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

tectonic setting of synorogenic gold deposits of the pacific rim abstract more than 420 million oz of gold were concentrated in circum pacific synorogenic quartz lodes mainly during two periods of continental growth one along the gondwanan margin in the palaeozoic and the other in the northern pacific basin between 170 and 50 ma these ores have many features in common and can be grouped into a single type of lode gold deposit widespread throughout clastic sedimentary rock dominant terranes the auriferous veins contain only a few percent sulphide minerals have gold silver ratios typically greater than 1 1 show a distinct association with medium grade metamorphic rocks and may be associated with large scale fault zones ore fluids are consistently of low salinity and are co2 rich in the early and middle palaeozoic in the southern pacific basin a single immense turbidite sequence was added to the eastern margin of gondwanaland deformation of these rocks in southeastern australia was accompanied by deposition of at least 80 million oz of gold in the victorian sector of the lachlan fold belt mainly during the middle and late devonian lesser devonian gold accumulations characterized the more northerly parts of the gondwanan margin within the hodgkinson broken river and thomson fold belts additional lodes were emplaced in this flyschoid sequence in devonian or earlier palaeozoic times in what is now the buller terrane westland new zealand minor post devonian growth of gondwanaland included terrane collision and formation of gold bearing veins in the permian in australia s new england fold belt and in the jurassic early cretaceous in new zealand s otago schists collision and accretion of dozens of terranes for a 100 m y long period against the western margin of north america and eastern margin of eurasia led to widespread latest jurassic to eocene gold veining in the northern pacific basin in the former location late jurassic and early cretaceous veins and related placer deposits along the western margin of the sierra nevada batholith have yielded more than 100 million oz of gold additional significant ore forming events during the development of north america s cordilleran orogen included those in the klamath mountains region california in the late jurassic and early cretaceous the klondike district yukon by the early cretaceous the nome and fairbanks districts alaska and the bridge river district british columbia in the middle cretaceous and the juneau gold belt alaska in the eocene gold bearing veins deposited during the late jurassic and early cretaceous terrane collision that formed the present day russian far east have been the source for more than 130 million oz of placer gold the abundance of gold bearing quartz carbonate veins throughout the gondwanan north american and eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata the common temporal association between gold veining and magmatism around the pacific rim reflects these thermal episodes melting of the lower thickened crust during arc formation slab rollback and extensional tectonism and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initiation of the ore forming processes

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

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

evolution from an oblique subduction back arc mobile belt to a highly oblique collisional margin the cenozoic tectonic development of thailand and eastern myanmar

measurements of salinity and volume of brine excluded from growing sea ice the volume of brine excluded from growing sea ice and its salinity were measured using a brine sampler the measurements were made in both laboratory and field under various growth conditions of the sea ice the salinity of the brine becomes higher and the volume flux decreases as the sea ice growth rate decreases consequently the salt flux of the brine decreases with decreasing growth rate in the case of sea ice growth at a constant rate as the sea ice becomes thicker the salinity of the brine excluded increases while its volume flux decreases however the salt flux is nearly independent of the ice thickness increase at least up to a thickness of 15 cm for sea ice growth rates between 1 7 10 5 and 1 4 10 4 cm s 1 and for a seawater salinity of 33 0 the brine salinity ranged from 42 3 to 92 7 the volume flux ranged from 6 3 10 6 to 3 4 10 5 cc cm 2 s 1 and the salt flux ranged from 6 4 0 7 to 1 5 10 6 g cm 2 s 1

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

global test of seismic event locations using three dimensional earth models to prepare to update location procedures at the international seismological centre isc we conduct a global test of location accuracy using two 3d earth models and three 1d models jeffreys bullens j b preliminary reference earth model prem ak135 with initial phase arrival times from different distance ranges the 3d models include one spherical harmonic model and one irregular grid model representing two important alternative model parameterizations our tests include a worldwide distribution of reference events from a previous study by smith and ekstrom 1996 and the ground truth database of the prototype international data centre for each test we use phase arrival times associated with the events in the isc bulletin and recompute hypocenters with the same algorithm used in the isc operations with teleseismic arrival times alone 25 the overall accuracy of our recomputed hypocenters is similar using either of the 3d models the teleseismic hypocenters from 3d models are on an average closer to the reference locations than the hypocenters computed using any of the 1d models but the improvement in results using ak135 is small when we use the irregular grid model with teleseismic regional and local initial arrival times together and fix to reference depths the accuracy of the epicenters is improved over the results with teleseismic times alone with a 3d model we are able to invert for depth for a larger fraction of earthquakes and our newly computed depths are more tightly clustered in a subduction zone than depths from the isc bulletin but not as tightly as depths computed by engdahl et al 1998 who used depth phases as well as direct phases in a test of all the locatable events from 1 month of the isc bulletin the irregular grid model improved residuals and formal location uncertainties without introducing large systematic changes in the hypocenters

joint seismic tomography for bulk sound and shear wave speed in the earth s mantle high quality p and s travel times are now available from careful reprocessing of data reported to international agencies a restricted data set has been extracted for which comparable ray coverage is achieved for p and s and used for a joint inversion to produce a three dimensional model for shear and bulk sound velocities represented in terms of 2 2 cells and 18 layers in depth through the mantle about 106 times for each of p and s are combined to produce 312 549 summary rays for each wave type linearizing about the ak135 reference model 583 200 coupled tomographic equations are solved using an iterative partitioned scheme clear high resolution images are obtained for both bulk sound speed and shear wavespeed the bulk and shear moduli have differing sensitivity to temperature and mineral composition and so the images of the two velocity distributions help to constrain the nature of the processes which produce the variations different heterogeneity regimes can be recognised in the upper mantle the transition zone most of the lower mantle and the lowermost mantle in the upper mantle many features can be explained by thermal effects but in some orogenic zones e g western north america the opposite sense of the bulk sound and shear wave speed variation requires compositional effects or volatiles to outweigh any thermal effects in the lower mantle pronounced narrow structures which may represent remnant subduction are most marked in shear the level of large scale variations in bulk sound speed compared to shear diminishes with depth in the lower mantle reaching a minimum near 2000 km below this depth the variability of both wave speeds increases near the core mantle boundary the variations of the two wave speeds show little concordance suggesting the presence of widespread chemical heterogeneity

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

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

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

influence of the st lawrence island polynya upon the bering sea benthos the influence of a polynya a persistent ice free region on water column production and subsequent transport to the shallow continental shelf benthos of the bering sea was evaluated by studying spatial patterns of organic material deposition benthic biomass community sediment metabolism benthic population structure and other potential indicators of enhanced organic carbon transport to benthic communities underlying the st lawrence island polynya despite suggestions that polynyas may be important localized centers of primary production in polar waters we found that the st lawrence island polynya does not obviously enhance the biomass of benthic communities directly below the polynya however southward flowing baroclinic currents generated as a result of brine injection at the polynya edge do appear to have an influence on the biomass and ecological structure of bering sea benthic communities south of st lawrence island these currents appear to affect mean sediment oxygen consumption surface organic carbon nitrogen ratios total organic content and bottom water ammonia by sweeping phytodetrital matter south and to the west of the island a particle reactive short lived natural radioisotope 7be used as an indicator of rapid days to weeks deposition of particulate material from the water column was detected only in surface sediments to the southwest of the island indicating enhancement of particle deposition to the southwest of the island finally the 18o content of tunicate cellulose was highest in the polynya region consistent with increased filter feeding in the late winter when the polynya is present and presumably promoting primary production in the open water the anadyr current consisting of nutrient rich deeper bering sea water that is upwelled onto the shelf in the gulf of anadyr flows west to east in the region south of st lawrence island throughout the year and is the major forcing function for high production in the region the interaction of anadyr water with the winter spring ephemeral polynya and associated baroclinic currents combine to positively influence benthic communities

using interstation amplitude correction factors to predict regional phase amplitudes abstract developing regional discriminants at any given seismic station requires a ground truth database of waveforms from both earthquakes and explosions recently installed stations used for seismic monitoring have no single charge explosions on which to base discriminants we have developed a procedure to map regional seismic amplitudes from surrogate stations which have a long recording history to newly installed operational stations this procedure uses an interstation amplitude correction factor iacf computed using a set of commonly recorded calibration earthquakes between the surrogate and operational station pair to predict seismic amplitudes at the new station using the iacf and historical explosion amplitudes from the surrogate station we tested the method using an earthquake aftershock sequence in pakistan recorded at the kyrgyzstan broadband seismic network the aftershocks had a range of depths and were clustered in a linear trend defining the fault rupture plane of the mainshock we computed iacfs for all possible station combinations at knet 45 combinations for all events and then computed a mean iacf value for each station pair using the mean iacf values we calculated predicted phase amplitudes at each station and compared the predictions to the actual values the observed predicted relationship performed well r 2 values 0 8 for all phases and frequency bands at frequencies above 6 hz the observed predicted relationship showed more scatter a trend not due to interstation distance source depth or spatial location of the calibration earthquakes we were able to reduce scatter in the observed predicted relationship by applying path corrections to the data suggesting that sensitivities in differing paths between certain surrogate operational station combinations do play a role in the effectiveness of the method we used this methodology to predict explosion values at the lop nor nuclear test site in china using a suite of nearby calibration earthquakes to calculate iacf values the results indicate good correlation between the observed and predicted amplitudes suggesting that the method can be used to simulate explosion characteristics at stations that have never recorded explosions comparing the iacf values from the calibration dataset near lop nor to those calculated for the earthquakes in pakistan we see some similarity for certain station combinations however on the whole there are differences that suggest that iacfs have a spatial variance and must be tuned to the region and path of interest for the method to be successful

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

pn and sn tomography across eurasia to improve regional seismic event locations abstract this paper has three motivations first to map p n and s n velocities beneath most of eurasia to reveal information on a length scale relevant to regional tectonics second to test recently constructed 3 d mantle models and third to develop and test a method to produce p n and s n travel time correction surfaces which are the 3 d analogue of travel time curves for a 1 d model our third motive is inspired by the need to improve regional location capabilities in monitoring nuclear treaties such as the nuclear comprehensive test ban treaty ctbt to a groomed version of the isc neic data we apply the tomographic method of barmin et al pure appl geophys 2001 augmented to include station and event corrections and an epicentral distance correction the p n and s n maps are estimated on a 1 1 grid throughout eurasia we define the phases p n and s n as arriving between epicentral distances of 3 and 15 after selection the resulting data set consists of about 1 250 000 p n and 420 000 s n travel times distributed inhomogeneously across eurasia the rms misfit to the entire eurasian data set from the p n and s n model increases nearly linearly with distance and averages about 1 6 s for p n and 3 2 s for s n but is better for events that occurred on several nuclear test sites and for selected high quality data subsets the p n and s n maps compare favorably with recent 3 d models of p and s in the uppermost mantle and with recently compiled teleseismic station corrections across the region the most intriguing features on the maps are the low velocity anomalies that characterize most tectonically deformed regions such as the anomaly across central and southern asia and the middle east that extends along a tortuous path from turkey in the west to lake baikal in the east these anomalies are related to the closing of the neo tethys ocean and the collision of india with asia the uppermost mantle beneath the pacific rim back arc is also very slow presumably due to upwelling that results from back arc spreading as is the red sea rift the tyrrhenian sea and other regions undergoing active extension

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

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

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

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

dike swarms on seward peninsula alaska and their implications for the kinematics of cretaceous extension in the bering strait region late cretaceous dike swarms on seward peninsula northwestern alaska represent the youngest local manifestation of a 115 75 ma magmatic event in the bering strait region magmatism accompanied and followed high grade metamorphism and ductile deformation a late cretaceous extensional tectonic setting for the region is suggested by the thickness and seismic reflection characteristics of the crust regional basin development formation of high strain tectonites with subhorizontal foliations bimodal magmatism and dike swarms the orientation of the dike swarms is used to address the kinematics of extension a diabase dike swarm in the kigluaik mountains consists of dikes that strike northeast 040 and dip steeply phenocrysts include plagioclase clinopyroxene orthopyroxene and hornblende geochemical data indicate that sio2 ranges from 48 to 56 and k2o from 1 2 to 4 0 the dikes are geochemically similar to the mafic to intermediate root of the 90 ma kigluaik pluton sr and nd isotope data show that initial 87 sr 86 sr ranges from 0 7070 to 0 7077 and initial end ranges from 0 85 to 2 90 field relations and 40 ar 39 ar geochronology bracket the dike ages between 90 and 84 ma diabase dikes in the york mountains are associated with normal faults that strike east west to east northeast dikes in the bendeleben mountains are both mafic and felsic but their orientations are unknown alkalic dikes in the darby mountains strike 030 050 similar to those in the kigluaik mountains regional relationships including the orientation of dikes normal faults mineral stretching lineations and other shear sense indicators suggest that between 110 and 90 ma extension on seward peninsula was generally oriented north south to north northwest south southeast

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

40 ar 39 ar thermochronology of white mica from the nome district alaska the first ages of lode sources to placer gold deposits in the seward peninsula

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