Modeling of Ionospheric Responses to Atmospheric Acoustic and Gravity Waves Driven by the 2015 Nepal M(w)7.8 Gorkha Earthquake

Abstract

Near- and far-field ionospheric responses to atmospheric acoustic and gravity waves (AGWs) generated by surface displacements during the 2015 Nepal Mw7.8 Gorkha earthquake are simulated. Realistic surface displacements driven by the earthquake are calculated in three-dimensional forward seismic waves propagation simulation, based on kinematic slip model. They are used to excite AGWs at ground level in the direct numerical simulation of three-dimensional nonlinear compressible Navier-Stokes equations with neutral atmosphere model, which is coupled with a two-dimensional nonlinear multifluid electrodynamic ionospheric model. The importance of incorporating earthquake rupture kinematics for the simulation of realistic coseismic ionospheric disturbances (CIDs) is demonstrated and the possibility of describing faulting mechanisms and surface deformations based on ionospheric observations is discussed in details. Simulation results at the near-epicentral region are comparable with total electron content (TEC) observations in periods (∼3.3 and ∼6-10 min for acoustic and gravity waves, respectively), propagation velocities (∼0.92 km/s for acoustic waves) and amplitudes (up to ∼2 TECu). Simulated far-field CIDs correspond to long-period (∼4 mHz) Rayleigh waves (RWs), propagating with the same phase velocity of ∼4 km/s. The characteristics of modeled RW-related ionospheric disturbances differ from previously-reported observations based on TEC data; possible reasons for these differences are discussed.