The seismogenic layer is the range of depths within the crust or lithosphere over which most earthquakes are initiated. Typically in continental crust this is in the uppermost 15 km. The base of this layer represents the downwards change in deformation mechanism from elastic and frictional processes associated with brittle faulting to a generally aseismic zone where ductile creep becomes the dominant process. The location of this change in deformation style is sometimes referred to as the Brittle-ductile transition zone.