Frequency-dependent seismic radiation process of the 2024 Noto Peninsula earthquake from teleseismic P-wave back-projection

A large devastating earthquake of Mw 7.5 struck the Noto Peninsula, Japan, on January 1st, 2024. Persistent seismic swarms have continued 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.