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The Rangipo fault, Taupo rift, New Zealand: An example of temporal slip-rate and single-event displacement variability in a volcanic environment

Pilar Villamor^,1, Russell Van Dissen^,1, Brent V. Alloway^,1, Alan S. Palmer^#,2 and Nicola Litchfield^,3

¹ GNS Science, P.O. Box 30-368, Lower Hutt 5040, New Zealand
² Institute of Natural Resources, Massey University, Private Bag 11-222, Palmerston North, New Zealand
³ GNS Science, P.O. Box 30-368, Lower Hutt 5040, New Zealand

Geomorphic mapping and paleoseismic studies reveal that the Rangipo fault, the eastern boundary of the southern section of the Taupo rift, New Zealand, has highly variable single-event displacement and slip rate in time. Variability in single-event displacement (0.1–1.2 m since 14 cal. ka) is possibly the result of different fault rupture modes: primary (unsegmented and segmented) and secondary. Variability in fault-slip rate is attributed to interactions with volcanic activity of the nearby Ruapehu volcano (11 km distant), the southernmost and largest andesitic volcanic edifice within the southern Taupo volcanic zone. The Rangipo fault has had a mean slip rate of 1.4 mm/yr since ca. 25 cal. ka (calibrated radiocarbon age in thousands of years before present), and a mean slip rate of only 0.2 mm/yr since 14 cal. ka. This implies that during the period between 14 and 17–25 cal. ka, the fault had a slip rate of 2–9 mm/yr. This period of increased slip rate coincided with the most voluminous eruptions from Ruapehu volcano in the past 100 k.y. We infer that there is an interaction between the Rangipo fault and Ruapehu volcano, although we cannot confirm the sense of the interaction (i.e., volcanofault or faultvolcano). The interaction could be related to pulsed rifting, where major rifting occurs in periods of accelerated faulting that coincide with extensive eruptions.

Key Words: Taupo volcanic zone • Taupo rift • active normal fault • active andesitic volcano • volcano-tectonic interactions • slip-rate variability • single-event displacement variability