T23D-2986
Temperature Anomalies in DFDP-2B Borehole, Alpine Fault, New Zealand: Implications for Hydrology and Stress in the Uppermost Crust
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Lucie Capova1, John Townend2, Rupert Sutherland3, Mai-Linh Doan4, Cecile Massiot1, Bernard P Celerier5 and DFDP Science Team, (1)Victoria University of Wellington, Wellington, New Zealand, (2)Victoria University of Wellington, School of Geography, Environment, and Earth Sciences,, Wellington, New Zealand, (3)GNS Science-Institute of Geological and Nuclear Sciences Ltd, Lower Hutt, New Zealand, (4)ISTerre Institute of Earth Sciences, Saint Martin d'Hères, France, (5)University of Montpellier II, Montpellier Cedex 05, France
Abstract:
A total of 16 temperature logs extending to a maximum depth of 893 m were acquired by wireline logging as part of DFDP-2B drilling operations in the Whataroa Valley, South Island, New Zealand. Temperature profiles acquired at different times after circulation record the evolution of temperatures towards equilibrium and thus allow us to estimate the thermal diffusivity of the rock environment in the Alpine Fault’s hanging wall. After drilling stopped, a multi-strand fibre-optic cable was installed along the full length of the 893 m-deep borehole. This cable has been used to make repeated temperature measurements on an approximately two-monthly basis since January 2015. Local temperature anomalies correlate with fractures identified in borehole televiewer and laterolog data. Zones where temperature profiles differ from the average geothermal gradient indicate thermal disturbance, caused by advection of heat by fluids. The identification and characterisation of flowing fractures provide insight into the permeability structure, stress field, and hydrogeological regime of the hanging wall of the central Alpine Fault.
