Characterisation of faults as earthquake sources from geomorphic data in the Tongariro Volcanic Complex, New Zealand

At the southern Taupo Rift, tectonic faults and volcanic edifices have interacted during the last 350 kyr. The NNE-striking Tongariro Volcanic Complex is bounded and displaced by four parallel normal faults: National Park, Waihi, Poutu and Upper Waikato Stream, which collectively define the Tongariro Graben. Offsets of geomorphic surfaces of known age and fault trace geometry were used to characterise the seismic parameters of these faults. Along-strike distribution of fault displacement suggests that these faults could rupture as a whole. However, geomorphic data and geometrical characteristics of surface ruptures suggest that they could also rupture in shorter segments. This study calculates higher slip-rates (∼2.6 ± 0.8 and 2.2 ± 1.9 mm/yr for Waihi and Poutu fault zones, respectively) and greater earthquake magnitudes (up to MW 7.2 ± 0.1 and 6.9 ± 0.1, respectively) than previous studies, suggesting an important seismic hazard for the Tongariro area.