Pennsylvania State University, United States

During Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stage 2 operations, Integrated Ocean Drilling Program (IODP) Hole C0010A was drilled and cased during IODP Expedition 319 and then subsequently instrumented with a temporary borehole monitoring system (a "SmartPlug"). The SmartPlug was recovered in November 2010 during IODP Expedition 332 and replaced with a "GeniusPlug." Both instruments were mounted beneath a Baker Hughes mechanically set retrievable casing packer. The casing packer was set just above the casing screen that intersects a major out-of-sequence splay fault, which branches off of the primary subduction thrust. The SmartPlug was designed to document ambient conditions and provide proxies for strain and fluid flow related to tectonic and seismic activity within the splay fault. This was achieved by recording formation pressures and temperatures. Two pressure sensors were used (resolution=10 ppb full-scale, i.e., approximately 0.7 Pa, equivalent to 0.07 mm of seawater head), one plumbed to the formation via the casing screens below the packer seal and the other to the section of the borehole above the packer seal to record ocean loading signals. Temperature was recorded with a platinum thermometer and by a self-contained miniature temperature logger (MTL) with a resolution of approximately 0.5 mK. The second-generation instrument package (i.e., GeniusPlug) consisted of a SmartPlug base unit to which an extension containing an OsmoSampler for fluid geochemistry and a FLOCS (flow-through osmo colonization system) unit for microbiology were added. We report on the design of both instruments, the proof-of-concept after successful deployment of both instruments and recovery of the SmartPlug, and preliminary data from the SmartPlug that documents hydrologic responses to predominantly oceanographic loading and teleseismic earthquakes. Additional data and samples are anticipated in 2012 upon recovery of the GeniusPlug, at which time the GeniusPlug will be replaced by a permanent multisensor, multilevel borehole observatory system that will be connected to the seafloor fiber-optic cable network (Dense Oceanfloor Network System for Earthquakes and Tsunamis).