为了确定穿过四川二滩坝区 F20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 F20断层的最后一次活动发生于第二期方解石贯入以前。此后,F20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 history of the F20-fault activity in Ertan, Sichuan province, some samples of calcite veins and nodule were collected within and outside the fault zone, and the age of the calcite was measured by the thermoluminescent technique. Based on the age,occurrence, degree of crystallization and the deformation characteristics, of calcite,the calcite veins in the region could be divided into 3 periodst the first is about 2.25m, y. age, the second 1.0-1.3 m.y.,and the third 0.35 m. y., Then it can be exactly determined that the latest activity of the fault is before the second period calcite intrusion. From then on, no more appa rent activity of the fault has occurred. It has great significance for evaluating seismic risk in Ertan dam region.