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  • 1
    Publication Date: 2015-11-05
    Description: In 1981, a powerful M L5.7 earthquake occurred 50 km away from the Aswan Reservoir dam. After the statistical analysis on the correlationship between long-term continuous seismicity occurrence and the reservoir water level variation attributed to the impoundment and drainage procedures, researchers believe that this event is a typical reservoir-triggered seismicity (Nature 301(6):14, 1983 ; Earthquake Activity in the Aswan Region, Egypt. Birkhäuser, Basel, pp. 69–86, 1995 ), although its triggering mechanism is poorly understood to date. To quantitatively address the triggering mechanism as well as its relationship with the characteristics of local geological settings around the reservoir region, in this paper, a fully coupled three-dimensional poroelastic finite element model of the Aswan reservoir is put forward by taking the consideration of the realistic observation data, for example, the high-resolution topography, water level fluctuation history, flood zone boundary and water depth variation, fault parameters, etc. Meanwhile, the change of Coulomb Failure Stress (ΔCFS) in correspondence to elastic stress and pore pressure variations induced by fluid diffusion is calculated. And the elastic strain energy accumulation in the reservoir region due to the impoundment load is obtained as well. Our primary results indicate that both the pore pressure and the coulomb stress on the seismogenic fault plane gradually increase with the respect of time while the water level rises. The magnitude of ΔCFS at the hypocenter of this major event is around 0.1 MPa, suggesting that the impoundment of the Aswan Reservoir possibly triggered the M L5.7 earthquake. The contribution of the elastic load is less than 3 percent of the total ΔCFS; on the other hand, the dynamic pore pressure change predominantly accounts for the contribution. The accumulative maximum surface deformation beneath the Aswan reservoir is up to 80 cm since its impounding began until the M L5.7 earthquake occurred. Although the total elastic strain energy accumulation caused by the impoundment water load is around 1.0 × 1010J, this energy density still insignificant compared to that of the vast reservoir inundation area, as it is only less than few percent of the total energy released by the major event, which confirms that the sustained regional geological loading controls the occurrence of this large reservoir-induced event. Furthermore, elastic loading and pore fluid pore pressure diffusion due to the impoundment of the Aswan reservoir might accelerate its occurrence. ©2015 Springer Basel
    Print ISSN: 0033-4553
    Electronic ISSN: 1420-9136
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 2008-04-01
    Description: Modeling tsunami wave propagation is a very challenging numerical task, because it involves many facets: Such as the formation of various types of waves and the impingement of these waves on the coast. We will discuss the different levels of approximations made in numerical modeling of 2-D and 3-D tsunami waves and their relative difficulties. In this paper new attempts are proposed to evaluate the hazards of tsunami’s and visualization of large-scale numerical results generated from tsunami simulations. Specialized low-level computer language, based on a parallel computing environment, is also employed here for generating FORTRAN source code for finite elements. This code can then be run very efficiently in parallel on distributed computing systems. We will also discuss the need to study tsunami waves with modern software and visualization hardware. ©2008 Birkhaueser
    Print ISSN: 0033-4553
    Electronic ISSN: 1420-9136
    Topics: Geosciences , Physics
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  • 3
    Publication Date: 2008-04-01
    Description: In this work we visualize tsunami and earthquake simulation results with graphics hardware acceleration. The rapid improvement in the computational power of graphics hardware and its programmability has made general computation on Graphics Processing Units (GPUs) very compelling. We generate Synthetic InSAR images using GPUs. Interference phenomena have formed the underlying theory for Interferometric Synthetic Aperture Radar (InSAR) in unveiling dynamical Earth movements. In our approach light path differences are defined by the surface values to be visualized. These path differences then modulate the lighting intensity to generate the interference patterns. We can interactively visualize surface deformation patterns by leveraging the computational power of GPUs. Our visualization method is applied to simulations of rupture fault displacements during the tsunamogenic earthquake events, which are vital to understanding the subsequent wave propagation. We also integrate the visualization results into Google Earth virtual globe to provide the geological context of the visualized regions. ©2008 Birkhaueser
    Print ISSN: 0033-4553
    Electronic ISSN: 1420-9136
    Topics: Geosciences , Physics
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  • 4
    Publication Date: 2015-09-01
    Description: The glacial trough is a common glacier erosion landscape, which plays an important role in the study of glacier erosion processes. In a sharp contrast with the developing river, which is generally meandering, the developing glacial trough is usually wide and straight. Is the straightness of the glacial trough just the special phenomenon of some areas or a universal feature? What controls the straightness of the glacial trough? Until now, these issues have not been studied yet. In this paper, we conduct systematic numerical models of the glacier erosion and simulate the erosion evolution process of the glacial trough. Numerical simulations show that: (1) while the meandering glacier is eroding deeper to form the U-shaped cross section, the glacier is eroding laterally. The erosion rate of the ice-facing slope is bigger than that of the back-slope. (2) The smaller (bigger) the slope is, the smaller (bigger) the glacier erosion intensity is. (3) The smaller (bigger) the ice discharge is, the smaller (bigger) the glacier erosion intensity is. In the glacier erosion process, the erosion rate of the ice-facing slope is always greater than that of the back-slope. Therefore, the glacial trough always develops into more straight form. This paper comes to the conclusion that the shape evolution of the glacial trough is controlled mainly by the erosion mechanism of the glacier. Thereby, the glacial trough prefers straight geometry. ©2015 Science China Press and Springer-Verlag Berlin Heidelberg
    Print ISSN: 1674-7313
    Electronic ISSN: 1869-1897
    Topics: Geosciences
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  • 5
    Publication Date: 2014-09-01
    Description: The electrical conductivity of Tibetan eclogite was investigated at pressures of 1.5–3.5 GPa and temperatures of 500–803 K using impedance spectroscopy within a frequency range of 10−1–106 Hz. The electrical conductivity of eclogite increases with increasing temperature (which can be approximated by the Arrhenius equation), and is weakly affected by pressure. At each tested pressure, the electrical conductivity is weakly temperature dependent below ∼650 K and more strongly temperature dependent above ∼650 K. The calculated activation energies and volumes are 44±1 kJ/mol and −0.6±0.1 cm3/mol for low temperatures and 97±3 kJ/mol and −1.2±0.2 cm3/mol for high temperatures, respectively. When applied to the depth range of 45–100 km in Tibet, the laboratory data give conductivities on the order of 10−1.5–10−4.5 S/m, within the range of geophysical conductivity profiles. ©2014 Science China Press and Springer-Verlag Berlin Heidelberg
    Print ISSN: 1674-7313
    Electronic ISSN: 1869-1897
    Topics: Geosciences
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  • 6
    Publication Date: 2014-03-01
    Description: The pressure-dependent elastic properties of the Fe–S system are important to understand the dynamic properties of the Earth’s interior. We have therefore undertaken a first-principles study of the structural and elastic properties of FeS2 polymorphs under high pressure using a method based on plane-wave pseudopotential density function theory. The lattice constants, elastic constants, zero-pressure bulk modulus, and its pressure derivative of pyrite are in good agreement with the previous experiments and theoretical approaches; the lattice constants of marcasite are also consistent with the available experimental data. Calculations of the elastic constants of pyrite and marcasite have been determined from 0 to 200 GPa. Based on the relationship between the calculated elastic constants and the pressure, which can provide the stability of mineral, it would appear that pyrite is stable, whereas marcasite is unstable when the pressure rises above 130 GPa. Static lattice energy calculations predict the marcasite-to-pyrite phase transition to occur at 5.4 GPa at 0 K. ©2013 Springer-Verlag Berlin Heidelberg
    Print ISSN: 0342-1791
    Electronic ISSN: 1432-2021
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 7
    Publication Date: 2013-01-01
    Description: Japan’s 2011 Tohoku-Oki earthquake and the accompanying tsunami have reminded us of the potential tsunami hazards from the Manila and Ryukyu trenches to the South China and East China Seas. Statistics of historical seismic records from nearly the last 4 decades have shown that major earthquakes do not necessarily agree with the local Gutenberg-Richter relationship. The probability of a mega-earthquake may be higher than we have previously estimated. Furthermore, we noted that the percentages of tsunami-associated earthquakes are much higher in major events, and the earthquakes with magnitudes equal to or greater than 8.8 have all triggered tsunamis in the past approximately 100 years. We will emphasize the importance of a thorough study of possible tsunami scenarios for hazard mitigation. We focus on several hypothetical earthquake-induced tsunamis caused by M w 8.8 events along the Manila and Ryukyu trenches. We carried out numerical simulations based on shallow-water equations (SWE) to predict the tsunami dynamics in the South China and East China Seas. By analyzing the computed results we found that the height of the potential surge in China’s coastal area caused by earthquake-induced tsunamis may reach a couple of meters high. Our preliminary results show that tsunamis generated in the Manila and Ryukyu trenches could pose a significant threat to Chinese coastal cities such as Shanghai, Hong Kong and Macao. However, we did not find the highest tsunami wave at Taiwan, partially because it lies right on the extension of an assumed fault line. Furthermore, we put forward a multi-scale model with higher resolution, which enabled us to investigate the edge waves diffracted around Taiwan Island with a closer view. ©2012 Springer Basel AG
    Print ISSN: 0033-4553
    Electronic ISSN: 1420-9136
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  • 8
    Publication Date: 2006-08-01
    Description: In Appling studies, the strain rate in China has been computed from using different methods, resulting in quite different estimates of the strain rate the geo-statistics from GPS velocity field of Chinese continent, we obtain the velocity value at each little regularly spaced grid point, by kriging interpolation and the component of strain rate for each volume element, using a method similar to the derivation of shape functions in the finite element algorithm. Therefore the distribution of the strain rate field in whole for the Chinese continent is presented. The result shows that the orientations of principal strain rates are consistent with those of the P and T axes of focal mechanisms. The distribution of maximum shear strain rate clearly delineates some major active fault zones surrounding the Tibetan Plateau. The maximum shear strain rate is comparable with that obtained from analysis of seismic moment release. In part of the Tibetan Plateau containing normal faults and pull-apart grabens, we obtain an extensional state of strain. The absolute value of the strain rate in West China is approximately 5 times larger than that of East China, and the pattern of the strain rate field in most of the Chinese continent is controlled by the India/Eurasia collision. ©2006 Birkhäuser Verlag, Basel,
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  • 9
    Publication Date: 1996-09-01
    Description: Finite-element modeling of the thermal regime across the Southern Alps of New Zealand has been carried out along two profiles situated near the Franz Josef and Haast valleys. The modeling involves viscous deformation beneath the Southern Alps, including both uplift and erosion, and crustal/lithospheric thickening, as a result of crustal shortening extending to 20 mm/y of a 25-km thick crust. Published uplift rates and crustal thickness variations along the two profiles are used to constrain the modeled advection of crustal material, and results are compared with the recent heat flow determinations, 190±50 mW/m2 in the Franz Josef valley and 90±25 mW/m2 in the Haast valley. Comparisons of the model with published K−Ar and fission track ages, show that the observed heat flow in the Franz Josef valley is consistent with observed zircon fission track ages of around 1 Ma, if the present-day uplift rate is close to 10 mm/y. Major thermal differences between the Franz Josef and Haast profiles appear to be due to different uplift and erosion rates. There is weak evidence that frictional heating close to the Alpine fault zone is not significant. The modeling provides explanations for the distribution of seismicity beneath the Southern Alps, and predicts a low surface heat flow over the eastern foothills due to the dominant thermal effect of crustal thickening beneath this region. Predicted temperatures at mid-crustal depth beneath the zone of maximum uplift rate are 50–100°C cooler than those indicated in previously published models, which implies that thermal weakening of the crust may not be the main factor causing the aseismicity of the central Southern Alps. The results of the modeling demonstrate that the different types of reset age data in the region within 25 km of the Alpine fault are critical for constraining models of the deformation and the thermal regime beneath the Southern Alps. ©1996 Birkhäuser Verlag
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  • 10
    Publication Date: 2013-05-01
    Description: We used two-dimensional numerical simulations to investigate small-scale convection in the upper mantle-lithosphere system with depth- and temperature-dependent viscosity. Our aim was to examine the mechanism of craton thinning by thermal convection. The model domain is 700 km deep and 700 km wide with a resolution of 71×71 nodes and 160000 markers. The velocity boundary conditions are free-slip along all the boundaries. A thermal insulation condition was applied at the two side walls, with constant temperatures for the top and bottom boundaries. We assumed an initial temperature of 273 K at the upper boundary and 1673 K at the lower boundary, and 1573 K at the bottom of the lithosphere (200 km depth) for the thick, cold, and stable North China Craton (NCC). We calculated the thermal evolution in the upper mantle when the temperature at its bottom is raised because of lower mantle convection or plumes. The temperature at the bottom of the upper mantle was set at 1773, 1873, 1973, and 2073 K for different models to study the temperature effect on the lithospheric thinning processes. Our end-member calculations show that with the bottom boundary raising the lithosphere can be thinned from a depth of 200 km to a depth of between 100 and 126.25 km. The thinning rates are at mm/y order of magnitude, and the thinning timescale is about 10 Ma. ©2013 Science China Press and Springer-Verlag Berlin Heidelberg
    Print ISSN: 1674-7313
    Electronic ISSN: 1869-1897
    Topics: Geosciences
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