基于台阵记录的土层山体场地效应分析  

Site effect of unconsolidated soil hill based on seismic array records

作　　者：卢育霞[1,2,3] 刘琨 王良[2] 魏来 李少华[1,2,3] 

机构地区：[1]中国地震局黄土地震工程重点实验室,中国兰州730000 [2]中国地震局兰州地震研究所,中国兰州730000 [3]甘肃省岩土防灾工程技术研究中心,中国兰州730000

出　　处：《地震学报》2017年第6期941-954,共14页Acta Seismologica Sinica

基　　金：中国地震局地震预测研究所兰州创新基地基本科研业务费项目(2015IESLZ05);国家自然科学基金(51248005)共同资助

摘　　要：选取2008年5月25日至8月7日期间由甘肃省文县上城山地形效应台阵获取的12次汶川地震余震事件(MS≥4.0),在分析其地震动基本参数的基础上,采用参考场地谱比(RSSR)法和水平-竖向谱比(HVSR)法,研究了不同地震作用下上城山地形台阵的场地效应.分析结果显示:随着高程和覆盖层的增加,记录台站地震动的PGA呈增大趋势,地震频谱形状由宽变窄;上城山台阵记录到的地震波在地形基阶频段(2—4 Hz)和浅部土层频段(7—9Hz)的幅值明显放大,RSSR曲线显示山顶NS向的土层频段谱比大于山体地形频段谱比;由于土层山体竖向地震动在中高频段放大,使得HVSR方法谱比结果在中高频段较RSSR方法所得结果明显偏低,而在山体基阶频段附近两种方法的谱比值接近.松散土层山体的台阵记录特征体现了地形和土层对地震动的联合作用,揭示了强震区起伏地形场地震害加重及地震滑坡集中发生的原因所在.Following the 2008 MS8.0 Wenchuan earthquake,a topographical array including four digital seismograph stations was installed along Shangcheng hill,Wenxian,Gansu Province,which is a piedmont diluvial terrace about 50-m high and made up of Quaternary silty clay and gravelly soil with thin layer of coarse sand.One of the stations was installed at a rock cave in northeastern Shangcheng hill,and the other three stations were respectively installed at the foot of the hill,hill slope and hill top.From May 25 to August 7,2008,a series of aftershocks of Wenchuan MS8.0 earthquake occurred,but only twelve events（MS≥4.0）were recorded at three of the four stations at least.In this study,seismic response of each station is evaluated as a function of frequency by reference site spectral ratio（RSSR）method and single-station horizontal to vertical spectral ratio（HVSR）based on all shear waves from the twelve earthquake events.The analyses lead to the conclusions that：（1） with the elevation climbing and soil thickening,the PGAs of the twelve events increase and the broadband seismic spectra gradually narrow to the characteristic frequency band;（2） dynamic amplification of Shangcheng hill occurs in both topographic characteristic frequency band（2--4 Hz）and shallow stratigraphic fundamental frequency band（7--9 Hz）in horizontal direction,while amplification caused by the soil stratigraphy near surface is comparatively more obvious than that by the topography in NS at hill top;（3） in medium-high frequency band,the spectral ratio from HVSR method is much lower than that from RSSR method due to the amplitude of seismic waves in vertical direction.The characteristics of seismic array records of the unconsolidated soil hill give expression to the combined effect of topography and soil stratigraphy,and reveal the reasons for the aggravation of structural damage and the concentration of seismic landslide on topographic site in strong ground motion zone.

关 键 词：台阵记录 地形-土层联合效应 参考场地谱比 水平-竖向谱比 地面运动 

分 类 号：P315.9[天文地球—地震学]