关键词: 震源深度, 强震活动, 地震地热说, 地震链

Abstract: A detailed analysis is made for the earthquake data with focal depth since 1970 on the most regians of China. A hypothesis is poposed to explain the analysis results, which leads to a new concept on the overall situation of major earthquakes in China. It is suggested that major events of China are driven by the earthquakes with middle-depth ard deep-depth sources which occurred at four "hot spots" in 1970s, that are located at Jilin Province, Xindoukushi of Xinjiang, Taiwan, and Rikeze of Tibet. A process of earthquake chain composed of an active period (1970～1982), adjustment period (1983～1992) and waning period (1993～1999) has been completed. Althouth the last period is still under going, a new circle of the earthquake chain may be developing since the M 7.0 deep event of Jilin on April 8, 1999.

Key words: Focal depth, Major earthquake, Hypothesis of seismo-geothermics, Hot spot