NanTroSEIZE Stage 3: Shallow Megasplay Long-Term
Borehole Monitoring System (LTBMS)1
Published December 2015
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The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) program is a coordinated, multiexpedition drilling project designed to investigate fault mechanics and seismogenesis along subduction megathrusts through direct sampling, in situ measurements, and long-term monitoring in conjunction with allied laboratory and numerical modeling studies. The fundamental scientific objectives of the NanTroSEIZE drilling project include characterizing the nature of fault slip and strain accumulation, fault and wall rock composition, fault architecture, and state variables throughout the active plate boundary system.
International Ocean Discovery Program (IODP) Expedition 365 will recover temporary monitoring instruments (a “GeniusPlug”) from previously drilled and cased Integrated Ocean Drilling Program Site C0010 and deploy a permanent long-term borehole monitoring system (LTBMS) in the same hole after deepening it to ~656 meters below seafloor (mbsf). These operations will complete preparations begun during Integrated Ocean Drilling Program Expedition 319 and continued during Integrated Ocean Drilling Program Expedition 332. This expedition will cover a period of 33 days, beginning on 26 March and ending on 27 April 2016.
Site C0010 is located 3.5 km north of Integrated Ocean Drilling Program Site C0004 and was first drilled during Expedition 319. Operations during that expedition included drilling through the megasplay fault zone and into its footwall using logging while drilling (LWD), setting casing with screens spanning the fault zone, and installation of a simple temporary observatory (a “SmartPlug”) to monitor fluid pressure and temperature in the screened interval. Major lithologic boundaries as well as the location of the megasplay fault at ~407 mbsf were identified in LWD data and were used to select a depth interval spanning the fault for placement of the two screened casing joints. Three distinct lithologic packages were observed at Site C0010: slope deposits (Unit I, 0–182.5 mbsf), thrust wedge (Unit II, 182.5–407 mbsf), and overridden slope deposits (Unit III, 407 mbsf to total depth). During Expedition 332, the SmartPlug was recovered and replaced with an upgraded version, the GeniusPlug, which includes a set of geochemical and biological experiments housed in a 30 cm extension. This GeniusPlug will be recovered and replaced with a permanent LTBMS, which will be later linked to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) submarine network. This Scientific Prospectus outlines the scientific rationale, objectives, and operational plans for Site C0010 and describes the contingency plan.
1Kopf, A., Saffer, D., and Toczko, S., 2015. Expedition 365 Scientific Prospectus: NanTroSEIZE Stage 3: shallow megasplay long-term borehole monitoring system (LTBMS). International Ocean Discovery Program. http://dx.doi.org/10.14379/iodp.sp.365.2015
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