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Abstract:
Large and shallow earthquakes (minimum magnitude 6.5) generate distinctive ionospheric disturbances detectable using radio signals emitted by Global Navigation Satellite Systems (GNSS). In the recent years, the number of satellites has increased drastically, allowing a refined coverage of the Earth, including the earthquake-prone zones. The subduction zones (e.g. Japan, Indonesia, South America), where most tsunamigenic earthquakes occur, are poorly instrumented because located offshore, far from the coasts. By measuring the integrated quantity of electrons along the satellite-receiver paths, the Total Electron Content (TEC), GNSS satellites offer the capability to sound the ionosphere in all directions, including far from the receiver when satellites can be tracked at low elevation. Besides the enhanced coverage, we further investigate the new capabilities carried out by the new frequencies (L5, E5) offered by the US Global Positioning System (GPS), the European Galileo as well as the Indian Regional Navigation Satellite System (IRNSS) for seismic source studies. We investigate past earthquakes with a multi-GNSS scenario and discuss how such observations can be usefully included in tsunami early-warning systems for the case of an underwater earthquake poorly instrumented. More specifically, we study the morphology of co-seismic TEC signatures derived from numerical modeling results of seismo-acoustic waves. Simulated using an acoustic ray tracing method, atmospheric perturbations are coupled with the ionospheric plasma through transport mechanism by the local geomagnetic field. The electron density perturbation is finally integrated along the known satellite-station line-of-sights, based on the information of GNSS satellite orbits.
