Analysis of late Holocene faulting within an active rift using lidar, Taupo Rift, New Zealand



Begg, J.G.1 & Mouslopoulou, V.
1 - GNS Science, Lower Hutt, New Zealand

Abstract - High-quality Light Detection and Ranging (lidar) data collected across the Rangitaiki Plains, the fastest extending section of the onshore Taupo Rift, New Zealand, reveal 122 active fault traces and provide new constraints on displacements, displacement rates and paleoearthquakes of the normal faults in the rift. The identified lineaments are scarps that record vertical offset of geomorphic surfaces (e.g., beach ridges, meander channel floors, river terraces, etc.) and trend parallel or sub-parallel to other active faults in the rift; these lineaments are interpreted to be active faults. Active fault traces trend ca 060° and their lengths range from 0.25 to 6 km. They mainly traverse and displace a diachronous landscape of ca 6.5kyr age, with throws that vary from 0.05 to 7 m and form a graben. Historic, geometric and kinematic constraints have been used to aggregate individual traces into eight fault zones that range in length from5 to 40 km. Displacement rates in the rift beneath the Rangitaiki Plains vary between and along individual faults by more than one and three orders of magnitude, respectively, over the last 0.64 and/or 1.72 kyr. Variability of displacement rates on individual faults arises from episodic slip accumulation during a minimum of 15 paleoearthquakes of variable slip and recurrence interval. Repeated fault movements have produced about 3 mm/yr of subsidence over the last ca 2 kyr within the rift (i.e. between the Edgecumbe and Matata faults) while relatively stable conditions have persisted (uplift/subsidence of 0–0.6mm/yr) on the rift shoulders for the last 3.3 to 6.5 kyr. These plain-wide signals of vertical movement were interrupted by short-lived episodes of rapid uplift (0–1.72 kyr) and subsidence (1.72 to ca 2.1 kyr) at the western and eastern margins, respectively, which we infer to result from prehistoric earthquakes.

Journal of Volcanology and Geothermal Research, 190, 152-167, 2010.