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Book Chapter

Andersonian wrench faulting in a regional stress field during the 2010–2011 Canterbury, New Zealand, earthquake sequence

By
R. H. Sibson
R. H. Sibson
1
Department of Geology, University of Otago, P.O. Box 56, Dunedin 9054, New Zealand
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F. C. Ghisetti
F. C. Ghisetti
2
Terrageologica, 129 Takamatua Bay Rd., RD1, Akaroa 7581, New Zealand
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R. A. Crookbain
R. A. Crookbain
3
Shell Exploration NZ Ltd, 167 Devon Street West, New Plymouth 4310, New Zealand
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Published:
January 01, 2012

Abstract

The initial Mw7.1 Darfield earthquake sequence was centred west of Christchurch City in the South Island of New Zealand but aftershocks, including a highly destructive Mw6.3 event, eventually extended eastwards across the city to the coast. The mainshock gave rise to right-lateral strike-slip of up to 5 m along the segmented rupture trace of a subvertical fault trending 085±5° across the Canterbury Plains for c. 30 km, in agreement with teleseismic focal mechanisms. Near-field data however suggest that the mainshock was composite, initiating with reverse-slip north of the surface rupture. Stress determinations for the central South Island show maximum compressive stress σ1 to be horizontal and oriented 115±5°. The principal dextral rupture therefore lies at c. 30° to regional σ1, the classic ‘Andersonian’ orientation for a low-displacement wrench fault. An aftershock lineament trending c. 145° possibly represents a conjugate left-lateral strike-slip structure. This stress field is also consistent with predominantly reverse-slip reactivation of NNE–NE faults along the Southern Alps range front. The main strike-slip fault appears to have a low cumulative displacement and may represent either a fairly newly formed fault in the regional stress field, or an existing subvertical fault that happens to be optimally oriented for frictional reactivation.

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Geological Society Special Publications

Faulting, Fracturing and Igneous Intrusion in the Earth’s Crust

D. Healy
D. Healy
University of Aberdeen, Scotland
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R. W. H. Butler
R. W. H. Butler
University of Aberdeen, Scotland
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Z. K. Shipton
Z. K. Shipton
University of Strathclyde, Scotland
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R. H. Sibson
R. H. Sibson
University of Otago, New Zealand
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Geological Society of London
ISBN electronic:
9781862396159
Publication date:
January 01, 2012

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