Simulation of Acoustic-Gravity Waves Generated by an Earthquake and Explanation of the Ionospheric Disturbance Observed During 2023 M 7.7 Turkey Earthquake

Abstract

We present a semi-analytic method that allows efficiently simulating acoustic-gravity waves (AGWs) excited by an earthquake source in a stratified lithosphere-atmosphere model. First, we introduce the surface harmonic vectors to transform the atmospheric governing equations and the elastodynamic equations from the frequency-space to frequency-wavenumber domain. Next, we compute the wavefields in the frequency-wavenumber domain using a global matrix method incorporating boundary conditions and the source contribution. Finally, we obtain the time-space responses through the wavenumber integration and fast Fourier transform. We use this method to investigate the characteristics of AGWs generated by an earthquake source. The results reveal two main types of AGWs: the epicenter AGW generated by seismic waves near the epicenter and the head AGWs generated by the seismic waves that travel along the free surface. The epicenter AGW shows lower frequency compared with the head waves. AGWs caused by earthquakes with different focal mechanisms exhibit different energy distributions. Particularly, both the epicenter and head AGWs caused by a vertical strike fault are weak along the strike direction. The epicenter AGW is very sensitive to the source depth comparing to the head AGW. We also find that the Earth structure has little effect on the epicenter AGW but a significant effect on the head AGWs. We use our method to simulate the ionospheric disturbance observed from the Doppler frequency shift data following the 2023 Turkey M 7.7 earthquake. The good agreement suggests that our method provides a good understanding of the lithospheric and atmospheric coupling.