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Seismic exploration at Fuji volcano with active sources�The outline of the experiment and the arrival time data�

Jun Oikawa+�, Tsuneomi Kagiyama+�a, Satoru Tanaka,�b, Hiroki Miyamachi-�, Tomoki

Tsutsui.�, Yasushi Ikeda/�, Hiroaki Katayama/�, Norimichi Matsuo0�, Hiromitsu Oshima1�,

Yuichi Nishimura1�, Keigo Yamamoto2�, Toshiki Watanabe3�, Fumihito Yamazaki3�, Hide-

fumi Watanabe+�, Toshitsugu Fujii+�, Setsuya Nakada+�, Minoru Takeo+�, Takao Oh-

minato+�, Takayuki Kaneko+�, Mitsuhiro Yoshimoto+�c, Toyotarou Takeda+�d, Etsurou

Koyama+�, Noboru Osada+�, Mamoru Saka+�, Toshio Haneda+�, Shinichi Hashimoto+�, Hi-

roshi Tsuji+�, Yoshiko Imoto+�, Taketo Shimano+�e, Akiko Furukawa+�, Takeshi Sagiya3�,

Iwao Fujii3�f, Yoshinari Hayashi3�, Rikio Miyajima3�, Mamoru Yamada3�, Takashi Okuda3�,

Takeo Itoh3�, Takeshi Hashimoto1�, Tokumitsu Maekawa1�, Atsuo Suzuki1�, Taku Itoh1�g,

Yasushi Miura1�, Sadato Ueki,�, Takeshi Nishimura,�, Kouichi Nita,�d, Mineji Satoh,�h,

Youichi Simomura,�, Kenji Nogami+*�, Sin’ya Onizawa+*�i, Hiroko Oyamada++�j, Jun

Funasaki/�, Shin Chikazawa/�, Kenji Fujiwara/�, Nobuo Hamada/�, Gen Aoki/�, Akimichi

Takagi/�, Tetsuya Yamamoto/�, Yutaka Hayashi/�, Masaki Kanao+,�, Mikiya Yamashita+,�b,

Hiroshi Shimizu0�, Atsushi Watanabe0�, Masahiro Korenaga0�k, Takahiro Ohkura+-�, Shin

Yoshikawa+-�, Sayaka Ikeda+-�l, Masato Iguchi2�, Takeshi Tameguri2�, Hiroshi Yakiwara-�,

Shuichirou Hirano-�

+�Earthquake Research Institute,University of Tokyo, ,�Graduate School of Science,Tohoku Univer-

sity, -�Faculty of Science,Kagoshima University, .�Faculty of Engineering and Resource Science,

Akita University, /�Japan Meteorological Agency, 0�Graduate School of Sciences, Kyushu Univer-

sity, 1�Graduate School of Science, Hokkaido University, 2�Disaster Prevention Research Institute,

* e-mail : [email protected] ©º++-�**-, |}��}»+M +�+�+�

� � � � � , -Bull. Earthq. Res. Inst.

Univ. Tokyo

Vol. 2+ ©,**1� pp. 1+�3.

¼ 71 ¼

Kyoto University, 3�Graduate School of Environmental Studies, Nagoya University, +*�Volcano

Fluid Research Center, Tokyo Institute of Technology, ++�Faculty of Science, Chiba University,+,�National Institute of Polar Research, +-�Graduate School of Science, Kyoto University, a Now at

Graduate School of Science,Kyoto University, b Now at Japan Agency for Marine-Earth Science and

Technology, c Now at Graduate School of Sciences, Hokkaido University, d Now retired, e Now at

Colledge of Environment and Disaster Research, Fuji Tokoha University, f Tono Research Institute

of Earthquake Science, g Now at JALWAVE COMPANY, LTD., h Now at Hakusan Corporation, i Now

at National Institute of Advanced Industrial Science and Technology, j Now at Earthquake Research

Institute, University of Tokyo, k Now at Railway Technical Research Institute, l Now at Japan

Meteorological Agency

Abstract

Fuji volcano (altitude -,110m) is the largest basaltic stratovolcano in Japan. In late August and

early September ,**-, seismic exploration was conducted around Fuji volcano by the detonation of

/** kg charges of dynamite to investigate the seismic structure of that area. Seismographs with an

eigenfrequency of , Hz were used for observation, positioned along a WSW-ENE line passing

through the summit of the mountain. A total of .03 seismic stations were installed at intervals of

,/*�/** m. The data were stored in memory on-site using data loggers. The sampling interval was

. ms. Charges were detonated at / points, one at each end of the observation line and - along its

length. The first arrival times and the later-phase arrival times at each station for each detonation

were recorded as data. P-wave velocities in the surface layer were estimated from the travel time

curves near the explosion points, with results of ,./ km/s obtained for the vicinity of Fuji volcano

and ..* km/s elsewhere.

Key words : Fuji volcano, seismic exploration, seismic velocity structure of volcano, National Pro-

ject for Prediction of Volcanic Eruption

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Fig. +. Tectonic setting around Fuji volcano, Japan and location map of the seismic exploration. EUR, NAM, PAC and

PHS stand for Eurasian, North American, Pacific and Philippine Sea plates, respectively. Solid triangles show active

volcanoes and open triangle indicates Fuji volcano. Stars and open circles indicate shot points and observation

points, respectively.

Table +. Shot times, locations of / explosions in the experiment.

The coordinates are presented by WGS2..

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Fig. ,. Seismic traces along the observation line for (a) S+, (b) S,, (c) S-, (d) S. and (e) K+. The vertical axis indicates a

distance from the shot S+ and the horizontal axis denotes travel time.

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ms�'/bPG���E�[U�� �7� D��NOP�&E�+** ms�'/bUEG���E(��/bU� [�� �7�A�D��/G�)*E�+/oU�&�7� L� G�)*E�+/orm� (00|� G��NOP!E,m�&�7�X@��� �KG�AB�-mU�@E�.U�7�A�D

�NOP!�� S+/ -/*�� S,/ ,,3�� S-/ -+.

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Fig. -. Travel time plots of first motions for each shot. The vertical axis indicates travel time and horizontal

axis are a distance from S+.

Fig. .. Travel time plots of later phases for S,. The vertical axis indicates travel time and horizontal axis are a

distance from S,. Times are reduced to 0 km/s. d indicates first motion. e, f andgindicate later phases.

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Fig. 0. Travel time plots of later phases for S.. The vertical axis indicates travel time and horizontal axis are a

distance from S.. Times are reduced to 0 km/s. ¸ indicates first motion. ¹ indicates later phase.

Fig. /. Seismic traces of east-west component along

the observation line for S.. The vertical axis indi-

cates a distance from the shot S+ and the horizontal

axis denotes travel time. Later phases are identified

between arrows.

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Table ,. Locations of observation points. The coordinates are presented by WGS2..

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Table ,. (continued)

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Table ,. (continued)

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Table ,. (continued)

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Table ,. (continued)

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Table -. Arrival times (arrival(s)), polarity (P) and quality rank of the first motion (R) at each station for all

shots. Ranks A, B, C indicate that accuracies of the first arrival times are within +* ms, -* ms, +** ms,

respectively, and polarities are determined. Rank D indicates that accuracy is within +** ms and polarity

is undetermined. Rank L indicates that accuracy is more than +** ms and polarity is undetermined.

Rank X indicates that no first motion is identified. Polarities of U and D indicate that directions of the

first motion are upward and downward, respectively. Polarity of X means undetermined one.

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Table -. (continued)

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Table -. (continued)

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Table -. (continued)

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Table -. (continued)

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Table -. (continued)

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Table -. (continued)

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Table -. (continued)

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Table -. (continued)

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Table -. (continued)

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Table .. Arrival times of the later phase for shot S,. Table /. Arrival times of the later phase for shot S..

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