The Inst.of Natural Sciences Nihon Univ.Proc.of The Inst.of Natural Sciences
Vol.24(1989)pp。53-62
Earthquake Prediction an(i Seismic Hazard
Analysis in Japan
Tsuneji RIKITAKE(Received October 31, 1988)
Probabilities of earthquake generation from active faults in Japan are evaluated basing on
crustal strain geodetically obtained over fault areas,From the data of earthquakes that oc・
curred on or very close to an active fault,the relation between the strain rate(7)and time
interval between a speci丘ed epoch,say the year2000,and the last earth(luake occ皿rence(T)
isstudied,s・thatthedistributi・ns・fTf・rthreeranges・fr,i.e.7<2×10-7/yr,2×10-7/yr
≦7<4×10-7/yr and4x10-7/yr≦プrespectivelyシare obtained. The distributions are approxi-
mated wlth Weibull distribution.With the aid of the parameters of Weibull distribution thus
determined,strain accumulation over an active fault is estimated on the assumption that the
strain rate is constant.Probability of crustal break or earthquake occurring in a time interva1,
10yr say,at the year2000is then evaluated by comparing the accumulated strain to the ul-
timate strain。Such an evaluation is made for all the active faults amounting to348in num・
ber。
As earthquake magnitude can be approximately assessed from the length of a fault,
ground motion at a site in terms of acceleration is readily calculated by making use of an
exisiting empirical relation between maximum mean horizontal acceleration,epicentral dis-
tance and magnitude。
Summing up the effects from all faults,it is then possible to evaluate probability of ground
motion at a site exceeding a certain acceleration level・100and300gals say・In this way
probability distribution of seismic hazard can be obtained all over the Japanese Islands,
The present zonation is different from existing ones,which are liable only to the average
of seismic hazard throughout historical and/or geological times,in the fact that the present
state of crustal strain accumulation is taken into account.In other words the estimated
seismic hazard is based on long-term earthquake prediction、
In addition to the probabilities due to inland active faults,probabilities of major earth-
quakes Qccurring in亡he sea suτrounding Japan are also evaluated in some way although no
accurate evaluation is possible.Combining on-and of〔一shore seismic activities,overa1玉zonation
of seismic hazard is put forward. It tums out that the probability representing seismic hazard
is highest in the Chubu and Kinki districts,Central Japan,and next highest in some parts of
Tohoku,Shikoku and Kyushu districts.
The probabihty distribution maps brought out in this paper may be useful for having
some idea about future seismic hazard in terms of ground acceleration although the absolute
value of probabi1呈ty may not be quite accurate.
Department of Earth Sclences,College of Humanitles and Sciences,
Setagaya-ku,Tokyo,156,Japan
一53一
Nihon University,25-40,Sakurajosui3-chome,
(1)
T.RIKITAKE
Intro“uction
Seismic hazard analyses in terms of maximum
seismic intensity,acceleration,velocity and the hke
have been made in Japan in the hope of bringing
out possible earthquake hazar(1s throughout the
country.Kawasumi(1951), who relied on the
earthquake record in history, obtained expectancies
of maximum seismic acceleration in gal for periods
of75,100and200yr,The distribution of expec-
tancy thus obtained is called the“Kawasumi map”
and w1dely used for designing earthquake-proof
construction in Japan,A similar analysis for max-
imum velocity was put forward by Kanai and Su-
zuki(1968)。
It apPears that the period covered by the
history of2,000yr or so is oftell too short for
evaluating seismic圭ty because retum period of large
earthquakes is longer than 1,000yr in some parts
of Japan.Wesnousky(1982)and Wesnousky et aL
(1984)evaluated inland seismicity averaged over a
much longer period on the condition that the past
activity of an active fault can be inferred from its
slip rate and length、 The fault activity thus
brought out is converted into the rate of earthquake
generation on a few assumptiolls. Taking the con-
tributions of all faults in an area of interest into
consideration,it is possible to estimate the average
time interval between seismic shakings of a given
strength for a site in the area.From such a time
interval,we can readily evaluate probab呈1ity of ground
shaking exceeding a certain level in a speci后ed time
interval provided earth(luake occurrence is stationary
alld random,and so occurrence frequency obeys the
Poisson distribution.
The zonation maps by Wesnousky(1982)and
W▼esnousky et al. (1984) are interesting in that the
earthquake hazards averaged over a period much
longer than that obtained by Kawasumi are present-
ed,It should be pointed out,however,that these
maps are good only for the average during the
period probably since recent geological era.As no
account of crustal strain accumulating in the area
covering all fault at present is taken into considera・
(2)
tion, the probability of ground shaking for a
prescribed time interval from a speci丘ed epoch can・
not be evaluated by the above method。
As the earthquake prediction program made
progress in Japan,the writer feels that something
more de丘nite can be said about probability of&n
earthquake occurring from an active fault basing
on the data taken by the program,For instance,
accumulation of crustal strain over a fault can in
many cases be monitored by repetition of geodetic
surveys, and so probability of crustal break related
to earthquake occurrence may in some cases be
evaluated by comparing accumulated stra1n to
ultimatestrainthatleadstothecatastrophe.Amethod of evaluating probability of a fault genera・
ting an earthquake as a function of time will be
presentedinthispaperbased・nthecrustalstrain
data(Rikitake,1983,1984).Summing up contribu-
tions of all active faults in Japan,probability of
ground shaking exceeding a certain level during a
prescribed time interval from a speci丘ed epoch can
then be calculated for any site.It thus becomes
possible to present a sort of zonation map of
ground shaking on the basis of long-term prediction
of earthquakes originating frっm active faults in
Japan.
The approach is different from those by Kawa・
sumi,Wesnousky and Wesnousky et aL in that the
probability is speci6ca11y obtained at a certain
epoch.The former studies are concerned only with
the average probability during historical and/or
geological t1mes.
This paper飯st of all describes how to evaluate
pr・babilities・faccelerati・n・fgr・undshakingex・
ceeding a certain value due to earthquakes origi・
nating from active faults on land,Zonations basing
on such probabilities will be shown in a form of
distribution map.
In the next place,the writer will try to evaluate
thepr・babilitiesduet・earthquakesintheseaareas
surrounding the Japanese Islands in order to
elucidate overall earthquake hazard in Japan・As
Wesnousky(1982)and Wesnousky et aL(1984)did,
there are some means of evaluating future seismic
一54一
Earthquake Prediction and Seismic Hazard Analysis in Japan
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' _ _ If;~~; ~/a r ;( ¥~L~ ~ ' / 's¥ ~ ~ ~'-/ ~t¥!~ 4 ¥r;~
Fig' I Active faults in JTapan (Research Group for Active Faults' 1980)'
activity in the sea area surrounding Japan even
though monitoring of crustal strain by means of
geodetic survey cannot be used.
The writer will evaluate probabilities of earth-
quake occurrence in a number of seismically active
areas in the seas adjacent to the Japanese Islands
in some way or other, so that the probabilities of
ground shaking due to these off-shore activities ex-
ceeding a certain level can be evaluated.
Finally, effects 0L inland and off-shore seismic
activities will be synthesized reaching zonations of
overall earthquake hazard in terms of probability
of ground acceleration exceeding certain levels for a
prescribed time interval from a specified epoch.
Strain Accumulation over Active Faults
An extensive catalog of active Laults in Japan
was put forward by Research Group for Active
Faults (1980), the distribution of active faults
having been shown by the group as can be seen in
Fig. 1.
Meanwhile, Geographical Survey Institute has
been conducting triangulation and trilateration sur-
veys of the precise geodetic networks composed of
the Ist- and 2nd-order triangulation stations a-
mounting to some 6,000 in number. As the survey
made progress, it becomes possible to see the
accumulation of crustal strain over most portions
of the Japanese Islands, if not all. Dividing the
accumulated strain by the number of years between
two surveys, which usually amounts to scores of
years, the crustal strain rate per year can be obtain-
ed. The rate of maximum horizontal shear strain
for an active fault is estimated as an average of
d
i
,~
1?o
~
,2
~ 3 / 1817
_ 9 5 12~ 10 1¥ I .~ 4 11 6 '-
o 4eO km
'c' g
Fig. 2
- 55 -
The 14 faults associated with a large earth-
quake in the past. I : West of Aomori, 2 : Senya. 3 : Shiroishi-Fukushima, 4 : Sagami trough S : Tanna, 6 : Suruga trough, 7 : Zenkoji-Iiyama, 8 : Atotsugawa, 9 : Neodani,
10: Yanagase. 11 : West of Suzuka, 12: Hi-ra, 13 : Yamasaki, 14: Shikano.
(3)
T。RIKITAKE
such rates for a number of triangles covering the
fault.Strain rates for348active faults can thus be
estimated.
For the14faults shown in Fig.2,we know
thatalargeearthquake・ccurfedinthepastinassociation with their movements,As the exact
dates of occurrence are infeπed from the history
for these earthquakes,we have the relation between
the strain rateプand the time interval T between a
speci丘edep・ch,theyear2000say,andtheyear・f
thelastearthquake・ccurrencef・rthefaults・In
addition to these faults,there are15examples of
earthquakesthat・ccurredinthepastveryc1・set・
a fault although no detail of fault movement is
available.
Examining theプーT relationship for these faults,
we see that there is a tendency that the retum
peri・d・fearthquake・ccurrencef・rahighstrain
丁
0 49
50 99
100 149150 199200 249250 299500 349550 399
0
FREαUεNCY
r(2
T
■■■■■■■1 2
- 1■■■■■■■■ 2
- 1 0 0 0
FREOUENCY
2≦k4 0 - 49
50 99
100 14915α 1ワ9
200 2奪9
250 299500 549350 399
T
〇 一
50
100150200250300350
脳■■■ 1
0 0口■■顧 1
■■■圏■團■■ 2
7
rate fault is shorter than that for a low rate one,
InFig.3aresh・wnthefrequencydistributi・ns・f
Tinyrf。rthethreeranges・fプ,Le・r<2×10-7/
yr,2x10-7ノシr≦7〈4×10-7yrand4x10-7/yr≦rin
regardt。thご27faults・nland。Weinfact・bserve
thatthepeak・ffrequencyshiftst・asmallervalue
。fT-rangeastheプーrangetakes・nalargervalue・
Letusden。tethepr・bability・fanearthquake
。ccurringbetweenTandT+∠Tbyμ(孟)whichis
assumed to be expressed by a Weibull distribution
such as
μ(T)=KT鵬 (1)in which parameters K and形are constants and K
>O and窺>一1。
When the probability of an earthquake occurr-
ingbetweenOandTisden・tedbyF(T)・wehave
F(T)=1-R(T)
where
R(T)一expHlμ(T)dT]
一exp[一KT ・/(翻)] (2)
Thepr・babilitydensity∫(T)isthengivenby
∫(T)=一dR/dT
=KT皿exp[一KT酬/(”3+1)] (3)
Parameters K and形can be determined from
ther-Trelati。nsandtake・nthevaluesgiveninTable l for respective r-ranges. The probability
densities are also obtained with the aid of these
parametersassh・wninFig・4f・rrespectiveプー「anges・
4999
1491992492993存9
399
0
o
FREOUENCY
45r
Fig.3
(4)
■■■■■■■■■■■ 5
■■■■■■■■ 2
0 0 0 0 0
The frequency distributions of time interval
(T)betw-een the year200Q and the year for
the last earthquake occurrence for threeranges of strain rate(プ),T andプare mea-
sured in units of year and 10 7/yr, respec’
tively.
> .012ト
罰Z,01田
o .008
>卜
一
ロ雛.004
く自コ
0002配’
匹
YR
3
2
o
Fig.4
一56一
50 1D巳 150 200 250 300 350 T l N YR
Probability densities of earthquake occur-
rence as a function of T at the year2000・
Curves,1,2and3correspond for the tbree
ranges・fstrainrate,i・e・1f・げ<2・2f・r2
≦7<4and3for4≦7。プis measured inunitsoflO-7/yr.
Earthquake Prediction and Seismic Hazard Analysis in Japan
ζ.012
5Z.01国
o ,008
>←
一
ロ.o園
くoユ
0、002
配
ら
Y罠13
N
\
Table l
Parameters K and”3for the two epochs2000and2010when T is measured in units of year.Strain
rateプis嫌easured in units of lo『7/yr.
Epochプ<2 2≦プ<4 4≦7
2K 解 K ”z K ”3
20005,14×10田51.101.78x10-40。9482,47×10-70。991
2010 7.03x10-5 1.01 4。12x10-5 1.26 8.97×10-7 2.27
0 50 鵬 150 200 250 300 350 T IN YR
Fig。5 Probabilit1y densities of earthquake occur-
rence as a function of T at the year2010.
Strain rate ranges are the same as those for
Fig.4.
Tab互e2τ’s for the two epochs.
Epoch プく2 2≦プ<4 4≦72000
2010
140
146
105
111
81.2
91.6
On the assumption that no earthquake occurs
until2010,similar probabilities are estimated,The
parameters are also given in Table1,while the
probability densities become as shown in Fig.5.It
seems likely,however,that some earthquakes occur
during2001-2010, so that the peaks of probability
density curve would in actuality shift to sma11er
valUes of T。
According to Geographical Survey Institute
(1981),it is reported that a42,5km base-line con・
necting two triangulation stations across Suruga Bay
has shortened by90and42cm during the periods
1884-1973and 1931-1973シrespectively. The base-
1ine crosses Suruga trough which is a typical active
fault. It appears,t}lerefore,that the strain rate 圭n
the direction of base-line has b㏄n almost constant
over the90-year period,As such steady develop・
ment of crustal strain is known for a number of
active∫aults,it is assumed in this paper that the
strain rate is constant。Although the strain rate
may considerably vary immediately before and after
an earthquake,the assumption of constant rate for
a period of亡he order of100yr may not be unrea-
sonable.
The strain accumulated during a period from
the last earthquake and the epoch at which data
analysis is conductedン say the years 2000and 2010
in the present case,is given by
・一∫r∫(T)dT∫『プ(孟)dオ (4)
When7=const.is assumed,we obtain
ε一∫rT∫(T)dT一τ (5)
where
τ=[K/(勉+1)]一1伽+1)r[(解+2)/(窺+1)](6)
in wh三ch r denotes a Gamma function。
On the basis of K and解given in Table1,τ
is calculated as given in Table2for the respective
strain ranges, Puttingτthus estimated into equa・
tion (5),the strain accumulation is obtained for a
fault for whichプis known。
Probability of Earthquake Generation
fromanActiveFault
Let us assume that the crustal strain so far
accumulated around an active fault was released at
the time o{the last earthquake originating from
that fault and that the strain has been accumulat・
ing again since then with the rate inferred from
geodetic surveys.In that case,strain accumulation
for any epoch can be estimated in a manner
mentioned in the last section.Comparing the
accumulated strain to the ultimate strain,which
was estimated by Rikitake(1975),it三s possible to
evaluate probability of a crustal break or an earth一
(luake taking place within a prescribed time interval
from a speciGed epoch,As such probability evalua-
tion of active faults has already been presented by
Rikitake (1984),no detailed account of evaluation
method is given here。
As we can estimate strain accumulation by the
一57一 (5)
T.RIKITAKE
years 2000 and 2010 based on 7 and τ already
obtained,the cumulative probabilities F2000and F2010
0f an earthquake occurring by the years 2000and
2010can be calculated.The probability of an earth・
quake occurring during2001-2010 is then obtained
as
F3=(F2。、。ぞ2。。。)/(1-F2。。。) (7)
on the con(1ition that no earthquake occurs by the
year 2000.
The probabilities of earthquake occurrence
within the10・yr period from the year2001are thus
evaluated for the 348 active faults distributed al呈
over the Japanese Islands.
Grouna Motion aue to Earth“uakes
Relatea to hlanαActive Faults
Matsuda (1977)proposed an empirical relation
between the magnitude M of an earthquake caused
by a fault movement and the fault Iength L such as
Mニ(1・gL+2。9)/0.6 (8)
where L is measured in units of kilometer.Equation
(8)is useful for estimating the earthquake magni-
tude when a fault moves。
On the other hand,Katayama(1974)obtained
a statistical relation between maximum mean hori、
zontal acceleration J in gal and epicentral distance
D in km which is given as
I・9ク=0,982-1.2901・9.D+0.466M (9)
in whichハ4is the earthquake magnitude.
Combining(9)with(8),maximum mean hori-
zontal acceleration 碗ゴ at the∫一th site due to the
movement of the.ノーth fault can readily be calculat・
ed.As the probability for each fault giving rise to
an earthquake has been obtained as mentioned pre-
vi・usly,itispossiblet・evaluatepr・babilityP却of
maximum mean horizontal acceleration at theゼーth
site exceeding a certain leve1.
When there areηfaults,the synthetic proba-
bility is given by
acceleration,In practice,distributions of maximum
mean horizontal acceleration exceeding100and300
gals for10-yr time interval from the year2001are
obtained as can be seen in Figs.6and7.
In the actual calculation of probab丑ities,faults
of which the length is shorter than5km are dis-
regarded,When a number of faults are located
very closely, they are sometimes represented by a
single fault。When a site,for which the proba・
bility is to be evaluated,is within a distance of5
km from a fault,σ=400gals is assumed.
Looking at Figs.6and7,it is apparent that
the probability is highest in the Chubu and Kinki
districts in Central Japan. This certainly reHects
the fact that many active faults are densely distri・
buted in the districts. There are a few areas of
relatively high probability hl the Shikoku,Kyushu
and Tohoku districts. The low probability in the
Kanto district,which includes the Tokyo area,is
certainly due to the fact that no active faults can
be recognized because of thick sediments covering
the Kanto plain and also that crustal strain moni.
tQring is di伍cult to conduct because many triangu・
lation stationS have been destroyed by human
aCtiVity in reCent yearS.
It is interesting to compare the probability dis-
tributions as shown in Figs,6and7to those given
by Wesnousky(1982)and Wesnousky et a1。(1984).
Apart from the absolute values of probability,dis-
tr二butions of earth(1uake hazard in terms of proba・
bility obtained in this study generally agree with
those by Wesnousky and his colleagues.There are
of course some differences between the two distri・
butions. For instance,the high probability area in
Central Japan in the Wesnousky map is somewhat
shifted to the east comparing to those in Figs,6
and 7, Such points are caused by the di鉦erence in
the basic assumption for evaluating hazard proba・
bility between the two studies,
ルP¢=1一π (1-P乞ゴ) ゴ=1
(10)
On the basis of equation (10), P〆s can be ca1-
culated for any site and for any Ievel of ground
(6)
OccurrenceProbabilityofO」f一曲ore
Earthquakes an{l Gro覗nd Motion on Land
Major earth(1uakes ofエM=7-80ccur in the sea
surrounding Japan,so that it is important to
58一
Earthquake Prediction and Seismic Hazard Analysis in Japan
’
ρo’
9
ら〃
◎
6
ア 1 『 1 P 一 『 1 』 コ ロ ドコ コ ド ア
⑳蓑綴鷲Vll
VIll
多
戯㈱朋1
⑱v
Vl
Fig,8 Seismic belts and clusters from where major
off-shore earthquakes around Japan are ori・
ginated.
estimate seismic hazard caused by off-shore earth-
quakes.The seismic belts or cfusters,from which
major interplate earthquakes are originated,are
shown in Fig8, Monitoring of crustal strain is
possible only for near-shore areas such as VI and
V旺a, so that evaluation of earth(王uake occurrence
probability is forced to rely on historical records of
seismicity in respective earthquake areas。
No detailed account of probability evaluation
is given here for the sake of simplicity。Only the
probabilities of a large earth(1uake ofハ4=70r over
occurring in the respective areas are evaluated and
given in Table3along with the Iocations of earth・
quake area,mean magnitudes,years of the Iast
earthquake and mean return periods.When the
number of data is su伍ciently large,we make use
of Weibull distribution for estimating mean retum
period and probability.Meanwhile,we have to rely
on Poisson distribution in the cases of scarce data
on the assumption that earthquake occurrence is
stationary and random。In the table,the last
column indicates which distribution is used by
notationsW(Weibu11)andP(Poisson),Earthquake
areas Nos. I and V旺 are divided into6 and 3
subareas, respectively, although the statistics for
evaluating Probabilities are conducted bas玉ng on the
data sets for the whole areas.
The probabilities of earthquake occurrence be-
ing thus evaluated,we can readily estimate probabi1-
ities at an on-shore site exceeding a specif三ed level of
Table3Probabilities of a large earth(1uake occurring from
off-shore earthquake areas(Iuring2001-2010。
No. Earthquake areaMean Mean
latitude Iongitude
(。N) (。E)
Mean Year of Mean last returnmagn1冒 earth- period tude quake (yr)
Probability
for Remark
2001-2010
IaIbIcIdIeIfH皿
wVwVEa
WbV匪c
皿
Off Hokkaido-Kurile
Off Aomori Pref。
Off Sanriku
Off Miyagi Pref.
Off Fukushima Pref.
Sagami trough
Nankai trough
Hyuganada Sea
44.5
44,0
43。3
42.6
42.2
40.7
40.7
39.4
38.2
37.2
34.7
34、7
33。9
32.9
32.1
151.2「
149,0
147.6
146.2
144.6
143.6-
142.4
144.4
142.0
141.6
139.8
138.3-
136。8
134.4-
132.1
7,9
7,3
7.7
7.4
7,5
8,0
8.0
7。0
1963
1958
1969
1973
1952
1968
1945
1933
1978
1938
1923
1854-1944
1946-
1984
85.3
69
107
34.9146
156
117
7。2
0.037- 0.050i lO.021
wO。017
0.070
0.026一
0.14
0.089
0.33
0.066
0.20
PPWPw
0.41-
0.044 WO.041-
0.66 W
一59一 (7)
T。RIKITAKE
ground acceleration on the condition that the Ka-
tayama formula(9)can be applied even to o旺・shore
shocks.Such probabilities can then be combined
with those from earthquakes due to inland active
faults obtained previously reaching synthetic
probabilities that represent overa11seismic hazard in
Japan for the10-yr period between the years2001
and2010,The probability distributions of maximum
mean horizontal acceleration exceeding 100and 300
gals are shown in Figs,9and10,respectively.
It is noticeable in these 且gures that the high
probabihty in the Chubu and Kinki districts predo-
minates even though the contribution of o狂一shore
earthquakes is taken into account.That the future
off-shore seismic activity expected in the Hyugana-
da Sea near Kyushu and off the Tokai area in the
middle Honshu results in relatively high probabil-
ities can also be clearly observed in the丘gures。As
major earth(1uakes in the Hokkaido-Kurile area
have already occurred in the later half of 1900’s,
theearthquakehazardduet・sh・cks・riginatingfrom the area is not high for the period in question.
It is no easy matter to evaluate probability of
a major earthquake occurring in Japan Sea because
oflackofdata,Averyroughestimate,however,1eads to a very low value amounting to a few per-
cent for a 10-yr period. It is therefore surmised
that the probability distributions shown in Figs.9
and 10are affected very little by Iarge earth(luakes
originating from the Japan Sea area.
Seismic HazarαWhen Low Strain Rate
Fa腿lts are Disregar-e盛
The above probabilities of earth(luake genera-
tion from active faults are evaluated on the
assumption that all the faults treated are capable of
generating an earthquake although many of them
are characterized by a low strain rate.Among the348
faults studied,strain rate for105faults is lower than
the average rate of maximum horizontal shear
strain of Japanese Islands as a whole as revealed
by the repetitioτl of the lst-order triangulation/
trilateration surveys.A Weibull distribution anal-
ysis of geodetic data for the lst-order surveys
(8)
Ieads to a mean rate amounting to 1、3×10-7/yr
(Rikitake,1983)。
When there are many faults which are assumed
to be independellt o{each other,we see that the
synthetic probability as calculated by formula(10)
becomes extremely high even though the probability
for each fault is not very high.Let us for instance
assume that there are10independent faults each
having a probability amounting to O.10,we see
that the synthetic probability is estimated as O.65。
When there are20faults,the probability becomes as
high as O。88.
In view of such a consideration,we suspect that
high probabilities of seismic hazard in some areas
as presented in Figs。6シ7,9,and10may be
brought about by the fact that there are many
壬aults even though the probability of earth(1uake
generation from each fau玉t is not quite high,At
the moment,there is no clue to judge whether a
fault is capable or not capable of generating an
earthquake、 But it would not be u皿easonable to
presume that a fault of which the strain rate is
substantially smaller than the average may not gene-
rate an earthquake after alL In other words such
a fault is totally dead in the sense of earthquake
generation。
Let us assume that a fault,of which the rate
is smaller than the average rate of general defor・
mation of the Japanese Islands or1。3x10-7/yr as
cited in the above has nothing to do with crustal
break or earthquake generation.The probability of
maximum mean horizontal acceleration at a site
exceeding respectively 100and300gals is then re-
evaluated.In spite of such elimination of low-rate
faults, it turns out that the general pattern of
probability distribution is not greatly altered,
especially in the Chubu-Kinki area w五ere the
probability is high although probabilities at sites
very close to an ignored fault become considerably
Iower. In view of this,no probability distribution
map for which the Iow-rate faults are disregarded
is presented for the sake of simplicity.
一60一
Earthquake Prediction and Seismic Hazard Analysis in Japan
Conclusion
Seismic hazard in terms of probabihty of ground
shaking exceeding a specified level is estimated in
Japan・nthebasis・factivefaultdistributi・nand
crustal strain accumulation.Unlike the existing
studies,that deal with only the average over his・
torical and/or geological times,the probability for
a prescribed time interval from a speci丘ed epoch
can be evaluated,so that it may be said that Iong-
term earthquake prediction is taken into account in
the evaluation.
It turns out that the highest probability apPears
in the Chubu and Kinki districts,Central Japan,
where many faults are concentrated,There are
some areas of next highest probability in the Shi・
koku,Kyushu and Tohoku districts。
If low strain rate faults are disregarded,the
probability lowers to some extent although the
general tendency of probability distribution is much
the same、
Probabilities of a large earthquake occurring in
theseasurroundingtheJapaneselslandscanbe
evaluated in some way or other though the
evaluation may not be quite accurate,The contri-
bution from such o鉦一shore seismic activities to on-
shore ground shaking can be combined with that
from inland active faults providing overall hazard
estimation in terms of probability of gromd acce1・
eration exceeding a certain leveL
The hazard maps presented here are di鉦erent
from the existing ones,which represent seismic
hazard averaged over a long Period, in the fact
that earthqake prediction in terms of probability of
earthquake occurring in a prescribed time interval
from a speci丘ed epoch is taken into consideration.
It is the writer’s belief that the seismic hazard
maps presented in this paper would be of some
usef。ranti-earthquakepr・graminJapaninthe
future.
Refere皿cesGeographical Survey Institute(1981).Crustal movement
in the Tokai district,Rψ.Coo74.Co”z”z.Eαπhα。
Pプ84乞α.,25,213-222(in Japanese),
Kanai,K.and T,Suzuki(玉968)・Expectancy of the
maximum velocity of earthquake motions at bed
rock,B%ZZ.Eαπhg灘た6R85.1n5孟,,τo妙o Uπ加,,46,
663-666.
Katayama,T.(1974).Statistical analysis of peak accelera-
tions of recorded earthquake ground motions,5E1-
S。41V-KE1〉Kyu,26,18-20、
Kawasumi,H.(1951).Measures of earthquake danger
and expectancy of maximum intensity throughout
Japan as inferred from the seismic activity in histori-
Cal times,β%lJ.Eαπ物襯為6R85,1π5オ.,To妙o U麗加・・
29,469-482。
Matsuda,T.(1977).Estimation of future destructive
earthquakes from active faults on land in Japan,」.
Phζy5.Eαπh,25,5麗汐ψ」,S251-S260,
Research Group for Active Faults(1980)・Active faults
in Japan,sheet maps and inventories,Uη幻8プ5⑳o/
7b々yo Pプε55,7b為ッo,」4♪‘zπ,363pp.(in Japanese),
Rikitake,T,(1975).Statistics of ultimate strain of the
earth・s crust and probability of earthquake occurren-
ce,7セ6勲o頚ツ5f65,26,1-2L
Rikitake,T.(1983).Active fault and crustal strain,
E碗んα.Pプ84㍑.R65,,2,167-189・
Rikitake,T,(1984).Strain rate of active fault and
earthquake risk,Eαプ‘h(z・P764∫o筑・R65・・ 2・277-303・
Wesnousky,S,G。(1982)、Crustal defomation and earthquake risk in Japan,Pゐ,五),Tんθ5∫5,Colπ甥6ガα
Uπ掬67麟ツ,Nθτσyo矯.
Wesnousky,S.G。,C.H.Scholz,K Shimazaki and T。
Matsuda(1984)。Integration of geological and seismo・
10gical data for the analysis of seismic hazard:a case
study・fJapan,B祝」1。S召枷.5・・.肋・,74・687-708・
一61一(9)
/
g
/
l~
L/~_. J~'~'(
<)g
~;~~¥
A 100 - 81 o/o
B 11 80-61 60- 41
D 1 40- 21 E ~I 20-11 E'] 10-0
~~l'
e~ o
e
e
/
O p
o
f o
Og
ve o
~e
6O-41 9~0 C
D 1 40-21 20- 11 E
10- O E'
Fig. 6 Probability in percent of a exceeding 100 gals in a tlme interval
of 10 yr from the year 2001 due to earthquakes originating from
inland active faults. a denotes the maximum mean horizontal acce le rat ion .
Fig. 7 Probability of a exceeding 300 gals in a time interval of 10 yr
from the year 9-001 due to earthquakes originating from inland
active faults.
/
Og
/
,"~~~
~~~
A 11 Io0-81~~
B 1 80-61 60-41
DII 40-21 E~~] 20-11 E'] lo-o
・f
e~ o
,
,
o
/
/
o
dP
o
<)d
~~~
~)
B 1 80-61 ~6 C J 60-41 D 1 40-21 E 1 20-11 E'] IO-O
o
Fig. 9 Probability of a exceeding 100 gals in the 10-year period as specified
before. Both the on. and off-shore seismicities are taken into
account.
Fig. 10 Probability of a exceeding 300 gals.
as those in the legend of Fig. 9.
Other conditions are the same