surface rupture of the 2005 kashmir pakistan earthquake and its active tectonic implications to provide a detailed record of a relatively rare thrust surface rupture and examine its active tectonic implications we have conducted field mapping of the surface rupture associated with the 2005 m w 7 6 kashmir earthquake despite the difficulty arising from massive earthquake induced landslides along the surface rupture we found that typical pressure ridges and warps extend northwestward for a distance of 70 km with a northeast side up vertical separation of up to 7 m neither the main frontal thrust nor the main boundary thrust is responsible for the earthquake but three active faults or fault segments within the sub himalaya collectively called the balakot bagh fault compose the causative fault although the fault exhibits substantial geomorphic expression of repeated similar surface ruptures only a part of it had been mapped as active before the earthquake the location of the hypocenter suggests that the rupture was initiated at a deep portion of the northern central segment boundary and propagated bilaterally to eventually break all three segments our obtained surface rupture traces and the along strike slip distribution are both in good agreement with results of prompt analyses of satellite images indicating that space geodesy can greatly aid in time consuming field mapping of surface ruptures assuming that the extensive fill terrace in the meizoseismal area was abandoned during 10 30 ka we tentatively estimate the earthquake recurrence interval and shortening rate on the balakot bagh fault to be 1000 3300 yr and 1 4 4 1 mm yr respectively these estimates indicate that the balakot bagh fault is not a main player of himalayan contraction accommodation graphic 1 selected field photographs and arcgis files of the mapped surface rupture traces and measured vertical separations are available in the electronic supplement to this article 1 embed inline graphic 1 gif

local seismic activity in the region of the assam gap northeast india abstract a tripartite array of vertical seismographs was operated for 5 5 months in late 1979 in the shillong massif area of northeast india during this time 719 local earthquakes were recorded of these 359 were located 2 4 m d 5 1 using for some events additional arrival times from the wwssn imd station shillong and some portable stations operated by the ngri rrl the area of the shillong massif and the mikir hills 60 km radius within our array showed a high seismicity rate of about four earthquakes per week with m d 3 1 4 this activity rate contrasted strongly with the assam gap where there were practically no earthquake sources detected by our array a seismic asperity seems to exist in the kopili valley between shillong and mikir hills which may have been the termination of the 1897 rupture and which could perhaps become the nucleation point for the next great assam earthquake based on these seismicity results and macroseismic data seeber and armbruster 1981 we estimate the length of the assam gap to be about 240 km frequency versus magnitude plots revealed b values of about 1 5 and suggested that within the array the locations were complete for m d 3 1 4 a comparison of local and teleseismic locations and magnitudes could be made only for the largest event which was located 300 km outside the array this comparison suggests that m d m b 0 5 and that the epicenter location errors outside the array are of the order of 40 km

seismotectonics in northeast india a stress analysis of focal mechanism solutions of earthquakes and its kinematic implications summary in northeast india three major plates interact along two convergent boundaries the himalayas and the indo burma ranges which meet at the assam syntaxis to clarify this tectonic interaction and the underlying dynamics we determine the regional seismotectonic stress from the stress inversion of 285 double couple focal mechanism solutions of earthquakes with an average magnitude of 5 we then compare the reconstructed stress regimes with the available information about geodetically determined relative displacements north south compression in a direction consistent with india eurasia convergence prevails in the whole area from the eastern himalayas to the bengal basin through the shillong mikir massif and the upper assam valley e w extension in tibet is related to this n s india eurasia convergence not only does the major n s compression affect the outer segments of the indo burma ranges it also extends into the descending slab of indian lithosphere below these ranges although stresses at depth are controlled by bending of the slab beneath the burmese arc the existence of widespread n s compression in the bengal basin far away from the himalayan front is compatible with the previously proposed convergence between a shillong mikir assam valley block and the indian craton e w compression inside this block supports the hypothesis of a component of eastward extrusion stress inversion of focal mechanism solutions in the indo burma ranges reveals a complex stress pattern the burmese arc and its underlying lithosphere experience nearly arcperpendicular extension with ese wnw trends in the northernmost ne trending segment and ene wsw trends in the main n s arc segment such extensional stress documented from many arcs is likely a response to pull from and bending of the subducting plate at the same time the indo burma ranges are under compression as a result of oblique convergence between the sunda and indian plates the maximum compressive stress rotates from ne sw across the inner and northern arc to e w near the bengal basin this rotation is consistent with the deformation partitioning reflected in the rotation of relative displacement vectors from a ssw directed sunda burma motion to a wsw directed burma india motion as a consequence of this partitioning the major belt parallel fault zones show a variety of movements across the main n s arc segment from right lateral slip in the inner ranges to oblique reverse dextral slip in the outer ranges and pure thrusting in the westernmost foreland belt

earthquake magnitude frequency epicentral distance and soft sediment deformation in sedimentary basins abstract empirical equations available for earthquake magnitude frequency and the maximum epicentral distance of liquefied sites versus magnitude are combined with the characteristic instantaneous sediment deposition rate at a station in a sedimentary basin to form a model for the local stratigraphic frequency of earthquake induced soft sediment deformation structures both the style of sedimentation and the characteristics of the earthquake source combine to determine the pattern of incidence of the structures in a basin the model is probably most directly applicable to the geodynamic interpretation of fluvial basins in which substantial volumes of readily liquefied sands accumulate at high local short term rates

genesis and diagnostic value of soft sediment deformation structures a review abstract soft sediment deformation structures are recognized as important diagnostic features in the rock record for determination of depositional environments and slope processes the diagnostic value of these structures is reevaluated by analysis of the parameters controlling sediment deformation soft sediment deformation is contemporaneous with deposition and occurs dominantly in course silt to fine sand the high depositional rate low permeability and low shear strength of grains within this sediment range maximize the occurrence of deformation the dominant mechanisms responsible for sediment deformation include 1 liquefaction or fluidization 2 reverse density gradation 3 slumping or slope failure and 4 shear stress in most cases a combination of these mechanisms occurs the processes function in a continuum producing features that are microscopic to megascopic in scale it is shown that the processes and thus the structures are not environment specific the true diagnostic value of the structures may be in defining hydrodynamic conditions and in interpreting paleocurrents and paleoclimatic and paleoseismic events ultimately for the best diagnostic results soft sediment deformation structures should be studied in association with all other available lithologic structural and paleontological information

luminescence chronology of the inland sand dunes from se india abstract records of past climate changes have been preserved variously on the earth s surface sand dunes are one such prominent imprint and it is suggested that their presence is an indicator of periods of transition from arid to less arid phases we report inland sand dunes from andhra pradesh se india spread over an area of 500 km 2 75 km inland from the east coast the dune sands are examined to understand their provenance transportation timing of sand aggradation and their relationship to past climates the dune distribution grain morphology and the grain size studies on sands suggest an aeolian origin physiography of the study area heavy mineral assemblage and abundance of quartz in the parent rocks indicate that the dune sands are largely derived from first order streams emanating from hills in the region and from weathering of the nellore schist belt it appears that the geomorphology and wind direction pattern both facilitated and restricted the dune aggradation and preservation to a limited area osl dating of 47 dune samples ranged from the present to 50 ka thereby suggesting a long duration of sand dune aggradation and or reworking history

the shillong plateau and the great 1897 assam earthquake previous analysis of triangulation data of the survey of india concluded that the great 1897 assam earthquake occurred on a south dipping fault near the northern edge of the shillong plateau which was named the oldham fault this attribution has been questioned on geological and geodetic grounds we refine the triangulation data adding recently discovered observations and demonstrate that they require average slip of 25 5 m on a fault that dips south at 40 beneath the plateau the best fitting solution to the geodetic observations gives a rupture length of 79 km however the chedrang fault immediately to the west of the oldham fault appears to have slipped as a subvertical tear fault during or shortly after the 1897 earthquake with over 10 m of down to the west normal sense slip this observation suggests that the western end of the main rupture approached within a few kilometers of the chedrang fault giving a length of 95 km for the rupture this range of parameters gives a magnitude 8 15 mw 8 35 for the earthquake the triangulation data cannot be satisfied by slip on the north dipping faults that border the southern edge of the shillong plateau nor by slip on a south dipping fault that has been postulated in the brahmaputra valley gps velocities show that up to 5 mm yr of shortening is taken up across the plateau and its borders this suggests via moment frequency relations that the interval between great earthquakes in the region is several thousand years but that earthquakes of magnitude 7 or greater should occur roughly once per century

the great 1950 assam earthquake revisited field evidences of liquefaction and search for paleoseismic events abstract extensive field investigations were carried out for the first time in the meizoseismal area of the great 1950 assam earthquake aimed at exploring the paleoseismic history of the ne indian region through documentation of liquefaction features and radiocarbon 14c dating trenching at more than a dozen locations along the burhi dihing river valley and within the alluvial fans adjoining the brahmaputra and dibang rivers resulted in the identification of more than a dozen very prominent liquefaction features sand dykes sills sand blows etc as evidences of large to great earthquakes 14c dating of the organic material associated with some of the features indicates a paleoseismic record of about 500 yrs archived by the sediments in this region compelling geological evidence s of the great 1950 earthquake are well constrained by 14c dating out of the two historically reported seismic events 1548 ad and 1697 ad from this region 14c dating could constrain the 1548 ad event though not distinctly further studies using combined 14c and osl dating may better constrain the seismo chronology of the study region

paleoseismic investigations in the kopili fault zone of north east india evidences from liquefaction chronology abstract we report the seismogenic liquefaction signatures observed in the kopili fault zone of the brahmaputra plains ne india this seismically active zone has previously been identified as the assam seismic gap and thus necessitates understanding its past seismicity and implied seismic hazard with this objective paleo seismic studies using seismogenic liquefaction features have been carried out in this region largely covered with the flood plain deposits of kopili and kalang rivers the trenches excavated at two locations revealed extensive liquefaction features with more than 20 sub parallel sand dykes having major orientation in ne sw direction a total of 29 samples from marker horizons have been processed to constrain chronology of the liquefaction features using optically stimulated luminescence osl and 14 c ams dating techniques the age constraints in terms of respective lower and upper bound age brackets for individual dykes suggest three time intervals of their formations i e i 250 25 yr bp ii between 400 to 770 yr bp and iii 900 50 yr bp these new ages of liquefaction features correspond to the occurrence timings of causative seismic events which are in addition to the known historical earthquakes and thus enhance our understanding of the paleoseismic history of this region during past 1000 years

earthquake imprints on a lacustrine deltaic system the kurk delta along the east anatolian fault turkey deltas contain sedimentary records that are not only indicative of water level changes but also particularly sensitive to earthquake shaking typically resulting in soft sediment deformation structures the kurk lacustrine delta lies at the south western extremity of lake hazar in eastern turkey and is adjacent to the seismogenic east anatolian fault which has generated earthquakes of magnitude 7 this paper reevaluates water level changes and earthquake shaking that have affected the kurk delta combining geophysical data seismic reflection profiles and side scan sonar remote sensing images historical data onland outcrops and offshore coring the history of water level changes provides a temporal framework for the depositional record in addition to the common soft sediment deformation documented previously onland outcrops reveal a record of deformation fracturing tilt and clastic dykes linked to large earthquake induced liquefactions and lateral spreading the recurrent liquefaction structures can be used to obtain a palaeoseismological record five event horizons were identified that could be linked to historical earthquakes occurring in the last 1000 years along the east anatolian fault sedimentary cores sampling the most recent subaqueous sedimentation revealed the occurrence of another type of earthquake indicator based on radionuclide dating 137cs and 210pb two major sedimentary events were attributed to the ad 1874 1875 east anatolian fault earthquake sequence their sedimentological characteristics were determined by x ray imagery x ray diffraction loss on ignition grain size distribution and geophysical measurements the events are interpreted to be hyperpycnal deposits linked to post seismic sediment reworking of earthquake triggered landslides this article is protected by copyright all rights reserved

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

plateau pop up in the great 1897 assam earthquake the great assam earthquake of 12 june 1897 reduced to rubble all masonry buildings within a region of northeastern india roughly the size of england and was felt over an area exceeding that of the great 1755 lisbon earthquake1 hitherto it was believed that rupture occurred on a north dipping himalayan thrust fault propagating south of bhutan2 3 4 5 but here we show that the northern edge of the shillong plateau rose violently by at least 11 m during the assam earthquake and that this was due to the rupture of a buried reverse fault approximately 110 km in length and dipping steeply away from the himalaya the stress drop implied by the rupture geometry and the prodigious fault slip of 18 7 m explains epicentral accelerations observed to exceed 1g vertically and surface velocities exceeding 3 m s 1 ref 1 this quantitative observation of active deformation of a pop up structure confirms that faults bounding such structures can penetrate the whole crust plateau uplift in the past 2 5 million years has caused the indian plate to contract locally by 4 2 mm yr 1 reducing seismic risk in bhutan but increasing the risk in northern bangladesh

near surface expression of early to late holocene displacement along the northeastern himalayan frontal thrust at marbang korong creek arunachal pradesh india we present the results of a paleoseismic trench investigation of an 8 m scarp at the mouth of marbang korong creek 27 58 26 0700 n 95 13 42 3000 e within the meizoseismal area of the 1950 assam earthquake along the northeast himalayan frontal thrust hft of india structural stratigraphic and growth stratigraphy relations observed in the trench are interpreted to indicate that expression of the scarp is due to uplift and folding of near surface sediments in response to hft displacement that reaches near the surface yet below the 5 m depth of the trench exposure the most recent contribution to scarp growth dates to fault displacement post 2009 cal yr b p it remains a matter of speculation whether or not the most recent event deformation is a result of the great 1950 assam earthquake that is reported on the basis of intensity data online material high resolution trench log 5 and table summarizing results and inputs of radiocarbon analysis of detrital charcoal samples

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

regional variation of coda q in kopili fault zone of northeast india and its implications abstract kopili fault has been experiencing higher seismic and tectonic activity during the recent years these kind of active tectonics can be inspected by examining coda wave attenuation and its dependence with frequency exploiting single back scattering model we have endeavored to measure coda q and its associated parameters such as frequency dependent factor n and attenuation coefficient covering seven lapse time windows spanning from 30 to 90 s and central frequencies 1 5 3 5 6 9 and 12 hz the average estimated values of qc increase s with frequency and lapse time window from 114 at frequency 1 5 hz to 1563 at frequency 12 hz for 30 s window length and from 305 at frequency 1 5 hz to 2135 at frequency 12 hz for 90 s window length the values of q0 and n are also estimated for the entire kopili fault zone for this study region the q0 values vary from 62 to 348 and n varies from 0 57 to 1 51 within the frequency range 1 5 to 12 hz furthermore depth variation of attenuation of this region reveals that there is velocity anomaly at depth 210 220 km as there arises sharp changes in and n which are supported by available data reported by other researcher for this region finally we have tried to separate the intrinsic and scattering attenuation for this area it is observed that the entire region is dominated by mainly scattering attenuation but we can see an increase in intrinsic attenuation with depths in two stations namely tzr and bkd furthermore the obtained results are comparable with the available global data

paleoliquefaction evidence and periodicity of large prehistoric earthquakes in shillong plateau india abstract the tectonic setting and the occurrence of the great assam earthquake m 8 7 of 1897 in the shillong plateau succeeded by three great earthquakes 1905 1934 and 1950 in the adjoining himalayan frontal arc indicates the vulnerability of the shillong plateau to large earthquakes the lack of seismicity records of the region earlier than 100 years and data on the recurrence of damaging earthquakes led us to investigate the paleoseismicity of the shillong plateau our paleoseismic investigations in the meizoseismal area of the 1897 earthquake revealed well preserved liquefaction and deformed syndepositional features at 10 selected sites in the alluvial deposits along two north flowing tributaries of the brahmaputra river these features are 14c dated using associated organic samples as the liquefaction of sediments was an important feature of the 1897 earthquake we identified this seismic event and other large major prehistoric earthquakes through paleoliquefaction and other coseismic structural deformation at the investigated sites in addition to the 1897 event we provide geological evidence for at least three large seismic events two of them occurred during 1450 1650 and 700 1050 ad the third predates 600 ad the analysis of the 14c data suggests a return period of about 400 600 yr for the large earthquakes in the shillong plateau this finding is the first of its kind from the himalaya and adjoining region

interpreting the style of faulting and paleoseismicity associated with the 1897 shillong northeast india earthquake implications for regional tectonism 1 the 1897 shillong assam northeast india earthquake is considered to be one of the largest in the modern history although oldham s 1899 classic memoir on this event opened new vistas in observational seismology many questions on its style of faulting remain unresolved most previous studies considered this as a detachment earthquake that occurred on a gently north dipping fault extending from the himalayan front a recent model proposed an alternate geometry governed by high angle faults to the north and south of the plateau and it suggested that the 1897 earthquake occurred on a south dipping reverse fault coinciding with the northern plateau margin in this paper we explore the available database together with the coseismic observations from the region to further understand the nature of faulting the geophysical and geological data examined in this paper conform to a south dipping structure but its location is inferred to be in the brahmaputra basin further north of the present plateau front our analyses of paleoseismic data suggest a 1200 year interval between the 1897 event and its predecessor and we identify the northern boundary fault as a major seismic source the shillong plateau bounded by major faults behaves as an independent tectonic entity with its own style of faulting seismic productivity and hazard potential distinct from the himalayan thrust front a point that provides fresh insight into the regional geodynamics

anelastic and compressible simulation of moist dynamics at planetary scales abstractmoist anelastic and compressible numerical solutions to the planetary baroclinic instability and climate benchmarks are compared the solutions are obtained by applying a consistent numerical framework for discrete integrations of the various nonhydrostatic flow equations moist extension of the baroclinic instability benchmark is formulated as an analog of the dry case flow patterns surface vertical vorticity and pressure total kinetic energy power spectra and total amount of condensed water are analyzed the climate benchmark extends the baroclinic instability study by addressing long term statistics of an idealized planetary equilibrium and associated meridional transports short term deterministic anelastic and compressible solutions differ significantly in particular anelastic baroclinic eddies propagate faster and develop slower owing to respectively modified dispersion relation and abbreviated baroclinic vorticity production these eddies also carry less kinetic energy and the ons

the 2016 mw 6 7 imphal earthquake in the indo burman range a case of continuing intraplate deformation within the subducted slab the 2016 m w 6 7 imphal earthquake is one of the largest and instrumentally well recorded seismic events to have occurred on the segment of the indo burman plate boundary where indian and burman plates converge in a roughly northeast direction similar to 3 4 cm yr this segment of the plate boundary has not generated any great earthquakes in the documented history but is noted for its complex intraslab deformation arc parallel compression and slip partitioning with the continental strike slip sagaing fault previous studies have noted a mix of faulting styles and hypocentral distribution indicating the inherent complexities within this segment based on the teleseismic moment inversion of 88 p and sh waveforms from 70 global broadband seismic stations we use the source model of the 2016 earthquake to corroborate the continuing intraslab deformation the earthquake is sourced at a depth of 55 km where the dip of the slab changes to similar to 50 degrees with the p axis oriented in the north northeast south southwest direction our analysis of azimuths and plunges of p axes of 214 earthquakes m w 4 5 global centroid moment tensor is consistent with this trend previous studies have noted two distinct types of intraplate earthquakes along this segment shallower events 25 75 km due to arc parallel bending and the deeper ones 90 150 km in response to slab pull interplate seismicity is almost absent and the potential for great earthquakes seems much lower compared with the rest of the eastern india plate boundary

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

the earthquake potential of the new madrid seismic zone the fault system responsible for new madrid seismicity has generated temporally clustered very large earthquakes in a d 900 100 years and a d 1450 150 years as well as in 1811 1812 given the uncertainties in dating liquefaction features the time between the past three new madrid events may be as short as 200 years and as long as 800 years with an average of 500 years this advance in understanding the late holocene history of the new madrid seismic zone and thus the contemporary tectonic behavior of the associated fault system was made through studies of hundreds of earthquake induced liquefaction features at more than 250 sites across the new madrid region we have found evidence that prehistoric sand blows like those that formed during the 1811 1812 earthquakes are probably com pound structures resulting from multiple earthquakes closely clustered in time or earthquake sequences from the spatial distribution and size of sand blows and their sedimentary units we infer the source zones and estimate the magnitudes of earth quakes within each sequence and thereby characterize the detailed behavior of the fault system it appears that fault rupture was complex and that the central branch of the seismic zone produced very large earthquakes during the a d 900 and a d 1450 events as well as in 1811 1812 on the basis of a minimum recurrence rate of 200 years we are now entering the period during which the next 1811 1812 type event could occur

metamorphic processes a celebration of the career contribution of ron vernon this special issue is in celebration of the career contribution of ron vernon it arises from the ron vernon symposium which was held as part of the 15th australian geological convention in sydney in 2000 to date ron has published more than one hundred scientific papers several books and contributed widely to international conferences he is the doyen in the multidisciplinary field of microstructures which spans petrology and structural geology however ron s range is phenomenal and he has contributed to many aspects of metamorphism magmatism and rock deformation he has drawn on data from his work in these areas to contribute widely to understanding thermal regimes crustal evolution and tectonics as exemplified by his ideas about htlp metamorphism and emplacement of granites ron has followed the scientific method in his work it has led him to many innovative interpretations some of which undermined established dogma by example ron has been a positive role model for the younger generation however for the older generation he has been something of a bete noire the papers in this special issue cover the range from low to high grade metamorphism from metasomatism to melting from microstructures to tectonics and from fieldwork to experiments it is our hope that in reading them you will take time to think about what has been achieved in the past 40 years and use this as motivation for what remains to be done

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

timing and return period of major palaeoseismic events in the shillong plateau india abstract the close temporal occurrence of four great earthquakes in the past century including the great assam earthquake of 1897 in the shillong plateau necessitated examination of the palaeoseismicity of the region the results from such investigation would definitely aid in addressing the problem of the earthquake hazard evaluation more realistically our recent palaeoseismological study in the shillong plateau has led us to identify and provide geological evidence for large major earthquakes and estimate the probable recurrence period of such violent earthquakes in parts of the shillong plateau and the adjoining brahmaputra valley trenching along the krishnai river a tributary of the river brahmaputra has unravelled very conspicuous and significant earthquake induced signatures in the alluvial deposits of the valley the geological evidence includes 1 palaeoliquefaction features like sand dykes and sand blows 2 deformational features like tilted beds 3 fractures and syndepositional deformational features like flame structures caused by coeval seismic events chronological constraints of the past large major earthquakes are provided from upper and lower radiocarbon age bounds in the case of the palaeoliquefaction features and the coeval timing of the palaeoseismic events is obtained from the radiocarbon dating of the organic material associated with the deformed horizon as well as buried tree trunks observed wide distances apart our palaeoseismic measurements which are the first from the area indicate that the shillong plateau has been struck by large major earthquakes around 500 150 1100 150 and 1500 150 yr bp in addition to the well known great seismic event of 1897 thereby the 14 c dates indicate a recurrence period of the order of 500 yr for large earthquakes in the shillong plateau

soft sediment deformation in contemporary reservoir sediment a repository of recent major earthquake events in garhwal himalaya abstracttwo discrete 10 20 cm thick zones of soft sediment deformation ssd structures in horizontal beds occur in a 2 35 m thick sandbar in the asan reservoir in the northwestern sub himalaya the sediment column shows uninterrupted fluviolacustrine deposition since 1975 the depositional and deformational features boundary conditions and sedimentation rate suggest that the discrete ssd features formed in an apparent reverse density gradient and were triggered by the 1991 uttarkashi and 1999 chamoli earthquakes these triggering events occurred within 100 150 km of the reservoir which lay in intensity zones v vi the observations correspond well to the empirical relationship between distances to a liquefaction zone from an epicenter the highly liquefiable sediments in the asan reservoir provide a unique depositional and tectonic setting to record ssd triggering of ssd by contemporary seismic events demonstrates the validity of interpretations of similar causes of ssd in older sediments this is pr

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