阿木尼克山山前地表破裂带与1962年6.8级地震关系的讨论

doi:10.3969/j.issn.0253-4967.2022.04.010

摘要/Abstract

摘要：

柴达木盆地北缘地区是地震频发地段, 历史上曾发生多次6.0级以上地震。自2003年德令哈6.6级地震以来, 柴达木盆地北缘地区又在2008年和2009年分别发生了6.3级和6.4级地震, 引起了广大研究者的高度关注, 该地区也因此成为研究的热点地区。文中通过遥感解译发现阿木尼克山山前的线性特征明显, 存在疑似地表破裂。断裂断错不同期的洪积扇、阶地与水系。通过实地地质考察发现其沿线发育断层陡坎、断层凹槽、地震鼓梁、水系扭错等地貌, 形成一条走向为 N30°~40°W、同震位移达2.3m, 长约22km的地表破裂。通过探槽开挖, 并结合地表遗迹、地质测年, 微地貌测量等方法, 确定断裂的性质以走滑为主、逆冲为辅。剖面显示断裂存在多期活动的特点, 最新一次活动断错至地表, 晚第四纪以来活动明显。根据震级与地表破裂的经验统计关系、同震位移与震级经验关系可知, 产生长22km的地震地表破裂所需的平均震级为6.79级, 形成长2.3m同震位移的平均震级为7.03级。结合地表破裂情况、探槽剖面资料、地质测年结果、地震地质灾害现象、经验公式计算结果并查阅历史地震目录、地方志等文献分析认为, 该地表破裂极有可能是1962年5月21日6.8级地震所致, 该历史地震的发震断裂为柴达木盆地北缘断裂的阿木尼克山段, 与微观震中存在偏差。

关键词: 北霍布逊湖, 阿木尼克山, 发震构造, 地表破裂, 历史地震

Abstract:

The investigation of seismogenic structure of historical strong earthquakes and the research on the genetic link between earthquakes and active faults are a basic seismogeologic work. In particular, the investigation of seismic surface rupture zones and the study of seismogenic structures are extremely important for understanding the characteristics of their tectonic activities. The determination of the macro-epicenter provides important evidence for the site selection for post-disaster reconstruction and avoidance. Due to the diversity of the rupture process in the focal area, the macro-epicenter and the micro-epicenter may not be identical. As the magnitude increases, the larger the focal area of an earthquake is, the more significant the gap between the macro-epicenter and the micro-epicenter will be.

The northern margin of the Qaidam Basin is an area with frequent earthquakes, where many earthquakes with magnitude above 6.0 occurred in the history. In the early and late 1990s, small earthquake swarms with long duration and high frequency occurred in this area, which caused considerable losses to the local industry. Since the Delingha earthquake of magnitude 6.6 in 2003, two earthquakes with magnitude 6.3 and 6.4 occurred in the northern margin of the Qaidam Basin in 2008 and 2009, which aroused great attention of researchers. A new research focus has emerged on this area, and many scholars conducted in-depth research on the faults of the northern margin of the Qaidam Basin.

The author conducted a preliminary remote sensing interpretation of the Amunikeshan Mountain segment of the northern margin of the Qaidam Basin and found that there is a very straight linear feature in the image of the Amunikeshan mountain front. On the basis of remote sensing interpretation, a related study was carried out on the Amunikeshan segment of the northern margin fault of the Qaidam Basin, which was considered to be a Holocene active fault. Since the late Holocene, the horizontal movement rate of the fault is 2.50~2.75mm/a, and the vertical movement rate is(0.43±0.02)mm/a. A 30km-long earthquake surface rupture zone was found in front of Mount Amunikeshan. It is preliminarily believed that the rupture might be caused by a strong historical earthquake. According to the catalogue of historical strong earthquakes and local chronicles, there were earthquakes of magnitude 6.8 and 6.3 occurring in this area on May 21, 1962 and January 19, 1977, respectively. There has been no detailed research report on these two earthquakes.

Through on-the-spot geological investigation, it is found that there are fault scarps, fault grooves, seismic bulges and ridges, twisted water system and other landforms developed along the line, forming a surface rupture zone with a strike of N30°-40°W, a coseismic displacement of 2.3m, and a length of about 22km. Through trenching and excavation, the trench section reveals several faults, indicating the characteristic of multi-stage activity. In the section, the faults ruptured to the surface, and the late Quaternary activity is obvious. Combining surface relics, geological dating, and micro-geomorphic measurements, it is determined that the nature of the fault is mainly strike-slip with thrust. The investigation has found many seismic geological disasters, such as landslides, rockfalls and ground fissures along the fault, which are judged to be generated in recent decades or centuries.

Based on the empirical statistical relationship between magnitude and surface rupture, and the empirical relationship between strike-slip fault and rupture length, the average magnitude required for producing a 22km-long earthquake surface rupture is 6.79, and the average magnitude for producing a 2.3m coseismic displacement is 7.03. In combination with the surface rupture, trench profile, geological dating, seismic geological disasters, empirical formula calculation, historical earthquake catalogue, local chronicles and other documents, it is considered that the rupture zone is most likely produced by the North Huobuxun Lake M6.8 earthquake on May 21, 1962, and its seismogenic fault is the Amunikeshan Mountain segment of the northern margin fault of the Qaidam Basin.

Since the study area has no permanent residents or buildings(structures), which are taken as the basis for inquiring and investigating the earthquake intensity, we are unable to draw the earthquake intensity map.

Key words: North Huobuxun Lake, Amunikeshan Mountain, seismogenic structure, surface rupture, historical earthquake

中图分类号:

P315.2

姚生海, 盖海龙, 殷翔, 刘炜, 张加庆, 袁建新. 阿木尼克山山前地表破裂带与1962年6.8级地震关系的讨论[J]. 地震地质, 2022, 44(4): 976-991.

YAO Sheng-hai, GAI Hai-long, YIN Xiang, LIU Wei, ZHANG Jia-qing, YUAN Jian-xin. A DISCUSSION ON THE RELATIONSHIP BETWEEN THE SUR-FACE RUPTURE ZONE IN FRONT OF THE AMUNIKESHAN MOUNTAIN AND THE 1962 M6.8 EARTHQUAKE[J]. SEISMOLOGY AND GEOLOGY, 2022, 44(4): 976-991.

图/表 12

图1 研究区的地质构造简图 1 前新生界; 2 火山岩; 3 古近系; 4 新近系; 5 第四系; 6 全新世断裂; 7 晚更新世断裂; 8 逆断层; 9 走滑断层; 10 研究范围。F1 大柴旦-宗务隆山断裂带; F2 大柴旦-托素湖断裂带; F3 柴达木盆地北缘断裂带; F4 柴达木盆地北中央断裂带

Fig. 1 Schematic geological structure of the research area.

图2 阿木尼克山山前影像图

Fig. 2 Amunikeshan mountain front images.

图3 断层地貌特征红色箭头指示断裂位置。a、 b 断层陡坎; c-f 挤压脊; g 地震凹槽; h 挤压脊及鼓包

Fig. 3 Geomorphic characteristics of fault.

图4 无人机拍摄的洪积扇Fan1上形成的挤压脊(a, c)与断层陡坎(b, d) 黄色箭头指示挤压脊, 红色箭头指示断层陡坎

Fig. 4 Pressure ridge(a, c)and fault scarp(b, d)developed in Fan1 of the alluvial fan captured by UAV.

图5 断裂沿线的水系走滑红色箭头指示断裂位置, 蓝色虚线为季节性河流。a 水系左旋走滑; b 水系同震位移; c 同震位移DEM图; d 冲沟位错恢复

Fig. 5 Strike-slip water system along the fault.

图6 探槽1的位置图 a 探槽在影像上的位置; b 探槽处的照片图(镜向NEE)

Fig. 6 Position map of Trench 1.

图7 探槽1(TC1)的剖面解译图

Fig. 7 Trench 1(TC1)profile interpretation.

图8 探槽2的位置 a 探槽在影像上的位置; b 探槽处的照片(镜向NEE)

Fig. 8 Position of Trench 2.

图9 探槽2(TC2)的剖面解译图

Fig. 9 Trench 2(TC2)profile interpretation.

图10 地震地质灾害的照片 a、 b 崩塌; c、 d 滚石; e-g 地裂缝

Fig. 10 Photos of earthquake geological disaster.

图11 1962年6.8级地震的微观震中和宏观震中分布图 F1 大柴旦-托素湖断裂; F2 柴达木盆地北缘断裂

Fig. 11 Distribution map of the micro-epicenter and macro-epicenter of the M6.8 earthquake in 1962.

表1 根据各类经验关系得到的破裂长度和同震位移

Table 1 The rupture length and coseismic displacement of earthquakes derived by applying different empirical relations

公式	震级/M	破裂长度L/km	同震位移D/m	公式来源
M=5.16+1.12logL	6.66	22		Wells et al., 1994
M=5.92+0.88logL	7.10	22		邓起东等, 1992
M=5.303+1.181logL	6.88	22		冉洪流, 2011
M=4.278+1.653logL	6.50	22		丁国瑜等, 1993
平均值	6.79
logD=-1.791+0.324M	6.64		2.3	冉洪流, 2011
logD=-3.37+0.53M	7.04		2.3	邓起东等, 1992
logD=0.9M-6.32	7.42		2.3	Wells et al., 1994
平均值	7.03

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