2016年新西兰凯库拉M_w 7.8级地震中场地效应分析

Analysis on site effects in the 2016 M_w 7. 8 Kaikoura earthquake sequence in New Zealand

为研究2016年新西兰凯库拉M_w7. 8级地震序列中的局部场地效应,采用参数化广义反演方法分离了126个台站在148个地震中获取的2445组记录的震源、传播路径和场地三项因素,得出了126个台站的场地反应函数,重点分析了基督城地区的19个台站和惠灵顿地区的14个台站的场地效应,基于张力样条插值法分别建立两个城市在0. 5～3. 0Hz频段的平均场地放大分布图。结果表明:场地放大受地质和岩土特性的影响显著,软土场地卓越频率低,低频段场地放大更显著而高频段则相对较弱,平原地区场地放大高于山区,沉积层较厚地区的场地放大效应更显著。这些现象很好地解释了地震动和震害的区域性差异,是完善抗震设计理论的有力依据。

In order to investigate the site effects in the 2016 M_w 7. 8 Kaikoura earthquake sequence in New Zealand,the generalized inversion technique was used to derive three factors of ground motions including source characteristics,site effects,and path attenuations. Totally 2445 strong-motion recordings obtained at 126 stations in 148 earthquakes were used in the inversion. The site effect functions of 126 stations were obtained,19 stations in Christchurch and 14 stations in Wellington area were selective analysis,and the tension spline interpolation method was utilized to derive the contour map of the average site amplification over the frequencies of 0. 5 ~ 3. 0 Hz in these two areas. The results show that: site amplification exhibits strong correlation with the geological and geotechnical characterization;lower predominant frequency is observed at the site with softer soil,and the amplitude of site amplification is larger at the low-frequency band but smaller at the high-frequency band;larger site response is observed in the mountainous area than in the plain area,and thicker soil deposit larger site amplification. These results explain well the regional differences of ground motion and earthquake damage observed in this earthquake,and could support for the improvement of seismic design theory.