the mutual interaction between continental scale ice sheets and atmospheric stationary waves the great continental ice sheets of the pleistocene represented significant obstacles to the northern hemisphere midlatitude westerlies they must therefore have forced large changes in the atmospheric circulation and consequently also in the patterns of accumulation and melting over the ice sheets themselves a simplified threedimensional coupled ice sheet stationary wave model is developed in order to understand the ice sheet s response to the circulation changes that it induces consistent with ice age climate simulations the ice sheet topography induces an anticyclonic circulation over the ice sheet causing a slight warming over the western slopes and a stronger cooling over the remainder the modeled feedbacks significantly affect the ice sheet configuration with the most important influences being the patterns of summer temperature and the topographically induced precipitation field the time evolution of the ice sheet is also changed by the atmospheric feedbacks and the results suggest the possibility of multiple equilibrium solutions

history and isostatic effects of the last ice sheet in southern british columbia abstract the late wisconsinan cordilleran ice sheet covered british columbia southern yukon territory and parts of alaska washington idaho and montana its major source areas were the high mountain ranges of the canadian cordillera and flow was strongly controlled by topography the last ice sheet began to develop about 30 000 25 000 14c yr ago but it did not achieve its maximum extent until 15 000 14 000 14c yr bp ice sheet growth was interrupted locally by stillstands and retreat ice sheet decay was rapid and was characterized by complex frontal retreat at the periphery accompanied locally by brief readvances and by downwasting and stagnation by 10 000 14c yr bp

the north american cordillera an impediment to growing the continent wide laurentide ice sheet abstractthis study examines the evolution of a continental scale ice sheet on a triangular representation of north america with and without the influence of the cordilleran region simulations are conducted using a comprehensive atmospheric general circulation model asynchronously coupled to a three dimensional thermomechanical ice sheet model the atmospheric state is updated for every 2 106 km3 increase in ice volume and the coupled model is integrated to steady state in the first experiment a flat continent with no background topography is used the ice sheet evolves fairly zonally symmetric and the equilibrium state is continent wide and has the highest point in the center of the continent this equilibrium ice sheet forces an anticyclonic circulation that results in relatively warmer cooler summer surface temperatures in the northwest southeast owing to warm cold air advection and radiative heating due to reduced cloudiness the second experiment includes a simplified representation of t

reduced atlantic storminess during last glacial maximum evidence from a coupled climate model the last glacial maximum lgm 21 000 yr before present was the time of maximum land ice extent during the last ice age a recent simulation of the lgm climate by a state of the art fully coupled global climate model is shown to exhibit strong steady atmospheric jets and weak transient eddy activity in the atlantic sector compared to today s climate in contrast previous work based on uncoupled atmospheric model simulations has shown that the lgm jets and eddy activity in the atlantic sector are similar to those observed today with the main difference being a northeastward extension of their maxima the coupled model simulation is shown to agree more with paleoclimate proxy records and thus is taken as the more reliable representation of lgm climate the existence of this altered atmospheric circulation state during lgm in the model has implications for understanding the stability of glacial climates for the possibility of multiple atmospheric circulation regimes and for the interpretation of paleoclimate proxy records

shallow creep along the 1999 izmit earthquake rupture turkey from gps and high temporal resolution interferometric synthetic aperture radar data 2011 2017 characterizing the spatiotemporal evolution of creep is essential to constrain fault slip budget and understand creep mechanism studies based on interferometric synthetic aperture radar and global positioning system gps satellite observations until 2012 have shown that the central segment of the 17 august 1999 mw 7 4 izmit earthquake on the north anatolian fault began slipping aseismically following the event in the present study we combine new interferometric synthetic aperture radar time series based on terrasar x and sentinel 1a b radar images acquired over the period 2011 2017 with near field gps measurement campaigns performed every 6 months from 2014 to 2016 the mean velocity fields reveal that creep on the central segment of the 1999 izmit fault rupture continues to decay more than 19 years after the earthquake in overall agreement with models of postseismic afterslip decaying logarithmically with time for a long period of time along the fault section that experienced supershear velocity rupture during the izmit earthquake creep continues with a rate up to 8 mm year a significant transient accelerating creep is detected in december 2016 on the sentinel 1 time series near the maximum creep rate location associated with a total surface slip of 10 mm released in 1 month only additional analyses of the vertical velocity fields show a persistent subsidence on the hanging wall block of the golcuk normal fault that also ruptured during the izmit earthquake our results demonstrate that afterslip processes along the north anatolian fault east southeast of istanbul are more complex than previously proposed as they vary spatiotemporally along the fault

simulation of dispersion in layered coastal aquifer systems abstract a density dependent solute transport formulation is used to examine ground water flow in layered coastal aquifers the numerical experiments indicate that although the transition zone may be thought of as an impermeable sharp interface with freshwater flow parallel to the transition zone in homogeneous aquifers this is not the case for layered systems freshwater can discharge through the transition zone in the confining units further for the best simulation of layered coastal aquifer systems either a flow direction dependent dispersion formulation is required or the dispersivities must change spatially to reflect the tight thin confining unit

the mechanisms that determine the response of the northern hemisphere s stationary waves to north american ice sheets abstractstationary waves describe the persistent meanders in the west east flow of the extratropical atmosphere here changes in stationary waves caused by ice sheets over north america are examin

stationary wave reflection as a mechanism for zonalizing the atlantic winter jet at the lgm abstractcurrent estimates of the height of the laurentide ice sheet lis at the last glacial maximum lgm range from around 3000 to 4500 m modeling studies of the lgm using low end estimates of the lis height show a relatively weak and northeastward tilted winter jet in the north atlantic similar to the modern jet while simulations with high end lis elevations show a much more intense and zonally oriented jet here an explanation for this response of the atlantic circulation is sought using a sequence of lgm simulations spanning a broad range of lis elevations it is found that increasing lis height favors planetary wave breaking and nonlinear reflection in the subtropical north atlantic for high lis elevations planetary wave reflection becomes sufficiently prevalent that a poleward directed flux of wave activity appears in the climatology over the midlatitude north atlantic this entails a zonalization of the stationary wave phase lines and thus of the midlatitude jet

variable density flow and solute transport simulation of regional aquifers containing a narrow freshwater saltwater transition zone variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful typically only cases involving wide transition zones have been simulated with variable density transport models possibly because of inaccuracies in the modeling approaches used the major components of a successful approach are threefold first functionally consistent approximation of terms involved in fluid velocity calculations is necessary in the case of galerkin finite element methodology a significant modification is required to the standard approach in order to achieve consistency second the simulator must be verified in a particular series of tests the usual tests using henry s problem for verification of density dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces third adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity the effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern oahu hawaii the transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed simulation of this common situation with an inconsistent approximation gives grossly incorrect results while simulation with a consistent model provides a robust tool for analysis of system hydrology

sea fetch observed by synthetic aperture radar two satellite synthetic aperture radar sar observations of the fetch in the bohai sea of china are presented the sea surface winds derived from sar data indicated a high wind of 15 16 m s that occurred in the fetch zone the winds are shown to have immediate direct mechanical forcing impacts on the significant wave heights hs of ocean surface gravity waves buoy measurements and numerical wave modeling results show that the hs increased to a maximum of 3 5 m in the semienclosed sea 3 h after the passage of the fetch winds and the high hs in the sea was sustained for a total of 6 h the weather research and forecasting wrf model implemented in our modeling simulation captured the wind field responsible for the evolution of the fetch event the model simulated surface horizontal winds agree with the sar derived winds in addition the vertical wind distribution reveals that the fetch wind field reached the 800 hpa level and the event lasted less than one day this study demonstrates the synergy of using sar imagery and the wrf model as effective tools to investigate the lateral and vertical structures of coastal wind

gulf stream and wind induced current variability on the georgia continental shelf winter 1978 low frequency longshore current fluctuations on the continental shelf off georgia and their relationships with local atmospheric forcing and gulf stream displacement were examined for a 3 month period from january to april 1978 acoustic travel time and bottom pressure measurements at a station on the continental slope were used to determine the depth of the main thermocline as an indicator of gulf stream displacement on the middle shelf current variability was dominated by local wind forcing at periods longer than 2 days with very little gulf stream influence longshore wind stress was the main driving force at periods longer than 4 days while cross shore wind contributed at shorter periods in contrast on the outer shelf current fluctuations in the upper layer were highly coherent with gulf stream displacement at a 12 day period and marginally coherent with longshore wind at a 6 day period linear regression analysis showed that gulf stream and local wind forcing accounted for most of the fluctuations in the upper layer over the shelf break for time scales greater than 5 days and at around 2 days a low multiple coherence window at 2 8 5 days was probably due to gulf stream frontal eddies in the lower layer over the shelf break the current fluctuations had a character intermediate between the upper layer currents gulf stream dominated and mid shelf currents wind dominated

an extraordinary breach of the gulf stream north wall by a cold water intrusion 1 a breach of the gulf stream gs north wall by a parcel of cold middle atlantic bight shelf water was observed from october 2 to 5 2001 by a sequence of noaa avhrr sea surface temperature sst images unlike the warm cold core rings generated by gs meanders the path of cold water eventually cuts into the gs subsequently the cold water remained intact and eventually penetrated and transversed the entire width of the gs this is readily apparent in the 3 day sst sequence analysis of wind data from a nearby cman station reveals a high over 12 8 m s and persistent 3 days alongshore wind event occurred prior to the breach an 11 year time series 1991 2001 of local wind measurements show that this type of strong and persistent wind situation is uncommon which may explain why the large scale surface shelf water breach of the gs has not been previously reported

maintenance of northern summer stationary waves in a gcm abstract the maintenance of northern summer stationary waves is studied with data from a 15 year integration of the general circulation model gcm experiment performed at the geophysical fluid dynamics laboratory the model has relatively high resolution rhomboidal 30 wavenumbers 9 vertical levels and simulates the summertime stationary waves reasonably well a steady linear baroclinic model is used to understand the various forcing mechanisms for the northern summer stationary waves the linear model response to global diabatic heating is found to play a dominant role in maintaining the summertime stationary waves in the gcm especially in the subtropics this response to diabatic heating shows a baroclinic structure in the vertical with a node at about 0 5 on the other hand stationary nonlinear interaction terms are found to be largely responsible for the extratropical equivalent barotropic stationary wave features it is hypothesized that this nonlinear interaction is a result of the therm

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

deformation due to the 17 august 1999 izmit turkey earthquake measured from spot images the geometry of the ruptured areas and the coseismic slip distribution data are key to highlighting the behavior of seismic faults this information is generally retrieved from field investigations and geodetic measurements or synthetic aperture radar sar interferometry here we show that spot images can also be used to accurately map the fault zone and to determine the slip distribution by subpixel correlation of images acquired before and after an earthquake the measured slip includes the contribution of possible distributed shear that might not be clearly expressed in surface ruptures and smoothes out possible along strike variability due to near surface fault complexities we apply the technique to the m s 7 4 1999 izmit earthquake our results reveal a 100 m wide and very linear fault zone that can be traced for 70 km from golcuk to akyazi along which supershear rupture has been inferred the obtained slip distribution compares well with the field measurements and is consistent with ground deformation measured at some distance from the fault zone using sar images very little deformation was accommodated off the main fault plane maximum slip is observed near sapanca lake at a small fault jog that has probably influenced rupture propagation

north atlantic eddy driven jet in interglacial and glacial winter climates the atmospheric westerly flow in the north atlantic na sector is dominated by atmospheric waves or eddies generating via momentum flux convergence the so called eddy driven jet the position of this jet is variable and shows for the present day winter climate three preferred latitudinal states a northern central andsouthernpositioninthena here theauthorsanalyzethebehavioroftheeddy drivenjetunderdifferent glacial and interglacial boundary conditions using atmosphere land only simulations with the ccsm4 climate model as state of the art climate models tend to underestimate the trimodality of the jet latitude the authors apply a bias correction and successfully extract the trimodal behavior of the jet within ccsm4 the analysis shows that during interglacial times i e the early holocene and the eemian the preferred jet positions are rather stable and the observed multimodality is the typical interglacial character of the jet during glacial times the jet is strongly enhanced its position is shifted southward and the trimodal behavior vanishes this is mainly due to the presence of the laurentide ice sheet lis the lis enhances stationary waves downstream thereby accelerating and displacing the na eddy driven jet by anomalous stationary momentum flux convergence additionally changes in the transient eddy activity caused by topography changes as well as other glacial boundary conditions lead to an acceleration of the westerly winds over the southernnaattheexpenseofmorenorthernareas consequently bothstationaryandtransienteddiesfoster the southward shift of the na eddy driven jet during glacial winter times

how fast is rupture during an earthquake new insights from the 1999 turkey earthquakes we report that during the two devastating 1999 earthquakes in turkey rupture propagated over a large part of the nearly 200km long fault zone at supershear speed approaching 5km s we present observations and modeling which confirm the original inference of supershear rupture during the izmit earthquake and we show that supershear rupture also occurred during the duzce earthquake we show that the rupture velocity measured about 2 times the shear wave velocity is the value predicted by theoretical studies in fracture dynamics we look for clues to explain these observations

direct observation of rupture propagation during the 1979 imperial valley earthquake using a short baseline accelerometer array abstract the 1979 imperial valley california earthquake m s 6 9 was recorded on the el centro differential array a 213 m long linear array of 5 three component digital accelerometers 5 6 km from the nearest tectonic surface rupture although absolute time was not recorded on the array elements a relative time base was established using the main shock hypocentral p wave and the p and s waves from a later aftershock a cross correlation technique was used to measure the difference in arrival times of individual seismic waves in a moving 0 6 to 1 2 sec window at each array element which would then be converted into the wave9s slowness 1 velocity along the array when applied to the main shock vertical and horizontal accelerograms results from both components of motion indicated that the early arriving energy came from a source to the south of the array and the source of the energy moved rapidly to the north of the array during the strong shaking the ground motions at the array elements were well correlated for about the first 11 sec of motion these observations suggest that we have observed the initiation of rupture south of the array and its subsequent propagation along the fault to a position north of the array in about 10 sec and that the energy was radiated from a fairly compact region around the rupture front if the observed vertical and horizontal ground motions are assumed to be caused by p and s waves respectively then the observed slownesses show irregularities which can be interpreted as implying that the observed high frequency ground motions originated at irregularly distributed regions on the fault surface or that the rupture velocity was variable or both one possible interpretation of the data suggests that the rupture proceeded at near p wave velocity over a 7 km long section of fault average rupture velocities of about 2 7 to 3 2 km sec at 8 km depth are consistent with the data and 2 8 km sec is weakly preferred under the assumption that rupture propagates at a fixed fraction of the shear velocity the large vertical pulse which had a peak acceleration of 1 7 g at e06 was emitted from the portion of the fault extending 25 to 30 km northwest of the hypocenter near meloland overpass and not from the point on the fault closest to the differential array nothing can be said about fault behavior southeast of the hypocenter

earthquake fault superhighways abstract motivated by the observation that the rare earthquakes which propagated for significant distances at supershear speeds occurred on very long straight segments of faults we examine every known major active strike slip fault system on land worldwide and identify those with long 100 km straight portions capable not only of sustained supershear rupture speeds but having the potential to reach compressional wave speeds over significant distances and call them fault superhighways the criteria used for identifying these are discussed these superhighways include portions of the 1000 km long red river fault in china and vietnam passing through hanoi the 1050 km long san andreas fault in california passing close to los angeles santa barbara and san francisco the 1100 km long chaman fault system in pakistan north of karachi the 700 km long sagaing fault connecting the first and second cities of burma rangoon and mandalay the 1600 km great sumatra fault and the 1000 km dead sea fault of the 11 faults so classified nine are in asia and two in north america with seven located near areas of very dense populations based on the current population distribution within 50 km of each fault superhighway we find that more than 60 million people today have increased seismic hazards due to them

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

northern hemisphere storm tracks during the last glacial maximum in the pmip2 ocean atmosphere coupled models energetic study seasonal cycle precipitation mid latitude eddies are an important component of the climatic system due to their role in transporting heat moisture and momentum from the tropics to the poles and also for the precipitation associated with their fronts especially in winter we study northern hemisphere storm tracks at the last glacial maximum lgm and their influence on precipitation using ocean atmosphere general circulation model oagcm simulations from the second phase of the paleoclimate modelling intercomparison project pmip2 the difference with pmip1 results in terms of sea surface temperature forcing fundamental for storm track dynamics is large especially in the eastern north atlantic where sea ice extends less to the south in oagcms compared to atmospheric only gcms our analyses of the physics of the eddies are based on the equations of eddy energetics all models simulate a consistent southeastward shift of the north pacific storm track in winter related to a similar displacement of the jet stream partly forced by the eddies themselves precipitation anomalies are consistent with storm track changes with a southeastward displacement of the north pacific precipitation pattern the common features of north atlantic changes in the lgm simulations consist of a thinning of the storm track in its western part and an amplification of synoptic activity to the southeast in the region between the azores islands and the iberian peninsula which reflects on precipitation this southeastward extension is related to a similar displacement of the jet partly forced by the eddies in the western north atlantic the synoptic activity anomalies are at first order related to baroclinic generation term anomalies but the mean flow baroclinicity increase due to the presence of the laurentide ice sheet is partly balanced by a loss of eddy efficiency to convert energy from the mean flow moisture availability in this region is greatly reduced due to more advection of dry polar air by stationary waves leading to less synoptic scale latent heat release and hence less precipitation also in terms of seasonality the stormy season is shifted later in the year by a few days to a month depending on the season and the model considered this shift does not directly reflect on the first order seasonal cycle of precipitation which also depends on other mechanisms especially in summer

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

temporal correspondence between pluvial lake highstands in the southwestern us and heinrich event 1 pluvial lakes were abundant in the southwestern united states during pleistocene glaciations particu larly in the great basin many of these lakes occupied closed basins therefore fluctuations of their water surface elevations are valuable sources of paleoclimate information histories of the largest lakes are well constrained whereas dozens of smaller lakes that were present in this region have received relatively little scientific attention given their dimensions these smaller lakes were climatically sensitive and can offer important information about quaternary climate variability here we present new ages for the highstands of three previously undated small lakes based on radiocarbon dating of gastropod shells recovered from beach ridges these results are combined with other published and unpublished 14 c ages to yield an extensive compilation of highstand shoreline ages for lakes of all sizes throughout the southwestern us the results indicate that although some lakes reached highstands during the last glacial maximum the strongest temporal correspondence is between highstands and heinrich event h1 these results are consistent with speleothem based reconstructions of effective moisture in the southwestern us which show increased precipitation during stadials of the last glacial cycle copyright 2012 john wiley sons ltd

ice sheets and sea level of the last glacial maximum this paper outlines the general issues regarding ice sheets and sea level of the last glacial maximum lgm which formed the basis of an epilog project workshop papers in this special issue of quaternary science reviews provide a comprehensive assessment of these issues from the perspective of geological reconstructions of ice sheet extent records of sea level change ice sheet modelling geophysical models of glacial isostatic adjustment and geochemical proxies of ice volume this new assessment has substantially narrowed the uncertainties in the total changes in ice sheets and sea level and their proxies suggesting a net decrease in eustatic sea level at the lgm ranging from 120 to 135 m r 2001 elsevier science ltd all rights reserved

understanding the seasonality of orographically forced stationary waves interaction between mechanical and thermal forcing abstract idealized simulations of the atmosphere s stationary response to the rockies tibetan plateau and the greenland ice sheet are made using a nonlinear quasigeostrophic model and are compared to observations observational data indicate low level heating cooling occurs above the rockies and tibet in the summer winter low level cooling is found above greenland in both seasons the atmosphere responds to both diabatic heating termed thermal forcing and low level flow being obstructed by the mountain s presence termed mechanical forcing the response to thermal and mechanical forcing together can be very different from the response to either forcing individually the presence of modest low level heating or cooling 1 5 k day 1 causes significant changes to the mechanical forcing and thereby to the stationary wave response for example while the nonlinear response to mechanical forcing and low level heating is characterized by a cyclone over the orography the response to mechanical forc

last glacial maximum and holocene climate in ccsm3 abstract the climate sensitivity of the community climate system model version 3 ccsm3 is studied for two past climate forcings the last glacial maximum lgm and the mid holocene the lgm approximately 21 000 yr ago is a glacial period with large changes in the greenhouse gases sea level and ice sheets the mid holocene approximately 6000 yr ago occurred during the current interglacial with primary changes in the seasonal solar irradiance the lgm ccsm3 simulation has a global cooling of 4 5 c compared to preindustrial pi conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at lgm tropical sea surface temperature sst cools by 1 7 c and tropical land temperature cools by 2 6 c on average simulations with the ccsm3 slab ocean model suggest that about half of the global cooling is explained by the reduced lgm concentration of atmospheric co2 50 of present day concentrations there is an increase in the antarctic circumpolar current an

an observational study of the northern hemisphere extratropical summertime general circulation abstract the three dimensional structure of the extratropical northern hemisphere summertime general circulation is documented by making use of twice daily operational analyses at nine pressure levels 1000 100 mb for 12 summers 1966 77 two distinct regimes of standing waves quite unlike the wintertime standing waves appear a subtropical regime which is clearly a monsoonal response to thermal forcing and a higher latitude regime in which the standing waves are of smaller scale and much weaker than in winter and tend to be equivalent barotropic in structure with almost no vertical tilt in the mid and upper troposphere while the transient eddies shift poleward from their wintertime location and are weaker in summer their properties and relation to the mean flow are much the same as blackmon et al 1977 lau 1978 1979a b and lau and wallace 1979 found for the winter in both seasons the regions of strongest transient activity generally coincide with the regions where the height scale of the m

abrupt reorganization of north pacific and western north american climate during the last deglaciation dramatic hydroclimate shifts occurred in western north america during the last deglaciation but the timing and mechanisms driving these changes are uncertain and debated and previous modeling has largely relied on linear interpolations between equilibrium snapshot simulations using a published transient climate simulation and a range of proxy records we analyze the region s climate evolution in order to identify the mechanisms governing hydroclimate shifts a rapid loss of ice around 14 000 years ago causes an abrupt reorganization of the circulation which precipitates drying and moistening of southwestern and northwestern north america respectively the atmospheric circulation transitions between two states on a timescale of decades to centuries during which time the westerly jet shifts north by about seven degrees in contrast to previous studies we find that changes in the water budget of western north america prior to this event are not attributable to variations in the position of the jet but rather to the intensity of moisture transport into the continent

on the enigmatic similarity in greenland δ18o between the oldest and younger dryas the last deglaciation 20 0 10 0 kyr b p was punctuated by two major cooling events affecting the northern hemisphere the oldest dryas od 18 0 14 7 kyr b p and the younger dryas yd 12 8 11

continental shelf circulation induced by a moving localized wind stress abstract a linear two dimensional model of a rotating stratified fluid is constructed to investigate the circulation induced by a moving localized line of surface stress this model is used to analyze the effect of moving cold fronts on continental shelf circulation the nature of the induced circulation depends on the relative magnitude of the translation speed of the storm and the natural internal wave speed if the surface stress moves slower than the internal wave speed the disturbance is quasi geostrophic and moves with the storm if the storm moves faster than the internal wave speed two sets of internal inertial waves are produced one set of waves is forced by the surface forcing and travels at the speed of the storm another set of waves is produced by reflection of the directly forced waves from the coastal wall we conclude that free surface deflection slope is responsible for the low frequency quasi geostrophic currents due to passing cold fronts the internal response is composed of t

northern winter stationary waves theory and modeling a review is provided of stationary wave theory the theory for the deviations from zonal symmetry of the climate to help focus the discussion the authors concentrate exclusively on northern winter several theoretical issues including the external rossby wave dispersion relation and vertical structure critical latitude absorption the nonlinear response to orography and the interaction of forced wave trains with preexisting zonal asymmetries are chosen for discussion while simultaneously presenting a decomposition of the wintertime stationary wave field using a nonlinear steady state model

a note on the charleston gyre the deflection of the gulf stream caused by a topographic feature the charleston bump located offshore of savannah georgia results in a quasi stationary cyclonic eddy the charleston gyre which is situated over the continental slope east of charleston and cape romain occasionally the upwelling associated with this eddy produces an enhancement in the surface layer primary production that is great enough to be detected by the nimbus 7 coastal zone color scanner czcs in this note a czcs image with simultaneous hydrography current and wind observations is presented that documents an unusual manifestation of the gyre in addition to the czcs image a seasat synthetic aperture radar sar image is included that clearly indicates the presence of the eddy adjacent to the gulf stream front

a numerical study on the atmospheric circulation over the midlatitude north pacific during the last glacial maximum abstract the dynamics of the atmospheric circulation change over the midlatitude north pacific under the boundary conditions during the last glacial maximum lgm have been studied by atmospheric general circulation models gcms with different ocean feedbacks three boundary conditions in the lgm were different from those of the present day pd ice sheet with elevated topography and high albedo atmospheric co2 concentration and insolation the ocean component was treated as follows a full circulation ocean with dynamical and thermal ocean feedback coupled general circulation model cgcm a slab ocean only with thermal feedback used to calculate the surface heat balance slab ocean gcm sgcm and no ocean feedback by fixing sea surface temperature sst with pure atmospheric dynamics agcm both cgcm and sgcm simulated a weakened pacific high pressure system in boreal summer during the lgm compared to the pd and an intensified aleutian low pressure system in winter both in summer and winter t

ground motion modeling of hayward fault scenario earthquakes part ii simulation of long period and broadband ground motions abstract we simulate long period t 1 0 2 0 s and broadband t 0 1 s ground motions for 39 scenario earthquakes m w 6 7 7 2 involving the hayward calaveras and rodgers creek faults for rupture on the hayward fault we consider the effects of creep on coseismic slip using two different approaches both of which reduce the ground motions compared with neglecting the influence of creep nevertheless the scenario earthquakes generate strong shaking throughout the san francisco bay area with about 50 of the urban area experiencing modified mercalli intensity vii or greater for the magnitude 7 0 scenario events long period simulations of the 2007 m w 4 18 oakland earthquake and the 2007 m w 5 45 alum rock earthquake show that the u s geological survey s bay area velocity model version 08 3 0 permits simulation of the amplitude and duration of shaking throughout the san francisco bay area for hayward fault earthquakes with the greatest accuracy in the santa clara valley san jose area the ground motions for the suite of scenarios exhibit a strong sensitivity to the rupture length or magnitude hypocenter or rupture directivity and slip distribution the ground motions display a much weaker sensitivity to the rise time and rupture speed peak velocities peak accelerations and spectral accelerations from the synthetic broadband ground motions are on average slightly higher than the next generation attenuation nga ground motion prediction equations we attribute much of this difference to the seismic velocity structure in the san francisco bay area and how the nga models account for basin amplification the nga relations may underpredict amplification in shallow sedimentary basins the simulations also suggest that the spudich and chiou 2008 directivity corrections to the nga relations could be improved by increasing the areal extent of rupture directivity with period

mechanics of 3 d shear cracks between rayleigh and shear wave rupture speeds abstract though mode ii shear fractures primarily strike slip earthquakes can not only exceed the shear wave speed of the medium but can even reach the compressional wave speed steady state calculations showed that speeds between the rayleigh and shear wave speeds were not possible thus defining a forbidden zone for more than 30 years it was believed that this result in which the rupture jumps over the forbidden zone also holds for 3 d ruptures in which mode ii and mode iii mainly dip slip faulting are mixed using unprecedentedly fine spatial and temporal grids we show that even in the simple configuration of homogeneous fault properties and linear slip weakening friction law a realistic 3 d rupture which starts from rest and accelerates to some higher velocity actually does pass smoothly through this forbidden zone but very fast the energy flux from the rupture tip is always positive even within the so called forbidden zone contrary to the 2 d case finally our results show that the width of the cohesive zone initially decreases then increases as the rupture exceeds the shear wave speed and finally again decreases as the rupture accelerates to a speed of 90 of the compressional wave speed

steering of westerly storms over western north america at the last glacial maximum the last glacial maximum hydroclimate over western north america differed from the modern climate a proxy model comparison suggests that the glacial storm track was squeezed and steered by atmospheric high pressure systems

seismic imaging of the 1999 izmit turkey rupture inferred from the near fault recordings we use near fault accelerograms to infer the space time history of rupture on the fault during the izmit earthquake the records show that the ground displacement and velocity near the fault were surprisingly simple rupture propagated toward the west at a velocity of about 3 km s and toward the east at a remarkably high average velocity of 4 7 km s over a distance of about 45 km before decelerating to about 3 1 km s on the eastern segment slip on the fault is particularly large down to a depth of 20 km on the central portion of the fault where it reaches about 7 m slip is large also below 10 km on the eastern fault segment and this may have contributed to the loading of shear stress on the duzce fault on the western fault segment large slip seems confined to shallow depths

influence of artificial channels on the source and extent of saline water intrusion in the wind tide dominated wetlands of the southern albemarle estuarine system usa saline water intrusion is degrading water quality in the channelized coastal wetlands of the southern albemarle estuarine system aes the source transport and fate of the saline water in the southern aes was determined by monitoring specific conductivity and water levels in small artificial channels the alligator river the alligator pungo canal and the groundwater system for 12 months results indicate that water levels are affected by wind tides which trigger the movement of saline water into the interior of the wetlands via the small canals the wind tides are mostly driven by episodic southerly winds pushing saline water into the canal network and the groundwater regime proximal to the alligator river the saline waters persist in the canals as long as the wind tide events last specific conductivities from canals and groundwater are shown to be unexpectedly higher closer to the source of the alligator river than toward the albemarle sound suggesting that the large alligator pungo canal facilitates the northward migration of saline water from the pamlico sound to the alligator river overwash and reversals in the flow directions between groundwater and surface water bodies suggest that saline water that is present during wind tide events may migrate into the groundwater system from surface water bodies the results of this study reveal that whereas the large alligator pungo canal channels saline water to the aes small artificial channels may also play significant roles in degrading water quality in the interior of channelized coastal wetlands

north american ice sheet build up during the last glacial cycle 115 21 kyr the last glacial maximum lgm outline and subsequent retreat pattern 21e7 kyr of north americanice sheets are reasonably well established however the evolution of the ice sheets during their build upphase towards the lgm between 115 and 21 kyr has remained elusive making it difficult to verifynumerical ice sheet models for this important time interval in this paper we outline the pre lgm icesheet evolution of the laurentide and cordilleran ice sheets by using glacial geological and geomorphologicalrecords to make a first order reconstruction of ice sheet extent and flow pattern we mappedthe entire area covered by the laurentide and cordilleran ice sheets in landsat mss images andapproximately 40 of this area in higher resolution landsat etm images mapping in aerial photographsadded further detail primarily in quebec labrador the cordilleran region and on baffin island our analysis includes the recognition of approximately 500 relative age relationships from crosscuttinglineations together with previously published striae and till fabric data these are used as the basis forrelative age assignments of regional flow patterns for the reconstruction of the most probable ice sheetevolution sequence we employ a stepwise inversion scheme with a clearly defined strategy for delineatingcoherent landforms swarms reflecting flow direction and configuration and linking these topreviously published constraints on relative and absolute chronology our results reveal that icedispersalcentres in keewatin and quebec were dynamically independent for most of pre lgm time andthat a massive quebec dispersal centre rivalling the lgm in extent existed at times when the sw sectorof the ice sheet had not yet developed the oldest flow system in eastern quebec labrador atlanticswarm had an ice divide closer to the labrador coast than later configurations a northern keewatin central arctic ice sheet existed prior to the lgm but is poorly chronologically constrained there is alsoevidence for older and more easterly cordilleran ice sheet divide locations than those that prevailedduring the late wisconsinan in terms of ice sheet build up dynamics it appears that residual ice capsafter warming phases may have played an important role in particular the location and size of remnantice masses at the end of major interstadials i e ois 5c and 5a must have been critical for subsequentbuild up patterns because such remnant uplands may have fostered much more rapid ice sheetgrowth than what would have occurred on a fully deglaciated terrain the ice sheet configuration duringstadials would also be governed largely by the additional topography that such residual ice constitutesbecause of inherent mass balance topography feedbacks

aspects of numerical and representational methods related to the finite difference simulation of advective and dispersive transport of freshwater in a thin brackish aquifer abstract the simulation of the transport of injected freshwater in a thin brackish aquifer overlain and underlain by confining layers containing more saline water is shown to be influenced by the choice of the finite difference approximation method the algorithm for representing vertical advective and dispersive fluxes and the values assigned to parametric coefficients that specify the degree of vertical dispersion and molecular diffusion that occurs computed potable water recovery efficiencies will differ depending upon the choice of algorithm and approximation method as will dispersion coefficients estimated based on the calibration of simulations to match measured data a comparison of centered and backward finite difference approximation methods shows that substantially different transition zones between injected and native waters are depicted by the different methods and computed recovery efficiencies vary greatly standard and experimental algorithms and a variety of values for molecular diffusivity transverse dispersivity and vertical scaling factor were compared in simulations of freshwater storage in a thin brackish aquifer computed recovery efficiencies vary considerably and appreciable differences are observed in the distribution of injected freshwater in the various cases tested the results demonstrate both a qualitatively different description of transport using the experimental algorithms and the interrelated influences of molecular diffusion and transverse dispersion on simulated recovery efficiency when simulating natural aquifer flow in cross section flushing of the aquifer occurred for all tested coefficient choices using both standard and experimental algorithms

the 1999 izmit earthquake sequence in turkey seismological and tectonic aspects the izmit duzce earthquake sequence is the largest sequence recorded by modern digital networks in the history of turkish earthquakes the m w 7 4 izmit mainshock occurred at 29 967 e and 40 729 n and 13 km depth at 00 hr 01 min 38 7 sec utc on 17 august 1999 and was preceded by at least eight immediate foreshocks of magnitude m l 3 0 aftershock locations show that a large region has become seismically very energetic following the mainshock and that most of the aftershock zone developed quickly in the first 3 days the distribution of the aftershocks illuminates numerous seismotectonic structures associated with the various branches of the north anatolian fault naf in the aftershock zone the seismicity pattern defines a rupture plane that extends about 80 km east and 75 km west of the mainshock epicenter confirming bilateral rupture during the mainshock the western aftershock activity is almost entirely located offshore extending along the axis of the izmit bay we show that the westernmost extent of the mainshock rupture reached the offshore region just 10 km south of the princes islands the dominance of strike slip motion is one of the main characteristics of the izmit sequence a number of significant aftershock clusters occur off the inferred mainshock rupture plane the spatial and temporal occurrence of these clusters show that they are triggered by the complex redistribution of stresses and dynamic strains imposed by the dislocation of the mainshock the focal mechanisms of the events located in the western end of the rupture zone show both strike slip and normal faulting mechanisms we infer that the yalova cluster was triggered by the mainshock the dominance of the normal faulting mechanisms supports the notion that dynamic extensional strains played a major role in triggering this cluster four events located off the princes islands indicate similar source mechanisms characterized by right lateral strike slip motion parallel to the strike of the northern boundary fault nbf and local trend of aftershock distribution this observation leads to a first order seismotectonic evidence that the nature of the nbf which is known to be a transtensional feature at the surface is dominated by strike slip motion at depth the coexistence of strike slip and extensional seismotectonic features in the sea of marmara highlights the importance of strain partitioning amongst shallow transtentional structures accommodating north south extension and deeper structures associated with the naf accommodating east west right lateral shear manuscript received 22 september 2000

the structure of shelf and gulf stream motions in the georgia bight abstract the structure of the current and temperature fields along 30 n over the mid shelf and western blake plateau in the south atlantic bight has been investigated by combining two moored instrument experiments in the summer of 1981 the shelf moorings were part of the second georgia bight experiment gabex ii and the gulf stream mooring data on the blake plateau have been described by lee and waddell 1983 empirical orthogonal functions eof in the frequency domain are used to extract shelf and gulf stream coherent current and temperature fluctuations in the two to 14 day period band three modes are found of which the first two are interpreted as gulf stream meander and frontal eddy circulations the difference between them is chiefly in the shelf motions the first mode is primarily restricted to the shelf edge whereas the second mode penetrates to the 40m isobath the third mode dominates at mid shelf and is the only mode that shows strong coherence with the windstress and local sea level fluctuations the relationship of the modes to the occurrence of mid and inner shelf cold sub surface intrusions generated by shelf edge gulf stream frontal eddies is examined all three modes are found to play a role in the initiation growth and decay of these structures

beryllium 10 chronology of early and late wisconsinan moraines in the revelation mountains alaska insights into the forcing of wisconsinan glaciation in beringia abstract we present 32 new cosmogenic 10be exposure ages from a moraine sequence deposited during the wisconsinan glaciation in the swift river valley revelation mountains western alaska range 10be ages from an early wisconsinan marine isotope stage 4 moraine average 59 7 3 6 ka n 9 excluding one outlier and 10be ages from a late wisconsinan marine isotope stage 2 terminal moraine inboard moraines and two recessional end moraines average 21 3 0 8 ka n 3 excluding two outliers 20 2 1 0 ka n 7 excluding three young outliers 19 6 1 0 ka n 2 excluding one outlier and 17 7 0 8 ka n 4 excluding two outliers respectively the early wisconsinan moraine age coincides with the close of mis 4 consistent with previous chronologies from beringia whereas southern hemisphere glaciers retreated prior to the onset of heinrich stadial 6 64 60 ka the mis 4 glacier advance in the swift river valley terminated at the close of heinrich stadial 6 possibly in response to abrupt north atlantic warming our late wisconsinan ages indicate significant initial glacier retreat between ca 21 3 17 7 ka prior to any significant increase in co2 likely in response to amplified warming from rising insolation preservation of mis 4 moraines in beringia has traditionally been ascribed to limited mis 2 glacier advance modulated by low regional moisture availability stemming from the exposed bering land bridge however we hypothesize that atmospheric re organization forced by the laurentide ice sheet resulted in relatively higher temperatures and drier conditions in beringia during mis 2 than mis 4 allowing for the preservation of early wisconsinan moraines

ice sheet influence on atmospheric circulation explains the patterns of pleistocene alpine glacier records in north america abstract we explore the hypothesis that the relative size of pleistocene ice sheets in north america modulated regional climate and alpine glaciation we compare pleistocene alpine glacier chronologies across north america with a comprehensive general circulation model using reconstructed ice sheet extents at peak glacial conditions during marine isotope stage mis 2 and mis 4 the effect of continent wide ice sheets on atmospheric circulation during mis 2 led to warming in beringia and cooling in the western us less expansive ice sheets during mis 4 resulted in weaker ice sheet modulation of atmospheric circulation this led to preservation of mis 4 moraines in beringia due to limited mis 2 glaciation resulting in a mis 2 4 moraine sequence and overriding of mis 4 moraines for sites with existing chronologies in the western united states during mis 2 resulting in a mis 2 6 moraine sequence our results highlight how influential ice sheets are for regional climate conditions

effects of a low velocity zone on a dynamic rupture dynamic crack earthquake simulations generally assume that the crustal material surrounding faults is laterally homogeneous tomographic and near fault seismic studies indicate that the crust near faults is instead comprised of rocks of varying material velocities we have tested the effects of adding material velocity variation to simulations of spontaneously propagating earthquakes we used two dimensional plane strain conditions coupled with a slip weakening fracture criterion and examined earthquakes on faults that bisect finite width low velocity zones embedded in country rock and earthquakes on faults that bound two different velocity materials when a fault bisects a low velocity zone the normal stress remains unchanged but both the rupture velocity and slip velocity pulse shape are perturbed the presence of the low velocity zone induces high frequency oscillations in the slip function near the rupture front when the fault is on the edge of the low velocity zone the oscillations are more pronounced and repeated sticking and slipping can occur near the rupture front for the slip weakening velocity independent friction model however the temporary sticking does not lead to permanent arrest of slip and slip duration is still controlled by the overall rupture dimension when an earthquake ruptures a fault juxtaposing a lower velocity material against a higher velocity material the normal stress across the fault near the crack tip is perturbed the sign of the normal stress perturbation depends on the direction of rupture leading in some cases to a directional dependence of rupture velocity when slip is accompanied by stress reduction a positive feedback develops between the normal and shear stress changes as previously noted by andrews and ben zion 1997 resulting in an apparently unavoidable grid size dependence in computation of stress change near the rupture front numerical experiments indicate however that the rupture velocity is insensitive to this zone size dependence which is highly localized immediately behind the crack tip the factors controlling the rupture velocity in the simulations including directional dependence are further elucidated by a new analytical solution for rupture of an asperity on a frictionless interface

decomposing observations of high frequency radar derived surface currents by their forcing mechanisms locally wind driven surface currents 1 the wind impulse response function and transfer function for high frequency radar derived surface currents off southern san diego are calculated using several local wind observations the spatial map of the transfer function reflects the influence of the coast on wind current dynamics near the coast within 20 km from the shoreline the amplitudes of the transfer function at inertial and diurnal frequencies are reduced due to effects of coastline and bottom bathymetry meanwhile the amplitude of low frequency currents increases near the coast which is attributed to the local geostrophic balance between cross shore pressure gradients against the coast and currents locally wind driven surface currents are estimated from the data derived response function and their power spectrum shows a strong diurnal peak superposed on a red spectrum similar to the spectra of observed winds current magnitudes and veering angles to a quasi steady wind are typically 2 5 of the wind speed and vary 50 90 to the right of the wind respectively a wind skill map is introduced to present the fractional variance of surface currents explained by local winds as a verification tool for wind data quality and relevance moreover the transfer functions in summer and winter are presented to examine the seasonal variation in ocean surface current response to the wind associated with stratification change

kinematics and correlation of the surface wind field in the south atlantic bight surface winds observed at charleston south carolina and at an offshore buoy located some 300 km to the east of charleston are analyzed to determine operational transformations for estimating the offshore winds from the coastal winds both the statistics describing the wind field at each station along with those describing the correlation between stations are found to be seasonally modulated ensemble averaged by season transfer functions computed by using the first 3 years of available data are applied to a fourth independent data year for assessing their predictive utility the transfer functions and predictability are both seasonally modulated and the transformation matrix is nondiagonal each offshore wind velocity component depends upon both coastal components

a dynamic link between high intensity precipitation events in southwestern north america and europe at the last glacial maximum abstract both hydroclimate proxies and modeling studies alike present compelling evidence for abundant precipitation in southwestern north america and europe at the last glacial maximum lgm however model simulations exhibit an apparent disagreement between changes in precipitation and the orientation of the midlatitude jet streams relative to modern this is surprising as it is well known from modern observations that the jet streams and storm tracks closely follow one another in the time mean the present study shows that a substantial fraction between 35 and 50 of the precipitation along the western seaboards of the northern hemisphere continents at the lgm is due to short lived high intensity events rather than a permanent rearrangement of the circulation moreover these precipitation events are shown to be dynamically linked by a wavenumber 5 stationary wave packet that is trapped in a midlatitude waveguide when the wave energy is concentrated in the eastern north pacific an atmospheric river is excited that makes landfall along the north american west coast days later when the wave packet has reached europe the north atlantic jet stream assumes a zonally oriented state that brings abundant precipitation to the western mediterranean sector understanding the dynamics of this teleconnection pattern is not only key for interpreting proxy data signals in past climates but may also be important for improving predictions of storm track dynamics and water resources availability in the face of climate variability and change

illuminating the near sonic rupture velocities of the intracontinental kokoxili mw 7 8 and denali fault mw 7 9 strike slip earthquakes with global p wave back projection imaging 1 the denali and kokoxili strike slip earthquakes are two of the longest recent intracontinental ruptures previous studies report a range of rupture velocities here we image these earthquakes by reverse time migration of the intermediate frequency p wave train recorded by global broadband seismometers this technique permits a relatively direct measure of rupture velocity speed and direction as constrained by the radiated seismic energy free from restrictive assumptions or rupture speed bounds placed on the solution we compare our results with published seismic gps displacement and surface slip inversion results both ruptures were initially subshear and transitioned over a distance no longer than 40 km to supershear speeds close to the p wave speed of 5 6 km s we investigate the accuracy of our results with synthetic data and experiment with using different imaging parameters and seismic subnetworks these tests allow us to rule out the possibility of subshear speeds along the supershear segments although we cannot exclude supershear speeds of 4 5 6 5 km s our most reliable rupture velocities of 5 6 km s are close to the local p wave speeds we hypothesize that these intracontinental faults have weak shear strengths or high breakdown slips or crustal rigidities and experience at least moderate slip or slip rate weakening our observations and previous published results lead us to speculate that very long surface extending faults with general homogeneity in prestress and fault strength together with smaller adjacent fault segments to provide triggering may be necessary ingredients for the sub rayleigh to supershear rupture speed transition in strike slip earthquakes

abrupt regime shifts in the north atlantic atmospheric circulation over the last deglaciation we analyze modeling results of the north atlantic atmospheric winter circulation from a transient climate simulation over the last 21 000 years in agreement with previous studies we find that the midlatitude jet stream assumes a strong stable and zonal disposition so long as the north american ice sheets remain in their continent wide last glacial maximum lgm configuration however when the laurentide lis and cordilleran ice sheets separate ca 14 000 years ago the jet stream abruptly changes to a tilted circulation regime similar to modern the proposed explanation is that the dominant stationary wave source in the north atlantic sector changes from the lis to the cordilleran mountain range during the saddle collapse as long as the lis dominates the circulation retains the zonal lgm state characterized by prevalent stationary wave reflection in the subtropical north atlantic when the cordillera takes over the circulation acquires its modern disposition

interactions between stationary waves and ice sheets linear versus nonlinear atmospheric response this study examines the mutual interaction between topographically forced atmospheric stationary waves and continental scale ice sheets using a thermomechanical ice sheet model coupled to a linear

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

coseismic and early post seismic slip associated with the 1999 izmit earthquake turkey from sar interferometry and tectonic field observations summary we use combined tectonic field observations and sar data to determine an improved model of the slip associated with the 1999 izmit earthquake which ruptured the north anatolian fault at the eastern end of the sea of marmara the leading goal is to understand the main features of the coseismic and post seismic deformation which are captured together in the sar data to achieve this we make a critical analysis of the ers1 2 sar data which allows atmospheric effects to be identified and removed we also use detailed field mapping and measurements of the earthquake surface rupture dislocations in elastic half space and a forward modelling strategy allow us to obtain a slip model by steps a trial and error approach is combined with conventional inversion techniques to determine the slip in the different regions of the fault the sar data are well explained with three main zones of high slip along the fault releasing a total moment of 2 3 10 20 nm mw 7 6 which is higher than the seismological estimates 1 7 2 0 10 20 n m the inhomogeneous slip distribution correlates with fault segments identified at the surface the izmit rupture appears to have extended 30 km west of the hersek peninsula into the sea of marmara with slip tapering fro m2mt ozero the western end of the rupture is located 40 km sse from istanbul we show that some features seen near to mudurnu and gevye and previously interpreted as slip on secondary faults are explained mostly as atmospheric effects correlated with the topography using our approach and the available gps data we obtain a slip model that represents the coseismic slip alone which suggests that the moment release during the main shock was 1 9 10 20 nm mw 7 5 consistent with the seismological estimates we conclude that the sar data include the effects of 2 m of fast after slip during the month following the main shock within a zone of the fault located 12 24 km below the epicentral region near the hypocentre at a depth of 18 km the fault appears to have experienced dynamic slip of 1 m associated with the main shock followed by 2 m of rapidly decelerating post seismic shear during the following month we suggest that the distribution of heterogeneous slip and loading along the different fault segments may be important factors controlling the propagation of large earthquake ruptures along the north anatolian fault

evidence for a supershear transient during the 2002 denali fault earthquake elastodynamic considerations suggest that the acceleration of ruptures to supershear velocities is accompanied by the release of rayleigh waves along the fault from the stress breakdown zone these waves generate a secondary slip pulse trailing the rupture front but manifest almost entirely in ground motion perpendicular to the fault in the near source region we construct a spontaneously propagating rupture model exhibiting these features and use it to explain ground motions recorded during the 2002 denali fault earthquake at pump station 10 located 3 km from the fault we show that the initial pulses on both the fault normal and fault parallel components are due to the supershear stress release on the fault whereas the later arriving fault normal pulses result from the trailing subshear slip pulse on the fault online material mpeg movies of rupture history and ground motion

methodological study of submarine groundwater discharge from a karstic aquifer in the western mediterranean sea summary a multiproxy approach of complementary techniques is applied to localise and quantify submarine groundwater discharge sgd from el maestrazgo jurassic aquifer an example of widespread carbonate coastal aquifer of the western mediterranean sea castellon spain unconventional water resources are critical in this area where highly populated resorts have been developed the aquifer has two main features of particular interest a karstic system with a deep saturated zone reaching 450 m and with no significant surface discharge occurring within the continental area on the other hand sgd can alter the condition of coastal marine environments reducing salinities and providing nutrients that can cause eutrophication and algal blooms the applied combined techniques make it possible to detect groundwater outflows using airborne thermal infrared tir images to monitor physico chemical anomalies in the sea and to quantify the submarine groundwater discharges by means of direct measurements and radium isotopic analyses three main coastal areas affected by sgd and a submarine spring located at 3 km from the coast which seems to be associated with tectonic discontinuities were localised the calculated fresh sgd from ra isotopes 375 mm 3 y 1 is in agreement with the mean aquifer recharge obtained by hydrogeological methods 394 mm 3 y 1