double ramp on the main himalayan thrust revealed by broadband waveform modeling of the 2015 gorkha earthquake sequence abstract the 2015 m w 7 8 gorkha earthquake sequence that unzipped the lower edge of the main himalayan thrust mht in central nepal provides an exceptional opportunity to understand the fault geometry in this region however the limited number of focal mechanisms and the poor horizontal locations and depths of earthquakes in the global catalog impede us from clearly imaging the ruptured mht in this study we generalized the amplitude amplification factor aaf method to teleseismic distance that allows us to model the teleseismic p waves up to 1 5 hz we used well constrained medium sized earthquakes to establish aaf corrections for teleseismic stations that were later used to invert the high frequency waveforms of other nearby events this new approach enables us to invert the focal mechanisms of some early aftershocks which is challenging by using other long period methods with this method we obtained 12 focal mechanisms more than that in the gcmt catalog we also modeled the high frequency teleseismic p waves and the surface reflection phases pp and sp to precisely constrain the depths of the earthquakes our results indicate that the uncertainty of the depth estimation is as small as 1 2 km finally we refined the horizontal locations of these aftershocks using carefully hand picked arrivals the refined aftershock mechanisms and locations delineate a clear double ramp geometry of the mht with an almost flat decollement sandwiched in between the flat dip 7 degrees portion of the mht is consistent with the coseismic rupture of the mainshock which has a well constrained slip distribution the fault morphology suggests that the ramps both along the up dip and down dip directions play a significant role in stopping the rupture of the 2015 gorkha earthquake our method can be applied to general subduction zone earthquakes and fault geometry studies

assessment of teleseismically determined source parameters for the april 25 2015 mw 7 9 gorkha nepal earthquake and the may 12 2015 mw 7 2 aftershock on april 25 2015 a major m w 7 9 thrust earthquake ruptured the deeper portion of the seismogenic plate boundary beneath nepal along which india is underthrusting eurasia an m w 7 2 aftershock on may 12 2015 extended the eastern down dip edge of the rupture these destructive events caused about 9000 fatalities and 23 000 injuries the overall rupture zone is about 170 km long and 40 80 km wide this region of the plate boundary previously experienced a large earthquake in 1833 and in 1934 a larger m s 8 0 event located to the east ruptured all the way to the surface the main himalayan thrust mht on which slip occurred in 2015 has a very low dip angle of 6 and the depth of the mainshock slip distribution is very shallow extending from 7 to 18 km the shallow dip and depth present challenges for resolving faulting characteristics using teleseismic data we analyze global teleseismic signals for the mainshock and aftershock to estimate source parameters evaluating the stability of various procedures used for remotely characterizing kinematics of such shallow faulting back projection and finite fault slip inversion are used to assess the spatio temporal rupture history and evidence for frequency dependent radiation along dip slip zone width constraints from near field geodetic observations are imposed on the preferred models to overcome some limitations of purely teleseismic methods radiated energy stress drop and moment rate functions are determined for both events

primary surface ruptures of the great himalayan earthquakes in 1934 and 1255 it is unclear where plate boundary thrusts generate giant rather than great earthquakes along the himalayas the source sizes and recurrence times of large seismic events are particularly uncertain since no surface signatures were found for those that shook the range in the twentieth century here we challenge the consensus that these events remained blind and did not rupture the surface we use geomorphological mapping of fluvial deposits palaeo seismological logging of river cut cliffs and trench walls and modelling of calibrated 14c ages to show that the mw 8 2 bihar nepal earthquake on 15 january 1934 did break the surface traces of the rupture are clear along at least 150 km of the main frontal thrust fault in nepal between 85 50 and 87 20 e furthermore we date collapse wedges in the sir valley and find that the 7 june ad 1255 earthquake an event that devastated kathmandu and mortally wounded the nepalese king abhaya malla also ruptured the surface along this stretch of the mega thrust thus in the past 1 000 years two great earthquakes 679 years apart rather than one giant eleventh century ad event contributed to the frontal uplift of young river terraces in eastern nepal the rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great himalayan events might exist the recurrence times of great himalayan earthquakes are difficult to assess because they rarely rupture the surface field mapping and 14c dating of offset fluvial deposits are used to identify two great himalayan quakes that ruptured the surface along the main plate boundary fault in ad 1255 and 1934

duplex in the main himalayan thrust illuminated by aftershocks of the 2015 m w 7 8 gorkha earthquake in april 2015 the lower locked portion of the main himalayan thrust ruptured beneath nepal causing the disastrous mw 7 8 gorkha earthquake elucidating the enigmatic geometry of this plate boundary fault is important for understanding the nucleation and arrest of large earthquake ruptures as well as the seismic hazard topography and tectonics of the himalaya here we interpret the geometry of the main himalayan thrust from the spatial distribution and rupture patterns of a dynamic sequence of aftershocks following the gorkha earthquake which were recorded by a rapidly deployed dense seismic network we find that the thrust comprises two north dipping subhorizontal planes that are connected by a system of bounded imbricate thrust faults this structure is known as a duplex we propose that this duplex acts as an impediment to plate convergence and accommodates tectonic stress along its complex system of faults such a prominent structure to the main himalayan thrust is consistent with surface geological studies but challenges geophysically derived conventional models with simpler geometries the main himalayan thrust comprises two fault planes connected by imbricated faults a structure that impedes convergence according to an analysis of the distribution and orientation of aftershocks of the 2015 gorkha earthquake in nepal

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

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

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 aftershock sequence of the 2015 april 25 gorkha nepal earthquake l b adhikari 1 u p gautam 1 b p koirala 1 m bhattarai 1 t kandel 2 r m gupta 1 c timsina 1 n maharjan 1 k maharjan 2 t dahal 2 r hoste colomer 3 4 y cano 3 m dandine 3 a guilhem 3 s merrer 3 p roudil3 and l bollinger3 1national seismological centre department of mines and geology lainchaur kathmandu nepal e mail adhikari research gmail com 2regional seismological centre department of mines and geology surkhet birendranagar nepal 3cea dam dif f 91297 arpajon france 4laboratoire de geologie ecole normale superieure cnrs 24 rue lhomond f 75004 paris france

rupture processes of the 2015 mw 7 9 gorkha earthquake and its mw 7 3 aftershock and their implications on the seismic risk abstract the rupture processes of the 2015 april 25 gorkha earthquake and its strongest aftershock occurred on may 12 in nepal are investigated by joint inversion of seismological and geodetic data synthetic test shows that the sedimentary layers in the source region play an important role in the rupture process inversion our optimized model of the mainshock shows that the rupture has a unilateral propagation pattern the dominant mechanism is pure thrust with maximum slip of 5 8 m the rupture scale extends 60 km along dip and 150 km along strike and the largest static stress change is 7 6 mpa the total seismic moment is 7 87 1020 n m equivalent to mw 7 9 most seismic moment was released within 80 s and the majority seismic moment was released at the first 40 s the rupture propagated in main slip asperity with a velocity of 3 0 km s the strong aftershock magnitude is about mw 7 3 and the peak slip is about 5 0 m close to the peak slip of the mainshock moreover the slips of the mainshock and the aftershocks are in good complementary suggesting a triggering relationship between them considering the strain accumulation the gorkha earthquake ruptured only part of the seismic gap alone thus still poses high earthquake risk especially in the west side of the mainshock rupture zone

source modeling of the 2015 mw 7 8 nepal gorkha earthquake sequence implications for geodynamics and earthquake hazards abstract the gorkha earthquake on april 25th 2015 was a long anticipated low angle thrust faulting event on the shallow decollement between the india and eurasia plates we present a detailed multiple event hypocenter relocation analysis of the mw 7 8 gorkha nepal earthquake sequence constrained by local seismic stations and a geodetic rupture model based on insar and gps data we integrate these observations to place the gorkha earthquake sequence into a seismotectonic context and evaluate potential earthquake hazard major results from this study include 1 a comprehensive catalog of calibrated hypocenters for the gorkha earthquake sequence 2 the gorkha earthquake ruptured a 150 60 km patch of the main himalayan thrust mht the decollement defining the plate boundary at depth over an area surrounding but predominantly north of the capital city of kathmandu 3 the distribution of aftershock seismicity surrounds the mainshock maximum slip patch 4 aftershocks occur at or below the mainshock rupture plane with depths generally increasing to the north beneath the higher himalaya possibly outlining a 10 15 km thick subduction channel between the overriding eurasian and subducting indian plates 5 the largest mw 7 3 aftershock and the highest concentration of aftershocks occurred to the southeast the mainshock rupture on a segment of the mht decollement that was positively stressed towards failure 6 the near surface portion of the mht south of kathmandu shows no aftershocks or slip during the mainshock results from this study characterize the details of the gorkha earthquake sequence and provide constraints on where earthquake hazard remains high and thus where future damaging earthquakes may occur in this densely populated region up dip segments of the mht should be considered to be high hazard for future damaging earthquakes

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

stress buildup in the himalaya the seismic cycle on a major fault involves long periods of elastic strain and stress accumulation driven by aseismic ductile deformation at depth ultimately released by sudden fault slip events coseismic slip distributions are generally heterogeneous with most of the energy being released in the rupture of asperities since on the long term the fault s walls generally do not accumulate any significant permanent deformation interseismic deformation might be heterogeneous revealing zones of focused stress buildup the pattern of current deformation along the himalayan arc which is known to produce recurring devastating earthquakes and where several seismic gaps have long been recognized might accordingly show significant lateral variations providing a possible explanation for the uneven microseismic activity along the himalayan arc by contrast the geodetic measurements show a rather uniform pattern of interseismic strain oriented consistently with long term geological deformation as indicated from stretching lineation we show that the geodetic data and seismicity distribution are reconciled from a model in which microseismicity is interpreted as driven by stress buildup increase in the interseismic period the uneven seismicity pattern is shown to reflect the impact of the topography on the stress field indicating low deviatoric stresses 35 mpa and a low friction 0 3 on the main himalayan thrust arc normal thrusting along the himalayan front and east west extension in southern tibet are quantitatively reconciled by the model

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

aftershock patterns of ms 7 earthquakes in the india asia collision belt anomalous results from the muzaffarabad earthquake sequence kashmir 2005 the seismicity rate triggered by the muzaffarabad kashmir 2005 m w 7 6 m s 7 7 earthquake is above the average when analyzing the aftershock rate of the 18 m s 7 0 events in the india asia collision belt between 1973 and 2008 all 17 m s 7 0 events occurred within 10 latitude and 20 longitude distance from the 2005 muzaffarabad earthquake epicenter we determined the huge aftershock productivity for this earthquake is not driven by a specific omori law parameter this anomaly in aftershock rate value corresponds to a relatively higher rate decay as measured by the p value and a larger density value in a higher background seismicity rate setting prestress conditions than the other 17 sequences respectively after normalizing by the mainshock size and by the magnitude range of observation we resolved the anomalies with a 95 confidence level for five aftershock sequences for either the duration the productivity the density or the background seismicity rate when we did not include the local processes that drive these specific anomalies two other global results emerged for the averaged data from the 18 m s 7 0 aftershock sequences first for all sequences background seismicity and duration are anticorrelated graphic 1 within the framework of rate and state friction law this result supports the assertion that the observed background seismicity rate can be used as a proxy for the stressing rate dieterich 1994 second we robustly resolve the dependence of aftershock productivity on the mainshock faulting styles for example the aftershock productivity for strike slip mainshocks is on average four times smaller than the productivity of thrust faulting mainshocks 1 embed inline graphic 1 gif

structural context of the 2015 pair of nepal earthquakes mw 7 8 and mw 7 3 an analysis based on slip distribution aftershock growth and static stress changes the great himalayan earthquakes are believed to originate on the main himalayan thrust and their ruptures lead to deformation along the main frontal thrust mft the rupture of the april 25 2015 mw 7 8 earthquake was east directed with no part relayed to the mft the aftershock distribution coseismic elevation change of 1 m inferred from the insar image and the spatial correspondence of the subtle surface deformations with pt2 a previously mapped out of sequence thrust lead us to explore the role of structural heterogeneities in constraining the rupture progression we used teleseismic moment inversion of p and sh waves and coulomb static stress changes to map the slip distribution and growth of aftershock area to understand their relation to the thrust systems most of the aftershocks were sourced outside the stress shadows slip 1 65 m of the april 25 earthquake the may 12 mw 7 3 earthquake that sourced on a contiguous patch coincides with regions of increased stress change and therefore is the first known post instrumentation example of a late distant and large triggered aftershock associated with any large earthquake in the nepal himalaya the present study relates the slip aftershock productivity and triggering of unbroken stress barriers to potential out of sequence thrusts and suggests the role of stress transfer in generating large great earthquakes

geochemical studies of crude oil generation migration and destruction in the mississippi salt basin abstract the main source for crude oil in the mississippi salt basin is the laminated lime mudstone facies of the lower smackover crude oil generation and migration commenced at a level of thermal maturity equivalent to about 0 55 vitrinite reflectance short range lateral migration of crude oil was focused to upper smackover and norphlet reservoirs but vertical migration also charged some overlying cotton valley rodessa lower tuscaloosa and eutaw reservoirs following migration from the lower smackover thermal maturity history of reservoir rocks controls the preservation of crude oil gas condensate and methane slow thermal cracking of crude oil occurred in deep upper smackover reservoirs resulting in formation of gas condensate and precipitation of solid bitumen the maximum thermal maturity for preservation of condensate is equivalent to about 1 3 vitrinite reflectance only methane pyrobitumen and nonhydrocarbon gases including hydrogen sulfide persist at higher levels of thermal maturity early destruction of methane in deep upper smackover reservoirs near the wiggins arch is driven by thermochemical sulfate reduction lesser availability of sulfate in norphlet reservoirs in lower mobile bay could account for methane preservation at higher levels of thermal maturity one basic geochemical strategy for further exploration of the mississippi salt basin is to focus exploration effort on traps with reservoirs in the thermal maturity window for hydrocarbon preservation another strategy is to avoid drilling traps with overmature reservoir rocks

long term growth of the himalaya inferred from interseismic insar measurement the rise and support of the 5000 m topographic scarp at the front of indian eurasian collision in the himalaya involves long term uplift above a mid crustal ramp within the main himalayan thrust mht system locking of the shallower portion of the flat ramp flat during the interseismic period also produces transient uplift above the transition zone however spatial and temporal relationships between permanent and transient vertical deformation in the himalaya are poorly constrained leading to an unresolved causal relationship between the two here we use interferometric synthetic aperture radar insar to measure interseismic uplift on a transect crossing the whole himalaya in central nepal the uplift velocity of 7 mm yr at the front of the annapurna mountain range is explained by an 18 21 mm yr slip rate on the deep shallow dipping portion of the mht with full locking of the mid crustal ramp underlying the high himalaya the transient uplift peak observed by insar matches spatially with the long term uplift peak deduced from the study of trans himalayan river incision although models of the seismic cycle involving thrusting over a ramp of fixed geometry predict an 20 km separation between the two peaks we argue that this coincidence indicates that today s mid crustal ramp in central nepal is located southward with respect to its average long term location suggesting that mountain growth proceeds by frontward migration of the ramp driven by underplating of material from the indian plate under the himalaya

implications for elastic energy storage in the himalaya from the gorkha 2015 earthquake and other incomplete ruptures of the main himalayan thrust abstract rupture in the 2015 m7 8 gorkha earthquake nucleated at the downdip edge of the main himalayan thrust mht near the transition from interseismic locking to aseismic creep beneath the tibetan plateau and propagated incompletely towards the main frontal thrusts mft despite the imposition of a substantial static strain in the mid decollement afterslip on the mht within a year of the earthquake had decayed to negligible levels earthquakes that incompletely rupture the mht 7

improved location procedures at the international seismological centre summary the international seismological centre isc is a non governmental non profit organization with the primary mission of producing the definitive account of the earth s seismicity the isc bulletin covers some 50 yr 1960 2011 of seismicity the recent years have seen a dramatic increase both in the number of reported events and especially in the number of reported phases owing to the ever increasing number of stations worldwide similar ray paths will produce correlated traveltime prediction errors due to unmodelled heterogeneities in the earth resulting in underestimated location uncertainties and for unfavourable network geometries location bias hence the denser and more unbalanced the global seismic station coverage becomes the less defensible is the assumption that is the observations are independent which is made by most location algorithms to address this challenge we have developed a new location algorithm for the isc that accounts for correlated error structure and uses all iaspei standard phases with a valid ak135 traveltime prediction to obtain more accurate event locations in this paper we describe the new isc locator and present validation tests by relocating the ground truth events in the iaspei reference event list as well as by relocating the entire isc bulletin we show that the new isc location algorithm provides small but consistent location improvements considerable improvements in depth determination and significantly more accurate formal uncertainty estimates we demonstrate that the new algorithm through the use of later phases and testing for depth resolution considerably clusters event locations more tightly thus providing an improved view of the seismicity of the earth

more major earthquakes at the nepal himalaya study on coulomb stress perspective abstract on april 2015 a major earthquake of 7 9 mw occurred in the nepal himalaya followed by 553 earthquakes of local magnitude greater than 4 0 within the first 43 days including another major event of 7 3 mw we resolve the static coulomb failure stress cfs change onto the finite fault models of 7 9 mw after elliott et al 2016 and galezka et al 2015 and its effect on associated receiver faults correlation of aftershocks with the enhanced cfs condition shows that the elliott et al 2016 model explains 60 4 and the galezka et al 2015 model explains about 47 7 of the aftershocks in high stress regions aftershocks were poorly spatially correlated with the enhanced cfs condition after the 7 9 mw main shock and can be explained by correlation with release of seismic energy from the associated secondarily stressed prominent thrust planes and transverse faults stress resolved on the associated receiver faults show increased stress on both transverse and thrust fault systems with the potential of triggering significant aftershocks or subsequent main shocks

the 2015 gorkha earthquake a large event illuminating the main himalayan thrust fault the 2015 gorkha earthquake sequence provides an outstanding opportunity to better characterize the geometry of the main himalayan thrust mht to overcome limitations due to unaccounted lateral heterogeneities we perform centroid moment tensor inversions in a 3 d earth model for the main shock and largest aftershocks in parallel we recompute s top and p to s receiver functions from the hi climb data set inverted centroid locations fall within a low velocity zone at 10 15 km depth and corresponding to the subhorizontal portion of the mht that ruptured during the gorkha earthquake north of the main shock hypocenter receiver functions indicate a north dipping feature that likely corresponds to the midcrustal ramp connecting the flat portion to the deep part of the mht our analysis of the main shock indicates that long period energy emanated updip of high frequency radiation sources previously inferred this frequency dependent rupture process might be explained by different factors such as fault geometry and the presence of fluids

a crust and upper mantle model of eurasia and north africa for pn travel time calculation abstract we develop a regional seismic travel time rstt model and method for use in routine seismic analysis the model parameterization is a global tessellation of nodes with a velocity profile at each node interpolation of the velocity profiles generates a 3d crust and laterally variable upper mantle velocity the upper mantle velocity profile at each node is represented as a linear velocity gradient which enables travel time computation in approximately 1 millisecond this computational speed allows the model to be used in routine analyses in operational monitoring systems we refine the model using a tomographic formulation that adjusts the average crustal velocity mantle velocity at the moho and the mantle velocity gradient at each node while the rstt model is inherently global our first rstt tomographic effort covers eurasia and north africa where we have compiled a data set of approximately 600 000 pn arrivals ten percent of the data set is randomly selected and set aside for testing purposes travel time residual variance for the validation data is reduced by 32 based on a geographically distributed set of validation events with epicenter accuracy of 5 km or better epicenter error using 16 pn arrivals is reduced by 46 from 17 3 km ak135 model to 9 3 km rstt model after tomography the median uncertainty ellipse area is reduced by 68 from 3070 km 2 ak135 to 994 km 2 rstt and the number of ellipses with area less than 1000 km 2 which is the area allowed for onsite inspection under the comprehensive nuclear test ban treaty is increased from 0 ak135 to 51 rstt

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

the impact of syn and post extension prograding sedimentation on the development of salt related rift basins and their inversion clues from analogue modelling abstract various studies have demonstrated the intrinsic interrelationship between tectonics and sedimentation in salt related rift basins during extension as well as during their inversion by compression here we present seven brittle ductile analogue models to show that the longitudinal or transverse progradation of sediment filling an elongate extensional basin has a substantial impact on the growth of diapirs and their lateral geometrical variations we use five extensional models to reveal how these prograding systems triggered diapir growth variations from proximal to distal areas relative to the sedimentary source in the models continuous passive diapir walls developed after a short period of reactive active diapiric activity during syn extensional homogeneous deposition in contrast non rectilinear diapir walls grew during longitudinal prograding sedimentation both longitudinal and transverse post extensional progradation triggered well developed passive diapirs in the proximal domains whereas incipient reactive active diapirs incipient roller like diapirs or poorly developed diapirs were generated in the distal domains depending on the modelled sedimentary pattern two models included final phases of 6 and 10 shortening associated with basin inversion by compression respectively to discriminate compressional from purely extensional geometries with the applied shortening the outward flanks of existing diapir walls steepened their dips from 8 17 to 30 50 likewise 6 of shortening narrowed the diapir walls by 32 72 with their fully closing salt welds with 10 of shortening we compare our results with the distribution of salt walls and minibasins of the central high atlas diapiric basin in morocco which was infilled with a longitudinally prograding mixed siliciclastic and carbonatic depositional sequence during the early middle jurassic with a minimum thicknesses of 2 5 4 0 km

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

surface ruptures of large himalayan earthquakes in western nepal evidence along a reactivated strand of the main boundary thrust the chronology of the seismic ruptures along the active faults of western nepal remains almost unconstrained despite their high seismogenic potential we present here a slip history of one of these structures a 120 km long reactivated segment of the main boundary thrust named the surkhet gorahi fault this slip history is based on geomorphologic and neotectonic mapping of active faults deduced from the analysis of a high resolution total station digital elevation model and 15 detrital charcoals radiocarbon ages constraining the age of deposition or abandonment of 4 alluvial terraces of the bheri river in botechaur our results show that the last two earthquakes occurred on this fault after 1860 and 640 bp respectively and accommodated slip greater than 8 m each a value corresponding to the incremental vertical offset of the terraces such events released a significant part of the slip deficit accumulated on the main himalayan thrust fault however given the geometry of this fault system as well as the date of occurrence of the last events the ruptures could be associated with major earthquakes also rupturing the main frontal thrust such as the great 1505 earthquake

matched filter detection of the missing pre mainshock events and aftershocks in the 2015 gorkha nepal earthquake sequence abstract the 25 april 2015 mw 7 8 gorkha nepal earthquake occurred at the bottom edge of the locked portion of the main himalayan thrust where the indian plate underthrusts the himalayan wedge the earthquake was followed by a number of large aftershocks but not preceded by any foreshocks within 3 weeks according to the neic or isc catalog however due to the limited station coverage of the local seismic network a large portion of events may not be reported in routine catalogs here we employ the matched filter technique to recover the undocumented earthquakes for the period beginning 80 days before through 30 days after the 2015 gorkha earthquake we detect twice as many aftershocks as those listed in the isc catalog we observe an along strike aftershock expansion after the mainshock and before the largest mw 7 3 aftershock that occurred on 12 may 2015 repeating earthquakes are found to the ese of the mainshock rupture area suggesting that the expansion may be partially driven by afterslip in addition we observe a significant increase in seismicity rate 3 4 days prior to the mainshock initiating 6 h after a m 5 2 earthquake located 240 km to the nw of the mainshock the increase of seismic activities occurs in a wide region around the gorkha principal slip zone indicating the effect of delayed dynamic triggering may contribute to the large scale unloading process prior to the 2015 gorkha mainshock

rupture process of the mw 7 9 2015 gorkha earthquake nepal insights into himalayan megathrust segmentation we investigate the rupture process of the 25 april 2015 gorkha earthquake mw 7 9 using a kinematic joint inversion of teleseismic waves strong motion data high rate gps static gps and synthetic aperture radar sar data the rupture is found to be simple in terms of coseismic slip and even more in terms of rupture velocity as both inversion results and a complementing back projection analysis show that the main slip patch broke unilaterally at a steady velocity of 3 1 3 3 km s this feature likely contributes to the moderate peak ground acceleration 0 2 g observed in kathmandu the 15 km deep rupture occurs along the base of the coupled portion of the main himalayan thrust and does not break the area ranging from kathmandu to the front the limitation in length and width of the rupture cannot be identified in the preearthquake interseismic coupling distribution and is therefore discussed in light of the structural architecture of the megathrust

intensity magnitude location and attenuation in india for felt earthquakes since 1762 a comprehensive consistently interpreted new catalog of felt intensities for india martin and szeliga 2010 this issue includes intensities for 570 earth quakes instrumental magnitudes and locations are available for 100 of these events we use the intensity values for 29 of the instrumentally recorded events to develop new intensity versus attenuation relations for the indian subcontinent and the himalayan region we then use these relations to determine the locations and mag nitudes of 234 historical events using the method of bakun and wentworth 1997 for the remaining 336 events intensity distributions are too sparse to determine mag nitude or location we evaluate magnitude and location accuracy of newly located events by comparing the instrumental with the intensity derived location for 29 cali bration events for which more than 15 intensity observations are available with few exceptions most intensity derived locations lie within a fault length of the instrumen tally determined location for events in which the azimuthal distribution of intensities is limited we conclude that the formal error bounds from the regression of bakun and wentworth 1997 do not reflect the true uncertainties we also find that the regression underestimates the uncertainties of the location and magnitude of the 1819 allah bund earthquake for which a location has been inferred from mapped surface deformation comparing our inferred attenuation relations to those developed for other regions we find that attenuation for himalayan events is comparable to intensity attenuation in california bakun and wentworth 1997 while intensity attenuation for cratonic events is higher than intensity attenuation reported for central eastern north america bakun et al 2003 further we present evidence that intensities of intraplate earth quakes have a nonlinear dependence on magnitude such that attenuation relations based largely on small to moderate earthquakes may significantly overestimate the magnitudes of historical earthquakes