aftsolve a program for multi kinetic modeling of apatite fission track data aftsolve is a computer program for deriving thermal history information from apatite fission track data it implements a new fission track annealing model that takes into account the known kinetic variability among different apatite species to fully utilize this model a fission track worker must obtain data that can be used to infer the kinetic characteristics of each apatite grain from which a measurement was taken such data can consist of etch figure lengths or chemical composition the benefit of this overall approach is that it allows useful information to be derived from previously unusable analyses extends the practical range of geological temperatures constrained by fission track analyses and increases overall confidence in model predictions aftsolve also incorporates the effects of fission track orientation relative to the apatite crystallographic c axis variation in initial track length and the biasing effect of 2 5 2 cf irradiation for enhancing confined horizontal track length detection aftsolve is written for windows operating systems and has a graphical interface that allows interactive input of thermal histories and real time generation of estimates for fission track length distributions and ages for up to six simultaneously modeled kinetic populations it also includes procedures for estimating the range of time temperature histories that are statistically consistent with a data set and constraints entered by the user

itrf2008 plate motion model 1 the itrf2008 velocity field is demonstrated to be of higher quality and more precise than past itrf solutions we estimated an absolute tectonic plate motion model made up of 14 major plates using velocities of 206 sites of high geodetic quality far from plate boundaries deformation zones and glacial isostatic adjustment gia regions derived from and consistent with itrf2008 the precision of the estimated model is evaluated to be at the level of 0 3 mm a wrms no gia corrections were applied to site velocities prior to estimating plate rotation poles as our selected sites are outside the fennoscandia regions where the gia models we tested are performing reasonably well and far from gia areas where the models would degrade the fit antarctica and north america our selected velocity field has small origin rate bias components following the three axis x y z respectively 0 41 0 54 0 22 0 64 and 0 41 0 60 95 per cent confidence limits comparing our model to nnr nuvel 1a and the newly available nnr morvel56 we found better agreement with nnr morvel56 than with nnr nuvel 1a for all plates except for australia where we observe an average residual rotation rate of 4 mm a using our selection of sites we found large global x rotation rates between the two models 0 016 ma and between our model and nnr morvel56 of 0 023 ma equivalent to 2 5 mm a at the earth surface

quantifying exhumation from apatite fission track analysis and vitrinite reflectance data precision accuracy and latest results from the atlantic margin of nw europe

the use of gps horizontals for loading studies with applications to northern california and southeast greenland received 23 august 2012 revised 15 january 2013 accepted 20 january 2013 published 25 april 2013 1 we describe how gps measurements of horizontal crustal motion can be used to augment vertical crustal motion measurements to improve and extend gps studies of surface loading we show that the ratio of the vertical displacement to the horizontal displacement combined with the direction of the horizontal motion can help determine whether nearby loading is concentrated in a small region for example in a single lake or glacier and where that region is we illustrate this method by applying it to two specific cases an analysis of gps data from northern california to monitor the level of lake shasta and the analysis of data from a single gps site in southeast greenland to determine mass variability of two large nearby outletglaciers helheim glacier and midgaard glacier the californiaexampleserves largely as a proof of concept where the results can be assessed by comparing with independent observations lake shasta tide gauge data in this case our greenland results show that both helheim and midgaard have experienced notable interannual variations in mass loss rate over the last decade helheim sm ass loss accelerated rapidly in mid 2003 decelerated in late 2005 and increased again in 2008 2009 before returning to about its pre 2003 rate in late 2010 midgaard s mass loss accelerated in mid 2004 and remained more or less constant before returning to its pre 2003 rate in late 2008

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

sedimentary basin inversion caused by igneous underplating northwest european continental shelf a considerable body of evidence indicates that many of the extensional sedimentary basins in the vicinity of the british isles underwent permanent exhumation during the tertiary the most dramatic indicator of this process is the present day absence of as much as 4 km of anticipated postrift thermal subsidence in basins just north and west of scotland any explanation of this observation must take into account the fact that the entire region has very small long wavelength free air gravity anomalies this important constraint implies either that the crust has been thickened or that low density material has been added to or formed from the lithosphere and rules out models that invoke flexural effects arising from the opening of the north atlantic tertiary epeirogeny is often attributed to compression that is assumed to be related in a general sense to alpine mountain building however to remove 3 km of sedi mentary rock from a basin 100 km wide requires 15 km of shortening minor tertiary compression is observed all over the continental shelf but nowhere is it sufficient to account for the required amount of uplift and erosion in addition exhumation dramatically increases from south to north whereas the observed compression decreases markedly in the same direction at the beginning of the tertiary rifting associated with the initiation of the iceland plume generated substantial volumes of melt inversion of rare earth element concentrations of mgorich igneous rocks suggests that a minimum of 5 km of melt was produced beneath at least part of the continental shelf we infer that much of this melt remains trapped within the lithosphere presumably close to the moho which acted as a density filter such underplating will generate rapid uplift

seasonal speedup along the western flank of the greenland ice sheet it has been widely hypothesized that a warmer climate in greenland would increase the volume of lubricating surface meltwater reaching the ice bedrock interface accelerating ice flow and increasing mass loss we have assembled a data set that provides a synoptic scale view spanning ice sheet to outlet glacier flow with which to evaluate this hypothesis on the ice sheet these data reveal summer speedups 50 to 100 consistent with but somewhat larger than earlier observations the relative speedup of outlet glaciers however is far smaller 15 furthermore the dominant seasonal influence on jakobshavn isbrae s flow is the calving front s annual advance and retreat with other effects producing outlet glacier speedups an order of magnitude larger seasonal melt s influence on ice flow is likely confined to those regions dominated by ice sheet flow

recurring dynamically induced thinning during 1985 to 2010 on upernavik isstrom west greenland this is the publisher s version also available electronically from http onlinelibrary wiley com

geodetic measurements of postglacial adjustments in greenland 1 we analyze data from seven continuous global positioning system gps receivers and one tide gauge all located along the edge of the greenland ice sheet to determine vertical uplift rates we compare our results with predictions based on the ice 5g deglaciation model of peltier 2004 results from the gps receiver at kellyville 1 2 1 1 mm a and from the tide gauge at nuuk 2 2 1 3 mm a indicate that ice 5g overestimates the subsidence rates at those locations by 2 1 and 1 1 mm a respectively kellyville and nuuk are located along the southwestern margin of the greenland ice sheet and the observed negative uplift rates are consistent with independent evidence that the ice margin along the southwestern edge readvanced during the last 8 ka to its current position the ice 5g glaciation deglaciation history includes a readvance between the latitudes of 62 n and 72 n the gps measurements suggest the ice 5g readvance may be too large or mistimed our gps results at qaqortoq located at the southern tip of greenland suggest a secular subsidence rate of 0 3 1 1 mm a while ice 5g predicts an uplift rate of 1 0 mm a ice 5g assumes no ice sheet readvance in south greenland including no readvance of the qassimiut lobe the difference of 1 3 1 1 mm a can tentatively be explained as due to a 33 km readvance of the qassimiut lobe during the last 3 ka for the other gps sites the observed predicted uplift rates are 3 6 1 1 0 1 mm a at thule 0 0 1 1 2 0 mm a at scoresbysund and 0 4 1 1 1 7 mm a at kulusuk for thule kulusuk and scoresbysund the differences between the observed and predicted rates are on the order of 1 3 3 7 mm a though with opposite signs and indicate that ice 5g does not exactly reproduce the correct rebound signal at those locations

bedrock displacements in greenland manifest ice mass variations climate cycles and climate change the greenland gps network gnet uses the global positioning system gps to measure the displacement of bedrock exposed near the margins of the greenland ice sheet the entire network is uplifting in response to past and present day changes in ice mass crustal displacement is largely accounted for by an annual oscillation superimposed on a sustained trend the oscillation is driven by earth s elastic response to seasonal variations in ice mass and air mass i e atmospheric pressure observed vertical velocities are higher and often much higher than predicted rates of postglacial rebound pgr implying that uplift is usually dominated by the solid earth s instantaneous elastic response to contemporary losses in ice mass rather than pgr superimposed on longer term trends an anomalous pulse of uplift accumulated at many gnet stations during an approximate six month period in 2010 this anomalous uplift is spatially correlated with the 2010 melting day anomaly

an inverse method of modeling thermal histories from apatite fission track data abstract apatite fission track ft ages and track length distributions are important sources of information about the thermal histories of rocks recent advances in the understanding of track annealing in apatite provide a solution to the forward problem of predicting ft ages and track length distributions that result from a given thermal history in this paper a method is presented to address the inverse problem estimation of the thermal history from ft data the inverse method uses an iterative approach the downhill simplex to systematically modify a starting thermal history to achieve satisfactory statistical agreement between the predicted and observed ft age and track length distribution however because of analytical uncertainties a unique thermal history does not exist monte carlo simulations are used to take into account the uncertainties in the data and yield a spectrum of possible thermal histories the results are based on the isothermal annealing model of laslett et al 1 chem geol isot geosci sect vol 65 but because the method uses forward predictions and not an analytical formula specific to a single annealing model alternative annealing models could be used within the same framework this method is an improvement in interpreting fission track data because the range of thermal histories permitted by the data can be evaluated to demonstrate the method it is applied to several sets of test data created by forward modeling of idealized thermal histories the results show that the age at which the sample cooled through its closure temperature and the most general features of the thermal history are revealed however data from partially annealed samples have wide spectra that reflect large uncertainties in the form of the thermal history for such samples ft data alone are not likely to provide strong tests of geologic hypotheses conversely geologic information may play a crucial role in constraining the thermal history spectrum in application to uplift related cooling this inverse method can provide much more realistic assessments of the cooling rate and its uncertainty than are otherwise possible

origin of the international terrestrial reference frame 1 with recent improvements in space geodesy the earth s center of mass cm and center of figure cf are no longer indistinguishable the current origin of the international terrestrial reference frame itrf is defined as the cm which shows measured seasonal variations of several millimeters to 1 cm with respect to true cm as scientists study earth s dynamic deformations on seasonal and shorter timescales and begin to compare observed geocenter motion with predictions from geophysical models the reference frame origin presents significant error due to missing the geocenter motion this paper discusses the nature of the origin of the itrf and explores the sensitivity of gps measurements to geocenter motion we find that since the values of nonlinear geocenter motion are not included in the positions of the itrf sites the behavior of the current itrf origin reflects cm on secular timescale but reflects cf on seasonal and short timescales the nature of the itrf origin depends on both the adopted kinematic model and unmodeled network motion the realized itrf origin should be defined by a new nomenclature to reflect its nature accurately by the new nomenclature the origin will maintain its current long term stability while improving its stability on seasonal timescales to the submillimeter level with the degree 1 deformation approach gps measurements are able to provide potentially valuable information on geocenter variations on seasonal and short timescales

greenland ice sheet melt extent 1979 1999 analysis of melt extent on the greenland ice sheet is updated to span the time period 1979 1999 and examined along with its spatial and temporal variability using passive microwave satellite data to acquire the full record the issue of continuity between the previous passive microwave sensors smmr ssm i f 8 and ssm i f 11 and the most recent ssm i f 13 sensor is addressed the f 13 cross polarized gradient ratio melt classification threshold is determined to be 0 0154 results show that for the 21 year record a positive melt trend of nearly 1 yr is observed but this trend falls just below the 90 significance level the observed melt increase does appear to be driven by conditions in the western portion of the ice sheet rather than the east where melt appears to have decreased slightly moreover the eruption of mount pinatubo in 1991 is likely to have had some impact on the melt but not so much as previously suspected the 1992 melt anomaly is 1 7 standard deviations from the mean finally the relationship between coastal temperatures and melt extent suggests an increase in surface runoff contribution to sea level of 0 31 mm yr for a 1 c temperature rise

accelerating uplift in the north atlantic region as an indicator of ice loss vertical motions of the rocky margins of greenland and antarctica respond to mass changes of their respective ice sheets but these motions can be obscured by ancient episodes of glacial advance or retreat an analysis of the acceleration of vertical motion indicates that accelerated ice loss in western greenland started in the late 1990s vertical motions of the rocky margins of greenland and antarctica respond to mass changes of their respective ice sheets1 2 however these motions can be obscured by episodes of glacial advance or retreat that occurred hundreds to thousands of years ago3 4 5 6 which trigger a delayed response because of viscous flow in the underlying mantle here we present high precision global positioning system gps data that describe the vertical motion of the rocky margins of greenland iceland and svalbard we focus on vertical accelerations rather than velocities to avoid the confounding effects of past events our data show an acceleration of uplift over the past decade that represents an essentially instantaneous elastic response to the recent accelerated melting of ice throughout the north atlantic region our comparison of the gps data to models for glacial isostatic adjustment suggests that some parts of western coastal greenland were experiencing accelerated melting of coastal ice by the late 1990s using a simple elastic model we estimate that western greenland s ice loss is accelerating at an average rate of 8 7 3 5 gt yr 2 whereas the rate for southeastern greenland based on limited data falls at 12 5 5 5 gt yr 2

elastic uplift in southeast greenland due to rapid ice mass loss this is the publisher s version also available electronically from http onlinelibrary wiley com

displacements of the earth s surface due to atmospheric loading effects on gravity and baseline measurements atmospheric mass loads and deforms the earth s crust by performing a convolution sum between daily global barometric pressure data and mass loading green s functions we estimate the time dependent effects of atmospheric loading including those associated with short term synoptic storms on surface point positioning measurements and surface gravity observations we calculate the response for both an oceanless earth and an earth with an inverted barometer ocean load responses for near coastal stations are significantly affected by the inclusion of an inverted barometer ocean peak to peak vertical displacements are frequently 15 20 mm with accompanying gravity perturbations of 3 6 gal baseline changes can be as large as 20 mm or more the perturbations are largest at higher latitudes and during winter months these amplitudes are consistent with the results of rabbel and zschau 1985 who modeled synoptic pressure disturbances as gaussian functions of radius around a central point deformation can be adequately computed using real pressure data from points within about 1000 km of the station knowledge of local pressure alone is not sufficient rabbel and zschau s hypothesized corrections for these displacements which use local pressure and the regionally averaged pressure prove accurate at points well inland but are in general inadequate within a few hundred kilometers of the coast

seasonal speedup of a greenland marine terminating outlet glacier forced by surface melt induced changes in subglacial hydrology we present subdaily ice flow measurements at four gps sites between 36 and 72 km from the margin of a marine terminating greenland outlet glacier spanning the 2009 melt season our data show that 35 km from the margin seasonal and shorter time scale ice flow variations are controlled by surface melt induced changes in subglacial hydrology following the onset of melting at each site ice motion increased above background for up to 2 months with resultant up glacier migration of both the onset and peak of acceleration later in our survey ice flow at all sites decreased to below background multiple 1 to 15 day speedups increased ice motion by up to 40 above background these events were typically accompanied by uplift and coincided with enhanced surface melt or lake drainage our results indicate that the subglacial drainage system evolved through the season with efficient drainage extending to at least 48 km inland during the melt season while we can explain our observations with reference to evolution of the glacier drainage system the net effect of the summer speed variations on annual motion is small 1 this in part is because the speedups are compensated for by slowdowns beneath background associated with the establishment of an efficient subglacial drainage system in addition the speedups are less pronounced in comparison to land terminating systems our results reveal similarities between the inland ice flow response of greenland marine and land terminating outlet glaciers

geodetic measurements in greenland and their implications we describe results from an ongoing experiment in greenland in which we are using absolute gravity and continuous global positioning system gps measurements to study vertical crustal motion at two locations along the edge of the ice sheet kellyville located about one third of the way up the western ice margin and kulusuk located along the eastern ice margin at about the same latitude as kellyville the gps measurements suggest average crustal uplift rates of 5 8 1 0 mm yr at kellyville and 2 1 1 5 mm yr at kulusuk there have not yet been enough absolute gravity occupations to permit useful secular gravity solutions at either location the negative uplift rate at kellyville is consistent with independent archeological and historical evidence that the southwestern edge of the continent has been subsiding over the last 3000 years but it is inconsistent with estimates of the earth s continuing viscoelastic response to melting ice during the early holocene which predict that kellyville is likely to be uplifting rather than subsiding by 2 0 3 5 mm yr the resulting 7 8 3 6 mm yr discrepancy between the observed and predicted uplift rates is too large to be caused by loading from present day changes in nearby ice however it is consistent with independent suggestions that the western ice sheet margin in this region may have advanced by 50 km during the past 3000 4000 years if this advance did occur and if the crustal subsidence it induces is not removed from altimeter measurements of greenland ice sheet elevations then the altimeter solutions could underestimate the true snow ice thickness change by 5 10 mm yr along portions of the western margin of the ice sheet

icelandic rhythmics annual modulation of land elevation and plate spreading by snow load we find strong correlation between seasonal variation in cgps time series and predicted response to annual snow load in iceland the load is modeled using green s functions for an elastic halfspace and a simple sinusoidal load history on iceland s four largest ice caps we derive e 40 15 gpa as a minimum value for the effective young s modulus in iceland increasing with distance from the eastern volcanic zone we calculate the elastic response over all of iceland to maximum snow load at the ice caps using e 40 gpa predicted annual vertical displacements are largest under the vatnajokull ice cap with a peak to peak seasonal displacement of 37 mm cgps stations closest to the ice cap experience a peak to peak seasonal displacement of 16 mm consistent with our model east and north of vatnajokull we find the maximum of annual horizontal displacements of 6 mm resulting in apparent modulation of plate spreading rates in this area

annual variations in gps measured vertical displacements near upernavik isstrom greenland and contributions from surface mass loading in response to present day ice mass loss on and near the greenland ice sheet steady crustal uplifts have been observed from the network of global positioning system gps stations mounted on bedrock in addition to the secular uplift trends the gps time series also show prominent annual variability here we examine the annual changes of the vertical displacements measured at two gps stations srmp and upvk near upernavik isstrom in western greenland we model elastic loading displacements due to various surface mass loading including three non ice components atmospheric pressure ocean bottom pressure continental water storage and one ice component i e surface mass balance smb we find that the contribution from atmospheric pressure changes can explain 46 and 78 of the annual amplitude observed in the gps verticals at srmp and upvk respectively we also show that removing the predicted loading displacements due to smb adversely increases the annual variance of the gps residuals however using the gps data alone we cannot identify the exact cause s of this discrepancy because the annual loading displacements are sensitive to the smb changes from over 85 of the ice sheet area alternatively by differencing vertical displacements between the two stations we find a good agreement between the modeled differential smb loading displacements and the gps residuals after removing non ice components our study highlights the necessity of correcting for non ice loading contributions in the gps measurements of crustal deformation to infer ice mass changes in greenland at annual periods

a two layer lithospheric compressional model for the tertiary uplift of the southern united kingdom reflection seismic records show that many of the mesozoic sedimentary basins of the southern united kingdom were compressed and uplifted inverted during the late cretaceous tertiary recent quantitative studies based on apatite fission track analysis and chalk porosity data show that uplift and erosion although concentrated in the inverted basins was regional and not limited to the recognized areas of crustal shortening inversion a two layer or heterogeneous model of lithospheric compression similar to two layer models of lithospheric extension may account for this pattern of uplift upper lithospheric shortening is accommodated by reverse movement on major reactivated extensional detachments causing inversion of pre existing basins pure shear shortening of the lower lithosphere is decoupled and may be laterally displaced from that in the upper lithosphere lower lithospheric shortening and thickening displaced from that in the upper lithosphere causes initial subsidence due to the submersion of cold dense lithosphere into the surrounding asthenosphere subsequent thermal re equilibration of the lower lithosphere may have generated the uplift without attendant crustal shortening witnessed by apatite fission track and chalk porosity data

seasonal dynamic thinning at helheim glacier a b s t r a c t we investigate three annual mass balance cycles on helheim glacier in south east greenland using tandem x interferometric digital elevation models dems bedrock gps measurements and ice velocity from feature tracking the dems exhibit seasonal surface elevation cycles at elevations up to 800 m a s l with amplitudes of up to 19 m from a maximum in july to a minimum in october or november concentrated on the fast flowing areas of the glacier indicating that the elevation changes have a mostly dynamic origin by modelling the detrended bedrock loading unloading signal we estimate a mean density for the loss of 671 70 kg m 3 and calculate that total water equivalent volume loss from the active part of the glacier surface flow speeds 1m day 1 ranges from 0 5 km 3 in 2011 to 1 6 km 3

gps measurements of crustal uplift near jakobshavn isbrae due to glacial ice mass loss 1 we analyze 2006 2009 data from four continuous global positioning system gps receivers located between 5 and 150 km from the glacier jakobshavn isbrae west greenland the gps stations were established on bedrock to determine the vertical crustal motion due to the unloading of ice from jakobshavn isbrae all stations experienced uplift but the uplift rate at kangia north only 5 km from the glacier front was about 10 mm yr 1 larger than the rate at ilulissat located only 45 km further away this suggests that most of the uplift is due to the unloading of the earth s surface as jakobshavn thins and loses mass our estimate of jakobshavn s contribution to uplift rates at kangia north and ilulissat are 14 6 1 7 mm yr 1 and 4 9 1 1 mm yr 1 respectively the observed rates are consistent with a glacier thinning model based on repeat altimeter surveys from nasa s airborne topographic mapper atm which shows that jakobshavn lost mass at an average rate of 22 2 km3 yr 1 between 2006 and 2009 at kangia north and ilulissat the predicted uplift rates computed using thinning estimates from the atm laser altimetry are 12 1 0 9 mm yr 1 and 3 2 0 3 mm yr 1 respectively the observed rates are slightly larger than the predicted rates the fact that the gps uplift rates are much larger closer to jakobshavn than further away and are consistent with rates inferred using the atm based glacier thinning model shows that gps measurements of crustal motion are a potentially useful method for assessing ice mass change models

geodetic secular velocity errors due to interannual surface loading deformation geodetic vertical velocities derived from data as short as 3 yr are often assumed to be representative of linear deformation over past decades to millennia we use two decades of surface loading deformation predictions due to variations of atmospheric oceanic and continental water mass to assess the effect on secular velocities estimated from short time series the interannual deformation is time correlated at most locations over the globe with the level of correlation depending mostly on the chosen continental water model using the most conservative loading model and 5 yr long time series we found median vertical velocity errors of 0 5 mm yr 1 over the continents 0 3 mm yr 1 globally exceeding 1 mm yr 1 in regions around the southern tropic horizontal velocity errors were seven times smaller unless an accurate loading model is available a decade of continuous data is required in these regions to mitigate the impact of the interannual loading deformation on secular velocities

troposphere mapping functions for gps and very long baseline interferometry from european centre for medium range weather forecasts operational analysis data 1 in the analyses of geodetic very long baseline interferometry vlbi and gps data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three parameter continued fraction in 1 sin elevation using the 40 years reanalysis era 40 data of the european centre for medium range weather forecasts for the year 2001 the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined unlike previous mapping functions based on data from numerical weather models isobaric mapping functions niell 2000 and vienna mapping functions vmf boehm and schuh 2004 the new c coefficients are dependent on the day of the year and unlike the niell mapping functions niell 1996 they are no longer symmetric with respect to the equator apart from the opposite phase for the two hemispheres compared to vmf this causes an effect on the vlbi or gps station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles the updated vmf based on these new coefficients and called vmf1 hereinafter yields slightly better baseline length repeatabilities for vlbi data the hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all vlbi international vlbi service for geodesy and astrometry ivs r1 and ivs r4 24 hour sessions of 2002 and 2003 the investigations concentrate on baseline length repeatabilities as well as on absolute changes of station heights

chalk porosity and tertiary uplift western approaches trough sw uk and nw french continental shelves porosities have been derived from sonic logs for the cenomanian maastrichtian chalk of 22 hydrocarbon exploration wells in the western approaches trough although the burial depth of the chalk studied ranges from 40 1500 m below sea bed porosities are all within the range 0 45 the most deeply buried chalk sequences exhibit close to normal porosity depth relations for offshore chalks abnormally low porosities in the remainder of the wells result from burial at greater depth than that presently observed low porosities were preserved during tertiary alpine related uplift of the area for a given well the magnitude of uplift not reversed by subsequent subsidence apparent uplift equals the displacement of its porosity depth relation from the normal relation along the depth axis apparent uplift in the western approaches trough ranges from 0 1 3 km in the western approaches trough chalk porosity data provide evidence of more widespread tertiary uplift than do seismic reflection records alpine related compression and uplift fault bounded basin inversion is apparent only on seismic records in the southern part of the trough brittany and south west channel basins whereas chalk porosity data suggest regional uplift occurred throughout the trough and adjacent highs chalk porosity data were also used to quantify tertiary uplift in the cleethorpes l well of the east midlands shelf the resultant value of 1 1km is considerably greater than that previously derived from shale sonic velocities approximately 0 3 km and slightly less than that based on apatite fission track analysis 1 3 1 7 km

thermal evolution of rifted continental margins new evidence from fission tracks in basement apatites from southeastern australia the palaeozoic granitic basement of southeastern australia shows a regular pattern of apatite fission track ages which is dominated by a rapid decrease in apparent age towards the rifted continental margin apparent ages away from the margin vary between about 230 and 360 myr but drop sharply to minimum values of around 80 myr near the coast just south of the sydney basin and 150 175 myr elsewhere along the coast fission track length information allows the age pattern to be interpreted as the result of partial to complete resetting of the older ages by a widespread thermal event at about 80 100 myr this event accompanied the rift phase of passive margin development and peaked just before the onset of sea floor spreading in the adjacent tasman sea the zone of reduced apatite ages is deeply embayed around the gippsland basin supporting the suggestion that it originated as a cretaceous failed arm of the tasman rift system the thermal event has affected apatites up to about 130 km from the margin and has produced a characteristic set of bimodal track length distributions in apatites with partially reset ages the bimodality gradually disappears towards the oldest apatite ages which have negatively skewed unimodal distributions the youngest apatites also tend towards unimodal length distributions indicating that thermal annealing of pre existing tracks in these samples went almost to completion maximum temperatures reached in samples presently exposed in the coastal area were thus probably about 110 120 c thermal activity was accompanied by considerable uplift across the region followed by gradual erosion to expose the present land surface post breakup erosion was generally greater towards the new coastline with near coastal samples being previously buried a probable 1 5 2 5 km

months long thousand kilometre scale wobbling before great subduction earthquakes megathrust earthquakes are responsible for some of the most devastating natural disasters1 to better understand the physical mechanisms of earthquake generation subduction zones worldwide are continuously monitored with geophysical instrumentation one key strategy is to install stations that record signals from global navigation satellite systems2 3 gnss enabling us to track the non steady surface motion of the subducting and overriding plates before during and after the largest events4 6 here we use a recently developed trajectory modelling approach7 that is designed to isolate secular tectonic motions from the daily gnss time series to show that the 2010 maule chile moment magnitude 8 8 and 2011 tohoku oki japan moment magnitude 9 0 earthquakes were preceded by reversals of 4 8 millimetres in surface displacement that lasted several months and spanned thousands of kilometres modelling of the surface displacement reversal that occurred before the tohoku oki earthquake suggests an initial slow slip followed by a sudden pulldown of the philippine sea slab so rapid that it caused a viscoelastic rebound across the whole of japan therefore to understand better when large earthquakes are imminent we must consider not only the evolution of plate interface frictional processes but also the dynamic boundary conditions from deeper subduction processes such as sudden densification of metastable slab

increased mass loss and asynchronous behavior of marine terminating outlet glaciers at upernavik isstrom nw greenland in order to model and predict future behavior of marine terminating glaciers it is essential to understand the different factors that control a glaciers response to climate change here we present a detailed study of the asynchronous changes in dynamic behavior of four adjacent marine terminating glaciers at upernavik isstrom ui northwest greenland between 1992 and 2013 velocities were stable for all outlets at ui between 1992 and 2005 the northernmost glacier started to accelerate and thin in 2006 and continued to do so into 2011 after which time the velocities stabilized the second most northerly glacier started to accelerate and thin in 2009 and continued to do so until the last observations in 2013 dramatically increasing the area affected by dynamically induced thinning the southern glaciers show little change with the most southerly glacier undergoing slight retreat and deceleration between 1992 and 2013 these observations point out the fact that the ui glaciers are reacting to climate change on different timescales the asynchronous behavior of the four neighboring glaciers is explained in terms of the individual glaciers geometry and terminus position the northernmost glacier is believed to have had a floating tongue between 1985 and 2007 which disintegrated in 2007 2008 this release of back stress destabilized the glacier causing it to accelerate and thin rapidly we suggest that the ice tongue broke up due to ocean warming induced thinning in the late 1990s recent response on ui glaciers is found to be related to increased surface melt our investigations suggest that three out of the four main glaciers in the ui are likely to be in unstable positions and may have the potential to rapidly thin and accelerate and increase their contribution to sea level in the future

multiple episodes of cenozoic denudation in the northeastern brooks range fission track data from the okpilak batholith alaska the northeastern brooks range of alaska is a complex mesozoic to cenozoic northward verging fold and thrust belt in response to regional compression shortening in the upper crust has occurred thr

evidence from apatite fission track analysis for the post devonian burial and exhumation history of the northern highlands scotland abstract devonian and older rock samples from outcrops in the northern scottish highlands have undergone protracted cooling since they reached palaeotemperatures of 110 c or more in the late palaeozoic to early mesozoic the results not only suggest that the northern highlands region has experienced kilometre scale exhumation since the late palaeozoic but also that devonian and possibly permo carboniferous sedimentation was probably more extensive than current outcrop patterns would imply a permian outcrop sample from the minches basin reached a maximum palaeotemperature of 70 90 c prior to the onset of cooling in the early tertiary while data from devonian and older samples suggest an acceleration in the rate of cooling in the early tertiary the magnitude of early tertiary palaeotemperatures on the mainland adjacent to the inner moray firth imf indicate similar amounts of tertiary exhumation to those derived from compaction analyses for the imf however to the west the magnitude of tertiary cooling cannot be solely ascribed to exhumation and a contribution of heating due to hydrothermal effects and or elevated heat flow associated with the tertiary igneous complex may also need to be invoked

thermal and tectonic history of selected taranaki basin new zealand wells assessed by apatite fission track analysis apatite fission track analysis afta has been applied to samples from four hydrocarbon well sections to study the thermal and tectonic history and the hydrocarbon prospectivity of the southern part of the taranaki basin new zealand data from three of the wells 1 fresne 1 north tasman 1 surville show that the successions were exposed to higher temperatures in the past through deeper burial cooling from elevated paleotemperatures was effected by late miocene uplift and erosion of 3 0 or 0 3 km of section in 1 fresne or 2 0 or 0 5 km in 1 surville and 1 0 or 0 3 km in 1 north tasman in the fourth well 1 kupe formations are currently at their maximum temperatures since deposition afta provides unique constraints on the timing of hydrocarbon generation in relation to trap formation the proposed source rocks in 1 fresne passed through the oil formation window 100 150 degrees c and into the zone of gas production 150 220 degrees c during the middle miocene prior to the formation of potential trapping structures those in 1 north tasman passed into the oil formation zone about the same time and source rocks in 1 surville have probably never been heated enough to produce oil afta indicates considerable prospectivity remains in the region of 1 kupe where generation would have occurred after trap formation

geodetic measurements reveal short term changes of glacial mass near jakobshavn isbrae greenland from 2007 to 2017 abstract the global positioning system gps and gravity recovery and climate experiment grace provide important geodetic datasets to study glacial mass change applying the multichannel singular spectral analysis to the gps measured vertical and horizonal crustal displacement and grace derived vertical displacement near jakobshavn isbrae ji in western greenland from 2007 to 2017 we reconstruct the short term loading displacements due to ice mass changes both the vertical and east displacements show strong seasonal variability they also reveal three episodes of transient displacements downward and eastward motion from late 2007 to around 2010 sustained upward and westward motion from 2010 to early 2013 and downward and eastward motion till late 2016 we also forward model the seasonal and transient displacements caused by surface mass balance smb and glacier dynamics our model agrees well with the geodetic observations and provides quantitative insights into the contribution from smb and ice dynamics to the ice mass changes we find that smb is the dominant contributor to the seasonal and transient displacements at three out of four gps sites aasi ilul and qeqe while at the fourth gps site kaga that is closest to the glacier the contributions to the transient displacements from smb and glacier dynamics are comparable the forward modeling also suggests that the dynamic mass change in the ji catchment underwent strong seasonal variations and these variations correlated more with the seasonal retreat and advance of the calving front than with the changes of glacial velocities our altimetry results reveal that the frontal portion of ji catchment lost 34 gt in 2012 and this loss of ice declined to only 11 gt in 2016 due to widespread thickening along the main flowline

crustal uplift due to ice mass variability on upernavik isstrom west greenland abstract we estimate the mass loss rate of upernavik isstrom ui using surface elevation changes between a spot 5 digital elevation model dem from 2008 and nasa s airborne topographic mapper atm data from 2010 to assess the validity of our mass loss estimate we analyze gps data between 2007 and 2011 from two continuous receivers upvk and srmp which are established on bedrock and located 65 and 2 km from the front of ui respectively we construct along track elevation changes on ui for several time intervals during 2005 2011 based on atm spot 5 and ice cloud and land elevation satellite icesat data to assess temporal changes of ui we estimate a mass loss rate of 6 7 4 2 gt yr over an area of 1600 km 2 the ice mass loss occurs primarily over the northern glacier of ui this pattern is also observed 40 km upstream where we observe glacier thinning at a rate of 1 6 0 3 m yr across the northern portion of ui and 0 5 0 1 m yr across the southern portion gps measurements suggest bedrock uplift rates of 7 6 0 6 mm yr upvk and 16 2 0 6 mm yr srmp the modeled ice mass loss of ui causes bedrock uplift rates of 1 3 0 6 mm yr upvk and 8 3 4 2 mm yr srmp including additional contributions from ice mass changes outside ui and from glacial isostatic adjustment gia we obtain total modeled uplift rates of 4 7 0 6 mm yr upvk and 13 8 4 2 mm yr srmp the modeled uplift rates from our ui ice mass loss are substantially lower indicating that additional mass loss is taking place outside of ui we obtain a difference of 0 6 mm yr between the modeled and observed relative uplift rates srmp relative to upvk suggesting that the mass loss of ui is well captured in the model we observe elevation changes from 15 to 40 m yr near the front during the period 2005 2011 indicating that ui undergoes large variations in thinning pattern over short time spans

the art of maturity modeling part 1 finding a satisfactory geologic model an example of one dimensional maturity modeling of the miti rumoi well a stratigraphic test drilled in a frontier area of japan is worked out in detail to illustrate how maturity modeling should be carried out prior to and during modeling an effort was made to integrate all available geological geochemical and geophysical concepts and data to create a single geologic model called here the good model that was as plausible and internally consistent as possible where data sets were internally inconsistent or in conflict with other data decisions had to be made about data reliability some vitrinite reflectance data subsurface temperatures and thermal conductivity measurements were rejected for a variety of reasons the justifications for these decisions which influenced the results of the modeling are discussed in detail using the good model we evaluated the timing and amount of oil and gas generation from coals in the haboro formation the only proposed source rocks in northwest hokkaido japan generation has occurred continually since the middle miocene but the fractional conversion of kerogen to hydrocarbons to date has been small as a result the total volume of hydrocarbons available for expulsion and migration from the haboro source rock probably is small unless very large volumes of coal are present the good model does not represent a unique solution however it thus should be regarded as one of a number of viable models rather than as the only correct one alternative models are considered in a companion paper the modeling process itself by which and during which we learn much about the geologic system is at least as important as the final numerical answer highly interactive modeling programs greatly aid in proper modeling

upper crustal velocity structure in the rose area of the east pacific rise we describe a method to constrain the seismic velocity structure of the upper 500 800 m of young oceanic crust conventional interpretations of seismic refraction profiles provide little or no information about this shallowmost crust the method described here requires the assumption of a linear velocity gradient and utilizes measured values of range travel time and slowness of the observed refracted waves results are reported from several refraction profiles that sample crust between 0 and 4 m y in age on the flanks of the east pacific rise at 12 n these data give an average gradient in the uppermost 800 m of the crust of 3 5 s 1 and a velocity at the seafloor of 2 5 km s ray path and travel time modeling show that the refracted waves sampling the uppermost part of the crust are effectively masked by reflections from the seafloor

geodetic and model data reveal different spatio temporal patterns of transient mass changes over greenland from 2007 to 2017 abstract much of the research to understand the ice mass changes of greenland ice sheet gris has focused on detecting linear rates and accelerations at decadal or longer periods the transient short term non secular mass changes show large variability and if not properly accounted for can introduce significant biases into estimates of long term ice mass loss rates and accelerations despite the growing number of geodetic observations in terms of spatial coverage types of observables and the extent of the time series studies of the transient mass changes over gris are lacking to address this limitation we apply multi channel singular spectral analysis to the gravity recovery and climate experiment grace mass concentrations mascon surface mass balance smb model output and ice discharge data to determine the transient mass changes over greenland over the decade 2007 to 2017 the goal of this analysis is to elucidate the spatio temporal variability of the ice mass change for the entire gris both the mascon and smb transient mass changes are characterized by a sustained mass gain from late 2007 to early 2010 a sustained mass loss from early 2010 to early 2013 and a mass gain from early 2013 to mid 2015 global positioning system sites deployed along the coast of greenland showed uplift from early 2010 to early 2013 and subsidence from early 2013 to 2015 consistent with the corresponding ice mass loss and gain of the entire gris the peak to peak amplitude of the transient mass change was estimated to be 294 27 gt from grace mascons and 252 16 gt from the smb where the latter value includes the effect of ice discharge the transient mass change due to ice discharge accounted for less than 10 of the total transient mass change our regional assessment reveals that the central west southwest northeast and southeast regions display similar time varying patterns as we found for the entire gris but the north and northwest regions show different patterns atmospheric circulation anomalies as measured by the greenland blocking index gbi are able to explain most of these transient anomalies more specifically high gbi associated high temperature was one of the main reasons for the transient mass loss of the entire gris during 2010 2012 while low gbi can explain the transient mass gain during 2013 2015 contrasting behaviors of precipitation anomalies in east and west greenland under abnormally high or low gbi conditions may explain the different patterns of the transient mass change in the northwest and the rest of greenland