Textual research of Wudu earthquake in 186 B.C. in Gansu Province, China and discussion on its causative structure

摘要

On the basis of the textual research on the historical earthquake data and the field investigation of Wudu earthquake occurred in 186 B.C., we suggest that the earthquake parameters drawn from the present earthquake catalogs are not definite and amendments should be made. The heavily-damaged area of this earthquake should be located between Jugan township of Wudu County and Pingding township of Zhouqu County. Its epicenter should be in the vicinity of Lianghekou in Wudu County with a magnitude of about 7～7 1/4 and an intensity of about Ⅸ～Ⅹ. The major axis direction of the heavily-damaged area should be in the WNW direction that is approximately consistent with the strike of the middle-east segment of Diebu-Bailongjiang active fault zone, and the origin time should match up to that of the latest paleoearthquake event[before (83±46) B.C.] obtained by the trench investigation.Certain seismic rupture evidences are still preserved on this fault segment. Therefore, we propose on the basis of comprehensive analysis that the causative structure of the M7～7 1/4 Wudu earthquake in 186 B.C. Should be in the middle-east segment of Diebu-Bailongjiang active fault zone.