长江三峡水电站坝址区断裂新活动年龄及地壳稳定性

A STUDY ON THE ACTIVITY OF MAJOR FAULTS IN THE THREE-GORGE DAM SITE AREA AND ITS SURROUNDINGS

长江三峡水电工程坝址区断裂新活动年龄分为两类:(1)>220×10~4a BP.和(2)(131-54)×10~4aBP.。坝区15公里范围内不存在近代活动断裂。地震基本烈度为Ⅵ度。地壳稳定性等级属稳定区。

In order to evaluate the seismic activity and crustal stability in the Three-Gorge hydropo-wer project area on Changjiang River, some new isotopic dating methods were used in determination of the ages of fault activity in and around the dam area. Analysis of the obtained data indicates that the age of the latest activity of the major faults around the project site is (145-20)×104a and two age data of the latest activity of the major faults in the dam area are 220×104a (as they had not been activated in the Quaternary time) and (131-54)×104a. As studied by the author, the lower limit of the age of latest fault activity in eastern China affecting on the stability of the project is identified to be 5×104a, that is, the fault with its age equal or less than the identified age data may be activated (creep or earthquake) in the period of operation of the project. Thus the faults in the Three-Gorge dam area do not belong to the engineering-active faults.Comprehensive analysis of the age data of latest fault activity, historic seismic and micro-seismic data indicates that no recently active faults exist in the area with diameter of 15 km around the projected Sandouping Dam site. Therefore, the crustal stability conditions in the dam area are good. Comprehensive analysis of fault activity, seismic parameters and crustal structure indicates that the crustal stability in the dam area is classified as a stable area. From viewpoint of the crustal stability the projected Sandouping Dam site is suitable for construc-'ion of a large dam.