Tectonic geomorphology of the San Andreas Fault zone from high resolution topography: An example from the Cholame segment   总被引：7，自引：0，他引：7  

J Ramn Arrowsmith  Olaf Zielke 《Geomorphology》2009,113(1-2):70

High resolution topographic data along fault zones are important aids in the delineation of recently active breaks. A 15 km-long portion of the south-central San Andreas Fault (SAF) along the southern Cholame segment contains well preserved tectonic landforms such as benches, troughs, scarps, and aligned ridges that indicate recurring earthquake slip. Recently acquired LiDAR topographic data along the entire southern SAF (“B4” project) have shot densities of 3–4 m^− 2. Computed from the LiDAR returns, Digital Elevation Models (DEMs) of 0.25 to 0.5 m resolution using local binning with inverse distance weighting and 0.8 m or larger search radii depict the tectonic landforms at paleoseismic sites well enough to assess them confidently. Mapping of recently active breaks using a LiDAR-only based approach compares well with aerial photographic and field based methods. The fault zone varies in width from meters to nearly 1 km and is comprised of numerous en echelon meter to kilometer-length overlapping sub parallel fault surfaces bounding differentially moving blocks that elongate parallel to the SAF. The semantic variations of what constitutes “active” and the importance of secondary traces influence the breadth and complexity of the resulting fault trace maps.  相似文献   

A pilot-scale field experiment for the microbial neutralization of a holomictic acidic pit lake     

Walter Geller  Matthias Koschorreck  Katrin Wendt-Potthoff  Elke Bozau  Peter Herzsprung  Olaf Büttner  Martin Schultze 《Journal of Geochemical Exploration》2009,100(2-3):153-159

A strategy to neutralize acidic pit lakes was tested in an upscaling process using field mesocosms of 26 to ca. 4500 m³ volume in the acidic pit Mining Lake 111 in Germany. After addition of the substrates Carbokalk and straw a neutral sediment layer formed, in which microbial sulfate and iron reduction as well as sulfide precipitation occurred. The net rate of neutralization was limited by the precipitation of iron sulfides rather than by microbial reactions. Oxidation of H₂S by ferric iron in the anoxic sediment lowered the net sulfate reduction rate. Seasonal fluctuations of iron sulfides in the sediment showed that the reaction products were not necessarily stable. The long-term success of the approach depends on the net partition of the precipitated iron-(mono-/di-) sulfide that is permanently buried in the anoxic sediment. It could be shown by field experiments that the long-term success of the neutralization depends on the spatial scale and duration of the experiments. Volumes from 26 to 4500 m³, exposition times from 4 months to 5 years, and increasingly thick coverings of the sediments with straw, from zero to 40 cm, were used. Net neutralization rates decreased from 41 meq m^− 2 d^− 1 in laboratory microcosms to a mean rate of 2.3 meq m^− 2 d^− 1 in the 4500 m³ field experiment. The results show that the success of the microbial treatment of acid pit lakes lastly depends on the limnological conditions in the lake that cannot be simulated by upscaling of simple laboratory experiments.  相似文献   

Consolidation around a point heat source (correction and verification)     

Aqeel Afzal Chaudhry  Jörg Buchwald  Olaf Kolditz  Thomas Nagel 《国际地质力学数值与分析法杂志》2019,43(18):2743-2751

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Novel basin modelling concept for simulating deformation from mechanical compaction using level sets     

Sean McGovern  Stefan Kollet  Claudius M. Bürger  Ronnie L. Schwede  Olaf G. Podlaha 《Computational Geosciences》2017,21(5-6):835-848

As sedimentation progresses in the formation and evolution of a depositional geologic basin, the rock strata are subject to various stresses. With increasing lithostatic pressure, compressional forces act to compact the porous rock matrix, leading to overpressure buildup, changes in the fluid pore pressure and fluid flow. In the context of petroleum systems modelling, the present study concerns the geometry changes that a compacting basin experiences subject to deposition. The purpose is to track the positions of the rock layer interfaces as compaction occurs. To handle the challenge of potentially large geometry deformations, a new modelling concept is proposed that couples the pore pressure equation with a level set method to determine the movement of lithostratigraphic interfaces. The level set method propagates an interface according to a prescribed speed. The coupling term for the pore pressure and level-set equations consists of this speed function, which is dependent on the compaction law. The two primary features of this approach are the simplicity of the grid and the flexibility of the speed function. A first evaluation of the model concept is presented based on an implementation for one spatial dimension accounting for vertical effective stress. Isothermal conditions with a constant fluid density and viscosity were assumed. The accuracy of the implemented numerical solution for the case of a single stratigraphic unit with a linear compaction law was compared to the available analytical solution [38]. The multi-layer setup and the nonlinear case were tested for plausibility.  相似文献   

A comparative simulation study of coupled THM processes and their effect on fractured rock permeability around nuclear waste repositories     

Jonny Rutqvist  Deborah Barr  Jens T. Birkholzer  Kiyoshi Fujisaki  Olaf Kolditz  Quan-Sheng Liu  Tomoo Fujita  Wenqing Wang  Cheng-Yuan Zhang 《Environmental Geology》2009,57(6):1347-1360

This paper presents an international, multiple-code, simulation study of coupled thermal, hydrological, and mechanical (THM) processes and their effect on permeability and fluid flow in fractured rock around heated underground nuclear waste emplacement drifts. Simulations were conducted considering two types of repository settings (1) open emplacement drifts in relatively shallow unsaturated volcanic rock, and (2) backfilled emplacement drifts in deeper saturated crystalline rock. The results showed that for the two assumed repository settings, the dominant mechanism of changes in rock permeability was thermal–mechanically induced closure (reduced aperture) of vertical fractures, caused by thermal stress resulting from repository-wide heating of the rock mass. The magnitude of thermal–mechanically induced changes in permeability was more substantial in the case of an emplacement drift located in a relatively shallow, low-stress environment where the rock is more compliant, allowing more substantial fracture closure during thermal stressing. However, in both of the assumed repository settings in this study, the thermal–mechanically induced changes in permeability caused relatively small changes in the flow field, with most changes occurring in the vicinity of the emplacement drifts.  相似文献   

Hybrid analytical and finite element numerical modeling of mass and heat transport in fractured rocks with matrix diffusion   总被引：1，自引：0，他引：1  

Christopher I. McDermott  Robert Walsh  Ralph Mettier  Georg Kosakowski  Olaf Kolditz 《Computational Geosciences》2009,13(3):349-361

Quantification of mass and heat transport in fractured porous rocks is important to areas such as contaminant transport, storage and release in fractured rock aquifers, the migration and sorption of radioactive nuclides from waste depositories, and the characterization of engineered heat exchangers in the context of enhanced geothermal systems. The large difference between flow and transport characteristics in fractures and in the surrounding matrix rock means models of such systems are forced to make a number of simplifications. Analytical approaches assume a homogeneous system, numerical approaches address the scale at which a process is operating, but may lose individual important processes due to averaging considerations. Numerical stability criteria limit the contrasts possible in defining material properties. Here, a hybrid analytical–numerical method for transport modeling in fractured media is presented. This method combines a numerical model for flow and transport in a heterogeneous fracture and an analytical solution for matrix diffusion. By linking the two types of model, the advantages of both methods can be combined. The methodology as well as the mathematical background are developed, verified for simple geometries, and applied to fractures representing experimental field conditions in the Grimsel rock laboratory.  相似文献   

Is the North Atlantic Oscillation reflected in Scandinavian glacier mass balance records?     

Atle Nesje   yvind Lie  Svein Olaf Dahl 《第四纪科学杂志》2000,15(6):587-601

The North Atlantic Oscillation (NAO) is one of the modes of climate variability in the North Atlantic region. The atmospheric circulation during the winter season in this region commonly displays a strong meridional (north–south) pressure contrast, with low air pressure (cyclone) centred close to Iceland and high air pressure (anticyclone) near the Azores. This pressure gradient drives the mean surface winds and the mid‐latitude winter storms from west to east across the North Atlantic, bringing mild moist air to northwest Europe. The NAO index is based on the difference of normalised sea‐level pressures (SLP) between Ponta Delgada, Azores and Stykkisholmur, Iceland. The SLP anomalies at these stations are normalised by division of each monthly pressure by the long‐term (1865–1984) standard deviation. Interannual atmospheric climate variability in northwest Europe, especially over Great Britain and western Scandinavia has, during the last decades, been attributed mainly to the NAO, causing variations in the winter weather over the northeast North Atlantic and the adjacent land areas. A comparison between the NAO index and the winter (December–March) precipitation between ad 1864 and 1995 in western Norway shows that these are strongly linked (correlation coefficient 0.77). Variations in the NAO index are also reflected in the mass balance records of glaciers in western Scandinavia. The NAO index is best correlated with mass balance data from maritime glaciers in southern Norway (e.g. Ålfotbreen R² = 0.51). The record of Holocene (last ca. 11 500 cal. yr) glacier variations of maritime glaciers in western Scandinavia is thus a proxy of pre‐instrumental NAO variations. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

ESR Dating of the Evolution of the Shuanghu Basin in the Northern Tibetan Plateau   总被引：3，自引：0，他引：3  

WU Zhenhan  JIANG Wan  Peter Blisniuk  BI Siwen  ZHANG Shukun  Olaf Kuchel  MAO Yi Institute of Geomechanics  CAGS  Minzu Xueyuan Nanlu  Beijing Institut fur Geowissenschaften  Universitat Potsdam  Postfach  D- Potsdam  Germany Liu Xinzhu 《《地质学报》英文版》1999,73(3):289-293

The Shuanghu basin is a NE-trending rift basin bounded by NE-striking normal faults and NW-striking shear-extensional faults of the northern Tibetan Plateau. Four samples from calcite veins in marginal faults and one sample from mudstone (S-3) were collected for dating the evolution of the Shuanghu basin by using the ESR spectrograph of EXM-type. Ages were calculated according to the close-equilibrium model on the basis of the measured ESR signal spectra of samples, providing good chronological information. It is known from the ESR dating that the extensional faulting and rifting of the Shuanghu area began at 4.92 Ma B.P., followed by regional folding in 3.56-1.36 Ma, NW-striking faulting in 0.60 Ma and normal faulting in 0.024 Ma in the Shuanghu basin.  相似文献   

Insect communities of Phragmites habitats used for sewage purification: Effects of age and area of habitats on species richness and herbivore-parasitoid interactions     

Olaf Athen  Teja Tscharntke   《Limnologica》1999,29(1):71-74

In 1994, 28 sewage purification plants based on common reed Phragmites australis were analyzed, to study fragmentation effects on diversity and on food web structure of insect communities. Purification plants differed in age (2 to 11 years) and area (10 to 2,500 m²). Both age and area were significantly correlated with species richness of herbivores. Populations of the two most abundant herbivores, the gall makers Lipara pullitarsis (Diptera, Chloropidae) and Giraudiella inclusa (Diptera, Cecidomyiidae), increased significantly with age and size of the Phragmites habitats, i.e. the purification plants. Incidence curves showed that only habitats older than 6 years and larger than 100 m² have a 50% probability of finding these two most abundant gall makers, and can correspondingly be considered to contribute to insect species conservation. Natural enemies were even more susceptible to habitat fragmentation than their phytophagous hosts or prey, thereby hampering possible biocontrol. Percent parasitism of both the Lipara and Giraudiella gall makers significantly increased with habitat age.  相似文献   

Methane in the southern North Sea: Sources, spatial distribution and budgets   总被引：3，自引：0，他引：3  

Maik Grunwald  Olaf Dellwig  Melanie Beck  Joachim W. Dippner  Jan A. Freund  Cora Kohlmeier  Bernhard Schnetger  Hans-Jürgen Brumsack 《Estuarine, Coastal and Shelf Science》2009,81(4):445-456

Measurements of methane (CH₄) so far have always shown supersaturation in the entire North Sea relative to the atmospheric partial pressure and the distribution of surface CH₄ reveals a distinct increase towards the shore. Since North Sea sediments presumably are an insignificant source for CH₄ the coastal contribution via rivers and tidal flats gains in importance.In this work, CH₄ data from the River Weser, the back barrier tidal flats of Spiekeroog Island (NW Germany), and the German Bight are presented. Results from the River Weser are compared to other rivers draining into the German Bight. Measurements in the tidal flat area of Spiekeroog Island highlight this ecosystem as an additional contributor to the overall CH₄ budget of the southern North Sea. A tidally driven CH₄ pattern is observed for the water column with maximum values during low tide. Tidal flat sediments turn out to be the dominating source because pore waters discharged during low tide are highly enriched in CH₄. In contrast, the freshwater contribution to the tidal flats by small coastal tributaries has almost no impact on water column CH₄ concentrations. The CH₄ level seems to be disturbed irregularly by wind forcing due to elevated degassing and prevention of advective flow when tidal flats remain covered by water.Based on our data, two model calculations were used to estimate the impact of tidal flats on the CH₄ budget in the German Bight. Our results demonstrate that the back barrier tidal flats of the east Frisian Wadden Sea contribute CH₄ in an order of magnitude between the Wash estuary and River Elbe and thus have to be considered in budget calculations.  相似文献