Evolving seismogenic plate boundary megathrust and mega-splay faults in subduction zone

Author(s): Kimura, G.; Hamahashi, M.; Fukuchi, R.; Yamaguchi, A.; Kameda, J.; Kitamura, Y.; Hashimoto, Y.; Hamada, Y.; Saito, S.; Kawasaki, R.
Author Affiliation(s): Primary:
University of Tokyo, Earth and Planetary Science, Tokyo, Japan
Kochi University, Applied Science, Kochi, Japan
Japan Agency for Marine Earth Science and Technology, IFREE, Kanagawa, Japan
Volume Title: AGU 2013 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2013; American Geophysical Union 2013 fall meeting, San Francisco, CA, Dec. 9-13, 2013. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Understanding the fault mechanism and its relationship to the seismo-tsunamigenesis is a key of the scientific targets of subduction zone and therefore NantroSEIZE project of IODP and future new drilling project of International Ocean Discovery Program keeps focusing on that. Mega-splay fault branched from plate boundary megathrust in subduction zone is located around the border between outer and inner wedges and is considered to cause great earthquake and tsunami such as 1960 Alaska earthquake, 1944 and 1946 Nankai-Tonankai earthquakes, and 2004 Sumatra earthquakes. Seismic reflection studies for the mega-splay fault in 2D and 3D in the Nankai forearc present the reflector with negative or positive polarities with various amplitudes and suggest complicated petrophysical properties and condition of the fault and its surroundings. The Nankai mega-splay fault at a depth of ≈5 km is going to be drilled and cored by NantroSEIZE experiments and is expected for great progress of understanding of the fault mechanics. Before drilling the really targeted seismogenic fault, we are conducting many exercises of geophysical and geological observations. The core-log-seismic integrated exercise for the exhumed mega-splay fault by drilling was operated for the Nobeoka thrust in the Shimanto Belt, Kyushu, Japan. The Nobeoka thrust was once buried in the depth >≈10 km and suffered maximum temperature >≈300 degree C. As the core recovery is ≈99%, perfect correlation between the core and logging data is possible. Thickness of the fault zone is >200 m with a ≈50 cm thick central fault core dividing the phyllitic hanging wall and the footwall of broken-melange like cataclasite. A-few-meter-thick discrete damage zones with fault cores are recognized by difference in physical properties and visual deformation textures at several horizons in the fault zone. Host rocks for those damaged zones are completely lithified cataclasites with abundant mineral veins, which record the older and deeper deformation in the maximum depth >10 km. Temperature difference between the hanging wall and footwall suggests the displacement along the Nobeoka thrust is >10 km, which is almost similar to the mega-splay fault in the Nankai Trough. Geological and physical properties of the Nobeoka thrust suggest an evolving process of the seismogenic mega-splay fault associated with seismogenic up-thrust of the inner wedge of the accretionary prism.
Year of Publication: 2013
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Faults; Integrated Ocean Drilling Program; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Pacific Ocean; Plate boundaries; Plate tectonics; Subduction; Subduction zones; Thrust faults; West Pacific
Record ID: 2015037319
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by, and/or abstract, Copyright, American Geophysical Union, Washington, DC, United States

Similar Items