cenozoic deformation of the tarim plate and the implications for mountain building in the tibetan plateau and the tian shan 1 the tarim basin in nw china developed as a complex foreland basin in the cenozoic in association with mountain building in the tibetan plateau to the south and the tian shan orogen to the north we reconstructed the cenozoic deformation history of the tarim basement by backstripping the sedimentary rocks two dimensional and three dimensional finite element models are then used to simulate the flexural deformation of the tarim basement in response to the sedimentary loads and additional tectonic loads associated with overthrusting of the surrounding mountain belts the results suggest that uplift of both the western kunlun shan and the tian shan orogens started during or before oligocene since the miocene mountain building accelerated in the western kunlun shan but showed segmented development in the tian shan the results also indicate reduced tectonic load along the altyn tagh fault since late miocene consistent with geological and geophysical evidence of the fault cutting the entire lithosphere and migrating southward during its cause of the cenozoic evolution

near real time mapping of peak ground acceleration and peak ground velocity following a strong earthquake during a disastrous earthquake the early assessment and timely reporting of the peak ground acceleration pga and peak ground velocity pgv maps will be crucial in an effective emergency response operation in this study we first derive an empirical relationship between m l and m w the pga and pgv attenuation relationships are deduced with data from the taiwan strong motion instrumentation program tsmip and the taiwan rapid earthquake information release system treirs site corrections of the attenuation relationships for shallow and large earthquakes in taiwan region are also obtained peak values of earthquake strong ground motion can be well determined in taiwan as soon as the earthquake location is determined and magnitudes are calculated by the treirs this peak ground motion value information can be immediately turned into the calculated pga and pgv maps that can be issued within two minutes of the earthquake origin time during any disastrous earthquake these maps are found to be very useful for immediate seismic damage assessment and dispatching of emergency response missions manuscript received 1 december 2000

age and significance of sequence boundaries on jurassic and early cretaceous rifted continental margins the age and significance of sequence boundaries on jurassic to early cretaceous rifted continental margins in three ocean basins have been documented the margins are the santos basin in the south atlantic the grand banks in the north atlantic and the beaufort sea in the arctic ocean large industry data bases were used for the interpretation of each area megasequence boundaries separate the major phases of basin evolution for example syn rift and post rift boundaries developed with an average periodicity of 49 m y sequence boundaries define the component parts of each megasequence and developed with a modal periodicity of 10 15 m y out of 27 total boundary ages most 16 are developed on just one margin only two possible age ranges overlap on all three margins ighty percent of the megasequence boundaries and 50 of the sequence boundaries show a direct causal connection with coeval faulting and or folding the rest of the boundaries appear as unstructured surfaces separating transgressive and or regressive sedimentary wedges and are interpreted to result from changes in the rate of basin subsidence sediment input and long term eustatic sea level these data do not support theories advocating synchronous worldwide boundary development resulting from periodic short term falls in global eustatic sea level only in like basins of the same age with identical subsidence and sediment input rates are boundaries likely to develop synchronously hence the concept of global synchroneity of sequence boundary development may well be an illusion creat d by the similarity in age of the majority of basins studied as a result of this study it seems wise discard the global approach to basin analysis

moment magnitude local magnitude calibration for earthquakes off canada s west coast local magnitude m l values of earthquakes off canada9s west coast are known to be underestimated by at least 0 5 magnitude units compared with other magnitude scales moment magnitude m w derived from moment tensor analysis provides the most robust estimate of the magnitude of earthquakes moment tensor analysis of regional seismic data in western canada is now possible due to the installation of more than 40 three component broadband stations in western canada the u s pacific northwest and southeast alaska moment tensor solutions are now possible down to m 4 0 more than 230 regional moment tensor solutions have been calculated off canada9s west coast at the geological survey of canada for 1995 2002 these solutions along with 14 previous solutions by oregon state university in 1994 1995 and 13 harvard solutions for 1984 1993 allow a systematic m w m l calibration for earthquakes in this region the study area extends from the queen charlotte islands region in the north to the area off the west coast of southern vancouver island at the northern end of the study area where there is little oceanic crust in the source receiver travel path m w is systematically larger than m l by 0 28 0 08 magnitude units at the southern end of the study area where there is a significant amount of ocean crust in the source receiver travel path m w is systematically larger than m l by 0 62 0 08 magnitude units calibration of m l with m w will allow the western canadian earthquake database to be used more effectively for tectonic studies and seismic hazard analysis

mesozoic large scale lateral extrusion rotation and uplift of the tongbai dabie shan belt in east china the tectonic convergence between the south china block and qinling belt that occurred in mesozoic time was not homogeneous along strike it was mainly concentrated in the shengnongjia and hannan domes which formed a pair of indentors along which the south china block penetrated the qinling belt as a consequence the tongbai dabie shan belt the eastern part of the qinling orogenic belt may have undergone large scale eastward extrusion clockwise rotation and uplift as indicated by its boundary deformation features it was originally located beneath the narrowest part of the qinling belt where it underwent ultrahigh pressure metamorphism in the early triassic

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

sedimentologic and tectonic origin of an incised valley fill sequence along an extensional marginal lacustrine system in the basin and range province united states implications for predictive models of the location of incised valleys incised valleys in extensional lacustrine systems should be common and significant petroleum targets yet documentation and analysis of these systems are limited and hence so are predictive models for their location geologic mapping of the miocene pliocene humboldt formation in knoll basin northeastern nevada has revealed a significant incised valley system formed along the lacustrine margins of an extensional basin the valley formed during a relative lake level fall and incised into lacustrine shoreface and offshore sandstone and subsequently was filled with fluvial and eolian sediment as lake level rose the valley s location was tectonically influenced it is situated in the hinge zone of a syncline near the tip of the range bounding fault system folding of the syncline was broadly synchronous with incision and filling and it appears to have localized the valley along the topographically low hinge zone furthermore the large relative lake level change that produced the valley is only recorded in strata in the syncline area suggesting that the location and cause of incision was greatly influenced by tectonics thus the location of similar incised valleys in other extensional basins may be predictable if comparable tectonic features and processes are recognized our study suggests that the best locations to develop and preserve incised valleys are near the tips of normal faults during periods of overall high tectonic subsidence specific areas along basin bounding faults where tectonically influenced incised valleys are more likely to form include fault propagation folds synthetic relay ramps near transfer faults and areas that have large changes in fault slip although lake volume changes caused predominantly by climate change can be an important factor in producing incised valleys tectonically influenced incised valleys are likely to be larger better preserved and more petroleum prone compared to climate controlled incised valleys

lg wave propagation in a laterally varying crust and the distribution of the apparent quality factor in central france the aim of this study is to evaluate the sensitix ity of lg waves to lateral changes of the earth s structure considering a simple model of uplift of the moho numerical simulations show that the geometrical attenuation of lg is not much affected by a smooth anomaly of the moho depth on the other hand the passing of the lg wave through the region of the moho uplift results in a clear deterioration of the wave shapes which confirms the occurrence of mode conversions the presence of an overlying sedimentary basin causes a local amplification of lg above the basin itself and the appearance behind the basin of a secondary surface wave guided in the sediments the effect of the basin on the lg wave is found to be reasonably taken into account by applying a local amplification function to the data we use a data set consisting of records of lg phases in france to test the conclusions of our numerical study the mapping of the apparent quality factor computed from lg at different frequencies confirms the interpretation of the strong attenuation of s waves around i hz in terms of scattering and shows the weak sensitivity of the amplitude of lg to smooth changes in the depth of the moho

formation of ripples in erodible channels formation of ripples and dunes in erodible channels is analyzed by using the hydrodynamic model developed by kobayashi and madsen this issue applying the continuity equation of sediment the propagation velocity of the wavy bed is expressed in terms of the net fluxes of bed load along the wavy bed and suspended sediment out of the bed load transport layer the spatial variation of the bed load transport rate is derived by analyzing the balance of forces acting on a representative bed load particle on a sloping bed the net flux of the suspended sediment out of the bed load transport layer is obtained by solving the diffusion equation for the suspended sediment near the bed the stability analysis predicts that a perturbation that is either fairly short or long relative to the depth of flow will initially grow depending on whether the flow is hydraulically smooth or fully rough thus the model explains why ripples are not observed in experiments involving fairly coarse sediments since in these cases the flow is rough turbulent

contemporary crustal deformation of northeast tibet from geodetic investigations and a comparison between the seismic and geodetic moment release rates abstract we processed the data recorded by 32 continuous gps stations from the crustal movement observation network of china and combined them with published gps observations in a common geodetic reference frame to better depict the ongoing crustal velocities and deformation field of northeast tibet the derived velocity field indicates that the deformation of northeast tibet is characterized mainly by crustal shortening coupled with the eastward extrusion of crustal material and clockwise block rotation we further used the gps velocity field to evaluate the strain rate tensors by the method of sandwell and wessel 2016 the strain rate field shows an obvious transition of the contraction rate from ne sw to nee sww and a decrease in the maximum shear strain rate from west to east was observed along the east kunlun fault and haiyuan fault indicating that the block rotation and lateral extrusion therein may be partitioned by ne sw oriented compression to some extent the inhomogeneity of the rotation strain rate implies that northeast tibet does not behave like a single rigid block but instead resembles a left lateral shear zone supporting the hypothesis that the northward transfer of motion along the east kunlun fault may play a significant role in the deformation style of this area the dilatation rate verified that most of northeast tibet experiences crustal thickening which coincides with the average uplift rate of 1 mm y revealed by gps velocities and channel steepness indices we also estimated the geodetic moment rates and compared them with the seismic moment rates estimated using the truncated gutenberg richter earthquake distribution the ratio of the seismic strain rate to the geodetic strain rate in the regions near the altyn tagh fault the qaidam basin adjoining the qilian mountains the haiyuan fault and the central part of the east kunlun fault are near unity indicating that the deformation in these areas is dominated by seismic release and may represent fully coupled seismogenic zones the occurrence of large earthquakes in the past estimated magnitudes m 6 coupled with a high geodetic deformation rate in these regions could indicate overdue m 6 earthquakes however other factors including the occurrence of creep and the long recurrence time of mw 8 0 earthquakes should be taken into consideration along the haiyuan fault by contrast in other regions including the southern and eastern parts of the haiyuan fault along the elashan fault and the northern qilian mountains the geodetic moment rate is higher than the seismic moment rate by a factor between 3 and 9 we propose that this phenomenon is related to the undersampling of long term earthquake rates within the seismic catalogue long term aseismic crustal deformation or a combination of these factors our study has implications for better comprehending the current seismotectonic pattern of northeast tibet

shear wave q structure and its lateral variation in the crust of china and surrounding regions summary we have obtained three layer crustal models of shear wave q q for several surface wave paths in china and peripheral regions using a single station multimode method in which amplitude spectra of fundamental mode and higher mode rayleigh waves computed for known source depths and mechanisms are compared to measured spectra the three layers totaling 60 km in thickness roughly comprise the entire crust in the tibetan plateau and include both the crust and part of the uppermost mantle in other regions where the crust is thinner q in the shallowest layer 10 km thick is lowest about 40 in the western portion of the tibetan plateau and highest about 250 in southeastern china in the middle layer at 10 30 km depth q is lowest 60 80 beneath tibet and the pamir thrust system and highest 120 140 in central china and parts of the sino korean platform uncertainties of q in the deepest layer at 30 60 km depth are much greater than in the upper two layers but available results suggest that q is lowest about 80 under the pamir thrust system and highest about 180 under southern mongolia the densities of event and station coverage although wanting in some regions allow us to develop the first regionalized maps of crustal q variation for continents the maps for depth ranges 0 10 km and 10 30 km generally show good agreement with q results obtained earlier with other phases and good correlation with the tectonics of this active region

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

structural style and its relation to hydrocarbon exploration in the songliao basin northeast china the songliao basin in northeast china is a mesozoic rift basin characterized by mesozoic and cenozoic hydrocarbon systems the songliao basin was initiated by southeast to northwest lithospheric extension during the late jurassic the extensional phase was dominated by two fault sets l shallow to moderately dipping normal faults and 2 steeply dipping transfer faults the extensional structures are characterized by half grabens a second short extensional tectonic overprinting phase occurred during the early qingshankou early albian 100 to 97 ma faults that occur in the quantou formation and the qingshankou formation are growth faults t2 faults which trend mostly nnw and occur predominantly at the sites of basement faults and structural bend zones located between sag and uplift and basement uplifts the basin broadly subsided during the denglouku quantou aptian 125 to 100 ma and the late qingshankou late albian 97 to 94 ma to yaojia nenjiang cenomanian to campanian 94 to 73 ma respectively positive inverted structures developed during the late cretaceous to the cenozoic in the songliao basin these are classified into two types positive inversion structures controlled by reactivation of early normal faults and inversion structures not controlled by earlier faults the major extensional structures exerted a range of controls on both sedimentation and deformation during the subsequent phases of basin evolution two thermotectonic rifting events during the late jurassic and early qingshankou play a major role in organic matter thermal evolution the timing of formation of structural traps in the basin matches that of hydrocarbon generation and migration structural traps formed during late jurassic early qingshankou and late cretaceous to paleocene 73 to 56 ma late jurassic organic rich source rock reached its peak oil generation from the time of deposition of member deng 3 4 of the denglouku formation 119 to 116 ma to that of member qing 1 of the qingshankou formation 100 to 97 ma qing 1 of the qingshankou formation and nen 1 of the nenjiang formation organic rich source rocks reached their peak oil generation from the time of deposition of the upper mingshui formation to that of the upper yi an formation and from the time of deposition of the taikang formation to that of deposition of the quarternary respectively

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

bedforms in a turbulent stream formation of ripples by primary linear instability and of dunes by nonlinear pattern coarsening it is widely accepted that both ripples and dunes form in rivers by primary linear instability the wavelength of the former scaling on the grain size and that of the latter being controlled by the water depth we revisit here this problem in a theoretical framework that allows to give a clear picture of the instability in terms of dynamical mechanisms a multi scale description of the problem is proposed in which the details of the different mechanisms controlling sediment transport are encoded into three quantities the saturated flux the saturation length and the threshold shear stress hydrodynamics is linearized with respect to the bedform aspect ratio we show that the phase shift of the basal shear stress with respect to the topography responsible for the formation of bedforms appears in an inner boundary layer where shear stress and pressure gradients balance this phase shift is sensitive to the presence of the free surface and the related effects can be interpreted in terms of standing gravity waves excited by topography the basal shear stress is dominated by this finite depth effect in two ranges of wavelength when the wavelength is large compared to the flow depth so that the inner layer extends throughout the flow and in the resonant conditions when the downstream material velocity balances the upstream wave propagation performing the linear stability analysis of a flat sand bed the relation between the wavelength at which ripples form and the flux saturation length is quantitatively derived it explains the discrepancy between measured initial wavelengths and predictions that do not take this lag between flow velocity and sediment transport into account experimental data are used to determine the saturation length as a function of grain size and shear velocity taking the free surface into account we show that the excitation of standing waves has a stabilizing effect independent of the details of the flow and sediment transport models consequently the shape of the dispersion relation obtained from the linear stability analysis of a flat sand bed is such that dunes cannot result from a primary linear instability we present the results of field experiments performed in the natural sandy leyre river which show the formation of ripples by a linear instability and the formation of dunes by a nonlinear pattern coarsening limited by the free surface finally we show that mega dunes form when the sand bed presents heterogeneities such as a wide distribution of grain sizes

lg coda q variation across eurasia and its relation to crustal evolution an extensive set of broadband and short period seismograms from regional seismic events has been used to derive a tomographic image of broad scale variations of lg coda q for most of eurasia the image indicates that lg coda q at a frequency of 1 hz varies between about 200 and 1000 lowest q values 800 are found in four regions the east european shield the siberian shield the indian shield and the southwestern and oldest portion of the altaid belt the pattern of lg coda q variation across eurasia suggests that crustal q in any region is directly proportional to the length of time that has elapsed since the most recent episode of large scale compressional tectonic activity or upper mantle heating that occurred there we interpret the low q as resulting largely from hydrothermal fluids generated by tectonic activity or heating that now reside in cracks and permeable portions of the eurasian crust crustal q increases with time after that activity as fluids are lost to the surface or absorbed by retrograde metamorphism

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

deltas of the lake malawi rift east africa seismic expression and exploration implications high resolution air gun sourced seismic reflection surveys over the offshore regions of five river deltas in lake malawi in the east african rift system reveal considerable variability in acoustic facies and stratigraphic architecture this variability can largely be attributed to the influences of different structural settings and to a lesser degree to high amplitude 100 400 m and high frequency 1000 to 100 000 yr fluctuations in lake level deltas on flexural and axial margins in the rift lake show well developed progradational geometries in contrast a delta on a steep accommodation zone margin distributes coarse sediments over a broad depositional apron rather than concentrating sediment in discrete progradational lobes as on the other deltas a large border ault margin river delta displays the most complex tectonic and stratigraphic architecture of all the deltas studied it contains several delta associated facies including prograding clinoform packages fan deltas stacked against a boundary fault and extensive subaqueous fans flexural margin lowstand deltas may be the most prospective for hydrocarbon exploration due to their large internally well organized progradational lobes and their close proximity to deep water high total organic carbon lacustrine source facies

ml measurements for northeastern united states earthquakes abstract local magnitudes m l are reported for 56 northeastern united states and canadian earthquakes using records from a pair of wood anderson torsion instruments which have operated at weston observatory since 1967 corrections to the richter m l formula are computed to take into account the difference in attenuation between southern california and the northeastern united states the corrected m l values for these events were compared to the previously reported magnitudes which had been calculated either from the nuttli 1973 m blg formula applied to 5 to 10 hz waves called m n or from a coda magnitude formula m c in general the m l determinations tend to underestimate the m n and m c values by about 0 4 magnitude units this confirms the fact that the m n scale is not appropriate when applied to high frequency waves as it is in the northeastern united states the reason for this appears to be in the relation of the period of the wave used in the magnitude determination to the corner period of the earthquake and earth response

exhumation of the dabie shan ultra high pressure rocks and accumulation of the songpan ganzi flysch sequence central china the presence of coesite and diamond bearing ultra high pressure uhp metamorphic rocks in the dabie and sulu regions central china suggests that a 100 km thick crustal section 4 x 106 km6 in volume has been denuded this volume is comparable to that represented by the 10 15 km thick middle to upper triassic flysch rocks in the songpan ganzi region regional geology and radiometric dates are compatible with an interpretation that the majority of these sedimentary rocks were derived from denudation of the orogenic belt between north and south china blocks following their latest paleozoic to triassic collision this correlation implies a high denudation rate of 4 mm yr that may have been in part promoted by tropical precipitation and extreme topographic relief for as long as 25 m y

unsteady flow in straight alluvial streams part 2 transition from dunes to plane bed the effect of suspended sediment on the modification of individual dunes in unsteady channel flow is analyzed the model is an extension of that developed by fredsoe 1979 in which the change of the dune dimensions was analyzed assuming that the transport of sediment mainly occurs as bed load by including suspended sediment it is possible to describe dune behaviour at high sediment transport rates for which the dunes are washed out so the bed at sufficiently high bed shear stress becomes plane the model is compared with laboratory experiments and the agreement is reasonable the effect of temperature variations on dune dimensions is incorporated in the analysis

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

relationship between peak ground acceleration peak ground velocity and macroseismic intensity in western chinarelationship between pga pgv and macroseismic intensity in western china

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

determination of seismic energy from lg waves seismic energy is a physical concept related to broadband information on the source radiation this is different from seismic moment which is related to low frequency information improved estimates of seismic moment and radiated energy can improve the scientific framework for interpreting observed seismicity in terms of physical source processes this study evaluates the utility of regional lg waves the dominant feature of seismograms for regional earthquakes for the estimation of radiated seismic energy the rms lg which is defined as the root mean square of lg wave ground velocity within a certain group velocity range is proportional to the square root of lg wave radiated energy flux we find that rms lg is a good quantity for estimating the energy release of earthquakes because a large fraction of the total seismic energy is radiated as lg waves we scale the network averaged rms lg value to a reference distance of 100 km for a set of 52 earthquakes in the northeastern united states using an empirically derived relation between rms lg and epicentral distance we apply the source parameters estimated for these earthquakes to boatwright s deceleration source model and calculate the total seismic energy expected to have been radiated by each event assuming it can be modeled by this source we then obtain for earthquakes in the northeastern united states the scaling of the total radiated seismic energy of earthquakes with network averaged rms lg values from synthetic seismograms it is found that different velocity structures have an effect on the efficiency of lg wave radiation using measurements of rms lg made from synthetics we find that the vertical strike slip source tends to radiate less lg wave energy than other source mechanisms manuscript received 4 february 1998

anatomy of a lacustrine stratigraphic sequence within the fourth member of the eocene shahejie formation along the steep margin of the dongying depression eastern china a comprehensive study on rift stratigraphy requires a solid understanding of sequence architecture along the steep margins of rift basins this study analyzes an eocene lacustrine sequence along the steep margin of the dongying depression in eastern china through integrated core well log and three dimensional seismic analyses the lacustrine sequence is bounded by unconformities and their correlative conformities at the base and top and consists of three systems tracts namely an early expansion systems tract eest late expansion early contraction systems tract leecst and late contraction systems tract lcst which record a lake expansion contraction cycle these systems tracts differ in thickness and development of depositional systems the eest is the thickest and contains well developed marginal and basinal fan systems with an overall retrogradational stacking pattern the well developed fan systems are the most striking features within the sequence the leecst is the most widespread and contains dominantly profundal sublittoral deposits the lcst is the thinnest with poorly developed fan systems and is characterized by significant erosion by fluvial incision the variable thickness and development of depositional systems in the three systems tracts are the responses to the interplay of sediment supply and accommodation space accommodation space establishes the framework for sedimentary infill and sediment supply determines spatial distribution and temporal evolution of depositional systems within each systems tract this study provides a lake expansion contraction scheme to divide a lacustrine stratigraphic sequence into systems tracts and highlights the feasibility of applying this approach in studying sequence stratigraphy along the steep margin of a lacustrine rift basin the results also provide understandings for the development distribution and evolution of depositional systems and their controlling factors along the steep margin of other rift basins in the world

formation and evolution of nonmarine petroleum in songliao basin china in large lake basins source rocks containing sapropelic kerogen have a high transformation ratio and a high potential for petroleum and they offer the material basis for the formation of a large nonmarine oil field on the basis of geologic and geochemical data and the results of thermal simulation of kerogen it is confirmed that the maturation sequence of kerogen is type i type ii and type iii

hydrocarbon migration and accumulation in the upper cretaceous qingshankou formation changling sag southern songliao basin insights from integrated analyses of fluid inclusion oil source correlation and basin modelling abstract the upper cretaceous qingshankou formation acts as both the source and reservoir sequence in the changling sag situated in the southern end of the songliao basin northeast china an integrated approach involving determination of hydrocarbon charging history oil source correlation and hydrocarbon generation dynamic modeling was used to investigate hydrocarbon migration processes and further predict the favorable targets of hydrocarbon accumulations in the qingshankou formation the hydrocarbon generation and charge history was investigated using fluid inclusion analysis in combination with stratigraphic burial and thermal modeling the source rocks began to generate hydrocarbons at around 82 ma and the hydrocarbon charge event occurred from approximately 78 ma to the end of cretaceous 65 5 ma when a large tectonic uplift took place correlation of stable carbon isotopes of oils and extracts of source rocks indicates that oil was generated mainly from the first member of qingshankou formation k 2 qn1 suggesting that hydrocarbon may have migrated vertically three dimensional 3d petroleum system modeling was used to evaluate the processes of secondary hydrocarbon migration in the qingshankou formation since the latest cretaceous during the late cretaceous hydrocarbon mainly originated from the qianan depression migrated laterally to adjacent structural highs subsequent tectonic inversion defined as the late yanshan orogeny significantly changed hydrocarbon migration patterns probably causing redistribution of primary hydrocarbon reservoirs in the tertiary the heidimiao depression was buried much deeper than the qianan depression and became the main source kitchen hydrocarbon migration was primarily controlled by fluid potential and generally migrated from relatively high potential areas to low potential areas structural highs and lithologic transitions are potential traps for current oil and gas exploration finally several preferred hydrocarbon accumulation sites have been identified by this work like western slope southern uplift and eastern slope helping reduce the risk on targeting hydrocarbon potential reservoirs in changling sag

genetic sequence stratigraphic framework depositional style and hydrocarbon occurrence of the upper cretaceous qyn formations in the songliao lacustrine basin northeastern china the qingshankou yaojia and nenjiang qyn formations in the songliao basin of northeastern china can be used to illustrate the application of sequence stratigraphic analysis in a lacustrine setting and to provide a good example of hydrocarbon occurrence in a lacustrine stratigraphic framework the qyn genetic stratigraphic sequence bounded by maximum flooding surfaces or beds is a low frequency second order sequence or supercycle in a lacustrine basin with a ramp margin use of subaerial unconformity and transgressive surfaces allows further subdivision of the qyn sequence into a progradational systems tract lowstand prograding complex and retrogradational systems tract delta system styles are dominated by the physiography and relative intensity of fluvial and wave rocesses q1 and n1 maximum flooding related deposits used to identify the qyn genetic stratigraphic sequence boundaries are the main petroleum source rocks and regional seals and play an important role in determining hydrocarbon distribution in the songliao basin the y1 lowstand prograding complex and y2 3 retrogradational systems tract in the northern part of the basin are the most important reservoir and producing intervals within the qyn sequence

high resolution geochemical analysis of organic matter accumulation in the qingshankou formation upper cretaceous songliao basin ne china abstract in the well known continental songliao basin the oil shale successions of the cretaceous qingshankou formation are excellent source rocks for oil the oil shale layers with high toc total organic carbon contents developed at the bottom of the formation they are divided into the lower oil shale toc up to 18 3 and the upper oil shale layer toc up to 14 4 the oil shale layers and accompanying mudstones are investigated by high resolution analyses of drill cores by pyrolysis organic petrology organic and inorganic geochemistry the results demonstrate the predominance of type i kerogen derived from algal microbial mats i e lamalginite however increased proportions of plant derived organic matter are indicated by rock eval parameters and the presence of vitrinite in the upper oil shale as evidenced from lower concentrations of hopanes higher sinking rates of organic matter om are suggested to have been responsible for a lower extent of microbial degradation during accumulation of the lower oil shale unit the environmental conditions are characterized by anoxic saline bottom water overlain by an extended zone of freshwater favorable for om production and preservation under these preconditions oil shale thickness and quality are governed by primary productivity related to accommodation space and nutrient supply redox conditions within the water column are the key factor controlling organic matter preservation

propagation of regional seismic phases lg and sn and pn velocity structure along the africa iberia plate boundary zone tectonic implications we used over 1000 regional waveforms recorded by 60 seismic stations located in northwest africa and iberia to map the efficiency of l g and sn wave propagation beneath the gulf of cadiz alboran sea and bounding betic rif and atlas mountain belts crustal attenuation is inferred from the tomographic inversion of l g pg amplitude ratios upper mantle attenuation is inferred from maps of sn propagation efficiency derived by inversion of well defined qualitative efficiency assignments based on waveform characteristics regions of l g attenuation correlate well with areas of thinned continental or oceanic crust significant sedimentary basins and lateral crustal variations comparison of the sn efficiency results with velocities obtained from an anisotropic pn traveltime inversion shows a fairly good correlation between regions of poor sn efficiency and low pn velocity a low pn velocity 7 6 7 8 km s 1 and significant sn attenuation in the uppermost mantle is imaged beneath the betics in southern spain in sharp contrast to the relatively normal pn velocity 8 0 8 1 km s 1 and efficient sn imaged beneath the alboran sea slow pn velocity anomalies are also imaged beneath the rif and middle atlas in morocco we do not identify any conclusive evidence of lithospheric scale upper mantle attenuation beneath the rif although the crust in the gibraltar region appears highly attenuating making observations at stations in this region ambiguous paths crossing the gulf of cadiz eastern atlantic and the moroccan and iberian mesetas show very efficient sn propagation and are imaged with high pn velocities 8 1 8 2 km s 1 the spatial distribution of attenuation and velocity anomalies lead us to conclude that some recovery of the mantle lid beneath the alboran sea must have occurred since the early miocene episode of extension and volcanism we interpret the low velocity and attenuating regions beneath the betics and possibly the rif as indicating the presence of partial melt in the uppermost mantle which may be underlain by faster less attenuating mantle in the light of observations from other geophysical and geological studies the presence of melt at the base of the betic crust may be an indication that delamination of continental lithosphere has played a role in the neogene evolution of the alboran sea region

a record of appalachian denudation in postrift mesozoic and cenozoic sedimentary deposits of the u s middle atlantic continental margin abstract the complex interplay between source terrain uplift basin subsidence paleoclimatic shifts and sea level change left an extensive sedimentary record in the contiguous offshore basins of the u s middle atlantic margin salisbury embayment baltimore canyon trough and hatteras basin isopach maps of 23 postrift lower jurassic to quaternary a allostratigraphic units coupled with a revised stratigraphic framework reveal that tectonism by regulating sediment supply accumulation rate dominated the interplay of forcing mechanisms tectonic pulses are evidenced by abruptly accelerated sediment accumulation marked latitudinal shifts in the location of depocenters and regional changes in lithofacies relatively rapid tectonic subsidence during the early and middle jurassic history of the basins may have enhanced sediment accumulation rates beginning in the late jurassic however subsidence rates decreased significantly though occasional short pulses of subsidence may have effected relative sea level rises sea level change heavily influenced the distribution and redistribution of sediments one they reached the basins and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins we conclude that source terrains of the central appalachian highlands were tectonically uplifted intensely weathered and rapidly eroded three times since the late triassic 1 early to middle jurassic aalenian to callovian 2 mid early cretaceous barremian and 3 late cenozoic middle miocene intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces geomorphic features commonly reported to characterize the central appalachian highlands this series of three irregularly spaced tectonic quiescent cycles does not however match the traditional four cycle concept of post triassic appalachian peneplanation

basin evolution and oil shale deposition during upper cretaceous in the songliao basin ne china implications from sequence stratigraphy and geochemistry abstract the controlling factors of oil shale formation within the upper cretaceous qingshankou and nenjiang formations of the songliao basin are investigated by petrological and geochemical methods sediment deposition was balanced by basin subsidence resulting in the accumulation of cretaceous strata of high thickness global sea level fluctuations have been related to periods of oil shale deposition within the basin the results indicate a comparable depositional environment during oil shale formation within the two upper cretaceous strata with respect to palaeotectonic and palaeoclimate but differences in the accommodation space during accumulation of the two formations the larger accommodation space during deposition of the nenjiang formation resulted in the higher thickness and wider distribution of the oil shale members total thickness 11 2 32 m distribution area 4 48 103 km2 within the basin as compared to the oil shale of the qingshankou formation total thickness 2 19 3 m distribution area 1 3 103 km2 further differences exist with regard to the palaeoenvironment of oil shale formation and primary productivity deposition of the qingshankou formation 1st member and nenjiang formation 1st member took place within a saline brackish lake under anoxic conditions in the bottom water preservation of organic matter is suggested to have been less favorable during deposition of the nenjiang formation 2nd member higher primary productivity is believed to be the responsible factor for the accumulation of organic rich sediments in the qingshankou formation 1st member the interplay of these two factors i e preservation productivity leads to the formation of oil shale in the qingshankou formation average toc 8 32 tocmax 13 52 average oil yield 5 57 with better hydrocarbon source rock potential and slightly higher oil yield during pyrolysis as in the nenjiang formation average toc 7 76 tocmax 9 7 average oil yield 5 54 primary productivity is suggested as the main controlling factor on differences in oil shale quality and source rock potential between the two formations whereas the variations in quality within each formation mainly depend on the preservation of organic matter the high thickness wide spatial distribution and excellent hydrocarbon potential of the upper cretaceous oil shales in the songliao basin are suggested to have been the result of large accommodation space stable palaeoenvironmental conditions and high primary productivity

lg coda q and its relation to the structure and evolution of continents a global perspective tomographic maps of lg coda q q lg c variation are now available for nearly the entire african eurasian south american and australian continents as well as for the united states q lg c at 1 hz q 0 varies from less than 200 to more than 1000 and q lg c frequency dependence varies between 0 0 and nearly 1 0 q 0 appears to increase in proportion to the length of time that has elapsed since the most recent major episode of tectonic or orogenic activity in any region a plot of q 0 versus time since that activity indicates that a single q 0 time relation approximates most mean q 0 values those that deviate most from the trend lay in australia the arabian peninsula and the east african rift the increase in q 0 with time may be due to a continual increase in crustal shear wave q q caused by the loss of crustal fluids and reduction of crustal permeability following tectonic or orogenic activity extrapolated values of q lg c at 5 hz using q 0 and values measured at 1 hz and assuming that is constant in all regions between 1 and 5 hz show a similar percentage wise increase with times that has elapsed since the most recent activity other factors that can reduce q 0 in continental regions include thick accumulations of sediment especially sandstone and shale of mesozoic age and younger severe velocity gradients at the crust mantle transition and possibly lateral variations in the depth thickness and severity of those gradients severe and large increases of q in the mid crust of some regions can cause relatively large values of even if the frequency dependence of q is small

sulfur isotope constraints on marine transgression in the lacustrine upper cretaceous songliao basin northeastern china abstract organic rich cretaceous source rocks of the petroliferous songliao basin in northeast china are considered to be lacustrine in origin but paleontological and organic geochemical evidence suggest episodic marine incursions as a test of this hypothesis we applied time series measurements of elemental and isotopic abundances on core and cutting samples to evaluate fluctuations in the sulfur and carbon cycles across the santonian campanian transition preserved in the upper yaojia and lower nenjiang formations the data reveal a spike in pyrite sulfur abundance and a marked negative excursion in 34s at the base of the nenjiang formation when the basin expanded to its maximal extent the elemental and isotopic data suggest that flooding was associated with rapid marine transgression that enhanced sulfate concentrations which promoted microbial sulfate reduction in anoxic bottom waters that were episodically euxinic subsequent restriction of the basin and a decline in marine influence is supported by progressive upsection 34s enrichment up to 30 in nenjiang member i which are interpreted to reflect the distillation of sulfate through enhanced pyrite burial followed by a gradual return to lacustrine conditions that prevailed in overlying strata

structural and sedimentary evolution of the southern songliao basin northeast china and implications for hydrocarbon prospectivity the southern songliao basin manifests itself as a wide rift system that developed in northeast china from the late jurassic to early cretaceous individual basins in the system experienced marked rift subsidence but the postrift subsidence was insignificant in most of the basins contrasting strikingly with the tectonic subsidence history of the northern songliao basin two types of rift basins are defined according to whether the basins underwent prominent postrift subsidence type 1 basins are characterized by thick postrift accumulations type 2 basins although experiencing minor postrift subsidence represent most of the southern songliao basin and can be subdivided in accordance with bounding fault geometry and areal extent basins bounded by high angle faults type 2a basins bounded by low angle faults type 2b and basins with limited spatial area type 2c many rift basins are expressed as narrow belts in map view and are composed internally of several segments linked through different types of transfer zones depositional processes and facies architecture of the basins are controlled primarily by dips and migration of active bounding faults synrift depocenters occur close to high angle bounding faults and deep lake deposition commonly persists through much of the synrift subsidence lacustrine deposition can be enhanced by the backward or toward the footwall stepping of active bounding faults depocenters controlled by low angle bounding faults in contrast tend to shift basinward through time and deep lake facies commonly develop in the middle stage of rifting at the end of the cretaceous basin inversion was evident in type 1 basins such as the shiwu basin on the north but other basins appear to have mostly escaped the contractional deformation gravitational collapse of the previously thickened crust is considered the cause for the generation of the rift basins and lateral flow of the ductile lower crust may explain the significantly induced postrift subsidence of type 2 basins effective plays occur in basins bounded by high angle faults and therefore type 1 and type 2a basins are suggested to be the main targets of future oil exploration synrift source rock maturation might be partially attributed to the heating of early cretaceous magmatism because shallower burial alone could not elevate temperatures high enough for petroleum generation

surface wave array tomography in se tibet from ambient seismic noise and two station analysis ii crustal and upper mantle structure summary we determine the 3 d shear wave speed variations in the crust and upper mantle in the southeastern borderland of the tibetan plateau sw china with data from 25 temporary broad band stations and one permanent station interstation rayleigh wave phase velocity dispersion curves were obtained at periods from 10 to 50 s from empirical green s function egf derived from ambient noise interferometry and from 20 to 150 s from traditional two station ts analysis here we use these measurements to construct phase velocity maps from 10 to 150 s using the average interstation dispersion from the egf and ts methods between 20 and 50 s and estimate from them with the neighbourhood algorithm the 3 d wave speed variations and their uncertainty the crust structure parametrized in three layers can be well resolved with a horizontal resolution about of 100 km or less because of the possible effect of mechanically weak layers on regional deformation of particular interest is the existence and geometry of low shear velocity layers lvls in some regions prominent lvls occur in the middle crust in others they may appear in the lower crust in some cases the lateral transition of shear wave speed coincides with major fault zones the spatial variation in strength and depth of crustal lvls suggests that the 3 d geometry of weak layers is complex and that unhindered crustal flow over large regions may not occur consideration of such complexity may be the key to a better understanding of relative block motion and patterns of seismicity

1 hz lg q tomography in central asia we have applied tomographic techniques to a data set of over 1700 regional distance lg amplitudes from 12 stations for paths inside a 30 by 40 region of central asia our purpose is to create high resolution path correction maps for use in regional distance source discrimination and magnitude determination as well as to study lg propagation characteristics in one of the most heterogeneous portions of the earth for 1 0 hz data tomography reduced variance 33 relative to a best fit uniform q model lgq varied with geologic region with low values in tibet the tien shan and the pamir range q 200 to 400 intermediate values in basins such as the tarim q 500 and high values for platforms and older crust q 800 the relatively efficient propagation across the tarim differs from the poor propagation that is generally observed across sedimentary basins

high resolution rayleigh wave slowness tomography of central asia 1 we compute short period high resolution surface wave slowness maps for central asia using bayesian tomography we focus on the region between 69 and 108 e and 29 and 54 n and used seismograms from more than 1100 events using multiple filter and phase matched filter techniques we measured the dispersion characteristics of the signals between 6 and 30 s period these rayleigh wave group velocity dispersion curves were used to compute high resolution half degree cell size slowness tomographic maps because short periods are primarily sensitive to upper crustal structures the images display low velocities associated with the tarim junggar and qaidam basins relatively high velocities are associated with mountainous tectonic features such as the tian shan we validated our maps using dispersion curves from 640 events that were not used to construct the tomographic model the model predictions show a significant variance reduction at short and intermediate periods 6 15 s with respect to the prior model our model also shows 15 improvement in surface wave detection capability with respect to previous one dimensional models these high resolution short period tomography maps can help improve regional magnitude estimations for construction of mb ms discriminants moreover the short period surface wave tomographic results show unprecedented resolution that reveals greater geologic detail than has previously been achieved using surface waves and that give us insight into the shear velocity structure of the crust underlying this part of asia

uppermost mantle velocities beneath china and surrounding regions 1 seismic p wave velocity variations in the uppermost mantle beneath china are tomographically imaged using pn wave travel time data the average velocity of the mantle lid beneath china is 8 05 km s with a range from 0 30 km s to 0 35 km s eastern china has slower mantle velocities and a thinner crust than western china different inversions performed for shorter ray path and longer ray path data sets separated the shallow and deep structure within the mantle lid velocities in the lower lid are no more than 0 2 km s faster than at the top the fastest velocities are beneath cratons which remained relatively undeformed despite orogenic events around their margins the pn velocity beneath southern tibet is faster than that beneath northern tibet suggesting that this contrast delineates the northern edge of the indian lithosphere on the southeastern margin of the tibetan plateau the panxi rift slow pn velocity exists in the lithosphere due to the transextensional tectonic environment in eastern china extension of the north china block produced a series of nne ssw trending rifts that cause slow mantle lid velocities these slow velocities extend to the base of the mantle lid suggesting that late cenozoic pacific subduction drove the rifting both high temperature and hydration may contribute to these low uppermost mantle velocities the shanxi rift along the east margin of the ordos platform is characterized by a slow mantle velocity in contrast the yinchuan rift on the west margin does not show any uppermost mantle velocity anomaly

crustal thickening and lateral extrusion during the indo asian collision a 3d viscous flow model abstract the 2000 km crustal shortening from the indo asian collision in the past 40 70 million years has been accommodated mainly by crustal thickening in the himalayan tibetan plateau and lateral extrusion of blocks of asian continents however the spatiotemporal evolution of crustal thickening and lateral extrusion hence the far field impact of the indo asian collision on asian tectonics remains controversial here we present a 3d viscous flow model that simulates the partitioning of crustal material between thickening and lateral extrusion during the indo asian collision the model assumes conservation of crustal mass and is constrained by the history of the indo asian plate convergence and by the present day topography of the himalayan tibetan plateau the results show that much of the early collision was absorbed by crustal thickening within the himalayan tibetan plateau however lateral extrusion of crustal material has gradually become dominant in the past 10 20 myr indicating increasing influence of the indo asian collision on asian tectonics

correction to variability of crustal attenuation in the northeastern united states from lg waves by jinghua shi won young kim and paul g richards

bayesian lg attenuation tomography applied to eastern asia bayesian attenuation tomography tarantola 1987 is being used to refine existing lg attenuation models in eastern asia the advantages of a bayesian approach to tomography are that large scale and high resolution tomographic models available from other well accepted studies can be used as prior background models the resulting refined tomographic model will blend into these prior background models moreover the uncertainties are well established in a bayesian framework we assume a general linear gaussian least squares model where the covariance matrix is partitioned into data and prior model components uncertain data are naturally down weighted and model components with small errors will be subject to little change amplitude tomography provides only an approximation to the propagation effects a seismic wave may experience for example phase blockage can occur over relatively short distances in the absence of any anelastic effects station centric kriged amplitude correction surfaces on top of the tomographic models may assist in identifying blocked paths because a signal to noise criterion is used to select amplitudes for the inversion the data are left censored and the resulting q 0 models will be biased high we examine the utility of a maximum likelihood data augmentation method to the left censored data problem schafer 1997 in this case we can only measure an upper bound to measured amplitudes on the basis of prephase noise data augmentation is used to impute the missing data values with their conditional expectation based on the relationship of amplitudes with other completely observed variables we have initially chosen a bivariate gaussian model for filling in missing amplitudes based on the relationship between amplitude and prephase noise we apply the technique to eastern asia for lg signals at 1 hz using data from 1651 earthquakes recorded at 12 stations tomographic patterns correlate well with those expected from geophysical considerations e g high attenuation in tibet and low attenuation up into the stable regions of kazakhstan many of the large cratonic basins surrounding the tibet plateau e g tarim junggar show reduced attenuation consistent with the hypothesis that they represent regions of stronger lithosphere data augmentation tends to increase attenuation in tibet particularly western tibet and the cratonic basins to the north of but not to the east of tibet in addition the resulting models are much smoother than models that do not account for censoring

evidence for intracontinental thrust related exhumation of the ultra high pressure rocks in china coesite and diamond bearing ultra high pressure metamorphic rocks produced during the triassic continental collision between the sino korean and yangtze plates are offset by about 530 km along the sinistral tanlu fault in eastern china the tanlu fault terminates abruptly south of the ultra high pressure metamorphic terrain in dabie shan and does not extend into the foreland fold belt along the yangtze river this suggests that in this region the mesozoic major sinistral displacement along the tanlu fault was transferred to southward directed thrusting which led to the exhumation of the ultra high pressure metamorphic rocks formed earlier postcollisional himalayan type intracontinental thrusting and concomitant erosion appear to be the main agents in the exhumation of the very high pressure metamorphic rocks in china

path specific velocity structure of western china from surface wave dispersion we develop one dimensional 1 d path specific velocity models in western china using new rayleigh and love wave group and phase velocity dispersion measurements for 20 events in the region the earthquakes were grouped into three geographic clusters from which we compute the average phase and group velocity dispersion we invert the average dispersion curves simultaneously for 1 d shear velocity models appropriate for the three central asian paths using three previous shear velocity models as initial models the models are validated by forward modeling waveforms of recent events the crustal thickness beneath western china in the vicinity of the lop nor test site is 50 60 km and our velocity models are consistent with major geologic features e g basins and mountain ranges and previous structural models for this region

ambient noise rayleigh wave tomography in western sichuan and eastern tibet abstract we perform rayleigh wave tomography in western sichuan and eastern tibet by applying the ambient noise method to broadband data recorded at 49 stations from the sichuan digital seismic network cross correlations of vertical component ambient noise data are computed in one hour segments and stacked over 7 months from june to december 2007 then rayleigh wave group dispersion curves from 6 to 48 s were measured using the multiple filter analysis method group velocity maps at periods from 8 to 44 s were inverted the resulting group velocity maps generally show good correlations with tectonic features the sichuan basin is clearly resolved with lower group velocities at the short periods 8 to 20 s due to thick sedimentary layers and a prominent low velocity zone exhibits in the middle crust beneath the eastern margin of the tibetan plateau the longmen shan thrust belt marks not only the rapid lateral velocity variation between the topographically high tibetan plateau and low elevation sichuan basin but also the transition from the thick crust beneath the tibetan plateau to the normal continental crust beneath the sichuan basin

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

lake type controls on petroleum source rock potential in nonmarine basins based on numerous empirical observations of lacustrine basin strata we propose a three fold classification of lacustrine facies associations that accounts for the most important features of lacustrine petroleum source rocks and provides a predictive framework for exploration in nonmarine basins where lacustrine facies are incompletely delineated 1 the fluvial lacustrine facies association is characterized by freshwater lacustrine mudstones interbedded with fluvial deltaic deposits commonly including coal shoreline progradation dominates basin fill resulting in the stacking of indistinctly expressed cycles up to 10 m thick in map view the deposits may be regionally widespread but laterally discontinuous and contain strong facies contrasts transported terrestrial organic matter contributes to mixed type i iii kerogens that generate waxy oil type i kerogen is hydrogen rich and oil prone type iii kerogen is hydrogen poor and mainly gas prone the luman tongue of the green river formation wyoming and the honyanchi formation junggar basin china provide examples of this facies association which is also present in the songliao basin of northeastern china the central sumatra basin and the cretaceous doba doseo basins in west central africa 2 the fluctuating profundal facies association represents a combination of progradational and aggradational basin fill and includes some of the world s richest source rocks deposits are regionally extensive in map view having relatively homogenous source facies containing oil prone type i kerogen examples include the laney member of the green river formation wyoming the lucaogou formation junggar basin china the bucomazi formation offshore west africa and the lagoa feia formation campos basin brazil 3 the evaporative facies association represents dominantly aggradational fill related to desiccation cycles in saline to hypersaline lakes and may include evaporite and eolianite deposits sublittoral organic rich mudstone facies are relatively thin but may be begin page 1034 quite rich and widespread the highest organic enrichment coincides with the deepest lake stages low input of land plant organic matter results in minimal lateral contrasts in organic content in some cases a distinctive type i s sulfur rich kerogen may generate oil at thermal maturities as low as 0 45 vitrinite reflectance equivalent examples include the wilkins peak member of the green river formation wyoming the jingjingzigou formation junggar basin china the jianghan and qaidam basins china and the blanca lila formation argentina

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

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

empirical mw ml mb and ms conversions in western china local magnitude m l body wave magnitude m b and surface wave magnitude m s which are saturated at certain values and may lead to an incorrect energy estimation of a large earthquake are largely used in quantifying the size of an earthquake in western china based on the catalog from the china earthquake data center cedc and moment magnitude m w provided by the global centroid moment tensor global cmt project we test the general orthogonal regression gor and the ordinary least squares ols methods in m w m l m s and m b conversions for earthquakes in three different tectonic structures of western china for m l and m b linear trends vary according to tectonic structures which implies different body wave attenuations in the three structures for m s the results are similar whether using the gor or the ols method but slopes of regression lines are not close to 1 which indicates routine misestimates of m s in western china the gor slopes are uniformly larger than the ols slopes in all magnitude conversions standard deviations are between 0 06 and 0 13 for the gor method but are between 0 12 and 0 25 for the ols thus the gor is found to be superior to the ols method and its use is recommended conversions of different magnitudes to m w not only imply different patterns of seismic wave attenuations but will also benefit immediate assessment of seismic damage after occurrence of a destructive earthquake in the future online material earthquake catalog and tables showing differences between magnitude estimates for m w m l m b and m s

variability of crustal attenuation in the northeastern united states from lg waves high quality digital seismograms from eight pairs of collocated earthquakes in the northeastern united states were analyzed to determine accurate source spectrum corner frequencies this was accomplished by applying the empirical green s function method to regional pg and lg or sg phases recorded by vertical component seismographs of the u s national seismographic network usnsn and the lamont doherty cooperative seismographic network lcsn stations the frequency band used was 0 5 16 hz for usnsn and 1 30 hz for lcsn records the source spectrum corner frequencies for the eight larger earthquakes of the event pairs magnitudes between mb lg 2 5 4 1 range from about 4 3 to 16 3 hz based on the comer frequencies obtained independently from the empirical green s function analysis sg or lg wave displacement amplitude spectra up to 30 hz were used to determine the crustal average q factors along 87 event station paths these paths crossed diverse tectonic features in the northeastern united states and were in the epicentral distance range of 41 to 1394 km we found that within the northeastern united states the crustal average qlg we obtained was frequency dependent and showed spatial variability which correlated fairly well with the major tectonic features in the region our attenuation measurements indicated low lg attenuation in the adirondack mountains with exposed precambrian grenville basement with qlg 905 f0 40 high lg attenuation in the central appalachian province with qlg 561 586 f0 46 0 47 and an intermediate lg attenuation in northern new england appalachians with q 705 f0 41

3 d velocity structure of the middle and upper crust in the yunnan region china using short period 1 18 s surface wave data recorded by 23 stations of the yunnan digital seismic network of china we determined phase velocities of the fundamental rayleigh wave along 209 paths by the two station narrowband filtering and cross correlation method followed by an inversion for phase velocity distributions at various periods using the ditmar yanovskaya method we then obtained a 3 d s wave velocity structure of the middle and upper crust in the yunnan region using the genetic algorithm the results show strong lateral variation of phase velocity in the region the short period phase velocity variation is closely related to thickness variation of sedimentary layer in the shallow crust within the depth range of 26 30 km the s wave velocity in the sichuan yunnan rhombic block is lower than in the surrounding areas most large earthquakes of m 6 0 in yunnan occurred in the transition zones between low and high velocities