Vaporization of fault water during seismic slip

Abstract

Laboratory and numerical studies, as well as field observations, indicate that phase transitions of pore water might be an important process in large earthquakes. We present a model of the thermo‐hydro‐chemo‐mechanical processes, including a two‐phase mixture model to incorporate the phase transitions of pore water, occurring during fast slip (i.e., a natural earthquake) in order to investigate the effects of vaporization on the coseismic slip. Using parameters from typical natural faults, our modeling shows that vaporization can indeed occur at the shallow depths of an earthquake, irrespective of the wide variability of the parameters involved (sliding velocity, friction coefficient, gouge permeability and porosity, and shear‐induced dilatancy). Due to the fast kinetics, water vaporization can cause a rapid slip weakening even when the hydrological conditions of the fault zone are not favorable for thermal pressurization, e.g., when permeability is high. At the same time, the latent heat associated with the phase transition causes the temperature rise in the slip zone to be buffered. Our parametric analyses reveal that the amount of frictional work is the principal factor controlling the onset and activity of vaporization and that it can easily be achieved in earthquakes. Our study shows that coseismic pore fluid vaporization might have played important roles at shallow depths of large earthquakes by enhancing slip weakening and buffering the temperature rise. The combined effects may provide an alternative explanation for the fact that low‐temperature anomalies were measured in the slip zones at shallow depths of large earthquakes.

Subseismic to Seismic Slip in Smectite Clay Nanofoliation

“…In addition, smectite‐rich gouges have a low hydraulic diffusivity of 2.3·10 −8 ≤ κ ≤ 10 −7 m 2 /s (typical values for smectite‐rich natural fault gouges,Faulkner et al, ; Wibberley, ), therefore the equilibration of the transient pore pressures due to pore volume decrease by shear compaction cannot occur during shear deformation at shear strain rates of ~6.6·10 −4 s −1 (calculated using slip rates of 0.5 μm/s and a gouge layer thickness of ~0.75 mm, Faulkner et al, ). At seismic slip rates, equilibration is further complicated as the pore pressure increase by shear compaction sums with the transient pore pressure increase induced by thermal pressurization of the pore fluids (Faulkner et al, ), by thermochemical pressurization resulting from the expulsion of water films from the basal planes (completed at T > 120–150 °C, Ferri et al, ), or by the vaporization of pore water (Chen et al, ). The combination of the low hydraulic diffusivity of smectite‐rich gouges with thermal pressurization effects implies that the mechanical behavior cannot be explained in a model without accurately measuring at least pressure, temperature, and porosity change.…”

Effect of Fluid Chemistry on the Interfacial Composition, Adhesion, and Frictional Response of Calcite Single Crystals—Implications for Injection‐Induced Seismicity

“…In fact, the temperature of the regions in the Earth crust reached by the injected fluid may be high, for example, 260 °C in Zoback and Harjes (), and the retrieved reservoir fluid from a geothermal well can be hot (Sanchez‐Alfaro et al, ). Studies also suggest that the temperature of the fluid may increase due to flashing heating at much higher slip rates (Rice, ), while the elevation of temperature at the asperity level can be significantly influenced by the thermophysical properties of the fluid (Acosta et al, ; Chen et al, ). The increase of temperature in our AFM experiments is estimated to be extremely small (1.42·10 ‐7 to 5.5·10 ‐4 °C; Cowan & Winer, ; Rabinowicz & Tanner, ).…”

Thermal Alteration of Pyrite to Pyrrhotite During Earthquakes: New Evidence of Seismic Slip in the Rock Record

“…However, as evident by the aforementioned faint bulk temperature anomalies around seismically active faults or by the lack of bulk pseudotachylytes, the average frictional heat over an entire fault zone could still be rather low. This may be explained by dynamic weakening mechanisms (e.g., flash heating and thermal [thermochemical] pressurization) or extra heat sinks (e.g., phase transitions of pore water and endothermic chemical reactions) (e.g., Chen, Niemeijer Fokker, ; Chen, Niemeijer, & Yao, , and references therein). As mentioned, pyrite is thermally unstable and readily decomposed to pyrrhotite at elevated temperatures.…”