Electromagnetic Trigger Effects in the Ionosphere–Atmosphere–Lithosphere System and Their Possible Use for Short-Term Earthquake Forecasting

Previously conducted numerical studies of the influence of class X solar flares on seismic activity have shown that the absorption of X-ray radiation from a solar flare in the ionosphere can cause pulsations of the geomagnetic field up to 100 nT and the corresponding generation of telluric currents in faults in the Earth’s crust with a density of up to 10^–6 A/m², which is comparable to the current density created in the Earth’s crust by artificial pulse sources and leading to the initiation of weak earthquakes in the Pamirs and Northern Tien Shan. To verify these numerical results, an analysis was conducted of the possible impact of the 50 strongest class X flares (1997–2023) on both global seismic activity and earthquake-preparation zones located only on the illuminated part of the globe. The method of superimposing epochs has established an increase in number of earthquakes M ≥ 4.5 within 10 days after a solar flare, especially in the area with a radius of 5000 km around the subsolar point (up to 68% for flare class >X5), compared to the same period before it. Analysis of aftershock activity of the strong Sumatra–Andaman earthquake (M = 9.1, December 26, 2004) showed that the number of aftershocks with magnitude M ≥ 2.5 increased more than 17 times after the X10.1 class solar flare (January 20, 2005) with a delay of 7–8 days. In addition, it has been shown that solar flares of class X2.3 and M3.64, which occurred after the Darfield earthquake (M = 7.1, September 3, 2010, New Zealand), in the area of subsolar points of which the aftershock zone was located, probably caused three strong aftershocks (M6.3, M5.2, and M5.9) with the same delay of 6 days on the Port Hills fault, which is the most sensitive to external electromagnetic influences in terms of its electrical conductivity and orientation. Taking into account the concept of earthquake forecasting based on trigger effects proposed by G.A. Sobolev, the possibility is discussed of using the obtained results for short-term forecasting as additional information along with known precursors.