Earthquake Predominant Ground Motion in the San Francisco Metropolitan Area Using Data from Microtremors and 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。这个项目涉及对旧金山盆地长周期微震的广泛测量。微震，或微地震，是由自然事件产生的地球的微小震动或振动，如海浪冲击海岸或道路交通。它们只能被敏感的仪器探测到，与地震无关，但可以用来更好地了解地震引起的地面震动过程。其目的是研究利用旧金山盆地的长周期微震来识别其固有振动频率接近于盆地主要运动的“关键”结构。该计划包括三个阶段：(1)测量盆地内约30个地点的长周期微震，在洛马普里塔地震期间，由于一些场地与强震位置重合，获得了记录，(2)对这些数据进行处理，(3)对这些数据进行分析，并将它们与洛马普里塔地震期间获得的强地面运动记录进行比较。特别重视滨海地区，该地区由非常软的沉积物组成，并发生了相当大的破坏。所有记录的数据都存储在软盘上，如有需要，可提供软盘。此外，还可以通过电子邮件查阅这些记录。

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. This project involves extensive measurements of long-period microtremors in the San Francisco basin. Microtremors, or microseisms, are small tremors or vibrations of the earth that are generated by natural occurrences such as the pounding of surf on the shore, or road traffic. They can be detected only by sensitive instruments and are not associated with earthquakes, but may be used to understand better the process of ground shaking due to earthquakes. The aim is to investigate the use of long-period microtremors in the San Francisco basin to identify "critical" structures having a natural frequency of vibration close to that of the predominant motion of the basin. The program consists of three phases: (1) The measurement of long-period microtremors at approximately 30 locations within the basin, with some of the sites coinciding with the locations were strong motion records were obtained during the Loma Prieta earthquake, (2) processing these data, and (3) analyzing these data and comparing them with the strong ground motion records obtained during the Loma Prieta earthquake. Special emphasis is being given to the Marina district which consists of very soft sediments and in which considerable damage occurred. All recorded data are being stored on floppy disks, which will be available upon request. In addition, the records will be accessible through electronic mail.