cenozoic global ice volume and temperature simulations with 1 d ice sheet models forced by benthic δ18o records variations in global ice volume and temperature over the cenozoic era have been investigated with a set of one dimensional 1 d ice sheet models simulations include three ice sheets representing glaciation in the northern hemisphere i e in eurasia north america and greenland and two separate ice sheets for antarctic glaciation the continental mean northern hemisphere surface air temperature has been derived through an inverse procedure from observed benthic 18o records these data have yielded a mutually consistent and continuous record of temperature global ice volume and benthic 18o over the past 35ma the simple 1 d model shows good agreement with a comprehensive 3 d ice sheet model for the past 3 ma on average differences are only 1 0 c for temperature and 6 2m for sea level most notably over the 35ma period the reconstructed ice volume temperature sensitivity shows a transition from a climate controlled by southern hemisphere ice sheets to one controlled by northern hemisphere ice sheets although the transient behaviour is important equilibrium experiments show that the relationship between temperature and sea level is linear and symmetric providing limited evidence for hysteresis furthermore the results show a good comparison with other simulations of antarctic ice volume and observed sea level

impacts of non plane waves on two station measurements of phase velocities summary to determine the regional shear wave velocities in the lithosphere it is frequently necessary to use two station dispersion curves we investigate the influence of non plane wave energy on such dispersion curves and compare them to two other better known sources of error deviations from great circle paths and uncorrelated noise to study the influence of nonplane waves created from distant heterogeneities we create complex wavefields in a laterally homogeneous medium by adding interfering waves to a main plane wave we then calculate the apparent phase velocity between two seismic stations located 100 400 km apart using realistic values for the sources of error we conclude that the contribution of each is similar for 200 km long profiles our conclusions on non plane waves are made under the assumption that non plane energy from distant heterogeneities varies randomly with hypocentre location if this is correct then only five to 10 events with different hypocentres are required to obtain a stable dispersion curve with less than 1 per cent error the influence of uncorrelated noise and non plane waves diminish for longer profiles while the errors due to great circle deviations are independent of profile length and systematically bias the dispersion curve to higher velocities we recommend the inclusion of some off profile broad band stations for surface wave studies on a regional scale because such supplementary stations make it possible to apply first order corrections for off great circle propagation the strong influence from the different sources of error combined with our lack of precise knowledge of the nature and amplitude of non plane energy implies that the interpretation of two station measurements should be restricted to major changes in regional earth structure

correcting the cenozoic δ18o deep sea temperature record for antarctic ice volume abstract the oxygen isotope signal in benthic foraminifera from deep sea cores is mainly determined by deep ocean temperature and land ice volume separating the temperature and ice volume signals is a key step in understanding the evolution of cenozoic climate except for the last few million years fluctuations in land ice volume were determined mainly by the size of the antarctic ice sheet here a simplified antarctic ice sheet model and composite deep sea oxygen isotope records are used to derive a deep sea temperature history for the cenozoic the ice sheet model is forced with the oxygen isotope record which is instantaneously corrected for the calculated ice volume therefore the resulting deep sea temperature and antarctic ice volume curves are mutually consistent the temperature record of lear et al science 287 2000 269 derived from the mg ca ratio in benthic calcite is also used to force the ice sheet model the resulting ice volume does not agree well with the ice volume history inferred by lear et al from a comparison of mg ca and 18 o records the most important points emerging from this study are the cenozoic 18 o record from benthic forams is a truly mixed signal ice volume and deep sea temperature contribute equally to the variance for the period of 45 to 30 ma ago 18 o temperatures are significantly lower than mg ca temperatures rapid nonlinear build up of a continental scale ice sheet on the antarctic continent can easily occur for a linear cooling rate it is unlikely that the method of lear et al provides a reliable measure of ice volume the cooling rate at the beginning of the pliocene is much larger in the 18 o temperature curves than in the mg ca temperature curve

lithospheric structure of the central andes based on surface wave dispersion 1 shear wave velocity is very sensitive to temperature anomalies and partial melt and can provide important insights on the state of the lithosphere with that aim in mind phase velocities of rayleigh and love waves have been inverted for the regionalized shear wave velocity structure of the lithosphere across the central andes this inversion reveals strong lateral variations of vs both across the range and along strike in the altiplano crust in the upper crust the main features of our models are prominent low velocity anomalies probably related to partial melt below the los frailes ignimbrite complex and the southern altiplano at lower crustal level the altiplano is characterized by lower vs than the surrounding regions we find that the transition from the altiplano to the puna is associated with a 7 km thickening of the crust at mantle depths the nazca plate is found to be overlaid by a dipping low velocity zone with decreasing intensity with depth our results favor the idea of a cold mantle lid underlying the whole central andes

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

constraints on absolute s velocities beneath the aegean sea from surface wave analysis summary the 3 d structure of the lithosphere beneath the aegean sea is investigated through surface wave dispersion analysis rayleigh and love waves recorded by 12 broad band stations installed for a duration of 6 months in the aegean region are processed through array analysis and wiener filtering data from three geofon stations in the area of crete were also used the resulting two station phase velocities are used to determine lateral variations of rayleigh wave phase velocities between periods of 20 and 100 s by a 2 d ray tomography method the obtained phase velocities are inverted to calculate variation of s wave velocity with depth using a combination of linearized inversion and a monte carlo based non linear inversion the absolute s wave velocity is resolved to a depth of approximately 200 km a highvelocity anomaly of 3 per cent is observed in the southern aegean attributed to the hellenic subduction in the northern part of the aegean in the prolongation of the north anatolian fault which is influenced by strong extensional movements we found low absolute s wave velocities at 50 100 km depth this supports a model of a distributed deformation of the upper mantle in the area separate rayleigh and love wave phase velocity inversions along common profiles reveal a strong love rayleigh discrepancy in the northern aegean down to at least 150 km depth i e most probably including the top of the asthenosphere

measuring surface wave phase velocities beneath small broad band arrays tests of an improved algorithm and application to the french alps the local measurement of dispersion curves of intermediate period surface waves is particularly difficult because of the long wavelengths involved we suggest an improved procedure for measuring dispersion curves using small aperture broad band arrays the method is based on the hypotheses of plane incoming waves and that averaging over a set of events with a good backazimuth distribution will suppress the effects of diffraction outside the array none of the elements of the processing are new in themselves but each step is optimized so we can obtain a reliable dispersion curve with a well defined uncertainty the method is based on the inversion for the slowness vector at each event and frequency using time delays between pairs of stations where the time delays deltat are obtained by frequency domain wiener filtering the interstation distance projected on to the slowness vector d is then calculated the final dispersion curve is found by at each frequency calculating the inverse of the slope of the best fitting line of all d deltat points to test the algorithm it is applied to synthetic seismograms of fundamental mode rayleigh waves in different configurations 1 the sum of several incident waves 2 an array located next to or above a crustal thickening and 3 added white noise using regular and irregular backazimuth distributions in each case a circular array of 23 km diameter and composed of six stations is used the algorithm is stable over a large range of wavelengths between half and a tenth of the array size depending on the configuration the situations of several simultaneously incoming waves or neighbouring heterogeneities are well handled and the inferred dispersion curve corresponds to that of the underlying medium above a strong lateral heterogeneity the inferred dispersion curve corresponds to that of the underlying medium up to wavelengths of eight times the array size in the configuration considered but further work is needed to better understand the limits under which the obtained dispersion curve is not biased in the case of 5 per cent spectral amplitude white noise the dispersion curve is also stable for wavelengths up to approximately eight times the array size but this limit depends of course strongly on the noise level the method is finally applied to data from two arrays in the french alps located 50 km apart it is possible to measure the dispersion curves up to wavelengths approximately ten times bigger than the array diameter the difference in the dispersion curves is compatible with a crustal and lithospheric thickening under the alps however the observed errors are large which result in severe limits on the interpretation in terms of lithospheric structure longer recording periods may help to reduce the errors otherwise the algorithm is likely to be of use mainly in areas where the lateral variations outside the array are smaller than those of the french alps

global ice volume variations through the last glacial cycle simulated by a 3 d ice dynamical model abstract a coupled ice sheet ice shelf bedrock model was run at 20 km resolution to simulate the evolution of global ice cover during the last glacial cycle the mass balance model uses monthly mean temperature and precipitation as input and incorporates the albedo mass balance feedback the model is forced by the grip and vostok derived temperature records and by sea level and solar radiation variations which are distributed spatially and seasonally model simulations show that at the last glacial maximum lgm a volume of ice representing about 65 m of sea level equivalent is stored on the eurasian continent whereas north america stores 42 m the other regions greenland tibet south america and antarctica contribute about 17 m to global sea level lowering at the lgm compared to present day sensitivity experiments show that the ice volumes of the eurasian and north american ice sheets are particularly sensitive to summer temperature changes finally the timing and mechanism of grounded ice formation and expansion for the last glacial were studied for the eurasian and north american continents ice sheet formation begins at 118 kyr bp in the barents and kara sea region over baffin island and in the high cordilleran range following a 4 c cooling alternating regions of ice sheet expansion by direct snowfall ice flow and grounding of ice shelves can be identified these relate to specific geomorphological traces and may as such help in model validation

seismic evidence for a moderately thick lithosphere beneath the siberian platform 1 we have built a sv wavespeed tomographic model for the upper mantle beneath the siberian platform and surrounding region derived from the analysis of more than 13 000 fundamental and higher mode regional waveforms the dense path coverage and rich higher mode content of the data allow building an upper mantle image with an horizontal resolution of a few hundred kilometers extending to 400 km depth the high velocity upper mantle lid or seismic lithosphere is 200 km thick beneath most of the siberian platform but may extend to 250 km depth beneath small areas a high velocity seismic lid also underlies a large region west of the siberian platform our observation of a 200 thick seismic lithosphere beneath the siberian platform on the slow moving eurasian plate similar to the thickness of the seismic lithosphere beneath precambrian terrains on the fast moving australian plate suggests that a moderately thick seismic lithosphere beneath precambrian terrains may be more common than previously supposed

ice sheet modelling characteristics in sea level based temperature reconstructions over the last glacial cycle a widely used method for investigating palaeotemperatures is to analyze local proxy records e g ice cores or deep sea sediment cores the interpretation of these records is often not straightforward and global or hemispheric means cannot be deduced from local estimates because of large spatial variability using a different approach temperature changes over the last glacial cycle can be estimated from sea level observations by applying an inverse method to an ice sheet model in order to understand the underlying physical mechanisms we used a 1 d ice sheet model and a 3 d coupled thermodynamic ice sheet ice shelf bedrock model to investigate the importance of several physical processes for the inverse temperature reconstructions results show that i temperature reconstructions are sensitive to the employed formulation of mass balance ii excluding thermodynamics in the ice sheet leads to a smaller temperature amplitude in the reconstruction and iii hysteresis in the non linear relation between sea level and temperature occurs as a consequence of ice redistribution in the process of merging and separation of ice sheets the ice redistribution does not occur if the geometry does not support the formation of a relatively flat dome which tends to be preserved in warming conditions

off great circle propagation of intermediate period surface waves observed on a dense array in the french alps array analysis is performed on surface waves recorded in the french alps using a small aperture 25 km temporary array of six broad band stations the analysis shows that both rayleigh and love waves deviate relative to the great circle path the deviations are particularly strong up to 30 between 20 and 40 s period to interpret these observations we first study the effect of large scale structures using ray tracing in a smooth laterally heterogeneous model of the earth second we evaluate the local effect by considering a model for the french alps including strong lateral heterogeneities around the array that were not taken into account in the ray tracing by combining these two possible causes of the observed deviations we propose an explanation for the general trend in the observed deviations finally we show that by taking into account azimuthal deviations phase velocities measured at a regional scale can be significantly improved

artificial optical bleaching of the aluminium center in quartz implications to esr dating of sediments abstract electron spin resonance esr dating of quartz extracted from sediments may contribute to elaborate a neogene and quaternary chronostratigraphy especially in the case of azoic deposits when methods such as thermoluminescence or k ar cannot be applied the esr method is applicable for aeolian littoral and fluvial sediments when quartz is zeroed or bleached by an optical phenomenon photoelectric effect due mainly to uv solar rays in this case esr dating on bleached quartz is based on the presence of paramagnetic substituted atoms in the crystal lattice the al center can be optically bleached and its signal intensity decreases in fossil samples versus exposure to the solar light after a long time the esr intensity reaches a plateau value corresponding to the electrons which cannot be extracted by the light energy these electrons represent a residual dose which must be subtracted from the total equivalent dose in order to obtain the archaeological dose our kinetic study has the objectives of obtaining a new modelization and to establish a correct time of natural bleaching for using quartz sample as appropriate for dating we have investigated samples from a fossil fluvial sand from the creuse river terraces system france our experimental bleaching curve obtained is compared with that one previously proposed by walther and zilles quat sci rev 13 1994 611

exploring uncertainties in the relationship between temperature ice volume and sea level over the past 50 million years over the past decade efforts to estimate temperature and sea level for the past 50 ma have increased in parallel efforts to model ice sheet changes during this period have been ongoing we review published paleodata and modeling work to provide insights into how sea level responds to changing temperature through changes in ice volume and thermal expansion to date the temperature to sea level relationship has been explored for the transition from glacial to interglacial states attempts to synthesize the temperature to sea level relationship in deeper time when temperatures were significantly warmer than present have been tentative we first review the existing temperature and sea level data and model simulations with a discussion of uncertainty in each of these approaches we then synthesize the sea level and temperature data and modeling results we have reviewed to test plausible forms for the sea level versus temperature relationship on this very long timescale there are no globally representative temperature proxies and so we investigate this relationship using deep sea temperature records and surface temperature records from high and low latitudes it is difficult to distinguish between the different plausible forms of the temperature to sea level relationship given the wide errors associated with the proxy estimates we argue that for surface high latitude southern hemisphere temperature and deep sea temperature the rate of change of sea level to temperature has not remained constant i e linear over the past 50 ma although the relationship remains ambiguous for the available low latitude surface temperature data a nonlinear form between temperature and sea level is consistent with ice sheet modeling studies this relationship can be attributed to 1 the different glacial thresholds for southern hemisphere glaciation compared to northern hemisphere glaciation and 2 the ice sheet carrying capacity of the antarctic continent

constraints on the velocity structure beneath the tornquist teisseyre zone from beam forming analysis summary the primary indicators of lateral heterogeneity in the earth are the slowness and azimuth of incoming seismic signals on a regional scale surface waves in the upper mantle and crust are often scattered and or refracted which results in deviations from the great circle azimuth the slowness and direction of propagation of an arriving wave packet provides information about the lateral heterogeneity and can be measured by performing beam forming on the recordings across an array of stations the azimuthal deviation gives a constraint on the transverse velocity gradient along the path in addition its frequency dependence gives information on the depth dependence of the heterogeneity we have performed beam forming of fundamental mode rayleigh waves in the period range of 20 to 100 s travelling from the south east of europe to the nars nl array in the netherlands the purpose of this study is to obtain new information about the velocity structure beneath the tornquist teisseyre zone ttz the ttz is known to be a transition between the higher seismic velocities in the thicker and older precambrian crust of the east european platform eep and the lower velocities in the thinner and younger palaeozioc crust of central and western europe tectonic europe te however the lateral velocity gradient and the depth extent of this transition are not very well constrained we have used events located at both sides of the ttz and both the direct rayleigh wave and its coda have been analysed on the one hand the deviation of the wave propagation paths relative to the great circle observed in the direct wave for the events on the eastern side of the ttz confirms earlier results i e it gives independent evidence for a thicker crust and up to 10 per cent higher velocities in the first 150 km of the upper mantle beneath the eep than beneath the te such a contrast also explains observed surface head waves refracted along the ttz on the other hand no energy reflected at the ttz is detected in the coda for the events on the western side from synthetic experiments based on a linearized theory we conclude that from this absence of reflections no lower bound can be imposed on the width of the transition zone across the ttz at different depths source mechanisms other than the ones for the events used are needed to observe these reflections at different depths for both a sharp and a smooth transition

a new method to estimate ice age temperatures on glacial time scales the waxing and waning of the eurasian and north american ice sheets depend largely on variations in atmospheric temperature as global sea level is primarily determined by the volume of these ice sheets there is a direct yet complex relation between global sea level and the northern hemispheric nh temperature this relation is essentially represented by a model of the nh ice sheets we use a thermomechanical ice sheet ice shelf bedrock model in conjunction with an inverse method to deduce a time series of nh temperature from 120 kyr bp until present that is consistent with the observed global sea level record the advantage of this method is that it provides the annual mean surface air temperature averaged over the nh continents north of 40 n the results reveal that ice age temperatures were 4 10 c lower than today which agrees with other temperature reconstructions however reconstructed temperatures are comparitively low during the early stages of the glacial a feature that is consistent with the rapid growth of the ice sheets the sensitivity of the results for uncertainties in precipitation rate in observed sea level and in some other model parameters is examined to quantify the error in reconstructed temperature during the glacial period 120 15 kyr bp surface air temperatures in the nh north of 40 n were 7 2 1 5 c lower than today s interglacial temperatures

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

a strong seismic velocity contrast in the shallow mantle across the zagros collision zone iran summary surface wave dispersion measurements are interpreted jointly with the inversion of teleseismic p wave traveltime residuals along a dense 620 km long temporary seismic profile across the zagros to investigate its upper mantle structure the s wave model determined from rayleigh wave dispersion in the zagros fold and thrust belt has high velocities from 4 5 0 2 km s 1 below the moho to 4 9 0 25 km s 1 at 200 km depth which are comparable to a shield like structure beneath the suture region from the main zagros thrust mzt to the urumiehdokhtar volcanic arc s wave velocities are lower than beneath the zagros in the top 50 km of the upper mantle with a minimum of 4 4 0 2 km s 1 at 80 km depth from 150 km and deeper s velocities are as high as beneath the zagros we suggest that part of the velocity difference at shallow depth is due to higher mantle temperatures and or higher fluid content beneath the northern half of the profile but that velocities are too high to support the hypothesis of mantle lid delamination under the suture zone teleseismic p traveltime relative residuals display a long wavelength variation along the transect with a difference of 1 1 s between negative residuals in the zagros simple folded belt and positive residuals in central iran this difference backprojects into a 6 7 per cent lateral variation of p wave velocity in the shallow upper mantle with higher vp beneath zagros and lower vp beneath central iran the main short wavelength variation of the residual is located in the suture region with late p arrivals in the region of the mzt and early arrivals in the sanandaj sirjan zone ssz using synthetic models of vp perturbations we show that the high velocities of the arabian platform have to extend laterally at least to the ssz to fit the observed p delays this model also predicts rayleigh wave phase velocities which are within the error bars of the observed dispersion it supports the model of crustal scale overthrusting at the mzt

luminescence dating of archaeological materials using a new technique based on single aliquot measurements abstract a dating method based on single aliquot luminescence dose determination was applied to quartz and feldspars from heated archaeological materials the problem of changes of sensitivity to radiation resulting from signal erasure in regeneration measurements was studied in some detail and a new method based on single aliquot regeneration measurements within an added dose framework which appears to eliminate the problem of sensitivity change is proposed preliminary dating results mainly using quartz obtained with the new method are presented

sensitivity of a greenland ice sheet model to ice flow and ablation parameters consequences for the evolution through the last climatic cycle sensitivity experiments are conducted to test the influence of poorly known model parameters on the simulation of the greenland ice sheet by means of a three dimensional numerical model including the mechanical and thermal processes within the ice two types of experiments are performed steady state climatic conditions and simulations over the last climatic cycle with a climatic forcing derived from the grip record the experiments show that the maximum altitude of the ice sheet depends on the ice flow parameters deformation and sliding law coefficients geothermal flux and that it is low when the ice flow is fast on the other hand the maximum altitude is not sensitive to the ablation strength and consequently during the climatic cycle it is driven by changes in accumulation rate the ice sheet extension shows the opposite sensitivity it is barely affected by ice flow velocity and the ice covered area is smaller for large ablation coefficients for colder climates when there is no ablation the ice sheet extension depends on the sea level an interesting result is that the variations with time of the altitude at the ice divide summit do not depend on the parameters we tested the present modelled ice sheets resulting from the climatic cycle experiments are compared with the present measured ice sheet in order to find the set of parameters that gives the best fit between modelled and measured geometry it seems that compared to the parameter set most commonly used higher ablation rate coefficents must be used

steady state characteristics of the greenland ice sheet under different climates the greenland ice sheet is modelled to simulate its extent and volume in warmer climates and also to find out whether the ice sheet would re form on theice free bedrock under present climatic conditions the ice sheet model is a three dimensional thermo mechanical model with a fine resolution grid thebedrock surface beneath the ice sheet was mapped using radio echo sounding measurements by the electromagnetic institute copenhagen the modelexperiments show that increased temperature will result in ice margin retreat but the ice sheet is relatively stable it takes a rather high temperature rise of atleast 6ic for the ice sheet to disappear completely which indicates that the ice sheet probably survived the last interglacial also it appears that the greenlandice sheet is not a mere relict ice mass from a previously colder climate but that the ice sheet will still re form on the bare bedrock under the present or evenslightly warmer climatic conditions

arrival angles of teleseismic fundamental mode rayleigh waves across the alparray the dense alparray network allows studying seismic wave propagation with high spatial resolution here we introduce an array approach to measure arrival angles of teleseismic rayleigh waves the approach combines the advantages of phase correlation as in the two station method with array beamforming to obtain the phase velocity vector 20 earthquakes from the first two years of the alparray project are selected and spatial patterns of arrival angle deviations across the alparray are shown in maps depending on period and earthquake location the cause of these intriguing spatial patterns is discussed a simple wave propagation modelling example using an isolated anomaly and a gaussian beam solution suggests that much of the complexity can be explained as a result of wave interference after passing a structural anomaly along the wave paths this indicates that arrival angle information constitutes useful additional information on the earth structure beyond what is currently used in inversions

rayleigh wave multipathing along the west coast of north america we have created a movie of surface ground motion for the 3 november 2002 denali fault earthquake based on spectral element simulations using crustal model crust2 0 mantle model s20rts topography and bathymetry model etopo5 and a finite fault slip model the movie features two anomalous wave packets that travel along the west coast of the north american plate following off great circle paths these wave packets are rayleigh waves with dominant periods around 20 sec which are also found in seismograms recorded by the southern cali fornia seismic network one of these packets is the direct surface wave whose group arrival time changes laterally as dictated by the shape of the oregon coast the other packet is a surface wave reflected by a lateral interface underneath the rocky moun tains a linear reflector parallel to the canadian coast offsetting it by a few hundred kilometers can explain its arrival time but the offsetting distance derived from the synthetic seismograms puts the reflector 350 km northeast of the result obtained from the data indicating a need to update the crustal and mantle models in this area online material animation of normalized simulated vertical displacement for the 2002 denali earthquake

reflection of seismic surface waves at the northern apennines abstract seismic surface waves with periods of 15 to 20 s are reflected laterally at the northern apennines for earthquakes originated and recorded in the wider alpine area a few hundred kilometres north of the apennines we can directly observe late arrivals of reflected regional surface waves these have a characteristic polarization of particle motion and often dominate the intermediate period surface wave coda love waves are the most prominent coda arrivals while reflected rayleigh waves show smaller amplitudes and become clear only after rotation of the recordings to the reflection incidence direction we can track the development of the love wave reflection along a temporary broad band transect across the northern apennines indicating the location of the reflector near to the highest topography from spectral element simulations of three dimensional wave propagation we attribute the reflection to a continuous 270 km long offset in the crust mantle boundary under the mountain belt with vertical throw of 20 km thus supporting a deep crustal root under the outer side of the apennines fold and thrust belt and significant crustal thinning on the inner side amplitude reflection coefficients for near normal incidence can be estimated as 7 for both love and rayleigh waves

initiation and development of the laurentide and cordilleran ice sheets following the last interglaciation abstract fossil records from sites overridden by or adjacent to the laurentide ice sheet indicate that the climate of the last interglaciation oxygen isotope substage 5e ca 130 116 ka was warmer than today following the last interglaciation the laurentide ice sheet first developed during stage 5 over keewatin quebec and baffin island along its northern margin the ice sheet reached its maximum extent of the last glaciation during stage 5 the ice sheet advanced across baffin island onto the continental shelf early during stage 5 5d whereas the advance into the western canadian arctic occurred late during stage 5 5b the ice sheet also may have advanced into the st lawrence lowland during substage 5b although this event may be younger stage 4 the hudson bay lowland became ice free during substage 5a retreat of the ice sheet on baffin island occurred during late stage 5 probably substage 5a the exact timing of retreat from the western canadian arctic is unknown but it occurred before 48 ka the southern sector including the st lawrence lowland was ice free during late stage 5 the hudson bay lowland may have remained ice free through stage 4 and much of stage 3 because of conflicting chronologies however it is more likely that this area was glaciated throughout stage 3 and perhaps stage 4 nevertheless the data demonstrate that the lowland was ice free during part of the last glaciation an independent ice cap developed over the appalachian uplands and advanced across nova scotia during stage 4 perhaps as far as the edge of the continental shelf the ice cap remained active over nova scotia as a setellite to the laurentide ice sheet throughout the remainder of the last glaciation the ice sheet advanced into the st lawrence lowland during stage 4 and subsequently overwhelmed the local ice cap in the appalachian uplands advancing perhaps into northern new england but not farther south the lowland remained covered by the ice sheet until late stage 2 the ice sheet may also have advanced into the lake ontario basin during stage 4 the position of the northern margin of the laurentide ice sheet during stage 4 is not known but it remained an unknown distance behind its maximum position reached during stage 5 cores from baffin bay indicate a substantial decrease in high latitude glaciation during stage 4 following retreat the keewatin sector of the ice sheet may have remained over much of northwestern canada as a quasi stable ice mass until it readvanced during stage 2 similarly the baffin island sector of the ice sheet may have remained largely intact the southern margin of the ice sheet may have advanced into the lake ontario basin and upper mississippi valley during the middle of stage 3 ca 50 ka reaching its maximum extent of the last glaciation during stage 2 ca 18 21 ka advance of the northern margin was younger ca 8 13 ka than that of the southern margin this advance was less extensive than the penultimate advance stage 5 paleoenvironmental records indicate that the last interglaciation in areas covered by and near the cordilleran ice sheet was as warm as or warmer than present the cordilleran ice sheet appears to have developed during stage 5 or 4 at that time it advanced over southern british columbia and into the northern puget lowland there is no record of this event in northern areas that were later covered by the ice sheet the ice sheet disappeared before 59 ka at the beginning of a lengthy nonglacial interval paleoenvironmental records indicate that climate was similar to the present during part of this interval the ice sheet was absent and glaciers probably were confined to mountain areas throughout stage 3 climatic deterioration marking the end of this nonglacial interval may have begun as early as 29 ka by 14 15 ka the ice sheet had achieved its maximum extent of the last glaciation because there are few suitable dating methods capable of resolving events beyond the radiocarbon limit and because sites that preserve a record of events from the last glaciation are spatially restricted we consider this synthesis as tentative and subject to significant revision as dating methods improve nevertheless this perspective of the north american ice sheets through the last glaciation demonstrates their complex and dynamic behavior and attendant rapid fluctuations in ice volume

reverse propagation of surface waves reflected from seamounts in the northwestern pacific abstract the reverse propagation of a surface wave traveling through the japanese islands from southwest to northeast was detected for major shallow earthquakes that occurred in northeastern japan the wave is predominant in the transverse component having a period of 20 sec and lasting longer than 200 sec the propagation velocity is around 3 8 km sec which is characteristic of a typical surface wave semblance analysis using a dense seismograph network shows that the wave was generated near the kyushu palau ridge southeast of kyushu island numerical simulation with a 3d finite element method can explain the surface wave reflection predominant in the transverse component as reflection from seamounts with a crustal root 10 km deeper than the moho discontinuity at the surrounding ocean floor the observed long duration of the reverse propagating surface wave might represent the superposition of a reflected wave from other seamounts and or the thick sedimentary layer along the nankai trough

terminating the 100 kyr ice age cycle we report a simulation of the most recent 100 000 year glaciationdeglaciation cycle of the late pleistocene ice age a simulation that delivers an ice sheet chronology that is in close accord with that inferred from the geological record our analyses are performed with a reduced model of the climate system that incorporates significant improvements to the representation of both climate forcing and mass balance response in a previously described theory based upon a coupled one level energy balance model ebm and vertically integrated ice sheet model ism the theory fully incorporates the influences of orbital insolation forcing glacial isostatic adjustment and variations in the atmospheric concentrations of greenhouse gases it correctly predicts the main geographical regions of the northern hemisphere that were glaciated at last glacial maximum 21 000 years ago as well as the abrupt termination of the glacial epoch that occurred subsequently the latter feature of the ice age cycle is obtained without the need to incorporate unconstrained and therefore controversial physical processes into the model a limitation of all previous attempts to understand this global scale climate cycle our analyses suggest that the radiative impact on surface glaciation due to the changing atmospheric concentration of co2 is critical to the ability of the model to deliver a synthetic history of glaciation and deglaciation that is in accord with inferences based upon surface geological and geomorphological evidence with the incorporation of this influence model predicted ice thickness distributions at last glacial maximum lgm are very similar to those of the recently described ice 4g reconstruction that was based upon the inversion of postglacial relative sea level histories

high resolution surface wave tomography beneath the aegean anatolia region constraints on upper mantle structure summary this study provides new constraints on the upper mantle structure from western greece to central anatolia using seismic data of permanent broad band networks recently installed in greece and turkey and from a two year temporary array simbaad experiment we used 200 seismic events recorded at 146 broad band stations with a typical interstation distance of 60 100 km across the study area the high resolution 3 d shear wave velocity model of the mantle is obtained by inversion of fundamental mode rayleigh wave phase velocity maps for periods between 20 and 195 s the tomography is based on ray tracing in heterogeneous media taking into account external propagation effects the horizontal resolution is approximately 100 km however small heterogeneities may suffer from some horizontal smearing and damping the vertical resolution is approximately 100 km the vertical smoothing is necessary to avoid unresolved spurious shear wave velocity oscillations in the upper mantle the errors on shear wave velocities in our 3 d model 0 02 0 1 km s 1 are significantly smaller than the amplitude of vs variations 0 3 0 5 km s 1 in spite of the vertical and horizontal smoothing our model shows details in the upper mantle structure never reached at regional scale in the area the overall structure is characterized by a low velocity zone 80 200 km depth reflecting a slow and warm asthenosphere underlying a thin lithosphere the southwesternmost termination of the low velocity anomaly corresponds to the northward dipping hellenic slab the detailed shear velocity structure of the upper mantle beneath anatolia appears to be far more geometrically complex than revealed in previous tomographic studies of the area at depths larger than or equal to 160 km velocities are overall high beneath anatolia partly due to the presence of dipping high velocity anomalies which we tentatively interpret as remnant slabs the southernmost high velocity anomaly beneath anatolia is separated from the eastern edge of the hellenic slab by a major low velocity anomaly which we interpret as the trace of asthenospheric mantle material rising inside a vertical slab tear beneath southwestern anatolia

upper mantle structure in southern norway from beamforming of rayleigh wave data presenting multipathing summary a model for the upper mantle sv wave velocity under southern norway is obtained by depth inversion of the average phase velocity of the rayleigh wave fundamental mode in the area the average dispersion curve is obtained in the period range 22 200 s by beamforming of 190 rayleigh waves recorded by the magnus network a temporary regional network of 41 broad band stations resolution of the beamforming procedure is increased by deconvolving the original beams from the array response function using the lucy richardson algorithm in addition to an average phase velocity beamforming gives us some information concerning the nature of the incoming wavefield we detect deviations of the wave propagation direction from the great circle paths which commonly reach 10 at a period of 25 s for the teleseismic events the amplitude of the deviations decreases with increasing period and with decreasing epicentral distance as expected the phase velocity measured by beamforming does not show any correlation with the deviation from great circle path suggesting that deviation does not bias phase velocity measurements we detect also significant multipathing with characteristics that vary rapidly with frequency the obtained sv wave velocity profile clearly shows that southern norway is underlain by a low velocity zone in the upper mantle and does not have shield like characteristics despite its location in the baltic shield these findings support the hypothesis that the high topography of southern norway is sustained by anomalous upper mantle material

esr dating of tephra with dose recovery test for impurity centers in quartz abstract the multiple aliquot regenerative additive method of esr electron spin resonance dating was applied to numazawa shibahara nm sb tephra from fukushima japan with dose recovery tests for impurity centers in quartz the age obtained from ti h center is consistent with the rtl red thermoluminescence and fission track ages while the ones from al and ti li center are overestimates the dose recovery test indicates that the equivalent dose estimate based on the ti h center agrees within 6 of the expected dose 370 gy the dose recovery test is a useful procedure for choosing the signal appropriate for dating

ice sheet inception subgrid hypsometric parameterization of mass balance in an ice sheet model studies of ice sheet inception and mountain glaciation are limited by model resolution in both atmospheric and glaciologic models the accumulation and ablation of snow and ice are controlled by local climate which is sensitive to topographic features that are subgrid in continent scale investigations climate patterns are complex in areas of high relief but the first order influence of elevation on temperature and atmospheric humidity is quantifiable and is central to glacier mass balance we make substantial improvements to the descriptions of accumulation and ablation in a large scale ice sheet model by incorporating subgrid topographic information the distribution of relief in the large scale model is estimated through a hypsometric parameterization based on the minimum maximum and median topographic elevation this permits accounting of high elevation accumulation and melting in deep valleys we combine this with a parameterization of downslope subgrid ice flux simulating but not explicitly describing the role of alpine glaciers the detailed budgeting of mass balance greatly improves our skill in modelling present day ice distribution in north america we anticipate similar improvements in our ability to model nucleation centres of the quaternary ice sheets this approach may also prove useful in projections of glacier and ice field response to climate change

surface wave propagation in central asia observations of scattering and multipathing with the kyrgyzstan broadband array we studied the propagation of rayleigh waves at regional distances in central asia using a combination of array processing techniques and surface wave analysis we present results from the detailed analysis of three representative events recorded by a 10 station broadband network that has been running in the central asian country of kyrgyzstan since 1991 an ms 5 1 event near ashkhabad turkmenistan an ms 5 8 event in south central tibet and the october 7 1994 nuclear explosion at lop nor we find there is a remarkable difference in the propagation characteristics of surface waves along these three paths the path from the event in turkmenistan is simple and is well approximated by propagation through a laterally homogeneous medium array processing shows the entire rayleigh wave train stacks coherently and arrives from an azimuth close to that predicted by a great circle path furthermore estimates of dispersion curves and fundamental mode signals determined for individual stations show little variation across the array the tibet and lop nor paths are completely different we find strong evidence for complicated multipathing and scattering effects along both of these paths we observe a three stage pattern in the tibet case 1 the early lowest frequency part of the rayleigh wave packet arrives as a coherent signal from close to the great circle path azimuth 2 this is overpowered in the period range around 20 s by a strong multipath signal that propagates across the array from a much more southerly azimuth and 3 periods below 20 s rapidly become incoherent and the signal does not have a well defined direction of propagation the lop nor path shows similar complexity on this path there is little dispersion for measurable periods greater than 10 s so the low frequency energy arrives in an airy phase the airy phase stacks somewhat coherently it stacks but significant power is lost in the best beam and slowness analysis shows it arrives from an azimuth 14 north of the great circle path azimuth like the tibet event the direction of propagation of the shorter periods cannot be resolved these results are consistent with crustal structure in central asia the multipathing and scattering from the tibet and lop nor events are not surprising given these waves propagate across highly variable crust and high topography resulting from the collision of india with eurasia the relative simplicity of the turkmenistan event path reinforces this as almost all of that path traverses the relatively undeformed turan platform of uzbekistan

esr dating of the rotoiti breccia in the taupo volcanic zone new zealand abstract electron spin resonance esr can be used to determine the time of formation of quartz in volcanic rocks based on the trapping of changes in the quartz resulting from environmental radiation the method has been used on quartz from a rhyolitic pyroclastic flow the rotoiti breccia deposited ne of rotorua new zealand it yields a date of 45 2 8 2 ka bp the mean of ages of 48 6 and 41 8 ka bp obtained from the al and ti centers respectively this result is in good agreement with previous 14c ages of 41 6 ka bp and 44 2 4 3 ka bp but does not agree with a date of 71 6 ka bp based on uranium disequilibrium we suggest that this discrepancy reflects the time difference between attainment of equilibrium at depth and the emergence time of the pyroclastic flow on the surface where radiation bombardment commenced

new insights into the lithosphere beneath the superior province from rayleigh wave dispersion and receiver function analysis we study the azimuthally anisotropic upper mantle structure of the superior craton and grenville province in ontario canada using rayleigh wave phase velocity data in the period range 40 160 s 152 two station dispersion measurements are combined in a tomographic inversion that solves simultaneously for isotropic and anisotropic terms using a least squares technique we perform a series of tests to derive optimal regularization smoothing and damping and to assess the resolution of and trade offs between isotropic and anisotropic anomalies the tomographic inversion is able to resolve isotropic phase velocity anomalies on a scale of 200 300 km and to distinguish between different anisotropic regimes on a 500 km scale across the study region isotropic phase velocity anomalies in the tomographic model span a range of up to 2 per cent around a regional average which is similar to the canadian shield dispersion curve of brune dorman 1963 with phase velocities up to 3 per cent above global reference models the amplitude of azimuthal phase velocity anisotropy reaches a maximum of 1 2 per cent a clear east west division of the study area based on both isotropic phase velocity anomalies and azimuthal anisotropy is apparent in the western superior isotropic phase velocities are generally higher than the regional average anisotropy is observed at all periods with ene wsw to ne sw fast propagation directions at periods 120 s the anisotropy likely results from frozen lithospheric fabric aligned with tectonic boundaries whereas the anisotropy at longer periods is interpreted to arise from present day sublithospheric flow the fast directions from published sks measurements are close to the fast rayleigh wave propagation directions throughout the period range sampled and the large sks splitting times may be accounted for by this near coincidence of fast propagation directions across most of eastern ontario phase velocities are lower than the regional average fast propagation directions rotate from nw se at 40 130 s period to wnw ese at periods 140 160 s the results suggest a difference in fast propagation directions between the anisotropic fabric frozen into the lithosphere and the fabric due to current and recent sublithospheric flow the superior craton and grenville province are characterized by large scale structural variations that reflect the complex tectonic history of the region this study highlights differences between the characteristics of eastern and western ontario and indicates the occurrence of multiple layers of anisotropy in the subcratonic upper mantle

the dynamic response of the greenland and antarctic ice sheets to multiple century climatic warming new calculations were performed to investigate the combined response of the greenland and antarctic ice sheets to a range of climatic warming scenarios over the next millennium use was made of fully dynamic 3d thermomechanic ice sheet models which were coupled to a two dimensional climate model the experiments were initialized with simulations over the last two glacial cycles to estimate the present evolution and were subsequently forced with temperature scenarios resulting from greenhouse emission scenarios which assume equivalent co2 increases of two four and eight times the present 1990 a d value by the year 2130 a d and a stabilization after that the calculations brought to light that during the next century short term effect the background evolution trend would dominate the response of the antarctic ice sheet but would be negligible for the greenland ice sheet on that timescale the greenland and antarctic ice sheets would roughly balance one another for the middle scenario similar to the ipcc96 is92a scenario with respective contributions to the worldwide sea level stand on the order of about 610 cm on the longer term however both ice sheets would contribute positively to the worldwide sea level stand and the most important effect would come from melting on the greenland ice sheet sensitivity experiments highlighted the role of ice dynamics and the height massbalance feedback on the results it was found that ice dynamics cannot be neglected for the greenland ice sheet not even on a century timescale but becomes only important for antarctica on the longer term the latter is related to an increased outflow of ice into the ice shelves and to the grounding line retreat of the west antarctic ice sheet which are both found to be sensitive to basal melting below ice shelves and the effective viscosity of the ice shelves stretching parameters to their limits yielded a combined maximum rate of sea level rise of 85 cm century21 of which 60 cm would originate from the greenland ice sheet alone

beno gutenberg contribution to seismic hazard assessment and recent progress in the european mediterranean region abstract the fundamental work of beno gutenberg has inspired and guided an appreciable part of research in modern seismology both from the experimental and the theoretical point of view among the several topics of seismology that have benefited from the fundamental contribution of gutenberg we consider particularly relevant the description of the asthenospheric low velocity channel the definition of the surface waves magnitude and the gutenberg richter law since they are pivotal tools for seismic hazard assessment the quite revolutionary model for the lithosphere asthenosphere system in the european area predicts the existence of almost aseismic lithospheric roots these roots are located in correspondence of most of the orogenic belts and interrupt the asthenosphere low velocity channel that has been identified by beno gutenberg in 1948 the model of the european upper mantle proposed for the first time in 1979 and subsequently refined has stimulated a considerable amount of research which has nicely confirmed the major innovative features of the early model at present the subduction of the lithosphere at continent continent collisions supported not only by seismological data is a widely accepted concept within the community of earth scientists even if it contradicts one of the basic dogmas of the original formulation of plate tectonics the proposed model for the alpine apennines area supplies a new and unifying framework for the interpretation of the quaternary magmatism at present generally accepted by petrologists and geochemists the theoretical basis for the gutenberg s surface wave magnitude calibration function has been supplied by the use of complete synthetic seismograms and thus it has been possible to formulate the theoretical m s depth correction the introduction of the depth correction for m s enables the computation of surface wave magnitude for all earthquakes regardless of their focal depth this is especially important for the quantification of subcrustal historical earthquakes for which the seismic moment may be difficult to estimate from recordings of early mechanical seismographs the new m s calibrating function yield both distance and depth independent magnitude estimates the analysis of the global seismicity using the seismotectonic regionalization in subduction zones mid oceanic ridge zones island arcs shows that a single gutenberg richter gr relation is not universally applicable and that a multiscale seismicity model can reconcile two apparently conflicting paradigms the self organized criticality mechanism and the characteristic earthquake concept the multiscale representation has been applied to italy where the zones at the space scale of 400 500 km quite well reproduce the shapes of the regions used to apply the globally tested cn intermediate term earthquake prediction algorithm

methodology for use of isotopic climate forcings in ice sheet models in ice sheet models an internally consistent calculation of climatic temperature forcing from ice core isotopic records requires that corrections be made for an ice core site s elevation changes such corrections can be important for two reasons first elevation change at an ice divide can be large compared to elevation change at the migrating ice margin resulting in erroneous estimates of marginal melt rate second the of precipitation at an ice divide responds less to regional climatic temperature changes than to local temperature changes of the same magnitude that are caused by elevation changes significant elevation change corrections may also be necessary for inferring the relationships used to calculate climatic temperature from a simple methodology incorporating both of these elevational effects is presented here further i recommend that the to temperature conversion relations used in ice sheet models should derive from independently reconstructed temperature and time series rather than from spatial correlations and justify this recommendation based on current understanding of the atmospheric isotopic distillation system

surface waveform tomography of the turkish iranian plateau summary the middle east is a tectonically complex region consisting of terrains as diverse as precam brian shields and young orogens the dominant tectonic feature is the turkish iranian plateau a recently elevated seismically active region along the zagros bitlis suture which results from the collision of the arabian plate with eurasia in this study we use surface waveform tomography to elucidate the upper mantle shear wave velocity structure beneath the turkish iranian plateau and adjacent regions the main large scale feature in the tomographic model is a low shear wave velocity anomaly in the uppermost mantle beneath the plateau this low velocity feature correlates with a long wavelength free air gravity anomaly and with recent volcanism whose geochemistry has a lower lithospheric mantle signature seismology gravity and volcanism all suggest the presence of a thin lithosphere and warm upper mantle beneath the turkish iranian plateau the upper mantle low shear wave velocity zone the high free air gravity and the deep lithospheric source depth for the basaltic volcanism are all consistent with a partial delamination of the lithosphere as a result of earlier lithospheric thickening resulting from the continental collision

esr dates and thermal behaviour of al and ti centers in quartz for the tephra and welded tuff in japan abstract a welded tuff in a geothermal area was dated by electron spin resonance esr and thermoluminescence tl the esr spectrum has a clear ti center signal and weak al center signal which resembles the spectrum of the volcanic ash crystal ash c1 shinshu japan annealed at 200 c for 20 hr in this volcanic ash the intensity of the al center signal selectively decreased with the heat treatment this result may suggest that this welded tuff sample was subjected to weak thermal annealing in the past and only the al center signal was reduced from esr the equivalent dose ed was 49 gy and the esr date was 0 043 ma for the al center and the ed value was 300 gy and the esr date was 0 26 ma for the ti center from tl the ed value was 39 gy and the tl date was 0 039 ma which are close to that of the al center signal using esr a detailed thermal annealing experiment at 400 800 and 1000 c for this sample rose and smoky quartz was performed to investigate the variety of esr signals of natural quartz and the influence of thermal annealing in the past

a three dimensional climate ice sheet model applied to the last glacial maximum a quasi three dimensional climate model sellers 1983 was used to simulate the climate of the last glacial maximum in order to provide climatic input forthe modelling of the northern hemisphere ice sheets the climate model is basically a coarse gridded gcm with simplified dynamics and was subject toappropriate boundary conditions for ice sheet elevation atmospheric co2 concentration and orbital parameters when compared with the present daysimulation the simulated climate at the last glacial maximum is characterized by a global annual cooling of 3 5deg c and a reduction in global annualprecipitation of 7 5 which agrees well with results from other more complex gcm s also the patterns of temperature change compare fairly with mostother gcm results except for a smaller cooling over the north atlantic and the larger cooling predicted for the summer rather than for the winter overeurasia the climate model is able to simulate changes in northern hemisphere tropospheric circulation yielding enhanced westerlies in the vicinity of thelaurentide and eurasian ice sheets however the simulated precipitation patterns are less convincing and show a distinct mean precipitation increase over thelaurentide ice sheet nevertheless when using the mean monthly fields of lgm minus present day anomalies of temperature and precipitation rate to drive athree dimensional thermomechanical ice sheet model it was demonstrated that within realistic bounds of the ice flow and mass balance parameters veryreasonable reconstructions of the last glacial maximum ice sheets could be obtained

contribution of dense array analysis to the identification and quantification of basin edge induced waves part ii application to grenoble basin french alps settled on a deep sediment filled valley the city of grenoble french alps faces important site effects large amplification and significant duration in crease of ground motion even for moderate size events in order to study multidi mensional site effects a very dense array composed of 29 three component seis mometers over a 1 km aperture was operated during spring 1999 in the center of the city a total of 18 events 6 local 4 regional and 8 teleseismic with an acceptable signal to noise ratio could be recorded over a 4 month period the complexity of the wave field and in situ seismic noise constraints led us to develop a procedure based on time frequency coherence and the multiple signal classification algorithm to iden tify and characterize wave arrivals cornou et al 2003 applying the procedure to the 18 records it is clearly indicated that ground motion inside the valley is domi nated by basin edge induced waves that carry 4 times more energy than the direct wave field regardless of the type of event considered in addition the basin induced wave field is composed of 60 rayleigh waves and 40 love waves when consid ering energy carried by the three components if one considers only the energy of horizontal components this proportion is 50 rayleigh waves and 50 love waves the diffraction phenomena are mostly constrained by the 3d structure of the basin regardless of the azimuth of the event a study of the relative contribution of 1d and 2d 3d effects on recorded ground motion suggests at least at frequencies below 1 hz that the difference between the standard spectral ratio and 1d transfer function or possibly the horizontal to vertical ratio receiver function and nakamura esti mates might be due mainly to laterally propagating waves

hydrographic variations in deep ocean temperature over the mid pleistocene transition abstract during the mid pleistocene transition the dominant 41 ka periodicity of glacial cycles transitioned to a quasi 100 ka periodicity for reasons not yet known this study investigates the potential role of deep ocean hydrography by examining oxygen isotope ratios in benthic foraminifera oxygen isotope records from the atlantic pacific and indian ocean basins are separated into their ice volume and local temperature hydrography components using a piece wise linear transfer function and a temperature calibration although our method has certain limitations the deep ocean hydrography reconstructions show that glacial deep ocean temperatures approached freezing point as the mid pleistocene transition progressed further analysis suggests that water mass reorganisation could have been responsible for these temperature changes leading to such stable conditions in the deep ocean that some obliquity cycles were skipped until precessional forcing triggered deglaciation creating the apparent quasi 100 ka pattern this study supports previous work that suggests multiples of obliquity cycles dominate the quasi 100 ka glacial cycles with precession components driving deglaciations

a 3 d model for the antarctic ice sheet a sensitivity study on the glacial interglacial contrast on the longer climatic time scales changes in the elevation and extent of the antarctic ice sheet have an important role in modulating global atmospheric and oceanographic processes and contribute significantly to world wide sea levels in this paper a 3 d time dependent thermomechanical model for the entire ice sheet is presented that is subsequently used to examine the effects of glacial interglacial shifts in environmental boundary conditions on its geometry the model takes into account a coupled ice shelf grounding line dynamics basal sliding and isostatic bed adjustment and considers the fully coupled velocity and temperature fields ice flow is calculated on a fine mesh 40 km horizontal grid size and 10 layers in the vertical for grounded and floating ice and a stress transition zone in between at the grounding line where all stress components contribute in the effective stress in the flow law there is free interaction between ice sheet and ice shelf so that the entire geometry is internally generated a simulation of the present ice sheet reveals that the model is able to yield realistic results a series of sensitivity experiments are then performed in which lower temperatures reduced accumulation rates and lower global sea level stands are imposed either singly or in combination by comparing results of pairs of experiments the effects of each of these environmental changes can be determined in agreement with glacial geological evidence we found that the most pronounced changes show up in the west antarctic ice sheet configuration they appear to be essentially controlled by variations in eustatic sea level whereas typical glacial interglacial changes in temperature and ice deposition rates tend to balance one another these findings support the hypothesis that the antarctic ice sheet basically follows glacial episodes in the northern hemisphere by means of sea level teleconnections grounding occurs more readily in the weddell sea than in the ross sea and long time scales appear to be involved it may take up to 30 40000 years for these continental shelf areas to become completely grounded after an initial stepwise perturbation in boundary conditions according to these reconstructions a steady state antarctic ice sheet may contribute some 16 m to global sea level lowering at maximum glaciation

esr dating of quaternary tephra from mt osore zan using al and ti centres in quartz abstract quaternary tephra of mt osore zan was dated by electron spin resonance quartz grains were separated from the tephra and esr signals of al and ti centres were measured at 77 k the signals of al and ti centres which have a complicated hyperfine structure were simplified by using wider field modulations width 5 gauss than usually used 0 5 1 gauss the influence of 5 gauss modulation width on the measurement of the signal intensity of al and ti centres was investigated the intensity of the signal increases linearly with gamma irradiation and total doses obtained were 178 to 273 gy and esr ages were 0 19 to 0 32 ma these ages agree with the estimated age of about 0 3 ma from the correlation of volcanic ash and terrace level

analysis of wave propagation in the valley of mexico from a dense array of seismometers a dense array of seismometers was installed and operated in the botanical garden of unam within the valley of mexico during april and may 1994 the slow surface velocities at the array require an approach to array analysis with the capability of measuring arrival time differences between stations of less than the sampling interval of the data applying the method to principal component seismograms from earthquakes at local and regional ranges from a number of directions provides the first quantitative information on the composition of the wave field incident upon mexico city phases that propagate through the entire crust such as the initial p and lg waves cross the array with the expected backazimuth on the other hand surface waves in the 2 5 to 5 sec period band which are sensitive to uppercrustal structure show systematic rotations of backazimuth these suggest changes in upper crustal structure or point scatterers located north and south of mexico city for earthquakes outside of the valley of mexico no significant energy was observed propagating across the array from the east from the lake zone thus although it is clear that seismic waves resonate within the lake zone little if any of this energy is transmitted into the hill zone where the array was located however long duration ground motions are observed at the array with evidence of multipathing a back projection of these late off azimuth arrivals indicates that their sources correlate with the boundaries of the quaternary volcanics of the trans mexican volcanic belt

the crust and uppermost mantle structure of southern peru from ambient noise and earthquake surface wave analysis abstract southern peru is located in the northern central andes which is the highest plateau along an active subduction zone in this region the nazca slab changes from normal to flat subduction with the associated holocene volcanism ceasing above the flat subduction regime we use 6 s to 67 s period surface wave signals from ambient noise cross correlations and earthquake data to image the shear wave velocity v s v structure to a depth of 140 km a mid crust low velocity zone is revealed and is interpreted as partially molten rocks that are part of the andean low velocity zone it is oblique to the present trench and possibly indicates the location of the volcanic arcs formed during the steepening of the oligocene flat slab beneath the altiplano plateau the recently subducted slab beneath the forearc shows a decrease in velocity from the normal to flat subduction regime that might be related to hydration during the formation of the nazca ridge which in turn may contribute to the buoyancy of the flat slab the mantle above the flat slab has a comparatively high velocity which indicates the lack of melting and thus explains the cessation of the volcanism above a velocity contrast from crust to uppermost mantle is imaged across the cusco vilcanota fault system and is interpreted as the boundary between two lithospheric blocks

the nature and cause of polarization anomalies of surface waves crossing northern and central eurasia summary results of a pilot experiment preliminary to a systematic study of surface wave polarization across eurasia are presented long period fundamental rayleigh and love waves recorded by the broad band seismic stations kiv kislovodsk and obn obninsk of the iris ida network deployed in the former soviet union fsu were analysed from 14 events to the north east east and south east of these stations in search of particle motion anomalies using a technique called frequency time polarization analysis ftpan all anomalies indicate deviations of wave propagation paths to the north relative to the great circle paths polarization anomalies at obn are uniformly small 5 significant frequency dependent polarization anomalies 5 20 are found for rayleigh and love waves arriving at kiv from teleseismic events at a wide range of backazimuths 26 103 polarization measurements are repeatable both for a number of nearly degenerate events and for reciprocal paths and vary smoothly and continuously as epicentral location is moved consequently such measurements are robust and can provide useful structural information the systematics of the frequency dependence of the polarization anomalies as epicentral position is moved from north to south display sensitivity to structures at a number of length scales results from synthetic experiments using coupled normal mode and gaussian beam synthetics reveal that 1 recently constructed long wavelength aspherical models produce polarization anomalies that are significantly smaller 5 at kiv but of the same sign negative as the observed anomalies and 2 the frequency dependence of the observed anomalies must result from a combination of structures of differing wavelengths with scale lengths ranging from regional to global thus polarization measurements provide new information about currently unmodelled structures a model that fits the polarization anomalies observed at kiv includes a regional scale low velocity feature near to kiv in order to fit the large magnitude short period polarization anomalies and a smaller magnitude continent scale increase in upper mantle velocities and or the reduction of crustal thickness from south to north in central eurasia in order to fit the broad band longer period anomalies the small scale low velocity feature is a model of the sedimentary basin of the sub caspian depression we conclude that measurements of polarization anomalies can be obtained accurately that they are reproducible that they contain currently unmodelled information and that they should prove to be useful in combination with velocity and amplitude information in future tomographic inversions especially to help focus global scale models to regional wavelengths

a comparison of different ways of dealing with isostasy examples from modelling the antarctic ice sheet during the last glacial cycle the bedrock isostatic response exerts a strong control on ice sheet dynamics and is therefore always taken into account in ice sheet models this paperreviews the various methods normally used in the ice sheet modeling community to deal with the bedrock response and compares these with a moresophisticated full earth model each of these bedrock treatments five in total are coupled with a three dimensional thermomechanical ice sheet model underthe same forcing conditions to simulate the antarctic ice sheet during the last glacial cycle the outputs of the simulations are compared on the basis of thetime dependent behavior for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over antarctica thiscomparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns it furthermoredemonstrates the deficiencies inherent to the diffusion equation in modeling the complex deformation within the mantle nevertheless when characteristicparameters are varied within their range of uncertainty differences within one single method are often of the same order as those between the variousmethods this overview finally tries to point out the main advantages and drawbacks of each of these methods and to determine which one is mostappropriate depending on the specific modeling requirements

antarctic ice volume and deep sea temperature during the last 50 myr a model study a simple quasi analytical model is used to study the sensitivity of the antarctic ice sheet to climate change the model is axisymmetrical and has a profile that only depends on the ice sheet radius the climatic conditions are represented by three parameters the altitude of the runoff line the accumulation rate above the runoff line and the balance gradient below the runoff line the ice sheet may extend into the sea at the grounding line the ice velocity is assumed to be proportional to the water depth for this set up an explicit algebraic expression for the total mass budget of the ice sheet can be derived after calibration of the model with respect to the present day ice sheet equilibrium states are studied for a wide range of temperatures the model predicts a maximum ice volume 3 4 for a temperature that is 2 5 k above the present value for a temperature increase of 7 k mass loss by runoff and calving are about the same in this case the ice volume is about 82 of the current value the ice sheet model is used to correct the cenozoic deep sea temperature record 18o record from benthic foraminifera in ocean sediments for antarctic ice volume the model is forced with the oxygen isotope record which is then corrected for the calculated ice volume therefore the resulting deep sea temperature and antarctic ice volume curves are mutually consistent it is concluded that for the last 35 106 years the 18o record truly is a mixed temperature ice volume record in which the contributions from these parameters have the same order of magnitude

the importance of thermodynamics for modeling the volume of the greenland ice sheet two different kinds of ice flow models one two dimensional 2 d and the other three dimensional 3 d have been used to test the importance of the thermodynamic response of the greenland ice sheet the basic difference between the two models is that the thermodynamics are neglected in the two dimensional model whereas these are incorporated in the three dimensional model the 2 d and 3 d models are compared in terms of volume response time and total volume of the ice sheet results indicate that the sawtooth character of the ice volume on glacial interglacial timescales is among other possible reasons a result of the thermodynamic coupling the changes in elevation over the last 130 000 years calculated with the three dimensional version are 230 m for the summit drill site and 190 m for the n grip site the standard deviation of the changes in elevation is 55 m for the summit site and 43 m for the n grip site the present day imbalance is merely a result of the rather constant climate over the last 10 kyr and is not determined by the thermodynamics consequently pleistocene temperatures do still exist in the ice sheet but are not important for volume calculations of the present day ice sheet for short term perturbation experiments in the future the pronounced sensitivity of the mass balance will determine the response of the greenland ice sheet whereas thermodynamics will play only a minor role

phase velocities of rayleigh and love waves in central and northern europe from automated broad band interstation measurements the increasingly dense coverage of europe with broad band seismic stations makes it possible to image its lithospheric structure in great detail provided that structural information can be extracted effectively from the very large volumes of data we develop an automated technique for the measurement of interstation phase velocities of earthquake excited fundamental mode surface waves in very broad period ranges we then apply the technique to all available broad band data from permanent and temporary networks across europe in a new implementation of the classical two station method rayleigh and love dispersion curves are determined by cross correlation of seismograms from a pair of stations an elaborate filtering and windowing scheme is employed to enhance the target signal and makes possible a significantly broader frequency band of the measurements compared to previous implementations of the method the selection of acceptable phase velocity measurements for each event is performed in the frequency domain based on a number of fine tuned quality criteria including a smoothness requirement between 5 and 3000 single event dispersion measurements are averaged per interstation path in order to obtain robust broad band dispersion curves with error estimates in total around 63 000 rayleigh and 27 500 love wave dispersion curves between 10 and 350 s have been determined with standard deviations lower than 2 per cent and standard errors lower than 0 5 per cent comparisons of phase velocity measurements using events at opposite backazimuths and the examination of the variance of the phase velocity curves are parts of the quality control with the automated procedure large data sets can be consistently and repeatedly measured using varying selection parameters comparison of average interstation dispersion curves obtained with different degrees of smoothness shows that rough perturbations do not systematically bias the average dispersion measurement they can therefore be treated as random but they do need to be removed in order to reduce random errors of the measurements using our large new data set we construct phase velocity maps for central and northern europe according to checkerboard tests the lateral resolution in central europe is 150 km comparison of regional surface wave tomography with independent data on sediment thickness in north german basin and polish trough confirms the high resolution potential of our phase velocity measurements at longer periods the structure of the lithosphere and asthenosphere around the trans european suture zone tesz is seen clearly the region of the tornquist teisseyre zone in the southeast is associated with a stronger lateral contrast in lithospheric thickness across the tesz compared to the region across the sorgenfrei tornquist zone in the northwest

sharp contrast in lithospheric structure across the sorgenfrei tornquist zone as inferred by rayleigh wave analysis of tor1 project data abstract this work is a part of the tor1 project 1996 1997 and is devoted to determining the lithospheric structure across the sorgenfrei tornquist zone in northern europe for the first time in europe a very dense seismic broadband array has offered the possibility of determining very sharp lateral variations in the structure of the lithosphere at small scales using surface wave analysis we measure phase velocities for rayleigh waves with periods ranging between 10 and 100 s both within arrays with apertures of 40 50 km small compared to the wavelength and along long profiles of at least 100 km dispersion curves are then inverted and shear wave velocity models down to the depth of 200 km are proposed we show that the sorgenfrei tornquist zone is a major tectonic feature within the whole lithosphere north east of this feature in sweden beneath the baltic shield no lithosphere asthenosphere boundary is observed to exist to depths of 200 km south west of the sorgenfrei tornquist zone beneath denmark we find a lithospheric thickness of 120 20 km the transition across the sorgenfrei tornquist zone is sharp and determined to be very steeply dipping to the south west we also demonstrate the existence of a sharp discontinuity between the lithospheres beneath denmark 120 20 km thick and beneath germany characterized by thicknesses of 50 10 km in the northernmost part and 100 20 km in the southwest this discontinuity is most likely related to the trans european fault at the surface

non linear surface wave phase velocity inversion based on ray theory summary the development of temporary and permanent broad band seismic arrays reinforces the need for advanced interpretation techniques in surface wave analysis we present a new method based on 2 d paraxial ray theory of inverting teleseismic surface wave phase information and constructing phase velocity maps on a regional scale measurements of local phase velocities and propagation directions of rayleigh waves taken from full waveform synthetic seismograms are used to validate the ray theory for smooth structures on a regional scale curved wavefronts created by heterogeneous structure outside the study area are taken into account through joint inversion for the phase velocity field and the shape of the incoming wavefronts in the forward ray tracing procedure the curved wavefronts are introduced through the boundary conditions by equating the slowness vector of the ray at the edge of the study region with the known gradient of the arrival time of the wave to make the inverse problem non singular we constrain the parameters in the inversion primarily by applying a smoothness criteria on the velocity field and on the incoming wave field inversions of synthetic data sets computed by direct ray tracing and by full waveform modelling show that for 100 km spacing between stations the minimum size of structure that we can image is approximately 150 km heterogeneities with a size approximately equal to the wavelength are reconstructed by the ray based inversion even though velocity variations are underestimated due to the wave field smoothing of the structures a minimum signal to noise ratio of 3 5 is necessary in order to correctly retrieve the phase velocity field inversion of a subset of the svekalapko data for 60 s period demonstrates the applicability of the method on real data

lithospheric and sublithospheric anisotropy beneath the baltic shield from surface wave array analysis abstract we report measurements of radial and azimuthal anisotropy in the upper mantle beneath southern and central finland which we obtained by array analysis of fundamental mode rayleigh and love waves azimuthally averaged phase velocities were analysed in the period range 15 to 190 s for rayleigh waves and 15 to 100 s for love waves the azimuthal variation of the rayleigh wave phase velocities was obtained in the period range 20 to 100 s the limited depth resolution of fundamental mode surface waves necessitated strong damping constraints in the inversion for anisotropic parameters we investigated the effects of non unicity on the final model by experimenting with varying model geometries the radial anisotropy beneath finland can be explained by a lithosphere at least 200 km thick predominantly 50 by volume composed of olivine crystals having their a axes randomly distributed in the horizontal plane on the contrary the measured lithospheric azimuthal anisotropy is small this can be reconciled with body wave observations made in the area that indicate a complex pattern of rapidly varying anisotropy below 200 250 km depth that is below the petrologic lithosphere as revealed by xenolith analyses conducted in the area the magnitude of the azimuthal anisotropy increases and would be compatible with a mantle containing 15 20 by volume of olivine crystals whose a axes are coherently aligned in the n ne direction the alignment of the a axes is off the direction of present day absolute plate motion in either the no net rotation or hot spot reference frame currently n55 n60 we interpret this mismatch as evidence for a complex convective flow pattern of the mantle beneath the shield which by inference is decoupled from the overlying lithosphere