three dimensional finite difference simulation of long period ground motions for the 2003 tokachi oki japan earthquake 1 to explore the generation and propagation mechanisms of long period ground motions we used a 3 d finite difference method to simulate wave propagation during the 2003 mw 8 3 tokachi oki japan earthquake a large scale computation with an inverted slip model and a geological and geophysical based velocity structure model successfully reproduced the overall characteristics of substantial observed velocity seismograms for a period range of 3 3 to 25 s significant long period ground motions of extended duration were observed in the yufutsu basin where oil tanks were damaged at tomakomai because of sloshing associated with the ground motions our simulation revealed that the combination of the large and shallow earthquake and the deep extent of the sedimentary basin generated long period ground motions with a duration of several hundred seconds the yufutsu basin contains an internal subbasin that deepens from east to west in contrast with the geometry of the overall basin that deepens from west to east the long period ground motions were amplified in both the eastern and western parts of the basin with the durations being greatly extended in the western part a series of computations with and without each of the velocity layers within the basin demonstrated that the basin response amplifies long period ground motions as expected and that the subbasin response is effective in amplifying and extending long period ground motions our quantitative 3 d finite difference simulations clarify the generation of disastrous long period ground motions that occurred in the yufutsu basin during the 2003 tokachi oki earthquake

controls upon the last glacial maximum deglaciation of the northern uummannaq ice stream system west greenland the uummannaq ice stream system uiss was a convergent cross shelf ice stream system that operated in west greenland during the last glacial maximum lgm this paper presents new evidence constraining the geometry and evolution of the northern sector of the uiss and considers the factors controlling its dynamic behaviour geomorphological mapping 21 new terrestrial cosmogenic nuclide tcn exposure ages and radiocarbon dating constrain lgm warm based ice stream activity in the north of the system up to 1400 m a s l intervening plateaux areas either remained ice free or were covered by cold based icefields beyond the inner fjords topography and bathymetry forced ice flow southwards into the uummannaq trough where it coalesced with ice from the south and formed the trunk zone of the uiss deglaciation of the uiss began at 14 9 cal ka bp rapid retreat from the lgm limit was forced by an increase in air temperatures and rising sea level enhanced by the bathymetric over deepening of the uummannaq and igdlorssuit sund troughs ice reached the inner fjord confines in the northern uummannaq area by 11 6 ka and experienced an ice marginal stabilisation in rink karrat fjord for up to 5 ka this was a function of topographic constriction and bathymetric shallowing and occurred despite continued climatic forcing in the neighbouring ingia fjord this did not occur following this period of stability ice within rink karrat fjord retreated reaching the present ice margin or beyond after 5 ka the presence of a major ice stream within a mid fjord setting during the mid holocene and the holocene thermal maximum 11 5 ka is in direct contrast to records of other ice streams throughout west greenland which suggest ice had retreated beyond its present margin by 9 7 ka this demonstrates the potential importance of topographic control on calving margin stability and its ability to override climatic forcing

introduction to this special section advances in seismic sensors seismic detectors have been around for centuries and seismic prospecting for many decades the variety of seismic sensors in modern surveys is dazzling they can measure particle velocity and acceleration pressure and pressure gradient strain and strain rate and multiple components z h1 h2 yaw pitch roll from near dc to hundreds or thousands of hertz in land marine borehole and extraterrestrial environments

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

multiple stage deglacial retreat of the southern greenland ice sheet linked with irminger current warm water transport 1 there is limited knowledge pertaining to the history of the greenland ice sheet gis during the last glacial interglacial transition as it retreated from the continental margins to an inland position here we use multiproxy data including ice rafted debris ird planktonic isotopes alkenone temperatures and tephra geochemistry from the northern labrador sea off southwest greenland to investigate the deglacial response of the gis and evaluate its implications for the north atlantic deglacial development the results imply that the southern gis retreated in three successive stages 1 early deglaciation of the east greenland margins by tephra rich ird that embrace heinrich event 1 2 progressive retreat during allerod culminating in major meltwater releases 18o depletion of 1 2 at the allerod younger dryas transition 12 8 13 0 kyr b p and 3 a final stage of glacial recession during the early holocene 9 11 kyr b p rather than indicating local temperatures of ambient surface water the alkenones likely were transported to the core site by the irminger current we attribute the timing of gis retreat to the incursion of warm intermediate waters along the base of grounded glaciers and below floating ice shelves on the continental margin the results lend support to the view that gis meltwater presented a forcing factor for the younger dryas cooling

vertical seismic profiling using distributed acoustic sensing with scatter enhanced fibre optic cable at the cu au new afton porphyry deposit british columbia canada abstract wireline logs and vertical seismic profile data were acquired in two boreholes intersecting the main mineralized zone at the cu au new afton porphyry deposit canada with the objectives of imaging lithological contacts fault zones that may have acted as conduits that channelled the mineralization and alteration zones log data provide physical rock properties for the main lithologies and alteration zones calliper logs reveal many faults and caved in zones generally indicating rocks with low integrity at the borehole wall the preponderance of these zones as indicated by the logs suggests that their response may dominate the seismic reflection wavefield outside fault zones compressional and shear wave velocities exhibit significant variability due to porosity the heterogeneity of volcanic fragmental rocks and alteration distributed acoustic sensing was used to acquire vertical seismic profiling data in the two boreholes surveyed with wireline logs straight and helically wound fibre optic cables housed standard fibres and a fibre engineered to increase the intensity of backscattering at the distributed acoustic sensing interrogator standard and engineered optical fibres placed in the two boreholes were daisy chained together to form two 5 km long continuous fibres that were interrogated at once with two interrogators a new generation of interrogator connected to the engineered fibres provided field data with lower noise level and higher signal to noise ratio these data with higher signal to noise ratio from straight fibre optic cable were processed and used for depth imaging depth images benefitted from new migration weights that account for the directional sensitivity of the straight fibre optic cable and limit the extent of migration artefacts migration results show several reflectors with shallow dips to the northwest some explained by faults intersecting the surveyed boreholes the main sub vertical lithological and alteration contacts at new afton generated downgoing reflections that were not considered in the migration

site amplification in the los angeles basin from three dimensional modeling of ground motion it is well established that sedimentary basins can significantly amplify earthquake ground motion however the amplification at any given site can vary with earthquake location to account for basin response in probabilistic seismic hazard analysis therefore we need to know the average amplification and intrinsic variability standard deviation at each site given all earthquakes of concern in the region due to a dearth of empirical ground motion observations theoretical simu lations constitute our best hope of addressing this issue here 0 0 5 hz finite difference finite fault simulations are used to estimate the three dimensional 3d response of the los angeles basin to nine different earthquake scenarios amplifi cation is quantified as the peak velocity obtained from the 3d simulation divided by that predicted using a regional one dimensional 1d crustal model average ampli fication factors are up to a factor of 4 with the values from individual scenarios typically differing by as much as a factor of 2 5 the average amplification correlates with basin depth with values near unity at sites above sediments with thickness less than 2 km and up to factors near 6 above the deepest 9 km and steepest dipping parts of the basin there is also some indication that amplification factors are greater for events located farther from the basin edge if the 3d amplification factors are divided by the 1d vertical sh wave amplification below each site they are lowered by up to a factor of 1 7 the duration of shaking in the 3d model is found to be longer by up to more than 60 seconds relative to the 1d basin response the simu lation of the 1994 northridge earthquake reproduces recorded 0 0 5 hz particle velocities relatively well in particular at near source stations the synthetic and observed peak velocities agree within a factor of two and the log standard deviation of the residuals is 0 36 this is a reduction of 54 and 51 compared to the values obtained for the regional 1d model and a 1d model defined by the velocity and density profile below a site in the middle of the basin dow respectively this result suggests that long period ground motion estimation can be improved consid erably by including the 3d basin structure however there are uncertainties con cerning accuracy of the basin model model resolution the omission of material with shear velocities lower than 1 km s and the fact that only nine scenarios have been considered therefore the amplification factors reported here should be used with caution until they can be further tested against observations however the results do serve as a guide to what should be expected particularly with respect to increased amplification factors at sites located above the deeper parts of the basin

validation of a 3d velocity model of the puget sound region based on modeling ground motion from the 28 february 2001 nisqually earthquake in this study we prepared a 3d velocity model suitable for modeling long period wave propagation in the puget sound region the model is based on products of the seismic hazard investigation in puget sound ships and geophysical information from other studies of the region the adequacy of the velocity model was evaluated based on analyses of goodness of fit between recorded and simulated ground motion velocity from the m 6 8 nisqually earthquake the earthquake was located about 60 km south of seattle with a hypocentral depth of 59 km the analyses were performed in the frequency range of 0 02 0 5 hz using data from 40 stations although our model covers a wide area of the puget sound region its quality is assessed in the seattle region in which the distribution of stations that recorded the nisqually earthquake was denser our 3d finite difference ground motion modeling suggests that the propagation of long period waves periods longer than 3 sec in the seattle basin is mostly affected by the deep basin structure the tomographic velocity model of parsons et al 2001 combined with the model of depth to the basement of the seattle basin of blakely et al 1999 was essential in preparing and constraining geometrical features of the proposed velocity model manuscript received 20 august 2003

the deglacial history of southeast sector of the greenland ice sheet during the last glacial maximum the southeast sector of the greenland ice sheet is currently experiencing rapid changes in mass balance and ice sheet dynamics at low elevations however to what extent these changes are typical of the behaviour of this sector of the ice sheet is uncertain as our understanding of the longer term controls on ice sheet dynamics in this region is limited two models exist for last glacial maximum lgm ice sheet configuration in east greenland the first minimum model envisages a restricted ice sheet with exposed nunataks in coastal areas and limited ice extent onto the continental shelf fed by ice flowing through bedrock troughs a second maximum model entails a thicker ice sheet with limited coastal nunataks and ice filling the coastal valleys and extending across the entire continental shelf radiocarbon dates on foraminifera collected from seabed cores on the southeast greenland continental shelf suggest that the ice sheet reached a maximum extent at ca 22 kcal yr before retreating perhaps as early as ca 17 kcal yr bp and reaching the present coast at ca 10 kcal yr bp this paper presents the results of a study designed to test these different ice sheet models based on geomorphological mapping and cosmogenic isotope analyses in the torqulertivit imiat valley an area to the east of the coastal town of ammassalik 26al and 10be measurements on abraded bedrock surfaces in terrain above local trimlines yield surface exposure ages of ca 11 8 9 9 ka this demonstrates warm based glacial erosion of high level surfaces ca 740 m asl followed by trimline formation during deglaciation and intense postglacial weathering our work constrains minimum ice thickness during the lgm to at least 740 m and supports a maximum ice sheet model in this sector of the gis ice sheet retreat from the continental shelf to the southern edge of sermilik fjord is dated to ca 11 1 9 7 ka and helps to constrain the timing of the early holocene retreat of the helheim glacier ice stream within the torqulertivit imiat valley age determinations from glacially abraded terrain above the local marine limit on the coast 11 1 9 7 ka and those from 10 km up valley 12 8 9 9 ka suggest rapid surface ablation during these intervals coincident with rapid atmospheric warming observed in the greenland ice core records

a 10be production rate calibration for the arctic we present a baffin bay 10 be production rate calibration derived from glacial deposits in western greenland and baffin island and test our results against published 10 be calibration datasets to develop an arctic 10 be production rate our calibration comprises i 10 be measurements from moraine boulders linked to a 14 c dated moraine at jakobshavn isfjord in western greenland ii an independent and previously published 10 be production rate at jakobshavn isfjord and iii re measured 10 be concentrations from a baffin island calibration site that is included in the north eastern north america dataset combined we calculate a sea level high latitude 10 be production rate for the baffin bay region of 3 96 0 07 atoms g 1 a 1 lal stone scaling model after testing the baffin bay rate against calibration sites in norway and north eastern north america we calculate a more conservative arctic production rate of 3 96 0 15 atoms g 1 a 1 the baffin bay and arctic 10 be production rates are indistinguishable from the north eastern north america 10 be production rate 3 91 0 19 atoms g 1 a 1 and yield overall uncertainties of 2 3 7 1s these production rates reduce systematic uncertainties in 10 be based chronologies of ice margin change and allow 10 be based chronologies to be more confidently compared with high resolution climate records such as those from greenland ice cores copyright 2013 john wiley sons ltd

late holocene expansion of istorvet ice cap liverpool land east greenland abstract the greenland ice sheet is undergoing dynamic changes that will have global implications if they continue into the future in this regard an understanding of how the ice sheet responded to past climate changes affords a baseline for anticipating future behavior small independent ice caps adjacent to the greenland ice sheet hereinafter called local ice caps are sensitive indicators of the response of greenland ice marginal zones to climate change therefore we reconstructed late holocene ice marginal fluctuations of the local istorvet ice cap in east greenland using radiocarbon dates of subfossil plants 10 be dates of surface boulders and analyses of sediment cores from both threshold and control lakes during the last termination the istorvet ice cap had retreated close to its maximum holocene position by 11 730 cal yr bp radiocarbon dates of subfossil plants exposed by recent recession of the ice margin indicate that the istorvet cap was smaller than at present from ad 200 to ad 1025 sediments from a threshold lake show no glacial input until the ice cap advanced to within 365 m of its holocene maximum position by ad 1150 thereafter the ice cap remained at or close to this position until at least ad 1660 the timing of this the most extensive of the holocene expansion is similar to that recorded at some glaciers in the alps and in southern alaska however in contrast to these other regions the expansion in east greenland at ad 1150 appears to have been very close to if not at a maximum holocene value comparison of the istorvet ice cap fluctuations with holocene glacier extents in southern hemisphere middle to high latitude locations on the antarctic peninsula and in the andes and the southern alps suggests an out of phase relationship if correct this pattern supports the hypothesis that a bipolar see saw of oceanic and or atmospheric circulation during the holocene produced asynchronous glacier response at some localities in the two polar hemispheres

constraining landscape history and glacial erosivity using paired cosmogenic nuclides in upernavik northwest greenland high latitude landscape evolution processes have the potential to preserve old relict surfaces through burial by cold based nonerosive glacial ice to investigate landscape history and age in the high arctic we analyzed in situ cosmogenic 10 be and 26 al in 33 rocks from upernavik northwest greenland we sampled adjacent bedrock boulder pairs along a 100 km transect at elevations up to 1000 m above sea level bedrock samples gave significantly older apparent exposure ages than corresponding boulder samples and minimum limiting ages increased with elevation two isotope calculations 26 al 10 be on 20 of the 33 samples yielded minimum limiting exposure durations up to 112 k y minimum limiting burial durations up to 900 k y and minimum limiting total histories up to 990 k y the prevalence of 10 be and 26 al inherited from previous periods of exposure especially in bedrock samples at high elevation indicates that these areas record long and complex surface exposure histories including significant periods of burial with little subglacial erosion the long total histories suggest that these high elevation surfaces were largely preserved beneath cold based nonerosive ice or snowfields for at least the latter half of the quaternary because of high concentrations of inherited nuclides only the six youngest boulder samples appear to record the timing of ice retreat these six samples suggest deglaciation of the upernavik coast at 11 3 0 5 ka average 1 standard deviation there is no difference in deglaciation age along the 100 km sample transect indicating that the ice marginal position retreated rapidly at rates of 120 m yr 1

new in situ 14c data indicate the absence of nunataks in west greenland during the last glacial maximum abstract in situ cosmogenic nuclide exposure age distributions on ice age nunataks act as past ice thickness indicators and provide valuable targets for ice sheet model simulations of the last glacial maximum several locations along west greenland have been identified as being potential nunataks due to their weathered nature and their high cosmogenic nuclide inventories with little evidence for ice sheet burial we present new in situ cosmogenic 14c measurements from four high elevation surfaces in the central uummannaq fjord system that were identified as potential nunataks in prior work building on previous work we model cosmogenic radionuclide production and decay and consider a range of ice sheet history scenarios since our results require more burial or shielding under ice than what independent methods suggest for holocene ice cap cover we propose that these locations were not nunataks during the last glacial maximum but rather were buried during the peak of the last glacial maximum however we cannot confirm whether these sites were buried by the greenland ice sheet or local glaciers

new constraints on greenland ice sheet dynamics during the last glacial cycle evidence from the uummannaq ice stream system this paper presents the first assessment of the uummannaq ice stream system uiss in west greenland the uiss drained 6 of the greenland ice sheet gris at the last glacial maximum lgm the onset of the uiss is a function of a convergent network of fjords which feed a geologically controlled trough system running offshore to the shelf break mapping cosmogenic radiogenic nuclide crn dating and model output reveal that glacially scoured surfaces up to 1266 m above sea level asl in fjord head areas were produced by warm based ice moving offshore during the lgm with the elevation of warm based ice dropping westwards to 700 m asl as the ice stream trunk zone developed marginal plateaux with allochthonous blockfields suggest that warm based ice produced till and erratics up to 1200 m asl but crn ages and weathering pits suggest this was pre lgm with only cold based ice operating during the lgm deglaciation began on the outer shelf at 14 8 cal kyrs b p with ubekendt ejland becoming ice free at 12 4 ka the uiss then collapsed with over 100 km of retreat by 11 4 ka 10 8 cal kyrs b p a rapid and complex response to bathymetric deepening trough widening and sea level rise coinciding with rapidly increasing air temperatures and solar radiation but which occurred prior to ocean warming at 8 4 cal kyrs b p local fjord constriction temporarily stabilized the unzipped uiss margins at the start of the holocene before ice retreat inland of the current margin at 8 7 ka

early holocene history of the west greenland ice sheet and the gh 8 2 event abstract the margin of the greenland ice sheet retreated rapidly during the first few thousand years of the holocene during this period of relative warmth known as the holocene thermal maximum ice core records identify a significant short lived cooling event at approximately 8 4 8 0 ka cal yr bp the gh 8 2 event associated with a 5 7 c fall in mean annual air temperature over the centre of the ice sheet in this paper we constrain the history of the ice sheet margin in disko bugt west greenland and that of a major ice stream jakobshavns isbrae during the early holocene which incorporates the interval of the gh 8 2 event our work is based on a new relative sea level curve and minimum age estimates for the timing of deglaciation from two field sites combined with a review of previously published research from the study area we identify important differences in the chronology of ice margin recession during the early holocene most noticeably the margin of jakobshavns isbrae retreated well inland of the adjacent ice sheet at this time we conclude that the early holocene fjord stade moraines in disko bugt do not record a uniform ice sheet margin response to the gh 8 2 event rather these moraines are diachronous and formed between c 10 8 ka cal yr bp their age varying as a function of the interplay between topography and ice sheet ice stream dynamics we hypothesise that one cause for the lack of an identifiable response to the gh 8 2 event is because topographic controls dominated ice sheet behaviour at this time in lowland areas any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin

modelled ice sheet margins of three greenland ice sheet models compared with a geological record from ice marginal deposits in central west greenland ice sheet modelling is an essential tool for estimating the effect of climate change on the greenland ice sheet the large spatial and long term temporal scale ofice sheet models limits the amount of data which can be used to test model results the geological record is useful because it provides test material on the timescales typical for the memory of ice sheets millennia this paper compares modelled ice marginal positions with a geological scenario of ice marginpositions since the last glacial maximum to the present in west greenland morphological evidence of ice margin positions is provided by moraines moraine systems are dated by 14c dated marine shells and terrestrial peat we compared three greenland ice sheet models there are distinct differences inmodelled ice margin positions between the models and between model results and the geological record disagreement between models and the geologicalrecord in the near coastal area are explained by the insufficient treatment of marginal processes in a tidewater environment a smaller than present ice sheetaround the warm period in the holocene holocene climatic optimum only pops up when an unsmooth forcing is used this underlines the importance ofshort term variations in climatic variables in determining ice margin positions in the past but also in the future

cosmogenic 26al 10be surface production ratio in greenland the assumed value for the cosmogenic 26al 10be surface production rate ratio in quartz is an important parameter for studies investigating the burial or subaerial erosion of long lived surfaces and sediments recent models and data suggest that the production ratio is spatially variable and may be greater than originally thought here we present measured 26al 10be ratios for 24 continuously exposed bedrock and boulder surfaces spanning 61 77 n in greenland empirical measurements such as ours include nuclides produced predominately by neutron induced spallation with percent level contributions by muon interactions the slope of a york regression line fit to our data is 7 3 0 3 1 suggesting that the 26al 10be surface production ratio exceeds the commonly used value of 6 75 at least in the arctic a higher 26al 10be production ratio has implications for multi nuclide cosmogenic isotope studies because it results in greater modeled burial durations and erosion rates

field testing of fiber optic distributed acoustic sensing das for subsurface seismic monitoring distributed acoustic sensing das is a relatively recent development in the use of fiber optic cable for measurement of ground motion discrete fiber optic sensors typically using a bragg diffraction grating have been in research and development and field testing for more than 15 years with geophysical applications at least 12 years old bostick 2000 and summary in keul et al 2005 however developments in recent years have sought to remove the need for point sensors by using the fiber cable itself as a sensor mestayer et al 2011 miller et al 2012

constraining multi stage exposure burial scenarios for boulders preserved beneath cold based glacial ice in thule northwest greenland abstract boulders and landscapes preserved beneath cold based non erosive glacial ice violate assumptions associated with simple cosmogenic exposure dating in such a setting simple single isotope exposure ages over estimate the latest period of surface exposure hence alternate approaches are required to constrain the multi stage exposure burial histories of such samples here we report 28 paired analyses of 10be and 26al in boulder samples from thule northwest greenland we use numerical models of exposure and burial as well as monte carlo simulations to constrain glacial chronology and infer process in this arctic region dominated by cold based ice we investigate three specific cases that can arise with paired nuclide data 1 exposure ages that are coeval with deglaciation and 26al 10be ratios consistent with constant exposure 2 exposure ages that pre date deglaciation and 26al 10be ratios consistent with burial following initial exposure and 3 exposure ages that pre date deglaciation and 26al 10be ratios consistent with constant exposure most glacially transported boulders in thule have complex histories some were exposed for tens of thousands of years and buried for at least hundreds of thousands of years while others underwent only limited burial these boulders were probably recycled through different generations of till over multiple glacial interglacial cycles likely experiencing partial or complete shielding during interglacial periods due to rotation or shallow burial by sediments our work demonstrates that the landscape in thule like many high latitude landscapes was shaped over long time durations and multiple glacial and interglacial periods throughout the quaternary

imaging the aquistore reservoir after 36 kilotonnes of co2 injection using distributed acoustic sensing abstractaquistore is a geologic co2 storage project that is using a deep saline formation as a storage reservoir from april 2015 to february 2016 approximately 36 kilotonnes of co2 were injected into the reservoir at a depth of 3130 3350 m we have developed an analysis of distributed acoustic sensing das 3d vertical seismic profiling data acquired in february 2016 marking the first seismic survey since injection began the vsp data were processed in parallel with baseline preinjection data from a november 2013 survey with the objective of detecting and characterizing the subsurface co2 plume and evaluating the repeatability of das in a reservoir monitoring project a single processing sequence was devised that 1 accurately imaged the reservoir for the baseline and monitor data and 2 attained adequate repeatability to observe time lapse differences related to the presence of co2 repeatability was somewhat compromised by the less advanced noise cancellation methodology of the das system used for

fluctuations of local glaciers in greenland during latest pleistocene and holocene time abstract this paper is the first to summarize research on fluctuations of local glaciers in greenland e g ice caps and mountain glaciers independent of the greenland ice sheet during latest pleistocene and holocene time in contrast to the extensive data available for fluctuations of the greenland ice sheet surprisingly little data exist to constrain local glacier extents much of the available research was conducted prior to wide spread use of ams radiocarbon dating and the advent of surface exposure and luminescence dating although there is a paucity of data generally similar patterns of local glacier fluctuations are observed in all regions of greenland and likely reflect changes in paleoclimate which must have influenced at least the margins of the inland ice absolute age data for late glacial and early holocene advances of local glaciers are reported from only two locations disko island and the scoresby sund region subsequent to late glacial or early holocene time most local glaciers were smaller than at present or may have disappeared completely during the holocene thermal maximum in general local glacier advances that occurred during historical time 1200 1940 ad are the most extensive since late glacial or early holocene time historical documents and more recent aerial photographs provide useful information about local glacier fluctuations during the last 100 yrs in all but one area north greenland local glaciers are currently receding from historical extents

a study on the response of a soft basin for incident s p and rayleigh waves with special reference to the long duration observed in mexico city abstract the responses of two types of soft basins for incident sh sv p and rayleigh waves in a 2 d elastic half space are investigated with special reference to the long duration of strong motions observed in mexico city during the michoacan mexico earthquake of 1985 first the difficulty for simple 1 d models to reproduce the later part of the accelerogram observed in mexico city is shown then the effect of a 2 d deep basin structure of a relatively large scale 10 km wide and 1 km deep and a moderate impedance ratio 2 5 is studied the results show that surface waves generated at the edges of the basin are clearly propagating inside the basin back and forth however the increase in duration by these surface waves is 20 sec at most introducing another much softer layer inside the basin we found that the calculated durations and envelop shapes become very similar to the observed ones because of the slowness of surface wave propagation these theoretical studies suggest that the exceptionally long duration observed in mexico city might be caused by a strong constructive interaction of soft surface layers with a deep basin structure beneath the city

erosion rates in fennoscandia during the past million years abstract the widespread existence of cosmogenic nuclides accumulated in bedrock prior to the last glaciation demonstrates the limited erosional efficacy of the most recent fennoscandian and laurentide ice sheets yet the deeper history of erosion in these landscapes repeatedly blanketed by ice remains essentially unknown here we present the first comprehensive ice sheet wide analysis of cosmogenic 10be data n 953 from the fennoscandian landscape we find 64 of all sampled bedrock surfaces contain 10be inheritance including 85 of blockfields and tors and 50 of ice carved terrain in addition to 27 of ice transported boulders recent ice sheets scoured landscapes well beyond glacial troughs and nuclide inventories reveal a patchy legacy of erosional effectiveness that diminishes at high elevations such that 89 n 55 of bedrock samples retain inheritance above 1600 m we exploit this widespread nuclide inheritance in a markov chain monte carlo based inversion model to estimate long term erosion rates and surface exposure histories from 113 paired 10be 26al bedrock samples nuclide inventories with or without inheritance convey equally important information about the erosional effectiveness of the last ice sheet we define cosmogenic nuclide memory as the residence time of bedrock samples inside the nuclide production window 2 m depth where 80 of the total nuclide production occurs the cosmogenic nuclide memory is set by mean erosion rate and varies from 10 ka for samples eroded 2 m during the last glaciation to 1 ma for the slowest erosion rates we find that mean erosion rates are well constrained compared to the ratio of exposure to burial the inclusion of bedrock erosion in our computations thwarts the capacity to constrain surface exposure history or identify former nunataks from paired 10be 26al data ice carved surfaces reflect diverse erosion histories that are not straightforward to interpret from surficial morphology alone relative to the 10 mm kyr benchmark for polar ice masses we report point based mean erosion rates that vary by more than three orders of magnitude with glacial troughs and areal scour terrain eroding at 1 to 100 mm kyr blockfields at 0 8 16 mm kyr and tors at 0 8 7 7 mm kyr 5th 95th percentiles

ice sheet grounding line dynamics steady states stability and hysteresis 1 the ice sheet ice shelf transition zone plays an important role in controlling marine ice sheet dynamics as it determines the rate at which ice flows out of the grounded part of the ice sheet together with accumulation this outflow is the main control on the mass balance of the grounded sheet in this paper we verify the results of a boundary layer theory for ice flux in the transition zone against numerical solutions that are able to resolve the transition zone very close agreement is obtained and grid refinement in the transition zone is identified as a critical component in obtaining reliable numerical results the boundary layer theory confirms that ice flux through the grounding line in a two dimensional sheet shelf system increases sharply with ice thickness at the grounding line this result is then applied to the large scale dynamics of a marine ice sheet our principal results are that 1 marine ice sheets do not exhibit neutral equilibrium but have well defined discrete equilibrium profiles 2 steady grounding lines cannot be stable on reverse bed slopes and 3 marine ice sheets with overdeepened beds can undergo hysteresis under variations in sea level accumulation rate basal slipperiness and ice viscosity this hysteretic behavior can in principle explain the retreat of the west antarctic ice sheet following the last glacial maximum and may play a role in the dynamics of heinrich events

preservation of arctic landscapes overridden by cold based ice sheets for nearly 40 years a massive well preserved glaciomarine delta more than 54 000 years old and ancillary landforms have formed the cornerstone of models positing limited ice sheet extent in arctic canada during the late wisconsinan we present exposure ages for large boulders on the delta surface which coupled with preservation of relict landforms demonstrate that the region was covered by minimally erosive cold based ice during the late wisconsinan our data suggest that surficial features commonly used to define the pattern of late wisconsinan ice movement cannot be used on their own to constrain late wisconsinan ice sheet margins in arctic regions

constraining quaternary ice covers and erosion rates using cosmogenic 26 al 10 be nuclide concentrations abstract paired cosmogenic nuclides are often used to constrain the exposure burial history of landforms repeatedly covered by ice during the quaternary including tors high elevation surfaces and steep alpine summits in the circum arctic regions the approach generally exploits the different production rates and half lives of 10 be and 26 al to infer past exposure burial histories however the two stage minimum limiting exposure and burial model regularly used to interpret the nuclides ignores the effect of variable erosion rates which potentially may bias the interpretation in this study we use a monte carlo model approach to investigate systematically how the exposure burial and erosion history including variable erosion and the timing of erosion events influence concentrations of 10 be and 26 al the results show that low 26 al 10 be ratios are not uniquely associated with prolonged burial under ice but may as well reflect ice covers that were limited to the coldest part of the late pleistocene combined with recent exhumation of the sample e g due to glacial plucking during the last glacial period as an example we simulate published 26 al 10 be data from svalbard and show that it is possible that the steep alpine summits experienced ice free conditions during large parts of the late pleistocene and varying amounts of glacial erosion this scenario which contrasts with the original interpretation of more or less continuous burial under non erosive ice over the last 1 myr thus challenge the conventional interpretation of such data on the other hand high 26 al 10 be ratios do not necessarily reflect limited burial under ice which is the common interpretation of high ratios in fact high 26 al 10 be ratios may also reflect extensive burial under ice combined with a change from burial under erosive ice which brought the sample close to the surface to burial under non erosive ice at some point during the mid pleistocene importantly by allowing for variable erosion rates the model results may reconcile spatially varying 26 al 10 be data from bedrock surfaces preserved over multiple glacial cycles suggesting that samples from the same high elevation surface or neighbouring alpine summits may have experienced similar long term burial under ice but varying amounts of glacial erosion

contributions and unrealized potential contributions of cosmogenic nuclide exposure dating to glacier chronology 1990 2010 abstract this paper reviews the application of cosmogenic nuclide exposure dating to glacier chronology exposure dating of glacial landforms has made an outsize impact on this field because the technique filled an obvious need that had already been recognized by glacial geologists by now hundreds of studies have used cosmogenic nuclide exposure dating to date glacial deposits and in fact it is rare to find a study of glacial geology or glacier chronology or any paleoclimate synthesis that makes use of such studies that does not involve exposure dating these developments have resulted in major contributions to glacier chronology and paleoclimate in particular i reconstructing antarctic ice sheet change ii establishing the chronology of late pleistocene and holocene glacier change in mountain regions where it was previously unknown iii establishing the broad chronological outlines of mountain glaciations prior to the last glacial maximum and iv gaining insight into subglacial erosional processes through the observation that many glaciated surfaces preserve cosmogenic nuclide inventories from long past ice free periods as well as the present one an important potential future contribution will be the application of the large data set of exposure dated glacier chronologies to better understand global and regional climate dynamics during lateglacial and holocene millennial scale climate changes however this contribution cannot be realized without significant progress in two areas i understanding and accounting for geologic processes that cause apparent exposure ages on glacial landforms to differ from the true age of the landform and ii minimizing systematic uncertainties in exposure ages that stem from cosmogenic nuclide production rate estimates and scaling schemes at present there exists an enormous data set of exposure ages on glacial deposits but these data cannot be used to their full potential in paleoclimate syntheses due to an inadequate understanding of geologic scatter and production rate uncertainties the intent of this paper is to highlight this situation and suggest some strategies for realizing this potential

field testing of modular borehole monitoring with simultaneous distributed acoustic sensing and geophone vertical seismic profiles at citronelle alabama a modular borehole monitoring concept has been implemented to provide a suite of well based monitoring tools that can be deployed cost effectively in a flexible and robust package the initial modular borehole monitoring system was deployed as part of a co2 injection test operated by the southeast regional carbon sequestration partnership near citronelle alabama the citronelle modular monitoring system transmits electrical power and signals fibre optic light pulses and fluids between the surface and a reservoir additionally a separate multi conductor tubing encapsulated line was used for borehole geophones including a specialized clamp for casing clamping with tubing deployment the deployment of geophones and fibre optic cables allowed comparison testing of distributed acoustic sensing we designed a large source effort 64 sweeps per source point to test fibre optic vertical seismic profile and acquired data in 2013 the native measurement in the specific distributed acoustic sensing unit used an idas from silixa ltd is described as a localized strain rate following a processing flow of adaptive noise reduction and rebalancing the signal to dimensionless strain improvement from repeated stacking of the source was observed conversion of the rebalanced strain signal to equivalent velocity units via a scaling by local apparent velocity allows quantitative comparison of distributed acoustic sensing and geophone data in units of velocity we see a very good match of uncorrelated time series in both amplitude and phase demonstrating that velocityconverted distributed acoustic sensing data can be analyzed equivalent to vertical geophones we show that distributed acoustic sensing data when averaged over an interval comparable to typical geophone spacing can obtain signal to noise ratios of 18 db to 24 db below clamped geophones a result that is variable with noise spectral amplitude because the noise characteristics are not identical with vertical seismic profile processing we demonstrate the effectiveness of downgoing deconvolution from the large spatial sampling of distributed acoustic sensing data along with improved upgoing reflection quality we conclude that the extra source effort currently needed for tubing deployed distributed acoustic sensing vertical seismic profile as part of a modular monitoring system is well compensated by the extra spatial sampling and lower deployment cost as compared with conventional borehole geophones

preliminary analysis of long period basin response in the los angeles region from the 1994 northridge earthquake long period 1 10 sec ground motions recorded in the los angeles basin region during the northridge earthquake show complex waveforms extended durations and multiple sets of arrivals which cannot be attributed solely to source processes or wave propagation within a plane layered medium these features suggest a strong interaction between the propagating seismic wave field and the laterally varying subsurface geologic structure of this region recorded motions at a hard rock site in the santa monica mountains scrs are smaller by nearly a factor of three in peak velocity compared to recordings at more distant sites in the adjacent northwest portion of the los angeles basin in addition although the rock site recording has a relatively simple wave shape the basin site recordings are dominated by late arriving large amplitude pulses of energy we interpret these arrivals to be surface waves which are generated by body waves interacting with the thickening margin of the basin a preliminary modeling analysis of these data indicates that a combination of both large scale deep basin and small scale shallow micro basin structures are needed to explain the observed responses

ice stream influence on west greenland ice sheet dynamics during the last glacial maximum this paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central west greenland and explores the evidence for a cross shelf ice stream at the last glacial maximum lgm to the east of sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow flowing ice sheet areas at the coast the effects of regional flow convergence caused by coastal fjord orientation routed ice into the sisimiut itilleq area where it formed an ice stream onset zone this funnelled ice into an offshore trough holsteinsborg dyb resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream holsteinsborg isbrae to the south of this striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast but were later redirected by the itilleq fjord ice which turned southwestward due to diffluent flow and deflection by holsteinsborg isbrae roches moutonnees in this area have low elongation ratios and high bedform density but do not provide unequivocal support for ice streaming as they are a product of both bedrock structure and changes in ice flow direction rather than enhanced flow velocities cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca 755 810 m above sea level in this region such ice thickness enabled holsteinsborg isbrae to reach the mid outer continental shelf during the lgm and to contribute to the formation of a trough mouth fan and the outer hellefisk moraines initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the bolling interstadial at ca 14 5 cal ka bp between 12 and 10 cal ka bp both increased air and ocean temperatures post the younger dryas and peak sea level rise up to the marine limit caused accelerated thinning and marginal retreat through calving although dating evidence suggests ice streams remained along the inner shelf coast boundary until at least ca 10 cal ka bp their longevity maintained by increased ice thickness and ice discharge copyright 2009 john wiley sons ltd

a new high resolution digital elevation model of greenland fully validated with airborne laser altimeter data a new digital elevation model of the greenland ice sheet and surrounding rock outcrops has been produced at 1 km postings from a comprehensive suite of satellite remote sensing and cartographic data sets height data over the ice sheet were mainly from ers 1 and geosat radar altimetry these data were corrected for a slope dependent bias that had been identified in a previous study the radar altimetry was supplemented with stereophotogrammetric data sets synthetic aperture radar interferometry and digitized cartographic maps over regions of bare rock and where gaps in the satellite altimeter coverage existed the data were interpolated onto a regular grid with a spacing of 1 km the accuracy of the resultant digital elevation model over the ice sheet was assessed using independent and spatially extensive measurements from an airborne laser altimeter that had an accuracy of between 10 and 12 cm in a comparison with the laser altimetry the digital elevation model was found to have a slope dependent accuracy ranging from 1 04 1 98 m to 0 06 14 33 m over the ice sheet for a slope range of 0 0 1 0 the mean accuracy over the whole ice sheet was 0 33 6 97 m over the bare rock areas the accuracy ranged from 20 to 200 m dependent on the data source available the new digital elevation model was used as an input data set for a positive degree day model of ablation the new elevation model was found to reduce ablation by only 2 compared with using an older 2 5 km resolution model which suggests that resolution induced errors in estimating ablation are no longer important

an isochron method for cosmogenic nuclide dating of buried soils and sediments we describe an improved method for dating buried paleosols using measurements of the cosmic ray produced radionuclides 10be and 26al in quartz grains and apply it to a sequence of intercalated tills and paleosols in central missouri usa that record plio pleistocene advances of the laurentide ice sheet a buried paleosol implies a period of surface exposure and nuclide accumulation followed by burial and a halt to nuclide production if the paleosol is formed in a sedimentary unit such as till this unit may also have been emplaced with unknown 26al and 10be concentrations inherited from past surface exposure if the inherited nuclide concentrations are the same at all depths in the soil as is true for well mixed sediments such as till then the 26al and 10be concentrations at different depths in the paleosol will show a linear relationship the slope of this line depends on the duration of burial of the paleosol but not on the inherited nuclide concentrations or on the sample depths thus one can date strata overlying buried paleosols by measuring 26al and 10be at multiple depths in the paleosol and calculating the burial age of the paleosol from the resulting isochron we focus on applying this approach to till paleosol sequences but the basic idea of forming an 26al 10be burial isochron with a set of samples that share the same burial age but differ in other aspects of their exposure history applies to other stratigraphic settings as well the method yields ages for four tills in missouri that are stratigraphically consistent agree with paleomagnetic age constraints and show that ice advanced into missouri near 1 25 ma near 0 8 ma and twice between ca 0 4 and 0 2 ma

elastic full waveform inversion of vertical seismic profile data acquired with distributed acoustic sensors distributed acoustic sensing das is a rapidly developing technology particularly useful for the acquisition of vertical seismic profile vsp surveys das data are increasingly used for seismic imaging but not for estimating rock properties we propose a workflow for estimating elastic properties of the subsurface using full waveform inversion fwi of das vsp data whereas conventional borehole geophones usually measure three components of particle velocity das measures a single quantity which is an approximation of the strain or strain rate along the fiber standard fwi algorithms are developed for particle velocity data and hence their application to das data requires conversion of these data to particle velocity along the fiber this conversion can be accomplished by a specially designed filter field measurements show that the conversion result is close to vertical particle velocity as measured by geophones elastic time domain fwi of a synthetic multi offset vsp dataset for a vertical well sho

minimal erosion of arctic alpine topography during late quaternary glaciation alpine topography in europe has been shaped by recent glaciations cosmogenic dating of summits in svalbard suggest that arctic alpine topography is a million years old and that subsequent glaciations have preserved rather than eroded the landscape the alpine topography observed in many mountainous regions is thought to have formed during repeated glaciations of the quaternary period1 2 before this time landscapes had much less relief1 2 3 however the spatial patterns and rates of quaternary exhumation at high latitudes where cold based glaciers may protect rather than erode landscapes are not fully quantified here we determine the exposure and burial histories of rock samples from eight summits of steep alpine peaks in northwestern svalbard 79 5 n using analyses of 10be and 26al concentrations4 5 we find that the summits have been preserved for at least the past one million years the antiquity of svalbard s alpine landscape is supported by the preservation of sediments older than one million years along a fjord valley6 which suggests that both mountain summits and low elevation landscapes experienced very low erosion rates over the past million years our findings support the establishment of northwestern svalbard s alpine topography during the early quaternary we suggest that as the quaternary ice age progressed glacial erosion in the arctic became inefficient and confined to ice streams and high relief alpine landscapes were preserved by minimally erosive glacier armour

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

distributed acoustic sensing for reservoir monitoring with vertical seismic profiling distributed acoustic sensing is a novel technology for seismic data acquisition particularly suitable for vertical seismic profiling it is a break through for low cost on demand seismic monitoring of reservoirs both onshore and offshore in this article we explain how distributed acoustic sensing works and demonstrate its usability for typical vertical seismic profiling applications such as checkshots imaging and time lapse monitoring we show numerous data examples and discuss distributed acoustic sensing as an enabler of seismic monitoring with 3d vertical seismic profiling key words borehole geophysics acquisition seismics time lapse monitoring

autochthonous block fields in southern norway implications for the geometry thickness and isostatic loading of the late weichselian scandinavian ice sheet the consistent geographical and altitudinal distribution of autochthonous block fields mantle of bedrock weathered in situ and trimlines in southern norway suggests a multi domed and asymmetric late weichselian ice sheet low gradient ice sheet profiles in the southern baltic region in the north sea and along the outer fjord areas of southern norway are best explained by movement of ice on a bed of deforming sediment although water lubricated sliding or a combination of the two may not be excluded the ice thickness distribution of the late weichselian scandinavian ice sheet is not in correspondence with the modern uplift pattern of fennoscandia early holocene crustal rebound was apparently determined by an exponential glacio isostatic rise later however crustal movements appear to have been dominated by large scale tectonic uplift of the fennoscandian shield centred on the gulf of bothnia the region of maximum lithosphere thickness

multiple independent records of local glacier variability on nuussuaq west greenland during the holocene abstract the sensitivity of mountain glaciers to small scale climate fluctuations makes records of their past extent among the best proxies for identifying spatio temporal climate variability here we build on the few existing holocene records of local glacier change in greenland by using three independent geochronological methods proglacial lake sediment analysis cosmogenic 10be surface exposure dating and in situ 14c burial modeling to reconstruct continuous records of holocene glacier variability on nuussuaq west greenland 10be ages of perched boulders indicate eastern nuussuaq was deglaciated between 11 0 and 10 5 ka radiocarbon dated sediments from two lakes on nuussuaq contain mineral rich layers between 9 6 and 9 0 and 8 7 8 0 cal ka bp that may be correlative with nearby ice sheet moraines deposited in the early holocene multiple proxies for glacier size indicate frequent high amplitude glacier fluctuations superimposed on net glacier growth during the late holocene with significant ice expansion phases at 3 7 ka 2 8 ka and throughout the past 2 ka mean 10be ages from five nested moraine crests confirm that local glacier extents on nuussuaq culminated during both the little ice age 1470 c e n 3 and 1750 c e n 3 and the preceding centuries 520 1320 c e n 11 results reveal that local glaciers on nuussuaq episodically advanced and retreated at centennial timescales throughout the holocene most likely in response to regional climate changes in west greenland superimposed on the progressive insolation driven cooling trend in the northern hemisphere our new 10be moraine chronologies coupled with other glacier size proxies corroborate an emerging pattern of significant summer cooling and glacier expansion in the centuries prior to the little ice age in the arctic

paired bedrock and boulder 10be concentrations resulting from early holocene ice retreat near jakobshavn isfjord western greenland we measured in situ cosmogenic 10 be in 16 bedrock and 14 boulder samples collected along a 40 km transect outside of and normal to the modern ice margin near sikuijuitsoq fjord in central west

mid pleistocene cosmogenic minimum age limits for pre wisconsinan glacial surfaces in southwestern minnesota and southern baffin island a multiple nuclide approach abstract paired 10 be and 26 al analyses n 14 indicate that pre wisconsinan glaciated bedrock surfaces near the northern baffin island and southern minnesota paleo margins of the laurentide ice sheet have long and complex histories of cosmic ray exposure including significant periods of partial or complete shielding from cosmic rays using the ratio 26 al 10 be we calculate that striated outcrops of sioux quartzite in southwestern minnesota southern margin were last overrun by ice at least 500 000 years ago weathered bedrock tors on the once glaciated uplands of baffin island northern margin are eroding no faster than 1 1 m myr 1 the equivalent of at least 450 000 years of surface and near surface exposure our data demonstrate that exposure ages and erosion rates calculated from single nuclides can underestimate surface stability dramatically because any intermittent burial and the resultant lowering of nuclide production rates and nuclide abundances will remain undetected

greenland rumbles louder as glaciers accelerate flow rates of many large glaciers in greenland and antarctica have accelerated recently greenland earthquakes produced from glacier motion and calving have also increased dramatically

holocene mountain glacier history in the sukkertoppen iskappe area southwest greenland abstract mountain glaciers and ice caps gic independent of the greenland ice sheet respond rapidly to climate variations and records of their past extent provide information on the natural envelope of climate variability here we use a multi proxy approach that combines proglacial lake sediment analysis cosmogenic nuclide surface exposure dating in situ 10be and 14c and radiocarbon dating of recently ice entombed moss to generate a centennial scale record of holocene gic fluctuations in southwestern greenland following local deglaciation 10 9 ka sediments from proglacial crash lake record a glacier advance at 9 ka that is indistinguishable from nearby ice sheet moraines implying a synchronous response of gic and the greenland ice sheet to a centennial scale climate event following this local glacier advance gic experienced net recession until 4 6 ka radiocarbon ages of in situ moss n 29 and crash lake sediments reveal intervals of glacier expansion at 1 8 1 2 and 0 7 ka that are superimposed on an overall trend of net glacier expansion throughout the late holocene in situ 14c concentrations from bedrock adjacent to radiocarbon dated moss samples further constrain the duration of ice cover through the holocene in this region we find that our glacier size proxy records during the past 4 ka are broadly consistent with relatively lower temperatures recorded in gisp2 and occur during or following intervals of volcanic perturbations thus we speculate that volcanic activity although less frequent and intense than in the early holocene and during the little ice age may have led to centennial scale variability imprinted on net glacier expansion due to decreasing summer insolation through the late holocene

ice sheet extent and early deglacial history of the southwestern sector of the greenland ice sheet the offshore and coastal geomorphology of southwest greenland records evidence for the advance and decay of the greenland ice sheet during the last glacial maximum regional ice flow patterns in the vicinity of sisimiut show an enlarged ice sheet that extended southwestwards on to the shelf with an ice stream centred over holsteinsborg dyb high level periglacial terrain composed of blockfield and tors is dated to between 101 and 142 ka using 26al and 10be cosmogenic exposure ages these limit the maximum surface elevation of the last glacial maximum ice sheet in this part of southwest greenland to ca 750 810 m asl and demonstrate that terrain above this level has been ice free since mis 6 last glacial maximum ice thickness on the coast of ca 700 m implies that the ice sheet reached the mid to outer continental shelf edge to form the outer hellefisk moraines exposure dates record ice surface thinning from 21 0 to 9 8 ka with downwasting rates varying from 0 06 to 0 12 m yr 1 this reflects strong surface ablation associated with increased air temperatures running up to the bolling interstadial gis1e at ca 14 ka and later marine calving under high sea levels the relatively late retreat of the itilleq ice stream inland of the present coastline is similar to the pattern observed at jakobshavn isbrae located 250 km north in disko bugt which also retreated from the continental shelf after ca 10 ka we hypothesise that the ice streams of west greenland persisted on the inner shelf until the early holocene because of their considerable ice thickness and greater ice discharge compared with the adjacent ice sheet

the seismic response of the los angeles basin california using strong motion data recorded in the los angeles region from the 1992 mw 7 3 landers earthquake we have tested the accuracy of existing three dimensional 3d velocity models on the simulation of long period 2 sec ground motions in the los angeles basin and surrounding san fernando and san gabriel valleys first the overall pattern and degree of long period excitation of the basins were identified in the observations within the los angeles basin the recorded amplitudes are about three to four times larger than at sites outside the basins amplitudes within the san fernando and san gabriel valleys are nearly a factor of 3 greater than surrounding bedrock sites then using a 3d finite difference numerical modeling approach we analyzed how variations in 3d earth structure affect simulated waveforms amplitudes and the fit to the observed patterns of amplification significant differences exist in the 3d velocity models of southern california that we tested magistrale et al 1996 graves 1996a hauksson and haase 1997 major differences in the models include the velocity of the assumed background models the depth of the los angeles basin and the depth location and geometry of smaller basins the largest disparities in the response of the models are seen for the san fernando valley and the deepest portion of the los angeles basin these arise in large part from variations in the structure of the basins particularly the effective depth extent which is mainly due to alternative assumptions about the nature of the basin sediment fill the general ground motion characteristics are matched by the 3d model simulations validating the use of 3d modeling with geologically based velocity structure models however significant shortcomings exist in the overall patterns of amplification and the duration of the long period response the successes and limitations of the models for reproducing the recorded ground motions as discussed provide the basis and direction for necessary improvements to earth structure models whether geologically or tomographically derived the differences in the response of the earth models tested also translate to variable success in the ability to successfully model the data and add uncertainty to estimates of the basin response given input scenario earthquake source models

a relict landscape in the centre of fennoscandian glaciation cosmogenic radionuclide evidence of tors preserved through multiple glacial cycles the presence of well developed tors boulder fields and weathering mantles in the parkajoki area of northeastern sweden near the centre of fennoscandian glaciation has been used to suggest that these landscapes were preserved during all glacial cycles since ice sheet initiation in the late cainozoic this implies that all successive large scale glaciations must have had frozen bed conditions across this area to allow for subglacial landscape preservation cosmogenic 10be and 26al data from three tors and a meltwater channel in the parkajoki area were used to test this hypothesis of landscape preservation through multiple glacial cycles apparent exposure ages of tor summit bedrock surfaces ranging between 79 and 37 ka in an area deglaciated at 11 ka are consistent with the interpretation of these features as relict landforms that have survived glaciation with little or no erosion single nuclide minimum exposure age data require that the tors have survived at least two complete glacial cycles this estimate is based on i the approximate duration of periods of ice sheet cover versus ice free conditions as deduced from the dsdp 607 marine benthic foraminifer oxygen isotope record in conjunction with ii a record of fennoscandian ice sheet flow traces and hence ice sheet extent and iii noting that cosmogenic nuclides are accumulated only during ice free periods in addition mean cosmogenic 26al 10be concentration ratios from two of the sites indicate a minimum model total history of 605 ka and a maximum erosion rate of 1 6 m ma 1 thus the numerical ages confirm the overall qualitative interpretation of landscape preservation through multiple glacial cycles

quantification of subaerial and episodic subglacial erosion rates on high latitude upland plateaus cumberland peninsula baffin island arctic canada abstract long term rates of subaerial and episodic subglacial erosion by predominately cold based ice cover are determined for tors on weathered plateaus on cumberland peninsula by measuring terrestrial cosmogenic nuclide concentrations in differentially weathered surfaces on a given tor we reconstruct the complex exposure and erosion history involving recurring cold based ice cover the style and rate of subaerial and subglacial erosion at multiple tor sites on cumberland peninsula are assessed with a monte carlo approach that computes plausible exposure histories based on a proxy record of global ice volume constant subaerial erosion rates by weathering are low

substantial agreement on the timing and magnitude of late holocene ice cap expansion between east greenland and the eastern canadian arctic a commentary on lowell et al 2013

a source synchronous filter for uncorrelated receiver traces from a swept frequency seismic source abstractwe have developed a novel algorithm to reduce noise in signals obtained from swept frequency sources by removing out of band external noise sources and distortion caused from unwanted harmonics the algorithm is designed to condition nonstationary signals for which traditional frequency domain methods for removing noise have been less effective the source synchronous filter ssf is a time varying narrow band filter which is synchronized with the frequency of the source signal at all times because the bandwidth of the filter needs to account for the source to receiver propagation delay and the sweep rate ssf works best with slow sweep rates and moveout adjusted waveforms to compensate for source receiver delays the ssf algorithm was applied to data collected during a field test at the university of california santa barbara s garner valley downhole array site in southern california at the site a 45 kn shaker was mounted on top of a one story structure and swept from 0 to 10 hz and back over

a field experiment of walkaway distributed acoustic sensing vertical seismic profile in a deep and deviated onshore well in japan using a fibre optic cable deployed inside coiled tubing abstract a two dimensional walkaway vertical seismic profiling survey using distributed acoustic sensing was conducted at an onshore site in japan the maximum depth and the deviation of the observation well were more than 4 000 m and 81 degrees respectively among the several methods for installing fibre optic cables we adopted the inside coiled tubing method in which coiled tubing containing a fibre optic cable is deployed the signal to noise ratio of the raw shot gather was low possibly due to poor coupling between the fibre optic cable and the subsurface formation resulting from the fibre optic cable deployment method and the existence of considerable tubewave noise nevertheless direct p wave arrivals p p reflections and p s converted waves exhibited acceptable signal to noise ratios after careful optimization of gauge length for distributed acoustic sensing optical processing and the application of carefully parameterized tubewave noise suppression one of the challenges in current distributed acoustic sensing vertical seismic profile data processing is the separation of p and s waves using only one component measurements hence we applied moveout correction using two dimensional ray tracing this process effectively highlights only reflected p waves which are used in subsequent subsurface imaging comparison with synthetic well seismograms and two dimensional surface seismic data confirms that the final imaging result has a sufficiently high quality for subsurface monitoring we acquired distributed acoustic sensing vertical seismic profile data under both flowing conditions and closed conditions in which the well was shut off and no fluid flow was allowed the two imaging results are comparable and suggest the possibility of subsurface imaging and time lapse monitoring using data acquired under flowing conditions the results of this study suggest that by adopting the inside coiled tubing method without drilling a new observation well more affordable distributed acoustic sensing vertical seismic profile monitoring can be achieved in fields such as co2 capture and storage and unconventional shale projects where monitoring costs have to be minimized

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

cosmogenic radionuclides from fiord landscapes support differential erosion by overriding ice sheets the interpretation of differentially weathered mountainous areas along the fringes of pleistocene ice sheets is fundamental for determining ice sheet behavior and thickness during the last glaciation two existing interpretations are either that highly weathered uplands remained as nunataks while freshly eroded troughs held outlet glaciers during the last glaciation or that uplands and lowlands were equally covered by ice but that it was differentially erosive as a function of its spatially variable basal thermal regime cosmogenic radionuclide measurements from 33 bedrock samples and 27 upland erratics from differentially weathered fi ord landscapes on northeastern baffi n island shed light on laurentide ice sheet lis dynamics and thickness tors on weathered upland surfaces have minimum 10 be ages between ca 50 and ca 170 ka n 12 whereas the majority of erratics perched in the uplands range from ca 10 to ca 13 ka n 14 indicating that the whole landscape was glaciated during the last glacial maximum lgm glacially sculpted bedrock n 7 near sea level refl ects the age of deglaciation and increasing amounts of isotopic inheritance in highelevation sculpted bedrock n 3 higher elevation intermediately weathered bedrock n 11 and highest elevation intensely weathered bedrock refl ect the weakening of erosive power as the ice sheet transitioned from fi ords to interfi ord plateaus cold based glaciation of uplands was contemporaneous with warm based glaciation in fi ords suggesting the presence of ice streams 26 al and 10 be concentrations measured in 10 bedrock samples indicate that tors have experienced a complex history of alternating periods of exposure burial and limited glacial erosion the paired isotope data reveal a minimum duration of burial of 80 500 k y presumably by cold based ice and indicate that the tors have an age of at least 150 580 ka these data together with other reconstructions of ice streams in the eastern canadian arctic suggest that ice streams were a large infl uence on northeastern lis dynamics throughout the late quaternary thus the northeastern lis was sensitively tied with north atlantic thermohaline circulation and abrupt climate change

meteoric 10 be as a tracer of subglacial processes and interglacial surface exposure in greenland abstract in order to test whether sediment emerging from presently glaciated areas of greenland was exposed near or at earth s surface during previous interglacial periods we measured the rare isotope 10be contained in grain coatings of sediment collected at five ice marginal sites such grain coatings contain meteoric 10be 10bemet which forms in the atmosphere and is deposited onto earth s surface samples include sediment entrained in ice glaciofluvial sediment collected at the ice margin and subglacial sediment extracted during hot water drilling in the ablation zone due to burial by ice contemporary subglacial sediment could only have acquired substantial 10bemet concentrations during periods in the past when the greenland ice sheet was less extensive than present the highest measured 10bemet concentrations are comparable to those found in well developed long exposed soils suggesting subglacial preservation and glacial transport of sediment exposed during preglacial or interglacial periods ice bound sediment has significantly higher 10bemet concentrations than glaciofluvial sediment suggesting that glaciofluvial processes are sufficiently erosive to remove tracers of previous interglacial exposures northern greenland sites where ice and sediment are supplied from the ice sheet s central main dome have significantly higher 10bemet concentrations than sites in southern greenland indicating greater preglacial or interglacial landscape preservation in central greenland than in the south because southern greenland has more frequent and spatially extensive periods of glacial retreat but nevertheless has less evidence of past subaerial exposure we suggest that 10bemet measurements in glacial sediment are primarily controlled by erosional efficiency rather than interglacial exposure length

modelling landscape evolution under ice sheets we use an ice sheet model glimmer with an erosion component to examine the evolution of landscapes under ice sheets over long time scales in hypothetical situations glimmer is a fully coupled thermomechanical 3 dimensional ice sheet model with a sliding component the model thus has the ability to predict ice thickness the distribution of areas at pressure melting point and basal velocities the erosion rate is assumed to be a simple linear function of the basal velocity and therefore erosion only occurs where the bed is not frozen and basal sliding is possible in addition sliding velocities are assumed to be related to basal water production thus giving a mechanism for smooth temporal and spatial transitions between eroding and non eroding portions of the bed the eroding glacial landscape system is modelled for long term persistent glaciation assuming a variety of initial landscapes results indicate that without the inclusion of basal water production in the calculation of sliding velocities any thermal feedbacks are exaggerated because of steep horizontal basal temperature gradients additionally bed morphology exerts a greater influence under low basal slip conditions because ice cannot respond readily to thermal instabilities we suggest that erosion and valley overdeepening may aid stabilisation of the thermal regime of an ice sheet and that it is possible to generate glacial signals in previously fluvial systems after only 100 kyr of glaciation at conservative erosion rates

quaternary evolution and ice sheet history of contrasting landscapes in uummannaq and sukkertoppen western greenland abstract constraining the history of the greenland ice sheet gis is important for improving our understanding of ice sheet dynamics and landscape evolution processes we analyzed in situ cosmogenic 10be and 26al in 26 rock samples from two high elevation landscapes adjacent to the gis minimally eroded by past glaciations and of differing character in uummannaq n 16 and sukkertoppen n 10 western greenland the uummannaq region is characterized by a marine embayment with islands and peninsulas where the margin of the gis is marine based whereas the sukkertoppen landscape resides within the wide terrestrial fringe outboard of the land terminating portion of the southwestern gis margin we targeted landscapes for sampling with highly weathered surfaces adjacent to cold based portions of extant ice caps indicated by preservation of fragile dead vegetation emerging from beneath retreating ice margins paired isotope results require differing surface histories between the two areas many surfaces in the uummannaq region have minimum exposure durations up to ca 300 kyr but with no significant burial most surfaces in the sukkertoppen region however yield complex exposure histories with minimum cumulative exposure durations up to ca 100 kyr and minimum cumulative burial durations up to ca 400 kyr yielding minimum total surface histories of up to 500 ka these findings suggest that parts of the uummannaq landscape may have been continuously exposed throughout much of the middle and late quaternary on the other hand the high altitude surfaces in the sukkertoppen region were largely preserved beneath minimally erosive cold based ice during the same period data from the uummannaq region thus stand in contrast not only to the sukkertoppen region but also to other sites surrounding baffin bay reported in previous studies we hypothesize that surfaces in the uummannaq region may have remained as nunataks above the last glacial maximum lgm ice sheet surface as well as prior glacial maxima due to significant ice surface drawdown by the uummannaq ice stream system uiss

blockfields old or new evidence and implications from some plateaus in northern norway evidence is presented from investigations on plateau top blockfields in still glaciated regions of north norway pits dug into these blockfields typically show profile depths 0 5 m and sometimes in excess of 1 m analysis of fines shows enrichment in the silt and clay sized fraction suggestive of prolonged chemical weathering chemical alteration of parent material is supported by xrd analysis which identifies a number of clay minerals present in blockfield samples a chemical weathering origin suggests that these plateau top blockfields are features which have considerable longevity in the landscape and have been forming since perhaps tertiary times the original weathering profiles have been destroyed by frost heaving mechanisms protection of the blockfield by cold based ice occurred during periods of glacial coverage

landscape preservation under fennoscandian ice sheets determined from in situ produced 10be and 26al some areas within ice sheet boundaries retain pre existing landforms and thus either remained as ice free islands nunataks during glaciation or were preserved under ice differentiating between these alternatives has significant implications for paleoenvironment ice sheet surface elevation and ice volume reconstructions in the northern swedish mountains in situ cosmogenic 10be and 26al concentrations from glacial erratics on relict surfaces as well as glacially eroded bedrock adjacent to these surfaces provide consistent last deglaciation exposure ages 8 13 kyr confirming ice sheet overriding as opposed to ice free conditions however these ages contrast with exposure ages of 34 61 kyr on bedrock surfaces in these same relict areas demonstrating that relict areas were preserved with little erosion through multiple glacial cycles based on the difference in radioactive decay between 26al and 10be the measured nuclide concentration in one of these bedrock surfaces suggests that it remained largely unmodified for a minimum period of 845 418 461 kyr these results indicate that relict areas need to be accounted for as frozen bed patches in basal boundary conditions for ice sheet models and in landscape development models subglacial preservation also implies that source areas for glacial sediments in ocean cores are considerably smaller than the total area covered by ice sheets these relict areas also have significance as potential long term subglacial biologic refugia

the potential of das in teleseismic studies insights from the goldstone experiment author s yu c zhan z lindsey nj ajo franklin jb robertson m abstract 2019 american geophysical union all rights reserved distributed acoustic sensing das is a recently developed technique that has demonstrated its utility in the oil and gas industry here we demonstrate the potential of das in teleseismic studies using the goldstone optical fiber seismic experiment in goldstone california by analyzing teleseismic waveforms from the 10 january 2018 m7 5 honduras earthquake recorded on 5 000 das channels and the nearby broadband station gsc we first compute receiver functions for das channels using the vertical component gsc velocity as an approximation for the incident source wavelet the moho p to s conversions are clearly visible on das receiver functions we then derive meter scale arrival time measurements along the entire 20 km long array we are also able to measure path averaged rayleigh wave group velocity and local rayleigh wave phase velocity the latter however has large uncertainties our study suggests that das will likely play an important role in many fields of passive seismology in the near future

control factors of spatial variation of long period strong ground motions in the yufutsu sedimentary basin hokkaido during the mw 8 0 2003 tokachi oki japan earthquake we successfully reproduced important features of long period 7 to 8 sec large amplitude ground motions observed in the yufutsu basin hokkaido during the m w 8 0 2003 tokachi oki japan earthquake through numerical simulation of wave propagation recordings from the dense nationwide strong ground motion networks in japan demonstrated significant spatial variation of long period strong ground motions within the yufutsu basin and revealed that the long period shaking in the tomakomai western port was the strongest of all the sites within the basin in interpreting or predicting long period strong ground motions in sedimentary basins the importance of deep basin structures such as the depth of bedrock with an s wave velocity over 3 km sec has been emphasized however the characteristics of the underground structure model of the yufutsu basin that explain the observations indicate that thickness of near surface

response of a land terminating sector of the western greenland ice sheet to early holocene climate change evidence from 10 be dating in the sondre isortoq region abstract the prevalence of land terminating greenland ice sheet margins is expected to increase as tidewater glaciers retreat onto land yet few studies have characterized the sensitivity of these slow moving margins to climatic variability the response of land terminating ice sheet sectors to climate forcing can be assessed by examining records of paleo ice margin positions preserved in ice sheet moraine systems in western greenland the extensive fjord stade moraine system was deposited by minor readvances or stillstands of the greenland ice sheet margin during early holocene net recession here we combine new moraine mapping and cosmogenic 10be exposure dating to constrain the timing of fjord stade moraine deposition in the sondre isortoq region we find that the fjord stade moraines are composed of a western stage and an eastern stage which we constrain to 9 7 0 7 ka n 7 1 sd and 9 0 0 3 ka n 7 1 sd respectively synchronous deposition of the fjord stade moraine complex across at least 350 km of western greenland implies a widespread response of the western greenland ice sheet to the 9 3 ka event furthermore these new moraine ages may correlate with laurentide ice sheet sourced freshwater pulses into the north atlantic ocean we also show that the response of the western greenland ice sheet to early holocene freshwater forcing was not restricted to fast flowing marine terminating outlet glaciers the land terminating margin in the sondre isortoq region halted or reversed its pattern of retreat in response to climatic change