A window into thousands of earthquakes: Results from the Deep Fault Drilling Project (DFDP)

Abstract

In 1941, two geologists, Harold Wellman and Richard Willett, traversed the length of Westland, mapping what would become one of the most influential continental faults in the world, New Zealand’s Alpine Fault (Wellman & Willet 1942). The Alpine Fault strikes down the western edge of the Southern Alps, a youthful mountain range on New Zealand’s South Island (Fig 1). Here, collision between the Australian and Pacific Plates forms peaks over 3000 m in elevation which trap rain-laden clouds, resulting in 5–15 m of precipitation a year in central and south Westland. Driven by gravity, the rain and snow migrate into fractures and voids along the Alpine Fault, becoming heated and saturated with reactive ions along the way. Within the fault zone, these fluids play a fundamental role in the processes that drive earthquake nucleation and rupture propagation. Measurements made, and rocks recovered, from boreholes drilled during phases one and two of the Deep Fault Drilling Project (DFDP) have enabled scientists to document and quantify these processes for the first time.