Frictional behavior of altered basement approaching the Nankai Trough

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http://abstractsearch.agu.org/meetings/2017/FM/T23A-0590.html
Author(s): Saffer, Demian M.; Ikari, Matt; Rooney, Tyrone O.; Marone, Chris
Author Affiliation(s): Primary:
Pennsylvania State University, Department of Geosciences, University Park, PA, United States
Other:
University of Bremen, Germany
Michigan State University, United States
Volume Title: AGU 2017 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2017; American Geophysical Union 2017 fall meeting, New Orleans, LA, Dec. 11-15, 2017. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The frictional behavior of basement rocks plays an important role in subduction zone faulting and seismicity. This includes earthquakes seaward of the trench, large megathrust earthquakes where seamounts are subducting, or where the plate interface steps down to basement. In exhumed subduction zone rocks such as the Shimanto complex in Japan, slivers of basalt are entrained in mélange which is evidence of basement involvement in the fault system. Scientific drilling during the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) recovered basement rock from two reference sites (C0011 and C0012) located seaward of the trench offshore the Kii Peninsula during Integrated Ocean Discovery Program (IODP) Expeditions 322 and 333. The basement rocks are pillow basalts that appear to be heterogeneously altered, resulting in contrasting dense blue material and more vesicular gray material. Major element geochemistry shows differences in silica, calcium oxides and loss-on-ignition between the two types of samples. Minor element geochemistry reveals significant differences in vanadium, chromium, and barium. X-ray diffraction on a bulk sample powder representing an average composition shows a phyllosilicate content of ∼20%, most of which is expandable clays. We performed laboratory friction experiments in a biaxial testing apparatus as either intact sample blocks, or as gouge powders. We combine these experiments with measurements of Pennsylvania slate for comparison, including a mixed-lithology intact block experiment. Intact Nankai basement blocks exhibit a coefficient of sliding friction of 0.73; for Nankai basement powder, slate powder, slate blocks and slate-on-basement blocks the coefficient of sliding friction ranges from 0.44 to 0.57. At slip rates ranging from 3×10-8 to 3×10-4 m/s we observe predominantly velocity-strengthening frictional behavior, indicating a tendency for stable slip. At rates of < 1x10-6 m/s some velocity-weakening was observed, specifically in intact rock-on-rock experiments. Our results show that basement alteration tends to reduce the tendency for unstable slip, but that the altered Nankai basement may still exhibit seismogenic behavior in the case of localized slip in competent rock.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Expedition 322; Expedition 333; IODP Site C0011; IODP Site C0012; Integrated Ocean Drilling Program; NanTroSEIZE; North Pacific; Northwest Pacific; Pacific Ocean; Shikoku Basin; West Pacific
Coordinates: N324944 N324945 E1365256 E1365254
N324453 N324453 E1365501 E1365501
Record ID: 2019016412
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