３．Co-seismic Displacements of the 1995 Hyogo-ken
Nanbu Earthquake
MANABU HASHIMOTO, TAKESHI SAGIYA,
HIROMICHI TSUJI, YUKI HATANAKA, and TAKASHI TADA
Geographical Survey Institute, Tsukuba 305, Japan
Journal of Physics of the Earth, Vol.44, P.255-279,1996
We present co-seismic displacements of the
Hyogo-ken Nanbu earthquake of January 17.
1995, detected
by continuous GPS (Global Positioning System)
observation, campaign type GPS survey and leveling.
Continuous GPS observation gives a consistent
pattern of displacements with those expected
from a right lateral slip on a NE-SW trending
vertical fault in far field: stations about
50 km east and west of the epicenter moved
toward the epicenter by about 4 cm, while stations
north and south moved away from the epicenter.
By comparing with line lengths obtained by
geodolite about 10 years ago, the campaign
type GPS revealed most control points on Awaji
Island moved to the southwest or south, which
may be attributed to the movement of the Nojima
Fault which cut the surface. On the other hand,
control points northwest of the Rokko fault
system moved toward the northeast and those
on the other side moved slightly to the west,
in and around Kobe. Leveling data revealed
uplift of 19 cm on the northwestern side of
the Suma Fault, a member of the Rokko fault
system, and subsidence of 7 cm just east of
this fault. Furthermore, up]ift of about 5
cm was observed in the central part of Kobe City,
and subsidence of 5 cm was detected east of
Kobe. There is no significant gap in horizontal
and vertical displacements around the northern
extension
of the Nojima Fault, which implies a complicated rupture process of this
event. Leveling on the east coast of Awaji Island revealed a significant
uplift of about 20 cm with slight subsidence at both edges of this uplift
region during the past 20 years. By fitting the above geodetic data, we
searched for an optimal set of parameters of a dislocation model. We assumed
six nearly vertical faults trending NE-SW from Kobe to Awaji Island on
the basis of aftershock distribution and focal mechanism. About 250cm of
the right lateral slip for the fault on Awaji Island is derived from large
horizontal displacements near the Nojima Fault. The fault in Kobe may be
divided into two segments with 100-200 cm slip by a slip-free zone which
roughly corresponds to the cluster of aftershocks. The southern part of
the Nojima Fault, segments near the Akashi Strait. and north of central
Kobe may have significantly large thrust components of 100 cm. We also
examined the possibility of buried faults bcneath the zones of severe damage.
Since this model cannot explain the observed geodetic data and the estimated
slips are inconsistent with focal mechanism, these possible buried faults
may not play a significant role, if any. 論文一覧へ戻る
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