The fact that major quakes can occur anywhere within very large ranges-including the entire length of faults or even whole tectonic plates-is another problem. For example, the 2008 Sichuan quake could have arisen anywhere within a 2900-km-long fault zone. Consequently, the areas above which the ionosphere might change are also very large.
另外，由於發生大地震前的「醞震範圍」相當廣闊，可能包含整條斷層、甚至整個板塊，如川震的醞震範圍就長達 2,900 公里，因此電離層產生變化的區域也很寬廣。