Kyoto, Japan -- Researchers at Kyoto University have proposed a new physical model that explores how disturbances in the ionosphere may exert electrostatic forces within the Earth's crust and potentially contribute to the initiation of large earthquakes under specific conditions.
The study does not aim to predict earthquakes but rather presents a theoretical mechanism describing how ionospheric charge variations -- caused by intense solar activity such as solar flares -- could interact with pre-existing fragile structures in the Earth's crust and influence fracture processes.
In the proposed model, fractured zones within the Earth's crust are assumed to contain high-temperature, high-pressure water, potentially in a supercritical state. These zones behave electrically like capacitors and are capacitively coupled with both the ground surface and the lower ionosphere, forming a large-scale electrostatic system.
When strong solar activity increases electron density in the ionosphere, a negatively charged layer can form in the lower ionosphere. Through capacitive coupling, this space charge may induce strong electric fields inside nanometer-scale voids within fractured crustal regions. The resulting electrostatic pressure could reach magnitudes comparable to tidal or gravitational stresses known to affect fault stability.
Quantitative estimates in the study suggest that ionospheric disturbances associated with large solar flares -- corresponding to increases in total electron content of several tens of TEC units -- could generate electrostatic pressures on the order of several megapascals within crustal voids.
Ionospheric anomalies, such as increased electron density, lowered ionospheric altitude, and slowed abnormal propagation of medium-scale traveling ionospheric disturbances, have been repeatedly observed prior to major earthquakes. Traditionally, these phenomena have been interpreted as consequences of stress accumulation within the Earth's crust.
The new model provides a complementary perspective by proposing a bidirectional interaction: while crustal processes may affect the ionosphere, ionospheric disturbances themselves may also exert feedback forces on the crust. This framework offers a possible physical explanation linking space weather phenomena and seismic processes without invoking direct causation.
The study discusses recent large earthquakes in Japan, including the 2024 Noto Peninsula earthquake, as examples that are temporally consistent with the proposed mechanism. In these cases, intense solar flare activity occurred shortly before the seismic events. The authors emphasize that such temporal coincidence does not establish direct causality, but is consistent with a scenario in which ionospheric disturbances act as a contributing factor when the crust is already in a critical state.
By integrating concepts from plasma physics, atmospheric science, and geophysics, the proposed model broadens the conventional view of earthquakes as purely internal Earth processes. The findings suggest that monitoring ionospheric conditions, together with subsurface observations, may help improve scientific understanding of earthquake initiation processes and seismic hazard assessment.
Future research will focus on combining high-resolution GNSS-based ionospheric tomography with space weather data to clarify the conditions under which ionospheric disturbances may exert significant electrostatic influence on the Earth's crust.
