seismic risk in turkey the aegean and the eastern mediterranean the occurrence of large magnitude earthquakes summary the file of turkish seismicity developed by kandilli observatory istanbul for earthquakes to 1970 is extended here up to 1978 using 1sc and pde data entries into this file are maintained on the surface wave magnitude scale m and conversion of body wave magnitude mb to m has been carried out where necessary using a formula derived for turkish earthquakes completeness analysis suggests that magnitudes m 4 5 may be used for statistical evaluation of seismic risk this file is analysed by a range of methods to provide a suite of risk forecasts forecasting results from least squares and maximum likelihood estimates of the whole process gutenberg richter cumulative frequency law of earthquake magnitude occurrence and from the part process of gumbel s first extreme value distribution all show small systematic differences in forecasts but all three methods lead to magnitude forecasts which fall well within the range of standard deviation however these forecasts are obtained by subdividing turkish seismicity in a cellular manner and many of these cells show curvature of the earthquake frequency magnitude distribution curve concave with respect to the origin gumbel s third asymptotic distribution of extreme values is chosen as an appropriate statistical description approximate upper bounds o to earthquake surface wave magnitude occurrence are evaluated and estimates of largest magnitudes expected over an interval of 75yr are forecast with uncertainties values of w are asymptotic uncertain and theoretically correspond to infinite return periods strain energy release diagrams are then invoked to estimate empirically the large magnitude m which is equivalent to the total strain energy which may be accumulated in a region this equivalent magnitude m is consistently less than w and there is a finite waiting time typically ranging from about 15 to 70 yr during which the energy equivalent to m3 may be accumulated

a nonlinear method to estimate source parameters amplitude and travel times of teleseismic body waves abstract we present a nonlinear waveform inversion method to determine source parameters under point source approximation depth source time function centroid moment tensor and seismic moment and also travel times and amplitudes of body waves from teleseismic records we demonstrate that our source time function estimates significantly improve correlation between observed and synthetics broadband seismograms the scaling of source dimensions with seismic moment is similar for deep and shallow events in the japanese subduction area for moment magnitudes between 6 1 and 7 5 we compare event depths and moment tensors obtained with our method to those reported by different institutions for a set of japanese earthquakes this comparison reveals that our method gives hypocentral depths closer to those obtained with regional arrays than other teleseismic methods the seismic moment is properly recovered but data weighting strongly influences the moment tensor solution focal mechanisms are biased by high frequency body wave amplitude variations due to crustal structure below the stations and by errors on the instrument responses body wave differential travel times are improved compared with phase picking measurements the high quality travel times will be exploited to obtain more precise event locations and higher resolution tomographic models online material coordinates of japanese earthquakes processed in this study

using repeating earthquakes to correct high precision earthquake catalogs for time dependent station delays waveform cross correlation allows one to measure the relative arrival times of similar microearthquakes with errors of less than 1 10 of 1 sample location algorithms based on these measurements have greatly improved images of earthquake distribution for the northern california seismic network catalog however the relative location errors implied by the scatter of relocated repeating earthquakes sometimes 10s of meters is often considerably larger than the errors estimated from monte carlo simulations meters using a priori estimates of the cross correlation errors i find that most of this discrepancy arises from unmodeled time varying station delays by identifying many clusters of repeating earthquakes presumed to rupture the same source and assuming the measured arrival time differences between event pairs to be due to the difference in origin time plus the difference in station delay it is possible to invert for time dependent station corrections the method is robust in that these corrections are consistent over many kilometers of fault and greatly reduce the scatter and residuals when relocating earthquake clusters not used in the station correction determination many of the largest delay changes some approaching 2 samples 20 ms are associated with changing station electronics at several stations an annual cycle is also clearly seen with amplitudes up to 0 5 samples some m 4 7 earthquakes have produced comparable transient delay changes after applying the station corrections the scatter within clusters of repeating earthquakes is reduced to a few meters and the apparent seismogenic thickness of many kilometer long sections of faults is only 10 20 m manuscript received 31 may 2001

amino acid epimerization implies rapid sedimentation rates in arctic ocean cores the palaeooceanography of the arctic ocean is less well known than any other ocean basin due to difficulties in obtaining cores and in providing a secure chronological framework for those cores that have been raised most recent investigators have suggested that low sedimentation rates 0 05 0 1 cm kyr 1 have characterized the deep basins over the past 5 myr refs 1 2 despite the glacial marine character of the sediment and proximity to major centres of shelf glaciation these calculations have been primarily based on the down core pattern in the inclination of magnetic minerals supported by uranium series 14c and micropalaeontological evidence here we analyse amino acid diagnesis in foraminifera from two gravity cores raised from the floor of the arctic ocean our results suggest that these cores span 200 kyr conflicting with the earlier estimate of 3 myr based on palaeomagnetic data the chronology of other arctic ocean cores and previous palaeoenvironmental interpretations need re evaluation

a possible station bias in travel time measurements reported to isc a station bias in the travel times of p waves may exist in the international seismological centre isc data base it appears that low gain seismographs report systematically late arrival times average station delays confirm this with low gain stations generally slower than high gain stations

origin nature and world climate effect of arctic ocean ice cover during the cenozoic an open water arctic ocean changed to the modern permanently ice covered condition significant world climate modification accompanied this change but the precise role of the arctic ocean in major pleistocene climate events is controversial the present ice cover averages 3 m thickness but there are theories that during the pleistocene it was antarctic like several thousand metres thick the time of origin of the ice cover is placed as young as 0 7 myr ago and as old as the middle miocene any theory concerned with origin nature and climatic response of the arctic ice cover must consider the ocean s sediment record

constraints on aspherical core structure from pkikp pcp differential travel times 1 we have assembled a data set of 302 differential pkikp pcp travel times that were recorded by seismic array stations of the international monitoring system this is an order of magnitude more data than all previous pkikp pcp observations combined the differential times were measured using a beam forming and cross correlation algorithm that has a precision of 1 2 sampling intervals 0 1 s the use of differential times mitigates the effects of hypocentral errors and heterogeneities in the crust and upper mantle leaving the data sensitive to deep earth structure the pkikp pcp times are especially sensitive to variations in the thickness of the liquid outer core the data are well fit by prem with residuals having a mean of 0 29 s and a standard deviation of 0 44 s and rule out lateral variations in outer core thickness of more than 4 km most of the geographically coherent residuals can be explained by lower mantle heterogeneities and ellipticity corrections however there remain at least three regions that seem to require aspherical core structure the anomalous data are best explained by long wavelength topography on the core mantle boundary cmb with peak to peak amplitude of 3 5 km the cmb topography is most likely maintained by isostatic compensation of thickness variations in a distinct layer at the base of the mantle

stable isotope data and depositional environments in the late quaternary arctic ocean there has been much speculation about the history of the arctic ocean particularly its response to the late quaternary climatic fluctuations1 8 as a result considerable data have been gathered from arctic ocean sediment cores to reconstruct glacial and interglacial arctic ocean palaeoenvironments8 9 but even with these data the reconstructions and the correlations with the quaternary chronostratigraphy have been unsatisfactory mainly because of the lack of detailed stratigraphical data such as those provided by stable oxygen isotope stratigraphy10 here we present stable isotope records from arctic ocean sediment cores which can be correlated convincingly with corresponding data from the north atlantic together with lithostratigraphical data they provide new evidence on arctic ocean history in relation to global late quaternary climatic fluctuations

reworked jurassic neogene calcareous nannofossils in the central arctic abstract over 130 different reworked calcareous nannofossil taxa ranging from the lower jurassic to the neogene are recorded in quaternary sediments from the central arctic ocean species with mesozoic and tertiary stratigraphic ranges occur together this suggests that the reworked specimens are not primarily derived from the local bedrock but are transported to the central arctic ocean from the surrounding shelves and landmasses sea ice provides a possible means of transport the reworked nannofossil assemblages in the arctic are a result of geologic and climatic developments in the source areas both during the time of their deposition and during their subsequent erosion and transportation in the quaternary only two specimens restricted to the lower jurassic were observed and none restricted to the middle and upper jurassic the lower cretaceous is represented by at least four species restricted to that interval together with other long ranging taxa the presence of micrantholithus speetonensis perch nielsen is the first record of this species outside northwest europe the other lower cretaceous species observed are all typical of temperate to high latitude assemblages of both the southern and northern hemispheres the nannofossils reworked from the upper cretaceous strata are the dominant component of the assemblages nephrolithus corystus wind is recorded in the northern hemisphere for the first time some of the distinctive high latitude species present in the southern hemisphere have not been observed in the arctic helioliths discoasters and sphenoliths indicate relatively warm surface water conditions in the arctic subarctic areas during the paleocene and eocene

sediments of the lomonosov ridge and makarov basin a pleistocene stratigraphy for the north pole sediments of 16 short cores taken as part of the lomonosov ridge experiment lorex can be organized into the first pleistocene stratigraphy for the north polar region this stratigraphy can be correlated with stratigraphic units described from the alpha chukchi areas 300 km distant the lorex cores include at least 12 sedimentary subunits differentiated by texture color and carbonate content the units are silty and arenaceous lutites and are principally glacial marine benthic and planktonic foraminifera degree of bioturbation and fe mn micro nodule abundance generally are positively correlated foraminifera in core b 8 from 3 956 m in the makarov basin may have been affected by ccd fluctuations that did not affect fossils in core b 24 from 1 600 m on the crest of the lomonosov ridge the 12 stratigraphic units were deposited during the late pleistocene and represent the same major sedimentary events as those of stratigraphic units k l and m of the amerasian basin this correlation is excellent evidence for the remarkable and widespread uniform depositional style of glacial marine sediment times of major glacial ice transport reflect deglaciation events in the central arctic ocean surface currents during deglaciation transport glacial ice in a more or less uniform pattern over at least 50 of the arctic ocean even thin sedimentary units deposited during relatively long time intervals are correlated over 500 000 km 2

implicit randomness in earthquakes 1 analytical number theory for two integers chosen at random provides a numerical method to estimate value an analysis of three datasets of earthquakes including earthquakes occurring in mainland china south california and all over the world thus allowed us to estimate with less than 3 0 relative deviation the complexity of earthquakes is expressed by implicit randomness and characteristics of seismicity if other physical precursors were not taken into account two or more earthquakes would be correlative with one another or an earthquake could be partly predictable on the basis of the event sequence itself with a ratio of about 40 at most

bias in reported seismic arrival times deduced from the isc bulletin summary the accurate timing of seismological data is crucial for most quantitative examinations in seismology we present evidence that traveltime data from many stations contain systematic variations in timing which can be identified by checking the median of station delay times as a function of time this function is expected to be constant but many deviations are found several hundred stations that report arrival times to the isc have been examined the median station delay times of almost 8 per cent of these stations show changes of more than 1 s and thus exceed the structural signal in the data temporal variations of 0 5 1 s are common changes in the distribution of observed earthquakes and other possible explanations of such variations have been tested and fail to explain most of the observations therefore the bulk of the observed changes must be caused by flaws in the timing of the data or by biased picking of arrival times for instance at one station with a strong annual variation of noise level the arrival times are on average picked several tenths of a second later during months with a high noise level because of their systematic nature these errors will not necessarily cancel out by using the large number of traveltimes in the isc bulletin and may therefore introduce a bias in many investigations if the observed timing variations are due to the recording equipment at the stations the errors will be present in the digital waveform data as well tomographic studies could potentially be affected but in particular studies of temporal variations of earth structure based on traveltime data e g inner core rotation need to be looked at with caution as results might be influenced by station effects the exact nature of the bias is study dependent and needs thorough investigation in each individual case

travel times and station corrections for p waves at teleseismic distances approximately 3300 shallow focus earthquakes and 1000 seismic stations have been used in a study of p wave travel times and station residuals including azimuthal effects the events were selected from a catalog containing 160 000 earthquakes and those having uniform distance and azimuthal coverage were systematically relocated and used to refine p wave travel times and station corrections station corrections are provided for 994 seismic stations the station corrections involve three terms the static effect and two cosine terms with appropriate phase shifts they exhibit general consistency over broad geographic areas and where coverage is dense often show abrupt changes from one geological province to another the cos 2 terms appear to be due to upper mantle anisotropy and they correlate with the stress direction in the crust

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

inference of core mantle boundary topography from isc pcp and pkp traveltimes we invert isc pcp and pkp absolute and differential traveltimes in an attempt to infer the long wavelength topography of the core mantle boundary cmb the data selection and processing methods are described and evaluated these travel time data are very noisy and the geographic distribution of the data is highly non uniform inhibiting reliable inference of cmb topography spatial averaging enhances the coherent component of the residual variance related to heterogeneity however the random component of the variance is much larger than the coherent component we show that for pcp data the coherent signal due to mantle heterogeneity overshadows that arising from the cmb and that the effects of mantle heterogeneity are mapped into our inferred cmb solutions the pcp data are not correlated across the spatial averaging bins and seem to have a strong bias due to small scale structure and or noise the non uniform geographic sampling of the data plays a role in the mapping of mantle heterogeneity onto the cmb spatial patterns of cmb models inferred from different phases do not agree amplitudes of seismically inferred cmb undulations vary greatly the sensitivity of inferred cmb models to the processing spatial averaging procedure and inversion techniques are investigated topographic amplitudes increase strongly with increasing input residual variance the power spectrum of inferred topography indicates that there are unmodelled heterogeneities that must be described with spherical harmonics of degree 6 and higher based on this work we conclude that reliable inference of long wavelength cmb topography is not likely with the current isc data set or with a spherical harmonic expansion truncated to degree and order 6

central arctic ocean response to pleistocene earth orbital variations abstract three central arctic ocean sediment cores were sampled for percentage carbonate number of foraminifera and texture these three parameters were used in spectral analyses to test the idea that the ice covered arctic ocean may respond to orbital forcing in a different manner than has been indicated for lower latitude ice free oceans the record for two of the cores represents approximately 1 my and the record for the third approximately 400 000 yr the 100 000 yr frequency is well represented in all of the cores a 40 000 yr frequency may be present as well an unexpected 70 000 yr frequency occurs in most of the spectra and may reflect nonlinear sedimentation rates or the combined effect of obliquity and eccentricity the strong 100 000 yr signal confirms that in spite of ice feedback the arctic ocean has responded to orbital forcing in much the same manner as have ice free oceans

pleistocene paleoceanographic correlations northern greenland sea to central arctic ocean abstract correlation of pleistocene paleoceanographic events across parts of the polar seas is accomplished with core mg 123 from the swedish ymer 80 cruise the 8 72 m sediment core one of the longest recovered from any part of the arctic ocean contains abundant microfossils and coarser grain sediment that are useful in interpretation and correlation of pleistocene events with shorter sediment cores in the central arctic ocean faunal and sediment correlations are constrained by 18 o correlations and a time series analysis that matches several possible sedimentation rates for mg 123 with central arctic ocean sedimentation rates and provides a best fit correlation of the cores the results of this study provide the first correlation of northern greenland sea southern arctic ocean sediment with that of the central arctic ocean more than 1000 km distant oceanic circulation patterns between the areas during the pleistocene involved increased circulation during interglacials with reduced circulation during glacials subpolar water was not present in the northern greenland sea during the past 600 000 years during this time alternating phases of the climate cycle show a strong relationship to the 100 000 year milankovitch cycle

calibration of the regional crustal waveguide and the retrieval of source parameters using waveform modeling regional crustal waveguide calibration is essential to the retrieval of source parameters and the location of smaller m 4 8 seismic events this path calibration of regional seismic phases is strongly dependent on the accuracy of hypocentral locations of calibration or master events this information can be difficult to obtain especially for smaller events generally explosion or quarry blast generated travel time data with known locations and origin times are useful for developing the path calibration parameters but in many regions such data sets are scanty or do not exist we present a method which is useful for regional path calibration independent of such data i e with earthquakes which is applicable for events down to m w 4 and which has successfully been applied in india central asia western mediterranean north africa tibet and the former soviet union these studies suggest that reliably determining depth is essential to establishing accurate epicentral location and origin time for events we find that the error in source depth does not necessarily trade off only with the origin time for events with poor azimuthal coverage but with the horizontal location as well thus resulting in poor epicentral locations for example hypocenters for some events in central asia were found to move from their fixed depth locations by about 20 km such errors in location and depth will propagate into path calibration parameters particularly with respect to travel times the modeling of teleseismic depth phases pp sp yields accurate depths for earthquakes down to magnitude m w 4 7 this m w threshold can be lowered to four if regional seismograms are used in conjunction with a calibrated velocity structure model to determine depth with the relative amplitude of the p nl waves to the surface waves and the interaction of regional spmp and ppmp phases being good indicators of event depths we also found that for deep events a seismic phase which follows an s wave path to the surface and becomes critical developing a head wave by s to p conversion is also indicative of depth the detailed characteristic of this phase is controlled by the crustal waveguide the key to calibrating regionalized crustal velocity structure is to determine depths for a set of master events by applying the above methods and then by modeling characteristic features that are recorded on the regional waveforms the regionalization scheme can also incorporate mixed path crustal waveguide models for cases in which seismic waves traverse two or more distinctly different crustal structures we also demonstrate that once depths are established we need only two stations travel time data to obtain reliable epicentral locations using a new adaptive grid search technique which yields locations similar to those determined using travel time data from local seismic networks with better azimuthal coverage

accuracy of modern global earthquake catalogs we compare several modem 1977 present worldwide earthquake catalogs to infer their completeness earthquake origin time and hypocenter location accuracy magnitude scalar seismic moment errors and difference between individual focal mechanism moment tensor solutions the harvard centroid moment tensor cmt us geological survey usgs mt usgs first motion fm focal mechanism pde and isc catalogs have been analyzed and compared the catalogs completeness and accuracy vary in time and depend on earthquake depth and tectonic environment we propose a new statistical method for evaluating catalog completeness and show the results for the cmt dataset a difference in frequency range of seismic waves used in earthquake processing leads to varying degrees of catalog completeness for foreshocks and aftershocks close in time earthquake origin time versus centroid time as well as hypocenter location versus centroid location can be explained well by earthquake scaling relations comparing moment magnitudes and regular earthquake magnitudes yields estimated magnitude uncertainties and shows that latter magnitudes poorly estimate earthquake size for large events moment errors reported in the cmt solutions are well correlated with the cmt gs mt magnitude difference and hence indicate magnitude uncertainty well a normalized seismic moment tensor has 4 d f and its accuracy can be represented as the non double couple non dc component value the 3 d angle phi of dc source rotation and a position of the rotation pole our results suggest that a routinely determined non dc component is in most cases only an artifact the distribution of the phi value varies over catalog time earthquake depth focal mechanism and magnitude the seismic moment errors and the value of the non dc component are indicative of the phi value for the best solutions the 3 d angle in the cmt catalog is on the order of 5 7degrees the cmt catalog is obviously the best dataset in completeness and accuracy of its detailed solutions our results specifying uncertainties and completeness of global earthquake catalogs can be used in studies of geodynamic processes tectonic deformation associated with earthquakes earthquake stress analysis and in many other applications of earthquake catalog data seismogram interpretation techniques can be reviewed and possibly revised in light of these results c 2002 elsevier science b v all rights reserved

new faunal and isotopic evidence on the late weichselian holocene oceanographic changes in the norwegian sea downcore studies of planktonic and benthonic foraminifera and 18o and 13c in the planktonic foraminifer neogloboquadrina pachyderma sin in two piston cores from the southern part of the norwegian sea suggest large changes in the oceanic circulation pattern at the end of oxygenisotope stage 2 and in the early part of stage 1 prior to oxygen isotope termination ia 16 000 13 000 yr b p an isolated watermass with lower oxygen content and temperature warmer than today existed below a low salinity ice covered surface layer in the norwegian sea close to termination ia well oxygenated deep water probably with positive temperatures was introduced this deep water which must have had physical and or chemical parameters different from those of present deep water in the norwegian sea could have been introduced from the north atlantic or been formed within the basin by another mechanism than that which forms the present deep water of the norwegian sea a seasonal ice cover in the southern part of the norwegian sea is proposed for the period between termination ia and the beginning of ib close to 10 000 yr b p the present situation with strong influx of warm atlantic surface water and deep water formation by surface cooling was established at termination ib

constraints on sst estimates for the northern north atlantic nordic seas during the lgm abstract a map of estimated calcification temperatures of the planktic foraminifer neogloboquadrina pachyderma sinistral tnps for the nordic seas and the northern north atlantic for the last glacial maximum was produced from oxygen isotopes with support of mg ca ratios to arrive at the reconstruction several constraints concerning the plausible salinity and 18 o fields were employed the reconstruction indicates inflow of temperate waters in a wedge along the eastern border of the nordic seas and at least seasonally ice free waters the reconstruction from oxygen isotopes shows similarities with mg ca based paleotemperatures in the southern and southeastern sector while unrealistically high mg ca values in the central nordic seas prevent the application of the method in this area the oxygen isotope based reconstruction shows some agreement with temperature reconstructions based on the modern analogue technique but with somewhat lower temperatures and a stronger internal gradient inside the nordic seas all told our results suggest a much more ice free and dynamic high latitude ocean than the climap reconstruction

tomographic inversions for mantle p wave velocity structure based on the minimization of l 2 and l 1 norms of international seismological centre travel time residuals we use international seismological centre isc p arrival data 1964 1987 and iterative algorithms which minimize the l1 and l2 residual norms to solve simultaneously for three dimensional p velocity variations in earth s mantle source mislocations and station corrections we find that the maximum velocity perturbations produced by the l1 minimization approximately 4 in our final model are relatively insensitive to smoothing and damping constraints therefore using an l1 norm criterion allows us to keep the bias introduced to the inversion to a minimum among the well resolved features contained in both the l1 and the l2 velocity models are a fast anomaly in the lower mantle beneath the tonga new hebrides subduction zone to a depth of 1670 km and another fast anomaly beneath the japanese island arc and eastern asia continuity between these anomalies and shallower fast anomalies is not clear a fast anomaly extending from 670 km to 2070 km depth appears beneath eastern north america the caribbean and north central south america a broad fast anomaly appears beneath eastern asia just above the core mantle boundary as well as several slow anomalies under the pacific basin of comparable size both models contain a circum pacific ring of 2 lower velocities in the depth range 0 200 km associated with back arc basins high velocities over 2 associated with the continental shields tend to disappear below 400 km though a significant region of high velocity remains beneath the siberian platform in the 400 to 670 km depth interval

simultaneous inversion for 3 d variations in shear and bulk velocity in the mantle until recently most of the seismic tomographic modeling has been addressing the question of lateral heterogeneity either in p or s wave velocities the s wave velocity variations are larger and hence provide stronger signal on long period waveforms the direct p travel times being the first arrivals on the other hand are most frequently reported in the international seismological centre isc bulletins in mineral physics experiments the variation in bulk velocity is more often measured to better understand the differences between vp and vp patterns and better link the results from mineral physics to those of seismic tomography we formulate the inverse problem in terms of relative perturbations in the shear velocity vs 12 and bulk sound velocity v k 12 we use a large data set which consists of waveforms waveform derived travel times and travel times from the isc bulletins the earthquakes are relocated using corrections for lateral heterogeneity the events which cannot be reliably determined are discarded the model is defined as spherical harmonics to degree 12 horizontally and as chebyshev polynomials to order 13 radially for both shear and bulk sound velocity the inversion is performed under smoothness constraint the resolution tests and bootstrapping analysis indicate that the model is well recovered particularly at long wavelength the results indicate a much larger variability of shear than bulk sound velocity the model explains observations well the most intriguing result obtained in this study is that the variations in shear velocity and bulk sound velocity are negatively correlated in the lowermost mantle the explanation is not very clear from the mineral physics point of view it is not unlikely that this could be explained in terms of thermal variation even though we are unwilling to rule out the possibility of large wavelength compositional variations

crust and upper mantle p and s wave delay times at eurasian seismic stations median crust and upper mantle p and s wave delay times based on residuals for teleseismic p and s wave arrival times included in the groomed isc neic database of engdahl et al bull seism soc am 88 1998 722 are estimated as functions of time and azimuth for eurasian seismic stations the effects of source and lower mantle 3 d structure on the station residuals are corrected by ray tracing all phase data to a depth of 400 km below the station through the 3 d p and s wave models of bijwaard et al j geophys res 103 1998 30055 and bijwaard seismic travel time tomography for detailed global mantle structure university of utrecht utrecht the netherlands 1999 179 pp respectively in general crust and upper mantle p and s station delays based on medians of azimuthally binned residuals are spatially coherent and can be qualitatively associated with eurasian tectonic features such as orogens and cratons as well as with structural elements such as sediment and crustal thickness and average uppermost mantle velocities paired p and s station delays are correlated with a rather poorly determined slope s p delay time ratio of about 1 9 2001 elsevier science b v all rights reserved

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

p and pcp travel time tomography for the core mantle boundary pcp arrival times reported to the international seismological centre isc are inverted for vertical travel time anomaly at the core mantle boundary cmb we first invert about 2 106 isc first p arrival data for the three dimensional 3 d structure of the mantle and hypocenter locations iteratively the pcp data are corrected for the relocated hypocenters and the 3 d structure this correction has reduced the observed pcp residuals the corrected pcp data are then inverted for the vertical travel time anomalies at the cmb which are due either to velocity anomaly or topographic anomaly the spherical average of the inverted structure requires either a velocity reduction in the boundary layer just above the cmb by 3 if the layer is 20 km thick or a lowering of the cmb by 3 km the heterogeneity pattern of the cmb is drastically different from that of the overlying d layer negative vertical travel time anomalies appear in the northern high latitude region and positive anomalies appear under southeast asia and middle to south america the lateral dimensions of these anomalies are of the order of 40 the anomalies can be interpreted as either a velocity perturbation in the boundary layer 7 if the layer is 20 km thick or an undulation of the cmb 7 km various tests including the error and resolution estimations indicate that these three anomalies are the significant resolvable features of the cmb these anomalies are also corroborated by the result of the joint inversion of p and pcp for both the 3 d mantle and the 2 d cmb assuming that the layer is laterally heterogeneous in iron content and deforms at the base in isostatic equilibrium with the outer core the pcp data are also inverted for the isostatic figure of the boundary layer the velocity perturbation in this case is 5 6 if the layer is 20 km thick and the cmb undulation is only 1 2 km regardless whether the cmb heterogeneity is due to velocity and or topographic perturbations it is dominant in the zonal component of degree 2 while the degree 2 pattern in the lower mantle including the d is dominant in sectorial component

planet within a planet rotation of the inner core of earth the time dependence of the orientation of earth9s inner core relative to the mantle was determined using a recently discovered 10 degree tilt in the axis of symmetry of the inner core9s seismic velocity anisotropy two methods of analyzing travel time variations for rays traversing the inner core on the basis of 29 years of data from the international seismological centre 1964 1992 reveal that the inner core appears to rotate about 3 degrees per year faster than the mantle an anomalous variation in inner core orientation from 1969 to 1973 coincides in time with a sudden change jerk in the geomagnetic field

pleistocene calcite lysocline and paleocurrents of the central arctic ocean and their paleoclimatic significance most previous references to the depth of the arctic ocean calcite lysocline have been based on comparison with the known north atlantic carbonate compensation depth foraminifera from cores taken at depths ranging from 2316 to 3956 m provide the first firm calcite lysocline constraints for the central arctic ocean these data suggest progressive lowering of the calcite lysocline to at least 3956 m during the past 1 5 m y interrupted by 300 m rises of the lysocline level that apparently correspond with interglacial and early glacial climate conditions most cores from less than 2450 m indicate variable foraminifera abundance but continual presence of foraminifera for the past 1 5 m y low abundances commonly occur in coarse textured sediment and are interpreted to represent low productivity during major deglaciations within certain equivalent lithostratigraphic units representing the past 1 5 m y there is an absence of foraminifera in cores from depths greater than 2450 m this absence of foraminifera is interpreted to be due to dissolution dissolution intervals are associated with fine grain sediments interpreted to represent interglacial and early glacial climate conditions the interpretation of a rise in the lysocline level during interglacials is in apparent disagreement with studies reported from lower latitudes in the atlantic ocean but is complementary with the hypothesis that formation of norwegian greenland sea deep water ngdw and cold canada basin deep water occurs during interglacials paleocurrent data from the lomonosov ridge and the adjacent makarov basin are interpreted to indicate that during periods of increased glacial ice influx into the arctic ocean system there was reduced current activity in the bottom and intermediate water masses relative to periods when little glacial ice was present this is in accord with the idea that ngdw affects intermediate and deep water circulation in the central arctic ocean and hence the calcite lysocline level

modeling the water masses of the atlantic ocean at the last glacial maximum 1 we produced gridded monthly sea surface boundary conditions for the atlantic ocean at the last glacial maximum lgm based on the sea surface temperature reconstruction of the glamap project we used an ocean general circulation model ogcm subject to these sea surface boundary conditions and a corresponding wind stress field from an atmospheric general circulation model to study the differences in the distribution of the main water masses between the lgm and the present our global ogcm is characterized by high vertical resolution low vertical diffusion and isopycnal mixing and hence allows for a realistic representation of the hydrology and circulation of the modern atlantic ocean according to a series of lgm experiments with an increasing sea surface salinity anomaly in the weddell sea the ventilated thermocline was colder than today by 2 3 c in the north atlantic ocean and in the experiment with the largest anomaly 1 0 beyond the global anomaly by 4 5 c in the south atlantic ocean its depth was reduced by 50 m on average most notably in the tropics in the north atlantic ocean the outcrop locations of the thermocline isopycnal surfaces migrated southward by 5 10 and the ventilation increased in the south atlantic ocean the mixed layer and thermocline water masses were dominated by cold water originating from drake passage and the import of warm water from the indian ocean was reduced to about 4 sv or 40 of its modern value antarctic intermediate water was colder by 3 4 c and could be traced as far as 10 n the meridional overturning rates of north atlantic deep water nadw and antarctic bottom water aabw in the atlantic ocean were similar to those of the present day experiment 9 10 sv and 4 sv respectively however nadw cooled by 2 5 c and aabw by 1 c aabw was near the freezing point of seawater at the surface and the saltiest water mass in the atlantic ocean even saltier than nadw we show that the differences between the lgm and the present day experiments can be traced back to the changes in the subpolar and interhemispheric sea surface density gradients

on the onset of p seismograms summary for more than 30 years seismologists have been encouraged to read p onsets to 0 1 s evidence is presented that the actual errors are significantly greater than this three main factors determine how accurately any particular onset is read 1 magnification and timescale of the display 2 signal to noise ratio and 3 the form of the p pulse radiated by the source if too low a magnification is used the first motion can have such a low amplitude that it is not identified and the reported onset is measured on a later arrival potentially the largest errors will occur for stations for which direct p leaves the source near a node in the earthquake radiation pattern if the signal to noise ratio is low weak nodal p may not be observed and the onset picked on a later large amplitude phase such as the surface reflection pp the size of the first motion relative to the maximum amplitude of p depends principally on the rise time of the p pulse for explosions where the rise time can be very short first motion on conventional sp seismographs may be more than one quarter of the maximum peak to trough deflection shown by p for some earthquakes where the rise time is over 0 5 s however first motion may be only 1 20 of the maximum peak to trough deflection and so may be lost in the noise examples are shown of seismograms that display such features estimates of the reading error in p have been determined using the joint epicentre method to estimate the relative epicentres and origin times of groups of explosions at two test sites degelen mt and shagan river in kazakhstan and for a series of aftershocks the 1976 gazli uzbekistan sequence as station terms take up deviations from standard traveltimes that are common to all disturbances in a group the residuals after applying the joint epicentre method should be a measure of observational error assuming that the effects of any lateral heterogeneity in the source region are negligible the joint epicentre studies show using p onsets measured on array seismograms that the standard deviations of the residuals on seven degrees of freedom for the degelen mt and shagan river explosions are 0 10 s and 0 14 s respectively whereas for the gazli earthquakes the standard deviation is 0 39 s the difference between the variances for the earthquakes and explosions being significant at 0 1 per cent level the results show that even for the onsets from explosion p waves recorded at arrays which are some of the most reliable data available observational errors are not consistently less than 0 1 s and for earthquakes the errors will often be 0 5 s or greater

seismic velocities at the core mantle boundary inferred from p waves diffracted around the core the very base of the mantle is investigated with core diffracted p wave pdiff travel times published by the international seismological centre isc for the period 1964 1987 apparent slownesses are computed for two station profiles using a difference method as the short period pdiff mostly sample a very thin layer above the core mantle boundary cmb a good approximation of the true velocity structure at the cmb can be derived from the apparent slownesses more than 27000 profiles are built and this provides an unprecedented pdiff sampling of the cmb the overall slowness distribution has an average value of 4 62 s deg which corresponds to a velocity more than 4 lower than that of most mean radial models an analysis of the residuals of absolute isc p and pdiff travel times is independently carried out and confirms this result it also shows that the degree of heterogeneities is significantly higher at the cmb than in the lower mantle a search for lateral velocity variations is then undertaken a first large scale investigation reveals the presence of coherent slowness anomalies of very large dimensions of the order of 3000 km at the cmb a tomographic inversion is then performed which confirms the existence of pronounced 8 10 lateral velocity variations and provides a reliable map of the heterogeneities in the northern hemisphere the influence of heterogeneity in the overlying mantle of noise in the data and of cmb topography is evaluated it seemingly proves minor compared with the contribution of heterogeneities at the cmb our results support the rising idea of a thin low velocity laterally varying boundary layer at the base of the d layer the two principal candidate interpretations are the occurrence of partial melting or the presence of a chemically distinct layer featuring infiltrated core material

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

the influence of path corrections and a three dimensional global p wave velocity model on seismic event location in kazakhstan we relocate 81 large nuclear explosions that were detonated at the balapan and degelen mountain subregions of the semipalatinsk test site in kazakhstan during the years 1978 to 1989 the absolute locations of these explosions are available as well as very accurate estimates of their origin times this ground truth information allows us to perform a detailed analysis of location capability we use a sparse network of stations with highly accurate first arrival picks measured using a waveform cross correlation method these high quality data facilitate very accurate location estimates with only a few phases per event we contrast two different approaches 1 a calibration based approach where we achieve improved locations by using path corrections and 2 a model based approach where we achieve improved locations by relocating in a recently published global 3 d p velocity model both methods result in large improvements in accuracy of the obtained absolute locations compared to locations obtained in a 1 d reference earth model ak135 the calibration based approach gives superior results for this test site in particular when arrival times from regional stations are included estimated locations remain well within a 1000 km2 region surrounding the ground truth locations when the path corrections for the balapan and degelen mountain subregions are interchanged but even for the short separation between these two regions we find variations in the path corrections that cause systematic mislocations the model based approach also results in substantially reduced mislocation distances and has the distinct advantage that it is in principle transportable to other source regions around the world

mid chain diols and keto ols in se atlantic sediments a new tool for tracing past sea surface water masses abstract long mid chain diols and keto ols in se atlantic surface sediments have been studied in relation to the properties of the overlying surface waters the strongest change in compound composition occurs over the angola benguela front 14 16 s south of the front 1 13 and 1 14 diols notably the 1 14c 28 and 1 13c 30 homologs increase relative to 1 15 diols the 1 13c 30 keto ol is almost absent north of the front these changes probably reflect differences in sea surface temperature persistence of stratification and upwelling at opposite sides of the front elevated relative abundances of the 1 15c 32 diol and 1 15c 32 keto ol below the congo river plume 6 s may be outflow related which should be tested on other river plumes lower relative abundances of 1 15 diols close to walvis bay might relate to a higher upwelling intensity compared to the other sites investigated the applicability of the observed surface patterns is tested down core for the penultimate deglaciation the temporal changes in diol and keto ol composition not only have their spatial counterpart in the se atlantic surface sediments they are also readily interpretable on the basis of the modern diol and keto ol assemblages as well as the palaeoenvironmental reconstructions based on other proxies

hypocenter location by pattern recognition 1 a novel approach to hypocenter location is proposed on the basis the concept of pattern recognition a new data misfit criterion for location is introduced which measures discrepancies between the observed arrival times of an event and those of nearby previous events in the arrival pattern misfit measure travel times predicted by an earth model are effectively replaced by information from an ensemble of previous observations thin plate spline interpolation and generalized cross validation are applied to interpolate and smooth the resulting misfit function which may then be used in standard location algorithms synthetic experiments show that in certain circumstances it is possible to achieve locations with errors smaller than those in the underlying database it is suggested that the arrival pattern approach exploits information on lateral heterogeneous earth structure contained in the database to constrain locations the arrival pattern approach is illustrated by relocating 395 ground truth events from the nevada test site 482 earthquakes from the marianas subduction zone and 457 earthquakes from the atlantic mid ocean ridge it is shown that picking errors and unmodeled small scale lateral heterogeneity are the most significant sources of event mislocation and that errors in the original locations of the database events make a much smaller contribution

whole earth structure estimated from seismic arrival times the arrival times of 10 compressional and shear phases p s pp pcp ss scs pk pab pk pbc pk pdf sk sac and two sets of differential times ss s410s and ss s660s are used to infer the earth s three dimensional structure with the exception of ss sds the raw data are composed of arrival times from the international seismological centre isc catalogue the isc events have been relocated using p and s phases and the ak135 radial earth model a total of 818 655 summary arrival times constrain lateral velocity variations in the crust mantle and core we also determine relocation parameters for all events stations corrections for each phase boundary topography 410 km 660 km core mantle boundary inner core boundary and inner core anisotropy variations our model of p and s velocity variations in the crust and mantle contains the general features observed in other body wave inversions a low velocity ring around the pacific ocean basin in the depth range 35 400 km high velocity anomalies associated with subducting slabs most prominent in the depth range 660 1070 km and high velocity anomalies surrounding the pacific basin just above the core mantle boundary in the outer core there is evidence of a latitudinal variation in velocity approaching 0 6 in magnitude with lower p velocities at the poles and higher velocities near the equator this pattern is observed throughout the outer core but is most prominent in the depth range 3671 4071 km and near the inner core boundary synthetic tests indicate that outer core features are moderately resolvable and inversions of random arrival times indicates that the anomalies are a factor of 2 above the estimated parameter noise level lateral heterogeneity in the inner core trades off with anisotropy resulting in poor resolution of isotropic velocity variations anisotropy in the inner core is predominantly subparallel to the earth s axis and of the order of 3 but this value can decrease if more inner core isotropic lateral heterogeneity is allowed a comparison of structure above and below the core mantle boundary cmb indicates that velocity heterogeneity is uncorrelated across the cmb but there is a moderate correlation between cmb topograpy and outer core heterogeneity an inversion in which the pk pdf residuals were absent indicates that the latitudinal pattern of outer core velocity variations is not due to the influence of inner core velocity structure

seismological study of the elevation of phase boundaries within the subducting lithospheric slabs abstract the depths of phase transformations corresponding to major velocity discontinuities differ in the subducting lithospheric slabs from those in the surrounding mantle mainly due to temperature differences we interpreted sets of p and s wave travel time observations which are anomalously late produced by 36 deep earthquakes in the tonga kermadec subduction zone as reflections from the two major velocity discontinuities in the surrounding mantle which are relatively deep and correspond to those independently obtained at the relatively shallow depths of 410 km and 600 km in the subducting slab in this region by kaila and krishna the inferred depths in the surrounding mantle for these two discontinuities respectively vary within 490 560 km and 630 680 km this implies that these discontinuities are relatively elevated by 80 150 km to 410 km depth and by 30 80 km to 600 km depth in the subducting slab in the tonga kermadec region these estimates of the elevation of the discontinuities within the subducting slab are in general agreement with those proposed by ringwood and others the present study thus provides new seismological evidence for the elevation of velocity discontinuities within the subducting slabs the velocity models considered in the present study also indicate lithospheric slab penetration well below the 600 km seismic discontinuity in the tonga kermadec region

inner core anisotropy in three dimensions the purpose of this paper is the investigation of cylindrical anisotropy in the inner core based on the travel time anomalies of the pkikp phase we use the arrival times reported in the international seismological centre bulletins for years 1964 1990 we select only earthquakes which have a good azimuthal coverage and a sufficiently large number of reporting stations the earthquakes are relocated using corrections for lateral heterogeneity computed for our most recent three dimensional mantle model we use a total of 313 422 observations of the df branch of pkp travel time anomalies within the epicentral distance ranges of 120 140 and 150 180 reported by 2335 stations for 26 377 earthquakes we process the data using an averaging procedure which we call cylindrical anisotropy stacking that enhances the effects of anisotropy but is expected to suppress those due to lateral heterogeneity and random errors the processed residuals show a remarkably consistent pattern this confirms the dominance of the cylindrical elastic anisotropy in the inner core with approximately a constant axis of symmetry this axis of symmetry is found to be tilted 10 5 1 from the earth s rotation axis in the direction 160 e 5 in the northern hemisphere in this new coordinate system we determine a four layer axisymmetric model of transverse anisotropy with each layer approximately 300 km thick the model shows that the anisotropy is strongest 3 within the innermost part of the core the travel time anomalies show significant 1 5 s longitudinal variations even when the tilt of the axis of symmetry is considered there is a substantial increase in the amplitude of the longitudinal variations which are dominated by the second and fourth harmonics for rays with bottoming depths exceeding 400 km below the inner core boundary the measurable tilt of the axis of symmetry and the presence of significant nonaxisymmetric signal may provide important clues with respect to the possible causes of anisotropy the increase in the anisotropy in the innermost part of the core departs from earlier inferences that anisotropy may be limited to the outermost 200 300 km of the earth s inner core

nuclear explosion locations at the balapan kazakhstan nuclear test site the effects of high precision arrival times and three dimensional structure abstract we have investigated the potential contributions of improved arrival times using waveform cross correlation and the use of three dimensional 3 d velocity models for seismic event location capability our analyses are applied to a dataset of nuclear explosions at balapan kazakhstan for which ground truth locations and some absolute origin times are available this ground truth information allows us to determine excellent origin time estimates for the remaining explosions the combination of excellent ground truth location information and high quality origin time estimates permits us to 1 carry out a detailed examination of the quality of isc picks 2 identify probable timing errors in the digital data 3 evaluate relative and absolute location capability using data from a sparse network 4 assess the influence of event signal to noise ratio snr on relative location accuracy 5 utilize the balapan events as a source array for 3 d tomography beneath the test site and 6 test the influence of 3 d structure local and global on relative location accuracy and precision in a controlled situation our principal finding is that improved arrival times are the primary contributor to improved locations joint and individual relocations of balapan events using the full digital dataset result in average mislocations of less than 1 km and 95 confidence regions of a compatible size to mimic a ctbt scenario more realistically we also carry out relocations using very few stations 4 10 observations location accuracy degrades somewhat but the high quality picks generally result in mislocations less than 10 km even for events with very large azimuthal gaps uncertainty is generally underestimated in these cases tests with artificially degraded snr show that mislocation increases slowly as snr decreases 3 d velocity structure makes a smaller contribution to relative location accuracy than accurate time picks travel time variations due to global 3 d structure vary little across the source region so that location scatter is not reduced when travel time corrections for global 3 d structure are applied travel time variations due to the local 3 d structure estimated using source region tomography are also modest applying travel time corrections that account for the local structure does yield slight location improvement

stable isotope stratigraphy of the arctic ocean fram strait to central arctic abstract a comparison of stable isotope and textural records of sediment cores from the fram strait and central arctic ocean to isotopic records from low latitude oceans indicates that the arctic mediterranean responded dynamically to climatic change during the pleistocene core mg 123 from the fram strait shows at least four significant low 18 o intervals 5 high 13 c intervals and five intervals with a low amount of coarse sediment the association of high 18 o values with coarse sediment intervals indicates increased glacial ice in the fram strait during glacial phases of the climate cycle peaks within the low 18 o intervals increase in magnitude from oldest to youngest suggesting that glacial interglacial transitions are pulsed the magnitude of the different low 18 o intervals increases from oldest to youngest this is interpreted to indicate that there has been a progressive intensification of the oceanographic response to glacial interglacial transitions in the fram strait during the past 524 ky time series spectral analysis suggests an age of approximately 524 ky for the oldest sediment in core mg 123 yielding an average sedimentation rate of approximately 1 66 cm 1000 yr stable isotope records from the central arctic ocean indicate that sedimentation rates are on the order of 1 3 mm 1000 yr the isotope records support the established central arctic ocean lithostratigraphy coarse sediment deposition in the central arctic is not as clearly related to glacial conditions as it is in the fram strait the oxygen isotope range of central arctic ocean records is accentuated relative to the global ice volume signal recorded from lower latitude cores this may be caused by variations in salinity temperature and thickness of the arctic ocean s low salinity surface layer oceanographic responses to climatic change recorded in the fram strait are also recorded in the central arctic ocean but with decreased resolution due to the magnitude of difference in the sedimentation rates between the two areas

spectra of mantle shear wave velocity structure summary we applied the stochastic method of gudmundsson davies clayton 1990 which was applied to isc p wave data to teleseismic isc s wave data to obtain an independent estimate of mantle structure we inverted the variance of s wave traveltime residuals of bundles of rays to obtain a description of the spectrum of lateral heterogeneity as a function of depth through the mantle the technique yields robust estimates of the traveltime scattering power the product of a characteristic scalelength of heterogeneity and the mean square of slowness perturbations we can estimate the characteristic scalelength half width from the autocovariance which can be reconstructed from the spectra hence by division we can estimate the root mean square slowness by extrapolating the variance of bundles of rays to bundles of zero cross sectional area we can also estimate the scale incoherent signal which is a plausible estimate of the noise in the data which is removed from the data we find that most of the structure generating shear wave traveltime residuals is located in the uppermost mantle about half of the structure is short scale harmonic degree 1 50 the large scale structure 1 50 has a half width of about 500 km in the upper half of the mantle this s wave half width is consistent with the p wave half widths determined by gudmundsson et al 1990 the s wave half width in the lower half of the mantle is poorly constrained it varies from 500 to 3000km which spans the better constrained value of 1200 km found by gudmundsson et al 1990 for p waves the incoherent scatter suggests that the signal to noise ratio of the s wave data set is around 1 5 assuming that the compressional and shear wave velocity variations are correlated then the signal weighted value of the ratio d in y ld in y is 2 as also found in normal mode studies this is much larger than the value of 0 8 1 4 suggested by laboratory experiments undertaken at atmospheric pressure there is no evidence of periodicity in the traveltime autocovariance this suggests little or no periodicity in the underlying convection the short half width through most of the mantle suggests high rayleigh number convection with its attendant small scale structures the power decreases by an order of magnitude or more in going from the upper mantle to the lower mantle the same as found by gudmundsson et al 1990 for p waves this large difference suggests either a change in convective regime and or a difference in the temperature sensitivity of elastic constants in both layers the increased short scale structure at the top of the mantle suggests that a large part of the seismic signature at this boundary is compositional since one would expect a red spectrum for a thermal boundary layer the derived spectra between 1 10 and i 50 are similar in shape to spectra from the mantle convection simulations of glatzmaier 1988 with a rayleigh number of 106 107 which would suggest layered convection if the comparison is valid

precursory arrivals to pp summary isc international seismological centre traveltime data have been investigated to reveal the source of precursory arrivals to the pp phase observed at epicentral distances around 100 the data include more than 25 000 traveltimes reported from 1971 to 1985 most of the lead times of the precursory arrivals are found to be less than 75 s and the frequency distribution of the lead times indicates that most of the precursory arrivals can be interpreted as scattering waves generated in the crust and the uppermost mantle however several peaks can be found in the frequency distribution especially for impulsive onsets these may correspond to certain types of deterministic waves such as p waves reflected from the bottom sides of the velocity discontinuities in the upper mantle or those reflected asymmetrically in the crust or the uppermost mantle many of the impulsive onsets included in these peaks have paths travelling through the tibetan region suggesting the possible velocity discontinuity around 190 km associated with the low velocity layer in this tectonically active region

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

global scale p wave tomography optimized for prediction of teleseismic and regional travel times for middle east events 1 data set development 1 we extend the bayesloc seismic multiple event location algorithm for application to global arrival time data sets bayesloc is a formulation of the joint probability distribution spanning multiple event location parameters including hypocenters travel time corrections pick precision and phase labels stochastic priors may be used to constrain any of the bayesloc parameters markov chain monte carlo sampling is used to draw samples from the joint probability distribution and the posteriori samples are summarized to infer conventional location parameters such as the hypocenter the first application of the broad area bayesloc algorithm is to a data set consisting of all well recorded events in the middle east and the most well recorded events with 5 spatial sampling globally this sampling strategy is designed to provide the ray coverage needed to determine lithospheric scale p wave velocity structure in the middle east using the complementary ray geometry provided by regional subhorizontal and teleseismic subvertical raypaths and to determine a consistent albeit lower resolution image of global mantle structure the data set consists of 5401 events and 878 535 p pn pp sp and pcp arrivals recorded at 4606 stations relocated epicenters are an average of 16 km from bulletin locations the data set included events that are known to an accuracy of 1 km a k a gt1 based on nonseismic information the average distance between gt1 epicenters and our relocated epicenters is 5 6 km for arrivals labeled p pn and pcp 92 90 and 96 are properly labeled with probability 0 9 respectively incorrect phase labels are found to be erroneous at rates of 0 6 0 2 1 6 and 2 5 for p pn pcp and depth phases pp and sp respectively labels found to be incorrect but not erroneous were reassigned to another phase label p and pn residual standard deviation with respect to ak135 travel times are dramatically reduced from 3 45 s to 1 01 s the differences between travel time residuals for nearly reciprocal raypaths are significantly reduced from the input event locations suggesting that bayesloc relocation improves data set consistency the reciprocity tests suggest that the dominant contribution to travel time residuals calculated from information provided in global bulletins is location and picks errors not travel time prediction errors due to 3 d structure modeling the whole multiple event system results in accurate locations and an internally consistent data set that is ideal for tomography and other travel time calibration studies simmons et al 2011 companion paper use the bayesloc processed data set to develop a 3 d tomographic image which further reduces residual standard deviation to 0 50 s

late pleistocene paleo oceanography of the norwegian greenland sea benthic foraminiferal evidence fluctuations in benthic foraminiferal faunas over the last 130 000 yr in four piston cores from the norwegian sea are correlated with the standard worldwide oxygen isotope stratigraphy one species cibicides wuellerstorfi dominates in the holocene section of each core but alternates downcore with oridorsalis tener a species dominant today only in the deepest part of the basin o tener is the most abundant species throughout the entire basin during periods of particularly cold climate when the norwegian sea presumably was ice covered year round and surface productivity lowered portions of isotope stages 6 3 and 2 are barren of benthic foraminifera this is probably due to lowered benthic productivity perhaps combined with dilution by ice rafted sediment there is no evidence that the norwegian sea became azoic the holocene and substage 5e the last interglacial are similar faunally this similarity combined with other evidence supports the presumption that the norwegian sea was a source of dense overflows into the north atlantic during substage 5e as it is today oxygen isotope analyses of benthic foraminifera indicate that norwegian sea bottom waters warmer than they are today from substage 5d to stage 2 with the possible exception of substage 5a these data show that the glacial norwegian sea was not a sink for dense surface water as it is now and thus it was not a source of deep water overflows the benthic foraminiferal populations of the deep norwegian sea seem at least as responsive to near surface conditions such as sea ice cover as they are to fluctuations in the hydrography of the deep water benthic foraminiferal evidence from the norwegian sea is insufficient in itself to establish whether or not the basin was a source of overflows into the north atlantic at any time between the substage 5e 5d boundary at 115 000 yr b p and the holocene

ice rafting history from the spitsbergen ice cap over the last 200 kyr abstract three piston cores taken from the mid to upper continental slope of the spitsbergen margin have been used to elucidate the calving history of the spitsbergen ice mass for the last 200 kyr the abundance of clasts larger than 2 mm was used as a measure of ice rafted detritus ird in the cores these clasts were counted from x ray photographs the fraction coarser than 63 m was also measured and compared to the clast counts to assess the validity of this parameter as a measure of ird content the correlation between clast counts and the fraction 63 m was poor and it was concluded that the fraction 63 m was a poor measure of ird in the spitsbergen cores in cores close to a major continental landmass or from an area of steep submarine relief the fraction 63 m is likely to be affected by factors other than ice rafting alone the ird peaks identified in this study were thought to be produced by the following advance of the spitsbergen ice cap during periods of increased moisture supply during interstadial periods mid stage 5 and stage 3 disintegration of a large ice mass on the continental shelf during deglaciations stages 6 5e 5b 5a and 2 1 boundaries summer melting of a large ice mass during glacial periods stage 6 a good correlation was found between interpreted ice advances from ird input to the spitsbergen margin and postulated ice advances from terrestrial evidence the ird peaks found from the spitsbergen margin appear to be produced by a different mechanism from that proposed for the production of the heinrich layers of the north atlantic these are thought to be produced by the collapse of the laurentide ice sheet once it reaches a threshold size correlation of heinrich layers produced from a mid latitude ice sheet with the ird events of the norwegian greenland sea is not possible due to their different mechanism of formation in fact there is possibly an antiphase relationship as heinrich layers are formed mainly during glacial periods whereas ird peaks in the greenland sea are produced during periods of rapid ice advance when moisture supply is high when relatively warm atlantic waters enter the norwegian greenland sea during interstadial periods as well as during melting events

abrupt climatic change during the last interglacial glacial cycle in the polar north atlantic abstract we have investigated five sediment cores from the margin and abyssal plain off western svalbard barents sea in the polar north atlantic we discuss the palaeoceanography and its relationship to glacial history during the last interglacial glacial cycle based on detailed stratigraphic analyses of planktic and benthic foraminiferal fauna oxygen and carbon isotopes on foraminifera ice rafted debris grains 500 m and radiocarbon dates the sediment cores combined cover the last interglacial glacial cycle including marine isotope stage mis 5 1 sedimentation rates are generally high ranging from 3 to 100 cm 1000 years atlantic water repeatedly reached the polar north atlantic during the last interglacial glacial cycle and was present for at least 50 of the total time interval periods having atlantic water advection termed hp zones hp high productivity are characterised by high planktic foraminiferal production a small increase of benthic and subpolar planktic foraminifera benthic foraminiferal and stable isotope data indicate active deep water formation during the hp zones in substage 5e there are indications of sea surface temperatures similar to those of today the major glaciations on svalbard during the last interglacial glacial cycle are related to hp zones some hp zones correspond to an early build up phase of the ice sheets peak glacials all correspond to one hp zone that subsequently is terminated by a meltwater event however periods with advection of atlantic water during mid mis 3 do not correlate to a glacial phase on svalbard but rather to the western fennoscandian ice sheet the records in the present study are correlated to the northeast atlantic the arctic ocean and to the greenland ice core record and show parallel millennial scale variability

a new absolute arrival time data set for europe summary the main aim of this study is to create a data set of accurate absolute arrival times for stations in europe which do not report to the international seismological centre isc waveforms were obtained from data centres and temporary experiments and a semi automatic picking method was applied to determine absolute arrival times for p and s phases 85 000 arrival times were picked whose distribution of residuals shows generally low standard deviations on the order of 0 5 0 7 s furthermore mean teleseismic station residuals reflect the properties of the underlying crust and uppermost mantle comparison to isc data for matching event stationphase combinations also confirms the good quality of the new absolute arrival time picks most importantly this data set complements the isc data as it fills regional data coverage gaps in europe

late quaternary sedimentation in the eastern arctic basin stratigraphy and depositional environment abstract the late quaternary history of the arctic basin is poorly known because most sediment cores seemed to have accumulated very slowly based on magnetostratigraphy on the order of one to a few millimeters per thousand years two short sediment cores from the eurasian basin of the arctic ocean have now been dated by means of o and c isotopic ratios the o isotope stratigraphy suggests that these sediments accumulated much faster on the order of one to four centimeters per thousand years than in the central arctic ocean the cores penetrated sediments belonging to isotope stages 1 3 and allow a detailed description of the depositional environment under the arctic ice cover during the last ice age and the ensuing climatic warm interval

arctic ocean chronology confirmed by accelerator 14c dating the role of the arctic ocean in earth s climatic and oceanographic development is significant but has become controversial because of disagreements concerning a reliable arctic chronology the first arctic ocean chronology based on u th and 14c data was in agreement with magnetostratigraphy developed later but these data have been challenged by recent amino acid diagenesis dates new accelerator 14c data support the earlier u th magnetostratigraphic dates and confirm the reliability of the established arctic ocean chronology

toward quantifying uncertainty in travel time tomography using the null space shuttle 1 the solution of large linear tomographic inverse problems is fundamentally non unique we suggest to explore the non uniqueness explicitly by examining the null space of the forward operator we show that with the null space shuttle it is possible to assess robustness in tomographic models and we illustrate the concept for the global p wave model mit p08 we found a broad range of acceptable solutions compatible with the travel time data the root mean square rms velocity perturbations vary from 0 2 to 0 6 in the lowermost mantle and from 0 3 to 1 3 in the upper mantle such large variations in average amplitudes prohibit meaningful inferences on temperature or chemical variations in the earth from tomographic models alone on a global scale much short wavelength structure resides in the null space of the forward operator suggesting that the data do not everywhere resolve structure on the smallest length scale 200 km allowed by the block parameterization used in mit p08 and similar models this indicates that great care should be taken when interpreting such structure as a practical measure we suggest that only those structures for which the wave speed perturbations do not change sign within the range of models permitted by the data should be considered robust with this criterion the model null space analysis shows that the high velocity anomalies in the lower mantle which are often interpreted as remnants of slabs of subducted lithosphere are required by the seismic data low velocity anomalies underneath for instance hawaii iceland and africa show varying degrees of robustness