宜昌葛洲坝库区西南邻域地壳垂直形变

THE VERTICAL DEFORMATION OF THE CRUST IN THE SOUTH-WEST AREA NEARBY YICHANG GEZHOU DAM RESERVOIR

本文通过近10年跨仙女山、天阳坪断裂带上6处短水准垂直形变资料分析,指出:控制葛洲坝库区西南邻域地壳垂直形变的是仙女山断裂;其断层东(下)、西(上)盘升降趋势,受力状态南北地段不一致,且发生明显的反向运动。前5年(1981—1985年),南段的东盘下降,区域力为挤压;北段东盘上升,区域力为拉张,1985年后发生明显的反向运动。库区南侧的天阳坪断裂的东段近期较稳定,西段变化则是受仙女山断层变化的影响,产生同步运动,东西向的区域力对断层两盘的作用一致。1988年12月16日兴山县北发生M_L为3.9级地震,认为与仙女山断层明显的反向运动关系密切,断层运动趋势及其与地震的关系有待今后进一步探索。由于库区西部仙女山断层的活动,能量有所释放,不可能发生大震,因此库区及大坝比较安全。

Based on the analysis of the vertical deformation data of six short leveling lines to cross fault of Xiannushan and Tianyangping last 10 years, in this paper the author points out that it is Xiannushan fault that control vertical deformation of the south-west area nearby the Gezhou dam reservoir:the tendency of risingfalling in the east (down)-west (up)flanks and the state of force are different in south-north section, and the obvious opposite motion have happened,During the first 5 years (1981-1985 year) in south section, the east flank is falling (down) and the section force of action is pressure to fault,in north section, the east flank is rising and the section force is tensile.After 1985 year,obvious opposite motion has happened and the crust of the east section of Tianyangping fault recently is stable in the south area of the reservoir. In west section the crust change is controlled by Xiannushan fault motion, at the same time it keeps in step motion with Xiannushan fault motion.In this area,force action of the west-east direction is uniform to both flanks of this fault.The earthquake M_L 3.9 had happened in the north section of Xingshan county on December 16, 1988.We think that it can be concerned with obvious opposite motion of Xiannushan fault. The relation between the tendency of its fault motion and the earthquake will he deeply explored later. Because of motion of fault and the releasing energy, the large earthquake can not occur,and the reservoir area and the dam is comparatively safe.