoclimate

residual analysis of teleseismic p wave energy magnitude estimates inter and intrastation variability p computing the magnitude of an earthquake requires correcting for the propagation effects from the source to the receivers this is often accomplished by performing numerical simulations using a suitable earth model in this work the energy magnitude m e is considered and its determination is performed using theoretical spectral amplitude decay functions over teleseismic distances based on the global earth model ak135q since the high frequency part above the corner frequency of the source spectrum has to be considered in computing m e the influence of propagation and site effects may not be negligible and they could bias the single station m e estimations therefore in this study we assess the inter and intrastation distributions of errors by considering the m e residuals computed for a large data set of earthquakes recorded at teleseismic distances by seismic stations deployed worldwide to separate the inter and intrastation contribution of errors we apply a maximum likelihood approach to the m e residuals we show that the interstation errors describing a sort of site effect for a station are within 0 2 magnitude units for most stations and their spatial distribution reflects the expected lateral variation affecting the velocity and attenuation of the earth s structure in the uppermost layers not accounted for by the 1 d ak135q model the variance of the intrastation error distribution describing the record to record component of variability is larger than the interstation one 0 240 against 0 159 and the spatial distribution of the errors is not random but shows specific patterns depending on the source to station paths the set of coefficients empirically determined may be used in the future to account for the heterogeneities of the real earth not considered in the theoretical calculations of the spectral amplitude decay functions used to correct the recorded data for propagation effects

middle cenozoic uplift and concomitant drying in the central rocky mountains and adjacent great plains when and how the central rocky mountains rockies of western north america gained modern topography remain controversial questions we reconstruct the middle and late cenozoic topography along a transect that extends from the great plains of western nebraska across the central rockies in wyoming based on reconstructed surface water d values from volcanic glass d values our data show gradual increases of surface water d values in both the central rockies and adjacent great plains during middle and late cenozoic time and the establishment of a similar to present surface water d gradient between the central rockies and western great plains before earliest oligocene time these observations suggest that the region underwent differential uplift to form relief similar to that of today before earliest oligocene time this uplift has caused regional drying and the gradual increase of surface water d values over the past 35 m y when placed in the context of other paleoaltimetry studies our work suggests that along our transect the central rockies and adjacent great plains underwent uplift during the late eocene and have not undergone any large magnitude 500 m uplift since that time

arctic ground squirrels of the mammoth steppe paleoecology of late pleistocene middens 24000 29450 14c yr bp yukon territory canada abstract this paper presents paleoecological analyses of 48 fossil arctic ground squirrel spermophilus parryii middens nests and caches recovered from ice rich loess sediments in the klondike region of west central yukon territory ams radiocarbon dates and stratigraphic association of middens with dawson tephra 25 300 14 c yr bp indicate these paleoecological data reflect the onset of glacial conditions of early marine isotope stage mis 2 and terminal mis 3 24 000 29 450 14 c yr bp plant macrofossils include at least 60 plant taxa including diverse graminoids poa elymus trachycaulus kobresia myosuroides steppe forbs penstemon gormanii anemone patens var multifida plantago cf canescens tundra forbs draba spp bistorta vivipara dwarf shrubs salix cf arctica s cf polaris sage artemisia frigida and rare trees picea mariana many of these taxa identified in the middens represent the first recorded fossils for these plants in eastern beringia and add to our knowledge of the floristic composition of pleistocene vegetation and biogeography in this region fossil beetles include typical members of the eastern beringian steppe tundra fauna lepidophorus lineaticollis and connatichela artemisiae and others suggesting predominantly dry open habitats cache forage selection is suggested by some plant taxa which were particularly frequent and abundant in the middens bistorta vivipara kobresia myosuroides ranunculus spp potentilla erysimum cf cheiranthoides poa carex and draba factors such as proximity of vegetation to burrows and abundance of fruits and seeds per plant were probably important in cache selection glacial conditions enabled arctic ground squirrels to form widespread and dense populations in regions such as the klondike in which they are rare or absent at present this fossil midden record supports previous hypotheses that suggest arctic ground squirrels evolved in and are well adapted to the open steppe tundra vegetation loessal soils and glacial climates of the mammoth steppe biome

the grip deuterium excess record abstract ice cores from greenland and antarctica are ideal archives for retrieving long time series of deuterium excess d d 8 18 o a parameter influenced by conditions prevailing in the oceanic regions which provide moisture for polar snow the central greenland grip deuterium excess record has recently been interpreted in terms of oceanic source temperatures both for the holocene and for the last glacial period this approach being less straightforward for the latter period because of changes in the precipitation seasonality between glacial and interglacial periods this article examines why a conventional or sea surface temperature interpretation of the grip excess record seems inconsistent with inferred site and source temperature changes in addition the grip excess record is extended back into the penultimate glacial period and we assess its geographic significance through a comparison with existing dye 3 and north grip data we examine why low d 18o slopes observed during glacial times are associated with low deuterium excess values similarities between the greenland grip and antarctic vostok excess records are discussed in terms of potential links with insolation and insolation gradient changes finally the isotope records in specific do events are examined in light of intruiging differences between the isotope ratios d or 18o and the excess records that may result from a feedback mechanism linked with freshwater oceanic input

critical parameters affecting bias and variability in site response analyses using kik net downhole array data because of the limited number of strong motion records that have measured ground response at large strains any statistical analyses of seismic site response models subject to strong ground motions are severely limited by a small number of observations recent earthquakes in japan including the m w 9 0 tohoku earthquake of march 2011 have substantially increased the observations of strong motion records that can be used to compare alternative site response models at large strains and can subsequently provide insight into the accuracy and precision of site response models using the kiban kyoshin network kik net downhole array data in japan we analyze the accuracy bias and variability precision resulting from common site response modeling assumptions and we identify critical parameters that significantly contribute to the uncertainty in site response analyses we perform linear and equivalent linear site response analyses at 100 kik net sites using 3720 ground motions ranging in amplitude from weak to strong 204 of these records have peak ground accelerations greater than graphic 1 at the ground surface we find that the maximum shear strain in the soil profile the observed peak ground acceleration at the ground surface and the predominant spectral period of the surface ground motion are the best predictors of where the evaluated models become inaccurate and or imprecise the peak shear strains beyond which linear analyses become inaccurate in predicting surface pseudospectral accelerations psa presumably as a result of nonlinear soil behavior are a function of vibration period and are between 0 01 and 0 1 for periods 0 5 s do not display noticeable effects of nonlinear soil behavior online material site specific information and model residuals at 100 kik net stations 1 embed inline graphic 1 gif

vegetation buried under dawson tephra 25 300 14c years bp and locally diverse late pleistocene paleoenvironments of goldbottom creek yukon canada paleoecological research at goldbottom creek in the klondike region of yukon territory nw canada documents an in situ riparian grassy meadow that was buried during the winter or early spring by dawson tephra near the onset of marine isotope stage mis 2 ca 25 300 14 c years bp analyses of vascular plant macrofossils bryophytes pollen insects and paleosols from the riparian meadow contrast with evidence for well drained upland steppe tundra habitats obtained from fossil arctic ground squirrel middens within the same valley the mesic valley bottom vegetation consisted of grasses deschampsia caespitosa alopecurus sedges carex horsetail equisetum cf palustre diverse bryophytes and few forbs upland habitats with dry loessal soils along the valley slopes contained graminoids elymus festuca kobresia myosuroides sage artemisia frigida and diverse steppe and tundra forbs phlox hoodii plantago cf canescens anemone patens var multifida bistorta vivipara draba these paleoecological data highlight the effect of topographic position and moisture on substrates and their control on local scale habitat variability this study represents the first recorded in situ riparian surface from the unglaciated pleistocene refugium of beringia and provides well documented evidence for local habitat heterogeneity and ecosystem structure within the mammoth steppe biome other radiocarbon dated paleoecological data from our study sites indicate that full glacial steppe tundra habitats in west central yukon territory were established during the later stages of the mis 3 interstadial by 29 000 14 c years bp the diverse data obtained through integration of multiple paleoecological methods

simulation of strong ground motion in northern iran using the specific barrier model summary in this study based upon the calibrated specific barrier model sbm against the latest available strong motion data ground motion prediction equations for soil and rock sites in northern iran are developed the sbm may provide the most complete simple and self consistent description of the faulting process which is applicable in both near fault and far field regions consequently the sbm may provide consistent ground motion simulations over the entire necessary frequency range and for all distances of engineering interests to determine source parameters in this study we used 163 three component records of 32 earthquakes with magnitude ranging from mw 4 9 to 7 4 in northern iran in the database records with hypocentral distances less than 200 km are chosen and only earthquakes whose moment magnitude estimates are available have been used furthermore using the best available information recording sites are classified into two main geologic categories rock and soil because of the lack of site amplification information in the most regions of the world including iran we used the h v ratio method for estimating the site amplification moreover the kappa factor that shows diminishing the high frequency amplitude is determined in this study two data sets are considered for determining the source parameters g and l and the h v ratio and the kappa factor only s wave part of signals is used in each analysis regression analysis is performed using random effects method that considers both interseismic event to event and coseismic within event variabilities to effectively deal with the problem of weighting observations from different earthquakes the residuals are controlled against available northern iranian strong ground motion data to verify that the model predictions are unbiased and that there are no significant residual trends with magnitude and distance at first it is assumed that no sign of self similarity breakdown is observed between the source radius and its seismic moment after controlling the results the modified sbm should be used as some deviations have been observed to verify the robustness of the results the number of observations is changed by removing various randomly selected data sets from the original database which results in unchanged results of the model stochastic simulations are then implemented to predict peak ground motion and response spectra parameters the stochastic sbm predictions are in relatively good agreement with other available attenuation relationships proposed for iran europe and middle east it has been shown that the proposed sbm of this study provides unbiased ground motion estimates over the entire frequency range of most engineering applications it provides a reliable and physically realistic yet computationally efficient way to model strong ground motions

autogenic dynamics of alluvial fans in endorheic basins outcrop examples and stratigraphic significance alluvial fans are relatively simple depositional systems due to the direct coupling of sediment sources and adjacent accumulation areas nonetheless general models of alluvial fan evolution and stratigraphy remain elusive due to the great sensitivity of such systems to allogenic controls and their strongly case specific responses autogenic processes intrinsic to alluvial fan dynamics can complicate stratigraphic architectures with effects not easily distinguishable from those of allogenic forcing a distinction is made here between lateral autogenic dynamics tied to spatial sediment distribution over fan surfaces and vertical autogenic dynamics related to independent incision aggradation cycles autogenic mechanisms have been highlighted recently by modelling studies but remain poorly constrained in field based studies examples are presented here from the margins of the cenozoic teruel and ebro basins spain where alluvial fans accumulated thick successions during phases of basin topographic closure and endorheic drainage which promoted forced aggradation fan successions consist of conformable architectures of stacked clastic sheets laterally continuous and with no evidence of internal unconformities inset architectures fan segmentation or preserved incised channels continuous aggradation in these closed basins strongly inhibited vertical autogenic dynamics in the form of fan head and through fan incision due to the forced rise in geomorphic base level and the creation of positive accommodation furthermore the lack of incised channels favoured widespread sediment transport and aggradation over broad fan sectors in relatively short time spans in contrast to the typical occurrence of active lobes and abandoned fan surfaces caused by lateral autogenic dynamics stratigraphic records of alluvial fans developed in endorheic basins are essentially complete and largely unaffected by autogenic processes the latter characteristic implies that they can be more unambiguously interpreted in terms of allogenic forcing because stratigraphic signatures are not complicated by the effects of complex fan autodynamics

interevent and interstation variability computed for the italian accelerometric archive itaca abstract the interevent and interstation ground motion variability of the updated italian strong motion database italian accelerometric archive itaca has been explored through the development of new empirical ground motion prediction equations gmpes for italy the regressions have been performed on 241 three component waveforms from 27 earthquakes with moment magnitudes ranging from 4 8 to 6 9 recorded by 146 stations at distances up to 200 km the site classification follows the schemes previously proposed for italy in which two soil classes are defined considering both shear wave velocity and deposit thickness the regression analysis uses the values of the explanatory variables magnitude fault distance site class and style of faulting recently revised in the framework of a project funded by the italian department of civil protection the equations have been derived for peak ground acceleration peak ground velocity and 5 damped spectral accelerations at 18 periods from 0 03 to 2 sec the residual variance has been decomposed into interevent interstation and record to record components by applying a random effect regression scheme the interevent and interstation error distributions have been analyzed as function of periods to detect sites and events for which predicted values significantly deviate from observations for periods up to 0 35 sec the interstation is the dominant component of variance indicating that an improvement in the site classification could lead to a refinement of the gmpes for longer periods the three components of variance provide similar contributions indicating that a reduction of the uncertainty can be achieved by reducing the epistemic uncertainty affecting the physical model the interevent error highlights the peculiarity of few earthquakes suggesting that the evaluation of regional gmpes can be important when specific scenario studies should be carried out the interstation variability allows us to detect stations with peculiar site response and to assess the goodness of the considered site classification scheme

permafrost evidence for severe winter cooling during the younger dryas in northern alaska 1 the younger dryas cold event a rapid reversion to glacial climate conditions at the pleistocene holocene transition has generally been attributed to the release of meltwater from the laurentide ice sheet to the north atlantic or arctic oceans the reaction of the north pacific region to this shutdown of the thermohaline circulation in the north atlantic during younger dryas is little understood in this paper we present the first radiocarbon dated centennial scale stable water isotope record from permafrost in northern alaska this late glacial winter climate reconstruction from barrow ice wedges demonstrates the existence of a younger dryas cold event formerly believed to be reduced or absent in this area our stable isotope data display a gradual change of the atmospheric moisture source conditions during the younger dryas likely associated with the successive opening of the bering strait

calibration of the specific barrier model to earthquakes of different tectonic regions the specific barrier model proposed and developed by papageorgiou and aki 1983a b 1985 provides the most complete yet parsimonious self consis tent description of the faulting process it applies both in the near fault and in the far field region thus allowing for consistent ground motion simulations over the entire frequency range and for all distances of engineering interest the model has been implemented in the stochastic method and calibrated with extended databases of response spectral amplitudes from earthquakes of intraplate regions mainly east ern north america events interplate regions and regions of tectonic extension spu dich et al 1999 database the ensemble average value of a key parameter of the specific barrier model the local stress drop dr l i s 161 bars for interplate earth quakes 114 bars for extensional regime earthquakes and 180 bars for intraplate earthquakes the high frequency source spectral levels of interplate and extensional regime earthquakes deviate significantly from self similar scaling the deviation is most likely caused by the effective source area and or irregularities in the rupture kinematics we account for their overall effects through a high frequency source complexity factor f in the source spectrum of the specific barrier model as a result inter and intraplate source spectra show similar high frequency levels at moderate magnitudes but intraplate earthquakes have higher spectral levels at the larger mag nitudes the interplate soil residuals show clear signs of nonlinear site response whereas only slight signs of such nonlinearity are observed for the extensional data set the regional models calibrated in this study are in reasonably good agreement with other regional attenuation relationships and provide a reliable and physically realistic yet computationally efficient way to model strong ground motions with implications for seismic hazard and risk analysis online material strong motion station and event station pair information

air temperature snow cover creep of frozen ground and the time of ice wedge cracking western arctic coast the time of ice wedge cracking is examined for several sites with young and old ice wedges along the western arctic coast the correlation between sharp air temperature drops and ice wedge cracking is highest where the snow cover is thin and least where the snow cover is thick the favoured duration and rate of a temperature drop that results in cracking is about 4 days at a rate of about 1 8 c d such temperature drops have a minimal effect in cooling the top of permafrost wherever there is an appreciable snow cover since short duration temperature drops often result in ice wedge cracking the thermal stresses that trigger cracking probably originate more within the frozen active layer than at greater depth in permafrost although most ice wedges tend to crack during periods of decreasing air temperatures about one third of those monitored have cracked during periods of increasing air temperatures long term measurements show that the active layer and top of permafrost move differentially all year in

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

influence of subduction zone structure on coastal and inland attenuation in mexico summary although it has been suggested in the past that the attenuation of seismic waves along the pacific coast of mexico and towards the continent differs the subject has been controversial and as yet unresolved here we re examine this issue using more extensive and higher quality data now available our analysis of more than 450 local and regional r 400 km records from interplate earthquakes 5 0 m w 8 0 10 h 30 km shows that the fourier spectral amplitudes at inland sites exceed those at coastal ones especially in the frequency range of 0 3 2 hz we find that site or source effects are not the cause of this difference the observed disparity of amplitudes is in fact a consequence of the efficient propagation of lg and sms phases along the convergence direction as it is confirmed by numerical modelling the simulations show that the energy radiated by interplate earthquakes is efficiently guided towards the continent by the wedge shape geometry and the structure of the subduction zone thus enhancing the inland wavefield beyond 100 150 km on the contrary for coastal paths there is a rapid drop of amplitude due to lateral heterogeneity and low crustal thickness corresponding to geometrical spreading terms of

northern hemisphere controls on tropical southeast african climate during the past 60 000 years the processes that control climate in the tropics are poorly understood we applied compound specific hydrogen isotopes d and the tex86 tetraether index of 86 carbon atoms temperature proxy to sediment cores from lake tanganyika to independently reconstruct precipitation and temperature variations during the past 60 000 years tanganyika temperatures follow northern hemisphere insolation and indicate that warming in tropical southeast africa during the last glacial termination began to increase 3000 years before atmospheric carbon dioxide concentrations d data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial scale events recorded in northern hemisphere monsoonal climate records this implies that precipitation in tropical southeast africa is more strongly controlled by changes in indian ocean sea surface temperatures and the winter indian monsoon than by migration of the intertropical convergence zone

the oxygen isotopic composition of seawater during the last glacial maximum high resolution oxygen and hydrogen isotope measurements were made on pore fluids from deep sea sediments from sites in the north and south atlantic the data provide direct measurements of changes in the isotopic composition of bottom waters during the last glacial maximum lgm results from ocean drilling program odp site 981 in the north atlantic currently bathed in north atlantic deep water nadw reproduces previous results from the ceara and bermuda rises constraining the glacial interglacial change in 18 o of the deep atlantic to be 0 7 0 8 results from site 984 which is located north of site 981 and at a shallower water depth yield a similar value 0 8 providing insight into the properties of glacial north atlantic intermediate water gnaiw sites from odp leg 177 in the south atlantic span the modern boundary between northern and southern sources of deep water data from the northern site 1088 yield a similar result to sites in the tropical and north atlantic 0 7 at the southern site 1093 located south of the polar front the change is substantially larger 1 1 representing the change in 18 o of southern source waters since the lgm these results confirm previous estimates that the global average change in 18 o of seawater is 1 0 0 1 hydrogen isotopes measured on pore fluids from three sites are consistent with the oxygen isotopes from these locations giving further support to these results at all sites studied the temperature of the deep ocean during the lgm calculated by combining the pore fluid results with oxygen isotope data from benthic foraminifera was within 1 c of the freezing point of seawater

environmental controls on the 2h 1h values of terrestrial leaf waxes in the eastern canadian arctic the hydrogen isotope composition of plant waxes preserved in lacustrine sediments is a potentially valuable tool for reconstructing paleoenvironmental changes in the arctic however in contrast to

mutual climatic range reconstructions of seasonal temperatures based on late pleistocene fossil beetle assemblages in eastern beringia abstract the mutual climatic range mcr method of paleoclimate reconstruction has been employed by paleoentomologists for the last decade a quantitative calibrated method mcr has many advantages over qualitative methods the method has now been developed for arctic faunas climate envelopes for beetle species found in eastern beringia have been compiled using a 25 km gridded north american climate database that pairs climate parameters with modern collection sites linear regressions of predicted on observed values yielded equations used to calibrate the mcr estimates this study presents the initial results from the mcr analysis of 46 fossil beetle assemblages from alaska and the yukon territory the assemblages range in age from about 150 000 9200 yr bp isotope stage six assemblages yielded estimates of mean july temperature tmax 4 5 c colder than at present assemblages associated with the old crow tephra oct dated approximately 140 000 yr bp likewise indicated tmax values well below modern levels isotope stage 5e faunas showed tmax values as much as 3 5 c warmer than modern early wisconsinan assemblages showed climatic cooling with tmax levels dropping as low as 6 c colder than at present a mid wisconsinan interstadial period is marked by warming of mean summer temperatures to near modern levels at some sites last glacial maximum assemblages reflect cooling of tmax to a level about 6 4 c colder than at present although most assemblages from this period yielded mean january temperatures above modern levels warming of summer temperatures began at least by 12 500 yr bp and warmer than modern tmax values were recorded from all assemblages between then and 9200 yr bp

sea level and deep sea temperature variability over the past 5 3 million years ice volume and hence sea level and deep sea temperature are key measures of global climate change sea level has been documented using several independent methods over the past 0 5 million years myr older periods however lack such independent validation all existing records are related to deep sea oxygen isotope 18o data that are influenced by processes unrelated to sea level for deep sea temperature only one continuous high resolution mg ca based record exists with related sea level estimates spanning the past 1 5 myr here we present a novel sea level reconstruction with associated estimates of deep sea temperature which independently validates the previous 0 1 5 myr reconstruction and extends it back to 5 3 myr ago we find that deep sea temperature and sea level generally decreased through time but distinctly out of synchrony which is remarkable given the importance of ice albedo feedbacks on the radiative forcing of climate in particular we observe a large temporal offset during the onset of plio pleistocene ice ages between a marked cooling step at 2 73 myr ago and the first major glaciation at 2 15 myr ago last we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep sea temperature a novel approach to the estimation of sea level and deep sea temperature has been used to determine these quantities over the past 5 3 million years this approach based on oxygen isotope records from the eastern mediterranean shows that temperature and sea level histories are broadly correlated but also show intriguing temporal offsets most records of past sea level variation and associated changes in ocean temperature rely on variations in oxygen isotopes recorded in deep sea marine microorganisms these signals unfortunately are confounded by other influences making it difficult to extract a clear climate related signal eelco rohling and colleagues now present a novel approach to estimating sea level and deep sea temperature variations for the past 5 3 million years the record based on oxygen isotope variations from the eastern mediterranean avoids the issues of the deep sea approach and generally corresponds to an independent record of the past 1 6 million years as expected temperature and sea level are broadly correlated but also show intriguing temporal discontinuities as at the initiation of plio pleistocene ice ages when a major sea level drop lagged a sharp temperature decline by several hundred thousand years

eastern beringia and beyond late wisconsinan and holocene landscape dynamics along the yukon coastal plain canada terrestrial permafrost archives along the yukon coastal plain northwest canada have recorded landscape development and environmental change since the late wisconsinan at the interface of unglaciated beringia i e komakuk beach and the northwestern limit of the laurentide ice sheet i e herschel island the objective of this paper is to compare the late glacial and holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice analyses at these sites involved a multi proxy approach including sedimentology cryostratigraphy palaeoecology of ostracods stable water isotopes in ground ice hydrochemistry and ams radiocarbon and infrared stimulated luminescence irsl dating ams and irsl age determinations yielded full glacial ages at komakuk beach that is the northeastern limit of ice free beringia herschel island to the east marks the late wisconsinan limit of the northwest laurentide ice sheet and is composed of ice thrust sediments containing plant detritus as young as 16 2 cal ka bp that might provide a maximum age on ice arrival late wisconsinan ice wedges with sediment rich fillings on herschel island are depleted in heavy oxygen isotopes mean delta o 18 of 29 1 parts per thousand this together with low d excess values indicates colder than modern winter temperatures and probably reduced snow depths grain size distribution and fossil ostracod assemblages indicate that deglaciation of the herschel island ice thrust moraine was accompanied by alluvial proluvial and eolian sedimentation on the adjacent unglaciated yukon coastal plain until similar to 11 cal ka bp during a period of low glacio eustatic sea level the late glacial holocene transition was marked by higher than modern summer temperatures leading to permafrost degradation that began no later than 11 2 cal ka bp and caused a regional thaw unconformity cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone thermokarst activity led to the formation of ice wedge casts and deposition of thermokarst lake sediments these were subsequently covered by rapidly accumulating peat during the early holocene thermal maximum a rising permafrost table reduced peat accumulation and extensive ice wedge growth resulted from climate cooling starting in the middle holocene until the late 20th century the reconstruction of palaeolandscape dynamics on the yukon coastal plain and the eastern beringian edge contributes to unraveling the linkages between ice sheet ocean and permafrost that have existed since the late wisconsinan

seasonality of the late pleistocene dawson tephra and exceptional preservation of a buried riparian surface in central yukon territory canada abstract the late pleistocene dawson tephra was deposited by one of the largest quaternary eruptions in northwestern north america its distribution is known sparsely from sites near the source area in southwestern alaska and central yukon territory where more than 20 occurrences are documented in the klondike region dawson tephra erupted about 25 300 14 c yr bp near the onset of the last glaciation and provides a stratigraphic marker across eastern beringia we report radiocarbon ages paleobotanical data and cryostratigraphic observations from a new dawson tephra locale at goldbottom creek in the klondike region of yukon territory which collectively indicate that the eruption occurred in the late winter or early spring multiple fining upward tephra rich ice beds are interpreted as remnants of surface icings which presently are common in the region during spring a buried in situ riparian meadow preserved below the icing and tephra consists of abundant tufted hair grass deschampsia caespitosa with interspersed horsetails equisetum cf palustre and mosses detrital plant remains and preserved in situ grass inflorescences entombed in the icing had expelled their fruits consistent with a late season surface when the icing was active the extraordinary thickness of dawson tephra in central yukon likely reflects reworking of a winter deposited tephra by snow melt in the spring following the eruption indicating that the primary thickness may be overestimated at valley bottom sites winter deposition of the tephra may have in part minimized the terrestrial ecological impacts of the eruption on zonal steppe tundra vegetation through the retransportation of tephra from hillslopes to the riparian areas where the tephra became incorporated into local fluvial systems

borehole versus isotope temperatures on greenland seasonality does matter new simulation results obtained with the hamburg atmosphere general circulation model echam 4 under maximum glacial boundary lgm conditions confirm the paleotemperatures on greenland determined by borehole thermometry the disagreement between 18o isotope based temperatures and the borehole temperatures of the lgm is not only reproduced by the model but the simulation results provide a plausible explanation paleotemperatures inferred from 18o measurements in ice cores are biased by a substantially increased seasonality of precipitation over greenland during the lgm during the glacial winter a much more zonal circulation prevents the effective transport of moisture to the greenland ice sheet and therefore reduces the contribution of isotopically strongly depleted winter snow to the annual mean isotope signal

last glacial maximum records in permafrost of the east siberian arctic palaeontological proxy data and cryolithological information from siberian arctic permafrost preserves records of late quaternary climate and environmental conditions in west beringia and their variability which results from interglacial glacial and interstadial stadial dynamics to date the last glacial maximum lgm period has been rather poorly represented in east siberian permafrost records here we present pollen sediment and ground ice stable water isotope data obtained from coastal exposures on bol shoy lyakhovsky island new siberian archipelago arctic ocean that mirror the coldest conditions during the sartan period between about 26 and 22 ka bp using pollen and sediment data for summer conditions and stable water isotope data for winter conditions the pollen record revealed a cold tundra steppe vegetation with characteristic predominance of grass pollen over sedge pollen while the stable isotope ice wedges data indicate extremely cold winter temperatures with mean values of d 18 oo f about 37 dd of about 290 combined with available regional lgm permafrost records that extend from the taymyr peninsula in the west to the yana river lowland in the east the new data set from bol shoy lyakhovsky island indicate that the regional appearance of lgm conditions depended on atmospheric circulation patterns that were influenced by the extent of the northern hemisphere glaciation

large arctic temperature change at the wisconsin holocene glacial transition analysis of borehole temperature and greenland ice sheet project ii ice core isotopic composition reveals that the warming from average glacial conditions to the holocene in central greenland was large approximately 15 c this is at least three times the coincident temperature change in the tropics and mid latitudes the coldest periods of the last glacial were probably 21 c colder than at present over the greenland ice sheet

tectonics and alluvial sedimentation of the upper oligocene lower miocene vasquez formation soledad basin southern california the upper oligocene lower miocene vasquez formation marks the earliest sedimentation in the soledad basin central transverse ranges southern california the vasquez consists primarily of alluvial sediments and presently appears as outcrops in three geographically restricted fault bounded sub basins the two southern sub basins vasquez rocks and texas canyon shared similar tectonic and depositional histories the northernmost sub basin charlie canyon appears to have had a distinct history the soledad basin originated as a predominantly orthogonal rift during the latest oligocene incipient subsidence was concentrated in the southeastern region of the basin as debris flow deposits accumulated as small thick alluvial fans draining local source areas adjacent to vasquez rocks sub basin intense rifting volcanism and rapid subsidence produced the half graben geometry of this sub basin as a source area rose to the south southeast across the active soledad fault coeval displacements along the vasquez canyon and pelona faults led to the asymmetric graben geometry of texas canyon sub basin as abundant detritus derived from an eastern southeastern source interfingered with small debris flow dominated fans along the pelona fault margin periodic faulting and source area uplift followed by tectonic quiescence and erosion produced thick upward fining alluvial megacycles in both sub basins major tectonic uplift in the ancestral san gabriel area led to drainage system enlargement increased water discharge into the depositional systems and deposition by hyperconcentrated flood and braided fluvial processes in both sub basins erosional dissection of mint canyon ridge allowed physical interconnection of the two depocenters at this time charlie canyon sub basin the northernmost vasquez depocenter displays no clast suites or alluvial megacyclicity to suggest close affinities with the other two depocenters a sequence of easterly derived braid plain sediments low in the section is overlain by a 1 600 m upward coarsening alluvial sequence this sequence reflects probable inception of the san francisquito fault uplift of a marine sedimentary quartz monzonite quartz diorite source terrane and northward progradation of an alluvial fan system post oligocene clockwise rotation of the soledad basin by as much as 40 degrees is indicated by paleomagnetic data of other workers restoration of the soledad basin to its oligocene orientation indicates that southeast northwest extension caused rifting and heralded vasquez deposition in small rapidly subsiding basins neither compressional deformation nor strike slip deformation seems to have been a significant factor during vasquez sedimentation the sedimentary and tectonic history of the soledad basin is consistent with a plate tectonic model involving extension in the north american plate north of the unstable mendocino triple junction

the principles of cryostratigraphy abstract cryostratigraphy adopts concepts from both russian geocryology and modern sedimentology structures formed by the amount and distribution of ice within sediment and rock are termed cryostructures typically layered cryostructures are indicative of syngenetic permafrost while reticulate and irregular cryostructures are indicative of epigenetic permafrost cryofacies can be defined according to patterns of sediment characterized by distinct ice lenses and layers volumetric ice content and ice crystal size cryofacies can be subdivided according to cryostructure where a number of cryofacies form a distinctive cryostratigraphic unit these are termed a cryofacies assemblage the recognition if present of i thaw unconformities ii other ice bodies such as vein ice ice wedges aggradational ice and thermokarst cave pool ice and iii ice sand and gravelly pseudomorphs is also important in determining the nature of the freezing process the conditions under which frozen sediment accumulates and the history of permafrost

seismic refraction evidence for steep faults cutting highly attenuated continental basement in the central transverse ranges california a 2 d upper crustal structural profile with seven steeply dipping faults was constructed from the los angeles region seismic experiment phase ii larse ii seismic refraction data recorded over the north central transverse ranges and adjacent mojave desert in southern california the profile extends to a depth of approximately 4 km the faults were identified from distinctive features in the seismic first arrival data while the velocity structure was determined from travel times and refined by forward modelling the resulting seismic velocity structure is correlative to the geological structure along the profile and is used to help constrain a geological cross section six of the seven faults detected from the seismic data correspond directly to geologically mapped faults in the central transverse ranges and adjacent mojave desert from south to north they are the pelona fault the san francisquito fault the clearwater fault the san andreas fault and two faults that cut the portal ridge the seventh fault is buried beneath quaternary deposits of the western mojave desert and appears to correlate with an additional fault that cuts portal ridge out of the section line the southernmost fault the pelona fault separates the younger vasquez formation in the south from the pelona schist in the north and is determined to be an intermediate 40 60 south dipping normal fault this coupled with field observations indicate that the pelona fault was instrumental in the late oligocene early miocene formation of the soledad basin and the structural ascent and exhumation of the pelona schist along the proto sierra pelona intrabasin ridge analogous neogene extensional deformation is found to have affected the western mojave desert region where faults 6 and 7 appear to have had north side down normal displacement and to have been instrumental in forming the western antelope basin a 6 0 km s 1 basal layer to our shallow seismic structure is correlated with the pelona schist south of the san andreas fault and with the tectonically related rand schist beneath the western mojave desert granitic and gneissic crystalline rocks which form regional upper plate complexes along the vincent thrust above the pelona schist and along the rand thrust above the rand schist yield consistently low seismic velocities as compared with the expected velocities for the constituent rock types these anomalous velocities are reconciled by the degraded structural and textural state of the upper plate crystalline rocks that resulted from extreme shearing brittle fracturing and related retrogressive hydration reactions starting during or shortly after the latest cretaceous early palaeocene underthrusting of the schists extension translation along the san andreas transform system and compressional faulting with the uplift of the transverse ranges further accentuated the basement deformations the integrated result is that the survival of the precambrian through mesozoic granitic crust of the region became a rootless and highly attenuated upper crustal layer

strong motion seismology strong motion seismology is concerned with earthquake ground motion in the amplitude range that poses the threat of human injury or property damage because the occurrence of strong motion cannot be predicted in advance and because the time between significant events at any one place may range from tens to thousands of years strong motion data is recorded on triggered instruments that typically must be maintained in readiness for years between periods of significant recording as a consequence the strong motion data set is sparse because of the engineering need for estimates of future ground motion the scope of the field of strong motion seismology encompasses seismic source theory and any other aspect of seismology that can provide insights helpful in making the best possible estimates given the limited data this relationship with the rest of seismology is a reciprocal one in that strong motion data gives perhaps the best information available on earthquake source processes

intra event spatial correlations for cumulative absolute velocity arias intensity and spectral accelerations based on regional site conditions abstract spatial correlations of ground motion intensity measures ims are essential for seismic analysis of spatially distributed systems in this paper geostatistical analysis is conducted to calculate the spatial correlations for cumulative absolute velocity cav arias intensity ia and spectral accelerations sa using a total number of more than 1500 earthquake records from nine recent earthquakes occurred in taiwan california and japan the results indicate that the spatial correlations for these ims are closely related to the regional site conditions and they can be predicted based on the spatial correlations of shear wave velocity in the top 30 m v s 30 in general an im recorded from a relatively homogeneous regional site condition tends to have a larger spatial correlation range than that from a heterogeneous site condition due to their intrinsic similarity to represent the integration of acceleration time histories cav and ia have similar spatial correlation coefficients besides the range of spatial correlation of sa generally increases as the spectral period increases simple predictive equations are proposed in this study to quantify the spatial correlations of cav ia and sa based on regional site conditions methods for data correction are also proposed to eliminate artificial correlations due to biased distance scaling and v s 30 estimation in the database finally monte carlo method is used to generate spatially distributed ims the results demonstrate that the annual frequency of exceedance curves for spatially distributed ims differ significantly if different ranges of spatial correlations are used

implications of volcanism in coastal california for the neogene deformation history of western north america 1 the geologic record of coastal california includes evidence of numerous volcanic centers younger than 30 ma that do not appear to have erupted in an arc setting by correlating these volcanic centers with specific slab windows predicted from analysis of magnetic anomalies on the pacific plate we add new constraints to tectonic reconstructions since 30 ma our correlations such as erupting the morro rock islay hill complex south of the pioneer fracture zone and the iversen basalt south of the mendocino fracture zone require larger displacements within western north america than advocated by most previous authors specifically we infer at least 315 km of motion between the sierra nevada and rigid north america at an azimuth of about n60 w and at least 515 km between baja california and rigid north america in a similar direction a consequence of inferring a large displacement of baja california is that the pacific north american plate boundary must have developed most of its current form prior to 10 ma we interpret a slab window developing between cocos and monterey plates after 19 ma that reconstructs under nearly all of the southern california volcanic centers dated at 18 14 ma most of the sedimentary basins associated with volcanic rocks show brief periods of rapid subsidence synchronous with volcanism followed by slow subsidence of variable but often extended duration consistent with rapid extension of cold lithosphere over recently introduced hot asthenosphere

ice complex formation in arctic east siberia during the mis3 interstadial abstract a continuous 15 m long sequence of ice complex permafrost yedoma exposed in a thermo cirque at the southern coast of bol shoy lyakhovsky island new siberian archipelago dmitry laptev strait was studied to reconstruct past landscape and environmental dynamics the sequence accumulated during the marine isotope stage 3 mis3 interstadial between 49 and 29 ka bp in an ice wedge polygon the frozen deposits were cryolithologically described and sampled on a vertical bluff between two ice wedges according to sedimentological and geochronological data the section is subdivided into three units which correlate with environmental conditions of the early middle and late mis3 period palynological data support this stratification the stable isotope signature of texture ice in the polygon structure reflects fractionation due to local freeze thaw processes while the signature of an approximately 5 m wide and more than 17 m high ice wedge fits very well into the regional stable water isotope record regional climate dynamics during the mis3 interstadial and local landscape conditions of the polygonal patterned ground controlled the ice complex formation the sequence presented here completes previously published mis3 permafrost records in northeast siberia late quaternary stadial interstadial climate variability in arctic west beringia is preserved at millennial resolution in the ice complex a mis3 climate optimum was revealed between 48 and 38 ka bp from the ice complex on bol shoy lyakhovsky island

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

upper crustal structure from the santa monica mountains to the sierra nevada southern california tomographic results from the los angeles regional seismic experiment phase ii larse ii in 1999 the u s geological survey and the southern california earthquake center scec collected refraction and low fold reflection data along a 150 km long corridor extending from the santa monica mountains northward to the sierra nevada this profile was part of the second phase of the los angeles region seismic experiment larse ii chief imaging targets included sedimentary basins beneath the san fernando and santa clarita valleys and the deep structure of major faults along the transect including causative faults for the 1971 m 6 7 san fernando and 1994 m 6 7 northridge earthquakes the san gabriel fault and the san andreas fault tomographic modeling of first arrivals using the methods of hole 1992 and lutter et al 1999 produces velocity models that are similar to each other and are well resolved to depths of 5 7 5 km these models together with oil test well data and independent forward modeling of larse ii refraction data suggest that regions of relatively low velocity and high velocity gradient in the san fernando valley and the northern santa clarita valley north of the san gabriel fault correspond to cenozoic sedimentary basin fill and reach maximum depths along the profile of 4 3 km and 3 km respectively the antelope valley within the western mojave desert is also underlain by low velocity high gradient sedimentary fill to an interpreted maximum depth of 2 4 km below depths of 2 km velocities of basement rocks in the santa monica mountains and the central transverse ranges vary between 5 5 and 6 0 km sec but in the mojave desert basement rocks vary in velocity between 5 25 and 6 25 km sec the san andreas fault separates differing velocity structures of the central transverse ranges and mojave desert a weak low velocity zone is centered approximately on the north dipping aftershock zone of the 1971 san fernando earthquake and possibly along the deep projection of the san gabriel fault modeling of gravity data using densities inferred from the velocity model indicates that different velocity density relationships hold for both sedimentary and basement rocks as one crosses the san andreas fault the larse ii velocity model can now be used to improve the scec community velocity model which is used to calculate seismic amplitudes for large scenario earthquakes

early wisconsinan mis 4 arctic ground squirrel middens and a squirrel eye view of the mammoth steppe abstract fossil arctic ground squirrel spermophilus parryii middens were recovered from ice rich loess sediments in association with sheep creek klondike and dominion creek tephras ca 80 ka exposed in west central yukon these middens provide plant and insect macrofossil evidence for a steppe tundra ecosystem during the early wisconsinan mis 4 glacial interval midden plant and insect macrofossil data are compared with those previously published for late wisconsinan middens dating to 25 2914c ka bp mis 3 2 from the region although multivariate statistical comparisons suggest differences between the relative abundances of plant macrofossils the co occurrence of steppe tundra plants and insects e g elymus trachycaulus kobresia myosuroides artemisia frigida phlox hoodii connatichela artemisiae provides evidence for successive reestablishment of the zonal steppe tundra habitats during cold stages of the late pleistocene arctic ground squirrels were well adapted to the cold arid climates steppe tundra vegetation and well drained loessal soils that characterize cold stages of late pleistocene beringia these glacial conditions enabled arctic ground squirrel populations to expand their range to the interior regions of alaska and yukon including the klondike where they are absent today arctic ground squirrels have endured numerous quaternary climate oscillations by retracting populations to disjunct interglacial refugia during warm interglacial periods e g south facing steppe slopes well drained arctic and alpine tundra areas and expanding their distribution across the mammoth steppe biome during cold arid glacial intervals

rupture dynamics and ground motion from 3 d rough fault simulations 1 we perform three dimensional 3 d numerical calculations of dynamic rupture along non planar faults to study the effects of fault roughness on rupture propagation and resultant ground motion the fault roughness model follows a self similar fractal distribution over length scales spanning three orders of magnitude from 102 to 105 m the fault is governed by a strongly rate weakening friction and the bulk material is subject to drucker prager viscoplasticity fault roughness promotes the development of self healing rupture pulses and a heterogeneous distribution of fault slip at the free surface and at depth the inelastic deformation generated by the large dynamic stress near rupture fronts occurs in a narrow volume around the fault with heterogeneous thickness correlated to local roughness slopes inelastic deformation near the free surface however is induced by the stress waves originated from dynamic rupture at depth and spreads to large distances 10 km away from the fault the present simulations model seismic wave excitation up to 10 hz with rupture lengths of 100 km permitting comparisons with empirical studies of ground motion intensity measures of engineering interest characteristics of site averaged synthetic response spectra including the distance and period dependence of the median values absolute level and intra event standard deviation are comparable to appropriate empirical estimates throughout the period range 0 1 3 0 s this class of model may provide a viable representation of the ground motion excitation process over a wide frequency range in a large spatial domain with potential applications to the numerical prediction of source and path specific effects on earthquake ground motion

nature and origin of a pleistocene age massive ground ice body exposed in the chapman lake moraine complex central yukon territory canada abstract a massive ground ice body was found exposed in the headwall of a thaw flow developed within the chapman lake terminal moraine complex on the blackstone plateau ogilvie mountains central yukon territory which is contemporaneous to the reid glaciation based on visible cryostructures in the 4 m high headwall two units were identified massive ground ice overlain sharply by 2 m of icy diamicton the nature and origin of the chapman lake massive ground ice was determined using cryostratigraphy petrography stable o h isotopes and the molar concentration of occluded gases co2 o2 n2 and ar entrapped in the ice a new technique in the field of periglacial geomorphology that allows to distinguish between glacial and non glacial intrasedimental ice collectively the results indicate that the chapman lake massive ground ice formed by firn densification with limited melting refreezing and underwent deformation near its margin given that the massive ground ice body consists of relict glacier ice it suggests that permafrost persisted at least locally on plateau areas in the central yukon territory since the middle pleistocene in addition the d value of chapman lake relict glacier ice suggests that the ice covering the area during the reid glaciation originated from a local alpine glaciation in the ogilvie mountains

within event and between events ground motion variability from earthquake rupture scenarios measurement of ground motion variability is essential to estimate seismic hazard over estimation of variability can lead to extremely high annual hazard estimates of ground motion exceedance we explore different parameters that affect the variability of ground motion such as the spatial correlations of kinematic rupture parameters on a finite fault and the corner frequency of the moment rate spectra to quantify the variability of ground motion we simulate kinematic rupture scenarios on several vertical strike slip faults and compute ground motion using the representation theorem in particular for the entire suite of rupture scenarios we quantify the within event and the between events ground motion variability of peak ground acceleration pga and response spectra at several periods at 40 stations all approximately at an equal distance of 20 and 50 km from the fault both within event and between events ground motion variability increase when the slip correlation length on the fault increases the probability density functions of ground motion tend to truncate at a finite value when the correlation length of slip decreases on the fault therefore we do not observe any long tail distribution of peak ground acceleration when performing several rupture simulations for small correlation lengths finally for a correlation length of 6 km the within event and between events pga log normal standard deviations are 0 58 and 0 19 respectively values slightly smaller than those reported by boore et al earthq spectra 30 3 1057 1085 2014 the between events standard deviation is consistently smaller than the within event for all correlations lengths a feature that agrees with recent ground motion prediction equations

cryostratigraphic record of permafrost degradation and recovery following historic 1898 1992 surface disturbances in the klondike region central yukon territory we present a detailed cryostratigraphic reconstruction of the degradation and recovery of near surface permafrost in the southern klondike goldfields central yukon territory two ice rich layers a

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