Brittle–ductile transition zone

[1] For quartz and feldspar-rich rocks in continental crust, the transition zone occurs at an approximate depth of 20 km,[2] at temperatures of 250–400 °C.

The transition zone is, therefore, the strongest part of the crust and the depth at which most shallow earthquakes occur.

In contrast, the lower region of the crust is highly resistive and its electrical conductivity is determined by physical factors such as depth and temperature.

Above the transition zone, the rock may deform ductilely if pore fluids are present and stress is applied gradually.

Along this fault line, researchers have directly observed changes in structure and strength profiles in transition zone.

Variation of strength with depth in continental crust and changes in dominant deformation mechanisms and fault rocks in a conceptual vertical fault zone .