Effects of river valley topography on anomalously high intensity in the Hanyuan town during the Wenchuan M_S8.0 earthquake
LI Ping;LIU Hong-Shuai;BO Jing-Shan;LI Xiao-Bo;YU Xiao-Hui;Institute of Disaster-Prevention;National Earthquake Infrastructure Service,China Earthquake Administration;
The Hanyuan town is located approximately 200 km to the macro-epicenter of the great Wenchuan M_S8.0earthquake.However,it is the only one within the intensity VIII zone,surrounded by a region of intensity VI.In landscape,this town lies on the second and third terraces of the Liusha River.The river valley topography has important influence on earthquake damage.Authors have obtained several geological profiles during the scientific survey and carried out the measurements of shear velocity in the typical boreholes in Hanyuan.To quantitativelyanalyze the effects of river valley topography on the intensity anomalies in this area,aprofile,perpendicular to the Liusha River and passing through the town,is selected as the computation model reflecting the differences of damage.Taking the pulse waves as the base inputs,the site amplification effects of the selected profile are studied by employing the finite difference method of wave propagation to analyze the effects of river topography on the high intensity anomalies.The results show that the frequencies of 1.0to 10 Hz are the most amplified by the site of Hanyuan town and the magnifying effects are more significant in the old town than in the new town.The sites in the old town have significant amplification effects on the ground motion of main shock during the Wenchuan M_S8.0earthquake and the peak accelerations of the old town greatly exceeded the specified value in the code of seismic design of buildings.The most significant frequencies amplified by the sites of the Hanyuan town are consistent with the concentrated energy frequency bands of the Wenchuan M_S8.0 earthquake,and the natural frequencies of buildings in the old town are just within these frequencies,thus leading to resonance effects to cause more significant amplification effects.This is one of the main causes inducing the intensity anomalies in the town during the Wenchuan M_S8.0earthquake.Therefore,the valley terrain has important influences on the ground motion,which should be considered in selecting project sites and seismic design.
【Fund】： 中国地震局地震科技星火计划项目(XH15067Y);; 国家自然科学基金项目(51508096 41172293);; 中央高校基本科研业务专项资金(ZY20140206)资助
【CateGory Index】： P315.9
【CateGory Index】： P315.9