Seismic imaging of the Waihemo Fault System in the southern Canterbury Basin off coastal Otago

Author:

van Haastrecht, Laurine Nathalie (Laurine)

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Abstract:

The Waihemo Fault System is a major crustal-scale structure that forms the northern boundary of the active north-east striking ranges of Otago, New Zealand. The fault system on the east coast of the South Island is orthogonal to the coast but its offshore geometry is poorly understood. The Waihemo Fault System originated in the Cretaceous as a set of crustal-scale northeast trending normal faults that reactivated as reverse faults in the Late Cenozoic. This study investigates the offshore extent of the Waihemo Fault System, how it changes offshore, and how this compares to the known nature of the onshore fault system.
Three multichannel seismic data sets were used in a comparison study to characterise the offshore section of the Waihemo Fault System. Petroleum industry exploration data from the 1980s were compared to recent seismic data from 2012 (RV Kaharoa 48-channel data with a generator-injector airgun source) and 2014 (RV Polaris II 24-channel data with a boomer source), with notably different depth penetration scales and seismic resolutions.
The Waihemo Fault System can be seen to extend from the basement through the overlying Tertiary sedimentary units, with the Shag Point Anticline visible on the northern side. The new high-resolution data, as well as the older exploration data, appear to partially confirm previously suggested offshore segment fault models, and extend the fault system further offshore. Strands of the Waihemo Fault System are shown to continue from onshore to offshore away from the coast with an approximate northwest-southeast strike. Within the first 5 km offshore, two fault strands are inferred to merge together with a larger main strand. Small conjugate faulting is present on the main strand; however, is discontinuous and did not produce a surface trace. A southeast plunging, anticlinal structure in the hanging wall was imaged, with lateral offset by the Waihemo Fault System. A gas feature is visible on two of the seismic lines. A previously inferred extension of the Titri Fault System in the area, running parallel to the coastline and extending from south of Dunedin, was not imaged but remains a possibility.

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xiv, 69 pages A4, seismic lines in back 8 250mm high, ~1m wide

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OU geology Identifier:

2014van_Haastrecht

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Location (WKT, WGS84):

POLYGON ((170.679218834379611 -45.670042188554518,170.855272927038868 -45.462716745033383,171.036352817015455 -45.364756165144449,171.278982924852983 -45.385342375258553,170.769774737987035 -45.699234243271711,170.679218834379611 -45.670042188554518))

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http://download.otagogeology.org.nz/temp/Abstracts/2014van_Haastrecht.pdf

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Citation

van Haastrecht, Laurine Nathalie (Laurine), “Seismic imaging of the Waihemo Fault System in the southern Canterbury Basin off coastal Otago,” Otago Geology Theses, accessed November 29, 2021, http://theses.otagogeology.org.nz/items/show/587.

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