ῒΐ  /,  (,**1)
 -  +.3ῌ+/3 ῕ ῔

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

+3-*   ,**1  +

3   ,**1  .

.  

Dike Intrusion Model of the +3-* o# Ito Earthquake Swarm Estimated from Leveling Data
Takuya NISHIMURA῍ and Makoto MURAKAMI῍
We examine vertical deformation observed by leveling during and after the +3-* Ito-oki earthquake swarm in
the Izu-tobu volcano group, eastern part of the Izu Peninsula, central Japan. Taking the mechanism of the swarm
activity after +31*’s in the same area into consideration, we estimate the source model which can explain theobserved uplift along the eastern coast of the Izu Peninsula. Although the observed deformation in +3-* allows
a wide range of parameters of a tensile fault as a source, it is reasonably explained by a near-vertical tensile fault
suggesting dike intrusion east o# Ito. The volume increases are estimated to be 2.2+*1 m- and +..+*2 mbefore and after April, +3-*, respectively. They are much larger than that for each episode of dike activities after+31*’s. Broad uplift with no seismic activity was observed during +3-+ῌ+3--. It is explained by either aspherical inﬂation source or a horizontal tensile fault at a depth of +* km, west of Ito. In both cases, the volume
increase is estimated about 0+*1 m-. Calculation of the Coulomb failure stress suggests that the dike intrusioneast o# Ito triggered the M1.- Kita-Izu earthquake occurred on November ,0, +3-*.
Key words : Izu-tobu volcano group, crustal deformation, leveling, tensile fault modelqrs tu"#Ivw"xyz"$+ῌ ῐ ῎ ῑ ῏







 +312  ! !"#$% &'( ,**0.

)*+,-*.

"#$% 0( & +332  //.-)-\&{0((+) "#  |"n}~}$#$

%  P f.)9\&%+{ 1 +31* 2-&D$.-\&%( -? "#%345678)9:; (Fig. +) $<8=>& -X)9:= +* km 9:''?: @A "BC "BDC)EF 0)>0 }~}$=( +* km 9: )<8$G=> "HIJK$L-M>&'( 0)"#$("H<8NOPQ&*678NO-R(,) #b ` ?? ++*ῌGPS S8T (EDM) UVW W-X$'>+,/ ¡: f""&¢£¤¥¦)b)9Y)-: Z[-"H$)-\&'*L¡( §I+# 

( ]0 "##^_`a*b¨© ),ª y--P( UV«& "##^

[cd$Qe9Y)-\0( f>)¬'& ..)UV

ghi

jkRlm$k'(!e!

Aoki et al., +333 ;Cervelli et al., ,**+ ; Hayashi and Morita, ,**- ; Morita et­« (1*ῌ2/ ) ¡¢®

)?O +312 /¯IPQ&°

al., ,**0 ;  ,**, ; Okada and Yamamoto, +33+ ; Okada

. +{-"HP/Y"#I +3-* )

et al., ,*** ; Tada and Hashimoto, +33+ ; Ukawa and Tsuka-*% &' (Fig. +)( +3-* "#hara, +330 )9\& /n9Y-"#%op±hP²¬"#I)> Nasu et al., +3-+ ; ³

 ´-*/ῌ*2++ µ¶·¬R!0¸ + 1¹2"º""HIlm»¼ih
Geography and Crustal Dynamics Research Center,
Geographical Survey Institute, + Kitasato, Tsukuba,

Ibaraki -*/ῌ*2++, Japan.
Corresponding author : Takuya Nishimurae-mail : t_nisimura@gsi.go.jp, º»¼%»® &150

Fig. +. Temporal change of vertical displacement at leveling benchmarks around Ito City (modiﬁed from
Geographical Survey Institute, ,**0). Vertical displacement is plotted relative to benchmark 3-,2. (Inset)
Location map of leveling benchmarks.
­ +. h]"/0®¯°±# P~ ,**0&®¯u ­ /0¸¹u ,**-   ,+-  MJMA /.3  .
 ,   / 

1  ! , "#$%

&'()*+,$-.



,,

 

 /01

+,>+? +31* @AB?

CDEFGH )IJKL;+M NO)&45+; P
XYTZ[\a ]^__ (+33*) `b+$c%de5+&+ `aK

?hvw|u;1)de5

+

3-.. P]hv   /01)d&e5 +3-*  -ῌ.

 +3-*  ++ῌ+, +3-*  +,
 +3-0  ,ῌ-QR Kuno, +3/.  ST7 UVW=

+3-* <f,/01T7g hvj, +3-* +;   hvw]yz/0 3-,2 P29:45+; +3-* <=µu;¶µ·

1)de5+; f,? +3-* h]<  +,x 

23145678  Tsuboi (+3-+, +3--)²$³´ /0 3-,2ῌ+3-+  +

 +3-,  +,ῌ+3--  -1)de5 5 1rs

 >+  +3-0 1b
Tsuboi (+3--)  )45+; ~K /01sT7LAGSAS P~ ,**+ g+;) f

=IJ) +31* @ABh]i<

+3-*  -ῌ.

 +3-*  ++ῌ+,

+3-,  +, - 1rs) 5+&+ῌ--

jklmno pKL;q\ XYTZ[

-

 ~

\d&rs >+tu;

 45+;/01s /01?5 1 u;?) ¡&+ ,ῌ ῑῐῒΐ῏῍῎¢hvwxyz{+|}/0z  ~1s¤!

0  1  d451|}/0£ 5 z1¥#3

KL;1 2 +3*.  11)¦45+; 5)S45 ] (MJMA 1.3) , +3,. `a§ ¨©ª«de5¬ ~,3 - 1 

89123'h +3-*

7-¹T# !º»¼`1



$% (Fig. ,c) )

!~   +3,1151

* [K

!U<'8v

LHIH 8vDC '

!!"#$  % & '($6$%M6:8v Abe (+312) !")* +, -' LAGSAS '.

HI1JNJ* x' 97 !  /)/0123  .)123'4+3-*ῌ+3--o (Fig. -b)  k7-@M8vGJ Tsuboi (+3--)  56* +3-*

97 !O$%JN@* 5$%<=

!HI'M P#

789 :; <=6

hk7-@M$%'V I Q<=I' ABCD

KR * 5 .ῌ,  S6* Fig. -c 89>?@ +3-*
8E

F! m G'H

I89J* 8

 LAGSAS 'ABK"

98C'4 LM>)IN

.)

O

* +,RSTP89K"Q)

-d  +3-*

< % +31*

U LM%'=Saq$% I'r IJ* Fig.
- c  +322

/ῌ1 tD +33* 5o' +323

0ῌ1 t ,o$%¡_¢T£#{*# !$%"89C +* km U&M 

7-DY6:7-p'f8v

 89C''V W0J$%"X('Fig. ,a $%¤* mI Fig. -d  +33-0ῌW0)5' * Y5 +, Z*+

1 tD +33.

1 tm +o$% 5no'[ \] ^,_` +3-+

G T# !%#{* 5no'y#?%  ^7-` +3,2#?% ].a 89 /, bcd,_e% D 3-..

8v7u 7-hk¥:&UVJk 8

bcd-7/% K"0fgH

v#zkT#

I* 5hS'5'

0fgHI89K"i1Fj

m 21Jk +,3'j+J*Fig. ,  'l-!4

 +3,.ῌ+3,/¦X@M'C65D W¦8v§Dm 0 4no57-p89+301

aq$%r6* ms +3-*

. tmno (Fig. ,a)  7-67u6L' +*.2 cm 8vw

* x +3-*!#{~ (Fig. -c) hkzH* 5no8v 8v7u7-¥W
Fig. .  Fig. ,  - raE ¨'U

 +31*

*

I89123

r I +3-*< %LM%'=Saq$%Y©' 65V* +323

T# !%'=S8++ tmno (Fig. ,b) v (Fig. .e)  ¨ ,* km @MDª'8v«m L' +-.. cm 8vw) yk 8v#6k 8v#Z¬ ­ * 8v#Z¬ 

)

9'zH

*

6:FNy +3-*
 +3-*(MJMA 1.-) #{<'?@S$%|m

* [K +33-ῌ+33.

!#{

no8v 8v#\z *!~$%L' - cm 2o (Fig. ,d)* mI 8v# +3-*

no (Fig. ,a-b)

 BzH yk Y29>%* 7-@M8v +3--

U C 

oD I Fig. +  Fig.

+3-+

'¤

D --

T#

8v (Fig. .d)  5°®32¯.ῌ++ t8v (Fig. .b) Y7o

* +3-*

 ®32¯r+3-*. tm8v®32*

E~89U±$%w]

 ²Jk 5°97 ! ³?@

*D  aq$%'V 7-hk6:

97 !<J´n'?@I D* YI , µ0

!o $%- ! 97 ! '=S$%|m,f%*E~ 789,_D

F_p  + $6 D DHI* 'l!

$% ¥[,**,%  yk +3-*

DD@s7-@ML' +..+ cm 'A68vw

+3-*

!'=S

¯ (Fig. .a) ¤* x97 ! > ,

 (Fig. ,e) C > .*T# +332++ t ,0 ;97 !

J 5no'3?HI !% DHI')­ 97 !'=* xno (Fig. ,c) 97!|}noJ1 H++ t w

D97

!4

noaq$% (Fig. -a)$%S65^* mI 5 #'¶_

·;)I 7- +31- k7-@M8vGJ* 58JI ¶_123D +3-*v 97 ! !HI1   Abe, +312%5VJV* mI Fig. , IhS' 7-@M*

hH  ²123D7-T# !%'=S* ¸ +311

$%S6u 

152

Fig. ,. Vertical displacement on the leveling route along the eastern coast of Izu Peninsula. Bars denote verticaldisplacement relative to the reference benchmark denoted as Ref. Lines in northern part of Izu peninsula
represents surface trace of the Tanna fault system ruptured by the +3-* Kita-Izu earthquake. Data period is
written.
m ,. nop qrstuvO^wx. my Ref. Qzh{|}~P~<[uvO^ P. no1t' +3-*  ^hab  P. m H' myzh,1.

-ῌ ΐῒ῏῎ῐ῍ῑ῔+ 

D /* EF GH: ; I4J$4KLM9N
 +31* ()*+,-. 
89:;OPQ'RST+U +31*  !"#$%&

!"#$%&'' +3-*   VWXYZ['U1. B

/0123456 7, \ ]O^'_`abcdef-QRST;<=>?@AB,C1++. gh ijk +3-*   l][\]. +3-*

Fig. -.

±·¸nmW ¹Aº»¼#$

153

Vertical displacement on the leveling route of Izu Peninsula. Symbols are the same as Fig. ,.
­ -. ±²³´[\V~.wµ¶ Na

­,

:;

  (Nasu et al., +3-+ ; Yoshida and Hama-

|./

da, +33+)  

SQR) Period B k  !" T^

 +31*

  }~.- wx

T *./ km   !"#x?>T`)c$  %&'() *+,-./QR) Period C k   Wl^0)

1/2 342 56!" 789  +31*:;  2<. =>) 78

 

/

fg T / km S^o 7B Period A, B

 2 ^ Ug`. 1/2 342

9 ?>@ / ) ABCDEFBG

  d#$e[56!" d$e  HIJK )L789 MNO MNO

, 

/

) $

P.?>O QR STU. Matsu’ura and Hase- 56!" T   +* km >) //2  V WX

gawa (+321)

OYZ  Okada (+32/) . [\]^@_`Na  +3-*

. bc2 Period A dFig.

,a. bfg ++ b Period B dFig. ,b.ae +3-*.be +3-*,d++ῌ+, bfg +3--

Fig. .de)789  QR . 2 M
NOP.?>O ' T
ABCDEFB    [\a de  [\] ABCDEFB- b Period C dFig.

@   [\ x \ )¡ [hi/ ) Na MNOQR\  ) .<.^ 

STU56!"j Period A#$@B789?>) c

MNOk  lmnmWl^o/./ fg +31*



pJ

  ./ \ ¢

.£¤¥ ¦§}~./ ^2¨. ©)   ª«J f ¬_`.

56!"#$ qr2<. +,*s ) tuv 2*s

2 Fig. . 2 ­  ®]OV¯#$.Y) c Period A k  !" wx^yz{

ZO °  ®] x \ )

 S 

154

Fig. .. Vertical displacement on the leveling route along the eastern coast of Izu Peninsula. Horizontal axis isdistance from benchmark J/,. Data period is written.
n .. opqrst uvwxSyz{|>} ~
7W n4./ 

s: mm  

 sa ῍ ῌ L : !": km a : ] J/, #uvS)5 Vn

U. V7WXYZ[\]^_`a b
Fig. / 45

#$%&'( *.22 )* (+,-./0&123) Table + 45 6

. 



+3-* 

789:;<1/=>?@A(4..+BC  DEFG *.+ HI 5JKLMNO

Period A (0&1XYZ[ a

P

678Q5;< DEFG *.3 RST

bG +31*

cdRefghii`j\XYZ[klJ5m

AºghiM +3-* <»O¼789:£¤g
Table +.

155

Estimated fault parameters4 ,**, ; Ukawa and Tsukahara, +330)  Period
B 

 

   !"#$%$&'( )*+,-./0 !12%3  
456789:8;+31* <=>?

' /0 !ABCD 
 +

@*3

!EFGHI

/0 !J2K(L Period

B /0 !  Period A M(NOP3
Yoshida and Hamada (+33+) M +3-* < - Q /Q:RSTU V6' S-P WX)* - QYZ[ )12\ L( ]^_`abc6d]^_6"efZghij)* k% l/0mnohi  p3q3rsthuvwxyd(z {|(& \)\  6d~}fx\} EFGJ2

K(c &| 3  fZR)*S+&'4  fC ~}f mnohi')*6d (Okada, +32/) ~} Period A  B 6p3q3 2.2+*1 m-, +..

+* m 6d +323 <>?789:g6  +2-,+*1 m- 6d Cervelli et al., ,**+ ;  ,**, ; OkaFig. /. Location map of the estimated fault model.
The rectangles show the locations of the estimatedtensile faults. The solid line on each rectangle
shows the upper edge of the fault. Open squares
represent the leveling benchmarks as of +3-*’s.
° /12%3 !gCD ±²
1
2%3/0 !CD³\ ´[µ¶·6³ ¸¹G  +3-* <=AºCD³da and Yamamoto, +33+  ~}\ )*& +3-* <78YZ6 '¡¢¡£¤d | M¥.

>"9:¦6j § +3-* <78YZ

1* ¦6d( (Yoshida and Hamada, +33+) +31* <>?8;\78¨©sª « +322 <78 -3 ¦¬6 +323 <78 -- ¦ p3­® p3>¯¨©s6+/ ¦>e6d M

9:YZ¦)yz{|¸z/ }156

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

TMN 9N9J0# )"80#MN"  )I UVJ (+33*)  +3-*(Nasu et al., +3-+)  ! " Period A



#

+323

$ % &'()  /ῌ+* km *+," - #*=98gU8_c

GPS   SAR OV0 DE

O M2 d  u

z@Ut Miyazaki et al.,,**.| )? M1 d WXY¡C.+/  / km 0 +,*1 234 0*1 56

V0 zZ¢0|)&')7"89 :;)

,**. ; Nakano and Hirahara, +331|

56 *  * #!"&'<£¤ - = [, R F}Z¢0) =98/#+*./ km ,> @ z@Ut Fialko,?9 "," h^9gU \<   V0 zFig.

$?89 :;)@ABC"DE  %,c  Fig. .c| ]¤8Z¢0 zFig. ,d  Fig. .d| - km F?G+ &4)956799W^)  _ WX

 H I JK Table +20)L *!

'(+  "," :;)"5

6MN  MNO>PQ+R, (RMS), S-.F? 

PQ

Q

Z¢0

 0]¤8F9 ??   Q . `F}Z¢0)+a"9 \+Period C

0y (Fig. ,d) ¥b?¦)y (Fig. ,e)



-

 ¥

0
-

CQO>79 )/T) 9U O8 V) IH)F}"89R cid§801?+MN2+9W3

j> 0F9 Z¢0mnopqO8

4

XY, Table + "$)Z456

 0y0¨+

z@Ut Pollitz et al., ,**+|

MN[5")7 e©)ª0+OW

MN 59 \], + 67ygU?9 \« fg hi

- O/^0 _) ` 0#

j ¬ER)­k0 99W^)

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) M /.3 c+ M/ d 89   :*e;"

f<WV0g

 Fig. -b  Period C ®  / 0)

   © /^0 7R¯
t / cm -.F9 POWl]JK Z¢0 y :* Z¢0

>hi $ j98 M/

mnopq (Fialko et al., ,**.) g="8 d   kk;"89   ??°"8^±gU Ri

="899 +31*l] mnopqr= ) > I&s7/^0<\9 @Ut Mw 0.*¬ER)70 9` RaAl]

F}Z¢0gU G

<WV0 BuCvwxy D z{E © 0# '(lmn!

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s:KC

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 Period C

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, +33.

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) :;):MNO"

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 JK) '()L, _> 0# +3-+ῌ+3-- ῔῍῕ΐ῍ῒ῎ῐ῏ῑ:;) P Q , zFig. /  Table +|Period C zFig.

NMNb"0#) N x,d  Fig. .d| R F}=98 S% I¼ +* km b"89  qr¸

+,- ./0 +3-* Z[T U"A.@

157

Fig. 0. Coulomb stress change caused by opening of the estimated tensile faults(CFS). A thick gray plane of abeachball represents the mechanism for calculating CFS. Gray region is positive CFS. Contour intervals
are *.+ MPa. No contours are plotted in the region where absolute CFS is larger than - MPa. Left panel
shows NS proﬁle at +-3.*E. The star represents the epicenter of the +3-* Kita-Izu earthquake.
 0. ' +3-*  ¡¢£A.@/¤¥C lCFSn* U¦§¨©6 CFSª«'¬­® UL¯4* §¨$°CFS ±$° * ²³©R´6 ** +MPa  µ¶³ -MPa NO²³©6¯ * ·¯4¸W¢ 6 [¹ +-3% ¢ * º»6 +3-*  Z
UU¼&4*p'% q)D'r*

 (,**0)  +33-ῌ+33.  SAR  3 km  +- km,.- 

1 km  !"# $

stVuv UwxRhyz{'%&'()* +,- ./01

6E|2}B1 stV U4`

23 4'56 +- km 78 '~` L} lr t ,**,n*6 ../>Z  UmstV( wxRhyz{+*1 m-  * ?@A.@B;$C

B1 Thatcher and Savage (+32,) 6 iy

2 9:6  1 km, ;$<=

6 &4DEF786G) ++ km st]HI JKL/0& M1 , NOG

C

6 *

(M 0.1) !{'r* `'PO (,**0) 6 QR+,-./0ST

U+3-*  Z

U +32* Z [ U

T U U(

"C

VVC4WXQR GPS Y-./0r (Morita et al., ,**0 ; Ukawa andZ[ \ +* km N?@]^_^`1ab4

Tsukahara, +330)*B1 cdefgh)* +33-

Thatcher and Savage (+32,) 6

ZU{

 +33. ijk';$<=

'

6 +.2>+*1 m- lm

# iy]* ,**0n )1+3-+ῌ+3-- +301  +313 +,- ef +ῌ- )*  QR6BB  iy]3 v

;$<=o86

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)""#$%&'(-./ 01CFS ; 2 3

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.)? +-3@"(



./ Fig. 0 (A) Fig. 0 BC 
""DE *., MPa .FGH" -IGJK.FI( .)GLMN
 BN! +3-*  O "P(BN!" G!QNGR/ῌ ῎ ῍ ῏>S"#(BN!T"= +3-*  O
"P($U%V  &'

RGLMN +31* (WX)Y*Z+[ (+,*@) \]^ (2*@) ;_`
+3-* (

! ,-F# ,.-a+*2

m (. +31* (WbcO-! ef0R 

"P/d" g +3-+ῌ+3-- %V  12345(hi<= +* km jkl mknon6-(BN!&'R ,-F#7 0a+*1 m- l BUY 85p
q<59: +31* (g1W rP#$%&'*;l Q +3-*   (B *+, -./56M *++ s(

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G

<t=ΐῒ

u= >vwxy( z?{|(}~ 
R @ABy( C3D( !}A  Q , EFEG (B#, 
H(lCI(JlN KchB
LMNB( Q)
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Japan. J. Phys. Earth, ,0, ,/-ῌ,1..
Aoki, Y., Segall P., Kato T., Cervelli P. and Shimada S.
(+333) Upward dike migration during the +331 seismic
swarm o# the Izu Peninsula, Japan, from inversion of
deformation data. Science, ,20, 3,1ῌ3-*.
Cervelli, P., Murray M. H., Segall, P., Aoki, Y. and Kato,
T. (,**+) Estimating source parameters from deforma-tion data, with an application to the March +331 earthquake swarm o# the Izu Peninsula, Japan. J. Geophys.
Res., +*0, ++,+1ῌ++,-1.
Fialko, Y. (,**.) Evidence of ﬂuid-ﬁlled upper crust fromobservations of postseismic deformation due to the +33,
M 1.- Landers earthquake. J. Geophys. Res., +*3, B*2.*+, doi : +*.+*,3/,**.JB**,32/.
Hayashi Y. and Morita Y. (,**-) An image of a magma
intrusion process inferred from precise hypocentral migrations of the earthquake swarm east of the Izu peninsula. Geophys. J. Int., +/-, +/3ῌ+1..
u= >v (,**0) K r "OPQR
S 10 ,+/ῌ,./.
 (,**,)  ZET IhR0 "Q ¡¢#$%&'(M£)
¤¥¦*¡ §¨ +++ ,,,ῌ,-,.
u©UVª«WX¬ªYZ ­ª®[ ª¯°\ª±]^ (,**+) >S"#*²M³H_`2+** ´ rµ u= >v7S 30 ,-ῌ-1.
Kuno, H. (+3/.) Geology and petrology of Omuro-yama
volcano group, north Izu. J. Fac. Sci., Univ. Tokyo, Sec.
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Matsu’ura, M. and Hasegawa Y. (+321) A maximum likelihood approach to nonlinear inversion under constraints. Phys. Earth Planet. Inter., .1, +13ῌ+21.
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fault zone frictional properties. Geophys. Res. Lett., -+, L*00,-, doi : +*.+*,3/,**-GL*+3.+*.
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] a (,**0)  5O "P(b¶)r _·¸O B,3 2/.
Nakano, T. and Hirahara, K. (+331) GPS observations of
postseismic deformation for the +33/ Hyogo-ken Nanbu
earthquake, Japan. Geophys. Res. Lett., ,., /*-ῌ/*0.
Nasu, N., Kishinouye, F. and Kodaira T. (+3-+) Recent
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Earthq. Res. Inst., 3, ,,ῌ-/.
c]de (,**,)  ¹º(hi (B "»¼»,o §¨ +++ +00ῌ+1..
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deformation after the +333 Hector Mine earthquake.
Science, ,3-, +2+.ῌ+2+2.
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 (+33*) +323   +3-*     !" .2" ,+ῌ,/.
#$%& (,**,) '()*+,-'(./012301243567/189: ;<" +++" ,--ῌ,.1.
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Tsuboi, C. (+3--) Vertical crustal displacement in the159

seismic region of Itô, on the east coast at the Idu Peninsula. Bull. Earthq. Res. Inst., ++, .22ῌ.33.
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=>?@A (,**-) BCDEFGHIJ K.+0Lῌ,**+
MND " 0*/p.
=OPQ (,**+)  RS - DT UVNDWX Y"-10p.
Z[\]- ^_ ` - a$bc- de f - g^hi(,**0) jk SAR lmnopqrst uvwxyz9{|}~ EF5 S +*0  " +.-ῌ+...
Yoshida, A. and Hamada, N. (+33+) Redetermination of
hypocenters of foreshocks, mainshock, and aftershocksof the Kita-Izu earthquake and the Ito earthquake swarmof +3-*. J. Phys. Earth, -3, -,3ῌ-...
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