选取日本熊本MW7.0地震断层距小于200 km的82个近场KiK-net台站记录到的三分量记录数据进行基线校正后,获得近场地面运动水平向的峰值加速度PGA、峰值速度PGV及周期为0.2,1,2,3,5和10s的加速度反应谱数据,并与美国NGA-West2的地震动预测模型相比较,研究熊本地震地表和井下地震动峰值及反应谱的衰减特征,通过比较KiK-net台站地表与井下记录结果,探讨浅层场地放大效应的影响.研究结果表明:①对于井下观测结果,NGA-West2的地震动模型对PGA和短周期0.2s的反应谱的预测值与井下观测值相比整体偏高,而PGV和较长周期地震动(如1,2和3s的反应谱)的预测值与井下观测值较为吻合;②地表观测记录的PGA,PGV和周期为0.2-3 s的反应谱残差整体上随vS30对数值的增大呈线性减小的趋势,而周期为5s和10s的长周期部分,其场地效应的影响很小;③相对于井下记录,地表记录的地震动PGA,PGV和周期为0.2,1和2s的反应谱有明显的放大,这种放大作用随浅层场地剪切波速的增大而减小;周期为3,5和10s时长周期地震动的放大效应很小.%We used the records of 82 near-field strong motion stations (KiK-net),which are within 200 km to the rupture fault of the Kumamoto MW7.0 earthquake,as database to derive near-field horizontal peak ground acceleration PGA,peak ground velocity PGV and spectra acceleration (period T=0.2,1,2,3,5,10 s),after baseline correction we further compared them with the NGA-West2 ground motion model predictions.We investigated the attenuation and residuals distribution characteristics of these intensity measures (IMs),and shallow siteamplification effects by comparing surface and borehole ground motion records.The following conclusions can be drawn from our study:In the boreholes,NGA-West2 predictions are obviously greater than observations of PGA and T=0.2 s spectra acceleration,but close to the measured value in long-period IMs (spectra acceleration with T=1,2,3 s) and PGV.On surface,the residuals of observed PGV and T=0.2-3 s spectra acceleration show linear decrease tendency with the increase of vS30,but the site effects affect little on the long-period spectra acceleration.Surface records are greater than borehole in PGA,PGV and T=0.2,1,2 s spectra acceleration,and the amplification effects decrease with the increase of shallow site shear velocity;whereas the site amplification has little effects on the long-period spectra acceleration with T=3,5,10s.
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