uplift and convergence along the himalayan frontal thrust of india along the himalayan thrust front in northwestern india terrace deposits exposed 20 to 30 m above modern stream level are interpreted to have been uplifted by displacement on the underlying himalayan frontal thrust a radiocarbon age limits the age of the terrace to 1665 215 calendar bc 3663 215 radiocarbon years before present yielding a vertical uplift rate of 6 9 1 8 mm yr in combination with published studies constraining the dip of the himalayan frontal thrust fault to about 30 in the study area the observed uplift rate equates to horizontal shortening across the himalayan frontal thrust of 11 9 3 1 mm yr and the slip rate of the himalayan frontal thrust of 13 8 3 6 mm yr this is similar to previously reported rate estimates along the himalayan arc based on displacement of older plio miocene age rocks or the much shorter records of geodesy and historical seismicity the similarity is consistent with the idea that convergence across the himalayan front has occurred at a relatively steady rate through time the seismic expression of this deformation includes several great m 8 historical earthquakes which due to lack of surface rupture during those events have been attributed to their occurrence on blind thrusts yet the occurrence of a possible fault scarp in the field area indicates that past earthquakes have been sufficiently large to rupture to the surface and produce coseismic scarps these observations suggest a potential for earthquakes along the himalayan frontal thrust larger than those observed historically

3d seismic imaging of the shallow plumbing system beneath the ben nevis monogenetic volcanic field faroe shetland basin seismic reflection data allow for the 3d imaging of monogenetic edifices and their corresponding plumbing systems this is a powerful tool in understanding how monogenetic volcanoes are fed and how pre existing crustal structures can act as the primary influence on their spatial and temporal distribution this study examines the structure and lithology of host rock as an influence on edifice alignment and provides insight into the structure of shallow sub volcanic monogenetic plumbing systems the anticlinal ben nevis structure located in the northerly extent of the faroe shetland basin ne atlantic margin was uplifted during the late cretaceous and early paleocene by the emplacement of a laccolith and a series of branching sills fed by a central conduit seismic data reveal that multiple intrusions migrated up the flanks of the ben nevis structure after its formation c 58 4 ma kettla equivalent and fed a series of scoria cones and submarine volcanic cones these monogenetic edifices are distributed around the crest of the ben nevis structure the edifices are fed from a complex network of sills and transgressive sheets involving lateral magma migration of tens of kilometres before extrusion at the surface this work highlights the importance of underlying basin structures in influencing the sites and development of subaerial monogenetic fields and the importance of lateral magma flow within volcanic systems supplementary materials the results of the statistical alignment analysis of the monogenetic edifices are available at https doi org 10 6084 m9 figshare c 3662809

vent distribution and its relation to regional tectonics cappadocian volcanics turkey abstract the distribution of polygenetic and monogenetic volcanoes of the neogene quaternary cappadocian volcanic province cvp is analyzed to investigate the relationship between vent location and regional tectonic lineaments two fault systems exist in the province one system miocene quaternary tuzgolu ecemis system is oblique whereas the other system late miocene pliocene cvp system is parallel to the long axis of the cvp the polygenetic volcanoes are aligned parallel to the second system but concentrate around the major faults of the first system regional offsets are proposed along the first fault system based on the distribution of the polygenetic volcanoes the monogenetic volcanoes group into five geographically distinct clusters in the western part of the cvp the monogenetic cones are aligned parallel to the cvp system whereas in the central part the cones are fed by dikes injected along the recent fractures of the tuzgolu ecemis system in the eastern part the monogenetic cones form along the radial fractures of the erciyes composite volcano

effect of stress fields on magma chamber stability and the formation of collapse calderas 1 the summits of many of the earth s and other planets larger volcanoes are occupied by calderas that formed by collapse into an evacuating underlying magma chamber these collapse calderas are typically several tens of square kilometers in area and are commonly elliptical in shape we show that the long axes of late quaternary collapse calderas in the kenya rift valley the western basin and range province the snake river yellowstone plateau and the iceland rift zone are parallel to the upper crustal minimum horizontal stress direction sh as determined by independent criteria we suggest that circular magma chambers beneath these volcanoes became elliptical by stress induced spalling of their chamber walls by a mechanism that is analogous to the formation of breakouts in boreholes and tunnels in breakouts the hole becomes elongate parallel to the far field minimum stress in the kenya rift late pleistocene caldera collapse was accompanied by a 45 rotation of sh and an increase in the magnitude of the maximum horizontal stress sh the breakout model predicts increasingly unstable caldera walls under these conditions a possible explanation for the sudden appearance of so many collapse events in a volcanic setting that had never experienced them before this mechanism of stress change induced collapse may have played a role in other caldera settings

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

volcanic vents rooted on extension fractures and their geodynamic implications in the ethiopian rift abstract most of the extension fractures located in the ethiopian rift are related to rift dynamics and they have consistently similar orientations for hundreds of kilometers the orientation of extension fracture gives the local extension direction which is perpendicular to its horns end segments of an extension fracture we have established clear geometrical relationships between tectonics and volcanism in the main ethiopian rift by interpreting high resolution images obtained from landsat tm and spot satellites and by quantitatively analyzing the geometry of extension fractures elongated vents and linear volcanic clusters applying the relationships obtained we show that extension fractures in the rift served as channels for magma rising to the surface and that extension fractures underlie most of the elongated volcanic vents and linear volcanic clusters the geometry of extension fractures beneath volcanic edifices can be deduced from the shape of elongated vents and pattern of linear volcanic clusters rooted on them utilizing the orientations of extension fractures directly observed and those inferred from elongated volcanic vents and linear clusters we found that the extension direction of the main ethiopian rift is northwest southeast and that the direction has been rotated clockwise for about 20 in the time interval 2 83 to 0 023 ma the recent axis of rift opening is oriented n40 and located closer to the southeastern escarpment giving an asymmetric geometry to the main ethiopian rift mer

active faults and state of stress in the central part of the trans mexican volcanic belt mexico 1 the venta de bravo fault the central part of the trans mexican volcanic belt is being deformed by seismically active west east striking normal faults that cause pronounced scarps structural and seismic along strike discontinuities allow the following segmentation 1 the western segment the area between morelia and the los azufres volcanic center is characterized by 25 km long fault scarps that define the cuitzeo graben and the santa ana maya horst which has a relief 850 m with respect to the cuitzeo graben the faults cut several quaternary scoria cones as well as alluvium 2 the central neotectonic segment extends between maravatio in the west and altamirano volcano in the east the most prominent structure of this segment is the 45 km long venta de bravo fault with a relief 300 m the february 22 1979 mb 5 3 maravatio earthquake occurred on this fault the late quaternary vertical slip rate along the easternmost part of the venta de bravo fault is estimated at 2 mm yr the lateral extension of the segment is defined by the limits of the venta de bravo fault and the eastern termination of the cuitzeo graben 3 the eastern segment is made up of the acambay graben the limit between the central and eastern segments is defined by an extensional jog between the venta de bravo and pastores faults which indicates a left lateral strike slip component the most recent rupture of this segment occurred in the november 19 1912 ms 6 9 acambay earthquake that caused vertical displacements 50 cm along the faults flanking the graben stress determinations based on quaternary scoria cone alignments the focal mechanism of the 1979 earthquake and the inversion of striation measurements indicate a stress field with sv sene snnw the fault striations as well as the focal mechanism indicate a minor but consistent left lateral strike slip component the observed stress and deformation can be explained by the superposition of two sources of stress isostatically compensated surface loads related to the high elevation of the trans mexican volcanic belt probably cause horizontal deviatoric tension and the observed crestal normal faults which strike parallel to the axis of the volcanic belt the observed left lateral strike slip component on the other hand can be explained by compressional far field stresses caused by loads at the boundary between the cocos and north american plates the orientation of the faults with respect to the direction of plate convergence is a prefered orientation for left lateral slip along the observed faults alternatively the observed left lateral strike slip component may accommodate trench parallel motion of crustal blocks in southwestern mexico

interseismic strain accumulation on the himalayan crustal ramp nepal the departement of mines and geology has been monitoring the seismicity of the central himalayas of nepal since 1985 intense microseismicity and frequent medium size earthquakes ml 4 tend to cluster beneath the topographic front of the higher himalaya this 10 20km deep seismicity also correlates with a zone of localized uplift that has been evidenced from geodetic data both microseismic and geodetic data indicate strain accumulation on a mid crustal ramp that had been previously inferred from geological and geophysical evidence this ramp connects a flat decollement under the lesser and sub himalaya with a deeper decollement under the higher himalaya and probably acts as a geometric asperity where strain and stress build up during the interseismic period the large himalayan earthquakes could nucleate there and probably activate the whole flat and ramp system up to the blind thrusts of the sub himalaya

the pattern of circumferential and radial eruptive fissures on the volcanoes of fernandina and isabela islands galapagos maps of the eruptive vents on the active shield volcanoes of fernandina and isabela islands galapagos made from aerial photographs display a distinctive pattern that consists of circumferential eruptive fissures around the summit calderas and radial fissures lower on the flanks on some volcano flanks either circumferential or radial eruptions have been dominant in recent time the location of circumferential vents outside the calderas is independent of caldera related normal faults the eruptive fissures are the surface expression of dike emplacement and the dike orientations are interpreted to be controlled by the state of stress in the volcano very few subaerial volcanoes display a pattern of fissures similar to that of the galapagos volcanoes some seamounts and shield volcanoes on mars morphologically resemble the galapagos volcanoes but more specific evidence is needed to determine if they also share common structure and eruptive style

geometric evolution of a plate interface branch fault system its effects on the tectonic development of the himalayas abstract crustal deformation due to fault slip depends strongly on fault geometry and fault geometry is changed by the deformation of the crust this feedback mechanism causes the geometrical evolution of the fault system we have studied the progress of the geometrical evolution of a plate interface branch fault system through numerical simulation based on elastic viscoelastic dislocation theory if the plate interface is smooth no significant change occurs in fault geometry if the plate interface has a ramp we observe the gradual horizontal motion of the ramp toward the hanging wall side of the interface at half the plate convergence rate the offset of the ramp decreases with time the dip angle of thrust faults branching from the plate interface increases more rapidly as the dip of the fault increases we have applied these results to the plate interface branch fault system at the india eurasia collision boundary and obtained a scenario for the tectonic development of the himalayas for the last 30 myr

present day kinematics at the india asia collision zone the collision of the indian subcontinent with asia drives the growth and evolution of the greater tibetan plateau region fault slip rates resulting from the relative motion between crustal blocks can provide a kinematic description of the distribution of presentday deformation i construct a three dimensional regional scale elastic block model of the india asia collision zone that is consistent with geodetic observations of interseismic deforma tion mapped fault system geometry historical seismicity and the mechanics of the earthquake cycle this mechanical model of the elastic upper crust yields a set of kinematically consistent fault slip rates and block motions that may serve to constrain dynamic models of continental crustal dynamics

current shortening across the himalayas of nepal summary underthrusting of the indian lithosphere beneath the himalayas occurs during the quaternary period along a gently north dipping main basal detachment main himalayan thrust mht from which the southernmost emergent ramp main frontal thrust mft branches historical seismicity shows that slip on the mht is frequently accommodated through m 8 shallow earthquakes but shows a seismic gap in western nepal this absence of major historical earthquakes in western nepal can be explained either by an aseismic slip on the mht or a longlived elastic strain accumulation to test these hypotheses the present day displacement field has been measured for a gps network formed of 35 sites the updated solution presented in this paper combines data from 1995 1997 1998 and 2000 measurements the lack of deformation less than 3 10 8 yr 1 through the outer belt does not fit with a regional aseismic slip along the southern part of mht a less than 3 mm yr 1 aseismic slip could nonetheless affect restricted areas of the outer belt in contrast a strain accumulation of more than 30 10 8 yr 1 is measured south of the higher himalayas in a zone where an intense microseismicity reflects a stress build up it is presumably generated by locking of the aseismic creep that occurs along the mht beneath the higher himalayas and tibet the displacement field is simulated by a dual dislocation model that takes into account the pattern of microseismicity and particularly a segmentation between central and western nepal the best fit between the measured and simulated displacement fields is obtained with 19 mm yr 1 thrust and 0 1 mm yr 1 dextral strike slip components along a 117 ne dislocation locked to a depth of 20 21 km beneath western nepal and 19 20 mm yr 1 thrust and 0 2 mm yr 1 dextral strike slip components along a 108 ne dislocation locked to a depth of 17 21 km beneath central nepal the width of the locked zone between the main frontal thrust and the creeping zone is of the same order but rather greater in western nepal than in central nepal therefore it is expected that m 8 earthquakes could occur in western nepal

tectonic and magmatic controls on the location of post subduction monogenetic volcanoes in baja california mexico revealed through spatial analysis of eruptive vents post subduction 12 5 ma to less than 1 ma monogenetic volcanism on the baja california peninsula mexico formed one of the densest intra continental areas of eruptive vents on earth it includes about 900 vents within an area 700 km long n s and 70 to 150 km wide w e this study shows that post subduction volcanic activity was distributed along this arc and that modes exist in the volcano distribution indicating that productivity of the magma source region was not uniform along the length of the arc vent clustering vent alignments and cone elongations were measured within eight monogenetic volcanic fields located along the peninsula results indicate that on a regional scale vent clustering varies from north to south with denser spatial clustering in the north on the order of 1 9 10 1 vents km2 to less dense clustering in the south on the order of 7 8 10 2 vents km2 san quintin san carlos jaraguay and santa clara are spatially distinct volcanic fields with higher eruptive vent densities suggesting the existence of individual melt columns that may have persisted over time in contrast the san borja vizcaino san ignacio and la purisima vent fields show lower degrees of vent clustering and no obvious spatial gaps between fields thus indicating an area of more distributed volcanism insight into the lithospheric stress field can be gained from vent alignments and vent elongation measurements within the fields located along the extinct subduction related volcanic arc elongation patterns of cinder cones and fissure fed spatter cones vent clusters and vent alignments trend nw se and n s within the santa clara field located more to the west within the forearc elongation patterns of the same volcanic features trend ne sw these patterns suggest that magmatism was more focused in the forearc and in the northern part of baja california than in its southern region within the extinct arc magma ascent created volcano alignments and elongate cones parallel to nw se to n s oriented tectonic structures in the forearc the existence of n s and ne sw oriented volcanic features indicates a rotation in the stress field orientation compared to the arc

spatially variable extension in southern tibet based on gps measurements 1 we use global positioning system gps data and kinematic block models to study the present day deformation of southern tibet gps data from 33 sites in southern tibet and nepal surveyed between 1991 and 2000 reveal 13 2 mm yr of n110 e extension between lhasa and shiquanhe 80 e 91 e of which 9 7 3 0 mm yr represents permanent extension of the tibetan crust the remaining 3 mm yr results from elastic deformation from the locked curving main himalayan thrust fault this extension is spatially nonuniform one half to two thirds of the permanent extension is concentrated across the yadong gulu rift with an opening rate of 6 5 1 5 mm yr most of the remainder occurs on or near the thakkola graben with little extension across the rifts between them differential velocities of sites north and south of the yarlung zangbo suture in western tibet imply that the suture or an adjacent structure may be active as a strike slip fault a numerical model suggests that right lateral strike slip on the yarlung zangbo suture may extend from the karakorum fault zone in the west at least to the yadong gulu rift in the east with 3 mm yr slip rate accommodating part of the eastward extrusion of tibet the convergence directions inferred from gps are consistent with slip vectors of earthquakes however the rate of slip of india beneath tibet along the himalaya is lower than those previously estimated we estimate a slip rate of 12 4 0 4 mm yr between longitudes 83 e and 88 e and 17 1 and 19 1 mm yr in the western and eastern himalaya respectively the variable slip rate correlates with the variable extension rate in southern tibet and we suggest that it results from variation in the deformation rate of the overriding tibetan crust we infer that the slower convergence rate in the central himalaya is significant

new criteria for systematic mapping and reliability assessment of monogenetic volcanic vent alignments and elongate volcanic vents for crustal stress analyses abstract linear arrays of monogenetic volcanic vent alignments represent an important source of stress strain data from volcanic regions of the earth and other planets currently however there is no standard methodology for mapping vent alignments or for assessing alignment reliability which are essential to defining a robust stress datum from vent alignments here we define a systematic method for defining monogenetic vent alignments by mapping the locations and shapes of vents elongation of vents into elliptical shapes is directly related to the trend of subsurface fissures that control alignments elongated vents therefore are critical for defining reliable regional vent alignments and also provide an independent means for assessing stress directions our reliability assessment system a b c d for vent alignments is based on the number of vents the standard deviation of vent center points from a best fit line the numbers and types of elongate vents the standard deviation of long axes of elliptical vents from a best fit line and in cases where alignments lack elongate vents by vent spacing distances we quantified morphometric parameters of well defined fissure fed vent alignments from polygenetic volcanoes and platform volcanic fields to establish appropriate threshold values for reliability assessments in this new method the combined analysis of vent locations and shapes optimizes the process of alignment mapping and the assessment of the reliability of alignments to be incorporated in stress analyses we provide quality ranking schemes for stress data derived from reliability assessed vent alignments and from elongate vents we demonstrate the utility of this new mapping and assessment methodology by analyzing monogenetic cinder cone fields within a platform volcanic field the san francisco volcanic field in arizona and within a volcanic field on the flank of a polygenetic volcano mount morning in antarctica

modelling the spatial distribution of present day deformation in nepal how cylindrical is the main himalayan thrust in nepal summary the structure of the himalayas in nepal is characterized by underthrusting of the indian lithosphere beneath the chain along the main himalayan thrust mht the mht is affected by major earthquakes of m 8 that have ruptured segments several hundred kilometres in length the study of historical seismicity underlines the existence of a significant seismic gap between the 1905 kangra and the 1934 bihar nepal earthquake areas in western nepal this contribution presents a numerical model of the interseismic deformation using the adeli 2 d finite element code a parametric study has been performed to estimate the influence of the topography the geometry of the flat ramp flat transition of the mht and its rheology the results of these runs are compared along three cross sections of eastern central and western nepal using various recordings of the active deformation of nepal neotectonics microseismicity gps velocities vertical displacement rates deduced from comparative levellings the results of this study suggest 1 a small amount of aseismic slip along the southern part of the mht and 2 an abrupt change in geometry of the mht between central and western nepal the stress build up in eastern and central nepal is produced by coupling of a bend flat ramp transition of the mht and a brittle ductile transition at the foot of the ramp in western nepal on the other hand stress build up is only induced by a brittle ductile transition located along the low angle part of the mht this difference suggests the presence of a lateral ramp on the mht to allow transition between the central and western nepal geometries of the mht this change in mht geometries between central and western nepal is also clearly marked in the himalayan relief an abrupt decrease in altitude and incision between central and western nepal

new kinematic and geochronologic evidence for the quaternary evolution of the central anatolian fault zone cafz as the kinematics of active faults that bound the anatolian plate are well studied it is now essential to improve our understanding of the style and rates of intraplate deformation to constrain regional strain partitioning and improve seismic risk assessments one of these internal structures the central anatolian fault zone cafz was originally defined as a regionally significant left lateral tectonic escape structure stretching for 700 km in a ne direction across the anatolian plate we provide new structural geomorphic and geochronologic data for several key segments within the central part of the cafz that suggest that the sinistral motion has been overstated the ecemis fault the southernmost part of the cafz has a late quaternary minimum slip rate of 1 1 0 4 mm a 1 slower than originally proposed farther north the erciyes fault has fed a linear array of monogenetic vents of the erciyes stratovolcano and 40ar 39ar dating shows a syneruptive stress field of ese wnw extension from 580 130 ka to 210 180 ka in the erciyes basin and central part of the cafz we mapped and recharacterized the erkilet and gesi faults as predominantly extensional these long term geological rates support recent gps observations that reveal ese wnw extension which we propose as the driver of faulting since 2 73 0 08 ma the slip rates and kinematics derived in this study are not typical of an escape tectonic structure the cafz is a transtensional fault system that reactivates paleotectonic structures and accommodates e w extension associated with the westward movement of anatolia

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

the motion and active deformation of india measurements of surface displacements using gps constrain the motion and deformation of india and india eurasia plate boundary deformation along the himalaya the gps velocities of plate interior sites constrain the pole of the angular velocity vector of india with respect to eurasia to lie at 25 6 1 0 n 11 1 9 0 e approximately 6 west of the nuvel 1a pole of 3 ma plate motion the angular rotation rate of 0 44 0 03 myr 1 is 14 slower than the long term rate of 0 51 myr 1 insignificant velocities between plate interior sites indicate that the exposed indian plate is stable to within 7 10 9 yr 1 the observed contraction vector across the himalaya 20 mm yr veers from n20 e in the northwest himalaya to n25 w in east nepal consistent with east west extension of southern tibet

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

convergence across the northwest himalaya from gps measurements 1 horizontal velocities of 26 global positioning system gps stations in the northwest himalayan region provide new constraints on the partitioning of india eurasia convergence and elastic strain accumulation about the locked main frontal thrust mft the northwest striking karakorum fault slips at 11 4 mm yr and contributes to east west extension of southern tibet and westward motion of the northwest himalaya towards nanga parbat rather than playing a role in eastward extrusion of tibet crustal shortening across the himalaya occurs within a zone centered about 100 km north of the siwalik foothills and the mft model inversions of the gps data indicate that the mft is locked over a width of 100 km comparison with geologic mft slip rate estimates suggests that this zone is building up a slip deficit at a rate of 14 1 mm yr and will eventually fail in future great earthquakes

an approach using sar ers images to relate extension fractures to volcanic vents examples from iceland and madagascar abstract a new approach to the study of geometric relationships between tectonic structures and volcanic vents is presented it is based on the mapping of tectonic and volcanic features using high resolution imagery including synthetic aperture radar sar images of the european remote sensing satellite number one ers 1 we have evidenced new faults 1 n striking normal faults in the husavik fault zone of the north atlantic ridge and 2 nw striking faults belonging to the husavik transform fault zone associated to drag folds which testify to a dextral strike slip movement component we show that most of the volcanic edifices are located on extension fractures responsible for fissure eruptions volcanic linear clusters and elongated volcanoes this relationship is studied first in iceland where the geodynamics is well known using sar ers 1 imagery applied to the montagne d ambre in northern madagascar using aerial photographs this approach makes it possible to identify faults and the regional plio quaternary direction of extension i e n65 e to n85 e volcanoes forming linear clusters together with elongated volcanoes are interpreted to be located on extension fractures s or z shape of the linear clusters allowed us to determine the tips of extension fractures and consequently the orientation of the regional tension alignments of extension fractures depending on their s or z shape permitted us to infer conjugated faults

emplacement of volcanic vents and geodynamics of central anatolia turkey abstract observations on synthetic aperture radar sar scenes of the european remote sensing ers satellite and digital elevation models dems complemented by field structural analysis permit a new understanding of relationships between tectonics and volcanism since the late miocene 10 ma in central anatolia volcanic edifices form elongate stratovolcanoes linear clusters and volcanic ridges they indicate emplacement on tension fractures and tail crack or horsetail features for instance the kara dag volcano is rooted on a tail crack which accommodates a horizontal left lateral throw component at a fault termination caldera complexes of cappadocia are associated with horsetail fault patterns the emplacement of volcanoes also benefits from larger scale tectonic structures the erciyes dag volcano is localized by the sultan saz releasing bend which opens along the sinistral strike slip ecemis fault deformation has been analysed from tension fractures which are perpendicular to the direction of extension and from field structural analysis on a regional scale the tectonic regime responsible for the distribution of volcanic vents in this area of convergence and lateral extrusion is not compression but extension the central taurus range is the thermally uplifted shoulder of the adana cilicia basin which is related to lithosphere thinning westward movements in the northwestern part of the studied area are influenced by the active back arc aegean extension situated to the west farther to the south the direction of motion turns southwest and south under the influence of the opening of the adana cilicia basin we interpreted that extension in the central anatolian plateau is related to crustal blocks moving above sub horizontal detachment surfaces located in the lower crust this is based on several facts the tuz golu fault zone is a within crust detachment the tuz golu basin does not affect the whole lithosphere because otherwise it would have been bordered by thermally uplifted shoulders movements change trend within a small 50 km region

an assessment of present day crustal deformation in the kumaun himalaya from gps observations abstract the india eurasia collision has created high mountains in the himalayan plate boundary system which has led to numerous earthquakes in this region and released part of the elastic strain accumulated over years in this study the present day deformation pattern is derived from geodetic mode global positioning system gps measurements obtained during 2005 2016 from 16 campaign sites in the kumaun province of the central himalaya gps derived horizontal velocity vectors are in the range of 1 9 mm yr and 27 38 mm yr with respect to stable india and eurasia reference frames respectively to understand the interseismic strain partitioning in the study region we consider the uniform slip dislocation model over the fault in an elastic isotropic and homogeneous half space medium the model indicates the main himalayan thrust mht fault is locked to a depth of 20 km and slips at a rate of 17 2 1 mm yr with a dip angle of 7 this mht slip rate build up corresponds to a moment deficit of 8 4 1 1018 nm yr due to locking of the fault beneath the kumaun himalaya the total seismic strain accumulation of 61 10 6 estimated from the geodetic data suggests the possibility of large earthquakes typically magnitude 8 and above with the recurrence interval of around 600 years in the kumaun himalayan region

physical processes of shallow mafic dike emplacement near the san rafael swell utah some 200 shonkinite dikes sills and breccia bodies on the western colorado plateau of south central utah were intruded from approximately 3 7 to 4 6 ma contemporaneous with mafic volcanism along the nearby plateau margin thicknesses of dikes range to about 6 m the log normal mean thickness is 85 cm despite the excellent exposures of essentially all dikes in strata of the jurassic san rafael group their number is indeterminate from their outcrop and spacing because they are everywhere greatly segmented by our grouping of almost 2000 dike segments most dikes are less than 2 km in outcrop length the longest is 9 km because the san rafael magmas were primitive and probably ascended directly from the mantle dike lengths in outcrop are much less than their heights the present exposures probably lie along the irregular upper peripheries of dikes that lengthen and merge with depth orientations of steps on dike contacts record local directions of dike fracture propagation about half of the measurements plunge less than 30 showing that lateral propagation at dike peripheries is as important as the vertical propagation ultimately responsible for ascent the san rafael dikes now exposed after erosion of about 0 5 1 5 km appear to thicken and shorten upward probably because near surface vesiculation enhanced magmatic driving pressures propagation likely ceased soon after the first dike segments began to feed nearby sills or vented to initiate small volume eruptions most of the dikes are exposed in clastic strata of the jurassic san rafael group they probably acquired their strikes however while ascending along well developed joints in massive sandstones of the underlying glen canyon group rotation of far field stresses during the emplacement interval cannot account for disparate strikes of the dikes which vary through 110 most lying between north and n25 w rather the two regional horizontal principal stresses were probably nearly equal and so the dominant n75 e direction of dike opening was not strongly favored across the center of the swarm about 10 to 15 dikes overlap and produce 15 20 m of dilation many are in sufficient proximity that later dikes should be thinner than earlier ones if neither the magma pressures nor regional stresses were changing during the emplacement interval however dike thicknesses vary systematically neither along the length of the swarm nor in proportion to the number of neighboring dikes it appears that crustal extension during the magmatic interval relieved compressive stresses localized by intrusion

a non conventional watershed partitioning method for semi distributed hydrological modelling the package aladhyn the extraction of the river network from a digital elevation model dem plays a fundamental role in modelling spatially distributed hydrological processes the present paper deals with a new two step procedure based on the preliminary identification of an ideal drainage network idn from contour lines through a variable mesh size and the further extraction of the actual drainage network and from the idn using land morphology the steepest downslope direction search is used to identify individual channels which are further merged into a network path draining to a given node of the idn the contributing area peaks and saddles are determined by means of a steepest upslope direction search the basin area is thus partitioned into physically based finite elements enclosed by irregular polygons different methods i e the constant and variable threshold area methods the contour line curvature method and a topologic method descending from the hortonian ordering scheme are used to extract the adn from the idn the contour line curvature method is shown to provide the most appropriate method from a comparison with field surveys using the adn one can model the hydrological response of any sub basin using a semi distributed approach the model presented here combines storm abstraction by the scs cn method with surface runoff routing as a geomorphological dispersion process this is modelled using the gamma instantaneous unit hydrograph as parameterized by river geomorphology the results are implemented using a project oriented software facility for the analysis of land digital hydrological networks aladhyn

coseismic and early postseismic deformation due to the 25 april 2015 mw 7 8 gorkha nepal earthquake from insar and gps measurements analysis of interferometric synthetic aperture radar insar and global positioning system gps data reveals coseismic and early postseismic 4 88 days surface displacements associated with the 25 april 2015 mw 7 8 gorkha nepal earthquake the pattern of early postseismic surface uplift and subsidence is found to be opposite to that of the coseismic motion insar and gps data were jointly inverted for coseismic and postseismic slip on the main himalayan thrust mht we consider a complex ramp flat ramp flat subsurface structure of the mht with four connected fault planes dipping toward north from the main frontal thrust mft the inverted coseismic slip distribution follows an elliptical pattern extending east southeastward from the hypocenter with maximum amplitude of 5 7 m above the upper edge of the midcrustal ramp we infer early postseismic afterslip 4 16 days of 0 2 0 47 m toward downdip of the coseismic slip asperity and another patch with 0 1 0 2 m slip toward east the shallow portion of the mht toward south is found to have remained unruptured during the earthquake nor did it slip aseismically after the earthquake suggesting possibility of large events in the future

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

spatial distribution of earthquake potential along the himalayan arc abstract to determine the spatial distribution of earthquake potential along the active himalayan arc we utilize gps measurements and earthquake data we derive horizontal velocity field and 2 d strain rates from a new set of 41 regional gps stations along with 446 published velocities we convert these strain rate tensors to geodetic moment rate build up within 24 contiguous segments and compare to the seismic moment rate release derived from a reassessed earthquake catalog of 900 years the geodetic to seismic moment rate ratio an indicator of stored strain energy varies from below unity to more than 50 in different segments the estimated geodetic moment rate ranges from 1 7 1018 nm yr to 10 2 1018 nm yr whereas the seismic moment rate ranges from 3 7 1016 nm yr to 5 1 1019 nm yr this variation between the geodetic and seismic moment rate corresponds to a moment deficit rate of 1 15 1017 nm yr to 7 97 1018 nm yr along various segments of the study region the above moment deficit rate provides an equivalent earthquake potential of magnitude 5 7 8 2 in different segments specifically the higher earthquake potential mw 8 0 corresponds to the segments in the central seismic gap and the northeast part of himalaya whereas the lower earthquake potential mw

the auckland volcanic field new zealand geophysical evidence for structural and spatio temporal relationships abstract geophysical data from the monogenetic auckland volcanic field reveal complex structural and spatio temporal relationships at different scales the volcanic field is coincident with regional magnetic and gravity anomalies that mark a major crustal suture and with a discontinuity marking a significant structural asperity here the linear regional magnetic anomaly splays into a wide band of nnw trending lineaments arising from serpentinised shear zones in the upper crust that matches the extent of the volcanic field and that may reflect a region of crustal weakness creating preferential permeability however there appears to be no simple correlation between the locations of individual vents and these lineaments that might delineate more shallow structural controls with this orientation probably as a consequence of other structural influences high resolution aeromagnetic data over the volcanic field show that the volcanoes have a wide range of magnetic signatures indicating a variability of subsurface structure scoria cone volcanoes typically have strong anomalies up to several 100 nt whilst tuff ring volcanoes typically have weak anomalies less than 50 nt though the surface geology is not always an indicator of the nature and extent of the subsurface deposits both cone and tuff ring volcanoes in the auckland field appear to be underlain by subsurface bowl shaped bodies of basalt implying that their eruption histories commonly involve lava ponding into early excavated craters the present geophysical data give no evidence for subsurface dyke like structures or for substantial near surface volumes of basaltic rocks where there are no known eruption centres or buried flows aeromagnetic and palaeomagnetic data suggest that a number of adjacent vents with an implied structural linkage may be contemporaneous though other examples occur where vents of clearly different ages exploit the same apparent structure a unique feature of the auckland field is that at least 5 widely separated and structurally unrelated volcanoes are contemporaneous these observations highlight the spatial and temporal heterogeneities that can occur in monogenetic fields and have an important bearing on recurrence rates and temporally linked eruptions which are probably more common than is generally supposed and are key factors in statistically based hazard assessments

migration of volcanism in the san francisco volcanic field arizona the remanent magnetization of volcanic rocks has been determined at 650 sites in the san francisco volcanic field in the southern part of the colorado plateau the polarity of remanent magnetization combined with k ar age determinations spatial and petrographic associations stratigraphic relations and state of preservation of the cinder cones provides a basis for assignment to known magnetic polarity epochs of 610 mafic vents and 100 intermediate to silicic flows flow sequences and vents the age assignments for basaltic rocks include 243 brunhes 0 73 ma vents 220 matuyama 0 73 to 2 48 ma vents and 147 pre matuyama 2 48 to about 5 0 ma vents basaltic volcanism migrated northeastward before matuyama time at a rate of 1 2 cm yr and eastward s87 5 e over the past 2 5 m y at a rate of 2 9 0 3 cm yr concomitant acceleration in total magma production from 75 to 1 400 10 6 km3 yr and frequency of basaltic eruptions from 1 per 17 000 yr to 1 per 3 000 yr occurred between 5 and 0 25 ma for the past 0 25 m y magma production 180 10 6 km3 yr and perhaps eruption frequency have decreased this evolutionary sequence coupled with the lead and strontium isotopic composition of the rocks can be explained by magmatism caused by shear heating at the base of the lithosphere we propose that this eastward drift of volcanic activity represents absolute westward motion of the north american plate our model is in agreement with a model in which the african plate is fixed to the deep mantle

paleoseismic evidence of great surface rupture earthquakes along the indian himalaya 1 toward understanding the relationship between strain accumulation and strain release in the context of the mechanics of the earthquake and mountain building process and quantifying the seismic hazard associated with the globes largest continental thrust system we describe the late quaternary expression and paleoseismic evidence for great surface rupture earthquakes at six sites along the himalayan frontal thrust hft system of india our observations span a distance of 250 km along strike of the hft uplifted and truncated fluvial terrace deposits resulting from the holocene displacements on the hft are preserved along canyons of the ghaggar markanda shajahanpur and kosi rivers dividing the elevation of the bedrock straths at each site by their ages yields estimates of the vertical uplift rate of 4 6 mm yr which when assumed to be the result of slip on an underlying thrust dipping at 20 45 are equivalent to fault slip rates of 6 18 mm yr or shortening rates of 4 16 mm yr trench exposures reveal the hft to fold and break late holocene surface sediments near the cities and villages of chandigarh kala amb rampur ganda lal dhang and ramnagar radiocarbon ages of samples obtained from the displaced sediments indicate surface rupture at each site took place after a d 1200 and before a d 1700 uncertainties attendant to the radiocarbon dating currently do not allow an unambiguous definition of the capping bound on the age of the displacement at each site and hence whether or not the displacements at all sites were contemporaneous trench exposures and vertical separations measured across scarps at rampur ganda lal dhang and ramnagar are interpreted to indicate single event displacements of 11 38 m dividing the observed single event vertical components of displacement by the estimated longer term uplift rates indicates 1330 3250 or more years should be required to accumulate the slip sufficient to produce similar sized displacements surface rupture appears to not have occurred during the historical 1905 kangra mw 7 7 1934 bihar nepal mw 8 1 and 1950 assam mw 8 4 earthquakes which also occurred along the himalayan front yet we observe clear evidence of fault scarps and displacements in young alluvium and progressive and continued offset of fluvial terrace deposits along the hft we suggest on this basis and the size and possible synchroneity of displacements recorded in the trenches that there exists the potential for earthquakes larger than recorded in the historical record and with the potential to rupture lengths of the hft greater than the 250 km we have studied

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

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

morphology of pyroclastic cones and tectonics the relationships between morphology and spatial distribution of 1315 quaternary pyroclastic cones and coeval faulting of the volcanic substrate are analyzed in the following regions with different structural settings tepic rift mexico ethiopian rift mexican volcanic belt canary archipelago and mount etna field data and analog experiments of tephra cone emplacement and collapse enable the definition of a number of parameters which can be used to infer the geometry of the fracture feeding the magma to a pyroclastic cone the strike of the feeding plane is directly related to 1 the elongation of cone base and crater 2 the location of depressions on the crater rim and 3 the alignment of pyroclastic cones in relation to a given vent spacing in addition the strike and dip of faults affect the direction of cone breaching these relationships are valid for volcanic substrate topographic surfaces with an inclination of less than 9 and are especially sensitive to fault escarpment and cone height lava and cone density and fault orientation with respect to the dip of the volcanic substrate topography relations 1 and 2 become more pronounced for regions undergoing extensional tectonics where edifices also have a larger dimension whereas breaching in the direction of the fault dip is more widespread in regions under extension breaching along the fault strike as well as the coincidence between fault strike and vent alignment are more frequent in regions with transcurrent or transtensional tectonics

mechanical modeling of circumferential and radial dike intrusion on galapagos volcanoes a distinctive and unusual pattern of eruptive fissures is observed on the active volcanoes of the galapagos islands reflecting circumferential dike intrusion near the calderas and radial dike intrusion on the volcano flanks elastic finite element models were used to investigate how a stress field could be produced and maintained to promote both circumferential and radial dike emplacement modeling results show that magma reservoirs of galapagos volcanoes are probably diapiric because this shape promotes both circumferential and radial intrusions but magma pressure alone cannot create the observed pattern of dikes loading by volcano growth and magma reservoir pressure could produce a stress field of suitable orientation but insufficient magnitude the intrusion of circumferential dikes could alter the stress field in a way that promotes future radial diking and vice versa faulting or slumping within the calderas or on the volcano flanks in response to repeated intrusions could also create a stress field conducive to continued intrusion

the comoros archipelago a right lateral transform boundary between the somalia and lwandle plates abstract the origin of the comoros archipelago in the mozambique channel is the subject of a longstanding controversy this volcanic chain has been successively interpreted as a hotspot track as built on an intraplate fracture zone or a passive margin or as the northern limit of a diffuse deformation zone in the nubia somalia plate system none of these interpretations being entirely satisfactory it is also possible that the volcanism of the comoros is a branch of the east african rift system and delineates the still poorly constrained northern boundary between the lwandle and somalia plates to better understand the origin of the comoros archipelago we combined a formal stress inversion of earthquake focal mechanisms and deformation structures faults and dykes observed on three islands mayotte anjouan and moheli with a morphologic study of the repartition of onshore and offshore volcanic vents in the area earthquake focal mechanisms and field observed deformation structures both yield a generalized strike slip regime with a maximum horizontal stress oriented nw se in tandem the study of topographic and bathymetric features shows that volcanic vents follow a preferential repartition along two trends n105 10 lineaments up to 100 km long and n145 10 less than 60 km long lineaments organized in an en echelon fashion earthquakes deformation structures and volcanic vents all consistently designate the comoros archipelago as an e w elongated 150 km wide zone of right lateral tear in the lithosphere because the clockwise rotation of somalia relative to lwandle requires the existence of such a right lateral shear zone we interpret the comoros archipelago as the northern boundary between the two plates this plate boundary is still in an immature state which is why it remained undetected until now

precision and accuracy of the calcite strain gage technique the twinned calcite strain gage technique allows the determination of strain magnitude and direction in mildly deformed sedimentary rocks in that the measurements required for the calculation are rather time consuming it is important to know the minimum number required to obtain a precision that is comparable with the accuracy of the result this paper documents a series of tests on three different limestones having different textures and porosities in order to determine the precision and accuracy of the technique as a function of the number of measurements and the number of perpendicular thin sections the tests show that for most purposes the best measurement strategy will be to make 25 measurements on each of two perpendicular thin sections the best determined principal strain axis is the one having a magnitude that is opposite in sign from the other two over the range of zero to 11 shortening the magnitude of the odd signed strain axis will than have a precision and accuracy of about 11 in magnitude and a precision and accuracy of about 6 to 8 in orientation differences in texture and porosity do not appear to have significant effects upon precision and accuracy

oblique convergence in the himalayas of western nepal deduced from preliminary results of gps measurements a gps network consisting of 29 sites was installed in central and western nepal with measurements taken in 1995 and partial remeasurements in 1997 data suggest 15 5 mm yr of n180 convergence between the higher himalayas and india a result that is consistent with n s shortening across the arcuate shape of the nepalese himalayas and an oblique underthrusting of the indian crust below the high himalayas of western nepal a 4 3 mm year e w extension and deviation of the principal shortening axes are inferred east of 83 e where quaternary faults darma bari gad fault system and thakkhola graben delineate a crustal wedge this wedge is located on the se projection of the karakorum fault and may segment the himalayan thrust belt the convergence between the outer belt of western nepal and india is less than 3 mm yr an attenuation consistent with creep on a dislocation locked beneath the lesser himalayas a preliminary model suggests that this n 120 e striking dislocation is affected by a 19 mm yr thrust component and a 7 mm yr right lateral component

relationships between volcanic patterns and neotectonics in eastern anatolia from analysis of satellite images and dem the late neogene to quaternary volcanism in eastern anatolia is related to the arabia eurasia convergence but a clear deformation pattern has not yet been established in this region we have used the distribution and shape of volcanoes and fault geometry as indicators of the tectonic regime volcanic edifices and related faults were analyzed in vertical view using sar ers spot images and a digital elevation model dem in several places adjacent volcanoes that form linear clusters or elongated volcanoes are clearly rooted on vertical tension fractures these are compatible with horizontal 3 striking 90 n associated with 1 horizontal strike slip regime or vertical extensional regime we mapped the recent faults that are directly associated to volcanoes volcanic vents are related to tail crack horsetail or releasing bend structures in this work it has been possible to define the ese striking 270 km long tutak hamur caldiran fault that forms a releasing bend testifying to right lateral motion extension is well documented for few places but no recent fold has been observed since 8 ma the tectonic system is principally strike slip most of the tension fractures being 2 to 10 km in length so we infer that they affect only part of the crust most strike slip fault zones are of several tens to a few hundred kilometers long and thus not of lithospheric scale therefore the channels used by the magma to reach the surface are crustal structures

structural control on volcanoes and magma paths from local to orogen scale the central andes case abstract assessing the parameters that control the location and geometry of magma paths is of paramount importance for the comprehension of volcanic plumbing systems and geo hazards we analyse the distribution of 1518 monogenic and polygenic volcanoes of miocene quaternary age of the central volcanic zone of the andes chile bolivia argentina and reconstruct the magma paths at 315 edifices by analysing the morphostructural characteristics of craters and cones then we compare these data with outcropping dykes tectonic structures and state of stress most magma paths trend n s nw se and ne sw in decreasing order of frequency the n s and nw se paths coexist in the northern and southern part of the study area whereas n s paths dominate east of the salar de atacama outcropping dykes show the same trends the regional holocene stress state is given by an e w greatest horizontal principal stress n s and nne ssw reverse faults and folds affect deposits of 4 8 3 2 and 1 3 ma bp especially in the central and southern study areas a few nw se left lateral strike slip faults are present in the interior of the volcanic arc part of which belong to the calama olacapato el toro fault the volcanic chain is also affected by several n s and nw se striking normal faults that offset pliocene and quaternary deposits the results indicate different scenarios of magma tectonic interaction given by n s normal and reverse faults and n s fold hinges that guide volcano emplacement and magma paths magma paths are also guided by strike slip and normal nw se faults especially in the northern part of the study area zones with verticalized strata with bedding striking ne sw also acted as preferential magma paths these data suggest that at convergence zones with continental crust shallow magma paths can be more sensitive to the presence and geometry of upper crustal weakness zones than to the regional state of stress

mountain building in the nepal himalaya thermal and kinematic model we model crustal deformation and the resulting thermal structure across the nepal himalaya assuming that since 20 ma shortening across the range has been primarily taken up by slip along a single thrust fault the main himalayan thrust mht fault and that the growth of the himalayan wedge has resulted mainly from underplating and to the development of a duplex at midcrustal depth we show that this process can account for the inverse thermal metamorphic gradient documented throughout the lesser himalaya lh the discontinuity of peak metamorphic temperatures across the mct as well as the distribution of age of exhumation across the range this study suggests that the metamorphic evolution of the range over about the last 20 million years is compatible with the kinematics of recent crustal deformation deduced from morphotectonic and geodetic studies

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

estimating the return times of great himalayan earthquakes in eastern nepal evidence from the patu and bardibas strands of the main frontal thrust the return times of large himalayan earthquakes are poorly constrained despite historical devastation of cities along the mountain range definitive links between events and specific segments of the main frontal thrust mft are not established and paleoseismological records have not documented the occurrence of several similar events at the same location in east central nepal however recently discovered primary surface ruptures of that megathrust in the a d 1255 and 1934 earthquakes are associated with flights of tectonically uplifted terraces we present here a refined longer slip history of the mft s two overlapping strands patu and bardibas thrusts in that region based on updated geomorphic neotectonic mapping of active faulting two 1 3 km long shallow seismic profiles and logging of two river cut cliffs three paleoseismological trenches and several pits with constraints from 74 detrital charcoals and 14 cosmogenic nuclide ages the amount of hanging wall uplift on the patu thrust since 3650 450 years requires three more events than the two aforementioned the uplift rate 8 5 1 5mm yr thrust dip 25 5 n and apparent characteristic behavior imply 12 17 5m of slip per event on the bardibas thrust discrete pulses of colluvial deposition resulting from the coseismic growth of a flexural fold scarp suggest the occurrence of six or seven paleo earthquakes in the last 4500 50 years the coeval rupture of both strands during great himalayan earthquakes implies that in eastern nepal the late holocene return times of such earthquakes probably ranged between 750 140 and 870 350 years

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

seismic moment frequency relation for shallow earthquakes regional comparison we determine the parameter values for the seismic moment frequency relation using flinn engdahl s regionalization of global seismicity and the harvard centroid moment tensor data the earthquake size distribution is approximated by the gamma law a version of the gutenberg richter distribution with an exponential taper at the maximum moment there is no statistically significant variation of the fj value the analog of the b value for all seismic regions except for the midocean ridge systems for the latter regions fj 0 93 whereas for all other zones fj 0 63 the maximum moment mxg can be statistically evaluated only for subduction zones treated as a whole mxg 10 21 2 x 10 22 newton m which corresponds to the worldwide mxg value for other regions as well as for single subduction zones mxg is determined by comparing the number of events in each zone with the seismic moment rate calculated on the basis of the nuvel 1 model of plate motion for subduction zones we obtain the estimate of mxg which agrees with the statistical value giving evidence that most tectonic deformation is released by earthquakes we test the hypothesis that no statistically significant variation in mxg occurs in subduction and continent collision zones the hypothesis cannot be rejected with available data for the midocean ridges the mxg estimate cannot be unambiguously determined it is quite possible that the estimate is significantly biased because only a small part of tectonic deformation at the ridges is released by earthquakes these results have importance in evaluating seismic risk and may also lead to developing a physical theory for earthquake generation

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

magnitude calibration of north indian earthquakes this article is concerned primarily with the evaluation of the size and location of northern indian and southern tibetan earthquakes during the last 200 yr it draws attention to the problems of assessing intensity of early and more recent earthquakes in a built environment which is different from that for which the intensity scale has been constructed and to the way in which isoseismals are drawn through a re evaluation of intensities and a reassessment of isoseismals a formula for the estimation of surface wave magnitude using isoseismal radii is derived this formula is used to estimate the surface wave magnitudes of 16 earthquakes that occurred in the region between 1803 and 1900 this study shows that it is possible to calculate accurate surface wave magnitudes for earthquakes that occurred before the advent of the scale and that there is no need to resort to empirical formulae for the assessment of the size and seismic moment release of pre 20th century earthquakes also derived are formulae for the conversion of ms to m0 in total locations surface wave magnitudes and m0 estimates are presented for 43 important events that occurred in the region between 1803 and 1974 eight of which were in the lower crust or were subcrustal we find that the m0 ms scaling for india yields smaller ms than the global relation and that the methodology used can help to evaluate more realistic slip rates as well as to address other issues related to earthquake hazard in northern india

miocene block uplift and basin formation in the patagonian foreland the gastre basin argentina abstract the intraplate fault block mountains and intermontane deposits of the gastre basin which are recorded more than 550 km east of the andean trench in central patagonia argentina are analyzed the gastre basin is one of the largest patagonian intermontane basins limited by uplifted blocks strongly oblique to the andean chain it was originated by reverse faulting and inversion of pre existing normal faults associated with a mesozoic rift basin and defined by older crustal heterogeneities the deformational event occurred during the middle miocene related to a short contractional episode 16 1 14 86 ma probably in response to an eastward migration of the andean fold and thrust belt during pliocene to quaternary times neither younger fault block uplifts nor reconfigurations of the basin occurred similarities between the study area and other parts of the patagonian foreland such as the presence of miocene reverse or inversion tectonics as well as the accommodation of the miocene sedimentary successions suggest that the gastre basin is part of a major late early to middle miocene broken foreland system i e the patagonian broken foreland that exhumed discrete fault block mountains and generated contemporary basins along more than 950 km parallel to the andean trench i e between 40 00 and 48 00 south latitude based on recent studies on the southern andean margin this continental scale contractional episode may be the result of a flat slab subduction segment nevertheless such a hypothesis is very difficult to support when analyzing such a large flat subduction segment along the entire patagonian trench this suggests the need to consider alternative flat slab trigger mechanisms or other factors in the generation of broken foreland systems

interseismic coupling on the main himalayan thrust we determine the slip rate and pattern of interseismic coupling on the main himalayan thrust along the entire himalayan arc based on a compilation of geodetic interferometric synthetic aperture radar and microseismicity data we show that convergence is perpendicular to the arc and increases eastwards from 13 3 1 7 mm yr to 21 2 2 0 mm yr these rates are comparable to geological and geomorphic estimates indicating an essentially elastic geodetic surface strain the interseismic uplift rate predicted from the coupling model closely mimics the topography suggesting that a small percentage of the interseismic strain is permanent we find that the fault is fully locked along its complete length over about 100 km width we don t find any resolvable aseismic barrier that could affect the seismic segmentation of the arc and limit the along strike propagation of seismic ruptures the moment deficit builds up at a rate of 15 1 1 10 19 n m yr for the entire length of the himalaya