Hot on the trail: Coseismic heating on a localized structure along the Muddy Mountain fault, Nevada

Abstract

Recent advances in the use of thermal proxies to identify past earthquake slip in exhumed faults have created an extraordinary opportunity to map the geometry of past ruptures in unprecedented detail. This approach can reveal along-strike differences in the structure and speed of earthquake slip. Here, we present organic thermal maturity data collected along the Muddy Mountain thrust in Nevada to investigate where it was within the fault that earthquake slip occurred and whether this is consistent along strike. We observe large changes in thermal maturity, which represent temperature-rise variations along the fault. Modeling of thermal maturity measurements yield peak temperatures of 760–1090 °C where the principal slip zone (PSZ) is narrowest (0.8 mm). Nearby where the PSZ is thicker (1.5 mm) these temperatures did not exceed 500 °C. Based upon estimates of temperature rise within a submillimeter PSZ, mean frictional work during earthquake slip was 6.3–7.1 MJm−2. These results show that thickness of the active slipping zone can vary at small spatial scales and development of a continuously narrow (<1 mm) slip layer is not required for earthquake propagation. Therefore, even for an earthquake with spatially uniform slip, we may observe large variations in heating and the effectiveness of thermally-activated dynamic-weakening mechanisms.