Aftershocks are generally weaker than the main quake, but buildings that have already been damaged are prone to collapse in an aftershock. 通常余震比主震弱，但是，在主震中受损的建筑往往因余震倒塌。
However, the earliest long-period seismographs recorded dispersive waves with large transverse displacement components in the main tremor. 但是，最早期的地震记录，就记录下了主震中具有很大横向位移分量的频散波。
