on the resource evaluation of marine gas hydrate deposits using sea floor transient electric dipole dipole methods methane hydrates are solid nonstoichiometric mixtures of water and the gas methane they occur worldwide in sediment beneath the sea floor and estimates of the total mass available there exceed 1016kg since each volume of hydrate can yield up to 164 volumes of gas offshore methane hydrate is recognized as a very important natural energy resource the depth extent and stability of the hydrate zone is governed by the phase diagram for mixtures of methane and hydrate and determined by ambient pressures and temperatures in sea depths greater than about 300 m the pressure is high enough and the temperature low enough for hydrate to occur at the seafloor the fraction of hydrate in the sediment usually increases with increasing depth the base of the hydrate zone is a phase boundary between solid hydrate and free gas and water its depth is determined principally by the value of the geothermal gradient it stands out on seismic sections as a bright reflection the diffuse upper boundary is not as well mar

biogenic silica record of the lake baikal response to climatic forcing during the brunhes abstract this work presents a detailed orbitally tuned biogenic silica record of continental paleoclimate change during the brunhes chron the brunhes matuyama boundary lies within the warm isotopic stage 19 in baikal and the boundaries between eight lithological cycles correspond to terminations in the marine oxygen isotope record the high amplitude and resolution of climatically driven changes in biosi content in lake baikal sediments permits tuning of almost every precessional cycle during the brunhes and reveals the structure of interglacial stages for example the last three interglacial stages mis 5 7 and 9 clearly consist of five substages a b c d e corresponding to precessional insolation peaks abrupt and intense regional glaciations in siberia during substages 5d and 7d were driven by extreme insolation minima during substage 9d cooling was more gradual in response to more moderate forcing the impact of strong glaciation is also observed in the middle of stage 15 where full glacial conditions appear to have lasted for over 30 000 yr during substages 15d 15c and 15b marine oxygen isotopic stage 11 appears to be the warmest period during the brunhes in the lake baikal record with at least three substages a new hypothesis is presented regarding the response of the lake baikal biosi record to insolation forcing based on the mechanism controlling modern diatom blooms biogenic silica production is hypothesized to be dependent on changes in the heat balance of the lake and consequently on changes in the thermal structure of the water column this mechanism is also sensitive to short term sub milankovich cooling events such as the mid eemian cooling the montaigu event during substage 5c and a cooling which appears to be analogous to the montaigu event during substage 9c the continuity of the lake baikal paleoclimate record its sensitivity to orbital forcing and its high resolution make it an excellent candidate for a new paleoclimatic stratotype section for continental asia

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

growth and destruction of gran canaria deduced from seismic reflection and bathymetric data the morphology and structure of the submarine flanks of gran canaria have been mapped using hydrosweep swath bathymetry and high resolution reflection seismic data the growth and destruction of the island has been characterized previously by three major periods of volcanic activity 16 9 ma 4 5 3 5 ma younger than 3 ma separatedby erosional intervals two major sector collapses along the west coast inferred from the coastal morphology are believed to have formed at the end of the shield building phase one is characterized by a 19 km wide reentrant along the northwestern coast that may have formed synchronously with the formation of the 20 km diametermiocene tejeda caldera high sedimentation rates around gran canaria 50 m myr tend to cover and bury major landslide blocks ssw off the island several canyons continue seaward into a major sediment fan a 9 5 km wide volcaniclastic ridge in this fan is interpreted to represent deposits of the pliocene subaerial roque nublo debris avalanche we tentatively interpret the slope break at a depth of 600 800 m as the transition between subaerial and subaqueous chilled lavas at the end of the shield building phase the subsidence caused by the volcanic load 30 000 km3 on the lithosphere may thus amount to no more than 800 m several canyons on the island can be traced down the submarine flanks to a depth of 3 5 km indicating that at least deeper portions below the level of subsidence were eroded by mass flows continuing seaward from the subaerial canyons four submarine volcanoes were identified west and northeast of the island

controlled source electromagnetic imaging on the nuggets 1 reservoir the marine controlled source electromagnetic csem sounding method is rapidly gaining acceptance as an exploration tool for detecting and delineating hydrocarbon reservoirs whereas seismic surveys can detect the structures that may contain hydrocarbons with great accuracy distinguishing hydrocarbon fluids from water within these structures is more problematic as a result less than a third of exploration wells result in a commercial discovery

internal structure of the western flank of the cumbre vieja volcano la palma canary islands from land magnetotelluric imaging 1 large scale mass wasting is a natural part of the evolution of volcanic islands where deformation and indications of flank instability such as large scale faulting and seismic and aseismic slip are common the cumbre vieja volcano on the island of la palma canary islands provides an ideal setting to address fundamental questions about the structure evolution and stability of island volcanoes the island of la palma is still in a shield building stage and it has been postulated that the western side of the island lies over a pre existing zone of weakness that can nucleate ruptures we undertook an audiomagnetotelluric amt survey over the proposed unstable western flank to try to image structures that may be associated with the zone of weakness the magnetotelluric method mt is a geophysical technique used to map the presence of fluids or image important structural contrasts the goals of this study were 1 to delineate the unstable flank 2 to map the structures underneath and 3 to determine the presence and geometry of fluids the results show a 1 km thick top resistive layer overlaying an area of reduced resistivity enhanced conductivity interpreted as a layer consisting of an alteration zone and also fluids our results confirm previous studies that suggested the existence of a western flank lying over collapse debris material and hyaloclastites and also they allow us to map part of the subaerial southern extent of the cumbre nueva units that lie beneath the more recent cumbre vieja rocks in addition dimensionality analysis maps the rotation of the dike emplacement off ridge along the western flank in an en echelon fashion

electromagnetic active source sounding near the east pacific rise an active source electrical conductivity sounding was carried out near the east pacific rise at 21 n the average electrical conductivity from 2 km beneath the seafloor into the upper mantle was found to be about 0 004 s m there is no evidence of fully molten magma at a distance of 7 km from the spreading axis the inferred conductivity with depth of the crustal rock is consistent with brace s model of connected seawater filled pores in rocks heated from beneath

boat towed radio magnetotelluric and controlled source audio magnetotelluric study to resolve fracture zones at aspo hard rock laboratory site sweden boat towed radio magnetotelluric rmt measurements using signals between 14 and 250 khz have attracted increasing attention in the near surface applications for shallow water and archipelago areas

dating of the upper pleistocene holocene volcanic activity of la palma using the unspiked k ar technique abstract combined unspiked k ar dating and detailed mapping have established the eruptive chronology of the cumbre vieja volcano in the canary islands the cv volcano is a large polygenetic volcano subaerial area 220 km2 subaerial volume 125 km3 elevation above sea level 2000 m which rests on the southern flank of the older taburiente cumbre nueva volcano we defined two stratigraphic units by their relationship to the development of coastal cliffs developed around the cumbre vieja volcano a cliff forming series and a scree forming series which is draped over the cliffs and forms the coastal platforms at their bases k ar ages were measured from 20 samples from the two series there are no discrepancies between k ar ages and the stratigraphy the k ar ages of one flow compare well with 14 c determinations 14 c 3 2 0 1 ka k ar 4 2 ka the ages of the scree forming series range from 3 2 ka to 21 2 ka the cliff forming series ages range from 20 2 ka to 123 3 ka but as the base of the sequence is not exposed the growth of the cumbre vieja volcano must have begun substantially earlier the boundary between the two coincides with the low sea level stand in the last glacial maximum which we infer to have been a period of intense coastal erosion dated samples from the upper part of the taburiente cumbre nueva volcano range in age from 853 10 ka to 566 8 ka the age of the youngest taburiente cumbre nueva volcano sample provides an upper bound on the age of the subsequent cumbre nueva giant lateral collapse

time evolution of deformation using time series of differential interferograms application to la palma island canary islands differential interferometry is a very powerful tool for detecting changes in the earth s crust where coherence conditions are good but is difficult to employ in some volcanic areas due to dense vegetation we apply two differential insar methods using the time series associated with the interferograms to perform a phase analysis on a data set for la palma island canary islands from the ers 1 and ers 2 european space agency esa satellites for the time period 1992 to 2000 both methods involve choosing a master image from the database and creating a series of interferograms with respect to this image the coherent pixel time series cpts technique chooses pixels with good average coherence aligns the unwrapped interferograms with a stable area and then performs an inversion to calculate the linear velocity to quantify the deformation the coherent target modeling ctm method calculates the temporal coherence of each pixel to identify stable targets and then determines the best velocity for each pixel by using a linear fit that maximizes the temporal coherence using these two methods we have been able to detect deformation on la palma island that has been previously undetectable by conventional insar methods there is a roughly circular region on the southern part of the island that is actively deforming at 4 to 8 mm yr this region is located near the teneguia valcano the host of the last known eruption on la palma in 1971 a thorough investigation of the possible sources for this deformation revealed that it was most likely created by a subsurface thermal source

stratigraphy and paleogeography of the sartan glaciation in west siberia abstract the paleogeography of the last glaciation in west siberia is outlined on the basis of detailed chronostratigraphy evidence indicates an ice sheet with a centre on the kara sea shelf the existence of ice dammed lakes that drained through turgai pass to the aral sea and onward to the caspian and black seas and traces of lateglacial transgression discussion involves problems connected with the hypothesis of retarded deglaciation astakhov 1992 which disputes the existence of a sartan ice sheet ice dammed basins and traces of lateglacial transgression the terraced plains of silt and clay previously considered to have been deposited in proglacial lakes are re interpreted to have formed by loess deposition modified by thermokarsting topography which resembled glaciated terrain appears to have developed during the holocene through glaciokarsting rather than by glaciation it is suggested that the new model of sartan glaciation renders unjustifiable contentions of its universal significance

reproducibility of uav based earth topography reconstructions based on structure from motion algorithms combination of uav based aerial pictures and structure from motion sfm algorithm provides an efficient low cost and rapid framework for remote sensing and monitoring of dynamic natural environments this methodology is particularly suitable for repeated topographic surveys in remote or poorly accessible areas however temporal analysis of landform topography requires high accuracy of measurements and reproducibility of the methodology as differencing of digital surface models leads to error propagation in order to assess the repeatability of the sfm technique we surveyed a study area characterized by gentle topography with an uav platform equipped with a standard reflex camera and varied the focal length of the camera and location of georeferencing targets between flights comparison of different sfm derived topography datasets shows that precision of measurements is in the order of centimetres for identical replications which highlights the excellent performance of the sfm workflow all parameters being equal the precision is one order of magnitude higher for 3d topographic reconstructions involving independent sets of ground control points which results from the fact that the accuracy of the localisation of ground control points strongly propagates into final results 2015 elsevier b v

the ramesses experiment iii controlled source electromagnetic sounding of the reykjanes ridge at 57 45 n summary a controlled source electromagnetic sounding survey centred on an axial volcanic ridge avr segment of the reykjanes ridge at 57 45aen was performed as part of the ramesses experiment low frequency 0 35 11 hz electromagnetic signals were transmitted through the crust to an array of horizontal electric field recorders at the seafloor to ranges of 15 km from the source which was a 100 m long horizontal electric dipole towed at heights of 50 80 m from the seafloor coincident seismic and magnetotelluric studies were conducted during the rest of the ramesses experiment data were interpreted using a combination of 1 d forward modelling and inversion and iterative forward modelling in two dimensions on the axis of the avr the resistivity at the seafloor is 1 v m there is a steep resistivity gradient in the upper few hundred metres of the crust with the resistivity reaching approximately 10 v ma t a depth of 500 m in order to explain the low resistivities the upper layer of the crust must be heavily fractured and saturated with sea water the resistivity increases with distance from the axis as the porosity decreases with increasing crustal age the most intriguing feature in the data is the large diverence in amplitude between fields transmitted along and across the avr axis a significant zone of low resistivity material is required at approximately 2 km depth beneath the ridge crest in order to explain this diverence it is coincident with the low velocity zone required by the seismic data and has a total electrical conductance in excellent agreement with the results of the magnetotelluric study the low resistivity zone can be explained by the presence of a body of partially molten basalt in the crust taken together these results provide the first clear evidence for a crustal magma chamber at a slow spreading mid ocean ridge the data constrain the melt fraction within the body to be at least 20 per cent with a melt volume suycient to feed crustal accretion at this segment of the ridge for of the order of 20 000 years since this body would freeze in the order of 1500 years this finding lends support to the hypothesis that at slow spreading rates crustal accretion is a cyclic process accompanying periodic influxes of melt from the mantle to a crustal melt reservoir

electrical resistivity structure of the valu fa ridge lau basin from marine controlled source electromagnetic sounding summary in december 1995 we carried out a comprehensive controlled source electromagnetic survey of the valu fa ridge at 22u25k si n the lau basin the valu fa ridge is ab ack arc spreading centre of intermediate spreading rate and is a site of extensive hydrothermal activity seismic studies have imaged a melt lens at an average depth of 3 2 km below the seafloor surrounded by a zone of lowered seismic velocity interpreted as a region of partial melt in the crust the electromagnetic experiment was part of a multidisciplinary study which included wide angle and reflection seismics bathymetry and potential field measurements electromagnetic signals at frequencies between 0 25 and 40 hz were transmitted from a horizontal electric dipole towed close to the seafloor and were recorded by an array of 11 sea bottom receivers at ranges of up to 20 km from the source over 80 hr of data consisting of the magnitude of the horizontal electric field at the seafloor were collected these data have extremely low scatter compared to similar data from previous surveys the data were interpreted using a combination of 1 and 2 d forward modelling and inversion the vertical resistivity gradient in the upper crust at the valu fa ridge is abnormally low with resistivities of less than 10 v m observed throughout layer 2 of the crust to a depth of 3 km this is significantly more conductive at depth than the axis of the slow spreading reykjanes ridge at 57u45kn and the fastspreading east pacific rise at 13un where similar data sets have been collected in the past although the structure of layer 2 is well constrained by the electromagnetic data its extremely low resistivity causes rapid attenuation of electromagnetic signals diffusing through it and hence the data are not sensitive to the structure in layer 3 in particular the structure of the melt lens or surrounding low velocity zone the seismic velocity structure of the valu fa ridge determined from the coincident wide angle seismic study is similar to that observed at other mid ocean ridges with a steep seismic velocity gradient through layer 2 although overall velocities are slightly lower the seismic velocity anomaly calculated relative to an average off axis structure is also small this suggests that the very low resistivities observed at the axis are not caused by an upper crust of abnormally high porosity however hot and or saline fluids permeating the crust can explain the low resistivities without affecting the seismic velocity since the conductive region extends unbroken from 3 km depth to the seafloor it is probable that these fluids circulate to or close to the magma chamber itself

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

three dimensional model of the feeder conduit of the 1983 eruption of mt etna volcano from ground deformation measurements a levelling network and a horizontal distance measuring network down mt etna s south flank were measured before during and after the 1983 eruption we analyse the large movements recorded using theoretical models of surface displacement to determine the shape and position of the feeder conduit that supplied magma to the eruption the results indicate that a dyke the top surface extending nearly horizontally connects the eruption site to a point near the southeast crater the top of the dyke lies at an altitude of 2400 m to 2500 m and dips between 75 and 90 to the west more tentative evidence indicates that the top of the active dyke dropped by about 150 m between the 25th and the 95th day of the eruption and that a small branching dyke 1 km long was emplaced to the east of the main dyke but did not attain the surface the implications of these observation are discussed

the russian component of an arctic ice sheet during the last glacial maximum abstract the extent of late weichselian glaciation in arctic russia remains a problem our model of 1995 1998 suggests a continuous and long lived ice sheet centered on the kara sea other reconstructions suggest a smaller and diachronous glaciation the vast majority of dates support the model of restricted glaciation we show that these dates are inconsistent with the geologic record of ice flow across the kara barents divide with second order glacial geology of kola peninsula and with evidence for glacial surges they are also inconsistent with late weichselian climate of the arctic with eurasian continental paleohydrology including meltwater drainage systems cataclysmic megafloods major transgressions of the caspian sea and with the entire paleogeographic context of northern eurasia we believe that due to impeded ventilation of the pleistocene arctic ocean these dates are often too old and that recycling and contamination of the samples would also contribute to the dating errors destructive impacts of late glacial ice sheet surges and megafloods upon the arctic glacial sequences would also aggravate the situation by ignoring the dates until these problems are addressed we find that the field evidence supports continuous glaciation of arctic russia at the lgm and that the resulting ice sheet was part of an arctic ice sheet that included an ice shelf in the arctic ocean and ice sheets in greenland and north america we present 3 d reconstructions of the arctic ice sheet and with an enlarged antarctic ice sheet we show that the ice volume is equivalent to an lgm sea level that was 130 135 m lower than at present the reconstructions depict the arctic ice sheet before and after massive thawing of the bed that allows partial gravitational collapse of the overlying ice with a minimal change in ice volume

quaternary glaciation in north western siberia new evidence and interpretation abstract the pleistocene history of north western siberia is hotly discussed by researchers as the extension and impact of ancient glaciers are subjected to major revision the representative object for this study is the siberian uval an upland at the right hand bank of the ob river the uval contains some stony debris and for a long time researchers considered it as a moraine of an ice sheet however the siberian uval represents a predominantly sandy 30 40 m river terrace its origin is associated with development of the river network ice floe drift tectonics and marine ingressions well developed paleosols in the terrace body add to the picture of the development the first paleosol was encountered at a depth of a few meters and two 14 c dates 25693 27748 cal bp soan 7550 and 34740 35440 cal bp beta 410187 confirm the soil formation as karga mis3 the second paleosol is in the center of undisturbed section of 30 40 m terrace and its 14 c dates 45 ka bp soan 7551 soan 7552 43 5 ka bp beta 410188 the warmer paleobotanical spectra obtained from it may suggest that the paleosol formed in the beginning of mis5 the stony debris either underlies or overlies the first paleosol and represents rare boulders and pebbles embedded in the top sandy part of the terrace the debris is a result of ice floe drift ancient glaciers developed only in the mountains surrounding northwestern siberia only and then the stony moraine material could be spread by river ice floe drift during the river floods and sea water ingressions extrapolations relying on the data obtained by study of modern glaciers in the mountains surrounding northwestern siberia as well of relics remained by ancient glaciers confirm this conclusion

geodetic and structural research in la palma canary islands spain 1992 2007 results we review the results of the geodetic and structural studies carried out on la palma island using geodetic and geophysical data during the period 1992 2007 insar and gps observation techniques were applied to study the existence of deformation on the island and gravity observations were carried out for structural studies gravity data were inverted using a nonlinear three dimensional gravity inversion approach to obtain the geometry of the anomalous bodies constructed in a random growth process with respect to an exponentially stratified background the main structural feature is a large central body under the caldera de taburiente with high density which was interpreted as the pliocene age uplifted seamount and a relatively dense intrusive plutonic complex magma body the cumbre vieja series is characterized by elongated minima distributed according to the rift structure insar results show a clear subsidence located on the teneguia volcano where the last eruption took place in 1971 a thermal source is the most probable origin for this deformation a gps network composed of 26 stations covering the total island surface was set up vertical displacements determined comparing the gps coordinates obtained in 2007 with coordinates determined in 1994 are consistent with the insar results obtained in the southern part of the island this is not the case for the northern part from the comparison of 2006 and 2007 coordinates it is clear that more time is needed to obtain significant displacements but observed trends are also consistent with insar results all the observed significant displacements are in stations located outside of the large high density central body

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

ten years of marine csem for hydrocarbon exploration marine controlled source electromagnetic csem surveying has been in commercial use for predrill reservoir appraisalandhydrocarbonexplorationfor10 years althougha recent decrease has occurred in the number of surveys and publications associated with this technique the method has become firmly established as an important geophysical tool intheoffshoreenvironment thisisaconsequenceoftwoimportant aspects associated with the physics of the method first it is sensitive to high electrical resistivity which although not an unambiguous indicator of hydrocarbons is an important property of economically viable reservoirs second although the method lacks the resolution of seismic wave propagation it has a much better intrinsic resolution than potential field methods such as gravity and magnetic surveying which until now have been the primary nonseismicdatasetsusedinoffshoreexploration althoughbymany measures marine csem is still in its infancy the reliability and noise floors of the instrument systems have improved significantly over the last decade and interpretation methodology has progressed from simple anomaly detection to 3d anisotropic inversion of multicomponent data using some of theworld sfastestsupercomputers researchdirectionspresently include tackling the airwave problem in shallow water by applying time domain methodology continuous profiling tools and the use of csem for reservoir monitoring during production

landslide monitoring with high resolution tilt measurements at the dollendorfer hardt landslide germany abstract to continuously monitor ground movement at the dollendorfer hardt landslide in konigswinter bonn germany a borehole and a platform tiltmeter both with a resolution of 0 1 rad were installed the station is complemented with two pressure transducers to control pore pressure and four thermistors installed at different depths precipitation data is from frankenforst manor about 2 km away the data shows clear correlation between tilt pressure and precipitation as well as daily temperature induced tilt oscillations to decompose the tilt signal we first differentiated the series three times with respect to time to separate the trend we then expanded the remaining signal into a fourier series that was truncated to cutoff signal corresponding to shorter periods than 10 days this way we separate the seasonal variation from the shorter period residual component the trend is predominantly linear amounting to a 1000 rad down slope tilt per year the residual is characterized by rainfall events we attempt to describe the tilt response to rain by a linear system with precipitation data as input and tilt signal as output the analysis shows that this model qualitatively explains several features of the tilt signal but there is also a dependence of the tilt signal on pore pressure and temperature the study shows that a continuous high resolution monitoring of slope deformation allows decomposition into different processes and is thus a reasonable basis to verify theoretical models

marine controlled source electromagnetic of the scarborough gas field part 3 multicomponent 2d magnetotelluric controlled source electromagnetic inversionsmulticomponent inversion

magma supply and storage at kilauea volcano hawaii 1956 1983 abstract shallow crustal magma reservoirs beneath the summit of kilauea volcano and within its rift zones are linked in such a way that the magma supply to each can be estimated from the rate of ground deformation at the volcano s summit our model builds on the well documented pattern of summit inflation as magma accumulates in a shallow summit reservoir followed by deflation as magma is discharged to the surface or into the rift zones magma supply to the summit reservoir is thus proportional to summit uplift and supply to the rift zones is proportional to summit subsidence the average proportionality constant is 0 33 10 6 m 3 rad this model yields minimum supply estimates because it does not account for magma which escapes detection by moving passively through the summit reservoir or directly into the rift zones calculations suggest that magma was supplied to kilauea during july 1956 april 1983 at a minimum average rate of 7 2 10 6 m3 month roughly 35 of the net supply was extruded the rest remains stored within the volcano s east rift zone 55 and southwest rift zone 10 periods of relatively rapid supply were associated with the large kapoho eruption in 1960 and the sustained mauna ulu eruptions in 1969 1971 and 1972 1974 bursts of harmonic tremor from the mantle beneath kilauea were also unusually energetic during 1968 1975 suggesting a close link between kilauea s deep magma supply region and shallow storage reservoirs it remains unclear whether pulses in magma supply from depth give rise to corresponding increases in shallow supply or if instead unloading of a delicately balanced magma transport system during large eruptions or intrusions triggers more rapid ascent from a relatively constant mantle source

remote reservoir resistivity mapping a method for surface estimation of reservoir properties wherein location of and average earth resistivities above below and horizontally adjacent to the subsurface geologic formation are first determined using geological and geophysical data in the vicinity of the subsurface geologic formation then dimensions and probing frequency for an electromagnetic source are determined to substantially maximize transmitted vertical and horizontal electric currents at the subsurface geologic formation using the location and the average earth resistivities next the electromagnetic source is activated at or near surface approximately centered above the subsurface geologic formation and a plurality of components of electromagnetic response is measured with a receiver array geometrical and electrical parameter constraints are determined using the geological and geophysical data finally the electromagnetic response is processed using the geometrical and electrical parameter constraints to produce inverted vertical and horizontal resistivity depth images optionally the inverted resistivity depth images may be combined with the geological and geophysical data to estimate the reservoir fluid and shaliness properties

bathymetric effects and corrections in marine csem data the effect of seafloor topographic variations on controlled source electromagnetic csem responses is investigated using a finite difference modeling approach for both petroleum and gas hydrate exploration scenarios in a deepwater reservoir model distortions in the inline electric field responses are mainly due to galvanic effects particularly at long transmitter receiver tx rx offsets and are characterized by persistent short wavelength anomalies at all tx rx offsets in the amplitude profiles in a shallow water reservoir model the contribution of inductive effects to bathymetric distortions is large at short tx rx offsets compared to the deepwater case whereas at long offsets the distortion pattern is mainly determined by the source receiver geometry relative to the sea surface because of the airwave effect rather than by the resistivity variations associated with the seafloor topography a simple correction technique which is an extension of the topographic correction procedure for magnetotelluric data is effective in removing the bathymetric distortions for the deep marine case but cannot be used for the shallow water case because of the airwave effect for a gas hydrate exploration model it is shown that the bathymetric response can be large enough to mask the target response because higher frequencies and shorter offsets need to be used to detect the shallow targets however the modeling study suggests that the shallow target response can be separated from the bathymetric distortions using the correction method

shallow flank deformation at cumbre vieja volcano canary islands implications on the stability of steep sided volcano flanks at oceanic islands abstract volcano flank instability has been recognized at many volcanoes around the globe structural morphological geodetic and geophysical evidence supports the continuous deformation of their flanks while identification of instability has been recognized in well documented examples until recently the initial stages of such processes have been difficult to capture using a combination of geological geodetic and geophysical data analysis we study the stability of the cumbre vieja new descending radar interferometric data covering a volcanologically quiet period between 1992 and 2008 at cumbre vieja indicate movement away from the satellite on the western volcano flank using an inversion of stacked velocity maps we determine the geometry and slip for a near horizontal dislocation beneath the western flank of cumbre vieja our ground deformation modelling results position and depth are in agreement with a low density anomaly constrained by gravity data the previously undetected intereruptive ground deformation at cumbre vieja volcano flanks was explained as an indicator of a kinematic passive response model of the flank where the flanks were mobilized only during periods of magmatic activity shallow dike intrusions and remained stable and undeformed during intereruptive periods here we present new results indicating that active creeping stress release due to gravitational loading is also a dominant deformation mechanism for current intereruptive periods at cumbre vieja which would contribute positively to the stabilization of the edifice and reduce the associated hazard related to the volcano flank dynamics this study at cumbre vieja can be considered as a prototype for similar volcanoes around the macaronesian islands group e g fogo teide el hierro pico and elsewhere

the assessment of marine gas hydrates through electrical remote sounding hydrate without a bsr marine gas hydrates prevalent in offshore sediments in canada and japan are a possible hydrocarbon resource a hazard to drilling and a source of a major greenhouse gas quantitative estimates of hydrate concentrations in deep sea sediment are difficult to obtain by conventional methods we have sought novel techniques specifically designed for assessment such as transient electric dipole dipole electromagnetics the latter method is based on the assumption of a reduced electrical conductivity in hydrate rich zones field trails of new apparatus on the cascadia margin have proven successful excellent data were collected and analysed using a differential phase method to reduce systematic error apparent resistivities collected on three lines demonstrate that the resistivity of the seafloor is remarkably uniform over the whole survey area the average hydrate concentration deduced with the aid of a reference model based on the electrical logs of odp holes 888 and 889 is about 17 26 of pore space 9 13 of sediment volume in the 100 m interval above the bsr the values are consistent with those obtained by other analyses further the presence of hydrate is predicted in a region to the east of 889b where there is no visible bsr

the november 2002 eruption at piton de la fournaise volcano la reunion island ground deformation seismicity and pit crater collapse an eruption on the eastern flank of piton de la fournaise volcano started on 16 november 2002 after 10 months of quiescence after a relatively constant level of activity during the first 13 days of the eruption lava discharge volcanic tremor and seismicity increased from 29 november to 3 december lava effusion suddenly ceased on 3 december while shallow earthquakes beneath the dolomieu summit crater were still recorded at a rate of about one per minute this unusual activity continued and increased in intensity over the next three weeks ending with the formation of a pit crater within dolomieu based on ground deformation measured by rapid static and continuous gps and an extensometer seismic data and lava effusion patterns the eruptive period is divided into five stages 1 slow summit inflation and sporadic seismicity 2 rapid summit inflation and a short seismic crisis 3 rapid flank inflation onset of summit deflation sporadic seismicity accompanied by stable effusion 4 flank inflation coupled with summit deflation intense seismicity and increased lava effusion and finally 5 little deflation intense shallow seismicity and the end of lava effusion we propose a model in which the pre intrusive inflation of stage 1 in the months preceding the eruption was caused by a magma body located near sea level the magma reservoir was the source of an intrusion rising under the summit during stage 2 in stage 3 the magma ponded at a shallow level in the edifice while the lateral injection of a radial dike reached the surface on the eastern flank of the basaltic volcano causing lava effusion pressure decrease in the magmatic plumbing system followed resulting in upward migration of a collapse front forming a subterranean column of debris by faulting and stoping this caused intense shallow seismicity increase in discharge of lava and volcanic tremor at the lateral vent in stage 4 and eventually the formation of a pit crater in stage 5

remote sensing of hydrocarbon layers by seabed logging sbl results from a cruise offshore angola detecting and assessing hydrocarbon reservoirs without the need to drill test wells is of major importance to the petroleum industry seismic methods have traditionally been used in this context but the results can be ambiguous another approach is to use electromagnetic sounding methods that exploit the resistivity differences between a reservoir containing highly resistive hydrocarbons and one saturated with conductive saline fluids modeling presented by eidesmo et al 2002 demonstrates that by using seabed logging sbl a special application of frequency domain controlled source electromagnetic csem sounding the existence or otherwise of hydrocarbon bearing layers can be determined and their lateral extent and boundaries can be quantified such information provides valuable complementary constraints on reservoir geometry and characteristics obtained by seismic surveying

an overview of geodetic volcano research in the canary islands the canary islands are mostly characterized by diffuse and scattered volcanism affecting a large area with only one active stratovolcano the teide pico viejo complex tenerife more than 2 million people live and work in the 7 447 km2 of the archipelago resulting in an average population density three times greater than the rest of spain this fact together with the growth of exposure during the past 40 years increases volcanic risk with respect previous eruptions as witnessed during the recent 2011 2012 el hierro submarine eruption therefore in addition to purely scientific reasons there are economic and population security reasons for developing and maintaining an efficient volcano monitoring system in this scenario geodetic monitoring represents an important part of the monitoring system we describe volcano geodetic monitoring research carried out in the canary islands and the results obtained we consider for each epoch the two main existing constraints the level of volcanic activity in the archipelago and the limitations of the techniques available at the time theoretical and observational aspects are considered as well as the implications for operational volcano surveillance current challenges of and future perspectives in geodetic volcano monitoring in the canaries are also presented

glacial history and palaeo environmental change of southern taimyr peninsula arctic russia during the middle and late pleistocene abstract we here reconstruct a glacial and climate history of arctic nw siberia for the last 600 000 years based on the stratigraphy and chronology of 35 studied river sections on the southern taimyr peninsula from this stratigraphic mosaic we have identified four glacial events marked by tills glaciotectonics which are intercalated with mainly marine sediments deposited in proglacial settings during transitions from glacial conditions into subsequent interglacials interstadials the traces of early shelf based kara sea ice sheet ksis glaciations in marine isotope stages mis 12 14 and 8 are sparsely preserved but these ice advances are suggested to have terminated far south into the central siberian uplands as also was the case with the younger taz glaciation mis 6 the inception phase of the latter glaciation was complex with ice advancing into a proglacial marine basin both from the south putorana anabar uplands and the north the deglaciation leading into the karginsky interglacial mis 5e was marked by the development of the southernmost ice marginal zones imzs on the taimyr lowlands the urdakh and sampesa imzs the most recent late pleistocene glacial cycle is recorded by three successively smaller ksis advances from the kara sea shelf onto taimyr of which only the first during early zyryanka mis 5d reached south of the byrranga mountains with its maximum extent marked by the jangoda syntabul severokokorsky imz retreat of the ice margin during mis 5c b was accompanied by deposition of glaciomarine sediment in the proglacial basin and deposition of large successions of delta sediments in the foothills of the byrranga mountains reaching 100 m above present sea level the region north of the byrranga mountains was subjected to two subsequent ksis glaciations during mis 4 and mis 2 while the area south of the byrranga mountains transitioned to a terrestrial environment from the middle into the lower zyryanka as evidenced by deposition of fluvial aeolian and ice complex yedoma sediments

controlled electromagnetic sources for measuring electrical conductivity beneath the oceans 1 forward problem and model study exact closed form expressions for the electromagnetic induction fields produced by vertical and horizontal current sources in the conducting ocean overlying a one dimensional earth are derived from the maxwell equations numerical methods for the evaluation of the solutions are given including correction for the finite size of real sources simple models of the electrical conductivity structure of the ocean crust and lithosphere are deduced from geologic petrologic and laboratory data and their electromagnetic response is modeled horizontal electric dipole sources produce much larger field amplitudes than their vertical counterparts for a given frequency and range and the horizontal electric field offers superior received signal performance reflections of electromagnetic waves from the sea surface and thermocline must be considered for low enough frequencies or long ranges estimates of the ambient noise level from natural electromagnetic sources in the frequency range 0 01 10 hz are presented the ability of controlled sources to determine features of the conductivity of the ocean crust and upper mantle especially low conductivity zones is demonstrated if the mantle conductivity is low enough horizontal ranges of 50 km and conductivity estimates to over 20 km depth can be achieved

geodetic analysis of dike intrusion and motion of the magma reservoir beneath the summit of kilauea volcano hawaii 1970 1985 we use leveling and trilateration data collected on kilauea volcano to constrain the location of deformation sources caused by magma accumulation intrusion and eruption for the 13 inflationary epochs examined combinations of an expanding point source and one or two opening rectangular dislocations mimic inflation of the summit reservoir and formation of dike s respectively the combined model adequately accounts for the deformation data and is consistent with the seismicity observed during each epoch for 10 deflationary epochs however the data require only a contracting point source confidence in these results is gained by noting that locations of the sources of both inflation and deflation are coincident within the observed uncertainties of the data the function of network geometry and the inversion procedure it appears therefore that magma accumulation at kilauea volcano may be characterized by the growth of dikes during inflation of the summit reservoir drainage of the reservoir on the other hand is not accompanied by significant closure of dikes in contrast to previous studies e g fiske and kinoshita 1969 dvorak et al 1983 that do not include the dislocation or dike growth component of summit magma accumulation and concluded that the source of inflation migrates over a 5 km2 area we find that a single magmatic reservoir source accounts for data collected during all inflationary and deflationary epochs results which compare favorably with those obtained from the point ellipsoid model can be used to estimate the distribution of stresses within the volcano in the near field of the source

process oriented use of geostatistics to analyse creeping para glacial features complex para glacial systems may show signs of destabilization leading to frequent and potentially hazardous debris flows understanding creeping permafrost displacement over a period of time is therefore crucial for hazard management and risks assessment this paper presents our methodology for estimating creeping permafrost displacement based upon data derived from various survey methods and demonstrates its relevance on the glacier bonnard system in southern switzerland geostatistical processing allowed estimation of the displacement intensity over the area of interest as well as assessment of the interpolation quality although the local measurement network needs to be refined the results largely improve the understanding of the bonnard para glacial system though highlighting the need to locally refine the measurement network in the present case the destabilized front advances at 1 m a and the upstream creeping part at 0 4 m a variance analysis also provide objective thresholds that could be used to distinguish underlying physical processes copyright 2015 john wiley sons ltd

useful characteristics of shallow and deep marine csem responses inferred from 3d finite difference modeling hydrocarbon reservoirs can be mapped if sufficient resistivity contrastsexistbetweenthemandtheirconfininglayers butpractical problems remain in target discrimination in deep and shallowwaters especiallyinthepresenceofheterogeneousoverburden wehavedevelopedanefficient3dstaggered gridfinite difference controlled source electromagnetic csem modeling code that enables study of the physics underlying some practical problems we undertook a comparative analysis of reservoir detection in 2000 m and 300 m deep waters using the simulated electric and magnetic field responses of a simple 3d reservoir we examined the effect of two types of near surface heterogeneitymimickingdisconnectedgascloudsand orpatchygeochemicalalterationhalosonthe3dreservoirresponse wefoundthat small scale shallowheterogeneitiescausedistortionsthatarealmost independent of the source frequency these persist at all source receiver offsets in the electric amplitude response in deep and shallow waters and phase response in shallow water they decrease in magnitude with increasing offset in deepwater phase response large scale near surface heterogeneities distort the horizontal electric field response more significantly than the small scale ones but the near surface response gets smaller in amplitude as the offset increases the distortions in shallow water are much smaller in magnitude than those for the deepwater case so that the reservoir signatures still are visible on the responseprofiles thismightbeconsideredasapositivefeaturefor shallow water inline electric field exploration the magnetic field responses for the orthogonal direction provide diagnostic target signatures that are similar to the inline electric field responsesindeepwaterbutthataredifferentinshallowwater the magnetic responses are affected by the airwave in a different manner from the electric field suggesting that combined 3d electric and magnetic field analysis might be vital for handling theairwaveproblem

using csem to monitor production from a complex 3d gas reservoir a synthetic case study the marine controlled source electromagnetic csem method is most commonly used in targeted exploration or appraisal studies as a tool for detecting and delineating hydrocarbon reservoirs see for example constable and srnka 2007 whereas seismic surveys can detect the structures that may contain hydrocarbons with great accuracy distinguishing hydrocarbon fluids from water within these structures is more problematic originally developed in the late 1970s young and cox 1981 the csem method uses a high powered horizontal electric dipole hed to transmit a low frequency electromagnetic signal through the sea floor to an array of multicomponent electromagnetic receivers bulk electrical resistivity of the sea floor can be determined at scales of a few tens of meters to depths of several kilometers in many cases this resistivity is driven by the fluid content and saturation of subsurface formations

enhanced subsurface response for marine csem surveying one of the main challenges of using marine controlled source electromagnetic csem sounding for hydrocarbon detection has been a relatively low resolution and restricted depth penetration in addition the use of csem in shallow waters has been perceived as particularly difficult a new robust method for enhancing marine csem subsurface response is particularly useful in shallow waters the method is designed to reduce acquisition imprints and attenuate the dominant primary airwave contribution synthetic examples show that it is possible to detect thin deeply buried 3d resistive bodies in a shallow water environment with a complex resistivity structure the results highlight the importance of a sufficient signal to noise ratio

a numerical comparison of time and frequency domain marine electromagnetic methods for hydrocarbon exploration in shallow water in shallow water the frequency domain controlled source electromagnetic method is subject to airwave saturation that strongly limits the sensitivity to resistive hydrocarbon targets at depth it has been suggested that time domain csem may offer an improved sensitivity and resolution of these deep targets in the presence of the airwave in order to examine and test these claims this work presents a side by side investigation of both methods with a main focus on practical considerations and how these effect the resolution of a hydrocarbon reservoir synthetic noisy data for both time domain and frequency domain methods are simulated using a realistic frequency dependent noise model and frequency dependent scaling for representative source waveforms the synthetic data studied here include the frequency domain response from a compact broadband waveform the time domain step response from a low frequency square wave and the time domain impulse response obtained from pseudo random binary sequences these data are used in a systematic resolution study of each method as a function of water depth relative noise and stacking length the results indicate that the broadband frequency domain data have the best resolution for a given stacking time whereas the time domain data require prohibitively longer stacking times to achieve similar resolution

focused source electromagnetic survey versus standard csem 3d modeling in complex geometries a novel focused source electromagnetic fsem method focusestheemfieldintheverticaldirectiontoprovidedeepreadingresistivitydata fsemoffersbetterspatialresolution and greater depth of investigation than the conventional controlled source electromagnetic csem method for land and marine em surveys we have proven the high efficiency of fsem by analyzing 3d models of various complex geologic formations in the presence of seafloor bathymetry shallow resistive gas hydrate overburdens and secondary gas reservoirs formed above deeper oil reservoirs combining the powerofourfocusingtechniquewiththepowerofour3dnumerical modeling method we have developed exceptionally challenging test cases to conclude that fsem automatically cancels unwanted shallow effects and allows simple visual interpretationofdeepreservoirresponses inaddition fsem is insensitive to imperfections in the setup geometry we achievetheseadvantagesusingapropercombinationofmeasurementsacquiredinthereceiverexcitedbytransmitterssituated at different space points the method is promising in anisotropicformationsaswell

new geodetic monitoring system in the volcanic island of tenerife canaries spain combination of insar and gps techniques even though volcanic activity in tenerife is characterized by the fact that eruptions do not normally occur more than once in the same volcanic edifice geodetic monitoring has mainly focused on the las canadas caldera where a geodetic micronetwork and a levelling profile are located a sensitivity test of this geodetic network showed a clear need to extend it to cover the full island for volcano monitoring purposes this conclusion together with the detection of two unexpected movements on the island using insar that were beyond the scope of the traditional geodetic network prompted the authors to design and observe a gps network covering the whole of tenerife the network was monitored in august 2000 the results obtained were accurate to 1 cm and confirm the deformation in the pinar de chio zone but are not definitive enough to confirm the displacements detected to the south of the village of garachico furthermore new cases of possible subsidence have been detected in areas where insar could not be used to measure deformation due to low coherence future observations will be necessary for further validation and to study the time evolution of the displacements and supplementary research must be conducted to determine the possible causes in particular if they are connected with the water pumping operations performed on the island one important result is that a new geodetic monitoring system based on two complementary techniques insar and gps has been set up on tenerife island this is the first time that the whole surface of any of the volcanic canary islands has been covered with a single network this research has displayed the need for further similar studies in the canary islands at least on the islands which pose a greater risk of volcanic reactivation

trans dimensional bayesian inversion of controlled source electromagnetic data in the german north sea this paper presents the first controlled source electromagnetic survey carried out in the german north sea with a recently developed seafloor towed electrical dipole dipole system i e hydra ii controlled source electromagnetic data are measured processed and inverted in the time domain to estimate an electrical resistivity model of the sub seafloor the controlled source electromagnetic survey targeted a shallow phase reversed seismic reflector which potentially indicates free gas to compare the resistivity model to reflection seismic data and draw a combined interpretation we apply a trans dimensional bayesian inversion that estimates model parameters and uncertainties and samples probabilistically over the number of layers of the resistivity model the controlled source electromagnetic data errors show time varying correlations and we therefore apply a non toeplitz data covariance matrix in the inversion that is estimated from residual analysis the geological interpretation drawn from controlled source electromagnetic inversion results and borehole and reflection seismic data yield resistivities of 1 m at the seafloor which are typical for fine grained marine deposits whereas resistivities below 20 mbsf increase to 2 4 m and can be related to a transition from fine grained holocene age to unsorted coarse grained and compacted glacial sediments pleistocene age interface depths from controlled source electromagnetic inversion generally match the seismic reflector related to the contrast between the different depositional environments resistivities decrease again at greater depths to 1 m with a minimum resistivity at 300 mbsf where a seismic reflector that marks a major flooding surface of late miocene age correlates with an increased gamma ray count indicating an increased amount of fine grained sediments we suggest that the grain size may have a major impact on the electrical resistivity of the sediment with lower resistivities for fine grained sediments concerning the phase reversed seismic reflector that was targeted by the survey controlled source electromagnetic inversion results yield no indication for free gas below it as resistivities are generally elevated above the reflector we suggest that the elevated resistivities are caused by an overall decrease in porosity in the glacial sediments and that the seismic reflector could be caused by an impedance contrast at a thin low velocity layer controlled source electromagnetic interface depths near the reflector are quite uncertain and variable we conclude that the seismic interface cannot be resolved with the controlled source electromagnetic data but the thickness of the corresponding resistive layer follows the trend of the reflector that is inclined towards the west

integration of electromagnetic and seismic data to assess residual gas risk in the toe thrust belt of deepwater niger delta during the last couple of years drilling activities in the deepwater thrust belt play of nigeria figure 1 have shown mixed results with some wells finding pay but others coming across low saturation gas and or brine sands in this frontier exploration context shell nigeria e p co snepco has been particularly successful in a number of toe thrust prospects where the key risk is trap integrity related to both earlier thrust faults and later extensional faults

controlled source electromagnetic sounding in shallow water principles and applications the marine controlled source electromagnetic csem method is being applied to the problem of detecting and characterizing hydrocarbons in a variety of settings until recently its use was confined to deepwater water depths greater than approximately 300 m because of the interaction of signals with the atmosphere in shallower water depths the purpose of this study was to investigate using a simple 1d analytical analysis the physics of csem in shallow water this approach demonstrates that it is difficult to simply decouple signals that have interacted with the earth from those that have interacted with the air using either frequency domain or time domain methods stepping away from wavelike approaches which if applied without care can be misleading for the diffusive fields of csem we demonstrate an effective way to mitigate the effect of the air in shallow water surveys by decomposing the em signal into modes and using only the mode least affected by interaction with the atmosphere such decompos

a past giant lateral collapse and present day flank instability of fogo cape verde islands fogo island is a large and extremely steepsided oceanic island volcano in the cape verde archipelago it has a large ca 9 km across east facing summit collapse structure the monte amarelo collapse with a probable volume of at least 150 200 km3 for most of its history the monte amarelo volcano had a small but productive central vent complex and radial rift zones fed by laterally propagating dykes shortly before the collapse the latter were replaced by north south trending arrays of en echelon vertically propagating dykes since the monte amarelo collapse the scar has partly filled with a new volcano the cha das caldeiras volcano the summit cone of this volcano the pico do fogo is a very young feature but has been abandoned in the most recent phase of activity from the 18th century onwards the same period has also seen the abandonment of earlier radial rift zones with laterally propagating dykes and their replacement with en echelon arrays of vents fed by vertically propagating dykes these form an n s trending array within the older collapse structure and are associated with seaward displacement of the eastern flank of the volcano within the old collapse structure the most recent eruptions those of 1951 and 1995 appear to be associated with episodes of flank instability manifested in n s surface fissuring and east facing normal faults these recent structural changes in the volcano parallel those which took place in the monte amarelo volcano prior to its collapse

sensitivity and inversion of marine electromagnetic data in a vertically anisotropic stratified earth the controlled source electromagnetic csem and magnetotelluric method mt are two techniques that can be jointly used to explore the resistivity structure of the earth such methods have in recent years been applied in marine environments to the exploration and appraisal of hydrocarbons in many situations the electric properties of the earth are anisotropic with differences between resistivity in the vertical direction typically much higher than those in the horizontal direction in cases such as this the two modes of the time harmonic electromagnetic field are altered in different ways implying that the sensitivity to the earth resistivity may vary significantly from one particular resistivity component scalar horizontal or vertical to another depending on the measurement configuration range azimuth frequency or water depth in this paper we examine the sensitivity of the electromagnetic field to a vertically anisotropic earth for a typical set of configurations compare inversion results of synthetic data characterizing a vertically anisotropic earth obtained using the isotropic and anisotropic assumptions and show that correctly accounting for anisotropy can prevent artefacts in inversion results

on the electrical nature of the axial melt zone at 13 n on the east pacific rise the first controlled source electromagnetic experiment directly on a ridge with the potential to identify the presence of an axial melt body beneath a fast spreading center was conducted at 13on on the east pacific rise epr in 1989 transmission for 36 hours was achieved by a deep towed horizontal electric dipole source of moment 6000 am operating at frequencies between 1 4 and 8 hz signals from the source were recorded by seven seafloor electric field receivers positioned both along the ridge crest and 5 km to the east on 100 000 year old crust data above ambient noise levels were obtained at ranges of up to 10 kin the results of modeling observed electric field amplitudes reveal that resistivities in the uppermost crust are very low 1 tim indicating a heavily fractured high porosity surficial layer below this topmost layer the upper 2 km of crust is found to be moderately resistive 100 tim we find no evidence for a large conductive axial melt body with dimensions on the order of kilometers in the middle or upper crust if a partial melt body is present which is continuous along strike and which comprises a connected and therefore conductive melt texture it must be of very limited volumetric extent this picture is consistent with recently proposed models of a thin sill like melt lens with across strike dimensions of no more than 1 km and probably with smaller vertical extent the larger region below the sill characterized by low seismic velocities must contain at best a very small melt fraction distributed in isolated pockets providing further evidence that the epr at 13on is currently in a state of relative magmatic quiescence

glacial geomorphology and recent glacial recession of the harmukh range nw himalaya abstract a comprehensive description of the glaciation and glacial geomorphology of the harmukh range northwest himalaya is reported first time in this study the geomorphic system of the range is dominated by glaciation and provides an excellent opportunity to assess the glacial fluctuations from the late quaternary to the present using a time series of the satellite data from 1992 to 2018 the glacier area snout and equilibrium line altitude ela changes of the existing glaciers in the harmukh range were estimated the glacier cover has receded from 7 47 0 58 km2 in 1992 to 6 24 0 62 km2 in 2018 a deglaciation of 16 46 0 24 the glaciers showed an upward shift in ela from 47 m to 80 m during the last two and a half decade the observations revealed that other than the climatic factors the ela change and glacier recessions are influenced by the glacier size mean altitude and the aspect of the glaciers further the high resolution google earth images supplemented by field observations were used for mapping various glacial geomorphic landforms the nature of glacial grooves overdeepenings the height of the lateral moraine deposits and trimlines indicated appreciable thickness of the former glaciers the pattern of the glaciated valleys revealed that the area has predominantly experienced alpine type of glaciation with most of the glaciers centred on the harmukh peak based on the shape and the number of lateral moraine ridges present it is suggested that the area has witnessed three major glacial advances by tracing the outer limits of the glacial valleys moraine boulders and ice scoured terrain it was estimated that the glaciers in the range covered 629 km2 during the glacial maxima the presence of numerous rock glaciers and debris free cirque glaciers on the north eastern slopes of the range indicated a strong climatic and topographical control on the pattern situation and extent of glaciers however there is a need for detailed field based mapping of the glacial geomorphology and geochronological study in order to better understand the nature and extent of paleo glaciation the observed glacier recession and the past climatic variations in this hitherto understudied glaciated region of the kashmir himalaya

ground deformation monitoring of a potential landslide at la palma canary islands abstract the southern part of the island of la palma comprises a north south oriented volcano known as the cumbre vieja the steep gradient and high aspect ratio of the volcano coupled with the prospect of future episodes of magma intrusion highlight the potential for large scale lateral collapse of the volcano as recorded earlier in the history of la palma and elsewhere in the canary islands historic eruptions of the cumbre vieja have occurred high up on the western flank of the volcano and along a single rift zone along the crest of the volcano the geometry of the recent activity and faulting which occurred during an eruption in 1949 indicates that a discontinuity may be present beneath the western flank of the volcano along which a future collapse may occur to identify any displacement of the western flank overlying the discontinuity a ground deformation network has recently been established on the volcano the initial network spanned the fault system that developed on the upper flanks of the cumbre vieja during the 1949 eruption this small network was measured in 1994 1996 and 1997 using infrared electronic distance measurement in 1997 the network was enlarged and re occupied using the global positioning system to incorporate the west flank and the southern part of the island although the results show that apparent displacements recorded during this period are within the error margins of the techniques employed the apparent movement vectors do suggest a coherent westward displacement of stations to the west of the 1949 fault system additional occupations of the network over the next few years will however be required to determine the reality or otherwise of this apparent coherent movement and thus to decide whether or not the western flank of the cumbre vieja is currently sliding seaward if not it can be inferred that the volcano is stable during inter eruptive periods

vertical vertical controlled source electromagnetic instrumentation and acquisition abstract vertical vertical controlled source electromagnetic is an alternative to other techniques for providing three dimensional resistivity images of the subsurface it utilizes a large and powerful vertical dipole transmitter and arrays of e field receivers with vertical and horizontal dipole sensors the necessary instrumentation and acquisition procedures which differ strongly from other controlled source electromagnetic methods are described in the paper

glaciers in the polar urals russia were not much larger during the last global glacial maximum than today abstract 10 be exposure dates from boulders indicate that the chernov moraines located only 1 km beyond the chernov glacier in the polar urals russia were formed during the time of the last global glacial maximum lgm six samples from large boulders on the moraine yielded a mean age of 21 5 2 3 std error kyr the distinct semicircular usa moraine is located beyond the western flank of the urals boulders in the valley between the chernov and usa moraines yielded some spread in 10 be ages but four out of seven yielded ages 50 60 kyr we conclude that the usa and chernov moraines represent the maximum glacier extent during marine isotope stages mis 4 and 2 respectively the exceptionally small extent of the lgm glacier is explained with a dry lgm climate but also with the fact that present day cirque glaciers in the polar urals are extremely favoured by topographical factors such as leeward accumulation and shadowing mountain walls advantages which decrease when the glaciers grow

decomposition in upgoing and downgoing fields and inversion of marine csem data abstractwe describe a data driven method to estimate the top formation resistivity using marine controlled source electromagnetic data the procedure exploits the fact that the airwave contributions are traveling up or down with a poynting vector close to the vertical axis the proposed method is based on forming an impedance in the same way as it is done in magnetotelluric processing the top formation resistivity is used to perform up down decomposition of the electric field below the seabed this procedure suppresses the contribution from the airwave in the resulting upgoing electric field and increases the data sensitivity to the subsurface resistivity distribution the upgoing electric field is used in the misfit kernel for an inversion scheme this is a method that is intended for use in shallow water inversion using the upgoing electric field means that the observed electric and magnetic fields contribute to the data misfit the optimization procedure seeks to reduce the misfit between the observe

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

west siberian plain as a late glacial desert the paper presents results of morphoscopic studies of quartz grains recovered from sands underlying surficial peat over the west siberian plain the field materials were collected in the course of the russian american expedition in 1999 2001 the data obtained proved the existence of a vast area in west siberia similar to cold deserts in appearance at the late glacial time and probably even as early as the last glacial maximum 18 20 ka bp the desert was confined to the arctic and temperate belts the southernmost part of the plain being an area of loess accumulation

decomposition of electromagnetic fields into upgoing and downgoing components this paper gives a unified treatment of electromagnetic em field decomposition into upgoing and downgoing components forconductiveandnonconductivemedia wheretheelectromagneticdataaremeasuredonaplaneinwhichtheelectricpermittivity magneticpermeability andelectricalconductivityareknown constants with respect to space and time above and below the plane of measurement the medium can be arbitrarily inhomogeneousandanisotropic in particular the proposed decomposition theory applies to marine em low frequency data acquired for hydrocarbon mapping where the upgoing components of the recordedfield guided and refracted from the reservoir that are of interest for the interpretation the direct source field the refracted airwave induced by the source the reflected field from the sea surface and most magnetotelluric noise traveling downward just below the seabed are field components that are considered to be noise in electromagneticmeasurements the viability and validity of the decomposition method is demonstrated using modeled and real marine em data also termed seabed logging sbl data the synthetic data are simulated in a model that is fairly representative of the geologic area wheretherealsblwerecollected theresultsfromthesynthetic data study therefore are used to assist in the interpretation of the realdatafromanareawith320 mwaterdepthaboveaknowngas province offshore norway the effect of the airwave is seen clearly in measured data after field decomposition just below the seabed the upgoing component of the recorded electric field has almost linear phase indicating that most of the effect of the airwavecomponenthasbeenremoved

marine csem of the scarborough gas field part 2 2d inversion we explored the application of 2d inversion of marine controlled source electromagnetic and marine magnetotelluric data to image an ambiguous target the scarborough gas reservoir off the west coast of australia lies in close repose to a layer in the overburden of similar resistivity thickness product and also is not far above the resistive basement making it a difficult electric target we found that the standard 2d smooth inversion method yielded models that were unable to resolve this ambiguous structural configuration we solved this problem by developing a two step workflow in which we first invert for a coarse background resistivity model e g anisotropic layers then invert for the minimum deviation from this background using a much finer model discretization the main purpose of our two stage workflow is to inject the knowledge into the inversion that the subsurface is composed of self similar geologic domains though the resulting models did not resolve fine scale structural details they might still be used to map the overall extent and bulk qualities of a target in an otherwise confounding setting

structural results for la palma island using 3 d gravity inversion 1 a recent gravity survey composed of 317 bench marks all over the island of la palma canary islands is used in combination with satellite data for regional aspects to obtain results about structural properties of the island connected with the tectonic environment and local volcanism to that end a nonlinear three dimensional gravity inversion approach is considered the inversion scheme provides in a nonsubjective form the geometry of the anomalous bodies constructed in a random growth process results from the inversion can be interpreted in the framework of the geologic evolution of this ocean island volcano as a complex composite volcano with a large central body with high density corresponding to the older intrusive part of the basalt complex new unexpected features are enlightened such as large thermal anomalies in the upper mantle southward of la palma as well as fracture en echelon zones associable to a slow active process of dislocation related to the recent volcanism in the southern half of the island the results obtained for la palma as a test site testify to the usefulness of the developed gravity inversion methodology for structural studies on islands in general

evidence for a persistent uplifting of la palma canary islands inferred from morphological and radiometric data abstract the morpho structural evolution of la palma canary islands is characterized by vertical movements responsible for or favoring large landslides in its northern part conglomerate terraces nowadays topographically hanged and re incised by the present day barranco de las angustias reveal a recent ongoing uplift process lava flows covered by this geological unit have been sampled and dated by the k ar cassignol technique at a mean age of 507 11 ka the minimum rate of uplift inferred of about 0 4 mm yr is similar to the one deduced from the abnormal elevation of the early submarine series staudigel and schmincke j geophys res 89 1984 11195 11215 this indicates that the northern shield may have experienced a global rise fairly constant throughout most of its geological history it probably results from the combination of regional atlas tectonic processes and the existence of a swell at the island scale this global rise together with the existence of a north south fault in the basement may have controlled triggering of the sw flank collapse of the northern shield and the subsequent concentration of magma along a southern still active topographic ridge the cumbre vieja cv morphological asymmetry of this structure may result from the destabilization of its distal western part favored by strong injections at the axis tilting processes along lateral listric faults can then explain the existence of slope break ups especially on the western side of the ridge such tectonic processes are likely responsible for local superimposed uplifting contributing to the genesis and development of huge western coastal cliffs even in sub historic and historic times we show that unlike many oceanic islands la palma island has experienced important positive vertical movements rather than subsidence

mapping thin resistors and hydrocarbons with marine em methods insights from 1d modeling the use of marine controlled source electromagnetic em csem sounding to detect thin resistive layers at depths below the seafloor has been exploited recently to assess the resistivity of potential hydrocarbon reservoirs before drilling we examine the sensitivity of the csem method to such layers with forward and inverse modeling in one and three dimensions the 3d modeling demonstrates that if both source and receivers are over a tabular 3d target 1d modeling predicts the observed response to very high accuracy experimental design can thus be based on 1d analysis in which hundreds of range and frequency combinations can be computed to find the optimal survey parameters for a given target structure modeling in three dimensions shows that the vertical electric field response is largest over the edges of a 3d target the 3d modeling also suggests that a target body needs to have a diameter twice the burial depth to be reliably seen by csem sounding a simple air wave model energy propagating from source to receiver via the atmosphere allows the effects of the target layer and atmosphere to be separated and shows where sensitivity to the target is diminished or lost because of finite water depth as a function of range frequency and seafloor resistivity unlike dc resistivity sounding the marine csem method is not completely t equivalent and in principle can resolve resistivity and thickness separately smooth inversion provides an estimate of the method s resolving power and highlights the fact that although the radial csem fields contain most of the sensitivity to the thin resistive target inverted alone they produce only increasing resistivity with depth inclusion of the radial mode csem data forces the recovery of the thin resistor but magnetotelluric data can be used more effectively to achieve the same result

evolution of a bank failure along the river danube at dunaszekcső hungary the banks of the river danube are one of the most susceptible areas to mass wasting in hungary in 2007 a large slump began to develop along the danube at dunaszekcs and jeopardized properties on land and navigation in the river several factors such as geological hydrogeological and morphological conditions recurrent flooding and erosion by the danube led to a gradual development of the large rotational slide slope failure has been monitored using gps precise levelling techniques and tiltmeters since october 2007 the expected location of the maximum lateral displacement and extrusion was indicated by gps measurements from the middle of november 2007 the main phase of the slope failure evolution i e the rapid movement on 12 february 2008 was indicated by accelerated tilting of the southern moving block prior to slumping small rise of the relatively stable part of the slope was measured after the rapid movements which may be explained either by the elastic rebound along the slip surface or by the intrusion of some plastic material into the lower section of the slope comparison of geodetic datasets and field observations with the timing of rainfall and water level changes of the danube suggested that hydrological properties subsurface flow processes soil physical properties infiltration and perched water table were primarily responsible for initiation of the studied slump a model of slope failure evolution is proposed here based on the monitoring and field observations

surface deformation in volcanic rift zones abstract the principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes some of which feed fissure eruptions elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift if eruption occurs the characteristic ridge trough ridge displacement profile changes to a single ridge centered at the fissure and the erupted lava alters the local topography a well developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events to investigate this process we compute the elastic displacements and stresses in a homogeneous two dimensional half space driven by a pressurized crack that may breach the surface a derivative graphical method permits one to estimate the three geometric parameters of the dike height inclination and depth to center and the mechanical parameter driving pressure rock stiffness from a smoothly varying displacement profile direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation notably normal faulting creates discontinuities in the profile geological structures open cracks normal faults buckles and thrust faults form because of stresses induced by dike emplacement and fissure eruption theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation

discrete element simulations of gravitational volcanic deformation 1 deformation structures and geometries 1 we have carried out two dimensional particle dynamics simulations of granular piles subject to frictional coulomb failure criteria to gain a first order understanding of different modes of gravitational deformation within volcanoes under uniform basal and internal strength conditions granular piles grow self similarly developing distinctive stratigraphies morphologies and structures piles constructed upon cohesive substrates exhibit particle avalanching forming outward dipping strata and angle of repose slopes systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults and slip along a basal decollement landslide forms grade from shallow slumps to deep seated landslide and finally to axial subsidence and outward flank displacements or volcanic spreading surface slopes decrease and develop concave up morphologies with decreasing decollement strength depositional layers tilt progressively inward spatial variations in basal strength cause lateral transitions in pile structure stratigraphy and morphology this approximation of volcanoes as coulomb granular piles reproduces the richness of deformational structures and surface morphologies in many volcanic settings the gentle slopes of hawaiian volcanoes and olympus mons on mars suggest weak basal decollements that enable volcanic spreading high angle normal faults favored above weak decollements are interpreted in both settings and may explain catastrophic sector collapse in hawaii and broad aureole deposits surrounding olympus mons in contrast steeper slopes and shallow detachment faults predominate in the canary islands thought to lack a weak decollement favoring smaller more frequent slope failures than predicted for hawaii the numerical results provide a useful predictive tool for interpreting dynamic behavior and associated geologic hazards of active volcanoes

the last ice sheet of the kara sea terrestrial constraints on its age abstract the ice dispersal features on the siberian mainland unanimously indicate that the last ice domes were positioned on the kara sea shelf and adjacent coastal plains the age of the last glacial maximum evokes much controversy the problem may be solved by sorting out the available radiocarbon dates both statistically and using geological common sense over 200 finite radiocarbon dates have been analysed 77 of the entire population represent sediments overlying the topmost till including dating the most reliable organics such as mammoth remains the rest of the dates 23 have been obtained from the underlying sediments mostly on materials readily prone to redeposition and contamination such as driftwood and shells the last culmination of the shelf ice sheet must have occurred beyond the range of the conventional radiocarbon method and after the last warm water sea transgression correlative to the eemian the early weichselian age for the last kara sea ice sheet is also supported by the lack of proglacial lacustrine sediments with finite radiocarbon dates in periglacial west siberia