Anisotropy of the near-field coseismic ionospheric perturbation amplitudes reflecting the source process: the 2023 February Turkey earthquakes

Abstract

The East Anatolian Fault in southern Turkey ruptured on 6 February 2023, causing a Mw 7.8 earthquake (EQ1), one of the largest strike-slip events recorded on land. ∼9 hr later, earthquake of Mw 7.7 (EQ2) occurred to the north of EQ1. We investigate here near-field coseismic ionospheric perturbations (CIP) caused by acoustic waves (AWs) excited by coseismic vertical crustal movements. We find that observed CIP periods were somewhat longer for EQ1 than EQ2. EQ1 also showed azimuthal dependence in CIP amplitudes that cannot be explained by known factors such as geomagnetism and line-of-sight geometry. Numerical experiments revealed that CIP by EQ1 can be well reproduced by assuming a suite of sources along the fault that successively ruptured. Small but significant dependence of amplitudes and periods on azimuths were caused by interference of AWs from multiple sources. We also found that CIP amplitudes of strike-slip earthquakes tend to be lower than dip-slip earthquakes.