汶川地震中陈仓区成为Ⅵ度烈度区中的Ⅶ度异常区的原因浅析

Preliminary study on the reason of Chencang district to be the anomalous zone with seismic intensity Ⅶ in the area with seismic intensity Ⅵ of Wenchuan earthquake

本文在宝鸡市震害考察、建筑物分布调查的基础上,利用宝鸡市地震小区划成果,结合对陈仓台站的汶川地震记录分析,得出陈仓区为5.12汶川8.0级地震Ⅶ度烈度异常区,是以下3种因素综合作用所致:(1)当地场地土层特性与其他地方不同,使得地震动强度较大;(2)异常区在地形上位于一个孤立突出的位置,地形的二维变化进一步放大了当地的地震动作用;(3)汶川地震记录表明,在宝鸡地区中、长周期地震动的成分较高、作用较大。故若有震害,将主要集中在中高层建筑(其自振周期为中长周期)。宝鸡市地震小区划地震动峰值分区的低峰值区中,由于汶川地震在此的地震动强度小,对所有建筑都不足以造成较重的震害;而在高峰值区中,仅陈仓区有大量中高层建筑分布,汶川地震在此的频谱特征和较强的地震动强度,造成了其独有的严重震害。

After investigating the earthquake damage and the building geographic distribution of Baoji city,quoting the achievements of ＂seismic ground motion micro-zoning of Baoji city＂ and analysising the acceleration records of Wenchuan Ms8.0 earthquake at Chencang staion,we found that the reason of Chencang district to be the anomalous zone with seismic intensity Ⅶ in the area with seismic intensity Ⅵ of Wenchuam earthquake is that it is a result from the common effect of the following 3 facters：（1）The site soil layer feature is so different that its seismic ground motion is more strong;（2）The anomalous zone in terrain is located in an isolated position of a prominence,this local two-dimensional topography made seismic ground motion more strong;（3）Analysising the acceleration records of Wenchuan Ms8.0 earthquake recorded in Baoji city,the middle or long period seismic waves are more strong.So if there is damage,it will be mainly concentrated in the middle or high storey buildings,which have middle or long natural vibration periods.Among all areas with high values of ground motions according to ＂seismic ground motion microzonation of Baoji city＂,only Chencang district has many middle or high storey buildings,so its damage is more serious.