structural geology and regional tectonic significance of the ramgarh thrust himalayan fold thrust belt of nepal 1 the ramgarh thrust is one of the major fault systems of the himalayan thrust belt in nepal and northern india the ramgarh thrust sheet is 0 2 2 0 km thick and can be traced along strike the entire length of the himalaya in nepal the fault generally places the oldest paleoproterozoic rocks in the lesser himalayan series upon younger lesser himalayan rocks or lower miocene foreland basin deposits regional balanced cross sections suggest that the ramgarh thrust had at least 120 km of initial south vergent displacement subsequently the frontal part of the thrust experienced further slip as the roof thrust for a large duplex in underlying lesser himalayan rocks ramgarh hanging wall strata are greenschist grade phyllite quartzite and augen gneiss all of which locally exhibit phyllonitic and mylonitic fabrics that indicate a top to the south sense of shear structural fabrics in the ramgarh thrust sheet are generally parallel to the fabrics in rocks above and below the thrust sheet regional and local mapping of the ramgarh thrust in nepal demonstrates that the fault always places a hanging wall flat upon a footwall flat except where local lateral ramps complicate its geometry similarly the structurally overlying main central thrust always places a hanging wall flat in greater himalayan series rocks upon the regionally flat ramgarh thrust sheet these geometric relationships preclude kinematic and thermal models that elevate greater himalayan and lower lesser himalayan rocks along high angle thrust ramps in the vicinity of the present traces of the ramgarh and main central thrust faults instead the corresponding footwall ramps for these thrusts must be located more than 100 km north of the current trace of the main central thrust the present steep dips of the ramgarh and main central thrust sheets can be attributed to tilting during emplacement of structurally lower thrust sheets within a large antiformal duplex that occupies most of the lesser himalayan zone the ramgarh thrust sheet overlaps a bed length of at least 100 km in lower miocene foreland basin deposits indicating that a significant amount of displacement on the thrust must have occurred after 15 ma growth of the lesser himalayan duplex and additional slip on the frontal part of the ramgarh thrust occurred from 12 to 5 ma the presence of a major greenschist grade metasedimentary thrust sheet composed of lesser himalayan rocks directly below the main central thrust suggests that the famous inverted metamorphism in this region is a result of structural inversion similarly the concept of a broad zone of intense shear strain related exclusively to emplacement of the main central thrust sheet is probably invalid in nepal

paleoseismic evidence from trench investigation along hajipur fault himalayan frontal thrust nw himalaya implications of the faulting pattern on landscape evolution and seismic hazard abstract the study area falls within the mesoseismal zone of 1905 kangra earthquake mw 7 8 two parallel nnw sse striking active fault scarps named as hajipur faults hf1 and hf2 along the northwestern end of the janauri anticline in the foothill zone have displaced floodplain sediments of the beas river the hf1 and hf2 represent the imbricate faults of the himalayan frontal thrust hft and are the result of lateral propagation of deformation from two fold segments i e jf1 and jf2 respectively in northwest direction along the strike ground penetrating radar gpr profiles and trenching across the hf2 reveal two low angle thrust fault strands f1 and f2 displacements of 7 5 m on f2 and 1 5 m on the associated branching faults f a f b and f c were observed total four stratigraphic units unit a gravel with a lens of medium sand unit a is the oldest overlain by units b medium to coarse sand unit c with fine to medium sand and unit d fine to medium sand with scattered gravel were observed in trench radiocarbon ages of the charcoal samples from unit b and unit d optical ages of sediments from units a b and c gpr data and trench log suggest two major events along f1 and f2 strands event i along f1 occurred during 2600 800 yr bp and event ii along f2 around 400 yr bp and before 300 yr bp given the uncertainty in dates it is suggested that the latest event occurred during 1500 1600 ad considering the oldest unit unit a exposed in trench with vertical displacement of 7 5 8 m age of 2600 500 yr bp and net displacement of 9 m during single event along low angle fault 25 implies slip rate 7 6 1 7 mm yr uplift rate 3 2 0 6 mm yr shortening rate 6 9 1 4 mm yr and recurrence interval 1160 250 yr for large magnitude event with mw 7 0 with the recurrence of 1100 yr the penultimate event probably occurred at around 1400 1500 yr bp given the recent gps based slip rate of 14 1 mm yr in kangra reentrant baneerjee and burgman 2002 the present study suggests that about half of this slip is consumed along the hft and that this fault is more active compared to those in the hinterland

revisiting the earthquake sources in the himalaya perspectives on past seismicity abstract the 2500 km long himalaya plate boundary experienced three great earthquakes during the past century but none of them generated any surface rupture the segments between the 1905 1934 and the 1897 1950 sources known as the central and assam seismic gaps respectively have long been considered holding potential for future great earthquakes this paper addresses two issues concerning earthquakes along the himalaya plate boundary one the absence of surface rupture associated with the great earthquakes vis a vis the purported large slip observed from paleoseismological investigations and two the current understanding of the status of the seismic gaps in the central himalaya and assam in view of the paleoseismological and historical data being gathered we suggest that the ruptures of earthquakes nucleating on the basal detachment are likely to be restricted by the crustal ramps and thus generate no surface ruptures whereas those originating on the faults within the wedges promote upward propagation of rupture and displacement as observed during the 2005 kashmir earthquake that showed a peak offset of 7 m the occasional reactivation of these thrust systems within the duplex zone may also be responsible for the observed temporal and spatial clustering of earthquakes in the himalaya observations presented in this paper suggest that the last major earthquake in the central himalaya occurred during ad 1119 1292 rather than in 1505 as suggested in some previous studies and thus the gap in the plate boundary events is real as for the northwestern himalaya seismically generated sedimentary features identified in the 1950 source region are generally younger than ad 1400 and evidence for older events is sketchy the 1897 shillong earthquake is not a decollement event and its predecessor is probably 1000 years old compared to the central himalaya the assam gap is a corridor of low seismicity between two tectonically independent seismogenic source zones that cannot be considered as a seismic gap in the conventional sense

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

rupture history and seismotectonics of the 1991 uttarkashi himalaya earthquake abstract the 19 october 1991 uttarkashi india earthquake occurred in the main thrust zone of the himalaya with a moment magnitude of 6 8 this event is characteristic of the present day motion on the thrust fault system we examine this earthquake using different sets of data in order to understand better the faulting process of a major earthquake in the himalayan region firstly the modeling of the teleseismic records indicates that the mechanism is similar to the published cmt and indicates a shallow between 10 and 15 km depth low angle thrust event in the vicinity of the source the earthquake was recorded by a network of accelerometers run by the university of roorkee six three component accelerometers were triggered within a radius of 60 km two of them were very close to the surface projection of the fault forward modeling of those records shows that the rupture propagated toward the west this forward modeling gives us the possibility to confirm the epicenter location and to evaluate the timing of the accelerograms the accelerogram records are inverted to obtain the distribution of slip on the fault plane the results show a complex rupture process the slip maxima 1 5 m occurred 10 km west and 15 km southwest of the hypocenter the slip source function obtained with near field data is similar to the function obtained from teleseismic records and shows a low moment release at the beginning of the rupture and a maximum rate of moment release 4 seconds after the relation between the slip distribution obtained by inversion isoseimals mapped faults and the aftershocks location is then discussed and we finally propose a seismotectonic interpretation of this earthquake the uttarkashi earthquake probably occurred along the detachment surface which coincides with the upper surface of the subducting indian lithosphere this detachment surface is gently dipping under the lesser himalaya and south of the vaikrita thrust the vaikrita thrust marks the line separating the very shallow dipping detachment along which big earthquakes like the uttarkashi earthquake could occur from the steeper dipping aseismic basement thrust this observation is important for correctly estimating the seismic hazard in the uttarkashi region

injection mechanism of clay rich sediments into dikes during earthquakes 1 clastic dikes may form by simultaneous fracture propagation in rocks and injection of clastic material into the fractures resulting from strong seismic shaking we studied the mechanisms of clastic dike formation within the seismically active dead sea basin where hundreds of clastic dikes cross cut the soft rock of the late pleistocene lacustrine lisan formation we analyzed the anisotropy of magnetic susceptibility ams of dikes with known formation mechanisms and defined the characteristic ams signatures mainly of dikes developed by injection process most of the dikes were emplaced due to fluidization of clay rich sediment and are characterized by triaxial ams ellipsoids the dominant triaxial ams ellipsoids along the dike widths suggest that the fluidization mechanism of clay rich sediment is different from the known liquefaction process of sand the ams analysis supported by field evidence indicates that the injection of clay rich sediment is characterized by two main regimes 1 vertical flow characterized by subvertical v2 axes and subhorizontal v1 and v3 axes the v2 axes may indicate the flow directions during fast flow 2 horizontal slow flow characterized by subvertical v3 axes and subhorizontal v1 and v2 axes a streaked ams pattern mainly composed of v2 and v3 axes represents a turbulent flow that generated local eddies simultaneously with the clastic transport the ams parameters along the dikes and possible grain imbrications along dike walls support organization of grains under high strain rates this application of the ams method provides a petrofabric tool for identifying seismites and inferring their flow kinematics in complex geologic areas

the 2003 m8 0 tokachi oki earthquake how much has the great event paid back slip debts 1 a great earthquake with m8 0 the 2003 tokachi oki earthquake occurred on september 26 2003 on the plate boundary south of hokkaido at about the same epicenter as that of the 1952 m8 2 tokachi oki earthquake we estimated the coseismic slip distribution using gps data to obtain consistent results with that inferred from waveform inversions a maximum slip larger than 5m exists around 30km nne from the epicenter though the slip deficit estimated there 80 mm yr by our recent study is based on a rather short period of observation 5 years to discuss the whole seismic cycle the maximum coseismic slip roughly accounts for the slip deficit accumulated in the past 51 years assuming that the back slip rate has been nearly constant since 1952 besides the area of the largest slip however an accumulated slip deficit still remains and should be released by seismic or aseismic slip which is now actually observed in part as postseismic slip

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

control on thrust tectonics in the himalayan foothills a view from a numerical model abstract the evolution of an intracontinental accretionary wedge is controlled by a the displacement of several thrust sheets along faults and an underlying decollement b the vertical motion of the rigid basement beneath the accretionary wedge and c superficial processes erosion sedimentation a numerical model is proposed based on the coulomb wedge theory a 2 5 d forward kinematic system progressive tilting of the underthrust basement and an erosion sedimentation model in order to characterise the sequence of fault activation in a thrust system and the syn orogenic sedimentation in such a system the siwalik belt the frontal thrust system of the himalayas represents a structure on which the model can be applied it presents mainly simple structures made of one fault system branched on an underlying decollement conglomerate deposits of the plio pleistocene upper siwalik are overthrust by miocene formations lower siwalik at the front of the wedge and along inner faults structural maps show that thrust sheets are laterally relayed and simultaneously emplaced the comparison between the deformation pattern in the himalayan foothills and the modelling results supports the concept that the himalayan thrust wedge has a steady state type evolution controlled by horizontal convergence and superficial mass transport and characterised by an irregular spatial and temporal distribution of shortening within the whole wedge during this evolution piggy back basins or strongly displaced internal sheets hide some thrust sheets the exhumation path of these sheets is then discontinuous though the shortening of the wedge is regular

toward understanding tectonic control on the mw 8 8 2010 maule chile earthquake the maule earthquake of 27th february 2010 m w 8 8 affected similar to 500 km of the nazca south america plate boundary in south central chile producing spectacular crustal deformation here we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous gps both in near and far field regions earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published gps insar and land level changes data using green s functions generated by a spherical finite element model with realistic subduction zone geometry the combination of the data sets provided a good resolution indicating that most of the slip was well resolved coseismic slip was concentrated north of the epicenter with up to 16 m of slip whereas to the south it reached over 10 m within two minor patches a comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap slip deficit distribution shows an apparent local overshoot that highlight cycle to cycle variability which has to be taken into account when anticipating future events from interseismic observations rupture propagation was obviously not affected by bathymetric features of the incoming plate instead splay faults in the upper plate seem to have limited rupture propagation in the updip and along strike directions additionally we found that along strike gradients in slip are spatially correlated with geometrical inflections of the megathrust our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts c 2012 elsevier b v all rights reserved

structural interpretation of the great earthquakes of the last millennium in the central himalaya abstract a major question about the himalaya remains open does a great earthquake like the mw 8 1 1934 earthquake release all the strain stored by the tibet india convergence during the preceding interseismic period and only that strain or can it also release a background store of energy that remained unreleased through one or more earlier earthquakes and so potentially engender giant events or a relatively random sequence of events to consider this question the history of the great earthquakes of the last millennium is investigated here by combining data provided by the historical archives of kathmandu trenches through surface ruptures isoseismal damage mapping seismites and the instrumental record in the kathmandu basin the location of the epicenter of the 1934 earthquake was determined from the arrival of high energy p waves that caused sedimentary dikes and ground fractures perpendicular to the epicenter azimuth the epicenter of the mw 7 6 1833 earthquake can therefore be determined analogously from dike orientation and its location to the ne of kathmandu indicates an overlap with the mw 8 1 1934 rupture the 1934 earthquake released strain not released by the 1833 earthquake comparison of the historical records of earthquakes in kathmandu with 14c ages from paleo seismic trenches along the himalayan front suggests that 1 the 1344 kathmandu event ruptured the surface as far away as kumaon and was therefore a giant mw 8 6 earthquake and 2 the 1255 event that destroyed kathmandu is attested by surface ruptures in central and western nepal and by seismites in soft sediment as far away as kumaon geometric and rheologic controls for the different types of ruptures during the medium mw 7 great mw 8 and giant mw 8 4 earthquakes are illustrated in structural cross sections it is found that the epicenters of great himalayan earthquakes are located on the basal thrust farther north or close to the locked zone which is defined from geodetic measurements of regional deformation during the interseismic period this suggests that great earthquakes initiate in a wide transition zone between exclusively brittle and exclusively creeping regimes the extent of which depends on the dip of the main himalayan thrust the succession of the great earthquakes during the last millennium has released all the 20 m millennial himalayan convergence even in the central seismic gap which has been locked since 1505 the millennial seismic release rate is close to the convergence rate nonetheless no evidence of a succession of characteristic earthquakes has been found the 1100 1833 and 1934 earthquakes in the eastern himalaya are characterized neither by constant displacement nor by constant recurrence furthermore some great earthquakes do not release all the strain elastically stored by the himalayan and tibetan upper crust after the 1255 event there was still the potential for a slip of several meters for the mw 8 1 1505 event this suggests a rather random release of seismic energy great earthquakes could occur anytime and in any part of the central himalaya furthermore a future giant earthquake of mw 8 6 cannot be excluded

possibility of biases in the estimation of earthquake recurrence and seismic hazard from geologic data abstract aseismic deformation is an integral part of the earthquake process and may lead to systematic biases in the estimation of earthquake size recurrence and attendant strong ground motions in seismic hazard analyses founded on the geologic description of the locations lengths and slip rates of active faults observations are reviewed and presented to suggest that large earthquakes systematically rupture to increasingly greater depths below the seismogenic layer and that the portion of slip on faults accommodated by aseismic processes may be inversely related to the length of rupture expected to occur on them if so the expected seismic moment per unit area of earthquakes on mapped faults may be systematically overestimated as a function of rupture length when derived from regressions of seismic moment and aftershock area and estimates of seismic moment rate derived from geologic measures of fault offset might be systematically overestimated as an inverse function of the length of rupture expected to recur on a fault

frontal and piggy back seismic ruptures in the external thrust belt of western nepal abstract this paper gives structural and morphological evidence for meter scale episodic displacement pulses along the mft and mdt during a complex sequence of thrusting in the sub himalayan fold and thrust belt the studied cross section is located in western nepal at a latitude of e 82 20 along this section the main dun thrust mdt is in a piggy back setting and comprises three splays that are spaced by less than 200 m the splays display the following sequence of motion 1 the medium splay was active 2 the internal splay was active and had a dip slip displacement of 3 m that could be the surface rupture of an earthquake 3 a period of quiescence occurred for all the splays of the mdt 4 the external splay is active the motion along the medium and internal thrust predates 70 kyr whereas motion along the external splay postdates 5468 5214 yr before j c the main frontal thrust mft is the most external himalayan thrust ten encased strath terraces are found at its hangingwall sudden 1 5 m uplift events could have induced their abandonment and could have been linked to 2 m slip events along the mft a value close to the lower bound inferred for co seismic slip along the basal detachment mht during m 8 earthquakes from the offset of a terrace level a displacement of 8 m is inferred between 1224 1280 yr after j c and 1828 1883 yr after j c it could be linked to a succession of several seisms along the mft this study suggests that a several thrusts that branch off the basal decollement are active faults b great earthquakes that occur along the outer part of the basal decollement of the himalayan thrust belt reach the surface at different location c only one thrust moves during one earthquake d the sequence of thrusting is successively out of sequence and in sequence and changes at an intermediate time scale between earthquake cycle and finite geometry of the thrust system

seismotectonics of the nepal himalaya from a local seismic network the national seismological network of nepal consists of 17 short period seismic stations operated since 1994 it provides an exceptional view of the microseismic activity over nearly one third of the himalayan arc including the only segment between longitudes 78 e and 85 e that has not produced any m 8 earthquakes over the last century it shows a belt of seismicity that follows approximately the front of the higher himalaya with most of the seismic moment being released at depths between 10 and 20 km this belt of seismicity is interpreted to reflect interseismic stress accumulation in the upper crust associated with creep in the lower crust beneath the higher himalaya the seismic activity is more intense around 82 e in far western nepal and around 87 e in eastern nepal western nepal between 82 5 and 85 e is characterized by a particularly low level of seismic activity we propose that these lateral variations are related to segmentation of the main himalayan thrust fault the major junctions between the different segments would thus lie at about 87 e and 82 e with possibly an intermediate one at about 85 e these junctions seem to coincide with some of the active normal faults in southern tibet lateral variation of seismic activity is also found to correlate with lateral variations of geological structures suggesting that segmentation is a long lived feature we infer four 250 400 km long segments that could produce earthquakes comparable to the m 8 4 bihar nepal earthquake that struck eastern nepal in 1934 assuming the model of the characteristic earthquake the recurrence interval between two such earthquakes on a given segment is between 130 and 260 years

the status of central seismic gap a perspective based on the spatial and temporal aspects of the large himalayan earthquakes abstract the central himalaya considered as a prominent seismic gap is generally believed to be the most vulnerable segment due for a great plate boundary earthquake m 8 two significant historical earthquakes are known to have occurred in this region in ad 1505 and 1803 interpreted by some workers as great earthquakes occurrences of these events question the validity of central himalaya being a seismic gap here we analyze the macroseismal data from the central himalaya and the gangetic plains and suggest that neither of these earthquakes can be qualified as a plate boundary type event and the size of at least the 1803 does not exceed mw 7 7 our studies further indicate that the central himalayan frontal thrusts may be undergoing a quiescence of 1000 years in terms of generation of great earthquakes assuming a steady elastic strain accumulation due to plate convergence and its simple translation as periodic great earthquakes such long quiescence may appear intriguing we suggest that the long term quiescence and the spatial and temporal clustering that characterize the distribution of large earthquakes in the himalaya is a manifestation of the tectonic deformation associated with a highly evolved fold and thrust belt our analyses also indicate that the large moderate earthquakes are mostly concentrated on higher level thrusts these structures probably accommodate most of the seismogenic slip in the himalaya and the rest of the strain could possibly be expended on passive folding consequently great earthquakes m 8 are relatively infrequent as in the case of central himalaya apparently leading to long periods of quiescence

the siwaliks of western nepal i geometry and kinematics abstract the siwalik group which forms the southern zone of the himalayan orogen constitutes the deformed part of the neogene foreland basin situated above the downflexed indian lithosphere it forms the outer part of the thin skinned thrust belt of the himalaya a belt where the faults branch off a major decollement md that is the external part of the basal detachment of himalayan thrust belt this decollement is located beneath 13 ma sediments in far western nepal and beneath 14 6 ma sediments in mid western nepal i e above the base of the siwalik group unconformities have been observed in the upper siwalik member of western nepal both on satellite images and in the field and suggest that tectonics has affected the frontal part of the outer belt since more than 1 8 ma several north dipping thrusts delineate tectonic boundaries in the siwalik group of western nepal the main dun thrust mdt is formed by a succession of 4 laterally relayed thrusts and the main frontal thrust mft is formed by three segments that die out laterally in propagating folds or branch and relay faults along lateral transfer zones one of the major transfer zones is the west dang transfer zone wdtz which has a north northeast strike and is formed by strike slip faults sigmoid folds and sigmoid reverse faults the width of the outer belt of the himalaya varies from 25 km west of the wdtz to 40 km east of the wdtz the wdtz is probably related to an underlying fault that induces a a change of the stratigraphic thickness of the siwalik members involved in the thin skinned thrust belt and particularly of the middle siwalik member b an increase from west to east of the depth of the decollement level and c a lateral ramp that transfers displacement from one thrust to another large wedge top basins duns of western nepal have developed east of the wdtz the superposition of two decollement levels in the lower siwalik member is clear in a large portion of the siwalik group of western nepal where it induces duplexes development the duplexes are formed either by far travelled horses that crop out at the hangingwall of the internal decollement thrust id to the south of the main boundary thrust or by horses that remain hidden below the middle siwaliks or lesser himalayan rocks most of the thrusts sheets of the outer belt of western nepal have moved toward the s sw and balanced cross sections show at least 40 km shortening through the outer belt this value probably under estimates the shortening because erosion has removed the hangingwall cut off of the siwalik series the mean shortening rate has been 17 mm yr in the outer belt for the last 2 3 ma

assessing the potential of internal erosion and suffusion of granular soils this study presents a new empirical criterion for assessing the potential of internal erosion and suffusion of granular soils this method considers the bimodal structure of a soil having a primary coarse fabric and loose finer particles based on the porosities influenced by the particle size distribution and the degree of compaction by comparing the representative particle size of a loose finer fraction with the controlling constriction size of a primary coarse fabric a distinct boundary between internally stable and unstable soils with respect to internal erosion may be found

space and ground based measurements of sulphur dioxide emissions from turrialba volcano costa rica remotely sensed measurements of sulphur dioxide so2 emitted by turrialba volcano costa rica are reported for the period september 2009 january 2011 these measurements were obtained using images from advanced spaceborne thermal emission and reflexion radiometer ozone monitoring instrument and a ground based uv camera these three very different instruments provide flux measurements in good agreement with each other which demonstrate that they can be integrated for monitoring so2 fluxes fluxes from turrialba increased fourfold in january 2010 following a phreatic explosion that formed a degassing vent in the w crater of turrialba since then the so2 flux has remained high 30 50 kg s but seems to be showing a slowly decreasing trend we interpret this evolution as the start of open vent degassing from a recently intruded magma body the opening of the degassing vent decreased the confining pressure of the magma body and allowed the gases to bypass the hydrothermal system

growth and lateral propagation of fault related folds in the siwaliks of western nepal rates mechanisms and geomorphic signature 1 we study the controls on drainage development in tectonically active regions using a numerical tectonic surface processes model combining tectonic uplift caused by fault related folding with erosion by fluvial incision hillslope diffusion and landsliding our model shows the fundamental control exerted by the dip of the detachment underlying the folds on drainage evolution when the detachment is horizontal the relative rates of tectonic uplift and fluvial incision control the evolution for a nonzero dip in contrast the lateral displacement gradient associated with fold propagation sets up a lateral slope behind the active structure which deflects the stream network we also demonstrate the importance of landsliding for the attainment of realistic and steady state topography in contrast discontinuous tectonic movements do not appear to influence the system we apply our model to the dundwa fault related fold ridge siwalik nepal we estimate a remarkably low mean propagation rate for different segments of the structure this finding together with the structure and morphology of the ridge leads us to propose that the ridge developed by linkage of several component segments the drainage evolution predicted when modeling this scenario compares favorably with field observations our models provide insights into the dynamics of fault related fold propagation in particular as a result of fault segment linkage estimates of propagation rate of these structures may be strongly scale dependent and the observed morphology and drainage patterns on fault related fold ridges may be controlled by fault geometry rather than by the relative rates of tectonics and surface processes

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

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

neogene shortening contribution to crustal thickening in the back arc of the central andes to illustrate the neogene shortening distribution in the back arc units of the central andes and to estimate the contribution of the shortening to crustal thickening two balanced crustal cross sections have been constructed across the northern and southern branches of the bolivian orocline total neogene shortening which varies from 191 to 231 km is accommodated by a crustal duplex below the cordillera oriental but is insufficient to produce the 70 km of crustal thickness evidenced by geophysical data below the altiplano the best explanation for this anomalous thickening seems to be crustal underplating by material tectonically eroded from the continental margin this process probably caused the altiplano uplift the subduction of oceanic lithosphere coupled with this underplating and a brief episode of gravity spreading of the altiplano constituted the driving forces that produced neogene shortening and development of the central andes