REDETERMINATION OF THE SURFACE RUPTURES CAUSED BY THE HONGYAPU,GANSU PROVINCE,M7 1/4 EARTHQUAKE OF 1609 |
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| Authors: | HUANG Xiong-nan YANG Xiao-ping YANG Hai-bo |
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| Affiliation: | Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China |
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| Abstract: | 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. 200km2. 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. MW7.0~MW7.4, close to the M7 1/4 suggested by previous studies. |
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| Keywords: | Fodongmiao-Hongyazi Fault Northern Qilishan Hongyapu earthquake in 1609 surface ruptures |
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