地震简问简答/Foreshocks, aftershocks - what's the difference?
Q: Foreshocks, aftershocks - what's the difference?
A: "Foreshock" and "aftershock" are relative terms. Foreshocks are earthquakes which precede larger earthquakes in the same location. Aftershocks are smaller earthquakes which occur in the same general area during the days to years following a larger event or "mainshock", defined as within 1-2 fault lengths away and during the period of time before the background seismicity level has resumed. As a general rule, aftershocks represent minor readjustments along the portion of a fault that slipped at the time of the main shock. The frequency of these aftershocks decreases with time. Historically, deep earthquakes (>30km) are much less likely to be followed by aftershocks than shallow earthquakes. (Univ. of Washington)
Foreshocks, Mainshocks, and Aftershocks Flash Animation
问：前震，余震有何差异？
答：“前震”和“余震”是两个相关的术语。前震是更大强度地震发生之前在同一位置发生的地震。余震是临近地区在“主震”发生后的几天到几年内发生的更小强度的地震，即余震发生在距（震中）1-2个断层的范围内，在本底地震恢复到原先级别之前的这段时间里（译注：本底地震指此地震区或地震带内没有明显构造标志的最大地震）。一般来说余震代表发生主震的断层的微小重调。余震的发生频率随着时间慢慢减小。从历史数据看，深度地震（>30千米）比浅层地震的余震少的多。（华盛顿大学）