In this study, we conducted a series of microtremor surveys to understand the contribution of soil amplifications to the heavy structural damage of wooden houses in downtown Mashiki, Kumamoto, Japan, during the 2016 Kumamoto earthquake. We analyzed the microtremor horizontal‐to‐vertical spectral ratios (MHVRs) of each observation site. A few previous studies have demonstrated the applicability of the earthquake horizontal‐to‐vertical spectral ratios (EHVRs) to identify velocity structures. Therefore, we transformed the MHVRs into pseudo‐EHVRs (pEHVRs) using the EHVR‐to‐MHVR ratio (EMR) method. We identified the velocity structures in Mashiki, according to the diffuse field concept (DFC) for earthquake, using the pEHVRs. We also estimated the seismological bedrock motions during the mainshock based on the DFC. We then performed the seismic ground response analyses of subsurface structures, using a 1D linear analysis and an equivalent linear analysis (ELA). Finally, we obtained the distribution maps of peak ground acceleration (PGA) and peak ground velocity (PGV) for Mashiki town. We obtained the following results: (a) the thickness of the soft sediment under the southwestern part of Mashiki is deeper than that under the northeastern part; (b) the thickness of the soft sediments was a primary cause of the heavy damage to buildings of Mashiki; (c) the ground motions estimated by the ELA method seemed to be close to the observed seismic ground motions in Mashiki; (d) the distribution of the estimated PGV in Mashiki had a close relationship with the damage ratio distribution of buildings; (e) the EMR method, along with the DFC for earthquake and the 1D ELA method, successfully simulated the strong motions that occurred during the mainshock in Mashiki.

中文翻译：

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基于微震水平与垂直光谱比的熊本町Mashiki镇浅表层结构的场地效应分析

在这项研究中，我们进行了一系列的微震调查，以了解在2016年熊本地震期间，土壤扩增对日本熊本市Mashiki市中心木屋严重的结构破坏的贡献。我们分析了每个观察点的微震水平与垂直光谱之比（MHVR）。先前的一些研究已经证明了地震水平-垂直频谱比（EHVR）在识别速度结构方面的适用性。因此，我们使用EHVR与MHVR的比率（EMR）方法将MHVR转换为伪EHVR（pEHVR）。我们根据地震的扩散场概念（DFC），使用pEHVR确定了Mashiki的速度结构。我们还基于DFC估算了主震期间的地震基岩运动。然后，我们使用一维线性分析和等效线性分析（ELA）对地下结构进行了地震地面响应分析。最后，我们获得了Mashiki镇的峰值地面加速度（PGA）和峰值地面速度（PGV）的分布图。我们得到了以下结果：（a）在Mashiki西南部的软沉积物的厚度比在东北部的软沉积物的厚度大；（b）软质沉积物的厚度是造成Mashiki建筑物严重受损的主要原因；（c）用ELA方法估算的地震动似乎与在Mashiki中观察到的地震地震动接近；（d）Mashiki中估计的PGV的分布与建筑物的损坏率分布有密切关系；（e）EMR方法，