A Study Of Holocene Palaeo-earthquake On The Yushu Fault Zone

The Yushu Fault zone in South-eastern Tibetan Plateau is a typical active fault zone,characterized by sinistral strike-slip faults.The field investigation has reveals a lot of relics along the fault traces of the segment of the Yushu Fault Zone,including push-up and pull-apart basins?sag ponds,and earthquake fault scarps.These phenomenons imply that the Yushu Fault is a seismetic fault in which co-seismic surface ruptures often occured in regular or irregular intervals.To determine the chronology of these holocene palaeo-earthquake,more than five trenches were excavated across the Yushu Fault Zone.All sediment samples we collected from the trenches were dated by using 14C methods.Palaeo-earthquake evidence,combined with 14C dating,shown that the Yushu Fault has generated at least 4 palaeo-earthquakes since holocene,whose ages are(170-260)±30aB.P.,(3185-3925)±30aB.P.,(6695-7150)±30aB.P.and 10400±40a B.P.respectively.The recurrence interval between two adjacent events isabout 3500a.So we advocate that the recurrence interval of palaeo-earthquake at the same place is 3500a.0ur research shown that the recurrence is not uniform with time,that is,the distribution of palaeo-earthquakes on the Yushu Fault is characterized by clustering.The first cluster period on the Yushu Fault zone is between7510 a B.P.and 6120aB.P.,and the second cluster period is from 4020aB.P.to 2810aB.P.The interval of the two cluster periods is 2100a.This result suggests that the Yushu Fault Zone had displayed a spatial discontinuity and a time-dependent seismic behavior.The strong earthquake activities on each segment of the fault zone had shown an alternative characteristics.