Cardiff University | Prifysgol Caerdydd ORCA
Online Research @ Cardiff 
WelshClear Cookie - decide language by browser settings

The Alpine Fault hangingwall viewed from within: structural analysis of ultrasonic image logs in the DFDP-2B Borehole, New Zealand

Massiot, Cécile, Célérier, Bernard, Doan, Mai-Linh, Little, Tim A., Townend, John, McNamara, David D., Williams, Jack ORCID:, Schmitt, Douglas R., Toy, Virginia G., Sutherland, Rupert, Janku-Capova, Lucie, Upton, Phaedra and Pezard, Philippe A. 2018. The Alpine Fault hangingwall viewed from within: structural analysis of ultrasonic image logs in the DFDP-2B Borehole, New Zealand. Geochemistry, Geophysics, Geosystems 19 (8) , pp. 2492-2515. 10.1029/2017GC007368

[thumbnail of Massiot_et_al-2018-Geochemistry,_Geophysics,_Geosystems.pdf]
PDF - Published Version
Download (16MB) | Preview


Ultrasonic image logs acquired in the DFDP‐2B borehole yield the first continuous, subsurface description of the transition from schist to mylonite in the hangingwall of the Alpine Fault, New Zealand, to a depth of 818 m below surface. Three feature sets are delineated. One set, comprising foliation and foliation‐parallel veins and fractures, has a constant orientation. The average dip direction of 145° is subparallel to the dip direction of the Alpine Fault, and the average dip magnitude of 60° is similar to nearby outcrop observations of foliation in the Alpine mylonites that occur immediately above the Alpine Fault. We suggest that this foliation orientation is similar to the Alpine Fault plane at ∼1 km depth in the Whataroa valley. The other two auxiliary feature sets are interpreted as joints based on their morphology and orientation. Subvertical joints with NW‐SE (137°) strike occurring dominantly above ∼500 m are interpreted as being formed during the exhumation and unloading of the Alpine Fault's hangingwall. Gently dipping joints, predominantly observed below ∼500 m, are interpreted as inherited hydrofractures exhumed from their depth of formation. These three fracture sets, combined with subsidiary brecciated fault zones, define the fluid pathways and anisotropic permeability directions. In addition, high topographic relief, which perturbs the stress tensor, likely enhances the slip potential and thus permeability of subvertical fractures below the ridges, and of gently dipping fractures below the valleys. Thus, DFDP‐2B borehole observations support the inference of a large zone of enhanced permeability in the hangingwall of the Alpine Fault.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Publisher: American Geophysical Union (AGU)
ISSN: 1525-2027
Date of First Compliant Deposit: 11 September 2018
Date of Acceptance: 23 April 2018
Last Modified: 03 May 2023 12:35

Citation Data

Cited 17 times in Scopus. View in Scopus. Powered By Scopus® Data

Actions (repository staff only)

Edit Item Edit Item


Downloads per month over past year

View more statistics