Distribution of seismic intensities of the November 6, 1988, Lancang-Gengma earthquakes and their surface ruptures in Yunnan Province, China |
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| Authors: | Hui Wang Zuji Qiang Zhuzhong Yuan Yanglong Wang Hua Zhang Xiang Zhao and Yishan Gu |
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| Institution: | (1) Institute of Geology, State Seismological Bureau, 100029 Beijing, China;(2) Seismological Bureau of Yunnan Province, 650041 Kunming, China |
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| Abstract: | On November 6, 1988, two earthquakes with magnitude>7 occurred on the Lancang-Gengma fault zone in south-west China. The extensive
destruction and loss of lives resulted mainly from widespread collapse of unreinforced masonry and mud brick structures; the
maximum preliminary intensity of the Lancang earthquakes was IX on the Chinese scale, which is similar to the Modified Mercall
scale, and the highest preliminary intensity of the Gengma earthquake was probably X.
The surface manifestation of tectonic activity of the Lancang earthquake was the occurrence of the earthquake-related extensional
ground cracks and small fault scarps in the epicentral region. The cracks with small fault scarps occurred mainly in four
relatively continuous north-northwest-trending linear zones that ranged from a few hundred meters to 6 km in length. The area
within which the cracks and small scarps occurred is 35 km long by 3 km wide. The maximum net throw and the dextral horizontal
offset were 1.5m and 1.4m, respectively.
Clear evidence of new surface faulting caused by the Gengma earthquake includes a series of relatively continuous north-northwest-trending
linear ground crack zones and a 5 km long section of fault scarps. The total length of the surface rupture zones of the Gengma
earthquakes is about 24 km, with 3.5m maximum net throw and 3m maximum right-lateral slip.
Both earthquakes were associated with surface faulting showing a combination of normal and right lateral motion. The distribution
of seismic intensities and surface rupture characteristics of these two earthquakes are discussed in this paper.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 344–353, 1991.
The research project was performed out under the direction of Professors. Xingyuan Ma and Yuntai Chen, and the field investigation
was performed with help of Kui Jiang and Junchang Zhang of the Seismological Bureau of Yunnan Province. Here the authors express
great appreciation. |
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| Keywords: | Lancang-Gengma earthquakes Yunnan Province seismic intensity surface ruptures fault scarps |
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