Scismi city of Matrmshiro micro carthquake swarm (*) 

J. C. J)lUKOPOULOS (**) - H. N. SltrVASTAVA (***) - T. TERA~Hl.MA 

Ricevuto il Il! Agosto 1\)70 

SU~D1AltY. - lllll'illg UIO jJrak swarJll adivity at ~rat";ll,.;hiro. micro. 
Cal'thqllakes were rc('oj'(le,l at ~llzaka a)l(1 l'IratHllKhiro (m F2\f magndie ,lata 
rp'(·ol',lcr. 'l'IlO (Iuta 80 obbillc,1 Wé'l'l' Ilt.ilizeil lo ,.;tllil.V l.he val'iatio](~ or b 
ill r,lltenberg-H.khto·r'~ fn;(lllP]((·Y·H(ilJi; nitlldll rnln.tion~hijJ givcll by log]o.' = 
" I -/131, whl'J'c M i~ the magllitn,1c all<I N is UIO 1l((Jllbcl' or t'arthlJ1Jake.~. 
It was [oullIl thal thc vulnc or b in .\latsu"hiro RW1U'lll i8 Hlon'· or lll.~,.; (~OnKtaHt 
in ;;llort inlcl'vul" oI lilllO bllt ,.)mllgl's , .. ignificlI.lltly for two dilfl'l'nHt jl('rio,lsof 
olmnrvation>\ of ~Ilzak!l.. Tlle vahw of /, from tirI' oh,.;erval,ion" al ;\Ia\..~IlHhiro 
has al"o hmm fOllml lo h(~ l'al hO!' ;\JI(ali aK "olllpar('([ lo that at S11)~uka. 

RrASSUN 'I'(). - DIIl'allte l'illtell,''o perioilo ili attivitiì. mi(~ro,.;iKmica av-
Vlllll1to a l'Irat ";ll"hiro, le mino";"o";He fllrono nl/.:i"t.ratn a SIl7.aka P 2\I'atHIlShil'u 
con Iln n'gidl'atorl' a Hij.stro ma,t:'lwlko F~J. I ,lali "oHi oltclluli fUl'OIlO uti-
lizzati l'C!' Ht1!,li~I.!,t· lo variazioni oli b. ,lalla rOrlJl\tla ili Gllhmlwrg-H.kllt.llr 
,.)11' ll'ga la [n' IIIwnza alla. mag-nitlHlo 

10g.N = /[ -".ll 
,10\'(' ..Il i.~ la wagllilwlo c,l X i.~ il lllllllC!'O ,Ici tCl'I'cmoli pl'csi in e.~alllC. 

Dalle of;81l1'vazionl fatte a ;\Iat.~ll~hiro (, .~tat.o trovato dw il valore di /, 
pe!' brevi int('rva.I1i (li tempo (, pii't o mFno ('o,.;tante, mentre yarin. HFn,.;ibil-
meHte a SU7.aka qnij.H,lo "i (,oH~i,]Prano ,I\H~ ,li\'I'Hi perio,li si~mit'i. Ilal COllo 
frolltO (1,01]', oSRervaziolll ~i è polllto ('ollslatare t'hl' il valol'c di li rdalivo 
a MahnHhll'O è allJ1Jallto pii't piet'olo (li IJ1H'llo ('akolato per ~";t,aka. 

l. - TN'rIWDUCTTO~. 

8eismicity of 1htSllShil'o ea l'tltqnake f!warm ha.~ beell t.lte subject 
of illt.el'est for the bst rew yen,l's. Some seinnologistH nmllely Sllyehiro, 

(.) Intel'Hij.tioHal Tnstit.llte of Seismology and Eart luluakl' Engineering 
Tokyo, Japall. 

(U) ScislIlolo!-(ical Lahoratory. Atlwns l:llivcrsily, Grcccc. 
( ••• ) !!lIlia ;\Ici.co!'ological DCjJarllllclll, Lo,li Roa,l, }l'cw D,oIhi 3. I![{!ia. 



178 J. C. DRAKOPOULOS - II. ~. "RIVASTAVA - T. TERASHDIA 

et n.1 (I) studied tho se.ismicit,y of t,he region for Celt earthquakes or 
ea rt,hqllakes of ratlwr large ll1agnitnde. In a series of lJal)ers, Hamada 
and JTn.giwn.rn. (~) relJOrted det,ailed re8lllts of tlw micro and ultra ll1icro-
ea rt,hqnakefl in the a rea of ::\Iu,t,SlIRhiro Ilfling high sensit,ivity trivart,ite 
observations recorded on magnetic data recorder. 'l'hey fonlld t,hn.t, 
the valne of b in Gutenbcrg-llichter's relation8hip (3) did not, clmnge 
signiflca.ntly with respect to difIcrent intervals of time. :Further, the 
valne of b dUl"ing UlC abnormalIy high activity wa.s flill1ilar to that 
for normal seismie l1ctivit,y. They also found that the Ishimot,o-lida's 
coclftcient "In (4) examined with reS}Jeet to nltrn. lI1icro-en.rLhqnH,kes 
showod la rger v a.lnc before two elimaxef! of flei:muc activity n.t the 
bcginning of Aprii and t,he end of August and the smH,lIer vH,lue 
l11)1)earcd jnflt a fter the climaxef!. 

Thc party for soiflmographir. obflervn.tion and soiflmological sec-
tion (~) obtained the valne of "In for overy lO days and tho valuos of 
b for each month flince 1Ifal'ch 1966. The value ofm at eH,ch fltation 
of obflcrvn.tion showed a sill1ilar belmvionr. 

The object of the IH'{\f!{lnt palmr if! to fltudy thc seismicity in lmr-
t,icuhlol" t,he variations of b in Gntenberg-Richtf>.r's l'elationshil) (3) within 
flllOrter int.erval of timo than studicd hithcrto with reference to t,he 
micro-earthqnakef! recorded at Smmka and :i\Tatsushil'O lmd COml1!H'e 
t,ho reslùts with t,llOse of other inve8t,igators. 

,, ~w .... ,, ~,~t. 
'"~ ,.~.ULt. 

Fig. l - Block dia.gram for micro-carthqllake o1.JServatiolls. 



SEIMIICI T Y 01' MATSUSJU1W MIC1W EARTlIQUAKE SWARM 1 iO 

'l'able l - 8UZAKA l (196,:;) 

Munitur 
Perioù 01 Ob~(\r\'ation I Xum1Jer of 

N° Pl'OIll '1'0 Eal' t1HIUakes 
- -

I ]kl'. 20 , 1411 1 Om Dlw. 20, l till 3"m 12 
2 1 ti ,i2 23 2" " 3 Dee. 21, OH 00 Ilee. 21, 12 42 31 
4 18 42 20 40 2 
,i 23 45 Ilrw. 2') -, 00 48 O 

" Ilox'. 22, 00 .51 01 44 O ; 01 '" 08 l" 
1 35 

8 08 17 12 31 " U 14 IO 16 55 33 
lO I i 3i 18 51 O 
]] 18 51 20 23 O 
12 20 38 lltw. 23, ])]) 27 37 
13 Ilox'. 23, 00 30 07 00 "' 14 Oli 00 Il 53 21 
l,:; 12 32 18 00 52 
lfi 18 O,i Dee. 24, 00 40 33 
17 Due. 24, 00 41 00 "H 3 
18 01 IO 07 30 40 
IO 08 Oli 14 33 37 
20 14 34 21 16 52 
21 21 I; D('I\ . 2,;, 00 06 18 
22 De!'. 2,;, 00 14 07 30 41 
23 08 34 13 O,i 26 
24 13 13 16 12 I; 
25 IO 17 In 47 32 
26 Ili 48 00 ,i.5 61 
2; De!:. 26, 00 ,,6 Dee. 26, 07 30 85 

Suzaka ]] (1066) 

50 Jun. 13, 011l12m ,J a ll. 13, 08"00,n 02 
51 lO 23 12 23 14 
52 12 2.5 1550 15 
,:;3 16 O" 17 lO 8 
,)4- I; Iii 21 36 I 60 ,i,i 21 ,,8 ,J an. 14, 00 lO 1 ,i6 
56 .Tali. 14, 00 Il OG 45 

I 
tii 

5i I lO 05 
12 14 7 

58 12 IO 1 H ,:;2 

I 
1.50 

,:;1) 

I 
I n 30 21 MJ i4 

60 21 51 23 35 n3 
1 1 

Matsush iro (10G6) 

I I May 21, 00"10m I May 21, 04h44m I 510 



180 ll II AKOI'OUr.OS .r. c. - S IIlVASTAVA Il . S. - 'l'EltAS Il D!A T. 

2. - INf:lTltU!lfENTA'l'lO-", AND COLLECTION OI<' nATA. 

'l'IHl experimental ,~I'I'}~llgellwllt for t.he observatioll of lIli(lI'o-eart.h-
qw~kes is giV()1l in -Fig. 1. 'fhe ouLpllt signalH frOlli t,hn't' moving ooil 
transducers oi 1 seo fnlO Ileriod wit.h It =!=- O.(i5 ,vere roeorde(l hy FM 

magnetic tape l'ecO!'der after alllpW-ieation. 
'rhe .~ensitiTit,y or thc transdueer iH 3.5 YoI1:/kine. Tlw respollse 

of Lhe dat.,~ of Ff.I was l\at Irom nc to 250 eIl,~ with a shal1) cut orT. 
'Plte gain of t.he aml)lifier was variahle dup01uling upon tlte grollllfl 
1l00se. 'rlte t.'"I)eS wCI'e rePI'(l(luced h'ypen galvallometer~ of natural 
frequency 30 cp.~ witlt a papm spee(l oI 30 lllm/.~ec. 

TIHI l)erio(l of observation alld the nUlnber of llIiero-e,~rLhqm1kes 
reeorded at, Slizalm amI Mat.sushiro are given in 'r,~hle 1. 

During t,he period oI observat,ioll at ì\Iat.~lIshiro approxilllately 2 
eartltquakes were recorded per llIinllt~l. 

3. - CAT.GV"LATION OF ]'L\GNI'l'1'DF~<; OI<' l\IICHO-EA1~'l'l1lìlIAT;:E.<;. 

'rlte ea.lcuh~t.jon oI nmgnitude of llIiel'O-ea.l-Lhqm1kes is bamd 011 t.he 
eOIlHidera tioll or atwnuatioll of seiSlllie waves with tlte epieentral 

dista.uee. 
Mumm atu et al (S), (lerive(l tlw following equatioll fol' c,~lellla.t,illg 

the magnitude frOlll Lhe ohservations oI miel'o-lmrLhquakeH in the 

vieillit,y of Gifu prefeetl1l'e. 

.ili = 1.25 log ~i" (kine) 1- 2.5 log T (lnu) + 1.0 [lJ 

whel'e A" i,~ Uw velociLy muplitude ,~Jl(l T is Llw h.Ypocentml diHtauce. 
HeCllllt.l.Y Tera~hillla (7) dl:'.1'ived the following equation Iol' the enlcul-
at.ion oI magnitude.~ of llliero-eal't.hquakes. 

M = log A"(T) + 1.5 log T + 2.35 [2] 
V'h have IIs0Il ellua.t.ion [2J in the pre8ellt stlllly fO!' Lhe ealeulatioll 

oI mngnitlt(le.~ of miero-earthqua ke8. 
Substitut.ing t.he inst.l'umental eOllHtantH and the hYl)()eelltral 

(listanees in equa tion [2J we get: 

- 0.-1-1 + 10gA -Fm' Suz,~ka monit.oring" recm'der 
sensitivit.'y,2011unimVolt [3J 



SEIS~IICITY Ù"'" ~J,\'rSlJSllmLl MleRO llAIlTIIQUA10: SWAIDI 1S1 

JI = - 0.84- + log A 

..ilI - 3,10 j- log A 

1<'01' Suzaka lllollitol'ing reeorder 
~en8it.ivity, 50mm,im Yolt. [4] 

l·'or )htsushil'o monit.ol'ing ]'N',ol'del' 
~en8it.ivity, 2mm/lIJ \'olt; [5J 

whel's .il is the doublo amplitllde as moaslll'ed on tllo St>.if!lllogl'am", 

! ! I l" \' , " 'l'I ! I I I 
, , , , 

I , ,i. .. I , , , , 

I I i 
. 

i i i l ; , , 
I , I 

I I I ' I • i I I 
I I I I 

I i I , I i I I ' " ... _. " , I I , 

Fig, 2 - Micro-eartlul!Jakes reeonled at ~uzaka 011 Ja11. 14-, 1\.166, 

I 

Fig, 3 - Mkl'o-cal'thquakcs 1'6001'<1e<1 at Matsushiro on May 21, 1966, 

AlI tho oarthquakos of trace amplitude greater than l mm recorded 
011 ~eismograms were ntilized for calclliating t.he magnitllde~ of llliero-
oal'thqllftkes_ 'l'he ea.rthqllake~ of m agnitndo largol' tlmn that COl'-
l'esponding- to tho traco amI)litude of 50 mm had to be omittod as 
t.he defloctions were too largo to be "\yit.hin the recol'ding papero 

The dlll'ation of P a mI.'; int.orval at Sllzaka wa~ appl'oxima tely 
2 second~. r and 8 phasos wore not quite cloar at Thhtsushiro due 



182 D U AKorO U LOS J. C. - S IH VASTAVA I I. N. - TImA1i Il DIA T. 

to the location of the f\eif\mometers in the el)icentral region. Typical 
micro·ea rt.hquaokes rccordecl at Suzaka and J\J atsushiro are shown in 
Fignres 2 aond 3 respectively. 

,1. - RBSULTS AND DISCUSSION. 

It is welI known th a t, the nnmber j'l of eart,hqlUvke8 during an 
a rbitmry interval of t,ime in a given seif\mic rl-lgion is l'elatoMI to mlv' 
gnitude Jf by 

log N = A'-bM. [lì] 

Many investigl~torH use t,hif\ equa tion in the form, 

log N = Ali + b (8-M) . [7J 

In the above equations the const anw A', Ali l~llli b are coefficients 
which flore determined from the da,t,a by t,}ie least sqlUvl'e met,}lIId and 
the v a.l'iances a re alf\o given. 

The values of A' or Ali vary wit,h the cluration of timc of the data, 
geographical location and choice of .di'IL 'l'he valne of b i8 reh~t,ively 
uniform. lIu,,,ever, cOllsidemble diffol'ence of UIJiniun exists regarding 
the v a riations of b with the focal depth, geogmphical looa.t,ion, foresllllck 
and aftershock seqnences, ea l'thquakEl sw al'ms ,Lnll vI)lc,oni ? eal't,}lqm~ke.'!. 

'l'he value of b increases as the (legree of hettlrogencity incl'ea.'!efl 
and a.'! tlw degree of symmetry of the al)plied stress decrcases. .A 
dElcreasc of b with depth h a s been fonnd by fleveml sei.~mologists. 

It has been fonnil ( ~ .U) that thEl v'olncR of b ,ore lal'ger for 'oftcl'shockR 
th an for foreshocks. 'l'he constants bi and b" of the fore- and after· 
shock scqucnccs of the s,ome main shock are connectl-lll by the l'el ation(O) 

bi '"'"" (0.11 ± 0.13) + (0.65 ± 0.11) ba . [S] 

Mogi (l~) 8hoWEl(1 exveriment,olIy that when foreshocks and aft,ershoch 
OCCUI' in the same volume the v altle b is sml~ller fol' fOl'eshocks than 
for aftershocks because the main shock ca.nsef\ new era cks an(l thUH 
the number of irregula.l' voints increasf\,~. The value b for earthquali:e 
swarmf\ is larger t,}Uvn fol' aftershocks or normal seismic a.otivity. 

Ishimoto amI Iirla C') 1)rOl)08ed l~ fOl'mnhv 

N(A) dA ~ H-m dA [9J 



SEIS~IICITY 01' )IATSUSIIIIW )lICIW EAUTlIQU.\KE ~W.lIDl 183 

where N is t,he ILlllnher of e'1.l'thquakes and A is the m.1.XimUlll tmee 
a.lllplitude. 'fhe coeffieients k andm are detel'lllined by t,he IE't\st 
square method. For..ti, it i~ suffieient, t,o oonf\idel' t,lw llla.xiul1Jln tmee 
t\mplit,nde of an arbit,rary chosen standal'd f\ei::!lllOgraph. COI'I'I\etiollS 
for dist a noe must IlO llla.de fl'om the point of observat.ion to tho opi-
centrai a rea. 



JK-l- lJ]{AKUl'UULU~ J. C, - SHI\'ASTAVA Il, ~. - TE]L\~I!DU T. 

SinCfl M -::: log A for Ollicolltral llista,llee eqll a l 1.0 100 klll a lld 
dA = AdllI it (!)"m be slwwn tlmt tll(' conHklo llt,s /; a llli III in tlw forllln-

!as [o] a llli [Hj a ro rolated by 

/; = '11/.-1, [lO] 

'l'lw 10g',.riLhm o( the onllln la.t,iye fW1llll']WY funct,ioll N(j'U) and 
tlw lllagnitllde of mic]'o-e,w Llt1lllaoko ref'onlod :~t. t)m:a,ka dllring tlte 
lWl'ioù ~Oth j o ::!oth I k.fll'llllwr 1965 is showll in tlw Fig. -L 'l'ho 
1llolH m: lol' kt'd with lejtl'],,~ A, 11, C, n, g a,lld 1<' indiclbt,e IlitII>l'ellt in-
tOl"yah o( time, It lll a y lw ,~eell tlmt, f~ ll tho six el1lTeH HI'O lj,pp]'oxiln-
n,t,efy p, lo]'a lllll wit.,h (', wh otlwr im}llyill)..!," that /; Ylj,lnOH mlluLillH nOIlKL a llt 
ill ~ho]'t, illte]'Ya l of (ime. 'l'1m f]'('(lllCney llm)..!,"llihule ]'olat.ioll~hip fo]' 

the~e <HlI'Y('S is (\X.IJI'I~,~H('d l)y 

( ,l) log N , .li5 .0:") jl! 
(II) log J..V , .-w .0:") ;li 
(O) log -.N :l .::!.1 . O!! M 

( li) log -.N . !]H .06 111 [11] 
(E) log N 1 . !ii! 1 .05 ;li 

(1") lo}.!; N 1 .. 1\) Il .!W M 

li'])..!,". (r)) giyeH Lite m ag"llitllde-froqul'lIey l'dn,t,ioll for nllotllOr 1H\]'iOlI 
of oh,~(~rvaLioll i, c,13th t.o l-it.h :\lH,~r 1!hW a l, Snzaka . AIUlOnglt t.,lle 
yahlO oI b iH sliglrUy difIcrellt., f]'OIll t1w )JI'eViOll8 set. oI ohHorva t.iolls 
(Fig. -i), tho v a lne of li 18 almof\1, Ht a tioll a l'y dlL]'ing" difIorl\nt int,crvafi; 

or tinte. '['[l(' ]'ef<lot.ioIlH hd,\n~I'1l lo}.!; N Vel'HIlS ;li a re giVOll a.s Iollow~: 

(A) log N 2 .~9 1 .19 M 

(Ii) log N ::! .18 1 .~\l M 

(O) log N , .O~ .1 !! Al 
( n) log N 1 .,sO 1 .18 111 lI::!] 
(El log N 1 .:3/ 1 .1G 111 
(P') log II 1 .39 .13 M 

fn t.his case wc Jmd to oxefUlle t,he lllaglliLIHle Slll a lllw Lfl all -- O .!) 

lwemlM' dlll'ing th is IwriOiI L[m sellHiLivil,y 01 Uw (b ta rC'eonlor wa.'! 
nlmllg(~11 with Lite 1'(~,~IlIL th a t.. Uw muth(Jlm kes of wmller llmgllituùos 
('onld Bot he roool'ùed tlm.J\1ghout tllo :pol'ÌOII of o!Jsel'v a tioll. rl'hi,~ i8 
the l'ea.soll why tlw cm'ves ùo not, Et. t,he dal,a fo]' t1le lll agniLndes lowm' 
t,ll a ll - O.:"), 

'l'he plot o[ log N Ve]"~IlH .M a L }h tf\lL8hi]'() is giveu ill :Fig. n, 
'l'he yalno of b l'mnains statiollal',Y dUl'illg ùiilerent intervuls of Lime 



• " - ~ • .. • • • • " 
" " " " • • • • • 
~ ~ v p " 

• o 

• • 

o 

• 

", ~ • • • • 

.. 
~ 

" • 

~ 

• 

• 

• 

• 

, .. • -.. '. • • • 
• , .. ", - • ~ " 
Nt'ì 

~ <! .. " 

• • 

r .. 
.. 

~ 
• , 

" 2 

~ .. 



~ 'lo ... ,.,"1 
• ... ~ . h 

U ~ 
, 'II ~ ., •• ~ 

• , \O." . ... lo ~ • \ ~ O ·~I· ~ '-' • • , 'lo:. ' .h • ,., , .. ~ o.,'" , • O • > 
U • • O , <l , 

O ' .0 5 , ., 
• • , . , • • 

1 
• c 

'.' o f ,. • 
" ,., o < ~ • o • > o o • " ~ • " • • > '.' o • • < > 

o • 
Lo 

, C 
, , , , 

o., 
o " " " ' ·0 > ,. 
• o < o., > 

; .. 
• 

-' .'L -) .1 -}.O -1." -'. -1,·1 -., -z. .~ -1.'1 · 1·\ -1."1. -'l·t -'1..- -" - l.' -n ·u -" - 1.'1 
" 

, 
]i'ig. 6 - I •• ,. v e r ... us JI J<1r !l iffere nl. inl.e rvtl.l,. 0 1 ti nl(' Te<'onl C'tl " i' Jahm!ihi ro ( 196H ). 



SEJ~~lICJTY 010' ~IAT~U~J-JJRO MIGRO l~ARTHQ,UAKE ~W."'IB[ 18i 

foJ' this period of obsel'vation although the value of b is srnallel' than 
t,lu~t a t Suzaka. Thc least squarlìs fit blìtween IOg" N ltnd . .:lf fOl' dif-
ferent bme int,ervals (Fig. 6) is given below: 

(A) log ],T 0.10 0.8..1- M 
(B) log ],T () .1H O .. ~3 . .:lf 
(C) log N () H O . 86 . .:lf 
(D) log N () 57 0.92 M [ 13] 
( l<J) log N () .88 0.97 N 
(F) log N 1 O" ."' 0.86 N 
(a) log ],T 1.38 - o 86 M . 

In Table II tlw cllmula tive fl'equency of N1rthquakes for ali cases is 
given. 

'l'abl .. Il - CU~IULATJ\'E FREQUEXCY OF ]<:AR1'IIQU.\KES 

• VrolIl Sm;aka I FI'Olil :-luzuka Il Frolll .\Iat..4u~hiro 

:.r ago CUIl!. 
I 

:\fag. CUlli. "rag. CUlli. 
M freq. ][ freq. ,l{ frl'q. 

-- - - -- -

- O . .J. H4!J -O . H 610 -3 2 510 
-0 . 3 7.J.2 -0 . 7 ;ii8 -3 . I 467 

-0 . 2 H4!J -O . ti 545 

I 
-3 O .J.36 

- 0 . 1 555 -O . fi ii22 -2 . D 3im 
0 . 0 4iiH -OA 47H -2 . 8 2% 

() . 1 :170 -0 . 3 3ii .. 2 , 23i 
o. 2 2Ui -0 . 2 320 -2 li 18ti 
O. 3 235 -0 . 1 261 -2 , l4i 
0 . 4 lill 0.0 20.J. -2 4 128 
0 . 5 l3ti O. j 158 -2 . 3 114 
O. I! 10H Il 2 130 -2 . 2 87 
O. i 83 0.3 08 -2 . 1 i3 
() . 8 70 Il 4 tiU -2 . 0 ti3 
O U 53 O 5 .J.ii -I . 0 ii 1 
1.0 '" Il li 3;; - I . 8 43 1.1 " Il 7 21! - I 

, 34 
1.2 19 O 8 \;j - I .I! 24 
1.3 5 

I 
O 9 7 - I . 5 III 

1.11 2 - 1.4 2 
1.1 I 

I 



I,'\X 1J 1I AKOPOliLOS .r. c. -- ~ U n-ASTAY,\ II. :\". - TERASnnlA T. 

Frolll 1;hc u,hovc result~ it may be sccn that, thc valuc or b is 
sta tionary in short intcl'val or time in earthqm~ke swarmi>. 'rhis 
result is simil a r to tlmt ohtainC!1 fOI" l ~ft,(wshock SI'qlwncllS (II). Ho\\'-
lWCI", in thcsc 1'1Ll"thqnakc swarms, thc vu,hw of li changcs significH. nt,]y 
in dilhwenl mont·h" 01" lli1rm'l'nt ])CriOlL of ohMlI""Va tion n. 

O. Ri) .8 

. .s - 2.:J 
Ftd,. lo :\Ial". 

rOI"l'·aHt'.r~ll(wk~, ~wal"lll ' l 
lIol"lIIal s\'i"mit'itJ' 

:\[lIl~II~llÌl"o i'W:l1"1II 

I U - l.n I 
,ApI". lo ,llIl!. 

[.S <).J. I 
,I III. to .\11g-. 

1l.!lii- I . .J.O 1/1, 2. [ !ili 
F~ lo. I ~Hi!i 

1.1 

O. :J,") 
0.7(; 

O.iiii±0.05 
1.13±O.O.J. 

O.lj lo I.:J 

r')l"e"ho('k~' :\rllt.~l1~hil'o 
aftel""[lOt~k~ 

rOl"c~IJ<,('k,,' CIIiII':lIl 
arteI"HIJ<)('k.~ l'urlh,[. 

Lal"g-e Pil1't.hq. ili ,liIT\'l'l'lIt, 
~I'i~mit~ n'.g-ioJI~ 

onlilllll"y parlll,[uakt,t; ! 
allll aft'I'T><h,,,'k ad,ivit.y 

AIIIIIIII"" 

Il1IllIf\!la .'\: Ilag-iwal"a 
I !llili, l't. I 

lIaJlL~\!la .'\: lIag-iwara 
InnO, l't. 2 

[laIJlf\!llI So. IIlI!.!,"ÌwlIl"a 
I !llili, l't, 3 ' 

l'al"t.y fOI" Spi~JllOg-l"a[)hi(' 
()h~t'.rl'at.ioll ([\Jtl7) 

[[ol"i (IHtr"i) 

Sl1,Vl'hiro. l't al. ([HO.J.) 

~ll:>'f\hiI"O (I ~Hi!i) 

Glltmllh'Tg $.: Ri"litl1r 
(I H;j.J.j" 

:-ìllzuki ([ ~j,")~j) 

In TaNc Hl, thc valucs or li l ~ll(lm ohta inc!l hy dilTm'ellt in-
vestigators are g-iven ror Jlatsushiro rcgion. Tt nmy be .~mltl t,hat thc 
vH.lllc of li COm])al'llS wnlI with thc clLrlicl' \vorkers. 

SUyllhil'O (l) noLiec!l a ~llhstl ~llt.ial dilTenmcc betwcen thc forcs-
hoeks and aftcrshocks in tlw b vahw whieh was fOlllld to he 0.35 
for tlw foreshocks l~nd 0,7(; for thc l ~ft(\rsll()(lb or l ~ Sllutll lH'I'Cc])tible 



SEIS)lI('ITY ()F ~L\TSlTSIITnO ~llcno EAH'I'IIQUA"KE ~WAIOI JHfI 

oarthqllako in tlw )Ia,tsnshiro rogiml. ComparmI with them Hw v a hw 
of li i~ larger l ~~ is expeetod far tllo oal'thqllakC' ,~warlll,~ al!!! aho sng-

gostml by the oxporilllonts of i\Iol!i (I~). 
H howovor, tlle v a lno o[ b for )Iatsnshiro l'el!iou l[nl'iul! file HWlU'm 

i,~ cOlllp a rod with t!mt of genomi SOiSlllicity OVOI' dil1(1!'(1Ut p!;\e!\i; in 
tho world (13), it is rathel' diflicult to 00110h1(10 tllat t!w ya!no i,~ Iliglw~t. 
dnl'ing tlw SWu,rlll. 01](\ of tlle pos~ihl0 l'oason,~ far thiH llis(,l'epancy 
is a,t,trihlltnd to t!w dittm'(mt gmphieal all(I nmtlH'lllMicallllotllods mpd 
[or detl1t'lllining b va!n(','l, )H1sidpH tlw 11.~e or dilferellt lltagnitude sl·all's. 

5. - COè'fCLTTSlON. 

'[']w abovll stlJ([Y hl'inl!s to light tlw iuterc~tilll! cOllelmiou thaj-
iu Il[l,rthqllfl,ko SWlUlil tho valno ai b l'olllaim station1H.v iu a sliOrt lime 
interval l~lthough it nmy cha,ngl' OVOI' dilferont ]wriod aI observat.illm. 

G. - ACKXOWLEDGEI'IIEN'l':'l. 

'l'he a.nthol's l~re ~'Tatpfu! to Dr. S. ()IllOte, ;\diul! llirnctor of 
lJ1tol'w~tioua,! Illstitute of Seislllo!ogy l ~IHl Eal'thqw~lw Enl!inoering, 
Tokyo, for eUCOllral!lllll(mt and far providing tllo lH'('eSslw~' [a,c,ili1il's 
Ior the IH't\~ml1 inv('stil!ation. 

(') SYUEHIIW S., A.~AIH T. & :'IL UIlTAK.:, POn'S/lfJckR (Imi Ai/rr".lwck.~ 
"-lecolllf!lwyiny Il PaGe}J/.ible h'arl,hquakl' iII Celi/mi .!ajJall-, "Pa]lllr~ 
,rlltt'O!". Geoph.y~. 1'okyo ",15, 71·88, (HHi-1-). 

(' ) ILuL\DA K &; T. HAGIWAI(A, lIjgh Sell".i/i!'i!.l! 1'ri}Jar/.itc O/"<frm/iol, 01 
JlII/~I/.".hiro BarlhgIHlke~, ,. Bull. EartlHl. R('~. In~t.." PurI 1, 121:1-
123.-., 1'111"1. 2, 1 2:111· I 21i1i. l'art, :{, HiIi7·IH'-'7, (I!llili), l'art -1-, Li!l· 

!\Hi (I !Hii). 

(") GlJl'llNIlEIW Il. & C. HICTlTEI\, 8r:isJJl.fcil!l o/11M.' 11'111'/11. Imd A~socilll,l'd f'hr-
'1II11I1C/I{I .• PrÌncctoll l~niver~ity Pm;;;; ", (1005). 

(') [SIII}IOTO .\1. & lillA K., ()/lsl'rl'lllillll~ il'l/)" [rs SriSI!lI'N Hllre(!i~lrls }J/l1" 
k Jl icroseismoyrn}Jhl' (!r/ll.N/rll il, f)rrll-ihl'llIcllt" Il 1111. Eurt li 'I. R('~. [n~L 
17, .J-.J-3 . .J-7K, (111311). 



190 fH ! AKOPOULOS .1. C. - S Il IVASTAVA II. N. - TERASIIIMA T. 

(') Purly for Sei~mogruphic Observatioll of ][atsus/dro Eal'thqnakcs and 
HeiwlIUlmetrieul Hcction, .l[alsu~hil'O BUl'lhquakes Obscl't'ed wilh a Ternpo. 
rary Seismogra!,hic Network, l'art 4,45, 887-9l7. (i9H7). 

(') ;-'TUltA)IATU I., et al. O!Jsc1Tutioll of .l[icro-earlhqll(lke~ in J[ino dislricl in 
Oifu Prefect.ure, Ceti trai .!o/lUn "J. of l'hp\. of the l';arth ", 11, 35·49, 
(191i3). 

(1) TERAsnBIA T., .l[agnillldc oj ]ficro'l'urthquuke alld tlw Hpectra oj JIicro· 
MlrUlqu(lk e IVavel,' ,. Bull. liltorn. Ill~t. ScislIl. Eal'tllq. Engin ", 5, 
31·101:!, (Hl(jl:!). 

(") SUY.~:l!JIW ~., j)iOel'mlc~ !J~tlt'eMI Ajll'1"8/wcks (llId F01'es/wekli in lhc RI~. 
l.alionship (lf ][agni/udc to l<'rcq-lIl'ne!! oj Occ-urrcllce lor the Gl'eal Chilwn 
b'urlhquuke io 1%0 "Bull. SPiSlll. Soc. AlIl.", 56, 185·200, (190H). 

(') ])ltAKOPOULOS ,j., Ghamc/eri~iie l'araml'lrr~ of Fore (llId Allcl'6hock Hc· 
quenecs iII Ihl' Hegi(ln oj (frecce, "Di88ertatioll ill Athen8 Univf'.rsity" 
( 19G8). 

(IC) ;-'TOGI IL, H/ud!! (lf E/rullie 8hod:s Caused b!!lhe Fraclurc 01 IIell'l·o.qeneo-us 
.l[alel'i(ll~ all{i IIs re/.alirJ!l.s lo Bar/hquakc Phcuollle/la, "Bull. Eal'thq. 
ReR. 1118t.. ",40. 125·174 (19H2h). 

(l') UTSU T., On the N(I/ll1'e oj Thrl'e A/.a8krW Aliershocks 1'3cquellees (lI 19ii7 
anri 19,;8, " Bull. ~eh\ll'. So!'. Am. ", 52, 279·297 (l962). 

('2) ;-'TOGi K., Home ])i8c-us~irHls rm AI/e1"8hock8 F01"Cshoeks al/d Earlhq·uakc 
Hworms - 'l'he Fmcture oj a HMni·lnfinile Body CallsetI by ali Inner 
Stress all~l Ils rdatio-//. lo thf- Earlhquakf- Phcnomcna, "Bull. I(nrlhll. 
Res. fast. ", 41, lili)·658, (l963b). 

(l~) ISACKS B. an,] UL!y.~:1t J., Scismie IV(wes with Freqllf-ncies Irom 1 lo 
100 r;ycll'8 pa 8eeoml Reconlcrlin a Deep Jline iu Northern NC1j' ./crsc!!, 
"Bull. ::)ei8nl. ::)01:. Am. ", 54. 1941·1979, (1904). 

(H) Hom M., .l[al8ushiro Burlhquake Slt'unn auri J/s PeriJ!hcral Scis1IIicily, 
"Bull. l';arthq. Rei<. last. ", 45, 489-503, (l967). 

(' 0) SUZUKI A., ,1 slalislical Sturiy on Ihe Oecurre/lec oj Hmall Bar/hquakcs, 
"::)ci. Rept. Tohoku Uaiv., ::)el'. 5, Geollhys." Il. 10·54, (1959).