2022年9月5日泸定县磨西发生Ms6.8强烈地震,震中距离磨西镇约7 km,此次强震导致磨西台地边缘产生了大量浅表滑坡灾害.本文通过调查、无人机测量、环境噪声测试及地形多谱放大分析(Simulator for mapped seismic response using a hybrid model,SiSeRHMap)等,对磨西台地地震效应进行研究.调查表明:(1)台地边缘发育同震滑坡90处,集中在台地东、西两侧边缘,以浅表层小型滑塌为主,破坏深度2～5 m,地形坡度多在50°以上.(2)33处环境噪声水平与竖向谱比(H/V)分析揭示,场地卓越频率以1～4 Hz低频为主,谱比放大系数随着离台地边缘距离增加先增大后减小,离台地边缘距离小于20 m的范围场地大多具有方向效应,优势方向趋近垂直临空面走向.(3)综合地形放大计算分析表明,磨西台地边缘破坏与其场地地形共振效应密切相关,在台地东、西两侧的坡度越大、地形越凸出、土体越松软的区域场地地震响应越强烈,易破坏.本研究对磨西台地灾后重建及抗震设防具有重要应用价值及理论意义.
Seismic Response of Moxi Terrace Induced by the Ms 6.8 Luding Earthquake on September 5th,2022,in Luding County,Sichuan,China
On September 5,2022,a severe earthquake of Ms6.8 occurred in Luding county,China,with its epicenter approximately 7 km away from Moxi Town.This earthquake triggered numerous shallow landslides along the edges of Moxi Terrace,a glacial landform constituted by glacial till,alluvial and colluvial sediments,and remnants of ancient debris flows.In this paper,the seismic effects on Moxi Terrace were investigated through surveys,unmanned aerial vehicle(UAV)measurements,ambient noise testing and multispectral topographic amplification analysis by SiSeRHMap methodology(simulator for mapped seismic response using a hybrid model).(1)A total of 90 co-seismic landslides were identified along the edges of the Terrace,primarily developed on the eastern and western flanks,featuring small-scale shallow collapses with 2-5 meters in depths,and slopes exceeding 50°.(2)By an examination of ambient noise levels and vertical-to-horizontal spectral ratios(H/V)at 33 sites on the Terrace,it found that the predominant frequencies of site were primarily low frequencies of 1-4 Hz.The amplification factor of H/V spectral ratio initially increased and then decreased with distance increasing from the Terrace edge.Most sites within 20 meters of the Terrace edge exhibited directional effects,with the dominant direction approaching to the perpendicular of the air face of the Terrace.(3)By SiSeRHMap method,it suggested that the collapses occurred on the edges of Moxi Terrace were consistent with resonance effect of site terrain.In areas with steeper slopes,more prominent topography,and softer soil on the eastern and western flanks of the Terrace,the seismic responses were more intense and prone to failure.This study has practical value and theoretical significance for post-disaster reconstruction and seismic fortification of Moxi Terrace.
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