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1948年川西理塘M7.3地震地表破裂特征及Riedel剪切构造分析
投稿时间:2020-04-09  修订日期:2020-07-03  点此下载全文
引用本文:
DOI:10.19762/j.cnki.dizhixuebao.2020291
摘要点击次数: 96
全文下载次数: 130
作者单位地址
刘亢 中国地震应急搜救中心 北京石景山区玉泉西街1号
李岩峰 中国地震应急搜救中心 北京石景山区玉泉西街1号
郭辉文 中国地质大学北京 
中文摘要:1948年发生在川西理塘的M7.3级地震,是近一个世纪以来发生在川滇菱形块体内部的一次重大的破坏性地震。本文利用差分GPS对此次地震产生裂缝带进行精确测量与统计分析,揭示地表破裂长度为36km。考虑到自然侵蚀与人类活动的影响,将前人调查汇总得到的41km作为最大值,而本次测量值作为最小值。地表破裂北端始于无量河以北,向南东沿藏坝盆地北东缘、德巫盆地东南缘,延伸至南端德巫乡北,在交德附近存在3km长的地表破裂空区,地表破裂分为南北两段。结合前人在震后调查中多次提到了原地相隔2-3分钟发生了2次地震,推测1948年理塘地震在3分钟内发生了2次大的破裂活动。根据震声描述推断发震断层破裂自北西开始,逐渐往南东方向传递。裂缝线密度统计结果表明,南部德巫段地表裂缝较连续,分布密度大,其中28km处为最大值50条,说明德巫盆地震害最为严重,推测宏观震中位于德巫盆地中部交德东南约5km处。Riedel剪切是地震断层初始破裂的主要类型,特别是在走滑型大地震地表破裂时表现更为明显。Riedel剪切分析结果指示1948年理塘地震同震地表破裂带中Riedel剪切构造主要由R剪切组成,发育雁列状排列的挤压鼓包(Push-up),以及少量R′剪切与T裂缝,Y型剪切带与主断裂面平行,地表破裂带缺少P型与X型剪切。R剪切裂缝约占95%以上,其优势方向为316°,与断裂走向Y呈16°夹角。建立了理塘地震裂缝带演化顺序,R和共轭R′剪切发生在最初阶段,然后相关性较大的T剪切与挤压鼓包可能同时出现,随着破裂的逐渐发展,挤压鼓包会进一步弯曲、旋转,形成反“S”形褶皱。综合多种地震、地质参数对比结果,揭示理塘断裂带与鲜水河断裂带(炉霍-道孚-康定段)的构造背景、形成机理相似;推测受川滇活动地块与边界鲜水河断裂带运动影响,后期在活动地块内部发育了平行的理塘断裂带;对于川滇活动地块的顺时针运动特征,东北边界的鲜水河断裂带承担了主要的左旋走滑分量,内部的理塘断裂带分担了部分走滑分量。
中文关键词:理塘地震  破裂长度  Riedel剪切  地震裂缝带  挤压鼓包
 
Determination of Surface Rupture Length and Analysis of Riedel Sshear Structure of Litang M7.3 Earthquake in West Sichuan in 1948
Author NameAffiliationAddress
Liu Kang National Earthquake Response Support Service 北京石景山区玉泉西街1号
Li Yanfeng National Earthquake Response Support Service 北京石景山区玉泉西街1号
Guo Huiwen China University of Geosciences (Beijing) 
Abstract:The Litang M7.3 Earthquake which happened in 1948 in the western Sichuan, is a major destructive earthquake in Sichuan-Yunan block in the past century. Using differential GPS, seismic fissures are accurately measured and analyzed. It is revealed that the length of surface rupture is 36 km. In consideration of the impact of natural erosion and human activities, the maximum value of 41km obtained from previous investigations is taken as the maximum value, while this measurement is taken as the minimum value. The north end of the surface rupture starts from the north of the Wulianghe river and extends southeastern along the northeastern margin of Zangba basin and the southeastern margin of Dewu Basin to the north of Dewu. There is a 3 km long surface rupture gap near Jiaode, and the surface fracture is divided into two sections, North and south. In the post earthquake investigation, many people mentioned that 2 earthquakes occurred in 2-3 minutes and it is speculated that the Litang earthquake in 1948 had two large rupture activities in three minutes. According to the description of seismic sound, it is inferred that the rupture of seismogenic fault started from the northwest and gradually transferred to the southeast. The statistical results of fracture linear density show that the surface fractures in the south of Dewu section are relatively continuous, with a large distribution density, and the maximum value is 50 at 28km, indicating that the most serious earthquake damage is in Dewu basin. It is speculated that the macro epicenter is located about 5km southeast of Jiaode in the middle of Dewu basin.Riedel shear is the main type of initial rupture of seismic fault, especially when the surface rupture of strike slip earthquake is more obvious. Riedel shear analysis indicates that the Riedel shear structure is mainly composed of R shear in the surface fracture zone of the 1948 Litang earthquake and developed a echelon of extruded bulges, a small amount of R′shear and T fracture, and Y-type shear zone parallel to the main fault plane. The surface fracture zone lacks p-type and X-type shear. R shear fracture is the main fracture, accounting for more than 95%, and its predominant direction is 316° with an angle of 16° between fracture strike Y and R shear fracture. The evolution sequence of Litang seismic fracture zone is established. R and conjugate R" shear occur in the initial stage, and then T shear and Push-up may occur simultaneously. With the gradual development of fracture, Push-up bend and rotate further, forming an anti-S-shaped fold. Based on the comparison results of various seismic and geological parameters, it is revealed that the structural background and formation mechanism of Litang fault zone and Xianshuihe fault zone (Luhuo-Daofu-Kangding section) are similar. It is speculated that the parallel Litang fault zone developed in the later stage of the active block due to the movement of the Sichuan-Yunnan active block and the Xianshuihe fault zone on the boundary. For the clockwise movement characteristics of the Sichuan-Yunnan active block, the Xianshuihe fault zone in the Northeast boundary bears the main left-hand strike slip component, and the Litang fault zone in the interior bears part of the strike slip component.
keywords:Litang earthquake  rupture length  Riedel shear  seismic fracture zone  Push-up
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