宁夏卫宁北山南缘断层探测与活动性初步鉴定

宁夏卫宁北山位于青藏高原、阿拉善和鄂尔多斯3大活动地块的交汇地带，查清该地区的活断层对厘清活动地块边界和规划中卫工业园区布局均具有重要意义。采用浅层地震勘探、钻孔联合剖面探测及槽探等手段，针对卫宁北山南缘推测断层开展综合探测，以便查清该断层展布情况和地层断错特征，并结合区域地层时代对比，初步鉴定已探明断层的活动性。结果表明：前人推测的地貌陡坎之下的卫宁北山南缘正断层并不存在，而在卫宁北山南缘地貌陡坎偏北基岩内发育一条逆冲断层，浅层地震勘探剖面揭示该断层上断点埋深35～40 m,钻孔联合剖面探测和槽探发现断层错断了石炭系和新近系，但未错断上覆的上更新统，表明该断层不是活动断层；另外，浅层地震剖面揭示在中卫盆地内部还发育一条北西西向的隐伏正断层，上断点埋深约60 m,但也未错动晚更新世以来地层，因而推测该断层不存在晚第四纪活动性。

A preliminary study on detection and activity of the southernmargin fault of Weiningbeishan, Ningxia

Weiningbeishan, Ningxia, is located at the convergence zone among three active blocks, i.e., the Tibetan Plateau, the Alax Block, and the Ordos Block. Detection of the active faults in this area is of great significance for clarifying the boundary of active blocks and planning the layout of Zhongwei Industrial Park. By means of shallow seismic exploration, drilling joint profile exploration, and trenching, this paper carried out a comprehensive exploration on the inferred fault at the southern margin of Weiningbeishan, found out the fault distribution and the characteristics of stratum dislocation, and preliminarily identified the activity of the proved fault. The results show that the normal southern margin fault of Weiningbeishan under the geomorphic scarp inferred by former researchers is not found, and a thrust fault is developed in the bedrock to the north of the geomorphic scarp. The shallow seismic exploration profile reveals that the buried depth of upper breakpoint of the fault is 35-40 m. The drilling joint profile surveying and tren-ching found that the fault offset the Carboniferous and Oligocene strata, however, the overlying Late Pleistocene sediments are not faulted, indicating the fault is not active. In addition, the shallow seismic profile reveals that a NWW-trending buried normal faultis developed in the Zhongwei basin, and the buried depth of upper breakpoint is 60 m. Combined with the stratigraphic age of the basin, we infer that the fault has not been active since the Late Pleistocene.