Stress release in exhumed intermediate and deep earthquakes determined from ultramafic pseudotachylyte

Stresses released by coseismic faults during subduction toward lawsonite-eclogite facies conditions in the Alpine subduction complex of Corsica can be estimated based on the energy required to form pseudotachylyte fault veins where shear strain can be measured. Congruent peridotite melting at ambient conditions of 1.5 GPa and 470 degrees C requires a temperature increase of 1280 degrees C to 1750 degrees C. We assume that more than 95% of the work is converted to heat during faulting, hence that the stress drop is nearly proportional to the amount of melting and inversely proportional to shear strain. Minimum estimates or released stress are typically greater than 220 MPa and as high as 580 MPa. The abundance of pseudotachylyte on small faults in the studied peridotite suggests that melting is very common on intermediate and deep earthquakes and that shear beating is important for seismic faulting at depth.