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/美国地质勘探局国家减少地震灾害计划的一部分，目的是调查10月17日洛马普里埃塔地震的影响。Loma Prieta地震期间，旧金山湾区记录到的强烈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，这可能是地壳底部的地震波临界反射的结果。这项建议的目标是使用包括地震序列的其他事件的记录的扩展数据库来执行进一步的分析和模拟，以便严格测试这一点和其他对观测到的大地面运动的解释。评估观测到的地面运动水平偏离预测水平的原因，对于估计圣安德烈亚斯和海沃德断层未来大地震的地面运动具有重要意义。它对美国的其他地区也有影响，例如西雅图-波特兰地区，在那里，震源深度较深的地壳地震可能同样会将遥远地点的地面运动提高到破坏性水平；而在西雅图、洛杉矶、盐湖城等盆地响应效应预计较大的地区。

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.