对于没有文字记载的史前灾变,例如地震,火山爆发、海啸等,人们是难以确知的。然而树木年轮就象一本史书,替人类记下了史前的自然灾变,成为人类研究史前灾变的宝贵资料。近年来,美国科学家高登.杰克比对生长在阿拉斯加地震断裂带上的树木年轮进行了取样测量,发现一九○四年强烈地震在树木年轮上留下了地震记录。他还发现一八八九年这里发生过七点八级地震。震前,树木生长缓慢,震后三年生长迅速,由此,科学 It is hard to know for prehistoric catastrophes without written records, such as earthquakes, volcanic eruptions, tsunamis and so on. However, the tree rings are like a history book, which records the prehistoric natural catastrophe for human beings and becomes the valuable information for the human study of prehistoric catastrophe. In recent years, US scientist Gordon Jackby sampled and measured tree-ring trees growing on the Alaskan earthquake fault zone and found that a strong earthquake in 1904 left an epicenter on tree rings. He also found that there was a 7.8-magnitude earthquake here in 1889. Before the earthquake, the trees grew slowly and grew rapidly three years after the earthquake, thus science