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继2013年芦山M_s7.0地震发生之后,龙门山断裂带南段的地震危险性得到广泛的关注。为了深化对龙门山断裂带南段晚第四纪活动性的认识,我们对横跨该断裂带的青衣江上游河段开展了河流阶地调查与测量。在卫星影像和高分辨率DEM分析的基础上,基于SCCORS系统对河流阶地进行了精细测量和对比,建立了青衣江上游河流阶地纵剖面图。阶地面高程显示,耿达-陇东断裂、盐井-五龙断裂和小关子断裂均垂直断错了青衣江二级以上阶地,表现为逆冲活动,其晚第四纪平均垂直错动速率分别为0.21~0.30mm/yr/0.12~0.21mm/yr和0.10~0.12mm/yr。晚第四纪以来,大川-双石断裂垂直错动量不大,金汤弧形构造带没有活动。通过青衣江河流阶地变形得到龙门山断裂带南段晚第四纪地壳缩短速率为0.48~0.77mm/yr。该缩短速率约为龙门山断裂带中段的一半。结合前人研究,认为龙门山南段前陆区吸收了一半以上的地壳缩短量,其未来地震危险性不容忽视。
Following the occurrence of the M_s7.0 Lushan earthquake in 2013, the seismic risk in the southern segment of the Longmenshan fault has received extensive attention. In order to deepen the understanding of Late Quaternary activity in the southern segment of the Longmenshan fault zone, we conducted a survey and measurement of the terraces of the rivers in the upper reaches of the Qingyi River across the fault zone. Based on the satellite images and the high-resolution DEM analysis, the SCMORS system is used to finely measure and contrast the river terraces, and the vertical section of the river terrace in the upper reaches of the Qingyi River is established. The terrestrial elevation shows that the Gengda-Longdong fault, the Yanjing-Wulong fault, and the Xiaooguanzi fault are vertically offset above the second-order terraces of the Qingyi River by thrusting. The average vertical slip rate of the Late Quaternary was respectively 0.21 to 0.30 mm / yr / 0.12 to 0.21 mm / yr and 0.10 to 0.12 mm / yr. Since the Late Quaternary, the Daochuan-Shishuang fault had a large vertical amount of slip and no movement of the arc-shaped tectonic belt. The Late Quaternary crustal shortening rate was 0.48 ~ 0.77mm / yr from the deformation of the Qinghai River terrace. This shortening rate is about half of the middle part of the Longmen Shan fault zone. Combined with previous studies, it is considered that the frontal area of the southern part of Longmen has absorbed more than half of the crustal shortening, and its future seismic risk can not be ignored.