variations associated with cores and gaps of a pacific narrow cold frontal rainband abstract a noaa p 3 instrumented aircraft observed an intense fast moving narrow cold frontal rainband ncfr as it approached the california coast on 19 february 2001 during the pacific coastal jets experiment airborne doppler radar data obtained while the frontal system was well offshore indicated that a narrow ribbon of very high radar reflectivity convective cores characterized the rainband at low levels with echo tops to 4 5 km and pseudo dual doppler analyses showed the low level convergence of the prefrontal air the ncfr consisted of gaps of weaker reflectivity and cores of stronger reflectivity along its length perhaps as a result of hydrodynamic instability along its advancing leading edge in contrast to some earlier studies of cold frontal rainbands density current theory described well the motion of the overall front the character of the updraft structure along the ncfr varied systematically along the length of the precipitation cores and in the gap regions the vertical shear of the c

mesoscale numerical modeling of meteorological events in a strong topographic gradient in the northeastern part of mexico a series of numerical experiments were carried out to study the effect of meteorological events such as warm and cold air masses on climatic features and variability of a understudied region with strong topographic gradients in the northeastern part of mexico we applied the mesoscale model mm5 we investigated the influence of soil moisture availability in the performance of the model under two representative events for winter and summer the results showed that a better resolution in land use cover improved the agreement among observed and calculated data the topography induces atmospheric circulation patterns that determine the spatial distribution of climate and seasonal behavior the numerical experiments reveal regions favorable to forced convection on the eastern side of the mountain chains eastern sierra madre and sierra de alvarez these processes affect the vertical and horizontal structure of the meteorological variables along the topographic gradient

mantle discontinuities beneath southern africa 1 seismic velocity discontinuities within the top 1000 km of the earth beneath southern africa are imaged by stacking about 1300 source normalized broadband seismograms recorded by the southern african seismic experiment the moho 410 and 660 kilometer discontinuities are clearly detected the mean mantle transition zone thickness is 245 km essentially the same as the global average suggesting that the transition zone is not anomalously warm thus the lower mantle african superplume beneath our study area has no discernible effect on transition zone temperature and is consequently confined to the lower mantle variations in transition zone thickness appear to be related to the presence or absence of thick lithosphere we do not detect several previously reported discontinuities beneath continents such as the hales or lehmann discontinuities and find no evidence for a 520 km discontinuity nor do we detect a previously proposed low velocity zone just above the transition zone

effects of inelasticity on the apparent depth and detectability of seismic discontinuities in the mantle 1 accurate determination of parameters about seismic discontinuities in the earth such as their depth existence and strength provides critical information about the physical and chemical states and dynamics of the earth s interior unfortunately those parameters can be strongly affected by factors that are not related to the discontinuities we use synthetic seismograms to estimate the influence of one of those factors inelasticity on the apparent depth and detectability of the 410 and 660 kilometer discontinuities obtained from stacking p to s converted phases pds our results show that when pds travels through a zone with lower than normal q values the observed depth of discontinuities could be tens of kilometers deeper than the real value and the stacking amplitudes and consequently the detectability and apparent strength are greatly reduced this study demonstrates the importance of taking q structure into account when seismologically detected discontinuity parameters are interpreted

the effect of water on the 410 km discontinuity an experimental study 1 in order to evaluate the effect of h on the pressure and transition interval of the olivine wadsleyite transformation synthesis experiments were carried out in hydrous and anhydrous peridotite compositions at 1400 c under hydrous near saturated conditions the pressure of the transition is 1 0 0 5 gpa lower than under anhydrous conditions in addition the two phase interval appears to broaden from about 0 4 gpa 12 km in the anhydrous system to as much as 1 3 gpa 40 km in the hydrous system under hydrous conditions the spatial distribution of olivine and wadsleyite appears to be controlled by h diffusion extrapolating previously measured diffusion coefficients for h in olivine and in liquids it appears that h diffusion driven by gravitational equilibration may serve to narrow the transition interval between olivine and wadsleyite

seismic signature of the mantle transition zone beneath eastern tibet and sichuan basin abstract the strong interaction between the eastward flow escaping from tibet and the rigid sichuan basin resulted in the rise of the longmenshan however the detailed dynamics in the mantle remains controversial in this study the structure of the mantle transition zone mtz beneath eastern tibet and sichuan basin is investigated using 5080 receiver functions from 51 broadband stations the depth of the 410 km discontinuity is close to the global average except for the longmenshan where the 410 and 660 km discontinuities are found to be depressed by up to 10 25 km and 5 10 km respectively the observed simultaneous depressions of the 410 and 660 km discontinuities distributed along the lms together with proofs from tomography and regional tectonics suggest that asthenospheric flow sinks into the mtz resulting in a high velocity zone as well as variation in the mtz thickness the depressions are not from the traditional clapeyron slopes or temperature variation also the depression of the 410 km discontinuity and the dehydration of wadsleyite are syngenetic both of which originate from the dry mantle flow traveling across the old 410 km interface

the numerical simulation of non supercell tornadogenesis part i initiation and evolution of pretornadic misocyclone circulations along a dry outflow boundary abstract high resolution three dimensional simulations are used to study misocyclone initiation and development along the leading edge of an outflow boundary model conditions were designed such that this development could be simulated independent of moist processes the outflow boundary is allowed to propagate into a region of southerly low level flow which results in a vertical vortex sheet along the outflow s leading edge lobe and cleft instabilities follow and provide perturbations for the subsequent development of horizontal shearing instabilities these growing instabilities are the inaugural circulations of leading edge misocyclones with wavelengths ranging from 1 6 to 3 2 km the structure of these modeled misocyclones compares favorably to observed pretornadic misocyclones along outflow boundaries in northeast colorado vortex sheet dynamics are observed to exert substantial control over the structure of the evolving outflow leading edge the vertical vortex sheet passes through discrete evoluti

low seismic velocity layers in the earth s crust beneath eastern siberia russia and central mongolia receiver function data and their possible geological implication analysis of teleseismic receiver functions at digital stations along the bratsk irkutsk ulanbaatar undurshil profile suggests that low velocity layers in the earth s crust exist not only beneath the baikal rift zone where such a layer was found earlier by deep seismic sounding dss but also beneath early paleozoic sayan baikal paleozoic mongolian early mesozoic mongolia okhotsk fold areas and beneath the siberian platform the reliability of detection of the low velocity layers by receiver function analysis has been checked by numerical modeling the results of this modeling demonstrate that receiver functions can reveal the low velocity layers in the crust if the initial model starting approximation is close to real velocity distribution and if the model medium is divided into thin layers averaged dss velocity model without low velocity layers was used as starting approximation for the inversion of observed receiver functions the low velocity layers are interpreted to reflect inhomogeneities of the earth s crust formed during its evolution most of these layers are presumed to correspond to thick mylonite zones related to large pre cenozoic thrusts the mylonites possess a great seismic anisotropy caused by the mineral orientation formed by the ductile flow in large thrust zones they can result in low velocity layers only for seismic waves whose rays are oriented perpendicular to the mylonite foliation i e in the direction of the minimum velocity the velocities along the foliation direction can be rather high therefore the low angle mylonite zones can be distinguished by the receiver function method which uses the waves from the teleseismic events with nearly vertically oriented rays the suggestion that the low velocity layers mark low angle thrusts is in agreement with gravity and geological data the amount of overthrusting is estimated to be as large as several hundred kilometers multichannel seismic profiling can be used to verify the existence and the deep geometry of the presumed thrusts d 2002 elsevier science b v all rights reserved

evidence for small scale mantle convection in the upper mantle beneath the baikal rift zone 1 inversion of teleseismic p wave travel time residuals collected along a 1280 km long profile traversing the baikal rift zone brz reveals the existence of an upwarped lithosphere asthenosphere interface which causes a travel time delay of about 1 s at the rift axis central high an area with early arrivals relative to the stable siberian platform of up to 0 5 s is observed on each side of the rift about 200 km from the rift axis flank lows while the location of the central high is approximately fixed in the vicinity of the rift axis those of the flank lows vary as much as 200 km with the azimuth of the arriving rays we use three techniques to invert the travel time residuals for velocity anomalies beneath the profile two of the techniques assume an isotropic velocity structure and one of them considers a transversely isotropic velocity model with a vertical axis of symmetry we use independent geophysical observations such as gravity active source seismic exploration and crustal thickness measurements to compare the applicability of the models other types of geophysical measurements suggest that the model involving transverse isotropy is a plausible one which suggests that the central high and flank lows are caused by the combined effects of an upwarped asthenosphere with a 2 5 lateral velocity reduction and a velocity increase due to transverse isotropy with a vertical axis of symmetry we consider the anisotropy to be the result of the vertical component of a lithosphere asthenosphere small scale mantle convection system that is associated with the rifting

velocity structure around the baikal rift zone from teleseismic and local earthquake traveltimes and geodynamic implications abstract we present new results on the velocity structure of the baikal rift zone asia deduced from a comparative teleseismic and local tomography analysis the aim of this paper is to better identify the role of deep mantle processes versus that of far field tectonic effects on the occurrence of extensional tectonics within a continental plate we use 36000 traveltimes of p refracted waves from the isc catalogues and pg and pn traveltimes of 578 earthquakes recorded by the russian regional network to determine a velocity model by the use of local and teleseismic inversion procedures the models show that some velocity patterns are continuous from the surface down to at least 400 km among them a narrow negative anomaly goes through mongolia and follows the southern and eastern margins of the siberian craton this structure is interpreted as a thin mantle plume rising beneath the rift axis however our results do not evidence any wide asthenospheric upwarp at this place other velocity anomalies observed near the surface are not deeply rooted in particular a negative anomaly is observed at shallow levels 48 km beneath the northern third of lake baikal which is disconnected from deeper structures it may be explained by the existence of underplated magmatic material at the bottom of the crust by comparing the geometry of deep rooted anomalies to the present day stress field patterns we conclude that the sub lithospheric mantle dynamics is not the main factor controlling extensional processes in the baikal rift however it does contribute to a thermal weakening of the lithosphere along a mechanical discontinuity bounding the siberian shield we finally conclude that three favourable conditions are gathered in the baikal area to generate extension far field extensional stress field mechanical inherited lithospheric weakness and heat supply further studies should help to precise the genetic link between these three factors

the s velocity structure of the east asian mantle from inversion of shear and surface waveforms summary the structure of the mantle beneath east asia down to 800 km depth is investigated using full waveforms of seismic shear and surface waves epicentral distances are limited to less than 40 in contrast with previous waveform inversions we avoid ray theoretical or path integral approaches instead we use 1 exact 3 d waveform sensitivity kernels that correctly reflect off path sensitivity and the existence of fresnel zones we apply 2 an accurate 3 d forward modelling technique based on a coupled mode multiple forward scattering approach allowing us 3 to iterate the inversion procedure through several 3 d models and 4 to evaluate the true misfit between the data and the synthetics for the 3 d model average lateral resolution of the model in regions with good path coverage is 400 km throughout the upper mantle in the depth range from 100 to 250 km the lateral resolution even approaches 200 km since wave front healing is taken into account the amplitudes of velocity perturbations are larger than in other tomographic models moreover the waveform sensitivity kernels provide an intrinsic physical smoothing of the model stabilizing the inversion finally owing to the use of exact sensitivities better resolution can be achieved with a given set of seismograms major features of the model are high velocity subducting slabs along the west pacific subduction zones stagnating at the 660 km discontinuity a strong low velocity zone between 80 and 250 km depth in the west pacific backarc regions a plume like low velocity feature beneath the southern tip of the baikal rift zone extending into the transition zone a low velocity region under the tien shan with connection into the transition zone and thick crust under tibet reaching its maximum thickness of approximately 80 km close to the 35th parallel the lithospheric mantle underneath southern tibet is very fast indicating underthrusting of the indian lithosphere in contrast the upper mantle beneath northern tibet exhibits average to slow values from the moho down to the 660 km discontinuity very high s velocities are again observed beneath the tarim basin the high velocity mantle lithospheres under southern tibet and the tarim join beneath the karakorum range at the western tip of the tibet plateau

processes affecting groundwater quality in arid zones the case of the bou areg coastal aquifer north morocco abstract the coastal aquifer of bou areg morocco has been studied to identify the main processes causing groundwater salinization using a multi tracer general chemistry and isotopes 2h 18o 13c 15nno3 18ono3 geochemical approach groundwater is characterized by the widespread occurrence of brackish waters tds no 3 reaching a maximum of 208 mg l 1 and cl lagoon samples represent a mixture of fresh water and sea water showing a na cl ratio in agreement with that of sea water and an excess of ca the high ca values represent the main peculiarity of the groundwater lagoon water system two types of groundwater could be identified i freshwater separated from the whole system and located at the limit of the irrigated area characterized by low tds depleted isotopic composition and relatively high quality and ii water mainly recharged by mountain runoff interacting with local recharge and acquiring salinity from different sources thus creating a complex system of dilute waters hydrochemical results confirm that the high salinity of the aquifer is caused by the coexistence of dissolution of evaporate rocks and carbonates from miocene strata water rock interaction and human impacts due to agricultural return flows the latter represents the main contribution to groundwater salinization especially in the central part of the aquifer as well as one of the main causes of the general increase in no 3 concentrations only locally in the southern part of the aquifer close to the city of kariat arkmane the high salinization observed may be attributed to the presence of lagoon water intrusion the isotopic composition of dissolved no 3 indicates manure and septic effluents especially in urban areas and in the central part of the plain and synthetic fertilizers in the agricultural zone as the main drivers for human induced pollution the study shows that agricultural return flow has significantly modified the chemistry of the system and it is a prime example of the human induced changes over coastal environments saline water intrusion from the lagoon in the shallow aquifer is negligible while discharge of polluted groundwater into the lagoon has been found to partially alter its quality

global mapping of topography on the 660 km discontinuity long period precursors to the ss seismic phase are used to produce global maps of topography for the discontinuity at 660 km depth in the upper mantle these maps indicate discontinuity depth variations of up to 30 km and suggest a correlation between regional depressions in the 660 km discontinuity and subduction zones a result more consistent with models in which the subducting slabs are deflected horizontally at the discontinuity than with models of unhindered slab penetration into the lower mantle

origin of groundwater salinity and hydrogeochemical processes in a confined coastal aquifer case of the rhone delta southern france the rhone delta south of france camargue 750 km2 is a coastal saline wetland located along the mediterranean sea the confined aquifer of this delta shows high values of electrical conductivity rising from the north 4 ms cm to the shoreline 58 ms cm this work aims to identify the origin of groundwater salinity and the geochemical processes occurring in this coastal confined aquifer according to the degree of salinity a natural tracing approach is considered using monthly sampling in 8 piezometers for chemical and isotopic analyses 18o 2h 13ctdic ionic and isotopic ratios demonstrate that strong salinities are due to a simple mixing between mediterranean seawater and freshwater seawater contribution reaches up to 98 at 8 km from the shoreline seawater intrusion induces a particular groundwater chemistry which varies with the degree of seawater contribution 1 in the less saline part of the aquifer seawater contribution 20 the intrusion induces so4 reduction which is confirmed by highly depleted 13ctdic values up to 19 the 13ctdic also reveals that methanogenesis processes may occur in the most reductive part of the aquifer due to so4 reduction the intrusion induces a shift in carbonate equilibrium leading to supersaturation with respect to dolomite and or magnesian calcite thus carbonate precipitation may occur in the area strongly influenced by seawater

alpine mantle transition zone imaged by receiver functions abstract assessing the thermal state of the mantle is essential to understand mantle dynamics and provides important clues about present and past tectonic regimes the tectonic processes related to the cenozoic subduction of the alpine tethys likely affected the regional upper mantle structure we use receiver functions to determine the mantle transition zone thickness beneath the greater alpine region as a proxy for its current thermal state compilation of a dataset of nearly 7000 high quality receiver functions from 98 stations yields a reliable and stable image of the alpine mantle transition zone significant signal from p to s conversions at the 410 and 660 km discontinuities is clearly observed the 410 km discontinuity is found at a depth close to that predicted by the iasp91 global model its seismic signature is generally strong except south of the alps signal from the 660 km discontinuity is strong continuous and emerges throughout the whole alpine region at depths greater than predicted by the global model the mantle transition zone is not or only slightly thickened 10 km north of the alps but is up to 40 km thicker than normal south of the alps and in the western alps outlining a roughly 300 km wide and 800 km long ene wsw directed anomaly thickening assuming conversions are due to olivine phase transformations suggests that the alpine mantle transition zone is at least 300 k colder than normal if the thickness anomaly were caused by equal amounts of shallowing and deepening of the 410 and 660 km discontinuity respectively however the thickness anomaly seems mainly due to depression of the 660 km discontinuity which suggests that temperature at the bottom of the mantle transition zone could actually be up to 800 k cooler than ambient mantle while temperatures at 410 km depth may be close to normal both location and amount of suggested thermal anomaly agree with tectonic reconstruction and large scale tomography models of the euro mediterranean region the cold material accumulated at the 660 km discontinuity is interpreted as remnants from the oceanic mantle lithosphere that detached from the eurasian plate after closure of the alpine tethys

mantle discontinuity structure beneath the colorado rocky mountains and high plains analysis of mantle discontinuity structure using converted p to s pas phases beneath colorado from the program for array seismic studies of the continental lithosphere passcal rocky mountain front rmf experiment reveals significant topography at the 410 and 660 km depth discontinuities and corresponding transition zone thickness variations a stack of all radial receiver functions resolves the 410 and 660 km discontinuities at average depths of 419 and 677 km respectively imaging of lateral variations in mantle discontinuity structure is accomplished by geographically binning the pds conversion points and then stacking the receiver functions in each bin to form spatial images analogous to common depth point stacking corrections for lateral velocity heterogeneity are calculated using the local s wave tomographic model of lee and grand 1996 and a constant lnvs lnvp scaling of 1 3 this scaling value is determined from the relative scaling between teleseismic p and s wave travel time residuals measured from the rocky mountain front deployment mantle discontinuity images using 150 km square bins show 20 km of 410 km discontinuity topography 30 km of 660 km discontinuity topography and up to 40 km of transition zone thickness variation features of the discontinuity structure include a 20 km depression of the 660 km discontinuity beneath western colorado and a gradual 10 km dip of the 410 km discontinuity beneath the high plains the thickening of the transition zone beneath southwest colorado is consistent with the presence of the subducted farallon slab in this region as imaged by van der lee and nolet 1997 in general our results show that the transition zone discontinuity structure is more complex than that predicted by the simple model of olivine phase boundaries modulated by vertically coherent thermal anomalies

upper mantle and mantle transition zone thermal and water content anomalies beneath ne asia constraints from receiver function imaging of the 410 and 660 km discontinuities abstract the 410 and 660 km discontinuities d410 and d660 bordering the mantle transition zone mtz beneath ne asia including ne china eastern mongolia and southern siberia are imaged in successive circular bins with a radius of 1 degree by stacking a total of 274 413 p to s radial receiver functions recorded by 799 broadband seismic stations after moveout correction based on the 1 d iasp91 earth model the resulting apparent depths of the discontinuities exhibit significant and spatially systematic variations three approximately n s elongated narrow zones with significantly thickened mtz are observed which may be associated with the thermal effect and dehydration of subducted slabs the major volcanoes in ne china are underlain by a d660 that is apparently depressed by 19 km which can be interpreted by the presence of an anomalously high water concentration in the lower mtz released from the stagnated slabs low wavespeed anomalies above the d410 west of the datong volcanic fields are underlain by an mtz with normal thickness and are attributable by dehydration of the leading portion of the stagnant pacific slab in the mtz that is revealed in an n s oriented narrow zone east of this area the lateral shift of the upper mantle low wavespeed zone and the area with thickened mtz may suggest a westward drift of the upper mantle relative to the subducted slab an abnormally thin mtz is observed beneath the hangay dome in central mongolia suggesting the possible existence of thermal upwelling from the lower mantle through the mtz

numerical modeling of precipitation cores on cold fronts abstract a nonhydrostatic three dimensional mesoscale model including cloud physics is used to simulate the structure of a narrow cold frontal rainband ncfr the model simulations reproduce the observed core gap structure of the ncfr trapped gravity waves triggered by regions of stronger convection on the cold front induce subsidence and regions of warming aloft in these regions precipitation is suppressed thereby creating precipitation gaps along the front separated by precipitation cores the advection of hydrometeors is responsible for the parallel orientation and the elliptical shapes of the precipitation cores gravity waves produce pressure perturbations just behind the cold front which modify the wind and thermal structure parts of the front behave locally like a gravity current traveling at the theoretical gravity current speed in a direction perpendicular to the local orientation of the front but the motion of the front as a whole is not well described by the gravity current spe

seismic imaging of mantle transition zone discontinuities beneath the northern red sea and adjacent areas summary the dramatic asymmetry in terms of surface elevation cenozoic volcanisms and earthquake activity across the red sea is an enigmatic issue in global tectonics partially due to the unavailability of broad band seismic data on the african plate adjacent to the red sea here we report the first comprehensive image of the mantle transition zone mtz discontinuities using data from the egyptian national seismic network and compare the resulting depths of the 410 and 660 km discontinuities with those observed on the arabian side our results show that when a standard earth model is used for time to depth conversion the resulting depth of thediscontinuities increases systematicallytowards theaxisoftheafro arabiandome aad from both the west and east relative to the westernmost area the maximum depression of the 410 km discontinuity is about 30km and that of the 660 km discontinuity is about 45km the observed systematic variations can best be explained by a model involving a hydrated mtz and an upper mantle low velocity zone beneath the aad models invoking one or more mantle plumes originated from the mtz or the lower mantle beneath the study area are not consistent with the observations

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

variability of precipitation along cold fronts in idealized baroclinic waves abstractprecipitation patterns along cold fronts can exhibit a variety of morphologies including narrow cold frontal rainbands and core and gap structures a three dimensional primitive equation model is used to investigate alongfront variability of precipitation in an idealized baroclinic wave along the poleward part of the cold front a narrow line of precipitation develops along the equatorward part of the cold front precipitation cores and gaps form the difference between the two evolutions is due to differences in the orientation of vertical shear near the front in the lower troposphere at the poleward end the along frontal shear is dominant and the front is in near thermal wind balance while at the equatorward end the cross frontal shear is almost as large at the poleward end the thermal structure remains erect with the front well defined up to the midtroposphere hence updrafts remain erect and precipitation falls in a continuous line along the front at the equatorward end the cores form

groundwater quality of porous aquifers in greece a synoptic review greece is dependent on groundwater resources for its water supply the main aquifers are within carbonate rocks karstic aquifers and coarse grained neogene and quaternary deposits porous aquifers the use of groundwater resources has become particularly intensive in coastal areas during the last decades with the intense urbanization tourist development and irrigated land expansion sources of groundwater pollution are the seawater intrusion due to over exploitation of coastal aquifers the fertilizers from agricultural activities and the disposal of untreated wastewater in torrents or in old pumping wells in the last decades the total abstractions from coastal aquifers exceed the natural recharge so the aquifer systems are not used safely over exploitation causes a negative water balance triggering seawater intrusion seawater intrusion phenomena are recorded in coastal aquifer systems nitrate pollution is the second major source of groundwater degradation in many areas in greece the high levels of nitrate are probably the result of over fertilization and the lack of sewage systems in some urban areas

two stage rupture of the 1999 mw 6 0 southern lake baikal earthquake summary the 1999 february 25 1858 hr southern lake baikal earthquake is evidently a two stage rupture when compared with its prominent foreshock mb 4 4 at 0537 hr on the same day and a prominent nearby earthquake mb 5 1 on 2000 may 31 the foreshock and 2000 may 31 earthquake have similar waveforms recorded at short period array stations at 21 79 the main shock p wave train including the surface reflections pp and sp appears most similar to that from the 2000 may 31 earthquake after a shift of 8 5 s from the p wave first arrival a model of two stage rupture with a smaller stage followed 8 5 s later by a larger rupture fits many aspects of the seismograms of the main shock whereas the 2000 may 31 seismograms can be fitted with a single source the main shock first stage rupture has moment 17 per cent of that of the second stage rupture their hypocentres are at depth 15 2 km from modelling pp and sp phases using a crustal model of a low wave speed sedimentary basin at the epicentral region the hypocentres of the two stages are the same to within the resolution of the modelling the 2000 may 31 hypocentre is at depth 13 km in the same model model seismograms at stations to the northwest and southeast have different time intervals between initial p and the surface reflections the longer p pp interval for the northwest stations can be explained by a thicker sedimentary basin at pp bounce points northwest of the epicentre the two stage rupture of the main shock could be responsible for the wide range of depths 7 21 km and mb 4 9 6 1 published in the international seismological centre catalogue

hydrochemical and statistical studies of the groundwater salinization in mediterranean arid zones case of the jerba coastal aquifer in southeast tunisia coastal aquifers are considered as major sources for freshwater supply worldwide especially in arid zones the weak rainfall as well as the intensive extraction of groundwater from coastal aquifers reduce freshwater budget and create local water aquifer depression causing both seawater intrusion and a threat to groundwater this phenomenon was observed in the jerba island which is located in southeast tunisia jerba s unconfined aquifer shows high values of groundwater salinity reaching locally 17 g l and a strong contrast between some zones of the aquifer high pumping rates and weak recharge disturb the natural equilibrium between fresh and saline water causing water salinization in most areas of the island this study aims at establishing the salinity map of the aquifer and identifying the origin of groundwater salinization the salinity map shows that zones characterized by low groundwater salinity are located in the center of the study area high groundwater salinities are observed near the coast and in some parts having low topographic and piezometric levels groundwater geochemical characterization and br cl and na cl ratios suggest that the origin of abnormal salinity is seawater intrusion considering groundwater salinity values and br concentrations a seawater intrusion map is established it shows that many areas of the unconfined aquifer are contaminated by mixed groundwater and seawater the statistical analysis demonstrates that high mineralization of the groundwater is due to gypsum and carbonate dissolution coupled with the mixed groundwater and seawater in many areas

density patterns of the upper mantle under asia and the arctic comparison of thermodynamic modelling and geophysical data based on the modified thermodynamic model we calculate the density of olivine pyroxene mixtures at different proportions of molecular masses in minerals at temperatures of 1000 1700 k and pressures up to 17 gpa the calculated density of the olivine pyroxene mixtures is compared with the prem model and the average density patterns of the asian and arctic regions estimated from the data on the rayleigh wave group velocity dispersion in upper mantle conditions taking into account the characteristic temperature profiles of different tectonic units in asia tibetan plateau khangay dome baikal rift and southern siberian platform and the arctic chukotka fold belt barents sea northern greenland and eurasia basin we discuss density patterns and features of the mantle composition underneath structures and to depths of 200 km where the most significant variations in their density patterns are observed the results obtained suggest some insights into the geodynamic evolution of the lithosphere in the study area the calculated density characteristics of the components in the upper mantle and the modelling of their composition are compared with average density patterns under the tectonic units in order to show the possibilities of previously developed equations of state it has been shown that the composition 0 9 mg0 9fe0 1 2sio4 0 1mgsio3 describes the prem model well in addition to the average velocity patterns of the study regions variations in mineralogical compositions are revealed between stable structures and the areas with high levels of tectonic and seismic activity the present paper could be of interest to geophysicists and mineralogists as it researches overlapping topics for both sciences indicating the relationship between seismicity and features of the deep structure of the upper mantle

asymmetric upwarp of the asthenosphere beneath the baikal rift zone siberia in the summer of 1991 we installed 27 seismic stations about lake baikal siberia aimed at obtaining accurately timed digital seismic data to investigate the deep structure and geodynamics of the baikal rift zone and adjacent regions sixty six teleseismic events with high signal to noise ratio were recorded travel time and q analysis of teleseisms characterize an upwarp of the lithosphere asthenosphere boundary under baikal theoretical arrival times were calculated by using the international association of seismology and physics of the earth s interior 1991 earth model and travel time residuals were found by subtracting computed arrival times from observed ones a three dimensional downward projection inversion method is used to invert the p wave velocity structure with constraints from deep seismic sounding data our results suggest that 1 the lithosphere asthenosphere transition upwarps beneath the rift zone 2 the upwarp has an asymmetric shape 3 the velocity contrast is 4 9 in the asthenosphere 4 the density contrast is 0 6 and 5 the p wave attenuation contrast t is 0 1 s

mantle transition zone discontinuities beneath the baikal rift and adjacent areas like most other major continental rifts the baikal rift zone brz in siberia ispresumably underlain by a hot and partially molten mantle which has a reduced seismicvelocity relative to surrounding areas recent seismic tomography studies however gaveconflicting results about the depth extent and even the existence of the low velocityanomaly beneath the brz suggesting that additional constraints are needed here wepresent results from stacking of about 1700 radial p to s receiver functions from asingle long running seismic station tly located at the sw tip of lake baikal a clearuplift of the 410 km discontinuity d410 with a magnitude of about 47 km relative tothe south margin of the siberian platform is observed beneath the rift currently availableseismic results suggest that the uplift is unlikely to be caused by addition of water tomantle transition zone mtz silicates but is the result of a 550 c reduction in temperaturein the vicinity of the d410 in addition the 660 km discontinuity d660 shows adownward trend toward the rift from the south suggesting that the entire mtz might havea low temperature beneath the rift the thickening of the mtz suggests a high velocityanomaly of about 2 in the mtz and rules out the possibility that the rifting is caused bya mantle plume originated in or beneath the mantle transition zone

east asia seismotectonics magmatism and mantle dynamics abstract in this article we review the significant recent results of geophysical studies and discuss their implications on seismotectonics magmatism and mantle dynamics in east asia high resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes which may reflect magma and fluids that affected the rupture nucleation of large earthquakes in subduction zone regions the crustal fluids originate from the dehydration of the subducting slab magmatism in arc and back arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab the intraplate magmatism has different origins the continental volcanoes in northeast asia such as changbai and wudalianchi seem to be caused by the corner flow in the big mantle wedge bmw above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well the tengchong volcano in southwest china is possibly caused by a similar process in bmw above the subducting burma microplate or indian plate the hainan volcano in southernmost china seems to be a hotspot fed by a lower mantle plume associated with the pacific and philippine sea slabs deep subduction in the east and the indian slab s deep subduction in the west down to the lower mantle the occurrence of deep earthquakes under the japan sea and the east asia margin may be related to a metastable olivine wedge in the subducting pacific slab the stagnant slab finally collapses down to the bottom of the mantle which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and cause the slab plume interactions some of these issues such as the origin of intraplate magmatism are still controversial and so further detailed studies are needed from now

evolution of groundwater salinity in the unconfined aquifer of bou areg northeastern mediterranean coast morocco the bou areg plain in the mediterranean coast at the north eastern of morocco is characterized by a semi arid climate the aquifer consists of two sedimentary formations of plio quaternary age the upper formation of fine silts and the lower one of coarse silts with sand and gravels the aquifer is underlain by marly bedrock of miocene age that dips toward the coastal lagoon of bou areg the hydrodynamic characteristics vary between 10 4 and 10 3 m s and transmissivities range between 10 4 and 10 1 m2 s the general direction of flow is sw to ne toward the lagoon the aquifer is crossed by the river selouane which also ends in the lagoon the groundwater is characterized by a high salinity that can reach 7 5 g l the highest values are observed in the upstream and in the downstream sectors of the aquifer the temporal evolution of the physico chemical parameters depends on the climatic conditions and piezometric variations the analysis of the spatio temporal distribution of the physico chemical parameters suggests different sources of groundwater salinization the seawater intrusion the influence of marly gypsum bearing terrains and the influence of anthropogenic products as the agricultural fertilizers which cause great nitrate concentrations that vary between 80 and 140 mg l

terrestrial heat flow in the south of east siberia abstract we summarize the results of heat flow studies in the paleozoic southern parts of the siberian platform mesozoic zabaikalye and cenozoic baikal rift activity areas it is established that regional heat flow values are greatly influenced by the latest tectonic activity rather than by the age of crust formation

late permian early triassic igneous activity in the attic cycladic belt attica new geochronological data and geodynamic implications article i nfo article history igneous rocks of the attic cycladic belt acb formed prior to the alpine orogeny have received relatively little attention especially regarding their crystallisation age new u pb shrimp zircon data from mylonitised metagranitoid rocks within metapelites and metabasites of the pentelikon mountain lower tectonic unit ltu of attica in combination with internal zircon characteristics reveal the following the metagranitoid precursor was very likely an i type pluton crystallising in two successive stages at 255 3 ma and 246 2 ma weighted mean 206 pb 238 u ages error at 95 c l these age results are respectively marginally older than and within un certainty of the 240 4 ma protolith age reported for metagranitoids of the same unit in the area of lavrion at tica they are in line with the protolith ages of several meta igneous rocks within the cycladic blueschist unit of aegean islands one core zircon domain and one single zircon grain yielded

seismic anisotropy and mantle flow beneath the baikal rift zone seismic studies have shown that continental rifts such as lake baikal and the great rift valley of east africa are like mid ocean rifts in that they lie above broad regions of asthenospheric upvvarp of much greater extent than the surface expression of rifting1 4 the direction of mantle flow in such regions can be investigated using the seismic anisotropy created by flow induced orientation of mantle olivine crystals5 8 seismic studies of the mid atlantic ridge have revealed upwelling mantle flow beneath the ridge and flow normal to the ridge axis on either side8 10 here we present results from an array of seismic stations across the baikal rift zone in southern siberia the splitting in arrival times of sks seismic waves indicates that the upper mantle beneath the rift zone is anisotropic with the fast direction which reflects the direction of mantle flow being horizontal and normal to the rift axis this suggests that the broad upwarp associated with this continental rift is caused by similar mantle flow to that at mid ocean rifts this may help to elucidate the processes involved in continental rifting

on the mesoscale structure of surface wind and pressure fields near tornadic and nontornadic cold fronts abstractobservations from a mesoscale network of automatic weather stations are analyzed for 15 u k cold fronts exhibiting narrow cold frontal rainbands ncfrs seven of the ncfrs produced tornadoes a time compositing approach is applied to the minute resolution data using the radar observed motion vectors of ncfr precipitation segments interpolated onto a 5 km grid the analyses resolve much of the small mesoscale structure in surface wind temperature and pressure fields postfrontal winds varied substantially between cases tornadic ncfrs exhibited a near 90 wind veer and little or no reduction in wind speed on ncfr passage these attributes were generally associated with large vertical vorticity horizontal convergence and vorticity stretching at the ncfr nontornadic ncfrs exhibited smaller wind veers and or marked decreases in wind speed across the ncfr and weaker vorticity convergence and vorticity stretching in at least four tornadic ncfrs increases in vorticity stretching preceded tor

characterization of a continuous very narrowband seismic signal near 2 08 hz we have detected a continuous seismic signal near 2 08 hz using data from a portable seismic array 1280 km long deployed in siberia and mongolia the signal can be observed on almost all the stations along the profile the amplitude and the frequency of the signal show a clear daily cycle and their temporal variations are similar at different stations suggesting that the signals observed at different stations have a common source we performed a nonlinear inversion of the amplitude of the signal and found that the geometrical spreading factor is about 0 6 implying that the signal is most likely to be a form of surface waves the source location found by the inversion is in the vicinity of the city of irkutsk which is about 50 km north of lake baikal

sks splitting beneath continental rift zones we present measurements of sks splitting at 28 digital seismic stations and 35 analog stations in the baikal rift zone siberia and adjacent areas and at 17 stations in the east african rift in kenya and compare them with previous measurements from the rio grande rift of north america fast directions in the inner region of the baikal rift zone are distributed in two orthogonal directions ne and nw approximately parallel and perpendicular to the ne strike of the rift in the adjacent siberian platform and northern mongolian fold belt only the rift orthogonal fast direction is observed in southcentral mongolia the dominant fast direction changes to rift parallel again although a small number of measurements are still rift orthogonal for the axial zones of the east african and rio grande rifts fast directions are oriented on average nne that is rotated clockwise from the n s trending rift all three rifts are underlain by low velocity upper mantle as determined from teleseismic tomography rift related mantle flow provides a plausible interpretation for the rift orthogonal fast directions the rift parallel fast directions near the rift axes can be interpreted by oriented magmatic cracks in the mantle or small scale mantle convection with rift parallel flow the agreement between stress estimates and corresponding crack orientations lends some weight to the suggestion that the rift parallel fast directions are caused by oriented magmatic cracks

variation of frontal and precipitation structure along a cold front a diagnostic study is presented to illustrate the sequence of events in which a warm conveyor belt wcb flow is drawn into the circulation of a developing extratropical cyclone and interacts with dry air aloft to produce distinctive precipitation structures the poleward boundary of the upstream end of the wcb was associated with a classical ana cold frontal structure the other end of the wcb flow closer to the cyclone centre was overrun by a dry intrusion of low wet bulb potential temperature air to give a split kata cold front the orientation of the surface cold front i e the wcb boundary changed significantly between these two parts but the orientation of the surface geostrophic flow within the wcb changed relatively little between the two parts the surface cold front was characterized in most places by a narrow cold frontal rainband composed of shallow line convection elements precipitation cores aligned nearly parallel to the surface geostrophic flow in the wcb the changing relationship between the frontal orientation and the direction of the surface flow accounts for the fact that the line convection elements occurred end to end to give almost two dimensional line convection along the classical ana part of the cold front but were non aligned and widely spaced along the split cold front part

hydrodynamic analysis of a mediterranean aquifer system with the use of hydrochemical and isotopical analysis as supporting tools the management of groundwater resources in coastal environments within the mediterranean basin has become of paramount importance especially in the light of global changes a typical example of such a hydrosystem is the lavrio basin in greece this research site involves two aquifer types granular and karstic formations that are hydraulically interconnected furthermore the proximity to the sea and the abstractions for irrigation and drinking water supply have led to the phenomenon of seawater intrusion the present study aims at analyzing the hydraulic hydrological and hydrogeological conditions of the area by means of hydrochemical and isotopical data interpretation as supporting tools which will inform and support the development of an integrated conceptual hydrogeological model of the area field investigations were conducted in order to collect piezometric and chemical data and use them to retrieve the quantitative and qualitative status of the local aquifer units new interpretation of an older dataset gave an insight into how the karstic aquifer behaves in terms of hydraulics the results have also demonstrated that there is a hydraulic connection between the different aquifers and the mediterranean sea while natural recharge was quantified for both aquifer types

organization and structure of clouds and precipitation on the mid atlantic coast of the united states part vi the synoptic evolution of a deep tropospheric frontal circulation and attendant cyclogenesis abstract interactions between an upper level frontal system and an initially weak surface cold front resulted in the production of a deep precipitating frontal structure over the south atlantic states on 26 27 january 1986 attendant with the intensification of the frontal circulation was the development of an intense marine cyclone off the delmarva peninsula the increase in frontal circulation strength is attributed to a favorable vertical superposition of the surface frontal trough and the upper level frontogenetic horizontal deformation field that resulted in a deep column of divergence over the surface frontal trough the surface cyclone developed partly and indirectly in response to the increase in warm air advection in the lower stratosphere which was directly related to an increase in the slope of the dynamic tropopause the increase in the slope of the tropopause is hypothesized to have been the result of the combined effect of adiabatic advection of low tropopause height in the cold air of t

olivine hydration in the deep upper mantle effects of temperature and silica activity 1 although water controls the biology and geology of the surface hydrogen is perhaps the most poorly constrained compositional variable in the bulk earth its concentration in the upper mantle appears to be controlled by its solubility as hydroxyl in the nominally anhydrous silicate phases olivine pyroxene garnet wadsleyite and ringwoodite here we describe a series of experiments showing that the solubility of h2o in olivine at 12 gpa increases with temperature to 8900 ppm by weight at 1250 c and decreases at higher temperature with the onset of melting sample characterization by infrared spectroscopy indicates that the primary hydration mechanism is the substitution of 2h for mg2 similar results obtained from samples coexisting with clinohumite low silica and with clinoenstatite high silica indicate that silica activity has minimal effect on hydration under these conditions single crystal x ray diffraction measurements constrain the volume of hydration and indicate significant m site vacancies hydrogen thus appears to become a geochemically compatible element as depths approach 400 km

analysis of potential field anomalies in lavrion mining area greece mining activities in lavrion began during the first millennium b c after the decline of ancient athens and then restarted more deliberately during the nineteenth century aeromagnetic data from a 1967 survey of the mining area was recompiled processed and interpreted for the present study the original flight lines were digitized and leveled and the international geomagnetic reference field igrf was removed the data were inverted by means of a terracing technique that defines separate domains of uniform distribution of physical properties that cause the magnetic anomalies the log power spectrum was computed along with the results of terracing it suggested the existence of two sources of the magnetic anomaly the long wavelength anomaly reflects a large concealed body that is most probably a granitic intrusion consistent with local geological evidence the source of the short wavelength anomaly is a strongly magnetized body attributed to the net effect of various thin magnetite bearing sulfide zones the anomalies were then separated in the wavenumber domain magnetic susceptibility measurements were made in situ on the exposed parts of the local formations three dimensional models whose effect simulates the observed anomalies were calculated results of the modeling show that the large magnetic body is buried at 0 68 km depth the small relatively shallow body is about 0 035 km thick and buried at 0 6 km depth the bodies do not show any corresponding gravity anomaly on the regional bouguer gravity anomaly map

significant crustal thinning beneath the baikal rift zone new constraints from receiver function analysis 1 thinning of the crust of more than 10 km is a major feature of typical continental rifts such as the east african ear and rio grande rgr rifts however numerous previous studies across the baikal rift zone brz which has similar surface expressions and tectonic history and more active seismicity relative to ear and rgr have resulted in contradicting amount of thinning ranging from almost none to more than 10 km we measure crustal thickness by stacking teleseismic receiver functions beneath 51 sites on the southern and central parts of the brz and adjacent siberian platform and sayan baikal mongolian foldbelt our measurements reveal that beneath the southern part of the platform the average crustal thickness is about 38 km which is about 7 km thinner than that beneath the foldbelt and the un rifted part of the brz the thinnest crust 35 km is found beneath the central part of the rift and represents a significant thinning of about 10 km relative to the un rifted parts of the brz index terms 7200 seismology 7203 seismology body wave propagation 7205 seismology continental crust 1242 citation gao s s k h liu and c chen 2004 significant crustal thinning beneath the baikal rift zone new constraints from receiver function analysis geophys res lett 31 l20610 doi 10 1029 2004gl020813

geochemical evolution and timescale of seawater intrusion into the coastal aquifer of israel this study is an attempt to quantify the geochemical processes and the timescale of seawater intrusion into a coastal aquifer from changes in the major ionic composition of the water and the natural distribution of the cosmogenic isotopes 14c and 3h for that purpose we sampled saline and brackish groundwaters from the israeli coastal aquifer a multilayer sampler mls was used to obtain very high resolution 10 cm profiles across the fresh saline water interface fsi the chemical and stable isotope data revealed three distinct water types end members that are located in different zones on the route to the coastal aquifer 1 slightly modified mediterranean seawater sws 2 slightly diluted with up to 20 fresh groundwater saline groundwater sds and 3 fresh groundwater fgw the sws samples generally show an excess of total alkalinity and total dissolved inorganic carbon dic and a depletion of 13cdic and 14cdic with respect to normal seawater indicating that anaerobic oxidation of organic matter is the first diagenetic reaction that affects seawater during its penetration into the bottom sediments sds waters appear when sws is slightly diluted gain ca2 and sr2 and is depleted in k suggesting that the main processes that transform sws into sds are slight dilution with fresh groundwater and cation exchange at the fresh saline water interface sds generally shows conservative mixing with fgw inspection of chemical data from coastal aquifers around the world indicates that intensive ion exchange in slightly diluted saline groundwater is a globally important phenomenon of seawater intrusion most of our saline groundwater samples contain substantial amounts of 3h suggesting that penetration of mediterranean seawater and its inland travel to a distance of 50 100 m onshore occurred 15 30 yr ago this is supported by the 14cdic mass balance that explains the relatively low 14cdic activities in the sds as influenced by diagenesis and not by simple radioactive decay

baikal rift zone structure and geodynamics abstract the cenozoic baikal rift zone is superimposed on the caledonian baikal fold belt representing the suture between the precambrian siberian craton and several microcontinents the baikal rift zone consists of a system of disconnected fault bounded basins and extensional and wrench faults that straddles a major arch having a topographic relief of 2 3 km rifting activity commenced during the oligocene and is still active as evident from high seismicity of the baikal rift zone across the baikal rift zone upper crustal extension is considerably smaller than would be expected from its crustal thickness which decreases by 8 11 km across the baikal basins as compared to the adjacent unextended areas the discrepancy between upper and lower crustal attenuation could be attributed to intrusion of a major diapir indeed geophysical data indicate that the sayan baikal dome coincides with such a diapir the top of which is located at the crust mantle boundary this intrusion is held responsible for oligocene and quaternary doming of the rift zone development of the intra continental baikal rift system is thought to be related to asthenospheric diapirism active rifting however intra plate stresses in conjunction with the himalayan collision may have played some role

seismic signatures of an altered crust and a normal transition zone structure beneath the godavari rift abstract the godavari rift valley in the south indian shield located over a paleosuture between the dharwar and singhbhum cratons is a very less studied region in terms of its deep seismic structure in the present study a total of 1559 receiver functions from 777 earthquakes registered by a 10 station network are utilized to investigate crust and mantle structure broadly the crustal architecture underneath the rift appears very complex with the presence of intracrustal layers and a weak moho compared to a sharp moho and a simple crust outside it detailed modelling of receiver functions at 6 stations using the nearest neighbourhood algorithm approach reveals a 40 km thick crust within the rift compared to a 33 km thick crust in the adjacent dharwar craton also the lower crustal character is found to be distinctly different with a faster lower crust beneath the rift a weak moho beneath the rift may be due to magmatic underplating the transition zone 660 410 km structure inferred from the common conversion point stacks of receiver functions can be interpreted in terms of the absence of a thermal anomalies within and above the mantle transition zone mtz b thin lithosphere or high temperatures in the uppermost mantle magmatic underplating within the crust and a normal mtz argue in favour of a rift formed due to lithospheric stretching without the influence of a mantle plume

the vertical structure of new england coastal fronts abstract aircraft data from the new england winter storms experiment newsex are used to examine the vertical structure of four new england coastal fronts the aircraft made multiple passes at varying elevations through the coastal fronts the observations were projected onto cross sections normal to the coastal fronts using frontal orientations determined from surface analyses and frontal velocities determined from a least squares fit to multiple frontal penetrations the frontal zones were found to be roughly 200 m wide rising sharply from the ground to a height of 150 m to 400 m over distances of 0 5 to 2 5 km before leveling off and rising gradually toward the mountains the underlying pools of cold air were similar in form and flow patterns to cold air damming structures observed elsewhere along the east coast the coastal fronts formed the leading edges of the cold pools air on the warm side of the fronts was neutrally stratified having been recently heated by the warm gulf of maine this warm a

seismic signatures of detached lithospheric fragments in the mantle beneath eastern himalaya and southern tibet abstract in this study we investigate the mantle transition zone mtz structure beneath eastern himalaya and southern tibet using 9000 high quality receiver functions from 96 broadband stations spanning the entire region the pervasive early arrival times 1 7 s compared to iasp91 of the p to s conversions from the 410 km discontinuity are attributed to the high shear wave velocities associated with the subducted indian and asian lithosphere s global and regional shear wave velocity models obtained from seismic tomography evince such high velocity anomalies both in the uppermost mantle and within the mtz in this complex collision environment in contrast the conversions from the 660 km discontinuity are either normal or delayed up to 1 s providing evidences for a thickened mtz beneath most of the study region although presence of water in the mtz can result in such a thickening issues like 1 low amplitudes of the p410s and p660s conversions 2 small dependence of their amplitudes with frequency 3 absence of a detectable low velocity layer atop 410 and 4 lack of evidence for a 520 km discontinuity preclude such an interpretation instead we attribute this thickening to lowered temperatures affected by the possible presence of detached cold and dense lithospheric slabs within the mtz such a detachment might have been facilitated either by convection or gravity removal of the lithosphere thickened due to continued subduction of the indian plate since the mesozoic

comprehensive crustal structure and seismological evidence for lower crustal flow in the southeastern margin of tibet revealed by receiver functions abstract the lower crustal flow model has become an interesting proposal to describe the growth and expansion of eastern tibet to date however the geophysical results are not definitive due to the non uniqueness of the solutions found through data inversion and the resolution limitations in this study the polarity of p to s converted phases at intra crustal interfaces are analyzed in order to reveal evidence for low seismic velocity and lower crustal flow in southeastern tibet we are interested in a joint study that is both a mapping of the crustal structure moho topography and poisson s ratio and an attempt to constrain an iclvz we have determined the crustal thickness and poisson s ratio from p prfs and s srfs receiver functions acquired in 108 permanent seismic stations deployed in the sichuan and yunnan areas also we have obtained 98 measurements of pms phase splitting parameters at the array stations the crustal thickness provided by prfs is consistent with that given by srfs it varies from 60 km in the songpan ganzi sg fold system and the northern part of the sichuan yunnan diamond shaped block sydsb near the eastern himalayan syntaxis to 33 km in southern yunnan the poisson s ratio varies mostly from 0 24 to 0 32 the highest values 0 28 0 32 are found along the axis formed by the longmenshan fault the lijiang jinhe fault and in the tengchong volcano area the value of 0 28 observed in sydsb and the sg fold system is attributed to the presence of a low velocity zone in the lower crust and partly to the great sediment thickness in sichuan basin the crust is clearly anisotropic in the southeastern margin of tibet the fast wave polarization direction exhibits a nw se regional bias while the time delay varies between 0 07 s and 1 27 s being the average 0 54 s 0 12 s implying the existence a strong shear zone in the lower crust based on the negative polarity observed after the direct p wave in teleseismic receiver functions we have detected an intra crustal low velocity zone iclvz in a wide region including east and southeast of tibet and southern yunnan so both the shear zone and iclvz suggest the existence of lower crustal flow the reverberation ppps and psps ppss phases at the moho are clearly weaker in sydsb and the sg fold system than in the indochina block and eastern yunnan implying that sydsb has a structure and tectonic history different from indochina on its west side and eastern yunnan on its east side the above results provide seismological evidence for a lower crustal flow spreading from the eastern tibet and that in its advance southward has invaded sydsb widely crossed the lijiang jinhe fault and reached southern yunnan

thickness of the lithosphere beneath the baikal rift zone and adjacent regions abstract methods of separation of gravity anomalies related to mantle density inhomogeneity are developed based on the inversion of these anomalies with regard to some constraints obtained from seismic data the map of lithospheric thickness beneath the baikal rift zone and adjacent regions was made the lithospheric thickness beneath the baikal rift zone is estimated to be 40 50 km i e the lithosphere is thinned here to a crustal thickness beneath the siberian platform the lithospheric thickness increases to 200 km and underneath the trans baikal region of moderate cenozoic tectonic activity it ranges from 75 to 160 175 km therefore a wide asthenospheric upwelling was revealed beneath the rift zone the data available on the configuration of the baikal depression and that of the crust and the lithosphere as a whole made it possible to estimate the magnitudes of extension at different lithospheric levels the significant increase in extension with depth implies that rifting in the baikal zone was caused by asthenospheric diapirism

seismic anisotropy and mantle flow seismic anisotropy in the mantle is primarily due to deformation induced lattice preferred orientation lpo of olivine crystals the aim of this paper is to better understand how such lpo is produced by flow and to learn whether observations of seismic anisotropy can be used to infer the local direction of flow within the mantle the basis of the work is a two dimensional theory which describes how lpo evolves during an arbitrary time dependent deformation ribe 1989 i investigate the evolution of lpo beneath ocean ridges above subducted slabs and in thermal convective flows the ocean ridge model predicts that the seismic anisotropy produced at a fast spreading ridge should be greater in magnitude than that produced at a slow spreading ridge and that the fast axis should be more nearly horizontal the subduction zone model predicts that strong seismic anisotropy should be produced above subducted slabs with the fast axis aligned with the slab regardless of the subduction angle the evolution of lpo in typical convective flows is extremely complex and depends strongly on such factors as the mode of heating and the surface boundary conditions in general there is no simple relation between the lpo and the local flow direction in any of the models considered the attempt to use seismic anisotropy to map flow patterns on a global scale is therefore probably unwarranted however the lpo does become aligned with the flow direction when the flow is a progressive simple shear such a flow occurs in limited portions of the mantle beneath the lithosphere at a fast spreading ridge above subducted slabs and in boundary layers beneath rigid surfaces such as continents observations of seismic anisotropy may therefore indicate the sense of shear at shallow depths in the mantle

offshore continuation of coastal groundwater systems predictions using sharp interface approximations and variable density flow modelling analytical sharp interface solutions and numerical variable density flow and transport modelling are used to study how far into the offshore the influence of meteoric continental groundwater systems extends under steady state flow and transport conditions results show that factors which favour the development of an extensive fresh water wedge in the offshore are 1 a high head or fresh water discharge at the coastline 2 a thick semi confined high permeability submarine aquifer 3 optimum but not necessarily maximum and minimum values for the thickness and permeability of the confining layer near the seafloor respectively sharp interface models tend to overpredict the seaward extent of fresh water considerably because in distal parts upward seepage rates through the overlying confining layer are too small to prevent salinisation by diffusion from the overlying sea and ensuing convective mixing by density differences within underlying aquifers the overprediction is particularly large for relatively low heads at the coastline and low permeabilities of the confining layer under favourable conditions fresh water connected to continental flow systems is predicted to occur up to several tens of kilometers offshore comparison of model predictions with observational data demonstrates that relatively fresh submarine pore waters off the coasts of new jersey us and suriname south america occur too far offshore to be explained by active flow systems indicating that they are paleo waters which formed during the pleistocene when sea levels were lower than at present

assessment of the impact of anthropogenic activities on the groundwater hydrology and chemistry in tarsus coastal plain mersin se turkey using fuzzy clustering multivariate statistics and gis techniques summary tarsus coastal plain tcp is an economically and ecologically important area situated in between the fertile fluvio deltaic plains of two rivers delicay and tarsus mersin se turkey where anthropogenic activities agricultural industrial and domestic are very intense twenty four water quality parameters were surveyed at 193 groundwater and 10 surface water sites during august 2008 the objective was to characterize the physico chemical properties of groundwaters in tcp assess the impact of anthropogenic activities on the groundwater hydrology and chemistry and identify the major hydrogeochemical processes occurring in the area groundwater samples were grouped into hydrochemically distinct and spatially continuous four water classes i e c1 c2 c3 and c4 using the fuzzy c means fcm clustering method where membership values were interpolated using the ordinary kriging technique principal components analysis pca was used to decipher various underlying natural and anthropogenic processes creating these distinct water classes four principal components pcs were extracted in pca which explained more than 73 of the total variance in water quality major factors responsible for the variations in chemistries of water classes are identified as 1 water rock interaction and nitrate contamination 2 salinization by seawater intrusion and evaporite dissolution 3 geogenic anthropogenic cr fe and mn and 4 anthropogenic zn pollution overexploitation of the aquifer is clearly evident especially at settlements located near the coastal zone where the water table is lowered 2 5 m below the sea level salinization is well known in the area and is attributed not only to seawater intrusion but also to dissolution of evaporitic series from the handere formation hydrochemical evidence also suggest that in the area subsurface paleo river channels and the deposits infilling the ancient lagoon area within quaternary recent alluvial deposits act as significant hydrological features where preferential groundwater flow occurs along them

crustal deformation in the baikal rift from gps measurements three years and four campaigns of global positioning system gps measurements 1994 1997 in the baikal rift zone largest active continental rift system in eurasia show crustal extension at a rate of 4 5 1 2 mm yr in a wnw ese direction a comparison with moment release of large historical earthquakes suggests that elastic strain is currently accumulating in the baikal rift zone along active faults that currently have the potential for a m 7 5 earthquake the gps derived extension rate in the baikal rift zone is at least two times greater than the prediction of most deformation models of asia this result could reflect the dynamic contribution of the pacific eurasia subduction to intracontinental deformation in asia in addition to the effect of the india eurasia collision

seismic evidence for water deep in earth s upper mantle water in the deep upper mantle can influence the properties of seismic discontinuities in the mantle transition zone observations of converted seismic waves provide evidence of a 20 to 35 kilometer thick discontinuity near a depth of 410 kilometers most likely explained by as much as 700 parts per million of water by weight

footwall mineralization during late miocene extension along the west cycladic detachment system lavrion greece the west cycladic detachment system wcds has been mapped from the western cycladic islands to lavrion mainland greece where several top to ssw low angle normal faults at different structural levels are observed near the detachment horizon hydrothermal fluid flow originating from miocene intrusions lead to high temperature carbonate strata bound pb ag zn ore deposits zircon u th he cooling ages from the mineralized footwall are 7 1 0 6 to 7 9 0 6 ma carbon and o isotope analyses of the carbonate host indicate high water to rock ratios during brittle deformation induced metasomatism and that this interaction unrelated to proximity of the intrusions plays the dominant role in the mineralization the late miocene geology of lavrion is strikingly similar to serifos island on the se termination of the wcds both characterized by strong localization of detachment faulting and the interaction of brittle deformation with the injection of fluids related to granitoid intrusions

surface microphysical observations within east coast winter storms on long island new york abstractsurface observations of ice habit and degree of riming were measured for 12 cyclone events over 3 winter seasons at stony brook new york on the northeast coast of the united states a total of 205 6 cm of snow accumulated during these storms with an average degree of riming of 1 25 out of 5 and snow to liquid ratio ranging from 3 1 to 17 1 there were consistent spatial patterns of habit and riming intensity relative to the cyclone structure cold type habits side planes and bullets commonly occurred within the outer comma head to the north and northeast of the cyclone center in the middle of the comma head moderately rimed dendrites plates and needles were observed close to the cyclone center heavy riming was observed with needles and graupel the western quadrant of the comma head had primarily plates and dendrites with little to no riming periods of light riming and high snow liquid ratios 13 1 are dominated by cold type habits dendrites and plates and have similar vertical m

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones part v the substructure of narrow cold frontal rainbands abstract the organization and structure of a narrow cold frontal rainband ncfr on the small mesoscale and the microscale have been investigated through quantitative radar reflectivity doppler radar observations airborne observations and surface measurements the ncfr was composed of small mesoscale regions of heavy precipitation called precipitation cores pcs oriented at an angle to the synoptic scale cold front in horizontal cross section the pcs were roughly elliptical in shape areas of lighter precipitation called gap regions grs separated the pcs the pcs were so oriented that their loading edges were regions of strong low level convergence the weather associated with the passage of a pc resembled that of a squall line gust front with concurrent windshifts and pressure checks occurring 5 min before heavy precipitation and a fall in temperature the changes in surface weather that accompanied the passage of a gr were more variable but tended to be less marked than for pcs thus the se

groundwater resource degradation in coastal plains the example of the cecina area tuscany central italy abstract the paper describes the degradation of the groundwater resources in the cecina area where seawater intrusion b contamination and no 3 pollution are all affecting the heavily exploited pleistocene aquifer over pumping has brought water levels to about 0 m a s l as far as about 7 km from the shore line thereby promoting the seawater intrusion the intrusion which is characterized by cation exchange phenomena and ca cl type waters enters the plain mostly through the shallower horizons the saline front which advanced from 0 5 to 1 km in 4 a has by now reached the foot of the hills to the east of the town where it is also affecting wells of the local aqueduct boron contamination linked to past discharge of industrial waste transported downstream by the river reached concentrations as high as 3 5 mg l in the mid 1980s although a decreasing trend is now under way b content is still close to 1 mg l the presence of high no 3 which together with the seawater intrusion represents a major issue for groundwater management in the area is linked to the widespread utilization of fertilizers nitrate concentration which reaches a maximum of about 300 mg l in the shallow aquifer horizons and then decreases rather regularly with depth is strongly influenced by precipitation however irrigation also contributes significantly to transporting the no 3 contamination to depth as clearly shown by 18 o data the severe decline in the quality of the groundwater resource in the cecina area is further compounded by an overall decrease in water availability in the region of tuscany as evidenced by long term monitoring of precipitation and fluvial discharge

the organization of convection in narrow cold frontal rainbands abstract narrow cold frontal rainbands are lines of intense precipitation that straddle surface cold fronts recent observational work has revealed that the rainfall within the band is organized into regularly spaced ellipsoidal cells called precipitation cores the rainband is coincident with a line of intense cyclonic shear associated with a low level jet that lies ahead of and parallel to the surface cold front numerous authors have suggested that the organization of cells in the rainband is the result of shear instability of the horizontal wind field to investigate this hypothesis a linear stability analysis was performed on an idealized frontal zone consisting of a line of convection coincident with a line of cyclonic shear to model the convective processes the air inside the rainband was assumed to be unstably stratified the presence of horizontal wind shear in an unstably stratified environment resulted in the existence of a mode with a short wave cutoff the coupling between the convective p

processes reshaping the nile delta promontories of egypt pre and post protection abstract shoreline positions established from beach profile surveys combined with wave data are jointly analyzed as a function of their contribution to coastal processes to investigate the interaction between waves shoreline orientation and coastal structures along the nile delta promontories rosetta burullus and damietta repeated beach profile surveys along the promontory sectors 64 km long in total have been analyzed to determine rates of shoreline changes prior to construction 1971 1990 and after construction of protective structures 1990 2000 the behavior of coastline pre and post construction indicates that coastal erosion fronting protective structures has declined in the case of the seawalls at the tips of the rosetta and damietta promontories or has been partially replaced by sand accumulation in the case of detached breakwaters at baltim east of burullus promontory and at ras el bar west of the damietta promontory as a consequence downdrift erosion has been initiated in local areas adjacent to these structures in the direction of longshore sediment transport the 5 km long seawall protecting the rosetta promontory has stopped the dramatic erosion of this highly eroded area formerly shoreward retreated 88 m year with adverse local erosion at its west and east ends being 3 and 13 m year respectively similarly the 6 km long seawall built on the eastern tip of the damietta promontory still under construction has nearly stopped the severe erosion which was formerly 10 m year the detached breakwaters at both baltim and at ras el bar have accumulated sand at accretion rates of 37 and 14 m year respectively this sand accumulation is associated with downdrift erosion of 25 and 13 m year at baltim and ras el bar respectively results reaffirm that the original erosion accretion patterns along the nile delta promontories have been reshaped due to the massive protective structures built during the last decade this reshaping along the examined promontories is generally controlled by the temporal variability in the intensity and reversibility of wave directions and associated longshore currents coastline orientation and by the existing coastal protection structures

upper mantle p velocity structure beneath the baikal rift from modeling regional seismic data 1 uppermost mantle p wave velocity structure beneath the baikal rift and southern margin of the siberian platform has been investigated by using a grid search method to model pnl waveforms from two moderate earthquakes recorded by station tly at the southwestern end of lake baikal the results yielded a limited number of successful models which indicate the presence of upper mantle p wave velocities beneath the rift axis and the margin of the platform that are 2 5 lower than expected the magnitude of the velocity anomalies and their location support the presence of a thermal anomaly that extends laterally beyond the rift proper possibly created by small scale convection or a plume like thermal upwelling

convection waves observations of gravity wave systems over convectively active boundary layers widespread gravity wave systems have been found to exist over convectively active boundary layers cbls in the presence of vertical wind shear in contrast to mountain waves these convection waves occur over flat terrain and are ubiquitous over fields of shallow fair weather cumuli or clear air thermals they extend vertically to at least 9km a m s l probably to the tropopause first discovered by glider pilots as thermal waves they have now been systematically investigated by research aircraft during the ncar convection wave project which also incorporates an effort in numerical simulation the flight results are reported in this paper while the numerical simulations are described in a companion paper typical wavelengths of convection waves were found to range from 5 to 15 km average 9 km and typical vertical motion amplitudes from 1 to 3 m s 1 in all cases vertical wind shear exceeded 3 10 3s 1 under these conditions cloud tops were measured to move with relative velocities of 8 to 10 m s 1 against their environment hence they present an obstacle to the surrounding airflow the analogy to mountainous obstacles launching gravity waves into the atmosphere is suggestive and borne out by the aforementioned numerical simulations which describe this process step by step the interaction between the cbl and the overlying stable layers is studied by spectral and cross spectral analysis of aircraft data including coherence and phase relations between wave motions and cloud population underneath consideration is given to other potential sources of the observed gravity waves at this stage the conclusions of our pilot study may be considered tentative some implications for further research are also discussed

hydrogeology and geochemistry of the multilayered confined aquifer of the pisa plain tuscany central italy the pisa plain contains a multilayered confined aquifer made up of pleistocene sands and gravels the groundwater from the wells tapping these horizons are generally of poor quality they exhibit significant tds relatively high cl content and considerable hardness during geothermal prospecting of the pisa plain about 80 wells ranging in depth from 20 to 250 m were sampled and both chemical major ions and isotope analyses were conducted the data collected show that tds is strongly influenced by hco3 and cl and that a 3 component mixing process affects the groundwater s chemical composition the end members of this mixing process have been identified as a diluted hco3 meteoric water which enters the plain mainly from the eastern and northern sides of the study area b cl rich water which largely characterizes the shallow sandy horizons of the multilayered aquifer system and has been attributed to the presence of seawater as also suggested by 18o data and c so4 rich groundwater which is linked to the hot groundwater circulation within mesozoic carbonate formations and at first sight seemed to affect only the gravelly aquifer a so4 rich water also contributes to the sandy aquifer it probably enters the plain both laterally from the margins of the pisan mountains and from depth but promptly undergoes substantial so4 reduction processes by bacteria that such processes are at work is suggested both by the low so4 and high hco3 concentrations found in the well waters and by their c and s isotope compositions the collected data have allowed zones with higher quality waters to be identified which may someday be used for the local water supply

mantle layering across central south america 1 imaging of seismic velocity discontinuities along a 3000 km profile across central south america at 20 s suggests that the depth variations of the 410 km d410 and 660 km d660 discontinuities are closely associated with the high velocity nazca slab and juxtaposed low velocity oceanic mantle beneath the slab the mantle transition zone thickness ranges from 220 km in the oceanic mantle to 270 km in a 600 km wide area occupied by the deflected nazca slab the slab deflection has also been suggested by previous studies of seismic tomography and seismicity this 50 km difference in the thickness corresponds to a lateral temperature variation of about 370 c between the two areas the depth of d410 shows a gradual eastward decrease of about 10 km along the profile corresponding to a temperature that is about 75 c cooler to the east this variation is probably related to changes in the upper mantle geotherms associated with the transition from tectonically active to stable upper mantle a low velocity anomaly in the upper mantle and mantle transition zone beneath eastern brazil previously detected by seismic tomography and interpreted as a fossil plume produced no detectable perturbation in transition zone thickness it is thus unlikely to extend to the transition zone or alternatively is not thermal in origin finally we have observed several possible second order discontinuities at the depths of 230 500 600 840 and 915 km beneath the western part of the study area

faults and tectonic stresses of the baikal rift zone abstract the cenozoic baikal rift system consists of a central extensional segment which links a southwestern and a northeastern sinistral shear segment statistical studies on fault length amount and sense of slip depth of crustal penetration and spacing has led to the establishment of empirical relationships which appear to apply also for non extensional regimes results are graphically displayed in figs 4 7 tectonic stress regimes were determined by means of fault and joint analyses and on the basis of seismological data results of both approaches are compatible and explain the evolution of the baikal rift zone in terms of tensional reactivation of pre existing crustal discontinuities

volcanism in the baikal rift 40 years of active versus passive model discussion abstract in this review we focus on the volcanism that occurred in transbaikalia siberia after the closure of the mongolia okhotsk ocean the closure happened in the early jurassic after that time lithosphere in transbaikalia went through two phases of rifting in the early cretaceous and again in the late cretaceous until present the latter rifting event is known as the baikal rifting we consider the chronology of the volcanism and basin formation in the baikal rift and show that there has been a complex relationship between the two extension initiated in the central part of the rift system this area is now occupied by lake baikal sedimentary basins initially developed by deepening and widening of the central part of the rift system and then by bilateral propagation of basin formation outwards volcanism was generally offset from the axial rift considering along axis distribution of volcanism it initiated in the central part of the system and propagated bilaterally to the modern rift ends we argue that tectonic stress controlled localization of the eruptive centres extension and shearing probably caused melting at mantle depth suggestive of the passive model of volcanism however when considering the baikal rift and adjacent non rifted regions of mongolia in a wider context of tectonics and volcanism of central and east asia it is not possible to rule out that the volcanism may be associated with mantle transition zone diapirs thus the active model of volcanism may also apply the diapirs are located by regional isostatic gravity anomalies and considered as upwelling parts of the upper mantle convective cell controlled by the pacific subduction and slab stagnation in the mantle transition zone we do not see any geochemical geophysical and geochronological evidence for involvement of deeper mantle to explain volcanism in either baikal rift non rifted regions of mongolia or anywhere else within central and east asia

numerical study of precipitation core gap structure along cold fronts abstract the mechanism responsible for the core gap structure of precipitation along narrow cold frontal rainbands ncfrs is investigated through analyses of idealized cloud resolving simulations of cold fronts the control simulation in which the prefrontal thermal stratification is characterized by a weak convective instability at low levels with convective available potential energy cape of 60 j kg 1 reproduces the typical alongfront variability of observed ncfrs the simulated ncfr is broken up into regularly spaced ellipsoidal cores oriented at a clockwise angle to the cold front while horizontal shear instability hsi has frequently been proposed as a mechanism leading to the alongfront variability of ncfrs no characteristic features of hsi are recognized in the simulated vertical vorticity field at the leading edge of the cold front the alongfront variability in precipitation is attributed to the formation of a wavelike disturbance just above the leading edge of the cold front the wave

imaging mantle discontinuities using multiply reflected p to s conversions abstract improving the reliability and accuracy in the determination of the depth to velocity discontinuities in the earth s mantle is essential for a better understanding of mantle dynamics as well as for addressing such fundamental questions as the origin of mantle plumes and fate of subducted slabs most existing techniques that utilize receiver function stacking which is perhaps the most commonly used method to image mantle discontinuities suffer from strong trade offs between the depth and velocity anomalies above the discontinuities here we propose and test a procedure that utilizes both the p to s converted phase pds and the multiply reflected and converted phase ppds at the discontinuities to simultaneously determine the depth of mantle discontinuities and velocity anomalies in the overlying layer the procedure includes masking the strong pp arrivals prior to computing receiver functions computing non plane wave travel times for pds and ppds for accurate moveout corrections and utilizing the discrepancies in the apparent discontinuity depths from pds and ppds to simultaneously estimate velocity anomalies and discontinuity depths that are independent of velocity anomalies application of the procedure to data recorded by stations in seven radius 1 5 circles along a 780 km n s profile centered at the yellowstone hotspot reveals lower than normal upper mantle and mtz velocities beneath yellowstone a positive temperature anomaly of 40 190 c in the vicinity of the 410 km discontinuity d410 and a lower than normal temperature in the vicinity of the 660 km discontinuity d660 the perceived hotspot is not associated with a localized depression of the d410 or an uplift of the d660 suggesting that the proposed mantle plume does not traverse the mtz beneath the profile

observation of a cold front with rope cloud abstract observations are presented of a cold front which passed over the florida peninsula and produced a rope cloud visible on satellite imagery the low level structure of the leading edge of the front is revealed with data from the 150 m tower at cape canaveral air force station it is shown that the leading edge of the front is very similar to thunderstorm gust fronts and the speed is predicted well by the gust front speed equation this indicates that the rope cloud is directly analogous to the arc cloud sometimes observed along thunderstorm gust fronts further the rope cloud appears to be a less intense manifestation of the forced convection that produces the narrow cold frontal rainbands observed in some other cold front studies

seawater intrusion and associated processes in a small coastal complex aquifer castell de ferro spain an attempt to identify the hydrogeochemical processes that accompany current or past intrusion of seawater in the castell de ferro coastal aquifer se spain was made using ionic deltas ionic ratios and saturation indices alluvial and coastal quaternary sediments and triassic marbles constitute this complex aquifer cation exchange dolomitization and calcite dissolution were identified as operating in the aquifer the cation exchange processes in the detrital materials are different from those in the marbles in addition it was determined that while the processes of marine intrusion associated with periods of low groundwater levels still persist in the detrital aquifer in the carbonate sector the flushing process characteristic of wetter conditions has begun

deep structure of the baikal rift zone revealed by joint inversion of gravity and seismology 1 the question of plate boundary forces and deep versus shallow asthenospheric uplift has long been debated in intracontinental rift areas particularly in the baikal rift zone asia which is colder than other continental rifts as previous gravity and teleseismic studies support the dominance of opposing mechanisms in the baikal rift we reconsidered both data sets and jointly inverted them this more effective approach brings insight into location of the perturbing bodies related to the extension in this region our new joint inversion method allows for inverting the velocity density relationship with independent model parametrization we obtain velocity and density models that consistently show 1 crustal heterogeneities that coincide with the main tectonic features at the surface 2 a faster and denser cratonic mantle nw of lake baikal that we relate to the thermal contrast between old and depleted archean siberian platform and paleozoic orogenic belt sayan baikal belt 3 three dimensional topographic variations of the crust mantle boundary with well located upwarpings and 4 the lithosphere asthenosphere boundary uplift up to 70 km depth with a nw dip our resulting velocity and density models support the idea of a combined influence of lithospheric extension and inherited lithospheric heterogeneities for the origin of the baikal rift zone index terms 1234 geodesy and gravity regional and global gravity anomalies and earth structure 7218 seismology lithosphere and upper mantle 8122 citation tiberi c m diament j deverchere c petit mariani v mikhailov s tikhotsky and u achauer deep structure of the baikal rift zone revealed by joint inversion of gravity and seismology

deep structure and origin of the baikal rift zone p wave velocity images are determined under the baikal rift zone in siberia by using teleseismic tomography our results show prominent low velocity anomalies in the upper mantle under the baikal rift zone and high velocity anomalies in the lithosphere under the siberian craton the low velocity anomalies are interpreted as a mantle upwelling plume which has played an important role in the initiation and evolution of the baikal rift zone the rift formation may be also controlled by other factors such as older prerift linear lithosphere structures favorably positioned relative to the upwelling and favorable orientation of the far field forces caused by the india asia collision