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 4 1 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 M 7~7 4 1 Wudu earthquake in 186 B.C. should be in the middle-east segment of Diebu-Bailongjiang active fault zone. Key words: Wudu earthquake in 186 B.C.; textual research of historical earthquake; causative structure; Diebu-Bailongjiang fault zone CLC number: P315.2; P315.5 Document code: A
On the basis of textual research on the historical earthquake data and the field investigation of 1219 A.D. Guyuan earthquake, we suggest that there is only one strong earthquake occurred in Guyuan area in 1219 A.D., instead of two or three strong earthquakes. We further suggest that the earthquake parameters recorded in the present earthquake catalogs are not definite and should be modified. The occurrence time of this earthquake should be about 11 am, August 7, 1219 A.D. and the heavily-damaged area of this earthquake, the VIII intensity area, should be located among the regions of Guyuan, Pingliang and Longde county cities. The epicenter area should be near Guyuan city. The magnitude of this earthquake is about 7 and it has intensity about larger than or equal to IX within the epicenter area. The major axis direction of the heavily-damaged area strikes in north-northwest that is approximately consistent with the strike of the Liupan Shan thrust fault zone. The new tectonic activity of the Liupan Shan thrust fault zone resulted in the M7 Guyuan earthquake in 1219 A.D.
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