Site Response and Soil Liquefaction in San Francisco Due to the 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(NEHRP)倡议的一部分，目的是调查1989年10月17日洛马普里塔地震的影响。旧金山提供了一个独特的机会，可以通过详细和全面的观测来比较两次地震的影响，目前存在于1906年和1989年的地震中。通过研究城市内的不同位置，可以评估填土厚度和密度、下伏软粘土的厚度和固结状态、地下水位、在相似水平的基岩地震作用下，基岩埋深影响地表反应和土层液化的发展。此外，地面响应与地下生命线系统的性能相结合，为量化土-结构相互作用对复杂结构的影响提供了额外的机会对紧急行动至关重要的网络。为了利用从1906年和1989年地震中获得的知识，该项目的结构包括三个方面的目标：(1)描述旧金山选定地点的地下地面条件和现场反应-这需要一个关于土壤状况的全面数据库，以及从城市以前的调查和震后勘察中获得的熟悉情况和特定地点的知识，(2)对选定地点的地点反应进行分析建模，并将这些分析结果与现场观测和地震数据进行比较，以证实和完善分析模型，以及(3)使用分析模型来预测未来可能发生的地震对旧金山市的影响，这些地震比洛马普里塔地震更大、更近。该项目涉及与美国地质调查局(USGS)和旧金山的岩土公司和市政机构的合作。美国地质勘探局正在选定的地点进行土壤钻探；岩土技术公司正在提供土壤钻探记录(数据)和岩土调查报告，以扩大关于地下条件和相关土壤性质的现有数据库。此外，城市机构，如旧金山消防局，参与评估现场响应特征可能如何影响供水，以及如何最好地设计和运行管道系统，以最大限度地减少局部严重地面震动和液化的影响。

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. San Francisco offers a unique opportunity to compare the effects of two earthquakes through detailed and comprehensive observations which now exist for the 1906 and the 1989 earthquakes. By studying different locations within the city, it is possible to evaluate how variations in fill thickness and density, the thickness and consolidation state of underlying soft clay, the water table, and the depth to bedrock affect the ground surface response and the development of soil liquefaction for similar levels of bedrock seismic motion. Moreover, ground response coupled with the performance of buried lifeline systems provides an additional chance to quantify the effect of soil-structure interaction on complex networks that are critical for emergency operations. To take advantage of the knowledge gained from the 1906 and 1989 earthquakes, this project is structured according to a three- fold set of objectives: (1) to characterize subsurface ground conditions and site response at select locations in San Francisco - this requires a comprehensive data base on soil conditions, as well as the familiarity and the site-specific knowledge gained from previous investigations and post-earthquake reconnaissance in the city, (2) to model analytically the site response at select locations, and to compare these analytical results with field observations and with seismic data in order to substantiate and refine the analytical models, and (3) to use analytical models to predict the effects on the city of San Francisco of possible future earthquakes that are larger and closer than was the Loma Prieta earthquake. This project involves cooperation with the U.S. Geological Survey (USGS) and San Francisco geotechnical firms and city agencies. The USGS is performing soil boring at selected locations; geotechnical firms are providing soil boring logs (data) and geotechnical investigation reports in order to expand the available data base on subsurface conditions and relevant soil properties. In addition, city agencies, such as the San Francisco Fire Department, are involved in evaluating how the site response characteristics might affect the water supply, and how best to design and operate the pipeline system so as to minimize the effects of locally severe ground shaking and liquefaction.