Structure of the plate boundary fault in the Japan Trench, and implications for slip behaviour

Author(s): Rowe, Christie D.; Tarling, Matthew; Kirkpatrick, James D.; White, Joseph Clancy; Ujiie, Kohtaro; Moore, James Casey; Regalla, Christine A.; Remitti, Francesca; Toy, Virginia G.; Wolfson-Schwehr, Monica
Author Affiliation(s): Primary:
McGill University, Earth & Planetary Sciences, Montreal, QC, Canada
Colorado State University, Fort Collins, CO, United States
University of New Brunswick, Canada
University of Tsukuba, Japan
University of California-Santa Cruz, United States
Pennsylvania State University, United States
University of Modena and Reggio Emilia, Italy
University of Otago, New Zealand
University of New Hampshire, United States
Volume Title: Geological Society of America, 2014 annual meeting & exposition
Source: Abstracts with Programs - Geological Society of America, 46(6), p.237; Geological Society of America, 2014 annual meeting & exposition, Vancouver, BC, Canada, Oct. 19-22, 2014. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: The 2011 Mw9.0 Tohoku-oki earthquake ruptured to the trench with maximum coseismic slip located on the shallow portion of the plate boundary fault. To investigate the conditions and physical processes that promoted slip to the trench, Integrated Ocean Drilling Program Expedition 343/343T sailed one year after the Tohoku-oki earthquake and drilled into the plate boundary ∼7 km landward of the trench, in the region of maximum slip. Core analyses show that the plate boundary decollement is localized onto an interval of smectite-rich, pelagic clay. Subsidiary structures are present in both the upper and lower plates, which define a fault zone ∼5-15 m thick. Fault rocks recovered from within the clay-rich interval contain a pervasive scaly fabric defined by anastomosing, polished and lineated surfaces with two predominant orientations. Scaly fabrics have been described in other subduction thrusts, landslides, and sub-glacial tills, but there is no constitutive understanding of the behaviour of anastomosing networks during shear deformation. We present analog models using lentils to simulate scaly fabrics, and describe the distribution and localization of shear during deformation. The scaly fabric is crosscut in several places by discrete faults across which the scaly fabric is truncated and rotated, or different rocks are juxtaposed. A very thin (∼5 micron) amorphous layer has been discovered in transmission electron microscope observations of the main discrete fault cutting the scaly fabrics. The mechanism of amorphization is unknown, but may be related to shear heating on a micro-localized seismic slip surface. We infer that the formation of both of these types of structures is controlled by the frictional properties of the clay: the distributed scaly fabric formed at low strain rates associated with velocity-strengthening frictional behavior, and the localized faults formed at high strain rates characterized by velocity-weakening behavior. The presence of multiple discrete faults resulting from seismic slip within the decollement suggests that rupture to the trench may be characteristic of this margin.
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Crust; Expeditions 343/343T; Faults; Integrated Ocean Drilling Program; Japan Trench; Japan Trench Fast Drilling Project; Lithosphere; North Pacific; Northwest Pacific; Oceanic crust; Oceanic lithosphere; Pacific Ocean; Plate boundaries; Plate tectonics; West Pacific
Coordinates: N375619 N375620 E1435449 E1435447
Record ID: 2015016116
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