On the North‐South Asymmetry of Co‐Seismic Ionospheric Disturbances During the 16 September 2015 Illapel M8.3 Earthquake

The Mw8.3 Illapel earthquake on 16 September 2015 induced ionospheric disturbances detected by Global Positioning System ground-based total electron content (TEC) observations, which display much stronger TEC perturbations above the northern region of the epicenter than above the southern region. To investigate the cause of the asymmetry, we extend the Wave Perturbation-Global Ionosphere-Thermosphere Model from using a point source representing the epicentral crustal movement to using an extended source including the ground motion caused by propagating seismic waves. The modeling results reveal that on average, 31% of the north-south asymmetry in the TEC perturbation magnitude is caused by the different ground motion strengths northward and southward of the epicenter, while the remaining 69% is attributed to the background ionospheric state including the magnetic field. In particular, the spatial variation of the background electron density and the magnetic field inclination angle contributes comparably to the north-south asymmetry.