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Expedition 314 Site C00031

Expedition 314 Scientists2

Background and objectives

Integrated Ocean Drilling Program Site C0003 (proposed Site NT2-01D) is located on the lower slope off Kii Peninsula, just seaward of the Kumano forearc basin. The Site C0003 summary log diagram is shown in Figure F1.

Goals at proposed Site NT2-01 included logging while drilling (LWD) of ~1000 m of the midslope region, across at least one major strand of the megasplay fault system (Fig. F2). This proposed site was intended to begin the downdip transect of the megasplay fault system by sampling a relatively shallow, presumably aseismogenic point on the fault zone at ~800 meters below seafloor (mbsf). The anticipated lithology was deformed terrigenous sediment, faults, and possible gas hydrate, though there is no clear bottom-simulating reflector at this site. Beneath the near-surface slope deposits, the acoustically transparent zone above the reflective thrust fault was predicted to be composed of highly deformed and faulted accretionary mélange and/or disrupted stratigraphy of slope deposits. Beneath the fault reflector, three-dimensional (3-D) seismic data suggested drilling would penetrate deformed but stratigraphically intact slope sediments overridden by the splay thrust fault.

Unfortunately, we encountered very difficult drilling conditions at Site C0003, such as especially pronounced caving and washout of likely fault zones and possibly sandy intervals, which caused the drill string to become irretrievably stuck before reaching the primary objective. We lost a complete LWD tool string and ~200 m of drill collars at this site. Nevertheless, real-time data transmission provided substantial logging data from the seafloor to ~530 m LWD depth below seafloor (LSF). This incident prompted the decision to add another site (C0004) in order to drill through the shallower part of the megasplay fault zone to meet the primary objective (see the “Expedition 314 Site C0004” chapter for details).

1 Expedition 314 Scientists, 2009. Expedition 314 Site C0003. In Kinoshita, M., Tobin, H., Ashi, J., Kimura, G., Lallemant, S., Screaton, E.J., Curewitz, D., Masago, H., Moe, K.T., and the Expedition 314/315/316 Scientists, Proc. IODP, 314/315/316: Washington, DC (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/​iodp.proc.314315316.115.2009

2 Expedition 314/315/316 Scientists’ addresses.

Publication: 11 March 2009
MS 314315316-115