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doi:10.2204/iodp.sp.343.2012

Risk and contingency

Contingency

Contingency operations for Expedition 343 are based on the current state of knowledge at the time of writing this Scientific Prospectus. These plans may be modified both before and during the expedition, based on continuing JFAST Project Management Team discussions. The Expedition 343 drilling schedule is shown in Table T1. The following operations are planned:

• Install riserless MTL observatory at proposed Site JFAST-3, Hole A, comprising an internal string suspending a mix of RBR and ANTARES MTLs; and

• Install riserless CORK observatory at proposed Site JFAST-3, Hole B, comprising external pressure sensors and internal thermistor string.

Risks

There are significant technical and logistical challenges for this project, including drilling in 7000 m water depth and conducting long-term monitoring of temperature and pressure. The drilling and monitoring plans presented are the result of extensive discussions, including the platform operators, and are considered to be feasible operations. A decision tree of operations for the various successes and failures of the operational plan is shown in Figure F8.

If operational difficulties prohibit completion of the primary borehole goals of the project, plans for drilling alternative sites have also been prepared for any remaining ship time. Boreholes of ~200 m can be drilled with LWD to obtain estimates of absolute stress levels from observations of borehole breakouts. Four possible sites (JFAST-5, JFAST-6, JFAST-7, and JFAST-8) are located at site survey crossing points, as shown in Figure F9. Estimates of the stress levels are important for evaluations of models of the fault coupling along the tip of the shallow megathrust. These sites can also be considered for drilling. If all the operations for the primary goals are completed ahead of schedule, these drilling sites will also be considered.

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