龙门山断裂带西南段现今地应力状态与地震危险性分析

ANALYSIS OF CURRENT GEOSTRESS STATE AND SEISMIC RISK IN SOUTHWEST SEGMENT OF LONGMENSHAN FRACTURE BELT

为了解汶川地震后龙门山断裂西南段现今地应力环境与地震发展趋势,对比分析2003,2008和2010年在宝兴、康定地区4个钻孔的水压致裂应力测量资料,初步揭示汶川地震后断裂西南段现今地应力环境与地震危险性。研究结果表明:龙门山断裂西南段,尤其是康定地区,地震后仍然积累有较高的地应力,震后应力调整以积累为主;龙门山断裂西南端的最大水平主应力已经达到断层活动应力临界下限值,断裂活动进入临界状态,未来具有发生逆断层活动的可能性;结合地应力测量结果、地震地质等资料认为,龙门山断裂西南端具有潜在大震危险性,值得重点关注和研究。研究成果对于龙门山西南段断裂活动性分析、地应力长期监测以及防灾减灾有重要意义。

Results ofgeostress measured respectively in 2003, 2008 and 2010 in four boreholes located in Baoxing County and Kangding district in Sichuan Province, together with seismic geological data, were used to study the geostress state and seismic risk in Southern segment of Longmenshan fracture belt after Wenchuan Ms 8.0 earthquake. The study results show that the present stress conditions do not appear to be totally relieved after the region tectonic stress field adjustment caused by Wenchuan earthquake, and the adjustment tendency of geostress is accumulated after Wenchuan earthquake in this region. Primary analysis reflects that the maximum horizontal principal stress values have reached the lower limit of fault activity in the Southwest segment of Longmenshan fracture belt. The fault has been in critical state and will probably slip in the way of reverse fault in the future. Based on the measured geostress state and earthquake migration data, there is a potential seismic risk in the Southwest segment of Longmensban fracture belt. It is suggested that more attention should be paid to this region. The research results have great significance for mobility analysis of fracture, long-term monitoring of geostresses and disaster prevention and mitigation in the Southwest segment of Longmenshan fracture belt.