ῒ῔  /-  (,**2)
 -  +-+ῌ+-0 ΐ ῕« ¬ ­ ® ] ¯ °F I 2±²  ³ J { ´ Kµ¶·¸¹º»¼-L M w ½ N,**2  + O ++ P,**2  0 O +, P

Relation between High Temperature and Low Resistivity in the Shallow Part of
the Northeastern Foot of Unzen Volcano
Shogo KOMORI῍, Tsuneomi KAGIYAMA῍, Mitsuru UTSUGI῍, Akihiko TERADA῍, Hiroyuki INOUE῍,Wahyu SRIGUTOMO῍῍, Yoshikazu TANAKA῍, Hideo HOSHIZUMI῍῍῍We conducted AMT,VLF-MT and high resolution electrical resistivity survey in the northeastern foot of theUnzen Volcano in order to compare shallow resistivity structure with temperature proﬁle of the borehole (USDP+). These surveys revealed that a low resistivity layer (.* · m) lies at .*ῌ/* m depth and a high resistivity layer(,** · m) lies below 0* m depth. The low and high resistivity layers correspond to the high temperature zone(-1 C, ., m depth) and temperature-decreasing zone,respectively. To examine the factor which decreases theresistivity and increases temperature at around .* m depth, we observed the feature of the drillcore samples ofUSDP-+ precisely. As a result, argillaceous impervious layer was found at 01ῌ+** m depth,just beneath the low
resistivity and high temperature zone. This suggests that groundwater is maintained shallower than 01 m depth
and that geothermal water decreases the resistivity of this zone.
Key words : Unzen Volcano, resistivity structure, temperature proﬁle, geothermal water, argillaceous impervious layer

QRST +, UVW0X! ., m 5Y-Z (-1 C) 0[K+ῌ ῐ ῎ ῑ ῏:\]6^_`3:a01@ "b#cAd2?B$efEAd X! +** m gX3h!Bb%ij][k3&l3'mn(oJp&i\]5q?rk)s@Ad[d2?tu 23MN6X! .* mv *+ w +33/  +33* ,06\x-J.y/

z00UV0h!J{|f}~Bv2?J

\J2@ (Nakada et al., +333) :\] 6. ]1 (,**,) 6 23h! 3 #cbtu23JA 0StE4JiJh!3d 5$e56gW6? 37./'01. (Fig. +) 23456 789

8-9? USDP-+ ;<G3z+0dA VLF-MT :;< (USDP) 3=>?@A +333 0;<0HI)J0CK L3MN Fig. ,BCDE,***  23;<G (USDP-+)3:5.;tu-40tA<I3 B40dA=1 (,***) 6h!>QRJCd G0BKA?@Ad2?B@ut0fE

Ah!34JB@ >QRJST@A , UV

232?6 <I4B0KA-9 ¡.0¢CJ£K?2¤ h!3¥DB¦0>.

63?J@Ad§E¨Bv2?J.

©F0dAX! *ῌ.* m@t@[Bu VLF-MT 6G=3ªHl (,,., kHz) JF z5h!B{|@ > 0*0ῌ2/*,   !
Earth and Planetary Science, Graduate School ofScience, Kyoto Univ, Kitashirakawaoiwake, Sakyo,
Kyoto 0*0ῌ2/*,, Japan Faculty of Mathematics and Natural Sciences
Bandung Institute of Technology, Jl. Ganesha +*Bandung .*+-,, Indonesia -*/ῌ2/01 +ῌ+ῌ+  1"#$%&'()&*+,Geological Survey of Japan, AIST, Tsukuba Central
1, Higashi +ῌ+ῌ+, Tsukuba -*/ῌ2/01, Japan
Corresponding author : Shogo Komorie-mail : komori@aso.vgs.kyoto-u.ac.jp

132<=>?@.ABC DEFGHIJKLMNOPQRSTFig. ,. Resistivity distribution in the northeastern footof Unzen Volcano by VLF-MT survey (Kagiyamaet al., ,**,). This survey area is shown in Fig. +.
Low resistivity zone extends from the upper side
to the down side along the stream. Arrow indicatesthe stream.

4U*V  U* WXU* AMT 9:YZ
5 +* kHz )[\]^_`a )[b]^1  c d* ,,., kHz e_` VLF-MT 9:f\ AMT 9: !
 VLF-MT !

 "#$%&'(  AMTVLF-MT )*+,-. /0*1  23
,**/45

+, 678  AMT 9:5 - ; Phoenix

gh MTU-/A iJjk VLF-MT 9:5
jljmnogh VL-+*+  Fig. + 9:pU qr (UZ-+, UZ-,, UZ--) s9: Fig. +. Observation points for the AMT & VLF-MTsurvey (UZ-+, UZ-,, UZ--) and location of surveylines for high resolution electrical resistivity survey(A-B, C-E, D-F, E-G).

rs USDP-+ tuv d* + wxyz{|}z5 Adaptive Damping Method ~ AMTINVprogram Oulu

 0Markku Pirttijärvi ! 23"%&'(  &'5 #X$%%& d*yzzJjz\%\* a  '23()



U*V 5  +322)

(y 5*+!%5\\ , 5V`-. / vG0(y¡¢ 1 23 )U* a 1
 23 4 AMT, VLF-MT )*4/)¥

(Ingham,,ῌ, AMTVLF-MT 9:!

24£¤

3+£

¤ Fig. - (a)  !  23 Fig. - (b) pU \!9:/\%¦ ,,., kHzb4(§24 \ ¨© 23 ª« 5sb ¬!)[]^c 5

 5sa USDP-+ ­KzL®¯°±9²( \³´s)(  µ V24£¤!* 23 5 - 9: ¦¶( +** m ·1^, AMTVLF-MT 

,ῌ+ ,5 ¶( * m+** m /0*

+*  · m ¸¹sº"!  6 USDP-+ tuv»7 UZ-, 9: 5 ¶( .*/* m 23 s(y8¼¸¹sp½!*¶ !"#$%&'()*133

 .* m +,'-./01)*2 34//23 Fig. - (a) 5  UZ-, 6 1072 + kHz,,., kHz 8 9: 10;'</= /0 > +** Hz+ kHz 8 9: 10 ?=@'7'ABCD2

E5F UZ-, 6 ! VLF-MT 'AMT J' 89GH2>2I5F

35F JIKLM

2 NOP&QRS5T - UVSWXYZ VLF-MT AMT  ++* kHz[\3 ]1 ^>2FJ'  5F _J5 `ab6cd
e/ USDP-+10fg Gh  $%WXcijj +klmOcn4- 

-ῌ+ AMTVLF-MT opcq fgG>h$%WX',rsAtuv'wcnx
J'cS'/0 ,**0  . y+klmOcn4
 Fig. + 6zc{| (A-B, C-G)   }~P~Pcxz   u CH-0*+ R c/zckz'/0/ 1
 10 0* kc/  +  (A-B) 5
kc . m  ,.* m  ,  .  (C-G)
5 kc / m  -** m '/ \ , C-E,  -  (Fig. +)   + D-F  . E-G 5FUSDP-+  ,.   + > ` z/01

 d

;^2 +*ῌ!@£c1 u¤¢¥¦"$%¡¢#§ (+33-) "c1
-ῌ, 
Fig. .  +klmO40$3$%WXopc{| USDP-+   z/ + 5

 QS `2+$%& ¨2#$%&!3 USDP-+

Fig. . (a) {|%© Xz/ J%©g¨$%WX ª¢«¬­®(¯°c±!01'²q3¯°c±!011'³´ 8&wSµ¶'/0%© Y 5{P6g¨$%fgWX
cN·' ¸ ,*-* m 3$%#¨2@3
Fig. -. (a) Sounding curves and (b) resistivity structures obtained by AMT & VLF-MT survey.

¸ .*/* m 59 +*  · m 5#¨/01J'2 J'¹  º§» (,***) 5$301,
rsAtuv'¹'j01¼½c{/01 

! "#$%& '  ()*+,-./01234567

134

  8 9: ; 9<=.
>?@; A + kHz ,:B
  CD9EF;9GH : IJ KL MNO!8 9 +1 k; J" O! #P;QH k

R :S :B9#$

TU V%9W
,&'UG  */* m   :(X)YZ[\] * ;+,&'
Fig. . (a) -^ Y _QH./` a/  /* m  F     ; + kHz ` AMT O !

    ,ῌ +bcdefc0 g1 ]Th  ,,., kHz VLF-MT O!!2 ijkl%Tmn3o\ 495GHFig. .. ,-D resistivity structure by high resolution
electrical resistivity survey. (a) A-B line. Thearrow X indicates the position of the USDP-+and the arrow Y indicates the position used forresistivity structure analysis. (b) C-G line.
The depth is measured from the ground surfaceof the left side of the survey line.

r6sTU/xyr6;z{ Fig. / (a) Fig. / (b)TU p q 7tuFHvbw
iZ[5GH)Y|8;&3|8iH}H_P +** Hz+ kHz B9~  Fig. - (a)g>?x?c09,  +** m :2 ,**  · m ;Tg USDP-+; <= (,***) 5GH

;>T 2;T  Fig. . (b) ? ,. !8  @A ?

+ !8;+,95GH B ~9 USDP-/ C GHATTS TS

USDP-++  ;<>b;7DY~EF {m9g ;G@;GPp <= (,***) 5H

GH<>b@ ;;

/ (a)_P HUGST. USDP-+ 

MNO!5GH 
\USDP-+ */* m `C 1  :(X)Y gI(T 9 pGH  /* m   :(X)Y)YK9L4

p AMTO!Z[ P ,ῌ, ¦P

 VLF-MT ;AMT O!2LTU%

W9 :(X)YUG 7DY~ DY~EF{m9g;1QH

g;;

Fig.

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Z= (+333) : FHG (,***) [\ (,**/)¯ 

VLF-MT ; AMT O!2LTU%9 - °±AT]

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9WU AMT :BO!2 Cg9WUW bcV%9GH ]Th  7tu
 Phoenix ºd MTU-/ A ».¼A½e%;`´ Curtis and Kelly, +33* ; : +33/ 7tu~¡¢£;T

VO;9;

`

Um\UaPp USDP-+

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12 34135

5" '#$6%
0ῌ ῎῔

78  -./19:  USDP-+   AMTVLF-MT   1 .*/* m ';<5(.*  · m)  0* +** m '=% (,**  · m) (>?@ AB  ,***  CD% (  1' E5(  5"

1

%

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%
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%N"< 'U% ' VW FGHIJKL?
&"4'X()"

1 R" CY*XZ  +,[\3D%]^#NXZ_)'U%
ῑ ῐFig. /. (a) Relation between the resistivity structure
and the temperature proﬁle in USDP-+. Resistivitystructure is determined by hybrid analysis of highresolution electrical resistivity survey and AMT.
Low resistivity zone in .*ῌ/* m depth corresponds
to the high temperature zone. High resistivity
zone in 0*ῌ+** m depth corresponds to the temperature decreasing zone. (b) Comparison of thesounding curve at UZ-, estimated by the hybrid
analysis with the observation.

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Curtis, B. and Kelly, W.E. (+33*) Resistivity-recharge
relationships -ﬁeld study. J. Hydrology, ++2, -3ῌ/-.
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Ingham, M. (+322) The use of invariant impedances inmagnetotelluric interpretation. Geophysical Journal, 3,,+0/ῌ+03.
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Nakada, S., Shimizu, H. and Ohta, K. (+333) Overview of
the +33*ῌ+33/ eruption at Unzen Volcano. J. Volcanol.
Geotherm. Res., 23, +ῌ,,.
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