甘肃红崖堡１６０９年７1/4级地震地表破裂再厘定

REDETERMINATION OF THE SURFACE RUPTURES CAUSED BY THE HONGYAPU,GANSU PROVINCE,M7(1/4) EARTHQUAKE OF 1609

位于祁连山北缘活动断裂带中段的佛洞庙-红崖子断裂发生过1609年红崖堡7(1/4)级地震。通过详细的地貌解译和地形测量,在比现代冲洪积扇和河床略高的次新地貌面上发现了全长约95km的地表破裂带,西起酒泉洪水坝河,东至肃南头道东湾。通过探槽研究和年代学测试,确认该破裂带的产生晚于公元元年。对比区域上前人对历史强震震中分布的研究,认为该地表破裂带即1609年红崖堡7(1/4)级地震地表破裂带。地形测量结果表明,1609年红崖堡地震以逆冲倾滑为主,平均垂向位移1.1m,最大垂向位移1.8m。局部由于走向的变化兼具右旋走滑(NNW走向的小泉段)或左旋走滑(NEE走向的红山村东段)。依据地表破裂长度、断层最大位移与断层倾角,估算出地震震级为M_W7.0~7.4,与前人认识(震级M7(1/4))接近。

The Hongyapu M7 1/4 earthquake in 1609 occurred on the Fodongmiao-Hongyazi fault,which is a Holocene active thrust in the middle segment of the northern Qilianshan overthrust fault zone,located in the north-eastern edge of the Tibet plateau.This earthquake caused death of more than 840 people,ruined the Hongyapu Village and had an affected area ca.200km 2.Previous work provided different opinions on the length of the earthquake surface rupture zone,such as 60km from the Bailanghe western riverbank to the Fenglehe eastern river bank,and only 11km from the Hongyazi village to eastern edge of the Hujiatai anticline.And the surface rupture zone appears in the western and middle segments of the Fodongmiao-Hongyazi fault zone.Our detailed geomorphic analysis and topographic survey found that the surface rupture zone with a total length of ca 95km is present on the new geomorphic surfaces which are slightly higher than the modern allvial-dilvial fans and riverbeds,which begins from the Hongshuiba river,Jiuquan in the west extending to the Toudaodongwan,southern Gansu in the east along the Fodongmiao-Hongyazi Fault.The surface rupture zone occurred later than 0 A D,proved by the study of trenchs and chronology.Compared to the previous research on the epicenters of the historical major earthquakes in and around the study region,this surface rupture zone is considereded to be the surface rupture zone of the Hongyapu earthquake of 1609 in Gansu provice.Average vertical co-seismic displacement of the 1609 Hongyapu earthquake is 1.1m with maximum 1.8m,dominated by thrusting.The NNW striking Xiaoqun segment shows thrust with a component of dextral strike slip and the NEE-trending East Hongshancun segment is also mainly thrust but with sinistral strike slipp.The lateral movement could be caused by the local change of the fault strike direction.Based on the length of surface ruptures,the maximum coseismic displacement and fault dipping,this event is estimated to be of ca.M W7.0～M W7.4,close to the M7 1/4 suggested by previous studies.