汶川8.0级地质发震断层逆冲活动的地震地貌与古地震初步研究

与河流阶地相关的地震地貌包括地震阶地和阶地断错两方面。地震阶地是古地震事件的直接反映； 阶地断错则是多次古地震事件的累积效应。文章在汶川8.0级地震破裂带调查的基础上，讨论了平行断裂的河流和横穿断裂的河流两种情况下的阶地发育特征。在此基础上，应用差分GPS测量技术，分别对虹口附近的地震阶地和映秀附近阶地断错现象进行了测量。研究结果表明，虹口附近地震阶地反映了自白沙河Ⅱ级阶地形成以来发生了5次规模基本相当的断错事件； 映秀附近的阶地累积位错量反映了不同级阶地经历了不同数量的地震事件，其中，Ⅱ级阶地形成以来大致经历了5次与汶川8.0级地震位错相当的地震事件。两个地点的地震阶地和阶地位错研究得到了一致的古地震次数。本文进一步讨论了前人对该区阶地的测年数据，从而推测得到汶川8.0级地震发震断层的古地震复发间隔约为4ka。

PRELIMINARY STUDY OF PALEOEARTHQUAKES BASED ON EARTHQUAKE TERRACE AND OFFSET TERRACE INVESTIGATION AFTER WENCHUAN MS8.0 EARTHQUAKE

Earthquake geomorphology related to river terrace includes earthquake terrace and offset terrace. Earthquake terraces were caused directly by individual paleoearthquakes while offset terraces are cumulative displacement of several paleoearthquakes. We observed terraces of a river that goes along the fault or cross the fault after the Wenchuan Ms8.0 Earthquake. As examples，we measured earthquake terraces nearby Honkou Town and offset terraces of Minjiang nearby Yingxiu Town using Real Time Kinematic GPS technique. The result is: (1)Earthquake terraces near Hongkou Town imply about 5 severe earthquakes occurred after Terrace Ⅱ of the Baisha River was formed; (2)Offset terraces near Yingxiu Town shows that different terraces had experienced various times of palaeoearthquakes. The Terrace II had been also cut by about 5 paleoearthquakes as severe as the Wenchuan MS8.0 Earthquake. Based on published ages of the terraces in this region，we suggest that the recurrence interval of severe earthquakes is about 4ka in this region.