Long-term slip rates and fault interactions under low contractional strain, Wanganui Basin, New Zealand

[1] The newly mapped Kapiti-Manawatu Fault System (KMFS) in southern North Island, New Zealand, accommodated similar to 3.5 km of basement throw over the last 3 Myr. Along-strike throw profiles are generated using seven stratigraphic markers, interpreted from seismic reflection profiles acquired < 3 km apart. The profiles are symmetrical about their point of maximum displacement, and cumulative profiles suggest that the reverse fault system behaves coherently. The KMFS originates from the reactivation of extensional structures, with fault lengths remaining constant over time. Contractional deformation started at circa 1750 +/- 400 ka. Maximum dip-slip rates along individual faults are 1.77 +/- 0.53 and 0.74 +/- 0.22 mm yr(-1) for the 0 - 120 and 120 - 1350 ka periods, respectively. The maximum cumulative throw rates across the KMFS are 4.9 +/- 1.5 and 1.5 +/- 0.5 mm yr(-1) for the same periods. Long-term strain rates across the KMFS are 2 - 5 times smaller than strain rates in the forearc basin of the Hikurangi subduction margin located less than 100 km to the east. The faults of the KMFS may extend to depth and link with the subducted Pacific plate.