biomarker maturity parameters for high maturities calibration of the working range up to the oil condensate threshold abstract in a study of oils and source rocks from the kimmeridge clay united kingdom and the hanifa qatar formations several biomarker maturity parameters with working ranges up to vr e vitrinite reflectance equivalent 1 0 oil condensate threshold have been identified and calibrated this represents a significant improvement compared to commonly used biomarker maturity tools sterane and hopane isomerisation with their maturity maximum of approximately vr e 0 7 early part of oil window these new parameters are 1 the absolute concentrations of steranes and hopanes decreasing gradually with increasing maturity 2 the ratio of tricyclic terpanes tricyclic terpanes hopanes increasing with maturity 3 the ratio of diasteranes 14 h 17 h steranes depending both on maturity and on source rock lithology and 4 the ratio of t s t m 22 29 30 trisnorneohopane 22 29 30 trisnorhopane increasing rapidly at very high maturities during artificial maturation experiments the biomarker maturities described in the natural samples were also known to be time temperature dependent up to rather severe laboratory heating conditions this corresponds with the working range up to high maturity levels as observed in the natural samples

coseismic slip distribution of the 2015 mw7 8 gorkha nepal earthquake from joint inversion of gps and insar data for slip within a 3 d heterogeneous domain

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

an improved set of a x parameters for fe mg ca garnets and refinements of the orthopyroxene garnet thermometer and the orthopyroxene garnet plagioclase quartz barometer

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

crustal density structure across the central indian shear zone from gravity data abstract the central indian shear zone is a distinct tectonic feature in the central part of india that separates the central indian tectonic zone from the bastar craton the complete bouguer anomaly map of the region encompassing central indian shear zone is characterised by a broad relative gravity high over central indian tectonic zone as compared to the bastar craton the paired gravity anomaly across the two crustal domains signifies that the central indian shear zone is a locus of density discontinuity along which the two crustal domains accreted horizontal gravity gradient analysis further demonstrates the northward subduction of the bastar craton beneath the bundelkhand craton 2 d gravity modelling along mungwani rajnandgaon profile constrained by seoni kalimati seismic section delineates a thick crust beneath the bastar craton as compared to the central indian tectonic zone northward dipping contact of the two crustal domains when projected on the surface coincides with the central indian shear zone with a well defined moho offset and crustal density discontinuity central indian shear zone represents a suture zone that separates the bastar craton from the central indian tectonic zone a low velocity 6 4 km s density 2 90 g cm 3 layer at the base of the crust and relatively lower density 3 21 g cm 3 subcrustal mantle may be the imprint of thermal remobilization beneath the central indian tectonic zone

a vitrinite reflectance kinetic model incorporating overpressure retardation abstract the models currently used to predict maturation and hydrocarbon generation in petroleum basins use time and temperature as controlling parameters a small number of studies have indicated that overpressure can retard maturation although some of the published information from experimental investigations appears to be conflicting careful examination of the experimental conditions shows that both vitrinite reflectance and hydrocarbon generation are retarded by overpressures overpressure appears to result in the retention of volatiles within the molecular structure which prevents the molecular reorganisation necessary to produce higher reflectance values using a database containing vitrinite reflectance from both overpressured and normally pressured wells a kinetic model presro has been developed in which overpressure modifies the arrhenius a factor the model has been tested on two different basins south china sea and sable exhibiting a range of time temperature overpressure characteristics the results suggest that the maturity and timing of the onset of hydrocarbon generation differ significantly from those predicted by current models

archaeabacterial lipids in drill core samples from the bosumtwi impact structure ghana meteorite impacts are associated with locally profound effects for microorganisms living at the terrestrial surface and the subsurface of the impact zone the bosumtwi crater in ghana west africa is a relatively young 1 07 myr structure with a rim to rim diameter of about 10 5 km in a preliminary study targeting the subsurface microbial life in the impact structure seven samples of the impact breccia from the central uplift of the bosumtwi crater were analyzed for the presence of typical archaeal membrane lipids gdgts these have been detected in four of the samples at a maximum depth of 382 m below the lake surface which is equivalent to 309 m below the surface sediment the concentration of the gdgts does not show a trend with depth and their distribution is dominated by gdgt 0 possible origins of these lipids could be related to the soils or rocks predating the impact event the hydrothermal system generated after the impact or due to more recent underground water transport

joint inversion of gps insar and teleseismic data sets for the rupture process of the 2015 gorkha nepal earthquake using a generalized abic method abstract various observations are made to invert for the source model of the 2015 gorkha earthquake previously published slip models involve different slip distributions and slip amplitudes to obtain a robust model we jointly invert for the rupture process of the gorkha earthquake using three types of observations global positioning system gps interferometric synthetic aperture radar insar and teleseismic p wave data three constraints i e spatial and temporal smoothness and minimum moment constraints are applied to regulate the rupture process the weight ratios between data sets and prior constraints are determined from a new developed generalized akaike s bayesian information criterion gabic weight determination method this gabic method can simultaneously and objectively weigh various kinds of observations and prior constraints rather than being limited to the two types in the traditional abic method the inverted slip model reveals the seismic moment of the earthquake is 9 40 10 20 n m released primarily in the first 60 s equivalent to mw 7 92 the rupture front propagates unilaterally along the strike direction and spreads in both the strike and dip directions the slip distribution shows one large slip patch with two peaks along the strike direction with a maximum slip amplitude of approximately 7 6 m and identifies large slips 2 m that occur in the updip section of the main himalayan thrust mht fault plane our results indicate that the released slip amplitude is larger than the accumulated slip amplitude since 1833 so the 2015 earthquake likely does not overlap with the 1833 earthquake

geological overview and cratering model for the haughton impact structure devon island canadian high arctic the haughton impact structure has been the focus of systematic multi disciplinary field and laboratory research activities over the past several years regional geological mapping has refined the sedimentary target stratigraphy and constrained the thickness of the sedimentary sequence at the time of impact to 1880 m new 40ar 39ar dates place the impact event at 39 ma in the late eocene haughton has an apparent crater diameter of 23 km with an estimated rim final crater diameter of 16 km the structure lacks a central topographic peak or peak ring which is unusual for craters of this size geological mapping and sampling reveals that a series of different impactites are present at haughton the volumetrically dominant crater fill impact melt breccias contain a calcite anhydrite silicate glass groundmass all of which have been shown to represent impact generated melt phases these impactites are therefore stratigraphically and genetically equivalent to coherent impact melt rocks present in craters developed in crystalline targets the crater fill impactites provided a heat source that drove a post impact hydrothermal system during this time haughton would have represented a transient warm wet microbial oasis a subsequent episode of erosion during which time substantial amounts of impactites were removed was followed by the deposition of intracrater lacustrine sediments of the haughton formation during the miocene present day intracrater lakes and ponds preserve a detailed paleoenvironmental record dating back to the last glaciation in the high arctic modern modification of the landscape is dominated by seasonal regional glacial and niveal melting and local periglacial processes the impact processing of target materials improved the opportunities for colonization and has provided several present day habitats suitable for microbial life that otherwise do not exist in the surrounding terrain

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

deep seismic soundings along hirapur mandla profile central india summary the crustal depth section along hirapur mandla profile has been computed in two steps from deep seismic sounding dss data the shallow section up to the crystalline basement is derived by inverting first arrival refraction travel times the upper vindhyan sediments velocity 4 5 km s have a maximum thickness of about 1 5 km at bakshaho the lower vindhyan sediments velocity 5 4 km s were deposited north of narmadason lineament between katangi and narsinghgarh in a graben developed in crystalline basement the thickness of the lower vindhyans increases from north to south towards katangi and the depth to the basement reaches 5 5 km near jabera the depth to the moho boundary varies from 39 5 km near tikaria to 45 km at narsinghgarh the narrow block between katangi and jabalpur forms a horst feature which represents the narmada son lineament forming the southern boundary of the vindhyan basin two dimensional ray tracing was performed generating travel time curves from various shot points which were matched with observed travel time data

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

hydrothermally enhanced magnetization at the center of the haughton impact structure haughton is a 24 myr old mid size apparent diameter 23 km complex impact structure located on devon island in nunavut canada the center of the structure shows a negative gravity anomaly of 12 mgal coupled to a localized positive magnetic field anomaly of 900 nt a field expedition in 2013 led to the acquisition of new ground magnetic field mapping and electrical resistivity datasets as well as the first subsurface drill cores down to 13 m depth at the top of the magnetic field anomaly petrography rock magnetic and petrophysical measurements were performed on the cores and revealed two different types of clast rich polymict impactites 1 a white hydrothermally altered impact breccia not previously observed at haughton and 2 a grey impact breccia with no macroscopic sign of alteration in the altered core gypsum is present in macroscopic veins and in the form of intergranular selenite associated with colored and zoned carbonate clasts this altered core has a natural remanent magnetization nrm four to five times higher than materials from the other core but the same magnetic susceptibility their magnetization is still higher than the surrounding crater fill impact melt rocks x ray fluorescence data indicate a similar proportion of iron rich phases in both cores and an enrichment in silicates within the altered core in addition alternating field demagnetization results show that one main process remagnetized the rocks these results support the hypothesis that intense and possibly localized post impact hydrothermal alteration enhanced the magnetization of the clast rich impact melt rocks by crystallization of magnetite within the center of the haughton impact structure subsequent erosion was followed by in situ concentration in the subsurface leading to large magnetic gradient on surface

thermal maturity of lower paleozoic sedimentary successions in arctic canada mean maximum graptolite reflectance values from numerous sections in arctic canada range from 0 6 in cornwallis island and northwestern devon island to 4 7 in ellesmere island we attribute this great lateral reflectance variation to differing burial depths of the graptolite bearing strata beneath thick synorogenic siliciclastic covers we attribute the low maturity of rocks in northern cornwallis and eastern bathurst islands to a maximum burial of about 2 km elsewhere we used the paleogeographic location and proximity to the ellesmerian overthrust wedge to interpret the measured reflectance values in northern ellesmere island where the highest graptolite reflectance values 4 7 occur as much as 9 6 km of synorogenic siliciclastics accumulated on a tectonically loaded carbonate shelf initial synorogenic siliciclastics encountered substantial submarine to basin relief and thus about 2 km of sediment were deposited prior to the initiation of deposition on the adjacent drowned shelf also the deep water sequence probably was underlain by attenuated continental crust adjacent to the southeastward advancing ellesmerian overthrust wedge together these factors caused deposition of as much as 7 6 km of sediment in western melville island and as much as 9 6 km in northeastern ellesmere island on the drowned shelf synorogenic stratal thicknesses were less a feature we attribu e to a thicker more rigid crustal sequence and greater distance from the ellesmerian tectonic loading we expect liquid hydrocarbons to be generated from the organic matter in the shales in areas with a graptolite r0 maximum gr0 max of less than 1 7 the presence of two types of solid bitumens having different reflectances morphologies and optical textures suggests that hydrocarbons were generated and migrated through the graptolite bearing strata we expect only gaseous hydrocarbons in areas where gr0 max exceeds 2 0 r0

precipitation sublimation and snow drift in the antarctic peninsula region from a regional atmospheric model 1 a regional atmospheric model with a horizontal grid spacing x of 14 km is used to study the surface mass balance components precipitation sublimation and snow drift in the region of the antarctic peninsula ap an integration is performed for the 7 year period 1987 1993 using a realistic forcing at the lateral model boundaries and at the sea surface output from this integration indicates that the precipitation reaches its maximum value on the northwestern slope of the ap where the upward motion in the atmosphere is largest uplift occurs upstream of the barrier affecting the precipitation distribution over sea the effect of the barrier on the precipitation distribution over the bellingshausen sea might have important implications for the ocean circulation in this region the mean precipitation over the grounded ice of the ap 1 20 m water eq yr 1 is 6 times larger than the mean value over all the grounded ice of antarctica our estimates for the surface sublimation and wind transport of snow over the grounding line toward the sea are 9 and 6 1 of the precipitation respectively in situ data of the wind distribution at three coastal sites located on the northern eastern and western sides of the ap are used to evaluate the modeled wind field which is important for the snow drift calculations for two of the three sites considered the prevailing wind direction and bimodal wind distribution are correctly represented by the model the calculated distribution of accumulation and ablation due to snow drift shows a complex pattern the wind removes snow from the spine of the ap where the near surface flow field diverges whereas deposition occurs mainly on the eastern slopes where the near surface flow field converges an intercomparison between two 7 year integrations at different horizontal resolution x 14 km and x 55 km shows that the precipitation on the northwestern slope is very sensitive to the model resolution in the x 14 km integration precipitation on the northwestern slope is higher than in x 55 km because of higher vertical velocities resulting in a 35 increase in average precipitation over the grounded ice of the ap

impact generated carbonate melts evidence from the haughton structure canada evidence is presented for the melting of dolomite rich target rocks during formation of the 24 km diameter 23 ma haughton impact structure on devon island in the canadian high arctic field studies and analytical scanning electron microscopy reveal that the s 200 m thick crater fill deposit which currently covers an v60 km 2 area in the center of the structure comprises fragmented target rocks set within a carbonate silicate matrix the silicate component of the matrix consists of si al mg rich glass the carbonate component is microcrystalline calcite containing up to a few wt si and al the calcite also forms spherules and globules within the silicate glass with which it develops microtextures indicative of liquid immiscibility dolomite clasts exhibit evidence of assimilation and may show calcite and rare dolomite overgrowths some clasts are penetrated by calcite and silicate injections along with the carbonate silicate glass textures the presence of pigeonite and spinifex textured diopside suggests that the matrix to the crater fill deposit was originally molten and was rapidly cooled this indicates that the impact event that generated haughton caused fusion of the predominantly dolomitic target rocks it appears that the ca mg component of the dolomite may have dissociated with mg entering the silicate melt phase while the ca component formed a caco3 dominant melt the silicates were derived by the fusion of lower paleozoic sandstones siltstones shales and impure dolomites evidence for melting is corroborated by a review of theoretical and experimental work which shows that caco3 melts at s 10 gpa and s 2000 k instead of dissociating to release co2 this work indicates that carbonate rich sedimentary targets may also undergo impact melting and that the volume of co2 released into the atmosphere during such events may be considerably less than previously estimated fl 2001 elsevier science b v all rights reserved

granulite belts of central india with special reference to the bhopalpatnam granulite belt significance in crustal evolution and implications for columbia supercontinent abstract the central indian collage incorporates the following major granulite belts 1 the balaghat bhandara granulite belt bbg 2 the ramakona katangi granulite belt rkg 3 the chhatuabhavna granulite cbg of bilaspur raigarh belt 4 the makrohar granulite belt mgb of mahakoshal supracrustals 5 the kondagaon granulite belt kggb 6 the bhopalpatnam granulite belt bgb 7 the konta granulite belt ktgb and 8 the karimnagar granulite belt kngb of the east dharwar craton edc we briefly synthesize the general geologic petrologic and geochronologic features of these belts and explain the precambrian crustal evolution in central india on the basis of the available data a collisional relationship between bastar craton and the edc during the paleo mesoproterozoic is reiterated as proposed by the earlier workers the tectonic evolution of only few of the orogenic belts bgb in particular of central india is related to columbia

geochemical study on a well in the western canada basin relation of the aromatic distribution pattern to maturity of organic matter abstract thirty one rock samples from a western canada basin well have been analysed for aromatics using glass capillary gas chromatography with simultaneous flame ionization and sulfur selective flame photometric detection a uniform aromatic distribution pattern with a marked predominance of di and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising cretaceous and jurassic sediments the very high relative abundance of sulfur aromatics at two narrow intervals in the triassic and mississippian is attributed to a major change in facies gradual changes with increasing depth have been observed for a series of compound ratios which had been calculated from the isomers of methyl and dimethylphenanthrene and their parent compounds these changes reflect the increasing thermal maturation of the sedimentary organic matter a methylphenanthrene index mpi has been introduced which exhibited a very good correlation with vitrinite reflectance data the mpi is the first maturity parameter which is based on a series of aromatic hydrocarbons this hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity e g vitrinite reflectance of source rocks

groundwater helium an indicator of active tectonic regions along narmada river central india abstract results of a survey of dissolved helium fluoride and electrical conductivity in groundwater from across the main stem of the narmada river between bharuch in the west and amarkantak in the east are reported this survey was undertaken to identify active tectonic regions based on locations of high helium concentrations interpreted as indicative of upward migration of deep fluids existence of deep fluids in this region has been hypothesised earlier based on various geophysical studies in the narmada rift basin a major tectonic feature in central india samples with high helium concentration are clustered in two broad regions with known intersecting faults indicating the possibility of plumes with high helium concentration being injected into shallower groundwater in these regions facilitated by these faults and fractures locations of groundwater samples having excess fluoride remarkably correspond to these two clusters of excess helium this suggests a possible commonality between the causal factor of excess helium and higher fluoride in groundwater which needs to be further investigated

estimating the return times of great himalayan earthquakes in eastern nepal evidence from the patu and bardibas strands of the main frontal thrust the return times of large himalayan earthquakes are poorly constrained despite historical devastation of cities along the mountain range definitive links between events and specific segments of the main frontal thrust mft are not established and paleoseismological records have not documented the occurrence of several similar events at the same location in east central nepal however recently discovered primary surface ruptures of that megathrust in the a d 1255 and 1934 earthquakes are associated with flights of tectonically uplifted terraces we present here a refined longer slip history of the mft s two overlapping strands patu and bardibas thrusts in that region based on updated geomorphic neotectonic mapping of active faulting two 1 3 km long shallow seismic profiles and logging of two river cut cliffs three paleoseismological trenches and several pits with constraints from 74 detrital charcoals and 14 cosmogenic nuclide ages the amount of hanging wall uplift on the patu thrust since 3650 450 years requires three more events than the two aforementioned the uplift rate 8 5 1 5mm yr thrust dip 25 5 n and apparent characteristic behavior imply 12 17 5m of slip per event on the bardibas thrust discrete pulses of colluvial deposition resulting from the coseismic growth of a flexural fold scarp suggest the occurrence of six or seven paleo earthquakes in the last 4500 50 years the coeval rupture of both strands during great himalayan earthquakes implies that in eastern nepal the late holocene return times of such earthquakes probably ranged between 750 140 and 870 350 years

charnockite geobarometers based on coexisting garnet pyroxene plagioclase quartz numerous geothermometers based on compositions of coexisting minerals have been calibrated experimentally or theoretically during the past 10 yr in contrast few continuous reaction geobarometers exist which have had wide application one based on the reaction of cordierite to garnet sillimanite and quartz is limited by a relatively narrow pressure range of application and also by conflicting calibrations1 2 because the mixing relations of mg and fe and the role of h2o in cordierite3 are not understood another successful barometer uses the assemblage garnet plagioclase al2sio5 and quartz4 5 continuous geobarometers based on the reaction of orthofer rosilite to fayalite plus quartz6 and on the aluminium content of enstatite in equilibrium with garnet7 have been used to a lesser extent the former barometer is limited by rarity of the requisite assemblage and the latter by uncertain experimental calibration for crustal rocks we calibrate here two mineralogical geobarometers from measured thermodynamic data the participating minerals pyroxenes garnet plagioclase and quartz are frequently associated in high grade metamorphic rocks calculation of pressures for several terrains show that the geobarometers yield reasonable and consistent results for the entire range of crustal pressures

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

highly heterogeneous precambrian basement under the central deccan traps india direct evidence from xenoliths in dykes abstract crustal or mantle xenoliths are not common in evolved tholeiitic flood basalts that cover huge areas of the precambrian shields yet the occasional occurrences provide the most direct and unequivocal evidence on basement composition few xenolith occurrences are known from the deccan traps india and inferences about the deccan basement have necessarily depended on geophysical studies and geochemistry of deccan lavas and intrusions here we report two basalt dykes rajmane and talwade dykes from the central deccan traps that are extremely rich in crustal xenoliths of great lithological variety gneisses quartzites granite mylonite felsic granulite carbonate rock tuff because the dykes are parallel and only 4 km apart and only a few kilometres long the xenoliths provide clear evidence for high small scale lithological heterogeneity and strong tectonic deformation in the precambrian indian crust beneath measured 87sr 86sr ratios in the xenoliths range from 0 70935 carbonate to 0 78479 granite mylonite the rajmane dyke sampled away from any of the xenoliths shows a present day 87sr 86sr ratio of 0 70465 and initial at 66 ma ratio of 0 70445 the dyke is subalkalic and fairly evolved mg no 44 1 and broadly similar in its sr isotopic and elemental composition to some of the lavas of the mahabaleshwar formation the xenoliths are comparable lithologically and geochemically to basement rocks from the archaean dharwar craton forming much of southern india as several lines of evidence suggest the dharwar craton may extend at least 350 400 km north under the deccan lava cover this is significant for precambrian crustal evolution of india besides continental reconstructions

source rupture process of the tecoman colima mexico earthquake of 22 january 2003 determined by joint inversion of teleseismic body wave and near source data the spatial and temporal slip distribution of the tecoman colima mexico earthquake is estimated from near source strong motion and teleseismic body wave data to perform a stable inversion we applied smoothing constraints and determined their optimal relative weights on the observed data using an optimized akaike s bayesian information criterion abic the source parameters are as follows strike dip slip 300 20 93 seismic moment m 2 3 1020 n m source duration 30 sec along strike distance 35 km along dip distance 70 km we found that the rupture process can be divided into three stages the rupture nucleated near the hypocenter stage i then it broke the first asperity centering about 15 km southwest from the epicenter stage ii and the rupture propagated to the northeast and the second asperity was broken stage iii we also estimated the shear stress change due to the rupture process of the mainshock on and around the major fault zone it appears that one cluster of aftershocks for the first 5 days which took place in and adjacent to the zones of stress increased due to the fault rupture during the mainshock but overall correlation between the aftershock location and the stress pattern is not clear manuscript received 14 may 2003

haughton impact structure structural and morphological aspects haughton is a complex meteorite impact structure of tertiary age on devon island in the canadian arctic the 20 5 km diameter site was formed in essentially flat lying paleozoic carbonates roughly 1700 m in thickness overlying precambrian gneisses the structure comprises three concentric rings surrounding a central basin with interior peaks the outer ring diameter 20 5 km is an annulus of peaks separating the allen bay dolomites of the regional plateau from the same unit that has been downdropped towards the crater interior along a series of circumferential faults the middle ring of peaks diameter 14 15 km comprises both faulted allen bay dolomites and blocks of the underlying bay fiord formation uplifted 250 m hills of the inner elliptical ring 3 5 5 5 km in diameter are also formed from bay fiord formation and the underlying eleanor river formation brought up 600 m an interconnected series of normal faults occupies most of the annulus between the inner and outer rings within the central b

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

origin of oils in helez region israel implications for exploration in the eastern mediterranean in this case study of oils in the helez brur kokhav oil field and nearby shows organic geochemical criteria were integrated with geologic data to identify the source rocks and migration paths of the oils the data presented which include terpenoid biomarkers isoprenoid ratios carbon preference indexes and stable carbon isotopes clearly indicate that the oils in helez brur kokhav ashdod and ashqelon wells are genetically related and were derived from the same source rocks rock extracts bitumen from the lower cretaceous gevaram shales differ geochemically from the oils whereas those of the jurassic barnea formation are similar some barnea samples are apparently stained by oil whereas others are indigenous rock extracts therefore we concluded that the barne samples represent both the rock type from which the oils were derived and the migration path the maturity of the oils determined by c29 20s 20r sterane ratio about 0 85 ro equivalent as compared with the maturation configuration in the area implies generation and expulsion from the barnea rock type at a depth of about 4 500 5 500 m the impervious blanket of gevaram shales covering the jurassic barnea limestone and the westward inclination of this unconformable boundary funneled the oils updip eastward the oils were trapped around the zero isopach line of the gevaram shales in jurassic and lower cretaceous rocks under a combination of stratigraphic and structural controls consequently further oil exploration should focus on 1 delineating the gevaram zero isopach line and identifying adjacent traps and 2 identifying barriers on the migration path below the gevaram seal

complex craters relationship of stratigraphy and rings to impact conditions one of the key issues associated with the understanding of large scale impacts is how the observable complex crater structural features e g central peaks and pits flat floors ring shaped ridges and depressions stratigraphic modifications and faults relate to the impactor s parameters e g radius velocity and density and the nonobservable transient crater measures e g depth of penetration and diameter at maximum penetration we have numerically modeled large scale impacts on planets for a range of impactor parameters gravity and planetary material strengths from these we found that the collapse of the transient cavity results in the development of a tall transient central peak that oscillates and drives surface waves that are arrested by the balance between gravitational forces and planetary strength to produce a wide range of the observed surface features in addition we found that the underlying stratigraphy is inverted outside of the transient cavity diameter overturned flap region but not inside this change in stratigraphy is observable by remote sensing drilling seismic imaging and gravity mapping techniques we used the above results to develop scaling laws and to make estimates of the impact parameters for the chicxulub impact and also compared the calculated stratigraphic profile with the internal structure model developed by hildebrand et al 1998 using gravity seismic and other field data for a stratigraphy rotation diameter of 90 km the maximum depth of penetration is 43 km the impactor diameter was also calculated from the scaling relationships we get for a 2 7 g cm 3 asteroid impacting at 20 km s or a 1 0 g cm 3 comet impacting at 40 km s an impactor diameter of 13 km and for a comet impacting at 60 km s an impactor diameter of 10 km

biomarker determination as a provenance tool for detrital carbonate events heinrich events fingerprinting quaternary glacial sources into baffin bay sedimentary deposits associated with heinrich events are anomalously rich in detrital carbonate off hudson strait the dominant carbonate is calcite whereas at distal sites in the north atlantic dolomite is dominant more diagnostic a significant source for dolomite is its outcrop at the northern end of baffin bay where major ice streams from the laurentide innuitian and greenland ice sheets converged the provenance of samples containing detrital carbonate mainly dolomite from a core in baffin bay has been confirmed using organic geochemistry to distinguish between alternative sources based upon the thermal maturity of organic matter in carbonates of the source region the core contained five distinct carbonate units dating between 14 and 51 cal ka bp and indicates significant ice stream instability associated with iceberg calving and significant volumes of meltwater the exact temporal relationship to heinrich events is not yet clear a long mid wisconsin interval 38 to 22 cal ka bp devoid of detrital carbonate suggests a major reduction in ice extent at high northern latitudes the core samples yield thermally sensitive biomarker ratios comparable to those from laurentian carbonates in the canadian arctic islands but unlike those from north greenland identifying the former region as their provenance however a late holocene sample from off newfoundland shows a stronger affinity with greenland 2007 elsevier b v all rights reserved

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

coseismic slip distribution of the 2008 mw 7 9 wenchuan earthquake from joint inversion of gps and insar data on 12 may 2008 the m w 7 9 wenchuan earthquake occurred at the eastern margin of the tibetan plateau along the longmen shan fault based on previous geological and geophysical studies and offset maps from advanced land observing satellite phased array type l band synthetic aperture radar alos palsar data a layered crustal structure and a five segment rupture model are established to study the coseismic deformation of this event using the constrained least squares method a preferred coseismic slip model is derived from global positioning system gps and interferometric synthetic aperture radar insar data in particular the helmert variance component estimation hvce method is used to determine the relative weight ratio between the gps and insar data in contrast to the initial weight ratio 0 752 0 246 0 002 among three type observations gps horizontal gps vertical and insar los displacement the final optimal weight ratio is found to be 0 473 0 279 0 248 and the overall root mean square rms misfit for all three datasets decreases from 9 15 cm without hvce to 5 46 cm with hvce as revealed by the preferred slip the slip changes obviously along the strike direction from southwest to northeast and exhibits four asperities close to hongkou town yuejiashan town beichuan county and nanba town respectively two major asperities are located on the hongkou and beichuan segments with the maximum slip close to 10 m the slips of hongkou yuejiashan and beichuan segments are dominated by the thrust movement with a significant right lateral strike slip component the qingchuan segment experiences a dominant right lateral strike slip with an average magnitude of 1 2 m most of the slip asperities are shallower than 10 km depth except for the southwest part near the hypocenter where the slip may exceed 20 km the seismic moment of the wenchuan earthquake is 8 19 1020 n m m w 7 91 based on the layered crust model which is slightly larger than that using a corresponding homogeneous crust model m w 7 87

structure of the deep crust beneath the central indian tectonic zone an integration of geophysical and xenolith data abstract xenoliths of garnet granulite and crustal eclogites in alkaline dykes from the northern margin of the dharwar craton suggest that the deep crust beneath this region is dominated by mafic granulite the granulites consist primarily of clinopyroxene orthopyroxene garnet and plagioclase clinopyroxene from most garnet bearing lithologies is eclogitic with jd ts 0 5 the jd component varies from 5 to 8 garnets from the granulites are similar to those in crustal eclogites whereas the ones from pyroxenites are akin to those in kimberlites composite xenoliths are indicative of interstratification of the lower crust by ultramafic rocks represented by pyroxenites and websterites that display prominent high density reflectors in deep seismic sounding profiles they represent cumulates in relict magma chambers and are expressed as conductors in magnetotelluric transects thermobarometric estimates for granulite xenoliths are 740 1094 c 0 71 1 3 gpa equivalent to depths of 20 40 km whereas those for pyroxenite xenoliths are 726 1042 c 0 57 1 05 gpa these provide for the first time a spatial context to these rock types suggesting derivation from lower crustal depths the lower crustal rocks beneath the central indian tectonic zone are near to their melting point as is evident from the anomalously high geothermal gradient due to which they show lower vps than those characteristic of typical garnet granulites the deep crust has undergone thickening both due to crustal inflation and under and intra plating beyond its original pre rift thickness overcompensating for the crustal thinning due to extension lateral flow of the lower crust has also contributed to crustal thickening in addition to under and intra plating transport of midcrustal rocks to the surface along ductile shear zones has caused additional crustal modification

geodetic model of the 2015 april 25 mw 7 8 gorkha nepal earthquake and mw 7 3 aftershock estimated from insar and gps data

source process of the 1995 kobe earthquake determination of spatio temporal slip distribution by bayesian modeling the kobe hyogo ken nanbu earthquake ms 6 8 occurred on 16 january 1995 in western japan bringing about a tremendous disaster we constructed its source model by determining a spatio temporal slip distribution using strong motion seismograms recorded at a number of stations near the hypocenter the source area is expressed using both a rough and a detailed subfault discretization system and a source time function expanded with a finite number of basis functions at each subfault is determined to perform stable inversions with many parameters we construct a bayesian model with unknown hyperparameters incorporating prior constraints on the smoothness of spatio temporal slip distribution in the observation equation using akaike s bayesian information criterion abic the optimal set of hyperparameters are objectively determined from observed data which enables us to uniquely determine a spatio temporal slip distribution after rough analysis in which the actual rupture area is estimated as 45 20 km we carried out a detailed analysis with a finer subfault discretization system 5 5 km in our final source model most of the slip exists beneath awaji island and the rupture below the city of kobe where the damage was most serious is relatively smaller the large slips of about 2 m in the shallowest subfaults located southwest of the hypocenter correspond to the surface offsets observed along the nojima fault the overall focal mechanism of the source is right lateral strike slip with a small thrust component while total seismic moment is 2 0 1019 nm the source time functions at shallow subfaults show a longer duration than those at deeper ones being hypothesized to represent a possible combined effect of low rupture propagation velocity and varying friction behavior in shallow regions of crust

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

sulfate minerals and organic compounds on mars strong evidence for evaporitic sulfate minerals such as gypsum and jarosite has recently been found on mars although organic molecules are often codeposited with terrestrial evaporitic minerals there have been no systematic investigations of organic components in sulfate minerals we report here the detection of organic material including amino acids and their amine degradation products in ancient terrestrial sulfate minerals amino acids and amines appear to be preserved for geologically long periods in sulfate mineral matrices this suggests that sulfate minerals should be prime targets in the search for organic compounds including those of biological origin on mars

dating of a regional hydrothermal system induced by the 1850 ma sudbury impact event new u pb geochronologic data from the sudbury structure directly link extensive hydrothermal activity in crater fill breccias with the 1850 ma impact event and constrain complex impact induced processes to 4 m y semiconformable alteration of breccias in the onaping formation includes silicification albitization chloritization calcitization and complex feldspathization which directly underlies zn cu pb ore deposits geochronologic data demonstrate a middle to lower crustal source for the crater fill deposit that was subsequently affected by the hydrothermal event at 1848 4 3 8 1 8 ma these and other data confirm that the crater fill breccia hydrothermal system sudbury igneous complex and its sublayer ni ore bearing units were emplaced as a result of impact the ages of events associated with the sudbury structure are now more closely constrained than in any other meteorite impact structure

a method for the joint inversion of geodetic and seismic waveform data using abic application to the 1997 manyi tibet earthquake geodetic imaging data and seismicwaveformdata have complementary strengthswhen considering the modelling of earthquakes the former particularly modern space geodetic techniques such as interferometric synthetic aperture radar insar permit high spatial density of observation and thus fine resolution of the spatial pattern of fault slip the latter provide precise and accurate timing information and thus the ability to resolve how that fault slip varies over time in order to harness these complementary strengths we propose a method through which the two data types can be combined in a joint inverse model for the evolution of slip on a specified fault geometry we present here a derivation of akaike s bayesian information criterion abic for the joint inversion of multiple data sets that explicitly deals with the problem of objectively estimating the relative weighting between data sets as well as the optimal influence of model smoothness constraints in space and time we demonstrate our abic inversion scheme by inverting insar displacements and teleseismic waveform data for the 1997 manyi tibet earthquake we test using a simplified fault geometry three cases insar data inverted alone vertical component teleseismic broad band waveform data inverted alone and a joint inversion of both data sets the insar only model and seismic only model differ significantly in the distribution of slip on the fault plane that they predict the joint inversion model however has not only a similar distribution of slip and fit to the insar data in the insar only model suggesting that those data provide the stronger control on the pattern of slip but is also able to fit the seismic data at a minimal degradation of fit when compared with the seismic only model the rupture history of the preferred joint inversion model indicates bilateral rupture for the first 20 s of the earthquake followed by a further 25 s of westward unilateral rupture afterwards with slip peaking at 7m in the upper 6 km of the fault this joint inversion approach is thus shown to be a viable method for the study of large shallow continental earthquakes and may be of particular benefit in cases where near field seismic observations are not available the authors 2014 published by oxford university press on behalf of the royal astronomical society

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

supercycle at the ecuadorian subduction zone revealed after the 2016 pedernales earthquake large earthquakes are usually assumed to release all of the strain accumulated since the previous event implying a reduced seismic hazard after them however long records of seismic history at several subduction zones suggest supercycle behaviour where centuries long accumulated strain is released through clustered large earthquakes resulting in an extended period of enhanced seismic hazard here we combine historical seismology results present day geodesy data and dense local observations of the recent mw 7 8 2016 pedernales earthquake to reconstruct the strain budget at the ecuador subduction zone since the great 1906 earthquake we show that the pedernales earthquake involved the successive rupture of two patches on the plate interface that were locked prior to the earthquake and most probably overlaps the area already ruptured in 1942 by a similar earthquake however we find that coseismic slip in 2016 exceeds the deficit accumulated since 1942 the seismic moment of every large earthquake during the twentieth century further exceeds the moment deficit accumulated since 1906 these results together with the seismic quiescence before 1906 highlighted by historical records and marine palaeoseismology argue for an earthquake supercycle at the ecuador colombia margin this behaviour which has led to an enhanced seismic hazard for 110 years is possibly still going on and may apply to other subduction zones that recently experienced a great earthquake large earthquakes are often assumed to reset the seismic hazard of a region analysis of recent and historical seismicity in ecuador suggests that this region may experience clusters of large earthquakes and extended periods of high seismic hazard

source parameters and seismogenic structure of the 2017 mw 6 5 mainling earthquake in the eastern himalayan syntaxis tibet china abstract on november 18 2017 a moderate to strong earthquake occurred at mainling county nyingchi city tibet which was the first moderate earthquake in the eastern himalayan syntaxis ehs region in the past five decades to gain a better understanding of the rupture mechanism and seismogenic structure of this earthquake the rupture process through a joint inversion of far field body wave data and interferometric synthetic aperture radar insar data was present in this study in addition the three dimensional 3d crustal density structure of the ehs area was inverted using the gravity data according to the joint inversion results of the rupture process the mainling earthquake lasted approximately 18 s and released energy of 8 32 1018 n m mw 6 5 the rupture was dominated by the thrust movement the maximum slip was approximately 0 83 m and the slip distribution was mainly concentrated at depths of 5 15 km in two patches according to the results of gravity inversion the density structure has good constraints on the source depth the mainling earthquake s epicenter was located near the junction of high and low density areas its rupture extended over nearly 40 km in the ese direction along the fault strike in addition the density structure also clearly shows a uniform density anomaly in this region which may be beneficial to the release of seismic energy the clockwise deformation of the erosion effect in the ehs superimposed over the uplifting and thrusting motion of the namche barwa nb area and the northward indentation effect of the indian block all of these processes have strengthened folding deformation and the accumulated of stress and an abnormally high density concentration within the nb area the sudden release of accumulated stress led to the occurrence of the mainling earthquake these are the seismogenic structure of the nb zone the regional structure and material characteristics indicates that the dongjiu segment of the dongjiu mainling shear zones dmsz lies in the density anomaly gradient belt with high density low velocity and high resistance media on its northeastern side which benefits the stress accumulation the earthquake activity and risks of this segment merits further attention

joint inversion of strong motion teleseismic geodetic and tsunami datasets for the rupture process of the 2011 tohoku earthquake 1 the 2011 tohoku earthquake was observed by dense strong motion teleseismic geodetic and tsunami networks we first inverted each of the datasets obtained by the networks separately for the rupture process of the earthquake we then performed checkerboard resolution tests for assessing the resolving power of these datasets in order to overcome the limited resolutions of the separate inversions and differences in their results we performed a quadruple joint inversion of all these data to determine a source model most suitable for explaining all the datasets in the obtained source model the maximum coseismic slip was approximately 35 m and the total seismic moment was calculated to be 4 2 1022 nm which yielded mw 9 0 the main rupture propagated not only in the strike direction but also in the dip direction and included both the deep area called the miyagi oki region and the compact shallow area near the japan trench

simultaneous inversion of waveform and geodetic data for the rupture process of the 1984 naganoken seibu japan earthquake summary a simultaneous inversion method of strong motion seismograms and geodetic data for inferring earthquake rupture process was developed we assumed a source model composed of many point sources of which slip vectors and rupture times are unknown parameters in addition to observed data we introduced smoothing constraints to determine many parameters without instability since the leastsquares solution depends on the relative weights of the smoothing constraints to a data misfit function we determined their values by minimizing akaike s bayesian information criterion abic by using abic we can objectively choose a unique model this inversion method was applied to the naganoken seibu japan earthquake of 1984 dividing a 15 x 10 km fault into 150 subfaults we obtained the minimum abic model with a seismic moment of 2 7 x los dyne cm this model has a slip peak in the eastern and shallow area of the assumed fault the high slip area is just under the areas where thrown out boulders were found by umeda et al 1987 and iio yoshioka 1988 comparing the aftershock distribution with the estimated slip distribution we found that the high slip area had few aftershocks this suggests that aftershocks are caused by the stress generated in the marginal region around the main shock slip the inversion analysis also revealed that there was a slight change in slip angle during the earthquake the high slip area has some amount of dip slip component while the slips in the other areas are almost purely right lateral

himalayan megathrust geometry and relation to topography revealed by the gorkha earthquake the himalayan mountain range has been the locus of some of the largest continental earthquakes including the 2015 magnitude 7 8 gorkha earthquake competing hypotheses suggest that himalayan topography is sustained and plate convergence is accommodated either predominantly on the main plate boundary fault or more broadly across multiple smaller thrust faults here we use geodetic measurements of surface displacement to show that the gorkha earthquake ruptured the main himalayan thrust fault the earthquake generated about 1 m of uplift in the kathmandu basin yet caused the high himalaya farther north to subside by about 0 6 m we use the geodetic data combined with geologic geomorphological and geophysical analyses to constrain the geometry of the main himalayan thrust in the kathmandu area structural analyses together with interseismic and coseismic displacements are best explained by a steep shallow thrust fault flattening at depth between 5 and 15 km and connecting to a mid crustal steeper thrust we suggest that present day convergence across the himalaya is mostly accommodated by this fault no significant motion on smaller thrust faults is required furthermore given that the gorkha earthquake caused the high himalayan mountains to subside and that our fault geometry explains measured interseismic displacements we propose that growth of himalayan topography may largely occur during the ongoing post seismic phase

evidence from borehole samples for the role of accessory minerals in lower crustal conductivity the high electrical conductivity of the lower continental crust as inferred from geophysical measurements1 has defied a simple explanation both pore saturating brines2 and interconnected carbon films3 5 have been proposed as conducting pathways but their relative importance remains uncertain and may vary from place to place6 so far attempts to address this question in the laboratory have had to rely on samples of metamorphic rock collected from surface exposures7 10 although these rocks almost certainly originated in the lower crust chemical alteration during their transport to and residence at the surface is likely to have affected their conducting properties here we report conductivity data for pristine crustal rocks recovered from depths of up to 4 6 km in the ktb boreholes in southern germany our results show that the electrical conductivity of accessory phases such as fe ti oxides and sulphides can enhance or even surpass the high conductivity produced by saline fluids

confirmation of the double asperity model for the 2016 mw 6 6 akto earthquake nw china by seismic and insar data abstract on november 25 2016 an mw 6 6 earthquake struck akto a county in the xinjiang autonomous region of china this earthquake nucleated on the dextral steep dip strike slip segment of the muji fault in the western tibetan plateau in this study we conducted a joint inversion using a higher number of data than in previous works i e teleseismic p and sh waveform near field seismic waveform and coseismic insar displacement data in order to analyze the spatiotemporal rupture process of this seismic event the results of the joint inversion showed that the event consisted in a primarily unilateral rupture toward east southeast along the muji fault and that 90 of the scalar seismic moment was released in the first 18 s moreover we confirmed the occurrence of two major asperities the first one located right next to the hypocenter and the second one 30 35 km east of the hypocenter the first asperity was found at a deeper depth than the second asperity additionally it was larger and had a smaller slip the results of the coulomb stress change analysis suggested that the rupture of the first asperity triggered the rupture of the second one the heterogeneity of the on fault slip revealed the heterogeneity of the inherent strength and stress of the muji fault moreover the clear slip deficit area characterized by a high coulomb stress might indicate a high seismic risk

the effects of meteorite impacts on the availability of bioessential elements for endolithic organisms meteorite impacts one of the most ubiquitous processes in the solar system have the ability to destroy as well as create habitats for life the impact process can increase the translucency and porosity of the target substrate as well as mobilize biologically relevant elements within the substrate for endolithic organisms this process has important implications especially in extreme environments where they are forced to seek refuge in the interior of rocks here we show that unshocked target rocks and rocks that have experienced pressures up to about 80 gpa from the haughton impact structure devon island canada possess a small but discernible change in bulk chemistry within the major oxide analysis however changes in the distribution of elements did occur with increasing shock level for both the sedimentary and crystalline target both the crystalline and sedimentary target rocks contain significant amounts of glasses at higher shock levels up to about 95 by volume which would improve the availability of these elements to potential microbial endoliths as glasses are more easily dissolved by organic acids the implication that impact events do not impoverish their capacity to serve as a substrate through volatilization is important with respect to analogous impact structures on mars after the deleterious effects of the direct meteorite impact any microorganisms on mars would have benefited from the input of heat the mobilization of a possible frozen groundwater system as well as increased translucency porosity and trace nutrient availability of the target substrate

resistivity structure of the central indian tectonic zone citz from multiple magnetotelluric mt profiles and tectonic implications the central indian tectonic zone citz is a major tectonic feature extending across the indian subcontinent it was formed in the paleoproterozoic when the bastar craton and the bundelkhand craton were sutured together this region is recognized in the geological record as a persistent zone of weakness with many tectonothermal events occurring over geologic time the weakness of this region may have caused the late cretaceous early tertiary deccan volcanism to have been localized in the citz the zone is still tectonically active as evidenced by sustained levels of seismic activity this paper presents the first systematic investigation of the resistivity structure of the citz using multiple magnetotelluric mt transects two dimensional 2d resistivity models were generated for five north south profiles that cross the citz and encompass an area of 60 000 km2 the models were based on the joint inversion of transverse electric te transverse magnetic tm and tipper hz data all the profiles showed a low resistive 10 80 m middle to lower crust beneath the citz with a crustal conductance of 300 800 s the presence of an interconnected fluid phase and or hydrous metallic minerals appears to be the most likely explanation for the elevated conductivity that is observed beneath the citz the presence of fluids is significant because it may indicate the cause of persistent weakness at crustal depths a northward dip of both the crustal conductive layer and coincident seismic reflections favor a northward polarity of the subduction process associated with the formation of the citz

the transfer of organic signatures from bedrock to sediment abstract a case study in the canadian arctic demonstrates how an organic geochemical signature in the regional bedrock can be transferred by erosion and redeposition to younger geological formations and surface sediments the hydrocarbon composition recorded in laurentian lower palaeozoic carbonate bedrock was incorporated into overlying miocene and quaternary formations and modern mass waste alluvium snow ice and proglacial deposits and further distant in ice rafted detritus the retention of the original geological organic signature is reflected in consistent thermal maturities hopane ratios and environmental indicators sterane distributions in the modern sediments the geological signature is variably mixed with a modern microbial organic signature reflected in high values of carbon preference index and diploptene these data show that hydrocarbon occurrences in bedrock may be detected by the analysis of surface detritus especially in carbonate terrains however they also indicate that environmental signatures may be misleading if they are inherited from older geological units

organic geochemistry of impactites from the haughton impact structure devon island nunavut canada organic matter in impactites from the 24 km wide and 39 ma old haughton impact structure canadian high arctic is a mixture of fossil and modern biological components the fossil component represents a conventional oil that was generated from lower palaeozoic marine source material before impact and permeates bedrock dolomites biomarker maturity parameters record the thermal effect of the mid tertiary impact maturity influenced sterane rearranged hopanoid and triaromatic steroid ratios all increase towards the centre of the impact structure where thermal alteration was greatest the heating was probably dominated by an impact related hydrothermal system as such systems last long enough for kinetically based thermal alteration to occur kinetically related biomarker data suggest that the hydrothermal heating lasted for c 5000 years biomarkers are also preserved in dolomite clasts within impact melt breccia and indicate strong thermal alteration modern biological contamination of the rocks is responsible for the superposition of two geochemical signatures which could be cyanobacteria non marine algae or higher plant matter onto the fossil component but they can be recognized and distinguished the data show that the impact structure system holds a record of both the pre impact organic signature and the thermal signature of the impact and thereby indicates that organic geochemistry is a valuable tool in documenting the response of rocks to impacts

the central india tectonic zone a geophysical perspective on continental amalgamation along a mesoproterozoic suture abstract the central india tectonic zone citz is a prominent divide and a major suture zone between the north indian and south indian crustal blocks the resistive upper crust as modeled in the magnetotelluric data from citz suggests a dominant tonalite trdondhjemite granodiorite composition associated with an accretionary complex characterized by mainly felsic rock components the highly conductive bodies in this zone might represent mafic ultramafic layered intrusives derived from a deeper reservoir of underplated basaltic magma related to the formation of the cretaceous deccan flood basalts the uniformly thick mafic lower crust below the cratons on both sides of the suture is interpreted as the accreted remnants of archaean and paleoproterozoic subducted slabs we redefine the nature of deep faults traversing the citz which were described as steep and penetrating the moho by previous workers and classify them as listric faults with gentle dips at depth seismic reflection data from the eastern side of the suture suggest a northwestward subduction of the bhandara craton reflection data from the central part of the citz show northerly dip in the southern part suggesting northward subduction of the dharwar craton however an opposite trend is observed in the northern part of the suture with a southward dip of the bundelkhand craton based on these features and in conjunction with existing magnetotelluric models we propose a double sided subduction history along the citz this would be similar to the ongoing subduction accretion process in the western pacific region which possibly led to the development of paired collision type and pacific type orogens one important feature is the domal structure along the central part of the suture with a thick felsic crust occurring between mafic and intermediate crust the high resistivity felsic domain suggests underplated sediments felsic crust that would have caused the doming our model also accounts for the extrusion of regional metamorphic belts at the orogenic core and the occurrence of high pressure ultrahigh temperature paired metamorphic belts within the suture

rupture process of the 2016 mw 7 8 ecuador earthquake from joint inversion of insar data and teleseismic p waveforms abstract the 2016 ecuador earthquake ruptured the ecuador colombia subduction interface where several historic megathrust earthquakes had occurred in order to determine a detailed rupture model interferometric synthetic aperture radar insar images and teleseismic data sets were objectively weighted by using a modified akaika s bayesian information criterion abic method to jointly invert for the rupture process of the earthquake in modeling the rupture process a constrained waveform length method unlike the traditional subjective selected waveform length method was used since the lengths of inverted waveforms were strictly constrained by the rupture velocity and rise time the slip duration time the optimal rupture velocity and rise time of the earthquake were estimated from grid search which were determined to be 2 0 km s and 20 s respectively the inverted model shows that the event is dominated by thrust movement and the released moment is 5 75 1020 nm mw 7 77 the slip distribution extends southward along the ecuador coast line in an elongated stripe at a depth between 10 and 25 km the slip model is composed of two asperities and slipped over 4 m the source time function is approximate 80 s that separated into two segments corresponding to the two asperities the small magnitude of the slip occurred in the updip section of the fault plane resulted in small tsunami waves that were verified by observations near the coast we suggest a possible situation that the rupture zone of the 2016 earthquake is likely not overlapped with that of the 1942 earthquake

constraints on early events in martian history as derived from the cratering record the shapes and densities of crater size frequency distribution curves are used to constrain two major events early in martian history termination of high obliteration rates and viability of the multiple impact origin of the crustal dichotomy distribution curves of fresh craters superposed on uplands intercrater plains and ridged plains display shapes and densities indicative of formation prior to the end of heavy bombardment this observation correlates with other geologic evidence suggesting a major change in the erosional regime following the last major basin size impact i e argrye in addition the multisloped nature of the curves supports the idea that the downturn in the crater size frequency distribution curves reflects the size frequency distribution of the impactors rather than being the result of erosion the crustal dichotomy formed prior to the heavy bombardment intermediate epoch based on distribution curves of knobby terrain if the dichotomy resulted from a single gigantic impact this observation places constraints on when this event happened an alternate theory for dichotomy formation the multiple impact basin idea is questioned since distribution curves of large basins as well as heavy bombardment era units are not represented by a 3 differential power law function this study finds fewer basins missing on mars compare to the moon and mercury than previously reported the area covered by these missing basins is less than that covered the northern plains

radar interferogram filtering for geophysical applications the use of sar interferometry is often impeded by decorrelation from thermal noise temporal change and baseline geometry power spectra of interferograms are typically the sum of a narrow band component combined with broad band noise we describe a new adaptive filtering algorithm that dramatically lowers phase noise improving both measurement accuracy and phase unwrapping while demonstrating graceful degradation in regions of pure noise the performance of the filter is demonstrated with sar data from the ers satellites over the jakobshavns glacier of greenland

waveform inversion using abic for the rupture process of the 1983 hindu kush earthquake abstract an inversion method was developed to infer earthquake rupture process from far field velocity waveforms we devise a source model that has variable slip and variable rupture velocity the fault plane is divided into many subfaults slip amplitude is assumed to be dependent on the subfaults and slip velocity at a point is assumed to be a triangle function of time rupture time is expressed by an interpolation equation using the rupture times at the corners of the subfaults the slip distribution and the rupture front motion are estimated by constrained least squares inversion we incorporate smoothing constraints on slip distribution and on rupture propagation into the observed data the degree of the constraints is controlled by hyperparameters the optimal values of the hyperparameters are determined by minimizing akaike s bayesian information criterion abic under the assumption of abic we can obtain a unique solution with reasonable resolution we apply this inversion method to the hindu kush earthquake of 30 december 1983 with a depth of 212 km we found that the rupture process of this earthquake was composed of two subevents the first subevent occurs near the initiation point of the rupture the centre of the second subevent region is approximately 20 km to the west of the first subevent the released moment of the second subevent is about seven times larger than that of the first subevent

multiarray rupture imaging of the devastating 2015 gorkha nepal earthquake sequence a rapid robust multiarray backprojection method was applied to image the rupture pattern of the 2015 gorkha nepal mw7 8 main shock and its mw7 3 aftershock backprojected teleseismic p wave trains from three regional seismic arrays in europe australia and alaska show that both earthquakes ruptured unilaterally and primarily eastward with rupture speeds potentially decreasing with depth the rupture of the main shock first extended eseward at 3 5 km s over 120 km with later rupture propagation further downdip on the eastern segment at 2 1 km s the aftershock ruptured the fault se of the main shock s ruptured plane it began to rupture updipward for 20 km at a speed around 1 2 km s then it may have accelerated to 3 5 km s for the next 50 km the apparent depth dependent rupture speeds of the two earthquakes may be caused by along dip heterogeneities in fault strength with a higher stress concentration on the updip part of the nepalese main himalayan thrust

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

thermal alteration of organic matter in an impact crater and the duration of postimpact heating the 24 km diameter tertiary haughton impact structure formed in rocks that contained preexisting liquid hydrocarbons biomarker ratios in the hydrocarbons show a consistent pattern of variation in degree of heating across the structure the heating reached a maximum at the crater center and is attributed to hydrothermal activity following impact kinetic modeling suggests a time scale of 5 k y for the heating at a maximum temperature of 210 c the short time scale suggests that in moderate sized craters which are abundant on mars heating is not so extensive that fossil or extant organic matter would be obliterated

evidence for an extensive intrusive component of the deccan large igneous province in the narmada son lineament region india from three dimensional magnetotelluric studies abstract the crustal electrical structure beneath the western segment of narmada son lineament zone in central india has been imaged using magnetotelluric mt data set of 153 stations distributed over a grid 7 8 km site spacing three dimensional modeling of this data set brought out several major crustal conductors with different geometries at different depth levels in the crustal column the conductive features correlating with gravity high anomalies and high seismic velocity zones are interpreted to be mafic ultramafic bodies derived from mantle we infer that these bodies represent the intrusive component of the large igneous province lip of the deccan volcanic episode triggered by the passage of the indian continent over the reunion hot spot during the late cretaceous the disposition and the geometry of the subsurface magmatic bodies which must have served as magma chambers for outpouring of the deccan lavas suggest that they are closely related to the plumbing geometry of the lip of the deccan volcanic episode

new evidence for persistent impact generated hydrothermal activity in the miocene ries impact structure germany the extent of impact generated hydrothermal activity in the 24 km sized ries impact structure has been controversially discussed to date mineralogical and isotopic investigations point to a restriction of hydrothermal activity to the impact melt bearing breccias specifically the crater fill suevite here we present new petrographic geochemical and isotopic data of postimpact carbonate deposits which indicate a hydrothermal activity more extended than previously assumed specifically carbonates of the erbisberg a spring mound located upon the inner crystalline ring of the crater show travertine facies types not seen in any of the previously investigated sublacustrine soda lake spring mounds of the ries basin in particular the streamer carbonates which result from the encrustation of microbial filaments in subaerial spring effluents between 60 and 70 c are characteristic of a hydrothermal origin while much of the primary geochemical and isotopic signatures in the mound carbonates have been obliterated by diagenesis a postimpact calcite vein from brecciated gneiss of the subsurface crater floor revealed a flat rare earth element pattern with a clear positive eu anomaly indicating a hydrothermal fluid convection in the crater basement finally the strontium isotope stratigraphic correlation of the travertine mound with the crater basin succession suggests a hydrothermal activity for about 250 000 yr after the impact which would be much longer than previously assumed

impact of topography on earthquake static slip estimates abstract our understanding of earthquakes is limited by our knowledge and our description of the physics of the earth when solving for subsurface fault slip it is common practice to assume minimum complexity for characteristics such as topography fault geometry and elastic properties these characteristics are rarely accounted for because our knowledge of them is often partial and they can be difficult to include in simulations however topography and bathymetry are known all over the earth s surface and recently developed software packages such as specfem x have simplified the process of including them in calculations here we explore the impact of topography on static slip estimates we also investigate whether the influence of topography can be accounted for with a zeroth order correction which accounts for variations in distance between subfaults and the surface of the domain to this end we analyze the 2015 mw 7 5 gorkha nepal and the 2010 mw 8 8 maule chile earthquakes within a bayesian framework the regions affected by these events represent different types of topography chile which contains both a deep trench and a major orogen the andes has a greater overall elevation range and steeper gradients than nepal where the primary topographic feature is the himalayan mountain range additionally the slip of the continental nepal event is well constrained whereas observations are less informative in a subduction context we show that topography has a non negligible impact on inferred slip models our results suggest that the effect of topography on slip estimates increases with limited observational constraints and high elevation gradients in particular we find that accounting for topography improves slip estimates where topographic gradients are large when topography has a significant impact on slip the zeroth order correction is not sufficient

impact induced hydrothermal activity within the haughton impact structure arctic canada generation of a transient warm wet oasis field studies and analytical scanning electron microscopy indicate that a hydrothermal system was created by the interaction of water with hot impact generated rocks following formation of the 24 km diameter 23 ma haughton impact structure hydrothermal alteration is recognized in two settings within polymict impact breccias overlying the central portion of the structure and within localized pipes in impact generated concentric fault systems the intra breccia alteration comprises three varieties of cavity and fracture filling a sulfide with carbonate b sulfate and c carbonate these are accompanied by subordinate celestite barite fluorite quartz and marcasite selenite is also developed particularly in the lower levels of the impact breccia sheet the fault related hydrothermal alteration occurs in 1 7 m diameter subvertical pipes that are exposed for lengths of up 20 m the pipes are defined by a monomict quartz carbonate breccia showing pronounced fe hydroxide alteration associated sulfides include marcasite pyrite and chalcopyrite we propose three distinct stages in the evolution of the hydrothermal system 1 early stage 200 c with the precipitation of quartz vapor phase dominated 2 main stage 200 100 c with the development of a two phase vapor plus liquid zone leading to calcite celestite barite marcasite and fluorite precipitation and 3 late stage 100 c with selenite and fibroferrite development through liquid phase dominated precipitation we estimate that it took several tens of thousands of years to cool below 50 c following impact during this time haughton supported a 14 km diameter crater lake and subsurface water system providing a warmer wetter niche relative to the surrounding terrain the results reveal how understanding the internal structure of impact craters is necessary in order to determine their plumbing and cooling systems

the aftershock sequence of the 2015 april 25 gorkha nepal earthquake l b adhikari 1 u p gautam 1 b p koirala 1 m bhattarai 1 t kandel 2 r m gupta 1 c timsina 1 n maharjan 1 k maharjan 2 t dahal 2 r hoste colomer 3 4 y cano 3 m dandine 3 a guilhem 3 s merrer 3 p roudil3 and l bollinger3 1national seismological centre department of mines and geology lainchaur kathmandu nepal e mail adhikari research gmail com 2regional seismological centre department of mines and geology surkhet birendranagar nepal 3cea dam dif f 91297 arpajon france 4laboratoire de geologie ecole normale superieure cnrs 24 rue lhomond f 75004 paris france

reaction kinetics of alkenone and n alkane thermal alteration at seismic timescales recent experiments and field observations have indicated that biomarker molecules can react over short timescales relevant to seismic slip thereby making these compounds a useful tool in studying temperature rise in fault zones however short timescale biomarker reaction kinetics studies have previously focused on compounds that have already experienced burial heating here we present a set of hydrous pyrolysis experiments on pleistocene aged shallow marine sediment to develop the reaction kinetics of long chain alkenone destruction change in the alkenone unsaturation ratio uk 37 and change in the n alkane chain length distribution our results show that biomarker thermal maturity provides a useful method for detecting temperature rise in the shallow reaches of faults such as subduction zone trench environments through the course of our work we also noted the alteration of total alkenone concentrations and uk 37 values in crushed sediments stored dry at room temperature for durations of months to years but not in the solvent extracts of these materials this result though parenthetical for our work in fault zones has important implications for proper storage of sedimentary samples to be used for alkenone paleotemperature and productivity analysis this article is protected by copyright all rights reserved

shock re equilibration of fluid inclusions in crystalline basement rocks from the ries crater germany this study examines the effects of shock metamorphism on fluid inclusions in crystalline basement target rocks from the ries crater germany the occurrence of two phase fluid inclusions decreases from shock stage 0 to shock stage 1 while single phase inclusions increase likely as a result of re equilibration in shock stages 2 and 3 both two phase and single phase inclusions decrease with increasing shock stage indicating that fluid inclusion vesicles are destroyed due to plastic deformation and phase changes in the host minerals however quartz clasts entrained in shock stage 4 melts contain both single phase and two phase inclusions demonstrating the rapid quenching of the melt and the heterogeneous nature of impact deformation inclusions in naturally shocked polycrystalline samples survive at higher shock pressures than those in single crystal shock experiments however fluid inclusions in both experimental and natural samples follow a similar trend in re equilibration at low to moderate shock pressures leading to destruction of inclusion vesicles in higher shock stages this suggests that shock processing may lead to the destruction of fluid inclusions in many planetary materials and likely contributed to shock devolatilization of early planetesimals

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

slip model of the 2015 mw 7 8 gorkha nepal earthquake from inversions of alos 2 and gps data we use surface deformation measurements including interferometric synthetic aperture radar data acquired by the alos 2 mission of the japanese aerospace exploration agency and global positioning system gps data to invert for the fault geometry and coseismic slip distribution of the 2015 mw 7 8 gorkha earthquake in nepal assuming that the ruptured fault connects to the surface trace of the main frontal thrust mft fault between 84 34 e and 86 19 e the best fitting model suggests a dip angle of 7 the moment calculated from the slip model is 6 08 1020 nm corresponding to the moment magnitude of 7 79 the rupture of the 2015 gorkha earthquake was dominated by thrust motion that was primarily concentrated in a 150 km long zone 50 to 100 km northward from the surface trace of the main frontal thrust mft with maximum slip of 5 8 m at a depth of 8 km data thus indicate that the 2015 gorkha earthquake ruptured a deep part of the seismogenic zone in contrast to the 1934 bihar nepal earthquake which had ruptured a shallow part of the adjacent fault segment to the east

influence of supercontinents on deep mantle flow abstract the assembly of supercontinents should impact mantle flow fields significantly affecting the distribution of subduction upwelling plumes lower mantle chemical heterogeneities and thus plausibly contributing to voluminous volcanism that is often associated with their breakup alternative explanations for this volcanism include insulation by the continent and thus elevated subcontinental mantle temperatures here we model the thermal and dynamic impact of supercontinents on earth like mobile lid convecting systems we confirm that insulating supercontinents over 3000 km extent can impact mantle temperatures but show the scale of temperature anomaly is significantly less for systems with strongly temperature dependent viscosities and mobile continents additionally for continents over 8000 km mantle temperatures are modulated by the development of small scale convecting systems under the continent which arise due to inefficient lateral convection of heat at these scales we demonstrate a statistically robust association between rising plumes supercontinental interiors for a variety of continental configurations driven largely by the tendency of subducting slabs to lock onto continental margins the distribution of slabs also affects the spatial positioning of deep mantle thermochemical anomalies which demonstrate stable configurations in either the sub supercontinent or intraoceanic domains we find externally forced rifting scenarios unable to generate significant melt rates and thus the ultimate cause of supercontinent breakup related volcanism is probably related to dynamic continental rifting in response to mantle reconfiguration events

the lithospheric mantle beneath the kerguelen islands indian ocean petrological and petrophysical characteristics of mantle mafic rock types and correlation with seismic profiles deep seated meta igneous xenoliths brought to the surface by alkali basaltic magmas from the kerguelen islands reveal that basaltic magmas have intruded the upper mantle throughout their geological evolution these xenoliths record volcanic activity associated with their early south east indian ridge location and subsequent translation to an intraplate setting over the kerguelen plume the meta igneous xenoliths sample two distinctive geochemical episodes one is tholeiitic transitional and one is alkali basaltic geothermobarometry calculations provide a spatial context for the rock type sequence sampled and for interpreting petrophysical data the garnet granulites equilibrated over a pressure range of 1 15 to 1 35 gpa and the garnet pyroxenite at 1 8 gpa ultrasonic measurements of compressional wave speed vp have been carried out at pressures up to 1 gpa and densities measured for representative samples of meta igneous xenoliths and for a harzburgite that represents the peridotitic mantle vp and density have also been calculated using modal proportions of minerals and appropriate elastic properties for the constituent minerals calculated and measured vp agree well for rock types with microstructures not complicated by kelyphitic breakdown of garnet and or pervasive grain boundary cracking pyroxene granulites have measured and calculated vp within the range 7 37 7 52 km s calculated velocities for the garnet granulites and pyroxenites range from 7 69 to 7 99 km s whereas measured and calculated vp for a mantle harzburgite are 8 45 and 8 29 km s respectively the seismic structure observed beneath the kerguelen islands can be explained by 1 a mixture of underplated pyroxene granulites and ultramafic rocks responsible for the 2 3 km low velocity transitional zone below the oceanic layer 3 2 varying proportions of granulites and pyroxenites in different regions within the upper mantle producing the lateral heterogeneities and 3 intercalation of the granulites and pyroxenites throughout the entire upper mantle column along with elevated temperatures accounting for the relatively low mantle velocities 7 70 7 95 km s

subhorizontal layering in the lower crust and its tectonic significance in the narmada son region india comparison of deep seismic sounding dss results of different profiles across the narmada son lineament nsl india indicates the anomalous nature of the crust along the ujjain ma han profile forward travel time and synthetic seismogram modeling using normalized record sections of refraction and wide angle reflection data acquired along the ujjain mahan deep seismic sounding profile across nsl brings into focus the presence of high velocity 7 0 7 3 km s subhorizontal layers from a depth of 8 12 km down to moho the tectonic implication of such reflections layering in the crust is discussed the two fault zones reported by earlier workers flanking the rift might have acted as feeders for the mantle material to intrude into the middle and lower crustal columns

deep crustal structure in central india using magnetotelluric studies summary magnetotelluric studies over the damoh jabalpur mandla anjaneya profile in central india have delineated vindhyan sediments which are about 5 km thick in the damoh katangi region the crust below the vindhyan sediments shows the characteristics of lower crust as observed from the relatively lower resistivity of about 200 v m and high seismic velocities p wave velocities of 6 5 km s x1 compared with 5 8 6 2 km s x1 in the surrounding region it is conjectured that the upper crust may have been completely eroded in the uplift and erosion process and thus the vindhyan sedimentation has occurred directly over the lower crust an anomalous conductivity is observed at depths of 10 12 km in the vindhyan crust the conductance of more than 1200 s observed here may be due to either the serpentinization of the mafic and ultramafic rocks or the presence of grain boundary graphites the thickness of the deccan traps is about 100 m near jabalpur and decreases near mandla on the south of mandla the archaean crust is exposed two crustal conductors are delineated below the deccan volcanics with a resistivity of about 30 v m the first on the immediate south of jabalpur seems to mark the southern boundary of the jabalpur horst block the second conductor was delineated about 40 km southeast of jabalpur coincident with a positive gravity anomaly of about 30 mgal deep seismic sounding studies do not show any significant density contrast associated with this conductive feature it is proposed that the gravity high may be due to the upwarp of the moho the high electrical conductivity is attributed to the fluids in the upper crust

geodetic data inversion using abic to estimate slip history during one earthquake cycle with viscoelastic slip response functions summary we developed a new method of geodetic data inversion to estimate slip history at a plate interface by using akaike s bayesian information criterion abic in this method we considered the effects of viscoelastic stress relaxation in the asthenosphere which cannot be neglected to estimate slip history at a plate interface during one earthquake cycle we also introduced a proper formulation to incorporate two sorts of partially dependent prior information into observed data by bayes rule by applying the new inversion method to levelling data for 1893 1983 in shikoku southwestern japan we reconstructed the pattern of space time variation in slip motion during one earthquake cycle including the 1946 nankai earthquake at the interface between the eurasian and the philippine sea plates the result shows that a steady slip motion at a plate convergence rate 40 mm yr 1 proceeds in the shallow and the deep regions through the entire earthquake cycle in the intermediate depth range 10 30 km on the other hand an instantaneous slip of approximately 4 m occurs at the time of the nankai earthquake after that this portion keeps in stationary contact until the occurrence of the next nankai earthquake if we neglect the effects of viscoelastic stress relaxation the inversion analysis gives geophysically unrealistic results

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

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

rupture process of the mw 7 9 2015 gorkha earthquake nepal insights into himalayan megathrust segmentation we investigate the rupture process of the 25 april 2015 gorkha earthquake mw 7 9 using a kinematic joint inversion of teleseismic waves strong motion data high rate gps static gps and synthetic aperture radar sar data the rupture is found to be simple in terms of coseismic slip and even more in terms of rupture velocity as both inversion results and a complementing back projection analysis show that the main slip patch broke unilaterally at a steady velocity of 3 1 3 3 km s this feature likely contributes to the moderate peak ground acceleration 0 2 g observed in kathmandu the 15 km deep rupture occurs along the base of the coupled portion of the main himalayan thrust and does not break the area ranging from kathmandu to the front the limitation in length and width of the rupture cannot be identified in the preearthquake interseismic coupling distribution and is therefore discussed in light of the structural architecture of the megathrust