PALEOSEISMOLOGIC STUDY ON THE SHIMIAN FAULT IN THE NORTHERN SECTION OF THE DALIANGSHAN FAULT ZONE

doi:10.3969/j.issn.0253-4967.2021.01.004

Abstract

Abstract: The Daliangshan fault zone(DF)constitutes an important part of the large-scale strike-slip Xianshuihe-Xiaojiang fault system(XXFS). Affected by the channel flow of the middle-lower crust in the western Sichuan region, the XXFS is strongly active, and large earthquakes occur frequently. On average, there is an earthquake of magnitude 7 or more every 34 years. However, the DF, as an important part of the middle segment of the XXFS, has only recorded several earthquakes with magnitude 5-6, and no earthquakes with magnitude over 6 have been recorded. The reason for the lack of strong earthquake records may be related to the lack of historical records in remote mountainous areas, but the main reason may be attributed to the active behavior of the faults. He et al.(2008)hold that the DF is a new fault, resulting from straightening of the middle section of the XXFS, and its activity gradually changes from weak to strong, and will probably replace the Anninghe-Zemuhe Fault. However, this view lacks evidence of strong earthquakes. In recent years, some scholars have studied the paleoearthquakes on the DF, and found the signs of strong earthquake activity, and considered that the fault has the seismogenic capacity of earthquakes with magnitude more than 7. These studies are mainly concentrated in the middle and southern segments of the DF. Although there are scattered activity data and individual trench profiles, direct evidence of Holocene activity and paleoearthquake data are very scarce in the northern part of DF. On the basis of the previous studies, combined with our detailed field geomorphological surveys, we excavated a set of two trenches at Lianhe village in Shimian Fault to reveal the direct evidence of fault activity in Holocene. From paleoseismic analysis and radiocarbon samples accelerated mass spectrometry(AMS)dating, four paleoseismic events are identified, which are E1 between 20925—16850BC, E2 between 15265—1785BC, E3 between 360—1475AD, and E4 between 1655—1815AD. The results of the latest two events should be relatively reliable, and the latest event may be related to the Moxi earthquake of magnitude 7^3/4 on June 1, 1786 or the Dalu earthquake of magnitude ≥7 on June 10, 1786. Among the four events revealed, three are since the Holocene, and the recurrence interval of the latest two events is about 800 years. Compared with other active faults at the triple junction, the recurrence interval is slightly longer than that at the northern segment of the Anninghe fault zone, but close to that at the Moxi segment of the Xianshuihe fault zone. Compared with the western segment of Xianshuihe Fault and the northern segment of Anninghe Fault, the Shimian Fault also has a higher seismic risk, which needs further attention.

Key words: Daliangshan Fault, Shimian Fault, Paleoearthquake, Xianshuihe-Xiaojiang fault system

摘要： 大凉山断裂带是大型走滑断裂鲜水河-小江断裂系的重要组成部分, 其活动性是认识和探讨青藏高原东南缘现今地震活动和构造变形机制的重要基础资料。相较于中段和南段, 关于大凉山断裂带北段活动性的相关研究成果, 尤其是古地震资料非常缺乏。文中基于野外地质地貌调查, 在石棉断裂联合村处开挖了一组(2个)探槽, 揭露出断裂全新世活动的直接证据。通过古地震分析和炭样加速器质谱仪(AMS)测年, 共获得了4次古地震事件: 事件E1: 20925—16850BC; 事件E2: 15265—1785BC; 事件E3: 360—1475AD; 事件E4: 1655—1815AD。其中包括全新世以来的3次事件, 最新2次事件的复发间隔骤然缩短, 反映断裂活动可能正在加剧。

关键词: 大凉山断裂, 石棉断裂, 古地震, 鲜水河-小江断裂系

CLC Number:

P315.2

FENG Jia-hui, CHEN Li-chun, WANG Hu, LIU Jiao, HAN Ming-ming, LI Yan-bao, GAO Shuai-po, LU Li-li. PALEOSEISMOLOGIC STUDY ON THE SHIMIAN FAULT IN THE NORTHERN SECTION OF THE DALIANGSHAN FAULT ZONE[J]. SEISMOLOGY AND GEOLOGY, 2021, 43(1): 53-71.

冯嘉辉, 陈立春, 王虎, 刘姣, 韩明明, 李彦宝, 高帅坡, 卢丽莉. 大凉山断裂带北段石棉断裂的古地震[J]. 地震地质, 2021, 43(1): 53-71.

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