Biomarker thermal maturity experiments at earthquake slip rates

Evidence of temperature rise is useful for identifying where within a fault zone earthquake slip has occurred, as well as some attributes of the earthquake such as energy output. Biomarker thermal maturity can elucidate structures within a fault zone that were hotter than surrounding rock, and therefore likely to have hosted earthquakes. We performed a series of friction experiments on thin gouge layers of Woodford shale at slip rates of 1 m/s. Our results show that biomarker thermal maturity can clearly delineate zones of slip that are as thin as 150 μm. We establish that the kinetics of methylphenanthrene reaction previously determined at longer durations and lower temperatures are applicable at seismic slip rates and timescales. Temperature estimates show that once the slipping zone reached ∼500 °C, biomarker reaction was significant, as predicted by the reaction kinetics. Our results demonstrate that temperature rise in fault zones is a function of both the work density and power density during the earthquake. Biomarker reactions, along with other Arrhenius-style reactions such as those that lead to dynamic shear weakening, are both a function of slip speed and frictional work.