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77
Bull. Earthq. Res. Inst.
Univ. Tokyo
Vol. pp.
* e-mail : [email protected]
An extensive onshore-o shore seismic refraction/wide-angle reflection experiment was under-
taken in . The profile line was extended from the eastern part of the Nankai trough to Central
Japan. The land profile line of -km length was laid from the Tokai district to the coastal region
of the Sea of Japan, crossing an expected fault area of the forthcoming Tokai earthquake, an
aseismic slip region north of the fault area, the Median Tectonic Line and the Niigata-Kobe Tectonic
line. On this profile, receivers were deployed to observe dynamite shots with kg
charge. Data obtained are of good quality, from which clear first arrivals are traced beyond
km o sets. The most important feature in these data is strong reflection from the subducted
Philippine Sea plate observed in the southernmost part of the profile. This paper presents the
outline of this seismic expedition and fundamental data obtained.
: crust, plate structure, subduction, Philippine Sea plate, Central Japan
Iidaka
Fig. Kodaira
aseismic slip
Kodaira
NNW-SSE
aseismic slip Ozawa
Sagiya km
NNW-SSE J -J
The Research Group for Seismic Expedition in Central Japan
et al.
et al.,
et al.,
et al.,
et al.
Abstract
Key words
Deep Seismic Refraction/Wide-angle Reflection
Profiling in Central Japan
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78
Fig. . Location map of the seismic expedition.
Six shots (J -J and T ) of -kg charges on
the onshore line are shown by stars. Our onshore-
o shore profile is running across the expected fault
area of the forthcoming Tokai earthquake indicated
by a pink area. The onshore line is also crossing
Median Tectonic Line (MTL) and the Niigata-Kobe
Tectonic line. The aseismic slip area in the Tokai
district (Ozawa ( )) is located west of the
southern part of our profile (south of J )). Receiver
points of the onshore line are indicated by small
circles.
Table . Shot time, location and charge size of seismic expedition.
Fig.
kg J -J
Texas kg T
J -T
Table
. mm, J -J . .
m, T . m
m
Fig.
J -J T
. . . . . . km s
Table J -
J Table
LS
Mark Products L- D
. Hz, . k
. ms
DAT
km
km Table
ms
L B . Hz
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79
Fig. . Travel-time diagrams near shot points. These observations were performed to determine
seismic velocities at the shallowest part of the crust.
J km m, C
m J S N
L
S Iidaka
J -J . . sec
GPS
J -J
km s
ms km s km s
SEGY format Barry
Fig. km s
reduction
velocity km s J -J Fig.
km
km
Fig. Table J Fig. e
. s J km
A . s B
et al.
et al.,
,
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Table . Receivers of seismic expedition., ,**+
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Table . (Continued),
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Table . (Continued),
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83
Table . (Continued),
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(a)
(b)
84
Fig. . Record sections. Horizontal axis is an o set in km from the individual shot point. Travel time is reduced
for a velocity of km/s. Remarkable later phases are indicated by arrows. (a) J . (b) J . (c) J . (d) J . (e) J .
(f) T .
- #
0 + , - . /
0
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85
Fig. . (Continued)-
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86
Fig. . (Continued)-
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(b)
(c)
(d)
87
Fig. . Travel-time plots. The reduction velocity is taken to be . km/s. The horizontal axis is an o set in km.
The quality of travel time data is shown with di erent symbols (see text for explanation). (a) J . (b) J . (c) J .
(d) J . (e) J . (f) T .
. 0 * #
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Fig. . (Continued).
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100
Barry, E.M., Cavers, D.A. and Kneale, C.W., , Recom-
mended standards for digital tape format,
, .
Iidaka, T., T. Iwasaki, T. Takeda, T. Moriya, I. Kumakawa, E.
Kurashimo, T. Kawamura, F. Yamazaki, K. Koike and G.
Aoki, , Configuration of subducting Philippine Sea
plate and crustal structure in the central Japan,
, doi : / GL ..
Iidaka, T., T. Takeda, E. Kurashimo, T. Kawamura, Y.
Kaneda and T. Iwasaki, , Configuration of subduct-
ing Philippine Sea plate and crustal structure in the
central Japan, , .
Kodaira, S., T. Iidaka, A. Kato, J-O Park, T. Iwasaki and Y.
Kaneda, , High pore pressure may cause silent slip
in the Nankai Trough, , .
Kodaira S., T. Iidaka, A. Nakanishi, J.-O. Park, T. Iwasaki
and Y. Kaneda, , Onshore-o shore seismic transect
from the eastern Nankai Trough to central Japan cross-
ing a zone of the Tokai slow slip event,
, .
.
Ozawa, S., M. Murakami, M. Kaidu, T. Tada, T. Sagiya, Y.
Hatanaka, H. Yarai and T. Nishimura, , Detection
and monitoring of ingoing aseismic slip in the Tokai
region, central Japan, , .
Sagiya T., S. Miyazaki and T. Tada, , Continuous GPS
array and present-day crustal deformation of Japan,
, .
Kate Miller
aseismic
slip
Iidaka
:
:
:
:
:
:
Ismail Husain
Fathi
Geophysics,
Geo-phys. Res. Letter,
Tectonophysics,
Science,
Earth PlanetsSpace,
Science,
Pure appl. geophys.,
et al.,
+31/
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Galen Kaip Amy
Kwiatkowski
C .
C . Received December ,
GPS Accepted March ,
.
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