Abstract <p>The hypothesis of the thermal trigger mechanism of the effect of electric current on porous fluid-saturated rock is considered, when Joule heating of fluid (mineralized water) in pores and cracks leads to an increase in pore pressure and a decrease in the effective strength of rock. Numerical estimates of current flow in a porous fluid-saturated medium have shown that the increase in fluid temperature and, as a consequence, its pressure in the pores is several percent, which, in principle, can explain the trigger effect of electric current when the geoenvironment is in a stress–strain state close to the ultimate strength of rocks. In experiments on a uniaxial press with cylindrical samples of artificial sandstone and marble in the form of a rectangular parallelepiped of square cross-section with different porosities, the response of acoustic emissions and deformation of the sample during sessions of electrical action was demonstrated. However, when the sample was exposed to electrical current density at a level of 10^–5 A/m², which is an order of magnitude higher than the numerical estimates of the current density created in the Earth’s crust by artificial sources in field conditions, the response of acoustic emissions and the change in transverse deformation of the sample to such an effect has not been established. This allows us to conclude that the electromagnetic initiation of earthquakes when rocks are exposed to a weak electric current cannot be explained by a thermal mechanism based on Joule heating of fluids in cracks and pores of rocks.</p>