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Geological and geophysical studies of the Nojima Fault from drilling: An outline of the Nojima Fault Zone Probe
Author(s) -
Ando Masataka
Publication year - 2001
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/j.1440-1738.2001.00349.x
Subject(s) - geology , fault (geology) , seismology , drilling , scientific drilling , seismometer , compression (physics) , materials science , composite material , metallurgy
The Nojima Fault Zone Probe was designed to study the properties and recovery processes of the Nojima Fault, which moved during the Hyogo‐ken Nanbu earthquake ( M JMA 7.2) of 1995. Three holes, 500 m, 800 m and 1800 m deep, were drilled into or near the fault zone by the Disaster Prevention Research Institute, Kyoto University. The 500 m and 800 m holes were drilled in November 1995, and in December 1996 the last hole reached its final depth of 1760 m. The significant results are: (i) Geological and geophysical reconstruction of the structure and evolution of the Nojima Fault was obtained; (ii) the maximum compression axis was found to be perpendicular to the fault, approximately 45° to the regional compression stress axis; (iii) micro‐earthquakes (m = –2 to +1) were induced by water injections 1–3 km from the injection points in the 1800 m hole; (iv) the fault zone was measured to be 30 m wide from microscopic studies of core samples. Instruments such as three‐component seismometers, crustal deformation instruments, and thermometers were installed in the holes.