关键词: 古地震, 活动断裂, 色尔腾山山前断裂

Abstract: The Sertengshan piedmont fault is a very important active fault. Along with the Langshan piedmont fault, it controls the northwest boundary of the Hetao fault-depression zone. We have carried out detailed investigation of fault activity and paleoseismology on east of Delingshan segment of this fault, on which little work has been done before. The result of investigation indicates that the geomorphic characteristics of late Quaternary activity on this segment of the Sertengshan piedmont fault are very remarkable, appearing as the offset and uplift of lacustrine deposits, alluvial fan and stream terraces, resulting in linear scarps and fault platforms. Taken the Xiaoshetai canal outlet as boundary, this fault segment can be subdivided into the Dashetai and Wulanhudong active fault segments characterized by different features. In the past 30ka BP,the average uplift rate of the upthrown side on the Dashetai segment is 0.19mm/a, while that of the upthrown side on the Wulanhudong segment is 0.20mm/a. One trench has been excavated on each active fault segment for paleoseismic investigation. As a result, the Hongming trench on the Dashetai segment has revealed that 4 paleoseismic events have occurred on this segment since about 32ka BP, the occurrence times of which are successively 31,690?1770, 23,000?1320, 15,420?870 and 7,440?440a BP. The corresponding displacements produced by these 4 events are 2.6, 1.6, 2.2 and 1.4m, respectively. The Wulanhudong trench on the Wulanhudong segment, has also revealed that 4 paleoseismic events have occurred on this segment since about 25ka BP, the occurrence times of which are successively 25,130?1430, 14,570?820, 11,660?650 and 7,220?400a BP. The corresponding displacements produced by these 4 events are 2.6, 1.8, 1.3, and 1.2m, respectively. The comparison of these paleoseismic events also indicates that the subdivision of east of Delingshan segment of the Sertengshan piedmont fault into 2 active fault subsegments is acceptable. Finally, according to the Displacement amount-constraining Method, it is confirmed that the acquired paleoseismic activity histories for the two segments are complete during the observed period of time.

Key words: paleoseismic event, active fault, Sertengshan piedmont fault