Expedition 365 summary

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doi: 10.14379/iodp.proc.365.101.2017
Author(s): Kopf, Achim; Saffer, Demian; Toczko, Sean; Araki, Eiichiro; Carr, Stephanie; Kimura, Toshinori; Kinoshita, Chihiro; Kobayashi, Reiji; Machida, Yuya; Rösner, Alexander; Wallace, Laura M.
International Ocean Discovery Program, Expedition 365 Scientists, College Station, TX
Author Affiliation(s): Primary:
University of Bremen, MARUM-Center for Marine Environmental Sciences, Bremen, Germany
Other:
Pennsylvania State University, United States
Japan Agency for Marine-Earth Science and Technology, Japan
Bigelow Laboratory for Ocean Sciences, United States
Kyoto University, Japan
Volume Title: Proceedings of the International Ocean Discovery Program; NanTroSEIEZE Stage 3; shallow megasplay long-term borehole monitoring system; Expedition 365 of the riser drilling platform from and to Shimizu, Japan; Site C0010, 26 March-27 April 2016
Volume Author(s): Kopf, Achim; Saffer, Demian; Toczko, Sean; Araki, Eiichiro; Carr, Stephanie; Kimura, Toshinori; Kinoshita, Chihiro; Kobayashi, Reiji; Machida, Yuya; Rösner, Alexander; Wallace, Laura M.
Source: Proceedings of the International Ocean Discovery Program; NanTroSEIEZE Stage 3; shallow megasplay long-term borehole monitoring system; Expedition 365 of the riser drilling platform from and to Shimizu, Japan; Site C0010, 26 March-27 April 2016, Achim Kopf, Demian Saffer, Sean Toczko, Eiichiro Araki, Stephanie Carr, Toshinori Kimura, Chihiro Kinoshita, Reiji Kobayashi, Yuya Machida, Alexander Rösner and Laura M. Wallace; International Ocean Discovery Program, Expedition 365 Scientists, College Station, TX. Proceedings of the International Ocean Discovery Program, Expedition Reports, Vol.365, 18p. Publisher: International Ocean Discovery Program, Washington, DC, United States. ISSN: 2377-3189 CODEN: IDSDA6
Note: In English. 52 refs.; illus., incl. sects., 2 tables, sketch map
Summary: The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is a coordinated, multiexpedition International Ocean Discovery Program (IODP) 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. IODP Expedition 365 is part of NanTroSEIZE Stage 3, with the following primary objectives: 1. Retrieval of a temporary observatory at Site C0010 that began monitoring temperature and pore pressure within the major splay thrust fault (termed the "megasplay") at 400 meters below seafloor in November 2010. 2. Deployment of a complex long-term borehole monitoring system (LTBMS) designed to be connected to the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) seafloor cabled observatory network postexpedition. The LTBMS incorporates multilevel pore pressure sensing, a volumetric strainmeter, tiltmeter, geophone, broadband seismometer, accelerometer, and thermistor string. Together with an existing observatory at Integrated Ocean Drilling Program Site C0002 and a planned future installation near the trench, the Site C0010 observatory allows monitoring within and above regions of contrasting behavior of the megasplay fault and the plate boundary as a whole. These include a site above the updip edge of the locked zone (Site C0002), a shallow site in the megasplay fault zone and its footwall (Site C0010), and a site at the tip of the accretionary prism (possible future installation at Integrated Ocean Drilling Program Site C0006). Together, this suite of observatories has the potential to capture deformation spanning a wide range of timescales (e.g., seismic and microseismic activity, slow slip, and interseismic strain accumulation) across a transect from near-trench to the seismogenic zone. Site C0010 is located 3.5 km along strike to the southwest of Integrated Ocean Drilling Program Site C0004. The site was drilled and cased during Integrated Ocean Drilling Program Expedition 319, with casing screens spanning a ∼20 m interval that includes the megasplay fault, and suspended with a temporary instrument package (a "SmartPlug"), which included pressure and temperature sensors. During Integrated Ocean Drilling Program Expedition 332 in late 2010, the instrument package was replaced with an upgraded sensor package (the "GeniusPlug"), which included a set of geochemical and biological experiments in addition to pressure and temperature sensors. Expedition 365 achieved its primary scientific and operational objectives, including recovery of the GeniusPlug with a >5 y record of pressure and temperature conditions within the shallow megasplay fault zone, geochemical samples, and its in situ microbial colonization experiment; and installation of the LTBMS. The pressure records from the GeniusPlug include high-quality records of formation and seafloor responses to multiple fault slip events, including the 11 March 2011 Tohoku M9 and 1 April 2016 Mie-ken Nanto-oki M6 earthquakes. The geochemical sampling coils yielded in situ pore fluids from the splay fault zone, and microorganisms were successfully cultivated from the colonization unit. The complex sensor array, in combination with the multilevel hole completion, is one of the most ambitious and sophisticated observatory installations in scientific ocean drilling (similar to that in Hole C0002G, deployed in 2010). Overall, the installation went smoothly, efficiently, and ahead of schedule. The extra time afforded by the efficient observatory deployment was used for coring in Holes C0010B-C0010E. Despite challenging hole conditions, the depth interval corresponding to the screened casing across the megasplay fault was successfully sampled in Hole C0010C, and the footwall of the megasplay was sampled in Hole C0010E, with >50% recovery for both zones. In the hanging wall of the megasplay fault (Holes C0010C and C0010D), we recovered indurated silty clay with occasional ash layers and sedimentary breccias. Mudstones show different degrees of deformation spanning from occasional fractures to intervals of densely fractured scaly claystones of up to >10 cm thickness. Sparse faulting with low displacement (usually <2 cm) is seen in core and exhibits primarily normal and, rarely, reversed sense of slip. When present, ash was entrained along fractures and faults. In Hole C0010E, the footwall to the megasplay fault was recovered. Sediments are horizontally to gently dipping and mainly comprise silt of olive-gray color. The hanging wall sediments recovered in Holes C0010C-C0010D range in age from 3.79 to 5.59 Ma and have been thrust over the younger footwall sediments in Hole C0010E, ranging in age from 1.56 to 1.67 Ma.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 07 Marine Geology and Oceanography; 20 Geophysics, Applied; Asia; Boreholes; Cores; Drilling; Earthquakes; Expedition 365; Far East; Faults; Geophysical methods; Geophysical profiles; Geophysical surveys; Honshu; IODP Site C0010; International Ocean Discovery Program; Japan; Kii Peninsula; Marine drilling; Marine sediments; Monitoring; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Pacific Ocean; Pore pressure; Pore water; Sedimentary rocks; Sediments; Seismic methods; Seismic profiles; Seismicity; Subduction zones; Surveys; Thrust faults; West Pacific
Coordinates: N331233 N331236 E1364113 E1364110
Record ID: 2017073015
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute.
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