  /*  (,**/)
 /  -.1ῌ-0+  GPS 


 ,**/  -  ,   ,**/  3  ,3  Magma Plumbing System of the Asama Volcano Inferredfrom Continuous Measurements of GPS
Makoto MURAKAMI
Continuous GPS measurements around the Asama volcano, central Japan, show a repetition of episodic inﬂations and deﬂations of the ediﬁce. A correlation is found among plume height, seismicity and crustal deformation measured by the GPS. During the inﬂation period, increase of seismicity and rise of plume height wereobserved. A planar magmatic source situated at about , km depth below the surface was inferred from the GPSdata during both the inﬂating and deﬂating periods. It is also suggested that a buoyant bubble-rich magma surges
episodically into the magma reservoir, then it loses the buoyancy through degassing process, and ﬁnally drains backto the further depth. Inﬂations of the ediﬁce preceding the eruption were registered in the GPS data before both,**- and ,**. crises, showing the usefulness of crustal deformation data for the prediction of the volcanic unrestof the Asama volcano.
Key words : crustal deformation, Asama volcano, GPS, magma plumbing system, degassing"+  



 +330 
*+

,-.



 GPS



!"#$%&'()/012340+

5

6789 :; <=>?

)A*4M+7DEF I"J,**.  3 *4SP!640+

0M

 ,**/!"D7DEF +3-* 1 /* +  0W,"-Mc 0.I/iEfgJ0P7DEM  +33*!"@ABC7DEF GH0IJ  (3/*,,+)

> Q%RH JH JP7,

 (3/*,02) KL (3/*,03) 5MN[ 40+ z9 M1 PS6MOP7@FPQ%RS

P GH040+ TUV0WXY
ZM PS[ \]\^ M!"87

7DEbDDMDF+33* 2lm3

Fig. + i-z GPS 

0.SP4 +* km 5d" GPS . MN 6&SP0W

Q%Re40fgb$hiE b-67 j[ ¡7b67DEF 8¢H19i bklm"@GH0n\]\opqrD40`9 £:bA;¤iE¥

DE_#`aD bMcS67@F1bD¦DJ

D7s%iEF

0.In§ km <=¨>©+ :;iE b? ª«  GPS ,J­E<= ®`M¯"@EF

GH0 (,,/02 m)  & tbu'\vwxt
yz40{|}&~I(iE+

¬"

40

 ²-*/ῌ*2++ ³´µrA«¶&· + B¸C¹  9+ º»¼}R%
Geography and Geodynamics Research Center, The
Geographical Survey Institute, +-Kitasato, Tsukuba,

!"fgSP 0W[AH
5M°X@Z±[A7DE bM PSb6
Ibaraki -*/ῌ*2++, Japan.
e-mail : mccopy@gsi.go.jp

 

348

L

Fig. +. A location map of observation sites around the Asama volcano (elevation ,/02 m). Black open circles
with site identiﬁcation numbers indicate permanent GPS stations operated by the Geographical Survey Institute(GSI). The station *-S*.0 is a site operating since February ,**., whereas *.3*0. and *.3*0/ are thoseinstalled after the September eruption. The black solid circle indicates the location of seismometer (JMA
station B) operated by the Japan Meteorological Agency (JMA et al., ,**.). The solid line connecting 3/*,,+
and 3/*,02 is the baseline whose distance change is plotted in Fig. ,. The elevations of the GPS sites,
3/*,,+, 3/*,02, 3/*,03, 3/*,1+ and 30*0+* are 31*.2, m, 030..0 m, 3.1.02 m, 2,*.,3 m and 1.2.** m,respectively.

  ,**-   & ῌ(3/*,,+) (3/*,02) Fig. ,  ! "# $ %'()*+, + -./012

 A  G 3456

7 5 E 89-ῌ ῑ῎῔ΐ῍῕῏῍ῐῒ4p |*4CqC\5 l 9b8 5-.Hs*4
H Fig. ,56*9 5 q

+!H, 1-( pHs!H   4 :; <=>?*@A , Bq ; Fig. , jH

CDEFGH I JKLMNOP*Q

79F +, cm .:9  @

NRS(TU@",QN / 0 /*1b

JKVW JMA-B,

Fig. + XY 4NZV[ F\]^_GPS¡34 ¢5£ 3¤6¥[ mm .

T` a LMNO34:b l9H (Hatanaka, et al., ,**-) |

P ,**. bcde6' \5 RS

*4QNZ¢5 QN¦¥7§¨*Sb Hf*GH V[89F '5

8b © q4GHp  9 ª GH JKVT7/ 2 9gZ 59gZFhi7/ )5FjgV*kl5 FmGHF

 oH( "E*GHv£89 QN¦¥*¢5£7§ , 9.

 !n 

89si_ :«ZH¢5 ;p_ T0

.¬v4GH sZQN4­$H_lq r"E*GHs t9H sZ3<®!H¯Z*G/ =9 9s!H

4F kb T79 (u)*QNZ%4| T0>?9H 4 QN

9H* sZ v wxw 0ry*GH

Zq  | 0°±!H£z{*kb | v4F #$TE }~

p@*AB4GH ²³

GPS QN*9HDE*S9 %4 GPS  l¢5£ ) 2%CD²jl´µE

QNZq  /&/ v4¢5F

C9HK89 '(   QN

  ·Iª$4 bµE*GHsF¸

FXY *)i_H

JZ9H %¹º K@>?!H »¼G¶*9Hs*HZ9H 3



Fig. ,. Time series plots of distance change between , GPS sites (3/*,,+ and 3/*,02) spanning over the Asama volcano.
Plume height and seismicity measured at JMA-B in Fig. + (Japan Metrological Agency et al., ,**.) are also plotted.
The hatched periods are those during which the distance extended. There is a correlation between extension of the
distance and plume height growth. Likewise, correlation between GPS and seismicity is recognizable except during
Period F, while seismicity was high despite the shortening of the distance. The overall change during +330 to ,**. wasa slight contraction.

GPS 
349

 A

350

   (Sagiya et al., ,***) 

  + 

 *., ppm GPS 

$%





! " ,* km  #& +  . mm '  ()*+!"),#(-)*;**s *`#5  +!"5 4a %&5hb Fig. - 00GPS +!3%& 2*6

Z/ <i ;* +! c
A de $f6 fO/1 ~V<  #

3 ,- 1g) fO* + km, -km, / km 4* 35KJp 5*;*/ b 1hB >Dij.$  /%& 01*2 3 ,**/I *¡Y3/1 (O* , km  J  f' ()*4*5 +*,-5 

O/1 kb , km uu¢h~V U

GPS +! 17%&*8kwxml3 Al 1g) fO m

3  /%&2* +! 3*%45 9

1 0£ ¤¥ >p cn¥5I yO*( +** km./6 0: ;<= #5  >u?aux@buy@cuxy@du, v?
avx@bvy@cvxy@dv ;A u, v B/1 C/1

Z;*  # $%6 ¢h~V  o5¤¥5  > ¦KJI  `§17%& x, y  +! BDEC auFdu, avFdv

Q{*N*O(¨  3 KJ5 ;*(G(H4I JK +*,-5  -* km 9L

©ª5«¦(  pq¬­h+! %&5*6.789:$ H4*;`: Okada (+32/) 

17%&5*   M N*O( "*6 +) -* km

Table + +!3%®2rUSo .7

90  /P<2=P 17%&5*;*$%so ~Vr;* *J53 

QR+!O( 17%&)/2>? *S

<i K( ]r ¯US 7

T U*VW X%&5YZ#Oh$%2Z   S¦K

5  # [@ \]^5Q_ b s~V #5hfO*;*

9A $%`a*C;*O(

0 b c] 3

17%&B* Fig. - d  \] Fig. ,=Pe

A +331  . f9C ] A b ?c +!4 g$O)Dh </#5   Al fO 1g) +..F- km
T}pJo 5 t?;* s¦(
5uv
r5r5 +!wx5t°  3 ;*i;* E jF =G5 Fig. - , b q )*N*Qy# ¯%&klmn Fig. , H ]oz{S ¦  ;**u*  p J  IJ]o

B, D, FC, E, G   KJ  (G(LM #5*d¯%bUS ] B *# ²7O

;* }³*$~h2 3 5 ] G#() qml*r5 <i ;**s%

A+!4 t)( 3 <i u6 v
kwxml NyO*Z5 zP j*{*QR#5 |E5 ±|o SzQ/ * Fig. . d  # )    3/*,03 >´µI 9¶ +!b 
<i$E· `§Q¸+!"*z#5 ¦  3/*,03  j`)T}hb kwxml*UQ~V+!"5 %Z;**s *P )<i *25 #  }5¹o 01*d2*2 ;*  Matsu’ura and Hasegawa (+321)

 c]·  ¨#5º­h Fig. / `:%

"K(

$%2Z Fig.  N

# +!  c»*d  #  +r<

Fig. - 2$% +!O( %& B ) "j5}) +Z/<+*,-5 W klmn#5*z

i** 2¼ } 5] %&  %Z AXq$o%&*g/1g(#5 ]O(  Fig. /#5*3  # $%%&B*LMO  $%01* ^3#5 Y % .rXq Z/ <i >[\/ 

%&klmn±1

c»

)

q ; Mogi, +3/2I $E ) 

Fig. . ;*O( $%c (- Y $]^*_ 3 ]^5 (G(*

317%&

3/*,03 r<g(hrJ¦

GPS Id¡¢¤©ª{|«¬«­®¯ 

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

 !"# $%& '( )*+351

qr/st@j!k"#uv )w 

Fig. , fgx Fig. - &*+g\&Qy&z,- ./0 1234%56789:&){|}"#-z~} Jk2- -;< =  Fig. . >?@-ABCDE F

f y& F2 &gGH& !&IJ KL) MNOP ,-)Q ,**/R ,-S >?@./0&5TUVEW

J) ,y"# a&{|}- )S,+  XY&Z[ ) - )>?@A\|-$]&^-Z[  ,_` >?@ a



)

-& >?@bc def Fig. / &gS-w  nyEEWgh*- 3/*,03 "# iY&j!k#klKYEW2 &m<) nop- Table , &¤ >?@ a§ 3/*,03 E

¡¢ =-£) Fig. 0,-&g2 ¥¦"#) ¨n&Fig. -. Horizontal displacements around the Asama volcano for each period. The regional tectonic trend, which
is an east-westward compression, is already removed in the ﬁgures. Note that the scales of displacements are
di#erent for periods. The horizontal displacements are basically of radial pattern. The similarity of thepatterns of di#erent periods suggests a common volcanic source that is persistently in activity extending overindividual periods of extension and contraction.

2 k

352

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

*\ *]\! ^(_ Fig. 0 

F`a D!bS  cd8?+! " #$%&()* km0 1+, - ' 

./% &23()* ,4- km

 789& :;56<=>?

@/(A & BCD56 E78DF

"78 eVWHfA#`g

h

GID56>Hij+, ]k5l 
m8 $n%op q$r&hG eVWD56>S
>>+ m8 s t%u!L'(vw

FGHI56%J KFL -/xy(z * &t%H)K ^{}VW<YH "

M

H<NOῌ

P>%FGIDQRSLT
+, U6 VWHX>PYZ[

 {| "VW

`g%,>+, GPS *})P >+%+zs +$n%H~ 
IH& H *)YL%+z ,tH- .6@

Table +. Comparison of residuals of ﬁtting assuming
point sources and a dike for each period.

,**,

/01 ; 2

"L%{3L|"%H4P

Z.%#% .6@

,*** 56s{$n% ; e7 ,**, <NO`g{}| "%

%0]r8+,P %)A "L| "%H978}
. : m8;!%6sD4w!<=AH>?Y+@..  : 



.ῌ+  !"m8

q$rh`a+& 

VW

wPA$

+ ,AB ,+*043

+* m +, (Table ,) - 78 B478 G EAD
0

-

F

()VWCDS * +.,+*1 m- () +.0+*1 m- +,A VWHP

H D8 <=F+,
>E & $rF
t/5lS $n%=A<D' S G LLH 78 G )AH¡H6>  I

6s

 D¢"X>£!L< ¤¥¤+,56 ,**. 5 3¦

 +* ¦_s§J6H¡A$¨d©gª«§¬­­ (SAR)   Ke7 ,**/
 ,+*0 m-#$%® ,**. 56s+

6H¡CH fA#)K ^A$
¯UC (Table ,) F°­­+,>

AD ±<D¤¥¤:/_u!L²³
The depth refers to the topographic surface, which isabout +*** meters above the mean sea level and ismeasured downward. The residual in the table is thesum of squares of di#erences between the observed andsynthesized values multiplied by the weights. The
hatch indicates the minimum value for the period.

56>´ HµS ¤¥¤H)A.L k¶">LH ¤¥¤ M·N;!L¸
OD+z¹N+56 ¤¥¤P-AQRS{  ¸OJº»H¤¥¤P-A¼?TGPS ¶PQ ·¸2ne¹o+,+º»¼353

Fig. .. Comparison of models assuming a point source (A) and a dike (B) for the Period G. Solid arrows
indicate observations, whereas open arrows illustrate displacements simulated by the best-ﬁt model for each.
The both models generally explain the observations well except 3/,03 whose northward displacement is
unexplained. A point source predicts an eastward movement at this site, which is not the case as seen in Fig.
/, suggesting that the dike model is more realistic.

      !" #$%* SO, PQ.\I o
Ve G 2xV *

f" Ve E M
=H

7I

&'()"* +,+-#$%./ {O ,**.

0123456 789.:; +,+

 r =27I& +,+x

< =" >.1?@-A2&"B'()2klI"! 34 

B

7C6BDEF).GH7IC? JK

LMNOPQ R 3S 4
T UVWBX8Y GZ2 [ 3\SI]^ GPS PQ _`a2bc +* de] -fIgh i^   7-bcj?

kl3-Bm ]Nm neo3- C^+,+Jpq , km 9r

3"st2DEF)

urIBmvw 7I3456 7C6
" xeX8II&ys"+,+^ z% ?IGH {|q} ] - 7+,+^.n+,+^I~ Fig. , C6 fV !" #$%&C
!rq'()23456 #$%
'C?+,+<-=" bW- +,+¡¢C^<mB?>.1

 £?A  7- ¤WUxe.¥?m^2IGH +,+¦3§Lxe B*& ¥?m^"'()¨©IB^6 7C6BªMB'()- ghV"
IGH
773GH C6B+,+A «7^6

"nst"+,+3-  - NL  7I ¬34^

fx-()

N- ­®¯°C± ²; B 7I

#$%Tb 

*xWB$ \-T34  

³ " ? +,+^-´µ-

´ 

354

µ

Fig. /. Time series plots of longitudinal and latitudinal displacements at 3/,03. Eastward or westward movements, which a point source model predicts, are not veriﬁed. Episodic displacements to the north occurred
during the hatched periods, but the temporal conformity with the volcanic activity which was seen in the
distance change between 3/*,,+ and 3/*,02 (Fig. ,) is unclear.

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

 .ῌ, 

st !abcde

j&8wx ?wx@ op!@ 
<  C *+,CBJK`&ghg.ῌ,ῌ+LA k YZX989! 

 ! "#$!%&'() *+,-,./ghgsLX)

012  ,**. 34-5627 89 :.
/;+<=>

?@ABC   -,D  :./6ghgX + wt.ῌ & 5X[9 ] |!%&

E FG H8 +33/ 3I SO, JKL +** tonῌday, P Q (,**/) !H& ,**. 3 3  MNOPQ ,**.R ;$ GPS STU}~¢£dCB*+,}~¤¥,- ¡JKd@ 4VW FCH8CB ;$MSO, !¦r& *.-- wt.ῌR

X"#$&YZX[9X§¨) M5 ©ª89 ghg! «=`&  '(\]^_& "#$!JK`&ab¬j&)R m SO, ­Q./

cde  *fghgijkl!m&n9&8op

op H,O !®¯&°`± ab|opXqr)   ghgijkl abcde!m& H,O !%& 'ystuv& , %wx 'yB  z{c

 ! JK./| }~!s&8wxX

 ./| }~!s&8wx k @! :./

+ %z{c ghg 8;CB !

+**ῌ )

JK` SO,  H,O ²L® ³ + : -CB

Fig. 0. Inﬂation and deﬂation sources derived from the inversion of GPS measurements assuming dikes. Periods refer to the designations in Fig. ,.
Note that the scales of displacements are di#erent among the periods. The periods A, C, E and G are those of extension, whereas B, D and F
are of contraction, respectively. Solid arrows indicate observations, whereas open arrows illustrate displacements simulated by the best-ﬁt
model for each period. The horizontal positions of dikes fall into a small area, which are a few kilometers west of the volcano summit. The
proximity among the estimated dikes for di#erent periods strongly suggests that inﬂation and deﬂation are caused by a common planar magma
reservoir. The estimated parameters are summarized in Table ,.

GPS 
355

¼ `

356
Table ,.

+

Summary of dike parameters.

The depth refers to the topographic surface, which is about +*** meters above the mean sea level. The lengthand the width are the lateral and vertical along-dip sizes of the dike, respectively. In this conﬁguration, thedip smaller than 3* degrees means a dike dipping to the south west.

SO,  +** ton   -** ton 

  ,*cm- (Lange and Carmichael, +33*)   !

| L-./% "#%y& + 0 8- + %& -.-'+*, m- ("#$

T % +.-'+*0 m-   | OP

23 !

-

 + )#$  +.,'+* m  

 + r % pq F &`  w

*% +,-./%01

OP ../'+*0 m- V% -L+,"#$  66 c%$   / -2345
07 891:;<   .

=>?@ "#A!  BCD, km EF$/** -B (/* MPa) GHIJ

 +,-** K   + !

"#$-** ton  -.0'+*- m- +  +.-'+*0 m- (  .

 -*ῌ - %6(  6o -wd(o( 6-%z{(V& OPp*&@\7  %V OPp+,./1ghx  -(  .
K -L./$ K01 !  MN

OP :+

%&Q m- ; Table , RS< T&U

0 8 \  

6 *! ;(

 

 %

 K 07 8XY YZ[\]^

V  W*&OP 07 8XY

OP"{ c(d *& YZ[\]^_` abc(de 

T&W¢#£¤ KT  w Fig.

f  .

%+,

ghi#$   SO, J
 66Kjklm (,**/) T n@o (*.-- wt.ῌ)$ pq F TYOP + qr %s@  +** ton  SO,  + qtr$- ¥(( ¡  ¦§¨C©$¤ª Dc

6p«7¬ .ῌ,ῌ, ῎῍ῌ,**.  3 ­%®¯ #°$ SO, r

 ,*** ton ῌ day 4J:,**/  0 ­±/< *% %! +** ton ῌ day'-0/ dayu*.**--v+.+'+*1 ton

TV  -,*** tonῌday ² 6K& OP³T

wghx& + ´z{  J ,./'zµ&(+,MN:#+*- kgῌm- $  yTw ...'+*0 m- (  6'lm ,**.< =( SO, z ,**- ¶) MN·³KMNOP=4Jz{ 6|} SO, Z~* 

y& w +,CXV%ac w^  

 6TY )·³ 

! z*¸1*& 6qgh($ ¹(+,Aº 0 8»X$ 6

GPS #rs¢ 

2T0_UV¼

357

  

$%$<u()~ ! LEv5

 GPS  

78$=> +,-  +-   ! "#$ % &34F1T/b/()* +,-  ./

'

Xa$

 j./c*) ,**. 0 12 (Table ,) ,34

56!/+,7 8 9
/ :;   ,<= .ῌ,ῌ- ++  Fig. , dL,4

 "#CeK"#'- $<! >?, "#@,  ABCD*/E,FG*/E@$3 kG



+,

W

P@T B :

2.0 mmῌyear, @T D : ++.2 mmῌyear, @T F : +,..

, <=7)    D* mmῌyearS ++, .ῌ,ῌ+ f.*"#EH* IJ$K* ()*:;,gG/)

4 ¡G/+h  +,$¢*  / 4, " ,,*** ton ! ,.* " P,**.  3ij) +,-Z@[dkG/C z#

QR,**/  / QS T#*/E$IJ

* j./* @,LE/ M(  N$O!

,  U

V?,W /.3X+*1 m- $% +)&Y'()*-Z,[ +* (\

7 k1'"# £()* 

 (Table ,)+@T[)  4#** ,<=  ABC]^,0_ !$`M>+/,\ -UV"¤k¥$x /d W) a$kC, ]@T/ UV,4l¦mE*

*+b,  c-@ - SO, !$*+[/

/dAefg

E1Tg§$ Fig. 1   +n  )  + / /X+*0 m-h, i- , Hj./<=7)  kH

o% z#'4 PC=~ @T FS + d 01,21,T3

M W(C ()* E

456* lB   mn789o $^G*  ¨©£Bp l¦ )~ UV,78pp:q/34k1'56 Wrs

4!qmE*  @]^ Wt-$;*-7<uv578=>() ,*w?x  ,(  +),@yAefgh c5-) z#'5
6* A0_v5/78=>{|,B}()*, W,MUVC ()/C

PC=~ DE: +330 ; Kazahaya et al.,- 
ªr*

M/78p,«7-*+,[ +) O!/

¬



M/

+33.S [kHj./ 34$;-*[ sZF)* j./*   +))~ v578F$ ]

t Fop§- Ft ­®

F@T 21kG@T

u6¯vwp0x$3Q!oK)  H ) IJ$*01mn

 2

E 3 F78,

T_ W)K,L() ,"#MNªr  &Y'() ABC Pry

N() ,<= lB  z°* S M±()* ,<=7) +N7[ G/' SO, =>, _i F =>{|j{$|o /dOP$*+ M  G,+ O8kt*F}d ²E$³´µ£

P$+7QR

x 21¯ ~+-STU7)*-* -7 8 2T_E F$]TV'- $<=, HWlB /*,) WXY 34Z[\]Z*+,   Fig. ,Aefgh$^_x  ]Z &`-ghax8F78 SO, , H,O 9H* +) .

, ¶9
 SO, !3¸

[ + $%#**-* / W56Z%
+R, k%$IJ+ : - ,·G, + " ,,*** ton

! 0,*** ton 21¹J$ /** F¹ P&m , kmS º%$ +-**K , FP$»$
$IJ, ,**.  3 Q0*F78!()/q P"l¦ ,,*** tonX,.* "S FtG IJ)~34 + T 0X+* m

*/,<=/E +.1X+*1 m- ,-  kP

1

-

¼ H

358

Fig. 1. Schematic illustration for the volume change of the magma chamber caused by episodic supply surges witha constant drain back. In this ﬁgure, I assume a constant outward ﬂow (drain back of magma), whose
contribution to the chamber volume is seen as a downward straight line, and episodic magma supplies
repeating every , years, which appear as steps. That we observe through geodetic measurements is the sum of
those two contributions as indicated by the thick line in the ﬁgure, which qualitatively simulates the behaviorof length change in Fig. ,.





G

# |r G`)C0- ,**. s|%    !"SO, 8# 2

Rx

%B ,**- s (Table ,) # $%&'()*+"\() # ,**.

,-./0# 1*2 +3+*1 m- 45

0G# x

06/7089 :;< ./ =>8?9)8# =@A45B  !"CDEFS;5 e()

# 7># ,**. s|RN E0*> Fig. 2 G# Fig. , 7

./G# HIJKL ./0-D

 3/*,,+῍3/*,02

CD# HIMNO %B )# 

P8QMRS

TUVW# O XY./ Z[G# 0-ῌ 45B
0-089 O ./\8]^>_45`0# O8 a( S CD O. bc d8!ef`g (Eichelberger et al., +320)#

h 8ei S CDP(
am#

S

GPS

,**. s + t ,**/ s / t

11*2 L w¡ G# 3 t + ¢|£Q¤¥ +* t¦Y§%!¨©8oª()0«  %G# ¬­®[<£¯°±° (SAR) ²"CD# ³|¯W´

8jikl8EF%[µ() ?# ,**/HI8 nop() C7 0¶)(# · *>-(*> 8
£Q . t¤¥# nCD

`)
.ῌ,ῌ.



,**.  q"8Qr

G +330 s . tBS

HI °LG

 % uvwL0A# =@§FBr0 . t¤¥ 3 t |G#

S

HI8 S

8# Fig. , CDlC*># uvwL8gBrY# §F i5 S g . x"() G# ,**. syz# {{?9`8 B> C# ³8 3 t¤

|}rG~B>C G# xG# ;¥58eCrY#

S 8?9`  + ¸t45  ¹G# HI(9 S 82

º(Y#S gG»GPS #-.ij ¶·d¸p¹<=<º»¼359

Fig. 2. Close-up view of the distance change of the same baseline of Fig. ,. Before spring of ,**. the baseline
was contracting. Then, around May the length change turned to the extension and it continued for several
months until the September eruption. After the eruption the baseline length stayed constant for about amonth and then the expansion resumed. It is suggested that the halt of expansion corresponds to the
extrusion of magma at the summit crater as observed by airborne SAR measurement (Oki et al., ,**/).

 

   !" #$%&'

(&  )*+ , -./01(%2uv 7 <=<vw . 5` 7xLynz$N{M&%& 3 5vw % <=<|}~f  , Kvw

 &34 3 56, 7 +* 589 :%;<%p &oQ 4=< >?@ SAR ABCD.

7

f0Qd %' pd ,.+E+*0 m- FG'7(%& HIJ ,**/34 K

5 ^*Q  K<=< ,**.  . 5 7 3 5LMNOPQRS

vw %q7 &4

U& V-.W( [* G *\]^

DZ_, *\] ^ 0.+E+*0 m- (Table ,) QT

X Y& V3 0Q

% 3 5`a;W(uv Fig. 3 oL,

4

Q

%



<=<&% ¡  K¢ <=<Qbcd

 4^q!"*Q$ \* £ vw

  +E+*0 m- efFG' 4 qf 8H¤Q¥<= SAR -.W( ;A +ῌ- +  D<&% ¦§¨ ©!W(%&&+ZgfQ hijkl %&m%4 ª«&4 L  ;y "7( i o ¡'+yo&o]Gno H& pq ¬­cQ '+
 ²A]GrsQt %&'7®¯­°±Q;%&&'+4(4-.Q³K°%y ´ µ &-.i

¼ °

360

"

Fig. 3. Schematic illustration of episodic magma ascent model. A : During the deﬂating period, the shallow
magma chamber deﬂates due to moderate degassing of dissolved volatile. Small emission of volcanic gases isobserved. B : During the inﬂating period, a bubble-rich magma ascents from the deeper magma reservoir
causing large emission of gases, the inﬂation of the shallow magma chamber and occasional lava extrusions.





T

V8 ; , +( GPSP+   ! "#$%*.3*0. =]Y *.3*0/ w- QRP& (Fig.

&'()*+,-(./(0%1,23

+)4 (~6q& ,**/ F 0 Tt9:;(

&4

cSP=  V; (f(,¡f¢£¤&1,]¥ ¦9

/ 

§9:;( <(?@?AB¨(] -©

156(78 9:;( <=:>

8 ¥t(,&4?@?(AB,CD(E +ῌ, F.G(H6I
-*J-&KLM(N1,O4 9:;( GPSPQRS +330 F . T$U V;

V WXY Z(Q+8S GPS QR$U[\*0GPS

PQRª «¬NH=]Y)­¡f¢,q®z¯-ª 9:;( <6S :J- ,**- F - T=]Y ,**. F 3 T( V( 6

> ?@?(AB, ]CD(EI-*^_%&`aTbH(cdefgh6ijk

J-&KLMN1,®8¥4 ?@?(°±li4Vm&nbGop6q&rS

 9:;6S s=tV^cn

S ²%&, , F + GbH(H6*J-&³´-tµ(¶H V%&®6S 4Vm&°bu&KLMq&4 GPS (QR+vw

±, µ6 °±,(·S ?@?(*!H6q&

xyz {|(}~MtN  PQRP

KLMq&4 GPS QR$U]*J- ,**- F%&1,,&4- T=]Y ,**. F 3 T(

V(¸S ¹ ,t`1(]  8 ?@?()nb]

aT¸bH(c(2:q¥1,g84!&>6 ;(N +2** m (9:;6S

+ - PQR+ *-S*. wS Fig. +  ]¥u&KLMq QR+vw]xw- ,**. F , T8QR$U-4 5 ,**. F 3yz {|(}~MtN  PQRP%&Vm&º»nb ,- GPSGPS Q¨¸¹>ºV bpqp»¼


῏

῎





 
%&

 


!"#$'( )*+,-./.01

 234 56

75810 

9:+ ;/<=> ?@AB+
CDE!"!F#G$7%H$CIJ5&K
L'/MNO 5 .0 (P)$HQ*RSST$0 +U7,Vῌ ῑ ῐ ῍Eichelberger, J. C., Carrigan, C. R., Westrich, H. R. and
Shannon, J. R. (+320) Non-explosive silicic volcanism.
Nature, -,-, /32ῌ0*,.
Hatanaka, Y., Iizuka, T., Sasawa, M., Yamagiwa, A.,
Kikuta, Y., Johnson, J. M. and Rocken, C. (,**-) Improvement of the analysis strategy of GEONET. Bull.
Geogr. Surv. Inst., .3, +ῌ-1.
-.WEXY/Z[X01\]X^234X56_-X
7 `a (,**.)  SO, 8 9 :(bcd ,**. ;ef<dgh=Pi p +3/.
56_-X?@AB (+330) jbk>/?lm
5810 nopqpk@rsn tci .0
3+ῌ+*..
Kazahaya, K., Shinohara, H. and Saito, G. (+33.) Excessive degassing of Izu-Oshima volcano : magma convection in a conduit. Bull. Volcanol., /0, ,*1ῌ,+0.
bAbuXvw2xy (,**.) bj n,**. ;bzn B .+ {|C}~cD E iii-+-3.
Lange, R. and Carmichael, I. (+33*) Understanding magmatic process, modern methods of igneous petrology,
Nicholls, J. and Russell, J., Eds., Mineral. Soc. Am : ,/ῌ

361

/3.
Matsu’ura, M. and Hasegawa, Y. (+321) A maximum
likelihood approach to nonlinear inversion under constraints. Phys. Earth Planet. Inter., .1, +13ῌ+21.
 F (+33*) G95 .0H5RS:( yIE 0/ 00/ῌj b2*1.
J1 K (,**-) bj LM5N$ OPcQcdN<d=Pi V*//ῌ
*+..
Mogi, K. (+3/2) Relations between the eruptions of various volcanoes and the deformation of the ground surfaces around them. Bull. Earthq. Res. Inst., Univ. Tokyo,-0, 33ῌ+-..
RJS4 (,**,) T5 bUV5
4lq c +++, No. ,, +00ῌ+1..
Y/ XwWHXX
 (,**/) YZV
bU[ : +330 ; ++ ῌ+333 ; / \ OPcQcd ,**/ N<d=Pi
V*//ῌ**+.
Okada, Y. (+32/) Surface deformation due to shear andtensile faults in a half-space. Bull. Seis. Soc. Am., 1/, ++-/ῌ
++/..
<]^E X J1 K X _`abX AHD (,**/)¡rc¢£d¤9M ¥ ¦SAR§ ¨5 b ,**. ;b5eDb9f© ª b/* .*+ῌ.+*.
Sagiya, T., Miyazaki, S. and Tada, T. (,***) Continuous
GPS array and present-day crustal deformation of Japan.
Pure and Applied Geophs., +/1, ,-*-ῌ,-,,.
«¬X­®`Xg¯ hX7°Xij \X_`kB X ± l X mn o X ²pqb X ]³r
 X ´@ s (,**,) , µt GPS ar5  ,***; ¶bu·¨ b .1 +0+ῌ+01.
9:XvGwxX9¶yXxWz ¦,**/§ b
 ,**. ; 3  + :b {|234 ª OPcQcd ,**/ N<d=Pi V*/0ῌ*+/.
¦}i~ ·p^§