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Title:: Determining the Site Effects of the 2014 Ludian M_S6.5 Earthquake Using HVSR Microtremor Method

Author(s):: LIN Guoliang; ZHANG Qian; CUI Jianwen; ZHAO Kun; YANG Liwei; (Yunnan Earthquake Agenoy,Kunming 650224,Yunnan,China)

Keywords:: Longtoushan; microtremor; spectral ratio; site effect; Ludian earthquake

摘要:: 2014年鲁甸6.5级地震导致龙头山镇位于洪积扇上的大量房屋倒塌,而位于河流阶地上的房屋破坏相对较轻。为找出造成该震害差异的原因,在龙头山镇布设间距50～200 m的高密度观测台阵进行连续地脉动观测,采用HVSR谱比法来研究该地区的场地地震响应,确定场地的卓越频率和放大系数。结果表明:HVSR谱比结果与钻孔资料给出的结果较为一致,位于洪积扇上的场地HVSR峰值频率介于1.5～5.0 Hz,河流阶地上的峰值频率多介于6.0～10 Hz,卓越频率值相对较小(5 Hz以下)的场地与地震中破坏最严重的区域较为相符。

Abstract:: The M_S6.5 earthquake occurred in Ludian County of Yunnan Province,2014 caused severe damage to a large number of buildings on the pluvial fan,resulting in seriously personnel casualty and the economic loss.However,the damage of buildings on the river terrace was relatively lightly.Therefore,to find out the reason for this differences of damage level,we deployed high density observation array with the interval of 50-200m in the Longtoushan Town to measure microtremor continuously,and used the HVSR(Horizontal to vertical spectral ratio)method to get the predominant frequency and amplification factor of the site to study the site earthquake effect.We found out that the result of HVSR method was consistent with the outcomes from drill data.The HVSR predominant frequencies on the pluvial fan were between 1.5～5.0 Hz,while the ones on the river terrace were between 6.0～10 Hz,and the sites with relatively small predominant frequencies(less than 5 Hz)were highly consistent with the worst damaged area.