Analysis of coseismic ionospheric disturbance of Alaska M7. 8 earthquake on July 22,2020

The characteristics of co-seismic ionospheric disturbances (CIDs) of the 2020 Alaska M(W)7.8 earthquake were explored. Using GNSS, ionosonde and seismograph data, we discussed from multiple perspectives of amplitude and waveform, spatiotemporal distribution, propagation velocity and direction, and time-frequency domain. The satellites G03, G04 and G09 detected three types of CIDs in the west of the earthquake, with a maximum disturbance amplitude of about 0.1 TECU (1 TECU=10(16) el/m(2)), and all propagated along the extension direction of the earthquake fault rupture (southwest direction); however, no CIDs were found in the north and east of the earthquake. The CIDs are divided into three types according to their velocity and center frequency. The first type is the CIDs with high-velocity propagation (the velocity is about 2.93 km center dot s(-1)), and the center frequency is about 11 mHz, which is consistent with the ionospheric disturbance characteristics excited by Rayleigh waves. The second type of the CIDs had the propagation velocities of about 1.69 km center dot s(-1) and 1.55 km center dot s(-1), and their center frequencies are about 4.5 mHz and 4.7 mHz, which are consistent with the ionospheric disturbance frequencies caused by sound waves. The third type of the CIDs had the propagation velocities of about 0.98 km center dot s(-1) and 1.11 km center dot s(-1), and the center frequency is about 2.9 mHz, The third type of CIDs may be another type of ionospheric disturbance caused by acoustic waves. Meanwhile, the location of the CIDs source estimated by the CIDs spatiotemporal data is very close to the epicenter, which further indicates that the ionospheric disturbance is excited by earthquakes. By analyzing the displacements of GNSS stations and seismographs, it is estimated that the propagation velocity of seismic Rayleigh waves in the southwest direction is in good agreement with the first type of CIDs. It is verified that the first type of CIDs is excited by Rayleigh waves, and the vertical displacement of the fault is an important factor causing the ionospheric disturbance. The peak frequency of F2 layer (f(0)F(2)) observed by ionosonde fluctuates significantly, and the propagation velocity of the detected CIDs is about 1.02 km center dot s(-1). The propagation velocity and direction are in good agreement with the CIDs detected by the satellites G03 and G04, therefore it is inferred that it belongs to the third type of CIDs.