CHARACTERISTICS OF LATE QUATERNARY ACTIVITY ALONG THE SOUTHERN BORDERFAULT ZONE OF WEIHE GRABEN BASIN

The Weihe graben basin located in the centre of Shaanxi, China, is a t ectonic depression on the southern border of Ordos massif, a subtecton ic unit in the Sino-Korean paraplatform. In the light of new informati on exhibited from geological mapping on the scale of 1:50,000, the act ive history and the feature of the Southern Border Fault Zone of Weihe graben basin have been researched. The fault zone may be subdivided i nto two segments: the piedmont fault of Huashan Mt. in the east sector and the northern border fault of Qinling Mts in the west sector. The research shows that new activity of the piedmont fault of Huashan Mt. is obvious since the Late Quaternary. A great number of relies of eart hquake deformation, such as the newest fault scarps, bedrock fractures , loess crevices, landslides and mountain creep, are distributed along this fault and its two flanks. This fault is most likely the causativ e fault zone of the Huaxian great earthquake in 1556 (M = 8). The anal ysis of two palaeoseismic profiles shows the earthquake recurrence int erval is 2000-2500 years for the Huashan Mt. piedmont fault, whereas 2 000-4000 years for the northern border fault of Qinling Mts.