The city of Pohang in South Korea experienced substantial damage following the M_L 5.4 earthquake on 15 November 2017. Damage surveys immediately after the earthquake revealed significant spatial variations in damage intensity across the epicentral area. We collected ambient noise data (three‐component seismic data) from 124 locations in Pohang, covering a total area of 17 km × 20 km, and applied the horizontal‐to‐vertical spectral ratio technique to estimate the resonance frequency, amplification factor and vulnerability of the ground to seismic shaking. Spatial variations exhibited by these three parameters are strongly correlated and consistent with variations in local geology. By comparing the distribution of the ground vulnerability index (Kg) with the damage distribution (or intensity) documented by the Korea Meteorological Administration following the earthquake, we confirm that the site effect is the prevailing effect that influences damage intensity in this region. We also demonstrate that Kg is an efficient proxy for identifying relatively fragile zones during ground shaking: in areas with a reported damage intensity of VIII, the proportion of the area with Kg > 20 is as high as 78.2%. Given that the study area has experienced a recent moderate earthquake, with significant economic consequences, our new results and analytical techniques will provide valuable information for future urbanization projects.

中文翻译：

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从水平到垂直的光谱比得出的地面脆弱性：与2017年韩国浦项ML 5.4地震造成的破坏分布比较

浦项制铁在韩国的城市经历了以下几个重大损害中号_大号11月15日2017年损害调查5.4级地震地震发生后立刻显露跨越震中区损坏强度显著的空间变化。我们从浦项的124个地点收集了环境噪声数据（三分量地震数据），覆盖了17 km×20 km的总面积，并应用了水平-垂直频谱比技术来估计共振频率，放大系数和易损性。地震动。这三个参数所表现出的空间变化与当地地质的变化密切相关且一致。通过比较地面脆弱性指数（Kg），并根据大地震后韩国气象局记录的破坏分布（或强度），我们确认了场地效应是影响该地区破坏强度的主要效应。我们还证明，Kg是在地面震动过程中识别相对脆弱区域的有效代理：在报告的破坏强度为VIII的区域中，Kg > 20的区域比例高达78.2％。鉴于研究区域最近遭受了中度地震，并带来了严重的经济后果，我们的新结果和分析技术将为未来的城市化项目提供有价值的信息。