Abstract:

Through the examination of a large number of seismic phenomena and thermodynamical analysis of seismic processes, we found the common characteristics of earthquakes which included plane zonation, correlation with faults, multiple seismic layers occurring in the lithosphere, high conductivity and low velocity layers in the deep part of the affected area, close relationship with water, short and sudden main quake, abnormal behavior of some animals and plants, topographic and geomorphological changes, and geochemical, geophysical and meteorological anomalies. As a whole, these characteristics can be divided into two kinds: one relates to faults affected by rock properties and force; and the other relates to water. In this study, focusing on fault depressurization and water phase transition, we improved the theory stating that the coupling of the singularity of critical point behavior of water during second-order phase transition, and fault depressurization in lithosphere, triggers earthquake. On this basis, we proposed the theory of earthquake triggering by the singularity of critica point behavior of water as follows: (1) Depressurization and water accumulation in brittle and ductile fractures (or zones) cause pressure decrease and temperature rise in some areas of crust and upper mantle; as temperature and pressure of water simultaneously reach the critical values of water, the second order phase transition is induced. (2) At the critical point of second order phase transition of water, change of water physico-chemical properties is abrupt. In particular, sudden change of solubility of solids in water abruptly weakens the local mechanical properties of the crust and upper mantle, while thermal pressure (i.e. thermal stress) approaches infinity, according to the Mie-Grüneisen formula, as water C_V approaches infinity during the second order phase transition. Fracturing depressurization causes the local temperature and pressure of the lithosphere to reach the critical values of water at the same time thus induces second order phase transition. These factors trigger the local hydro-thermal explosion to form earthquake. And (3) Earthquake magnitude is positively correlated with the amount of local accumulation of water undergoing second order phase transition in faults. The critical behavior of water, i.e., sudden change of many physico-chemical properties, is the source of various anomalies in geochemistry, geophysics, plant and animal growth, meteorology and so on, and is also the main indicator in earthquake monitoring.We also briefly discussed correlation between earthquakes and hydro-thermal metallogeny or oil and gas formation or other geological processes. The theory we proposed here is mainly used to explain the mechanism of strong earthquakes in the Earth’s crust.

Key words: the singularity of critical point behavior, second order phase transition, mutation, depressurization, water, seismic origin