论文部分内容阅读
1985年以来,在加州中部帕克菲尔德镇附近的圣安德烈斯断层上,以地震预报为核心的试验已经取得了进展。1857年以来,帕克菲尔德以22年一次的平均间隔经历了6次中等地震,最近的一次6级地震是在1966年。另一次中等地震立刻就要出现的概率也很高,但认定它发生在1993年前的概率达95％的研究结果,现在看来显然是过于简单化了。帕克菲尔德断层分段的鉴别工作原先是以圣安德烈斯断层地表迹线所显示的几何特征为基础的,但是近来的微震研究业已显示这些特征并未延伸到孕震深度。另一方面,大地测量与帕克菲尔德下方断裂上现在已积累起相当于1966年地震时的位移量的位移亏空的断层闭锁段的存在相一致。1992年10月的一次4.7级地震,以发布6级地震发生概率为37％的72小时公众警报将帕克菲尔德试验引向其最高警戒水平。然而,这一警报被证明是一次虚报。在帕克菲尔德收集的多数资料显示,圣安德烈斯断层的这一段,应变正以恒定速率积累,但是也已记录到对这一性质的某些有意义的偏离。这里,我们将概述关于下一次帕克菲尔德地震究竟什么时候可能发生这一问题的科学论证,并对最新的地球物理观测结果进行总结。
Experiments centered on earthquake prediction have progressed since 1985 on the San Andres Fault near Parkfield, California. Since 1857, Parkerfield has experienced 6 moderate earthquakes at 22-year intervals, the most recent of which was in 1966. The probability of another moderate earthquake occurring immediately is high, but the findings, which found it to have occurred 95% of the time before 1993, now appear to be clearly simplistic. The identification of Parkfield faults was originally based on the geometric features shown by the San Andreas fault surface trace, but recent microseismic studies have shown that these features do not extend to seismogenic depth. On the other hand, geodetic coincides with the presence of a fault-deficient fault block that has now accumulated a displacement equivalent to that of the 1966 earthquake below Parkfield’s fault. A 4.7-magnitude earthquake in October 1992 brought the Parker test to its highest alert level with a 72-hour public alert on a 37% probability of a magnitude 6 earthquake. However, this alert proved to be a fake. Most of the information collected at Parkfield shows that during this period of the San Andrrasian fault, strain is accumulating at a constant rate, but some meaningful deviations from this property have also been recorded. Here, we will outline the scientific justification for when this problem may occur at the next Parkfield Earthquake, and summarize the latest geophysical observations.