地震基本烈度应以长期地震预报为基础,加上影响场(烈度衰减规律)的考虑而得。由于地震预报问题尚未解决,所以实际上往往不是这样做的。早期的方法是以历史上遭遇的最高烈度为准。这一准则显然并不合理,尤其是它没有给定时间范围,而工程建设是有时间性的。譬如说,某地历史上最高烈度记录为十度,但在两千年中就只有这么一次,而在该地要建的一项工程只使用一百年,显然这一百年中碰到一个十度地震的机会并不大,按十度设防就未必恰当。后来有一些工作中提出了十度以上地震不原地重复的看法。这种提法未免有些绝对化,实际上我们只能说在多长时间和多大范围内不重复,或者说重复的概率小到怎样的地步。由此可见,鉴定一个地方的基本烈度,时间性和概率性都是必须加以考虑的。 The basic earthquake intensity should be based on the long-term earthquake prediction and the consideration of the influence field (intensity attenuation law). As the problem of earthquake prediction has not been solved, it is often not the case in practice. The early method was based on the highest intensity ever encountered in history. Obviously, this criterion is not reasonable. In particular, it does not have a given time frame and construction is time-consuming. For example, the record of the highest intensity in a certain place in history was recorded as ten degrees, but it was only once in two thousand years. Only one hundred years was required for a project to be built there. Obviously, in this century, one ten Degree of earthquake opportunities are not large, according to ten degrees fortification may not be appropriate. Later some work proposed the view that the earthquakes of more than ten degrees did not repeat themselves. This formulation is somewhat inelegant, and in fact we can only say how long and to what extent the non-repetition, or how small the probability of duplication. From this it can be seen that the basic intensity, timeliness and probability of identifying a place must be taken into account.