1988年云南澜沧-耿马地震的烈度分布及地表破裂

THE DISTRIBUTION OF SEISMIC INTENSITIES AND SURFACE RUPTURE IN THE LANCANG-GENGMA (YUNNAN PROVINCE,CHIN A ) EARTHQUAKES OF NOVEMBER 6, 1988

1988年11月6日,在云南省西南部的澜沧-耿马断裂带上发生了两次大于7级的地震.地震造成的严重破坏和人员伤亡主要是由于极震区内抗震性能极差的毛石房、砖柱土坯房的大量倒塌所致.澜沧地震的震中基本烈度可达Ⅸ度,耿马地震极震区烈度达Ⅹ度.澜沧地震构造活动的地表证据主要是出现在极震区内的张性地裂缝带和小断层陡坎.地裂缝带和小断坎主要出现在四条相对连续的北北西走向的狭窄地带内,其长度从几百 m 到6km 不等.澜沧地震地表破裂带长约35km,宽约3km,最大垂直位移量和最大右旋水平位移量分别为1.5m 和1.4m.耿马地震地表断裂活动的明显证据包括一系列北北西走向的地裂缝带和一段长约5km的地震断层陡坎.耿马地震地表破裂带长约24km,其最大垂直位移3.5m,最大右旋水平位移为3m.两次地震形成的地表破裂带均具有右旋-正断层性质.本文讨论了这两次地震的 度分布及地表破裂特征.

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 earthquake was IX on the Chinese scale , which is similar to the Modified Mercalli 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 6km 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 l-5m and l-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 earthquake is about 24km, 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.