NEW CHRONOLOGICAL CONSTRAINT ON THE CO-SEISMIC SURFACE RUPTURE SEGMENTS ASSOCIATED WITH THE LITANG FAULT

doi:10.3969/j.issn.0253-4967.2015.02.009

Abstract

Abstract:

Detailed mapping shows that there are two segments of co-seismic surface ruptures on the Litang-Dewu left-lateral strike-slip fault. The north segment is about 25km long, with a strike about 135°NE. The maximum horizontal left-lateral displacement on the north one is~1.8m and located at the high floodplains on the north side of the Wuliang River near Cun'ge village, offsetting the linear ridges that were left behind by human activity. The south segment is about 41km, striking generally about 146°NE. The maximum horizontal left-lateral displacement is located at the piedmont near the north side of the Rongjia mountain pass and the river floodplain scarp here is offset about 3.2m. There is a surface rupture gap about 11km between these two co-seismic surface rupture segments. The distribution of the co-seismic surface ruptures acquired by detailed mapping in the field survey, the earthquake event revealed by the trench, the AMS-¹⁴C dating result, the historical records of earthquakes at least since AD 1729 in the study area and the visiting on the local people, show consistently that the northern co-seismic surface rupture segment is most possibly produced by the 1729 Litang earthquake. The 1948 Litang earthquake was only responsible for the southern surface rupture segment. However, if only according to the 2 sigma calendar calibrated results of ¹⁴C dating, it cannot be excluded the possibility that the north segment maybe was produced by some older large earthquake occurring at some time during the AD 1420 to AD 1690. The moment magnitude(M_W)of the 1729 earthquake is about 6.7 and that of the 1948 earthquake is about 7.0 calculated from the empirical relations between the earthquake magnitude and the rupture length.

Key words: co-seismic surface rupture, historical earthquake, seismic hazard assessment, Litang Fault, the 1948 Litang earthquake

摘要：

在开展理塘左旋走滑活动断裂带的同震地表破裂实测填图基础上, 结合历史地震资料及地震事件测年, 对该断裂带的最新同震地表破裂形成年代和震级进行了重新厘定。结果表明: 理塘活动断裂带的最新同震地表破裂可分为南、北2段, 其中北段最长约25km, 最大左旋错动量1.8m; 南段最长约41km, 最大左旋错动量3.2m。综合探槽揭露的地震事件及AMS-¹⁴C测年结果和历史地震资料的分析结果, 北段和南段同震地表破裂应为2次地震沿理塘断裂带不同段先、后破裂的结果, 属典型的分段破裂现象。其中北段破裂极可能是历史记载的1729年地震活动的产物, 而南段由1948年大地震所产生。根据震级和地表破裂长度的经验关系计算结果, 前者的矩震级(M_W)约为6.7, 后者约为7.0。2次大地震沿同一断裂分段破裂的现象表明, 该断层带尚未破裂的段可能是未来强震活动的危险地段。

关键词: 同震地表破裂, 历史地震, 地震危险性评价, 理塘断裂带, 1948年理塘地震

CLC Number:

P315.3⁺2

ZHOU Chun-jing, WU Zhong-hai, ZHANG Ke-qi, LI Jia-cun, JIANG Yao, TIAN Ting-ting, LIU Yan-hui, HUANG Xiao-jin. NEW CHRONOLOGICAL CONSTRAINT ON THE CO-SEISMIC SURFACE RUPTURE SEGMENTS ASSOCIATED WITH THE LITANG FAULT[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(2): 455-467.

周春景, 吴中海, 张克旗, 李家存, 蒋瑶, 田婷婷, 刘艳辉, 黄小巾. 川西理塘活动断裂最新同震地表破裂形成时代与震级的重新厘定[J]. 地震地质, 2015, 37(2): 455-467.

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