Holocene Paleoseismic Activity Along the Northern Piedmont Fault of the Hengshan Mountain, South of Datong Basin in Shanxi Province

摘要

Our field investigation indicates that the northern piedmont fault of the Hengshan Mountain has dislocated proluvial fan and terrace I of the gully mouth on the northern border of the Hengshan Mountain. Stratigraphic age data indicates that the surface layer in the middle and rear part of the proluvial fan and on the terrace I of the gully mouth on the mountain border consists of sediments of about 5200 ～ 6800a B. P. The Hezhuang and Niucaoyu trenches excavated in the front of Hengshan Mountain revealed that 3 paleoseismic events have occurred along the northern piedmont fault of Hengshan Mountain since the early Holocene. The 3 paleoseismic events occurred in 2260 +- 190 ～ 4370 +- 150a BP, nearly 5628 +- 150a BP, and 8083 +- 250 ～ 8430 +- 720a BP, respectively, and their recurrence interval is 2313a, 2628a and 2471a on average. The coseismic vertical displacement produced by these events is 1.0 ～ 3.0m. The elapsed time of the latest movement along the fault has exceeded the recurrence interval of these paleoearthquakes. Thus, there exists the possibility of strong earthquake occurrence along the fault from now onward, so the fault is in need of observation.