Characterizing the seismogenic zone of a major plate boundary subduction thrust: Hikurangi Margin, New Zealand

Abstract

[1] The Hikurangi subduction margin, New Zealand, has not experienced any significant (>M w 7.2) subduction interface earthquakes since historical records began $170 years ago. Geological data in parts of the North Island provide evidence for possible prehistoric great subduction earthquakes. Determining the seismogenic potential of the subduction interface, and possible resulting tsunami, is critical for estimating seismic hazard in the North Island of New Zealand. Despite the lack of confirmed historical interface events, recent geodetic and seismological results reveal that a large area of the interface is interseismically coupled, along which stress could be released in great earthquakes. We review existing geophysical and geological data in order to characterize the seismogenic zone of the Hikurangi subduction interface. Deep interseismic coupling of the southern portion of the Hikurangi interface is well defined by interpretation of GPS velocities, the locations of slow slip events, and the hypocenters of moderate to large historical earthquakes. Interseismic coupling is shallower on the northern and central portion of the Hikurangi subduction thrust. The spatial extent of the likely seismogenic zone at the Hikurangi margin cannot be easily explained by one or two simple parameters. Instead, a complex interplay between upper and lower plate structure, subducting sediment, thermal effects, regional tectonic stress regime, and fluid pressures probably controls the extent of the subduction thrust's seismogenic zone.Components: 20,324 words, 15 figures.

Investigating subduction earthquake geology along the southern Hikurangi margin using palaeoenvironmental histories of intertidal inlets

“…Figure A1.1A is based on a coupling model from Wallace et al (2008) and Fig. A1.1B is based on a coupling model from Wallace et al (2009). Both of the couplings behind these two vertical deformation models fit the onshore GPS velocities equally well.…”

“…MFS: Marlborough fault system; NIDFB: North Island dextral fault belt. B, Distribution of interseismic coupling at the Hikurangi margin interpreted from campaign GPS measurements (Wallace et al 2009). C, Localities and active faults of the southern Hikurangi margin, encompassing the lower North Island and north-western South Island.…”

“…Evidence for past subduction earthquakes includes subsided tidal marshes and coral reefs and, elsewhere, uplifted beaches; both are often associated with synchronous tsunami deposits. In the central Hikurangi margin sudden subsidence of intertidal sediments and associated tsunamis are probable evidence of past subduction earthquakes at c. 5550 and c. 7000 years BP (Cochran et al 2006;Wallace et al 2009). Along the southern Hikurangi margin pervasive active upper plate faulting causes coastal deformation (Fig.…”

“…The hazard of subduction earthquakes along the Hikurangi margin is therefore highly uncertain at present (e.g. Wallace et al 2009). Globally, almost all palaeoseismic records of subduction earthquakes have been obtained from the coastal zone (e.g.…”

Holocene rupture of the Repongaere fault, Gisborne: Implications for Raukumara Peninsula deformation and impact on the Waipaoa Sedimentary System

“…1B): (1) the backarc, characterised by the Taupo volcanic Zone (TvZ) and normal faults of the Taupo Rift; (2) the basementcored backstop (axial ranges), which is crossed by obliquenormal faults of the North island Fault System (moulsopoulou et al 2007a,b, 2009); (3) the now partly uplifted inner forearc, which is cut by normal faults (including the Repongaere Fault); and (4) the still submerged outer forearc, deformed by reverse faults and associated folds. The subduction interface lies at a depth of c. 15 km near the east coast and c. 30 km below the crest of the Raukumara Ranges (ansell & Bannister 1996;Wallace et al 2009). …”