Design of an Air Conductivity Meter for Earthquake Anomaly Detection via Lithosphere–Atmosphere–Ionosphere Coupling Mechanism With Effective Range of 10^–15–10^–9 S/m

When significant electromagnetic disturbances occur over seismogenic regions, the electrical conditions at Earth’s surface are analyzed based on an electric field penetration model for seismo-ionospheric research in this article. The simulation results indicate that in order to generate an additional electric field of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-3}$ </tex-math></inline-formula> V/m at the bottom of the ionosphere, the abnormal current density at Earth’s surface should be at least <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-9}$ </tex-math></inline-formula>–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-8}$ </tex-math></inline-formula> A/m2. Considering that the maximum observed vertical atmospheric electric field before an earthquake is approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{4}$ </tex-math></inline-formula> V/m, which is insufficient to cause obvious disturbance of electron density in the ionosphere, another parameter that may affect current density anomalies, namely air conductivity, is investigated. First, this article designs and develops a portable low-energy air conductivity meter for earthquake anomaly monitoring, which can observe the air conductivity in real time and transmit the observation results to the cloud. In response to probable seismic air conductivity anomalies, the observation range of the instrument is expanded to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-15}$ </tex-math></inline-formula>–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-9}$ </tex-math></inline-formula> S/m, which can better capture irregularity in the atmosphere during the earthquake preparation or occurrence period. Then, the air conductivity meter is verified and theoretically analyzed by laboratory experiments, and the air conductivity increases by orders of magnitude in an environment filled with radon gas. It is concluded that radioactive gases emitted from seismogenic areas before and after earthquakes are able to increase air conductivity. Meanwhile, the influence of other factors (including relative humidity, air temperature, air pressure, and pollutants) on air conductivity is investigated through laboratory experiments and theoretical research. The proposed air conductivity meter for earthquake anomaly monitoring is promising for explaining abnormal disturbances in seismo-ionospheric phenomena related to direct current (dc) electric fields associated with earthquakes.