土层结构对汉源烈度异常的影响

汶川MS8.0大地震在远离震中近200 km的汉源县县城产生了高烈度异常, 其原因比较复杂．为了分析土层结构对汶川大地震中汉源县老县城高烈度异常的影响, 在汉源县城震害科学考察基础上, 依据地震烈度异常的分布情况, 在背后山滑坡前缘地带布设5个工程地质勘察钻孔, 获得了汉源县老县城场地土层结构资料．在现场测试和室内试验的基础上, 给出了汉源县老县城场地各层土体动力学参数．本文利用汶川地震九襄强震台的强震记录, 结合其台站的场地资料反演给出了汉源县老县城的基岩地震动时程, 作为地震反应分析的基岩输入地震动．在此基础上利用土层地震反应一维等效线性方法对汉源县老县城场地进行了地震反应分析, 并将计算所得结果与Ⅵ度区其它强震台站获得的强震记录进行比较．研究结果表明, 汉源县老县城土层结构对地震动的放大作用导致地表地震动异常, 是汉源县老县城高烈度异常的主要原因之一． 

Effects of soil structure on abnormal intensity in Hanyuan old town

Hanyuan town,Sichuan, is200 kmaway from the epicenter of the 2008 Wenchuan great earthquake, yet high abnormal seismic intensity was observed there. In order to analyze the effects of soil structure on the abnormal intensity at Hanyuan old town, based on scientific investigation on seismic damage distribution there, five boreholes were drilled on the frontal landslide slope of theBeihouMountainand the data of soil layer structures were obtained. On the basis of field test and laboratory experiment, the dynamic parameters of soils in different layers in Hanyuan old town were deduced. By inverting the strong motion data recorded at Jiuxiang strong-motion station and associate site information of this station, the time-history of ground motion was derived, and was taken as input bedrock waves for ground seismic response analysis. With 1-D equivalent linearization wave motion method, which is widely used in ground response analysis, Hanyuan old town ground motion parameters were calculated. The calculation result was compared with the strong motion record corresponding to intensity Ⅵ during the Wenchuan earthquake. The analysis result shows that the soil structure of Hanyuan old town region amplified ground motion, hence leading to abnormal ground motion. This is one of the main reasons for abnormal intensity.