2025-07-01 北海道大学
能登半島地震によるP波の放射領域：（左）0.03-0.3Hz、（右）0.1-1.0Hz。破壊継続時間全体で累積したP波の放射領域を示している。（5秒間毎のスナップショットは図2を参照。）
＜関連情報＞
- https://www.hokudai.ac.jp/news/2025/07/2024pd.html
- https://www.hokudai.ac.jp/news/pdf/250701_pr.pdf
- https://www.sciencedirect.com/science/article/abs/pii/S0012821X25003073?via%3Dihub
遠地P波のバックプロジェクション解析による2024年能登半島地震の周波数依存した地震波放射過程 Frequency-dependent seismic radiation process of the 2024 Noto Peninsula earthquake from teleseismic P-wave back-projection
Kotaro Tarumi, Kazunori Yoshizawa
Earth and Planetary Science Letters Available online: 20 June 2025
DOI:https://doi.org/10.1016/j.epsl.2025.119509
Highlights
- The source process of the 2024 Noto earthquake is imaged by P-wave back-projection.
- Multi-frequency back-projection images reveal complex fault rupture sequences.
- Main source rupture propagates bilaterally toward inland and offshore regions.
- High-frequency P-waves are radiated before the rapid main rupture propagation.
- Frequency-dependent P-wave radiations reflect the effects of complex fault geometry.
Abstract
A large devastating earthquake of Mw 7.5 struck the Noto Peninsula, Japan, on January 1st, 2024. Persistent seismic swarms have preceded the main rupture around the hypocenter since 2020, likely driven by crustal fluids migrating upward from the lower crust. In this study, we investigated the frequency-dependent seismic radiation process using multi-frequency teleseismic P-wave back projection. The resulting source process reveals complex frequency-dependent behavior, which can be divided into four episodes. The initial episode lasts 15–20 s, characterized by high-frequency energy preceding low-frequency radiation. The second episode is marked by intense high-frequency P-wave emission with the absence of low-frequency signals. Then, intensive low-frequency P-waves are radiated from the source region, with ruptures propagating bilaterally from the hypocentral area toward the southwestern inland (third episode) and northeastern offshore (fourth episode) regions. The fluid-rich condition near the hypocenter likely plays an important role in controlling fault rupture, contributing to the observed complex rupture processes. The intricate fault geometry around the source region may have also contributed to the characteristic frequency-dependence of P-wave radiation during this earthquake.
