Ionospheric TEC changes immediately before and after the 2010 Mentawai earthquake, Indonesia

The October 25, 2010, Mentawai earthquake (Mw 7.9) occurred off the coast of southern Sumatra. He and Heki (2017 JGR) confirmed Mw dependence of the properties of the TEC (Total Electron Content) anomalies immediately before 18 earthquakes (Mw 7.2-9.2) using GNSS (Global Navigation Satellite System) data. Here we analyze the vertical TEC (VTEC) data from the SuGAR (Sumatra GPS Array) network before and after the Mentawai earthquake to confirm if the VTEC anomaly before this earthquake follows the same scaling laws. These laws suggest that a small VTEC increase appears ~20 minutes before the earthquake, and the anomaly would reach ~2 % of the background value. This was exactly the case for the VTEC changes immediately before the Mentawai earthquake. Considering the hypothetical mechanism of such TEC anomalies (Muafiry & Heki, JGR 2020), the anomaly is expected to emerge to the north of the hypocenter, and this was also the case.

Upward propagating air waves excited at the surface by coseismic crustal uplift/subsidence make ionospheric disturbances in 8-10 minutes (acoustic wave) and >40 minutes (internal gravity wave) after earthquakes. We also analyzed such coseismic ionospheric disturbance of the 2010 Mentawai earthquake. We found the gravity wave signatures were very clear, which is unusual for an earthquake of this size. The Mentawai earthquake is a typical tsunami earthquake, and its slower fault slip than regular earthquakes might have caused large internal gravity wave signatures relative to the acoustic wave signature.