Deep Arrays for Earthquake Response, San Francisco Bay Area

这一行动是为了支持与美国地质调查局(USGS)合作--以及可能与加州矿产和地质分部(CDMG)合作--在旧金山湾区安装两个深层阵列，目的是测量预计将在旧金山湾区发生的大地震期间的地面运动和地下水压力的升高。这些记录将为地震学、地震工程学和地震减灾研究提供有价值的数据：这些数据目前还不存在。1989年10月17日加利福尼亚州洛马普里塔地震的地表测量表明，深层粘土场地水平地面加速度峰值的视放大比预期的高100%或更多；然而，目前还没有土壤剖面的测量数据来显示基岩和地表之间的放大过程。强震的其他地点也没有这种类型的数据。旧金山湾区极有可能(30年后67%)发生比洛马普里塔地震更强烈的地震；因此，旧金山湾区是建立深层加速度计阵列以提高预测能力的绝佳地点。目前正在对该地区的地点进行勘测，并已确定了几个有希望的地点。一个由来自美国和加拿大主要大学以及美国地质勘探局和CDMG的地震减灾领域著名研究人员和管理人员组成的咨询小组将就场地及其仪器的一般要求提供建议，以及仪器的位置，以最大限度地发挥所恢复的数据的作用。小组成员在地球科学、岩土工程和现场数据测量方面拥有专业知识。洛马普里塔地震以及世界各地以往的大地震造成的破坏表明，需要测量两种不同类型的数据，以改进地震减灾方法：在强震引起的地面震动期间测量深层粘土矿床中的地面运动放大；强震时饱和砂土中的地面运动和地下水压力的增加。这些测量值可以通过两个单独的野外阵列获得，或者在饱和砂土和深层粘土沉积物适当组合的地点通过组合阵列获得。根据1988年9月关于“美国土工试验指定场地”的研讨会和1990年11月关于“动态土壤性质和场地特征”的研讨会的建议，建立了这些阵列。这些场地将成为指定的岩土试验场地，向所有感兴趣的研究人员开放。这些地点将可用于研究与地震无关的岩土现象，但预计所选地点总体上将更适合于研究所讨论的地震引起的现象。

This action is to support the installation, in collaboration with the U.S. Geological Survey (USGS) - and possible collaboration with the California Division of Mines and Geology (CDMG) - of two deep arrays in the San Francisco Bay area, with the objective of measuring ground motions and the elevation of ground water pressure during the large earthquake that is expected to occur in the San Francisco Bay area. These recordings will provide valuable data for seismological, earthquake engineering and earthquake hazard mitigation studies: these data do not exist at present. Surface measurements from the October 17, 1989 Loma Prieta, California earthquake showed that the apparent amplification of the peak horizontal ground acceleration at deep clay sites was higher by 100% or more than would have been anticipated; yet no measurements in the soil profile showing how amplification progressed between bedrock and the ground surface are available. Nor are data of this type available at other locations for strong-motion earthquakes. There is a significant probability (67% in 30 years) that an earthquake producing greater intensity of motion than the Loma Prieta event will occur in the San Francisco Bay area; it is thus an excellent location to establish a deep accelerometer array to improve prediction capabilities. Sites are being surveyed in the area, and several promising locations have been identified. An advisory panel consisting of eminent researchers and administrators in earthquake hazard mitigation, from major universities in the United States and Canada, and from the USGS and CDMG, will provide advice on the general requirements for the sites and their instrumentation, as well as on the location of instruments to maximize the usefulness of the data recovered. The panel members have expertise in earth science, geotechnical engineering, and field data measurements. The damage caused by the Loma Prieta earthquake, as well as previous major earthquakes worldwide, point to the need to measure two different types of data so as to improve earthquake hazard mitigation methods: The measurement during strong earthquake-induced ground shaking of the amplification of ground motions in deep clay deposits; and the ground motions and the increase in ground water pressure in saturated sands during strong earthquakes. These measurements could be obtained through two separate field arrays, or a combined array at a site which has the appropriate combination of saturated sands and deep clay deposits. The establishment of these arrays follows the recommendations of the September 1988 workshop on "Designated Sites for Geotechnical Experimentation in the United States", and the November 1990 workshop on "Dynamic Soil Properties and Site Characterization". These sites will become designated geotechnical test sites, open to all interested researchers. The sites will be available for research into geotechnical phenomena not associated with earthquakes, but it is expected that the sites chosen will, in general, be more suitable for investigation of the earthquake-induced phenomena discussed.