Active faults, paleoseismology, and historical fault rupture in northern Wairarapa, North Island, New Zealand

Abstract

Active faulting in the upper plate of the Hikurangi subduction zone, North Island, New Zealand, represents a significant seismic hazard that is not yet well understood. In northern Wairarapa, the geometry and kinematics of active faults, and the Quaternary and historical surface-rupture record, have not previously been studied in detail. We present the results of mapping and paleoseismicity studies on faults in the northern Wairarapa region to document the characteristics of active faults and the timing of earthquakes. We focus on evidence for surface rupture in the 1855 Wairarapa (M W 8. Estimates of slip rates provided by these data suggest that a larger component of strike slip than previously suspected is occurring within the upper plate and that the faults accommodate a significant proportion of the dextral component of oblique subduction. Assessment of seismic hazard is difficult because the known fault scarp lengths appear too short to have accommodated the estimated singleevent displacements. Faults in the region are highly segmented, disconnected, and probably structurally immature, which implies that apparent geometric discontinuities at the surface may not be significant barriers to rupture propagation at depth and that the surface rupture record significantly under-represents the seismic slip on faults in the region.

Infrared-stimulated luminescence dating of late Quaternary aggradation surfaces and their deformation along an active fault, southern North Island of New Zealand

“…Beyond Mauriceville, the line of the fault is uncertain but there are several sub-parallel recently active strands within Miocene mudstone that presumably trace its course (Lensen, 1970;Grapes and Wellman, 1988;Grapes, 1991Grapes, , 1999Schermer et al, 2004).…”

Using displaced river terraces to determine Late Quaternary slip rate for the central Wairarapa Fault at Waiohine River, New Zealand

“…Despite this, the magnitude and distribution of its single-event displacement or its Late Quaternary slip rate remain poorly constrained. Estimates of 1855 single-event dextral displacements on the Wairarapa Fault range from as high as c. 18.5 m at Pigeon Bush on the southern part of the fault (Rodgers & Little 2006) to as low as 4Á7 m on the Alfredton Fault, discontinuously linked to the northern end of the Wairarapa Fault (Schermer et al 2004). Estimates of the Late Quaternary dextral slip rate along the central Wairarapa Fault range from 6.5 mm a…”

“…A number of recent studies have quantified the singleevent dextral displacements and placed constraints on the Late Quaternary slip rates for different sections of the Wairarapa Fault (e.g. Van Dissen & Berryman 1996;Schermer et al 2004;Rodgers & Little 2006). Variations in slip rate and single-event displacement northwards along the Wairarapa Fault are the subject of another manuscript.…”

Defining the geometric segmentation and Holocene slip rate of the Wellington Fault, New Zealand: The Pahiatua section

“…The slip-rate decrease is documented for the eastern strand of the NIDFB, which includes the Wairarapa Fault, from Palliser Bay (Fig. 1) to Cape Kidnappers in Hawke's Bay (Beanland 1995;Van Dissen & Berryman 1996;Beanland & Haines 1998;Schermer et al 2004). For the western strand of the NIDFB, which is dominated by the Wellington, Mohaka, Ruahine, and Whakatane Faults (Fig.…”