We derived a three-dimensional S-wave velocity model for the San-in area of southwest Japan to examine heterogeneous structures such as tectonic faults. Many earthquakes occur in this area, but much of the activity has been relatively recent, so the fault distribution has yet to be fully clarified. Here, we used continuous ambient noise data from a dense seismic network, deployed from November 2009 to extract Rayleigh and Love wave dispersion data between station pairs, and then applied a direct surface wave inversion to the phase velocities of each station pair to determine a three-dimensional S-wave velocity model. In the resulting model, faults and a previously unrecognized tectonic boundary appeared as low-velocity anomalies or velocity boundaries, and the velocity anomalies were also associated with many past earthquake hypocenters. These results contribute to our understanding of heterogeneous structures caused by recent tectonic motion and of possible future tectonic activity, such as intraplate earthquakes. Surface wave tomography using ambient noise recorded in dense seismic networks could also be applied in other parts of the world to reveal new heterogeneous geological structures (i.e., unrevealed tectonic faults) and could contribute to disaster mitigation.

中文翻译：

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使用由环境噪声表面波层析成像获得的 3D S 波速度结构识别日本西南部山阴地区的新生构造边界

我们推导出了日本西南部山阴地区的三维 S 波速度模型，以检查构造断层等异质结构。该地区发生了多次地震，但大部分活动都是相对较新的，因此断层分布尚未完全阐明。在这里，我们使用从 2009 年 11 月部署的密集地震网络中的连续环境噪声数据来提取台站对之间的瑞利和洛夫波频散数据，然后将直接表面波反演应用于每个台站对的相速度，以确定三个维 S 波速度模型。在得到的模型中，断层和以前未被认识的构造边界表现为低速异常或速度边界，速度异常也与许多过去的地震震源有关。这些结果有助于我们了解由最近的构造运动和未来可能发生的构造活动（例如板内地震）引起的异质结构。使用密集地震网络中记录的环境噪声的表面波层析成像也可应用于世界其他地区，以揭示新的异质地质结构（即未揭示的构造断层），并有助于减轻灾害。