Metropolitan Tokyo is subject to significant seismic hazards because it is located near a triple junction of tectonic plates and because it sits atop the soft and thick sediments of the Kanto sedimentary Basin. Numerical simulations of earthquake ground motions rely on accurate velocity models of the basin elastic and anelastic structure, which remains to be improved. Here, we leverage the density of permanent stations of the Metropolitan Seismic Observation network seismic network to construct a high-resolution radially anisotropic (V_SV ≠ V_SH) shear wave velocity model of the Kanto basin. We construct surface waves using ambient seismic noise cross correlations. In sedimentary structures, it is common for several surface-wave modes to arise and to couple in time, so we use local sub-arrays to extract the phase velocity of the fundamental mode and first overtone of Rayleigh and Love waves at short periods (1–7 s). We find that a strong and negative shear-wave anisotropy (−5%) is confined to the upper 300 m depth range, and a strong and positive anisotropy (+5%) at greater depths. We interpret them as a result of the vertical cracks from repeated earthquake damage and sediment stratigraphy in the Kanto Basin. Because anisotropy models are not routinely used in physics-based ground motion prediction, our study motivates the consideration of seismic anisotropy in sedimentary basins for the ground motion of future earthquakes.

中文翻译：

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关东沉积盆地明显的地震各向异性：使用密集阵列、环境噪声地震学和多模态表面波成像的案例研究

东京都面临着严重的地震灾害，因为它位于构造板块的三重交界处附近，并且位于关东沉积盆地的软而厚的沉积物之上。地震地震动的数值模拟依赖于盆地弹性和非弹性结构的精确速度模型，该模型仍有待改进。在这里，我们利用 Metropolitan Seismic Observation network 地震网络的永久台站的密度来构建高分辨率径向各向异性 ( V _SV  ≠  V _SH) 关东盆地的横波速度模型。我们使用环境地震噪声互相关构造表面波。在沉积构造中，常见的几种面波模式会同时出现并及时耦合，因此我们使用局部子阵列来提取短周期内瑞利波和洛夫波的基模和第一泛音的相速度（1 –7 秒）。我们发现强负横波各向异性（-5%）局限于上部 300 m 深度范围，而强正各向异性（+5%）则在更深的深度范围内。我们将它们解释为关东盆地反复地震破坏和沉积地层学造成的垂直裂缝。由于各向异性模型通常不用于基于物理的地震动预测，