Abstract Typical rocks at shallow depths of seismogenic faults are fluid-rich gouges. During earthquakes, on-fault frictional heating may trigger thermal pressurization and dynamic fault weakening. We show that melting, rather than pressurization, occurred during the 2008 MW 7.9 Wenchuan earthquake, China. One year after we found an ~2-mm-thick, glass-bearing pseudotachylyte (solidified melt) i...