A geometric model to estimate slip rates from terrace rotation above an offshore, listric thrust fault, Kaikōura, New Zealand

Abstract

The Kaikōura Peninsula lies at the transition from subduction to continental collision at the southern end of the Hikurangi subduction system. This study uses a 2012 lidar survey over the Kaikōura Peninsula to re-map a flight of four uplifted Late Pleistocene marine terraces at high resolution. The lidar shows that the terraces are being progressively tilted landwards in a manner consistent with listric thrust faulting offshore. The fault, known as the Kaikōura Peninsula Fault, dips shallowly at c.30° to the northwest at depth and probably truncates the Seaward segment of the Hope Fault in the footwall of the Jordan Thrust. Geometric analysis of the tilt, using ages based on previous dating and a regional sea level curve, suggests that slip rates on the Kaikōura Peninsula Fault have ranged between 2.3 ± 1.5 mm/yr and 4.1 ± 1.3 mm/yr over the Late Pleistocene. The elevations of Late Holocene fringing beaches track regional sea level changes, apart from a departure indicating a single uplift event (penultimate earthquake) in the late 18th to earliest 19th century (1702–1838 CE), followed by uplift in the 2016 Kaikōura earthquake. The slip rate calculated from beach uplift, including the Kaikōura earthquake, is consistent with longer term rates. The accumulation of the slip over only c.220 years following >2000 years of quiescence suggests that the offshore thrust and associated faults exhibit clustered behavior, possibly as a result of keystone faulting.