Coal maturation by frictional heat during rapid fault slip

The detection of frictional heating effects along faults provides key insight into the dynamics of earthquakes and faulting. Thermal maturity of organic matter has been considered a possible fault-thermometer that records the frictional heat signature of ancient earthquakes. However, whether or not organic matter can mature on the order of seconds, typical earthquake rise time, remains uncertain. Here we present the results of experiments aimed at revealing coal maturation by frictional heat generated at slip velocities representative of natural earthquakes of up to 1.3 m/s. Our results show that coal can mature coseismically in similar to 11 seconds at temperatures induced by frictional heat ranging from 26 to 266 degrees C. Even with a temperature rise to only 28.7 degrees C over 15 m displacement in similar to 3.2 hours, coal can slightly mature within a shear localized zone. The commonly used kinetic model of vitrinite maturation cannot predict the experimental results. A kinetic model involving the effect of flash temperature at grain contacts and mechanochemical effects on reaction kinetics is necessary to better estimate heat generation along a fault. Citation: Kitamura, M., H. Mukoyoshi, P. M. Fulton, and T. Hirose (2012), Coal maturation by frictional heat during rapid fault slip, Geophys. Res. Lett., 39, L16302, doi:10.1029/2012GL052316.