【摘要】 龙门山逆冲推覆构造带中段山前断裂的存在和最新活动时代一直是个争论的问题.石油地震探测资料和浅层地震剖面揭示该断裂的存在,并断错了第四系;野外调查表明,龙门山中段山前存在明显的线性地貌特征,山前断裂断错晚了更新世晚期的洪积台地;探槽剖面揭示距今约1500a之前在山前断裂上曾发生过一次地表破裂型事件,而该断裂未来具备发生强震的潜势.断错地貌的差分GPS测量和年代学分析显示山前断裂晚第四纪垂直滑动速率大于0.36mm/a,其与龙门山中段主干断裂活动强度相当,说明龙门山山前断裂在龙门山逆冲推覆构造带的变形中也承担着重要的作用.该研究不仅能为成都平原的地震危险性评价提供基础资料,也有助于全面理解青藏高原东缘的隆升机制.更多还原

【Abstract】 The existence and the latest active time of the range-front fault along the mid-segment of the Longmen Shan thrust belts are controversial for a long period.Petroleum seismic reflection and high-resolution shallow seismic reflection profile discovered the existence of the range-front fault which offset the Quaternary strata.Based on detailed field observation,we found that there is an obvious linear feature along the mid-segment of the Longmen Shan front and the range-front fault that displaced the late Quaternary alluvial terrace.Trench log indicates that a surface-rupture event occurred before ~1500 a along the range-front fault.Differential GPS surveying and dating of alluvial terrace show that the range-front fault during late Quaternary had a vertical slip rate bigger than 0.36 mm/a,approximately equivalent to that along the main faults of the Longmen Shan thrust belts,which demonstrates that the range-front fault also took an important role in accommodating the deformation of the Longmen Shan thrust zone.This study not only provides the fundamental data for seismic hazard assessment of the Chengdu Plain,but is helpful for the overall understanding of uplift mechanism of east Tibet.更多还原