山西地堑系洪洞8级地震地表破裂带的北延截止位置及其发震构造运动特征研究

1303 Hongtong Ms 8 earthquake at Shanxi Province is the first event with magnitude larger thanof M8.0 in China from historical documents. The research on the geometry, kinematics of the earthquake surface rupture of the earthquake and its seismogenic faulting, is very important for understanding the active tectonic evolution of the Shanxi Graben system and even the North China in theoretical significance and strong earthquake hazard assessment in the near future. However, there is still some different understanding, such as how the length and its geometry extending of the coseismic rupture zone? and how the faulting manner of its seismotectonic (Huoshan Piedmont Fault, HPF) and its difference and connection with other active faults? This proposal will be after the work achieved in study on “1/50000 scale geological mapping of south section (between Huozhou and Hongtong) of the HPF” and preliminary investigation for the proposal at north section (between Huozhou and Jiexiu) of the HPF, based on the research methods such as symbol fault profile interpretation analysis, comprehensive interpretation using remote sensing images, and quantitative tectonic geomorphology analysis, focusing on 1) identify the latest rupture at favorable trench sites and determine the deadline of northward extension using remote sensing interpretation, 2) comprehensive variety of means of paleo-earthquake(including historical earthquake) trench investigation at several favorable topography selected before pre-study, tectonic geomorphology parametric analysis and rock fault plan exposed cosmogenic nuclide dating, to study the faulting pattern of the HPF during Late Quaternary, and furture 3) research its coordination between the size of the rupture and its estimated earthquake magnitude combined the results between the north and south section according to its faulting modle.

1303洪洞8级地震是依据文献确认的我国第一个8级大地震，开展该次地震的破裂带及发震构造研究对山西地堑系的新构造历史和未来强震危险性评价都有重要意义。然而，目前对于该次地震地表破裂带的规模还存在不同认识，如破裂带的延伸长度及其结构如何？其发震构造霍山山前断裂的晚第四纪活动样式具有怎样的特点，与周边其它断裂有何区别与联系？本项申请将在“霍山山前断裂（南段）1/5万地质填图”和预研究的基础上，应用多断层剖面精细分析、遥感综合解译和定量构造地貌分析方法，以断裂北段（霍州以北）为重点，开展1）有利地貌部位最新破裂事件探槽识别和区间段的遥感综合解译，确定破裂带北延截止位置，2）综合多个大型剖面古地震事件分析、北段构造地貌参数分析和暴露基岩断层面宇宙成因核素测年，研究霍山山前断裂的晚第四纪活动特征；进一步3）结合霍山山前断裂的活动模式讨论破裂带规模与给定震级两者之间关系。

山西地堑系是鄂尔多斯东缘东边界，其中部的霍山山前断裂曾发生根据史料确定的大陆内部的第一个M8.0地震1303年洪洞地震。围绕该次历史强震和相应的反震构造的详细研究对认识地堑系太原盆地和临汾盆地的地震危险性具有重要意义。. 本项目的主要研究内容：（1）1303洪洞8级地震地表破裂带的北延规模；（2）霍山山前断裂的活动方式研究。. 本项目在3年执行期内取得的主要认识： （1）1303年洪洞8级地震的地表破裂带长度约90km，南端自临汾盆地东北部的洪洞东北起始，沿着霍山山前西麓延伸，经霍州、灵石，止于介休东南，即北延截至太原盆地南部而非霍州以东，破裂带表现为断层陡坎、槽谷、地震滑坡等变形现象，单次破裂的平均位错量为2m；（2）霍山山前断裂的活动方式以正断为主，而非之前认为的右旋走滑，这从多方面参数得到相互印证，全新世共发生3次地震事件，平均复发间隔2000年，根据破裂规模得到的1303地震矩震级规模为Mw7.1-7.6要小于之前的历史地震震害评定震级，正断层活动受其几何规模存在震级上限；（3）沿着霍山断裂解译出1303年地震的同震滑坡体1.1万余处，主要位于临汾、太原盆地之间的黄土丘陵，据此建议将地震震中自现在的洪洞向北移动至霍州附近，同震滑坡与宏观震中相匹配，位于盆地内的古建筑震害当属盆地松散层的震害方法效应所致，而非一定是震中位置。. 本项目执行期间取得了结果的科学意义：（1）1303年洪洞地震地表破裂带90km，到达介休东南，沿断裂带解译1.1万余处同震滑坡，确认霍山断裂为一条正断层，而非右旋走滑断层，根据震级规模1303地震矩震级为Mw7.1-7.6级，存在震级上限受断层规模限制的问题；（2）洪洞地震的宏观震中建议向北移动60 km部分解释了之前困惑的临汾盆地1303洪洞地震（包含临汾盆地北部、太原盆地南部及介于之间的灵石凸起）和1695临汾地震（仅局限于临汾市周边）两次8级地震震中相距仅40km的问题。