Preliminary Study on Precursors to the 1923 Great Kanto Earthquake of Magnitude 7.9

Tsuneji RIKITAKE

Abstract

Geoscientific and macroscopic data precursory to the 1923 Kanto earthquake of magnitude 7.9 are collected from existing literature. As a result, 66 data of various disciplines, for which the precursor time can be approximately identified, are obtained. They are anomalous changes in hot spring, animal behaviour, seismic activity, underground water, crustal move- ment and the like. Three peaks of precursor time (T) which is measured in units of day appear for loglo T=0.0-1.0, 1.0--0.5 and 1.5-2.0. Such a conclusion seems to agree with the mode of precursor appearance prior to other great earthquakes in Japan such as the 1944 Tonankai earthquake of magnitude 7.9. It is hopefully expected that a more intensive search for precursors to the Kanto earthquake will bring out many more data which are useful for earthquake prediction study.

l. Introductio'n

The 1923 Kanto earthquake of magnitude 7.9 is certainly the worst earthquake in the history of Japan. As the earthquake and the associated damage were a terrible shock to the Japanese people of those days, many reports, either scientific or non- scientific, on the Kanto earthquake were published after the earthquake. It is highly likely, therefore, that fairly many instances of premonitory effect could be collected by reading through existing publications. Many people, who experienced the earthquake, are still alive, so that an extensive inquiry survey could be done. Under the circum- stances, the author believes that extensive studies on precursors to the Kanto earth- quake should be made in a fashion similar to the Ansei Tokai and Tonankai earth- quakes (Association for the Development of Earthquake Prediction, 1982, 1983) . As far as the author knows, no such thorough investigations of precursors to the Kanto earthquake have been conducted. What the author presents in this paper is only the preliminary results so far obtained by the author and his collaborators. The Kanto earthquake having occurred about sixty years ago, seismic and other geoscientific observations were not quite developed as they are now. It cannot be helped, therefore, that only precursor-1ike phenomena of limited number were reported on the

Department of Earth Sciences, College of Humanities and Sciences, Nihon University, Setagaya- ku, Tokyo, Japan -3 Proceedings of the Institute of Natural Sciences (1986) basis of geoscientific obs:ervations. On the contrary, there are fairy many reports on macroscopic precursors such as changes in underground water level, hot spring, anomalous animal behaviour and so on. This is probably due to the fact that the earthquake hit the densely-populated South Kanto area. It is also likely that terrified people looked back very seriously and recollected strange phenomena which they had experienced before the earthquakes.

2. Geoscientific and nracroscopic precursors

Geoscientiflc as wel][ as macroscopic precursors to the Kanto earthpuake collected so far are respectively listed in Tables I (a) and I (b) in a summarized form. The pre- fectures in and around the Kanto area are indicated in the table with abbreviations T (Tokyo) , C (Chiba) , K (Kanagawa) , S (Shizuoka) , Y (Yamanashi) and Sa (Saitama) . respectively. Much of pre-earthq:uake crustal movement as revealed by triangulation surveys and rhombus distance measurements were reported by Fujii and Nakane (1979) , Tsuboi (1933) and Geographical Survey Institute (1972, 1981, 1983) . Imamura (1928 a, b) reported on an anomalous ground tilting started early in the morning of earthquake day. A number of observations of sea level at the seashore mostly 1;'.'ith the eye clarified that the southern coast of Kanto area had beep. subsiding over a period of scores of years. However, uplift of the ground in areas close to the epicenter such as the extremity of Miura Peninsula seemed likely to have started about 2 months before the earthquake. It is extremely interesting to note that a tide gauge at the Yokosuka Navy Shipyard began to register an anomalous change in the sea level early in the morning of earthquake day. The h_igh _seismicity in the Kanto area during a period of 10-20 years before the Kanto earthquake is well k･nown (Sekiya, 1971 ; Suyehiro and Sekiya, 1972) . Rikitake (1982) pointed out a tendency that the epicenters of moderately large earthquake occuring during the several year period before the main shock tended to move toward the epicenter of the main shock. No remarkable foreshock activity immediately before the Kanto earthquake was reported althou*"h several small shocks had been occuring in an area near the epicenter of coming earthquake in a period of a few months prior to the main shock. Earth current measl~lrements had been carried out in Sendai in Northeast Japan even in such an early period of geoelectric study in Japan. Notwithstanding a large epicentral distancnce a:D~lounting to 350 km. Shiratori (1925) observed an anomalous disturbance in earth potential between two electrodes buried in the ground. The dis- -4- Pre11minary Study on Precursors to the1923Great Kanto Earthquake of Magn量tude7．9

Table1（a）Ge・scienti五cprecurs・rst・the1923Kant・earthquake．

Epicentralprecurs。r No。 Observation spot distance Description time （km）

Discip賎ne3crustalmovement l S・uthKant・ 30 30yr It is concluded that the anomalous strains with contraction in NNW・SSE directiQn occurred about thirty years before the 1923 Kanto earth・ quake，the contractions were reversed during the time of the earthquake，and the strains are now accumulating with contraction in NNW・SSE direction after the earthquake．1） 2 M三taka（T） 60 3yr An anomalous increase in the rhombus area in the compound of the Tokyo Astronomica互Ob・ servatory started about 4 years prior to the earthquake．2） 3 Hongo（T） 70 8hr An Omori－type horizontal pendulum seismograph of long period at the Tokyo Imperial University recorded a sudden westward tilt from about O4・0010cal time on September1，1923． The Kanto earthquake occurred at 11．580n that day． According to the author’s experience，however， the seismograph suf〔ers much friction and is un－ stable，so that the record may not be guiteτe。 liable．3）

1）iscip1最ne＝αustalm・vementbyti“eobsewation 4S・uthempart・f 20－5060－70yr In the southem part of Boso Peninsula and Miura Boso Peninsula and Peninsula，it has been noticed that the seas五〇re Miura Peninsula had been subsiding since60－70yr preceding the Kanto earthquake。 There were many points where the roads along the shore were submerged， The amounts of subsidence during the period seem likely to be80and50cm respectively for Boso and Miura Peninsulas．4） 5 Aburatsubo（K） 18 2yr Since the beginning of observation， the groun（l at Misaki had been subsiding with a mean rate of l cm／yr。 Since1921，however，the gromd tended to uplift with a rate of3cm／yr．4） 6 Tateyama（C） 42 1－2yr The height of sea level had increased since1－2 yr before the earthquake，so that the sea reaches almost the hedges of houses at the beach．5》 7Arasaki（K） 18 15－16m The height of sea level increased by20cm or s（》 since around May－June，1920．5） 80dawara（K） 18 一 The height of sea level seems likely to have up－ heaved wit蓋a rate of about20cm／yr before the earthquake．5）

5 Proceedings of the Institute of Natuml Sc五ences（1986）

Epicentral Precursor No． Observation sp・tdistance time Description （km）

9Choshi（C） 145 8m The sea level had become higher by21cm than that for the last year in May， June and July。 It became nearly30cm higher immediately before the earthquake．6） 101ioka（C） 135 8m The Ievel of sea water was so high that no huts for sea bathers could be built on the ordinary Places・fthebathingres・rtattheKujukuri beach．7） 11 Aburatsubo（K） 18 2m The sea level at Misaki lowered by14cm in July－August． It appears that the ground there upheaved by at least8cm in July－August・9） 29 The tide・gauge at the Yokosuka Navy Shipyard 12 Yokosuka （K） 7．5hr fbeg an to record an anomalous saw・toothed change since O4．30 10cal time．8）

Discipline＝earthquake 13Wakayama prefecture 400 1500d The number oHelt earthquakes in Wakayama Prefecture began to increase since 1500 days prior to the Kanto earthquake．9） 14 Sagami Bay 0 3．5m No earthquake activity immediately before the earthquake． However，there were frequent earth－ quakes in Sagami Bay，the epicental area of the present earthquake，during a perlod from May to August20、10） 15 Hongo（T） 72 25d According tQ the observation at．the Tokyo Im－ 15d perial University，there were unfe正t earthquakes 8d on August7，0n August17and24，there were ■espectively one felt earthquakes、 These quakes are located near the epicenter of the Kanto earth・

quake．4） 16 Yokosuka（K） 30 7d Small shocks on August25，28and 30， No 4d foreshocks immediately prior to the Kanto earth－ 2d quake，5）

Discipline：eartk currents

17 Sendai 350 Several hr An anomalous change in earth potential was ob・ （Miyagi Prefecture） served by Shiratori． The change started several hours before the earthquake occurrence． The earth potential was largely disturbed at the time of earthquake occurrence． Such disturbances continuedforsometimeaftertheearthquake。11）

6 Prehminary Study on Precursors to the1923Great Kanto Earthquake of Magnitude7．9

Table1（b）Macroscopicprecursorstothe1923Kantoearthquake，

Epicentτal Precursor No。 Observatまon spot distance Description time （km）

Discioline；rumbling l Shonan （K） 20 Several d Rumblings were heard o長Shonan and less fish・ catch was reported．12） 2 Miura Peninsula（K） 25 1－2d Rumblings were heard o鉦Miura Peninsula．4》 3 Shinagawa（T） 601mmed1ately ArumblingsQunding“goh”washeard。13） before 4Kimitsu（C） 50 3－5s Arumblinglikethewhirofanairplanepropel・ Ier or丘ring of a gun was heard3－5seconds before the earthquake occurrence，14） 5 Sanuki （C） 45 3－4s A rumbling Iike the sound from a running train was heard3－4seconds before the earthquake occurrence．The sound was coming from the S600Wdirection，14） 6Minato（C） 42 1mmediately A rumbling like the whir of an airplane prope1・ before lerwasheardfromtheS100Wdirection。14） 7 Honjo（T） 73 1mmediately Astrangesoundlikeastormfromtheground before bottom was heard，15）

Discipline un－ergrounαwater 8 Lake Yamanaka（Y） 60 3m According to Mr．D．Amano，the headman of Nakano Village，the Lake Yamanaka started to get muddy at May－June，1923．There is no river which flows into the lake，while the water springs up from the lake bottom．6）

9 1zu Nagaoka （S） 46 Well water turned whitish before tke earthquak6． It became muddy after the earthquake，6） 10 Shinagawa（T） 60 2－3m The water at段well in a Buddhism temple start・ ed to smell strangely．After the earthquake，it became gradually clear．But no such change was found for a well in front of the temple．6） 11 1sehara（K） 30 21m The water level at a well in Ota Village lowered since about2months before the earthquake．It recovered after the earthquake．6） 12Hadano（K） 33 The same as the above at a well in Hadano Village． No exact date is available．6）

13 Kameido（T） 70 The same as the above．6） 14 Takinogawa（T） 75 Awellcou正（lnotbeusedbecausethewatergot muddy，No exact date is available．6）

7 Proceedings of the Institute of Natural Sciences（1986）

Epicentralprecurs。r No． Observation spot distance time Description （km）

15 Shinagawa（T） 60 36d It was ascertained by an expert that the welI water at several wells in Shinagawa dried up toward the end of July。 The investigation was made because the local people suspected that the phenomenon might be a kind of precursor to a large earthquake．Such an anomalous change in well water was also observed before the1855 Ansei Edo earthquake。 The well completely dried up on July27．6）

16 Yokohama（K） 42 5－6d In a river in Yokohama，many五sh Hoated and died， River water got muddy， this being a phenomenQn called“Nigashio”（bitter tide）。16）

17 Shizuoka （S） 97 2－3d The well water in the govemor’s residence in Shizuoka City got muddy2－3days before the earthquake．6）

DisciOline＝ kot spring 18Atami（S） 33 8m The geyser stopped to gush at December20， 1922．6）

19 1zu Nagaoka （S） 46 7d The amount of hot spring water decreased at the north spring one week before the earthquake． However， it increased after the earthquake． Meanwhile，the amount at the south spring de・ creased after the earthquake．17）

20 Atami（S） 33 1d The geyser gushed hot water for40minutes on August31in contrast to the ordinary gush period of5－20minutes．6） 21Hakone（K） 36 6hr The hot spring water at a hote玉at Dogashima got mud（1y at O6．000n September1。6）

22 Hakone（K） 33 6hr The hot spring water at Tonosawa got muddy in the moming on September1．10）

23 1zusan （S） 32 3hr According to Y。Miyayama，a student at the Meteorological Schoo1，the temperature of the Izusan hot spring became so h1gh that no one could bathe．17）

24 1to （S） 34 3hr The amount o｛hot spring water increased in the moming on September1．This is the report of the chief of Ito police station．17）

8 Preliminary Study on Precursors to the1923Great Kanto Earthquake of Magni亡ude7．9

濫線ぎa1Pr曼curs・r No． Observation spot Description （km） tme

Discipline ammalous animal behaviour （1） Mammals

25 Shinagawa（T） 60 4d Rats disappeared．12） 26 Nagasaki（T） 71 2d Rats ran away from the house．18）

27 Kanda（T） 70 3hr 40rats were captured by a trap at one time．19）

28 Akihabara（T） 70 1mmediately A cow pull圭ng a cart suddenly stopped raising before its forefeet when the great shock hit，18）

（2）Fish 29 0ff Kinkazan 400 98d Out－of－season丘sh catch of mackerel pikes on May （Miyagi Prefecture） 25， 1923，20）

30 Sea near Tokyo In spite of usual fish catch of horse mackerehn summer，many mackere1，sometimes as Iong as 30cm or more，were caught this year．16） 31 Tama（T） 56 1m Many eels and daces appeared in brooks which usedtobealmostdryinordinaryyears．16） 32 Kawasaki（K） 55 1m Cat丘sh propagated unusually．16） 33 Kamakura（K） 23 1week Many shrimps were found at the shore of Kama－ kura．16）

34 Kamakura（K） 23 1week Many gobies were found at the shore of Kama・ kura．16）

35 Sagami Bay Less fish catch in Sagami Bay．No bonito and tunny apPeared in the deep interior of the bay．12）

36 Sagami Bay O Severa夏d Fish catch decreased in Sagami Bay．12）

37 Hayama（K） 20 Several d According to the Belgian ambassador，a trans． parent， raddish五sh， probably a kind of deepsea one，Hoate（1to the sea surface．20）

38 1zu （S） 30 Severa豆d Fishermen in Izu saw a deepsea丘sh called“Shige” Hoated up to the sea surface．12）

39 0dawara（K） 28 Deepsea fish appeared at the seashore of Oda－ wara．8） 40 Hachioli（T） 60 5d Great catch of sweet丘sh in River Tama．16） 41 Mukojima（T） 74 2－3d Mr．T．Akatsukasa，the deputy minister of educa・ tion，saw many catfish jumped up on a pond at a restaurant downtown Tokyo immediately before the earthquake， It was reported that the 五sh had been active these a few days．4），21）

9 Proceedings of the Institute of Natural Sciences（1986）

Epicentra1Precurs。r No． Observation spot distance time Description （km）

42 Yokohama（K） 42 1－2d Many crabs moved towards land．16） 43 Yokohama（K） 42 l d Sar盛ines came into haτbour in shoals．16） 44 Tokyo Bay 60 l d No fish catch by casting nets，16）

45 Izusan （S） 30 l d Many red snappers，gray mullets and sea basses were caught near Atami。16）

46 Tsurumi（K） 50 1d Gray mullets floated to surface．16） 47 － 1d Mr．H．Kishinami，a painter，put a cat丘sh in a large bowl for the purpose of sketching． He felt strange because the五sh did not stop moving。16）

48 Kugenuma（K） 21 1d Mr．T．Shibagaki，the architecture chief at the Ministry of Educat圭on， 丘shed by a casting net three backetful cat五sh of30cm in length．4），12）

49 Lake Yamanaka 60 1d Great catch of crucian carp．12），16） 50 River Sakawa（K） 20－40 l d Great catch of sweetfish。16）

51 River Ara（T） 60－110 l d Great catch of sweet丘sh，16） 52 Kawaguchi（Sa） 80 Catfish propagated unusua11y only in the earthqu。 akeyear．16）

53 Kamata（T） 55 1d Many crucian carp were caught at a pond in Kamata．12）

54 1shinomaki 400 18hr Countless gray mullets went up a river・20） （Miyagi Prefecture） 55 Sagami Bay 6hr Many dead deepsea codfish were floating on the sea surface．16）

56 Senju（T） 75 4－5hr Carpandcruciancarpn・atedt・surfaceata pond at Senju．20）

57 Nihonbashi（T） 68 2－3hr Many丘sh Hoated and were in agony at Nihon・ bashi．16）

58 0ff Sunosaki（C） 35 2hr Plankton came up to sea surface at the mouth of Tokyo Bay．12）

59 Okinoshima Is．（C） 35 2hr Many bonitoes were caught in Tateyama Bay。12） 60 O長Kamogawa（C） 64 一 Much五sh catch of sardine。No catch after the earthquake．12）

61 River Sagami （K） 30 2hr Many sweet丘sh and daces were caught、16）

62 River Kanna 120 一 Surprisingly large number of eels were seen・ （Gumma Prefecture） They were sticking their head out of stone holes．16）

10一 Preliminary Study on Precursors to the1923Great Kanto Earthquake of Magnitude7．9

Nα・bservati・nsp・t濫欝a’p瑠ls・r Description

63 Anegasaki（C） 68 All eels in a reservoir at Anegasaki disappeared before the earthquake．20） （3）Insects 64 Yamanash玉Prefecture 98 2－3m Wasps d1sapPeared． Discipline； earthquake lig騒t 65 Honjo（T） 73 3．5d Apillarof五resomethinglikeathunderlight was seen for30minutes．No sound was accom・ pained． The light was most intense towards the west as if it was daylight time。22） 66 Tokyo 68 1．5d AsoundlesslightovertheskyofTokyolasted a fairly long time．22）

67 0nahama 250 15hr Fishermen saw something bright in the west sky （Fukushima Prefecture） off Onahama in midnight the day before the earthquake．22） 68 Pt．Nojimazaki（C） 50 Afurious五repillarwasseentowardsthesouth－ east of Pt．Nojimazaki．8） 69 Fukagawa（T） 69 6hr Aflashinglightwasseentowardsthedirection of Tokyo Bay in the moming of the earthquake day．22） I）iscipline： super蹴atural IDower

70 Kanda（T） 70 Mr．K．Sakuma，a dietman，said that a white fox，the envoy of a god of a shrine in the town， appeared before the earthquke． This part of Tokyo did not su丘er from the f辻e because the god defended the town．23） Discipline：anomalousweather 71 Shinagawa（T） 60 12d Since around August20，thunderclaps were heard fr・m10・夕c1・ckinthemorningtillduskevery－ day．No thunderlight was observed、13）

72 Boso Peninsula（C） 60 7d It was terribly dark at the sea bottom，so that the fishermen failed to丘sh．8） 73 HonjQ（T） 73 6hr The sky was reddish w血en a child of15years old got up in the moming．13）

1）Fuii圭and Nakane（1979），2）Tsuboi（1933），3）Imamura（1928a，b），4）Shnsai Yobo Kyokai（1977）， 5）Yokosuka－shi Sh五nsa圭shi Kankokai（1932），6）Shinsai Yobo Chosakai（1925），7）Mizuochi（1983）， 8）Da圭Nlhon Kyoiku Tsushinsha（1923），9）Kanamori（1972），10）Mizuochi（1983），11）Shiratori （1925），12）Musha（1957），13）Sぬinagawa・ku，Tokyo－to（1978），14）Geological Survey of Japan（1925）， 15）Kaizosha（1924），16）Suyehiro（1976），17）Central Meteorological Observatory（1924），18）Mejiro Police Station，Metropolitan Police Board（1977），19）Nagai（1923），20）Musha（1935），21）Musha （1932b），22）Musha（1932a），23）Kanto Daishlnsai Sh葦ryobu（1924），

一11一 Proceedings of the Institute of Natural Sciences (1986) turbance started several hours before the Kanto earthquake. Even after the earthquake, the disturbance continued for some time. Reports on rumbling are not many. There are a few reports, however, that some detonation-1ike sounds were heard off the Miura and Shonan areas facing Sagami Bay. There are fairly many reports on precursory anomalies of underground and lake water. Report No. 15 in Table I (b) on the well water at Shinagawa in Tokyo is especially interesting because of the detailed description and of its resemblance to that at the time of the 1855 Edo earthquake (M=6.9) . Looking at the precursory anoma- lies of hot spring water summarized in Table I (b) , it seems certain that hot springs in the lzu-Hakone area adjacent to the epicentral area were under some premonitory effect of the Kanto earthquake. Quite a few reports on anomalous animal behaviour are available as can be seen in Table I (b) . The number of reports of flsh is especially large. This is certainly due to the effort made by Professor Y. Suyehiro, a famous ichthyologist, who is very much interested in the anomalous behaviour of flsh in relation to earthquake phenomena. The readers may notice that there is no report on bird behaviour. The author thinks, however, that such lack of data reflects the fact that no extensive and systematic investigations on anomalous animal behaviour has as yet been carried out in relation to the Kanto earthquake. It is highly likely that many more precursory data could be (rbtained by an extensive study which should be conducted in the future.

3. Characteristics of precursors

A preliminary statistical study of the precursors to the Kanto earthquake is made on the basis of the data so far collected as will be pesented in the following. (1) Precursor time Fig. I shows the histogram of logarithmic precursor times of the whole data set of precursors listed in Tables I (a) and I (b) . The precursor time T is measured in units crf day. The frequency is counted for each interval of 0.5 for logro T. In the flgure, we see that three peaks of frequency appear for logro T=0.0-1.0, -1.0--0.5 and l.5-2.0. It is interesting to note that these ranges of loglo T for which the peaks appear approximately agree with those for the precursors to the Tonankai earthquake (Association for the Development of Earthquake Prediction, 1983) . It may be that the overall tendency of precursor appearance is more or less the same for great earthquakes in the Tokai-Kanto area. Figure 2 shows the frequency distribution of geoscientific precursor times. The spectrum of precursor time is rather broad in this case. When the histograms for different disciplines, say crustal movement (including sea level change) and earth-

- 12 - Preliminary Study on Precursors to the 1923 Great Kanto Earthquake of Magnitude 7.9 quake activity, are drawn separately, we 18 notice that the peaks occur at ranges dif- ferent with one another as can be seen in IG

Figs. 3 and 4. It is premature, however, 14 to conclude that the characteristic precursor 12 time is different from discipline to dis- cipline because the number of available 10 precursors is small. 8 A similar histogram for the macro- scopic precursor data is shown in Fig. 5. Comparing the histogram to that in Fig. 1, 4 we observe that the histogram in Fig, I is 2 largely affected by the histogram for macro- scopic precursors. Such a fact cannot be -2 -1 O 1 2 3 4 avoided because the number of data for Fig. I Histogram of logarithmic precursor time for the whole data of pre- macroscopic precursors is larger than that cursors to the Kanto earthquake. for geoscientific precursors. Precuasor time T is measured in Figs. 6, 7 and 8 show separately the units of day. The interval of each range is O.5. histograms for underground water, hot spring and anomalous animal behaviour. Scantiness of data prohibits us from conclud- ing any prevailing ranges of precursors for underground water and hot spring. How- ever, the peak around logro T= O-1 for the histogram of anomalous animal behaviour in Fig. 8 seems significant. Such a tendency can also be seen in the histogram of anomalous animal behaviour for the Tonankai earthquake (Association for the Develop' ment of Earthquake Prediction, 1983) and that for the lzu-Ohshima Kinkai earthquake

6

4

2

-2 -1 O 1 2 3 4 Fig. 2 Histogram of logarithmic precursor time for the data of geoscientific phenomena.

- 13 - Pr㏄eedings of the Instltute of Natural Sciences（1986）

4 2

一2 一1 0 1 2 3 4 Fig． 3 Histogτam of logarithmic precursor time fGr the data of crustal movement．

4 2

Fig。4 Histogram of logarithmic precursor time for the data of earthquake activity．

1 1

10 8 6 4 亀 2 2

一2 一1 0 1 2 3 一l o 1 2 3

Fig， 5 Histogram of logarithmic precursor Fig．6 Histogram of logarithmic precursor＝time time for the macroscopic data． for the data of underground wateL

14 Preliminary Study on Precursors to the 1923 Great Kanto Earthquake of Magnitude 7.9

14

12

10

8 G G 4 4 2 2 -2 -1 O 1 2 3 _2 -1 O 1 2 3 Fig. Histogram of logarithmic precursor time Fig. 8 Histogram of logarithmic precursor for the data of hot spring. time for the data of anomalous animal behaviour.

Table 2 The ranges of logro T (T is measured in units of day) for which the peaks of precursor time frequency occur and the number of precursor data for respective disciplines for the Kanto earthquake.

Discipline Number of data Range of loglo T

Hot spring 7 -l--O. 5 Anomalous animal behaviour 31 O-1 Earthquake activity 8 O. 5-1. 5 Underground water 6 1. 5-3 Crustal movement 12 2~3

(M= 7.0, 1978) (Rikitake, 1981) . Summarizing what the author stated in this section, the ranges of logro T for which the peaks of precursor time frequency for respective disciplines occur are given in Table 2 in which the numbers of data are also listed. In spite of the scarcity of data, it seems likely that Table 2 suggests that precursors of a particular discipline appear for a particular band of precursor time. It is pre- mature, however, to conclude that such a tendency is firmly established until more data sufEcient for an exact statistical study are accumulated. As a tentative conclusion of the preliminary study of precursors to the 1923 Kanto earthquake, we may say that the mode of precursor appearance for the earthquake is not much different from that of the 1854 Ansei Tokai and 1944 Tonankai earthquakes

- 15 - Proceedings of the Institute of Natural Sciences (1986)

l t

l 3 14{t24~li Itt

551 tr~F7iLi:~72V1 44 i 3 5 5j~ X ~ Ot KANTO EQ.

t ~ 30km

Fig. g (a) Spots where a precursor was observed before the Kanto earthquake. The numerals indicate respective disciplines of precursor : (1) anomalous animal behaviour, (2) earthquake activity, (3) crustal movement, (4) underground water, (5) hot spring, (6) earth potential, (7) rumbling, (8) earthquake light, (9) supernatural power and (O) anomalous weather.

(Association for the Development of Earthquake Prediction, 1982, 1983). No more analysis such as basing on a Weibull distribution of precursor time is carried out for the present data set. Such a detailed analysis will be made after collecting some more precursor data in the future. (2) Spots where a precursor is observed The spots where a precursor is observed are shown in Figs. 9 (a) and 9 (b) . It is natural that many reports came from highly populated and much damaged areas. The author feels, however, that the data from Chiba Prefecture and lzu Ohshima Island are too scanty. Future study for digging out precursor data of the Kanto earthquake may hopefully supplement this point. Fig. 10 represents the frequency versus epicentral distance relation. It appears that the larger the distance is, the smaller is the number of precursor data. The drop of frequency for 40-60 km may be due to the fact that the population was thin in the Tanzawa and Tama areas to the west of highly-populated Tokyo and Yokohama areas in those days. Many of the data used m thrs pap'r were collected by M N. Mizuochi, one of

- 16 - Preliminary Study on Prec皿sors to the1923Great Kanto Earthquake of Magnltude7。9

夢 1

X KANTOEQ．

㎞ 0 100 200 一’一一一 2

Fig，9（b） Additional spots where a precursor was observed before the Kanto earthquake．The meanings of numerals are given in the Iegend of Fig．9（a）．

30

20

10

O 20406080100120140160 Fig． 10 Frequency versus epicentral distance relation of the precursors to the Kanto earthquake。

一17一 Proceedings of the Institute of Natural Sciences（1986） the author’s former students at the College of Humanities and Sciences，Nihon University．The author thanks him for his e仔ort．

References

Association for the Development of Earthquake Prediction，Precursors to the Ansei Tokai and Tonankai Earthquakes，106pp．，1982（in Japanese）・ Association for the Development of Earthquake Prediction，Precursors to the Tonankai Earth・ quake with Supplements to the Ansei Tokai Earthquake，204pp・，1983（in Japanese）・ Central Meteorologica正Observatory，Kanto Daishinsai Chosa Hokoku，Jishin Hen（Rep。on the Kanto Earthquake），61PP、， 1924 （in Japanese）。 Dai Nihon Kyoiku Tsushinsha，Kanto Dai Shinsaishi（The Great Kanto Earthquake），351pp，，

1923 （in Japanese）． Fujii，Y。and K．Nakane，Anomalous crustal strain prior to the1923Kanto，Japan，earth・ quake as deduced from analysis of old triangulation data，Pure AppL Geophys，，117，1301－

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18一 Preliminary Study on Precursors to the1923Great Kanto Earthquake of Magnitude7，9

Japanese）。 Nagai，S。，（ed．），TaishQ Shinsai Ki（Report of the Taisho Earthquake Disaster），Taisho Shinsal Kiroku Hensankai，Tokyo，227pp・，1923（in Japanese）・ Rikitake，T．，Anomalous animal behaviour preceeding the1978earthquake of magnitude7．O that occurred near Izu・Oshima Island，Japan，In Current Research in Earthquake Prediction I7 edited by T．Rikitake，Center for Academic Publications Japan，Tokyo／D．Reidel Publish－ ing Company，Dordrecht，69－80，1981． Rikitake，T．，Do foreshock epicenters move toward the main shock epicenter？，Earthq．Predict、

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225， 1972， Suyehiro，Y。，Namazu Jishin Kanchiho（A method of Detecting Earthquakes by Cat五sh）， Shodensha，Tokyo，232pp，，1976（in Japanese）． Tsub・i，C。，lnvestigati・n・nthedef・mati・n・ftheearth’scrustf・undbyprecisege・detic means，Jap．J．Astr．Geophys．，10，93－248，1933・ Yokosuka－shi Shinsaishi Kankokai，Yokosuka－shi Shinsaishi，Yokosuka・shi Shinsaishi Kanko・ kai，Yokosuka，336PP。，1932，

Note a－dωin proof3 Precursor data for the Kanto earthquake amQunting tQ 914 in total number were collected by later stu（玉ies，The result of analysis of these data will be reported elsewhere in

the future．

19