Three-Dimensional Vp Imaging Across the Interseismically Locked Southern Hikurangi Margin, Wellington, New Zealand

Abstract:

We present a three-demensional Vp model for the southern portion of the North Island, New Zealand, where the Pacific Plate is subducting beneath the Australian plate at a rate of c. 42 mm/yr, The region provides a unique opportunity to investigate the frictional properties, geometry, and seismic potential of a shallow, locked megathrust fault. Here the coupled plate interface is 20-30 km deep beneath land and can be sampled with onshore/offshore data from 3 sides. We have previously published a 2D Vp model [Henrys et al., 2013] incorporating coast-to-coast onshore-offshore transect of 50 stations and utilising first arrivals from offshore multichannel seismic (MCS) sources on either side. The transect velocity model also combined first arrivals from 800 stations with 100 m spacing recorded from 12 in-line, 500 kg onshore dynamite explosions. We have expanded the transect data to include first arrivals from the dense temporary array of 50 seismometers augmented with 25 regional GeoNet instruments together with offshore airgun sources from MCS lines crisscrossing two sides of the array. We combine all shot and earthquake recordings to simultaneously invert for velocity structure and earthquake hypocenters in the densely sampled volume.

Henrys, S., et al. (2013), SAHKE geophysical transect reveals crustal and subduction zone structure at the southern Hikurangi margin, New Zealand, Geochemistry, Geophysics, Geosystems, doi:10.1002/ggge.20136.