The Influence of Critical Reflections on Ground Motions Recorded in San Francisco and Oakland During the 1989 Loma Prieta Earthquake

该项目是美国国家科学基金会/美国地质勘探局在国家减少地震危害方案（NEHRP）下的倡议的一部分，目的是调查1989年10月17日洛马普列塔地震的影响。在Loma Prieta地震期间，旧金山湾区记录的强地面运动超过了标准经验衰减关系预测的水平。对这些记录的初步分析表明，这可能是地壳底部对地震波进行关键反射的结果。这项提议的目的是利用一个扩展的数据库，包括地震序列中其他事件的记录，进行进一步的分析和模拟，以便严格检验这种解释和其他对观察到的大地面运动的解释。​评估这种观测到的与预测的地面运动水平偏离的原因，对于估计未来圣安德烈亚斯和海沃德断层上大地震的地面运动具有重要意义。它对美国其他地区也有影响，如西雅图-波特兰地区，在那里，震源深度较深的地壳地震可能同样会使遥远地区的地面运动达到破坏性水平；以及在西雅图、洛杉矶、盐湖城和其他流域响应效应预计会很显著的地区。

This project is part of the NSF/USGS initiative within the National Earthquake Hazard Reduction Program (NEHRP) to investigate the effects of the Loma Prieta earthquake of 17 October 1989. The strong ground motions recorded in the San Francisco Bay Area during the Loma Prieta earthquake exceeded the levels predicted by standard empirical attenuation relations. A preliminary analysis of these records suggests that this may have been a result of critical reflections of the seismic waves from the base of the crust. The objective of this proposal is to perform further analyses and simulations using an expanded data base that includes recordings of other events of the earthquake sequence in order to rigorously test this and other explanations for the large ground motions observed. Evaluating the cause of this observed departure from predicted levels of ground motion has important implications for estimating ground motions from future large earthquakes on the San Andreas and Hayward faults. It also has implications for other regions in the United States such as the Seattle-Portland region where crustal earthquakes having deep focal depths may similarly elevate ground motions to damaging levels at distant locations; and in the Seattle, Los Angeles, Salt Lake City and other regions where basin response effects are expected to be significant.