synchronizing intercontinental seismic networks using the 26 s persistent localized microseismic source accurate instrument clocks are essential for quantitative studies in seismology recent studies demonstrate that ambient seismic noise can be used to detect clock time drift for ocean bottom seismometers obss or inland seismometers with internal hardware or software problems but the short period 20 s interstation rayleigh waves extracted from ambient seismic noise are too weak for intercontinental seismic station pair correlations and thus are less effective for synchronizing sparse global seismic networks the 26 s persistent localized microseismic source in the gulf of guinea radiates strong seismic signals that can be recorded on global stations thus providing an alternative approach for synchronizing seismometers at large interstation distances in this study we test the feasibility of synchronizing seismic stations in africa north america and europe using the 26 s signals in the noise cross correlation functions we find that the clocks at the tam and obn stations are relatively stable during the years from 2002 to 2009 an 1 s time shift occurred at the ccm station from 2006 to 2009 and the clock drift was not constant we also detected about 150 s time shifts at the kowa station in october 2012 and up to 500 s in january 2013 we validate our results via comparison with the ambient noise method by stehly et al 2007 and teleseismic p wave arrival time residuals the method proposed in this study can be used to calibrate the obss in the north atlantic by synchronizing their clocks with the precisely calibrated inland seismometers

joint inversion for crustal and pn velocities and moho depth in eastern margin of the tibetan plateau abstract a classical problem in seismic tomography is the trade off between a discontinuity location and the velocity of the medium for that reason crustal tomography and pn tomography are typically done separately by isolating first arriving pg and pn waves although this avoids the contamination of secondary arrivals because of the existence of the moho lots of good data are discarded and as a result the lower crust is particularly poorly constrained here we design an iterative scheme to invert jointly for the velocities of the whole crust and the pn waves as well as the moho depth we use a spherical pseudo bending ray tracing method for the heterogeneous crust and include secondary pg waves at large distances we applied the method to the eastern and southeastern margin of the tibetan plateau where this method is particularly useful because of the rapid variation of crustal structure and moho depth our data include arrival times from chinese provincial and national earthquake bulletins and our own hand picks the results show significant features including slow upper crust but fast lower crust under sichuan basin rapid moho variation and slow pn in the plateau and fast pn in the borderland separated by major boundaries and faults the mid lower crust in the plateau is relatively slow compared to the average model and sichuan basin and poisson s ratio is anomalous exceeding 0 3 which is consistent with weak mid lower crust in the plateau

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

upper mantle structure and geodynamics of the sumatra subduction zone from 3 d teleseismic p wave tomography abstract teleseismic waveforms from a passive array of 63 seismic stations are applied to image the 3 d p wave velocity structure of the mantle in the sumatra subduction zone in this study 102 teleseisms with good signal to noise ratios were selected in total 1627 p wave relative arrivals have been extracted with high accuracy based on multi channel cross correlation and adaptive stacking methods with this dataset we conducted the 3 d tomographic inversions for the 3 d p wave velocity structure of the upper mantle in the sumatra subduction zone the tomographic results suggest significant lateral variations of p wave velocity in the mantle the trench parallel low velocity features in the upper mantle reveal that there may be a trench parallel flow associated with 3 d mantle flow beneath the subducting slab the subducting indo australian plate is also clearly imaged as a continuous high velocity anomalous zone in the mantle along the sumatra island beneath southern sumatra there could have a lateral detachment of high velocity anomaly from 560 km to the deep part of the slab which may imply the slab tearing if it is true we could infer that this tear in the slab may be terminated around 17 5 ma the advancing speed of the indo australian plate increasing from north sumatra to south sumatra plays a key role in the slab tear which suggests likely that the northeastward subducting of the indo australian plate along the sunda trench and the southeastward clockwise motion of the sunda shelf may form a torque tracing the sumatra island that facilitated the clockwise rotation of the fast moving plate with the oblique subduction of the indo australian plate the asymmetric distribution of stresses along this torque on either side may induce the slab tearing

plate interactions crustal deformation and magmatism along the eastern margins of the tibetan plateau abstract in order to investigate the deep structure and dynamics of the triangular colliding system of the eastern tibetan plateau tp as well as the yangtze platform and the qinling dabie fold belt a large number of p and s wave arrival times from both local and teleseismic earthquakes were used to generate high resolution tomographic images beneath the eastern margins of tp the results of this study show that the western margin of the minjiang fault is characterized by low velocity low v anomalies in sharp contrast to the high velocity high v anomalies that are derived from the eastern part this means that the minshan uplift zone is imaged as high v and acts as a barrier to the eastward escape crustal flow which leads to obvious segmentation of the longmenshan fault lmsf zone between velocity belts that are concatenated into the minjiang fault because high v anomalies are clearly imaged in this study to extended depths of ca 450 km we consider the yangtze platform containing the sichuan basin to comprise craton like lithosphere this study reveals the presence of a low v belt extending to a depth of ca 250 km between the sichuan basin and the ordos block which probably represents the migration pathway of upwelling asthenosphere materials from tibet at the same time low v zone with a downdip depth of ca 500 km accompanied by an approximately 400 km rectangular high v body is imaged under the tengchong volcano we interpret the high v body and the low v zone as evidence for the subducted indian plate and the volcanic magma source respectively the results of this study reveal a number of new features of structural heterogeneities relative to deep coupling between the tibet and the yangtze platform as well as the relationship between the sichuan basin and the ordos block and the original source of the tengchong volcano the results presented here enable us a better understanding of the plate interaction crustal deformation and magmatism of the tengchong volcano along the eastern margins of tp

models of the upper mantle beneath the central north island new zealand from speeds and anisotropy of subhorizontal p waves pn 1 the central north island of new zealand shows significant variations in pn wave speeds over small distances ranging from 8 5 0 2 km s to 7 4 0 1 km s over a distance of 150 km a combination of national network seismometers local volcanic seismic monitoring networks and temporary deployments are used to collect arrival times from local events during the period of 1990 2006 the data set consists of approximately 11 200 pn observations from 3000 local earthquakes at 91 seismograph sites we have created a method that allows us to model the predominant wavelength features of p wave speeds in the uppermost mantle as well as estimating values of mantle anisotropy and irregularities in the crust beneath stations using least squares collocation the resulting model shows distinct variations in uppermost mantle pn velocities velocities of less than 7 5 km s are found beneath the back arc extension region of the central volcanic region and under the taranaki volcanic region indicating the presence of water and partial melt the region to the east shows extremely high velocities of 8 3 8 5 km s where the p waves are traveling within the subducting pacific slab slightly lower than normal mantle velocities of 7 8 8 1 km s are found in the western north island suggesting a soft mantle pn anisotropy estimates throughout the north island show predominately trench parallel fast directions ceasing to nulls in the west anisotropy measurements indicate the strain history of the mantle null anisotropy measurements suggest an undisturbed mantle suggesting that mantle beneath the western north island is young

crustal structure across longmenshan fault belt from passive source seismic profiling 1 we analyse receiver functions from 29 broad band seismographs along a 380 km profile across the longmenshan lms fault belt to determine crustal structure beneath the east tibetan margin and sichuan basin the moho deepens from about 50 km under songpan ganzi in east tibet to about 60 km beneath the lms and then shallows to about 35 km under the western sichuan basin the average crustal vp vs ratios vary in the range 1 75 1 88 under songpan ganzi in east tibet 1 8 2 0 under the lms and decrease systematically across the nw part of the sichuan basin to less than 1 70 a negative phase arrival above the moho under songpan ganzi and sichuan basin is interpreted as a ps conversion from the top of a low velocity layer in the lower crust the very high crustal vp vs ratio and negative polarity ps conversion at the top of lower crust in east tibet are inferred to be seismic signatures of a low viscosity channel in the eastern margin of the tibetan plateau the lateral variation of moho topography crustal vp vs ratio and negative polarity ps conversion at the top of the lower crust along the profile seem consistent with a model of lower crust flow or tectonic escape

structure of the crust beneath the southeastern tibetan plateau from teleseismic receiver functions abstract southeastern tibet marks the site of presumed clockwise rotation of the crust due to the india eurasian collision and abutment against the stable sichuan basin and south china block knowing the structure of the crust is a key to better understanding of crustal deformation and seismicity in this region here we analyze recordings of teleseismic earthquakes from 25 temporary broadband seismic stations and one permanent station using the receiver function method we find that the crustal thickness decreases gradually from the tibetan plateau proper to the sichuan basin and yangtze platform but that significant intra crustal heterogeneity exists on shorter lateral scales 0 30 are detected beneath the southeastern margin of tibet but in the sichuan basin and southeastern yangtze platform the values are close to the global average combined with high regional heat flow and independent evidence for mid crustal layers of high electric conductivity the large intra crustal s wave velocity reduction 12 19 and the intermediate to high average crustal poisson s ratios are consistent with partial melt in the crust beneath parts of southeastern tibet these results could be used in support of deformation models involving intra crustal flow with the caveat that significant lateral variation in location and strength of this flow may occur

observations on regional variability in ground motion amplitude from six mw 6 0 earthquakes of the north south seismic zone in china observed ground motion intensity for six earthquakes of mw 6 0 6 2 that occurred in china s north south seismic zone nssz was compared with predicted medians from the bssa14 model the resulting between event be and within event wes residuals for peak ground acceleration and pseudo spectral acceleration up to 5 0 s were used to investigate the impact of source effects and path propagation on the regional variability in observed ground motion amplitude within the nssz although the magnitude and fault type were similar among the six earthquakes the results showed that their source effects were significantly different which contributed in part to the regional variability in observed ground motion amplitude estimated values for stress drop were found to mirror the trend in variation of the be values for short period ground motions in the six earthquakes this suggests that stress drop is an important factor for accurate representation of source effects and should be considered in the functional form of ground motion prediction equations anelastic attenuation of ground motion was found to be considerably different in local areas of the nssz which may constitute the primary reason for the regional variability in the observed ground motion amplitude the variation in wes values confirmed that regional adjustment of anelastic attenuation in the bssa14 model is applicable to some local areas i e around the longmenshan fault but not to the nssz in its entirety

the characteristics of high frequency attenuation of shear waves in the longmen shan and adjacent regions abstract a database of 1597 accelerograms from more than 500 events 3 3 m s which is the key parameter controlling the shape of fourier acceleration spectrum at high frequency in stochastic simulation the results indicate that is independent of magnitude but clearly dependent on near surface geology site condition and epicenter distance the obtained dependences of on distance in the songpan garze orogen sgo and western sichuan basin wsb are 0 0001427 and 0 0001031 s km respectively the average 0 of the horizontal component of the wsb and sgo ranges from 0 0144 to 0 0469 s and from 0 0321 to 0 0539 s respectively the dependence of on site condition shows opposite tendencies in the wsb and sgo in the sgo it suggests that v s 30 cannot fully represent the features of near surface geology which is believed to be the main contributor of furthermore we observed that the spatial distributions of 0 of the horizontal and vertical components are closely related to elevation and velocity images at 0 10 km depth respectively the correlations of and elevation in the longmen shan southeastern alps and northern dinarides region and anza seismic network are studied the results show good correlation and indicate that elevation may be used as a complementary parameter to develop a regional model in addition to the correlation

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

pn tomography with moho depth correction from eastern europe to western china we proposed a modified pn velocity and anisotropy tomography method by considering the moho depth variations using the crust 1 0 model and obtained high resolution images of the uppermost mantle pn velocity and anisotropy structure from eastern europe to western china the tomography results indicate that the average pn velocities are approximately 8 0 and 8 1 km s under the western and eastern parts of the study area respectively with maximum velocity perturbations of 3 4 we observed high pn velocities under the adriatic sea black sea caspian sea arabian plate indian plate and in the tarim and sichuan basins but low pn velocities under the apennine peninsula dead sea fault zone anatolia caucasus iranian plateau hindu kush and in the yunnan and myanmar regions generally regions with stable structures and low lithospheric temperatures exhibit high pn velocities low pn velocities provide evidence for the upwelling of hot material which is associated with plate subduction and continental collision processes our pn velocity and anisotropy imaging results indicate that the adriatic microplate dives to the east and west the hot material upwelling caused by subduction beneath the tibetan plateau is not as significant as that in the caucasus and myanmar regions the lithosphere exhibits coupled rotational movement around the eastern himalayan syntaxes and the areas to the north and south of 26 n in the yunnan region are affected by different geodynamic processes our newly captured images of the uppermost mantle velocity and anisotropy structure provide further information about continental collision processes and associated dynamic mechanisms

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

total energy of deep low frequency tremor in the nankai subduction zone southwest japan we estimated the total seismic energy of deep low frequency tremor in the nankai subduction zone southwest japan over an 11 year period for precise estimation the continuous time sequence of tremor activity was carefully detected using a procedure designed to minimize false negative detections the estimated spatial distribution of accumulated total energy of tremor indicates high energy area in the western shikoku region tremor activity rate defined as the yearly average of total tremor energy per unit area was investigated in each area throughout the nankai subduction zone the tremor activity rate was spatially variable being high in areas west of the kii channel the channel is marked by a complex plate geometry and low in areas east of the channel the plate convergence rate shows the same spatial pattern as that for tremor activity we infer that tremor activity is influenced by accumulated strain due to plate convergence

structural heterogeneity of the longmenshan fault zone and the mechanism of the 2008 wenchuan earthquake ms 8 0 we determined detailed 3 d images of p and s wave velocity vp vs and poisson s ratio in and around the longmenshan lms fault zone by using a large number of p and s wave arrival times from the aftershocks of the 2008 wenchuan earthquake ms 8 0 and other local events our results show that the structure of the lms fault zone north of the wenchuan main shock is very different from that south of the main shock the southern section of the lms fault zone contains a broad zone with low vp low vs and high anomalies while the northern segment exhibits more scattered heterogeneities corresponding to most of the aftershocks which occurred there a prominent low vp low vs and high anomaly exists directly beneath the wenchuan main shock hypocenter suggesting that in addition to compositional variations fluid filled fractured rock matrices may exist in the lms fault zone which may have influenced the generation of the large wenchuan earthquake our tomographic results provide sound seismic evidence for the hypothesis that an upward intrusion of lower crustal flow occurred along the lms fault zone in addition most small earthquakes before the 2008 wenchuan main shock occurred around the guanxian jiangyou fault while the wenchuan aftershocks were mainly concentrated on the yingxiu beichuan fault suggesting that the rupture process of the wenchuan earthquake may belong to an out of sequence thrusting event a suggestion which is in good agreement with the results from geological surveys and also quite similar to the rupture processes of the 1999 chi chi earthquake m 7 5 and the 2005 kashmir earthquake m 7 6 a few aftershocks occurred close to the blind guangyuan dayi fault in the sichuan basin suggesting that this blind fault was also ruptured by the wenchuan earthquake consistent with geological surveys

pre seismic deformation detected from regional gnss observation network a case study of the 2013 lushan eastern tibetan plateau china ms 7 0 earthquake abstract gnss global navigation satellite system observation is complicated by the presence of noise local benchmark motion un modeled atmospheric and other effects more subtle signals have existed the individual gnss time series but have undetected due to its low signal to noise ratio snr we introduce here a new method to extract spatially and temporally coherent signals by analyzing data from entire gnss networks simultaneously using free net solutions daily gnss network is performed a similarity transformation by constraining one location and one direction the deformation signal is extracted by analyzing the change of the gnss geometry net form integrating the location baseline length and direction information of all gnss stations from entire networks combined with area strain the deformation characteristic are further interpreted we apply the method for the 2013 lushan ms 7 0 earthquake and find a significant pre seismic deformation anomaly with the locked status and negative acceleration in the first shear strain and direction change time series implying a strong sinistral shear tectonic forces have happened in seismic source area and can intensify the pregnancy of the earthquake the phenomena can be well supported and explained by the experiment results of rock fracture in the laboratory it s inferred that a processes from stable locked status to negative acceleration change may be the most characteristic of pre seismic deformation

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

seismic structure of the longmen shan region from s wave tomography and its relationship with the wenchuan ms 8 0 earthquake on 12 may 2008 southwestern china 1 using arrival time data we determined seismic structure of the longmen shan by s wave tomography and studied its relations with the ms 8 0 earthquake in wenchuan southwestern china our results suggest that the longmen shan fault belt is a rheologic boundary between the eastern tibetan plateau and the sichuan basin and the deep crust of the entire longmen shan is significantly thickened by ductile deformation the upper structure of the eastern tibetan plateau is cored by the high velocity pengguan massif its collision with the sichuan basin is the most direct reason for the seismic ruptures on the longmen shan fault belt north of wenchuan while the lack of earthquakes south of wenchuan is related to the weakness of the crust therefore the ms 8 0 earthquake occurred in a strongly heterogeneous region the variations in the crustal structure largely controlled the initial rupture of the ms 8 0 earthquake and aftershock activity

complex deformation of central and north china through pn velocity and anisotropy tomography using our recently developed pn tomography method we obtain high resolution pn velocity and anisotropy structures of uppermost mantle beneath the central and north china which provide useful insight concerning the mechanism of intraplate mantle dynamics the consistency between the new pn model and seismic reflection refraction profiles demonstrates the high quality of our model based on the pn anisotropy structure surrounding the alxa block we infer that material extrusion from northeastern tibet was impeded and turned to the west and south edges of the alxa block the pn structures beneath the sichuan basin and songpan ganzi orogen suggest that the stable sichuan basin impeded material extrusion from the tibetan plateau and caused material from tibet to be extruded separately along the west and northwest edges of the sichuan basin to the north of the sichuan basin we infer that the extrusion has ceased within the songpan ganzi orogen rather than to further east the high pn velocities beneath the qinling orogen do not support the proposal of large scale eastward material escaping flow in the shallow mantle beneath the western qinling orogen the pn velocity distribution beneath the north china craton indicates that hot material from the mantle is more likely to upwell beneath deep faults or active orogenic areas our model indicates that the northern and central parts of the ordos block retain stable structures at the uppermost mantle while its southeastern has been reworked by hot material

crustal structure variation along 30 n in the eastern tibetan plateau and its tectonic implications abstract we determined crustal structure along the latitude 30 n through the eastern tibetan plateau using a teleseismic receiver function analysis the data came mostly from seismic stations deployed in eastern tibet and western sichuan region from 2004 to 2006 crustal thickness and vp vs ratio at each station were estimated by the h k stacking method on the profile the mean crustal thickness and vp vs ratio were found to be 62 3 km and 1 74 in the lhasa block 71 2 km and 1 79 near the bangong nujiang suture 66 3 km and 1 80 in the qiangtang block 59 8 km and 1 81 in the songpan garze block and 42 9 km and 1 76 in the yangtze block respectively the estimated crustal thicknesses are consistent with predictions based on the topography and the airy isostasy except near the bangong nujiang suture and in the qiangtang block where the crust is 5 10 km thicker than predicted indicating that the crust may be denser possibly due to mafic underplating we also inverted receiver functions for crustal velocity structure along the profile which reveals a low s wave velocity zone in the lower crust beneath the eastern tibetan plateau although the extent of the low velocity zone varies considerably the low velocity zone together with previous results suggests limited partial melting and localized crustal flow in the lower crust of the eastern tibetan plateau

active deformation of asia from kinematics to dynamics using estimated strain rates across the actively deforming region of asia to infer variations in viscous stress it is shown that gradients of stress point uphill toward the center of tibet where gravitational potential energy per unit surface area reaches a maximum thus the dynamics of the deformation seem to obey the equation of creeping flow which expresses a balance between gradients in stress and the gravitational body force this balance in the region of the tibetan plateau yields an estimate of 10 22 pascal second for the average viscosity of the tibetan lithosphere which is only about 10 to 100 times greater than the viscosity of the convecting upper mantle

mineralium deposita change and continuity 2012 has been a year of transition for mineralium deposita after 4 years as co editor patrick j williams has steppeddown in june to fully concentrate on his consulting busi ness during patrick s tenure mineralium deposita hascontinued to grow as a top journal for research on mineraldeposits we are grateful for his dedicated work and wishhim the best of luck for the future the council of the society for geology applied tomineral deposits sga has appointed georges beaudoinfrom universite laval quebec canada as the new co editor of the journal georges has been on the editorialboard since 2001 bernd lehmann from technischeuniversitat clausthal clausthal germany remains asco editor three new associate editors joined the editorialboard in 2012 these are david craw university of otago dunedin new zealand albert gilg technische universitatmunchen munich germany and robert linnen westernuniversity london canada associate editor noel c whitehas stepped down after many years of service and we thankhim for his energic and careful work the journal continues to attract a high level of sub missions of about 120 140 papers per year since 2011 a mineralium deposita volume contains about 1 000printed pages with color print free of charge to allauthors we have a wide distribution across the world through subscriptions and more than 300 online dealswith aggregators and consortia mineralium deposita isaccessible to more than 7 700 institutions worldwide this is a strong incentive to submit research to mineraliumdeposita and to gain large exposure the world of scientificpublishing is changing quickly and direct download ofpapers published in mineralium deposita has grownfrom about 98 000 in 2008 to 133 000 in 2011 for anannual rate of increase of approximately 10 approx imately 20 of downloads are for papers publishedonline first and for the calendar year whereas about60 of downloads are for papers published since 1997 roughly 44 of downloads are from the asia pacificregion china 18 australia 10 whereas europeaccounts for 28 germany 6 uk 4 northamerica for 16 usa 8 canada 7 and bothafrica and south america each account for 6 as editors of mineralium deposita we are committed todiligent review of submissions in 2011 the average timefrom submission to acceptance including author correctionsof revised versions was 217 days slightly down from239 days in 2010 however this distribution is highlyskewed and most papers were handled within 150 days after acceptance a paper is published online with a doiwithin approximately 3 weeks this ensures rapid publica tion and allows the new papers to be read downloaded andcited immediately such that your work reaches the scientificcommunity quickly the research submitted to mineraliumdeposita is sourced from a large number of countries withtop contributors in 2011 being china 30 canada 15 and australia 11 as we wish to ensure high scientificquality we accept on merit approximately 40 of thesubmissions from year to year since 2006 the annualimpact factor if of mineralium deposita has variedbetween 1 25 and 2 06 with a value of 1 68 in 2011 close to the average 10 year if of 1 66 we are dedi cated to publish high quality innovative and challeng ing papers in mineralium deposita and we work toimprove the standing of the journal the two most citedpapers to date published in mineralium deposita in2010 were by r r keays and p c lightfoot on thecrustal sulfur contamination that causes formation ofmagmatic ni cu sulfide deposits keays and lightfoot2010 andbyn koglin h e frimmel w e lawrieminter and h braetz on the trace element compositionof pyrite from mesoarchean and paleoproterozoic placerdeposits koglin et al 2010

mapping the deep lithospheric structure beneath the eastern margin of the tibetan plateau from gravity anomalies 1 various authors have investigated the mechanism of lateral support of the lithosphere in maintaining the uplift of the tibetan plateau based on gravity data and elastic flexural modeling in the south of the plateau across the himalayas and in the north and the northwest across the altyn tagh and west kunlun shan however the degree of the regional compensation and lateral support to the east of the tibetan plateau has remained unknown in this paper we present a lithospheric flexure model by interpreting gravity and topography to understand the first order problem of lateral support of the lithosphere at the eastern margins of the tibetan plateau the flexural modeling constrains the geometry and strength variation of the lithosphere from the eastern margin of tibet past the longmen shan ranges on to the sichuan basin a lithosphere of intermediate strength te 45 km beneath the sichuan basin is weakened te 36 km by the thrusting underneath the eastern margin of the tibetan plateau the strength variations indicate that about 10 km of the crustal material of the lithosphere has been ripped off and integrated into the thickened upper crust of the tibetan plateau which however has no appreciable strength the stiffness of the lithosphere keeps the tibetan plateau relatively stable at its eastern margin and enables the weight of the plateau to be supported in the east by the sichuan lithospheric deformation in the southern longmen shan area is more pronounced than in the northern region

low velocity crustal flow and crust mantle coupling mechanism in yunnan se tibet revealed by 3d s wave velocity and azimuthal anisotropy abstract we used teleseismic data recorded by a permanent seismic network in yunnan se tibet and measured the interstation rayleigh wave phase velocity between 10 and 60 s a two step inversion scheme was used to invert for the 3d s wave velocity and azimuthal anisotropy structure of 10 110 km the results show that there are two low velocity channels between depths of 20 30 km in yunnan and that the fast axes are sub parallel to the strikes of the low velocity channels which supports the crustal flow model the azimuthal anisotropy pattern is quite complicated and reveals a complex crust mantle coupling mechanism in yunnan the n s trending luzhijiang fault separates the dianzhong block into two parts in the western dianzhong block the fast axis of the s wave changes with depth which indicates that the crust and the lithospheric mantle are decoupled in the eastern dianzhong block and the western yangtze craton the crust and the lithospheric mantle may be decoupled because of crustal flow despite a coherent s wave fast axis at depths of 10 110 km in addition the difference between the s wave fast axis in the lithosphere and the sks splitting measurement suggests that the lithosphere and the upper mantle are decoupled there in the baoshan block the stratified anisotropic pattern suggests that the crust and the upper mantle are decoupled

the contribution of postcritical moho reflections sms to ground motions of the 2008 mw 7 9 wenchuan earthquakethe contribution of postcritical moho reflections sms to ground motions

split philippine sea plate beneath japan 1 the shape of the philippine sea plate subducting beneath western japan is a crucial factor in understanding earthquakes and volcanic activity we propose that the subducted plate was split along an extinct ridge due to an abrupt change of subduction direction followed by elastic deformation of the plate and an accumulation of stress near the ridge this shape is consistent with receiver function images the distribution of deep tremor sources the seismicity and focal mechanisms of intraplate earthquakes and the distribution of anomalous ratios of helium isotopes in ground water the movement history of the plate can explain active tectonics in western japan in the last 2 4 ma the location history of the volcanic front and the tear control where fluids ascend in the crust and these fluids are responsible for the generation of large earthquakes and volcanoes

pn uppermost mantle tomography of central tibet implication for mechanisms of n s rifts and conjugate faults abstract the north south convergence between the indian and eurasian continents since cenozoic has produced the tibetan plateau and east west extension structures have also developed since late cenozoic whether these extensional structures are limited to the crust or extend to the deep lithosphere remains controversial the uppermost mantle serves as a link between the crust and deep lithosphere the velocity structure of which provides an important constraint on exploring the mechanism of extensional structures based on pn traveltime data recorded by the sandwich network in central tibet we use the interstation traveltime difference method to obtain the uppermost mantle velocity structure our results show significant velocity differences for the uppermost mantle beneath the conjugated strike slip faults and rifts which indicates their different formation mechanisms the high pn velocity beneath the conjugated strike slip faults support an eastward horizontal shear at the base of the upper crust rather than the lower crust has contributed to the development of the conjugated strike slip faults the low pn velocity beneath the rifts in lhasa may provide evidence for the rifts cutting through the entire crust and reflect the connection between the formation of the rifts and deep tectonic activities the most prominent features in our results are the low pn velocity zones beneath the tangra yum co rift tyr the pumqu xianza rift pxr and the zone between the two rifts and we explain the low pn velocity as the top of the mantle wedge upon the subducting indian lithospheric slab

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

rayleigh wave phase velocity maps of tibet and the surrounding regions from ambient seismic noise tomography ambient noise tomography is applied to the significant data resources now available across tibet and surrounding regions to produce rayleigh wave phase speed maps at periods between 6 and 50 s data resources include the permanent federation of digital seismographic networks five temporary u s program for array seismic studies of the continental lithosphere passcal experiments in and around tibet and chinese provincial networks surrounding tibet from 2003 to 2009 totaling 600 stations and 150 000 interstation paths with such a heterogeneous data set data quality control is of utmost importance we apply conservative data quality control criteria to accept between 5000 and 45 000 measurements as a function of period which produce a lateral resolution between 100 and 200 km across most of the tibetan plateau and adjacent regions to the east misfits to the accepted measurements among passcal stations and among chinese stations are similar with a standard deviation of 1 7 s which indicates that the final dispersion measurements from chinese and passcal stations are of similar quality phase velocities across the tibetan plateau are lower on average than those in the surrounding nonbasin regions phase velocities in northern tibet are lower than those in southern tibet perhaps implying different spatial and temporal variations in the way the high elevations of the plateau are created and maintained at short periods 20 s very high velocities are imaged in the tarim basin the ordos block and the sichuan basin these phase velocity dispersion maps provide information needed to construct a 3 d shear velocity model of the crust across the tibetan plateau and surrounding regions

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

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

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

slow earthquakes linked along dip in the nankai subduction zone we identified a strong temporal correlation between three distinct types of slow earthquakes distributed over 100 kilometers along the dip of the subducting oceanic plate at the western margin of the nankai megathrust rupture zone southwest japan in 2003 and 2010 shallow very low frequency earthquakes near the nankai trough as well as nonvolcanic tremor at depths of 30 to 40 kilometers were triggered by the acceleration of a long term slow slip event in between this correlation suggests that the slow slip might extend along dip between the source areas of deeper and shallower slow earthquakes and thus could modulate the stress buildup on the adjacent megathrust rupture zone

accounting for lateral variations of the upper mantle gradient in pn tomography studies 1 the effect of an upper mantle velocity gradient on regional arrival times has been approximated by a cubic distance term which can be extended to two dimensions for use in tomographic studies to demonstrate this we add a laterally varying upper mantle gradient to the standard pn time term tomography technique and apply to a data set from asia compiled using ground truth event location criteria we observe strong lateral variations in the gradient ranging from 0 001 to 0 003 s 1 with high gradients associated with the tethys convergence zone the gradient patterns may reflect lateral variations in the thermal gradient of the mantle lid variance reduction is 63 with respect to pn tomography without gradients adding gradients allows the use of longer path lengths improving velocity image definition in high gradient regions with sparse station distribution such as tibet

refining the image of the san andreas fault near parkfield california using a finite difference travel time computation technique abstract the parkfield area seismic observatory paso was a dense telemetered seismic array that operated for nearly 2 years in a 15 km aperture centered on the san andreas fault observatory at depth safod drill site the main objective of this deployment was to refine the locations of earthquakes that will serve as potential targets for safod drilling and in the process develop a high for passive seismological techniques resolution image of the fault zone structure a challenging aspect of the analysis of this data set was the known existence of large 20 25 contrasts in seismic wavespeed across the san andreas fault the resultant distortion of raypaths could challenge the applicability of approximate ray tracing techniques in order to test the sensitivity of our hypocenter locations and tomographic image to the particular ray tracing and inversion technique employed we compare an initial determination of locations and structure developed using a coarse grid and an approximate ray tracer thurber c roecker s roberts k gold m powell m l and rittger k 2003 earthquake locations and three dimensional fault zone structure along the creeping section of the san andreas fault near parkfield ca preparing for safod geophys res lett 30 3 10 1029 2002gl016004 with one derived from a relatively fine grid and an application of a finite difference algorithm hole j a and zelt b c 1995 3 d finite difference reflection traveltimes geophys j int 121 2 427 434 in both cases we inverted arrival time data from about 686 local earthquakes and 23 shots simultaneously for earthquake locations and three dimensional vp and vp vs structure included are data from an active source seismic experiment around the safod site as well as from a vertical array of geophones installed in the 2 km deep safod pilot hole drilled in summer 2002 our results show that the main features of the original analysis are robust hypocenters are located beneath the trace of the fault in the vicinity of the drill site and the positions of major contrasts in wavespeed are largely the same at the same time we determine that shear wave speeds in the upper 2 km of the fault zone are significantly lower than previously estimated and our estimate of the depth of the main part of the seismogenic zone decreases in places by 100 m tests using virtual earthquakes borehole receiver gathers of picks for surface shots indicate that our event locations near the borehole currently are accurate to about a few tens of meters horizontally and vertically

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

asperity of the 2013 lushan earthquake in the eastern margin of tibetan plateau from seismic tomography and aftershock relocation summary the mw 6 6 lushan earthquake occurred on 2013 april 20 in the eastern margin of tibetan plateau and was about 50km away from the 2008 mw 7 9 wenchuan earthquake rupture zone by using arrival times from portable and permanent seismic stations local earthquake tomography and aftershock relocation were conducted by using 41955 first p and 42687 first s arrivals low vp vs high vp and vs anomaly are found in the source region which is well consistent with the aftershock distributions the ruptured fault plane might be a blind thrust and is well defined by the vp vs structure and aftershock seismicity high velocity and lowvp vs anomalies may suggest the mafic or ultramafic materials thrust from mid lower crust and define the asperity that concentrated stresses responsible for seismogenesis in contrast low vs anomalyisfoundinthegapbetweenthewenchuanandlushanearthquakes suggesting of ductile rocks with low stress

trace element characteristics of different pyrite types in mesoarchaean to palaeoproterozoic placer deposits a comparative in situ la icp ms trace element study on pyrite from three different variably auriferous archaean to palaeoproterozoic palaeoplacer deposits in the ouro fino syncline quadrilatero ferrifero brazil the elliot lake area north of lake huron se canada and several deposits within the witwatersrand basin south africa revealed systematic differences between morphologically different pyrite types and between the various palaeoplacer deposits especially the ni and au concentrations as well as co ni and mo ni ratios were found to be systematically different in detrital compact detrital porous and post sedimentary hydrothermal pyrite grains from different source areas high co ni ratios and low au concentrations are typical of post sedimentary pyrite which is hydrothermal in origin in contrast relatively low co ni ratios and high au contents characterise detrital porous banded and concentric pyrite grains au 1 ppm which are syn sedimentary in origin in the elliot lake area and the witwatersrand basin detrital compact rounded pyrite is characterised by high co ni ratios which is in agreement with derivation from a hydrothermal source low au concentrations in this pyrite type support the contention of the gold and the pyrite in these deposits coming from different source rocks in contrast derivation from an originally diagenetic pyrite is suggested for the detrital compact pyrite in the ouro fino syncline because of low to intermediate co ni ratios high au contents may indicate a genetic relationship between pyrite and gold there systematic differences exist between the three areas with respect to au ni co mo and cu distributions in detrital pyrite which reflects differences in the provenance a predominantly mafic ultramafic source is indicated for the ouro fino a felsic source for the elliot lake and a mixed felsic mafic provenance for the witwatersrand pyrite populations independently of pyrite type the higher au endowment of the studied witwatersrand and ouro fino conglomerates are also reflected by an overall higher au concentration in the respective pyrite grains compared to the relatively au poor samples from elliot lake in general a strong positive correlation between au and pb levels in the various pyrite grains is noted analogous to pb which is well known for not being easily accommodated in the pyrite crystal lattice but occurring as discrete pbs phases au is considered to be present mainly in the form of discrete au phases in minute pores and interstices of the pyrite grains rather than within the pyrite lattice

constraints on crust mantle transition zone with pn waveforms a case study of eastern china and southern korean peninsula abstract the seismic velocity structure of the crust mantle transition zone cmtz provides key constraints on crustal dynamics and can be studied with pn wave which propagates horizontally along the moho discontinuity in this study we first explore an effect of velocity gradient structures in the cmtz through synthetic pn waveforms and demonstrate that the shape of pn changes from step like to pulse like when the cmtz becomes from sharp to a gradient velocity structure respectively we then use pn waveforms of the regional earthquakes the july 2012 mw 4 8 earthquake in east china and the september 2016 mw 5 1 earthquake in south korea to examine the cmtz structures to the west and east of the yellow sea and thus to constrain tectonic affinity between the eastern china and southern korean peninsula the pn waveforms from the mw 4 8 event in east china show that the moho in southern yangtze craton is sharp whereas there may be a gradient structure in cmtz with a 6 10 km thickness in northern yangtze craton the pn waveforms from the mw 5 1 event in south korea show that the cmtz in south korea is also sharp similar to the southern yangtze craton observed difference in cmtz structures suggest that sulu orogenic belt may extend along the north of the gyeonggi massif in korea

the role of gravitational potential energy in active deformation in the southwestern united states in orogenic belts intrinsic buoyancy and extrinsic boundary forces act on the continental lithosphere determining the relative importance of these forces is fundamental to understanding the dynamics of continental deformation in the western united states estimates of gravitational potential energy show that given available constraints on rheology buoyancy forces are sufficient to produce the wide variety of rates and styles of observed deformation including absence of deformation this underscores the importance of gravitational potential energy for deformation in orogenic belts

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

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

seismically constrained thermo rheological structure of the eastern tibetan margin implication for lithospheric delamination article i nfo the eastern tibetan margin bordered by the longmen shan range exhibits significant lateral differences in the lithospheric structure and thermal state to investigate the roles of these differences in mountain building we construct a thermo rheological model along a wide angle seismic profile across the eastern tibetan margin based on recent seismic and thermal observations the thermal modeling is constrained by the surface heat flow data and crustal p wave velocity model the construction of the rheological envelopes is based on rock me chanics results and involves two types of rheology a weak case where the lower crust is felsic granulite and the lithospheric mantle is wet peridotite and a strong case where the lower crust is mafic granulite and the litho spheric mantle is dry peridotite the results demonstrate 1 one high temperature anomaly exists within the uppermost mantle beneath eastern tibet indicating that the crust in eastern tibet is remarkably warmer than thatinthe sichuanbasin and 2 therheologicalstrengthofthe lithosphericmantlebeneatheasterntibetiscon siderably weaker than that beneath the sichuan basin the rheological profiles are in accord with seismicity dis tribution by combining theseresults with the observed crustal lithospheric architecture pn velocity distribution and magmatism in the eastern tibetan margin we suggest that the delamination of a thickened lithospheric mantle root beneath eastern tibet is responsible for the growth of the eastern tibetan margin

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

lateral variations in compressional velocities beneath the tibetan plateau from pn traveltime tomography summary a back projection algorithm is applied to 353 p traveltime measurements to image the lateral variations in compressional velocity in the uppermost mantle in and around tibet prior to the tomographic inversion we refined the apparent p slowness measurements based on a recently developed relocation procedure zhao helmberger 1991 and mathematical formulations of zhao 1993 these refinements are crucial in obtaining a high quality velocity image we obtained an average p velocity value for the uppermost mantle of 7 93 kms l and an average mantle p velocity gradient of 3 1 x lo s for tibet the final 2 d p velocity image in the uppermost mantle is characterized by a large 7 to 9 in dimension low velocity down to about 7 78 km s region in north central tibet and by large high velocity up to 8 11 km s i regions in the western and eastern flanks of tibet the crustal thickness is greater than 70 km inside the tibetan plateau it decreases toward the southern eastern and western boundaries of the plateau at and beyond these boundaries the crustal thickness is similar to those beneath the eurasian shield rigorous analyses of resolution and error suggest that 1 there is a pronounced difference between the tomographic velocity image obtained with and without the refinements to the p slowness measurements indicating a significant improvement in the quality of our inversion by these refinements 2 random errors in measuring earthquake origin times and locations and in the p arrival times should not cause errors of more than 0 1 km s in the velocity image 3 the resolution is generally within 6 to 10 the velocity image obtained in this study is consistent with previous s p traveltime studies and geothermal petrological studies and is consistent with a mantle convection model in which a convective upwelling is occurring in north central tibet and downwellings occurring in the surrounding regions molnar 1988 1990

the relation between cu au ratio and formation depth of porphyry style cu au mo deposits constraints on gold and copper ore grades in porphyry style cu au mo deposits are re examined with particular emphasis on published fluid pressure and formation depth as indicated by fluid inclusion data and geological reconstruction defining an arbitrary subdivision at a molar cu au ratio of 4 0 104 copper gold deposits have a shallower average depth of formation 2 1 km compared with the average depth of copper molybdenum deposits 3 7 km based on assumed lithostatic fluid pressure from microthermometry the correlation of cu au ratio with depth is primarily influenced by the variations of total au grade despite local mineralogical controls within some ore deposits the overall cu au ratio of the deposits does not show a significant correlation with the predominant type of cu fe sulfide i e chalcopyrite or bornite primary magma source probably contributes to metal endowment on the province scale and in some individual deposits but does not explain the broad correlation of metal ratios with the pressure of ore formation by comparison with published experimental and fluid analytical data the observed correlation of the cu au ratio with fluid pressure can be explained by dominant transport of cu and au in a buoyant s rich vapor coexisting with minor brine in two phase magmatic hydrothermal systems at relatively shallow depth approximately 3 km and greater confining pressure is likely to precipitate copper molybdenum only while sulfur complexed gold remains dissolved in the relatively dense vapor upon cooling this vapor may ultimately contract to a low salinity epithermal liquid which can contribute to the formation of epithermal gold deposits several kilometers above the au poor porphyry cu mo deposit these findings and interpretations imply that petrographic inspection of fluid inclusion density may be used as an exploration indicator low pressure brine vapor systems are favorable for coprecipitation of both metals leading to au rich porphyry copper gold deposits epithermal gold deposits may be associated with such shallow systems but are likely to derive their ore forming components from a deeper source which may include a deeply hidden porphyry copper molybdenum deposit exposed high pressure brine vapor systems or stockwork veins containing a single type of intermediate density inclusions are more likely to be prospective for porphyry copper molybdenum deposits

constraining p wave velocity variations in the upper mantle beneath southeast asia we have produced a p wave model of the upper mantle beneath southeast se asia from reprocessed short period international seismological centre isc p and pp data short period p data of the annual bulletin of chinese earthquakes abce and long period pp p data we used 3d sensitivity kernels to combine the datasets and mantle structure was parameterized with an irregular grid in the best sampled region our data resolve structure on scale lengths less than 150 km the smearing of crustal anomalies to larger depths is reduced by a crustal correction using an a priori 3d model our tomographic inversions reveal high velocity roots beneath the archean ordos plateau the sichuan basin and other continental blocks in se asia beneath the himalayan block we detect high seismic velocities which we associate with subduction of indian lithospheric mantle this structure is visible above the 410 km discontinuity and may not connect to the remnant of the neo tethys oceanic slab in the lower mantle our images suggest that only the southwestern part of the tibetan plateau is underlain by indian lithosphere and thus that the upper mantle beneath northeastern tibet is primarily of asian origin our imaging also reveals a large scale high velocity structure in the transition zone beneath the yangtze craton which could have been produced in multiple subduction episodes the low p wave velocities beneath the hainan island are most prominent in the upper mantle and transition zone they may represent counter flow from the surrounding subduction zones and may not be unrelated to processes beneath eastern tibet 2005 elsevier b v all rights reserved

anisotropic pn tomography in the western united states pn travel times are affected not only by lateral variations in crust and mantle velocity but also by significant amounts of laterally varying anisotropy to investigate uppermost mantle anisotropy a tomography algorithm was reformulated to include lateral variations in both velocity and horizontal anisotropy and it was applied to pn travel time data from the western united states results show that anisotropy is as important in explaining the travel time residuals as are the velocity variations a detailed resolution study examined the trade off between the velocity variations and the anisotropy variations and showed that both could be resolved for regions with good ray path coverage pn anisotropy beneath the western united states has maximum amplitudes of 0 3 km s 7 5 when resolved on a length scales of around 3 the orientations of pn anisotropy often correlate well with those inferred from shear wave splitting results this correlation suggests that orientation of mantle anisotropy does not change significantly with depth for many regions the orientation of the pn anisotropy can be correlated with some of the tectonic processes which occur within the western united states for example the fast direction of pn anisotropy parallels the northeast direction of subduction of the juan de fuca plate beneath the northwest pacific coast suggesting that there the anisotropy is related to subduction driven deformation the fast direction of pn anisotropy also parallels the strike of the san andreas fault system in central california indicating that shear strains along the plate boundary may be responsible for the anisotropy there within the great basin the pn anisotropy varies substantially and both partial melting and small scale convection within the uppermost mantle could be responsible for these anisotropy variations

numerical modeling of eastern tibetan type margin influences of surface processes lithospheric structure and crustal rheology the eastern tibetan margin is characterized by a steep topographic gradient and remarkably lateral variations in crustal lithospheric structure and thermal state gps measurements show that the surface convergence rate in this area is strikingly low how can such a mountain range grow without significant upper crustal shortening in order to investigate the formation mechanism of the eastern tibetan type margins we conducted 2d numerical simulations based on finite difference and marker in cell techniques the numerical models were constrained with geological and geophysical observations in the eastern tibetan margin several major parameters responsible for topography building such as the convergence rate the erosion sediment rate and the presence of partially molten crust were systematically examined the results indicate that the presence of partially molten material in the middle lower crust can make a positive contribution to the formation of steep topography but it is not a necessary factor a steep topographic gradient may be a characteristic feature when a thin lithosphere with thick crust converges with a thick lithosphere with thin crust in the context of a high erosion rate the longmen shan range still gains and maintains its steep high topography to the present this could be explained by exerting a large push force on tibet side our numerical experiments suggest that topographic characteristic across the eastern tibetan type margins is mainly derived from isostatic equilibration forces and intensive convergence between two continental lithospheres with totally different rheological properties

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

interstation pg and sg differential traveltime tomography in the northeastern margin of the tibetan plateau implications for spatial extent of crustal flow and segmentation of the longmenshan fault zone abstract interstation pg and sg differential traveltime tomography is performed in the northeastern margin of the tibetan plateau providing reliable mid lower crustal velocity images while minimizing errors from earthquake mislocation and origin time prominent low p and s velocities p and s in the northeastern tibetan plateau are bound to the east by the minjiang fault and the southwest segment of the longmenshan fault zone lmsfz in contrast relatively high p and s velocities 6 1 km s for v p and 3 7 km s for v s are found beneath the sichuan basin and in the triangular region bound to the west by the minjiang fault and to the east of the northeast segment of the lmsfz significant low velocity anomalies suggest a weak mid lower crust that flows beneath the eastern tibetan plateau while the high velocities beneath the sichuan basin indicate a rigid cold and stable crust the strong lithospheric mantle beneath the sichuan basin inferred from previous studies may act as a barrier to the eastward escape of crustal flow from the eastern tibetan plateau the segmentation of the lmsfz is reconfirmed by the distinct mid lower crustal velocities in the southwest and northeast segments high velocity and low conductivity anomalies in the mid lower crust beneath the eastern minshan uplift and the western qinling orogen suggest that no crustal flow reaches this area

tomographic image of the crust and upper mantle beneath the western tien shan from the manas broadband deployment possible evidence for lithospheric delamination abstract we combine teleseismic p arrival times from the recent manas deployment of broadband sensors with p and s arrival times from local events recorded by the genghis deployment and analog observations from the kyrgyz institute of seismology to generate a high resolution 20 km image of elastic wavespeeds in the crust and upper mantle beneath the western tien shan the total data set consists of 29 006 p and 21 491 s arrivals from 2176 local events recorded at 144 stations along with 5202 p arrivals from 263 teleseismic events recorded at 40 stations the most significant feature in our image of the mantle beneath the tien shan is a pair of large elongated high wavespeed regions dipping in opposite directions from the near surface to depths of at least 400 km these regions appear to be continuous and extend upwards to bounding range fronts where the tarim basin is being overthrust by the kokshal range on the south side and the kazach shield underthrusts the kyrgyz range on the north side while it is tempting to interpret these high wavespeed anomalies as evidence for contemporary subduction of continental lithosphere such a scenario is difficult to reconcile with both the timing of the orogen and the size of the wavespeed anomaly we suggest instead that they represent downwelling side limbs of a lithospheric delamination beneath the central part of the tien shan possibly by siphoning of the bordering continental lithosphere as the central part descends

shear wave velocity structure of the shallow sediments in the bohai sea from an ocean bottom seismometer survey abstractto investigate the seismic velocity structure of the shallow sediments in the bohai sea of china we conducted a shear wave velocity inversion of the surface wave dispersion data from a survey of 12 ocean bottom seismometers obss and 377 shots of a 9000 in3 air gun with obs station spacing of approximately 5 km and air gun shot spacing of approximately 190 m high quality scholte wave data were recorded by the obss within 0 4 5 km offset we retrieved the scholte wave phase velocity dispersion for the fundamental mode and first overtone in the frequency band of 0 9 3 0 hz with the phase shift method and inverted for the shear wave velocity structure of the shallow sediments with a damped iterative least squares algorithm pseudo 2d shear wave velocity profiles with a depth of approximately 400 m revealed coherent features of relatively weak lateral velocity variation we also estimated the uncertainty in shear wave velocity structure based on the pseudo 2d profiles from six trial inversions wi

uppermost mantle structure of the eastern margin of the tibetan plateau from interstation pn traveltime difference tomography abstract tomographic inversion with interstation pn differential traveltime data provides a reliable velocity image of the uppermost mantle across the longmenshan fault belt which borders the eastern tibetan plateau and sichuan basin low pn velocities pn velocities 8 1 km s appear beneath the sichuan basin to the east suggesting a relatively weak upper mantle beneath eastern tibetan plateau and a strong upper mantle beneath the sichuan basin the pn velocities are consistent with the proposition that the rigid and stable lithosphere of the sichuan basin may act as a barrier to the eastward escape flow of the ductile crust of the eastern tibetan plateau consistency of pn velocities with the smoothed topography crustal thickness and bouguer gravity implies that the dynamic processes of the lithospheric mantle should be responsible for the crustal thickening and relief of uplift in the eastern tibetan plateau however the longmeshan fault belt appears to be separated into two segments by the huya and leidong faults as manifested by significant discrepancies in topography gradient seismic activity rupture process and aftershock distribution of wenchuan earthquake this segmentation is also supported by difference in pn velocities along the strike of the fault belt suggesting different tectonic environments in the crust and lithospheric mantle understanding of the mechanism for the segmentation requires further investigation

spatial distribution of seismic energy rate of tectonic tremors in subduction zones the sizes of deep tectonic tremors have never been accurately evaluated as a physical quantity here we estimate tremor size as the band limited seismic energy rate at 2 8 hz with accurate evaluation of the path attenuation and site amplification of seismic waves in four subduction zones nankai cascadia jalisco and south chile the size frequency statistics of seismic energy rate which are characterized by the median measure for each subregion are spatially variable the spatial variations are categorized into three types with each type corresponding to a different tremor migration behavior in type a regions where tremor zone is wider seismic energy rates are highly variable in the dip direction and tremor activities are usually initiated in the less energetic tremor zone some of them further penetrate into the energetic tremor zone and subsequently migrate for long distances in the strike direction type b regions are characterized by relatively narrow tremor zones minor variations in energy rates in the dip direction and long distance migration in the strike direction type c regions are characterized by isolated clusters of tremor activities without migration and by independent failure of each small tremor cluster given that the spatial distributions of tremor energy rates reflect heterogeneities in the strength of the plate interface such distributions which would be controlled by the width of tremor zone may determine the regional style of slow earthquake behavior some energetic tremor regions act as switches that trigger large slow slip events especially in type a regions

a low velocity belt beneath northern and eastern tibetan plateau from pn tomography 1 new pn tomography on tibetan plateau tp and neighboring region is conducted with data assembled from various sources the improved pn tomographic image delineates several distinct geophysical regimes that are approximately separated by geological boundaries at surface dense distribution of the stations in the eastern half of the plateau allows us to infer a 3d view of crustal thickness variation of the region the most striking feature is the bended low velocity belt lvb which extends from west to east beneath qiangtang block and songpan ganzi fold belt sgfb in northern tp and then turns consistently southward with sgfb beneath eastern tp and further south to indo china the consistency between geological boundaries on surface and sharp velocity contrast boundaries in uppermost mantle may suggest strong deformation coupling between crust and at least uppermost mantle if not whole lithosphere a north south striking lvb is also observed cutting through the southern tp coinciding with the yadong gulu rift at surface our tomographic results are generally consistent with dynamic models that involve with underthrusting in the southern tp shortening in the northern tp and extrusion to the east and the southeast furthermore our results suggest significant east west variations in the structure and dynamics