Energetics of chemical alteration in fault zones and its relationship to the seismic cycle

Joseph Jacobs, & James P. Evans

Published 2006, SCEC Contribution #993

We examine the composition of small and medium-displacement faults in the western San Bernardino Mountains, southern California, in order to determine the nature and degree of alteration in faults. The development of clay-rich fault gouge is clearly syntectonic, and the reactions that produced the fault gouge are endothermic. We suggest and test they hypothesis that a primary source of energy to drive these reactions is the heat produced by earthquakes. We use standard thermodynamic values for enthalpies of formation to show that for the Eastwood fault, a fault ~ 7 km long, syntectonic alteration could consume approximately 20 % of the energy available from the repeated earthquakes that slipped along the fault. Many of the reactions that take place in and around faults to produce clay and mica minerals are endothermic, suggesting that chemical reactions can be a significant sink of energy produced in earthquake ruptures in faults in the upper 10 km of the crust. Consumption of heat by chemical reactions in and around faults would also result in a reduced heat flow anomaly associated with the fault.

Citation
Jacobs, J., & Evans, J. P. (2006). Energetics of chemical alteration in fault zones and its relationship to the seismic cycle. In Jacobs, J., Evans, J. P., , & (Eds.), AGU Monograph on Earthquake energy budgets, (170, pp. 181-191) , : AGU