河西走廊西端花海断裂晚第四纪活动特征

花海断裂是位于河西走廊西端阿尔金断裂系北侧花海盆地内的一条活动断裂，对该断裂活动性的认识不仅有助于评估该区的地震危险性，而且对深入理解青藏高原向北扩展过程中块体相互作用具有重要的科学意义。遥感解译与地震地质调查表明，花海断裂仅局限于花海盆地内，长度约25 km。断裂走向NNW,南端起自花海镇以南，向北经小泉、大泉、双泉子后穿过山水河，向北逐渐消失在北山山前大型冲积扇前。地貌上，花海断裂南部表现为线性延伸的断层陡坎，北段构成了风成砂丘与冲洪积扇的界线。在断裂北段跨断层陡坎进行了探槽开挖，探槽揭露和光释光年代学测试结果表明，该断裂最新一次古地震事件的时间距今约5万年，全新世以来没有明显的活动迹象，为晚更新世活动断裂。结合陡坎位错分析，花海断裂晚第四纪以来垂直滑动速率小于0.03 mm/a。区域大地构造动力学背景分析表明，花海断裂是在青藏高原向北扩展作用下盆地内形成的次一级活动断裂，是高原外围块体对青藏高原向外扩展的响应。

Characteristics of Late Quaternary activities alongthe Huahai fault in western Hexi Corridor

Huahai fault, an active fault developed in Huahai basin, is located on the north side of Altyn Tagh fault, western end of Hexi Corridor. The understanding of the fault activity is helpful to evaluate the seismic risk in this area, and also has important scientific significance for in-depth understanding of the interaction between the Qinghai-Tibet Plateau and surrounding blocks during the northward expansion. The results of remote sensing interpretation and seismic geological survey show that the Huahai fault is mainly developed in the Huahai basin, with a length of about 25 km and a fault strike of NNW. From south to north, the Huahai fault starts from the south of Huahai Town, then passes through Xiaoquan, Daquan, Shuangquanzi, and Shanshui river, and gradually disappears in front of the alluvial fans at Beishan Mountain. In geomorphology, the southern part of Huahai fault shows a linear fault scarp, and the northern part forms the boundary between aeolian sand mound and alluvial diluvial fan. Three trenches were excavated across the fault scarp in the north section of the fault. The OSL dating results suggest that the latest paleoseismic event along the fault occurred about 50 000 years ago, and no distinct evidence of fault activity was found since Holocene. Therefore, the Huahai fault is a Pleistocene active fault, and the vertical slip rate since Late Quaternary is less than 0.03 mm/a. The analysis results of regional geodynamic background show that the Huahai fault is a secondary active fault formed in Huahai basin under the northward expansion of the Qinghai-Tibet Plateau.