Textual research of 1219 A.D. Guyuan earthquake in Ningxia Hui autonomous region, China and discussion on its causative structure

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.