Tectonic Setting and the Features of the Surface Rupture Zone caused by the Mani Earthquake (Ms7.9) in 1997

Abstract

On 8 November 1997, an Ms7.9 earthquake occurred at the northern edge of Qiangtang basin in Mani of the Xizang autonomous region. The Qiangtang area lies in northern Tibet where nobody inhabits, the climate is cold, the air is thin and the field investigation condition is very arduous. In this work LANDSAT images are used to study the geological tectonic background of the earthquake. The result shows that the earthquake occurred in the NEE trending Margai Caka-Rola Co fault zone, which is an active deep fault since the Holocene. CBERS-1 images of 1/100000 scale reveal the geometric characteristics of the surface rupture zone caused by the event. The trace of the Mani surface rupture zone is linear and composed of fissures, swells and dammed pools, which can be used to measure the length and segmentation of the rupture zone. The analysis shows that the major surface rupture zone of the earthquake, which is 110km long and trending 70°N~80°E, appears at the northern edge of the Qiangtang basin, Baixue Lake plain which lies in the southern foot of the Suijia Mountains, and extends eastward to the western bank of the Shuangduan Lake. The surface rupture zone can be divided into 3 sections: Baixue Lake-Margai Caka section, Margai Caka-Chaoyang Lake section and Chaoyang Lake-Shuangduan Lake section. The analysis of multi-phase MSS and TM images indicates that the surface rupture is the result of re-fracturing along an old fault.