顺义地裂缝成因与顺义-良乡断裂北段第四纪活动性讨论

本文通过钻孔地层对比方法研究了顺义一良乡断裂北段的第四纪活动性，资料显示该断裂在第四纪期间呈现强弱交替的分期活动特征，距今315万年以来有3个较强活动期和3个较弱活动期，前三者分别距今266～315、171～228、73～147万年，后三者距今分别为228．266、147～171、0～73万年。中更新世晚期以来断裂活动不明显。超量开采地下水导致地面不均匀沉降是造成顺义地裂缝现今活动的主要原因。

Quaternary Activities of Northern Segment of the Shunyi-Liangxiang Fault

The Quaternary activities of northern segment of the Shunyi-Liangxiang fault are discussed based on the contrast of drilling strata across the fault. The fault present active and silent substages alternantly in Quaternary. Since 3150ka B.P., there are 3 active substages and 3 silent stages. The active substages are from 3,150ka to 2,660ka B.P., from 2,280ka to 1,710ka B.P. and from 1,470ka to 560ka B.P. The silent substages are from 2,660ka to 2,280ka B.P., from 1,710 ka to 1,470 B.P., and from 730ka B.P. to present. This segment went into silence since 730ka.From Junying to Xiaodongzhuang, there is a active groung fissure zone developed along the Shunyi-Liangxiang fault,4km long, 10m wide, pulling apart building wall and cement ground. The fissure exhibits vertical displacement of southeast side falling, which accords with the movement of the Shunyi-Liangxiang fault in early Quaternary. The fissure appeared after the Tangshan earthquake in 1976, and developed rapidly in the 1980s. The fissure accord in development procedure with Pinggezhuang ground subsidence center 2km southeast of it. The ground fissure is a consequence of uneven ground subsidence from excessive exploitation of ground water divided by the Shunyi-Liangxiang fault, independent of the creeping of the fault.