A seismic velocity profile across the central South Island, New Zealand, from explosion data

Abstract

Abstract Data from a seismic experiment across the central South Island, New Zealand, were used to model the crustal structure of the Australia‐Pacific plate continent‐continent boundary to a depth of c. 40 km. Large explosions were detonated off each coast and in Lake Tekapo and recorded on 19 seismographs deployed in a line from Timaru to just south of Fox Glacier, and on the Pukaki Seismograph Network. In the upper crust, a clear difference was found between the seismic velocities in Permian and younger rocks, in agreement with findings from other studies. Within the Permian schists and greywackes, the P‐wave velocity is 5.8 km/s to 2.7 km depth and 6.0 km/s below, contrasting with 5.4 km/s in the Triassic greywackes which form the basement near Lakes Pukaki and Tekapo in the central part of the survey area. Strong second arrivals from a layer 24 km deep at the east coast, and dipping inland at 3.4°, were seen from both offshore shots. The true velocity of the arrivals was determined to be 7.2 km/s. Ar...