Ambient noise cross-correlation functions and three-dimensional S-wave velocity structure in the Noto Peninsula, Japan

The three-year-lasting earthquake swarm in the Noto Peninsula, Japan, led to the 2024 Noto earthquake (moment magnitude 7.5). To reveal structural controls on the swarm evolution and the large earthquake generation, we imaged the three-dimensional S-wave velocity structure beneath the Noto Peninsula using ambient noise surface wave tomography with dense seismic observations. This dataset provides the cross-correlation functions of the densely observed ambient seismic noise and the estimated three-dimensional S-wave velocity structure model. We computed the multicomponent cross-correlation functions for the pairs of 22 seismic stations (composed of 12 seismic nodes and 10 short-period permanent stations). The observation data spanned 32 days, from October to November 2023. The cross-correlation functions in the vertical-vertical, vertical-radial, radial-radial, and transverse-transverse components yielded the estimates of dispersion curves of Rayleigh and Love waves. The dispersion curves of the fundamental-mode Rayleigh and Love waves in the frequency range of 0.10–0.45 Hz were used to estimate isotropic S-wave velocity structure via two-dimensional phase velocity tomography and a series of local 1D inversions. Our results show a high-velocity body collocated with the major slip zone of the 2024 Noto earthquake, a region the preceding swarm avoided. This observation strongly suggests that the structural heterogeneity beneath the Noto Peninsula controlled the swarm evolution and the generation of the 2024 Noto earthquake.

日本能登半岛持续三年的地震群引发了2024年能登地震（矩震级（moment magnitude）7.5）。为揭示该地震群演化与大震孕育的构造控制机制，本研究借助密集地震观测开展的环境噪声面波层析成像（ambient noise surface wave tomography）技术，对能登半岛下方的三维S波速度结构进行了成像。本数据集包含密集观测得到的环境地震噪声互相关函数（cross-correlation functions），以及反演获得的三维S波速度结构模型。研究针对22个地震台站（seismic stations）的台站对（包含12个地震节点（seismic nodes）与10个短周期固定台站（short-period permanent stations）），计算了多分量互相关函数。观测数据的时间跨度为2023年10月至11月，共计32天。通过垂直-垂直、垂直-径向、径向-径向以及横向-横向分量的互相关函数，研究获取了瑞利波（Rayleigh waves）与洛夫波（Love waves）的频散曲线（dispersion curves）。本研究选取0.10–0.45 Hz频率范围内的基阶瑞利波与洛夫波频散曲线，通过二维相速度层析成像（phase velocity tomography）与一系列局部一维反演，估算得到各向同性S波速度结构（isotropic S-wave velocity structure）。研究结果显示，一处高速体与2024年能登地震的主要滑动区域（slip zone）重合，而该区域恰好是前期地震群未波及的地带。这一观测结果有力表明，能登半岛下方的构造非均质性（structural heterogeneity）控制了地震群的演化与2024年能登地震的孕育过程。