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 /  ,,-ῌ,-. ῕ ῔,**+ 

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Temporal Change of the Pressure Source Estimated by Tilt Records
During the ,**+ Hakone Swarm Activity
῍, Hiroshi ITO῍,
Yasushi DAITA῍, Toshikazu TANADA῍, Toshiya TANBO῍
Masatake HARADA῍ and Kazutaka MANNEN῍
Remarkable changes were observed by tiltmeters installed in the Hakone caldera during the ,**+ intenseswarm activity. Using the records of the tiltmeters as well as the GPS data acquired by the Geographical Survey
Institute (GSI), we investigate the pressure source which produced the crustal deformation. We divide the period
from May ,- to September 3 into ﬁve stages based on the changes in the direction and the rate of tilt at
Komagatake Station. The overall model during the whole period is composed of a Mogi-source at a depth of 1
km (volumetric expansion : 1.++*0 m-) and two shallow open cracks (depth range *ῌ*., km ; volumetric expansion *.+/ῌ*./++*0 m-). The tilt changes in each stage, including that in the ﬁrst stage at the time when theswarm activity had not yet commenced, is well explained by the expansion of the same cracks, which is considered
to show the validity of our pressure models. The strike of the crack in owakidani and that near Komagatake are
WNW-ESE and NW-SE, respectively. The S-wave splitting analysis (Honda and Tanada, ,**0) indicatesexistence of cracks in those directions around the source region, and many ﬁssures in the NW-SE direction are
observed on the surface of the ﬁeld (Kobayashi et al., ,**0). However, local earthquakes are not distributed
along the direction, but the epicentral area extends from south to north as a whole. This feature di#ers from thatof the swarm activity occurring in the region east-o# Izu Peninsula, in which extension of hypocentral distribution
is estimated to correspond to the zone of dike intrusion. We consider that up-rising steam or volcanic gases
compelled to open the pre-existing cracks to produce the crustal deformation in the ,**+ Hakone swarm activity.
It is plausible that the two-crack pressure source of our model represents a set of many small cracks or the largest
one in the source region.
Key words : Hakone volcano, earthquake swarm, crustal deformation, temporal change, tiltmeter+ῌ ῐ ῎ ῑ ῏

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K:[@ ; (+321) VPZ]: ,/*ῌ**-+ !"#$%! /20
 /012345
Hot Springs Research Institute of Kanagawa Prefecture, /20 Iriuda, Odawara, Kanagawa, ,/*ῌ**-+,
Japan.
  : 3-*ῌ+.*/ 
67 02

 &'()*+,-.
Tateyama Caldera Sabo Museum, 02 bunasaka, asikuraji, tateyama, toyama, 3-*ῌ+.*/, Japan.
Corresponding author : Yasushi Daitae-mail : daita@onken.odawara.kanagawa.jp

 ! " #$%

224

Fig. +. (a) Location of tiltmeters, and (b) epicenters and cross sections of earthquakes during
the period from June +, through October -+, ,**+. KOM, KZR, KZY, TNM and SSN
represent Komagatake, Koziri, Kozukayama, Tonomine and Susono, respectively.

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225

, 6 789,$%-: ..;< 

*=>$% ?!-@A "#-
BC%,

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&'%FG12:H5I%, J K
&*- J>*L &'5MNO4
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

bc* 0dAe(KZR) jkl (KOM)

f0g (KZY) hi- km )1g)2'3 4

5 (TNM) n6 (SSN), km o( / km pqrAs&'( 0tg &'.7
  (Fig. +)

 &'( 

uv8 , w 8xsyz{* J,|,}9: +**     *.**1 mradian m~ mrad NN" + ;*: <    ,**+  + #$% +, #    +33*
* &' Fig. ,Fig. ,. Tide-removed tiltmeter data for the period fromJanuary to December, ,**+, with daily numbers ofearthquakes and daily precipitation.

H &' BAYTAP-G (Tamura et al., +33+)
:=w:2< *   bc >?$%@12 + A2:

C .D ./E_G

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 FG

+

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 +

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2> :0D* 3 # 3 ++  ./CE 0**O 2 J ¢£ : KZR

Pw KZY

EW w* 3 #$$%&'%F=Q5 

mm   - !"

/ # ,- $% KOM*u~: ¡, J E *.,1 mrad 
Q9 *.*. mrad ῌ day, ~ mrad ῌ day  + A2:
E Q9 HO 2 KOM )*&¤&'5¥RH>¦S

'+%,- KOM./ ,**+  + #$%-12 KZR

Pw KZY+, # * &'§¨©A Fig. -



¢£





FG

:ª

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/ # ,3 «$% KOM&'%FJ, * u~:$%u~: G: *.+. mrad (*.*+ mrad/day) ,2 KOM ª ._­®
²&'5³-´T

2

B*: FG   ῌD / # ,- ,2  ῍D / # ,3  ,**,a ῌD῍D 5  Yµ

0 # ++   ¶D A2῎D 0 # +, 2*12·¸XBC%, ῌD(&,-   ¹ºD»12῏D 0 # ,. 

 KOM )*&'+%,-1 # ,-   ¼D ῐD 1 # ,. 3

῎ 0  +, ,-  : 

# 3 

/ D" S/ 2 ~ D WX½



12 0 # +, ¼_ KOM

./ 89/:;<=:>?@ AB/CDEFGH

226
Table +.

Tilt change and change rate at each observation point over the stage of I to V.

IJ$1234)

./0 ,**,a KL"(M NOPQR"#$5S$TU$
TNM 45 *.,3 mrad (*.*, mrad/day)  @

N *+, -1235VWXY ZU[\]5^_` Q"U$a"1234) .
/0 ,**,aSSN bc$#( dNe]fU 5gU

 N 12 O" -123bc$#5
NS hi4 *.2 mradῌmonth 
mradῌmonth @ EW hi4 *.+1

jklmfU]fb*+,- ./0 ,**,b 01234567
U$nop  6, qqrstIJU1234)- ./0 ,**,a U`u, M Nbvw

Qxyz5{"$ cc|} *.0. mrad(*.*0 mrad/day)   

῎ 0  ,. 1  ,-  : 
KOM 45῍p5vw~
Fig. -. Tide-removed tilt-down vector diagram at KOM
for the period from January to December, ,**+.


"



U -p N5 ,.+/ mrad (*.*1 mrad/day)4) vw~" 0  ,. 5 I qQ"# + b +*** c$#5ῌp



"

 N " vw~

0  ,3 e4)  -  dNd 56,Uu O" ,- 4 N5

"#$%&' ) "u" 0  ,3 *..* mrad (*.*- mrad/day) U"$dN+   N5

ῌpb# - b"5*+,UuI 4 "+ 0  +, b KZY 45¡4]fU¢@) 1  ,+ eb5vw~vw N £¤"#@

U ¡vw N£¤5

+  !"#$%&'() 

KZY 45 0  ,. u,vw~


@

U

Lub

N5 0.3+ mrad (*.,- mrad/day) 4)  ¥(dN dO῎pb5 ῍p ( +   N

, ¦§IJ[U ^¨©pb6, ./ dNd KZY vw N5ª«"#$0 ,**,b -p KZY  N5 +.+/ mrad (*.+*¬b67

mrad/day) 4)

KZR 45 vw~

KZR 45 dNe]fU¢

vw

N

N5



­

"#$ -*.-1 mrad (*.*- mrad/day) 4) O" VWXYday) 

@"# +.3* mrad (*.*0 mrad/

U

TNM 45 ῍p@ N "N5 +.+. mrad (*.*. mrad/day) 4)

,**+ \]^ L&' =IJN9 )
SSN % &'( )! **+, +.++ mrad (*.*.
mrad/day) "d =KLklmnopqr MaGCAP-V %s ,**2  #KOM % "d  &"*  <t9

  ,..+ mrad (*.*/ mrad/day) %DL ++K; x WXYZ

       !"#$! )c;== .}E/!.}0123STU Okada (+33,)+  Q *.++ mrad = - KL;@ABC * ~MC?45S - !" ./ 012 MaGCAP-V) -
KZY % &'(-d6% 1 8 ,+7 ++** :8!



<! &'

 1 8 ,-&'(Q 1 8 ,+)c;==Q

=MC{@)! KZY &'  A%8c;^DE=F!" x F;>?

$'=u('vw , )**z;ῌt{|  ,yc;= KOM

KZR

_ =! M.`a -ῌ, !%bc.  e#fg$@!hij^.

῍ 1  ,. 3  3  :

Q +

227

*" 2 8 +"d=!"

=&'(

345 67% 1 8 ,1

 j IJ9:;Kmnopq

BC1N'


-ῌ+ 





0 8 +,>? 3 8 3

%7 - 89



H

+

,* :

{H^K^u(-C"; |;MCCIJc; , H@ABC:!".*)J%K KZR %?C<KL <7 - 89 **+,]^9>?BAYTAP-G (Tamura et al., +33+)"d)! KZR

2 8 /

TU

r%D; K* ,y#$ &'u(T &' <^ K!";LD;
TNM * ~ SSN % &'(ῌt==1

? ++  RST<!" + HGIJ= KZY * ~ KOM  L">?Mc;%t9 N+! ,**+ j OPQbc=EF?C;
 GEONET T  GIJT O

T U- PVW** M'; Mx!
-

"** MGIJ= , H@ABCGEONET % \hiXhAXY=!ZG ¡u(-C"*¢^_£ ,**, M + HGIJ 23STU ; Mogi, +3/2 %  T OT H[U- E- \ ]((Strike) &'¤ (Dip) @A `a=!"¥ &'T n¦Y§¦¨W

L"_bSTU

IJ;%D; !>! KZY © KOM &' 

ªc! , H@ABC](=&'¤ d«

IJc; 5¬ ­UKIJe:c;fg

hzK>L ¡i T OT U-

D; <<%@ABC (Okada, +33,) :!"

u(-C^©&' >?{d x ®j!

j JSTU)¯; ¬ ­UKIJ; °kc;&'#T 2z%GIJ

H"

+ l@ABCSTU (A+)  KZY K&

.m!  GEONET T >?GI'J** M¡i M`aQ=  N9

6^DE=no!&(D.; pC;&'#T ±L" &' IJ;<=>? @ABC D;=EFc; STUªcc;

IJ%;WXYZ  ]^t9_brK bcST

xh:! KZY &'[67²+q7% STUH[U-!"; , km %

U=!" !;==Q

KZY &'

u(-C 0 8 +,;³´µC, l@ABCSTU (B+)  KOM &' 

%7 - 89j  H".

IJ%; x h:!  , !%¶· x ];u 3 8 3>? st=!

*<KL {d%<C_bSTU=¸¹<=^=! -ῌ+ !%MC H"¶·; R  IJN9<=>? KOM 6  )J?> c;  ]^xt»+ ,**+vºc; KOM w?CI  JD;= : !

  &'(^t99)!";<=

 / 8>? 3 8 >z"t9 . H z MCC>? 5m ¼yic;<=©m ¼½c;

G9 H"IJ.*<KL MG

<=KQEF?C <<%z{N9OP==Q &'(R

CSTUV! WXYZ)! KOM + H@AB[ KOM

67 897:;:<=> ?@7ABCD

228

Fig. .. A source model for the crustal deformation in months from June +, to September 3, ,**+ (Basicmodel). Gray dots indicate epicenters and cross sections of earthquakes.

Fig. /. Comparison of horizontal displacements observedat GPS stations of GSI with those calculated by thebasic model.

EFGH IJK FL KOM MN
O,PQ RSTU, km 5 ((V unique &ILW5XN

IJ]^ )*+,_`abc0d 0 1 +, 23

TUKefEFg&L Y Z[\
hijkH

4 3 1 3 25  - l1d +m`  Fig. . K

KOM

tuvwK xlyz> + km TU 1 km KZ[u#$ %&'( {]^ (Fig. 0, Table ,) Z[OnK-opq B, rs!"|}~ n RSTU *., km   B+ EF{q4abCu%

ῌ>z>-opq A+ xlyn RST

LX3'( %]^  +,_`K( `U * km ῌz>-opq B +  - ~L f EF t(-opq B+ g~K

Kv %LX3'( 5( %EFv'(GH&%t &GPS   (Fig. /)

 T|}~

KOM abKsUq

%f EF Table , Ktu +

(V |}~

KOM zL

 (,**,) EFu - ~Z[\u%

TUKe & L f EF|(,)}~L+ (,**,) EF,)*+,/340 ῑ  ῒ0 : / 1 ,3 23
4 0 1 ,- 25  C xlyn-opq +ῌ- &'

KOM K

L`t( / 1 ,3 23

4 0 1 ,- 25d-ῌ, ῍ΐῐῌῑ῏ῒ῎¦§d¨©K  L  (

KOM `fK ῌ KOM `LzLtῑῒ0 EFGH %0 ¡¢£¤K

`L¥V4q%3

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L­4q(῔0 )*+,¹0  . 0dKº»'~§d¼½((+) )*+,-./ ῐ0 : / 1 ,- 234 ,2 25 
KOM KNzL *.,1 mrad u TNM-opq34 / km ²Rq((, -opq A- B- u K  c !"#$ %&'(IJ]^ Fig. 1  Table , Ktu,**+ 
Table ,.

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

229

Parameters of each of the source models.

Fig. 0. A source model for the period from May ,to May ,2, ,**+, before the swarm activity started(Stage I).

,  !"# (A-, B-) $%&'( )* +Fig. 1. A source model for the period from May ,3to June ,-, ,**+ (Stages II and III). Gray dots
indicate epicenters and cross sections of earthquakes.

,-./ 012/ 3012/4567

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YUR JZ SSN [ KZR \]^_`"2ab7  

230

Fig. 2. A source model for the period from June ,.
to July ,-, ,**+ (Stage IV). Gray dots indicate
epicenters and cross sections of earthquakes.

Fig. 3. A source model for the period from July ,. toSeptember 3, ,**+ (Stage V). Gray dots indicate
epicenters and cross sections of earthquakes.

  !"#$%&'()*!+,-./01 2

34567! 8'9: ;;<=>?@1';ABCD'9:AEF 7

A8( KZR !GHI3J'(KL89(-)

 ῎ : 0  ,.  1  ,- 

KOM %&'(QRB>!

 3O89 0  ,. 

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7 , `!abc !defHI%`'( ; ^!gh%i>jkXYA , `!abc<!MNA&&lm<P> -> n oa A. B.

bc Bab81BqBr('r9A8(s81

A67 3p.8(KL89

 A !tuvw   +  x9> +  +*-MN Fig. 2 A Table , %O8(P7 , `!abc' abc yz {| }~BA%GW- (,)

m ῌday A1> ῎A8( +ῌ-  %89 ;!MNA89 89Br( ῎%`'(-!_C3

YA67

B8(& n oabc Bab81BqBr('r9>A8(<D7;A%17 + x9>!tuvw

 /+*- m-ῌday %8('7B ῎A8( ,ῌ%`'(ῌ῍A67A abc  A < *.3

-  <P> '

+* m ῌday B -+* m ῌday  B < ,+* m ῌday
-

-

-

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B 2+*- m-ῌday A n--- vw8(&>!2AiT8('7

(.)



%

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KZY %&'(}~|A! 2A!B 7 abc  B

2B8('7

91

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<1
;!

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'7¯!°BP7 ±²% ; ^<A!"<¨

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+Z~

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(3-*.,) " &3,<=*+I,% IM7r678

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7

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3pN , " FG;< I, nSB=" UVHI45

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E-,:(OPQ,B8 FG  A7 " o0123pE8

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,B 

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N ," ¡-JMEy( 3M012 G,¢= S ,%" KOM E  - £J  M38 % " ,**1 ; Okada and YamaE%F" ,**-# 

moto, +33+ ; Okada et al., ,*** ;# K d-J:" o0123p>" E+

E" I +* km B:6" [!

¢7T4¤¥¦§¨978"bcUVV,XY" W©,

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

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deB3,-Ya 

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23/N ? ,**2 84

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:;<&=>?> 9%:;7 GEONET #$AB*CD;>?EF G++,NOP*H

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I_ 01 +*.ῌ+*1.
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i§ (,**-) ª´%& µ¶«(+3+1+30*) ;  )u·` .2 .,/ῌ..-.
Mogi, K. (+3/2) Relations between the eruptions of various volcanoes and the deformations of the ground surfaces around them. Bull. Earthq. Res. Inst., -0, 33ῌ+-..
  (,**+) ,**+  1 @  , )I ,**+ st:IKL^p@
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 '() (,**+) ,**+  0ῌ2 @ ,)I- 30 JKLI.
 H
M +,+ῌ+,,.
Okada, Y. (+33,) Internal deformation due to shear andtensile faults in a half-space. Bull. Seism. Soc. Am., 2,,+*+2ῌ+*.*.
Okada, Y. and Yamamoto, E. (+33+) Dyke intrusion modelfor the +323 seismovolcanic activity o# Ito,central Japan.
J. Geophys. Res., 30, +*-0+ῌ+*-10.
Okada, Y., Yamamoto, E. and Ohkubo, T. (,***) Coswarm
and preswarm crustal deformation in the eastern Izu
Peninsula, central Japan. J. Geophys. Res., +*/, 02+ῌ03,.
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>; ` ^a]bII_ 2* ./ῌ.2.
Tamura, Y., Sato, T., Ooe, M. and Ishiguro, M. (+33+) A
procedure for tidal analysis with a Bayesian information
criterion. Geophys. J. Int., +*., /*1ῌ/+0.
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