Chen Yu

Stress may induce apparent resistivity changes. Clarifying the deformation process of the source media is critical for determining the correlations between resistivity variations and earthquake occurrence. In this study, the stress state of a medium was analyzed by integrating GPS measurements, the spatiotemporal evolution of the load/unload response ratio (LURR), geochemical monitoring, and synchronous apparent resistivity changes preceding the 2020 Mw 6.0 Jiashi earthquake. The medium hosting the Kalpin Observatory underwent elastic deformation before 2019, and the synchronous decreases in the E–W and N–S apparent resistivities from 2015 can be attributed to N–S-dominated compressive stress. The microdamage stage occurred in 2019, with subsequent E–W apparent resistivity variation amplitudes that were ~0.4 Ωm higher than those in previous years. This difference is a result of microdamage to the medium owing to tensile stress during the seismogenic process. The spatiotemporal evolution of the LURR and gas seepage monitoring data also indicate that the medium was damaged prior to the earthquake. Variations in the apparent resistivity measured at the Kalpin Observatory indicate that the medium underwent elastic deformation, followed by microdamage, until stress triggered the earthquake.

A large scale of abnormities from ground-based electromagnetic parameters to ionospheric parameters has been recorded during the Wenchuan MS8.0 earthquake. All these results present different anomalous periods, but there seems one common climax leading to a lithosphere-atmosphere-ionosphere electromagnetic coupling (LAIEC) right on May 9, 3 days prior to the Wenchuan main shock. Based on the electron-hole theory, this chapter attempts to estimate the “energy source” magnitude driving this obvious coupling with the Wenchuan focus zone parameters considered. The simulation results show that the total surface charges fall in ~107–108 C, and the related upward electric field is ~108–109 V/m. These corresponding parameters are up to 109 C and 1010 V/m when the main rupture happens, and the order of the output current is up to 107 A. The electric field increasing in the interface between the Earth’s surface and the atmosphere, on one hand, can cause electromagnetic parameter abnormities of ground-based observation, with the range beyond 1000 km. On the other hand, it can accumulate air ionization above pre-earthquake zone and lead to ionospheric anomaly recorded by some spatial seismic monitoring satellites.