Earthquakes generated by fluid overpressure: Insights from cryptoexplosive breccias

The genetic mechanism of earthquakes remains puzzling even though some hypotheses for earthquake generation have been proposed. A new genetic model of earthquake was established by studying the dynamical relationship between earthquake generation and cryptoexplosion. More and more cryptoexplosive breccias that were naturally produced by explosion or detonation below the surface have been found throughout the world. The endogenic cryptoexplosive breccias (CEBs) have been found at hundreds of sites in China, most of which were dated in the Yanshanian period, some in Preyanshanian, and dozen in the Himalayan period. The breccias are characterized by the angular fragments produced by hydrothermal and magmatic explosions, the network and jigsaw textures, and the matrices that originated from magma or geothermal fluids. The high energy fluids derived from the lower mantle accumulated at some places during upward migration, at which the fluid explosions occurred when the fluid pressure exceeded the confined pressure of the host rocks. As a result, innumerable paleoearthquakes were produced by the prevailing cryptoexplosions in the geological history. Such geological processes never end, as geothermal and volcanic activities do. Therefore, cryptoexplosion can be ascribed as the most primary mechanism of earthquake generation.