美国对自然灾害的承受力越来越弱,主要是因为人口密集程度及社会财富集中的改变——更多的人和更多的社会性基础结构设施越来越集中在易发生灾害的地方。就20世纪大部分时间来说,美国已大大节省了破坏性灾害造成的损失所消耗的费用。自1906年旧金山地震后,其主要城市没有遭到巨大地震(震级≥8.0)的破坏;自1926 The United States has become weaker and weaker for natural disasters, mainly because of the changes in population density and concentration of social wealth - more and more social infrastructure facilities are increasingly concentrated in areas prone to disasters. For most of the twentieth century, the United States has greatly saved the costs of the damage caused by devastating disasters. Since the San Francisco earthquake in 1906, its major cities have not been damaged by huge earthquakes (magnitude ≥ 8.0); since 1926