陕西咸阳东地震砂土液化的发现及意义

Discovery and Implications of Sand Liquefaction in Eastern Xianyang,Shaanxi Province

地震砂土液化是研究历史地震和古地震的重要手段,其结果对评价一个地区的地震危险性有重要意义。通过对陕西咸阳黄家沟、长兴村砂土液化平面和剖面特征的调查,明确了该地区砂土液化为地震诱发产生。对上述两地砂土液化所穿过的文化层进行考古鉴定,综合分析认为砂土液化形成于明朝时期,对应的地震可能是1556年华县8?级地震、1568年西安东北6?级地震或1487年临潼6?级地震。依据在渭河盆地发现的其他砂土液化,对其有争议的公元前780年岐山≥7级地震和公元600年秦陇6~7级地震的震中和震级进行讨论,认为公元前780年地震的震级定为8级有待更多的证据,公元600年秦陇地震震中应不在西安附近。这一结论为渭河盆地几条主要活动断裂的地震危险性评价提供了新的旁证资料。

Researching on seismic sand liquefaction is one of the important methods of studying historical earthquakes and paleoearthquakes. Its result has great meaning in evaluating regional seismic risk. The horizontal and sectional characteristics of sand liquefaction in the Huangjiagou and Changxing villages in Xianyang City, Shaanxi Province were investigated. The sand liquefaction was clearly induced by earth quakes. According to the archaeological identification of the cultural layers, where the dikes of the two sites both pass through, the sand liquefaction might have formed during the Ming Dynasty. Moreover, the corresponding earthquake was the 1556 Huaxian M8^1/4 earthquake, the 1568 M6 ^3/4 earthquake in eastern Xi＇an, or the 1487 Lintong M6^1/4 earthquake. The controversial epicenters of the Qishan M≥7 earthquake in 780 B.C. and the Qin Long M=6-7 earthquake in 600 A.D. were discussed based on the other sand liquefactions we found in the Weihe Basin before. Defining the epicenter of the 780 B.C. earth quake as magnitude 8 needed more evidence. The epicenter of the 600 A.D. earthquake should not be near Xi＇an. The conclusion provides new circumstantial data for the seismic hazard evaluation of several main active faults in the Weihe Basin.