Ionospheric changes immediately before the 2025 March 28 Mw7.7 Myanmar earthquake

We studied ionospheric changes associated with the 2025 March 28 Myanmar earthquake (Mw7.7) using global navigation satellite system receivers to measure ionospheric electrons, as a part of the project to predict earthquake precursors. The total electron contents above the fault changed their trends ~36 minutes before the earthquake, with the positive anomaly reaching ~1 per cent of the background. These quantities fit well with the past ~20 cases despite relatively large day-to-day variability due to high geomagnetic activities. The positive anomaly was sandwiched by two negative anomalies to the north and the south, suggesting within-ionosphere electron transportation along geomagnetic fields possibly driven by surface positive electric charges released from the fault.