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排序方式: 共有61条查询结果,搜索用时 15 毫秒
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Mathematical Geosciences - 相似文献
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In this paper, we consider wave propagation in a periodically layered medium with orthorhombic symmetry. The weak-contrast approximation is utilized to derive the low-frequency dispersion in effective properties for P, S1 and S2 waves. We show that the dispersion term for all effective properties is controlled by the second-order contrasts in elastic properties from the layers. We also compute the sensitivity matrices for second- and fourth-order coefficients from eigenvalues of frequency-dependent system matrix associated with kinematic parameters for individual wave modes. 相似文献
54.
The presence of triplications (caustics) can be a serious problem in seismic data processing and analysis. The traveltime curve becomes multi‐valued and the geometrical spreading correction factor tends to zero due to energy focusing. We analyse the conditions for the qSV‐wave triplications in a homogeneous transversely isotropic medium with vertical symmetry axis. The proposed technique can easily be extended to the case of horizontally layered vertical symmetry axis medium. We show that the triplications of the qSV‐wave in a multilayered medium imply certain algebra. We illustrate this algebra on a two‐layer vertical symmetry axis model. 相似文献
55.
Images acquired by the LRO NAC allow 3D phase-ratio imagery of several areas in the crater Giordano Bruno. This is a new optical, remote-sensing technique that allows a determination of the optical roughness of the lunar surface. Our study confirms complicated impact melt movement on the flanks and the floor of the crater. In many cases, however, flow structures seen on the inner wall can be attributed to regolith/debris taluses rather than impact melt flows. It was found that the whirlpool-like formation seen near the western side of the crater Giordano Bruno has a small central depression that can be interpreted as either a vortex cavity or a feature which resembles such a vortex formed by viscous flows coming from the crater flanks. We discuss several features that confirm the young age of the crater, concluding, however, that it was not formed within human history; its age is, likely, on the order of 1 My. 相似文献
56.
Yuriy Elesin Taras Gerya Irina M. Artemieva Hans Thybo 《Arabian Journal of Geosciences》2010,3(4):477-497
We present a new 2D finite difference code, Samovar, for high-resolution numerical modeling of complex geodynamic processes.
Examples are collision of lithospheric plates (including mountain building and subduction) and lithosphere extension (including
formation of sedimentary basins, regions of extended crust, and rift zones). The code models deformation of the lithosphere
with viscoelastoplastic rheology, including erosion/sedimentation processes and formation of shear zones in areas of high
stresses. It also models steady-state and transient conductive and advective thermal processes including partial melting and
magma transport in the lithosphere. The thermal and mechanical parts of the code are tested for a series of physical problems
with analytical solutions. We apply the code to geodynamic modeling by examining numerically the processes of lithosphere
extension and basin formation. The results are directly applicable to the Basin and Range province, western USA, and demonstrate
the roles of crust–mantle coupling, preexisting weakness zones, and erosion rate on the evolutionary trends of extending continental
regions. Modeling of basin evolution indicates a critical role of syn-rift sedimentation on the basin depth and a governing
role of Peierls deformation in cold lithospheric mantle. While the former may increase basin depth by 50%, the latter limits
the depth of rift basins by preventing faulting in the subcrustal lithosphere. 相似文献
57.
Closure and opening of oceans on time‐scales of a few hundred million years is a fundamental tectonic process on Earth, typically referred to as a “Wilson cycle”. Subduction of oceanic and continental crust leading up to and during continent–continent collision can refertilize and enrich the orogenic continental lithospheric mantle in heat‐producing elements. The resulting thermal anomaly weakens the lithosphere and, along with structural weaknesses (e.g. sutures), make this orogenic lithosphere more prone to rifting given an extensional stress field. Thermal modelling shows that anomalously hot lithosphere can focus asthenospheric upwellings over time‐scales of a few hundred million years. Processes related to closure of oceans thus provide a mechanism for later localization of rifting and an extensional driving force. 相似文献
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Vitaliy D. Rusov Vladimir N. Vaschenko Elena P. Linnik Оksana T. Myhalus Yuriy A. Bondartchuk Vladimir P. Smolyar Sergey I. Kosenko Strachimir Cht. Mavrodiev Boyko I. Vachev 《Journal of Atmospheric and Solar》2010,72(5-6):389-397
The solution of energy-balance model of the Earth global climate and the EPICA Dome C and Vostok experimental data of the Earth surface palaeotemperature evolution over past 420 and 740 kyr are compared.In the framework of proposed bifurcation model (i) the possible sharp warmings of the Dansgaard-Oeschger type during the last glacial period due to stochastic resonance is theoretically argued; (ii) the concept of climatic sensitivity of water in the atmosphere, whose temperature instability has the form of so-called hysteresis loop, is proposed, and based on this concept the time series of global ice volume over the past 1000 kyr, which is in good agreement with the time series of δ18O concentration in the sea sediments, is obtained; (iii) the so-called “CO2 doubling” problem is discussed. 相似文献
59.
Philipp Balling Yuriy Maystrenko Magdalena Scheck-Wenderoth 《Environmental Earth Sciences》2013,70(8):3505-3522
With this paper, we assess the present-day conductive thermal field of the Glueckstadt Graben in NW Germany that is characterized by large salt walls and diapirs structuring the graben fill. We use a finite element method to calculate the 3D steady-state conductive thermal field based on a lithosphere-scale 3D structural model that resolves the first-order structural characteristics of the graben and its underlying lithosphere. Model predictions are validated against measured temperatures in six deep wells. Our investigations show that the interaction of thickness distributions and thermal rock properties of the different geological layers is of major importance for the distribution of temperatures in the deep subsurface of the Glueckstadt Graben. However, the local temperatures may result from the superposed effects of different controlling factors. Especially, the upper sedimentary part of the model exhibits huge lateral temperature variations, which correlate spatially with the shape of the thermally highly conductive Permian salt layer. Variations in thickness and geometry of the salt cause two major effects, which provoke considerable lateral temperature variations for a given depth. (1) The “chimney effect” causes more efficient heat transport within salt diapirs. As a consequence positive thermal anomalies develop in the upper part and above salt structures, where the latter are covered by much less conductive sediments. In contrast, negative thermal anomalies are noticeable underneath salt structures. (2) The “thermal blanketing effect” is caused by thermally low conductive sediments that provoke the local storage of heat where these insulating sediments are present. The latter effect leads to both local and regional thermal anomalies. Locally, this translates to higher temperatures where salt margin synclines are filled with thick insulating clastic sediments. For the regional anomalies the cumulative insulating effects of the entire sediment fill results in a long-wavelength variation of temperatures in response to heat refraction effects caused by the contrast between insulating sediments and highly conductive crystalline crust. Finally, the longest wavelength of temperature variations is caused by the depth position of the isothermal lithosphere–asthenosphere boundary defining the regional variations of the overall geothermal gradient. We find that a conductive thermal model predicts observed temperatures reasonably well for five of the six available wells, whereas the steady-state conductive approach appears not to be valid for the sixth well. 相似文献
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