validation of lateral fluid flow in an overpressured sand shale sequence during development of azeri chirag gunashli oil field and shah deniz gas field south caspian basin azerbaijan abstract data collected over the past 15 years from exploration appraisal and production in the offshore south caspian sea validates the previously developed model of lateral fluid flow from the overpressured basin center to the basin margins within the sandstone aquifers of the pliocene productive series specifically new data confirm the predictions that 1 although both sandstones and shales are overpressured sandstones are generally less overpressured than shales 2 there is a lateral regional gradient in sandstone overpressure decreasing from the basin center to the basin margin and 3 the impact on the pressure field from local features such as mud volcanoes or local faults is limited additional pressure data combined with regional seismic mapping suggests variations in lateral fluid flow in different stratigraphic intervals these data show that the less continuous sandstones of the upper and lower productive series are closer to the surrounding shale pressures as they are less well connected to the basin margin outlet whereas continuous sandstones in the middle productive series show the highest amount of lateral pressure transfer from the basin center and are therefore at lower pressures than the surrounding shales pressure data from development wells at the azer chirag gunashli oil field and the shah deniz gas condensate field reveal local variations in sandstone and shale overpressure resulting from the lateral pressure transfer affect traugott and heppard 1994 traugott 1996 swarbrick and osborne 1998 yardley and swarbrick 2000 across large high relief structures well connected sandstones transmit fluid pressures from the adjacent deep overpressured synclines into the shallower crest of the structure pressures in sandstones decrease updip along a hydrostatic gradient 0 433 psi ft the pressure gradient in the shales however will change according to the shale overpressure gradient in the south caspian basin the overpressure gradient in the shales varies between 0 6 and 0 9 psi ft therefore the relative overpressure between the sandstones and shales varies along structural dip there are a number of important implications to exploration appraisal and development because of large scale lateral fluid flow lateral fluid flow has consequences for the sealing capacity of sandstone reservoirs and the variable position of hydrocarbon to water contacts around a structural accumulation this requires each sandstone shale couplet be considered separately for pore pressure prediction basin scale 3d models were constructed to better understand the implications of basin scale fluid flow within and between individual reservoirs at each structure

thermal anomalies in the central indian ocean evidence for dewatering of the bengal fan seafloor heat flow measurements in the central indian ocean are locally higher than predicted by lithospheric cooling models these anomalously high heat flow values occur in a region affected by folding and faulting of oceanic crust and overlying distal bengal fan sediments three closely spaced sites drilled during ocean drilling program leg 116 dated the onset of deformation in this area at about 7 8 ma here apatite fission track thermochronometric data from sites 717 and 718 and numerical simulations are used to 1 quantify the effects of bengal fan sedimentation on seafloor heat flow 2 evaluate the thermal history of sediments penetrated at these two sites and 3 constrain mechanisms responsible for anomalous seafloor heat flow in this area at the rates sediments were deposited along the distal fan 350 m m y numerical simulations predict a 6 to 9 reduction in present day heat flow at the seafloor relative to heat flow through the base of the lithosphere at site 717 thermal history simulations assuming heat transfer dominated by conduction are consistent with available down hole temperature measurements and apatite fission track data site 718 is located 8 km south of site 717 and 2 km south of a high angle fault that offsets oceanic crust by about 300 m a previously published detailed heat flow survey conducted around site 718 documented seafloor heat flow ranging from 44 to 166 mw m2 over kilometer scale distances in addition a monotonic 10 to 20 reduction in the mean length of fission tracks in apatite from 560 to 960 m below the seafloor at site 718 implies bottom hole temperatures of the order of 50 60 c for a time period greater than a few million years both the seafloor heat flow and apatite fission track data argue for localized possibly intermittent advection of heat by lateral updip migration of pore fluids in the vicinity of site 718 taken together the heat flow data and temperature range inferred from the apatite fission track data at site 718 imply a fluid source in the upper crust upward movement of pore fluids at velocities of less than 1 cm yr through a basement sediment boundary maintained at temperatures ranging from 65 to 80 c is capable of explaining both sets of observations as a hypothesis to reconcile existing observations i suggest that the anomalous thermal structure in the central indian ocean represents a joint response to compaction driven dewatering of the bengal fan and local enhancement of the vertical permeability in the upper crust and sediment pile due to intraplate deformation

a two dimensional model of overpressure development and gas accumulation in venture field eastern canada 1 we used a basin scale model to reconstruct the development of overpressures in a sedimentary basin the area of application is the venture gas field nova scotia canada it is in an overpressured zone in which sedimentation rates have been relatively low since 90 ma and where large horizontal stresses have been evidenced we investigated the importance of overpressure mechanisms using the institut francais du petrole temispack model which integrates compaction hydraulic fracturing fluid flow heat transfer and the formation and migration of hydrocarbons we first constructed a reference model using geological geochemical and physical data second we studied sensitivity of the model to several input parameters and from this deduced additional constraints the modeled permeability along faults and of shaly beds interlayered in the reservoirs must be very low to enable both the local and regional distributions of overpressure and gas to be reproduced several runs of the reference model studying the relative importance of possible overpressuring mechanisms and the relative contribution of plausible source rocks to gas accumulations showed that gas generation and accumulation and lateral compression contribute little to overpressuring which is mainly accounted for by compaction disequilibrium in spite of low sedimentation rates faults and shaly beds play an important role in maintaining the overpressure gas generation in the reservoir units or close to them does not contribute significantly to the field gas accumulations gas sources are likely to be found in the underlying formations

flexural plate subsidence sedimentation rates and structural development of the super deep south caspian basin abstract on a 270 km long seismic line across the west central and central parts of the south caspian basin an inverse flexural plate method is used to recover original uploaded plate parameters the original plate shows remarkable consistency of parameters determined from the 12 second deep seismic line with average rigidity d 1023 6nm bending moment m 1016n dip angle 0 14 and in line compressive stress of 1012 3n m 1 by sequentially adding the sedimentary units to the average bare basement it is shown that the geometry of the basin at jurassic time had a major downward warp and high sedimentary fill to the west leaving the eastern section open to possible erosion during early and middle cretaceous time the deep western part of the basin was then filled by sediments during late tertiary quaternary time and a new depocenter created across the central and western parts of the basin this newer depocenter was then filled during pliocene quaternary time the combined flexure of the basement plate and corresponding sediment fill behaviors with time are indicative of corresponding lithologic variations across the basin and with suspected organic rich sediments the integrated description of basement sediments and depocenter behavior points to the utility of the inverse procedure for improving our understanding of basinal evolution the value of rigidity is comparable to estimated oceanic crust values in line with the suspected tethys oceanic fragment of an island arc below the sediments the shift in depositional behavior with time from west to more northerly across the line of section is tied to the orogenic rise of the caucasus mountains to the north of the section and to the continued subduction of the talysh vandam plate fragment northward today the transpressional nature of the basin and the resolution of the in line compressive stress into components perpendicular to the great caucasus 70 and also perpendicular to the west caspian deep laid fault 25 30 are both in accord with the 25 30 km of present day sedimentary cover including the variations of thicknesses of seismic stratigraphic units along the section from azerbaijan in the west to nearly the turkmenian border in the east

geohistory thermal history and hydrocarbon generation history of the north west south caspian basin abstract both the hydrocarbon potential of and excess fluid pressure build up in the thick 25 30 km sedimentary pile of the northwestern part of the south caspian basin were evaluated using a one dimensional fluid flow compaction model the model consists of three parts a geohistory model a thermal history model and a hydrocarbon generation model input data for the model are commonly used depth values of geological parameters lithofacies formation thicknesses stratal ages porosity permeability pore pressure temperature total organic carbon content type of organic matter vitrinite reflectance and other maturity indicators in order to bracket oil generation in terms of timing and depth location two extreme thermal histories were modeled paleoheat flow values at one half and twice the present day values with a linear variation through time to present day measured values the most intensive oil generation occurs during the last 5 2 my when the oil window is confined to depths between 5 7 5 km in the northwest 7 10 km in the west onshore part of the study area and 8 11 km in the central and southwestern parts of the area below the oil window cracking occurs of oil into gas rapid sedimentation which took place in the middle pliocene through quaternary results in overpressure build up across all of the study area maximum values of excess fluid pressure of 300 400 atm at 6 10 km are reached in the central and southeastern parts of the area where the sedimentation rate is the highest isobaric contours of excess pressure are then at shallow depths compared to the previous history of the area because there is a laterally decreasing trend of excess pressure oriented from the central and western parts of the area to the northeast and in addition the sand shale ratio is increasing in the same direction inferences that can be drawn on the most probable hydrocarbon migration directions suggest recent flows towards the northeast with hydrocarbon accumulations of gas and light oil likely to be more prevalent in the northeastern sands

heterogeneous lithosphere and the underlying mantle of the indian subcontinent abstract p and s receiver functions prfs and srfs respectively for 21 broad band seismograph stations of the india meteorological department imd illuminate lithosphere and the underlying mantle of some previously poorly sampled regions of the indian sub continent our analysis demonstrates that the archean and early proterozoic lithospheric keel of the indian shield has been reworked by younger processes we find very low s wave velocities in the uppermost mantle from 4 0 to 4 3 km s to the north of the deccan volcanic province kutch region and aravalli craton 1 in the south southern granulite terrain and sri lanka 2 and in the north east gangetic plane bengal basin and singhbuhm craton 3 the anomalies 1 and 2 may extend into the transition zone early arrivals of the s410p seismic phase are indicative of anomalously high vp vs ratio 1 9 in the upper mantle of the low velocity regions whereas late arrivals in the western himalaya ladakh and western tibet are consistent with the previously found indications of anomalously low vp vs ratio a transition from the high s velocity mantle lid to a layer of slightly lower velocity is seen in part of the data but a straightforward interpretation of this transition as the lithosphere asthenosphere boundary is problematic a mafic s velocity in the upper crust and a pronounced low s velocity layer in the lower crust beneath the eruptive center is practically the only specific feature in the lithosphere that may be linked to the deccan traps a separation in depths between the 410 km and 660 km discontinuities varies laterally in a range from 240 to 270 km the largest uplift of the 410 km discontinuity up to 390 km is observed beneath the foothills of the himalaya where it is caused by cooling of the transition zone by the ongoing continental collision

the upper mantle beneath ninetyeast ridge and broken ridge indian ocean from surface waves summary the rayleigh wave group velocities are used to determine the upper mantle structure of the aseismic ridges of the eastern indian ocean i e the ninetyeast ridge and the broken ridge naturaliste plateau for comparison profiles are studied across the bay of bengal and to the west of the ninetyeast ridge the group velocities are associated with the regions by the pure path method models are obtained down to 150 200 km for the profiles on and off ninetyeast ridge and down to 100km for broken ridge they reveal that except for a thick anomalous crust the structure beneath these ridges is quasi oceanic for the ninetyeast ridge however the uppermost 30 km of the mantle have lower velocities such low velocities are also obtained for the walvis ridge by chave for the paths off ridge no such low velocities are obtained indicating a small lateral extension of this anomaly a thermal origin is ruled out while a model with serpentinized peridotites as proposed by bowin which fits the gravimetric data is able to explain the low velocities of the uppermost mantle beneath the ninetyeast ridge

modelling generation and dissipation of overpressure in sedimentary basins an example from the halten terrace offshore norway a pressure simulator modelling the dynamic overpressure history in sedimentary basins is developed using a pressure compartment methodology simple models for porosity reduction are used for controlling pressure generation and different empirical models are used to estimate the lateral and vertical sealing dissipation mechanisms the equations describing the flow of formation water between the pressure compartments are used to calculate the resulting pressure dissipation on a geological time scale the methodology is tested and applied to the jurassic fangst group in the halten terrace area offshore norway dynamic allocation and an explicit numerical solution technique ensure a fast and accurate solution of the flow equations the results suggest a the probable mechanisms and processes that have generated the overpressure b the timing and location of hydraulic fracturing and c the nature and behaviour of the overpressure in addition to the overpressure history

lateral fluid flow in a compacting sand shale sequence south caspian basin the article lateral fluid flow in a compacting sand shale sequence south caspian basin by john d bredehoeft rashid d djevanshir and kenneth r belitz aapg bulletin v 72 no 4 april 1988 p 416 424 needs the following corrections there are several typographical errors that were the author s error equation 2 should be equation 2 equation 3 should be equation 3 although the equations were incorrect in the article the associated discussion and equations 4 and 5 are based upon the correct expressions as shown above table 3 the calculated regional sand permeabilities is also incorrect the hydraulic conductivity which in our case has the units of meters per second was incorrectly converted to millidarcys values in meters per second were multiplied by the standard conversion 1 m sec equals 1 04 108 md in retrospect this conversion was a conceptual error table 3 should read table 3 calculated regional sand permeabilities acknowledgment we appreciate the comments of stan lohman who brought our attention to these errors end of article last page 1525

hotspots mantle plumes flood basalts and true polar wander persistent long lived stationary sites of excessive mantle melting are called hotspots hotspots leave volcanic trails on lithospheric plates passing across them the global constellation of fixed hotspots thus forms a convenient frame of reference for plate motions through the orientations and age distributions of volcanic trails left by these melting anomalies hotspots appear to be maintained by whole mantle convection in the form of upward flow through narrow plumes evidence suggests that plumes are deflected little by horizontal flow of the upper mantle mantle plumes are largely thermal features and arise from a thermal boundary layer most likely the mantle layer just above the core mantle boundary experiments and theory show that gravitational instability drives flow beginning with the formation of diapirs such a diapir will grow as it rises fed by flow through the trailing conduit and entrainment of surrounding mantle the structure thus develops a large spherical plume head and a long narrow tail on arrival at the base of the lithosphere the plume head flattens and melts by decompression producing enormous quantities of magma which erupt in a short period these are flood basalt events that have occurred on continents and in ocean basins and that signal the beginning of major hotspot tracks the plume supported hotspot reference frame is fixed in the steady state convective flow of the mantle and is independent of the core generated axial dipole paleomagnetic reference frame comparison of plate motions measured in the two frames reveals small but systematic differences that indicate whole mantle motion relative to the earth s spin axis this is termed true polar wander and has amounted to some 12 since early tertiary time the direction and magnitude of true polar wander have varied sporadically through the mesozoic probably in response to major changes in plate motions particularly subduction zone location that change the planet s moments of inertia

synthesis and model of formation water flow alberta basin canada based on a large amount of publicly available data several studies have previously examined the flow of formation waters in different parts of the alberta basin offering various interpretations as to the causes of the observed pressure regime and flow pattern however there has been no synthesis of these diverse studies on a basin wide basis accordingly these studies are critically reviewed in this paper and synthesized in a new basin scale model of the flow of formation waters in the alberta basin the proposed regional scale model has significant implications for understanding hydrocarbon migration pathways ore genesis the geothermal regime and deep waste disposal in the alberta basin several flow systems each one driven by a different mechanism are identified together with the main processes leading to the nonhydrostatic pressures observed in the basin two megahydrostratigraphic successions and associated flow systems are recognized the first succession corresponds to the pre cretaceous passive margin stage of basin development and consists of thick carbonate dominated aquifer systems separated by shaly aquitards and evaporitic aquicludes a northeastward basin scale flow system is driven by basin topography with recharge in montana and discharge in northeastern alberta southwest to northeast regional scale flow adjacent to the fold and thrust belt is probably the result of past tectonic processes the salinity of formation water in pre cretaceous aquifers is high and generally increases both northward and with depth this variability is the result of increased water rock reactions mineral solubility with increased temperatu e and of incomplete flushing by meteoric water as a result of salinity variations flow retarding buoyancy effects can be important the second megahydrostratigraphic succession corresponds to the post jurassic foreland stage of basin evolution and consists of thick shaly aquitard systems and relatively thin sandstone aquifers in the southwestern part of the basin flow in isolated aquifers is driven southwestward by erosional rebound in the thick intervening shales downdip toward the fold and thrust belt the salinity of formation waters in the post jurassic aquifers is low mixing of waters and interference between the major flow systems takes place along the pre cretaceous unconformity where successively older pre cretaceous aquifers subcrop from west to east flow in shallow lo al systems at the top of the sedimentary succession is driven by local topography

wellbore reservoir coupled simulation to study thermal and fluid processes in a co2 based geothermal system identifying favorable and unfavorable conditions in comparison with water using co2 as a heat transmission fluid to extract geothermal energy is currently considered as a way to achieve co2 resource utilization and geological sequestration as a novel heat transmission fluid the thermophysical properties of co2 are quite different from those of water co2 has many advantages such as larger mobility and buoyancy resulted from the lower density and viscosity this will reduce the consumption of pressure driving the circulation and save the energy of external equipment the cycle even can be achieved by siphon phenomenon under a negative circulating pressure difference however there are still some disadvantages for co2 as the heat transmission fluid such as small heat capacity leading to a less heat at the same mass flow rate at the same time because of the lager expansion and compression coefficient for co2 changes in temperature and pressure may cause a more complex flow and thermodynamic processes the lager compressibility makes it possible to get high temperature at the bottom of the injection well whereas the lager expansion coefficient makes the temperature drop rapidly along the production well therefore how to scientifically control the production pressure to guarantee sufficient high temperatures at the head of production well and thereby improve the efficiency of heat extraction are the key issues needed to be further addressed the geological and geothermal conditions correspond to the central depression of the songliao basin located in the northest of china this depression has a high geothermal gradient and heat flow in this article a classic idealized five spot reservoir model coupled with wellbores is used for simulations and analyses the objectives of the present work are 1 to investigate the fluid flow and thermal processes of supercritical co2 along the wellbore and in the reservoir 2 to understand the heat extracting mechanism 3 to identify advantages and disadvantages of using co2 as the heat transmission fluid and 4 to provide a theoretical basis for the selection of heat transmission fluid

overpressures in the anadarko basin southwestern oklahoma static or dynamic fluid pressures were estimated from mud weights and wellhead shut in pressures along a north south linear trend through the anadarko basin in southwest oklahoma fluid pressures above hydrostatic start at a depth of about 2 5 km on a normalized scale where hydrostatic pressure equals 0 and lithostatic pressure equals 1 estimates of fluid pressures were found to range from 0 4 to 0 8 over a depth range of 4 7 km using scale analyses and a simple numerical model we evaluated two end member hypotheses compaction disequilibrium and hydrocarbon generation as possible causes of overpressuring in the anadarko basin if compaction disequilibrium is the primary cause of present day overpressures in the anadarko basin the anadarko basin is required to have an average permeability of 10 23 m2 10 8 md or lower if geopressures in the anadarko basin result from hydrocarbon generation average basin permeabilities can be as high as 10 21 m2 10 6 md scaling these average permeabilities down to thicknesses of 100 m or less implies permeabilities lower than 10 25 m2 10 10 md are required in the most optimistic scenario the lowest permeabilities ever measured on sedimentary rocks are in the neighborhood of 10 22 10 23 m2 10 7 10 8 md thus it is not possible to reconcile the existence of overpressures in the anadarko basin with classic hydrodynamic theories that maintain that aquicludes do not exist either some unknown process is generating excess fluid pressures or the anadarko basin contains pressure seals geopressure models that invoke compaction disequilibrium and are commonly applied to cenozoic basins undergoing rapid sedimentation e g the gulf coast basin of the southeastern united states do not appear to apply to the anadarko basin the anadarko basin belongs to a group of cratonic basins that are tectonically quiescent and characterized by the association of abnormal pressures with natural gas begin page 146

a deterministic seismic hazard map of india and adjacent areas a seismic hazard map of the territory of india and adjacent areas has been prepared using a deterministic approach based on the computation of synthetic seismograms complete with all main phases the input data set consists of structural models seismogenic zones focal mechanisms and earthquake catalogues there are few probabilistic hazard maps available for the indian subcontinent however this is the first study aimed at producing a deterministic seismic hazard map for the indian region using realistic strong ground motion modelling with the knowledge of the physical process of earthquake generation the level of seismicity and wave propagation in anelastic media synthetic seismograms at a frequency of 1 hz have been generated at a regular grid of 0 2 x 0 2 by the modal summation technique the seismic hazard expressed in terms of maximum displacement d m a x maximum velocity v m a x and design ground acceleration dga has been extracted from the synthetic signals and mapped on a regular grid over the studied territory the estimated values of the peak ground acceleration are compared with the observed data available for the himalayan region and are found to be in agreement many parts of the himalayan region have dga values exceeding 0 6 g the epicentral areas of the great assam earthquakes of 1897 and 1950 in northeast india represent the maximum hazard with dga values reaching 1 2 1 3 g the peak velocity and displacement in the same region is estimated as 120 177 cm s 1 and 60 90 cm respectively

thermophysical rock properties of the crystalline gonghe basin complex northeastern qinghai tibet plateau china basement rocks the basement of the gonghe basin complex gbc mainly consists of plutonic rocks which in general are suitable for geothermal applications knowledge of the rock properties of the deep basement formations is of fundamental importance for unconventional geothermal applications such as enhanced geothermal systems an outcrop analogue study at the margin of the gbc was conducted to improve the understanding of the petrophysical rock properties and enhance the data availability for numeric simulation and resource assessment approaches in total 148 samples were derived from 21 sampling locations at the margin of the gbc area and mountain ranges within lithologically the sample set was divided in three sample types 1 syenogranite 2 granite and biotite granite 3 granodiorite petrophysical properties such as grain density bulk density porosity intrinsic matrix permeability compressional and shear wave velocities as well as thermal properties like thermal conductivity and thermal diffusivity were analyzed on oven dry specimens under laboratory conditions ambient temperature atmospheric pressure unconfined compressive strength was additionally measured on selected samples the resulting dataset shows averaged bulk densities ranging between 2 59 and 2 73 g cm 3 and porosities from 0 2 to 1 7 matrix permeability is lower than 1 10 18 m2 averaged thermal conductivity ranges from 2 34 to 3 19 w m 1 k 1 compressional wave velocity from 3 6 to 6 2 km s 1 and unconfined compressive strength from 128 to 241 mpa petrophysical data are correlated with mineral content and grain size to show the influence of petrography on petrophysical properties although the petrophysical rock properties were analyzed at laboratory conditions and therefore deviate from in situ properties at reservoir conditions the presented dataset enhances the knowledge of petrophysical rock properties within the study area for further geothermal applications a first prediction of in situ reservoir conditions was performed on laboratory data based on empirically determined pressure and temperature dependencies of thermal conductivity thermal diffusivity specific heat capacity and compressional wave velocity

correlation alteration and origin of hydrocarbons in the gca bahar and gum adasi fields western south caspian basin geochemical and multivariate statistical assessments abstract geochemical as well as multivariate statistical analyses pca were carried out on 20 crude oil samples from middle pliocene production series mpps of guneshli chirag azeri gca bahar and gum adasi fields in the western south caspian basin scb pca analysis employed to source specific biomarkers distinguishes the oils into two types one being divided into two sub types type 1 gca oils type 2a bahar field oils and type 2b gum adasi field oils indirect oil to source rock correlations to available source rock data from previous studies suggest that type 1 oils located in the apsheron balkhans uplift area are derived from basinal shales of the oligocene lower miocene middle maikop formation type 2a and 2b oils located in the gum deniz bahar shakh deniz trend area are more likely derived from shelf edge shales of the upper maikop formation and the middle upper miocene diatom suite respectively biomarker maturity study reveals that type 1 oils mean rc 0 78 are more mature than type 2 oils mean rc 0 71 source rocks which generated these oils were at generation depth interval between 5200 m 112 c and 7500 m 153 c at the time of expulsion this indicates that the western scb oils experienced significant long range vertical migration along the deep seated faults to accumulate in the mpps reservoirs post accumulation biodegradation process was only observed in the guneshli field where bacterial alteration level 4 began between 4 2 and 2 6 mybp and stopped with the deposition of the overlying impermeable upper pliocene akchagyl formation subsequent light hydrocarbon c1 c16 charge into the guneshli fields caused precipitation of asphaltenes which is evidenced by high resin to asphaltene ratios for the present day guneshli oils evaporative fractionation examined using the scheme of thompson 1987 showed high correlations of the aromaticity b parameter toluene n c7 and parafinicity f parameter n c7 mch with the rc maturity and c27 c29 sterane ratio organic matter type this implies that thompson s approach should be used with caution in the scb among the several mechanisms rapid and thick deposition of pliocene sediments and subsequent high heating rate on the maikop formation and diatom suite is probably the most plausible way of explaining the origin of light hydrocarbons in the guneshli and bahar fields

sensitivity of 3d thermal models to the choice of boundary conditions and thermal properties a case study for the area of brandenburg ne german basin based on newly available data of both the structural setting and thermal properties we compare 3d thermal models for the area of brandenburg located in the northeast german basin to assess the sensitivity of our model results the structural complexity of the basin fill is given by the configuration of the zechstein salt with salt diapirs and salt pillows this special configuration is very relevant for the thermal calculations because salt has a distinctly higher thermal conductivity than other sediments we calculate the temperature using a femethod to solve the steady state heat conduction equation in 3d based on this approach we evaluate the sensitivity of the steady state conductive thermal field with respect to different lithospheric configurations and to the assigned thermal properties we compare three different thermal models a a crustal scale model including a homogeneous crust b a new lithosphere scale model including a differentiated crust and c a crustal scale model with a stepwise variation of measured thermal properties the comparison with measured temperatures from different structural locations of the basin shows a good fit to the temperature predictions for the first two models whereas the third model is distinctly colder this indicates that effective thermal conductivities may be different from values determined by measurements on rock samples the results suggest that conduction is the main heat transport mechanism in the brandenburg area

impact of single inclined faults on the fluid flow and heat transport results from 3 d finite element simulations the impact of inclined faults on the hydrothermal field is assessed by adding simplified structural settings to synthetic models this study is innovative in carrying out numerical simulations because it integrates the real 3 d nature of flow influenced by a fault in a porous medium thereby providing a useful tool for complex geothermal modelling the 3 d simulations for the coupled fluid flow and heat transport processes are based on the finite element method in the model one geological layer is dissected by a dipping fault sensitivity analyses are conducted to quantify the effects of the fault s transmissivity on the fluid flow and thermal field different fault models are compared with a model where no fault is present to evaluate the effect of varying fault transmissivity the results show that faults have a significant impact on the hydrothermal field varying either the fault zone width or the fault permeability will result in relevant differences in the pressure velocity and temperature field a linear relationship between fault zone width and fluid velocity is found indicating that velocities increase with decreasing widths the faults act as preferential pathways for advective heat transport in case of highly transmissive faults whereas almost no fluid may be transported through poorly transmissive faults

sedimentation and tectonics of the sylhet trough bangladesh the sylhet trough a sub basin of the bengal basin in northeastern bangladesh contains a thick fill 12 to 16 km of late mesozoic and cenozoic strata that record its tectonic evolution stratigraphic sedimentologic and petrographic data collected from outcrops cores well logs and seismic lines are here used to reconstruct the history of this trough the sylhet trough occupied a slope basinal setting on a passive continental margin from late mesozoic through eocene time subsidence may have increased slightly in oligocene time when the trough was located in the distal part of a foreland basin paired to the indo burman ranges oligocene fluvial deltaic strata barail formation were derived from incipient uplifts in the eastern himalayas subsidence increased markedly in the miocene epoch in response to western encroachment of the indo burman ranges miocene to earliest pliocene sediments of the surma group were deposited in a large mud rich delta system that may have drained a significant proportion of the eastern himalayas subsidence rates in the sylhet trough increased dramatically 3 8 times from miocene to pliocene pleistocene time when the fluvial tipam sandstone and dupi tila formation were deposited this dramatic subsidence change is attributed to south directed overthrusting of the shillong plateau on the dauki fault for the following reasons 1 pliocene and pleistocene strata thin markedly away from the shillong plateau consistent with a crustal load emplaced on the northern basin margin 2 the shillong plateau is draped by mesozoic to miocene rocks but pliocene and younger strata are not represented suggesting that the massif was an uplifted block at this time 3 south directed overthrusting of the shillong plateau is consistent with gravity data and with recent seismotectonic observations sandstone in the tioam has a marked increase in sedimentary lithic fragments compared to older rocks reflecting uplift and erosion of the sedimentary cover of the shillong plateau if the dauki fault has a dip similar to that of other himalayan overthrusts then a few tens of kilometers of horizontal tectonic transport would be required to carry the shillong plateau to its present elevation uplift of the shillong plateau probably generated a major 300 km westward shift in the course of the brahmaputra river

thermal hydraulic measurements and modelling of the brine circuit in a geothermal well wellhead temperature and pressure are critical parameters of a geothermal well their prediction requires knowledge of the geofluid properties and detailed thermal modelling of the well and formation high salinity and gas content complicate the task this article presents a comprehensive thermal hydraulic wellbore model which is parameterized and validated with data from the gross schoenebeck site and used for a long term prognosis geofluid properties are calculated based on the specific gas and salt contents by determining the vapour liquid equilibrium

depth extent of cratons as inferred from tomographic studies we address the question of the depth extent of mantle high velocity zones under ancient cratons by using seismic velocity maps from recent mantle tomographic studies we divided old continents into two age provinces 800 1700 ma middle proterozoic and older than 1700 ma archean and early proterozoic the areas included in these age provinces are cross correlated with the tomography at different depths to quantify the global occurrence of high velocity anomaly hva extensions beneath cratons statistically significant hvas underlie the oldest cratons to a depth of 250 km there is no significant consistent correlation between tomography and younger cratons the older cratons have correlated hvas extending to depths varying from 100 to 450 km there is no significant difference in the average velocity anomaly beneath the early proterozoic part and the archean part of the canadian shield whereas the middle proterozoic part does not contain any hva the mantle under early precambrian crust is distinctly different from mantle elsewhere we propose two different hypotheses to explain these results 1 cratons of early proterozoic age or older contain ancient and deep physically attached roots or 2 these cratons contain a small permanent physical root that induces cold downwellings beneath it a root thickness of 200 km can be explained by an feo poor olivine rich mineralogy whereas a requirement of high strength probably demands in addition a volatile poor composition different root depths for cratons of similar age may be related to their location in the various supercontinents in which they were involved and to their subsequent deformational history or they may represent different snapshots in time of transient roots such as thermal boundary layers

modeling anomalous surface wave propagation across the southern caspian basin the south caspian basin contains one of the thickest sedimentary deposits in the world intermediate frequency 0 02 0 04 hz fundamental mode rayleigh waves propagating across the basin are severely attenuated but apparent attenuation is significantly less for both low and high frequencies we have modeled the response of surface waves in a simplified rendition of the south caspian basin model of mangino and priestley 1998 using a hybrid normal mode 2d finite difference approach to gain insight into the features of the basin that cause the anomalous surface wave propagation we have varied parameters of the basin model and computed synthetic record sections to compare with the observed seismograms we have varied the moho depth beneath the basin the shape of the basin boundaries the thickness and shear wave q of the sediments and mantle and the water depth of these parameters the intermediate frequency surface waves are most severely affected by the sediment thickness and shear wave attenuation all models fail to satisfy observations for frequencies of 0 05 hz and above and this failure is attributed to significant 3d wave propagation effects caused by focusing and scattering of surface waves by basin structures

a preliminary site selection system for a co2 ages project and its application in china because of the high costs involved in co2 sequestration in deep saline formations it has been difficult for its widespread application in the short term recently however a new technology called combined geothermal production co2 sequestration technology has made the technique more attractive not only by increasing the co2 storage capacity but also by decreasing the operational costs through the utilization of geothermal energy either directly or for the purpose of producing electricity a co2 aided or co2 involved geothermal extraction system co2 ages is presented based on existing technologies and the new ideas of combined geothermal production co2 sequestration introduced in this paper this system can be used to extract geothermal energy from sedimentary aquifer formations low medium temperature at different stages the purpose of this paper is to set up an evaluation system for selecting a suitable site for this co2 ages system there are both similarities and differences in the procedure needed for selecting a site for a conventional pure co2 sequestration and for this co2 ages system both are carried out at different scales including basin region and target formation scales the biggest difference is the temperature gradient which plays an opposite role in the two systems by using the preliminary ranking and screening method presented in this paper it can be shown that the bohaiwan songliao and qiangtang basins have the highest potential for the application of this co2 ages technology however if co2 sequestration is considered alone the ordos tarim and bohaiwan basins should be selected as the best three operational sites in china while preliminary evaluation methods can provide some useful information on the selection of the best sites for the combined geothermal production co2 sequestration technology more detailed work is still required because of the strong uncertainties that exist in the determination of the upper and lower boundaries for each indicator

geophysical constraints on the link between cratonization and orogeny evidence from the tibetan plateau and the north china craton abstract understanding the geodynamic process of orogeny and cratonization and their transition is among the key topics of research in evaluating the link between plate tectonics and continental dynamics the tibetan plateau and the north china craton ncc two key areas in mainland china offer excellent laboratories to understand continental tectonics over a broad span of earth history particularly the deep structure of the lithosphere as imaged from geophysical data on the tibetan plateau and the ncc provide important clues in understanding orogeny and cratonization the tibetan plateau is the largest and highest plateau on earth in terms of mean altitude and is an important region for understanding the mechanisms of continent continent collision and cenozoic plateau uplift the ncc is an archean craton that underwent lithospheric disruption during the mesozoic here we reconstruct the main features of the structure of the crust and upper mantle from surface wave tomography and gravity modeling in tibet and its neighboring regions in order to understand the modality of the convergence and collision process between the indian and eurasian plates and the influence of this process on the uplift of the plateau in the ncc geological geochemical geophysical and tectonic investigations demonstrate that lithospheric destruction mainly occurred in the eastern block the crustal structure of the ncc is reconstructed from ambient noise surface wave tomography and the different possible disruption mechanisms are evaluated the vs shear wave velocity tomography results and the density structure of the crust and upper mantle to about 350 km depth demonstrate the lateral variation of the thickness of the metasomatic lid between the south and north of the bangong nujiang suture bns and the west and east of tibet which suggest that the leading edge of the subducting indian slab reaches the bns the subduction angle of indian plate indicates a transition from steep to shallow from the west to east tibet sections depicting the gravitational potential energy suggest that mantle flow contributes to the subduction of the indian plate as far as the bns and the transition from the asthenospheric layer to the metasomatic lid overlaps with the transition from north south shortening in south tibet to eastward tectonic escape in north tibet qiangtang and songpan ganzi blocks both vs and models suggest the following 1 north southward lower crust flow beneath the eastern ncc and interaction between the westward mantle flow and eastward escape flow beneath the central ncc in addition to the earlier proposed mechanisms of delamination and thermal erosion played important roles in the lithospheric disruption of the archean craton 2 mantle flow plays an important role in the continental tectonic transition between neighboring tectonic blocks and within the cycle between orogeny and cratonization

mineral water interaction fluid flow and frio sandstone diagenesis evidence from the rocks the spatial distribution of burial diagenetic cements in sandstones of the frio formation is related to permeability and fluid flow the relationship between sandstone diagenesis and fluid flow implies that the modification of the rocks is largely the outcome of reactions between the detrital and authigenic minerals and the formation water in the pores during burial formation water preferentially flowed through the most porous and permeable sandstones diagenetic alteration is more extensive in permeable sandstones because the minerals in those rocks were exposed to significantly more pore volumes of reactive water each of which accomplished a small amount of diagenetic work consequently porous and permeable units were also the preferred sites of diagenetic mineral p ecipitation the heterogeneous distribution of authigenic minerals in sandstones is a result of changing preferential flow paths due to diagenetic modification during burial sandstones that are not the most porous or permeable at the time of deposition commonly preserve the best reservoir quality at depth because they are less modified by diagenesis petrographic analyses indicate that the sio2 needed for the quartz overgrowths in the sandstones had an allochthonous source dgr18o values for diagenetic quartz imply that the mineral precipitated from rapidly ascending hot formation water quartz overgrowths are most abundant in distal shelf facies sandstones where the isolated nature of the sandstones in a predominately shaly section maximized preferential fluid flow mass balance calculations show that thousands of pore volumes of formation water are required to supply the sio2 needed for the quartz overgrowths in the sandstones the amount of water required to produce the diagenetic modification of the sandstones is much larger than the amount of water present in the entire frio formation impl ing that reuse of formation water is an important and necessary process during diagenesis

deep 3d thermal modelling for the city of berlin germany this study predicts the subsurface temperature distribution of germany s capital berlin for this purpose a data based lithosphere scale 3d structural model is developed incorporating 21 individual geological units this model shows a horizontal grid resolution of 500 500 m and provides the geometric base for two different approaches of 3d thermal simulations 1 calculations of the steady state purely conductive thermal field and 2 simulations of coupled fluid flow and heat transport the results point out fundamentally different structural and thermal configurations for potential geothermal target units the top of the triassic middle buntsandstein strongly varies in depth 159 2 470 m below sea level and predicted temperatures 15 95 c mostly because of the complex geometry of the underlying permian zechstein salt the top of the sub salt sedimentary rotliegend is rather flat 2 890 3 785 m below sea level and reveals temperatures of 85 139 c the predicted 70 c isotherm is located at depths of about 1 500 2 200 m cutting the middle buntsandstein over large parts of berlin the 110 c isotherm at 2 900 3 700 m depth widely crosscuts the sedimentary rotliegend groundwater flow results in subsurface cooling the extent of which is strongly controlled by the geometry and the distribution of the tertiary rupelian clay the cooling effect is strongest where this clay rich aquitard is thinnest or missing thus facilitating deep reaching forced convective flow the differences between the purely conductive and coupled models highlight the need for investigations of the complex interrelation of flow and thermal fields to properly predict temperatures in sedimentary systems

groundwater upwelling near bay st elaine salt dome in southeastern louisiana as inferred from fluid property variations fluid pressures temperatures and salinities derived from 62 well logs were mapped in three vertical cross sections across the bay st elaine salt dome in southeastern louisiana to qualitatively determine groundwater flow patterns around the dome near hydrostatic conditions prevail in the sand rich shallow section from depths of 0 to 2 5 km however fully enclosed within the hydropressured section are lenses of slightly overpressured sediments which slope up toward the dome hydraulic heads may be as much as 500 m above ground level within these enclosed lenses in some strongly overpressured sediments deeper than 2 5 km hydraulic heads are as much as 2500 m above ground level pore water salinities increase with depth within the hydrostatically pressured section fr m 0 wt at the surface to maximum values of 10 12 wt at the top of the overpressured section within the overpressured section salinities decrease to as little as 6 wt with increasing depth immediately adjacent to the northeastern flank of the dome is a steeply dipping lobe of relatively fresh waters 6 wt sodium chloride that separates the flank of the dome from saltier 8 10 wt waters away from the dome this low salinity water mass appears to be connected to similar low salinity waters in the overpressured section and is postulated to be due to pore water upwelling from a depth of 4 km to a depth of about 1 5 km

a proposed super thick sedimentary basin bay of bengal a super thick 22km sedimentary basin under the northern bay of bengal is proposed the hypothesis is based on data from surface wave dispersion seismic refraction sn attenuation and geology we present new high frequency sn data which indicate a cold upper mantle beneath the bay of bengal we propose that the oceanic crust in this region is in fact nearly normal and that the sedimentary section is at least 6 km thicker than previously thought with velocities at the base of the sediments having been increased to near 6 5 km sec by high pressure metamorphism reinterpretation of the refraction data indicate a post india asia collision thickness of over 16 km

structure and emplacement of mud volcano systems in the south caspian basin the term mud volcano system is coined to describe the set of structures associated with a constructional edifice mud volcano and feeder complex that connects the volcano to its source stratigraphic unit three dimensional 3 d seismic data from the south caspian basin are used to investigate the structural elements and evolution of these systems mud volcano systems initiate via early kilometer scale biconic edifices termed pioneer cones these are fed by fluidization pipes tens of meters in width subsequent kilometer scale mud volcanoes grew via persistent extrusion fed by numerous additional fluidization pipes injected in the country rock this subvolcanic intrusion complex creates a densely intruded cylindrical zone similar in cross section to gryphon swarms observed at an outcrop onshore wall rock erosion and compaction of the intruded zone leads to the collapse of a downward tapering cone enveloping the cylindrical zone capped by ring faults that define a kilometer scale caldera that downthrows the overlying mud volcano mud volcanoes get buried during basin subsidence and can look like intrusive laccoliths at first glance on seismic data reactivation of mud flow through a conduit system generates a stack of superimposed mud volcanoes through time large volcanoes continue to dewater during burial and may locally remobilize this model of mud volcano evolution has similarities with igneous and salt tectonic systems to reduce drilling and geologic uncertainty mud volcano system extent and impacts on a reservoir can be assessed on 3 d seismic data simon stewart received his ph d from the imperial college london in 1992 in 1992 2000 he was seismic interpreter at amerada hess in support of exploration and appraisal drilling in the north sea in 2000 he moved to bp and has since worked on structural geology and well planning in the americas middle east and the former soviet union his special interest is in the integration of structural geology and seismic interpretation richard davies received his ph d from the university of edinburgh in 1995 in 1995 2003 he was with mobil and exxonmobil working on field development and exploration the north sea the west of shetlands and the west niger delta deep water slope in 2003 2005 he was a senior lecturer in earth sciences at cardiff university united kingdom currently he is professor and director of cerees center for research into earth energy systems durham university united kingdom his special interest is in seismic scale expression of fluid migration and diagenesis

seismic velocities beneath central and southern britain from broad band surface waves abstract fundamental mode rayleigh waves recorded across the uk broad band network have been analysed to produce phase velocity curves in the period range of 12 to 85 s an inter station method has been used for two paths across southern england the resulting mean phase velocity curve has been compared with a mean curve derived using three stations in central britain lateral refraction characteristics of tripartite phase velocities have been analysed and shown to be less than 5 at periods of greater than 15 s forward modelling to s wave velocity depth profiles using a hedgehog search procedure suggests that central britain is underlain by a thicker crust than southern england with a steady velocity increase down to the moho for southern england low velocities are apparent either at the base of the crust or in the uppermost mantle for both regions sub crustal lithosphere velocity is contrained to be between 4 6 and 4 7 km s 1 with a layer thickness of less than 140 km for southern england and between 80 and 160 km for central britain both regions appear to exhibit low velocity zone lvz development however for central britain more data are required to place better constraints on the magnitude of the lvz channel velocities in the lower crust have been used to place constraints on poisson s ratio which appears to decrease northwards from greater than 0 27 beneath southern england to between 0 25 and 0 27 beneath central britain the distributions of p wave velocities s wave velocities and poisson s ratio have been interpreted of compositional variation and or fluid content within the lower crust

structural model of the lithosphere asthenosphere system beneath the qinghai tibet plateau and its adjacent areas abstract the deep structure of the lithosphere asthenosphere system as imaged from geophysical data of the qinghai tibet plateau the highest on the earth provides important clues in understanding its orogenic processes here we reconstruct the main features of the structure of the crust and upper mantle from surface wave tomography in the qinghai tibet plateau and its adjacent areas in order to understand the modality of the convergence and collision process between the indian and eurasian plates based on rayleigh waves dispersion theory we collected long period and broad band seismic data from the global and regional seismic networks surrounding the study area 20 n 50 n 70 e 110 e after applying instrument response calibration and filtering group velocities of the fundamental mode of rayleigh waves are measured using the frequency time analysis ftan combining the published dispersion data a 2 d surface wave tomography method is applied to calculate the lateral variations of group velocity distribution at different periods in the range from 8 s to 150 s the hedgehog non linear inversion method is performed to obtain shear wave velocity vs versus depth models of the crust and upper mantle for 181 cells with size 2 2 in order to identify the cellular representative models we applied the local smoothness optimization method lso fairly detailed structural models of the lithosphere asthenosphere system have been defined the vs models demonstrate the lateral variation of the thickness of the metasomatic lid between the south and north of the bangong nujiang suture bns and the west and east of tibet the variation in thickness of the metasomatic lid may suggest that the leading edge of the subducting indian slab reaches up to bns

mantle discontinuities beneath the deccan volcanic province abstract mantle discontinuities beneath the deccan volcanic province dvp are imaged using about 900 seismograms from a network of six broadband stations deployed in the dvp along a 350 km long north south profile paralleling the west coast of india teleseismic receiver function analysis of the data enabled distinct identification of the moho 410 and 660 km discontinuities presence of sub moho low velocity zones with velocity reductions in the range of 0 1 0 4 km s have been brought out through modeling of receiver function stacks at individual stations the arrival times of p410s and p660s are normal as predicted by the iasp91 model and the mantle transition zone thickness is 252 km which is close to the global average this study reveals that the upper mantle beneath dvp south of the narmada rift does not exhibit any anomalous signatures associated with a mantle plume a shield like lithosphere coupled with the presence of an upper mantle low velocity zone confined to shallow depths beneath dvp imposes constraints on the mechanisms feasible for deccan volcanism the present study does not favour the plume impact plume incubation models instead necessitates searching for clues offshore west coast of india and exploring alternate mechanisms

estimation of biot s effective stress coefficient from well logs effective stress governs the mechanical response of rock formations to variations in stress and pore pressure which affect wellbore stability and reservoir integrity during drilling and production biot s coefficient is employed to calculate effective stresses from total stress and pore pressure therefore the measurement of biot s coefficient becomes crucial however the laboratory measurement of biot s coefficient is expensive and laborious this paper presents three methods for computing biot s coefficient using logging data the first method calculates biot s coefficient using the existing empirical correlations between porosity and biot s coefficient the second and third methods calculate biot s coefficient using dynamic rock and solid bulk modulus computed using rock and solid wave velocities respectively however the second and third methods calculate the necessary solid wave velocities in different ways the second method calculates solid shear and compressive velocities vs and vp using a newly developed correlation between the differential pressure porosity and wave velocity of sandstone the third method calculates solid wave velocities based on the significant finding that the vp vs ratio with respect to the s wave velocity is constant for sediments including highly compacted sand case studies were undertaken using logging data from the gulf coast gas wells it was found that biot s coefficient calculated using the first method was highly dependent on the chosen relation while the coefficients calculated using the second and third methods were related to well logs results from the third method show that biot s coefficient deflects to higher values in situations where gamma ray surveys read low api values this is in agreement with the phenomenon that rocks with a smaller api should have lower a clay content and bigger value of biot s coefficient therefore the third method is more reliable and also requires fewer input parameters

numerical studies on co2 injection brine extraction process in a low medium temperature reservoir system co2 sequestration in deep saline formations has been proved to be an effective method for reducing greenhouse emissions into the atmosphere however pure sequestration of co2 will add to the costs incurred by both industries and governments a win win method of co2 injection and hot brine water extraction can become attractive to the investors as it will not only increase the storage capacity of the injected co2 but also offset the costs by selling and using the produced hot water for industrial agricultural or household purposes for instance water from very hot geothermal reservoirs t 150 c can be used for electricity generation in power plants and water from low medium temperature reservoirs the most predominant in natural systems are more popular for direct use e g in heating systems household hot water baths aquaculture etc in this paper low medium geothermal reservoirs widely distributed in china especially those in the ordos basin were selected for the numerical case studies using tough2mp with the eco2n module for the simulations generally simulation parameters were taken from the ordos basin where the first full integration co2 sequestration project had been operated since 2010 the simulations in the base case study lasted 35 years based on the lifespan of a normal geothermal project shallow re injection systems were also considered to investigate the influence of thermal breakthrough pressure perturbation etc results show that injection of cold co2 causes sharp decrease in temperature in the reservoir region near the injection well which is enlarged with continuous injection the region near the production well is dominated by different fluid phases during the co2 driven process including a single water phase a two phase fluid water and co2 and a phase of almost pure co2 results also show that the co2 breakthrough lags far behind the pressure response in the geothermal production system before breakthrough the injected co2 pressurizes the reservoir improving the overall performance of the geothermal reservoir furthermore the heat extraction efficiency of co2 based system is obviously higher than h2o based system

deep seismic structure of the indian shield western himalaya ladakh and tibet abstract p and s receiver functions from seismograph stations in the indian shield western himalaya ladakh and tibet are processed with a method which provides estimates of the p and s velocities and their ratio as a function of depth the time difference between the p660s and p410s phases in the north of the indian shield and the lesser himalaya is 1 0 1 5 s larger than the normal 24 s this is an effect of a low temperature with implication that the consumed material of the indian shield has reached the transition zone the waveforms of the p410s and s410p phases at some stations in the indian shield are indicative of a thin a few tens of kilometers low s velocity layer atop the 410 km discontinuity which is usually related to mantle upwelling the mantle s velocity under the indian shield at depths less than 180 km is 4 4 4 5 km s much lower than the 4 7 km s typical for precambrian shields we explain this low s velocity mainly by a recent tertiary metasomatic alteration of the high velocity mantle keel beneath the western himalaya ladakh and western tibet but not eastern tibet the s velocity in the mantle at depths less than 100 150 km is around 4 7 km s vp vs is anomalously low and we argue that this high velocity layer is a remnant of the mantle lithosphere of the northern greater india at most locations in the indian shield high s velocities 3 5 km s and more are dominant in the middle and lower crusts and the elevated s velocity is accompanied by an increased vp vs ratio 1 8 2 1 versus the standard 1 73 in the foothills of the himalaya the crust is 50 55 km thick and consists almost entirely of a high s velocity 3 7 km s and more rock with the increased vp vs ratio in the middle and the standard vp vs ratio in the lower crust this observation suggests that the upper crust of the indian plate is scraped off in the collision zone whereas the high velocity lower crust is subducted jointly with the mantle lithosphere the high velocities are responsible for the p wave teleseismic travel time anomaly of 1 s relative to ladakh under the himalaya the vp vs ratio in the crust is normal which suggests a change in composition relative to the crust of the indian shield under ladakh and tibet the anomalously high vp vs ratio in the crust is observed again beneath tibet our analysis reveals a low velocity crustal zone of partial melt between the 20 km and 45 km depths previously the 45 km discontinuity was interpreted as the effect of eclogitization

strike slip fault bridge fluid pumping mechanism insights from field based palaeostress analysis and numerical modelling abstract we present a finite element study of stress perturbation in evolving compressive and extensional strike slip fault bridges the results are compared with a fracture study of a compressive bridge at st donats uk horizontally interbedded calcareous mudstone and bioclastic calcilutite at st donats have a distinct vertical permeability anisotropy this sedimentary sequence behaves as a set of horizontal aquifers the fluid flow in these aquifers is sensitive to mean stress gradients paleostress analysis of field fracture data verified by finite element modelling indicates a rotation of 1 towards parallelism with boundary faults inside the growing compressive bridge boundary faults and bridge faults recorded numerous fluid flow events the modelled mean stress pattern shows a regional maximum within the bridge and local maxima minima pairs at boundary fault tips finite element modelling of an extensional bridge indicates that 3 rotates towards parallelism with boundary faults the mean stress pattern is similar to the pattern in compressive bridge but with maxima and minima locations interchanged the stress patterns are reestablished by each stress build up preceding the rupturation of the boundary faults throughout the development stages of strike slip fault bridges mean stress gradients developed pre failure control the fluid flow in fractures of the strike slip fault system at and after the end of each stress build up and the fluid flow in boundary faults post failure fracture reactivation and new fracture generation within an evolving bridge is a process consisting of multiple successive events that retain the storage capacity of the bridge rupture and sealing of the main bounding faults is a step wise process that opens and closes fluid conduits between areas with different pressures

saline groundwater in mono basin california 2 long term control of lake salinity by groundwater mono lake is a perennial closed basin lake that has existed for at least 700 kyr this 46 m deep alkaline lake s present concentration is about 90 000 ppm total dissolved solids well logs show that beneath part of the lake saline groundwater of concentration 18 000 ppm extends to the bottom of the basin fill aquifer rogers and dreiss this issue numerical simulations indicate that redistribution of the basin s solutes between the lake and underlying saline groundwater body driven by late quaternary lake level changes may be responsible for the high present day solute content of mono lake at low lake levels the high lake concentration causes solute loss via free convection this might occur more rapidly through faults or fractures the saline fresh groundwater interface position reflects a balance between the saline groundwater density and the force of inflowing fresh groundwater discharging near the shoreline at higher lake stages the shoreline discharge zone moves toward the basin edge and the unrestrained saline groundwater mass subsides drawing solutes from the lake into the basin sediments falling lake levels again constrict the saline groundwater beneath the lake forcing saline water into the lake and increasing its solute content the sediment permeability below the lake is the major control on the solute transfer rate between the lake and the groundwater reservoir only the larger longer term lake stage changes cause saline groundwater movement depending on the assumed basin fill aquifer permeability equilibration of the saline groundwater and lake solute content with lake stage changes requires hundreds to thousands of years simulations suggest that the historical conditions where a more saline mono lake 50 000 90 000 ppm overlies less concentrated groundwater apparently 18 000 ppm could be due to the still present impact of late pleistocene lake high stands mono lake s historical salinity data have a large scatter but suggest a 5 decrease in the lake s solute content over the last 50 years we estimated the diffusive solute flux into lacustrine sediments for this period from core data the salinity data are consistent with a combination of solute diffusion into sediments and an equal or greater model predicted advective solute loss to groundwater

modelling of fractured carbonate reservoirs outline of a novel technique via a case study from the molasse basin southern bavaria germany fluid flow in low permeable carbonate rocks depends on the density of fractures their interconnectivity and on the formation of fault damage zones the present day stress field influences the aperture hence the transmissivity of fractures whereas paleostress fields are responsible for the formation of faults and fractures in low permeable reservoir rocks fault zones belong to the major targets before drilling an estimate for reservoir productivity of wells drilled into the damage zone of faults is therefore required due to limitations in available data a characterization of such reservoirs usually relies on the use of numerical techniques the requirements of these mathematical models encompass a full integration of the actual fault geometry comprising the dimension of the fault damage zone and of the fault core and the individual population with properties of fault zones in the hanging and foot wall and the host rock the paper presents both the technical approach to develop such a model and the property definition of heterogeneous fault zones and host rock with respect to the current stress field the case study describes a deep geothermal reservoir in the western central molasse basin in southern bavaria germany results from numerical simulations indicate that the well productivity can be enhanced along compressional fault zones if the interconnectivity of fractures is lateral caused by crossing synthetic and antithetic fractures the model allows a deeper understanding of production tests and reservoir properties of faulted rocks

continental scale body wave tomography of india evidence for attrition and preservation of lithospheric roots we assemble p and s waveforms of 2301 teleseismic earthquakes registered at 413 broadband seismic stations spanning the indian plate from the southern tip of india to the himalayan collision belt and generate an accurate data set of 52 050 p and 30 423 s arrival times through the multichannel cross correlation approach these traveltimes are then inverted to obtain 3 d p and s velocity structures of the subcontinent at a 2 2 lateral resolution the heterogeneous nature of the indian lithospheric mantle revealed in this study suggests that the lithospheric roots are not uniformly thick on a regional scale the key cratonic segments of the indian shield are characterized by pockets of high velocity anomalies 3 at shallow depths 300 km with the diamondiferous regions like wajrakarur revealing high shear wave anomalies down to 300 km in contrast to the southern deccan volcanic province dvp the northwestern dvp is underlain by low velocity anomalies at similar depths suggesting that the upper mantle retains imprints of deccan volcanism which was facilitated by the reactivation of the rift systems

lithosphere of the dharwar craton by joint inversion of p and s receiver functions summary the archean dharwar craton in south india is known for long time to be different from most other cratons specifically at station hyderabad hyb the ps converted phases from the 410and 660 km mantle discontinuities arrive up to 2 s later than in other cratons of comparable age which implies lower upper mantle velocities to resolve the unique lithosphere asthenosphere system of the dharwar craton we inverted jointly p and s receiver functions and teleseismic p and s traveltime residuals at 10 seismograph stations this method operates in the same depth range as long period surface waves but differs by much higher lateral and radial resolution we observe striking differences in crustal structures between the eastern and western dharwar craton edc and wdc respectively crustal thickness is of around 31 km with predominantly felsic velocities in the edc and of around 55 km with predominantly mafic velocities in the wdc in the mantle we observe significant variations in the p velocity with depth practically without accompanying variations in the s velocity in the mantle s velocity there are azimuthdependent indications of the hales discontinuity at a depth of 100 km the most conspicuous feature of our models is the lack of the high velocity mantle keel with the s velocity of 4 7 km s 1 typical of other archean cratons the s velocity in our models is close to 4 5 km s 1 from the moho to a depth of 250 km there are indications of a similar upper mantle structure in the northeast of the indian craton and of a partial recovery of the normal shield structure in the northwest a division between the high s velocity western tibet and low s velocity eastern tibet may be related to a similar division between the northeastern and northwestern indian craton

surface heat flow and probable evolution of deccan volcanism abstract in the light of surface heat flow observations as well as other related geological and geophysical data the origin of the deccan basalts has been examined the indian lithosphere after its detachment from gondwanaland apparently traversed a rising plume at la reunion which virtually bored through the lithosphere to emerge as the deccan trap volcanism on the surface subsequent volcanic and plutonic activity appears to have continued not only up to the oligocene as is indicated by the alkaline magmatic activity observed near the junction of the three prominent features the west coast faults the narmada son tapti lineament and the cambay graben but also up to the mio pliocene as indicated by the heat flow and gravity data over the cambay graben the dyke swarms and sills which are mostly post trappean evolved from the lithosphere after the indian plate moved away from the hot spot

3d geometry of a shale cored anticline in the western south caspian basin offshore azerbaijan abstract the internal structure of one of the common fold structures in the western margin of the south caspian basin scb has been characterized in 3d using a depth migrated seismic cube in offshore azerbaijan the fold corresponds to a nnw sse anticline with a basinward vergence i e eastwards because in this direction of the margin the scb is floored by a probable oceanic crust the anticline has two culminations cut by mud diapirs and is bounded by two parallel rim synclines with contrasting sedimentary thickness this anticline deforms congruently the thick productive series ps messinian to late pliocene whereas the most recent sequences we reconstruct the existence of two episodes of folding during deposition of the uppermost ps sequences ca 3 5 3 4 to 3 1 ma fold uplift initiated with a significantly lower rate than sedimentation during this epoch folding was accompanied by basin tilting and by faulting in a basinward normal fault with a limited right lateral strike slip component motion along this fault zone promoted the downdip flow of a weak layer formed by fluid and mud rich sediments maykop formation which also migrated along strike to build up the growing anticline henceforth fold growth accelerated and sedimentary units like the akchagyl 3 1 1 7 ma were deposited preferentially in the subsiding flanks seafloor upwarping due to folding conditioned the sediment transport and large deltas adapted their prograding pattern to the growing anticline crest this structure resembles a detachment fold with a leading east vergent forelimb nevertheless the occurrence of progressive tilting accompanying sedimentation and folding or the mud inflation of the fold core by deep flow parallel to the anticline axis make this example in the scb a special example of this fold type

shear velocity structure of the laterally heterogeneous crust and uppermost mantle beneath the indian region abstract the shear velocity structure of the indian lithosphere is mapped by inverting regionalized rayleigh wave group velocities in time periods of 15 60 s the regionalized maps are used to subdivide the indian plate into several geologic units and determine the variation of velocity with depth in each unit the hedgehog monte carlo technique is used to obtain the shear wave velocity structure for each geologic unit revealing distinct velocity variations in the lower crust and uppermost mantle the indian shield has a high velocity 4 4 4 6 km s upper mantle which however is slower than other shields in the world the central indian platform comprised of proterozoic basins and cratons is marked by a distinct low velocity 4 0 4 2 km s upper mantle lower crustal velocities in the indian lithosphere generally range between 3 8 and 4 0 km s with the oceanic segments and the sedimentary basins marked by marginally higher and lower velocities respectively a remarkable contrast is observed in upper mantle velocities between the northern and eastern convergence fronts of the indian plate the south bruma region along the eastern subduction front of the indian oceanic lithosphere shows significant velocity enhancement in the lower crust and upper mantle high velocities 4 8 km s are also observed in the upper mantle beneath the ninetyeast ridge in the northeastern indian ocean

development of a semi analytical method to calculate depth dependent temperature and stress changes investigation of micro seismicity at unterhaching uha gt 2 geothermal well since october 2007 when the hydrothermal production of geothermal energy from the deep underground started at unterhaching near munich germany several micro seismic events have been observed three of the five strongest events with local magnitudes ml ranging from 2 0 to 2 4 occurred in 2008 and were partially felt by the residents the reasons for these events are not clear these micro seismic events could have been induced by a variety of factors the strongest micro seismic event was observed soon after the injection of cold water pointing to an intrinsic relationship between micro seismic event and cold water injection one of the possible reasons for the observed micro seismic events could be the reinjection of cooled thermal water into the hotter underground inducing stress redistribution and shear failures in the reservoir formations around the injection wellbore uha gt 2 to justify this reason further investigation will be carried out in another simulation study to verify whether the shear failures induced by cold water injection were the major cause for the occurrence of these micro seismic events nevertheless before the simulation of shear failures temperature profiles in both the wellbore and surrounding rocks as well as their corresponding thermal stresses during cold water injection should be established in this study in this paper a new semi analytical simulation method has been developed to calculate simultaneously the temperature profiles in the wellbore and the surrounding rock formations and also determine the corresponding thermal stresses in the surroundings near wellbore field and subsequently verified by analytical solution results show that great tensile thermal stresses in the reservoir were initiated by the injection of the cooled thermal water in the injection wellbore uha gt 2 the results of the simulated thermal stresses indicate a great potential for the ensuing shear failures to affect an extensive area and could be used as input data for the planned shear failure simulations in the future

the main characteristics of the lithosphere asthenosphere system in italy and surrounding regions we present a summary of the available information on rayleigh wave dispersion data for the italian area the dispersion curves can be grouped into two main families according to their shape one with an almost linear trend in the period range from 40 to 150 sec the other with a relatively flat portion in the period range from 40 to 80 sec the inversion of these data shows that there are strong lateral variation in the lithosphere system a very rapid transition in the lithospheric thickness from about 130 km to about 30 km as well as in the s wave velocity of the lithosphere and asthenosphere

shortening budgets and the role of continental subduction during the india asia collision abstract the india asia collision provides a remarkable example of diffused deformation because the zone of compressive strain extends far into the hinterland of the himalaya molnar and tapponnier s science 189 1975 419 concept of india as a rigid indenter responsible for the diffused deformation has been widely accepted perhaps uncritically this review gives a reappraisal of landmark papers by dewey et al philos trans r soc london a 327 1988 379 eclogae geol helv 82 1989 717 which discussed the shortening budget in se asia and the evidence for the amount and the rate of the convergence between india and asia taking place after the initial collision of these continents at roughly 55 50 ma evidence for the total convergence comes from magnetic anomaly palaeomagnetic and volumetric balancing studies the results are consistent in showing about 1800 2100 km convergence between india and asia in the western sector 2475 km in the central and 2750 2800 km in the eastern sector the rate of convergence between india and asia over the period since initial collision is roughly 5 cm year however the possible long term rate of convergence within the himalaya is considerably less i e 1 5 2 0 cm year a fraction of the total convergence this shortfall can be made up by adding to the rate for the himalaya alone the convergence rates in other parts of the diffused zone of compressive strain i e tibet tien shan altai this works well for the post oligocene but not for the earlier post collisional history when the areal extent of thrust fold tectonics was much more limited possibly the apparent shortening deficit before the miocene was made up by strike slip faulting but with the notable exception of the red river fault evidence for widespread pre miocene strike slip faults is not convincing summation of the amount of shortening in thrust fold regimes in the himalaya and its hinterland falls short of that required by the total convergence figures quoted above the deficit arises firstly because of the likelihood that pre collisional crustal shortening of uncertain areal extent in tibet reduces tibet s contribution 40 according to dewey et al philos trans r soc london a 327 1988 379 eclogae geol helv 82 1989 717 to the shortening budget for the cenezoic revised shortening budgets are presented on the assumption that most of the lhasa block southern tibet was already thickened prior to collision this thickening is difficult to quantify secondly balanced cross sections from various parts of the himalaya give 60 70 shortening that is only about 500 km roughly half of the shortening proposed by dewey et al the conclusion of le pichon et al tectonics 11 1992 1085 that only indian mid upper crust is involved in the himalayan thrust sheets is supported but it needs to be reassessed in the light of the recognition of eocene oligocene thickening in the himalaya this early crustal thickening antedates the sequence of thrusts which started with the main central thrust and therefore the shortening estimates based on balanced cross sections probably underestimate the total shortening in the himalaya the prospect of substantial underthrusting of india beneath tibet minimizes the amount of horizontal shortening of tibetan lithosphere during the cenozoic the conclusion is that either the total convergence deduced from geophysical and volumetric work is too large or the deficit must be made up by shortening mechanisms other than thrust fold regimes i e strike slip faulting which serves to move rocks out of the way of india

investigation of a new hdr system with horizontal wells and multiple fractures using the coupled wellbore reservoir simulator tough2mp well eos3 geothermal energy is renewable sustainable and available in large amounts the hot dry rock hdr systems in particular have the largest potential for long term sustainability and therefore draw a lot of attention the combination of horizontal wells and the technology of multiple transverse fractures technology is an attractive approach of such hdrs which is called in this paper as the specific egs enhanced geothermal system the main objective of this paper is to study the heat extraction over a period of 20 years by water circulating in a deep geothermal reservoir using this specific egs the wellbore flow module t2well eco2n is implemented in the parallelized simulator tough2mp as a new code tough2mp well eos3 which enables coupled wellbore reservoir simulations using this newly developed code the sensitivity of heat extraction against various parameters of the formation and fractures is assessed the influences of the fracture geometry and the space of two neighborhood fractures on the geothermal energy performance are analyzed according to the results in this paper the injection rate the wellbore radius and the fracture permeability are three main influence factors for the distribution of total flow through individual fractures a large injection rate a small wellbore radius and a large fracture width will cause the short circuit effect which reduces the performance of this specific egs compared with the classic hdr system doublet or triplet vertical wells single fracture this specific egs has a much higher performance and a longer duration of the economic production furthermore the horizontal wells can also be drilled in both directions of the minimum horizontal stress instead of in just one direction so that the energy performance is doubled and the investment cost per kw energy production is decreased and the advantage of this specific egs is significantly enlarged

modeling subsurface flow in sedimentary basins groundwater flows that arise in sedimentary basins from the effects of topographic relief buoyant convection sediment compaction erosional unloading and combinations of these driving forces can be described using quantitative modeling techniques models can be constructed to consider the effects of heat and solute transport petroleum migration and the chemical interaction of water and rocks the accuracy of model predictions however is limited by the difficulty of predicting hydrologic properties of sediments on regional dimensions estimating past conditions such as topographic relief and knowledge of how physical and chemical processes interact over gelogic time scales progress in basin modeling will accelerate as hydrologic research efforts are better integrated with those of other specialities such as sedimentology rock mechanics and geochemistry

seismic heterogeneities in the indian lithosphere abstract rayleigh wave group velocity distributions over the indian region were obtained by the backus gilbert method for time periods 15 25 40 50 and 60 s the observed velocity variations reveal sharp lithospheric heterogeneities in this region southern peninsular india is marked by high velocities in contrast to the northern indo gangetic plain and the himalaya highest surface wave velocities are observed over the southern part of the deccan traps and the dharwar craton whereas the metamorphic terrains and rift zones exhibit anomalous low velocities the nepal himalaya and indo burmese collision zones are characterised by contrasting velocities which reflect their diverse orogenesis the bay of bengal is marked by an anomalous 6 12 higher velocity as compared with the indian continental region for the periods 25 50 s

pore pressure variation within the tuscaloosa trend morganza and moore sams fields louisiana gulf coast repeat formation tester rft mark of schlumberger pore pressure data from the lower tuscaloosa formation upper cretaceous are analyzed across a pressure transition zone in two gas fields of the tuscaloosa trend louisiana documenting a pressure seal within a sandstone dominated interval that maintains a pressure anomaly of 20 mpa pressure measurements within the formation span a depth interval of 5500 6060 m and are limited to the crests of rollover structures associated with growth faults the onset of overpressure occurs at a depth between 5620 m and 5690 m in two fault blocks while the strata are displaced across the fault by 100 to 120 m suggesting that the pressure seal may be near horizontal crosscutting stratigraphic boundaries the pressure seal zone is as thin as 38 m and occurs within interbedded sandstones and shales overpressures in all wells of the moore sams field and in two wells of the morganza field follow local hydrostatic gradients indicating that portions of the overpressured zone are in fluid communication though isolated from shallower normally pressured fluids in other wells overpressures increase with depth in a stair step manner to 117 mpa at depths of 5 9 km the occurrence of the pressure seal in interbedded sandstones and shales where higher permeability is expected suggests that the sandstones of the seal zone are unusually tight a companion petrographic study of sandstones near the pressure seal suggests that extreme compaction of the sandstones after dissolution of grain supporting cements may have contributed to the low permeability of the seal zone

upper mantle structure of the british isles from rayleigh wave dispersion summary fundamental mode rayleigh wave phase velocities have been measured over the period range 15 140 s for two paths within the british isles from southern scotland esk parallel to the trend of the caledonides to south west ireland val and from esk to southern england wol errors generated in these observations during the processing sequence have been examined in detail and empirically derived uncertainty bounds have been placed on the data inversion of the dispersion velocities to s wave velocity depth profiles using the hedgehog technique yields a set of models for the caledonides path esk val which are similar to typical continental aseismic platforms with a well developed low velocity channel of shear velocity vs 4 2 4 4 km s 1 lithosphere thickness is in the range 110 190 km with a sub moho velocity of 4 525 4 6 km s 1 although the lithosphere along the other path esk wol has comparable velocities it must be at least 140 km thick beneath this the low velocity channel is less pronounced vs 4 4 kms 1 or absent hence this profile appears distinct from that for the caledonides and is significantly different to that for the north sea region instead it is shield like and is not distinguishable from profiles for the baltic shield and parts of hercynian france

lithospheric thickness and mechanical strength of the indian shield abstract we determined the relative mechanical strength of the indian subcontinent by a robust coherence method based on multitaper spectral analysis on overlapping windows of equal size representing the elastic properties of the lithosphere by a transitional coherence wavelength we bypass the need to input rheological variables such as young s modulus or poisson s ratio which have been shown to vary on other continents we compare our measurements in terms of age and find that regions underlain by proterozoic basement are on average stronger than regions of archaean age this is in stark contrast to the common assumption that mechanical strength should increase progressively with time this suggests they are indeed mechanically distinct and that the transitional coherence wavelength adequately captures this distinction between regions of relative strength difference conversions of these values to absolute effective elastic thickness show a greater overlap which is due to the many strong assumptions required in obtaining such absolute values and argues against their usage as a robust and well constrained property of the elastic lithosphere

the deep geothermal potential of the berlin area in this study we model the geothermal potential of deep geological formations located in the berlin region in germany berlin is situated in a sedimentary geological setting northeastern german basin comprising low enthalpic aquifers at horizons down to 4 5 km depth in the berlin region the temperature increases almost linearly with depth by about 30 k per kilometer thus allowing for direct heating from deep aquifer reservoirs in principle our model incorporates eight major sedimentary units jurassic keuper muschelkalk upper middle lower buntsandstein zechstein salt and sedimentary rotliegend owing to lack of available petro physical rock data for the berlin region we have evaluated literature data for the larger northeastern german basin to develop a thermodynamic field model which regards depth corrected equations of state within statistical intervals of confidence integration over the thicknesses of the respective structural units yields their heat in place energy densities associated with the pore fluid and the rock matrix under local conditions in joule per unit area at the surface the model predicts that aquifers in the middle buntsandstein and in the sedimentary rotliegend may well exhibit energy densities about 10 gj m 2 for the pore fluids and 20 gj m 2 to 40 gj m 2 for the rock matrices on average referring these figures to the city area of berlin about 892 km2 a significant hydrothermal potential results which however remained undeveloped until today for the reason of present development risks the model accounts for these risks through statistical intervals of confidence which are in the order of 60 to 80 of the trend figures to minimize these uncertainties scientific field explorations were required in order to assess the petro physical aquifer properties locally

basin dewatering near salt domes and formation of brine plumes a previous study noted the occurrence of a subsurface brine plume with more than 160 g l sodium chloride perched above welsh salt dome in southwestern louisiana plumes of saline groundwaters have been reported above other gulf coast salt domes as well the u s geological survey code sutra was used to model the formation of brine plumes around a generic salt dome by basin dewatering along the flanks of the dome and also to study the gravitational instability of a brine plume initially perched above a dome in the absence of an externally impressed driving force for upwelling the simulations take into account the effect of salt concentration gradients on brine density the first set of simulations showed that a brine plume initially perched above a salt dome sank rapidly in the absence of an overpressured section where observed perched brine plumes above salt domes must therefore be either 1 young 2 ma if formed by basin dewatering and vertical fluid expulsion along the flanks of salt domes or 2 formed by a continuous mechanism the second set of simulations modeled the dewatering of a thick initially overpressured sedimentary section extending from a depth of 3 km to a depth of 10 km the deflation rate of the overpressured section profoundly depended on whether or not a permeable conduit along the flank of the dome existed which could collect water expelled radially inward to the flank of the dome from the overpressured sediments and focus it upward along the flank of the dome in most simulations the volume of compaction water was limited to only 10 of the total volume of overpressured sediment around the dome and there was an ample amount of compaction water for a perched brine plume to form in fact when a perched brine plume formed it formed very quickly in 0 01 m y after a negligible degree of deflation of the overpressured section it is conceivable that if cycles of conduit sealing and seal rupturing occurred perched brine plumes could be formed several times during deflation conditions necessary for the formation of a perched brine plume are as follows 1 waters must be focused laterally toward the dome within in the overpressured section 2 there must be a conduit of sediment with relatively high vertical permeability along the flank of the dome and 3 sediments above the dome must be more permeable than sediments along the flank of the dome for some simulations the average linear velocity of upward flow along the flanks of the dome was 3 m yr possibly of large enough magnitude to cause a thermal anomaly if perched brine plumes form by basin dewatering the thermal buoyancy effects associated with such a thermal anomaly may make the plumes rise to depths shallower than indicated in the simulations here the inability of the code sutra to simultaneously model heat and solute transport did not permit an evaluation of this

accretionary tectonics of burma and the three dimensional geometry of the burma subduction zone the geometry of the burma wadati benioff zone wbz has been determined by fitting a trend surface parameterized with eight effective degrees of freedom to 184 well located hypocenters the dip of this surface which passes through the middle of the wbz varies from about 50 in the north near the eastern himalayan syntaxis to about 30 in the bay of bengal area the eastern edge of the indo burman ranges closely follows the map projection of the 60 km depth contour of the wbz the curvature of the indo burman ranges is controlled by the geometry of the interface between the more steeply dipping part of the indian plate and the leading edge of the overriding burma platelet shallow earthquakes beneath the indo burman ranges are primarily confined to the underthrusting indian plate their focal mechanisms indicate strike slip faulting and north south shortening parallel to the eastern margin of the indian plate

continent like crustal thickness beneath the bay of bengal sediments observed dispersion of fundamental mode rayleigh and love waves across the bay of bengal to wwssn and indian seismograph stations suggests increasing crustal thickness northward from an approximate 15 km thick oceanic crust south of the latitude of the southern tip of india to a more continent like thickness of approximately 25 km at 20 n and over 35 km at the northernmost part of the bengal fan the dispersion data are not consistent with models which simply add the increasing sedimentary thickness on top of a normal oceanic crust the sediment thicknesses and crust velocities are controlled by extensive seismic refraction results and are in agreement with clearly observed sedimentary higher mode waves recorded at the indian seismograph stations madras and vishakapatnam several hypotheses might explain this surprising result 1 1 the blanketing effect of the sediments with consequent temperature rise has brought about differentiation of basalt to increase the crustal thickness r n singh personal communication 2 2 the change in moho depth represents dynamic isostatic adjustment such as a phase change boundary which is lowered because of temperature or pressure perturbations from the sedimentary blanket or from pressure perturbations of plate collision 3 3 the collision has underthrust a wedge of low velocity material beneath the oceanic crust 4 4 the northern bay of bengal is actually fortuitiously continental or continent like possibly as a result of the influence of the 90 ridge especially in the northern part if the explanation is 1 2 or 3 the result is important to our understanding of crust and upper mantle dynamics it is suggested that further controlled studies be performed to verify the result

saline groundwater in mono basin california 1 distribution mono lake california is a perennial closed basin saline lake up to 2 km of sediments have accumulated below the lake and a well log shows that saline groundwater of concentration 18 000 ppm extends to the bottom of the basin fill we investigated the groundwater system with the variable density flow and solute transport code sutra to determine if the basin s recharge and inferred groundwater salinity are consistent with observational data steady state model predictions of the position and shape of the interface separating saline from fresh groundwater are consistent with the salinity profile derived from the spontaneous potential sp log of a geothermal well on the lake s shoreline we also inferred the basin wide saline groundwater distribution and concentration from experiments with a steady state model of the entire basin groundwater system hydrologic variations around the lake determine the position of the saline fresh groundwater interface higher recharge rates characteristic of the sierra nevada shoreline push the interface far beneath the lake the interface probably lies below the shoreline around much of the rest of the lake on the low recharge northeastern shoreline the interface top may lie outside the lake edge this positions the saline groundwater discharge zone just below the playa surface and contributes to development of salt flats on the recently exposed former lake bed simulations suggest that the basin fill permeability may not have significant anisotropy possibly owing to extensive faulting which increases vertical permeability for an anisotropic basin fill the resultant increased channeling of recharge beneath the lake readily overcomes the opposing force of the saline groundwater density and it is flushed out of the basin sediments a simple permeability representation of the basin lithology with low permeability below the lake and an anisotropic transition to higher permeability outside the lake reasonably represents the well and spring water salinity observations

flood basalts and large igneous provinces from deep mantle plumes fact fiction and fallacy abstract flood basalts large igneous provinces and all intraplate magmatism are almost unanimously ascribed to features called mantle plumes in current geodynamics literature in the starting plume model flood basalts and any associated hotspot tracks have been ascribed to the melting of a large plume head and a narrow tail respectively and the deccan flood basalt province of india and the laccadives maldives chagos reunion island volcanic chain in the indian ocean are widely thought to be an excellent example supporting this model however the existing geodynamic thermal petrological geochemical and geochronological constraints on deccan volcanism do not require or support a mantle plume origin a new interpretation made here rules out any role for the reunion plume in deccan volcanism and even questions the notion that the reunion hotspot is the manifestation of an underlying reunion plume the laccadives reunion hotspot track is viewed here as caused by a southward propagating fracture based on the published radiometric age data and the ultimate cause of deccan volcanism is argued to be mega scale lithospheric rifting the appreciation of the great original areal extent of the deccan nearly as far as the southern tip of peninsular india solves the hitherto unsolved problem of the cause of the uplift of the 1500 km long western ghats escarpment this cause being combined surface erosion and magmatic underplating hypothesized mantle plumes do not appear responsible for most large igneous provinces instead their very existence is questionable no geological evidence of any kind geochemical petrological thermal topographic requires mantle plumes the self contradictions and special pleading that proliferate in plume explanations are unjustified and unnecessary if one accepts based on various grounds that a globe encircling enriched mantle layer the perisphere may overlie a deeper depleted mantle which is the source of morb the systematic geochemical variations along the laccadive reunion chain can be explained by this model and are not consistent with a plume tail experiencing entrainment from surrounding morb mantle as in the current plume model hotspot tracks may not reflect plate motion above stationary deep mantle upwellings but the stress state of the lithosphere as originally proposed decades ago the locations of large igneous provinces hotspots and hotspot tracks are strongly controlled by lithospheric architecture and history they are not placed randomly on the globe indifferent to the surface geology neither are large igneous provinces sudden chance events within the vastness of geological time which plume theories typically allege

evidence for anisotropy in north east africa from geographical and azimuthal distribution of rayleigh wave velocities and average upper mantle structure long period surface waves from wwssn gdsn sro and geoscope stations are analysed to obtain the dispersion of surface waves in the north east of africa lateral variations of rayleigh wave velocities are retrieved simultaneously with the average azimuthal anisotropy as a first result the low velocity anomaly under the red sea is apparent at all periods a second result is a nearly north south direction of maximum group and phase velocities this azimuthal anisotropy direction is in agreement with the direction of absolute plate motion in this region anisotropy is also evidenced by simultaneous inversion of love and rayleigh wave dispersion along the path tam agd in the resulting models isotropic and anisotropic very low mantle sv wave velocities extend up to the moho for sh waves we find a strong discrepancy with sv waves sh wave velocities being higher by 5 down to 200 km under the crust this is characteristic of lithospheric polarization anisotropy the s wave anisotropy polarization and azimuthal found in this region including the red sea is compatible with the absolute motion of the african plate it can be interpreted considering the low lithospheric s velocities as a consequence of plastic flow in the weak lithosphere of an anomalous mantle this anisotropy evidenced here on s waves may be due as pn and lithospheric s wave anisotropy found in other continental areas to dynamical processes related to plate motion

the deep thermal field of the glueckstadt graben with this paper we assess the present day conductive thermal field of the glueckstadt graben in nw germany that is characterized by large salt walls and diapirs structuring the graben fill we use a finite element method to calculate the 3d steady state conductive thermal field based on a lithosphere scale 3d structural model that resolves the first order structural characteristics of the graben and its underlying lithosphere model predictions are validated against measured temperatures in six deep wells our investigations show that the interaction of thickness distributions and thermal rock properties of the different geological layers is of major importance for the distribution of temperatures in the deep subsurface of the glueckstadt graben however the local temperatures may result from the superposed effects of different controlling factors especially the upper sedimentary part of the model exhibits huge lateral temperature variations which correlate spatially with the shape of the thermally highly conductive permian salt layer variations in thickness and geometry of the salt cause two major effects which provoke considerable lateral temperature variations for a given depth 1 the chimney effect causes more efficient heat transport within salt diapirs as a consequence positive thermal anomalies develop in the upper part and above salt structures where the latter are covered by much less conductive sediments in contrast negative thermal anomalies are noticeable underneath salt structures 2 the thermal blanketing effect is caused by thermally low conductive sediments that provoke the local storage of heat where these insulating sediments are present the latter effect leads to both local and regional thermal anomalies locally this translates to higher temperatures where salt margin synclines are filled with thick insulating clastic sediments for the regional anomalies the cumulative insulating effects of the entire sediment fill results in a long wavelength variation of temperatures in response to heat refraction effects caused by the contrast between insulating sediments and highly conductive crystalline crust finally the longest wavelength of temperature variations is caused by the depth position of the isothermal lithosphere asthenosphere boundary defining the regional variations of the overall geothermal gradient we find that a conductive thermal model predicts observed temperatures reasonably well for five of the six available wells whereas the steady state conductive approach appears not to be valid for the sixth well

the geothermal potential of the underground of the salento peninsula southern italy the low enthalpy geothermal energy systems exploit the underground as a heat reservoir by coupling it with highly efficient heat pumps in winter the energy stored in the subsoil can be transferred to the surface to heat buildings whereas in summer the surplus heat in buildings can be transferred back to the ground providing a cooling action despite the high costs for installation low enthalpy geothermal systems have high energy efficiency and therefore contribute to energy saving to the use of renewable energy sources to environmental sustainability the effects on the hydrogeological cycle are often negligible and to the reduction in fuel consumption and in gas emissions in this paper a simple methodology is proposed to assess the geothermal potential of the underground of the salento peninsula southern italy at the regional scale by calculating the equivalent thermal performance of the subsoil which expresses the thermal power that is potentially extractable and useful to heat or cool a building since the possibility of exploiting the underground as a heat reservoir depends on the physical properties and water saturation of rocks previous detailed studies on the hydrostratigraphic setup of the region are the basis for this analysis of geothermal potential the equivalent thermal performance depends on the thermal efficiencies of different lithological units whose ranges of values for heating only are provided in literature for this case study a stochastic approach has been applied several combinations of thermal efficiencies were randomly selected from the intervals of reference values for every hydrostratigraphic formation and the corresponding minimum depths below the ground surface that must be reached to get the desired equivalent thermal performance are computed the results show that the underground of the salento peninsula has great potentialities for heating of buildings except for some coastal areas because the saltwater intrusion phenomenon could cause problems for the realization of low enthalpy geothermal energy systems

crust and upper mantle velocity structure beneath north and central india from the phase and group velocity of rayleigh and love waves abstract crust and upper mantle velocity structure is determined using the fundamental mode rayleigh and love waves for 23 different paths across north and central india the earthquakes occurring in kashmir nepal himalaya burma and nearby regions and recorded at hyderabad new delhi and kodaikanal seismic stations are used for dispersion studies frequency time analysis ftan using the multiple filter technique is done for the fundamental mode surface waves to estimate group velocities from the time periods of 13 71 s the single station technique is used to estimate rayleigh and love wave phase velocities at time periods of 15 75 s velocity structure down to a depth of 120 km is determined using both rayleigh and love wave phase and group velocities the crustal thickness is found to be 50 km with 4 km sedimentary thickness for the northern india across burma to new delhi path and 44 km for the central india across kashmir nepal himalaya and northeast india to hyderabad and kodaikanal path a low velocity zone v p 8 4 km s v s 4 15 km s is found from 100 km below the surface velocity structure shows that the shield structure of the peninsula extends up to northernmost india below sub himalayan regions with an overlying sedimentary thickness of 4 km the lower value of observed group velocity and higher phase velocity across northern and central india may be caused by the presence of varying sedimentary thickness in the northernmost part of india the indo gangetic plain below the sub himalayan region the observed lower value of rayleigh wave group velocities below 40 s time periods can be explained by assuming a thin layer of a high contrast material with a p wave velocity of 4 6 km s an s wave velocity of 2 5 km s a density of 3 24 g cm3 and a thickness of 3 km centred above the moho

fluid dynamics driving saline water in the north east german basin in several areas of the north german basin saline water comes close to or even reaches the surface available data from wells indicate that brine stratification is under unstable conditions in the deeper underground in order to analyse the possible transport mechanisms 3d thermohaline simulations have been carried out for two different scenarios the 3d regional model 230 330 km indicates that salty water is driven to the surface by hydrostatical forces from the surrounding highlands in addition a smaller scale model 10 10 km has been constructed with a grid resolution accounting for possible convective flow the results indicate that convective flow may play a dominant role in areas with minor topography in summary the complex pattern of near surface occurrences of saline water probably results from the interaction of hydrostatic and thermal forces

depositional architecture provenance and tectonic eustatic modulation of miocene submarine fans in the shikoku basin results from nankai trough seismogenic zone experiment seismostratigraphy coring and logging while drilling during integrated ocean drilling program expeditions 319 322 and 333 sites c0011 c0012 show three miocene submarine fans in the ne shikoku basin with broadly coeval deposits at ocean drilling program site 1177 and deep sea drilling project site 297 nw shikoku basin the sediment dispersal patterns have major implications for paleogeographies at that time the oldest finer grained kyushu fan has sheet like geometry quartz rich flows were fed mostly from an ancestral landmass in the east china sea during prolonged hemipelagic mud deposition at c0011 c0012 similar to 12 2 to 9 1 ma sand supply continued at sites 1177 and 297 sand delivery to much of the shikoku basin halted during a phase of sinistral strike slip to oblique plate motion after which the daiichi zenisu fan similar to 9 1 to 8 0 ma was fed by submarine channels the youngest fan daini zenisu similar to 8 0 to 7 6 ma has sheet like geometry with thick bedded coarse grained pumiceous sandstones the pumice fragments were fed from a mixed provenance that included the collision zone of the izu bonin and honshu arcs the shift from channelized to sheet like flows was favored by renewal of relatively rapid northward subduction which accentuated the trench as a bathymetric depression increased sand supply appears to correlate with long term eustatic lowstands of sea level the stratigraphic position and 3 d geometry of the sandbodies have important implications for subduction related processes including the potential for focused fluid flow and fluid overpressures above and below the plate boundary fault in sheet like sands pathways for fluid flow have greater horizontal permeability compared with those in channel sands

global love wave phase velocity variation and its significance to plate tectonics abstract global love wave phase velocity variation was constructed for periods between 80 and 200 s by using approximately 9000 paths from 971 earthquakes with m 5 5 the data set was from gdsn and geoscope networks between 1980 and 1987 we examined both the spherical harmonic expansion method and the block parameterization method with a simple constant damping parameter approach synthetic tests showed that more accurate results were obtained by the block parameterization method than by the spherical harmonic expansion method we adopted the block inversion method with a nearly equal area block 5 5 near the equator discretization the general pattern of the resulting maps were consistent with previous global and local studies with a discretization of 5 by 5 the maps were detailed enough to test some plate tectonic models for the pacific atlantic and indian oceans surface wave velocities increased smoothly to plate ages older than 100 ma simple forward modeling showed that seismic phase velocity variation with a continuous thickening of lithosphere up to about 150 ma fits the present observation disagreeing with the model deduced from the heat flow and ocean depth data which change variations at about 60 80 ma the seismic phase velocity variations in different oceans showed systematic differences at younger ages and convergence beyond 100 ma the difference at younger ages implies a failure of scaling derived from a simple thermal boundary layer model for oceanic plates age seismic phase velocity relationships on each side of ridges were also examined and asymmetric velocity variations were found which suggests differences in thermal states from one side of the ridge to the other in order to further examine the thermal state of the lithosphere average age phase velocity relations were established for each ocean and subtracted from phase velocity variation maps the results indicated broad low velocity regions in the south pacific super swell region the south and west indian ocean and high velocity regions east of the east pacific rise and in the north to northeast indian ocean the results reflect the asymmetry of phase velocity variation about ridges there is some correlation between hot spot locations and low velocity anomalies but additional large scale thermal anomalies exist under old oceanic plate

shear velocities qβ and the frequency dependence of qβ in stable and tectonically active regions from surface wave observations summary velocities and attenuation coefficient values of rayleigh waves within the south american continent and indian subcontinent have been determined in order to study velocity structure and qp structure as well as their lateral variation in those regions single station and two station data are combined to yield dispersion and attenuation data from periods of a few seconds to periods between 60 s and 100 s for each region both types of data are inverted using differential inversion schemes this inversion process is found to sometimes allow the location of velocity discontinuities in the models directly from the dispersion data qp models obtained from the inversion process are not constrained to have high values at large depths a problem with earlier methods used to invert surface wave attenuation data the shear velocity models for the indian shield and eastern south america are similar to one another and have somewhat slower velocities than those reported for shield regions of north america the shear velocity models for the himalaya and andes are similar to one another in crustal thickness but the velocities in the andes are lower than those in the himalayas in the uppermost mantle a low velocity zone can marginally be resolved in the upper mantle beneath the himalaya but not beneath the other regions in this study qp models obtained for the stable regions of eastern north america and eastern south america exhibit similar qp values at mantle depths the indian shield however has much lower qp values in both the crust and upper mantle a result which may be related to the unusually high heat flow observed for that stable region for the tectonically active regions of western north america western south america and the himalaya is considerably lower than qp for the stable regions throughout most of the crust and upper mantle minimum mantle values appear to be about 120 for stable regions and 40 or less for tectonically active regions thus qp values in the upper mantle appear to vary regionally by a factor of 3 or more whereas shear velocities in the same regions vary by no more than 13 per cent

deep gases discharged from mud volcanoes of azerbaijan new geochemical evidence abstract this paper presents new geochemical data of hydrocarbon rich gases released from some mud volcanoes of azerbaijan methane is considerably the most abundant component of all the sampled gases which show d ch 4 and 13 c ch 4 values likely related to a dominant thermogenic source these gases are characterized by the presence of more than 20 different cyclic compounds with concentrations up to several mol mol a similar gas composition has recently been found to characterize many mud volcanoes of the northern apennines and sicily italy the data of the azerbaijan mud volcanoes corroborate the notion that cyclic compounds can be considered reliable tracers for hydrocarbon gas production at considerable depths and temperatures up to 120 150 c which correspond to a 6 5 8 3 km depth range assuming an average geothermal gradient of 18 c km this depth interval is consistent with both the depth of potential source rocks imaged seismically beneath some mud volcanoes and the results of previous estimates that used the 13 c 12 c values of methane and ethane such deep sourced gases and material fluidized clayey mass and rock fragments ascend into the core of anticlines and accumulate at shallower reservoirs where fold parallel outer arc faults or fold orthogonal fractures may penetrate and transfer the fluids to the surface finally the basically equivalent composition of the different hydrocarbon groups c 2 c 10 alkanes aromatics and cyclic determined in the gases sampled in both azerbaijan and italy manifests the lack of evident relationships between the chemistry of light hydrocarbons and the type of source rock

the interdisciplinary use of overpressure abstract overpressure is a polysemic word that has a variety of meanings within and across different disciplines this is likely to be a particular problem in analysis of geothermal resources where reservoir engineers volcanologists and structural geologists may each confidently use overpressure but mean different things we suggest that to avoid confusion the term should be carefully and accurately defined whenever used and ideally only used to mean fluid pressure in excess of hydrostatic pressure

the role of turbidites on compaction and dewatering of underthrust sediments at the toe of the northern barbados accretionary prism new evidence from logging while drilling odp leg 171a abstract recently obtained logging while drilling data sets from odp leg 171a enable a detailed correlation of sediments among drill sites and an estimate of the change of bulk densities among them in this analysis three different lithologies from the underthrust sediments of the barbados accretionary prism were picked up and volumetric strains were calculated by comparing bulk densities of correlated intervals results showed that the interbedded mudstones in turbidites have experienced larger volumetric strain while massive claystones have not the mudstone beds sandwiched both above and below by relatively highly permeable sandstones are interpreted to have undergone dewatering because laterally continuous sandstones have acted as effective drains for dewatering the existence of the turbidite sandstones in the underthrust package and the migration of warm fluid along the sandstones might explain why high heat flow is observed at the ocean floor at site 672 where turbidite sandstones exist but not at site 543 where turbidites were not deposited

subsurface thermal conductivity assessment in calabria southern italy a regional case study determining the suitability of a local area at a regional or local scale for the geothermal application of low enthalpy systems requires the knowledge of rock thermal conductivity values to evaluate the possibility of low enthalpy heat exchange a digital cartographic tool is also needed to synthesize the thermal properties of the underground this tool should be easily accessible and upgradeable and thus suitable for territorial planning and environmental control in order to address these key issues a methodological approach was developed within the framework of the national vigor project dedicated to evaluating the geothermal potential in southern italy in this paper the region of calabria was selected as a case study around 70 samples that were representative of the main geological formations were collected from all over the area thermal property tests were carried out both in dry and wet conditions using a thermal device in accordance with the modified transient plane source method the thermal conductivity values were then compared with data from the international literature in order to consider the influence of the entire stratigraphic sequence on the thermal conductivity parameters a geostatistical analysis of the available lithostratigraphic data was performed using the matlab toolbox modalstrata specially developed for this purpose a comprehensive geothermal subsurface characterization of calabria was thus obtained

reply to comment on a numerical model of compaction driven groundwater flow and heat transfer and its application to the paleohydrology of intracratonic sedimentary basins by craig m bethke