Simulation of a lithosphere-atmosphere-ionosphere electromagnetic coupling prior to the Wenchuan M_S8.0 earthquake

Abstract. Continuously to a previous work on qualitatively investigating the probable electromagnetic interacting process among lithosphere, atmosphere and ionosphere, this work aims to quantitatively establish an electromagnetic coupling model among these three spheres prior to the Wenchuan earthquake. Firstly, a underground finite length electrical dipole in a half-space model has been employed to estimate the possible “energy source” for an observable 1.3 mV m^-1 electrical field registered at 1440 km Gaobeidian station during the Wenchuan event. The result shows that the seismo-telluric current covers ~10⁵–10⁶ kA if the measuring frequency f = 0.01–10 Hz considered. The central magnitude of the vertical electrical field caused by the current at 0.01 Hz on the Earth’s surface can be up to kV m^-1. Then, this vertical field acts as an input into an electric field penetration model. It is shown that this field attenuates quickly at the atmosphere and completely vanishes at the top ionosphere and produces a 0.1 mV m^-1 additional electrical field at the ionospheric bottom. Through the TIE-GCM, this additional electrical field causes 0.01 % ionospheric variations on electron density and TEC near the Wenchuan epicenter, as well as near its magnetically conjugated point. Further, the simulations have also been discussively performed on frequencies of 1 Hz and 10 Hz. The results demonstrate that the variations of electron density present their maximum values at the height of ~300–400 km and the varied percentages of ionospheric parameters have been beyond 10 %, the same magnitude as what has been registered during the Wenchuan shock.