Coseismic recrystallization during shallow earthquake slip

Abstract

Solidified frictional melts, or pseudotachylytes, remain the only unambiguous indicator of seismic slip in the geological record. However, pseudotachylytes form at >5 km depth, and there are many rock types in which they do not form at all. We performed low- to high-velocity rock friction experiments designed to impose realistic coseismic slip pulses on calcite fault gouges, and report that localized dynamic recrystallization may be an easy-to-recognize microstructural indicator of seismic slip in shallow, otherwise brittle fault zones. Calcite gouges with starting grain size −1 , and total displacements between 1 and 4 m. At coseismic slip velocities ≥0.1 m s −1 , the gouges were cut by reflective principal slip surfaces lined by polygonal grains 2 + CaO. The recrystallized calcite aggregates resemble those found along the principal slip surface of the Garam thrust, South Korea, exhumed from