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265

JMA

JMA

Bull. Earthq. Res. Inst.

Univ. Tokyo

Vol. pp.

* e-mail : satow@eri.u-tokyo.ac.jp

Earthquake Research Institute, the University of Tokyo

JGI Inc.

Graduate School of Science, Chiba University

The seismogenic source fault of the Noto Hanto earthquake (M . ) runs beneath the

northwestern part of the Noto peninsula and its o shore trending ENE-WSW. To reveal the rela-

tionship between a seismogenic source fault and geologic structure, shallow, high-resolution seismic

reflection and refraction profiling was undertaken across the source fault along the western coast of

the Noto peninsula for km distance. The seismic source was a vibroseis and seismic data were

recorded by fixed channels. The P-wave refraction analysis delineated the three layered velocity

structure down to km ; . km/s, . km/s and . km/s layers. The . km/s layer, which corre-

sponds to the lower Miocene fluvial sediments, shows northward thickening with steps. On the

resultant depth converted seismic section, south and north-dipping, faults are interpreted based on

the systematic change on dip-angle of the reflectors in the lower Miocene fluvial sediments. By

comparing with the aftershock distribution, the deeper extension of the south-dipping fault corre-

sponds to the source fault of the Noto Hanto earthquake.

: Noto Hanto earthquake, earthquake source fault, seismic reflection profiling, geo-

logic structure, central Japan

.

M . Sakai

ENE-WSW ; ;

; Ozawa

km

Yamada ; Sakai

*

Hiroshi Sato *, Shinji Kawasaki , Susumu Abe , Naoko Kato , Iwasaki Takaya , Tanio

Ito

et al.,

et al.,

et al., et al.,

Abstract

Key words

Seismic Reflection Profiling Across the Onshore Source

Area of the Noto Hanto Earthquake, Central Ja-

pan

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Fig. . Geological map showing the seismic line “Monzen ”.

Major geologic structure is after Editorial committee of civil engineering geologic map of Hokuriku ( ).

Pre-N : mainly pre-Neogene rocks with minor distribution of lower Miocene andesite.

Fig.

Kano ;

. km Fig.

Lopez and Ishiwatari,

ENE-WSW

Table

ENE-WSW Industrial Vehicle Interna-

tional EnviroVibe

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et al.,

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267

Table . Data acquisition parameters for the Monzen

seismic survey.

Fig. . Examples of shot gathers of the Monzen seismic survey.

A : a shot gather for reflection profiling at VP , B : a shot gather for refraction analysis at VP . Location of

shot points is shown in Fig. .

Fig. A

. . .

G-DAPS A

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B

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Trace Edit

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Fig. . Surface structure determined by time-term analysis.

(a) time-terms,

(b) velocities of second layer,

(c) topography and geometry of surface low velocity layer.

Fig. . Optimum stacking velocities determined by

velocity analysis.

Deconvolution

: :

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Refraction Statics

mal Moveout NMO

Fig. V .

. km s V Residual Statics

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Fig. . Filtered stacked section and post stacked, migrated time section of the Monzen seismic line.

F-X : km s

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Fig. . Depth converted seismic section (A) and its geologic interpretation (B) of the Mozen seismic line. F and

F : inferred fault, Red and black broken lines : boundary of velocity layers deduced from the refraction analysis.

m, m

m

Fig. B CMP

CMP F ; Fig. B

. km CMP . km s

m . km s . km s,

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Fig. . Velocity model of the Monzen seismic line obtained by refraction analysis.

(a) Comparison between theoretical travel time curves (solid lines) and first arrival data (solid circles).

(b) Ray diagrams corresponding to the first arrivals from seven shot points.

(c) Velocity model with inferred P-wave velocities (in km/s).

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F

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m

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syn-rifting succession, northern Noto Peninsula, Japan :

Fig. . Comparison between geologic structure and aftershock distribution. Aftershock distri-

bution is after Sakai ( ) and Yamada ( ). The aftershocks were projected to

the plane, which is perpendicular to the strike of the source fault and passes through the center

of the seismic line (Line in Figure from Sato ), and rotated to the general strike

of the CMP line of the seismic section. On this figure the dip angle of source fault shows

apparent dip angle.

Evidence for short-term uplifting precedent to the

rapid opening of the Japan Sea, , .

.

p.

.

Lopez, C. J. and Ishiwatari, A., , Petrogenesis of the

tholeiitic basalt, calc-alkaline basaltic andsite and high

magnesian andesite lava succession of the Oligo-

Miocene Anamizu Formation in northeastern Noto Pen-

insula,central Japan, , .

no.

CD.

Ozawa, S., H. Yarai, M. Tobita, H. Une and T. Nishimura,

, Crustal deformation associated with the Noto.

Hanto Earthquake in in Japan,

, ..

Sakai, S., A. Kato, T. Iidaka, T. Iwasaki, E. Kurashimo, T.

Igarashi, N. Hirata, T. Kanazawa and the group for thep.

joint aftershock observation of the Noto Hanto

Earthquake, , Highly resolved distribution of after-.

shocks of the Noto Hanto Earthquake by a denseKano, K., T. Yoshikawa, Y. Yanagisawa, K. Ogasawara and

seismic observation, , .T. Danhara, , An unconformity in the early Miocene

:

:

et al. et al.

et al.,

Island Arc,

J. Min. Petrol. Sci.,

Earth Planets Space,

Earth Planets Space,

2

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273

.

Sato, H. and K. Amano, . Relationship between tecton- Yamada, T., K. Mochizuki, M. Shinohara, T. Kanazawa, S.

ics, volcanism, sedimentation and basin development, Kuwano, K. Nakahigashi, R. Hino, K. Uehira, T. Yagi, N.

Late Cenozoic, central part of Northern Honshu, Japan. Takeda and S. Hashimoto, , Aftershock observation

Sediment. Geology, , . of the Noto Hanto earthquake in using ocean bot-

tom seismometers, Earth Planets Space (in press).

Yamaji, A., , Rapid intra-arc rifting in Miocene north-

. east Japan, Tectonics, , .

Received January ,

Accepted March ,

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