Decoding multiple source signatures in coseismic ionospheric disturbances of the 2024 January Mw7.5 Noto-Peninsula earthquake, Central Japan

Abstract

Vertical crustal movements associated with large earthquakes excite various kinds of atmospheric waves. They propagate upward and often disturb ionosphere. Here, I report a case for the 2024 January 1 M_w7.5 earthquake that occurred in the northern tip of the Noto Peninsula, Central Japan, using a dense network of multi-GNSS receivers. A rectangular-shaped positive anomaly of ionospheric total electron content emerged ∼9 min after the mainshock. The initial sharp peak was composed of two acoustic wave pulses excited at the two ends of the fault spanning ∼100 km. It was followed by a series of smaller-amplitude broad peaks, the largest of which was possibly excited by a slow fault rupture near the NE edge of the fault ∼8 min after the mainshock. These signatures become large where the wavefronts overlap with those of medium-scale traveling ionospheric disturbances, suggesting possible enhancement of the coseismic signals by downward displacements of high electron density regions in the ionosphere.