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221.
Boris Gurevich Miroslav Brajanovski Robert J. Galvin Tobias M. Müller Julianna Toms-Stewart 《Geophysical Prospecting》2009,57(2):225-237
Natural fractures in hydrocarbon reservoirs can cause significant seismic attenuation and dispersion due to wave induced fluid flow between pores and fractures. We present two theoretical models explicitly based on the solution of Biot's equations of poroelasticity. The first model considers fractures as planes of weakness (or highly compliant and very thin layers) of infinite extent. In the second model fractures are modelled as thin penny-shaped voids of finite radius. In both models attenuation is a result of conversion of the incident compressional wave energy into the diffusive Biot slow wave at the fracture surface and exhibits a typical relaxation peak around a normalized frequency of about 1. This corresponds to a frequency where the fluid diffusion length is of the order of crack spacing for the first model and the crack diameter for the second. This is consistent with an intuitive understanding of the nature of attenuation: when fractures are closely and regularly spaced, the Biot's slow waves produced by cracks interfere with each other, with the interference pattern controlled by the fracture spacing. Conversely, if fractures are of finite length, which is smaller than spacing, then fractures act as independent scatterers and the attenuation resembles the pattern of scattering by isolated cracks. An approximate mathematical approach based on the use of a branching function gives a unified analytical framework for both models. 相似文献
222.
Paul J. Umhoefer Tobias Schwennicke† Maya T. Del Margo Gabriela Ruiz-Geraldo† James C. Ingle Jr. ‡ William McIntosh§ 《Basin Research》2007,19(2):297-322
Transtensional basins are sparsely described in the literature compared with other basin types. The oblique‐divergent plate boundary in the southern Gulf of California has many transtensional basins: we have studied those on San Jose island and two other transtensional basins in the region. One major type of transtensional basin common in the southern Gulf of California region is a fault‐termination basin formed where normal faults splay off of strike‐slip faults. These basins suggest a model for transtensional fault‐termination basins that includes traits that show a hybrid nature between classic rift and strike‐slip (pull‐apart) basins. The traits include combinations of oblique, strike‐slip and normal faults with common steps and bends, buttress unconformities between the fault steps and beyond the ends of faults, a common facies pattern of terrestrial strata changing upward and away from the faults into marine strata, small fault blocks within the basin that result in complex lateral facies relations, common Gilbert deltas, dramatic termination of the margin of the basin by means of fault reorganization and boundary faults dying and an overall short basin history (few million years). Similar transtensional fault‐termination basins are present in Death Valley and other parts of the Eastern California shear zone of the western United States, northern Aegean Sea and along ancient strike‐slip faults. 相似文献
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224.
Ákos Török Tobias Licha Klaus Simon Siegfried Siegesmund 《Environmental Earth Sciences》2011,63(4):675-693
A novel approach of studying dust, black crust and host limestones by using various techniques is presented in this paper.
Samples were collected from limestone monuments located in rural, urban and industrial areas in Germany and Hungary. The paper
focuses on differences in the mineralogical composition, major and trace element distribution of materials and their total
polyaromatic hydrocarbons (PAH) concentration having different exposure to air pollutants. High concentration of gypsum was
found in laminar and dendritic black crusts and even in the dust of both urban and rural areas, despite the low concentration
of SO2 in rural atmospheric environments. The black crusts show a typical microfabric with distinct layers of various gypsum–calcite
mineral associations, silt-sized mineral fragments and black particle content. In dust, newly formed gypsum crystals were
found along with mineral fragments, and siliceous and, less frequently, carbonaceous fly ash particles. High concentration
of lead was found both in the samples of urban and rural areas of Germany and Hungary. Lead mostly accumulates in dust and
also in the black crust. Highest lead concentrations were found not on the surface of the black crust, but close to the crust/limestone
boundary according to LA-ICPMS analyses. It indicates that despite the ban of leaded petrol, lead is still present in the
dust and the in the soiled zones of the built environment. Similarly to lead, no significant difference in the total PAH content
of dust and crust samples were found in the two countries. Dusts are equally enriched in PAH in both countries, whereas black
crusts contain fewer amounts. Most of the aqueous extracts of the samples were saturated with respect to sulphate, which also
indicate the presence of gypsum, whilst in some German samples unsaturated conditions were detected. In summary, by using
a combination of these analytical techniques, it was possible to distinguish rural and urban samples and to outline the role
of dust in bringing pollutants to the stone surface. It is suggested that the analysed dust and stone samples indicate not
only present, but also the past, pollution fluxes and as a consequence stones similar to sediments or surface waters can be
used as environment indicators. 相似文献
225.
Henny A.J. Van Lanen Gregor Laaha Daniel G. Kingston Tobias Gauster Monica Ionita Jean‐Philippe Vidal Radek Vlnas Lena M. Tallaksen Kerstin Stahl Jamie Hannaford Claire Delus Miriam Fendekova Luis Mediero Christel Prudhomme Ekaterina Rets Renata J. Romanowicz Sébastien Gailliez Wai Kwok Wong Mary‐Jeanne Adler Veit Blauhut Laurie Caillouet Silvia Chelcea Natalia Frolova Lukas Gudmundsson Martin Hanel Klaus Haslinger Maria Kireeva Marzena Osuch Eric Sauquet James H. Stagge Anne F. Van Loon 《水文研究》2016,30(17):3097-3104
226.
Computing spatially distributed sediment delivery ratios: inferring functional sediment connectivity from repeat high‐resolution digital elevation models 下载免费PDF全文
High‐resolution digital elevation models (DEMs) from repeat LiDAR (light detection and ranging) or SfM (structure from motion) surveys have become an important tool in process geomorphology. The spatial pattern of negative and positive changes of surface elevation on raster DEMs of difference (DoD) can be interpreted in terms of geomorphic processes, and has been used for morphological budgeting. We show how the application of flow routing algorithms and flow accumulation opens new opportunities for the analysis of DoD. By accumulating the values of the DoD along downslope flowpaths delineated on a DEM, these algorithms lend themselves to computing the net balance, i.e. sediment yield (SY), for the contributing area of each cell. Doing the same for the negative subset of the DoD yields a minimum estimate of erosion (E) within the contributing area. The division of SY by E yields (a maximum estimate of) the sediment delivery ratio (SDR), that is the proportion of material eroded within the contributing area of each cell that has been exported from that area. The resulting SDR is a spatially distributed measure of functional sediment connectivity. In this letter, we develop the computationally simple approach by means of an example DoD from a lateral moraine section in the Upper Kaunertal Valley, Austrian Central Alps. We also discuss advantages, assumptions and limitations, and outline potential applications to connectivity research using field‐, laboratory‐, and model‐based DoD. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
227.
Nickschick Tobias Flechsig Christina Meinel Cornelia Mrlina Jan Kämpf Horst 《International Journal of Earth Sciences》2017,106(8):2915-2926
International Journal of Earth Sciences - The Hartoušov mofette field in NW Bohemia, Czech Republic, is characterized by strong CO2 degassing from the Lithospheric Mantle. In a test survey... 相似文献
228.
229.
Ronny Boch Xianfeng Wang Tobias Kluge Albrecht Leis Ke Lin Hannes Pluch Florian Mittermayr Andre Baldermann Michael E. Bttcher Martin Dietzel 《Sedimentology》2019,66(2):604-635
The well‐known Erzberg site represents the largest siderite (FeCO3) deposit in the world. It consists of various carbonates accounting for the formation of prominent CaCO3 (dominantly aragonite) precipitates filling vertical fractures of different width (centimetres to decimetres) and length (tens of metres). These commonly laminated precipitates are known as ‘erzbergite’. This study focuses on the growth dynamics and environmental dependencies of these vein fillings. Samples recovered on‐site and from mineral collections were analyzed, and these analyses were further complemented by modern water analyses from different Erzberg sections. Isotopic signatures support meteoric water infiltration and sulphide oxidation as the principal hydrogeochemical mechanism of (Ca, Mg and Fe) carbonate host rock dissolution, mobilization and vein mineralization. Clumped isotope measurements revealed cool formation temperatures of ca 0 to 10°C for the aragonite, i.e. reflecting the elevated altitude Alpine setting, but unexpectedly low for aragonite nucleation. The 238U–234U–230Th dating yielded ages from 285·1 ± 3·9 to 1·03 ± 0·04 kyr bp and all samples collected on‐site formed after the Last Glacial Maximum. The observed CaCO3 polymorphism is primarily controlled by the high aqueous Mg/Ca ratios resulting from dissolution of Mg‐rich host rocks, with Mg/Ca further evolving during prior CaCO3 precipitation and CO2 outgassing in the fissured aquifer. Aragonite represents the ‘normal’ mode of erzbergite formation and most of the calcite is of diagenetic (replacing aragonite) origin. The characteristic lamination (millimetre‐scale) is an original growth feature and mostly associated with the deposition of stained (Fe‐rich) detrital particle layers. Broader zonations (centimetre‐scale) are commonly of diagenetic origin. Petrographic observations and radiometric dating support an irregular nature for most of the layering. Open fractures resulting from fault tectonics or gravitational mass movements provide water flow routes and fresh chemical reaction surfaces of the host rock carbonates and accessory sulphides. If these prerequisites are considered, including the hydrogeochemical mechanism, modern water compositions, young U‐Th ages and calculated precipitation rates, it seems unlikely that the fractures had stayed open over extended time intervals. Therefore, it is most likely that they are geologically young. 相似文献
230.
Tobias Lienen Klas Lüders Hannah Halm Anke Westphal Ralf Köber Hilke Würdemann 《Environmental Earth Sciences》2017,76(6):261
Aquifer thermal energy storage may result in increases in the groundwater temperature up to 70 °C and more. This may lead to geochemical and microbiological alterations in the aquifer. To study the temperature effects on the indigenous microbial community composition, sediment column experiments at four different temperatures were carried out and the effluents were characterized geochemically and microbiologically. After an equilibrium phase at groundwater temperature of 10 °C for 136 days, one column was kept at 10 °C as a reference and the others were heated to 25, 40 and 70 °C. Genetic fingerprinting and quantitative PCR revealed a change in the bacterial community composition and abundance due to the temperature increase. While at 25 °C only slight changes in geochemical composition and gene copy numbers for bacteria were observed, increasing concentrations of total organic carbon in the 40 °C column were followed by a strong increase in bacterial abundance. Thermophilic bacteria became dominant at 70 °C. Temporary sulfate reduction took place at 40 and 70 °C and this correlated with an increased abundance of sulfate-reducing bacteria (SRB). Furthermore, a coexistence of SRB and sulfur-oxidizing bacteria (SOB) at all temperatures indicated an interaction of these physiological groups in the sediments. The results show that increased temperatures led to significant shifts in the microbial community composition due to the altered availability of electron donors and acceptors. The interplay of SRB and SOB in sedimentary biofilms facilitated closed sulfur cycling and diminished harmful sulfur species. 相似文献