kinematic models of fluvial terraces over active detachment folds constraints on the growth mechanism of the kashi atushi fold system chinese tian shan during detachment folding the relationship between differential uplift and shortening depends on the mechanism of fold growth such as limb rotation or hinge migration and may vary over the lifetime of a fold thus neither long term shortening rates nor the present fold geometry unambiguously constrain the kinematics of fold growth where rivers cut through growing anticlines flights of abandoned fluvial terraces act as passive kinematic markers as shortening progresses the terraces become deformed and thereby preserve critical information about the kinematics and evolution of active fold growth to constrain recent fold growth across three detachment folds in the kashi atushi fold system in the sw tian shan china we surveyed flights of deformed terraces and compared them with geometric models of successively emplaced horizontal unconformities terraces across pregrowth strata deformed by hinge migration limb rotation and a combination of the two migration of angular hinges and curved hinge zones were also compared each kinematic model predicts both a distinct geometry for the deformed terraces and contrasting angular relationships between the terraces and the pregrowth strata notably limb rotation and migration of curved hinge zones result in progressively rotated terraces that cut across pregrowth strata whereas all limb lengthening models result in parallelism between pregrowth strata and terrace straths across much of the fold the kashi atushi terraces show clear evidence of abandoned axial surfaces concentrated deformation near the core of the folds and progressive tilting with age when compared to the model predictions the folds are likely growing by a combination of limb rotation in the tight cores of the folds and hinge zone migration of pregrowth strata across the flanks of the folds

tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

lateral variation of crustal structure and composition in the cathaysia block of south china and its geodynamic implications abstract in order to clarify lateral variations in the crustal structure and composition of the cathaysia block in south china which was affected by violent mesozoic and cenozoic tectono magmatic activities we studied the crustal thickness and the poisson s ratio in this region using the h stacking method of teleseismic receiver functions our results show that the poisson s ratio varies between 0 20 and 0 29 and the crustal thickness ranges from 26 to 34 km in the cathaysia block the crustal thickness and poisson s ratio show considerable variations across the lishui haifeng fault the southeast coast magmatic belt is characterized by poisson s ratios 0 25 and a crustal thickness of 28 33 km reflecting probably intermediate to mafic compositions of the crust the southwestern part of the cathaysia fold belt exhibits a crustal thickness of 27 30 km and poisson s ratios

imaging the moho and the main himalayan thrust in western nepal with receiver functions the crustal structure of western nepal is studied for the first time by performing receiver function analysis on teleseismic waveforms recorded at 16 seismic stations the moho geometry is imaged as it deepens from 40 km depth beneath the foothills and the lesser himalaya to 58 km depth beneath the higher himalayan range a midcrustal low velocity zone is detected at 15 km depth along 55 km horizontal distance and is interpreted as the signature of fluids expelled from rocks descending in the footwall of the main himalayan thrust our new image allows structural comparison of the moho and of the main himalayan thrust geometry along strike of the himalayas and documents long wavelength lateral variations the general crustal architecture observed on our images resembles that of central nepal therefore western nepal is also expected to be able to host large m w 8 megathrust earthquakes as the 1505 ce event plain language summary we investigate the earth s crust in western nepal we use 16 stations to detect waves from faraway earthquakes and using these we make an image of the structure of the crust we find that the crust is getting thicker beneath the himalaya and that fluids are locally present in the upper part of the crust as this image is similar to the one we know in central nepal where major earthquakes happened it is possible that major earthquakes will also happen in western nepal in the future without knowing when

a 130 ka reconstruction of rainfall on the bolivian altiplano new efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the bolivian altiplano on the southern altiplano 10 lake oscillations have been identified from this new unified chronology each coincident with north atlantic cold events such as heinrich events h5 h2 h1 and the younger dryas by coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the southern bolivian altiplano over the last 130 ka these modeling efforts underscore the relative aridity of the altiplano during the rare and small lake cycles occurring between 80 and 20 ka when colder temperatures combined with little or no change in rainfall produced smaller paleolakes relative aridity between 80 and 20 ka contrasts with the immense tauca lake cycle 18 1 14 1 ka which was six times larger than modern lake titicaca and coincided with heinrich event 1 this improved paleolake record from the southern altiplano reveals a strong link between central andean climate and atlantic sea surface temperature gradients during the late pleistocene even though today rainfall variability is driven mostly by pacific sea surface temperature anomalies associated with el nino southern oscillation however not all heinrich events appear to result in lake expansions most conspicuously during the global cold interval between 80 and 20 ka when the altiplano and amazon basin were relatively arid

slab derived fluids and quartz vein formation in an accretionary prism otago schist new zealand regional quartz vein formation and the fluxes flow paths and sources of metamorphic fluids were investigated in the mesozoic accretionary prism of new zealand by using a new chemical mass balance analysis of outcrops samples were collected at meter or submeter intervals along outcrop length traverses and combined to obtain average chemical compositions of whole outcrops mass balance analysis used zr as an immobile reference frame and as a monitor of sedimentary sorting processes sio2 zr systematics produced by sedimentary processes differ greatly from those caused by metasomatic mass transfer of silica allowing evaluation of vein formation mechanisms relatively undeformed metasedimentary outcrops of low metamorphic grade mostly prehnite pumpellyite facies are nearly unveined and characterized by sedimentary compositional trends more deformed outcrops of higher metamorphic grade mostly greenschist facies contain 10 30 vol quartz veins these outcrops underwent mass addition of externally derived silica into quartz veins accompanied by addition of na and removal of k and w average silica additions suggest a time integrated fluid flux of 104 105 batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document m 3 fluid end document batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document m 2 rock end document for fluids ascending through the prism dehydration of spilitized oceanic crust subducting beneath the prism is the most probable source for this large fluid flux and could also have caused the na k metasomatism the w removed from deep levels of the prism may have been deposited in focused retrograde au w quartz veins at shallow levels by ascending fluids transfer of sio2 from subducting slabs into accretionary prisms is a plausible mechanism for long term bulk silica enrichment of the continents beyond that possible by magmatic differentiation

mt and reflection an essential combination summary at many localities in the world there have been coincident comprehensive electromagnetic em studies and seismic reflection profiles conducted unfortunately over many more regions the seismic reflection images are interpreted without the constraints afforded by electrical conductivity information this paper is an attempt to convince the reader that a collocated magnetotelluric mt study should in almost every case be made wherever a seismic reflection survey is undertaken examples are shown from six studies in which the em results aided the geological tectonic interpretations of the seismic sections also difficulties with the mt technique are discussed and the interpretations of conducting zones within the lower crust are examined finally a generalised model is proposed for the continental crust that may account for both the reflectivity and conductivity of the zone at the top of the lower crust

three dimensional dynamic response analyses of cogswell dam the recorded strong motions at cogswell dam during the 1987 whittier narrows and 1991 sierra madre earthquakes provide a valuable opportunity to evaluate the applicability of established engineering procedures for evaluating the dynamic response of dams with highly three dimensional geometries in addition these records provide an opportunity to back calculate the dynamic properties of rockfill materials which cannot be easily measured in the laboratory or in situ peak transverse crest accelerations of 0 15 g and 0 42 g were recorded during the whittier narrows and sierra madre earthquakes respectively combined with analyses of the trailing portions of these strong motion records the field data cover a wide range of induced shear strains two dimensional and three dimensional dynamic response analyses were performed using established engineering procedures and their results are compared with the recorded responses dam canyon interaction and topographic effects appear to have influenced the seismic

the angle of reach as a mobility index for small and large landslides the relations between the angle of reach fahrboschung and other indexes expressing the mobility of landslides and vertical drop horizontal reach and volume of landslide mass have been analyzed by means of simplified plots and regression equations results for 204 landslides of all sizes show that whatever the mechanism of motion all kinds of landslides experience a continuous reduction of the angle of reach with volume increase this reduction starts from the smallest sizes scattering in this relation is mostly due to mechanisms of motion and to both obstacles and topographic constraints on the path this synthesis indicates that small landslides less than 0 5 106 m3 in relative terms display excesses of travel distance similar to large landslides since most small landslides are not expected to develop any change in the mechanism of progression while moving the decrease in the reach angle with volume suggests that scale effects should be taken into account the angle of reach is found to be

crustal structure of the pannonian basin the alcapa and tisza terrains and the mid hungarian zone abstract the pannonian basin of central europe is one of the key examples of miocene continental extension that is easily accessible to surface seismological investigation it comprises two major crustal blocks alcapa and tisza which abut along a poorly understood structure referred to as the mid hungarian zone mhz the whole being surrounded by the arc of the carpathian mountains the alps and the dinarides using data from the cbp carpathian basins project temporary broadband seismic array of 46 stations deployed across the western pannonian basin in 2006 2007 we calculated receiver functions that constrain the variation of crustal thickness across the basin and derive a map of moho depth across a nw se oriented swath about 450 km long and 75 km wide the measured moho depths show no significant change in crustal thickness between alcapa and tisza terrains but the moho is not or very weakly imaged along a ca 40 km wide strip centred on the mhz moho depths within the pannonian basin are typically in the range 25 30 km and increase toward the periphery of the basin our measurements are generally consistent with earlier vp models from controlled source seismic surveys and recent vs models determined by tomographic analysis of ambient noise signals the lack of a sharp moho image beneath the mhz suggests that the crust mantle boundary in that zone may consist of a gradual increase in velocity with depth the relatively constant crustal thickness across the two domains of the pannonian basin suggests that thinning to the same final state is controlled thermally this structural characteristic seems to be governed by a large scale balance of gravitational potential energy that is insensitive to the separate prior histories of the two regions

the continental extension discrepancy and anomalous subsidence pattern in the western qiongdongnan basin south china sea abstract passive margins are first order tectonic features on earth formed by polyphase extension and breakup of continental lithosphere it is accepted that mildly extended basins in the proximal margin form largely by uniform continental thinning but the continental extension in deepwater is much debated here we choose a line from the western qiongdongnan basin in the magma poor south china sea margin to further explore the style of continental extension and the corresponding subsidence patterns where high resolution seismic and heat flow data are available structural analysis reveals that the basin architecture is extremely asymmetric and mainly controlled by the se directed normal faults soling into a low angle detachment fault however fault timings nicely show that the faults form through polyphase rifting and from inside outwards and do not follow a simple sequential faulting like the west iberia margin where the upper and lower crustal deformation are strongly coupled perhaps the fault order here reflects a much weaker and decoupled lower crust then we divide the basin into five zones and calculate the average fault derived extension factors moreover the whole crustal extension factors are also estimated after assessing the initial crustal thickness on basis of the backstripped subsidence and the lithospheric extension factors are numerically modeled using a coupled lithosphere and basin scale model constrained by the heat flow and sedimentation data results show that along the profile the overall lithospheric extension is much less than that of the whole crust and only at the south end of the profile does lithospheric extension exceeds the whole crust showing lithospheric depth dependent thinning the whole crustal extension is roughly equal to the faults derived extension in the northern part displaying no extension discrepancy in the middle part the whole crustal extension is less than the faults derived extension denoting inverse extension discrepancy while the whole crustal extension is in far excess of the faults derived extension in the southern part showing obvious positive extension discrepancy we infer that the inverse and positive discrepancy of crustal extension was likely to be caused by landward directed lower crustal flow driven by the horizontal pressure arising from the combination of the differential extension in the faulted upper crust in the mantle lithosphere and the differential sedimentation during the syn rift period

two crustal low velocity channels beneath se tibet revealed by joint inversion of rayleigh wave dispersion and receiver functions abstract competing geodynamic models such as rigid block extrusion continuous deformation and the mid lower crustal flow have been proposed to describe the growth and expansion of eastern tibet however the dynamic processes responsible for plateau evolution and deformation remain poorly understood partly due to resolution limitations of previous models of lithospheric structure on the basis of joint inversion of rayleigh wave dispersion and receiver functions using data from a newly deployed seismic array we have obtained a high resolution 3d image that reveals the distribution of low velocity zones lvzs with unprecedented clarity the prominent feature of our model is two low velocity channels that bound major strike slip faults in se tibet and wrap around the eastern himalaya syntaxis consistent with the clockwise movement of crustal material in this region most large earthquakes in this region occurred in the boundaries of the lvzs we propose that ductile flow within these channels in addition to shear motion along strike slip faults played a significant role in accommodating intensive lithospheric deformation during the eastward expansion of tibet in the cenozoic

mid late pleistocene osl chronology in western amazonia and implications for the transcontinental amazon pathway abstract the origin of the transcontinental amazon drainage system remains unrevealed sedimentary deposits formed from the neogene in the amazonas and solimoes basins constitute natural archives for reconstructing this event in space and time however paleoenvironmental and chronological analyses focusing on these deposits or even their basic mapping are still scarce to allow such investigation in this context primary interests are fluvial strata related to the lithostratigraphic ica formation mapped over a widespread area in western amazonian lowlands although long regarded as plio pleistocene in age this unit has not yet been dated and its overall depositional setting remains largely undescribed the main goal of the present work is to contribute for improving facies analysis and chronology of these deposits approaching an area in southwestern amazonia and another in northern amazonia which are located more than 1000 km apart despite this great distance the sedimentological and chronological characteristics of deposits from these two areas are analogous hence facies analysis revealed paleoenvironments including active channel abandoned channel point bar crevasse splay and floodplain which are altogether compatible with meandering fluvial systems similarly optically stimulated luminescence osl dating revealed thirty three ages ranging from 65 4 16 9 to 219 6 25 1 ky in addition to three outliners of 54 0 7 6 337 3 36 9 and 346 6 48 6 ky and nine 97 1 9 9 to 254 8 23 8 ky for the areas in southwestern and northern amazonia respectively these data lead to establish that deposits mapped as ica formation over a vast area of western brazilian amazonia have a mid late pleistocene age rather than the previously inferred plio pleistocene age it follows that if plio pleistocene deposits exist in this region they remain to be dated and must be restricted to a narrow belt in western amazonia as well as isolated occurrences underlying the mid late pleistocene strata characterized herein the combination of data from this work with previously published provenance studies supports main andean sediment sources only in the mid late pleistocene it is proposed that before this time the amazon river was restricted to eastern amazonia being separated from western amazonian drainage basins due to the presence of the purus arch erosion and or subsidence of this geological feature would have promoted the connection of these drainage systems ultimately with the expressive record of the transcontinental amazon pathway into the atlantic ocean in the mid late pleistocene

new evidence from seismic imaging for subduction during assembly of the north china craton comment the frozen in information in the crust plays an important role in improving our understanding of cratonic formation and evolution and plate tectonics in the precambrian the trans north china orogen is a continent continent collision belt generated by the assembly of the north china craton the mechanism and modality of the collision are disputed here we present a seismic image of the western block and the trans north china orogen of the north china craton derived using receiver function analysis of the teleseismic records from a dense array a low velocity zone extending from the middle crust to the moho is interpreted as a remnant of upper middle crustal material associated with westward dipping subduction beneath the western block of the north china craton crustal uplift and magmatic underplating resulting from subsequent tectonic events were responsible for modifying the remaining subduction architecture the western boundary of the trans north china orogen is located west of the boundary earlier identified by surface investigation the results combined with previous seismic imaging in the eastern north china craton provide insight into the amalgamation of the eastern and western blocks and the subsequent tectonic deformation of the north china craton

a physically based multi hazard risk assessment platform for regional rainfall induced slope failures and debris flows abstract rainfall induced slope failures and debris flows are two major hazards in mountainous areas a physically based multi hazard risk assessment platform for regional rainfall induced slope failures and debris flows has been developed in this study the platform enables prompt assessment of risks posed by regional rainfall induced slope failures and debris flows across multiple catchments which is required in landslide risk management in a large area it considers the contribution of slope failures to debris flows and the scenario of a location impacted by multiple slope failures or debris flows or both the contribution of slope failures to debris flows is considered by adding the increased amount of channel deposit from slope failures to the source material of debris flows the platform is applied to a highway near the epicentre of the 2008 wenchuan earthquake the platform predicts the impact areas and runout distances of regional debris flows reasonably well the risk assessment results indicate that both slope failures and debris flows pose a great danger to travellers along the road shortly after the earthquake due to the presence of a large amount of loose landslide deposits on steep terrains the materials from the slope failures triggered during a storm substantially increase the channel deposit volume leading to significantly increased debris flow volume and risk a multi hazard risk assessment approach is necessary to consider the scenario of a location impacted by multiple slope failures or debris flows or both since assessing risks of slope failures and debris flows separately may underestimate the risk

full fit reconstruction of the south china sea conjugate margins although the south china sea margins have been well studied there are no full fit reconstructions that document the complex rifting history in a regional geodynamic context we restored conjugate margins to their original late cretaceous unstretched geometries and generated the first full fit reconstructions of the south china sea conjugate margins the impact of magmatic underplating on restoration and full fit reconstruction was estimated quantitatively the full fit reconstruction model includes restoration uncertainties and results in minimum gaps and overlaps between the restored conjugate margin geometries based on our restoration the full fit reconstruction and the continental basement thickness distribution we estimate that there was more extension of continental basement on the western part of the conjugate margins compared with the eastern margin prior to the initiation of seafloor spreading therefore the mid ocean ridge initially formed in the east and propagated westward to open the south china sea seafloor spreading propagated along the xisha trough during nw sub basin formation but continental breakup occurred along the southern side of the zhongsha xisha islands where the lithosphere was probably weaker than along the xisha trough consistent with the geometry and evolution of the nw sub basin and the southward jump of the mid oceanic ridge c 2015 elsevier b v all rights reserved

prolonged post rift magmatism on highly extended crust of divergent continental margins baiyun sag south china sea three dimensional 3d seismic borehole and geochemical data reveal a prolonged phase of post rift magmatism on highly extended crust of the baiyun sag south china sea two volcanic complexes are identified and described in the context of continental rifting and diachronous continental breakup of the south china sea biostratigraphic data from exploration wells by7 1 and by2 complemented by k ar datings from core samples confirm that magmatic activity in the baiyun sag occurred in two main stages 1 a first episode at the base of the miocene 23 8 ma and 2 a second episode occurring at the end of the early miocene 17 6 ma the relative location of volcanic complexes in the baiyun sag and their stratigraphic position reveals prolonged magmatism inboard of the ocean continent transition zone during continental breakup we suggest that magmatism in the baiyun sag reflects progressive continental breakup in the south china sea with the last volcanic episode marking the end of a breakup sequence representing the early post rift tectonic events associated with the continental breakup process seismic and borehole data from this breakup sequence records diachronous magma emplacement and complex changes in depositional environments during continental breakup c 2016 the authors published by elsevier b v

microstructural analyses of a giant quartz reef in south china reveal episodic brittle ductile fluid transfer abstract a long lived hydrothermal system at the heyuan fault south china has led to the development of a giant quartz reef now partially exhumed along its length for more than 40 km systematic analyses and focused microstructural studies have been undertaken to unravel a complex formation history of repeated fracturing hydrothermal fluid flow and sealing cycles resulting in a dynamic permeability across the fault zone the change in morphology and decreasing grain size with time further indicates the move from slow ductile opening to fast seismic events quartz reef formation has been estimated to occur within a range of 200 350 c based on evaluation of i quartz deformation microstructures ii chlorite and mica geothermometry and iii review of comparable quartz reef studies additionally a set of physico chemical formation conditions have been identified which compose the quartz reef window these are i significant volume of fluid ii fluid sources from meteoric metamorphic and or from mantle origin iii considerable time integrated fluid fluxes iv sio2 oversaturation due to a temperature change b sudden pressure drop or c chemical change e g fluid mixing v accommodation space to grow the reef vi channel permeability and vii cap rock seal to trap the fluid flow the mechanism of quartz reef growth is here interpreted as the brittle ductile analogue of the brittle fault valve model

seismic imaging of mid crustal structure beneath central and eastern north america possibly the elusive grenville deformation iris passcal instrument center at the new mexico institute of mining and technology socorro new mexico usa u s national science foundation nsf national science foundation nsf ear 1261681 u s department of energy national nuclear security administrationnational nuclear security administrationunited states department of energy doe nsfnational science foundation nsf ear 1251515 ear 1251329 ear 1250988

three dimensional back analysis of saturated rock slopes in discontinuous rock a case study two historic block failures on the left abutment of pacoima dam california are back analysed using three dimensional limit equilibrium analysis water pressures within the boundary joints are int

from mountain summits to roots crustal structure of the eastern alps and bohemian massif along longitude 13 3 e abstract the crustal structure of the eastern alps and adjacent tectonic units investigated in this work sheds new light on the relationship of surface geology to geodynamic processes operating at depth of particular interest are the nature of a previously proposed moho gap south and east of the tauern window the plate tectonic affinity of the steeply dipping eastern alpine slab and the relationship of the alps to the neogene sedimentary basins and the bohemian massif to address these questions we use various seismological approaches based on converted waves from the temporary passive experiment easi eastern alpine seismic investigation a complementary experiment of the alparray project the easi is a densely spaced 540 km long seismic network along 13 3 e we operated for more than a year the uppermost crustal structures in and near the alps exhibit dipping layers and or tilted anisotropy that correlate well with surface geology observations the moho despite its variable appearance is clearly identified along most of the swath the variscan lithospheric blocks beneath the bohemian massif are imaged with sub vertical boundaries beneath the eastern alps the shape of the moho is consistent with bi vergent orogenic thickening with a steeper and deeper reaching adriatic plate plunging northwards beneath the european plate in the north at the junction of these plates at depth around the previously proposed moho gap the root of the eastern alps is a broad trough characterized by a zone of low velocity gradient that is up to 20 km thick transitioning between crust and mantle our receiver function results corroborate earlier lithosphere upper mantle seismic tomography images and highlight the adriatic affinity of the eastern alpine slab the zigzag deployment pattern of stations in the easi experiment also allows distinction of short wavelength variations perpendicular to the profile both within the shallow and the deep crust this underlines the importance of applying 3d imaging in complex geodynamic systems

the structure and evolution of deepwater basins in the distal margin of the northern south china sea and their implications for the formation of the continental margin abstract although it is generally accepted that the south china sea margin can be classified as a magma poor rifted margin little is known about the structural style of the distal margin and how the distal deep basins evolved observations and data from the northern south china sea margin suggest that the deepwater basins distal margin domain are commonly underlain by a highly extended continental crust and detachment fault systems have been interpreted in places we have interpreted a large seismic data set covering deepwater basins in the northern south china sea the interpreted moho on reflection seismic profiles indicates that the crustal thickness varies along sections perpendicular to the coast which is the first order criterion to divide the whole margin into a proximal domain necking zone and distal domain furthermore the underlying extremely stretched crust

different expressions of rifting on the south china sea margins abstract rifting of continental margins is generally diachronous along the zones where continents break due to various factors including the boundary conditions which trigger the extensional forces but also the internal physical boundaries which are inherent to the composition and thus the geological history of the continental margin being opened quite recently in the tertiary in a scissor shape manner the south china sea scs offers an image of the rifting structures which varies along strike the basin margins the scs has a long history of extension which dates back from the late cretaceous and allows us to observe an early stretching on the northern margin onshore and offshore south china with large low angle faults which detach the mesozoic sediments either over triassic to early cretaceous granites or along the short limbs of broad folds affecting palaeozoic to early cretaceous series these early faults create narrow troughs filled with coarse polygenic conglomerate grading upward to coarse sandstone because these low angle faults reactivate older trends they vary in geometry according to the direction of the folds or the granite boundaries a later set of faults characterized by generally e w low and high angle normal faults was dominant during the eocene associated half graben basement deepened as the basins were filling with continental or very shallow marine sediments this subsequent direction is well expressed both in the north and the sw of the south china sea and often reactivated earlier detachments at places the intersection of these two fault sets resulting in extreme stretching with crustal boudinage and mantle exhumation such as in the phu khanh basin east of the vietnam fault a third direction of faults which rarely reactivates the detachments is ne sw and well developed near the oceanic crust in the southern and southwestern part of the basin this direction which intersects the previous ones was active although sea floor spreading was largely developed in the northern part and ended by the late miocene after the onset of the regional mid miocene unconformity known as mmu and dated around 15 5 ma latest miocene is marked by a regional basement drop and localized normal faults on the shelf closer to the coast the se margin of the south china sea does not show the extensional features as well as the northern margin detachments are common in the dangerous grounds and reed bank area and may occasionally lead to mantle exhumation the sedimentary environment on the extended crust remained shallow all along the rifting and a large part of the spreading until the late miocene when it suddenly deepened this period also corresponds to the cessation of the shortening of the nw borneo wedge in palawan sabah and sarawak we correlate the variation of margin structure and composition of the margin mainly the occurrence of granitic batholiths and mesozoic broad folds with the location of the detachments and major normal faults which condition the style of rifting the crustal boudinage and therefore the crustal thickness

seismic imaging of the transitional crust across the northeastern margin of the south china sea abstract crustal structure across the passive continental margin of the northeastern south china sea scs is presented based on a deep seismic survey cooperated between taiwan and china in august 2001 reflection data collected from a 48 hydrophone streamer and the vertical component of refraction reflection data recorded at 11 ocean bottom seismometers along a nw se profile are integrated to image the upper 1 6 2 4 km s lower 2 5 2 9 km s and compacted 3 4 5 km s sediment the upper 4 5 5 5 km s middle 5 5 6 5 km s and lower 6 5 7 5 km s crystalline crust successively the velocity model shows that the thickness 0 5 3 km and the basement of the compacted sediment are strongly varied due to intrusion of the magma and igneous rocks after seafloor spreading of the scs furthermore several volcanoes and igneous rocks in the upper middle crust 7 10 km thick and a high velocity layer 0 5 km thick in the lower crust of the model are identified as the ocean continent transition oct below the lower slope in the northeastern margin of the scs a thin continent nw of the oct and a thick oceanic crust se of the oct in the continental margin of the northeastern scs are also imaged but these transitional crusts cannot be classified as the oct due to their crustal thickness and the limited amount of the volcano the magma and the high velocity layer the extended continent next to the gravity low and a sag zone extended from the sw taiwan basin may have resulted from subduction of the eurasian plate beneath the manila trench whereas the thick oceanic crust may have been due to the excess volcanism and the late magmatic underplating in the oceanic crust after seafloor spreading of the scs

crustal structure and contact relationship revealed from deep seismic sounding data in south china abstract a 400 km long wide angle seismic profile in the south china crosses three tectonic domains southeast continental margin of yangtze block northwest continental margin of cathaysia block and south china suture zone separating these two blocks the crustal velocity model constructed from traveltime fitting shows that the crust thickness thins from the northwest to the southeast along the profile it also reveals the crustal contact relationship between the yangtze and cathaysia blocks where the wuchuan sihui fault is the boundary between them combining this profile with two more profiles in the continental south china and three profiles in the northern margin of south china sea constructs a continent ocean transition section this cross section reveals that the moho depth shallows gradually along the cross section from the yangtze block to the cathaysia block and the northern margin of south china sea but shallows abruptly in the continent ocean transition to the south china sea

deep crustal structure of the conjugate margins of the sw south china sea from wide angle refraction seismic data abstract the south china sea is the largest marginal basin of se asia yet its mechanism of formation is still debated a 1000 km long wide angle refraction seismic profile was recently acquired along the conjugate margins of the sw sub basin of the south china sea over the longest extended continental crust a joint reflection and refraction seismic travel time inversion is performed to derive a 2 d velocity model of the crustal structure and upper mantle based on this new tomographic model northern and southern margins are genetically linked since they share common structural characteristics most of the continental crust deforms in a brittle manner two scales of deformation are imaged and correlate well with seismic reflection observations small scale normal faults grabens horsts and rotated faults blocks are often associated with a tilt of the velocity isocontours affecting the upper crust the mid crust shows high lateral velocity variation defining low velocity bodies bounded by large scale normal faults recognized in seismic reflection profiles major sedimentary basins are located above low velocity bodies interpreted as hanging wall blocks along the northern margin spacing between these velocity bodies decreases from 90 to 45 km as the total crust thins toward the continent ocean transition the continent ocean transitions are narrow and slightly asymmetric 60 km on the northern side and no more than 30 km on the southern side indicating little space for significant hyper stretched crust although we have no direct indication for mantle exhumation shallow high velocities are observed at the continent ocean transition the moho interface remains rather flat over the extended domain and remains undisturbed by the large scale normal faults the main decollement is thus within the ductile lower crust

age of the subducting pacific slab beneath east asia and its geodynamic implications abstract we study the age of the subducting pacific slab beneath east asia using a high resolution model of p wave tomography and paleo age data of ancient seafloor our results show that the lithosphere age of the subducting slab becomes younger from the japan trench 130 ma to the slab s western edge 90 ma beneath east china and the flat stagnant slab in the mantle transition zone mtz is the subducted pacific plate rather than the proposed izanagi plate which should have already collapsed into the lower mantle the flat pacific slab has been in the mtz for no more than 10 20 million years considerably less than the age of the big mantle wedge beneath east asia 110 million years hence the present flat pacific slab in the mtz has contributed to the cenozoic destruction of the east asian continental lithosphere with extensive intraplate volcanism and back arc spreading whereas the destruction of the north china craton during the early cretaceous 140 110 ma was caused by the subduction of the izanagi or the paleo pacific plate

influence of earthquakes on the stability of slopes earthquakes are a major trigger for instability of natural and man made slopes often the instability of slopes due to an earthquake causes more destruction and kills more people than the actual earthquake itself a comparison is made between different methodologies to analyze the potential stability of slopes during earthquakes theoretically it seems simple to calculate the stability of a slope during an earthquake in reality however the stability is influenced by so many parameters that are either not known or which influence is so poorly known that a decent estimation of stability cannot be made offshore the situation is worse because proper data required for stability calculations are even less available than onshore on and offshore erosion and weathering create continuously slopes that may become unstable during a future earthquake offshore also sedimentation creates continuously new slopes another fundamental problem in stability analysis is the complicated and largely unknown behavior of seismic waves in three dimensions in natural materials the lack of accurate data and the unknown behavior of seismic waves in three dimensions make estimations of slope stability during an earthquake unreliable

the effects of a tectonic stress regime change on crustal scale fluid flow at the heyuan geothermal fault system south china abstract the south china heyuan fault zone provides unique crustal exposure to study the meso macroscale architecture of evolving fracture networks in response to a change in tectonic stress regime and associated changing fluid flow pathways multiple generations of fracturing across the fault zone reveal its structural evolution related to the change in stress regime from extensional since the mesozoic to transpressive in the cenozoic which coincides with generations of growth and fracturing on the microscale low angle mode i fractures quartz veining and a giant quartz reef 75 m wide and 40 km long were formed due to a combination of chemo mechanical mechanisms including a crucial phyllonite cap rock during the extensional phase this evolved through to a predominately sub vertically aligned shear fracture network exhibiting only minor quartz precipitation these open fractures are attributed to the transpressive regime experienced since the cenozoic in which strike slip faults cross cut the heyuan fault we propose that this sub vertical fracture network provides the fluid flow pathway supplying the present day hot springs by penetrating through the phyllonite seal which previously enabled sio2 accumulation additionally further quartz reef building would likely be reduced due to i lack of seal integrity and ii an unfavourable tectonic setting to channel the flow and provide accommodation space

effects of water and melt on seismic velocities and their application to characterization of seismic reflectors the effects of a silicate melt and water on seismic velocities are compared at relatively small fluid fraction less than 20 vol on the basis of a theoretical model of composite materials to show that the two fluids are clearly characterized by the velocity ratio vp vs for a silicate melt vp vs increases with increasing fluid fraction when a significant reflection is expected vp vs becomes much larger than 2 for water vp vs decreases as the fluid fraction increases to 10 vol then it increases but it remains similar to a solid state value about 1 8 unless the amount of water exceeds 15 vol this will be a good measure to distinguish between two candidates for seismic reflectors partially molten rocks and rocks containing free water if a reflector can be treated as a thin low velocity layer the velocity ratio in it can be estimated from the frequency dependence of reflection coefficient

crustal stretching style variations in the northern margin of the south china sea linking deep seismic profiles with regional scale gravity inversion is a powerful tool to deduce the architecture of rifted margins and their structural evolution here we map upper and lower crustal thicknesses of the northern south china sea scs margin in order to investigate the occurrence of depth dependent crustal extension from the proximal to the distal margin by comparing upper and lower crustal stretching factors we find that the northern margin of the scs is segmented in three parts 1 sedimentary basins where upper crust is stretched more than lower crust 2 distal margin where lower crust is stretched more than upper crust 3 mostly proximal margin regions where the two layers have similar stretching factors our results suggest that sedimentary basins and distal margin prominently feature depth dependent extension however accommodated by different processes while differential thinning within sedimentary basins appears to be governed by lateral pressure variations inducing lower crustal flow we suggest the distal margin to be affected by a combination of mantle flow induced lower crustal shearing and sequential fault activity during crustal hyper extension

landslides triggered by the avaj iran earthquake of june 22 2002 abstract the 2002 avaj iran earthquake mw 6 5 triggered many landslides over an area of about 3600 km 2 in this paper we describe a ground based field study conducted during several days immediately after the earthquake and pre and post earthquake landslide inventory maps that were prepared the landslides due to earthquake include 47 fall and topple zones 9 slides and 3 lateral spreads the largest slide is a rockslide 150 100 m which occurred southeast of the village of changureh the main results of this study are the density of earthquake triggered landslides decreases away from the fault zone in a manner that is asymmetric with respect to direction although several slides and lateral spreads were seen the most common types of triggered landslides are falls and topples the area throughout which landslides occurred and maximum epicentral and fault zone distances of landslides are comparable to similar data from other historical earthquakes landslides mostly occurred in the most susceptible geologic units in which there were many landslides before the earthquake new disrupted slides and falls generally occurred in ancient fall zones but no information about reactivation of coherent slides is available

cascadia subducting plate fluids channelled to fore arc mantle corner ets and silica deposition in this study we first summarize the constraints that on the cascadia subduction thrust there is a 70 km gap downdip between the megathrust seismogenic zone and the episodic tremor and slip ets that lies further landward there is not a continuous transition from unstable to conditionally stable sliding seismic rupture occurs mainly offshore for this hot subduction zone ets lies onshore we then suggest what does control the downdip position of ets we conclude that fluids from dehydration of the downgoing plate focused to rise above the fore arc mantle corner are responsible for ets there is a remarkable correspondence between the position of ets and this corner along the whole margin hydrated mineral assemblages in the subducting oceanic crust and uppermost mantle are dehydrated with downdip increasing temperature and seismic tomography data indicate that these fluids have strongly serpentinized the overlying fore arc mantle laboratory data show that such fore arc mantle serpentinite has low permeability and likely blocks vertical expulsion and restricts flow updip within the underlying permeable oceanic crust and subduction shear zone at the fore arc mantle corner these fluids are released upward into the more permeable overlying fore arc crust an indication of this fluid flux comes from low poisson s ratios and vp vs found above the corner that may be explained by a concentration of quartz which has exceptionally low poisson s ratio the rising fluids should be silica saturated and precipitate quartz with decreasing temperature and pressure as they rise above the corner

lithospheric structure in the cathaysia block south china and its implication for the late mesozoic magmatism abstract mesozoic granitoids are widely distributed in south china but the mechanism for generating the felsic magmas is still in debate to understand the possible origin of the granitoids we use joint inversion methods and forward modelling of receiver functions to reveal the lithospheric structure in the cathaysia block the joint inversion of receiver functions and surface wave dispersion with p velocity constraints is applied to a dense array in the cathaysia block and the specific crustal vp vs ratios obtained from a generalized h stacking method are introduced to the traditional joint inversion for passive seismic stations the detailed structures provide valuable knowledge of the geological processes 1 the present day lithosphere is 60 70 km thick which has been thinned since the late mesozoic with reference to geochemical data 2 there is a lack of high vp and vs in the lower crust in this region the results may have limited resolution on the localized magmatic underplating but they do not support the extensive magmatic underplating at the late mesozoic other factors could be the mechanism for the granitoid formation in this region

the mechanism of high speed motion and damming of the tangjiashan landslide abstract understanding the mechanisms of landslide failure and resulting damming processes is crucial for constraining the hazard chain associated with landslide damming events on may 12 2008 the wenchuan earthquake caused a large number of secondary hazardous events such as landslides and collapses most of which occurred in high mountain gorges in these areas the sliding distance of landsides is often very short and the landslides are often characterized by high speed short distance and damming using the tangjiashan landslide damming events induced by the wenchuan earthquake as a model this paper reconstructs the three dimensional failure and associated damming caused by the landslide based on a detailed geological investigation of the landslide area and using the dynamic finite element technique the study proposes a four stage model for the failure and damming process of the tangjiashan landslide earthquake induction and progressive destruction of the slide body destruction and high speed sliding of the slide body slide body impact disintegration and river blockage for the formation of a damming body and vibration compression the average speed of the tangjiashan landslide reached a maximum value of 22 m s about 30 s after the earthquake and the landslide reached stability about 60 s later

rifting and magmatism in the northeastern south china sea from wide angle tomography and seismic reflection imaging we present a new travel time tomography velocity model and seismic reflection images that delineate the rift architecture and magmatic features of the rifted margin in the northeastern south china sea these data reveal moderately stretched crust 25 km thick along the continental shelf and thin but laterally variable crustal thickness in the distal margin along the continental slope crust rapidly thins to 4 km in a basin characterized by tilted fault blocks that sole into a low angle detachment strain was localized to a degree within the highly stretched basin but failed to progress to breakup and seafloor spreading crust in the distal margin is 12 15 km thick few extensional structures are apparent in the distal margin but seismic velocities are suggestive of highly thinned and magmatically intruded continental crust the magmatic features we interpret include volcanic zones at the top of the basement that deform or disrupt overlying postrift strata sills intruded into the postrift sedimentary section and a high velocity 6 9 7 5 km s lower crustal layer that we take to be magmatic underplating or pervasive lower crustal intrusions these features primarily occur in the distal margin and may have been emplaced during postrift seafloor spreading the postrift magmatism may have been induced by convective removal of continental lithosphere following breakup and the onset of seafloor spreading in the south china sea

seismic imaging of a mid crustal low velocity layer beneath the northern coast of the south china sea and its tectonic implications abstract low velocity layer lvl within the continental crust is usually closely associated with tectonic events thus it may reflect ongoing processes or offer a chance to backtrack the evolutional history mid crustal lvl has been reported in the northern coast of the south china sea scs by several geophysical studies but the 3d distribution of lvl in the whole coastal area is still poorly known here we perform a receiver function study based on 67 broadband seismological stations we use the common conversion point method to construct structures of the moho as well as intra crustal interfaces we image sharp intra crustal negative velocity gradient broadly distributed in the eastern cathaysia block with depth increasing from 10 km in the nw to 12 16 km in the se the corresponding amplitude of the negative interface shows variable values from 0 03 to 0 1 with an evidential trend of strengthening eastwards we interpret the negative gradient as top of the lvl produced by accumulation of fluids from dehydration of the paleo pacific subduction plate the mid crustal lvl tends to act as weak domains during continental rift and the lateral variation of the lvl may be one possible reason explaining the along strike variation in crustal stretching in the northern scs rifted margin

a method for producing digital probabilistic seismic landslide hazard maps abstract the 1994 northridge california earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability these data sets include 1 a comprehensive inventory of triggered landslides 2 about 200 strong motion records of the mainshock 3 1 24 000 scale geologic mapping of the region 4 extensive data on engineering properties of geologic units and 5 high resolution digital elevation models of the topography all of these data sets have been digitized and rasterized at 10 m grid spacing using arc info gis software on a unix computer combining these data sets in a dynamic model based on newmark s permanent deformation sliding block analysis yields estimates of coseismic landslide displacement in each grid cell from the northridge earthquake the modeled displacements are then compared with the digital inventory of landslides triggered by the northridge earthquake to construct a probability curve relating predicted displacement to probability of failure this probability function can be applied to predict and map the spatial variability in failure probability in any ground shaking conditions of interest we anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure

crustal thickness and poisson s ratios of south china revealed from joint inversion of receiver function and gravity data abstract crustal thickness and poisson s ratio are two important parameters for understanding the crustal structure composition and deformation of the south china block due to the complicated crustal structure and poor signal to noise ratio of teleseismic data at dozens of stations in south china the receiver function h stacking produces large uncertainty and deviation when estimating these two crustal parameters in this paper we improve the technique of the joint inversion of receiver function and gravity data and utilize it to improve the estimates of crustal thickness and poisson s ratio in south china we calculate the receiver functions of 245 permanent seismic stations from the teleseismic data recorded during 2013 2015 and then carry out the joint inversion on the receiver functions and the complete bouguer gravity anomalies data the joint inversion reduces the uncertainty of each single method inversion and enhances the accuracy of estimation our results demonstrate that the crustal thickness ranging 26 1 46 5 km is large in the nw 38 46 5 km and small in the se 26 34 km with a nne trending gradient zone along the line of yichang jishou baise in central south china the crustal poisson s ratio ranging 0 20 0 31 is high 0 28 0 31 in most of the northern south china intermediate 0 26 0 29 around the eastern coastal area very low 0 20 0 24 within the jiangnan orogenic belt and around the southern coastal area and slightly low 0 22 0 26 in other places with the constraints of previous geological and geophysical studies we suggested that the notable low value belt of crustal poisson s ratio between the lines of shitai jiujiang yiyang jishou baise and shaoxing jiangshan pingxiang yongzhou guigang beihai represents the possible suture zone between yangtze and cathaysia sub blocks in south china during the neoproterozoic

how does the continental crust thin in a hyperextended rifted margin insights from the iberia margin the discovery of hyperthinned continental crust and exhumed mantle on present day deep water rifted margins leads to two fundamental questions 1 in detail how does the crust thin in extension and 2 what controls extreme crustal thinning and mantle exhumation reflection and refraction seismic lines across the iberian margin show decoupling levels in the crust cut by structures that eventually transfer deformation to mantle levels the region of decoupled extension appears to be more broadly distributed on the northern iberian margin and more localized on the southern margin based on drill hole data the transition from decoupled to coupled deformation occurred during tithonian time ca 145 ma this evolution from decoupled to coupled deformation may help explain the crustal architecture of the iberian margin an apparent delay of subsidence across the hyperextended coupled zone of the iberian margin may indicate that crustal thinning had to occur simultaneously with lithospheric necking and the advection of heat related to lithospheric mantle thinning

the poisson ratio of the australian crust geological and geophysical implications the poisson ratio which depends on the vp vs ratio provides much tighter constraints on the crustal composition than either the compressional or the shear velocity alone the crustal poisson ratio can be determined from the joint analysis of the travel times of waves converted at the moho and of crustal multiples reflected at the top of the moho we have analyzed the records of the permanent stations installed on the australian continent complemented by the data of the skippy experiment the results reveal substantial variations in the poisson ratio in the different tectonic units for the proterozoic crust an increase of the poisson ratio with increasing crustal thickness is systematically observed while for the phanerozoic crust the poisson ratio tends to decrease for increasing crustal thicknesses these observations are in remarkable agreement with the results of the deep seismic soundings that were performed in the former soviet union the variations observed in the proterozoic provinces can perhaps be explained by underplating of mafic materials at the base of the crust fl 2000 elsevier science b v all rights reserved

imaging the indian subcontinent beneath the himalaya new seismic images reveal the geometry of the indian plate as it passes beneath the himalayan plateau several important subsurface features of vanished india are revealed including a shear zone above the base of the indian crust beneath the himalaya and conversion of the deep indian crust into denser rock the rocks of the indian subcontinent are last seen south of the ganges before they plunge beneath the himalaya and the tibetan plateau they are next glimpsed in seismic reflection profiles deep beneath southern tibet1 yet the surface seen there has been modified by processes within the himalaya that have consumed parts of the upper indian crust and converted them into himalayan rocks2 3 the geometry of the partly dismantled indian plate as it passes through the himalayan process zone has hitherto eluded imaging here we report seismic images both of the decollement at the base of the himalaya and of the moho the boundary between crust and mantle at the base of the indian crust a significant finding is that strong seismic anisotropy develops above the decollement in response to shear processes that are taken up as slip in great earthquakes at shallower depths north of the himalaya the lower indian crust is characterized by a high velocity region consistent with the formation of eclogite a high density material whose presence affects the dynamics of the tibetan plateau

the thor suture zone from subduction to intraplate basin setting the crustal seismic velocity structure of northwestern europe shows a low p wave velocity zone lvz in the lower crust along the caledonian thor suture zone tsz that cannot be easily attributed to avalonia or baltica plates abutting the tsz the lvz appears to correspond to a hitherto unrecognized crustal segment accretionary complex that separates avalonia from baltica explaining well the absence of avalonia further east consequently the northern boundary of avalonia is shifted 150 km southward our interpretation based on analysis of deep seismic profiles places the lvz in a consistent crustal domain interpretation a comparison with present day examples of the kuril and cascadia subduction zones suggests that the lvz separating avalonia from baltica is composed of remnants of the caledonian accretionary complex if so the present day geometry probably originates from pre variscan extension and eduction during devonian carboniferous backarc extension the reinterpretation of deep crustal zonation provides a crustal framework in which the northern limit of avalonia corresponds to the southern limit of the deep north german basin and the northern limit of prolific gas reservoirs and late mesozoic inversion structures 2016 geological society of america

a crustal structure profile across the northern continental margin of the south china sea an ocean bottom seismometer obs geophysical experiment was carried out across the northern continental margin of the south china sea two dimension kinematic ray tracing was used to construct synthetic records and to define the geological model along the obs profile according to the calculation and interpretation of refracted p wave phases the crustal thickness decreases from 22 km obs 1 in littoral area to 8 km obs 15 in deep sea the lower slope structured by volcanism changes sharply in moho depth from 22 to 9 km the volcanoes over the lower slope were markers of ocean continental transition zone a high velocity layer hvl with an average thickness of 4 km was found in the base of the lower crust over the shelf and slope the south china sea was originated by the passive rifting of south china continent and seafloor spreading however geological and geophysical data collected in the northern margin of the south china sea show a small amount of magma intruded into or erupted onto the crust during pull apart and breakup further analysis shows that the hvz in the base of the thinned continental crust was related to magmatism that occurred after the cessation of seafloor spreading of the south china sea magmatism during the crustal extension and breakup is very weak therefore the northern continental margin of the scs is classified as non volcanic passive margin the southern margin of the south china sea has a crust with a steady thickness of 18 24 km which is different from the nor them margin of the south china sea with a gradually thinned crust they constitute an asymmetrically conjugated pair of passive margins c 2001 elsevier science b v all rights reserved

depths and focal mechanisms of crustal earthquakes in the central andes determined from teleseismic waveform analysis and insar 1 we investigate the depths of crustal earthquakes mw 5 5 earthquakes from the global cmt catalog and previous work spanning 1944 2007 for 38 well recorded events we use teleseismic p and sh waveforms to model the strike dip rake focal depth and source time function we use insar observations of surface deformation from 9 earthquakes to compare inferred fault parameters with the waveform inversions and global catalogs to assess their accuracies while the depths from the insar and waveform analyses generally agree within error horizontal and depth errors in global catalogs are 10 to 50 km as found elsewhere as noted in previous work the majority of crustal earthquakes occur in the eastern cordillera and foreland regions of the central andes although a few normal and strike slip earthquakes occur beneath the altiplano plateau and in the forearc in southern peru and northernmost chile we propose a new interpretation of one of the basement thrusts shira mountain peru as a pop up block on the basis of our new earthquake depths we confirm that earthquakes in the flat slab areas of peru and argentina are within the sometimes aseismic lower crust lower crustal earthquakes are globally found in all types of tectonic settings only when the thermal lithosphere is more than 80 km thick and the amount of recent shortening extension is 30

deep penetration seismic soundings across the northern margin of the south china sea twenty reversed two ship expanding spread profiles esps with maximum source receiver offsets of 100 km were collected in three transects across the rifted northern margin of the south china sea source receiver offset versus two way travel time x t data were mapped into the intercept time versus ray parameter p domain and velocity depth solutions were obtained by a combination of sum inversion in the p domain and ray tracing in both the p and x t domains arrivals from the moho were detected on 17 of the esps the depths to moho determined for individual esp interpretations have reproducibilities of 0 1 km to 3 km in most cases the moho depth has been determined to within 1 5 km moho depths determined in this investigation represent a significant improvement over previous estimates of moho along the margin from gravity data variations in present day crustal thickness measured from top of prerift basement to moho are one measure of the amount and nature of the crustal thinning associated with the rifting of continental crust preceding the formation of the adjacent south china sea basin the esp interpretations reveal that across the eastern portion of the south china margin the crust appears to thin more or less continuously toward the continent ocean boundary in the west esp interpretations also show a general trend of seaward crustal thinning but in addition indicate at least two instances of focused localized crustal thinning crustal velocities and the relative proportion of upper crust vp 6 4 km s are used to identify areas of the south china margin with similar and contrasting crustal structures variations in these properties are believed to result primarily from contrasting prerift crustal structure across the margin however magmatic underplating during rifting depth dependent extension and pleistocene igneous intrusions may also have contributed to the variations in present crustal structure reliable information about variations in crustal thickness and velocity structure across and along the south china margin is an important prerequisite to understanding better the nature of the spatially variable rifting processes which dominated the formation of this margin

characterizing the main himalayan thrust in the garhwal himalaya india with receiver function ccp stacking abstract we use common conversion point ccp stacking of ps receiver functions to image the crustal structure and moho of the garhwal himalaya of india our seismic array of 21 broadband seismometers spanned the himalayan thrust wedge at 79 80 e between the main frontal thrust and the south tibet detachment in 2005 2006 our ccp image shows the main himalayan thrust mht the detachment at the base of the himalayan thrust wedge with a flat ramp flat geometry seismic impedance contrasts inferred from geologic cross sections in garhwal imply a negative impedance contrast velocity decreasing downward for the upper flat located beneath the lower himalaya and a positive impedance contrast velocity increasing downward for the ramp located beneath the surface trace of the munsiari thrust or mct i at the lower flat located beneath the higher himalaya spatially coincident measurements of very high electrical conductivities require the presence of free fluids and we infer a negative impedance contrast on the mht caused by ponding of these fluids beneath the detachment our seismic image indicates that the upper flat of the mht is 10 km below sea level and dips north at 2 connecting to a mid crustal ramp which is 10 km high and dips at 16 the lower flat is 20 25 km below sea level and dips at 4 the main central thrust mct appears as a negative impedance contrast dipping at 16 the moho is nearly horizontal at 35 45 km depth beneath the sub himalaya and lower himalaya deepening to 50 km or more beneath the higher himalaya this depth is 10 25 km shallower than in the nw indian himalaya and 5 10 km shallower than in central nepal requiring significant along strike variations in crustal thickness the observed thickness of subducted indian crust in garwhal is 20 28 km

the role of seismic triggering in a deep seated mudstone landslide china historical reconstruction and mechanism analysis abstract deep seated mudstone landslides are widely distributed in northwest china the zhengjiamo landslide occurred in 734 ce near taijing tianshui region it was triggered by the main shock of the historical ms 7 0734 ce earthquake the earthquake also induced a wide range of landslides in this area with hundreds of fatalities and many houses destroyed by landslide debris based on a detailed field survey borehole data and mapping a detailed geological reconstruction of the slope was achieved and the geo mechanical features of the claystone involved in the landslide were obtained using the particle flow code to simulate the mechanism of the zhengjiamo landslide the features of the landslide dynamics were obtained using a 5 stage model during the landslide process the slip mass at the front and upper edges exhibited higher mobility than at the rear and bottom edges furthermore the contact bond strength of the sliding body gradually weakened the model indicates that the particle bond strength has a larger influence on the maximum runout distance and landslide debris morphology than the type of weak intercalated layers the slip mass presented a rotational slide pattern and remained on the slip plane throughout the sliding process finally the earthquake uplifted the slope toe which prevented the slip mass from gliding the modelled scenario provided a reasonably good fit to the actual topography verifying the modelling results after the historical earthquake with the clay minerals swelling and shrinking under rainfall and efflorescence conditions the structure of the soft rock changed contributing to the weakening of the sliding rock mass the landslide gradually crept and evolved to its current topography

the effect of a mainshock on the size distribution of the aftershocks author s gulia l rinaldi ap tormann t vannucci g enescu b wiemer s abstract 2018 american geophysical union all rights reserved a systematic decay of the aftershock rate over time is one of the most fundamental empirical laws in earth science however the equally fundamental effect of a mainshock on the size distribution of subsequent earthquakes has still not been quantified today and is therefore not used in earthquake hazard assessment we apply a stacking approach to well recorded earthquake sequences to extract this effect immediately after a mainshock the mean size distribution of events or b value increases by 20 30 considerably decreasing the chance of subsequent larger events this increase is strongest in the immediate vicinity of the mainshock decreasing rapidly with distance but only gradually over time we present a model that explains these observations as a consequence of the stress changes in the surrounding area caused by the mainshocks slip our results have substantial implications for how seismic risk during earthquake sequences is assessed

crustal structure across the san andreas fault southern california from teleseismic converted waves crustal structure along a 140 km long profile across the san andreas fault saf in southern california was imaged by stacking teleseismic p s converted phases recorded by a dense short period seismic array the crust mantle discontinuity moho is visible as a continuous feature at a depth around 30 km but is offset 6 to 8 km beneath the saf a small moho disruption can also be seen under the eastern california shear zone ecsz these results suggest that the saf and ecsz extend through the entire crust the moho upwarp under the san gabriel mountains indicates that the mountain ranges were lifted en masse as a result of crustal buckling under horizontal compression

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

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

the role of silica redistribution in the evolution of slip instabilities along subduction interfaces constraints from the kodiak accretionary complex alaska abstract quartz veins from a subhorizontal shear zone in the kodiak accretionary complex in southwest alaska record cycles of cracking and sealing contemporaneous with simple shear and analysis of the vein array in the context of silica dissolution diffusion and precipitation leads to the conclusion that the time needed to seal after a fracture event overlaps with the time scales associated with the recurrence of slip instabilities along active megathrusts the central belt of the kodiak accretionary complex is interpreted as a shear zone developed adjacent to a paleo decollement that was active in the late cretaceous based on large strain magnitudes recumbent isoclinal folds and regional cleavage patterns that depict rotation of the steep cleavage that characterizes most of the kodiak formation into the horizontal fabrics of the central belt within this regional shear zone crack seal veins composed of quartz with phyllosilicate inclusion bands are spaced at less than a cm but en echelon vein arrays are spaced at 500 cm these arrays indicate top to the southeast shear on southeast dipping brittle ductile shear zones vein textures indicate cracking and sealing of thin veins in the matrix but thicker veins in en echelon sets record initial cracking and sealing followed by periodic collapse of fracture porosity at a frequency that is lower than the frequency of crack seal cycles silica depletion zones in the wall rock adjacent to veins indicate local transport of silica by diffusion by combining the maximum time in which diffusion could dominate over advection with the time needed to precipitate the quartz associated with one crack seal band we show that a reasonable range of p or pressure difference between matrix and crack can produce crack seal bands in less than 10 days this time frame is less than the recurrence of earthquakes and similar to the duration of some slow earthquakes in nature therefore silica redistribution could play a role in modulating the frequency of plate boundary slip instabilities along convergent plate boundaries

the south china sea margins implications for rifting contrasts abstract implications regarding spatially complex continental rifting crustal extension and the subsequent evolution to seafloor spreading are re examined for the northern and southern rifted margins of the south china sea previous seismic studies have shown dramatic differences in the present day crustal thicknesses as the manifestations of the strain experienced during the rifting of the margin of south china although the total crustal extension is presumed to be the same along the margin and adjacent ocean basin the amount of continental crustal extension that occurred is much less along the east and central segments of the margin than along the western segment this difference was accommodated by the early formation of oceanic crust creating the present day south china sea basin adjacent to the eastern margin segment while continued extension of continental crust was sustained to the west using the observed cross sectional areas of extended continental crust derived from deep penetration seismics two end member models of varying rift zone widths and varying initial crustal thicknesses are qualitatively examined for three transects each model implies a time difference in the initiation of seafloor spreading inferred for different segments along the margin the two models examined predict that the oceanic crust of the south china sea basin toward the west did not begin forming until sometime between 6 12 my after its initial formation 32 ma toward the east these results are compatible with crustal age interpretations of marine magnetic anomalies assuming rifting symmetry with conjugate margin segments now residing along the southern portions of the south china sea basin implies that the total width of the zone of rifting in the west was greater than in the east by about a factor of two we suggest the most likely causes of the rifting differences were east west variations in the rheology of the pre rift crust and associated east west variations in the thermal structure of the pre rift lithosphere the calculated widths of rifted continental crust for the northern and southern margins when combined with the differential widths of seafloor generated during the seafloor spreading phase indicate the total crustal extension that occurred is about 1100 km and is remarkably consistent to within 10 for all three eastern central western segments examined

quantitative impact of structural inheritance on present day deformation and seismicity concentration in intraplate deformation zones abstract structural inheritance i e paleo tectonic areas acting as weakened domains appear to be a key element localizing the seismicity in intraplate deformation zones however the impact of structural inheritance on the observed present day seismicity and strain rate concentration remains to be quantified in this study we quantify through 2d numerical modeling the localization and amplification factor of upper crustal strain rates induced by structural inheritance our 2d models are constrained by intraplate velocity boundary conditions and include rheology laws that accounts for inherited strain weakening in both the brittle and ductile layers of the lithosphere the role of structural inheritance is investigated for different localization of the weakened domain in the lithosphere for an average intraplate geotherm moho temperature ca 500 c brittle weakening i e inherited faults alone induces a limited amplification factor of upper crustal strain rates of ca 4 ductile weakening can increase the amplification factor to ca 7 when localized in the lower crust but has no effect when localized in the lithospheric mantle overall the amplification factors of upper crustal strain rates vary between 1 and 27 depending on the location of the weakened area in the lithosphere and on the different possible net driving forces crustal strengths amounts of weakening and geotherms these model amplification factors are in reasonable agreement with those derived from gps and seismicity data over large spatial scale several hundreds of kilometers in north america

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

quantitative risk analysis for earthquake induced landslides emamzadeh ali iran abstract earthquake induced landslides are among the most destructive slope movements not only because of their size and magnitude but also because of the synergistic action with the earthquake the consequences are higher due to the earthquake shaking and the landslide effect studies on landslides triggered by seismic activities are not as extensive as rainfall induced landslides in this study a quantitative risk analysis approach was used to calculate the risk for people exposed to the threat of earthquake induced landslide in emamzadeh ali north of iran emamzadeh ali was selected as it has already experienced some landslides and is located in a tectonically active region a numerical model was used in this study to carry out the stability analysis of the slope under both static and dynamic conditions a quantitative probabilistic approach was developed for determining the frequency and magnitude of the process in addition the values of vulnerability for each building were calculated the highest risks individual risk to life and societal risk to life are in the area of the stone mine on the head of the slope and close to the toppling activities north east of the study area

dipping seismic reflectors electrically conductive zones and trapped water in the crust over a subducting plate the lithoprobe program across the northern cascadia subduction zone at vancouver island has obtained geophysical data that suggest a dipping zone of trapped free pore water in the overlying continental crust land and marine multichannel seismic reflection profiles show several bands of reflectors the primary one at a depth of about 30 km is about 5 km thick dips inland and appears to coincide with an electrically conductive layer defined by magnetotelluric data the downgoing oceanic crust is imaged as a thin reflector dipping at about 15 and 10 km deeper than the primary reflector a location that is consistent with seismicity and seismic refraction data both the reflectors and the conductor have been modeled by near horizontal lamellae with 1 4 saline water porosity detailed geothermal measurements defining heat flow that decreases inland indicate that the dipping bands are nearly isothermal at a temperature of 400 500 c it is suggested that free water generated by dehydration of the downgoing oceanic plate migrates upward until reduced temperature results in hydration reactions and mineral precipitation that forms an impermeable barrier low vertical permeability is required to keep the water from separating to the top of the layer this can be reconciled with the low electrical resistivity if pore interconnection is through thin grain boundary tubes as predicted by theoretical equilibrium pore geometry although very small effective grain size is necessary an abrupt transition from high permeability to very low permeability is predicted at a several percent porosity in agreement with the modeled porosity such pore geometry with low permeability may be restricted to temperatures above about 400 c i e in greenschist to amphibolite facies conditions where grains will deform to equilibrium geometry and cracks are annealed the region above the reflective and conductive band is estimated to be within blueschist conditions consistent with the inferred high seismic velocity from refraction data and high density from gravity data

along strike segmentation of the south china sea margin imposed by inherited pre rift basement structures abstract multibeam bathymetric seismic and borehole data are used to investigate a large scale strike slip structure the baiyun liwan fault zone in the northern south china sea this fault zone comprises nw to ne striking faults and negative flower structures that were generated by oblique extensional displacement notably the interpreted data reveals that the baiyun liwan fault zone was active during the cenozoic recording intense magmatism and accommodating significant intraplate deformation during progressive continental rifting and ocean spreading it bounds two distinct crustal segments and played a significant role in segmenting the northern margin of the south china sea the geometry of faults and strata within the baiyun liwan fault zone also controlled local sediment routing and depocentre evolution during the cenozoic as basement and syn rift structures change markedly across the baiyun liwan fault zone we propose this structure to be inherited from a lithospheric scale fault zone separating the mesozoic arc from forearc related terrains we therefore stress the importance of pre existing structures in the development of rifted margins with the example provided by the baiyun liwan fault zone having profound implications for palaeogeographic reconstructions in the south china sea at present the baiyun liwan fault zone is incised by the pearl river canyon and eroded by recurrent submarine landslides forming a major area of sediment bypass towards the abyssal plain

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

fluvial terraces as quantitative markers of late quaternary detachment folding and creeping thrust faulting in the peruvian huallaga basin abstract in the western huallaga basin located in the peruvian subandes a series of nine fluvial terraces with elevations of up to 160 m above current floodplain level fp were formed against the biabo anticline the terraces are progressively more folded with age and terrace elevation and present growth strata suggesting ongoing folding of the anticline optically and infrared stimulated luminescence osl and irsl dating of fluvial terrace sediments yielded ages of 10 8 0 7 ka for the t2 24 2 2 ka for the t4 and 46 9 ka for the t7 terrace uniform uplift rates of 2 mm a 1 for the past 46 ka were calculated terrace profiles and two new seismic profiles that cross the biabo anticline longitudinally and transversally were used to calculate shortening rates of 2 6 mm a 1 for the anticline over the past 46 ka our calculations took into account potential contributions of detachment thrusting parallel to the biabo fold and reverse tear faulting perpendicular to the fold tip as visible on the seismic sections a maximum uplift rate of 0 62 mm a 1 due to reverse thrusting of the bellavista tear fault for the past 46 ka could have contributed to the overall uplift of the bellavista terraces based on trigonometric relationships a reverse fault slip rate of 0 86 mm a 1 and an age of 137 ka were calculated for this fault in the eastern part of the huallaga basin a series of two fluvial terraces were formed with elevations of 13 15 m and 30 m fp and with osl ages of 6 9 0 7 ka for t1 and 30 2 3 1 ka for t2 the interpretation of a third new seismic profile crossing the study area in combination with field observations and trigonometric relationships shows that the terraces were formed by a complex system of oblique ramp and strike slip faulting resulting in uplift and shortening rates of 1 mm a 1 and 1 96 mm a 1 between 30 2 ka and 6 9 ka respectively and uplift and shortening rates of 2 mm a 1 and 3 70 mm a 1 from 6 9 ka until the present reverse slip of the shapaja oblique ramp that was responsible for uplift of the terraces was calculated at 2 19 mm a 1 for the period 30 2 to 6 9 ka and 4 15 mm a 1 from 6 9 ka until the present measured total slip in combination with the calculated slip rates allowed an age calculation of 181 ka for the shapaja thrust ramp our inferences showed that the studied tectonic structures absorb most of the present day deformation in the huallaga basin the calculated uplift and shortening rates are compatible with published present day crustal movement velocities and miocene to present shortening rates for various studied sites of the tropical subandes and suggest that it is deforming at a relatively uniform rate the timing of sedimentation of the terrace sediments may have corresponded to periods of increased precipitation which occurred coeval with the heinrich events of the northern hemisphere terrace records similar as ours have been described for other tectonically highly active areas in the tropical subandes but not in the tectonically less active amazonian lowlands it is suggested that uplift rates of at least 1 mm a 1 are needed to preserve suborbital climate cycles as individual terraces the tropical subandes could therefore be a new key area to investigate the interactions between tectonics suborbital climate forcing and fluvial response during the late quaternary