interglacial collapse of crary trough mouth fan weddell sea antarctica implications for antarctic glacial history abstract in this study we investigate the stratigraphy of a trough mouth fan in the weddell sea to determine possible relationships between basin floor stratigraphy and glaciation on antarctica seismic data from the basin floor show a deep broad and elongate erosional channel filled by thick chaotic facies deposits basin floor fans and channel levee deposits from seismic stratigraphy analysis of basin floor stratigraphy we infer that this channel formed by large volume mass wasting sourced from poorly sorted glacial sediments from crary trough mouth fan and dronning maud land slopes correlation to odp leg 113 site 693 suggests that the mass wasting of the slopes occurred in the early pliocene we surmise that collapse occurred during an early pliocene interglacial and was related to major drawdown of the antarctic ice volume collapse was probably triggered by rebound and relative sea level fall a mathematically predicted geoidal effect related to antarctic ice volume reduction the record of this major ice volume reduction is not manifest in the trough mouth fan but rather is manifest in the basin floor stratigraphy as a major backfilled erosional channel which extends far beyond the trough mouth fan

radiocarbon constraints on ice sheet advance and retreat in the weddell sea antarctica we report here the results of a study aimed at providing radiometric age control on glacial events in the weddell sea during the late quaternary sediment cores from the eastern continental shelf where the east antarctic ice sheet was grounded have recovered glacial marine sediments resting on tills and the latter deposits predate the isotope stage 2 last glacial maximum sediment cores from the continental slope and rise sampled a prominent ice rafted debris layer and radiocarbon ages indicate that this ice rafting event took place prior to 26 000 yr b p thus the combined data indicate that significant deglaciation of the weddell sea continental shelf took place prior to the last glacial maximum our data also suggest that the ice masses that border the weddell sea are more extensive than they were during the previous glacial minimum

the death mask of the antarctic ice sheet comparison of glacial geomorphic features across the continental shelf abstract multibeam swath bathymetry data seismic lines and shallow cores were collected seaward of all of the major drainage outlets of the antarctic ice sheet from the pennell coast of north victoria land to the northwestern weddell sea the results show that during the last glacial maximum the ice sheet extended onto the outer shelf in all areas to the shelf break in many swath bathymetry and deep tow sidescan sonar data from the continental shelf also record the geomorphology left by the retreating ice sheet glacial troughs occur offshore of all major glacial outlets in each drainage area except for parts of the ross sea the inner shelf is characterized by acoustic basement interpreted as crystalline substrate the geomorphology of these inner shelf areas consists of erosional features such as grooves that show that ice flow tended to follow the structural grain of the bedrock outer shelf areas are floored by sedimentary substrate where the direction of ice flow was more directly offshore and depositional features characterize the seafloor in these areas the signature of the grounded ice consists of till deposits and large scale geomorphic features mega scale glacial lineations drumlins occur within the region of contact between crystalline and sedimentary substrates meltwater channels also have been imaged in both inner and outer shelf settings while the presence of meltwater across the shelf has long been suspected we present here the first multibeam image of a meltwater channel on the outer continental shelf of antarctica at the shelf break gullies are in all areas where we know ice reached the shelf break we note the remarkable similarity in form of mega scale glacial lineations observed on the outer shelf over sedimentary substrate across all areas surveyed typically measuring 200 600 m crest to crest this suggests that the shape of these landforms is governed by the same process in each drainage area and that process was occurring under a large area of the ice sheet the erosional and transitional features show much variability in form and distribution

southern weddell sea shelf edge geomorphology implications for gully formation by the overflow of high salinity water 1 submarine gullies are the most common morphological features observed on antarctic continental slopes the processes forming these gullies however remain poorly constrained in some areas gully heads incise the continental shelf edge and one hypothesis proposed is erosion by overflow of cold dense water masses formed on the continental shelf we examined new multibeam echo sounder bathymetric data from the weddell sea continental slope the region that has the highest rate of cold dense water overflow in antarctica ice shelf water isw cascades downslope with an average transport rate of 1 6 sverdrups sv in the southern weddell sea our new data show that within this region isw overflow does not deeply incise the shelf edge the absence of gullies extending deeply into the glacial sediments at the shelf edge implies that cold high salinity water overflow is unlikely to have caused the extensive shelf edge erosion observed on other parts of the antarctic continental margin instead the gullies observed in the southern weddell sea are relatively small and their characteristics indicative of small scale slides probably resulting from the rapid accumulation and subsequent failure of proglacial sediment during glacial maxima

bathymetry of the amundsen sea continental shelf implications for geology oceanography and glaciology the amundsen sea continental shelf is one of the most remote areas of coastal antarctica and was relatively unexplored until the late 1980s over the last two decades increased oceanographic and geological interest has led to several cruises that resulted in sufficient bathymetric data to compile a fairly detailed regional map of the amundsen continental shelf we have combined available multibeam and single beam bathymetry data from various sources and created a new regional bathymetry of the amundsen sea continental shelf and margin deep trough systems that dominate the inner shelf are aligned with present glaciers and separated by shallower ridges shaped by paleo ice streams these features merge into a small number of broader troughs on the middle shelf and shoal seaward they now serve as conduits and reservoirs for relatively warm circumpolar deep water this new compilation is a major improvement over previously available regional maps and should aid the numerical modeling of ocean circulation the reconstructions of paleo ice streams and the refinement of ice sheet models

ice ocean processes over the continental shelf of the southern weddell sea antarctica a review 1 interactions between the southern ocean and the weddell sea ice shelves are important both to the antarctic ice sheet and to the production of globally significant water masses here we review the interaction between the filchner ronne ice shelf and the shelf sea in which it floats the continental shelf processes leading to the production of weddell sea deep and bottom waters from the original off shelf source waters are discussed and a new view is offered of the initial production of high salinity shelf water data from ship based measurements at the ice front from glaciological methods and from measurements made within the sub ice shelf cavity itself are used to describe the pattern of flows beneath the ice shelf we also consider the variability observed within the cavity from tidal to interannual time scales and finish with a discussion of future research priorities in the region

modeling surface deformations at complex strike slip plate boundaries two new versions of the physical base traction model of li and rice 1987 have been developed to study the loading processes and surface deformation near plate boundaries with geometric complexities including a shallow creeping fault segment and two subparallel faults predictions of surface velocity and surface slip rate for the region between the san andreas fault and the pacific coast at the latitude of the parkfield cholame segment using model parameters based on geologic geodetic and seismic considerations were found to be in good agreement with contemporary geodetic field data not used in constraining model parameters also predicted surface velocity for the salton sea coachella valley area were fit to recently derived contemporary geodetic data and very large baseline interferometry data although here the model parameters are not well constrained

the crary fan a trough mouth fan on the weddell sea continental margin antarctica abstract multichannel seismic investigations show the presence of a large trough mouth fan deposit on the continental margin in the southern weddell sea a characteristic feature of the fan is relatively few but large canyons and or channels which appear to have been stable for long periods levees associated with the channels may reach thicknesses of more than 1 km drilling during odp leg 113 recorded the presence of glaciers in east antarctica since early oligocene time and the seismic stratigraphic evidence suggests that the submarine fan is largely composed of glacigenic sediments the channel levee systems and complexes indicate several growth phases apparently controlled by glacial interglacial climate fluctuations with maximum fan growth during glacial periods the present interglacial period is characterized by strong and erosive flow of ice shelf water running down the western slope of the fan and carrying only minor amounts of suspended matter the fan is essentially sediment starved during interglacial periods the dimensions of the channel levee complexes and the persistent loci of sediment supply suggest that turbidite sedimentation resulted from melting of wet based glaciers at or near the shelf edge which has consequently prograded 70 80 km seaward

numerical simulation of the filchner overflow the plume of ice shelf water isw flowing into the weddell sea over the filchner sill contributes to the formation of antarctic bottom water the filchner overflow is simulated using a hydrostatic primitive equation three dimensional ocean model with a 0 5 2 sv isw influx above the filchner sill the best fit to mooring temperature observations is found with influxes of 0 5 and 1 sv below a previous estimate of 1 6 0 5 sv based on sparse mooring velocities the plume first moves north over the continental shelf and then turns west along slope of the continental shelf break where it breaks up into subplumes and domes some of which then move downslope other subplumes run into the eastern submarine ridge and propagate along the ridge downslope in a chaotic manner the next western ridge is crossed by the plume through several paths despite a number of discrepancies with observational data the model reproduces many attributes of the flow in particular we argue that the temporal variability shown by the observations can largely be attributed to the unstable structure of the flow where the temperature fluctuations are determined by the motion of the domes past the moorings our sensitivity studies show that while thermobaricity plays a role its effect is small for the flows considered smoothing the ridges out demonstrate that their presence strongly affects the plume shape around the ridges an increase in the bottom drag or viscosity leads to slowing down and hence thickening and widening of the plume

satellite image derived velocity field of an antarctic ice stream the surface velocity of a rapidly moving ice stream has been determined to high accuracy and spatial density with the use of sequential satellite imagery variations of ice velocity are spatially related to surface undulations and transverse velocity variations of up to 30 percent occur such large variations negate the concept of plug flow and call into question earlier mass balance calculations for this and other ice streams where sparse velocity data were used the coregistration of images with the use of the topographic undulations of the ice stream and the measurement of feature displacement with cross correlation of image windows provide significant improvements in the use of satellite imagery for ice flow determination

a note on the development of the bathymetry of the continental margin west of the antarctic peninsula from 65 to 71 s and 65 to 78 w multibeam data collected during the united states southern ocean global ocean ecosystems dynamics cruises in 2001 and 2002 aboard the r vib nathaniel b palmer were augmented with available multibeam and centerline bathymetry data from a variety of sources to compile a bathymetric data set for the continental shelf west of the antarctic peninsula this new bathymetry data set provides an improvement in the resolution of the bathymetry of the region the improved data set was used to construct a high resolution bathymetric map of the continental margin west of the antarctic peninsula from 65 to 71 s and from 65 to 78 w

strain accumulation in southern california 1973 1984 repeated surveys of selected lines from five trilateration networks along the san andreas fault in southern california have been used to deduce the 1973 1984 strain accumulation records at five localities the secular rate of engineering shear strain accumulation is about 0 3 rad yr with the plane of maximum shear parallel to the local strike of the san andreas fault the secular rate of accumulation of areal dilatation is negligible the data were examined to detect evidence for fluctuations in the rate of strain accumulation for this examination 19 lines were removed from the data set four because they exhibited an obvious coseismic offset and 15 others because they contained at least one very anomalous measurement that could reasonably be attributed to a survey blunder the incidence of such blunders appears to be one in every 75 measurements the remaining data consist of 104 lines with an average of 10 measurements each although the strain accumulation plots for the five networks may exhibit marginally significant temporal fluctuations we are not convinced that those fluctuations are greater than could be attributed to survey error in particular we are unable to demonstrate that the 1973 1979 southern california strain anomaly reported by savage and others is real given the uncertainty in the random and systematic errors in measurement the strain measurements in southern california are marginally consistent with linear in time strain accumulation the strain accumulation plots for the salton network clearly established that unlike the deformation reported after the 1940 imperial valley earthquake no acceleration in the shear strain rate has yet been observed following the 1979 imperial valley earthquake

continuation of a deep borehole stress measurement profile near the san andreas fault 2 hydraulic fracturing stress measurements at black butte mojave desert california hydraulic fracturing stress measurements were obtained in the black butte drill hole 18 km northeast of the san andreas fault in the mojave desert at depths from 251 to 635 m in all tests the least and greatest horizontal principal stresses s h and s h respectively exceeded the vertical stress s indicating a thrust faulting stress regime a single good quality hydraulic fracture impression from 309 m depth indicates an s h direction of n41 e 10 this s h direction should be interpreted with caution because it is based on only one observation this orientation is fairly compatible with nearby surface stress measurements but is incompatible with most of the hydraulic fracturing stress orientations reported from comparable depths in the mojave desert and is not favorable for right lateral slip on either the san andreas fault or nw striking faults present farther to the east the stress regime measured in the black butte hole is comparable to that measured at nearby shallow depths but differs from the strike slip or transitional strike slip to thrust faulting stress regime present at similar depths in two nearby holes crystallaire 4 km northeast of fhe san andreas fault and hi vista 32 km northeast of the san andreas fault the s h direction measured in these holes is approximately 60 counterclockwise of that observed in the black butte hole the differences in stress magnitudes and orientation among these holes substantiate previous indications of local variations in stress in the upper kilometer of the crust in this area and cast doubt on the validity of linear elastic models in which the effects of the san andreas fault dominate the stress field in the western mojave desert

the role of subglacial water in ice sheet mass balance subglacial water can significantly affect the velocity of ice streams and outlet glaciers of ice sheets depending on the geometry and capacity of the subglacial hydrologic system increased surface melting in greenland over the coming decades may influence the ice sheet s mass balance furthermore subglacial lakes in antarctica can modulate ice velocities and act as nucleation points for new fast flowing ice streams in the coming decades significant changes in the polar regions will increase the contribution of ice sheets to global sea level rise under the ice streams and outlet glaciers that deliver ice to the oceans water and deformable wet sediments lubricate the base facilitating fast ice flow the influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system water moving rapidly through a well connected system of conduits or channels will have little impact on ice sheet velocities but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet and thereby trigger increased ice sheet velocities in greenland the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice sheet mass balance in antarctica subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice flow tributaries climate models of ice sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics

divergent trends in land and ocean temperature in the southern ocean over the past 18 000 years reconstructions of land and ocean temperatures over the past 18 000 years in the high southern latitudes have shown conflicting trends analyses of temperatures on campbell island south of new zealand confirm this behaviour and lead to the suggestion that it reflects changes in the position and intensity of the westerly winds over the past 18 000 years sea surface temperatures for the southern ocean do not align with those of the adjacent high latitude landmasses during the late glacial period the ocean surface warmed rapidly to present day temperatures1 whereas the land warmed only slowly as evidenced by the lagged response of forest and glaciers2 3 however in the holocene epoch land based records suggest strong warming whereas marine records indicate that ocean surface temperatures cooled here we present reconstructions of summer temperature for campbell island in the southern ocean over the past 16 500 years based on fossil pollen we find a pronounced warming 12 500 11 000 years ago a cooling until 9 200 years ago and a rapid warming to a peak between 6 000 and 5 000 years ago followed by minor cool intervals from 5 200 4 000 3 000 1 700 and 700 100 years ago as expected our temperature reconstructions show a late glacial lag behind nearby records of sea surface temperature6 7 and opposing trends in the holocene we suggest that this discrepancy arises because land based reconstructions record summer temperatures whereas marine proxies generally reflect annual temperatures we conclude that the divergence of the records therefore reflects changes in the seasonality of atmospheric heat transport as atmospheric heat transport is tied to the southern hemisphere westerly winds we attribute our observed changes to shifts in the position and intensity of the southern westerlies

source parameters for the 1952 kern county earthquake california a joint inversion of leveling and triangulation observations coseismic leveling and triangulation observations are used to determine the faulting geometry and slip distribution of the july 21 1952 mw 7 3 kern county earthquake on the white wolf fault a singular value decomposition inversion is used to assess the ability of the geodetic network to resolve slip along a multisegment fault and shows that the network is sufficient to resolve slip along the surface rupture to a depth of 10 km below 10 km the network can only resolve dip slip near the fault ends the preferred source model is a two segment right stepping fault with a strike of 51 and a dip of 75 sw the epicentral patch has deep 6 27 km left lateral oblique slip while the northeastern patch has shallow 1 12 5 km reverse slip there is nearly uniform reverse slip epicentral 1 6 m northeast 1 9 m with 3 6 m of left lateral strike slip limited to the epicentral patch the seismic moment is m0 9 2 0 5 1019 n m mw 7 2 the signal to noise ratio of the leveling and triangulation data is reduced by 96 and 49 respectively the slip distribution from the preferred model matches regional geomorphic features and may provide a driving mechanism for regional shortening across the comanche thrust and structural continuity with the scodie seismic lineament to the northeast

late weichselian submarine debris flow deposits on the bear island trough mouth fan sedimentary processes on the bear island trough mouth fan during the last glacial were studied using high resolution reflection seismics and gravity cores the fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km2 the large debris flows were generated when the barents sea ice sheet reached the shelf break glacigenic sediments transported to the grounding line were temporarily stored on the upper slope due to the high sedimentation rate the sediments were unstable and earthquakes oversteepening and or build up of excess pore pressure triggered sediment release generating large debris flows sediments were also eroded and incorporated during the downslope flow debris flows were the most important sediment distributing process due to the relatively high shear strength low flow mobility of the glacigenic diamicton and the low fan gradient the weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the early and mid weichselian the barents sea ice sheet might have reached the shelf break twice during the late weichselian on average one large debris flow comprising 18 km3 of sediments was released between every 35 to 75 years during the last glacial maximum

strain accumulation in southern california 1973 1980 frequent surveys of seven trilateration networks in southern california over the interval 1973 1980 suggest that a regional increment in strain may have occurred in 1978 1979 prior to 1978 and after late 1979 the strain accumulation has been predominantly a uniaxial north south compression this secular trend was interrupted sometime in 1978 1979 by an increment in both north south and east west extension in five of the seven networks the onset of this change appears to have occurred first in the networks farthest south the changes occurred without any unusual seismicity within the networks but the overall seismicity in southern california was unusually low prior to and has been unusually high since the occurrence the average principal strain rates for the seven networks in the 1973 1980 interval are 0 17 mu strain yr north south contraction and 0 08 mu strain yr east west extension although the observed increment in strain could be related to unidentifed systematic error in the measuring system a careful review of the measurements and comparison with three other measuring systems reveal no appreciable cumulative systematic error

strain on the san andreas fault near palmdale california rapid aseismic change frequently repeated strain measurements near palmdale california during the period from 1971 through 1980 indicate that in addition to a uniform accumulation of right lateral shear strain engineering shear 0 35 microradian per year across the san andreas fault a 1 microstrain contraction perpendicular to the fault that accumulated gradually during the interval 1974 through 1978 was aseismically released between february and november 1979 subsequently november 1979 to march 1980 about half of the contraction was recovered this sequence of strain changes can be explained in terms of south southwestward migration of a slip event consisting of the south southwestward movement of the upper crust on a horizontal detachment surface at a depth of 10 to 30 kilometers the large strain change in 1979 corresponds to the passage of the slip event beneath the san andreas fault

the role of lateral drag in the dynamics of ice stream b antarctica the partitioning of resistive force between the bed and sides of ice stream b antarctica is obtained for three large areas that have been measured using repeat aerial photogrammetry problems associated with data errors and local variations in ice strength and velocity are reduced by considering the areally averaged budget of forces for each photo block results indicate that the bed under ice stream b must be very weak and unable to provide muche resistance mechanical control on this ice stream emanates almost entirely from the lateral margins

flow of the west antarctic ice sheet on the continental margin of the bellingshausen sea at the last glacial maximum geophysical data show that during the last glaciation the west antarctic ice sheet wais drained to the continental shelf edge of the bellingshausen sea through a cross shelf bathymetric trough belgica trough as a grounded fast flowing ice stream the drainage basin feeding this ice stream probably encompassed southwestern palmer land parts of southern alexander island and the bryan coast of ellsworth land with an area exceeding 200 000 km2 on the inner continental shelf streamlined bedrock and drumlins mapped by swath bathymetry show that the ice stream was fed by convergent ice flow draining from eltanin bay and bays to the east as well as by ice draining the southern part of the antarctic peninsula ice sheet through the ronne entrance the presence of a paleoice stream in belgica trough is indicated by megascale glacial lineations formed in soft till and a trough mouth fan on the continental margin grounding zone wedges on the inner and midshelf record ice marginal stillstands during deglaciation and imply a staggered pattern of ice sheet retreat these new data indicate an extensive wais at the last glacial maximum lgm on the bellingshausen sea continental margin which advanced to the shelf edge in conjunction with ice sheet reconstructions from the antarctic peninsula and pine island bay this implies a regionally extensive ice sheet configuration during the lgm along the antarctic peninsula bellingshausen sea and amundsen sea margins with fast flowing ice streams draining the wais and antarctic peninsula ice sheet to the continental shelf edge

use of total grain size distributions to define bed erosion and transport for poorly sorted sediment undergoing simulated bioturbation abstract flume experiments were conducted using poorly sorted beds made to resemble those glacial deposits that blanket the antarctic seafloor today flow within the flume was gradually increased over 2 cm s 1 increments up to 20 cm s 1 an initial run was made without altering the bed and two additional runs were made in which the bed was mechanically mixed in order to simulate bioturbation initial and efficient transport of a given size particle was determined using total grain size distribution data for samples taken from the residual bed from trays placed at different elevations above the floor of the flume and from the water column using this method we were able to measure the current velocities at which initial movement occurred as well as relate different modes of transport for given size ranges to current velocity without mixing the bed current velocities greater than 16 cm s 1 were required to initiate particle movement but because the bed became armored this initial movement was not reflected in the total grain size distribution of the bed with mixing a residual bed containing little silt and clay was produced at velocities of only a few centimeters per second once fines were removed from the bed sand sized material began to move by either traction or saltation a curve relating current velocity to sediment transport by bed load traction and saltation intermittent suspension and suspension is presented the results of our flume experiments demonstrate how sorted sediments are presently being derived from cohesive often overcompacted poorly sorted glacial sediments on high latitude continental shelves where measured current velocities are less than 20 cm s 1 the antarctic seafloor for example furthermore we have gained important information about the true meaning of grain size data as it relates to current velocity mean grain size sorting and skewness reflect not only current velocity but also the efficiency with which the bed was mixed therefore attempts to reconstruct paleovelocity using only these parameters may be meaningless

the determination of displacement fields from geodetic data along a strike slip fault observations of angles or distances between stations of a geodetic network are commonly used to infer information about the movement of the surface of the earth the absence of any observations external to the network leads to an ambiguous displacement field existing techniques for eliminating this ambiguity are all unsatisfactory in some respect the best technique an inner coordinate solution is not appropriate for networks located in a strike slip fault environment the inner coordinate solution zeros the rotation of all stations about their center of mass along a strike slip fault like the san andreas however motion normal to the fault is less likely than motion parallel to the fault the solution presented here an outer coordinate solution finds the rotation of the network that minimizes the components of displacement normal to the fault since motion along a strike slip fault is generally expected to be parallel to the fault the displacements obtained with the outer coordinate solution are more reasonable than those obtained with other techniques examination of a trilateration network near san francisco bay demonstrates the large effect that the choice of adjustment technique can have on the inferred relative motion of the two sides of the fault the inner coordinate solution gave a rate of about 1 mm yr whereas the preferred outer coordinate solution rate was 36 mm yr

crustal strain near the big bend of the san andreas fault analysis of the los padres tehachapi trilateration networks california in the region of the los padres tehachapi geodetic network the san andreas fault saf changes its orientation by over 30 degree from n 40 degree w close to that predicted by plate motion for a transform boundary to n 73 degree w the strain orientation near the saf is consistent with right lateral shear along the fault with maximum shear rate of 0 38 plus minus 0 01 mu rad yr at n 63 degree w in contrast away from the saf the strain orientations on both sides of the fault are consistent with the plate motion direction with maximum shear rate of 0 19 plus minus 0 01 mu rad yr at n 44 degree w the strain rate does not drop off rapidly away from the fault and thus the area is fit by either a broad shear zone below the saf or a single fault with a relatively deep locking depth the fit to the line length data is poor for locking depth d less than 25 km for d of 25 km a buried slip rate of 30 plus minus 6 mm yr is estimated the authors also estimated buried slip for models that include the garlock and big pine faults in addition to the saf slip rates on other faults are poorly constrained bymore the los padres tehachapi network the best fitting garlock fault model had computed left lateral slip rate of 11 plus minus 2 mm yr below 10 km buried left lateral slip of 15 plus minus 6 mm yr on the big pine fault within the western transverse ranges provides significant reduction in line length residuals however deformation there may be more complicated than a single vertical fault a subhorizontal detachment on the southern side of the saf cannot be well constrained by these data the authors investigated the location of the saf and found that a vertical fault below the surface trace fits the data much better than either a dipping fault zone located south of the surface trace less

geodetic measurement of deformation in the central mojave desert california data from triangulation and trilateration surveys made during 1934 1982 are used to calculate shear strain rates in the central mojave desert of california for the region between the helendale and camp rock faults the shear strain rate was determined to be 0 16 0 03 strain yr with maximum right lateral shear strain occurring on a plane oriented n41 w 5 if we assume that this deformation is due to right lateral motion across the northwest trending local faults the average shear straining corresponds to a relative displacement of 6 7 1 3 mm yr across this portion of the network accounting for 12 of the predicted 56 mm yr of relative motion between the north american and pacific plates from the camp rock fault eastward across the network there is a transition from significant to very low strain rates examination of nine focal mechanisms and their relation to the local geology and the strain data suggests that most of the long term displacement occurs on the major northwest trending faults oriented nearly along the direction of relative motion between the north american and pacific plates secondary faulting controlled by a coulomb anderson failure mechanism or by slip on preexisting faults can account for the occurrence of earthquakes on faults of other orientations

extent and dynamics of the west antarctic ice sheet on the outer continental shelf of pine island bay during the last glaciation abstract swath bathymetry and topas sub bottom profiler acoustic data reveal the presence of a major cross shelf bathymetric trough containing streamlined subglacial bedforms formed in soft till that extends to the continental shelf edge of outer pine island bay amundsen sea west antarctica the new data indicate that the west antarctic ice sheet wais extended to the shelf edge of pine island bay during the last glaciation and was drained by a grounded fast flowing palaeo ice stream through this outer shelf trough topography and subglacial geology are likely to have exerted a strong control on the development and location of palaeo ice streams in pine island bay topas records show that mega scale glacial lineations are formed in an acoustically transparent sediment layer interpreted to be soft till and are inferred to be the product of subglacial sediment deformation beneath the palaeo ice stream the flat to irregular nature of the basal reflector of the acoustically transparent layer of soft till implies that a combination of groove ploughing of the substrate and subglacial sediment deformation were important processes beneath the palaeo ice stream in the outer trough of pine island bay as well as palaeo ice streams elsewhere in antarctica therefore the formation of the soft till layer and possibly associated subglacial bedforms are likely to be a function of these palaeo ice stream processes in a regional context the wais extended to the continental shelf edge of the bellingshausen amundsen and ross seas and was drained by a number of palaeo ice streams during the last glaciation

the sedimentary legacy of a palaeo ice stream on the shelf of the southern bellingshausen sea clues to west antarctic glacial history during the late quaternary a major trough belgica trough eroded by a palaeo ice stream crosses the continental shelf of the southern bellingshausen sea west antarctica and is associated with a trough mouth fan belgica tmf on the adjacent continental slope previous marine geophysical and geological studies investigated the bathymetry and geomorphology of belgica trough and belgica tmf erosional and depositional processes associated with bedform formation and the temporal and spatial changes in clay mineral provenance of subglacial and glaciomarine sediments here we present multi proxy data from sediment cores recovered from the shelf and uppermost slope in the southern bellingshausen sea and reconstruct the ice sheet history since the last glacial maximum lgm in this poorly studied area of west antarctica we combined new data physical properties sedimentary structures geochemical and grain size data with published data shear strength clay mineral assemblages to refine a previous facies classification for the sediments the multi proxy approach allowed us to distinguish four main facies types and to assign them to the following depositional settings 1 subglacial 2 proximal grounding line 3 distal sub ice shelf sub sea ice and 4 seasonal open marine in the seasonal open marine fades we found evidence for episodic current induced winnowing of near seabed sediments on the middle to outer shelf and at the uppermost slope during the late holocene in addition we obtained data on excess pb 210 activity at three core sites and 44 ams c 14 dates from the acid insoluble fraction of organic matter aio and calcareous micro fossils respectively at 12 sites these chronological data enabled us to reconstruct for the first time the timing of the last advance and retreat of the west antarctic ice sheet wais and the antarctic peninsula ice sheet apis in the southern bellingshausen sea we used the down core variability in sediment provenance inferred from clay mineral changes to identify the most reliable aio c 14 ages for ice sheet retreat the palaeo ice stream advanced through belgica trough after similar to 36 0 corrected c 14 ka before present b p it retreated from the outer shelf at similar to 25 5 ka b p the middle shelf at similar to 19 8 ka b p the inner shelf in eltanin bay at similar to 12 3 ka b p and the inner shelf in ronne entrance at similar to 6 3 ka b p the retreat of the wais and apis occurred slowly and stepwise and may still be in progress this dynamical ice sheet behaviour has to be taken into account for the interpretation of recent and the prediction of future mass balance changes in the study area the glacial history of the southern bellingshausen sea is unique when compared to other regions in west antarctica but some open questions regarding its chronology need to be addressed by future work c 2010 elsevier ltd all rights reserved

strain effects near palmdale associated with the san fernando earthquake 1971 abstract field data from the southeast palmdale network in california are the basis for a practical strain analysis with triangulation data available for the year 1938 and 1958 and trilateration data at 1 year intervals from 1971 to date a uniform although small strain accumulation over the last forty years appears to be evident from this data set a possible soceismic strain jump of 2 strain in both shearing strain components related to the 1971 san fernando earthquake may be postulated in the observations however it was already pointed out previously that this coseismic strain jump needs further qualifications due to the corrupting influence of uncertainties in the network height differences this particular situation arises because triangular data have to be compared with trilateration data for the computation of the coseismic strain changes to clarify this situation the height differences of the southeast palmdale network were determined by trigonometric levelling in spring 1981 the effect of this new height data on the interpretation of the coseismic strain change is discussed in detail a comparison of this result with strain model calculations is presented

tectonic motions and systematic errors in leveling and trilateration data for california abstract we examined leveling and trilateration data for southern california we used mathematical models that allow for both tectonic motion and systematic errors for both data types we find evidence of systematic errors the leveling data reveal no significant tectonic motion except the direct effects of earthquakes trilateration data show steadily accumulating shear strain but previously reported episodic dilatations probably result from systematic errors

evolution of subglacial bedforms along a paleo ice stream antarctic peninsula continental shelf geophysical data from the antarctic peninsula continental shelf reveal streamlined subglacial bedforms in a cross shelf trough bedforms exhibit progressive elongation with distance along the trough and record flow of a paleo ice stream from the antarctic peninsula ice sheet during the last glacial maximum downflow evolution of the bedforms indicates increasing flow velocities as the ice stream traversed the shelf this in turn is related to a transition from crystalline bedrock on the inner shelf to a soft sedimentary substrate on the outer shelf although streaming flow operated across both substrates the highest flow velocities occurred over the soft bed spatial variation in the inferred nature of fast flow from sliding to subglacial sediment deformation and or ploughing was also lithologically controlled these data highlight the control of subglacial geology on ice stream dynamics in the geological record and demonstrate a direct relationship between the formation of streamlined subglacial bedforms and paleo ice streams

comments on near surface stress and displacement in a layered elastic crust and stress in a stratified crust overlying a buried screw dislocation by p c leary

interaction of the san andreas fault creeping segment with adjacent great rupture zones and earthquake recurrence at parkfield three dimensional finite element calculations are employed to study interactions in space and time between the creeping segment of the san andreas fault in central california and the adjacent currently locked zones of the 1857 and 1906 great earthquakes vertically the model consists of an elastic upper crust over a maxwell viscoelastic region representing the entire lower crust or a narrower horizontal detachment layer and a stiffer and more viscous upper mantle the crust has a single vertical fault extending to the top of the mantle at 25 km depth in zones along strike corresponding to the 1857 and 1906 events the top 12 5 km of the fault is locked against slip except in great earthquakes below the locked zones and everywhere along the creeping region between them the fault is freely slipping the model parameters are compatible with seismological and geological observations and with a ratio of maxwell relaxation time to the relaxing layer thickness in the range 1 to 2 yr km as established by li and rice 1987 and fares and rice 1988 based on fits to geodetic data along the san andreas fault an imposed constant far field shear motion and periodic 1857 and 1906 type earthquakes generate slip rates along the creeping fault segment that evolve in time throughout the entire earthquake cycle shortly after an adjacent great earthquake slip rates in the creeping zone are higher than the far field velocity while later in the cycle they are lower hence time dependency should be accounted for when measurements of fault slip are used to estimate the plate motion if parkfield earthquakes are a response to a time dependent loading of the type simulated here their recurrence interval would tend to lengthen with time since the 1857 event thus the hypothesis of characteristic periodic earthquakes at parkfield may not provide the best estimate of the occurrence time of the next event using for example the statistics of past events and assuming that parkfield earthquakes are a response to a slip deficit near middle mountain and that the elastic crustal layer is 17 5 km thick we find that the next event is predicted for about 1992 9 years if the lower crust is a 7 5 km thick layer having a material relaxation time of 15 years and 1995 11 years if the 7 5 km thick lower crust is characterized by a relaxation time of 7 5 years these values may be compared to the 1988 7 years estimate based on periodicity in time the modeling results also indicate that the interaction between the 1857 and 1906 rupture zones is small

climate evolution at the last deglaciation the role of the southern ocean abstract two sediment sequences recovered close to and south of the present polar front 50 53 s in the atlantic sector of the southern ocean were analysed in order to evaluate the environmental evolution of the southern ocean surface over the last deglaciation and the holocene our reconstruction is based on radiocarbon dated records of diatom based sea surface temperature and sea ice proxies and planktic foraminiferal stable isotopes the onset of the deglacial warming and gradual southward retreat of the winter sea ice field between 18 and 17 cal kyr bp occurrence of a thermal reversal centered at ca 13 cal kyr bp antarctic cold reversal or acr and early holocene occurrence of the climatic optimum well correlate with climatic reconstructions available from the indian southern ocean and from antarctic ice cores time correspondence of southern ocean warming and heinrich event 1 in the north atlantic is compatible with the transmission of the climate signal from the northern to the southern hemisphere through the bipolar seesaw our data support modeling results suggesting that the northern hemisphere bolling warming and turn on of the north atlantic deep water formation are triggered by gradual warming and sea ice retreat in the southern ocean meltwater shedding into the southern ocean associated with the acr may maintain northern hemisphere warming during the allerod the development of sea surface warming and sea ice retreat is compatible with a southern ocean control on the atmospheric co2 increase during the deglaciation during the early holocene 9 7 cal kyr bp our southern core records renewed surface ocean cooling and northward readvance of the winter sea ice field such early holocene cooling is common to cores from the high latitude atlantic sector and might be brought about by expansion of the weddell gyre circulation at that time

flow dynamics and till genesis associated with a marine based antarctic palaeo ice stream geophysical and geological data indicate that during the last glacial cycle a palaeo ice stream drained the antarctic peninsula ice sheet apis through marguerite bay to the edge of the continental shelf via a bathymetric trough marguerite trough mega scale glacial lineations msgl in outer marguerite trough are formed in an acoustically transparent sediment unit consisting of a soft deformation till the association of msgl with deformation till indicates that bed deformation occurred beneath the ice stream and the thickness of the subglacial deforming layer was on the order of several metres msgl within outer marguerite trough are related to a pre existing thick sequence of soft sediments on the outer shelf and are inferred to have formed by a combination of subglacial sediment deformation by attenuation from a point source and groove ploughing morphologically the msgl differ in several respects from those documented elsewhere and this variation suggests a polygenetic origin for this subglacial landform an initial advance of the apis across the marguerite bay continental shelf at the lgm deposited a stiff subglacial till following this advance the ice margin within marguerite trough retreated 70 100 km before stabilising and depositing a grounding zone wedge an ice stream then developed in the trough and extended to the shelf edge forming a soft deformation till development of the ice stream may have been a glacio dynamic response to regional deglaciation subsequent retreat of the marguerite trough ice stream was underway by 13 490 uncorrected 14c years before present based on the geophysical and core data ice stream retreat appears to have been rapid and it contrasts with reconstructions of palaeo ice streams from other locations in antarctica this implies marked regional variations in antarctic ice stream dynamics during late quaternary deglaciation

consistent generation of ice streams via thermo viscous instabilities modulated by membrane stresses accurate computation of ice stream location and dynamics is a key aspiration for theoretical glaciology ice sheet models with thermo viscous coupling have been shown to exhibit stream like instabilities using shallow ice approximation mechanics but the location and width of these streams depends on the numerical implementation and are not unique we present results from thermo viscously coupled ice sheet models incorporating membrane stresses spontaneous generation of fast flowing linear features still occurs under certain parameter regimes with computed stream widths between 20 km to 100 km comparable with observations these features are maintained as the grid size is decreased the thermo viscous feedback mechanism that generates ice streams under the shallow ice approximation still operates now selecting a unique stream size computations of thermo viscous ice flows should include membrane stresses when the bed is approximately flat e g parts of antarctica and former ice sheets of the northern hemisphere previous calculations of spontaneous ice stream generation using the shallow ice approximation should be reassessed citation hindmarsh r c a 2009 consistent generation of ice streams via thermo viscous instabilities modulated by membrane stresses geophys res lett 36 l06502 doi 10 1029 2008gl036877

flow and retreat of the late quaternary pine island thwaites palaeo ice stream west antarctica multibeam swath bathymetry and sub bottom profiler data are used to establish constraints on the flow and retreat history of a major palaeo ice stream that carried the combined discharge from the parts of the west antarctic ice sheet now occupied by the pine island and thwaites glacier basins sets of highly elongated bedforms show that at the last glacial maximum the route of the pine island thwaites palaeo ice stream arced north northeast following a prominent cross shelf trough in this area the grounding line advanced to within similar to 68 km of and probably reached the shelf edge minimum ice thickness is estimated at 715 m on the outer shelf and we estimate a minimum ice discharge of similar to 108 km 3 yr 1 assuming velocities similar to today s pine island glacier similar to 2 5 km yr 1 additional bed forms observed in a trough northwest of pine island bay likely formed via diachronous ice flows across the outer shelf and demonstrate switching ice stream behavior the style of ice retreat is also evident in five grounding zone wedges which suggest episodic deglaciation characterized by halts in grounding line migration up trough stillstands occurred in association with changes in ice bed gradient and phases of inferred rapid retreat correlate to higher bed slopes supporting theoretical studies that show bed geometry as a control on ice margin recession however estimates that individual wedges could have formed within several centuries still imply a relatively rapid overall retreat our findings show that the ice stream channeled a substantial fraction of west antarctica s discharge in the past just as the pine island and thwaites glaciers do today

the sedimentary record of the last glaciation in the western bellingshausen sea west antarctica implications for the interpretation of diamictons in a polar marine setting upper quaternary marine sediments recovered from the west antarctic continental margin are characterized by a distinct lithological succession allowing the reconstruction of past environmental changes massive homogenous diamictons were deposited elsewhere on the margin during the last glacial period when grounded ice masses advanced across the shelf sedimentological investigations using a multi proxy approach and examination of the margin topography suggest that during this time a deformation till and subsequently a glaciomarine till were deposited on the shelf while glaciogenic debris flows were deposited on the slope and rise the comparison of the clay mineral assemblages in the matrix of the diamictons with clay mineral assemblages of potential source areas reveals distinct pathways of grounded ice flow on the shelf lithogenic sandy muds overlying the diamictons were deposited by meltwater flows and or marine currents on the shelf and by turbidity currents and marine currents on the slope and rise respectively the sedimentation of the sandy muds denotes a deglaciation stage when grounded ice started to retreat from the shelf but semi permanent sea ice coverage still hampered biological productivity bioturbated foraminifer bearing sediments were deposited in a glaciomarine setting during the present interglacial period when sea ice cover was only seasonally present and a marine current related to the southern boundary of the antarctic circumpolar current winnowed the seafloor on the outer shelf slope and rise

clay mineral provenance of sediments in the southern bellingshausen sea reveals drainage changes of the west antarctic ice sheet during the late quaternary the belgica trough and the adjacent belgica trough mouth fan in the southern bellingshausen sea pacific sector of the southern ocean mark the location of a major outlet for the west antarctic ice sheet during the late quaternary the drainage basin of an ice stream that advanced through belgica trough across the shelf during the last glacial period comprised an area exceeding 200 000 km 2 in the west antarctic hinterland previous studies mainly based on marine geophysical data from the continental shelf and slope focused on the bathymetry and seafloor bedforms and the reconstruction of associated depositional processes and ice drainage patterns in contrast there was only sparse information from seabed sediments recovered by coring in this paper we present lithological and clay mineralogical data of 21 sediment cores collected from the shelf and slope of the southern bellingshausen sea most cores recovered three lithological units which can be attributed to facies types deposited under glacial transitional and seasonally open marine conditions the clay mineral assemblages document coinciding changes in provenance the relationship between the clay mineral assemblages in the subglacial and proglacial sediments on the shelf and the glacial diamictons on the slope confirms that a grounded ice stream advanced through belgica trough to the shelf break during the past thereby depositing detritus eroded in the west antarctic hinterland as soft till on the shelf and as glaciogenic debris flows on the slope the thinness of the overlying transitional and seasonally open marine sediments in the cores suggests that this ice advance occurred during the last glacial period clay mineralogical acoustic sub bottom and seismic data furthermore demonstrate that the palaeo ice stream probably reworked old sedimentary strata including older tills on the shelf and incorporated this debris into its till bed the geographical heterogeneity of the clay mineral assemblages in the sub and proglacial diamictons and gravelly deposits indicates that they were eroded from underlying sedimentary strata of different ages these strata may have been deposited during either different phases of the last glacial period or different glacial and interglacial periods additionally the clay mineralogical heterogeneity of the soft tills recovered on the shelf suggests that the drainage area of the palaeo ice stream flowing through belgica trough changed through time c 2009 elsevier b v all rights reserved

a unified analysis of crustal motion in southern california 1970 2004 the scec crustal motion map 1 to determine crustal motions in and around southern california we have processed and combined trilateration data collected from 1970 to 1992 vlbi data from 1979 to 1992 and gps data from 1986 to 2004 a long temporal coverage required in part by the occurrence of several large earthquakes in this region from a series of solutions for station positions we have estimated interseismic velocities coseismic displacements and postseismic motions within the region from 31 n to 38 n and east to 114 w the final product includes estimated horizontal velocities for 1009 gps 190 trilateration and 16 vlbi points with ties between some of these used to stabilize the solution all motions are relative to the stable north american reference frame snarf as realized through the velocities of 20 gps stations this provides a relatively dense set of horizontal velocity estimates with well tested errors for the past quarter century over the plate boundary from 31 n to 36 5 n these velocities agree well with those from the plate boundary observatory which apply to a later time period we also estimated vertical velocities 533 of which have errors below 2 mm yr most of these velocities are less than 1 mm yr but they show 2 4 mm yr subsidence in the ventura and los angeles basins and in the salton trough our analysis also included estimates of coseismic and postseismic motions related to the 1992 landers 1994 northridge 1999 hector mine and 2003 san simeon earthquakes postseismic motions increase logarithmically over time with a time constant of about 10 days and generally mimic the direction and relative amplitude of the coseismic offsets

glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and the barents sea a review abstract studies of glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and barents sea show that during periods of limited glacial coverage interstadials large amounts of material may be brought into the sea mainly by meltwater the major load is deposited relatively close to the icefront 1 at times of maximum glacial extent grounded ice extends onto the shelf with the shelf edge as the outer limit and land and inner shelf areas are eroded main glacial depositional sites are then the outer shelf and shelf edge the sedimentary environment outside an ice shelf is characterized by low clastic supply mainly deposited from icebergs due to low turbidity and a supply of nutrient rich water biogenic matter accumulates leading to a glaciomarine sequence rich in bioclastics sea level lowering results in grounding and seaward expansion of the ice shelf subsequent eustatic rise causes the grounded ice to float deglaciation and sea level rise reduces clastic input to the shelves glacial sediments are reworked and carbonates may accumulate forming tillite carbonate sequence e g late precambrian break up of marine ice sheets such as the barents sea ice sheet seems to have taken place stepwise in response to eustatic rise and climatic changes

earthquake focal mechanisms in the eastern transverse ranges and san emigdio mountains southern california and evidence for a regional decollement earthquake focal mechanisms obtained from p wave first motions are presented for the eastern transverse ranges and the san emigdio mountains in southern california the former region shows a predominance of strike slip faulting whereas quaternary faults in the region show thrust motion we suggest that the observed strike slip mode of deformation cannot continue indefinitely without the occurrence of more thrust faulting fault deformation in the san emigdio mountains inferred from focal mechanisms is in accord with displacements across quaternary faults in the area this study and a search of the literature has yielded 19 mechanisms with shallow dipping nodal planes previous workers have interpreted such mechanisms as evidence for a regional decollement if such a regional decollement exists these data give some indication of its regional extent slip directions inferred from the focal mechanisms with shallow dipping nodal planes show some regional consistency but this pattern cannot be entirely explained with current tectonic models a comparison of the stress drop of an event having a shallow dipping nodal plane with an event with steeper planes gave inconclusive results

marine geological constraints for the grounding line position of the antarctic ice sheet on the southern weddell sea shelf at the last glacial maximum abstract the history of grounded ice sheet extent on the southern weddell sea shelf during the last glacial maximum lgm and the timing of post lgm ice sheet retreat are poorly constrained several glaciological models reconstructed widespread grounding and major thickening of the antarctic ice sheet in the weddell sea sector at the lgm in contrast recently published onshore data and modelling results concluded only very limited lgm thickening of glaciers and ice streams feeding into the modern filchner and ronne ice shelves these studies concluded that during the lgm ice shelves rather than grounded ice covered the filchner and ronne troughs two deep palaeo ice stream troughs eroded into the southern weddell sea shelf here we review previously published and unpublished marine geophysical and geological data from the southern weddell sea shelf the stratigraphy and geometry of reflectors in acoustic sub bottom profiles are similar to those from other west antarctic palaeo ice stream troughs where grounded ice had advanced to the shelf break at the lgm numerous cores from the southern weddell sea shelf recovered sequences with properties typical for subglacially deposited tills or subglacially compacted sediments these data sets give evidence that grounded ice had advanced across the shelf during the past thereby grounding in even the deepest parts of the filchner and ronne troughs radiocarbon dates from glaciomarine sediments overlying the subglacial deposits are limited but indicate that the ice grounding occurred at the lgm and that ice retreat started before 15 1 corrected 14c kyrs before present bp on the outer shelf and before 7 7 corrected 14c kyrs bp on the inner shelf which is broadly synchronous with ice retreat in other antarctic sectors the apparent mismatch between the ice sheet reconstructions from marine and terrestrial data can be attributed to ice streams with very low surface profiles similar to those of ice plains that had advanced through filchner trough and ronne trough at the lgm considering the global sea level low stand of 130 m below present a low surface slope of the expanded lgm ice sheet in the southern weddell sea can reconcile grounding line advance to the shelf break with limited thickening of glaciers and ice streams in the hinterland this scenario implies that ice sheet growth in the weddell sea sector during the lgm and ice sheet drawdown throughout the last deglaciation could only have made minor contributions to the major global sea level fluctuations during these times

a major trough mouth fan on the continental margin of the bellingshausen sea west antarctica the belgica fan a 330 km length of the little known continental shelf edge and slope of the bellingshausen sea west antarctica is investigated using multibeam swath bathymetric and sub bottom profiler evidence the shelf break is at 650 700 m across the 150 km wide belgica trough and to either side is about 500 m when full glacial ice advanced across the shelf to reach the shelf break it was partitioned into fast and slow flowing elements with an ice stream filling the trough this had important consequences for the nature and rate of sediment delivery to the adjacent continental slope off belgica trough the upper continental slope has convex outward contours indicating a major sedimentary depocentre of gradient 1 2 degrees acoustic profiles and cores from the depocentre show a series of diamictic glacigenic debris flows the depocentre is interpreted as a trough mouth fan built largely by debris delivered from the ice stream the slope is steeper beyond the trough margins at up to 6 degrees the main morphological features on the bellingshausen sea slope are gully systems and channels major canyons and late quaternary slides are absent most gullies and channels are found on the fan gullies are about 15 25 m deep a few hundred metres wide and some are 25 km long the largest channel is over 60 km long about a kilometre wide and 10 to 15 m deep the channels provide pathways for sediment by passing of the upper slope and transfer to the continental rise and beyond by turbidity currents gullies on the bellingshausen sea margin cut through debris flows on the slope assuming the debris flows are linked mainly to downslope transport of diamictic debris when ice was at the shelf edge under full glacial conditions then those gullies cut into them formed during deglaciation belgica fan is 22 000 km 2 in area and about 60 000 km 3 in volume it is the largest depocentre identified to date on the continental margin of the west antarctic ice sheet fed by an interior ice sheet basin of approximately 200 000 km 2 c 2008 elsevier b v all rights reserved

ice sheet extent of the antarctic peninsula region during the last glacial maximum lgm insights from glacial geomorphology we present marine geological and geophysical data for the antarctic peninsula that call for a larger ice sheet reconstruction during the last glacial maximum lgm than suggested by previous studies such glacial reconstructions are important for quantifying post lgm sea level rise and providing boundary conditions for general circulation models megascale glacial lineations on the continental shelf surrounding antarctica provide documentation for grounded ice that was streaming swath bathymetry data nbp02 01 reveal lineations in each of the major glacial troughs except for smith trough which features grooves and bedrock drumlins 0 5 3 km spacing 1 20 elongation ratios on crystalline bedrock we place the maximum extent of ice at the seaward limit of the lineations at or near megascale glacial lineations imaged in this study and other areas surrounding antarctica including the ross sea pine island bay have a consistent morphology with elongation ratios of 80 1 and spacings of 200 600 m mode of 300 m in contrast lineations bundles canals et al 2000 in the gerlache boyd trough exhibit larger spacing 1 5 km and the upstream portions 7 km are carved directly into bedrock rather than till as suggested by previously unpublished air gun 120 hz seismic data these features have yet to be dated however they are believed to have been active during the lgm radiocarbon dates in glaciomarine sediments foraminifera and organic matter from seven glacial troughs indicate that megascale glacial lineations were formed during the lgm other geomorphic features such as the grounding zone wedge in the northwestern weddell sea formed when the ice sheet was retreating the initial retreat of the grounded ice from the outer shelf occurred by 18 500 cal yr b p the inner shelf was mostly ice free by 13 000 cal yr b p this is significantly earlier than numerical models which suggest antarctic deglaciation began at 12 000 cal yr b p this also suggests the peninsula area contributed to global sea level rise associated with meltwater pulse mwp 1a

morphology and sedimentary processes on the continental slope off pine island bay amundsen sea west antarctica morphology and sedimentation on the pine island bay continental margin eastern amundsen sea is investigated using swath bathymetry parametric subbottom profiler topas records and sediment cores a major cross shelf trough extends to the continental shelf edge at 114 w through which fast flowing ice drained the west antarctic ice sheet under full glacial conditions the slope adjacent to the trough mouth is 4 whereas to the east and west it is steeper a bulge in bathymetric contours beyond and east of the trough mouth indicates some slope progradation elsewhere seismic reflection profiles indicate major shelf aggradation and minor slope progradation networks of gullies and channels dominate the slope adjacent to pine island bay in front of the trough mouth gullies at the shelf edge and uppermost slope connect directly with channels that continue to the continental rise other gullies connect indirectly with channels further downslope topas records indicate that gully channel systems acted as conduits for coarse grained sediment transfer cores comprise turbidites representing channel deposits and diamicton facies deposited by debris flows sandy turbidites interbedded with hemipelagic muds occur on the rise and abyssal plain the west antarctic ice sheet extended to the shelf edge during full glacials delivering water saturated till and turbid water directly to the continental slope along a line source gully channel systems are probably a product of sediment gravity flows derived from the release of water saturated till and turbid water along the ice sheet margin perhaps augmented subsequently by downslope flow of dense cold and saline water associated with sea ice production during the holocene the gully channel systems enable sediment to bypass the continental slope spatial variations in gully channel system morphology along the amundsen sea continental slope are probably linked to differences in sediment gravity flow processes and the rate and composition of sediment delivered to the shelf edge from the ice sheet cored sediments on the slope and abyssal plain record the widespread presence of turbidite sands indicating that downslope transfer of glacier derived sediments has taken place this supports our interpretation that submarine channels are derived from and are conduits for mass wasting submarine channels on the upper slope continue into the abyssal plain as far north as 67 s they are separated by sediment drifts and sediment waves resulting from the interaction between downslope turbidity current processes and along slope bottom currents similar deep sea sedimentary processes operate along much of west antarctica and the western side of the antarctic peninsula

distribution of glacial geomorphic features on the antarctic continental shelf and correlation with substrate implications for ice behavior surveys were conducted seaward of all the major drainage outlets of the antarctic ice sheet from the pennell coast north victoria land to marguerite bay antarctic peninsula the results show that the ice sheet extended onto the outer shelf glacial troughs occur offshore of all major glacial outlets where the substrate is crystalline bedrock ice flow tended to follow the structural grain of the bedrock deposited little sediment and eroded the underlying bedrock where ice flowed over relatively soft more easily eroded sedimentary strata the direction of ice flow was more directly offshore and depositional features characterize the sea floor in these areas the signature of the grounded ice consists of till deposits and large scale geomorphic features drumlins occur within the region of contact between crystalline and sedimentary substrates the different geological substrates are interpreted to have exerted a fundamental control on the behavior of past ice sheets the troughs in the areas of bedrock composed of sedimentary substrate are interpreted to have been occupied by relatively fast flowing ice ice streams and the troughs in the areas of crystalline substrate are interpreted to have been occupied by slower moving ice the area between these two zones was characterized by ice acceleration and is marked by drumlins

crustal deformation in great california earthquake cycles periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model a depth l h extending downward from the earth s surface at a transform boundary between uniform elastic lithospheric plates of thickness h is locked between earthquakes it slips an amount consistent with remote plate velocity vpl after each lapse of earthquake cycle time tcy lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress the plates are coupled at their base to a maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions compatible with plate velocity are transmitted to the surface plates the coupling is described approximately through a generalized elsasser model we argue that the model gives a more realistic physical description of tectonic loading including the time dependence of deep slip and crustal stress buildup throughout the earthquake cycle than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone parameters of the model are chosen to fit seismic and geologic constraints and the apparent time dependence of surface strain rates along presently locked traces of the 1857 and 1906 san andreas ruptures we fix vpl 35 mm yr tcy 160 years and l 9 11 km based on earthquake nucleation depths the geodetic data are then found to be described reasonably within the context of a model that is locally uniform along strike and symmetric about a single san andreas fault strand by lithosphere thickness h 20 30 km and elsasser relaxation time tr 10 16 years we therefore suggest that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps crust mantle transition zone and has an effective viscosity between about 2 1018 and 1019 pa s depending on the thickness assigned to the asthenospheric layer predictions based on the chosen set of parameters are also consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces although the fit is degraded by asymmetry relative to the fault and by slip on adjacent fault strands

aseismic crustal deformation in the transverse ranges of southern california abstract geodetic data at a plate boundary can reveal the pattern of subsurface displacements that accompany plate motion we model these displacements as the sum of rigid block motion and the elastic effects of frictional drag between blocks the frictional interactions are represented by uniform dislocation on each of several rectangular fault patches we then estimate the block velocities and fault parameters from geodetic data our bayesian inversion procedure employs prior estimates based on geological and seismological data we apply the method to the transverse ranges using prior data from bird and rosenstock 1984 and geodetic data from the usgs trilateration networks and nasa vlbi measurements our model consists of 12 blocks and 27 rectangular fault patches the block motion inferred from the geodetic data has the same order of magnitude as the geologic estimates and for many faults the agreement is excellent however the geodetic data imply a displacement rate of about 20 mm yr 1 across the san andreas fault while the geologic estimates exceed 30 mm yr 1 the final model implies about 6 mm yr 1 of crustal shortening normal to the trend of the san andreas fault this is about half the rate implied by the prior model most of this shortening occurs on the sierra madre cucamonga and the white wolf fault systems aseismic fault motion is a major contributor to plate motion and the thickness of the frictional surface varies considerably from one fault to another the geodetic data can help to identify faults that are suffering rapid stress accumulation in the transverse ranges those faults are the san andreas san gabriel sierra madre pleito and white wolf faults

glacigenic sediments on a passive continental margin as exemplified by the barents sea abstract reflection seismics data borehole data and gravity cores have been used to map the sedimentary facies of the epicontinental southwestern barents sea its continental margin and adjacent coastal areas an upper unconformity with a glacially eroded morphology extends over most of the continental shelf up to 300 m of stratiform glacigenic sediments overlie this unconformity these sediments can be grouped into seismic units which are separated by smooth or irregular erosional surfaces each sequence may be up to 150 m thick normally with a lateral extent of 100 300 km three dominant seismic signatures may be discerned semi transparent stratified and chaotic reflection patterns these sediments are partly glacifluvial in origin but on the whole they represent more or less tectonized glacimarine deposits the deeper troughs on the continental shelf contain an undeformed postglacial glacimarine marine trough fill the greatest thickness up to 1000 m of glacigenic sediments occurs at the shelf break and below the upper slope the depocentres are situated at trough mouth fans the sediments comprise several prograding sequences with a complex sigmoid oblique character indicating alternating upbuilding and depositional bypass erosion in the topset segment small and large scale slide scars are observed on the upper slope and debris lobes on the lower slope a marked progradation seems to have occurred during the plio pleistocene glacial periods this progradation also resulted in an unstable slope with various types of sediment gravity flows currents flowing along the slope were established during interglacials and gullying by cold dense shelf water and downslope transport occurred maximum net sedimentation rates are 0 2 m ka continental slope 0 4 m ka shelf break 0 1 m ka shelf stratiform diamictons 1 m ka shelf trough fills and 60 m ka fjord trough fills

slope failure dynamics and impacts from seafloor and shallow sub seafloor geophysical data case studies from the costa project holocene and slightly pre holocene submarine landslide are found both in high latitude glacial dominated margins and in lower latitude river dominated margins this paper constitutes a major assessment on some of the best studied submarine instabilities in the world we review and update from original data and literature reports the current state of knowledge of storegga traenadjupet and finneidfjord slides from the mid norwegian margin afen slide from the faeroe shetland channel big 95 slide and central adriatic deformation belt cadeb from continental slope and inner continental shelf settings off the ebro and po rivers in the mediterranean sea canary slide west of the westernmost youngest canary islands and gebra slide off the northern tip of the antarctic peninsula in the southern hemisphere i e those studied in the continental slope stability costa project the investigated slides range in size from the gigantic 90 000 km2 and almost 3000 km3 storegga slide to the tiny 1 km2 and 0 001 km3 finneidfjord slide not only do individual submarine landslides rarely involve processes precisely fitting with pre established categories mostly based on subaerial research but also they display complex mechanical behaviors within the elastic and plastic fields individual events can involve simultaneous or successive vertical to translational movements including block detachment block gliding debris flow mud flow and turbidity currents the need for an in depth revision of the classification criteria and eventually for a new classification system based on the new imaging capabilities provided by modern techniques is more than obvious we suggest a new system which for the moment is restricted to debris flows and debris avalanches volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides the assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey cadeb a shore parallel prodelta detached from its source is the exception to the good correlation found between across slope width and alongslope length with slide area height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas which prevent farther forward expansion of the deposit such as gebra and big 95 in such cases over thickened deposits are found a particularly loose and fluid behavior can be deduced for slides showing an over thinned character such as the canary slide that traveled 600 km scar areas and slip planes have been investigated with particular emphasis although slide headwalls might present locally steep gradients up to 23 for storegga slide the slope gradients of both the failed segment margins and the main slip planes are very low max 2 and usually around 1 and less an exception is the finneidfjord slide 20 5 that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure mechanically distinct low permeable clayey weak layers often correspond to slip planes beyond the slide headwall since not only formation of these weak layers but also sedimentation rates are climatically controlled we can state that slide pre conditioning is climatically driven too run out distances reflect the degree of disintegration of the failed mass of sediment the total volume of initially failed material and transport mechanisms including hydroplanning commonly specific run outs could be attributed to distinct elements such as cohesive blocks and looser matrix as nicely illustrated by the big 95 slide total run outs usually correspond to matrix run outs since the coarser elements tend to rest at shorter distances outrunner blocks are finally a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass in addition to pre conditioning factors related to geological setting and sedimentation conditions a final trigger is required for submarine landslides to take place which is most often assumed to be an earthquake in high latitude margins earthquake magnitude intensification because of post glacial isostatic rebound has likely played a major role in triggering landslides although it cannot be totally ruled out there is little proof at least amongst the costa slides that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers

regional deformation near palmdale california 1973 1983 the tehachapi trilateration network spans the intersection of the san andreas and garlock faults in southern california in the big bend region of the san andreas fault analysis of data from 1973 1983 shows strain differences between the northwest and southeast regions of the network and slip at depth on both faults the palmdale network spanning the san andreas fault entirely within the tehachapi network showed increases of about 1 strain in both east west and north south extension in late 1979 the tehachapi strains also jumped at this time but the magnitude of the increase was only about one third that of palmdale the principal strain rates for tehachapi over the time interval 1973 1983 are e 1 0 08 0 01 strain yr and e 2 0 12 0 01 strain yr with the 1 axis directed n76 e strains were also computed for two subregions the principal strain rates for the southeast tehachapi region are e 1 0 14 0 02 strain yr and e 2 0 16 0 02 strain yr with the 1 axis directed n73 e this result differs significantly from the principal strain rates at palmdale e 1 0 21 0 02 strain yr e 2 0 17 0 01 strain yr with the 1 axis directed n71 e for the northwest tehachapi region e 1 0 11 0 02 strain yr and e 2 0 06 0 02 strain yr with the 1 axis directed n93 e

a late cretaceous turonian coniacian high latitude turtle assemblage from the canadian arctic three turtles are present in a turonian coniacian age high latitude vertebrate assemblage from axel heiberg island borealochelys axelheibergensis gen et sp nov a generically indeterminate eucryptodire and a trionychid the assemblage differs from most late cretaceous turtle assemblages from north america in that members of the paracryptodira are absent the absence of this group is interpreted as a result of latitudinal differentiation of turtle assemblages in north america during the late cretaceous the level of diversity of turtles in the axel heiberg assemblage is comparable to that of mid latitude assemblages associated with a mean annual paleotemperature of 14 c adding to the evidence for high mean annual temperatures at high latitudes during turonian coniacian times

in situ fluid pressure measurements for earthquake prediction an example from a deep well at hi vista california short term earthquake prediction requires sensitive instruments for measuring the small anomalous changes in stress and strain that precede earthquakes instruments installed at or near the surface have proven too noisy for measuring anomalies of the size expected to occur and it is now recognized that even to have the possibility of a reliable earthquake prediction system will require instruments installed in drill holes at depths sufficient to reduce the background noise to a level below that of the expected premonitory signals we are conducting experiments to determine the maximum signal to noise improvement that can be obtained in drill holes in a 592 m well in the mojave desert near hi vista california we measured water level changes with amplitudes greater than 10 cm induced by earth tides by removing the effects of barometric pressure and the stress related to earth tides we have achieved a sensitivity to volumetric strain rates of 10 9 to 10 10 per day further improvement may be possible and it appears that a successful earthquake prediction capability may be achieved with an array of instruments installed in drill holes at depths of about 1 km assuming that the premonitory strain signals are in fact present

contemporary plate motion and crustal deformation the measurement of relative plate velocities during the past few years is a signal accomplishment in earth science leading to refinement of the precepts of steady motion of plate interiors and cyclic deformation along plate margins regrettably deformation premonitory to an earthquake has yet to be detected with confidence delineation of the spatial and temporal buildup of strain between earthquakes however has put limits on models of the earthquake cycle a diverse set of fault structures and crustal rheologic conditions can explain the pattern of surface strain accumulation and release along strike slip faults in contrast the geometry of thrusts and normal faults revealed by earthquake deformation has been found to differ markedly from expectations geodetic observations have proved vital to monitor the ascent of magma through the earth s crust and to predict volcanic eruptions at the earth s surface episodic vertical and horizontal deformation in southern california remains a subject of dispute if anything it is less certain than it once seemed

predicted variation of stress orientation with depth near an active fault application to the cajon pass scientific drillhole southern california preliminary measurements of the stress orientation at a depth of 2 km in the cajon pass scientific drillhole about 3 6 km from the san andreas fault in southern california indicate that the local direction of maximum compression is nearly normal to the fault zone the measurements have been interpreted to indicate that the regional orientation of the maximum compression is normal to the fault and taken as evidence for a very weak fault the orientation of the regional maximum compression expected from plate tectonic arguments is about 66 ne from the strike of the fault geodetic data indicate that the orientation of maximum compressive strain rate is about 43 ne from the strike of the fault and show nearly pure right lateral shear acting parallel to the fault these apparent conflicts in the inferred orientation of the axis of maximum compression may be explained in part by a model in which the fault zone is locked over a depth interval in the range of 2 5 to 15 km but is very weak above and below that interval an analytic solution for this model predicts orientations of the principal stresses that are nearly parallel or normal to the fault for observations made close to the fault and above and below the locked zone but an orientation consistent with plate tectonic estimates at depths corresponding to that of the locked interval this solution does require however a few mm yr of creep at the surface on the san andreas or nearby sub parallel faults such as the san jacinto which has not yet been observed or a shallow zone near the faults of distributed deformation

the depositional pattern and distribution of glacial interglacial sequences on the antarctic peninsula pacific margin the outer shelf on the antarctic peninsula pacific margin south of 63 30 s is underlain by pliocene pleistocene prograding sequences which have been produced mainly by the action of ice sheets grounded out to the shelf edge at times of glacial maximum most sediment in these sequences has probably been transported to the margin in a deforming basal till which implies deposition on a broad front a line source a representative prograding sequence mapped across an extensive network of multichannel seismic reflection lines has an elongate depocentre on the upper palaeoslope which is consistent with the grounded ice sheet model however it is likely that each sequence recognized on existing multichannel seismic data represents several ice advances depth to surface maps reveal a broad variation along the margin in the amount of progradation reflecting differences in sediment supply the pattern of progradation and the bathymetry of the outer shelf suggest that the main depocentre in the area studied was fed by an ice stream at times of glacial maximum seismic lines across the margin farther to the southwest indicate the existence of other depocentres several broad depositional lobes have probably coalesced to form the extensive outer shelf the present continental slope is smooth and steep and is not cut by major canyons a downslope change in seismic facies and scouring on the uppermost rise probably reflect downslope transitions from slumps to debris flows to turbidity currents these processes are likely to be most active at times of glacial maximum deep drilling data indicate that the rise sediments consist mainly of terrigenous turbidite and ice rafted detritus a marked upward change in seismic facies on the continental rise indicates a change to a higher energy sedimentary regime and appears to correlate with the start of glacial progradation on the shelf

reconstruction of the west antarctic ice sheet in pine island bay during the last glacial maximum and its subsequent retreat history abstract marine geological and geophysical studies were conducted to determine the late quaternary glacial history of the west antarctic ice sheet in pine island bay antarctica the data set includes sea floor imagery in the form of multibeam swath bathymetry and deep tow side scan sonar surveys distribution of sedimentary deposits and basal surface conditions are revealed through intermediate resolution seismic data and chirp 3 5 khz sub bottom profiles sedimentary deposits were sampled with piston cores and calcareous material was dated using ams radiocarbon techniques results from the study indicate the ice sheet was grounded on the outer shelf during its maximum extent sometime in the past thick ice flowing slowly and resting on crystalline bedrock was influenced by significant amounts of subglacial meltwater on the inner shelf thinner but more rapidly flowing ice characterized the seaward extent of the ice sheet which was grounded on a sedimentary substrate deglaciation occurred in two phases beginning soon after the last glacial maximum the outer most extension of the ice sheet retreated gradually pausing on a bathymetric high on the middle shelf by 16 000 14c years ago between 16 000 and 12 000 14c years ago ice sheet retreat resumed and may have proceeded rapidly to reach a present day position by 10 000 14c years ago

impacts of bottom corrugations on a dense antarctic outflow nw ross sea 1 prominent seabed corrugations axially oriented roughly down slope are present along the antarctic continental slope we use analytical and numerical model results to assess the potential impact of these corrugations on outflows of dense shelf water that contribute to antarctic bottom water down slope flow increases with increasing corrugation height and varies with along slope wavelength for parameters appropriate to the northwest ross sea where heights and wavelengths are 10 20 m and 1 5 km respectively we estimate that the corrugations increase the down slope transport of dense water relative to the smooth bottom case by 13 corrugations enhance entrainment and reduce along slope speed of the dense outflow larger amplitude corrugations 100 m observed in other regions may impact outflows elsewhere around the poorly mapped antarctic continental margin our results emphasize the need to consider small scale local topography when modeling dense outflows

geodetic measurements of horizontal strain near the white wolf fault kern county california 1926 1993 the white wolf fault located north of the big bend segment of the san andreas fault is the ne sw trending left lateral oblique reverse fault responsible for the ms 7 8 1952 kern county earthquake we combined global positioning system gps measurements with historical triangulation and trilateration data to determine changes in the strain rate over 7 decades 1926 1993 we reanalyzed the historical geodetic data and calculated an elevated preseismic 1926 1952 maximum shear strain rate of 0 62 0 16 strain yr across the white wolf fault the maximum shear strain rate decreased with distance toward the garlock fault to 0 09 0 08 strain yr in the decade following the earthquake 1952 1963 the near fault was high 0 85 0 23 strain yr and decreased to 0 23 0 13 strain yr across the garlock fault in 1993 we resurveyed many of the same monuments with gps receivers to estimate fault crossing and off fault strain rates for the preceding 30 years across the white wolf fault the maximum shear strain rate dropped to 0 19 0 07 strain yr the azimuths of the maximum principal strain rates for the 1963 1993 epoch rotate from a fault normal orientation 57 15 across the white wolf fault to 11 3 e across the garlock fault

precision of geodolite surveys a reply to jackson and cheng jackson and cheng have suggested that the changes in areal dilatation measured in geodolite surveys by the u s geological survey may be simply an artifact of the measuring system although systematic error could conceivably account for the observed excursions in dilatation we maintain that the specific criticisms by jackson and cheng are incorrect the excursions in dilatation cannot be attributed to the offset correction nor to proportional error associated with temperature the absence of both errors is demonstrated by using data that are particularly sensitive to the two effects

ice shelf water overflow and bottom water formation in the southern weddell sea 1 cold shelf waters flowing out of the filchner depression in the southern weddell sea make a significant contribution to the production of weddell sea bottom water wsbw a precursor to antarctic bottom water aabw we use all available current meter records from the region to calculate the flux of cold water 1 9 c over the sill at the northern end of the filchner depression 1 6 0 5 sv and to determine its fate the estimated fluxes and mixing rates imply a rate of wsbw formation referenced to 0 8 c of 4 3 1 4 sv we identify three pathways for the cold shelf waters to enter the deep weddell sea circulation one path involves flow constrained to follow the shelf break the other two paths are down the continental slope resulting from the cold dense water being steered northward by prominent ridges that cross the continental slope near 36 w and 37 w mooring data indicate that the deep plumes can retain their core characteristics to depths greater than 2000 m probably aided by thermobaricity the plume water at this depth can flow at a speed approaching 1 m s 1 implying that the flow is occasionally supercritical we postulate that such supercriticality acts to limit mixing between the plume and its environment the transition from supercritical to slower more uniform flow is associated with very efficient mixing probably as a result of hydraulic jumps

the velocity field along the san andreas fault in central and southern california the velocity field within a 100 km broad zone centered on the san andreas fault between the mexican border and san francisco bay has been inferred from repeated surveys of trilateration networks in the 1973 1989 interval the velocity field has the appearance of a shear flow that remains parallel to the local strike of the fault even through such major deflections as the big bend of the san andreas fault in the transverse ranges of southern california across strike profiles of the fault parallel component of velocity exhibit the expected sigmoidal shape whereas across strike profiles of the fault normal component of velocity are flat and featureless no significant convergence upon the fault is observed even along the big bend sector of the fault simple dislocation models can explain most of the features of the observed velocity field but those explanations are not unique about 35 mm yr of relative plate motion is accounted for within the span of the trilateration networks geologic studies indicate that the secular slip rate on the san andreas fault is about 35 mm yr the agreement between these two estimates implies that most of the strain accumulation is elastic and will be recovered in subsequent earthquakes the relative motion observed across the san andreas fault 35 mm yr plus that observed across the eastern california shear zone 8 mm yr accounts for most 43 mm yr of the observed north america pacific relative plate motion 47 mm yr