TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 56 (No. 12), pp. 1233-1240, 2004

Structural evolution of the Nojima fault (Awaji Island, Japan) revisited from the GSJ drill hole at Hirabayashi

Anne-Marie Boullier1, Koichiro Fujimoto2, Hisao Ito3, Tomoyuki Ohtani4, Nynke Keulen5, Olivier Fabbri6, David Amitrano7, Michel Dubois8, Philippe Pezard9

1L.G.I.T.-CNRS, Joseph Fourier University, Grenoble, France
2Tokyo Gakugei University, Japan
3Geological Survey of Japan, AIST-Earthquake Research Group, Tsukuba, Japan
4Gifu University, Japan
5Department of Earth Sciences, Basel University, Switzerland
6Franche Comt University, BesancŁon, France
7ENS Mines Nancy, France
8Department of Earth Sciences, Lille University, France
9ISTEEM, Montpellier University, France

(Received May 25, 2004; Revised November 19, 2004; Accepted December 1, 2004)

Abstract: Following the Hyogoken Nanbu earthquake (January 17, 1995, Mw=7.2), three drillholes were sunk through the Nojima Fault (Awaji Island, Japan). Textural and petrographic studies of the Geological Survey of Japan (GSJ) drill cores allow recognition of two deformation episodes. The first one is older than the deposition of the Middle to Late Eocene Kobe Group, corresponds to a left-lateral movement on the Nojima fault and is expressed by pseudotachylytes, kinking of biotite crystals in the low-strain rocks and an intense laumontite hydrothermal alteration. The second one displaces the basal unconformity of the Kobe group, corresponds to a right-lateral reverse displacement and is expressed at least by carbonate-filled hydraulic fractures and thin gouge zones. Different important deformation mechanisms are recorded by the fault rocks, but questions relating to the attribution of deformation and alteration features to one or other deformation episodes remain unresolved.
Key words: Nojima, fault, seismic, aseismic, deformation, veins, laumontite, carbonates.

Corresponding author E-mail: Anne-Marie.Boullier@obs.ujf-grenoble.fr

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