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Site C00101

Expedition 319 Scientists2

Background and objectives

Integrated Ocean Drilling Program (IODP) Expedition 319 Site C0010 (proposed Site NT2-01J) is a riserless drilling site located 3.5 km along strike of previously drilled and cored IODP Site C0004 (Figs. F1, F2) and was planned to penetrate the megasplay fault at ~410 meters below seafloor (mbsf) and ~150 m into the footwall. A summary of Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) drilling around Site C0010 is shown in Figure F1. The operational and scientific objectives at this site were to

  • Collect logging-while-drilling (LWD) and measurement-while-drilling (MWD) data to 560 mbsf to complement LWD and core data collected during IODP Expeditions 314 and 316 at Site C0004 (Kinoshita et al., 2008; Kimura et al., 2008) in order to

    • Characterize the lithology, physical properties, and structural geology of the shallow slope apron, thrust wedge, megasplay fault, and overridden slope apron and

    • Correlate observations between Sites C0004 and C0010 to assess along-strike variations in physical properties and fault zone architecture;

  • Install casing to ~550 mbsf with screened joints (~20 m of screened interval) spanning the megasplay fault as defined from logging data in order to provide hydraulic communication between instruments inside casing and the fault zone in preparation for planned observatory installation in 2010, 2011, or beyond;

  • Conduct a "dummy run" of the instrument package (including a strainmeter and broadband seismometer) to evaluate shock and acceleration caused by hole reentry and instrument emplacement, for future installation of a strainmeter and seismometer package at this site as part of a permanent observatory; and

  • Suspend the hole with a temporary monitoring system (a "smart plug") affixed to a retrievable casing packer (bridge plug), in order to record pore pressure and temperature within the screened interval of the formation.

The temporary instrument package will provide continuous monitoring during the time between drilling of the site (this expedition) and permanent observatory installation. This planned permanent observatory will monitor seismicity, volumetric strain, tilt, pore pressure, and temperature (Fig. F3). Together with a second planned long-term observatory installation at Site C0009, it will constitute the initial phase of a distributed observatory network spanning the region above the aseismic–seismic transition on the plate boundary at depth.

Based on interpretation of three-dimensional (3-D) seismic reflection data and the results of drilling at Site C0004 during Expeditions 314 and 316 (Kinoshita et al., 2008; Kimura et al., 2008), the anticipated geology from the top of the section to the planned total depth (TD) was an ~200 m thick sequence of slope apron deposits composed of silty mudstone with some thin sand and ash layers overlying an ~210 m thick zone of fractured mudstone comprising a thrust wedge in the hanging wall of the megasplay fault (e.g., Moore et al., 2009). The fault juxtaposes the thrust wedge above with overridden slope apron sediments below, which consist of silty mudstone with numerous sand beds and some ash (Kimura et al., 2008; Moore et al., 2009). The character of the megasplay fault zone in seismic reflection images differs markedly between Sites C0004 and C0010. At Site C0004, there are two distinct reflectors at the base of the thrust wedge, and both coring and LWD data document the presence of two main fault zones separated by an ~50 m thick "fault-bounded package" (e.g., Kimura et al., 2008). In contrast, at Site C0010, the megasplay is imaged as a single sharp reflector in the seismic data, suggesting that the fault zone would be thinner and perhaps have a simpler architecture than at Site C0004.

1Expedition 319 Scientists, 2010. Site C0010. In Saffer, D., McNeill, L., Byrne, T., Araki, E., Toczko, S., Eguchi, N., Takahashi, K., and the Expedition 319 Scientists, Proc. IODP, 319: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.319.104.2010

2Expedition 319 Scientists' addresses.

Publication: 31 August 2010
MS 319-104