TDChanges in Coulomb failure function due
to the occurrence of the M7.2 Kobe Earthquake of
January 17, 1995, as a possible measure of the change
in seismicity
MANABU HASHIMOTO
Crustal Dynamics Departent, Geographical survey Institute,
Kitasato 1, Tsukuba, Ibaraki 305, Japan
"Earthquake
Proof Design and Active Faults", ed. Y. Kanaori,
Developments in Geotechnical Engineering, Vol.81, p.181-197,
Elsevier Science B.V.,1997
We calculated changes in Coulomb failure function
(CFF) for a geodetic fault model of the M7.2 Kobe
Earthquake of January 1 7, 1995, to investigate
the possible
relationship between the occurrence of the main shock and the following increase
in seismicity in the surrounding area. The modeled fault, which was derived
from geodetic data, consists of six nearly vertical
planes trending in the NE-SW direction
with dominant right-lateral strike-slip and some thrust components. We calculate
CFF changes for several focal mechanisms which are usually seen in the Kinki
district or are consistent with the type of active faults there, and compare
its distribution with the seismicity observed after the main shock. Calculated
CFF for right-lateral slip on NE-SW trending vertical planes or left-lateral
slip on NW-SE trending vertical planes, which are dominant focal mechanisms
in this area, increases along the northeastern
extension of the source region and
around the Yamasaki fault, a conjugate fault located northwest of the source
region. In the former region a drastic increase in number of earthquakes were
observed after the main shock. The activation of seismicity was also observed
near the Yamasaki fault. CFF decreases in the north of the source region, where
the size of earthquakes became smaller than before the main shock. CFF may
decrease a little in the Wakayama region, where
no notable changes in seismicity were
observed. The Kobe Earthquake may have loaded stresses which might lead to
right-lateral slip on the eastern half of the Arirna-Takatsuki
Tectonic Line and segments of
the Median Tectonic Line in the Wakayama and Tokushima regions. Since these
faults have no record of M7 or greater events during
at least 400 years, we should be
aware of the seismicity around these tectonic lines.
_ΆκΦίι
|
