Beschreibung
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.