Fault ruptures triggered by large rhyolitic eruptions at the boundary between tectonic and magmatic rift segments: The Manawahe Fault, Taupō Rift, New Zealand

The Manawahe Fault is located at the boundary between the tectonic Whakatane and the magmatic Okataina segments of the Taupō Rift. We investigate prehistoric ground surface fault ruptures and their timing in association with volcanic eruptions of the Okataina Volcanic Centre (OVC), using geomorphic fault mapping, paleoseismic trenching, ground penetrating radar and shallow drillcores. Paleoseismic trench data across the major strand shows that the Manawahe Fault ruptured at least seven times in the last c. 9.5 cal. ka (with a possible rupture 8 just prior to c. 9.5 cal. ka). At least four of these surface fault ruptures occurred during, or immediately prior to, volcanic eruptions. These eruptions, named Whakatane (c. 5.5 cal. ka – 1 fault rupture), Mamaku c.8 cal. ka −1 fault rupture), and the Rotoma (c. 9.5 cal. ka - 2-3 fault ruptures), were all sourced from the nearby Haroharo Volcanic Complex nested within the OVC, one of the two currently active volcanic lineaments within the OVC. Ground penetrating radar and drillcore data show that the Manawahe Fault has a slip rate of c. 3 mm/yr and that it only formed recently (< 26.5 ka ago), much more recently than the last caldera forming eruption, the c. 61 ka Rotoiti eruption. Fault rupture recurrence is 1580–2000 years. We discuss possible modes of ruptures of the Manawahe Fault in association with modes of volcanic unrest and magmatic processes; whether these prehistoric ruptures were seismogenic or not, and what the implications are for volcanic and seismic hazard.