The Alpine Fault, New Zealand, near Milford Sound and to the southwest

Abstract

From 70 km northeast of Milford Sound (44.14° S, 168.55° E) to the coast at Milford Sound (44.53° S, 167.83° E) the trace of the Alpine Fault is nowhere more than 1.2 km from the arc with a centre at 48.81° S, 173.20° E and a radius of 628 km (5.65° latitude). Earthquake epicentres indicate that the arc defines the position of the fault just off Fiordland's outer coast and then to near the north end of Puysegur Trench at 46.9° S, 165.25° E. Along the fault vertically to a depth of 10 km the Fiordland rocks are 0.6 Mg/m³ denser than those to the northwest. Displaced post-glacial topography at and near Milford Sound shows that the dip of the fault is southeast at 75 ± 5° and that the faulting is pure dextral at a rate of at least 46 ± 5 mm/yr.