关键词: 古地震, 全新世, 西张探槽, 交城断裂带, 山西

Abstract: Xizhang trench is located at 10 kilometers northwest of the Taiyuan City,Shanxi Province,and it was excavated at the front of a NNW-trending scarp of 4.6m height on the northern segment of the Jiaocheng Fault zone.The dimensions of the trench are 108m in length,8m in width,and 10m in depth.There are 18 strata revealed in the trench.The upper stratum is sandy loam;the upper stratum of the downthrown block of the fault is gravel,the lower stratum is interbed of brown loam and sandy loam.The strata on the upthrown block of the fault are sandy loam containing gravel.The trench shows 3 fault planes,and the upper fault point on the fault plane is 1.5m deep from the ground surface,the newest dislocated stratum is(3.74±0.06)ka BP.The trench reveals a lot of deformation traces,such as fault plane,dislocated strata,colluvial wedge and the dipping of formation.The relation between the strata and the faults in the trench shows that 3 paleoearthquake events have occurred at the Jiaocheng Fault zone since Early Holocene,they are about(3.74±0.06)～(3.06±0.26)ka BP,(8.35±0.09)～(3.74±0.06)ka BP,and(10.66±0.85)～(8.35±0.09)ka BP,respectively.The average interval of the events is2.6～3.6ka.The minimum coseismic vertical displacements of the 3 events are 3.0m,2.5m,and 3.2m,respectively.The significance of Xizhang trench is that the Jiaocheng Fault used to be active thousands years ago,though there wasn't M≥7 earthquake recorded in historical words.The evidence of newest activities of the Jiaocheng Fault zone during Holocene is important for earthquake safety assessment of Taiyuan City in the future.

Key words: paleoearthquake, Holocene, Xizhang trench, Jiaocheng Fault, Shanxi