Association of Ionospheric Signatures to Various Tectonic Parameters During Moderate to Large Magnitude Earthquakes: Case Study

Abstract

The sudden ground movement associated with Mw > 6.5 earthquakes is considered a potential source of ionospheric electron density perturbations over the fault region. Coseismic ground displacement is a function of various seismic source parameters such as moment magnitude, focal depth, and focal mechanism etc. We study here the distinct effects of vertical ground displacement, moment magnitude and focal depth on coseismic ionospheric perturbation (CIP) amplitudes during moderate-to-large earthquakes. We analyze GPS-total electron content variations during 59 dip-slip earthquakes that occurred in the last 20 years. Our study reveals that though CIP amplitudes are primarily controlled by moment magnitude, they are also sensitive to the earthquake focal depth. To understand the influence of focal depth on the displacement field and therefore on CIP amplitudes, we present a simple synthetic test, for a depth range of 0–200 km, highlighting that the maximum vertical ground displacement decreases logarithmically with increasing focal depth while the volume (i.e., integrated vertical ground displacement) of uplifted/subsided material varies very marginally. We conclude that CIP is sensitive to the wavelength of co-seismic vertical displacement field and that seismic energy propagation to the overlying atmosphere during deep earthquakes is not adequate to generate detectable CIP.