ῒ῔  .3  (,**.)
 -  +.-ῌ+/+ ΐ ῕    ,**-  ,+-  ,**.  //  Pseudo Reﬂection Proﬁling of Shallow Structure in Unzen Volcano
Tomoki TSUTSUI῍, Takeshi MATSUSHIMA῍῍ and Hiroshi SHIMIZU῍῍Pseudo Reﬂection Proﬁling (PRP) is introduced as an e#ective method for shallow seismic study ofvolcanoes. PRP is applied to seismic exploration records in Unzen Volcano in +33/ and two reﬂection proﬁles areobtained. A reﬂection proﬁle of E-W line shows more complicated appearance of reﬂection phases in HeiseiShinzan side than that in another side of the survey line. Another reﬂection proﬁle of N-S line includes convex
phases in the west of Heisei-Shinzan. Two of these reﬂections are common in both proﬁles and can be located at
the boundary of the shallow aseismic region which was pointed out in the other geophysical study. Since theseresults are consistent with the previous reﬂection study and PRP requires free source location, PRP will be one of
the useful method for surveying shallow structure of volcanoes.
Key words : Unzen volcano, shallow structure, controlled seismic method, Pseudo Reﬂection Proﬁling, passive
seismic method.

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Ee£D%/+,-* E¤01$$A Df0 :/T8:$g:Ahi@%Dfj/()* 1$6s./¥7-¦ "%7§"U!"k#l$mQn%&Qo%7-* "¨¦~0Df (Fig. +)0 +,-* E'p.qrsDB6Et$Q%0 CAu.7-E:f/V7'p.q"()3/©"%/vDE(w!"xayNza{|aHKª8~'2=Q%q11«$p -* ¬9~{HV7)}~-"%Dh%­:=$A;3=f0 C;3E.- ®*+*ῌ2/*, ¯<°v±²= +ῌ+¯<³±±´±"
Faculty of Engineering and Resource Sciences, Akita
University, +ῌ+ Tegata-Gakuen-cho, Akita *+*ῌ2/*,,Japan.
 ®2//ῌ*2.- µ¶·°¡ ,ῌ/0.3ῌ,3¸¹³±³±º ±»¼º
Institute of Seismology and Volcanology, Faculty ofSciences, Kyushu University, ,ῌ/0.3ῌ,3 Shin-yama,Shimabara, Nagasaki 2//ῌ*2.-, Japan.
Corresponding author : Tomoki Tsutsui
e-mail : tom@buttan.mine.akita-u.ac.jp

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D S (z) P (z)$#!-qr$,OP  S (z) P (z) >s&.tuvwr OP  fg@hijklm@
Fig. +. Illustrations of reﬂection proﬁling. (a) A
concept of Pseudo Reﬂection Proﬁling. Multiple reﬂections are extracted from a transmitted
seismogram and are used as a component of areﬂection proﬁle. (b) The conventional reﬂection survey.

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145

Fig. ,. Geometry of the +33/ seismic experiment in Unzen volcano. Solid squares are temporary stations andopen circles are shot points. Solid triangles are major summits. The thick frame presents a target area of
this study.

   Fig. . (b)  Fig. / (b) !

"#$%&' t (t)t**#L.!uv-eawux. AyD z{R Fig. . (c) .-uop|E.( Umakoshi
et al. (,**+) .}~ ,.0y../ km .hd+havsurface(.)

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  C    D   >  HTDL  Focal

Area . Rs.u-( Fig. / (c)  AyD =|>Fig. . (c)  AyD H-I-PQR Fig. . (b)( Fig. / (b) .-lmn oFKKpqre( H-I- Fig. . (c)( Fig. / (c) Fig. / (c)VR¡.¢w£]¤.¥ ¦¢VR (  Fig. . (c) .V,-lmnst( FKK  A  B =| wu C  D  +.WyW+, km XY$%&' *.0146 Fig. -. Shot records for the shot S. at the stations in the target area. Horizontal axis denotes travel time. A
leftmost number of each trace is the maximum amplitude and a rightmost letters indicate a correspondinginstrument code number. “W-E” marks the original seismograms of Fig. . (b) and “N-S” marks those forFig. / (b), respectively.





147Fig. .. A Pseudo Reﬂection Proﬁle of the line W-E. The top panel (a) shows a close up of Fig. ,. The middlepanel (b) shows a Pseudo-Reﬂection Proﬁle of the line W-E. A bottom panel (c) shows a trace of prominent
phases in (b) and seismological aspects, the Focal Area and HTDL, by Umakoshi et al. (,**+). Marks “A””D” indicate clear phases at the right portion.

148 Fig. /. A Pseudo Reﬂection Proﬁle of the line N-S. The top panel (a) shows a close up of the target area. Themiddle panel (b) is a Pseudo-Reﬂection Proﬁle of the line N-S. A bottom panel (c) shows a trace ofprominent phases in (b) and estimated HTDL (Umakoshi et al., ,**+). Marks “A”-”D” indicate clear phases.

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 FKK 

149

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=E}~' E D  FFGxy

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O-MPwB +E+E DE :>F24, km 35*+N-S  4.2y6 C'D  "78 9 :;<9=*>:>xyqop Q ROw¡¢9£FM{W9+ D E X?@?ABC () * E D DE FG (,**,) HI !"#FKK JK LM=EN$ %O

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N$ 

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 +?9M=E  A'D 78 :;+,6^r@3 HTDL 3 (Umakoshi et al., ,**+)

.s *+  A  B +,6^r@3

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Aki, K. and Richards, P. G. (+32*) Quantitative seismology. W. H. Freeman and Company, 3-, p.
Clearbout, J. F. (+302) Synthesis of a layered medium fromits acoustic transmission response. Geophysics, --, ,0.ῌ,03.
L ¤G 2, S (+331) +33/ 3e4YIN$5f
6^xy8T% 1, +01ῌ+2-.
¥ (+331) N$5fzpo 7+EULYIV+, -D WXN$ YI ., +0/ῌ+1*.
Nishi, K. (,**+) A three dimensional robust seismic ray
tracer for volcanic regions. Earth Planets Space, /-, +*+ῌ+*3.
F YGD HG¦:§GZW[GF \m(,**,) ^# 7+Ee4YI Y[5f¨© 6ª]^«(¬ ,**, 3­ F¬ V*/.ῌ
*+/.
Tanaka, S., Hamaguchi, H., Nishimura, T., Yamawaki, T.,Ueki, S., Nakamichi, H., Tsutsui, T., Miyamachi, H.,Matsuwo, N., Oikawa, J., Ohminato, T., Miyaoka, K.,Onizawa, S., Mori, T. and Aizawa, K. (,**,) Threedimensional P-wave velocity structure of Iwate Volcano,Japan from active seismic survey. Geophys. Res. Lett., ,3,+*, +*.+*,3/,**,GL*+.32-.
Tsutsui, T. (+33,) Pseudo Reﬂection Proﬁling method : ane$cient complement to the CDP method. Geophysical
Prospecting, .*, +/ῌ-*.
Umakoshi, K., Shimizu, H. and Matsuwo, N. (,**+)
Volcano-tectonic seismicity at Unzen Volcano, Japan,+32/ῌ+333. J. Volcanol. Geotherm. Res., ++,, ++1ῌ+-+.
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X (z)UV$WXFJ/Y $3

Fig. A+. A model of zero-o#set seismogram R (z)at the top of horizontal layers. Vertical travel
time of each layer is t. Reﬂection andtransmission coe$cients are ri and ti at the ithinterface.

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ῌ (z)  R

z 

 (B+) (B-)

ῌ (z) "#$%&'! F (z) G (z) R!( )*+
T,z-.

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T *,+ῌz-(B.)

T (z)! 12 345 ! T (z)  08967)*:;!

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,DEFG HIJK-Fig. A,. A model of transmitted seismogram T (z)from vertical incident impulse.