Co-seismic ionospheric total electron content disturbances of Turkey earthquake doublet in 2023 detected by Beidou geostationary satellites

The M7.8 and M7.5 earthquakes that occurred on 6 February 2023 in Turkey caused co-seismic ionospheric disturbances, and ionospheric total electron content (TEC) disturbances can be detected by Beidou geostationary satellites. The 17 GNSS continuous observation stations from IGS Net around the epicenters receive electromagnetic wave signals emitted by two Beidou geostationary satellites located above the equator at a frequency of 1 Hz. That allows us to obtain the TEC time series at fixed ionospheric piercing points (IPPs). Disturbances triggered by the M7.5 earthquake propagate farther and have a larger amplitude in general traveling at least 1600 km northwest and 800 km south and reaching the furthest area of the study with the maximum amplitude of about 2.5 TECU. For Mw 7.8 earthquake, the disturbances can be observed about 800 km northwest of the epicenter while no significant disturbances detected further away and the maximum amplitude of the disturbances is about 0.25 TECU. The TEC disturbances propagation speeds corresponding to the M7.5 and M7.8 earthquakes are 2.77 km/s and 2.60 km/s as the results of least squares fitting performed on epicentral distances and travelling times of the disturbances with the greatest amplitude. The speeds are closer to Rayleigh waves velocity of about 3 km/s at the surface rather than acoustic waves velocity of about 1 km/s in the ionosphere. The velocity of propagation for the co-seismic ionospheric disturbances, as determined by utilizing the Beidou geostationary satellites during two earthquakes, is consistent with that of the Rayleigh waves determined from the seismometers. Meanwhile, the velocity exhibits directional disparities for M7.5 earthquake.