Fault Zone Drilling
IODP-MI/ICDP Workshop on Fault Zone Drilling: Developing a Global Perspective
This workshop will bring together active team members (both scientists and engineers) of fault-zone drilling projects for an open and detailed exchange of results, ideas, and experiences, fostering cooperation and synergy in interpretation of findings, experiment design, and technology development. Despite the different tectonic environments and specific scientific objectives, all of these diverse projects share the challenges of drilling into unstable active faults with an emphasis on in situ measurements. Development of the technological capability to successfully drill, test, sample and instrument the active fault environment is critical to the success of all the projects.
From the SeaGaia Resort in Miyazaki, Japan, this workshop will include a one-day field trip to spectacular coastal exposures of a plate boundary thrust fault system exhumed from seismogenic depth.
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The past few years have seen the initiation of a number of high profile fault zone drilling projects (Table 1). Each of these projects has unique objectives and scientific drivers, yet they share the fundamental goal of seeking direct access to zones of active deformation of the Earth's crust. This burgeoning interest in active fault drilling is taking place in the context of very rapidly growing research efforts on the mechanics and dynamics of faulting processes, integrating rock mechanics, seismology, geodesy, frictional physics, and fluid-fault interactions. Earthquakes and their attendant effects such as tsunami represent one of the greatest natural hazards to society, yet detection of precursory warning signals-not to mention their prediction-remains elusive.
Table 1: Major Active Fault Zone Drilling Projects
Extant rheological models for how faults behave depend on specific physical properties at the fault interface and in the surrounding rock volume, such as coefficients of friction, permeability, pore fluid pressure, state of stress, and elastic stiffnesses - all parameters that can best be addressed in situ , by drilling, sampling, and monitoring active fault zones in the subsurface.
The core purpose of this workshop is to provide a forum for an open and detailed exchange of scientific and technical knowledge, ideas, lessons learned, and fundamental science drivers among the various projects. The workshop will bring together participants from all the active fault zone drilling projects, to address both science and technology of drilling, sampling, testing, and long-term monitoring of active faults, especially those at plate boundaries.
The various active FZ drilling projects, both on land and at sea, are in different stages of completion, ranging from projects that are still in the planning to those that are essentially complete. While the large-scale questions are at least in part shared, each current project addresses a unique tectonic setting, point in the seismic cycle, or relationship between seismic and aseismic deformation, and each has its own scientific drivers and experiment design. Pursuit of all of these projects affords a much more complete picture than any of them in isolation, yet raises the challenge of how to keep communication and information exchange open among this international diversity of complex projects. Additionally, the scientific rationale for many of these projects was developed in the 1990s; the science of fault zone physics has advanced rapidly in the past 5 years, and the time is right for an assessment and update of the fundamental questions driving fault zone studies.
Fault zone drilling projects are different in important respects from most other scientific drilling efforts. In general, fault zone targets include discontinuities and small, anomalous intervals in large rock volumes, rather than the stratigraphic succession. The targets of interest are often the exact locations of poorest drilling conditions, such as a highly - fractured and potentially overpressured fault volume. The scientific approach commonly focuses on obtaining very extensive downhole measurements, logs, cores, and seismic structure in and around these fault zone environments. Measurements at the time of drilling as well as long-term observations are emphasized. Furthermore, the practices and experience of industry drilling do not transfer easily to fault zone projects. Specialized drilling and borehole engineering techniques are required to achieve project goals, and much of the expertise lies in the scientific drilling community. Though there is overlap among the various continental and ocean drilling groups, all will benefit from an opportunity for exchange.
Professor Gaku Kimura of the University of Tokyo will lead a field trip to spectacular and dramatic coastal outcrop exposures of a subduction zone thrust fault near the town of Nobeoka, about 1.5 hours by coach bus from the meeting location. This fault zone is the subject of substantial current research effort, and has been interpreted as a well-preserved, exhumed example of a fault active in the plate boundary interface (the "megathrust"). Visiting this fault zone as a group of scientists and engineers together will help us develop an appreciation for the complexity of fault rocks, challenges of targeting them by drilling, and ways to infer 3-D structure from a 1-D borehole. Further field trip information will be provided soon.
This may be published as a special issue of the new journal Scientific Drilling . We have secured the agreement of the editors.