承蒙卢刚相助，从国外查询维基百科，得到资料如下：

Bigger earthquakes have more _and larger aftershocks _and the sequences can last for years or even longer especially when a large event occurs in a seismically quiet area

很吃惊，原来真的是这样，那也就是说，仍需做好防震措施。

不过余震会越来越少。

The rate of aftershocks decreases quickly - the decrease is proportional to the inverse of time since the main shock. This means the second day has about 1/2 the number of aftershocks of the first day _and the tenth has about 1/10 the number of the first day.

How long this lasts depends on the size of the main shock (bigger earthquakes have more aftershocks) _and how active the region was before the main shock (if the region was seismically quiet before the main shock, the aftershocks continue above the previous rate for a longer time). Thus, an aftershock can occur weeks or decades after a main shock.

多了解一些相关知识，可以避免不必要的伤亡，假如不知余震的可怕，可能会放心地回到家中。

我们想知道，发生大地震前，地震的监测在哪里？

请阅读http://blog.vsharing.com/qsxiao/A682106.html 地震知识手册中，有相关地震预报的部分。