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为了确定穿过四川二滩坝区 F_(20)活断层的活动历史,采集了断层带内及其两侧的方解石脉、方解石团块,用热释光技术测定了这些方解石的年龄。根据方解石的热释光年龄以及他们的产状、结晶程度和变形等特征,可把该区的方解石分为三期:第一期为225万年左右;第二期为100—130万年左右;第三期为35万年左右。从而比较准确地确定了 F_(20)断层的最后一次活动发生于第二期方解石贯入以前。此后,F_(20)断层没有再发生过明显的活动。这对评定二滩坝区的地震危险性有重要的意义。
In order to determine the activity history of the F 20 active fault in the dam area of Ertan, Sichuan, the calcite veins and calcite agglomerates were collected in the fault zone and on both sides of the fault zone. The ages of these calcites were determined by using the thermoluminescence technique. According to the calcite’s age and the age of their thermoluminescence, their occurrence, degree of crystallization and deformation characteristics, the calcite can be divided into three phases: the first period is about 2.25 million years; the second period is about 100-130 million years The third period is about 350,000 years. Thus, the last activity of the F 20 fault occurred more accurately before the second calcite penetration. Since then, no obvious activity has occurred in F_ (20) fault. This is of great significance for assessing the earthquake risk of Ertan dam area.