mobility of rare earth and other elements during crystallization of peralkaline silicic lavas abstract pantellerite lavas of the dormant caldera volcano mayor island new zealand have thick nonhydrated obsidian selvages at the tops and bases and crystalline microspherulitic interiors the flows were chemically homogeneous on emplacement but the crystalline portions have lost significant na f cl cs y and ree percentage losses of y and ree may exceed 60 ce yb ratios decrease by as much as 20 but eu eu ratios are unchanged loss of y and ree is attributed to the expulsion at near solidus temperatures of y ree 3 chloride complexes but other complexing agents may have contributed to this mobility na is also lost in the same manner groundwater has introduced mg and sr and leached or redistributed na cs and halogens analysis of hydrated glassy plinian pumice shows that secondary hydration has not affected y and ree concentrations the elements na mg f cl sr cs y and ree are highly mobile during the crystallization of peralkaline silicic melts and should not be used in petrogenetic evaluations these elements but not y and ree are also redistributed during secondary hydration processes magmas of undersaturated peralkaline composition will be similarly affected

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

characterization of airborne carbonate over a site near asian dust source regions during spring 2002 and its climatic and environmental significance 1 during spring 2002 three dust storm events were monitored by filter sampling in xi an near an asian dust source region of northwest china the carbonate co32 fraction was determined by sample acidification and thermal evolution the co32 accounted for 8 0 0 8 of particles with aerodynamic diameter 2 5 m pm2 5 during dust storms and 4 7 3 0 of pm2 5 between storms the ratios of calcium to carbonate carbon were consistent with those of calcite caco3 the 13c and 18o abundances in dust storm samples were 2 7 0 7 and 5 8 1 5 which differed from 8 3 1 9 for 13c and 10 8 2 0 for 18o during normal conditions the 13c is positively correlated with 18o values r 0 78 this first measurement of isotopic abundance in asian dust indicates the potential to quantify its contribution at distant locations using receptor models by increasing the alkalinity of ocean water in the pacific ocean and buffering the atmospheric acidity of east asia the large amounts of airborne co32 as high as 44 8 tg yr 1 entrained by asian dust may provide an important atmospheric alkaline carbon reservoir for large scale climatic and environmental changes

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

geodetic measurement of crustal motion in southwest china global positioning system measurements performed over a 2 4 yr period confirm the xianshuihe xiaojiang fault system as one of the primary active structures in southwest china stations southwest of these faults show southerly motions of 5 15 mm yr relative to the western sichuan basin and stations in a 200 km geodetic network located northwest of the basin move at only 0 5 mm yr these results are consistent with clockwise rotation of southwestern sichuan and western yunnan about the eastern tibetan syntaxis accommodated by left lateral slip of 12 4 mm yr on the xianshuihe xiaojiang fault system the results imply that if eastward extrusion of crustal material from the plateau occurs at present it is not accommodated by east west shortening along the margin of the plateau and must involve wholesale eastward motion of low lying regions to the east

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

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

nonlinear characteristics of paleoseismicity in china detailed studies of historical seismicity and paleoseismological data for major late quaternary faults in china reveal spatial and temporal patterns in paleoseismic activity associated with these faults analysis of space time distributions of late quaternary faults and consideration of new models for deformation of the asian continent provide a basis for proposing a division of china and surrounding areas into five active tectonic provinces slip rates for active faults are highest in the himalayan collision zone between the indian and eurasian plates and gradually decrease away from the collision zone into the adjacent active tectonic provinces paleoearthquake recurrence intervals in the active tectonic provinces of china reflect seismogenic properties that are closely related to the position of these provinces relative to the converging indian and eurasian plates average recurrence intervals are 2000 years to as little as 310 900 years for active faults in the qinghai tibetan active tectonic province whereas recurrence intervals are 2000 4500 years in the xinjiang active tectonic province and longer than 2000 years to as much as 7250 years in the north china active tectonic province although average recurrence intervals are closely related to the slip rates of late quaternary faults no simple linear relationship exists between recurrence interval and slip rate further analysis of paleoseismicity on major active faults shows that there are temporal variations in recurrence intervals the case studies also indicate that for some provinces faults or fault segments there are three paleoseismic patterns linear logarithmic and stepped in the logarithmic and stepped patterns the earthquake temporal sequence is characterized by active periods earthquake clusters with relatively short recurrence intervals and quiet periods lack of clustering and relatively long recurrence intervals

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

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

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

northwest trending middle cenozoic left lateral faults in southern yunnan china and their tectonic significance abstract the northwest striking jianshui qujiang and chuxiong faults and probably the zhongdian fault south china show evidence for different amounts of middle cenozoic pre pliocene and post early paleogene left lateral displacement that range from 6 to 25 km the age and orientation of the left lateral faults suggest that the faults are related to a regional deformational event associated with important left lateral shear on the ailao shan shear zone which lies 50 70 km to the south identification of these faults extends left lateral shear during this deformational event farther to the northeast than previously recognized unlike the ailao shan shear zone these faults do not appear to be part of a through going nw trending shear zone these faults are interpreted to be the northernmost part of a nw trending boundary whose main structure the left lateral ailao shan shear zone forms a broad zone of mylonitic rocks bounding a crustal fragment that rotated clockwise around the eastern himalayan syntaxis following middle cenozoic left lateral displacement only the jianshui and qujiang faults exhibited a reversal of displacement in post miocene time this reversal is interpreted to be the result of counterclockwise rotation within the broad n s striking left lateral xiaojiang fault zone none of the post miocene displacement on these two faults appears to be related to post miocene right lateral displacement on the red river fault system the chuxiong fault may have reversed its early left lateral displacement but evidence from surface geology for young and active right lateral displacement is not clear the zhongdian fault appears to have undergone only left lateral displacement some of which may be middle cenozoic in age and some post miocene in age active displacement on the zhongdian fault is interpreted to mark the eastern boundary for a small crustal fragment that rotates clockwise around the eastern himalayan syntaxis

transformation of displacement between strike slip and crustal shortening in the northern margin of the tibetan plateau evidence from decadal gps measurements and late quaternary slip rates on faults abstract studies of late quaternary geological slip rates and the gps decadal slip rates along the major strike slip faults in the northern margin of the tibetan plateau show that slip rates remain relatively constant along the middle sections of each fault and decrease rapidly toward the ends our recent studies suggest that the slip rates are low

lateral extrusion in transpression zones the importance of boundary conditions the homogeneous transpression strain model formulated by sanderson and marchini journal of structural geology 6 449 458 1984 has proved to be a useful tool in the analysis of complex three dimensional deformation patterns however some of the boundary conditions introduced in the mathematical model may be unrealistic and unnecessarily restrictive in this paper a strain matrix for unconfined transpression and transtension is derived in which material is allowed to move not only vertically but also horizontally in and out of the deforming zone parallel to its length lateral extrusion three end member plane strain components are defined wrench simple shear pure shear in xy lateral stretch and pure shear in yz vertical stretch these biaxial strains can be viewed as the apices of a strain triangle for unconfined transpression or transtension the edges of the triangle correspond to triaxial pure shear non coaxial biaxial lateral extrusion and the triaxial confined transpressional or transtensional strain of sanderson and marchini during unconfined transpression the orientation and in particular the geometry k value of the finite strain ellipsoid depends upon not only the amount of shortening across the zone and the amount of strike slip parallel to the zone but also upon the ratio of vertical to lateral stretch this can present serious difficulties when attempting to use finite strains to infer the direction and magnitude of zone boundary displacements examples of transpression zones in which there is evidence of a component of lateral extrusion are described from sw cyprus and central scotland these examples illustrate that antithetic strike slip shearing is a kinematic requirement of laterally unconfined transpression implying that synchronous shear sense indicators may give opposite senses of movement in shear zones specific geometric and mechanical boundary conditions together with internal fault zone rheologies may favour the lateral extrusion of material kinematic partitioning can occur to form fault bounded domains in which end member biaxial and or non coaxial strains are developed analysis of such domains can give a clearer understanding of regional scale triaxial deformations these findings illustrate the importance of establishing displacement boundary conditions when qualitatively or quantitatively analysing crustal deformation zones

investigation on the dynamic rupture of the 1970 ms 7 7 tonghai yunnan china earthquake on the qujiang faultinvestigation on the dynamic rupture of the 1970 ms 7 7 tonghai yunnan china earthquake on the qujiang fault

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

asymmetrical river valleys and their tectonic significance in the maxianshan area ne tibetan plateau abstract the geometry of river networks is particularly sensitive to active tectonic deformation morphotectonic analyses conducted using geomorphic indices and numerical models are useful methods with which to identify such deformation the northeastern ne margin of the tibetan plateau is characterized by active tectonics easily erodible bedrock and well developed valleys and is thus an ideal region for studying the effects of tectonics on the landscape evolution here we firstly identify the systemic asymmetrical valleys in the maxianshan area ne tibetan plateau to quantitatively analyze the asymmetrical characteristics of these valleys identified in the southern maxianshan 33 parallel streams were investigated by using two drainage basin analytical techniques namely the transverse topographic symmetry factor t and asymmetry factor af our results show that the mean t value is 0 14 magnitude and 319 08 direction and the majority of the af results are

characteristics of the active xiaojiang fault zone in yunnan china a slip boundary for the southeastward escaping sichuan yunnan block of the tibetan plateau abstract the xiaojiang fault zone within the yunnan province china is one of the most active fault zones of the southeastern edge of the tibetan plateau this n s trending 400 km long fault zone defines the southern part of the eastern boundary of the sichuan yunnan block which is escaping southeastward from the tibet plateau and rotating around the eastern himalayan syntaxis the middle section of the fault zone splits into two branches each branch fault consists of several en echelon faults basins of various ages have developed on the step overs between the secondary faults the left lateral strike slip rate along the eastern branch is up to 9 mm a and that on the western branch is 7 mm a more than 10 m 6 historic earthquakes have occurred along the fault zone the largest was the 1833 songming earthquake of m 8 four earthquake rupture zones were discovered along the fault zone 15 trenches have been excavated along every major segment of the fault zone and 4 5 paleoearthquakes have been distinguished along the xiaojiang fault zone the average strong earthquake recurrence interval is 2000 2500 years

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

an empirical relationship between thermal conductivity and elastic wave velocities in sandstone measurements in three samples of very clean quartz sandstone in the porosity range 4 16 under dry and 100 water saturated conditions show that p and s wave velocities are linearly correlated with thermal conductivity the experimental results agree with the theoretical relation between seismic velocities predicted by the kuster and toksoz model 1974 and thermal conductivity predicted by weighted geometric mean

generic along strike segmentation of afar normal faults east africa implications on fault growth and stress heterogeneity on seismogenic fault planes understanding how natural faults are segmented along their length can provide useful insights into fault growth processes stress distribution on fault planes and earthquake dynamics we use cumulative displacement profiles to analyze the two largest scales of segmentation of 900 normal faults in afar east africa we build upon a prior study by manighetti et al 2009 and develop a new signal processing method aimed at recovering the number position displacement and length of both the major i e longest and the subordinate secondary segments within the faults regardless of their length age geographic location total displacement and slip rate 90 of the faults contain two to five major segments whereas more than 70 of these major segments are divided into two to four secondary segments in each hierarchical rank of fault segmentation most segments have a similar proportional length whereas the number of segments slightly decreases with fault structural maturity the along strike segmentation of the afar faults is thus generic at its two largest scales we summarize published fault segment data on 42 normal reverse and strike slip faults worldwide and find a similar number two to five of major and secondary segments across the population we suggest a fault growth scenario that might account for the generic large scale segmentation of faults the observation of a generic segmentation suggests that seismogenic fault planes are punctuated with a deterministic number of large stress concentrations which are likely to control the initiation arrest and hence extent and magnitude of earthquake ruptures

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

geological and geomorphic evidence for activity of the mengzi fault along the southeastern margin of the tibetan plateau abstract few studies have been conducted on the activity of the mengzi fault system which is located to the southeast of the sichuan yunnan block the mengzi fault is distributed along the eastern margin of the mengzi basin however little is known about the location length and activity of the fault or the occurrence of paleo earthquakes during the late quaternary this paper studies the geometric distribution and activity of the fault via remote sensing imagery interpretation fault outcrops in the area faulted landforms and chronological analyses the results show that the mengzi fault extends from nandong kaiyuan basin in the north through the eastern margin of the mengzi basin to pingbian in the southeast eventually intersecting with the honghe fault the mengzi fault is approximately 250 km long and is characterized as a reverse strike slip fault we survey and calculate the offset gullies and terraces dislocated by the fault combined with sample dating we calculate the horizontal slip rate of the fault since 30 ka bp to be 0 91 1 56 mm a three paleo events since 30 40 ka bp are observed with a 10 ka major earthquake recurrence period we analyze the relationships among the mengzi fault southern xiaojiang fault and qujiang jianshui fault and note a slip rate loss of 8 mm a from the southern xiaojiang fault that was absorbed by reverse dextral strike slip faulting and lateral shortening of the qujiang jianshui fault and the mengzi fault the mengzi fault plays an important role in the adjustment of the large slip rate reduction along the southern xiaojiang fault moreover the mengzi fault has a similar tectonic position to the seismogenic faults of the 2008 wenchuan earthquake 2013 lushan earthquake and 2014 ludian earthquake and the mengzi fault and southern xiaojiang fault both accumulate the energy generated by the southeastward movement of the sichuan yunnan block studies on the mengzi fault are helpful for renewing our understanding of the tectonic patterns of the southeastern sichuan yunnan block and delimiting the boundary of the southeastern block margin furthermore because the cities of mengzi and kaiyuan are located along the mengzi fault this study has practical significance for earthquake disaster mitigation

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

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

varied thermo rheological structure mechanical anisotropy and lithospheric deformation of the southeastern tibetan plateau abstract to investigate the lithospheric structure and deformation of the tibetan plateau we present thermo rheological models for two transects across the southeastern tibetan plateau se tibet showing strong lateral heterogeneity the geodynamic implications are also investigated in relation to gps motions seismic anisotropy seismicity distribution and crustal isostatic state the unmatched pattern between pms and sks splittings which even intersect at right angles to the south of 26 n suggests the crust mantle decoupling constrained by a brittle load bearing layer at the uppermost mantle beneath the indochina block the decoupling may occur below the uppermost mantle the strong crust beneath the south china plate and indochina block implied by the seismicity distribution has two thick brittle load bearing layers indicating a coupled system the crust beneath the emeishan large igneous province elip also has two brittle load bearing layers but the brittle deformation is restricted to the topmost 10 km of the upper and lower crust only one brittle load bearing layer resides in the upper crust in the other part of the chuandian block combining with gps and pms splitting we can infer that the weak crust with seismicity restricted into the depth of

role of the red river shear zone yunnan and vietnam in the continental extrusion of se asia the 1000 km long nw se striking left lateral ailao shan red river shear zone runs from the southeastern corner of tibet to the gulf of tonkin and the south china sea it has been used as the prime example of a lithospheric scale strike slip fault that has accommodated between 500 and 1000 km of southeastwards extrusion of indo china away from the indian plate indentor central to the model of continental extrusion is that such faults cut through the entire lithosphere that shear heating resulted in high grade metamorphism and local anatexis and that the ages of sheared granites along the fault also date the timing of strike slip shearing however structural data from the red river shear zone clearly show that vertical strike slip faulting post dated metamorphism and granite emplacement most granites along the shear zone are mantle related granodiorites or within plate alkali granites formed prior to shearing along the red river shear zone left lateral kinematic indicators are ubiquitous within the red river mylonites but they are always lower temperature fabrics formed after peak sillimanite metamorphism and after granite crystallization it is suggested that left lateral strike slip shearing along the red river shear zone started after 21 ma not at 35 ma as previously thought and the fault was purely a crustal structure none of the geological features used to propose the 500 1000 km offsets are robust and the total finite offset remains unknown

late cenozoic to holocene deformation in southwestern sichuan and adjacent yunnan china and its role in formation of the southeastern part of the tibetan plateau from at least 2 4 ma to present crust in the southeastern part of the tibetan plateau west of the convex east xianshuihe xiaojiang fault system has deformed internally and rotated clockwise around the eastern himalayan syntaxis the northwest striking ganzi fault zone bounds the rotating crust on the north and has a total left slip of 78 100 km of which 60 km is transferred to the xianshuihe fault zone across a diffuse transfer zone and 22 40 km is absorbed by bending of older structures and crustal shortening crustal shortening is expressed along and east of the eastern end of the ganzi fault zone by mountains capped by permanent glaciers locally rising nearly 1000 m above the average elevation of the tibetan plateau a similar transfer of left slip into shortening occurs farther south across the xianshuihe fault in the high mountains around and east of gongga shan 7556 m the northwest striking convex east left lateral litang fault zone lies southwest of the ganzi xianshuihe xiaojiang fault zone and appears to be less well developed but otherwise similar to the ganzi fault zone the batang chenzhi and other northeast striking right lateral faults of small displacement occur within the rotating crustal fragment together with the left slip faults they accommodate east west shortening northeast of the eastern himalayan syntaxis south of this region of shortening the crust is extending to form grabens within the dali and southern xiaojiang fault systems and in the tengchong volcanic province the progressive change from shortening southward into extension is related to variations in strain that characterize the region from northeast to southeast of the eastern himalayan syntaxis the assemblage of structures in southwestern sichuan geometrically resembles structures of eocene to miocene age in southern yunnan that were positioned northeast of the eastern himalayan syntaxis similar to present day southwestern sichuan at the time of their development the similarity in the structural development in the two areas indicates that crust northeast of the syntaxis underwent a common evolution as the syntaxis migrated northward during the past 50 m y structures in sichuan are less fully developed than older structures in southwestern yunnan and can serve as a guide to reconstruct the progressive tectonic development in the region of the syntaxis deformation in these areas indicates that plateau formation has been complex inhomogeneous and diachronous at scales from 1000 km to less than 100 km

spatial variations in damage zone width along strike slip faults an example from active faults in southwest japan abstract field investigations reveal spatial variations in fault zone width along strike slip active faults of the arima takatsuki tectonic line attl and the rokko awaji fault zone rafz of southwest japan which together form a left stepping geometric pattern the fault zones are composed of damage zones dominated by fractured host rocks non foliated and foliated cataclasites and a fault core zone that consists of cataclastic rocks including fault gouge and fault breccia the fault damage zones of the attl are characterized by subsidiary faults and fractures that are asymmetrically developed on each side of the main fault the width of the damage zone varies along faults developed within granitic rocks of the attl and rafz from 50 to 1000 m in contrast the width of the damage zone within rhyolitic tuff on the northwestern side of the attl varies from 30 to 100 m the fault core zone is generally concentrated in a narrow zone of 0 5 5 m in width consisting mainly of pulverized cataclastic rocks that lack the primary cohesion of the host rocks including a narrow zone of fault gouge

nested strike slip duplexes and other evidence for late cretaceous palaeogene transpressional tectonics before and during india eurasia collision in thailand myanmar and malaysia the late cretaceous palaeogene structural and tectonic events in the northern region of sundaland represent a poorly known but potentially important orogenic development in se asia extensive late cretaceous s type granites extending from malaysia through thailand to myanmar have long been used to infer an episode of crustal thickening an inference supported by the presence of late cretaceous eocene ophiolites in myanmar however structural evidence for a well developed associated fold and thrust belt has been lacking apatite and zircon fission track studies of thailand indicate a broad regional uplift from about 80 ma to 40 ma suggesting an episode of crustal thickening but the uplift amount is modest and not that expected for a major fold and thrust belt left lateral motion on major nw se trending strike slip fault zones mae ping and three pagodas faults in myanmar and thailand has been attributed to himalayan tibetan escape tectonics this paper demonstrates that the fault zones are considerably more complicated than just nw se trends they are a network of branching faults with important north south trends as well as nw se trends they form large scale nested strike slip duplex structures and affect a region over 1000 km long and up to 250 km wide this diffuse branching network of strike slip fault trends may represent a substantial late cretaceous palaeogene transpressional belt himalayan escape tectonics represent later increments of deformation with both oligocene sinistral and late oligocene recent dextral reactivation