earthquake generation in different stress states abstract a method of numerical simulation of an earthquake sequence is presented based on the stress evolution equations and the new rebound theory a zone of earthquake preparation is modelled by a medium filled with parallel antiplane cracks some statistical properties of the numerically simulated sequences are discussed it follows that a complete representation of a cumulative energy diagram requires that energies released in the creep events should also be included

crack fusion dynamics a model for large earthquakes the physical processes of the fusion of small cracks into larger ones are nonlinear in character a study of the nonlinear properties of fusion may lead to an understanding of the instabilities that give rise to clustering of large earthquakes we have investigated the properties of simple versions of fusion processes to see if instabilities culminating in repetitive massive earthquakes are possible we have taken into account such diverse phenomena as the production of aftershocks the rapid extension of large cracks to overwhelm and absorb smaller cracks the influence of anelastic creep induced time delays healing the genesis of juvenile cracks due to plate motions and others a preliminary conclusion is that the time delays introduced by anelastic creep may be responsible for producing catastrophic instabilities characteristic of large earthquakes as well as aftershock sequences however it seems that nonlocal influences i e the spatial diffusion of cracks may play a dominant role in producing episodes of seismicity and clustering

segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

contribution of icelandic ice caps to sea level rise trends and variability since the little ice age 1 in total icelandic ice caps contain 3600 km3 of ice which if melted would raise sea level by 1 cm here we present an overview of mass changes of icelandic ice masses since the end of the 19th century they have both gained and lost mass during this period changes in ice volume have been estimated both through surface mass balance measurements performed annually since 1990 and differencing of digital elevation models derived from various satellite and airborne observations while the glaciers showed little mass loss as the 20th century began losses increased rapidly after 1925 peaked in the 1930s and 1940s and remained significant until the 1960s after being near zero or even positive during the 1980s and early 1990s glacier mass budgets declined considerably and have since the mid 1990s shown an average annual loss of 9 5 1 5 gt a 1 contributing 0 03 mm a 1 to sea level rise since 1995 interannual variability in mass loss is high ranging from 2 7 to 25 3 1 5 gt a 1 corresponding to surface mass balances of 0 2 to 2 2 0 15 m we a 1 this variability is driven by climate fluctuations and also by transient reduction of albedo due to volcanic eruptions

seismically imaged shallow and deep crustal structure and potential field anomalies across the eastern dharwar craton south indian shield possible geodynamical implications abstract the time bound crustal evolution and subsequent deformation of the cuddapah basin nellore schist belt and eastern ghats terrain of eastern dharwar craton which have undergone sustained geodynamic upheavals since almost 2 0 billion years remain enigmatic an attempt is made here to integrate newly available potential field data and other geophysical anomalies with deep seismic structure to examine the generative mechanism of major crustal features associated with this sector our study indicates that the initial extent of the cuddapah basin sedimentation may have been much larger extending by almost 50 60 km west of tadipatri during paleoproterozoic period which subsequently shrank due to massive erosion following thermal uplift caused by sw cuddapah mantle plume below this region crust is still quite warm with moho temperatures exceeding 500 c similarly nallamalai fold belt rocks bounded by two major faults and extremely low gravity may have occupied a large terrain in western cuddapah basin also before their abrasion no geophysical signatures of thrusting are presently seen below this region and thus it could not be an alien terrain either in contrast nellore schist belt is associated with strikingly high positive gravity possibly caused by a conspicuous horst structure and up dipping mafic crustal layers underneath that resulted due to india east antarctica collision after the cessation of prolonged subduction 1 6 0 95 ga further the crustal seismic and gravity signatures would confirm presence of a totally distinct geological terrain east of the cuddapah basin but the trace of eastern ghats belt is all together missing instead all the geophysical signatures point out to presence of a proterozoic sedimentary terrain east of nellore schist belt it is likely that the extent of prorerozoic sedimentation was much larger than thought today in addition presence of a seismically detected gondwana basin over nellore schist belt apart from some recently discovered similar subsurface gondwana occurrences in intracratonic parts would indicate that dharwar craton was rifting even during gondwana period thereby challenging the long held view of cratonic stability

secular variations of the earth s apparent resistivity monitoring carried out by the generalized magnetovariation gmv and geomagnetic depth sounding gds methods has shown a valuable variability of yearly apparent resistivities from the yr 1911 to 2010 for the selected european geomagnetic observatories these deep soundings were carried out by the two methods mentioned above correspondingly for shorter and longer periods in the range from 8 h to a month the possible changes in the source signals through an uncorrelated part of the observed field were mainly suppressed by robust coherence based statistical data processing the detected resistivity variations have periods of more than several yr while inequality of induction arrows obtained by the gmv method may be seen already during a couple of yr the 11 yr variability of the apparent resistivity correlates with wolf numbers with some phase lags the variations with shorter periods have been found to change synchronously with the number of the earthquakes at a region including some seismically active areas in europe the peculiarities and possible origins of the phenomenon are discussed

a model for repetitive cycles of large earthquakes the theory of the fusion of small cracks into large ones reproduces certain features also observed in the clustering of earthquake sequences by modifying our earlier model to take into account the stress release associated with the occurrence of large earthquakes we obtain repetitive periodic cycles of large earthquakes a preliminary conclusion is that a combination of the stress release or elastic rebound mechanism plus time delays in the fusion process are sufficient to destabilize the crack populations and ultimately give rise to repetitive episodes of seismicity

thermo mechanical structure of the southern part of the indian shield and its relevance to precambrian basin evolution abstract the thermal and mechanical structures of the southern part of the precambrian indian shield have been estimated using available heat flow data and shear stress profiles from olivine rheology these and other geological geochronological and geophysical data including deep seismic studies dss profiles of proterozoic cuddapah basin on south indian shield are utilized to examine thermal models for the evolution of precambrian intracratonic platform basins on the archean lithosphere of indian shield evidence of mantle perturbations and cycles of thermal events are documented to be important in the cuddapah basin s evolution haxby et al s 1976 thermal model has been shown to explain the cuddapah basin s flexuring and magnitude of subsidence

influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas abstract dmowska r and lovison l c 1992 influence of asperities along subduction interfaces on the stressing and seismicity of adjacent areas in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 23 43 we have investigated the influence of large scale fault inhomogeneities in large subduction earthquakes on the style of deformation and seismic behavior of the incoming oceanic plate and slab at intermediate depths during the earthquake cycle the zones of the large subduction events of rat islands 1965 alaska 1964 and valparaiso 1985 have been searched for earthquakes with m b 5 0 if available and for time periods as long as possible it has been found that in general the seismicity in the incoming oceanic plate clusters in front of asperities areas of highest seismic moment release and strongest locking and is positioned relative to them in the direction of plate motion it is usually lacking in areas adjacent to non asperities that is to zones that slip during the main event but with appreciably smaller seismic moment release and possibly slip seismically aseismically during the whole cycle similar behavior occurs in the downgoing slab at intermediate depths where seismicity during the cycle clusters but less strongly than in the oceanic crust next to asperities and down dip from them we infer that the locking of asperities causes higher stresses associated with the earthquake cycle itself to occur in areas adjacent to asperities both up dip and down dip from them along the direction of plate motion and that such stressing is much less pronounced in the areas adjacent to non asperities this opens the possibility of identifying the areas of highest seismic moment release in future subduction earthquakes and carries implications for where the highest deformation and possibly precursory phenomena and or nucleation of a future event might occur

seismic imaging across the eastern ghats belt cuddapah basin collisional zone southern indian shield and possible geodynamic implications abstract the evolutionary nature of the area encompassing cuddapah basin nellore schist belt and the ongole domain of eastern ghats belt south india which contains paleo neoproterozoic imprints of thick sedimentation intense magmatism subduction accretion and possible collision between eastern dharwar craton and east antarctica is still being debated an attempt has been made here to decipher the deep crustal structure and tectonics of this region by reprocessing deep seismic sounding data acquired earlier through the modeling of first arrival refraction and wide angle reflection travel times the derived crustal seismic velocity structure reveals that the intracratonic proterozoic cuddapah basin containing only 4 km thick sediment is bounded by two major faults the moho reaching fault detected on its eastern boundary demarcates cuddapah basin from the nellore schist belt although a deep normal fault is mapped within the nallamalai fold belt but no thrusting signatures are apparent almost all the crustal layers beneath nellore schist belt and the ongole domain of eastern ghats belt show distinct eastward dipping trend conforming to an upthrusted feature suggesting possible presence of a collisional suture besides the areas lying east of cuddapah basin appear to be an accreted orogenic terrain beneath which lower crust has upwarped substantially the entire stretch of the studied region is underplated by unprecedently thick 20 km high velocity 7 0 7 4 km s magma layer above the moho indicating strong crust mantle thermal perturbation and massive subcrustal erosion further an expression of a deep seated mantle thermal anomaly has also been found below the parnapalle region of the sw cuddapah basin beneath which deeper crustal layers have exhumed

crustal structure and domain tectonics of the dharwar craton india insight from new gravity data abstract the precambrian dharwar craton of peninsular india comprises three distinct crustal domains namely the western dharwar craton wdc the eastern dharwar craton edc and the eastern ghats mobile belt egmb the domain boundaries are demarcated by bipolar positive and negative gravity anomalies measured along a 600 km long udipi kavali seismic line the two and half dimensional modelling of the gravity anomalies well constrained by available seismic depth sections identified the two contact zones one occurs between the wdc relatively low density and the edc intermediate density to the east of the chitradurga schist belt and the second occurs between the edc and the egmb high density to the east of cuddapah basin as west verging thrust faults the three layer crustal structure is up to 41 km thick beneath the wdc thinning to 37 km beneath the west coast under the edc the depth of the moho varies from 38 km towards the west to 40 km beneath the cuddapah basin and decreases to a depth of 35 km beneath the egmb a high density steeply inclined ridge like body is modelled between 5 and 20 km depth beneath the closepet granite and a similar body is modelled under the egmb it is suggested that the three domains of the dharwar craton were brought and welded together at the suture zones in the period from late archaean to late proterozoic through collisional tectonics the apparent offsets in the moho depth may be the imprint of the relative domain movement that probably was initiated by the convergent plate motion the steeply inclined ridge like high density bodies are interpreted as stacked lower crustal blocks from the convergent tectonic setting the cuddapah basin with a 10 km thick shelf marine sedimentary sequence is interpreted as a peripheral foreland basin abutting the egmb a lopolith of likely mafic composition is modelled at 10 km depth and is interpreted as a product of juvenile magmatism beneath the edc

dynamics of a zone of four parallel faults a deterministic model we consider a two dimensional model for quasi static evolution of four parallel faults the model is based on the physics of continuum with slips along the faults long range interactions a distribution of barriers and asperities a velocity dependent friction healing and reactivation of cohesive forces and a mutual causality between faulting and tectonic forces all taken into account both the long term time series of seismic activity and details of seismic and aseismic crustal deformations during each phase of the earthquake cycle are produced by the model it is shown that the system whose evolution is described by a set of deterministic differential equations may exhibit periodic or quite irregular despite its assumed symmetry behavior depending on model parameters

volume changes of vatnajokull ice cap iceland due to surface mass balance ice flow and subglacial melting at geothermal areas 1 we present observed changes in the geometry of western vatnajokull over a period of about ten years which are caused by the surface mass balance ice flow both during surges and quiescent periods and basal melting due to geothermal and volcanic activity comparison of two digital elevation models shows that from 1985 to 1998 the outlet glaciers have lost 14 5 km3 on the average 1 m yr 1 evenly distributed over the area of 1360 km2 however the marginal areas of four outlets have gained up to 80 m in elevation and the uppermost parts have subsided similarly during surges altogether 26 3 km3 were transported from the accumulation areas to the ablation areas of which 19 3 km3 are attributed to surges comparison of dem s from august 1997 and august 1998 revealed 10 ice cauldrons produced by subglacial geothermal activity of which some were previously unknown

structure of the earth s crust and upper mantle below hindustan and the northern part of the indian ocean from geophysical data abstract the crustal cross section of the indian shield is refined on the basis of data obtained in the cooperative indian soviet deep seismic sounding dss research and from the use of a new interpretation technique crustal velocity parameters are studied and the main blocks and faults are identified the hypsometric position of the blocks is determined gravity field interpretation using dss and explosion seismology data has made it possible to characterize the structure of the entire tectonosphere for the area africa hindustan eastern coast of the bay of bengal it is confirmed that the continents have a normal continental crust that passes into the oceanic type under the ocean in the somali trough especially in the bay of bengal sediments are very thick the laccadiv isles have crust which is oceanic in composition the rift zone of the karlsberg ridge has deep seated asthenospheric roots the lithospheric density increases as the distance from the ridge grows the asthenosphere is developed everywhere but it is thinner and denser below the continent than below the ocean

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

measurement of ice sheet topography using satellite radar interferometry detailed digital elevation models dems do not exist for much of the greenland and antarctic ice sheets radar altimetry is at present the primary in many cases the only source of topographic data over the ice sheets but the horizontal resolution of such data is coarse satellite radar interferometry uses the phase difference between pairs of synthetic aperture radar sar images to measure both ice sheet topography and surface displacement we have applied this technique using ers 1 sar data to make detailed i e 80 m horizontal resolution maps of surface topography in a 100 km by 300 km strip in west greenland extending northward from just above jakobshavns isbrae comparison with a 76 km long line of airborne laser altimeter data shows that we have achieved a relative accuracy of 2 5m along the profile these observations provide a detailed view of dynamically supported topography near the margin of an ice sheet in the final section we compare our estimate of topography with phase contours due to motion and confirm our earlier analysis concerning vertical ice sheet motion and complexity in ers 1 sar interferograms

outflow channels with deltaic deposits in ismenius lacus mars abstract a connected series of outflow channels in the ismenius lacus quadrangle are identified for the first time and characterized using high resolution stereo camera images of mars express the context camera images of mars reconnaissance orbiter and the topography of the mars observer laser altimeter these channels named okavango valles which stretch over 400 km south to north and join the northern plains were identified from braided channels scour groove marks poorly sinuous valleys and depositional landforms discharge rates were estimated to 0 1 5 10 6 m 3 s 1 from analysis of the topography of scour marks pathways of channels segments were extracted from topography showing a unique source at a breached crater rim suggesting overflow from ponded depressions a series of delta fans are observed inside depressions along the channel pathways the presence of these deltas formed in former bodies of water is a compelling argument for formation of this outflow channel system by fluvial flows the similarity of these flows with other outflow channels on mars proves that volcanically related outflows cannot explain all such features in addition this study also shows that catastrophic floods are able to create fan deltas in transient lakes this example has to be taken into account in the interpretation of late stage fans associated with poorly branched valleys and single channels

surges of glaciers in iceland surges are common in all the major ice caps in iceland and historical reports of surge occurrence go back several centuries data collection and regular obser vationover thelast several decadeshave permitteda detailed descriptionof several surges fromwhich it is possible to generalize onthe nature of surging in icelandic glaciers com bining the historical records of glacier front variations and recent field research we sum marize the geographic distribution of surging glaciers their subglacial topography and geology the frequency andduration of surges changes in glacier surface geometry during the surge cycle and measured velocity changes comparedto calculatedbalance velocities wenotetheindicatorsofsurgeonsetanddescribechangesinice waterandsedimentfluxes duringa surge surgesaccomplishasignificantfractionofthetotalmasstransportthrough the main outlet glaciers of ice caps in iceland and have important implications for their hydrology ouranalysisof the data suggeststhat surge type glaciersin icelandarecharac terizedbygentlysloping surfacesandthatthey movetoo slowlytoremain inbalance given their accumulation rate surge frequency is neither regular nor clearly related to glacier size or massbalance steeply sloping glaciers whetherhard or soft bedded seemto move sufficiently rapidly to keep inbalance with the annual accumulation

tectonic evolution in the archaean and proterozoic kre high heat flow probably favoured global hotspot activity with crustal growth of iceland type through vertical magmatic accretion the tectonic environment for the generation of about 3 9 2 5 ga granite gneiss greenstone terrains with volurnlnous production of tonalite trondhjemite granodlorite magmas is still uncertain and both piate ma and intrapiate scenarios arc possible deformanon atylea in greenstones and adjacent high grade orthognersses with intercalated shallow water supracrustal assemblages suggest extensive horizontal shortening and crustal interstacking this probably resulted from collisional and or rotational motion and produced significant intracrustal melting as early as 3 9 ga by the end of the archaean and locally much earlier crustal thicknesses reached 35 50 km or more and the cxtl aordinary hhlding to erogenic deformation may have been due to delamination and crustal subduction towards the end of the proterozoic evidence for modern style plate tectonics becomes abundant through the recognition of laland a16 accretion ophiolite obducdon foreland thrust and fold belts and exotic terranes one of the best documented example for this tectonic environment is the arabian nubian shield 4lthough it is doubtful whether modern plate tectonic settings can serve as analogues for all precambrian tectonic styles it i clear that global crustal evolution since the early archaean was governed by the motion of plates which repeatedly came togethel tv fotm supercontinents and then dlspersetl again we shall not understand the detailed mechanism of precambrian crustal itlton cs before we learn horn lo irltejpret recent large scale crustal deformation and its causes

the level of the grimsvotn subglacial lake vatnajokull iceland monitored with spot5 images abstract we describe the vertical displacement field of an ice shelf floating on a subglacial lake grimsvotn located underneath the vatnajokull ice cap iceland the uplift is measured using the correlation of two satellite optical spot5 images acquired 5 days apart with similar non vertical incidence angles this is the first time correlation of optical images has been used to measure vertical displacements our technique is suitable for mapping short term elevation changes of glaciers if the surface features are preserved vertical displacements can be measured every 25 m with an accuracy of about 0 5 m the uplift map of grimsvotn shows that 10 9 1 km 2 of ice was floating between 11 and 16 august 2004 the ice shelf rose by 1 7 0 6 m indicating that the volume of liquid water in the lake increased by 0 018 0 007 km 3 our field observations show that surface melting due to meteorological processes contributed 70 of the accumulated water hence the rest originated from ice melted by the subglacial geothermal activity the power required to melt 0 005 km 3 water equivalent of basal ice in 5 days is 4000 mw the applicability of the technique can be extended to volcanology and seismology and even landslides or subsidence when finer resolution optical images become available applied to two pairs of images it could solve for the 3 dimensional displacements of the earth s surface

what controls dead ice melting under different climate conditions a discussion abstract in the geological record hummocky dead ice moraines represent the final product of the melt out of dead ice processes and rates of dead ice melting in ice cored moraines and at debris covered glaciers are commonly believed to be governed by climate and debris cover properties here backwasting rates from 14 dead ice areas are assessed in relation to mean annual air temperature mean summer air temperature mean annual precipitation mean summer precipitation and annual sum of positive degree days the highest correlation was found between backwasting rate and mean annual air temperature however the correlation between melt rates and climate parameters is low stressing that processes and topography play a major role in governing the rates of backwasting the rates of backwasting from modern glacial environments should serve as input to de icing models for ancient dead ice areas in order to assess the mode and duration of deposition a challenge for future explorations of dead ice environments is to obtain long term records of field based monitoring of melt progression furthermore many modern satellite borne sensors have high potentials for recordings of multi temporal digital elevation models dems for detection and quantification of changes in dead ice environments in recent years high accuracy dems from airborne laser scanning altimetry lidar are emerging as an additional data source however time series of high resolution aerial photographs remain essential for both visual inspection and high resolution stereographic dem production

early proterozoic melt generation processes beneath the intra cratonic cuddapah basin southern india early proterozoic tholeiitic lavas and sills were emplaced during the initial phase of extension of the intra cratonic cuddapah basin southern india ar 40 ar 39 laser fusion determinations on phlogopite mica from the tadpatri fm mafic ultramafic sill complex constrain the age of the initial phase of extension and volcanism in the basin at 1 9 ga despite their early proterozoic age the igneous rocks are unmetamorphosed undeformed and remarkably fresh they exhibit a wide range in mgo contents 4 28 wt and have undergone varying degrees of accumulation or crystal fractionation variable la nb ratios 1 2 3 7 and epsilon nd values 1 to 10 suggest that some but not all of the mafic rocks have been affected by crustal contamination this appears to have taken place in magma chambers at similar to9 kbar i e the base of the continental crust forward modelling of major and trace elements fe and nd and inverse modelling of rare earth elements suggest that the primary cuddapah melts were generated by similar to10 15 partial melting of a lherzolite mantle source this corresponds to a mantle potential temperature of similar to1500degreesc the thickness of the mechanical boundary layer predicted by the geochemical modelling is 70 km with a minimum initial lithospheric thickness of 120 kin this corresponds to a stretching factor of 1 6 1 8 richter s 1988 secular cooling model for the earth predicts that at 1 9 ga the ambient mantle had a potential temperature of similar to1500degreesc i e similar to200degreesc hotter than phanerozoic mantle if the cooling model is correct then proterozoic lithospheric stretching and mantle melting beneath the intra cratonic cuddapah basin could have been caused by passive rather than active rifting

transient electric variations associated with large intermediate depth earthquakes in south aegean abstract a telluric station was installed on crete in the south aegean in order to investigate the existence of transient electric variations before large near intermediate depth earthquakes during the experiment two transient electric variations not correlated with geomagnetic variations were recorded and associated with two time isolated intermediate depth earthquakes with local magnitude m l 5 8 and 4 8 respectively finally a qualitative discussion on the form of the electric signal based on the charge dislocation model is presented

seismic imaging of the proterozoic cuddapah basin south india and regional geodynamics abstract cuddapah basin has been believed to be one of the largest intra cratonic proterozoic sedimentary basins of india situated in the eastern part of the dharwar craton of the south indian shield which is magmatically infested and contain thick column of sediments its overall sedimentary thickness as well as the nature of crustal evolution has remained enigmatic based on deep seismic sounding and other geological studies in the past it was perceived that this basin may contain as much as 10 12 km thick sediments the results of our present analysis derived up to a depth of 12 km reveals five layered upper crust associated with velocities i 4 50 km s ii 5 20 5 30 km s iii 5 50 5 80 km s iv 5 85 6 00 km s and v 6 40 km s out of which second and third layers correspond to upper and lower cuddapah sediments the results suggest the presence of only 4 0 km thick sediments in the deepest part of the basin below the nallamalai fold belt which has its implications in the developmental history of the basin a thermal driving force was invoked by earlier workers to account for estimated 10 12 km thick sediments however the present estimate of only 4 km basement depth in the cuddapah basin shows that the role of the thermal driving force may be marginal particularly in the deeper eastern cuddapah as isostatic subsidence due to sedimentary accumulation alone is enough to explain the basin depth further a basement sag of about 10 km would have logically needed lateral extension of the order of several hundreds of kilometers however as our present estimate of the sediment thickness gets reduced from earlier 10 km to only 4 km the size of the basin 44 500 km 2 would be in conformity with isostatic subsidence due to sedimentary accumulation hypothesis the structural features derived from present analysis like maximum depth observed near the thrust suture on the basin margin from where it decreases away from it its association of shallow marine sediments the arcuate shape of the basin along with its areal dimension resembles foreland basin between continent continent collisions

application of fracture mechanics to the simulation of seismicity and recurrence of characteristic earthquakes on a fault we present a fault model consisting of a large number of collinear cracks and intervening asperities for the simulation of seismicity and recurrence of large earthquakes on a fault we apply fracture mechanics to the analysis of the interaction of cracks and to the consideration of fracture condition our fault model gives rise to a complex frequency distribution of event sizes even if no externally imposed spatial inhomogeneity is assumed for the distribution of cracks and asperities and a homogeneous statistical distribution is assumed for fracture strengths the frequency distribution of event sizes is found to be bimodal with no intermediate size event in all the calculations for the smaller events the frequency distribution shows a power law behavior whereas the larger size events denote ones that rupture the whole fault statistically the same frequency distributions are obtained for inhomogeneous distributions of crack lengths and fracture strengths the occurrence of events that rupture the whole fault is shown to be periodic when the fault is isolated the magnitudes of these large events generally increase with increasing recurrence period for given fault length and rate of remote loading the events having a longer recurrence period have a shorter fault length for given magnitude and rate of remote loading if there are fault interactions the periodicity in the recurrence of the large events that would be observed for the isolated fault disappears and the recurrence of the large events becomes complex

possible mechanism of rockbursts in coal mines one of the important questions of rockburst prevention is the understanding of the mechanism of rockburst source this question can be effectively studied by direct seismic observations in the rockburst regions for this purpose the distribution ofp wave onset signs and the inversion of first motion amplitudes were utilized as the basic method in such a way the coal mine regions in poland upper silesia and in czechoslovakia kladno coal mine district were studied as part of the polish czechoslovak rockburst investigation project more than 250 rockburst events were recorded here in the decade 1977 1983 and analyzed the results of the statistical analysis of these data allow us to formulate and introduce a model of the rockburst source with an implosion component the suitability of this conception was verified by laboratory simulation conditions it was confirmed that the seismoactive displacements with a clear implosive component were recorded in the neighbourhood of a stress concentrator weakened by holes the results of both the field observations and laboratory tests were in good agreement with the theoretically derived radiation patterns for a combined shear implosive source and also with the theoretical conception of such a source based on real geometrical configurations of mine excavations and tectonic dislocations

imprints of a proterozoic tectonothermal anomaly below the 1 1 ga kimberlitic province of southwest cuddapah basin dharwar craton southern india summary a detailed 2 d modelling of the seismic structure and other geological and geophysical signatures across the cuddapah basin of the southern indian shield suggests upwarping of highvelocity and high density layers which are observed close to the surface below the southwestern part of the basin this anomalous feature is constrained by i a strong gravity high anomaly of about 55 mgal ii a 100 km wide high conductivity anomaly resistivity 100 m extending from surface to a minimum depth of 50 km in the mantle lithosphere and iii large scale massive intrusive activity these features are interpreted to be an expression of a thermal anomaly which may have acted like a plume during the proterozoic and could well correspond to a 1 1 ga kimberlitic activity below this region the thin granitic gneissic crust is underlain by well differentiated high velocity layers possibly due to underplating and densification of much of the crust by extruded magma

lithospheric mantle deformation beneath the indian cratons abstract the nature of deformation of the deep continental roots beneath the archean early proterozoic terrains opens the question whether these ancient terrains have had stable roots since the precambrian or whether recent plate motions have deformed them in view of this we make an attempt to study the thermal structure beneath the cratonic regions of the indian shield which vary in lithospheric thickness from 65 km in the singhbhum craton to 148 km in the archean dharwars the average depth of 104 km to the top of the underlying asthenosphere is consistent with other termination methods and is in fact less than half the 200 400 km depth found in other stable areas of the earth similarly the average reduced heat flow of about 35 mw m2 and moho temperature of about 550 c range 400 730 c for the indian cratons are also much higher than their counterparts elsewhere our study indicates a large scale deformation of the cratonic mantle lithosphere beneath the indian shield since the mesoproterozoic c

a 300 year surge history of the drangajokull ice cap northwest iceland and its maximum during the little ice age over the last 300 years each of the three surge type outlet glaciers of the drangajokull ice cap in northwest iceland has surged 2 4 times there is valuable historical information available on the surge frequencies since the little ice age lia maximum because of the proximity of the surging outlets reykjarfjar arjokull leirufjar arjokull and kaldalonsjokull to farms and pastures and monitoring of these glaciers since 1931 we have reconstructed the surge history of the drangajokull ice cap based on geomorphological mapping sedimentological studies and review of historical records geomorphological mapping of the glacier forefields reveals twice as many end moraines as previously recognized this indicates a higher surge interval than earlier perceived a clear relationship between the surge interval and climate cannot be established surges were observed more frequently during the 19th century and the earliest 20th century compared with the relatively cool 18th century and the late 20th century

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

glacial isostatic adjustment and the viscosity structure underlying the vatnajokull ice cap iceland we examine the dependence of glacial isostatic adjustment gia due to changes in the vatnajokull ice cap iceland on the underlying viscosity structure iceland offers a unique case study for gia research with a thinner elastic lithosphere underlain by a low viscosity zone or asthenosphere as opposed to regions such as fennoscandia or north america described by a thicker lithosphere while not necessarily featuring an asthenosphere

c o sr and nd isotope systematics of carbonates of papaghni sub basin andhra pradesh india implications for genesis of carbonate hosted stratiform uranium mineralisation and geodynamic evolution of the cuddapah basin abstract the cuddapah basin cb is one of a series of proterozoic basins that overlie the archaean cratons of india and contains a unique stratiform carbonate hosted uranium mineralisation in the present work we discuss stable c o and radiogenic nd sr isotope systematics of carbonates of the papaghni sub basin in order to understand uranium ore forming processes and geodynamic evolution of the cb uranium mineralised dolomites umds of the basal vempalle formation show a significantly lighter 1 5 c isotope signature compared to that of open marine stromatolitic sub tidal facies suggesting input of isotopically lighter carbon through in situ remineralisation of organic matter om this implies deposition in a hydrologically restricted redox stratified lagoonal basin wherein exchange with open oceanic dissolved inorganic carbon dic was limited persistent bottom water anoxia was created and maintained through consumption of dissolved oxygen do by decaying om produced in oxidised surface water zone significantly more radiogenic end t of umd 6 31 0 54 compared to that of dharwar upper crust 8 64 3 11 indicates that dissolved constituents did not originate from the dharwar craton rather were derived from more juvenile exotic sources possibly from a continental arc dissolved uranyl ions u 6 were introduced to the basin through fluvial run off and were reduced to immobile uranous ions u 4 at the redox interface resulting in precipitation of pitchblende and coffinite carbonate horizons of upper vempalle formation and tadpatri formation show progressively more radiogenic nd isotope compositions signifying increased juvenile arc contribution to the papaghni sub basin through time which is also corroborated by the presence of younger zircons 1923 22 ma in pulivendla quartzites we propose that the papaghni sub basin opened as a back arc extensional basin at 2 ga as a result of westerly directed subduction of oceanic crust beneath the eastern indian continental margin the papaghni back arc basin eventually evolved to upper cuddapah foreland basin with collision of the dharwar craton and napier block of antarctica at 1 6 ga possibly during the final stage of amalgamation of the columbia supercontinent

poisson s ratio behaviour in various crystalline rocks application to the study of the earth s interior the study of poisson s ratio behaviour in various crystalline rocks under different temperatures and pressures shows this parameter to depend upon the rock composition rather than upon p t conditions the results of this study are presented in the form of a comparison of z distributions within the consolidated crust and continental upper mantle and the specific variations of in crust and mantle rocks underlying the voronezh crystalline massif vcm these investigations which are based upon seismic and seismological data as well as high pressure experiments should clarify in particular the composition and petrology of the earth s interior

effects of subglacial geothermal activity observed by satellite radar interferometry we use one day synthetic aperture radar sar interferograms from data of the earth remote sensing satellites ers 1 and ers 2 to study ice flow and uplift of two surface depressions within the vatnajokull ice cap iceland the ice cauldrons are created by melting at sub glacial geothermal areas meltwater accumulates in a reservoir under the cauldrons over 2 to 3 years until it drains in a jokulhlaup under the ice dam surrounding the reservoir the ice surface in the depressions drops down by several tens of meters during these draining events but rises again as ice flows into the depressions until a jokulhlaup occurs again using sar interferograms we quantify an uplift rate of about 2 to 18 cm day within the jokulhlaup cycle varying with the surface slope of the depressions the uplift rate is high during the first months after a jokulhlaup when the cauldron is relatively deep with steep slopes but the uplift rate decreases as the cauldron is gradually filled a simple axisymmetric model simulating the ice flow into one of the depressions describes quantitatively the filling rate of the cauldron and qualitatively the shape of the ice flow field the best fit model has an ice flow law parameter a0 that is about one order of magnitude lower than typically estimated for temperate glaciers

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

gravity study along the kavali udipi deep seismic sounding profile in the indian peninsular shield some inferences about the origin of anorthosites and the eastern ghats orogeny abstract the crustal section along a 600 km long profile across the indian peninsular shield between kavali on the east coast and udipi on the west coast running approximately along 14 n latitude can be represented by a generalised three layer crustal model in accordance with the interpretation of gravity data along this profile based on the structural picture obtained from deep seismic soundings dss kaila et al 1979 these three crustal layers are an upper layer of density 2 70 g cm 3 corresponding to an average p wave velocity v p of 6 2 km sec an intermediate layer of density 2 75 g cm 3 v p 6 5 km sec and a deeper layer of density 2 85 g cm 3 v p 6 8 km sec crust of varied thicknesses and comprising the above three layers sits in general on upper mantle rocks of 3 3 g cm 3 corresponding to v p 8 2 km sec the regional gravity anomaly pattern along the profile can convincingly be explained as being due to the combined effect of intracrustal structural features and the configuration of the moho boundary as developed through tectonic activities along a number of faults detected by dss in the eastern portion of the profile corresponding to the cuddapah basin there exists an additional deep crustal layer of density 3 05 g cm 3 v p 7 2 km sec and an emplacement of highdensity material at shallow depths along weak zones on the eastern margin of the cuddapah basin this magmatic high density mass at shallow depth may extend as a linear subsurface feature along the entire eastern ghats belt as evidenced by the continuity of the similar gravity anomaly pattern and may be responsible for the eastern ghats orogeny and uplift this feature may be responsible for the plutonic activity to which the origin of anorthosite rocks found along the eastern ghats can be associated in the western part of the cuddapah basin the basaltic layer has thickened considerably with its top reaching a shallow depth of about 8 km this thickening of the basaltic layer is considered responsible for the generation of numerous dykes and sills in this region

model for intermediate term precursory clustering of earthquakes a causal sequence of an earthquake swarm extended quiescence foreshocks and main shock can be understood in terms of an aggregation model of crack growth and ultimate fusion on a multiplanar earthquake fault system the rheological model is one of accelerated crack growth under conditions of slip weakening coupled with a slow recovery of static friction after fracture once a slip feature has been generated that spans a large part of the available geometry a stress shadow is cast on other neighboring cracks that strongly retards and inhibits crack growth thus initiating the quiescent phase abruptly the success of the model depends on the assumption that nonlinear rheology regulates the rate of slip and that earthquake faults are not simply connected surfaces but instead have many strands

mantle derived fluids in the basement of the deccan trap evidence from stable carbon and oxygen isotopes of carbonates from the killari borehole basement maharashtra india we report here for the first time geochemical mineralogical and stable carbon and oxygen isotopic data on the crystalline basement rocks of the 1993 killari earthquake region of maharashtra india which is covered by a thick suite of deccan volcanics our results revealed the hitherto unknown amphibolite granulite nature of the 2 5 ga basement which contains 2 00 2 28 wt of co2 the stable carbon 13c and oxygen 18o isotopic measurements on carbonates separated from two basement samples kil 13 440 5 m depth and kil 20 499 6 m depth collected from the klr 1 borehole drilled in the epicentral region showed the respective values of 6 23 and 6 22 versus pdb for 13c and 7 94 and 8 11 versus smow for 18o the samples plot in the primary igneous carbonatite field indicating the mantle origin of the carbonates derived through the process of mantle metasomatism from the deep mantle carbon reservoir this would suggest large scale crust mantle thermal fluid interaction beneath the killari seismogenic region which is characterized by massive upwarping of the high velocity mafic crust and retrograde metamorphism

earthquake premonitory processes evolution of stresses and electric current generation the principles and assumptions of the earthquake premonitory and rebound theory are reviewed the theory based on a continuum model of fracturing processes the stress evolution equations describe the dynamic processes governing a continuous distribution of dislocations special attention is paid to the problem of electric current generation in a seismic source zone electric current is considered as reflecting the rate of polarization which is influenced by motion of the charge bearing dislocations the relationship between the current density and stress accumulation rate is derived

spot5 hrs digital elevation models and the monitoring of glacier elevation changes in north west canada and south east alaska abstract monitoring the response of land ice to climate change requires accurate and repeatable topographic surveys the spot5 hrs high resolution stereoscopic instrument covers up to 120 km by 600 km in a single pass and has the potential to accurately map the poorly known topography of most glaciers and ice caps the acquisition of a large hrs archive over ice covered regions is planned by the french space agency cnes and spotimage france during the 2007 2008 international polar year ipy here we report on the accuracy and value of hrs digital elevation model dem over ice and snow surfaces a dem is generated by combining tools available from cnes with the pci orthoengine se software using hrs images acquired in may 2004 over south east alaska usa and northern british columbia canada the dem is evaluated through comparison with shuttle radar topographic mission srtm dem and icesat data on and around the glaciers a horizontal shift of 50 m is found between the hrs and srtm dems and is attributed to errors in the srtm dem over ice free areas hrs elevations are 7 m higher than those of srtm with a standard deviation of 25 m for the difference between the two dems the 7 m difference is partly attributed to the differential penetration of the electromagnetic waves visible for hrs microwave for srtm in snow and vegetation we also report on the application of sequential dems srtm dem in february 2000 and hrs dem in may 2004 for the monitoring of glacier elevation changes we map the topographic changes induced by a surge of one tributary of ferris glacier maximum surface lowering of 42 10 m and rising of 77 10 m are observed in the 4 years time interval thinning rates up to 10 2 5 m yr are observed at low altitudes and confirm the ongoing wastage of glaciers in south east alaska

non riemannian and fractal geometries of fracturing in geomaterials the mechanism of earthquakes is presented by use of the elastic dislocation theory with consideration of the continuous dislocation field the general problem of medium deformation requires analysis based on non riemannian geometry with the concept of the continuum with a discontinuity no more continuum here we derive the equilibrium equation navier equation for the continuous dislocation field by introducing the relation between the concepts of the continuous dislocation theory and non riemannian geometry this equation is a generalization of the laplace equation which can describe fractal processes like diffusion limited aggregation dla and dielectric breakdown 1313 moreover the kinematic compatibility equations derived from navier equation are the laplace equations and the solution of navier equation can be put in terms of functions which satisfy the biharmonic equation suggesting a close formal connection with fractal processes therefore the relationship between the non riemannian geometry and the fractal geometry of fracturing damage in geomaterials as earthquakes can be understood by using the navier equation moreover the continuous dislocation theory can be applied to the problem of the earthquake formation with active folding related with faulting active flexural slip folding related to the continuous dislocation field

glacier volcano interactions deduced by sar interferometry glacier surface displacements produced by geothermal and volcanic activity beneath vatnajokull ice cap in iceland are described by field surveys of the surface topography combined with interferograms acquired from repeat pass synthetic aperture radar images a simple ice flow model serves well to confirm the basic interpretation of the observations the observations cover the period october 1996 january 1999 and comprise a the ice flow field during the infilling of the depressions created by the subglacial gjalp eruption of october 1996 b the extent and displacement of the floating ice cover of the subglacier lakes of grimsvotn and the skafta cauldrons c surface displacements above the subglacier pathways of the jokulhlaups from the gjalp eruption site and the grimsvotn lake d detection of areas of increased basal sliding due to lubrication by water and e detection of spots of temporal displacement that may be related to altering subglacial volcanic activity at the depression created by the gjalp eruption the maximum surface displacement rate away from the radar decreased from 27 cm d 1 to 2 cm d over the period january 1997 january 1999 the observed vertical displacement of the ice cover of grimsvotn changed from an uplift rate of 50 cm d 1 to sinking of 48 cm d 1 and for skafta cauldrons from 2 cm d 1 to 25 cm d 1

the 20th century retreat of ice caps in iceland derived from airborne sar w vatnajokull and n mýrdalsjokull we present observations of the long term recession of surging outlets of icelandic ice caps in response to 20th century climate in august 1998 synthetic aperture radar sar data covering the western part of vatnajokull and the northern part of m rdalsjokull in southern iceland were acquired with the danish airborne emisar radar system polarimetric and interferometric sar data reveal the margins of the present ice caps as well as a series of terminal moraines in the fore field these moraines date back to the maximum neoglacial extent at the end of the 19th century and the outermost allow reconstruction of the margin at that time the data offer a unique opportunity to estimate the area decrease of these ice caps in the 20th century the influence of the fluctuations of the surge type outlets constituting most of w vatnajokull area and a good part of n m rdalsjokull area is minimal since they had all recently surged in 1998 as was presumably the case when the outermost moraines were formed the major contributor to the area decrease is therefore climate changes in the 20th century even though the glacier retreat has been interrupted by short lived surges moraines associated with most of the surges in w vatnajokull in the 20th century are observed in the sar data including the most recent surges in the 1990s interestingly no push moraines were observed in front of the surge advance but the moraines appear when the glaciers start retreating we estimate that the collective decrease of the outlets of western vatnajokull since maximum neoglacial extent of each outlet is 109 km2 6 7 corresponding to an average retreat of 850 m over a 130 km long margin in the same period the outlet slettjokull in n m rdalsjokull has decreased by 33 km2 20 corresponding to an average retreat of 1500 m over a 20 km long margin

surges of outlet glaciers from the drangajokull ice cap northwest iceland abstract surface elevation and volume changes of the drangajokull surge type glaciers reykjarfjar arjokull and leirufjar arjokull were studied by comparing digital elevation models that pre date and post date their most recent surges annual glacier frontal measurements were used to estimate average ice velocities during the last surge of the glaciers the observations show a distinct ice discharge most of which was from the upper reservoir areas down to the receiving areas during the surges the surface draw down in the reservoir areas was usually 10 30 m during the surges while the thickening of the receiving areas was significantly more variable on the order of 10 120 m despite a negative geodetic net mass balance derived from the digital elevation models the reservoir areas have been gaining mass since the surge terminations this surface thickening along with considerable ablation of the receiving areas will most likely return the glacier surface profiles to the pre surge stage our results indicate that a greatest surface thinning in the upper reservoir areas of drangajokull rather than proximal to the equilibrium line during vatnajokull surges and b development of drangajokull surges that resembles svalbard surge type glaciers rather than vatnajokull surge type glaciers the contrasting surge characteristics could be explained by differences in glacier geometry topography and substratum of the drangajokull and vatnajokull surge type glaciers

exposed cross sections through the continental crust implications for crustal structure petrology and evolution abstract the continental crust is exposed in cross section at numerous sites on the earth s surface these exposures which appear to have formed by obduction along great faults during continental collision may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle from an examination of five complexes which meet these criteria it is concluded that the most prominent layering in the crust is not compositional but metamorphic the lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks respectively post metamorphic granitic intrusions are common at intermediate to shallow levels position of discontinuities in refraction velocity where present commonly correspond to changes in composition or metamorphic grade with depth the continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by cocorp field observations coupled with geochemical data indicate a complex evolution of the lower crust which can include anatexis multiple deformation polymetamorphism and reworking of older crustal material the complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments

seismically derived gondwana and proterozoic sediments east of cuddapah basin south indian shield and its possible geotectonic implications the study area situated east of the intracratonic proterozoic cuddapah basin that covers nellore schist belt ongole domain of the eastern ghats belt and adjacent east coast terrain forms a geodynamically important segment of the dharwar craton this region came into focus due to proposition that during paleoproterozoic to mesoproterozoic era it underwent persistent oceanic subduction continent continent collision and multi stage accretional growth in view of this we have reprocessed in detail the deep seismic sounding data over this region and integrated the obtained results with other geophysical studies to decipher the deep subsurface crustal structure underneath the derived shallow seismic section across this region showed the presence of a thin layer 250 m of gondwana sediments with a distinct velocity of 4 20 km s and a lateral dimension of about 40 km around vinjamuru region of the nellore schist belt another important finding has been the depiction of 5 3 and 5 5 km s velocity sediments comparable to upper and lower cuddapah sediments between nellore schist belt and the east coast indicating the possible presence of an additional proterozoic sedimentary terrain named here as east coast sedimentary basin overlying the concealed archean crystalline basement the presence of this sedimentary terrain which is separated from the cuddapah basin by an exhumed horst like feature situated below nellore schist belt would indicate proterozoic sedimentation in a much larger area during columbia and rodinia supercontinental assembly periods than hitherto known importantly no seismic trace of the eastern ghats belt has been found between nellore schist belt and the east coast it appears that during the gondwana period entire eastern segment of the east dharwar craton has been persistently rifting uplifting and eroding together with other gondwana grabens in india thereby leaving behind only a thin veneer of gondwana sediments at many places in view of the presence of number of gondwana occurrences all along the east coast it is felt that the rifting during the gondwana period may have been a prelude to india antarctica breakup with final separation between the two taking place much later during early cretaceous

analysis of the electromagnetic field recorded in the friuli seismic zone northeast italy abstract some examples of unusual telluric activity were found during the italian polish magnetotelluric measurement campaign in the friuli seismic zone 1987 1988 the standard procedure for the elimination of the induction component from the telluric recordings and the calculation of the transfer functions were first applied however due to a high noise level in the observed telluric fields in the northern alpine region it appeared indispensable to develop new methods for the detection of any tectonically related component of the telluric field the common function defined as the average curve derived from two telluric stations and multiplied by the correlation coefficients moving window procedure allowed an increase in the telluric activity time changes of variances to be traced before and during seismic events in september 1987 and february 1988 another approach was based on the time frequency isoline calculations of the poynting vector of electromagnetic field positive isoline values opposite to the usual downward direction of this flux were discovered and correlated with a course of seismic activity some good results were found for the time intervals studied some considerations on a mechanism for the generation of an electric current in a zone of seismic preparation are discussed an accumulation of stress leads to an oriented motion of the charged charge bearing dislocations the mechanism consists of the formation of a kind of polarization current induced by the motion of these dislocations

the purana basins of southern cratonic province of india a case for mesoproterozoic fossil rifts abstract since its cratonization in the palaeoproterozoic southern peninsular india witnessed the development of a number of large intracratonic sedimentary basins traditionally referred to as purana basins spanning in age from late palaeoproterozoic through neoproterozoic the localization of these intracratonic basins namely pranhita godavari pg chattisgarh and cuddapah basins is apparently controlled by pre existing sutures and or weak zones the pg basin and the cuddapah basin host unconformity bound thick sediment dominated successions attesting to several cycles of fluvial shallow marine to shelf slope basin sedimentation deposition was punctuated by block uplifts resulting in local hiatuses and or volcanic upheavals leading to intercalation of thin but persistent basaltic flows and acid tuffs and ignimbrites basin margin deep faults apparently played a role in the facies distribution in these basins based on these features we propose that these basins initiated as continental rifts which however never opened up into a full fledged ocean basin but links with open seaway are evident from frequent occurrence of deposits representing tidal and storm influence particularly in upper part of the chattisgarh succession spatial distribution of facies and sediment thickness in the cuddapah and pg basins suggest that an open seaway existed to the east of the south indian cratonic province during the mesoproterozoic while similar criteria point to the existence of an open seaway north of the chattisgarh basin development history including nature of inversion suggest that the southern cratonic province of india existed as a single large continental mass since the mesoproterozoic in spite of episodes of supercontinent build up and fragmentation involving india and east gondwana during the proterozoic

ice volcano interactions during the 2010 eyjafjallajokull eruption as revealed by airborne imaging radar 1 during the eruption of the ice covered eyjafjallajokull volcano a series of images from an airborne synthetic aperture radar sar were obtained by the icelandic coast guard cloud obscured the summit from view during the first three days of the eruption making the weather independent sar a valuable monitoring resource radar images revealed the development of ice cauldrons in a 200 m thick ice cover within the summit caldera as well as the formation of cauldrons to the immediate south of the caldera additionally radar images were used to document the subglacial and supraglacial passage of floodwater to the north and south of the eruption site the eruption breached the ice surface about four hours after its onset at about 01 30 utc on 14 april 2010 the first sar images obtained between 08 55 and 10 42 utc show signs of limited supraglacial drainage from the eruption site floodwater began to drain from the ice cap almost 5 5 h after the beginning of the eruption implying storage of meltwater at the eruption site due to initially constricted subglacial drainage from the caldera heat transfer rates from magma to ice during early stages of cauldron formation were about 1 mw m 2 in the radial direction and about 4 mw m 2 vertically meltwater release was characterized by accumulation and drainage with most of the volcanic material in the ice cauldrons being drained in hyperconcentrated floods after the third day of the eruption meltwater generation at the eruption site diminished due to an insulating lag of tephra

configuration of the late paleoproterozoic supercontinent columbia insights from radiating mafic dyke swarms abstract remnants of 2 1 1 8 ga orogens can be recognized in nearly every craton assembled within reconstructions of the rodinia supercontinent although no particular pattern of laterally extensive orogenic belts emerges these cratons may be the fragments of an older supercontinent formed in response to the collision and accretion of even older cratons during the early earth history paleomagnetic constraints have played a limited role in many previous reconstructions of the early precambrian supercontinent mainly because of the poor age control and a large scatter of the paleomagnetic poles the geometry of giant radiating dyke swarms and orogenic belts provide important constraints for the reconstruction of the pre rodinian supercontinent some early unmetamorphosed and undeformed mafic dyke swarms in north china southern peninsular india and north america share coeval age of 1 85 ga if these continents are assembled the overall pattern exhibited by the mafic dyke swarms appears to constitute a giant radiating swarm with a piercing point between the cuddapah rift in south india and the xiong er aulacogen in north china this suggests that the north china craton indian craton and canadian shield may be fragmented from the same landmass the reconstruction of 1 85 ga giant radiating dyke swarm attempted in this paper suggests that the north china craton india craton and canadian shield were united together to form a landmass within the columbia supercontinent before its extension and break up the 1 90 1 85 ga andean style north orogenic belt suggests that a subduction zone existed on the northern margin of the north china craton wopmay orogenic belt developed in a 1 88 1 84 ga continental volcano plutonic arc which is interpreted as the product of eastward subduction of oceanic lithosphere the transantarctica orogenic belt in east antarctica may be another candidate to be linked with the subduction zone the north orogenic wopmay orogenic and transantarctica orogenic belts could be connected to form a continuous subduction zone the orogenic comparison strengthens the configuration of the columbia supercontinent proposed by the reconstruction of the giant radiating dyke swarm the laurentia west australia and east antarctica were relatively stable from 1 85 ga to 1 20 ga as inferred from the data on dyke swarms magmatism and the paleomagnetism these continents constituted the core of the columbia supercontinent in the late paleoproterozoic time the north china craton and indian craton were however separated from the columbia supercontinent during the mesoproterozoic time

collision tectonics in the late precambrian eastern ghats mobile belt mesoscopic to satellite scale structural observations regional mapping of a section across the eastern ghats mobile belt egmb north of the godavari graben in eastern peninsular india by using landsat thematic mapper data enables recognition of a number of shear zones lineaments and structural domes and basins a conspicuous megashear occurs at the western boundary of the granulite facies rocks of the egmb adjacent to the archean granite greenstone craton the confinement of a suite of alkaline igneous rocks to this shear zone is a notable feature the strike extensions of this shear belt extend through to the elchuru alkaline complex prakasam district andhra pradesh and the syenite plutons of koraput district orissa the contrasting lithologies metamorphism and structural history on either side of the shear zone suggests that it might be a precambrian suture zone the mesoscopic structural features in the egmb include prominent foliation with moderate to steep dips folds faults shears s c fabrics pinch and swell structures and other linear fabric elements these observations favour the consideration of drastic crustal shortening and thickening and a complex deformational sequence the major rock units in this part of egmb comprise garnetiferous sillimanite gneisses quartzites and calc granulites forming the khondalitic suite of rocks and a wide variety of charnockitic rocks the contact of the two rock units is generally sheared and often migmatised the structural fabric suggests two major tectonic events an essentially horizontal tectonic regime resulting in thrust systems and associated structures subsequently followed by strike slip tectonics characterized by high shear strains features such as westward verging thrusts large scale recumbent folds major shear zones structural domes and basins indications of tectonic crustal shortening extensive calc alkali magmatism and widespread migmatization in the region are attributed to collisional processes during proterozoic times the spatial disposition of the egmb and its linkage with the distribution of similar rock units during the late precambrian time in a global tectonic scenario are discussed

stratigraphic and structural development of the precambrian cuddapah basin s e india abstract the present work recognizes a subdivision of the cuddapah basin into 3 separate main units of deposition some of the earlier correlations proved to be untenable for practical reasons king s widely used stratigraphy is retained where possible in a revised form we recognise the cuddapah group 2000 1490 1450 ma nallamalai group 1490 1450 1090 870 ma and the kurnool group 1090 870 500 ma on the basis of surface geology mapping and photo interpretation we discern 5 tectonic zones the boundaries of these zones coincide with deep crustal faults encountered in a deep seismic sounding survey three phases of tectonic activity are 1 1 crustal movements resulting in broad folds affecting the cuddaph rocks exposed in the western area followed by 2 2 folding of the nallamalai rocks east of the rudravaram line and 3 3 later folding and metamorphism in the eastern tectonic zones structural sections allow an interpretation of an eastward continuation of the cuddapah basin rocks into the highly metamorphosed series underlying the eastern ghats complex a colour geological map and sections are included

rbsr ages of proterozoic kimberlites of india evidence for contemporaneous emplacement abstract rb sr analyses of leached phlogopite macrocrysts from kimberlite pipes 1 2 5 and 7 in south india give concordant ages of 1091 20 1092 15 1093 20 and 1091 10 ma respectively indicating contemporaneous emplacement of these pipes the present results are in contradiction with earlier measurements groundmass mineral assemblages with low rb sr ratios give a tight set of initial sr ratios at 0 7029 2 0 7019 2 0 7029 2 and 0 7030 4 suggesting derivation of the primary kimberlite magma from a relatively uniform and depleted mantle source a similar age and initial sr isotopic ratio of one sample of the majhgawan lamproite from central india imply that the proterozoic kimberlite lamproite activities in india though widely separated in space were nearly contemporaneous

regional stress field as determined from electromagnetic radiation in a tunnel abstract the paper presents the results of electromagnetic radiation emr measurements in the feuerberg tunnel in southwest germany emr is associated with small scale fracturing processes the measured numbers of emr impulses are shown to be proportional to shear stresses from the correlation of emr and shear stresses along the long axis of the tunnel orientations and magnitudes of the horizontal principal stresses are determined the major horizontal principal stress is 3 6 0 3 mpa and has an azimuth of 143 6 the minor principal horizontal stress is 2 1 0 3 mpa zones in the tunnel are located where low shear stresses occur because vertical overburden and horizontal stresses are equal in these zones also minimum radiation was detected a possible stress accumulation close to a fault is suggested by higher emr values in a part of the tunnel orientations and magnitudes of the horizontal principal stresses which are derived from the measurements of emr correlate well with conventional stress measurements it is suggested that the cross section measuring method described in the study is used to determine regional stress fields as well as to investigate endangered zones with high stresses in underground facilities which may be critical with regard to stability

new earthquake rebound theory abstract the model adopted in this paper assumes that a medium is permeated with a continuum field of defects and that a flow of defects describes an advanced state of deformation leading to fracturing the obtained system of equations describes a field of internal stresses and a relative flow velocity of cracks the form of equations shows that before an earthquake a field of internal stresses reaches its maximum and that this moment corresponds to a specific silent gap expressed by the disappearance of the relative velocity field of cracks later on there starts a rebound process with an opposite sense of relative velocities with decrease of defect density joining of cracks and with a main process of earthquake release

sedimentation and magmatism in the paleoproterozoic cuddapah basin india consequences of lithospheric extension abstract the cuddapah basin is one of many proterozoic intracontinental sedimentary basins across peninsular india the basin comprises several unconformity bounded successions the lowermost of which the papaghni group and overlying chitravati group are intruded by dolerite sills that contact metamorphosed their host rocks a mafic ultramafic sill from the base of the tadpatri formation in the chitravati group was previously dated at c 1885 ma and interpreted to be part of a large igneous province lip we have dated two samples of a felsic tuff from the upper part of the tadpatri formation at 1864 13 ma and 1858 16 ma combining data from the two samples yields a weighted mean date of 1862 9 ma mafic sills intrude rocks stratigraphically above the tuffaceous beds indicating that mafic magmatism continued until after c 1860 ma given that the sills intruded lithified rocks some of the sills may be considerably younger than 1860 ma mafic volcanic rocks are also known from below the unconformity at the base of the chitravati group within the basal papaghni group c 1890 ma collectively these data indicate that mafic sill emplacement spanned more than 30 myr so that it is likely to have been a protracted event or a series of events and therefore unlikely to represent a lip the time span for mafic magmatism is more compatible with episodic lithospheric extension passive rifting during basin evolution than it is with a mantle plume active rifting

structural trends in the cuddapah basin from deep seismic soundings dss and their tectonic implications abstract structural trends in the upper proterozoic cuddapah basin at the basement level and at the moho level have been discussed based on deep seismic sounding dss studies results of dss studies along the alampur koniki profile profile 2 of fig 1 crossing the northern part of the cuddapah basin have been discussed in detail these results combined with the results of the kavali paranpalle section of the kavali udipi dss profile profile 1 of fig 1 kaila et al 1979 crossing the basin on its southern flank along with geological data and earthquake epicentral locations are used to explain the structural trends of the area it has been shown that the cuddapah basin was first created in its western part by downfaulting of the crustal block between faults 7 and 14 towards the west and fault 6 in the east fig 1 subsequently the eastern part was downfaulted against fault 6 before the commencement of upper cuddapah sedimentation further downfaulting towards the north along fault 5 created the srisailam block minor scale downfaulting between faults 7 and 13 in the west and fault 6 in the east and fault 8 in the north gave rise to the kurnool sub basin at a later stage similar downfaulting east of fault 9 and north of fault 5 gave rise to the palnad sub basin both these sub basins received kurnool sediments after the close of kurnool sedimentation the blocks between faults 4 and 6 along profile ii and between 11 and 6 along profile i were uplifted at the basement level thus giving rise to the nallamalai hills and iswarakuppam dome fig 1 the low angle thrust fault 3 on the eastern margin of the cuddapah basin might be a post cuddapah phenomenon the low angle thrust fault 2 probably occurred in the post dharwar period faults 1 17 and 10 near the east coast of india seem to be comparatively younger probably of mesozoic time along which the coastal block is downfaulted giving rise to the sedimentary basins

relative contribution of surface mass balance and ice flux changes to the accelerated thinning of the mer de glace alps over 1979 2008 by subtracting surface topographies from 1979 1994 2000 and 2008 we measured ice thinning rates increasing from 1 m a 1 1979 1994 to more than 4 m a 1 2000 2008 on the tongue of the mer de glace the relative contributions of changes in surface mass balance and ice fluxes to this acceleration in the thinning are estimated using field and remote sensing measurements between 1979 1994 and 2000 2008 surface mass balance diminished by 1 2 m w e a 1 mainly because of atmospheric warming mass balance changes induced by the growing debris covered area and the evolving glacier hypsometry compensated each other meanwhile the mer de glace slowed down and the ice fluxes through two cross sections at 2200 m a s l and 2050 m a s l decreased by 60 between 1979 1994 and 2000 2008 two thirds of the increase in the thinning rates was caused by reduced ice fluxes and one third by rising surface ablation however those numbers need to be interpreted cautiously given our inability to respect mass conservation below our upper cross section an important implication is that large errors would occur if one term of the continuity equation e g surface mass balance was deduced from the two others e g elevation and ice flux changes

magneto telluric recordings from the friuli seismic zone northeast italy abstract magneto telluric measurements were undertaken in the friuli seismic area of north east italy the purpose was to find possible correlations between magneto telluric signals and seismic activity two stations were operational between july 1987 and june 1988 apparent resistivity curves were found for september 1987 and january 1988 data and a magneto telluric inversion problem was solved artificial noise and natural disturbances of the electromagnetic field especially those related to tectonic processes are discussed

elastic properties of amphibolite and granulite facies mid crustal basement rocks of the deccan volcanic covered 1993 latur killari earthquake region maharastra india and mantle metasomatism abstract present study provides a new data set of p and s wave velocities and density of metasomatized mid crustal amphibolite and granulite facies basement rocks of the 1993 latur killari earthquake region of maharashtra india which is concealed below a thick suite of deccan volcanics this includes laboratory tests geochemical analysis and petrographic examination on 29 fresh cored samples selected from the depths between 351 7 m and 616 8 m of the klr 1 borehole drilled in the earthquake epicentral zone these samples show a wide range in sio2 content from 52 2 to 70 0 wt majority of these samples are characterized by intermediate composition with a mean density of 2 85 g cm3 range 2 72 3 06 g cm3 and average p and s wave velocities of 6 23 km s 5 83 6 61 km s and 3 56 km s 3 21 3 96 respectively they also contain quite high amount of feot and cao with respective means of 9 76 and 6 59 wt average poisson s ratio is 0 25 together with respective values of young s bulk and rigidity modulus at 90 8 gpa 62 0 gpa and 36 3 gpa inspite of having higher densities some of the biotite and feo rich samples exhibit unusually low velocities consequent to metasomatic activity our study demonstrates that the mantle metasomatic alteration and retrogression of the underlying high velocity mafic crust under the latur killari earthquake region accompanied by geodynamic process of uplift and erosion during the geologic past has led to severe changes in the petrophysical and elastic properties of the studied rocks

the impact of jokulhlaups on basal sliding observed by sar interferometry on vatnajokull iceland we have analyzed insar data from the ers 1 ers 2 tandem mission to study the ice dynamics of vatnajokull iceland during jokulhlaups from the skaftacauldrons and the grimsvot n geothermal area which drained under the tungnaarjokull and skei ararjokull outlets respectively during the initial phase of a grimsvotn jokulhlaup in march 1996 the velocity of skei ararjokull increased up to three fold relative to observed velocities in december 1995 over an area up to 8 km wide around the subglacial flood path accumulation of water was observed at one location in the flood path during a small jokulhlaup from the skaftacauldrons in october 1995 the velocity on tungnaarjokull increased up to four fold over a 9 km wide area the velocity increase was observed 1 5 days before the floodwater was detected in the river skafta a reduced glacier speed as the flood peaked in skaftaindicates evolution of the subglacial drainage system from sheet to tunnel flow the glacier acceleration and local uplift observed in the early phase of both jokulhlaups supports the concept that increased water inflow in a narrow tunnel system causes water pressure to rise and forces water into areas outside the channels thus reducing the coupling of ice with the glacier bed

radioactivity heat flow and rifting of the indian continental crust the relationship between heat flow q and heat production a in india is quite different for the northern and southern parts of the peninsula in the north locations in a variety of tectonic settings including gondwana rifts show a linear relationship between q and a with a common reduced heat flow q about 40 mwm 2 in southern india the heat production of surface rocks is greater than is expected for the measured heat flow relative to other continental shields g is high in northern india and about average in the south apparently the indian crust evolved with a content of radioactive elements higher than in most shields and the southern part of the peninsula has undergone regional depletion in the lower crust and possibly upper mantle this depletion may coincide with a regional granulite event about 2 500 m y ago the high heat flow and heat production in northern india may explain several unique characteristics of the indian peninsula one feature is the continued reactivation of rif

deep crustal electrical signatures of eastern dharwar craton india abstract wide band magnetotelluric mt investigations were carried out along a profile from kavali in the east to anantapur towards west across the eastern ghat granulite terrain eggt eastern dhanvar craton edc and a proterozoic cuddapah basin this 300 km long profile was covered with 20 stations at an interval of 12 18 km the mt data is subjected to robust processing decomposition and static shift correction before deriving a 2 d model the model shows a resistive crust 10 000 30 000 ohm m to a depth of 8 10 km towards west of the cuddapah basin the mid crust is less resistive about 500 ohm m and the lower crust with a slight increase in resistivity about 1 500 ohm m in the depth range of 20 22 km the resistivity picture to the east of the cuddapah basin also showed a different deep crustal structure the resistivity of upper crust is about 5 000 ohm m and about 200 ohm m for mid and lower crust the sediment resistivity of cuddapah basin is of the order of 15 20 ohm m mt model has shown good correlation with results from other geophysical studies like deep seismic sounding dss gravity and magnetics the results indicate that the lower crustal layers are of intermediate type showing hydrous composition in eastern dhanvar craton

earthquake recurrence and risk assessment in circum pacific seismic gaps the development of the concept of seismic gaps regions of low earthquake activity where large events are expected has been one of the notable achievements of seismology and plate tectonics its application to long term earthquake hazard assessment continues to be an active field of seismological research here i have surveyed well documented case histories of repeated rupture of the same segment of circum pacific plate boundary and characterized their general features i find that variability in fault slip and spatial extent of great earthquakes rupturing the same plate boundary segment is typical rather than exceptional but sequences of major events fill identified seismic gaps with remarkable order earthquakes are concentrated late in the seismic cycle and occur with increasing size and magnitude furthermore earthquake rup ture starts near zones of concentrated moment release suggesting that high slip regions control the timing of recurrent events the absence of major earthquakes early in the seismic cycle indicates a more complex behaviour for lower slip regions which may explain the observed cycle to cycle diversity of gap filling sequences