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Seismic Zones (seismic + zone)

Distribution by Scientific Domains
Earth and Environmental Science50%

Selected Abstracts

Near-lithostatic pore pressure at seismogenic depths: a thermoporoelastic model

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006
Francesca Zencher
SUMMARY A model is presented for pore pressure migration through a transition layer separating a meteoric aquifer at hydrostatic pressure from a deeper reservoir at lithostatic pressure. This configuration is thought to be pertinent to the South Iceland seismic zone (SISZ) and to other tectonically active regions of recent volcanism, where volatiles are continuously released by ascending magma below the brittle,ductile transition. Poroelastic parameters are computed for basaltic rock. The model is 1-D, the fluid viscosity is temperature dependent and rock permeability is assumed to be pressure dependent according to a dislocation model of a fractured medium. Environment conditions are considered, pertinent to basalt saturated with water at shallow depth (case I) and at mid-crustal depth (case II). If the intrinsic permeability of the rock is high, no significant effects are observed in the pressure field but advective heat transfer shifts the brittle,ductile transition to shallower depths. If the intrinsic permeability is low, the pressure-dependent permeability can propagate near-lithostatic pore pressures throughout most of the transition layer, while the temperature is practically unaffected by advective contributions so that the rock in the transition layer remains in brittle condition. Geometrical parameters characterizing the fracture distribution are important in determining the effective permeability: in particular, if an interconnected system of fractures develops within the transition layer, the effective permeability may increase by several orders of magnitude and near-lithostatic pore pressure propagates upwards. These modelling results have important bearings on our understanding of seismogenic processes in geothermal areas and are consistent with several geophysical observations in the SISZ, in connection with the two 2000 June M= 6.5 earthquakes, including: (i) fluid pressure pulses in deep wells, (ii) low resistivity at the base of the seismogenic layer, (iii) low VP/VS ratio and time-dependent seismic tomography, (iv) heterogeneity of focal mechanisms, (v) shear wave splitting, (vi) high b -value of deep foreshocks, (vii) triggered seismicity and (viii) Radon anomalies. [source]

Hybrid platform for high-tech equipment protection against earthquake and microvibration

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 8 2006
Y. L. Xu
Abstract To ensure the high quality of ultra-precision products such as semiconductors and optical microscopes, high-tech equipment used to make these products requires a normal working environment with extremely limited vibration. Some of high-tech industry centres are also located in seismic zones: the safety of high-tech equipment during an earthquake event becomes a critical issue. It is thus imperative to find an effective way to ensure the functionality of high-tech equipment against microvibration and to protect high-tech equipment from damage when earthquake events occur. This paper explores the possibility of using a hybrid platform to mitigate two types of vibration. The hybrid platform, on which high-tech equipment is installed, is designed to work as a passive isolation platform to abate mainly acceleration response of high-tech equipment during an earthquake and to function as an actively controlled platform to reduce mainly velocity response of high-tech equipment under normal working condition. To examine the performance of the hybrid platform, the analytical model of a coupled hybrid platform and building system incorporating with magnetostrictive actuators is established. The simulation results obtained by applying the analytical model to a high-tech facility indicate that the proposed hybrid platform is feasible and effective. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Localization analysis in softening RC frame structures

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2003
Ali R. Khaloo
Abstract This paper discusses the sensitivity of softening reinforced concrete frame structures to the changes in input ground motion and investigates the possibility of localizations for this type of structure in static and dynamic analysis. A finite element model is used in which the sections resisting force are calculated using a proposed differential hysteretic model. This model is especially developed for modelling softening behaviour under cyclic loading. To obtain parameters of the differential model the moment,curvature of each section is evaluated using a microplane constitutive law for concrete and bi-linear elasto-plastic law for reinforcements. The capability of the procedure is verified by comparing results with available experimental data at element level, which shows good accuracy of the procedure. The effect of possible changes in ground motion is assessed using a non-stationary Kanai,Tajimi process. This process is used to generate ground motions with approximately the same amplitude and frequency content evolution as those of base ground motion. The possibility of localization in static and dynamic loading is investigated using two structures. A measure for the possibility of localization in code-designed structures is obtained. This study indicates that localization may occur in ordinary moment-resisting structures located in high seismic zones. Localization may result in substantial drift in global response and instability due to P,, effect. Also, it is shown that the structure becomes very sensitive to the input ground motion. It is concluded that allowance by some design codes of the use of ordinary moment-resisting frames in regions with high seismicity should be revised or improvements should be made in the detailing requirements at critical sections of these structures. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Heat Flow Pattern in the Mainland of China and Its Geodynamic Significance

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2000
WANG Yang
Abstract On the basis of 723 heat flow measurements in the mainland of China and over 2000 data from the global heat flow data set, the authors compiled the heat flow map of the mainland of China and its adjacent areas to exhibit the overall variation of the heat flow pattern in the mainland. The heat flow pattern of the mainland is complex, and can not be simply summarized as "low in the north and west and high in the south and east". Significant difference exists between eastern and western China in the spatial pattern of heat flow. Divided by the 105°E meridian, heat flow values in eastern China show a westward-decreasing trend; and a northward variation is observed in western China. The high-heat flow regions correspond to tectonically active belts such as Cenozoic orogens and extensional basins, where mantle heat flow is high; and the low-heat flow regions correspond to stable units such as the Tarim and Yangtze platforms. This heat flow pattern is controlled by India-Asia collision in the west and Pacific plate subduction in the east. The lateral variation in lithospheric strength corresponds to the heat flow variation, and there is a generally reversely proportional relation between heat flow and lithospheric strength in the mainland of China. The mosaic pattern of present deformation in the mainland results from lateral rheological heterogeneity. The good coincidence between weak strength domains and seismic zones demonstrates the intrinsic relation between the strength heterogeneity and regional seismicity pattern in the mainland of China. [source]