estimating the full scale flexural and compressive strength of first year sea ice sea ice salinity density and temperature data were used to develop new methods for determining the bulk brine volume and porosity of sea ice floes methods for estimating full thickness ice sheet strength based on large scale field tests are presented the relationships among bulk sea ice properties strain rate and strength are illustrated a new constitutive equation was developed for predicting the full thickness horizontal compressive strength c of first year sea ice as a function of the applied strain rate and bulk porosity in the form c b2e 1 n bm where parameters b2 n and m are about 2 7 103 3 and 1 respectively and e and b are the ice strain rate and ice floe bulk porosity of sea ice respectively an example of the first year sea ice indentation force against a 90 m wide structure is given estimating sea ice strength based on remote ice conductivity measurements is also discussed conceptually

stress evolution in southern california and triggering of moderate small and micro size earthquakes we calculate the evolution of stresses in southern california extending the study of deng and sykes 1997 by increasing from 6 to 36 the number of earthquakes for which coseismic changes in stress are computed and by expanding from m 6 to m 1 8 the range of magnitudes m of events whose focal mechanism solutions are examined in the context of the evolving stress field the cumulative stress on a given date is calculated with respect to an arbitrary zero baseline just before the 1812 wrightwood earthquake by taking into account the long term stress loading associated with 98 fault segments and coseismic stress changes for 36 significant earthquakes our calculations indicate that more than 85 of m 5 earthquakes from 1932 1995 occurred in regions of positive change in coulomb failure function cff most of the remaining about 15 earthquakes that occurred in areas of negative cff fall very close to boundaries between positive and negative cff some of which are sensitive to the less well controlled slip distributions of the earliest historic events calculations also show that from 1981 until just before the 1992 landers earthquake more than 85 of small m 3 and micro size m 1 8 shocks in the seeber and armbruster 1995 catalog with mechanisms involving either nw trending right lateral or ne trending left lateral strike slip faulting occurred in regions of positive cff the ratio of encouraged to all small and micro size events reaches a high value of about 88 if an apparent coefficient of friction between 0 0 and 0 6 is used the highest percentage of earthquakes occurred in areas where stress is about 1 mpa above the 1812 baseline most 66 events occurred in regions of cff between 0 0 and 2 0 mpa the upper limit indicates that the approximate range of stress variation in the earthquake cycle is of the order of 2 0 mpa the fact that the locations of most moderate small and micro size earthquakes are still related to stress changes remaining from large historical events might be used to constrain slip distribution of some of those earthquakes and to constrain the locations of future significant events

influence of water column anoxia and sediment supply on the burial and preservation of organic carbon in marine shales abstract previous work has suggested that the laminated organic rich and bioturbated organic poor shales of the camp run member of the late devonian early mississippian new albany shale formed under anoxic and oxygenated bottomwater conditions respectively and that the interbedding of the two facies was due to the vertical oscillation of a water column anoxic oxic boundary where it impinged on the basin margin we have extended this analysis by examining the chemical and mineralogical differences between the two shale facies in a single borehole core by seeking evidence for deposition of the laminated shales under bottom water oxia or anoxia and by determining whether the laminated shales formed when the carbon supply to the sea floor was higher the results of this study show that the laminated and bioturbated shales are mineralogically and chemically distinct relative to al an index of the aluminosilicate content si ti fe p na ba co cr cu mo ni v zn and zr are all higher whereas mn ca mg and sr are lower in the laminated compared with the bioturbated shales the differences are due to a higher quartz feldspar titanite ilmenite and zircon content in the laminated shales probably indicating a coarser grain size and the greater abundance of manganoan calcite in the bioturbated shales dissolved oxygen was present in bottom waters during the deposition of some of the laminated shale intervals because of the presence of manganoan calcite a phase that can only form in sediments with an oxic surface in addition the organic matter preserved in the two shale types is isotopically different 13corganic values are 1 9z permil lighter on average in the laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals possibly indicating a larger fraction of terrestrial organic matter in the latter 15n values are 1 9z permil lighter on average in laminated compared with bioturbated intervals suggesting that nutrient drawdown was less during the deposition of the organic rich laminated shales the chemical mineralogical and isotopic contrasts between the two shale facies of the camp run member indicate that the conditions of sedimentation were different during their deposition the difference was possibly related to variations in sea level which would have caused the camp run shoreline to move closer to and farther from the core site causing in turn the deposition of coarser and finer grained sediments that contained different mixtures of marine and terrestrial organic matter bottomwater conditions were anoxic during deposition of most laminated intervals bottom water anoxia or dysoxia led to decreased burial and preservation of the essential nutrient phosphorus in the laminated organic rich shales relative to the rocks deposited beneath better oxygenated bottomwaters increased availability of phosphorus in the water column on long timescales leads to increased productivity and a higher settling flux of organic matter causing bottom water oxygen levels to fall this is consistent with the nitrogen isotope evidence suggesting that production was probably higher during the deposition of the organic rich shales thus production variations coupled with enhanced sedimentary regeneration of phosphorus from sediments related to low oxygen bottom water concentrations provide a general mechanism for the formation of the alternating facies of this member of the new albany shale

the january 1992 franklin lake northwest territories earthquake sequence abstract on 4 january 1992 an m blg 6 0 earthquake occurred in a relatively aseismic section of the boothia ungava seismic zone near franklin lake in the eastern northwest territories and was the third large earthquake to have occurred in eastern canada since 1988 we have determined the source properties of this earthquake by modeling both body and surface waves the focal mechanism indicates a combination of thrust and strike slip faulting on a northwest striking plane with the rupture initiating at a depth of 9 km the p axis of this focal mechanism is consistent with those of nearby earthquakes and with the regional stress field which is dominated by near horizontal northeast compression m s and m b are about one unit of magnitude less than m blg which may be a result of directivity there is some evidence based on a shift in corner frequency with azimuth that the fault ruptured to the southeast maximum likelihood estimates of the recurrence rates for the seismic zone suggest that although the earthquake was unusually large for the immediate epicentral area it was not anomalous with respect to the seismic zone as a whole a comparative analysis of the mainshock and aftershocks indicates that the aftershocks tended to be shallower than the mainshock and probably had a larger component of dip slip motion

geochemical and isotopic evidence for paleoredox conditions during deposition of the devonian mississippian new albany shale southern indiana the upper part of the new albany shale is divided into three members in ascending order these are 1 the morgan trail member a laminated brownish black shale 2 the camp run member an interbedded brownish black and greenish gray shale and 3 the clegg creek member also a laminated brownish black shale the morgan trail and camp run members contain 5 to 6 total organic carbon toc and 2 sulfide sulfur isotopic composition of sulfide in these members ranges from 5 0 to 20 0 c s plots indicate linear relationships between abundances of these elements with a zero intercept characteristic of sediments deposited in a non euxinic marine environment formation of diagenetic pyrite was carbon limited in these members the clegg creek member contains 10 to 15 toc and 2 to 6 sulfide sulfur isotopic compositions of sulfide range from 5 0 to 40 the most negative values occur in the uppermost clegg creek member and are characteristic of syngenetic pyrite formed within an anoxic water column abundances of carbon and sulfur are greater and uncorrelated in this member consistent with deposition in as euxinic environment in addition dop degree of pyritization values suggest that formation of pyrite was generally iron limited throughout clegg creek deposition but sulfur isotopes indicate that syngenetic water column pyrite becomes an important component in the sediment only in the upper part of the member at the top of the clegg creek member a zone of phosphate nodules and trace metal enrichment coincides with maximal toc values during euxinic deposition phosphate and trace metals accumulated below the chemocline because of limited vertical circulation in the water column increased productivity would have resulted in an increased flux of particulate organic matter to the sediment providing an effective sink for trace metals in the water column phosphate and trace metals released from organic matter during early diagenesis resulted in precipitation of metal rich phosphate nodules

tsunami hazard assessment of coastal south africa based on mega earthquakes of remote subduction zones the nuclear structural engineering pty and the national research foundation through the technology and human resources for industry programme project thrip tp2011061400009

seismic source modeling seismic source modeling is taken to mean the modeling of seismograms to investigate kinematic properties of the earthquake source current trends such as the use of other data types e g geodetic measurements of coseismic deformation and the explicit consideration of source dynamics when modeling seismograms are beginning to blur this definition but i will adhere to it in this review i have divided seismic source modeling into teleseismic regional and near source modeling teleseismic modeling has the advantage of global coverage for earthquakes of magnitude 5 5 and larger but does not provide much more than point source parameters regional distance modeling has the advantage of a more rapid assessment of earthquake source properties but is complicated by relatively complex wave propagation the coverage is also limited to areas of broadband regional networks typically continental areas of developed countries near source modeling has the potential for detailed imaging of source properties but very few earthquakes occur in regions with sufficient instrumentation to allow this i have also included a section on historical earthquakes because of the additional issues that seismologists face in working with pre wwssn data and because of the important issues such as earthquake recurrence that require historical data in addition to reviewing the progress in seismic source modeling during the last four years i have also briefly reviewed some of the progress in understanding earthquake physics and hazards that has come about because of basic research in earthquake source modeling

gas hydrate occurrence on the continental slope of the northern south china sea high resolution multi channel seismic data and geological samples were collected during two research cruises of the r v fendou 4 in 1999 and 2000 studies on these data and samples together with results from sites 1143 1145 and 1148 of odp leg 184 suggest that the geological structure on the continental slope of the northern south china sea is favorable for the formation of gas hydrates bottom simulating reflectors bsrs and geochemical anomalies which indicate the existence of gas hydrates have been recognized in sediments of the xisha trough the dongsha rise and the accretionary wedge of the manila subduction zone these gas hydrates are generated by two different mechanisms depending on the tectonic regime and the seismic and geochemical characteristics the first applies to the passive continental margin of the nor them south china sea on the dongsha rise and in the xisha trough the gas hydrates are associated with diapiric structures active faults slumps and gravity flows as well as high late cenozoic sedimentation rates their seismic expression includes bsrs seismic blanking zones and velocity anomalies the second mechanism is operative on the active continental margin along the manila subduction zone especially in the accretionary wedge here gas hydrate occurrence is marked by widespread bsrs and acoustic pull down possibly related to the existence of free gas in the sediments beneath the bsr the thickness of the seismic blanking zones averages 250 m suggesting that the stable gas hydrate zone has about the same thickness c 2005 elsevier ltd all rights reserved

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

carbon and oxygen isotope composition of carbonate in bulk sediment in the southwest taiwan basin south china sea methane hydrate decomposition history and its link to mud volcano eruption abstract anaerobic oxidation of methane aom coupled with sulfate reduction sr generates authigenic carbonate which has the unique carbon and oxygen isotope composition in sulfate methane transition zone smtz the carbon and oxygen isotope composition of carbonate in sediments which can be used to revel the variable methane flux is affected by the percentage of aom driven carbonate in sediments to investigate the methane hydrate decomposition history in the southwest taiwan basin we analyzed a 13 m long sediment core for grain size carbonate and elemental carbon contents and stable carbon and oxygen isotopes composition of carbonate 13ccarb and 18ocarb the ams 14c dating results and carbonate content reveal that a turbidity current occurred at around 14 ka b p which reversed sediment accumulation between 455 and 885 cm in depth combining the chronological framework and 13ccarb values we identified that the methane hydrate decomposition scale began to decrease at 14 ka b p moreover we discovered that three transiently enhanced methane hydrate decomposition events occurred from then on although the 13ccarb and 18ocarb variability are as expected the low 18ocarb values are inconsistent with the previous theory which favors 18o enriched in aom driven authigenic carbonate thus we suggest that a large amount of 18o depleted water which originally migrated from southwest taiwan island was injected into surface sediment along with the eruption of mud volcanos as the terminal electron accepter of aom sr reaction the exogenous 18o depleted water leads its special oxygen isotope to be inherited by the authigenic aom driven carbonate the proposed theory provides new insights on the authigenic carbonate in methane hydrate area and the association between methane hydrates and mud volcanoes

lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the gulf of california a test of the hypothesis that hydrogen rich organic matter accumulates preferentially in sediments under oxygen minima has been carried out by examining the composition of laminated and homogeneous diatomaceous sediments of the guaymas basin in the gulf of california the laminated sediments occur where an intense oxygen minimum intersects the slope around the margins of the basin above and below the depth of the oxygen minimum the sediments are homogenized by a burrowing infauna the two sediment types have very similar bulk chemical and mineral compositions and the organic matter is overwhelmingly marine the total organic carbon contents and rock eval parameters hydrogen and oxygen indices of the two sediment types are not significantly different whereas a road organic carbon maximum in the homogeneous sediments is centered at roughly 1200 m depth on the slope of the basin this maximum lies deeper than the core of the oxygen minimum thus both the concentration and the nature of the organic matter in the sediments of this highly productive marginal marine basin are not related to the concentration of dissolved oxygen in the bottom waters

rupture patterns and preshocks of large earthquakes in the southern san jacinto fault zone we relocated the large 1937 1942 and 1954 earthquakes in the san jacinto fault zone the epicenters of the main shocks aftershocks and some preshocks were determined using empirical station corrections from recent small events in the study areas the 1937 ml 5 9 earthquake has an epicenter between the surface traces of the san jacinto and buck ridge faults and aftershocks suggest about 7 km of rupture predominantly to the northwest a significant increase in small earthquake activity occurred about formula yr before this event the 1954 m l 6 2 earthquake is located at the southeast end of the mapped trace of the san jacinto fault and aftershocks suggest about 15 km of rupture further southeast into an area of folded young sediments with no surface fault trace this event was preceded by a cluster of small earthquakes which occurred within an 8 hr period 10 weeks before the main event and in the eventual rupture zone the 1942 m l 6 3 earthquake is located southwest of the southeast end of the coyote creek fault large aftershocks of this event are spread over a 15 by 18 km area southwest of the coyote creek fault and are not associated with any one fault the relation of the 1942 event to the san jacinto fault zone is not simple

quantitative interpretation for gas hydrate accumulation in the eastern green canyon area gulf of mexico using seismic inversion and rock physics transform gas hydrate can be interpreted from seismic data through observation of bottom simulating reflector bsr it is a challenge to interpret gas hydrate without bsr three dimensional qualitative and quantitative seismic interpretations were used to characterize gas hydrate distribution and concentration in the eastern green canyon area of the gulf of mexico where bsr is absent the combination of qualitative and quantitative interpretation reduces ambiguities in the estimation and identification of gas hydrate sandy deposition and faults are qualitatively interpreted from amplitude data the 3d acoustic impedance volume was interpreted in terms of high p impedance hydrate zones and low p impedance free gas zones gas hydrate saturation derived from p impedance is estimated by a rock physics transform we interpreted gas hydrate in the sand prone sediments with a maximum saturation of approximately 50 of the pore space sheet like and some bright spot gas hydrate accumulations are interpreted the interpr

strong motion modeling of the imperial valley earthquake of 1979 twelve three component strong motion displacement records are modeled for the 1979 imperial valley earthquake to recover the distribution of slip on the imperial fault plane the final model for which point source responses are calculated by a discrete wavenumber finite element technique uses a structure with gradients in material properties rather than layers the effects of a velocity gradient are investigated by comparing synthetics with a layer over a half space model using generalized rays it is shown that a uniform fault rupture model on a rectangular fault plane does not explain the data the preferred fault model has slip concentrated below 5 km in the basement material and between the epicenter 5 km south of the international border and highway 80 within this region there appears to be two localized areas of larger dislocations one just north of the border near bonds corner and a second under interstate 8 at meloland overpass a major arrival associated with large amplitude vertical accelerations up to 1 7 g is identified in the el centro array records this arrival has an s p time of approximately 2 3 sec at many of the array stations and is modeled as originating from a localized source 8 km to the south of the array the moment is estimated to be 5 0 10 25 dyne cm from the strong motion records which is consistent with teleseismic body wave estimates the preferred fault model is strike slip with a 90 dip the average strike is 143 however to explain vertical waveforms near the fault trace a corrugated or wiggly fault plane is introduced the average rupture velocity is in the range 2 5 to 2 7 km sec 0 8 to 0 9 times the basement shear wave velocity the preferred model has unilateral rupture propagation to the north although the data would allow a small amount of propagation to the south the estimated stress drop for the entire fault plane is only 5 to 10 bars however the stress drop over the more localized sources is about 200 bars the fault model is consistent with the pattern of seismicity and observations of aseismic creep in the imperial valley and suggests that the southern half of the imperial fault acts as a locked section which breaks periodically

relationship between sea ice freeboard and draft in the arctic basin and implications for ice thickness monitoring we have confirmed our earlier finding that the probability density function pdf of ice freeboard in the arctic ocean can be converted to a pdf of ice draft by applying a simple coordinate transformation based on the measured mean draft and mean elevation this applies in each of six 50 km sections north of greenland of joint airborne laser and submarine sonar profile obtained along nearly coincident tracks from the arctic basin north of greenland and tested for this study detailed differences in the shape of the pdf can be explained on the basis of snow load and can in principle be compensated by the use of a more sophisticated freeboard dependent transformation the measured density ratio r actually mean draft mean elevation ratio for each section was found to be consistent over all sections tested despite differences in the ice regime indicating that a single value of r might be used for measurements done in this season of the year the mean value r from all six sections is 7 89 on the assumption that all six values are drawn from the same population the standard deviation is 0 55 for a single 50 km section and thus 0 22 for 300 km of track in attempting to infer ice draft from laser measured freeboard we would therefore expect an accuracy of about 28 cm in 50 km of track if mean draft is about 4 m and about 11 cm in 300 km of track these accuracies are compatible with the resolution of predictions from numerical models a simple model for the variability of r with season and with mean ice thickness gives results in reasonable agreement with observations they show that although there is a large seasonal variability due to snow load there is a stable period from november to april when the variability is chiefly dependent on the mean ice thickness alone thus in principle r can be mapped over the arctic ocean as a basis for interpreting survey data better field data are needed on the seasonal and spatial variability of three key quantities area averaged snow load mean density of first year and multiyear ice including the effect of ridging with these two ice regimes and density of near surface water

identification and numerical modelling of hydrocarbon leakage in the lower congo basin implications on the genesis of km wide seafloor mounded structures abstract we present a combined approach of interpretation of 2d seismic reflection data and numerical modelling of hydrocarbon generation and migration across the southern slope of the lower congo basin in order to investigate the factors controlling timing and distribution of hydrocarbon leakage in this area we identified three main families of past and present day leakage features 1 mid upper miocene seismic chimneys concentrated basinwards and ending up on buried pockmarks 2 plio pleistocene chimneys rather clustered to the east of the study area and ending up in seafloor pockmarks and 3 fewer scattered chimneys identified within the miocene sequences ending up in shallow enhanced reflectors flat spots stratigraphic and structural elements seem to control the distribution of these features at least two major events of leakage occurred during the middle late miocene and intermittently during the pliocene present external factors as sediment supply are associated to the miocene leakage event whilst internal structural elements probably triggered the pliocene to present day leakage a major seabed morphological feature represented by a margin paralleled belt of more than 1 km wide mounds was identified above growth faults to the east of the study area data constrained 2d hc generation and migration modelling suggests a genetic link between these structures and vertical migration leakage of thermogenic methane sourced from either currently mature oligo miocene source rocks or secondary cracking and further expulsion from over mature upper cretaceous source rocks hence the mounds are likely to represent a lineation of methane derived carbonate build ups despite the natural limitations of a 2d migration model when combined and calibrated with observations from seismic data it can be used as a valid tool to assess petroleum migration routes in sedimentary basins to the best of our knowledge this is the first integrated approach combining both seismic observations and numerical modelling carried out in the angola basin

possible pingo fields in the utopia basin mars geological and climatical implications abstract the presence of pingos on mars has been hypothesized since the period of the viking mission in fact a diverse range of pingo like features has been found at various martian sites including elysium chryse and utopia planitiae in the northern lowlands due to the morphology and the geological setting some of those features were interpreted in different ways creating some controversies as happened in athabasca valles this reflects the complexity of interpreting these features by remote sensing and multiple plausible interpretations of the same feature with the objective of identifying new possible pingos or rootless cones on mars we selected a study area in utopia planitia 10 55 n 210 260 w where the presence of both features is possible due to its geological history volcanic and hydrological we analyzed more than 2100 mars orbiter camera moc narrow angle images in addition to viking thermal emission imaging system themis and high resolution stereo camera hrsc images together with mars orbiter laser altimeter mola derived digital elevation models dems with a geographic information system gis we found in 94 moc narrow angle images dome cone and ring shaped features we analyzed them from morphological and morphometrical points of view in order to compare them with relevant features on mars and earth we tested different possible origins for those features following the approach of multiple working hypotheses we conclude that the dome cone and ring shaped features could be pingos which is in agreement with their geological settings regarding the driving heat source for the formation of the purported pingos we propose the existence of a heat source possibly a magma chamber underneath the surface of the utopia basin together with possible climatic shifts the past activities of the heat source may have caused melting of ground ice the pingo growth due to freezing of the water would have occurred during the following cold climatic conditions

detection of gas hydrates in faults using azimuthal seismic velocity analysis vestnesa ridge w svalbard margin accepted for publication in journal of geophysical research solid earth copyright 2020 american geophysical union further reproduction or electronic distribution is not permitted

thickness and density of snow covered sea ice and hydrostatic equilibrium assumption from in situ measurements in fram strait the barents sea and the svalbard coast modern satellite measurements of sea ice thickness are based on altimeter measurements of the difference in elevation between the snow or ice surface and the local sea surface for retrieval of sea ice thickness it is assumed that the ice is in hydrostatic equilibrium and that the snow load on the ice and the density of the sea ice and sea water are known this study presents data from in situ sea ice thickness drillings and snow and ice density measurements from fram strait the barents sea and the svalbard coast in the european arctic the error in the altimetry ice thickness products is assessed based on the spatial variability of snow and ice density and snow thickness data ice thickness uncertainty related to snow depth was found to be 40 cm radar altimeter and 90 cm laser altimeter while uncertainty related to ice density is 25 cm for both techniques the assumption of hydrostatic equilibrium at the scales of the measurements 10 100 m was found to hold better in the case of level landfast ice near svalbard than for fram strait drift ice which consists of mixed ice types where the deviation between the calculated and measured ice thicknesses was on average 0 5 m

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

the superstition hills california earthquakes of 24 november 1987 the 24 november 1987 superstition hills earthquakes occurred on the conjugate northwest striking right lateral superstition hills fault and a previously unknown northeast striking left lateral structure defined by a lineation of hypocenters extending from the superstition hills fault to the brawley seismic zone master event locations of the earthquakes using caltech usgs seismic network data reveal the following the first main shock 33 4 9 n 115 47 7 h 10 6 km m s 6 2 0154 gmt on the northeast striking structure and its foreshocks co locate events on the northeast structure cluster in space and time and some aftershocks occur in the brawley seismic zone the second main shock 33 0 9 n 115 50 9 w h 1 9 km m s 6 6 1315 gmt on the superstition hills fault was 12 hr after the first main shock and initiated at shallow depth where the two trends join aftershocks of the second main shock lie in a northwest trend between the superstition hills and superstition mountain faults and have a sharply defined western edge the extent of the northwest trend aftershocks is not coincident with surface rupture on the superstition hills fault in general the earthquakes in the northeast trend are deep and the earthquakes in the northwest trend are shallow we compare the earthquake distribution to the distribution of crystalline basement rocks defined from a refraction study of fuis et al 1982 the earthquake locations and extent of aftershock activity appear to be controlled by the presence of crystalline basement rocks

estimating small scale snow depth and ice thickness from total freeboard for east antarctic sea ice abstract deriving the snow depth on antarctic sea ice is a key factor in estimating sea ice thickness distributions from space or airborne altimeters using a linear regression to model snow depth from observed total freeboard or the snow ice surface elevation relative to sea level is an efficient and promising method for the estimation of snow depth for instruments which only detect the uppermost surface of the sea ice conglomerate e g laser altimetry however the antarctic pack ice zone is subject to substantial variability due to synoptic scale weather forcing ice formation motion and melt undergo large spatio temporal variability throughout the year in this paper we estimate snow depth from total freeboard for the arise 2003 sipex 2007 and sipex ii 2012 research voyages to the east antarctic pack ice zone using in situ data we investigate variability in snow depth and show that for east antarctica relationships between snow depth and total freeboard vary between each voyage at a resolution of metres to tens of metres we show how regression based snow depth models track total freeboard and generally over estimate snow depth especially on highly deformed sea ice and at sites where ice freeboard makes a substantial contribution to total freeboard for a set of 3192 records we obtain an in situ mean snow depth of 0 21 m 0 19 m using a regression model derived from all in situ points we obtain the same mean with a slightly lower variability 0 16 m using voyage specific subsets of the data to derive regression models and estimate snow depth mean snow depths ranged from 0 19 m model derived from sipex observations to 0 25 m model derived from sipex ii observations while small these discrepancies impact ice thickness estimation using the assumption of hydrostatic equilibrium mean in situ ice thickness for all samples is 1 44 m 1 19 m using empirical models for snow depth ice thickness varies from 1 0 to 1 8 m with the best match to the in situ mean given when snow depth is derived using a snow depth model from all observations 1 53 m 1 55 m however mean values only tell part of the story when investigating the sea ice thickness distribution here we explicitly show how modelling snow depth and ice thickness based on a total freeboard signal compares with in situ observations this provides insight into the confidence we place in ice thickness distributions derived using a total freeboard signal and empirically derived models for snow depth

the chronology and tectonic style of landscape evolution along the elevated atlantic continental margin of south africa resolved by joint apatite fission track and u th sm he thermochronology atlantic type continental margins have long been considered passive tectonic settings throughout the entire postrift phase recent studies question the long term stability of these margins and have shown that postrift uplift and reactivation of preexisting structures may be a common feature of a continental margin s evolution the namaqualand sector of the western continental margin of south africa is characterized by a ubiquitously faulted basement but lacks preservation of younger geological strata to constrain postrift tectonic fault activity here we present the first systematic study using joint apatite fission track and apatite u th sm he thermochronology to achieve a better understanding on the chronology and tectonic style of landscape evolution across this region apatite fission track ages range from 58 3 2 6 to 132 2 3 6ma with mean track lengths between 10 9 0 19 and 14 35 0 22 m and mean u th sm he sample ages range from 55 8 31 3 to 120 6 31 4ma joint inverse modeling of these data reveals two distinct episodes of cooling at approximately 150 130ma and 110 90ma with limited cooling during the cenozoic estimates of denudation based on these thermal histories predict approximately 1 3 km of denudation coinciding with two major tectonic events the first event during the early cretaceous was driven by continental rifting and the development and removal of synrift topography the second event during the late cretaceous includes localized reactivation of basement structures as well as regional mantle driven uplift relative tectonic stability prevailed during the cenozoic and regional denudation over this time is constrained to be less than 1 km

relations between mud volcanoes thrust deformation slope sedimentation and gas hydrate offshore north panama abstract seamarc ii swath mapping and migrated seismic reflection data show a high concentration of mud volcanoes in the primary sediment depocentre along the lower slope of a thrust belt offshore north panama the mud volcanoes are 0 4 2 0 km wide sonar reflectivity backscattering sediment cores and seismic stratigraphic relations indicate that the depocentre contains thick sequences of basinal turbidites which are ponded between the anticlinal ridges the ridges are composed of the deformed turbidites of the colombian basin and exhibit a strong bottom simulating reflector bsr apparently associated with a gas hydrate layer based on the concentration of mud volcanoes along the crests of the anticlinal ridges in the depocentre and the structural position of the bsr we suggest that folding along the deformation front sediment ponding leading to differential loading methane migration and accumulation in the anticlines and gas hydrate formation are important factors in the development of mud volcanoes in this region

the relation between arctic sea ice surface elevation and draft a case study using coincident auv sonar and airborne scanning laser 1 data are presented from a survey by airborne scanning laser profilometer and an auv mounted upward looking swath sonar in the spring beaufort sea the air snow surface elevation and water ice draft surfaces were mapped at 1 1 m resolution over a 300 300 m area data were separated into level and deformed ice fractions using the surface roughness of the sonar data the relation r d f between draft d and surface elevation f was then examined correlation between top and bottom surfaces was essentially zero at full resolution requiring averaging over patches of at least 11 m diameter to constrain the relation largely because of the significant error 15 cm of the laser instrument level ice points were concentrated in two core regions corresponding to level fy ice and refrozen leads with variations in r attributed primarily to positive snow thickness variability deformed ice displayed a more diffuse cloud with draft having a more important role in determining r because of wider deformed features underwater averaging over footprints similar to satellite altimeters showed the mean surface elevation typical of icesat to be stable with averaging scale with r 3 4 level and r 4 2 deformed the minimum elevation within a footprint characteristic reported for cryosat was less stable significantly overestimating r for level ice r 5 and deformed ice r 6 the mean draft difference between measurements and isostasy suggests 70 m as an isostatic length scale for level ice the isostatic scale for deformed ice appears to be longer than accessible with these data 300 m

the seismic source parameters of the 1991 costa rica aftershock sequence evidence for a transcurrent plate boundary the april 22 1991 valle de la estrella costa rica earthquake ms 7 6 was a back arc thrusting event associated with the underthrusting of the caribbean plate beneath central america a network of three passcal type portable instruments was deployed to monitor the aftershock activity in southern costa rica 2 to 6 weeks after the main shock the waveforms recorded on three component midperiod seismometers were used to recover source information for 15 small aftershocks magnitudes between 3 2 and 4 4 with a linear moment tensor inversion method we conducted several tests to investigate the effects of unknown structure and event mislocation on source parameter recovery the longer period waveforms in general are less sensitive to the effects of the structural details so that the essential source information can be successfully extracted from the waveform data the earlier part of the seismic wave forms has proven to be the most important carrier of the source information a gross crustal model can be used to describe the structure for the source study the small changes in the waveform character resulting from the mislocation of the events or inexact green s functions generated from the oversimplified crustal model do not prohibit us from the recovery of the source orientation at local distances in contrast the determination of the focal depth is subject to uncertainty because of the lack of detailed structural information our focal mechanisms are generally in good agreement with p wave first motion fault plane solutions determined from a local short period network the aftershocks show a clear spatial segmentation based on focal mechanism type most aftershocks near or southeast of the main shock were thrusting events with focal mechanisms similar to the main shock in contrast a cluster of aftershocks northwest of the main shock showed dominantly left lateral strike slip motion on a northeasterly striking nodal plane this suggests that a diffuse deformation zone exists in central costa rica and is characterized by left lateral strike slip motion this diffuse transcurrent deformation zone coincides with several geologic and geophysical features and perhaps is a result of the slower subduction rate of the buoyant cocos ridge than its adjacent segments along the middle america trench mat the diffuse transcurrent boundary may intersect with the north panama deformed belt npdb near limon costa rica and is very likely a plate boundary for the proposed panama block

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

3d seismic analysis of the ak fault orange basin south africa implications for hydrocarbon leakage and offshore neotectonics abstract a high resolution 3d reflection seismic dataset was used to achieve a detailed description of the half graben bounded ak fault in the ibhubesi gas field of the offshore orange basin seismic analysis of the fault involved the combination of both the conventional seismic interpretation and seismic attributes the main objective of the study was to provide insights into hydrocarbon leakage and neotectonic activity along the west coast shelf of south africa the ak fault is among the several half graben bounded faults that formed in the late jurassic to early cretaceous during the separation of the south american and the african continents the ak fault consists of five seismically detectable segments whose evolution reflects characteristics of both the coherent and the isolated end members model of segmented fault origin diapiric structures that are direct indicators of vertical fluid movement were also observed along the ak fault system providing evidence of significant roles that the fault plays in promoting the vertical migration of hydrocarbon in the orange basin recent reactivation of the fault has also occurred along an oblique extensional regime that is dominated by normal dip slip faulting with minor shear components along the tips

waveform modeling of the november 1987 superstition hills earthquakes long period body wave data recorded at teleseismic distances and strong motion data at pasadena for the superstition hills earthquakes of 24 november 1987 are modeled to obtain the source parameters we will refer to the event that occurred at 0153 ut as eq1 and the event at 1316 ut as eq2 at all distances the first earthquake appears to be a simple left lateral strike slip event on a fault striking ne it is a relatively deep event with a source depth of 10 km it has a teleseismic moment of 2 7 10 25 dyne cm the second and more complex event was modeled in two ways by using eq1 as the green s function and by using a more traditional forward modeling technique to create synthetic seismograms the first method indicated that eq2 was a double event with both subevents similar but not identical to eq1 and separated by about 7 5 sec from the synthetic seismogram study we obtained a strike of 305 for the first subevent and 320 for the second both have dips of 80 and rakes of 175 the first subevent has a moment of 3 6 10 25 which is half that of the second we obtain depths of at least 6 km the teleseismic data indicate a preferred subevent separation of 30 km with the second almost due south of the first but the error bounds are substantial this would suggest that the subevents occurred on conjugate faults the strong motion data at pas however imply a much smaller source separation with the sources probably produced by asperities

tectono sedimentary controls on the likelihood of gas hydrate occurrence near taiwan abstract marine sediments on the continental slope of the ne south china sea have appropriate thickness methane generating potential and occur in a suitable pressure temperature regime to host gas hydrate evidence for gas hydrate the bottom simulating reflector bsr is observed to the south of taiwan on reflection seismic records and can be used to suggest that gas hydrates are widely distributed the tectono sedimentary framework south of taiwan bears directly upon methane generation and the likelihood of the presence of significant gas hydrate deposits three zones of probable hydrate occurrence have been delineated along the margins of the ne south china sea 1 in a thick accumulation of sediment along the northern passive margin 2 along a more thinly sedimented eastern active collisional margin and especially 3 in a zone of thick originally passive margin sedimentation into which the collisional margin has encroached obliquely

top bottom multisensor remote sensing of arctic sea ice the arctic sea ice cover has been studied using near simultaneous observations by passive and active synthetic aperture radar sar microwave sensors upward looking and sidescan sonars a lidar profilometer and an infrared sensor data from two aircraft and a submarine over an approximately 100 km track of central arctic sea ice were registered and analyzed to evaluate the characteristics of the ice cover and the utility of each sensor in ice studies the results of comparative and correlation analyses are as follows the probability density functions of ice draft from sonar and elevation from lidar were found to be almost identical when isostasy is taken into account this result suggests that the basic ice thickness distribution can be derived from the surface topography measurements alone reasonable correlation was found between sar backscatter and ice draft or elevation especially when scales were adjusted such that 15 20 sar pixels were averaged however surface roughness derived directly from standard deviations in the lidar elevation data was found to be poorly correlated to the sar backscatter these results indicate that the sar values are affected more by scattering from the ice than from the snow covered surface the active and passive microwave sensors are shown to generally complement each other as the two sensors are especially sensitive to different physical properties of the sea ice undeformed first year ice showed low backscatter values but high brightness temperatures while some multiyear ice showed high backscatter values and low brightness temperature however surfaces identified as multiyear ice by the passive system have a large spread in the unaveraged sar backscatter indicating limitations when using a one channel sar for ice type identification at the highest resolution also ridged ice identified by sonar and sar data covers a large range of passive microwave emissivity suggesting considerable variability in the age and salinity of this type of ice significant variations about 0 11 in the minimum emissivity of consolidated multiyear ice are observed in different regions of the arctic using the high resolution 30 m passive microwave data this suggests that regional variations in texture and scattering characteristics of multiyear ice in the arctic are present likely influenced by different histories of formation of the ice in different regions

fluid flow and origin of a carbonate mound offshore vancouver island seismic and heat flow constraints a 1 5 km long 1 km wide and 70 80 m high carbonate mound was identified on the mid slope region of the subduction accretionary sedimentary prism offshore vancouver island 3 5 km west of ocean drilling program odp site 889 and integrated ocean drilling program iodp site u1327 seabed video images show the presence of seafloor carbonate as well as chemosynthetic communities a high resolution single channel seismic survey with close line spacing recording coherent reflectivity down to about 400 m beneath the seafloor provided acoustic images of this mound and of the gas hydrate bottom simulating reflector bsr beneath it the mound is interpreted to have developed as a structural topographic high in the hanging wall of a large reverse fault formed at the base of the current seaward slope the fault zone provides pathways for fluids including gas to migrate to the seafloor where diagenetic carbonate forms and cements the near surface sediments to examine the thermal effect of possible upward fluid flow beneath the mound heat flow at the mound and in the neighbouring region was calculated from the depth of the bsr below the seafloor these data were combined with heat flow calculated over a broader region from previous multi channel seismic data heat flow within the flattest portion of the surrounding 4 km by 8 km region averages 74 mw m2 taking this value to represent the regional or background heat flow a simple 2d analytical method was used to calculate theoretical heat flow variations due to topography across the mound most of the variability is explained by topographic effects including a local 6 mw m2 negative anomaly over the central mound and a large 20 mw m2 positive anomaly over the mound steep side slope however just south of the mound there is a 6 7 mw m2 positive anomaly in a 2 km long band that has predominantly flat seafloor most of this anomaly is probably unrelated to topographic effects but rather likely due to warm upward fluid flow along faults or fracture zones

an irregular feather edge and potential outcrop of marine gas hydrate along the mauritanian margin the dissociation of marine hydrate that surrounds continental margins is thought to be an agent for past and future climate change as the water depth decreases landwards the base of the hydrate stability zone progressively shallows until hydrate can occur at or immediately below the seabed where an increase in bottom water temperature can cause dissociation but the true extent of these most vulnerable hydrate deposits is unknown here we use exceptional quality three dimensional 3 d seismic reflection imagery offshore of mauritania that reveals a rare example of a bottom simulating reflection bsr that intersects the seabed and delineates the feather edge of hydrate the bsr intersects the seabed at the 636 m isobath but along the 32 km of the margin analysed the intersection is highly irregular intersections and seismic evidence for hydrate less than 4 3 m below the seabed occur in seven small localised areas that are 0 02 0 45 km2 in extent we propose gas flux below the dipping base of the hydrate to these places has been particularly effective the intersections are separated by recessions in the bsr where it terminates below the seabed seawards of the 636 m isobath recessions are areas where the concentration of hydrate is very low or hydrate is absent they are regions that have been bypassed by gas that has migrated landwards along the base of the hydrate or via hydraulic fractures that pass vertically through the hydrate stability zone and terminate at pockmarks at the seabed an irregular feather edge of marine hydrate may be typical of other margins

sedimentary geochemistry of manganese implications for the environment of formation of manganiferous black shales the sedimentary geochemistry of manganese is dominated by the redox control of its speciation higher oxidation states mn super 3 and super 4 occurring as insoluble oxyhydroxides in well oxygenated environments and the lower oxidation state mn super 2 being much more soluble in oxygen deficient settings its geochemical behavior is therefore quite different in oxic and anoxic environments and where oxic and anoxic conditions are juxtaposed mn is recycled between the two environments in modern marine sediments mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating pelagic sediments of the deep ocean and in surficial deposits of continental margin environments diagenetic recycling of mn in the latter causes surficial deposits to have larger mn enrichments than in many pelagic sediments bottom sediments of permanently anoxic basins show no enrichments and have mn concentrations that are controlled solely by the aluminosilicate fraction manganese carbonates kutnohorite and calcic rhodochrosite are found only in anoxic sediments accumulating beneath surface oxic horizons and therefore under oxygenated bottom waters in many nearshore environments such enrichments are due to delivery of mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved pore water mn levels can reach saturation with respect to a mixed mn ca carbonate phase in such sediments the diagenetic origin for these phases is shown by their carbon isotope compositions which typically indicate a carbon source from decomposing organic matter the presence of mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters on the basis of this information it is proposed that in contrast to several current explanations for the formation of mn carbonates kutnohorite and rhodochrosite in ancient organic rich shales limestone and marl sequences and in many mn ore deposits the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters by analogy with the present mn carbonates could not have formed in the bottom waters of anoxic basins these diagenetic phases however did form where mn was supplied at a high rate namely by the burial of oxyhydroxide enriched surface sediments to a subsurface anoxic environment this situation could only have occurred under oxygenated bottom waters the presence of mn carbonates in ancient black shales and in some carbonate rich rocks lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters probably in continental margin settings

modelling the spread of oil under fast sea ice using three dimensional multibeam sonar data 1 a substantial portion of the world s remaining oil and gas reserves are found in the arctic exploration pressure will intensify as sea ice thinning and retreat continue and the subsequent production could involve spills or blowouts under various kinds of sea ice existing models for the spread of oil under ice are inadequate because they are unable to replicate the complexity or uniqueness of different ice regimes through the novel combination of 3 d under ice imagery from an autonomous under water vehicle auv and oil trajectory modelling we demonstrate that it is possible to overcome these deficiencies results suggest that we are presently underestimating the spread of oil under sea ice by an order of magnitude this is an important result with wide ranging ramifications as it suggests that our present ability to contain and recover oil under ice is limited

m 6 earthquakes in southern california during the twentieth century no evidence for a seismicity or moment deficit abstract a broadly based report on seismic hazards in southern california wgcep 1995 concluded that the predicted seismicity exceeds that observed since 1850 a subsequent independent analysis argued that infrequent huge m 8 earthquakes are needed to explain the low rate of large earthquakes jackson 1996 frequency magnitude relationships and earthquake reporting suggest that the 1903 to 1997 catalog we present here with a b value of 1 0 and a rate of m 6 shocks of 0 42 to 0 49 yr 1 is nearly complete in contrast the 1850 to 1994 catalog used by wgcep is incomplete before the turn of the century and thus its reported seismicity rate of 0 32 m 6 shocks yr 1 is too low principally because the wgcep 1995 model results in b values of up to 4 0 for regions of lesser and blind faults the rate of m 6 shocks off the san andreas system predicted by the wgcep 1995 model is three times greater than that observed in this century because they obtained b 0 4 for m b 2 2 for m 7 3 on major faults their expected rate of m 7 san andreas shocks is twice as high as observed thus part of the seismicity and moment discrepancy identified by wgcep was caused by use of an incomplete catalog and part was caused by inappropriate b values we obtain a southern california moment release rate of 8 to 12 10 18 n m yr 1 which cannot be distinguished from the moment release estimated by fault slip or the moment accumulation inferred from plate motions or geodetically measured shear strain we thus find no evidence for a moment deficit significant aseismic moment release or for rare m 8 earthquakes off the san andreas fault system finally the number of m 6 earthquakes per decade does not depart significantly from a poisson process during this century and thus we find no evidence that the rate of seismicity is increasing now or at any other time since 1900

sea ice thickness from airborne laser altimetry over the arctic ocean north of greenland 1 we present a new method to measure ice thickness of polar sea ice freeboard heights using airborne laser altimetry combined with a precise geoid model giving estimates of thickness of ice through isostatic equilibrium assumptions in the paper we analyze a number of flights from the polar sea off northern greenland and estimate accuracies of the estimated freeboard values to be at a 13 cm level corresponding to about 1 m in absolute thickness

passive margin evolution and its controls on natural gas leakage in the southern orange basin blocks 3 4 offshore south africa using a 2d seismic dataset that covers part of the southern orange basin offshore south africa we reconstructed the geological evolution of the basin this evolutionary model was then used to investigate the occurrence of natural gas within the sedimentary column and the distribution of gas leakage features in relation to the observed sedimentary and tectonic structures developed in the post rift succession since the early cretaceous the cretaceous succession has been subdivided into five seismic units the highest sedimentation rates occur within the barremian aptian unit c1 and the turonian coniacian unit c3 two cenozoic units t1 and t2 have been distinguished these show a sudden decrease in sedimentation rate for the whole of the cenozoic three phases of gravitational tectonics with two late cretaceous phases of mass movement in the northern study area and cenozoic slumping in the southern study area have been related to sedimentation rates sea level changes paleoenvironmental evolution and regional tectonics the occurrence of natural gas leakage follows a coast parallel distribution within the study area in the near shore part at water depths shallower than 400 m massive gas chimneys penetrate through the sediment layers and reach the near surface within an intermediate narrow band between 300 and 500 m water depth the gas migrates more diffusely through sub vertical faulted cretaceous sediments while in the outer part of the basin through the cretaceous and cenozoic gravitational wedges only very few signs of gas accumulation and migration can be seen along the faults a conceptual model has been established with the aptian source rock generating gas in the outer part of the basin this source rock underlies the cenozoic wedge in the south and the thick cretaceous wedge in the north and is a postulated source for the natural gas within the sedimentary column this thermogenically generated gas does not migrate directly through the gravitational faults and the above lying sediments but moves buoyancy driven up dip along stratigraphic layers to escape through the sediments to the sea floor in the inner shelf area

geochemistry of recent toc rich sediments from the gulf of california and the black sea major and minor elements incl ag as ba cd co cr cu mn mo ni pb sr v zn have been determined in recent sediments from the gulf of california upwelling area and black sea sapropels in order to reinterpret their chemical composition in view of reliable seawater and plankton data the chemistry of the gulf of california sediments reflects regeneration processes which occur in the water column i e only a small fraction 10 of elements like cd which in seawater are coupled to the labile nutrients c n p is buried in the sedimentary column in contrast elements like the more resistant nutrients si undergo a deeper regeneration cycle ba several trace metals which are present in comparatively higher concentrations in seawater as mo u v and at the same time are reactive under reducing conditions and or are able to form stable sulfides are fixed in the sediments during early diagenesis the early diagenetic behavior of ba is closely related to bacterial sulfate reduction the formation of barite concretions is discussed anoxic conditions in the water column act as ideal traps for a number of redox sensitive and or stable sulfide forming elements a simple trace metal balance calculation shows that the chemical composition of black sea sapropels is controlled by fluvial and mediterranean seawater element input and the accumulation rate of terrigenous detrital material

glacial to interglacial changes in surface nitrate utilization in the indian sector of the southern ocean as recorded by sediment δ15n we present a new approach for paleoceanographic reconstruction of surface nutrient utilization in the southern ocean it has been observed in the contemporary ocean that due to preferential uptake of 14no3 during photosynthesis the 15n of planktonic organic matter increases with increasing nitrate depletion in surface waters our results demonstrate that the 15n signal produced in surface waters is reflected in the underlying surface sediments core top 15n is inversely correlated with surface nitrate concentration along a transect across the subtropical convergence and the polar front in the southeast indian ocean these results are consistent with a four box model showing that the nitrogen isotopic composition of sinking organic matter depends on percent nitrate utilization in the euphotic zone by comparing the 15n of surface sediments with that measured in the glacial sections of several cores we infer changes in the intensity and latitudinal distribution of nitrate uptake in this region during the last glacial maximum these preliminary results argue against increased biological uptake of nutrients in southern polar waters as a major mechanism for glacial lowering of atmospheric co2 they also suggest that subantarctic waters in the se indian sector became more nutrient depleted as they migrated northward increased nitrate depletion might have also occurred slightly south of the glacial polar front we use a six box model to explore the possible impact of this observation on atmospheric co2

an assessment of state of the art mean sea surface and geoid models of the arctic ocean implications for sea ice freeboard retrieval state of the art arctic ocean mean sea surface mss models and global geoid models ggms are used to support sea ice freeboard estimation from satellite altimeters as well as in oceanographic studies such as mapping sea level anomalies and mean dynamic ocean topography however errors in a given model in the high frequency domain primarily due to unresolved gravity features can result in errors in the estimated along track freeboard these errors are exacerbated in areas with a sparse lead distribution in consolidated ice pack conditions additionally model errors can impact ocean geostrophic currents derived from satellite altimeter data while remaining biases in these models may impact longer term multi sensor oceanographic time series of sea level change in the arctic this study focuses on an assessment of five state of the art arctic mss models ucl13 04 dtu15 13 10 and a commonly used ggm egm2008 we describe errors due to unresolved gravity features inter satellite biases and remaining satellite orbit errors and their impact on the derivation of sea ice freeboard the latest mss models incorporating cryosat 2 sea surface height measurements show improved definition of gravity features such as the gakkel ridge the standard deviation between models ranges 0 03 0 25 m the impact of remaining mss ggm errors on freeboard retrieval can reach several decimeters in parts of the arctic while the maximum observed freeboard difference found in the central arctic was 0 59 m ucl13 mss minus egm2008 ggm the standard deviation in freeboard differences is 0 03 0 06 m

morphology of sea ice pressure ridges in the northwestern weddell sea in winter altimeter during winter weddell outflow study with the german r v polarstern in 2006 an optimal cutoff height of 0 62 m derived from the best fits between the measured and theoretical ridge height and spacing distributions was first used to separate pressure ridges from other sea ice surface undulations it was found that the measured ridge height distribution was well modeled by a negative exponential function and the ridge spacing distribution by a lognormal function next based on the ridging intensity ri the ratio of mean ridge sail height to mean spacing all profiles were clustered into three regimes by an improved k means clustering algorithm ri 0 01 0 01 0 026 denoted as c1 c 2 and c3 respectively mean and standard deviation of sail height was 0 99 0 07 m in regime c1 1 12 0 06 m in c2 and 1 17 0 04 m in c3 respectively while the mean spacings and standard deviations were 232 240 m 54 20 m and 31 5 6 m these three ice regimes coincided closely with distinct sea ice regions identified in a satellite radar image where c1 corresponded to the broken ice in the marginal ice zone and level ice formed in the larsen polynya c2 corresponded to the deformed first and second year ice formed by dynamic action in the center of the study region and c3 corresponded to heavily deformed ice in the outflowing branch of the weddell gyre the results of our analysis showed that the relationship between the mean ridge height and frequency was well modeled by a logarithmic function with a correlation coefficient of 0 8 although such correlation was weaker when considering each regime individually the measured ridge height and frequency were both greater than those reported by others for the ross sea compared with reported values for other parts of the antarctic the present ridge heights were greater but the ridge frequencies and ridging intensities were smaller than the most extreme of them meanwhile average thickness of ridged ice in our study region was significantly larger than that of the coastal ross sea showing the importance of deformation and ice age for ice conditions in the northwestern weddell sea

gaia s breath global methane exhalations abstract methane ch 4 is the most abundant organic compound in the earth s atmosphere where it acts as a greenhouse gas and thus has implications for global climate change the current atmospheric ch 4 budget however does not take into account geologically sourced ch 4 seepage geological sources of ch 4 include natural macro and micro seeps mud volcanoes and other miscellaneous sources such as gas hydrates magmatic volcanoes geothermal regions and mid ocean ridges macro seeps contribute 25 tg teragrams ch 4 yr to the atmosphere whereas micro seepage contributes perhaps 7 tg ch 4 yr mud volcanoes emit 5 tg ch 4 yr and miscellaneous sources emit 8 tg ch 4 yr to the atmosphere thus the total contribution to the atmosphere from geological sources is estimated to be 45 tg ch 4 yr which is significant to the atmospheric organic carbon cycle and should be included in any global inventory of atmospheric ch 4 we argue that the atmospheric ch 4 global inventory of the interplanetary panel on climate change must be adjusted in order to incorporate geologically sourced ch 4 from naturally occurring seepage

evidence of a widespread paleo pockmarked field in the orange basin an indication of an early eocene massive fluid escape event offshore south africa abstract the detailed interpretation and seismic attribute analysis of 2d and 3d seismic reflection data sets revealed the presence of a distinct seismic horizon displaying circular and elongated depressions in early eocene sediments along the northwestern slope of the orange basin on the southwest african margin their occurrence within a single seismic horizon indicates a contemporaneous formation process we interpret the depressions as paleo pockmarks which occur as single pockmarks predominantly nne ssw aligned pockmark trains and coalescing elongated pockmarks the paleo pockmarked surface covers an area of 2800 km 2 and has been mapped by integrating the 3d dataset with industrial 2d seismic grids the spatial and temporal occurrence of the paleo pockmarks is associated to two episodes of rapid sedimentation during the late maastrichtian to paleocene comprising fine grained shelf eroded material we propose that they were formed during the early eocene by the seepage of both 1 overpressured pore fluids from disequilibrium compaction of upper maastrichtian sediments and 2 thermogenic gas from underlying cretaceous mature source rocks we show that the location of the pockmarks is controlled by the underlying faults system of the paleo slope the paleocene eocene transition is known for its series of hyperthermal events characterized by negative excursions of the carbon isotope curve the early eocene widespread event of fluid and thermogenic gas escape identified in this work can be an example of the type of carbon release processes occurring in hydrocarbon prone sedimentary basins during this time

ml m0 as a regional seismic discriminant the m b m s ratio determined by teleseismic observations has proven to be an effective discriminant for explosive sources tend to be significantly richer in short period energy than are earthquakes unfortunately this method is limited by the detection threshold of teleseismic surface waves however recent advances in instrumentation allowing low amplitude surface wave measurements coupled with new analytical techniques make it feasible to use regional waveform data to determine the long period source excitation level of low magnitude events we propose using the ratio of m l local magnitude to m 0 scalar seismic moment as an analogous regional discriminant we applied this criterion to a data set of 299 earthquakes and 178 explosions and found that this ratio seems to be diagnostic of source type for a given m 0 the m l of an explosion is more than 0 5 magnitude units larger than that of an earthquake this separation of populations with respect to source type can be attributed to the fact that m l is a short period 1 hz energy measurement whereas seismic moment is determined from long period body wave phases period 4 s and surface waves 10 to 40 sec using regional stations with sources 200 to 600 km away the effective threshold for magnitude measurements for this discriminant is found to be m l 3 1 for earthquakes and m l 3 6 for explosions this method does require the determination of regional crustal models and path calibrations from master events or by other means

spatial and temporal variations in seismicity in the imperial valley 1902 1984 earthquakes with m l 4 5 that occurred between 1932 and 1973 in the imperial valley region and their related foreshocks and aftershocks are relocated using station delays derived from calibration events that were well recorded at regional distances between 1979 and 1981 the relocated seismicity shows that there was an increase in seismicity in regions northeast of the imperial fault 5 to 6 yr prior to the 1940 m s 7 1 imperial valley earthquake a study of intensity reports for felt earthquakes prior to 1932 also suggests an increase in seismicity in regions surrounding the imperial fault as early as 1917 isoseismal patterns description of the mainshock sequence and patterns of seismicity before and after the 1915 imperial valley earthquakes suggest that the earthquakes occurred off the imperial fault in this case seismicity between 1906 and 1940 would nearly encircle the portion of the imperial fault that ruptured during 1940 in both the 1940 and 1979 imperial valley earthquake sequences aftershocks of m l 4 5 occurred only for 2 months following the mainshock the aftershock sequences were followed by periods of quiescence lasting up to 10 yr in the region within 30 km of the mainshock this is in contrast to m l 6 0 earthquakes occurring near the edges of the imperial valley that had aftershocks of m l 4 5 occurring for up to 4 yr after the mainshock these differences may be related to the high heat flow within the imperial valley

ocean waves across the arctic attenuation due to dissipation dominates over scattering for periods longer than 19 s the poorly understood attenuation of surface waves in sea ice is generally attributed to the combination of scattering and dissipation scattering and dissipation have very different effects on the directional and temporal distribution of wave energy making it possible to better understand their relative importance by analysis of swell directional spreading and arrival times here we compare results of a spectral wave model using adjustable scattering and dissipation attenuation formulations with wave measurements far inside the ice pack in this case scattering plays a negligible role in the attenuation of long swells specifically scattering dominated attenuation would produce directional wave spectra much broader than the ones recorded and swell events arriving later and lasting much longer than observed details of the dissipation process remain uncertain average dissipation rates are consistent with creep effects but are 12 times those expected for a laminar boundary layer under a smooth solid ice plate

on the uncertainty of sea ice isostasy during late winter 2007 coincident measurements of sea ice were collected using various sensors at an ice camp in the beaufort sea canadian arctic analysis of the archived data provides new insight into sea ice isostasy and its related r factor through case studies at three scales using different combinations of snow and ice thickness components at the smallest scale 1m point scale isostasy is not expected so we calculate a residual and define this as zjey to describe vertical displacement due to deformation from 1 to 10m length scales we explore traditional isostasy and identify a specific sequence of thickness calculations which minimize freeboard and elevation uncertainty an effective solution exists when the r factor is allowed to vary ranging from 2 to 12 with mean of 5 17 mode of 5 88 and skewed distribution at regional scales underwater airborne and spaceborne platforms are always missing thickness variables from either above or below sea level for such situations realistic agreement is found by applying small scale skewed ranges for the r factor these findings encourage a broader isostasy solution as a function of potential energy and length scale overall results add insight to data collection strategies and metadata characteristics of different thickness products

broadband modelling of regional seismograms imperial valley to pasadena summary this paper addresses broadband wave propagation along a corridor from imperial valley to pasadena california the path consists of 50 km of slow basin structure with a shallow moho followed by 250 km of relatively normal southern california structure approaching pasadena events occurring in the valley produce extended body wave codas which carry a dispersive waveform imprint along with longer period rayleigh waves many features of these seismograms at periods greater than a few seconds can be modelled by applying a finite difference technique to a 2 d structure shorter periods display complex behaviours not easily modelled by present techniques especially for shallow events events occurring in the normal structure produce broadband sh waveforms that can be modelled analytically if some extra empirically derived alignment parameters determined from calibration events are used these parameters are determined by adjusting traveltime differentials between the decomposed wavefield s ss etc for example delays in ss relative to s correspond to local corrections for sediment cover for a particular source region source complexity such as asperities and directivity become increasingly important at shorter periods as demonstrated by numerical experiments and observation

roughness of weddell sea ice and estimates of the air ice drag coefficient the roughness of a sheet of sea ice encodes its deformational history and determines its aerodynamic coupling with the overlying air and underlying water here we report snow surface ice surface and ice underside roughness computed from 47 surface elevation profiles collected during a transect of the weddell sea the roughness for each surface parameterized as the standard deviation of the surface elevation segregates according to whether or not a floe has been deformed deformed ice has greater roughness than undeformed ice regardless of deformational history the underside roughness is almost always greater than the snow surface and ice surface roughnesses which are nearly equal roughness spectra for all three surfaces and for both deformed and undeformed ice roll off roughly as k 1 when the wavenumber k is between 0 1 and 3 rad m 1 the snow surface and underside spectra roll off somewhat faster than k 1 and the ice surface spectra roll off somewhat slower than k 1 both top and underside arctic ice roughness spectra on the other hand have been reported to roll off faster than k 2 we speculate that the excess spectral intensity at high wavenumbers in the antarctic ice surface spectra results from the small scale roughness that the ice sheet had on consolidation this excess high wavenumber spectral intensity persists in the ice surface spectra of second year ice evidently once formed the ice surface remains unchanged on the microscale until the entire ice sheet melts with a remote measurement of roughness we should be able to decide whether an ice floe is deformed or undeformed our spectral analysis hints that remote sensing may also be able to differentiate between first year and second year ice from the snow surface spectra we compute a roughness scale that parameterizes the air ice momentum coupling and lets us estimate the neutral stability drag coefficient referenced to a height of 10 m cdn10 typical cdn10 values are 1 1 1 4 10 3 over undeformed ice and 1 3 1 8 10 3 over deformed ice

gas hydrates free gas distribution and fault pattern on the west svalbard continental margin summary a 3 d tomographic analysis of seismic velocity and attenuation fields is presented with the purpose to analyse the intimate relation of gas hydrates and free gas distribution with the fault pattern the 3 d four component seismic data have been acquired offshore western svalbard the analysis of the subbottom topography of the base of the stability field of gas hydrates indicated by the bottom simulating reflector and the thickness of the underlying free gas bearing zone suggest a fault induced compartmentalization of the gas reservoir the proposed fluid and gas circulation scheme assumes deep sourced warm fluids moving upwards mainly along high permeability faults and fractures below the gas hydrate stability zone faults change from being a pathway of fluid flow to being barriers to fluid flow in the hydrate stability zone consequently below the hydrate stability zone free gas is transferred from the permeable faults to non faulted but fault bounded sediments where it accumulates below the base of the hydrate stability zone producing a significantly thicker free gas layer the tomographic approach is therefore proposed as an effective procedure to provide detailed information on 3 d p and s wave velocity and attenuation distribution in marine sediments and specifically to examine the details of the distribution of the gas hydrates and of the free gas for which the dependence on the vp vs and qp is now fairly well known

arctic ocean gravity geoid and sea ice freeboard heights from icesat and grace 1 icesat laser measurements provide a high resolution mapping of the sea ice surface of the arctic ocean which can be inverted to determine gravity anomalies and sea ice freeboard heights by a lowest level filtering scheme in this paper we use updated terrestrial gravity data from the arctic gravity project in combination with grace gravity field models to derive an improved arctic geoid model this model is then used to convert icesat measurements to sea ice freeboard heights with a coarse lowest level surface method the derived freeboard heights show a good qualitative agreement to the coverage of multi year sea ice however comparison to an airborne lidar underflight north of greenland shows that the lowest level filtering scheme may introduce a bias we finally use the icesat and grace results to derive new gravity anomalies by fourier inversion the satellite only gravity field shows all major tectonic features of the arctic ocean and has an accuracy of 6 mgal compared to recent airborne gravity data illustrating the usefulness of icesat data for gravity field determination

offshore mud volcanoes and onland faulting in southwestern africa neotectonic implications and constraints on the regional stress field abstract recently discovered mud volcanoes in the orange basin offshore southwestern africa denote the existence of neotectonic faults in the submerged continental shelf interpretation of seismic lines perpendicular to the trend of the alignment of the mud volcanoes shows flower structures diagnostic of strike slip faulting along a n nnw direction analysis at the regional scale of onland neotectonic features in southwestern africa shows that recent faulting occurred both in central namibia and namaqualand south africa and that it created both n nnw and nw trending lineaments it is proposed that the newly discovered offshore neotectonic activity and the onland structures described in this paper represent the structural expression of the same stress field these structures form a set of conjugate transtensive faults which constrain the regional horizontal greatest compressive stress in a nw nnw direction such stress orientation also supported by in situ stress measurements defines the so called wegener stress anomaly the predominant present day stress field of southwest africa the wegener anomaly is incompatible with the stress orientation required by plate scale tectonic constraints mainly in the form of recently published gps motion values for the african plate

comparison of the sea ice thickness distribution in the lincoln sea and adjacent arctic ocean in 2004 and 2005 results of helicopter borne electromagnetic measurements of total ice plus snow sea ice thickness performed in may 2004 and 2005 in the lincoln sea and adjacent arctic ocean up to 868 n are presented thickness distributions south of 848 n are dominated by multi year ice with modal thicknesses of 3 9 m in 2004 and 4 2 m in 2005 mean thicknesses 4 67 and 5 18 m respectively modal and mean snow thickness on multi year ice amounted to 0 18 and 0 30 m in 2004 and 0 28 and 0 35 m in 2005 there are also considerable amounts of 0 9 2 2 m thick first year ice modal thickness mostly representing ice formed in the recurring refrozen lincoln polynya results are in good agreement with ground based electromagnetic thickness measurements and with ice types demarcated in satellite synthetic aperture radar imagery four drifting buoys deployed in 2004 between 868 n and 84 58 n show a similar pattern of a mean southward drift of the ice pack of 83 18 km between may 2004 and april 2005 towards the coast of ellesmere island and nares strait the resulting area decrease of 26 between the buoys and the coast is larger than the observed thickness increase south of 848 n this points to the importance of shear in a narrow band along the coast and of ice export through nares strait in removing ice from the study region

gas hydrate and mud volcanoes on the southwest african continental margin off south africa widespread occurrence of bottom simulating reflectors bsrs has been detected in multichannel seismic profiles on the upper continental slope in the southern periphery of the orange river delta probably indicating the presence of large quantities of gas hydrate in this area this report is the first to show the presence of bsrs on seismic records on the southwest african continental margin south of the walvis ridge another remarkable feature in the area is the occurrence of a large number of mud volcanoes the distribution of the bsrs and the location of the mud volcanoes are controlled by the locations of active faults the gas hydrate in this region may consist of a mixture of microbial and thermogenic gas whereas much of the gas flowing through the mud volcanoes probably originated from deep seated aptian source shales

the underside topography of sea ice over the continental shelf of the beaufort sea in the winter of 1990 a spatial section of draft across 348 km of sea ice was obtained by moored subsea sonars in the beaufort sea in the winter of 1990 the ice field was a mixture of first year and multiyear types with mean draft of the order of 3 m level ice of 0 to 4 m draft occupied approximately 50 of the section within this fraction draft values of 0 and 1 5 m were most common while at 2 to 3 m draft a noticeable contribution was made by rafted first year ice deformed ice was observed to a maximum draft of nearly 27 m keels within the section were identified using both the rayleigh criterion and a new criterion based on level ice both criteria defined exponentially distributed populations but with different e folding scales the observations revealed an ice cover whose statistical properties are consistent with other data from the periphery of the polar pack in the beaufort sea but which are much more severe than those of ice found in the seasonal ice zone only a few tens of kilometres to the south the cross sectional shape of individual keels was highly variable but on average the distribution of ice within a keel was an exponential function of draft the topography of both first year and old ice subsections of the data was fractal in character with a dimension of about 1 5 for both ice types the average mass of sea ice per unit area was estimated as 2540 2970 kg m 2 with 68 73 of this mass contributed by deformed ice the large uncertainties in these estimates arise because the porosity of keels and the burden of snow or melt water upon the ice are not known

evolution of the stress field in southern california and triggering of moderate size earthquakes a 200 year perspective changes in stress in southern california are modeled from 1812 to 2025 using as input 1 stress drops associated with six large 7 0 7 5 earthquakes through 1995 and 2 stress buildup associated with major faults with slip rates 3 mm yr as constrained by geodetic paleoseismic and seismic measurements evolution of stress and the triggering of moderate to large earthquakes are treated in a tensoffal rather than a scalar manner we present snapshots of the cumulative coulomb failure function acff as a function of time for faults of various strike dip and rake throughout southern california we take acff to be zero everywhere just prior to the great shock of 1812 we find that about 95 of those well located m 6 earthquakes whose mechanisms involve either strike slip or reverse faulting are consistent with the coulomb stress evolutionary model that is they occurred in areas of positive acff the interaction between slow moving faults and stresses generated by faster moving faults significantly advanced the occurrence of the 1933 long beach and 1992 landers events in their earthquake cycles coulomb stresses near major thrust faults of the western and central transverse ranges have been accumulating for a long time future great earthquakes along the san andreas fault especially if the san bernardino and coachella valley segments rupture together can trigger moderate to large earthquakes in the transverse ranges as appears to have happened in the santa barbara earthquake that occurred 13 days after the great san andreas shock of 1812 maps of current acff provide additional guides to long term earthquake prediction

digital terrain mapping of the underside of sea ice from a small auv 1 in april 2007 the first three dimensional digital terrain mapping of the underside of sea ice to be done from an ice launched autonomous underwater vehicle auv was carried out at an ice camp in the beaufort sea using the gavia vehicle which could be launched and recovered through 3 1 m holes gavia was equipped with a geoswath 500 khz interferometric sonar system which yielded swaths of typical width 80 m the imagery showed the morphological distinctions between first year fy and multi year my ice undersides the contrast between the shapes of fy and my ridges and the appearance of refrozen leads ice drafts were validated by drilling and it was found that ridge slope statistics and local probability density functions pdfs of draft could be derived with high precision the special opportunities offered by access to 3 d mapping are pointed out

impact of cretaceous sea level rise and anoxic events on the mesozoic carbonate platform of yugoslavia the adriatic dinaric carbonate platform of yugoslavia was influenced by rapid sea level rise and an oceanic anoxic event during the cenomanian turonian open marine biota such as planktonic foraminifera radiolarians and locally even ammonites associated with and bracketed by successions of typical shallow water carbonates indicate partial drowning of substantial areas of the platform during this time suggestive furthermore that the rate of increase of water depth was locally great enough to outpace carbonate production the presence of carbon rich and fish bearing platy limestones commonly cherty as an associated coeval facies indicates the development of anoxic or euxinic environments and the stromatolitic laminations in such rocks are attributed to the action of bacterial mats it is suggested that an extensive column of deoxygenated water developed in the neighboring marche umbrian adriatic deep water basin and was carried on to the carbonate platform during the cenomanian turonian transgression

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

a re examination of historic earthquakes in the san jacinto fault zone california the high level of seismic activity and the potential for large earthquakes in the san jacinto fault zone southern california make it desirable to have accurate locations and source parameters for as many previous events as possible prior to the installation of a dense seismic network in this region earthquakes were located using only a few stations with generally poor azimuthal coverage resulting in considerable uncertainty in the locations we relocate and obtain moment estimates for historic pre wwssn earthquakes in the western imperial valley by comparing the waveforms and travel times with recent earthquakes in the region all the events are in the m l 5 5 to 6 5 range the historic earthquakes of interest occurred in 1937 1942 and 1954 we use the 1968 borrego mountain 1969 coyote mountain and 1987 elmore ranch earthquakes as calibration events we employ regional and teleseismic data from continuously operating stations with pasadena debilt berkeley ottawa and st louis recording most of the events the waveforms imply that all the events are almost pure strike slip events on vertical or near vertical faults approximate values for the strikes were obtained and are within the range of observed strikes for well studied earthquakes in this region the earthquakes are relocated by comparing s p and surface wave s travel times of historic events with the presumably well located recent events the relocations require only a small change in location for the 1954 event and a larger adjustment in the 1942 epicenter it also appears that the 1969 earthquake may have been mislocated the moment estimates are obtained by direct comparison of the maximum amplitudes the moment estimates imply that the 1968 and not the 1942 earthquake is the largest to have occurred in the region this century previous magnitude estimates suggested the 1942 event was larger

a seismic reflection profile across the cascadia subduction zone offshore central oregon new constraints on methane distribution and crustal structure in 1989 we conducted an onshore offshore seismic experiment to image the crustal structure of the cascadia forearc in this paper we discuss the processing and interpretation of a multichannel seismic reflection profile across the continental margin that was collected as part of this effort this profile reveals several features of the forearc that were not apparent in an earlier coincident reflection profile one of the most important of these features is a very strong bottom simulating reflection bsr beneath the midslope region that is nearly continuous from water depths of about 1500 m to 600 m where it appears to crop out on the seafloor the pressure and temperature conditions at the bsr derived from our observations are remarkably consistent with the experimentally determined phase diagram for a methane hydrate seawater system over a broad range of temperatures and pressures assuming hydrostatic pressure and the temperature gradiant measured near the base of the continental slope during ocean drilling program odp leg 146 interval velocities and reflection coefficients derived from the data indicate that the bsr represents a contrast between sediment with a small amount of hydrate overlying sediment containing free gas consistent with results obtained during leg 146 although the regional distribution of the anomalously strong bsr beneath the midslope is poorly known we speculate that it may be related to apparent slope instability the data also provide constraints on the thickness and geometry of the siletz terrane which is the basement beneath the shelf and acts as the subduction zone backstop a deep reflection which might mistakenly be interpreted to be moho if coincident large aperture data were not available is interpreted to be the base of the siletz terrane a recently active strike slip fault zone that overlies the seaward edge of the siletz terrane suggests that the siletz terrane controls the location of decoupling of the subduc tion complex from the rest of the forearc

tectonic geomorphology and hydrocarbon induced topography of the mid channel anticline santa barbara basin california the geomorphology of the western sector of the mid channel anticline mca santa barbara southern california suggests the actively growing fold is laterally propagating to the west the presence of fold scarps and cross faults that segment the structure suggests that buried faults that are producing the folding are present at shallow depths the summit area of the anticline at the last glacial maximum 22 to 19 ka was probably a small late pleistocene island evidence for presence of the island includes what appears to be terrestrial erosion and is supported by assumption of sea level change and rates of uplift and subsidence pockmarks and domes ranging in diameter from 10 to 100 m and several meters deep are present along the crest and flanks of the mca these features appear to be the result of hydrocarbon emission their formation has significantly modified the surface features producing simple to complex erosional and or constructional topography a large pockmark near the anticline crest dated by two calibrated ams radiocarbon dates of 25 3 and 36 9 ka continues to emit hydrocarbon gases we term the topography produced by hydrocarbon emission as hydrocarbon induced topography hit 2007 elsevier b v all rights reserved

interaction of the san jacinto and san andreas fault zones southern california triggered earthquake migration and coupled recurrence intervals two lines of evidence suggest that large earthquakes that occur on either the san jacinto fault zone sjfz or the san andreas fault zone safz may be triggered by large earthquakes that occur on the other first the great 1857 fort tejon earthquake in the safz seems to have triggered a progressive sequence of earthquakes in the sjfz these earthquakes occurred at times and locations that are consistent with triggering by a strain pulse that propagated southeastward at a rate of 1 7 kilometers per year along the sjfz after the 1857 earthquake second the similarity in average recurrence intervals in the sjfz about 150 years and in the mojave segment of the safz 132 years suggests that large earthquakes in the northern sjfz may stimulate the relatively frequent major earthquakes on the mojave segment analysis of historic earthquake occurrence in the sjfz suggests little likelihood of extended quiescence between earthquake sequences

a statistical analysis of arctic pressure ridge morphology individual pressure ridges were identified on both sensors the shape on the upward looking sonar was used to obtain draft and apparent slopes and width of each ridge while the orientation of the ridge as revealed by the side scan sonar was used to convert these figures into absolute slopes and width the data set comprises 729 ridges it was found that in addition to ridge spacing ridge drafts fit a lognormal distribution better than a negative exponential that the mean draft of ridges diminishes with downstream distance in the trans 3polar drift stream at about 0 625 m per degree suggesting a faster melt rate for ridge bottoms than for the ice as a whole and that ridge widths and slopes also fit lognormal distributions an empirical relationship was found relating ridge slope to the ratio of half width to draft the mean ridge slope varied with location but always lay in the range 21 7 to 26 5

a review of methane and gas hydrates in the dynamic stratified system of the blake ridge region offshore southeastern north america abstract the blake ridge region lies on the passive margin of southeastern north america and contains a large amount of methane gas hydrate the methane and methane gas hydrate are predominantly biogenic apparently produced by co2 reduction reflection seismics indicate that bottom simulating reflectors bsrs enclose 55 000 km2 with high amplitude bsrs covering 26 000 km2 ocean drilling program odp leg 164 drilled three deep holes on a 10 km long transect sites 994 995 and 997 water depth 2770 2798 m based on sampling and geochemical thermal seismic and borehole geophysical measurements gas hydrates are most likely present between 190 and 450 m in sediment column gas hydrate is most often disseminated throughout the sediment column although concentrations occur within specific sedimentary horizons within supposed fault zones and at the base of gas hydrate stability bghs where methane recycling produces more pervasive concentrations of gas hydrate estimates of gas hydrate inventory are based on a variety of methods including geochemical proxies vertical seismic profiling electric logging and measurements of in situ methane over the entire sediment column at least 2 4 of pore space volume 1 2 sediment volume is occupied by methane gas hydrates but average and maximum estimates are 5 4 and 12 respectively extrapolation of vertical gas hydrate and methane inventory over the area containing high amplitude bsrs yields estimates of 67 406 gt gigatons 1015 g of methane gas hydrate or 9 52 gt of methane and 2 6 27 gt of methane occurring as gas bubbles below the bghs average values are 185 gt of gas hydrate and 24 gt of methane as gas hydrate any gas hydrate occurring outside the area underlain by bsrs as suggested by geochemical evidence or that associated with low amplitude bsrs may increase these estimates by an unknown factor various data give conflicting pictures of mass transport with blake ridge sediments the data can be reconciled by viewing the upper sedimentary section accumulation of gas hydrate in the blake ridge sediments depends on the amount of methane leaving the system versus the amount of methane entering the gas hydrate stability zone ghsz over geologic time although there are some point sources of methane loss from the sediments e g seafloor seeps odp site 996 of unknown magnitude most of the documented methane loss occurs through diffusion and consumption at the sulfate methane interface smi by anaerobic methane oxidation amo 2 108 mol year 1 methane entering the ghsz at a rate of 1 3 109 mol year 1 indicates a methane trapping efficiency of 85 129i measurements suggest that the blake ridge system has accumulated gas hydrate over as much as 55 million years

source characteristics of earthquakes along the southern san jacinto and imperial fault zones 1937 to 1954 abstract body waveform inversion techniques are used to study the source parameters of four earthquakes occurring between 1937 and 1954 along the southern san jacinto and imperial faults 1937 buck ridge 1940 imperial valley 1942 borrego mountain and 1954 salada wash events all earthquakes had simple rupture histories with the exception of the 1940 imperial valley main shock which consisted of at least four subevents whose relative locations indicate unilateral rupture toward the southeast earthquakes in regions of high heat flow 80 mw m 2 had focal depths near the base of the seismogenic zone 8 to 10 km the 1937 buck ridge earthquake located in a region of lower heat flow however appears to have occurred at a shallow 3 2 km depth the location mechanism and aftershock distribution for the 1942 borrego mountain earthquake suggest it could have occurred along the split mountain fault a recently identified northeast trending cross fault located between the elsinore and coyote creek faults or along an unnamed fault that parallels the trend of the coyote creek fault moment and rupture length estimates obtained from this study agree well with estimates obtained in previous studies that used different data sets

sea ice surface roughness estimates from airborne laser scanner and laser altimeter observations in fram strait and north of svalbard we present sea ice surface roughness estimates i e the standard deviation of relative surface elevation in the arctic regions of fram strait and the nansen basin north of svalbard acquired by an airborne laser scanner and a single beam laser altimeter in 2010 we compare the scanner to the altimeter and compare the differences between the two survey regions we estimate and correct sensor roll from the scanner data using the hyperbolic response of the scanner over a flat surface measurement surveys had to be longer than 5 km north of svalbard and longer than 15 km in fram strait before the statistical distribution in surface roughness from the scanner and altimeter became similar the shape of the surface roughness probability distributions agrees with those of airborne electromagnetic induction measurements of ice thickness the ice in fram strait had a greater mean surface roughness 0 16m vs 0 09m and a wider distribution in roughness values than the ice in the nansen basin an increase in surface roughness with increasing ice thickness was observed over fast ice found in fram strait near the coast of greenland but not for the drift ice

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member

taking a look at both sides of the ice comparison of ice thickness and drift speed as observed from moored airborne and shore based instruments near barrow alaska data from the seasonal ice zone observing network sizonet acquired near barrow alaska during the 2009 10 ice season allow novel comparisons between measurements of ice thickness and velocity an airborne electromagnetic survey that passed over a moored ice profiling sonar ips provided coincident independent measurements of total ice and snow thickness and ice draft at a scale of 10 km once differences in sampling footprint size are accounted for we reconcile the respective probability distributions and estimate the thickness of level sea ice at 1 48 0 1 m with a snow depth of 0 12 0 07 m we also complete what we believe is the first independent validation of radar derived ice velocities by comparing measurements from a coastal radar with those from an under ice acoustic doppler current profiler adcp after applying a median filter to reduce high frequency scatter in the radar derived data we find good agreement with the adcp bottom tracked ice velocities with increasing regulatory and operational needs for sea ice data including the number and thickness of pressure ridges coordinated observing networks such as sizonet can provide the means of reducing uncertainties inherent in individual datasets

faulted structure of the bottom simulating reflector on the blake ridge western north atlantic abstract high resolution multichannel seismic data collected from the blake ridge in the western north atlantic by the naval research laboratory s deep towed acoustics geophysics system dtags show that the bottom simulating reflector bsr in this area is the reflection from the interface between an approx 440 m thick section of hydrate bearing sediment overlying and approx 5 m thick layer of methane gas rich sediment the high resolution attainable by the deep tow seismic system reveals normal fault offsets of approx 20 m in the bsr these growth faults may provide a path for vertical migration of methane initially concentrated beneath the hydrate bearing sediment enabling hydrate to form throughout sediment above the bsr because the bsr represents a methane gas methane hydrate phase boundary rather than a lithologic or diagenetic horizon the observed off set of the bsr itself reflects discontinuities in the pressure temperature field across the fault zones where they intersect the bsr directional ambient noise bottom scattering deep towed array geophysical system ocean bottom seismometer towed array