图2  吴忠、灵武地区主要断裂及历史地震震中分布图

Fig．2   Major faults and the epicentral

         distribution of historical earthquakes

         in Wuzhong and Lingwu areas

         ①黄河大断裂；  ②前筐子-马家湖隐伏断裂；  ③牛首山北麓断裂； 

         ④牛首山西麓断裂