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+

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
+31*  ! "#¹ 

º/0(,*++)+ῌ+1 ¸< L

¹»¸h ¼  ¸  ½ ¸ !,*+* ' +* ( +2 )* ,*++ ' + ( +. )*Features of Hypocental Area of Swarm Earthquakes in Hakone Volcano
in +31*’s Revealed by Re-Analysis Using S-P Data
¹ Comparison with Recent Activities ¹
Ryou HONDA῍, Hiroshi ITO῍, Youhei YUKUTAKE῍, Masatake HARADA῍ and Akio YOSHIDA῍
The Hot Springs Research Institute (HSRI) has developed seismic observation network in Hakone volcano
since +302. In the ﬁrst decade of the observation by the HSRI, hypocenters were determined by using S-P times
and the Omori equation and were conﬁned in the Owakudani geo-thermal area. This is remarkable, because
earthquakes are known to occur in an extended area in the Hakone caldera recently. In this paper, we try to
clarify whether the past hypocenters are real. For the purpose we introduce a ﬁtness value to estimate the mostprobable location of swarm activity based on the S-P times. First, we calculate synthetic S-P times from every
grid point that covers the Hakone caldera with a spacing of /** m for all observation sites. Then, Root Mean
Square (RMS) between observed S-P times for each earthquake in a certain swarm activity and the synthetic S-Ptimes is calculated for all the grid points. The ﬁtness value given to grid points is deﬁned as the summation of theinverse RMS for all earthquakes belonging to the swarm activity concerned. It is considered that the grid points
with large ﬁtness values exhibit the most probable area of the swarm activity. From the analysis we found thatearthquakes in the period of +31* s occurred in an extended region from Mt. Kintoki to Motohakone, not conﬁned
to the Owakudani area. Some of the swarms seem to have occurred near Lake Ashi. In conclusion, we thinkthat hypocentral distribution of swarm earthquakes in the past is not much di#erent from that in recent years andswarm activities in the Hakone caldera have occurred in a similar way at almost the same region since +31* s.
Key words : Earthquake swarms, Hakone volcano, Historical earthquake distributions+ῌ ῐ ῎ ῑ ῏+,-. ..- km /01234 +3/3 '56 0* '5789:;<=>?@ABCD EF +* km G

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/20, Iriuda, Odawara, Kanagawa ,/*ῌ**-+, Japan
Corresponding author : Ryou Hondae-mail : ryou@onken.odawara.kanagawa.jp

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"+,*-./  01 2)34
5 6 +313 78 22 ! P

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A6 J S-P %$ *45/ +302ῌ
+312 #$"G  %K85/@L

M " NOPQR@-S5 6 ,*** T 
U2VP. 6H2") WX"

Fig. +. Tectonic setting around the study area is shownin the top panel and the bottom panel showsobservation sites of the seismograph network of
the Hot Springs Research Institute (HSRI) of
Kanagawa Pref. Solid circles and squares indicate
observation sites at the present and those in +31*’s,
respectively. Dotted line shows caldera somma.
Thick dotted lines indicate plate boundaries of thePhilippine Sea Plate and solid lines represent active
faults. A shadowed area represents central corn.
Gray lines indicate contour lines at +** m interval.

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S-P $%+05  +31* 6789

3+312 :.;< . mmῌs  =,. $>?!@AB$".C0 D #$$>%
EE S-P $%+F

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+322 W% Lee and Lahr (+31/) ! hypo 1+ 0(

 P 1XY S 123$>+Z[\'!8J(C]  
16  ^4 - _+95`6 78
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op +33, : q=>r?@] 0R sj@rtt@(  uAv 2, :.wx =,uA 3jy=,@ ( +323 z{q=B

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0! Z[I~J.l<+mnopq=  +33/

z{ win  KLM  +33, +N(

Fig. ,. Distribution of hypocenters relocated by Honda
and Ito (,**3) using a conventional method which
is based on the Omori’s equation and S-P times.
Epicentral distribution is shown in the left top panel.
The right top and left bottom panels represent
cross sections in the N-S and E-W directions,
respectively. The right bottom panel shows numberof earthquakes in each depth range.

!f +33/ z{8J(hypo1+ ./01 234+X<0\'.V! hypomh (Hirata and Matsu’ura,(( 59D+5.,0! +31* +321) '(

0! 1RK S

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OP8Q0 5J

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 !   "#859_0x! +312 :.
8+&( Rl<+mnop"u( 0! r?"( X

 ]Z

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NT `  !xE$8590R+!  L5,( 0$I©uAS-P $% & '( )*)+, -+F8J(+C & ,  Y-^D (,**3)
5J((  +302 

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9
+

+312 W%85

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dej³+k+^´ lµ , km mn¶^, q( . km <aE ¼r * km P-0

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, ^¢£¤¥D_.7+]00- ^¢£¤¥E_.

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. G_db8}«a0V! )K^¢£¤¥¬f¦H F­®¯b}P.
c / km G deP.c , km .V!
/ -

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±

7+89²%,ghi! ,*** z{& -  (a) (l) 7+y@[r?+

X< 89·0¸ 0V!D]! ,**+ ¹ ºo¦H» dep9.+]X< & - k½.8 L+4,  -./0

Fig. -. Hypocentral distribution of swarm earthquakes occurred in the period from ,*** to ,**3. The central
panel is the map view. The left panel is the cross section in which earthquakes in region A are projected.
The right panel is same as the left panel except that earthquakes in region B are projected. Gray circles
represent the earthquakes occurred in the ,**+ swarm activity which was the largest one since +302. Blackcircles show the swarm earthquakes except for those in ,**+. Remarkable swarm activities are classiﬁed into
clusters indicated from (a) to (l). Occurrence data of each activity is shown in Fig. /. Hypocenters ofthese earthquakes are determined based on the Double Di#erence method (Waldhauser and Ellsworth, ,***).

12(34)%567%8 9:!4;<=>?@%A1 ,** m  7% &EF1 1* G! ** HI  

(OWD) J 3 KLMN  SMY

 1O'(P)8Q %8 6 & 8RS(J(3 TUVW + XYZ , Hz [\]!^_`ab;*"c(#
kJlm$%n  2&(o8<!(%pqF

D c1'rFs-   S-P

+312 

(L ,, D) J - d) e$f%ghij LS 1*** J

tWuvUw(1E34
-ῌ+

BCD



x) y

 +,0* z

{ .a

 *Fs|*!+},~ -Hn-.<8' +-0 z73

 BC!(%* *&  &  S-P ! +302ῌ+312 1

W   x)/1E340 6 7%A S-P  (RMS)  ! " #$%&! '() *& J[ A RMS 8ry)

1* G* H |* !+},~  8)&!J1$%!(42) 9

J

4 1)4 RMS J[ RMS 8

S-P  ! 1* G S-P  J #$%*.*/ 3H!(% 80  *&!

) 1
 1* G

8SEF(6731)44$%

8+}

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 ,**2  0  ,**3  . |*Fs NNT, KMY
[dJ*



#



$ 81FsJ56

  %J5 1* G

D KKY, OSS 717%

7%  ~*  ¡tWuvUw¢e£~J¤<¥ BJ8¦46( !§{/  +, ,**3 1E34xA!¨

GPS 1E34©9Jx)

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 OWK 6 73O:ª­®¯°±8)%1²4 tWuvUw(  * 

<³y  =´µ!(34)% *&  ¶·aJ(% 8¸¶¹;º»¼>½16 4)%&!8%~

S-P  

+31* 

5

Fig. .. (a) Hypocentral distribution of earthquakes determined by HSRI routine analysis in the period of
temporary observation (Jun. ,**2-Apr. ,**3). (b) Solid circles show earthquakes for which RMS between
S-P time of the observation and any one of the old record of S-Ps is less than *.*/ sec. Open circles
represent hypocenters of the corresponding earthquakes determined by the conventional method that was usedin +31*’s (after Honda and Ito, ,**3).

   1*  S-P   ! " #$    %& '()* +

-./

7

8 +321 9 :;( 0** m (KKY)  +,01 m(KMY) ' 0** m BC+ D E

0( 123 456- '(<=>6?@9A./

2** m ',FGH IJ0K%& -'LM/ N - )*!QRS( ,.* T U

W X/Y/)* + 9Z /[ (-  ''P  V\]M/ -/ 
3 459NM/^H$_0 d eM!QRS

ic$jk9lm/ 7Wn)*'(aj\tu #7)* 9. a'  O S-P 'P

$7`7WX/ab(  BCc$ !
"fa7

gh( 3 456)*+ o pq

7 c$ rs )* vwW'P  :;(xyj\tuz@9{|'}  c$)*a~7 & /  & - 0 "IW

9 $ 9 9P $l/ KKY # # P KZY ' S-P  $ <=>?'~7,**2  3  +, %

"'PW KZY ' S-P ( +.+ 'P' !QRS'e0!-ῌ, ῒΐ S-P ῐ῏ῌ῍ῑ῎'( )*&/  gh0
S-P $V0  +31* ,./ $$! " #9

/ - $!

A & 0 X(   9 )7  X +31* - '(-  * (%& 'P

! " #'}

0'^W X # rsaj&()*' !QR

9A./7I Pc$9¡  +

S

'P

'( gh0(:;(oI 7`/¢£W (! " #A./ X¤ ¥ X¦ $l,(§-

X/Y/ ,./ rs /.* $7%&¨!QRS !}^7 ©i'( ªD.«9!}^'P : ¬­ ®¡  /** m ¯'°©i' ±7 ²³9-$(´ )* '!/ S-P  µ¶7·^ § gh¸&(¹)* SSN $ KIN WL

 + º + º)* S-P »0  !/ S-P 

7 ' )!# $ RMSµ¶7 RMS 9 *.*/ 'B¼$½

>? @AB CDEFGHIJKLIMN

6

OPQ5R  S&TU'OPQ5VWX 7
RYZ7[\5]^_ &+`5a(b&cdDe  'OPQ5VWX ;fSf;&TU&ghiPjklZfm S&[\n5]^+`&`o. pq&r -. hiPjkl&
st:;uv/w7"xy z{|}~&cd5#
Joint Hypocenter Determination  Kissling et al., +33.

  1  (Yukutake, et al., ,*+*a  ! + "# $%&'()!*+,&-./012 3456789&&:;<="

Table +. O-C residuals of P- and S-wave arrival times
used as the site correction at each station in +31*’s.
These O-C residuals are estimated from data observed at stations of recent observation network in
the period from ,*** to ,**3. We adopted those O-C
residuals, which are obtained for the nearest station
belonging to same geological structure, as the site
corrections for old stations listed in the table.

Fig. /. Frequency distributions of S-P times at KZY
for swarm activities occurred in the period from,*** to ,**3. Swarm activity (a) has the smallest
average S-P times and activity (l) has the largest
value. Locations of swarm activities are shown in
Fig. -. Occurrence date, total number of earthquakes and average of S-P times are given at the
top of each histogram.

Fig. 0. An example of the conventional method for an earthquake in Sep. +,, ,**2. The black star
indicates epicenter obtained by the routine analysis. White stars are epicenters obtained with theconventional method. The left and center panels are results by data of the temporary observation at
old sites (solid circles) only, and the right panel is those by data of old sites together with data of SSN
and KIN. Omori’s coe$cient used for the examples are shown in the left top of each panel.

S-P 

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

+31*  !"#7$%&'( )*+,-. / 0123. 4 56+789:;< =>? @A
BCD ;< EF?G. H 2 I JKL?  MNO S-P BPQ? O H .b 
4  56+789: =>? RLS.
 UVIWX S-P =>
^B_`:

a

bc?

-.** m ig

BYZ[\]

 ddef

56+789:;<2PQ?

T?

.

;<B

T? ghj;LIklimA2n

Fig. 1. Velocity structure model used for the calculation of S-P times (after, Yukutake et al., ,*+*a).

A. opI q4r1A.2 P4I stO4 uv? wxy_`: z{? .
/ - |}~-.[\]^;?A

(2S.  gq.BO[\2[qFig. 2. Distribution of ﬁtness values obtained by using S-P data observed in +31*’s. Open circles show
epicenters of earthquakes shown in Fig. .b whose depths enter within /** m from the depth indicated at the
top of each map. Fitness values are normalized by its maximum value in each depth range. The max of theabsolute ﬁtness values in each depth range is given at the bottom of each panel. Note that distribution of theﬁtness value is similar to the epicentral distribution of earthquakes at depths shallower than -.** m.

8  

*.+ !"#$%&'()*

0 )') - km 1234567#893:0 ;3 3 RMS H+,-./
1<=>?@AB +302 C'D +312 CEF8G*.*/ !1I#0JKL?MN%O

PQRS  TUVW0X YZ[\]^H67_[`ab  cd45V8)X efgh*X# i(jk 0 KKY  S-P lQ?mV nop4

0'?q)N(/ 45#r*3stu#

45vwxy? zN {PQRVo|)N }~tu** m  + km  +.. km fg/p mnop4#*NTU3 +31+

 t **p4VW0X KL?MN%O

C 1  +31, C -  +31- C +,  +31. C +,  . 

_[`

/

0W/'?hV)Xq)N;+* / ; +* 'D 453 tuV3 ,O_[` (+*** m) 1Itu#tu3 . O_[` (,*** m) 1IVD*{#ῌ+31+ C 1 p4TU

KKY  + CQV*N S-P lQg67?;

6' z++ V 1 noTUV8)XD*NYZ[\]^H¡45¢£g3 , km 1I#X

67?; +, Vq% S-P lQg67J¤ O¥0"¦J ,l§g'D¨B*© ª6«¬q*X0 45­®Np4/X {Fig. 3. Frequency distributions of the distance between the hypocenter determined by the routine analysis andthe grids that satisfy the ﬁtness criterion. Note that the hypocenters were relocated with the velocity
structure and site corrections shown in Fig. 1 and table +, respectively. The averages and standard
deviations are given in meters at the left top of each panel.

Fig. +*. Maximum distance distributions of grids on which ﬁtness values are assinged. The distance is supposed
to indicate the resolution in each of the direction. The averages and standard deviations are given in km at
the right top of each panel.

S-P 

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

+31*  !"#9

Fig. ++. S-P time distribution at KKY for earthquakesin +31+. Histograms of S-P times for each of
three-month periods are shown in (a)-(d). Thatfor the whole year is shown in (e). Gray bars
represent S-P times for earthquakes whose locations
were determined based on the Omori equation.

$%& (+31,) '()* S-P + *./ , +.* ,-+./ 0

*1234567 * km 89:;< = >>  S-P  *., ,?@ABCD E ++eF@=: GHI+JK *..

*.2 , *.2  +., , L=M:+C= *..  *.2 ,

GHI NKOP* 1 Q-OPRSTUVW  S-P +X

9YZ [ \]^

+_ M: KKY T`)*ab c defghHij;-OP)L :kb;<= lmnopqrCD E +,  S-P 
ABCDF<=JK-OP ! k]s=: 12345 ,.** m 89OP+ *..ῌ*.2 ,GHItu> vwxyz{; -3** m 89OP+*.2ῌ+., ,GHItus=:|}<= - km R{ :M~)*Hm\] :+/:+ vwxyz)* ,.** m lmno

pqr+1W ) 089OP+L :F  :<=

> KKY 9 KZY )ab;< 9OP (l) (k)  S-P  +.*ῌ+., ,B :9 M: (l)  (k) :!OPSL=

Fig. +,. Distribution of ﬁtness values for the activity
in July +31+. The ﬁtness values are normalized
by its maximum value. Two regions with large
ﬁtness values are clearly seen near OWD at thedepth of ,.** m and in the west coast of Lake
Ashi at the depth of -3** m.

ῌ +31,  - Q . Q-OP

M-*'()t:s=)1OP)LR QT  ,** T ab

D E +-¢£¤¥¦§ ¨j-+ab;<  S-P +

CD> = ;©ª« @=: + Q- Q*./ , +.* ,+./12389+

GHI+ *.0  *.2 , . Q  0 QGHI+ *.2  +.*!:;<=+ ¬}­ $%& +31-  S-P ABC

/F=: *., , +., ,) ¡/,L=M: ® =OP!+¯P> SL



10

Fig. +-.

!" #$%&'()*+,)-.

Same as Fig. ++ except for the events in +31,.

 /0123456 7 +. 8

9  :;<=8>?@ABCDE"F "B NNT GHIJ KBLMN OBPQRGHIJSTUVWXYJZW4[\@W  ]/0^ Z_`a/0>bc

B defgh

ij +3** m,.** m klmO῎ij ,3** m no ῍ pJq

 rs

S-P Mt^56

*.0ῌ*.2  us

x bc
ῌ

*.2ῌ+.* vw

+31- y +, z`a/0+31- y{uB | IJST?@}~U`a/0

[_[\@ +, z . ?`a/0
B

.* 5J? ' +31. KKY Jj

 S-P M + yt^56 7 +/ B *..*.0
 *.2+.,  

123456 7 +0 JB KIN GHij +3** m4d[῍p q S-P M *.2+., /0B῍pvwx   ' (+31.)   
yB S-P M -ῌJj[`aj @ |-3 BJ?

j @W  `aBt^56

¡a¢£j @W[W  B¤S¥@
SMY JdW¦§ q ¨Fig. +.. Distributions of ﬁtness values at various depths
for events in March through April, +31,.

' +31. a¢£j `a¨ ©ª123456 7+0 «¬defgh 3** m GH/0Jq­«j I  S-P M -ῌ[`aB .0 z

STU¨\ y8±?@?@W

'

efGHq\®¯°q 
῍+31. y`a/0

yB +, z +/ ¨j+0 ¨²@ 3* 5+31. ¨  defGHq\ry/0³´ +/ `a·¸?@Wbc

 ¹\@ `a?

 !" +31/ KKY Jj  S-P M + yµ¶[/0@º῏q+, z/0a¢pBLMNGHJq\

t^5687 +1 »x ¼? +, z/0 y8±?`a/0>Bd

JB KKY J S-P Mº῏q\B - ½¼²J

S-P 

Fig. +/.

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

+31*  !"#11

Same as Fig.++ except for the events in +31-.

$% &'( +31/ )  +, *+,-./ 01)

- 234 S-P 0$% 5 / 67./89:;<=> ?@ABCDE:FGRMS 0 *.*/ H3I 5 - 6JKA$% +

LA S-P MNOP0QRS 5 NNT A ++6+T MNOP0$P UTB0 *.+ HV
W *.//ῌ*.0/ H A$% (XY2A5WZR - T[\ S-P MNOP0$%JKA ]R NNT ^_%GUTB0`B  a NNT 3bXY
2Acd0eZ +5f7g+,-!
RA5g +,-VGhW5 S-P 0
5BPGMNOZ VWij+A$ Gkl
Z% mmA589:;<=> ?@AB +Ln - T+JKopq%A5g %_
gSgrst u ],-\v w! xy
q%G .z{| + }rst89:;<=>}~    +2 %. 89:;<=>0`B 5 KKY  +31- +,- ]  +3** m,.** m A + * *KZ% S-P 0 + H,-A$%
.0 *$% *..*.0 Hs5 OWD 

Fig. +0. Distributions of ﬁtness values at various depths
for events in December +31-.

 .** m 89:;<=>}~q%
ῌ +302  +31* +,-mm)A 1* + ! 0 +,-0cdZ +302  +31*

R +0S  ]] f7g
DsF0j +002  03 5

1yZ +0 

 +3a, b 7mA - ./^§¨

1y0S

+31* T5 *..*.2 H,-!G *.2+., H,-!
0xYZ%  ,* 5 + * - *K0Sg 5
rst

,-0$

 

89:;<=>}~ %G  ,+.  ¡¢£ f¤`¥¦A`

7,-

B>G% "¡¢£ +.** m A

w! ©_  +31*  KKY A S-P ª\}~89:;<=>0`B  7+5 KKY A



12

Fig. +1.

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

Same as Fig. ++ except for the events in +31..

 S-P 

*.2+., !"#$%&'()"*+,&-$ +31* ."/0123-4567
89:;<=45>?@ABCD 7 *..
*.2 !'()"8B@ S-P EFG%5HI

JKLMB5NO"6PQR,&STB T-T

UVWX/0126Y KKY  S-P 

K *.0 !PZ&D[\;<T-MB-$]^$_ ^%[\PY`T56abcde(fXgM12PhT@B&>?$%&+302 . +303 .12 KKY  S-P ij

klPF& 1* .m

noKF$%& ,Mp

S-P K *..*.2 !

*.2+., !126K=

q 0rsRt5/0uv +*ῌ wj xy0rKsN$%@BMB*..*.2 !'()"8B@

 S-P Kz_-8{HIJ|(}KMB
-$[\< ~_XgB/0PhT@B&QR
g%& *.2+., !'()"8B@ +31* .m
6B=&K MK$ /0"*+,&- R,&STB B%"T@ 02
03 . *..  *.2 !'()K.P@=&

-$ [\< K5&126=45>?$%&.ῌ ῍

Fig. +2. Distributions of ﬁtness values at various depths
for events in +31..

῎ +31* ."T5/0"8B@,  126M$ QRg%50r6g

S-P B>?PT_T ^0r6< <T5/012g@ 0r6QRP45 ^klx£7¤T@B&A"#?& ¡5 Y¥¦§%¡ ¢"=&A"[\"/0K¨YT@B5M_©6"/0KTMBB45 ª

1* ."]B@«¬-$­®¯ °±²;<¡³

<12m =&B´µ/0KT@B5Kk-45 ¶ ,, "+3/3 .¡/00r6"8B@ [\·¸QRT5¹5&126P@º/»C¼M_°±²;<=&BY¥¦§©½" 

. (,**-) +3+1 .-$

S-P  +31* !"#$%&'(

13

Fig. +3. Histograms of S-P times for (a) the events in+302 and (b) the events in +303.

Fig. ,*.

Same as Fig. ++ except for the events in +31*.

)*+, -./01234,56789

Fig. ,+. Distributions of ﬁtness values at various depths
for the events in +31*.

,:; <=> ?@)AB CDE2FG HI#$%& JG  +31+  KLMNO

 ,**1  , ,&  +31,  ,**3 b  +31-  1.  #$ ,**+ #$34,G P ,- Q, RSTUVW

gh KZY ijk

G cWXBG Ad2 %Z[\]e , f

KINlm nG  opqrstu *./ lmRv

ijk FG , w xyz{tb
+312 2~%w  (+3/.)

XB%&2FGY %Z[\]^_;;`a%

aG567]FG] AB2) M+ |}Gg~U opqrstunG  ] M* 2F; M-*.- txwg

%

$

,

 P - ,#$~%34n 

WXBG P ,.

opqrstu m2) M+ |}Gg~%)F 

14  M*./  !"# $%
&'() *+,-./012%34567)8+312 926 ,- :;()<==>?@ABCD

+E#(FGHIJ= >?@ABCD

KLM%3NOP. QRS/0 TUL !"TUL<.2)VW%#X#YZ[JX\M

6.%3]I(#^W[Z _`abGcd*+!",- 9e !"fgh.<

 i +Ejklm.#+Eno@pq rsGW3%TUtVu#X# 6
X#M]IZ[Fig. ,,. Source regions of swarm activities obtainedin this paper. The year of the events and depthof major activity are shown in the panel.

Fig. ,..

Fig. ,-. Histogram of magnitude for earthquakes in
the period from +302 through +312. Magnitudesof these earthquakes are obtained by the Tsuboi’s
formula using displacement amplitudes.

Histograms of magnitude for earthquakes in each of the activities shown in Fig. -.

S-P *+, -. # +323 $  %

34567. $ /890:+31* /0 12

15

 $ ; # ::<& =>?@AB,C$ /890D

$ E# FG ' "H I!"JKJ#$L%&'M( +N(O PQ )*R  $  
  !"#& Yukutake
et al. (,*+* a) 

1+,S-TU,./V0  DoubleDifference 1 (Waldhauser and Ellseworth,,***) ,,*** 0& WAB$ 2X0,;.

 1 3456,

 $ W7Y89ZX:9ῌ;8<Y<

,[ & =#/;>?@A$ :>
39A


\

Fig. ,/. Monthly number of earthquakes, whose S-Ptime is less than , sec, in the period from +30+ to,**2. Numbers of earthquakes in a year are
shown for +33., ,**+, ,**., ,**0 and ,**2
because of huge number of earthquakes (themonthly number of earthquakes exceeded 0**).
A dotted line shows April +323 in which theobservation network was reconstructed.

#$ pull-apart ]B ^ 0 !" & Q $ Yukutake et al., (,*+*b) $ ,**3 >D  C2D&E

2 ` abc:d0 $ WHeZ=>0

D  #

Wfghij: !k$ )*  *,mn LM

$ 0 _FG <&
?@AB

IJ& lK0D , C2$ 
H#X,o  X Z$ <NO

 12 pPQ0 &*+

89D TS: $ T (,**-) $ +3+1 $ -v0D , _F!"# +3/3 0

# #<& /9*")*D

T $ HeZUw%

VxW+T <yz"$ Q V(D}'M Z~ &CZ0[} X} #$ /0
_" JKJ`Gy89
GZX$ ]BG2XQ Ab & ,**+ 0$ GPS \2g"##'I!"1,Z:!" $ KOM v KZY 34

X_1,Z:{#'&  KOM $ LM

$ 0



2j #'Mq

HrsthusL%&

R

Q

\ 

X{|E!"H$ YWDA

\ ]W^+0 Z

 X&
Qa y$ 0

 12

 X' #e$ \D D cde<!"#&  $hi$ 1* jkQ\f

1* k# 2* jk  l & m ,/ $ / 

S-P *+, nI

fQR,[ ' 1V0 ZZ(& +301 Q$D L ' <Y *+'

8 (e o¡p#PB ' "H$ (e$M & qr (,**3) $ 34¢s. #t+30+( <& +30*  # +313 Q$ £¤6>u:9ῌ;8$ ::9ῌ;;8¥¦s§us,¨0tS-' & /890

$ s§us v)¥¦  !"

D

34'

'M *)*¬yZªw ,[ &ª$ «x$ ea y©# FGL%&­z{0

D z#y_" ®¯s`}1 _Xy~ ' "H$ ±

r$ ,**+(z#} #$ !"O%1

> GPS ,

L%'M  s§us< )*,**0  v ,**2 s§us)` s§us,³´ 
. &?@ #$ 0

°f|$ !"JKJD 'M,² _FGZ<&'  $ ,**+ $# ,**3  #$ g"# $ D*µ0 /89
D TS

Q0 & Fqr (,**3) $ GPS 567,+302ῌ+312 0

6 #$ µ+0

125y»X: D =¶#$1·5¸M,¹$ e&CZº8¦¼I! 2 km

# +* km e,½:$ ;:7Y

16



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

 / km !"#$

-./*0+"1 !2$ 34 156

%&' ()$!*" +!,
78!95:!"

#$& %&';<5-!
ΐ()=:$>)*'?@<5!ABA!CDE7F+

ῒGHE, ,*

-./IJKLM01N2O()=:5:' 3P Q 4 6#'#5

67R8GH S9!2=:;72$ <=#

25:T>U?@VAE ABAWXBC

$#7DEYZ[\]^FE  VA_`a bc":!?@=8 Oki and Hirano, +31* ; G

HdI JKLaHdIM KL-./NO ,*+* ; e/O ,*+*  P9ABAF78<

IfOQ CLgORhS:$F172$ <5&'T2=&UVi"E5: WX:$=#Xjkl\YZmn\EYop LRZ<

qr[s\tu(E  ]qP +* km ^v

8_8:$272$

 low Vp, low Vp/Vs bJ', !'=:

cZ!dYyefE !gz5hi:$F17(Nakamichi et al., ,**1) 7$ Nakajima et al., (,**+a)2$

wx`,$8 a

{2= |j:$27E}kb7l%Wmn~o E Wm  p !2=$!1 lowVp high Vp/Vs bJ!2=qr Ss low VpῌVs!5E H,O 'z:{$
2=:<5|}",!t~2=: Nakajima etal. (,**+b) EsWmr[(  ]q low Vp, low Vs, high Vp/Vs JT9+
2$ABA( H,O '[\$W  #5 ;  H,O b b J' low
Vp, low Vs, low Vp/Vs !2= @=:!s2$ "&ABACD!?@W'=#=: QS X<¡ 
 XJE KIN ] q< ,/ km ^ v,)= low
VpῌVs bJ<8&££¤E2 low VpῌVs bJ<8&P:
P9SX W low VpῌVs J VA!6#XJ5¦¤ECD§ !&b¨= r[©s$¨E ª«m\¬­@= VA+ £,®5¦ ªL5«m\¬&©9;$s\' ¯6£!5!V9/ῌ ῎ ῍ ῏
+302

( 12

7"VALGHR#¤"#$ S-P =(°±²¥+ ³¦
2 R§=XJ")$ tu
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Hirata N. and Matsu’ura M. (+321) Maximum-likelihood
estimation of hypocenter with origin time eliminatedusing nonlinear inversion technique, Phys. Earth Planet.
Inter., .1, /*ῌ0,.
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Three-dimensional velocity structures of Mount Fuji and
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17Oki, Y. and Hirano T. (+31*) The geothermal system of the
Hakone Volcano. Geothermics SP. Iss. , : ++/1ῌ++00.
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Yukutake, Y., Tanada T., Honda R., Harada M., Ito H.
and Yoshida A. (,*+*a) Fine fracture structures in thegeothermal region of Hakone volcano, revealed by wellresolved earthquake hypocenters and focal mechanisms,
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Yukutake Y., Ito H., Honda R., Harada M. and Yoshida
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