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Three-dimensional crustal structure influences on wave propagation and generation of strong ground motion in the greater San Francisco Bay region.

机译：三维地壳结构影响大旧金山湾地区的波传播和强地面运动的产生。

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摘要

Recent development of three-dimensional finite-difference codes allows simulation of earthquakes using realistic three-dimensional earth models. These and other developments have shifted emphasis in seismology from earthquake prediction to estimation of location and magnitude of damage in future earthquakes. The accurate calculation of ground motions for future large earthquakes depends upon detailed knowledge of three-dimensional (3D) geologic structure and the earthquake source process, as well as sufficient computational resources. Knowledge of subsurface geologic structure in the San Francisco Bay Area is quite good relative to many areas, and this knowledge has been incorporated into a 3D velocity model of the Bay Area. With access to a 3D finite-difference code (E3D) developed by Shawn Larsen at Lawrence Livermore National Laboratory and use of super-computing resources at Livermore, we are able to complete calculations for simulations of a number of San Francisco Bay Area earthquakes. These include a small 1993 Rodgers Creek event recorded at Berkeley Seismological Laboratory, the 1989 Loma Prieta event recorded on the U.S. Geological Survey and Calif. Div. of Mines and Geology network of strong motion stations, and a number of small South Bay events (including the 8/12/98 San Juan Bautista EQ) recorded on a temporary USGS/UCB/PASSCAL Santa Clara array. In each of these cases, comparison of synthetic results (synthetic seismograms and plots of maximum horizontal ground velocity) from E3D to recorded data from the event gives an excellent opportunity to both judge the usefulness and the constraints necessary in using finite-difference modeling and the validity of the velocity model as it is now constructed.; Results show that 3D finite-difference modeling produces waveforms that are often quite comparable to recorded data, and that fit the data considerably better than synthetics waveforms derived with a 1D velocity model. It is also possible to explore the sensitivity of the, synthetics to the major geologic structures in the velocity model, such as pronounced lateral velocity contrasts across the major strike-slip faults and extensive basins of alluvial velocities. Understanding the effects of such long wavelength structure is especially important when considering that most earthquakes locate on or close to faults' velocity contrasts, and often also near basins. For example, in simulations of the Loma Prieta earthquake, it is apparent that the refraction of energy by the San Andreas Fault serves to reduce ground motions at stations located along the San Francisco Peninsula, and the Quaternary and Tertiary alluvial basins of the San Francisco Bay Area are found to amplify and extend the duration of ground motions in the Santa Clara Valley, Livermore Valley and San Pablo Bay. In conclusion, it appears that the 3D model as it is currently defined accurately describes the spatial variation of peak ground velocity in the f 0.5 Hz band, which suggests that this model may be used to estimate ground motions for future earthquake scenarios.
机译：三维有限差分码的最新发展允许使用逼真的三维地球模型来模拟地震。这些和其他发展已将地震学的重点从地震预测转移到了对未来地震破坏的位置和震级的估计。未来大地震的地震动的准确计算取决于对三维（3D）地质结构和震源过程的详细了解，以及足够的计算资源。相对于许多地区，旧金山湾区的地下地质结构知识非常好，并且该知识已被纳入湾区的3D速度模型中。可以访问劳伦斯·利弗莫尔国家实验室（Lawrence Livermore National Laboratory）的肖恩·拉尔森（Shawn Larsen）开发的3D有限差分代码（E3D），并利用利弗莫尔的超级计算资源，我们可以完成许多旧金山湾区地震模拟的计算。其中包括在伯克利地震实验室记录的1993年罗杰斯河小事件，在美国地质调查局和加利福尼亚分公司记录的1989年洛马普里塔事件。强大运动台站的矿山和地质网络，以及在临时USGS / UCB / PASSCAL圣克拉拉阵列上记录的一些小型南湾事件（包括8/12/98 San Juan Bautista EQ）。在每种情况下，将E3D的合成结果（合成地震图和最大水平地面速度图）与事件记录的数据进行比较，都提供了极好的机会，既可以判断使用有限差分建模的实用性和必要条件，也可以使用现在构造的速度模型的有效性。结果表明，3D有限差分建模所产生的波形通常与记录的数据具有相当的可比性，并且与通过1D速度模型得出的合成波形相比，拟合数据的性能要好得多。也有可能在速度模型中探索合成物对主要地质结构的敏感性，例如跨越主要走滑断层和冲积速度广泛盆地的明显横向速度对比。考虑到大多数地震都位于断层的速度对比上或附近，而且往往也位于盆地附近，因此了解这种长波长结构的影响尤为重要。例如，在对Loma Prieta地震的模拟中，很明显，圣安德烈亚斯断层的能量折射有助于减少沿着旧金山半岛以及旧金山湾第四纪和第三纪冲积盆地的站点的地震动。在圣塔克拉拉山谷，利弗莫尔山谷和圣巴勃罗湾，发现该区域可扩大并延长地面运动的持续时间。总之，目前定义的3D模型似乎准确地描述了f <0.5 Hz频带内峰值地面速度的空间变化，这表明该模型可用于估计未来地震场景的地震动。

著录项

  • 作者

    Stidham, Christiane Wilson.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Geophysics.
  • 学位 Ph.D.
  • 年度 1999
  • 页码 316 p.
  • 总页数 316
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地球物理学;
  • 关键词

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