摘要
基于高分辨率SPOT影像解译、关键地点的野外构造地貌调查和活动断裂测量以及错断沉积物的光释光测年(OSL),确定了龙门山断裂带西南段主要活动断裂的分布特征及其晚第四纪活动特征,发现后龙门山断裂带——五龙-冷碛镇断裂是一条晚更新世活动的右旋走滑断裂,没有明显的挤压逆冲活动形迹。根据次级断层的地层切割关系和沉积物测年结果,确定了沿该断裂带晚更新世两期走滑活动事件:一期发生在86～88ka,另一期发生在36～48ka。中央断裂带——双石-西岭断裂也具有右旋走滑活动特征,但其活动性相对较弱。这两条主要断裂在全新世没有明显的活动形迹,表明龙门山断裂带西南段构造活动性较弱。现今以中小地震为主,地震震源机制解显示以走滑应力机制占主导,与现今应力测量确定的逆冲应力状态不一致。这些观察和测试结果为龙门山断裂带西南段未来强震危险性评价提供了重要的依据。
The SW segment of the Longmenshan fault zone remains unruptured during the May, 12, 2008 Wenchuan earthquake. The question what could be the potential of seismic rupture of this segment has attracted a lot of attentions. This paper investigates Late Quaternary active faults and their kinematic behavior of the SW segment of the Longmenshan fault zone, based on high resolution SPOT imagery interpretation,field observations of active fault morphology and measurements of active faults,as well as stimulated luminescence dating（OSL） of Late Quaternary lacustrine and fans deposits. It is found that the back Longmenshan fault zone,namely the Wulong-Lengqi fault,is a Late Pleistocene dextral strike-slip fault, with no obvious evidence for reverse faulting. Two strike-slip events have been determined from the secondary faults and OSL dating results along this fault zone at two sites. The early one occurred in 86 - 88ka, and the late one in 36 - 48ka. The Central Longmenshan fault,namely the Shuangshi-Xiling fault, shows evidence for Late Quaternary right-slip motion, but the degree of its activity is relatively low along its SW segments and seems to be intensified northeastwards. Young colluvial fans and river terraces （T1, T2） across these two faults have not been offset, suggesting that the faults were not ruptured since the latest Pleistocene. Duo to the lack of offset markers, slip rate on these faults has not been firmly determined. The seismicity of this segment is characterized by low frequent, middle to small magnitude earthquakes, and the focal solution of earthquakes shows dominance of strike-slip faulting regime. This is not consistent with those determined by in situ stress measurements that show dominance of reverse faulting regime. These observations and results provide key appraisals for future assessment of earthquake hazards of the SW segment of the Longmenshan fault zone.
出处
《第四纪研究》
CAS
CSCD
北大核心
2010年第4期699-710,共12页
Quaternary Sciences
基金
国家重点基础研究发展规划项目(973项目)"龙门山地质构造断裂带及其与汶川蕴震动力条件分析"(批准号:2008CB425702)资助
关键词
龙门山断裂带
晚第四纪
活动断裂
光释光测年(OSL)
dating（OSL） Longmenshan fault zone, Late Quaternary, active fault, optically stimulated luminescence
