The structure and seismic potential of the Aotea and Evans Bay faults, Wellington, New Zealand

Abstract

ABSTRACTThe active Aotea and Evans Bay faults underlie Wellington Harbour/Te Whanganui a Tara, and are inferred to extend south beneath Wellington City and eastern suburbs. The Aotea Fault dips east, has reverse displacement, and projects onshore beneath the western flank of Mount Victoria/Matairangi and Te Aro, where a basement fault has been inferred previously. East of Mount Victoria, the Evans Bay Fault may dip west and extend southward beneath the Rongotai isthmus. Marine seismic-reflection profiles tied to dated sediment cores indicate vertical separation rates of ∼0.6 ± 0.3 mm/yr on both the Aotea and Evans Bay faults, and evidence of at least two, and one, seafloor-rupturing earthquakes during the last 10,000 years on each fault, respectively. Previously, neither fault has been recognised specifically in seismic hazard assessments of New Zealand. We infer that earthquakes activating these faults have magnitude Mw ≥ 7, potential rupture lengths exceeding 30 km, and possibly involve multiple faults.