ῒΐ  /.  (,**3)
 .  +1/ῌ+20 ῕ ῔ BL  
,**3 5 - 6 +0 789 ,**3 5 1 6 ,1 78:Ground Deformation Associated with BL-type Earthquake Swarms at Sakurajima Volcano
Yuki TATEO῍ and Masato IGUCHI῍
Sakurajima volcano experiences, in addition to repeated vulcanian eruptions, intermittent small eruptions
similar in style to strombolian eruptions. These strombolian-like eruptions are associated with swarms of BL-type
earthquakes dominated by low frequency components (+ῌ- Hz). Ground deformation associated with BL-type
earthquake swarms was detected by water-tube tiltmeters and extensometers in an underground tunnel. Tilt andstrain records were corrected by BAYTAP-G to account for the tidal e#ect. Gradual tilt change of crater-side-up(,*ῌ-,* nrad) and extension of the ground (2ῌ+1* nstrain) continued for -ῌ-* hours before the BL swarms. The
inﬂation was temporarily suspended for *./ῌ+3 hours, and was then followed by deﬂation associated with BL
swarms. The degree of tilt and strain change was in the same order as that for vulcanian eruptions ; however theduration of inﬂation processes is longer than that of a vulcanian explosion (by several minutes to several hours).
The inﬂation rates (,ῌ,2 nrad/h, ,ῌ+0 nstrain/h) prior to BL swarms are smaller than those prior to vulcanianeruptions (,*ῌ3* nrad/h, +*ῌ/* nstrain/h). In the deﬂation process, tilt change of crater-side-down (.*ῌ-**nrad) and contraction of the ground (,*ῌ+0* nstrain) continued for +ῌ0./ hours and was accompanied by BL
swarms. The deﬂation rates (+1ῌ++- nrad/h, +,ῌ/1 nstrain/h) accompanying BL swarms are small. The
deﬂation rates of +/- of the vulcanian eruptions exceeded the upper limit of the deﬂation rate that accompanied
the BL swarms. The depth of the source of pressure that is thought to induce the ground deformation associatedwith BL swarms is estimated to be -ῌ. km for both inﬂation and deﬂation processes (assuming the Mogi source tobe horizontally located at the center of crater). No di#erence in depth is detected for vulcanian eruptions.
Volcanic gases were emitted in the inﬂation process prior to BL swarms, however volcanic gas emission stopped
in the inﬂation process prior to vulcanian eruptions. It is inferred that prior to vulcanian eruptions, the top of the
conduit is plugged by a lava dome derived from cooled and degassed magma, and the internal pressure rapidly
increases. In contrast, prior to BL swarms, the upper conduit is loosely choked and the internal pressure
gradually increases due to the intrusion of new magma from a deeper source. The di#erence in inﬂation rates may
be caused by the degree of choking of the upper conduit. BH-type earthquakes dominated by high frequency
components (/ῌ2 Hz) occurred alongside inﬂation prior to a BL swarm. The inﬂation rate almost reached the
maximum rate prior to BL swarms that occurred without pre-BH-type earthquakes. It is inferred that a highinﬂation rate due to choking of the conduit is the cause of BH-type earthquakes.
Key words : ground deformation, BL-type earthquake swarms, Sakurajima volcano+ῌ ῐ ῎ ῑ ῏;<=!+> + ?6@AB +./!=!,HIJ/!KL,MNM(OPQ4RS

T(UVWJ K(XYJ/.ZRS([\1],^,^V =!_`ab+_c(de fYJ =!gh

, mῌ7+CD;EFG

ViW23Z (Lipman et al., +32+)

jklm=!,nSSo,MNM+pW,^V_c(qr stQ4RS./o uv,=!,HIJ/!K+de fY(w()*+!,-./0123/.4 +32* 5 / 6 +2 7

B34 xy!;< ,**. 5 3 6 + 7+z{|=!},K~}=!({JZ$% %! . +klz{|=!+ -./23+ῌ+.+3  +1,,ῌ+3 !"#$%&'
Sakurajima Volcano Research Center of DPRI, Kyoto
Univ., Sakurajima-Yokoyama, Kagoshima, 23+ῌ+.+3,3 y@ABF

Japan.
Corresponding author : Masato Iguchi
e-mail : iguchi@svo.dpri.kyoto-u.ac.jp)*+K%,-176

 += 

> (*.*-  *.++ mrad) $&  . - //0,./ km 3

 LHMN"1$2

O & BL 

4512H=P)Q312/R

 & +323 ST2 6789: (+- Hz) $Q& = >. A

U0; <VFW=X[\]^@_A`$.H +a
2/#

bB1

CD%c& ,**0' EF ]9defgh>1$Y

?Z%& +323' 

BL 

 ,**-** m&  

A *, km GiH 2.& ?2jk& CDCl R#/ --* :(-IV

GmhJ KH12HH Rn o IV

$+BmhpM >  qr2/#= >F0.&  <BL

(Iguchi et al., ,**2)' )*"+,

iP-N2

stO u2& PQRS R#/ +** '(-IB s$v
Q& $v

AVz sBLA +** m Y1 s5
[

' 2

}@_A`MZ~)/z+12Hqr2/#(Iguchi

H& I$  %J& +* '(et al., ,**2)'-$./# $012/#(Iguchi,+33.)'

H& BL $Y./# OIV$<= >F0 -& BL 

A_A$6A

wT Y.& xU9: Vy{CDC$W R#/|2#/# @X  qr2/#

?Z%& +323'.H$/& BL $Y
HB\./#( CDC$$]^12$& ?Z % 

& BL Y _  [(Kaneshima(+323)

R#/

IV$+#/012/#"#' BL 5 _

et al., +330)' +3// `-a.

4bFc*./&
78

5$Qd12/# ' e"F& #

9: (/2 Hz) $=X

%Jf pGF"#

2 ' +321 ` 3  . g BL Y5  ' hij67kl3 4 : 56789:;

BH  & +323 $_./mg !(- BH $n.H-- ,.1 km

?Z%& +323& BL Y _./CD

33 R#/  

C$\.H$012 ' .-. BH ?

ifo$ +* mm & Jffo$ +* Pa 2p$["& BL 5qG 

F^./# ' ,**2 `r-]^12 CDC\wT$s:t12

1231  $2.H' Jff/#"#' BL Y _ s57u

o$ /** Pa Fvr %?Z& +33*& w$-+= >#12Hp $ & ,***& - km ? xGyOM [#/^x>12/R&





%& +32-' )/"#12 xn
& +321 ` ++  +1 g  ,*.* } 9
$"#.HuM2/#

?Z%1& +322'

5CDC¡¢£ ./# ' ?Z(+322) .A -  . km Y.&

U

CDCQ¦" )/WB©/# ]z > [#/{|  '
?

~67

& a

H +320  +322 `Rn5$5

2.H BL YFq

b & ?(¤=R)¥z >Fb.&  F^x>F§¨H'* ªH&  c )Q& CDC¡¢£ ^./# ' &:&OM( _.

HR)¥CDC Q Rn _A >F«#/7u$+%.& ¤ <%

F|- .& CDCXH@X « [#/¬.H'' ? x= >$ *.*+*.- mrad& Mz>$ **.,/(+*0 '  Fz+ _A`Y1A -CDC QY1 q
,0 km -& (IV$+%<= >& ?2@2& A BCD

C\-CDC"# q
2/#

bB1

-/; ,.1 km 

H° R#/312/#(HAR ; Fig. +)' ­:±.²(Ishihara, +33*)'  ! "#$& EF! "#

,ῌ ῎ῐ῍ῑΐ῔ῒ῏῕=R)¥z >a.C

G (Kamo and Ishihara, +323)&

´ & ?A
1 --* m­:

Q& ? ,/ m ³?


/* m

µ$¶·H/M./# ' 3°­:h ¸9¹º LHMN"1$"#/;

Fc#"$OMy

±.²HF®¯12/RQ& »

$ ' h ¸9¹º®¯12-., m 3-a Vn&

U  ¼u½¼

. /0 BL 1 !2 3 4 

177

Fig. +. Map showing the location of tiltmeters and extensometers in the underground tunnel at Harutayama (HAR : solid circle). Also shown are Seismometers (HIK : open circle), a tide gauge (HAK :reversed triangle) and the video camera equipped
main observatory (SVO : diamond).

56789:0;678 <=>? , @ (WT-R, WT-T) /AB&C&

DEF&$GH - @ (EX-+ (R), EX-, (T), EX--)
9:IJK;/ LMN +OK ,2 m

N+++E

 P

Fig. ,. Tilt and strain records associated with (a)vulcanian eruptions, and (b) BL-type earthquake
swarms. Seismicity is represented by amounts ofseismic energy released in +*-m intervals.

   ++

;+ (Ishihara, +33* ; Kamo and Ishihara, +323 ) Q
RS TUVP
WK_V@* R @@* T @`V

+320+322    

;++,n oO     p*BqrE sty&z,g OriginLab Corporationy&z
T} Origin Pro 1J{|}~@

dBz&$

 Digitizer &$  st*yBD B

 WKXY Z[/+; \;+,]^

9a,b` c$defghijiM*\,j]kl* 4j3 muvwH xK+ (Fig. ,a)+322  , - 0++  .3   +-  ,1  o, BL 1 !

 <=>? WT-R @ ]v9nK o,GH

(EX-R, EX-T) /+;

+** nstrain

2

, @

!*

Vb`yz$, EE{ZVwH"9nK (Fig. ,b) BL/ ,* 

1 !

 #K,$)%&*

+ +* ()y&z*~@,

V



¦*

!3

! 2 Y§¨``

!3 ¯,`;  +.1 km

he/

°-



 !*£  '¡`i9 Fig. , b4@

+9¤J¥ 9 ©;+ª«  ¬­® +*¦
$b` ±.

!67 (HIK ; Fig. +) /0 +* Z!"#$%&'()* +, +321  ++ - +.
 -0 

)¢*nb`9

Fig. , c$def/A BL 1

gV

\XY

c$def
'¡nstrain _K;+ +/. ZY +/* nrad>? o,/+; .* nstrain

/+; ..

G¢"967J

9'¡)¢*VZ[!"#$%&'()9u¥0º;+ bK- 
-ῌ+ 
Fig. , V4. /0>?/A" ²³*´¥µ0;+ Ishihara (+33*)
¸678 (HAK ; Fig. +) ¶·¸`¹$z]67

P% >?"` ZM5»¼*½1 EFGHIJ

178

Fig. .. Tilt and strain records associated with BL-type
earthquake swarms (after correction for tidal e#ects
by using BAYTAP-G). Seismic energy released in+*-minute intervals is also shown. Periods of Vulcanian eruptions are denoted by “expl.”.

  BAYTAP-G 
KILD#MN)O) BAYTAP-G KIPQRS# -TUV=WX(EX-T) YZTWX (WT-R) Y'([\B%]
Fig. -. Representative tidal correction. (a) Originaltilt and strain records and tidal level at station
HAK. Dashed lines show times of low tide. (b)Tilt and strain records after correction for tidal
e#ects by using BAYTAP-G (heavy lines) and byusing the tidal level at station HAK (thin lines).

-ῌ, 



+321 > +, ? +. @ +0 @^.KI_YZ` +* X;a!bcdefgh

ijk

Fig.

. <= +, ? +. @ + :lABmnA)

!"`<=

!"

OoCp9 +3:;j]pqr ] #WXY

3* nrad #WX UVWX

WXst`uv]O wxyD#!"c z{^| ,, nstrain } ] ,*,+ : BL ~!bO ^; M , :;O

 !"=]\ ^.WXOiO $wD

)*+ (WT-R :  .* nrad)Y # ^.X^ ` ]^EX-T : 3 nstrain)  ] BL ~!bO

./012345 BAYTAP-G 678 +32. ; Tamura
et al., +33+ ` ^.WX`st ]
BAYTAP-G `

^.WX`st ] `z{Y^KIS ijk
Fig. - <= +322 > + ? , @ 0 :AB 1 :CD+ ? - @ / :AB 0 :CD] BL ~!b¢!"*+`<=YZ,-# $%&% '(,- (EX-R :  +* nstrain,] +. @ ,- :lABmnA)!"`<=

!"O,3 :;r]

+0 @ . :l# WT-R WX# +.* nrad# EX-R Y.. nstrain EX-T WXY.* nstrain } ] $_ 

# + nrad#  

¡ # - nstrain¡£¤) B¥ ¦Cv] w§¨O9 . :;rD# BAYTAP-G D|^`]KID

N 2 :lAB BL ~!bO o\|© SOªB%]O «:;¬ ­ ­

9 +, :; *+ (WT-R : ,.* nrad)

BAYTAP-G KIO ®%]^`!",- (EX-R : 02 nstrain, EX-T : 03 nstrain)]KIv ]^.WXO¯)
OB%# + ? , @|° )±

+ ? - @ * :³LD,* :lCDO®%] *+,-²Y # BL ~!b+* Xadefgh´µ¶#p ^`]KID# + ? + @ ,+ :YZ +]O mnA)

? , @ +3 :¸¹ Fig. - º»D< ] AB

¼)½`sN - mkine · s,

MD +./ mkine, · s }

²n²D# ¤·¡ ¤®

*+,-. BL /0123456708(5179

9 ,* nrad :#;<=08῏>?@A&'()?67 .2 B BL /012345CD ῏>EF,GH IJ(5ῒKLMNOP
Q?RS  TTUVW῕?῎D῕()ῒ?XY Z  [\ ] !"#CD^ῑ_PQ?@
Fig. . @G7 BL /016708(5`aA.bcd῏>  eFdfgh?iIJj. Zk Llmlno,GHῐpqNrstCDuS. vwxyz{ +*|}U.U +* |O()ῒ~A. BL /0123nodfNO? / nrad ῌf|?ghKA LTdfNO?.K῏>e
F?@A|K.

fNO? / nrad 

K() D|?C-. BL /0123nogh&'

fNO?

() DG^ ,* nrad :D$% ῑ_O|&'ῒ`aA.῏>K

|? BL /0123

 ῏>no +* |O&'()ῒ -  -* | ῔  / nrad ?
K  Nr?῏>noNrK
noK

 ῏>

 - ῔ ()ῒ/ nrad  N L Nr?
῏>gKghnoK



n

o^῍ - ῔ ()ῒ/ nrad 
N / nrad  Nr? noKῐ - ῔ / nrad f N / nrad fFig. /. Relationship between the amount of inﬂation
ground deformation and the duration of time preceding BL-type earthquake swarms and vulcanianeruptions. (a) Tilt change of crater-side-up. (b)Areal dilation.

NrU.  !"#CD^ gh?
D῍U. , BL /0123`aA.῏>,GHghU !"#3^ - ῔  / nrad :K.d / nrad fl£¤¥Fig. . $%  Tl08(5 D"#U.
Fig. /  BL /012345K

!"# ,*3* nradῌh +*/* nstrainῌh [S BL /012345`aA.#;<=08
῏>EFbcd¡a D.TK¢d.
῏>  EFgh¦K§aA. ¨©ªΐ?
Fig. 0 @A gh .2 «¬{7­ ., «¬!"#CD῏>  EF(5ῒKLMNOPQ?@
 BL /012345`aA.῏>EF(5ῒ&'() ,*  -,* nrad VW῕() 2  +1* nstrain U{,D®]fl LMNO *./  +3 NOU
  ¯<  !"#U`aA.῏>EF"#noKK^ IJ¦°±  gh +*|}vwxdf®]fld   !"#$%&'()ῒ ,*-.* nradIJU^L(5ῒ BL /0123

VW῕()ῒ .+3* nstrain K²³´. ¯

67&'() .*  -** nrad VW ῕ () ,*  +0*< BL /0123`aA.῏>EFMNO

nstrain U  -  -* NOU MNO ,* NO + ΐ?D

,3* nrad VW῕()ῒ -+/* nstrain K²³´!"#MNO +* | 2 NO[S.Kµ!"#$%&'()ῒ +*. (Fig. 1) ¯< BL /012367 I¶·D (5ῒ?MNOU¸¹º(5»¼KA

JMNO +  0./ NOU .K BL /01`aA.&'()U ,,2 nradῌh,$% +* |, NO[S.K·D BL /0123

VW῕U ,+0 nstrainῌh K  T}½¹º »¼ +1++- nradῌh ¹ºIJ»¼V!"#'()*+,-.

180

Fig. 0. Examples of records of tilt. Suspension ofprocesses is indicated by bracket lines. Dates
referr to the start of upward tilt.

/012 +,/1 nstrainῌh &34 56789:;&<= +..,3 nradῌh 2,,* nstrainῌh !> ?
@ABCDE>FG>HG ICJH25
6789:;KLMN?@A BL OMPQR
S . TUADE&3V W 56789:;
0, XY ,- X (-1ῌ) G BL OMPQRYZ[@A\D]&3 ++- nradῌh ^_2H.ῌ ῎ῒ῏῍ῐῑIshihara (+33*) > H`ab6 (Mogi, +3/2) c12 BL OMPQRdefghi! <KLZ[jklEgm !n/?o1

pqrstu;,Yv!1

BL OMPQRwde12xnfghi

lEgm

Fig. 1. Relationship between amounts of deﬂation
ground deformation and duration of time associated with BL-type earthquake swarms andvulcanian eruptions. (a) Tilt change of craterside-down. (b) Areal dilatation.

 ,.0  ... km Myz{|n/}~ .  +*-  1  +*. m- !/ 567

+*. m- !>4 (Fig. 2b) BL OMPQRw!567

89:; ,.+  ..* km n/}~ .  +*-89:;& {n/ H>

+* m !DE>H > V (Fig. 2a) W

 n/ BL OMPQR 56789:;!  W xnfghilEgm !Z[ >H 56789:; n/}jklEgm  n/?o! 

~G +* m B&3

HG > V

/

-

.

-

G>!n/?

oG>L_G z/0!?o Ishihara (+33*) &  , km z/0!?o G *Hm!1 z/0GH
¤AG>H>V

Ishihara (+33*)  56789:;deMN?

lEgmi ,  0 km !/4 n/}~G2HG &G - km ¡¢£Y1 n/}~H mm&¥¦1MN?

xnZ[jklEgm JH2 $§ Ishihara (+33*)  !"#$%&¨©Gª  BL OMPQRKLxnZ[3& mH «¬­-H 

jklEgm!®_ 

 ,.0  ../ km n/

 2+*-1+*. m- !/ ° 5678

9:;³ ,.+.., km n/  -+*-3

?oz/0!;,¯± G -῍+ ²SL­-H´;,¯µ¶!hk´;,BL  

181

     !" #
 $% &'()

*+,-. /01

2 34 BL ,  &'(5 634 7 8 ,9:9;< =.>% <?
@ABCD E%FG,H6 IJ K
L4>  BL ,M5NOPQDR
6/S,F.,TU *./+3 VW,X!Y NOPQDR6/F.

SM &'(#  &'(S,015 9:9;<,=S,1!
Z

/,

KL4>  [\] (+32-)

R>^ NOPQD,_,7`S5 , a,bcd
e  4>  fg,bcde5 NOPQDhi j,_,! "k hi j5_,7`S5#l mn $#  > " o,bcdeM5_5p%SM7`#  >! "k& fg,bcde5q j,'<rst (Ishihara, +33*)"k >5 f7,u*;<%$6,mn2'( R /, v%.>
  NOPQD,,#(5w> axy&'(Mz6 _{M5 , )*,bcde,
_,p%S,7`"k#,7`S! ,*ῌ-/ mῌsFig. 2. Relationship between depth and volume changeof the pressure source for (a) inﬂation process and(b) deﬂation process. Solid and open circles
indicate BL-type earthquake swarms and vulcanianeruptions, respectively.

 [\] (+32-) 5|}/~  BL 

qV,_5%+M=.> ,M S
!|}/  5, +322 - .  +- .,_,p ,/012  2* w,7`S!|}//+* mῌs

26 BL 

9:

9;<,=S5d d1 52/,,3" F. L 

4,,54 #ly> ,M 6j,S,015TU)

/Mz

75*+,-.,|}/6 #ly!8L  |6 BL , # S5NOPQD 7 *+,-.-y$>^ 9}:/# ;F. ,<= a>?,l7@4>$ Ishihara (+33*) ,AM5

xK! BL , NOPQD

B ',0#lV 6q% +322 - .  +- .,.C,D

!q 

2 

Z D! Fig. 3¡# U(¢'( £¤¢¥4, &!¡#VWE + M5 BL ,/ῌ ῍῎~9:F¦1

BL   , 

=.>

 1 V -* 

NOPQD  ,§>,¨©

ª «¬32T (+. nrad/h) U (- nstrain/h) h/ w> # TU!­lT#*+,-i% VWE , ,VWEM5 +* W,®

.5 ¥34 -. km Mz  Ishihara (+33*) 5¯O°d}±75 *.1 mkine, · s ²NOPQD # ¥4,,T U

;F. VWE +_5$ Z 345G9:5 -. . km ²- z 634   ,

³6,9;<,=´HMl  %~,

7 5h+Mz 3 9;<,=!µ.¶R~­lT.>BL , 6

# ,TUM/ ,-. *+J#  5 BL ,·¸¹

5Iº%+M52

TUS5»

3

 

¼½ ++ V ,* 34 +, V ,,

182῔ῒΐ῎ῌ῍῏ῑῐ

Fig. 3. Relationship between ground deformation and surface
phenomena. (a) Tilt and strain records on April +-, +322.
Ground deformation records are divided into 1 time intervals :+ : . h .* mῌ1 h -* m ; , : 1 h -* mῌ++ h ,* m ; - : ++ h ,* mῌ+, h ,, m ; . : +, h ,, mῌ+, h .* m ; / : +, h .* mῌ+0 h ** m ;0 : +0 h ** mῌ+1 h ,* m ; and 1 : +1 h ,* mῌ+2 h ,* m. Seismicenergy for +*-minute intervals is also shown. Bracketed numbers with arrows indicate the time of capture of photographs(b) of surface phenomena above the summit crater.

. /0 BL 1234 56#*78 - *9:;

1* nradῌh  /-< -* nstrainῌh/-<=> 78

183   
BL 123=<-?

! " #$

@A()(* - *BCDEF# GHGIJ %<-?K<-,* L (Iguchi, +33.) ??

-+5 M ?*7*N*"O P <# !Q" 6##>=<-()(Q A-- RSTUV*W

8* = +GH GIJN /-<$X

YZ[*\]P >?

(Ishihara, +32/) $?  ?*ab,N

$XYZ[\]

<->k(l$ ?*)#  2mnSoZ*+r s,# - Fig. ,ae=>+5  Gl

%?

'

+ !*%^ _`'*#N&c**'dQe'9:; fghij
 p* , #p* +q6 ()( A/-<  6#=</ 

-.t= 2mnSoZs, +r'?

Quv?'w/x*y

$ ?*?

()( A %Quv?=<- | 0}=>? Qe~' ,= 78 ,-/-< r *()(*

 ()( A *r>>()

 ;<, " $XYZ[ +(B0}'   !*w/@ 6? k(

12#$ ?*7  GHGIJ* % +, 7 ,,  RSTUV'  3

M*#*GH %  -@A'dfgQe' 78 . +, 7 .*   * %6      9: : +* nrad ῌ h, 4 ^  : 2

nstrainῌh => 78 / ?*7 78 , 2mnSoZ^5+K<?*

z{?

-. km$!

uv?>$()( A *0<-- GHGIJ*

,*  Ishihara (+32/)/ p* + p* ,'?

/-<()( A *6IJ

+|



9 78 0 Q< BL 12*3Q-v p* - # ()( A *|'dfg'p*

K> 78 1 RST

UV ¡'@* %%*<¤'?



6#=>()(*6IJ +\] <

P #v * +0 7+1 7 ,* **.

GIJ*"% &'()( B *+,-*# EF 7-GH*GIJ* %  

!

RSTUV*W P $XYZ[  N

*.3 mkine, · s r*.t BL 12*3 ¡'

>&



0}"

8l=<$XYZ[  p* , # ()(:r *()(;  > | *
GHGIJ %;Q¥0 r ¢K</ *p£

 =' p* - #   | *0}"  

0}<-*# ()(: r *(¦§=<-+5 j y  *()()(*; ;<, '¨< r;©#$ ª'  0}=*= «>'?

  r *=<-- BL 12*3W* *()(*&p

'?

*#

$XYZ[?­GX® =< % 

! *w /@¬i  p* . # RSTUV - =< " 0}"¯ "$ RSTUV@W*

GIJ =< %*# @  !*%^()(&'  !*w/@ = Av- =<> !²#v  !*( *°± ()( A+r' p* /

GH/+¯/-< ()( B * Q0}=<--" # Q'*# p* ,)(*©7 =>k(l,$ ?



*78 -*.0BL 12*3 ¡'p*  *./i N

+3 78* .9 p * Q< BL 1  2*3  Q  5 '/-<2mnSoZ^5mkine, · s r *W*78 , 

*GHGIJ* %" ¥0;=<-?

d  fgp*

QB'    0}=>?   ! *

* BL 1234

w/*Q{> >&12#$³5* {> ?*78*GH* %

´   | *0}" ;'DE µ-<¶=<j> L!*"

;Q Fig. +*e' BL 123=<-p* + # !

()( #></ J·¸¹º»V ¼>8

 Fig. 3 *78 0 #+2 7

¡=<C +./ 78*.9p=p*#$*W*78 / +,3-?
EFL#v .9p* /-<L !*"A  ½

Q Fig. +*e' p* .

/-<()(%  p* / #  ()( B *j !

184

Fig. +*. Schematic illustration of the internal change of the conduit inferred from ground deformation and surface
phenomena. Illustrations +ῌ1 correspond to time intervals in Fig. 3. Vinin indicates the volume of magma
emitted as volcanic ash and gas ; Voutout indicates the volume of magma supplied from the magma reservoir.
Symbols “A” and “B” represent magma, which supplied into the conduit in di#erent stage. A schematic of
the ground deformation of tilt and strain changes is shown.

"#$%&'()*  +, 0 -&%.+, /  Nogami et al. (,**0) . /0123 BL 4

56 789: ;<=>$ ?:

@A BCDEFGHIJ9:K

K

78 RST D U$ BL 4@A BC IJ"LC M  NO PQ

B

VWXYQZ[789:K\]: E78RS$KN^_-`a_ b+, 0 .@c >de$%& +,fg hijT ./0123Ek5l6&<mn:

Dq$%&  . BL 4@A BCDEIJ



op78$%9:B
B

htuvHwx yH&Fz()* 
B

"L*

M 

NO

PQVWXYQ

?p$ (Cashman et al., ,***) rCjT H

B .H?C DMk  C $K|} wx y%

BL

4@ABC$ FGHI%787|}9: uvH ¡+,¢()*

+, 1

+, . -&% ©

M  /012

3f. {|}~

9:%& D

lM 
C

+,D

A . BL 4@A BCDE

K5

fgrCjTH& $K

%A .;<"#$%5 *K

M

B



f&H&

f C  $%"H

rCjTW

D£TM ()*  +, ¤ +. ¥ ,- +/ ¥ ,, ¦H§¨+, (Fig. .) f. - © /01ªC%A M¬%h­<9:®*HK¯.
;<=>$ +, -.rCjT  s



A

A

"

³`´HH Kµ @c H§¨
 ³`+, . D % +, /¶·<¢ ()*23«: BL 4@A BCDE¡¢K .+, - . D«$K~ °
+, / 0 1 <=$K5 ±² 
Fig. / q$K /0123 BL 4@ABC¸M¹ºop

"»¼. -** nrad ½, BL  

185

 Fig. +*  !"#$ %" km

+ BL ,-'.

/ (Iguchi, +33.) BH -+0 12+345+6789 %" ' :!"#;3<=#>?@'$''.%ABCD'E+

BL &'()*'F/G3 5' BH -$' 2 FH

=#FI'JKJ&'LM)/'+NOG

P' Q(P'+/)3< +31. *RS'BL ''+0#T+UG V',W-.X3 VY /'JKJ&'LM)*Z0MG Figs.
3 +* [ / -) \1-3]"+T0ῌ ῍+ ^!"3+78IG / _4<*

BL '$`-+3#' :4, b5-6

ῐ
a2FIR='

5+7IF34

$'%ABCD'Ec/6+-GY  '3

+)

JKJ'=#d'ef3+%ABCD' :3

g8h'9i :;j<0 >9i :;Z0MG5+3* b5-3['` *./+3+BL ', --*O

'=>[ck BL '%" +?%ABCD'E+=#c3I@S AB[l

FI'JKJ&'LMmC-5+3 5'D,)o

0i5-sG(%"%" 3<

BL cpqr

BL ',-QE'F;+ABcn

tuv3HI #JKJJwp

km 'MxK-

$'LM3JKJ;FI Nogami et al. (,**0) -)%" + BL )*N<MG'Do+? -  .

BL ',-9i +* 2:;[%"    Qy'O%(PQRcS BL 

 ,*-,* nrad  2+1* nstrain

LM3JKJIT %" Jwp

* %"`'JKJIT-++321 * 3 H . U    BL     ,BH  |g +323 WXU$FI g8

h''9ic-~ |g +323

'z'

9i :;'3 ,,2 nradῌh+4
,+0 nstrainῌh* %"  VM< {&F4,-}YMG Z

R'5+FI BL ',-g8

BAYTAP-G )*a2[x\]h''9i :;%" +?JKJ

c+5 5' BH 'g8h^*FI=#d'JKJ'_)4n0i5M

3 ,0 nrad ῌ h, :;c-G+`00 BL ',-g8

3 +. nstrainῌh +IG BL 'h''9i :;[X&F3Qwp'N<

9i'

,- 3 (,ῌ,2 nrad/h, ,ῌ+0 nstrain/h)a 0'b %" '6$Q+ +bcd5+OF BL 

wp'N<=-5+FI b#' :!",-d'JKJ'_[ /'9i :;3FI`0MG BL 'sG3e  3c0<3Do

+%" ,-/'sGe3 BH c'F/G3 BH ''fgMG+78IG



'N<IG/''h3QyN<

3'iIG35+FI #-῏%A)4{< ^!"+`0MG

jcklZ~mn cH Z~ |g +323

' :!"JKJ'῎

Qon cpqn ¡rs¢cd'_ 'sGe3£¤ct8'F

u0> vQ¥¦§¨w'©xyªz«[{/G3 |)%" ,-¬S­rK®D¯ ¡rcu0> °}§

9i F;[/ :5+`0M¨w~±²tK³´cµM¶u0>

G +321 * 3 H . U' BH '



cn0i5-sG('M -.. km *BL &%" ,-9i F;cn0
i5-sG('M'¼ BH 
= #  f -½ O = +ῌ,./ km Q u g= ,ῌ-./+ '·+V z«'s¢¸c¹

-cº73*> a »
>-



186

ῌ ῏ ῎ ῍
 !"! (,**0) ,**. #$%&'(
678'59:  /+ 3+ῌ+*+.
Cashman, K.V., Sturtevant, B., Papale, P. and Navon, O.
(,***) Magmatic fragmentation. In Encyclopedia ofVolcanoes (Sigurdsson, H. ed.), Academic Press, San
Diego, .,+ῌ.-*.
 (+323) )*+ BLBH ]^_`abc ;<=>?@ABC#D d -, e B-+ +-ῌ,,
Iguchi, M. (+33.) A vertical expansion source model forthe mechanisms of earthquakes originated in the magma
couduit of an andecitic volcano : Sakurajima, Japan.
Bull. Volcanol. Soc. Japan, -3, .3ῌ01.
 (,***) )*+,-P,,-f_:ghijk lm*n ,, No. / -+/ῌ-,-.
 (+33*) P,o&'(6*+
pqrstABHIuvwxIst ;<=>?@ABC#D -- B-+ +ῌ+,.
LMNO (+32-) yz{|}[\~P,'59: ;<=>?@
ABC#D ,0 B-+ 3ῌ,+.
Iguchi, M., Yakiwara, H,. Tameguri, T., Hendrasto, M.
and Hirabayashi, J. (,**2) Mechanism of explosive eruption revealed by geophysical observations at the Sakurajima, Suwanosejima and Semeru volcanoes. J. Volcanol.
Geotherm. Res., +12, +ῌ3.
G != (+32.) *n|} BAYTAP O
ABCD -, 1+ῌ2/.
Ishihara, K. (+32/) Dynamical analysis of volcanic explosion. J. Geodyn., -, -,1ῌ-.3.
 (+322) *n>o'WUHI ¡¢£SWXg¤¥ ;<=>?@ABC#D -+ B-+ /3ῌ1-.
Ishihara, K. (+33*) Pressure sources and induced grounddeformation associated with explosive eruptions at anandesitic volcano : Sakurajima volcano, Japan. In Magma


Transport and Storage (Ryan, M.P. ed.), John Wiley &Sons, --/ῌ-/0.

 (+323)  
)*+,-./ (+)01*+2,34'5
9: ;<=>?@ABC#D -, B-+ +ῌ++.
1EFG (+322) HIJK
 -- ,03ῌ,1+.
LMNO (+32-) P,QR'STU&VSWXYZ[\'59: ;<=>?@ABC#D ,0 B-+ +ῌ1.
Kamo, K. and Ishihara, K. (+323) A preliminary experiment on automated judgment of the the stages of eruptive activity using tiltmeter records at Sakurajima, Japan.
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