基于实测记录分析场地因素对海底地震动特性影响

Effect of site factors on the characteristics of offshore ground motions based on strong motion observation records

目前基于海底实测记录的分析发现海底与陆地地震动特性存在明显差异,但难以进一步确定海底地震动特性的影响因素。在以往研究的基础上对比同次地震中相邻海底台站间地震动特性的差异,并分析造成差异的原因。以日本K-NET地震台网中6个海底强震台站及其相邻不同场地条件陆地台站监测的8次强震记录为研究对象,通过分析强震记录的峰值加速度、水平放大系数谱、竖向与水平反应谱的比谱等,对比分析不同海底台站地震动的特性,以及海底台站与相邻不同场地条件陆地台站地震动特性的差别。研究发现:(1)海底与陆地竖向地震动存在明显差异;(2)不同海底台站间地震动特性亦存在较大差异和明显的规律性,海底场地条件、地形等场地因素对海底地震动特性的影响较大;(3)海底水平向地震动反应谱的特征周期较大,谱特性介于陆地中硬土与软土场地间。

Present research on strong motion records show that the characteristics of offshore ground motions are obviously different from those of onshore ground motions,but it is difficult to further determine the influencing factors of offshore ground motions.Based on previous research,the differences of ground motion characteristics between adjacent offshore stations during the same earthquake were compared and the reasons were analyzed.The strong motion records from six offshore stations and adjacent onshore stations with different site conditions were selected in the K-NET of Japan.The V/H PGA ratio,amplification factor spectrum,and V/H spectral ratio of strong motion records from different stations were analyzed,then the ground motion characteristics from six offshore stations and the difference of ground motion characteristics between offshore and onshore stations with different site conditions were studied.The results showed that:(1)there are obvious differences in offshore and onshore vertical ground motions;(2)the ground motion characteristics of different offshore stations,which are greatly influenced by site factors,also have great difference and obvious regularity;(3)the characteristic period of offshore horizontal seismic response spectrum is large,and the spectral curve is between those of medium hard-soil and soft-soil sites.