title investigation of microearthquakes -on seismicity...
TRANSCRIPT
Title Investigation of Microearthquakes -On Seismicity -
Author(s) HASHIZUME, Michio
Citation Bulletin of the Disaster Prevention Research Institute (1969),19(2): 67-85
Issue Date 1969-11
URL http://hdl.handle.net/2433/124769
Right
Type Departmental Bulletin Paper
Textversion publisher
Kyoto University
Bull. Disas. Prey. Res. Inst., Kyoto Univ., Vol. 19, Part 2, No. 159, Nov. 1969 67
Investigation of Microearthquakes
—On Seismicity—
By Michio HASHIZUME
(Manuscript received August 30, 1969)
Abstract
On the hypocenters of microearthquakes observed by the seismological network at-tached to the Tottori Microearthquake Observatory of the Disaster Prevention Research Institute of Kyoto University. The outline of observed data, method of hypocenter determination and seismicity maps are presented.
About 1500 hypocenters of microearthquakes were determined using the data obtained at five seismological stations from Aug. 1964 to June 1968. About 980 of them were determined within the standard deviation 0.15 sec by the method of hypocenter determi-nation discussed in this paper.
1. On the Observed Data
The observation of microearthquakes in the northern part of the Kinki and the western part of the Chugoku areas was started on July 1963 at Mikazuki station, Hyogo Pref. by the Tottori Microearthquake Observatory attached to the Disaster Prevention Research Institute of Kyoto University. After that, new
NS E W V PICK UP P. U. P. U.
41 4 • 1. PRE-AMPLIFIER PRE. AMP. PRE . AMP.
100V AC 4 4 4 HIGH CUT FILTER FILTER
FILTER VOLTA GE 1 y 1
REGULATOR MAIN-AMPLIFIER MAIN . AMP. MAIN . AMP.
T T 1 T
TAL GALVANOMETER GAL. GAL.
CLOCK RECORDER REC . NEC .
60% tr 100)/ 6058 DIO BATTERY —
TIMERASIGNAL —NMOTER DRIVER
Fig. 1 Outline of observation system.
68 Al. HASHIZUME
Table 1 Outline of observation stations attached to the Tottori Microeathquake Observatory.
MIKAZUKI FUNAOKA OYA HIKAMI IZUMI
Abbreviation MZ FO OY HM IZ
Latitude (E) 1134°26' 40". 51 134°16' 02". 1 134°39' 52". 21 135°02' 36". 6 134°53' 15". 5 Longitude (N) 34°59' 12". 0 35°19' 49". 9 35°20' 02". 3 35°13' 35". 5 34°58' 20". 0 Height (m) 200 200 260 250 230
I I Lat. (km) 0.33 38.48 38.86 26.94 - L 27 Long. (km) -0.10 -16.26 19.93 54.50 40.35
Components I 1V 2H 1 IV 1V 2H IV 2H IV Sensitivity
(e kine/orn)14001 400 400 400 400 Origin of coordinate : 134°26' 44". 6 (E)
34°59' 01". 3 (N) 1V means 1 set of vertical component.
2H means 2 sets of horizontal component. NS and EW. (1968 July present)
Table 2 Outline of instruments.
Instrument
Seismogram Natural Voltage Output** Internal
period sensitivity impedance resistance (sec) (v/1(ine) (k51) (1(12)
Vertical 1.0 2.6-3. 1 1. 0
Horizontal 1. 0 3. 3-3. 6 3-6 1.0
Amplifier Direct current amplifier &
Galvanometer ' Maximum amplitude : 40mm/p-p
Natural frequency : 50c/s Overall sensitivity : about lcm/mv
•
* Voltage sensitivity is expressed as output voltage against velocity displacement of ground.
** Output impedance is adjusted as damping constant h= O. 707. (1968 July present)
S T 30 stations were constructed
ST 30IIby and by and the seismo- 4 K CI 10 logical network now consists
' ' of five stations . In this
paper some descriptions
I N 1 K(3 as 0.5 0.25µF 0.5 OUT are presented mainly on T I-IF PFT T NF the data obtained bythis
II
I 1 _network. •___0The outline of the pre-
Fig. 2 Circuit of high cut filter. sent network, outline of
Investigation of Mierviiirthquakes 69
- —
==ll••••^^ IMM0/111^=111111SIMIIIIMII
IMMPIIII NMI 111111
0.1 1111111 11111 1111 aZIO•111•1^MIIMICISBI
c.) A=MMIONI^IMMWE M^1=11^•••• MI
w 411•1=11111^0111aMMIIIIIII
,
0.1 1 10 100 Fig. 3 Overall frequency response curve.
observation instruments and observation systeria diagram are shown in Table 1, Table 2 and Fig. 1 respectively. The natural frequency of seismometers is 1.0 c/s and it has strong higher mode near 30 c/s. This higher mode vibration stimulated by ground noise or sound disturbs the seismograms. And the high cut filter shown in Fig. 2 is used at the position shown in Fig. 1. The overall frequency response curve is shown in Fig. 3. The characteristics of the seismo-
grams are kept constant during the whole period of observation. A set of apparatus in an observation system and an example of a seismogram
are shown in Photo 1 and Photo 2 respectively. The time mark is recorded every second and it is controlled by 'X'tal clock, and the X'tal clock is checked every hour by N. H. K (Japan Broadcasting Corporation) time signal.
The terms of seismograms reading are date, P and S time and their accuracy, P initial sense, P-F time, maximum amplitude and its period and some remarks. These terms are punched on a card, and the compilation and some corrections are done by electronic computer. There were some alternations of the observa-tion system, and they are all shown in the volume of data on the same titles).
There is the Takatsuki branch that belongs to the Tottori Microearthquake Observatory. The outline of the seismological network of the Takatsuki branch is shown in Table 3. The seismograms are all one component (V), and although they are soot writing the time accuracy is not so good because only minute marks are recorded on them. So, without any comment, no data are used in this
paper or the succeeding papers. All the data used were reexamined by the author himself, and the time ac-
curacy is as for the data of P time ± 0. 05, and as for S-P time ±0. 1 sec. Data used in this paper are confined to maximum S-P times less than 18 sec, and
they are shown in the volume of datal). Before June 1965 the observation system was not so complete, so only the data that were well observed at more than three stations are used.
70 M. HAMILZUME
- ' -.• • - -
-g1i ,'„'>':t',"_4,:t....;,-:,cf-7,,;.X...,-1`•`:' art;cite-(4,4,,,,s0--;.,,,,• 14I-.,71-- 141“ar:*! - ---,-,d,
Photo 1 Apparatus of observation system.
-.=-E-=====-=Emffeg "Z-s-ttier-±=Eri-mert-st-sp-10-.3.- -NE-,--ig',./..1E-RE-E-4.4: c.e.-a-s,-----„....E=E--E--1-E-s-r--7..a.-E=atEe-za EEEEglugNmEur=.5-'2gINNiamm-dgEERIIERmam#megmgagg: telta1E-NEIPltifflS.211112-211IfIE-Ettr-4-Bill° IEElppiqp2474-HgffiNalgAlmareallIEIgEEiliggaggpftillt-,. -1-z-:---%32-ntagifitanteffpg-Eit-Zi-adlEglti71 -.:-T2i7.1"; ---2-sh-57--aaa-4e 0-.-fazzonmmt-eitiELENziaE-s-oricl=tittegw .gE.zaigt-ffig =7-f-'ff=2;=Ne@g-gaitEsitlIgegflkffsgsgmg-g aEatm:4-mmtSa= -=E ==p-a.wat-"N=E'71FW'If17.1=2E.RasEsssEsgmess
ggEES==iagt4=7T,=',2.:=M,7711Fi:",1,4,,Y.7,.77745,7. .„Igr.F2EL-F4me ,1t-E.,-?-1.7MffigeWer-flleaMEEEE' .,r .,...„.„sa_=.. =======ssasssEssxgmt,.,Nammg=p==_== gl.g'2W2R-=:----Rag y---.am1R.t.,*ssENsEssi .Ess4g e---mENEREsAEEMIEE10:10MggN,gglITup.ls.... NEBEEEZEEEffmOsgSsERallEIE6144gEllIP5=" asesms==sgsRs'=,,sr ,aggss,,,,E=S_ge=n , 4m:g, iliZ-Eggi..-=saAns---/-ti==g-sigmblEas.-=-g--E-E ..raigEvaER: ===.....-...m-a=sgEgffSsEsEggEWEIElEIMErE=ERNssWssEE I ====assEssss=====saaEA@EE _am_a== _=Elms=ErEssm_ ,,Eg=ms=EM=MEgERN€ffis=s4E..--rea=i-EsmsEr=nm=S• SESSMEggssE2EegssEassM=W...m==mffssE E EsE=waSmaSa ER-Er:...-lSsigmE.E.FigeasidENEEEgisigEN§§g=1EEEMIggilsg-sing• ="44's-4-anaE=B=-"-17•-th'E•a'-=i=-S==isoa"Es==EE_:xeE.--srr=-sa--=ia.-.=.- •r.wi-.a,eEev-ai'-•e.'..l't''-'r--.''*"=-:t&-.--W.tg.Egi.ig=ERE•Esn.ar:g--,IiEai-isi.•-=,.r_--
-
li t'-•"-:W'l"-2=a'r-.'m-ra=--a.-gEEr:a.ri:iiNE'EE--q.-T-E:.-:---g--ge:--g i..E"'#gi1".C''K':t"1'-Tg-ntS2§ga=g'§a.$rNuI:-=-as:s-:R:.ELWFS:,tgri- 7 sa=s= ireSnaigrztI rekgRE---24=2ERK' .7411"--4:1111311--SligigaBEF-triZE-2 iigkiartsin:.i.�..kiaki •• -lis-.=4w-14=-E---r,-3-..--2..E.v.,:tals§-e„:L=.11--.-1-gitc-s.-
-- -- - r =====tE.:EF-E-=EEEN=7÷ .-saa-a.E.E-ssFAE-4.Fr..5eFEERmega azi.aardErt . EEN-0=EEF --=Ea-=',.-.EMEW.....--,Er-.51-ati.E.ME.E=MaRErega-E-aa..-ar4 ==5a=====E _gmreEE=itn-t-EirimE=g,..2=-askrita..- .====ms7=s-igm- ft"&"--11WSiarir-_=20.r.-En==."...asit,E=4 .....m====_===3,__2,...g.E
==-==_= t-
====-=====__ ___=-1=r-r=E.tt-_a.====e.g1Z-_,EffeE2=4"E=farigai=a--.2- _agE;-_-soRr-=&-a--.r-rlf..7tEssrogggatglINE2-nRE.-Et--Egszkzt-Eziag: gP-EirlP:raff:1t:th.P.Ears-NFazigat-timptgtifEif-;;;;;===;_ag, -az -
_ ____— ======= ------------=_-7,-- -- ___===== =====
=
=E-asio.47?-mr-z-ms-s--
Photo 2 Example of a seismogram.
Investigation of Minvearthquakes 71
Table 3 Outline of observation stations attached to the Takatsuki branch of the Tottori Microearthquake Observatory.
ABUYAMA MYOKEN YAG1 KAMI- KYOHOKU TANTO GAMO
Abbreviation AB MK YG KG KH TT
Latitude (E) 135034'22". 41135°28'18". 0 135°30'46". 01135°45'56".3' 135°39'43" '134°58'38".1 Longitude(N) 34°51'34". 34°55132". 01 35'04'04". 35M3'32 0, 35°10'37" 35°30'2r. 5
Lat. (km) 1 103.00 I 93.71 97.38 120.46 110.92 48.38 Long. (km) -13.78 I -5.76 9.33 , 8.34 21.44 58.00
TANNAN KOBE TSUNA I IKEHARA ROKKO IWAO
Abbreviation TN KB TU IK RK IW
Latitude (E) 135°12'50". 0.135010'34". 0 134°53'05". 61135°59'05". 7,135°10'31". 2136°07'56". 0 4Longitude (N)• 35°01'55". 8, 34°44'05". 4 34'25'04". 81 34°02'00".8 34°44'05".4 34°52'57". 0
Lat. (km) 70A2 66.79 40.24 14L35 66.73 154.09 Long. (km) 5.38 -27.61 -62.76 -105.40 -27.61 -11.23
(1968 July present)
2. On the Method of Hypocenter Determination
The program for hypocenter determination is as follows :- The principle is to search for the best fitted point in the plain of a varying
depth as for the observed P times or P and S times and theoretical traveltime calculated from a known crustal structure.
In this paper the hypocenter domain is limited within ±250 km on the coordi-nate of Table 1. Depth is determined at the interval of 1 km up to 15 km and then 2 km up to 37 km.
As for the accuracy or some other discussions another paper is prepared2). Some notations are described for the following discussions :-
Suffix j : station identification P° time : origin time
T time : traveltime Z : depth X", Y" : coordinate of station
P time : onset time of initial P wave S-P time : S-P duration time
P time : calculated travel time
( 1) In a case where more than three P times and more than one S time are available :-
a) To determine origin time.
Assuming Poisson's ratio u= O. 2402 and using Pi and (S-P); time we put, P°;= Pt- 1. 4 08 X (S-P);. (2.1)
We assume the mean value of ri to be origin time P'. Then the travel time is reduced as,
Ti= Pi-Po (2.2)
72 M. HASNIZUME
If even only one datum of S-P time can be available the traveltime is determined by this method.
b) To determine initial value of X and Y. Setting mesh on the surface of Z=0 of which the grid spacing is 12. 5
km, the best fitted point to hypocenter is searched for on the cross point of the mesh by stage e) as the initial value of hypocenter determination .
In this procedure the mesh can be rough in the area where the deviation is greater than a certain value.
c) To search for the epicenter. We set nine new points X', Y' as,
(X' = X±d' or X' = X Y±d' or In Y (2.3)
d'=d/1. 8 where X and Y is the initial value of the epicenter and d the grid
spacing. The best fitted point to the epicenter is chosen by stage e) and it is newly set as the initial value X and Y. This procedure is re-
peated until the grid spacing constant d is 200 m. d) To search for the depth.
Stage c) is repeated on the plane Z-11. H is varied by 1 km up to 15 km of depth, and more than 15 km of depth by 2 km, but if the deviation
calculated by stage e) is greater than a certain value some steps can be jumped. For Z=0 the epicenter is determined by stage b) and stage c).
For Z>0 stage b) is deleted and the calculated most probable point of the
just upper plane is set as the initial value of X and Y. The point of the least deviation S is searched as the most probable hypocenter.
e) To calculate the deviation. We calculate the traveltime Tic for the distance Di between stations XP,
Yr and X, Y by stage f) at the depth H, and put as :—
3= (2(Ti - TiT)34. (2.4) where 5 is defined to be the deviation at X, Y and Z.
f) To calculate the traveltime. ,5 6 7 8KrA Traveltime curves are calculated
on the base of the crustal struc- ture shown in Fig. 4. The struc- ture is a slightly modified struc- 10-
ture of Model II researched in this district by explosion seismo-
a_ logy3). These traveltime curvesw 20- are divided minutely and memo- o
rized. Traveltime is calculated by the interpolation of distance. 30-
The time accuracy is within 1/100 sec.
( 2 ) In a case where S-P time is not 40- available and more than four P KM
times are available. Fig. 4 Crustal structure used to Calculating Tr by stage f) for calculate traveltime.
Investigation of Microeanliguakes 73
X, Y and Z, we put the origin time P° as :— P=I(PJ-77)/Ej (2 .5)
Then we repeat the above procedure in the same manner as the case using S -P time . The least deviated point and origin time are searched as the
most probable hypocenter and origin time . In a case where S-P time is used and crustal structure is known
, the equation to determine the epicenter at the depth H is :—
(TiVj) 2 = (XJ"—X) 2 + Yr — 10' (2.6) where V.; is the mean apparent velocity from the assumed epicenter to the observation station. In the above method the determination of the most
probable point at the depth H is to determine the minimun value of a' that is :—
52= .(7.1—T:19)2/= E(T —1V(X ist — X)z + (Y i"— })ar/ Zi (2 .7)
at32 acv ax ay=0 (2.8)
In other words a is the standard deviation of the observed data to the deter mined hypocenter. Mathematically the minimum point of this equation is very complicated , and
we have some possibility of mistaking another minimum point to be the most probable point. In this sense stage b) is important. If the mesh to give the initial value is rough, then in some cases a very large value of deviation a and mistaken hypocenter is determined . The length of the grid spacing may depend on the seismic network size and the number of stations . In this case 12.5 km is given.
For the hypocenter that has a value of a more than 0.10 sec, all data was checked by the graphical method or by varying the initial value slightly , and it was con-fi
rmed so as not to mistake epicenter more than 0.3 km or so. In the case of using P time only it is more complicated , but in our case almost
all the earthquake that can not be read with the S-P time are rather large earth -quakes which are reported in the bulletin of the J . M. A. (Japan Meteorological Agency) and the results could be compared to them .
As was mentioned already , the time accuracy of data for P time is within ±0.05 sec, but some unknown errors are left such as the origin time
, crustal structure, regional travel time anomalies , so that more minute discussion than deviation less than 0.15 sec may be nonsense .
There are some data as to local traveltime anomalies by explosion seismology in Table 4. All the onset times of P wave are clearly read within ±0 .01 sec. From those results about ±0.1 sec of traveltime correction is needed if confined only to those data, but since it does not affect the result so much , we have left it f
or further reseach work. The inaccuracy of S-P time affects the origin time . In some cases residual
JPi° from mean origin time, that is:— 4P.t° 1.408 x (5— P)1 (2.9)
exceeds ±0.3 sec, but it is elucidated that it does not affect the hypocenter determination so much2).
The list of standard deviation 5 and its number of earthquakes N , the number of earthquakes observed at each station and the number of stations used in
74 M. HASHIZUME
Table 4 Data for local traveltime anomalies by explosion seismology.
1st and 2nd Kurayosi Explosion4) Tomieda quarry blast 1967 Nov. 30 06h 30.n
4 P-0- /6 Shot point : 134°22'03". 2 ( Y=41. 687) 35°21'43”. 1(X= —7. 122)
FO 1 39. 85 1 0.52 MZ ' 71.36 0.33 4 P-4/6
OY 75.28 0.53 FO 9.69 32.38
1st Hanabusa Explosion° OY 27. 10 32. 34 MZ 41.95 32.61
4 P-0- 4/6 BM 63.36 32.58
HM 143.00 0. 35 I Z 64.02 32.55
Table 5
a) Number of earthquakes of which hypocenters are determined within a cirtain value of standard deviation 8.
• _ .
.3.<0. 05 o. cio�s<o. 10 O. 10<d<0. 15 a i.s.�a
941 438 132 19
Total 1530
( Among them the number of earthquakes determined by P time only is 8)
b) Number of earthquakes observed at each station.
MZ FO OY HM IZ
1346 1 722 I 1309 li 1260 1384 c) Number of stations used in determining hypocenter for each
earthquake and its number of earthquakes.
Station 3 4 5
Earthquake 503 623 404
determining the hypocenter for each earthquake are in Table 5. The most difficult point to level up in the accuracy of hypocenter determina-
tion is how to keep the accuracy of obsevation and reading seismograms of each station of each earthquake.
3. On the Determination of Magnitude
The determination of magnitude is after Muramatsu's formula for microearth-
quakes), M = 1. 25 log (V) + 2. 50 log (R) —6. 50 (3. 1)
where V is the maximum amplitude in p kine, in our case the maximum ampli-tude of vertical component is used and R the epicentral distance.
Investigation of Mieroearthquakes 75
There is some questions of applying this equation and the corresponding energy
and magnitude relation,
E=11. 8+1. 5M (3.2) to our
network.
Then as the first step in applying equation (3 . 1), we calculate the residual JMJ, reduced magnitude determined by each station M
I from its mean value M, that is :—
AMJ-Mi-M (3.3) I
n Table 6 the mean value of AM and mean epicentral distance R is shown for
Table 6. The mean value of residual magnitude .4 M and mean epicentral distance R for each station . N is the number
of earthquakes used in this calculation . - - -
- -
- - -- --
Station MZ I FO OY HM IZ
4 M 0. 04 -0 . 04 -0. 02 -O. 10 O. 09 R (km) 76.4 I 94 .7 79.2 63.0 58 .2
678 333 674 631 I 734
• each station. N is the number of earthquakes used in this calculation . From this result it needs about 20% of amplitude correction in linear scale for our
network. As for FO the mean epicentral distance is not so great as that of the stations
MZ or OY and the amplitude correction is the same as the others , but the number of data used is fairly small . The reason why is because there were often no observation periods due to some accidents . Then there is a possibility that the seismicity level is underestimated around station FO .
If AM.; is due to second coefficient of the right side of equation (3 . 1), it must be changed as follows by the least square curve fitting .
M= 1. 25 log ( V) + 2. 90 log (R) - const . (3.4) But some consideration must be paid to the calibration of the instruments , d
eviation of seismicity from each station , focal mechanism, and so on. As we have not so much data , then at the first step we do not use equation
(3.4) but use (3. 1) because the difference between the two equations does not seem to have a decisive effect on our discussion .
By the characteristics of the galvanometer , the amplitude is saturated more than 2. 0 cm (about 800 p kine), so some device is needed to estimate the real
calve of the scaleout amplitude . Tsumura found a certain relation between P-F time (from onset time of initial P time to Coda time) and the amplitude for
microearthquakeso. But we find this relation does not hold in our case . We find the relation shown in Fig . 5, of which the abscissa is the time interval
in seconds from the onset time of S inferred from the hypocentral distance determined by the above method, to the time when the amplitude becomes less than 2. Ocm, and the ordinate is the amplitude in m kine after equation (3 . 1) using the magnitude determined by the J . M. A. (open circle) , or determined
only by unsaturated seismograms (solid circle) . In Table 6 the data thus determined is not used.
76 M. HASHIZUME
rnK/NE 0 o 0 0
0 0 100- o
o
o o
• t• °g • o
0
. o
•• • ••0 • • 0 • • • o
• • • • ° •
0 • • 10-ea o 0 0
• • • •
•
1 e
1 L ,, , 0 10 20 30 40 SEC
Fig. 5 Curve for estimating the amplitude of a saturated seismogram. Abscissa is the time interval in seconds from the onset time of
S inferred from the hypocentral distance to the time when the amplitude becomes less than 2.0 cm, and the ordinate is the amplitude in m kine after equation (3-1) using the magnitude
determined by the J. M. A. (open circle), or determined only by unsaturated seismograms (solid circle).
In Fig. 6 the magnitude (M)—NI . . . accumlated frequency (N) rela- 1000 tion is shown. At a glance on this t
figure we find Gutenberg—Richter's \ relation, \
log n(M)= a — bM (3.6)
which does not hold in this district. N't. If we manage to fit straight lines, 1 00-
their coeficientsf 1; are culculated by the method of Utsu7), \\
\\., 1.2 <M<2.2; b=0.89
2.2<M; b=0.52 .. ., .
and for M less than 1.2 hypocenter 10- \‘. could not be determined uniformly. ‘,
Seismograms begin to saturate N more than M = 2. 0, for M more \ than 4.0 magnitude is determined'\\ by the J. M. A. And the magni-tude between 2.2 and 4.0 the ampli. . , tude is estimated by Fig. 5. The _1 0 1 2 3 4 5 NI value b =0.89 is the same as the Fig. 6 Magnitude (M) and accumu-value in this district8L lated frequancy(N) relation.
Investigation of Microearthquakes 77
If in equation (3. 1) the constant term is less than 6.5 by 1.0, then Fig. 6 is little changed and our curve may be one straight line connecting the microearth-
quake to the large earthquake. We have left this problem for further research. In the volume of (laical) all the earthquake from Aug . 1964 to June 1968 is
listed for date, origin time, epicenter X, and Y focal depth Z and its probable domain, standard deviation, magnitude and station observed .
4. On Seismicity
The seismicity map of the northwestern part of the Kinki and the eastern
part of the Chugoku districts is shown in Fig. 7. In this figure the end of shore line is nearly the limited boundary on determining the hypocenter in this paper .
Fig. 8 a, b and c is the seismicity map, from Aug. 1964 to June 1966, from July 1966 to June 1967 and from July 1967 to June 1968 respectively. As was mentioned already before the June 1965 observation system was not complete so the seismicity is much underestimated.
Fig. 9 a, b and c is the seismicity map of magnitude M as 1.0�M, 2. 0 M and 3.0�M respectively.
z
o 16as e °0 0 0 (
0
eirc...4 .,
---, 00maii,nr‘felV2ma ;,-4a arba
1 ee'e aa°ra%a 10
pa
aaftgae® ,. La e DEt2.z,ea S Sotho Celli°. : ...
a e.Aws ® vatoiffro. __go.00. 7 ."Eg .kr , .7:®iit--;;:cai.. 02, o
•
z-.°,4ol:1
.
. 06,.20.a5Lob(v::.o ..E ,o,o O • 26a",4:'.OFc'C
1
._11,zon :.c 2 . 0
e
. z . 4---1-,./, a1'
,,,,o,. z " a
cm a ; ala . 0 STATION
I 16 o • 2 6'2 sc.3—5
23. 26 ; , • S_ 0 10 20 32 40 50
I KM)
Fig. 7 Seismicity map of the northwestern part of the Kinki and the eastern
part of the Chugoku districts. The end of shore line is nearly the limited boundary on determining the hypocenter.
78 M. HASHIZUME
0
z
: •
A a z,z
: „a, = , ,,,a
I' r. z ® z_ z PT,.'. -9‘, '` z z z . 0 z zz ka Zia 2 22'-AazF, is
.223":_.27: =i 4 4Zz g. 7 "Z,'IN-.)7124 -4;'-i kvi:
4 2 r _GO : 51, lia tje. 9,1, a
a /' s a° a N
4' z_ z 2 '''''' . k 3&
' I
ciV , zID STATION
e 2
?....\ 3—5 •6
' 7--I\ D 0 I 9 20 30 40 50
(KM)
Fig. 8 (a ) Seismicity map from Aup 1969 to June 1966. In this period seismicity is under estimated.
4 a
,
, a,7 .I z.i'Thi
. .. „„ , '
2§ z" o 4a ; . " 9Ur-zf1 . a Z1es j1 09® 2a2F;W
aa3 Iaa2 Lb :aatzlg. ., .graC
accaleit 2 @z(2 0Fl
9a00NaN ztoir. ''
2 E .1 a r e z . I ' ri. 91 ib I"
: r•a
a z ;J, a 0 0 0 ® STATION aI
0Z2 s E amt
,:35 •6— a
a0 10 2030 40 50 2
( KM)
Fig. 8 (b) Seismicity map from July 1966 to June 1967.
Investigation of Microearthquakes 79
a
. - „ ..
„ z
W a , ,
, za z o ® r 7 z
, k ,,,z!z
N ®rnotiO vz . /4"ti. 2 r' - • ' — a
0
..::4)1:::,r,"117?"„7:1.7).Cer:::: 99 If .a. , : % • C
••:.,
_.a
091a
zz /-zIf,__::
1 0 STATION ^e1
a s.•2 oi 3-5
• 6— 0CI' 0 •`c'II0 c 0 10 20 30 40 50
(KM)
Fig. 8 ( c ) Seismicity map from July 1967 to June 1968.
n
0
, 2 a m B .. o
a 9ado .
az " a
----\)) a . rie, ®z :a a az '
,, t4 aA a.1
ziI, 9) n®
, 'el°4301tjte% : a 00
II 7. a a 0 0 07122°140a° 0®~ 00°00
in aT4aa
cl a aSe , m 24 ait'''Pet®
°
0 a2a a
aa a aeanW2: i0''caa °aNt 0°
0lb10 a.:
°
.0 e 0 is 7000 ° °.
2a a 2 °
a STATION ,,..,,,,,, :ie •
a11r9r77 d° ''II''‘I“ • 1 • • 2 a• 3-5
aEI.I3 a • a•- • S— •00 a a ? lo JO 30 40 50
(04) Fig. 9 (a) Seismicity map of magnitude M as 1. O<M.
80 M. HASHIZUME
a a / 4 2 z
z7
N ore Zel3Pr°
1
9 y--7 [1;;;;)
or
STATION z I
a 2 3-5
) 0 10 20 30 40 50 (Kw
Fig. 9 ( b) Seismicity map of magnitude M as 2.0<M.
A 0 E-4
CC:21 0001111:10N
a 2 a 5-5
0 10 20 3C 40 57
Ii0e)
Fig. 9 ( c ) Seismicity map of magnitude M as 3.0�M.
Investigation of Microearthqztakes 81
. • —
0
o • • • • 0 - .9 I • • • • • • I s • ,
res'— ^ 4 44 . .
,!! - I ° • .. . • 0 6..• ,npo a't
!•6. .?"'i-Z , E 04'
Fig.10 ( a ) Fig.10 ( b ) Distribution of epicenters determined Distribution of epicenters determined
by J. M. A. from 1926 to 1954. by J. M. A. from 1955 to 1964.
N
Li— 1020 30 KM
Fig. 11 Histogram of frequency (N)-depth.
For reference the seismicity map of rather large earthquakes by the J. M. A. is shown in Fig. 10 a and b. The coincidence between the microearthquake seismi-city map and the rather large earthquake seismicity map is not necessarily good .
The histogram of frequency-depth is shown in Fig. 11. Fig. 12 a, b, c, d, e and f is the seismicity map of the focal depth d(km) as
0<d<5, 5<d�10, 10<d15, 15<d<20, 20<d<30, and 30<d�40 respectively. The details of seismicity and quarternary geotectonics and related problems will
be discussed in succeeding papers,).
82 M. HASHIZUME
0
a
0 0
•P p .
reof.crl' 0 ...'—‘\11 • °mm1. 20r4aia 0 as i 20ea me.0o e•'' 02 Sa a otinaa
z
a210s 2,,je 0 Do 0o •sa'.% A •
,4 0 64. za #'•:: 0 0pale
0 2
Az o aa a p sen9:1200 ."e ... 2 Sa pm a914' a
z 7 P aoo taN
i
glIkLii.
(!;;;j1 .. 77 t ARIS STATION 0I
Ou 2 .:.:oe 3-5
• 6—
o ip 29 30 40 5D
(KW
Fig. 12 (a) Seismicity map of the focal depth d as 0<d<5
a
0
a 0
-A n 00 I IR. ~®„Ivora11m•0 Ø.
a ®4.4 a° co •
la ala aLaa "cafaPP°if•aeala°KaiH „IL,~
®0 e ,-"- e;40 .1%.
f
.Q4."I A3 °a 2 0 %die mm
2 40 ° Y
° I •
N
MI 60
0
0 1: 2) OM 0
GiD STATION CI /
le 2 .=a a 3 —5 • 5 —
0 10 20 30 LO 50 ^...--1.- (154)
Fig. 12 (b) Seismicity map of the focal depth d as 5<d<10.
Investigation of Microearthquakes 83
"
72'2.1 •I•2
2Era2zz/
16.17/."'62i 3- 2,1, a a 7b 620,1 .
RE"
sla 5 ta 2 ,
0 a
STATION m
e 2 • 3-5 • 5— o 10 20 30 40 50
( Fig. 12 ( c ) Seismicity map of the focal depth d as 10<r/,115.
n @
a ncik
n n
IC;) gI STATION
m 2 s 3 —5
—
0 10 20 30 40 50
(NM)
Fig. 12 (d) Seismicity map of the focal depth d as 15<e/20.
84 M. HASHIZUME
4\
0
it 0 o
1
N-t 0 57AT / ON
71 1 CI 2
iae /73 —5 • 6— ( \
0 10 20 90 40 50
INN)
Fig. 12 (e) Seismicity map of the focal depth d as 20<d30.
0
0
•
STATION
I 0 1
2 g 2 3 3 —5 1
• 6 — 0 10 20 30 40 50
INN)
Fig. 12 ( f ) Seismicity map of the focal depth d as 30<d<40.
Investigation of microeartlupeakes 85
Acknowledgements
Most of the data in this study was provided by the Tottori Microearthquake Observatory attached to the Disaster Prevention Research Institute of Kyoto Uni-
versity. The author wishes to express his sincere thanks to the following members :—
Director Dr. Y. KISHIMOTO
Seismologists Mr. K. MIND
Mr. K. OIKE Mr. R. NISHIDA
Technicians Mr. S. NAKAO Mr. Y. TSUSHIMA
Mr. S. MATSUO
Seismogram Mrs. M. KOGA interpreters Mr. S. YABE
Station Mr. M. YABE
keepers Mr. R. OGURA
Mr. T. SHIKATA Mr. G. HOSOMI
Mr. Y. UENAKA Financial aid was granted by the fund for special work of this Institute.
References
1) Hashizume, M.: Investigation of Microearthquakes - Data - (in press). 2) Hashizume, M. : Investigation of Microearthquakes -On the Accuracy of Hypo-
center Determination -(in press). 3) Hashizume, M. et al, : Crustal Structure in the Western Part of Japan Derived
from the Observation of the First and Second Kurayosi and the Hanabusa Ex-
plosions, Part 2, Crustal Structure in the Western Part of Japan, Bull. Earthq. Res. Inst., Vol. 44. 1966. pp. 109-120.
4) The Research Group for Explosion Seismology : Crustal Structure in the Western Part of Japan Derived from the Observation of the First and Second Kurayosi
and the Hanabusa Explosions, Part 1, Observation of Seismic Waves Generated by the First and Second Kurayosi and the Hanabusa Explosions, Bull. Earthq.
Res. Inst., Vol. 44. 1966. pp. 89-107. 5) Muramatsu. I. et at : Observation of Microearthquakes in Mino District in Gifu
Prefecture, Central Japan, Jour. Phys. Earth, Vol. 11, No.2, 1963. pp.35-48. 6) Tsumura, K. : Determination of Earthquake Magnitude from Total Duration of
Oscillation, Bull. Earthq. Res. Inst, Vol. 45. 1967. pp.7-18. 7) Utsu, T.: A Method for Determining the Value of b in a Formula log n=a—bM
Showing the Magnitude-Frequency Relation for Earthquakes, Geophys. Bull. Hokkaido Univ., Vol. 13, 1965, pp. 99-103 (in Japanese).
8) Hamamatsu, 0. : Seismicity of Shallow Earthquakes in and near Japan During 1926 to 1956, Quatr. Jour. Seisms., 25, 1960, pp.97-108 (in Japanese).
9) Hashizume, M. : In preparation with the same title.