gutenberg s surface wave magnitude calibrating function theoretical basis from synthetic seismograms the surface wave magnitude as originally defined by gutenberg 1945 appears to be the most stable quantity rating the strengths of seismic sources it is based on the ground displacement produced by a nearly monochromatic wave train the calibrating function underlying the magnitude definition was obtained from observations of the amplitudes as a function of epicentral distance for a wealth of earthquakes no distinction was made as to focal depths thus the calibrating function depends on one parameter the epicentral distance only subsequent attempts to introduce a focal depth correction were not successful in practice and one and the same calibrating function continues to be applied to events with focal depths ranging from 0 to about 70 km assuming a strike slip point source located inside a standard earth model synthetic seismograms of the fundamental mode sh love wave are computed for a range of focal depths and azimuths amplitude distance curves are obtained and averaged over the azimuths the curves are the basis for improved calibrating functions average depth corrections are obtained and applied to some populations of seismic events the corrected surface wave magnitudes are internally more consistent than the uncorrected ones usually published applying the depth correction to published surface wave magnitudes and considering themb ms relation for a sample of earthquakes and explosions it has been established that for a given intensity of short periodic radiation the 20 s radiation intensity can vary by orders of magnitude while it is known that the 20 s radiation intensity is generally lower for explosions than for earthquakes it turns out to be even lower if the depth correction is applied yielding a clearer separation between both classes of seismic events

millennial scale fluctuations of the european ice sheet at the end of the last glacial and their potential impact on global climate abstract reconstructing northern hemisphere ice sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes to date research efforts have mainly focused on the north american laurentide ice sheets lis leaving the potential role of the european ice sheet eis and of the scandinavian ice sheet sis in particular largely unexplored using neodymium isotopes in detrital sediments deposited off the channel river we provide a continuous and well dated record for the evolution of the eis southern margin through the end of the last glacial period and during the deglaciation our results reveal that the evolution of eis margins was accompanied with substantial ice recession especially of the sis and simultaneous release of meltwater to the north atlantic these events occurred both in the course of the eis to its lgm position i e during heinrich stadial hs 3 and hs2 31 29 ka and 26 23 ka respectively and during the deglaciation i e at 22 ka 20 19 ka and from 18 2 0 2 to 16 7 0 2 ka that corresponds to the first part of hs1 the deglaciation was discontinuous in character and similar in timing to that of the southern lis margin with moderate ice sheet retreat from 22 5 0 2 ka in the baltic lowlands as soon as the northern summer insolation increase from 23 ka and an acceleration of the margin retreat thereafter from 20 ka importantly our results show that eis retreat events and release of meltwater to the north atlantic during the deglaciation coincide with amoc destabilisation and interhemispheric climate changes they thus suggest that the eis together with the lis could have played a critical role in the climatic reorganization that accompanied the last deglaciation finally our data suggest that meltwater discharges to the north atlantic produced by large scale recession of continental parts of northern hemisphere ice sheets during hs could have been a possible source for the oceanic perturbations i e amoc shutdown responsible for the marine based ice stream purge cycle or so called he s that punctuate the last glacial period

regional bias in estimates of earthquake ms due to surface wave path effects continental earthquakes have long been known to have anomalously high surface wave magnitudes relative to their seismic moments a recent global study of shallow earthquakes by ekstrom and dziewonski 1988 confirmed this and found other regional systematic anomalies in the ms m relationship it is important to determine the source of these anomalies in order to understand the controls on earthquake source radiation and to obtain accurate estimates of historical seismic strain rates in this study the magnitudes of 82 earthquakes from eight different tectonic regions are recalculated using a simple surface wave path correction to determine whether path effects are responsible for the observed anomalies the magnitudes of continental earthquakes are reduced by an average of 0 2 magnitude units an improvement in fit to the global average significant at the 98 level surface wave path effects are clearly responsible for the high ms observed in continental areas there is a small decrease in scatter in the other areas but lateral refraction of the surface waves at plate boundaries prevents the simple correction from having a significant effect there is no evidence in the observed anomalies however for any dependence of earthquake source type on tectonic setting it is clear that to obtain reliable unbiased estimates of regional seismic strain rate and hazard a local moment magnitude relationship should be preferred to a global one

homogeneous moment magnitude calibration in switzerland an earthquake catalog containing a uniform size estimate is important for long term seismic hazard assessment in regions of low to moderate seismicity during the update of the earthquake catalog of switzerland ecos we performed regression analyses to convert all earthquake size information in ecos to physically meaningful moment magnitude m w for 34 events in and near switzerland we determined seismic moment thus m w by regional waveform inversion independent m w estimates for the same events do not exist however m w from european mediterranean events obtained in the same way agree with m w from harvard cmt solutions all other size estimates m l m d m b m s and intensities are calibrated relative to these 34 events teleseismic m s and m b from international data centers are directly regressed against m w most observations in ecos consist of local magnitudes m l m d and intensities for local magnitudes we first calibrated the swiss seismological service s m l then we calibrated magnitudes from observatories in neighboring countries france germany italy using only events in the border region e g france switzerland modern instrumental records exist only since the mid 1970s we calibrated the macroseismic dataset which represents by far the largest period in the catalog by determining surface wave magnitude m s for stronger twentieth century swiss earthquakes from analog seismograms these m s which were converted to m w connect intensities and m w after calibration all 20 300 events in ecos have a unified m w including a class type uncertainty estimate based on the original magnitude scale ecos covers the period 250 2001 from 44 n to 51 n and 4 e to 13 e the largest event in ecos is the 1356 m w 6 9 basle earthquake

deglaciation of a marine based ice sheet late weichselian palaeo ice dynamics and retreat in the southern barents sea reconstructed from onshore and offshore glacial geomorphology abstract marine and terrestrial datasets swath bathymetry 2d and 3d seismic and remote sensing data are used to map the megascale glacial geomorphology of the southern barents sea seafloor northern fennoscandia and the kola peninsula giving new insights into the dynamics and behaviour of the barents sea ice sheet during retreat the glacial geomorphology indicates clear spatial and temporal variations in ice dynamics with evidence for both active ice streaming and frozen bed conditions at the maximum and during deglaciation a five stage reconstruction of the late weichselian deglaciation is proposed at the late weichselian maximum ice covered the whole of the barents sea shelf and the configuration and dynamics of the ice sheet were controlled by the bjornoyrenna bear island trough ice stream this was fed by source areas in the central and north eastern barents sea and in the fennoscandian mainland deglaciation was initiated along the western continental margin available dating results show that this occurred after 19 cal ka bp the bjornoyrenna ice stream retreated rapidly ice margin retreat rates of 275 m a 1 but was periodically grounded as evidenced by a well developed series of grounding zone wedges this was followed by an advance of two short lived ice streams from the eastern sector of the ice sheet into the south western barents sea these ice streams advanced and retreated very rapidly with no evidence for ice margin standstills correlation to dated cores suggests an age of around 16 000 cal ka bp for this readvance the period of operation of these two ice streams was coincident with maximum ice extent along the eastern margin in russia the western barents sea ice margin then retreated onshore with deglaciation continuing at a reduced rate the initiation of deglaciation coincided with rising global eustatic sea level acceleration of calving due to grounding line floatation rapidly opened up a major calving bay in bjornoyrenna encouraging rapid loss of the marine based ice the retreat rate stabilised only once the ice sheet retreated onshore and calving ceased we note that the observed pattern of rapid retreat with high variability in ice streaming for the marine based barents sea ice sheet is similar to that of the marine based sectors of the late weichselian british laurentide and west antarctic ice sheets

rare earth elements and neodymium isotopes in sedimentary organic matter abstract we report rare earth element ree and neodymium nd isotope data for the organic fraction of sediments collected from various depositional environments i e rivers n 25 estuaries n 18 open ocean settings n 15 and cold seeps n 12 sedimentary organic matter som was extracted using a mixed hydrogen peroxide nitric acid solution 20 h2o2 0 02 m hno3 after removal of carbonate and oxy hydroxide phases with dilute hydrochloric acid 0 25 m hcl a series of experimental tests indicate that extraction of sedimentary organic compounds using h2o2 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates however this contamination is expected to be minor for ree because measured concentrations in h2o2 leachates are about two orders of magnitude higher than in the above mentioned phases the mean ree concentrations determined in the h2o2 leachates for samples from rivers estuaries coastal seas and open ocean settings yield relatively similar levels with ree 109 86 ppm mean s n 58 the organic fractions leached from cold seep sediments display even higher concentration levels 285 150 ppm mean s n 12 the h2o2 leachates for most sediments exhibit remarkably similar shale normalized ree patterns all characterized by a mid ree enrichment compared to the other ree this suggests that the distribution of ree in leached sedimentary organic phases is controlled primarily by biogeochemical processes rather than by the composition of the source from which they derive e g pore river or sea water the nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions in contrast the som extracted from marine sediments display end values that typically range between the end signatures for terrestrial organic matter inferred from the analysis of the sedimentary detrital fractions and marine organic matter inferred from the analysis of local surface seawater a notable exception is the case of organic matter om fractions leached from cold seep sediment samples which sometimes exhibit end values markedly different from both terrigenous and surface seawater signatures this suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes recycling pore water ree characterized by a distinct isotopic composition overall our results confirm that organic matter probably plays an important role in the oceanic ree budget through direct scavenging and remineralization within the water column both the high ree abundances and the shape of shale normalized patterns for leached som also suggest that om degradation in sub surface marine sediments during early diagenesis could control to a large extent the distribution of ree in pore waters benthic fluxes of organic bound ree could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins neodymium isotopes could provide useful information for tracing the origin terrestrial versus marine and geographical provenance of organic matter with potential applications in paleoceanography in particular future studies should further investigate the potential of nd isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation

ice streams as the arteries of an ice sheet their mechanics stability and significance ice streams are corridors of fast ice flow ca 0 8 km year within an ice sheet and are responsible for discharging the majority of the ice and sediment within them consequently like the arteries in our body their behaviour and stability is essential to the well being of an ice sheet ice streams may either be constrained by topography topographic ice streams or by areas of slow moving ice pure ice streams the latter show spatial and temporal patterns of variability that may indicate a potential for instability and are therefore of particular interest today pure ice streams are largely restricted to the siple coast of antarctica and these ice streams have been extensively investigated over the last 20 years this paper provides an introduction to this substantial body of research and describes the morphology dynamics and temporal behaviour of these contemporary ice streams before exploring the basal conditions that exist beneath them and the mechanisms that drive the fast flow within them the paper concludes by reviewing the potential of ice streams as unstable elements within ice sheets that may impact on the earth s dynamic system d 2002 elsevier science b v all rights reserved

moment tensor solutions for small and moderate earthquakes in the ibero maghreb region 1 we applied time domain moment tensor inversion of local and regional waveforms to small and moderate mw 3 5 5 7 shallow earthquakes from the iberian peninsula northern morocco and northern algeria for the 6 years period from november 1995 to march 2002 and the previous network of autonomously recording seismograms nars experiment moment tensor solutions were obtained for 58 events considerably increasing the total number of available solutions in the study area for each event we performed a moment tensor inversion and a double couple grid search for simple faulting events the grid search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation the computed mechanisms show regional consistency a large part of the iberian peninsula is characterized by normal faulting mechanisms with sw ne oriented t axes thrusting and se nw compression is dominant in algeria in the alboran sea the westernmost part of the mediterranean and the transition between both regimes strike slip mechanisms dominate with approximately n s oriented p axes this pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations

the signature of strain magnitude in tills associated with the vistula ice stream of the scandinavian ice sheet central poland abstract at oborki in central poland we examined a 3 m thick late weichselian basal till deposited by the vistula ice stream a multi proxy approach involving a study of grain size grain roundness crushing index petrographic composition till fabric and till micromorphology in a closely sampled vertical profile was applied to decipher till formation and ice movement mechanisms the till consists of a succession of four texturally and structurally different units generated by a combination of processes related to effective stresses exerted on the bed by active ice deformation intergranular advection clast ploughing and localized basal decoupling played important roles during till formation micromorphological analysis reveals that the most common s matrix microstructures are grain lineations grain stacks turbate structures till pellets and crushed grains microshears dominate whereas plasmic fabric is not well developed we use grain roundness crushing indices and microshear geometry to determine subglacial strain magnitude in the till matrix microfabric and macrofabric s 1 eigenvalues together with i l indexes indicate low shear strains in the order of 10 10 2 strain estimates vary depending on the particle sizes used suggesting a plastic mode of till deformation all proxies studied suggest complex and temporally variable subglacial conditions under the marginal part of the vistula ice stream probably caused by changes in till rheology related to fluctuating porewater pressures fast ice flow was facilitated by a combination of bed deformation and enhanced basal sliding on a thin water layer our results may also be representative for other terrestrially based pleistocene ice streams moving over soft beds

southwest scandinavia 40 15 kyr bp palaeogeography and environmental change twelve palaeogeographical reconstructions illustrate environmental changes at the southwest rim of the scandinavian ice sheet 40 15 kyr bp synchronised land sea and glacier configurations are based on the lithostratigraphy of tills and intertill sediments dating is provided by optically stimulated luminescence and calibrated accelerator mass spectrometry radiocarbon an interstadial sequence ca 40 30 kyr bp with boreo arctic proglacial fjords and subarctic flora and occasional glaciation in the baltic was succeeded by a last glacial maximum sequence ca 3020 kyr bp with the closure of fjords and subsequent ice streams in glacial lake basins in kattegat and the baltic steadily flowing ice from sweden bordered the norwegian channel ice stream a deglaciation sequence ca 20 15 kyr bp indicates the transgression of arctic waters retreat of the swedish ice and advance of baltic ice streams succeeded by a return to interstadial conditions when ameliorated ice free conditions prevailed in maritime regions glaciers advanced through the baltic and when interstadial regimes dominated the baltic glaciers expanded off the norwegian coast the largest glacier extent was reached in the north sea around 29 kyr bp about 22 kyr bp in denmark and ca 18 kyr bp in the baltic our model provides new data for future numerical and qualitative landform based models copyright c 2003 john wiley sons ltd less

european mediterranean regional centroid moment tensors 1997 2000 the mediterranean region is seismically very active and undergoing rapid deformation earthquakes as strong as m 6 are present but relatively rare on the other hand moderate magnitude seismicity 4 5 m 5 5 is widespread and often damaging an improved knowedge of moderate magnitude earthquakes can contribute significantly to a better understanding of active tectonics in the region harvard centroid moment tensors cmt today represent the most widely used reference for reliable source mechanisms but modelling seismic sources with the cmt technique for earthquakes with magnitude less than m 5 5 5 is quite difficult since 1997 we are using an extension of the standard cmt algorithm to compute regional centroid moment tensors rcmt for moderate magnitude earthquakes mw as low as 4 0 analyzing intermediate period surface waves from regional and teleseismic seismograms we routinely apply the algorithm to european mediterranean seismicity to produce a catalog of seismic moment tensors for events with magnitude between 4 5 and 5 5 which generally are not included in the harvard cmt catalog in this paper we show the results for earthquakes that occurred between 1997 and 2000 consisting of 252 solutions and we discuss the characteristics of the catalog and the areas where these new data are most relevant

influence of provenance and transport process on the geochemistry and radiogenic hf nd and sr isotopic composition of pleistocene glacial sediments minnesota usa abstract we develop a broad geochemical dataset from 50 samples of pleistocene glacial till matrix including three lacustrine samples representing four sediment provenances collected from across minnesota usa such a dataset is useful both in the context of regional studies of glaciation and in efforts to understand how provenance and glacial processes impact the geochemistry of sediment archives the principal sediment sources of the four provenances include materials from the archean proterozoic canadian shield the proterozoic midcontinent rift paleozoic carbonates and cenozoic and mesozoic clastic sediments we measured major element geochemistry in all till samples in both

recent antarctic ice mass loss from radar interferometry and regional climate modelling observed estimates of ice losses in antarctica combined with regional modelling of ice accumulation in the interior suggest that east antarctica is close to a balanced mass budget but large losses of ice occur in the narrow outlet channels of west antarctic glaciers and at the northern tip of the antarctic peninsula

structural and rheological implications of lower crustal earthquakes below northern switzerland abstract a detailed study of the recent seismicity in the northern alpine foreland of switzerland reveals that earthquakes with magnitudes between 0 9 and 4 2 occur not only in the upper part of the crust but contrary to observations in most other intracontinental settings seismicity extends down to depths of about 30 km in the lower crust observed p wave velocities in the focal region of even the deepest earthquakes are less than 6 3 km s 1 the average value of poisson s ratio for the entire focal depth range 6 30 km lies between 0 23 and 0 24 focal mechanisms are mostly a combination of strike slip and normal faults with consistent orientations of p and t axes but without any systematic dependence on focal depth from geological observations regional strain rates are of the order of 10 13 s 1 two dimensional temperature modelling indicates that temperatures in the lower crustal seismogenic zone are well above 450 c under the assumption of a dry environment the observed p wave velocities and poisson s ratios imply either a granitic or quartz rich gneissic composition or possibly a gabbroic quartz free granulite the deformation would be governed either by the rheology of quartz or of plagioclase the onset of ductility observed in laboratory studies lies around 300 c for quartz and around 450 c for plagioclase thus conditions in the lower crust beneath northern switzerland appear to be incompatible with the occurrence of either brittle failure or plastic instabilities as is implied by the existence of earthquakes alternatively lower crustal earthquakes could be a manifestation of the presence of fluids in the lower crust fluids under near lithostatic pressure either evolved in situ from metamorphic reactions or from infiltration from the mantle would tend to decrease the effective stress on pre existing faults and thus allow brittle friction failure to occur at depths where under dry conditions or low fluid pressures only ductile deformation would be expected

continental scale transport of sediments by the baltic ice stream elucidated by coupled grain size and nd provenance analyses abstract we introduce a methodology for determining the transport distance of subglacially comminuted and entrained sediments we pilot this method on sediments from the terminal margin of the baltic ice stream the largest ice stream of the fennoscandian ice sheet during the last glacial maximum a strong correlation r2 0 83 between the end and latitudes of circum baltic river sediments enables us to use end as a calibrated measure of distance the proportion of subglacially transported sediments in a sample is estimated from grain size ratios in the silt fraction

subglacial sediment dispersal and till composition dispersal of subglacial sediment down ice from its bedrock source assumes the form of a negative exponential decay curve dispersal decay curves can be quantified by their decay constants half distances half lives and total transport distances mapped dispersal decay curves associated with pleistocene ice sheets in north america and europe identify several scales of dispersal ranging from local kilometers to continental 100 s to 1000 s km scales till composition reflects the various scales of dispersal local scales short transport distances result in tills that reflect underlying bedrock whereas continental scales long transport distances result in tills derived largely from sources far up ice a number of parameters proposed as influencing subglacial sediment dispersal and transport distances do not explain the range of scales observed although they may explain minor variations kilometers in transport distances topography and basal ice velocity sliding velocity are interpreted as

characteristics of the heat balance of the greenland ice sheet for modelling les donnees du bilan thermique recoltees au cours de l egig de 1959 a 1967 sont appliquees au calcul du deplacement de la ligne d equilibre du au changement climatique

micro meteorological conditions for snow melt conditions meteorologiques des periodes de debut et de fin des fontes des neiges et glaces de glaciers alpins on utlise la temperature de l air l humidite les rayonnements total global reflechi le coefficient d echange turbulent utilise est 18 5 wm 2 k 1 il apparait que la neige peut fondre a 10 c et rester solide a 10 c

how glaciers entrain and transport basal sediment physical constraints abstract simple insights from the physics of ice water and sediment place constraints on the possible sediment transport behavior of glaciers and ice sheets because glaciers concentrate runoff streams generated by glaciers transport much sediment and may erode bedrock rapidly deforming glacier beds also can transport much sediment particularly in marginal regions rapid sediment entrainment producing thick debris rich basal zones may occur by regelation into subglacial materials and by freeze on from rising supercooled waters numerous other mechanisms may be important but primarily near ice margins especially those of advancing or fluctuating glaciers several sediment entrainment mechanisms may be active beneath a single glacier but one process is likely to be dominant at any place and time

patterns of quaternary ice sheet erosion and deposition in fennoscandia and a theoretical framework for explanation it has long been recognised that the formerly glaciated area of fennoscandia shows large spatial differences in thicknesses of quaternary deposits mainly tills and exhibits distinct patterns of glacial scouring and deep linear erosion the reasons for this striking zonation have been elusive and in particular the relative roles of mountain ice sheets mis and full sized fennoscandian ice sheets fis in shaping the landscape surface need clarification on the basis of current advances in our understanding of the climate evolution and basal thermal organisation of ice sheets we perform spatio temporal qualitative modelling of ice sheet extent and migration of erosion and deposition zones through the entire quaternary and proceed to suggest an explanatory model for the current spatial pattern of quaternary deposits and the two different types of erosion zones we use the spatial distribution of fjords and deep non tectonic lakes for delineating zones of deep glacial erosion and relict landscapes as markers for frozen bed conditions on the basis of the amount of exposed bedrock the landscape was classified into a tripartite system of drift thickness thick drift intermediate drift thickness absence of drift scoured zones it is found that a centrally placed central and northern sweden zone of thick drift cannot be explained by deposition under fis style ice sheets but is instead likely to be the combined result of marginal deposition of fluctuating mis style ice sheets primarily during the early and middle quaternary and the inefficiency of later east centered fis style ice sheets in evacuating this drift from underneath their central low velocity and possibly frozen bed areas the western fjord zone of deep glacial erosion formed underneath both mis and fis style ice sheets during the entire quaternary while the eastern lake zone of deep glacial erosion is exclusively related to mis style ice sheets and formed largely during the early and middle quaternary the scouring zones formed under conditions of rapid ice flow towards bathymetrically defined calving margins of fis style ice sheets they likely reflect process patterns of the last two or three fis style ice sheets the three landscape zones differ in their degree of permanence with the deep erosion zones being a long lasting legacy in the landscape more likely to be enhanced than obliterated by subsequent glacial events the thick drift cover zone once established appears to have been surprisingly robust to erosion by subsequent glacial events the scouring zones appear to be the most recent and ephemeral of the three zones with possible major alterations during single glacial events

regional moment tensor determination in the european mediterranean area initial results the broadband seismic network in the european mediterranean area provides high quality data we invert these regional three component data for the source parameters of moderate to strong earthquakes in the entire european mediterranean area regional seismograms have a good signal to noise ratio even for moderate sized events that are too small for teleseismic analysis the magnitude threshold for source parameter determination can thus be significantly lowered the threshold depends on the average event station distances within dense broadband networks we analyze mw 3 0 earthquakes in areas far from broadband seismic stations the lower bound is mw 4 5 4 8 still considerably lower than the teleseismic analysis threshold about mw 5 0 5 3 for larger events we perform rapid moment tensor analysis using near real time data solutions are posted within hours after event occurrence in a second step we merge near real time and later available data to obtain a regional moment tensor catalog of moderate to large earthquakes for the entire european mediterranean area within less than 1 year we have analyzed 67 earthquakes ranging in size from mw 2 9 to 7 5 the solutions cover the seismically active areas of the european mediterranean area particularly important are solutions for slowly deforming regions where large earthquakes that could be analyzed with teleseismic data occur infrequently the solutions are reliable for events with independent source parameter estimates the agreement is generally high the solutions are robust variations in epicentral parameters source depth or exact choice of stations do not affect source parameter estimates strongly the moment magnitudes provide a unified estimate of earthquake size for the european mediterranean area we perform regression analyses to link our moment magnitudes with local body and surface wave magnitudes

retention of greenland runoff by refreezing implications for projected future sea level change melting produced at the surface of subfreezing permeable firn does not freely percolate but instead refreezes near its point of origin raising the firn temperature and decreasing the pore space if sufficient meltwater is introduced the firn will warm to 0 c and subsequent water will fill the remaining pore space without freezing only after the residual water content of the firn is exceeded will water flow through the firn and possibly escape as runoff this process prevents summer melt on high arctic glaciers and ice caps from escaping in its entirety and it must be accounted for in modeling glacier runoff on the basis of surface energy balance a model is presented here which describes in a simple way the transient process of infiltration refreezing and runoff in a future warming climate the model is applied to greenland for which predictions of runoff induced sea level rise that do not consider the refreezing process could be as much as 5 0 cm too high over 150 years

evidence of bias in estimations of earthquake size magnitudes of earthquakes determined using traditional methods show systematic deviations dependent on tectonic setting from accurate estimates of earthquake size magnitudes are overestimated for most of the continental earthquakes underestimated for mid oceanic ridges and differences of varying sign are obtained for subduction zones this is important in evaluating the seismic risk or consideration of effects such as the seismic versus aseismic strain release as seismic moments determined from magnitudes can be wrong by as much as a factor of four

determination of timing and location of water movement and ice layer formation by temperature measurements in sub freezing snow measurements of temperature in snow along a vertical profile during the onset of spring melting are used to calculate spatial and temporal temperature gradients and terms of the conduction equation with an internal energy production term are calculated heat transfer information is combined with stratigraphic observations made during melting and allow detailed determination of the timing and location of heterogeneous water movement and of refreezing internal energy production is interpreted as latent heat of refreezing of percolated meltwater times and locations of flow and refreezing of meltwater are calculated and compared to stratigraphic observations of layering and changes in density and liquid water content sequences of melt piping layering and refreezing seen in calculations and in stratigraphy demonstrate retarded flow at fine to coarse transitions flow along such transitions and refreezing at the transitions to form ice layers downslope flow is also observed in the absence of an impermeable horizon to redirect flow from the vertical

genesis of dispersal plumes in till in regions formerly covered by continental ice till sheets may contain distinctive clastic particles derived from local bedrock sources such as ore bodies such particles especially in thicker tills may be distributed in three dimensional dispersal trains or plumes developments in our understanding of glacial erosion entrainment and deposition over the past two or three decades help clarify formation of these plumes much of the debris in the basal ice of ice sheets is likely incorporated at places where water is freezing onto the base of the ice sheet this water largely a product of melting of basal ice further upglacier has migrated downglacier under the influence of a gradient in the hydraulic potential controlled primarily by the ice surface slope and secondarily by basal topography and thermal regime refreezing occurs over a substantial distance along flow so as the ice moves away from an ore body material eroded from the body is later elevated above the bed by refreezing of more meltwate

glacial curvilineations new glacial landforms produced by longitudinal vortices in subglacial meltwater flows abstract the glacial landscape of the dobrzyn plateau in central poland contains a complex suite of enigmatic bedforms consisting of elongate and sinuous sediment ridges occurring within an anabranched network of tunnel channels terminating at a former ice margin marked by extensive glaciofluvial fans the term glacial curvilineations is proposed to describe these enigmatic bedforms that occur as fields of parallel sinuous ridges separated by troughs the regional pattern of glacial curvilineations replicates the morphology and pattern of tunnel channel margins and suggests a common genesis tunnel channels and glacial curvilineations are eroded in the interbedded diamictons and glaciofluvial sediments of the plateau we propose that tunnel channels and glacial curvilineations are the products of subglacial meltwater erosion curvilineations are erosional remnants produced by longitudinal vortices within the tunnel channel forming flows parallelism of curvilineations reflects spacing of turbulent structures within the subglacial flow tunnel channel margins also control the sinuosity of curvilineations by dictating both the path and curvature of longitudinal vortices arguments for meltwater erosion are strengthened by the presence of extensive glaciofluvial fans at tunnel channel termini they are the depositional counterparts to the extensive subglacial fluvial dissection of the plateau understanding curvilineation genesis may shed light on glacier hydrologic processes tunnel channels develop abruptly in the plateau surface suggesting localized point sources of meltwater such as drainage of subglacial and or supraglacial lakes the extent of tunnel channels and lateral continuity of glacial curvilineations suggests broad sheet like flows as wide as a few kilometres

an improved method for extracting marine sediment fractions and its application to sr and nd isotopic analysis the radiogenic isotopic composition of both detrital and fe mn fractions in marine sediments can be used in paleoceanography to infer changes of bottom water circulation we have examined various chemical techniques for the analysis of sr and nd isotope ratios in these fractions and present a robust method that can be used to separate both the fe mn oxides and the detrital fraction from a marine sediment sample for isotopic analysis our sequential leaching procedure involves the use of 10 acetic acid followed by 1 m hydroxylamine hydrochloride in 25 acetic acid to remove the carbonate component and the fe mn oxide fraction respectively the applicability of our chemical procedure is illustrated with examples from a marine sediment core raised from the northern cape basin southeast atlantic ocean

deglaciation of fennoscandia abstract to provide a new reconstruction of the deglaciation of the fennoscandian ice sheet in the form of calendar year time slices which are particularly useful for ice sheet modelling we have compiled and synthesized published geomorphological data for eskers ice marginal formations lineations marginal meltwater channels striae ice dammed lakes and geochronological data from radiocarbon varve optically stimulated luminescence and cosmogenic nuclide dating this is summarized as a deglaciation map of the fennoscandian ice sheet with isochrons marking every 1000 years between 22 and 13 cal kyr bp and every hundred years between 11 6 and final ice decay after 9 7 cal kyr bp deglaciation patterns vary across the fennoscandian ice sheet domain reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins for example the ice sheet margin in the high precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice marginal deposits in many fjords and coastal valleys retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern sweden and rapid retreat of the calving ice margin in the baltic basin our reconstruction is consistent with much of the published research however the synthesis of a large amount of existing and new data support refined reconstructions in some areas for example the lgm extent of the ice sheet in northwestern russia was located far east and it occurred at a later time than the rest of the ice sheet at around 17 15 cal kyr bp we also propose a slightly different chronology of moraine formation over southern sweden based on improved correlations of moraine segments using new lidar data and tying the timing of moraine formation to greenland ice core cold stages retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet with the lowest rates on the high elevation and maritime norwegian margin retreat rates compared to the climatic information provided by the greenland ice core record show a general correspondence between retreat rate and climatic forcing although a close match between retreat rate and climate is unlikely because of other controls such as topography and marine versus terrestrial margins overall the time slice reconstructions of fennoscandian ice sheet deglaciation from 22 to 9 7 cal kyr bp provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the fennoscandian ice sheet and are an important resource for testing and refining ice sheet models

the sources and transport of sr and nd isotopes in the baltic sea we have determined the concentration and isotopic composition of sr and nd in waters from the baltic sea the baltic sea is an intracontinental stratified brackish water estuarine like system and the rivers emptying into it drain a suite of terranes ranging from proterozoic archean in the north to phanerozoic in the south the sampled brackish waters range in salinity from seawater sw at 35 289 to a minimum of 2 460 at the surface in the innermost part of the gulf of bothnia the sr concentrations show generally conservative behavior indicating a simple two component mixing however small deviations 3 70 from a perfect mixing line reveal that the imprints from rivers with different sr concentrations are preserved in the blending strontium concentrations from a depth profile across the redoxcline in the baltic proper indicate that vertical particle transport alters the sr concentration in the water our estimated concentration of sr in the average freshwater input to the baltic is 0 03 ppm which is only about 0 4 of the sw concentration the sr isotopic data range from e sr sw 0 in seawater to e sr bw sw 7 8 in the least saline baltic water bw sample in the gulf of bothnia the isotopic composition of sr versus 1 sr in the baltic sea follows an almost perfect mixing line which shows that seawater sr is mixed with much more radiogenic components calculated end member values of e sr sw for each sample show that the riverine input into the gulf of bothnia has e sr sw 120 200 and 10 50 e units in the baltic proper these values are in general agreement with direct measurements of river waters in each region however the calculated values in the gulf of bothnia are lower than the measured river water input in this region which indicates the presence of less radiogenic sr presumably originating from the river waters draining the southern part of the basin which are partially transported northward and mixed with sr from the gulf of bothnia rivers the nd concentration in the baltic sea is not conservative varying between 5 and 45 ppt with the highest concentrations in the bottom waters due to vertical particulate transport a plot of e nd o in baltic water yields a good correlation with the calculated freshwater end member e sr sw the data show that it is possible to unravel the different freshwater sources into the baltic and to identify the zones of particulate removal of both non conservative species such as the ree and of quasi conservative species such as sr the use of isotopic tracers in this estuarine environment may provide a much better insight into mixing and element transport it should also be possible to trace lateral movements of freshwater inputs

laurentide ice streaming on the canadian shield a conflict with the soft bedded ice stream paradigm elucidating the controls on the location and vigor of ice streams is crucial to understanding the processes that lead to fast disintegration of ice flows and ice sheets in the former north american laurentide ice sheet ice stream occurrence appears to have been governed by topographic troughs or areas of soft sediment geology this paper reports robust evidence of a major paleo ice stream over the northwestern canadian shield an area previously assumed to be incompatible with fast ice flow because of the low relief and relatively hard bedrock a coherent pattern of subglacial bedforms drumlins and megascale glacial lineations demarcates the ice stream flow set which exhibits a convergent onset zone a narrow main trunk with abrupt lateral margins and a lobate terminus variations in bedform elongation ratio within the flow set match theoretical expectations of ice velocity in the center of the ice stream extremely parallel megascale glacial lineations tens of kilometers long with elongation ratios in excess of 40 1 attest to a single episode of rapid ice flow we conclude that while bed properties are likely to be influential in determining the occurrence and vigor of ice streams contrary to established views widespread soft bed geology is not an essential requirement for those ice streams without topographic control we speculate that the ice stream acted as a release valve on ice sheet mass balance and was initiated by the presence of a proglacial lake that destabilized the ice sheet margin and propagated fast ice flow through a series of thermomechanical feedbacks involving ice flow and temperature

palaeoglaciology of an ice sheet through a glacial cycle the european ice sheet through the weichselian abstract satellite images provide unique means of identifying large scale flow generated lineations produced by former ice sheets they can be interpreted to reconstruct the major elements which make up the integrated large scale structure of ice sheets ice divides ice streams interstream ridges ice shelves calving bays the evolving palaeoglaciological structure of the european ice sheet during its decay from the last glacial maximum lgm is reconstructed by reference to these components and in the context of a new map showing isochrons of retreat during the retreat phase in particular the time dependent dynamic evolution of the ice sheet and the pattern of ice stream development are reconstructed crossing lineations are widespread the older ones are suggested to have formed during molten bed phases of ice sheet growth and preserved by frozen bed conditions during the glacial maximum particularly in areas which lay during deglaciation beneath ice divides and inter ice stream ridges both areas of slow flow and possibly frozen bed conditions four phases of growth a1 to a4 and five phases of decay r1 to r5 are used to describe the major climatically and dynamically determined stages in the evolution of the ice sheet through the last glacial cycle the growth and decay patterns are quite different and associated with major shifts in the ice divide reflecting growth from the fennoscandian mountains and decay away from marine influenced margins these patterns were determined by the locations of nucleation areas spatial patterns of climate and calving at marine margins the prevalence of streaming within the retreating ice sheet suggests that the mean elevation of the ice sheet was lower than predicted from glaciological models which do not include streaming and that this might reconcile glaciological models and earth rheology models which infer paleao ice sheet thickness by inverting sea level data

fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model the evolution of ice sheet configuration and flow pattern in fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model i e a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets the model uses mapped flow traces and deglacial melt water landforms as well as relative chronologies derived from cross cutting striae and till lineations as input data flow trace systems were classified into four types i time transgressive wet bed deglacial fans ii time transgressive frozen bed deglacial fans iii surge fans and iv synchronous non deglacial event fans using relative chronologies and aggregation of fans into glaciologically plausible patterns a series of ice sheet configurations at different time slices was erected a chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume geological evidence exists for several discrete ice sheet configurations centred over the scandinavian mountain range during the early weichselian the build up of the main weichselian fennoscandian ice sheet started at approximately 70 ka and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern norway this configuration had a flow pattern which is poorly reproduced by current numerical models of the fennoscandian ice sheet at the last glacial maximum the main ice divide was located overthe gulf of bothnia a major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the scandinavian mountain chain widespread areas of preserved pre late weichselian landscapes indicate that the ice sheet had a frozen bed core area which was only partly diminished in size by inward transgressive wet bed zones during the decay phase

reappraisal of surface wave magnitudes in the eastern mediterranean region and the middle east there have been many attempts to improve parametric catalogues for surface wave magnitudes for earthquakes of this century and many of these attempts have been based on empirical adjustments to homogenize and complete catalogues without recourse to the instrumental data with which these magnitudes have been calculated using the prague formula with station corrections and a substantial volume of amplitude and period readings of surface waves culled from station bulletins we calculated uniformly the magnitude of all significant earthquakes 1519 in all in the eastern mediterranean region and in the middle east between 1900 and 1998 we also calculated station corrections and their variation with time and examined the effect of distance adjustment of the prague formula on m s estimates we find that the current procedure of averaging station magnitudes underestimates m s this underestimation depends on the variance and on the number of station magnitudes available for the calculation of m s which can be as large as 0 3 magnitude units or more we also find that station corrections have a rather small overall effect on event magnitude of less than 0 1 except when the number of observing stations is small in which case the correction may reach 0 3 magnitude units event magnitudes derived from station magnitudes with distance adjustment calculated from the original prague formula are on average 0 1 units larger than m s without distance correction we find that for shallow events gutenberg s estimates are on average larger by 0 12 units and show a significant scatter with a standard deviation three times the mean value we find similar differences and scatter for surface wave magnitudes estimated by other workers and agencies

samarium neodymium elemental and isotopic systematics in sedimentary rocks abstract trace element sm nd th sc and nd isotopic data for sedimentary rocks are examined in order to evaluate 1 1 possible secular trends in the composition of the sedimentary mass and upper continental crust 2 2 the role of tectonic setting in controlling the chemical and nd isotopic composition of the sedimentary mass when plotted against either sedimentation age or average provenance age determined mainly from nd model ages sm nd in sedimentary rocks decreases abruptly from about 0 21 to 0 19 at the archean proterozoic transition consistent with a change towards a more felsic upper crustal composition the change is only somewhat less pronounced for turbidite sediments than for those of continental affinity a trend toward increasing sm nd approaching or exceeding archean values is observed for phanerozoic turbidites this latter change is interpreted as indicating undifferentiated young crust as a component in the sediment which has been lost from the older post archean record due to sedimentary and igneous intracrustal recycling processes when plotted against sedimentation age th sc ratios exhibit a trend directly comparable to that of sm nd in this case th sc increases abruptly at the archean proterozoic boundary from about 0 5 to 1 0 and then decreases to about 0 7 during the phanerozoic nd isotopic composition of modern sediments is affected by tectonic association with those deposited at active margin settings tending to have higher nd reflecting younger provenance and higher and more scattered sm nd reflecting less homogenized and differentiated provenance it is likely that these distinctions can be traced back for about 1 2 ga but with the current data base are not readily resolved in older sedimentary rocks the degree to which the preserved sedimentary mass is open to new additions from the mantle either through replacement during sedimentary recycling or sediment mass growth is highly variable but averages about 15 25 during the phanerozoic

genesis of hummocky moraines by thrusting in glacier ice evidence from svalbard and britain irregular mounds of glacial debris commonly referred to as 9hummocky moraine9 until recently were linked to ice stagnation during rapid climatic amelioration however recent work in scotland has demonstrated that some hummocky moraine dating from the younger dryas event c 10 000 years bp was the product of deposition at active ice margins observations at modern high arctic glacier margins in svalbard 76 80 n indicate that some moraines of this type form under a dynamic glaciological regime mainly by thrusting in active polythermal ice undergoing strong longitudinal compression this situation is particularly common where there is a transition from warm based ice in the interior of a glacier to cold based ice at the margins or snout from their morphological similarity rectilinear slopes facing up glacier and irregular downglacier faces and apparent stacking of slabs of sediment of subglacial derivation it is concluded that some assemblages of british moraines are also the product of thrusting this process appears to be most dominant in polythermal glaciers rather than in temperate glaciers on this basis it is tentatively suggested that the younger dryas in britain was characterized by a climatic regime similar to that in svalbard today mean annual temperature 5 c 400 1000 mm precipitation and that the associated glaciers may have been of polythermal character

linking danube river activity to alpine ice sheet fluctuations during the last glacial ca 33 17 ka bp insights into the continental signature of heinrich stadials abstract offshore archives retrieved from marine lacustrine environments receiving sediment from large river systems are valuable quaternary continental records in the present study we reconstruct the danube river activity at the end of the last glacial period based on sedimentological mineralogical and geochemical analyses performed on long piston cores from the north west black sea margin our data suggest that the danube river produced hyperpycnal floods throughout the ca 33 17 ka period four main periods of enhanced danube flood frequency each of 1 5 3 kyr duration are recorded at ca 32 5 30 5 ka equivalent to the first part of heinrich stadial hs 3 at ca 29 27 5 ka equivalent to greenland stadial 4 at ca 25 3 23 8 ka equivalent to hs 2 and at ca 22 3 19 ka based on mineralogical and geochemical data we relate these events to enhanced surface melting of the alpine ice sheet ais that covered 50 000 km2 of the danube watershed at the last glacial maximum lgm our results suggest that i the ais growth from the inner alps to its lgm position in the northern alpine foreland started from ca 30 5 ka ended no later than ca 25 3 ka and was interrupted by a melting episode ca 29 27 5 ka ii the ais volume drastically decreased from ca 22 3 to 19 ka as soon as summer insolation energy at the ais latitude increased and iii hss strongly impacted the ais mass balance through enhanced summer surface melt this together with evidence of severely cool winters and the rapid expansion of sea ice in the north atlantic implies strong seasonality in continental europe during stadials

lake sediment based paleoseismology limitations and perspectives from the swiss alps abstract in regions with moderate seismicity and large intervals between strong earthquakes paleoseismological archives that exceed the historical and instrumental timescale are needed to establish reliable estimates of earthquake recurrence for long return periods in several regions lake sediments have shown to be suitable for paleoseismological studies by causally linking characteristic sedimentological features to historic earthquakes studies on single lakes however do neither allow determining the paleoepicentre nor the paleomagnitude for the potential paleoearthquakes here we compile using shaking induced mass movements and micro deformations summarized as sedimentary event deposits seds the sedimentary paleoseismic record of 11 lakes from switzerland over the last 10 000 years the large dating uncertainty attributed to such deposits up to 250 years does not allow us to conclusively test for one large earthquake hypothesis when comparing the different lake records and therefore represents one of the major limitations of this approach instead using a new approach of exploring the normalized frequency of occurrence averaged over a larger area the compiled dataset reveals striking periods of enhanced occurrence of seds in the studied lakes during several phases of the past 10 000 years centered at 9700 6500 and during the last 4000 cal yr bp moreover we use a calibrated intensity attenuation relation in order to model scenarios of possible epicentral areas and ranges of magnitudes of paleoearthquakes we differentiate two cases i a single earthquake scenario if seds occur simultaneously in various studied lakes or ii a multi earthquake scenario if seds in the studied lakes cluster within a time interval the modelled scenarios allow us to propose maximally possible magnitudes of large paleoearthquakes constituting an important input for seismic hazard assessment in the swiss alps

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

record of the vistula ice lobe advances in the late weichselian glacial sequence in north central poland during the last glacial maximum lgm the vistula ice lobe was one of the key morphological elements at the southern margin of the scandinavian ice sheet in north central poland the area of the vistula ice lobe experienced two ice sheet advances of varied extent the older one is correlated with the leszno brandenburg phase and the younger one is correlated with the poznan frankfurt phase sedimentological research and luminescence dating of the late weichselian glacial sequence in the vistula ice lobe area was conducted a new scenario of the late weichselian ice events in the area is presented the limit of the leszno phase within the vistula ice lobe was much smaller than had been accepted previously and its age is estimated to be about 20 300 bp significant ice sheet retreat was

abrupt drainage cycles of the fennoscandian ice sheet continental ice sheets are a key component of the earth s climate system but their internal dynamics need to be further studied since the last deglaciation the northern eurasian fennoscandian ice sheet fis has been connected to the black sea bs watershed making this basin a suitable location to investigate former ice sheet dynamics here from a core retrieved in the bs we combine the use of neodymium isotopes high resolution elemental analysis and biomarkers to trace changes in sediment provenance and river runoff we reveal cyclic releases of meltwater originating from lake disna a proglacial lake linked to the fis during heinrich stadial 1 regional interactions within the climate lake fis system linked to changes in the availability of subglacial water led to abrupt drainage cycles of the fis into the bs watershed this phenomenon raised the bs water level by 100 m until the sill of the bosphorus strait was reached flooding the vast northwestern bs shelf and deeply affecting the hydrology and circulation of the bs and probably of the marmara and aegean seas

effects of climatic perturbations on the equilibrium line altitude west greenland perturbation analysis is applied to the heat balance at the egig line west greenland with respect to climatic changes the shift of the equilibrium line altitude is obtained for perturbations of temperature absolute humidity cloudiness and annual accumulation the total net ice ablation at the egig line increases by 45 with a perturbation of 1 k

seismic moment from regional surface wave amplitudes applications to digital and analog seismograms accurate consistent earthquake size estimates are fundamental for seismic hazard evaluation in central europe seismic activity is low and long term seismicity available as intensities from written historical records has to be included for meaningful assessments we determined seismic moments m 0 of 25 stronger twentieth century events in switzerland from surface wave amplitude measurements these m 0 can be used to calibrate intensity moment relations applicable to preinstrumental data we derived the amplitude moment relation using digital data from 18 earthquakes in and near switzerland where independent m 0 estimates exist the surface wave amplitudes were measured at empirically determined distance varying reference periods t for amplitudes measured at t the distance attenuation term of the surface wave magnitude relation s log a t max 1 66 log is independent of distance for log m 0 m s c e we get log m 0 s 14 90 uncertainties of 0 3 for the 14 90 constant correspond to a factor of 2 m 0 uncertainty which was verified with independent data our relation allows fast direct m 0 determination for current earthquakes and after recalibration of the constant the relation can be applied anywhere we applied our relation to analog seismograms from early instrumental earthquakes in switzerland that were collected from several european observatories amplitude measurements from scans were performed at large amplifications and corrected for differences between t and actual measurement periods the resulting magnitudes range from m w 4 6 to 5 8 for the largest earthquake in switzerland during the twentieth century uncertainties for the early instrumental events are on the order of 0 4 magnitude units online material moment tensor analysis of 14 recent earthquakes