陕南汉中盆地西部梁山南缘断裂隐伏段的活动性鉴定

Activity identification of the buried segment of Liangshan south margin fault in the west of Hanzhong basin

汉中盆地是青藏高原、秦岭与大巴山—龙门山差异隆升区中间的新生代断陷盆地,是重要的地质体连结点.通过新近开展的汉中市活断层探测工作中的地面地质调查、浅层地震勘探与钻孔联合地质剖面分析等工作认为,汉中盆地内部存在一条活动断裂,即梁山南缘断裂.浅层地震勘探资料显示,梁山南缘断裂错断多套第四纪以来的地层,错距自下而上逐渐减小.钻孔联合地质剖面显示,梁山南缘断裂错断晚更新世中晚期以来的砾砂及卵石层,距今58ka的砾砂层错距约为6m.这些现象首次揭示了汉中盆地内部梁山南缘断裂的最新活动时代和活动性质.

Hanzhong basin is a Cenozoic faulted basin located in the differential uplift region among Qinghai-Xizang plateau, Qinling mountain and Dabashan-Longmenshan. It is a connection hub among them. Based on the analysis of ground geological survey, shallow seismic prospecting and composite drilling geologic profile carried out recently in active fault surveying of Hanzhong, we recognized that there is an active fault in Hanzhong basin, namely the Liangshan south margin fault. Shallow seismic investigation data indicate that this fault cuts many sets of Quaternary strata in Hanzhong city and the offsets are reduced gradually from bottom up. Composite drilling geologic profiles show that this fault breaks sand and gravel strata of the middle and late period of Late Pleistocene. The offset is about six meters. These phenomena show the latest activity age and nature of the Liangshan south margin fault in Hanzhong for the first time.