Structure and paleoearthquake records of active submarine faults, Cook Strait, New Zealand: Implications for fault interactions, stress loading, and seismic hazard

Abstract

[1] A new interpretation of active faulting in central Cook Strait, New Zealand, reveals tectonic structures associated with the spatial transition from subduction to continental transform faulting. Marine seismic reflection profiles and multibeam bathymetric data indicate that there are no throughgoing crustal faults connecting the North Island Dextral Fault Belt and the Marlborough Fault System in South Island. The major faults terminate offshore, associated with 5-20 km wide step-overs and a change in regional fault strike. This structure implies that propagation of strike-slip earthquake ruptures across the strait is not probable. Faulted sedimentary sequences in the Wairau Basin (Marlborough shelf), correlated to glacioeustatic sea level cycles, provide a stratigraphic framework for fault analysis. A high-resolution study of the postglacial (<20 ka) vertical displacement history of the Cloudy and Vernon faults reveals up to six and five paleoearthquakes since 18 ka, respectively. These long-timescale records indicate variable recurrence intervals and possibly variable stress drop, thus conforming to the variable slip model of earthquake behavior. Integration of these data with other submarine and terrestrial paleoearthquake records indicates the presence of clustered earthquake sequences involving multiple faults. Different sequences do not always involve the same faults. It appears that earthquake clustering is driven by fault interactions that lead to specific loading conditions favoring the triggering of earthquakes on major faults in relatively short time intervals. Present-day regional Coulomb stress distribution has been calculated in two scenarios considered to represent minimum and maximum loading conditions. The models, incorporating secular tectonic loading and stress changes associated with major crustal earthquakes, indicate high stress loading in a large part of central Cook Strait. These conditions may favor the triggering of future damaging earthquakes in this region.Citation: Pondard, N., and P. M. Barnes (2010), Structure and paleoearthquake records of active submarine faults, Cook Strait, New Zealand: Implications for fault interactions, stress loading, and seismic hazard,

Understanding the potential for tsunami generated by earthquakes on the southern Hikurangi subduction interface

“…However, major faults may coalesce in the crust and sole at the décollement (Eberhart-Phillips et al 2014). For example, there may be a kinematic connection between the Kekerengu Fault in the South Island and the Wairarapa Fault in the North Island (Wallace et al 2012a), although they do not appear to constitute a clear, through-going structure (Pondard & Barnes 2010). Bathymetry data offshore Wairarapa and the Marlborough coast show that the shelf break and a number of prominent ridges are cored by large splay faults emerging from the plate boundary.…”

“…The locations of active faults beneath Cook Strait ( Figure 1B) indicate there is a general discontinuity between the faults in the lower North Island and the Marlborough Fault System (Pondard and Barnes 2010). No through-going fault traces connecting North and South islands are observed on multibeam bathymetry data.…”

“…Here the Pacific Plate is subducted westwards beneath the Australian Plate. The transition from Hikurangi subduction to the strike-slip Marlborough Fault System occurs within Cook Strait and the northeastern corner of the South Island (Carter et al 1988;Little and Roberts 1997;Barnes et al 1998;Pondard and Barnes 2010;Wallace et al 2012a). Northeast-striking dextral strike-slip faults occur in the North Island forearc (the North Island Dextral Fault Belt; NIDBF) and also in the South Island, where they form the Marlborough Fault System (MFS).…”

“…Field et al 1997;Mountjoy et al 2009;Barnes et al 2010;Pondard and Barnes 2010). These lines were acquired to determine shallow fault geometry (up to 5 km depth) and sedimentary basin stratigraphy, but lacked the large source volumes needed to image the plate boundary at 10-30 km depth.…”

National Seismic Hazard Model for New Zealand: 2010 Update

“…The largest change to the Stirling et al (2002) model is the extension of the faults offshore into Cook Strait and eastern Marlborough (e.g., Barnes and Audru, 1999a, b;Barnes and Pondard, 2010;Pondard and Barnes, 2010). One key finding of these recent studies is confirmation that faults do not directly link across Cook Strait with the North Island dextral fault belt, that strike-slip faulting extends into the southern Hikurangi margin, and that the offshore extent of the Wairau fault is limited to about 40 km in Cook Strait (cf.…”