Textual Research on the July 7,1590 A. D. Southeastern Yongjing Earthquake in Gansu Province

According to historical records,in July of 1590 A.D.,a destructive earthquake occurred near Lintao county in Gansu Province,in which "… city walls and houses collapsed,and countless people and domestic animals were killed".In the same month,Binggou town in eastern Qinghai Province(now northeastern Ledu county),was also damaged by an earthquake.These two earthquakes were listed as two different cases in the published earthquake catalogues,recorded separately as the Lintao M_S5.5 earthquake with epicentral intensity Ⅶ in Gansu Province and the Ledu M_S5.0 earthquake with epicentral intensity Ⅵ in Qinghai Province.However,based on comprehensive analysis of research on historical records and field investigations,it is concluded in this paper that these two earthquakes could be the same one with magnitude 6.5 and epicentral intensity Ⅷ～Ⅸ.Its epicenter was in the Maxian Mt.,which is located in southeastern Yongjing and its seismogenic structure might be the mid-western segments of the north fringe fault zone of Maxian Mt.of Lanzhou.