基于HVSR的DONET1海底地震动场地效应研究

为基于谱比方法研究海底地震动场地效应，选取日本DONET1台网的20个海底台站2014—2021年记录的1634组地震数据，对其进行筛选和处理后，利用水平与竖向谱比（HVSR）方法考虑不同布设对海底5组节点台站（KMA、KMB、KMC、KMD、KME）谱比特征的影响。研究结果表明:KMA与KME节点台站具有相似的场地特征，KMB与KMD节点台站分散布置在2种场地，KMC节点台站场地与其他节点均不相似，这与长期地质调查结果相似；海底台站谱比曲线呈多峰值现象，其中KMB、KMC、KMD分组台站利用HVSR方法识别的主频变异性较高，KMA、KME分组台站主频较稳定；相同地形条件下，布设方式相同的海底台站谱比曲线随频率分布相似，海底复杂场地条件下，采用装沙沉底方式布置的台站识别场地条件时出现偏差；海底复杂因素对掩埋沉箱方式布设的台站谱比曲线的影响主要集中在频率<5 Hz的低频处；海底复杂因素对未埋入海底台站谱比曲线的影响主要集中在频率为5—10 Hz的高频处。研究结果可为海底地震动场地效应研究提供参考。

The Study of Site Effect of DONET1 Offshore Ground Motions Based on HVSR

For study the site effect, a group of 20 stations in the DONET1 network, which was used for earthquake and tsunami warning, have been deployed on the seafloor as large earthquakes of magnitude continue occur in offshore around the world and cause serious secondary disasters. In this paper, based on the 1634 group offshore ground motion data recorded by 20 offshore stations (4 stations in a group named KMA, KMB, KMC, KMD, KME) in the DONET1 network, the spectral ratio characteristics of offshore stations were studied by HVSR method after data processing. The results shows: (1) The stations in the KMA and KME groups may be located in the same geological state on the seafloor, and the stations in the KMB and KMD groups may be distributed in two different geological states on the seafloor. The stations in the KMC group are different from those in the previous geological state, which is similar to the results of long-term geological survey. (2) The spectral ratio curves with multiple peaks, and with large variation coefficient of dominant frequency for offshore stations. (3) The HVSR curves of offshore stations with the same buried conditions and topographic condition have good consistency. In complex seafloor, site buried with sand conditions is deviated due to the influence of caisson sand filling when identification of site conditions use spectral ratio method. The influence of complex seafloor factors on the HVSR curve of stations with buried caisson is mainly at the low frequency of less than 5 Hz.The influence of complex seafloor factors on the HVSR curves of unburied offshore stations is mainly concentrated on the high frequency range of 5—10 Hz.The results can provide a reference for the study of the site effect of offshore ground motion.