Biomarkers as a Fault Paleothermometer
What's Cooking?: Using the Thermal Maturity of Organic Matter to Evaluate Frictional Heating on Faults
How much heat is generated during earthquakes? We expect to see a thermal signature from earthquakes because of the energy that presumably goes into frictional heating. By detecting temperature rise in fault zones, we can determine whether that fault, or a specific structure within a fault zone, has experienced an earthquake. If the amount of heating on a fault can be measured, the energy budget during earthquakes could be constrained.
Pratigya Polissar and I developed a new measurement for detecting frictional heating on faults using the thermal maturity of extractable organic molecules (Polissar et al., 2011; Savage et al., 2014). We have verified that this measurement is sensitive to frictional heating through studies of faults that contain pseudotachlyte (frictional melt) and thus were unequivocally heated during an earthquake (Savage et al., 2014). We have developed a laboratory apparatus for short, high-temperature hydrous pyrolysis experiments to measure the kinetics of biomarker reactions at fault-relevant timescales (Sheppard et al, 2015). Our results have constrained the maximum earthquake and possible ranges of fault width and friction on an ancient strand of the San Andreas Fault (Polissar et al., 2009; Sheppard et al., 2015), the energy budget for a large subduction zone paleoearthquake (Savage et al., 2014) and the presence of multiple earthquake-hosting strands in the shallow wedge sediments ruptured during the tsunami-generating 2011 Tohoku earthquake (Rabinowitz et al., in prep).