  Theoretical approaches to earthquake instabilities propose shear dominated
instabilities as a source mechanism. Here we take a fresh look at the role of
possible volumetric instabilities preceding a shear instability. We investigate
the phenomena that may prepare earthquake instabilities using coupling of
Thermo-Hydro-Mechano-Chemical (THMC) reaction-diffusion equations in a THMC
diffusion matrix. We show that the off-diagonal cross-diffusivities can give
rise to cross-diffusion slow (no inertia) pressure waves and propose that a
resonance phenomenon of the long-wavelength limit causes constructive
interference and triggers the seismic moment release.

Geophysics;Pattern Formation and Solitons