Assessing the Rayleigh Surface Wave Characteristics From Ionospheric Observations During the Mw 9.1 Tohoku‐Oki Earthquake

Abstract

This study re-examines ionospheric responses to the Mw 9.1 Tohoku-Oki earthquake of 11 March 2011, using data from nearly 1200 GEONET GPS receivers distributed across Japan. The focus is on co-seismic ionospheric perturbations (CIP) induced by Rayleigh surface waves, referred to here as Rayleigh wave-generated co-seismic ionospheric perturbations (RAW-CIP). Significant RAW-CIP signatures were observed in Total Electron Content (TEC) time series from multiple GPS satellites. From the spatiotemporal evolution of these perturbations, their propagation velocities and amplitude variations were estimated. Concurrently, seismic data from 64 broadband stations across Japan were analyzed to derive period-dependent group velocities using dispersion curve analysis and amplitudes of Rayleigh surface waves. A comparative assessment revealed that Rayleigh waves with periods between 10 and 50 s were most effective in coupling with the ionosphere. The average propagation velocities of these surface waves showed good agreement with those of RAW-CIP, and their amplitude variations also correlated well. These findings highlight that low-frequency Rayleigh surface waves can be reliably characterized using ionospheric observations, as they effectively manifest in the ionosphere.