ῒΐ  /+  (,**0) /  ,3+ῌ-*3 ῕ ῔














,**/  +,  ,0  !" ,**0  1  ,*  #$Ground Deformation and Magma Reservoir at Aso Volcano :Location of Deﬂation Source Derived from Long-term Geodetic Surveys
Yasuaki SUDO῍, Tomoki TSUTSUI῍῍, Makoto NAKABOH῍῍῍,Miyuki YOSHIKAWA῍῍῍῍, Shin YOSHIKAWA῍ and Hiroyuki INOUE῍
So far the ground deformation associated with a magma supply system of Aso Volcano had not been discussed
because any clear signals in ground deformations and volcanic earthquake activity had been hardly observed near
the Nakadake active crater during its activity enhancement cycles. In this article, however, the deﬂation source
and magma supply system is investigated by the long-term geodetic surveys. The secular subsidence is observedin the Kusasenri area about - km west of the Nakadake active crater from the +3/+’s levelling survey in compiled
levelling surveys along the Bouchuu-line since +3-1. While the ground deformation near the active crater has
been obscure. The source of this deﬂation near the Kusasenri area is estimated on the basis of the sphericalpressure source model through the non-linear least square method with using recent survey data which include the
Bouchuu-line and an extended survey route. The deﬂation source is located beneath the Kusasenri area at about/ km depth. However, recent volume changes at the spherical deﬂation source are smaller than before +3/3.
The location of the deﬂation source coincides with the low P- and S-wave velocity body in the -D seismic velocity
structure. This fact supports a hypothesis that the low seismic wave velocity body represents a magma reservoir.
Therefore this magma reservoir beneath the Kusasenri area must be connected to the Nakadake active crater.
We inferred a rigid conduit in the magma supply system from the obscure ground deformation in the vicinity of
the Nakadake crater.
Key words : Aso Volcano, ground deformation, magma reservoir, --D seismic wave velocity structure, magma
supply system+ῌ ῐ ῎ ῑ ῏

QRST10< UVW" Malone et al., +32+ ; McNutt,%&'()*+,-./01" ,-()'23.45+330 +X$Y Z[1\]" 8,/^_Z'`./01+61" 7.8,()93:;<=" (),>'?&@

5" ,-().45+aCLO)PQRST" Z'bc

&A,-BCD'EFGH'IJKCL.MN+O)P

defgfhijk4'lmP

p203ῌ+.*. qrstuvwtuxyz{|J}J}~#}C} ,-
Aso Volcanological Laboratory, Graduate School of
Science, Kyoto University, Kawayou, MinamiAso,
Aso, Kumamoto 203ῌ+.*., Japanp*+*ῌ*2/, } +ῌ+J}}}
Faculty of Engineering and resource science, Akita
University, +ῌ+, TegataGakuencho, Akita *+*ῌ*2/,,
Japan

ed.STnno<p203ῌ,,-, qrstuJNPO  f ¡¢£
NPO Kyushu Biomass Forum, Ohhori, Akamizu,
Aso, Kumamoto 203ῌ,,-,, Japanp203ῌ,,-, qrstu +3-*ῌ+¤$tu,-¥¦§
Aso Volcano Museum, +3-*ῌ+ Akamizu, Aso, Kumamoto 203ῌ,,-,, Japan
Corresponding author : Yasuaki Sudoe-mail : yas@aso.vgs.kyoto-u.ac.jp

CDs4Mt·u¸M ¹M5vwºM5 »M·¢¼x

292

 Dieterich and Decker, +31/ ; Murray et al., +33/SVT U&4

.HJ

 V

12RWJf-.WWJ,t    

!

"#$%



 +3-,0&'()*+ (Sassa,'(    ,-.

+3-/) +3-1

/01234 5 (+3/.)  +3-1

 + 6  1 6 *,-78'( '( +3/-

9%:&;;<,

Sassa (+3-/) =&4 + > 9< *.2?

+./  

@A.

3BC

D"E.F(

R S +

Jf
M

M,t+ ,fg9<VS +A

TAB;J`9&wfX 12  YZ

0  +323a,+323b, +33*a, +33*b, +33*c, +33+a, +33+b, +33+c, +33,,+33- W4P

;'(

K1[\JA]%^R_1234 =AWJ& Sassa (+3-/, +3-0) 2 G H< !I"E.F(2JK"&4+ N2 



L # M $ (+32.)  N  O  +3/2t NOf'( 2 6 ' (TAB;@}3V.12

9%Q.t; ¡R`W/5,;%%Q&4f

 +, 6 *,-%*JP%Q&.a> ¢ L# +30, +30. ; L#Mb +302 ; £cR N2 J S T& '&(U)E¤ +30. ; ¥dM$ +3/2 ; CD +312 +32. +32/ ; Sudo,+32+-* S T+-* ; AVL-+, +- +. ,V+322 ; efM$ +31* ; Wada et al., +31* ; 5M¦§

. 3RJK"&R+3/2

WX

RY+,&-.

&'& S T(¥,K1a

12 -..%Q1234. Z[Z\]^_ `ab/0cde2RR *4; JfX Dg!I%1h1i2jk
f-312RR NW, lmggjk¡RH ;<fh;<f 3V.
12¨ ©i +312 +32/ +321 ; ©iMª +32. ; YZ

0  +323a, +323b, +33*a, +33*b,+33*c, +33+a, +33+b, +33+c, +33,, +33- *4 '(Z[Z\]^_%4(' a4P 

gs2 ¡RfWS; Tjx, 3

-%/0&

V.12RR L#M$ +312 +32. ; L#M©

M+332

+331

M+333

M,**.

i +32/ ; £c¤M$ +31. +312 +32. ; £c¤Mkl

4
%5, +3-1'(n*, N 1*o

6< 7Y+,&/01234-78%p%f4(a2jk %qP Z[Z8*+J`9%b/a+32/ ; ©iMb +312 +32. ; CDM5 +33/ 1( S

T9yª«+3 m®nS(¥,K1&4¯Kg%°Jop







J.s;,t NW,/h< 








wx

;-.%:raW%;-.%uv

;-. +3.*, SVTU&4

.  H&'(Z[Z\]^_%4(' a 

3

g;.qr,tae, 

T¬­, +312M.12.

;@} JfM

3V

ggjk ggs2

3V.12RRWJ.-.JR


=yI;

±



,;K

;<%1²,Y;+,&-.12R4 f''e(¨ 

w?<%|RWJ,t W2*,12

-.'( Dg!I%1h1i2jk

 T.S +34

T z312 > o{,

AB;M

;@}

JfXAB~CD (,**+,,**.) ,&uvtX

4

 Fig. +NE

12XF.Y+,&F(2 ae

 Gc*+MHG~MI HMJKM T
LMMNO~MT;M

gZ[Z\]^_ `ab/.12W'4 ¢ uv4X;@} '³aJ´(2X. < +3/2'( +3/3



%°RW2*,F(2R'44P,tµX

HM ~M

PMNOHQM ~M R~M
H MJKMGc*+JRXF,W2*,;.@}&3R *4H ;<,Rf-  

-% Fig. ,

a

%5,

t¡'X- , ¡t ¶J¡ Fig. , , 

!"#Q ³´³µw¶+·8 ¸¹º»?¶ 

  !"#$%
& (Bouchuu-line) '()*+, +1 km-./, 1.*m 01%&2 34567((AVL-+ῌAVL-+1):;<, + km 8901(AVL-XX +/,) =>?@A B C DEF01%&& GHF 
I C JKL MN OPQRS=!"#$%TU&(Yoshida-line)

VW0& (Akamizu-line) X Y

Z[)\01(BM+*.*+ῌBM+*.+/)  +322 ]^>? )01%&2 :X_8 (BM+*.*/ῌBM+*.*2)N`a&bc

B

C DE2N01

BM+*.*2ῌBM+*.+/ d7e BM+*.*+ῌBM+*.*/ fghi@

A 01%&_8TUW0& GHF I C&01jkN `al)7K +3-1 ]fg
34567( mn@A d jkopN qrstA) ,**. ]jkuvopy FAw2xl +/z{|} +312 +32. ; {|~ +32/ ;T +3/.CF8 +3/1 ]N!"#$% 7&01

AVL-, fg AVL-+- w2=@A))v :AD D2 )Q= \( B C F)v FAw2 +/ o01jkw v )(  +3/1 ]D D_YI C w) FADEI01 dB N $%\201 = ¡@A) ¢£gf\¤¥=¦gA §¨N:

01 ¢©B ª Cw) «a )TUW0&2N +323 ]OPQR
S7¬v 01jk=stA)C F)v +331
] z­ +. o 01jk2N&jk®y  ¯01%&= OPQRSTUW0&
MB

J01jks() z­ +. ojk +331 ] /° +331 ] ++±+, ° +332 ] 0±1 ° +333 ] -±.

293

Fig. +. The process of volcanic activity at Aso
Nakadake crater. At the weakly active stage
there is a hot and super acid water lake in thecrater, with a diameter of about ,** m, a
temperature of about 0*², and a greenish whitecolor. The water level is maintained fromgroundwater and fumaroles, and does notchange. The ingredient responsible for thegreen color is iron. When the volcano becomes
more active, its temperature rises up to theboiling point, evaporation is promoted, and the
hot water level decreases gradually, and many
mud eruptions (small phreatic explosions) occur
intermittently, ejecting hot water and old rockfragments of / m diameter or more to distancesof up to + km outside of the crater. At the bottom of crater many small pits open, with diameters of several meters, ejecting high temperature volcanic gases and ashes, and becoming
incandescent. After this a lot of volcanic ash
is ejected accompanied by intense rumblings,
ﬂames several tens of meters high, and ejectionof volcanic rocks. So the vents expand, growing to a size of tens of meters diameter, andeventually cover the entire crater bottom. In
this stage a lot of ash is ejected to some tens ofkilometers height. The volcanic activity thenbecomes even more intense and a Strombolian
type eruption stage begins. For some weeks ormonths the volcanic activity is at a high levelwith violent rumblings, and ejection of many
fresh magma fragments and ashes. A Strombolian type eruption becomes gradually weaker
and the volcanic activity ceases. The volcanic
ash deposited around the crater is washed into
the crater by rainwater and the crater wallcollapses. Then the bottom of crater is buried
and the ﬂoor at the crater bottom begins toappear again. A lake covering the whole craterbottom is again gradually formed, as the craterﬁlls with hot water. The water level goes up
gradually, and becomes more stable. A phreatic explosion can still occur if there is somepower remaining in the volcanic activity. Thisis the end of the eruption cycle. In this way, asa calm period ensues, the lake becomes green
and a cycle is completed. This is one volcanic
cycle at Aso Volcano. And at every active
stage a lot of volcanic ashes are ejected during
the time when new vents are opened. These are
the main characteristic of the eruptions of Aso
Volcano.

XYZ?[\]^_[ ` a[bcdef[bc g[]hij294

Fig. ,. Index maps of Aso Caldera showing levelling benchmarks and levelling routes with benchmarks at thecentral cones. Triangles show tops of notable central cones. In the Aso Caldera map, solid circles indicate
benchmarks of AVL (Aso Volcanological Laboratory of Kyoto University) and open circles indicate
benchmarks of GSI (The Geographical Survey Institute). In the levelling route map, solid circles indicate
signiﬁcant benchmarks and open circles indicate auxiliary benchmarks.

 . 

;

 +331  
-ῌ++3.,   . /  +3-1 ΐῌῐ +3/- ΐ῏῍῎ῑ῔῕ῒ +3/1 !"#$%&'(

!

)


/!0 1&'( +3/-  2. 1  )*45

 ,  1    +3/+  2. 00 +3/-  2. 1   ,-0 ?54@;A* Fig. - + ,- +3-1 . + ,3

AVL-+ :;<=>

!"67890!"

BCDE E'F0 +3.,  2. /  , )*,-0 G !"HIJKE@LCM50 NI
OE5GP,QRST> 40 +3/+ 
2. 0  U45-!" AVL-++ VW1%

1234mn&Y[d*&

Fig. -. Vertical displacements observed along thelevelling route of Bouchuu-line in Aso central
cones. The benchmark of AVL-+ was held
ﬁxed. Displacements during the period from
+3-1 to +3/- were calculated by comparing
results of the +3-1’s survey.



295

Fig. .. Secular vertical displacements observed at
the benchmark AVL-+. near the Nakadake
active crater during 01 years from +3-1 to ,**..
Each displacement was calculated by comparing
the result of +3-1’s survey.

  0     3  +3/3

! "#$% &'()
 / ! & +3/++3., 0 ! * +, +**-*./0 *123456 +373489:;< +3.+3.0.ῌ1 = > +3.1

-ῌ. = > +3.3
+3/+0 = > +, = >/ῌ+, = > +3.2+, =ῌ+3/*-ῌ3 = > +3.3

, = > +3/*. =ῌ

3 = 34?@ABCDCE:F.G( 5H +3/*.=

IJKLMNO.

)PQ $ RS:8O:348 TU
VHHG(W<) QX +3-1
+ ! $% +3., / ! Y 56 + 37 

ZXY[\].^  CD8>34?CE8._
a$%bcd  + 37[`G(Q. +3.2

Fig. /. Vertical displacements observed along thelevelling route of Bouchuu-line at Aso central
cones. The benchmark of AVL-+ was held
ﬁxed. Displacements during the period from
+3/2 to +3/3 were calculated by comparing
results between the +3/2’s survey and the +3/3’ssurvey.

ZXY[.G( Q&S348.)
 +3.,"#ef / ! & +3/+ 0 ! &: !  ghiU:$PQ5&* yz.{-K )PQ. 
. ,**.

 +/ Y|

6 + 37 j AVL-+. kl! mno-ῌ,p&q%$)  AVL-+.  AVL-+gh 2 "# +3/2

&r ghiUs%t +3-1

+3/2  0 


0 = ,.

 + "#$%

}NO 1 =$% 2 = $~UQ $op&.  AVL-+ ou&- +&F.ghiUQ :$% ,**.

Y +/ "#efoQ +3-1
Fig. .

vw  +3-1

v) +3-1
! Y
+3/+

 + "#ox& + ! $% +3.,

:.^. +3., 0 ! *q%$

p%U T +3/2 / / ! &: ! .

 2 ! & +3/3

 3 !

.% +3/-

 1 ! &IJ  AVL-, $%AVL-+- *mn.F

Q$.&:PX:. Fig. .
AVL-+.  +3/2

vwRS 2 ! & +3/3

 3 ! "#* {-K:yz."iU
T d*.FRS:H$o Fig. /µGHIrJ¶K·r ¸rq¹L+ºrq¹ »r¶w¼M

296



.

+3-1 0%=> Fig. -, Fig. /, Fig. 0 -./0%12 -_. km MN"]

C+

RS\

H

*

$? +3/-  1  0%GE&`:a5  

+3/- baZ`

V:MN"]

H?:%:cd#ef$g%
cd#ef$g%:Z , 6hijklm&(: n 6o +33-   +-  ^p ,**.   +/   
&(hijklm A "' +  ?5n 6
Fig. 0. Vertical displacements observed along thelevelling route of Bouchuu-line at Aso central
cones. The benchmark of AVL-+ was held
ﬁxed. Displacements during the period from
+3/3 to ,**. were calculated by comparing
results from the +3/3’s survey. The benchmark
of AVL-+, had been destroyed during the +311’s
survey and the +32+’s surveys.

o
 +.  +33-   +-  q( r so +323 +331  )B:hijklm B "' ,  1* Qhijklm &%hijklm&(:*+

o AVL-+

0% AVL-+.

+3-1 0% +/ tZ,

E&($ - + ./2u!-o +- 0%;<&( 

Fig. -

+3/2  2 +331 

+33-

\QvPow.x (AVL-XX +/,) y"

   +3/3   3  ( ow AVL-XX + ῌ ,zE&  AVL-+   .x AVL-XX .{/

 ! "# $ %&

AVL-XX!I0|}~$E&(?

AVL-+. '  1'(a( E%  AVL-+,'($ AVL-+-)' * $+%&  AVL-+-   , AVL-+-

-./0%12 , km 

 *$ +3/2  0 34

 +331   +.  o?

./2130%13 i4*q(rso-o$y &vZ 5 

0#506(7 89:($ )( g%E&:MN267

+3/3  ,**. 

a5'-o$|E&(: #eg%8-ῌ-+3/3   3  0% ,**.   +/ ;<&:=> Fig. 0  ?


@AB



 +3/3 

9 '0%#eg%:Z :; : +-+ < *- => -, < /. = ? *.* m(*.*, *.*, *.*) (m) C0% :=>$&D&

&D&>K :Kva@w E&( &%=>FG;&(:  #eE v(+%&: +3/+ 0%H!I

Fig. - JKA$'( Z :E&( $<0 '<L  AVL-2 0% AVL-+-MN0%O 0P +311   ++  0%.ῌ+  +33- ,**.  !"+32+   +, QRS *$GE&:? Fig. 0  +3/3 +32+ 

# $%&'%#+33- 0% ,**.  +* ZQ+32+ H!5$U'hijklm A 0% Bo¡^¢C£ Marquardt'V( W HJK$X(YE& "' - &( DE¤h¥ ¦§d#e¤h¥

6 Z

T

: +311 U[%6) +%&$ !\+

(Mogi, +3/2) ¨ d#e cd#e f$MN"]: AVL-+* 0% AVL-+- Q: :Y cd#ef$$-oo0%©&^  /_0 cm !#H( $<0

:21ª «%E&: Bo¡^¢C£;5F:Vd#ef$¬\  0
% / km E­%:®¯l°±i²a³´C\AC 

297

Fig. 1. Locations of deﬂation sources BCU and BYA and the levelling routes with benchmarks at the central
cones in Aso Volcano. Triangles show tops of notable summits among central cones. The cross markindicates the initial coordinate of deﬂation sources. A large open ellipsoid BCU indicates the location of
deﬂation source during the period of about +* years from +33- to ,**.. Lengths of each axis represent
standard deviations. The source BCU is derived from the spherical deﬂation source model by the +33-’s and,**.’s surveys along the Bouchuu-line. The depth of this source is about / km below the sea level. A smallersolid ellipsoid BYA indicates the location of deﬂation source during the period of about . years from +33- to+331. Lengths of each axis represent standard deviations. The source BYA is derived from the sphericaldeﬂation source model by the +33-’s and +331’s surveys along the Bouchuu-line and the +323’s and +331’s
surveys along the Yoshida-line and the Akamizu-line in the southern west ﬂank of Kusasenri. The depth of
the source BYA is estimated at about /.2 km below the sea level beneath the southern region of Kusasenri near
Mt. Eboshi. The +323’s levelling data were obtained by GSI.



Fig. 1     !"!
# $$%&'() . *

!"!

O \ $]^_`DC%abcO
defQRSg%h"i!jklKmnOO^o?p Fig. 1q12 NIUV+, -  x, y, z, k* -./0 1234

WCCD rO IUVW%stuvO

5!"678 A 9:

p ?

12;<=

@AB

wxE

 Fig. 1 FE 5!"678

Op 5!"678 A yzvqA 9: FGHI JE - *@ABKLM

{% |}~  /.**,..+ km p

0 N;<COP $%@ABK  +33-

QRSTIUVWXYZ [4 $C

%..+3/.*3+* m C12  $>?@ABCCD

Table +

o? ,**.

 ++
0

-

 

³FG0NH´µ¶N ·NM¸IJ¹NM¸ ºN´»¼K

298

Table +. The coordinates of deﬂation source for
BCU-Model BCU 

Table ,. The coordinates of deﬂation source for
BYA-Model

  RSTU! c

"Q,</;+.ῌ,  +33- +331 



 BCU VW?<+ BCU 

$%C!r34J VW?<+54
"DE!# C5 /.2-+..3 km &Z# =)A $%B C<+DE+ +33- >? +331 5 . [_+lm n "5-.00+.3,+*0 m-  C<+ {|# 
 BYA 

M N O5

-B4567

P*+89B+  B -B4# QNMNO5  Table ,  RSTU

FGHI&56 )JK@L5+331 7

162]"3 A 

34#  567 89:;4# <=!

6



!"# $%&'()*+ ,

!# -. /012
7 >?@ B 

0" Fig. 1   !rC<+P*+cSr.ῌ-  !"#$%&Fig. 1 rC< BCU  RSTUB4VW+ BYA  B XYJ+Z#  K@

A# u6)  b162])

LMNO5 7 [\]-B4^TC&*4B <"# u 7p

!)J &_`#  !" +33- >? +331 :;?<+MNO5 )8H56 . [  )a!%b34# MNO5

9XY+W!J;?< =+# Fig. 1 !" +323 K@L)cW47 P*4dZ#
e +. f7+331 

=![\) 2 "Z&*4

B!J

rC<# BYA   BCU

 A# 162]:H;!<u"o=34B

& , g7 89#hJ+*4# i

~*4# +33- >? ,**. [dp

&-jdB+ k-" +323 >? +331  ¡56 /;"# Fig.

=!lm n$"o!J3+# 

1  BYA k-"MNO5

"DE?¢@£¤ + km 7¥

dp +323 K@L789q])%rC<4B&>*+!# s&t[)S>!J;?<# 54

&

q]" *.**- m !J3+!J uj
vw" Fig. . rC<56' AVL-+. x(y /' ()*+,*-.#/01 +3/2  ,**. z=B!J +311 {|# 56' AVL-+. %"o)}$~*4B;>?!J=+# ujvw"56  MNO5
' BM+*.*1 dp +331 7

234567
 BYA B4# <=! !A?<+ +3/2 >? ,**. ¦[567 89>q]d?lm n 34+  J+*

K@LWo567   *;#4B+6"# § a3+,

+# +32+ !J j}!M N O5

<!J)# BC¨©ª«¬­®

89 . ,34 n¯¨©3#+323 >? +331  2 [,7&+W# +ῌ, U+ *.**- m q]34-

7D -  (-) °*4lm n 3+;+  B 3+ ~*4# . !(89 Table - r

VW?<lm n " +33- >? +331 =!
 . ,&&

Table - !" +311 {|lm n$)B±<[+* ²+*0 m- E!J)rC<4B 7 [\)/





Table -. Volume Changes and Rates of BYA-Model for +3/2-,**.

Table .. Residuals and Errors at each Benchmark in meters (underline represents that residual value ismore than two times of error value )299

µqr_Fs¶t·Fu ¸F¹vw<ºF¹v »F¶<¼x300   Table - Fig. 0

AVL-2

.
='(



!

!

+~I6=.q V67 :Pb(#,"# AVL-+,   $%&'( +33- "# ,**. )*





AVL-+. (Fig. .) +&,

0123456

7897: Table .

&, Table . ;< )*: .=> ? 97: >@ 97A7:B+C m &,
Table . A7 , D<97HI ! J K97L

8#MN# #97
"OPKQ

AVL-+-

N#, R(P +3/2῍+3/3F+30-῍+311  , G)*
AVL-+- .ST UP+O+K !

AVL-+- lI

(KSM) !

!

!, &M

AVL-+- SJ"W97

N# +312 J'6: P !
AVL-+- K-d.qcLg0 4

Y=O :WM&"+,<V' !

=:E ,

+3/2῍+3/3F+3/3῍+30-F+30-῍+311  - G)*B+ !

AVL-+- D + km H+312  3 ^ +3 &J'6

+311 DZ

-  ./)*

!

!

AVL-+- N  <U e.qCOPQ #"rs:%&t   3 A!

V} B 

AVL-+-  : R;[S(Fig. 2, Table /, 0), U( )V

T:aO

* .  BCU 234

V} BYA 234#u  ,
3 A !

AVL-+-  :97:& !, "#  e.qCO~~W=  +~V'97"W

~-QI j5 ..2 kmk X!Y7 -*ῌ $KQ

X# +311 Y DZ)*97A7#$%".V
I+[+ Table .
+3/2῍+3/3 )*P,

!

AVL-+- 97\*.+0-]*.**/ m  +3/2  0 ^ ,. &

'(

)'

_ 1 ^"# 2 ^ "P* 2 `aM:b+& "#c ,'-deO ,  !

AVL-+- .qZ CO.qCOPQP¡C ! 8:

P, "

!

AVL-+-  :¢£njBCU 234k   j[PQk  X!Y7K"#P\¤CO7"W¥,u9 3 B !

AVL-+-  

. :/fPg01hb(#, GY:P+QP+ e.qPQCO$I 2)**i j3 0.0 k VI45 + *£#"O ,iaM  +3/2῍+3/3 )*67 
 +3/2  0 ^)' lM mYnopP BYA 234.q8.q

VLrs!

AVL-+- 97 *.*+-+]*.**0* m  97 +3/3῍+30- )*.vPuw[QO ++- ST

AVL-+- :|&97G ]

BYA 234^_K67:tP, 

8:tP+b(#,u9 +30-῍+311 )*

D<"# +3/2῍+311 )*N#V
' !

!

AVL-

pP

+30- D]n X#Na8"

8 + $§*¨©4X  ub
X#Na" ª_c«d8,UP97x:PK:
AVL-+- 67 8;0 

<PYO yz Vg01+b(#

P, 



Table .

`¦&

h 4:o!

V{ AVL-+- =

>?&

!

AVL-++ +* 97 AVL-+- #@:P, # !

97.A7 +./ 

D<:P, D<"#

!

AVL-+- &K97  ! Ayz8&BC.'8, GYI 6=.q V67

0ῌ+ 

]U V'  ef234:gPe.q:¬
N 01 e.qhijWK ¬N# , m­®uG6¯8hij °¦m'

=9 -±. km CO

8,

:Pb(#, Y  )*D

u9 hijW  .= ²³²kYIb

AVL-0 :|&F97+8#M(#6lmn%o¯`¦´pP,

mE!

P I .ST97G V}A7:b+&Sudo and Kong (,**+)   m

­

®

_`abTcdefeghijkNlTcdmn3opj

301

Fig. 2. Locations of deﬂation sources determined without AVL-+-. The display scheme is the same as theprevious ﬁgure. The depth of the source BCU is about ..2 km below the sea level. The depth of the source
BYA is estimated at about /.3 km below the sea level beneath the southern region of Kusasenri near Mt.
Eboshi.

Table /. The coordinates of deﬂation source for
BCU-Model without AVL-+- - 
   !" # -$. km %

&'()*+,-.

/-0,-.

1Fig. 3 ; 2 3456789:;<2=>?,-.@AB-,-.C D2E > 0 km 1FGH

Table 0. The coordinates of deﬂation source for
BYA-Mod el without AVL-+-I  P 

J@K S ?L?

MNOPQRS.TU= 2VW X

W - km XYZ[\] P 

J@K S TU]^.IC
D

]  P 

] +*ῌ 89 ,/302    

Fig. 3. The seismic wave velocity perturbations modiﬁed from Sudo and Kong (,**+). AVL is Aso Volcanological Laboratory. A heavy solid line delineates the outline of the caldera. Perturbations are contoured
at +*ῌ intervals with solid and dashed lines indicating velocities faster and slower than the average model,
respectivery. Top : Horizontal P- and S- wave velocity perturbation sections at the depth of 0 km, at which
the velocity resolution is very good. Bottom : Vertical P- and S- wave velocity perturbation sections at - km
X-axis, at which the velocity resolution is very good above 2 km depth.

VWXY E*/0/-.¼4 £*FG>¼

303^_C<`$aXY bc%:; &d$ 
VWXY( Ne'f( )* g
hiXYS+j$  (hi XkC<A
lm5( EXYno,p2-^_(  N2 (hXYno,pq.r/$
s<5Q2 Fig. +* Q2%tuv*+ ,-. 

!/0/-.C<Z2

0wXk- x<C1y!z23.hir/$ {. XYS &g |*g+*5
g%<8-} XYZZ(~+b 3h( /0/-.C<XYno$p$ U=%3.538 i 0wXk4 XYS+( 2 Xk !5 XYS+5

b

XYZ ( /0/-.C<no$  Z (pk Xk(6#+}` %E Xk !noF-. 7$$Fig. +*. Model of magma supply system in Aso
Volcano. Nakadake Crater is now active.
LPT-Source indicates the source of long period
tremor with a period of about +/ seconds(Yamamoto et al., +333a, +333b). The magma
reservoir is located from --D tomography of Pand S- wave velocities (Sudo and Kong, ,**+).
A conduit from the magma reservoir to thecrater is kept to be its shape.

.8$ LM &G
8  & 9a+&8 . no+ !:-.77-+}42(58 
FG18

3$%

+312 < 3  +3 =>w

!(

;(

&(

2%

?& XY ¡ +313 )¢<£&Z(j$  -%  '!

/0/-.1( VWXY{s ¤}C<1
8 XYS¥¦  @A§¨©§ ª§«¬>ῌ S  ,*ῌ  

!^_gB­2  +*ῌ  P ,*ῌ S  -*ῌ 

1ῌ ῍ ῐ ῏ ῎(Mavko, +32* ; Sato et al., +323)   VWXY{!" #$% &'()ῌ
*+   ,-. !/0/-.12

3$

  /0/-.+$(! ,*ῌ4-*ῌ 5678&

9 -4. km ²C5³¯´ µD8  °bLM#< a XYZZ(~gb+ E*([1ZXk 0wXk;(rF+ b

0¶Xk·YGC<0wXk¸H}AB¹( 

':;< 8=+(  &'>®¯%AB - °± &IJº4 £rF+ c ABLM,

KLtuv5M %F?@ABC<DE<%FG>

G35®b FG0wXkC<N¸ -4.

HIJK2

km O%    ABL

M.DE<%FG( N>C<:; /0/-.OP5Q2

RS 0ῌ, ῒ῕ΐῑ῔

 , TU=%VWXYXYZ ![\(-]"#<%/0/-.FG>

d;D- ABLMC<3$%FG>

 &C<3$%'(K2 ; !/0/-.12 0wXkXYZG

:;< e FG(/0/-.OP5»P8 :;

¶NoJQp·F¸Q1 ¹Qm_qrºQm_ »Q·¼s

304


f 

 

      !"#$%

&' () *+,
"

-

./0#123

#4156
 )7891:; <=>?@ 0;" A("#$<=&B @C A1D
E

(F#GH1I0/J#4; K$#L

M!AN":#/O41  PQ '?$0
56?R; ST%&'"561/( U&AV$῏῎78#/)W*X+A4YR,Z .; - [.\]^_`abcd)W?YR efcd)Wgh #i+A4; ; j/0k12

Klm

3Qn72784o5p6 +323 *78q
r?71; s/ 8t0u ; , 9:9v;w<x=>y?@z{)WA|#}B?7. ?~C .; t0uῌ ῑ ῐ ῍
Dieterich, J. H. and Decker, R. W. (+31/) Finite element
modeling of surface deformation associated with volcanism. J. Geophys. Res., 2*, .*3.ῌ.+*,.
DEF (+30,)   G)%H
1 +ῌ+0.
1
DEF (+30.)  G)%H1(,)
3 3ῌ+0.
DEFQH I (+302)  % P
+- 2.ῌ3..
H1 (+)
DEFQ JQ 3* (+312) KxL'
78 +311 * H1  M +  +311  +0ῌ+2.
DEFQNOQH IQ J (+32.) K78 +32+ * Kl-*baxL' M ,  +32+ 
R 
,,ῌ,2.
DEFQ 'P (+32/) 'QR0 S]^KT U \]^VW]^Zr //ῌ0-   (+30.) H1 (+) M , 
3%X-%DP ¡J21ῌ32.
 Q?YQ¢Z[\ (+31.)  +3 +,-ῌ+,/.
 L+]£^0  Q_¤`Qa3b¤Q?YQ3c¤Q
c¥¦Q§¨d¥ (+312) e L x  L  '  M + +K +311  ,-ῌ-*.
  Q ?Y Q a3b¤ Q fP[Q ©ghª(+32.) +313
e L+K* / «¬l +32+ * ++ « 
xL'M ,  +32+  --ῌ-2.
 Q?Y (+32/)  L+]
QR0 S]^KT£^0 U \]^VW]^Zr 0.ῌ
02.
[.\0\]^­i (+313) ®-
P( Kl +312 * 3 « +3 j¯c°kP
T Ulm±± +. 12ῌ2*.
[.\0\]^­i (+323a) 
 
%¬l
P'qr +323 * + «²+323* + «
T Ulm±± .- 00ῌ1+.
[.\0\]^­i (+323b)  %P +322 * +323 * + « + j²/ « 1 j /« 2 j ² / « 3 j ¬l% +322 * 1 « ²+323 * / « +0 j 'qr
T Ulm±± .. +,1ῌ+-,.
[.\0\]^­i (+33*a) 
 
%PQ
%Q³QQ´
T Ulm±± .0 .0ῌ/2.
µn'
[.\0\]^­i (+33*b) 
®-
T Ul
( Kl +33* * . « ,* jT m±± .1 1+ῌ2-.
[.\0\]^­i (+33*c) ®-T Ulm±±( +33* * / «²+* «.2 2*ῌ21.
[.\0\]^­i (+33+a) ®-T Ulm( +33* * +* «²+33+ * + «±± .3 --ῌ-2.
[.\0\]^­i (+33+b) ®-T Ulm±±( +33+ * , «²/ «/* -,ῌ-1.
[.\0\]^­i (+33+c) ®-T Ulm( +33+ * , «²+33+ * +* «±± /+ .+ῌ./.
[.\0\]^­i (+33,) ®-T Ulm( +33+ * +* «²+33, * / «±± /- ,.ῌ,3.
[.\0\]^­i (+33-) ®-T Ulm( +33, * 0 «²+33- * , «±± // ,0ῌ.+.
Malone, S. D., Endo, E. T., Weaver, C. S. and Ramey, J. W.
(+32+) Seismic monitoring for eruption prediction. US.
Geol. Surv. Prof. Pap., +,/*, 2*-ῌ2+-.
Marquardt, D. W. (+30-) An algorithm for least squareestimation of nonlinear parameters. J. Soc. Indust. App.
Mathem., ++, .-+ῌ..+.
Mavko, G. M. (+32*) Velocity and attenuation in partiallymolten rocks. J. Geophys. Res., 2/, /+1-ῌ/+23.
McNutt, S. R. (+330) Seismic monitoring and eruption

 !%t(v®¯®°±²u]§³%t(v´µ%¶·u
forecasting of volcanoes : a review of the state-of-theart and case histories. In Monitoring and Mitigation ofVolcano Hazards (Scarpa, R. and Tilling, R.I. eds), 33ῌ
+.0. Springer.
Mogi, K. (+3/2) Relationship between eruptions of various
volcanoes and the deformation of the ground surfaces
around them. Bull. Earthq. Res. Inst., -0, 33ῌ+-..
Murray, J. B., Pullen, A. D. and Saunders, S. (+33/)
Ground deformation surveying of active volcanoes. In
Monitoring Active Volcanoes (McGuire, B., Kilburn, C.
R. J. and Murray, J. eds), ++-ῌ+/*, UCL Press Lmt.
 (+32+) +   -*,.
 (+312)  !"#$%&'( !%)*+, -. + / +3110 12 .ῌ2.
 (+32/)  ! 3#$%&'(!4%5678%9:;<=>?@ ABC -D;<
EFGH;<IJ12K0 -1ῌ.,.
 (+321) :  !%LM%NO !P& Q
RSA;T1 -* B-+ +3ῌ,2.
UV WX (+312)  !Y%ZL [\=-. + /
 !%)*+,>?$]+3110 12 +3ῌ,,.
U^ _` (+32.)  !"#$%&'( -+32+ T0  !%)*+, -. , / +32+0
12 1ῌ+0.
UV WX (+32.)  !Y%ZL [\=(,)  !%)*+,-. , />?$]+32+0 12 ,3ῌ-,.
Press, W. H., Teukolsky, S. A., Vettering, W. T. and Flannery, B. P. (+33,) NUMERICAL RECIPES in FORTRAN. The art of scientiﬁc computing. Second edition,
Cambridge press, 30- p.
Sassa, K. (+3-/) Volcanic micro-tremors and eruptionearthquakes (Part + of the geophysical studies on the
Volcano Aso). Mem. Coll. Science, Kyoto Imp. Univ.,
Ser., A, +2, /, ,/.ῌ,3-.
Sassa, K. (+3-0) Micro-seismometric study on eruptions of
the Volcano Aso (Part , of the geophysical studies on the
Volcano Aso). Mem. Coll. Science, Kyoto Imp. Univ.,
Ser., A, +3, +, ++ῌ/0.
Sato, H., Sacks, I. S. and Murase, T. (+323) The use oflaboratory velocity data for estimating temperature andpartial melt fraction in the low-velocity zone : Comparison with heat flow and electrical conductivity studies. J.
Geophys. Res., 3., /023ῌ/1*..
abRcUdefgUhijUik (+3/2) 305! - -/ῌ.,.
!=lm? !Pn(%,oep` (+312) !Pn(%q] -+310r+311 T0  !%)*+, -. + /0 12 -+311 T 2r+,s0 +ῌ- +312.
oep` (+32.) !Pn(%q] -+312r+32, T0  !%)*+, -. , /0 12 -+32+ T 2r+,s0 +ῌ0 +32..
oep` (+32/)  !=lm? !Pn(%t(u+32- T +32. T%q]v !'(u!4%567
8%9:;<=>?@ ABC  wx /3 TyD;<EFGHz{AB|};< (+) ;<IJ12K
.3ῌ/. +32/.
Sudo, Y. (+322) Development of device for successive
spectral analysis of volcanic micro-tremors. Proceedings
Kagoshima International Conference on Volcanoes +322,--+ῌ--., +322.
oep`U~  (+33/)  !=lm?% s ^ ++ 1/ῌ13.
Sudo, Y. and Kong, L. S. L. (,**+) Three-dimensional seismic velocity structure beneath Aso Volcano, Kyushu,
Japan. Bull. Volcanol., 0-, -,0ῌ-...
oep` (,**+)  !% !'(%|u!u s ,- /./ῌ//*.
oep` (,**.) UUv ! K
 +.. p.
xiUUoep` (+31*) !Pn(%,! +/ +ῌ3.
%
Wada, T., Kamo, K. and Sudo, Y. (+31*) Measurement ofkinetic energy of volcanic micro-tremors. Special Contributions, Geophysical Institute, Kyoto University, +*, +.3ῌ+/2, +31*.
Yamamoto, M., Kawakatsu, H., Kaneshima, S., Mori, T.,
Tsutsui, T., Sudo, Y. and Morita, Y. (+333) Detection ofa crack-like conduit beneath the active crater at Aso
volcano,Japan. Geophysical Res. Lett., ,0, -011ῌ-02*.
Yamamoto, M., Kawakatsu, H., Kaneshima, S., Iidaka, T.,
Oikawa, J., Watada, S., Morita, Y., Mori, T., Tsutsui, T.,
Sudo, Y., Yoshikawa, S., Hashimoto, T. and Nakabo, M.
(+333) ASOBOI31 : Aso seismic observation with broadband instruments in +331. Bull. Earthq. Res. Inst. Univ.
Tokyo, 1., ,01ῌ,2/.
~ (+3/.)  !%t(= ¡ -. +10 & 1 +/+ῌ+/..
~¢kU£¤]¥ (+3/2)  !%¦#§ !Pn! - +.1ῌ+/-.
(= ¡-)¨© ª«¬­0306  + A+33-ῌ,**.

   

 , B





+323ῌ+331 +33-ῌ+331

307

308

    

 K> ῏ῑ -Marquardt ^ijkNlJ45ῌ῎῍ῐn?op

FGHIGJKLCq rM@ANON0X s

   (Mogi, +3/2)   (x, y, z) 


309

!" aS # DP $%&'() (xS , yS , zS) *+,-. /0  DUz
12() (xr , yr , zr)3  (+) 456
Dr
D
ῌ
῎
9
῍1D,8r,3-ῌ, 1Dr,8rr,3-ῌ,῏

DUz7k*(+)::D71zS9z3, Dr71zr9z3, r7;1xS9x3,81yS9y3,<,rr7;1xr9x3,81yr9y3,<, k*7

1l8,m3a-SDP*=> l, m,m1l8m3?@ABC*= 6DEFGHIGJKLC?M@ANON x, y, z, k*
LPQRS*=

6 :.TUM@ANON x, y, z,LCtuvw .xwyw56 .
x, y, z, k * 0X

cPuv6(;DUz<
ῌ9-D1xs9x3 9 9-Dr1xr9x3῎7k*
῍ 1D,8r,3/ῌ,(x
1Dr,8rr,3/ῌ, ῏(;DUz<
ῌ9-D1ys9y3 9 9-Dr1yr9y3῎7k*
῍ 1D,8r,3/ῌ,(y
1Dr,8rr,3/ῌ, ῏(;DUz<
ῌ ,D,9r, 9 ,Dr9rr ῎7k*
῍1D,8r,3/ῌ, 1Dr,8rr,3/ῌ,῏(z

6  .

LX

M@ANONVW:X(,)(;DUz< ῌDrD῎79
῍1D,8r,3/ῌ, 1Dr,8rr,3/ῌ,῏(k*-y DP w}~DV ?

k* M@ANONVW:X 6 YM@AN

ON k* 

M@ANONz.{.sLC?| (,) 

DV7

M@ANON x, y, z, k* ?QRSZ[

p
k*
1+9V3

(-)

\]^ _`aB (Marquardt, +30-) bcPaB*-. 6 $ V ?J *= 6 ::*6 M@ANONaBdeK@fgNhP?

? V7*.,/ 6 rNOH0X ~Press et al. (+33,) m46Marquardt ^ijkNlJ

? z.{.aB-.M@ANON k*  (-) 
46