土层特性变异性对场地传递函数的影响

Influence of Variability of Soil Characteristics on Site Transfer Function

选取日本Kik-Net强震数据库中软(FKSH14)、硬(FKSH12)两类场地,建立场地概率模型。应用Monte Carlo技术随机生成50组场地剖面,分别计算场地的传递函数STF及STF标准差,讨论场地土层厚度、剪切波速,以及两者组合工况对场地传递函数的标准差的影响。结果显示:对于硬土场地,场地特征频率标准差相对于软土场地较大,且剪切波速变异性的影响略大于土层厚度变异性的,两者组合工况的影响最大;而对于软土场地,土层厚度、剪切波速变化工况下,场地特征频率的标准差相当,略低于两者组合工况;对于软、硬两类场地,土层厚度与剪切波速两者组合工况下的STF标准差略大于单一量变化工况,但3种工况下的场地STF标准差相差不明显;场地STF标准差在场地自振频率附近的频率段取值较大,极值点与场地STF的极值点相对应;基于实际地震记录的场地传递函数标准差高于模拟的结果,但是两者极值点对应的频率范围吻合。

Two Kik-Net seismic strong-motion stations, which are installed on hard ground （FK- SH12） and soft site （FKSH14） in Japan, were selected and the corresponding probability site models were established. Fifty site soil profiles were randomly generated for hard ground and soft site via Monte Carlo simulation, and then the site transfer functions（STFs） were calculated as well their standard deviations, respectively. The standard deviations of STFs were discussed in three cases, i.e. , varying subsoil thicknesses （Case I）, varying subsoil shear wave velocity sim- ultaneously （Case II）, and varying subsoil thickness and shear wave velocity simultaneously （Case III）. The results show that the standard deviations of site characteristic frequencies of hard ground are overall larger than those of soft site; the standard deviation of site characteristic fre- quency of hard ground is the smallest in Case I, followed by Case II, while in Case III the stand- ard deviation of site characteristic frequency is the largest;the standard deviations of soft site characteristic frequencies in case I and Case II are comparative but weakly smaller than that in Case III; the standard deviations of STFs in case III for soft site and hard ground are slightly lar- ger than those in Case I and Case II, but the standard deviations in the three cases are not consid- erably different; the standard deviations of STF are fairly large in the vicinity of site predominant frequencies with peak values corresponding to peak values of relevant mean STF; the STF stand- ard deviations based on real seismic records are particularly larger than the simulated, while the frequencies at the peak value ranges are consistently matched.