LATE-QUATERNARY ACTIVITY OF THE YALAHE FAULT OF THE XIANSHUIHE FAULT ZONE, EASTERN MARGIN OF THE TIBET PLATEAU

doi:10.3969/j.issn.0253-4967.2020.02.016

Abstract

Abstract: Complex geometrical structures on strike-slip faults would likely affect fault behavior such as strain accumulation and distribution, seismic rupture process, etc. The Xianshuihe Fault has been considered to be a Holocene active strike-slip fault with a high horizontal slip rate along the eastern margin of the Tibetan plateau. During the past 300 years, the Xianshuihe Fault produced 8 earthquakes with magnitude≥7 along the whole fault and showed strong activities of large earthquakes. Taking the Huiyuansi Basin as a structure boundary, the northwestern and southeastern segments of the Xianshuihe Fault show different characteristics. The northwestern segment, consisting of the Luhuo, Daofu and Qianning sections, shows a left-stepping en echelon pattern by simple fault strands. However, the southeastern segment(Huiyuansi-Kangding segment)has a complex structure and is divided into three sub-faults: the Yalahe, Selaha and Zheduotang Faults. To the south of Kangding County, the Moxi segment of the Xianshuihe Fault shows a simple structure. The previous studies suggest that the three sub-faults(the Yalahe, Selaha and Zheduotang Faults of the Huiyuansi-Kangding segment)unevenly distribute the strain of the northwestern segment of the Xianshuihe Fault. However, the disagreement of the new activity of the Yalahe Fault limits the understanding of the strain distribution model of the Huiyuansi-Kangding segment. Most scholars believed that the Yalahe Fault is a Holocene active fault. However, Zhang et al.(2017)used low-temperature thermochronology to study the cooling history of the Gongga rock mass, and suggested that the Yalahe Fault is now inactive and the latest activity of the Xianshuihe Fault has moved westward over the Selaha Fault. The Yalahe Fault is the only segment of the Xianshuihe Fault that lacks records of the strong historical earthquakes. Moreover, the Yalahe Fault is located in the alpine valley area, and the previous traffic conditions were very bad. Thus, the previous research on fault activity of the fault relied mainly on the interpretation of remote sensing, and the uncertainty was relatively large. Through remote sensing and field investigation, we found the geological and geomorphological evidence for Holocene activity of the Yalahe Fault. Moreover, we found a well-preserved seismic surface rupture zone with a length of about 10km near the Yariacuo and the co-seismic offsets of the earthquake are about 2.5~3.5m. In addition, we also advance the new active fault track of the Yalahe Fault to Yala Town near Kangding County. In Wangmu and Yala Town, we found the geological evidence for the latest fault activity that the Holocene alluvial fans were dislocated by the fault. These evidences suggest that the Yalahe Fault is a Holocene active fault, and has the seismogenic tectonic condition to produce a large earthquake, just like the Selaha and Zheduotang Faults. These also provide seismic geological evidence for the strain distribution model of the Kangding-Huiyuansi segment of the Xianshuihe Fault.

Key words: the Xianshuihe Fault, the Yalahe Fault, Late-Quaternary fault activity, seismic surface rupture

摘要： 走滑断裂几何结构的复杂性往往影响着断裂上的应变积累与分配、大地震的破裂过程等。鲜水河断裂带是青藏高原东南缘一条强烈活动的次级块体边界断裂带, 其在惠远寺—康定之间叉分为3支次级断层: 雅拉河断层、色拉哈断层和折多塘断层。前人认为这3条断层不均匀地分配了鲜水河断裂慧远寺以北段的应变。然而, 关于雅拉河断层晚第四纪活动性的分歧制约了对这种应变分配模式的认识。文中通过遥感解译和野外调查发现: 在雅拉措一带仍残留有一段长约10km的地震地表破裂带, 同震水平位错2.5~3.5m; 断层晚第四纪地表活动行迹一直向S延至雅拉乡附近。这些证据表明雅拉河断层为全新世活动断层, 与色拉哈断层、折多塘断层一样具有孕育和发生强震、大地震的构造能力, 同样参与鲜水河断裂带的应变分配。

关键词: 鲜水河断裂, 雅拉河断层, 晚第四纪活动性, 地震地表破裂

CLC Number:

P315.2

LIANG Ming-jian, CHEN Li-chun, RAN Yong-kang, LI Yan-bao, WANG Dong, GAO Shuai-po, HAN Ming-ming, ZENG Di. LATE-QUATERNARY ACTIVITY OF THE YALAHE FAULT OF THE XIANSHUIHE FAULT ZONE, EASTERN MARGIN OF THE TIBET PLATEAU[J]. SEISMOLOGY AND GEOLOGY, 2020, 42(2): 513-525.

梁明剑, 陈立春, 冉勇康, 李彦宝, 王栋, 高帅坡, 韩明明, 曾蒂. 鲜水河断裂带雅拉河段晚第四纪活动性[J]. 地震地质, 2020, 42(2): 513-525.

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