研究2001年昆仑山口西地震和2008年汶川地震前的中源地震活动特征，与唐山地震前的特征进行比较，发现：3次大地震前曾发生6或7次h≥60 km的中源地震，且“大震前中源地震活跃的时间跨度T”约5年或5年多。这是大震前中源地震活动最主要的两个特征，包含了孕育大地震的一些重要信息。其他特征还有：中源地震的活动—平静交替、临近大地震前的地震平静、呈条带分布和(或)地震空区等特征，这与大震前壳内地震活动性的一些特征类似。

The characteristics of the mediumdepth events′ seismicity before the Kunlun Mountain earthquake in 2001 and the Wenchuan earthquake in 2008 are not only studied in this paper, but also compared with those before the Tangshan earthquake. It is concluded that: there were 6 to 7 mediumdepth events with h≥60 km before the 3 main quakes. Moreover, the “time span T of the active mediumdepth earthquakes before the large earthquake” is about or more than 5 years. These two characteristics are the principal, which include some important information to generate large quakes. Other characteristics are as follows: an activequiet alternating phenomenon of mediumdepth events exists; there is a preseismic quiet stage of the large earthquake; the mediumdepth events present a beltlike distribution and/or form a seismic gap. All of these are similar to those of the crustal seismicity before a large quake.