Abstract On 20 January 2024, a deep‐focus earthquake (Mw 6.6, depth 607 km) struck near Tarauacá, Brazil, within the subducted South America Nazca Plate. Although it produced no surface damage, the event generated clear co‐seismic ionospheric disturbances (CSIDs) detectable in GNSS‐based Total Electron Content (TEC) data from the Brazilian RBMC network. The disturbances appeared as “N” and inverted “N” waveforms in the slant TEC and emerged 8–13 min after the mainshock, with a maximum dTEC of 0.08 TECU, propagating radially at ∼880 92 m/s. To examine the physical origin of these signatures, we used an acoustic‐gravity wave model that takes the ground vertical velocity as input and simulates the accompanying CIDs. The simulation successfully reproduced the observed key features of the CSIDs, confirming that the disturbances were driven by acoustic waves launched by ground vibrations. Despite the earthquake's large depth, three factors appear to have enhanced CSID observability: ionospheric pierce points with elevation angles below , daytime ionospheric conditions at 16:00 LT, and the event's equatorial location. Spectral analysis showed dominant frequencies of 3.80–4.84 mHz, characteristic of infrasonic‐acoustic waves generated by earthquakes according to previous studies. This study presents the first documented CSIDs associated with an earthquake in the Brazilian sector and demonstrates that even deep‐focus earthquakes can produce measurable ionospheric responses when observational geometry and background conditions are favorable. The combined TEC analysis and modeling provide new insights into solid Earth–ionosphere coupling and highlight the use of GNSS‐based monitoring in seismic studies.
Adebayo et al. (2026) studied this question.