distributed energy balance modeling of snow cover evolution and melt in rugged terrain tobacco root mountains montana usa summary a distributed energy balance model was developed for simulating snowpack evolution and melt in rugged terrain the model which was applied to a 43 km 2 watershed in the tobacco root mountains montana usa used measured ambient data from nearby weather stations to drive energy balance calculations and to constrain the model of liston and sturm liston g e sturm m 1998 a snow transport model for complex terrain journal of glaciology 44 148 498 516 for calculating the initial snowpack thickness simulated initial snow water equivalent ranged between 1 cm and 385 cm w e water equivalent with high values concentrated on east facing slopes below tall summits an interpreted satellite image of the snowcover distribution on may 6 1998 closely matched the simulated distribution with the greatest discrepancy occurring in the floor of the main trunk valley model simulations indicated that snowmelt commenced early in the melt season but rapid meltout of snow cover did not occur until after the average energy balance of the entire watershed became positive about 45 days into the melt season meltout was fastest in the lower part of the watershed where warmer temperatures and tree cover enhanced the energy income of the underlying snow an interpreted satellite image of the snowcover distribution on july 9 1998 compared favorably with the simulated distribution and melt curves for modeled canopy covered cells mimicked the trends measured at nearby snow pillow stations by the end of the simulation period august 3 28 of the watershed remained snow covered most of which was concentrated in the highest parts of the watershed where initially thick accumulations had been shaded by surrounding summits the results of this study provide further demonstration of the critical role that topography plays in the timing and magnitude of snowmelt from high mountain watersheds

crustal deformation of the eastern tibetan plateau revealed by magnetotelluric imaging the ongoing collision of the indian and asian continents has created the himalaya and tibetan plateau through a range of deformation processes these include crustal thickening detachment of the lower lithosphere from the plate delamination and flow in a weakened lower crust 1 6 debate continues as to which of these processes are most significant 7 in eastern tibet large scale motion of the surface occurs but the nature of deformation at depth remains unresolved a large scale crustal flow channel has been proposed as an explanation for regional uplift in eastern tibet 6 8 9 but existing geophysical data 10 11 do not constrain the pattern of flow magnetotellurics uses naturally occurring electromagnetic waves to image the earth s subsurface here we present magnetotelluric data that image two major zones or channels of high electrical conductivity at a depth of 20 40 km the channels extend horizontally more than 800 km from the tibetan plateau into southwest china the electrical properties of the channels imply an elevated fluid content consistent with a weak crust 12 13 that permits flow on a geological timescale these findings support the hypothesis that crustal flow can occur in orogenic belts and contribute to uplift of plateaux our results reveal the previously unknown complexities of these patterns of crustal flow many previous studies of the indiaasia

miocene to present activity along the red river fault china in the context of continental extrusion upper crustal rotation and lower crustal flow detailed mapping of field relationships along the red river fault reveals information about the distribution and magnitude of slip along the fault about its interactions with other regional fault systems and the relationship between river incision and growth of the eastern margin of the tibetan plateau the red river fault is complex consisting of up to four strands and is dominated by right lateral strike slip displacement evidence for an extensional component of displacement is strongest along the northern part of the fault and decreases to the southeast to zero southeast of a major bend in the fault results of this study indicate dextral displacement on the red river fault is probably at least 40 km 15 16 km of which predates incision of the red river in pliocene time or later and probably also predates plateau growth and development of other regional fault systems long term average slip rate on the red river fault is a minimum of 5 mm yr however regional active tectonics are characterized by rotation of the upper crust around the eastern himalayan syntaxis bounded to the east by the xianshuihe xiaojiang fault system which deflects but does not cut the red river fault the distributed nature of the xianshuihe xiaojiang fault system as it approaches the red river fault is important for accommodating shearing across the strong crustal anisotropy formed by the red river fault and ailao shan shear zone the red river fault appears to terminate in the extending dali fault system in northwest yunnan pliocene surface uplift river incision and rotation around the eastern himalayan syntaxis are inconsistent with the pre pliocene displacement on the red river fault and lateral extrusion along the ailao shan shear zone advocated by the extrusion model this suggests a significant change in crustal conditions on the southeast margin of the tibetan plateau in pliocene time possibly the result of lower crustal flow

miocene jiali faulting and its implications for tibetan tectonic evolution the karakoram jiali fault zone kjfz comprises a series of right lateral shear zones that southerly bound the eastward extrusion of northern tibet relative to india and stable eurasia here we present new 40 ar 39 ar age data from the puqu and parlung faults two easternmost branches of the jiali fault zone which indicate a main phase of the kjfz shearing from v18 to 12 ma thus the tibetan eastward extrusion bounded by principal strike slip fault zones started and was probably most active around the middle miocene an interval marked also by active east west extension in southern tibet the coincidence of these two tectonic events strongly suggests a common causal mechanism which is best explained as oblique convergence between india and asia under the framework of this mechanism the extension in southern tibet is not a proxy for the plateau uplift the kjfz activity was furthermore coincident with right lateral displacements along the gaoligong and sagaing faults in southeast asia this defines a miocene deformation record for the regional dextral accommodation zone that in response to the continuing india asia collision may have accounted for the initiation and prolonged history of clockwise rotation of the tibetan extrusion around the eastern himalayan syntaxis 2002 elsevier science b v all rights reserved

an analysis of snow cover patterns in a small alpine catchment snow cover patterns in a 9 4 km2 basin in the austrian alps are examined during spring and summer 1989 digital mono plotting from oblique aerophotographs is used for mapping on the basis of a square grid with 25 m spacing snow cover as mapped during nine surveys is analysed as a function of elevation and slope during winter conditions the snow cover is found to be much better related to these terrain features than during the late ablation period

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

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

distributed snow process modelling an image processing approach an approach to spatially distribute a snow process model by segmenting images of land cover terrain and snow properties is reported a small 1 7 ha study area with an existing database was selected for this preliminary evaluation the methodology was carried out over a relatively flat valley bottom at camp grayling michigan meteorological measurements on two sides of the area showed only small differences so uniform meteorological variables were assumed over the site initial snow cover conditions were reconstructed and were distributed over the area using snow maps and sparse snow pit measurements one metre resolution terrain soil vegetation and snow type maps were individually processed into class maps these layers were then combined to produce a segmented class map where the attributes from the data layers were known for each class a one dimensional model of snow processes was run for each class then the results were mapped back into images shallow snow conditions provided high sensitivity of ablation patterns to meteorological conditions over a 72 h period the model performance was assessed by comparing predicted and observed ablation patterns the error in total snow covered area was less than 9 however the location errors were greater predicted snow where no snow was observed and observed snow where no snow was predicted extensive error analysis was not justified because of the lack of multiple point measurements of snow properties

the world stress map database release 2016 crustal stress pattern across scales abstract knowledge of the present day crustal in situ stress field is a key for the understanding of geodynamic processes such as global plate tectonics and earthquakes it is also essential for the management of geo reservoirs and underground storage sites for energy and waste since 1986 the world stress map wsm project has systematically compiled the orientation of maximum horizontal stress shmax for the 30th anniversary of the project the wsm database has been updated significantly with 42 870 data records which is double the amount of data in comparison to the database release in 2008 the update focuses on areas with previously sparse data coverage to resolve the stress pattern on different spatial scales in this paper we present details of the new wsm database release 2016 and an analysis of global and regional stress pattern with the higher data density we can now resolve stress pattern heterogeneities from plate wide to local scales in particular we show two examples of 40 60 shmax rotations within 70 km these rotations can be used as proxies to better understand the relative importance of plate boundary forces that control the long wave length pattern in comparison to regional and local controls of the crustal stress state in the new wsm project phase iv that started in 2017 we will continue to further refine the information on the shmax orientation and the stress regime however we will also focus on the compilation of stress magnitude data as this information is essential for the calibration of geomechanical numerical models this enables us to derive a 3 d continuous description of the stress tensor from point wise and incomplete stress tensor information provided with the wsm database such forward models are required for safety aspects of anthropogenic activities in the underground and for a better understanding of tectonic processes such as the earthquake cycle

late cenozoic tectonic evolution of the ailao shan red river fault se tibet implications for kinematic change during plateau growth surface uplift river incision shear zone exhumation and displacement along active faults have all interacted to shape the modern landscape in the southeastern margin of the tibetan plateau the ailao shan red river fault a major structure in the tectonic evolution of southeastern asia is an excellent recorder of these processes we present new stratigraphic structural and low temperature thermochronologic data to explore its late cenozoic tectonic and geomorphic evolution the stratigraphic and structural observations indicate that the major bend in the fault was a releasing bend with significant miocene sedimentation in the early middle miocene but became a restraining bend with abundant shortening structures developed after the late miocene reversal of displacement we also document exhumation of the shear zone from two low temperature thermochronologic transects new apatite u th he ahe data and published thermochronologic results reveal two accelerated cooling episodes backed by stratigraphic and geomorphic observations the first rapid cooling phase occurred from ca 27 to 17 ma with removal of cover rocks and exhumation of the shear zone the second accelerated cooling episode revealed by our ahe data commenced at 14 13 ma lasting 2 3 myr the ailao shan range may have risen to its modern elevation with high relief topography developing due to river incision we interpret the onset of this rapid exhumation to reflect renewed plateau growth associated with lower crustal flow

a review on active tectonics and deep crustal processes of the western sichuan region eastern margin of the tibetan plateau abstract one of remarkable geological and geomorphological features in continental china is the presence of a north south trending tectonic zone which separates the seismically active tibetan plateau to the west from the tectonically stable south china and ordos blocks to the east the zone also owns a name of north south seismic belt as a large number of great historical earthquakes occur on it the most recent one the 2008 wenchuan earthquake attests its recent tectonic activity in this review i take the western sichuan region as an example to probe the structural styles and kinematic pattern as well as deep geological process associated with tectonic deformation of the north south trending zone through integrated studies on active faults gps crustal deformation and geophysical structure we show that deformation in the western sichuan is governed by interactions among three crustal blocks songpan chuandian and south china of distinctive rheological properties under the tectonic framework that eastward growth of the soft eastern tibet is blocked by the hard lithosphere of the south china block the left lateral xianshuihe fault continues to the north south trending fault system without crustal shortening to form a bounding fault to limit the northern extend of the magnificent clockwise rotation of crustal material around the eastern himalaya syntax upper crust of the three blocks is dominated by brittle deformation whereas the ductile flow of lower crust would drag the brittle upper crustal blocks to move with respect to each other the relative motions among the brittle upper crustal blocks cause strain accumulations among their bounding faults to generate large earthquakes deformation of the western sichuan region can thus be described in terms of combined model of rigid block movement and continuous deformation we suggest this combined model can be applied to entire continental china

three dimensional velocity field of present day crustal motion of the tibetan plateau derived from gps measurements 1 using the measurements of 750 gps stations around the tibetan plateau for over 10 years since 1999 we derived a high resolution 3 d velocity field for the present day crustal movement of the plateau the horizontal velocity field relative to stable eurasia displays in details the crustal movement and tectonic deformation features of the india eurasia continental collision zone with thrust compression lateral extrusion and clockwise rotation the vertical velocity field reveals that the tibetan plateau is continuing to rise as a whole relative to its stable north neighbor however in some subregions uplift is insignificant or even negative the main features of the vertical crustal deformation of the plateau are the following a the himalayan range is still rising at a rate of 2 mm yr the uplift rate is 6 mm yr with respect to the south foot of the himalayan range b the middle eastern plateau has a typical uplift rate between 1 and 2 mm yr and some high mountain ranges in this area like the longmen shan and gongga shan have surprising uplift rates as large as 2 3mm yr c in the middle southern plateau there is a basin and endorheic subregion with a series of ns striking normal faults showing obvious sinking with the rates between 0 and 3 mm yr d the present day rising and sinking subregions generally correspond well to the cenozoic orogenic belts and basins respectively e at the southeastern corner of the plateau there is an apparent trend that the uplift rate is gradually decreasing from between 0 8 and 2 3 mm yr in the inner plateau to between 0 5 and 1 6 mm yr outside the plateau with the decrease of terrain height

new constraints on the structure thermochronology and timing of the ailao shan red river shear zone se asia new structural petrographic and 40ar 39ar data constrain the kinematics of the asrr ailao shan red river shear zone in the xuelong shan xls geochronological data reveal triassic early tertiary and oligo miocene thermal events the latter event 33 26 ma corresponds to cooling during left lateral shear in the fansipan fsp range thrusting of the sapa nappe linked to left lateral deformation and cooling of the fsp granite occurred at 35 ma rapid cooling resumed at 25 29 ma as a result of uplift within the transtensive asrr in the daynuiconvoi dncv foliation trends nw se but is deflected near large scale shear planes stretching lineation is nearly horizontal on steep foliations shear criteria indicate left lateral shear sense zones with flatter foliations show compatible shear senses petrographic data indicate decompression from 6 5 kbar during left lateral shear temperatures 700 c 40ar 39ar data imply rapid cooling from above 350 c to below 150 c between 25 and 22 ma without diachronism along strike along the whole asrr cooling histories show two main episodes 1 rapid cooling from peak metamorphism during left lateral shear 2 rapid cooling from greenschist conditions during right lateral reactivation of the asrr in the nw part of the asrr xls diancang shan we link rapid cooling 1 to local denudations in a transpressive environment in the sw part ailao shan and dncv cooling 1 resulted from regional denudation by zipper like tectonics in a transtensive regime the induced cooling diachronism observed in the ailao shan suggests left lateral rates of 4 to 5 cm yr from 27 ma until 17 ma dncv rocks always stayed in a transtensive regime and do not show cooling diachronism the similarities of deformation kinematics along the asrr and in the south china sea confirms the causal link between continental strike slip faulting and marginal basin opening

crustal deformation in the india eurasia collision zone from 25 years of gps measurements the india eurasia collision zone is the largest deforming region on the planet direct measurements of present day deformation from global positioning system gps have the potential to discriminate between competing models of continental tectonics but the increasing spatial resolution and accuracy of observations have only led to increasingly complex realizations of competing models here we present the most complete accurate and up to date velocity field for india eurasia available comprising 2576 velocities measured during 1991 2015 the core of our velocity field is from the crustal movement observation network of china i ii 27 continuous stations observed since 1999 56 campaign stations observed annually during 1998 2007 1000 campaign stations observed in 1999 2001 2004 and 2007 260 continuous stations operating since late 2010 and 2000 campaign stations observed in 2009 2011 2013 and 2015 we process these data and combine the solutions in a consistent reference frame with stations from the global strain rate model compilation then invert for continuous velocity and strain rate fields we update geodetic slip rates for the major faults some vary along strike and find that those along the major tibetan strike slip faults are in good agreement with recent geological estimates the velocity field shows several large undeforming areas strain focused around some major faults areas of diffuse strain and dilation of the high plateau we suggest that a new generation of dynamic models incorporating strength variations and strain weakening mechanisms is required to explain the key observations seismic hazard in much of the region is elevated not just near the major faults

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

modelling snow melt and snowcover depletion in a small alpine cirque canadian rocky mountains spatial and temporal patterns of areal snowcover depletion scd were studied over a small 0 6 km 2 alpine cirque within the canadian rocky mountains using a combined approach of daily acquisition of remotely sensed imagery together with meteorological observations and snowmelt modelling digital terrestrial photographs were georeferenced using a novel software tool together with a high resolution digital elevation model and used to derive measurements of fractional snowcovered area sca over the cirque manual snow surveys carried out in the pre melt period were used to describe the initial frequency distribution of snow water equivalent swe values over the cirque and indicated a lognormal distribution of swe when surveys were stratified by terrain features rates of snowmelt were simulated using a physically based snowmelt energy balance model snobal driven by observed meteorological conditions at a nearby station which were adjusted for slope orientation and exposure by making corrections to observed incoming shortwave and longwave radiation components in the cold regions hydrological model platform simulated melt rates were then applied to the approximated swe distributions to model the decline in sca over the spring the model was found to perform well for the simulation of snowmelt based on point observations of swe at the meteorological station and produced a close correspondence between simulated and observed scd curves representing two opposing slopes within the cirque the results show that both the pre melt distributions of swe and the spring melt rates exhibit considerable spatial variability between distinct slope units within the cirque and that this variability has a significant impact on simulated scd assuming a unimodal pre melt frequency distribution and conditions of spatially uniform snowmelt over complex terrain such as this can lead to large errors in the simulation results it is suggested that modelling applications intended to represent snowmelt dynamics and areal scd in similar alpine environments consider the effects of spatial variation in swe distribution and melt energetics between slopes

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

snow accumulation distribution inferred from time lapse photography and simple modelling the spatial and temporal distribution of snow accumulation is complex and significantly influences the hydrological characteristics of mountain catchments many snow redistribution processes such as avalanching slushflow or wind drift are controlled by topography but their modelling remains challenging in situ measurements of snow accumulation are laborious and generally have a coarse spatial or temporal resolution in this respect time lapse photography shows itself as a powerful tool for collecting information at relatively low cost and without the need for direct field access in this paper the snow accumulation distribution of an alpine catchment is inferred by adjusting a simple snow accumulation model combined with a temperature index melt model to match the modelled melt out pattern evolution to the pattern monitored during an ablation season through terrestrial oblique photography the comparison of the resulting end of winter snow water equivalent distribution with direct measurements shows that the achieved accuracy is comparable with that obtained with an inverse distance interpolation of the point measurements on average over the ablation season the observed melt out pattern can be reproduced correctly in 93 of the area visible from the fixed camera the relations between inferred snow accumulation distribution and topographic variables indicate large scatter however a significant correlation with local slope is found and terrain curvature is detected as a factor limiting the maximal snow accumulation copyright 2010 john wiley sons ltd

optimal interpolation of spatially discretized geodetic data abstract we present an algorithm to calculate horizontal strains or strain rates through interpolation of geodetically derived displacements or velocities this is an underdetermined inverse problem to derive smoothly distributed strains or strain rates using spatially discretized geodetic observations a priori information in the form of weighted smoothing is critical to facilitate the solution at a given site the horizontal displacement or velocity field in its vicinity is approximated by a bilinear function and represented by rigid block translation rotation and strains or their rates the weighted displacement or velocity data in the neighborhood are used to estimate the field parameters through a least squares inversion procedure optimal weightings are prescribed for the neighboring data based on their distances to the interpolation site and their spatial coverage nonelastic strains resulted from surface fault rupture and creep may also be excluded from the solution we apply this method to the southern california earthquake center crustal motion map version 4 0 velocity field and derive the strain rate field in southern california our result shows that 1 distance dependent weighting can be optimally achieved by employing either a gaussian or quadratic decay function with the former offering a slightly sharper result than the latter 2 spatially dependent weighting is important to improve the interpolation and can be done by invoking either an azimuthal weighting or a voronoi cell areal weighting function 3 the strain rate pattern in southern california is dominated by dextral shear of the san andreas fault saf system and the secondary faults surrounding the big bend of the saf strike at oblique angles with respect to the maximum shear direction suggesting that tectonic deformation field on and off the saf is dominated by mechanic processes of the saf

propagation of surface uplift lower crustal flow and cenozoic tectonics of the southeast margin of the tibetan plateau surface uplift of the southeast margin of the tibetan plateau is interpreted to have progressed from the northwest near the tibetan border to the southeast in the red river region of the central yunnan province china this interpretation is based on existing thermochronologic data and new mapping and sedimentologic and paleobotanic data demonstrating incision in the headwaters of the red river in pliocene time or later together with previously published data demonstrating surface uplift and a gradient in crustal thickness in the absence of upper crustal shortening this is strong evidence for growth of the southeast margin of the tibetan plateau through lower crustal flow displacement along the ailao shan red river shear zone slowed or ceased in early pliocene time and the xianshuihe xiaojiang fault system initiated accommodating diffuse deformation and rotation around the eastern himalayan syntaxis we suggest a kinematic link between the change in mode of deformation and the introduction of a weak crustal layer through lower crustal flow

structure and tectonic geomorphology of the qujiang fault at the intersection of the ailao shan red river fault and the xianshuihe xiaojiang fault system china abstract the northwest striking qujiang fault is located at the southeastern tip of the sichuan yunnan block which is bounded by the ailao shan red river fault and the xianshuihe xiaojiang fault system the qujiang fault is one of the most seismically active faults in western yunnan china and is considered to be the seismogenic fault of the 1970 ms 7 7 tonghai earthquake in this study we examine the geometry kinematics and geomorphology of this fault through field observations satellite images and dems it is a holocene active fault characterized by dextral strike slip movements with dip slip components it can be divided into northwest and southeast segments depending on different kinematics the northwest segment from baiyizhai to wujie shows right lateral strike slip with normal components whereas it is characterized by dextral movements with the northeast wall thrusting over the opposite in the southeast segment from wujie to miaobeishan the geophysical data combined with our investigations indicate that the fault dips steeply to the ne at depth while secondary faults with different dip directions developed at shallow surface owing to fault bifurcation during the tonghai earthquake a blind fault may have developed on the southwest wall resulting in aftershocks concentrated to the southwest of the surface raptures multiple tectonic landforms are developed along the fault the right lateral holocene slip rate was determined to be 2 84 3 27 mm year based on radiometrically dated offset gullies our analyses show that the present deformation at the intersection of the ailao shan red river fault and the xianshuihe xiaojiang fault system is partitioned into a shortening distributed over a region 150 km wide and a right lateral strike slip localized on the qujiang and jianshui faults since the late pleistocene the qujiang fault has been playing an important role in accommodating the ongoing se directed movements of the sichuan yunnan block creating strong earthquakes to release strain energy

the nature of the ailao shan red river asrr shear zone constraints from structural microstructural and fabric analyses of metamorphic rocks from the diancang shan ailao shan and day nui con voi massifs abstract the structural geology timing of shearing and tectonic implications of the asrr shear zone one of the most striking lineaments in southeast asia have been the topics of extensive studies over the past few decades the xuelong shan xls diancang shan dcs ailao shan als and day nui con voi dncv metamorphic massifs along the shear zone have preserved important information on its structural and tectonic evolution our field structural analysis detailed microstructural and fabric analysis as well as the quartz sillimanite and garnet fabric studies of the sheared rocks from the massifs demonstrate the dominant roles of three deformation episodes during cenozoic tectonic evolution in the shear zone among the contrasting structural and microstructural associations in the shear zone d2 structures which were formed at the brittle to ductile transition during large scale left lateral shearing in the second deformation episode predominate over the structural styles of the other two deformation episodes discrete micro shear zones with intensive grain size reduction compose the characteristic structural style of d2 deformation in addition several types of folds early shearing folds f 2 1 and late shearing folds f 2 2 were formed in the sheared rocks including discrete to distributed mylonitic foliation stretching lineation and shear fabrics e g mica fish domino structures as well as sigma and delta fabrics a sequence of microstructures from syn kinematic magmatic flow high temperature solid state deformation to brittle ductile shearing is well preserved in the syn kinematic leucocratic intrusions deformation structures from the first episode d1 are characterized by f1 folds and distributed foliations s1 in rocks due to pure shearing at high temperatures they are preserved in weakly sheared d2 rocks along the eastern margin of the als belt or in certain low strain tectonic enclaves within the shear zone furthermore semi brittle deformation structures such as hot striae and discrete retrogression zones are attributed to normal slip shearing in the third deformation episode d3 which was probably locally active along the eastern flank of the dcs range for example there are four quartz c axis fabric patterns in the mylonitic rocks including type a point maxima type b y point maxima with crossed girdles superimposition type c quadrant maxima as well as type d point and quadrant maxima combination they are consistent with microscopic observations of microstructures of high temperature pure shearing low temperature simple shearing and their superimposition integrated microstructural analysis and fabric thermometer studies provide information on both high temperature up to 750 c and dominant low temperature 300 600 c deformations of quartz grains in different rock types sillimanite and garnet fabrics especially the latter were primarily formed at the peak metamorphism during high temperature pure shearing the above structural microstructural and fabric associations were generated in the tectonic framework of the indian eurasian collision the low temperature microstructures and fabrics are attributed to left lateral shearing along the asrr shear zone from 27 to 21 ma during the southeastward extrusion of the indochina block which postdated high temperature deformation at the peak metamorphism during the collision

polystage deformation of the gaoligong metamorphic zone structures 40ar 39ar mica ages and tectonic implications abstract the gaoligong metamorphic zone is located southeast of the eastern himalayan syntaxis in western yunnan china the zone is characterized by four stages of deformation d1 d4 d1 structures record early compressive deformation during the indosinian orogeny which formed tight to isoclinal f1 folds of bedding with a penetrative s1 foliation developed parallel to fold axial planes mid crustal horizontal shearing during d2 resulted in overprinting of d1 structures d1 and d2 structures are associated with granulite facies metamorphism d3 doming resulted in late crustal thickening and the development of a regional nw se trending f3 antiform synchronous with or slightly subsequent to d3 deformation the zone experienced d4 ductile strike slip shearing resulting in its exhumation to shallow crustal levels and retrograde metamorphism granitic d4 mylonites predominantly yield 40 ar 39 ar mica ages of 15 16 ma indicating that d4 dextral strike slip shearing occurred in the miocene weakly deformed leucogranite and protomylonite yield 40 ar 39 ar ages of 10 11 ma suggesting that ductile strike slip shearing continued to the late miocene the new 40 ar 39 ar data indicate that escape related deformation along the gaoligong strike slip shear zone occurred in the miocene in association with recent geophysical studies and on the basis of the structural crystal preferred orientation cpo and geochronological data presented in this paper we suggest that the gaoligong metamorphic zone formed in response to intracontinental transpression in the southeast of tibet characterized as intense deformation and metamorphism at middle upper crustal levels

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

clockwise rotations recorded in redbeds from the jinggu basin of northwestern indochina paleomagnetic data have been used to infer clockwise rotations and significant southward motion of the indochina block during cenozoic extrusion from the india asia collision zone because the cenozoic of the indochina block has been sparsely sampled to date and is key to determining the timing of this tectonic motion we performed an extensive paleomagnetic study on paleocene to oligocene redbeds and middle miocene sandy silts from the jinggu basin 23 5 n 100 7 e in northern indochina paleomagnetic results from the redbeds pass fold tests but they show exclusively normal polarity there is controversy however on the age assignment to the lower part of the succession if the age of the redbeds is indeed paleogene this indicates a prefolding remagnetization associated with oligocene deformation of the indochina block if the age of the redbeds would be late cretaceous their magnetization may be primary and deposition could have taken place during the cretaceous normal superchron however the abundance of secondary hematite in the redbeds in combination with the biostratigraphy which indicates a paleogene age for at least the upper two formations of the redbeds in the jinggu basin implies a pervasive remagnetization the middle miocene sediments pass both the fold test and the reversals test and contain magnetite as well as hematite as carriers suggesting a primary magnetization our large data set from the redbeds 2000 paleomagnetic directions demonstrates an 30 35 clockwise rotation of the jinggu basin with respect to eurasia for both scenarios i e when compared to a ca 100 ma pole if the redbeds carry a primary natural remanent magnetization or to a ca 30 ma pole if the sequence is remagnetized the middle miocene results however indicate that the jinggu basin experienced no significant 2 5 6 rotation with respect to eurasia since no major deformation has occurred within northern indochina during late cretaceous to eocene times our results reflect a major clockwise rotation of the indochina block during its oligocene to early miocene extrusion from the india asia collision zone

diffuse deformation in the se tibetan plateau new insights from geodetic observations the southeastern tibetan plateau is a key component in the india eurasia collision zone which is characterized by spatially prevalent strike slip fault systems with devastating earthquakes however slip rates on some of these faults are still poorly constrained hindering an understanding of kinematic and dynamic processes in this region we analyze contemporary crustal deformation in the se tibetan plateau based on the latest dense geodetic observations slip rates on a set of dextral nw nnw striking faults are determined using a 3 d elastic half space dislocation model our results show that boundary faults such as the red river and lancangjiang faults yield dextral slip rates ranging from 1 to 3 mm a similar to those of other small scale sub parallel faults such as the chuxiong qujiang and wuliangshan faults additionally sinistral slip of the xiaojiang fault may have partly transferred to transpressional slip on the qujiang jianshui and central red river faults which increase seismicity on these faults new seismic relocation results geodetic measurements and existing structural observations show the geometry of this dextral fault system at the depth which may be restricted above or within the rheologically weak mid lower crust rather than cutting into the mantle results confirm that the se tibetan plateau is characterized by on going diffuse deformation between the sagaing and xianshuihe xiaojiang faults driven by the northward advance of the eastern himalayan syntaxis and southward crustal extrusion distributed right lateral movements occurred along the nw nnw striking fault system

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

magnetostratigraphy of the xiaolongtan formation bearing lufengpithecus keiyuanensis in yunnan southwestern china constraint on the initiation time of the southern segment of the xianshuihe xiaojiang fault the late cenozoic extensional basins in yunnan province southwestern china which are kinematically linked with the regional strike slip faults can provide meaningful constraints on the fault activity history and tectonic evolution of the southeast margin of the tibetan plateau semtp and further on the geodynamic evolution of the tibetan plateau however this has been severely impeded by the lack of precise age constraints on the timing of fault activity to better constrain the timing of fault activity and the tectonic rotation of semtp we undertook a high resolution magnetostratigraphic study on the xiaolongtan formation in the xiaolongtan basin which is located at the southern tip of the xianshuihe xiaojiang fault and is well known by the presence of hominoid lufengpithecus keiyuanensis rock magnetic experiments indicate that magnetite is the main remanence carrier correlation to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic and biostratigraphic data our correlation suggests that the xiaolongtan formation sedimentary sequence spans from chron c5ar 1r to chron c5n 2n which indicates that the age of the xiaolongtan formation ranges from 10 ma to 12 7 ma and that the ages of the two sedimentary layers possibly bearing the hominoid l keiyuanensis are 11 6 ma or 12 5 ma the basal age of the sediments is 12 7 ma which indicates that the activation of the southern xianshuihe xiaojiang fault was initiated at this time the overall mean paleomagnetic direction d 353 2 i 34 2 95 2 1 n 166 documents a counter clockwise vertical axis rotation of 8 3 with respect to eurasia which is the response to the activity of the left lateral xianshuihe xiaojiang fault

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

optically stimulated luminescence dating as a tool for calculating sedimentation rates in chinese loess comparisons with grain size records understanding loess sedimentation rates is crucial for constraining past atmospheric dust dynamics regional climatic change and local depositional environments however the derivation of loess sedimentation rates is complicated by the lack of available methods for independent calculation this limits interpretation of the environmental changes revealed by the loess record in particular while the quaternary neogene chinese loess and red clay sequences have the potential to provide detailed records of past sedimentation and climate change there is great uncertainty concerning i the influences on sediment grain size and accumulation and ii their relationship through time and across the depositional region this uncertainty has led to the widespread use of assumptions concerning the relationship between sedimentation rate and grain size in order to derive age models and climate reconstructions to address this uncertainty detailed independent age models based on optically stimulated luminescence dating undertaken at 10 to 40 cm intervals at five sections across the loess plateau in china have been used to calculate sedimentation rates and make comparisons with grain size changes over the late pleistocene and holocene the results demonstrate that sedimentation rates are site specific extremely variable over millennial timescales and that this variation is often not reflected in grain size changes in the central part of the loess plateau the relationship between grain size and sedimentation rate appears most complex suggesting an interplay between local conditions at source and sink and a changing emplacement mechanism this observation further undermines the common use of loess sedimentation age models that rely on a derived relationship between grain size and sedimentation rate from a type section the results also highlight the difficulty in assigning specific environmental causes to sedimentation rate changes and to a lesser extent grain size shifts

large river offsets and plio quaternary dextral slip rate on the red river fault yunnan china using multispectral spot images and 1 100 000 topographic data we present an improved map of the active red river fault zone between midu yunnan china and hanoi vietnam the fault zone is composed of parallel strands one of which the yuanjiang fault was previously undetected there also appears to be a component of extension all along the fault zone such extension increases toward the se from yunnan to the south china sea coast and the vector describing the motion of south china relative to indochina points within the n45 135 e quadrant we attempt to assess the plio quaternary dextral slip rate on the red river fault rrf by restoring large river offsets and searching for the largest plausible one across much of yunnan the fault is perpendicular to local catchments that drain into the red river from precise mapping of the river courses on spot satellite images and on 1 100 000 topographic maps numerous multiple offsets along the fault can be detected and reconstructed the lack of correlation between the apparent offsets and the lengths of the rivers upstream from the fault suggests either that the drainage system was in large part established prior to the onset of dextral slip along the fault or that frequent captures have occurred we thus try to find the best fit between series of river channels upstream and downstream from the fault by progressively restoring the dextral displacement in increments of 500 m up to an offset of 50 km for each increment we measure the misfits root mean squares rms between the upstream and downstream channels the best fit and smallest rms are obtained for an offset of 25 0 5 km that we interpret to represent the clearest large right lateral displacement recorded in the geomorphology along the active red river fault since dextral motion is likely to have started around 5 myr the most probable average plio quaternary slip rate on the fault is of order of 5 mm yr we attribute the apparent lack of seismic activity on a large stretch of the fault to millennial recurrence times between great earthquakes our study shows that relatively small drainage systems can keep a good record of fairly large cumulative fault offsets

fault spacing in continental strike slip shear zones abstract strike slip shear zones with sub parallel arrays of evenly spaced faults are widely observed in nature but the controls on the spacing between major faults are unclear we analyze a 2 d model and develop a scaling law relating the fault spacing to structural and rheological parameters in the continental crust we find that fault spacing positively correlates with brittle layer thickness viscous lower crust thickness and strength contrast between active faults and surrounding intact blocks and is inversely correlative with lower crust viscosity this is corroborated for either a zero shear traction decoupled or a prescribed velocity coupled basal boundary condition in the 2 d analytical solution the zero shear traction boundary condition represents low viscosities in the lowermost crust or the topmost mantle that may decouple deformations from mantle flow the prescribed velocity boundary condition emphasizes basal drag tractional forces imparted on the lower crust by a strong mantle for a viscous layer that is thicker than half of its average fault spacing models with either of the boundary conditions produce the same results otherwise a thinner viscous layer with a linear velocity condition tends to produce smaller fault spacings than a no shear model all else being equal these theoretical models are comparted to data from shear zones in california the marlborough fault zone in new zealand and central tibet modeling indicates that the effective viscosity of the viscous layer underlying the brittle layer in all of the selected areas is 2 10 20 to 4 10 21 pa s the subducted oceanic plate attached to the lower crust of the eastern marlborough fault zone also appears to influence fault spacing in the overriding plate

strain accumulation across the eastern california shear zone at latitude 36 30 n the motion of a linear array of monuments extending across the eastern california shear zone ecsz has been measured from 1994 to 1999 with the global positioning system the linear array is oriented n54 e perpendicular to the tangent to the local small circle drawn about the pacific north america pole of rotation and the observed motion across the ecsz is approximated by differential rotation about that pole the observations suggest uniform deformation within the ecsz strike n23 w 26 nstrain yr 1 extension normal to the zone and 39 nstrain yr 1 simple right lateral shear across it with no significant deformation in the two blocks the sierra nevada mountains and southern nevada on either side the deformation may be imposed by right lateral slip at depth on the individual major fault systems within the zone if the slip rates are death valley furnace creek fault 3 2 0 9 mm yr 1 hunter mountain panamint valley fault 3 3 1 6 mm yr 1 and owens valley fault 6 9 1 6 mm yr 1 however this estimate of the slip rate on the owens valley fault is 3 times greater than the geologic estimate

present day crustal vertical movement inferred from precise leveling data in eastern margin of tibetan plateau abstract we collect precise leveling data observed in the period of 1970 to 2012 around the eastern margin of the tibetan plateau and process the data to acquire present day crustal vertical velocity field vertical rates of 9 gps sites are employed as a priori constraints to define the reference frame the velocity field shows that most of the regions in the eastern margin of the tibetan plateau are undergoing uplift the gongga shan and west qinling are uplifting at maximum rates of 5 8 1 0 mm a and 6 0 1 3 mm a respectively a 2 d buried dislocation model is used to infer normal or reverse dip slip rates the result indicates that the reverse slip rate along the longmen shan fault is 4 2 0 5 mm a followed by the daliangshan and longriba faults with the rates of 3 7 0 5 mm a and 2 8 0 3 mm a respectively thezemuhe and northern section of the xiaojiang fault have the normal slip rates of 2 3 1 0 mm a and 2 9 0 4 mm a respectively combining vertical velocity field with gps derived horizontal velocity field we investigate the characteristics of crustal movement and dynamic mechanism the 3d velocity field indicates that the helan shan is uplifting and the yinchuan graben is subsiding the 3d crustal movement of the liupan shan region is segmented with the area in the vicinity of the northern liupan shan fault uplifting and the area in the vicinity of southern liupan shan fault subsiding respectively the subsidence of the central and southern sichuan yunnan terrain is caused by the near east west extension the budget of horizontal material influx suggests that movements of the upper and lower crust are rather different in most of the region excessive material influx into the lower crust upper mantle underneath most of the sub blocks seems required to maintain the uplift rates inferred from leveling providing evidence for the existence of lower crustal flow in this region

geodetic estimates of fault slip rates in the san francisco bay area bourne et al 1998 have suggested that the interseismic velocity profile at the surface across a transform plate boundary is a replica of the secular velocity profile at depth in the plastosphere on the other hand in the viscoelastic coupling model the shape of the interseismic surface velocity profile is a consequence of plastosphere relaxation following the previous rupture of the faults that make up the plate boundary and is not directly related to the secular flow in the plastosphere the two models appear to be incompatible if the plate boundary is composed of several subparallel faults and the interseismic surface velocity profile across the boundary known each model predicts the secular slip rates on the faults which make up the boundary as suggested by bourne et al the models can then be tested by comparing the predicted secular slip rates to those estimated from long term offsets inferred from geology here we apply that test to the secular slip rates predicted for the principal faults san andreas san gregorio hayward calaveras rodgers creek green valley and greenville faults in the san andreas fault system in the san francisco bay area the estimates from the two models generally agree with one another and to a lesser extent with the geologic estimate because the viscoelastic coupling model has been equally successful in estimating secular slip rates on the various fault strands at a diffuse plate boundary the success of the model of bourne et al 1998 in doing the same thing should not be taken as proof that the interseismic velocity profile across the plate boundary at the surface is a replica of the velocity profile at depth in the plastosphere

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

miocene emplacement and deformation of the konga shan granite xianshui he fault zone west sichuan china geodynamic implications the presently active sinistral xianshui he strike slip fault xsh is a lithospheric scale strike slip fault in the eastern himalaya in the study area this fault affects the eastern edge of the konga shan granitic massif where it has caused both brittle and ductile deformation a rbsr isochron and nd and pb isotope study of three samples and a upb zircon study of a single sample were completed on the granite upb data indicate a granite emplacement age of 12 8 1 4 ma the rbsr isochrons show that the granite emplacement and the deformational event were synchronous at around 12 10 ma minimum age for deformation the nd and pb isotope compositions of whole rocks and k feldspars indicate the involvement of proterozoic continental crust which is confirmed by upb systematics indicating inherited zircons sinistral faulting along the xsh began at the latest at 12 ma and marks the extrusion toward the east of the west sichuan and south china blocks following their extrusion along the red river fault zone between 50 and 21 ma

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

the xuelongshan high strain zone cenozoic structural evolution and implications for fault linkages and deformation along the ailao shan red river shear zone abstract new structural geometric petrographic and u pb zircon data constrain the kinematics of the xuelongshan high strain zone northermost parts of the ailao shan red river shear zone in the xuelongshan range mylonitic foliation mainly trends nw se on steep foliation and flatted foliation mineral stretching lineation is various from gentle to steep and ductile shear senses indicate a left lateral top to the northwest shear movement on the eastern limb and a left lateral top to the southeast shear on the western limb of the range these dome related ductile geometries and kinematics namely d1 deformation represent regional high temperature metamorphism due to crustal thickening the superimposed sinistral strike slip shearing of d2 deformation occurred locally along the earlier domal fabrics metamorphism migmatization and the emplacement of leucogranitic veins associated with partial melting were syntectonic with the regional scale upright antiform la icp ms u pb dating of zircons reveals the late permian triassic and oligocene thermal events the latter event ca 33 26 ma or possibly earlier from the leucogranitic veins corresponds to the regional metamorphism during crustal thickening along the xuelongshan these data indicate that the jiali xuelongshan diancangshan ailao shan high strain zones can belong to a system around the eastern himalayan syntaxis ehs and that the xuelongshan zone played a role in linking other segments between the tibet to indochina in cenozoic

crustal structure beneath se tibet from joint analysis of receiver functions and rayleigh wave dispersion new constraints on the pattern of crustal flow in se tibet are obtained from joint analysis of receiver functions and rayleigh wave dispersion with a newly deployed seismic array the crust in the sichuan yunnan diamond block has an average thickness of 45 km and gradually thins toward the indo china block to the west and the yangtze block to the east high vp vs ratios are detected to the west of the xiaojiang fault but not in the yangtze block to the east the s wave velocity profile reveals that intra crustal low velocity zones ic lvzs are strongly heterogeneous with two lvzs in the middle and mid lower crust respectively in marked contrast to previous observations of a single lvz combined with other observations the two ic lvzs are interpreted as isolated channels of crustal flow at different depths beneath se tibet resulting in the observed complex pattern of radial anisotropy and further elucidating patterns of flow and deformation

pliocene to present morphotectonics of the dien bien phu fault in northwest vietnam abstract the north to northeast trending dien bien phu fault dbpf zone appears to the south of the red river fault rrf zone sharing the spatial alignment of the xianshuihe xiaojiang fault xxf and extending over a distance of 150 km from yunnan china through northwest vietnam into laos although the dbpf is one of the most conspicuous active fault systems in indochina it is less studied than the rrf and xxf and its quantified kinematics remain mostly unknown our detailed modern fault trace mapping compiled from topographic maps stereographic aerial photos aster satellite imageries and field reconnaissance reveals new information on the fault geometry the slip magnitude and distribution along the fault and the relationship between river channel offset and fault activity the geometry of the modern dbpf is complex consisting of single strands and stepovers abundant geomorphic expressions along the dbpf illustrate that the modern fault is dominated by sinistral motion and the present left lateral component of motion is also clearly demonstrated by the existence of numerous rivers offsets multiple offsets of geomorphic features along the fault are recognized and reconstructed and the largest sinistral displacement on the dbpf is ca 12 5 km based on drainage network restoration because sinistral motion likely initiated approximately 5 ma the most probable pliocene to present average slip rate on the dbpf is on the order of 2 5 mm yr based on the slip rate the dbpf could generate an earthquake with a magnitude greater than m w 7 and a recurrence interval of 500 to 1000 yr the combined gps velocity fields observed from northwest vietnam and south china reveal approximately 2 to 3 mm yr left lateral slip across the dbpf and significant east west extension exists in the western crustal block of dbpf although the boundary fault system of the active crust rotation around the eastern himalayan syntaxis i e xxf does not cut the rrf the pliocene to present activity along the dbpf favors the possibility that the tectonic shear has been transmitted across the rrf and taken up on the dbpf the results of this study suggest that the modern dbpf zone acts as a reactivated fault with a different slip sense from its previous phase and plays a role as an eastern boundary of the crustal deformation in northern indochina

two phase exhumation along major shear zones in the se tibetan plateau in the late cenozoic three continent scale shear zones are arguably the most outstanding structural features in the southeastern tibetan plateau and therefore their tectonic and landscape evolution have significant implications for understanding the history and mechanisms of intracontinental mountain building and plateau growth this study presents low temperature thermochronology from the gaoligong and chongshan shear zones glsz and cssz and quantitative analyses of fluvial longitudinal profiles of tributaries in the salween drainage which lies between the shear zones apatite and zircon u th he data reveal a two stage exhumation history for both shear zones rapid and prominent cooling in the middle miocene followed by a second lower magnitude cooling event in the late miocene to early pliocene ductile transpressional shearing is inferred to have caused the first cooling continuing until 11 ma the northward migration of the tectonic events along the mogok metamorphic belt and glsz and synchronous dextral displacement along the jiali fault indicate the dominant role of the north advancing eastern himalayan syntaxis on the surrounding structures increased river incision is identified in the middle salween drainage leading to two segment river profiles and further exhumation along the glsz and cssz the tributary transient response could result from temporal changes in uplift or adjustments of the trunk channel to climatic change furthermore glaciers play an important role in shaping the landscape of the upper reaches of catchments in the northern segment of the shear zones different drivers for the two exhumation events may reflect distinct stages of plateau growth characterized by different crustal deformation patterns

cenozoic exhumation of the ailaoshan red river shear zone new insights from low temperature thermochronology continental scale shear zones play an important role in accommodating block extrusion and rotation as shown by deformation on the ailaoshan red river shear zone asrrsz in the se tibetan plateau this study presents 13 apatite u th he 11 zircon u th he and three apatite fission track dates together with thermal modeling in the ailaoshan and xuelongshan segments alsz and xlsz of the shear zone to investigate its cenozoic exhumation history and mechanism which are critical for understanding its tectonic and landscape evolution our results combined with published chronologic data reveal that shear zone rocks along the alsz experienced prominent and rapid cooling from high temperature 500 c to 120 60 c at a rate of 75 100 c myr during 29 17 ma with northwestward younging onset a second lower magnitude accelerated cooling occurred at 14 10 ma along the alsz at a rate of 20 30 c myr with a later initiation on the xlsz at 5 ma and continuing to present with a cooling rate of 20 c myr thermal modeling reveals a single rapid cooling phase with a rate of 17 14 c myr in the eocene to early oligocene for samples outside the shear zones these three fast cooling episodes are directly related to deformation stages including crustal shortening across the se plateau sinistral ductile shearing along the asrrsz and dextral faulting with a dip slip component on the red river and weixi qiaohou faults along the shear zone flanks furthermore the northward migration of kinematic reversal and associated cooling along strike since the mid late miocene likely reflects the northward advance of the eastern himalayan syntaxis

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

structure kinematics and ages of transpression during strain partitioning in the chongshan shear zone western yunnan china abstract the chongshan shear zone extends from the eastern himalayan syntaxis to the lincang granitic pluton in yunnan province china the structure and kinematics show that the shear zone comprises mainly of mylonitic gneiss migmatite and schist with a dextral dominated strike slip motion in an n s trending northern segment and a sinistral strike slip shear in nw se trending middle and southern segments both were developed under a bulk regional scale sinistral transpression shrimp and la icpms u pb and 40 ar 39 ar dating reveal two tertiary magmatic events along the zone followed by younger sinistral strike slip shear the eocene magmatic event c 55 38 ma followed by metamorphism at c 36 ma happened before the strike slip motion the strike slip shear along the zone began c 32 ma which generated shear heating from 32 to 22 ma the 40 ar 39 ar ages of syn kinematic micas range from 19 to 14 ma and indicate that the strike slip shear continued to this time with coeval transpressional exhumation and uplift of the metamorphic rocks along the biluoxueshan chongshan chain the chongshan zone is thus a cenozoic shear zone which was contemporaneous with motion on the left lateral ailao shan red river shear zone and the right lateral gaoligong shear zone and should be important in accommodating the northwards movement of india during collision during oligocene to miocene times the continental block that was extruded between the ailao shan red river and gaoligong shear zones was dismembered into at least two major fragments by the chongshan shear zone

intracontinental deformation within the india eurasia oblique convergence zone case studies on the nantinghe and dayingjiang faults the most striking structural features in the interior of the shan plateau southeast of the eastern himalayan syntaxis are a series of ne trending faults that exhibit sinistral movement and an arcuate geometry their origin and tectonic evolution remain poorly understood furthermore a switch in slip sense is recorded along many of these faults but the timing of kinematic reversal is still unclear hindering an understanding of the causal geodynamic mechanisms we conducted an integrative study of apatite and zircon u th he thermochronology ar ar geochronology and structural and geomorphic analysis to decipher the evolution of two major ne trending faults the nantinghe and dayingjiang faults at least three deformation stages are identified within the nantinghe fault zone including top to the se ese thrusting dextral ductile strike slip shearing and sinistral movement zircon and apatite u th he data collected from the northeastern terminus of the nantinghe fault reveal rapid cooling in the early miocene combined with the ar ar data from sinistrally sheared mylonite left lateral movement on the nantinghe fault is inferred to have initiated as early as ca 20 ma the dayingjiang fault reactivated as a sinistral brittle fault along the dextral yingjiang shear zone a two stage thermal history is identified along the shear zone with prominent cooling during dextral ductile shearing in the early to mid miocene followed by a lower magnitude cooling episode at ca 11 ma caused by sinistral transtension along the dayingjiang fault the evolution of the nantinghe and dayingjiang faults suggests that the ne trending fault system in the shan plateau may have developed along preexisting structures and underwent diachronous slip sense inversion in the late cenozoic the northward advance of the eastern himalayan syntaxis caused a major change in both the regional stress field and fault geometries in the eastern india eurasia oblique convergence zone contributing to the inversion of fault kinematics

paleomagnetic constraints on the mesozoic cenozoic paleolatitudinal and rotational history of indochina and south china review and updated kinematic reconstruction abstract paleomagnetic data have long been used to hypothesize that the cenozoic extrusion of the indochina block along the left lateral ailao shan red river fault as a result of the india asia collision may have been associated with a major southward paleolatitude shift of as much as 10 15 and a vertical axis rotation of as much as 25 40 however although numerous paleomagnetic studies have been conducted in the southeast margin of the tibetan plateau and in the indochina region during the last few decades the detailed rotation as well as the latitudinal displacement of the indochina block remain controversial because of apparently contradicting paleomagnetic results geological constraints also yield contrasting estimates on the amount of displacement along different segment of the ailao shan red river fault 700 200 km in the northwest but only 250 km in the southeast in this paper the available paleomagnetic data from the southeast margin of the tibetan plateau and indochina as well as the south china block from jurassic and younger rocks are compiled and critically reviewed using the new paleomagnetic toolkit on paleomagnetism org our results show that 1 the south china block has declinations that reveal no significant rotations relative to eurasia since latest jurassic inclinations are consistently shallower than expected which is likely the result of inclination shallowing in sedimentary rocks 2 there is no paleomagnetically resolvable southward motion of the indochina block with respect to eurasia based on the paleomagnetic data paleomagnetic inclinations are in fact lower than expected probably due to inclination shallowing in sediments 3 paleomagnetic declinations reveal large more or less coherently rotating blocks in the northern indochina domain and the se tibetan margin that rotated up to 70 clockwise much more than the 10 15 rotation of the stable se part of the indochina block these blocks are bounded by fold thrust belts and strike slip faults which we interpret to have accommodated these block rotations during the cenozoic we designed a new tool on the online open access portal paleomagnetism org that allows testing whether euler rotations in a kinematic reconstruction fulfill paleomagnetic data using this tool we built a first order kinematic reconstruction of rotational deformation of northwest indochina in cenozoic we show that the northwestern part of indochina extruded 350 km more along the ailao shan red river fault than the southeastern part accommodated by internal northwest indochina rotation and deformation estimates of 250 km of extrusion of the southeastern part of the indochina then predicts 600 km of left lateral motion along the northwestern part of the ailao shan red river fault which reconciles the small and large estimates that prevail in the literature of extrusion of indochina from the tibetan realm during the cenozoic india asia collision