岷县漳县6.6级地震黄土场地放大效应地脉动测试研究
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摘要
2013年7月22日甘肃岷县漳县MS6.6级地震在极震区出现了黄土场地放大效应,为了从理论上解释黄土场地放大效应的原理,本文利用地脉动测试了极震区2个典型的黄土场地进行研究。结果发现:在黄土覆盖地区场地卓越频率特征显著,即在同一区域内山顶卓越频率较低,集中在1～2Hz,山沟卓越频率较高,集中在3～6Hz;同时,黄土场地随着高程的增加表现为厚黄土分布特征,其场地卓越频率在1.3～1.8Hz,与地震观测波的卓越频率1.0Hz接近,呈现出较明显的场地放大效应。结果与实际受灾情况相符。
An MS6.6 earthquake occurred on July 22,2013,in Minxian-Zhangxian,Gansu province,and the amplification effect of the loess site appeared in meizoseismical area.To explain the principle of amplification effect of loess site in theory,we measured and researched two typical loess sites by using microtremor measurement.The results show that,the damage of adobe house is more serious on the summit than on the gully.On the summit the damage of adobe house is serious and there are even entire collapses,but on the gully there are cracks and not collapse of adobe house.The intensity difference between the summit and gully is intensity Ⅰ ～ Ⅱ,which shows obvious amplification effect of the massif.In the paper,we have made contrastive study of the predominant frequency of microtremor measurement by choosing two typical areas of the obvious amplification effect of loess site at the meizoseismal area(intensity 8),which are Yongxing village and Daleng village,Majiagou village and Xinglin village in Meichuan town,Minxian County.At Yongxing village and Majiagou village,the damage of adobe house is serious and there are entire collapses.However,at Daleng village and Xinglin village,there are cracks and not collapse of the same adobe house.The earth pulsation has rich geophysics information,which is aggregation of body wave and surface wave.In the paper,the principle,test method and causes of ground microtremors are introduced.According to engineering examples,the determination for the predominant period of a site is described,moreover,its application in evaluation for the category of the site and soil and the effect of different site conditions on the characteristics of frequency spectrum are analyzed.The results show that the thick soil and thin soil structure obviously affect the frequency spectra of the ground microtremors,and there are corresponding relationships between them.The research results show:the characteristic of predominant frequency of the site is obvious in the covered loess area,in which the predominant frequency is lower on the summit than on the gully,the range of which is 1～2Hz and 3～6Hz respectively;Meanwhile,with the increase of the altitude of the loess site,which shows the distribution characteristic of thick loess,the range of the site predominant frequency is 1.3～1.8Hz,which is similar to the predominant frequency 1 Hz of earthquake observation wave and shows obvious amplification effect of the site,which is the same with the actual damage fact.
An MS6.6 earthquake occurred on July 22,2013,in Minxian-Zhangxian,Gansu province,and the amplification effect of the loess site appeared in meizoseismical area.To explain the principle of amplification effect of loess site in theory,we measured and researched two typical loess sites by using microtremor measurement.The results show that,the damage of adobe house is more serious on the summit than on the gully.On the summit the damage of adobe house is serious and there are even entire collapses,but on the gully there are cracks and not collapse of adobe house.The intensity difference between the summit and gully is intensity Ⅰ ～ Ⅱ,which shows obvious amplification effect of the massif.In the paper,we have made contrastive study of the predominant frequency of microtremor measurement by choosing two typical areas of the obvious amplification effect of loess site at the meizoseismal area(intensity 8),which are Yongxing village and Daleng village,Majiagou village and Xinglin village in Meichuan town,Minxian County.At Yongxing village and Majiagou village,the damage of adobe house is serious and there are entire collapses.However,at Daleng village and Xinglin village,there are cracks and not collapse of the same adobe house.The earth pulsation has rich geophysics information,which is aggregation of body wave and surface wave.In the paper,the principle,test method and causes of ground microtremors are introduced.According to engineering examples,the determination for the predominant period of a site is described,moreover,its application in evaluation for the category of the site and soil and the effect of different site conditions on the characteristics of frequency spectrum are analyzed.The results show that the thick soil and thin soil structure obviously affect the frequency spectra of the ground microtremors,and there are corresponding relationships between them.The research results show:the characteristic of predominant frequency of the site is obvious in the covered loess area,in which the predominant frequency is lower on the summit than on the gully,the range of which is 1～2Hz and 3～6Hz respectively;Meanwhile,with the increase of the altitude of the loess site,which shows the distribution characteristic of thick loess,the range of the site predominant frequency is 1.3～1.8Hz,which is similar to the predominant frequency 1 Hz of earthquake observation wave and shows obvious amplification effect of the site,which is the same with the actual damage fact.
引文
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[2]Yabe T,Xiao Feng,Yuki Taka,et al.The Coast-rained Interpolition Profile Method for Multiphase Analysis[J].J.Comput.Phys.,2001,169:556593.
[3]师黎静,陶夏新,赵纪生.地脉动台阵方法的有效分析[J].岩土力学与工程学报,2006,25(8):1683-1690.SHI Li-jing,TAO Xia-xin,ZHAO Ji-sheng.Validation of Microtremors Array Method[J].Chinese Journal of Geothechnical Engineering,2006,25(8):1683-1690.(in Chinese)
[4]李智玲.表层微动的基本原理及在抗震作用中的作用[M].北京:地震出版社,1991:198-202.LI Zhi-lin.Function in Aseismic Effect andFundamental Principle of Surface Microseism[M].Beijing:Earthquake Publishing House,1991:198-202.(in Chinese)
[5]Seekins L,Wennerberg L,Mwrgherinti,et al.Siteamplification at Five Location in San Francisco,California,A Comparison of S-waves,Codas and Microtremors[J].Bull.Seism.Soc.Am.,1996,86:627-635.
[6]上海市地质调查研究院.上海地球物理勘探技术应用与发展[M].上海:上海科技出版社,2010:165-167.Shanghai Research Institute of Geological Survey.Application and Development of Geophysics Prospection Technique in Shanghai[M].Shanghai:Shanghai Technique Press,2010:165-167.(in Chinese)
[7]王振东.浅层地震勘探应用技术[M].北京:地质出版社,1988.WANG Zhen-dong.Applied Technique of Shallow Seismic Exploration[M].Beijing:Geological Publishing House,1988.(in Chinese)
[8]Sophia Hassiotis,Jeong Carrett D.Identification of Stiffness Reduction Using Natural Frequencies[J].Journal of Engineering Mechanic,1995,10:1106-1113.
[9]薄景山,李秀领,李山有.场地条件对地震动影响研究的若干进展[J].世界地震工程,2003,19(2):11-15.BO Jing-shan,LI Xiu-ling,LI Shan-you.Some Progress of Study on the Effect of Site Condition on Ground Motion[J].World Earthquake Engineering Geology,2003,19(2):11-15.(in Chinese)
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