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doi:10.2204/iodp.proc.314315316.113.2009 Expedition 314 Site C00011Expedition 314 Scientists2Background and objectivesIntegrated Ocean Drilling Program (IODP) Site C0001 (proposed Site NT2-03B) targets the uppermost 1000 meters below seafloor at the seaward edge of the Kumano Basin uplift (outer arc high) where the megasplay fault system branches and approaches the surface (see Figs. F1, F2 in the “Expedition 314 summary” chapter). The Site C0001 summary log diagram is shown in Figure F1. Both inline and cross-line three-dimensional (3-D) seismic lines crossing Site C0001 are shown in Figure F2. Locations of drill holes at Site C0001 are plotted in Figure F3 with 3-D seismic profile coverage. The upper 1000 m drilled during this expedition provided an opportunity to access the thrust sheets uplifted by several branches of the megasplay fault system, as well as a thin overlying slope sediment cover sequence. The nature of the material in these thrust sheets was unknown. As with proposed Site NT2-01 (Sites C0003–C0005), the acoustically nonreflective nature of this section suggests that it may be composed of chaotically deformed accretionary prism sedimentary mélange transported from significantly greater depth. The principal objective at this site was to obtain in situ density, resistivity, gamma ray values, porosity, P-wave velocity, and photoelectric factor (PEF) data through logging-while-drilling (LWD) and seismic-while-drilling operations. Together with later core samples, logs from this site discriminate among the structural possibilities and provide data on physical properties, strength, composition, and structure of the hanging wall of the main megasplay branch. The upper 1000 m of drilling at this site penetrated one or more subsidiary splay branches near the updip end of the splay system, affording an opportunity to compare fault development with Sites C0003–C0005. LWD data at this site will also provide critical “pilot hole” information for later riser-based drilling. To achieve the ~3500 m total depth objective using the riser and weighted drilling mud involves setting multiple casing strings, the depth of each of which depends on the least principal stress, fracture strength of the formation, and pore fluid pressure gradient. The key part of this casing plan is the “top-hole” portion, where tolerances on mud weight are tight. Planning the casing program, therefore, requires excellent information on physical properties in the uppermost 1000 m. |
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