 

92./  46<?1CGEFBCDH$'CG%&$'CH%&5 46=;>
@346@IA
A46'-+
$'DB%E,
46:7 "#8*
! 0 465)(SK  ' 











 j

jhTV&J[ 









 p

kh*,4.%Q)17/3-70%"#



jj




lhdN&U]$]X









lo

mh]XC&FYR=eO%"#





nn



nh\M%"#









pq

ohtr%();D>` 







ql



8bfITV%ca #@H !_G6?<Wg       














qq


            
        














jlj


17/4+7supiii&LBPE^:$AQ23*52&Z9














jmn

 ª®¦¤ 90/26-@/,¢µR¤`R<73>A1
,( *
ÛÙµRÔ,90/26-@/dZQ¾ßk×², ÁÆ*')µRÔ90/26-@/Q,¾*
ÜÙ4:?-@/Q¾ßÔ  KY,VK*`Ô¼,-@/*Ø4:?-@/Ù')¦¤*\ ( *Rl*{s,*  *k×² Á,Æ*')`Ô¼-@/Q,¾*
ÝÙ`EaÄwuÖ¿Jß`¥É,ÀÉ,»±$È
%')ÌÉxc ¬s-@/Q,\D* ,À"*ÞÙÏÊ³ËÅ'*ÑeRMßÏÊ³ËÅ')90/26-@/ijw'!Ì (TmÑeS»,¶ÑeRMN»µ90/26-@/QÒÊ'! yeR M+dZ 9.>8A;@B5$È$ÒÊ,( * &9.>8A;@B5$È$'*Ôb§DI´*
[WnfhCº}Øz©¨ÂoÙ Ô¸´,«½90/
26-@/k×,¶ *Í´#Ô½´uÖ,¿J*&Ô]Ç`¥ÉÀ,¶(Ô¸´]_àá¬s°_kÓ`Ô¼,Í´-@/Q,¾*&º,¶ «½ÒL ~ÑU)«½v^5=:? £¡jpËÅLÑ

*­H'kÓk×Ðg q|ÜÚrÜ (Ðg  (ª®Ã¹PÎ'tO¦¤&k× Xµ Õpf » Gv&Á¯£·, Fj*

1
  SU[Xt 45 YF k)'3.0N-0SUTDAlmn  SU$@Xt Jb "H k)'3.0N-0SUT#DAl  SU$@Xt

 E; kGMT.070d%?l  SU$@Xt OQ je k)'3.0N-0SUTP10cCSU*l                                  mo  SU$@Xt +& /I kh5.0M0d2*#DAlmp_tmn 8=nr9:G.0,gSU>DA  mo 8=nq9:  mp 8=nr9:8=ns9: 



RBVa

fBVa

(^

8=nq9:



8=nr9: 

 

8=ns9:(^



 



 

 
Yamaoka, K. Strategy of earthquake prediction research in Japan and the role of active
monitoring.: Proceedings of the Active Geophysical Monitoring of the earth
lithosphere. 12-16 September, 2005 Novisibirsk, Russia, 28-31, 2005.
Tsuruga,K., Y.Hasada, T.Kunitomo, J. Kasahara, R.Ikuta, T.Watanabe, K.Yamaoka et al.:Monitoring of the State of Inter-plate coupling using reflection phase. Proceedings of
the Active Geophysical Monitoring of the earth lithosphere. 12-16 September, 2005
Novisibirsk, Russia, 23-27, 2005.
Saiga, A., Yamaoka, K., Kunitomo, T. and Watanabe, T. Continuous observation ofseismic wave velocity and apparent velocity using a precise seismic array and
ACROSS seismic source, Earth Planets Space,58,8,993-1005,2006.
OQje45YF]i\WZ6    K:L<`!

2

=`"#&"s.T+8;5hkH Ir64   
Watanabe,T., Ikuta,R., Yamaoka.K., Soma,T. and Fujii, N. Continuous Active Seismic
Observation using ACROSS source and Seimometer Array, Proceedings of the 8th
SEGJ International Symposium, 369-372. 2006.
Saeki,M., Khosaka,T. and Kaneko, S.: Phase ambiguity resolution based on Linear
modeling of DD carrier phase. Proceedings of ION GNSS06. 26-29, 2006.

Watanabe, T., Ikuta, R., Soma, T., Saiga, A., Miyajima, R., Fujii, N., Yamaoka, K.,
Tsuruga, K., Kunitomo, T., Hasada, Y., Kasahara, J., Kumazawa, M., Satomura, M.,
Feasibility experiment for Active Monitoring of Inter-plate Coupling in Tokai region.
---A dense array measurement---, Eos Trans. AGU, 86(52), Fall Meet. Suppl.,
Abstract NG33B-0174, 2005.
Soma, T., Watanabe, T., Ikuta, R., Saiga, A., Miyajima, R., Yamaoka, K., Tsuruga, K.,
Kunitomo, T., Hasada, Y., Kasahara, J., Satomura, M., Kumazawa, M., Fujii, N.,
Detection of Reflected Waves from Plate Boundary Using ACROSS Source andSeismic Array, Eos Trans. AGU, 86(52), Fall Meet. Suppl., Abstract NG33B-0177,
2005.
Yamaoka, K., Watanabe, T., Fujii, N., Ikuta, R., Miyajima, R., Monitoring Experiment inTokai, Japan : ACROSS source designed for a phased array, Eos Trans. AGU, 86(52),
Fall Meet. Suppl., Abstract NG33B-0176, 2005.
[y/W_a|>?oNx J<@0~dfDqY9V
Q_q*c)'{X(g!&5w$`GfeL
Sb'Pzl5u\%vUKR5^FMj;z3
 B8,  dfD[y/W_a|>?oN<@0~q*c)5w$`'Pzlu\%]CEZ$vUKR
5^FMj;z3  B8,   
Ikuta, R., Watanabe, T., Soma, T., Yamaoka, K., Kunitomo, K., Feasibility experiment for
active monitoring of inter-plate coupling in Tokai region using ACROSS, Eos Trans.
AGU,87(52), Fall Meet. Suppl., Abstract NG51A-1012,2006.
2A/), [y/W, n-ap9, >?oN, _a|, Hi-net%zlS

tZmO}71, KR5;, 2007 Bi:8,,

P1-003.
Watanabe, T., Furukawa, T., Hasada, Y., Ikuta, R., Yamaoka, K., Time-evolution of later
phases in the transfer functions obtained by a permanent seismic source and receivers

3

(ACROSS), Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract NG41A-0147,
2007.
Hasada, Y., Watanabe, T., Yamaoka, K., Itoh, H., Fujii, N., Kumazawa, M., Interpretationof frequency dependence in transfer functions acquired by seismic ACROSS, Eos
Trans. AGU, 88(52), Fall Meet. Suppl., Abstract NG41A-0148, 2007.
Ikuta, R., Yamaoka, K., Watanabe, T., Temporal changes in emission characteristic ofelastic wave by vibrator source and its correction, Eos Trans. AGU, 88(52), Fall Meet.
Suppl., Abstract NG41A-0149, 2007








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




4



 l%#LJXRSxS:}*594
FSa,7-9e8adcW } dc% v
aND>& !kMK&Qf $"a~dc%
I LJXRSLeb¡w[RSVNeb¢?=&
S~8a~ '02(+%;pq`#E< LJXRSyPSYOrZ8s,79+-.3veNZG\zBo|&q`E#'02(+ 1./69)UCn%

aNZ{T&gOqta~dc%
A jhH£]`Ym@RSO`i^u^dc%

5

_

6
ÿÿþ$*" vùÅÂ,¹s¹3Z·0*"$Ï¨Æ"$Z·#*#¼ÀLAPÝ0¾}"vùZÊ#ËÏbð" $¼ÀLAP"wZ·<JMQT<NS#ïÝ .v¿<JMQT?! #>TET:SFMT?3
ÃzÞ«<JMQT<NSÚ#òÅ !10¹s¹ZÊ"ô
+'<JMQT<NS# 0¯ö"'$í! I9IW"ô0¼ÀìÎ#ËÏ Ç4"Ù210
 U»#! .#-!<JMQT<NS$Z·$ }ø#vX#½3LC?T0*#ß· Ý!0#-!ß·¾¢º£+`û10#$ GPS "-0·vß·0
vú#y$vù#ù¸" 0&/,¹" 0I9I#Íh! 3Èj¡/vù#ù¸,¹#uf¸LAP3]|6SDT=NS"-vX
 #-! å 0 3|0  0 vù! #±èÆvùµh+vX#fx#yi3j¡0Ø .1 /LC?OS9#AT?$Ã0  0¤10 ! .®(,f#yi#ôê" Ì!ô_.

"$1 .''¾}#LC?OS9#AT?$Ã.1
!#-"¾¢º$Z·<JMQT<NS"0LC?OS9#A
T?$ GPS "-0v°yh"õ.10# ¾½0
 #-!¾½#Y }0Ó~dù¸#ËÏ$!LC?OS9´#©Ò"rËÏ0^×0  0 ¥ËÏãü$Ó~dù¸<>@K#òÅ}Ãi#UÁ^×.
10 ë*0Ó~dù¸" Ã0ù¸$ç#'2/"a +/tæ0"-îf3ÅÂ0+#0tæ$
AC ;THLT?"-ýhtæ^×3 GPS "-.10¢e"p¤0-"âà10#Ö§AT?R7TÑ#vh`n3áñ0Û
×GPS #¢e"p¤;SGOS91 / 1%ù¸·|Û×#ó#p¤ k10"!01$#ù¸Û×#Ä¤Æ!cº/[#LC?OS9#*#dù¸#w¥\ª!0& +#0
 ¥ãü$£ÔÆ"$¦¶v"²(é)GQTB­ú .#j3 0*ÊÉä¬ "0qlz{#V³ß·"58R>ù¸3ÍâÜm#ù¸3ó÷3Ðâ×0"-ù¸5Q6#g§3ËÏ0"0¥ù¸$++Ām#ù¸Û×3Õ(o2ù¸

7Qzk?;=Rur " }a#5^t`Tou!  yJurjhFTqM9S}a%'1(}a#ur!76jh!
 AX_CU !%'1(}aurFT!V<CE

ur%'1(}a8r!Wlpv~ur@>NILeG
Llpn|OC}cP3{dlp)2*45^t`TToyohashi’m
FT!"7HBQTokiYfMorimachiur """=K:yg[ZXbCnL)2*4\wlpT uris#!!


CEC6-&/,2_.04+ ]x$!AD

A—X_CU !%'1(}aurFT

8

ît L{è´R× }.©±sì ì³tðr¾tñ.$
st!õóóó ,5@9=4;68FI8D;Að°Çp2îtñ)Um°sìHbðq ÙMñ Ð²/AEI> r¾· 0'yu .st.

 36F8 ì³ÍÈ!ì³ÍÈ ,sKk S0° A
EI>wº , e° +" ¥æxb1r¾· xcÑåfË  1ÀÕ .Ï .ÝUm°sì AEI>wº ¿§¼* -#-T. ÀÕ/* -#-(`xb)r¾ xb1e¤.Ê,/. +xb36F
8ì³ , Zh ¥æxb1®Ü.+AEI>wº ·1C?
:I.fË1.  .
 $Î ì³1Úë1ëÎgÔÈj§áÛ.+
ì³ , Zh¶k1.~ï(ÌPo!NÄ äi+-õg ì³ ÔÈ    aª1Ó.'~ï1ÌÆ
~ï!õóó÷ö¦ , ~¢'P Ö Ãul.
ôöò©±sìst .36F8~ï É _Å(Þ# Ý[~ï °1¹¡ r¾·1C?:DG7 .fË Á/.ðYoshioka and Iwasa, 2006ñ
 ~ï!sì»¸_r¾ *.&ßâ.sì!  .1Á.$±t .e¯« (sì1»¸.38B
D<4ît e  Án/.ðFujie et al. 2000ñ0¡í r¾ z v!sì° ßâ) e 1Án.$r¾ v!sì° ßâÆªe z (Án. /, ~ïHÐ²O~!sì°1¹¡í r¾1C?:I .fË1Á.Nakatani (2001)+.¡í !¡í .½ ÒíÂ®W.Ê,/à·X|.¬^! Ðµ ,Ñå. fË.½ ÒíÂ!rV
rV Ò.¡í ~êÒ.ã\ íÂ.$¡í1ßâ-e.° !½ ÒíÂçY.Ê,/.
'°1¹.+-¡í r¾ç.¨Ø¼u1.
  .Ê,/.  +Ðµ ,©±sì }ì³t 36F8 ì³+.~ï1Ì©±sì ì³t d\QJ!ét K\ éJ
.C?:DG7 £.]µ1]¹$­%Ó)øùúÃ

9

 6U93#

 #C!   !

PM  Hi-net YfA=7e` f:=a[ "!
0Q$'-(!>?L4;ZF93#C!   !5]?!/RD<78!
 cJa[!$'-(eOVWS@\ !GVW
"1^DeO!+&%)*$,%2H#Ib!TS.K_NBE7^DeO#a[GXd! reference

Fujie G., Kasahara, J., Hino, R., Sato, T. and Shinohara, M. : Inhomogeneous
crustal structure and seismic activity at the plate subduction zone, off Sanriku
region. Journal of Geography (Chigaku Zasshi), 109, 497-505, 2000.
Nakatani, M. Cnceptual and physical clarification of rate and state frition;
frictional sliding as a thermally activated rheology. J. Geophys. Res., 106,
13347-13380, 2001.
Yoshioka, N. and Iwasa, K. : A laboratory experiment to monitor the contact state ofa fault by transmission waves. Tectonophysics, 221-238, 200610      \`veITW¡{ÓĉJqkgswaI0-DK*ĔÜ[ĞğĠÍIÏ:DĔ9>W+?JïÒF:DJjxgubxhJcwmswa2Ğğ
ĠÍIÏ9XD-9/<XL*ĆđJăē2Č4ēXD-@¢I0DRĆJÏ2óE,W+7JÞK*/L Hi-net JT.HÊüJĘÁ
³¡ĔøÛðJûď2 äóFHW7FE,V*ĔÜ9/äÀE3XL¡{ÓĉJqkgswa2ÖĄæ©ÌIE3WT.IHW7FE,W+ :1:H2U*<MDJjxgv_x2»=:R²ÍÔìIĞğĠÍIÏ
:D-WZ5EKH4*v_xITBDKĜ8F*,W-KĜÍđÕIĞğĠ
ÍIÏ<WA5JRJR,W+?J@Q*jxgcwmswaJg]pwa
ILUC32ã;WïÒFHW+N@¡ĔúJüñ¢ÄITBDKl]funt2Ę-¢ÄR,V*?JT.H¸ĖIC-DRò«<W»ö2,W+ ëíJÐÿIWI*v_xJ¾ó2JāIGJT.I¸Ė[}/W
1IC-Dò«<W+ĝ)ĜěK;QI ¡{J¡Ĕ×Æß¾J£[FU/WÅõ[Đå<W7FKºJ¡ĔÝ¯ëíJå­J@QIKßIĎöH7FE,W+/LÝ¯J¡{I,WFò/U
XD-WoaoANVJčK*ÎHGITWîÃ£2ª³£[´3Ă7:*¶¾×Æß¾2£<W7F2¿9XW+Ýċ[oao2zË<WĒIRÝċF?JąJ¡Ĕ×Æß¾J£2Ï¹9XW+R:R7JT.H£2FU/UXXLÝ¯JâùA5EH4Ý¯ØÛIR¦34Āá<W+N@¡ĔÈ®ĕEK^imswaJµ³£ITV¡Ĕ×JćĊS¬Ç2£
<WFò/UXD-W+¼£ITBDÈ®ĕ¤JÙ±2£<W7
FITBD¶¾×Æß¾2£<WE,Y.+ÚčJ¡ĔÈ®J£[[¶¾
×ITBDéW7F2E3XL*¡ĔÈ®JàÂ[qkgx:*¡ĔåãÛI
CH6W7FRóIHW1R:XH-+7JT.Iy÷|£F½ZXW¡{J¡Ĕ×ÆĈ³R*°ç~JXèSÙJ§ ITBDėôI£<W+7J
7FKÙ[P°êJ¡Ĕ×Ĉ³2ÙJ§ ·ÂS§ ª³ITV¦34£
ZWF-.ëíę/L*& "!!!&!$'  ! ĚITBDéUXD-W7FE,W+
 yÉ*¶¾×Ĉ³[ÛXL¡ĔJé2E3WFF-.Ï¹Kh]rgwdx
þ&# "%(% ITVR@U9X*Ñ¡Ĕ×Ĉ³£[Û¨<Wëí2H9XD3@+?JIR11ZU=¥4JýOK11¢ÊHþWT+ħßĘ¯ÕIé½Jw4@C/@>,:3:G4S=I
xDP+~1K'#&#  J\Z]rIXP?/C "
ĦV>ĒĦDďÎIÎģXÕ;U>OI§īXĆ/+äÛEÐ:>üİ
mpúIħßĘ¯IĭħßĘ¯Iü  Hó²;UĮXÕ:C/U,RTĬßIĩDJ) )( (! 4íĝğ¬H2/CäÛEÐ:> IħßĘ¯IXÕ:C/U,}ĝsÓčĭ ĮPđĨßHR
U±»ßĘ¯IĂTĕ:â¦X­ÁôĞõğ¬DĆ/+ ®IvĥJU3ÝħHÐ:C I±»ßĘ¯IafelñGXÕ:>,8IR0H±»ß{Çê»IXÕ;UJý-ED.U4+Ā7SVC5>, Ĕ®èåsÙy ĮHRT+ØøH¸9V>Ø°ßXðí9<Uħã`afn4ăÔ9V>,´SJ8IØ°ßħã`afn4+¶ÑHG/Ĭ/ĳĲÚEÎģ¥¦»DwÖęE=Ië¾XohdtD5UĄ»XÅ@C/U8EXù
:>,8I_rclgHB6`afnJ ĭ)&(!*$#(&$!!
(($#!'"$)&µH )&(!*$#(&$!!$)(#%&(#!*'("ĮEz7SV+´SXxºE;U^qtlHR@CĢðöû4£
OSV>,  Jìě+E6HÏ HĖL>R0GħðíQæ¬H27Uħ
ß{Çê»IÎģXohdt;UÁÞE:CăÔ9V>, DJ=IR
0GXĈ3SĚĀñHohdt;U8EX¼¦:C/U,=I>OIĜĉ
GÂćĢðHJıAIĜĉGČĪ4.U,uAJwáě3SÀ@C6U¹ªG
NDES1U>OHĳĲÚXĬOU8ED.U,P0uAJąçïI¹ªG
ÎģXES1U>OHį×QàěòHĐ;UXÄ91Cį¥¦:>XġÎģĚĀ:Cė;U8ED.U, DJ=VSIČĪXĊÜ
;U>OHØ°ßXî/C/U,
 É©9V>Ø°ßJ¤Ď4ā³D.UĤTFYGH«ÃQ©XĂTĕ:CP=IßÌJ:G/,N>Ø°ßJÎģĩIDi[bHPVC:N@C/CP+
ktp\ÆHR@CßÌĩDjqaEGT¡5G  ÚX·U
8E4D5U,êHÉ©9V>Ø°ßIÐIÍÌIÎģH¨:CĦËktp
\ÆĭXMF8;8EHRT+ßÌĩDJuIßÌ¿E:CXT;8E4D5U,N>ĚĀñGØ°ßIċĠÎģXġ6;VK;UM
F+ HR@C·SVUßÌĩI¿Ì41CĆ6,=IÿÒ+i[bJRT 6I¿HË9VUIH¨:+Ø°ßJ+=IÐIÍÌIÎģH¨:C  4G9VC/UĤT+uI¿HÆ9VU,:>4@CÎģ
X37VK37UMF  Ú4È9VU, ¥¦:>XġÎģė;U>OHP+Ø°ßXî/U8EI|»4.
U,ġÎģXė;U>OHJ²çI8EG4SēI­òX÷:C:N

12

E=HM=G+*-JQB-ì¸<À8).(+°´.rÝÃ<Åz573]RLQ(æ¨çÞ_8)(8-5+°´<'æ¨çáÊÞ_8).ÏÌ-<ñ28#(+ÏÌ-ÖÌ9"rÝ-Ã-<ñ28)3äÑ(8èê4²·{
i+*,57}9+9ÏÌrÝ-Ã-´\£º{i8wX
µã-{i<)68)<ÄÂ)'8,)%'!-5+ÏÌrÝ
-{i.I=C¸)+8ÏÌrÝ-Ã{i-î<¶6<!-{i<Ð°8)ÏÌ-!-3-,j8)3g6+ÎÂÙï,+8 (.-5+ <®8Î-$n a,Ñ)98

Í,&'-×^<Ø18÷ ÷õøùûúüü-ÕåÏÌ÷ ÷ öõøùûúüü-m¾ .°´<wX,Þ_%'"_p<Ò¬8),5%'wX®à)!-»-¨ç{k-x<5)3-(8«-¡­ABFO)q¯, ABFO.ì¸ÏÌòÞ_ÏÌó)n_ÏÌ6+8òt÷óõì¸ÏÌ.wÃ,%7u9°´-´<wX,¤8õì¸ÏÌ)'.ô.`"37-sÛ,58âf,5%'°´<Á¿ 8ÏÌ<À'8õ9.[-¦³,±0'È +d±ÜÂ§(8))ôÁ¿8f,'b8ëf-h¼56(8õ -5,'Á¿"°´<é9"y(n_8;(8ô!-¨-©3äÑ+¹.ÕåÏÌ<ì¸,qª 8)(8õ@UKQ,5%'
ì¸a6qª_p<Þ8)3m¾Â,.oÍ(8_pË-¥Ö+*½8W(-dÉ}+8!(.ì¸)ÕåÏÌ-Z¦< ,58È +¨Ô,qª 8),"&'.È +¨e<8).~{+
ç%"

Àk9"½v(.±ÜÂÇl,  M=>SÆ

3-È-¨e<,b98)(8ì¸ÏÌ<ði8PUDU.|ã6Y8JQBc-ß,5%'d8)(85,ÖÔ9'8õ!-"2Y8JQBc< ¨Ô,qª 8#(ì¸6Á¿8_p<,qª 8)(8õn_a3ô {¢-D=NT?< 
9/5õ-5,Þn_-qª ,qª,57oÍ,+%"(ôâé9"y(-qªí,§,+%"õ 'ô
lV-°´<À"#(.wì(Ó):-Ú¨-x.6

13

W  47A:9:<?'QG 'ugWQG#,% GPS
qM%Ts!GR3Pc0

1$'(*",$0`Y%K_n'UxniK'vbxf%$0jE%|!0VX'y"n'UxniK3Tq%}{0%(VUxn3Uxn\1).#)Uxn\'\Us
3  #0#%. ! \Us'n"0  'onH'UxniK'n'vbx3Tq%m^0#"0'.$iK(DeUxn'
U/%K_'`Y(+&Uxn\a%$0'.%!n'
UxniK"GR3Pc0#%./ 2-0q'hZ3c0#"
0  QG  G1!0GR(F#ka3]%Ld1n'vbx$'" '.$GR3r,Nz~%Pc"0.$ 3tr,O$( #%"! I3=C@6\l! ~'GRi
K3P/Jpw"0
'[S%  \l';5>B8 

14

qM%Ts!

|Ç!Ç iw?ºxÂstackÃ?|%I±*$I?@²&C:E=%#© =o>y29q3IMv
i3I6D>@/?G&=°«:tm:$I#
 ;/K*"3->m)I>"¹ª>´¼3I6D>@­=´»*±:$I#g>  [UW:T^bXa?VcRM  :Pb\`bO29 m?´¼MuI;"  ZNW±;=I#e;=89@/?¨?VcR»:@Á)=%*"´¼FT^bXa*'I/;M¬'I;:+I7.´»MH29(%6B&*?k*hn>=I2Ä´¼°«µ³?®¡
E3#5/:¬'l1J6?*½s½ºx}´¼°«Â
¢29 Ã:$I#  :@$Id?½0;>iwM¶2$L49%IÅ|M >¦3Å5?½½¿@À)H·i1J9%I?z?j:$JAG%#LJLJ@¸ºx?½½¿M  §>µ29%I#/?~x·i3I@  ?j:$JA´¼1JI#
5Jf?zM8
6FYNQm@ºx{*'I>26*89iw*¤£>89%,#iw;_bS]YNQ?@¯,¥HJ9%IG&>"Â @ºx{Ã:p29%,#C6½½¿?m?Æ?zmÂiw;29%IE?Ã;5Jf?zm;?*ºx{:<?G&>r3I)@|Ç!È>¦29$I#|@  ?z>3I  *ºx{>G8
9<?G&>r3I)M¦26E?:$IÅ  @zf ?¾;29

15

!01  (+(,&"*.()(+(#'$%

-

 

/

16õùö)T /ê{.Õ8ä ìíõê{¬ììíö÷/Ù§ud)9ø 7;96-ê{§ù.{-/!2(.~·§.hz/|Î,F?\)Þë:9øê{§r!9-÷ê{¬ììí.¨§m.ùb.hz.F?\¸ (ø#:*|¬-Â³9~·§¤m.~·§5¿,&(*;9ø#./ù.m75;96- NT
*,8÷Ôlwë¬ì.æ§*,9*;9øúúûøxhÚÖ* (.¡Û¯c ðºÚÖÅÂ!9²·/²Ë,¬oõÀÆ-/ o¬ö-|® (,hz<åh (9* %{÷ÞëÚÖ.j-Ûµ:9òÇ/õùöüý¦.K?V\E²Ë,¬oõo¬ö-|® (9*øõúö=P[

Eáé5}4(¾¢¬ìÆ- (9*)9ø#:$:-'(Á£*ÀÆ,ó¼-'(b^-Üà!9õùö`Ä.°»¬/v¬Ý<»-¶47:(9À ;:;:/v¬Ý-69°»¬< -6&( Í.Ð)«-¥-k:9*)96-,&%
.¬o.²Ë<Þë-Â!%4-/  ¦.K?V\E<-|®"9*)9
ØÉ7:(96-  ¦/ç±´â

*NYKHEUõö*0:95.6gÃ:9ç±´â/©+8¦!9Èì.ïi<NIKY) 95.)9UYLTZDG-6&(´âÆÏu-LW\QYs)9*5&(Ã7:(9 ,7  ¦1.kq.p-=P[E.=\L@?X=JS>YK]¡Û)8#.¾¢Ý¹lf.¾¢<y!9êÛ,ÛÑ-,&( 3.
î¼)9è÷=\L@?X=J-Ã7:9

  S>YK].BM

OAS/½CJ*~·§685eß:9÷S>YK]_,{BMOASaã.~·§¾¢­5ñ:9ø#:- (/­ÒÆ,
G\TX\Eìí685/9-Êìí)hz<A]R]G\TX\E %
NIKYS>YK]<ª (ômÜ×< 95.)9A]R]G\TX\
E<!9%4=\L@?X=JS>YK].BMOAS~·§<Þë!9hz.~·§685tm-ôß!9*)÷¾¢.¢-ÌÓ<g¡Û,*n¼917   7çòãß3&1  ¼J>.68,G-G6óÚ!F À:7Â68íÄÈê7<!¡¿2F,G8ąĆ¼7iX[pRn]R7Ë¾!UohkoSË¾3'2C#ÈêÖw#1(? D2
F,G6¢&_l[VSi28OpdpUohkoSJ(F.@6  
Üª7ýË¾J  6Â%*F°ä!Fs\jobl 3åÏ28Ā28il\hmRUJy)ĀĂ\jobl6Ă07  ¼JE¬1F.@TX`ú2öE65F
& &5!DÐ±ú28!/1F6ì;.C6OpdpUohkoS3_W[lgLl[p6C/1ØÖ7U
ohkoSË¾J¯F.@©5vÙÐ±J¯F$3!2"F=.æá
61A_l[VSi8  f]`Üª7æá!qâÖ2F76¢&íÄÈê28*+  f]`Üª2Fþăÿ  7çòãß3&1äÊ%GF÷ÉÖÐ±3&1ÁAðä578Àô ±2F  28rJuIFøË7Àô J»F$3JØÖ3&1F.@çòãß6Àô ±!äÊ%GFqâ6çòãß7Ð±7Àô 68#7ä!F!,7Á7A78Íª 6CFA72Fçòãß7ÍªJq 6}0¤A°ä2F!Íª6¢&1ñ³5çòãß
JxF$3Aðä2F Ð6Íª6½³5ep^8To_oUp2EĀqâ6¸·7Íª{±CEAqÃ8²āî¦gLl[p68To_oUp!ÓDG1F72Ā 28KanSgLl[p7Ð±6Ð6ÛÝJyāz9NMkKXõÅ6Ó
DGFnpeXgLl[p8Íª!(F3P]`Ogtë7vÙÐ±6
"5®û!FíÄÈê7  ¼JÓ.548P]`Og7w
npeXgLl[pJÓF.@  2ÓF~:7®û8" KanSKohþhkKohÿ7Ð±AÍª6C/1(Fî¦OgZ]`!Íª (F$3JÉ6(FA!   28µJÓ5.

@OgZ]`7®û85§Ñ7ÍªÐ±8Ó1F¸·6{(F!Ð±7,H/.¸·JÓF3Íª7®û8QjoZl(F6E=.Í
ª|¾7w¸·JÓF$36CE¡¿6 ªÜª6¹%F$3!
á2F ¼6AÍªÐ±!Fðä5A78  ¼7Î÷2
F!Ā±á7C  ¼ãßJÓG9$GA ªÜª8ïµ2"FþĄÿ,7s6à´(;"$3AFāKohB  ¼7Þ­±8ðä2F  2ÓFÆ«Ë8î¦8cMY6AG1FÞ­±!²3cMYº§7"¶3£%¶2ðÔ&1FÆ«Ë7º§!&1&==.ùÞÇ6C/1ýèË!ÕÒ&.E  è6C/1ÕÒ%*.#7Æ«Ë7ô6¨Ì!é"1B¥7Ë¾µ!ÕÒ(F& &5!DĀçòãß
7ùÞ­±8×BZoUp547ùÞ­±6È;1î¦8ü65D5Üª

18

=(PĒ
¤ÀCeWlug\{}`KĄô@Č=(P&  =DCì³»Sª4<)P8J%-\ygq4<Dă-¼)&ÖA¢ĊLÉ6B
nWb@?C´ċ=\ygq5Pï»-§.)&
H8 CÏ²ÓC¿°Dÿ¯CnWb{rz =(P8J%]x}knWbH=A÷ą5P1>C=.PeWlug\{}`-¸ô-(P& ç­A¶3Q8Ï²ÓSĎ)º«±=÷ą5P8JAD CÕSî½
5P¸ô-(P&4,4@-N«ĈADä'CèAM:<5F<S«×5P1>D ĉ=(P1>-¦)&ÍCå=D«ĈCè>õÑÒSá5&Ĕ$ĕĒ×«ß@Č>õÑCÅæ
Ĕ$ĕ$ēĒÜ4<)P "!åH==üF8M*@Ø=ÈććĄ÷ąòíSäč,ù48&
7CADÆ©C÷ąòíSÜ4<cpjCÂðCIAM:<®¹48KCK(
P&7QNA;)<E>>+OÄØ4<+0ďēĐ >  A¤Às~kSÜ48KC&¤Às~kSéIR68÷ąòíDÐûß¬ÇAó=.P& L

s~kAD¦Ê@äč-(O%¸ô>3QP»ïA(R68ÌäSā¾=.P>)*Õ-(P&RQRQK C÷ąòí>4<% >¤Às~kSéIR68_ahvSù48& D»ï-Ď)G?¦0Cfw}mzÃSMO
Ď)^}qy}]ÓÃ=Ø5P1>-ïA@P& ¤Às~kD  Èö,NCdWu}]S^}qy}]C¥ĂÉAÜ)P1>-=.PKCSÜ
)8&¤ÀÅÒDþÍÐû£=(O%tzfq{\^AM:<¦fw}mz@3Q<)P& >4<D  C % ď×¡DÚÛÎĐSÜ)8&

s~kDYn~qaâCs~k7CKCADU}fXWyUapVzd~-òà3Q<)@)8JA¥ĂCUl|]pVzd~SÜ4<)P&^}qy}]CdWu}]D¥ĂC  Èöď!#  ,NÞÚ
5Pē CSÜ)8&1C  ÈöD  ¶AM:<¯ÈÝËÔÈ,N  tW\|ã Cç±S;1>-=.PM*Aøö3Q<)P& ¤À
s~k=Dđ(Pt~\SjyZ~A4<¤ÀSĆ¨48µDđ Èö,N
ê3QPē AÉ4<¤À4đ C·ÙogpT~AĀëúý3QPĒ7
CogpT~,NªÈć2>Ci~dS  -O94<adg[}]ÁS
ñ*Ē1CM*A4<>/Q@0đ AÉ48adg[}]Sñ:<)PĒ

19ęĞĚĠġ¢ÃIâ/B9 þĎ)HG9}è©ªº9ß4:9Ġġ¢ÃIâG9$DĠġ¢Ã:RufuXsiosWI,G/Açæ5,G9ÙÄ±DFBLs_QNoLZhMp]u9S`bRhÙÄIĘ&ÿª4%
G.9/ALdrWhMp]u9àº¢9µĔ#E>5J69$HG(5$4%G?/võæ89  ¢Ã:^Ndl`VqsY$³&  g`b|w9ï´IÀ2B9I¾4%G¼:(9D 7à¸IÀ2ÆđđČþĎùòIkuVnscęÍĚ8Ā~Iĕ*/(9þĎùò: 9«ėË#EÚĄ*¤&9ĂČ7au]I·*3G(9ùò9Óß:ě£ċVr`V59Ë4GĠġ¢Ã9 ěÊñæ7XsiosWÙÄ9    769Vr`VIkZ]uVr`V5*3Ġġ¢Ã8y!3CG¹û$F.9Vr`V.9B9I  Æ8Ë)-G¹û$
G!;  9XsiosWËI·/ 8:ě  Ģ5#  
9kZ]uVr`V$¹û57GĜ.9D 7ÙÄI  8Ë)-G(5:¿øæ8¬Å47(5$G¼$Ā~*/þĎùò4:kZ]uVr`
VI²Æ  Æ8Ë)-G(5:%EA3Z]`UsWđęĉ² êĚ9Đ¦9]NlsWI  8Ë*.9¶:ô9×ÈäÁ§8Ë*3aY]N[,G(58*/
.9 ô9×ÈäÁ§9ï´:  ë´$Çĉ
4 Æý8Ö=G5:G#8»?/{ē*/Ė5*3  Ë9Ý
9/A8Z]`UsWËđ9Ê¶8ĝĞê9ÓÜÆđ$á+G(9µĔ
9úÕ:þĎ·¶8÷ ¹û$GZjVbp<9µĔ5úÕØ:¶8ć
=G
ęğĚ°ā9au]rTu °ā)H3Gau]rTu9z8B\hb9¢É0'4Æđđöìþ
Ďùò5*3âG(5$4%GB9$Gå®¯ÏęÍĚ9   B.9
v24ě :Þ®8"'GÐĊÂÌ9/A8Đä)H/­ąč4Ęºó7au]rTu4GęÎãtÛěĚ
Ĝ¼:å®¯ÏęÍĚ8ĕ*  

9hKumOPLę\hbĚI¢É*3BEě  â9Æđđöì
þĎùò5*3â4%GD 8*/(9au]rTu9ď½:  ÆýIù
*­tąč4Gß8G?/,48  Iă!GÄ$9¥¨î9éíÒĒ8ā¡)H3"F¬Å8 9¥üÑ«ėI÷!G(5Bß9v24G(9au]rTu:ĈÔÖĆ9  ¢ÃIâ3G$euc9ð8DF²Æ  8Ë,G(5:xó4GĜ*/$13Z]`UsWđ9Đ¦9]NlsW9@I  Æý8Ë)-GD 8713G20

 i'!¢{|ÅÆ<   ¡t$?0>#5XCZ6q5Í
Îum@ 0>8,ÏÐÑc75i:Á4}v31x&0
>/8=w£4ÏÐÑc25»~@³&0»~4!3>;4DXLD5k@ue$*0>#?6·«4FYRUYE(>
°>MZJXCZ40ÏÐÑ4i$*>2&06¦¸3
1>,-  6PBIWSVÃ51=ÊÌQLN5
q5ÍÎ@_ &0>
x¾5KBOTLDWYG6ÊÈQLN]\1>
ADXH5g`2&0_ (>sh46pdPBI@´º(>-"5 °1>sh4;.06+5 4¶=3,9z 5AYR@^&,#5AYR4/06b§40rj(>ÊËÊÇ    5µ~°n2y¨ $0+?<5»f»¹hq´º¯­46$8%83´º[5µ~°n
>+?<@]\4@&0y¨@®>4  

5;3Ã©@¤&,²165pÀ²16®,#2:3;3lÂ¡(>oÊÌ À5k8,6FYRUYEkÉÈÄ)?,sh5kªa5ue@¥(¬6FYRUYE»½Ò5s
h5k@·«¼1¥&,:5¿MZJ5sh46
o55s1FYRUYE$?>2±3(#21 >21

°´± p~k1CQJNQBj1=%/%<08;y®-t  p~1E?MQB>¦$;LDERAPFA1%<j¯n,.1
80<;>¡X#8 1ohs0d#+gDEF@QBb«1ªq)/  0i#'1z2[1APFA0i#+  p~>71-$;4([1APFA02_5192/71-Vr$;
180[1,/oh02 ¨"<(w2gDEF@QB«1q6-=:,WS&%!=%0%<;#(*+'1w
2cS1j|],2,%jl1|]0Yf<)#+#4
1`>180; [¥1APFA%<;-Tj%<(80;#(*+,2APFA1%<>j1%<-5/$UDEF@QBb«1©"°DEF@QB«­±>  -$;-'<2«¯n,2¤#(Yf9 
v1  ¬08:Yf>e:\#( -0x$;'1ohj¯n,2Z1Yf1    p~-   ¬1    p~-15£5]0/;U²Yf2}af0 1w-$;-Yf2j¯n,2IOD-/:5£5]12   ¬1    p~'171,;

m 2-5 GRECQJNQB0´³µ1¢u;oh1^Y
f-DKAHOYf ,;3DKAHO0$'§<+;1{22\|./:"1tc2 ff0 -  ./9T g0{./:T   VhcxX-2   #.0wbR$;:*5  1dcO1f]h-2@HDEH?i2P1Vhc=u,2\|1{1i.Jm&:*
5SJ1NT_Q.%,nj$;:%%/8<'-6)1Vhc8';,%4.ltc1   Za1{-/i=@HDEH?%,%4
SJ1NT_Q.%,2nj- /!/:zW|}02Vhc ';*YU
0yVhcpK-@HDF$;:Y`=k%,:z"1YUyP2SJ1V
hc-+*f]hywbR$;*YU0SJ1Vhc-2n$;'yor=3,%4zor1[ $2yf - f0 Lqe[0/:)1Y`1 1^QMc2


W| W|~0,E@HDF07+,@HDEH?sv=ZR$(*YU1B>ACGI1ZR23    m
#%']{rf $ 6#c[,wx,]{r(,ql),z-        m
)*5>@A:L<,4  i)5]{r )#);JA;, 6  )5)wx,]{rpWPd+~65pW,ufT-wx,ql,  )*5
 N, 6-|_+`5^(4&y_,SQk15#0!6"6,| +i8s'gU+ 68X4)-a*c[e~h+]{r 6^+*5c[+-/6(7^+*%#c[|6#BM@+i'PO,2*V8s)+24;JA;, 6,o8X4)(5   }3R65RY- t+\v'5#0RY,Z]{b b(D9?EKMuj+*5=LFHL<(=LFI
#c[,t{n2.]{rEKM>G;CI24

pjU,z)]|p&5'.)!'&500YSTST'\z)s*\u%#b[*,SZ,@J=DL'%~65s+r*5'9k$#@J=DL*)5i$%s9
z!5#/*,SZt0@J=DL'%652*SZ9K?NIL%16-2'*)5 ^¦¨*,@BC<N>  ?NIKN> &s+r* +f+5YS&#b[+sa+SZ'@J=DL9%
5SZ,  *% 

'£

+zh|'%5¤E:A'%SZ+  +Uo9k$#E:A9W%5s+f,  $%0¥?NIL+  *)3)
@J=DL&.5'~6%
5'85+ ,g§&me#v'P!5&sa+SZ977'K?NIKN>%SZ+@J=DLt0)50+9
l!K?NIKN>,)q{5R-y+2*sVS
Z,HOK;cn*2$%
 '65&,?NIKN> ,s¡&,@BC<N>]u¢&5sa&K?NIL!5#/*,«¬9_e%
7'cX"%HOK;cn9%16-2^¦©*,97

9cX"#

b[*SZQd+]|pjU+ FMO(+2*cX!59#0+&^¦ª @BC<N>w+Px}#b[+@J=D
LSZ+GO=+]*4`+@J=DL~65

25

#J!YNUZbd?`Sc]`cR=G89~q09'I vj>´>
.>2K:#J  6,°09`Sc]`cR05;*=YNUZbd)
=<89$J-;)L(J!
{ÇÈ?4>G%=09¼Á|:`Sc]`c
R05F>;Ä4KMnA\d`O~09T^QXaM¤05F>:#J!³g=±º)<+<Iª$_NcT^QXa)05-;)L(J!ÂÇÃ>À µ»¯­=G89?  ´;>y=m&J5E= y£p=Sc]`
cRMe¢=l3/JM<$}x)#J!Sc]`cRl?Æ"Ç¥¦;<J!4>}x>T^QXaB>ÀB>¶i?©s:#J!TVWPcRzM  4>%7>¼M  ;1J; zÁ|:>jw?

 >

jw; ÂÃ>  ¨½>  ~;>¡D¸D§o:® .K
J!{ÇÉ=?¿=>#Jµ»¯­=G89t».K5µ»M¤1!e³
09L(JG%=jw:#J¬T^QXa>zI=¨½>  ~=
1JT^QXa)³&9$J!
 jw)se>zo>}x=? µ».K5jwo>M k
1K@G$>:©s:#J!0(0<)HËÌ~·>}x>G%=jwo)²#J}x=? ¨½=GJ#Jz[dQ>)I)h>jwo=¹<
89YNU=<890C%!05)89s=M°1J6,:?fro:#J!4>}x=?>G%<:°M1JÅ TVWPcRz)¥:#J}x=? jw?  >k>zo>¬ «x:® .KJ!5;&@TVWPcRz)  ¥>}x=? 

{ÇÊ «>ÀM°05«!¨½>À)uI¾

26

-Y-i,] "8*)8!!+6Xe(!0* -Y{]/-] .Td,+8-5+lf,.cy 9%X
e-  ;( -Y-i,] "8*;£18u-*+6Xe-i.  -Y-1,"8z8$-¨cy!
%Xe;`],^"8%2,-5+\;"8*5

 




0%

 

 )7V;EFGARC-[«,:#8%2-@MQSF)8)
.[«6·DRLP6  ¥]KSO?m~!%¯¶.  ¥-DRLP)8$-5+KSO?m~;µ¬'(rk"8°W;"*,57><RI>-vª.b)8$-;j²´,"°U,><RI>-vª,58EMBHPJSB-s7(8*:8°%&!¯-W,57  -nY-i{]}(69(!0-)¯©-i{],.h28*)+°­³®g -6 m~-DRLORCF=NRC+¡,p!(6lf8
3!9+9.©-i6&lf-_*(3g)8
(DRLORCF=NRC4©-i-6;V-6*!(-5,") .aV .rk-DRLORC¥§ .DRLORC-
6;V)!%3-)8-5,DRLORC4i-6.|q-6*!(¢¤)8) .rkZ±-ot¦,x*"
8-lf|q- wZ.27
 3¡oDº& 3j²2>2r.@> >0=12wD  ´1#@)913j²w2rD  ´1#@¼@(2|j²2>2¢¨p3 ´/0?Ñ
"A3Á×ELaQ2n{/$-®-@   ´2n{2|13Nc]_cMSG^cM2>/$-3  ³´/0@Á2Nc]_cM2SG^cM3w@/$-:"A=?3'+/#Ï(>
 2LaUL2~¥2u7´2<>Ð.B>½¦e2Í3°­$08$BË§»·2°­&@£¥2j²w25 .BÏÖÐEcTHG_EQ\F`Sd1,-Á2VdSy.3qv#A@EXaMn{2~¥D>%9ad[Q\F`Sd1=+-XGKQW~¥ÏNc]_cM~¥2ÔÓÕÐ=?:Î:2Dy?É- "A3HG_EOcM1=+-XGKQW~¥
=?:Î~¥2n{r?À#A-Ñk~¥2n{1Æ0+@)9.@¹«Ë2=0~¥ >%9~¥2C
+-0n{.3Nc]_cM2Ê2HG_EOcM2ÌDÄ!@¼
@"AEcTHG_EQ\F`Sd2±.@  2=1Ë§.°­&@£¥2~¥>%9C+-@|13HG_EOcMDÅ&@¼3ª VPS`Nc]_cM~¥3ad[Q\F`Sd2JUWI\/ªÇm1¾.@  .3È>A)2£¥D®@)9Ãs
0Nc]_cM~¥D¾&A4HG_EQ1=@n{2Æ¯DÄ!@"/.@)*$6+) ad[Q\F`SdD®0/Î~¥D}9)2YGRrn{1Æ0+--$6 ¤2©.ft10@
ad[Q\F`Sd3n{1ÌDg0´2Î~¥1JUWI\D¾
&A4=
 l4ad[Q\F`Sd1ZSbdQ¬2\F`SdD®)|D¸=ÒZSbdQ\F`Sd3JUWI\2¬¶;.@hC?1ÁÂ2¬.@/¬@ÒELaQ2zn»·/$-¬1
Í10@j²¬3µx1¿i&@/


28

 

(*5·'Â ->FH=Lk·Ã-L:QET,'5¸%&>FH=Lk,sc+y&-

 

5-

 




>FH=Lk,wx-#&,qi·(@SGSAT,wx+2%&/5¸,$@SGSAT,wx,U£+ ·}\-vswx#1,'1 

¹}'5¸"'  ,}\8 (&·>FH=Lk8Z 5k|p,  ^}µ  ¶·L:QET,Ã¿¼( 5(·Wsb,}\- (*5¸,qi·r,} sc 5(W-  sc 5(+*4·t+v
*sb81#3 ¸+k«8­ 5#0+8´ 5(·24v*sb§m(*5,' 5§5¸  n,±¡o*),²+24´ª³¤*qi+-V¨,2+e'-**5¸[.]hk¼º 'ASMPS?k»ºº ,qi¼º ,½^,´ª'5¾º <;P9BS?+2%&¼º +¬*%&/u,k`8!&5qi+-1%(¦°'a*qi1 5g¢5(%&RTKDL:QET,>FH=L8X
©x 5(,®sb,²_&/,²8z 5#0+-·=TJTASMPS?8¥¸9IR?RTKDL:QET,>FH=Lk8d`+´©x 5(j+·<;P9BS?{**52*ASMPS?k'=TJTASMPS?8¥¸",·GCEQ
L:QE+2%&´k|p8f4¯#+ASMPS?8®~µGBNT
BOS¶Y8 6.2¸o,ÀÁsl'-,2*Y¥76&
5#0·wx*85('5¸29ÙßÚÀ1$A@PGTZQI^`L ¡É5  5Ë§6³Á%!at8046  VQSf©,-+;
5-1Ñ4  VQS>  VQS4Ì&@;580 Ê4l°$
A@=43-+ 5|n5+:À3  5PGTZQI^`L6

25·5;50Bn~5bÓoÙØ^X]Ú1cÓoÙqÂ¼Ú4
C"/»/9@ 8'n~5Ø^X]5Ä0@Ö325 3n~pv$A/;Ø%3^X]0@#1¢8%n~Ø&@1Ø%+Îq0^
X]5$  5n~ª$A/%8+:4
n~5MYIS]g$A/%8
 #5w¤Ds«&@+:463!1;Þ.5¨@Ý.:5¨6
MOQH`JD&@Õ4n~50u?¸D%/Ç%C(@¨0@#5¹¤ 5Îq5×6´²4$!3@#5¨6£5­¯¥3205MOQH`J5Õ4;¾CA/@#10?d5 UGN4=-/MOQH`J5w¤}¬%43@#1DÍ@h0@Þ.:5¨
6<<5ÈE,¨0@ÃÐ¿º0MOQH`JD&@Õ4Ø%+
Îq5n~D););MOQH`Jk>{?Ô/<@¨0@)5Õ
4n~DMOQH`J%3-+ÎqDÃÐ%//5k5Õ4»
&@À@.8?

 




1kD&@#14&@##0MOQH`JD&@yÑ5)A*
A5  ±³5K`W]5MOQH`JD  1%/ÃD%/"7=
. 4  5qÂ¼D25^X]4Ä&A7=D»=
)5+:
46n~5Ïx4iUGNDÅm&@#A6a½4ÏxUGN1%/µ>A/@;50@Û¦5=4»A7=ÜRLO]n~46Ïx5¡zj5r9?$A@FT_Jn~6¡;Ér95oÙ8+
6FT_Jn~DÆ3¡ 5r9Ú4e:>A@)A  4iUG
N43@UGN6\`P[1»/=Ïx5¡zj50a5¶®D-+;543@.8?¶®Ò 6Ïx5¡zjD 1&@1


30

 

  


&(5 *Wz  +&(6iZD:?+JMAI&476*%D:?*FLN>H;CK+c{)34Ok&(6iZD:?*c{h%*FLN+  )
6FN@EK*R 4t476Ps*`+c{h%*rf>H;CKFLNo+~h*D:?FLN*  T&/(&%6*%c{h%*iZD:?*FLN+
&(6!"  +<MGK{%6*U  

*Sa*c{qh)

6eY2D:?*FLN351\Wl(63)k$,3¡}j*=>BI)#$ ACROSS *^S&$~[bg9y *w
&pd)#$Q$!(4ACROSS *^S*!0)V|=>BIu%6&v87$.*+
ACROSS 9]6P%+(+"bx %}j*=>BI) ACROSS *^S&$X_')#$6 %)-!3)mn LS8000SH *3((=>BI+

31

ACROSS `PW

a(tk§¯±,

ACROSS 35:A¨#)¹& n¯U*

ACROSS `PWa) ACROSS ]|Y n ¹ylUg)35:A
W )$L¶»·GPSACROSS `P

Xe¾¿m *)¸¶¼·

zHM pq)¸)¹'£s¯ ´'*)ld¸r ³589/G1  ))¹& 35:ATin¯U*inojµ :EBI835:A
¢"& ¹35:A;I8m¬(LT8500)%uw¶·35:A '*)35:Am*;I8 C-D8.A
©P '­P*`P R *Ti%ª;I8,^° )}^°Q ³[³®d7>< ²*\ACROSS `N   )a,) +)
ACROSS `«{  35:A,¥O)LT8500;I8m:EBI8J¬¤¡*24 =9<kAD mf GPS

Xe¾¿m ±)& 35:A,xb)6G2I 'SZ,;48Dm)¬V!)

h¼»º ¦v¤-0F5µPc,
½ººÀ¤@-?IDjµ¡_~:EBI
8,K£°%

32

&bg"1BO91PE(wV "#- 1PE]"#+. -"!Zz-KR6R!*-c¤# 10PPM/ "

,a.^-":;?J#@R<v¼!

u" AD vr0

 -"1P=53L1;D2M<R"Àvh0}! -( ACROSS "k­©#x& ":;?Ja. -#u AD vr"I;<R8O>80 GPS e!
o --o#Ç£!=4>8.wÇÆI38O£
Yd".! +. -­©#

."X0®.$ ACROSS "k,"ª0 -´[-YU!|Á!²¾0

j§0¢ ¶"½¸_!³© ACROSS Â!*-\n0$!³©.H1GRMtÂ±"@R<0·¹ -¬?NKR<­©0²¾Å¶#°f±¡!*½¸_! ACROSS Â
­©)H1GRM¯³` ³©. -Å 1998  12  + 1999 Ç!  ACROSS Â­©0¦ÇQÀº¨»·0Å""\n#¬?NKR<0Wpl~w{k\.Äq 100 £ÇÀ;<>7P90Å.+0%µ/-!*ÊÉ"« \n²¾ +.Ä:;?J" + ! -Ås 2-10 !¢"# 1998 
12  25  + 1999 Ç 13 &"\n0%µ/("-|Á"|Ã# 12  14  +y& - i¾¿yÀj,¬?NKR<!*-i¾#T²"À"'²¾. -Â­©#Èm0o!»·

sÈÇÇ sÈÇÆ"S¼0w(";F8AMCR8t" 1/1000 ¥"½ ®+.-

33

--/ 20ÐHz  302.5Hz ×Øm¿g$--#]·¯"v,DQ6° ¹*-,40Hz SÁ"¹*-,:F6@LDQ6°$Ë¿"),(#,
¬ 20 Æ#:;>5P7#\ 80dB "Á~*- ,-*#Wa# ( SN #³

SN 

20Hz cÀ/n#gÑ11 ,n,:F6@L". $, Ä , . ,Ä#Ë$Wa#DQ6#¬ 1/1000 ! ,/ AD me#G:;Q6N>6#-"),(#± ,:;>5P7ÆÇ

100 ¦!#c#-$ 10-5Hz !,¤ ,c

20Hz, *G:;Q6N>6 GPS #[Â{#-$ 10-6 §{± *-,-*#Ä#Wa#COQ$$R#DQ6#COQ *-(#,z" 10-3 §{#-, *COQ$ 10-6 #
-"!,#Ro#DQ6"z#m]( 10-6 #4Q<Q!+ -") $_Y!²/ ,¹! ,ÑÔÏ&'
 «uZsyWa8:?IÌACROSSÍ¢ ,»Å·¯ÎÆ^Æ´¨k»Å·¯ \,Ï#·¯#¸T$ÌÐÍÕÖmGPS ["b ,ÎÌÑÍ¡lm]"v rs ,ÎÌÒÍ®| X- ,Î,Ï#) !²/Æ^Æ´¨k»Å·¯/t ,'# µ£dÊ +Î-"U ¾x¸f/½VÏt£"dÊ!,ÌÐÍAD m#G:;Q6N>6#¾xÎ
ÌÑÍÎ
ÌÒÍb#*Î
ÌÓÍ0P=32K0:E1L;QÎ
ÌÔÍ<2AH>6MP9¼
sÎ" }É½V/Îvª/¥Ï#­ 10-4 #«{$ i# µ
_Y"Ã, . Ï&p#?MJQ;8:?I# h©
nq#wjÈºB>@OQ6"¢*-,¶?MJQ;·¯

ACROSS #`W·¯¢ , ,/¿%Ï#­Î

# ACROSS #`W·¯$_Y"t¢£, . Ï

この章に関する文献
森田裕一・浜口博之（1996） 火山帯構造探査のための高精度小型データロガーの開発．火山，41，127-139.
Nur, A. (1972) Dilatancy, pore fluids, and premonitory variations of ts/tp travel
times, Bull. Seismol. Soc. Am., 62, 1217-1222.

34

O'Connel, R.J. and Budiansky, B., (1974) Seismic velocities in dry andsaturated cracked solids. J. Geophys. Res., 79, 5412-5426.
Riesenberg, P. and Aki, K. (1974) A precise, continuous mesurements ofseismic velocity for monitoring in situ stress, J. Geophys. Res., 79,
399-406.
Schmeling, H., (1985) Numerical models on the influence of partial melt onelastic, andelastic and electric properties of rocks. Part I: elasticity andanelasticity.

Phys. Earth. Planet. Inter., 41, 34-57.

Sholtz, C. H., Sykes, L.R. and Aggarwal, Y.P. (1973) Earthquake prediction: A
physical basis, Science, 181, 803-810.
佐野修・柳谷俊(1998) 地殻の精密連続観測から何がわかるか．月刊地球、20、
172-176.
Yukutake, H., Nakajima, T. and Doi, K. (1988) In situ measurements of elastic
wave velocity in a mine, and the effects of water and stress on theirvariation. Tectonophys., 149, 165-175.
Wu, T. T. (1966) The effect of inclusiion shape on the elastic moduli of a
two-phase material. Int. J. Solid. Struct., 2, 1-8.

35
3°®o«^VX ¬¡
 >¢z£*¬¡!
&&!o«^VX£+ ¬¡!³[ ¬.$_-*`¨¦*(r­L *Dx ~a" U|.l*&  - )' ¤*°[ ¬!d¦U|* d¦U|!E´¯s+~a ± U| 8259c  *±[.$_-B§~ad¦*= ~a U|8259
+* -)+C~a U| ¥-+*  (±[ ¬.$_-*(U|.F)P  *
jd¦g ¬! (~tU|.$P*#±[ d¦g¬ Eq.iW*()r­LDx ~aU|.$P Z* , ¬¡ ±[ h_!592g U|T #59
2g U|T.F)P%!±[ ¬.$_-§~ad¦*(592.{  * e 3°!^VX£+¬¡ N ¬.Qw*% ¶µ*¬¡!d¦g ¬.³[$_-* * e²±!³[ ¬(U|.y*te*³ M
d¦g¬¡. M A nM d¦¬L© **R&) E. *³[ ¬¡!°d¦ ;<4 e &)E*(Qw+`= b}d¦*pJ $_-d¦*e ?@~a U|T.*\J $_-d¦*e p\~a U|T.*  vfY(=kª §d¦.*~.mK*()
 I]OU|THT._y* Z)
 U|~t uS!- %++ ¬.Qw¬ 71036/:0G*
36

 3-  *(   ,#)( $21 &

/. 0 ,# %' " +!

37ĄăĀÌß948BIE
ôÇnfi )ÉÇå¬ okz~K²Ýµ# Ìè!SM 9

48BIE·X£ò'+&¥ÊÎáû­óñ|Sd U©'
p.+
ĂÿVÛuí (2003.10 -)ăÿK²ÝµÀuâ§ (2005.04.14)
ĄÿuÆâ§ (2005.08.02)
ąÿnfi/2F9jP (2005.12  06.03)
Ćÿ/2F9ø¶ÚÖZ (2005.12.21)
ćÿ1=CIï¦ZbÆ ßÖ(2006.03.07)
Ĉÿ³»¹H^hÚÖZ (2006.03.14)
ĉÿìæàlÂã (2006.04.28)
Ċÿt¤PþðH°¸Hø¶wËÿ (2006.07.13-08.02)
ĂāÿcuÆ¨Þ (2006.08.04)
ĂĂÿù5G2DI<Hï¦ßÖ(2006.08 - 09.10)
Ăăÿ5G2DI<Hø¶ßÖ (2006.09.20)
ĂĄÿ÷¯ÑÔßÖâ (2006.12.21)
Ăąÿb79;A ßÖâ (07.02-03)ĄĄĀK²ÝµßÖx ÍÍ bÒ'*Rr!okz~ K²Ýµu\/2F9ø¶ÚÖ-ßÖþsăÿ
să +mLs!u ªÃsø¶ÚÖ ßÖ¼+Ýµ u!Çìù *%Q )!g_õ,x+&øe(+qéT®# ê l×!$.½u 60:!
Òąāċ{ÙĂĆċ$+ Ýµ!'' Yu-`*Å*ë*sN ´Õ(*'yW!ä-v&x+ &ø¶!W ă1þsÿßÖ+±]È!º¿[¡ ("ø¶ ßÖOÏ+ sĄ!¢ÓÄßÖ«}+ø¶ÚÖ-üe+& bÆ!Ý
µ ¿ ýç9?I9ßÖ+ø¶ÚÖ%îÕ-+ø¶ÚÖ!ö)+! &* Øeç ÐçÁ @FÜú*(+ a¼ 'ă
+J!¾ '*/2F9ø¶!>/DG3 (38NK9LK   P@V8SRKW $Z)X796(> 2 [NM !#"ZI0COE:GNM(> P@V8
(> [NM ,-;\5  P@V8
A4O?Q'<5 DYL1B&4.]]^+*623%FTH= !#"ZIUQ&4/J

39

=croxoO1j

U??i\}yZ c !SF #"?ac.|?i\} L8 #"
xo3tbQU??i\}$k"tbQU?0_v'%&*([IwyZ qaRZ$EV=—qaRZbn"U?Ki@Q "bn Line1
 h>~2$;bn Line2bD$=,A  
tbQNdG  _vvbro$6l"GH" qaRZMzR^ Pf?{s$fc/9W `ge 
 =RZ]B"RZ:7HACTp<)ACe-
JAC54EV +bn "vbmY$uX = ="40V7)]K\O  L^;a7  "8*  L^;

Kb[*  L^; aJ4F gMUih
.0<c` FRN! XM@B08Ce#-_?!
+0<0V d!f2  L^; E .0< AM
! 5>O^;,:QPTH =! %DMUjZ#1S_?B0 1S3@^; 6 'M! MUjTH#W 1S3@^; 6 

 "

L

jMUi$@(9(9 )]  L^;&DYG/%^;I_
QPTH =! 



























41

./1)&  ",!'

.01%! #   -* +-$
!( 
42

"FHJ7;D <C5.2=0:16 GH@
A+,' 4( B?!<)@A+ 

"FIJ7;E <C5.2=0:1/#"*!>
$8 &-<C5.2:139 A+% <

43{9h MGUST5n p]+,1-qVzJCE(q*{JCE(+,1-qQV"o
W(v&L4qI~ %'!
'((qHz dS/2@*wt' 
 '!' qOaN~K)$jaNx
A_*wt'  ' Z^w$D4Oq*u!blOaNF^\$f<s$

6%#'mXaNxA_*wt'  '^ =e6  Jqr|q;?u'  PJCE(q'6> 03.
7:[!& g}(' :[!& 6
7ki&y8Y*`' $:[*Rc' H'PJCE(qI*~B*wt

44

I6mqbf? %r

I6mqbrf?jR$7kA{f?>ijRX8A{)*3+'LyJS$98r'C_$C_y']+/5+@GT  &H8tsn'B
F$BF$ r:rx#l`w
!$BF'"tsn'zeBF$ !h='BF $ IrLy'dD jR$p mZ
!Q |\~'dD dD Nb  Vg
'DNb#LuYM}W$  U;$#E K$ IId~,14-'c[" 7
r'<JS$jR$A{X7~,14-'o (["va$7.250'l[$Ly
.250o (,14-^\'O.250~P

45

z(z&
zNTw#f NTwL( &K?=[@Fxi}vpN#08<3R"&'& 
pRY (u&"08<3(n!I(~)ajC(BRYFxK@
 Q08<3(n)Uy(D&kW&08<316,927POM Fx?A(on!-<+9>3S`\V  ^_%`\ Z ls &ls( "^_%`\V  16,927(oEC^_%`\(V&

 Q $08<3(n)XeUy&prqmdt=GJ(b{g]($QQpHc|&5:/.*4;>1h $p(Hc&46

+*),(!&%  "  

+**,&%' #$  (!  47      !" 48+), ./*'  

+)-( #"%"!& $   

  



49

32410$"*( 0$"75678#- &%,+  ) 678  /!  .+"'

















50

ØÙÕ½É¿ Ñ¢"¼³'D.8½É¿Gµ1.½É¿:X¸¡9u9{8¼³'D.wsÑº @;pÁ9  ¸¡£9amG¨69­ 9am GADC!G¾<. ½É¿:Øq8F.BÑ¢9q¿OTRVMGy7"A~(.~
5OTRVM:^Z9ÆB

½É¿

Ñ¢

É¿Ë|


®Öq

 

®×q




  
   

®Øq


 

 

  


[
p
ÓÔ
  y¾p   



y¾


y¾p


É¿¯]


X¹
 
X¹




     


X¹






   Ñ¢:
ÛÜy¾8@BÉ¿(3C
IKUL9Ñ¢:q¿v9Ñ¢4C"q¿GÈ±ª8yj',!2-9yjGW}Ì8«8²BÃ*&58@BpÀY4W}ÌÎ45;5;87AH/·9G©§',C5&E8¥"C¶9OTRVM90[py¾py¾
y¾p:ÛÜy¾9OTRVMG¶(3C./(ÛÜy¾513?©§h"q¿9×\8`(3C.>?o8yj*C ¶90[p5:ÛÜy¾9t9p4Cy¾p5:y¾*Cp9G¤c94¶(.?94C~Ï8©a*Cp9
GPTLQJNL4¬(3Cy¾5:pGxi',C98!%CÌ5 ',C98!%CÌ9¦4C&9¦8@Bz#$*C5©§*Cam9¥"p8A+W}8Â$7C(!(-9e/%iÇC: Ç9gn"z#$7C.>SVM9ÄÍ"$7C(."13&9b:~Ï8É¿G(7"AC­ °Òª8>C&587Cy¾
p:ÛÜy¾G²BÃ*ÌÌÎ4C~Ï8©§*Cpe9ÌÎ:&9y¾p9Å57C=.-9p:[pG+A*&58@BpÌÎGyj',74d_G+A*&5"k´4C-9.>×l9Ñ¢Go)pw4É¿(7"A?amGeÐ4#C59"&99f£4C rØÖÚ8:®Öq½É¿8@CX¸¡9sÑº9»ÊG¬(.X51

y{p$&a2 1wb%s-g$¢£¢c%jida2 1a{M%^&5:I<|aQ[${$m4N1"!5:I<|$.1Q[&]zrdM!
"("(%oU$2#,T%Q[$P0m4N#!5:I<%Q[4Y1"&3 1#/ILC<D6G?L$. Y!2'EI><-X!1` &ILC<D6G?L4
v4 15:I<%Q[&]zri/2 1,ILC<D6G?L$.0]uS)%m&OhM~!1"31 ` 
  $&{p]%   {}$1Q[ZQlk4&5:I<Q[4\+]zroU&Q[4\*#]zroU!
1n &%ep!%B7=HFG4 1  & Kt%<?@9J;$.1lk!1

2{}$ -Q[4!1

%Q[&D87=A5H7$.1Wv4 #-%!0D87=A
5H7Wv4V2'sfR%¢¡xq_Wv1



















52

;ljn Sj:Z_\X`<K@4VN?BdOTjmi+/&,c>IYU >IYU FE=<dWgpqpkhX`".#dO176) ,%/ LG".#17X` D./(#) ,% LG./(#) ,%".#17E=b  a8J2179f 3Q
R 

;ljo Sj:Z_\178] Hi-net VNP5H MC0^VNPHi-net VNP'!$-*,A[".#1
7e'!$-*,




53

):9; 0:(264'5 Hi-net 1-/ #%+*3"7.#%& ,$8#%& ,$ !

 












54

  

 S¬,¢­tX$´ª§(5u³+®±¯8r05)&,Y*lµ$¥(-#63¨lµ+&'/)05¼º¹  ´ª§,\d~,Vai ´ª§­§},®±¯(´,\d~+ZU,Vai«&%$
º·°h¯+MQAxm¯!5oi5¹»·\d~+  m¯£z,.3&5¹

n¼1¹2007 y 7  2  1 3 2 ,¶T·k¸(W)\¸(U)DO<,w¹º·+&'n¼º+5R²¶ y     3  ·,  ´ª§,k,w¸\¸DO<,w8 !¹   c  ¡(±¯j8°¯"$³¸DO<|+q*x*^ '5¹   c  ¡,e}  ¡²8 q
$1,8n¼ + !¹ k¸\¸DO<-  ¡),>PJNP=(5¸,³,MQA,
f8u³+¬v!5)¸/%'53¤z3gzm¯¸
4s,2+©f¡¦¹L;F@K-3MQA+°h¯?:C
BP=+[G:@`%'{dm¯ ¸d~_,p\8b'x*\§+#)!5I9QEHC<]+25±f)765¹?:CBP=55

a¢ 2 a¢ 1 ( 1 r 54 V 11 M 60 6nd K0^
xpO?G8 O') 10 0( 4 # 100 (9>=C
032 aL( ) 54 V 11 6(A7:EI<'SY3&/&gUl# 2  &,'`q](Z)  r(  V  '53"2(r(?G8(Q6yLT"(vN'!"CH=?.(a  # 2 @=??G8(Q# 1
|'   z#)&1(i#;H0)3"d&Q6$ "2 aL($)33w`0`'W1tc[`0w`'W1tc[6"1%0.;H6Lk'R
1&eb"2$0z(Zq]$z(h`('P){/'2  s'(}) No.1No.2 z#\u~' "2 + No.1#/1i' "2¡'!"
ofEI<O'gh' 30ptJ^# 8000pt i*0!"2
PD Xj(BFDI<f(_# 4£m) 4pt1/1000 ` i
'-

56

+ *)!&&*      "  
(%'*    )!$#*

57f ACROSS j{x,%/2'q^aue

 4 3bvVNtB No.1 ACROSS j{x
ER!\Fi ,%/2'^>?G$a ^>sX\F!aZ ,%/2'M @ "["!(1(1$<Y!*-4)4 "^>!y_nmJ`97|DW$Y
! cU "!(1pT d, M pT DJRIg`FAI6(1=` n  :@ 5^>m !LG5r (1^>$!J` NI 
[Hz]

(1)

M 5^>m !LG(1^>6J` NO 
[Hz]

(2)

lO(15^>$m !LGCM @ *-4)4"H LXw  S!J` NR 
[Hz]

(3)

! "5r ^>]~J`^>Qk !y_ #"!J;\F$}P" "$Cd !
!f ACROSS {x14.4,%/2' D=299d=34, n=19
!5, 10, 15Hz @ $J  ,%/2'^>K!y_nmJ`z8i "! "Ig`ho *-&+0$}P!

58

Zoml

D _ C R 5Hz

10Hz

15Hz

<`9$N;$I 53.594@

107.19160.78J`9$N;$I 41.406@

82.811124.2219.16538.32957.494ON;WL-6$N;$I@onnl\S F?(M>$GgH=aK\i   j'hT$,8/7+P:c#^Xk  hT[X# %   b_k  hT[X# %  
b_!\S'Yl.7347+%   &  k180e%  &  V
e!YiZonjl
Zo2l=aK\]d$2)*5B".7347+CROk$"$hT$b_CROl

D_CRO 5 Hz
.7347+

No.1

20 kHz

3,4,5

10 Hz
No.2

15 Hz

No.1

No.2

No.1

No.2

10,11,12,

25,26,27,

17,18,19,

50,51,52,

13

28,33,34,

20

53,54

14,15,16

43,44,45,

35,36,37,
38,39,40
41,42
100 kHz

0,1,2

6,7,8,921,22,23,
24,29,30,

46,47,48,

31,32

49

 No.1 hT[X' 5Hz, 10Hz, 15Hz !D_f$]di3,10,17j'Eoo#UlAQ# No.2 hT$]d(25,50)'Eop#Ul59

8ccbNo.1 ]IQN3X@STZb.FDM2a/FA?"&#*b20kHz !,%)
, , 50s [b=^ 5,10,15Hz ]IYV\TZb

8cdbNo.2 ]IQN3X@STZb.FDM2a/FA?"&#*b20kHz !,%)
, , 50s [b= 10Hza4 15Hz ]IYV\TZb5Hz YVTZJ
8 1 GW =L$(,b TZ_Pa]I7V6HB `UH(,"&#*b0OGW  No.1 ]I; DM215A?-E< b8 160Hz >9 No.2 C :a0]I 10Hz YV\ 10kHz "&#*K8ceR No.1  2kHz 
8kHz '+#A?"&#*_P60

AvwuNo.1 nUrEs
tNo.2 nUr<s 10Hz ji mN]9glr4sIG$,"'.r5su=AoX&2%th 200Hz  3 Q(%02$) .%uDu+-1#Jfcp68>W ;_Hu+-1#PKB>bLYX?TMekdON]9!1+/2*u $,"'. No.1 AvxtNo.2 Avy[ uAvxqat4SN]9  ji?TM!1+/2*C:7dd^VuRF@i!1+/2*
ji?TMW uVAvyji?TM3` C:AvxZ\u61

SS 1  No.1 p}w(=5<>4# 200Hz <>1,3&:.# @mguHAm`\,6)/:[ 5Hz10Hz 15Hz p#


No.1 pROiNi$|c d"  No.2  W sQ "!5%9=* +83/{l,6)/:!MSAmvsG5%9=*kb!,6)/:2>)Bo "!No.1No.2 hOnfW DbC
!,6)/:2>)Y_!GjEVZ2>)"!!2>) 0'-;5: tF
xX
 K],6)/:I q No.1 pOnf?z`LTL! DbCY_!Onf2>)! !Jy#e!{#U~#!a! 
G7>.R  ^y0'-;5: 
tF zPrx"!

62

!342! 2
No.2 0'*) +. 200Hz 1 
2&%( 1&$#2" 10Hz1 15Hz 0'-,/ +.263yxtSKWb^O>G\ 2RfTN[h7SKWb^Phg d8 nVb^mh^ :@_=Ui  SKWb^n> 5M6
3E

G\QLe  64xoZn>G\a  vr:@) 0;^wr) 0sS'0"4lO%-h^xr.1',("&sk]DFyxvt:@) 0;^ t No.1sNo.2 nVb^?9<XA_&+1&jsJY!0#/d8qCyzr


Cyz No.1(H)) 0$1*/,("&3sNo.2(B)) 0'0"ch^tNo.1 ) 0^ X!0#/`Ip Let

No.1 ) 0$1*/,("&3^ qCyvurt64

Q  No.1 ;.(>0yuQQ5%={I$O!xQ@!xQ

600mm &=+<$ @8<3RW;.(>0~c-9eb,>6<82*/l 3 zjh(?T! 300mm)$# No.2 @,>6<82*/l" D yuQ
5%=T}s 200mm q

eb "No.12 @F&=)>8<3RW

Q No.2 ;.(>0yuQQ5%={I$@!xQO!xQ s 400mm &=+<$ @8<3RW;.(>0~c-9eb GM5%=$Ju "kZo4'7$-91:>6Vg"[w"A|t4'7NK_$ Ei$ "5%=0=*@~c-9yu 0=*NKnSCu!L 
k$am]X U^$! &=)>$`~c-9$yu " 5%=@&=+<dPEA 0'7?@8<3H"
0'7~c-9$yu "5%=p-9Y\WfrHB@ 
v

65

qmhb 50kg(NF)nCVP 20HznOLWP 4 WnAWOL?hv13kg d^!orm'0#<"aDRM@P f N/fw4

eF!lN 

I>M@Pmj@:fXu%]H !lf G "G]cmo
 f<w20/4=5Hz !oDRM@P# 5Hz !@[-,FP K 
f=1/2pi sqrt(K/m)  K=(2pif)^2 x m=(6.3x5)^2 x 13 =13 N/mmnk[-,
FPw@[-,FPp1.4 nk[-,FP ksw9.3 N/mm !smiM'0qOLW k?h

130Nn7 X QBk[-,FP9.3

N/mm 9 6   !    ' 0  o EA2006 l KX:20N/mm,  KZ:110N/mm,
mZ:830N, mX:145Nm
oKX

20N nf uHz ]H nN/f=3o:f

X 0.13 ]H!o )4%Y'0n&4%25+E\/3+ZnEB )$.l6;#
8S/3+T!)$.mo)4%Y'0JKFP_=96QU oqmhb 100kgnCVP 20HznOLWP 4 WnAWOL?hv25kg d^!orm'0#<"aDRM@P f N/fw4

eF!of<w

20/4=5Hz !oDRM@P 5Hz !@[-,FP K  K=(2pif)^2 xm=(6.3x5)^2 x 25 =25 N/mm !k[-,FPw@[-,FPp1.4 nk[-,FP ksw17.9 N/mm !smiM'0qOLW k?h

250Nn7 X QBk[-,FP18

N/mm 96!'0oEB4004 lKX:32N/mm, KZ:210N/mm,
mZ:1,000N, mX:195Nm
oKX

32N nf uHz ]H nN/f=3o:

fX 0.13 ]H!otsso15)/*%(ng`DFo66

5;)2*"(I~{|B`b y?u%LoYNaQAJMgz

I~{| B`O5;)2*"(y$;/8u^u<?y2*"(G E?u
2 cSyY28+JM z sY2*"(q&4.*,Tzmdy[k_pjt\I~{}B`f1:b
3 WmdzB`b v=lCwO?md 3 cSyE?md 1 cSx
%LKoYy7'!;)Dr R:#8l9 6JM

z
I~{} \mdwf1:Ibxy9 6JMz9 6. 0UFl>i]&4y83X>iz9 6P9 6Zn@he-*+H hVz67µµ°=r).90ªvxws1:. #dK{®¥¯©%
Y®NM[UV~V <¨/7;5D@¯ ³±±·^¸l²iº³iXh&=r).90ªv6:23:0
jxws1:._1:.HB¥}{ % & t).90LeE48;-:/"%!$Tf48;.}{ dK& APdK&{¥}$&
dK&!a} %JQ( p % SEM YEDX®FIo¯"xws?¥Om£uW(µµ²°"GV­b§"%Y a}Y(Sky($(  %B  #¥% ' %²±±¹
Rµ²µ =r).90dK&¥}Rµ²¶ GV­b§Y¥}{

{

=r).90dK&¥}¤\z®Rµ²µRµ²¶¯C>|c 
²¯«]Z ®²±¹`C>¯
-6    ®ng³±¹,+74*71;(¡¢¥%¯³¯ky%´¯­b§Y%¬¦Gq %
µ¯­b§Y%} }%

68

 P5OJ2 NDR.YVYSGAIJ2 NDGR.Y
VZS0@AI /,C?ND1L,

Q H 6YYW
W USEMTEDX J2F8
 '9!"%# No.V<;:$&"-+ ND?@> SEM
R4?J2S EDXR)E*7SJ2 F8 .YV[.YWZB .Y16 ND?M3= SEM-EDX *7
V.Y17 ND?M3= SEM-EDX *7
WR.(  K*S.Y18 ND?M3= SEM-EDX *7
WR.(  K*S.Y19 ND?M3= SEM-EDX *7
X

69

20   SEM-EDX   

22 

21   SEM-EDX     SEM-EDX 23   SEM-EDX   

25   SEM-EDX   

24   SEM-EDX   70 zq,E-cNRgL
769ljicnRz E"*) ,u!
u]Ye~28/5,\h@)

~

28/5x,' $y ~MGQa_zq,28/5W{)}IOvZjic%

f)~

~

%<28/5jic ,WC)
}WC)?o D~~|Jmzq,E-jic,F28/5x,y)

~D^|Jmjic ,F28/5x,y)

~

**28/5x '28/5r?x,S ~jic4;31;5 'jicNR []B )28/5FCjic?o,`$E"*)zy,sp)
&`$zqE[y}769lVjiczE[y~ []
}* TktP E#z,E#wB ,28/5F> ) jic,F"$zE[y XK&( ' IU+*)~H 26 =b.092 No.1 
jic3:0Awld

71"!&$('+[02] #"!)[.0]

$   *,-[/]% 

72  iiidVB
 30VB&P
iiifd 4S6GUHVBCr I5 NL9@7VBfb Z; #NL$A</XOZ;FEY8[_KS)-,Z;] M #%$aNTN '+-* fhQZ;FE&:Vb
30_KS)-,Z;]TC&P_KS)-,Z;]1TCaJIS G imej SUJhA<bC oednjyfdfe`
Si oediyedle`Mn oedj`30
Cr oedneyfdge`"Z;#NL$\R Cr>%$Si !I5%$$ 2?UHI5%  
gb Z(.^ DW\R NL$A<^Z(.FE%%tgjpthjptijp$tgjp
gjKSp&edgj`>

&P=JthjpKSp

&edhj`tijpedij`>p  TC&P
thjpTC
poedhgyedhm
tuoedfjyedhj`
qvoedkyedn`soedehe`toedehj`pxoedh`ruoedg`
pwoedg`
rucpwoedhj`

73

&P $thj´»(2F  Cr

d$-,`¦y!,'ÇÆÉÃMH

Ç%Äd$-Å'­a,/{e,d$-
'&v¸U-¤ 
Cu  Zn

U¾,¤p#0 6D=A Cu  ZnU-,ÈÅ´_ *,ja´_!
5C/O|,@9F:F ¼« ·g N.-, ´_ *º¼ L,!Iz ,²13C7
P  }^-¹s!º <BF3¼© d$-
Ä§'WX ,Å Ki º¾ToÂv½¯p¡ *!¼ §/vn!#0± /Nº/V¿¼!¯p- ¼ , !´_³\Á Àt¨+m <BF3º  ¼« @9F:F Y*-,&¤ ,
Ki¼ © ¯p- *´_³\Á ¥'´_qf <BF2D4!¤ *-,ÉÅ´2F» *,ja´(2F» Cu  Zn Cu ( Znd$- *´(2F» ¥,!x.-,ÊÊÊÉÆ ToÂv½¯p¡ ¤p
 Ki}^-°!G¬Àt¬ , Âv½¯p,© 'º+n ) l/µ,nbk£ [¢ c~  ¯p-  *#0"
 n º,! a¹, . ÄEDX V¡ *'bÅ  # ®¯p%,ªÁ § ¹§ n . d$-
,-!]wªÁ§ *'¼ ©x.-, Àtr#0¯p-ÄZ¶Å´_ Q,Q5C(¹s<BF3)+>1@D4O|h Y*-,&¼© d$-,!'l¤ ,Ä²13C7 ja¹s<BF3Jl ¹§ © Å
SEMEEDX
X¯p¡ÄS?8;D4ËS

SEM R u*-,Å *'¼©!¯p-

74   s<P5=jM
 &(.+{Ylg7vxI?E Nn"vA!s< P5"h6d9TeU Cr `z V8#"ZOX "
 ,-0'/)H@%u":s< r;|Qi \"D>"

B 27 Wq&(.+s<7t},-0'/)k~    r;|*.! fS] " B Wq&(.+9m4[#Rs< }NU~7tr;|" s< ,-0'/)%p  *.r;
"fS] ao " Qi ^\"yc ^\"L$#" 2yc^\w

s< Qiw%OG"

3G
~yc^\w%[]~yc s<}NU~Cb^\

~Qi7tr;|Ftr;|C1^\~7tr;|_K  []~Ftr;|_K%  []~r;|J}*.J~   [] []ycs<^\"s<!

Qiw

75­¤¥¨[³]+-L V[±´3] t-ª¡«*¯­¤©¡§[±´3]ORd-²¤[±´]_Rd-²¥[±´]Ra4D a
-°[±´]*k |*®[±´2]!
®­²¤° ²¥° ­¥¦¡¤¦¡¤§¦¡§ ¥¬¡¬¦¡¤§¦¡§ ­¨©© [±´2]kS-µ*µ­¯¢®
 ­¤©¡§¢¨©©
 ­£¡£¥¬£ [±´] ­£¡¥¬ [´´] #) |T\-X*XR!£¡¦[´´]ck
** | Pyxu7E3b
&?;D ^S %) #s*4D k -f!

|T\10C=/C7FU+~z'*k4D Jl
R'*")iyx J]G`h(+*§§§§¡ YP@E>:D40;@E> jN
 |  ( *YP@E> DF7 jN! |T\!
 .3D6 b Qw#yxu-[V*YH?8;!¥´c*e,+*.3D6oI (YH*%o¦´c* YH?8;!(`*W)gmn!YH?8;!¤´#+ )r- M}{v* * 'qKM}*p!2A<9F5BE |&~z Z$$

76

.3-gBn24)4o N9  ]n.3-#3+424)"$)424)QF tqxuqwo/3*+3(!:
5HTR ]
rrsp\d j[XW=D f>?_K m ,14&ViGU b f>8LCnYl`v0*4+4o N9 6 S<,14%3'e J  7"&2(;ggB@EMcO^nfk%4N9Ao]j[XW=D!PZnj[XWh o;gTRIa]

77

78

IF=4   d^rkm%H±~$µªÄ®ª&N$¼Â2ÂÎ`%Ä®ª-# .Ä%3D5"  /"_«! / !& Ä3D5"gÄ³3D52 Ê¯Ä®ª-%Ta%toÇ2/ ¸Å% ¢¿W$&±¦2x/"!#£!¡$hÎÌÌÑuÏf±2§¨/ ÐÍË&*$ gÄm!&lºK! n%i~-%LÊ\q%)2[$].Y*$D8F@F3D52 /ÈÃ¥$vÉÊ-$¾T
V!+3D52}0'Q|%i~$6?C7F2ÁKÊn%i~%LÊ\q2[$].Y"!/ÈDF;F$vÉ
Ë%35>432 ACROSS Ta!o/¤G9=<B%o¶oÇ" PJ2
/Ë M`%Ä®ª2 Ê0--%Ta2g­3D5!]x/Ë $t
%O2jÊg­3D5W!%Ta6?C7F%Zs2¹(/ËoÇ!&PJ%M2¸Å"/Ë
?DGJH&B5<;)2/C* %$ !'87E
>1"6 -9()2/!' #                     DF;F¾T%*$&R$b1 R2¹ce%Ta
y°! /Ë%ibÊR2j ib$&Ä®ª%R2
j # &#-# Ë #R$p

 R2¹ Ta¾T2©.½"&¿"6?C7F%Æ! /Ë!¯%Ä®ª-#/e%Ta2YÊw!²/À$ce%Ta" X
/"2·)/Ë?DHJH
H &B5<;!':,3AE+@.0 ¸Å 1 !S.Yce%Ta2 #R2- »b1Ê±3D5W%Q|%i~$6?C7F2ÁK/tA:FE2S/Ë
 PJ!&I´¸ÅÍÊÎ$pzUoÇ2# {n0/[2¡ËÐÎË¸Å 1 ¸Å 1 " ]x>F:-#/eTa%b}2¬ Ë
0$,.Ê

79c C\Wt9  2 @|_nj9A"B C\W9A
 R

"e 

is

FM t9 {VC\W7vyW?N $'0*p^is

FM t9{VdC\WOg"N }5w~DD|_ 1000m {!FQUt\C\W 10.015 -/+C\W:H 5 -/+FM CZ 50 f200 fx>w
qw7vyW!!Xh<C\Wh<}C\WOg~ L[(x,y)C\WOg F(f,x,y)64Mlb J8]mkP 

(1)f C\W(x0, y0)|_L[Vp  P \uK 4000m/sVs  S \uK 2500m/s Q  quality factor  100DUt\C\W 10.015 -/+C\W:H 5 -/+FM CZ 50 f1km {! 200
fx>w qw7vyWP,S \uK!! 4km/s, 2.5km/s3200 fxqwFM
CZ 50 f 4 ,2'o  43qw 195 f 0 f"T# 10 f"SGp^ar IEYz  0 f=&%.$)1(}`!; ~o 80MM 1 =~dJlduD
real part{ imaginary part9100Hz *7357)z 50Hz 2&',1%<Y_"|# :9`QM200 s
zTFM Ji 50 s08/n 3  cJlduD#<R`Q
B

M08/ 3 n cJldZt X!$# cJld
ZtJldb}lJld%Nm 10.015+0.02N HzN edw $#cJldZtx MJlduD?G 3  .6@%a 08/I$#h\[O P  08/nd 1/4 # %\K#VoguD?G  1/4 A[O%a#SM
1 guD=~d% 50 sk 4 -(+47FC#$$-(+47lWHJld]B>r /2rad $#200 s
>r2L^ #yEq;# $AlWI$#Jld]B

10.0150.02nHz # !vf#lW%wp#j

Ul cos2ft >rB f=10.0150.02n 

81

(2)
.Á50 ¡Á100 ¡Á150 ¡Á200 ¡00-1/2Á-Á-3/2Á00/ -/Â -pc10.0150.005nHz /vm #",®f# Ácos2ft "Uµc#TR"«0/Â(3)


&. 4 /EN8"" 3 ¿Ã"QPÀ# 1/200Hz^"pc ;MGK00$6IM>K0/:N=B/Â¦eXk-:N=B2j.º q"/ 50 ¡"°·"'2j.b´d a/Á;MGK0µc"p¤AN@2¬¹ /Â}]
¯+¦eXk"vm2§/ÂOª ¦eXk2¹»Dt½
;MGJM9l"¹2t)¼ #p¦eXk 54J3<
M9g"*ÁC46=Bp/ 1/2Dt"y[ Z?
L"2w++0$,Â"W#­ Q;MGJM9p2zAN@"u w# Á³FNJ5x0$;MGJM9 {¦eAN@2/  /Ân p¦e2£¹»½;
MGJM9lpc"¹2t)vm #Á¦eiAN@¸"g Z?L"2w+$,ÂiAN@¸#"vm^u2o( 50¡¹/Â¦e54J3<M9¿g%"5DK7N"0b À50 ¡"AN@2d.bÁ"g Z?L"2h/Â"W
;MGKp¤µc\ /Â

 _V #sÆÃ"-5 ¡¿195 ¡À - 45 ¡&" 50 ¡Ty" 150 ¡2Z?L/Â"°·2FNJ5xp=H8BK2sÆÄÂ¦eAN@" 3/4 2j.º"# 4 YÂsÆÄR"zsÁsÆÃ"=H8BK"¾?L"AN@¶!m1/O©/ ±/ÂsÆÅ#S¨"~2*"/ÂS¨"~# , 10-4 /Â*"p¤"z # 1 ¢/"ÁS-N  104 TR"Xk |#²~"¥r`/Â

82

*OML?F  (6507L!P?,  @ELGP-CKAP>CL"P?
,  (6507IGKA9JK&H%4 2'D L3+*P"*A)C'3+L#;= <L*ONL*OM"?,  (6507&H%4 2'.LGPCLAP>CL:B8)-10-4  10-4L

?F$1(652'(6507/

L

83

 2
 Bv'yz#SriOa Srib~' 1 RSridIGP'F" $!'nE|'!  Q&Dc
Ve*59+<'A #]t61<;'F#C?N=SridIVQiSridI'Qd VQNiHW'qv u#]tKmk  X #% Bv!{x  10.015Hz  P rGPSrib~g\jJ

t=0 /427-823'T} v1)7N*,
/7:<.8;U P rhY#@v y >_o(0,0)'f( 35m $ $#P r^ 4000m/s #_o(x, y)r$#
` g(t,x,y)C?


(4)


f=10.015Hz #TBv!N=Sri10.015Hzb~r`/427-823No.1  No.2
E|[0:Z!v No.1 v No.2 @QdlpML#wsc

84

 AcBS\>F,0.1+2./J((o^%\>F,
0.1+2./[p;8UMe 2 :')'q E\$N] ')&%#pErs,0.1+2.
/ 64$'UMg_*a qq   (5) pp

'qErs$'BS\PUM<LW79IR 5%bO' 
='qErs. ErrD\VQd\PUM<LqJ%o^ No.1 !po^ No.2 !p5f
BSUM<LqNo.1  No.2 7`K-3qBSUM<LW79IR 5%bO'q(1000m n(@ 1.68 bOpY 1.60 bO)

 Z5o^7`*% N]G?*h$q o^ No.2 7`* 2f35/4000 l%'q35/4000 5o^min 35m *jO 4000m/s  P \k"Xm'q '\>FYC HUM*TpW79IR 12%85`,

U¡£?{ *M<Tzn10.015Hzgzd37582956[ *{No.1 &{ No.2 &>QiNo.2 { No.1 {YA 2f35/4000
-, )u=>{HsA\.,)Qiz
JVl_oADXh.k,  ,U¡¥ { 1km }A\oAl_E.{ No.2 A. 0¦30deg *[ pI4;37582956O l_G],OU.,A\4; 90oSKL
A\ 30 +PA\prWrZl_\0oSt rW

12% `U¡¢U¡¤N~, xRvmC.nTzniGzJV.Qi,b 1 eTzngn.{ No.1{ No.2 i>{A\4;QiP GrWl_G].U¡¢|jdU¡ 
FTzn.QiVQ(l_G]d M<TznVQ#$Rv
,2 {(35m)

5¦15Hz z(266¦800m)y"^Z

'#/M<Tzn %,(,qTzn
-!, chz` Bz -!b 5 aw),fG
W +DXh %, ,@= *x0:1. ,

86

.QSP .QR,?;7D?6:4$3P2L@ No.1 OL@ No.2 O!F*9:4$3P*9:4$3<"#08 12%C5 (1000m K > 1.65 C5O
G 1.45 C5)PNo.2 L@"B No.1 L@ 1 2f35/4000 J P.QTPL@ No.1 1L@ No.2 "BJMEIN O'A 1km K A(>(=H- G ) ?&/$3P2U=%
P)U:4$3P:4$3+"B <"#08 10%C5 P

87

FP av=[IWN=MK }d No.1 }d No.2 3oCVW
N=MNo.1  No.2 8iL)/CVWN=MY89JT 5%kPF 
D`(1000m |#A 670 kP^ 640 kP)%.&rg s~ 1 X;rm!2 }dxh"EaXt: :B D E
aXEaXSlyXQ #" j #s~ 2 X;rm!
fY}d"EaXSlyX8i$q_2u> 6Ob,*10$H
7UY8a?G'+-(1${4 " j #
]}dpnwnxz 35m EaXV= 515Hz {4PC 5%kP" 5c #"8i$H@ Za?G'+-(1{4PC}d4e$4R"DR<2H@I   
%.&wn\#"

88

H 11bnkGBO 1km EP?e3piskKS=o 8 cL> 4 c vZ`D> 4 c WvZ IVY

3pi qa 3 R@Jrm;9\XQp
4.5Hz xMr 3 R@

-8 %(+610  100 /25/-8 %(+

6LS7000 47

-8 %(+

62GB "5- +.1(#0-16 %(+62 

6{l~_ 15V, 60Ah3 y|~A<jfN-16 %(+
-8 %(+647{l~_d}^Ch!7$bzwqaTg

No.1 b 10.0155HzNo.2 b 10.00755Hz zw
8y|m]:y|No.1 b 10.00755HzNo.2 b 10.0155Hz zwm u 1 EU[t*7&FC,()27'( 8y| m89

$>EDFFM )<(40FM )<A/(40 8!7 @065;  C
(2 TB)<+ 3,4- FM )< 9C.=4:(40 c  )<:(40B(A-1)
1C )< FM )<&'

(A-2)
C

B

C

B":@0%#8!7 @0*?

C

(A-3)

C

(A-4)

  F(t)



90

&~/nyQ7G)\dD6= F(t)31$k[ '(A-5)G A-5

Aq?T T C s=2/T% F(t)OxYn?YQ c )2J~)zP;4'n?YQ cns|n{rRQ}6=L8
 o'

>('

S9c;!?YQAq)AqE XHYI ~?T T e&v?YQAq.j)g"Aq?YQYI m/T|mhZQ}?YQL8 >(~G 1  cos 2t 2t/T
2mt/T &~dU
)

"

' 'G 5 

f N"~#& F(t) cns|n{rRQ}6=L8> <g@ A-1  0 W % 5 W 50 Wb.`,+*-yQ)]
WQVua0 & .i&~?YQL8ME D/s mB
('  :'5AqE 5Hz~Aq?T 5 ^(D/s=25 &~25 W_F,+*-yQpw s&'AqE 5Hz~Aq?T 50^(D/s=250  250 W_FKl'

91 A-1 

92

QPTR285N
 0>J@:OAIG63LK $*D 28H  $*7MTRTRD.!'/ )/%B?&, 14ECIGSTU<K=9  TR28)/%OA28IG;F(-#"+*  193

:6`V?
ACROSS-SGGPS IZ

-2
'-)

Ch.1

2$+3'(MPB-J6204)
Ch.2

*/"<+
*/"<Com

10MHz
;*/"

10MHz
;*/"
U*/"

F5

U*/"
;*/"
A
B
Z
Com
U*/"
A
B

AD +3'(MPB-J3176)

RS-232C






&/ ,($3b&/ ,($3Com
MD,($3bMD,($3Com[@ ComLPOYWRC2)3$RC.03+3'(MPB-J2503)=ES    






        






MDAG>

K\
]\

aC7J
aC7J Com
.#%&
^\
7J
Com

GPS/FM !2&13XTQPOYWRC2)3$RC[@ Com
_H,3'
N8B4
XT ComN89F5
N89 Com








      
    




 
 
 





 
  
 
 

2
94

GPS-FM (8AD 6)

5':*# LED 1-*
GPS-FM&+9



1M

AD 
1-2 /)20
2-2 /)20
1-3 
2-3 

260k

!%,."
3101

No.1 5'3102

No.2 5'3105

No.1 *

3106

No.2 *

3103

No.1 /)203104

No.2 /)20

3114

No.1



3201

No.2



M24FM

DC24V
4301

No.1 *

4302

No.2 *

4301



4302

43

7A

4416

(

1B

6501
6502

7$(


2A
6A



M24D
DC24V
3
95

GPS %-ACROSS-SGGPS  10Mpps1($ ACROSS-SG 21*

,&"

#'+!

10MHz


D-sub 9 Out+ (1)

*


(MPB-J6204)

GND

Ch1





2

ACROSS-SG.

GPS %-

 Out- (6)GND (9)

7201
7202
S31



1L1+
1L1- (L)
1L2+
1L2- (L)Ch2

1A+
1A- (L)A21 (A22)A31 (A32)

A)

1B+
1B- (L)

B21 (B22)
B31 (B32)

B)

1Z+
1Z- (L)Z21 (Z22)
Z31 (Z32)

Z)

2L1+
2L1-(L)

Com11 (Com12)
Com21 (Com 22)
Com31 (Com 32)

2B+
2B- (L)2Z+
2Z- (L)
GND

PC /RS232C0

4
96

AD !) No.1SNo.2T
&#)UAC#)+/

UA:FKI?QU()?QM1 (&(+/L6VAC9 $)"

DC=< Pt100 C95>2

C9

%

 GPS-FM (')$ LED JG*.

U24V =<O

PU87@S$)" OFF @T
AD !)
(MPB-3176)
(&(+/

AIN1
Com1

R3

-N

5VUM4@S$)" ON @T
C95>2

1M

AIN2
Com2

5>V
5V ,/

0V



Sp2 0ETV
B;V

1-a (2-a)
1-b (2-b)
1-c (2-c)AC3103 (3104)

HAKIM1M24FM

M1 Com

260k
260k

AIN3
Com3

1M
3114 (3201)
7120 (7510)
7121 (7521)

AIN4
Com4

(

)M1

&

GPS-FM (')$

DC24V

5
97


)+5 1

# GPSFM'4GPS-FM

4.,4#"*2p2 %35

(MPB-J2503)

OUT1BC

!&(6501

OUT1BB1

#0

1

# Com

6502
OUT2ACOUT2AA

4401

OUT6AA

4415


OUT6AC.,OUT7AC

4416

OUT7AA#
M24D
OUT3BCOUT3BB

4309(4311)

OUT3ACOUT3AA

4310 (4312)

$,/
-,/

6
98

M. Sc.
Dissertation

Correction of near-source instability for long-termmonitoring with ACROSS

Noriko SUTO

Department of Earth & Environmental Sciences
Graduate School of Environmental Studies
Nagoya University
Mar. 200799

Contents

Abstract

1.

Introduction

2.

Instrumentation of the Experiment2-1. Awaji site
2-2. Experiment in Awaji site

3.

Analysis and Result3-1. Application of methods in Yamaoka et al., 2001
3-2. Result of methods in Yamaoka et al., 2001
3-3. Improvement of the method
3-4. Process for analysis
3-5. Result of the improved method

4.

Conclusion

Acknowledgements

Reference

Figure100

Abstract
Unexpected temporal variation due to near-source effect on the ACROSS(Accurately Controlled Routine Operated Signal System) signal is successfully reduced
using near-source signal of the source vibration. The ACROSS vibrator for practical use
was deployed neat the Nojima fault to detect the temporal variations of seismic
velocity after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Ikuta et al., [2002] madea 15-month continuous monitoring for the temporal variation in the travel time of P- andS- wave from Jan. 2000 to Apr. 2001. The elastic waves emitted form the ACROSS
vibrators located at the surface were observed with seismometers at 800m and 1700m in
depth. Though they detected a change in seismic velocity due to shakings of teleseismic
events, they observed the long–term variations with the amplitude of 2ms for both P and
S waves, which have good correlation to the temperature change and rainfall. The major
cause of these variations was identified to be that of a near-source property whichchanges the source vibration. Most of the temporal variations are attributed to that ofnear-source region which seems to be mostly affected by rainfall. In this study, we tried
to remove the near-source effect in order to detect the small change in deeper part of theground that was not able to be detected in Ikuta et al., [2002].
In this study the correction is made in two ways. First we attempted to devide thesignal into long-term and short-term variations. Second the method proposed by
Yamaoka et al., [2001] was modified to make a better performance. As a result, we canreduce the effect of near-source variation in quite good performance compare withmethod Yamaoka et al., [2001].

1. Introduction
Monitoring the temporal variation of a state within the earth is important especiallyfor predicting earthquake occurrence or volcano eruption. Many techniques have been
invented since the beginning of the history of earth observation. Seismic activity is mostwidely used to monitor the temporal variation of the crust. For example,

1101

magnitude-frequency distribution has been used to investigate the temporal and spatial
variation of the stress or strength within the crust (e.g. Wiemer & Wyss 1997). Seismic
activity prior to large or great earthquakes has recently been used to predict the time of
the main shock (e.g. Bufe & Varnes 1993). Fault mechanism solutions and theirtemporal variation give the spatial and temporal variation of stress orientation (e.g. Zhao
et al., 1997). Strainmeters are used to make direct measurements of strain of rocks inthe crust. In spite of the efforts to reduce the effect of meteorological noise on
strainmaters, very few observations have reported on the precursor strain change before
large earthquakes. For this purpose propagation property of seismic wave is a good
indicator. Many efforts have been made to detect the temporal change in seismic
velocity and amplitude.
The ACROSS system was developed in order to detect the temporal variation of theseismic velocity of the Earth’s interior: The principal aim of the ACROSS system is todetect the velocity change associated with earthquake and/or volcanic eruption.
[Kumazawa and Takei, 1994]. For this purpose, two technical issues arise. First, agood signal-to-noise ratio (SNR) of signal which brings the seismic velocity
information to the targets (e.g. source nucleation region of earthquake or magma
chambers ), is required. An excellent SNR can be obtain by using accurately controlled
sinusoidal waves as the source signal, which is directly related to the design of the
instrument itself. The second issue is the temporal stability of the system that makes thenatural variation visible. This includes not only the technique to reduce the effect of theenvironmental condition on the system itself but also the technique to calibrate thetemporal variation of the elastic and/or inelastic property of the surrounding rock, which
may vary with some meteorological effects.
The temporal variation of seismic velocity near the Nojima Fault, which ruptured
during the 1995 Hyogo-ken Nanbu (Kobe) earthquake (Mw; 6.9), was monitored using
ACROSS. Ikuta et al., [2002] made a 15 months continuous monitoring of the temporalvariation in the P- and S- wave travel time from Jan. 2000 to Apr. 2001. The elastic
waves emitted form the ACROSS vibrators located at the surface were observed using
seismometers at 800m and 1700m in depth. They observed long–term variations with

2102

the amplitude of 2ms for both the P and S waves. Furthermore, they detected sudden
decrease of S wave and velocity at time when the 2000 Western-Tottori earthquake(Mw; 6.6) and the Geiyo earthquake (Mw; 6.4) occurred. The near-source variations arevery similar to the travel time variations at the 800m. The major cause of thosevariations was identified to be a near-source property that changes the source vibration
through dynamic interaction between the source and the surrounding media. The phasevariation in the source vibration is primarily governed by the rigidity of the surroundingrock. The lower the rigidity, the more the phase of vibration delays [Juan et al., 1971].
Most of the temporal variations are attributed to that of near-source region which seems
to be mostly affected by rainfall (Fig.1) [Ikuta and Yamaoka, 2004].
Ikuta and Yamaoka [2004] corrected the effect of the near-source variation using thesignal that was recorded by the seismometers around the source. The correction wasmade only for the data with in a time-window of two months long, because thecorrection for the whole data at one time was not successful.
In this study, we tried to remove the effect of the near-source vibration for the wholeobservation period to find the small change in deeper part of the ground that was notable to be detected in the previous analysis.
2. Instrumentation of the Experiment2-1. Awaji site
Two ACROSS sources are installed near the fault of the 1995 Hyogo-ken Nanbu
earthquake (Mw; 6.9) in Awaji Island (Fig.2). The two vibrators in this test site havedifferent eccentric moments to cover the wider frequency ranges with a small variation
in force. They are designed to produce a sinusoidal wave up to 35Hz and 25Hz with amaximum force of 2.0×105 N, referred to as the HF (High Frequency) and LF (Low
Frequency) units, respectively. Two deep boreholes with 800m and 1700m were drilled
at 50m and 200m from the ACROSS sources. At the bottom of each borehole,
three-component velocity-type seismometer is deployed. The changes in the3103

propagation property between the sources and the seismometers in the boreholes weremonitored.
The Fourier amplitude spectra of the observed in 800m borehole data are shown in
Fig.3, where the ACROSS signal is recognized as multiple lines in the spectrum.

2-2. Experiment in Awaji site
The temporal variation of seismic velocity near the Nojima Fault, which ruptured
during the 1995 Hyogo-ken Nanbu (Kobe) earthquake (Mw; 6.9), was detected using
ACROSS. Ikuta et al., [2002] made a 15 months continuous monitoring of the temporalvariation in the P- and S- wave travel time from Jan. 2000 to Apr. 2001. They observed
long–term variations with the amplitude of 2ms for both the P and S waves. They
assumed that near-source variations are very similar to the travel time variations at the
800m. The major cause of those variations was identified to be a near-source property
that changes the source vibration through dynamic interaction between the source andthe surrounding media Most of the temporal variations are attributed to that ofnear-source region which seems to be mostly affected by rainfall [Ikuta and Yamaoka,
2004] (Fig.1). They placed four three-component velocity sensors around the
ACROSS sources to observed the movement of near-source vibration. Three of themare placed on the foundation and one is deployed in the 10m-deep borehole (Fig.4). We
attempted to correct near-source effect that appears commonly on the signal of the
800m borehole and the seismometers near the source.
3. Analysis and Result3-1. Application of method in Yamaoka et al., 2001
As we can assume that the near-source effect appears commonly on the signal of the
800m borehole, we can remove it using the signal that is recorded by the seismometernear the source. We first applied the method proposed by Yamaoka et al., [2001] toreduce the effect of the temporal variation of the source.

4104

We assumed that the observed vibration of the seismometer, O, is a product of thetransfer function, G, and source function, S. In this analysis S is assumed to be therecord of four three-component velocity sensors and deployed in the 10m-deep boreholeas the source function. In our observation G and S are assumed to vary slightly withtime and are divided into the time-invariant term and the time-variant term. The
observed vibration is represented by:O(ω,t) = (G0(ω) +δG(ω,t))(S0(ω) +δS(ω,t))(3-1)

Here ω is the angular frequency used in the ACROSS signal, and t is the time. G0 and S0
denote the time invariant parts of G and S, respectively. We assumed that time-variant
terms are small compared to the time-invariant term S and denote them with δ. Ignoringhigher order fractions, Equation (3-1) can be rewritten as:O(ω,t) = G0(ω) (S0(ω) +δS(ω,t)) +δG(ω,t)S0(ω)(3-2)

We obtained G0 by the following procedure. Assuming that the source function S is
described with M parameters of seismometers, we wrote the vibration at a seismometerwith a liner combination of the source function and residual as:
Oi (k) = G0ijSj(k) + Ri(k)(i = 1,…,3; j = 1,…,M; k = 1,…,N)(3-3)

where i denotes each component of the vibration of the seismometer, j denotes that ofthe vibration of the basement around the source, and k denotes the serial number ofsamples. Note G0ij is independent of time.
G0ij and Ri were obtained using least-squares fitting to the observed data. Then, thepredicated temporal variation is written as
Oi(k)pre = G0ijSj(k)

(3-4)

5
105

using the transfer function, G0ij, obtained here. Comparing the temporal variation of thepredicted vibration with those observed, we can see that they are quite similar to eachother, meaning that the observed temporal variation at the seismometer is attributed
mostly to that of the foundation’s movement.
In this calculation the temporal variation of the medium, δG(ω,t), is the residual of
fitting Ri. Following Equation (3-2), the residual is written as:
Ri(k)= δG0ij(k)S0j(3-5)

What we want to obtain here is the vibration of the seismometer after of thetemporal variation of the foundation, and it is written as:(G0ij+δGij(k)) S0j= G0ij S0j+ Ri(k)(3-6)

From Equation (3-1),
G0ij S0j=< Oi(k)>(3-7)

in which <> denotes the average over time k. In this procedure we can obtain thetemporal variation without near-source effect.
3-2. Result of method in Yamaoka et al., 2001
As shown in Ikuta and Yamaoka (2004), the data in relatively short period of time
are well corrected using the method that is described above. To evaluate theperformance of the method for long-term data we applied the above method again forthe same data obtained in Ikuta et al. (2002). We tried to correct 800m-borehole dateusing transfer function on all frequency. In Fig.5 and Fig.6, the original date andcorrected date both in real and imaginary part are shown, which are corrected using therecords of the three seismometers deployed on the surface and one at the 10m borehole.
We show the results for two frequencies, 13.0 Hz and 19.1Hz, which corresponds tothe frequency in the middle of the frequency band generated by LF and HF unit,
respectively. In the long–term data, only the variations with long period were removed,

6106

but the variation with short period does not change. Fig.7 shows the standard deviation
for all frequencies on 800m-borehole observation. Fig.8 shoes the standard deviation
when applied the Yamaoka et al., [2001]. The variation of short period component
corresponds to daily changes. This suggests that the temporal variation in the motions of
the source can be devided into several modes, which have different transfer functions.
Therefore, the correction with single transfer function fails for long-term data.
We propose a reason why the method cannot remove the effect of the near-source
vibration. We assumed that the temporal variation at near-source signal can be divided
into at least two modes, short-term and long-term variation. The short-term variation
contains daily variation due to atmospheric temperature. The long-term variation
contains seasonal change due to drying or wetting of soil material near the source.
3-3. Improvement of the method
From the result that is shown above, we assumed that the temporal variation atnear-source signal can be divided into at least two modes, short-term and long-term
variation. We apply low pass filter both on observed data and near-source data to divide
the data into long-term and short-term variation. Moreover we improved the method by
Yamaoka et al., [2001].
We start with the same assumption that is proposed by Yamaoka et al., [2001], inwhich they assumed that the observed vibration of the seismometer, O, is a product of
the transfer function, G, and the near-source vibration of the function, S. Here we canwrite O and S as:O(ω,t)=G(ω)S(ω,t)(3-8)

In the analysis we assume S cannot fully represented by the record of near-source
vibration. We assume S is represented by two spaces, one is represented by near- source
vibration Sk and the rest is denoted as Su. In this notation k means ‘kown’ and u means‘unkown’.
Deviding S into two space Sk and Su, Equation (3-8) can be rewritten as:7107

O(ω,t)=Gk(ω,t)Sk(ω,t)+Gu(ω,t)Su(ω,t)(3-9)

in which, Gk and Gu care the transfer function that corresponds to a Sk and Su,
respectively. Dividing each term into time variant and invariant terms,
O0+δO=(Gk0+δGk)(Sk0+δSk)+(Gu0+δGu)(Su0+δSu)= Gk0Sk0+ Gk0δSk+δGkSk0+δGkδSk+ Gu0 Su0 + Gu0δSu+δGu Su0+δGuδSu(3-10)

We assumed that time-variant terms are small compared to the time-invariant term S, O
and denotes them with δ, respectively. We can assume that the contribution of Sk to O
is larger enough than that of Su, we can ignore higher order fractions correcponding to
Su. Therefore equation (3-10) can be rewritten as:
O0+δO= Gk0Sk0 + Gk0δSk + δGkSk0+Gu0Su0(3-11)

We calculate the average for both side of the equation (3-11):
O0= Gk0Sk0+Gu0Su0(3-12)

subtracting (3-12) form (3-11)
δO=Gk0δSk+ δGkSk0(3-13)

Gk0 andδGkSk0 are obtained using least-squares fitting to the time-variant term ofobserved data.
3-4. Process for analysis(Process 1)
First we applied low pass filter both on observed data and near-source data to divide
the data into two data set with long-term and short-term variations (Fig.9 and Fig.10).
We assumed that the long-term vibration includes seasonal change, and the short-term

8108vibration includes daily change. Fig.11 shows standard deviation for the long-term andshort-term variation on 800m-borehole observation.
(Process 2)
We applied the improved method on long-term and short-term variation,
respectively. We have suggested that the temporal variation of the motions of the source
can be dividing into several modes, which have different transfer functions. We
calculated transfer function both on long-term variation and short-term variation
separately. In Fig.12 and Fig.13, the original and corrected data of the real part andimaginary part are shown for long-term vibration and short-term vibration. We canreduce seasonal change on long-term vibration, and daily change on short-term
vibration. Fig.14 shows standard deviation when applied the improved method on
long-term and short-term variation.
(Process 3)
We add corrected long-term and short-term variation and obtain the final data inwhich the effect of near-source variation are corrected.
3-5. Result of the improved method
Fig.15 and Fig.16 shows the original data and the corrected data using the improvemethod that is described above. The data are corrected with the records of three
seismometers deployed on the surface and the one at the 10m borehole. We show theresults for two frequencies, 13.0Hz and 19.1Hz for examples.
In this result, temporal variations are reduces both in real part and imaginary part.
We calculated the standard deviations for all frequency. Fig.17 shows the standard
deviation of data corrected by the improve method. The standard deviation of new
methods is reduced by more than 0.5 to 0.8 orders of magnitude. When we compare itwith method of Yamaoka et al., [2001] (cf. Fig.5, Fig6 and Fig.7), it appeared that the
reduction of near-source effect using New Analysis works very well, especially UD, NS
components.

9109

4. Conclusion
We have successfully removed the temporal variation that is commonly appeared on
the signal both on receivers and near-source movement using the signal that is recordedby the seismometer near the source. We modified the method proposed in Yamaoka etal., [2001] to be able to correct the data in long-term observation. In the original method
it is difficult to reduce the common variation from long-term data, in which daily andseasonal variations are included, though it works for short-term data, in which daily
variation predominates.
We assumed that the temporal variation at near-source signal can be divided into atleast two modes, short-term and long-term variation. The short-term variation contains
daily variation due to atmospheric temperature. The long-term variation contains
seasonal change due to drying or wetting of soil material near the source.
In the new method we developed, we separate the whole data using low pass filter todivide the data into long-term and short-term variation. We also expressed the source
function with two independent spaces that is and is not able to be expressed withobserved signal at near-source seismometers. As a result, we can reduce the effect ofnear-source variation in quite good performance, especially UD, NS components.
Acknowledgements
A number of people have generously cooperated in this study. In particular, Prof. K.
Yamaoka, Dr. R. Ikuta, Prof. T. Watanabe, Dr. Y. Hasada, Prof. N. Fujii, in the field.
This research is fully supported by member of the ACROSS team.
We thank to Prof. K. Yamaoka, Dr. R. Ikuta in the University of Tokyo and Prof. T.
Watanabe in Nagoya University, who were great help in improving the this study.
Reference

10110

BuFE C. G ＆ VARES D. 1993 Predicitive modeling of the seismic cycle of theGreater San Francisco Bay region, Journal of Geophysical Research 98, 9871-83
Kumazawa, M., Y. Takei, Active method of monitoring underground structures bymeans of ACROSS.1 Purpose and principle, Abstracts of the Seismological Societyof Japan 2, 158, 1994
Ikuta, R., Temporal variation in the elastic properties in shallow crust detected withACROSS, Thesis for doctor of Science, Department of Environmental Studies,
Nagoya University, 2004, in Japanese
Ikuta, R., Yamaoka, K., Miyakawa, K., Kunitomo, T. and Kumazawa, M, Continuous
monitoring of Propagation velocity of seismic wave using ACROSS, Geophys. Res.
Lett., 29, doi; 10.1029/2001GL013974, 2002.
Ikuta R. and Yamaoka K, Temporal variation in the shear wave anisotropy detectedusing Accurately Controlled Routinely Operated Signal System (ACROS), J.
Geophys. Res., 109, B09305, doi; 10.1029/2003JB002901, 2004.
Juan, E Luco. and Russell, A Westmann., A. M. Asce., Dynamic response of circularfooting, Journal of the Engineering Mechanics Division, ASCE, 97, EM5, pp.
1381-1395, 1971
Misu, H., Active monitoring of upper crust using ACROSS-seismic array system–Identification of later phases observed in a long term continuous experiment at
Awaji Island-, Thesis for master of Science, Department of Earth and Planetary
Sciences Nagaya University, in JapaneseMisu, H, Reduction of the near-surface effect on the ACROSS signal recorded byreceivers at far-field, Thesis for master of Science, Division of Earth andPlanetary Sciences, Graduate School of Environmental Studies, Nagaya
University

11111

WIMER S. ＆ WYSS M. 1997. Mapping the frequency-magnitude distribution inasperities: An improved technique to calculate recurrence time?, Journal ofGeophysical Research 102, 15115-28
Yamaoka, K., Ikuta R., K. Miyakawa, T. Kunitomo, M. Kumazawa, A precise method
for continuous monitoring of the temporal variation of wave propagation,
Yamaoka, K., T. Kunitomo, K. Miyakawa, K. Kobayashi, M. Kumazawa, A trial formonitoring temporal variation of seismic velocity using an ACROSS system, The
Island Arc, 10, 336-347, 2001.
Miyakawa, K. Kobayashi, M. Kumazawa, A trial for monitoring temporal variation ofseismic velocity using an ACROSS system, The Island Arc, 10, 336-347, 2001.
AZHAD D., KANAMORI H. ＆ WIENS D. 1997. State of stress before and after the
1994 Northrige earthquake, Geophysical Research Letters 24, 519-22

12
112

1
0

a)

P

-1

1
0

SV

-1

SH

Rainfall(mm/day)

1
0
-1
100
50

0

b)

Delay time
(ms)

800m
1700m

Precipitation

10

Source

-1
Jan
15

Feb
24

Apr
4

May
14

Jun
23

Aug
2

Sep
11

Oct
21

NS
EW
Nov Jan
Feb
30
9
18

2000

2001

Fig. 1a) Temporal variation in the arrival time of P, transverse-S, and radial-S waves detectedby the 800m (red line) and 1700m (blue line) borehole sensors along with
precipitation.
The vertical arrows on the calendar axis indicate the date of the 2000 Western
Tottri and the 2000 Geiyo earthquakes.
b) Temporal variation in the phase of near-source vibration. Time delay averaged overfrequencies is used in the plot. The delays in two horizontal directions are estimatedassuming a rigid body motion of the source region. (Ikuta et al., 2002)

13
113

a)
c)
Osaka
North

Awaji Island

Nojima fault

South

0

b)

1700m borehole

600

main

800m
1700m

800m borehole

500m branch

1200
Seismometer
ACROSS Source

Fig. 2
Location of the ACROSS experiment site near the Nojima fault.
a) Location of the Nojima fault (Heavy line).
b) Location of the ACROSS vibrator (star) and the 1700m and 800m boreholes(triangles). Heavy gray lines are the surface trace of the boreholes.
c) North-South vertical cross section.
(modified Ikuta et al., 2002 )

14
114

a)
Amplitude [m/s]8

X 10‐8

0

-8
0

20

100

time (s)b)
Amplitude [m/s]

80

60

40

10-10
10-12
10-14
10

15

20

25

frequency (Hz)Fig. 3a) Example of one-hour stacked records for the vertical component of the
800m-borehole sensor.
b) Fourier amplitude spectra of the record shown in a). The separate lines in the
spectrum correspond to the signal of ACROSS. Two robes ranging from 10 to 16 Hz
and from 16.1 to 22.1 Hz correspond to the LF and HF units, respectively.
(Ikuta et al., 2004)

15
115

8.5m

ACROSS Source
Left
LF unit HF unit

(35Hz max)

10m

(25Hz max)

Right

10m-borehole

CenterSeismometer

Fig. 4
Arrangement of instrument in the building where the ACROSS source was situated.
Four seismometers (center, right, left, 10m-borehole) which placed near the edges of thefoundation to measure its vibration.

16
116a) 13.0 Hz

Real pa rt of Original date

Imaginary part of Original date‑8
1.5 x 10

2

Amplitude (m/s)

1.5

EW

1

x 10 ‑8

UD

1
0.5

0.5

0
0

UD

‑0.5

‑1

NS

Amplitude (m/s)‑2
10/01 01/01 04/01 07/01 10/01 01/01 04/01

Imaginary part of Correction

Real part of Correction

1.5

x 10‑82

x 10 ‑8

1.5

EW

1

EW

1.5

‑1
10/01 01/01 04/01 07/01 10/01 01/01 04/01

b)

NS

0.5

UD

1
0.5

0.5

0
0

NS

‑0.5

‑0.5

UD

‑1

NS

‑1.5

‑1
10/01 01/01 04/01 07/01 10/01 01/01 04/01

EW‑2
10/01 01/01 04/01 07/01 10/01 01/01 04/01

Time date

Time date

Fig.5a) Temporal variation of the ACROSS signal that is observe at 800m-boreholefrom Jan. 2000 to Apr. 2001. The signal at 13.0Hz, which is the middle of the frequency
range of LF (Low Frequency) unit, is shown for an representative example. Both realand imaginary parts are shown separately. Blue line shows the variation of UD
component, red line shows NS component and green line shows EW component. They
include seasonal and daily changes.
b)

The same signal that are shown in a) after the correction with the method

proposed by Yamaoka et al. (2001). Note that the long-term vibrations are reduced,
while short-term vibrations are not reduced.

17
117b)19.1HzaImaginary part of Original date

Real part of Original date

Amplitude (m/s)

20

x 10‑9

2
1.5

EW

15

0.5
0

NS

5

UD

EW

‑1.5

‑5
10/01 01/01 04/01 07/01 10/01 01/01 04/01

Amplitude (m/s)

UD

‑0.5
‑1

0

20

NS

1

10

b)

x 10 ‑8‑2

10/01 01/01 04/01 07/01 10/01 01/01 04/0

Imaginary part of Correction

Real part of Correction

x 10 ‑92

x 10‑8

1.5

15

EW
10

1

NS

0.5

UD

0

NS
5

0.5

UD

0

EW

‑1
‑1.5

‑5
10/01 01/01 04/01 07/01 10/01 01/01 04/01‑2
10/01 01/01 04/01 07/01 10/01 01/01 04/01

Time date

Time dateFig.6a) Temporal variation of the ACROSS signal that is observe at 800m-boreholefrom Jan. 2000 to Apr. 2001. The signal at 19.1Hz, which is the middle of the frequency
range of HF (High Frequency) unit, is shown for an representative example. Both realand imaginary parts are shown separately. Blue line shows the variation of UD
component, red line shows NS component and green line shows EW component. They
include seasonal and daily changes.
b)

The same signal that are shown in a) after the correction with the method

proposed by Yamaoka et al. (2001). Note that the long-term vibrations are reduced,
while short-term vibrations are not reduced

18
118

a)
‑9
2 x 10

UD

1.5
1
0.5
0
8.8

standard deviation

b)

10.8

12.8

14.8

16.8

c)
8

18.7

20.7

22.7

16.7

18.7

20.7

22.7

16.7

18.7

20.7

22.7

NS

‑9

6 x 10
5
4
3
2
1
0
8.8

16.7

10.8

12.8

14.8

x 10‑9

16.8

EW

6
4
2
0
8.8

10.8

12.8

14.8

16.8

Frequency [Hz]Fig.7
Standard deviation of the tempral variation of ACROSS signal for all the freuqnecies

that is observed at the 800m-borehole. a) UD component b) NS component c) EW
component. The frequencies from 8.0 Hz to 17.0 Hz and from 15.1 Hz to 23.1 Hz
correspond to the LF and HF units, respectively.

19
119

a)

‑10
x
10
6

UD

4
2

standard deviation

0

8.8 10.8 12.8 14.8 16.8 16.7 18.7 20.7 22.7
b)
‑10
x
10
6

NS

4
2
0

8.8 10.8 12.8 14.8 16.8 16.7 18.7 20.7 22.7
c)

‑10
x
10
6

EW

4
2
0

8.8 10.8 12.8 14.8 16.8 16.7 18.7 20.7 22.7
Frequency
Fig.8
Standard deviation after correction by the method proposed by Yamaoka et al.,[2001]. a) UD component b) NS component c) EW component. The frequencies from
8.0 Hz to 17.0 Hz and from 15.1 Hz to 23.1 Hz correspond to the LF and HF units,
respectively.

20
120a) 13.0 Hz Real partshort‑term vibration

long‑term vibration

1.5

x 10

‑8

1
0.5

0.5

0

0

‑0.5

‑0.5

‑1

Amplitude [m/s]

1

‑1
01/01

x 10

‑9

‑1.5
04/01

07/01

10/01

01/01

01/01

04/01

04/01

date

07/01

10/01

01/01

04/01

date

b) 13.0 Hz imaginary partlong‑term vibration

Amplitude [m/s]1.5‑

short‑term vibration

‑8
x 10

1.5

1

‑9
x 10

1

0.5

0.5

0
0

‑0.5

‑0.5

‑1

‑1

‑1.5
‑2

‑1.5

01/01 04/01 07/01 10/01 01/01

04/01

01/01 04/01 07/01 10/01 01/01

date

04/01

date

Fig.9
a)

Long-term and short-term temporal variation of the real part of 13.0 Hz todivide the data into long-term and short-term variation at 800m-borehole date from2000 to Apr. 2001.

Blue line shows the variation of UD component, red line shows NS

component and green line shows EW component. They include seasonal change anddaily change.
b)Long-term and short-term temporal variation of the imaginary part of 13.0 Hz

to divide the data into long-term and short-term variation at 800m-borehole date from
Jan. 2000 to Apr. 2001. They include seasonal and daily changes.

21121a) 13.0 Hz Real part
‑
x 10

20

Amplitude [m/s]

short‑term vibration

long‑term vibration

19.1

6

15

4

10

2

5

0

0

‑2

‑5

‑9
x 10

‑4

01/01 04/01 07/01 10/01 01/01

04/01

01/01 04/01 07/01 10/01 01/01

date

04/01

date

b) 19.1 Hz Imaginary partshort‑term vibration

long‑term vibration

Amplitude [m/s]

1.5

‑8
x 10

6

1

x 10

4

0.5
0

2

‑0.5

0

‑1

‑2

‑1.5
‑2
01/01 04/01 07/01 10/01 01/01

‑4
04/01

date

01/01 04/01 07/01 10/01 01/01

04/01

date

Fig.10a)Long-term and short-term temporal variation of the real part of 19.1 Hz todivide the data into long-term and short-term variation at 800m-borehole date from2000 to Apr. 2001. 13.0 Hz is the middle of the frequency by HF. Blue line shows thevariation of UD component, red line shows NS component and green line shows EWcomponent. They include seasonal and daily changes.
b)Long-term and short-term temporal variation of the imaginary part of 19.1 Hz

to divide the data into long-term and short-term variation at 800m-borehole date from
Jan. 2000 to Apr. 2001. They include seasonal and daily changes.

22
122long-term vibraion

standard deviationa) UDshort-term vibraion

‑9
x 10

2

6

1.5

‑9
x 10

4

1
2

0.5
0

0

8,8

standard deviationb) NSstandard deviation

c) EW

8

14.8 16.7

22.7

‑9
x 10

1

8,8

14.8 16.7

22.7

8,8

14.8 16.7

22.7

8,8

14.8 16.7
22.7
Frequency

‑9
x 10

6
4

0.5

2
0

3

8,8

14.8 16.7

0

22.7

‑9
x 10

3

2

2

1

1

0

0

8,8

14.8 16.7
Frequency

22.7

‑9
x 10

Fig.11
Standard deviation for long-term and short-term variation observed at the
800m-borehole date. a) UD component b) NS component c) EW component. The
frequencies from 8.0 Hz to 17.0 Hz and from 15.1 Hz to 23.1 Hz correspond to the LF
and HF units, respectively.

23123a) 13.0 Hz Real partshort‑term vibration

long‑term vibration

Amplitude [m/s]

1.5

‑8
x 10

1

1

0.5

0.5

0

0

‑0.5

‑0.5

‑1
‑1.5
01/01 04/01 07/01 10/01 01/01‑1
01/01 04/01 07/01 10/01 01/01

‑9
x 10

04/01

04/01

date

date
b) 13.0 Hz Imaginary partshort‑term vibration

long‑term vibration

Amplitude [m/s]

1.5

‑8
x 10

1.5

‑9
x 10

1

1
0.

0.5

0

0

‑0.

‑0.5

‑1

‑1

‑1.5

‑1.5

‑2
01/01 04/01 07/01 10/01 01/01

01/01 04/01 07/01 10/01 01/01

04/01

04/01

date

date
Fig. 12a)Corrected long-term and short-term variation of the signal at 13.0 Hz that isobserved at 800m-borehole date from 2000 to Apr. 2001. We applied the improved
method that is proposed in this study.

Blue line shows the variation of UD component,

red line shows NS component and green line shows EW component. Note that both thelong-term and short-term vibrations are reduced.
b)

Corrected temporal variation of the imaginary part of 13.0 Hz to divide the data

into long-term and short-term variation on 800m-borehole date from Jan. 2000 to Apr.
2001. We applied improve the method by [Yamaoka et al., 2001]. Note that thelong-term and short-term vibrations are reduced.
.
24
124

a) 19.1 Hz Real partshort‑term vibration

long‑term vibration

Amplitude [m/s]

20

‑9
x 10

6

15

4

10

2

5

0

0

‑2

‑5

‑4

01/01 04/01 07/01 10/01 01/01

‑9
x 10

01/01 04/01 07/01 10/01 01/01

04/01

04/01

date

date
b) 19.1 Hz Imaginary partshort‑term vibration

long‑term vibration

Amplitude [m/s]

1.5

‑8
x 10

6

1

‑9
x 10

4

0.5
0

2

0.5

0

‑1

‑2

1.5
‑2
01/01 04/01 07/01 10/01 01/01

‑4
04/01

01/01 04/01 07/01 10/01 01/01

date

04/01

date

Fig.13a)Corrected temporal variation of the real part of 19.1 Hz by the divide the data

into long-term and short-term variation on 800m-borehole date from 2000 to Apr. 2001.
We applied improve the method by [Yamaoka et al., 2001]. Blue line shows thevariation of UD component, red line shows NS component and green line shows EWcomponent. Note that the long-term and short-term vibrations are reduced.
b)

Corrected temporal variation of the imaginary part of 19.1 Hz by the divide thedata into long-term and short-term variation on 800m-borehole date from Jan. 2000 to
Apr. 2001. We applied improve the method by [Yamaoka et al., 2001]. Note that thelong-term and short-term vibrations are reduced.
25125a) UD
short-term vibration

long-term vibration

standard deviation

2

‑9
x 10

2

1.5

1.5

1

1

0.5

0.5

16.7

0

0

8,8
b) NS
2

standard deviation

‑9
x 10

14.8

16.7

8,8

22.7

‑9
x 10

2

1.5

1.5

1

1

0.5

0.5

0

standard deviation

8

16.7

22.7

14.8

16.7

22.7

14.8

16.7

22.7

0

8,8
c) EW

14.8

‑9
x 10

14.8

16.7

8,8

22.7

‑9
x 10

8

6

6

4

4

2

2

0

‑9
x 10

0

8,8

14.8

16.7

22.7

8,8

Frequency

Frequency

Fig. 14
Standard deviation for long-term and short-term variation observed when applied
improve the method by [Yamaoka et al., 2001] to divide the data into long-term andshort-term variation, respectively. a) UD component b) NS component c) EW
component. The frequency from 8.0 Hz to 17.0 Hz and from 15.1 Hz to 23.1 Hz
corresponds to the LF and HF units, respectively.

26
126

Fig. 15a) Temporal variation of the ACROSS signal that is observe at 800m-boreholefrom Jan. 2000 to Apr. 2001. The signal at 13.0Hz, which is the middle of the frequency
range of LF (Low Frequency) unit, is shown for an representative example. Both realand imaginary parts are shown separately. Blue line shows the variation of UD
component, red line shows NS component and green line shows EW component. They
include seasonal and daily changes.
b)

The same signal corrected by the method proposed in this study. The long-term

vibration reduced, short-term vibration reduced.
.

27
127

b)19.1Hz
Imaginary part of Original date

Real part of Original datex 10‑9Amplitude (m/s)

20

1.5

EW

15

NS

1
0.5

10

0

NS

5

UD

‑0.5
‑1

0

UD

‑2

10/01 01/01 04/01 07/01 10/01 01/01 04/01

15

EW

‑1.5

‑5

10/01 01/01 04/01 07/01 10/01 01/01 04/01

Real part of correction date

Imaginary part of correction date‑9x 10‑8

x 10

1

EW

Amplitude (m/s)

x 10 ‑8

2

NS

0.5

10

NS

UD

0

5

‑0.5
0

EW

‑1

UD

‑1.5

‑5

10/01 01/01 04/01 07/01 10/01 01/01 04/01

10/01 01/01 04/01 07/01 10/01 01/01 04/01

Time date

Time date

Fig.16a) Temporal variation of the ACROSS signal that is observe at 800m-boreholefrom Jan. 2000 to Apr. 2001. The signal at 19.1Hz, which is the middle of the frequency
range of HF (High Frequency) unit, is shown for an representative example. Both realand imaginary parts are shown separately. Blue line shows the variation of UD
component, red line shows NS component and green line shows EW component. They
include seasonal and daily changes.
b)

The same signal corrected by the method proposed in this study.

long-term vibration reduced, short-term vibration reduced.

28
128

The

a) UD
6

‑10
x 10

4
2

standard deviation

0
8.8

a) NS

x 10

10.8

12.8

14.8

16.8

16.7

18.7

20.7

22.7

10.8

12.8

14.8

16.8

16.7

18.7

20.7

22.7

10.8

12.8

14.8

16.8

16.7

18.7

20.7

22.7

‑10

6
4
2
0
8.8

a) EW
1

‑9
x 10

0.5

0
8.8

Frequency
Fig.17
Standard deviation for long-term and short-term variation observed when applied
improve the method by [Yamaoka et al., 2001]. a) UD component b) NS component c)
EW component. The frequency from 8.0 Hz to 17.0 Hz and from 15.1 Hz to 23.1 Hz
corresponds to the LF and HF units, respectively.

29
129

130

Earth Planets Space, 58, 993–1005, 2006

Continuous observation of seismic wave velocity and apparent velocity using aprecise seismic array and ACROSS seismic source
Atsushi Saiga1∗ , Koshun Yamaoka2 , Takahiro Kunitomo3 , and Toshiki Watanabe4
1 Graduate School of Science, Nagoya University, Nagoya 468-8602, Japan

2 Earthquake Prediction Research Center, Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan
3 Tono Geoscience Center, Japan Nuclear Cycle Development Institute, Gifu 509-5132, Japan

4 Research Center for Seismology, Volcanology and Disaster Mitigation, Nagoya University, Nagoya 468-8602, Japan(Received September 28, 2005; Revised May 28, 2006; Accepted May 29, 2006; Online published September 16, 2006)

We report the results of continuous monitoring—using a seismometer array—of the travel time of seismic
waves generated by an ACROSS artificial seismic source. The seismometer array, which was deployed in asurface vault located 2.4 km from the source, recorded both direct P- and S-waves and refracted P- and Swaves that traveled along a velocity boundary between the granite basement and overlying sedimentary rocks.
We analyzed temporal variation in differential travel time and apparent velocity for these phases for a periodof 1 month and found significant temporal variation in the differential travel time. Most of the variation can be
attributed to changes in environmental conditions, such as atmospheric temperature and rainfall. Variation is evenobserved in the seismogram that is located 50 m from the vibration source, although much smaller variation isobserved in the vibration of the foundation to which the source is attached. The spectral study revealed that theeffects of temperature and rainfall depend strongly on the frequency range used by ACROSS and that a large
variation occurs in the 15- to 20-Hz range, especially between 17 and 20 Hz. The environmental effect on thetemporal variation is comparable to the record of refracted S waves and that of a distance of 50 m, whereas a larger
variation was observed in the direct S wave. This result shows that the signal is affected by the environmental
change near the vibration source. The environmental effect can be drastically reduced when the signal from the
15- to 20-Hz range is eliminated in the analysis.
Key words: Active monitoring, seismometer array, ACROSS, temporal varia tion, spectral analysis.

1.

Introduction

prior to moderate magnitude earthquakes in central California even though seismic velocity was carefully monitored
using quarry blasts of precisely controlled timing. Theseauthors concluded that in order to successfully monitor velocity changes, additional careful studies would be required
within incipient source regions using wave paths that propagate through the source region. The question of whether itis practically possible to measure velocity changes resulting
from changes in tectonic stress, however, remains controversial.
The scattering of seismic waves is a potentially effective
method of detecting changes in physical properties, such asattenuation properties, as it can be used to sample an entire
crustal volume, such as a rupture zone. Sato (1988) reported
a significant increase in the scattering and attenuation ofseismic waves prior to and following the 1984 Western
Nagano earthquake (Ms=6.8). Similarly, Hiramatsu et al.
(2000) recorded an increase in coda Q−1 following the 1995
Hyogoken-Nanbu earthquake and attributed this change tovariations in static stress that resulted from the earthquake.
Changes in the anisotropy of seismic waves have also been
∗ Now at Institute of Seismology and Volcanology, Faculty of Sciences,
detected in association with seismic events. For example,
Kyushu University, Shimabara, Nagasaki 855-0843, Japan.
temporal changes in the time delay of split shear waves
have been observed immediately prior to earthquake events
c The Society of Geomagnetism and Earth, Planetary and Space SciCopyright !
ences (SGEPSS); The Seismological Society of Japan; The Volcanological Society (e.g. Crampin et al., 1990; Bokelmann and Harjes, 2000).
of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sci- This phenomenon has been explained by applying a theences; TERRAPUB.
ory of extensive dilatancy anisotropy (Crampin, 1987) in
Various methods have been tested for their sensitivity andreliability to detect changes in the propagation properties ofseismic waves related to changes in the travel medium (seeCrampin et al., 1990; Li et al., 1998; Niu et al., 2003).
Changes in stress and fluid distribution, for example, canaffect propagation properties, such as the velocity, attenuation, dispersion and anisotropy of seismic waves.
Laboratory experiments indicate that the velocity of elastic waves in rocks is strongly dependent upon the natureof the stress field (Birch, 1960). This relationship is attributed to the increasing stiffness and seismic velocity
of rocks under high stress that results from the closureof structural defects such as cracks and joints. Semenov(1969) monitored the velocity of direct P- and S-waves andrecorded reductions in the V p/V s ratio immediately prior
to large earthquakes; these observations are the forerunners
to the dilatancy-diffusion theory (Nur, 1972; Sholtz et al.,1973). In contrast to these findings, McEvilly and Johnson (1974) failed to detect any variation in the V p/V s ratio

993
131

994

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS

which the differential stress field dictates the preferentialalignment of newly formed or growing cracks. Saiga et al.
(2003) reported temporal variation in the time delay of split
shear waves resulting from static stress changes associatedwith a moderate magnitude earthquake. These observations
demonstrate the sensitivity of the propagation properties ofseismic waves to changes in applied stress; however, theseresearchers were not always able to analyze events of similar source parameters. Successive earthquakes with identical source parameters, such as hypocenter and focal mechanism, are ideally required for accurate monitoring of the
propagation properties of seismic waves.
An accurate and continuous experiment is necessary todetect temporal variations in seismic velocity within theearth’s crust. Reasenberg and Aki (1974) conducted an experiment that involved measuring the travel time of an airgun shot signal over a distance of 200 m. They detected avariation in travel time of 1 ms, which can be correlated tothe effects of the earth’s tide. Yamamura et al. (2003) conducted long-term observations using a piezoelectric transducer over a distance of 12 m, and also detected variations
in travel time that show a strong correlation with the earth’s
tide. Furumoto et al. (2001) demonstrated that characteristic temporal changes in seismic wave velocity can be related
to tidal stress and a secular stress accumulation resulting
from repeated observation explosions. There are, however,few studies that have undertaken the accurate and continuous long-term monitoring of seismic velocity using an artificial source.
A system that uses an artificial source and which is capable of continuous and precise monitoring of the propagation properties of seismic waves within the crust has alreadybeen developed (Kumazawa and Takei, 1994; Yamaoka etal., 2001). This system is called the Accurately Controlled
Routinely Operated Signal System (ACROSS). The vibrator in the ACROSS system generates a signal with a centrifugal force of a rotating eccentric mass. The rotation isprecisely synchronized to global positioning system (GPS)timing, which provides large numbers of stacks for data thatare also sampled in synchrony with GPS timing at a receiver. Given a 1-week stacking, the signal generated by the
ACROSS vibrator can be detected at seismic stations morethan 100 km from the source (Yamaoka and Ikuta, 2004;
Yoshida et al., 2004). The vibrator used in this study can
produce a maximum force of 2×105 N, but one can barely
feel the vibration even at a distance of 10 m.
Ikuta et al. (2002) monitored temporal variations in travel
time for 15 months using a surface-deployed ACROSS
source and seismometers at depths of 800 m and 1700 m
in boreholes along the Nojima fault zone, which was thefault zone that ruptured during the 1995 Hyogo-ken Nanbu(Kobe) earthquake. The authors were able to measure temporal variation in the travel time of direct waves over a long
period with high accuracy. Ikuta and Yamaoka (2004) detected sudden delays and subsequent gradual recovery in thetravel time of direct P- and S-waves generated by the 2000
Western-Tottori earthquake (Mw=6.6) and the 2001 Geiyo
earthquake (Mw=6.4). The delays were also accompanied
by an increase in shear wave splitting. These authors interpreted the measured variation as resulting from an increasein pore pressure within preferentially aligned cracks in theuppermost crust due to strong seismic shaking. The importance of this study is that the authors were able to demonstrate that seismic velocity could be monitored over a long
period of time at a high accuracy.
Based on the above experiments, all of which revealed
the potential of the ACROSS system, we sought to utilize
seismometer arrays to detect and monitor various phases
included in the ACROSS signal. Niu et al. (2003) detected a temporal variation in the seismogram of repeatedmicroearthquakes measured by seismic stations. Their results revealed a change in the location of scatterers within afault zone related to an aseismic deformation event. In thecurrent study, we set out to document precise observations
using a seismic array with the aim of investigating temporalvariations in the seismic wave velocity and apparent velocity of various phases propagating through the crust. The
observation site that we selected for this study is a researchsite located deep underground, where subsurface structure
is well understood and where many observational facilities,
such as strainmeters, groundwater wells and seismometers,
are already deployed.

2.

Site Description and System Deployment

2.1 Observation array
We deployed a seismic array within a vault used for theobservation of crustal deformation. As our aim was to detect temporal variations in the propagation properties ofseismic waves, it was important to minimize artificial variations resulting from the observation system. We therefore deployed both seismometers and the data-logging system in the vaults, where temperature remains constant towithin 0.1◦ C for the entire year. The array comprised 15
137°13'137°15'40°N

Mizunami
Tono mine(ACROSS source)
35°23'

borehole
seismometer

N126°E
30°N

2.4
km

130°E

140°E

Mizunami vault(Seismometer array)sourcefoundation
seismometer

1

8

1km

N32°E

A

35°21'H
N58°W
Extensometer
seismometer

Fig. 1. Map of the experiment site. The ACROSS sources and seismometer array are deployed in the Tono mine and in a vault used for the observation of crustal deformation in Mizunami, respectively. Solid circles
denote seismometers. The seismometer array is 64×64 m at the intervalof 8 m ,as a cross shape along extensometers. Open circles and an open
rectangular denote three ACROSS sources, which have rotation axes inthe vertical and the horizontal direction, respectively. The ACROSS
sources are covered with a foundation.

132

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS

three-component velocity sensors (Mark Products Inc.; L28LBH) with a natural frequency of 4.5 Hz and sensitivityof 0.61 V/(cm/s). The seismometers were deployed linearlyat 8-m intervals in two tunnels that intersect at right angles.
The vault that housed the seismometer array is located
2.4 km from the ACROSS source used in this study (Fig. 1)
and is constructed within Neogene sedimentary rock of the
Mizunami group that overlies the Cretaceous granite basement. The ACROSS source was deployed on the surface ofthe Mizunami group; phases that propagate through the sedimentary rock and granite basement can therefore be monitored by the array with good resolution.
2.2 Data logging system for array observation
The logging system consisted of an amplifier and PC withinbuilt digitizers. The signals from the seismometers were
amplified to ensure that ground noise was in excess of thequantization noise of the digitizer. The signal was digitized
by A/D converters with synchronization to GPS timing. We
adopted a sampling rate of 1 kHz to reduce the effect of antialiasing filtering, although the signal of the ACROSS source
was <30 Hz. The filter was used to reduce the noise above
Nyquist frequency, which otherwise overlaps with the frequency band of the ACROSS signal through the aliasing
effect. The cut-off frequency of the anti-alias filter was set
at 250 Hz, which was high enough to suppress the phase
effect on the frequency band of the ACORSS signal. Delaytimes due to channel switching in the digitizing process andsignal transmission from seismometers were measured andcorrected as appropriate.
2.3 GPS synchronization for array observation
The signals from seismometers were digitized in synchronization with GPS timing. For synchronization, weused a 1 pulse-per-minute (PPM) code and 1 kilo-pulse-persecond (KPPS) code that were generated by a GPS clock.
The data sampling, which is synchronized to the 1 KPPS
code, starts every hour with synchronization to the 1 PPM
code. The accuracy of the timing is kept to within 0.1 µs ofuniversal time.
As the logging system was installed approximately 200
m from the entrance of the vault, we had to transmit thecodes to the data logger from the GPS clock that is locatedby the entrance. We used differential line-drivers and differential line-receivers for transmitting both the 1 PPM and1 KPPS signals to avoid the effect of large common-mode
noise. The delay time involved in transmitting signals wascorrected as appropriate.
2.4 Source deployment
The ACROSS vibrators used in this study were deployedin the Tono mine, Gifu prefecture, Japan. Three ACROSS
vibrators with different eccentric moments were deployed.
The low-frequency (LF) vibrator produced a force of 2×105
N at a frequency of 25 Hz, the mid-frequency (MF) vibrator
produced 1.9×105 N at a frequency of 35 Hz and the highfrequency (HF) vibrator produced 1.6×105 N at a frequencyof 50 Hz. The vibrator force is generated by the centrifugal
force of a rotating eccentric mass and is therefore proportional to the square of the rotational velocity. The ACROSS
vibrators were firmly fixed to a foundation of steel-framed
concrete structure, which was constructed in a rectangularhole of dimensions 6 (length)×3.5 (width)×2.3 m (depth).

995

The eccentric masses of the LF and MF units rotate arounda vertical axis, whereas that of the HF unit rotates around a
horizontal axis. Three accelerometers were installed on thefoundation to monitor any movement.
The vibration of the source was synchronized to GPS
timing (Yamaoka et al., 2001). The rotation of the mass
is modulated in frequency to produce plural spectral peaks
simultaneously. The modulation is repeated at a constantinterval, resulting in the production of a stable force foreach spectral peak.

3.

Obtaining the Transfer Functions

3.1 Virtual linear vibrator
The ACROSS vibrators generate acceleration through therotation of eccentric mass around an axis, although linear
acceleration is often useful for sources of seismic signals. In
most rotational vibrators (e.g. Alekseev et al., 2005), linear
acceleration is produced by rotating two motors in opposite
directions. In contrast to traditional vibrators, we synthesize
a linear acceleration with the data of a single rotor. The motor of the ACROSS vibrator switches its rotational direction
at 1-h intervals, and we were able to synthesize a linear motion by combining the signals of two successive hours. The
great advantage of this method is that we can synthesize alinear acceleration in any direction at every hour. The synthesized data Y θ in the direction θ is obtained via a linear
combination (Kunitomo and Kumazawa, 2004) as:Y θ (ω) = Y n (ω) exp (iθ) + Y r (ω) exp (−iθ)(1)

where Y n and Y r are the observed spectrums when the
ACROSS source rotates in clockwise and counterclockwise
directions, respectively, and ω is the angular frequency ofthe signal.
The force at the source is also synthesized in a similarway:
X θ (ω) = X n (ω) exp (iθ) + X r (ω) exp (−iθ)(2)

where X n and X r are the spectrums of the generated force
when the source rotates in clockwise and counterclockwise
directions, respectively. We can then use these data toobtain transfer functions for different components of thevibrations.
3.2 Transfer function
The transfer function between the force generated at thesource and the signal observed at the array is obtained via
a deconvolution of observed waveform by source signal in
the frequency domain:G θk (ω) = Ykθ (ω) / X θ (ω)(3)

where G θk represents the transfer function of the k-th component of the receivers for a linear acceleration at the sourcein the direction θ.
A waveform in the time domain is obtained by applying
an Inverse Fourier Transform (IFT) to the transfer function
in Eq. (3). In the operation of the ACROSS source, weused a frequency modulation technique to produce plural
frequency components simultaneously. Figure 2 shows anexample of these waveforms and the spectrum for a virtual

133

996

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS

(a)

-8

10

Amplitude (N)

x105
1
0
-1
20

80

100

Amplitude (N)

104
102
100
15

(b)

20
Frequency(Hz)25

18.95Hz-91014.00Hz14.00Hz

-10

10

30

18.95Hz

Amplitude (m/s)

x10-8
-11

2

10

0

101

-2
0

20

-8

10
Amplitude (m/s)

4060
Time(second)

Amplitude (m/s)

0

40
60
Time(second)

80

10-12

Amplitude(m/s/N)

15

0

25

30

later phases

10
Time(second)-11

10
Amplitude(m/s/N)

20
Frequency(Hz)x10-11
S wave-2 P wave
0

20

-13

10

-15

10

104
1 week

Fig. 3. Variation in the amplitude of the signal and noise components witha greater number of stacks in the first experiment. Gray lines show thesignal and noise components around 18.95 Hz; black lines show thosearound 14.00 Hz. The level of signal components is almost constant incontrast to the level of noise that decreases with stacking.

10

2

103
1 day

Number of stacks

100

-10

(c)

102

15

20
Frequency(Hz)2530

Fig. 2. (a) Theoretical force generated at the ACROSS sources: A waveform (top); the amplitude spectrum (bottom). The gray and the blacklines indicate signals of the ACROSS sources and noises, respectively.
(b) (Top) A record at seismometer C. (Bottom) The amplitude spectrum. (c) (Top) A transfer function between the source and seismometerC in the time domain. (Bottom) The transfer function in the frequency
domain.

linear vibration in the radial direction; Fig. 2(a) shows aforce generated at the ACROSS source. The force is calculated theoretically from the rotation velocity of the eccentric mass. Figure 2(b) shows a record at a seismometer at
the center of the array for 150-h stacking. As a same modulation is repeated every 20 s, signals from the source appear
every 1/20 Hz in the frequency domain; these are called thesignal components, whereas others are termed noise com-ponents. The signal-to-noise ratio (SNR) can be estimatedfrom the ratio of the amplitudes of the signal and noise components, which is about 102 in this experiment. By using
the signal components for source and receivers, we can obtain transfer functions. Figure 2(c) shows the transfer function in both the frequency and time domains. The signal
components with small amplitudes are omitted in the transfer function in the frequency domain. The transfer functionin the time domain is calculated using these data. Several
phases with large amplitudes are found in the transfer function in the time domain [Fig. 2(c)].
A signal leakage is apparent in the transfer function in
the time domain, especially around 20 s in Fig. 2(c). The
leakage may have resulted from an inappropriate selectionof window function when applying the IFT. This effectalso occurs in other parts of the transfer function in thetime domain, and small later phases might be concealedby the leakage effect. We use cosine-taper windows in thefollowing analysis as an optimum window function.

4.

Phase Identification and Estimation of Temporal Change

We conducted three experiments with the aim of detecting temporal variations in the travel times of waves propagating along various paths between the source and the receivers. Table 1 shows the operation parameters of the
ACROSS source used in the experiments.

Table 1. Transmit parameter of the ACROSS sources.
Number of Time Period of Source Type
Source TypeTime Period of Center Frequency
Moduration
Generated Force [N]experiments Experiments (Rotation axis) (Type of frequency) FM [second][Hz]
Amplitude [Hz]1
1 weekVertical
MF
10
21.45
2.5
0.6×105∼0.9×105
Vertical
LF
10
16.50
2.5
0.6×105∼1.2×105
2
4 daysHorizontal
HF
20
30.00
10.00
0.3×105∼1.0×105
Vertical
LF
20
15.01
5.00
0.3×105∼1.3×105
31 monthVertical
MF
20
25.53
2.50
0.8×105∼1.2×105
Vertical
LF
20
17.52
2.50
0.7×105∼1.3×105

134

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS
(V-V)

997

(R-V)
1x10-11
Seismometer A

Seismometer A

Seismometer B

Seismometer B

Amplitude (m/s/N)

Amplitude (m/s/N)

1x10 -11

Seismometer C
Seismometer D
Seismometer E
Seismometer F
Seismometer G

Seismometer C
Seismometer D
Seismometer E
Seismometer F
Seismometer G

Seismometer H

Seismometer H

-11

1x10
Seismometer 1

Seismometer 1

Seismometer 2

Seismometer 2

Amplitude (m/s/N)

Amplitude (m/s/N)

1x10 -11

Seismometer 3
Seismometer C
Seismometer 5
Seismometer 6
Seismometer 7

Seismometer 3
Seismometer C
Seismometer 5
Seismometer 6
Seismometer 7

Seismometer 8

0

1

2

(V-R)

3
Time (second)4

5

Seismometer 8

0

6

1

2

(R-R)

3
Time (second)

4

5

6

1x10-11

Amplitude (m/s/N)

Amplitude (m/s/N)

1x10 -11

1x10-11

Amplitude (m/s/N)

Amplitude (m/s/N)

1x10 -11

0

1

2

3
Time (second)

4

5

0

6

1

2

3
Time (second)

4

5

6

(T-T)
Seismometer A

Amplitude (m/s/N)

Seismometer B
Seismometer C
Seismometer D
Seismometer E
Seismometer F
Seismometer G
Seismometer H

1x10-11
Seismometer 1

Amplitude (m/s/N)

Seismometer 2
Seismometer 3
Seismometer C
Seismometer 5
Seismometer 6
Seismometer 7
Seismometer 8

0

1

2

3
Time (second)

4

5

6

Fig. 4. Three component waveforms at the array for each component of the vibration. (V-V) Waveform at the vertical component for the verticalcomponent of vibration. (V-R) Waveform at the radial component for the vertical component of vibration. (R-V) Waveform at the vertical component
for the radial component of vibration. (R-R) Waveform at the radial component for the radial component of vibration. (T-T) Waveform at thetransverse component for the transverse component of vibration. The frequency band 10.01–20.01 Hz is used for the radial and the transverse
component of vibrations. A broader frequency band, which ranges from 20.00 to 40.00 Hz, is used for the vertical component of vibrations. Arrows
denote an arrival of marked phases.

In the first experiment, we examined the efficiency ofstacking to obtain a SNR that is large enough to enable
the identification of phases. Figure 3 shows the variationin the amplitude of signal and noise components versus thenumber of stacks obtained in the first experiment. We wereable to obtain a SNR of approximately 100 for each signal
component by stacking the data for a period of 1 week.
In the second experiment, a broad-frequency band wasused for the source signal. The use of a broadband signal as a source produced superior time resolution of phasesin the transfer functions. In this experiment we operated
the source with changing rotation direction to obtain thetransfer function corresponding to linear vibrations of various directions. For radial and vertical vibrations, the trans-

fer functions had larger amplitudes in the vertical and radial components than in the transverse component. For thetransverse vibrations, the transfer function had a large amplitude in the transverse component. Working under the assumption that P- and S-wave behavior in an isotropic homogeneous medium can be applied in this site, we separated the P- and SV -waves from the S H -wave in the transfer functions. Wherever possible, we attempted to detectvarious phases as in an isotropic homogeneous medium.
Figure 4 shows the three-component waveforms at thearray for each component of the vibrations. In the verticalcomponent of vibrations, four phases are evident at approximately 0.6, 0.8, 1.2 and 1.6 s of travel time. Four more
phases are also evident in the radial component of vibra-

135

998

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS(semblance analysis)Slowness (s/km)

0.6

0.5

0.4

0

0.2
-0.5
x 10-121

2

3Time (second)

4

5

1

0.4

0.5

0.3
0.2

0

0.1
-0.5

0
0

1

2

3
Time (second)

4

5

(R-V)

0.5

0.3

0.1
-0.5
0

-12

5 x 1000123Time (second)

4

5

6

semblance
0.5
0.4

0.5

0.3
0.2

0

0.1
-0.5
0

-12

5 x 1000123Time (second)

4

5

(T-T)

semblance

6

1

1

6

semblance
0.6
1

0.4

Slowness (s/km)

Slowness (s/km)

0.2

0Amplitude(m/s/N)0-12

5 x 100.4(V-R)

semblance
0.5(modified semblance analysis)Slowness (s/km)

6

Slowness (s/km)

001

Amplitude(m/s/N)

0

5

0.5

0

0.2

0.4
0.5
0.2

0

-0.5

-0.5
0

x 10 -11

Amplitude(m/s/N)

Amplitude(m/s/N)

semblance
0.5

0.8

1
Slowness (s/km)(V-V)

semblance

1
0
0

1

2

3
Time (second)

4

5

(R-R)

6

0

x 10 -12

2
0

0

1

2

3
Time (second)

4

5

6

semblance

Slowness (s/km)

1
0.4
0.5

0

0.2

Amplitude(m/s/N)-0.5
0x 10 -11

1
0
0

1

2

3
Time (second)

4

5

6

Fig. 5. (a) An example of the semblance map calculated in this study. (Top) A semblance map for an ordinary semblance analysis representing theradial component waveform at the array for the radial component of vibration. Time windows in the calculation are 0.1 s in both the numerator anddenominator. (Bottom) A semblance map for a modified semblance analysis. Time windows in the calculation are 0.1 s in the numerator and 0.3
s in the denominator. (b) Semblance map for the modified semblance analysis at each component waveform at the array for the vertical, radial andtransverse component of vibration. Symbols for figures denote the component waveform at the array and the component of the vibration, as shown in
Fig. 5.

tions at approximately 1.9, 2.3, 3.2 and 5.2 s. In the transverse component of vibration, there were two clear phases
at approximately 1.3 and 1.6 s. In the following sections weinvestigate these ten phases to determine their wave properties.
4.1 Semblance analysis of the ACROSS signal
To extract the spatially coherent component of the
ACROSS signal, we used the semblance method (Neidell
and Tanar, 1971) as a coherency measure for multi-channel
data. The semblance value S jn , as a function of time andapparent slowness, is expressed as
"K
%
J/2
#
$ 2
!
!
g jk t j , αnS jn =

j=−J/2

K·

J/2
!

k=1

K
!

j=−J/2 k=1

(4)

#
$2
g jk t j , αnwhere g jk denotes a wavefield at the j-th sample and k-th
seismometer, and J and K are the number of samples inthe select windowand#$ seismometers, respectively. In thisequation, g jk t j , αn is obtained using an inverse Fourier

136

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS

0.4
αr= 0.25
αt= -0.1
1-1-1

Radial component ofapparent slowness

0

1

0

Radial component ofapparent slowness

αr= 0.25
αt= -0.1

1

-1

0

0

-1

αr= 0.25
αt=-0.25

1
-1

1

0

1

-1

1.27 (second)

0

1

2

0

-1

0
0

αr= 0.45
αt= -0.2
-1

0

1

-2

0

-1

1.60 (second)
Transverse componentof apparent slowness00
αr= 0.55
αt= 0.25
0

-2
1

-2

0

2

1.88 (second)-10
αr= 0.45
αt= -0.4
0

0.5

0

-0.5
-0.5

0

0.5

0.5

0

-0.5
-0.5

0

0.5

0.6
0

0.4
αr= 0.45
αt= -0.3

1
-1

0

0.2

1
0
-1
-1
0
1
Transverse component

1

1.6 (second)

-2
1

0.8

Radial component ofapparent slowness

0

-1

0.5

semblance

-1

2

1

1

1.3 (second)

2

-1

0

0

Radial component-11

αr= 0.65
αt= 0.05

1

2

-0.5
-0.5

-1
-2

0

Vertical component

1

-2

0

Radial component

5.30 (second)

-1

0.5

Radial component

Vertical component

0

0

-1

0.2

3.25 (second)

-1

-1

0.4
αr= 0.45
αt= -0.5

Radial component

0.82 (second)

1

0.6
0

Vertical component

0

0

0.8

Vertical component

-1

0.2

1

semblance-

Vertical component

0.6
0Transverse componentof apparent slowness

0.8

-1

1

2.30 (second)

semblance
Vertical component

Transverse componentof apparent slowness

0.62 (second)

999

2
0
αr= 0.55
αt= 0

1
-1

0

1

1
0
-1
-1
0
1
Transverse component

Fig. 6. (Left) Semblance map for an ordinary semblance analysis as a function of the radial and transverse component of apparent slowness for eachphase. Negative of the radial component of apparent slowness shows an arrival from the source direction. (a) 0.62, 0.82, 1.27, 1.60, 1.88, 2.30, 3.25
and 5.30 s for the vertical and radial components of the vibrated directions. (b) 1.30 and 1.60 s for the transverse component of the vibrated directions.
(Right) Particle motion of each phase. Circle indicates a start point of particle motion.

transformation as,
#
$
&
$$'
# #
g jk t j , αn = IFT G lk · exp iωl t j − αn · xk

(5)

where xk is the position vector of the seismometer, αn isapparent slowness and t j is time. IFT denotes inverse theFourier transformation.
Figure 5 provides an example of a semblance map calculated in this study. The figure shows the time-slowness
plot of the semblance value for the radial component at
the receivers for the case of radial vibration at the source.

The axis of slowness is oriented in the receiver-source direction. There are many peaks of high semblance values
even where signal amplitude is small. In this experiment
we used a signal with a limited frequency band; side-lobes
are therefore inevitable in the resultant transfer function in
the time domain. As such, a traditional semblance calculation, in which the information of amplitude vanishes, isinappropriate. Consequently, we introduce a modified semblance method that takes into account the signal amplitude,
and we expand the time window of the denominator in the

137

1000

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS

Fig. 7. (a) Velocity structure under the array site down to 200 m. Thereis a pronounced change in the elastic wave boundary around 100 m. (b)Schematic figure of a velocity structure under the experiment site.

semblance calculation. This operation enables us to detect a
coherent signal with a large amplitude. We determined thetime window of the numerator and the denominator for 0.1
s and 0.3 s, respectively. Figure 5(a) also shows the resultsof the modified semblance calculations. The lower figureof the semblance map shows the averaged amplitude of denominators in a window of time and space. The averaged
amplitude serves as a weighting in the modified semblancecalculation. A clear peak in semblance values is evident at
0.6 s in the modified semblance map; the weighting suppresses spurious peaks in semblance values derived fromthe traditional one, such as the peak around 0.6 s. In thisoperation, we can clearly determine the travel time and apparent slowness of each phase.
Figure 5(b) shows the results of the modified semblancecalculations for each component of vibrations, and Fig. 6
shows a contour map of semblance values as a function of
the radial and transverse components of apparent slowness
αr and αt at the arrival time of each phase. Negative αr indicates an arrival of waves from the source direction. For
the P- and SV -components, coherent phases are apparent
at 0.62 s and 1.27 s, with apparent velocities of approximately 3.7 km/s and 2.0 km/s, respectively. It appears thatthese phases did not arrive directly from the direction of thesource but arrived from a direction slightly to the north of
the source. Coherent phases are also apparent at 0.82, 1.60,
1.88 and 2.30 s. with apparent velocities of about 3.7, 1.7,
1.7 and 1.5 km/s, respectively. Other coherent signals withlarge apparent velocities occur at 3.25 and 5.30 s. For theS H -component, we detected coherent phases at 1.3 and 1.6
s, with apparent velocities of 1.8 and 1.8 km/s, respectively.
4.2 Identification of waves
Geophysical logging exploration was used to investigate
velocity structures to a depth of several hundred meters at
the experiment site (TRIES, 2001; Fig. 7). A pronounced
velocity boundary exists at about a depth of 100 m, which isthe boundary between the granitic basement and overlying
sedimentary layers. The velocity of the sedimentary layers is approximately 2.0 km/s for P-waves and 1.0 km/s for
S-waves, while basement granite records velocities of 4.3
km/s for P-waves and 2.3 km/s for S-waves. The wave ob-served at 0.62 s has an apparent velocity of 3.7 km/s, whichcorresponds to P-wave velocity in the basement layer. Particle motion of the wave is in a sub-vertical direction. These
results show that the wave observed at 0.62 s is the refracted
P-wave traveling through basement rocks. Similarly, thewave observed at 1.27 s has an apparent velocity of 2.0
km/s, which corresponds to the S-wave velocity in basement rocks. Particle motion of the wave shows a nearlyradial direction. These results indicate that the wave observed at 1.27 s is the refracted S-wave traveling throughthe basement rocks. The refracted wave arrived at the array
a little northerly of the source direction, indicating that theboundary dips southward.
Coherent phases arriving after the refracted P-wave andthe refracted S-wave are found at 0.82 and 1.60 s, with apparent velocities of approximately 3.7 km/s and 1.7 km/s,
respectively. Although the apparent velocities of thesephases are similar to those of the refracted waves, they arrived before the surface waves, which arrived at 1.88 and2.30 s, with apparent velocities of 1.7 km/s and 1.5 km/s,
respectively. We therefore propose that the 0.82 and 1.60
s waves are a direct P-wave and a direct S-wave, respectively. The arrival times of these phases supports this interpretation. Other coherent phases with high apparent velocity are found at 3.25 and 5.30 s, with apparent velocitiesof 2.8 km/s and 1.5 km/s, respectively. We interpret thesephases to represent waves reflected from the deeper parts ofthe velocity boundary; however, the aperture size of the array used in this study was too small to resolve the detailed
apparent velocity of these phases.
In terms of the S H -component, S H -waves are recorded
at 1.3 and 1.6 s, with apparent velocities of 1.8 and 1.8 km/s,
respectively. We interpret these two phases to represent therefracted and direct S H -waves, respectively.
4.3 Estimation of differential travel time and differential apparent velocity
To examine small delays or advances in travel time forthese phases, we calculated the cross-spectral density between a reference waveform and an observed one. The two
waveforms are extracted with the same time window. The
cross-spectral density, Clk , is calculated as follows:&#$'
G lk = FT IFT G jk · h j

ref ∗
obs
Clk = G lk · G lk
(l = 1, · · · , L;(6)
k = 1, · · · , K )(7)where FT denotes the Fourier transformation, ∗ denotes
a complex conjugate and h j is an applied window function. Differential travel times for a sensor and a frequency$tlk (l = 1, · · · , L; k = 1, · · · , K ) are obtained by dividing the phase difference of the cross spectrum by an angular frequency:$tlk = angle (Clk ) /ωl(8)

where angle denotes a phase angle of the Clk .
We estimated the average differential travel time and differential apparent slowness from differential travel time forall the elements of the array. Assuming that a phase arrives
at the array as a plane wave, the differential travel time $τat the origin of the array and the differential apparent slow-

138

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS
x 10

(a)

-3

the refracted P-wave (0.62 second)
the refracted S-wave (1.27 second)

Differential
travel time(s)

1

0

-1

(b)

5
0
2

x 10 -4

0.5 ms1/1

08

15Time (day)x 10 -3-1

1 ms
x 10 -4

0.5 ms1/1

08

15Time (day)(c)
Time delay(seconds)

15

0

1/1

08

15
Time (day)22

the direct P wave (0.82 second)the direct S wave (1.60 second)

0.06
0.04
0.02
0
0.02
0.04

0.04
0.02
0

1/1

08

15
Time (day)

22

15

10

10
5
0
-5

980

01/01

01/08

Time(day)

01/15

5
0
-5
1/1

08

15
Time (day)220Fig. 9. Temporal variation in a differential apparent slowness for (a) the
refracted P-wave, and the refracted S-wave, (b) the direct P-wave andthe direct S-wave. (c) Temporal variation in the atmospheric temperature and precipitation.

0

-10
1000

10

10

-10

Precipitation(mm)

Atmospherictemperature(degree)

0.02

0.1 ms

-1

960

0.04

22

0

Atmosphericpressure
(hPa)

(e)

0.06

(c)

1x10-4

(d)

0.04

0.06
Estimated
error(s/km)

0

0
0.02

Atmospherictemperature(degree)

Estimated
error(s)

5

0.02

(b)

0

-2

the refracted P-wave (0.62 second)
the refracted S-wave (1.27 second)

0.04

22

the direct P wave (0.82 second)the direct S wave (1.60 second)1
Differential
travel time(s)Estimated
error(s/km)-2

Differential
apparent slowness(s/km)

Estimated
error(s)

1 ms

0.06

Precipitation(mm)2

Differential
apparent slowness(s/km)

(a)

1001

01/22

Fig. 8. Temporal variation in the differential travel time for (a) the
refracted P-wave and the refracted S-wave, (b) the direct P-wave andthe direct S-wave. The data stacked in 12 h was used for the evaluation.
Error was estimated by deviations in the differential travel time from theestimated plane as an uncertainty. (c) Time delay in the radial motion of
the source foundation. The time delay is expressed as the average of thedelays over the frequency range that the ACROSS source generated. (d)Atmospheric temperature and precipitation, (e) Atmospheric pressure.

ness $α are expressed as$tlk = $τ + $α · xk

(9)

Wlk |Clk |(10)

The differential apparent slowness corresponds to a change
in the elastic wave velocity of the medium immediately
beneath the receivers or to the incident angle of the wavethat encounters the receivers. The values of $τ and $α areevaluated by the weighted least squares method with thefollowing weighting:

The error is estimated from the deviation of differential
travel time from the estimated plane as an uncertainty.
We use data obtained by stacking for 12 h around eachtime in the observation period. Data measured at the beginning of the experiment are used as a reference. A 0.4-s
hanning window was used to extract each phase.
It is difficult to estimate the variation in differential apparent slowness for phases of small amplitude. To address this problem, we spatially stacked data, focusing ona phase with appropriate phase shift, and calculated a crossspectrum density. The differential travel time is obtained byaveraging the differential travel times at each frequency.

5.

Temporal Variations in Travel Time and Apparent Velocity

We used observational data from the seismic array tomonitor differential travel time and differential apparent
slowness for various phases with a high semblance value.
The results for each phase are presented below.
5.1 Refracted P-waves and S-waves
Figure 9(a) shows temporal variation in differential apparent slowness. The variation corresponds to that of theincident angle or to the spatially heterogeneous variation ofelastic wave velocity just beneath the site of array. Temporal variations in the elastic wave velocity beneath the arraycan result from meteorological effects as well as other factors.
We first compared the variations in travel time with variations in atmospheric temperature, precipitation and atmospheric pressure [Fig. 8(d) and 8(e)]. The variation in travel
time shows a similar pattern to variations in atmospherictemperature, with delays for periods of decreasing atmospheric temperature. Large variations are observed when
the temperature is less than −5◦ C. Figure 10(a) showsa correlation between a differential travel time for the refracted S wave and atmospheric temperature. In this figure
we demonstrate the correlation by a solid line for the period between January 21, 900 hours, and Jan 25, 900 hours,
when the atmospheric temperature is relatively low. The
correlation coefficient in this period is −0.72, although thecorrelation coefficient for the whole period is −0.17. These
results demonstrate that atmospheric temperature affects
travel time variation. It is highly unlikely that the changes
in atmospheric temperature affected the observation system

139

1002

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS

(b)

0.6

0.6

0.4

0.4
Time delay (ms)Time delay (ms)

(a)

0.2
0
-0.2
-0.4
-0.6

0.2
0
-0.2
-0.4
-0.6

-15

-10

-5

0

5

10

15

-15

Atmospheric temperature (degree)

-10

-5

0

5

10

15

Atmospheric pressure (hPa)Fig. 10. (a) Correlation between a differential travel time for the refracted S wave and atmospheric temperature. Each value is shown by subtracting ashort period trend, which is evaluated by a moving average over 2 days. Solid line shows the correlation in a period between Jan 21, 900 hours, andJan 25, 900 hours, when the correlation coefficient is high. (b) Correlation between a differential travel time for the refracted S wave and atmosphericpressure. Solid line shows the correlation in the period between Jan 21 9:00 and Jan 25 9:00.

(a)

-3

Differential
travel time(s)4 x 10the surface wave (2.15 second)

20

Estimated
error(s)

1 ms
-2
-4
5 x 10
0

(b)

1/1
x 10

0.5 ms08

Time (day)

15

22

-3

the reflected wave (3.22 second)
Differential
travel time(s)20Estimated
error(s)

-2

5
0

1 ms
x 10 -4
Time (day)

1/1

08

Time (day)15

0.5 ms
22

(c)
10

10

Precipitation(mm)

Atmospherictemperature(degree)

15
5
0
-5
-10

1/1

08

15
Time (day)220Fig. 11. (a) Temporal variation in differential travel time for the surface
wave (2.15 s). (b) Temporal variation in differential travel time forphases with a high apparent velocity (3.25 s). Data were stacked for
48 h in these phases because the amplitude of these phases was small.
(c) Temporal variation in atmospheric temperature and precipitation.

and elastic wave velocity near the array as the seismometers
were deployed in a temperature-constant vault. The effectsof rainfall and barometric pressure are scarcely apparent inthese data [Fig. 10(b)]. The correlation coefficient of therefracted S wave to barometric pressure is −0.01.
Figure 8(a) shows the temporal variation in differential
travel time for the refracted P- and S-waves for which prop-

agation properties were determined. The differential travel
time shows a cyclic variation with a period of 1 day. The
maximum amplitude of the variation is approximately 0.5
ms, which corresponds to 10−3 of a velocity change. Longterm and step-like variations are also apparent, with amplitudes of approximately 0.5 ms. The uncertainty in the
differential travel time, which arises from the frequencydependent deviation, is estimated to be within 0.1 ms, whichcorresponds to a precision of 10−4 . The variations in velocity change observed in this experiment are therefore statistically significant.
We compared the variation in the travel time with a variation in the motion of the source foundation [Fig. 8(c)]. Although the rotation of the eccentric mass in the source isprecisely controlled with reference to GPS timing, the motion (i.e. acceleration) of the source is strongly affected bychanges in the elastic or inelastic properties of the groundsurrounding the source. For example, if the stiffness of thesurrounding ground decreases, the amplitude of the motionof the source increases. Inelastic properties such as Q may
also affect the motion of the source. Saeki (2000) demonstrated that the energy emitted from the source and dissipated around the source is proportional to the phase delayof the motion of the source.
Phase variation on the source foundation shows similar
patterns to variation in atmospheric temperature. This indicates that changes in atmospheric temperature affect theelastic property of the ground surrounding the source. The
temporal variation in travel time observed at the array, however, is still fivefold greater than the variation that can be
explained by phase variation of the source motion. No
comparable pattern of temporal variation is apparent in the
differential apparent slowness. The effects of daily variation in atmospheric temperature do not penetrate far into
the ground, but do affect the physical properties of theground to depths of approximately 1 m. The observed refracted wave travels along the bedrock-sediment boundary
at a depth of approximately 100 m for most of the distance140

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS
(a)

(a)

x10 -34

Differential
travel time (s)16.02Hz
17.02Hz
18.02Hz
19.02Hz

3 ms

-6
1/1

(b)

x10

1/8
-3

1/15
Time(day)

1/22

0
-2

1/1
x10-3

(b)
Differential
travel time (s)

0

-4

1/15
Time(day)

1/22

1/28

the direct S wave (1.60 second)

2
0
-2
-4

3 ms

-6
1/1

1/15
Time(day)

4

1/22

1/28

1/1

(c)

Differential
travel time (s)

0
-2
-4

3 ms

(d)

1/15
Time(day)

4

1/22

1/28

Differential
travel time (s)

-4

3 ms

1/8

1/15
Time(day)

1/22

1/15
Time(day)

1/22

1/8

1/15
Time(day)

1/28
10

0
1/28

1/22

(Radial component)

0
-2
-4

3 ms
1/1

(e)

15
10
5
0
-5
-10
1/1

Fig. 12. Frequency dependence of temporal variations in differential travel
time for the phases of (a) the refracted S-wave, (b) the direct S-wave,(c) radial motion of the source foundation and (d) the main wave withlargest amplitude observed at the borehole seismometer (around 0.1 s).
The width of the frequency range from which we selected the signal
components is 2 Hz, which is centered at the frequency shown in thelegend. This figure shows the temporal variations in the lower frequency
band of 15.02–20.02 Hz. (e) Temporal variation in atmospheric temperature and precipitation.

between the source and receivers; it is likely that variation in
the physical properties of the near-surface medium causes
the observed variation in travel time.
5.2 Direct P- and S-waves
Figure 8(b) shows the temporal variation in differential
travel time for the direct P- and S-waves. These variations
are statistically significant; the uncertainty of the travel time
is within 0.1 ms for the observation period.
Variations in the direct P- and S-waves are different fromthose of the refracted waves, with the variation in direct
waves being less affected by the variation in atmospherictemperature than refracted waves. Marked changes in the
differential travel time of direct waves are observed at timesof rainfall. The observed changes involve an instantaneous
delay in travel time followed by a gradual recovery. The
amplitude of the change is >1.0 ms, and the change lasts
2 days or more. Such phase variations are not observedin the motion of the source foundation, nor in the temporalvariation in apparent velocity at the array site. The effects ofatmospheric temperature and barometric pressure are barely
apparent in these data.

1/28

2

1/8

1/15
Time(day)

1/22

1/8

1/15
Time(day)

1/22

1/28
10

Atmospherictemperature(degree)Atmospherictemperature(degree)

15
10
5
0
-5
-10
1/1

3 ms
1/1
x10-3

-6
1/8

Precipitation
(mm)

1/1

-4

4

0

-6

(Radial component)

0(Radial component)

-2

1/28

-2

(d)

2

1/22

2

-6
1/8

1/15
Time(day)4(Radial component)

1/1
x10 -3

1/8
-3

x10

2

-6

3 ms

-6
1/8

x10 -3(c)Differential
travel time (s)

1/8

4

-2

Differential
travel time (s)

3 ms

-6
1/28

2

(e)

24.03Hz25.03Hz26.03Hz27.03Hz-4

the direct S wave (1.60 second)4

the refracted S wave(1.27 second)

2

0
1/28

Precipitation(mm)

Differential
travel time (s)

0
-2
-4

Differential
travel time (s)

-3

x10
4

the refracted S wave(1.27 second)

2

1003

Fig. 13. Frequency dependence of temporal variations in differential
travel time for the phases shown in Fig. 12(a)–(d). This figure shows
the temporal variations in the frequency band of 23.03–28.03 Hz. (e)Temporal variation in atmospheric temperature and precipitation.

5.3 Surface wave and reflected waves
Figure 11 shows the temporal variation in the surface
wave and the phase that arrived at the array from a downward travel path. As the amplitudes of these phases were
small, the data were stacked for 48 h. Marked variation canbe correlated with times of rainfall for the surface wave.
The origin of this variation must also be related to rainfall
along the path of the surface wave.
One of the advantages of array observation is in detecting the reflection of phases from deeper parts of the crust.
From the data in Fig. 6, we can detect phases with highapparent velocity that are interpreted as representing the reflected wave that propagated from below. The data werealso stacked over the elements of the array by assuming thatthe wave propagated vertically. As uncertainty is within 0.5
ms for the observation period, no marked variation can becorrelated with other observation data.
5.4 Frequency dependence of the temporal variationin differential travel time
We investigated the frequency dependence of the temporal variation in differential travel time to take advantageof the frequency-discreteness of the ACROSS signal. Figure 12(a) and (b), and Figure 13(a) and (b) show the frequency dependence of the temporal variation in differential
travel time for the refracted and the direct S-wave. In thisanalysis, the signal components in the specified range of
frequency are selected from the stacked data set, and the

141

1004

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS

(a)
2

x 10

-3

the refracted P wave (0.62 second)
the refracted S wave (1.27 second)

Differential
travel time (s)

1

0

-1

Estimated
error(s)

1 ms
-2
-4
1x 10
0

(b)
2

1/1

0.1 ms08

2228

x 10 -3

the direct P wave (0.82 second)the direct S wave (1.60 second)1
Differential
travel time (s)15Time (day)0-1

Estimated
error(s)

1 ms
-2
-4
1 x 1001/1

0.1 ms08

15
Time (day)

22

28

(c)
10

10

Precipitation(mm)

Atmospherictemperature(degree)

15
5
0
-5
-10

1/1

08

15
Time (day)220Fig. 14. Temporal variation of (a) the refracted P- wave and S- waves, (b)the direct P-wave and S-waves except for a frequency band of 15–20
Hz. (e) Temporal variation in atmospheric temperature and precipitation.

differential travel times are estimated in the same way as
Section 4.3. The width of the frequency range from which
we selected the signal components is 2 Hz, which is centered at the frequency shown in the legend. A strong frequency dependency is clearly observed in this figure. The
temporal variation in the differential travel time appears to
be sensitive to the variation in atmospheric temperature andrainfall, especially in the frequency range centered at 18.02
Hz and 19.02 Hz. Although the variations show a similar
pattern in the direct and the refracted S-waves, the amplitude of the variation is much larger in the direct S-wave.
The differential travel times for the direct S-wave change
in the opposite manner for 18.02 Hz and 19.02 Hz with respect to atmospheric temperature; therefore, the variations
in travel time are cancelled out when averaged over all frequency components, and only a minor relationship appears
for atmospheric temperature [Fig. 8(b)]. On the other hand,
they change in the same manner with respect to rainfall,
which is clearly seen for the rain on January 4, making theeffect of rain remain after the variations in travel time havebeen averaged over all frequency components.

6. Discussion and Conclusions
In the investigation reported here we have attempted to
identify a region that is affected by atmospheric temperatureand rainfall using the vibration signal on the source foundation and at a borehole seismometer, which is about 50 m
away from the ACROSS source. Figures 12(c) and (d) and13(c) and (d) show the frequency dependence of a temporal variation in the radial motion of the source foundationand the initial part of the wave at the borehole seismometer.
The variation at the borehole seismometer shows a similar
pattern to the variation in the refracted S-wave and the direct S-wave. The amplitude of the variation at the borehole
seismometer is comparable to that of the refracted S-wave.
On the other hand, the amplitude at the source foundation ismuch smaller than that of the borehole seismometer. Thus,
we may conclude that the main cause of the temporal variation exists in the region that is very close to the source. The
reason why the variation in the direct S-wave is larger than
the reflected S-wave may be attributed to the ray path of thedirect S-wave, which travels through a relatively shallow
part of the ground that can be more affected by the weather
condition.
The variation in weather conditions, such as temperatureand rainfall, contributes to the variation in the property ofthe medium near the surface. As the ACROSS vibrator is
deployed on the surface, it may be strongly affected by thechange in weather conditions. Saeki (2000) documented
that compliance of the medium immediately surrounding
the seismic source affects the energy of the radiated wave
and its phase delay. This compliance is dependent upon theshear wave velocity in the medium around the source andthe angular frequency of the force generated by the source.
Once the angular frequency of the generated force is accurately controlled, we need to monitor shear wave velocity
near the source, as this appears to vary with weather conditions.
The environmental effects can be removed from thewaves to take advantage of the frequency-discreteness of
the ACROSS signal. As the environmental effect is relatively large in the frequency between 15 and 20 Hz, we removed the data corresponding to 15–20 Hz from our analysis. Figure 14 shows the temporal variation of the refracted
wave and the direct wave, with the exception of a frequency
band of 15–20 Hz. We were able to remove the effect andobtain the travel time with less effect by environmental conditions.
We can investigate depth variation in elastic wave properties using various phases with different wave paths. In
this study, we investigated depth variation using only direct
and refracted waves, as there is a clear boundary in termsof elastic wave velocity at this site. If more boundaries
exist, we can investigate more clearly the depth variationsin the elastic wave properties of the rock medium, whichmight be expected to include cracks and possibly aquifers
or similar features. Furumoto et al. (2001) compiled thestress sensitivity of a seismic wave velocity as a function of
baseline length for the temporal variations related to tidal
stress, tectonic stress and coseismic stress. The stress sensitivity over a baseline length is related to depth variations inthe stress sensitivity because a seismic wave travels throughdeeper levels with an increase in epicentral distance. Velocity change is dependent on the degree of defect developmentin the rock mass, including cracks and pores, and this varies
with depth. Furumoto et al. (2001) suggest that accurate
and continuous monitoring over a long distance is required
to determine the stress sensitivity of seismic wave velocity.
An experiment using the ACROSS source is one of the most142

A. SAIGA et al.: ACTIVE SEISMIC MONITORING WITH SENSOR ARRAY AND ACROSS

valuable methods of investigating the stress sensitivity.
Acknowledgments. We would like to acknowledge the use ofdata for elastic wave velocity by geophysical logging exploration
carried out by the Tono Research Institute of Earthquake Science.
We would also like to express our thanks to N. Fujii, T. Yamauchi
and R. Ikuta for their useful comments. Reviews by Y. G. Li andP. G. Silver greatly improved the manuscript.

References
Alekseev, A. S., Chichinin, I. S. and Korneev, V. A., Powerful lowfrequency vibrators for active seismology, Bull. Seismol. Soc. Am., 95,
10–17, 2005.
Birch, F., The velocity of compressional waves in rocks to 10 kilobars, Part
1, J. Geophys. Res., 65, 1083–1102, 1960.
Bokelmann, G. H. R. and H.-P. Harjes, Evidence for temporal variation ofseismic velocities within the upper continental crust, J. Geophys. Res.,
105, 23,789–23,894, 2000.
Crampin, S., Geological and industrial implications of extensive dilatancy
anisotropy, Nature, 328, 491–496, 1987.
Crampin, S., D. C. Booth, R. Evans, S. Peacock, and J. B. Fletcher,
Changes in shear-wave splitting at Anza near the time of the North Palm
Springs Earthquake, J. Geophys. Res., 95, 11,197–11,212, 1990.
Furumoto, M., Y. Ichimori, N. Hayashi, Y. Hiramatsu and T. Satoh, Seismic wave velocity changes and stress build-up in the crust of the KantoTokai region, Geophys. Res. Lett., 28, 3737–3740, 2001.
Hiramatsu, Y., N. Hayashi, M. Furumoto, and H. Katao, Temporal changes
in coda Q-1 and b-value due to the static stress change associated withthe 1995 Hyogo-ken Nanbu earthquake, J. Geophys. Res., 105, 6141–
6151, 2000.
Ikuta, R. and K. Yamaoka, Temporal variation of shear wave anisotropy
detected with ACROSS, J. Geophys. Res., 109, B09305, doi:10.1029/
2003JB002901, 2004.
Ikuta, R., K. Yamaoka, K. Miyakawa, T. Kunitomo, and M. Kumazawa,
Continuous monitoring of propagation velocity of seismic wave using
ACROSS, Geophys. Res. Lett., 29, 13, 10.1029/2001GL013974, 2002.
Kumazawa, M. and Y. Takei, Active method of monitoring undergroundstructures by means of ACROSS. 1. Purpose and principle, Abstr. Seismol. Soc. Jpn., 2, 158, 1994.
Kunitomo, T. and M. Kumazawa, Active monitoring of the Earth’s structure by the seismic ACROSS—Transmitting and receiving technologiesof the seismic ACROSS, Proc. 1st Int. Workshop Active Monitoring
Solid Earth Geophysics, 181–184, 2004.
Li, Y.-G., J. E. Vidale, K. Aki, F. Xu, and T. Burdette, Evidence of shallow fault zone strengthening after the 1992 M7.7 Landers, California,
earthquake, Science, 279, 217–219, 1998.

1005

McEvilly, T. V. and L. R. Johnson, Stability of P and S velocities from
central California quarry blasts, Bull. Seismol. Soc. Am., 64, 343–353,
1974.
Neidell, N. S. and M. T. Taner, Semblance and other coherency measures
for multichannel data, Geophysics, 36, 486–497, 1971.
Niu, F., P. G. Silver, R. M. Nadeau, and T. V. McEvilly, Migration ofseismic scatterers associated with the 1993 Parkfield aseismic transient
event, Nature, 426, 544–548, 2003.
Nur, A., Dilatancy, pore fluids and premonitory variations of ts/tp travel
times, Bull. Seismol. Soc. Am., 62, 1217–1222, 1972.
Reasenberg, P. and K. Aki, A precise, continuous measurement of seismic
velocity for monitoring in situ stress, J. Geophys. Res., 79, 5412–5426,
1974.
Saeki, M., Theoretical study of the ability of the ACROSS source to generate seismic wave field, MSc., University of Tokyo, Tokyo 2000.
Saiga, A., Y. Hiramatsu, T. Ooida, and K. Yamaoka, Spatial variation in
the crustal anisotropy and its temporal variation associated with themoderate size earthquake in the Tokai region, central Japan, Geophys.
J. Int., 154, 695–705, 2003.
Sato, H., Temporal change in scattering and attenuation associated withthe earthquake occurrence—A review of recent studies on coda waves,Pure Appl. Geophys., 126, 465–497, 1988.
Scholz, C. H., M. Wyss, and Y. P. Aggarwal, The physical basis for earthquake prediction, Science, 181, 803–810, 1973.
Semenov, A. N., Variation in the travel-time of transverse and longitudinal
waves before violent earthquakes, Bull. Acad. Sci. USSR, Phys. Solid
Earth, 3, 245–248, 1969.
TRIES, Geophysical log of TGR350; Tono Research Institute of Earthquake Science, 2001.
Yamamura, K., O. Sano, H. Utada, Y. Takei, S. Nakao, and Y. Fukao, Longterm observation of in situ seismic velocity and attenuation, J. Geophys.
Res., 108, B6, 2317, 10.1029/2002JB002005, 2003.
Yamaoka, K. and R. Ikuta, Feasibility of reflection monitoring for plate
coupling using ACROSS System, Proceedings of the 1st International
Workshop on Active Monitoring in the Solid Earth Geophysics, 126–
129, 2004.
Yamaoka, K., T. Kunitomo, K. Miyakawa, K. Kobayashi, and M. Kumazawa, A trial for monitoring temporal variation of seismic velocity
with ACROSS system, Island Arc, 10, 336–347, 2001.
Yoshida, Y., H. Ueno, and Y. Ishikawa, The observation and analysis of
ACROSS signals by seismic networks—Determination of the transfer
function. Proc. 1st Int. Workshop Active Monitoring Solid Earth Geophysics, 258–261, 2004.
A. Saiga (e-mail: saiga@sevo.kyushu-u.ac.jp), K. Yamaoka, T.
Kunitomo, and T. Watanabe

143

144

145

146

147

148

149

150