公元842年甘肃碌曲地震考证与发震构造分析

TEXTUAL RESEARCH OF LUQU EARTHQUAKE IN 842 AD IN GANSU PROVINCE AND ANALYSIS OF ITS CAUSATIVE STRUCTURE

唐会昌二年（公元842年）,在中国西北的汉藏交界地区（现甘肃省东南部地区）发生了一次大地震,造成“地震裂,水泉涌,岷山崩,洮水逆流三日”的严重震害.经过对这次地震史料的系统梳理、考证和综合分析,认为其极震区大致位于今甘肃省甘南藏族自治州碌曲、卓尼和迭部三县交界的光盖山—迭山山区,发震时间很可能为唐会昌二年十二月二十四日（公元843年1月31日或27日）,震级可达7～71/2级,震中烈度达Ⅸ～X度.在这次地震破坏区附近发育了临潭-宕昌断裂、光盖山-迭山断裂和迭部-白龙江断裂等3条以挤压逆冲为主兼具左旋走滑特征的晚第四纪活动断裂带.根据近年来对上述断裂的最新考察结果和对该区现今小震活动的对比分析,认为这次地震应与其中的光盖山-迭山断裂西段的最新构造活动有关,为这次地震的发震断裂.光盖山-迭山断裂为中国大陆近10多年来7级以上大震主体活动区——巴颜喀拉块体北部边界断裂（东昆仑断裂）东段的重要分支断裂,具备发生7级以上大震的构造条件.

An earthquake with MS6.6 occurred near the border between Minxian and Zhangxian counties in southeastern Gansu Province on July 22,2013.This earthquake caused serious personnel casualties and property damages.According to the field investigation,the intensity of the epicenter area is about Ⅷ,the causative structure is a branch fault of the eastern segment of Lintan-Dangchang active fault.The southeastern region of Gansu Province is located at the eastern boundary of Tibetan active block.A series of strike-slip faults with thrust components are developed and their combination is complicated and a series of strong or even large earthquakes occurred in this area in the history and present-days,and one of them is the Luqu earthquake occurring in 842 AD at the boundary of Han and Tibet area （now the southeastern area of Gansu Province）.The earthquake caused seismic rupture,spring gushing,landslip in the Minshan Mountains and countercurrent of the Taohe River for three days.According to the detail textual research of historical references and field investigation,the epicenter area of this earthquake locates at the Guanggaishan-Dieshan mountain area,at the border area between Luqu County,Zhuoni County and Diebu County in the Gannan Tibetan Autonomous Prefecture.The date of the Luqu earthquake is possibly on the 24th day of the twelfth month of the second year of Huichang Reign in Tang Dynasty,that is,on January 31 or 27,843 AD,and the magnitude of this earthquake is about 7～ 71/2,the intensity near the epicenter area is about nine to ten.There are three late Quaternary active fault zones of thrust with left-lateral components,namely,Lintan-Dangcang Fault,Guanggaishan-Dieshan Fault and Diebu-Bailongjiang Fault.According to the comparative analysis of the field investigation of active faults in recent years and present seismic activity,we think that Luqu earthquake is the result of new activity of Guanggaishan-Dieshan Fault,the causative fault of this earthquake.This fault is an important branch fault of the eastern segment of northern boundary faults of Bayan Har block （Eastern Kunlun Fault zone）,a main activity area of large earthquakes with magnitude larger than 7 in Chinese continent in the recent 10 years,and has the tectonic condition to generate M≥7 large earthquakes.