longriba fault zone in eastern tibet an important tectonic boundary marking the westernmost edge of the yangtze block global positioning system gps measurements across eastern tibet reveal a sharp velocity gradient zone located about 150 km west of the longmen shan frontal thrust zone where eastward block motion of tibet decreases from 12 mm yr to 3 mm yr over a distance of less than 10 km in order to investigate the tectonic cause for this rapid change in gps velocity together with systematic review on the available geological and geophysical data in easternmost tibet we provide new constraints on the tectonic feature of the longriba fault zone from advanced land observing satellite phased array type l band synthetic aperture radar data we propose that the ne striking longriba fault zone is the key structure responsible for the observed sharp gradient in gps velocities in addition the evidence indicates that the longriba fault zone instead of the longmen shan fault zone marks the westernmost edge of the yangtze crustal block given the irregular western margin of the yangtze block the longriba fault zone represents part of the actual tectonic boundary between the songpan ganzi terrane and the yangtze block the newly identified western edge of the yangtze block implies a paleocontinent ocean boundary at depth this boundary was a potential weak zone and may have been exploited during the formation of the longriba fault zone the results of this paper should advance our understanding of the tectonic relationship between the songpan ganzi terrane and yangtze block and provide additional constraints for studies of the geodynamic response of eastern tibet to the ongoing india eurasia collision

dynamic topography produced by lower crustal flow against rheological strength heterogeneities bordering the tibetan plateau summary dynamic stresses developed in the deep crust as a consequence of flow of weak lower crust may explain anomalously high topography and extensional structures localized along orogenic plateau margins with lubrication equations commonly used to describe viscous flow in a thin gap geometry we model dynamic stresses associated with the obstruction of lower crustal channel flow due to rheological heterogeneity dynamic stresses depend on the mean velocity u viscosity and channel thickness h uniquely through the term u h 2 these stresses are then applied to the base of an elastic upper crust and the deflection of the elastic layer is computed to yield the predicted dynamic topography we compare model calculations with observed topography of the eastern tibetan plateau margin where we interpret channel flow of the deep crust to be inhibited by the rigid sichuan basin model results suggest that as much 1500 m of dynamic topography across a region of several tens to a hundred kilometres wide may be produced for lower crustal material with a viscosity of 2 10 18 p asfl owing in a 15 km thick channel around a rigid cylindrical block at an average rate of 80 mm yr 1

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

prediction of lateral variability in fracture intensity using multicomponent shear wave surface seismic as a precursor to horizontal drilling in the austin chalk summary a method of multicomponent multisource shear wave interpretation utilizing the output of the alford rotation for separating the fast and slow particle motion stacks in azimuthally anisotropic media yielded a qualitative prediction of lateral fracture intensity variation prior to horizontal drilling the method exploits a fundamental difference between the two particle motion stacks when vertical aligned fractures are the source of the shear wave splitting the fast shear wave s1 section is insensitive to the lateral variation in fracture intensity since its particle motion is parallel to the fractures hence reflectivity on the s1 cdp stacked section should be likewise insensitive to fractures the slow shear wave s2 section however possesses particle motion perpendicular to the fracture planes so variation in lateral fracture intensity will affect velocity and reflectivity examination of the reflectivity on the two sections for a seismic line reveals laterally consistent reflector strength on the s1 section for the austin chalk the horizon of interest but laterally inconsistent reflector strength for the same horizon on the s2 section in the study area reflector dimming on the s2 section was interpreted as indicating fracture intensity maxima horizontal drilling confirmed both fracture azimuth and intensity predictions and resulted in significantly higher initial hydrocarbon production than for surrounding wells

thermal maturation potential source rocks and hydrocarbon generation in mesozoic rocks lougheed island area central canadian arctic archipelago abstract significant oil and gas accumulations occur in and around lougheed island arctic canada where hydrocarbon prospectivity is controlled by potential source rock distribution and composition the middle to upper triassic rocks of the schei point group e g murray harbour and hoyle bay formations contain a mixture of types i and ii organic matter tasmanales marine algae amorphous fluorescing bituminite these source rocks are within the oil generation zone and have hi values up to 600 mg hc g corg the younger source rocks of the lower jurassic jameson bay and the upper jurassic ringnes formations contain mainly gas prone type ii iii organic matter and are marginally mature vitrinite reflectance profiles suggest an effective geothermal gradient essentially similar to the present day gradient 20 to 30 c km maturation gradients are low ranging from 0 125 to 0 185 log ro km increases in subsidence rate in the early cretaceous suggest that the actual heat flow history was variable and has probably diminished from that time the high deposition rates of the christopher formation shales coincide with the main phase of rifting in aptian albian times uplift and increased sediment supply in the maastrichtian resulted in a new sedimentary and tectonic regime which culminated in the final phase of the eurekan orogeny burial history models indicate that hydrocarbon generation in the schei point group took place during rifting in early cretaceous long before any eurekan deformation

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

damped regional scale stress inversions methodology and examples for southern california and the coalinga aftershock sequence 1 we present a new focal mechanism stress inversion technique to produce regional scale models of stress orientation containing the minimum complexity necessary to fit the data current practice is to divide a region into small subareas and to independently fit a stress tensor to the focal mechanisms of each subarea this procedure may lead to apparent spatial variability that is actually an artifact of overfitting noisy data or nonuniquely fitting data that does not completely constrain the stress tensor to remove these artifacts while retaining any stress variations that are strongly required by the data we devise a damped inversion method to simultaneously invert for stress in all subareas while minimizing the difference in stress between adjacent subareas this method is conceptually similar to other geophysical inverse techniques that incorporate damping such as seismic tomography in checkerboard tests the damped inversion removes the stress rotation artifacts exhibited by an undamped inversion while resolving sharper true stress rotations than a simple smoothed model or a moving window inversion we show an example of a spatially damped stress field for southern california the methodology can also be used to study temporal stress changes and an example for the coalinga california aftershock sequence is shown we recommend use of the damped inversion technique for any study examining spatial or temporal variations in the stress field

structure and paleoearthquake records of active submarine faults cook strait new zealand implications for fault interactions stress loading and seismic hazard 1 a new interpretation of active faulting in central cook strait new zealand reveals tectonic structures associated with the spatial transition from subduction to continental transform faulting marine seismic reflection profiles and multibeam bathymetric data indicate that there are no throughgoing crustal faults connecting the north island dextral fault belt and the marlborough fault system in south island the major faults terminate offshore associated with 5 20 km wide step overs and a change in regional fault strike this structure implies that propagation of strike slip earthquake ruptures across the strait is not probable faulted sedimentary sequences in the wairau basin marlborough shelf correlated to glacioeustatic sea level cycles provide a stratigraphic framework for fault analysis a high resolution study of the postglacial 20 ka vertical displacement history of the cloudy and vernon faults reveals up to six and five paleoearthquakes since 18 ka respectively these long timescale records indicate variable recurrence intervals and possibly variable stress drop thus conforming to the variable slip model of earthquake behavior integration of these data with other submarine and terrestrial paleoearthquake records indicates the presence of clustered earthquake sequences involving multiple faults different sequences do not always involve the same faults it appears that earthquake clustering is driven by fault interactions that lead to specific loading conditions favoring the triggering of earthquakes on major faults in relatively short time intervals present day regional coulomb stress distribution has been calculated in two scenarios considered to represent minimum and maximum loading conditions the models incorporating secular tectonic loading and stress changes associated with major crustal earthquakes indicate high stress loading in a large part of central cook strait these conditions may favor the triggering of future damaging earthquakes in this region

evidence for mechanically coupled lithosphere in central asia and resulting implications the recent dramatic increase in seismic anisotropy and surface global positioning system gps data for central asia permits a comprehensive examination of the mantle s role in mountain building a joint analysis of 178 shear wave splitting and 2000 gps observations using a new technique reveals that the crust and lithospheric mantle deform coherently arguing for crust mantle mechanical coupling during deformation the observed spatial variations in anisotropy refl ect the large scale pattern of lithospheric deformation as well as a change in deformational style from simple shear on the tibetan plateau transitioning to pure shear in surrounding regions

why the 2002 denali fault rupture propagated onto the totschunda fault implications for fault branching and seismic hazards 1 the propagation of the rupture of the mw7 9 denali fault earthquake from the central denali fault onto the totschunda fault has provided a basis for dynamic models of fault branching in which the angle of the regional or local prestress relative to the orientation of the main fault and branch plays a principal role in determining which fault branch is taken geoearthscope lidar and paleoseismic data allow us to map the structure of the denali totschunda fault intersection and evaluate controls of fault branching from a geological perspective lidar data reveal the denali totschunda fault intersection is structurally simple with the two faults directly connected at the branch point 227 2 km east of the 2002 epicenter the 2002 rupture diverges southeast to become the totschunda fault we use paleoseismic data to propose that differences in the accumulated strain on each fault segment which express differences in the elapsed time since the most recent event was one important control of the branching direction we suggest that data on event history slip rate paleo offsets fault geometry and structure and connectivity especially on high slip rate short recurrence interval faults can be used to assess the likelihood of branching and its direction analysis of the denali totschunda fault intersection has implications for evaluating the potential for a rupture to propagate across other types of fault intersections and for characterizing sources of future large earthquakes

teleseismic shear wave splitting in se tibet insight into complex crust and upper mantle deformation we measured shear wave splitting of teleseismic xks phases i e sks skks and pks recorded by more than 300 temporary chinarray stations in yunnan of se tibet the first order pattern of xks splitting measurements shows that the fast polarization directions change at 26 27 n from dominant n s in the north to e w in the south while splitting observations around the eastern himalayan syntax well reflect anisotropy in the lithosphere under left lateral shear deformation the dominant e w to the south of 26 n is consistent with the maximum extension in the crust and suggest vertically coherent pure shear deformation throughout the lithosphere in yunnan however the thin lithosphere 80 km could account for only part 0 7 s of the observed splitting delay times t 0 9 1 5 s anisotropy in the asthenosphere is necessary to explain the nw se and nearly e w in these regions the ne sw can be explained by the counter flow caused by the subduction and subsequent retreat of the burma slab the e w is consistent with anisotropy due to the absolute plate motion in se tibet and the eastward asthenospheric flow from tibet to eastern china accompanying the tectonic evolution of the plateau our results provide new information on different deformation fields in different layers under se tibet which improves our understanding on the complex geodynamics related to the tectonic uplift and southeastward expansion of tibetan material under the plateau

mapping stress and structurally controlled crustal shear velocity anisotropy in california we present shear velocity anisotropy data from crustal earthquakes in california and demonstrate that it is often possible to discriminate structural anisotropy polarization of the shear waves along the fabric of major active faults from stress induced anisotropy polarization parallel to the maximum horizontal compressive stress stress directions from seismic stations located near but not on the san andreas fault indicate that the maximum horizontal compressive stress is at a high angle to the strike of the fault in contrast seismic stations located directly on one of the major faults indicate that shear deformation has significantly altered the elastic properties of the crust inducing shear wave polarizations parallel to the fault plane

organic matter apatite pyrite relationships in the botneheia formation middle triassic of eastern svalbard relevance to the formation of petroleum source rocks in the nw barents sea shelf abstract the middle triassic botneheia formation of eastern svalbard edgeoya and barentsoya comprises an organic carbon rich fine grained clastic succession 100 m thick that makes the best petroleum source rock horizon in the nw barents sea shelf the succession records a transgressive regressive interplay between the prodelta depositional system sourced in the southern barents sea shelf black shale facies of the lower and middle parts of the muen member and the open shelf phosphogenic system related to upwelling and nutrient supply from the panthalassic ocean phosphogenic black shale facies of the upper part of the muen member and the blanknuten member the relationships between organic matter authigenic apatite and pyrite in these facies allow to characterize the relative roles of redox conditions and oceanic productivity in the organic carbon preservation the accumulation of terrestrial and autochthonous marine organic matter in the black shale facies occurred under dominating oxic conditions and increasing upward productivity related to early transgressive phase and retrogradation of the prodelta system the phosphogenic black shale facies deposited in an oxygen minimum zone omz of the open shelf environment during the late transgressive to regressive phases under conditions of high biological productivity suppressed sedimentation rates and changing bottom redox the phosphatic black shales occurring in the lower and upper parts of the phosphogenic succession reveal depositional conditions indicative of the shallower part of omz including high input of autochthonous organic matter into sediment oxic to dysoxic episodically suboxic and or anoxic conditions intense phosphogenesis and recurrent reworking of the seabed the massive phosphatic mudstone occurring in the middle of the phosphogenic succession reflects the development of euxinia in the deeper part of omz during high stand of the sea high input of autochthonous organic matter in this environment was coupled with mineral starvation and intermittent phosphogenesis in mature sections in eastern svalbard the petroleum potential of the botneheia formation rises from moderate to good in the black shale facies and from good to very good in the phosphogenic black shale facies attaining maximum in the massive phosphatic mudstone

seismic signature of the collision between the east tibetan escape flow and the sichuan basin abstract gps displacement vectors show that the crust in east tibet is being squeezed in an easterly direction by the northward motion of the indian plate and the sichuan basin is resisting this stream and redirecting it mainly towards indochina the longmen shan containing the steepest rise to the high plateau anywhere in tibet results from the strong interaction between the east tibetan escape flow and the rigid yangtze block sichuan basin but the kinematics and dynamics of this interaction are still the subject of some debates we herein present results from a dense passive source seismic profile from the sichuan basin into eastern tibet in order to study the deep structure of this collision zone using p and s receiver function images we observe a sudden rise of the lithosphere asthenosphere boundary lab from 120 to 150 km beneath the sichuan basin and from 70 to 80 km beneath eastern tibet in contrast the depth of the crust mantle boundary moho increases from 36 to 40 km beneath the sichuan basin and from 55 to 60 km beneath eastern tibet the 410 km discontinuity is depressed below eastern tibet by about 30 km although the 660 remains at nearly the same depth throughout the lms from these observations we conclude that the mode of collision that occurs between tibet and the sichuan basin is very different to that found between india and tibet in southern tibet we observe in essence the subduction of the indian plate which penetrates northwards for several hundred kilometers under central tibet the very thin mantle part of the lithosphere beneath eastern tibet may indicate delamination or removal of the bottom of the lithosphere by hot asthenospheric escape flow this process leads to the exceptionally steep topography at the eastern tibetan margin as a result of gravitational buoyancy this view is supported by the very unusual depression of the 410 km discontinuity beneath eastern tibet which could be caused by the dynamics of the sub vertical downward asthenospheric flow

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

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

new insights into the generation of the 2013 lushan earthquake ms 7 0 china global seismic waveform inversion can provide information on where the 2013 ms 7 0 lushan earthquake occurred in sichuan province china and how its aftershock sequence expanded to investigate the generation mechanism of the lushan earthquake and its relation to the 2008 wenchuan earthquake ms 8 0 50 temporary seismic stations were installed in the source area following the lushan earthquake crustal stress data were also collected along the longmen shan fault zone lmfz to reveal its influence on the generation of the lushan earthquake seismic imaging and crustal stress analysis have revealed that the lushan earthquake occurred in a distinct area with high velocity vp vs low poisson s ratio and high crustal stress the high velocity zone at the lushan source may reflect precambrian metasedimentary or igneous rock in the seismogenic layer which enables the accumulation of high crustal stress to generate large earthquakes however a sharply contrasting gap zone with low velocity high anomalies is clearly imaged in the upper crust under the concatenated area between the lushan and wenchuan earthquakes seismic images indicate that the low velocity gap zone is associated with fluid bearing ductile flow from the lower crustal materials of tibet being pushed into a weakened segment of the lmfz this study suggests that the 2013 lushan earthquake may have been triggered by high crustal stress accumulation together with high coseismic stress further increased by the wenchuan earthquake in the metamafic seismogenic layer contrasting rheological variations in the crust and crustal stress changes along the lmfz control the rupture processes that generated the lushan and wenchuan earthquakes as well as the generation of new earthquakes in the future

stress distribution near the seismic gap between wenchuan and lushan earthquakes the wenchuan m s 8 0 earthquake and lushan m s 7 0 earthquake unilaterally fractured northeastward and southwestward respectively along the longmenshan fault belt the aftershock areas of the two earthquakes were separated by a gap with a length of nearly 60 km we have determined the focal mechanisms of 471 earthquakes with magnitude m 3 from jan 2008 to july 2014 near the seismic gap using a full waveform inversion method normal thrust and strike slip focal mechanisms can be found in northern segment but in a significant contrast focal mechanisms of the earthquakes in the southern segment are dominated by thrust faulting based on the determined source parameters we further apply a damped linear inversion method to derive the regional stress field the southern segment is characterized by an obvious thrust faulting stress regime with a nearly horizontal maximum compression that orients in se nw direction the stress environment in the northern segment is a lot more complicated the maximum compressional stresses appear to rotate around the asperity near west of the dujiangyan city stress field also shows strong variation with time and depth before 2009 the seismic activities are more concentrated on the pengxian guanxian fault and yingxiu beichuan fault with dominant strike slip faulting and normal faulting while after 2009 the seismic activities are dominated by thrust faulting from north to south while the activities are more concentrated on the wenchuan maoxian fault in northern segment and pengxian guanxian fault in southern segment the maximum compressional stresses vary in different depths from north to south thus may imply the decoupled movement in shallow and in depth

paleoseismic events on the shuangshi dachuan fault of the seismic gap longmen shan thrust belt eastern margin of the tibetan plateau abstract over a five year period the longmen shan thrust belt was the source of the 2008 ms 8 0 wenchuan earthquake and the 2013 ms 7 0 lushan earthquake leaving a seismic gap between the seismogenic structures of these two earthquakes in this study we report on a trenching and dating program to assess the rupture behavior of the shuangshi dachuan fault as well as analyzing its geological significance and discussing the seismic potential of the seismic gap one paleoseismic event 5382 385 yr b c and another possible event 1013 1560 yr a d were identified in our study based on geological physiognomy fault geometry and paleoseismic events etc and geophysical marks etc the shuangshi dachuan fault in the seismic gap can be divided into two segments a southern segment 1 and a northern segment 2 based on six trenches across the shuangshi dachuan fault in the seismic gap using the event window method at least four paleoseismic events are identified 120 435 yr b p 720 905 yr b p 2475 2717 yr b p 2335 3830 yr b p closest to 3830 yr b p the change in characteristics such as strike main stress maximum dislocation of single paleoseismic events and strike fault activity trace from segment 1 to segment 2 reflect the character of the longmen shan thrust belt transition zone vertical displacements of single earthquakes from the six trenches in the seismic gap are similar and small 0 2 0 4 m the reason for which may be that the seismic gap is a weak part in the upper crust of ductile rocks with low stress the seismic capacity of the seismic gap is likely ms

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

crustal anisotropy from moho converted ps wave splitting analysis and geodynamic implications beneath the eastern margin of tibet and surrounding regions abstract in addition to crustal thickening distinctly different mechanisms have been suggested to accommodate the huge convergences caused by the continental collision between india and eurasia as the transition zone between the two grand tectonic domains of asia the tethys and the pacific east tibet and its surrounding regions are the ideal places to study continental deformation pervasive rock deformation may produce anisotropy on the scale of seismic wavelengths thus seismic anisotropy provides insight into the deformation of the crust and mantle beneath tectonically active domains in this study we calculated receiver function pairs of radial and transverse components at 98 stations located in sichuan and yunnan provinces china we selected 7423 pairs with high signal to noise ratio snr and unambiguous moho converted ps phases pms to measure the pms splitting owing to the crustal anisotropy both the crustal thickness and the average crustal vp vs ratio were calculated simultaneously by the h k stacking method the geodynamic implications were also investigated in relation to surface geological features gps velocities absolute plate motion apm sks skks splitting and other seismological observations in addition to the fast polarization directions fpds of the crustal anisotropy we observed a conspicuous sharper clockwise rotation around the eastern himalayan syntaxis than was revealed by gps velocities the distributed fpds within and near the main active fault zones also favored the directions parallel to the faults this implied that the deformation of a continuous medium revealed by gps motions is a proxy for the deformation of the brittle shallow crust only while the main active faults and the deep crustal interiors both play important roles in the deep deformation our results suggest that the deformation between the crust and upper mantle within the northernmost section of the indochina block is decoupled due to the large difference in the directions between the observations related to the crust gps and crustal anisotropy and mantle apm and mantle anisotropy focusing on the transition zone between the plateau and the south china and indochina blocks we suggest that the motion of the central yunnan sub block is a southeastward extrusion by way of tectonic escape there is less deformation in the deep crust and the motion is controlled by the active boundary faults of the ailaoshan red river shear zone to the west and the xianshuihe xiaojiang fault to the east the lower crustal flow within the plateau southeastward reached the lijiang xiaojinhe fault but further south it was obstructed by the central yunnan sub block

the elastic anisotrophy of shales shales constitute about 75 of the clastic fill sedimentary basins and have a decisive effect on fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure the elastic stiffnesses of a shale with partially oriented clay particles is expressed in terms of the coefficients w sub lmn in an expansion of the clay particle orientation distribution function in generalized legendre functions application is made to the determination of the anellipticity of shales for transverse isotrophy the anellipticity quantifies the deviation of the p wave slowness curve from an ellipse and is shown to depend on a single coefficient w sub 400 in the expansion of the clay particle orientation distribution function if w sub 400 is small the anellipticity may be neglected as is apparently the case for a near surface late tertiary shale studied by winterstein and paulson strongly aligned clay particles result in a positive value of w sub 400 and a positive anellipticity in agreement with the majority of the field measurements however less well ordered shales could have a significantly positive second moment w sub 200 but only a small positive or even negative value of w sub 400 for such shales the anellipticity would be small or negative despite amore preferred alignment of clay particles in the bedding plane numerical examples of clay particle orientation distribution functions leading to zero or negative anellipticity are given less

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

p sh conversions in layered media with hexagonally symmetric anisotropy a cookbook reflectivity synthetic seismograms demonstrate that the type layering and orientation of 1 d anisotropy influences strongly the coda of teleseismic p waves at periods t 1 sec particularly p sh converted waves we assume the simplest form of anisotropy described by an elastic tensor with a symmetry axis of arbitrary orientation the resulting phase velocities vary as cos 2 with respect to that axis using three families of simple crustal models we compare the effects of an anisotropic surface layer with reverberations caused by both thick and thin layers of anisotropy at depth if anisotropy in the surface layer is significant the polarization of direct p can be distorted to generate a transverse component followed by ps and a prominent shear reverberation converted from direct p at the free surface if the anisotropic layer is buried the first and often the most prominent arrival on the transverse component is the p to sh conversion at its upper surface if the anisotropic layer is sufficiently thin p to sh conversions from its boundaries interfere to form a derivative pulse shape on the transverse component which could be mistaken as the signature of shear wave splitting if is horizontal compressional p and shear s anisotropy both produce similar waveform perturbations with four lobed azimuthal patterns suggesting that a weighted stack of p coda from different back azimuths would improve signal to noise for tilted between the horizontal and vertical however the effects of p and s anisotropy differ greatly the influence of p anisotropy on p to s conversion is greatest for a symmetry axis tilted at 45 to the vertical where its azimuthal pattern has two lobes rather than four combinations of p and s anisotropy typically lead to a composite azimuthal dependence in the p coda reverberations

seismic anisotropy in eastern tibet from shear wave splitting reveals changes in lithospheric deformation abstract knowledge about seismic anisotropy can provide important insight into the deformation of the crust and upper mantle beneath tectonically active regions here we focus on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china we measured shear wave splitting of core refracted phases sks and skks at a temporary array of 25 iris passcal stations we calculated splitting parameters using a multi channel and a single record cross correlation method multiple layers of anisotropy cannot be ruled out but are not required by the data a fresnel zone analysis suggests that the shallow mantle between 60 and 160 km depth is the most likely source of anisotropy the polarization directions reveal a pronounced transition from primarily north south in the north sichuan to mostly east west orientations in the south yunnan in the southern part of the study region that is south of 26 n the fast polarization directions do not correlate well with known surface features and geodetic estimates of the crustal displacement fields whereas gps campaigns provide evidence suggesting north south crustal flow across the red river fault the pattern of anisotropy argues against such flow in the upper mantle these observations support models that allow differential movement of upper crust relative to lithospheric mantle in the northern part of the study region the relationships are more ambiguous and coherent deformation of the crust and mantle lithosphere cannot be excluded the interpretation of the shear wave splitting results is non unique but we suggest that the observed n s transition reflects a fundamental change in deformation regime across our study region it may be related to lateral variations in lithospheric rheology or may mark a transition from the direct impact of the continental collision to dominance of the far field strain field associated with regional subduction processes understanding the nature of the lateral change in deformation regime may prove critical for our understanding the geotectonic evolution of eastern tibet

the kinematics of northern south island new zealand determined from geologic strain rates relative motions within the distributed plate boundary zone of northern south island new zealand are determined through an inversion of geologic strain rate estimates the quaternary fault slip rate estimates define the shear strain rates and rock uplift rates provide information on the horizontal divergence rates an erosion rate to rock uplift rate ratio along with a crustal compensation factor is estimated in order to convert rock uplift rates to horizontal divergence rates because of the uncertainty in erosion rates horizontal divergence rates are given a large standard error of the three horizontal strain rate components obtained from these data completely define the horizontal velocity gradient tensor strain rate distributions are matched with spline polynomial functions which can be constrained to behave rigidly within specified regions such as the pacific or australian plates inversion of the strain rate distribution assuming uniform erosion rates across the northern south island yields a velocity field that has small differences in both magnitude 10 larger and direction with the nuvel 1a plate motion model between pacific and australian plates a revised strain rate data set obtained from a variable erosion model in which erosion rates are a linear function of the log of the average annual rainfall magnitudes yields a velocity field with expected directions that are indistinguishable from the nuvel 1a plate motion model between pacific and australian plates but velocity magnitudes are still 10 15 higher than the plate motion model therefore the average values of slip rate on strike slip faults in marlborough required by the nuvel 1a plate motion model are typically close to the low end of the published range of slip values for those structures the major strike slip structures within the marlborough region are accommodating 80 100 of the total plate motion between australia and pacific plates on northern south island as much as 20 of the relative motion could be accommodated by shear generated by folding or thrust faulting with a single orientation between the major structures the magnitude of plate motion contributed by the major faults indicates that the distributed geodetic shear strains measured across northern south island and discussed by bibby 1981 and walcott 1984 are not a form of irrecoverable strain but rather a feature of the strain field that will eventually be released primarily as concentrated slip on the strike slip structures within the region strain modeling indicates that the earthquake moment release over the last 150 years within the northwest nelson province which is west of the marlborough region is at least half an order of magnitude higher than the long term rate of moment release overall the northwest nelson region is playing only a minor role in taking up the long term plate motion

regional maturity as determined by organic petrography and geochemistry of the schei point group triassic in the western sverdrup basin canadian arctic archipelago abstract maturity and source rock potential of organic rich beds in the triassic schei point group in the sverdrup basin arctic canada have been investigated using reflected light microscopy and the results are compared with other maturity parameters determined geochemically i e rock eval and biomarker maturation parameters the samples evaluated belong to the eden bay member of the hoyle bay formation and contain a predominance of marine algal material in the form of tasmanales and dinoflagellates along with mixed terrestrial organics the rock matrix is dominantly carbonate with some shaly input indicating that the rocks were deposited in an iron poor highly euxinic environment with few exceptions there is good agreement between parameters determined using microscopy namely r o max and r gq and geochemical parameters t max hi dia c 27 dia c 27 reg c 27 steranes s s r c 29 steranes the ternary diagram showing the abundance of normalized c 27 c 28 and c 29 regular steranes indicates a mostly marine depositional environment for the schei point source rock this is confirmed by the abundance of marine fauna and flora in these samples analytical results from several different techniques indicate that the source rocks become more mature from the margin towards the axis of the sverdrup basin this is due in part to the increase in overburden of sediments in the axis of the basin also the high thermal conductivity of salt has strongly influenced the maturity of schei point source rocks over the crest of the salt cored structures i e well hazen f 54 and the proximity of salt has enhanced maturation levels at well rock point j 43 the sections investigated were also considered to have an excellent gas potential due to their higher than average toc content

new evidence for the chronology of the eurekan orogeny from south central ellesmere island discovery of a post orogenic coarse grained sandstone and pebble to cobble conglomerate unit on south central ellesmere island provides important new evidence for the chronology of the eurekan orogeny in the eastern arctic archipelago palynological studies indicate an early miocene age for these deposits which rest with marked angular unconformity on mid paleocene strata in adjacent areas strata of the eureka sound formation as young as middle eocene are folded thereby bracketing the major orogenic phase of the eurekan orogeny on southern ellesmere island as post middle eocene to pre early miocene furthermore the occurrence of the coarse grained sandstone and conglomerate deposits indicates an early miocene phase of epeirogenic relative uplift of southeastern ellesmere island and possible coeval tectonism along the margin of baffin bay the discovery and dating of these post orogenic deposits provide additional chronological evidence for tectonism that constrains paleogeographic and paleo plate rec

distinct upper mantle deformation of cratons in response to subduction constraints from sks wave splitting measurements in eastern china abstract interaction between the subducting slab the overriding continental lithosphere and mantle flow are fundamental geodynamic processes of subduction systems eastern china is an ideal natural laboratory to investigate the behavior and evolution of cratonic blocks within a subduction system in this study we investigate deformation of the upper mantle beneath eastern china we present seismic shear wave splitting measurements from three networks consisting of over 483 broadband stations with 157 stations giving a total of 516 results the splitting parameters exhibit complex regional patterns but are relatively coherent within individual tectonic units tectonic blocks exhibited distinctive fast directions relative to regional features the dominant attitude of fast directions for the north china craton was subparallel to the direction of subduction whereas fast directions for southeastern china were perpendicular to the direction of subduction the shear wave splitting measurements were interpreted according to a high resolution tomographic body wave velocity model combining these two datasets showed that the predominant geodynamic models for the region mantle plume mantle wedge and flat slab subduction models are incompatible with the observations presented here we suggest that the north china craton yangtze craton and the cathaysia block have undergone different deformational events due to differing mantle flow patterns and distinct spatial and temporal subduction histories of the pacific and philippine sea plates

high latitude meteoric δ 18 o compositions from the cenomanian bastion ridge formation axel heiberg island canadian arctic archipelago a palaeoclimate proxy from the sverdrup basin

relationships between thermal maturity indices calculated using arrhenius equation and lopatin method implications for petroleum exploration thermal maturity can be calculated with time temperature indices tti based on the arrhenius equation using kinetics applicable to a range of types ii and iii kerogens these ttis are compared with tti calculations based on the lopatin method and are related theoretically and empirically via vitrinite reflectance to the petroleum generation window the ttis for both methods are expressed mathematically as integrals of temperature combined with variable linear heating rates for selected temperature intervals heating rates control the thermal maturation trends of buried sediments relative to arrhenius ttis lopatin ttis tend to underestimate thermal maturity at high heating rates and overestimate it as low heating rates complex burial histories applicable to a range of tectonic environments illustrate the different exploration decisions that might be made on the basis of independent results of these two thermal maturation models

tectonic history from vitrinite reflectance summary the degree of organic metamorphism of carbonaceous matter is expressed in terms of the reflectance of vitrinite vitrinite reflectance is a function of temperature and time a model relating vitrinite reflectance to temperature and time is proposed from published vitrinite reflectance temperature time nomograms a plot of the logarithm of vitrinite reflectance versus depth gives a linear curve for vitrinite reflectance greater than 0 3 per cent in a sedimentary basin which has had a constant geothermal gradient throughout its tectonic history the geothermal gradient c km 1 is equal to the slope of the curve multiplied by 194 8 the model is also applied to sedimentary basins with decreasing geothermal gradient with time i e cooling continental margin basins the vitrinite reflectance model is demonstrated to be consistent with observed reflectance data and tectonic information from the sydney bowen surat and gippsland basins in eastern australia

on the relation between seismic anisotropy and finite strain because seismic anisotropy in the upper mantle is due primarily to lattice preferred orientation lpo of olivine crystals induced by deformation observations of anisotropy can provide constraints on mantle deformation and flow in this paper we use a previously published theory for deformation induced lpo ribe and yu 1991 to quantify the relation between seismic anisotropy and deformation for two model compositions a pure olivine dunite aggregate and a harzburgite comprising 70 olivine and 30 enstatite analytical and numerical solutions of the governing equations show that the predicted lpo and hence also the seismic anisotropy depends only on the finite strain and not on the deformation path by which that strain is produced the magnitude of the anisotropy depends only on the ratios c1 c2 and c2 c3 where c1 c2 c3 are the lengths of the principle axes of the finite strain ellipsoid and the directions of maximum and minimum compressional wave velocity vp coincide with the axes c1 and c3 respectively we calculate the percent anisotropies for compresional and shear waves propagating along the three principle axes of the finite strain ellipsoid as functions of the axial ratios c1 c2 and c2 c3 for our two model compositions however inferences of the magnitude of finite strain obtained using these results are likely to be minimum estimates because our theory neglects the effects of dynamic recrystallization finally we present as a byproduct of this study a new direct method for calculating the finite strain produced by an arbitiary deformation history

state of stress before and after the 1994 northridge earthquake the state of tectonic stress in the epicentral area of the 17 january 1994 northridge earthquake mw 6 7 is investigated by applying a stress inversion method to p wave polarity data from earthquakes in northridge from july 1981 to january 1994 and from the northridge aftershocks during january 1994 to december 1995 a 3 d crustal model is used to trace the rays taking off from the hypocenter which reduced the effects of large structural heterogeneities on the determination of the stress tensor we found significant temporal changes of stress orientations induced by the northridge earthquake the principal pressure p axis is oriented n32 e from 1981 to june 1992 and n30 e from 28 june 1992 to 16 january 1994 suggesting that the stress field in northridge was not affected by the 1992 landers earthquake during two weeks following the northridge mainshock the p axis is oriented n13 e which is a significant 17 change from that before the earthquake n30 e between february 1994 and august 1995 the p axis orientation changes from n18 e to n26 e and finally ends up at n34 by the end of 1995 which is close to that before the northridge earthquake these results suggest that the stresses rotated coseismically then rotated more slowly back to their original orientation the aftershocks caused by the mainshock changed the stress distribution in the crust which showed up as a regional stress change the stress recovery appears to have completed within two years after the mainshock which is very short compared to the time scale of the earthquake cycle

influence of igneous intrusions on thermal maturity and optical texture comparison between a bituminous marl and a coal seam of the same maturity abstract the impact of a 120 cm thick dike on dispersed organic matter in the triassic marry harbour mh bituminous marl in the raanes peninsula ellesmere island arctic canada was studied using reflected light microscopy and rock eval pyrolysis results were compared to a coal seam of similar maturity that was thermally altered by an igneous intrusion the mh bituminous marl is mature and within the oil window ro 0 94 whereas the coal is high volatile b bituminous rank ro 0 80 thermal alteration impacted differently the organic rich marl than the coal seam most of the heat generated by the intrusive emplacement in contact with coal is spent transforming coal to coke in the plastic layer zone similar to the process that coal undergoes in industrial coking operations in contrast the thermal alteration of sedimentary rocks occurs over longer distances as a result of the absence of a plastic layer zone the impact zone of the 120 cm thick igneous intrusion was greater in the mh bituminous marl which became thermally altered ro 2 34 at 190 cm from the contact with the dike on the contrary the coal became thermally altered ro 5 0 by a 240 cm alkali basalt intrusion twice the thickness of the mh dike and its impact zone was only 65 cm heat and hot volatile matter produced by the thermal decomposition of organic matter and minerals carbonate dehydration of clay minerals in contact with the igneous intrusion body is transferred through the sedimentary rock matrix by convection through fractures this transformation is evident by the occurrence of the pyrolytic carbon at various distances in the fractured mh marl from contact the hydrogen index hi shows a similar trend to that of the remaining source potential s2 both parameters decrease systematically toward the dike and go through a minimum at 20 cm from the dike contact as the indigenous organic matter is converted to hydrocarbons or devolatilized at the dike contact both s2 and hi have higher values these trends are similar to those of the volatile elements h and cl in the intruded coal seam the free hydrocarbons s1 showed a slightly different trend than s2 and hi it increased initially from 300 cm and reached a maximum at about 190 cm from the dike contact before decreasing continually and reaching a minimum at 20 cm from the contact at the dike contact the s1 increased slightly similar to the hi and s2 the presence of oil droplets trapped in carbonate concretions in combination with the highest value of oil expelled from the source rock based on s1 toc at distance of 190 cm from dike is an indication of the influence of contact metamorphism on oil generation locally furthermore it indicates that intrusion of igneous dikes into the bituminous mh marl resulted in an increase of organic matter maturation locally and in hydrocarbon generation

upper mantle velocity structure beneath the tibetan plateau from pn travel time tomography we inverted 1510 p arrival times from regional distances 333 1600 km in and around the tibetan plateau to map the lateral velocity variation within the uppermost mantle previous studies have placed first order constraints on upper mantle velocities but relied on data recorded almost exclusively at stations outside of the plateau we improve resolution by using 40 events recorded at stations within the tibetan plateau we combine these data with observations obtained from the international seismological centre isc to extend our coverage by including pn arrivals from 85 additional plateau events relocated in previous studies and recorded at stations in and around the tibetan plateau we use synthetic travel time data to evaluate the resolution of our data set the observations provide good resolution to about 1 over most of the plateau and surrounding regions our results show average pn velocities that are about 3 lower in the northern plateau relative to the southern plateau these variations correlate well with major tectonic features and previous geophysical observations in the qiangtang terrane of the northern plateau an area known to be inefficient for sn propagation pn is slow relative to both the plateau south of the banggong nujiang suture and the tectonically stable tarim basin north of the plateau this is strong evidence for the existence of partial melt within the uppermost mantle beneath the northern tibetan plateau however when laboratory estimates of relationships between temperature velocity and attenuation are applied a relatively small temperature variation 240 to 370 c is required to explain our pn velocity observations when combined with geochemical constraints from volcanics in the northern plateau our results strongly suggest that the mantle lid is intact beneath the northern plateau this result would preclude tectonic models involving wholesale delamination of the mantle lithosphere in the northern tibetan plateau

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

local stress perturbations associated with the 2008 wenchuan m 8 0 earthquake near the longmenshan fault zone in the eastern margin of the tibetan plateau abstract the 2008 wenchuan m 8 0 earthquake induced local stress perturbations near the longmenshan lms fault zone using in situ measurements and stress tensor inversions from focal mechanisms we investigated the post earthquake perturbed stress field at shallow depths 1 2 km in the upper crust above a basal attachment 5 18 km as well as in the middle crust beneath a basal attachment 19 32 km at shallow depths in the beichuan jiangyou section the maximum principal stress 1 orientations changed from a pre earthquake orientation of nww to a post earthquake orientation of nee however near the baoxing an xian and qingchuan mianxian sections the pre earthquake 1 orientation of nw nww was largely unaltered before the mainshock in the upper crust above the basal detachment the entire lms fault zone exhibited a consistent 1 orientation of nw nww however after the earthquake some sections such as the beichuan nanba section achieved 1 orientations of nee that were distinctly different from the pre seismic stress field in the middle crust beneath the basal detachment the stress field was mostly unchanged the crust beneath the basal detachment along the eastern margin of the tibetan plateau is dominated by nww oriented maximum principle stress and strain directions and a thrust faulting stress regime along the entire lms fault zone these observations are representative of the southeastward motion of the bayan har block and its ongoing collision with the south china block along the lms thrust belt the spatially heterogeneous stress field that occurred in the upper crust 18 km after the mainshock was most likely caused by the co seismic static stress changes associated with the wenchuan earthquake prior to the onset of seismic activity the deviatoric stress magnitudes were estimated at less than 22 mpa and 4 mpa at depths of 10 km and 20 km respectively suggesting that the mainshock fault zone has a relatively low fault strength to overcome in order to initiate significant co seismic rupture and aftershocks especially in the crust beneath the basal detachment these smaller deviatoric magnitudes are indicative of the weaker fault materials that resides in the lms region

viscoplastic self consistent and equilibrium based modeling of olivine lattice preferred orientations implications for the upper mantle seismic anisotropy anisotropy of upper mantle physical properties results from lattice preferred orientation lpo of upper mantle minerals in particular olivine we use an anisotropic viscoplastic self consistent vpsc and an equilibrium based model to simulate the development of olivine lpo and hence of seismic anisotropy during deformation comparison of model predictions with olivine lpo of naturally and experimentally deformed peridotites shows that the best fit is obtained for vpsc models with relaxed strain compatibility slight differences between modeled and measured lpo may be ascribed to activation of dynamic recrystallization during experimental and natural deformation in simple shear for instance experimental results suggest that dynamic re crystallization results in further reorientation of the lpo leading to parallelism between the main 010 100 slip system and the macroscopic shear thus modeled simple shear lpos are slightly misoriented relative to lpos measured in natural and experimentally sheared peridotites this misorientation is higher for equilibrium based models yet seismic properties calculated using lpo simulated using either anisotropic vpsc or equilibrium based models are similar to those of naturally deformed peridotites errors in the prediction of the polarization direction of the fast s wave and of the fast propagation direction for p waves are usually 15 moreover overestimation of lpo intensities in equilibrium based and vpsc simulations at high strains does not affect seismic anisotropy estimates because these latter are weakly dependent on the lpo intensity once a distinct lpo pattern has been developed thus both methods yield good predictions of development of upper mantle seismic anisotropy in response to plastic flow two notes of caution have nevertheless to be observed in using these results 1 the dilution effect of other upper mantle mineral phases in particular enstatite has to be taken into account in quantitative predictions of upper mantle seismic anisotropy and 2 lpo patterns from a few naturally deformed peridotites cannot be reproduced in simulations these abnormal lpos represent a small percent of the measured natural lpos but the present sampling may not be representative of their abundance in the earth s upper mantle

differential strain transfer longmen shan thrust belt eastern tibetan plateau margin implications for seismic hazards abstract southeastward strain transfer in the middle southern longmen shan lms thrust belt not only can promote the development of fault related folds and earthquakes in the piedmont but also affect the seismogenic capacity of the middle southern lms thrust belt however the detailed transfer process remains elusive in this work we combine structural profile re analysis sandbox modeling and seismic statistics to illustrate the strain transfer process our main results indicate that 1 the thickness of the shallow detachment e g middle lower triassic gypsum salt strata is probably the main factor for differences in southeastward strain transfer within the domain between the middle southern lms thrust belt and weiyuan moxi anticline this is also supported by our sandbox model 2 the seismogenic capacity in the southern lms thrust belt is probably proportional to the corresponding shortening of the range front blind thrust rfbt thus seismogenic capacity in the seismic gap zone is weaker than those of other segments of the southern lms thrust belt which is probably

concealed quaternary strike slip fault resolved with airborne lidar and seismic reflection the grizzly valley fault system northern walker lane california 1 the grizzly valley fault system gvfs strikes northwestward across sierra valley a low relief basin situated within a network of active dextral slip faults in the northern walker lane california quaternary motion along the grizzly valley fault system has not been previously documented we used high resolution 0 25 m airborne lidar data in combination with high resolution p wave seismic reflection imaging to evaluate quaternary deformation associated with the gvfs we identified suspected tectonic lineaments using the lidar data and collected seismic reflection data along six profiles across the lineaments the seismic reflection images reveal a deformed basal marker that we interpret to be the top of tertiary volcanic rocks overlain by a 120 450 m thick suite of subhorizontal reflectors that we interpret to be plio pleistocene lacustrine deposits three profiles image features that we interpret to be the principal active trace of the gvfs which is a steeply dipping fault zone that vertically offsets the volcanic rocks and the lacustrine basin fill these data suggest that the gvfs may have been active in latest quaternary time because 1 the lidar data show subtle surficial geomorphic features that are typical of youthful faulting including a topographic lineament marked by an 1 m high ridge composed of discontinuous left stepping lobes and 2 the seismic profiles demonstrate shallow faulting of the lacustrine strata that coincides with the left stepping ridge this investigation illustrates the potential for unidentified low rate strike slip faults in basins and emphasizes the value of high resolution topographic data and subsurface imaging as a means of identifying these structures

heterogeneity and anisotropy of the lithosphere of se tibet from surface wave array tomography 1 understanding the geotectonic evolution of the southeastern tibetan plateau requires knowledge about the structure of the lithosphere using data from 77 broadband stations in sw china we invert rayleigh wave phase velocity dispersion curves from ambient noise interferometry t 1 0 40 s and teleseismic surface waves t 2 0 150 s for 3 d heterogeneity and azimuthal anisotropy in the lithosphere to 150 km depth our surface wave array tomography reveals 1 deep crustal zones of anomalously low shear wave speed and 2 substantial variations with depth of the pattern of azimuthal anisotropy upper crustal azimuthal anisotropy reveals a curvilinear pattern around the eastern himalayan syntaxis with fast directions generally parallel to the main strike slip faults the mantle pattern of azimuthal anisotropy is different from that in the crust and varies from north to south the tomographically inferred 3 d variation in azimuthal anisotropy helps constrain the source region of shear wave splitting south of 26 n off the high plateau most of the observed splitting can be accounted for by upper mantle anisotropy but for stations on the plateau proper with thick crust crustal anisotropy cannot be ignored on long wavelengths the pattern of azimuthal anisotropy in the crust differs from that in the mantle this is easiest explained if deformation varies with depth the deep crustal zones of low shear wave speed and presumably mechanical strength may represent loci of ductile deformation but their lateral variation suggests that in se tibet localized crustal channel flow and motion along the major strike slip faults are both important

upper mantle seismic velocities and anisotropy in china determined through pn and sn tomography 1 we have obtained velocity images of the uppermost mantle beneath china by performing tomographic inversion of both pn and sn traveltimes from the annual bulletin of chinese earthquakes 99 139 pn arrivals and 43 646 sn arrivals were selected pn anisotropy was also obtained simultaneously with pn velocity average pn and sn velocities are 8 05 and 4 55 km s respectively and maximum velocity perturbations are about 3 4 the pn and sn velocities are low in eastern china and high in western china particularly high velocities are associated with old basins for example tarim junggar turpan hami qaidam and sichuan and stable craton for example ordos low sn velocities are found mainly throughout north china in addition velocities are relatively low beneath the central tibetan plateau and the north south seismic zone along 103 e in tarim and central china where we observe strong anisotropy the fast pn velocity directions are consistent with the directions of maximum principal compressive stress as well as directions of crustal movement determined from global positioning system beneath the india eurasia collision zone the pn anisotropy direction is parallel to the collision arc and nearly perpendicular to both the direction of maximum compression and crustal movement resulting from pure shear deformation both the velocity variations and anisotropy indicate that the tibetan plateau was extruded and the mantle material beneath the plateau has flowed around the east himalaya syntax while the remaining material has diverted northwestward beneath the tarim basin

new images of the crustal structure beneath eastern tibet from a high density seismic array abstract an east west trending high density seismic array was deployed along the eastern margin of the tibetan plateau to investigate its eastward expansion the 160 km long array spans the ruoergai basin minjiang fault minshan mountains tazang fault and west qinling the array included 330 short period seismographs spaced at 500 m intervals which recorded teleseismic 3 component waveforms over a one month period p wave receiver functions calculated from 35 teleseismic events provided an image of crustal structure the results show a massive thrust nappe structure around the minshan mountains and beneath the minjiang fault we suggest that this nappe formed after the closure of the paleo tethyan ocean the resultant triassic thrusting contributed to partial uplift of the eastern ruoergai basin and the minshan mountains in middle to late miocene time receiver function images show that the tazang fault is a crustal scale rupture cutting across the moho the western tazang fault appears as a nearly vertical strike slip fault accommodating left lateral shear at the terminus of the eastern kunlun fault after clockwise rotation from an approximate east west orientation to a nearly north south orientation the eastern tazang fault became a west dipping thrust fault which caused crustal thickening beneath the minshan mountains and the west qinling our results suggest that late cenozoic uplift of the eastern margin of the plateau is produced by eastward overthrusting and crustal shortening processes that absorbed slip along the tazang and kunlun faults

on the evolution of seismogenic faults in the longmen shan eastern tibet abstract a fundamental debate exists regarding the geometry and depth extent of seismogenic faults in eastern tibet along the longmen shan geologic and seismic reflection data reveal a belt of low to moderate angle thrust faults some of which may have been activated in devastating earthquakes in 2008 mw 7 9 wenchuan and 2013 mw 6 6 lushan however geologic and geodetic constraints on these ruptures suggest rupture along relatively high angle listric reverse faults here we use a combination of focal mechanisms determined from 276 aftershocks ms 4 0 with well determined waveforms and aftershock distributions from the 2008 event to determine subsurface fault geometry our results imply that seismogenic slip occurred along relatively high angle structures that cross cut low angle imbricate faults imaged in reflection seismic data thus we suggest that current geometric models of seismogenic faults may not fully represent the distribution of subsurface seismic hazard along the heavily populated sichuan basin

crustal structure and deformation under the longmenshan and its surroundings revealed by receiver function data abstract the convergence of india and eurasia and the obstruction from the rigid sichuan basin cause the longmenshan lms to have the steepest topographic gradient at the eastern margin of the tibetan plateau however the mechanisms of surface uplift are still controversial in this paper we estimate the crustal structure and deformation under the lms and its surroundings by analyzing a large amount of receiver function data recorded by regional seismic networks of the china earthquake administration we apply a comprehensive splitting measurement technique on ps conversion phase at the moho moho ps splitting to calculate crustal anisotropy from azimuthal variations of receiver functions our results show that most of the seismic stations beneath the lms area exhibit significant seismic anisotropy with the splitting time of 0 22 0 94 s and a fast polarization direction of nw se while less or even no crustal anisotropy has been observed under the sichuan basin comparing the fast polarization directions of moho ps splitting with the indicators of lithospheric deformation such as shear wave splitting absolute plate motion and global positioning system imply a consistent tendency of deformation between the lower crust and upper mantle but decoupling deformation in the crust beneath the lms area we further compare moho ps splitting time to that estimated from previous sks splitting indicating that crustal anisotropy is an important source of the sks splitting time in this study area in addition a thick crust 50 km with high vp vs values 1 74 1 86 is also observed using the h stacking method these seismic observations are consistent with the scenario that the lms area has been built by the lower crustal flow combined with the seismic reflection refraction profile and geology studies we further suggest that the lower crustal flow may extrude upward into the upper crust along the steeply dipping strike faults under the lms area resulting in the surface uplift of the lms

complex multilayered azimuthal anisotropy beneath tibet evidence for co existing channel flow and pure shear crustal thickening of the two debated end member models for the late cenozoic thickening of tibetan crust one invokes channel flow rapid viscous flow of the mid lower crust driven by topography induced pressure gradients and transporting crustal rocks eastward and the other pure shear faulting and folding in the upper crust with viscous shortening in the mid lower crust deep crustal deformation implied by each model is different and would produce different anisotropic rock fabric observations of seismic anisotropy can thus offer a discriminant we use broadband phase velocity curves each a robust average of tens to hundreds of measurements to determine azimuthal anisotropy in the entire lithosphere asthenosphere depth range and constrain its amplitude inversions of the differential dispersion from path pairs region average inversions and phase velocity tomography yield mutually consistent results defining two highly anisotropic layers with different fast propagation directions within each the middle crust and the asthenosphere in the asthenosphere beneath central and eastern tibet anisotropy is 2 4 per cent and has a nne ssw fast propagation azimuth indicating flow probably driven by the nne ward shallow angle subduction of india the distribution and complexity of published shear wave splitting measurements can be accounted for by the different anisotropy in the mid lower crust and asthenosphere the estimated splitting times that would be accumulated in the crust alone are 0 25 0 8 s in the upper mantle 0 5 1 2 s depending on location in the middle crust 20 45 km depth beneath southern and central tibet azimuthal anisotropy is 3 5 and 4 6 per cent respectively and its e w fast propagation directions are parallel to the current extension at the surface the rate of the extension is relatively low however whereas the large radial anisotropy observed in the middle crust requires strong alignment of mica crystals implying large finite strain and consistent with high rate horizontal flow together radial and azimuthal anisotropy suggest eastward mid crustal channel flow in central tibet along the regional topography gradient in ne high tibet mid crustal azimuthal anisotropy is 4 8 per cent and has wnw ese and nw se fast propagation directions parallel to the net extension at the surface these fast directions are inconsistent with channel flow following the sw ne regional topography gradient instead they suggest similar net deformation in the decoupled shallow and deep crust in the brittle upper crust it is accommodated by strike slip faulting in the ductile mid lower crust by shear oriented at 45 to the faults although mid crustal flow beneath ne tibet may transport some material towards the plateau periphery at a low region average rate the dominant mid crust deformation pattern is shear parallel to the plateau boundary this implies that channel flow from central tibet is not the main cause of the on going crustal thickening farther northeast

a heat flow profile across the sverdrup basin canadian arctic islands an average geothermal gradient of 25 5 mk m and an average heat flow of 46 5mw m2 have been determined for 16 out of 20 analyzed wells along a profile across the sverdrup basin in the canadian arctic these estimates based on deep bottom hole temperature bht data from exploration wells and the permafrost base boundary temperature together with assumed heat conductivities from net rock analysis are surprisingly low and disagree with previously published results based on shallow data the differences may be due to the dramatic changes in boundary temperature conditions from moderate subsea conditions to ground surface low temperatures as a result of marine regression because of these effects it appears that deep bht temperature data are valuable in providing information about the deep heat flow the heat flows thus determined indicate that the basin has approached thermal equilibrium

thermal maturation by vitrinite reflectance of woodford shale anadarko basin oklahoma the woodford shale upper devonian lower mississippian a black shale widely regarded as an important hydrocarbon source rock has attained thermal maturity to postmaturity with respect to the generation of liquid hydrocarbons in most of the anadarko basin in western oklahoma untreated whole rock well cuttings and core material from selected 10 ft intervals of the woodford shale in 28 wells were examined under reflected white light thermal maturation was determined by measuring the reflectance in oil immersion ro of first generation vitrinite particles a minimum of 45 reflectance measurements were recorded for each well representing one or more sample intervals the woodford shale was sampled at depths from 5 060 ft 1 542 m in the northeastern shelf to 25 115 ft 7 655 in the deepest part of the basin a systematic increase in mean vitrinite reflectance meanro with depth was observed over much of the anadarko basin from northeast to southwest across the basin mean ro increases from 0 48 to 2 61 high temperatures have raised the woodford shale to anthracite rank in two wells 4 29 and 4 89 ro in the deep anadarko basin an isoreflectance map for the woodford shale indicates those areas of the basin where the thermal history of the shale is optimum for preserving liquid hydrocarbons mean ro of 0 5 to 2 0 computer generated plots of vitrinite reflectance versus depth provide a regression equation that predicts the vitrinite reflectance of the woodford shale at any depth in the anadarko basin and determines the amount of erosion

crustal thickening versus lateral expulsion in the indian asian continental collision since the beginning of the continental collision between india and asia there has been about 2500 km of convergence and the northward movement of india has been accommodated by major internal deformation of the asian lithosphere the crustal thickening in and around the tibetan plateau is clearly a direct consequence of this collision but there is considerable debate as to whether a large fraction of the indentation has been accommodated by eastward motion of the lithospheric blocks of southeastern asia and southern china numerical experiments described here test this hypothesis for a range of indentation geometries and rheological models of the lithosphere we employ a thin viscous sheet model of the lithosphere with a depth averaged nonlinear viscous rheology described by a stress strain rate exponent n and including gravitational buoyancy forces scaled by the dimensionless argand number ar the eastern boundary for the collision region is described as a lithostatic boundary the precollision normal stress is determined by static balance and that constant stress is applied throughout the collision the experiments show that during collision the eastern boundary is smoothly displaced to the east at a rate about 1 4 of the indentation rate with only minor variation due to geometry or rheology crustal thickening rates in the region of the plateau are reduced by between 10 and 25 of the corresponding rates determined for similar experiments with a rigid eastern boundary to generalize from the results of these experiments the total north south shortening strain produced by the collision is partitioned between crustal thickening and eastward displacement in the ratio of at least 3 1 and more probably 4 1

multimode rayleigh wave inversion for heterogeneity and azimuthal anisotropy of the australian upper mantle summary we present an azimuthally anisotropic 3 d shear wave speed model of the australian upper mantle obtained from the dispersion of fundamental and higher modes of rayleigh waves we compare two tomographic techniques to map path average earth models into a 3 d model for heterogeneity and azimuthal anisotropy method i uses a rectangular surface cell parametrization and depth basis functions that represent independently constrained estimates of radial earth structure it performs an iterative inversion with norm damping and gradient regularization method ii uses a direct inversion of individual depth layers constrained by bayesian assumptions about the model covariance we recall that bayesian inversions and discrete regularization approaches are theoretically equivalent and with a synthetic example we show that they can give similar results the model we present here uses the discrete regularized inversion of independent path constraints of method i on an equal area grid with the exception of westernmost australia we can retrieve structure on length scales of about 250 km laterally and 50 km in the radial direction to within 0 8 per cent for the velocity 20 per cent for the anisotropic magnitude and 20 for its direction on length scales of 1000 km and longer down to about 200 km there is a good correlation between velocity heterogeneity and geologic age at shorter length scales and at depths below 200 km however this relationship breaks down the observed magnitude and direction of maximum anisotropy do not in general appear to be correlated to surface geology the pattern of anisotropy appears to be rather complex in the upper 150 km whereas a smoother pattern of fast axes is obtained at larger depth if some of the deeper directions of anisotropy are aligned with the approximately n s direction of absolute plate motion this correspondence is not everywhere obvious despite the fast 7 cm yr 1 northward motion of the australian plate more research is needed to interpret our observations in terms of continental deformation predictions of sks splitting times and directions an integrated measure of anisotropy are poorly matched by observations of shear wave birefringence

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

complex layered deformation within the aegean crust and mantle revealed by seismic anisotropy continental lithosphere can undergo pervasive internal deformation often distributed over broad zones near plate boundaries however because of the paucity of observational constraints on three dimensional movement at depth patterns of flow within the lithosphere remain uncertain endmember models for lithospheric flow invoke deformation localized on faults or deep shear zones or alternatively diffuse viscous fluid like flow here we determine seismic rayleigh wave anisotropy in the crust and mantle of the aegean region an archetypal example of continental deformation our data reveal a complex depth dependent flow pattern within the extending lithosphere beneath the northern aegean sea fast shear wave propagation is in a north south direction within the mantle lithosphere parallel to the extensional component of the current strain rate field in the south central aegean where deformation is weak at present anisotropic fabric in the lower crust runs parallel to the direction of palaeo extension in the miocene the close match of orientations of regional scale anisotropic fabric and the directions of extension during the last significant episodes of deformation implies that at least a large part of the extension in the aegean has been taken up by distributed viscous flow in the lower crust and lithospheric mantle

revelation of organic matter sources and sedimentary environment characteristics for shale gas formation by petrographic analysis of middle jurassic dameigou formation northern qaidam basin china abstract the 7th member of middle jurassic dameigou formation j2d7 in northern qaidam basin china was proposed to have good hydrocarbon generating potential in previous studies here we apply an integrated petrographic and geochemical analysis to investigate the depositional environment real thermal maturity and shale gas potential of organic matter om rich assemblage the relatively high content of c29 regular sterane 56 8 62 8 and vitrinite predominance in maceral composition suggesting plenty of higher plant input combined with the high pristane phytane ratio pr ph 2 8 8 2 and low gammacerane index 0 2 0 4 reveals oxic water column with in situ depositional condition of carbonaceous mudstone when the lower j2d7 was deposited the maceral composition of oil shale at the upper part of j2d7 is mainly amorphous om with small proportion of reworked vitrinite and inertinite consistent with a mainly algea and small amount of exogenous om input when associated with low pr ph 0 8 and high gammacerane index 4 3 the oil shale was deposited in an anoxic saline water column with mainly zooplankton om source the geochemical and petrographic result implies a transitional environment ranging from suboxic semi saline to oxic fresh water environment with varying proportion of higher plant and algae input by in situ deposition and distant transportation for the mudstone at the middle part of j2d7 by use of random reflectance ro distribution two sedimentary environment microcycles which are confirmed by maceral composition from the depth of 1983 m to 1962 m and 1954 m to 1931 9 m are differentiated within the homogenous mudstone section the variation of om input condition and alternation of depositional environment led to accumulation and deposition of various kinds of abundant om when j2d7 was deposited although the om has actually low maturity at oil window with vitrinite reflectance around 0 6 according to the petrographic results the liptinite inherited from higher plants especially suberinite is the main maceral to generate gaseous hydrocarbons at the low maturity which implies that the dameigou formation j2d7 of qaidam basin is of gas potential

subsurface structure and spatial segmentation of the longmen shan fault zone at the eastern margin of tibetan plateau evidence from focal mechanism solutions and stress field inversion abstract as the eastern margin of the tibetan plateau the longmen shan fault zone lmsfz is characterized by a complex structural style and strong seismicity such as the 2008 wenchuan ms8 0 and 2013 lushan ms7 0 earthquakes in order to better understand the subsurface geometry of the lmsfz we inverted 391 focal mechanism solutions fms of earthquakes m 3 5 that occurred between 2009 and 2016 in the longmen shan region using seismic waveforms subsequently we calculated the stress field based on the fmss the results show that the lmsfz is dominated by a thrust faulting stress regime with subhorizontal nw se trending maximum principal stress 1 and subvertical minimum principal stress 3 indicating a lateral compression due to the southeastward movement of the bayan har block changes in fault dips at 10 km depth are inferred as the result of a shallow level detachment layer which may also promote shortening of the upper crust and uplift of the longmen shan based on differences in subsurface fault geometry stress field and geomorphological evidence we divide the lmsfz into two segments by beichuan county the southwestern segment has a listric fault geometry while the northeastern segment is dominated by subvertical transpressional strike slip faults according to the fmss results we suggest that the lixian fault is a tear fault accommodating different thrusting rates in the eastern margin of the bayan har block the normal faulting earthquakes in the lixian area are caused by local extension resulting from the sinistral shear movement of lixian fault in a strike slip faulting stress regime it is suggested that under the continuous southeastward movement of the bayan har block and the obstruction of the rigid sichuan basin stress is accumulating along the southwestern segment of the lmsfz to which accordingly a high seismic hazard is ascribed and which should be carefully monitored

spatial and temporal variations of stress field in the longmenshan fault zone after the 2008 wenchuan china earthquake summary we investigate the temporal and spatial patterns of the regional stress field along the longmenshan fault zone lfz following the 2008 wenchuan mw7 9 earthquake regional broadband seismic records are used to determine the focal mechanisms and centroid source depths of 400 aftershocks of magnitudes 3 3 mw 5 9 the focal mechanisms are then used to invert for the temporal and spatial variations of the regional stress field results show clear spatial changes in the directions of principle stress axes as well as the faulting types along the lfz the regional stress field is in an overall thrust regime with nearly horizontal maximum compressional axis in the southern section of the lfz in addition to the primarily thrust background with maximum compressional axis perpendicular to the main fault zone strike slip component is also present in the middle section the maximum compressional axis varies spatially changing abruptly from perpendicular to parallel to the lfz in the northernmost section the stress environment becomes primarily strike slip our result suggests that the collision of indian and eurasian plates led to the first order feature of the stress field in the study area the geometry of blocks and faults the lower crustal flow as well as the shallow crustal property difference are the major factors to controlling the local stress field temporal variations of stress field suggest that the mainshock caused a large stress disturbance at early stage in certain areas of lfz and the stress field variations with depth imply a different deformation pattern and different stress background in the shallow and lower crust

amphibole and lower crustal seismic properties abstract measurements of seismic anisotropy frequently offer insights of the deformation kinematics in situ within the earth in the continental crust seismic anisotropy is commonly ascribed to regionally aligned lattice preferred orientation lpo of mica crystals however determinations of composition suggest that the deep continental crust contains rather little mica in this contribution the role of amphibole a far more plausible constituent especially for deep continental crust of basic composition is assessed a field analogue approach is adopted where the lpo are measured correlated with the strain state of the rocks and used to calculate the seismic properties the seismic properties may be up scaled through the specimen using the modal proportions of the constituent mineral phases to examine the role of composition in controlling the intensity of seismic anisotropy seismic properties are computed using an array of modal compositions so called rock recipes the case history comes from the central block of the lewisian of nw scotland where a regional basic dyke swarm the scourie dykes is locally deformed within amphibolite facies shear zones conditions that are representative of the deep crust shear strain profiles across a 100 m wide shear zone using deflected banding in the host gneisses yield values of 0

timing of granite emplacement and cooling in the songpan garze fold belt eastern tibetan plateau with tectonic implications abstract new u pb and rb sr geochronology on syn and post orogenic granites provide constraints on the timing of major tectonic events in the songpan garze fold belt west sichuan china the ma nai granite was probably syn kinematic with the main deformation and yields an age of 197 6 ma that is interpreted as an upper age limit of the indosinian event zircons and apatites from the post kinematic rilonguan granite also yield jurassic ages 195 6 and 181 4 ma the post orogenic markam massif gives two ages of 188 1 and 153 3 ma both granites are undeformed and cut structures in the triassic sedimentary rocks these results demonstrate that the major deformation and decollement tectonics in the songpan garze fold belt occurred prior to the early jurassic the wide range of ages obtained for post kinematic granites from early jurassic to late jurassic suggests that locally magmatic activity persisted for a long time at least 50 ma after the indosinian compressional tectonism no tertiary ages have been obtained suggesting that these granites were not affected strongly by the india asia collision

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

preliminary geometry displacement and kinematics of fault ruptures in the epicentral region of the 2016 mw 7 8 kaikōura new zealand earthquake

the kinematics of a transition from subduction to strike slip an example from the central new zealand plate boundary 1 we develop a kinematic model for the transition from subduction beneath the north island new zealand to strike slip in the south island constrained by gps velocities and active fault slip data to interpret these data we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region convergence related to the hikurangi subduction margin becomes very low offshore of the northern south island indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate as suggested by previous studies this result has implications for understanding the likely extent of subduction interface earthquake rupture in central new zealand easterly trending strike slip faults such as the boo boo fault are the key features that facilitate the transfer of strike slip motion from the northern south island faults further north into the southern north island and onto the hikurangi subduction thrust our results also indicate that the transition from rapid forearc rotation adjacent to the hikurangi subduction margin to a strike slip dominated plate boundary with negligible vertical axis rotation in the south island occurs via a crustal scale hinge or kink in the upper plate compatible with paleomagnetic and structural geological data despite the ongoing tectonic evolution of the central new zealand region our study highlights a remarkable consistency between data sets spanning decades gps thousands of years active faulting data and millions of years paleomagnetic data and bedrock structure

maturity studies and source rock potential in the southern sverdrup basin arctic canada abstract the purpose of the study is to better understand the relationship between organic matter optical properties and the presence of potentially large oil and gas accumulations in arctic canada the type and thermal maturity of the dispersed organic matter of the mesozoic formations in the southern sverdrup basin melville island have been studied using organic petrology and rock eval pyrolysis all types of organic matter are present in the strata of mesozoic age hydrogen rich liptinite is dominated by alginite botryococcus and tasmanites dinoflagellate cysts and amorphous fluorescing matrix sporinite cutinite resinite and liptodetrinite made up the lesser hydrogen rich exinite vitrinite reflectance in cretaceous sediments ranges from 0 36 to 0 65 ro in jurassic sediments it ranges from 0 40 to 1 0 ro and in the triassic from 0 45 to 1 30 ro showing an overall increase with depth of burial cretaceous sediments of the deer bay formation are thermally immature and contain organic matter of terrestrial origin the upper jurassic shales of the ringnes formation contain predominantly organic matter of liptinitic and exinitic origin with a considerable vitrinitic input at optimum maturation levels potential source beds of this formation would have a good hydrocarbon generating potential the hydrocarbon potential however would be limited to the generation of gases due to the leanness of the source rocks parts of the lower jurassic jameson bay formation are organic rich and contain a mixed exinitic vitrinitic organic matter botryococcus colonial algae but visible organic matter is dominated by high plant remains mainly spores the schei point group shales and siltstones contain organic matter of almost purely marine origin whereas the predominantly higher plant derived organic matter found in the deer bay jameson bay and partly in the ringnes formations have higher toc among the schei point group samples the cape richards and eden bay members of the hoyle bay formation are richer in toc 2 0 than the murray harbour formation cape caledonia member this may reflect differences in the level of maturity or in the depositional environment more anoxic conditions for the former regional variations in the level of thermal maturity of mesozoic sediments in sverdrup basin appear to be a function of burial depth the mesozoic formations thicken towards the basin centre nne direction reflecting the general pattern of increasing thermal maturity north of sabine peninsula however the regional thermal maturation pattern of the mesozoic is not solely a reflection of the present day geothermal gradient which indicates that anomalous zones of high geothermal gradient may have existed in the past at least since when the mesozoic sediments attained maximum burial depth the contour pattern of the regional variation of maturity at the base of numerous triassic formations is similar to that of the structural contours of the sverdrup basin indicating that present day maturation levels are largely controlled by basin subsidence

eastward expansion of the tibetan plateau by crustal flow and strain partitioning across faults the tibetan plateau is expanding eastwards but the modes of deformation are poorly understood high resolution seismic images from the region identify localized zones of weak crustal rocks as well as deep faults implying that deformation occurs through a combination of crustal flow and movement of rigid blocks of crust