Time filter

Source Type

Diez A.,Alfred Wegener Institute for Polar and Marine Research | Diez A.,Karlsruhe Institute of Technology | Eisen O.,Alfred Wegener Institute for Polar and Marine Research | Eisen O.,University of Heidelberg | And 3 more authors.
Annals of Glaciology | Year: 2013

Two seismic surveys were carried out on the high-altitude glacier saddle, Colle Gnifetti, Monte Rosa, Italy/Switzerland. Explosive and vibroseismic sources were tested to explore the best way to generate seismic waves to deduce shallow and intermediate properties (<100 m) of firn and ice. The explosive source (SISSY) excites strong surface and diving waves, degrading data quality for processing; no englacial reflections besides the noisy bed reflector are visible. However, the strong diving waves are analyzed to derive the density distribution of the firn pack, yielding results similar to a nearby ice core. The vibrator source (ElViS), used in both P-and SH-wave modes, produces detectable laterally coherent reflections within the firn and ice column.We compare these with ice-core and radar data. The SH-wave data are particularly useful in providing detailed, high-resolution information on firn and ice stratigraphy. Our analyses demonstrate the potential of seismic methods to determine physical properties of firn and ice, particularly density and potentially also crystal-orientation fabric. Source

Schmitt D.R.,University of Alberta | Wilson T.J.,Ohio State University | Jarrard R.D.,University of Utah | Paulsen T.S.,University of Wisconsin - Oshkosh | And 3 more authors.
46th US Rock Mechanics / Geomechanics Symposium 2012 | Year: 2012

A set of hydraulic fracturing stress measurements were carried at depths of up to 1400 m below the rig floor at the bottom of the ANDRILL South McMurdo Sound borehole. The measurements were accomplished in open hole through indurated and low permeability glacial diamicts and shales. A 2000-m long wireline hosted straddle packer system was used that allowed for relatively rapid deployment; and seventeen successful measurements were made. Good breakdown pressures were observed in most of the tests; and this allowed constraints to be placed on the magnitude of the greatest horizontal compression. Correspondingly, the vertical stress was calculated by integrating the densities obtained from physical property logging of the nearly continuous core. In all cases, this vertical stress magnitude was intermediate between the horizontal stress values, and consequently indicating a strike-slip stress environment exists at this location. Copyright 2012 ARMA, American Rock Mechanics Association. Source

Hoecht G.,DMT Petrologic GmbH | Rost F.,DMT Petrologic GmbH | Luschen E.,Leibniz Institute For Angewandte Geophysik
76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014 | Year: 2014

In common-reflection-surface (CRS) imaging the data space is parameterized by operators that are expected to overlap in a continuous manner along events in the image space. These circumstances are employed in the operator-oriented scheme which integrates neighboring operators and, thereby, introduces multiple operators in the stacking process. Azimuth-dependant stacking velocities allow to account for a general type of model and are included in the hyperbolic CRS formula. We demonstrate the application of the operator-oriented CRS stacking method and the impact of azimuth-dependant stacking velocities in the context of a 3D WAZ land data set acquired over a crystalline basement. Source

Kuhn P.,University of Tubingen | Techmer A.,Leibniz Institute For Angewandte Geophysik | Weidenfeller M.,Landesamt fur Geologie und Bergbau Rheinland Pfalz
Quaternary Science Reviews | Year: 2013

Lower to middle Weichselian loess, loess derivatives and buried soils of the loess-paleosol sequence Alsheim (Central Europe) were characterised by particle size distribution, geochemical and micromorphological data. High rates of sedimentation with alternating phases of relocation are the main cause for a much less differentiation into Middle and Upper Weichselian loess-paleosol units of the Alsheim loess-paleosol sequence compared to other loess-paleosol sequences (e.g. Nussloch near Heidelberg), whereas the Lower Weichselian has distinct phases of pedogenesis resulting in Ah, Bw and Btw horizons.To distinguish between different loess deposits locally and intraregional, the degree of fineness is an easily applicable and suitable tool, though inappropriate for interregional comparisons. The chemical index of alteration (CIA) is low (<50=no weathering) for loess deposits in the Alsheim loess-paleosol sequence, which is in contrast to the worldwide compiled loess samples with CIA values ranging from >53 to <70 (Gallet etal., 1998). The highest weathering was detectable for Btw horizons with CIA values >70.A direct quantitative estimation of mean annual palaeotemperature and mean annual palaeoprecipitation can be provided by calculations based on geochemistry of soil horizons and sediments. The present mean annual precipitation (MAP) in the Mainz Basin is 789mm. In contrast, palaeoprecipitation data suggest a 150mm higher amount for the Last Interglacial (Btw horizon), a much lower amount of around 300-400mm MAPP (periods of loess and sandy loess deposition) and a MAPP of <500mm for Weichselian Interstadials (humus zones and Bw horizons). The calculated mean annual palaeotemperature (MAPT) for Interstadials with 8.9°C for Bw horizons or with 9.6°C for humus zones (or to 2K lower, considering the relation of the present MAT of the Mainz Basin with the MAT of Germany) seems to be a good approximation of the MAPT for Lower and Middle Weichselian Interstadials. A MAPT of 8.7°C (or 6.7°C) for Stadials (loess and sandy loess samples) is higher than other temperature estimations for Weichselian Stadials in Europe.Micromorphology shows compacted granular structure and moderately to strongly developed pedality as characteristic properties for aquatic loess, whereas channel microstructure with no pedality is typical for loess deposits. Spongy microstructure suggests a classification of the Lower Weichselian Mosbach Humus Zones as Chernozems. The Eemian paleosol (Btw horizon in Als III) has only weak clay illuviation, characteristic for drier regions in Europe.Palaeoclimate and soil formation of the Last Glacial-Interglacial cycle calculated from geochemistry and micromorphological data are in good accordance with other proxy data in Central Europe. This suggests that paleoclimate reconstruction based on palaeopedological analyses could be successfully implemented in Europe. Such data may provide a useful alternative to other proxies for correlating European records. © 2013 Elsevier Ltd. Source

Dahm T.,University of Hamburg | Kuhn D.,NORSAR | Ohrnberger M.,University of Potsdam | Kroger J.,Geologisches Landesamt Hamburg | And 4 more authors.
Geophysical Journal International | Year: 2010

Shallowly situated evaporites in built-up areas are of relevance for urban and cultural development and hydrological regulation. The hazard of sinkholes, subrosion depressions and gypsum karst is often difficult to evaluate and may quickly change with anthropogenic influence. The geophysical exploration of evaporites in metropolitan areas is often not feasible with active industrial techniques.We collect and combine different passive geophysical data as microgravity, ambient vibrations, deformation and hydrological information to study the roof morphology of shallow evaporites beneath Hamburg, Northern Germany. The application of a novel gravity inversion technique leads to a 3-D depth model of the salt diapir under study. We compare the gravity-based depth model to pseudo-depths from H/V measurements and depth estimates from small-scale seismological array data. While the general range and trend of the diapir roof is consistent, a few anomalous regions are identified where H/V pseudo-depths indicate shallower structures not observed in gravity or array data. These are interpreted by shallow residual caprock floaters and zones of increased porosity.The shallow salt structure clearly correlates with a relative subsidence in the order of 2 mm yr -1. The combined interpretation of roof morphology, yearly subsidence rates, chemical analyses of groundwater and of hydraulic head in aquifers indicates that the salt diapir beneath Hamburg is subject to significant ongoing dissolution that may possibly affect subrosion depressions, sinkhole distribution and land usage.The combined analysis of passive geophysical data may be exemplary for the study of shallow evaporites beneath other urban areas. © 2010 The Authors Journal compilation © 2010 RAS. Source

Discover hidden collaborations