Imaging beneath the Taranaki fault, New Zealand ? A feasibility study for wide-angle seismic surveys

The Taranaki overthrust fault at the the eastern boundary of New Zealand's most significant hydrocarbon province, the Taranaki Basin, presents a challenge to the exploration industry. Seismic imaging of potential hydrocarbon traps beneath the fault is difficult using conventional streamers with lengths of up to 6 km, mainly because the high velocities of overthrust greywacke deviate rays to large offsets. We present a modelling study of the feasibility of wide-angle experiments to undershoot the fault. We performed raytracing to predict ray coverage at horizons beneath the fault as a proxy for expected image quality. Our results suggest that by increasing the length of seismic streamers from 6 to 12 km, which is possible with modern streamers, ray coverage across potential hydrocarbon traps would increase significantly. Deeper targets, which would be of interest for studying the tectonic evolution of the Taranaki Basin and the source rock distribution, will require ``true' wide-angle experiments with ocean bottom seismometers. We also predict significant coverage with P-to-S mode-converted waves. Elastic full-wavefield modelling using a simplified velocity model suggests strong mode conversion on the greywacke/sediment interfaces.