© ICDP, the International Continental Scientific Drilling Program, 1996-2020

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Deep Fault Drilling Project (DFDP), Alpine Fault, New Zealand: Phase 2 - conditions at 1.5 km depth

Oceania, New Zealand, South Island, Alpine Fault

new full-proposal: ICDP-2011/01
for the funding-period starting 2011-01-15
by Rupert Sutherland, John Townend, Virginia Gail Toy
Abstract
Determining what temperatures, stresses, and chemical conditions prevail within active faults is fundamental to understanding how faults evolve and produce earthquakes. The Alpine Fault’s geometry, rapid and precisely-known slip rates, well-studied surface exposures, and >40 years of intensive research make it a site of global importance for research into the mechanics and evolution of large faults and the conditions under which earthquakes occur. Unlike many other major faults, however, the Alpine Fault has not produced large earthquakes in historic times, providing an opportunity to study a major fault late in the cycle of stress accumulation ahead of a future earthquake. Phase 1 of the Deep Fault Drilling Project (January–February 2011) will collect rock cores and wireline logs, and install an observatory in the near-surface of the Alpine Fault (150 m depth). Phase 2 of the project (this proposal) aims to determine ambient conditions on the Alpine Fault beneath near-surface anomalies and, for the first time, to precisely estimate the thermal, stress, and hydraulic states of the Alpine Fault in the mid-crust. The intended fault intersection depth of 1500 m is based upon numerical models that show the thermal, stress, and hydraulic anomalies caused by local topography to be large within 1000–1500 m of the surface. Measurements in the lower part of the borehole, beneath the perturbed zone, will enable us to determine gradients characteristic of greater depths. Measurements in the upper part of the borehole will be used to determine bulk rock properties and hence we will be able to construct 3D thermal and hydraulic models of the near-surface. Fresh rock cores from the fault zone beneath these near-surface effects will provide new insight into the mechanisms of deformation that occur in the mid-crust on a major plate-bounding fault. Finally, the borehole observatory that we will install will provide long-term monitoring of a fault estimated to have a 25% probability of rupture in the next 30 years, providing a unique opportunity to study transient behavior in the event of a large earthquake. We have assembled a large international team of researchers to undertake Alpine Fault drilling and allied research. We are seeking US$1.3M to complete the DFDP-2 phase of research. We have secured the other 50% of the drilling budget from a range of sources.
Scientific Objectives
  • The Deep Fault Drilling Project is motivated by a long-standing scientific question: what are the physical conditions in the mid-crust under which large, active continental faults evolve and generate earthquakes? We will drill two vertical boreholes in the lower Whataroa Valley: one situated within 150 m of the Alpine Fault trace and the second to intersect the fault at a target depth of 1500 m and reach a total depth of 1600 m. The objectives of our first (150 m) borehole, DFDP-2A, are to:
  • 1. Confirm the precise location and dip of the fault plane at the southwestern valley flank;
  • 2. Construct a geophysical observatory for cross-borehole and long-term analysis; and 3. Collect a set of rock cores and wireline logs through the shallow fault zone. The precise location of our second borehole will be informed by results from the first and by detailed geophysical surveys. The objectives of borehole DFDP-2B (1600 m) are to:
  • 1. Characterize fault zone lithologies and structures using rock cores and wireline logs;
  • 2. Determine in-situ temperatures, fluid pressures, and stresses via wireline logging and low-volume minifrac tests;
  • 3. Measure bulk rock permeability using hydraulic tests; and 4. Install a resilient permanent observatory around the fault at 1500 m depth.
Keywords
Active faults, Alpine fault, Brittle, DFDP, Ductile, ICDP-2011/01, New zealand, Seismogenic zone
Location
Oceania, New Zealand, South Island, Alpine Fault: -43.31607077, 170.3254968

© ICDP, the International Continental Scientific Drilling Program, 1996-2020

www.icdp-online.org