Abstract: The May 12,2008 M_S 8.0 Wenchuan earthquake in Sichuan Province,China produced a 240km long co-seismic surface rupture zone along the Longmenshan Central Fault.Our investigation focuses mainly on the three regions along the co-seismic surface ruptures,i.e.the Nanba Town and the Fenghuang village on the northern segment of the rupture zone,and the Yingxiu town on the southern segment.We studied the river terraces in these regions offset by the active fault,measured the surface ruptures and the fault scarps on the multilevel terraces and obtained the height of the fault scarps on each terrace,namely,the cumulative vertical slip of the active fault recorded by terrace,through data calculation and analysis.If we use the vertical slip of this earthquake as the average vertical slip of the paleoearthquakes,then the ratio of the cumulative vertical slip of each terrace to this average vertical slip is the cumulative times of paleoearthquakes recorded by each terrace.The research results show that T₁ of every study area has undergone only one paleoearthquake event ever since its formation,T₂ about 5 paleoearthquake events,T₃ about 9～11 paleoearthquakes and T₄ about 20 paleoearthquakes.Based on the research result of this paper,and combined with the previously dating ages of the terraces,we can obtain some reliable data about the recurrence intervals of the paleoearthquakes.

Key words: M_S 8.0 Wenchuan earthquake, Longmenshan Fault, faulted landform, terrace measurement, earthquake surface rupture, paleoearthquake

摘要： 2008年5月12日,四川省汶川县内发生M_S 8.0地震。此次地震沿龙门山中央断裂产生1条长达200km的同震地表破裂带。文中选择位于地震地表破裂带北段的南坝镇、凤凰村以及南段的映秀镇这3个地点,以被断层错断的河流阶地为研究对象,对多级阶地面上的地震地表破裂及断层陡坎地貌进行了野外实测工作。经过测量数据的计算和分析,得到了各级阶地上断层陡坎的高度,该值即为该阶地记录的地震断层的累积垂直位错量。若以本次地震的垂直位错量作为古地震位错量的均值,则可计算得到每级阶地累积的地震次数。研究结果表明,各点T₁阶地形成以来仅经历过1次事件,即本次地震事件;T₂阶地形成以来约经历了5次事件;T₃阶地形成以来约经历了9～11次事件;T₄阶地形成以来约经历了20次事件。在本文研究的基础上,结合前人的阶地测年数据,则可获得古地震复发间隔的可靠数据。

关键词: 汶川8.0级地震, 龙门山断裂, 断错地貌, 阶地测量, 地震地表破裂, 古地震