surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

formation and evolution of the tancheng lujiang wrench fault system a major shear system to the northwest of the pacific ocean abstract in the northwestern peri pacific tectonic belt on the continental margin of east asia there is a series of major faults trending ne nne i e the tancheng lujiang wrench fault system this fault system extends more than 5000 km with a width of 800 1000 km in the continent and a general strike of n30 e on the basis of the results of special research on the major faults and a lot of new information about the fault system the authors discuss early mesozoic triassic jurassic period sinistral transcurrent faulting in the different regions it is suggested that in the eastern continent of east asia the e w trending tectonic pattern of the paleozoic and beginning of the mesozoic appear in the nuclei of the sino korean continent massif and the yangtze continent massif these ancient continent massifs accreted both southwards and northwards which finally led to their collision and suturing to the angura continent massif later this tectonic framework was changed greatly by the tancheng lujiang wrench fault system along which left lateral horizontal displacement of 1000 1500 km took place since the mesozoic the dislocation and deformation of horizontal displacement of the tancheng lujiang fault system produced a series of structures trending ne nne in the continental margin which have greatly transformed the ancient structures of the preceding mesozoic this is an important diktyogenese in the continent of east asia during the horizontal displacement motion of these faults the folds nappes and decollement structures pull apart basins and subductions within the continent occurred in the continent at the same time some large sinistral ductile shear zones of horizontal displacement appeared the depth of the deformed horizon of ductile shear which belongs to simple shear was controlled by the tectonic element and distance away from the continental margin whilst the ductile shear deformation occurred the fault dynamo thermal metamorphism and the fault remelting took place and magma activity appeared within the continent in the mesozoic the fault zones used to be high energy zones and recently became the seismic belts within the continent formation of the tan lu fault system was due to the collision between the southern and northern blocks its large sinistral horizontal displacement in the mesozoic was closely related to the kula plate moving northwards therefore the continent disintegrated by shearing which produced some new terranes the shear edge belt was formed between the continent and ocean the change of relative motion between the continent and pacific ocean plate transformed the tan lu fault system into first extension and then compression clarifying the characteristics of the tan lu fault system is an important key in understanding the evolution of the east asia continent since the mesozoic

high resolution 3 d crustal shear wave velocity model reveals structural and seismicity segmentation of the central southern tanlu fault zone eastern china abstract the early mesozoic collision between the north and south china cratons resulted in different tectonic and geologic structures including the tanlu fault zone one way to understand the geodynamic processes beneath these structures is by studying the velocity structures and spatial distribution of earthquakes in the region we performed ambient noise tomography for the region around the central southern tanlu fault zone using the vertical component of continuous ambient noise data obtained in central east china empirical green s functions were retrieved from ambient noise cross correlation functions from which we extracted the rayleigh wave phase velocity dispersion curves and performed quality control on the dispersion data the direct surface wave tomography method was used to invert all phase velocity dispersion data for the 3 d shear wave velocity model in the crust and uppermost mantle our results show velocity segmentations with high velocity structures existing beneath orogenic belts and uplifts within the first 10 km depths which correspond to the high pressure ultra high pressure metamorphic rocks in the area the existence of high velocity structures beneath orogenic belts at shallow depths implies that the exhumation of eclogites is confined to the uppermost crust generally fault zones in this area are characterized by a low velocity from 0 to 5 km and relatively high velocity in the lower part of the upper crust and the middle crust the spatial distribution of earthquakes along tanlu fault reveals two seismicity zones the southern segment and the suqian tancheng segment with a low velocity transitional zone at suqian which suggests that the two segments respond differently to stresses regions of dense earthquake distribution correspond to the transition zones of high to low shear wave velocities which could be as a result of instability in the upper mantle and variation in compositions of crustal materials

triassic polyphase deformation in the feidong zhangbaling massif eastern china and its place in the collision between the north china and south china blocks the feidong zhangbaling massif is located between the dabieshan and sulu areas along the tan lu fault in eastern china five tectonic metamorphic events are distinguished there the earliest deformation d1 corresponds to a southward compression that occurred during subduction of the south china block below the north china block top to the south shearing is coeval with late permian early triassic blueschist facies metamorphism and possibly with the development of south verging recumbent folds in the neoproterozoic paleozoic sedimentary cover of the south china foreland the main ductile deformation d2 is an extensional one characterized by top to the north shearing coeval with the early stage of exhumation of the high pressure rocks a top to the nw ductile shearing and microfolds overturned to the northwest belong to a second deformational phase of exhumation d3 which is distinct from the main event d2 previous 40ar 39ar mica dates ranging between 245 and 212 ma suggest late permian early triassic ages for the d1 to d3 events the d4 event produced ne sw trending folds in the sedimentary cover interpreted as gravity collapse structures a late cretaceous brittle extensional event d5 controls the opening and infill of continental half grabens in the study area the tan lu fault is a cretaceous brittle normal fault the lack of ductile deformation presented along the tan lu fault suggests that it did not play a significant role in the exhumation of high pressure metamorphic rocks

palaeomagnetic constraints on the collision and rotation of north and south china the eastern half of china is dominated by the north china block ncb and south china block scb separated by a complex fold system that trends roughly east west interpretation of the geology of this fold belt has led to a variety of estimates of the age of amalgamation of these two blocks1 7 palaeomagnetic results are few and have also been subject to conflicting interpretations8 11 here we present our own palaeomagnetic results for late permian rocks for both the scb and ncb and summarize other relevant palaeomagnetic data by reinterpreting the polarity given in some previous studies we are able to synthesize the results for the widespread emeishan basalts of the scb and to suggest a new model for the collision and relative rotation of the two blocks

foraminifera as markers of holocene sea level fluctuations and water depths of ancient harbours a case study from the bay of elaia w turkey abstract the absence of common sea level indicators in the study area of elaia pergamum s harbour city in hellenistic and roman times forced to establish a new reliable indicator which was found in the foraminifera associations in connection with the transgressive contact the strength of this indicator is the exclusion of post depositional compaction accompanied by a well dated archaeological index point at a breakwater the micropalaeontological indicator enabled the establishment of a reliable regional sea level curve rsl curve for the bay of elaia it is in good agreement with other curves for the aegean region and in general agreement to the glacio hydro isostatic model for the region our sea level curve proves for the first time at a continental site on the turkish aegean coast the today s sea level peak water depth modelling for the so called closed harbour of elaia reveals the capacity to fully accommodate the common ship classes of hellenistic and early roman times until around 150 ce while water depth estimates for the so called open harbour of the city verifies the usage of the adjacent ship sheds during elaia s prime

a thinned lithospheric image of the tanlu fault zone eastern china constructed from wave equation based receiver function migration 1 we apply the newly proposed wave equation based receiver function poststack migration method to the northern china interior structure project broadband data to image the lithospheric structure of the tanlu fault zone area in eastern china our migration result reveals a 60 to 80 km thick present day lithosphere beneath the study region significantly thinned from the paleozoic lithosphere of 180 km the lithosphere asthenosphere boundary lab is coherently imaged along the 300 km east west profile displaying an arc like shape with its apex roughly coincident with the transverse location of the tanlu fault zone on the surface an obvious uplift from 36 km to 32 km of the moho is also clearly detected right below this fault zone the coincidence of the imaged moho uplift and the lab apex with the surface location of the tanlu fault zone provides seismological evidence for the steep geometry and deep penetration of the fault system and indicates that the tanlu fault zone might have acted as a major channel for anthenosphere upwelling during the mesozoic cenozoic continental extension and lithospheric thinning in eastern china frequency analysis and synthetic modeling suggest that both the moho and the lab are sharp and strong the latter in particular is constrained to have a 3 7 drop in s wave velocity over a depth range of 10 km or less such a rapid velocity change at the base of the lithosphere in the study region cannot be solely explained by thermal variation but likely reflects the presence of volatiles or melt in the asthenosphere or is partially attributed to the compositional contrast between the preserved depleted and dehydrated cratonic lithospheric veneer and the uplifted hydrated and fertile asthenospheric materials

seismic tomographic imaging of the crust and upper mantle under the central and western tien shan orogenic belt 1 detailed 3 d tomographic images of p and s wave velocity vp vs and poisson s ratio under the central and western tien shan orogenic belt are determined by using a large number of high quality p and s wave arrival times from local earthquakes the results show that under the tien shan orogenic belt high vp high vs and low anomalies are revealed in the upper and middle crust possibly indicating the existence of the paleozoic crystalline basement rocks while low vp low vs and high anomalies appear in the lower crust and upper mantle perhaps suggesting that the hot and wet material is upwelling under the tien shan orogenic belt from the mantle some high vp high vs and low anomalies are tilted toward the tien shan along with the seismicity these are found in the collision zones between the tien shan and the tarim basin in the south and the kazakh shield in the north and suggest the underthrusting of the tarim and kazakh lithosphere beneath the tien shan meanwhile some low vp low vs and high anomalies are imaged in other parts of these collision zones perhaps indicating the intrusion of the hot and wet material into the crust from the upper mantle these results indicate that both the upwelling of the hot and wet material and the underthrusting of the tarim and kazakh lithosphere may have played an important role in the mountain building under the tarim and fergana basins low vp low vs and high anomalies are revealed in the upper crust while high vp high vs and low anomalies are visible in the lower crust and upper mantle these may reflect the existence of less compacted sedimentary material in the shallow crust and more highly compacted craton like structures in the deeper crust and upper mantle under the basins the talas fergana fault shows an obvious tectonic boundary between central and western tien shan the central tien shan displays high vp high vs and low anomalies in the upper and middle crust while western tien shan exhibits low vp low vs and high anomalies however the pattern of seismic structure between central and western tien shan reverses in the lower crust such a correlation may extend down to the upper mantle suggesting that the talas fergana fault may be a lithospheric scale boundary additionally a columnar low vp and low vs anomaly is clearly observed around the turning point of the talas fergana fault from the nwn to nww trending orientations and may indicate that the fault provides a channel for the hot and wet material upwelling from the mantle to the surface

paleomagnetic constraints on the geodynamic history of the major blocks of china from the permian to the present paleomagnetic study of china and its environs has been the center of a major international effort for the last 10 years in this paper we critically review all available paleomagnetic poles of upper permian to tertiary age from the main blocks of china with the goal of placing constraints on models of the formation and the subsequent deformation of the region after selecting reliable poles by applying objective criteria we divide our analysis into first order motions of blocks and second order deformation within blocks for first order analysis apparent polar wander paths are constructed for the major blocks we discuss the compatibilities and contradictions between the geological and paleomagnetic records a sequence of paleogeographic configurations taking into account geological constraints but remaining within paleomagnetic uncertainties is presented in general the major blocks were probably in contact throughout the permian and triassic but the jurassic was the key age during which most of the movement toward china s present configuration took place our reconstructions include certain details which are suggested by the paleomagnetic record but whose geological signatures seem to have been hidden by subsequent events during the cretaceous chinese poles agree with poles from other continents transferred onto eurasia at the second order we observe that for almost each period with sufficient data the paleomagnetic poles are streaked along a small circle centered on the sampling region indicating that much of china has been affected by small 20 differential rotations this we interpret as deformation caused in part by the extrusion of the chinese blocks away from the indian collision the complete annotated list of poles is given as an appendix

timing of the north south china collision from new middle to late mesozoic paleomagnetic data from the north china block we collected paleomagnetic samples from 43 sites of middle and upper jurassic and cretaceous rocks along a 250 km wide east west trending belt located north of the suture between the north and south china blocks in each case laboratory treatment isolates dual polarity antipodal magnetizations that are demonstrably pre folding the paleomagnetic poles show very good coherence with coeval poles from other localities from the north china block ncb suggesting the apparent polar wander path apwp from the ncb is not distorted by post middle jurassic local vertical axis block rotations a comparison of the ncb apwp with that from the south china block suggests that collision continued after the early jurassic and ended no later than the late jurassic a cusp in the ncb apwp coincides with a marked angular unconformity that separates middle jurassic from upper jurassic and younger sediments together these observations indicate that the scissor like collision and associated deformation ceased at the middle to late jurassic boundary 159 ma the time of rapid 1 ma relative angular velocity between the two plates 225 to 190 ma coincides with a peak in u pb and ar ar dates obtained from metamorphic rocks in the suture the combined late jurassic and cretaceous paleomagnetic data from both blocks suggest that the united china plate traveled 2000 km north relative to eurasia during the late jurassic before docking in the cretaceous this younger collision event is also marked by a cusp on the cretaceous part of the eurasian apwp

collision between the north and south china blocks a crustal detachment model for suturing in the region east of the tanlu fault a crustal detachment model based on the interpretation of linear aeromagnetic anomalies surface geological observations and deep seismic profiles is proposed for the continent continent collision between the north and south china blocks east of the tanlu fault the model suggests that during the mid mesozoic collision between the two continental blocks the upper crust of the south china block in the subei yellow sea region was detached from the lower crust and thrust over the north china block for 400 km whereas the lower part of the lithosphere was subducted under the north china block along a subsurface suture running east from nanjing the sinistral offset of the qinling suture by the tanlu fault is only 110 120 km in the deep crust much less than previously suggested

crustal structure and exhumation of the dabie shan ultrahigh pressure orogen eastern china from seismic reflection profiling comment and reply comment yuan et al 2003 1 published a deep seismic reflection profile of the dabie shan ultrahigh pressure uhp orogen acquired by the chinese geological survey the seismic profile provides new insight into the crust structures of the orogen and gives us a better understanding of this specific uhp

structure of the upper mantle and transition zone beneath southeast asia from traveltime tomography 1 tomographic images of the mantle beneath east asia were obtained from the inversion of traveltime data from global and regional seismograph networks and from temporary arrays on and around the tibetan plateau our results are consistent with previous studies but the unprecedented resolution of mantle heterogeneity provides new insight into the large scale tectonic framework of the continental india asia collision in the western part of the study region and subduction of the oceanic lithosphere in the east in the realm of continental collision west of 100 e a relatively slow p wave speed characterizes the upper mantle beneath much of the tibetan plateau but the wave speed is high beneath cratonic india the southern and western part of the tibetan plateau hindu kush and the tian shan in the subduction realm east of 110 e the main structures are i pronounced low wave speed anomalies at a depth of between 100 and 400 km beneath asia s southeastern seaboard and the back arc regions of ongoing subduction ii narrow fast anomalies in the upper mantle beneath major subduction zones and iii widespread fast anomalies at a depth of 500 700 km beneath the sea of japan the northern part of the philippine sea plate and southeastern china if the latter anomalies represent stagnant slabs their fragmented nature and large lateral extent suggest that they are produced by different episodes of subduction beneath western pacific island arcs along the old se margin of asia or during the mesozoic collision of cratonic units in southeast asia attribution to ancient subduction systems implies that slab fragments can reside in the transition zone for at least several tens of millions of years shallow slow anomalies beneath the red river fault region connect to deep anomalies beneath the south china fold belt and south china sea suggesting a causal relationship between the evolution of the continental lithosphere of sw china and deeper mantle processes between the collision and the subduction realms tomography reveals high wave speed continental roots beneath the western part of the north china craton ordos block and the south china or yangtze craton sichuan basin to a depth of 300 km

active faulting in and along the qinling range china inferred from spot imagery analysis and extrusion tectonics of south china abstract since the beginning of the india asia collision about 2500 km of convergence has been accommodated by crustal thickening in and around the tibetan plateau and by extrusion of tibetan blocks and of the south china block the relative amounts of convergence accommodated by the two mechanisms are however still largely a matter of debate the main purpose of the present study is to determine the rate of left lateral movement between south china and north china during the late cenozoic this movement is accommodated by offsets along the more than 1000 km long e w trending qinling fault system which separates the south china block from the north china block and terminates to the east in the right lateral ndashs trending tanlu fault zone physiographic features typical of active faulting such as triangular facets along scarps and drainage deviations have been observed on spot images throughout the qinling fault system recent active faulting involves both left lateral strike slip and normal dip slip which are partitioned laterally east of the weihe graben two major faults the luonan and danfeng faults of the qinling fault system slip left laterally a cumulative slip rate of about 7 2 2 2 mm yr between the qinling shan south china and the hua shan north china has been estimated using quaternary morphological offsets in contrast the qinling frontal fault which bounds the cenozoic weihe graben to the south exhibits abundant evidence of normal faulting that accommodated large post early eocene vertical displacement in the graben crustal extension estimated from published seismic profiles and boreholes across the weihe graben contributes to a late cenozoic rate of left lateral movement of 2 0 5 mm yr in a n140 e direction between the hua shan and the ordos block combining these yields a rate of left lateral movement of 8 5 2 5 mm yr in a n100 e direction between south china and the ordos block is achieved additionally the ordos block rotates counterclockwise relative to gobi mongolia resulting in nw se crustal extension along the yinchuandashhetao grabens this is estimated from published seismic sections and adds a component of left lateral movement of 4 1 mm yr in a n125 e direction between south china and gobi mongolia the total rate of left lateral movement of south china with respect to gobi mongolia is 12 4 mm yr in a n110 e direction the eastward decrease of the left lateral strike slip on the active qinling fault system may be explained by the partitioning of left lateral movement on the faults bounding the dabie shan to the south and north and by a book shelf mechanism of counterclockwise rotating blocks separated by active ne sw right lateral faults in the dabie shan

crustal structure beneath the dabie orogenic belt from ambient noise tomography abstract the qinling dabie sulu orogenic belt in east central china is the largest high and ultrahigh pressure hp and uhp metamorphic zone in the world the dabie mountains are the central segment of this orogenic belt between the north china and yangtze cratons this work studies the nature of the crustal structure beneath the dabie orogenic belt to better understand the orogeny to do that we apply ambient noise tomography to the dabie orogenic belt using ambient noise data from 40 stations of the china national seismic network cnsn between january 2008 and december 2009 we retrieve high signal noise ratio snr rayleigh waves by cross correlating ambient noise data between most of the station pairs and then extract phase velocity dispersion measurements from those cross correlations using a spectral method taking those dispersion measurements we obtain high resolution phase velocity maps at 8 35 second periods by inverting rayleigh wave phase velocity maps we construct a high resolution 3d shear velocity model of the crust in the dabie orogenic belt the resulting 3d model reveals interesting crustal features related to the orogeny high shear wave velocities are imaged beneath the hp uhp metaphoric zones at depths shallower than 9 km suggesting that hp uhp metaphoric rocks are primarily concentrated in the upper crust underlying the high velocity hp uhp metamorphic zones low shear velocities are observed in the middle crust probably representing ductile shear zones and or brittle fracture zones developed during the exhumation of the hp uhp metamorphic rocks strong high velocities are present beneath the northern dabie complex unit in the middle crust possibly related to cooling and crystallization of intrusive igneous rocks in the middle crust resulting from the post collisional lithosphere delamination and subsequent magmatism a north dipping moho is revealed in the eastern dabie with the deepest moho appearing beneath the northern dabie complex unit consistent with the model of triassic northward subduction of the yangtze craton beneath the north china craton

indentation induced tearing of a subducting continent evidence from the tan lu fault zone east china abstract vertical tearing of oceanic slabs has been well documented at subduction zones it remains unclear whether a subducting continent can tear vertically origin of the continental scale tan lu fault zone tlfz in east china provides an example of the vertical tearing of the subducting continent at the convergent stage the dabie and sulu orogens between the north china plate ncp and the yangtze plate yzp are left laterally offset about 400 km along the ne striking tlfz but the fault zone terminates abruptly at the southeastern corner of the dabie orogen suggesting unique origin of the fault zone we present structural evidence to show that the tlfz initiated as a sinistral fault zone that is exposed in ductile shear belts just to the east of the dabie orogen our muscovite 40ar 39ar dating results coupled with existing age data indicate that the tlfz formed at 240 230 ma middle triassic when the yzp continental crust was subducted beneath the ncp along both the dabie and sulu sutures we also show that se directed extrusion of the subducted crust in the dabie orogen occurred during 230 209 ma late triassic and overprinted contractional deformation in the tlfz to the southeast of the dabie orogen syn collisional folds and thrusts in the yzp to the east of the tlfz exhibit evidence for large scale dragging by the sinistral fault zone whereas those in the ncp to the west are perpendicular to the tlfz without obvious evidence for drag combining these lines of evidence with published data on the tectonic evolution of the two orogenic belts we propose an indentation induced continent tearing model for the origin of the tlfz we suggest that the present southern boundary of the ncp represents its original shape with a promontory in front of the dabie orogen at the oceanic subduction stage the overriding ncp promontory led to vertical tearing of the subducting oceanic plate along the tlfz which formed the eastern boundary of the promontory once the rigid ncp indenter collided with the passive yzp along the dabie orogen the oceanic slab tear propagated into the yzp lithosphere resulting in long distance low angle subduction of the yzp underneath the ncp indenter and nne ward horizontal motion of the torn yzp east of the tlfz until the final collision at the sulu orogen thus the indentation induced the vertical tearing of the subducting yzp along the tlfz

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

upper mantle tomography and dynamics beneath the north china craton 1 a high resolution tomographic model of the upper mantle beneath the north china craton ncc is determined using a large number of precisely hand picked teleseismic p wave arrival times the results are generally consistent with previous results but high quality arrivals provide new insights into the dynamics beneath the ncc obviously north south trending low velocity low v zones are revealed down to 300 400 km depth under the shanxi rift and tanlu fault zone while a north south trending high velocity high v zone representing the remainder of detached lithosphere is visible down to 200 km depth under the western portion of eastern ncc high v anomalies representing the detached lithosphere are detected at 200 400 km depth under central and eastern ncc under the ordos block high v anomalies are visible above 400 km depth indicating intact lithosphere broad high v anomalies representing the stagnant pacific slab are imaged with a low v anomaly from datong volcano to the edge of bohai sea in the mantle transition zone beneath eastern and central ncc suggesting that the pacific slab has subducted to central ncc but with a gap a continuously y shaped low v structure is clearly imaged under datong volcano and bohai sea from the lower mantle through this gap in the mantle transition zone to the upper mantle indicating the existence of a lower mantle plume these results suggest that in addition to the subduction of the pacific plate the plume has also played an important role in lithospheric destruction by thermal erosion of the asthenosphere and detachment of the lithosphere beneath the ncc

seismic images under the beijing region inferred from p and pmp data abstract in this study a new tomographic method is applied to over 1500 high quality pmp moho reflected wave travel time data as well as over 38 500 high quality first p wave arrivals to determine a detailed 3d crustal velocity structure under beijing and adjacent areas results of detailed resolution analyses show that the pmp data can significantly improve the resolution of the model in the middle and lower crust after the pmp data are included in the tomographic inversion our new model not only displays the tectonic feature appeared in the previous studies but also reveals some new features the zhangjiakou bohai sea fault zone zhang bo zone is imaged as prominent and continuous low velocity low v anomalies in the shallower crust while in the middle and lower crust it shows intermittent low v anomalies extending down to the uppermost mantle furthermore the pattern of low v anomalies is different along the zhang bo zone from the southeast to the northwest indicating that there exist large differences in the dynamic evolution of taihangshan and yanshan uplifts and north china depression basin prominent low v anomalies are visible under the source area of the 4 july 2006 wen an earthquake m 5 1 suggesting that the occurrence of the wen an earthquake is possibly related to the effect of the crustal fluids probably caused by the upwelling of the hot and wet asthenospheric materials due to the deep dehydration of the stagnant pacific slab in the mantle transition zone the fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the wen an earthquake this is somewhat similar to the cause of the 1695 sanhe pinggu earthquake and the 1976 tangshan earthquake in the region as well as the 1995 kobe earthquake in japan and the 2001 bhuj earthquake in india

an attempt to detect temporal variations of crustal structure in the source area of the 2006 wen an earthquake in north china abstract lei et al 2008 revealed a low velocity low v anomaly in the lower crust under the source area of the 4 july 2006 wen an earthquake m 5 1 in north china in this work we tried to investigate the temporal variations of the crustal structure by using a number of p and pmp moho reflected wave arrival times recorded by 107 digital seismic stations from earthquakes that occurred separately in 2002 2003 2004 and 2005 2006 to determine p wave velocity structures in and around the source area of the wen an earthquake in different periods our results show that tomographic images inferred from the data sets in different years are all dominated by a low v anomaly in the lower crust under the wen an source area however there exist some differences in the p wave velocity image in the wen an source area inferred from the p and p pmp data sets suggesting that the pmp data have improved the tomographic images in the middle and lower crust but the results from the 2005 2006 p and p pmp data sets all show a relatively lager increase of the low v anomaly under the wen an source area in the amplitude and extent as compared with those from the 2003 and 2004 p and p pmp data sets incorporating the previous results if this low v anomaly may indicate the existence of fluids then our results suggest that the occurrence of the wen an earthquake is not only related to the long term influence of fluids that decrease the effective normal stress on the fault plane but also closely associated with the drastic increase of such influence however this study is just an experimental work and the results are still preliminary because the resolution scale of the present tomographic model is much larger than the wen an source area and our extensive tests show that different samplings of seismic rays from different data sets have affected the details of the tomographic images suggesting that the present sparse data coverage can hardly detect reliably any temporal variations of the velocity anomalies in the wen an source area in future studies it is necessary to improve the resolution of crustal tomography to the size of the rupture zone and utilize identical seismic ray paths from the same pairs of sources and receivers in order to detect any temporal variations of the crust structure in the source area of a large earthquake

high resolution 3 d crustal structure beneath ne china from joint inversion of ambient noise and receiver functions using necessarray data abstract we used ambient noise data recorded by the necessarray a portable seismic array deployed in northeast china to construct rayleigh wave phase velocity dispersion curves and obtain phase velocity maps for periods from 6 to 40 s s wave velocity structure beneath ne china is obtained by joint inversion of the phase velocities and receiver functions our results show good correlation between crustal velocity structure and geological features at shallow depths the songliao basin is separated into two small sub basins by a fast velocity anomaly corresponding to a southwest uplifted horst and the southern sub basin is associated with the kailu depression a low velocity anomaly extending from the lower crust to uppermost mantle beneath the changbaishan mountain range is consistent with p and s wave tomography models the mantle low velocity has been interpreted as a local mantle upwelling attributed to the subducting pacific slab induced return flow finally the s wave velocity in the mid and lower crust is lower beneath the xing an mongolia orogenic belt xmob than beneath the changbaishan mountain range this was not expected since the changbaishan mountain range has experienced more extensive volcanic activity in the cenozoic including the currently active changbaishan and jingpohu volcanoes than the xmob we infer that the mid and lower crust of the xmob is mainly felsic in composition and propose that the low shear wave velocity of the mid and lower crust beneath the xmob could be the consequence of removal of deep mafic crust through a continental accretion and subsequent delamination event in the paleozoic or via convection removal induced by the rollback of the flat subducted paleo pacific slab during the middle mesozoic

tectonic characteristics of the central segment of the tancheng lujiang fault zone shandong peninsula eastern china abstract the tancheng lujiang fault zone tlfz in the central segment in the shandong peninsula eastern china is composed of four major faults called f1 f4 from east to west forming a 50 km wide zone detailed field study demonstrates that neogene volcanic and sedimentary strata quaternary deposits and topographic surfaces cover the fractured zones of faults f3 and f4 and are not deformed or displaced the same rocks and surfaces on faults f1 and f2 however are clearly displaced the geological and seismological data show that the f1 and f2 are presently active as a major seismic zone in eastern china whereas the f3 and f4 have been inactive since the neogene fabrics of foliated cataclastic rocks generated in the fracture zones show left lateral strike slip on the f3 and f4 between cretaceous and neogene time and high angle reverse or normal faulting with a dextral component on faults f1 and f2 in late quaternary time field evidence and analysis of the fabrics of fault related rocks reveal the changes of shear sense and activity of faults f1 f4 of the central segment of the tlfz from cretaceous to quaternary time in the shandong peninsula

neogene volcanism and holocene earthquakes in the tanlu fault zone eastern china abstract in this paper we study the relationship between neogene volcanism and holocene earthquakes in the tanlu fault eastern china we find that fault segments through which neogene and quaternary magma have extruded do not show holocene slip because they are covered by unfaulted basalts in contrast fault branches that are away from the quaternary volcanic centers display quaternary faulting and are responsible for earthquakes as recorded both historically and geomorphologically therefore magma intrusion appears to modify fault activity in two different ways 1 within the faults the cooling magma serves as a cohesion or barrier welding the faults so that they become stronger in resisting slip 2 beneath the faults the upwelling magma promotes slip of faults above the magma body and hence generation of earthquakes physically the first case results from contraction of the cooling magma which causes a relative increase in fault normal stress so that the fault failure resistance is enhanced the second case results from the upward dynamic force and the heat brought in by the magma body both of which cause the effective fault normal stress to decrease so that the fault failure resistance is reduced that could explain why earthquakes occur on faults bypassing the volcanic centers as typified in the yishu fault zone and in the regions where heat flows are relatively high as shown in the bohai bay area

an improved method to extract very broadband empirical green s functions from ambient seismic noise the extraction of green s functions by cross correlation of continuous seismic records at station pairs is best achieved in a diffuse wave field where energies radiated by random sources have equal power to partially satisfy the diffuse wave field condition original seismic records must be normalized as they are highly nonstationary and may have amplitude variations of orders of magnitude within the cross correlation time window we adapt a frequency time normalization method to obtain seismograms with an even spectrum at all times within the data processing unit compared with the commonly used one bit normalization the new method improves the signal to noise ratio of empirical green s functions by a factor of 2 and increases the effective data recording duration by a factor of 4 assuming random local and instrument noise it yields useful rayleigh waves at periods up to 300 s for program for array seismic studies of the continental lithosphere passcal type deployments and 600 s for permanent stations with very broadband sensors thus the new method makes it possible to extend surface wave signals to frequencies beyond those in traditional earthquake based surface wave tomography at both the high and low frequency ends

syn collisional transform faulting of the tan lu fault zone east china origin of the continental scale tan lu fault zone tlfz east china remains controversial about 550 km sinistral offset of the dabie orogenic belt dob and sulu orogenic belt sob is shown along the ne nne striking tlfz syn collisional sinistral ductile shear belts in the tlfz have been identified thirteen phengite bulk separates from the mylonites were dated by the 40ar 39ar method they gave cooling ages of the 198 181 ma for the shear belts along the eastern margin of the dob and 221 210 ma from the western margin of the sob distribution of the foreland basin deposits suggests that sinistral offset of the dob and sob by the tlfz took place prior to deposition of the upper triassic strata the marginal structures around the dob and sob support syn collisional faulting and indicate anticlockwise rotation of the dob during the displacement the folding and thrust faulting related to crustal subduction coeval with the tan lu faulting is older than the foreland basin deposition related to the orogenic exhumation several lines of evidence demonstrate that the tlfz was developed as a syn collisional transform fault during latest middle to earliest late triassic time when the dob and sob experienced crustal subduction of the south china block scb eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting

broadband ambient noise surface wave tomography across the united states 1 this study presents surface wave dispersion maps across the contiguous united states determined using seismic ambient noise two years of ambient noise data are used from march 2003 through february 2005 observed at 203 broadband seismic stations in the us southern canada and northern mexico cross correlations are computed between all station pairs to produce empirical green functions at most azimuths across the us coherent rayleigh wave signals exist in the empirical green functions implying that ambient noise in the frequency band of this study 5 100 s period is sufficiently isotropically distributed in azimuth to yield largely unbiased dispersion measurements rayleigh and love wave group and phase velocity curves are measured together with associated uncertainties determined from the temporal variability of the measurements a sufficient number of measurements 2000 is obtained between 8 and 25 s period for love waves and 8 and 70 s period for rayleigh waves to produce tomographic dispersion maps both phase and group velocity maps are presented in these period bands resolution is estimated to be better than 100 km across much of the us from 8 40 s period for rayleigh waves and 8 20 s period for love waves which is unprecedented in a study at this spatial scale at longer and shorter periods resolution degrades as the number of coherent signals diminishes the dispersion maps agree well with each other and with known geological and tectonic features and in addition provide new information about structures in the crust and uppermost mantle beneath much of the us

the muzaffarabad pakistan earthquake of 8 october 2005 surface faulting environmental effects and macroseismic intensity the mw 7 6 muzaffarabad earthquake of 8 october 2005 occurred on a lateral equivalent of the main ramp of the hymalaia frontal thrust and is the result of the collision tectonics between the indian and eurasian plates the epicentre was located near the town of basantkot muzaffarabad and the focal depth was about 13 km the muzaffarabad earthquake provides unequivocal evidence about the localization of severe damage intense ground shaking and secondary environmental effects near the surface expression of the source fault we analyse its nature and impact on man made structures and the physical environment on the basis of a detailed survey and macroseismic study of the affected areas conducted by the micro seismic studies programme mssp team ishfaq ahmad research laboratories pakistan atomic energy commission immediately after the mainshock assisted by a careful review of the subsequent data and literature in the course of the field survey the displacement and surface expression of the causative fault and accompanying secondary environmental effects were observed at a number of places along a capable thrust fault structure we refer to this structure as the kashmir thrust kt capable fault following the terminology of local research geologists in pakistan the seismological evidence of this structure is already known in the literature as the indus kohistan seismic zone a complex clearly segmented at least 112 km long surface rupture was mapped along the kt the maximum values of vertical displacement on the order of 4 to 7 m were observed mainly between muzaffarabad and balakot along the central segment of the rupture 52 km associated with maximum slip at depth and a major portion of the energy release both the nw alai segment 38 km and se bagh segment 22 km are characterized by scattered minor surface ruptures with a few centimetres of displacement accompanied by extensive surface cracking landslides and severe damage concentrated in a narrow belt along the fault trace a maximum intensity of xi on the modified mercalli intensity mmi scale and on the environmental seismic intensity scale esi 2007 was recorded in the epicentral area between muzaffarabad and balakot extremely severe damage and very important secondary environmental effects in the hanging wall adjacent to the trace of the causative fault plane are mainly due to near fault strong motion and rupture directivity effects to our knowledge this is the first study to present field observations over the whole near field of the earthquake and to include the intensity map of the entire meizoseismal region the geological society of london 2009

geophysical evidence on segmentation of the tancheng lujiang fault and its implications on the lithosphere evolution in east china abstract the north south trending tancheng lujiang tanlu fault belt extends from northeast china to the dabie sulu orogenic belt for a length of more than 3000 km this fault belt probably has close links with the lithosphere evolution seismic activity and mineral resource concentration in east china surface geological mapping and studies on sedimentation and basin formation have indicated segmentation at the southern middle and northern domains of the fault here we employ geophysical constraints to evaluate these fault segments unlike previous geophysical studies focused on laterally varying crust mantle seismic velocity structure across the fault in this study we have integrated a variety of geophysical data sets such as crustal p wave velocity earthquake occurrence and released seismic energy seismogenic layer thickness surface heat flow and geothermal field to understand the deep structure and strength of the lithosphere along the tanlu segmented fault belt the results demonstrate remarkable crustal scale north to south segmentation this major fault the geophysical evidence and some geochemical constraints suggest that the tanlu fault belt probably served as a channel for melt and fluid percolation and exerted a significant control on the lithosphere evolution in east china

preliminary phanerozoic polar wander paths for the north and south china blocks polar wander paths for the north and south china blocks suggest that 1 both were parts of gondwana in the palaeozoic 2 the north china block accreted to siberia in the late permian and 3 the south china block accreted to the north china block in the middle triassic to the early jurassic comparison of the polar wander path for the south china block with that for northern eurasia suggests that relative motion of over 4 000 km has occurred between them

flake tectonics in the sulu orogen in eastern china as revealed by seismic tomography 1 seismic tomographic image reveals a crocodile like p waves velocity structure beneath the sulu orogenic belt which marks the subduction collision zone between the sino korean block sk and yangtze block yz in eastern china it may imply that the upper crust of the yz was detached from its lower crust and thrust over the sk for a maximum of 400 km in the sulu region whereas the remnant of the subducted yangtze lithosphere was lay beneath the sk this crustal detached structure flake tectonics might have occurred after the triassic subduction collision

the structural and tectonic relationships of the major fault systems of the tan lu fault zone with a focus on the segments within the north china region abstract the jiashan lujiang yishu and bohai segments have been the most tectonically active parts of the tan lu fault system since the mesozoic any analysis of faulting processes in the tan lu system is highly dependent on the relationships among the three segments here we divide the tan lu system into three styles of faulting strike slip faulting regional extensional faulting and listric normal faulting on the basis of emap data seismic profiles and geological evidence we suggest that 1 the strike slip faults which formed in the late jurassic include mainly the jiashan lujiang fault the deep parts of the chihe taihu fault and the guhe sanbing fault these three faults have had the most dramatic effect on the jiashan lujiang segment the strike slip style of faulting produced a huge positive flower structure that extends between the deep section of the chihe taihu fault and the guhe sanbing fault and overlaps with the position of the zhangbaling ductile shear zone 2 the regional extensional style of faulting whose characteristics are reflected best in the yishu fault zone is composed of the changyi dadian anqiu quxian yishui yangtou and tangwu gegou faults all of which were active during the early cretaceous these extension dominated faults extend southwards to the jiashan and hefei basins and die out in front of the dabie mountains to the north the faults penetrate the deeper parts of the weibei depression where they controlled cretaceous deposition in graben horst graben structures 3 the listric normal faults which were initiated in the paleogene generally occur around the bohai bay basin and include a series of ne trending faults in the weibei depression such as the tandong and tanxi faults these listric faults differ from the regional extensional faults in their localized occurrence and association with basin formation our study indicates that these three styles of faulting varied not only in timing and mechanical properties but developed at different levels at different locations resulting in different tectonic relationships and the formation of different geologic features in the different segments of the tan lu master system

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

crustal heterogeneity and seismotectonics of the region around beijing china abstract a detailed three dimensional 3 d p wave velocity model of the crust and uppermost mantle under the chinese capital beijing region is determined with a spatial resolution of 25 km in the horizontal direction and 4 17 km in depth we used 48 750 precise p wave arrival times from 2973 events of local crustal earthquakes controlled seismic explosions and quarry blasts these events were recorded by a new digital seismic network consisting of 101 seismic stations equipped with high sensitivity seismometers the data are analyzed by using a 3 d seismic tomography method our tomographic model provides new insights into the geological structure and tectonics of the region such as the lithological variations and large fault zones across the major geological terranes like the north china basin the taihangshan and the yanshan mountainous areas the velocity images of the upper crust reflect well the surface geological and topographic features in the north china basin the depression and uplift areas are imaged as slow and fast velocities respectively the taihangshan and yanshan mountainous regions are generally imaged as broad high velocity zones while the quaternary intermountain basins show up as small low velocity anomalies velocity changes are visible across some of the large fault zones large crustal earthquakes such as the 1976 tangshan earthquake m 7 8 and the 1679 sanhe earthquake m 8 0 generally occurred in high velocity areas in the upper to middle crust in the lower crust to the uppermost mantle under the source zones of the large earthquakes however low velocity and high conductivity anomalies exist which are considered to be associated with fluids the fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the large crustal earthquakes

crustal radial anisotropy beneath the dabie orogenic belt from ambient noise tomography summary in this study we continue our previous work of imaging isotropic shear velocity to study the crustal radial anisotropy beneath the dabie orogen and surrounding regions by jointly analysing rayleigh wave and love wave dispersion curves in addition to processing the vertical component data to retrieve rayleigh waves we collect horizontal component continuous ambient noise data and retrieve love waves from cross correlations of horizontal component noise data between station pairs then we measure love phase velocity dispersion curves at periods from 8 to 35 s using a spectral method and perform surface wave tomography to obtain high resolution phase velocity maps finally we determine crustal radial anisotropy by inverting the local phase velocity dispersion curves of rayleigh and love waves our model of crustal radial anisotropy reveals complex anisotropic patterns associated with the dynamic processes of continent continent collisions and post collision reworking between the north china craton and the yangtze craton in the huabei basin the radial anisotropy is positive throughout the entire crust corresponding to areas with extensional tectonics developed since the middle mesozoic in the jianghan basin strong positive radial anisotropy in the middle and lower crust is observed most likely resulting from subhorizontal alignment of seismic anisotropic materials under the crustal extensional deformation in the eastern dabie orogenic belt the radial anisotropy beneath northern dabie complex ndc appears positive in the upper and lower crust and negative in the middle crust the positive radial anisotropy in the upper crust is probably because of the presence of igneous rocks with anisotropic minerals aligned subhorizontally under the action of the extensional tectonics during igneous extrusion and emplacement whereas the positive radial anisotropy in the lower crust is probably because that subhorizontal alignment of anisotropic materials induced by magmatic underplating formed after the delamination of the orogeny in the middle crust finite strains associated with the vertical intrusion of deep magma might cause crystalline anisotropic minerals aligned vertically resulting in observed negative radial anisotropy in the western dabie orogenic belt positive radial anisotropy is present in the whole crust except beneath the hong an ultrahigh pressure uhp area where radial anisotropy is negative in the middle crust similar to ndc the hong an uhp probably experienced similar thermal geodynamic processes as the eastern dabie and the negative radial anisotropy might be also the result of vertical alignment of anisotropic minerals caused by the vertical intrusion of deep magma strong localized negative radial anisotropy in the middle crust beneath the xinyang area is imaged most likely caused by the vertical alignment of anisotropic minerals crystallized from the vertically intruding mafic magma originated from the upper mantle during the volcanism

the structure of the crust and uppermost mantle beneath south china from ambient noise and earthquake tomography summary two years of continuous recordings of ambient seismic noise observed at 354 stations in south china from 2009 to 2010 are used to estimate rayleigh wave group and phase velocity maps from 6 to 40 s period these results are merged with rayleigh wave phase velocity maps from 25 to 70 s period derived from earthquakes in the same time frame eikonal tomography generates the dispersion maps which by monte carlo inversion are used to estimate a 3 d vsv model of the crust and upper mantle down to a depth of 150 km across all of south china with attendant uncertainties a clear image emerges of the west yangtze block a region of the western yangtze craton characterized by relatively thick crust 40 km overlying a seismic mantle lithosphere that extends to at least 150 km that may have been the nucleus for the formation of the yangtze craton in the archean and may present a present day obstacle to the eastward expansion of tibet the west yangtze block contrasts with the thinner crust 30 km and mantle lithosphere 70 80 km beneath the eastern yangtze craton and south china foldbelt these observed differences are consistent with processes associated with flat slab subduction in the mesozoic that may have eroded the lithosphere of the eastern yangtze craton and the south china foldbelt

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