modeling mountain building and the seismic cycle in the himalaya of nepal a host of information is now available regarding the geological and thermal structure as well as deformation rate across the himalaya of central nepal these data are reconciled in a two dimensional mechanical model that incorporates the rheological layering of the crust which depends on the local temperature and surface processes over geological timescale 5 ma the 20 mm yr estimated shortening rate across the range is accommodated by localized thrust faulting along the main himalayan thrust fault mht the mht reaches the surface along the foothills where it is called the main frontal thrust fault mft the mht flattens beneath the lesser himalaya and forms a midcrustal ramp at the front of the higher himalaya consistent with the river incision and the anticlinal structure of the lesser himalaya farther northward the mht roots into a subhorizontal shear zone that coincides with a midcrustal seismic reflector aseismic slip along this shear zone is accommodated in the interseismic period by elastic straining of the upper crust increasing the coulomb stress beneath the front of the higher himalaya where most of the microseismic activity clusters negligible deformation of the hanging wall requires a low apparent friction coefficient less than 0 3 on the flat portion of the mht on the ramp might be as high as 0 6 sensitivity tests show that a rather compliant quartz rich rheology and a high radioactive heat production in the upper crust of 2 5 w m 3 is required erosion affects the thermal structure and interplays with crustal deformation a dynamic equilibrium is obtained in which erosion balances tectonic uplift maintaining steady state thermal structure topography and deformation field using a linear diffusion model of erosion we constrain the value of the mass diffusivity coefficient to 0 5 1 6 l0 4 m 2 yr this study demonstrates that the data are internally consistent and compatible with current understanding of the mechanics of crustal deformation and highlight the role of viscous flow in the lower crust and of surface erosion in orogeny processes on the long term as well as during interseismic period

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

detailed rupture imaging of the 25 april 2015 nepal earthquake using teleseismic p waves we analyze the rupture process of the 25 april 2015 nepal earthquake with globally recorded teleseismic p waves the rupture propagated east southeast from the hypocenter for about 160 km with a duration of 55 s backprojection of both high frequency hf 0 2 to 3 hz and low frequency lf 0 05 to 0 2 hz p waves suggest a multistage rupture process from the low frequency images we resolve an initial slow downdip northward rupture near the nucleation area for the first 20 s stage 1 followed by two faster updip ruptures 20 to 40 s for stage 2 and 40 to 55 s for stage 3 which released most of the radiated energy northeast of kathmandu the centroid rupture power from lf backprojection agrees well with the global centroid moment tensor solution the spatial resolution of the backprojection images is validated by applying similar analysis to nearby aftershocks the overall rupture pattern agrees well with the aftershock distribution a multiple asperity model could explain the observed multistage rupture and aftershock distribution

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

accelerating seismic crustal deformation before the izmit nw turkey large mainshock of 1999 august 17 and the evolution of its aftershock sequence summary the large izmit nw turkey mainshock 1999 august 17 mw 7 6 followed by another large earthquake on 1999 november 12 mw 7 2 caused extensive damage and loss of life in a zone approximately 170 km long along the coastal area of the gulf of izmit and further east to adapazari and duzce on the basis of the critical earthquake concept and by applying a recently developed optimization algorithm an elliptical area surrounding the 1999 august 17 mainshock epicentre was identified in which accelerating moderate magnitude seismic activity started in 1981 and culminated in the generation of the mainshock on the other hand the space and time distribution of the aftershocks of the first mainshock 1999 august 17 and the time variations of the b value of the gutenberg richter recurrence law and the mean aftershock magnitude suggest that the second mainshock 1999 november 12 might have been anticipated

the estimation of green s function from local earthquake recordings and the modelling of the site response abstract a method is presented for the modelling of the site response from the deconvolution of local earthquake recordings the green s function for the propagation medium is obtained by using the assumption of minimum phase propagation for a stratified absorptive earth model as deconvolution criterion the application of this technique to theoretical data shows that local synthetic seismograms can be deconvolved with high accuracy the site response for an actual site bhb in the swabian jura southwest germany has been estimated by integrating over a number of green s functions obtained for different incidence angles thus enhancing the effects of the superficial layers and reducing the effects of the deeper structure the comparison between accelerograms modelled with the obtained average site response and an observed accelerogram yields a good fit in peak and rms acceleration and strong motion duration

asperities and barriers on the seismogenic zone in north chile state of the art after the 2007 mw 7 7 tocopilla earthquake inferred by gps and insar data the mw 7 7 2007 november 14 earthquake had an epicentre located close to the city of tocopilla at the southern end of a known seismic gap in north chile through modelling of global positioning system gps and radar interferometry insar data we show that this event ruptured the deeper part of the seismogenic interface 30 50 km and did not reach the surface the earthquake initiated at the hypocentre and was arrested 150 km south beneath the mejillones peninsula an area already identified as an important structural barrier between two segments of the peru chile subduction zone our preferred models for the tocopilla main shock show slip concentrated in two main asperities consistent with previous inversions of seismological data slip appears to have propagated towards relatively shallow depths at its southern extremity under the mejillones peninsula our analysis of post seismic deformation suggests that small but still significant post seismic slip occurred within the first 10 d after the main shock and that it was mostly concentrated at the southern end of the rupture the post seismic deformation occurring in this period represents 12 19 per cent of the coseismic deformation of which 30 55 per cent has been released aseismically post seismic slip appears to concentrate within regions that exhibit low coseismic slip suggesting that the afterslip distribution during the first month of the post seismic interval complements the coseismic slip the 2007 tocopilla earthquake released only 2 5 per cent of the moment deficit accumulated on the interface during the past 130 yr and may be regarded as a possible precursor of a larger subduction earthquake rupturing partially or completely the 500 km long north chile seismic gap

india and sunda plates motion and deformation along their boundary in myanmar determined by gps using a regional gps data set including 190 stations in asia from nepal to eastern indonesia and spanning 11 years we update the present day relative motion between the indian and sundaland plates and discuss the deformation taking place between them in myanmar revisiting measurements acquired on the main boundary thrust in nepal it appears that points in southern nepal exhibit negligible deformation with respect to mainland india including these points using a longer time span than previous studies and making an accurate geodetic mapping in the newest reference frame allows us to refine the present day indian motion our results confirm that the current motion of india is slower than predicted by the nuvel 1a model and in addition our india eurasia motion is significantly 5 mm yr slower than previous geodetic determinations this new indian motion combined with a refined determination of the sundaland motion gives way to a relative india sunda angular velocity of 20 2 n 26 1 e 0 370 myr in itrf2000 predicting a relative motion of 35 mm yr oriented n10 at the latitude of myanmar there the sagaing fault accommodates only 18 mm yr of right lateral strike slip only half of the shear component of motion we present two models addressing how and where the remaining deformation may occur a first model of distributed deformation implies convergence on the arakan subduction the northern continuation of the now famous sumatra andaman trench and wrench faulting in the arakan wedge the second model uses localized deformation where deformation observed west of the sagaing fault is entirely due to elastic loading on a faster and oblique arakan subduction 23 mm yr this latter model predicts that a major earthquake of mw 8 5 may occur every century on this segment of the subduction

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

strong motion modeling of the imperial valley earthquake of 1979 twelve three component strong motion displacement records are modeled for the 1979 imperial valley earthquake to recover the distribution of slip on the imperial fault plane the final model for which point source responses are calculated by a discrete wavenumber finite element technique uses a structure with gradients in material properties rather than layers the effects of a velocity gradient are investigated by comparing synthetics with a layer over a half space model using generalized rays it is shown that a uniform fault rupture model on a rectangular fault plane does not explain the data the preferred fault model has slip concentrated below 5 km in the basement material and between the epicenter 5 km south of the international border and highway 80 within this region there appears to be two localized areas of larger dislocations one just north of the border near bonds corner and a second under interstate 8 at meloland overpass a major arrival associated with large amplitude vertical accelerations up to 1 7 g is identified in the el centro array records this arrival has an s p time of approximately 2 3 sec at many of the array stations and is modeled as originating from a localized source 8 km to the south of the array the moment is estimated to be 5 0 10 25 dyne cm from the strong motion records which is consistent with teleseismic body wave estimates the preferred fault model is strike slip with a 90 dip the average strike is 143 however to explain vertical waveforms near the fault trace a corrugated or wiggly fault plane is introduced the average rupture velocity is in the range 2 5 to 2 7 km sec 0 8 to 0 9 times the basement shear wave velocity the preferred model has unilateral rupture propagation to the north although the data would allow a small amount of propagation to the south the estimated stress drop for the entire fault plane is only 5 to 10 bars however the stress drop over the more localized sources is about 200 bars the fault model is consistent with the pattern of seismicity and observations of aseismic creep in the imperial valley and suggests that the southern half of the imperial fault acts as a locked section which breaks periodically

numerical simulation of three dimensional faulting processes with heterogeneous rate and state dependent friction abstract miyatake t 1992 numerical simulation of three dimensional faulting processes with heterogeneous rate and state dependent friction in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 223 232 numerical simulations of three dimensional faulting processes with heterogeneous rate and state dependent friction were carried out by using a multi mass spring model the rate and state dependent friction law proposed by dieterich and later developed by ruina has much capability to simulate a wide variety of source processes e g precursory slip post seismic slip co seismic slip creep events and earthquake cycles since the original equation is a stiff ordinary equation which has rapidly decaying solutions and is difficult to solve we modified the equation so that numerical computation are made stable this rate and approximate state dependent friction law is applied to a single degree of freedom elastic system to compare its dynamical behaviours with those of the original friction law and found that our friction law was a good approximation of the original formula then we apply this modified friction law to a multi mass spring model to simulate a whole earthquake source process in this paper we studied mainly the effect of heterogeneity of frictional parameters three types of barriers i e a strong barrier a weak barrier and a relaxation barrier can be simulated by certain frictional parameters for each case large mainshocks occurred repeatedly in the case of a weak barrier the barrier region slipped with some delay time during the mainshock i e the occurrence of a multiple shock in the case of a strong barrier the barrier region was left unslipped during the mainshock a small part of this barrier region slipped sequentially as small aftershocks and eventually the entire barrier region slipped as the largest aftershock a fault with a relaxation barrier was also left unslipped during the mainshock similarly to a strong barrier case but a small part of the barrier slipped as creep events

the mw 8 0 antofagasta northern chile earthquake of 30 july 1995 a precursor to the end of the large 1877 gap abstract an m w 8 0 earthquake occurred on 30 july 1995 in the antofagasta region northern chile the main rupture corresponding to thrust faulting developed from 10 to 50 km in depth along the subduction interface between the nazca and the south american plates the 1995 earthquake took place just south of the large seismic gap where a great earthquake m 9 had occurred in 1877 most of the 1995 rupture was located within a local network consisting of nine short period stations that had been previously installed at the southern end of the 1877 gap and the aftershock sequence could be accurately monitored little destruction resulted from the 1995 earthquake in spite of its large size ground acceleration in antofagasta reached 29 of gravity a tsunami wave 2 to 2 5 m high was observed along the coast from mejillones to taltal one strong foreshock m w 6 2 occurred in the 1995 hypocentral region 6 months before the main event body wave modeling of broadband seismograms from the global network along with the analysis of the aftershock distribution allows us to propose a well constrained model for the whole rupture process some additional details of the rupture were obtained from an accelerometer record at antofagasta the main rupture started as a double even with thrust mechanism below the southern part of the mejillones peninsula and it propagated southward in a n200 e direction with an average velocity of 2 8 km sec it ended near the trench in normal faulting the total rupture area and seismic moment are 185 90 km 2 and 1 2 10 28 dyne cm respectively the aftershock distribution delineates a well defined rupture surface along the subduction interface the distribution of epicenters during the first 20 h of aftershock activity shows a sharp northern boundary beneath the mejillones peninsula hence the 1995 main rupture did not propagate north of the mejillones peninsula into the 1877 gap aftershocks during the following 2 weeks indicate a growth of the initial rupture zone toward the north the mechanisms of the strongest aftershocks are similar to that of the mainshock the down dip termination of the main rupture corresponds to the maximum depth 50 km of the region that had been identified as the locked part of the subduction interface from the analysis of the microseismicity recorded by the local network prior to the 1995 event a well constrained dislocation model is proposed for the 1995 main rupture which produces surface displacements in good agreement with available observations of coastal uplift and gps measurements the dislocation model as well as global positioning system gps measurements indicate that the 1995 earthquake generated e w extension in the coastal region of antofagasta the atacama fault located 40 to 50 km above the 1995 main rupture showed small fresh surface ruptures near sierra remiendos 70 km to the sse of antofagasta with a maximum vertical offset of 20 cm this offset corresponds to normal faulting which is in agreement with the e w co seismic extension the mejillones peninsula appears to be the surface expression of a barrier that interrupted the propagation of the 1995 rupture to the north into the region of the 1877 gap modeling of static stress changes induced by the antofagasta earthquake indicates an increase in compressive stresses along a direction transverse to the trench immediately to the north of the 1995 rupture surface thus the chances for the reactivation of the 1877 gap after this event are greater now

seismicity and one dimensional velocity structure of the himalayan collision zone earthquakes in the crust and upper mantle 1 earthquakes beneath the himalayan collision zone occur at depths between near surface and around 100 km below sea level after relocating earthquakes with two one dimensional 1 d velocity models we found a clear bimodal depth distribution for earthquakes in the himalayas of eastern nepal and the southern tibetan plateau and evidence that some earthquakes originate at upper mantle depths seismicity in nepal shows an accumulation of earthquakes along the front of the himalayan arc with a seismic gap between longitudes 87 3 e and 87 7 e although upper crustal seismicity along the topographic front of the high himalaya is consistent with a region of high strain accumulation associated with convergence on the main himalayan thrust fault microearthquakes do not necessarily occur on this fault instead they concentrate in the hanging wall seismic activity in the sub himalaya and the terai plains is almost exclusively limited to the vicinity of the location of the magnitude 6 5 20 august 1988 udayapur earthquake with most of the earthquakes in the lower crust and the upper mantle clusters of earthquakes in the lesser and high himalayas and south tibet tethyan himalayas mark very well defined zones of seismicity at depths between 50 and 100 km confirming the presence of earthquakes in the upper mantle in the region of continental collision the occurrence of earthquakes at sub moho depths favors the idea that the continental upper mantle deforms by brittle processes

giant ice rings on lakes baikal and hovsgol inventory associated water structure and potential formation mechanism observations of giant ice rings on lake baikal russia have recently sparked scientific and public interest however there is still no clear consensus on their origins here we provide an inventory of the ice rings based on satellite imagery and photography for 1974 2014 we have identified 45 rings on lake baikal compared with 13 previously known and also for the first time four rings for the neighbouring lake hovsgol mongolia the results of our hydrographic surveys beneath the ice rings in lake baikal in 2012 2014 and in lake hovsgol in 2015 show the presence of warm double convex lens like eddies before and during manifestation of ice rings we suggest that these eddies are the driving factor for the formation of ice rings in these lakes we reassess the existing hypotheses of ice ring formation and discuss the potential mechanisms of eddy formation

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

upper crustal shortening and forward modeling of the himalayan thrust belt along the budhi gandaki river central nepal a balanced cross section along the budhi gandaki river in central nepal between the main central thrust including displacement on that fault and the main frontal thrust reveals a minimum total shortening of 400 km minimum displacement on major orogen scale structures include 116 km on the main central thrust 110 km on the ramgarh thrust 95 km on the trishuli thrust and 56 km in the lesser himalayan duplex the balanced cross section was also incrementally forward modeled assuming a generally forward breaking sequence of thrusting where early faults and hanging wall structures are passively carried from the hinterland toward the foreland the approximate correspondence of the forward modeled result to observe present day geometries suggest that the section interpretation is viable and admissible in the balanced cross section the trishuli thrust is the roof thrust for the lesser himalayan duplex the forward model and reconstruction emphasize that the lesser himalayan duplex grew by incorporating rock from the footwall and transferring it to the hanging wall along the main himalayan thrust as the duplex developed the lesser himalayan ramp migrated southward the movement of lesser himalayan thrust sheets over the ramp pushed the lesser himalayan rock and the overburdens of the greater and tibetan himalayan rock toward the erosional surface this vertical structural movement caused by footwall collapse and duplexing in combination with erosion exhumed the lesser himalaya

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

line of sight displacement from alos 2 interferometry mw 7 8 gorkha earthquake and mw 7 3 aftershock interferometric synthetic aperture radar insar is a key tool for the analysis of displacement and stress changes caused by large crustal earthquakes particularly in remote areas a challenge for traditional insar has been its limited spatial and temporal coverage especially for very large events whose dimensions exceed the typical swath width of 70 100 km this problem is addressed by the alos 2 satellite whose palsar 2 instrument operates in scansar mode enabling a repeat time of 2 weeks and a swath width of 350 km here we present insar line of sight displacement data from alos 2 palsar 2 observations covering the mw 7 8 gorkha nepal earthquake and its mw 7 3 aftershock that were acquired within 1 week of each event the data are made freely available and we encourage their use in models of the fault slip and associated stress changes the mw 7 3 aftershock not only extended the rupture area of the main shock toward the east but also left a 20 km gap where the fault has little or no coseismic slip we estimate this unslipped fault patch has the potential to generate a mw 6 9 event

integrated seismic source model of the 2015 gorkha nepal earthquake we compared spatiotemporal slip rate and high frequency around 1 hz radiation distributions from teleseismic p wave data to infer the seismic rupture process of the 2015 gorkha nepal earthquake for these estimates we applied a novel waveform inversion formulation that mitigates the effect of green s functions uncertainty and a hybrid backprojection method that mitigates contamination by depth phases our model showed that the dynamic rupture front propagated eastward from the hypocenter at 3 0 km s and triggered a large slip event centered about 50 km to the east it also showed that the large slip event included a rapid rupture acceleration event and an irregular deceleration of rupture propagation before the rupture termination heterogeneity of the stress drop or fracture energy in the eastern part of the rupture area where aftershock activity was high inhibited rupture growth high frequency radiation sources tended to be in the deeper part of the large slip area which suggests that heterogeneity of the stress drop or fracture energy there may have contributed to the damage in and around kathmandu

the el asnam algeria earthquake of 10 october 1980 multiple source mechanism determined from long period records we present a study of the el asnam algeria earthquake of 10 october 1980 from a large collection of long period surface and body wave records the focal mechanism of the main shock is well constrained by the p wave first motions at teleseismic distances and field observations it was a thrust event on a plane striking n45 e and a dip angle of 54 to the north it had a small component of left lateral motion 83 ouyed et al 1981 gaudemer et al 1981 this earthquake was very well recorded on wwssn stations and on gdsn and ida digital stations with a good azimuthal distribution from these records we confirm the focal solution and obtain a seismic moment m o 5 1026 dyne cm the p wave seismograms indicate a complex source we show that it is not sufficient to model the source by a multiple event but it is also necessary to include a propagation effect in order to explain accurately the waveform with assumptions based on field observation of the surface breaks we model the p waves including two discontinuities of the propagation along the fault plane and obtain a good agreement of the waveform

andean structural control on interseismic coupling in the north chile subduction zone segmentation can influence the extent of earthquake rupture and event magnitude large megathrust earthquakes result from total rupture of relatively continuous segments of the subduction interface segmentation is attributed to variations in the frictional properties of the seismogenic zone or to topographic features on the down going plate structures in the overriding plate may also influence segmentation but their importance has been dismissed here we investigate the links between interface segmentation at the north chile seismic gap and a crustal scale fault structure in the overriding plate that forms a coastal scarp of about 1 km in height we use satellite interferometric synthetic aperture radar insar and global positioning system gps data to measure interseismic surface deformation between 2003 and 2009 and compare the deformation with rupture extent during well documented earthquakes from these data we infer the degree of coupling and segmentation at depth we find that along a 500 km long segment the base of the strongly coupled seismogenic zone correlates with the line of the surface coastal scarp and follows the outline of the mejillones peninsula this correlation implies that large scale structures in the overriding plate can influence the frictional properties of the seismogenic zone at depth we therefore suggest that the occurrence of megathrust earthquakes in northern chile is controlled by the surface structures that build andean topography

the 14 november 2001 kokoxili tibet earthquake high frequency seismic radiation originating from the transitions between sub rayleigh and supershear rupture velocity regimes seismic array based analysis of the major kokoxili earthquake tibet 14 november 2001 yields an unambiguous reconstruction of the seismic rupture history and relates it to the generated seismic radiation we demonstrate that after a classical sub rayleigh velocity stage the rupture speed has jumped to supershear values close to compressional wave velocity over a 175 km long fault segment before abruptly slowing down in the late part of the earthquake the transition locations between these three phases are correlated with the fault geometry and are associated with the most energetic radiation this observation proves that the rupture velocity changes as theoretically predicted are a primary source of high frequency seismic radiation this result requires reconsidering the origins of seismic damage generally attributed to slip variations

strong motion prediction using mathematical modeling techniques abstract the parkfield california earthquake of 1966 produced the first recording of ground motion in the immediate vicinity of an earthquake fault the simplicity of displacement pulse observed at station 2 aroused great interest among seismologists working in the area of earthquake source mechanism since then numerous theoretical works on simulating strong motion have been carried out starting with the use of a simple kinematic model assuming a uniform slip over a fault plane the assumption of uniform slip had to be modified to explain the strong motion observed during the parkfield earthquake of 1966 the borrego mountain earthquake of 1968 the san fernando earthquake of 1971 the imperial valley earthquake of 1979 the el asnam earthquake of 1980 and others through these studies the simulation technique has been advanced to include a more realistic medium in the beginning most methods used green9s function for an unbounded homogeneous medium then the free surface effect the effect of a sedimentary layer as well as laterally heterogeneous basin structure have been included in the simulation the above simulation studies were however restricted to relatively low frequency waves represented in a displacement or velocity seismogram in order to predict an acceleration seismogram dominated by high frequency waves hybrid models have been proposed in which gross features of rupture propagation are specified deterministically but the details of the process are described by a stochastic model specified by a small number of parameters the application of these models to several california earthquakes revealed encouraging results that some of the key parameters of the model are stable among earthquakes mathematical modeling techniques will play an important role in the prediction of strong motion for a great earthquake in california as well as for major earthquakes outside california based on the records of moderate earthquakes already acquired in california

interseismic coupling segmentation and mechanical behavior of the central chile subduction zone global positioning system gps measurements carried out in chile over the last two decades showed that an entire portion of the nazca south america subduction zone 38 s 24 s was locked over this period of time the induced accumulation of elastic deformation in the upper plate was not released until the recent maule earthquake of 27 february 2010 mw 8 8 that ruptured the southern part of this section locking or coupling between the two plates varies both with depth and along strike here we use our own gps data an updated solution of our extended network in central chile combined with other published data sets to quantify the spatial variations of the coupling that prevailed before the maule earthquake using a simple elastic model based on the back slip assumption we show that coupling variations on the subduction plane are sufficient to explain the observed surface deformation with no need of a sliver in central chile we identify four segments characterized by higher coupling and separated by narrow areas of lower coupling this segmentation is in good agreement with historical and recent seismicity in chile in particular the narrow zones of lower coupling seem to have stopped most large seismic ruptures including maule s these zones are often associated with irregular bathymetric or coastal features fracture zones or peninsulas finally coseismic and early post seismic slip distribution of the maule earthquake occurring either in previously highly or weakly coupled zones map a complex distribution of velocity weakening and velocity strengthening patches on the subduction interface

dynamics of the 2015 m7 8 nepal earthquake the 2015 m7 8 nepal earthquake ruptured part of the main himalayan thrust beneath kathmandu to study the dynamics of this event we compute p wave spectra of the main shock and of two large aftershocks to estimate stress drop and radiated energy we find that surface reflections depth phases of these shallow earthquakes produce interference that severely biases spectral measurements unless corrections are applied measures of earthquake dynamics for the main shock are within the range of estimates from global and regional earthquakes we explore the azimuthal and temporal variations of radiated energy and highlight unique aspects of the m7 8 rupture the beginning of the earthquake likely experienced a dynamic weakening mechanism immediately followed by an abrupt change in fault geometry correlation of backprojection results with frequency dependent variations in the radiated energy rate and with the suggested geometry of the main himalayan thrust yields new constraints on dynamic ruptures through geometrical barriers

linearized inversion for fault rupture behavior application to the 1984 morgan hill california earthquake we present a technique to infer the rupture history of an earthquake from near source records of ground motion unlike most previous studies each point on the fault is assumed to slip only once when the rupture front passes with a spatially variable slip intensity in this parameterization the data are linearly related to slip intensity but nonlinearly related to rupture time we perform a linearized inversion for slip intensity and rupture time by iteratively perturbing an assumed starting model the inverse problem for the model perturbation is solved using a tomographic back projection technique smoothing and inequality constraints are applied to ensure that the resulting solution is stable and feasible asymptotic ray theory is used to calculate theoretical seismograms and partial derivatives with respect to model parameters in test cases with noisy synthetic data sets we found that it is possible to distinguish between rupture models having variable slip amplitude and models having variable rupture velocity provided the station coverage is adequate we apply the technique to recordings of the april 24 1984 morgan hill earthquake the results indicate that slip amplitude on the fault plane was extremely variable and that the rupture front did not propagate uniformly away from the hypocenter in particular rupture was delayed on a 12 km2 section of the fault approximately 14 km to the southeast of the hypocenter the rupture front surrounded the region which subsequently failed with a component of rupture propagation back toward the hypocenter similar behavior has been observed in dynamic rupture models with stress or strength inhomogeneities this segment of the fault ruptured with a large slip amplitude releasing 12 of the total seismic moment from 4 of the total area of the aftershock zone the surface trace of this section of the fault is characterized by a complex left step that could act to increase the normal stress acting across the fault however the distribution of aftershocks suggests that the fault at depth is simpler and that it may bend to the right in either case our rupture model suggests that this segment of the fault represents an asperity which initially resisted rupture but eventually ruptured massively we estimate the shear fracture energy for this earthquake to be 2 106 j m2

strong motion seismology although this is the first review on this topic to appear in a quadrennial report the roots of strong motion seismology extend back to at least 1932 when far sighted engineers in the seismological field survey of the u s coast and geodetic survey installed rugged fieldworthy instruments designed to make on scale recordings of large earthquakes carder 1964 these instruments are called accelerographs for their output closely mimics ground acceleration hudson 1979 the original instruments and their offspring have provided a wealth of information about ground motions of direct use to engineers due in large part to the continued devotion of the seismological field survey now part of the branch of engineering seismology and geology at the u s geological survey the number of recordings has increased substantially particularly in the last two decades and multiple recordings of a few california earthquakes have provided the data necessary to begin to unravel the complexities of the ground motions and to predict these motions on an empirical basis although seismologists used accelerograph records in studies of earthquake energy and ground motion attenuation as long ago as 1942 gutenberg and richter 1942 1956 widespread seismological use of the records began with aki s 1968 analysis of the 1966 parkfield earthquake

aftershock seismicity of the 2010 maule mw 8 8 chile earthquake correlation between co seismic slip models and aftershock distribution 1 the 27 february 2010 maule chile mw 8 8 earthquake is one of the best instrumentally observed subduction zone megathrust events here we present locations magnitudes and cumulative equivalent moment of the first 2 months of aftershocks recorded on a temporary network deployed within 2 weeks of the occurrence of the mainshock using automatically determined onset times and a back projection approach for event association we are able to detect over 30 000 events in the time period analyzed to further increase the location accuracy we systematically searched for potential s wave arrivals and events were located in a regional 2d velocity model additionally we calculated regional moment tensors to gain insight into the deformation history of the aftershock sequence we find that the aftershock seismicity is concentrated between 40 and 140 km distance from the trench over a depth range of 10 to 35 km focal mechanisms indicate a predominance of thrust faulting with occasional normal faulting events increased activity is seen in the outer rise region of the nazca plate predominantly in the northern part of the rupture area further down dip a second band of clustered seismicity showing mainly thrust motion is located at depths of 40 45 km by comparing recent published mainshock source inversions with our aftershock distribution we discriminate slip models based on the assumption that aftershocks occur in areas of rapid transition between high and low slip surrounding high slip regions of the mainshock

on the use of dislocations to model interseismic strain and stress build up at intracontinental thrust faults creeping dislocations in an elastic half space are commonly used to model interseismic deformation at subduction zones and might also apply to major intracontinental thrust faults such as the main himalayan thrust here we compare such models with a more realistic 2 d finite element model that accounts for the mechanical layering of the continental lithosphere and surface processes and that was found to fit all available constraints on interseismic and long term surface displacements these can also be fitted satisfactorily from dislocation models the conventional back slip model commonly used for subduction zones may however lead to a biased inference about the geometry of the locked portion of the thrust fault we therefore favour the use of a creeping buried dislocation that simulates the ductile shear zone in the lower crust a limitation of dislocation models is that the mechanical response of the lithosphere to the growth of the topography by bending of the elastic cores and ductile flow in the lower crust cannot be easily introduced fortunately these effects can be neglected because we may assume to first order a stationary topography moreover we show that not only can dislocation models be used to adjust surface displacements but with some caution they can also provide a physically sound rationale to interpret interseismic microseismicity in terms of stress variations

earthquake source spectra in eastern north america source spectra for earthquakes of 3 m 7 in eastern north america ena are determined from regional seismograph recordings strong motion records teleseismic data and modified mercalli intensity data the inclusion of mmi data is made possible by the finding that the felt area of an earthquake is an accurate measure of its high frequency spectral level at the source current ground motion relations for ena are based on a brune source model with a stress parameter of 100 bars this model is a poor fit to ena source spectra for events of m 4 at high frequencies 5 to 10 hz observed spectral amplitudes are more nearly matched by a brune stress parameter of 200 bars intermediate frequency amplitudes near 1 hz are matched by a stress parameter of approximately 50 bars an empirical two corner source model is proposed to describe ena source spectra for events of 4 m 7

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

p wave complexity and fault asperities the borrego mountain california earthquake of 1968 results from a synthetic seismogram analysis of the short period p waves from the borrego mountain earthquake of 9 april 1968 m l 6 4 are used to model the strong motion recording at el centro a short period long period deconvolution analysis of the teleseismic p waves suggested that a two source model would fit the data much better than the single source model presented by burdick and mellman 1976 forward and inverse modeling of the data demonstrated that two sources each of less than 2 sec duration the second occurring 2 2 sec after the first and both being at about 8 km depth best fit the short period waveforms from this model long period synthetics were generated which were found to be quite compatible with the data this source model was also used to synthesize the strong motion sh displacement velocity and acceleration records from el centro california the close match of synthetics and data is used to argue that short period waveforms contain much information about asperities which play a crucial role in the near source strong motions from an earthquake the borrego mountain event probably began with the failure of a fault asperity the evidence for this is the several hundred bars stress drops of the two short period sources and the probable location of these sources in a place where there was almost no aftershock activity or postseismic creep on the fault

nonlinear soil response a reality geotechnical models consistently indicate that the stress strain relationship of soils is nonlinear and hysteretic especially at shear strains larger than 10 5 to 10 4 nonlinear effects such as an increase in damping and reduction in shear wave velocity as excitation strength increases are commonly recognized in the dynamic loading of soils on the other hand these effects are usually ignored in seismological models of ground motion prediction because of the lack of compelling corroborative evidence from strong motion observations the situation is being changed by recently obtained data explicit evidence of strong motion deamplification accompanied by changes in resonant frequencies are found in the data from the 1985 michoacan mexico and the 1989 loma prieta california earthquakes the events recorded by the vertical and surface accelerograph arrays in taiwan as well as a number of other events throughout the world evidence of nonlinear behavior becomes apparent beyond a threshold acceleration of 100 to 200 gal nonlinearity is considerable in cohesionless soil but may be negligible in stiff soils the findings of recent years indicate that nonlinear site effects are more common than previously recognized in strong motion seismology

joint inversion of insar gps teleseismic and strong motion data for the spatial and temporal distribution of earthquake slip application to the 1999 izmit mainshock the space time distribution of slip of the 17 august 1999 izmit earthquake is investigated by inverting synthetic aperture radar sar interferometry and global positioning system gps data together with teleseismic broadband and near field strong motion records surface offsets are used as an added constraint special emphasis is given to analysis of the resolution of the different data sets we use a four segment finite fault model and a nonlinear inversion scheme allowing slip to vary in amplitude direction and duration as well as variable rupture velocity from the inversion of synthetic data we find that the best spatial resolution can be expected in the upper half of the fault model above 12 km where coverage of the interferometric sar data is good western half of the rupture and near the gps and strong motion stations teleseismic data are found to have a lower resolution that is more evenly distributed over the fault model the joint inversion of all the data sets has an increased resolving power compared with the separate inversions and gives a more robust description of the space and time distribution of slip our study shows the importance of resolution tests in evaluating the reliability of earthquake kinematic models and it confirms that an excellent fit of a single kind of data does not necessarily imply a good retrieval of the kinematic properties of an earthquake the izmit rupture which is almost pure right lateral strike slip faulting is dominated by the bilateral breaking of a central asperity located between 29 7 e about 10 km west of the city of golcuk and 30 4 e eastern margin of sapanka lake with slip reaching 6 8 m in the depth range 6 12 km the western termination of the rupture is found near the city of yalova but large slip ends around 29 7 e about 10 km east of hersek delta a second area of large slip is required by all the data sets further east toward the city of duzce between 30 7 e and 31 1 e karadere and duzce faults this eastern slip zone which is separated from the main central asperity by an area of greatly reduced slip is less well constrained by the data however a strong motion station near the city of duzce helps to locate a high slip patch near 31 1 e in the depth range 6 12 km the total seismic moment resulting from the joint inversion is 2 4 1027 dyne cm most of the energy release occurred in a short time less than 15 sec corresponding to the bilateral breaking of the central asperity rupture propagation is relatively uniform and fast toward the west with a rupture velocity close to 3 5 km sec propagation of large slip toward the east is initially slower but it accelerates during a short time interval about 10 sec after rupture nucleation eastward progression then slows down to less than 2 km sec after 15 sec and rupture almost vanishes in amplitude ca 20 sec after initiation rupture propagation then proceeds on the easternmost karadere and duzce fault segments east of 30 7 e from 22 to ca 50 sec supershear rupture propagation is not required for modeling the waveforms considered in this study the hypocenter of the duzce earthquake which occurred 3 months later 12 november 1999 m w 7 2 is located in the immediate vicinity of the easternmost slip patch of the izmit earthquake manuscript received 28 july 2000

thermal structure and exhumation history of the lesser himalaya in central nepal the lesser himalaya lh consists of metasedimentary rocks that have been scrapped off from the underthrusting indian crust and accreted to the mountain range over the last 20 myr it now forms a significant fraction of the himalayan collisional orogen we document the kinematics and thermal metamorphism associated with the deformation and exhumation of the lh combining thermometric and thermochronological methods with structural geology peak metamorphic temperatures estimated from raman spectroscopy of carbonaceous material decrease gradually from 520 550 c below the main central thrust zone down to less than 330 c these temperatures describe structurally a 20 50 c km inverted apparent gradient the ar muscovite ages from lh samples and from the overlying crystalline thrust sheets all indicate the same regular trend i e an increase from about 3 4 ma near the front of the high range to about 20 ma near the leading edge of the thrust sheets about 80 km to the south this suggests that the lh has been exhumed jointly with the overlying nappes as a result of overthrusting by about 5 mm yr for a convergence rate of about 20 mm yr this implies underthrusting of the indian basement below the himalaya by about 15 mm yr the structure metamorphic grade and exhumation history of the lh supports the view that since the mid miocene the himalayan orogen has essentially grown by underplating rather than by frontal accretion this process has resulted from duplexing at a depth close to the brittle ductile transition zone by southward migration of a midcrustal ramp along the main himalayan thrust fault and is estimated to have resulted in a net flux of up to 150 m 2 yr of lh rocks into the himalayan orogenic wedge the steep inverse thermal gradient across the lh is interpreted to have resulted from a combination of underplating and post metamorphic shearing of the underplated units

thrust tectonics crustal shortening and the structure of the far eastern nepal himalaya balanced and restored structural sections across the far eastern nepal himalaya have been constructed in order to determine the structure and evolution of the himalayan orogenic wedge and the amount of tectonic shortening the region has undergone since the initiation of thrusting along the main central thrust mct the far eastern nepal himalaya is comprised of three distinct thrust bound tectonic packages the higher himalayan crystalline thrust sheet the lesser himalayan metasediment thrust package and the sub himalayan imbricate fan the higher himalayan crystallines consisting of kyanite and sillimanite bearing gneisses intruded by the miocene jannu leucogranites have been thrust over the lesser himalayan metasediments along the mct for a distance of 140 km to 175 km the lesser himalayan metasediments are a 12 km thick unit consisting primarily of phyllites metaquartzites and mylonitic augen gneisses in which garnet biotite and chlorite metamorphic zones are exposed in progressively deeper structural levels the lesser himalayan metasediment thrust package is underlain by a decollement the main detachment fault mdf which lies at a calculated depth of between 6 and 10 km underneath the mahabharat lekh and at a calculated depth of 20 to 25 km north of the tamar khola dome the tamar khola dome overlies a footwall ramp along the mdf where the mdf cuts upsection through the lesser himalayan metasediments the lesser himalayan thrust package probably has an internal structure aproximating a hinterland dipping duplex with the mct and the mdf corresponding to the roof and floor thrusts respectively both the tamar khola thrust an out of sequence breach thrust and the main boundary thrust mbt are splay thrusts off of the mdf the sub himalaya consisting of nonmetamorphosed sedimentary rocks displays an emergent imbricate fan geometry and is underlain by the southern continuation of the mdf which lies at a depth of 5 5 km to 6 km beneath the siwalik hills folding and thrusting within the lesser himalayan thrust package and the sub himalayan imbricate fan have accomodated 45 to 70 km of tectonic shortening total north south shortening across the higher lesser and sub himalaya of far eastern nepal south of the tibetan plateau has been of the order of 185 km to 245 km and has occurred at an average rate of 7 4 mm to 15 3 mm per year since the initiation of the mct between 16 and 25 ma

a broadband study of the 13 august 1978 santa barbara earthquake the santa barbara earthquake of 13 august 1978 provides an opportunity to perform a broadband investigation of body waves for a well recorded moderate size m l 5 1 event the long and short period teleseismic body waves are modeled in the time domain to construct a source time function which is consistent in the period range of 1 to 20 sec the long period records indicate an overall duration of 6 sec while the short period records reveal the fine scale character of the slip history consisting of two sharp pulses separated by about 1 sec the source mechanism determined from this analysis is a moderately dipping 30 ne thrust with significant left lateral slip the moment was determined to be 1 1 10 25 dyne cm the earthquake was also reasonably well recorded on accelerographs in the near field the modeling of the strong motion displacements was a two step procedure 1 the displacements were modeled alone and 2 in an attempt to achieve consistency between the local and far field time functions the qualitative features of the teleseismic short period time function were used to predict the displacements if the two sources in the short period time function are allowed to have different mechanisms the displacements can be modeled quite well this suggests that the overall faulting process was rough and the multiple source character suggested at high frequencies is due to high stress drop asperities the two sources are modeled as asperities separated by 1 5 km the first source has a mechanism consistent with the teleseismic solution while the second source is more steeply dipping the total moment determined from the strong motion data is 3 5 10 24 dyne cm or one third the long period moment this is consistent with other recent studies which suggest that the high frequency strong ground motion is controlled by the distribution of asperities even though the sum of their moments may be small compared to the overall moment this study also shows the importance of teleseismic short periods in predicting the local displacements

the 2012 mw 8 6 sumatra earthquake evidence of westward sequential seismic ruptures associated to the reactivation of a n s ocean fabric 1 the 11 april 2012 mw 8 6 earthquake offshore sumatra is the largest of the rare great intraplate earthquakes of the instrumental era this major strike slip event occurred in the diffuse zone of deformation that accommodates differential rotation between indian and australian plates we perform a back projection analysis calibrated with well located aftershocks of short period teleseismic p waves recorded by the european array to image the rupture process during the mainshock in complement a love wave analysis is conducted for tracking azimuthal change in the apparent global source duration due to the source spatio temporal extent the combined analysis reveals a complex rupture pattern characterized by three main episodes of energy release the latest being located 370 km west of the epicenter on the ninety east ridge with a delay of 120 s we interpret the 11 april 2012 mw 8 6 offshore sumatra earthquake as a complex westward propagating sequence of dynamically triggered strike slip fault ruptures associated to the reactivation of the inherited nne striking sea floor fabric the dynamic triggering mechanism could result from the interaction between transient surface wave stress perturbations and fluids

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

rupture imaging of the mw 7 9 12 may 2008 wenchuan earthquake from back projection of teleseismic p waves 1 the mw 7 9 wenchuan earthquake of 12 may 2008 was the most destructive chinese earthquake since the 1976 tangshan event tens of thousands of people were killed hundreds of thousands were injured and millions were left homeless here we infer the detailed rupture process of the wenchuan earthquake by back projecting teleseismic p energy from several arrays of seismometers this technique has only recently become feasible and is potentially faster than traditional finite fault inversion of teleseismic body waves therefore it may reduce the notification time to emergency response agencies using the iris dmc we collected 255 vertical component broadband p waves at 30 95 from the epicenter we found that at periods of 5 s and greater nearly all of these p waves were coherent enough to be used in a global array we applied a simple down sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function arf we also considered three regional subarrays of seismometers in alaska australia and europe that had apertures less than 30 and p waves that were coherent to periods as short as 1 s individual arfs for these subarrays were skewed toward the subarrays however the linear sum of the regional subarray beams at 1 s produced a symmetric arf similar to that of the groomed global subarray at 5 s for both configurations we obtained the same rupture direction rupture length and rupture time we found that the wenchuan earthquake had three distinct pulses of high beam power at 0 23 and 57 s after the origin time with the pulse at 23 s being highest and that it ruptured unilaterally to the northeast for about 300 km and 110 s with an average speed of 2 8 km s it is possible that similar results can be determined for future large dip slip earthquakes within 20 30 min of the origin time using relatively sparse global networks of seismometers such as those the usgs uses to locate earthquakes in near real time

intraplate deformation of the indian subcontinent 1 while deformation at the earth s surface primarily occurs along tectonic plate boundaries major earthquakes have shaken regions deep within continental interiors three of the largest m 7 5 historic intraplate earthquakes occurred within the indian subcontinent suggesting the possibility of significant intraplate deformation we consider surface velocities determined from new gps data collected at 29 continuous gps stations and 41 survey mode gps stations in india between 1995 and 2007 to find a north south shortening rate of 0 3 0 05 nanostrain yr 1 which may be accommodated by 2 1 mm yr of more localized convergence across central india southward motions at 4 7 mm yr of sites on the shillong plateau in northeast india reflect rapid shortening and high earthquake hazard associated with active thrust faults bounding the plateau the width and magnitude of the elastic strain accumulation field across the himalaya varies little from 76 90 longitude but the strain is more broadly distributed and convergence rates are higher along the eastern 200 km of the range

ten year recurrence time between two major earthquakes affecting the same fault segment earthquake ruptures stop when they encounter barriers impeding further propagation these barriers can theoretically originate from changes of geometry or nature of the seismic faults or from a strong lowering of the tectonic stresses typically due to the occurrence of a recent major earthquake we show here that this latter mechanism can be ineffective at stopping rupture expansion the 17 november 2013 magnitude 7 8 scotia sea earthquake has propagated into a 100 km long zone already ruptured 10 years ago by a magnitude 7 6 earthquake given the plate velocities between scotia and antarctic plates 8 9 mm yr simple recurrence models would have predicted that the segment affected by the 2003 earthquake could not be reruptured by a major earthquake during several hundreds of years this earthquake pair indicates that the variations of the tectonic stress during the seismic history of the fault are small compared to the stresses dynamically generated by a large earthquake

the bermuda earthquake of march 24 1978 a significant oceanic intraplate event the bermuda earthquake m 6 occurred near the westerly extension of the kane fracture zone roughly 370 km southwest of the island of bermuda it is one of the largest oceanic intraplate earthquakes to occur off the eastern coast of north america because of its size and location it has provided an excellent set of wwssn body waves they can be used to infer its depth and faulting parameters by waveform modeling techniques the results indicate a north northwest striking thrust mechanism strike n20 w dip 42 ne rake 90 with the hypocenter located at a depth of 11 km which for an oceanic crust places it predominantly in the mantle the event had a seismic moment of 3 4 1025 dyne cm and its time history was modeled with a symmetric trapezoidal time function 3 s in duration the north northwest strike of the event is in good agreement with the bathymetry of the area the epicenter being close to the southwestern edge of the bermuda rise the strike of the event is also close to that of the inferred extensions of the present ridge fracture zones in the region the presence of such fracture zones is indicative of local weak zones in the lithosphere the bermuda earthquake most likely is associated with one of these zones of weakness and is the result of the application of present day stress imposed on the region by the north american plate in the direction of its absolute motion this is an important event in terms of understanding and estimating seismic hazard on the eastern seaboard of north america

coupled tectonic evolution of andean orogeny and global climate abstract the largest tectonic relief breaking the earth s surface 13 km vertically is at the subduction margin of the andes which generates routinely megathrust earthquakes mw 8 5 and drives the paradigmatic andean orogen here we present key geologic evidence to reassess first order features of geomorphology and tectonics across the central andes where the orogen includes the altiplano plateau and attains its maximum integrated height and width the andean subduction margin has a stepped morphology dominated by the low relief atacama bench which is similar to a giant uplifted terrace slopes gently over a width of 60 100 km from the andes to the pacific and runs over more than 1000 km of coastal length we find that the genesis of stepped morphology at the andean seaboard is due to concomitant development of large west vergent thrusts parallel to the subduction interface and increasing aridity in the atacama desert which keeps an unprecedented large scale record of interplaying tectonics and cenozoic climate change incorporating our results with published geological knowledge demonstrates that andean orogeny is characterized by trench perpendicular bivergent and trench parallel bilateral growth over the past 50 myr associated with positive trench velocity toward the continent trench advance and subduction of a wide slab under south america we hypothesize that a global plate tectonic reorganization involving long lasting viscous mantle flow has probably forced both andean orogeny and global climate cooling since 50 ma in contrast two important stepwise pulses of increasing aridity and trench perpendicular andean growth appear to be results of changes in erosion rates due to global late eocene and middle miocene cooling events

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

scardec a new technique for the rapid determination of seismic moment magnitude focal mechanism and source time functions for large earthquakes using body wave deconvolution accurate and fast magnitude determination for large shallow earthquakes is of key importance for post seismic response and tsumami alert purposes when no local real time data are available which is today the case for most subduction earthquakes the first information comes from teleseismic body waves standard body wave methods give accurate magnitudes for earthquakes up to mw 7 7 5 for larger earthquakes the analysis is more complex because of the non validity of the point source approximation and of the interaction between direct and surface reflected phases the latter effect acts as a strong high pass filter which complicates the magnitude determination we here propose an automated deconvolutive approach which does not impose any simplifying assumptions about the rupture process thus being well adapted to large earthquakes we first determine the source duration based on the length of the high frequency 1 3 hz signal content the deconvolution of synthetic double couple point source signals depending on the four earthquake parameters strike dip rake and depth from the windowed real data body wave signals including p pcp pp sh and scs waves gives the apparent source time function stf we search the optimal combination of these four parameters that respects the physical features of any stf causality positivity and stability of the seismic moment at all stations once this combination is retrieved the integration of the stfs gives directly the moment magnitude we apply this new approach referred as the scardec method to most of the major subduction earthquakes in the period 1990 2010 magnitude differences between the global centroid moment tensor cmt and the scardec method may reach 0 2 but values are found consistent if we take into account that the global cmt solutions for large shallow earthquakes suffer from a known trade off between dip and seismic moment we show by modelling long period surface waves of these events that the source parameters retrieved using the scardec method explain the observed surface waves as well as the global cmt parameters thus confirming the existing trade off for some well instrumented earthquakes our results are also supported by independent studies based on local geodetic or strong motion data this study is mainly focused on moment determination however the scardec method also informs us about the focal mechanism and source depth and can be a starting point to study systematically the complexity of the stf

constraints on himalayan deformation inferred from vertical velocity fields in nepal and tibet spirit leveling data from the nepal himalaya between 1977 and 1990 indicate localized uplift at 2 3 mm yr in the lesser himalaya with spatial wavelengths of 25 35 km and at 4 6 mm yr in the greater himalaya with a wavelength of 40 km leveling data with significantly sparser spatial sampling in southern tibet between 1959 and 1981 suggest that the himalayan divide may be rising at a rate of 7 5 5 6 mm yr relative to central tibet we use two dimensional dislocation modeling methods to examine a number of structural models that yield vertical velocity fields similar to those observed although these models are structurally nonunique dislocation models that satisfy the data require aseismic slip rates of 2 7 mm yr on shallow dipping faults beneath the lesser himalaya and rates of 9 18 mm yr on deep thrust faults dipping at 25 n near the greater himalaya unfortunately the leveling data cannot constrain long wavelength uplift 100 km across the himalaya and unequivocal estimates of aseismic slip in central nepal are therefore not possible in turn the poor spatial density of leveling data in southern tibet may inadequately sample the processes responsible for the uplift of the greater himalaya despite these shortcomings in the leveling data the pattern of uplift is consistent with a crustal scale ramp near the greater himalaya linking shallow northward dipping thrust planes 3 6 beneath the lesser himalaya and southern tibet aseismic slip on the potential rupture surface of future great earthquakes beneath the nepal himalaya south of this ramp appears not to exceed 30 of the total convergence rate between india and southern tibet resulting in an accumulating slip deficit of 13 8 mm yr

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

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