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doi:10.2204/iodp.proc.332.105.2011

Introduction

The multiexpedition Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) will complete a transect of holes drilled through the Nankai accretionary prism, with coring, logging, and long-term monitoring experiments examining faults and wall rock at various depths, ultimately including the seismogenic part of the subduction thrust fault (Fig. F1A). As part of operations at IODP Site C0010, a mechanically set retrievable packer (Baker Hughes A3 Lok-Set) equipped with a small instrument package to monitor pore pressure and temperature was installed inside a 10⅝ inch casing string during IODP Expedition 319 (see Saffer et al., 2009). This instrument package, termed a “SmartPlug,” was deployed for 1 y at 374 meters below seafloor (mbsf), immediately above a screened casing interval within the shallow megasplay fault zone (Fig. F1B) (Saffer, McNeill, Byrne, Araki, Toczko, Eguchi, Takahashi, and the Expedition 319 Scientists, 2010). The instrument package included a data logger, a temperature sensor within the data logger housing, a self-contained temperature sensor, and two pressure gauges. These pressure sensors monitored (1) below the packer seal in a screened interval that is open to the fault zone and (2) above the packer seal to serve as a hydrostatic reference open to the overlying water column. Both temperature sensors were just below the packer (Fig. F2A). The SmartPlug instruments developed in 2009 monitored formation pore pressure and temperature from the time the bridge plug was set (23 August 2009) until they were retrieved during IODP Expedition 332 (7 November 2010). In 2010, an upgraded version of the plug, termed “GeniusPlug,” was developed. It relies on the SmartPlug design but replaces its end cap (the bullnose) with a second unit of the same diameter and adds 30 cm length (Fig. F2B). It hosts a continuous fluid sampler (OsmoSampler; Jannasch et al., 2004) and a microbiological colonization experiment (flow-through osmo colonization system [FLOCS]; Orcutt et al., 2010).

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