segmentation of the himalayan megathrust around the gorkha earthquake 25 april 2015 in nepal abstract we put the 25 april 2015 earthquake of nepal mw 7 9 into its structural geological context in order to specify the role of the segmentation of the himalayan megathrust the rupture is mainly located nw of kathmandu at a depth of 13 15 km on a flat portion of the main himalayan thrust mht that dips towards the n ne by 7 10 the northern bound of the main rupture corresponds to the transition towards a steeper crustal ramp this ramp which is partly coupled during the interseismic period is only locally affected by the earthquake the southern bound of the rupture was near the leading edge of the lesser himalaya antiformal duplex and near the frontal footwall ramp of the upper nawakot duplex the rupture has been affected by transversal structures on the western side the judi lineament separates the main rupture zone from the nucleation area on the eastern side the gaurishankar lineament separates the 25 april 2015 rupture from the 12 may 2015 mw 7 2 rupture the origin of these lineaments is very complex they are probably linked to pre himalayan faults that extend into the indian shield beneath the mht these inherited faults induce transverse warping of the upper lithosphere beneath the mht control the location of lateral ramps of the thrust system and concentrate the hanging wall deformation at the lateral edge of the ruptures the mht is therefore segmented by stable barriers that define at least five patches in central nepal these barriers influence the extent of the earthquake ruptures for the last two centuries the 1833 mw 7 6 earthquake was rather similar in extent to the 2015 event but its rupture propagated south westwards from an epicentre located ne of kathmandu the patch south of kathmandu was probably affected by at least three earthquakes of mw 7 that followed the 1833 event a few days later or 33 years 1866 event mw 7 2 later the 1934 earthquake mw 8 4 had an epicentre 170 km east of kathmandu may have propagated as far as kathmandu and jumped the gaurishankar lineament this combined structural approach and earthquake study allows us to propose that the mht in the central eastern himalaya is segmented by stable barriers that define barrier type earthquake families however for each individual earthquake within a family the rupture histories could be different furthermore the greatest earthquakes could have broken the barriers and affected the patches of several families the concept of a regular recurrence of characteristic earthquakes is therefore misleading to describe the succession of himalayan earthquakes

implications of felt area magnitude relations for earthquake scaling and the average frequency of perceptible ground motion abstract observed relations between felt area and moment magnitude m for stable continental regions scr and california earthquakes can be explained by a simple model with geometrical spreading attenuation q 1 and earthquake stress drops that remain constant from m 4 to 8 differences in the slopes of the observed felt area m relations between scr and california earthquakes are consistent with differences in q between these tectonic settings fitting the felt area m data to the model yields an estimate of f q where f is the average frequency of minimum perceptible ground motion using fits to the data and instrumentally derived values of q i find that f is between about 2 and 4 hz i present an estimate of the spectral acceleration level associated with the lower limit of perceptibility

a catalog of felt intensity data for 570 earthquakes in india from 1636 to 2009 eight thousand three hundred thirty nine intensity observations have been evaluated for earthquakes that occurred on the indian subcontinent and surround ing plate boundaries from the seventeenth century to the present they characterize 570 earthquakes more than 90 of which occurred in the past two centuries the electronic supplement to this article lists these data using european macroseismic scale ems 98 intensities with their geographic coordinates we summarize these data graphically in the form of a spatially averaged intensity map for the subcontinent a map that emphasizes the features of many previously published earthquake hazard maps for the indian plate but which more faithfully depicts regional amplification and attenuation we also estimate the probable return time for future damaging shaking in five of india s largest cities

preliminary observations from the 3 january 2017 m w 5 6 manu tripura india earthquake abstract on 3 january 2017 a m w 5 6 earthquake occurred in dhalai district in tripura india at 14 39 03 ist 09 09 03 utc with an epicentre at 24 018 n 4 9 km and 91 964 e 4 4 km and a focal depth of 31 6 0 km the focal mechanism solution determined after evaluating data from seismological observatories in india indicated a predominantly strike slip motion on a steeply dipping plane the estimated focal depth and focal mechanism solution places this earthquake in the indian plate that lies beneath the overlying indo burmese wedge as in the 2016 manipur earthquake a strong motion record from shillong india appears to suggest site amplification possibly due to topographic effects in the epicentral region in tripura damage assessed from a field survey and from media reports indicated that the macroseismic intensity approached 6 7 ems with damage also reported in adjacent parts of bangladesh a striking feature of this earthquake were the numerous reports of liquefaction that were forthcoming from fluvial locales in the epicentral region in tripura and at anomalous distances farther north in bangladesh the occurrence of the 2017 manu earthquake emphasises the hazard posed by intraplate earthquakes in tripura and in the neighbouring bengal basin region where records of past earthquakes are scanty or vague and where the presence of unconsolidated deltaic sediments and poor implementation of building codes pose a significant societal and economic threat during larger earthquakes in the future

300 mw baspa ii india s largest private hydroelectric facility on top of a rock avalanche dammed palaeo lake nw himalaya regional geology tectonic setting and seismicity article i nfo this study aims for the characterization of the geological setting of 300 mw baspa ii india s largest private hydroelectric facility which was built on top of a relict rock avalanche dammed palaeo lake baspa valley nw himalaya geologically the hydroelectric installation is located in the higher himalayan crystalline just above the active karcham normal fault which is reactivating the early miocene main central thrust one of the principal himalayan faults the area is seismically active and mass movements are common at ca 8200 yr bp the baspa river was blocked behind a 142 10

interseismic strain accumulation along the western boundary of the indian subcontinent 1 despite an overall sinistral slip rate of 3 cm yr few major earthquakes have occurred in the past 200 years along the chaman fault system the western boundary of the india plate with the eurasia plate gps and insar data reported here indicate sinistral shear velocities of 8 17 mm yr across the westernmost branches of the fault system suggesting that a significant fraction of the plate boundary slip is distributed in the fold and fault belt to the east at its southernmost on land segment 26 n near the triple junction between the arabia eurasia and india plates we find the velocity across the ornach nal fault is 15 1 13 4 16 9 mm yr with a locking depth probably less than 3 km at latitude 30 n near the town of chaman pakistan where a m6 5 earthquake occurred in 1892 the velocity is 8 5 6 8 10 3mm yr and the fault is locked at approximately 3 4 km depth at latitude 33 n and further north insar data indicate a velocity across the chaman fault of 16 8 2 7 mm yr the width of the plate boundary varies from several km in the south where we observe 2 mm yr of convergence near the westernmost strike slip faults to a few hundreds of km in the north where we observe 6 9 mm yr of convergence and where the faulting becomes distinctly transpressional the shallow locking depth along much of the transform system suggests that earthquakes larger than those that have occurred in the historical record would be unexpected and that the recurrence interval of those earthquakes that have occurred is of the order of one or two centuries similar in length to the known historical record

on the paleoseismic evidence of the 1803 earthquake rupture or lack of it along the frontal thrust of the kumaun himalaya the foothills of the himalaya bordered by the main frontal thrust mft continue to be a locus of paleo seismological studies one of such recent studies of trench stratigraphy near the central indian himalayan foothills malik et al 2016 has reported multiple ruptures dated at 467 570 1294 1587 and 1750 1932 ce the last offset has been attributed to the uttarkashi earthquake of 1803 and the penultimate faulting with lesser confidence to an earthquake in 1505 ce we tested these claims by logging an adjacent section on a shared scarp and the new trench site however revealed a stratigraphic configuration partially in variance with from what has been reported in the earlier study our findings do not support the previous interpretation of the trench stratigraphy that suggested multiple displacements cutting across a varied set of deformed stratigraphic units leading up to the 1803 rupture the current interpretation posits a single episode of a low angle displacement at this site occurred between 1266 ce and 1636 our results suggest a single medieval earthquake conforming to what was reported from the previously studied neighboring sites to the east and west the present study while reiterating a great medieval earthquake questions the assumption that the 1803 earthquake ruptured the mft although a decollement earthquake the 1803 rupture may have been arrested midway on the basal flat and fell short of reaching the mft somewhat comparable to a suite of blind thrust earthquakes like the 1905 kangra and the 1833 nepal earthquakes

intensity attenuation model evaluation for bangladesh with respect to the surrounding potential seismotectonic regimes an effort has been made through this study to evaluate the existing intensity attenuation model ipe for the potential seismotectonic regimes in and around bangladesh to reach the goal the seismicity of the concerned tectonic regimes has been analyzed apart from evaluating the appropriate intensity model this research has also assessed the predictive performance of epicentral intensity estimation different magnitude types have been made uniform by converting into moment magnitude and subsequently into the modified mercalli intensity scale mmi the epicentral intensity conversion following li in chinese earthquakes seismological press beijing 1980 fits best for the study area among the utilized four predictive equations the epicentral intensity conversion from the moment magnitude shows that small to moderate earthquakes get significantly overestimated suitable attenuation models have been applied to the different tectonic regimes based on the criteria of using the ipes among all the utilized ipes the relation of bakun et al bull seismol soc am 93 190 202 2003 exhibits the highest standard deviation 1 61 in attenuation with distance although the szeliga et al s bull seismol soc am 100 2 570 584 2010 attenuation relation has a standard deviation of 1 22 the intensity decay is little even for the greater distance 800 900 km up to mw 7 0 the ipe of bindi et al geophys j int 187 1 327 337 2011 shows realistic attenuation scenario with 1 3 however at lower magnitude range mw 7 0 the intensity starts to decay sharply still the ipe of bindi et al 2011 is more realistic in comparison of the shakemaps of the past and in terms of convincible intensity decay with greater distance 500 900 km however the intensity close to the epicenter gets very high mmi xi or larger value for the major events mw 8 5 although the ipe of chandler and lam j asian earth sci 20 7 775 790 2002 has distance constraints its performance is acceptable considering the attenuation scenario with distance along with the lowest standard deviation 0 92 considering the seismic events from the only strike slip churachandpur mao fault of the study area bakun and wentworth bull seismol soc am 87 6 1502 1521 1997 relation has been applied to determine the attenuation pattern

seismicity patterns in the himalayan plate boundary and identification of the areas of high seismic potential abstract space time distribution of earthquakes along the himalayan plate boundary has been investigated with a view to discerning fluctuations in seismicity rates associated with great earthquakes the possibilities of epicentre migration and gaps in seismic activity data from 1800 to 1976 were considered this study shows that all great earthquakes m 8 0 were preceded by seismically quiescent periods of at least 19 years furthermore earthquake quiescence has also been recognised to follow the great earthquakes three possible trends of migration of epicentres of great earthquakes have been recognised 1 1 the first trend starts from the 1905 kangra earthquake the epicentres of subsequent earthquakes migrating eastwards along the plate boundary 2 2 the second trend of migration starts from the great nepal earthquake of 1833 associated with eastward migration 3 3 the third trend commences from the great assam earthquake of 1897 and shows a westward migration of earthquake epicentres the middle section of the himalayan convergent plate boundary 80 e to 90 e in general displays a relatively low level of seismicity as compared to the adjacent sections a remarkable decrease in seismicity following the year 1970 has been observed along a section of the himalaya which lies to the east of the rupture zone of the great 1905 kangra earthquake since 1970 the seismicity rate has also dropped in the region lying in between the rupture zones of the great assam earthquakes of 1897 and 1950 as has earlier been reported by khattri and wyss 1978 such decreases in the level of seismicity along active plate boundaries have been demonstrated to be indicative of building up of stresses leading to future great earthquakes mogi 1969 mccann et al 1979

paleohydrology of china lake basin and the context of early human occupation in the northwestern mojave desert usa abstract considerable prior research has focused on the interconnected pluvial basins of owens lake and searles lake resulting in a long record of paleohydrological change in the lower owens river system however the published record is poorly resolved or contradictory for the period encompassing the terminal pleistocene 22 000 to 11 600 cal bp and early holocene 11 600 8200 cal bp this has resulted in conflicting interpretations about the timing of lacustrine high stands within the intermediate basin of china lake which harbors one of the most extensive records of early human occupation in the western great basin and california here we report a broad range of radiocarbon dated paleoenvironmental evidence including lacustrine deposits and shoreline features tufa outcrops and mollusk ostracode and fish bone assemblages as well as spring and other groundwater related deposits a k a black mats from throughout china lake basin its outlet and inflow drainages based on 98 radiocarbon dates we develop independent evidence for five significant lake level oscillations between 18 000 and 13 000 cal bp and document the persistence of groundwater fed wetlands from the beginning of the younger dryas through the early holocene 12 900 8200 cal bp including the transition from ground water fed lake to freshwater marsh between about 13 000 and 12 600 cal bp results of this study support and refine existing evidence that shows rapid high amplitude oscillations in the water balance of the owens river system during the terminal pleistocene and suggest widespread human use of china lake basin began during the younger dryas

interseismic coupling in the central nepalese himalaya spatial correlation with the 2015 mw 7 9 gorkha earthquake geodetic measurements conducted in the himalaya over the last two decades have shown that the shallow portion of the main himalayan thrust mht was entirely locked during the interseismic period the induced elastic strain accumulated on the mht beneath the lesser himalaya was not released until the 2015 gorkha mw 7 9 earthquake which ruptured the north edge of the locked portion of the mht we utilized our own global positioning system gps data from southern tibet combined with published geodetic velocities to quantify the spatial variations of the coupling that prevailed before the gorkha earthquake the refined coupling model shows that the mht was strongly locked coupling 0 5 in the uppermost 15 km of crust corresponding to a downdip width of 100 km this model suggests a sharp transition zone of strain accumulation with a rapid decrease in the coupling coefficient from 1 0 to less than 0 2 along 50 km of the mht coinciding with the locations of microseismicity we also determined slip models for the 2015 gorkha earthquake and its mw 7 3 aftershock considering the ramp flat ramp flat structure of the mht we found that 85 of the total moment released by the gorkha earthquake was concentrated on the partially coupled transition portion of the mht indicating that the earthquake mainly ruptured the brittle ductile transition zone the coseismic coulomb failure stress increased along the southern and western parts adjacent to the rupture zone pushing these two regions closer to failure the moment deficits that have accumulated in these regions could trigger mw 8 0 and mw 8 3 earthquakes respectively

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

on the epicenter determination of historical earthquakes attested to by sparse intensity data sets abstract historical earthquakes have to be parameterized for seismic hazard analyses although there may be only a few intensity assignments available for them we studied epicenter determination for 18 million synthetic samples of 3 11 intensity data points idps the idp distributions corresponded to earthquakes that occurred offshore close to the coast or onshore we assumed an ordinal variable an attenuation relationship and a point source the attenuation relationship was utilized to encompass every idp of a sample using a lower and upper radius that corresponded to the respective intensity the epicenter must fit all the intensity rings simultaneously the successes and failures of epicenter determination were monitored for a fixed magnitude and depth we investigated where the epicenter was found its uncertainty and its uniqueness small location uncertainties may be obtained for the smallest samples but increasing the sample size led to a larger proportion of small uncertainties provided that intensities were error free a large range of intensities in the sample a short distance to the true epicenter and to a lesser extent a small azimuthal gap were indicators of a good solution a location uncertainty of 20 km and smaller is realistic in many cases but uncertainties of 5 km are extremely seldom occurrences the proportion of good locations was reduced when the intensities were erroneous epicenters were determined for the earthquakes of 26 april 1458 in central italy 14 july 1765 in sweden and 23 december 1875 in the eastern united states

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

seismological geodetic macroseismic and historical context of the 2016 mw 6 7 tamenglong manipur india earthquake abstract the 2016 mw 6 7 tamenglong earthquake in the state of manipur in northeastern india on 4 january 2016 at 04 35 indian standard time 3 january 23 05 utc was the strongest earthquake to strike manipur since 1988 using data from indian stations we constrain the hypocentral depth of the mainshock at 59 3 8 km and determine a strike slip mechanism with a moderate reverse component on a steeply dipping plane though coseismic offsets from gps measurements from four nearby sites were inadequate to provide further constraints on the focal mechanism they were consistent with the magnitude and hypocentral depth of the earthquake the epicentre of the mainshock was located 15 km west of the churachandpur mao fault cmf but it was unrelated to this structure and was instead a typical intra slab earthquake within the indian plate a strong motion instrument at the loktak power station lok 56 km from the epicentre recorded a peak ground acceleration pga of 0 027g while a pga of 0 103g was recorded at shillong shl at an epicentral distance of 111 km we also present macroseismic observations from 461 locations in north eastern india and the adjacent areas for this earthquake the highest intensities 7 ems were observed in the manipur valley and in the hills to the west while shaking was perceptible as far as delhi and jaipur lastly we present a catalogue of 333 felt earthquakes in manipur from 1588 1 ce to 1955 derived from the royal chronicle of the kings of manipur known as the cheitharon kumpapa discuss important historical earthquakes in the region and also estimate intensity magnitudes for the 1852 mi 6 5 0 8 1869 mi 7 1 0 7 1880 mi 6 3 0 7 and 2016 mi 6 8 0 8 earthquakes

the 19 january 2011 mw 7 2 dalbandin earthquake balochistan abstract the 19 january 2011 m w 7 2 dalbandin earthquake at 01 23 a m local time 18 january 2011 20 23 utc occurred south of the makran balochistan volcanic arc at a depth of 70 km and was followed by two globally recorded aftershocks it appears to have occurred on a normal fault within the subducting arabian ormara plate where it descends beneath a southern promontory of the eurasian plate an unusual feature of this earthquake was that it was felt from tehran to delhi and from the northern persian gulf states to central asia a radial felt extent of up to 1400 km however it caused few fatalities and relatively modest damage from the european macroseismic scale ems 98 intensities at 242 locations that are based on media reports and a field visit to the epicenter we compare the attenuation of intensity with distance from the dalbandin earthquake with observations from other intermediate focus earthquakes in the indian subcontinent we also briefly discuss other similar historical earthquakes in western balochistan as well as the potential for site response in the city of karachi in lieu of the varied intensities experienced during earthquakes since the mid twentieth century online material tabulated summaries of macroseismic accounts from 242 locations in the indian subcontinent central asia and the middle east where the 19 january 2011 dalbandin earthquake was felt

evidence of a large triggered event in the nepal himalaya following the gorkha earthquake implications toward enhanced seismic hazard a dc double couple constrained multiple point source moment tensor inversion is performed on the band passed 0 008 0 10 hz displacement data of the 25 april mw 7 8 2015 nepal mainshock from 17 broadband stations in india our results reveal that the 25 april event strike 324 dip 14 rake 88 ruptured the north dipping main himalayan thrust mht at 16 km depth we modeled the coulomb failure stress changes cfs produced by the slip on the fault plane of the 25 april nepal mainshock a strong correlation with occurrences of aftershocks and regions of increased positive cfs is obtained below the aftershock zone of the 2015 nepal mainshock we notice that predicted cfs at 16 km depth show a positive coulomb stress of 0 06 mpa at the location of the 12 may 2015 event these small modeled stress changes can lead to trigger events if the crust is already near to failure but these small stresses can also advance the occurrence of future earthquakes the main finding of our cfs modeling implies that the 25 april event increased the coulomb stress changes by 0 06 mpa at 16 km depth below the site of the 12 may event and thus this event can be termed as triggered we propose that the seismic hazard in the himalaya is not only caused by the mainshock slip on the mht rather the occurrence of large triggered event on the mht can also enhance our understanding of the seismic hazard in the nepal himalaya

gps measurements from the ladakh himalaya india preliminary tests of plate like or continuous deformation in tibet observations of relative motion in a geodetic network in ladakh india and across southern tibet indicate slow shear on the karakorum fault rapid east west extension across the whole of southern tibet and constant arc normal convergence between india and southern tibet along the himalayan arc measurements of ten campaign style and six permanent sites with global positioning system gps precise geodesy provide these bounds on the style and rates of the large scale deformation in the tibet himalaya region divergence between sites at leh ladakh india and shiquanhe western tibet as well as slow relative motion among sites within the ladakh network limit right lateral slip parallel to the karakorum fault to only 3 4 5 mm yr this low rate concurs with a recent estimate of 3 4 mm yr for late holocene time but disagrees with the much higher rate of 30 35 mm yr that has been used to argue for plate like behavior of the tibetan plateau convergence between ladakh and the indian subcontinent at 18 8 3 mm yr at 224 17 1 differs little from estimates of convergence across the central segment of the himalaya finally lengthening of the baseline between leh ladakh and lhasa in southeastern tibet at 17 8 1 mm yr or between leh and bayi farther to the southeast at 18 3 mm yr is consistent with an extrapolation of rates of east west extension of the tibetan plateau based both on shorter gps baselines e g lhasa simikot and on diverging slip vectors of earthquakes in the himalaya we interpret these results to indicate that tibet behaves more like a fl uid than like a plate

joint approach combining damage and paleoseismology observations constrains the 1714 a d bhutan earthquake at magnitude 8 0 5 the region of bhutan is thought to be the only segment of the himalayas not having experienced a major earthquake over the past half millennium a proposed explanation for this apparent seismic gap is partial accommodation of the india asia convergence further south across the shillong plateau yet the seismic behavior of the himalayan megathrust is unknown here we present historical documents from the region reporting on an earthquake in 1714 ad and geological evidence of surface rupture to constrain the latest large event in this area we compute various earthquake scenarios using empirical scaling relationships relating magnitude with intensity source location and rupture geometry our results constrain the 1714 ad earthquake to have ruptured the megathrust in bhutan most likely during a m7 5 8 5 event this finding reclassifies the apparent seismic gap to a former information gap and implies that the entire himalayan arc has a high level of earthquake potential

why the new madrid earthquakes are m 7 8 and the charleston earthquake is m 7 estimates of magnitudes of large historical earthquakes are an essential input to and can seriously affect seismic hazard estimates the earthquake intensity observations modified mercalli intensities mmi and assigned magnitudes m of the 1811 1812 new madrid events have been reinterpreted several times in the last decade and have been a source of controversy in making seismic hazard estimates in the central united states observations support the concept that the larger the earthquake the greater the maximum felt distance for the same crustal attenuation and local soil conditions magnitude should be the main influence on intensity values at large distances we apply this concept by comparing the mean mmi at distances of 600 1200 km for each of the four largest new madrid 1811 1812 earthquakes the 1886 charleston south carolina earthquake the 1929 m 7 2 grand banks earthquake and the 2001 m 7 6 bhuj india earthquake we fit the intensity observations using the form mmi a c dist 0 8 log dist to better define intensity attenuation in eastern north america ena the intensity attenuation in cratonic india differs from ena and is corrected to ena using both the above estimate and published intensity relations we evaluate source marine geophysical q and stress drop information as well as a 1929 milne shaw record at chicago to confirm that the 1929 grand banks earthquake occurred in ena crust our direct comparison of mean intensities beyond 600 km suggests m 7 5 7 3 7 7 and 6 9 for the three new madrid 1811 1812 mainshocks and the largest aftershock and m 7 0 for the 1886 charleston south carolina earthquake with an estimated uncertainty of 0 3 units at the 95 confidence level based on a monte carlo analysis our mean new madrid and charleston mainshock magnitudes are similar to those of bakun and hopper 2004 and are much higher than those of hough and page 2011 for new madrid online material tables of mean modified mercalli intensity for 800 1200 and 600 1000 km distance ranges and figures of least squares fit for all intensity measures used and for frequency dependent q in easternmost canada

active tectonics and earthquake potential of the myanmar region this paper describes geomorphologic evidence for the principal neotectonic features of myanmar and its immediate surroundings we combine this evidence with published structural geodetic and seismic data to present an overview of the active tectonic architecture of the region and its seismic potential three tectonic systems accommodate oblique collision of the indian plate with southeast asia and extrusion of asian territory around the eastern syntaxis of the himalayan mountain range subduction and collision associated with the sunda megathrust beneath and within the indoburman range and naga hills accommodate most of the shortening across the transpressional plate boundary the sagaing fault system is the predominant locus of dextral motion associated with the northward translation of india left lateral faults of the northern shan plateau northern laos thailand and southern china facilitate extrusion of rocks around the eastern syntaxis of the himalaya all of these systems have produced major earthquakes within recorded history and continue to present major seismic hazards in the region

evidence for a great medieval earthquake 1100 a d in the central himalayas nepal the himalayan orogen has produced three thrust earthquakes with moment magnitude m w 7 8 to 8 5 during the past century yet no surface ruptures associated with these great earthquakes have been documented here we present paleoseismic evidence from east central nepal that since 700 a d a single earthquake ruptured the frontal thrust fault at 1100 a d with a surface displacement of 17 5 3 meters and a lateral extent and size that could have exceeded 240 kilometers and m w 8 8 respectively ruptures associated with m w

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

seismotectonic perspectives on the himalayan arc and contiguous areas inferences from past and recent earthquakes abstract spread over countries including pakistan india nepal bhutan and china the himalayan mountain chain the most spectacular result of the indo eurasian plate collision is a locus of destructive earthquakes past earthquakes from this region have impacted vast swathes of frontal himalaya and stretches of alluvial plains south of the range front risk from future earthquakes has increased considering the burgeoning population and an ever expanding built environment in the region while considerable ambiguities exist on the locations ruptures and sizes of the earthquakes during the first half of the last millennium 1255 1344 and 1505 ce those during the latter half 1803 and 1833 ce are quite well documented all reported from the central himalayan segment comprising eastern nepal kumaun and garhwal while dormancy prevailed in the central segment in the intervening period the himalayan arc elsewhere witnessed three large great earthquakes in the last century namely 1905 kangra mw 7 8 1934 bihar nepal mw 8 2 and 1950 upper assam mw 8 6 the last one being the largest intra continental earthquake in the recorded history the april 25 gorkha nepal earthquake mw 7 8 located in the central seismic gap terminated the period of low level seismic productivity that followed the 1950 event the himalayan arc and its contiguous regions are now being investigated using various tools including paleoseismology quite understandably the interpretations and tectonic models do not always converge given the diverse quality and type of data the data from variously sized modern day earthquakes sourced in the diverse structural settings of the himalaya provide better constraints on the source properties of the himalayan earthquakes the source complexity and diversity is a striking point of interest for the post 1950 events and at least some of them seem to deviate from the generally accepted model of great ruptures on a shallow dipping detachment a prime example of such anomalies is the 2005 kashmir earthquake mw 7 6 sourced on an out of sequence thrust the sources of the 1991 uttarkashi mw 6 8 1999 chamoli mw 6 6 and the 2015 gorkha nepal mw 7 8 earthquakes all in the central himalayan segment are attributed to the ramp flat on the down dip part of the main himalayan thrust mht in contrast the 2011 sikkim mw 6 9 and the 2016 imphal mw 6 7 earthquakes are intraplate events sourced within the subducting slab source models of modern day earthquakes 1991 2016 discussed in this paper bring out this plurality of mechanisms expected of a complex subduction cum collisional boundary this review presents the status of current seismotectonic understanding of the himalaya from the analyses of significant earthquakes from the past as well as recent events with a focus on the central himalayan segment

the akato tagh bend along the altyn tagh fault nw tibet 1 cenozoic structure smoothing by vertical axis rotation and the effect of topographic stresses on borderland faulting

post earthquake aggradation processes to hide surface ruptures in thrust systems the m8 3 1934 bihar nepal earthquake ruptures at charnath khola eastern nepal the charnath khola is a large river crossing the himalayan thrust system in the region devastated by the great m8 3 1934 bihar nepal earthquake fluvial terraces are abandoned along the river and at the base of a 20 m high cumulative thrust escarpment a trench across the fault scarp exposed siwalik mudstone siltstone overthrusting quaternary units and three colluvial wedges interfingered with fluvial sands the 85 accelerator mass spectrometry radiocarbon dates from detrital charcoals sampled in the trench a river cut and river terraces constrain the timing of the sedimentary processes following the last two major earthquakes in 1934 and 1255 ce although several samples straddle the main earthquake horizon associating it with the 1934 earthquake based solely on radiocarbon ages remains challenging the 49 detrital charcoal ages found in the pre earthquake and postearthquake units fall between 65 and 225 bp a period with a flat calibration curve many of these radiocarbon ages are suspected to include a part due to inbuilt time i e age of the wood at the time of burning transport time and reworking processes which are difficult to resolve considering these ages at their face value could lead to dates older than the actual earthquake dates we suggest that a part of this chronological bias is also related to a local postseismic aggradation pulse of 4 to 5 m of sediments which is documented in the trench and terraces this fluvial sequence hiding the most recent surface rupture is likely related to landslide sediment deposition triggered by the 1934 bihar nepal earthquake

estimating earthquake magnitudes from reported intensities in the central and eastern united states a new macroseismic intensity prediction equation is derived for the central and eastern united states and is used to estimate the magnitudes of the 1811 1812 new madrid missouri and 1886 charleston south carolina earthquakes this work improves upon previous derivations of intensity prediction equations by including additional intensity data correcting magnitudes in the intensity datasets to moment magnitude and accounting for the spatial and temporal population distributions the new relation leads to moment magnitude estimates for the new madrid earthquakes that are toward the lower range of previous studies depending on the intensity dataset to which the new macroseismic intensity prediction equation is applied mean estimates for the 16 december 1811 23 january 1812 and 7 february 1812 mainshocks and 16 december 1811 dawn aftershock range from 6 9 to 7 1 6 8 to 7 1 7 3 to 7 6 and 6 3 to 6 5 respectively one sigma uncertainties on any given estimate could be as high as 0 3 0 4 magnitude units we also estimate a magnitude of 6 9 0 3 for the 1886 charleston south carolina earthquake we find a greater range of magnitude estimates when also accounting for multiple macroseismic intensity prediction equations the inability to accurately and precisely ascertain magnitude from intensities increases the uncertainty of the central united states earthquake hazard by nearly a factor of two relative to the 2008 national seismic hazard maps our range of possible 1811 1812 new madrid earthquake magnitudes increases the coefficient of variation of seismic hazard estimates for memphis tennessee by 35 42 for ground motions expected to be exceeded with a 2 probability in 50 years and by 27 35 for ground motions expected to be exceeded with a 10 probability in 50 years

large and great earthquakes in the shillong plateau assam valley area of northeast india region pop up and transverse tectonics abstract the tectonic model of the shillong plateau and assam valley in the northeast india region the source area for the 1897 great earthquake ms 8 7 and for the four 1869 1923 1930 and 1943 large earthquakes m 7 0 is examined using the high precision data of a 20 station broadband seismic network about 300 selected earthquakes m 3 0 recorded during 2001 2009 are analysed to study the seismicity and fault plane solutions the dominating thrust reverse faulting earthquakes in the western plateau may be explained by the proposed pop up tectonics between two active boundary faults the oldham brahmaputra fault to the north and the dapsi dauki thrust to the south though the northern boundary fault is debated the more intense normal and strike slip faulting earthquakes in the eastern plateau mikir massif and in the assam valley on the other hand are well explained by transverse tectonics at the long and deep rooted kopili fault that cuts across the himalaya and caused the 2009 bhutan earthquake mw 6 3 it is conjectured that the complex tectonics of the shillong plateau and transverse tectonics at the kopili fault make the region vulnerable for impending large earthquake s

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

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

paleoseismological evidence of surface faulting along the northeastern himalayan front india timing size and spatial extent of great earthquakes the similar to 2500 km long himalayan arc has experienced three large to great earthquakes of m w 7 8 to 8 4 during the past century but none produced surface rupture paleoseismic studies have been conducted during the last decade to begin understanding the timing size rupture extent return period and mechanics of the faulting associated with the occurrence of large surface rupturing earthquakes along the similar to 2500 km long himalayan frontal thrust hft system of india and nepal the previous studies have been limited to about nine sites along the western two thirds of the hft extending through northwest india and along the southern border of nepal we present here the results of paleoseismic investigations at three additional sites further to the northeast along the hft within the indian states of west bengal and assam the three sites reside between the meizoseismal areas of the 1934 bihar nepal and 1950 assam earthquakes the two westernmost of the sites near the village of chalsa and near the nameri tiger preserve show that offsets during the last surface rupture event were at minimum of about 14 m and 12 m respectively limits on the ages of surface rupture at chalsa site a and nameri site b though broad allow the possibility that the two sites record the same great historical rupture reported in nepal around a d 1100 the correlation between the two sites is supported by the observation that the large displacements as recorded at chalsa and nameri would most likely be associated with rupture lengths of hundreds of kilometers or more and are on the same order as reported for a surface rupture earthquake reported in nepal around a d 1100 assuming the offsets observed at chalsa and nameri occurred synchronously with reported offsets in nepal the rupture length of the event would approach 700 to 800 km the easternmost site is located within harmutty tea estate site c at the edges of the 1950 assam earthquake meizoseismal area here the most recent event offset is relatively much smaller 2 5 m and radiocarbon dating shows it to have occurred after a d 1100 after about a d 1270 the location of the site near the edge of the meizoseismal region of the 1950 assam earthquake and the relatively lesser offset allows speculation that the displacement records the 1950 m w 8 4 assam earthquake scatter in radiocarbon ages on detrital charcoal has not resulted in a firm bracket on the timing of events observed in the trenches nonetheless the observations collected here when taken together suggest that the largest of thrust earthquakes along the himalayan arc have rupture lengths and displacements of similar scale to the largest that have occurred historically along the world s subduction zones

a comprehensive assessment of ground motions from two 2016 intra slab earthquakes in myanmar abstract we map the distribution of macroseismic intensities from the mw 6 9 kani and the mw 6 8 chauk intra slab earthquakes in 2016 in myanmar using the 1998 european macroseismic scale ems 98 by interpreting data gathered from field surveys community responses sent via social media to the myanmar earthquake committee mec and digital news reports our macroseismic maps for both events provide better spatial data coverage in myanmar india and bangladesh than community derived macroseismic maps e g u s geological survey s did you feel it in myanmar this was driven by improved telecommunication that has allowed social media such as the burmese language facebook portal of the myanmar earthquake committee mec to reach into rural areas from where reports of shaking effects from earthquakes have been previously unavailable our analysis of both the macroseismic intensities and strong motion observations from india and myanmar suggests the two earthquakes had different source properties the comparison of our intensity data with instrumental strong motion records also suggests the peak ground motion intensity relationship by worden et al 2012 generally performs well for both earthquakes in addition ground motion behaviour within the burma and indian plates can be related to different existing ground motion prediction equations gmpes and intensity prediction equations ipes for subduction zones and for stable continental regions respectively we therefore suggest these effects will need to be considered in future regional seismic hazard models or shake maps for this region when evaluating the impact of the future events

estimating locations and magnitudes of earthquakes in eastern north america from modified mercalli intensities we use 28 calibration events 3 7 m 7 3 from texas to the grand banks newfoundland to develop a modified mercalli intensity mmi model and associated site corrections for estimating source parameters of historical earthquakes in eastern north america the model batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mathrm mmi 1 41 1 68 times mathbf m 0 00345 times delta 2 08 mathrm log delta end document where is the distance in kilometers from the epicenter and m is moment magnitude provides unbiased estimates of m and its uncertainty and if site corrections are used of source location the model can be used for the analysis of historical earthquakes with only a few mmi assignments we use this model mmi site corrections and bakun and wentworth s 1997 technique to estimate m and the epicenter for three important historical earthquakes the intensity magnitude m i is 6 1 for the 18 november 1755 earthquake near cape ann massachusetts 6 0 for the 5 january 1843 earthquake near marked tree arkansas and 6 0 for the 31 october 1895 earthquake the 1895 event probably occurred in southern illinois about 100 km north of the site of significant ground failure effects near charleston missouri manuscript received 14 march 2002

coseismic deformation fields and a fault slip model for the mw7 8 mainshock and mw7 3 aftershock of the gorkha nepal 2015 earthquake derived from sentinel 1a sar interferometry abstract coseismic deformation fields caused by the moment magnitude mw 7 8 mainshock and mw7 3 aftershock of the 2015 gorkha nepal earthquake are obtained by analyzing sentinel 1a iw ascending and descending interferometry data results show that the deformation field associated with the mw7 8 mainshock roughly resembles a prolate ellipse extending from the epicenter about 20 east by south the main region of deformation is about 160 km by 110 km comprising a large southern area of uplift and a small northern area of subsidence assuming that rupture occurred in a homogeneous elastic half space the coseismic fault slip models of the mainshock and aftershock are inverted based on a shallow dip fault constrained by the three data sets sentinel 1a iw descending data ascending data and alos 2 descending data separately or in combination mainshock slip distributions generated from all three data sets are similar and inversion constrained by all three in combination reveal a comprehensive fault slip model indeed coseismic slip is mainly distributed within a narrow 40 km zone to the north of the main frontal trust mft and at 6 15 km subsurface depth in addition the maximum slip in this event was about 5 1 m the mw7 8 mainshock ruptured the deep part of the seismogenic zone while the region between the southern boundary of the rupture area and the mft remained locked therefore a considerable earthquake risk remains to the south of kathmandu the inverted coseismic slip of the mw7 3 aftershock was concentrated in a small area close to and southeast of the epicenter with maximum displacement of about 3 m finally because there is no overlap between the two slip areas of the mainshock and aftershock the gap between them about 15 km in length has additional potential to generate future earthquakes

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

a probabilistic estimate of the most perceptible earthquake magnitudes in the nw himalaya and adjoining regions nw himalaya and its neighboring region 25 40 n and 65 85 e is one of the most seismically hazardous regions in the indian subcontinent a region that has historically experienced large to great damaging earthquakes in the present study the most perceptible earthquake magnitudes mp are estimated for intensity i vii horizontal peak ground acceleration a 300 cm s2 and horizontal peak ground velocity v 10 cm s in 28 seismogenic zones using the two earthquake recurrence models of kijko and sellevoll bulletin of the seismological society of america 82 1 120 134 1992 and gumbel s third asymptotic distribution of extremes giii both methods deal with maximum magnitudes the earthquake perceptibility is calculated by combining earthquake recurrence models with ground motion attenuation relations at a particular level of intensity acceleration and velocity the estimated results reveal that the values of mp for velocity v 10 cm s show higher estimates than corresponding values for intensity i vii and acceleration a 300 cm s2 it is also observed that differences in perceptible magnitudes calculated by the kijko sellevoll method and giii statistics show significantly high values up to 0 7 0 6 and 1 7 for intensity acceleration and velocity respectively revealing the importance of earthquake recurrence model selection the estimated most perceptible earthquake magnitudes mp in the present study vary from mw 5 1 to 7 7 in the entire zone of the study area results of perceptible magnitudes are also represented in the form of spatial maps in 28 seismogenic zones for the aforementioned threshold levels of intensity acceleration and velocity estimated from two recurrence models the spatial maps show that the quetta of pakistan the hindukush pamir himalaya the caucasus mountain belt and the himalayan frontal thrust belt kashmir kangra uttarkashi chamoli regions exhibit higher values of the most perceptible earthquake magnitudes mw 6 0 these spatially distributed values indicate good agreement with high seismic hazard zones in previously published hazard maps based on seismicity maximum expected earthquake magnitudes during specific time intervals and maximum expected acceleration these maps have useful implications in preparing earthquake selection criteria for the anti seismic design of non critical structures in the study region

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

characteristics of deformation and past seismicity associated with the 1819 kutch earthquake northwestern india the 1819 earthquake in kutch northwestern india is one of the most significant events to have occurred in a plate interior setting despite being the second largest among the stable continental region scr earthquakes this event has not been analyzed within the context of present day understanding of earthquake seismology coseismic changes related to this earthquake include massive ground deformation in a wide low lying tidal flat area although detailed historic accounts of this earthquake exist many questions regarding the mode of deformation and the seismic history of the region remain unresolved we explored the region nearly 180 years after the earthquake and the information gathered adds to our understanding of this event and provides a fresh perspective on this unique intraplate seismogenic zone a 90 km long tract of elevated land with a peak height of 4 3 m is the most visible surface expression of this earthquake we surveyed and analyzed the morphological features of this scarp and also carried out exploratory trenching in this region the scarp morphology is suggestive of a growing fold related to a buried north dipping thrust rather than a discrete fault that could have resulted from a surface rupture the extensive liquefaction field associated with the earthquake offered an ideal setting to explore the paleoearthquake history age data of liquefaction features suggest that a previous event of comparable size must have occurred 800 1000 years ago seismic activity appears to be related to the reactivation of an ancient rift in a stress regime that is dominated by nearly north south compression

seismic structure of the crust and the upper mantle beneath the himalayas evidence for eclogitization of lower crustal rocks in the indian plate 1 variations in the seismic velocity structure of the himalayan collision zone include significant differences between its north and south portions with transitions in physical properties across the greater himalaya we combined p and s wave traveltimes from a temporary broadband seismic network in eastern nepal and southern tibet with arrival times at the permanent station network of the department of mines and geology of nepal to determine the seismic velocity structure across the himalaya using local earthquake tomography and traveltimes of regional earthquakes the p to s velocity ratio vp vs structure marks the difference between the indian plate and the overlying materials with the vp vs ratios being high for the former and low for the latter we also found a significant increase in the uppermost mantle seismic velocities from south to north reaching p wave velocities vp over 8 4 km s north of the greater himalaya these high vp values do not seem to be the result of biases due to anisotropy in the upper mantle beneath the greater and tethyan himalayas instead we suggest that rocks in the lower crust of the underthrusting indian plate undergo metamorphism to eclogite as they plunge to greater depth beneath the mountain range explaining the high seismic velocities

active faulting in apparently stable peninsular india rift inversion and a holocene age great earthquake on the tapti fault we present observations of active faulting within peninsular india far from the surrounding plate boundaries offset alluvial fan surfaces indicate one or more magnitude 7 6 8 4 thrust faulting earthquakes on the tapti fault maharashtra western india during the holocene the high ratio of fault displacement to length on the alluvial fan offsets implies high stress drop faulting as has been observed elsewhere in the peninsula the along strike extent of the fan offsets is similar to the thickness of the seismogenic layer suggesting a roughly equidimensional fault rupture the subsiding footwall of the fault is likely to have been responsible for altering the continental scale drainage pattern in central india and creating the large west flowing catchment of the tapti river a preexisting sedimentary basin in the uplifting hanging wall implies that the tapti fault was active as a normal fault during the mesozoic and has been reactivated as a thrust highlighting the role of preexisting structures in determining the rheology and deformation of the lithosphere the slip sense of faults and earthquakes in india suggests that deformation south of the ganges foreland basin is driven by the compressive force transmitted between india and the tibetan plateau the along strike continuation of faulting to the east of the holocene ruptures we have studied represents a significant seismic hazard in central india

fold and thrust partitioning in a contracting fold belt insights from the 1931 mach earthquake in baluchistan 1 surface deformation associated with the 27 august 1931 earthquake near mach in baluchistan is quantified from spirit leveling data and from detailed structural sections of the region interpreted from seismic reflection data constrained by numerous well logs mean slip on the west dipping dezghat bannh fault system amounted to 1 2 m on a 42 km 72 km thrust plane with slip locally attaining 3 2 m up dip of an inferred locking line at 9 km depth slip also occurred at depths below the interseismic locking line in contrast negligible slip occurred in the 4 km near the interseismic locking line the absence of slip here in the 4 years following the earthquake suggests that elastic energy there must either dissipate slowly in the interseismic cycle or that a slip deficit remains pending its release in a large future earthquake elastic models of the earthquake cycle in this fold and thrust belt suggest that slip on the frontal thrust fault is reduced by a factor of 2 to 8 compared to that anticipated from convergence of the hinterland a partitioning process that is presumably responsible for thickening of the fold and thrust belt at the expense of slip on the frontal thrust near the latitude of quetta gps measurements indicate that convergence is 5 mm yr hence the minimum renewal time between earthquakes with 1 2 m mean displacement should be as little as 240 years however when the partitioning of fold belt convergence to frontal thrust slip is taken into account the minimum renewal time may exceed 2000 years

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

insar constraints on the source parameters of the 2001 bhuj earthquake 1 we present insar results of the coseismic displacement field for the january 2001 bhuj earthquake using insar data along multiple tracks we determine the optimal source parameters of the earthquake the deformation pattern is first modeled assuming uniform slip on an elastic dislocation a grid search is used to constrain the source location and finiteness assuming a strike rake and dip consistent with seismic studies an inversion for the distributed slip places oblique reverse slip at depth with strike slip motion resolved at shallower depths the estimated size of the event is mw 7 6 results also suggest that the postseismic response is minimal

the 26 january 2001 m 7 6 bhuj india earthquake observed and predicted ground motions although local and regional instrumental recordings of the devastating 26 january 2001 bhuj earthquake are sparse the distribution of macroseismic effects can provide important constraints on the mainshock ground motions we compiled available news accounts describing damage and other effects and interpreted them to obtain modified mercalli intensities mmis at 200 locations throughout the indian subcontinent these values are then used to map the intensity distribution throughout the subcontinent using a simple mathematical interpolation method although preliminary the maps reveal several interesting features within the kachchh region the most heavily damaged villages are concentrated toward the western edge of the inferred fault consistent with western directivity significant sediment induced amplification is also suggested at a number of locations around the gulf of kachchh to the south of the epicenter away from the kachchh region intensities were clearly amplified significantly in areas that are along rivers within deltas or on coastal alluvium such as mudflats and salt pans in addition we use fault rupture parameters inferred from teleseismic data to predict shaking intensity at distances of 0 1000 km we then convert the predicted hard rock ground motion parameters to mmi by using a relationship derived from internet based intensity surveys that assigns mmi based on the average effects in a region the predicted mmis are typically lower by 1 3 units than those estimated from news accounts although they do predict near field ground motions of approximately 80 g and potentially damaging ground motions on hard rock sites to distances of approximately 300 km for the most part this discrepancy is consistent with the expected effect of sediment response but it could also reflect other factors such as unusually high building vulnerability in the bhuj region and a tendency for media accounts to focus on the most dramatic damage rather than the average effects the discrepancy may also be partly attributable to the inadequacy of the empirical relationship between mmi and peak ground acceleration pga when applied to india the mmi pga relationship was developed using data from california earthquakes which might have a systematically different stress drop and therefore a different frequency content than intraplate events when a relationship between response spectra and mmi is used we obtain larger predicted mmi values in better agreement with the observations

quantifying the media bias in intensity surveys lessons from the 2001 bhuj india earthquake many seismologists have looked at the 26 january 2001 bhuj earthquake as a key modern calibration event that could be used to improve estimates of magnitudes of large historic mainshocks in stable continental regions since no instrumental data are available for important historic events such as the 1819 allah bund india and the 1811 1812 new madrid central u s mainshocks calibration hinges on comparisons of the macroseismic effects of these earthquakes with those of comparable modern earthquakes for which a reliable instrumentally determined moment magnitude is available however although such a comparison is conceptually straightforward in practice it is complicated by potentially significant inconsistencies in methods used to quantify macroseismic effects in different regions and or times for the bhuj earthquake extensive intensity data sets have been compiled and published from both media accounts and detailed direct surveys comparing the two provides a quantification of the previously suspected media bias whereby earthquake effects can be exaggerated in media accounts this bias is a strong function of intensity level with substantial bias at the highest shaking levels and significantly less bias at low intensities because only sparse documentary data are in general available for older historic earthquakes the results of this study suggest that their inferred intensity distributions might be similarly biased we further use the survey based intensity values to develop a new relationship between intensities and ground motions

revisiting the 1991 uttarkashi and the 1999 chamoli india earthquakes implications of rupture mechanisms in the central himalaya abstract the central himalaya has attracted much attention due to its potential to host a great earthquake an inference based on the history of earthquakes and the geodetic slip estimates the largest and earliest historically documented earthquake in the central himalaya occurred in 1803 m 7 7 near uttarkashi on its western part much before the great event of 1934 mw 8 2 located farther to the east both of which were felt severely in the gangetic plain south of the mountain front the seismotectonic model by seeber and armbruster 1981 predicts that large great earthquakes originate on the main himalayan thrust mht and their ruptures propagate southward to the main frontal thrust mft the rupture of the april 25 2015 mw 7 8 gorkha nepal earthquake however was southeast directed with a southwest directed slip and its mw 7 3 aftershock on may 12 also showed a similar slip direction post 2015 we revisited the 1991 uttarkashi mw 6 7 and the 1999 chamoli mw 6 5 earthquakes in india both of which had originated on the mht flat but show ssw directed slips as reported in this study ruptures of both these earthquakes fell short of reaching the mft just as the historically documented 1803 earthquake but their shaking effects were felt in the southern plains these observations compel us to conclude that the varying rupture modes exhibited by the himalayan earthquakes are controlled primarily by the geometry of the flat ramp flat system

postseismic deformation following the april 25 2015 gorkha earthquake nepal afterslip versus viscous relaxation abstract the postseismic deformation consecutive to the april 25 2015 gorkha earthquake mw 7 9 is estimated in this paper based on a cgnss network installed prior to the earthquake and supplemented by 6 cgnss stations installed after the main shock postseismic displacement are obtained from daily time series corrected for interseismic deformation and seasonal variations the maximum postseismic displacement is found north of the rupture area where locally it reached 100 mm between the date of the earthquake and late 2016 the postseismic deformation affects the northern part of the rupture area but not the southern part along the southern part of the main himalayan thrust mht three hypotheses for the mechanisms controlling postseismic deformation are tested through numerical simulations of the postseismic time series i viscous relaxation ii afterslip or iii a combination of these two mechanisms we can exclude postseismic deformation controlled by viscous relaxation of a thick deformation zone along the northern and lower flat of the mht however it is impossible to discriminate between postseismic deformation controlled by either afterslip along the mht northern part of the rupture zone crustal ramp and lower flat of the mht or a combination of afterslip along the mht northern part of the rupture zone crustal ramp and viscous relaxation controlled by a thin 3 4 km thick low viscosity body centered on the lower flat of the mht the occurrence of afterslip along the northern part of the upper flat of the mht and its longitudinal variations have been established thanks to the densification of gnss network by our team presented in this paper

broad band lg attenuation modelling in the middle east summary we present a broad band tomographic model oflg attenuation in the middle east derived from source and site corrected amplitudes absolute amplitude measurements are made on handselected and carefully windowed seismograms for tens of stations and thousands of crustal earthquakes resulting in excellent coverage of the region a conjugate gradient method is used to tomographically invert the amplitude data set of over 8000 paths over a 45 40 region of the middle east we solve for q variation as well as site and source terms for a wide range of frequencies ranging from 0 5 to 10 hz we have modified the standard attenuation tomography technique to more explicitly define the earthquake source expression in terms of the seismic moment this facilitates the use of the model to predict the expected amplitudes of new events an important consideration for earthquake hazard or explosion monitoring applications the attenuation results have a strong correlation to tectonics shields have low attenuation whereas tectonic regions have high attenuation with the highest attenuation at 1 hz found in eastern turkey the results also compare favourably to other studies in the region made using lg propagation efficiency lg pg amplitude ratios and two station methods we tomographically invert the amplitude measurements for each frequency independently in doing so it appears the frequency dependence of attenuation in all regions is not compatible with the power law representation of q f an assumption that is often made

coseismic postseismic and interseismic coulomb stress evolution along the himalayan main frontal thrust since 1803 the himalayan main frontal thrust is the most active fault in the himalayan subduction zone with a high degree of locking and a large thrust rate gaps on the himalayan main frontal thrust have been free of strong earthquakes for hundreds of years and the surrounding areas are densely populated so it is significant to study the evolution law and the current status of stress along the himalayan main frontal thrust based on a lithospheric viscoelastic layered medium model we analyzed the interseismic stress accumulation along the himalayan main frontal thrust and the coseismic and postseismic stress disturbance on the fault surface caused by nine mw 7 5 earthquakes since 1803 the results showed that the stress disturbance along the himalayan main frontal thrust caused by historical earthquakes have promoted most of the subsequent earthquakes but the coseismic and postseismic stress changes caused by the historical earthquakes on the faulty surface of subsequent earthquakes are not significant because of the long distance between strong earthquakes interseismic stress enhanced the stress level of the majority of fault planes in the study area and played a dominant role in the stress evolution and strong earthquake preparation along the himalayan main frontal thrust the recurrence interval of mw 7 5 7 9 earthquakes on the himalayan main frontal thrust is 70 250 years and the recurrence interval of mw 8 earthquakes which rupture the whole seismogenic layer may be longer than 500 years this agrees with historical seismic records the elapsed time of strong earthquakes in the four seismic gaps is between 460 and 915 years and the possibilities of mw 8 earthquakes in the future 10 years always exist including a probability of higher than 50 in three seismic gaps the peak of cumulative coulomb stress in the seismic gaps is more than 1 mpa and the seismic hazard on the himalayan main frontal thrust needs further attention

isoseismal map of the 2015 nepal earthquake and its relationships with ground motion parameters distance and magnitude abstract a devastating earthquake of mw 7 8 struck central nepal on 25th april 2015 6 11 25 ut which resulted in more than 9000 deaths and destroyed millions of houses standing buildings roads and electrical installations worth 25 30 billions of dollars are reduced to rubbles the earthquake was widely felt in the northern parts of india and moderate damage have been observed in the northern part of up and bihar region of india maximum intensity ix according to the usgs report was observed in the meizoseismal zone surrounding the kathmandu region in the present study we have compiled available information from the print electronic media and various reports of damages and other effects caused by the event and interpreted them to obtain modified mercalli intensities mmi at over 175 locations spread over nepal and surrounding indian and tibet region we have also obtained a number of strong motion recordings from india and nepal seismic network and developed an empirical relationship between the mmi and peak ground acceleration pga peak ground velocity pgv we have used least square regression technique to derive the empirical relation between the mmi and ground motion parameters and compared them with the empirical relationships available for other regions of the world further seismic intensity information available for historical earthquakes which have occurred in the nepal himalaya along with the present intensity data has been utilized for developing an attenuation relationship for the studied region using two step regression analyses the derived attenuation relationship is useful for assessing damage of a potential future large earthquake earthquake scenario based planning purposes in the region

probabilistic seismic hazard assessment for himalayan tibetan region from historical and instrumental earthquake catalogs the himalayan tibetan region has a long history of devastating earthquakes with wide spread casualties and socio economic damages here we conduct the probabilistic seismic hazard analysis by incorporating the incomplete historical earthquake records along with the instrumental earthquake catalogs for the himalayan tibetan region historical earthquake records back to more than 1000 years ago and an updated homogenized and declustered instrumental earthquake catalog since 1906 are utilized the essential seismicity parameters namely the mean seismicity rate the gutenberg richter b value and the maximum expected magnitude m max are estimated using the maximum likelihood algorithm assuming the incompleteness of the catalog to compute the hazard value three seismogenic source models smoothed gridded linear and areal sources and two sets of ground motion prediction equations are combined by means of a logic tree on accounting the epistemic uncertainties the peak ground acceleration pga and spectral acceleration sa at 0 2 and 1 0 s are predicted for 2 and 10 probabilities of exceedance over 50 years assuming bedrock condition the resulting pga and sa maps show a significant spatio temporal variation in the hazard values in general hazard value is found to be much higher than the previous studies for regions where great earthquakes have actually occurred the use of the historical and instrumental earthquake catalogs in combination of multiple seismogenic source models provides better seismic hazard constraints for the himalayan tibetan region

toward a consistent model for strain accrual and release for the new madrid seismic zone central united states 1 at the heart of the conundrum of seismogenesis in the new madrid seismic zone is the apparently substantial discrepancy between low strain rate and high recent seismic moment release in this study we revisit the magnitudes of the four principal 1811 1812 earthquakes using intensity values determined from individual assessments from four experts using these values and the grid search method of bakun and wentworth 1997 we estimate magnitudes around 7 0 for all four events values that are significantly lower than previously published magnitude estimates based on macroseismic intensities we further show that the strain rate predicted from postglacial rebound is sufficient to produce a sequence with the moment release of one mmax6 8 every 500 years a rate that is much lower than previous estimates of late holocene moment release however mw6 8 is at the low end of the uncertainty range inferred from analysis of intensities for the largest 1811 1812 event we show that mw6 8 is also a reasonable value for the largest main shock given a plausible rupture scenario one can also construct a range of consistent models that permit a somewhat higher mmax with a longer average recurrence rate it is thus possible to reconcile predicted strain and seismic moment release rates with alternative models one in which 1811 1812 sequences occur every 500 years with the largest events being mmax 6 8 or one in which sequences occur on average less frequently with mmax of 7 0 both models predict that the late holocene rate of activity will continue for the next few to 10 thousand years

stress transfer and connectivity between the bhutan himalaya and the shillong plateau abstract within the northern indian plate the shillong plateau is a peculiar geodynamic terrane hosting significant seismic activity outboard the himalayan belt this activity is often used as an argument to explain apparent reduced seismicity in the bhutan himalayas although current geophysical and geodetic data indicate that the bhutan himalayas accommodate more deformation than the shillong plateau we aim to quantify the extent to which the two geodynamic regimes are connected and potentially interact through stress transfers we compiled a map of major faults and earthquakes in the two regions and computed co seismic stress transfer amplitudes our results indicate that the bhutan himalayas and the shillong plateau are less connected than previously suggested major earthquakes in either of the two regions mainly affect transverse faults connecting them causing up to 40 bar coulomb stress change however this effect is clearly less on thrust faults of the either region up to 1 bar only the mw 8 25 1897 assam earthquake that affected the shillong plateau did not cause a stress shadow on the main himalayan thrust in bhutan as previously suggested similarly the mw 8 0 5 1714 bhutan earthquake had negligible impact on stress accumulation on thrust faults bounding the shillong plateau furthermore the main process shaping the regional stress patterns continues to be interseismic loading with complex boundary conditions in a diffuse deformation field involving the bengal basin and indo burman ranges while both the bhutan himalayas and the shillong plateau exhibit a compressional regime their stress evolutions are more weakly connected than hypothesized although our modelling suggests lateral increase in stress interactions from west less to east more in the bhutan himalayas a clearer picture will only emerge with better constrained fault geometries slip rates crustal structure and seismicity catalogues in the entire region of distributed deformation

frequency dependent lg attenuation in the indian platform we use seismograms from regional earthquakes recorded on digital seismographs in peninsular india to determine the frequency dependent q of lg for the indian platform we measure lg attenuation by determining the decay of spectral amplitudes with distance the available data suggest some spatial variation in attenuation but a much denser ray path coverage would be required to validate such observations we therefore combine all the measurements of overlapping regions that span both the shield and intervening terranes to obtain an average value of attenuation for the indian platform lg q 665 10 with the frequency exponent n 0 67 0 03 this average value of lg attenuation for the indian platform is similar to the average for other stable regions of the globe

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

first paleoseismic evidence for great surface rupturing earthquakes in the bhutan himalayas the seismic behavior of the himalayan arc between central nepal and arunachal pradesh remains poorly understood due to the lack of observations concerning the timing and size of past major and great earthquakes in bhutan we present here the first paleoseismic study along the himalayan topographic front conducted at two sites in southern central bhutan paleoseismological excavations and related oxcal modeling reveal that bhutan experienced at least two great earthquakes in the last millennium one between the seventeenth and eighteenth century and one during medieval times producing a total cumulative vertical offset greater than 10 m along with previous studies that reported similar medieval events in central nepal sikkim and assam our investigations support the occurrence of either i a series of great earthquakes between a d 1025 and a d 1520 or ii a single giant earthquake between a d 1090 and a d 1145 in the latter case the surface rupture may have reached a total length of 800 km and could be associated with an earthquake of magnitude mw 8 7 9 1

possible influence of subducting ridges on the himalayan arc and on the ruptures of great and major himalayan earthquakes abstract subduction of bathymetric features such as ridges seamounts fractures etc on the subducting plate influences the arc morphology and earthquake ruptures we analyse their effect on the development of the arcuate shape of the himalayan arc and on the ruptures of great and major himalayan earthquakes besides the two most prominent ridges in the indian ocean namely the chagos laccadive deccan ridge and the 90 e ridge which are assumed to extend up to the himalayan arc at least three major subsurface ridges have been mapped on the underthrusting indian plate under the indo gangetic plains it appears that the subduction of the two most prominent ridges contributed to the development of the arcuate shape of the himalayan arc the interaction and subduction of the other subsurface ridges probably influenced the himalayan arc morphology by causing a localised cusp in the frontal topography also these ridges probably acted as barriers to the ruptures of the major and great himalayan earthquakes

a spectral analysis of the 21 may 1997 jabalpur india earthquake mw 5 8 and estimation of ground motion from future earthquakes in the indian shield region the jabalpur earthquake 23 08 n 80 06 e h 36 km is the first event in the indian peninsular shield region to be well recorded by a newly installed 10 station broadband seismographic network using these data we estimate q of lg wave in the indian shield region as q 508 0 48 1 20 hz the corrected source spectrum with m 5 4 1024 dyne cm reported in the harvard cmt catalog and an 2 source model requires a stress parameter p of 420 bar to explain high frequency spectral level the computed seismic energy from the records is 7 4 1020 erg which yields an apparent stress and brune stress drop of 62 and 270 bars respectively the analysis of the jabalpur earthquake provides some elements for the estimation of ground motions during future earthquakes in the indian shield region based on the results of the jabalpur earthquake and on studies of tectonically similar region of eastern north america we assume that 1 the sources follow an 2 model 2 s waves dominate at r 100 km and lg waves dominate at r 100 km 3 q f 508 0 48 4 the ground motion is a bandlimited finite duration gaussian white noise and 5 the effective duration of the ground motion equals 1 c 0 05 r where fc is the corner frequency we apply random vibration theory rvt to compute various measures of ground motion such as a max and v max at near source distances the source finiteness is approximately taken into account the attenuation curves for 5 5 mw 7 and for p of 100 400 bar are presented as expected the predicted values with p 420 bar agree reasonably well with the limited jabalpur data an a max of 150 gal is predicted in the epicentral region of this earthquake the predicted curves imply p 100 bar for the latur earthquake of 1993 mw 6 1 h 2 5 km to explain a max 1 g and the reported isoseismal intensities in the epicentral region for koyna earthquake of 1967 mw 6 3 the inferred a max and v max from isoseismal intensities and the recorded strong motions at the koyna dam site are in agreement with the prediction curves for p 100 bar the rvt predictions seem reasonable but need validation from more strong motion data which is presently lacking

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

the nature of the crust in southern india implications for precambrian crustal evolution 1 we present crustal thickness and poisson s ratio determinations from receiver function analyzes at 32 sites on the archaean and proterozoic terrains of south india the crustal thickness in the late archaean 2 5 ga eastern dharwar craton varies from 34 39 km similar crustal thickness is observed beneath the deccan volcanic province and the cuddapah basin the most unexpected result is the anomalous present day crustal thickness of 42 51 km beneath the mid archaean 3 4 3 0 ga segment of the western dharwar craton since the amphibolite grade metamorphic mineral assemblages 5 7 kbar paleopressures in this part of western dharwar craton equilibrated at the depths of 15 20 km our observations suggest the existence of an exceptionally thick 57 70 km crust 3 0 ga ago beneath the exhumed granulite terrain in southernmost india the crustal thickness varies between 42 60 km the poisson s ratio ranges between 0 24 0 28 beneath the precambrian terrains indicating the presence of intermediate rock type in the lower crust these observations of thickened crust suggest significant crustal shortening in south india during the archaean

source characteristics of the 2015 m w 7 8 gorkha nepal earthquake and its m w 7 2 aftershock from space geodesy abstract on april 25 2015 a destructive m w 7 8 earthquake struck the capital of nepal kathmandu killing more than 8800 people and destroying numerous historical structures we analyze six coseismic interferograms from several satellites alos 2 sentinel 1 a and radarsat 2 as well as three dimensional displacements at six gps stations to investigate fault structure and slip distribution of the gorkha earthquake using a layered crustal structure the best fit slip model shows that the preferred dip angle of the mainshock fault is 6 3 5 and the major slip is concentrated within depths of 8 15 km the maximum slip of 6 0 m occurs at a depth of 11 km 70 km south east of the epicenter the coseismic rupture extends 150 km eastward of the epicentre with a cumulative geodetic moment of 7 8 10 20 nm equivalent to an earthquake of m w 7 84 we also investigate the m w 7 2 aftershock on 12 may 2015 using another three postseismic interferograms from alos2 radarsat 2 and sentinel 1 a the insar based best fit slip model of the largest aftershock implies that its major slip is next to the eastern lower end of the mainshock rupture with a similar maximum slip of 6 m at a depth of 13 km this study generates various coseismic geodetic measurements to determine the source parameters of the m w 7 8 gorkha earthquake and 12 may m w 7 2 afershock providing an additional chance to understand the local fault structure and slip extent

regional seismic intensity anomalies in the korean peninsula and its implications for seismic hazard potentials the strength of seismic ground motion is a consequence of seismic source strength and medium response the dependence of seismic amplitudes and seismic intensity on regional geological structures and crustal properties in the stable intraplate region around the korean peninsula is investigated an instrumental seismic intensity scale based on spectral accelerations are proposed after calibrating with the reported macroseismic intensities a representative seismic intensity attenuation curve for the korean peninsula is given by i m text l l h 0 998 pm 0 222 1 72 pm 0 04 m text l 0 322 pm 0 027 text ln l 2 h 2 0 00608 pm 0 00049 sqrt l 2 h 2 where i m text l l h is the seismic intensity at an epicentral distance l in km for an earthquake with local magnitude m text l and focal depth h in km seismic intensities decay slowly with distance in the korean peninsula the observed decay rate for the korean peninsula is comparable with those for other stable intraplate regions while are lower than those for active regions the regional seismic intensity anomalies present a characteristic correlation with geological structures positive seismic intensity anomalies appear in the yeongnam massif okcheon belt and gyeongsang basin while negative seismic intensity anomalies in the gyeonggi massif the regional seismic intensity anomalies display positive correlations with crustal thicknesses crustal amplifications and seismicity density and negative correlations with heat flows positive seismic intensity anomalies are observed in the yeongnam massif and gyeongsang basin suggesting high seismic hazard potentials in the regions the regional crustal properties may provide useful information on potential seismic hazards

estimating earthquake location and magnitude from seismic intensity data analysis of modified mercalli intensity mmi observations for a training set of 22 california earthquakes suggests a strategy for bounding the epicentral region and moment magnitude m from mmi observations only we define an intensity magnitude m i that is calibrated to be equal in the mean to m m i mean m i where m i mmi i 3 29 0 0206 i 1 68 and i is the epicentral distance km of observation mmi i the epicentral region is bounded by contours of rms m i rms m i m i rms m i m i where rms is the root mean square rms m i m i is the minimum rms over a grid of assumed epicenters and empirical site corrections and a distance weighting function are used empirical contour values for bounding the epicenter location and empirical bounds for m estimated from m i appropriate for different levels of confidence and different quantities of intensity observations are tabulated the epicentral region bounds and m i obtained for an independent test set of western california earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes the analysis strategy is particularly appropriate for the evaluation of pre 1900 earthquakes for which the only available data are a sparse set of intensity observations

differences in attenuation among the stable continental regions 1 there are systematic differences in the attenuation of damaging earthquake ground motions between different stable continental regions scrs seismic intensity and weak motion data show that the attenuation in seismic waves for eastern north america ena is less than for india africa australia and northwest europe if ena ground motion attenuation relations are used in seismic hazard models for other scrs as is commonly done then the estimated ground motions and resulting hazard may be too large if an attenuation model that averages observations from ena and the other scrs is used to estimate the magnitudes of large historical earthquakes in ena as is the case for recent estimates of m for the 1811 1812 new madrid missouri and the 1886 charleston south carolina events then the magnitude estimates for these events will be too large as will be the resulting hazard

structural segmentation controlled the 2015 mw 7 8 gorkha earthquake rupture in nepal the ongoing collision of india with asia is partly accommodated by slip on the main himalayan thrust mht the 25 april 2015 m w 7 8 gorkha earthquake is the most recent major event to rupture the mht which dips gently northward beneath central nepal although the geology of the range has been studied for decades fundamental aspects of its deep structure remain disputed here we develop a structural cross section and a three dimensional geologically informed model of the mht that are consistent with seismic observations from the gorkha earthquake a comparison of our model to a detailed slip inversion data set shows that the slip patch closely matches an ovalshaped gently dipping fault surface bounded on all sides by steeper ramps the gorkha earthquake rupture seems to have been limited by the geometry of that fault segment this is a significant step forward in understanding the deep geometry of the mht and its effect on earthquake nucleation and propagation published models of fault locking do not correlate with the slip patch or our fault model in the vicinity of the earthquake further suggesting that fault geometry was the primary control on this event our result emphasizes the importance of adequately constraining subsurface fault geometry in megathrusts in order to better assess the sizes and locations of future earthquakes

source area and rupture parameters of the 31 december 1881 mw 7 9 car nicobar earthquake estimated from tsunamis recorded in the bay of bengal 1 on the morning of 31 december 1881 a submarine earthquake beneath the andaman islands generated a tsunami with a maximum crest height of 0 8 m that was recorded by eight tide gauges surrounding the bay of bengal since the earthquake occurred 8 years before the construction of the world s first teleseismic recording seismometer little has been known about its rupture parameters or location waveform and amplitude modeling of the tsunami indicate that it was generated by a mw 7 9 0 1 rupture on the india andaman plate boundary resulting in 10 60 cm of uplift of the island of car nicobar the rupture consisted of two segments the northern 40 km long segment is separated from the southern 150 km long segment by a 100 km region corresponding to the westward projection of the west andaman spreading center the main rupture occurred between 8 5 n and 10 n with a total area of 150 km 60 km dipping 20 e with a mean slip of 2 7 m the recurrence time for 1881 type events is estimated to be 114 200 years on the basis of inferred gps convergence rates and inferred plate closure vectors although slip partitioning in the region may extend this estimate by as much as 30

pre and post seismic deformation related to the 2015 mw7 8 gorkha earthquake nepal we analyze time series from continuously recording gps stations in nepal spanning the pre and post seismic period associated to the m w7 8 gorkha earthquake which ruptured the main himalayan thrust mht fault on april 25th 2015 the records show strong seasonal variations due to surface hydrology after corrections for these variations the time series covering the pre and post seismic periods do not show any detectable transient pre seismic displacement by contrast a transient post seismic signal is clear the observed signal shows southward displacements consistent with afterslip on the mht using additional data from stations deployed after the mainshock we invert the time series for the spatio temporal evolution of slip on the mht this modelling indicates afterslip dominantly downdip of the mainshock rupture two other regions show significant afterslip a more minor zone updip of the rupture and a region between the mainshock and the largest aftershock ruptures afterslip in the first 7 months after the mainshock released a moment of 12 8 0 5 10 19 nm which represents 17 8 0 8 of the co seismic moment the moment released by aftershocks over that period of time is estimated to 2 98 10 19 nm geodetically observed post seismic deformation after co seismic offset correction was thus 76 7 1 0 aseismic the logarithmic time evolution of afterslip is consistent with rate strengthening frictional sliding according to this theory and assuming a long term loading velocity modulated on the basis of the coupling map of the region and the long term slip rate of 20 2 1 1 mm yr afterslip should release about 34 0 1 4 of the co seismic moment after full relaxation of post seismic deformation afterslip contributed to loading the shallower portion of the mht which did not rupture in 2015 and stayed locked afterwards the risk for further large earthquakes in nepal remains high both updip of the rupture area of the gorkha earthquake and west of kathmandu where the mht has remained locked and where no earthquake larger than m w7 5 has occurred since 1505

finite element modelling of the 2015 gorkha earthquake through the joint exploitation of dinsar measurements and geologic structural information abstract we investigate the co seismic effects of the mw 7 8 gorkha earthquake through a finite element modelling approach that jointly exploits space borne dinsar deformation measurements and geologic structural information our model permits to retrieve the coseismic displacements with a very good accuracy and to confirm the finding of earlier studies suggesting that the slip reaches a maximum value of about 7 m at a depth of 7 15 km along the main himalayan thrust mht and occurs in an area about 30 km northern of kathmandu in particular the main shock ruptured the deep part of the seismogenic zone of mht with rather small displacement values retrieved along the splay faults main frontal thrust mft main boundary thrust mbt in the southern region a relevant aspect of our results is the imaging of about 3 m of displacement in correspondence to the shallow portion of the main central thrust mct to the north and of the munsiari mahabharat thrust mt to the south this finding may be associated to a possible mechanism for accommodating the mht sourced deformation on the adjacent thrusts highlighting a passive role of the hinterland structures as receiver faults of the displacements transferred from earthquakes originating on the mht in addition the proposed model allow us to map the stress field distribution evaluated through von mises failure criteria associated to the main seismic event this result is in good agreement with the hypocentral distribution and mechanism of the investigated aftershocks

paleoseismic evidence of a surface rupture along the northwestern himalayan frontal thrust hft abstract new paleoseismic evidence is presented from the bhatpur n 31 18 16 28 e 76 9 50 00 trench site along the himalayan frontal thrust hft on western margin of the janauri anticline in nw himachal himalaya india the latest surface rupture at this site demonstrates coseismic displacement of at least 9 3 m radiocarbon dating of trench samples indicates that the surface ruptures occurred at a d 1400 1460 after comparison with other trench results along the himalayan front two scenarios are presented of the latest surface rupturing earthquake event in the northwestern indian himalaya 1 a single event surface rupturing for a minimum fault length of 450 km or 2 two events of different lateral extent according to the former scenario the latest surface rupture occurred between a d 1404 and 1422 the latter scenario suggests the latest surface rupture occurred between a d 1404 and a d 1460 in the northwestern extent from kala amb to hajipur with 9 0 m of coseismic displacement over a minimum fault length of 200 km yet another surface rupture event in the southeastern extent from kala amb to ramnagar has occurred between a d 1282 and a d 1422 with displacement ranging from 16 0 m to 26 0 m and a minimum surface rupture length of 230 km on the basis of these observations and historical earthquakes it is suggested that the potential for earthquakes larger than those in the historical records are capable of producing surface rupture lengths greater than the 200 to 230 km or 450 km in the northwestern indian himalayan front

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

ground motion scaling in the kachchh basin india deduced from aftershocks of the 2001 mw 7 6 bhuj earthquake we studied the excitation propagation and site effects in the kachchh basin of india by using ground motion recordings from a temporary seismograph network deployed to study aftershocks of the m w 7 6 bhuj earthquake of 26 january 2001 the kachchh basin has been proposed as a useful analog region for studying hazard in other earthquake prone but slowly deforming regions such as the central united states the earthquakes we studied ranged in size from about m 2 to m 5 2 and travel paths ranged from a few kilometers to about a hundred kilometers there was a broad range of focal depths among the aftershocks so the data were divided into two overlapping subsets to test the sensitivity of the derived propagation and source parameters to focal depth parameters we constrained include the source excitation terms related to stress drop a frequency dependent attenuation operator a geometric spreading function and an operator to account for site effects our results indicate that seismic wave attenuation in kachchh crust is very low similar to other continental intraplate areas such as central and eastern north america we also estimated seismic moments and stress drops for the earthquakes by fitting single corner frequency source model spectra to the observed spectra corrected for propagation by using our derived parameters stress drops were found to scale with seismic moment and to be rather high overall by using a stochastic point source model to estimate mainshock ground motions we found that the distance decay of expected peak ground motions assuming a stress drop of 15 20 mpa compare well with the scant observations for the bhuj earthquake ground motion predictions for kachchh based on bhuj aftershock data support the idea that the region may have similar hazard to proposed analog areas in north america