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51.
为弄清山西夏县中心地震台水氡震前异常的原因 ,对山西夏县中心地震台热水井水氡 1984年以来的观测资料用概率论的数据处理方法进行了处理 ,以负异常的发震原理进行了分析 ,结果表明震前负异常的发震概率为 70 %。 相似文献
52.
昆仑山口西8.1级地震前青海省形变及地温前兆特征分析 总被引:6,自引:0,他引:6
通过对青海省地倾斜、地应力、深井地温3种前兆手段在昆仑山口西8.1级地震前异常的分析与研究,得出了强地震远场前兆的一些初步特征,并与近场前兆异常特征做了比较,这对该省今后强震短期预报将是有益的。 相似文献
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J. J. Bommer M. B. Benito M. Ciudad-Real A. Lemoine M. A. Lpez-Menjívar R. Madariaga J. Mankelow P. Mndez de Hasbun W. Murphy M. Nieto-Lovo C. E. Rodríguez-Pineda H. Rosa 《Soil Dynamics and Earthquake Engineering》2002,22(5)
The small Central American republic of El Salvador has experienced, on average, one destructive earthquake per decade during the last hundred years. The latest events occurred on 13 January and 13 February 2001, with magnitudes Mw 7.7 and 6.6, respectively. The two events, which were of different tectonic origin, follow the patterns of the seismicity of the region although neither event has a known precedent in the earthquake catalogue in terms of size and location. The earthquakes caused damage to thousands of traditionally built houses and triggered hundreds of landslides, which were the main causes of fatalities. The earthquakes have clearly demonstrated trends of increasing seismic risk in El Salvador due to rapid population expansion in areas of high shaking and landslide hazard, exacerbated by deforestation and uncontrolled urbanisation. The institutional mechanisms required for the control of land use and building practice are very weak and present a major obstacle to risk mitigation. 相似文献
56.
An instrumental validation is attempted of an innovative approach devoted to the quick individuation, from macroseismic data, of site amplification phenomena able to significantly modify seismic hazard levels expected on the basis of average propagation effects only. According to this methodology, two evaluations of hazard are performed at each investigated locality: the former, obtained by epicentral intensity data ‘reduced’ at the site through a probabilistic attenuation function and, the latter, computed by integrating such data with seismic effects actually observed at the site during past earthquakes. The comparison, for each locality, between these two hazard estimates allow to orientate the identification of those sites where local amplifications of earthquake ground motion could be significant. In order to check such methodology, indications obtained in this way from macroseismic data are compared with the estimates of transfer functions performed through the HVSR technique applied to microtremors. Results concerning municipalities located in a seismic area of Northern Italy indicate a good agreement between macroseismic and instrumental estimates. 相似文献
57.
It is generally accepted that both deterministic and statistical approaches are useful for the characterization of earthquake hazard. Although the most reliable estimates of seismic hazard can only be based on an improved understanding of the earthquake mechanism, efficient utilization of the appropriate methods provided by recent statistical theories is also important in seismic risk analysis. This is especially true in regions where the connection between seismicity and geologic structure is tenuous at best. We are particularly interested in developing better statistical treatments of data for regions with little known seismic activity. To this end, we have applied three statistical methods to the historical record of seismicity in relatively quiet regions of eastern North America. These are: (1) the threshold method for tail inference, a new theory for modeling earthquakes with sizes above a given threshold, (2) the ‘bootstrap’ technique in which the characteristics of an unknown population are simulated by replacing the true population by an estimated one, and (3) a technique to estimate the number of earthquakes below a given size, in order to compensate for the under-reporting of small earthquakes in most catalogs. A combination of these techniques has been used to estimate the probabilities of future large earthquakes for the regions studied. Because of limitations imposed by existing catalogs, the size estimate used has been maximum intensity. 相似文献
58.
《CT理论与应用研究》编辑部 《CT理论与应用研究》2002,11(1):48-51
在《CT理论与应用研究》杂志1994~2001年本杂志“刊标”的基础上,在其上方增加了象征三维体视学成像的三角形四面体的透视图;该刊标的右下侧为医学断面成像扫描仪(包括各种X-CT机与核磁共振MRI扫描仪等);其左下侧为三维地幔速度模型和地球核的示意图,切出有两个地幔剖面,表示纵波速度二维变化的剖面。该速度剖面系根据赵大鹏教授的理论和计算方法,按照地球上的两个大圆弧做计算和绘制的彩色图,排在本期封4:第一大圆弧,从北极经西巴基斯坦(28°N, 64°E)到马尔代夫群岛(3°N,73°E);第二大圆弧从马尔代夫群岛点(3°N,73°E)连接巴布新几内亚之南点(12°S,150°E),来计算两剖面速度分布并作图的结果,其具体分布参见封4的两条彩色剖面和相应的地理位置图。由于赵教授这篇论文[1]在中国国内只有很少数图书馆收藏,在Elsevier Science的EPSL网站上一般人只能查到摘要,本刊对于该地幔速度模型的制作方法和所用数据资料,该模型的优越性和特征进行了叙述,他所用的地震事件数目,多达7128个;用于层析反演成像的震相到时数多到近一百万条。该速度如下的特点:在所采用的速度结构中,包含用几个复杂形状的地质速度界面,如莫霍面,以及下沉板块的分界 相似文献
59.
Chad Trabant Clifford Thurber William Leith 《Physics of the Earth and Planetary Interiors》2002,131(2):155-171
We utilized nuclear explosions from the Degelen Mountain sub-region of the Semipalatinsk Test Site (STS), Kazakhstan, to assess seismic location capability directly. Excellent ground truth information for these events was either known or was estimated from maps of the Degelen Mountain adit complex. Origin times were refined for events for which absolute origin time information was unknown using catalog arrival times, our ground truth location estimates, and a time baseline provided by fixing known origin times during a joint hypocenter determination (JHD). Precise arrival time picks were determined using a waveform cross-correlation process applied to the available digital data. These data were used in a JHD analysis. We found that very accurate locations were possible when high precision, waveform cross-correlation arrival times were combined with JHD. Relocation with our full digital data set resulted in a mean mislocation of 2 km and a mean 95% confidence ellipse (CE) area of 6.6 km2 (90% CE: 5.1 km2), however, only 5 of the 18 computed error ellipses actually covered the associated ground truth location estimate. To test a more realistic nuclear test monitoring scenario, we applied our JHD analysis to a set of seven events (one fixed) using data only from seismic stations within 40° epicentral distance. Relocation with these data resulted in a mean mislocation of 7.4 km, with four of the 95% error ellipses covering less than 570 km2 (90% CE: 438 km2), and the other two covering 1730 and 8869 km2 (90% CE: 1331 and 6822 km2). Location uncertainties calculated using JHD often underestimated the true error, but a circular region with a radius equal to the mislocation covered less than 1000 km2 for all events having more than three observations. 相似文献
60.
We examined the hypothesis that minima in local recurrence time, TL, or equivalently maxima in local probability, PL, may map asperities in the Kanto and Tokai areas of Japan, where the earthquake catalog of the National Research Institute for Earth Science and Disaster Prevention (NIED) is complete at the M=1.5 (M1.5) level. We mapped TL (PL) based on the a- and b-values of the nearest earthquakes within 20 km of every node of a grid spaced 0.01° for M7 target events. Only earthquakes within the top 33 km were used. The b-values increase strongly with depth, in several areas. Therefore, some of the TL (PL) anomalies are not revealed if data from the entire crustal seismogenic zone are mixed. Thus, we mapped TL (PL) separately for the top 15 km and the rest of the depth range, as well as for the entire seismogenic crust. The resulting TL- and PL-maps show that approximately 12% of the total area shows anomalously short recurrence times. Out of six shallow target events with M≥6.5 and which occurred since 1890, five are located within the anomalous areas with TL <450 years. We interpret this to mean that areas with anomalously short TL map asperities, which are more likely than other areas to generate future target events. The probability that this result is due to chance is vanishingly small. The great Kanto rupture of 1923 appears to have initiated in the most significant asperity we mapped in the study area. One anomaly is located in the northeastern part of the area of the proposed future rupture of the Tokai earthquake, and another one at its southwestern corner. The absolute values of TL calculated are uncertain because they depend on the size of the volume used for the calculation. 相似文献