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61.
The seismic ground motion of a test area in the eastern district of Naples is computed with a hybrid technique based on the mode summation and the finite difference methods. This technique allows us the realistic modelling of source and propagation effects, including local soil conditions. In the modelling, we consider the 1980 Irpinia earthquake, a good example of strong shaking for the area of Naples, which is located about 90 km from the epicenter.The detailed geological setting is reconstructed from a large number of drillings. The sub-soil is mainly formed by alluvial (ash, stratified sand and peat) and pyroclastic materials overlying a pyroclastic rock (yellow neapolitan tuff), representing the neapolitan bedrock. The detailed information available on mechanical properties of the sub-soil and its geometry warrants the application of the sophisticated hybrid technique.As expected, the sedimentary cover causes an increase of the signal's amplitudes and duration. If thin peat layers are present, the amplification effects are reduced, and the peak ground accelerations are similar to those observed for the bedrock model. This can be explained by the backscattering of wave energy at such layers, that tend to seismically decouple the upper from the lower part of the structure.For SH-waves, the influence of the variations of the S-wave velocities on the spectral amplification is studied, by considering locally measured velocities and values determined from near-by down-hole measurements. The comparison between the computed spectral amplifications confirms the key role of an accurate determination of the seismic velocities of the different layers.The comparison performed between a realistic 2-D seismic response and a standard 1-D response, based on the vertical propagation of waves in a plane layered structure, shows considerable difference, from which it is evident that serious caution must be taken in the modelling of expected ground motion at a specific site. 相似文献
62.
In situ seismic attenuationQ−1logs are derived from borehole velocity profiles and reveal sharp boundaries between morphologies of the extrusive volcanic layers in intermediate- and slow-spreading oceanic crust.Q−1logs are calculated from the scattering attenuation associated with vertical velocity heterogeneity in Ocean Drilling Program Holes 504B and 896A and in Hole 395A, located in 5.9–7.3 Ma crust on the Pacific and Atlantic plates, respectively. Our results strongly tie crustal properties to seismic measurables and observed geological structures: we find that the scattering attenuation can be used to identify the extrusive volcanic sequence because it is closely related to changes in the degree of vertical heterogeneity. We interpret a distinct decrease in the Q−1log at the transition below the extrusive volcanic layer to correspond with the seismic layer 2A/2B boundary. The boundary is located at 465 m depth below the sea floor in both Hole 395A and 504B, although this is likely to be a coincidence of the sediment thickness at these sites. Layer 2A is estimated to be approximately 150 m thick in Hole 504B and > 300 m thick in Hole 395A. Cyclic sequences of high-porosity pillows and low-porosity massive units in the uppermost 100 m of volcanics in Hole 395A result in large velocity heterogeneities which cause > 5 times more attenuation in this layer than in Hole 504B. In Hole 896A, by contrast, fewer pillows, more massive flows, and a greater volume of carbonate veins decrease the velocity heterogeneity and attenuation significantly over only 1 km distance from Hole 504B. We conclude that the attenuation in the extrusive volcanics of the ocean crust is largely controlled by variation in local heterogeneity and morphology as well as by subsequent hydrothermal alteration. The observed differences inQ−1profiles and layer 2A thickness at these sites may be attributed to variations in the volume and duration of volcanic activity at mid-ocean spreading centers for these Pacific and Atlantic ridge segments. 相似文献
63.
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65.
利用高分辨率卫星影像进行地震损失评价所需的城市特征识别 总被引:2,自引:0,他引:2
高分辨率卫星影像已经在一些国家的民用领域得到应用。利用高分辨率卫星影像来收集地震损失评价所需要的各类城市信息不仅高效和有较好的时间分辨率,而且它可以减少以往所必需的大量的代价高昂且费力的城市调查。基于在印度城市台拉登所做的研究,讨论了如何利用高分辨率卫星影像进行城市特征识别的一些问题,同时也简单论述了利用GIS/RS软件综合所得的数据以便用于地震损失评价的方法。 相似文献
66.
R.M.W. Musson 《Bulletin of Earthquake Engineering》2004,2(1):101-112
Three sites in the UK are taken, representative of low, medium and high hazard levels (by UK standards). For each site, the
hazard value at 10−4 annual probability is computed using a generic seismic source model, and a variety of ground motion parameters: peak ground
acceleration (PGA), spectral acceleration at 10 Hz and 1 Hz, and intensity. Disaggregation is used to determine the nature
of the earthquakes most likely to generate these hazard values. It is found (as might be expected) that the populations are
quite different according to which ground motion parameter is used. When PGA is used, the result is a rather flat magnitude
distribution with a tendency to low magnitude events (\le 4.5 ML) which are probably not really hazardous. Hazard-consistent scenario earthquakes computed using intensity are found
to be in the range 5.8–5.9 ML, which is more in accord with the type of earthquake that one expects to be a worst-case event
in the UK.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
67.
IntroductionItisdefinitelystipulatedintheLawofthePeople'sRepublicofChinaonProtectingagainstandMitigatingEarthquakeDisastersthattheseismicsafetyevaluationmustbemadeformajorprojects(includinglifelineprojects)and,accordingtotheresultsobtained,theseismicresistancerequirementsshouldbedetermined.Thenecessityofseismicsafetyevaluationhasbeenrecog-nizedgradually,butthetopicontheeffectofsafetyevaluationhasnotbeenreferredmuch.Gener-allyspeaking,althoughmostpeopleapprovethesocialeffectofsafetyevaluatio… 相似文献
68.
数值预报产品在夏季持续高温预报中的释用 总被引:6,自引:0,他引:6
利用 1999~ 2 0 0 2年 6~ 8月 96~ 192h日本数值预报产品 85 0hPa气温与吉林省的日平均气温、阶段性高温及极端最高气温 (长春市 )资料 ,通过线性分析 ,找出了日本数值预报产品的 85 0hPa气温与吉林省地面日平均气温、阶段性高温及极端最高气温的对应关系 :吉林省 6~ 8月日平均气温在 96~ 192h的 85 0hPa日本数值预报长春站日平均值上加 6 6~ 4 1℃ ,6~ 8月的极端最高气温在相应的日本数值预报产品上加 9 3~ 13 0℃。 相似文献
69.
The Zhangjiakou–Penglai seismotectonic zone (ZPSZ) lies in the northern part of North China and extends along the Zhangjiakou–Beijing–Tianjin–Bohai Bay–Penglai–Yellow Sea. It is about 900 km long and some 250 km wide in a northwest direction. The great Sanhe-Pinggu (MS=8.0) earthquake occurred on September 1679 and the Tangshan (MS=7.8) earthquake on July 1976 caused serious economic and life losses. According to some differences in crust structure and regional tectonic stress field, the ZPSZ is divided into western and eastern segment by the 117°E line for study on long-term seismic hazard analysis. An analysis of Gutenberg–Richter's empirical relation of earthquake-frequency and time process of historic and recent earthquakes along the eastern and western segments shows that the earthquake activity obeys a Poisson process, and these calculations indicate that the earthquake occurrence probability of MS=6.0–6.9 is 0.77–0.83 in the eastern segment and the earthquake occurrence probability of MS=7.0–7.9 is 0.78–0.80 in the western segment of the ZPSZ during a period from 2005 to 2015. 相似文献
70.
Transformation of Residuals to Avoid Artifacts in Geostatistical Modelling with a Trend 总被引:1,自引:0,他引:1
Trend modelling is an important part of natural resource characterization. A common approach to account for a variable with a trend is to decompose it into a relatively smoothly varying trend and a more variable residual component. Then, the residuals are stochastically modelled independent of the trend. This decomposition can result in values outside the plausible range of variability, such as grades below zero or ratios that exceed 1.0. We transform the residuals conditional to the trend component to explicitly remove these complex features prior to geostatistical modelling. Back transformation of the modelled residual values allows the complex relations to be reproduced. A petroleum-related application shows the robustness of the proposed transformation. Furthermore, a mining application shows that when this conditional transformation is applied to the original variable, instead of the residual, simulated values are assured to be nonnegative. 相似文献