Shear zone broadening controlled by thermal pressurization and poroelastic effects during model earthquakes
Jiangzhi Chen, & Alan W. RempelPublished 2015, SCEC Contribution #6147
As a result of the comminution that takes place over numerous earthquake cycles, mature faults are characterized by thick layers of pulverized gouge with finite porosity that is saturated with water at seismogenic depths. The heat generated during earthquakes raises the gouge temperature and thermal expansion of the pore fluid, and surrounding solids produce elevated pore pressures that cause fault strength to decrease in the process known as thermal pressurization. Building upon this framework, we describe a model that imposes a plane-strain configuration and shows that the stress variations caused
by porothermoelasticity promote the Mohr-Coulomb failure of previously undeformed regions. Except in special cases where the friction is rate strengthening, we find that the frictional strength must vary throughout the post-failure region, which we identify in our model with the shear zone. We introduce a strain rate function that describes the overall influence of distributed slip on energy dissipation and fault strength as the shear zone thickness expands. Using typical fault parameters at 7 km depth, the shear zone reaches several millimeters of thickness after 1 s sliding at an overall rate of 1 m/s. The expansion of the shear zone limits the temperature rise to several hundred degrees Celsius, and the average fault strength falls to about a tenth of the static frictional strength.
Citation
Chen, J., & Rempel, A. W. (2015). Shear zone broadening controlled by thermal pressurization and poroelastic effects during model earthquakes. Journal of Geophysical Research, 120, 5215–5237. doi: 10.1002/2014JB011641.
