ῒΐ  /0  (,*++)
 0  ,*+ῌ,+, ῕ ῔=  ´ µ¶  · ¸> ? 6 ¹@ A B {  º J» ¼½
,*++  + S 1 T ,*++  ++ S ,3 TThe Shallow Seismic Reﬂection Structure in the Northeastern Part of the Sakurajima Volcano
with the Pseudo-Reﬂection Method῍῍῍,Tomoki TSUTSUI῍, Mikihiro IMAI῍῍, Kazuki TSUSHIMA῍῍῍, Naofumi YAGI῍῍῍῍῍
Masato IGUCHI῍῍῍῍῍ and Takeshi TAMEGURI῍
Shallow seismic reﬂection structure down to , km b. s. l. in Sakurajima Volcano is presented with anapplication of Pseudo-Reﬂection proﬁling. Data used in this study are obtained through a controlled source
seismic experiment, the ,**2 Sakurajima project. Two ﬁnal proﬁles are obtained after the processing for the lines
NS and EW. Prominent reﬂective horizons can be recognized in shallow part of the both proﬁles. Complicatedpattern of the reﬂection horizons is correlated as a cross section of piled-up lava ﬂows. Thicknesses of thehistorical lava ﬂows are recognized and some unknown lava ﬂows are also detected in both proﬁles. However, lessreﬂective zone appear in +** to 2** m b. s. l. in the proﬁle. The less reﬂective zone is inferred as pyroclastic
materials from underwater eruptions because the zone corresponds to the low resistive layer in the resistivity
proﬁle. These results can be contributed to discuss evolution history and explosion mechanisms.
Key words : Sakurajima volcano, Shallow seismic structure, Seismic exploration, Pseudo-Reﬂection proﬁling

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Faculty of Engineering and Resource science, Akita
Fujitsu Software Technologies Limited.
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,0+ῌ**,/   +  ,  , Corresponding author : Tomoki Tsutsui
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Japan Oil, Gas and Metals National Corporation.
e-mail : tom@geophys.mine.akita-u.ac.jp.

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Fig. +. A geometry of the observation. The labels KD and MD represent the major summits of Sakurajima,
Kita-dake and Minami-dake, respectively. (a) Location of the shot points and the seismic lines. The
origin is the station KUR. Solid stars locate the shot points which are used for the analysis. Solid boxes
are the seismic stations. Triangles are the major summits. Thick rectangle indicate the range of (b). (b)The seismic lines and background knowledge. Geological regions are bounded after Kobayashi (+32,) andlabeled with bold alphabetical letters as follows ; E : recent materials, f : fan deposit, S : +3.0’s lava, T : +3+.’slava, A : +113’s lava, B : +.1+’s and +.1/ῌ10’s lava, N : 10.’s lava, K : Kitadake lavas, KP : Kitadakeparasitic cones, and b : substratum rocks. Larger solid boxes locate drilling sites ; SHR : Shirahama, andKUR : Kurokami. Solid circles mark the resistivity sounding stations after Kanda et al.(,**2) and arelabeled at the end station of each line. Seismic stations are described as those in (a) and are labeled withbold letters at the end stations.

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203

Fig. ,. Observed seismograms. Each trace was normalized with its peak amplitude. (a) S*+ in Line NS. (b) S*+
in Line EW. (c) S*. in Line NS. (d) S*. in Line EW. (e) S*/ in Line NS. (f) S*/ in Line EW.

+32, &'() * (Fig. +b) +, NS -./0,ῌ ῏῍῎ῑΐ

12345 N 6ῐ45 S 7845 B 94,**2 :;<= 1 >?@ABCDEF)

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lm;<nYZ[o Up.

7845 B ] ^*Fig. + qr,,+sῌt !u+s 2 bvs./w* , xyxzX\ , x+,X{/[| - }~+,o"#m;<ghF)[  (S*+, S*., S*/)  d , ,**3 wZ῎ [u+s

X**+AX+,/A ./$[*+, NS    S*+ Fig. ,c  ,d  S*. Fig. ,e  ,f  S*/

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BPF K!._`)*+* Fig. /a, b (45 ,2
Hz BPF K!.aU:%b&c('(5d':)*%:e&* .:fJ *ghG+ ,  2 Hz BPF [.3i%(G+j;%(5
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=> S*/ 3 .

8'n/0(?5 CV<@<%fi Fig. 0 (45 'n/0 / :Fig. -.

Data processing ﬂow.

%7( CV <@<if%i<45%%i( ]$uv ,./ :A<:(B5:4&*J *(06\$8'n/0 / :\]$8 )*+*

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

Fig. .. Result of the trace mixing. (a) Three-point mixing, (b) Five-point mixing for the shotS*/ in Line NS. The traces are ordered the same as those in Fig.,e.

Fig. /.

Band-pass ﬁltered seismograms for the shot S*/ in Line NS. (a) ,ῌ2 Hz, (b) ,ῌ+0 Hz.
The traces are ordered the same manner as those in Fig. ,e.

205



206



  

Fig. 0. Distribution of Median CV for the lag time.
The circles for the /s correlation window, theboxes for the +*s window, the triangles for the +/s
window, and the diamonds for the ,*s window areplotted. The /s window is applied to the actual
analysis.

Fig. 1. Raw Pseudo-Reﬂection proﬁle along Line NS
for the shot S*/. The datum is located at *., km
above sea level. The horizontal axis presents
distance from the northern end of the line. The
vertical axis is lag time or two way time. Theiramplitude is normalized with the zero-lag value.

 ! "#$%&'()*+,./012,3&45678) *+,-./0
12,9:;<=>)?@ "#$%&'@ABCD
B *.+ῌBE,FGHIJKL<=>M.NOIPQ,R (Yilmaz, ,**+) S ) T)*+,-./012,@U>HIJVW>)?@XY ,  2 Hz BPF S!Z[\]^_%`

a) *+,-./0

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1 fgW>hiBjklmno  pqrB_%

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Fig. 2. Equivalent incident seismograms for each shot.
Each seismogram was normalized and was scaledwith percentage for its zero lag amplitude.

kxBZ[yz6{ |T6a}|)A|~|B
@W>*+,-./012,]^_%cdKW>

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} a}|)]^_%cdB<nBjkl{*.+ km 6>}|>. 

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, +32+K ¡¢£¤ ¥¦ ,**2 UY§¨©¡¢£¤ ª«¦ , ,**2 a}|)]^_%cdf !k¬7w
Fig. ++ a { NS B Fig. ++ b { EW B]^_%cdBk¬eW ­®¯{ Fig. + @e<|>qp
°jB±e ®¯{²³\_%´µ¶W ·¸\qp°j{ (+32,) @U>m ¹º»¼ (K) B½j{(+32+) BpqpB°

Fig. 3. Deconvolved Pseudo-Reﬂection proﬁle along
Line NS for the shot S*/. Display method is thesame as that of Fig. 1.

 !"#$

207

Fig. +*. Stacked Pseudo-Reﬂection proﬁle. (a) Line NS, with the same display method as thatof Fig. 1. (b)Line EW. The datum in the panel b is located at *.. km above the sea level.
The horizontal axis is distance from the east end of the line.

%&' (  )*+,  Appendix -.

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208

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Fig. ++. Interpretations of the proﬁles. (a) Line NS, (b) Line EW. The display methods are
the same as those of Fig. +*. Geological descriptions are labeled with capital letters in
Fig. +. Important phases are labeled with Roman numerals I to V. The basement isinferred from the gravity basement by Komazawa et al. (,**2).

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

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 %&'()  NS II5  6  7 (KUR)  8  +** m   KUR (DEF!% (+333)
R +*. m0

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SHR  +*, m!"#$ 1*+,-./012m

$9 :!";

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Fig. ++ 6k0

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

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9Q(e <=m 6>O_e [O' EW

 II (A9bJR0[#0 3(q:rQO_ Q>seO !"# A(Be'[#0 Cjt

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KUR 8  IIIy< KUR (D8 

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O LMek(ifPQ# B# 3 XYZ,#R(9j9|@}B~@#O9j9hx[*@9 0( KUR 8.ῌ-    III

 NS

y<

   S  % (,**2)*+T< )+0Q 3J  U[|

Di EW3(4 * km 8u 8VPf O#0(WQ@}B~@*@ w72O % 6XO #0if3

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i

%eHIOse \% (,**2) (i NSu(8q(]^.O^(e ()  EW
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P Q Q NS_e  NS (DE IV  2 V)Ou

a E0 O  EW

JvW3PQ D"_ O]b <(6GQc(+312) O'[9 +-*** dYW<#OuJ v e# O+/* m fP'[Qg9 [¡h ,+312 2_qJRj

(i

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2 [Oi¢9ZY

lm[O #03(Pw72O anb JR#0¤¥"ob¦§¨©eª (i,pq

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:;   ,*G-*2 H    /24c2 6 ##>'j J2῎ ῍ ῑ ῌAvseth, P., Mukerji, T., and Mavko G. (,**/) Quantitative
Seismic Interpretation, Cambridge University Press, -/2
pp.
Bruno, P. P. G., and Castiello, A. (,**3) High-resolution
onshore seismic imaging of complex volcanic structures :An example from Vulcano Island, Italy, J. Geophys.
Res., ++., B+,-*-, doi : +*.+*,3/,**2JB**/332.
Cerveny, V. and Psencik, I. (,**,) Ray-theory amplitudes
and synthetic seismograms in ,-D inhomogeneous isotropic layered structures. Program package SEIS. In :Seismic Waves in Complex --D Structures, /-ῌ0/. Report+,, Dep. Geophys., Charles Univ., Prague,
Daneshvar, M. R., Clay, C. S., and Savage, M. K. (+33/)
Passive seismic imaging using microearthquakes, GEOPHYSICS, 0*, ++12ῌ++20.
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Hidayati, Sri, Ishihara, K., and Iguchi, M. (,**1) Volcanotectonic earthquakes during the Stage of magma Accumulation at the Aira Caldera, Southern Kyushu, Japan,
Bull. Volcanol. Soc. Japan, /,, 0, ,23ῌ-*3.
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Ikawa, T., Abe, S., and Kawabe, Y. (+33,) Undergroundstructure and magmatic activity of Izu-Oshima volcano,Japan, as inferred from seismic reﬂection survey, J.
Volcanol. Geotherm. Res., .3, +*/ῌ++1.
Tsutsui, T. (+33,) Pseudo Reﬂection Proﬁling Method : ane$cient complement to the CDP method Geophysical
Prospecting .* +/ῌ-*.
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Yilmaz, O. (,**+) Velocity analysis and Statics corrections,in Seismic data analysis, SEG, ,1+ῌ.0+.
Yokoyama, I., and Ohkawa, S. (+320) THE SUBSURFACE STRUCTURE OF THE AIRA CALDERAAND ITS VICINITY IN SOUTHERN KYUSHU,
JAPAN, J. Volcanol. Geotherm. Res., -*, ,/-ῌ,2,.
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corresponding travel time curve. Cross markers are observed travel times. Circle markers
are calculated travel times.

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212

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Fig. A-. Correlation between calculated travel time andaltitude. The solid line is the recurrence curve.

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