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| Titel |
Mechanical properties of foliated cataclasites from the Nobeoka thrust |
| VerfasserIn |
Hiroko Kitajima, Miki Takahashi, Gaku Kimura, Asuka Yamaguchi, Saneatsu Saito, Mari Hamahashi, Rina Fukuchi, Jun Kameda, Yohei Hamada, Koichiro Fujimoto, Yoshitaka Hashimoto, Yujin Kitamura, Shoko Hina, Mio Eida |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094669
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| Publikation (Nr.) |
 EGU/EGU2014-10096.pdf |
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| Zusammenfassung |
| Understanding the mechanics of plate boundary earthquakes requires a sound investigation of
the deformation style and mechanical behavior not only within plate boundary faults but also
in the surrounding rocks. It is critical to quantify the strain accumulation and accommodation
in the entire subduction systems. Recent studies suggest that heterogeneous deformation and
strain distribution in mélanges observed in many ancient accretionary prism outcrops are
related to slow slip events and low frequency earthquakes [Fagereng and Sibson, 2010;
Kitamura and Kimura, 2011]. However, there are few experimental studies to describe
mechanical properties of mélanges and foliated cataclasites. Here, we report on triaxial
deformation experiments on foliated cataclasites from the footwall of the Nobeoka thrust,
Japan.
The Nobeoka thrust, which is exhumated in Kyushu, southwest Japan, is considered as
one of the ancient out-of-sequence faults. The Nobeoka thrust fault core, hanging wall, and
foot wall rocks were recently cored and logged in a vertical borehole as a NOBELL project
[Hamahashi et al., in press]. The Nobeoka thrust is recovered at 41.3 m from the ground. The
hanging wall (0-41.3 m coring interval) is composed of the Kitagawa Group of phyllite of
alternating beds of sandstone and shale, while the footwall (41.3-255 m) is composed
of the Hyuga Group of foliated cataclasite consisting of scaly shale, tuffacious
shale, sandstone, and acidic tuff. For deformation experiments, we used foliated
catacalsite core samples, which are in better quality and less weathered than outcrop
samples. Cylindrical samples with a diameter of 20 mm and a length of 30 mm were
subsampled from the cores. The cylindrical specimen were deformed at an axial
displacement rate of 0.05-0.5 μm/s, corresponding to strain rates of 1.6 x10-6-1.6 x10-5
s-1, and at a temperature of 250 °C and an effective pressure (Pe) of 120 MPa
(confining pressure of 200 MPa and pore pressure of 80 MPa) or 20 MPa (confining
pressure of 200 MPa and pore pressure of 180 MPa). The temperature was chosen
based on the estimated temperature (250-300 °C) at which the footwall foliated
cataclasites were formed [Kondo et al., 2005]. The two different effective pressures of
120 MPa and 20 MPa correspond to the stress conditions at ~8 km (geothermal
gradient of ~30 °C/km) with hydrostatic pore pressure and lithostatic pore pressure,
respectively.
The preliminary results show that the foliated cataclasite samples, taken from the coring
interval of 153 m, deform in a brittle manner at Pe = 20 MPa. The strengths reach at 80-90
MPa at peak following a strain weakening to residual strengths of 40-60 MPa. At Pe = 120
MPa, on the other hand, the foliated cataclasite deforms in a brittle-ductile transition
manner and steady-state strength is ~ 300 MPa. We will present more experimental
results and microstructure observations of the experimentally deformed samples. |
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