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941.
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在对新疆1973年以来年度地震预测情况进行综合研究基础上,重点分析了乌恰-喀什周围地区年度预测的阶段性特点,并对这一地区1900年以来M≥6地震和1972-2008年M≥5.5地震活动特征进行了的研究.认为对该区域地震活动规律性特点认识不足,没有遵循本地区地震活动的基本规律对地震趋势进行客观判断,是造成地震危险区预测效果较差的主要原因.依据地震活跃与间歇的特点认为2008年底开始乌恰-喀什周围地区将进入一个新的活跃时段,这一地区可能仍将继续被划定为年度强地震危险区. 相似文献
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946.
四川汶川系列地震距太原基准地震台约1000km,介于近震与远震之间,震相特殊,识别困难。本文通过对汶川主、余震和四川其他地区远震波形的对照,及对主要震相周期、幅度及波形特点的分析,认为PN、SG两个震相是太原地震台记录四川汶川地震的主要定位震相。 相似文献
947.
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949.
The determination of seismic amplitude amplification is a fundamental contribution to seismic hazard assessment. While often
only high-frequency amplitude variations (>1 Hz) are taken into account, we analyse broadband waveforms from 0.14 to 8.6 Hz
using a temporary network of 32 stations in and around the earthquake-prone city of Bucharest. Spectral amplitudes are calculated
with an adaptive multiple-taper approach. Across our network (aperture 25 km × 25 km), we find a systematic northwest/southeast-oriented
structural influence on teleseismic P-wave amplitudes from 0.14 to 0.86 Hz that can be explained by constructive interference
in the dipping Cenozoic sedimentary layers. For higher frequencies (1.4–8.75 Hz), more local site effects prevail and can
be correlated partly among neighbouring stations. The transition between systematic and localised amplitude variations occurs
at about 1 Hz. 相似文献
950.
This study focuses on the southeast Capital area of North China (38.5–39.85° N, 115.5–118.5° E). Shear-wave splitting parameters
at 20 seismic stations are obtained by a systematic analysis method applied to data recorded by the Capital Area Seismograph
Network (CASN) between the years 2002 and 2005. Although some differences in the results are observed, the average fast-wave
polarization is N88.2° W ± 40.7° and the average normalized slow wave time delay is 3.55 ± 2.93 ms/km. The average polarization
is consistent with the regional maximum horizontal compressive stress and also with the maximum principal strain derived from
global positioning system measurements in North China. In spite of the uneven distribution of faults around the array stations
that likely introduce some amount of scatter in the shear-wave splitting measurements, site-dependent polarizations of fast
shear wave are clearly observed: in the northern half of the study area, the polarizations at CASN stations show E–W direction,
whereas in the southern half the polarizations exhibit a variety of possible azimuths, thus suggesting dissimilar stress field
and tectonic frame in both areas. Comparing the splitting results with those previously obtained in the northwest part of
the region, we find a difference in polarization of about 20° between the southeast and northwest parts of the Capital area;
also, in the southeast Capital area the average time delay is smaller than in the northwest Capital area, thus making clear
that the magnitude of crustal seismic anisotropy is not the same in the two zones. Being the shear-wave splitting polarizations
in the southeast Capital area, which lies on the basin, clearly different from the observed polarizations in the northwest
Capital area, where uplifts and basin converge, it is quite evident that the shear-wave splitting results are consequence
of the tectonics and stress field affecting the two regions. 相似文献