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Title:: Reservoir-induced Seismicity and Geological Tectonic Environment of Manwan and Dachaoshan Reservoirs in the Middle Reaches of Lancangjiang River of Yunnan

Author(s):: MAO Yu-ping; WANG Yang-long; FU Hong; LI Mao-xian; HU Ke; (Earthquake Administration of Yunnan Province, Kunming 650224, Yunnan, China)

Keywords:: middle reaches of Lancangjiang River; reservoir-induced seismicity; tectonic environment; Yunnan

摘要:: 位于云南澜沧江中段的漫湾和大朝山两电站水库位置相邻、大小相仿,坝高和库容均达到可能诱发地震的规模,都处于构造复杂的逆断层环境,但蓄水后库区地震活动水平明显不同,其中漫湾水库有明显的诱发地震活动,而大朝山水库蓄水5年来库区未出现地震活动明显增强现象。通过对漫湾和大朝山两电站水库蓄水后库区地震活动、库区地层和断层特点、地震活动与库区地层和断层特点的关系进行分析,认为沿断层的库水渗透、岩溶塌陷、水库规模、高应力环境、规模较大断裂的通过和断层力学环境等,并不是这两个电站水库诱发地震活动的主要因素; 而马街、腰街、哨街一带发育有NE和NW向断层,且多为正断层性质,断面多倾向水库一侧,这些断层的破裂可能是诱发水库地震集中发生的重要原因。

Abstract:: Both Manwan and Dachaoshan reservoirs were constructed in the middle reaches of Lancangjiang River,Yunnan. They are border upon, and alike in many aspects. For example, both are located in complex tectonic environment of thrusts, have almost the same scale, and the dam height and capacity all reach the level to induce earthquake. However, their post-impoundment seismicities are very different. Significant reservoir-induced seismicity(RIS)occurred in the Manwan reservoir area after the reservoir impounding; but the seismicity had not increased in the Dachaoshan reservoir area in 5 years after impounding. Based on the post-impoundment seismicity, the strata and the characteristics of the faults in the reservoir areas, we conclude that the RIS in the Manwan and Dachaoshan reservoir areas should not be attributed to the permeation of water, karst collapse, reservoir scale, stress environment, large active faults running through the reservoir areas, and the property of faults to a great extent, may be caused by the rupture of NE- and NW-trending faults developing along Majie, Yaojie,and Shaojie. Of these faults,most are normal faults, and the fault planes lean to the reservoirs.