deep crustal electromagnetic structure of central india tectonic zone and its implications magnetotelluric data at 45 locations along the mahan khajuria kalan profile in the central india tectonic zone are analysed this 290 km long profile yields data in the period range 0 001 1000 s across the tectonic elements of the study region bounded by purna fault gavligarh fault tapti fault narmada south fault and narmada north fault multi site multi frequency analysis suggests n70 e as the geoelectric strike direction data rotated into the n70 e strike direction are modelled using a non linear conjugate gradient scheme with error floors of 10 for both apparent resistivity and phase components two dimensional magnetotelluric model yields conductors that correlate with known faults in the study region and regional seismicity presence of a 30 mgal gravity high together with the observed conductive bodies less than 20 ohm m in the deep crust beneath the purna graben and tapti valley is explained by the process of magmatic underplating the conductive bodies beneath the mahakoshal rift belt and vindhyans accompanied by regional gravity lows of the order 70 mgal are attributed to the presence of deep crustal fluids following the re activation model proposed for the entire region the conductors 20 ohm m at various depth levels correspond to mafic magmatic and or fluid intrusions controlled by deep seated faults that seem to tap reservoirs beyond the crust mantle boundary the shallow depth localized faults also seem to have facilitated further upward movement of these underplated material and fluids release during this process

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

deep lower crustal earthquakes in central india inferences from analysis of regional broadband data of the 1997 may 21 jabalpur earthquake summary the only instance of a confirmed deep lower crustal earthquake occurrence in the indian shield region has been that of the 1938 satpura earthquake m 6 3 of central india reportedly at a depth of about 40 km moment tensor inversion of regional broadband waveform data of the 1997 may 21 jabalpur earthquake mw 5 7 confirms yet another such earthquake at about 35 km depth in the central part of the narmada son lineament nsl zone the study is based on a refined velocity model obtained using a traveltime grid search method a reverse fault mechanism is obtained which for a palaeo rift valley zone indicates the possibility of reactivation of a pre existing fault under the influence of the ambient stress field due to the india eurasia plate collision forces the occurrence of earthquakes at lower crustal depths quite unusual for the indian shield region indicates a possible causative mechanism related to crust mantle interaction based on the close proximity of the two deep earthquakes and their disposition with respect to the local trend of the central part of the nsl we suggest a model of stress accumulation due to horizontally elongated or elliptical possibly serpentinized mafic intrusives in the lower crust to explain the occurrence of deep earthquakes in the heart of the indian shield

passive seismological imaging of the narmada paleo rift central india abstract the narmada son lineament nsl is a prominent nearly e w trending tectonic feature dividing india into the peninsular and extra peninsular regions it marks the possible suture between two contrasting geological settings termed proto continents lying to the north and south of it various views prevail about the nature of the rift zone the present study delineates the seismic structure of the crust using p wave receiver functions at 10 broadband seismic stations installed along a profile across the nsl the results from common conversion point ccp stacking reveal a near continuous image of the moho boundary with the amplitudes of the ps conversions from the moho being weaker at stations within the rift modelling the receiver functions employing nearest neighborhood algorithm approach brings out a distinct 15 km thickening of the crust and a complex nature of the moho within the rifted zone we find that the backazimuthal variations of the sv and sh receiver functions at the permanent station jabalpur can be explained better by introducing azimuthal anisotropy in the middle and lower crust with the fast axes perpendicular to the rift axis also we find substantial evidence of post rifting magmatic underplating in the lower crust which could be reminiscence of deccan volcanism and or reunion plume path

crustal and upper mantle structure of peninsular india and source parameters of the 21 may 1997 jabalpur earthquake mw 5 8 results from a new regional broadband network abstract in the past two years a permanent network of 10 broadband seismographs has become operational in the indian peninsular shield region in this article we analyze the data recorded by this network with two goals 1 to lay ground for a quick estimation of source parameters of future earthquakes in the region and 2 to estimate the source parameters of the destructive jabalpur earthquake of 21 may 1997 mw 5 8 which occurred within the network toward these goals we measure rayleigh and love wave group velocity dispersion curves in the period range of 10 to 75 sec and invert these curves to estimate the crustal and the upper mantle structure below the indian shield region our best model consists of a two layer crust the upper layer is 14 km thick with a shear wave velocity v s of 3 55 km sec the corresponding values for the lower layer are 25 km and 3 85 km sec v s for the upper mantle is 4 65 km sec based on this structure we perform a moment tensor mt inversion of the bandpassed 0 05 0 02 hz seismograms of the jabalpur earthquake the best fit is obtained for a source located at a depth of 42 km with a seismic moment m 0 of 7 7 10 24 dyne cm and a focal mechanism with strike 61 dip 64 and rake 74 these source parameters are similar to those previously reported in the literature demonstrating that a routine mt inversion of moderate and large indian penisular earthquakes is now possible a careful examination of the seismograms and modeling of the two closest records reveal that the jabalpur earthquake nucleated in the lower crust at a depth of 36 km it consisted of two subevents separated in time by 0 65 sec with the second subevent located 2 km above the first one the total source duration was 1 4 sec

observation and inversion of surface wave group velocities across central india abstract surface wave group velocities across central india are measured from computer plots of frequency time analysis using multiple filter technique periods range from 5 to 56 sec for fundamental mode rayleigh wave 5 to 16 sec for first higher mode rayleigh wave and 5 to 49 sec for fundamental mode love wave the wave paths from koyna earthquakes to bokaro cross purely through the peninsular plateau the group velocities for these paths are found to be similar to those of surface waves recorded at poona from earthquake which lie to the northeast of bokaro in sub himalayan regions from this it is concluded that the shield structure of the peninsula extends to the sub himalayan regions to northeast of the peninsular plateu with a negligible part of sedimentary layer group velocities of fundamental mode rayleigh and love waves are also obtained for the paths from koyna earthquakes to shillong and are found to be similar to the above mentioned group velocities except at very low periods where group velocities are affected by the small part of each path through thick sedimentary layer of bengal basin northern limit of this basin sedimentary layer has been identified mean and standard deviation of observed group velocity at each period are obtained for each of rayleigh fundamental rayleigh first higher and love fundamental modes the group velocities closely agree with those obtained earlier for the path between new delhi and kodaikanal and are also found to be similar to those observed in some shield regions monte carlo inversion method is applied and crust and upper mantle structure of the indian shield across central india is obtained crustal structure obtained shows a marked resemblance to the results obtained earlier through body wave study

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

seismic evidence for significant crustal thickening beneath jabalpur earthquake 21 may 1997 source region in narmada son lineament central india 1 we investigate crustal properties beneath the deep crustal 35 km jabalpur earthquake of 21 may 1997 narmada son lineament nsl central india in search of a possible cause of stress accumulation in the region teleseismic receiver functions computed at nine digital seismographs along a 250 km long profile suggests moho downwarp to 52 km across the width of the lineament in contrast with an average 40 km depth elsewhere in addition the crust beneath the nsl has higher vp vs of 1 84 compared to 1 73 in the surrounding suggestive of a high density mafic mass at depth that compensates the crustal root also supported by small topographic variation 200 m across the lineament presence of such an anomalous mass in the deep crust may lead to gravitationally induced stresses in the lower crust that contribute to the failure of rock along the pre existing narmada son fault leading to the earthquake in deep crust

periodic variation of stress field in the koyna warna reservoir triggered seismic zone inferred from focal mechanism studies abstract the koyna warna region in western india is globally recognized as the premier site of reservoir triggered seismicity rts associated with the koyna and warna reservoirs the region is characterized by continuous seismic activity observed since several decades including the world s largest triggered earthquake of m6 3 which occurred in koyna in 1967 while the role of reservoirs in triggering earthquakes has been widely discussed the actual tectonic mechanism controlling earthquake genesis in this region is hardly understood the koyna warna region is exclusively governed by earthquakes of strike slip and normal fault mechanism distinct from the thrust faulting seen in other active zones in the indian region in the present study a comprehensive catalog of 50 focal mechanism solutions of earthquakes that occurred during the last 45 years in the koyna warna region is developed both from previous literature and from moment tensor inversion studies by the authors using broadband data from a local seismic network operating since 2005 the seismicity and fault plane data have enabled precise delineation of trends of the major causative faults which are further accentuated using the double difference technique stress inversion of the focal mechanism data has provided the best fitting principal compressive and tensile stress field of the region which in conjunction with the deciphered fault zones provides a feasible model of seismogenesis in this region based on the observed temporal variation of faulting mechanism a model of alternating cycles of predominantly strike slip and normal faulting is proposed which is attributed to a periodic peaking and relaxation respectively of the horizontal compressive stress field in this region due to the indian plate collision with eurasia

magnetotelluric studies in the central india tectonic zone implications for intraplate stress regimes and generation of shallow earthquakes abstract the central india tectonic zone citz dissects the indian peninsula into the northern and southern crustal blocks the citz has been a seismically active region since the precambrian whereas the relatively deep crustal earthquakes near the narmada faults in the eastern part of the citz have been well investigated the mechanisms for the shallow earthquakes in the western part remain unknown here we present results from a new magnetotelluric study to derive the crustal structure and to understand its implications our data show a thick and highly resistive 500 ohm m crust in the south of tapti river as against a less resistive one in the north these results in conjunction with heat flow values indicate that the crust below the southern part has stable continental cratonic signatures on the northern side of the tapti river we infer the ascent of basaltic magmas from the mantle into the shallow crust and crystallization into layered intrusions these mafic ultramafic bodies could be a potential cause for the shallow earthquakes in the western part of the citz the mafic ultramafic bodies below the crust of citz would locally modify the intraplate stresses which in turn would facilitate the occurrence of earthquakes due to reactivation of pre existing faults thus the large accumulation of strain energy in the deep crust beneath the region can be attributed to the presence of high stress bodies emplaced at depth during the deccan volcanic activity

an inversion method to analyze the rupture processes of earthquakes using near field seismograms a new and very practical nonlinear least square inversion method has been developed to investigate the dislocation distribution and the character of rupture propagation on an earthquake fault plane the problem is parameterized using a model in which the fault is composed of subfaults which start rupturing with arbitrary magnitudes at arbitrary times the performance of the method is examined by numerical simulations and the method proves useful for the analysis of source processes of earthquakes including complicated cases such as multiple events the source process of the naganoken seibu earthquake of 1984 has been analyzed using strong motion seismograms the dislocation distribution and the character of rupture propagation have been successfully obtained

frequency sensitive moment tensor inversion for light to moderate magnitude earthquakes in eastern africa 1 we provide a procedure for the routine determination of moment tensors from earthquakes with magnitudes as low as mw 4 4 using data recorded by only a few permanent seismic stations at regional to teleseismic distances waveforms are inverted for automatically determined frequency pass bands that depend on source receiver locations as well as the earthquake magnitude inversion results are stable against small variations in the frequency band and provide low data variances i e a good fit between observed and modelled waveform traces the total frequency band used for our procedure ranges from 10 mhz to 29 mhz periods of 35 s to 100 s this enables us to determine focal mechanisms for earthquakes that were not derived previously by routine procedures of cmt or other agencies as a case study we determine focal mechanism solutions of 38 light to moderate magnitude earthquakes in eastern africa between 1995 and 2002

the role of precambrian mylonitic belts and present day stress field in the coseismic reactivation of the pernambuco lineament brazil abstract the pernambuco lineament is a steeply dipping continental scale ductile shear zone rooted within the precambrian lithosphere of intraplate northeastern brazil it was formed during the brasiliano orogeny 600 ma and reactivated during the pangea breakup in the cretaceous when it controlled fault propagation and sediment accumulation in several rift basins the region is now under an e w trending horizontal compression and n s trending extension and faulting occurs predominantly in a strike slip regime we investigated two aftershock sequences and the preexisting tectonic fabrics along the pernambuco lineament in order to evaluate the role of these fabrics in the coseismic reactivation of continental scale structures the lineaments consist of a main ene wsw trending mylonitic belt about 2 3 km wide and two secondary ne trending mylonitic belts about 100 m wide they both present steeply dipping mylonitic foliations and shallowing plunging stretching lineations the mylonites present granitoid protoliths and mineral parageneses that range from amphibolite to greenschist facies brittle deformation overprints the ductile fabric in all mylonitic belts in 1991 coseismic reactivation nucleated along the ene wsw striking 3 3 5 6 km deep normal fault of less than 1 km in length in the main mylonitic belt in 2002 seismicity migrated to a ne trending secondary mylonitic branch and moved as a right lateral strike slip 1 2 km long 3 8 4 9 km deep fault plane both fault segments reactivated the mylonitic foliation and form part of a major system we conclude that the interplay between the present day stress field and preexisting fabrics controls seismogenic fault location attitude and kinematics the pernambuco lineament is an example of a long lived continental scale structure where selective reactivation has occurred other shear zones in the region also show a long history of brittle reactivation and present similar orientation in relation to the present day stress axes they might be dormant structures prone for reactivation under the present day stress field

origin and evolution of intracratonic thermal fluids from central western peninsular india abstract the chemical and isotopic composition of several thermal springs and associated gas phases in a large sector of central western peninsular india has been investigated such springs have meteoric isotopic signature and emerge after very well developed convective circulation at depth along important tectonic structures such as the son narmada tapti rift zone and the west coast fault chemical components in both gas and liquid phases and geothermometric estimations suggest that such springs are not related to the presence of any active hydrothermal systems at shallow depth in any of the studied areas the hottest convective water emerges at tattapani at near boiling point for water at atmospheric pressure 90 c in association with an n2 rich gas phase of clear meteoric signature since such fluids do not carry any corrosive components they could be conveniently exploited for industrial purposes such as drying processes from a tectonic point of view the presence of thermal emergences scattered in a wide area along geologically well defined structures which also generate frequent moderate earthquakes suggests that such structures are active although the isotopic composition of thermal springs points to a meteoric origin their feeding aquifers are not topographically driven as in most active alpine orogenic belts the relative high quantity of total helium in the associated gas phase suggests also that they are really deep old long circulating waters we propose for such waters the term intracratonic thermal waters since the isotopic signature of he in the gas phase does not show any release of primordial 3he in any of the areas of spring emergence based on the quite low 3he 4he ratio in the gas phase we suggest also that in spite of its morphological shape the narmada son tapti rift zone cutting the indian subcontinent in two is more related to paleo suture rather than to a mid continental rift system

diffusion wave model for simulating storm water runoff on highway pavement surfaces at superelevation transition on a curved section of highway the cross slope of the road is often designed to be superelevated to balance the centrifugal force and gravity applied on vehicles the accumulation of storm water runoff sheet flow near superelevation transitions may significantly increase due to the extended flow path and converging flow lines a two dimensional finite volume based diffusion wave model is developed to simulate the sheet flow on these geometrically complex surfaces both dirichlet and neumann type boundary conditions are developed for open boundaries based on kinematic wave theory results show that the distribution of sheet flow is closely related to the cross slope longitudinal slope rainfall intensity and the width of the road the analysis of sheet flow characteristics on superelevation transition areas suggests that the optimal longitudinal slope in the range of 0 3 0 4 minimizes the depth of storm water runoff on the road surface

source parameters of two rift associated intraplate earthquakes in peninsular india the bhadrachalam earthquake of april 13 1969 and the broach earthquake of march 23 1970 abstract the bhadrachalam earthquake of april 13 1969 and the broach earthquake of march 23 1970 are two major intraplate earthquakes associated with paleorift zones in the stable continental region of peninsular india these two events shook very large portions of the peninsula and casualties were reported for the broach earthquake ancient rifts have recently been identified as a major seismogenic tectonic feature for intraplate seismicity in stable continental regions p wave first motions and waveforms of long period teleseismic p and sh waves have been modeled to constrain the focal mechanisms and to determine the source parameters for the earthquakes previous investigators proposed multiple fault plane solutions for each of the events in this paper some of the early solutions are eliminated and the best source mechanism is derived for each earthquake for the bhadrachalam earthquake the focal mechanism determined is predominantly strike slip strike 245 dip 72 rake 358 the strike direction of the ne sw trending nodal plane is in good agreement with the trend of the observed isoseismals and is probably the fault plane the seismic moment is 4 59 1024 dyne cm and the moment magnitude mw is determined to be 5 7 the focal depth and the static stress drop are estimated to be 10 km and 17 bar respectively the strike slip motion represents a reactivated fault motion under the present day stress field for the broach earthquake the focal mechanism determined is reverse faulting with a strike slip component strike 273 dip 58 rake 130 the direction of the e w striking nodal plane is in good agreement with the mapped narmada fault dislocation direction of fissures and the trend of the isoseismals the seismic moment and moment magnitude are determined to be 1 39 1024 dyne cm and 5 4 respectivety the focal depth and the stress drop are estimated to be 11 km and 9 bar respectively the reverse motion of this event represents an inverted slip or tectonic inversion within a rift zone under the present day compressional stress field some rift associated earthquakes are characterized by large multiple shocks with significant strike slip motions the two indian earthquakes however occurred as regular main shock aftershock sequences and represent a different mode of strain release these two earthquakes also represent events with low stress drops and relatively long recurrence intervals the interpretation of this last observation is uncertain and needs more study in the future

seismogenesis in the stable continental interiors an appraisal based on two examples from india characteristics of two recent moderate earthquakes from india 1993 killari mw 6 1 and 1997 jabalpur mw 5 8 are presented in this paper to illustrate the influence of geologic and tectonic setting on the nature of seismicity in stable continental regions scrs the killari event which occurred in the middle of a cratonic region of low background seismicity long recurrence interval and poorly developed neotectonic features may be qualified as a common type of scr event this earthquake is also characterized by a shallow focal depth and a long sequence of aftershocks in contrast the jabalpur earthquake shows a spatial association with a well defined tectonic structure with significant background seismicity a remarkable feature of this earthquake is its deep focus not commonly observed in scr seismicity this event was associated with fewer aftershocks unlike most other scr earthquakes analogous events are found in other shield regions as well based on their general characteristics a broad classification of moderate scr earthquakes is attempted here two broad groups have been identified in this study 1 a set of deep focus earthquakes that are related to intracratonic paleorifts and 2 shallow focus earthquakes associated with discrete faults in the less deformed precambrian terrains a synthesis of earthquake data from different geologic environments will improve our understanding of the seismogenesis in the shield regions 1999 elsevier science b v all rights reserved

lithospheric s wave velocity structure of the bastar craton indian peninsula from surface wave phase velocity measurements abstract interstation phase velocities of surface waves are measured through a cross correlation method across the bastar craton in the eastern part of the indian peninsula the periods of love waves lie between 15 and 91 sec and those of rayleigh waves lie between 13 and 104 sec the observed phase velocities are close to the theoretical dispersion curves for the crust and upper mantle structure ip11 obtained earlier for central india in the indian peninsula through inversion of surface wave group velocities however for periods higher than 70 sec the theoretical curves remain above the observed data in ip11 the upper mantle low velocity zone lvz starts downward at a depth of 140 km the s wave velocity v s in the lvz of ip11 is decreased based on the recent studies and the modified structure ip11l is obtained the theoretical dispersion curves of ip11l improve the fit to the observed data particularly at higher periods the lithospheric part of ip11l is then improved through genetic algorithm inversion with more stratification in the structure for a better fit to the observed data such inversion generated the model ip11ba for the bastar craton the crustal thickness of this craton is found to be 40 1 0 6 km with the thickness of the upper crust as 15 3 0 7 km which is less than the corresponding thickness of 20 km in southern india in the upper crust v s shows a small increase with depth having an average value of 3 508 km sec and in the lower crust v s 3 934 km sec these values of v s for the crust of the bastar craton are nearly the same as those found in southern india below the moho down to a depth of 70 km ip11ba shows a constant v s of 4 577 km sec and then increases slowly to 4 609 km sec at the top of the lvz

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 evolution of the vindhyan basin vis a vis the narmada son lineament central india from deep seismic soundings abstract the evolution of the vindhyan basin has been studied from deep seismic soundings block tectonics appear to be active throughout the geological history in this region the crust is divided into four major blocks by deep faults at narsinghgarh katangi and jabalpur the crustal block between narsinghgarh and katangi forms a graben in the crystalline basement giving rise to the great vindhyan basin in which precambrian vindhyan sediments of about 5 5 km thickness are deposited the crustal block between katangi and jabalpur is a horst block which represents the narmada son lineament a crustal depth section obtained from wide angle reflections shows a large number of reflector segments up to the mono boundary indicating crustal heterogeneity the boundary faults at the northern and the southern ends of the vindhyan basin extend up to the moho the crustal thickness varies from 39 5 to 45 km

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

on the mechanism and source parameters of the deep crustal jabalpur earthquake india of 1997 may 21 constraints from aftershocks and changes in static stress summary the 1997 may 21 jabalpur earthquake mb 6 0 occurred in the lower crust of the ene wswtrending narmada son palaeorift zone in central india known as the narmada son lineament nsl we correlate the aftershock distribution of this earthquake with the computed changes in static stress caused by slip on the earthquake rupture in order to constrain some of the source parameters of the main event we estimate that the downdip edge of the earthquake rupture extended up to a depth of about 38 km and that the majority of the aftershocks occurred due to unclamping in the hangingwall near the downdip edge of the rupture considering the intermediate to moderately high heat flow in the region we suggest that 1 high pore pressure in the lower crust which developed due to the dehydration of the serpentinite body during previous episodes of thermo tectonic processes 2 a lower frictional coefficient possibly arising due to fractured rocks at depth 3 a higher strain rate and 4 the favourable influence of n s compression due to the motion of the indian plate are responsible for the infrequent earthquakes in the lower crust of the nsl zone

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

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

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

nature of continental crust along the narmada son lineament inferred from gravity and deep seismic sounding data abstract the narmada son lineament nsl is a very prominent feature on the tectonic map of india and divides the indian peninsula into two parts the northern part characterised by lower elevations and more positive bouguer gravity anomalies as compared to the southern part the lineament is characterised by a gravity high practically all along its length four published deep seismic sounding dss profiles across the nsl give vital information concerning its origin an analysis of the bouguer gravity field along these profiles has been carried out using all available geological and velocity density information the analysis reveals that the areas immediately south of the nsl are characterised by higher density crust in comparison to the areas north of it this increase in density could have taken place during mesozoic to tertiary times when major tectonic volcanic activity took place over peninsular india the presence of deep seated faults sediments and anomalous crust shows that the lineament has some characteristics of a rift valley

evidence for lower crustal ductile strain localization in southern new york historic triangulation data have been analysed to determine whether intraplate seismicity is associated with ongoing ductile deformation in the lower crust the model we have attempted to test is basically analogous to strain accumulation and release along plate boundary strike slip faults like the san andreas fault in california that is beneath an elastic seismogenic upper crust 20 km thick strain is preferentially localized within ductile shear zones in the lower crust due to broad scale plate driving forces the localized lower crustal ductile strain causes stress and strain to accumulate elastically in the brittle crust which is eventually released in crustal earthquakes at greater depths this localized shear deformation probably develops into pervasive ductile flow numerous geodetic measurements along the san andreas fault confirm that earthquakes in the brittle upper crust are produced by the release of elastic strain that results from ongoing ductile shear or slip in the lower crust1 2 we have found evidence of high rates of crustal deformation in southern new york which suggest that localized ductile shear is occurring in the lower crust

the lifetime probability density function for solute movement in the subsurface zone abstract the conceptual basis and physical significance of the solute lifetime probability density function pdf and its important special case the travel time pdf are discussed the field scale measurement and use of these two pdfs in characterizing solute mass transfer and solute concentrations in the subsurface zone are described along with their physical interpretation as lifetime or travel time spectra the relation between the travel time pdf and mechanistic models of subsurface solute transport e g the convection dispersion equation is illustrated with an application to three dimensional reactive solute movement in a sand aquifer

an overview on the seismic zonation and microzonation studies in india abstract the present study presents a review on the progressive development of the seismic zonation map of india both from official agencies and also from independent individual studies the zonation map have been modified and updated regularly with the occurrence of major destructive earthquakes over the years in the indian subcontinent with the addition of new data this study discusses the criteria chosen for the progressive zonation and the major earthquakes that were responsible for retrospection of the earlier published maps the seismic zonation maps of india have also been prepared by various independent workers by adopting different approaches to achieve the purpose of the zonation despite the endeavors from various sources to provide a solution for the problem of earthquake hazards in india there were many limitations on the zonation map as it gives the picture at a regional scale mostly on the bedrock level without addressing the local site conditions but nevertheless the seismic zonation map gives basic guidelines for any region to know the hazard scenario and if any city or urban population is under threat from seismic point of view further site specific seismic microzonation may be carried out in the international scenario the global seismic hazard assessment program gshap in 1999 prepared a hazard map for world in terms of peak ground acceleration pga with a 10 probability of exceedance in 50 years but it turned out to be an underestimation of the hazard parameter when compared with the observed pga to tackle the problem of seismic hazards there was a need to have a detail study on the local site conditions in terms of its geological geophysical and geotechnical properties with the advent of better instrumentation and knowledge on the mechanics of earthquakes it was possible to identify zones of hazards at a local level and this gives rise to the study of seismic microzonation seismic microzonation work has been carried out in india in some of the strategic important mega cities and industrial build up that has the potential of being damaged from future earthquakes as has been shown in the past though the microzonation map is not the final output map as it can still be updated at later stage with more input data it does provide a more realistic picture on the site specific seismic hazard