2014年鲁甸地震龙头山镇盆地共振效应研究

Study on the basin resonance effect in Longtoushan Town during the 2014 Ludian earthquake

2014年的云南鲁甸县M W 6.1级地震中,位于震中的龙头山镇遭受了严重的破坏,烈度达IX度。文中基于钻孔和地形资料建立的二维场地模型,并利用显式有限元方法分析了SV波作用下场地放大效应。模型由一个狭长浅盆地和位于其下方由强风化白云质灰岩构成的深盆地组成。研究表明,当仅考虑狭长浅盆地或一维土层模型时,龙头山镇结构倒塌和严重破坏区域地震动放大与该区域的台站53LLT观测的放大频带差别甚大。考虑深盆地的影响时,这一区域的振动以自振频率为2.2 Hz的二维盆地共振为主,共振频率与台站处观测到的放大频带更为接近,共振显著地放大了该区域的地震动,增长了地震动持续时间。盆地共振效应可能是导致该区域结构倒塌和严重破坏的一个主要原因。

During the 2014 Ludian earthquak(M W 6.1),the Longtoushan town in Ludian county suffered severe damage and the earthquake intensity reached IX degrees.In this paper,the site effect under input SV waves is studied using a two-dimension model established based on boreholes and topography data and by the explicit finite element method.The two-dimension model consist of a narrow shallow basin a deep basin with depth formed by strongly weathered dolomite limestone under the shallow basin.The results show that when only considered the narrow shallow basin or a one-dimensional soil layer model,the amplification frequency band of strong motions in the collapse and severe damage area of Longtongshan town is greatly different from the observed at the station 53LLT in this region.When considered the deep basin,the strong motions in this region are mainly consist of two-dimensional basin resonance with resonant frequency of 2.2 Hz,which is closer to the amplified band observed at the station 53LLT.The basin resonance significantly amplifies the ground motion in the collapse and severe damage area and increased the ground motion time.The basin resonance effect may be a major cause of structural collapse and severe damage in the region.