seismic structure of the crust and uppermost mantle of north america and adjacent oceanic basins a synthesis we present a new set of contour maps of the seismic structure of north america and the surrounding ocean basins these maps include the crustal thickness whole crustal average p wave and s wave velocity and seismic velocity of the up permost mantle that is pn and sn we found the following 1 the average thickness of the crust under north america is 36 7 km standard deviation s d 8 4 km which is 2 5 km thinner than the world average of 39 2 km s d 8 5 for continental crust 2 histograms of whole crustal p and s wave velocities for the north amer ican crust are bimodal with the lower peak occurring for crust without a high velocity 6 9 7 3 km sec lower crustal layer 3 regions with anomalously high average crustal p wave velocities correlate with precambrian and paleozoic orogens low average crustal velocities are correlated with modern extensional regimes 4 the average pn velocity beneath north america is 8 03 km sec s d 0 19 km sec 5 the well known thin crust beneath the western united states extends into north west canada 6 the average p wave velocity of layer 3 of oceanic crust is 6 61 km sec s d 0 47 km sec however the average crustal p wave velocity under the eastern pacific seafloor is higher than the western atlantic seafloor due to the thicker sediment layer on the older atlantic seafloor

crustal structure of the western new england appalachians and the adirondack mountains we present an interpretation of the crustal velocity structure of the new england appalachians and the adirondack mountains based on a seismic refraction wide angle reflection experiment in eastern north america extending from the adirondacks in new york state through the northern appalachians in vermont and new hampshire to central maine modeling of the eastern portion of the profile within the new england appalachians shows a subhorizontal layered crust with upper crustal velocities ranging from 5 5 to 6 2 km s a midcrustal velocity of 6 4 km s and a lower crustal velocity of approximately 6 8 km s crustal thickness increases from 36 km beneath maine to 40 km in vermont little evidence is seen for structures at depth directly related to the white mountains or the green mountains a major lateral velocity change in the upper and mid crust occurs between the appalachians and the adirondacks this boundary projecting to the surface beneath the champlain valley dips to the east beneath the green mountains and extends to a depth of 25 km below the eastern edge of the connecticut valley synclinorium in vermont the tahawus complex a series of strong horizontal reflections at 18 24 km depth beneath the adirondack highlands is seen to dip eastward beneath vermont upper crustal rocks in the adirondack mountains have poisson s ratios of 0 28 0 01 that can be correlated with the marcy anorthosite pois son s ratios of 0 24 0 01 calculated for rocks of the connecticut valley synclinorium indicate a siliceous upper crust in vermont the lower crust is considered to be best represented by intermediate to mafic granulites a high poisson s ratio 0 26 0 27 tends to support a mafic lower crust in the new england appalachians this seismic refraction wide angle reflection experiment provides further evidence for the obduction of the allochthonous western appalachian units onto grenvillian crust above a zone of detachment that penetrates at least to midcrustal depths and was the locus of successive paleozoic thrusting

ground motion relations for eastern north america predictive relations are developed for ground motions from eastern north american earthquakes of 4 0 m 7 25 at distances of 10 r 500 km the predicted parameters are response spectra at frequencies of 0 5 to 20 hz and peak ground acceleration and velocity the predictions are derived from an empirically based stochastic ground motion model the relations differ from previous work in the improved empirical definition of input parameters and em pirical validation of results the relations are in demonstrable agreement with ground motions from earthquakes of m 4 to 5 there are insufficient data to adequately judge the relations at larger magnitudes although they are consistent with data from the saguenay m 5 8 and nahanni m 6 8 earthquakes the underlying model parameters are constrained by empirical data for events as large as m 6 8

the complete synthesis of seismic crustal phases at regional distances using a new method to evaluate green s functions for elastic layered media we compute complete synthetic seismograms at regional distances for an earthquake in the earth crust we choose as source parameters the ones inferred for an earthquake in central france and compare the computed seismograms to the ones recorded at several short period stations of the french seismic network the major features of the records including complexity and duration are well reproduced by the synthetics lg waves which are the prominant phase are shown to be guided waves made up of sh and sv waves incident on the moho at angles of incidence more grazing than the critical angle and multiply reflected within the crust the length of the computed lg wave coda extends between group velocities of 3 5 and 2 8 km s and is in good agreement with the data

crustal structure of accreted terranes in southern alaska chugach mountains and copper river basin from seismic refraction results seismic refraction data were collected along a 320 km long transect line in southern alaska crossing the prince william chugach peninsular and wrangellia terranes and along several shorter lines within individual terranes velocity structure in the upper crust less than 9 km depth differs among the four terranes in contrast layers in the middle crust 9 to 25 km depth in some cases extend across projected terrane boundaries the following observations can be made 1 an intermediate velocity layer 6 4 km s at 9 km depth extends across the deep projection of the suture between the chugach and peninsular terranes suggesting that the northern chugach and southern peninsular terranes are detached and rest on a deeper terrane of unknown origin 2 the top of a gently north dipping sequence of low and high velocity layers 5 7 7 8 km s more than 10 km thick extends from near the surface in the southern chugach terrane to more than 20 km depth beneath the southern peninsular terrane this sequence truncated by the suture between the prince william and chugach terranes is interpreted to be an underplated terrane made up of fragments of the kula plate and its sedimentary overburden that were accreted during subduction in the late mesozoic and or early tertiary during or between times of accretion of the prince william and chugach terranes 3 a thick crustal root with a laminated sequence at its top extends from a depth of 19 km to as much as 57 km beneath the northern peninsular and wrangellia terranes this root extends across the deep projection of the suture between the peninsular and wrangellia terranes although resolution of this apparent crosscutting relationship is relatively poor this root may represent tectonically or possibly magmatically emplaced rocks the lower crust beneath the prince william chugach and southern peninsular terranes includes a north dipping 3 to 8 km thick section of subducting oceanic crust

seismic amplitude tomography for crustal attenuation beneath china summary amplitude tomography reconstructs seismic attenuation directly from recorded wave amplitudes we have applied the tomography to amplitude data reported in the annual bulletin of chinese earthquakes and interpreted the regionally varying crustal attenuation in terms of tectonics the seismic amplitudes were originally recorded for determining the m l and m s magnitudes they generally correspond to the maximum amplitudes of the horizontal components of the short period s waves and intermediate period rayleigh waves both sets of measurements are sensitive to crustal structure the peak amplitudes from m l amplitudes spread spherically with significant dispersion and scattering m s amplitudes show cylindrical spreading with little dispersion average crustal q values for attenuation at 1 hz are 737 and 505 for m l and m s respectively with substantial regional variations frequency dependence in the attenuation is also indicated regions with the lowest attenuation high q values are beneath the south china block sichuan basin ordos platform the daxinganling and the korea craton these tend to be tectonically inactive regions which are generally dominated by intrusive and cratonic rocks in the upper crust regions with the highest attenuation low q values are beneath bohai basin yunnan eastern songpan ganzi terrain margins of the ordos platform and the qilian shan these are predominantly active basins grabens and fold belts the continental margin also highly attenuates both s and surface waves

seismic attenuation tomography in southwestern china insight into the evolution of crustal flow in the tibetan plateau abstract crustal flow in southwestern china is commonly attributed to the continental collision between the indian and the eurasian plates therefore studying crustal flow in this area can provide valuable insight into the collisional process the quality factor q is an indicator of seismic wave attenuation that provides constraints on lithology rheology and geodynamic processes which are vital for interpreting the nature of the crustal flow in a given region in this study we used local seismic waveforms to obtain regional attenuation models for p qp and s qs waves in the sichuan yunnan region syr the emeishan large igneous province elip is characterized by high qp and qs values in the middle yunnan block myb at depths greater than 5 km the qp and qs values in most of the fault zones surrounding the myb were lower than 300 indicating that the material within crustal faults causes high waveform attenuation our results suggest that the crustal flow was diverted into two channels in the northern myb due to resistance from the elip to illuminate the tectonic dynamics of the syr we propose a simple model that explains both the evolution of the crustal flow and the variation in the seismic wave attenuation

attenuation tomography of the earth s mantle a review of current status resolving the lateral variations of attenuation in the deep mantle by tomographic methods holds potential for constraining its thermal structure and dynamics it is a challenging subject which has been addressed by only a few studies until now we here review the main motivations behind pursuing this challenge the difficult issues involved in separating effects of anelastic attenuation from scattering and focusing due to propagation in 3 d elastic structure and finally discuss the current status of global attenuation tomography

lg attenuation in northeast china using necessarray data nishath r ranasinghe 1 andrea c gallegos 1 andrea r trujillo 1 2 alexander r blanchette 1 eric a sandvol 3 james ni 1 thomas m hearn 1 youcai tang 4 5 stephen p grand 4 fenglin niu 5 6 yongshun j chen 7 jieyuan ning 7 hitoshi kawakatsu 8 satoru tanaka9 and masayuki obayashi9 1department of physics new mexico state university las cruces nm 88001 usa e mail nrana001 nmsu edu 2apache corporation 303 veterans airpark lane 600 midland tx 79705 usa 3department of geological sciences university of missouri 101 geology bldg columbia mo 65211 usa 4jackson school of geosciences the university of texas at austin austin tx 78712 usa 5state key laboratory of petroleum resource and prospecting and unconventional natural gas institute china university of petroleum beijing 102249 china 6department of earth science ms 126 rice university houston tx 77005 usa 7institute of theoretical and applied geophysics sess peking university beijing china 8earthquake research institute the university of tokyo tokyo japan 9institute for frontier research on earth and evolution japan agency for marine earth science and technology yokosuka japan

crustal structure of mainland china from deep seismic sounding data abstract since 1958 about ninety seismic refraction wide angle reflection profiles with a cumulative length of more than sixty thousand kilometers have been completed in mainland china we summarize the results in the form of 1 a new contour map of crustal thickness 2 fourteen representative crustal seismic velocity depth columns for various tectonic units and 3 a pn velocity map we found a north south trending belt with a strong lateral gradient in crustal thickness in central china this belt divides china into an eastern region with a crustal thickness of 30 45 km and a western region with a thickness of 45 75 km the crust in these two regions has experienced different evolutionary processes and currently lies within distinct tectonic stress fields our compilation finds that there is a high velocity 7 1 7 4 km s layer in the lower crust of the stable tarim basin and ordos plateau however in young orogenic belts including parts of eastern china the tianshan and the tibetan plateau this layer is often absent one exception is southern tibet where the presence of a high velocity layer is related to the northward injection of the cold indian plate this high velocity layer is absent in northern tibet in orogenic belts there usually is a low velocity layer lvl in the crust but in stable regions this layer seldom exists the pn velocities in eastern china generally range from 7 9 to 8 1 km s and tend to be isotropic pn velocities in western china are more variable ranging from 7 7 to 8 2 km s and may display azimuthal anisotropy

tomographic inversion of pn travel times in china 1 pn travel times are useful for studying crustal and uppermost mantle structure and regional tectonics because they are affected by crustal velocity and thickness as well as uppermost mantle velocity and anisotropy we obtained 57 740 pn travel time picks from 5433 earthquakes and 307 stations from chinese national and provincial earthquake bulletins and the international seismological center bulletins to invert for pn velocity variation and anisotropy and station delays in china our inversion reveals significant features that correlate with surface geology the main results are as follows 1 the pn velocities show a mosaic of very fast and very slow anomalies mirroring the heterogeneous geology of china at the surface the pn velocities are high beneath the major basins in the west sichuan qaidam west tarim tulufan and junggar and low in areas of active volcanoes myanmar and western yunnan and quaternary volcanism in northern tibet in seismically active areas in north china and tien shan and in the southern part of south china the hainan plume 2 the pn anisotropy beneath the major basins in the west is generally weak strong anisotropy is found beneath high deformation regions the tibetan plateau southeastern margin of the tibetan plateau western tien shan and part of north china suggesting the anisotropy is likely related to recent large scale tectonic activity 3 a large area of north china shows prominent low pn velocity beneath archean basement with thin crust our observations are consistent with rifting lithospheric thinning and mantle upwelling in the region the pn anisotropy is consistent with a dextral simple shear in the nne direction in the lithosphere mantle during the last and ongoing major deformation period 4 the pn velocity in northern tibet is generally lower than that in the south southern tibet has significant e w structure low velocity anomalies can be traced from northern tibet across southwestern tibet and south central tibet to near the india plate anisotropy is absent beneath much of the himalaya block but consistent anisotropy with e w fast direction is present beneath the lhasa block and large anisotropy up to 4 is observed in low velocity regions of the northern and western tibet complex station delays in the eastern margin of the plateau suggest that the whole crust may be highly deformed the anisotropy pattern in the southeastern margin of the tibetan plateau suggests a mantle lithospheric deformation similar to the clockwise rotation of material observed at the surface 5 crustal thicknesses inferred from our station delays are consistent with previous models which correlate well with surface topography

emplacement mechanism and lateral correlation of pyroclastic flow and surge deposits in northen st kitts lesser antilles thick accumulations of pyroclastic deposits have emanated from the mt misery volcano on st kitts lesser antilles during two major eruptive episodes 2 3000 and 41000 a bp systematic logging of coastal sections in the northern part of the island has revealed a variety of deposits including pyroclastic flows surges and intermittent air fall palaeosols and one laterally persistant surge deposit provide important marker horizons permitting correlation of the intervening and less persistent flow deposits block and ash flows traditionally termed nuee ardentes can be subdivided into andesitic pelean type and basaltic andesite st vincent type deposits closely corresponding to the products of historic pyroclastic eruptions in the lesser antilles finer grained ash flows are equally voluminous and comprise scoria semi vesicular andesite and mixed magma and ash deposits a significant pyroclastic surge component has been recognized with characteristic bedforms field evidence suggests that there is a continuous gradation between flow and surge deposits collectively the pyroclastic flow deposits are all of the small volume type and are commonly stratified with poor to moderate sorting and coarse tail grading where thickly developed they show an internal depositional sequence compatible with the standard ignimbrite flow unit well developed bedforms include steeply incised u shaped gullies eroded by the infilling flows the depositional characteristics of these pyroclastic flows appears to be a function of the physical properties of the magma on eruption initial flow magnitude potential energy and degree of topographic channel formation in general grain size and the erosive potential of the flow increases with increasing channel formation whilst sorting and the degree of stratification decrease the development of graded bedding is however apparently unaffected

application of regional phase amplitude tomography to seismic verification we have applied tomographic techniques to amplitude data to quantify regional phase path effects for use in source discrimination studies tomography complements interpolation kriging methods by extending our ability to apply path corrections into regions devoid of calibration events as well as raising levels of confidence in the corrections because of their more physical basis our tomography technique solves for resolvable combinations of attenuation source generation site and spreading terms first difference regularization is used to remove singularities and reduce noise effects in initial tests the technique was applied to a data set of 1488 1 0 hz p g l g amplitude ratios from 13 stations for paths inside a 30 by 40 box covering western china and surrounding regions tomography reduced variance 60 relative to the power law distance correction traditionally applied to amplitude ratios relative p g l g attenuation varied with geologic region with low values in tibet intermediate values in basins and high values for platforms and older crust spatial patterns were consistent with previous path effect studies in asia especially local earthquake coda q relative spreading was consistent with expected values for p g and l g relative site terms were similar to one another yet some tradeoff with attenuation was evident tomography residuals followed systematic trends with distance which may result from the evolution from direct to coda phases focusing model tradeoff or data windowing effects examination of the residuals using a kriging interpolator showed coherent geographical variations indicating unmodeled path effects the residual patterns often follow geological boundaries which could result from attenuating zones or minor blockages that are too thin to be resolved or that have anisotropic effect on regional phases these results will guide efforts to reparameterize tomography models to more effectively represent regional wave attenuation and blockage the interpolated residuals also can be combined with predictions of the tomographic model to account for path effects in discrimination studies on a station by station basis

seismic lg wave q tomography in and around northeast china 1 we investigate regional variations in the lg wave quality factor q in northeast china and its vicinity with a tomographic method digital seismic data recorded at 20 broadband stations from 125 regional events are used to extract lg wave spectra tomographic inversions are independently conducted at 58 discrete frequencies distributed log evenly between 0 05 and 10 0 hz we simultaneously invert for the lg wave q distribution and source spectra at individual frequencies without using any a priori assumption about the frequency dependence of the q model and source function the best spatial resolution is approximately 1 1 in well covered areas for frequencies between 0 4 and 2 0 hz the lg q shows significant regional variations and an apparent relationship with regional geology we use a statistical method to investigate the regional variations of lg q and their frequency dependence the average q0 1 hz lg q in the entire investigated region is 414 sedimentary basins are usually characterized by lower average q0 values from 155 to 391 while volcanic mountain areas have relatively high average q0 values from 630 to 675 lg q generally increases with increasing frequency however the frequency dependence has complex nonlinear features on a double logarithmic scale indicating that the commonly adopted power law relationship may be oversimplified in a broad frequency band the frequency dependence varies in different geological areas with larger variations seen at lower frequencies

ml amplitude tomography in north china we have selected 10 899 m l amplitude readings from 1732 events re corded by 91 stations as reported in the annual bulletin of chinese earthquakes abce and have used tomographic imaging to estimate the lateral variations of the quality factor q0 q at 1 hz within the crust of northern china estimated q0 values vary from 115 to 715 with an average of 415 q0 values are consistent with tectonic and topographic structure in eastern china q0 is low in the active tectonic regions having many faults such as the shanxi and yinchuan grabens bohai bay and tanlu fault zone and is high in the stable ordos craton q0 values are low in several topographically low lying areas such as the north china taikang hefei jianghan subei yellow sea and songliao basins whereas it is high in mountainous and uplift regions exhibiting surface expressions of crystalline basement rocks the yinshan yanshan taihang qinlin dabie and wuyi mountains and luxi and jiaoliao uplifts quality factor estimates are also consistent with pn and sn velocity patterns high velocity values in general correspond with high q0 and low velocity values with low q0 this is consistent with a common temperature influence in the crust and uppermost mantle

mirror symmetry of the crust in the oil gas region of shengli china abstract the concept of mirror image symmetry describes the correlation between the bottom of a sedimentary basin and the top of the underlying mantle the degree of mirror symmetry is analyzed here using thickness data from mesozoic cenozoic sedimentary basins and the moho depth with the purpose of investigating the implications for tectonics and exploratory practices in oil gas bearing basins our attention is focused on different tectonic elements of a multi scale tectonic partition in the oil gas region of shengli southeast of bohai bay china by applying standard least squares analysis methods to both datasets we obtained the average thickness h of the consolidated crust and the mirror symmetry factor a for every tectonic unit thereby allowing us to explore the correlation between the bottom depth of a sedimentary basin and the top of the underlying mantle a detailed analysis of data uncertainties and their potential effects led to small fluctuations of h and a within a narrow band around the mean values of 33 26 km and 1 43 respectively thus the results can be considered valid if they are constrained by these error bounds the issues of crust mantle interaction and the deviation of the crust from isostatic equilibrium are also addressed for their tectonic implications other structural parameters related to the deep rooted crust beneath the tectonic elements that make up the study region such as the ratio r of the thickness of the consolidated crust to the absolute value of the symmetry factor the ratio k of the maximum sediment thickness to the maximum uplift of the mantle and the product kh are also evaluated for their implications in geophysical prospecting the symmetry signature of the crust is compared to the symmetry of other sedimentary basins in china and in the world suggesting symmetry as a feasible prognostic tool in exploration for oil gas reservoirs the key result is that those locations where oil gas reservoirs have been found to date are basins in which the crust mantle interaction is active and the crust is isostatically compensated both of those parameters can be quantitatively constrained conversely oil and gas reserves are poor or nonexistent in regions where the crust mantle interaction is inactive and the crust is far from isostatic equilibrium however an intermediate case between these two extreme scenarios wherein the crust mantle interaction is rather moderate but the crust is in a state close to isostasy cannot be entirely ruled out

an overview of the earth crust under china abstract we assess the results of a number of deep seismic soundings performed in china over the last few decades and study the variations in crustal structure in 18 tectonic units comprised of three platforms and 15 fold systems thickness data on 344 mesozoic cenozoic sedimentary basins as well as data on moho depth are collected in order to discuss the relationship between the thickness of the basins and the average thickness of the consolidated crust in each tectonic unit the degree of mirror image symmetry between mesozoic cenozoic sedimentary basins and the uplifting topmost parts of the mantle is herein analyzed using deep geophysical data on sedimentary basins by applying standard methods of least squares analysis to both datasets we have obtained both the average thickness of the consolidated crust and the mirror image symmetry factor for every platform and tectonic fold system thereby allowing us to explore the correlation between the depths of the bottom of the sedimentary basins and the top of the uplifting mantle the thickness of the consolidated crust in china is found to be between 20 and 63 km following a pattern of gradual thickening from east to west expressed in terms of spatial seismicity and the concentration of seismic energy and according to the sharing out of earthquake hypocenters in the top 80 km of the earth the rheology of the area does not appear to suit the widely accepted jelly sandwich model for the continents which does not seem to be entirely valid in china the findings on the mirror image symmetry factor show that this parameter varies mainly in the range 0 5 to 1 8 compared with each other tectonic unit most of the tectonic systems in china appear to be isostatically compensated tibet is an exception in that the symmetry factor is positive for the gangdise nyainqentanglha 1 0 and himalayan 0 1 fold systems implying that these tectonic zones are far from being in the isostatic equilibrium of the other regions we have also analyzed the zoning characteristics through the logarithmic relationship ln r ln h a using the average thickness of the consolidated crust and the absolute value of the symmetry factor the key finding is that regardless of geographical location all the values of r h a for those sedimentary basins in which oil gas reservoirs have to date been found fall into the narrow range of values between 19 38 and 37 40 there is some appeal in a possible relationship involving the ratio of crustal thickness to symmetry factor more so when the results obtained appear to suggest a prognostic tool for exploratory practice in relation to oil gas reservoirs

mesozoic sedimentary evolution of the northwest sichuan basin implication for continued clockwise rotation of the south china block we present new sedimentary data integrated into a regional mesozoic stratigraphic framework to provide a detailed picture of spatio temporal variations in deposition and depocenter migration of the northwest sichuan basin the mesozoic sedimentary evolution is utilized to interpret basin subsidence history and to unravel coeval basin margin tectonics the northwest sichuan basin together with the songpan ganzi terrane behaved as a passive margin south of the qinling paleo tethys from late paleozoic to early middle triassic times and then evolved into a peripheral foreland basin in response to collision of the north and south china blocks since the late middle triassic coeval with strong north south contraction of the songpan ganzi terrane in the late triassic sinistral transpressional deformation of the longmen shan belt led to flexural subsidence of the adjacent western sichuan basin renewed basin margin fold thrust activity triggered recurrence of flexural subsidence of the northwest sichuan basin since the middle jurassic with the depocenter eventually shifting to the northwestern corner of the basin in the early cretaceous sedimentary evolution of the northwest sichuan basin and the basin margin deformation imply that the south china block had been rotating clockwise relative to the north china block throughout the mesozoic with an interim period of early jurassic tectonic quiescence a model is advanced that invokes clockwise rotation of the south china block as a driver for tectonic evolution of both the basin and adjoining structural belts and provides an explanation for several salient features that are otherwise puzzling

tomographic regionalization of crustal lg q in eastern eurasia 1 we measure q of crustal lg waves in eastern eurasia using the reliable two station methods more than 5 000 spectral ratios are collected over 594 interstation paths and are used to determine values of lg q0 and q at 1 hz and its frequency dependence over these paths these values are used to derive tomographic models of laterally varying q0 and with resolutions between 4 and 10 the q0 model contains values that vary between 100 and 900 q0 are the lowest in the tibetan plateau increase to moderate levels towards the east and north and reach maxima in the siberian and eastern europe cratons q0 values correlate well with regional tectonics most values are between 0 14 and 0 50 with a mean of 0 18 these values are lower than those obtained previously using either an lg coda q method or a method of simultaneous inversion of source spectra and q

the effect of crustal structure on strong ground motion attenuation relations in eastern north america strong ground motion attenuation relations are usually described by smoothly decreasing functions of distance however consideration of wave propagation in the crust suggests that attenuation relations should be more complex such complexity may be present in strong ground motion data for eastern north american earthquakes which show amplitudes in the distance range of 60 to 150 km that lie above the trends at smaller and greater distances using a wavenumber integration method to compute green s functions and close in recordings of several earthquakes as empirical source functions we have generated synthetic seismograms that are in good agreement with regional and strong motion recordings of eastern north american earthquakes from these synthetic seismograms we have shown that the observed interval of relatively high amplitudes may be attributable to postcritically reflected s waves from the moho the presence and location of the interval of relatively high amplitudes is highly dependent on the crustal velocity structure and may therefore be expected to show regional variation however for any realistic structure model there will be a transition in the attenuation relation from an interval at shorter distances less than about 100 km that is dominated by direct waves to an interval at greater distances that is dominated by postcritically reflected waves the synthetic seismograms have response spectral velocities that match those of the recorded data and their m blg values are in good agreement with observed values

attenuation of lg in the western us using the usarray 1 the unprecedented breadth and density of the usarray allows us to resolve lateral variations of 1 hz lg attenuation to 0 5 degrees over much of the western united states we collected over 31 000 lg amplitudes from 547 events and 408 stations of the initial usarray footprint two dimensional tomographic inversion yielded q ranging from 60 to 550 with a variance reduction of 47 relative to the best fit constant q model q 155 q is low over most of the region with lowest values associated with recent volcanic activity and active shear zones high q is found in older stable crust notably the colorado and columbia plateaus while smaller islands of high q are associated with batholiths including the sierra nevada peninsular and bitterroot ranges the western mojave and okanogan highlands as well as other areas of competent crust such as the harcuvar range and two topographically bounded blocks in the basin and range

a novel technique for measuring lg attenuation results from eastern canada between 1 to 10 hz spectral amplitudes of regionally recorded lg waves are studied in detail between 0 6 and 10 hz using vertical component velocity seismograms of the eastern canada telemetered network stations and a supplementary seismic research observatory type station at glen almond gac quebec we find that the site responses vary among these stations by more than a factor of 3 within the frequency range of interest furthermore they are found to be strongly frequency dependent consequently it is essential that they be taken into consideration in studies of lg wave attenuation and lg source spectra of regionally recorded seismic events we present a new method of measuring interstation surface wave attenuation which is closely related to the conventional two station method while retaining all the desirable features of the conventional two station method the new technique which we will call the reversed two station method allows simple direct one parameter determination of the lg wave attenuation from sparse spectral data in a manner unaffected by station site effects and associated instrument error the reversed two station method is successfully tested over weakly attenuating short 53 to 210 km interstation paths in eastern canada a difficult experimental condition by normal standards the lg attenuation coefficient 0 6 to 10 hz in eastern canada is found to be frequency dependent and of the form f 0 0008 f 0 81 km 1 at higher frequencies the lg attenuation appears to be essentially frequency independent this latter finding is preliminarily interpreted as evidence that regionally recorded lg waves in the canadian shield are as in the case of lg waves propagating through the structurally complex appalachian province contaminated by the high frequency coda of sn waves the lg contamination over the shield paths becomes severe starting at 14 hz twice the frequency above which the lg signal propagating over the appalachian province becomes completely dominated by non lg arrivals

lateral variations of crustal seismic attenuation along the indepth profiles in tibet from lg q inversion 1 fourier spectra of crustal guided lg waves are collected to study seismic attenuation or q along the indepth profiles the 1 hz lg q q0 values are measured between many pairs of two stations and input to a back projection algorithm to obtain laterally varying q0 models along the indepth iii profile in central tibet the q0 model consists of low and nearly constant values of 90 these low values are consistent with abnormally high temperature as well as partial melts in the crust along the indepth ii profile in southern tibet the q0 values increase southward they are extremely low 60 over the northernmost segment but increase by a factor of 2 over a distance of 100 km between the indus yalong suture and the kangmar dome farther south and into the high himalayas q0 values are higher than 300 regional rayleigh waves observed along the northern indepth ii profile are used to infer a low velocity low q layer at midcrustal depths between 15 and 30 km in southern tibet the aqueous fluid trapped in the upper crust and a midcrust partial melting zone associated with the underthrusting of the indian lithosphere are the likely causes of the high lg attenuation in southern tibet low q rather then a systematic lg conversion along a dipping moho is the main cause of the previously observed lg blockage over paths crossing the southern tibetan boundary

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

salsa3d a tomographic model of compressional wave slowness in the earth s mantle for improved travel time prediction and travel time prediction uncertainty abstract the task of monitoring the earth for nuclear explosions relies heavily on seismic data to detect locate and characterize suspected nuclear tests motivated by the need to locate suspected explosions as accurately and precisely as possible we developed a tomographic model of the compressional wave slowness in the earth s mantle with primary focus on the accuracy and precision of travel time predictions for p and pn ray paths through the model path dependent travel time prediction uncertainties are obtained by computing the full 3d model covariance matrix and then integrating slowness variance and covariance along ray paths from source to receiver path dependent travel time prediction uncertainties reflect the amount of seismic data that was used in tomography with very low values for paths represented by abundant data in the tomographic data set and very high values for paths through portions of the model that were poorly sampled by the tomography data set the pattern of travel time prediction uncertainty is a direct result of the off diagonal terms of the model covariance matrix and underscores the importance of incorporating the full model covariance matrix in the determination of travel time prediction uncertainty the computed pattern of uncertainty differs significantly from that of 1d distance dependent travel time uncertainties computed using traditional methods which are only appropriate for use with travel times computed through 1d velocity models

yield estimation of the 25 may 2009 north korean nuclear explosion we collect nine vertical component broadband seismograms from the 25 may 2009 north korean nuclear explosion for a regional seismic network in which eight stations also recorded the 9 october 2006 north korean nuclear test comparing the observed waveforms and spectra from the two events we estimate that the amplitudes of the records from the second event are approximately five times those from the first one additionally we use 599 vertical broadband seismograms from 82 regional events recorded on the regional network between december 1995 and may 2009 to calibrate the network lg wave magnitude the calibrated network is used to calculate the lg wave body wave magnitude m b lg 4 53 for the 25 may 2009 north korean nuclear explosion based upon 15 first arrivals from the two north korea nuclear explosions the regional pn velocity in the northeast china north korea region is calculated to be 8 0 km s this result along with the regional geological structures suggests that the north korean test site nkts is located at a relatively stable continental region we thus use a modified fully coupled magnitude yield relation to estimate the explosion yield and the result shows that the yield of the 25 may 2009 north korean nuclear test is approximately 2 35 kt under the minimum burial depth assumption online material epicentral parameters computed m b lg and corrected m b lg for 82 events used in the study

reconciling deep seismic refraction and reflection data from the grenvillian appalachian boundary in western new england abstract the grenvillian appalachian boundary is characterized by pervasive mylonitic deformation and retrograde alteration of a suite of imbricated allochthonous and parautochthonous gneisses that were thrust upon the grenvillian continental margin during the lower paleozoic seismic reflection profiling across this structural boundary zone reveals prominent dipping reflectors interpreted as overthrust basement slices parautochthons of the green mountain anticlinorium in contrast a seismic refraction study of the grenvillian appalachian boundary reveals a sub horizontally layered seismic velocity model that is difficult to reconcile with the pronounced sub vertical structures observed in the green mountains a suite of rock samples was collected from the green mountain anticlinorium and measured at high pressures in the laboratory to determine the seismic properties of these allochthonous and parautochthonous gneisses the laboratory measured seismic velocities agree favorably with the modelled velocity structure across the grenvillian appalachian boundary suggesting that the rock samples are reliable indicators of the rock mass as whole samples of the parautochthonous grenvillian basement exposed in the green mountains have lower velocities by about 0 5 km s than lithologically equivalent units exposed in the eastern adirondack highlands velocity reduction in the green mountain parautochthons can be accounted for by retrograde metamorphic alteration hydration of the paragneisses seismic anisotropies ranging from 2 to 12 in the mylonitized green mountain paragneisses may also contribute to the observation of lower seismic velocities where the direction of ray propagation is normal to the foliation the velocity properties of the green mountain paragneisses are thus insufficiently different from the mantling appalachian allochthons to permit their resolution by the ontario new york new england seismic refraction profile

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

evaluation of nga west2 and chinese ground motion prediction equations for developing seismic hazard maps of mainland chinaevaluation of nga west2 and chinese gmpes for developing seismic hazard maps of mainland china

gravity constraints on the structure of the northern margin of tunisia implications on the nature of the northern african plate boundary summary bouguer gravity data were analysed to determine the general crustal and upper mantle structure in northern tunisia residual gravity anomalies were determined by removing the gravitational effect of crustal thickness variations imaged by regional seismic experiments residual gravity anomalies contain short wavelength anomalies superimposed on a long wavelength component that decreases in amplitude northward towards the tunisian coastline an edge enhancement analysis e g enhanced analytic signals of the short wavelength anomalies suggests a previously unknown east west trending gravity anomaly south of 37 n with source depths of between 3 and 7 km modelling of residual and bouguer gravity anomalies indicate that there are two possible solutions for the residual gravity decrease in northern tunisia 1 thickening of cenozoic and mesozoic sediments north of a strike slip fault or 2 a crustal and uppermantle low density zone interpreted as being crustal material of the remnant subducted african plate the latter result is favoured based on seismic tomographic images of the mediterranean region which implies that subducting material exists under the african coast geological interpretations suggesting that the tell atlas may be a thrust wedge accreted by underplating of the african continental crust and seismic refraction models indicating a thinning of sediments in northern tunisia the east west trending gravity anomalies south of 37 n correspond to an important structural feature that may be related to either a structural boundary e g a transform fault or subduction beneath the african plate

a statistical model for ground motion produced by earthquakes at local and regional distances to adapt random process theory techniques for statistical estimation of peak ground motion to more realistic earth models we constrain the parameters of duration geometrical spreading and spectral shape by modeling the main ground motion as being the result of major contributions by the direct s wave and supercritically reflected s waves the results of our modeling are constrained to be consistent with values from full wave synthetics for the test models the combination of estimation theory and theoretical amplitude spectrum of the main ground motion within the ergodic window successfully predicts the mean peak vertical ground displacements velocities and accelerations of the 1982 miramichi earthquakes in new brunswick canada in addition upon considering the effects of source depth and crustal structure for the november 25 1988 saguenay earthquake m 5 8 in quebec canada the predicted mean peak horizontal ground accelerations match the observed data very well the effects of source depth and crustal structure on the peak ground motion are complicated for different source sizes and at different epicentral distance ranges

along strike variation in subducting plate seismicity and mantle wedge attenuation related to fluid release beneath the north island new zealand abstract we analyze seismicity in the subducted slab of the hikurangi subduction zone along a 600 km length beneath the north island new zealand the volcanic character changes along strike with extremely productive rhyolitic volcanism in the central taupo volcanic zone moderate andesitic volcanism in the northern and south central zones and subduction without volcanism in the southernmost hikurangi zone we have relocated slab earthquakes with 3 d velocity models the relocated seismicity shows more detail of the varied distribution and abundance of slab seismicity which below 50 km depth may be related to embrittlement from high fluid pressure the depth of the buoyant subducted hikurangi plateau ranges from 40 to 140 km depth at depths where the subducting slab interacts with the mantle wedge along arc variation in slab seismicity is a fundamental characteristic with patches of abundant seismicity separated by low seismicity zones the largest most numerous patch at 150 220 km depth underlies a pronounced low qp zone in the mantle wedge which is associated with the rhyolite dominant taupo caldera extensive melt in the region of low qp requires high h 2 o flux from the underlying slab the abundant taupo seismicity suggests a correlation between melt production and regions of earthquake fracture permeability following embrittlement which promote migration of dehydration fluid the hydration history of the incoming slab may be a key factor in producing variations in dehydration and intraslab fluid migration broader extensive outer rise yielding and hydration may have occurred near the approach of the re entrant hikurangi plateau forming the slab section that currently has high seismicity slab seismicity deepens from 240 to 330 km along arc as the subduction rate increases from 40 mm yr the southwestern slab seismicity is bounded by an unusually narrow zone with 110 km depth extent this is inferred to be a dehydration front related to heating at a slab edge that is located 70 km further southwest

crustal structure beneath the eastern margin of the tibetan plateau and its tectonic implications 1 two crustal cross sections through the eastern margin of the tibetan plateau are jointly determined from deep seismic sounding the e w trending line aa passes through the western sichuan plateau including the songpan garze terrane and the longmenshan fault belt and ends in the sichuan basin a part of the yangtze craton line bb has a trend of nne and crosses the songpan garze terrane two dimensional crustal structures along the profiles were jointly determined by the additional use of existing deep seismic sounding data our seismic velocity models indicate that the western sichuan plateau and the sichuan basin have crustal thicknesses of 62 and 43 km average crustal p wave velocities of 6 27 and 6 45 km s and lower crustal vp 6 5 km s thicknesses of 27 and 15 km respectively density models constructed from the seismic velocity models are consistent with observed bouguer gravity anomalies we infer that collision between the tibetan plateau and the yangtze craton has caused thickening of the lower crust and uplift of the western sichuan plateau we detect a low velocity layer in the upper crust of the western sichuan plateau but observe no equivalence in the sichuan basin west dipping thrusts may detach into this low velocity layer the seismic phase pmp in the western sichuan plateau has low amplitude suggesting high attenuation in the lower crust qp of 100 300 we suggest that the high attenuation is a consequence of lower crustal flow caused by the large lower crustal thickness beneath the western sichuan plateau

uncertainty in earthquake source imaging due to variations in source time function and earth structure abstract one way to improve the accuracy and reliability of kinematic earthquake source imaging is to investigate the origin of uncertainty and to minimize their effects the difficulties in kinematic source inversion arise from the nonlinearity of the problem nonunique choices in the parameterization and observational errors we analyze particularly the uncertainty related to the choice of the source time function stf and the variability in earth structure we consider a synthetic data set generated from a spontaneous dynamic rupture calculation using bayesian inference we map the solution space of peak slip rate rupture time and rise time to characterize the kinematic rupture in terms of posterior density functions our test to investigate the effect of the choice of stf reveals that all three tested stfs isosceles triangle regularized yoffe with acceleration time of 0 1 and 0 3 s retrieve the patch of high slip and slip rate around the hypocenter however the use of an isosceles triangle as stf artificially accelerates the rupture to propagate faster than the target solution it additionally generates an artificial linear correlation between rupture onset time and rise time these appear to compensate for the dynamic source effects that are not included in the symmetric triangular stf the exact rise time for the tested stfs is difficult to resolve due to the small amount of radiated seismic moment in the tail of stf to highlight the effect of earth structure variability we perform inversions including the uncertainty in the wavespeed only and variability in both wavespeed and layer depth we find that little difference is noticeable between the resulting rupture model uncertainties from these two parameterizations both significantly broaden the posterior densities and cause faster rupture propagation particularly near the hypocenter due to the major velocity change at the depth where the fault is located online material figures of inverted rupture models trade off curve and posterior probability density function

a back projection method for imaging large scale lateral variations of lg coda q with application to continental africa summary a new method is developed which uses back projection tomography to regionalize large scale lateral variations of coda q for lg waves which have traversed long continental paths successful use of this method requires precise and stable single trace measurements of lg coda q xie nuttli 1988 the method converges rapidly and requires minimal computer storage it also allows quantitative estimation of resolution and error in imaging lateral variations of coda q the spatial resolution of this method is limited by the uneven spatial coverage of the data base by our limited knowledge of lg coda generation and by the trade off between the stability and the spatial resolution of the coda q inversion the method is applied to a large set of digital lg coda data from africa where large scale lateral variations of lg coda q are found to correlate well with major tectonic features most of africa is stable and like other stable regions has relatively high coda q values the lowest values of coda q are associated with the african rift system other regions of low q values include the atlas mountains and cape fold belt regions of mesozoic and younger deformation the lateral variation of frequency dependence of lg coda q correlates in most regions with that of q at 1 hz our analysis of the spatial resolution of this method indicates that the resolving power of lg coda q imaging is comparable to that of velocity tomography using long period surface waves using empirical approaches we estimate that uncertainties in lg coda q and its power law frequency dependence parameter are less than about 60 and about 0 2 respectively for most of africa

density structure of the lithosphere in the southwestern united states and its tectonic significance we calculate a density model of the lithosphere of the southwestern united states through an integrated analysis of gravity seismic refraction drill hole and geological data deviations from the average upper mantle density are as much as 3 a comparison with tomographic images of seismic velocities indicates that a substantial part 50 of these density variations is due to changes in composition rather than temperature pronounced mass deficits are found in the upper mantle under the basin and range province and the northern part of the california coast ranges and adjacent ocean the density structure of the northern and central southern sierra nevada is remarkably different the central southern part is anomalous and is characterized by a relatively light crust underlain by a higher density upper mantle that may be associated with a cold stalled subducted plate high densities are also determined within the uppermost mantle beneath the central transverse ranges and adjoining continental slope the average density of the crystalline crust under the great valley and western sierra nevada is estimated to be up to 200 kg m 3 higher than the regional average consistent with tectonic models for the obduction of oceanic crust and uppermost mantle in this region

joint inversion of receiver functions and surface waves with enhanced preconditioning on densely distributed cndsn stations crustal and upper mantle structure beneath china we present shear wave velocity structure beneath china by joint modeling of teleseismic receiver function and rayleigh wave group velocity dispersion data observed at 1000 permanent broadband seismic stations in the chinese national digital seismic network cndsn a ray parameter based stacking method is employed to minimize artifacts in stacking receiver functions from different sources the rayleigh wave dispersion curve is extracted from group velocity tomographic models at all applicable periods enhanced preconditions are applied on the linearized iterative inversion to regularize and balance multiple types of data the velocity profile inversion at each station starts from an initial model derived from sediments crustal thickness vp vs ratio and pn sn models this multistep approach not only reduces uncertainty and nonuniqueness of the velocity inversion but also efficiently fills information gap in each data set we then generate a 3 d s velocity model by combining and smoothing all the 1 d models the obtained 3 d model reveals crustal and upper mantle velocity structures that are well correlated with tectonic features of china for example our model shows a clear east west bimodal distribution at 35 km deep low velocity in the crust beneath central and eastern tibetan plateau and sedimentary structure in major cratons and basins our model is consistent with existing tomographic models in large scale but provides more structural details in regional and local scales

lithospheric structure beneath trans carpathian transect from precambrian platform to pannonian basin celebration 2000 seismic profile cel05 1 in 2000 a consortium of european and north american institutions completed a huge active source seismic experiment focused on central europe the central european lithospheric experiment based on refraction or celebration 2000 this experiment primarily consisted of a network of seismic refraction profiles that extended from the east european craton along and across the trans european suture zone region in poland to the bohemian massif and through the carpathians and eastern alps to the pannonian basin the longest profile cel05 1420 km is the focus of this paper the resulting two dimensional tomographic and ray tracing models show strong variations in crustal and lower lithospheric structure clear crustal thickening from the pannonian basin 24 25 km thick to the trans european suture zone region 50 km together with the configuration of the lower lithospheric reflectors suggests northward subduction of mantle underlying carpathian pannonian plate under the european plate this however conflicts with strong geological evidence for southward subduction and we present three tectonic models that are to not totally mutually exclusive to explain the lithospheric structure of the area 1 northward old subduction of the pannonian lithosphere under the east european craton in the jurassic lower cretaceous 2 a collisional zone containing a crocodile structure where carpatho pannonian upper crust is obducting over the crystalline crust of the east european craton and the carpathian pannonian mantle lithosphere is underthrusting cratonic lower crust and 3 lithosphere thinning due to the effects of neogene extension and heating with the slab associated with young subduction southward in the miocene having been either detached and or rolled back to the east in the last case the northwestward dipping in the lithosphere can be interpreted as being due to isotherms that could represent the lithosphere asthenosphere boundary in the pannonian region

high resolution regional seismic attenuation tomography in eastern tibetan plateau and adjacent regions 1 the q of regional seismic phases lg and pg within the crust is assumed as a proxy for crustal q and q which is used as a constraint of crustal rheology we measure regional phase q of the eastern tibetan plateau and adjacent areas this method eliminates contributions from source and site responses and is an improvement on the two station method tsm we have generated tomographic images of crustal attenuation anomalies with resolution as high as 1 in general we observe low q in the northernmost portions of the tibetan plateau and high q in the more tectonically stable regions such as the interior of the qaidam basin the calculated site responses appear to correlate with topography or sediment thickness furthermore the relationship between earthquake magnitudes and calculated source terms suggest that the rtm method effectively removes the source response and may be used as an alternative to source magnitude

pgq model for nepal himalaya abstract we investigate the spatial variations of pg attenuation structure in nepal himalaya we implement the two station method on 2325 waveforms obtained from 435 events recorded at 151 stations deployed across nepal himalaya to measure the pg wave quality factor q these station station measurements are inverted further for investigating the spatial variations of pg attenuation using a back projection algorithm the model contains variations across the region with much of the region being dominated by high attenuation it is observed that the areas around the existing faults and lineaments exhibit very low q values a few exceptional high q pockets are observed to be limited predominantly in the north western side of our study area we hypothesize that intrinsic attenuation plays a major role in causing the high apparent pg attenuation in the crust of nepal himalaya this may be mainly caused by highly pressurized fluids trapped within a thin low velocity layer lvl at shallow depths moreover it is interesting to observe that all the past earthquakes of m w 7 since 1934 fall into the regions of low q values but not the lowest it may be anticipated that the very low q areas are too weak to sustain the accumulation of high energy release during a large magnitude earthquake therefore the observed low q structures across the study area may imply a weak crust and subsequently a favorable zone for future rupture

the seismic velocity structure of the newfoundland appalachian orogen the deep structure of the newfoundland appalachian orogen is investigated by analyses of three intersecting seismic refraction wide angle reflection profiles which traverse the gander and dunnage zones or central mobile belt of newfoundland a simultaneous travel time inversion for velocity and interface was applied to the in line seismic refraction wide angle reflection data and constrained by synthetic amplitude models the results of the modeling procedure show a subhorizontally layered crust with upper crustal velocities ranging from 5 4 to 6 2 km s a midcrustal velocity of 6 25 6 35 km s and a lower crustal velocity of 6 7 0 2 km s the top of the lower crust is marked by a series of prominent reflections between 18 and 23 km depth which suggest a complex layered velocity interface strong laterally coherent moho reflections indicate a sharp crust mantle transition at 35 3 km the uppermost mantle has a velocity of 8 0 0 2 km s and a reflecting horizon at 55 km depth suggests an increase to velocities approaching 8 5 km s normal moveout corrections applied to fan profiles provide constraining evidence for the reflecting horizon at the top of the lower crust and laterally continuous moho reflections at 11 12 s two way travel time comparisons with a coincident deep seismic reflection profile show that the refraction and reflection mohos match to better than 2 3 km bulk poisson s ratios of 0 23 0 24 for the whole crust calculated from pmp sms travel times suggest a crust dominated by quartzofeldspathic lithologies and a notable absence of voluminous mafic additions to the lower crust the absence of a deep crustal root coupled with the bulk intermediate composition inferred for the lower crust from the seismic refraction wide angle data implies that the crust beneath central newfoundland has undergone multiple periods of reactivation and equilibration following successive orogenic episodes

surface seismic and electrical methods to detect fluids related to faulting in the absence of drilling surface based geophysical methods are necessary to observe fault zones and fault zone physical properties at seismogenic depths these in situ physical properties can then be used to infer the presence and distribution of fluids along faults although such observations are by nature indirect and become less exact with greater depth multiple observations of a range of such geophysical properties as compressional and shear seismic velocity vp and vs vp v5 ratio related to poisson s ratio resistivity and attenuation in and adjacent to fault zones offer the greatest hope of making inferences of the fault zone geometry fluids in the fault zone and fluid reservoirs in the surrounding crust for simple geometries fault zone guided waves can provide information on fault zone width and velocities for faults of the order of 200 m wide to address the question of whether a narrow fault zone can be imaged well enough at depths of seismic rupture to infer the presence of anomalously high fluid rock ratios we present synthetic seismic tomography and magnetotelluric examples for an ideal case of a narrow fault zone with a simple geometry large changes in material properties and numerous earthquakes within the fault zone a synthetic 0 5 km wide fault zone with 20 velocity reduction is well imaged using local earthquake tomography when sequential velocity inversions are done the true fault width is found even to 9 km depth although the calculated amplitude of the velocity reduction is lower than the actual amplitude vp vs is as well determined as vp magnetotelluric imaging of a synthetic fault zone shows that a conductive fault zone can be well imaged within the upper 10 km further a narrow 1 km very low resistivity 3 ohm m fault core can be imaged within a broad 5 km low resistivity 10 ohm m fault zone illustrating that regions of a fault containing large quantities of interconnected fluids within a broader conductive fault zone should be detectable thus variations in fluid content and fluid pressure can be inferred from electrical and seismic methods but there will always be uncertainty in these inferences due to the trade off with other factors such as intrinsic variations in porosity mineralogy and pore geometry the best approach is combined modeling of varied seismic and electrical data

crustal structure of the southeastern grenville province northern new york state and eastern ontario the grenville province exposes an oblique cross section through mid lower crustal lithologies that were pervasively deformed and subjected to regional thermal overprinting during the grenvillian orogeny 1 1 ga the southeastern grenville province is divided into two subterranes by the carthage colton mylonite zone a 110 km long lineament characterized by intense ductile shear and igneous intrusion which separates the amphibolite facies metasediments of the central metasedimentary belt to the west from the granulite facies metaplutonics of the central granulite terrane to the east the recognition of distinct lithotectonic domains separated by zones of intense ductile shear in the grenville province raises questions concerning the deep structure of these subterranes and in particular the means by which the mid lower crustal rocks exposed in the grenville province were emplaced seismic refraction wide angle reflection data were acquired to investigate the deep structural interrelationships within the southeastern grenville province a travel time inversion for velocity and interface depth was applied to the seismic data together with constraints from amplitude modeling to produce a seismic velocity model of the crust in the southeastern grenville province in the central metasedimentary belt the upper crust is characterized by velocities in the range 6 3 6 4 km s and a poisson s ratio of 0 26 0 01 which are attributed to quartzofeldspathic rocks farther east in the central granulite terrane upper crustal velocities of 6 55 km s and a poisson s ratio of 0 28 0 01 are associated with the marcy anorthosite the seismic homogeneity of the upper crust in the region of the carthage colton mylonite zone suggests that this boundary is a shallow feature limited to the upper 2 3 km of the crust the deep crustal structure of the southeastern grenville province is characterized by two discrete and laterally discontinuous seismic interfaces in the central metasedimentary belt the top of the lower crust is delineated by an eastward dipping interface at 24 28 km depth in the central granulite terrane prominent en echelon reflections referred to as the tahawus complex form a gently arched dome at 17 22 km depth interpretation of the tahawus complex as a zone of layered mafic cumulates is supported by its high velocity 7 1 km s and poisson s ratio 0 27 0 02 the lower crust is characterized by a velocity of 7 0 7 2 km s and an anomalously high poisson s ratio of 0 30 0 02 which are representative of pyroxene garnet granulites in contrast velocities of 6 8 7 0 km s are modeled beneath the central granulite terrane and appear to signify a lateral change in composition the moho lies at 44 45 km depth and is characterized by pronounced en echelon reflection segments suggesting compositional interlayering around the crust mantle boundary the velocity of the upper mantle is 8 0 8 2 km s an anomalous upper mantle layer with a reversed velocity of 8 6 km s dips eastward from 50 to 60 km depth beneath the southeastern grenville province our results indicate that remnants of magmatic intrusions that mobilized and thickened the crust during the grenvillian orogeny are preserved in the mid lower crust as a layered cumulate body tahawus complex and in the upper mantle as an eclogitic lens possibly delaminated from the overthickened crust during uplift of the southeastern grenville province

seismic yield determination of soviet underground nuclear explosions at the shagan river test site summary a study of p and lg based source size estimators has been conducted for 101 presumed underground nuclear explosions at the shagan river test site near semipalatinsk ussr a systematic variation in the relative patterns across the test site has been observed when comparing the p wave estimators world wide mb and ulm and the lg based observations rms lg determined from norsar and grafenberg array recordings these variations correlate well with geological features determined from satellite imagery and suggest in particular that the northeast and southwest portions of the test site divided by the chinrau fault are characterized by distinct geophysical properties a difference in m p mlg bias of as much as 0 15 magnitude units exists between these two subareas available data indicate that the mlg observations are very consistent with published yields and suggest that the magnitude yield relationship for p wave based estimators can be significantly improved by introducing regional bias corrections we have determined such corrections for three subareas of the test site and used the corrected mh and ym observations in combination with the lg data in a weighted averaging scheme to arrive at yield estimates for all events in the database for the explosion of 1988 september 14 we obtain yield estimates from the three estimators ranging from 106 to 118 kt which is consistent with the independently derived estimates of 115 122 kt quoted by sykes ekstrom 1989 a further assessment of the validity of our results would require access to independently measured yields of additional explosions

revisions in the pyroclastic stratigraphy of mt misery volcano st kitts lesser antilles 14c ages and recognition of pyroclastic flow deposits new radiocarbon dates reveal that unlithified pyroclastic deposits erupted from mt misery st kitts principally the mansion series range from older than 42 000 years to younger than 1750 years b p previously published accounts of mt misery have only described air fall deposits however a newly recognized sequence of pyroclastic flow deposits within the mansion series is dated as 2000 to 3000 years b p the presence of these young deposits indicates that mt misery like other lesser antillean volcanoes also has a potential pyroclastic flow volcanic hazard

considerations in phase estimation and event location using small aperture regional seismic arrays the global monitoring of earthquakes and explosions at decreasing magnitudes necessitates the fully automatic detection location and classification of an ever increasing number of seismic events many seismic stations of the international monitoring system are small aperture arrays designed to optimize the detection and measurement of regional phases collaboration with operators of mines within regional distances of the arces array together with waveform correlation techniques has provided an unparalleled opportunity to assess the ability of a small aperture array to provide robust and accurate direction and slowness estimates for phase arrivals resulting from well constrained events at sites of repeating seismicity a significant reason for the inaccuracy of current fully automatic event location estimates is the use of f k slowness estimates measured in variable frequency bands the variability of slowness and azimuth measurements for a given phase from a given source region is reduced by the application of almost any constant frequency band however the frequency band resulting in the most stable estimates varies greatly from site to site situations are observed in which regional p arrivals from two sites far closer than the theoretical resolution of the array result in highly distinct populations in slowness space this means that the f k estimates even at relatively low frequencies can be sensitive to source and path specific characteristics of the wavefield and should be treated with caution when inferring a geographical backazimuth under the assumption of a planar wavefront arriving along the great circle path moreover different frequency bands are associated with different biases meaning that slowness and azimuth station corrections commonly denoted sascs cannot be calibrated and should not be used without reference to the frequency band employed we demonstrate an example where fully automatic locations based on a source region specific fixed parameter template are more stable than the corresponding analyst reviewed estimates the reason is that the analyst selects a frequency band and analysis window which appears optimal for each event in this case the frequency band which produces the most consistent direction estimates has neither the best snr or the greatest beam gain and is therefore unlikely to be chosen by an analyst without calibration data

broad band lg attenuation modelling in the middle east summary we present a broad band tomographic model oflg attenuation in the middle east derived from source and site corrected amplitudes absolute amplitude measurements are made on handselected and carefully windowed seismograms for tens of stations and thousands of crustal earthquakes resulting in excellent coverage of the region a conjugate gradient method is used to tomographically invert the amplitude data set of over 8000 paths over a 45 40 region of the middle east we solve for q variation as well as site and source terms for a wide range of frequencies ranging from 0 5 to 10 hz we have modified the standard attenuation tomography technique to more explicitly define the earthquake source expression in terms of the seismic moment this facilitates the use of the model to predict the expected amplitudes of new events an important consideration for earthquake hazard or explosion monitoring applications the attenuation results have a strong correlation to tectonics shields have low attenuation whereas tectonic regions have high attenuation with the highest attenuation at 1 hz found in eastern turkey the results also compare favourably to other studies in the region made using lg propagation efficiency lg pg amplitude ratios and two station methods we tomographically invert the amplitude measurements for each frequency independently in doing so it appears the frequency dependence of attenuation in all regions is not compatible with the power law representation of q f an assumption that is often made

volcanic hazards on st kitts and montserrat west indies pyroclast flows constitute the main potential hazard on both st kitts and montserrat radiocarbon dating indicates that the last major series of eruptions on st kitts occurred about 2000 years ago although a more recent phase of activity 1620 50 years b p produced the pyroclast surge and blast deposits of the steel dust series on montserrat the last major eruptive episode occurred about 19000 years ago and there is rather uncertain evidence for a small near historic eruption pyroclast flow material tends to have a basaltic andesite composition on st kitts and that of a more siliceous andesite on montserrat at mt misery st kitts the present configuration of the summit region has exercised considerable control over the distribution of pyroclast flows and the western side of the volcano remains the most vulnerable to future activity of this kind the summit morphology of the soufriere hills montserrat is more complex and appears to have changed during relatively recent times making the preferred pathway down the eastern slopes over the less populated side of the island pyroclast falls regarded as a negligible hazard on montserrat may attain a critical destructive thickness of c 50 cm once every few thousand years on st kitts lava flows which may be considered unimportant on montserrat are also likely to be a minor and very infrequent hazard on st kitts

investigation of the moho discontinuity beneath the chinese mainland using deep seismic sounding profiles abstract we herein describe the depth distribution of the moho beneath the chinese mainland determined via compilation and resampling of the interpreted results of crustal p wave velocity structures obtained from deep seismic soundings dsss performed since the pioneering dss work carried out in the qaidam basin in 1958 for the present study 114 wide angle seismic profiles acquired over the last 50 years were collated we included results for crustal structures from several profiles in japan and south korea to improve the reliability of the interpolation of the moho depth distribution our final moho map shows that the depth of the moho ranges from 10 to 85 km the deepest moho discontinuity at approximately 70 85 km beneath the tibetan plateau was formed by ongoing continent continent collision the moho beneath the eastern north china craton at a relatively constant 30 35 km has endured mantle lithosphere destruction the moho depths determined from active seismology are consistent within 3 5 km with results obtained from gravity inversion and surface wave tomography the spatial variation of the moho depth crustal formation and composition of different tectonic blocks contribute to controls on the spatial distribution of the seismicity and rheology in the crust beneath mainland china

estimating the model resolution matrix for large seismic tomography problems based on lanczos bidiagonalization with partial reorthogonalization summary the propack package developed by larsen is able to efficiently and accurately estimate singular values and vectors for large matrices based on the lanczos bidiagonalization with partial reorthogonalization we incorporate the pavtial reorthogonalization package propack package into the double difference seismic tomography code tomodd and estimate the model resolution matrix for large seismic tomography problems compared to previous least squares qr lsqr based methods for estimating the model resolution matrix the propack based method calculates the full resolution matrix and thus gives a complete description of how well the model is resolved several observations are drawn from the application to data from the 2001 eruption of mt etna for this example it is reasonable to use ray sampling density information to characterize the model resolution qualitatively the model resolution resulting from just velocity inversion bears a close linear relationship to that from simultaneous inversion but always overestimates resolution and the inversion system using differential times has a greater ability to resolve the source region structure than the system using absolute times

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

the crust of cathaysia age assembly and reworking of two terranes abstract u pb dating and hf isotope data from detrital zircons have been used to analyse the crustal evolution of the eastern and western parts of the cathaysia block in se china zircons from the oujiang river in eastern cathaysia indicate that the basement is dominantly paleoproterozoic 1850 1870 ma 2100 2400 ma in age with minor archean components it was extensively reworked in jurassic cretaceous time 100 155 ma to produce the widespread yanshanian magmatic suite both the 1850 1870 ma event and the yanshanian magmatism show wide ranges in hf isotope composition consistent with mixing between crustal and juvenile magmas marked downstream changes in the relative proportions of zircon age populations emphasize the care required in using detrital zircon data to estimate continental growth rates zircons from the north river indicate that the crust of western cathaysia was generated mainly during neoproterozoic time although it contains some archean 2500 3500 ma to mesoproterozoic components this crust was strongly reworked during caledonian ca 450 ma indosinian ca 240 ma and early yanshanian ca 160 ma thermal events there is little evidence for juvenile crustal growth in any of these events although the yanshanian granitoids of the eastern and western parts of the cathaysia give similar mean hf model ages consistent with published nd model ages this is a coincidence they have different crustal sources the distinct patterns of crustal evolution suggest that eastern and western cathaysia may represent separate microcontinents accreted to the older yangtze craton and transposed by extensive strike slip faults

shear velocity and vp vs ratio structure of the crust beneath the southern margin of south china continent abstract we here present the results of the inverse modeling of crustal s phases recorded from a 400 km long seismic profile with azimuth nearly n30w from lianxian near hunan province to gangkou island near guangzhou city guangdong province in the southern margin of south china continent the finding in this case is that many shot gathers provided by this wide angle seismic experiment show relatively strong reflected and refracted s phases in particular some crustal refractions sg waves and moho reflections sms waves or simply sm waves the p wave velocity structure of the crust and uppermost mantle was already obtained through the interpretation of vertical component shot gathers now with constraints introduced by the p wave velocity architecture and after picking up s wave traveltime data on the seismograms we have obtained the s velocity model of the crust by adjusting these traveltimes but keeping the geometry of the crustal reflectors our results demonstrate 1 the average crustal s velocity is about 3 64 km s to the northwest of the wuchuan sihui fault and 3 62 km s to the southeast of this fault 2 relatively constant s velocity of about 3 42 km s for the upper crust 3 55 km s for the middle crust and laterally varying shear velocity around 3 82 km s for the lower crust 3 correspondingly vp vs ratio is 1 73 for the upper crust 1 71 for the middle crust and 1 74 for the lower crust both shear velocities and vp vs ratio correlate well with the major active faults that break the study area and show significant changes especially in the upper crust high poisson s ratio 1 8 is observed at shallow depth beneath the minzhong depression to the southeast of the wuchuan sihui fault and the huiyuan depression in the southern margin of south china continent in contrast a very low vp vs ratio 1 68 is observed between 8 and 14 km depth beneath huiyuan at deeper depth a high vp vs ratio 1 76 is observed in the lower crust beneath the minzhong depression

strong lg wave attenuation in the middle east continental collision orogenic belt abstract using lg wave q tomography we construct a broadband crustal attenuation model for the middle east the q lg images reveal a relationship between attenuation and geological structures strong attenuation is found in the continental collision orogenic belt that extends from the turkish and iranian plateau to the pamir plateau we investigate the frequency dependence of q lg in different geologic formations the results illustrate that q lg values generally increase with increasing frequency but exhibit complex relationships both with frequency and between regions an average q lg value between 0 2 and 2 0 hz q lg 0 2 2 0 hz may be a critical index for crustal attenuation and is used to infer the regional geology low q lg anomalies are present in the eastern turkish plateau and correlate well with low pn velocities and cenozoic volcanic activity thus indicating possible partial melting within the crust in this region very strong attenuation is also observed in central iran the afghanistan block and the southern caspian sea this in line with the previously observed high crustal temperature high conductivity layers and thick marine sediments in these areas suggests the high lg attenuation is caused by abnormally high tectonic and thermal activities

resolution uncertainty and whole earth tomography 1 using the arrival times of 10 distinct phases from the international seismological center catalogue p s pp pcp ss scs pkpab pkpbc pkpdf sksac and two sets of differential times ss s410s and ss s660s we estimate the p and s velocity structure of the whole earth mantle outer core and inner core boundary topography of four interfaces within the earth hypocentral relocation parameters and station corrections the entire catalogue is relocated and reassociated using the radial velocity model ak135 both p and s phases are used in the relocation of over 41 000 events in depth isotropic velocity variations within the earth are parameterized by 22 layers lateral variations in shear and compressional velocity within the layers are represented by one of two grids in the mantle each layer is subdivided into 4560 equal volume cells of dimension 3 3 at the equator however in the outer and inner core the cell size is increased to 6 6 this change in grid spacing accounts for decreasing cell volumes with depth and variations in sampling between the mantle and core previous attempts using a fine grid throughout the earth resulted in poor resolution of core structure with the current grid the resolution of velocity heterogeneity in the mantle and outer core is comparable in the upper and midmantle the well resolved cells lie beneath eurasia and a narrow zone surrounding the mantle beneath the pacific basin in the lowest mantle the resolution decreases significantly an examination of the averaging kernels associated with six locations near the base of the mantle reveals the significant lateral and vertical averaging inherent in estimates of compressional velocity in well sampled regions of the outer core we are able to resolve compressional velocity variations in our 6 6 cells however velocity variations in the inner core are poorly constrained at the scale of our blocks in well sampled regions of the mantle and outer core model parameter standard deviations remain below 0 25 for much of the inner core the standard deviations are quite large exceeding 0 5 narrow high velocity anomalies are imaged in the upper mantle associated with subduction zones in a number of locations such as beneath the americas these features extend well into the lower mantle in the outer core heterogeneity is generally lower in magnitude of the order of 0 5 the most notable feature in the outer core is a systematic shift to slightly higher velocity in addition we find a roughly symmetric distribution of heterogeneity at the base of the outer core compressional velocities are generally higher in the equatorial regions and lower at the poles

lg attenuation in the central and eastern united states as revealed by the earthscope transportable array abstract lg waveforms recorded by earthscope s transportable array ta are used to estimate lg q 0 in the central and eastern united states ceus attenuation is calculated based on lg spectral amplitudes filtered at a narrow band from 0 5 to 1 5 hz two station and reverse two station techniques are used to calculate q 0 values 39 events occurring from 2010 to 2012 and ranging from magnitude 3 to magnitude 6 are used in this study 39 258 and 4 627 interstation q 0 values are determined using the two station and reverse two station techniques respectively the results show northeast trending high q 0 regions low attenuation ranging from eastern new mexico to wisconsin regions of low q 0 high attenuation are seen along the minnesota wisconsin border the gulf coastal plain gcp along the south dakota nebraska border and along the oklahoma texas border a positive correlation between heat flow sediment thickness recent tectonic activity fluids and low q 0 was observed areas with low heat flow thin sediment cover no recent tectonic activity and a lack of fluids were observed to have consistently high q 0 these new models use a greater amount of data attain more coverage than previous studies and better constrain attenuation this increase in detail can improve high frequency ground motion predictions of future large earthquakes for more accurate far field hazard assessment and improve the overall understanding of the structure and assemblage of the ceus

shallow seismic structure of kunlun fault zone in northern tibetan plateau china implications for the 2001 ms8 1 kunlun earthquake summary the shallow seismic velocity structure of the kunlun fault zone klfz was jointly deduced from seismic refraction profiling and the records of trapped waves that were excited by five explosions the data were collected after the 2001 kunlun ms8 1 earthquake in the northern tibetan plateau seismic phases for the in line record sections 26 records up to a distance of 15 km along the fault zone were analysed and 1 d p and s wave velocity models of shallow crust within the fault zone were determined by using the seismic refraction method sixteen seismic stations were deployed along the off line profile perpendicular to the fault zone fault zone trapped waves appear clearly on the record sections which were simulated with a 3 d finite difference algorithm quantitative analysis of the correlation coefficients of the synthetic and observed trapped waveforms indicates that the kunlun fault zone width is 300 m and s wave quality factor q within the fault zone is 15 significantly s wave velocities within the fault zone are reduced by 30 45 per cent from surrounding rocks to a depth of at least 1 2 km while p wave velocities are reduced by 7 20 per cent a fault zone with such pand s low velocities is an indication of high fluid pressure because vs is affected more than vp the low velocity and low q zone in the klfz model is the effect of multiple ruptures along the fault trace of the 2001 ms8 1 kunlun earthquake

amplitude ratio tomography for regional phase q 1 we image regional seismic phase attenuation q by extending amplitude ratio techniques which are widely used to determine average q within a sampled region to obtain laterally varying q structure using tomographic techniques the method assumes that source radiation is isotropic and that the amplitude ratios can be modeled by a two dimensional q map and relative site terms application to 2286 1 hz lg amplitudes from 816 events recorded at 35 central and east asia stations yields a misfit of 0 09 log10 units a variance reduction of 73 relative to the uniform q model that best fits the data and laterally varying q from 100 to 1000 with patterns closely following regional geology the image is resolved on average to 2 5 with resolution peaking at 1 5 in the best covered areas which is remarkable given the sparse station geometry employed the high resolution results from the dense distribution of earthquake sources and is aided by the increased confidence in source locations provided by merging catalogs from many different agencies

crustal attenuation within the turkish plateau and surrounding regions the lateral variations of seismic attenuation in the crust of turkey and surrounding regions have been imaged from the inversion of interstation lg q measurements this study develops the first tomographic model for lg q 0 in this region that model is consistent with previous more qualitative lg attenuation models that showed inefficient or blocked lg across the eurasian arabian plate boundary in general the northern arabian platform has low to normal lg q 0 values 250 350 whereas high q 0 values 670 800 occur in the southern arabian plate additionally we have found a dramatic decrease in lg q 0 across the bitlis suture the plate boundary between the arabian and eurasian plates beneath the turkish plateau our high to moderate lg attenuation values q 0 100 200 probably originates from both scattering and intrinsic attenuation due to the tectonic complexity and the widespread young volcanics in the region we conclude that the lowest q 0 values for the east anatolian plateau 70 100 and the portion of western turkey around the menderes massif 60 150 are probably caused by intrinsic attenuation we find low to normal lg q 0 values 150 300 beneath the part of the taurus mountains in western anatolia these higher values may be related to the nature of the crust in the tauride mountain belt we also mapped the lateral variations in lg and observed a fairly consistent negative correlation between and lg q 0 in the northern middle east

exploration in the shetland faeroe basin using densely spaced arrays of ocean bottom seismometers recent exploration activity in the peripheral regions of the shetland faeroe basin offshore northwest scotland has led to the discovery of some of the largest oil reserves on the united kingdom uk continental shelf we present results from two ocean bottom seismometer profiles acquired by mobil north sea ltd across the center of the shetland faeroe basin these data provide a powerful tool for delineating long wavelength velocity variations and thus have potential for reducing the nonuniqueness associated with conventional seismic exploration methods analysis of the first arrival traveltime data using both forward and inverse ray based techniques produces a well constrained velocity depth model of the basin fill we estimate that the uncertainty in the velocity structure is 5 from a series of trial and error perturbations applied to the final models the velocity structure of the faeroe basin has three principal layers 1 a near surface layer with velocities in the range 1 6 to 2 2 km s 2 a 3

crustal radial anisotropy across eastern tibet and the western yangtze craton 1 phase velocities across eastern tibet and surrounding regions are mapped using rayleigh 8 65 s and love 8 44 s wave ambient noise tomography based on data from more than 400 program for array seismic studies of the continental lithosphere and chinese earthquake array stations a bayesian monte carlo inversion method is applied to generate 3 d distributions of vsh and vsv in the crust and uppermost mantle from which radial anisotropy and isotropic vs are estimated each distribution is summarized with a mean and standard deviation but is also used to identify highly probable structural attributes which include 1 positive midcrustal radial anisotropy vsh vsv across eastern tibet spatial average 4 8 1 4 that terminates abruptly near the border of the high plateau 2 weaker 1 0 1 4 negative radial anisotropy vsh vsv in the shallow crust mostly in the songpan ganzi terrane 3 negative midcrustal anisotropy 2 8 0 9 in the longmenshan region 4 positive midcrustal radial anisotropy 5 4 1 4 beneath the sichuan basin and 5 low vs in the middle crust 3 427 0 050 km s of eastern tibet midcrustal vs 3 4 km s perhaps consistent with partial melt is highly probable only for three distinct regions the northern songpan ganzi the northern chuandian and part of the qiangtang terranes midcrustal anisotropy provides evidence for sheet silicates micas aligned by deformation with a shallowly dipping foliation plane beneath tibet and the sichuan basin and a steeply dipping or subvertical foliation plane in the longmenshan region near vertical cracks or faults are believed to cause the negative anisotropy in the shallow crust underlying tibet

spectral inversion of lg from earthquakes a modified method with applications to the 1995 western texas earthquake sequence spectral inversion of lg from earthquake sources is subject to significant errors due to random and systematic deviation of the lg spectra from idealized theoretical models i present an analysis of these errors and demonstrate that their effects tend to increase with decreasing frequency and recording distance i propose modifications to the inverse method of xie 1993 to reduce these errors the modifications include a more robust q estimator and the added capability of incorporating a priori knowledge into the inversion the modified method is applied to lg spectra from the 1995 western texas earthquake mw 5 7 i measured average two station q values for selected station pairs as well as the source rise time of the mainshock with an empirical green s function approach these served as a priori knowledge for the simultaneous inversion for lg seismic moment m corner frequency fc and path q the result of the inversion indicates that lg source radiation is nearly isotropic the m and fc values estimated using lg from the mainshock and two aftershocks are typical for lg from central and eastern north american earthquakes with m scaling with fc 4 and m and fc being 3 3 1016 n m and 0 3 hz respectively for the mainshock the 1 hz lg q correlates with tectonic environments increasing from about 200 for westerly paths to above 700 for easterly paths two station q measurements suggest that as previously discovered for eurasia the frequency dependence of lg q may be variable with distance if the distance spans a wide range 103 km

radiocarbon redating of contaminated samples from a tropical volcano the mansion series of st kitts west indies heavy rainfall and dense vegetation on tropical volcanoes produce abundant carbonized wood in pyroclastic deposits in addition to easy contamination of this wood by root systems and soluble humic material because the physical nature of the charcoal varies some samples are more prone to contamination two independent studies of the same volcano mt liamuiga on st kitts in the lesser antilles sometimes using samples from the same carbonized tree yielded a systematic difference in radiocarbon ages an exchange of samples and a re investigation of three physically distinct types of charcoal yielded the following results rare hard dense charcoal lacking contamination which had yielded a spurious age of 2860 years bp was redated at 1845 58 years bp common soft friable charcoal with good cellular structure proved to be susceptible to contamination a field decontamination technique utilized by one group seems significant as it yields older ages than when only routine laboratory pre treatment was used indicating that the latter technique only partly removes the dried and hard residue produced by the decomposition of modern plant rootlets a previous date of 24870 years bp obtained from powdery charcoal in a horizon beneath the mansion series contradicted ages older than 41000 years bp from common friable charcoal in the lower mansion series the soft powdery charcoal was re investigated using a sample collected a few centimeters from the original although field decontamination of this sample was not possible more extensive laboratory treatment yielded an age of ca 43000 years bp again proving that routine laboratory pretreatments are inadequate a revised geochronology for the mansion series is described and a cautionary discussion is presented for the benefit of investigators using radiocarbon ages to date volcanic deposits

yield estimates of nevada test site explosions obtained from seismic lg waves a methodology is presented for determining the yield of underground nuclear explosions from lg wave amplitudes the methodology is applied to nevada test site nts explosions for which the data from short period vertical component analog seismographs at three stations are used to develop calibration curves for unsaturated material and water saturated rock source conditions the latter curves are found to provide reasonably accurate estimates of the yields of explosions in other areas of the united states and in the french sahara suggesting that they may be applicable to all continental areas if so they also can provide an estimate of the bias of mb p magnitudes between different continental sites for example the lg data from nts explosions indicate a 0 31 0 02 magnitude unit bias between nts and eastern north america similar to the approximately 0 33 unit bias found between western and eastern north america previously by use of earthquake data

why is it downhill from tonopah to las vegas a case for mantle plume support of the high northern basin and range a major abrupt southward decline in elevation 800 m with an accompanying increase in bouguer gravity anomaly 80 mgal crosses a seismically active region of southern nevada at about 37 n the steepness of the gravity gradient requires significant crustal density contrast some of which is probably caused by the plutonic roots of voluminous tertiary volcanism to the north but the amplitude of the anomaly requires additional contrast within the mantle the topographic step probably developed in mid miocene time coincident with the arrival of the starting head of the yellowstone thermal plume at the base of the lithosphere a plausible combination of crustal and deep buoyancy sources related to the heat and melt input of an anomalously hot asthenospheric source is consistent with gravity seismic heat flow and isotopic observations and explains the origin of the topographic step

a crustal model of the ultrahigh pressure dabie shan orogenic belt china derived from deep seismic refraction profiling we present a new crustal cross section through the east west trending ultrahigh pressure uhp dabie shan orogenic belt east central china based on a 400 km long seismic refraction profile data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35 km thick crust consisting of three layers upper middle and lower crust with average seismic velocities of 6 0 6 0 2 km s 6 5 6 0 1 km s and 6 8 6 0 1 km s the crust reaches a maximum thickness of 41 5 km beneath the northern margin of the orogen and thus the present day root beneath the orogen is only 6 5 km thick the upper mantle velocity is 8 0 6 0 1 km s modeling of shear wave data indicate that poisson s ratio increases from 0 24 6 0 02 in the upper crust to 0 27 6 0 03 in the lower crust this result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies our seismic model indicates that eclogite which is abundant in surface exposures within the orogen is not a volumetrically significant component in the middle or lower crust much of the triassic structure associated with the formation of the uhp rocks of the dabie shan has been obscured by post triassic igneous activity extension and large offset strike slip faulting nevertheless we can identify a high velocity 6 3 km s zone in the upper 5 km depth crustal core of the orogen which we interpret as a zone of ultrahigh pressure rocks a north dipping suture and an apparent moho offset that marks a likely active strike slip fault

crust upper mantle seismic velocity structure across southeastern china abstract one in line wide angle seismic profile was conducted in 1990 in the course of the southeastern china continental dynamics project aimed at the study of the contact between the cathaysia block and the yangtze block this 380 km long profile extended in nw se direction from tunxi anhui province to wenzhou zhejiang province five in line shots were fired and recorded at seismic stations with spacing of about 3 km along the recording line we have used two dimensional ray tracing to model p and s wave arrivals and provide constraints on the velocity structure of the upper crust middle crust lower crust moho discontinuity and the top part of the lithospheric mantle p wave velocity s wave velocity and v p v s ratio are mapped the crust is 36 km thick on average albeit it gradually thins from the northwest end to the southeast end offshore of the profile the average crustal velocity is 6 26 km s for p waves but 3 6 km s for s waves a relatively narrow low velocity layer of about 4 km of thickness with p and s wave velocities of 6 2 km s and 3 5 km s respectively marks the bottom of the middle crust at a depth of 23 km northwest and 17 km southeast at the crust mantle transition the p and s wave velocity change quickly from 7 4 to 7 8 km s northwest and 8 0 to 8 2 km s southeast and from 3 9 to 4 2 km s northwest and 3 9 to 4 5 km s southeast respectively this result implies a lateral contrast in the upper mantle velocity along the 140 km sampled by the profile approximately the average v p v s ratio ranges from 1 68 1 8 for the upper crust to 1 75 for the middle and 1 75 1 85 for lower crust with the interpretation of the wide angle seismic data jiangshan shaoxin fault is considered as the boundary between the yangtze and the cathaysia block

crustal flow pattern beneath the tibetan plateau constrained by regional lg wave q tomography abstract as a prominent geophysical anomaly unusually high seismic wave attenuation is observed in the crust and upper mantle of the tibetan plateau particularly along its northern area theoretical and laboratory investigations show that the strong seismic attenuation can indicate high temperatures and partial melting which may decrease the viscosity of the material and cause it to flow thus seismic attenuation distribution may provide useful constraints to the crust flows if they exist using lg wave q tomography we construct a 0 05 10 0 hz broadband high resolution crust attenuation model for the tibetan plateau and its surrounding regions the maximum spatial resolution is approximately 1 0 1 0 in well covered areas and for frequencies between 0 05 and 1 5 hz this attenuation model reveals an apparent low qlg belt stretching along the northern and eastern tibetan plateau combining the lg wave q model with other geophysical data two possible crust flow channels are found in the tibetan plateau the main flow channel is from north to east and then turns to southeastern tibet along the western edge of the rigid sichuan basin while a second channel starts from southern tibet and crosses the eastern himalayan syntaxis

lith5 0 a revised crustal model for canada based on lithoprobe results summary during the last 15 yr numerous seismic refraction experiments have been conducted overthe canadian landmass most as part of the lithoprobe initiative the new results providethe basis for revising existing global models of crustal structure e g crust5 1 mooney et al 1998 which do not incorporate the new lithoprobe data the crustal model discussedhere lith5 0 combines the lithoprobe and crust5 1 data to provide better constraints oncrustal structure in canada the objectives of the study are to 1 compile available new datainto a single consistent database of crustal thickness and velocity including the uppermostmantle pn velocity and 2 to construct a revised 5 5 crustal model of the canadianlandmass in a format that is generally compatible with existing global models the lithoproberesults suggest a 5 5 km average root mean square rms crustal thickness difference betweenlith5 0andcrust5 1 evenwiththeincorporationofthenewdata thegeographiccoveragein north and central canada remains sparse the new model does not explicitly incorporategeological constraints but instead relies on spherical spline interpolation for extrapolatingvalues into regions that lack control to illustrate the implications of this new crustal model we use lith5 0 to correct for the isostatically compensated crustal heterogeneity in order toobtain improved estimates of the dynamic surface topography the latter provides importantconstraints on the density structure of the uppermost mantle