Geometry of the Hikurangi subduction thrust and upper plate, North Island, New Zealand

• Published in: Geochemistry, geophysics, geosystems : G3 Vol. 10; no. 2; pp. np - n/a
• Main Authors: Barker, Daniel H. N., Sutherland, Rupert, Henrys, Stuart, Bannister, Stephen
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 01.02.2009
• Subjects: Dipping; earthquake; Failure; forearc; Roughness; Sediments; seismic reflection; Slabs; Slopes; subduction; tectonics; Thrust; Wedges; New Zealand; PSE, New Zealand; PSE, New Zealand, North I., Hawke's Bay, Hawke Bay; New Zealand, North I., Northland, Hikurangi; New Zealand, North I
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2008GC002153

We use 2800 line km of seismic reflection data to map the offshore character and geometry of the Hikurangi subduction thrust and outer forearc wedge to depths of ∼15 km. For 200 km along‐strike south of Hawke Bay, the subduction thrust is relatively smooth, dips less than 8°, and the wedge is characterized by accretion of young sediment and topographic slopes of less than 3°. In Hawke Bay and north for 200 km, a kink in the subduction thrust is apparent, with a downdip increase in dip to angles greater than 8° at depths of 10–15 km; there is a corresponding steepening of the topographic slope to greater than 3° outboard of the kink and the wedge is characterized by lithified sedimentary rock and slope failure. The kink in the subduction thrust is a locus of inherent weakness in the subducting slab; we suggest its occurrence relates to a northward increase in subduction rate that controls initial slab dehydration and fluid release rates and hence intraslab deformation patterns. The subduction thrust geometry, in combination with a northward increase in subducting plate roughness and decrease in the amount of sediment accreted, causes the observed spatial change in character of the subduction thrust and forearc wedge.