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1.
《中国科学D辑(英文版)》2006,(3)
The Chi Chi earthquake (Mw7.6) occurred at 17:47 UTC on Sept. 20,1999 (01:47 September 21, 1999, local time) in central Taiwan. CWB located the epi- center at (120.82°E; 23.85°N) and the focal depth 8 km. Chi Chi earthquake is the best documented earth- quake ever recorded. The abundance and quality of its near-source observations present an unparalleled op- portunity for studying the rupture history from a close distance. More than 400 free field digital accelerome- ters with 3-compon… 相似文献
2.
Tsunami education activities, materials, and programs are recognized by the National Tsunami Hazard Mitigation Program (NTHMP) as the essential tool for near-source tsunami mitigation. Prior to the NTHMP, there were no state tsunami education programs outside of Hawaii and few earthquake education materials included tsunami hazards. In the first year of the NTHMP, a Strategic Plan was developed providing the framework for mitigation projects in the program. The Strategic Plan identifies education as the first of five mitigation strategic planning areas and targets a number of user groups, including schools, businesses, tourists, seasonal workers, planners, government officials, and the general public. In the 6 years of the NTHMP tsunami education programs have been developed in all five Pacific States and include print, electronic and video/film products, curriculum, signage, fairs and workshops, and public service announcements. Multi-state education projects supported by the NTHMP include TsuInfo, a bi-monthly newsletter, and Surviving a Tsunami, a booklet illustrating lessons from the 1960 Chilean tsunami. An additional education component is provided by the Public Affairs Working Group (PAWG) that promotes media coverage of tsunamis and the NTHMP. Assessment surveys conducted in Oregon, Washington, and Northern California show an increase in tsunami awareness and recognition of tsunami hazards among the general population since the NTHMP inception. 相似文献
3.
Comparison of the time-domain electromagnetic field from an infinitesimal point charge and dipole source 总被引：2，自引：0，他引：2
An electromagnetic field is generated through the accelerating movement of two equal but opposite charges of a single dipole. An electromagnetic field can also be generated by a time-varying infinitesimal point charge. In this study, a comparison between the electromagnetic fields of an infinitesimal point charge and a dipole has been presented. First, the time-domain potential function of a point source in a 3D conductive medium is derived. Then the electric and magnetic fields in a 3D homogeneous lossless space are derived via the relation between the potential and field. The field differences between the infinitesimal point charge and the dipole in the step-off time, far-source, and near-source zones are analyzed, and the accuracy of the solutions from these sources is investigated. It is also shown that the field of the infinitesimal point charge in the near-source zone is different from that of the dipole, whereas the far-source zone fields of these two sources are identical. The comparison of real and simulated data shows that the infinitesimal point charge represents the real source better than the dipole source. 相似文献
4.
Praveen K. Malhotra 《地震工程与结构动力学》1999,28(11):1309-1326
Ground motions affected by directivity focusing at near-field stations contain distinct pulses in acceleration, velocity, and displacement histories. For the same Peak Ground Acceleration (PGA) and duration of shaking, ground motions with directivity pulses can generate much higher base shears, inter-storey drifts, and roof displacements in high-rise buildings as compared to the 1940 El Centro ground motion which does not contain these pulses. Also, the ductility demand can be much higher and the effectiveness of supplemental damping lower for pulse-like ground motions. This paper presents a simple interpretation of the response characteristics of three recorded and one synthetic near-field ground motions. It is seen that for pulse-like ground motions—similar to any other ground motion—the Peak values of Ground Acceleration, Velocity, and Displacement (PGA, PGV and PGD) are the key response parameters. Near-field ground motions with directivity effects tend to have high PGV/PGA ratio, which dramatically influences their response characteristics. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
5.
在过去的20年里，近场问题受到了地震学家和土木工程师的共同关注，一方面原因旨在阐明地震本身的机理，解释新现象；另一方面是由于地震动作为一种主要的输入荷载，在某些情况下将对整个结构设计的最终结果起到控制作用. 同时试验和评估等其它领域的相关研究也均以指定的荷载形式为前提，荷载形式的变化直接影响了土木工程中的诸多方面，所以希望研究这种荷载的规律并获得其与结构反应之间的关系. 本文回顾了近场问题研究的历史，介绍了近年来国内外针对近场地震动所展开的相关研究工作，其中包括近场地震动本身的特性与近场地震动对土木工程结构的影响等方面，指出了目前存在的问题和进一步应该研究的方向，对于近场问题的深入研究具有一定的参考价值. 相似文献
6.
Introduction The characteristics of ground motions recorded near the fault of an earthquake are quite dif- ferent from the usual far-field ground motions. After the original recognition of their differences in the Port Hueneme earthquake in 1957, a great lot of inhabited structures and lifeline systems were damaged in the major earthquakes happened in the following years. The damages were beyond minds of seismologists and engineers. A quite rational reason is the lack of enough knowledge of t… 相似文献
7.
The tight sandstone gas in Upper Paleozoic Formation of the northern Ordos Basin is a typical giant unconventional tight gas province. Evidences from geochemistry, reservoir geology and paleo-tectonic setting all verify that the present-day tight sandstone gas accumulation in the Ordos Basin is the result of near-source accumulation. The evidences are listed as following: tight sandstone gas is mainly distributed in the area with high gas-generating strength; gas composition was not subjected to fractionation; gas saturation significantly decreases with the distance away from the source rocks; gas isotopes suggest their origin is the same and maturity is consistent with in-place source rocks; reservoirs have experienced three types of densification digenesis, including intense compaction, siliceous cementation and calcareous cementation, which took place before the formation of a large amount of tight sandstone gas, forming tight reservoirs with low porosity and permeability, fine pore throat and great capillary resistance; the paleo-structural gradient ratio is small from the main hydrocarbon generation period to present. It is indicated the present distribution of tight sandstone gas in the northern Ordos Basin is the result of near-source and short-distance migration and accumulation. 相似文献
8.
Jian Wu Yanxiang Yu Institute of Geophysics China Earthquake Administration Beijing China 《地震学报(英文版)》2010,(1):87-93
This paper proposes that on the basis of near-source saturation characteristic of ground motion, the peak ground motion acceleration and the acceleration response spectra of diffuse earthquakes affecting the nuclear facility site can be determined by the statistic method. In view of the problem of insufficient statistic samples due to fewer qualified strong earthquake records on the bedrock site, it also proposes that according to the features of ground motion response of the soil, the acceleration records ... 相似文献
9.
Shi Shaoxian 《中国地震研究》2004,18(4):348-356
Three methods of extracting the information of anomalies of a precursory group are put forward, i.e., the mathematical analyses of the synthetic information of earthquake precursors(S), the inhomogeneous degree of precursory groups ( ID ) and the values of short-term and impending anomaly in near-source area (NS). Using these methods, we calculate the observational data of deformation, underground fluid and hydrochemical constituents obtained from different seismic stations in the Sichuan-Yunnan region and conclude that the synthetic precursory anomalies of a single strong earthquake with Ms6.0 differ greatly from those of the grouped strong earthquakes, for the anomalous information of precursory groups are more abundant. The three methods of extracting the synthetic precursory anomaly and the related numerical results can be applied into the practice of prediction to the grouped strong earthquakes in the Sichuan-Yunnan region. Inhomogeneons degree (ID) of synthetic precursory anomaly can be identified automatically because it takes the threshold of distributive characteristics of the anomalies of precursory group as its criterion for anomaly. 相似文献
10.
A simple source inversion scheme for displacement seismograms recorded at short distances 总被引：2，自引：1，他引：1
We have implemented and tested a simple inversionscheme to retrieve source parameters of small andmoderate earthquakes recorded at close distances. Theinversion assumes that such events may be approximatedby a point-source shear dislocation, and the mediummay be considered an infinite space. Theoreticalseismograms used in the inversion include near- andintermediate-field contributions. The effect of freesurface is approximately taken into account bymultiplying the infinite-space synthetics by two. Thelocation of the event is assumed to be known. Based onan examination of the data, the user chooses thelength of the record and the weight of each trace tobe used in the inversion. The shape of the source-timefunction is estimated from the observed seismograms.A grid search is performed to determine the focalmechanism and the seismic moment which minimizes theerror between the observed and the syntheticseismograms. For two or more recordings, the inversiongives a solution which is consistent with thefirst-motion data and/or the moment tensor inversionof regional seismic waves. If only a singlethree-component recording is available then theinversion yields more than one equally acceptablefocal mechanisms. In such cases, the first-motionpolarities or a prior knowledge of the tectonics ofthe region is essential to constrain the solution. Thetest of the method on near-source broadband recordingsof small and moderate earthquakes in Mexico and theaftershock sequence of 1997 Umbria-Marche, Italy showsthat it gives fast, and surprisingly robust andreliable estimation of source parameters. 相似文献