Modeling of seismically-induced infrasonic acoustic wave signals in Earth’s electromagnetic field

Abstract:

Recent studies have reported magnetic field fluctuations following intense seismic hazard events (e.g. Hao et al., JGR, 118, 2013; Aoyama et al., EPS, 68, 2016). It was demonstrated that associated infrasonic acoustic waves (IAWs), generated by permanent and transient surface deformations, can serve as a source of ionospheric dynamo effects and can be separated from other sources of magnetic fluctuations (Zettergren and Snively, GRL, 46, 2019). However, the quantitative analysis of these fluctuations, with the use of realistic (spatially distributed, rather than axisymmetric) IAW sources, has not yet been performed. Here, we conduct the numerical investigation of coseismic IAW propagation and their imposed fluctuations in ionospheric plasma and Earth’s electromagnetic field during the 2015 M8.3 Chilean earthquake. We specify surface deformations from 1) forward seismic wave propagation simulation with SPECFEM3D-Globe codes (Komatitsch and Tromp, GJI, 149, 2002), based on the kinematic slip model by United States Geological Survey (USGS) and 2) temporal and spatial offset dynamics based on the kinematic slip model by (Melgar et al., GRL, 43, 2016). These simulated time-dependent deformations are then used to excite IAWs at the ground level of a numerical 3-D nonlinear compressible neutral atmosphere model MAGIC, that is coupled with a 3-D nonlinear multi-fluid ionospheric dynamics model GEMINI (Zettergren and Snively, JGR, 120, 2015; Inchin et al., JGR, 125, 2020). Simulations include the effective generation of ionospheric dynamo currents driven by IAWs and ensuing magnetic field disturbances. We investigate qualitative features of the generated ionospheric disturbances, and their quantitative temporal, spatial, and spectral characteristics. Modeling results are validated through comparisons with near-epicentral total electron content (TEC) and ground-level magnetometer data. Our results demonstrate that ground-based magnetometer observations may provide additional insight into the coupled earthquake-atmosphere-ionosphere physical processes.