viscosity and finite strength of the mantle as determined from water and ice loads summary some recent examples of transient earth loads lake bonneville utah glacier bay alaska northeast greenland indicate that both the viscosity and finite strength of the mantle are lower than is commonly presumed a time constant 1 e of 4000 years is estimated for lake bonneville and of 1000 years for northeast greenland a strain rate of 10 14 is typical these figures imply viscosities in a homogeneous half space ranging from 1020 to 1021 poises an upper limit of finite strength is set by lake bonneville at a few times 106 dyn cm2 if mountain ranges like the sierra nevada or himalaya are regarded as dynamically supported rather than static systems this low value is not incompatible with other geologic observations

fluid flow and late diagenesis of fault infill carbonates in the aptian dolostones at jabel semmama kasserine area western central tunisia abstract in western central tunisia kasserine area dolomitization of jabel semmama aptian limestones of the serj formation fm led to the dolostones of the orbata fm these dolostones are cross cut by several generations of faulting and fracturing the current study focused on e w trending faults and fractures system incorporating carbonate infills and freshwater flows which have stimulated continental diagenetic processes the faulting fracturing and rock fluid interactions yielded nine fault infill diagenetic and tectonic sedimentary phases the purpose of studying the tectonic stresses and the nine phases was to elucidate their late impact on the aptian dolostone reservoir quality this enquiry was based on lithological tectonic microfacies and oxygen carbon o c isotopes investigations analyses of stable o c isotopes are performed on crushed and dedolomitized dolostones as well as on calcite cement laminae and spherulites c1 c2 the crushed and dedolomitized dolostones 18o and 13c data averages 4 0 v pdb 1 75 v pdb remain close to the moderately depleted results of the aptian replacive dolostone host rocks averages 3 6 v pdb 2 0 v pdb inversely calcite cement laminae and spherulites c1 c2 yielded strikingly depleted oxygen values 18o averages 7 77 v pdb 8 0 v pdb pointing out to freshwater controlled diagenesis the discrepancy between the two records 0 23 v pdb is ascribed to cooling during the precipitation of calcitic cement spherulites the divergence between the two depleted 13c values of the two cements c1 c2 averages 6 19 v pdb and 4 0 v pdb is attributed to climatic control wet dry alternations that controlled the micritization phenomenon the latter orchestered the release of ca12co3 being more mobile than ca13co3 this process is in agreement with the strong variation of fluid flow supplies vadose phreatic transcribed in the lithology as cement phases lamellar spherulites gelatinous vadose and granular the study series record two major climatic changes a wet period encompassing phases p1 p4 and a dry period extending on phases p5 p9 two short cool and wet episodes accompany this period the nine tectonic sedimentary and diagenetic phases occurred into two periods through the telogenetic stage uplift they started at the miocene pliocene during the atlasic foldings along e w faults and fractures phases p1 p6 and continued throughout the quaternary period villafranchian along a reactivation of the same direction phases p7 p9 we believe that the nine phases arose after the oae s organic matter maturity and thus had nearly no impact on any early oil migration while the earlier diagenesis phases remain the most useful for the reservoir quality

physical properties of the lithosphere asthenosphere system in europe abstract all the geophysical fields considered evidence a clear structural difference between the adriatic sea ionian sea basin on one side and the tyrrhenian sea western mediterranean basin on the other the former displays continental type characteristics while the latter shows features definitely related to young ocean basins lateral variations in the thickness of the high velocity sub crustal layer the lid are clearly evidenced in the whole european area the lateral changes in the shear wave velocities of the lithosphere asthenosphere system are quite pronounced gravity data imply a positive density contrast 0 03 0 07 g cm 3 in the upper mantle related to almost aseismic high velocity lithospheric roots which seem to characterize many orogenic belts the analysis of a transect along the longitudinal axis of the alps seems to indicate that relevant lateral variations in density are present in the lithospheric part of the mantle

physical structural and isotopic characteristics and growth processes of fast sea ice in lutzow holm bay antarctica a sea ice ocean study was conducted off queen maud land and enderby land antarctica from 1990 to 1991 by the japanese antarctic research expedition observations of multiyear land fast sea ice were made in lutzow holm bay over a period of 2 years to determine the snow and ice characteristics and ice growth processes the snow depth in the bay reached large values of 1 0 to 1 5 m during the winter season at offshore locations from the analysis of ice thickness measurements it is confirmed that the fast ice with deep snow cover grew little in winter but substantially thickened during the summer months on the basis of ice core structure salinity and stable isotopic composition we conclude that the summer growth was caused by upward growth at the top of the ice to which snow ice and superimposed ice formation contribute these processes were the primary contributors to sea ice growth and characteristics only where the snow accumulation was large in areas of low snow accumulation there was no surface growth superimposed ice formation on sea ice in antarctica has not been reported previously evidence for snow cover melting which is a prerequisite for superimposed ice formation was also found

three dimensional p wave velocity image under the carpathian arc abstract an inversion of p wave travel time residuals from selected earthquakes in the distance range 30 98 to two seismic station networks was used to model p wave velocity anomalies down to 250 km depth in the first inversion experiment a region between 43 5 47 5 n and 21 29 e was modelled using 35 seismic stations while in the second one a region between 44 47 n and 25 29 e was modelled using 19 seismic stations the 4 layer block model of the first inversion offers 19 reduction in residual variance while the 5 layer block model of the second one offers 26 reduction the rest being explained by noise and smaller scale heterogeneities the obtained velocity anomalies correlate remarkably well with the gravity anomalies and with the tectonic model for the vrancea region of fuchs et al 1979

thin crust and active upper mantle beneath the southern sierra nevada in the western united states abstract analysis of seismic refraction wide angle reflection travel time and seismic amplitude data collected during the 1993 southern sierra nevada continental dynamics sscd project resolves a small crustal root 40 42 km thick centered 80 km west of the sierran topographic crest the sscd experiment consisted of a west east profile across the sierra nevada at approximately 36 5 n and a north south profile extending the length of owens valley located eastward of the sierran topographic crest two dimensional finite difference travel time inversion of p g and p n arrivals resolves upper crustal velocities of 6 0 to 6 4 km s 1 within the sierran batholith and basin and range an upper crustal west dipping wedge of higher velocities 6 8 7 2 km s 1 consistent with ophiolitic material underlying the great valley sedimentary sequence and higher velocities in the lower crust beneath the basin and range 6 8 7 0 km s 1 than those beneath the sierran batholith 6 6 km s 1 low average p n velocities 7 6 7 9 km s 1 and a laminated transitional moho imaged beneath the sierran batholith also differ from the higher p n velocities 7 9 8 0 km s 1 and sharp first order moho observed beneath the basin and range the crust decreases in thickness both westward of the root to 28 34 km beneath the great valley and eastward to 35 km beneath the highest sierran topography and decreases further to 27 30 km beneath the basin and range crustal thickness also appears to increase southeast to northwest from 29 30 km beneath the garlock fault in the south to 38 40 km beneath the north end of chalfant valley juxtaposition of the crustal model with previous p wave tomography models of the south ernmost sierra nevada upper mantle reveal that the thickest sierran crust on the west east profile overlies a pronounced upper mantle high velocity anomaly 5 whereas the region of laminated moho overlies a flanking upper mantle low velocity region 3 the upper mantle velocity anomalies relatively low p n and relatively flat moho observed beneath the sierran crest suggest that the recent uplift of the sierra nevada is due to asthenospheric flow and or lithospheric thinning beneath the southeastern sierra nevada and basin and range

natural fractures in a united kingdom shale reservoir analog cleveland basin northeast england faults and fractures within the well exposed lower jurassic cleveland ironstone and whitby mudstone formations may provide insights into the tectonic history of gas prospective mississippian shale in northern england subvertical opening mode fractures occur throughout the cleveland basin bed parallel fractures some of which contain blocky calcite fills occur preferentially within well bedded clay rich mudstones of the cleveland ironstone and whitby mudstone formations at jet wyke and port mulgrave subvertical fractures display abutting or curving parallel relationships with under and overlying bed parallel fractures together these observations suggest that bed parallel fractures at times acted as free surfaces some bed parallel fractures curve toward and branch from calcite filled fault slip surfaces indicating that bed parallel fracturing and normal faulting were synchronous occurring within a regional stress field with vertical maximum principal stress this apparent paradox can be explained by normal compaction followed by cementation and coupling between pore pressure and minimum horizontal stress driven by poroelastic deformation or incipient slip along critically stressed normal faults causing elevation of horizontal stress in excess of the vertical stress within clay rich units propagation of bed parallel fractures was enhanced by dilatational strains adjacent to normal fault planes bed parallel fractures have not been observed within more rich units at the top of the whitby mudstone formation at whitby east cliff or within well bedded clay rich shale at saltwick nab this observation is consistent with the lack of normal faulting at saltwick nab and the whitby mudstone formation having been drained by structural and or stratigraphical juxtaposition against permeable middle jurassic sandstones at both these localities

the sea ice thickness distribution in the northwestern weddell sea we present new data on distribution of snow and sea ice thicknesses in the northwestern weddell sea the data were obtained through direct measurements along 19 profiles each approximately 100 m long on 17 different floes located between 54 46 w and 59 64 s the overall probability density functions pdfs for ice thicknesses reflect the complex mixture of first second and multi year ice to be expected in the outflowing branch of the weddell gyre further differentiation of the data reveals four distinct thickness classes which reflect differences in the formation and subsequent histories of the ice encountered these classes i iv represent strongly deformed first year ice less deformed first and second year ice and deformed second or multi year ice respectively each of the classes is characterized by a specific set of quantities related to ice texture and surface snow characteristics and by distinct pdfs for snow and ice thicknesses in addition geometric surface and bottom roughness characteristics differ significantly for each of the floe classes

joint sets that enhance production from middle and upper devonian gas shales of the appalachian basin the marine middle and upper devonian section of the appalachian basin includes several black shale units that carry two regional joint sets j1 and j2 sets as observed in outcrop core and borehole images these joints formed close to or at peak burial depth as natural hydraulic fractures induced by abnormal fluid pressures generated during thermal maturation of organic matter when present together earlier j1 joints are crosscut by later j2 joints in outcrops of black shale on the foreland northwest side of the appalachian basin the east northeast trending j1 set is more closely spaced than the northwest striking j2 set however j2 joints are far more pervasive throughout the exposed devonian marine clastic section on both sides of the basin by geological coincidence the j1 set is nearly parallel the maximum compressive normal stress of the contemporary tectonic stress field shmax because the contemporary tectonic stress field favors the propagation of hydraulic fracture completions to the east northeast fracture stimulation from vertical wells intersects and drains j2 joints horizontal drilling and subsequent stimulation benefit from both joint sets by drilling in the north northwest south southeast directions horizontal wells cross and drain j1 joints whenever present then staged hydraulic fracture stimulations if necessary run east northeast i e parallel to the j1 set under the influence of the contemporary tectonic stress field thereby crosscutting and draining j2 joints

a sequence stratigraphic interpretation of a mudstone dominated succession the lower jurassic cleveland ironstone formation uk microfacies analysis using optical and backscattered electron imagery has been undertaken on 37 samples from the cleveland ironstone formation staithes yorkshire uk four lithofacies were encountered clay rich mudstones silt rich mudstones sand rich mudstones and concretionary carbonates two types berthierine siderite rich ironstones and apatite rich concretionary horizons successive units were found to stack systematically into upward coarsening units on a small 0 1 1 0 m scale upward coarsening and upward fining packages were also found on a larger 1 0 3 0 m scale the small scale upward coarsening units are interpreted to be parasequences while the large scale upward fining and upward coarsening packages are interpreted to be retrogradational and progradational parasequence sets respectively the ironstones occur at the level where the stacking patterns change from being overall progradational to retrogradational while the apatite rich concretionary units occur at the level where the stacking patterns change from being retrogradational to progradational the concretionary carbonates are interpreted to have formed close to at major stratal surfaces the ironstones are interpreted to be either the correlative equivalent of sequence boundaries or part all of the forced regressive system tract while the apatite rich units are interpreted to have precipitated close to at maximum flooding surfaces condensed sections and or major transgressive surfaces

linking paleogene denudation and magmatic underplating beneath the british isles a simple flexural model is used to explore the relationship between magmatic underplating and denudation first we show how denudation can be calculated as a function of underplating the distribution and density of underplate are obviously important parameters in determining the wavelength and amplitude of denudation however the denudational pattern can be considerably modulated by the flexural rigidity of the lithosphere several other parameters also play a significant role for example we show how variations in pre existing bathymetry and in present day topography affect denudational calculations we have applied our simple algorithm to the problem of paleogene underplating beneath the british isles forward and inverse modelling of travel time data from a wide angle seismic experiment which traversed the british isles suggests that a large pod of high velocity material occurs at moho depths beneath the irish sea the shape and inferred density of this pod are used to calculate the amplitude and wavelength of denudation for different flexural rigidities we compare our predictions with the observed pattern of paleogene denudation and conclude that the bulk of the observed denudation can be accounted for by magmatic underplating associated in a general way with the iceland plume notwithstanding this agreement there is compelling evidence for additional mild uplift events especially during the neogene these mild events may reflect fluctuating dynamic topography associated with the iceland plume

seismic images of the deep structure of the san andreas fault system central coast ranges california three dimensional inversion of teleseimic p wave travel time residuals recorded at the u s geological survey central california array has resolved small scale approx tens of kilometers crustal and upper mantle heterogeneity down to depths of 90 km beneath the california coast ranges upper crustal lateral velocity variations of 8 correlate closely with surface geology lower than average velocities are associated with thick tertiary sedimentary fill and higher than average velocities with basement exposures lower crustal velocity heterogeneity of 4 appear to reflect crustal thickness variations a thinner crust is indicated southwest of the san andreas fault and northwest of san pablo bay a linear zone of low velocities 0 to 40 subparallel to the san andreas fault was resolved in the upper mantle the preferred interpretation is that the low velocities indicate a narrow upwarp of asthenosphere to unusually shallow depths approx 45 km beneath the coast ranges such an unusual upper mantle structure may have been produced by the northwestward migration along the california coast of a transiently unstable mendocino triple junction the inversion results also indicate the possibility of partial decoupling of the crust from the upper mantle

travel time residuals and three dimensional velocity structure of italy jeffreys bullen p and pkp travel time residuals observed at more than 50 seismic stations distributed along italy and surrounding areas in the time interval 1962 1979 indicate the complex velocity pattern of this region strong lateral velocity inhomogeneities and low velocity zones are required to explain the observed pattern of residuals in particular late arrivals of about 1 sec are observed in the apenninic mountain range requiring both greater crustal thickness and low velocity layers coherent with seismic refraction data and surface wave dispersion measurements the seismic stations located in the western and eastern alps indicate the presence of high velocities in the western alps the strong azimuthal variation of residuals and the high values of early arrivals have a close relationship to the ivrea body an intrusive crustal complex characterized by a velocity as high as 7 7 2 km sec a travel time inversion performed with theaki et al 1977 block model confirms the peculiar characteristics and the sharp variations in the lithosphere of the whole italian region with values of velocity perturbations between many adjacent blocks ranging in size from 50 to 100 km and independent from the earth parametrization chosen reaching values up to 10 in the lithospheric part and 5 in the asthenosphere 3 d inversion requires also high velocity along the tyrrhenian coastal margin equivalent to an uprise of major crustal and lithospheric discontinuities along this part of the italian peninsula moreover low velocity material must be present in the northern part of the adriatic foreland in the lithosphere asthenosphere system closely related to the stress and seismicity pattern and the lateral bending of the lithosphere in the same region

dynamics of the wind driven sea level variation around antarctica coastal sea level variation around antarctica is characterized by a coherent circumpolarly in phase fluctuation correlated with the antarctic oscillation aao this study addresses the dynamics of the winddriven sea level variation around antarctica a realistic barotropic numerical model reproduced well the observed sea level around antarctica from numerical model experiments the authors demonstrate that the forcing responsible for the coastal sea level is the wind stress at the coastal boundary both the dominant coherent signal and westward propagating signals are identified in the model and these signals are trapped over the shelf and slope around antarctica as a mechanism of these trapped signals the authors consider analytical solutions of the oceanic response to alongshore wind stress over the shelf and slope in the circumpolar domain in these solutions besides the shelf wave mode a wavenumber zero mode appears and characterizes the coastal dynamics around antarctica at periods from 10 to 200 days the coherent sea level can be explained quantitatively by the solution of this wavenumber zero mode with a 5 10 day damping time scale the spectral peaks of the westward propagating signals can be explained by the resonance of the shelf wave mode the wavenumber zero mode can respond to the wavenumber zero forcing at any frequency and the degree of response increases with decreasing frequency in addition the wavenumber zero component of wind stress corresponding to the aao variation is a dominant forcing therefore the coherent sea level variation around antarctica is preferably generated and becomes a dominant feature in the circumpolar domain particularly at lower frequencies

scattering of continental shelf waves at a discontinuity in shelf width abstract an analytical solution is presented for the scattering of a free shelf wave incident upon a discontinuity in shelf width in a barotropic ocean the discussion of solutions relying on backscattered free waves with large wavenumbers which may not exist in a realistically stratified ocean is avoided by considering only the range of parameters over which energy transmission is nearly 100 there is a substantial transfer of energy to modes other than that of the incident wave the mode most readily excited is that which has the cross shelf structure most closely coinciding with that of the incident wave the resultant presence of multiple modes produces a strong alongshelf modulation in flow intensity and phase progression downstream of the scattering region which may affect the interpretation of shelf wave observations a nondispersive long shelf wave pulse is shown to scatter into a train of pulses of differing mode number each propagating at its own flee wave speed

variation of upper layer dynamics during breakup of the seasonal ice cover in hudson bay the present study describes circulation and stratification changes associated with the melt and breakup of the seasonal ice cover in the coastal waters of southeast hudson day field work was carried out at a station located 25 km north of the great whale river buoyancy fluxes and dissipation rates were calculated as well as changes in potential energy surface velocity data were partitioned into frequency bands and complex demodulated throughout the sampling period most of the current energy was found to be in the semi diurnal tidal band after ice breakup however low frequency and inertial motions became relatively more important in response to direct wind forcing at the sea surface changes in amplitudes and phases of the major tidal constituents occurred and are related to the presence of the sea ice cover between early april and mid june semi diurnal current amplitude doubled while its phase shifted by 45 to 60 degrees in early june the ice cover was sufficiently dispersed to allow the surface turbulence to overcome the buoyancy flux and mix the upper water column

receiver function and geometric tomography along the monterey microplate to test slab delamination or lithospheric drip models of the isabella anomaly california abstract two hypotheses were tested for the origin of the isabella tomographic anomaly which has been interpreted as either a lithospheric drip jones et al 1994 ducea and saleeby 1998 or a remnant of the farallon plate possibly attached to the monterey microplate wang et al 2013 p wave receiver functions and travel time residuals based on teleseismic events recorded by 41 stations were used to construct simple geometric tomography models of the isabella anomaly and to test whether the monterey microplate or a similar fragment of the farallon slab can be connected with the location of the anomaly the travel time residual pattern was modeled with a slab geometry composed of a high velocity rectangular block and a lithospheric drip was modeled as a dipping cylindrical anomaly both gave statistically similar fits but the cylindrical block appears less well constrained than the rectangular block the top surface of the best fit rectangular block was located at 50 km below the great valley and dips 65 northeast toward the sierra nevada with 100 km thickness west of the isabella anomaly receiver function p to s converted phases from the top and bottom surfaces of the oceanic crust of the monterey microplate were modeled as late arriving negative positive dipole signals such dipoles are observed at times that place their origin at 10 km below the moho at the coast ranges these converted phases from the oceanic crust could also be traced from the coast ranges to the great valley where the top surface of the slab model is located the combined result of the receiver functions and a geometric tomography model is consistent with the fossil slab hypothesis which initiated as a flat subduction system that later went through a delamination process online material figures of receiver functions sorted by back azimuth and ray parameter at 31 stations

on upper mantle seismic heterogeneities beneath fennoscandia abstract three dimensional seismic mapping of the upper mantle beneath fennoscandia baltic shield using an ach type of inversion technique in combination with p wave travel time residual observations from the local seismograph network gave the following results the central parts of the baltic shield are characterized by relatively high seismic velocities down to approximately 300 km those parts of the shield most affected by the caledonide orogeny exhibit relatively low velocities particularly in the uppermost 100 km depth interval the lower part of the upper mantle 300 600 km does not exhibit pronounced seismic velocity anomalies and in this respect is in contrast to results from similar studies in regions subjected to neotectonic processes like parts of central and southeastern europe the seismic anomaly pattern in the presumed thickened lithosphere is in quantitative agreement with similar ones derived from surface wave dispersion analysis and inversion of electrical measurements the general orientation of these anomalies coincides with that of the glacial uplift

delineation of a low velocity body under the roosevelt hot springs geothermal area utah using teleseismic p wave data to assess the nature of the heat source associated with the roosevelt hot springs geothermal area we have investigated the p wave velocity structure of the crust and uppermost mantle in the vicinity of the mineral mountains southwest utah a region of late cenozoic rhyolitic and basaltic volcanic activity a roughly square 30 30 km array of 15 seismographs centered on the mountains was operated for a period of 46 days during which 72 teleseismic events were recorded with sufficient quality for calculation of p wave traveltime residuals relative residuals using the array average for each event as reference show a clear pattern of azimuthal variation of up to 0 3 sec this pattern implies the existence of a localized region of relatively low velocity material extending up from the upper mantle to depths of about 5 km under the mineral mountains a three dimensional 3 d inversion of the data confirms this conclusion and yields a model featuring a region of low velocity 5 to 7 percent less than

seasonal current variations observed in western hudson bay yearlong current meter data from western hudson bay show that the annual ice cover modifies the currents currents observed at three depths are dominated by barotropic semidiurnal tidal currents which reach amplitudes of 28 cm s 1 during the ice covered season the tidal currents and tidal heights observed inshore decrease and their arrival times are advanced monthly mean currents set predominantly to the south and east in accordance with the cyclonic circulation pattern of the bay mean current speeds are less than 4 cm s 1 and are made up of wind driven and density driven components their onshore offshore components vary in phase with the ice buildup and ice breakup seasons of the annual ice cover storm generated inertial currents are as strong as the tidal currents but rotate clockwise opposite to the tidal current direction they decrease with depth and are absent during the ice covered season inertial currents below the pycnocline lead those in the surface mixed layer by more than 180 simulating an upward phase velocity passing weather systems also generate 5 to 6 day periodic currents which slightly decrease but are coherent with depth they reach magnitudes of up to 25 cm s 1 and occur throughout the year regardless of the ice condition

18o concentrations in sea ice of the weddell sea antarctica we present data on ice texture salinity and delta o 18 obtained from identical sections of ice cores during the winter weddell sea project 1986 on rv polarstern from july through august 1986 in the longitude range between 5 degrees w and 7 degrees e we find no uniquely definable relationship between delta o 18 values and ice texture in a particular section however most of the snow ice as well as some sections of frazil ice ar found to have negative delta o 18 concentrations this is due to varying degrees of admixtures of meteoric ice snow and sea water during formation of snow ice in contrast to common assumptions our results seem to indicate that a snow cover contributes positively to sea ice growth rather than slowing down the overall growth rate based on a simple model we have estimated the contributions of meteoric ice mean of 3 3 and the combined meteoric ice sea water fraction a minimum of 7 6 to the total ice thickness for the majority of the sampled floes although this is only a moderate contribution to the overall mass balance in the absence of congelation growth it nevertheless enhances ice growth in general this hypothesis is dependently supported by our snow and ice thickness data wadhams and others 1987 which demonstrate that the depression of the snow ice interface below the water line i e a negative freeboard and the formation of snow ice is a common occurrence in the weddell sea therefore we hypothesize that the major part of the observed apparent increase in ice thickness between our inbound and outbound tracks of wwsp 86 may not be derived from regular thermodynamically driven congelation growth but rather from the snow ice component in floes of the weddell sea

development and properties of sea ice in the coastal regime of the southeastern weddell sea from october to december 1986 a program consisting of sea ice core analysis in combination with sea ice observations was carried out from the icebreaker r v polarstern as part of the winter weddell sea project the ship operated in the central and southeastern weddell sea with interests focusing on the ice shelf front between 70 s and 77 s where a system of coastal polynyas extended for several tens to hundreds of kilometers opened and maintained despite temperatures well below freezing by offshore wind forcing three wind controlled ice formation regimes may be distinguished 1 for wind speeds 10 m s the ice cover is heavily ridged and rafted 50 and formation of granular ice predominates of the total length of cores sampled in the coastal regime 32 consisted of columnar and 35 of granular ice in addition we observed two unique ice classes along the coast platelet ice formed through consolidation of underwater ice platelets underneath the solid ice cover contributed 11 to our core samples another 22 consisted of intermediate columnar granular ice which originates under the dynamic hydrographic conditions of the near ice shelf region

rayleigh wave phase velocities small scale convection and azimuthal anisotropy beneath southern california 1 we use rayleigh waves to invert for shear velocities in the upper mantle beneath southern california a one dimensional shear velocity model reveals a pronounced low velocity zone lvz from 90 to 210 km the pattern of velocity anomalies indicates that there is active small scale convection in the asthenosphere and that the dominant form of convection is three dimensional 3 d lithospheric drips and asthenospheric upwellings rather than 2 d sheets or slabs several of the features that we observe have been previously detected by body wave tomography these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern sierra nevada and walker lane region sinking lithosphere beneath the southern central valley upwelling beneath the salton trough and downwelling beneath the transverse ranges our new observations provide better constraints on the lateral and vertical extent of these anomalies in addition we detect two previously undetected features a high velocity anomaly beneath the northern peninsular range and a low velocity anomaly beneath the northeastern mojave block we also estimate the azimuthal anisotropy from rayleigh wave data the strength is 1 7 at periods shorter than 100 s and decreases to below 1 at longer periods the fast direction is nearly e w the anisotropic layer is more than 300 km thick the e w fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms pure shear in the lithosphere due to n s tectonic shortening and simple shear in sublithosphere mantle due to mantle flow

seasonal variations of the antarctic coastal ocean in the vicinity of lutzow holm bay during the period of 1990 1992 year round oceanographic observations were conducted in the vicinity of lutzow holm bay east antarctica it was found that the thickness of the winter water ww layer characterized by a cold fresh oxygen rich water exhibits its maximum in the austral fall typically 500 m and its minimum in the austral summer typically 350 400 m the associated density variation of the water column explains only about one third of the seasonal variations in sea level at the coast which suggests a large seasonal variation in barotropic coastal flow prominent freshening occurs in the ww layer during fall this appears to be caused by the accumulation of ww whose upper portion is freshened in the preceding summer these seasonal variations appear to occur every year we propose that the seasonal variation in the ww layer is mainly caused by the seasonal variation in the wind over the coastal ocean in fall the prevailing easterly wind intensifies which increases the ekman convergence of ww in the coastal ocean while in summer the opposite occurs

sea ice growth in ongul strait antarctica a two year study was conducted on the growth processes of sea ice in ongul strait antarctica routine measurements of snow depth and ice thickness were made and sea ice cores were collected to assess their structure temperature and salinity the snow depth varied from 0 to about 1 m in the winter months the growth rate is higher in bare ice regions than in snow covered regions however over the year the ice thickness itself is lower in the bare ice regions than in the snow covered regions sea ice in the snow covered regions increased in thickness in spring rather than in winter due to the formation of snow ice and by ice formation related to the melting of snow cover

upper mantle shear velocities beneath southern california determined from long period surface waves we used long period surface waves from teleseismic earthquakes recorded by the terrascope network to determine phase velocity dispersion of rayleigh waves up to periods of about 170 sec and of love waves up to about 150 sec this enabled us to investigate the upper mantle velocity structure beneath southern california to a depth of about 250 km ten and five earthquakes were used for rayleigh and love waves respectively the observed surface wave dispersion shows a clear love rayleigh wave discrepancy that cannot be accounted for by a simple isotropic velocity model with smooth variations of velocity with depth separate isotropic inversions for love and rayleigh wave data yield velocity models that show up to 10 anisotropy transverse isotropy however tests with synthetic love waves suggest that the relatively high love wave phase velocity could be at least partly due to interference of higher mode love waves with the fundamental mode even after this interference effect is removed about 4 anisotropy remains in the top 250 km of the mantle this anisotropy could be due to intrinsic anisotropy of olivine crystals or due to a laminated structure with alternating high and low velocity layers other possibilities include the following upper mantle heterogeneity in southern california such as the transverse range anomaly may affect love and rayleigh wave velocities differently so that it yields the apparent anisotropy higher mode love wave interference has a stronger effect than suggested by our numerical experiments using model 1066a if the high love wave velocity is due to causes other than anisotropy the rayleigh wave velocity model would represent the southern california upper mantle velocity structure the shear velocity in the upper mantle moho to 250 km of this structure is on average 3 to 4 slower than that of the tna model determined for western north america

natural fractures in the barnett shale and their importance for hydraulic fracture treatments gas production from the barnett shale relies on hydraulic fracture stimulation natural opening mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone knowledge of both the present day maximum horizontal stress which controls the direction of hydraulic fracture propagation and the geometry of the natural fracture system which we discuss here is therefore necessary for effective hydraulic fracture treatment design we characterized natural fractures in four barnett shale cores in terms of orientation size and sealing properties we measured a mechanical rock property the subcritical crack index which governs fracture pattern development natural fractures are common narrow 0 05 mm 0 002 in sealed with calcite and present in en echelon arrays individual fractures have high length width aspect ratios 1000 1 they are steep 75 and the dominant trend is west northwest other sets trend north south the narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability but the population may follow a power law size distribution where the largest fractures are open the subcritical crack index for the barnett shale is high indicating fracture clustering and we suggest that large open fractures exist in clusters spaced several hundred feet apart these fracture clusters may enhance permeability locally but they may be problematic for hydraulic fracture treatments the smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments because the maximum horizontal stress trends northeast southwest and is nearly normal to the dominant natural fractures reactivation widens the treatment zone along multiple strands

review of pore pressure prediction challenges in high temperature areas pore pressure prediction relies heavily on interpretation of seismic and well attributes such as velocity resistivity and density which capture porosity changes during shale compaction under vertical loading relationships such as eaton 1975 were developed in the gulf of mexico using a relatively simple lithological mix of geologically young sandstones and shale mudrocks at relatively low temperatures an alternative approach using data from the same region was more deterministic also with vertical stress e g hottman and johnson 1965 bowers 1995 another approach using mean stress developed by harrold et al 2000 used similar sand and shale sequences at relatively low temperatures from data in southeast asia basins all the above approaches can be shown to provide acceptable prediction of pore pressure in shale mudrocks in young rapidly deposited siliciclastic sequences such as the baram delta brunei tingay et al 2009 and along the west african margin swarbrick et al 2011 the re

three dimensional seismic structure beneath southwest japan the subducting philippine sea plate abstract a three dimensional seismic structure beneath southwest japan has been investigated in detail by applying an inversion method this analysis clearly reveals the present and possibly the past subduction of the philippine sea plate beneath southwest japan beneath the izu peninsula the philippine sea plate does not appear to subduct but collides against the continental asian plate here and its thickness appears thinnest at most about 30 km from the tokai to the shikoku regions the high velocity zone corresponds well to the zone of subcrustal earthquakes down to a depth of about 60 70 km indicating that the subduction of the present philippine sea plate does not reach below this depth here however a small high velocity portion appears at depths between 100 km and 150 km beneath a part of the kinki region and probably extends to the chugoku region where no corresponding seismic activities exist these high velocities might be an indication of the remnants of the past subduction of the philippine sea plate in the kyushu region the high velocity zone continues down to a depth of about 150 km or even to 200 km in the southern part corresponding to a steeply inclined seismic zone the philippine sea plate in this region appears to be thicker than in regions east of the kyushu palau ridge it was also found that there exist narrow low velocity zones intervening within the philippine sea plate where two aseismic ridges the kyushu palau and shichito iwojima ridges extend northwards and the nankai trough shows warping these low velocity zones give support to the buoyant subduction hypothesis it also appears that lateral heterogeneities existing within and around the subducting plate are closely related to the mode of rupture of large earthquakes occurring around there

palaeopressure reconstruction to explain observed natural hydraulic fractures in the cleveland basin abstract natural fractures observed within the lower jurassic shales of the cleveland basin show evidence that pore pressure must have exceeded the lithostatic pressure in order to initiate horizontal fractures observed in cliff sections other field localities do not show horizontal fracturing indicating lower pore pressures there deriving the burial history of the basin from outcrop vr and heat flow data gives values of sedimentation rates and periods of depositional hiatus which can be used to assess the porosity and pore pressure evolution within the shales this gives us our estimate of overpressure caused by disequilibrium compaction alone of 11 mpa not sufficient to initiate horizontal fractures however as the thermal information shows us that temperatures were in excess of 95 c secondary overpressure mechanisms such as clay diagenesis and hydrocarbon generation occurred contributing an extra 11 mpa of overpressure the remaining 8 5 mpa of overpressure required to initiate horizontal fractures was caused by fluid expansion due to hydrocarbon generation and tectonic compression related to alpine orogenic and atlantic opening events where horizontal fractures are not present within the lower jurassic shales overpressure was unable to build up as high due to proximity to the lateral draining of pressure within the dogger formation the palaeopressure reconstruction techniques used within this study give a quick assessment of the pressure history of a basin and help to identify shales which may currently have enhanced permeability due to naturally occurring hydraulic fractures

fresnel zone inversion for lateral heterogeneities in the earth we propose a different kind of seismic inversion from travel time or waveform inversion for lateral heterogeneities in the earth fresnel zone inversion amplitude and phase delay of data in several frequency ranges are inverted for model space around ray paths with a width corresponding to the considered frequency so that primary effect of finiteness of wavelength be included for vertically heterogeneous media frechet derivatives for inversion are obtained very efficiently using the paraxial ray approximation with nearly similar amounts of computation compared to travel time inversion as an example frechet derivatives are computed for a teleseismic observation system for a three dimensional structure in the lithosphere beneath an array of seismic stations even if the used frequency is around 2 hz the width of frechet derivatives cannot be neglected particularly near the bottom of the lithosphere sensitivity of model parameters to observations is moreover different in our approach from conventional travel time inversion it is zero along ray paths but large slightly away from them some model calculations show that travel time inversion particularly with models divided into very fine meshes or blocks might give misleading results an example of inversion for a simple camembert model in the event that travel time inversion gives no reliable results shows how this technique works with much smaller data sets and computation than waveform inversions

the ice thickness distribution across the atlantic sector of the antarctic ocean in midwinter during the first leg of the winter weddell sea project antarktis v 2 cruise of f s polarstern the entire width of the antarctic sea ice zone was traversed in the vicinity of 0 longitude in the period july 18 to september 10 1986 ice thicknesses were measured by direct drilling and by helicopter profiling using an exstar 100 mhz impulse radar system in addition aerial photography of the ice cover was done from 100 to 2000 m altitude using a 70 mm aerial camera mounted in the helicopter the results of the point measurements drilling are reported in this paper together with an indication of how the radar and photography data will be used to extend them so as to yield area averaged ice thickness distributions it was found that the main ice type across the entire width of the ice cover was consolidated pancake ice occurring in vast floes this formed out of a 250 km wide band at the advancing ice edge which comprised a concentrated field of individual pancakes in a matrix of frazil ice preferred thicknesses of undeformed floes were 40 60 cm of ice covered with 5 15 cm of snow the individual pancakes attained almost all of this thickness before consolidation subsequent congelation growth was slow estimated at 0 4 cm d 1 the floes contained much small scale roughness on the upper and lower surfaces due to rafting of pancakes at the time of consolidation but pressure ridging was modest except in the far south a few very thick 8 11 m multiyear floes were observed embedded in the pack at latitudes beyond 66 s

fossil slabs attached to unsubducted fragments of the farallon plate as the pacific farallon spreading center approached north america the farallon plate fragmented into a number of small plates some of the microplate fragments ceased subducting before the spreading center reached the trench most tectonic models have assumed that the subducting oceanic slab detached from these microplates close to the trench but recent seismic tomography studies have revealed a high velocity anomaly beneath baja california that appears to be a fossil slab still attached to the guadalupe and magdalena microplates here using surface wave tomography we establish the lateral extent of this fossil slab and show that it is correlated with the distribution of high mg andesites thought to derive from partial melting of the subducted oceanic crust we also reinterpret the high seismic velocity anomaly beneath the southern central valley of california as another fossil slab extending to a depth of 200 km or more that is attached to the former monterey microplate the existence of these fossil slabs may force a reexamination of models of the tectonic evolution of western north america over the last 30 my

effect of landfast sea ice on coastal currents driven by the wind the present study examines the effects of landfast sea ice on the response of a homogeneous coastal ocean to wind forcings under the longwave approximation for a fluctuating wind continental shelf waves are induced by an infinite stress curl due to the existense of the ice edge as well as by the torque due to the topographic change the amplitude and sign of each shelf wave mode excited by the forcing depend strongly on the ice edge location the alongshore velocity field which can be represented as the sum of all the shelf wave modes has a maximum in amplitude at the ice edge with a strong lateral shear which is a result of the infinite stress curl the amplitudes of alongshore velocity and sea level near the coast are greatly reduced as the ice edge advances the response to a steady wind is also examined and it is found that even for the same wind the velocity distributions depend strongly on the ice edge location for instance the current direction near the coast is the same as that of the wind stress in the case of no fast ice whereas it is opposite in the case where the ice edge is located at the shelf break the present theory is applied to the continental shelf off enderby land antarctica and it gives the possible explanation for the observed features that the current variability its coherence with the wind and the prevailing current direction depend much on the extent of landfast sea ice

upper mantle heterogeneities beneath central europe summary an inversion of isc travel time data from selected earthquakes in the distance range 30 90 to 53 stations in central europe has been used to model velocity down to 600 km depth the model explains 0 1 0 2s of the residuals as for other array studies leaving 0 5 s unexplained as noise the uppermost 100 km of the mantle and crust contains inhomogeneities that correlate remarkably well with the geology this may be due to deep seated thermal anomalies or in some areas to delays introduced by passage of the rays through sedimentary cover the deeper anomalies are smaller and unrelated to those in the lithosphere which suggests that the asthenosphere is decoupled from the rigid lithosphere the structure at 600 km depth is again quite inhomogeneous and might be due to undulations of the 650 km discontinuity the models show some suggestion of a high velocity slab trending from east to west beneath the alps

low frequency currents and continental shelf waves in the southern weddell sea abstract the salient features of low frequency current fluctuations obtained from an analysis of eight current meter records from the continental shelf and slope of the southern weddell sea are compared to baroclinic and barotropic theories a simple baroclinic theory of internal waves is used successfully to predict high frequency spectral cutoff values from low frequency velocity ellipse calculations made from the continental slope mooring data the success of this theory indicates that the higher spectral energy levels observed over the slope compared to the shelf are probably due to baroclinic motions a barotropic model of free continental shelf waves probably by saint guily 1976 is adapted for the local topography and the predictions of the model compared to observations coherences and phases between moorings separated by 10 and 160 km in the along shelf direction provide substantial evidence of the existence of shelf waves as predicted by the theory for periods of 3 60 days and for the lowest

mechanical controls on horizontal stresses and fracture behaviour in layered rocks a numerical sensitivity analysis in layered materials the deformation style orientation confinement and 3d connectivity of natural fractures is generally impacted by changes in sedimentary facies and alternations in mechanical properties in this study we address this effect and perform a numerical sensitivity analysis mechanical properties confining pressures and interfacial frictions are varied for a three layered model to investigate and quantify the relation between contrasting material properties the principal horizontal stresses and fracture behaviour i e deformation style and orientation firstly the results show that tensile stresses develop in the stiffer layers due to the contrasting elastic parameters the magnitude of these stresses is dependent on the ratio between the elastic parameters of stiffer and softer layers i e estiff esoft and stiff soft there are no horizontal tensile stresses when applying a compressive horizontal confining pressure approx 1 5 of the applied vertical stress implementing an interfacial friction lower than 0 2 will result in decoupling of the layers resulting in slip on the layer boundaries and no tensile stresses within the stiffer layers further the acquired numerical results are in good agreement with previously conducted laboratory work finally we discuss whether the presented results can be used for better relating contrasting mechanical properties to potential fracture deformation styles and orientations in layered outcrops or subsurface reservoirs

coherent sea level response to the antarctic oscillation 1 large scale sea level variations around antarctica were studied and their relationship with atmospheric variations was investigated tide gauge data at five coastal stations were used coherent sea level variations were clearly detected for all stations on intraseasonal time scales the coherent variations had significant negative correlations with an index of the atmospheric annular mode variation antarctic oscillation coherence was significant for periods from 10 to 100 days with negligible time lag the negative correlation is consistent with the mechanism that a high low westerly anomaly leads to a stronger weaker northward ekman drift and causes divergence convergence around antarctica

thermal history reconstruction using apatite fission track analysis and vitrinite reflectance a case study from the uk east midlands and southern north sea apatite fission track analysis afta is a method of obtaining ther mal history information in sediments in sections that have been hotter in the past afta provides estimates of maximum palaeotemperatures and the time at which a sedimentary section began cooling from maximum palaeotempera tures it is useful for studying the thermal history of sequences containing source rocks and can provide information critical to the understanding of the timing of oil generation integration of afta and vitrinite reflectance vr data allows a coherent thermal history framework to be established and a formal method of analysing palaeogeothermal gradients has been developed by combining afta and vr data this approach allows definition of the major facets of thermal history based on directly measurable parameters rather than on assumed values of palaeo heatflow and provides rigorous estimates of the amount of uplift and erosion the case study demonstrates the application of this approach to the east midlands shelf region here afta data have revealed an episode of maximum palaeotemperatures prior to cooling commencing at around 60 ma combined afta and vr data show that this cooling was due to kilometre scale early ter tiary uplift and erosion under near normal geothermal gradients our estimates of uplift and erosion are significantly greater than those of pervious workers and show that uplift and erosion was not restricted to the recognized axes of inversion but was regional in extent this has implications for the evolution of source rock maturity in this region and in other basins in around the uk where afta has indicated early tertiary heating and where the extent and amount of tertiary uplift and erosion may have also been underestimated by previous workers apatite fission track analysis afta tm is a method of obtaining thermal history information in sediments and is particularly useful for studying the thermal history of sequences containing hydrocarbon source rocks as well as providing estimates of maximum palaeotemperatures afta provides a direct estimate of the time at which a sedimentary section began cooling from its maximum palaeotemperature a key advantage over traditional geochemical methods in many situations this knowledge is critical to the understanding of the timimg of oil generation and migration in relation to trap formation information on the timing of maximum palaeotempera ture can also be of significant value in the interpretation of vitrinite reflectance vr data and combination of afta and vr data allows a consistent integrated thermal history interpretation the afta technique is applied most usefully in sedimentary sections which have been hotter in the past than they are at the present day it is therefore applicable to large regions of britain and the uk continental shelf that have been subject to deeper burial in the past or affected by other sources of heating the basis of the technique has

three dimensional seismic inhomogeneities in the lithosphere and asthenosphere evidence for decoupling in the lithosphere and flow in the asthenosphere newly discovered three dimensional seismic velocity anomalies in the earth s lithosphere and asthenosphere are interpreted in terms of decoupling in the lithosphere and flow in the asthenosphere a rough estimate of flow in the asthenosphere under california was made using stokes law on the basis of the size of anomalies and density contrast estimated from the velocity contrast the result depends on the cause of velocity anomalies if they are due to any effect which obeys birch s law the flow is as rapid as that of morgan s 1972 plume driving the plate motion on the other hand if they are due to partial melts in thin cracks or at grain boundaries the flow is negligible in accordance with elsasser s 1971 model of plate tectonics driven quietly by the ridge push and slab pull in which the asthenosphere under the base of the plate is only passively dragged the result of cockerham and ellsworth 1979 1980 that the low velocity zone in the mantle under central california appeared to have preserved the shape of the downgoing slab for up to 10 m y supports elsasser s rather than morgan s model the shapes of low velocity bodies found by iyer and his colleagues under several geothermal areas in the western united states may be interpreted in terms of decoupling between the upper brittle lithosphere and the ductile substratum the misalignment of the axis of the low velocity column from the center of the granite outcrop in the roosevelt hot springs area utah and the inclined low velocity column under the geysers clear lake region california indicate a decoupled lithosphere in these areas whereas the upright column found under yellowstone national park suggests an intact lithosphere there

development of sea ice in the weddell sea we report on the development and physical properties of sea ice in the central and eastern weddell sea the investigations were part of the winter weddell sea project 1986 which extended over the months of july through december major elements of the glaciological part of this study included continuous shipborne observations of sea ice conditions and occasional helicopter reconnaissance flights extensive measurements of snow and ice thicknesses at daily ice stations and detailed analyses of sampled ice cores from each ice station textural investigations of the sampled ice revealed the dominance of frazil ice in the central weddell sea and the occurrence of an additional ice class called platelet ice together with the commonly known frazil and congelation ice in the coastal region of the eastern weddell sea these results in combination with the visual ice observations reveal two major mechanisms for sea ice generation in the antarctic which were not sufficiently well accounted for in previous investigations in the central weddell sea a cycle of pancake ice formation and its growth into consolidated floes seems to be the dominant process of the advancing sea ice edge in the coastal waters the growing sea ice cover consists to a considerable degree of ice platelets which are formed in the underlying water column in front of the ice shelf edges thus congelation ice growth which is mainly controlled by atmospheric thermodynamic forcing seems to be of less importance in the central and south eastern weddell sea than for example in the arctic basin

petroleum geochemistry of the kimmeridge clay of onshore southern and eastern england abstract the kimmeridge clay is considered a major oil source rock for the north sea hydrocarbon province the formation is also developed onshore in an organic rich mudstone facies this paper examines the possibility of onshore oil generation from the kimmeridge clay geochemically onshore basin margin sediments contain rich potential source horizons with mainly type l type ll oil prone kerogen but are immature some deeper cleveland basin sediments have reached marginal maturity burial history reconstruction suggests significant formation palaeoburial depths in central areas of the cleveland and wessex basins computed vitrinite isoreflectance contours show the wealden and isle of wight kimmeridge clay to be thermally mature basin modelling suggests an early palaeogene onset of oil generation in parts of the cleveland basin while maximum oil generation could have been reached by the formation base in the isle of wight area during the late cretaceous although basin subsidence ceased in the neogene in the weald and isle of wight where the formation is still deeply buried oil generation probably continued for some time during uplift thus significant quantities of oil could have been generated whether or not this oil is present today however would depend on the correct timing of suitable migration and trap structures

seasonal evolution of an ice shelf influenced fast ice regime derived from an autonomous thermistor chain ice shelves strongly interact with coastal antarctic sea ice and the associated ecosystem by creating conditions favorable to the formation of a sub ice platelet layer the close investigation of this phenomenon and its seasonal evolution remains a challenge due to logistical constraints and a lack of suitable methodology in this study we characterize the seasonal cycle of antarctic fast ice adjacent to the ekstrom ice shelf in the eastern weddell sea we used a thermistor chain with the additional ability to record the temperature response induced by cyclic heating of resistors embedded in the chain vertical sea ice temperature and heating profiles obtained daily between november 2012 and february 2014 were analyzed to determine sea ice and snow evolution and to calculate the basal energy budget the residual heat flux translated into an ice volume fraction in the platelet layer of 0 18 0 09 which we reproduced by a independent model simulation and agrees with earlier results manual drillings revealed an average annual platelet layer thickness increase of at least 4 m and an annual maximum thickness of 10 m beneath second year sea ice the oceanic contribution dominated the total sea ice production during the study effectively accounting for up to 70 of second year sea ice growth in summer an oceanic heat flux of 21 w m 2 led to a partial thinning of the platelet layer our results further show that the active heating method in contrast to the acoustic sounding approach is well suited to derive the fast ice mass balance in regions influenced by ocean ice shelf interaction as it allows subdiurnal monitoring of the platelet layer thickness

sea ice structure and biological activity in the antarctic marginal ice zone ice cores obtained during october november 1981 from weddell sea pack ice were analyzed for physical chemical and biological parameters frazil ice which is associated with dynamic turbulent conditions in the water column predominated 70 both floe thickness and salinity indicate ice which is less than 1 year old chemical analyses particularly with regard to the nutrients revealed a complex picture phosphate values are scattered relative to the dilution curve nitrate and silicate values are lower than expected from simple scaling with salinity and suggest diatom growth within the ice nitrite values are higher in the ice than in adjacent waters frazil ice formation which probably concentrates algal cells from the water column into ice floes results in higher initial chlorophyll a concentrations in the ice than in adjacent waters this mechanical concentration is further enhanced by subsequent reproduction within the ice ice core chlorophyll ranged from 0 09 to 3 8 mg m3 comparable to values previously reported for this area but significantly lower than values for antarctic coastal fast ice the dominance of frazil ice in the weddell is one of the major differences between this area and others consequently we believe that ice structural conditions significantly influence the biological communities in the ice

current variability under landfast sea ice in lutzow holm bay antarctica current measurements were made under landfast sea ice in lutzow holm bay antarctica in 1991 in spite of no direct wind forcing and negligible thermohaline forcing currents with a magnitude of 0 1 0 3 m s 1 were observed it is suggested that current variability strongly depends on the extent of the landfast ice on the eastward continental shelf before the fast ice edge extends to the shelf break the current at ongul strait located near the continental coast is highly coherent with the wind with a time lag of 1 1 5 days and somewhat coherent with the adjusted sea level with no time lag at periods of 6 8 days after the fast ice edge is stably located along the shelf break the current is not at all coherent with the wind or sea level we infer that the variability at periods of 6 8 days is mainly due to the first mode shelf wave excited by the wind stress over the eastward continental shelf the direction of the prevailing current at ongul strait changed drastically from southward the same direction of the wind to northward in may although the prevailing wind direction did not change this change in timing coincides with the rapid development period of the fast ice extent

upwarp of anomalous asthenosphere beneath the rio grande rift continental rifts are possible analogues of mid ocean ridges although major plate tectonic features are less clearly observed1 current thermal models of mid ocean ridges2 4 consist of solid lithospheric plates overlying the hotter less viscous asthenosphere with plate thickness increasing away from the ridge axis the lithospheric lower boundary lies at or near the melting point isotherm so that at greater depths higher temperatures account for lower viscosity lower seismic velocities and possibly partial melting upwarp of this boundary at the ridge axis concentrates heat there thus lowering densities by expansion and raising the sea floor to the level of thermal isostatic equilibrium at slow spreading ridges a major central graben forms owing to the mechanics of magma injection into the crust5 topography heat flow gravity and seismic studies support these models on the continents a low velocity channel has been observed although it is poorly developed beneath ancient cratons6 9 plate tectonic models have been applied to continental basins and margins10 12 but further similarities to the oceanic models remain elusive topographic uplift is often ascribed to airy type isostatic compensation caused by crustal thickening rather than thermal compensation in the asthenosphere here we discuss the rio grande rift in southwestern united states teleseismic p wave residuals show that regional uplift is explained by asthenosphere uplift rather than crustal thickening

mechanisms controlling rupture shape during subcritical growth of joints in layered rocks during joint propagation the orientation of plume lines on joint faces allows for mapping the path taken by the crack tip line during rupture growth rupture shapes in layered clastic sediments of the devonian catskill delta finger lakes district new york indicate joint growth through three stages where velocity of the tip line v tl varies as a function of the crack tip stress intensity k i the initial stage of growth is characterized by a rupture of approximately circular or elliptical shape that expands from an initiation fl aw with a velocity v tl in some cases primary growth involves self correction where an elliptical rupture redistributes the crack tip stress so that the rupture returns to a more stable circular shape the crack tip line eventually propagates to a bedding interface where properties of either a plastic or a noncohesive bedding interface cause v tl 0 along a portion of the tip line the onset of secondary growth occurs when the rupture tip line intersects both bedding interfaces and splits into two discontinuous segments that propagate synchronously as a single coherent rupture nonuniform nonsystematic v tl eventually interferes with the rupture s ability to grow coherently and thus leads to the transition to tertiary growth characterized by the detachment of the coherent rupture into one or more independently propagating noncoherent tip lines throughout all three stages of rupture growth the k i dependent v tl points to subcritical propagation variation from a smooth to rough plume morphology is consistent with propagation through region i of the subcritical regime with a transition at v tl 10 5 m sec rupture velocity may enter region ii of the subcritical regime but such a broad range of k i must be crossed to reach region iii and quasistatic behavior at the critical stress intensity k ic that region ii acts as a barrier through which few joints pass thus greatly limiting the number of postcritical joints in the catskill delta if not in the crust of the earth

small scale convective instability and upper mantle viscosity under california thermal calculations and convection analysis constrained by seismic tomography results suggest that a small scale convective instability developed in the upper 200 kilometers of the mantle under california after the upwelling and cooling of asthenosphere into the slab window associated with the formation of the san andreas transform boundary the upper bound for the upper mantle viscosity in the slab window 5 x 10 19 pascal seconds is similar to independent estimates for the asthenosphere beneath young oceanic and tectonically active continental regions these model calculations suggest that many tectonically active continental regions characterized by low upper mantle seismic velocities may be affected by time dependent small scale convection that can generate localized areas of uplift and subsidence

the european african collision and its effects on the lithosphere asthenosphere system abstract in the european area lateral changes in the shear wave velocities of the lithosphere asthenosphere system are quite pronounced gravity data imply a positive density contrast 0 03 0 07 g cm 3 in the upper mantle related to almost aseismic lithospheric roots which seem to characterize many orogenic belts the analysis of a transect along the longitudinal axis of the alps seems to indicate that relevant lateral variations in density are also present in the lithospheric part of the mantle

velocity density properties of the lithosphere from three dimensional modeling at the geysers clear lake region california the analysis of travel time delays from 94 teleseisms recorded at the geysers clear lake california region reveals a broad area of delay centered at mount hannah and encompassing the geysers geothermal field a three dimensional velocity inversion of the delays indicates that the source of the delays is a low velocity body largely within the top 30 km of the lithosphere velocity decreases of as much as 20 are observed in the top 15 km near mount hannah and diminish with depth no significant velocity fluctuations are observed below 60 km the block model of velocity perturbations resulting from the teleseismic residual inversion is used to predict the observed bouguer gravity field by solving for the relation between velocity and density perturbation comparison between the predicted gravity and observed gravity indicates that the same body responsible for the teleseismic delays accounts for the long wave length 30 mgal bouguer gravity minima at mount hannah the results of the velocity density modeling suggest that the material beneath mount hannah and the geysers may be partially molten and somewhat more silicic than the surrounding medium supplemental table is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 006 1 00 payment must accompany order

speculations on the thermal and tectonic history of the earth summary the connection between the earth s thermal history and convection in the mantle is exploited to elucidate the early evolution of the earth it appears probable that convection extending over almost all of the mantle has dominated vertical heat transport throughout the whole of the earth s history only in boundary layers at the surface and at a depth of 650 700 km is conduction likely to be important the resulting evolution appears to be consistent with geological observations on early precambrian rocks various arguments are put forward in favour of two horizontal scales of convective flow in the mantle at depths less than 650 km the large scale flow is related to the motion of major plates and must be ordered over distances of more than 5000 km its evolution and energetics are discussed and there are no obvious problems in maintaining the proposed convective motions small scale flow with an extent of the order of 500 km appears necessary both to explain the heat flow through older parts of the earth s surface and to reconcile the geophysical observations with the results of numerical experiments though the existence of the small scale flow is at present speculative various tests of its presence are proposed

correlation between abnormal pore pressure and tectonic jointing in the devonian catskill delta using the preferred orientation of chlorite we measured vertical compaction in 53 samples from the devonian catskill delta in central new york state the marine part of this delta contains three levels based on different amounts of vertical compaction these levels correspond roughly to 1 black shales at the base 2 prodelta turbidites and 3 a cap of shallow water sediments including abundant storm washed shell hashes deposited within the wave base the cap is normally compacted whereas the lower two levels are undercompacted tectonic cross fold joints that propagated during the late paleozoic alleghanian orogeny are restricted to the deeper undercompacted levels of the catskill delta whereas unloading cross fold joints pervade the cap the correlation between undercompaction and the distribution of tectonic joints indicates that abnormal fluid pressure was a key mechanism during the propagation of these joints

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

upper mantle heterogeneities beneath eastern europe abstract p wave travel time residuals for seismograph stations in eastern europe as reported by isc for the years 1964 1977 were used for constructing a seismic image of upper mantle heterogeneities in the network region for the depth range 0 100 km dominant tectonic features like the pannonian basin and the aegean sea and western turkey correlate well with pronounced velocity lows which a ppear to extenddown to a 300 km depth the velocity anomaly patterns in the depth intervals 300 500 km and 500 600 km are broadly similar but quite different from those of shallower depths the observed seismic heterogeneities are briefly discussed in terms of large scale tectonic and geophysical heat flow characteristics of eastern europe

organic geochemistry of the early toarcian oceanic anoxic event in hawsker bottoms yorkshire england a comprehensive organic geochemical investigation of the hawsker bottoms outcrop section in yorkshire england has provided new insights about environmental conditions leading into and during the toarcian oceanic anoxic event t oae 183 ma rock eval and molecular analyses demonstrate that the section is uniformly within the early oil window hydrogen index hi organic petrography polycyclic aromatic hydrocarbon pah distributions and tricyclic terpane ratios mark a shift to a lower relative abundance of terrigenous organic matter supplied to the sampling locality during the onset of the t oae and across a lithological transition unlike other ancient intervals of anoxia and extinction biomarker indices of planktonic community structure do not display major changes or anomalous values depositional environment and redox indicators support a shift towards more reducing conditions in the sediment porewaters and the development of a seasonally stratified water column during the t oae in addition to carotenoid biomarkers for green sulfur bacteria gsb we report the first occurrence of okenane a marker of purple sulfur bacteria psb in marine samples younger than 1 64 ga based on modern observations a planktonic source of okenane s precursor okenone would require extremely shallow photic zone euxinia pze and a highly restricted depositional environment however due to coastal vertical mixing the lack of planktonic okenone production in modern marine sulfidic environments and building evidence of okenone production in mat dwelling chromatiaceae we propose a sedimentary source of okenone as an alternative lastly we report the first parallel compound specific c13 record in marine and terrestrial derived biomarkers across the t oae the c13 records of short chain n alkanes acyclic isoprenoids and long chain n alkanes all encode negative carbon isotope excursions cies and together they support an injection of isotopically light carbon that impacted both the atmospheric and marine carbon reservoirs to date molecular c13 records of the t oae display a negative cie that is smaller in magnitude compared to the bulk organic c13 excursion although multiple mechanisms could explain this observation our molecular petrographic and rock eval data suggest that variable mixing of terrigenous and marine organic matter is an important factor affecting the bulk organic c13 records of the t oae

seismic tomography of the lithosphere with body waves a pair of papers in 1976 lead authored by kei aki heralded the beginning of the field of seismic tomography of the lithosphere the 1976 paper by aki christoffersson and husebye introduced a simple and approximate yet elegant technique for using body wave arrival times from teleseismic earthquakes to infer the three dimensional 3 d seismic velocity heterogeneities beneath a seismic array or network teleseismic tomography similarly a 1976 paper by aki and lee presented a method for inferring 3 d structure beneath a seismic network using body wave arrival times from local earthquakes local earthquake tomography following these landmark papers many dozens of papers and numerous books have been published presenting exciting applications of and or innovative improvements to the methods of teleseismic and local earthquake tomography many by aki s students

velocity structure of the pamir hindu kush region possible evidence of subducted crust the arrival times of compressional p and shear s waves from approximately 580 microearthquakes recorded by a temporary array in the pamir hindu kush region in central asia are used to deduce one and three dimensional velocity structures of this region the results for one dimensional structures imply that the moho is at 70 5 depth also there is a velocity reversal near 160 km depth which is inferred to be the beginning of the low velocity zone this reversal continues to depths of approximately 230 km below 230 km velocities are somewhat higher than those of normal mantle at similar depths 9 3 km s versus 8 4 km s for p waves the outstanding feature of the results for three dimensional velocity structures is a broad 40 km centrally located region with 8 to 10 lower velocities than those in the surrounding regions this low velocity region envelopes the seismic zone at depths between 70 and 150 km the region may actually extend beyond these depths but the results for shallower and deeper structure lack sufficient resolution to decide several tests using both hypothetical and real data were performed to estimate the reliability of the three dimensional solutions the results of these tests suggest that the inferred velocities are reasonably accurate representations of the average velocities in the blocks although one must be cautious of the effects of averaging in interpreting the solution the low velocity region is inferred to be a manifestation of substantial quantities of subducted continental crust therefore while subduction has occurred in the pamir hindu kush the results of the three dimensional inversions suggest that continental rather than only oceanic lithosphere has been subducted to depths of at least 150 km appendices are available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 013 1 00 payment must accompany order

sealing efficiency of shales the sealing efficiency of shale layers is studied through the hydraulic parameters which are required for sustaining overpressure during geologically significant periods assuming a 1d sedimentary complex composed of a sealing layer overlying a permeable one we give approximate solutions for the dissipation of a given initial overpressure the time constant for relaxation involves the thickness hydraulic conductivity and specific storage of the seal and also those of the permeable layer the values of the various hydraulic parameters are discussed it is argued first that the specific storage corresponding to plastic deformation during burial compaction is larger than the one which would correspond to elastic deformation when taking into account i plausible values for specific storage of the upper shale layer and ii the storage effect of the lower permeable layer it is found that a shale layer of several tens of m with an hydraulic conductivity of the order of 10 15 ms 1 maintains overpressure for 1 myr for such hydraulic parameter values in the absence of on going pressuring forces initial overpressures would decay with a time constant corresponding to a decrease by a factor e 2 7 of 1 myr this is interpreted as supporting a dynamic origin for observed abnormal pressures