Temperature Measurements and Active Faulting

Temperature measurements associated with active faults can be useful for studying the total energy balance, and especially the dynamic frictional levels during faulting of large earthquakes. However, temperature anomalies across faults or temperature changes associated with earthquakes are relatively rare. We make some simple calculations to estimate the temperature changes that should be observed across a fault for large earthquakes. For example, a temperature profile at 500 m depth across a fault that slipped 2 meters, at a time 6 months following the earthquake, shows a temperature anomaly of about 0.2 degrees, assuming an apparent coefficient of friction of 0.6. For an apparent coefficient of friction of 0.3, the anomaly reduces to about 0.05 degrees. The differences in the apparent coefficient of friction should be resolvable with the current temperature sensor instruments we are developing for borehole measurements. Estimating the apparent coefficient of friction is important for understanding the mechanics of faulting. The level of friction, and thus the amount of heat produced during an earthquake, has been a controversial issue in seismology for several decades. Timely measurements of the temperature profile across the fault following large earthquakes may be able to answer these long-standing questions about the level of dynamic friction.