Melting of fault gouge at shallow depth during the 2008 MW 7.9 Wenchuan earthquake, China

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) in gouges retrieved 732.6 m depth from first borehole Earthquake Fault Scientific Drilling Project. The matrix is enriched barium cut by barite-bearing veins, which provide evidence co- postseismic fluid percolation. Because can be rapidly altered presence percolating fluids, its preservation suggests gouge melting a recent large possibly earthquake. Rock friction experiments on deformed conditions expected for seismic slip showed generation pseudotachylytes. This result, along with second zone attributed to earthquake 589.2 depth, implies occur accommodated multiple faults. conclusion consistent surface faulting ruptures propagated