Skip to main content
U.S. flag

An official website of the United States government

Permeability reduction in granite under hydrothermal conditions

January 1, 2001

The formation of impermeable fault seals between earthquake events is a feature of many models of earthquake generation, suggesting that earthquake recurrence may depend in part on the rate of permeability reduction of fault zone materials under hydrothermal conditions. In this study, permeability measurements were conducted on intact, fractured, and gouge-bearing Westerly granite at an effective pressure of 50 MPa and at temperatures from 150° to 500°C, simulating conditions in the earthquake-generating portions of fault zones. Pore fluids were cycled back and forth under a 2 MPa pressure differential for periods of up to 40 days. Permeability of the granite decreased with time t, following the exponential relation k=c(10−rt). For intact samples run between 250° and 500°C the time constant for permeability decrease r was proportional to temperature and ranged between 0.001 and 0.1 days−1 (i.e., between 0.4 and 40 decades year−1 loss of permeability). Values of r for the lower-temperature experiments differed little from the 250°C runs. In contrast, prefractured samples showed higher rates of permeability decrease at a given temperature. The surfaces of the fractured samples showed evidence of dissolution and mineral growth that increased in abundance with both temperature and time. The experimentally grown mineral assemblages varied with temperature and were consistent with a rock-dominated hydrothermal system. As such mineral deposits progressively seal the fractured samples, their rates of permeability decrease approach the rates for intact rocks at the same temperature. These results place constraints on models of precipitation sealing and suggest that fault rocks may seal at a rate consistent with earthquake recurrence intervals of typical fault zones.

Publication Year 2001
Title Permeability reduction in granite under hydrothermal conditions
DOI 10.1029/2000JB000010
Authors C.A. Morrow, Diane E. Moore, D. A. Lockner
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Geophysical Research B: Solid Earth
Index ID 70022773
Record Source USGS Publications Warehouse