Seismology without Seismometers: Determining of Seismological Parameters from Ionospheric TEC Measurements. Recent Advances in the Ionospheric Seismology

Abstract:

Ionospheric seismology is a new branch of geophysics aiming to study ionospheric response to such natural hazards as earthquakes, tsunamis and volcano eruptions. One of the very modern and exciting applications of the ionospheric seismology is the use of ionospheric measurements to determine parameters of seismic source and tsunamis, in addition to the “traditional” seismological measurements.

It is now experimentally proved that earthquakes with moment magnitudes Mw>6.8 are very much probable to cause ionospheric perturbations, referred to as co-seismic ionospheric disturbances (CID). The CID are usually N-shaped, in response to propagation of compression-rarefaction wave launched from the ground. Besides the primary waves generated directly by the co-seismic crustal displacements, it is possible to observe multi-mode CID propagation, especially in places with good instrumental coverage. These multiple modes are triggered and correspond to the surface Rayleigh waves (3.0-3.5 km/s), free gravity waves, tsunami propagation, etc. When the observations take place directly over the seismic fault regions, ionospheric measurements can help to obtain information on the dimensions on seismic fault and its location, as it was shown on the example of the Tohoku-oki earthquake (Astafyeva et al., JGR, DOI: 10.1002/jgra50556, 2013).

The next step toward the use of the ionospheric measurements for seismological purposes is to analyze resemblance in generation of tsunamis and CID. For this purpose, we analyze ionospheric response to strike-slip earthquakes that occurred in 2001-2013. We show that, unlike tsunamis, earthquakes with small vertical component of the co-seismic ground motion, can generate sufficiently large ionospheric perturbations. Therefore, independently on a focal mechanism, larger earthquakes generate larger ionospheric perturbations.