a potential source of atmospheric sulfur from penguin colony emissions 1 samples of fresh penguin excrements and lake sediments composed of aged penguin excrements were collected on an antarctic peninsula island gases emitted from these samples were collected and analyzed for volatile organosulfur compounds no dimethyl sulfide dms was found however dimethyl trisulfide dmts dimethyl tetrasulfide dmtts and dimethyl pentasulfide dmps were found among the numerous organic compounds emitted from fresh penguin droppings these sulfur compounds account for as mush as 13 5 of the emitted gases but they have not been reported previously in atmospheric gases and therefore may represent a hitherto undetected source of atmospheric sulfur to evaluate the potential contribution of this non dms biogenic source to the atmospheric sulfur reservoir at high southern latitudes measurements of various chemical species in aerosols at several coastal antarctic locations were analyzed and compared the locations include zhongshan station china and dumont d urville france in east antarctica tentative calculations based on assumptions of similar aerosol sources and composition at these locations show that in areas downwind from large penguin colonies up to 5 5 10 5 nmol m 3 sulfur may be attributed to penguin emissions on a per penguin basis depending on the size of penguin population at a given location sulfur from this non dms source may account for 5 15 of the total non sea salt nss sulfur in these areas such high contributions may significantly impact the atmospheric sulfur burden and alter the sulfur budget in the high southern latitudes

structural attributes and paleostress analysis of quaternary landforms along the vigodi fault vf in western kachchh region abstract in this paper we elucidated deformational and kinematic characteristics of the nw se trending vigodi fault vf and its associated subsidiary faults in the western kachchh basin we applied paleostress inversion technique to understand the past stress regime from the acquired fault slip data the subsidiary faults strike nw se and ne sw and slickensided surfaces are well developed on the fault planes we present slip analysis and changes in the stress reorientation using the plane solutions to identify the principal stress axis 1 position regionally to obtain pressure tension and null axis pbt stress ratio and principal 1 axis we used the right dihedron method using the win tensor and t tecto software s respectively geomorphologically the vf zone comprises of bedrock strath terraces towards the upthrown block and fill terraces on the downthrown block of the fault development of fault scarps warped quaternary sediments slit canyons within quaternary sediments river nick points and deflected rivers are the major striking features observed along the strike length of the vigodi fault the analyses indicate that ne sw compressional stress dominates the regional area and the local area is affected by transpressional stress exhibiting oblique slip motion the combined observations made from the present investigation can be used to estimate seismic hazard and mitigation planning of the study area

crust beneath the northwestern deccan volcanic province india evidence for uplift and magmatic underplating the northwestern deccan volcanic province of india and its pericratonic rift basins were reactivated during different stages after the breakup of india from the gondwanaland and collision with the asian plate in this study we present results of crustal thickness and average crustal vp vs ratios beneath this plume affected region using common conversion point imaging and h k stacking analysis of 6893 receiver functions using data from a network comprising 58 broadband seismic stations sited on diverse tectonic terrains we find large variations in crustal thickness with the moho depths varying from 28 to 43 km in the kachchh rift 28 to 38 km in the cambay rift 39 5 41 5 km in the north and eastern parts of the cambay rift and 29 to 39 km in the saurashtra region and south gujarat a moho upwarp of 6 to 7 km in the saurashtra region can be attributed to positive buoyancy and uplift due to thermal influx affected by the reunion plume high crustal vp vs ratios beneath the kachchh rift 1 8 to 2 05 coastal areas of saurashtra 1 75 to 2 06 and north gujarat 1 81 to 1 85 indicate dominance of a mafic ultramafic crust high regional heat flow high electrical conductivity large intracrustal s wave velocity reduction and high average crustal poisson s ratios are consistent with partial melt related to the process of magmatic underplating in the lower crust at other stations the crust appears to be felsic with vp vs ratios in the range of 1 57 to 1 76

an insight into crack density saturation rate and porosity model of the 2001 bhuj earthquake in the stable continental region of western india abstract the 2001 bhuj earthquake mw 7 6 source zone is examined in the light of crack density e saturation rate and porosity parameter using new data set derived from a large aftershock sequence recorded by the gujarat seismic network gsnet during november 2006 december 2009 processes of rupture initiations of the mainshock and its aftershock sequence are better understood by synthesizing the dynamic snapshots of the source zone using the new dataset pattern of crustal heterogeneities associated with high e high and high anomalies at depths varying from 20 km to 25 km is similar to those of earlier study by mishra and zhao 2003 the anomalous zone is found extended distinctly by 50 60 km in the lateral direction indicating the reinforcement of cracks and fractured volume of rock matrix due to long aftershock sequence since 2001 bhuj earthquake in the source area it is inferred that the presence of a fluid filled fractured rock matrix with super saturation may have affected the structural and seismogenic strengths of the source zone and is still contributing significantly to the geneses of earthquakes in and around the source zone anomalous pattern of high e with wider distribution of high indicates the existence of micro cracks in the lower crust while high suggests the cementation of cracks through permeation of residual magma metamorphic fluids into the hypocenter zone the results suggest that the existence of residual fluids in the fractured rock matrix in the mid to lower crust might have played a key role in triggering the 2001 mainshock and is still responsible for its continued long aftershock sequences

evidence for high velocity in koyna seismic zone from p wave teleseismic imaging three dimensional p wave velocity structure of the crust and upper most mantle beneath the koyna seismic zone ksz was determined by inverting 780 p wave teleseismic travel times recorded by a 20 station digital network the velocity image obtained through damped least square was tested for its resolution using checkerboard approach the results of the inversion show strong lateral velocity variations of 6 to 7 within the study region a high velocity anomaly 2 to 5 in the upper and lower crust beneath the ksz is flanked by lower velocity 2 to 5 anomalies on either side the correlation of high velocity with the seismic zone suggests that the earthquakes are occurring in more rigid rocks with increasing ability to store strain energy and release it as brittle failure

the 1994 northridge earthquake 3 d crustal structure in the rupture zone and its relation to the aftershock locations and mechanisms a detailed 3 d p wave velocity structure of the crust in the epicentral area of the 17 january 1994 northridge earthquake is determined by using 104 709 arrival times from 1673 northridge aftershocks and 2948 other local earthquakes a test performed using the data from the nearby portable stations suggests that the aftershock hypocenters relocated with the obtained 3 d model are accurate to about 2 km we found that regions with high aftershock activity are generally associated with faster p wave velocities the velocity is high around the main south dipping fault of the 1994 northridge earthquake and the north dipping fault of the 1971 san fernando earthquake a linear distribution of strike slip aftershocks was found along a ne sw boundary between high velocity and low velocity structures to the west of this boundary a cluster of large shallow aftershocks with mixed mechanisms occurred in or near the border of a low velocity area while to the east aftershocks with thrust mechanisms occurred in a high velocity area these observations suggest that lateral variations of crustal properties are closely related to the fault segmentation in the transverse ranges a better understanding of these features is important for long term seismic hazard assessment in the los angeles area

a low seismic wavespeed anomaly beneath northwestern india a seismic signature of the deccan plume abstract seismic tomography of the indian region using p wave arrival times reveals an approximately cylindrical region of lowered seismic velocities in the upper mantle to the north of the gulf of cambay and the present exposure of the deccan flood basalts this anomaly with low velocities interrupts the characteristically high seismic velocities in the lithosphere beneath peninsular india and extends from shallow depth down to a more extensive low velocity zone beneath 200 km the centre of the low velocity anomaly lies just below the earliest alkaline magmatism which has been directly associated with the deccan plume in the northern portion of the cambay graben these magmatic events precede the main deccan flood eruptions by at least 3 myr the lowered seismic wavespeeds link into the ancient narmada lineament and to some extent to the south but here unfortunately the tomographic image runs out of resolution synthetic tests indicate that such a zone of lowered wavespeeds can be recovered with some loss of amplitude towards the south the association of the current seismic anomaly with the deccan traps is intriguing since the cambay graben remains a place of raised heat flow one explanation would be that the seismic anomaly represents the signature of the initial conduit through which plume material forced its way through the lithosphere beneath the cambay rift the zone of lowered seismic velocities beneath the indian lithosphere might then represent the remains of the initial plume head which would need to have moved with india over the 65 myr since the deccan eruptions

booming plutons source of microearthquakes in south carolina 1 loud shallow microearthquakes m 3 0 occurring in the vicinity of granitic plutons represent a different category of seismicity compared to other recognized seismic sources in south carolina we demonstrate this difference by comparing the locations of microearthquakes in the vicinity of three granitic plutons in south carolina with the results of two dimensional numerical modeling and analytical studies the less rigid plutons embedded in more rigid country rock were loaded by applying ambient tectonic plate stresses along the direction of maximum horizontal compression the results of modeling showed that regions of computed high stresses lie on the periphery of the plutons and coincide with both the observed locations of seismicity and with lobes of elevated stresses obtained by analytical calculations for a weak pluton subjected to a homogenous stress field the amplitude of the modeled stresses appears to be a function of the shape and size of the pluton

source parameters and tectonic implications of aftershocks of the mw 7 6 bhuj earthquake of 26 january 2001 we present and discuss the spatial distribution of more than 1000 aftershocks of the largest continental intraplate earthquake to occur during the modern seismological period the data were recorded on a network of eight portable digital seismographs deployed for 3 weeks starting 17 days after the mainshock we have calculated high quality single event locations based on a 1d velocity model determined for the region for earthquakes with magnitudes between 2 and 5 aftershock locations reveal activity concentrated on a nearly east striking south dipping plane trapezoidal in outline the active zone tapers from about 45 km along strike at the shallow end which is about 5 km deep to no more than 25 km long at a depth of 35 km the total rupture area was about 1300 km 2 we estimate the static stress drop of the mainshock at 16 2 mpa aftershocks extend nearly through the entire crust with concentrations in the lower crust at about 26 km and in the upper crust at about 10 km the fault that ruptured was not mapped at the surface and not known to have been active prior to the 2001 earthquake the aftershock data are consistent with the bhuj earthquake resulting from reactivation in contraction of a fault formed under extension within a failed rift

seismic imaging of the aftershock zone of the 2001 mw 7 7 bhuj earthquake india 1 detailed seismic tomography reveals that the 2001 mw 7 7 bhuj earthquake was associated with a 10 14 increase in vp and vs and a 10 decrease in vp vs in the 10 to 35 km depth range covering a 2750 km2 area beneath the aftershock zone this anomaly could be attributed to the existence of a lithological heterogeneity or a pluton of mafic composition that might have intruded during the rifting in early jurassic 160 ma the banni basin and the wagad uplift are found to be associated with high velocity intrusive bodies extending from 5 to 35 km depth a few patches of low vp and vs and high vp vs between 10 to 30 km depth have also been detected on the causative 45 south dipping north wagad fault nwf for the 2001 mainshock which may be attributed to a fluid filled fractured rock matrix

spatiotemporal variation of fractal properties in the source zone of the 2001 mw 7 7 bhuj earthquake the kachchh seismic zone ksz in gujarat india has been experiencing earthquakes since the occurrence of the 2001 m w 7 7 bhuj mainshock which led to a homogeneous catalog of 2808 earthquakes of m w 3 0 between 2001 and 2011 this enabled us to investigate the spatiotemporal variation of fractal dimensions d b values and seismic velocities in the ksz through 3d mapping of these three independent parameters the estimated fractal dimensions for the gedi fault gf events range from 0 7 to 1 0 whereas those of north wagad fault nwf events vary from 1 2 to 2 4 the b values for gf events also show smaller values in comparison to the nwf events the d values associated with events occurring in the main rupture zone mrz of the 2001 mainshock vary from 1 6 to 2 1 whereas those associated with events occurring in the surrounding unrifted zones show a wider range of variation from 1 2 to 2 4 we also observe that events associated with the nwf satisfy the aki s relationship d 2 b aki 1981 whereas events associated with gf do not follow this relationship both b and d values tend to increase with an increase in the earthquake density which could be connected with the process of disintegration of crustal rocks in the mrz where large material heterogeneities in terms of low and high seismic velocity patches are being mapped through local earthquake velocity tomography through examining the temporal changes in b and d values we notice several episodes of abnormally low b and d values associated with the occurrences of bursts of seismic activity in 2001 2005 2006 2008 and 2010 this decrease in b and d values is attributed to a reduction in rock friction in the causative fault zone at 10 35 km depths probably due to the presence of metamorphic fluids or volatile co2 thereby enhancing the probability of occurrence of stronger earthquakes

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

iterative de convolution of the local waveforms characterization of the seismic sources in kachchh india abstract the deviatoric and double couple dc constrained moment tensor inversions of multiple point sources 10 20 s for regional or local earthquakes developed by zahradnik et al 2005 has been applied on the data of nine significant bhuj aftershocks of mw4 4 mw5 6 recorded at three component 5 15 accelerograph and 5 11 seismograph stations epicentral distances

tectonics and crustal structures related to bhuj earthquake of january 26 2001 based on gravity and magnetic surveys constrained from seismic and seismological studies abstract gravity and magnetic data of the kachchh basin and surrounding regions have delineated major e w and nw se oriented lineaments and faults which are even extending up to plate boundaries in the north arabian sea and western boundary of the indian plate respectively the epicentral zone of bhuj earthquake and its aftershocks is located over the junction of rann of kachchh and median uplifts viz kachchh mainland and wagad uplifts which are separated by thrust faults gravity data with constraints from the results of the seismic studies along a profile suggest that the basement is uplifted towards the north along thrust faults dipping 40 60 south similarly gravity and magnetic modeling along a profile across wagad uplift suggest south dipping 50 60 basement contacts separating rocks of high susceptibility and density towards the north one of these contacts coincides with the fault plane of the bhuj earthquake as inferred from seismological studies and its projection on the surface coincides with the e w oriented north wagad thrust fault a circular gravity high in contact with the fault in northern part of the wagad uplift along with high amplitude magnetic anomaly suggests plug type mafic intrusive in this region several such gravity anomalies are observed over the island belt in the rann of kachchh indicating their association with mafic intrusions the contact of these intrusives with the country rock demarcates shallow crustal inhomogeneities which provides excellent sites for the accumulation of regional stress a regional gravity anomaly map based on the concept of isostasy presents two centers of gravity lows of 11 to 13 mgal 10 5 m s2 representing mass deficiency in the epicentral region their best fit model constrained from the receiver function analysis and seismic refraction studies suggest crustal root of 7 8 km deep crustal inhomogeneity under them for a standard density contrast of 400 kg m3 it is therefore suggested that significant amount of stress get concentrated in this region due to a buoyant crustal root b regional stress due to plate tectonic forces and c mafic intrusives as stress concentrators and the same might be responsible for the frequent and large magnitude earthquakes in this region including the bhuj earthquake of january 26 2001

variations of seismic velocities in the kachchh rift zone gujarat india during 2001 2013 abstract we herein study variations of seismic velocities in the main rupture zone mrz of the mw 7 7 2001 bhuj earthquake for the time periods 2001 05 2006 08 2009 10 and 2011 13 by constructing dvp dvs and d vp vs tomograms using high quality arrival times of 28 902 p and 28 696 s waves from 4644 precise jhd joint hypocentral determination relocations of local events differential tomograms for 2001 05 reveal a marked decrease in seismic velocities low dvp low dvs and high d vp vs in the mrz at 5 35 km depths during 2001 10 which is attributed to an increase in crack fracture density higher pore fluid pressure resulted from the intense fracturing that occurred during the mainshock and post seismic periods while we observe a slight recovery or increase in seismic velocities 2011 13 this could be related to the healing process lower pore fluid pressure due to sealing of cracks of the causative fault zone of the 2001 bhuj mainshock the temporal reduction in seismic velocities is observed to be higher at deeper levels more fluid enrichment under near lithostatic pressure than that at shallower levels fluid source for low velocity zone lvz at 0 10 km depths with high d vp vs could be attributed to the presence of meteoric water or soft alluvium sediments with higher water content while fluid source for lvz at 10 35 km depths could be due to the presence of brine fluids released from the metamorphic dewatering and volatile co2 emanating from the crystallization of carbonatite melts in the asthenosphere in fractures and pores we also imaged two prominent lvzs associated with the katrol hill fault zone and island belt fault zone extending from shallow upper crust to sub crustal depth which might be facilitating the deeper circulation of metamorphic fluids volatile co2 thereby the generation of lower crustal earthquakes occurring in the kachchh rift zone

changes in lead concentration in antarctic penguin droppings during the past 3 000 years anthropogenic lead pb has been found in antarctic seawater surface snow and ice cores here we analyzed a 3 000 year record of lead concentration in lake sediments affected by penguin droppings we found that lead concentration in penguin droppings has significantly increased during the last 200 years especially in the last 50 years as compared to low and stable lead levels prior to the industrial revolution this clearly indicates that global environmental pollution has influenced the antarctic ecological system heavy metal pb may find its way into the food web bioaccumulate and be passed along the chain to penguins

seismic velocity and poisson s ratio tomography of the crust beneath east anatolia abstract eastern anatolia is a region in the early stages of continent continent collision and so provides a unique opportunity to study the early development of continental plateau located within the alpine himalayan fold thrust fault belt the anatolian plateau is geologically very complex with over half of the surface area covered with late cenozoic volcanics of diverse composition the plateau is also seismically active and is dissected by numerous seismogenic faults predominantly of strike slip motion in this study we determine 3 d tomographic images of the crust beneath eastern anatolia by inverting a large number of arrival time data of p and s waves from the obtained p and s wave velocity models we estimated the poisson s ratio structures for a more reliable interpretation of the obtained velocity anomalies our tomographic results are generally consistent with the major tectonic features of the region high p and s wave velocity anomalies are recognized near the surface while at deeper crustal layers low seismic wave velocities are widely distributed poisson s ratio exhibits significant structural heterogeneities compared to the imaged velocity structure the seismic activity is intense along highly heterogeneous zones and is closely associated with pre existing faults in the central and western parts of the study area results of the checkerboard resolution test indicate that the imaged anomalies are reliable features down to a depth of about 40 km the low velocity high poisson s ratio zones in the middle to lower crust are consistent with many geophysical observations such as strong sn attenuation low pn and sn velocity and the absence of mantle lid implying the presence of partial melt in the uppermost mantle

depositional systems and sequence stratigraphy of mesozoic lacustrine rift basins in ne china a case study of the wulan hua sag in the southern erlian basin abstract the deltaic and lacustrine sediments respectively in the syn and post rift stages are recorded during the cretaceous at the wulan hua sag erlian basin inner mongolia in this study the mesozoic depositional system and sequence stratigraphic framework are recognized in the wulan hua sag using core well log and seismic data five sedimentary facies have been identified including fan delta braided delta shallow lacustrine deep lacustrine and sublacustrine fan during cretaceous at the wulan hua sag one first order sequence msq1 three second order sequences ssq1 ssq2 and ssq3 and five third order sequences sq1 sq2 sq3 sq4 and sq5 are classified by subaerial unconformities along the basin margins and correlative conformities in the central part of the basin during the depositional period of sq1 sq2 and sq3 the depocenter controlled by lake level fluctuations migrated from southern to northern part companying with multiple to single provenance supplies the characteristics of sedimentary facies and sequence stratigraphy in the wulan hua sag are commonly controlled by faults provenance and depocenters the development of the third order sequences is dominated by tectonism and sediment supplies as well as lake level changes driven by climate the favorable targets for hydrocarbon located in the lowstand system tract of sq1 sq2 and sq3 at the southern parts of the wulan hua sag

preliminary geochemical evidence of groundwater contamination in coral islands of xi sha south china sea geochemical data on dissolved major minor and trace constituents in groundwater samples from xi sha coral islands paratas islands reveal the main processes responsible for their geochemical evolution multivariate statistical analysis indicates four sources of solutes 1 seawater intrusion due to limited groundwater recharge 2 leaching of heavy metals from imported granite soil 3 leaching of toxic elements such as as due to guano soil erosion and historical phosphatic guano mining and 4 local and regional contamination characterized by high loadings of cu ag and hg although process 1 dominates the geochemical characteristics of the groundwater process 4 indicates the significant role of anthropogenic impact by local e g cu and regional e g hg sources such contamination in groundwater will potentially impose adverse effects on the fragile ecosystem of the coral islands it is necessary to monitor microorganisms associated with human feces in the nearshore water column as well as nutrient levels in coastal waters in order to further assess the impact of human activities on the ecosystem of these islands

an appraisal of the 2001 bhuj earthquake mw 7 7 india source zone fractal dimension and b value mapping of the aftershock sequence we examined seismic characteristics b value and fractal dimension of the aftershock sequence of the january 26 2001 bhuj earthquake mw 7 7 that occurred in the kutch failed rift basin western margin of the stable continental region scr of india a total of about 2 000 events m 2 0 were recorded within two and a half months immediately after the main shock some 795 events were precisely relocated by simultaneous inversion these relocated events are used for mapping the frequency magnitude relation b value and fractal correlation dimension dc to understand the seismic characteristics of the aftershocks and the source zone of the main shock the surface maps of the b value and dc reveal two distinct tectonic arms or zones of the v shaped aftershock area western zone and eastern zone the b value is relatively higher 1 6 in the western zone compared to a lower value 1 4 in the eastern zone the dc map also shows a higher value 1 2 1 35 in the western zone compared to a lower dc 0 80 1 15 in the eastern zone this implies a positive correlation between dc and b value two cross sections e w and n s are examined the e w sections show similar characteristics higher b value and higher dc in the western zone and lower in the eastern zone with depth the n s sections across the fault zones however show unique features it imaged both the b and dc characteristics convincingly to identify two known faults the kutch mainland fault and the south wagad fault swf one stepping over the other with a seismogenic source zone at depth 20 35 km the source zone at depth is imaged with a relatively lower b and higher dc at the fault end of the swf showing a negative correlation these observations corroborated with the seismic tomography as well as with the proposed geological tectonic model shed a new light to our understanding on seismogenesis of the largest scr earthquake in india in the recent years

mantle derived spinel lherzolite xenoliths from the deccan volcanic province india implications for the thermal structure of the lithosphere underlying the deccan traps abstract petrography mineral and host rock chemistry of the mantle derived spinel lherzolite xenoliths in the nephelinites of kutch a late variant of the deccan traps province india are reported the xenoliths register equilibration temperatures between 920 70 c and 1060 50 c and an ascent time between 19 and 168 days representing a palaeogeotherm of minimum heat flow between 60 and 70 mw m 2 the xenoliths possibly came from the oceanic lithosphere under the deccan field following the cretaceous eocene fragmentation of gondwanaland

seismic imaging of the 2001 bhuj mw7 7 earthquake source zone b value fractal dimension and seismic velocity tomography studies abstract we use precisely located aftershocks of the 2001 mw7 7 bhuj earthquake 2001 2009 to explore the structure of the kachchh seismic zone by mapping the 3 d distributions of b value fractal dimension d and seismic velocities from frequency magnitude analysis we find that the catalog is complete above mw 3 0 thus we analyze 2159 aftershocks with mw 3 0 to estimate the 3 d distribution of b value and fractal dimensions using maximum likelihood and spatial correlation dimension approaches respectively our results show an area of high b d and vp vs ratio values at 15 35 km depth in the main rupture zone mrz while relatively low b and d values characterize the surrounding rigid regions and gedi fault gf zone we propose that higher material heterogeneities in the vicinity of the mrz and or circulation of deep aqueous fluid volatile co2 is the main cause of the increased b d and vp vs ratio values at 15 35 km depth seismic velocity images also show some low velocity zones continuing in to the deep lower crust supporting the existence of circulation of deep aqueous fluid volatile co2 in the region probably released from the eclogitasation of olivine rich lower crustal rocks the presence of number of high and low velocity patches further reveals the heterogeneous and fractured nature of the mrz interestingly we observe that aki 1981 s relation d 2b is not valid for the spatial b d correlation of the events in the gf d2 1 2b zone however the events in the mrz d2 1 7b show a fair agreement with the d 2b relationship while the earthquakes associated with the remaining parts of the aftershock zone d2 1 95b show a strong correlation with the aki 1981 s relationship thus we infer that the remaining parts of the aftershock zone are probably behaving like locked un ruptured zones where larger stresses accumulate we also propose that deep fluid involvement may play a key role in generating seismic activity in the mrz therefore a similar episode of deep fluid inflow could play a crucial role in causing the next strong earthquakes in the surrounding blocks of nwf

the 1995 kobe earthquake seismic image of the source zone and its implications for the rupture nucleation in order to understand what may have triggered the 1995 kobe japan earthquake and how the rupture proceeded after initiation we determined high resolution three dimensional 3 d p and s wave velocity and poisson s ratio structures in the kobe epicentral area and relocated the aftershocks with the obtained 3 d velocity model we used 64 337 p and 49 200 s wave high quality arrival times from 3634 kobe aftershocks and local microearthquakes recorded by both permanent seismic networks and portable stations that were set up following the kobe mainshock significant velocity variations of up to 6 are revealed in the aftershock area we found that areas with high aftershock activity are generally associated with low poisson s ratio which may be the strong and competent parts of the fault zone and were apt to generate aftershocks the kobe mainshock hypocenter is located in a distinctive zone characterized by low p and s wave velocities and a high poisson s ratio this anomaly exists in the depth range of 16 to 21 km and extends 15 to 20 km laterally this anomaly may be due to a fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake our interpretation has been supported by many pieces of evidence from hydrological geochemical seismological and geophysical investigations conducted at the kobe earthquake region

imaging of vp vs and poisson s ratio anomalies beneath kyushu southwest japan implications for volcanism and forearc mantle wedge serpentinization abstract we determine detailed 3 d vp and vs structures of the crust and uppermost mantle beneath the kyushu island southwest japan using a large number of arrival times from local earthquakes from the obtained vp and vs models we further calculate poisson s ratio images beneath the study area by using this large data set we successfully image the 3 d seismic velocity and poisson s ratio structures beneath kyushu down to a depth of 150 km with a more reliable spatial resolution than previous studies our results show very clear low vp and low vs anomalies in the crust and uppermost mantle beneath the northern volcanoes such as abu kujyu and unzen low velocity anomalies are seen in the mantle beneath most other volcanoes in contrast there are no significant low velocity anomalies in the crust or in the upper mantle between aso and kirishima the subducting philippine sea slab is imaged generally as a high velocity anomaly down to a depth of 150 km with some patches of normal to low seismic wave velocities the poisson s ratio is almost normal beneath most volcanoes the crustal seismicity is distributed in both the high and low velocity zones but most distinctly in the low poisson s ratio zone a high poisson s ratio region is found in the forearc crustal wedge above the slab in the junction area with shikoku and honshu this high poisson s ratio could be caused by fluid filled cracks induced by dehydration from the philippine sea slab the poisson s ratio is normal to low in the forearc mantle in middle south kyushu this is consistent with the absence of low frequency tremors and may indicate that dehydration from the subducting crust is not vigorous in this region

magnetotelluric studies in the epicenter zone of 2001 bhuj earthquake abstract some earthquakes to mw5 level are occurring along two faults viz kachchh mainland fault and south wagad fault near the epicenter of mw7 7 bhuj earthquake of 2001 these faults are not the causative fault of the 2001 earthquake and suspect for future large earthquake in absence of detail geophysical surveys the sub surface orientation of these faults was not known and mt profiles have proved useful in delineating the subsurface trends two mt profiles having lengths of 24 km and 15 km with an inter station spacing of 1 3 km are taken about 10 km east and west of the epicenter of mw7 7 2001 bhuj earthquake respectively the profiles are in nearly n s direction to detect the faults which trend e w in the area from 2 d inversion of mt data of 23 stations it is found that there are two distinctive conductive features matching with the south wagad fault and kachchh mainland fault south of it both being about 10 km apart the south wagad fault is seen extending to banni low lying area 30 km west of the present trace

sediments in palaeo notches potential proxy records for palaeoclimatic changes in antarctica abstract many climatic proxy materials such as ice cores coastal and lacustrine sediments and abandoned penguin rookeries have been used to study palaeoclimatic changes and the palaeoenvironmental evolution of antarctica in this paper we report another geological record well preserved sedimentary sequences in the palaeo notches in marine terraces of fildes peninsula king george island based upon grain size distribution and microtexture geochemical element compositions and radiocarbon dating we identified the sediments in one palaeo notch as lacustrine sediments most likely deposited in a small palaeo lake from these data we inferred that between 4000 and 3000 yr b p a moderate chemical weathering occurred and the climate was warmer and more humid than present in good agreement with the findings from other climatic proxy materials we believe that the sediments in palaeo notches provide another reliable proxy material for studying the palaeoclimate and the palaeoenvironment in antarctica

fluids below the hypocentral region of latur earthquake india geophysical indicators a set of geophysical measurements and observations was undertaken to investigate the nature of the crust beneath the epicentral region of the deadly mw 6 1 latur earthquake of september 30 1993 with an estimated focal depth of 2 6 km and the associated well defined but subtle surface ruptures it is a rare stable continental region scr earthquake with surface rupture the focal depth of 69 out of 73 well located aftershocks is less than 5 5 km broad band 10 10 3 hz magnetotelluric mt soundings reveal the presence of an anomalously high conductivity zone at a shallow depth range of 6 10 km consistent with this result is the observation of a pc phase lagging behind the pg phase by about 0 6 to 0 8 sec in the aftershock seismograms indicating a low velocity layer lvl at 7 to 10 km depth a bouguer gravity low of 5 m gal nearly coincident with this feature is also observed above evidences indicate that the focal zone of the latur earthquake sequence is limited to depths of about 5 to 6 km in the upper crust by an underlying low velocity and high conductivity layer we interpret this high conductive low velocity layer as a fluid filled fractured rock matrix the inferred stress regime including due to uplift of the deccan plateau triggered by erosion of basalt cover is likely to be confined mostly in the upper part of the crust existence of a low velocity high conductivity fluid filled layer will enhance stress concentration in the uppermost brittle part of the crust causing mechanical failure

sinking mafic body in a reactivated lower crust a mechanism for stress concentration at the new madrid seismic zone we propose a geodynamic model for stress concentration in the new madrid seismic zone nmsz the model postulates that a high density mafic body situated in the deep crust directly beneath the most seismically active part of the nmsz began sinking several thousands of years ago when the lower crust was suddenly weakened based on the fact that deformation rates in the nmsz have accelerated over the past 9 k y we envision the source of this perturbation to be related to the last north american deglaciation excess mass of the mafic body exerts a downward pull on the elastic upper crust leading to a cycle of primary thrust faulting with secondary strike slip faulting after which continued sinking of the mafic body reloads the upper crust and renews the process this model is consistent with the youth of activity the generation of a sequence of earthquakes and the velocity evolution during interseismic periods which depend upon the density contrast of the mafic body with respect to the surrounding crust its volume and the viscosity of the lower crust

crustal heterogeneities beneath the 2011 talala saurashtra earthquake gujarat india source zone seismological evidence for neo tectonics abstract during the 1st decade of the 21st century the study area of talala saurashtra of western india witnessed three damaging earthquakes of moderate magnitude year 2007 mw 5 0 mw 4 8 and in the year 2011 mw 5 1 that generated public panic in the region the last damaging moderate earthquake of the 20th october 2011 in talala region 21 09 n 70 45 e located at about 200 km south to the devastating 2001 bhuj 23 412 n 70 232 e mainshock mw 7 6 jolted the entire saurashtra region of gujarat a long series of aftershocks followed hereafter recorded at nine seismograph accelerograph stations hypocenters of aftershocks were relocated accurately using absolute and relative travel time double difference method in this study we for the first time determined 3 d tomographic images of the upper crust beneath the 2011 talala earthquake source zone by inverting about 1135 p and 1125 s wave arrival time data estimates of seismic velocities v p v s and poisson s ratio structures offer a reliable interpretation of crustal heterogeneities and their bearing on geneses of moderate earthquakes and their aftershock sequences beneath the source zone it is found that the 2011 talala mainshock hypocenter depth 6 km is located near the boundary of the low and high velocity v p v s and the source zone is associated with low anomalies guarded by the prominent high anomalies along the active fault zone having strike slip motion beneath the earthquake source zone the pattern of distribution of v p v s and its association with occurrences of aftershocks provide seismological evidence for the neo tectonics in the region having left lateral strike slip motion of the fault

transient electromagnetic investigations in a tectonic domain of the kachchh intraplate region western india a morphotectonic study of the kachchh mainland fault

results from local earthquake velocity tomography implications toward the source process involved in generating the 2001 bhuj earthquake in the lower crust beneath kachchh india to comprehend the source processes of the 26 january 2001 bhuj earthquake sequence of m w 7 7 and its influence on the seismic hazard of the kachchh we estimate various seismological parameters using reliable and accurate aftershock data the estimated parameters led to several important findings including the delineation of an east west trending south dipping 45 fault north wagad fault nwf which touches the surface about 25 km north of kachchh mainland fault kmf the aftershock zone is confined to a 60 km long and 40 km wide region lying between the kmf to the south and nwf to the north extending from 10 to 45 km depth focal mechanism solutions of the mainshock and 25 significant aftershocks of m w 3 0 obtained from waveform inversion of broadband data and local earthquake moment tensor inversion suggest that the region between the kmf and nwf is mainly characterized by reverse faults with east west trend and southerly dip matching with the geological faults in the region the tomographic inversion technique is used to invert 5516 p wave travel times and 4061 s p travel time differences from 600 aftershocks recorded at 8 18 stations tomographic results suggest a regional high velocity body characterized by high v p 7 0 8 5 km sec high v s 4 0 4 8 km sec and low 0 24 0 26 with a head extending 60 km in north south and 40 km in east west at 10 40 km depths this high velocity anomaly is inferred to be a mafic pluton rift pillow which might have intruded during the rifting time 135 ma this crustal mafic pluton must be contributing significantly in accumulating large crustal stresses resulting in the generation of large earthquakes in this intraplate area another important result of our study is the detection of a low velocity zone low v p 6 5 7 0 km sec low v s 3 6 4 0 km sec large 0 26 0 265 within the mafic body at the hypocentral depth of the mainshock 18 25 km which is inferred to be a fluid filled trapped aqueous fluid resulting from metamorphism fractured rock mass the analysis of depth distribution of b values suggests a high b value zone between 15 and 25 km depths which further supports this contention hence the presence of fluids at the hypocenter might have facilitated the occurrence of the 2001 bhuj earthquake within the inferred mafic body in the lower crust

a seismotectonic model for western hawaii based on stress tensor inversion from fault plane solutions for 57 fault plane solutions of earthquakes with magnitude ml 3 0 located west of the southwest rift zone of mauna loa volcano in hawaii which occurred between 1972 and 1988 the dominant focal mechanisms 44 events are decollement type with one nodal plane nearly horizontal dip 30 the average slip vector of the upper crust on the decollement plane points in an azimuth of 260 toward the ocean away from mauna loa s southwest rift zone at an angle of about 150 with respect to the ne sw oriented rift two other types of focal mechanisms are present normal faults four events and strike slip faults with normal component nine events the orientation of the principal stresses was derived by minimizing the sum of the misfits between the theoretical and observed fault geometry for each focal mechanism after subdividing the data set into three different regions we found that the stress tensor is not homogeneous in west hawaii the orientation for the stress tensor is best resolved in the area located between latitudes 19 27 n and 19 4 n and longitudes 155 7 and 155 9 w where the greatest principal stress directions within the 95 confidence limits are nearly vertical with some spreading to the west their plunge varies between 53 and 85 the intermediate and least principal stresses are mostly horizontal and have similar magnitudes their plunge varies between 1 and 36 the area between latitudes 19 4 and 19 6 n and longitudes 155 7 and 156 w is characterized partly by near vertical and partly by east west oriented greatest principal stresses the least principal stresses are approximately horizontal and have magnitudes similar to the intermediate principal stresses in the two areas where the stress tensor was well resolved the principal strain directions differed from the principal stress directions by 30 in the plunge suggesting that the faulting in western hawaii takes place on a weak plane but this result could not be established at the 95 confidence level the tectonic model proposed for west hawaii is similar to the model for the kalapana region the strain is accumulated through magmatic intrusions in the southwest rift zone of mauna loa and the earthquakes occur along a zone of weakness composed of oceanic sediment at about 10 km depth the west flank of mauna loa slips in the direction away from the rift

stress rotation in the kachchh rift zone gujarat india double difference relocations of the 1402 kachchh events 2001 2006 clearly delineate two fault zones viz south dipping north wagad fault nwf and almost vertical gedi fault gf the relocated focal depths delineate a marked variation of 4 and 7 km in the brittle ductile transition depths beneath gf and nwf respectively the focal mechanism solutions of 464 aftershocks using 8 12 first motions show that the focal mechanisms ranged between pure reverse and pure strike slip except for a few pure dip slip solutions the stress inversions performed for five rectangular zones across the kachchh rift reveal both clockwise and anticlockwise rotation 7 32 in the 1 orientation within the rupture zone favoring a heterogeneous stress regime with an average n s fault normal compression this rotation may be attributed to the presence of crustal mafic intrusives 5 35 km depth in the rupture zone of the 2001 bhuj main shock results suggest a relatively homogeneous stress regime in the gf zone favoring strike slip motion with a fault normal n s compression

magnetotellurics study to identify subsurface resistivity structure in the eastern part of kachchh little rann area of gujarat india a magnetotelluric mt survey has been conducted in the eastern part of the kachchh region of gujarat state crossing little rann starting from adesar village in the north to enjar village in the south where limited geophysical data is available the profile has been acquired in the n s direction having a total length of 52 km with the interstation spacing of 3 4 km from two dimensional 2d inversion of the mt data four conductive zones are identified the analysis reveals that the depth of the basement varies from 1 2 km in the south to 1 8 km in the north the first conductive zone is found at a distance of 3 km in the south of adesar and is identified at the location of the kanmer fault kf the eastern extension of south wagad fault swf and might be the kf the second conductive zone is found at a distance of 42 km in the south of adesar and 13 km north of enjar village and is located at the contact zone of kachchh and saurashtra peninsula at the location of the north kathiawar fault nkf it is inferred as the nkf the third conductive zone at a distance of 27 km in the south of adesar is found between the first and second conductor this is interpreted as a step fault formed during the rifting process of kachchh the lower crust below 20 km is found conductive 120 m and might indicate the presence of fluid filled mafic ultramafic rocks in the lower crust

seismic tomography in the southern margin of the sichuan basin insight into the plateau craton interaction and seismotectonics in the se tibetan plateau abstract the expansion of the tibetan plateau in its southeastern margin causes high seismic hazards in southwest china even if some earthquakes are located far away from the expansion frontier in the southern sichuan basin in this study we determined the high resolution p wave velocity structure of the crust beneath the southern margin of the sichuan basin with an updated data set we find low velocity anomalies in the upper and lower crust whereas high velocity anomalies between them large earthquakes are spatially related to the low velocity anomalies in the lower crust the results indicate that the southern margin of the sichuan basin has been weakened laterally by the deep crustal extrusion related to the expansion of the se tibetan plateau we infer that the shallow crust might have been broken in association with the strike slip faults during the plateau expansion leading to large earthquakes

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

upper mantle seismic anisotropy in the intra continental kachchh rift zone gujarat india abstract shear wave splitting study of 411 sks skks phases covering backazimuth range of 13 to 305 recorded by 12 broadband stations in the kachchh rift has led to estimates of fast axis orientations and splitting times for 118 good measurements the average vector mean of fast axis orientation 86 14 corresponds to the e w axis of the kachchh rift and the delay time 1 6 s is attributed to the 184 km thick upper mantle layer with 4 anisotropy the anisotropic character observed for the kachchh rift kr is comparable to other continental rifts and these are related to the high temperature lattice preferred orientation fabric of olivine inherited from the mantle flows the source of the rift axis parallel anisotropy is traced to the rift parallel flows within the 76 6 km thick lithosphere additionally the rift parallel pockets of partial melts also induce anisotropy within the asthenosphere both these are inherited from the plume lithosphere interaction during the deccan reunion plume episode 65 ma

the utilization of sequence stratigraphy in reservoir geology initial applications of sequence stratigraphy focused on basin analysis and exploration problems as finer scale studies were conducted using well logs and outcrops it has become possible to apply the concepts to improving reservoir performance investigations of the fine scale sequence stratigraphy of carbonates has led to its application to enhance production in the complex paleozoic carbonate reservoirs of the permian and paradox basins studies of coastal plain and shallow marine sediments in the colorado plateau and alberta basin has led to effective utilization in alberta basin reservoirs outcrop of and subsurface investigations of fluvial and deltaic sediments in the north sea has improved performance of jurassic reservoirs in the north sea geophysicists are refining statistical and numerical techniques for defining the seismic facies within reservoirs in indonesia africa and the gulf of mexico several sequence stratigraphic concepts are available for application e g genetic sequences t r sequences forced regressions etc allowing the data to speak for itself rather than slavish adherence to only one theory has greatly improved the utilization of sequence stratigraphy at the reservoir level

tomographic p wave velocity images of the loma prieta earthquake asperity tomographic inversion is applied to delay times from local earthquakes to image 3 d velocity variations surrounding the main rupture of the 1989 loma prieta earthquake the 55 times 45 square km region is represented by blocks of 1 km per side laterally and by 8 layers of varying thickness to 18 km depth high quality p wave arrival times recorded on the usgs calnet array from 549 crustal earthquakes with depths of 0 to 25 km were used as sources preliminary results note several velocity variations 5 12 that correlate with specific characteristics of the 1989 rupture these include prominent high velocity anomalies near the mainshock hypocenter and prominent low velocity anomalies where the dip of the san andreas fault appears to change significantly the termination of prominent low velocity features existing primarily in the hanging wall to depths of 7 9 km correlates with the top of the rupture zone high velocity variations along the fault dominate where aftershock activity is high the high velocity anomaly located at depth along the fault is interpreted as imaging the asperity on which the loma prieta earthquake occurred

3 d seismic structure of the northeast india region and its implications for local and regional tectonics abstract in this study we attempted to estimate 3 d p wave velocity structure of northeast india region using the first arrival data of local earthquakes that were recorded by about 77 temporary permanent local seismic stations the data set the published bulletins include 3494 p wave travel times and 3064 s p travel times from 980 local earthquakes that were located with a minimum of six observations the located earthquakes having a travel time root mean square rms residual 0 49 s and azimuthal gap 180 are selected to compute a 1 d velocity model for the region which is used as initial model for the subsequent 3 d inversions our results demonstrate that the computed 3 d velocity model has significantly improved hypocenter locations of the selected 980 earthquakes by reducing the rms error 0 06 by about 88 with respect to that by the 1 d velocity model the reconstructed p wave velocity v p structure with relocated events reveal strong heterogeneity in lateral as well as in vertical direction corresponding to the local and regional geology tectonics of the region high v p is mapped beneath the shillong plateau mikir hills and in the vicinity of indo burma ranges at shallower crust v p structure is imaged between the shillong plateau and mikir hills at 20 km depth which corresponds to the kopili fault the kopili fault system extends down to 30 km depth as evidenced by the low v p a high v p is imaged below the mikir hills at 40 km depth which is possibly the stress concentrator for high seismic activity along the kopili fault particularly at the fault end the bengal basin south of the shillong plateau is identified as a low v p zone extending down to a depth of about 20 km that indicates the thick alluvium sediments

oceanographic mechanisms and penguin population increases during the little ice age in the southern ross sea antarctica abstract the adelie penguin is a well known indicator for climate and environmental changes exploring how large scale climate variability affects penguin ecology in the past is essential for understanding the responses of southern ocean ecosystems to future global change using ornithogenic sediments at cape bird ross island antarctica we inferred relative population changes of adelie penguins in the southern ross sea over the past 500 yr and observed an increase in penguin populations during the little ice age lia 1500 1850 ad we used cadmium content in ancient penguin guano as a proxy of ocean upwelling and identified a close linkage between penguin dynamics and atmospheric circulation and oceanic conditions during the cold period of 1600 1825 ad a deepened amundsen sea low asl led to stronger winds intensified ocean upwelling enlarged ross sea and mcmurdo sound polynyas and thus higher food abundance and penguin populations we propose a mechanism linking antarctic marine ecology and atmospheric oceanic dynamics which can help explain and predict responses of antarctic high latitudes ecosystems to climate change

the 1992 landers earthquake sequence earthquake occurrence and structural heterogeneities the june 28 1992 mw 7 3 landers earthquake occurred in the southeastern mojave desert california over 10 000 aftershocks of the earthquake were recorded by the caltech usgs southern california seismic network scsn in 1992 to investigate the relationship between complexities in the crustal structure and variations in seismicity we have used a tomographic method to invert 145 098 p wave arrival times from 3740 landers earthquake aftershocks and 1148 other events recorded by 60 permanent and temporary scsn stations we determined a detailed p wave tomographic image with a spatial resolution of about 5 km and relocated the hypocenters with the obtained 3 d velocity model the results show a correlation between seismicity patterns and velocity patterns and a tendency for regions rich in seismicity to be associated with higher velocities the higher velocity areas are considered to be strong and brittle parts of the fault zone which are apt to generate earthquakes in contrast low velocity areas are probably more ductile and weaker allowing aseismic slippage

seismic images under the beijing region inferred from p and pmp data abstract in this study a new tomographic method is applied to over 1500 high quality pmp moho reflected wave travel time data as well as over 38 500 high quality first p wave arrivals to determine a detailed 3d crustal velocity structure under beijing and adjacent areas results of detailed resolution analyses show that the pmp data can significantly improve the resolution of the model in the middle and lower crust after the pmp data are included in the tomographic inversion our new model not only displays the tectonic feature appeared in the previous studies but also reveals some new features the zhangjiakou bohai sea fault zone zhang bo zone is imaged as prominent and continuous low velocity low v anomalies in the shallower crust while in the middle and lower crust it shows intermittent low v anomalies extending down to the uppermost mantle furthermore the pattern of low v anomalies is different along the zhang bo zone from the southeast to the northwest indicating that there exist large differences in the dynamic evolution of taihangshan and yanshan uplifts and north china depression basin prominent low v anomalies are visible under the source area of the 4 july 2006 wen an earthquake m 5 1 suggesting that the occurrence of the wen an earthquake is possibly related to the effect of the crustal fluids probably caused by the upwelling of the hot and wet asthenospheric materials due to the deep dehydration of the stagnant pacific slab in the mantle transition zone the fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the wen an earthquake this is somewhat similar to the cause of the 1695 sanhe pinggu earthquake and the 1976 tangshan earthquake in the region as well as the 1995 kobe earthquake in japan and the 2001 bhuj earthquake in india

seismic imaging of source region in the 1976 ms 7 8 tangshan earthquake sequence and its implications for the seismogenesis of intraplate earthquakes

stress in the indo australian plate cloetingh s and wortel r 1986 stress in the ind austr ian plate in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 49 67 we modelled the state of stress in the indo australian plate in order to investigate quantitatively variations observed in tectonic style the numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere estimates are presented for the average net resistive forces at the himalayan collision zone the suction force acting on the overriding indo australian plate segment at the tonga kermadec trench and the drag at the base of the lithosphere our modelhng shows a concen ation of compressive stresses of the order of 3 5 lcbar in the ninetyeast ridge area the effects of the compressive resistance associated with himalayan collision and subduction of young lithosphere off the northern part of the sunda arc are focused in this region the stress field as calculated gives a consistent explanation for the observed concentration of seismic activity stein and okal 1978 and significant deformation in the oceanic crust weissel et al 1980 mcadoo and sandwell 1985 in the area the calculated stress field in the area adjacent to the southeast and central india ridges is characterized by tension parallel to the spreading axis this explains the concentration of near ridge normal faulting seismicity with t axes subparaile1 to the spreading ridge in the indian ocean as recently observed by bergman et al 1984 and wiens and stein 1984 the regional stress field along the strike of the sunda arc varies from compression seaward of and parallel to the sumatra trench segment to tension perpendicular to the java flores segment this explains the selective occurrence of well developed grabens seaward off the java flores segment of the trench observed by hilde 1983 our modelling shows that the observed rotation of the stress field denham et al 1979 in the australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down going slab in each of these the state of compression in west and central australia is induced by the action of resistive forces at the himalayan and banda arc collision zones the joint occurrence of high levels of compression in the plate s interior and normal faulting seismicity in the near ridge areas is a transient feature unique to the present dynamic situation of the indo australian plate

crustal seismic structure beneath the deccan traps area gujarat india from local travel time tomography abstract the gujarat region in western india is known for its intra plate seismic activity including the mw 7 7 bhuj earthquake a reverse faulting event that reactivated normal faults of the mesozoic kachchh rift zone the late cretaceous deccan traps one of the largest igneous provinces on the earth cover the southern part of gujarat this study is aimed at bringing light to the crustal rift zone structure and likely origin of the traps based on the velocity structure of the crust beneath gujarat tomographic inversion of the gujarat region was done using the non linear passive source tomographic algorithm lotos we use high quality arrival times of 22 280 p and 22 040 s waves from 3555 events recorded from august 2006 to may 2011 at 83 permanent and temporary stations installed in gujarat state by the institute of seismological research isr we conclude that the resulting high velocity anomalies which reach down to the moho are most likely related to intrusives associated with the deccan traps low velocity anomalies are found in sediment filled mesozoic rift basins and are related to weakened zones of faults and fracturing a low velocity anomaly in the north of the region coincides with the seismogenic zone of the reactivated kachchh rift system which is apparently associated with the channel of the outpouring of deccan basalt

coulomb static stress variations in the kachchh gujarat india implications for the occurrences of two recent earthquakes mw 5 6 in the 2001 bhuj earthquake region summary double difference algorithm was used to relocate aftershock sequences of two mw 5 6 kachchh earthquakes india which have occurred on 2006 march 7 and april 6 along almost vertical strike slip gedi fault gf and south dipping reverse north wagad fault nwf respectively the relocated focal depths delineate a marked variation of 4 and 7 km in the brittle ductile transition depths beneath gf and nwf respectively we modelled the coulomb failure stress change cfs produced by the 2001 mainshock and 2006 gedi events on an optimally oriented plane a strong correlation with occurrences of aftershocks and regions of increased cfs is obtained on both the faults the predicted cfs on the gf increased by 0 14 mpa at 3 km depth where the 2006 march 7 mw 5 6 event occurred the variation in brittle ductile transition depths may be related to the perturbation in geothermal gradient resulted from the presence of intrusives or varying saturation state of fluid filled fractured rock matrix beneath both the fault zones

seismic tomography structure of the 1993 killari earthquake source area the aftershock sequence of the 30 september 1993 killari earthquake in central india recorded by 14 temporary seismograph stations was used for seismic tomography study of the source area about 1500 p and 1200 s phases were inverted by the local earthquake tomography method the tomography structures revealed in this study shed new light in understanding seismotectonics of the killari earthquake sequence the contact of the low velocity and high velocity zones has been the source area for the mainshock manuscript received 24 july 2001

assessing the previous activity at the source zone of the 2001 bhuj earthquake based on the near source and distant paleoseismological indicators 1 the m w 7 7 2001 bhuj kachchh earthquake was not associated with any primary surface rupture but it produced secondary faulting folding and liquefaction this study highlights the potential of a secondary rupture and proxies like lateral spreads and sandblows in unraveling the past activity related to the 2001 source chronological constraints of an older lateral spread and far field paleoliquefaction features combined with archeological data provide evidence for occurrences of two previous earthquakes at the 2001 source zone about 4000 and 9000 years ago distinct stratigraphic evidence for at least one previous offset dated at 4424 656 years could be detected at a stepover zone associated with a dextral secondary fault reactivated during the 2001 earthquake the studies imply longer interseismic intervals for the 2001 source zone in comparison with the source zone of the 1819 earthquake located toward the northwestern part of the rann of kachchh the spatial and temporal correlation of previous events derived on the basis of the available paleoseismic data from the region suggest not only repeated activity at the 2001 source but possibility for additional potential sources in parts of kachchh and cambay basins although we infer a longer recurrence interval for the 2001 bhuj earthquake source our study points to the fact that these additional sources may have the potential to rupture in the future considering the long elapsed time

electrical conductance map for the kachchh rift basin constraint on tectonic evolution and seismotectonic implications geomagnetic field variations recorded by an array of magnetometers spread across the kachchh rift basin are reduced to a set of induction arrows as a diagnostic of lateral electrical conductivity variations a non uniform thin sheet electrical conductance model is developed to account for the salient induction patterns it indicates that the imaged conductivity anomalies can be related to the sediment filled structural lows in between the fault bounded uplifts it is suggested that sagging structural lows preserved the marine sediments deposited during the mesozoic sea transgression and later developed into first order embayment basins for the deposition of sediments in association with late eocene transgression depth integrated electrical conductance helped in mapping two depo centres along the ene wsw trending banni half graben bounded by the kachchh main fault on the south and second along the vinjan depression formed in response to the subsidence between the vigodi fault and westward extension of the katrol hill fault together with the westward bending of the median high presence of metamorphosed graphite schist clasts in shale dominated mesozoic sequence and or thin films of carbon resulting from the thermal influence of deccan activity on carbonate rich formations can account for the high electrical conductivity anomalies seen in the depo centres of thick mesozoic and tertiary sediments additionally two high conductivity zones are imaged encompassing a block defined by the 2001 bhuj earthquake and its aftershocks in agreement with gravity magnetic and seismic velocity signatures aqueous fluids released by recrystallizing magmatic bodies intruded in association with deccan trap activity account for mapped high conductivity zones high fluid pressure in such a fractured domain surrounding the intruded magmatic plugs perturb the regional stress concentrations to produce frequent and low magnitude aftershocks in the shallow section of the epicentral track of the 2001 bhuj earthquake

surface deformation and tectonic background of the 2019 ms 6 0 changning earthquake sichuan basin sw china abstract the june 17 2019 ms 6 0 changning earthquake at a depth of 3 5 km struck the changning anticline fold system no active faults have been observed in the region some studies have attributed the earthquake to the regional shale gas exploitation following the earthquake we conducted a field survey to investigate co seismic surface deformation in the area and observed many surface fractures and uplifted areas our work indicated that the deformation followed a riedel shear pattern the fractures and uplifted areas represent t fractures and s extrusions respectively the observed riedel shear pattern is indicative of left lateral strike slip motion to ascertain the relationship between the riedel shear pattern and regional tectonics we investigated the trends in layer striations and fault scratches the results indicated that there were two stages in the evolution of the anticline in the first stage the principal compressive stress that dominated the original formation of the anticline trended ne sw in the second stage the regional principal compressive stress shifted to the current e w trend generating oblique motion that included reverse and left lateral components we propose that the tectonic stress field in this region had a strong bearing on the focal mechanism of the mainshock and the co seismic surface deformation both the eastward expansion of the xianshuihe area and southeastward expansion of the longmen shan have affected the current changning anticline fold system

sediment thicknesses and qs vs qp relations in the kachchh rift basin gujarat india using sp converted phases delineation of the top sedimentary structure and its qs vs qp relationship using the travel time difference of direct s and converted sp phase is key to understanding the seismic hazard of any sedimentary basin area we constructed filtered displacement waveforms from local etna episensor acceleration recordings as well as local velocity recordings of aftershocks of the 2001 bhuj earthquake recorded by the kachchh seismological network of the national geophysical research institute ngri hyderabad india during 2001 2004 stations are within 15 70km of epicenters and the resulting displacement waveforms are generally simple displaying prominent p sp and s wave pulses particle motion of p and s waves suggest near vertical raypaths consistent with preliminary depth estimates the direct s wave on the horizontal component is characterized by lower frequency content than the converted sp phase on the vertical component this difference in frequency content between s and sp phases can be explained in terms of different attenuation effects for p and s waves in the unconsolidated sediments the sp phase is generated by s to p phase conversion at the base of mesozoic sediments of the kachchh basin travel time inversion velest of 2565 p and 2380 s arrivals from 658 well located aftershocks recorded at 8 14 three component local seismic stations led to 1 d velocity models indicated very slow sediments in the upper 0 2 km depth range vp 2 92 km s and vs 0 90 km s and an increasing trend of velocities with depth at 2 40 km depth the estimated sediment thicknesses beneath 12 accelerograph and 6 seismograph sites from the estimated velocity model and the travel time difference between s and converted sp phases reaches a maximum of 1 534 0 117 km beneath bandri near the location of 2001 bhuj mainshock and attains a minimum sediment thickness of 0 858 0 104 km beneath ramvav and burudia the spectral ratios between sp and s from 159 three component accelerograms have been used to study seismic wave attenuation in the kachchh rift basin the estimated qs vs qp relations for 12 accelerograph sites vary from qs 0 184 qp at chobari to qs 0 505 qp at dudhai for stations chobari chopdwa jahawarnagar vondh and tapar the spectral ratio slopes and hence the calculated qs vs qp relations are effectively the same and the correlation coefficients are quite high 0 91 0 93 stations adhoi manfara new dudhai dudhai and sikara have similar qs vs qp relationships to each other and also have high correlation coefficients 0 78 0 87 the spectral ratios for stations anjar and ramvav are small and poorly constrained resulting in less reliable qs vs qp relations this could be due to noisy data fewer available waveforms or scattering due to velocity heterogeneities and or interface irregularities

high pore fluid pressures at bhuj inferred from 90 flips in shear wave polarizations summary shear wave splitting above local earthquakes in the aftershock zone of the 2001 m w7 6 bhuj earthquake display a spatial variation of anisotropy related to crack orientation at most seismic stations the fast polarization directions are approximately nne ssw parallel to the inferred directions of maximum horizontal stress suggesting the dilatancy induced anisotropy resulting from approximately stress aligned parallel vertical microcracks in contrast the fast polarization directions at station samkhyali skl very close to the epicentre of the main shock are fault parallel approximately ew and almost orthogonal to the stress aligned polarizations elsewhere ape modelling and observations elsewhere suggest that these are 90 flips in shearwave polarizations caused by propagation through microcracks containing fluids at critically high pore fluid pressures surrounding the seismically active fault plane the presence of high pore fluid pressures on all seismogenic faults also explains the high scatter in shear wave time delays the average path normalized delay time varies from 2 to 4 ms km 1 except at station skl where higher delays of up to 13 ms km 1 are found the large scatter in measured time delays is caused by cracks saturated with high pressure pore fluids these observations can be explained by the presence of both normal stress aligned and 90 flipped shear wave polarizations at bhuj this suggests that the kutch mainland fault is a major tectonic feature

seismic images of the continental moho of the indian shield abstract deep seismic reflection profiling has imaged different patterns of the moho across the indian shield with a variety of tectonic environments from archean to recent the character of the moho varies from a discrete strong event the base of strong coherent lower crustal sub horizontal reflections the base of dipping lower crustal reflections into mantle to no clear reflection boundary the seismic reflection data suggest a laminated lower crust in several places and offsets in the moho at others kinematic and dynamic modeling of wide angle reflection data across the mesoproterozoic south delhi fold belt and the central indian tectonic zone suggests a laminated lower crust for these regions in general the lower crust of the indian shield is heterogeneous a clear moho is identified in some of the precambrian orogenic belts and sedimentary basins along with reflective lower crust whereas the cratonic areas exhibit a diffused moho post collisional extensional process such as orogenic collapse delamination magmatic intrusions low viscosity ordering and underplating might have played a role in the generation of lower crustal laminated zone and formation of a younger moho the termination of lower crustal reflectivity at the moho with a transparent upper mantle need not necessarily indicate homogeneous upper mantle

inversions for earthquake focal mechanisms and regional stress in the kachchh rift basin western india tectonic implications abstract more than a decade after the 2001 m w 7 7 bhuj earthquake in western india aftershocks up to m w 5 0 are still continuing around the rupture zone in the kachchh rift basin over the years some surrounding faults in the region have been activated and a transverse fault generated an m w 5 1 earthquake in 2012 most of the earthquakes occur in the lower crust at depths between 15 and 35 km we have determined focal mechanism solutions of 47 earthquakes m w 3 2 5 1 that were recorded by a 60 station broadband network during 2007 2014 within an area of 50 km radius of the 2001 main shock south dipping nodal planes in most of the solutions correlate well with the active faults the earthquakes near the epicenter of the 2001 main shock primarily show reverse faulting mechanisms the surrounding earthquakes in the area however show predominantly strike slip mechanisms the p axes of the earthquakes mostly oriented in north south and the t axes in east west however the orientations of the p and t axes exhibit more complexity near the source area of the main shock stress field inversion of the solutions yields a dominant north south compression which is consistent with the ambient tectonic stress field owing to the northward movement of the indian plate with respect to the eurasian plate the geodetic measurements are in reasonable agreement with our results

occurrences of large magnitude earthquakes in the kachchh region gujarat western india tectonic implications abstract moderate to large damaging earthquakes in the peninsular part of the indian plate do not support the long standing belief of the seismic stability of this region the historical record shows that about 15 damaging earthquakes with magnitudes from 5 5 to 8 0 occurred in the indian peninsula most of these events were associated with the old rift systems our analysis of the 2001 bhuj earthquake and its 12 year aftershock sequence indicates a seismic zone bound by two linear trends nnw and nne that intersect an e w trending graben the bouguer gravity values near the epicentre of the bhuj earthquake are relatively low 2 mgal the gravity anomaly maps the distribution of earthquake epicentres and the crustal strain rate patterns indicate that the 2001 bhuj earthquake occurred along a fault within strain hardened mid crustal rocks the collision resistance between the indian plate and the eurasian plate along the himalayas and anticlockwise rotation of the indian plate provide the far field stresses that concentrate within a fault bounded block close to the western margin of the indian plate and is periodically released during earthquakes such as the 2001 m w 7 7 bhuj earthquake we propose that the moderate to large magnitude earthquakes in the deeper crust in this area occur along faults associated with old rift systems that are reactivated in a strain hardened environment

crustal heterogeneity in bulk velocity beneath the 2001 bhuj earthquake source zone and its implications in order to resolve an enigmatic issue relating to the existence of fluid related or temperature related anomalies at the mainshock hypocenter of the 2001 bhuj india earthquake m w 7 6 an estimate of the 3d bulk sound velocity structure is made from the inverted high quality p and s arrival times from a total of 368 aftershocks recorded by 12 temporary seismic stations installed following the 2001 bhuj earthquake results reveal strong lateral and vertical heterogeneity in bulk velocity graphic 1 beneath the source zone the 2001 bhuj mainshock and its aftershock source zones are associated with anomalously high bulk sound velocity high graphic 2 indicating high bulk elastic strength of the source rocks at the mainshock hypocenter due to high pore pressures of the fully saturated cracked rocks associated with solute precipitation through the processes of acoustic fluidization and cementation the interpretation of bulk velocity tomograms suggests that the processes of mineral dehydration and permeation of sea surface water through several active quaternary faults down to the deep crust might have contributed to in situ fluid related material heterogeneity in bulk velocity within the fluid filled fractured rock matrix in the paleorift zone at the 2001 bhuj mainshock hypocenter which in turn increased pore pressure lowered the effective stress and brought the system into a brittle failure high graphic 3 in the intersecting fault geometry in the fractured rock matrix at the mainshock hypocenter can be taken as evidence for the strong role of fluids in association with the intraplate earthquake of the indian peninsula 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif

stress perturbation associated with the amazonas and other ancient continental rifts the state of stress in the vicinity of old continental rifts is examined to investigate the possibility that crustal structure associated with ancient rifts specifically a dense rift pillow in the lower crust may modify substantially the regional stress field both shallow 2 0 2 6 km depth breakout data and deep 20 45 km depth crustal earthquake focal mechanisms indicate a n to nne maximum horizontal compression in the vicinity of the paleozoic amazonas rift in central brazil this compressive stress direction is nearly perpendicular to the rift structure and represents a 75 rotation relative to a regional e w compressive stress direction in the south american plate elastic two dimensional finite element models of the density structure associated with the amazonas rift as inferred from independent gravity modeling indicate that elastic support of this dense feature would generate horizontal rift normal compressional stresses between 60 and 120 mpa with values of 80 100 mpa probably most representative of the overall structure the observed 75 stress rotation constrains the ratio of the regional horizontal stress difference to the rift normal compressive stress to be between 0 25 and 1 0 suggesting that this rift normal stress may be from 1 to 4 times larger than the regional horizontal stress difference a general expression for the modification of the normalized local horizontal shear stress relative to the regional horizontal shear stress shows that the same ratio of the rift normal compression relative to the regional horizontal stress difference which controls the amount of stress rotation also determines whether the superposed stress increases or decreases the local maximum horizontal shear stress the potential for fault reactivation of ancient continental rifts in general is analyzed considering both the local stress rotation and modification of horizontal shear stress for both thrust and strike slip stress regimes in the amazonas rift case because the observed stress rotation only weakly constrains the ratio of the regional horizontal stress difference to the rift normal compression to be between 0 25 and 1 0 our analysis is inconclusive because the resultant normalized horizontal shear stress may be reduced for ratios 0 5 or enhanced for ratios 0 5 additional information is needed on all three stress magnitudes to predict how a change in horizontal shear stress directly influences the likelihood of faulting in the thrust faulting stress regime in the vicinity of the amazonas rift a rift normal stress associated with the seismically active new madrid ancient rift may be sufficient to rotate the horizontal stress field consistent with strike slip faults parallel to the axis of the rift although this results in a 20 40 reduction in the local horizontal shear stress within the seismic zone sparse stress data in the vicinity of the seismically quiescent midcontinent rift of the central united states suggest a stress state similar to that of new madrid with the local horizontal shear stress potentially reduced by as much as 60 thus the markedly different levels of seismic activity associated with these two subparallel ancient rifts is probably due to other factors than stress perturbations due to dense rift pillows the modeling and analysis here demonstrate that rift normal compressive stresses are a significant source of stress acting on the lithosphere and that in some cases may be a contributing factor to the association of intraplate seismicity with old zones of continental extension

3d crustal resistivity structure beneath the wagad aftershock zone of the 2001 bhuj earthquake kutch india heterogeneous resistivity structure controlled by widespread fluid infiltration and clues to aftershocks pattern abstract the epicentral region of the 26 january 2001 bhuj earthquake 7 7 m w in the kutch region of india has been experiencing a vigorous and unique intraplate aftershock activity which shows a v shaped pattern and n ne migration along the western margin of the wagad uplift located to the northeast of the mainshock this study presents 3d resistivity structure of the wagad aftershock zone imaged using magnetotelluric mt data to understand the crustal geoelectric structure and subsurface geometry of faults lineaments which could provide critical inputs to evaluate and strengthen the earthquake generation mechanism and aftershocks pattern the obtained 3d conductivity structure showed a thick 3 km and homogeneous conductive 1 30 m layer of tertiary mesozoic sedimentary cover in the area a highly heterogeneous upper and middle crust characterized by a mix of conductive 300 m structures is imaged below the sedimentary cover enhanced conductivity zones showed spatial correlation with the surface trace of various faults lineaments and are interpreted as fluid enriched zones in the crust which play a critical role in earthquake triggering significantly higher fluid enrichment noticed in the crust below two minor faults khadir transverse fault ktf and manfara fault mf which are hitherto considered to have an insignificant role in the seismogenesis of the area the aftershock events seem to occur mostly on the resistive parts of the crust and its pattern shows good alignment with the anomalous conductive zones associated to the above two faults the results provide a strong clue to infer that the ktf and mf have a vital role in the observed aftershock activity and control the v shaped aftershocks pattern

depositional systems and sequence architecture of the oligocene dongying formation liaozhong depression bohai bay basin northeast china the sequence stratigraphic framework and depositional systems of an oligocene lacustrine rift succession in the liaozhong depression of bohai bay basin in northeastern china were investigated using seismic profiles complemented by well logs and cores seven sequences are identified on the basis of unconformities on basin margins and correlative conformities in the basin center depositional systems are associated with systems tracts within sequences lowstand systems tracts are dominated by sublacustrine fans transgressive systems tracts are mainly composed of beach bar deposits and highstand systems tracts are characterized by deep lacustrine fan or braid delta deposits episodic tectonic movement was the principal factor that controlled the development of the sequences lake level changes resulting from climatic oscillations may have controlled the development of these sequences the balance between tectonic subsidence and sediment supply controlled the type of lake basin the bohai bay basin was a balanced fill basin in the early and middle stages of the dongying formation and evolved into an overfilled basin at the end of deposition of the dongying formation this study enhances the understanding of depositional system configuration and systems tracts in a typical rift basin and proposes that the most favorable sandstone reservoirs are developed in sublacustrine fan deposits relative lowstand sublacustrine fan deposits capped by relative highstand prodelta or deep lacustrine mudstones form the highest potential lithostratigraphic traps

tomography of the source area of the 1995 kobe earthquake evidence for fluids at the hypocenter seismic tomography revealed a low seismic velocity 5 and high poisson s ratio 6 anomaly covering about 300 square kilometers at the hypocenter of the 17 january 1995 magnitude 7 2 kobe earthquake in japan this anomaly may be due to an overpressurized fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake

evidence for right lateral strike slip environment in the kutch basin of northwestern india from moment tensor inversion studies abstract the kutch region located in northwestern part of india is an ancient rift basin that was active until cretaceous period the region falls close to the india arabia and the india eurasia plate boundaries and has experienced devastating earthquakes in the past namely the 1819 allah bund earthquake the 1956 anjar earthquake and the 2001 bhuj earthquake to understand the tectonics of this region with respect to the adjacent plate boundaries we invert seismic waveform data of 11 earthquakes in this region recorded by a network of the institute of seismological research isr during 2007 2009 the study yields focal mechanism solutions of reverse fault and strike slip type mechanism the inferred fault planes correlate well with the local trends of the known tectonic faults while the principal stress directions derived from stress inversion based on a linearized least squares approach trend agreeably with the ambient stress field directions a consistently right lateral sense of shear is found on all the local faults as derived from each of the matching planes of the focal mechanism solutions computed in the present study it is inferred that in the kutch region a right lateral strike slip environment prevails along predominantly ew to nw se oriented deep seated pre existing faults in an otherwise compressive stress regime this in conjunction with the left lateral movements along the girnar mountain in southern saurashtra inferred from previous studies indicates a westward escape of the kutch saurashtra block as a consequence of the northward collision of the indian plate with respect to the eurasian landmass

postseismic deformation and stress changes following the 1819 rann of kachchh india earthquake was the 2001 bhuj earthquake a triggered event 1 the 2001 mw 7 6 bhuj earthquake occurred in an intra plate region with rather unusual active seismicity including an earlier major earthquake the 1819 rann of kachchh earthquake m7 7 we examine if static coseismic and transient postseismic deformation following the 1819 earthquake contributed to the enhanced seismicity in the region and the occurrence of the 2001 bhuj earthquake 100 km away and almost two centuries later based on the indian shield setting great rupture depth of the 2001 event and lack of significant early postseismic deformation measured following the 2001 event we infer that little viscous relaxation occurs in the lower crust and choose an upper mantle effective viscosity of 1019 pas the predicted coulomb failure stress dcfs on the rupture plane of the 2001 event increased by more than 0 1 bar at 20 km depth which is a small but possibly significant amount stress change from the 1819 event may have also affected the occurrence of other historic earthquakes in this region we also evaluate the postseismic deformation and cfs in this region due to the 2001 event positive cfs from the 2001 event occur to the nw and se of the bhuj earthquake rupture

post seismic crustal deformation and strain rate in bhuj region western india after the 2001 january 26 earthquake summary the mw 7 6 bhuj earthquake in gujarat western india which occurred on 2001 january 26 was a major intraplate event in the indian subcontinent to study the characteristics of transient post seismic deformation at the earth s surface to elucidate the distribution of strain accumulation rate and so understand the earthquake recurrence process five gps campaigns were conducted at 14 sites in bhuj region during 2001 2002 the daily variations in the site position coordinates and the baselines during the early after shock period i e for 21 d starting from 2001 february 10 march 2 showed no short term post seismic crustal deformation neither logarithmic nor exponential function could be well fitted to any of the components of the time series of the position co coordinates indicating no discernable contribution from viscoelastic relaxation poroelastic rebound or afterslip mechanisms the estimated velocity field in itrf2000 spanning five epochs during 2001 2002 has an average of 50 mm yr 1 in north northeast direction to obtain a better perspective of post seismic deformation in the epicentral track the residual velocity field has been expressed in an india fixed reference frame the residual velocity of 11 62 mm yr 1 in a north northwest direction and 5 24 mm yr 1 towards the south seen at sites south and north of the epicentre respectively indicates localized ongoing convergence in the epicentral region at sites away from the epicentre no significant deformation took place the estimated principal strain from the velocity field gives average compression and extension rates of 0 07 and 0 04 micro strain yr 1 respectively a zone of maximum compressive strain rate of 0 30 micro strain yr 1 with azimuth of 11 delineated north of the epicentral region shows good agreement with seismic deformation along the blind fault derived from earthquake focal mechanisms these results suggest ongoing transpressional deformation across the area with a blocked structure embedded between the north wagad fault and south wagad fault this deformation may be related to the present neo tectonic compressive stress regime of the indian plate due to its nne movement against the collision front in the north and its proximity to the triple junction in the western continental margin of the study area

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

a new insight into crustal heterogeneity beneath the 2001 bhuj earthquake region of northwest india and its implications for rupture initiations the seismic characteristics of the 2001 bhuj earthquake mw 7 6 has been examined from the proxy indicators relative size distribution 3d b value mapping and seismic tomography using a new data set to understand the role of crustal heterogeneities in rupture initiations of the 2001 bhuj earthquake of the gujarat india one of the disastrous indian earthquakes of the new millennium the aftershocks sequence recorded by 22 seismograph stations of gujarat seismic network gsnet during the period from 2006 to 2009 encompassing approximately 80 km 70 km rupture area had revealed clustering of aftershocks at depth of 5 35 km which is seismogenic layer responsible for the occurrence of continued aftershocks activity in the study region the 3d b value mapping estimated from a total of 3850 precisely located aftershocks with magnitude of completeness mc 2 7 shows that a high b value region is sandwiched within the main shock hypocenter at the depth of 20 25 km and low b value region above and below of the 2001 bhuj main shock hypocenter estimates of 3 d seismic velocity vp vs and poisson s ratio structure beneath the region demonstrated a very close correspondence with the b value mapping that supports the similar physicochemical processes of retaining fluids within the fractured rock matrix beneath the 2001 bhuj mainshock hypocenter the overall b value is estimated close to 1 0 which reveals that seismogenesis is related to crustal heterogeneity which in turn also supported by low vs and high structures the high b value and high anomaly at the depth of 20 25 km indicate the presence of highly fractured heterogeneous rock matrix with fluid intrusions into it at deeper depth beneath the main shock hypocenter region low b value and high vp in the region is observed towards the north east and north west of the main shock that might be an indication of the existence of relatively competent rock masses with negligible volume of cracks that may have contained over pressurized fluids without molten rocks

crustal heterogeneity and seismotectonics of the region around beijing china abstract a detailed three dimensional 3 d p wave velocity model of the crust and uppermost mantle under the chinese capital beijing region is determined with a spatial resolution of 25 km in the horizontal direction and 4 17 km in depth we used 48 750 precise p wave arrival times from 2973 events of local crustal earthquakes controlled seismic explosions and quarry blasts these events were recorded by a new digital seismic network consisting of 101 seismic stations equipped with high sensitivity seismometers the data are analyzed by using a 3 d seismic tomography method our tomographic model provides new insights into the geological structure and tectonics of the region such as the lithological variations and large fault zones across the major geological terranes like the north china basin the taihangshan and the yanshan mountainous areas the velocity images of the upper crust reflect well the surface geological and topographic features in the north china basin the depression and uplift areas are imaged as slow and fast velocities respectively the taihangshan and yanshan mountainous regions are generally imaged as broad high velocity zones while the quaternary intermountain basins show up as small low velocity anomalies velocity changes are visible across some of the large fault zones large crustal earthquakes such as the 1976 tangshan earthquake m 7 8 and the 1679 sanhe earthquake m 8 0 generally occurred in high velocity areas in the upper to middle crust in the lower crust to the uppermost mantle under the source zones of the large earthquakes however low velocity and high conductivity anomalies exist which are considered to be associated with fluids the fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the large crustal earthquakes

the 2001 bhuj earthquake tomographic evidence for fluids at the hypocenter and its implications for rupture nucleation 1 the january 26 2001 bhuj earthquake mw 7 6 is one of the most catastrophic indian earthquakes we have investigated the 3 d seismic velocity and poisson s ratio structures of the bhuj source area to understand the probable cause of triggering the earthquake we used 1948 p and 1865 s wave high quality arrival times from 331 aftershocks recorded at a temporary seismic network significant variations up to 5 in velocity and 10 in poisson s ratio are revealed in the aftershock area the mainshock is located in a distinctive zone characterized by high vp low vs and high poisson s ratio in the depth range of 20 to 30 km and extending 15 to 30 km laterally this feature is very similar to that of the 1995 kobe earthquake zhao et al 1996 the anomaly may be due to a fluid filled fractured rock matrix which might have contributed to the initiation of the bhuj earthquake

three dimensional velocity structure seismicity and fault structure in the parkfield region central california this study examines the three dimensional velocity structure in a 60 by 80 km region containing the parkfield segment of the san andreas fault we use local earthquake and shot p arrival times in an iterative simultaneous inversion for velocity and hypocentral parameters using the three dimensional model we relocated 5251 events that occurred from 1969 to 1991 as well as the 1966 aftershocks and computed 664 fault plane solutions the san andreas fault saf characterized by a sharp across fault velocity gradient is the primary feature in the velocity solution there is a 5 20 lateral change in velocity over a 4 km width the contrast being sharper where there is better resolution the model also shows significant variations in the velocity and in the complexity of the velocity patterns along the saf the largest across fault velocity difference is below middle mountain where a large volume of low velocity material impinges on the saf from the northeast this material is inferred to be overpressured and may be key to understanding the unusual behavior in the parkfield preparation zone a 20 km long high velocity slice is imaged northeast of the saf near gold hill its along fault length corresponds to the length of the maximum slip in 1966 the relocated seismicity shows that the san andreas fault is a planar vertical fault zone at seismogenic depths ninety percent of the fault plane solutions that are on or near the saf were right lateral strike slip on subvertical fault planes that parallel the saf thus the surface fault complexities do not appear to extend to depth and therefore do not explain the rupture character at parkfield at parkfield variations in material properties play a key role in fault segmentation and deformation style our observations suggest that there may be a general relation between increasing velocity and increasing ability of the rocks to store strain energy and release it as brittle failure

relocations and local earthquake tomography implications toward the mafic pluton induced crustal seismicity in kachchh gujarat india for last 18 years abstract the study presents new probable crustal model based on precise double difference relocations of 2420 aftershocks of the 2001 bhuj earthquake mw7 7 during 2001 16 and combining other geophysical and geological studies in the region which will lead to a better understanding of the cause of uninterrupted aftershock activities in the region relocations of aftershocks delineate two main seismic clusters in the central aftershock zone caz i e eastern a1 and western a2 the alignments of relocated hypocenters of the aftershocks delineate three main fault segments viz the south dipping north as well as south wagad faults and north dipping kachchh mainland fault relocations also detect some zones of devoid of aftershocks with a typical dimension of 3 9 km within the caz which could be related to locales of future earthquakes seismic velocity tomograms depict that both seismic clusters a1 and a2 are associated with high velocity anomalies inferred to be mafic plutons below the wagad and banni regions respectively the e w depth section of relocated hypocenters delineates an 18 km variation of the seismogenic base which could be attributed to the increase in crustal maficness due to the intrusion of mafic plutons below the caz stress inversions of selected focal mechanisms depict a rotation of 44 in the 1 orientation within the caz which could be attributed to large local stresses induced by mafic plutons the continued seismicity at kachchh is proposed to be caused by the presence of large stresses associated with mafic plutons owing to the n s plate compression associated with northward movement of the indian plate wherein crustal fluid flows aqueous metamorphic fluids or volatile co2 might provide the triggering to generate continued aftershock activities at kachchh india

comparative tomography of reverse slip and strike slip seismotectonic provinces in the northern south island new zealand abstract actively deforming crust and upper mantle around the obliquely convergent pacific australia plate boundary in the northern south island of new zealand have been investigated by seismic tomography using data from a temporary c 50 station network plus geonet the alpine wairau fault principal component of the plate boundary at the surface transects the study area separating the buller nelson bn province of active compressional inversion involving steep reverse faulting to the northwest from the marlborough fault system ma dominated by dextral strike slip faulting to the southeast in the course of this study ma hosted the 2013 seddon earthquake sequence m5 9 6 6 and the 2016 m7 8 kaikoura earthquake active fault structures and present seismicity are associated with a heterogeneous distribution of low velocity and vp vs anomalies elsewhere there is a general association between crustal seismicity and low velocity zones along major fault structures within both the ma and bn seismotectonic provinces along which high vp vs anomalies are locally conspicuous areas of active crustal seismicity are also generally characterized by high vp vs for instance the hypocentre and aftershocks of the 2016 m7 8 kaikoura earthquake overlie a low velocity region with high vp vs the coincidence of anomalously low vp and vs and anomalously high vp vs with zones of high electrical conductivity defined by a previous mt transect is consistent with the notion that upward migration of overpressured hydrothermal fluid from the subducting slab at depth leads to a heterogeneous distribution of overpressured fluid in and around the base of the crustal seismogenic zone weakening the overlying crust and promoting seismic rupture along major fault systems it seems possible that the association of mid crustal low velocity zones with anomalously high vp vs may diagnose rupture preparation zones where frictional strength is being lowered by the build up of fluid overpressure concurrent with accumulating shear stress so that eventual fault failure is dual driven

the 6 june 2003 bardwell kentucky earthquake sequence evidence for a locally perturbed stress field in the mississippi embayment this article describes an unusually well behaved unusually well documented central and eastern united states ceus earthquake sequence detailed analysis of regional and local waveform data from the 6 june 2003 bardwell kentucky earthquake indicates that the mainshock has the seismic moment of m 0 1 3 0 5 10 15 n m m w 4 0 and occurred at a depth of about 2 1 km on a near vertical fault plane a temporary seismic network recorded 85 aftershocks that delineate an east trending fault approximately 1 km in length the hypocenters illuminate a vertical plane between 2 0 and 2 7 km depth the centroid of the aftershock distribution is at 36 875 n 89 010 w and a depth of 2 4 km the aftershock cluster is interpreted as a circular fault area with a radius of 0 44 0 03 km this source radius yields a static stress drop 67 14 bars for the mainshock the focal mechanism for the mainshock has strike 90 dip 89 and rake 165 with a subhorizontal p axis trending 135 a formal stress inversion based on the focal mechanisms of the mainshock and ten aftershocks indicates the maximum compressive stress trends 104 with a plunge of 5 the local stress field near bardwell is therefore rotated about 40 clockwise relative to 65 for eastern north america as a whole the bardwell earthquakes have the opposite sense of slip to earthquakes with east trending nodal planes that occur near new madrid missouri this requires a significant local rotation of the stress field over a distance of 60 km

rupture process of the 26 january 2001 mw 7 6 bhuj india earthquake from teleseismic broadband data we investigate the rupture process of the 26 january 2001 bhuj india m w 7 6 earthquake through inversion of teleseismic broadband body waves this earthquake ranks as one of the most important recent events due to its occurrence within a stable continental interior where such events are rare the bhuj earthquake occurred on a moderately dipping blind thrust fault within an ancient failed rift about 70 of the seismic moment released in the earthquake was confined to a very small area 375 km2 surrounding the hypocenter and at depths below 12 km the static stress drop of the bhuj earthquake is anomalously high 20 mpa the source time history of the event indicates very rapid onset to the moment release and most likely high slip velocities within the deep asperity this suggests that some of the damage near the epicenter may have been caused by anomalously high frequency ground motions the teleseismic data also indicate the presence of a second area of large slip in the shallow part of the bhuj fault although the depth extent of this shallow large slip area is not resolved comparisons of the predicted ground motions with observed intensities suggest that substantial slip occurred in the upper 10 km of the fault in order to explain the distribution of high intensities to the west and northwest of the fault the upper surface layers near the bhuj fault consist of unconsolidated low rigidity sediments and alluvium the upper 10 km of the bhuj fault may therefore be in a conditionally stable region that normally deforms through aseismic creep and can sustain seismic rupture only when dynamically stressed by rupture of the high strength deep asperity we suggest that this deep asperity may be related to a lithologic anomaly of ultramafic composition

two dimensional seismic image of the san andreas fault in the northern gabilan range central california evidence for fluids in the fault zone a joint inversion for two dimensional p wave velocity vp p to s velocity ratio vp vs and earthquake locations along the san andreas fault saf in central california reveals a complex relationship among seismicity fault zone structure and the surface fault trace a zone of low vp and high vp vs lies beneath the saf surface trace safst extending to a depth of about 6 km most of the seismic activity along the saf occurs at depths of 3 to 7 km in a southwest dipping zone that roughly intersects the safst and lies near the southwest edge of the low vp and high vp vs zones tests indicate that models in which this seismic zone is significantly closer to vertical can be confidently rejected a second high vp vs zone extends to the northeast apparently dipping beneath the diablo range another zone of seismicity underlies the northeast portion of this vp vs high the high vp vs zones cut across areas of very different vp values indicating that the high vp vs values are due to the presence of fluids not just lithology the close association between the zones of high vp vs and seismicity suggests a direct involvement of fluids in the faulting process

a 1 800 year record of arsenic concentration in the penguin dropping sediment antarctic heavy toxic metals have been widely investigated in the antarctic however there are rare reports on arsenic up to now here we analyzed a 1 800 year record of arsenic concentration in lake sediments affected by penguin droppings we found that arsenic enriches in the penguin dropping sediments with 12 41 0 45 g g on dry weight which is about two times higher than the one in the background sediments with absence of penguin historical change in arsenic concentration was found to significantly correlate with the fluctuation of penguin number indicating that penguin activity will result in the enrichment of arsenic somewhere in the maritime antarctic

fault geometry of the mw 7 7 western india intraplate earthquake constrained from double difference tomography and fault plane solutions abstract globally one of the largest intraplate earthquakes of m w 7 7 occurred on 26 january 2001 in the kachchh rift basin krb western india the continuing long aftershock sequence over decades has generated much debate on the seismogenic fault s we have analyzed more than 10 000 aftershocks m w 1 0 recorded by a 50 station broadband network in the region during 2006 2014 a total of 834 aftershocks m w 2 4 each recorded by at least eight broadband seismic stations with a minimum of eight p and six s phases are relocated in this study by double difference tomography tomodd method the relocated aftershocks and velocity images reveal a near vertical or steeply south dipping deeper structure as the source zone of the mainshock and aftershocks the structure correlates well with the geologically mapped south wagad fault swf among the other geologically known faults the kachchh mainland fault kmf and the gedi fault gf are also well identified in the seismic sections further fault plane solutions of 109 aftershocks having m w 3 5 corroborate well with the known faults the geological model and seismological observations suggest that the swf overstepped the kmf and intersects it at depth the intersecting fault zone is the source area for the deeper 10 35 km reverse faulting earthquakes in the krb at the fault end of the swf a heterogeneous velocity structure is imaged which is attributed to a fluid filled rock matrix that triggered the mainshock on the other hand the gf is reported to be a later activated fault to the north of swf it generated some shallower aftershocks 0 20 km mostly by strike slip mechanisms