evidence for an earthquake cycle in nw outer himalaya near 78 e longitude from precision levelling observations a levelling line along the saharanpur dehradun mussoorie highway crosses the nw outer himalaya the line has been surveyed over most parts of its length several times at irregular intervals since 1861 the observations show that there was coseismic uplift along the line during the great kangra earthquake of 1905 but most benchmarks have started subsiding in the decades following the earthquake this is seen as evidence that the upper crust along and adjoining the levelling line experiences a cyclic process of strain accumulation and release in great earthquakes

estimation of strain distribution using gps measurements in the kumaun region of lesser himalaya abstract the continuous process of continent continent collision between the indian and the eurasian plates has led to the formation of the himalayan range and continuously caused earthquakes in the region large earthquakes with magnitudes of 8 and above occur in this region infrequently releasing the elastic strain accumulated over years around the plate boundary geodetic measurements can help estimate the strain distribution along the fault system these measurements provide information on active deformations and associated potential seismic hazards along the himalayan arc in order to understand the present deformation around the plate boundary we collected gps data during three campaigns in the years of 2005 2007 at 16 sites in the kumaun region of the lesser himalaya horizontal velocity vectors estimated in itrf2000 are found to be in the range of 41 50 mm yr with an uncertainty level of the order of 1 mm yr the velocity field indicates that the present convergence of around 15 mm yr takes place in the kumaun himalaya further we estimate the strain components in the study area for understanding the currently active tectonic process in the region the estimated dilatational strain indicates that the northern part near the main central thrust mct is more compressional than the southern part maximum shear strain is mostly accommodated in the northern part too the maximum shear and dilatational strain rates are about 1 0 and 0 5 strain yr it is seen that the distribution of high shear strain spatially correlates with seismicity the maximum of extensional and compressional strains due to the force acting along the main central thrust mct in the nw se direction are found to be 0 4 and 0 1 strain yr respectively the maximum shear strain in the northern part of the himalaya appears to be associated with the convergence of the region proposed by other geophysical studies

thermotectonic history of the chiplakot crystalline belt in the lesser himalaya kumaon india constraints from apatite fission track thermochronology abstract fission track ages and confined track length distribution of apatite samples separated from the chiplakot crystalline belt ccb of the lesser himalayan crystalline lhc zone located to the south of the main central thrust mct munsiari thrust mt in kumaon india have been determined ages from the ccb along the kali and darma valleys fall in two distinct groups in the northern part of the ccb the ages range from 9 8 0 6 to 7 6 0 6 ma with a weighted mean of 9 6 0 1 ma while in the southern part the ages vary from 17 9 0 9 to 12 9 1 1 ma with a weighted mean of 14 1 0 1 ma the bimodal distribution of track lengths indicates that the ages are mixed ages rather than simple cooling ages the apatite fission track aft ages and already published structural data of the ccb suggest a complex erosional denudation history within the upper 3 4 km of the crust of the ccb the ages further indicate that the ccb was thrust into place earlier than the middle miocene i e at the time of development of the mct since then these rocks have remained within the upper 3 km of crust and were affected by only moderate to slow erosion and exhumation these results have important implications for the tectonic evolution of the lhc zone to the south of the mct mt the exhumation of the lhc zone in different parts of the himalaya was not uniform in the kumaon himalaya it was not controlled as in the himachal himalaya by any major tectonic event since it was thrust over the lesser himalayan meta sedimentary lhms zone and underwent moderate to slow erosion and exhumation

interseismic strain accumulation on the himalayan crustal ramp nepal the departement of mines and geology has been monitoring the seismicity of the central himalayas of nepal since 1985 intense microseismicity and frequent medium size earthquakes ml 4 tend to cluster beneath the topographic front of the higher himalaya this 10 20km deep seismicity also correlates with a zone of localized uplift that has been evidenced from geodetic data both microseismic and geodetic data indicate strain accumulation on a mid crustal ramp that had been previously inferred from geological and geophysical evidence this ramp connects a flat decollement under the lesser and sub himalaya with a deeper decollement under the higher himalaya and probably acts as a geometric asperity where strain and stress build up during the interseismic period the large himalayan earthquakes could nucleate there and probably activate the whole flat and ramp system up to the blind thrusts of the sub himalaya

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

slip distribution beneath the central and western himalaya inferred from gps observations summary underthrusting of the indian plate beneath the himalaya has been the cause of many hazardous thrust faulting earthquakes along the arc moderate earthquakes with magnitudes of 5 occur frequently in this region releasing the elastic strain accumulated over many years around the plate boundary these events can be attributed to slip deficits where the indian and eurasian plates are locked during interseismic periods geodetic measurements can help discriminate the distribution of the interlocking areas and the steadily slipping areas beneath the himalaya to understand the deformation across the central and western himalaya and the associated slip on thrust faults campaign mode gps data were collected in the garhwal kumaun region of the western himalaya gps sites velocities show that the deformation is currently concentrated between the lesser and higher himalaya horizontal velocities are used to estimate the slip distribution for the estimation a model of the interseismic surface deformation caused by buried non uniform creep dislocation nuc on a curved fault surface is used the slip distribution shows that there might be structural discontinuity on the fault between the kumaun and garhwal regions of the himalaya the estimated slip rate at the depth around 20 40 km in the central himalaya and at the depth of 15 km in the western himalaya is 10 mm yr 1 the nuc model indicates that the shallow part 20 km of the thrust fault system along the plate boundary is almost locked the locking depth appears to be deep in the central himalaya and shallower in the western himalaya further most of the historical large seismic events are observed to have occurred in an area with a slip velocity less than 10 mm yr 1 i e in a locked zone at the plate interface

configuration of the indian moho beneath the nw himalaya and ladakh 1 teleseismic receiver function analysis of seismograms recorded on a 700 km long profile of 17 broadband seismographs traversing the nw himalaya shows a progressive northward deepening of the indian moho from 40 km beneath delhi south of the himalayan foredeep to 75 km beneath taksha at the karakoram fault similar studies by wittlinger et al 2004 to the north of the karakoram fault show that the moho continues to deepen to 90 km beneath western tibet before shallowing substantially to 50 60 km at the altyn tagh fault the continuity of the indian moho imaged in the receiver functions reported here along with those of wittlinger et al 2004 suggest that in this part of the himalayan orogen the indian plate may penetrate as far as the bangong suture and possibly as far north as the altyn tagh

modeling fluid transfer along california faults when integrating pressure solution crack sealing and compaction processes 1 several models pertaining to earthquake cycles imply intermittent fluid flow through fault during the interseismic period increase in fluid pressure from hydrostatic to lithostatic values is a crucial parameter in mechanisms leading to earthquakes to achieve such pressures geodynamic processes gouge compaction fluid flow and changes in permeability are required previous models have postulated that changes in permeability by self healing are faster than the effects of geodynamic processes we consider the different mechanisms and rates of crack sealing near active fault on the examples of uplifted californian faults we find that natural crack sealing is normally not achieved by a rapid self healing process pressure solution with mass transfer from solution cleavage to cracks appears to be a more important mechanism for crack sealing and creep during postseismic deformation the geometry of transfer path and experimental data have been used to model crack sealing rates by pressure solution which are estimated to be rather slow similar to the recurrence time of some earthquakes such slow changes in permeability may be crucial factors in controlling the increase in fluid pressure and consequently the mechanism of critical failure in faults then numerical modeling of fluid pressure and transfer around active faults has been performed integrating a slow change in permeability by crack sealing gouge compaction and fluid flow from depth this modeling shows various location and evolution of fluid overpressure during the interseismic period depending on these processes and allows one to estimate the amount of fluid transferred from depth during interseismic periods

the motion and active deformation of india measurements of surface displacements using gps constrain the motion and deformation of india and india eurasia plate boundary deformation along the himalaya the gps velocities of plate interior sites constrain the pole of the angular velocity vector of india with respect to eurasia to lie at 25 6 1 0 n 11 1 9 0 e approximately 6 west of the nuvel 1a pole of 3 ma plate motion the angular rotation rate of 0 44 0 03 myr 1 is 14 slower than the long term rate of 0 51 myr 1 insignificant velocities between plate interior sites indicate that the exposed indian plate is stable to within 7 10 9 yr 1 the observed contraction vector across the himalaya 20 mm yr veers from n20 e in the northwest himalaya to n25 w in east nepal consistent with east west extension of southern tibet

a review of crust and upper mantle structure beneath the indian subcontinent this study has been supported by a grant from the ministry of earth sciences moes iitkgp ckh

seismotectonics and crustal stress field in the kumaon garhwal himalaya abstract we present fault plane solutions of 94 well located small to moderate sized 1 5 ml 5 4 earthquakes which occurred in the kumaon garhwal himalaya during 2005 2008 using p wave polarity and body wave amplitudes these earthquakes show a mixture of thrust normal and strike slip type mechanism with a majority of thrust type most of the thrust earthquakes occur at a depth of 8 22 km in the main central thrust mct zone and the lower himalaya the spatial distribution of these earthquakes suggest that the strain resulting from the ongoing collision of the indian plate with the eurasian plate is being consumed by thrust fault movement mainly on the north dipping munsiari thrust and south dipping tons thrust the strike slip earthquakes are mainly observed in the lower himalaya as well as around the munsiari region in the mct zone the normal earthquakes are also observed in different parts of the kumaon garhwal himalaya and the gangetic plain their occurrence is attributed to the local structure s as well as the flexure of the indian plate stress tensor inversion of the calculated fault plane solutions indicates that the maximum compressive stress in the gangetic plain is n s directed and near vertical whereas in the kumaon garhwal himalaya it is near horizontal and nne ssw directed and correlating with the prevailing stress condition due to northward movement of indian plate

crustal rheology of the himalaya and southern tibet inferred from magnetotelluric data the collision between the indian and asian continents which began about 70 million years ago involved a convergence of at least 1 400 km and raised the tibetan plateau since crustal material is too buoyant to be transported downwards into the earth s interior the mechanisms at work in plateau formation are important in understanding the evolution of the continents yet still a matter of debate geophysical observations in the himalaya and tibet using ultra low frequency radio waves now reveal that a partially molten layer is present along the entire length of the himalaya this weak layer implies that widespread crustal flow is occurring and explains many features of plateau evolution the cenozoic collision between the indian and asian continents formed the tibetan plateau beginning about 70 million years ago since this time at least 1 400 km of convergence has been accommodated1 by a combination of underthrusting of indian2 and asian lithosphere crustal shortening3 horizontal extrusion4 and lithospheric delamination5 rocks exposed in the himalaya show evidence of crustal melting1 6 and are thought to have been exhumed by rapid erosion and climatically forced crustal flow7 8 magnetotelluric data can be used to image subsurface electrical resistivity a parameter sensitive to the presence of interconnected fluids in the host rock matrix even at low volume fractions here we present magnetotelluric data from the tibetan himalayan orogen from 77 e to 92 e which show that low resistivity interpreted as a partially molten layer is present along at least 1 000 km of the southern margin of the tibetan plateau the inferred low viscosity of this layer is consistent with the development of climatically forced crustal flow in southern tibet

catastrophic mass movement of 1998 monsoons at malpa in kali valley kumaun himalaya india abstract a devastating landslide on 18 august 1998 near malpa village in kali valley of higher kumaun himalaya killed 221 persons the landslide was a complex rock fall debris flow the mass movement generated around one million cubic metres of debris and partially blocked the kali river malpa gad a tributary of kali being blocked completely the rock mass failed primarily due to the near vertical slopes hanging over the valley along joints the formation of structural wedges along the free face the sheared rock mass due to the close proximity of major tectonic planes and the enhanced pore water pressure due to prolonged heavy precipitation in the preceding days the mesoscopic shear zone exhibiting ramp and flat structure in quartzites shows a southward thrust movement that might have generated shear stress in the rocks the slide clearly demonstrates the distressed state of the rock mass in the himalayan region due to the ongoing northward drift of the indian plate

crust and mantle structure across the basin and range colorado plateau boundary at 37 n latitude and implications for cenozoic extensional mechanism we present new evidence on the seismic velocity and density of the crust and upper mantle along a 200 km long transect across the eastern basin and range and western colorado plateau at 37 n latitude receiver functions computed from the p waveforms recorded with 10 portable broadband stations deployed along the transect were used to estimate crustal thickness variations the crust is 30 35 km thick within the eastern basin and range and increases over a distance of 100 km at the western edge of the colorado plateau reaching a maximum of approximately 45 km east of the hurricane fault the timing of crustal multiples within the reciever functions were used to estimate the v p v s of the crust along the profile and we found that the western colorado plateau crust is characterized by a high poisson s ratio 0 28 0 29 indicative of a crust with an average mafic composition we estimated the upper mantle lid thickness along our profile based on teleseismic p wave travel times and constraints provided by gravity data our data and available geophysical constraints are most consistent with a lithosphere that thickens from an average thickness of 60 km beneath the basin and range to 100 km beneath the western colorado plateau although the basin and range lithosphere may have significant thickness variations the thick strong mafic crust and thicker mantle lid under the colorado plateau can account for the relative geologic stability and subdued magmatism of the plateau during laramide compression and cenozoic extension compared to surrounding regions the crustal and lithospheric thinning across the tectonic boundary occurs over a short distance 100 km suggesting it is a geologically young feature produced by a predominantly mechanical response to late cenozoic extension our new lithosphere model at 37 n latitude is consistent with the existence in early cenozoic time of a flat subducted slab at 100 km depth and a relict sevier laramide 50 60 km thick crustal welt and 60 100 pure shear extension values of 1 6 2 0 during the late cenozoic

aftershocks of the march 1999 chamoli earthquake and seismotectonic structure of the garhwal himalaya the aftershocks of the chamoli earthquake m b 6 3 of 28 march 1999 are analyzed to understand the seismotectonic structure of the garhwal himalaya the permanent as well as temporary microearthquake network data are used the mainshock occurred on the basement thrust by thrust faulting the aftershocks on the other hand are triggered at the seismogenic faults to the south of the main central thrust mct by thrust faulting as well as by strike slip faulting and all the events occurred above the plane of detachment basement thrust the mct is not the seismogenic fault

electrical structure of the himalaya of central nepal high conductivity around the mid crustal ramp along the mht twelve broadband magnetotelluric mt soundings were performed across the himalaya of central nepal in 1996 in order to determine the electrical structure of the crust and its relation to geological structures and active tectonics the mt impedance tensors were obtained for frequencies between 0 001 and 500 hz the 2 d section derived from joint inversion of te and tm mode after rri and groom bailey decomposition shows high conductivity in the foreland basin 30 m that contrasts with the resistive indian basement 300 m and lesser himalaya 1000 m in addition our mt sounding reveals a major conductive feature beneath the front of the higher himalaya also characterized by intense microseismic activity and the position of a mid crustal ramp along the major active thrust fault mht this high conductivity zone probably reflects metamorphic fluids released during underthrusting of the indian basement and pervading well connected microcracks induced by interseismic stress build up or distributed brittle deformation around the ramp

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

thrust geometries and deep structure of the outer and lesser himalaya kumaon and garhwal india implications for evolution of the himalayan fold and thrust belt the kumaon garhwal region of the himalaya lies near the center of the himalayan fold and thrust belt we have drawn two balanced cross sections 100 km apart through the outer and lesser himalaya the cross sections incorporate all the surface well log and earthquake seismic data currently available from the region two branch line maps showing trailing and leading branch lines and cutoff lines of the major thrusts in the region are also drawn the three dimensional deep structure of the outer and lesser himalaya is interpreted based on the balanced cross sections and the branch line maps deep structure of the higher and tethyan himalaya is extrapolated based on surface geology and is subject to revision as more surface and seismic data become available from these areas a sequential evolutionary model for the kumaon himalaya along the eastern pindari section is proposed according to this model the kumaon himalaya evolved by an overall forelandward progression of thrusting with some reactivation along the munsiari thrust mt the main boundary thrust mbt and the main central thrust mct we use structural stratigraphic and radiometric criteria to place time constraints on the motion of these thrusts earliest motion along the mbt may have occurred in early middle paleocene but the main episode probably started in late eocene and may still be continuing emplacement of the mt had occurred by middle late eocene whereas the mct shows activity around 20 ma thus exhibiting break back thrusting with respect to the mt shortening estimates are obtained from the pindari section minimum shortening in the sedimentary thrust sheets of the outer and lesser himalaya is 161 km or 65 as a first approximation we have also restored the crystalline sheets in order to obtain shortening estimates for the entire himalaya minimum shortening for the himalaya after restoring the mct sheet varies from 354 76 to 421 km 79 these estimates were further combined with published data from the area between the mct sheet and the indus tsangpo suture zone itsz minimum shortening between the indo ganga foreland and the itsz thus obtained lies in the range 687 754 km or 69 72 we compare our shortening estimates with those available from the pakistan and nepal himalaya

role of fluids in faulting inferred from stress field signatures the stress orientation signature of weak faults containing high pressure fluids has been observed for segments of the san andreas fault system in southern california the inferred lithostatic fluid pressures extend into the surrounding relatively intact rock in a zone scaling with the width of the interseismic strain accumulation repeated strain related fracturing and crack sealing may have created low permeability barriers that seal fluids into the network of currently active fractures

sediment thickness beneath the indo gangetic plain and siwalik himalaya inferred from receiver function modelling abstract the indo gangetic plain and the adjoining siwalik himalaya are the seismically most vulnerable regions due to high density of human population and presence of thick sediments that amplify the seismic waves due to an earthquake in the region we investigate the sedimentary structure and crustal thickness of the region through joint inversion of the receiver function time series at 14 broadband seismograph locations and the available rayleigh velocity data for the region results show significant variability of sedimentary layer thicknesses from 1 0 to 2 0 km beneath the delhi region to 2 0 5 0 km beneath the indo gangetic plain and the siwalik himalaya as we progress from the delhi to the indo gangetic plain we observe a decrease in the shear velocity in sedimentary layer from 2 0 km s to 1 3 km s while the layer thickness increases progressively from 1 0 km in south to 2 0 5 0 km in the north average s velocity in the sedimentary layer beneath the siwalik himalaya is 2 1 km s crustal thicknesses varies from 42 in the delhi region 48 km in the indo gangetic plain 50 km in the western part of siwalik himalaya to 60 km in the kumaon region of siwalik himalaya

structural control on along strike variation in the seismicity of the northwest himalaya an overview of seismicity along the northwest himalaya exhibit along strike segmentation intricately controlled by the subsurface topographic ridges on the underthrusting indian plate as well by rift and nappe structures in the overriding wedge of the himalaya the segmentation exists for thrust dominated large magnitude earthquakes m 6 seated on the active detachment beneath the outer and lesser himalaya segmentation also prevails for moderate and small magnitude earthquakes concentrated in a narrow himalaya seismic belt hsb straddling northern lesser himalaya and southern higher himalaya numerical calculations of stress distribution favour that the degree of seismicity in the hsb is a good proxy to the presence of mid crustal ramp connecting the locked section of active detachment to aseismically slipping detachment beneath higher himalaya further gap or diffused pattern in the concentrated seismicity in the hsb in agreement with mapped high electrical conductive structure suggests ramp structure may be absent where underthrusting delhi hardwar ridge interacts with the himalaya arc in the nappe dominated tectonics the accommodation of the accumulating strains on the listric thrust faults produces increased frequency of moderate magnitude earthquakes and thereby possibly influences stress level on the detachment this may explain relatively less frequent occurrences of large earthquake in the kangra chamba region compared to that in the garhwal himalaya the low level seismicity in the simla region may also be influenced by the active kaurik chango rift in the higher himalaya as the former casts a stress shadow on the latter

electrical resistivity cross section across the garhwal himalaya proxy to fluid seismicity linkage abstract magnetotelluric mt measurements along a profile cutting across the garhwal himalaya of india are inverted to obtain 2 d electrical resistivity structures of the himalayan wedge and of the underthrusting indian plate the imaged resistivity cross section is dominated by a low angle north east dipping intra crustal high conducting layer ic hcl with an average thickness of 5 km at transition from the lesser himalaya to the higher himalaya the ic hcl is marked by a ramp structure across which its top jumps from a depth of 8 km to 13 km high conductivity of the layer is caused by pounding of upward propagating metamorphic fluids trapped by tectonically induced neutral buoyancy in compression regime of the himalaya the mechanical weakening effects of the fluids counteract the fault normal stresses thereby facilitating thrust type earthquakes on a plane imaged as the top of the ic hcl it is suggested that in the himalaya collision belt like the active subduction zone the active seismic plane forming seat of large and great earthquakes is located a few kilometers above the top of the down going plate in this tectonic setting the high conductance ramp symbolizes a block of low shear strength and high strain which under the deviatoric stresses release accentuated stresses into the brittle crust thereby generating small but more frequent earthquakes in the narrow himalayan seismic belt in response to either the co seismic pumping or the stress transfer during inter seismic period the upward infiltration of fluid fluxes into the over pressurized zones sufficiently reduces the shear strength of local thrusts and shear zones turning these into locales of concentrated seismicity

average crustal thickness and poisson s ratio beneath the kali river valley kumaon himalaya abstract crustal thickness and poisson s ratios were estimated at 13 broadband seismological stations established in a profile along the kali river valley kumaon central himalaya the seismological profile extends from the indo gangetic plain igp in the south to the higher himalaya in the north passing through the sub and lesser himalaya the receiver function rf method has been adopted to investigate the crustal structure beneath the profile time domain iterative deconvolution method has been adopted for rf computation the h k stacking method has been adopted to analyze the rfs for obtaining average crustal thickness and poisson s ratio of the crust beneath each station the study reveals that the crustal thickness beneath the igp is 38 km which gradually increases up to 41 km at the northernmost station located in the higher himalaya the values of vary from 0 23 to 0 28 the value of is low in the sub himalaya and outer lesser himalaya suggesting more of a felsic composition of crust a significantly high value of 0 28 is observed in the dharchula region of the chiplakot crystalline belt which is coincident with a large number of micro to moderate magnitude earthquakes forming a cluster at shallow to mid crustal depths the high poisson s ratio is possibly due to the presence of fluids partial melts at mid crustal depth the presence of fluids influences the rheological property and controls the mechanical and shear strength of crustal rocks producing a cluster of seismicity observed beneath the dharchula region

carbonate geochemistry of vadose water recharging limestone aquifers abstract thrailkill j and robl t l 1981 carbonate geochemistry of vadose water recharging limestone aquifers in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 195ndash 208 vadose water from lower carboniferous rocks in kentucky u s a was analyzed monthly in mammoth cave and in the caves and overlying soil at two other caves calcite saturation and equilibrium co 2 pressures of water were calculated after correcting for ion pairing and activity coefficients soil gas co 2 concentrations were determined directly both small flows of water which were usually depositing speleothems vadose seepages and larger flows vadose flows were studied some of the vadose seeps were often undersaturated with respect to calcite and showed little variation in ca content cv ca 7 while others were supersaturated and showed positive correlations between ca and soil co 2 or between ca and discharge at least some of the vadose seepages were believed to have been closed to co 2 introduction after leaving the soil zone in the soil co 2 varied with soil type moisture and season ca increased with depth but saturation with respect to calcite was not reached three types of vadose water may thus reach the aquifer undersaturated with respect to calcite 1 vadose flows which transit the vadose zone rapidly 2 low ca vadose seepage which is closed to co 2 as it transits the vadose zone and which may remain undersaturated with respect to calcite even after ventilation and 3 high ca vadose seepage which leaves the soil zone slightly undersaturated probably because of insufficient residence time

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

crust and mantle beneath western himalaya ladakh and western tibet from integrated seismic data abstract to understand deep structure of the western himalaya ladakh and western tibet we conduct an integrated analysis of teleseismic body wave recordings from the linear array of 16 portable broadband seismographs along a profile running through the himalaya to the karakoram the database includes p and s receiver functions teleseismic p and s residuals and observations of shear wave splitting in sks the analysis reveals beneath the himalaya a cold region at a depth of several hundred kilometers this anomaly can be caused by remnants of tethys subduction and perhaps is unrelated to the ongoing process the present day process is reflected in velocities beneath the lesser himalaya intermediate between those of the crust and the upper mantle this observation can be explained by scraping off the ductile lower crust of the underthrusting indian plate and accumulation of the high velocity crustal material in the frontal region of the thrust zone a representative value of the crustal thickness at the profile is 65 km and at most stations there is no evidence for a low velocity layer at mid crustal depths which makes crustal channel flow unlikely seismic waves in the upper 200 km of the mantle are faster than in global iasp91 model and the structure includes a low velocity layer sandwiched between two high velocity layers we interpret the lower layer as an image of subducted mantle lithosphere of the indian plate shear wave splitting is different in the south and the north in the south the fast direction of anisotropy is normal to the trend of the himalaya and can be interpreted as an effect of the ne motion of the indian lithosphere in the north the fast direction is oriented e w and can be explained by the fabric left in the presently extinct subduction zones in eastern tibet a similar analysis of the p and s receiver functions reveals upper mantle with the s velocities about 5 lower than in the west the mantle in the vicinity of station lsa lhasa contains a low s velocity layer between 160 km and 230 km depths with a velocity reduction of 0 2 km s underlain by the lehmann discontinuity

imaging laterally varying regional heterogeneities from seismic coda using a source array analysis abstract seismic coda is composed of scattered waves originated from various kinds of heterogeneities whose locations are not confined in the great circle ray path direction between the source and receiver we devise a technique to image laterally varying regional heterogeneities using single station seismograms for clustered events we analyze regional seismic records of the borovoye seismic station for the balapan nuclear explosions in kazakhstan scattered waves that arrive coherently over the source arrays are extracted by directional beamformings the locations of scatterers responsible for the scattered waves are mapped from the beamforming direction travel time and slowness equivalently phase velocity the illuminated locations of heterogeneities are highly correlated with the structural variations in surface topography crustal thickness and sedimentary thickness the influence of the structural variations on seismic waves is quantified in terms of scattering intensity and quality factor the scattering properties are observed to vary with phase due to the difference in frequency content and phase velocity the proposed technique appears to be useful for a study of active tectonic regions with limited monitoring stations

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities