Contribution of Ionospheric Sounding to the Study of Large Subduction Earthquakes, the Case of the Mw 7.8 Pedernales Earthquake (2016, Ecuador)

Large earthquakes (Mw > 6.5) in the shallow subduction zone are powerful sources of destructive tsunamis. The uplift at the source related to those events also triggers coseismic ionospheric disturbances (CIDs) that are routinely detected using Global Navigation Satellite Systems (GNSS) multi-frequency measurements. Developed over the last two decades, this novel observation method offers a unique view of the rupture history of subduction earthquakes, as it sounds the area directly above the rupture. In this presentation, we first review the historical research linking the seismic source characteristics to the CIDs observed using GNSS-derived Total Electron Content (TEC) measurements. We then report on CIDs associated with the Mw 7.8 Pedernales megathrust earthquake, April 2016 in Ecuador. Using a model based on acoustic ray tracing and ionospheric coupling, we simulate the observations and show that the best fitting model allows to localize the maximum of uplift and thus, the tsunami initiation zone consecutive to the offshore rupture at depth. Finally, we highlight how ionospheric measurements by multi-GNSS receivers can contribute to better and more rapidly assess the tsunamigenic potential of an underwater earthquake.