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Thermal anomaly around the Nojima Fault as detected by fission‐track analysis of Ogura 500 m borehole samples
Author(s) -
Tagami Takahiro,
Hasebe Noriko,
Kamohara Hidenori,
Takemura Keiji
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.1440-1738.2001.00344.x
Subject(s) - borehole , geology , fission track dating , fault (geology) , seismology , outcrop , crust , anomaly (physics) , geophysics , geochemistry , geotechnical engineering , tectonics , physics , condensed matter physics
To better understand heat generation and transfer along earthquake faults, this paper presents preliminary zircon fission‐track (FT) length data from the Nojima Fault, Awaji Island, Japan, which was activated during the 1995 Kobe earthquake (Hyogo‐ken Nanbu earthquake). Samples were collected of Cretaceous granitic rocks from the Ogura 500 m borehole as well as at outcrops adjacent to the borehole site. The Nojima Fault plane was drilled at a depth of 389.4 m (borehole apparent depth). Fission‐track lengths in zircons from localities > 60 m distance from the fault plane, as well as those from outcrops, are characterized by the mean values of ≈10–11 μm and unimodal distributions with positive skewness, which show no signs of an appreciable reduction in FT length. In contrast, those from nearby the fault at depths show significantly reduced mean track lengths of ≈6–8 μm and distributions having a peak around 6–7 μm with rather negative skewness. In conjunction with other geological constraints, these results are best interpreted by a recent thermal anomaly around the fault, which is attributable to heat transfer via focused fluids from the deep interior of the crust and/or heat dispersion via fluids associated with frictional heating by fault motion.