assessment of groundwater contamination around active dumpsite in ibadan southwestern nigeria using integrated electrical resistivity and hydrochemical methods investigation of groundwater contamination due to leachate migration in a solid waste disposal site was done using both geophysical and hydrochemical methods the main goals were to delineate groundwater contamination due to leachate percolation and thus assessment of quality of groundwater from nearby hand dug wells bordering the dumpsite for drinking purpose a total of ten resistivity traverses were acquired within and outside the dumpsite using wenner configuration with constant electrode separation ranging from 5 to 25 m the 2d resistivity data were processed and inverted using res2dinv and res3dinv softwares respectively geochemical assessment of groundwater samples were carried out according to apha standards while hydrochemical facies of the sampled groundwater was evaluated using piper trilinear software the inverse resistivity models of the subsurface from 2d and 3d imaging revealed low resistivity value less than 10 m suspected to be leachate while 3d inverse sections allowed delineation of leachate weathered layer bedrock and seepage path from the dumpsite the extent of migration was more pronounced in the southern part of the dumpsite hence possible contamination of shallow groundwater system as dumpsite ages the results of physico chemical analyses showed the groundwater samples to be within the limits of who nsdwq for drinking purpose however higher values of concentrations of most analyzed parameters were noticed in well 1 due to its nearness to dumpsite and well 10 due to agricultural activities respectively interpretation of piper diagram showed cahco3 to be dominant facie in the area while alkaline earth metals text ca 2 text mg 2 and weak acids hco3 co3 are dominant cations and anions during both climatic seasons groundwater in the study area is of hard fresh and alkaline in nature

dynamic analysis and field investigation of a fluidized landslide in guanling guizhou china abstract on june 28 2010 a large catastrophic landslide was triggered by a heavy rainfall in guanling guizhou china this catastrophic event destroyed two villages and caused 99 casualties the landslide involved the failure of about 985 000 m 3 of sandstone from the source area the displaced materials traveled about 1300 m with a descent of about 400 m covering an area of 129 000 m 2 with the final volume being accumulated to be 1 840 000 m 3 approximately to provide information for hazard zonation of similar type of landslides in the same area we used a dynamic model dan3d to simulate the runout behavior of the displaced landslide materials and found that a combined frictional vollemy model could provide the best performance in simulating this landslide and the runout is precisely duplicated with a dynamic friction angle of 30 and a pore pressure ratio r u of 0 55 for the materials at the source area and with vollemy parameters of friction coefficient f 0 1 dimensionless and turbulent coefficient 400 m s 2 the simulated results indicated that the duration of the movement is estimated at about 60 s for a mean velocity 23 m s to examine the effectiveness of simulation by means of dan3d and also to evaluate the reactivation potential of these displaced landslide materials depositing on the valley we used electrical resistivity tomography ert method to survey the depth and internal structure of landslide deposits the ert results showed that dan3d gave a good prediction on the shape and runout distance of the landslide deposits although the predicted maximum depths of landslide deposit on some areas were differing from those obtained by ert method

structure of an island arc wide angle seismic studies in the eastern aleutian islands alaska new seismic wide angle data from the eastern aleutian islands show a mafic composition and a 30 km thick island arc crust traveltimes of p and s refracted arrivals and prominent crustal and mantle reflectors observed to offsets of over 300 km were used to derive velocity models for the eastern aleutian arc between the islands of atka and unimak using a three dimensional finite difference modeling and tomography code we interpret the highest crustal p wave velocities of 7 2 7 4 km s between about 12 and about 22 km depth to the south and north of the main volcanic line as remainders of preexisting oceanic crust into which arc magma is intruded apart from the pieces of oceanic crust the velocities suggest an overall mafic composition for the arc composed mainly of metabasalts diorite and diabase in the upper crust and garnet granulite or amphibolite to hornblendite in the lower crust reflected arrivals from the subducting pacific plate at depths of 45 55 km beneath the fore arc together with pn show a mantle wedge with p wave velocities as low as 7 4 km s increasing with depth to about 8 1 km s with an average of about 7 7 km s a mantle composition that grades from mainly pyroxenite probably ultramafic cumulates near the moho to dunite at greater depths best explains these observed velocities

carbon cycle in the coastal zone effects of global perturbations and change in the past three centuries abstract the coastal zone consisting of the continental shelves to 200 m including bays lagoons estuaries and near shore banks is an environment that is strongly affected by two much bigger environmental reservoirs adjacent to it the land and open ocean in the coastal zone as elsewhere in the earth system the biogeochemical cycle of carbon is coupled to and driven by the cycles of nitrogen and phosphorus through biological transfer processes human activities in the past 300 years have become an increasingly important geological factor with respect to the coastal zone through four major environmental perturbations 1 c n and s emissions from fossil fuel burning 2 changes in land use activities resulting in gaseous c emissions increased dissolved and particulate loads organic matter transport and feedbacks to biological production 3 application of inorganic nitrogen and phosphorus containing fertilizers and 4 discharges of sewage containing reactive organic c n and p in addition the mean global surface temperature of the planet has increased over this period of time by approximately 1 c perhaps also because of human activities starting with the year 1700 as a base for the industrial age perturbations on land we analyzed the consequences of these five perturbations to the carbon cycle in the coastal zone using the thirteen reservoir process driven model totem for the coupled c n p s biogeochemical cycles an indicator of the reliability of the model is the good agreement of its results showing the time course of increasing atmospheric co 2 concentrations since the year 1700 with the observational results reported in the literature during the past three centuries there has been a significant increase in the amount of organic carbon transported from land and stored in coastal zone sediments of the total transported about 65 was stored in sediments and the remaining 35 primarily recycled through exchange with the atmosphere and open ocean the imbalance between the amounts of organic carbon produced by gross photosynthesis and remineralized has apparently increased slightly in favor of remineralization corresponding to an increase in the degree of heterotrophy of the global coastal zone this process along with the release of co 2 from the formation of caco 3 counteracts the invasion of co 2 from the atmosphere to coastal waters that is driven by the rise in atmospheric co 2 concentrations an analysis of a possible reduction or full collapse of the oceanic thermohaline circulation as believed to have occurred in the past and a possibility for future centuries indicates that the co 2 transfer from the atmosphere to coastal waters would increase while that from the atmosphere to open ocean surface waters would decrease if such an event took place this is attributable to a reduced supply to the coastal zone of dissolved inorganic carbon by coastal upwelling from the deeper ocean a process linked to the global conveyor belt of the thermohaline circulation to date fossil fuel co 2 emissions to the atmosphere changes in land use practices and sewage discharges have been the three main factors affecting the carbon cycle in the global coastal zone the latter inputs from land have apparently produced a slight increase in the heterotrophy of the global coastal zone however increases in the inputs of nutrient nitrogen and phosphorus from land to the coastal zone in the future may drive its trophic state toward net production and storage autotrophy thereby also increasing its potential role as a sink for atmospheric co 2 the direction of future change in net ecosystem production in the coastal zone strongly depends on changes in the relative magnitudes of organic carbon and nutrient n and p fluxes to the coastal zone via rivers provided the upwelling fluxes remain constant

role of subsurface loads and regional compensation in the isostatic balance of the transverse ranges california evidence for intracontinental subduction bouguer gravity anomalies in the transverse ranges of southern california show a pronounced asymmetry in north south profiles across the mountains and a characteristic shape which is largely insensitive to variations in the topographic load along strike while individual gravity topography profile pairs could be consistent with a number of isostatic compensation mechanisms the unusual relationship between gravity and topography in the san bernardino mountains severely limits the class of acceptable models if the bouguer gravity field is caused by flexure of the crust mantle boundary the simplest solution consistent with the data in the western transverse ranges the san gabriel mountains and the san bernardino mountains models the great valley and mojave provinces to the north as a 50 km thick elastic plate supporting the mountains which are underthrust by a much weaker plate to the south the best fit to the gravity data in the san bernardino mountains requires a terminal bending moment on the southern plate beneath the mountains the magnitude of the terminal bending moment decreases to the west in the san gabriel and western transverse ranges we equate the load responsible for this terminal moment with the high velocity slablike feature mapped in the upper mantle beneath the transverse ranges using seismic tomography the coupling between the subsurface load and the overlying lithosphere suggests that the slab represents lithospheric subduction with an extremely small density contrast rather than a small scale convective feature

variability of 14c reservoir age and air sea flux of co2 in the peru chile upwelling region during the past 12 000 years abstract the variability of radiocarbon marine reservoir age through time and space limits the accuracy of chronologies in marine paleo environmental archives we report here new radiocarbon reservoir ages r from the central coast of chile 32 s for the holocene period and compare these values to existing reservoir age reconstructions from southern peru and northern chile late holocene r values show little variability from central chile to peru prior to 6000 cal yr bp however r values were markedly increased in southern peru and northern chile while similar or slightly lower than modern r values were observed in central chile this extended dataset suggests that the early holocene was characterized by a substantial increase in the latitudinal gradient of marine reservoir age between central and northern chile this change in the marine reservoir ages indicates that the early holocene air sea flux of co2 could have been up to five times more intense than in the late holocene in the peruvian upwelling while slightly reduced in central chile our results show that oceanic circulation changes in the humboldt system during the holocene have substantially modified the air sea carbon flux in this region

investigating fluvial features with electrical resistivity imaging and ground penetrating radar the guadalquivir river terrace jaen southern spain abstract a geophysical survey has been conducted on the lowest terrace levels and the present day floodplain of the current course of the guadalquivir river passing through the province of jaen spain using two techniques electrical resistivity imaging eri and ground penetrating radar gpr three areas have been selected in one of these sectors los barrios there is an old quarry where there are excellent outcrops that allow for the calibration of the survey techniques facies associations on these outcrops are typical of meandering rivers with sequences of channel fills lateral accretion of point bars and floodplain facies the usefulness of the two methods is analysed and compared as a support for stratigraphic and sedimentological studies the geometry and lithofacies of subsurface deposits were characterised using eri and compared with field observations a total of 5 electrical resistivity imaging profiles were obtained the changes in electric resistivity highlight granulometric differences in terrace sediments this technique can thus be used to identify the morphology of these bodies the lithofacies silt sand or gravel and buried channel pattern in addition 16 gpr profiles using 100 and 250 mhz antennas were acquired indicating terrace morphology and the filling of the sedimentary bodies in a more detailed manner than in eri the study thus allows for inferring the existence of channel migration the lateral accretion of point bars and the presence of vertical accretion deposits attributable to the floodplains

air sea co2 fluxes in the near shore and intertidal zones influenced by the california current 1 the study of air sea co2 fluxes fco2 in the coastal region is needed to better understand the processes that influence the direction and magnitude of fco2 and to constrain the global carbon budget we implemented a 1 year january through december 2009 paired study to measure fco2 in the intertidal zone the coastline to 1 6 km offshore and the near shore 3 km offshore off the north western coast of baja california mexico a region influenced by year round upwelling fco2 was determined in the intertidal zone via eddy covariance while in the near shore using mooring buoy sensors then calculated with the bulk method the near shore region was a weak annual net source of co2 to the atmosphere 0 043 mol co2 m 2 y 1 where 91 of the outgassed fco2 was contributed during the upwelling season sea surface temperature sst and pco2 from upwelling showed the strongest relationship with fco2 in the near shore suggesting the importance of meso scale processes upwelling fco2 in the intertidal zone were up to four orders of magnitude higher than fco2 in the near shore wind speed showed the strongest relationship with fco2 in the intertidal zone suggesting the relevance of micro scale processes results show that there are substantial spatial and temporal differences in fco2 between the near shore and intertidal zone likely a result of heterogeneity we suggest that detailed spatial and temporal measurements are needed across the coastal oceans and continental margins to better understand the mechanisms which control fco2 as well as reduce uncertainties and constrain regional and global ocean carbon balances

crustal structure transition from oceanic arc to continental arc eastern aleutian islands and alaska peninsula abstract the aleutian island arc crosses from the pacific ocean to the north american continent at the island of unimak 3 d finite difference traveltime inversion of our onshore offshore seismic reflection refraction data gives a velocity model of the crust and uppermost mantle the arc crust is on average 30 km thick but thickens to almost 40 km under the western alaska peninsula the transition from oceanic arc to continental arc is characterised by a decrease in average velocity in the upper crust from about 6 5 km s to less than 6 0 km s with no systematic change in the velocity of the lower crust throughout our study area in the upper 15 km of the crust the highest velocities are observed in the fore arc just south of the volcanic line in the lower crust the lowest velocities of just 6 2 km s are found close to the volcanic line the uppermost mantle is quite heterogeneous with velocities ranging from 7 6 to 8 2 km s in part due to the thermal gradient from cold fore arc to hot back arc whereas the aleutian oceanic fore arc has higher seismic velocities than average continental crust throughout the crust the peninsula section is close to the continental average in the upper c 20 km of the crust we infer that repeated episodes of arc magmatism can produce a felsic to intermediate upper crust as is observed in the continents but arc magmatism produces a thicker mafic lower crust than the average continent retains some of the excess mafic material in the island arc crust can be attributed to pre existing oceanic crust which is less evident or absent in a continental arc

electrical imaging of sliding geometry and fluids associated with a deep seated landslide la clapiere france this paper deals with the applicability of electrical resistivity tomography ert for the recognition of large landslide structures at depths which have never previously been imaged accurately one of the most studied and instrumented deep landslides in europe is taken as an example the la clapiere landslide the first stage of the study consisted of an accurate geological mapping taking into account a morphological analysis of gravitational deformations this allowed a very fine definition of the landslide structure that could be compared with three provided ert profiles performed within the landslide body very good correlations were obtained for the determination of sub horizontal structures and associated fluid circulations it confirmed the position of the sliding surface that reached a maximum depth of 100 m forward computing was however necessary to determine the influence and then the presence of vertical discontinuities it supports the use of ert as an efficient tool for large scale landslide imaging such as deep seated landslides copyright 2010 john wiley sons ltd

surface nmr within a geophysical study of an aquifer at haldensleben germany the surface nuclear magnetic resonance snmr method has been tested at a site in haldensleben northern germany to assess the suitability of this new method for groundwater exploration and environmental investigations more information is obtained by snmr particularly with respect to aquifer parameters than with other geophysical techniques snmr measurements were carried out at three borehole locations together with 2d and 1d direct current geoelectrics as well as ground penetrating radar and well logging induction log gamma ray log and pulsed neutron gamma log permeabilities were calculated from the grain size distributions of core material determined in the laboratory it is demonstrated that the snmr method is able to detect groundwater and the results are in good agreement with other geophysical and hydrogeological data using the snmr method the water content of the unsaturated and saturated zones i e porosity of an aquifer can be reliably determined this information and resistivity data permit in situ determination of other aquifer parameters comparison of the snmr results with borehole data clearly shows that the water content determined by snmr is the free or mobile water in the pores the permeabilities estimated from the snmr decay times are similar to those derived from sieve analysis of core material more thus the combination of snmr with geoelectric methods promises to be a powerful tool for studying aquifer properties less

application of a two dimensional electrical tomography technique for investigating landslides along the amman dead sea highway jordan electrical tomography geophysical surveys were conducted with the syscal r2 resistivity instrument at the location of instantaneous rock failure of a few 1 000s m3 along the amman dead sea highway jordan providing a ground image for investigating landslide sites which caused material damage and closed the road this slide occurred along two major fault planes after heavy rainfall in a rock consisting of a succession of shale marl and marly limestone layers which were folded tilted and fractured three electrical tomography profiles were performed along the axis of the slope to assess the landslide risk in such potential unstable areas the results obtained based on two dimensional inversion of field data have allowed mapping of the shale zones at depths which are characterized by a lower resistivity value and have demonstrated that the rupture was initiated at the contact between the shale mass black colored and the massive limestone white yellowish brown colored

field experiment provides ground truth for surface nuclear magnetic resonance measurement a field experiment was conducted in the high plains aquifer central united states to explore the mechanisms governing the non invasive surface nmr snmr technology we acquired both snmr data and logging nmr data at a field site along with lithology information from drill cuttings this allowed us to directly compare the nmr relaxation parameter measured during logging t2 to the relaxation parameter t2 measured using the snmr method the latter can be affected by inhomogeneity in the magnetic field thus obscuring the link between the nmr relaxation parameter and the hydraulic conductivity of the geologic material when the logging t 2 data were transformed to pseudo t2 data by accounting for inhomogeneity in the magnetic field and instrument dead time we found good agreement with t 2 obtained from the snmr measurement these results combined with the additional information about lithology at the site allowed us to delineate the physical mechanisms governing the snmr measurement such understanding is a critical step in developing snmr as a reliable geophysical method for the assessment of groundwater resources citation knight r e grunewald t irons k dlubac y song h n bachman b grau d walsh j d abraham and j cannia 2012 field experiment provides ground truth for surface nuclear magnetic resonance measurement geophys res lett 39 l03304

constraints on the structure of the himalaya from an analysis of gravity anomalies and a flexural model of the lithosphere the intracontinental subduction of india beneath the himalaya presents several similarities to that occurring at island arcs we study one of those similarities by analyzing gravity anomalies across the himalaya assuming that the topography is supported by the indian elastic plate flexed under the weight of both the overthrust mountains and the sediments in the ganga basin we first examine in detail the effects of each of the following parameters on the configuration of the elastic plate and on the gravity anomalies the flexural rigidity the position of the northern end of the elastic plate the amount of underthrusting of such a plate beneath the range and the density contrasts between the crust and mantle and between the sediments and the crust a plate with a constant flexural rigidity of about 0 7 1025 n m between 0 2 and 2 0 1025 n m allows a good fit to the data from the lesser himalaya and the ganga basin such a plate however cannot underthrust the entire himalaya instead the gravity anomalies show that the moho steepens from only about 3 beneath the lesser himalaya to about 15 beneath the greater himalaya this implies a smaller flexural rigidity beneath the greater himalaya 0 1 to 1 0 1023 n m than beneath the ganga basin and the lesser himalaya even with a thin weak plate beneath the greater himalaya the weight of the mountains depresses the plate too much unless an additional force or moment is applied to the plate the application of a bending moment unit length to the end of the plate of about 0 6 1018 n m is adequate to elevate the indian plate and to bring the calculated gravity anomalies in agreement with those observed both the smaller flexural rigidity and the bending moment can be understood if we assume that part or all of the indian crust has been detached from the lower lithosphere that underthrusts the greater himalaya we study the tectonic implications of these results by means of a series of idealized balanced cross sections from the collision to the present that reproduce several important features of the geology of the himalaya and predict an amount of eroded material comparable to that in the ganga basin and the bay of bengal these cross sections include high grade metamorphic rocks near the main central thrust and a steeper dip of it there than in the lesser himalaya they predict rapid uplift only in the greater himalaya and at the foot of the lesser himalaya

air sea carbon dioxide fluxes in the coastal southeastern tropical pacific comprehensive sea surface surveys of the partial pressure of carbon dioxide pco2 have been made in the upwelling system of the coastal 0 200 km from shore southeastern tropical pacific since 2004 the shipboard data have been supplemented by mooring and drifter based observations air sea flux estimates were made by combining satellite derived wind fields with the direct sea surface pco2 measurements while there was considerable spatial heterogeneity there was a significant flux of co2 from the ocean to the atmosphere during all survey periods in the region between 4 and 20 south latitude during periods of strong upwelling the average flux out of the ocean exceeded 10 moles of co2 per square meter per year during periods of weaker upwelling and high productivity the co2 evasion rate was near 2 5 mol m2 yr the average annual fluxes exceed 5 mol m2 yr these findings are in sharp contrast to results obtained in mid latitude upwelling systems along the west coast of north america where the average air sea co2 flux is low and can often be from the atmosphere into the ocean in the peruvian upwelling system there are several likely factors that contribute to sea surface pco2 levels that are well above those of the atmosphere in spite of elevated primary productivity 1 the upwelling source waters contain little pre formed nitrate and are affected by denitrification 2 iron limitation of primary production enhanced by offshore upwelling driven by the curl of the wind stress and 3 rapid sea surface warming the combined carbon nutrient and oxygen dynamics of this region make it a candidate site for studies of global change

integrated geophysical studies at ancient itanos greece the results of an integrated geophysical survey at the archaeological site of itanos crete are presented and discussed at hellenistic itanos which is located near the seashore the buried ruins are partially under the saline water table the purpose of this geophysical survey was to map buried relics of buildings streets and walls of ancient itanos in particular the usefulness of combining conventional geophysical mapping techniques and high resolution imaging methods in delineating shallow targets of archaeological interest at such complex archaeological sites is studied magnetic gradient soil resistance and electromagnetic measurements were taken in grids covering an area of approximately 16 000 m2 processing of geophysical maps included filtering with the gradient and first derivative operators in the space domain and the upward continuation and butterworth filters in the wavenumber domain emphasis is given to the mathematical description of the processing steps the integration of the geophysical measurements revealed the existence of a well and three parallel walls verified by excavation ground probing radar and electrical tomography sections crossing the parallel walls showed the vertical extent of these features ground penetrating radar time slices and 3d electrical tomography depth slices were used for the verification of specific anthropogenic anomalies which were detected on the geophysical maps a shallow seismic survey was carried out in an effort to locate and map the ancient port the combination of a wide spectrum of geophysical prospecting techniques was successful in delineating the buried relics enhancing the information context regarding the hellenistic settlement of itanos together with its port and necropolis the geophysical survey at itanos demonstrates that the integrated approach is appropriate for archaeological investigations at complex sites like itanos

allochthonous terranes in alaska implications for the structure and evolution of the bering sea shelf abundant evidence has been gathered in support of the concept that much of the pacific margin of north america consists of allochthonous terranes that were accreted during mesozoic and early tertiary time in particular southern alaska is almost completely composed of separate terranes whose stratigraphy and paleomagnetism indicate distant origins the bering sea continental shelf is among the largest shelves in the world almost half as large as alaska itself some of the allochthonous terranes in alaska probably continue beneath the continental shelf but their distribution beyond the shoreline has not been determined we believe that much of the continental shelf is probably composed of allochthonous terranes in much the same way as southern alaska geophysical data from the bering continental shelf have been used to test this hypothesis although inconclusive without extensive drilling multichannel seismic profiles and magnetic data indicate the composite character of the shelf basement the magnetic anomalies can be separated into specific domains of limited extent these magnetic variations suggest a corresponding variation of rock terranes beneath the shelf in addition multichannel seismic profiles show possible thrust faults within the shelf basement that could be sutures between separate terranes

effects of upwelling tides and biological processes on the inorganic carbon system of a coastal lagoon in baja california abstract the role of coastal lagoons and estuaries as sources or sinks of inorganic carbon in upwelling areas has not been fully understood during the months of may july 2005 we studied the dissolved inorganic carbon system in a coastal lagoon of northwestern mexico during the strongest period of upwelling events along the bay different scenarios were observed for the distributions of ph dissolved inorganic carbon dic and apparent oxygen utilization aou as a result of different combinations of upwelling intensity and tidal amplitude dic concentrations in the outer part of the bay were controlled by mixing processes at the inner part of the bay dic was as low as 1800 mol kg 1 most likely due to high water residence times and seagrass co 2 uptake it is estimated that 85 of san quintin bay at the oceanic end acted as a source of co 2 to the atmosphere due to the inflow of co 2 rich upwelled waters from the neighboring ocean with high positive fluxes higher than 30 mmol c m 2 d 1 in contrast there was a net uptake of co 2 and hco 3 by the seagrass bed zostera marina in the inner part of the bay so the p co 2 in this zone was below the equilibrium value and slightly negative co 2 fluxes of 6 mmol c m 2 d 1 our positive nep and dic values indicate that bahia san quintin was a net autotrophic system during the upwelling season during 2005

integrated geoelectrical resistivity hydrochemical and soil property analysis methods to study shallow groundwater in the agriculture area machang malaysia integrated geoelectrical resistivity hydrochemical and soil property analysis methods were used to study the groundwater characteristics of sandy soils within a shallow aquifer in the agriculture area machang a pilot test investigation was done prior to the main investigation the area was divided into two sites test site 1 is non fertilized test site 2 is the former regularly fertilized site from the surface to depths of 75 cm a lower average resistivity was obtained in test site 2 around 0 37 less than in test site 1 the presence of nitrate and chloride contents in pore water reduced the resistivity values despite the low moisture content the ph values for the whole area range from 4 11 to 6 88 indicating that the groundwater is moderately to slightly acidic in the southern region concentration of nitrate is considered to be high 20 mg l while it is nearly zero in the northern region in the south the soil properties are similar however the geoelectrical model shows lower resistivity values around 18 m at the sites with relatively high nitrate concentration in the groundwater 20 mg l conversely the sites with low nitrate concentration reveal the resistivity values to be higher 35 m basement and groundwater potential maps are generated from the interpolation of an interpreted resistivity model the areas that possibly have nitrate contaminated groundwater have been mapped along with groundwater flow patterns the northern part of the area has an east to west groundwater flow pattern making it impossible for contaminated water from the southern region to enter despite the northern area having a lower elevation

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

methods for calculating frechet derivatives and sensitivities for the non linear inverse problem a comparative study1 a fundamental step in the solution of most non linear inverse problems is to establish a relationship between changes in a proposed model and resulting changes in the forward modelled data once this relationship has been established it becomes possible to refine an initial model to obtain an improved fit to the observed data in a linearized analysis the frechet derivative is the connecting link between changes in the model and changes in the data in some simple cases an analytic expression for the frechet derivative may be derived in this paper we present three techniques to accomplish this and illustrate them by computing the frechet derivative for the id resistivity problem for more complicated problems where it is not possible to obtain an expression for the frechet derivative it is necessary to parameterize the model and solve numerically for the sensitivities partial derivatives of the data with respect to model parameters the standard perturbation method for computing first order sensitivities is discussed and compared to the more efficient sensitivity equation and adjoint equation methods extensions to allow for the calculation of higher order directional and objective function sensitivities are also presented finally the application of these various techniques is illustrated for both the 1d and 2d resistivity problems

groundwater nmr in conductive water a surface method of groundwater prospecting using nuclear magnetic resonance nmr in the earth s magnetic field is under study the technique is employed for hydrogeological surveys down to a depth of about 100 m the advantage of this method is that an nmr signal can be observed only in the presence of groundwater a circular wire loop with a diameter of 100 m is laid out on the ground to excite and receive the nmr signal an oscillating current with a rectangular pulse shape is passed through the loop with the carrier frequency being equal to the proton resonance frequency in the earth s field the excitation pulse is followed by a nuclear induction emf caused by the free larmor precession in the earth s field of practical importance is the effect of the electrical conductivity of the ground on a groundwater nmr survey finite ground conductivity can result in induced currents that can screen the nmr signal the calculations of nmr signals are based on the transformation of maxwell s equations in terms of magnetic hertz potentials through use of the reciprocity principle groundwater nmr is measured with an instrument designed at the institute of chemical kinetics and combustion russian academy of science novosibirsk experiments were conducted in the altay region of russia both nmr signal amplitude and phase were measured and compared with the calculated results for horizontally stratified media borehole logs and vertical resistivity profiles were also used for evaluation of results the conductivity is shown to affect both phase and amplitude of the nmr signal at resistivities of a few to a few tens of ohm m depending on the depth of the water saturated layers there is good agreement between calculated and experimental data it is also established that the measurements of only nmr amplitude and phase are not sufficient for determining groundwater salinity

velocity estimation by the common reflection surface crs method using ground penetrating radar data in this paper we describe the use of the common reflection surface crs method to estimate velocities from ground penetrating radar gpr data applied to multicoverage data the crs method provides as one of its outputs the time domain rms velocity map which is then converted to depth by the familiar dix algorithm combination of the obtained depth converted velocity map with electrical resistivity in situ measurements enables us to estimate both water content and water conductivity these quantities are essential to delineate infiltration of contaminants from the surface after industrial or agricultural activities the method was applied to gpr data and compared with the classical nmo approach the results show that the crs method provides a physically more meaningful velocity field thus improving the potential of gpr as an investigation tool for environmental studies

determination of mechanisms and hydrogeological environments of gangxianlane landslides using geoelectrical and geological data in central taiwan electrical resistivity tomography ert single point resistance logging with time lapse and geological and groundwater level data are utilized to determine the mechanism of and a hydrogeological model of the gangxianlane landslide in the west central part of taiwan the rock surface and geometry of the colluviums were found by integrating ert and borehole data the iso resistivity line in the bedrock broadly followed the bedding plane indicating that the contribution of lithology to resistivity exceeds that of groundwater the results of single point resistance logging with time lapse and borehole data reveal that the bedrock has low permeability which is associated with poorly developed joints and fractures the fine grain content part including the clayey layer almost parallel to the bedding plane of the bedrock and between the colluvium and the bedrock in the upper part of the landslide served as the slip surface and is believed to have been recently produced it can block and retain water in the colluviums accordingly this slip surface has the potential to re slip in the future another slope failure involved rock collapse by a well developed open release joint close to the huoshaoping terrace it is also related to groundwater flow over a large gradient from the huoshaoping terrace it is a key to determining whether this landslide will expand in the future

tectonic evolution of the bristol bay basin southeast bering sea constraints from seismic reflection and potential field data 1 we interpret the tectonic evolution of the bristol bay basin also known as the north aleutian basin on the basis of a deep seismic reflection profile lithologic data from a well unreversed seismic refraction profiles a bathymetry profile a magnetics profile forward modeling of a gravity profile and flexural modeling of a basin wide paleosurface we present evidence that 1 an early or middle eocene through late miocene phase of extension led to fault controlled subsidence 2 a late eocene through early miocene phase of volcanic arc loading led to flexural subsidence which was amplified by additional factors possibly including lithospheric cooling tectonic compression reverse or thrust faulting or small scale intrusions of dense magma and 3 a late miocene through holocene resurgence of arc volcanism and a northward prograding delta continued or possibly increased flexural subsidence in the back arc region our interpretations imply that the fault controlled subsidence in the bristol bay basin is genetically linked to that found in the other outer bering shelf basins but the subsequent flexural subsidence of these basins is not related more fundamentally our observations suggest that the basin s evolution is unusual and has components typically found in both back arc extension and retroarc foreland flexure basins

the jettencave southern harz mountains germany geophysical observations and a structural model of a shallow cave in gypsum anhydrite bearing rocks abstract gypsum and anhydrite are soluble rocks where fissures and bedding partings can be enlarged with time by the dissolution of the mineral species through water the selective enlargement results in sub surface voids acting as preferential flow path for the drainage of the rock with time larger cavities develop and a network of cave passages can evolve if the enlarged cave voids are not too deep under the surface geophysical measurements can be used to detect identify and trace these structures we have used gravity measurements grav electrical resistivity imaging eri self potential measurements sp electrical conductivity measurements ec and ground penetrating radar gpr above the cave jettenhohle a cave located in the southern harz mountains in germany the jettencave is developed in the hauptanhydrit formation of the permian zechstein sequence characterised by large breakdown rooms and an exposed water table the overburden of the cave is only around 10 15 m and dolomitic rocks are located in close vicinity we present results from our geophysical surveys in vicinity of the cave we are able to identify the cave geometry from grav eri and gpr measurements which distinguish the local lithology of the permian zechstein rocks in the area from the eri and ec measurements we derive information on the void volume in the soluble rocks we finally present a three dimensional structural model of the jettencave and its surroundings based on our geophysical results and the hydrological interpretation

surface nmr applied to an electroconductive medium1 an integrated electromagnetic and nuclear magnetic resonance nmr method is proposed for investigating highly conductive soil areas using a simple model of a homogeneous half space and the same antenna for both methods a significant improvement in the nmr data interpretation is obtained a case study has shown fair agreement between the results from computer modelling field tests and data from a nearby observation well the electromagnetic method and the half space model were selected for easy integration into an existing instrument used for the nmr method a more accurate knowledge of the conductivity distribution with depth will further improve the final result

electrical resistivity imaging for the characterization of the montaguto landslide southern italy abstract electrical resistivity tomography surveys were carried out for the characterization of the montaguto earth flow located in the southern apennines chain campania region southern italy the earth flow investigated is one of the largest and most complex landslides in europe with a length of 3 1 103 m a width ranging between 45 and 420 m and an area of about 6 6 105 m2 in the spring of 2010 a large reactivation of the earth flow heavily damaged some strategic infrastructures in order to mitigate the effects of the mass movement considerable efforts were carried out by the italian national civil protection department dpc to tackle the emergency the aim of the study was to contribute to a more accurate geometric reconstruction of the landslide body and to improve the knowledge of the geological setting due to the lithological characteristic of the outcropping lithotypes i e faeto flysch calcarenite clay and marl and villamaina unit sand and silty clay the electrical resistivity contrasts were not very pronounced however the high resolution of the electrical tomographies was the key to observe the presence of both lateral and vertical discontinuities that were associated with lithological boundaries structural features and sliding surfaces the results of the geoelectrical surveys could be considered for planning additional and more appropriate actions aimed at the stabilization of different portions of the montaguto landslide

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

a survey of current trends in near surface electrical and electromagnetic methods electricalandelectromagnetice emmethodsfornearsurface investigations have undergone rapid improvements over the past few decades besides the traditional applications in groundwater investigations natural resource exploration and geological mapping a number of new applications have appeared these include hazardous waste characterizationstudies precision agricultureapplications archeological surveys and geotechnical investigations the inclusion of microprocessors in survey instruments development ofnewinterpretationalgorithms andeasyaccesstopowerful computers have supported innovation throughout the geophysical community and the e em community is no exception most notable are development of continuous measurement systems that generate large dense data sets efficiently these have contributed significantly to the usefulness of e em methods by allowing measurements over wide areas without sacrificing lateral resolution the availability of theseluxuriantdatasetsinturnspurreddevelopmentofinterpretation algorithms including laterally constrained 1d inversionaswellasinnovative2d and3d inversionmethods taken together these developments can be expected to improve the resolution and usefulness of e em methods and permit them to be applied economically the trend is clearly towarddensesurveyingoverlargerareas followedbyhighly automated post acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost effectivemanner

evidence for formation of a flexural backarc basin by compression and crustal thickening in the central alaska peninsula the north aleutian basin is a large cenozoic sedimentary basin in the northern part of the central alaska peninsula and the southern bering shelf the gravity anomaly pattern the geometry and the structure of the basin suggest that if formed by downward flexure of the backarc lithosphere basin modeling suggests that the flexure was driven by the emplacement of surface and subsurface loads having densities comparable to those of oceanic crust and mantle rocks at approximately the position of the present day volcanic arc and forearc the authors suggest that the inferred loads consist of tectonically thickened mafic crustal materials lying beneath the arc and forearc of the central alaska peninsula the crustal thickening may have occurred within a dominantly transpressional regime resulting from oblique convergence between the north american and pacific plates during the cenozoic

meshik and aleutian arcs tertiary volcanism on alaska peninsula alaska abstract the meshik and aleutian arcs of the alaska peninsula are magmatic arcs of predominantly calc alkaline affinity the meshik arc primarily of eocene and oligocene age is in part stratigraphically equivalent to early series rocks of the aleutian islands its northeasternmost outcrops lie south of mother goose lake but rocks of the arc occur in the subsurface as far north as becharof lake the aleutian arc is of middle miocene to holocene age it extends from hayes volcano in the southern alaska range to buldir island in the aleutians on the alaska peninsula the dominant major volcanic rock types in both arcs range from leuco basalt to dacite plutonic rocks of the aleutian arc crop out in many places on the peninsula including the devils and agripina bay batholiths ock types of the plutons are commonly quartz diorite granodiorite and lesser tonalite plutonic rocks of the meshik arc are less common though compositionally similar to aleutian arc plutonic rocks both the aleutian and meshik arcs exhibit a shift in the locus of magmatism over time available data document a shift in the magmatic locus of the aleutian arc about 50 km northwestward from the pacific coast in the middle miocene to its present position less definitive evidence suggests that the meshik arc shifted a similar distance to the southeast during eocene and oligocene time although segmentation of the aleutian arc is well described less evidence exists to suggest similar segmentation of the meshik arc end of article last page 683

mean surface circulation and mesoscale turbulent flow characteristics in the eastern south pacific from satellite tracked drifters 1 circulation of the eastern south pacific region 10 34 s 70 100 w was studied using drifting buoy trajectories from 1979 to 2003 three different current regimes were highlighted the south equatorial current flowing westward north of 26 s with surface velocities of 7 8 cm s 1 the south pacific current an eastward current of 2 cm s 1 south of 25 30 s and the chile peru current a northwestward flow of 6 cm s 1 found to the east of 82 w and south of 22 s the velocity variance distribution showed the regional flow to be anisotropic in nature maps of eddy kinetic energy obtained from drifter measurements and satellite altimetry data showed similar patterns with higher energy levels near the south american coast the lagrangian time and length scales of the turbulent flow revealed typical values of 5 9 0 6 days and 40 7 5 4 km in the zonal direction and of 3 5 0 4 days and 29 3 4 km in the meridional direction the estimated diffusivities were 4 9 0 5 107 cm2 s 1 and 2 6 0 3 107 cm2 s 1 in the eastward and northward directions respectively finally we estimated the respective role of horizontal advection and lateral diffusion on the mixed layer heat and salt budgets near the coast the lateral turbulent fluxes in the surface layer were two times larger than the horizontal transports associated with the large scale circulation mean horizontal heat and salt diffusive fluxes were around 25 w m 2 and 50 g m 2 d 1

low frequency electromagnetic exploration for groundwater on mars 1 water with even a small amount of dissolved solids has an electrical conductivity orders of magnitude higher than dry rock and is therefore a near ideal exploration target on mars for lowfrequency diffusive electromagnetic methods models of the temperature and frequency dependent electrical properties of rock ice water mixtures are used to predict the electromagnetic response of the martian subsurface detection of ice is difficult unless it is massively segregated in contrast liquid water profoundly affects soundings and even a small amount of adsorbed water in the cryosphere can be detected subcryospheric water is readily distinguishable at frequencies as low as 100 hz for fresh water to 10 mhz for brines these responses can be measured using either natural or artificial sources ulf signals from solar wind and diurnal heating perturbations of the ionosphere are likely and disturbances of regional crustal magnetic fields may also be observable spherics or elf vlf signals from lightning discharge would provide optimal soundings however lightning may be the least likely of the possible natural sources among the active techniques only the time domain electromagnetic tdem method can accommodate a closely spaced transmitter and receiver and sound to depths of hundreds of meters or more a ground or aircraft based tdem system of several kilograms can detect water to a depth of several hundred meters and a system of tens of kilograms featuring a large fixed rover or ballistically deployed loop can detect water to several kilometers depth index terms 0694 electromagnetics instrumentation and techniques 0925 exploration geophysics magnetic and electrical methods 6225 planetology solar system objects mars 5494 planetology solid surface planets instruments and techniques keywords mars water electromagnetic magnetotelluric tdem

using magnetic resonance imaging for experimental analysis of fine sediment infiltration into gravel beds sedimentologists recognize that development of a fine resolution truly threedimensional analytical tool is essential if the internal structure of an opaque material is to be examined this paper therefore seeks to i test the viability of magnetic resonance imaging for sedimentological research and ii investigate fine sediment infiltration into gravel beds the results of six experiments are analysed quantitatively using imagej post processing software data indicate that magnetic resonance imaging based measurements of particle axes and volumes are comparable with standard laboratory techniques furthermore the technique permits visualization and analysis of differences in the pattern of fine sediment infiltration median particle diameter d into a framework of gravel median particle diameter d data clearly illustrate a siltation process for samples of d d 34 and a sealing process for samples of d d 7 where the seal is restricted to a depth equal to 2d this pore scale visualization is valuable to the understanding of hydraulic sediment habitat interactions

cenozoic plate reconstruction of the south china sea region abstract reconstructions of the south china sea region at 60 ma 40 ma 30 ma 20 ma 10 ma and 5 ma are presented we have attempted to place the south china sea basin in a regional tectonic framework the tectonic evolution of the major blocks surrounding the south china sea were analyzed as well as the relative motions of the indian and australian plates we have tried to correct the tectonic models available in this region a 3 d graphics terminal was used to derive rotation poles for the different tectonic blocks and our model was then tested to determine its self consistency when the model conflicted with previous interpretations the input data were evaluated for alternative explanations at least two and possibly three stages of extension can be recognized in this region the earliest one active in the late cretaceous to eocene involved nw se extension the second one active from the late eocene to early miocene involved north south extension the third stage of extension which probably trended nw se can be dated as post oligocene the first extensional event produced the ne sw trending proto south china sea and a series of sedimentary basins along the south china margin following the southeastward extrusion of indochina the proto south china sea was mostly consumed at the palawan trough renewed north south extension in the south china continental margin started the present day south china sea spreading in the oligocene the southeastward extrusion of indochina blocked by sundaland resulted in the nw se trending opening of the south china sea basin in the early miocene collision of the north palawan microcontinental block with the west philippines block stopped the opening of the south china sea at the end of early miocene spreading activity switched to the sulu sea basin in the middle miocene but collision between the sulu ridge and the west philippines at mindanao halted the opening of the sulu sea at the end of the middle miocene in the late miocene greater india continued its northward path and seems to have ripped open the andaman sea in the pliocene subduction along the northern manila trench placed the north luzon arc on a collision path with the east asia continental margin at taiwan our reconstructions along with detailed geological and geophysical information may be used as a predictive tool for basin evolution models and block interactions in this region the development of the south china sea basin the gulf of thailand the malay basin and the central thailand basins are the result of collision induced extensional forces the sulu celebes and sumatra basins were formed as a consequence of prolonged subduction the opening of the pearl river mouth west natuna south china sea sulu and possibly celebes basins were terminated by various plate collisions during the course of plate reorganizations major boundary faults have changed their slip senses during different stages of evolution

assessing preferential seepage and monitoring mortar injection through an earthen dam settled over a gypsiferous substrate using combined geophysical methods abstract for several decades the sant llorenc de montgai reservoir has experienced different problems that could affect the safety of the engineering structure for this reason several corrective actions have been taken over the years here we present a study involving complementary geophysical methods including electrical resistivity tomography seismic refraction tomography and frequency domain electromagnetic surveys the analysis of the inverted electrical resistivity tomography cross sections combined with the seismic refraction results and land subsidence monitoring data show the likely mechanism of abnormal seepage the areas where mortar injections were applied as a corrective measure are also clearly delineated in addition the evolution of the state of the embankment has been established from two successive electrical resistivity tomography surveys in the last two decades the results show areas where corrective mortar injections have been effective while in other areas new abnormal seepage has been detected the lithological heterogeneity of the bedrock especially the dissolution of gypsum rich rocks induced subsidence effects and caused abnormal seepage in different areas along the embankment our results indicate how corrective solutions can be optimized to reduce the cost of corrective engineering interventions

two and three dimensional electrical resistivity imaging at a heterogeneous remediation site geometrically complex heterogeneities at a decommissioned sour gas plant could not be adequately characterized with drilling and 2d electrical resistivity surveys alone in addition 2d electrical resistivity imaging profiles produced misleading images as a result of out of plane resistivity anomalies and violation of the 2d assumption accurate amplitude and positioning of electrical conductivity anomalies associated with the subsurface geochemical distribution were required to effectively analyze remediation alternatives forward and inverse modeling and field examples demonstrated that 3d resistivity images were needed to properly reconstruct the amplitude and geometry of the complex resistivity anomalies problematic 3d artifacts in 2d images led to poor inversion fits and spurious conductivity values in the images at depths close to the horizontal offset of the off line anomaly three dimensional surveys were conducted with orthogonal sets of wenner and dipole dipole 2d resistivity survey lines the

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

sinkhole structure imaging in covered karst terrain 1 ground penetrating radar gpr and resistivity techniques have been widely used to map the locations of sinkholes in covered karst terrain to determine whether a sinkhole is a likely preferential conduit for groundwater flow however requires higher resolution imaging than that used in conventional sinkhole mapping surveys field observations combined with simulated surveys for a 15 m diameter 3 m deep sinkhole in west central florida are used to assess the resolution of gpr and resistivity surveys targeting the semiconfining unit that floors the sinkhole depression 2d resistivity surveys clearly show the central depression as well as resistivity contrasts between the cover sediments within and outside of the sinkhole but are inadequate for resolving breaches in the semiconfining unit or underlying conduits a 3d gpr survey resolves vertical structure on the order of tens of centimeters within the semiconfining unit as well as indicators of conduits that extend several meters beneath the central depression 3d gpr thus holds promise for imaging hydrologically significant features of sinkholes

mapping the descent of indian and eurasian plates beneath the tibetan plateau from gravity anomalies the collision of india with asia has produced a complicated continental continental plate boundary involving folding and faulting of variable trends and styles within and along the margins of the tibetan plateau numerous lines of evidence including the development of two scales of folding in tibet suggest that the lowermost crust is behaving in a ductile fashion this weak lower crust might then decouple the fundamental plate tectonic motions in the uppermost mantle from the complex pattern of surface faulting in this study we use bouguer gravity anomalies to map out the geometry of indian and eurasian plate interactions in the mantle beneath the plateau based on both the inferred geometry of the moho and lateral variations in lithospheric strength determined from mechanical modeling in our preferred model the lithosphere beneath tibet consists of two distinct units 1 the underthrust to the north indian plate which sutures with the eurasian plate in the upper mantle below the yarlung zangpo suture or the gangdese igneous belt 200 400 km north of the main boundary thrust and 2 the underthrust to the south eurasian plate a subducting slab of indian upper mantle extends about 200 km into the asthenosphere north from the mantle suture and exerts a bending moment of about 3 5 1017 n on the indian plate thus the mantle lithosphere appears to be behaving in the simple fashion of converging oceanic plates while the more buoyant continental crust deforms under high gravitational potential in a complex pattern controlled by its lateral and vertical strength heterogeneity

latitudinal change of remineralization ratios in the oceans and its implication for nutrient cycles 1 a new three end member mixing model is introduced to obtain remineralization ratios of organic matter in the water column remineralization ratios p n corg o2 of organic matter in the deep water column change systematically from the northern atlantic to the southern oceans then to the equatorial indian and the northern pacific oceans more or less along the global ocean circulation route of deep water average remineralization ratios of organic matter for the northern atlantic ocean are p n corg o2 1 16 1 73 8 137 7 and for the southern oceans p n corg o2 1 15 1 80 3 133 5 those values are similar to the traditional redfield ratios of p n corg o2 1 16 106 138 for marine plankton except for the low corg p ratio average remineralization ratios for the equatorial indian ocean are p n corg o2 1 10 1 94 5 130 7 and for the northern pacific ocean p n corg o2 1 13 1 124 11 162 11 the apparent low n p ratio for both ocean basins suggests that organic nitrogen was converted partly into gaseous n2o and n2 by bacteria through nitrification denitrification processes in a low oxygen or reducing microenvironment of organic matter throughout the oxygenated water column the actual n p ratio of remineralized organic matter is probably around 15 1 the o2 corg ratio of remineralized organic matter also decreases systematically along the global ocean circulation route of deep water indicating changes in relative proportions of biomolecules such as lipids proteins nucleic acids and carbohydrates no temporal trends of remineralization ratios are detected when comparing the results obtained by geosecs and woce data sets

comment on enhanced open ocean storage of co2 from shelf sea pumping in a well designed north sea study thomas et al 1 1 found that atmospheric carbon dioxide co2 was absorbed by continental shelf water and was eventually exported into the north atlantic ocean the work confirmed preliminary observations in the same area 2 2 3 3 and provided

low altitude permafrost research in an overcooled talus slope rock glacier system in the romanian carpathians detunata goală apuseni mountains abstract ground and air temperature monitoring geophysical soundings and dendrological investigations were applied to a basaltic talus slope rock glacier system from detunata site in the apuseni mountains western romanian carpathians to verify the presence of sporadic permafrost at 1020 1110 m asl well below the regional limit of mountain permafrost the near 0 c mean annual ground surface temperatures imposed by the large negative annual thermal anomalies of the ground up to 7 4 c together with the high resistivity values and the occurrence of trees with severe growth anomalies support the presence of permafrost at this location temperature measurements and ground air circulation experiments proved that the so called chimney effect is the main process favoring the ground overcooling and allowed for the construction of a model of ground air circulation in complex morphology deposits the texture and porosity of the debris were quantified along with the local morphology in order to evaluate their role upon the chimney circulation the debris porosity was found to be very high promoting intense ground overcooling during the cold season including the periods of high snow cover due to the development of snow funnels it efficiently reduces the heat transfer during summer thus contributing essentially to permafrost preservation in compound morphologies the depressed and low lying features are the cold zones subjected to winter overcooling and summer chill while the high positioned and convex up landforms become warm air evacuation features with positive thermal anomalies tree ring measurements showed that the growth of cold affected trees is higher during colder intervals years to decades probably as a consequence of the weakened katabatic air outflow during cooler summers the dendrological analysis of multi centennial spruces and their growth rates also provided palaeoclimatic inferences for the last 200 years

reconstructing palaeochannel morphology with a mobile multicoil electromagnetic induction sensor abstract field methods to map and reconstruct the morphology of buried river systems are highly dependent on spatial interpolation conventional methods such as standard borehole survey allow a detailed vertical reconstruction of the shallow subsurface but leave lateral connections between sample locations open to interpretation geophysical survey techniques have recently introduced more detail mobile electromagnetic induction emi survey combines high density sampling with full lateral coverage but fails to produce detailed information about vertical facies changes recently multicoil emi survey added vertical discrimination potential to this lateral continuity in this study we present an integrated approach for reconstructing the morphology of a known palaeochannel segment by modelling the depth to the sandy substrate in addition a calibration method based on a limited number of auger data is proposed in a first phase the modelling procedure was evaluated along two transects on a test site showing palaeochannel depths ranging from 1 to 4 m beneath the surface in a second phase the morphology of the entire site was reconstructed these three resulting depth models were then compared with auger observations and electrical resistivity tomography ert data the high correlation coefficients 0 9 between observed and modelled depths showed that even in complex pedological environments palaeochannel morphology could be predicted precisely using multicoil emi data therefore we concluded that a multicoil emi survey proves to be an efficient and reliable solution for mapping and reconstructing the morphology of the shallow subsurface

electric and magnetic tomographic approach for the geophysical investigation of an unexplored area in the archaeological site of pompeii southern italy the joint application of electric and magnetic techniques for near surface exploration represents a very useful tool for archaeological investigation and can provide a quantitative contribution to describe the spatial distribution of buried objects in this work we show a new advanced tomographic approach based on the parallel inversion of magnetic and electric observed data aimed at the reconstruction of the subsoil of a still unexplored area of the archaeological site of pompeii southern italy the survey was performed in collaboration with pompeii s archaeological commission the comparison between the results obtained from the tomographic inversions of both electrical and magnetic data was carried out in terms of the data inversions which allowed us to obtain information about the location of the buried geophysical sources in the investigated subsoil the results obtained seem to be in a good agreement both for the position of the geophysical sources and for their dimensions

structure and composition of the aleutian island arc and implications for continental crustal growth we present results of a seismic reflection and refraction investigation of the aleutian island arc designed to test the hypothesis that volcanic arcs constitute the building blocks of continental crust the aleutian arc has the requisite thickness 30 km to build continental crust but it differs strongly from continental crust in its composition and reflectivity structure seismic velocities and the compositions of erupted lavas suggest that the aleutian crust has a mafic bulk composition in contrast to the andesitic bulk composition of continents the silicic upper crust and reflective lower crust that are characteristic of continental crust are conspicuously lacking in the aleutian intraoceanic arc therefore if island arcs form a significant source of continental crust the bulk properties of arc crust must be substantially modified during or after accretion to a continental margin the pervasive deformation intracrustal melting and delamination of mafic to ultramafic residuum necessary to transform arc crust into mature continental crust probably occur during arc continent collision or through subsequent establishment of a continental arc the volume of crust created along the arc exceeds that estimated by previous workers by about a factor of two

air sea co2 fluxes along the coast of chile from co2 outgassing in central northern upwelling waters to co2 uptake in southern patagonian fjords 1 carbon system parameters measured during several expeditions along the coast of chile 23 s 56 s have been used to show the main spatial and temporal trends of air sea co2 fluxes in the coastal waters of the eastern south pacific chilean coastal waters are characterized by strong pco2 gradients between the atmosphere and the surface water with high spatial and temporal variability on average the direction of the carbon flux changes from co2 outgassing at the coastal upwelling region to co2 sequestering at the nonupwelling fjord region in chilean patagonia estimations of surface water pco2 along the patagonian fjord region showed that while minimum pco2 levels strong co2 undersaturation occurs during the spring and summer period maximum levels including co2 supersaturation occur during the austral winter co2 uptake in the patagonia fjord region during spring summer is within the order of 5 mol c m 2 yr 1 indicating a significant regional sink of atmospheric co2 during that season we suggest that the co2 sink at patagonia most probably exceeds the co2 source exerted by the coastal upwelling system off central northern chile

crustal structure in the southern bering shelf and the alaska peninsula from inversion of surface wave dispersion data dispersion of surface waves in the southern bering shelf bristol bay and the alaska peninsula is investigated for a study of the regional crustal structure our data consist of five shallow earthquakes located along the aleutian arc and recorded by long period three component seismographs sited in south central alaska both love and rayleigh group velocities are obtained through the application of the phase matched filtering technique the results are converted to equivalent pure path data by appropriate adjustment using the published information for the continental alaska treating the shear velocity of each layer as an independent parameter the pure path group velocities of love and rayleigh waves are jointly inverted in order to obtain a satisfactory agreement between the theoretical and the observed dispersion characteristics estimates of the resolving power of the inversion and uncertainty of the final velocity structure show substantial improvement over the previously published models with their crustal thicknesses ranging between 33 and 36 km none of the final models displays structural characteristics reminiscent of an oceanic crust over the northernmost path across the bristol bay we found an indication of a weak low velocity zone five per cent reduction relative to the lid velocity whose prominence diminishes towards the south

evaluation of landfill disposal boundary by means of electrical resistivity imaging this paper deals with an employment of electrical resistivity imaging eri for survey of leachate content on the waste disposal site in northern israel the research consisted of conducting ten eri lines and drilling investigation wells data simulation used a 2d earthimager inversion program analysis of 2d eri interpretation results shows that determination of the boundary between the landfill body bottom intensively saturated with leachates and underlying layers of highly water saturated fat nonconsolidated clays presents a challenge however statistical analysis of eri data indicates that standard deviation and confidence interval of a set of resistivity data measured in the landfill body are significantly larger than those in underlying clays moreover maximum changes of these parameters are found on the boundary between landfill body and underlying soil thus reflecting natural differences in scattering of resistivity data measured in these two objects

influence of mixing on cfc uptake and cfc ages in the north pacific thermocline 1 a diagnostic isopycnal advection diffusion model based on a climatological geostrophic flow field is used to study the uptake of chlorofluorocarbons cfcs into the portion of the thermocline that outcrops in the open north pacific 26 6 kg m 3 in addition to advection isopycnal diffusion is required to match the cfc data collected during the world ocean circulation experiment woce in the early 1990s using reduced outcrop saturations of 80 95 for isopycnals outcropping in the northwestern north pacific 25 4 kg m 3 together with an isopcynal interior diffusivity of 2000 m2 s 1 and enhanced diffusion 5000 m2 s 1 in the kuroshio extension region further improves the model data agreement along isopycnal diffusion is particularly important for isopycnals with shadow zones pool regions in the western subtropical north pacific that are isolated from direct advective ventilation the isopycnal mixing causes an estimated increase in cfc 12 inventories on these isopycnals compared to advection only ranging from 10 20 25 6 kg m 3 to 50 130 26 6 kg m 3 over the subtropics in 1993 this contribution has important consequences for subduction rate estimates derived from cfc inventories and for the location of the subsurface cfc maxima when tracer ages are derived from the modeled cfc distributions time evolving mixing biases become apparent that reflect the nonlinearities in the atmospheric cfc time histories comparison with model calculated ideal ages suggests that during the time of woce 1993 ventilation ages based on cfc 12 were biased young by as much as 16 24 years for pcfc 12 ages of 25 years underestimating ideal ages by as much as 40 50

comparison between four electrode arrays in delineating sedimentary layers of alluvial fan deposits in eastern iraq using a 2d imaging technique a resistivity survey is performed in the northern badra area eastern iraq using a two dimensional 2d imaging technique the mean goal is to compare four electrode arrays dipole dipole wenner schlumberger schlumberger reciprocal and wenner to examine their resolution and ability in delineating the layers in complex sedimentary deposits six 2d imaging stations applied in the study area the first two stations 2ds1 and 2ds2 are selected to make the comparison the comparison results showed that wenner schlumberger s inverse models provide optimal results corresponding to the deep subsurface layers and they show the best resolution with depth compared to the other arrays therefore it is useful in determining the layers especially in areas with high inhomogeneity and also with the long survey line the wenner array presents a high sensitivity to high background noise and or a long survey line its inverse model is incapable of recognizing the layers in 2ds1 but it gives good images when the noise level becomes small and or a shorter long survey line is used however its resolution is still less than that of the wenner schlumberger array the schlumberger reciprocal array successfully delineates the layers but its inverse models do not show optimal matching with the lithology sections of the boreholes bh1 and bh2 the dipole dipole array is incapable of determining the underlying layers due to the decrease in its vertical resolution when there is an increase in depth and or noise contamination however it is suitable to use in very shallow investigations no more 30 40 m depth and needs high quality data measurements

thermal modeling of the chugach metamorphic complex heating from hot young subducting oceanic lithosphere and from a subducting spreading center has been proposed to explain the metamorphism and associated plutonism observed in former accretionary prism sedimentary rocks in the gulf of alaska we evaluated the thermal effects on the overlying accretionary wedge by heat conduction from a hot young subducting slab through numerical modeling the temperature limiting parameter in the modeling is the age of the subducted crust the rate of convergence angle of subduction amount of radiogenic heating and values of thermal conductivity are of secondary importance in determining temperatures in the accretionary prism a possible former setting for the subduction of young oceanic crust is recorded in the valdez metasedimentary rocks in the chugach metamorphic complex of the chugach terrane in southern alaska petrologic data indicate that rocks now at the surface were at 10 km depth when they were metamorphosed under greenschist facies conditions 350 400 c and subsequently intruded by felsic plutons using parameter values appropriate for chugach terrane rocks our results indicate that for accretionary prisms less than 20 km thick oceanic lithosphere aged 1 0 ma or less must be subducted in order to obtain temperatures greater than 300 c at 10 km depth within the prism we also modeled the transient heating of the accretionary prism due to the cessation of subduction of young oceanic lithosphere recent seismic refraction surveys from the trans alaska crustal transect have been interpreted to show underplated sedimentary rocks and relict oceanic crust beneath the chugach mountains transient heating due to cessation of subduction or underplating of hot oceanic crust does not appreciably relax the requirement of subducting oceanic crust aged 1 0 ma or less in order to attain temperatures greater than 30o c at 10 km depth however at depths greater than 25 km it may provide the heat necessary to generate hot fluids and felsic magma which can augment the temperatures at shallow depths by advection of heat as well as produce the postmetamorphism or synmetamorphism emplacement of the anatectically derived plutons observed in the chugach mountains our modeling requires subduction of such young crust that subduction of a spreading ridge was probable although underplating of extremely young oceanic crust would also have provided sufficient heat to cause the formation of the chugach metamorphic complex

contribution of magnetic resonance soundings for characterizing water storage in the unsaturated zone of karst aquifers understanding the role of the unsaturated zone in aquifer recharge and contaminant attenuation processes is a major challenge for the protection and management of karstic water resources we present the potential of the magnetic resonance soundings mrs geophysical method for characterizing the vadose zone of karst aquifers composed of epikarst and infiltration layers to investigate the hydraulic functioning of the durzon karst system located on the larzac plateau southern france we used the mrs method at 16 sites the mrs results have been compared with available geologic information and to core water content measurements the remarkable spatial variability of the mrs response observed in the study area makes it possible to determine ranges of water storage properties in relation to the lithology of the investigated carbonate formations dolomite marly and siliceous limestone all soundings found either constant or increasing mrs water content with depth which demonstrates that the infiltration zone might be the major water storage entity for permanent water storage with important consequences for recharge quality and quantity these results show the feasibility and potential of the mrs method for the characterization of the karst unsaturated zone and for understanding the vertical distribution of water content which impacts the overall functioning of karst systems read more http library seg org doi 10 1190 geo2015 0411 1

a global merged land air sea surface temperature reconstruction based on historical observations 1880 1997 abstract a merged land air sea surface temperature reconstruction analysis is developed for monthly anomalies the reconstruction is global and spatially complete reconstructed anomalies damp toward zero in regions with insufficient sampling error estimates account for the damping associated with sparse sampling and also for bias uncertainty in both the land and sea observations averages of the reconstruction are similar to simple averages of the unanalyzed data for most of the analysis period for the nineteenth century when sampling is most sparse and the error estimates are largest the differences between the averaged reconstruction and the simple averages are largest sampling is always sparse poleward of 60 latitude and historic reconstructions for the polar regions should be used with caution

a comparison of time domain electromagnetic and surface nuclear magnetic resonance sounding for subsurface water on mars 1 the time domain electromagnetic tdem method has enjoyed wide success in terrestrial groundwater exploration and the contrast in electrical conductivity between dry overburden and groundwater containing even a small amount of dissolved solids on mars will yield a robust response however moist clays or even ores e g massive hematite will also be electrically conductive and could be mistaken for aquifers on mars if proper geologic context is lacking surface nuclear magnetic resonance snmr is the only noninvasive geophysical method that responds nearly uniquely to water as the measured emf is proportional to the proton precession frequency which in turn is proportional to the planet s static magnetic field snmr signals are comparatively weak using small systems of several kilograms and several watts the exploration depth of snmr is one to two orders of magnitude smaller than tdem the latter can detect water to depths up to a few kilometers whereas the former is limited to depths of a few tens of meters there is no improvement in snmr signal to noise with increasing static field where penetration is controlled by aquifer salinity skin depth as reasonable integration times cannot substantially increase the exploration depth much larger transmitter current or loop mass either requiring system masses of tens to hundreds of kilograms are the only way to implement snmr for exploration to depths of at least hundreds of meters in spite of some ambiguity in target identification tdem is recommended for the first generation of in situ active source em measurements for groundwater on mars

internal structure and conditions of permafrost mounds at umiujaq in nunavik canada inferred from field investigation and electrical resistivity tomography a systematic approach was used for the interpretation of the electrical resistivity tomography carried out on two permafrost mounds at umiujaq in nunavik canada to assess their internal structure and conditions prior information under the form of a geocryologic model of the permafrost mounds was integrated in the inversion of the pseudo section of apparent electrical resistivity the geocryologic model was developed from the synthesis of previous field investigations including shallow and deep sampling temperature and electrical resistivity logging and cone penetration tests performed in the permafrost mounds values of electrical resistivity were ascribed to the different layers making of the geocryologic model to define a synthetic resistivity model of the permafrost mounds used as a reference model to constrain the inversion the constrained resistivity model clearly show the presence of ice rich cores in the permafrost mounds underscored by high resistivity values in excess of 30 000 m while t

the opening of the andaman sea where is the short term displacement being taken up the short term spreading velocity in the andaman sea a marginal basin inboard of the western sunda arc is calculated using the strain rate tensor which in turn is obtained from summing seismic moment tensors of normal faulting earthquakes a velocity of displacement is also obtained for the right lateral sagaing fault which is the northern continuation of the andaman spreading system using earthquakes in a 22 year period 1964 1986 the maximum spreading velocity in the andaman sea is found to be oriented in a n 19 w direction with a speed of 0 05 cm yr the north south relative velocity along the sagaing fault is 0 5 cm yr for strike slip earthquakes between 1971 and 1992 historical earthquakes in the andaman sea do not significantly add to the short term spreading velocity because there are no earthquakes with ms 6 0 for the sagaing fault however when moment tensors from earthquakes since 1908 are used the relative velocity is 5 7 cm yr a figure close to the 3 72 cm yr long term 13 ma rate of opening of the andaman sea these results suggest that strain due to the opening of the andaman sea is seismic along the sagaing fault and aseismic along the andaman sea spreading system probably because the spreading centers and transform faults in the andaman sea are short and cannot accomodate large earthquakes

hydrogeological interpretation and potential of the new magnetic resonance sounding mrs method abstract this study reviews the up to date hydrogeological contribution of the new geophysical magnetic resonance sounding mrs method and presents new interpretation ideas and potential regarding various hydrogeological applications the main advantage of the mrs method as compared to other geophysical methods is in its water selectivity mrs is commercially available but is also the subject of r d to minimize a number of limitations related not only to data acquisition but also to hydrogeological data interpretation the two main mrs output data types are free water content mrs and decay time constant t d relations between mrs and effective porosity specific yield and specific storage are discussed in the framework of an original groundwater storage concept t d is correlated empirically with hydraulic conductivity however such correlation is not yet quantified for various rock types so t d has to be calibrated by borehole data as an improvement of the data interpretation a proposal of a new multi decay approach is presented the advantage of such analysis is that it combines storage and flow property characteristics in assessing water content at various pore size fractions and the disadvantage is that it is applicable only at large signal to noise ratios five case examples are used to show that combined interpretation of mrs and t d can be used to evaluate subsurface hydrostratigraphy although such analysis is vulnerable to equivalence error and its resolution decreases with depth mrs with large volume averaging schema and current limitation to 1d approach is already suitable for groundwater modelling applications and for evaluation of groundwater potential in the mrs measurement scale 100 100 m 2 but is not yet optimized for well siting mrs can detect water in the unsaturated zone which can be potentially used in real time subsurface flux monitoring field experiments indicate that mrs is not appropriate for groundwater salinity detection no field experiments have yet been made to detect hydrogenated compounds like hydrocarbons and tracers in the subsurface