The largest tsunami are generated by seafloor uplift resulting from rupture of offshore subduction-zone megathrusts. The rupture of the shallowest part of a megathrust often produces unexpected outsize tsunami relative to their seismic magnitude. These are so called ‘tsunami earthquakes’, which are difficult to identify rapidly using the current tsunami warning systems, even though they produce some of the deadliest tsunami. We here introduce a new method to evaluate the tsunami risk by measuring ionospheric total electron content (TEC). We examine two Mw 7.8 earthquakes (one is a tsunami earthquake and the other is not) generated in 2010 by the Sunda megathrust, offshore Sumatra, to demonstrate for the first time that observations of ionospheric sounding from Global Positioning Systems (GPS) can be used to evaluate the tsunamigenic potential of earthquakes as early as eight minutes after the mainshock.
One Sentence Summary: Ionospheric perturbations resulting from large earthquakes can provide additional information to tsunami warning systems on the tsunamigenic potential of the event, as early as eight minutes following rupture initiation.