ICDPInternational Continental Scientific Drilling Program

The mid-crust is the locus of several fundamental geological and geophysical phenomena: these include the transitions from brittle to ductile behaviour and from unstable to stable frictional sliding; earthquake nucleation and predominant moment release; the peak in the crustal stress envelope; the transition from predominantly cataclastic to mylonitic fault rocks; and mineralisation associated with fracture permeability. 

The Alpine Fault, New Zealand, is a globally significant dextral-reverse fault that is thought to fail in large earthquakes (c. Mw 7.9) every 200-400 years and last ruptured in 1717 AD. Ongoing uplift has rapidly exhumed a crustal section from c. 20 km, providing a young (<1 Myr), well-preserved sample of mid-crustal structures currently active at depth.